Presence of Vasoactive Intestinal Polypeptide‐Like Immunoreactivity in the Cholinergic Electromotor System of Torpedo marmorata

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Abstract
Vasoactive intestinal polypeptide (VIP)‐like immunoreactivity was detected in the cholinergic electromotor system of Torpedo marmorata using a combination of immunohistochemical assays, radioimmunoassay, and HPLC. The immunohistochemical assays revealed that the distribution of VIP‐like immunoreactivity in the electric lobes, electromotor nerves, and electric organ is comparable to that of the stable cholinergic synaptic vesicle marker vesicle‐specific proteoglycan. Ligation of the electromotor nerves caused a marked accumulation of VIP‐like immunoreactivity in the lobes (180%) and the proximal portions of the electromotor nerves (130%) and a decrease in the electric organ (‐50%), when measured by radioimmunoassay using synthetic VIP (porcine sequence) as the standard. VIP‐like immunoreactivity in extracts of electric lobes electromotor nerves, and electric organ was eluted from a semipreparative reverse‐phase HPLC column as a single peak with a retention time similar to that of porcine VIP. Rechromatography at higher resolution on an analytical column indicated diversity between the molecular forms of VIP‐like immunoreactivity extracted from electric lobe and electric organ, suggesting the possibility of posttranslational processing.