Neuropeptide Y modulation of A1 noradrenergic neuron input to supraoptic vasopressin cells

Abstract

A1 noradrenaline (NA) neurons provide a direct excitatory input to supraoptic nucleus (SON) vasopressin (VP) cells. Many A1 cells contain neuropeptide Y (NPY) and past studies have established that NPY exerts excitatory postsynaptic effects on VP cell activity. We have now investigated whether NPY might also modulate A1 input to VP cells via presynaptic mechanisms. Experiments done in pentobarbitone-anesthetized rats demonstrated that SON application of NPY (10 μM) excited VP cells but also depressed their response to activation of the A1 input. These two effects were not correlated, suggesting independent mechanisms. The putative Y 1 agonist [Leu 31,Pro 34]NPY (10 μM) also excited VP cells but did not alter their response to activation of the A1 input. In contrast, the putative Y 2 receptor agonist Ac-[Leu 28,Leu 31]NPY 24–36 mimicked the synaptic depression produced by NPY but did not significantly alter spontaneous activity. These data are consistent with the proposal that NPY acts on Y 1-like receptors to excite VP cells but can also act on a presynaptic Y 2-like receptor to depress A1-VP cell synaptic transmission.