Calretinin immunoreactivity in the inferior lobe of the hypothalamus and associated nuclei of the firemouth cichlid, Thorichthys meeki

Abstract

The distribution of the calcium-binding protein calretinin (CR) was examined by an immunohistochemical method using specific antibodies. CR is involved in the visual system, and the inferior lobe of the hypothalamus represents a multisensory integration center in cichlids. The focus of the present study was to analyze the distribution of CR immunoreactivity in a cichlid fish, the firemouth cichlid, Thorichthys meeki, for the hypothalamic inferior lobe and for the torus lateralis, nucleus glomerulosus, nucleus posterior tuberis, and corpus mamillare as associated nuclei of the hypothalamus. CR-immunoreactive (CR-ir) cell bodies were visualized in the lateral and medial part of the diffuse nucleus of the inferior lobe, ventral portion of the central nucleus of the inferior lobe, torus lateralis, nucleus glomerulosus, and nucleus posterior tuberis. CR-ir fibers could be detected in the dorsal portion of the central nucleus of the inferior lobe and corpus mamillare. The strongest labeling of CR-ir neuropil was observed in the lateral part of the diffuse nucleus of the inferior lobe, outer zone of the periventricular nucleus of the inferior lobe, torus lateralis, nucleus glomerulosus, and nucleus posterior tuberis. CR is abundantly present in the inferior lobe of the hypothalamus and associated nuclei. The role of CR in highly active processes in the inferior lobe of cichlids will be discussed.