The antipyretic effects of centrally administered vasopressin at different ambient temperatures

Identification and characterization of mesotocin and V1a-like vasotocin receptors in a urodele amphibian, Taricha granulosa

The cDNA sequences encoding the mesotocin receptor (MTR) and vasotocin 1a receptor (VTR-1a) were identified in a urodele amphibian, the rough-skinned newt, Taricha granulosa. Saturation binding of [(3)H]oxytocin (OT) to the Taricha MTR (tMTR) was best fit by a two-state model; a high affinity-low abundance site and a lower affinity-high abundance site. Competition-binding studies found the following rank-order affinities for the tMTR: mesotocin (MT)>OT≈vasotocin (VT)>vasopressin (VP)>isotocin (IT). Inositol phosphate (IP) accumulation studies demonstrated functional activity of both the tMTR and Taricha VTR-1a (tVTR-1a) in a heterologous cell culture system. The rank-order potencies for the tMTR were MT>OT>VT≈VP>IT. The combined binding and IP results indicate that VT may act as a partial agonist of the tMTR. Rank-order potencies for the tVTR-1a were VT>VP>MT≈OT>IT. For both receptors, stimulation of IP accumulation was blocked by d(CH(2))(5)[Tyr(Me)(2)]AVP (Manning compound) and d(CH(2))(5)[Tyr(Me)(2),Thr(4),Tyr-NH(2)]OVT (OTA). OTA was a more potent antagonist for the transiently expressed tMTR while Manning compound was relatively more potent at inhibiting IP accumulation in tVTR-1a expressing cells. In contradiction to earlier assumptions, the absolute IC(50) of Manning compound was lower for the tMTR (27nM±13) than the tVTR-1a (586nM±166) indicating its potential higher affinity for the tMTR, a finding with special relevance to interpretation of comparative studies investigating the behavioral and physiological actions of neurohypophysial peptides in non-mammalian species.

Effects of intracerebroventricular infusions of arginine vasopressin in sheep

In sheep, neither the in vivo effect of vasopressin administered by a method other than systemic infusion nor the central effects on behavior from the perspective of stress regulation has been fully elucidated in an intact animal. We examined changes in behavioral, adrenocorticotropic, and autonomic nervous functions after intracerebroventricular infusions of arginine vasopressin (AVP) to elucidate its central role. Intracerebroventricular infusions of AVP (0, 0.12, 1.2 and 12 microg/500 microl/30 min) evoked a dose-related increase in plasma cortisol concentration. There were significant treatment-related effects on the total duration of sham-chewing (Friedman's test, X2=12.75, p=.0052), on the total duration of bar-biting (Friedman's test, X2=15.0, p=.0018), and on the total duration of rubbing (Friedman's test, X2=12.0, p=.0074). AVP 12 microg treatment induced a greater degree of sham-chewing and bar-biting than the other three treatments did (Nemenyi multiple comparisons: p<0.1). These findings indicate, together with our previous findings, that AVP has the same corticotropic potential as corticotropin-releasing hormone infused intracerebroventricularly in equal molar concentrations. Although the degree to which central stress signaling pathways are involved in these responses remains speculative, the relationships between stereotypies and central AVP are of particular interest.

Conformational solution studies of (Sar7)desamino- and (MeAla7)desamino-vasopressin analogues using NMR spectroscopy

Solution structures of two analogues of vasopressin with an amino acid sequence of c[Mpa1-Tyr2-Phe3-Gln4-Asn5-Cys6]-Xaa7-Arg8-Gly9-NH2 (Xaa = Sar [I] or MeAla [II]) were established using ROE and the 3J(HNH alpha) couplings. Each of the peptides was found to exist in two stable isomers, pertaining to the cis or trans status of the Cys6-Xaa7 peptide bond, thus giving rise to four study objects. Two methods for studies of the conformational properties of the structures were compared. In the first, the algorithm consisted of three steps: (i) An Electrostatically Driven Monte-Carlo (EDMC) search for low-energy conformations. (ii) Simulations of the NOESY spectra and the vicinal couplings for these conformations. (iii) Determination of the statistical weights of the conformations with the ANALYZE package, so as to meet the best fit of the averaged NOE intensities and couplings to the experimental data. In the second method, the distance constraints and the torsion angles were used as the usual constraints in the Distance Geometry and Simulated Annealing algorithms. The flexibility of the pressin ring and the C-terminus was characterized by a large number of families of conformations. The presence of the beta-turn at position 4,5 was confirmed for all low energy structures found. The use of the EDMC method for the elaboration of the NMR data for small flexible peptides yielded an adequate description of their conformational diversity and is the method of choice for the analysis of their solution structures.

Antipyretic effect of arginine vasotocin in toads

Arginine vasotocin (AVT) is a nonmammalian analog of the mammalian hormone arginine vasopressin (AVP). These peptides are known for their antidiuretic and pressor effects. More recently, AVP has been recognized as an important antipyretic molecule in mammals. However, no information exists about the role of AVT in febrile ectotherms. We tested the hypothesis that AVT is an antipyretic molecule in the toad Bufo paracnemis. Toads equipped with a temperature probe were placed in a thermal gradient, and preferred body temperature was recorded continuously. A behavioral fever was observed after lipopolysaccharide (LPS) was injected systemically (200 microg/kg). Systemically injected AVT (300 pmol/kg) alone caused no significant change in body temperature, but abolished LPS-induced fever. Moreover, a smaller dose of AVT (10 pmol/kg), which did not affect LPS-induced fever when injected peripherally, abolished fever when injected intracerebroventricularly. We therefore conclude that AVT plays an antipyretic role in the central nervous system, by means of behavior, in an ectotherm, a fact consistent with the notion that AVT/AVP elicits antipyresis by reducing the thermoregulatory set point.

Central CO-heme oxygenase pathway raises body temperature by a prostaglandin-independent way

Recently, the carbon monoxide (CO)-heme oxygenase pathway has been shown to play an important role in fever generation by acting on the central nervous system, but the mechanisms involved have not been assessed. Thus the present study was designed to determine whether prostagandins participate in the rise in body temperature (T(b)) observed after induction of the CO-heme oxygenase pathway in the central nervous system. Intracerebroventricular (ICV) injection of heme-lysinate (152 nmol/4 microl), which is known to induce the CO-heme oxygenase pathway, caused an increase in T(b) [thermal index (TI) = 5.3 +/- 0.5 degrees C. h], which was attenuated by ICV administration of the heme oxygenase inhibitor ZnDPBG (200 nmol/4 microl; TI = 2.5 +/- 1.7 degrees C. h; P < 0.05). No change in T(b) was observed after intraperitoneal injection of the cyclooxygenase inhibitor indomethacin (5 mg/kg), whereas indomethacin at the same dose attenuated the fever induced by ICV administration of lipopolysaccharide (LPS) (10 ng/2 microl) (vehicle/LPS: TI = 4.5 +/- 0.5 degrees C. h; indomethacin/LPS: TI = 1.7 +/- 1.0 degrees C. h; P < 0.05). Interestingly, indomethacin did not affect the rise in T(b) induced by heme-lysinate (152 nmol/4 microl) ICV injection (vehicle/heme: TI = 4.5 +/- 1.4 degrees C. h; indomethacin/heme: TI = 4.2 +/- 1.0 degrees C. h). Finally, PGE(2) (200 ng/2 microl) injected ICV evoked a rise in T(b) that lasted 1.5 h. The heme oxygenase inhibitor ZnDPBG (200 nmol/4 microl) failed to alter PGE(2)-induced fever. Taken together, these results indicate that the central CO-heme oxygenase pathway increases T(b) independently of prostaglandins.

Voles and vasopressin: a review of molecular, cellular, and behavioral studies of pair bonding and paternal behaviors

Several lines of evidence have implicated the neurohypophyseal peptide, vasopressin (VP), in the mediation of complex social behaviors including affiliation, aggression, juvenile recognition and parental behavior. Recent studies in microtine rodents using cellular, molecular and behavioral approaches provide additional evidence suggesting a role for VP in the formation of pair bonding and male parental care. Monogamous and promiscuous voles differ in social behaviors such as mating-induced pair bonding, selective aggression, and male parental care. Comparative studies have demonstrated that they also differ in dynamics of VP synthesis and release associated with reproduction, in the distribution pattern and regional quantity of VP receptors, and in the promoter sequence of the V1a receptor gene. In monogamous prairie voles, (Microtus ochrogaster), brain administration of VP induces pair bonding and male parental care whereas administration of the VP antagonist diminishes these behaviors. Together, these data suggest that VP is involved in the regulation of social behaviors in monogamous voles and differences in the brain VP system may underlie species differences in behavior and life strategy in voles.

Vasopressin acting at V1-type receptors produces membrane depolarization in neonatal rat spinal lateral column neurons

Vasopressin-immunoreactive fibers have been visualized in the area of spinal lateral horn cells, including spinal sympathetic preganglionic neurons. The presence and nature of vasopressin receptors on neurons in this area were addressed using whole-cell patch-clamp techniques in transverse spinal cord slice preparations from neonatal rat. Bath applications of Arg8-vasopressin (VP) induced a slow-onset membrane depolarization accompanied by spike discharges and membrane oscillations. In voltage-clamp, applications of VP induced a reversible, tetrodotoxin-resistant and dose-dependent inward current in 90% of tested cells. This effect was blocked by a V1 receptor antagonist [D-(CH2)5 Tyr (Me)-VP], whereas a V2 receptor agonist [desamino-(D-Arg8)-vasopressin] was ineffective. Furthermore the applications of oxytocin produced significantly smaller depolarizations when compared with VP suggesting that, at least in the neonatal lateral horn cells, vasopressin rather than oxytocin is more effective ligand. Both the amplitude and duration of the VP effect were enhanced after intracellular dialysis with GTP-gamma-S, a non-hydrolyzable GTP analogue, whereas the inward current was significantly reduced after intracellular dialysis with GDP-beta-S, a stable analogue of GDP that competitively inhibits G-proteins. The observation that the VP-induced net inward current reversed at a potential close to the equilibrium for potassium ions and was associated with a decrease in membrane conductance in a majority of tested cells suggest mediation through closure of a leak potassium conductance. These data indicate that SPNs and other lateral horn cells possess functional G-protein-coupled V1-type vasopressin receptors that, in adult spinal cord, may contribute to CNS regulation of autonomic nervous system function.

Vasopressin's depolarizing action on neonatal rat spinal lateral horn neurons may involve multiple conductances

Vasopressin-immunoreactive fibers have been visualized in the area of spinal lateral horn cells, including spinal sympathetic preganglionic neurons (SPNs). The presence and nature of vasopressin receptors on 125 neurons in this area were addressed using whole-cell patch-clamp techniques in transverse spinal cord slice preparations from neonatal rat (11-21 days). Local pressure applications of Arg-vasopressin (AVP, 1 microM) induced a slow-onset membrane depolarization accompanied by spike discharges and membrane oscillations. In voltage-clamp, applications of AVP (10 nM-1 microM) induced a reversible, tetrodotoxin-resistant and dose-dependent inward current in 90% of tested cells. This effect was blocked by a V1 receptor antagonist [D-(CH2)5 Tyr (Me)-AVP], whereas a V2 receptor agonist [desamino-(D-Arg8)-vasopressin] was ineffective. Both the amplitude and duration of the AVP effect were significantly modified after intracellular dialysis of non-hydrolysable G-protein modulators. I-V relationships, examined in 75 cells, suggested two conductances. In 36 cells the net AVP current reversed approximately -102 mV, was associated with a decrease in membrane conductance and yielded linear I-V plots, suggesting mediation through closure of a resting potassium conductance. In a further 26 cells the I-V lines remained almost parallel in the voltage range used in this study (-130 to -40 mV), while the membrane conductance was decreased in a majority of these cells. In the remaining 13 cells the net AVP current was estimated to reverse approximately -30 mV and was associated with a small increase in membrane conductance, suggesting mediation through opening of a nonselective cationic conductance. These data indicate that the majority of SPNs and other lateral horn cells possess functional G-protein-coupled V1-type vasopressin receptors in the neonatal spinal cord. In the adult spinal cord, some of these receptors are likely to participate in CNS regulation of autonomic nervous system function.

AVP mediates the attenuated febrile response to administration of PGE1 in rats near term of pregnancy

Rats have an attenuated febrile response to intracerebroventricular injection of PGE1 near the term of pregnancy, the mechanism of which is unknown. The present experiments were carried out to test the hypothesis that arginine vasopressin (AVP), functioning as an endogenous antipyretic substance in the central nervous system, mediates this attenuated febrile response. The febrile response to intracerebroventricular injection of 0.2 microg PGE1 was determined in pregnant and nonpregnant rats after an intracerebroventricular injection of either vehicle or a vasopressin V1-receptor antagonist. After intracerebroventricular administration of vehicle, intracerebroventricular administration of 0.2 microg PGE1 produced significant increases in core temperature in both nonpregnant and pregnant animals. The increase in core temperature, however, was attenuated both in magnitude and duration in pregnant compared with nonpregnant animals. After intracerebroventricular administration of a vasopressin V1-receptor antagonist, intracerebroventricular administration of 0.2 microg PGE1 produced significant increases in core temperature that were similar in nonpregnant and pregnant animals. Our data support the hypothesis that a pregnancy-related activation of AVP as an endogenous antipyretic substance in the central nervous system attenuates the febrile response to intracerebroventricular administration of PGE1 near term of pregnancy in rats.

CNS cell groups projecting to sympathetic outflow of tail artery: neural circuits involved in heat loss in the rat

In the rat, approximately 20% of total body heat-loss occurs by sympathetically mediated increases in blood flow through an elaborate system of arteriovenous anastomoses in the skin of its tail. In this study, the CNS cell groups that regulate this sympathetic outflow were identified by the viral transneuronal labeling method. Pseudorabies virus was injected into the wall of the ventral tail artery in rats that had their cauda equina transected to eliminate the somatic innervation of the tail. After 4-7 days survival, the pattern of CNS transneuronal labeling was studied. Sympathetic preganglionic neurons in the T11-L2 (mainly L1) levels of the intermediolateral cell column (IML) were labeled by 4 days. After 5 days, sympathetic pre-motor neurons (i.e., supraspinal neurons that project to the IML) were identified near the ventral medullary surface; some of these contained serotonin immunoreactivity. Additional groups of the sympathetic premotor areas were labeled by 6 days post-injection, including the rostral ventrolateral medulla (C1 adrenergic neurons), rostral ventromedial medulla, caudal raphe nuclei (serotonin neurons in the raphe pallidus and magnus nuclei), A5 noradrenergic cell group, lateral hypothalamic area and paraventricular hypothalamic area (oxytocin-immunoreactive neurons). Seven days after the PRV injections, additional cell groups in the telencephalon (viz., bed nucleus of the stria terminalis, medial and lateral preoptic areas and medial preoptic nucleus), diencephalon (viz., subincertal nucleus, zona incerta as well as dorsal, dorsomedial, parafascicular, posterior and ventromedial hypothalamic nuclei) and midbrain (viz., periaqueductal gray matter, precommissural nucleus, Edinger-Westphal nucleus and ventral tegmental area) were labeled. The discussion is focused on the CNS cell groups involved in the control of body temperature and fever.

Characterization of vasopressin receptors in cultured cells derived from the region of rat brain circumventricular organs

The aim of the present study was to characterize vasopressin receptors within the two circumventricular organs located in the lamina terminalis of the rat brain, namely the organum vasculosum of the lamina terminalis and the subfornical organ. Cells derived from both structures were isolated, cultured and intracellular Ca2+ concentrations were measured in single fura-2 loaded neurons and astrocytes after application of vasopressin and various vasopressin analogues. Subsequent to Ca2+ measurements, the identification of neurons and astrocytes was verified using immunocytochemistry with cell type-specific antibodies. High proportions of subfornical organ (34%) and organum vasculosum laminae terminalis (28%) neurons exhibited increased intracellular Ca2+ concentration after exposure to 1-1000 nM vasopressin. Within single cells, the response was dose-dependent. Similar results were obtained in subfornical organ (62%) and organum vasculosum laminae terminalis (38%) astrocytes with minor differences in the transient amplitude and pattern distribution when compared with neurons. Since omission of extracellular Ca2+ preserved vasopressin responsiveness, it is likely that intracellular stores were the main source of mobilized Ca2+. The preincubation of neurons and astrocytes with the V1 receptor-specific antagonist d(CH2)5[Tyr(Me)2]8-arginine vasopressin (10-100 nM) selectively and reversibly blocked the vasopressin-mediated response. Oxytocin-induced Ca2+ transients (0.32-1000 nM), which were observed in 32% (63%) or organum vasculosum laminae terminalis and in 54% (42%) of subfornical organ neurons (astrocytes), were not affected by the V1-specific antagonist. These data indicate the presence of a V1-like vasopressin receptor and an oxytocin receptor in cultured neurons and astrocytes from both circumventricular organ structures. In addition, the exposure to the highly selective V2 receptor agonist, 1-desamino,8-D-arginine vasopressin, evoked Ca2+ transients almost exclusively in organum vasculosum laminae terminalis neurons (eight of 18 tested). Only 1 (n = 14) subfornical organ neuron and none of the astrocytes tested (n = 26) responded to 1-desamino,8-D-arginine vasopressin. Since 1-desamino,8-D-arginine vasopressin acting via "classical" V2 receptors is not expected to affect the intracellular Ca2+ concentration, these data indicate the tissue and cell type-specific expression of a 1-desamino,8-D-arginine vasopressin-sensitive vasopressin receptor in neurons of the organum vasculosum laminae terminalis. In summary, the results indicate a heterogeneity of neurohypophyseal peptide receptor subtypes in the primary cell culture of both circumventricular structures.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization and characterization of vasopressin binding sites in the rat brain using an iodinated linear AVP antagonist

The binding characteristics and central distribution of 125I-Linear AVP antagonist, a new ligand for vasopressin binding sites, are described in the following studies. Saturation studies performed on rat brain septal membranes demonstrated that 125I-Linear AVP antagonist binds to a single class of sites with high affinity (55 pM) and limited capacity (88 fmol/mg protein). In autoradiographic studies, 125I-Linear AVP antagonist labeled brain areas known to contain vasopressin receptors without binding to neurophysins. 125I-Linear AVP antagonist also labeled sites in cortex, hypothalamus, ventral tegmental area and substantia nigra. In competition studies, 125I-Linear AVP antagonist binding was most readily blocked by AVP and a selective V1a agonist. Oxytocin and a selective V2 ligand were effective only in micromolar concentrations. A selective oxytocin agonist was virtually ineffective in blocking 125I-Linear AVP antagonist binding. In regions that contain a high density of oxytocin binding sites, however, oxytocin-displaceable binding was observed. In agreement with studies on peripheral tissues, the binding profile generated from these studies indicates that 125I-Linear AVP antagonist binds to vasopressin receptors of the V1a subtype. These results suggest that 125I-Linear AVP antagonist is a valuable ligand for the study of central AVP receptors.

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

Intracerebroventricular injection of arginine vasotocin induces elevation of blood pressure in anesthetized trout

The present investigation assessed the ability of the neurohypophysial nonapeptide arginine vasotocin (AVT) to centrally regulate the cardiovascular activity in fish. Intracerebroventricular (ICV) injection of AVT (0.4 to 50 ng/kg b.wt.) in anesthetized trout resulted in a dose-related increase in blood pressure (BP) without any consistent changes in heart rate. For doses of AVT ranging from 2 to 50 ng/kg b.wt., BP remained elevated during at least 25 min after ICV injection. Systemic (intraarterial) administration of the same doses of AVT appeared to be less efficient than ICV injection, except for the highest dose (50 ng/kg) which evoked a similar rise in BP as that observed after ICV administration. In contrast to AVT, a high concentration of neuropeptide Y (10 micrograms/kg b.wt., ICV) caused only a slight increase of BP. The results suggest that AVT acts centrally to regulate BP in fish. These data, together with the widespread distribution of AVT-immunoreactive fibers and AVT binding sites in the brain, support the notion that, in fish, AVT may play neuromodulator and/or neurotransmitter functions.

E-series prostaglandins and arginine vasopressin in the modulation of male sexual behavior

Studies carried out recently in the author's laboratory have suggested that fever accompanies copulation in the male rat. Given the action of prostaglandin-E (PGE) in the genesis of fever and given the integrative role of the medial preoptic area (MPOA) in the expression of both fever and male sexual behavior, two hypotheses were advanced concerning male copulation. The first concerns PGE in facilitating transmission in MPOA pathways mediating mounting, intromission and ejaculation. The second concerns arginine vasopressin, a presumed "natural antagonist" of PGE, in inhibiting such transmission and eventually making the male refractory to the receptive female. Several experiments were suggested for testing each hypothesis.

Antipyretic doses of centrally administered vasopressin reach physiologically meaningful concentrations in the brain of the rat as evaluated by microdialysis

It was important to determine whether vasopressin (AVP) injected intracerebroventricularly (i.c.v.) in the rat reached the site of action within the ventral septal area (VSA) in sufficient concentrations to account for its physiological effects. Microdialysis was used to evaluate this hypothesis. The exchange rate across the dialysis tubing was determined in vitro to be 0.40%. After placement of the microdialysis cannula in the VSA of the rat the recovery of i.c.v. injected labelled or cold AVP was 0.23 and 0.20%, respectively. Maximum concentrations of AVP in the extracellular fluid of the VSA was determined to be 10.7 nM after 10 ng i.c.v. and hence extrapolated to be 1.07 nM after 1 ng i.c.v. or 2.65 nM after 2.5 ng i.c.v. between which lies the threshold dose of AVP for its antipyretic effects. This can be compared with a reported Kd for these receptors of 1.06 nM as determined by receptor binding assay.

Criteria for establishing a physiological role for brain peptides. A case in point: the role of vasopressin in thermoregulation during fever and antipyresis

This paper has attempted to present and discuss the criteria necessary for the evaluation of a specific physiological role for a peptide in the CNS. These criteria are based on many experimental approaches to the problem and conclusions must be supported by the weight of the evidence. These criteria were illustrated by examining the hypothesis that AVP is an antipyretic neurotransmitter involved in regulating febrile increases in Tb by release and action in the VSA of the brain. The weight of the evidence in this case implies that this hypothesis is essentially correct. The only serious conflicting evidence comes from the work with Brattleboro rats. It is hoped that further research will resolve these discrepancies or result in a suitably modified hypothesis.

Antipyresis due to centrally administered vasopressin differentially alters thermoregulatory effectors depending on the ambient temperature

The intracerebroventricular (i.c.v.) administration of arginine vasopressin (AVP), in the febrile rat elicits an antipyresis at cold, warm and neutral ambient temperatures. These experiments were conducted, therefore, to elucidate the thermoregulatory effector mechanisms responsible for this antipyretic effect. At 25 degrees C, AVP-induced antipyresis was mediated by tail skin vasodilation while metabolic rate was unaffected. At 4 degrees C, the antipyresis produced by AVP was approximately double that seen at 25 degrees C. This effect appeared to be mediated exclusively by inhibition of heat production since the metabolic rate decreased markedly following AVP. This antipyresis at 4 degrees C was accompanied by cutaneous vasoconstriction. At 32 degrees C, neither vasomotor tone, metabolic rate nor evaporative heat loss could be shown to contribute to the small antipyretic effect elicited by AVP. We conclude from these data that i.c.v. AVP is producing antipyresis by affecting the febrile body temperature set-point mechanism since the thermoregulatory strategy to lose heat varies at different ambient temperatures and the decrease in body temperature cannot be shown to be due to changes in a single effector mechanism.