The role of the subfornical organ in drinking induced by angiotension in the Japanese quail, Coturnix coturnix japonica

Circulating Isotocin, not Angiotensin II, is the Major Dipsogenic Hormone in Eels

Angiotensin II (AngII) is generally known as the most important dipsogenic hormone throughout vertebrates, while two other neurohypophysial hormones, vasopressin and oxytocin, are not dipsogenic in mammals. In this study, we found that systemic isotocin, but not vasotocin, is the potent dipsogenic hormone in eels. When injected intra-arterially into conscious eels, isotocin, vasotocin and AngII equally increased ventral aortic pressure dose-dependently at 0.03-1.0 nmol/kg, but only isotocin induced copious drinking. The dipsogenic effect was dose-dependent and occurred significantly at as low as 0.1 nmol/kg. By contrast, a sustained inhibition of drinking occurred after AngII, probably due to baroreflexogenic inhibition. No such inhibition was observed after isotocin despite similar concurrent hypertension. The baroreceptor may exist distal to the gill circulation because the vasopressor effect occurred at both ventral and dorsal aorta after AngII but only at ventral aorta after isotocin. By contrast, intra-cerebroventricular (i.c.v.) injection of isotocin had no effect on drinking or blood pressure, but AngII increased drinking and aortic pressure dose-dependently at 0.03-0.3 nmol/eel. Lesioning of the area postrema (AP), a sensory circumventricular organ, abolished drinking induced by peripheral isotocin, but not i.c.v. AngII. Collectively, isotocin seems to be a major circulating hormone that induces swallowing through its action on the AP, while AngII may be an intrinsic brain peptide that induces drinking through its action on a different circumventricular site, possibly a recently identified blood-brain barrier-deficient structure in the antero-ventral third ventricle of eels, as shown in birds and mammals.

Neural populations for maintaining body fluid balance

Fine balance between loss-of water and gain-of water is essential for maintaining body fluid homeostasis. The development of neural manipulation and mapping tools has opened up new avenues to dissect the neural circuits underlying body fluid regulation. Recent studies have identified several nodes in the brain that positively and negatively regulate thirst. The next step forward would be to elucidate how neural populations interact with each other to control drinking behavior.

Mapping the brain of the chicken (Gallus gallus), with emphasis on the septal-hypothalamic region

There has been remarkable progress in discoveries made in the avian brain, particularly over the past two decades. This review first highlights some of the discoveries made in the forebrain and credits the Avian Brain Nomenclature Forum, responsible for changing many of the terms found in the cerebrum and for stimulating collaborative research thereafter. The Forum facilitated communication among comparative neurobiologists by eliminating confusing and inaccurate names. The result over the past 15yearshas been a standardized use of avian forebrain terms. Nonetheless, additional changes are needed. The goal of the paper is to encourage a continuing effort to unify the nomenclature throughout the entire avian brain. To emphasize the need for consensus for a single name for each neural structure, I have selected specific structures in the septum and hypothalamus that our laboratory has been investigating, to demonstrate a lack of uniformity in names applied to conservative brain regions compared to the forebrain. The specific areas reviewed include the distributions of gonadotropin-releasing hormone neurons and their terminal fields in circumventricular organs, deep-brain photoreceptors, gonadotropin inhibitory neurons and a complex structure and function of the nucleus of the hippocampal commissure.

Drinking by amphibious fish: convergent evolution of thirst mechanisms during vertebrate terrestrialization

Thirst aroused in the forebrain by angiotensin II (AngII) or buccal drying motivates terrestrial vertebrates to search for water, whereas aquatic fish can drink surrounding water only by reflex swallowing generated in the hindbrain. Indeed, AngII induces drinking through the hindbrain even after removal of the whole forebrain in aquatic fish. Here we show that AngII induces thirst also in the amphibious mudskipper goby without direct action on the forebrain, but through buccal drying. Intracerebroventricular injection of AngII motivated mudskippers to move into water and drink as with tetrapods. However, AngII primarily increased immunoreactive c-Fos at the hindbrain swallowing center where AngII receptors were expressed, as in other ray-finned fish, and such direct action on the forebrain was not found. Behavioural analyses showed that loss of buccal water on land by AngII-induced swallowing, by piercing holes in the opercula, or by water-absorptive gel placed in the cavity motivated mudskippers to move to water for refilling. Since sensory detection of water at the bucco-pharyngeal cavity like 'dry mouth' has recently been noted to regulate thirst in mammals, similar mechanisms seem to have evolved in distantly related species in order to solve osmoregulatory problems during terrestrialization.

Renin-angiotensin system in vertebrates: phylogenetic view of structure and function

Renin substrate, biological renin activity, and/or renin-secreting cells in kidneys evolved at an early stage of vertebrate phylogeny. Angiotensin (Ang) I and II molecules have been identified biochemically in representative species of all vertebrate classes, although variation occurs in amino acids at positions 1, 5, and 9 of Ang I. Variations have also evolved in amino acid positions 3 and 4 in some cartilaginous fish. Angiotensin receptors, AT₁ and AT₂ homologues, have been identified molecularly or characterized pharmacologically in nonmammalian vertebrates. Also, various forms of angiotensins that bypass the traditional renin-angiotensin system (RAS) cascades or those from large peptide substrates, particularly in tissues, are present. Nonetheless, the phylogenetically important functions of RAS are to maintain blood pressure/blood volume homeostasis and ion-fluid balance via the kidney and central mechanisms. Stimulation of cell growth and vascularization, possibly via paracrine action of angiotensins, and the molecular biology of RAS and its receptors have been intensive research foci. This review provides an overview of: (1) the phylogenetic appearance, structure, and biochemistry of the RAS cascade; (2) the properties of angiotensin receptors from comparative viewpoints; and (3) the functions and regulation of the RAS in nonmammalian vertebrates. Discussions focus on the most fundamental functions of the RAS that have been conserved throughout phylogenetic advancement, as well as on their physiological implications and significance. Examining the biological history of RAS will help us analyze the complex RAS systems of mammals. Furthermore, suitable models for answering specific questions are often found in more primitive animals.

Differential responses of the vasotocin 1a receptor (V1aR) and osmoreceptors to immobilization and osmotic stress in sensory circumventricular organs of the chicken (Gallus gallus) brain

Past studies have shown that the avian vasotocin 1a receptor (V1aR) is involved in immobilization stress. It is not known whether the receptor functions in osmotic stress, and if sensory circumventricular organs may be involved. An experiment was designed with four treatment groups including a 1h immobilization acute stress (AS) group, an unstressed acute control (AC), a third given an intraperitoneal (ip) hypertonic saline injection (HS) and isotonic saline controls (IC) administered ip. One set of chick brains was perfused for immunohistochemistry while a second was sampled for quantitative RT-PCR. Plasma corticosterone (CORT) and arginine vasotocin (AVT) concentrations were significantly increased in the immobilized and hypertonic saline groups (p<0.01) compared to controls. Intense staining of the V1aR occurred throughout the organum vasculosum of the lamina terminalis (OVLT) and subseptal organ (SSO)/subfornical organ (SFO). The immunostaining allowed the boundaries of the two circumventricular organs (CVOs) to be described for the first time in avian species. Both treatment groups showed marked morphological changes in glia within the OVLT and SSO/SFO. The avian V1aR, angiotensin II type 1 receptor (AT1R), and transient receptor potential vanilloid receptor 1 (TRPV1) mRNA levels were increased in the SSO/SFO in hypertonic saline treated birds compared to isotonic controls. In contrast, the latter two genes (AT1R and TRPV1) were significantly decreased in the OVLT of birds subjected to hyperosmotic stress, while all three genes were significantly up-regulated after immobilization. Taken together, results show a possible differential function for the same receptors in two anatomically adjacent CVOs.

Hormonal control of drinking behavior in teleost fishes; insights from studies using eels

Marine teleost fishes drink environmental seawater to compensate for osmotic water loss, and the amount of water intake is precisely regulated to prevent dehydration or hypernatremia. Unlike terrestrial animals in which thirst motivates a series of drinking behaviors, aquatic fishes can drink environmental water by reflex swallowing without searching for water. Hormones are key effectors for the regulation of drinking. In particular, angiotensin II and atrial natriuretic peptide are likely candidates for physiological regulators because of their potent dipsogenic and antidipsogenic activities, respectively. In the eel, these hormones act on the area postrema in the medulla oblongata, a circumventricular structure without blood-brain barrier, which then regulates the activity of the glossopharyngeal-vagal motor complex. These motor neurons in the hindbrain innervate the upper esophageal sphincter muscle and other swallowing-related muscles in the pharynx and esophagus for regulation of drinking. Thus, the neural circuitry for drinking in fishes appears to be confined within the hindbrain. This simple mechanism is much different from that of terrestrial animals in which thirst sensation is induced through hormonal actions on the subfornical organ and organum vasculosum of the lamina terminalis that are located in the forebrain. It seems that the neural and hormonal mechanism that regulates drinking behavior has evolved from fishes depending on the availability of water in their natural habitats.

Area postrema, a brain circumventricular organ, is the site of antidipsogenic action of circulating atrial natriuretic peptide in eels

Accumulating evidence indicates that circulating atrial natriuretic peptide(ANP) potently reduces excess drinking to ameliorate hypernatremia in seawater(SW) eels. However, the cerebral mechanism underlying the antidipsogenic effect is largely unknown. To localize the ANP target site in the brain, we examined the distribution of ANP receptors (NPR-A) in eel brain immunohistochemically using an antiserum specific for eel NPR-A. The immunoreactive NPR-A was localized in the capillaries of various brain regions. In addition, immunoreactive neurons were observed mostly in the medulla oblongata, including the reticular formation, glossopharyngeal-vagal motor complex, commissural nucleus of Cajal, and area postrema (AP). Trypan Blue, which binds serum albumin and does not cross the blood–brain barrier, was injected peripherally and stained the neurons in the AP but not other NPR-A immunopositive neurons. These histological data indicate that circulating ANP acts on the AP, which was further confirmed by physiological experiments. To this end, the AP in SW eels was topically destroyed by electric cauterization or were by chemical lesion of its neurons by kainic acid, and ANP (100 pmol kg–1) was then injected into the circulation. Both heat-coagulative and chemical lesions to the AP greatly reduced an antidipsogenic effect of ANP, but the ANP effect was retained in sham-operated eels and in those with lesions outside the AP. These results strongly suggest that the AP, a circumventricular organ without a blood–brain barrier, serves as a functional window of access for the circulating ANP to inhibit drinking in eels.

The dipsogenic effect of the renin-angiotensin system in elasmobranch fish

This study investigated the control of drinking in elasmobranch fish through manipulation of the homologous renin-angiotensin system (RAS). The smooth muscle relaxant papaverine was found to increase basal drinking levels in the European lesser-spotted dogfish, Scyliorhinus canicula, almost 20-fold. However, this response was significantly reduced with the coadministration of the angiotensin-converting enzyme inhibitor captopril which had no effect when administered alone. Captopril was also found to block a 7-fold increase in drinking rate following administration of homologous angiotensin I in S. canicula. Finally, administration of homologous angiotensin II produced a dose-dependent response in drinking rate in two species of elasmobranchs, S. canicula and the Japanese dogfish, Triakis scyllia. These results demonstrate a central role of the RAS in the control of drinking in elasmobranch fish.

Angiotensin, thirst, and sodium appetite

Angiotensin (ANG) II is a powerful and phylogenetically widespread stimulus to thirst and sodium appetite. When it is injected directly into sensitive areas of the brain, it causes an immediate increase in water intake followed by a slower increase in NaCl intake. Drinking is vigorous, highly motivated, and rapidly completed. The amounts of water taken within 15 min or so of injection can exceed what the animal would spontaneously drink in the course of its normal activities over 24 h. The increase in NaCl intake is slower in onset, more persistent, and affected by experience. Increases in circulating ANG II have similar effects on drinking, although these may be partly obscured by accompanying rises in blood pressure. The circumventricular organs, median preoptic nucleus, and tissue surrounding the anteroventral third ventricle in the lamina terminalis (AV3V region) provide the neuroanatomic focus for thirst, sodium appetite, and cardiovascular control, making extensive connections with the hypothalamus, limbic system, and brain stem. The AV3V region is well provided with angiotensinergic nerve endings and angiotensin AT1 receptors, the receptor type responsible for acute responses to ANG II, and it responds vigorously to the dipsogenic action of ANG II. The nucleus tractus solitarius and other structures in the brain stem form part of a negative-feedback system for blood volume control, responding to baroreceptor and volume receptor information from the circulation and sending ascending noradrenergic and other projections to the AV3V region. The subfornical organ, organum vasculosum of the lamina terminalis and area postrema contain ANG II-sensitive receptors that allow circulating ANG II to interact with central nervous structures involved in hypovolemic thirst and sodium appetite and blood pressure control. Angiotensin peptides generated inside the blood-brain barrier may act as conventional neurotransmitters or, in view of the many instances of anatomic separation between sites of production and receptors, they may act as paracrine agents at a distance from their point of release. An attractive speculation is that some are responsible for long-term changes in neuronal organization, especially of sodium appetite. Anatomic mismatches between sites of production and receptors are less evident in limbic and brain stem structures responsible for body fluid homeostasis and blood pressure control. Limbic structures are rich in other neuroactive peptides, some of which have powerful effects on drinking, and they and many of the classical nonpeptide neurotransmitters may interact with ANG II to augment or inhibit drinking behavior. Because ANG II immunoreactivity and binding are so widely distributed in the central nervous system, brain ANG II is unlikely to have a role as circumscribed as that of circulating ANG II. Angiotensin peptides generated from brain precursors may also be involved in functions that have little immediate effect on body fluid homeostasis and blood pressure control, such as cell differentiation, regeneration and remodeling, or learning and memory. Analysis of the mechanisms of increased drinking caused by drugs and experimental procedures that activate the renal renin-angiotensin system, and clinical conditions in which renal renin secretion is increased, have provided evidence that endogenously released renal renin can generate enough circulating ANG II to stimulate drinking. But it is also certain that other mechanisms of thirst and sodium appetite still operate when the effects of circulating ANG II are blocked or absent, although it is not known whether this is also true for angiotensin peptides formed in the brain. Whether ANG II should be regarded primarily as a hormone released in hypovolemia helping to defend the blood volume, a neurotransmitter or paracrine agent with a privileged role in the neural pathways for thirst and sodium appetite of all kinds, a neural organizer especially in sodium appetit

Angiotensin II receptor subtypes in the duck subfornical organ: an electrophysiological and receptor autoradiographic investigation

The pharmacology of angiotensin II (AngII) receptors was investigated in the brain of ducks using receptor autoradiographic and electrophysiological methods. Using 125I[Val5]AngII as a ligand, specific binding was observed in sections of the duck adrenal gland and in several brain areas involved in body fluid homeostasis. Displacement studies using the same antagonists as used for classifying mammalian AngII receptor subtypes revealed that the rank order of potencies in competition with AngII receptors in the adrenal gland and in the subfornical organ was: AngII > CGP-42112A > losartan > PD-123319. Electrophysiological recordings from spontaneously active neurons of duck SFO slices revealed that the majority of neurons could be excited by AngII (10(-7) M). The excitatory effect of AngII could be partially inhibited by CGP-42112A (10(-5) M), which proved to be more effective than equimolar losartan and far more effective than PD-123319. These data suggest that the neuronal AngII receptors in the SFO are pharmacologically distinct from the mammalian AT1- and AT2-receptors. Further, central AngII receptors of ducks share common pharmacological characteristics with AngII receptors in the duck adrenal gland and peripheral organs of other bird species.

Water deprivation and subfornical organ activity in the pigeon a [14C]2-deoxyglucose study

Following varying degrees of water deprivation (0, 24 and 72 h), functional activity in the subfornical organ (SFO) of pigeons was measured using the [14C]2-deoxyglucose method. Increasing levels of water deprivation produced a significant increase in glucose uptake in SFO. The magnitude of the effect was systematically correlated with morphologically defined SFO subdivisions.

Ontogenesis of the angiotensin II (ANGII) receptor system in the duck brain

The ontogenetic development of the central nervous angiotensin II (ANGII) receptor system in the duck was studied at embryonic days E20 and E27 and at postnatal days P3 and P14 by computerized semiquantitative autoradiography employing the receptor antagonist 125I[1Sar,8Ile]ANGII as radioligand. For circumventricular structures involved in the sensing of brain-intrinsic (AV3V region) or blood-borne (subfornical organ, SFO) ANGII, binding sites for 125I[1Sar,8Ile]ANGII were first detectable at E27, with a steady rise in binding density up to P14. The choroid plexus of the lateral (PCVL) and third (PCVIII) cerebral ventricles responsible for cerebrospinal fluid (CSF) production were endowed with maximal ANGII receptor densities at E20 with subsequent reduction to constant medium (PCVIII) or low (PCVL) values. Besides the choroid plexus, the magnocellular paraventricular nucleus (PVN) was the only structure presenting ANGII specific binding sites at E20, although at low density. As for the SFO and AV3V region, labelling of ANGII binding sites in the PVN increased continuously during development to high values at P14. Nuclear components of the limbic system (archistriatum, amygdala and habenular complex) did not reveal specific labelling by the radioligand at E20 with constant, moderate binding densities evaluated for E27, P3 and P14. In the duck brain, functionally related structures exhibited a homogeneous ontogenetic development of their ANGII receptor system.

Response to angiotensin II after selective lesioning of brain regions believed to be involved in water intake regulation

The subfornical organ (SFO) and organum vasculosum lamina terminalis (OVLT) are regions of the brain that border the third ventricle (outside the blood-brain barrier) and have been implicated in the control of water intake elicited by angiotensin II (ANGII). Studies were conducted in which the response to injected ANGII following lesions of the SFO (LSFO) or OVLT (LOVLT) in broiler chicks was observed. Three groups of birds were used for each trial: lesioned and ANGII-injected (LI); not lesioned and ANGII-injected (NLI); and not lesioned and saline-injected (NLC). In Experiment 1, water intake of LISFO was decreased through 3 h postinjection (P less than .01). Intakes of LISFO and NLCSFO were not significantly different through 1 h postinjection. The OVLT did not have an effect on cumulative water intake in response to intramuscular ANGII. Water intakes of LIOVLT and NLIOVLT did not differ from each other, but were significantly higher than NLCOVLT (P less than .05) at .5 and 1 h postinjection. Feed intake was unaltered by SFO or OVLT lesions. Feed intake was suppressed and water intake increased by ANGII injection. The present study indicates that the SFO, but not the OVLT, plays a role in ANGII-induced water intake in broiler chicks.

Water and NaCl intake of chicks as mediated by angiotensin II, renin, or salt deficiency

Water, feed and NaCl intakes were measured in response to angiotensin II (ANGII) injected SC and ICV, and renin injected ICV, as well as to dietary salt deficiency in female broiler chicks (Gallus domesticus). In the first experiment, SC (100 micrograms/bird) and ICV (10 micrograms/bird) ANGII injection resulted in increased initial water intake. An additive effect on drinking was noted in response to consecutive daily SC injections. In addition, feed efficiency and growth were depressed following repeated ANGII injections (p less than 0.001). In a 2nd experiment, ICV ANGII stimulated increased cumulative water intake through 18 hours postinjection (p less than 0.05). Intake of 3.0% NaCl solution and feed was unaffected through 48 hours. Renin (1 microgram ICV) failed to affect cumulative water intake up to 48 hours postinjection. In the third experiment, dietary salt deficiency reduced feed intake after just 48 hours on salt-deficient diets (p less than 0.01), and growth and feed efficiency were significantly impaired (p less than 0.001) through 20 days of age. Intakes of NaCl solutions (0.8, 0.7 or 0.6%), however, were unaffected in salt-deficient vs. control birds. While the chicks in these experiments demonstrated a consistent drinking response to ANGII when injected peripherally or centrally, a salt appetite could not be elicited in these birds by components of the renin-angiotensin system or by dietary salt depletion.

Locations and properties of angiotensin II-responsive neurones in the circumventricular region of the duck brain

1. In brain slice preparations from the hypothalamus of domestic ducks, single-unit activity was recorded extracellularly to investigate location and properties of angiotensin II (AngII)-responsive neurones in various periventricular regions. 2. When exposing the slice to 10(-7) M-AngII in the perfusion medium, more than 65% of the neurones recorded in the subfornical organ (SFO) were activated (49 out of 75) and none inhibited. In the magnocellular (MC) region of the paraventricular nucleus (PVN) only four out of eighty-one neurones were influenced by AngII; one was inhibited and three were activated. In the anterior third ventricle region (A3V) two out of twenty-one neurones were activated by AngII. In the dorsal periventricular (PeV) region, one out of thirty-seven neurones was activated and one inhibited. The changes in firing rate of AngII-responsive neurones at comparable doses of AngII were generally large in the SFO and A3V but were small in neurones from the MC and PeV regions. 3. Analysis of AngII-responsive SFO neurones consistently revealed a dose-dependent stimulation with a threshold at 10(-9) M-AngII. The AngII antagonist 1Sar-8Ile-AngII (4 x 10(-7) to 10(-6) M) caused reversible, complete or partial suppression of responsiveness to 10(-7) M-AngII. Synaptic blockade with a medium low in Ca2+ and high in Mg2+ did not abolish AngII responsiveness in eight out of ten SFO neurones tested. 4. Angiotensin III affected neither AngII-responsive nor AngII-insensitive neurones. When eighteen AngII-responsive neurones were exposed to hypertonic stimulation (+20 to +30 mosmol/kg) by adding NaCl to the perfusion medium, only one neurone was stimulated and two were inhibited. 5. The results indicate that: (a) the SFO is a specific target for circulating AngII; (b) although neurones in the A3V responsive to AngII are rare, the pronounced excitation of those which were found suggest that neurones in this region might serve as targets for AngII acting from the brain side; (c) neurones in the MC region do not seem to function as direct AngII targets; (d) neuronal AngII responsiveness in the duck's hypothalamus seems to be specific inasmuch as activation by AngII (i) is readily blocked by an AngII antagonist, (ii) cannot be induced by AngIII, and (iii) is not associated, as a rule, with responsiveness to hypertonic stimulation.

Increase in basal firing rate and sensitivity to angiotensin II in subfornical organ neurones of ducks adapted to salt water

1. The influence of salt adaptation on spontaneous firing rate of subfornical organ (SFO) neurones and on their responsiveness to angiotensin II (AngII) (10(-10)-10(-7) M) were studied in vitro on hypothalamic brain slices taken alternately from ducks kept on either fresh water (FW ducks) or saline of 500 mosmol/kg for 8 weeks (SW ducks) as their only water supply. The animals were of the same age and were housed and fed identically. In SW ducks plasma osmolality and AngII plasma concentrations were typically increased. 2. Recording SFO single-unit activity in the AngII-free control perfusion medium disclosed significantly higher spontaneous firing rates in SW than in FW ducks with an average difference of 2.5 spikes/s. 3. With approximate threshold concentrations of AngII for activation of SFO neurones of 10(-10) M in slices from SW ducks and of 10(-9) M in slices from FW ducks, the fractions of neurones excited by AngII increased dose dependently in each group and were consistently larger in the slices from SW ducks. Average maximum increases in discharge rate during AngII-induced excitation also increased dose dependently and were higher at each AngII dose in SFO neurones from SW as compared to FW ducks. 4. Mean latencies of neuronal excitation decreased with increasing AngII doses in both groups of neurones but were significantly shorter in slices from SW than FW ducks. The shorter latencies in SW ducks corresponded to their enhanced sensitivity to AngII. Mean half-times of the disappearance of AngII-induced activation were determined after stimulation with 10(-7) M-AngII and were identical in SW and FW ducks, indicating no difference in kinetics in AngII-neurone interaction. 5. AngII-responsive SFO neurones in slices from SW ducks did not respond to AngIII and activation by AngII was abolished in the presence of the specific antagonist 1Sar-8Ile-AngII. 6. In the magnocellular portion of the paraventricular nucleus, the occurrence of AngII-responsive neurones was as infrequent in SW ducks (2 out of 45) as in FW ducks (0 out of 36). 7. The results indicate that adaptation to salt water in ducks selectively enhanced basal activity and responsiveness to AngII of the SFO neurones. This is a functional correlate of the up-regulation of AngII-receptor density observed in the SFO of the same species in the course of adaptation to salt water. Both adaptive adjustments seem to provide tighter coupling between systemic and central control of salt and fluid balance in conditions of chronic salt stress.

Projections of the nucleus of the tractus solitarius in the pigeon (Columba livia)

With the aid of autoradiographic and histochemical (WGA-HRP) tracing techniques, the projections of the nucleus of the tractus solitarius (nTS) in the pigeon have been delineated and related to the viscerotopic organization of the nucleus. As in mammals, nTS projects to both brainstem and forebrain structures. At medullary levels, projections were seen to nTS itself, to the dorsal motor nucleus of the vagus and to the subjacent and more ventral reticular formation. There is a substantial projection to the parabrachial nuclear complex with terminations in all its subnuclei and minor projections to locus coeruleus and several mesencephalic areas, including the ventral area of Tsai, the nucleus of the ascending brachium conjunctivum, and the compact portion of the tegmental pedunculopontine nucleus. At diencephalic levels, projections to the hypothalamus (magnocellular periventricular nucleus, stratum cellulare internum and externum) and dorsal thalamus were seen. Terminal fields within the basal telencephalon included the nucleus of the pallial commissure, the bed nucleus of the stria terminalis, and the nucleus accumbens. The organization of nTS projections in pigeons is correlated with the pattern of inputs to specific nTS subnuclei. Lateral tier subnuclei receiving cardiovascular and pulmonary inputs project upon the ventrolateral reticular formation and the ventrolateral parabrachial complex. Medial tier subnuclei receiving gustatory and gastrointestinal inputs project upon dorsal and medial parabrachial nuclei. Transparabrachial projections arise from nTS subnuclei receiving little or no primary input from the viscera.

The role of the subfornical organ in the drinking behavior of the pigeon

Pigeons with radiofrequency lesions that damaged the subfornical organ (SFO) (n = 4) or that isolated it from adjacent structures (n = 5), but not sham-lesioned pigeons, were unresponsive to blood-borne (i.p.) ANG II (100 micrograms/pigeon) in the immediate postoperative period and for 60 days thereafter. These animals were less sensitive to hypovolemic challenge (20% PEG), but they responded normally to 24 h of water deprivation and to cellular dehydration. Despite their unresponsiveness to bloodborne ANG II, the lesioned pigeons drank normally to 10 ng of i.c.v. ANG II given as early as 10 days after surgery, and they drank reliably and vigorously but less in total volume to 100 ng i.c.v. They also drank quickly, vigorously, and in normal total volume to i.c.v. tachykinins and bombesins, and to the peripheral (i.p.) bombesins. Peripheral (i.m.) tachykinins produced only low volume and variable drinking in all birds tested regardless of brain damage. The SFO of the pigeon, like that of the mammal, is essential for drinking evoked by blood-borne ANG II and is not necessary for thirst aroused by ANG II acting from within the cerebral ventricles. Lastly, it does not mediate the dipsogenic effects of the tachykinins or the bombesins.

Food and water intake response of turkeys to intracerebroventricular injections of angiotensin II

The effects of intracerebroventricular (ICV) injections of angiotensin II on food and water intake were studied in adult Medium White turkey hens. Food intake was not significantly affected by ICV injections of angiotensin II. The ICV injection of 50, 100, and 200 ng of angiotensin II significantly increased water intake in a dose-dependent manner. The dipsogenic effect of angiotensin II was significantly attenuated by Saralasin, an angiotensin blocker. These results suggest that angiotensin II functions in neural pathways within the central nervous system to control water intake, but not food intake, in turkeys.

Effects of Leu5-enkephalin on natural and angiotensin II-induced drinking in the Japanese quail (Coturnix coturnix japonica)

Natural drinking behavior was inhibited by intracranial (ic) injections of Leu5-enkephalin (LEN) (30 and 60 micrograms/100 g) for 60 min, but not by iv injections (30 and 100 micrograms/100 g) in the Japanese quail. Drinking induced by angiotensin II (AII) (30 and 50 micrograms/bird, ip) was also inhibited for 60 min by LEN (40, 60, and 100 micrograms/100 g, ic), given 5 min after the AII injections. Naloxone (3 mg/bird, ip) attenuated the inhibition of LEN (60 micrograms/100 g, ic) and when administered alone (3 mg/bird, ip) induced copious drinking. These results indicated that LEN binds with central opiate receptors to inhibit natural and AII-induced drinking and that endogenous enkephalins physiologically inhibit drinking.

Mechanisms for induction of drinking with special reference to angiotensin II

The Japanese quail drinks water vigorously after water deprivation, haemorrhage and administration of hypertonic saline solution. Most avian species responded to angiotensin II (AII) by drinking, but carnivorous birds and those originating in arid regions were insensitive. The receptive sites for AII were the subfornical organ (SFO) and the preoptic area (POA) in the Japanese quail. Catecholaminergic fibers proceed from the POA to the SFO. Dipsogenic information generated by AII at the POA is transferred to the SFO through the catecholaminergic nerve fibres. Plasma AII increased following dehydration and haemorrhage and returned to a normal level immediately after rehydration. Following dehydration, arginine vasotocin, aldosterone and corticosterone increased in plasma as well as AII. A single intraperitoneal injection of AII induced increases of arginine vasotocin, aldosterone and corticosterone in plasma. It seems that AII functions as a trigger for release of these other hormones during dehydration.

Extrahypothalamic peptidergic neurosecretion. II. Neurosecretion in the subfornical organ of Rana esculenta L

In the subfornical organ of Rana esculenta, three basic structural elements can be demonstrated by light microscopic and immunohistological techniques used for the demonstration of products of the neurosecretory system. These elements are: (i) neurones and their processes, which the constituents of the subfornical organ proper, (ii) afferent axons of the preoptic nucleus, and (iii) subependymal cells with coarse processes. The vesicular inclusions of the two former structures correspond to the neurophysin vesicles with respect to their size, structure and reactivity. The vesicles of the subependymal cells belong to the same size class, possess a somewhat granular internal structure and react atypically after the application of the ultrahistochemical technique for the identification of neurophysin vesicles. Presumably, their content is a glycoprotein with a high proportion of cystine. The peptidergic axons of the preoptic nucleus projecting to the subfornical organ form neuroneuronal synapses.

Involvement of catecholaminergic nerve fibers in angiotensin II-induced drinking in the Japanese quail, Coturnix coturnix japonica

Monamine distribution in a septohypothalamic area was investigated in the Japanese quail using a histochemical fluorescence method. This area includes the subfornical organ (SFO) and the preoptic area (POA) which are inferred dipsogenic receptor sites for angiotensin II (AII) in the Japanese quail. Nerve fibers showing yellow-green fluorescence were found between the POA and the SFO. Thwy traversed from the POA to the SFO, and some fibers seemed to terminate on the neurons in the SFO. After a low dose of reserpine, a considerable number of fluorescent perikarya were found in the POA. These fibers and perikarya appeared to be of primary catecholamine judging from the fluorescence color. Following transection of these fibers, fluorescence disappeared from the fibers located on the SFO side of the transection plane, while it became a little more intense on the POA side. After transection, microinjection of AII into the POA was no longer effective in induction of drinking. On the other hand, sham operation or transection in areas other than between the POA and the SFO produced only minute changes in those fluorescent fibers and had little effect on the dipsogenic potency of AII injected into the POA. These results suggest that information of AII perceived at the POA is transferred to the SFO via those primary catecholamine-containing nerve fibers, which effect induced drinking.

Ultrastructure of the subfornical organ of the chicken (Gallus domesticus)

The SFO of the chicken is divided in half by a large central blood sinus; ventrally it is covered by a thin layer of ependyma (including tanycytes, dendrites, and axons) which connects the two lateral halves and protrudes as a midsagittal crest into the lumen of the third ventricle. The ependyma consists predominantly of tanycytes with long basal processes which terminate upon perivascular spaces. These cells have an extensive Golgi apparatus and abundant lysosomes; their cellular apices containing polyribosomes and a few vesicles frequently protrude into the ventricle. In addition to astrocytes, oligodendrocytes, and microglial cells, there is another glial cell population that is distinguished by the presence of parallel stacks or spherical to ovoid conglomerates of rough ER and their unique location, i.e., limited to areas ventral and ventral-lateral to the large blood sinus. Two types of neurons are present: neurons in which there is a paucity of granulated vesicles and occasional vacuoles in both the cytoplasm and nuclei, the second type of neuron elaborates many granulated vesicles. Numerous puncta adhaerentia are observed between adjacent neuronal perikarya and between glial processes and neuronal perikarya. Diverse axon types are found within the chicken SFO. Axo-dendritic and axo-somatic axon terminals and presynaptic axon dilations contain assorted combinations of electron-lucent and granulated vesicles of different maximal diameters. Based on the morphology of these axons, cholinergic, peptidergic, and serotoninergic fibers are described. There are two additional groups of axons whose classification awaits further investigation. The chicken SFO differs from the mammalian SFO in several respects: it possesses an ependyma with secretory and/or absorptive tanycytes predominating; it is divided midsagittally by a central blood sinus; its lateral and dorsal limits are nebulous; a previously undescribed peculiar type of glial cell is found in a limited portion of the organ; supraependymal neurons are lacking.