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Department of Physiology, University of Kentucky, Lexington, Kentucky 40536
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
ACKNOWLEDGEMENTS
FOOTNOTES
REFERENCES
ABSTRACT 
Xu, Fadi, and Donald T. Frazier. Respiratory-related
neurons of the fastigial nucleus in response to chemical and mechanical challenges. J. Appl. Physiol. 82(4):
1177-1184, 1997.
Responses of cerebellar respiratory-related
neurons (CRRNs) within the rostral fastigial nucleus and the phrenic
neurogram to activation of respiratory mechano- and chemoreceptors were
recorded in anesthetized, paralyzed, and ventilated cats. Respiratory
challenges included the following: 1) cessation of the ventilator for a
single breath at the end of inspiration (lung inflation) or at
functional residual capacity, 2)
cessation of the ventilator for multiple breaths, and
3) exposure to hypercapnia. Nineteen
CRRNs having spontaneous activity during control conditions were
characterized as either independent (basic, n = 14) or dependent (pump,
n = 5) on the ventilator movement. Thirteen recruited CRRNs showed no respiratory-related activity until
breathing was stressed. Burst durations of expiratory CRRNs were
prolonged by sustained lung inflation but were inhibited when the
volume was sustained at functional residual capacity; it was vice versa
for inspiratory CRRNs. Multiple-breath cessation of the ventilator and
hypercapnia significantly increased the firing rate and/or
burst duration concomitant with changes noted in the phrenic neurogram.
We conclude that CRRNs respond to respiratory inputs from
CO2 chemo- and pulmonary
mechanoreceptors in the absence of skeletal muscle contraction.
respiratory control; cerebellum; hypercapnia; lung inflation; movement of skeletal muscles
INTRODUCTION THE RELATIVE IMPORTANCE of the cerebellum in the
regulation of responses to respiratory challenges has received previous
attention. Partial or whole ablation of the cerebellum
significantly attenuated the ventilatory responses to hypercapnia or
hypoxia in cats and dogs, primarily by reduction of respiratory
frequency (14, 22, 23). In vagotomized cats, cerebellectomy inhibited
the diaphragmatic response to inspiratory tracheal occlusion, and this
inhibition was significantly diminished by spinal cord dorsal
rhizotomies at C3-7 (6, 24).
Cerebellar respiratory-related neurons (CRRNs) have been reported in
the cerebellum of the carp (1) and, more specifically, in the rostral
fastigial nucleus (FNr) of spontaneously breathing cats (7, 11). With
use of extracellular recording, investigators (11) observed that units
in the FNr with spontaneous phasic activity correlated with the
respiratory rhythm. About one-half of the CRRNs were responsive to
intracarotid infusion of sodium cyanide and tracheal occlusion applied
for several breaths. These results suggest that the cerebellum (FNr) is
capable of modulating respiratory chemo- and mechanoreflexes. CRRNs can
be driven by activation of carotid body chemoreceptors and stimulation
of mechanoreceptors (respiratory muscle). However, questions still
remained as to whether CRRNs are responsive to activation of
CO2-sensitive chemoreceptors
and/or vagal pulmonary mechanoreceptors and whether
spontaneously active CRRNs depend on inputs emanating from contracting
respiratory and other skeletal muscles.
To examine these questions, anesthetized, paralyzed, and ventilated
cats were used to test CRRN and phrenic neurogram (PN) responses to
selective stimulation of pulmonary mechano- and
CO2 chemoreceptors. On the basis
of their phase relationship with the PN neurogram, 32 CRRNs were
classified as follows: basic (independent of ventilator movement), pump
(dependent on ventilator movement), and recruited (showed no
respiratory-related activity until breathing was stressed). With the
exception of pump CRRNs, the firing pattern of CRRNs was significantly
modulated during single-breath cessation of the ventilator at
end-inspiratory lung volumes [lung inflation (LI)] or at
functional residual capacity (FRC), multibreath (MB) cessation of the
ventilator, and inhalation of a hypercapnic gas mixture. The
characteristics of the responses of the CRRN were mirrored by
concomitant changes in the PN. Recruited CRRNs that were
either silent or displayed a tonic discharge pattern during control
developed phasic respiratory activity when respiratory challenges were
applied. The finding that the firing behavior of CRRNs could be altered
by hypercapnia and manipulation of vagal input in paralyzed cats
suggests that CRRNs in the FNr are capable of responding to and
integrating information from CO2
chemo- and pulmonary mechanoreceptors in the absence of skeletal
(respiratory) muscle contraction.
METHODS Eight adult cats of either gender were initially anesthetized with an
intraperitoneal injection of thiopental sodium (50 mg/kg), and the
anesthetic level was maintained with chloralose (40 mg/kg iv). To
prevent brain edema during surgery, 4 mg dexamethasone were injected
the day before and 2 mg on the day of the experiment. The left femoral
vein and artery were cannulated. The former was utilized for anesthetic
supplement and the latter for monitoring arterial blood pressure (ABP;
model P23AA, Statham) and periodic analysis of arterial blood gases
(1306 pH/blood-gas analyzer, Instrumentation Laboratory). Rectal
temperature was monitored continuously (model 73ATA, Yellow Springs
Instruments) and maintained at ~38°C via a heating pad and a
radiant-heat lamp.
A tracheotomy was performed below the larynx by blunt dissection.
Tracheal pressure (Ptr) was monitored via a differential pressure
transducer (model PM5T, Statham) attached to the cannulas. Animals were
subsequently paralyzed with gallamine triethiodide (4 mg/kg for
induction followed by continuous supplement of 4 mg · kg Animals were placed in a Kopf stereotaxic apparatus, and openings were
made in the occipital skull (detailed in Ref. 24). Bleeding was
controlled by bone wax and absorbable hemostat (Surgicel and/or
Gelfoam). The dura was removed, and the underlying tissue was covered with mineral oil.
The right C5 cervical phrenic
nerve rootlet was isolated via a dorsal approach and cut.
The central end of the nerve was mounted on a bipolar recording
electrode and then covered with petroleum jelly to prevent drying. Raw
signals of the PN were filtered (300-3,000 Hz) and amplified by
using a preamplifier (model P15, Grass Instruments) before being
displayed on a storage oscilloscope (model 5103n, Tektronix). The
amplified signals were in turn processed by an integrator with 100-ms
time constant (moving average; model MA-821RSP, Charles Woel
Enterprises) to obtain an integrated PN
(
1 · h1)
and artificially ventilated (model 55-0798, Harvard Apparatus). In the
spontaneously breathing animals, supplemental anesthesia was
administered as needed to suppress corneal and withdrawal reflexes.
After paralysis of the animal, supplemental anesthetic was administered
when irregularities were observed in ABP, heart rate, and respiratory
rate and pattern. To minimize movement of brain by
mechanical ventilation, a bilateral pneumothorax was created. The inlet
of the ventilator was controlled by a three-way valve so that the
animal was allowed to inhale room air (appropriate supplemental gas
mixture) or hypercapnic gas mixtures.
PN). Stereotaxic coordinates (15)
were used to position a tungsten microelectrode (~5 M
) in the
vicinity of the FNr. CRRN activity was electrically isolated and
amplified through a preamplifier (model P511K, Grass Instruments) and
displayed on the storage oscilloscope described above. Single units
were identified by using the criterion of spike-amplitude uniformity.
100 Torr, respectively). End-tidal
PCO2
(PETCO2) was continuously
monitored (model 78356A, Hewlett-Packard) and kept at ~35 Torr by
adjustment of the ventilator and the inhaled gas mixtures. Tidal volume
of the ventilator was usually adjusted at 
25 ml with a frequency 35
breaths/min to minimize inputs from afferents of the chest wall and
diaphragm. These ventilator parameters were kept constant before and during a given respiratory challenge.
When the neuronal baseline activity and/or PN became stable
under control conditions, the animal was randomly exposed to
1) cessation of the ventilator at
either LI or FRC for a single breath to manipulate the stimulation of
pulmonary mechanoreceptors; 2) cessation of the ventilator for MBs to initially manipulate the activity of pulmonary mechanoreceptors and, subsequently, the activity
of chemoreceptors because of developing hypercapnia and hypoxia; and
3) hypercapnic gases (7%
CO2-93%
O2) for ~1 min to activate
CO2 sensory receptors. The
intervals allowed for recovery after the stimulation were 10 breaths
for LI and FRC and 5 min for MBs and hypercapnia,
respectively. By utilizing the initial site as a
reference, the recording microelectrode was then moved to another tract
and the protocols repeated. ABP, Ptr, PN, PN, and
unit activity of CRRNs (inspiratory or expiratory) were continuously recorded on videotape via a pulse code modulation recording adaptor (model 3000A, Vetter Digital) and monitored by Grass polygraph (model
7D recorder) for later data analysis. After completion of
the experiment, the accuracy of the electrode placements was confirmed
by direct-current lesion (20 µA, 2 min).
The animals were killed by administration of additional anesthetic, and
the brain stem and the cerebellum were removed and placed in 10%
Formalin. After at least 3 days of immersion fixation, the brain stem
and the cerebellum were frozen, and 50-µm sections were cut and
mounted. The location of the marking lesions was drawn with camera
lucida.
Data analysis.
A window slope-height discriminator (model 74-60-1, Frederick Haer) was
used to electrically isolate the discharge of a single unit, and a
histogram of the integrated neural spike frequency was constructed from
an rate-interval monitor (model 74-40-5, Frederick Haer).
In general, time base settings in the rate mode were 5 Hz/0.2 s or 10 Hz/0.1 s. The level of the band-pass filter was adjusted to minimize
the background noise. To delineate the burst characteristics of neurons
and the PN with and without added respiratory challenges, the signals
were replayed onto a high-speed thermographic recorder (model TA2000,
Gould) in real time.
Inspiratory- or expiratory CRRNs were classified by identifying whether
the neuronal burst duration occurred primarily during the corresponding
phase of the PN. Neurons that displayed respiratory phasic activity
under control conditions (without respiratory challenges) were
subcatalogued as basic CRRNs, whereas neurons having respiratory phasic
activity that depended on either ventilator movement or respiratory
stress were listed as pump and recruited CRRNs, respectively. The
population of each group was expressed as percentage of all recorded
CRRNs. ABP, PETCO2,
end-tidal PO2
(PETO2), firing rate and
duration of CRRNs, inspiratory time
(TI) and expiratory time
(TE) (denoted on PN), and peak
of PN were recorded. The control values were
obtained by the average of the relevant variables of five breaths just
before application of respiratory stimuli. The responses were
determined by measuring respiratory variables of
1) the first inspiratory phase after
cessation of the ventilator at FRC,
2) the first expiratory phase after
cessation of the ventilator at LI, and
3) the maximum responses (both
inspiratory and expiratory phase) during application of MB cessation of
the ventilator and hypercapnia. One-way analysis of
variance with the Student-Newman-Keuls post hoc test was used to
identify significance of the differences among the three types of
neuronal firing patterns during control. The differences of the control
activity of the CRRNs and their responses to respiratory challenges
(LI, FRC, MB cessation of the ventilator, and hypercapnia) were
compared and examined by using the same statistics. All data are
presented as means ± SE. Significance was considered at
P < 0.05.
RESULTS
Thirty-two CRRNs were recorded, which included 15 inspiratory (basic = 5, recruited = 5, and pump = 5) and 17 expiratory (basic = 9 and
recruited = 8). Fourteen (44%) of these neurons displayed phasic
respiratory-related activity during control conditions and were
arbitrarily classified as basic neurons. Thirteen (41%) were initially
either silent or fired tonically during control but showed
phasic-related activity with respiratory challenges (recruited
neurons), and five (15%) were clearly driven by the ventilator (pump
neurons). The average firing rate of the CRRNs was 40.5 ± 5.1 Hz
with a range from 0 (recruited) to 110 Hz. Figure 1 illustrates the location of CRRNs and the
distribution of basic, recruited, and pump CRRNs (inspiratory and
expiratory neurons). For all data reported, the placement of the
recording electrode within the vicinity of the FNr was verified
histologically.
An example of a basic CRRN firing pattern is shown in Fig.
2. This unit displayed bursting behavior
under control conditions that was correlated with the expiratory phase
of the preceding PN activity. Five CRRNs displayed respiratory-related
phasic activity dependent on the pumping action of the ventilator. As
shown in Fig. 3, the discharges of a pump
CRRN was closely related to the volume changes precipitated by the
ventilator (see Ptr trace). When the ventilator was stopped the unit
was silent although the PN activity persisted. After MB cessation of
the ventilator, an immediate reappearance of the neuronal discharge was
coordinated with the ventilator but not associated with phrenic nerve
activities. The peak value of PN was enhanced
during MB cessation because sustaining the lung volume at FRC reduced the vagal inhibitory effect on inspiration.
PN), and tracheal pressure (Ptr) (similar to
those in Figs. 3, 4, 5, 6, 7, 8). This expiratory CRRN showed phasic discharge
that was clearly coordinated with silent period of phrenic nerve
activity. imp/sec, Impulses/s.
, Stimulation on; 
,
stimulation off.
Recruited CRRNs exhibited either tonic firing behavior
(n = 10) or no activity at all
(n = 3) under control conditions.
Their respiratory-related phasic activity did not emerge until
respiratory challenges were applied. Representative discharge patterns
of CRRNs exposed to respiratory challenges are presented in Figs. 4, 5, 6, 7, 8. Figure 4 shows an expiratory
phasic CRRN response to cessation of the ventilator at both LI and FRC
for a single breath. A sustained LI throughout expiration
resulted in a prolongation of the neuronal burst duration and the
expiratory phase of the PN. When
the lung volume was sustained at FRC, the expiratory neuronal firing
was inhibited but the inspiratory duration and amplitude of the
PN were increased. Table
1 summarizes the responses of CRRNs and
phrenic nerves to respiratory challenges. If the lung
volumes were sustained at FRC, firing rate and duration,
TI, and peak
PN of inspiratory CRRNs were significantly
increased (n = 5;
P < 0.05). However, with LI
(n = 2), burst durations of
inspiratory CRRNs during control conditions (2.3 and 2.2 s) were
dramatically shortened (0.8 and 0.7 s). In contrast, firing rate and
duration and TE of expiratory
CRRNs were dramatically prolonged (n = 7, P < 0.05) when LI was sustained
at the end of inspiration but were inhibited by sustained lung volumes
at FRC (n = 3).
, ventilator on; 
,
ventilator off) resulted in prolongation of neuronal burst duration (expiratory phasic CRRN) with concomitant change in expiratory duration of PN. With sustained deflation (functional residual capacity;
, on; , off) neuronal firing was inhibited, whereas PN
showed increase in inspiratory duration and augmentation of inspiratory
drive.
and .
, ventilator on; , ventilator
off).
, Stimulation on; stimulation off.
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A representative sample of a CRRN response to cessation of the ventilator for MBs is depicted in Fig. 5. The firing rate and burst duration of this expiratory basic CRRN did not show detectable changes in the initial breath but were gradually and dramatically elevated as the cessation period was extended, with these changes persisting for a few breaths after restoration of the artificial ventilation. This result suggests that the neuron was more sensitive to chemical drive (CO2 and/or O2) than to mechanical stimulation. In an attempt to differentiate responsiveness of CRRNs to CO2 chemoreceptors, hypercapnia was utilized to more directly stimulate CO2 chemoreceptors. The response of an inspiratory CRRN to hypercapnia is illustrated in Fig. 6. Compared with the control, the neuronal firing rate and burst duration were significantly increased during hypercapnia, in concert with similar effects noted on the PN.
Recruited CRRNs are defined as those neurons that were silent or displayed tonic activity during control conditions but were phasically modulated when the breathing was stressed. An example of a recruited-tonic CRRN is shown in Fig. 7. This expiratory CRRN displayed tonic discharge that was not correlated with the respiratory cycle during control conditions. However, respiratory-related phasic discharges emerged within the background of tonic discharges during MB cessation of the ventilator. An inspiratory recruited-silent CRRN is illustrated in Fig. 8. This neuron was silent during control, but respiratory-related phasic discharges appeared during MB cessation of the ventilator.
The group data of responses of CRRNs to cessation of the ventilator for
MBs and hypercapnia are listed in Table 1. MB cessation of the
ventilator increased firing rates (inspiratory and expiratory) and peak
values of PN of basic and recruited CRRNs, and it
prolonged neuronal and PN burst duration
(P < 0.05). Cessation of the
ventilator for MBs eliminated pump neuronal firing. Among 27 basic and
recruited CRRNs, 10 neurons failed to respond to single-breath
cessation, but 17 were responsive to both single-breath and MB
cessation of the ventilator. Successful recording of single units
throughout hypercapnic stimulation was made for 13 CRRNs. Hypercapnia
enhanced neuronal firing rate of 11 inspiratory and expiratory basic
and recruited CRRNs with no effect on the activity of two pump neurons.
Neurons that responded to hypercapnia also responded to MB cessation of
the ventilator (7 of which responded with single-breath cessation). In
addition, responses of CRRNs to respiratory challenges are
qualitatively similar to changes noted on the PN (inspiratory duration
and peak values of PN).
It should be noted that previous studies have reported large populations of neurons having a tonic firing pattern that was not associated with respiratory phase even with respiratory challenges (7, 11). In our paralyzed preparation, we encountered many neurons that displayed no detectable respiratory modulation with and without stressed breathing. Seven of them were recorded and showed no significant difference between control and MB cessation of the ventilator (29.1 ± 4.8 vs. 34.5 ± 6.3 Hz).
In the present study, LI and FRC, compared with control, did not significantly alter values of ABP (130 ± 11.0 vs. 135.5 ± 13.3 mmHg), PETCO2 (34.7 ± 1.6 vs. 33.8 ± 2.6 Torr), and PETO2 (97.8 ± 3.0 vs. 98.5 ± 2.6 Torr). However, ABP and PETCO2 values obtained in response to MB cessation of the ventilator (152.7 ± 5.8 mmHg and 44.2 ± 5.2 Torr, respectively) and to hypercapnia (155.6 ± 6.2 mmHg and 54.5 ± 5.8 Torr, respectively) were markedly increased (P < 0.05). With MB cessation of the ventilator, PETO2 values were reduced to 82.2 ± 3.2 Torr (P < 0.05), whereas during hypercapnia PETO2 elevated to the values >100 Torr.
DISCUSSION
Three types of respiratory-related neurons (basic, pump, and recruited) were found within the cerebellar fastigial nucleus with no apparent clustering. The firing behavior of these neurons was modulated by selective stimulation of vagal afferents. Manipulation of lung volume was used to vary vagal activity emanating from pulmonary mechanoreceptors. Potentially complicating effects of respiratory and skeletal muscles afferents on the CRRNs during sustained LI were minimized by muscle paralysis. For expiratory CRRNs, we observed that a sustained LI resulted in a prolongation of the burst duration with a concomitant increase in the interburst interval of the PN. Conversely, when the lung volume was sustained at FRC, the burst duration of the expiratory CRRNs was inhibited while the inspiratory duration and amplitude of the PN were increased. Responses of inspiratory CRRNs to these stimuli were just the opposite of those of expiratory CRRNs. Neurons possessing some of the firing characteristics of pump-type cells (4) were also encountered. These neurons fired when the lungs were inflated by the ventilator but were silent when inflation was withheld, suggesting dependency on vagal input (see Fig. 3). Our postulate that CRRNs neurons are involved in regulation of vagal-mediated respiratory responses is supported by other anatomic and functional data. First, projections from vagal afferents to the cerebellum and the FN have been documented. Hennemann and Rubia (8) recorded evoked potentials in lobes V and VI of the cerebellum when the cervical vagus was electrically stimulated. By injecting horseradish peroxidase into various parts of the cerebellar cortex and nuclei, Zheng et al. (25) demonstrated that there are direct projections from vagal nuclei to the FN in the cat. Second, functional interaction between the cerebellum and vagal afferents have also been reported to influence respiration. For example, cerebellectomy had little effect on inspiratory muscle response to inspiratory tracheal occlusion; however, cerebellectomy in concert with bilateral vagotomy significantly inhibited this response (24). In addition, removal of the cerebellum decreased inspiratory and expiratory duration, but these changes were no longer obtained if cerebellectomy was subsequently followed by bilateral vagotomy (18).
Another major finding was that firing rates of basic and recruited CRRNs were significantly increased when the animal was exposed to a hypercapnic gas mixture, suggesting that CRRNs receive and respond to information from CO2 chemoreceptors. Several lines of studies support cerebellar (FNr) contribution to respiratory responses to hypercapnia. Functional projections from central CO2 chemoreceptors to the cerebellum and its nuclei has been documented recently (9). By using c-fos as a marker to identify the chemoreceptors on medullary ventral surface of rats, James et al. (9) found that when these chemoreceptors were activated by acidic stimulation, c-fos-positive cells were detected in the brain stem as well as cerebellar nuclei. By utilizing whole or partial ablation, investigators have shown an important role of cerebellum and FNr in respiratory response to CO2 (12, 14, 21, 22). Mansfeld and Tyukody (12) described that cerebellectomy depressed the ventilatory response to inhalation of 10 and 20% CO2 in anesthetized dogs. With the same preparation, Sanapati et al. (14) observed that eupneic breathing and the ventilatory response to 4 or 6% CO2 were depressed after ablation of the anterior lobe of the cerebellum. Our laboratory (21, 22) reported that cerebellectomy or FNr lesions reduced the ventilatory response to progressive hypercapnia primarily by decreasing respiratory frequency. In addition, electrical stimulation of the FNr showed that phrenic nerve activity was dramatically altered in decerebrated or anesthetized cats (3, 10, 17). Combining these results with our data, we infer that CRRNs are able to integrate the information from CO2 chemoreceptors and pulmonary mechanoreceptors and in turn modulate the respiratory motor output.
All CRRNs recorded in our experiments responded to MB cessation of the ventilator, whereas 37% of them failed to respond to single-breath cessation of the ventilator (FRC or LI). These results show that CRRNs have differential responses to mechanical and chemical perturbations and thereby suggest that a more profound cerebellar involvement in chemo- rather than pulmonary mechanoreflexes. Indeed, investigators, using ablation of the cerebellum or the FNr, have demonstrated cerebellar (FNr) contributions to respiratory response to hypercapnia (12, 14, 21, 22) and hypoxia (11, 23). In contrast, with respect to respiratory mechanoreflexes, cerebellectomy failed to affect diaphragmatic activities evoked by application of inspiratory tracheal occlusion (24), although it altered electromyographic activity of the transversus abdominis muscle elicited by a continuous expiratory threshold load (19).
Interestingly, we found a population of neurons that show no respiratory-related activity (silent or tonic) during control conditions but display phasic respiratory-related activity with increasing respiratory challenges. This finding is in agreement with the acknowledged cerebellar role in the control of breathing; i.e., the cerebellum is involved in respiratory-stressed responses but is not critical for eupneic breathing. It is generally accepted that during eupneic breathing, cerebellectomy or FN lesions have little effect on minute ventilation, diaphragm electromyographic activity, and inspiratory activity of phrenic efferents in decerebrate (16) and anesthetized cats (22, 24).
We addressed the question as to whether the presence of CRRNs is dependent on the input from skeletal muscle contraction. The rationale was derived from the fact that recruited FN neurons (not related to respiration) have been recorded in the monkey that were silent until skeletal muscle voluntary movements occurred (2). In addition, firing patterns of cerebellar respiratory-movement-sensitive neurons in the carp were shown to be sensitive to mechanical loading of the buccal or the opercular system (1). Some CRRNs of spontaneously breathing cats have also been shown to respond to passive limb movement (11). Moreover, as described in the introduction, respiratory responses elicited by respiratory muscle voluntary contraction are modulated by the cerebellum (5, 6, 19, 24). Our results that paralysis of respiratory muscles or cessation of the ventilator (to eliminate passive movement of respiratory muscles) failed to abolish activity of CRRNs (except pump neurons) demonstrate that the phasic nature of these CRRNs does not depend on sensory feedback elicited by voluntary and/or passive movements of respiratory (skeletal) muscles.
In our experiment, the average value and the range of firing frequencies of CRRNs recorded during control conditions are very close to those previously reported in spontaneously breathing cats (28.8 ± 2.9 Hz with a range of 0-90 Hz, Ref. 11). The percentages of inspiratory and expiratory neurons recorded in the present study were 47 and 53%, respectively. These data show a little more balance between inspiratory and expiratory neurons than do those reported by Gruart and Maria (7), who found a predominance of expiratory CRRNs (76%). This difference of cell populations (inspiratory vs. expiratory CRRNs) may be due to the fact that our data were obtained in anesthetized and paralyzed cats, whereas theirs were collected in alert cats. Moreover, our recording region was localized in the FNr, but theirs included other cerebellar nuclei (interposed nuclei).
The amplitudes of the discharges of CRRNs recorded in this study could be varied continuously by moving the electrode tip over ~50 µm, suggesting that most of the recordings were related to somata rather than axons. Previous experiments involving electrical stimulation of the FNr also support neuronal involvement (20). After regional injection of kainic acid into the FN to destroy cell bodies (13), the respiratory responses to electrical stimulation previously observed in anesthetized cats were abolished.
In summary, three types of CRRNs were observed in this study, i.e., basic, recruited, and pump neurons. The presence of activity of basic and recruited CRRNs was not dependent on the inputs elicited by contraction of respiratory and other skeletal muscles. The responses of CRRNs to cessation of the ventilator for a single breath (either LI or FRC) or MBs and to hypercapnia mirrored changes noted in the PN. We found a population of recruited CRRNs that were either tonic or silent during control but developed respiratory-related phasic discharges when respiratory challenges were applied. We conclude that there are CRRNs that have a presence that is independent of inputs from respiratory and skeletal muscles. These CRRNs are capable of responding to and/or integrating information from CO2 chemoreceptors and vagal afferents (pulmonary mechanoreceptor). The appearance of recruited CRRNs supports the cerebellar involvement in respiratory control during stressed breathing.
ACKNOWLEDGEMENTS
The authors express their appreciation to members of the University of Kentucky Respiratory Group for helpful comments and critiques.
FOOTNOTES
Address for reprint requests: D. T. Frazier, Dept. of Physiology, Univ. of Kentucky, Lexington, KY 40536.
Received 2 May 1996; accepted in final form 18 November 1996.
REFERENCES
| 1. | Ballintijn, C. M., P. G. M. Luiten, and P. J. W. Jüch. Respiratory neuron activity in the mesencephalon, diencephalon and cerebellum of the carp. J. Comp. Physiol. 133: 131-139, 1979. . |
| 2. | Bava, A., R. Grimm, and D. S. Rushmer. Fastigial unit activity during voluntary movement in primates. Brain Res. 288: 371-374, 1983. [Medline] . |
| 3. |
Bradley, D. J.,
J. P. Pascoe,
J. F. R. Paton,
and
K. M. Spyer.
Cardiovascular and respiratory responses evoked from the posterior cerebellar cortex and fastigial nucleus in the cat.
J. Physiol. (Lond.)
393:
107-121,
1987.
|
| 4. |
Cohen, M. I.,
and
J. L. Feldman.
Discharge properties of dorsal medullary inspiratory neurons: relation to pulmonary afferent and phrenic efferent discharge.
J. Neurophysiol.
51:
753-776,
1984.
|
| 5. |
Farber, J. P.
Expiratory effect of cerebellar stimulation in developing opossums.
Am. J. Physiol.
252 (Regulatory Integrative Comp. Physiol. 21):
R1158-R1164,
1987.
|
| 6. |
Frazier, D. T.,
F. Xu,
R. Taylor,
and
L.-Y. Lee.
Respiratory load compensation. III. Role of the spinal cord afferents.
J. Appl. Physiol.
75:
682-687,
1993.
|
| 7. | Gruart, A., and J. Maria. Respiration-related neurons recorded in the deep cerebellar nuclei of the alert cat. Neuroreport 3: 365-368, 1992. [Medline] . |
| 8. | Hennemann, H. E., and F. J. Rubia. Vagal representation in the cerebellum of the cat. Pflügers Arch. 375: 119-123, 1978. [Medline] . |
| 9. | James, S. D., C. O. Trouth, R. M. Douglas, R. W. Durant, and J. S. Allard. Localization of C-fos in response to acidic stimulation of the ventrolateral medulla. Soc. Neurosci. Abstr. 21: 1882, 1995. . |
| 10. |
Lutherer, L. O.,
and
J. L. Williams.
Stimulating fastigial nucleus pressor region elicits patterned respiratory responses.
Am. J. Physiol.
250 (Regulatory Integrative Comp. Physiol. 19):
R418-R426,
1986.
|
| 11. | Lutherer, L. O., J. L. Williams, and S. J. Everse. Neurons of the rostral fastigial nucleus are responsive to cardiovascular and respiratory challenges. J. Auton. Nerv. Syst. 27: 101-112, 1989. [Medline] . |
| 12. | Mansfeld, G., and V. Tyukody. Atemzentrum und narkose. Arch. Int. Pharmacodyn. 54: 219, 1936. . |
| 13. | Matyja, E. Ultrastructural evaluation of the damage of postsynaptic elements after kainic acid injection into the rat neostriatum. J. Neurosci. Res. 15: 405-413, 1986. [Medline] . |
| 14. | Sanapati, J. M., S. K. Jain, B. Parida, A. Panda, and M. Fahim. The influence of cerebellum on carbon dioxide response in the dog. Jpn. J. Physiol. 40: 471-478, 1990. [Medline] . |
| 15. | Snider, R. S., and W. T. Niemer (Editors). A Stereotaxic Atlas of The Cat Brain. Chicago, IL: Univ. of Chicago Press, 1964. . |
| 16. | Speck, D. F., and C. L. Webber, Jr. Cerebellar influence on the termination of inspiration by intercostal nerve stimulation. Respir. Physiol. 47: 231-238, 1982. [Medline] . |
| 17. | Williams, J. L., S. J. Everse, and L. O. Lutherer. Stimulating fastigial nucleus alters central mechanisms regulating phrenic activity. Respir. Physiol. 76: 215-228, 1989. [Medline] . |
| 18. | Williams, J. L., P. J. Robinson, and L. O. Lutherer. Inhibitory effect of cerebellar lesions on respiration in the spontaneously breathing, anesthetized cat. Brain Res. 399: 224-231, 1986. [Medline] . |
| 19. |
Xu, F.,
and
D. T. Frazier.
Cerebellar role in the load-compensating response of expiratory muscle.
J. Appl. Physiol.
77:
1232-1238,
1994.
|
| 20. | Xu, F., and D. T. Frazier. Medullary respiratory neuronal activity modulated by stimulation of the fastigial nucleus of the cerebellum. Brain Res. 705: 53-64, 1995. [Medline] . |
| 21. | Xu, F., and D. T. Frazier. Role of the fastigial nucleus in respiratory response to hypoxia and hypercapnia (Abstract). FASEB J. 9: A427, 1995. . |
| 22. |
Xu, F.,
J. Owen,
and
D. T. Frazier.
Cerebellar modification of ventilatory response to progressive hypercapnia.
J. Appl. Physiol.
77:
1073-1080,
1994.
|
| 23. |
Xu, F.,
J. Owen,
and
D. T. Frazier.
Respiratory response to hypoxia attenuated by ablation of the cerebellum or fastigial nuclei.
J. Appl. Physiol.
79:
1181-1189,
1995.
|
| 24. |
Xu, F.,
R. F. Taylor,
L.-Y. Lee,
and
D. T. Frazier.
Respiratory load compensation. II. Cerebellar role.
J. Appl. Physiol.
75:
675-681,
1993.
|
| 25. | Zheng, Z., E. Dietrichs, and F. Walberg. Cerebellar afferent fibres from the dorsal motor vagal nucleus in the cat. Neurosci. Lett. 32: 113-118, 1982. [Medline] . |
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