Effects of Withdrawal from Cocaine Self-Administration on Rat Orbitofrontal Cortex Parvalbumin Neurons Expressing Cre recombinase : Sex-Dependent Changes in Neuronal Function and Unaltered Serotonin Signaling.

The orbitofrontal cortex (OFC) is a brain region involved in higher-order decision-making. Rodent studies show that cocaine self-administration (CSA) reduces OFC contribution to goal-directed behavior and behavioral strategies to avoid drug intake. This change in OFC function persists for many weeks after cocaine withdrawal, suggesting involvement in the process of addiction. The mechanisms underlying impaired OFC function by cocaine are not well-understood. However, studies implicate altered OFC serotonin (5-HT) function in disrupted cognitive processes during addiction and other psychiatric disorders. Thus, it is hypothesized that cocaine impairment of OFC function involves changes in 5-HT signaling, and previous work shows that 5-HT and 5-HT receptor-mediated effects on OFC pyramidal neurons (PyNs) are impaired weeks after cocaine withdrawal. However, 5-HT effects on other contributors to OFC circuit function have not been fully investigated, including the parvalbumin-containing, fast-spiking interneurons (OFC), whose function is essential to normal OFC-mediated behavior. Here, 5-HT function in naive rats and those withdrawn from CSA were evaluated using a novel rat transgenic line in which the rat parvalbumin promoter drives Cre-recombinase expression to permit identification of OFC cells by fluorescent reporter protein expression. We find that whereas CSA altered basal synaptic and membrane properties of the OFC neurons in a sex-dependent manner, the effects of 5-HT on these cells were unchanged by CSA. These data suggest that the behavioral effects of dysregulated OFC 5-HT function caused by cocaine experience are primarily mediated by changes in 5-HT signaling at PyNs, and not at OFC neurons.Cocaine addiction involves the inability to change behavior having negative consequences and to adopt beneficial behaviors. The orbitofrontal cortex (OFC) is a brain region involved in this behavioral flexibility, and OFC function is impaired after cocaine use. Moreover, signaling by the neurotransmitter serotonin (5-HT) is impaired in OFC pyramidal neurons (PyNs) after cocaine. However, whether other types of neurons are affected by cocaine is unknown, and we asked whether changes occur in another class of OFC cells known as parvalbumin interneurons. We report that cocaine changed the activity of parvalbumin interneurons in a sex-dependent manner but did not alter 5-HT effects. This suggests that the effects of cocaine on 5-HT function in OFC involves PyNs and not parvalbumin interneurons.