Anatomical Organization of the Rat Subfornical Organ

The subfornical organ (SFO) is a sensory circumventricular organ located along the anterodorsal wall of the third ventricle. SFO lacks a complete blood-brain barrier (BBB), and thus peripherally-circulating factors can penetrate the SFO parenchyma. These signals are detected by local neurons providing the brain with information from the periphery to mediate central responses to humoral signals and physiological stressors. Circumventricular organs are characterized by the presence of unique populations of non-neuronal cells, such as tanycytes and fenestrated endothelium. However, how these populations are organized within the SFO is not well understood. In this study, we used histological techniques to analyze the anatomical organization of the rat SFO and examined the distribution of neurons, fenestrated and non-fenestrated vasculature, tanycytes, ependymocytes, glia cells, and pericytes within its confines. Our data show that the shell of SFO contains non-fenestrated vasculature, while fenestrated capillaries are restricted to the medial-posterior core region of the SFO and associated with a higher BBB permeability. In contrast to non-fenestrated vessels, fenestrated capillaries are encased in a scaffold created by pericytes and embedded in a network of tanycytic processes. Analysis of c-Fos expression following systemic injections of angiotensin II or hypertonic NaCl reveals distinct neuronal populations responding to these stimuli. Hypertonic NaCl activates ∼13% of SFO neurons located in the shell. Angiotensin II-sensitive neurons represent ∼35% of SFO neurons and their location varies between sexes. Our study provides a comprehensive description of the organization of diverse cellular elements within the SFO, facilitating future investigations in this important brain area.

Raspberry Consumption Attenuates Angiotensin II-Induced Oxidative Stress in the Subfornical Organ in Male Sprague-Dawley Rats

Objectives To examine whether raspberry (RB) attenuates oxidative stress induced by angiotensin (Ang) II in the subfornical organ (SFO) of the brain in rats. Methods Male Sprague-Dawley rats were fed an AIN-93M diet with or without 10% w/w freeze-dried RB powder for seven weeks. At week 4, rats were implanted with subcutaneous osmotic minipumps that delivered 0.9% saline (Control) or Ang II (270 ng/kg body weight/day) for another three weeks. Brain region-specific tissue punches were collected from flash-frozen sections containing the SFO. NADPH oxidase (NOX) 2 and 4 and superoxide dismutase (SOD) 1 and 2 were measured in SFO using western blot. Results were analyzed using one-way ANOVA followed by Tukey post hoc test. Data were normalized to control and are expressed as means ± standard deviation. Results Ang II significantly increased NOX2 expression compared to control (1.24 ± 0.1, n = 5, vs 1.00 ± 0.07-fold, n = 3, P = 0.009) while RB supplementation significantly attenuated Ang II-induced increases in NOX2 (0.91 ± 0.05-fold, n = 4; P = 0.0006). Ang II also increased NOX4 expression compared to control (2.11 ± 1.2, n = 9, vs 0.98 ± 0.4-fold, n = 6, P = 0.04), but RB supplementation did not significantly attenuate this effect (1.30 ± 0.36-fold, n = 10, P = 0.11). RB increased expression of SOD1 (1.52 ± 0.20-fold, n = 4) compared to control (1.00 ± 0.15-fold, n = 3, P = 0.009) and Ang II alone (1.08 ± 0.16-fold, n = 5, P = 0.01). On the other hand, Ang II treatment decreased SOD2 expression compared to control (0.62 ± 0.05, n = 5, vs 1.00 ± 0.09-fold, n = 3, P = 0.0001), but the RB supplementation did not prevent this effect (0.72 ± 0.07-fold, n = 4, P = 0.16). Conclusions Our findings suggest that RB supplementation decreases Ang II-induced oxidative stress in the SFO by decreasing NOX2 and increasing SOD1 expression. Future investigations are warranted to elucidate the effects of RB on oxidative stress pathways in the SFO. Funding Sources This work was supported by the Agriculture and Food Research Initiative (grant no. 2019–67,017-29,257/project accession no. 1,018,642) from the USDA National Institute of Food and Agriculture.

The subfornical organ drives hypertension in polycystic kidney disease via the hypothalamic paraventricular nucleus

AimsHypertension is a prevalent yet poorly understood feature of polycystic kidney disease. Previously, we demonstrated that increased glutamatergic neurotransmission within the hypothalamic paraventricular nucleus produces hypertension in the Lewis Polycystic Kidney (LPK) rat model of polycystic kidney disease. Here, we tested the hypothesis that augmented glutamatergic drive to the paraventricular nucleus in Lewis polycystic kidney rats originates from the forebrain lamina terminalis, a sensory structure that relays blood-borne information throughout the brain.Methods and resultsAnatomical experiments revealed that 38% of paraventricular nucleus-projecting neurons in the subfornical organ of the lamina terminalis expressed Fos/Fra, an activation marker, in LPK rats while <1% of neurons were Fos/Fra+ in Lewis control rats (P = 0.01, n = 8). In anaesthetized rats, subfornical organ neuronal inhibition using isoguvacine produced a greater reduction in systolic blood pressure in LPK vs. Lewis rats (−21±4 vs. −7±2 mmHg, P < 0.01; n = 10), which could be prevented by prior blockade of paraventricular nucleus ionotropic glutamate receptors using kynurenic acid. Blockade of ionotropic glutamate receptors in the paraventricular nucleus produced an exaggerated depressor response in LPK relative to Lewis rats (−23±4 vs. −2±3 mmHg, P < 0.001; n = 13), which was corrected by prior inhibition of the subfornical organ with muscimol but unaffected by chronic systemic angiotensin II type I receptor antagonism or lowering of plasma hyperosmolality through high-water intake (P > 0.05); treatments that both nevertheless lowered blood pressure in LPK rats (P < 0.0001).ConclusionOur data reveal multiple independent mechanisms contribute to hypertension in polycystic kidney disease, and identify high plasma osmolality, angiotensin II type I receptor activation and, importantly, a hyperactive subfornical organ to paraventricular nucleus glutamatergic pathway as potential therapeutic targets.