The medial preoptic and anterior hypothalamic regions of the rhesus monkey: cytoarchitectonic comparison with the human and evidence for sexual dimorphism.

Examination of thionin-stained sections through the hypothalamus of the rhesus monkey revealed nuclei that resemble the first, second and third interstitial nuclei of the anterior hypothalamus (INAH1-3) of the human. Volumetric analysis of these nuclei in a small sample of monkeys suggests that the nucleus that resembles INAH3 is larger in males than in females. INAH1-3 have each been reported to be larger in men than in women and each has been considered as a potential candidate for homology with the much-studied sexually dimorphic nucleus of the preoptic area (SDN-POA) of the rat. Positional and cytoarchitectonic criteria suggest that of these nuclei, INAH3 and its potential counterpart in the rhesus monkey are the best candidates for homology with the SDN-POA. While the criteria employed in the present study may be used to suggest homologies, they are not adequate to confirm them. Confirmation of the homologies suggested here must rely on other considerations such as connectivity, neurotransmitter and peptide content, and function. It is hoped that the present report will stimulate interest in further examinations of the rhesus hypothalamus that will test both the suggested homologies and the evidence for sexual dimorphism. Copyright 1998 Elsevier Science B.V.