Expression of c-Fos Protein and Activity of NO Synthase in the Mesolimbic Dopaminergic Structures and Dorsolateral Striatum of Rats Realizing Operant Food-Procuring Reflexes

Abstract

We studied the quantitative distributions of c-Fos-immunopositive (Fos-ip) and NADPH-diaphorasereactive (NADPH-dr) neurons in the mesolimbic and nigrostriatal dopaminergic (DAE) midbrain structures (at levels −5.3 to −6.04 mm caudally from the bregma) and in the dorsolateral striatum (−1.4 to −2.56 mm from the bregma) of the rat brain. Measurements were performed on intact animals, those after 24 h-long food deprivation, and rats after repetitive realization of operant food-procuring reflexes (n = 4 in all the three groups). In rats realizing operant reflexes for 30–40 min each day during 12 days, the mean number of Fos-ip neurons within frontal sections of the lateral part of the substantia nigra (SNL) significantly (P < 0.05) exceeded that in control and starving animals at all the levels examined. Such exceedance was also observed within borders of the ventral tegmental area (VTA). In rats realizing operant reflexes, Fos-ip neurons were grouped bilaterally in the mediodorsal part of the dorsolateral striatum (CPu), while distribution of the labeled cells in control and starving animals was relatively even across the entire area of frontal sections of this structure. The intensity of c-Fos expression in the CPu after realization of operant reflexes observed at the levels from −1.4 to −2.56 caudally from the bregma was significantly (P < 0.05) smaller than that in control animals. Significant numbers of NADPH-dr neurons were found only in the SNL and CPu; the mean numbers of such neurons in the examined structures showed no considerable differences in animals of all experimental groups. Relatively specific patterns of c-Fos expression and NADPH-diaphorase activity in the SN, TA, CP, and also in the central amygdalar nuclei found after realizations of operant reflex movements by the animals confirm the existence of clear correlations between motor and motivational/affective phenomena in the subcortical structures involved in the performance of complex emotionally charged motor acts.