Inactivation of the bed nucleus of the stria terminalis in an animal model of relapse: effects on conditioned cue-induced reinstatement and its enhancement by yohimbine

Abstract

Rationale: Drug-associated cues and stress increase craving and lead to greater risk of relapse in abstinent drug users. Animal models of reinstatement of drug seeking have been utilized to study the neural circuitry by which either drug-associated cues or stress exposure elicit drug seeking. Recent evidence has shown a strong enhancing effect of yohimbine stress on subsequent cue-elicited reinstatement; however, there has been no examination of the neural substrates of this interactive effect.

Objectives: The current study examined whether inactivation of the bed nucleus of the stria terminalis (BNST), an area previously implicated in stress activation of drug seeking, would affect reinstatement of cocaine seeking caused by conditioned cues, yohimbine stress, or the combination of these factors.

Methods: Male rats experienced daily IV cocaine self-administration, followed by extinction of lever responding in the absence of cocaine-paired cues. Reinstatement of responding was measured during presentation of cocaine-paired cues, following pretreatment with the pharmacological stressor, yohimbine (2.5 mg/kg, IP), or the combination of cues and yohimbine.

Results: All three conditions led to reinstatement of cocaine seeking, with the highest responding seen after the combination of cues and yohimbine. Reversible inactivation of the BNST using the gamma-aminobutyric acid receptor agonists, baclofen + muscimol, significantly reduced all three forms of reinstatement.

Conclusion: These results demonstrate a role for the BNST in cocaine seeking elicited by cocaine-paired cues, and suggest the BNST as a key mediator for the interaction of stress and cues for the reinstatement of cocaine seeking.

Fig. 1

a Schematic diagram illustrating placements of injection cannulae as confirmed through histology (modified from Paxinos and Watson 1997). Coronal sections depicted are −0.2 to −0.6 mm from bregma along the A/P coordinates. Placements are shown within (circles) or outside of (triangles) the BNST. Please note some overlap in placements. The majority of BNST placements were in the dorsomedial portions of the BNST, with a few placed in more ventral locations. b A representative photomicrograph of BNST placements

Fig. 2

Responses (mean±SEM) on the active (ACT) and inactive (INACT) levers during cocaine self-administration (left panel) and the last 7 days of extinction responding before reinstatement (right panel)

Fig. 3

Responses (mean±SEM) on the active (previously cocaine-paired) lever for the last day of extinction responding before testing (EXT), and following saline vehicle or baclofen–muscimol (B/M) infusions into the BNST for conditioned cue-induced reinstatement tests (CUE), yohimbine-induced reinstatement tests (YOH), and yohimbine+cue-induced reinstatement tests (CUE+YOH). Significant differences (Student–Newman–Keuls test) are indicated for reinstatement compared with extinction level responding (*p<0.05) or vehicle vs B/M (†p<0.05)

Fig. 4

Responses (mean±SEM) on the active (previously cocaine-paired) lever for the last day of extinction responding before testing (EXT), and following saline vehicle or baclofen-muscimol (B/M) infusions directed at the BNST for conditioned cue-induced reinstatement tests (CUE), yohimbine-induced reinstatement tests (YOH), and yohimbine+cue-induced reinstatement tests (CUE+YOH) in animals with cannulae located outside of the BNST. Significant differences (Student–Newman–Keuls test) are indicated for reinstatement compared with extinction level responding (*p<0.05)