Effetto della separazione materna nella regolazione dell'attività neuronale nel test del labirinto a croce elevato in topi maschi adolescenti Mecp2-null e wild-type

Rett syndrome is a rare and severe genetic disease, which affects predominantly girls. The onset of symptoms varies between the 6th and 18th month of life. Approximately in 95% of cases, Rett syndrome is caused by mutations in the gene Methyl-CpG binding protein 2 (MECP2) gene, located on chromosome X. This gene encodes the multifunctional protein MeCP2, especially abundant in the brain, whose main function is to regulate the activity of other genes; in particular, it is a transcriptional repressor and a reader of epigenetic marks. Previous studies have shown that traumatic and stressful events at an early age produce important epigenetic changes, but the interaction between early life stress and Mecp2 deficiency that could shape anxious responses later in life has not been studied in mouse models. Thus, in this study, we examined the levels of activation of several brain nuclei involved in the regulation and display of different anxious behaviors in adolescent Mecp2-null and wild-type male mice. Mice were previously subjected to a standard protocol of early-life stress, namely maternal separation (MS-3h) every day until postpartum day 21; after that, animals were exposed to an anxiogenic test, the elevated plus maze (EPM). We then explored the expression of the product of the early-immediate gene C-FOS, a marker of neuronal activation. Furthermore, we studied the number of cells that co-expressed C-FOS and vasopressin (AVP) in the paraventricular nucleus of the hypothalamus. In fact, AVP is a neuropeptide involved in the control of the secretion of corticosteroids into the bloodstream; when a shock occurs, a strong lowering of blood pressure follows and the AVP leads to an increased secretion of ADH generating an increase in blood pressure. Our hypothesis was that the activity of neural nuclei controlling anxious behavior would be decreased both in Mecp2-null mice and MS-WT as compared to naive WT. To test this hypothesis, we analyzed the areas of the brain that, after the EPM test, most increase their activation, such as the ventral part of the lateral septum (LSV), the paraventricular hypothalamic nucleus (Pa) and the paraventricular thalamic nucleus (PV). Further, we checked the activation of the dentate gyrus of the hippocampus, an area related to memory and cognition (DG). Behavioral data from the lab show that Mecp2-null males display a reduction in anxiety in EPM, as compared to wild-type controls, and this result is supported by the data of the present thesis showing a significantly lower activation of the paraventricular nuclei in mutant mice. Data from the DG, showing no differences between groups, support that the differential neuronal activation is specific of the nuclei regulating anxiety and stress. Moreover, wild-type animals subjected to maternal separation also display a reduced activity of the paraventricular nucleus, also in agreement with behavioral data. Our results indicate that AVP-positive cells are not differentially activated. Hence, we hypothesize that neurons containing CRF (corticotropin-releasing factor), a peptide hormone implicated in stress, might be the ones involved in this differential response. Taken together, our results suggest that lack of Mecp2 mimics the effect of early life stress in altering the activity of the paraventricular nucleus of the hypothalamus.