Caudate unit activity and somal diameters in intact and nigral lesioned cats

Spontaneous and evoked activity of the caudate neurons to central and peripheral stimuli after brain lesions

The involvement of the cerebral cortex, commissural fibers and thalamus on caudate-caudate relations was studied in locally anesthetized, paralysed and artificially ventilated cats. This type of experimental preparation was necessary since a complete suppression of spontaneous and evoked activity is produced by subanesthetic doses of general anesthesia. Two types of caudate action potentials were encountered on the basis of their waveform characteristics: biphasic and triphasic spikes, the former being the largest population (80%). These waveforms were independent of the microelectrode resistance and the distance to recorded neurons. However, their responses were very similar to both central and peripheral stimuli. Caudate stimulation depressed the spontaneous discharges of the majority of the responsive units recorded within the opposite nucleus, while striatal neurons were activated by stimulation of the contralateral cortex. Decortication, thalamic lesion (motor nuclei and massa intermedia) and section of the corpus callosum decrease the firing rates of caudate neurons with biphasic spikes, while the discharges of the neurons with triphasic action potentials remained unchanged. Bilateral ablation of the cerebral cortex decreased the responsiveness of striatal neurons to contralateral nucleus and sciatic nerve and reduced the number of spontaneously active cells per recording tract. Section of the commissural fibers also depressed the caudate responses to the contralateral nucleus, and to the opposite precruciate cortex, although thalamic lesion did not affect the responsiveness of caudate cells to both central and peripheral stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Central and peripheral modulation of spontaneous neuronal activity in the caudate nucleus

The modulatory action of the caudate on the neural activity of the contralateral nucleus was studied in locally anesthetized, paralysed and artificially ventilated cats. This type of preparation was necessary because of a complete suppression of spontaneous spike activity after subanesthetic doses of general anesthesia. Two types of caudate action potential were characterized according to their waveform: biphasic and triphasic spikes, with a predominance of the former. These waveforms appeared to be independent of recording distance; however, their responses were similar to both central and peripheral stimuli. Caudate stimulation modified the spontaneous activity of the majority of the single units recorded within the opposite nucleus. This effect was mainly inhibitory and keeps up certain somatotopic distribution in the rostrocaudal extent of the nucleus. Kainic lesion of the site of stimulation suppressed the responses in the contralateral caudate nucleus, whereas the responses to substantia nigra and precruciate cortex remained unaltered. On the other hand, stimulation of the precruciate cortex opposite to the recording sites always excited the caudate neurons. The responses evoked by stimulation of ipsilateral substantia nigra and of contralateral sciatic nerve followed a similar pattern to those elicited by caudate stimuli. These results suggest a mostly inhibitory effect of the caudate on neuronal activity within the opposite nucleus, which is reinforced by the action of central and peripheral somatosensory inputs.