Stress-induced changes of central GABAergic function in rats

The effects of acute and repeated immobilization stress on central GABAergic function were examined in rats by evaluating the changes of the cardiovascular responses to intracerebroventricular injection of GABA. The depressor and bradycardia responses of GABA were attenuated significantly by immobilization stress for 6 h (from -5.5 +/- 0.7 kPa and -75 +/- 25 bpm to -2.3 +/- 0.9 kPa and -27 +/- 16 bpm respectively, for GABA 200 micrograms). These effects of stress were neither mimicked by administration of hydrocortisone, nor abolished by pretreatment with adrenalectomy or diazepam, but they were attenuated significantly by pretreatment with isoniazid. These results indicated that immobilization stress for long duration causes subsensitivity of central GABA receptors, in which the down-regulation mechanism may be involved.