Sources of presumptive glutamergic/aspartergic afferents to the rat ventral striatopallidal region

Abstract

The distribution of presumptive glutamergic and/or aspartergic neurons retrogradely labeled following injections of 3H-D-aspartate (3H-D-Asp) into the ventral striatopallidal region was compared with the distribution of neurons labeled by comparable injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP). The afferents labeled by 3H-D-Asp were a subset of those labeled by WGA-HRP. The major sources of afferents to the nucleus accumbens and olfactory tubercle that could be labeled by 3H-D-Asp were in the medial frontal and insular cortices; the olfactory cortex; the lateral, basolateral, and basomedial amygdaloid nuclei; and the midline nuclear complex of the thalamus. The corresponding afferents to the ventral pallidum arose in the central, medial, and basomedial amygdaloid nuclei and the midline thalamic nuclei. In addition, the nucleus of the lateral olfactory tract was moderately or heavily labeled by 3H-D-Asp injections into all three areas, and cells were labeled in the subiculum following injection in the anteromedial part of the nucleus accumbens. Conversely the ventral striatopallidal structures themselves were, at best, sparsely labeled by any of the 3H-D-Asp injections. Neurons in the substantia nigra, ventral tegmental area, dorsal raphe, and locus coeruleus were labeled by WGA-HRP but not by 3H-D-Asp, except for an occasional cell in the raphe. The results indicate that 3H-D-Asp is a specific retrograde tracer and suggest that there are widespread, presumably excitatory, glutamergic and/or aspartergic inputs to the ventral striatum and pallidum.