MODULATORY ROLE OF CATECHOLAMINES IN THE TRANSSYNAPTIC EXPRESSION OF C-FOS IN THE RAT MEDIAL PREFRONTAL CORTEX INDUCED BY DISINHIBITION OF THE MEDIODORSAL THALAMUS - A STUDY EMPLOYING MICRODIALYSIS AND IMMUNOHISTOCHEMISTRY

We studied the interaction of catecholaminergic and thalamic afferents of the medial prefrontal cortex (PFC) by analyzing the effects of cat echolamine depletion on thalamus-induced c-fos expression in the PFC o f freely moving rats. Thalamic projections to the PFC were pharmacolog ically activated by perfusing the GABA-A receptor antagonist bicuculli ne (0.03 mM or 0.1 mM) through a dialysis probe implanted into the med iodorsal thalamic nucleus. Bicuculline perfusion induced Fos-like immu noreactivity in the thalamic projection areas, including the PFC, and in the thalamic nuclei surrounding the dialysis probe. 6-Hydroxydopami ne lesions of the ventral tegmental area causing a 70-80% depletion of catecholamines in the PFC did not influence the increase in the numbe r of Fos-like immunoreactive nuclei in the prefrontal cortex in respon se to thalamic stimulation. However, densitometric image analysis reve aled that the intensity of Fos-like immunoreactivity in the PFC of les ioned rats perfused with 0.1 mM bicuculline was higher than in corresp ondingly treated controls. The behavioral activity to bicuculline perf usion, an increase of non-ambulatory activity (0.03 mM) followed by lo comotion and rearing (0.1 mM), was not changed in 6-hydroxydopamine-le sioned rats. It is suggested that the thalamically induced c-fos respo nse is directly mediated by excitatory, presumably glutamatergic, tran smission and not indirectly by an activation of catecholaminergic affe rents of the PFC. The increase in the intensity of Fos-like immunostai ning in strongly stimulated, catecholamine-depleted rats suggests that catecholamines modulate the degree to which thalamic activity can act ivate the PFC of awake animals. (C) 1997 Elsevier Science B.V.