Noradrenaline up-regulates the neuronal and the inducible nitric oxide synthase isoforms in magnocellular neurons of rat brain slices.

Nitric oxide (NO) and noradrenaline (NA) are suggested to be implicated in the regulation of neuropeptide secretion in the supraoptic nuclei (SON) and the paraventricular nuclei (PVN) of the hypothalamus. Our study demonstrates short-term interactions between NA and the activity and expression of NO synthase (NOS) in magnocellular neurons, by using an ex vivo model of hypothalamic slices. In the SON as well as in the PVN, total NOS activity exhibited a time-dependant increase after an incubation with NA. In the SON, this increase of total NOS activity was in part the consequence of stimulation of the iNOS activity. Coimmunodetections showed that cells expressing the inducible form of NOS were not astrocytes but magnocellular neurons. Steady-state levels of iNOS and nNOS mRNA were dramatically enhanced by NA, particularly in the SON. Consequently, we provide new evidence that iNOS could play an important role in multiple physiological functions, including extracellular fluid balance, lactation, and parturition.