Stem/progenitor cells in the developing human cerebellum: an immunohistochemical study.

The aim of this study was to analyze, by immunohistochemistry, the occurrence of stem/progenitor cells localized in the different niches of the developing human cerebellum. To this end, cerebellar samples were obtained from 3 fetuses and 3 newborns ranging, respectively, from 11 to 24 and from 30 to 38 weeks of gestation. Specimens were 10% formalin-fixed, routinely processed and paraffin-embedded; 3 µm-tick sections were immunostained with anti-SOX2 and PAX6 antibodies. Our study evidenced SOX2 and PAX6 immunoreactivity in precursors cells in all six developing human cerebella. SOX2 was expressed in precursors of different neural cell types, including Purkinje neurons, stellate cells, basket cells and Golgi cells. In the cerebellar cortex, SOX2 expression changed during gestation, being highly expressed from the 20th up to the 24th week, whereas at the 30th and at the 34th week SOX2 immunoreactivity was restricted to the Purkinje cell layer and the inner zone. Cerebellar human cortex was negative at the 38th week of gestation. PAX6 immunoreactivity was restricted to granule cell precursors in the external granule layer (EGL), being detected at all gestational ages. Our study indicates SOX2 and PAX6 as two useful markers of stem/progenitor cells that highlight the different germinative zones in the developing human cerebellum.

Sex differences in the outcome of juvenile social isolation on HPA axis function in rats.

Women are more likely than men to suffer from anxiety disorders and major depression. These disorders share hyperresponsiveness to stress as an etiological factor. Thus, sex differences in brain arousal systems and their regulation by chronic stress may account for the increased vulnerability to these disorders in women. Social isolation is a model of early life stress that results in neurobiological alterations leading to increased anxiety-like and depressive-like behaviors. Here we investigated the sex difference in the effects of post-weaning social isolation on acute stress sensitivity and behavior in rats. In both sexes, social isolation at weaning reduced basal levels of the neuroactive steroid allopregnanolone in the brain and of corticosterone in plasma. Moreover, acute stress increased plasma corticosterone levels in both group-housed and socially isolated male and female rats; however this effect was greater in male than female rats subjected to social isolation. Intriguingly, group-housed female rats showed no change in plasma and brain levels of allopregnanolone after acute foot-shock stress. The absence of stress-induced effects on allopregnanolone synthesis might be due to the physiologically higher levels of this hormone in females vs. males. Accordingly, increasing allopregnanolone levels in male rats blunted the response to foot-shock stress in these animals. Socially isolated male, but not female, rats also display depressive-like behavior and increased hippocampal brain-derived neurotrophic factor (BDNF). The ovarian steroids could "buffer" the effect of this adverse experience in females on these parameters. Finally, the dexamethasone (DEX) suppression test indicated that the chronic stress associated with social isolation impairs feedback inhibition in both sexes in which an increase in the abundance of glucocorticoid receptors (GRs) in the hippocampus was found. Altogether, these results demonstrate that social isolation affects neuroendocrine reactivity to stress, plasticity and emotionality in a sexually dimorphic manner.