OVERLAPPING CORTICOSTRIATAL PROJECTIONS FROM THE SUPPLEMENTARY MOTOR AREA AND THE PRIMARY MOTOR CORTEX IN THE MACAQUE MONKEY - AN ANTEROGRADE DOUBLE-LABELING STUDY

The purpose of the present study was to determine if the cortical effe rents from homologous body regions of the supplementary motor area (SM A) and the primary motor cortex (MI) project to separate or to overlap ping regions in the striatum. In order to investigate the dual cortico striatal projections, we employed an anterograde double labeling parad igm in which two tracers could be simultaneously detected in the same histological section. Prior to the injections, the forelimb representa tion in the two cortical motor areas was identified by using intracort ical microstimulation in four Japanese monkeys (Macaca fuscata). Multi ple injections of biotinylated dextran amine (BDA) were made into the forelimb regions of MI and wheatgerm agglutinin conjugated horseradish peroxidase (WGA-HRP) was injected into the arm region of the SMA. In additional animals, the tracers were reversed such that BDA was inject ed into the SMA and WGA-HRP was injected into the MI. The tissue was p rocessed sequentially using different chromogens in order to visualize both tracers in a single section. We analyzed the distribution of the ipsilateral anterograde label. The striatal labeling from each cortic al area basically consisted of a wide band of patchy dense labeling in terrupted by lighter labeling. The SMA striatal projections were locat ed mainly within the putamen, distributing from the level of the anter ior commissure to the most posterior extent of the putamen. At an inte rmediate level, the label spread obliquely from the ventrolateral edge of the putamen dorsomedially as far as the lateral edge of the caudat e nucleus. The label from the MI was observed in comparable portions o f the putamen, although the SMA projections were shifted more anterior and dorsomedial to the MI projections and the heaviest projections fr om the SMA and the MI were separately located. On the basis of the dou ble anterograde labeling technique, we found considerable overlap main ly in the central portion of the putamen from the SMA and MI forelimb representation. These results suggest that the homologous body regions of the SMA and MI send widespread, and substantially overlapping proj ections, to portions of the striatum. (C) 1996 Wiley-Liss, Inc.