Substance P and calcitonin gene-related peptide intrinsic choroidal neurons in human choroidal whole-mounts

Abstract

To determine the presence in the human choroid of substance P (SP)-and calcitonin gene-related peptide (CGRP) positive intrinsic choroidal neurons (ICNs), choroidal whole-mounts were processed for indirect immunofluorescence. An antibody to a component of the neuronal cytoskeleton, neurofilament 200 kDa (NF-200), was combined with antibodies to SP and to CGRP (neuropeptides proper to the sensory nervous system). The human choroid possesses numerous SP(+) and CGRP(+) ICNs. These neurons were observed in the suprachoroid, both in isolation and forming microganglia. For both types of ICNs studied, neurons were more numerous in the temporal than in the nasal regions. In both locations, SP(+) and CGRP(+) ICNs were more abundant in the central choroid (the choroid underneath the macular area of the retina), with cell density diminishing outwards to the choroidal periphery. There were no appreciable differences between the two populations of ICNs studied in terms of size, morphology or immunostaining characteristics. In conclusion, given that peripheral sensory innervation could be involved in the regulation of both choroidal blood flow and vascular architecture, the SP(+) and CGRP(+) ICNs described for the first time in the present work may be involved in these mechanisms of vascular regulation.