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

Abstract

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.

Estrogenic stimulation of neurite growth in midbrain dopaminergic neurons depends on cAMP/protein kinase A signalling

“…This includes differentiative events on the cellular level but also the formation of neural systems. By affecting neurogenesis (Byne and Bleier, 1987;Dodson et al, 1988), and by stimulating cell survival/death (Arai et al, 1996), neurite growth (Toran-Allerand, 1976; VanderHorst and Holstege, 1997), and synapse formation (Matsumoto and Arai, 1976;Garcia-Segura et al, 1989), as well as the maturation of functional properties of neurons (Arnold and Gorski, 1984;Raab et al, 1995a), the estrogenic environment appears to be instrumental in influencing the development of neural networks. Importantly, estrogen exposure of the developing brain is considered to be a prerequesite for the masculinization of brain structures and function resulting in sexual dimorphisms within the CNS (reviewed by Madeira and Lieberman, 1995;McEwen et al, 1997).…”

Medial preoptic sexual dimorphisms in the guinea pig. I. An investigation of their hormonal dependence

“…It is characterized and distinguished from its surround not only by its greater cell density, but also by its density of cells with steroid hormone receptors (Sar and Stumpf, 1975a, b;Sheridan et al, 1975;Stumpfet al, 1975;Warembourg, 1977) and by its patterns of neurogenesis. In the guinea pig the sexually dimorphic nuclei are the last nuclei in the medial preoptic region in which neuronal proliferation ceases, and they are the only nuclei in the region in which significant neuronal proliferation occurs after the onset of fetal gonadal activity (Byne et al, 1987). Thus, from the moment of their production, the developmental course of neurons destined for the sexually dimorphic nuclei may be influenced by sex differences in the levels of gonadal steroids.…”

Sex differences in cell migration in the preoptic area/anterior hypothalamus of mice

“…These mechanisms include; neurogenesis, cell migration, cell death, and cell specification. There has been little evidence for sex differences in neurogenesis (Jacobson and Gorski, 1981;Byne et al, 1987;Park et al, 1996). In the current study, we quantitatively analyzed data from animals exposed to BrdU on E14 and sacrificed 1-3 days later.…”

“…Other than determining their hormonal dependence, it has been more difficult to clarify the mechanisms by which these sex differences arise (reviewed in Tobet and Hanna, 1997). Four major mechanisms that have been examined include neurogenesis (Jacobson and Gorski, 1981;Byne et al, 1987;Park et al, 1996), cell migration (Jacobson et al, 1985;Park et al, 1996), cell death (Jacobson et al, 1985;Dodson and Gorski, 1993;Davis et al, 1996;Park et al, 1998), and phenotypic specification (Simerly et al, 1997;Park et al, 1997). Depending on the species, there may be some relative strength attributed to one mechanism more than another (e.g., phenotypic specification in ferrets) (Park et al, 1997), but without convincing generalizability across species.…”