Effects of amphetamine and cocaine treatment on c-Fos, Jun-B, and Krox-24 expression in rats with intrastriatal dopaminergic grafts.

Activation of dopaminergic (DA) transmission by psychostimulants increases c-fos expression. d-Amphetamine-induced c-fos activation is reduced in the neostriatum deprived of DA afferents. Dopaminergic grafts implanted into the denervated neostriatum induce a c-fos hyperexpression when challenged with d-amphetamine, which is correlated with the exaggerated compensation of d-amphetamine-induced rotation. The aim of the present study was to test the generality of this phenomenon and the effects of DA grafts on the expression of three immediate early gene-coded proteins (c-Fos, Jun-B, Krox-24) following a challenge with either d-amphetamine or cocaine. c-fos basal expression was low in the neostriatum and was increased by the administration of psychostimulants. These effects were blocked by the DA lesion and restored by the DA grafts. A c-fos hyperexpression was observed within the grafted neostriatum, which was correlated with the compensation of d-amphetamine- or cocaine-induced rotation. Basal levels of Jun-B- and Krox-24-LI nuclei were high within the neostriatum. Administration of d-amphetamine or cocaine did not influence the expression of these IEG-coded proteins. Jun-B expression was not affected by the surgical procedure. In contrast, lesion of DA afferents of neostriatum decreased Krox-24 basal expression, an effect reversed by the grafts. Thus, the expression of c-fos but not Jun-B or Krox-24 appeared to be a good marker for the rotational behavior exhibited by DA-grafted rats challenged with drugs that increased DA transmission. This generalized c-fos overshoot indicates an abnormal activation of postsynaptic neurons by dopamine and points to its value as an indicator of the deleterious effects of DA grafts.