DIRECT SPINAL PROJECTIONS TO LIMBIC AND STRIATAL AREAS - ANTEROGRADE TRANSPORT STUDIES FROM THE UPPER CERVICAL SPINAL-CORD AND THE CERVICALENLARGEMENT IN SQUIRREL-MONKEY AND RAT

With the anterograde tracers Phaseolus vulgaris-leucoagglutinin (PHA-L ) and biotinylated dextranamine (BD), direct spinal connections from t he upper cervical spinal cord (UC; C1 and C2) and the cervical enlarge ment (CE; C5-T1) were demonstrated in various striatal and limbic nucl ei in both squirrel monkey and rat. Within each species and from each spinal level, the total number of terminals seen in the limbic and str iatal areas was approximately 50-80% of the number seen within the tha lamus. Labeled terminal structures were seen in the hypothalamic nucle i, ventral striatum, globus pallidus, amygdala, preoptic area, and sep tal nuclei. In both species, the number of labeled terminals in limbic and striatal regions was larger from UC than from CE, although the di stributions to each nucleus varied with the specific lamina injected. In both species and from both UC and CE, approximately one-half of the projections to striatal and limbic areas terminated in the hypothalam us. The only region that demonstrated a topographical organization was the globus pallidus, where terminals from the CE were located dorsome dially to those from the UC. In the rat, UC and CE injections into the lateral dorsal horn and pericentral laminae resulted in the largest n umber of limbic and striatal terminations. The proportion of ipsilater al terminations was greatest when the medial laminae in the UC or the lateral dorsal horn in the CE received injections. Analysis of the mor phology of these spinohypothalamic and spinotelencephalic terminals sh owed that, in the squirrel monkey, terminals from CE injections were l arger than terminals from UC injections; no such size difference was e vident in the rat. However, limbic and striatal terminals in the rat w ere generally larger than those in the squirrel monkey following injec tions into the UC or CE. The exact function of these direct spinal pro jections to various striatal and limbic areas in primates and in roden ts remains to be determined. These findings, however, support recent i maging studies that suggest that the limbic system plays an important role in the mediation of chronic pain, perhaps directly through these spinolimbic and spinostriatal pathways. (C) 1996 Wiley-Liss, Inc.