The continued pairing of salient cues with drugs of abuse results in increased drug craving and relapse. Although cortical areas have been implicated in facilitating the learning of reward- predictive cues, the exact circuit mechanisms remain unclear. The insular cortex (IC) is an interesting target due to its role in processing cues associated with food availability as well as the delivery of drugs. Preliminary work reports an IC projection to the ventral bed nucleus of the stria terminalis (vBNST), a portion of the extended amygdala, acting as a relay station to integrate descending cortical inputs with limbic afferents. We hypothesize that reward-predictive cues activate IC projections that synapse onto projection neurons in the vBNST serving to activate the mesolimbic dopamine pathway resulting in acquisition of cue-reward association. I have observed that the IC sends a glutamatergic projection to the vBNST; and optogenetic stimulation of this pathway results in reward-related behavior in mice. My preliminary findings also demonstrate that administration of the dopamine receptor antagonist, cis-(Z)-flupenthixol dihydrochloride, significantly decreases reward-related behavior during IC-vBNST optical stimulation. Furthermore, IC-vBNST circuit silencing during the learning phase of a Pavlovian behavioral task resulted in decreased conditioned responding during cue presentation. These preliminary findings demonstrate the necessity of the IC-vBNST pathway in the association between reward and its predictive cues. Several experiments are proposed to further characterize the circuit utilizing ex-vivo slice eletrophysiology. We also plan to behaviorally disambiguate the value of the circuit in either the learning of reward-predictive cues or expression of behavior. Exploration of this pathway may uncover a critical circuit node involved in cue-induced reward seeking.
An addict's surrounding environment is littered with salient cues that may lead to intense drug craving making their transition to sobriety an uphill battle. The insular cortex provides a novel site for examining the acquisition of reward-predictive cues. My research will shed light on a projection from the insula to a prominent limbic area, the ventral bed nucleus of the stria terminalis, and establish the pathway as a potential therapeutic target for treatment in drug relapse.
