Infralimbic pyramidal neurons gate learned suppression of cocaine-conditioned behavior in male mice.

Infralimbic cortex (IL) pyramidal neurons (PNs) have been implicated in suppressing instrumental cocaine seeking, yet their causal contribution to Pavlovian extinction and subsequent retrieval remains unclear. Using CaMKIIα promoter-driven chemogenetics, we bidirectionally modulated IL PN activity across extinction training, extinction expression, and primed reinstatement in a cocaine-conditioned place preference (CPP) paradigm in male mice. Manipulating IL PN activity during the extinction phase did not alter the progressive reduction of CPP across intermediate probe sessions, suggesting no effects on the formation of extinction. In contrast, acute inhibition of IL PNs impaired extinction expression, whereas stimulation did not further enhance performance, indicating that extinction retrieval is dependent on a sufficient level of IL PN activity that is likely achieved under baseline conditions. During cocaine-primed reinstatement, acute inhibition of IL PNs exacerbated the recovery of conditioned responses, while stimulation was critical to prevent reinstatement, suggesting that IL-mediated behavioral suppression is sensitive to the motivational state. Although coordinated activity in IL projection targets, including the nucleus accumbens shell, the basolateral and central amygdala, and the lateral entorhinal cortex, was observed during extinction expression and reinstatement, this activity did not explain additional variance beyond IL PN activity. Together, these findings highlight IL PNs as a central node in the expression of Pavlovian extinction and in shaping vulnerability to cocaine-induced relapse-like behavior.