Tyrosine hydroxylase deficit in the chemoafferent and the sympathoadrenergic pathways of the Mecp2 deficient mouse.

Mutations in the gene encoding the transcriptional methyl-CpG binding protein 2 (Mecp2) cause a wide range of neurological disorders and the better known of these diseases is Rett syndrome (RS). Mecp2 deficiency has been previously associated to catecholaminergic dysfunction in the mouse brainstem. Here we report a catecholaminergic deficit in the peripheral nervous system of the Mecp2-/y males and heterozygous Mecp2+/- female mice. We used immunoquantification associated to densitometry to evaluate the amount of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis, in the key organs of the chemoafferent and sympathoadrenergic pathways: the carotid body (CB), the petrosal ganglion (PG), the superior cervical ganglion (SCG) and the adrenal medulla (AM). Our results show that the TH staining level is weaker in the CB (-15%), PG (-26%), SCG (-34%), AM (-35%) of Mecp2-/y mice and to a lesser extent in the PG (-11%) and AM (-18%) in Mecp2+/- mice. We evaluated in vivo the chemoreflex sensitivity of Mecp2-/y mice using whole-body plethysmography to record the breathing of Mecp2-/y mice in normoxia and in response to acute hypoxia (10% O(2)). Our results show that the hypoxic ventilatory response is significantly increased in Mecp2-/y mice (+50%) demonstrating in vivo disturbances of the chemoafferent pathway. In conclusion, our results offer new insights to better understand the mechanisms leading to autonomic dysfunction in RS.