EFFECT OF ELECTRICAL-STIMULATION OF THE CEREBRAL-CORTEX ON THE EXPRESSION OF THE FOS PROTEIN IN THE BASAL GANGLIA

The protein Fos is a transcription factor which is quickly induced in response to a variety of extracellular signals. Since this protein is expressed in a variety of neuronal systems in response to activation o f synaptic afferents, it has been suggested that it might contribute t o activity-dependent plasticity in neural networks. The present study investigated the effect of cortical electrical stimulation on the expr ession of Fos in the basal ganglia in the rat, a group of structures t hat participate in sensorimotor learning. Results show that the repeti tive application of electrical shocks in restricted areas of the cereb ral cortex induces an expression of Fos mostly confined to the striatu m and the subthalamic nucleus. The induction which can be elicited fro m different cortical areas (sensorimotor, auditory and limbic areas) d oes not require particular temporal patterns of stimulation but rather depends on the total number of shocks delivered during a given period of time. Moreover, it appears to be rather independent of the number of spikes discharged by the activated cells. In the striatum, the dist ribution of immunoreactive neurons is precisely delineated and conform s to the known topographical organization of stimulated corticostriata l projections. As demonstrated using a variety of double labelling tec hniques (combination of the immunocytochemical detection of Fos with t he autoradiography of mu opioid receptors, calbindin immmunocytochemis try, in situ hybridization of preproenkephalin and preprotachykinin A messenger RNAs), striatal neurons which express Fos are mostly localiz ed in the matrix compartment and concern equally enkephaline and subst ance P containing efferent neurons. In the subthalamic nucleus, Fos ex pression evoked by cortical stimulation is also confined to discrete r egions of the nucleus, the localizations corresponding to the primary projection site of the stimulated cortical cells. These results indica te that in addition to its phasic synaptic influence on the basal gang lia, the cerebral cortex could exert a long-term effect on the functio nal state of this system via a genomic control. Since the basal gangli a are involved in sensorimotor learning and motor habit formation, it is tempting to speculate that the activity-dependent Fos induction at corticostriatal and subthalamic synapses may contribute to consolidate the functionality of the neuronal networks activated during the compl etion of given motor tasks. (C) 1997 IBRO. Published by Elsevier Scien ce Ltd.