The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre-existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.ß

Autosomal recessive polycystic kidney disease (ARPKD) is an early onset genetic disorder characterized by numerous renal cysts resulting in end stage renal disease. Our study aimed to determine if metabolic reprogramming and tryptophan (Trp) metabolism via the kynurenine pathway (KP) is a critical dysregulated pathway in PKD. Using the Lewis polycystic kidney (LPK) rat model of PKD and Lewis controls, we profiled temporal trends for KP metabolites in plasma, urine, and kidney tissues from 6- and 12-week-old mixed sex animals using liquid and gas chromatography, minimum n = 5 per cohort. A greater kynurenine (KYN) concentration was observed in LPK kidney and plasma of 12-week rats compared to age matched Lewis controls ( P ⩽ .05). LPK kidneys also showed an age effect ( P ⩽ .05) with KYN being greater in 12-week versus 6-week LPK. The metabolites xanthurenic acid (XA), 3-hydroxykynurenine (3-HK), and 3-hydroxyanthranilic acid (3-HAA) were significantly greater in the plasma of 12-week LPK rats compared to age matched Lewis controls ( P ⩽ .05). Plasma XA and 3-HK also showed an age effect ( P ⩽ .05) being greater in 12-week versus 6-week LPK. We further describe a decrease in Trp levels in LPK plasma and kidney (strain effect P ⩽ .05). There were no differences in KP metabolites in urine between cohorts. Using the ratio of product and substrates in the KP, a significant age-strain effect ( P ⩽ .05) was observed in the activity of the KYN/Trp ratio (tryptophan-2,3-dioxygenase [TDO] or indoleamine-2,3-dioxygenase [IDO] activity), kynurenine 3-monooxygenase (KMO), KAT A (kynurenine aminotransferase A), KAT B, total KAT, total KYNU (kynureninase), KYNU A, KYNU B, and total KYNU within LPK kidneys, supporting an activated KP. Confirmation of the activation of these enzymes will require verification through orthogonal techniques. In conclusion, we have demonstrated an up-regulation of the KP in alignment with progression of renal impairment in the LPK rat model, suggesting that KP activation may be a critical contributor to the pathobiology of PKD.

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.

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Laryngeal stimulation that generates swallow activity is accompanied by laryngeal adduction along with central shutdown of breathing (apnoea) to execute safe swallowing without aspiration. The neural control of this is poorly understood. We hypothesized that the temporal precision of these separate phenomenon i.e., laryngeal adduction and apnoea during swallow is controlled by swallow burst generating neurons in the nucleus tractus solitarius (NTS) that project simultaneously to the caudal nucleus ambiguus (NA) for laryngeal adductions and to the Bӧtzinger complex (BötC) for apnoea. The present study aimed to provide anatomical support for the existence of such dual projecting neurons in the NTS. Retrograde tracing experiments were performed on adult male anaesthetised Sprague Dawley rats (n=2). Each rat received two microinjections of a retrograde tracer: cholera toxin B‐fluorescent conjugate (CTB‐555) into the BötC and unconjugated CTB into the NA. Following a recovery period of 5‐6 days the rats were euthanased and perfused transcardially with 4% paraformaldehyde with immunohistochemistry performed to visualize those neurons traced by the unconjugated CTB. The rostral to caudal distribution of labelled neurons in the NTS was determined by analysing multichannel tile images with fluorescent microscopy. Among the single labelled neurons in the caudal NTS a small number of double‐labelled neurons were identified. The double‐labelled neurons were found caudal to obex with ≤ 25 per section (n=2). This study supports the existence of neurons in the caudal NTS with simultaneous projection to NA and BötC and which could be potential candidates for the control of laryngeal adduction and apnoea during swallowing.