Cholinergic-Dependent Metaplasticity in the Amygdala-Insula Pathway During Incubation of Cocaine Craving.

The time-dependent increase in drug seeking during abstinence, termed 'incubation of craving' is believed to play a major role in the persistent risks of relapse. This phenomenon is associated with synaptic plasticity changes across brain structures involved in reward processing, executive functions, emotion regulation and inhibitory control. The basolateral amygdala (BLA) and the anterior insular cortex (aIC) are two interconnected structures involved in processing internal and external drug-related cues and are known to play a role in drug craving. However, whether chronic cocaine alters synaptic plasticity within the BLA-aIC circuit and how these changes evolve during abstinence remains unclear. Here, using cocaine self-administration and in vivo electrophysiological recordings in anesthetized male rats, we demonstrate that, while long-term potentiation in the BLA-aIC pathway remains intact, long-term depression is disrupted throughout abstinence in both cocaine- and sucrose-rats, indicating a persistent impairment in synaptic weakening mechanisms. Importantly, a loss of depotentiation was observed after late but not early abstinence, and was specific to cocaine self-administration, identifying it as a hallmark of incubation of craving. Systemic, but not local intra-aIC, blockade of muscarinic receptors with atropine restored depotentiation and reduced cocaine-seeking behavior. Finally, qPCR analysis revealed region-specific transcriptional adaptations, with upregulation of muscarinic, NMDA and AMPA receptor transcripts in the BLA and a selective decrease of Grin2a in the aIC. Together, these findings point to cholinergic regulation of BLA-aIC metaplasticity as a candidate mechanism underlying incubation of cocaine craving.