Noradrenergic inputs enhance the response of neurosecretory cells to osmotic stimulation.

Extracellular recordings from neurosecretory cells in the hypothalamic paraventricular nucleus (PVN) displayed either an excitation or no response following electrical stimulation (5 Hz) of the A1 noradrenergic region of the ventrolateral medulla, and exhibited either an increase or no effect in neuronal activity in response to intracarotid injections of hypertonic saline (0.2 M, 0.05 ml). The neurons responded to both the electrical and osmotic stimuli, A1 region stimulation at the subthreshold current (80-90% of the threshold required to evoke the response) significantly enhancing the facilitatory response caused by the osmotic stimulation. These results suggest that the A1 region may serve to potentiate the responsiveness of PVN neurosecretory cells in response to changes in plasma osmolality.