TRH microdialysis into the RTN of the conscious rat increases breathing, metabolism, and temperature.
Thyrotropin-releasing hormone (TRH) injected into the retrotrapezoid nucleus (RTN) of anesthetized rats produces a large, prolonged stimulation of ventilatory output (C. L. Cream, A. Li, and E. E. Nattie. J. Appl. Physiol. 83: 792-799, 1997). Here we inject or dialyze TRH into the RTN of conscious rats. In 6 of 17 injections (200 nl, 3.1 +/- 1.7 mM), ventilation (VE) increased 31% by 10 min, with recovery by 60 min. With dialysis, each animal of one group (n = 5) received, in random order, 10 mM TRH, 10 mM TRHOH (a metabolite of TRH), and artificial cerebrospinal fluid (aCSF); each animal of a second group (n = 5) received aCSF and 1 mM TRH. TRHOH and aCSF had no sustained effects. TRH (1 mM) increased VE (32%, P < 0.02, by 10 min, with recovery by 60 min), O(2) consumption (VO(2); 19%, P < 0. 03), and body (rectal) temperature (T(re); 0.5 degrees C, P < 0.09). TRH (10 mM) increased VE (78%, P < 0.01, by 10 min, with no recovery at 60 min), VO(2) (48%, P < 0.01), and T(re) (1.0 degrees C, P < 0. 01). TRH also induced arousal. The tissue volume affected in dialysis, estimated by spread of dialyzed fluorescein (332.3 mol wt, mol wt of TRH = 362.4), was 1,580 +/- 256 nl for 10 mM (n = 5) and 590 +/- 128 nl for 1 mM (n = 5). We conclude that 1) the RTN is involved in the integration of VE, VO(2), T(re), and arousal and 2) TRH may establish the responsiveness of RTN neurons.
Cream
C
C
Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire 03756-0001, USA.
Nattie
E
E
Li
A
A
D000818:Animals; D001143:Arousal; D001831:Body Temperature / Q000187:drug effects; D001933:Brain Stem / Q000166:cytology / Q000187:drug effects*; D002245:Carbon Dioxide / Q000378:metabolism; D002555:Cerebrospinal Fluid / Q000378:metabolism; D017551:Microdialysis; D010101:Oxygen Consumption / Q000187:drug effects; D010991:Plethysmography; D012123:Pulmonary Ventilation / Q000187:drug effects*; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D013990:Tidal Volume / Q000187:drug effects; D013997:Time Factors
D002245:Carbon Dioxide; D013973:Thyrotropin-Releasing Hormone