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J Appl Physiol 97: 1787-1795, 2004; doi:10.1152/japplphysiol.01394.2003
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Ventilatory behavior during sleep among A/J and C57BL/6J mouse strains

Lee Friedman,1 Abby Haines,2 Ken Klann,2 Laura Gallaugher,2 Lawrence Salibra,2 Fang Han,3 and Kingman P. Strohl2

1The MIND Institute, Albuquerque, New Mexico 87106; 2Department of Medicine, Case Western Reserve University, and the Louis Stokes Veterans Affairs Medical Center, Cleveland, Ohio 44106; and 3Department of Medicine, People's Hospital, Beijing University, Beijing 100029, China

Submitted 29 December 2003 ; accepted in final form 7 June 2004


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
The pattern of breathing during sleep could be a heritable trait. Our intent was to test this genetic hypothesis in inbred mouse strains known to vary in breathing patterns during wakefulness (Han F, Subramanian S, Dick TE, Dreshaj IA, and Strohl KP. J Appl Physiol 91: 1962–1970, 2001; Han F, Subramanian S, Price ER, Nadeau J, and Strohl KP, J Appl Physiol 92: 1133–1140, 2002) to determine whether such differences persisted into non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Measures assessed in C57BL/6J (B6; Jackson Laboratory) and two A/J strains (A/J Jackson and A/J Harlan) included ventilatory behavior [respiratory frequency, tidal volume, minute ventilation, mean inspiratory flow, and duty cycle (inspiratory time/total breath time)], and metabolism, as performed by the plethsmography method with animals instrumented to record EEG, electromyogram, and heart rate. In all strains, there were reductions in minute ventilation and CO2 production in NREM compared with wakefulness (P < 0.001) and a further reduction in REM compared with NREM (P < 0.001), but no state-by-stain interactions. Frequency showed strain (P < 0.0001) and state-by-strain interactions (P < 0.0001). The A/J Jackson did not change frequency in REM vs. NREM [141 ± 15 (SD) vs. 139 ± 14 breaths/min; P = 0.92], whereas, in the A/J Harlan, it was lower in REM vs. NREM (168 ± 14 vs. 179 ± 12 breaths/min; P = 0.0005), and, in the B6, it was higher in REM vs. NREM (209 ± 12 vs. 188 ± 13 breaths/min; P < 0.0001). Heart rate exhibited strain (P = 0.003), state (P < 0.0001), and state-by-strain interaction (P = 0.017) and was lower in NREM sleep in the A/J Harlan (P = 0.035) and B6 (P < 0.0001). We conclude that genetic background affects features of breathing during NREM and REM sleep, despite broad changes in state, metabolism, and heart rate.

ventilation; respiratory control; genetics

AMONG MAMMALS, THE PATTERN and depth of breathing vary, may be modified by a number of factors including chemical drive and respiratory loading, and are independent of respiratory mechanics (4, 15, 48, 49). During resting breathing, an individual in a species exhibits a recognizable pattern among many possible airflow profiles (1), and, in a human at rest, variability is small (~3%) on measures of respiratory timing [frequency (f), inspiratory time (TI), and TI/total breath time (TT)] compared with those for tidal volume (VT) or ventilatory drive (~8%) (35). Taken together, these observations suggest that, in the adult mammal, there are core features in ventilatory pattern generation operating at a eupneic level during wakefulness.

Sleep is a period in which there is reduced arousal to external stimuli, and ventilatory responses to hypoxia or hypercapnia are reduced (16). In addition, the transition to sleep is accompanied by pronounced changes in autonomic outflow and vascular tone (10). Nevertheless, Shea et al. (36) observed in humans the pattern of breathing during wakefulness, the "personalité ventilatoire," to persist into non-rapid eye movement (NREM) sleep, suggesting that an individual's breathing pattern was preserved, despite the changes in proprioception and cardiopulmonary physiology associated with that state (11). This literature is based on a small sample; moreover, observations of ventilatory behavior were largely confined to NREM sleep. Rapid eye movement (REM) sleep is a state distinct from NREM sleep, having phasic neural events, autonomic fluctuations, and other potentially destabilizing events to brain stem control mechanisms (28). Studies in humans appear to confirm a change in cardiovascular control occurring with REM sleep, compared with NREM sleep (5). There is a view that the brain in the state of REM sleep may express an essential individuality, if not physiologically then psychologically (17), so that, despite the instability of this state, it is possible that an "individuality" of breathing might also be present.

The study of in-bred animals potentially avoids the confounding effects of age, illness, and other environmental exposures that confound studies in humans, while permitting control of genes and diet in a manner that cannot be done in the studies of humans.

The hypothesis was that the differences in f that are known to occur between the A/J (Jackson Laboratory strain) (AJ) and C57BL/6J (B6) mouse strains during wakefulness would persist into sleep. The broad findings confirm this hypothesis and document strain-by-sleep state interactions in ventilatory behavior that are different from heart rate (HR), suggesting that genetic mechanisms operate in a rather specific way to produce differences in the control of breathing in adult male mammals.


   METHODS
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 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Animals.   Experiments were performed on three strains of inbred mice: B6, AJ mice from Jackson Laboratory (Bar Harbor, ME), and A/J Harlan mice from Harlan Bio-Products for Life (Indianapolis, IN) (AJH). The AJH have been a commercial colony, separated from the AJ since 1978 (Dr. R. J. Russell, personal communication). Sets of animals (n = 3–5 males of each strain at a time) were purchased and housed at the Animal Resource Center at Case Western Reserve University under standard conditions of 7 AM to 7 PM light-dark cycles for 2 wk until 5 days before implantation, when they were put in constant light. This was performed to standardize the environmental conditions for light-dark during those times that the animals were housed over the monitoring period; this area could not be controlled for light-dark cycling. Animals were provided standard laboratory chow and water ad libitum. Animals were kept in individual cages in the laboratory for the days needed to complete the protocol. The study was approved by the Case Western Reserve University School of Medicine Institutional Animal Care and Use Committee, was in agreement with the National Institutes of Health Guide for the Care and Use of Laboratory Animals, and was performed under the supervision of the Animal Care Facility.

Surgery.   Animals were anesthetized for electrode implantation by using isoflurane gas anesthesia (0.1–0.5% balance air or oxygen). Following anesthetic induction, the head and neck were shaved and washed with an antimicrobial agent, the animal was placed onto a heating pad, and the head was positioned in a stereotaxic alignment device (Cartesian Research). Depth of anesthesia was judged by response to touch, pain, and tail pinch, as well as observation for movements, and the mixture of isoflurane was adjusted accordingly. A midline incision was made to expose the skull and neck muscle posterior to the skull. Four holes were drilled (0.25 mm) through the skull. The EEG electrodes were constructed of 25-cm lengths of insulated stainless steel wire (0.21-mm diameter), with 0.5 mm of insulation removed at the end to form the contact, and the electrode wires were inserted into the drilled holes and positioned to contact the dura (27, 30). The medial anterior EEG electrode was placed 2 mm in front of bregma and 0.5 mm lateral of the midline; the medial posterior electrode was positioned 2 mm behind bregma and 1 mm lateral of the midline. The lateral anterior EEG electrode was placed 0.5 mm behind bregma and –2 mm lateral of the midline, whereas the lateral posterior EEG electrode was located 1 mm in front of lambda and –3 mm lateral of the midline. Two electromyogram (EMG) electrodes were formed by knotting the stainless steel wire, burning off the insulation, and suturing the knotted portion onto the surface of the neck muscle posterior to the dorsal area of the mouse skull. The wires were secured and cemented to the skull by using dental acrylic, which formed a hard head cap. The average time for the implantation of electrodes was 30 min. Animals recovered from anesthesia in ≤10 min. In summary, each animal was instrumented with four cortical EEG leads and two nuchal EMG leads, yielding three bipolar channels of data: a lateral EEG channel to distinguish general cortical EEG changes with sleep state, a medial EEG channel focusing on the hippocampal theta rhythm (51), and an EMG channel detecting levels of muscle tone across the sleep states.

Measurements of ventilatory behavior.   Ventilation was assessed by using a whole body plethysmograph by the open-circuit method (8), modified for monitoring sleep in the mouse (27, 30). Briefly, the round lucite chamber (600-ml volume) was modified with a "chimney" (100-ml volume) topped by a rubber stopper to permit an airtight seal. The monitoring leads were given sufficient slack (~2–4 cm) in the chimney and were on a swivel to allow the animal to move freely within the chamber. The leads exited through the rubber stopper and connected to a Grass model 15 recording system (Astro-Med, West Warwick, RI). Bedding chips were placed on the floor of the chamber, in an insufficient amount to permit a nesting burrow. Calibration volumes (0.01-, 0.02-, and 0.03-ml pulses of air) were sequentially introduced into the chamber (using a syringe) before and after a study with the chamber empty. These impulse volumes were used to test system stability (leakage, transducer drift, etc.) to ensure that data integrity was maintained during the study and served as a "calibration" for the estimation of VT. A thermometer-hydrometer probe was used to monitor ambient temperature and humidity.

An outlet port was connected to a vacuum sufficient to create a bias flow of 300 ml/min through the chamber. The chamber was connected to one side of a pressure transducer (Validyne DP45, Validyne Engineering), with a sensitivity of ±2 cmH2O, referenced to a chamber of equal volume and shape. As the animal breathed, swings in chamber pressure were converted to a signal, which, in turn, was analyzed for components of ventilatory behavior.

The fractional content of CO2 and O2 was measured by sampling the gas exiting the chamber (Beckman OM-11 and LB-2 analyzers, Beckman Instruments, Pittsburgh, PA). Oxygen and carbon dioxide levels, sampled from the line to the vacuum source, were continuously measured and recorded each epoch, and values were also collected from room air gas entering the chamber. Oxygen consumption and carbon dioxide production are calculated by determining the difference between the gas concentrations entering and leaving the chamber.

Experimental protocols.   Each animal was allowed 3 days to recover from surgery before any recordings were performed. There were then 3 recording days, each separated by 1 day: day 3 (or 72 h after surgery and recovery) for acclimatization and days 5 and 7 (Fig. 1). For each study, each animal was placed in the chamber for 15 min and then recorded for ~5 h between the hours of ~10 AM and ~3 PM.



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  		Fig. 1. Schema of the measurement protocol. EMG, electromyogram; JAX, Jackson Laboratories.

 
Signal collection.   The lateral EEG, medial EEG, nuchal EMG/electrocardiogram (ECG), and ventilation signal were amplified and filtered with a Grass model 15 system. Amplitude gain was adjusted for each mouse to provide an optimal range. The signals were filtered by using the built-in Grass filters and were set at 1–100 Hz for the lateral (cortical) EEG, 3–30 Hz for the medial EEG (to over-represent hippocampal theta activity), and 30–100 Hz for EMG; the signal from the pressure channel was connected to a direct-current channel for the ventilatory signal. All signals were entered into an analog-to-digital converter (16-bit, National Instruments, PCI-MIO-16E) and sampled at 512 samples/s. All signals were stored for offline analysis.

State scoring and ventilatory and HR signal evaluations were assessed in 4-s epochs (39). The computer program displayed four channels (lateral EEG, medial EEG, nuchal EMG/ECG, and ventilation) for three epochs (12 s) simultaneously. The records were scored in 4-s epochs.

Two trained observers scored each epoch visually as active wakefulness, quiet wakefulness, NREM, REM sleep, or movement time. The typical criteria were employed; i.e., wakefulness was characterized by a low-voltage, high-frequency EEG pattern (based on the lateral EEG channel) in association with an elevated and variable EMG. Active wakefulness was distinguished from quiet wakefulness on the basis of the EMG level. NREM sleep was defined by an increase in (lateral) EEG amplitude and a decrease in EEG frequency and, in particular, by the presence of high-amplitude delta waves (0.5–4 Hz). The EMG was generally low and stable during NREM sleep. REM sleep was defined by low-amplitude, high-frequency lateral EEG, regular theta waves (4.5–8.5 Hz) in the medial EEG, and the lowest recorded EMG tonic level with occasional phasic EMG bursts. The category for movement time included the following: movement artifact, temporary poor signal quality usually following an arousal, and presence of high-voltage spike-and-wave discharges seen exclusively in the AJ. A spike-and-wave discharge was defined as a sharp discharge pattern with an average spike peak amplitude at least 75% greater than that of surrounding EEG activity and a pattern lasting more than four cycles and was observed best in the lateral lead (1–100 Hz); the average rate was ~6 Hz (21). Interrater concordance was 91% overall and 96% for the main states of interest: quiet wakefulness, NREM, and REM sleep.

The ventilation signal was disrupted by movement artifact during epochs of active wakefulness or movement time and hence was not scored. Epochs containing sighs were also excluded from analysis. The onset of inspiration and expiration were detected based on changes in the slope of the chamber pressure swings. For each epoch, the start of inspiration, peak inspiration, and expiration were automatically indicated, but the operator was provided with flexible tools for editing the position of the automatically placed marks. Once the onset points were accepted, a series of measures were automatically collected for each epoch, including peak-to-peak time for respiratory rate (f; breaths/min) and peak-to-trough voltage for "inspiratory volume" relative to the calibration signal (VT; µl), and a subsequent calculation of minute ventilation (E; ml/min; VT x f). Derivative values discussed in RESULTS included TT, TI, and expiratory time, used to compute the elements of respiratory phase switching or TI/TT and mean inspiratory drive (VT/TI) (26).

HR was obtained from the ECG contribution to the nuchal EMG trace. The QRS spike from nuchal EMG was detected by using an adjustable-threshold algorithm, based on a moving EMG average and its standard deviation. The first step in the detection of HR from the EMG signal was to down-sample to 256 samples per second by averaging adjacent samples. Next, a moving average was computed based on 25 samples (0.05 s, number of samples was user adjustable). If the signal was >3.5 SD (user adjustable) above the moving average, then an ECG spike was detected, if at least 40 samples (0.08 s, user adjustable) had elapsed since the last ECG spike. The HR over the 4-s epoch was stored, according to each epoch scored.

Analysis of variance revealed that values for sleep state within a strain varied between days 3 and 5 but not between days 5 and 7 of testing. In the B6 and AJ strains, there was an increase in wakefulness and a reduction in NREM in days 5 and 7 compared with day 3 (P < 0.003). In contrast, values for ventilatory behavior and HR according to a given state showed no difference among study days in any animal. Nevertheless, data from the first day of recording (day 3) were not utilized in the analyses. We examined the effect of length of recording time with t-tests within a strain on values for ventilatory behavior, HR, and metabolism. Values were similar in the first hour of recording to the last hour of a 5-h recording (P = 0.057). Early studies suggested that extending the recording length to >5 h appeared to result in an increase in wakefulness (statistics not performed), possibly as water and food were restricted by the design of the testing chamber. Therefore, results from each animal from the initial 5 h of recording for days 5 and 7 were pooled for analysis by strain.

All results are expressed as means ± SD. The effect of strain, state, and their interaction were tested with mixed-model ANOVA designs (SAS Proc Mixed). The role of age and weight as covariates were assessed in each model. Mouse was treated as a random effect, and state and strain were treated as fixed effects. Post hoc simple effects were tested with protected t-tests. The level of statistical significance is provided, and values of P < 0.05 were considered significant.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Ten B6, 8 AJ, and 8 AJH animals completed the protocol. Mean ± SD age of the animals was 88 ± 10, 69 ± 10, and 84 ± 25 days for AJ, AJH, and B6 mice, respectively [degrees of freedom (df) = 2, 23, F = 2.68; P = 0.09]. Mean weight of the animals was 23.9 ± 2.1, 24.1 ± 2, and 25.4 ± 3.8 g for AJ, AJH, and B6 mice, respectively (df = 2, 23, F = 0.81; P = 0.46). Although there were no differences among strains in these values, we examined the influence of age and weight as covariate factors in the mixed-model ANOVA analysis of f, VT, and E. Age and weight were never significant covariates in any model, and, therefore, these variables were dropped in the final analyses. The temperature in the chamber and the humidity were 23.2 ± 0.6°C and 74 ± 8%, respectively; and these values did not vary on days of testing among strains (df = 2, 23; F = 1.09; P = 0.30). Temperature of the animals was measured before and after testing. Values were 35.4 ± 0.6, 35.6 ± 0.5, and 35.8 ± 0.5°C for AJ, AJH, and B6 mice, respectively (df = 2, 23, F = 2.55; P = 0.09).

Over the 10 h of data analysis from days 5 and 7, the average percentage of time spent in each state was 3% for quiet wakefulness, 47% for NREM, 7% for REM sleep, and 5.5% for arousals from sleep, with the remainder (~35%) in active wakefulness or movement time. There were differences in the number of observations of state among the three strains (df = 8, 40; F = 4.1; P = 0.001), and post hoc analyses localized differences to active sleep and to arousals. The AJH exhibited more REM (8.9%) compared with AJ (5.5%) and B6 (6.3%) (P = 0.026), and the B6 exhibited fewer arousals (3.7%) compared with AJ (5.7%) and AJH (7.2%) (P < 0.0001). The results of analyses on ventilatory behavior and metabolism are based on comparisons of similar amounts of quiet wakefulness and NREM sleep and sufficient (>5% of epochs), but unequal, amounts of REM sleep.

Ventilatory behavior.   Examples of recorded variables from two of the strains with the greatest divergence in breathing patterns are shown in Fig. 2. Values for ventilatory behavior (and for additional traits), as recorded during EEG-defined states, are shown in Table 1. The results of the mixed-model ANOVA analyses are presented in Table 2 (for overall strain-by-state comparisons). The post hoc analyses for sleep state contrasts by strain are presented in Table 3, and those for the differences among strains according to state are presented in Table 4.



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  		Fig. 2. Examples of recordings are shown for the strains with the greatest divergence in ventilatory behavior [C57BL/6J (B6) and A/J JAX from Jackson Laboratory] in each state. Six panels are screen captures of 4-s epochs, and each has the same format. First signal is the EEG from the lateral electrode (vertical bar is 100 µV). The second is the EEG from the medial anterior electrode (theta channel: vertical bar is 100 µV). The third signal is the nuchal EMG (vertical bar is 15 µV). The fourth signal is the plethysmographic signal from which values of respiratory frequency (f) and tidal volume (VT) are derived. Values for each state are provided for reference. Quiet Wake, quiet wakefulness; NREM, non-rapid eye movement sleep; REM, rapid eye movement sleep.

 

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  		Table 1. Ventilatory traits, metabolism, and heart rate

 

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  		Table 2. F-tests for strain, state, and the strain-by-state interaction for key measures

 

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  		Table 3. P values for sleep-state contrasts by strain

 

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  		Table 4. Comparisons of strains by state

 
The values during quiet wakefulness show a difference in f and VT in AJ and B6, consistent with the patterns previously reported in uninstrumented AJ and B6 animals during presumed wakefulness (8, 9, 43, 47) (Fig. 3). However, there is also a difference in f between AJH and AJ strains in all stages of sleep, with the AJ exhibiting the lowest values in each state compared not only with AJH but also with B6 animals (P < 0.001). The AJH and B6 animals differed only in f in REM sleep (P < 0.01). VT, statistically, showed little difference among strains; however, the trend was for VT to be lower in AJH and B6 strains. E was similar, and the E adjusted for weight did not differ among strains.



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  		Fig. 3. Mean ± SD values are shown for f (breaths/min) (A), heart rate (beats/min) (B), relative VT (µl) (C), and minute ventilation (f x VT as ml/min) (D). AJ, A/J JAX strain; AJH, A/J strain from Harlan Laboratory; Q, quiet wakefulness; N, NREM sleep; R, REM sleep.

 
HR varied in a more complex manner than ventilatory variables, with values for HR during NREM lowest in the B6 strain (P < 0.001). In all three strains, there occurred a reduction in HR comparing wakefulness and REM sleep with NREM (P < 0.02).

The data were further examined to establish the relative relationships of phase switching as represented by TI/TT, relative to central inspiratory drive, as represented by mean inspiratory flow (26). Figure 4 provides a graphical display of these data. The phase switching components or TI/TT varied according to strain (Table 2) and showed state (Table 4) and strain-by-state effects (Table 3). TI/TT was lower for AJ in wakefulness and NREM but equivalent to the other strains in REM sleep. Mean inspiratory flow showed strain and state effects, as well as strain-by-state effects. In each strain, mean inspiratory flow was least in REM sleep compared with wakefulness or NREM sleep.



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  		Fig. 4. Relationship between mean inspiratory (Insp) flow [VT/inspiratory time (TI)] and duty cycle (TI/TT) for each strain in each state [quiet wakefulness (A), NREM sleep (B), REM sleep (C)]. Values are means ± SD. Symbols are the same as in Fig. 3.

 
Effects of metabolism.   Oxygen consumption and carbon dioxide production did vary by strain and state, but showed no state-by-strain interaction (Tables 2 and 3). Similar to E, E corrected for carbon dioxide production or for oxygen consumption was similar among all three strains and did show state and state-by-strain interaction (Table 2).

Correlation of state and HR.   HR could be reliably recorded in seven animals from each strain. HR showed significant differences according to strain and state (Tables 2 and 4). State-by-strain effect was significant but less pronounced. In the AJH and B6, HR was lower in NREM than in REM sleep, in contrast to breathing pattern changes and with indexes of respiratory control (mean inspiratory flow and TI/TT) that are the most different in REM sleep. The lowest values found were in NREM sleep in the B6 mouse (P = 0.05). Thus HR control mechanisms are not uniquely correlated with mechanisms for respiratory control of VT and f.


   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
This study describes a significant strain effect on the f and pattern of breathing during wakefulness that occurs in NREM and into REM sleep, as well. This effect occurred independent of metabolism, as judged by whole body measurements of oxygen consumption and carbon dioxide excretion. HR, one measure of cardiovascular control, showed strain and state effects and a pattern of state-by-strain effect that was different from that of TI/TT or mean inspiratory flow.

Previous studies of breathing during sleep have focused on the mean changes in each component in the transitions from wakefulness to the different stages of sleep. In humans, there is a fall in f and VT, with values in NREM sleep being lower than those in wakefulness and values in REM sleep often different in REM than in NREM sleep (24). One general conclusion is that such studies of state-dependent physiology are not merely descriptive but are essential for a complete characterization of factors affecting this regulatory system. In the present study, such state effects were observed in most respiratory variables and in HR, but not in oxygen consumption or carbon dioxide production. Thus across this species there are distinct influences of strain, as a surrogate marker of genetic diversity, on the patterns of change in these regulated variables.

The primary variable of f and TI/TT exhibited characteristic mouse strain differences and state-by-strain interactions. One strain, the B6, showed an increase in f in REM sleep, whereas in both A/J strains f was reduced in REM, compared with NREM sleep. The B6 f response is not usually found in humans but is consistent with original observations of the effects of sleep in the unanesthetized cat (29). All strains, however, exhibited reductions in VT, E, and mean inspiratory flow, and a lengthening of TI/TT observed in that seminal study (29), findings consistent with state influences on respiratory control.

Metabolism exhibited strain and state effects but no state-by-strain interaction; in addition, when corrected for metabolism, the pattern of state-by-strain interactions observed for ventilation did not change. The flow-through method for the measurement of metabolism detects whole body events and would change slowly relative to the rapid transitions in state that can occur in mice. However, differences were in the amounts of REM and arousals from sleep observed among strains, rather than the amounts of quiet wakefulness, active wakefulness, and NREM sleep. Oxygen consumption did not vary with strain, perhaps because measurements were made during states without gross body movement, such as quiet wakefulness and NREM and REM sleep. There was a strain difference in the production of carbon dioxide in wakefulness, and values for carbon dioxide production did vary with state. Nevertheless, average sleep bout length may vary over time as a function of time of day or strain (6), and organ system differences in metabolism do occur with state (14, 19, 20, 25, 52). However, the direction of change was similar between strains, and the pattern was such that effects with regard to metabolism would not alter the conclusions of the study, namely that strain differences in ventilatory behavior persist into sleep.

The changes in mean inspiratory flow (VT/TI) are in the direction of change anticipated by vagally mediated stretch receptors in the AJ strain; namely, a longer TI was associated with a smaller VT (3, 50). However, in the B6, VT was independent of TI. We speculate that vagal reflex modulation of VT may differ between strains, and the relative influence of cholinergic drive on VT may differ with regard to state, as is suspected for the cardiovascular control system (12).

HR, although only one component of the cardiovascular control, was different by strain and by state and exhibited a state-by-strain interaction. There is one report of HR measured along with blood pressure in the B6 mouse that did not find variations with HR according to state (32); of note, the HR was higher than what was found in the present study. Direct comparisons among laboratories are difficult, given the differences in study techniques and methods, especially in regard to acclimatization issues. Differences among strains are interesting to contemplate with regard to the current ideas on the impact of sleep on the range of vagal tone and coupling of cardiovascular functions to sleep (22). With regard to the aims of the present study, the differences in ventilatory behavior between strains did not track with these variations in HR.

In humans, a "very first night effect" on sleep-wake behavior must be taken into account in the study of sleep (23). In this study, we observed differences in relative amounts of sleep states and wakefulness between strains on day 3 compared with day 5, which we attribute to anesthetic effects. However, strain differences in ventilatory behavior during each state persisted over all study days. This finding is consistent with studies in humans that suggest that a "first night effect" does not occur with regard to the ventilatory events (breathing and oxygen saturation) in each sleep state, even in patients with impaired respiratory mechanics (7) or sleep apnea (18).

There are circadian effects on cardiopulmonary function, and we restricted the time of testing to the midday hours. In addition, studies were performed in conditions of constant light. Hence, there may be diurnal effects on regulation, and such effects may differ among strains. This would have required 24-h recordings and the construction of a chamber that would permit access to water and food. As the recording times were substantial, finer analyses might have disclosed such circadian influences (33, 34); however, the study was not constructed to detect a circadian effect, either by design or by the timing of the recording.

There are observations of sleep and breathing in rodent models, yet these are limited to one strain or species (13, 32, 40). The noninvasive method for measuring ventilatory behavior has little inherent inaccuracy with regard to f, but more potential inaccuracy with regard to ventilatory depth (38), and this chamber was modified further to manage the simultaneous measurements of sleep and breathing. In the present study, unanesthetized animals were tested under environmentally similar circumstances (chamber size, material, temperature, and humidity, etc., being equal). The main conclusion about strain differences in breathing can be made only by using f, the technical measurement of which is not influenced by body temperature or chamber temperature and humidity. Considering the limitations of flow barometric plethysmography, the absolute values of VT or E presented here should be indicative only. The consistency of observations among published reports among laboratories (8, 43) and over time (8, 9) of the different patterns of breathing (slower and deeper in the AJ, and rapid-shallow in the B6) makes it less likely that technical issues or instrumentation produced artifactual state variation and strain differences.

While mechanisms related to either brain structure or function might explain strain differences, another factor that might explain differences would be pulmonary function, which also shows more similarity in identical twins than in nonidentical twins or in the general population (31). Our laboratory's previous study (31), however, found only minor differences in respiratory mechanics between the AJ and B6 strains.

During the course of this study, we observed that the AJ strain exhibited spike-and-wave discharges, mostly during NREM (~75% of events) (37). These events did not alter the conclusions concerning strain differences, as there were differences between AJH and B6 strains, strains without such a trait. In addition, we eliminated those epochs 4 s before, during, and after spike-and-wave discharges, to reduce the immediate confounding effect(s) of spike-and-wave discharges. Nevertheless, in the AJ, unlike the AJH, f values did not vary by state. TI/TT was different in the AJ in quiet wakefulness and in NREM sleep from the other two strains; however, in REM, both A/J strains assumed a similar phase switching pattern. Another feature was that the AJ had no significant difference in HR between NREM and REM sleep. As such, EEG abnormalities are often correlated with polymorphic variations in ion channels regulating neuronal excitability (2). We speculate that subtle genetic differences in the AJ may not only produce epileptiform discharges but also influence cardiopulmonary behavior across states in epochs distant from such overt discharges.

We and others suspect that differences among inbred strains likely occur as a result of genetic factors (9, 41). Gene expression directs the development and function of mechanical or neural components of the respiratory control system, which apparently operate in a loosely coupled manner. Such properties are transmitted by inheritance (42, 44). Such variations are not just curious phenomenon. Differences in the pattern of breathing determine, to a significant extent, the degree of lung damage observed in response to environmental exposure to ozone (45, 46). Strain differences in the manner of response to reoxygenation (8, 38) and the observations reported here indicate that such differences could operate in humans to modify the expression of sleep-disordered breathing. We suspect that these differences between strains occur as a result of the multiple genes and gene interactions rather than the action(s) of one gene.


   GRANTS
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 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
During the conduct of this study, L. Friedman was a faculty member in the Department of Psychiatry at Case Western Reserve University and F. Han was a visiting professor in the Department of Medicine at Case Western Reserve University. This work was supported in part by National Heart, Lung, and Blood Institute (NHLBI) Grant HL64278, National Center for Research Resources Grant RR12305, and the Research Service of the Department of Veterans Affairs. K. P. Strohl held a NHLBI Sleep Academic Award (KO7 HL03650).


   FOOTNOTES
 

Address for reprint requests and other correspondence: K. P. Strohl, VAMC 111j(w), 10701 East Blvd., Cleveland, OH 44106 (E-mail: KPSTROHL{at}aol.com).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Benchetrit G, Shea SA, Dinh TP, Bodocco S, Baconnier P, and Guz A. Individuality of breathing patterns in adults assessed over time. Respir Physiol 75: 199–209, 1989.[CrossRef][ISI][Medline]
  2. Berkovic SF and Scheffer IE. Genetics of the epilepsies. Epilepsia 42: 16–23, 2001.[CrossRef]
  3. Clark FJ and von Euler C. On the regulation of depth and rate of breathing. J Physiol 222: 267–295, 1972.[Abstract/Free Full Text]
  4. Daubenspeck JA and Farnham MW. Temporal variation in the VT-TI relationship in humans. Respir Physiol 47: 97–106, 1982.[Medline]
  5. Dempsey JA, Smith CA, Harms CA, Chow C, and Saupe KW. Sleep-induced breathing instability. University of Wisconsin-Madison Sleep and Respiration Research Group. Sleep 19: 236–247, 1996.[ISI][Medline]
  6. Franken P. Long-term vs. short-term processes regulating REM sleep. J Sleep Res 11: 17–28, 2002.[CrossRef][ISI][Medline]
  7. Gothe B, Hanekamp LM, and Cherniack NS. Reproducibility of ventilatory measurements during sleep on different nights in patients with chronic obstructive pulmonary disease. J Lab Clin Med 109: 608–616, 1987.[Medline]
  8. Han F, Subramanian S, Dick TE, Dreshaj IA, and Strohl KP. Ventilatory behavior after hypoxia in C57BL/6J and A/J mice. J Appl Physiol 91: 1962–1970, 2001.[Abstract/Free Full Text]
  9. Han F, Subramanian S, Price ER, Nadeau J, and Strohl KP. Periodic breathing in the mouse. J Appl Physiol 92: 1133–1140, 2002.[Abstract/Free Full Text]
  10. Harper RM. The cerebral regulation of cardiovascular and respiratory functions. Semin Pediatr Neurol 3: 13–22, 1996.[CrossRef][Medline]
  11. Haxhiu MA, Mack SO, Wilson CG, Feng P, and Strohl KP. Sleep networks and the anatomic and physiologic connections with respiratory control. Front Biosci 8: d946–d962, 2003.[ISI][Medline]
  12. Head GA. Cardiac baroreflexes and hypertension. Clin Exp Pharmacol Physiol 21: 791–802, 1994.[ISI][Medline]
  13. Horner RL, Liu X, Gill H, Nolan P, Liu H, and Sood S. Effects of sleep-wake state on the genioglossus vs. diaphragm muscle response to CO2 in rats. J Appl Physiol 92: 878–887, 2002.[Abstract/Free Full Text]
  14. Hoshi Y, Mizukami S, and Tamura M. Dynamic features of hemodynamic and metabolic changes in the human brain during all-night sleep as revealed by near-infrared spectroscopy. Brain Res 652: 257–262, 1994.[CrossRef][ISI][Medline]
  15. Jennings DB and Szlyk PC. Ventilation and respiratory pattern and timing in resting awake cats. Can J Physiol Pharmacol 63: 148–154, 1985.[Medline]
  16. Joseph V, Pequignot JM, and Van Reeth O. Neurochemical perspectives on the control of breathing during sleep. Respir Physiol Neurobiol 130: 253–263, 2002.[CrossRef][ISI][Medline]
  17. Jouvet M. Paradoxical sleep as a programming system. J Sleep Res 7: 1–5, 1998.
  18. Katz ES, Greene MG, Carson KA, Galster P, Loughlin GM, Carroll J, and Marcus CL. Night-to-night variability of polysomnography in children with suspected obstructive sleep apnea. J Pediatr 140: 589–594, 2002.[CrossRef][ISI][Medline]
  19. Lenzi P, Cianci T, Guidalotti PL, Leonardi GS, and Franzini C. Brain circulation during sleep and its relation to extracerebral hemodynamics. Brain Res 415: 14–20, 1987.[Medline]
  20. Lenzi P, Zoccoli G, Walker AM, and Franzini C. Cerebral circulation in REM sleep: is oxygen a main regulating factor? Sleep Res Online 3: 77–85, 2000.[Medline]
  21. Letts VA, Kang MG, Mahaffey CL, Beyer B, Tenbrink H, Campbell KP, and Frankel WN. Phenotypic heterogeneity in the stargazin allelic series. Mamm Genome 14: 506–513, 2003.[CrossRef][ISI][Medline]
  22. Lombardi F and Parati G. An update on: cardiovascular and respiratory changes during sleep in normal and hypertensive subjects. Cardiovasc Res 45: 200–211, 2000.[Free Full Text]
  23. Lorenzo JL and Barbanoj MJ. Variability of sleep parameters across multiple laboratory sessions in healthy young subjects: the "very first night effect." Psychophysiology 39: 409–413, 2002.[CrossRef][ISI][Medline]
  24. Lydic R. State-dependent aspects of regulatory physiology. FASEB J 1: 6–15, 1987.[Abstract]
  25. Madsen PL, Linde R, Hasselbalch SG, Paulson OB, and Lassen NA. Activation-induced resetting of cerebral oxygen and glucose uptake in the rat. J Cereb Blood Flow Metab 18: 742–748, 1998.[CrossRef][ISI][Medline]
  26. Milic-Emili J and Grunstein MM. Drive and timing components of ventilation. Chest 70: 131–133, 1976.[Free Full Text]
  27. O'Donnell CP, Schaub CD, Haines AS, Berkowitz DE, Tankersley CG, Schwartz AR, and Smith PL. Leptin prevents respiratory depression in obesity. Am J Respir Crit Care Med 159: 1477–1484, 1999.[Abstract/Free Full Text]
  28. Orem J. Excitatory drive to the respiratory system in REM sleep. Sleep 19: S154–S156, 1996.[ISI][Medline]
  29. Orem J, Netick A, and Dement WC. Breathing during sleep and wakefulness in the cat. Respir Physiol 30: 265–289, 1977.[CrossRef][ISI][Medline]
  30. Polotsky VY, Wilson JA, Smaldone MC, Haines AS, Hurn PD, Tankersley CG, Smith PL, Schwartz AR, and O'Donnell CP. Female gender exacerbates respiratory depression in leptin-deficient obesity. Am J Respir Crit Care Med 164: 1470–1475, 2001.[Abstract/Free Full Text]
  31. Redline S, Tishler PV, Lewitter FI, Tager IB, Munoz A, and Speizer FE. Assessment of genetic and nongenetic influences on pulmonary function. A twin study. Am Rev Respir Dis 135: 217–222, 1987.[ISI][Medline]
  32. Schaub CD, Tankersley C, Schwartz AR, Smith PL, Robotham JL, and O'Donnell CP. Effect of sleep/wake state on arterial blood pressure in genetically identical mice. J Appl Physiol 85: 366–371, 1998.[Abstract/Free Full Text]
  33. Seifert EL and Mortola JP. The circadian pattern of breathing in conscious adult rats. Respir Physiol 129: 297–305, 2002.[CrossRef][ISI][Medline]
  34. Seifert EL and Mortola JP. Circadian pattern of ventilation during acute and chronic hypercapnia in conscious adult rats. Am J Physiol Regul Integr Comp Physiol 282: R244–R251, 2002.[Abstract/Free Full Text]
  35. Shea SA and Guz A. Personnalite ventilatoire–an overview. Respir Physiol 87: 275–291, 1992.[CrossRef][ISI][Medline]
  36. Shea SA, Horner RL, Benchetrit G, and Guz A. The persistence of a respiratory "personality" into stage IV sleep in man. Respir Physiol 80: 33–44, 1990.[CrossRef][ISI][Medline]
  37. Strohl KP, Gallaugher L, Freidman L, Gosenhauser I, Klann K, Price ER, Hill A, Singer J, Lander E, and Nadeau J. Sleep-Related Epilepsy in the Mouse. Washington, DC: Society for Neuroscience, 2003, p. 642–643.
  38. Subramanian S, Han F, Erokwu BO, Dick TE, and Strohl KP. Do genetic factors influence the Dejours phenomenon? Adv Exp Med Biol 499: 209–214, 2001.[ISI][Medline]
  39. Tafti M and Franken P. Invited review: genetic dissection of sleep. J Appl Physiol 92: 1339–1347, 2002.[Abstract/Free Full Text]
  40. Tagaito Y, Polotsky VY, Campen MJ, Wilson JA, Balbir A, Smith PL, Schwartz AR, and O'Donnell CP. A model of sleep-disordered breathing in the C57BL/6J mouse. J Appl Physiol 91: 2758–2766, 2001.[Abstract/Free Full Text]
  41. Tankersley CG. A genomic model for differential hypoxic ventilatory responses. Adv Exp Med Biol 475: 75–85, 2000.[ISI][Medline]
  42. Tankersley CG, DiSilvestre DA, Jedlicka AE, Wilkins HM, and Zhang L. Differential inspiratory timing is genetically linked to mouse chromosome 3. J Appl Physiol 85: 360–365, 1998.[Abstract/Free Full Text]
  43. Tankersley CG, Fitzgerald RS, and Kleeberger SR. Differential control of ventilation among inbred strains of mice. Am J Physiol Regul Integr Comp Physiol 267: R1371–R1377, 1994.[Abstract/Free Full Text]
  44. Tankersley CG, Fitzgerald RS, Levitt RC, Mitzner WA, Ewart SL, and Kleeberger SR. Genetic control of differential baseline breathing pattern. J Appl Physiol 82: 874–881, 1997.[Abstract/Free Full Text]
  45. Tankersley CG, Fitzgerald RS, Mitzner WA, and Kleeberger SR. Hypercapnic ventilatory responses in mice differentially susceptible to acute ozone exposure. J Appl Physiol 75: 2613–2619, 1993.[Abstract/Free Full Text]
  46. Tankersley CG and Kleeberger SR. Ozone-induced inflammation and altered ventilation in genetically susceptible mice: a comparison of acute and subacute exposures. Toxicol Lett 72: 279–289, 1994.[CrossRef][ISI][Medline]
  47. Tankersley CG, Rabold R, and Mitzner W. Differential lung mechanics are genetically determined in inbred murine strains. J Appl Physiol 86: 1764–1769, 1999.[Abstract/Free Full Text]
  48. Tobin MJ, Chadha TS, Jenouri G, Birch SJ, Gazeroglu HB, and Sackner MA. Breathing patterns. 1. Normal subjects. Chest 84: 202–205, 1983.[Abstract/Free Full Text]
  49. Tobin MJ, Mador MJ, Guenther SM, Lodato RF, and Sackner MA. Variability of resting respiratory drive and timing in healthy subjects. J Appl Physiol 65: 309–317, 1988.[Abstract/Free Full Text]
  50. Trenchard D. Role of pulmonary stretch receptors during breathing in rabbits, cats and dogs. Respir Physiol 29: 231–246, 1977.[CrossRef][ISI][Medline]
  51. Welsh DK, Richardson GS, and Dement WC. A circadian rhythm of hippocampal theta activity in the mouse. Physiol Behav 35: 533–538, 1985.[CrossRef][Medline]
  52. Zoccoli G, Bach V, Cianci T, Lenzi P, and Franzini C. Brain blood flow and extracerebral carotid circulation during sleep in rat. Brain Res 641: 46–50, 1994.[CrossRef][ISI][Medline]



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