GONADAL HORMONE REGULATION OF NEURONAL-GLIAL INTERACTIONS IN THE DEVELOPING NEUROENDOCRINE HYPOTHALAMUS

Recent evidence indicates that, in addition to their well known effect s on neurons, gonadal steroids may exert part of their neural effects through astroglia. In adult female rats astroglia participate in the p hasic remodelling of synapses that takes place during the estrous cycl e in the arcuate nucleus of the hypothalamus under the influence of es tradiol. Astroglia also appear to be involved in the genesis of sex di fferences in synaptic connectivity. Gonadal steroids influence hypotha lamic astroglia differentiation in vitro and in vivo. In monolayer mix ed neuronal-glial cultures from fetal rat hypothalami, estradiol induc es a progressive differentiation of astrocytes from a flattened epithe lioid morphology to bipolar, radial and stellate shapes. This effect o f estradiol on astroglia is dependent on the expression of specific mo lecules on the neuronal surface, such as the polysialic acid-rich form of the neural cell adhesion molecule. In the rat arcuate nucleus in s itu, perinatal androgen influences astroglia gene expression and diffe rentiation, resulting in a sex difference in astroglia organization by postnatal day 20. By this day, the amount of neuronal surface covered by astroglial processes is higher in males than in females. This diff erence in the coverage of neuronal surface by astroglia may be directl y related to the reduced number of synaptic contacts that is establish ed on the soma of male neurons compared to females.