Sexually dimorphic distribution of calcium-binding protein, calretinin in the preoptic area of the freshwater catfish, Clarias batrachus (Linn.)

Preoptic area (POA) plays an important role in the hormonal regulation of the pituitary gland in vertebrates. In this study we report the sexually dimorphic distribution of calcium-binding proteins calretinin (CR) in the POA in the freshwater catfish, Clarias batrachus. Nissl staining highlighted the presence of the nucleus praeopticus periventricularis (NPP) and other subdivisions of the nucleus praeopticus (NPO), including supraoptic (NPOs), paraventricular (NPOp) and magnocellular (NPOm) divisions. In NPO, CR immunoreactivity was noted only in females but not in males. In both sexes, CR stained perikarya were found in the NPP. Sexually dimorphic localization of CR in the POA supports the notion that CR may play a gender-specific role and may be involved in hormonal regulation in fishes.