Fenfluramine-induced c-fos in the striatum and hypothalamus: a tract-tracing study.

Systemic administration of DL-fenfluramine (20 mg kg-1), an indirect serotonergic agonist, induced widespread FOS-like protein in the rat caudate putamen (CPu), paraventricular nucleus (PVn) of the hypothalamus and several intralaminar thalamic nuclei. To ascertain whether the dopaminergic nigrostriatal system coordinated transcriptional effects on the CPu, discrete microinjections of dextran into the substantia nigra (cell group A9) were evaluated for retrograde axonal transport. The protein product was induced preferentially in medium-sized spiny nerve cells of the CPu. Dextran microinjections into the PVn demonstrated that perikarya bearing FOS-like protein projected their extensions directly to thalamic nuclei and indirectly to immunopositive neurons of the striatum. The significance of these latter results is discussed in terms of a possible dopaminergic mechanism.