ETHANOL ENHANCES MEDIAL AMYGDALOID INDUCED INHIBITION OF PREDATORY ATTACK BEHAVIOUR IN THE CAT: ROLE OF GABAA RECEPTORS IN THE LATERAL HYPOTHALAMUS

The present study tested the hypothesis that the suppressiveeffects of ethanol upon predatory attack behaviour in the catinvolve a pathway from the medial amygdala to the lateral hypothalamus,and that these suppressive effects are mediated by -aminobutyricacid (GABA_A receptors located in the lateral hypothalamus. Cannulaelectrodes were implanted into the lateral hypothalamus forelicitation of predatory attack behaviour and for microinjectionsof the GABA_A receptor antagonist, bicuculline. Monopolar stimulatingelectrodes were implanted into the medial amygdala from whichsubseizure levels of electrical stimulation suppressed predatoryattack behaviour. In the first phase of the study, we comparedresponse latencies for predatory attack behaviour followingsingle stimulation of the lateral hypothalamus alone with thosefollowing paired trials of dual stimulation of the medial amygdalaplus lateral hypothalamus. Dual stimulation significantly suppressedpredatory attack. In the second phase of the study, peripheralethanol administration (in doses of 0.01, 0.5 and 1.0 g/kg,i.p.) enhanced the suppressive effects of medial amygdaloidstimulation in a dose- and time-dependent manner in which peakeffects were obtained 60 min post-injection. In the third phaseof the study, bicuculline (0.15 nmol) was microinjected intothe lateral hypothalamus both prior to and following pairedtrials of dual stimulation. Drug infusion blocked the suppressiveeffects of medial amygdaloid stimulation upon predatory attackbehaviour elicited from the lateral hypothalamus, indicatingthe importance of GABA_A receptors in mediating this suppression.In the fourth phase of the study, bicuculline, microinjectedinto the lateral hypothalamus at the time when ethanol's effectswere maximal (i.e. 60–80 min post-ethanol administration),totally blocked the suppressive effects of medial amygdaloidstimulation as well as the enhancing effects of ethanol uponmedial amygdaloid suppression of this form of aggressive behaviour.In the last phase of the study, bicuculline (0.15 nmol) infusioninto the lateral hypothalamus significantly reduced the suppressiveeffects of ethanol (10g/kg, i.p.) upon predatory attack behaviourelicited from the lateral hypothalamus. These results supportthe hypothesis that ethanol's suppressive effects upon predatoryattack behaviour in the cat are mediated, at least in part,by GABA_A receptors in the lateral hypothalamus. The presentand recent findings in our laboratory support the view thatGABA_A receptors in the lateral hypothalamus are activated, inturn, by a GABAergic pathway which arises from the medial hypothalamuswhose neurons receive inputs from the medial amygdala.