NEURONAL RESPONSES IN PREFRONTAL CORTEX AND NUCLEUS-ACCUMBENS DURING HEROIN SELF-ADMINISTRATION IN FREELY MOVING RATS

Chronic multi-channel single unit recordings of neuronal responses in prefrontal cortex (NAC) and nucleus accumbens (NAc) were made in 9 mal e Sprague Dawley rats to determine patterns of neuronal activity durin g heroin self-administration. Up to 32 neurons were recorded simultane ously in these two brain regions while rats lever pressed on a continu ous reinforcement schedule for intravenous infusion of heroin (30 mu g /kg/infusion). The variety of neuronal responses observed before and a fter each self-administered heroin infusion can be classified accordin g to the following categories: (1) neurons that increased or (2) decre ased their activity immediately before the lever press; (3) neurons th at increased or (4) decreased their activity after the heroin infusion ; and, (5) neurons that did not alter their activity either before or after the lever press for heroin infusion. The majority (69% in the PE C and 65% in the NAc) of neurons sampled fell into this last category of no change, indicating that a selected fraction becomes active durin g this specific task. In general, NAc neurons displayed more post-hero in responses than PFC neurons while the proportion of neurons showing responses before the lever press was similar in the mPFC and the NAc. This initial description of the responses of PFC and NAc neurons durin g heroin self-administration suggests that the neuronal circuit of the mesocorticolimbic system is involved in heroin self-administration. T his circuit appears to contribute both to the initiation of drug-seeki ng behavior (pre-lever press phasic neuronal responses), as well as th e action of heroin infusion itself (post infusion phasic neuronal resp onses) by activation of different subsets of neurons.