Sex Steroid Hormones Regulate the Expression of Growth-associated Protein 43, Microtubule-associated Protein 2, Synapsin 1 and Actin in the Ventromedial Nucleus of the Hypothalamus

The ventromedial nucleus of the hypothalamus is well known for its involvement in the regulation of the female reproductive behavior. The dendritic trees of neurons in its ventrolateral division (VMNvl), the dendritic spines, and the dendritic and spine synapses undergo alterations along the estrous cycle. Because these changes are conspicuous, we thought of interest to examine the influence of sex steroids in the levels of the structural proteins of axons and dendrites. The VMNvl of female rats at all phases of the estrous cycle was labeled for growth-associated protein-43, microtubule-associated protein 2, synapsin 1 and actin. The intensity of the labeling was measured using a modified Brightness–Area–Product method that is sensitive to variations the size of the VMN. The brightness per unit area of these proteins did not undergo significant variations over the estrous cycle, except synapsin 1 that was significantly reduced in diestrus relative to the remaining phases of the ovarian cycle. Conversely, the Brightness–Area–Product of all labeled proteins changed along the estrous cycle and was greater at proestrus than at all other phases. Our results show the presence of estrous cycle-related oscillations in the levels of the structural proteins that are involved in dendritic and synaptic plasticity.