Dissociating Motivational From Physiological Withdrawal in Alcohol Dependence: Role of Central Amygdala κ-Opioid Receptors

Abstract

Chronic intermittent alcohol vapor exposure leads to increased dynorphin (DYN) A-like peptide expression and heightened kappa-opioid receptor (KOR) signaling in the central nucleus of the amygdala (CeA) and these neuroadaptive responses differentiate alcohol-dependent from non-dependent phenotypes. Important for therapeutic development efforts is understanding the nature of the stimulus that drives dependence-like phenotypes such as escalated alcohol self-administration. Accordingly, the present study examined the impact of intra-CeA KOR antagonism on escalated operant alcohol self-administration and physiological withdrawal symptoms during acute withdrawal and protracted abstinence in rats previously exposed to chronic intermittent alcohol vapor. Following operant training, rats were implanted with intra-CeA guide cannula and exposed to long-term intermittent alcohol vapor exposure that resulted in escalated alcohol self-administration and elevated physiological withdrawal signs during acute withdrawal. Animals received intra-CeA infusions of the KOR antagonist nor-binaltorphimine (nor-BNI; 0, 2, 4, or 6 μg) prior to operant alcohol self-administration sessions and physiological withdrawal assessment during acute withdrawal and protracted abstinence. The results indicated that site-specific KOR antagonism in the CeA ameliorated escalated alcohol self-administration during both acute withdrawal and protracted abstinence test sessions, whereas KOR antagonism had no effect on physiological withdrawal scores at either time point. These results dissociate escalated alcohol self-administration from physiological withdrawal symptoms in relation to KOR signaling in the CeA and help clarify the nature of the stimulus that drives escalated alcohol self-administration during acute withdrawal and protracted abstinence.

Figure 1

Histological confirmation of infusion sites targeting the CeA. Filled circles: • denote correct cannulae placement, whereas an ‘X' indicates a nor-BNI-treated misplacement that was included in the negative control group. Note that for the sake of simplicity, the cannula sites depicted here show placements in only one hemisphere but are meant to reflect the bilateral locations of each cannula tip. Coronal sections taken from The Rat Brain in Stereotaxic Coordinates (Paxinos and Watson, 2005).

Figure 2

Mean (+SEM) alcohol self-administration following chronic intermittent alcohol vapor exposure (represented by the solid line). Animals were tested during acute withdrawal and received a single dose of nor-BNI (0, 2, 4, or 6 μg; n=5/6 per group). Following dependence induction during acute withdrawal, alcohol self-administration was significantly escalated (δ=P<0.001). Nor-BNI attenuated escalated alcohol self-administration (main effect of dose, *P<0.05; **P⩽0.01 when compared with vehicle). aCSF, artificial cerebrospinal fluid; Base, baseline; NC, negative control.

Figure 3

Mean (+SEM) total physiological withdrawal scores during acute withdrawal. Nor-BNI did not alter physiological withdrawal measures when compared with vehicle controls. NC, negative control.

Figure 4

Mean (+SEM) alcohol self-administration during protracted alcohol abstinence. Animals treated with nor-BNI (n=4–6/group) showed a dose-dependent reduction in escalated alcohol self-administration (main effect of dose, ^‡‡P<0.01; *P⩽0.05 and **P<0.01 when compared with vehicle).

Figure 5

Mean (+SEM) total physiological withdrawal scores during protracted abstinence. Nor-BNI did not alter physiological withdrawal measures when compared with vehicle controls.