TRPV1 channel activity triggered by hyperosmotic stimulation increases phosphorylated NOS activity in rat supraotic slices (1182.10)

Abstract

Magnocellular neuroendocrine cells (MNCs) in the supraoptic (SON) and paraventricular nucleus (PVN) of the hypothalamus release vasopressin (VP) from axons and somata/dendrites in response to hyperosmotic stimulation. Transient receptor potential vanilloid 1 (TRPV1) channels mediate osmosensory transduction and axonal neurosecretion in SON MNCs. Our lab has shown that osmotic‐stimulated somatodendritic VP responses occur in a TRPV1‐ and NOS‐dependent manner. Since TRPV1 activation may result in NO production, our current study examined the interaction between TRPV1 and NO synthase (NOS) under hyperosmotic conditions. Acutely dissected SON slices were prepared from adult male Holtzman rats perfused with sucrose‐enriched aCSF under deep anesthesia. Slices were treated with hyperosmotic stimulation in the presence and absence of TRPV1 antagonist SB366791 (1.5 μM) and later post‐fixed. Using double‐label immunohistochemistry for phosphorylated stimulatory residue of neuronal NOS (p‐nNOS ser1412) and combined VP‐neurophysin (PS41) and oxytocin‐neurophysin (PS38) we found elevated p‐nNOS immunoreactivity in MNCs under hyperosmotic conditions but not always in the presence of SB366791, suggesting that increased NO signaling may occur downstream of TRPV1 channel activity. By analogy to other neuroendocrine systems p‐nNOS ser1412 may participate in neuropeptide secretion perhaps by coupling with NMDAr on MNCs. We also immunoprobed for downstream signaling partners of NOS and found expression of sGC (beta subunit), an enzyme that converts GTP to cGMP.We conclude that hyperosmotic stimulation activates TRPV1 channels that produce stimulatory phosphorylation of nNOS leading to somatodendritic release of VP from supraoptic MNCs.Grant Funding Source: Supported by American Physiological Society