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Methyl CpG binding protein 2 (MeCP2) is a member of the methylated DNA binding protein family able to modulate the transcription of target genes. Mutations in MECP2 lead to a wide range of neurological phenotypes and the better known of these diseases is Rett Syndrome. All patients having a mutation in MECP2 are mentally retarded and most of them exhibit dysfunctions in autonomic processes that are controlled by the brainstem. Previous studies have shown that Mecp2 is developmentally and spatially regulated throughout the rodent brain but none of them investigated the brainstem. In the present study, we have quantified the levels of expression of the Mecp2 mRNA by real time PCR and MeCP2 protein by immunoquantifications, in different areas of the mouse brainstem during the postnatal development (P0, P7, P21, P35 and P55). We focused on regions of the pons and the medulla oblongata directly involved in the regulation of autonomic functions. Our results show that the expression of MeCP2 is heterogeneously expressed throughout the postnatal mouse brainstem. MeCP2 expression in each area studied is restricted to neurones. The developmental pattern is mainly characterized by a postnatal decrease of the Mecp2 mRNA and an increase of the MeCP2 protein staining level in spite of the local variability. However, we were not able to correlate the developmental expression of MeCP2 in a given area of the brainstem with autonomic dysfunctions occurring in the presence of a mutation in Mecp2.

The postnatal development of tyrosine hydroxylase activity has been studied in the brainstem catecholaminergic cell groups (A1C1, A2C2, A5, A6, A7), involved in cardiorespiratory control. In rat, at birth and at postnatal days P3, P7, P14, P21 ant P68, we used a microdissection technique followed by in vivo measurement of the tyrosine hydroxylase (TH) activity, the rate-limiting enzyme in catecholamine synthesis. There is two successive marked increases in TH activity: at P3 in every catecholaminergic cell groups (A1C1, +225%; A2C2, +300%; A5, +190%; A6, +205% compared to birth) and during the third postnatal week with a peak of TH activity at P14 (A6, +90% above the P7 level) or at P21 (A1C1, +715%; caudal A2C2, +585%; rostral A2C2, +15%; A5, +445%; A7, +180% compared to P7). The data suggest the existence of two temporal windows during the neurochemical development of the catecholaminergic cell groups, which correspond to two metabolic transitions. The first one could be related to the intra-, extrauterine transition and the second one, to a deep energetic phase of maturation in the rat brain, closely related to the maturation of cardiorespiratory processes.