Hypothermic effect of GABA in conscious restrained rats and its modification by monoaminergic blocking drugs.

Gamma-aminobutyric acid (GABA) was injected intraperitoneally (i.p.) in conscious restrained rats and the effects on core temperature were observed. GABA (250-1000 mg/kg) produced a dose-dependent decrease in core temperature at an ambient temperature of 22 +/- 1 degree C. GABA-induced hypothermia (1000 mg/kg) was attenuated by pretreatment with reserpine (2 mg/kg, i.p.), p-chloro-phenyl-alanine (300 mg/kg, i.p.), yohimbine (0.25 mg/kg, i.p.) or methysergide (2.5 mg/kg, i.p.). Neither alpha-methyl-p-tyrosine (200 mg/kg, i.p.), nor phenoxybenzamine (5 mg/kg, i.p.), nor pimozide (0.5 mg/kg i.p.) antagonized GABA-induced hypothermia. Pretreatment with either propranolol (10 mg/kg, i.p.) or bicuculline (3 mg/kg, i.p.) potentiated hypothermia induced by GABA. It is concluded that hypothermia produced by i.p. injection of GABA could be due to release of serotonin by activation of bicuculline-insensitive GABA receptors located on central serotonergic neurons.