Functional heterogeneity in dopamine release and in the expression of Fos-like proteins within the rat striatal complex

The dorsolateral striatum, and the core and shell of the nucleus accumbens are three major anatomical regions of the striatal complex. The shell is co nsidered as a part of the extended amygdala, and is involved in the control of motivation and reward. The core and the striatum are considered central to sensory motor integration. In this study we compared the responses of t hese three regions to mild stress and drugs of abuse by measuring extracell ular dopamine (DA) concentrations and Fos-like immunoreactivity (Fos-LI). T he results are summarrized as follows. (i) In unchallenged conditions, extr acellular DA concentrations were highest in the dorsolateral striatum and l owest in the core, whereas Fos-LI was highest in the shell and lowest in th e dorsolateral striatum. (ii) After challenges that increase DA by depolari zing DAergic neurons (injection stress or 2 mg/kg morphine), the shell pres ented the largest increase in DA levels and Fos-LI. (iii) After the adminis tration of a DA-uptake blocker (15 mg/kg cocaine), the percentage increase in DA was still largest in the shell. However, the absolute increase in DA and Fos-LI in the shell and the dorsolateral striatum were similar. (iv) Af ter a full D-1 agonist (SKF82958), Fos-LI was highest in the shell and lowe st in the dorsolateral striatum. In conclusion, the nucleus accumbens shell seems to be the area of the striatal complex most functionally reactive to stress and drugs of abuse. However, the dorsolateral striatum and the core appear functionally distinct, as for most of the parameters studied these two regions differed.