Distribution of kappa opioid receptor-like immunoreactivity in guinea pig hippocampal formation

Abstract

The guinea pig hippocampal formation contains components of a functional kappa opioid system: prodynorphin-derived peptides and at least two distinct kappa receptor subtypes, kappa1 (k1) and kappa2 (k2) receptors 1,2. By autoradiography, k1 binding sites are present predominantly in the molecular layer of the dentate gyrus, while k2 binding appears moderately dense throughout the guinea pig hippocampual formation. However, precise localization of hippocampal kappa receptors has not been reported, although such a high-resolution localization is important to better understand hippocampal opioid systems. The purpose of the present study was to determine the ultrastructural localization of hippocampal kappa opioid receptors. To this end, we developed and characterized a novel antiserum against a peptide fragment of a cloned kappa receptor, and determined the light and electron microscopic localization of this kappa receptor-like immunoreactivity in guinea pig brain sections.