Involvement of GABA in environmental temperature-induced change in body temperature.

Acute exposure of adult male albino rats (110-120 g) to higher environmental temperature (40 +/- 1 degrees C) increased body temperature (BT). This increase of BT was also dependent on the duration of exposure. Treatment with muscimol (1 mg/kg, i.p.), a GABA agonist, produced hypothermia at room temperature (28 +/- 1 degree C) and resistance to increase the body temperature when exposed to higher temperature (40 +/- 1 degree C). Administration of bicuculline (1 mg/kg, i.p.), a GABA antagonist, on the other hand, enhanced BT more than that observed in control (normal) rat exposed to higher temperature (40 +/- 1 degree C), although at room temperature bicuculline treatment did not show any effect on BT. Pretreatment with ethanolamine-O-sulfate (EOS) (2 g/kg, s.c.), a GABA transaminase inhibitor, to rats exposed to higher temperature increased BT as in control (normal) rat. Inhibition of central GAD activity with mercaptopropionic acid (MPA) (70 mg/kg, i.p.) produced resistance to increase BT during its period of action when rats were exposed to higher environmental temperature (28 +/- 1 degree C). These results thus suggest that central inhibitory neuron, GABA, plays a regulatory role in thermoregulation.