Postnatal and ovariectomic regulation of postsynaptic density protein-95 in the hippocampus of female Sprague-Dawley rats.

Postsynaptic density protein-95 (PSD-95) is hypothesized to control the excitatory-to-inhibitory ratio and plays an important role in the regulation of hippocampal synaptic plasticity, synaptogenesis, and learning and memory. In this report, we used immunoblotting to study the effects of aging and ovariectomy (OVX) on the expression of PSD-95 in the hippocampus of female rats. The results indicated that postnatal expression of hippocampal PSD-95 correlated with the fluctuation of circulating female sex hormones such as estrogen. Neonatal PSD-95 level was very low, but dramatically increased within the first month. The highest expression of PSD-95 was detected at postnatal day 30 (P30) and significantly decreased by 18 months. In the adult hippocampus, OVX significantly decreased PSD-95 expression within the first week, but it had recovered to adult levels 2 weeks later. Taken together, we conclude that circulating ovarian hormones may play a crucial role in the regulation of excitatory synapses within the hippocampus. Depletion of ovarian hormones can transiently and dramatically decrease the level of excitatory synapses for a limited time.