Synaptosomal-associated protein of 25 kD (SNAP-25) is a component of SNARE complex and plays a crucial role in neurotransmitter release from presynaptic terminals. A number of studies have shown that SNAP-25 expression in adult brain is regulated by gonadal steroids, particularly estradiol (E2). We recently found that subcellular SNAP-25 distribution in deep cerebellar nuclei of neonatal male rats is also modified by E2 treatment (Manca et al., Neuroscience 2014). However it is not well defined whether and how gonadal steroids may regulate SNAP-25 expression in neonatal period. In the present study, we analyzed SNAP-25 expression in the cerebellum, hypothalamus and hippocampus on postnatal day (PD) 10 in both male and female C57BL/6J mice to characterize possible sex and regional differences in SNAP-25 expression in developing brain. We also examined the effects of gonadectomy (GDX) at birth and E2 treatment on the expression of SNAP-25 on PD10 in male mice. Western blot analysis revealed that SNAP-25 expression in intact male mice was significantly lower than in female mice in the cerebellum and hippocampus. On the other hand, there was no sex difference in SNAP-25 levels in the hypothalamus. The levels of SNAP-25 in cerebellum and hippocampus in male mice GDX'ed on PD 0 were significantly higher than those in gonadally intact male and similar to those found in gonadally intact female mice. Interestingly, subcutaneous injection of estradiol-benzoate (1.5 µg/day, in sesame oil) on PD1-3 in GDX'ed male mice resulted in a significant increase of SNAP-25 levels compared to vehicle treated control groups in all brain regions studied. These results suggest that endogenous levels of gonadal steroids may be responsible in region specific sex differences in the expression of SNAP-25 in developing mouse brain. Our finding of up-regulation of SNAP-25 expression by exogenous estrogen treatment is consistent with our previous findings in the cerebellum in neonatal male rats and those reported in other functionally related proteins such as syntaxin, synaptophysin and spinophilin from the hippocampus of overiectomized female rats.

SS and PM contributed equally to this work.