The influence of striatum on the substantia nigra: a study using the spreading depression technique.

Effects of changes in striatal neurone activity on substantia nigra (SN) unit activity were studied in rats. Striatal changes were produced by the spreading depression (STSD) induced by perfusing the head of striatum with 0.06 M KCl via a push-pull cannula. In the medial part (caudate) striatal neurones are silent, with the arrival of STSD they exhibit a brief excitation coinciding with the onset of a slow wave of depolarisation in the extracellular steady potential. In the lateral part (putamen) striatal neurones are active, they undergo an arrest of their spontaneous activity for about 1 minute following the brief excitation. Antidromic activation of SN reticulata (SNr) neurones was attempted from the superior colliculus (SC). The majority of the 54 SNr neurones (96%) exhibited changes in firing rate during STSD. Ten neurones underwent brief single or repetitive changes of the same duration as the brief striatal excitation. Eight presented an initial brief change of activity followed by a longer duration inverse change in firing rate. Eighteen exhibited multiple brief changes followed by or superimposed on a long lasting decrease of firing rate and 50% of them were nigrotectal neurones. Sixteen neurones presented long duration biphasic changes in firing rate. Two SNr neurones and the 12 substantia nigra compacta (SNc) neurones studied were unaffected. Some neurones received both inhibitory and facilitatory striatal controls. In total thirty-nine neurones were inhibited and 47 facilitated, the origin of these effects from caudate and putamen are discussed. The excitatory action may be due to either a direct excitatory pathway or to a relayed effect of the inhibitory GABAergic pathway.