Nicotine-induced Fos expression in the nucleus accumbens and the medial prefrontal cortex of the rat: role of nicotinic and NMDA receptors in the ventral tegmental area.

We have previously shown that the nicotine-induced dopamine release in the nucleus accumbens can be attenuated by local administration into the ventral tegmental area (VTA), of antagonists at nicotinic and N-methyl-D-aspartate (NMDA), but not alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors. In the present study, we investigated the role of nicotinic and NMDA receptors in the VTA for the expression of Fos-like immunoreactivity (FLI) in the shell and core of the nucleus accumbens and in the medial prefrontal cortex (mPFC) of the rat after acute nicotine administration. Systemically administered nicotine increased FLI in both the mPFC and the nucleus accumbens when compared to saline controls, although this effect was more pronounced, and reached statistical significance in the nucleus accumbens, especially in the core region. When mecamylamine was delivered by reverse dialysis into the VTA, the systemic nicotine-induced FLI was significantly attenuated in the nucleus accumbens. Similarly, the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP-5), infused locally in the VTA, also antagonized the nicotine-induced FLI in the nucleus accumbens. Neither mecamylamine nor AP-5 alone affected basal FLI levels in any of the structures studied. Local administration of nicotine in the VTA increased FLI in the nucleus accumbens but not in the mPFC. Since the nicotine-induced FLI is probably due to an increased dopamine release in both the nucleus accumbens and the mPFC, we conclude that FLI in the nucleus accumbens is mediated, to a large extent, through the activation of dopamine neurons via nicotinic and NMDA receptors in the VTA, whereas the nicotine-induced FLI in the mPFC is subjected to a differential control mechanism, tentatively involving nicotinic receptors at the terminal level of the mPFC-projecting dopamine neurons.