Intravenous cocaine, morphine, and amphetamine preferentially increase extracellular dopamine in the "shell" as compared with the "core" of the rat nucleus accumbens.

TLDR

The nucleus accumbens, a key target of drugs of abuse, contains anatomically and histochemically distinct shell and core subregions. This study examined how intravenous cocaine, amphetamine, and morphine alter extracellular dopamine in the shell versus core of the rat nucleus accumbens using microdialysis. Freely moving rats received doses known to support self‑administration while vertically implanted concentric microdialysis probes recorded dopamine levels. Morphine (0.2–0.4 mg/kg) and cocaine (0.5 mg/kg) selectively raised dopamine in the shell; higher cocaine (1.0 mg/kg) and low‑dose amphetamine (0.125 mg/kg) increased dopamine in both regions but more in the shell, whereas the highest amphetamine dose (0.25 mg/kg) raised dopamine equally, demonstrating a preferential shell effect at self‑administration doses.

Abstract

The nucleus accumbens is considered a critical target of the action of drugs of abuse. In this nucleus a "shell" and a "core" have been distinguished on the basis of anatomical and histochemical criteria. The present study investigated the effect in freely moving rats of intravenous cocaine, amphetamine, and morphine on extracellular dopamine concentrations in the nucleus accumbens shell and core by means of microdialysis with vertically implanted concentric probes. Doses selected were in the range of those known to sustain drug self-administration in rats. Morphine, at 0.2 and 0.4 mg/kg, and cocaine, at 0.5 mg/kg, increased extracellular dopamine selectivity in the shell. Higher doses of cocaine (1.0 mg/kg) and the lowest dose of amphetamine tested (0.125 mg/kg) increased extracellular dopamine both in the shell and in the core, but the effect was significantly more pronounced in the shell compared with the core. Only the highest dose of amphetamine (0.250 mg/kg) increased extracellular dopamine in the shell and in the core to a similar extent. The present results provide in vivo neurochemical evidence for a functional compartmentation within the nucleus accumbens and for a preferential effect of psychostimulants and morphine in the shell of the nucleus accumbens at doses known to sustain intravenous drug self-administration.