The distribution and colocalization of neuropeptides in fish cardiac neurons
Abstract
Most if not all intracardiac nerve cell bodies in four species of teleost fish and a primitive air breathing fish contained immunoreactivity (IR) to vasoactive intestinal peptide (VIP). Intracardiac nerve cell bodies contained no other neuropeptide although galanin (GAL)-, substance P (SP)- and calcitonin gene-related peptide (CGRP)-IR were detected in cardiac axons. Varicose VIP-IR axons were observed in close association to the cardiac muscle in the sinus venosus and atrium, but not in the ventricle. Slightly less than half the total number of VIP-IR axons also contained colocalised GAL-IR. A smaller number of varicose axons containing colocalised SP- and CGRP-IR were also present in the sinus venous and atrium. In addition, a subpopulation of CGRP-IR axons present in the sinus venosus and atrium did not contain SP-IR. SP-IR axons lacking CGRP-IR formed boutons around the axon hillock and soma of the majority of VIP-IR nerve cell bodies. Associated with a small number of VIP/-ganglion cells were VIP/- boutons. No neuropeptides were observed in the ventricle of any species of fish studied here. These results suggest that a VIP-like peptide is localised in the cholinergic postganglionic parasympathetic neurons. Associated with ...Continue Reading
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