The organization of somatosensory activity in dorsolateral striatum of the rat

Cortically driven immediate-early gene expression reflects modular influence of sensorimotor cortex on identified striatal neurons in the squirrel monkey

Current understanding of basal ganglia function emphasizes their involvement in the focal, context-dependent release of motor and cognitive circuits in the brainstem and frontal lobes. How such selective action can arise despite the existence of massively convergent inputs from the cerebral cortex is unknown. However, anatomical work has suggested that specificity could be achieved in corticostriatal circuits by modular patterns of convergent and divergent cortical inputs to striatal projection neurons. To test for such modular activation of striatal neurons, we electrically microstimulated physiologically identified sites in the primary somatosensory (SI) and primary motor (MI) cortex of the squirrel monkey. We compared the efferent fiber distributions anterogradely traced from these sites to the distributions of striatal neurons activated by microstimulation to express Fos- and Jun B-like immediate-early gene proteins. We show that the microstimulation of sensorimotor cortex induces Fos and Jun B expression in localized cell clusters in the putamen and that these clusters match the anatomical input fiber clusters (matrisomes). The modular activation of striatal neurons by sensorimotor cortex seems likely. Unexpectedly, >75% of the Fos-positive nuclei in densely labeled cell clusters were in enkephalin-immunoreactive neurons. This expression pattern suggests that the primate sensorimotor cortex exerts a differential influence on the enkephalinergic (indirect pathway) as opposed to the substance P/dynorphin (direct pathway) projection neurons of the putamen. The densely labeled clusters of Fos-labeled enkephalinergic neurons occurred within larger zones containing sparsely distributed Fos-labeled parvalbumin neurons. Moreover, when the cortical stimulation induced expression of Fos-like protein only in sparsely distributed neurons, almost every putamenal neuron expressing Fos was a parvalbumin-containing (GABAergic) interneuron. These patterns suggest a model in which the primate sensorimotor cortex can target parvalbumin-containing inhibitory interneurons, which in turn depress the remaining neuronal activity within and around matrisomes in a feed-forward manner until sufficient coherent cortical input can overcome the inhibition to influence selectively enkephalinergic projection neurons in the activated matrisomes. Tuning of cortical input by striatal interneurons thus may be an important mechanism by which broader anatomical connections are dynamically adjusted to achieve selective flow of information through the basal ganglia.

Effects of cerebral cortical and striatal lesions on autotomy following peripheral neurectomy in rats

Peripheral nerve lesions have been reported to produce deafferentation pain and persistent changes at various levels of the central nervous system. Using autotomy in rats following leg denervation, as a model for deafferentation pain, we studied the effect of various cerebral lesions on this abnormal behavior. Under deep anesthesia, rats were subjected either to massive hemidecortication or to subtotal hemispherectomy (involving parts of basal ganglia and limbic areas), which was followed 1 week later by a denervation of the ipsilateral or contralateral leg. Hemidecortication significantly delayed autotomy from 7.8 +/- 2.8 to 25.6 +/- 2.1 days without reducing its incidence, whereas hemispherectomy abolished the incidence of autotomy in the contralaterally denervated leg and delayed its onset from 7.8 +/- 2.8 to 34 +/- 6.1 days and decreased its incidence (from 100% to 60%) in the ipsilaterally denervated leg. Chemical lesions of the neostriatum produced similar effects on autotomy to those produced by hemispherectomy. Hemispherectomized and striatum-lesioned rats that failed to elicit autotomy in the contralaterally denervated leg were subjected after 7 weeks to denervation of the ipsilateral leg. Sixty to seventy percent of these rats showed autotomy and in half of them the attack was directed simultaneously to both legs. These results suggest an involvement of the cerebral cortex and a stronger contribution of subcortical structures (like striatum and limbic system) in the processing of nociceptive information.