Influence of glucocorticoids on dopaminergic transmission in the rat dorsolateral striatum

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Abstract
Glucocorticoid hormones exert strong influences on central neurotransmitter systems. In the present work, we examined the functional consequences of corticosterone suppression on the dopaminergic transmission in the dorsolateral striatum by studying the expression of Fos‐like proteins and extracellular dopamine levels. Glucocorticoid hormones were suppressed by adrenalectomy, and the specificity of the effects assessed by restoring physiological plasmatic corticosterone concentrations. We show that, in the dorsolateral striatum, glucocorticoids modify postsynaptic dopaminergic transmission. Suppression of glucocorticoids decreased the induction of Fos proteins in response to a direct agonist of dopamine D1 receptors (SKF 82958, 1.5 mg/kg, i.p.), but not the release of dopamine induced by morphine (2 mg/kg, s.c.) or the density of the limiting enzyme of dopamine synthesis, tyrosine hydroxylase. In contrast to the dopaminergic response to morphine, the response to cocaine (15 mg/kg, i.p.) was modified by the suppression of corticosterone. In this case, adrenalectomy increased cocaine‐induced changes in extracellular dopamine but did not modify the expression of Fos‐like proteins. This absence of changes in cocaine‐induced Fos‐like proteins might result from a compensatory mechanism between the increase in the dopaminergic response and the decrease in the functional activity of dopamine D1 receptors. The increased dopaminergic response to cocaine also contrasts with the decreased response previously observed in the shell of the nucleus accumbens [Barrot et al. (2000) Eur. J. Neurosci., 12, 973–979]. The present data highlight the profound heterogeneous influence of glucocorticoids within dopaminergic projections.

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