Prefrontal cortical manipulations alter the effects of intra-ventral striatal dopamine antagonists on fixed-interval performance in the rat

The nature of the functional relationships between areas of prefrontal cort ex and Ventral striatum remain undefined. This study was designed to examin e functional interactions between activity in two areas of prefrontal corte x, the prelimbic (PL) and agranular insular (AI) areas, and ventral striata l (VS) dopamine (DA) function. Interactions were assessed using a Fixed Int erval (FI) schedule of reinforcement shown previously in our laboratory to be modulated by VS DA function. The study compared changes in FI performanc e following intra-VS DA antagonist injections alone (SCH23390 + eticlopride ) to those observed when either saline or saline + lidocaine were injected into prefrontal cortex after the intra-VS DA antagonist injections. The int ra-VS DA antagonists alone decreased FI response rates and increased postre inforcement pause times at both dose combinations (1/0.1 and 3/0.3 mu g of SCH23390/eticlopride per side). Neither saline nor saline + lidocaine injec ted into the PL area of prefrontal cortex altered the effects of intra-VS D A antagonists on FI performance. Saline administration into the Al area of prefrontal cortex, however, eliminated the FI rate-decreasing effects of in tra-VS DA antagonists. The agent or mechanism of this effect, whether it be saline, the act of inserting the cannulae into the cortical tissue, or the act of injecting fluid into this tissue, is not clear. This effect of AI s aline was prevented by coadministration of lidocaine with saline into AI. T hese results, coupled with those from a previous experiment examining lesio n effects in PL and AI on FI performance (Evans SB, Cory-Slechta DA. The ef fects of temporary lesions of the insular and medial prefrontal cortex on f ixed-interval schedule-controlled behavior in the rat, Soc Neurosci Abstr 1 996;22(1):159) suggest that PL might exert a tonic influence on VS DA funct ion, since FI response rates gradually increase over a 2-week period follow ing lesions of PL. In contrast, AI, although not normally modulating FI per formance, can apparently influence VS DA function, possibly when alteration s in activity are invoked in AI. (C) 2000 Elsevier Science B.V. All rights reserved.