Localization of angiotensin II receptor binding in rabbit brain by in vitro autoradiography

Abstract

Binding of 125I-[Sar1,Ile8] angiotensin II (AII) to sections of brains from both wild and laboratory rabbits was determined by in vitro autoradiography. In the forebrain, specific high density binding was observed in the olfactory bulb, organum vasculosum of the lamina terminalis (OVLT), subfornical organ, median eminence, lateral septum, median preoptic nucleus and hypothalamic paraventricular, supraoptic and arcuate nuclei. In the midbrain, binding of the radioligand was observed in the interpeduncular and parabrachial nuclei, in the locus coeruleus, and ventrolateral pons. In the hind brain, there was dense binding of 125I-[Sar1,Ile8] AII to the nucleus of the solitary tract (NTS) and to both rostral and caudal parts of the reticular formation of the ventrolateral medulla oblongata. Weaker specific binding of the radioligand to the molecular layer of the cerebellum, to the nucleus of the spinal trigeminal tract, dorsal motor nucleus of the vagus, area postema, and to a band of tissue connecting the NTS to the ventrolateral medulla was also observed. Binding of the ligand to circumventricular organs such as the OVLT, subfornical organ, and median eminence suggests that these are sites in the brain of the rabbit at which blood-borne AII may exert influences on the central regulation of fluid balance and pituitary hormone secretion, although AII of neuronal origin could also act at these sites. Binding of the radioligand in several other brain regions suggests that angiotensin II of cerebral origin may be involved in a number of different aspects of brain function in the rabbit. The finding of dense binding in the NTS and ventrolateral medulla, which are involved in autonomic activity and are also sites of catecholamine-containing neurons, raises the possibility of angiotensin interaction with these neurons and involvement in autonomic function.

The angiotensin type 2 receptor of angiotensin II and neuronal differentiation: from observations to mechanisms

“…Early studies from Mendelsohn et al (1988) and Unger et al (1988) established, using biochemical and pharmacological approaches, the existence of a renin-angiotensin system in the brain. The various components (angiotensin-converting enzyme, Ang II and Ang II receptors) are found in areas of the brain involved in the regulation of fluid and electrolyte balance and in the regulation of arterial pressure (Severs & Daniels-Severs 1973, Phillips 1987, as well as in structures involved in cognition, behavior and locomotion.…”

Angiotensin and baroreflex control of the circulation

“…The NTS is the nucleus containing the primary termination of baroreceptor and chemoreceptor afferents (52) but, more importantly, in most species including humans, cats, rabbits and rats, the NTS contains the highest concentration of Ang receptors within the medulla (4,53). Thus, it is not surprising that this nucleus has been suggested as a main region for Ang influencing baroreceptor afferent information (8,54) as well as the integration of chemoreceptor afferents (54).…”

“…There is a very close association between the location of Ang II receptors and many important brain nuclei involved in cardiovascular regulation (3,4). Much interest has been focused on the actions of Ang in the forebrain circumventricular regions such as the subfornical organ and organum vasculosum laminae terminalis which regulate thirst, body fluid and blood pressure (1,5), as well as in the area postrema (6).…”

The physiological role of AT1 receptors in the ventrolateral medulla

“…The striking association between AT 1 receptors and medullary cardiovascular nuclei raises the question as to the precise functions mans (3)(4)(5). These receptors are primarily of the AT 1 subtype (6,7).…”