Since both the medial amygdala and paraventricular nucleus in the MH contain AVP-synthesizing neurons, and altered activity of amygdalar AVP as a consequence of stress or opiate withdrawal contributes to anxiety-like and drug-seeking behaviors [16, 30, 31], we examined the mRNA levels of AVP in these two brain regions and of its V1b receptor in the AP. In the Me/BLA, one-way ANOVA revealed a significant effect of the Group [F(2,23) = 8.96, p<0.01] (Fig. 3A). Newman-Keuls post hoc tests showed that the AVP mRNA level in the H-RI rats was significantly higher than that of L-RI rats (p<0.05) and that of NR rats (p<0.01). The presence of individual differences in groups created by median split was confirmed by a significant positive correlation between the Me/BLA AVP mRNA levels and foot shock-induced responding on the active lever during the stress induced reinstatement (r = 0.56, n = 20, p<0.05) (Fig. 3B). When the AVP mRNA levels were analyzed with heroin-induced lever responding in all heroin self-administration rats, no significant correlation was found (data not shown). No group differences in the AVP mRNA in the MH (Fig. 3A) or the V1b mRNA in the AP were found (Table 1).
