Medial preoptic sexual dimorphisms in the guinea pig. II. An investigation of medial preoptic neurogenesis.

Neurogenesis was studied in the medial preoptic area of the guinea pig by the method of tritiated thymidine autoradiography. Eight cytoarchitectonic divisions were examined, 4 of which display sexual dimorphism and 4 that do not. Neurogenesis in the nonsexually dimorphic divisions was found to end at embryonic day (E) 27, while in each of the sexually dimorphic divisions neurogenesis continued after this and persisted until at least E31 in the central compact and principal portions of the medial preoptic nucleus. Since the testes become active at E25 in the guinea pig (Resko, 1970), it is possible that gonadal secretions influence the proliferation and subsequent developmental processes of neurons destined for the sexually dimorphic nuclei.