Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA257

Poster Communications

TRPV4 is expressed in vasopressinergic neurons of the magnocellular region of the rat paraventricular nucleus of the hypothalamus.

F. Shenton1, S. Pyner1

1. Durham University, Durham, United Kingdom.

The paraventricular nucleus of the hypothalamus (PVN) is critical for sensing and responding to changes in plasma osmolality1. Increased osmolality activates the PVN to promote arginine vasopressin (AVP) release and sympathetic nerve activity to end organs2. The transient receptor potential vanilloid type 4 channel (TRPV4), may be involved in systemic osmoregulation and there is some evidence to support a physiological role for TRPV4 in the PVN osmosensing nuclei3. TRPV4 is expressed in the PVN where it is co-localised with AVP containing cells3. In the PVN of rat and mouse, TRPV4 and calcium activated potassium ion channels have been shown to couple as osmosensors4. Intracerebroventricular administration in mice of hypotonic artificial cerebrospinal fluid decreases blood pressure but not heart rate and inhibition of the TRPV4 ion channel abolishes this effect5. These studies demonstrate a role for TRPV4 in osmosensing within the PVN but they do not establish which neurons express the channel. We used retrograde labelling of PVN- spinally projecting preautonomic neurons with immunohistochemistry to determine which neurons express TRPV4 and its relationship with cell groups involved in osmosensing and cardiovascular homeostasis. Experiments were performed on six male Wistar rats in accordance with the Animals (Scientific Procedures) Act, 1986 and the European Commission Directive 86/609/EEC. The rats were anaesthetised intraperitoneally (IP) with medetomidine (0.25ml/100g) and ketamine (0.06ml/100g) prior to spinal cord injection of Fluorogold (FG). Fluorogold (2%) was pressure injected into the left intermediolateral region at T2. Post-operatively, buprenorphine (0.01ml/100g) was administered and animals allowed to recover for 7-10 days. Following this, animals were humanely killed (pentobarbital 60mg/kg IP), perfuse-fixed (4% PFA) and brain and spinal cord removed. Immunohistochemistry to reveal TRPV4, AVP and oxytocin (OXT) in the PVN was carried out on free floating sections. Tissues was examined using confocal microscopy to determine their relationship with preautonomic PVN neurons. Preautonomic neurons identified by the presence of FG did not express TRPV4. All TRPV4 neurons were found to be vasopressinergic with TRPV4 expressing neurons making up 63% of the total vasopressinergic population. There was no evidence of TRPV4 being expressed on oxytocinergic neurons. A minority of preautonomic neurons were found to express OXT or AVP. TRPV4 was localised to the vasopressinergic magnosecretory neurons within the PVN. These neurons release AVP to modulate preautonomic neuronal activity in response to plasma osmolality disturbances. Our study indicates an anatomical basis to inform the mechanism by which changes in plasma osmolality alter sympathetic nerve activity.

Where applicable, experiments conform with Society ethical requirements