Calcitonin gene-related peptide-like immunoreactivity marks putative visceral sensory pathways in human brain

Calcitonin gene-related peptide serves as a neuromodulator in several ascending visceral sensory pathways from the parabrachial nucleus to the thalamus, amygdala and the visceral sensory cortex in rats, but these pathways have not been studied in primates. We have examined the distribution of calcitonin gene-related peptide-like immunoreactive innervation of the corresponding areas of the human brain, including the cortex, diencephalon and brainstem. We report the finding of three populations of calcitonin gene-related peptide-like immunoreactive cells that are homologous to those that have been characterized in the rat: the external lateral and external medial parabrachial subnuclei and the posterior intralaminar thalamic complex, including the subparafascicular, lateral subparafascicular and peripeduncular nuclei. In addition, scattered calcitonin gene-related peptide-like immunoreactive cells were found in the periventricular hypothalamus. Calcitonin gene-related peptide-like immunoreactive terminals were found in regions homologous to the projection areas of the external medial and external lateral parabrachial subnuclei in the rat, including the ventroposterior parvicellular nucleus of the thalamus, the central nucleus of the amygdala, the bed nucleus of the stria terminalis and the insular cortex; and in the terminal field of the posterior intralaminar thalamic complex, including the amygdalo-striatal transition region and the insular cortex. These results suggest that, similarly to other species, calcitonin gene-related peptide may also serve as a marker for ascending visceral sensory pathways in the human brain.