Matrix metalloproteinases MMP2 and MMP9 are upregulated by noradrenaline in the mouse neuroendocrine hypothalamus.

Magnocellular neurons of the hypothalamic supraoptic nuclei (SON) are involved in the synthesis and release of two major neuropeptides: oxytocin (OT) and arginine-vassopressin (AVP). Neurochemical plasticity in this system is induced by physiological conditions such as lactation, parturition and dehydration, and may be accompanied by reversible structural plasticity affecting neurons, astrocytes and the extracellular matrix (ECM). The noradrenergic system plays a critical role in triggering this chemical plasticity associated with structural plasticity. Matrix metalloproteinases (MMPs) are good candidates for involvement in the ECM remodelling observed in structural plasticity. We investigated the possible regulation of the two gelatinases, MMP2 and MMP9, by noradrenaline (NA) in the mouse neuroendocrine hypothalamus. We looked for the presence, location and activity of MMP2 and MMP9 in the SON, using an ex vivo experimental model of mouse hypothalamic slices incubated for 4 h with 10(-4) m NA. We showed that: (i) immunoreactivity for MMP2 and MMP9 was detected not only in AVP-positive and OT-positive magnocellular neurons, but also in astrocyte processes in control and NA-treated slices; (ii) the number of MMP2- and MMP9-positive cells increased after incubation with NA; (iii) MMP2 and MMP9 displayed markedly higher levels of gelatinolytic activity after NA treatment. These results suggest that both MMP2 and MMP9 are regulated by NA, and could therefore also be involved in structural plasticity within the SON.

Vasopressin and galanin expression in the hypothalamus of two African rodents, Taterillus gracilis and Steatomys caurinus, subjected to water-restriction.

The expression of arginine-vasopressin (AVP) and galanin (GAL) was studied by immunohistochemistry and in situ hybridization in the hypothalamus of two species of African rodents. In the wild, these animals experience successive arid and wet seasons that alternately stimulate their antidiuretic and diuretic systems. In this study, animals were subjected to both standardized laboratory conditions and to eight days of water-restriction. Under both sets of conditions, AVP and GAL were detected in the supraoptic nucleus (SON), paraventricular nucleus (PVN), and median eminence (ME). AVP and GAL responses to water-restriction differed in the two species, as did behavioral adaptations to the hot-dry season. In Taterillus gracilis, AVP- and GAL-LI (like immunoreactivity) peptide and mRNA levels increased in the SON. AVP-LI peptide and mRNA levels increased in the PVN, whereas only AVP-LI peptide levels increased in the ME. Pituitary gland AVP pools were unchanged by water deprivation, whereas urinary AVP levels and osmolality increased. The AVP response is typical of that of desert rodents, favoring survival under conditions of water-restriction. In Steatomys caurinus, which estivates, AVP and GAL-LI peptide levels decreased in the hypothalamus, as they did in the laboratory rat. In the SON, AVP, and GAL mRNA levels increased, whereas, in the PVN, only AVP mRNA levels increased. Pituitary gland AVP levels decreased, whereas urinary AVP levels and osmolality increased. In both species, the changes in the amount of GAL-LI peptide appeared to be closely linked to changes in AVP levels, suggesting that this peptide is involved in the osmoregulatory response to water-restriction.