Anxiolytic-like effects induced by medial prefrontal cortex inhibition in rats submitted to the Vogel conflict test

Abstract

Conflicting results have been obtained in studies aimed at investigating the role of the ventral portion of the medial prefrontal cortex (vMPFC), which comprise the prelimbic cortex (PL) and infralimbic cortex (IL), on anxiety responses in rodents evoked by animal models such as fear conditioning, elevated plus maze or social interaction. This may reflect the use of different lesion techniques and/or experimental paradigms based on distinct behaviors properties. Among the latter, the Vogel punished-licking test has been widely used to measure anxiety. However, the role of the vMPFC on anxiety-like behavior evoked by the Vogel model has not been evaluated. Thus, the present study verified the effects of acute and reversible bilateral inhibition of the vMPFC on the behavioral responses in the Vogel conflict test. After 24 h of water deprivation, male Wistar rats were subjected to an initial 3-min non-punished (pretest) drinking session. After an additional 24-h period of water deprivation they were exposed to a 3-min punished-licking session (test).Bilateral microinjections of lidocaine 2% (200 nL) or CoCl(2) (1 mM/200 nL) into the PL or IL produced similar anticonflict effects, increasing the number of punished licks. No responses were observed when lidocaine 2% was microinjected into vMPFC surrounding structures such as the cingulate cortex area 1, the corpus callosum and the tenia tecta. In control experiments the drugs did not change the number of unpunished licks nor had any effect in the tail-flick test. The present results, therefore, indicate that the vMPFC is involved in the behavioral responses elicited by punished stimuli.