Objective:The development of hypertension in the Lewis polycystic kidney (LPK) disease model of kidney disease is caused, in part, by neuronal overactivity in the subfornical organ (SFO). Circulating proinflammatory cytokines, namely TNFα, are suggested to act in the central nervous system to produce an increase in neuronal excitability. As circulating cytokines are increased in kidney disease, we hypothesised that TNFα acts on the SFO to increase neuronal activity, therefore contributing to the development of hypertension in this animal model.Design and Methods:Urethane anaesthetised Lewis control (n = 23 total) and LPK (n = 18 total) animals were instrumented to record blood pressure and perform microinjections of TNFα (1–300pg/50nl), TNFα receptor 1 (TNFRI) neutralising antibody (1ng/50nl) or minocycline (0.5 μg/50nl), an inhibitor of microglial activation.Results:Exogenous TNFα microinjected into the SFO elicited a significant pressor response in the Lewis control but not the LPK animals (9 ± 2 mmHg vs -1 ± 3 mmHg, Lewis vs LPK peak change from baseline, P = 0.04). Acute inhibition of actions of local TNFα via administration of TNFRI neutralising antibody in the SFO did not reduce mean arterial blood pressure in Lewis control or LPK animals (1 ± 1mmHg vs -1 ± 1mmHg, Lewis vs LPK change from baseline, P = 0.59). Acute blockade of the actions of all proinflammatory cytokines on microglia via microinjection of minocycline in the SFO did not reduce blood pressure in Lewis control or LPK animals (-1 ± 1mmHg vs -1 ± 1mmHg, Lewis vs LPK change from baseline, P = 0.11). Prior microinjection of TNFRI neutralising antibody into the SFO abolished the pressor response observed upon microinjection of TNFα in Lewis rats (9 ± 2 mmHg vs 1 ± 1 mmHg, TNFα vs TNFα after TNFRI Ab peak change from baseline, P = 0.01), whereas prior microinjection of minocycline into the SFO only attenuated the pressor response observed upon TNFα microinjection in Lewis rats (9 ± 2 mmHg vs 3 ± 1 mmHg, TNFα vs TNFα after Minocycline peak change from baseline, P = 0.04)Conclusions:Overall, these findings demonstrate that although hypertension observed in the LPK is sustained by an increase in SFO activity, the short-term control of mean arterial blood pressure activity is not dependent on the actions of endogenous TNFα or generalised microglial activation by proinflammatory cytokines in the SFO.

Objective:An overactive glutamatergic projection from the subfornical organ (SFO) to the paraventricular nucleus (PVN) is associated with the development of hypertension. Despite this, the functional relationship of this pathway under normotensive conditions remains poorly defined within the literature. Without this knowledge, it remains unknown if a dysfunction of this pathway is the underlying cause of hypertension or rather simply a consequence of the underlying hypertensive disease pathology. As such, the aim of this study is to identify the short-term function of the SFO and PVN pathway under normotensive conditions.Design and Methods:An optogenetic viral vector (pAAV-CaMKIIa-hChR2 (H134R)-EYFP) was microinjected into the SFO of Lewis rats (n = 5). Three weeks later, rats were anaesthetised and instrumented to record blood pressure and sympathetic nerve activity, administer intravenous drugs and to photo-stimulate glutamatergic SFO neurons.Results:Photostimulation of glutamatergic SFO neurons produced a pressor response that was abolished by inhibition of neuronal transmission within the PVN (9 ± 1mmHg vs 3 ± 1mmHg peak change from baseline, baseline vs PVN inhibition, n = 2 rats, 3 replicates per rat). In a separate cohort (n = 3 rats, 5 replicates per rat), we determined if the pressor response elicited was dependant on the sympathetic nervous system and/or the release of the vasoactive hormone vasopressin. Blockade of sympathetic vasomotor outflow attenuated the pressor response by 76%, whereas combined inhibition of sympathetic outflow and vasopressin 1a receptors attenuated the pressor response by 88%. Finally, photostimulation of glutamatergic SFO neurons led to a peak increase in sympathetic nerve activity (n = 2) that was abolished by phenylephrine administration, suggesting that the neuronal circuitry underpinning this response is barosensitive.Conclusions:This study demonstrates that the pressor response elicited by glutamatergic SFO neurons is dependent on the PVN and is largely mediated by the sympathetic nervous system via barosensitive neuronal circuitry. Chronic activation of this pathway will be undertaken to determine if an overactivation of this neuronal pathway induces hypertension in normotensive animals.