FREE POSTSYNAPTIC DENSITIES IN THE HIPPOCAMPUS OF THE FEMALE RAT

THE number of synapses in the adult, female hippocampal CA1 region flu ctuates naturally across the estrous cycle in an ovarian steroid-depen dent manner. This phasic variation in synapse number occurs without id entifiable degenerating synapses. Ultrastructural correlates of the dy namic aspect of this synapse loss and synapse formation thus remain un described. During early development, one hallmark of synaptogenesis is the presence of free postsynaptic densities (PSDs). Here we report th at the incidence of free PSDs in CA1 fluctuates across the rat estrous cycle. The number of free PSDs is greatest on the afternoon of proest rus and is significantly decreased on the afternoon of estrus, 24 h la ter. We hypothesize that these free PSDs reflect synapse turnover in t he adult CA1 region. (C) 1998 Rapid Science Ltd.