Spine-type densities of hippocampal CA1 neurons vary in proestrus and estrus rats.

Spines-mediated synaptic activity has been associated to learning ability. Dendritic spines from hippocampal CA1 pyramidal neurons of proestrus rats have been reported to be more numerous than in estrus animals, but some behavioral studies have reported a better performance during the estrus stage of the estrous cycle. Because spine shape has been shown to be strongly related to the post-synaptic processing of information, a quantitative morphological study related to the proportional density of each type of spine, was conducted in Golgi material of hippocampal CA1 pyramidal cells of proestrus and estrus rats. After three regular estrous cycles had been asserted, seven Sprague-Dawley female adult rats in proestrus and eight in estrus, were used. Mushroom-shaped spines from hippocampal pyramidal cells predominated in proestrous rats, being 15.1% more numerous in this stage than in estrus; while thin spines were the predominant type of spine in estrous animals, being 15.5% more abundant in estrus than in proestrus. The predominance of the mushroom-shaped or thin spines in the hippocampal CA1 pyramidal neurons during the respective stages of the rat estrous cycle, could be related to the organization of the hippocampal activity-dependent mnemonic information.