FURTHER EVIDENCE THAT THE CENTRAL NUCLEUS OF THE AMYGDALA IS ASSOCIATED WITH THE ETHANOL-INDUCED LOCOMOTOR RESPONSE

The effect of ethanol on the number of Fos-like immunoreactive (Fos-li ) neurons was previously studied in the C57BL/6J (B6) and DBA/2J (D2) inbred mouse strains (Hitzemann and Hitzemann, Alcohol. Clin. Exp. Res . 21:1497-1507, 1997). The data obtained suggested that the locomotor activation response to ethanol found in the D2 but not the B6 strain w as associated with an increase in the number of Fos-li neurons (a puta tive measure of synaptic activity) in the central nucleus of the amygd ala (CeA), but not in other brain regions, including the basal ganglia . The current study was performed to obtain data supporting a role for the CeA in the locomotor response. B6D2 F-2 intercross animals were p henotyped for their locomotor response to ethanol (1.5 g/kg). The anim als from the extreme phenotypes (>1 SD from the mean) were denoted as very high and very low activity (HH, LL) and differed in their ethanol response by >91000 cm/15 min (baseline activity was similar in both p henotypes: 5,500 cm/15 min). These extremes especially differed from t he parental strains in that the LL group showed a significant ethanol- induced inhibition of activity. After 2 weeks, HH and LL animals were rechallenged with 1.5 g/kg of ethanol or saline and the number of Fos- li neurons determined 1 hr later. In the HH group, ethanol increased t he number of Fos-li neurons >600%, whereas in the LL group the increas e was 170% (difference: p < 0.001). The increase in the HH group was p rincipally located in the GABA neuron-rich lateral aspect of the CeA a nd not in the medial posterior-ventral division or the caps division. No significant difference was found between groups in the Fos response for the basolateral or lateral amygdala. Other brain regions were als o examined, including the basal ganglia, the hippocampus (CA1, CA3, an d dentate gyrus), the bed nucleus of the stria terminalis, and several cortical regions. In some regions (e.g., the bed nucleus), a signific ant ethanol effect was detected, but it did not differentiate the HH a nd LL groups. Overall, the data obtained further argue that the CeA ha s an important role in regulating the acute locomotor response to etha nol.