Inactivation of the central nucleus of the amygdala reduces the effect of punishment on cocaine self-administration in rats

Continued cocaine use despite the negative consequences is a hallmark of cocaine addiction. One such consequence is punishment, which is often used by society to curb cocaine use. Unfortunately, we know little about the mechanism involved in regulation by punishment of cocaine use. The fact that cocaine addicts continue to use cocaine despite potentially severe punishment suggests that the mechanism may be impaired. Such impairment is expected to critically contribute to compulsive cocaine use. This study was aimed at testing the hypothesis that the central nucleus of the amygdala (CeN) plays a critical role in such regulation. To this end, rats were trained to press a lever to self-administer cocaine under a chained schedule: a response on one lever (cocaine-seeking lever) led to access to the other lever (cocaine-taking lever), on which a response was reinforced by cocaine and cues. Thereafter, responses on the seeking lever were punished by footshock with a probability of 0.5. Cocaine self-administration (SA) was significantly suppressed by punishment in an intensity-dependent manner. Interestingly, rats trained with daily 6-h (extended access) but not 2-h (limited access) sessions showed resistance to the lower intensity of punishment. Inactivation of the CeN induced a robust anti-punishment effect in both groups. These data provided evidence that the CeN is a critical neural substrate involved in regulation by punishment of cocaine SA. Rats with a history of extended cocaine SA appeared to be less sensitive to punishment. The decreased sensitivity could result from the neuroplastic changes induced by extended cocaine SA in the CeN.