Yc. Han et al., ETHANOL ENHANCES MEDIAL AMYGDALOID INDUCED-INHIBITION OF PREDATORY ATTACK BEHAVIOR IN THE CAT - ROLE OF GABA(A) RECEPTORS IN THE LATERAL HYPOTHALAMUS, Alcohol and alcoholism, 32(6), 1997, pp. 657-670
The present study tested the hypothesis that the suppressive effects o
f ethanol upon predatory attack behaviour in the cat involve a pathway
from the medial amygdala to the lateral hypothalamus, and that these
suppressive effects are mediated by gamma-aminobutyric acid (GABA(A))
receptors located in the lateral hypothalamus. Cannula electrodes were
implanted into the lateral hypothalamus for elicitation of predatory
attack behaviour and for microinjections of the GABA(A) receptor antag
onist, bicuculline. Monopolar stimulating electrodes were implanted in
to the medial amygdala from which subseizure levels of electrical stim
ulation suppressed predatory aback behaviour. In the first phase of th
e study, we compared response latencies for predatory attack behaviour
following single stimulation of the lateral hypothalamus alone with t
hose following paired trials of dual stimulation of the medial amygdal
a plus lateral hypothalamus. Dual stimulation significantly suppressed
predatory attack. In the second phase of the study, peripheral ethano
l administration (in doses of 0.01, 0.5 and 1.0 g/kg, i.p.) enhanced t
he suppressive effects of medial amygdaloid stimulation in a dose-and
time-dependent manner in which peak effects were obtained 60 min post-
injection. In the third phase of the study, bicuculline (0.15 nmol) wa
s microinjected into the lateral hypothalamus both prior to and follow
ing paired trials of dual stimulation. Drug infusion blocked the suppr
essive effects of medial amygdaloid stimulation upon predatory attack
behaviour elicited from the lateral hypothalamus, indicating the impor
tance of GABA(A) receptors in mediating this suppression. In the fourt
h phase of the study, bicuculline, microinjected into the lateral hypo
thalamus at the time when ethanol's effects were maximal (i.e. 60-80 m
in post-ethanol administration), totally blocked the suppressive effec
ts of medial amygdaloid stimulation as well as the enhancing effects o
f ethanol upon medial amygdaloid suppression of this form of aggressiv
e behaviour. In the last phase of the study, bicuculline (0.15 nmol) i
nfusion into the lateral hypothalamus significantly reduced the suppre
ssive effects of ethanol (1.0 g/kg, i.p.) upon predatory attack behavi
our elicited from the lateral hypothalamus. These results support the
hypothesis that ethanol's suppressive effects upon predatory attack be
haviour in the cat are mediated, at least in pari, by GABA(A) receptor
s in the lateral hypothalamus. The present and recent findings in our
laboratory support the view that GABA(A) receptors in the lateral hypo
thalamus are activated, in turn, by a GABAergic pathway which arises f
rom the medial hypothalamus whose neurons receive inputs from the medi
al amygdala.