Abstract
The neurohormones arginine-vasopressin (AVP) and oxytocin (OT) synthesised in supraoptic and paraventricular nuclei of neurohypophysis regulate lactation, systemic water homeostasis and nociception. Using transgenic rats expressing AVP and OT tagged with fluorescent proteins we demonstrate that both neurohormones are expressed in sensory neurones both in vitro, in primary cultures, and in situ, in the intact ganglia; this expression was further confirmed with immunocytochemistry. Both neurohormones were expressed in nociceptive neurones immunopositive to transient receptor potential vannilloid 1 (TRPV1) channel antibodies. The AVP and OT-expressing DRG neurones responded to AVP, OT, 50 mM K + and capsaicin with [Ca 2+ ] i transients; responses to AVP and OT were specifically blocked by the antagonists of V 1 AVP and OT receptors. Probing the extracellular incubation saline with ELISA revealed AVP and OT secretion from isolated DRGs; this secretion was inhibited by tetanus toxin (TeNT) indicating the role for vesicular release. Expression of OT, but not AVP in DRG neurones significantly increased during lactation. Together, the results indicate novel physiological roles (possibly related to nociception and mood regulation) of AVP and OT in the sensory neurones. It is a truth universally acknowledged that neurohypophyseal hormones arginine vasopressin (AVP) and oxytocin (OT) are synthesized in the magnocellular neurosecertory cells (MNCs) of the paraventricular and the supraoptic nuclei (PVN and SON respectively) of the hypothalamus. These hormones are secreted from MNCs axons that terminate in the posterior pituitary into the systemic circulation; OT and AVP secretion is linked to highly idio-syncratic electrical activities of MNCs 1. The neurohormones exert multiple effects on peripheral tissues and cells through activating dedicated metabotropic receptors for vasopressin (V 1a , V 1b and V 2) and oxytocin (OT-R) with well defined pharmacology 2-5. Several sporadic studies reported expression of AVP and OT outside of the neurohypophysis; immunore-activity for both hormones was, for example, detected in ~50% of rat dorsal root ganglia (DRG) neurones 6,7. Similarly, oxytocin was found (by radioimmunoassay) in human lumbar DRGs 8. These observations, however, were not universally confirmed; neither AVP nor OT were identified in DRGs from guinea-pig, cat, rat or rabbit 9-11. Exposure of DRG neurones to AVP or OT caused accumulation of inositol phosphates, suggesting the