Neurochemical characterization of extrinsic nerves in myenteric ganglia of the guinea pig distal colon

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    Abstract

    Extrinsic nerves to the gut influence the absorption of water and electrolytes and expulsion of waste contents, largely via regulation of enteric neural circuits; they also contribute to control of blood flow. The distal colon is innervated by extrinsic sympathetic and parasympathetic efferent and spinal afferent neurons, via axons in colonic nerve trunks. In the present study, biotinamide tracing of colonic nerves was combined with immunohistochemical labeling for markers of sympathetic, parasympathetic, and spinal afferent neurons to quantify their relative contribution to the extrinsic innervation. Calcitonin gene-related peptide, vesicular acetylcholine transporter, and tyrosine hydroxylase, which selectively label spinal afferent, parasympathetic, and sympathetic axons, respectively, were detected immunohistochemically in 1±0.5% (n=7), 15±4.7% (n=6), and 24±4% (n=7) of biotinamide-labeled extrinsic axons in myenteric ganglia. Immunoreactivity for vasoactive intestinal polypeptide, nitric oxide synthase, somatostatin, and vesicular glutamate transporters 1 and 2 accounted for a combined maximum of 14% of biotinamide-labeled axons in myenteric ganglia. Thus, a maximum of 53% of biotinamide-labeled extrinsic axons in myenteric ganglia were labeled by antisera to one of these eight markers. Viscerofugal neurons were also labeled by biotinamide. They had distinct morphologies and spatial distributions that correlated closely with their immunoreactivity for nitric oxide synthase and choline acetyltransferase. As reported for the rectum, nearly half of all extrinsic nerve fibers to the distal colon lack the key immunohistochemical markers commonly used for their identification. Their abundance may therefore have been significantly underestimated in previous immunohistochemical studies.

    Original languageEnglish
    Pages (from-to)742-756
    Number of pages15
    JournalJournal of Comparative Neurology
    Volume523
    Issue number3
    DOIs
    Publication statusPublished - 2015

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