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Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire 03756-0001
Received 6 March 1997; accepted in final form 30 April 1997.
Cream, Carlos L., Aihua Li, and Eugene E. Nattie. RTN
TRH causes prolonged respiratory stimulation. J. Appl.
Physiol. 83(3): 792-799, 1997.
We injected
thyrotropin-releasing hormone (TRH; 10 nl; 0.25, 0.5, 1.0, or 10 mM),
its inactive free acid form (TRHOH; 1 mM), or a metabolite with low
TRH-receptor binding affinity, histidine-proline diketopiperazine (cHP;
1 mM), into the retrotrapezoid nucleus of anesthetized rats. Injection
location was verified by anatomic analysis. Lower doses (0.25-0.5
mM) significantly increased both the product of integrated phrenic
amplitude and frequency
(
Phr · f) and f for 20-30
min compared with artificial cerebrospinal fluid control injections. Higher doses (1.0-10 mM) produced greater and long-lasting
stimulation of
Phr · f,
Phr, and f and of blood pressure. This
stimulation reached values 150% of baseline and durations of 270 min
after a single injection. TRHOH (1 mM ) or cHP (1 mM) had no effect on
Phr but increased f, as did 1 mM TRH. We conclude
that TRH has a very powerful stimulatory effect in the retrotrapezoid
nucleus region on
Phr · f, with
the
Phr response seemingly specific for TRH
receptors. Similar responses of f to TRHOH and cHP suggest it may be
nonspecific.
control of breathing; ventrolateral medulla; thyrotropin-releasing hormone free acid; histidine-proline diketopiperazine; blood pressure; respiratory regulation; retrotrapezoid nucleus
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