Cytoarchitectural analysis of the quail preoptic area. Evidence for a sex‐related dimorphism in the medial preoptic nucleus

Abstract
Studies using the Nissl method on thick paraffin sections of the preoptic region of the Japanese quail hypothalamus reveal a complex cytoarchitecture with several differentiated nuclei. The most prominent nucleus is the medial preoptic nucleus whose staining and volume appear sexually dimorphic. A higher number of intensely stainable neurons are present in males than in females, probably reflecting different metabolic rates in the two sexes. The volume of the medial preoptic nucleus is also larger (40Z) in males than in females. Present results represent the first description of a sex‐related dimorphism in the hypothalamus of non‐mammalian vertebrates.