Lever Pressing and Nose Poking in the Rat Medial Prefrontal Cortex

Abstract

The rodent medial prefrontal cortex (mPFC) is thought to be associated with a wide range of cognitive functions such as memory and goal-directed behavior. It can be further separated into two subregions, the prelimbic (PL) and infralimbic (IL) cortices. Common techniques employed to investigate functions of the mPFC, such as learning to nose poke or lever press for reward, are assumed to be regulated by the same brain regions and thus utilized interchangeably in research. This study questions that assumption and hypothesizes that nose poking and lever pressing are different behaviors regulated by different subregions of the mPFC. By examining and comparing acquisition of the two operant behaviors in rats trained on a fixed-ratio 1 schedule to respond to sucrose delivery by nose poking and lever pressing, respectively, the study considers the innate learning differences between the two behaviors. The study also considers effects of PL DREADD inactivation on acquisition, extinction, and reinstatement of both actions. Though receptor expression was confirmed with immunohistochemistry, PL inactivation yielded no significant behavioral effects. Inherent learning differences between the two behaviors, however, were indicated by the disparity in the number of days rats spent acquiring the respective behaviors. Although preliminary, the results of the study suggest that a larger sample size and analysis of both subregions of the mPFC may help to elucidate the role of the mPFC in different learning behaviors.