Calcitonin gene-related peptide (CGRP) immunoreactive projections from the thalamus to the striatum and amygdala in the rat

The organization of calcitonin gene-related peptide-like immunoreactive (CGRPir) innervation of the amygdala and caudate-putamen in the rat was examined by using immunohistochemistry for CGRP combined with retrograde transport of the fluorescent dye fluoro-gold, as well as anterograde transport of Phaseoleus vulgaris leucoagglutinin (PHA-L). The lateral part of the central nucleus of the amygdala and the amygdalostriatal transition zone was densely innervated by CGRPir terminals at all anterior-posterior levels. More caudally, the lateral part of the caudate-putamen also had large numbers of CGRPir terminals. Injections of fluoro-gold into the amygdala and amygdalostriatal transition area followed by immunohistochemistry for CGRP revealed double-labeled neurons in the subparafascicular, lateral subparafascicular, and posterior intralaminar nuclei of the thalamus and peripeduncular nucleus. Injections into the caudate-putamen demonstrated double-labeled neurons in the more lateral parts of this same nuclear complex. PHA-L injections into the posterior thalamic nuclei from which the CGRPir projections arise confirmed the medial-to-lateral organization of the projections to the amygdala and striatum. The subparafascicular nucleus and the rostral portion of the lateral subparafascicular nucleus primarily projected to the medial amygdala and the amygdalostriatal transition area, while the more lateral cell groups, including the caudal part of the lateral parafascicular, posterior intralaminar, and peripeduncular nuclei projected to the lateral amygdala and the caudate-putamen. These CGRPir projections may be involved in mediating conditioned autonomic and behavioral responses to acoustic stimuli or somatosensory stimuli.