Morphological Changes Induced by the Absence of Ovarian Hormones in Nucleus Accumbens of Ovariectomized Rats

Abstract

Ovariectomy (OVX) has been widely used to explore the effect of ovarian hormones on brain regions. It has been observed that estrogen in OVX rats increases the dopaminergic function in nucleus accumbens (NAcc). To determine whether absence or presence of estradiol changes the dendritic structure of some dopaminergic neurons, we investigated the consequences of a daily injection for 2 weeks of 17-beta estradiol (E2) on the dendritic morphology of NAcc neurons in two groups of rats, immediately or 10 weeks administered after OVX. The structure of dendrites was measured by using the Golgi-Cox procedure followed by a Sholl analysis. We found a reduction in the number of spiny dendrites of the medium spiny neurons of the NAcc in animals in which E2 was administrated without delay after OVX. However, when the same treatment was administered 10 weeks after OVX, not any difference was observed. Independently of the hormone treatment, rats from the group of 10 weeks after OVX showed a reduction in the number of spiny dendrites of the medium spiny neurons when compared with their counterparts at 2 weeks. Data suggest that estrogens or their absence regulate synaptogenesis in the NAcc.

Pregnancies alters spine number in cortical and subcortical limbic brain regions of old rats

“…Several reports suggest that changes in estrogen levels result in changes in the number of dendritic spines in cortical regions, such as the PFC, the hippocampus, and the basolateral amygdala (Inagaki, Frankfurt, & Luine, ; Luine & Frankfurt, ; Woolley, Gould, Frankfurt, & McEwen, ). In addition, the administration of estradiol (E2) to ovariectomized rats increased the dendritic spine number in the pyramidal neurons of the CA1 region of the hippocampus and MSN of the NAcc (Kato et al, ; Quiñones, Camacho‐Abrego, Rivera, Flores, & Picazo, ; Wooley & McEwen, ). It is clear that during the estrous cycle, low levels of estradiol are related to a reduced number of synaptic spines and high estradiol levels are related to a higher number of dendritic spines (Chen et al, ; Woolley and McEwen, ).…”

Role of Estrogens on Some Cognition-Related Aspects

“…In the same line, OVX induces a decrease in the dendritic spines density at hippocampus [80], prefrontal cortex [85,86] and even in nucleus accumbens [87], which is in line with a decrease in recognition memory [85] and with an increase in the number of hippocampal pre-synaptic buttons [88]. For instance, OVX increases the dendritic branch number and spine density of pyramidal cells from parietal cortex observed four months after the removal of ovaries [89], while a daily treatment with E2 for two weeks, decreases the number of branches of dendrites of layer II/III pyramidal cells in the entorhinal cortex [90] and the spine density in neurons from nucleus accumbens [87]. For instance, OVX increases the dendritic branch number and spine density of pyramidal cells from parietal cortex observed four months after the removal of ovaries [89], while a daily treatment with E2 for two weeks, decreases the number of branches of dendrites of layer II/III pyramidal cells in the entorhinal cortex [90] and the spine density in neurons from nucleus accumbens [87].…”

“…Spine density also varies along estrous cycle since rats in proestrus (when high levels of E2 are present) have a higher density of spines in the CA1 region in comparison to estrous [81,84]. In the same line, OVX induces a decrease in the dendritic spines density at hippocampus [80], prefrontal cortex [85,86] and even in nucleus accumbens [87], which is in line with a decrease in recognition memory [85] and with an increase in the number of hippocampal pre-synaptic buttons [88]. However, removal of ovaries can differentially alter the dendritic morphology in other areas not related directly with cognition.…”