Anatomical Organization of the Rat Subfornical Organ

Abstract

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.

Three‐plane description of astroglial architecture and gliovascular connections of area postrema in rat: Long tanycyte connections to other parts of brainstem

“…Pekny (2001) found that a lack of GFAP decreases the effect of BBB. Similar differences were found in the OVLT (Kálmán et al, 2019;Prager-Khoutorsky & Bourque, 2015) and, although less consequently, in the SFO (Hicks et al, 2021;Pócsai & Kálmán, 2015).…”

“…In the AP, both components occur in the lateral border zone, whereas in the SFO and OVLT only narrow strips along the borderlines of the peripheral and central areas displayed immunopositivity to both GFAP and vimentin. In the OVLT this characteristic was shown by the rostroventral part adjacent to the optic chiasm (Prager‐Khoutorsky & Bourque, 2015), whereas in the SFO by the ventromedially located glial population (Hicks et al., 2021) . In the AP, the junctional ventral zone (at McKinley et al., 2003; Morita et al., 2016; “commissural NTS” at Dallaporta et al., 2010) displays similar mixed patterns of GFAP and vimentin like the lateral border zone.…”

Constitutive cell proliferation and neurogenesis in the organum vasculosum lamina terminalis and subfornical organ of adult rats

“…Previous studies have demonstrated that pericyte coverage determines vascular permeability, 70 and established the key role of pericytes in maintaining the BBB. 71 However, since sensory CVOs lack a complete BBB due to the presence of a dense population of leaky capillaries, 54,55,72 the role of pericytes in these areas remains ambiguous. It is conceivable that CVO pericytes have additional functions requiring constitutive renewal and/or proliferation.…”

Fasting increases circulating angiotensin levels and brain Agtr1a expression in male rats

“…ANG II/AT 1 R signalling has also been implicated in food intake and metabolic control 2,3 . One of the main brain sites for peripheral ANG II action is the subfornical organ (SFO), a circumventricular structure related to the control of several autonomic functions, neuroendocrine regulation and behavioural responses 4,5 . Nevertheless, other brain regions associated with neuroendocrine control of hydromineral and metabolic balance also express AT 1 Rs and are directly and/or indirectly (via SFO) responsive to ANG II, such as the hypothalamic paraventricular nucleus (PVN) and the arcuate nucleus (ARC) 6–8 .…”

“…2,3 One of the main brain sites for peripheral ANG II action is the subfornical organ (SFO), a circumventricular structure related to the control of several autonomic functions, neuroendocrine regulation and behavioural responses. 4,5 Nevertheless, other brain regions associated with neuroendocrine control of hydromineral and metabolic balance also express AT 1 Rs and are directly and/or indirectly (via SFO) responsive to ANG II, such as the hypothalamic paraventricular nucleus (PVN) and the arcuate nucleus (ARC). [6][7][8] In the PVN, ANG II stimulates the activity and release of vasopressin (AVP), oxytocin (OXT) and corticotrophin-releasing hormone (CRH) secretion, 9 whilst in the ARC it modulates resting metabolic rate by acting on the Agouti-related peptide (AGRP)-producing neurones.…”