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Cocaine- and Amphetamine-Regulated Transcript Peptide in the Rat Epididymis: An Immunohistochemical and Electrophysiological Study¹

^a Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614 ^b Department of Physiology, Hong Kong Chinese University, Shatin, Hong Kong ^c Phoenix Pharmaceuticals, Inc., Mountain View, California 94043

ABSTRACT

Cocaine- and amphetamine-regulated transcript (CART) is a novel family of peptides, of which CART peptide fragments 55–102 and 62–102 are reported to be the endogenous, physiologically active peptides. Immunohistochemical studies with an antiserum directed against the CART peptide fragment 55–102 revealed CART-like immunoreactive (CART-LI) nerve fibers in the rat epididymis. The number was highest in the cauda epididymis and became progressively fewer toward the caput epididymis; the vas deferens exhibited an abundance of CART-LI fibers. Injection of the retrograde tracer Fluorogold (Fluorochrome, Inc., Englewood, CO) to the junction between the vas deferens and cauda epididymis labeled a large number of neurons in the major pelvic ganglion, some of which were CART-positive. Double-labeling the ganglion sections with tyrosine hydroxylase (TH) and CART antisera revealed that CART-LI and TH-LI were expressed in two distinct populations of ganglion cells. Some of the TH-LI cells in the ganglia, however, were covered with web-like CART-LI endings. The effects of CART peptide 55–102, referred to herein as CART, on anion secretion in the form of short circuit currents (Isc) were assessed in cultured epithelia. The CART (1 to 5 µM) applied to the basolateral or apical side of the cultured epithelia caused no significant responses on Isc, whereas lys-bradykinin (1 µM) produced a large Isc response in the same preparations. Our results show that CART-LI is present in a population of rat pelvic ganglion cells, which may give rise to CART-LI nerve fibers as observed in the vas deferens and the epididymis. The biological function of CART in the rat epididymis is not known, but it apparently is not involved in ion secretion across the epithelium.

FOOTNOTES

First decision: 25 May 2000.

¹ Supported by NIH grants NS18710 and NS39646 from the Department of Health and Human Services (NJD) and CUHK4293/99M from the Research Grant Council Hong Kong (P.Y.D.W.).

² Correspondence: Nae J. Dun, Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, P.O. Box 70577, Johnson City, TN 37614. FAX: 423 439 8773; dunnae{at}etsu.edu

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