The effect of intraseptally applied vasopressin on thermoregulation in the rat

Drug-induced therapeutic hypothermia after asphyxial cardiac arrest in swine

A feasibility study was performed to compare an investigational drug, HBN-1, to forced cooling to induce hypothermia after resuscitation in a translation model of asphyxial cardiac arrest in swine. Serum and cerebral spinal fluid neuron-specific enolase activity (sNSE and csfNSE) were measured after cardiac arrest as surrogate markers of brain injury. In a block design, swine resuscitated from 10 minutes of asphyxial cardiac arrest were infused intravenously with HBN-1 or iced saline vehicle (forced hypothermia [FH]) 5 to 45 minutes after return of spontaneous circulation (ROSC). External cooling in both groups was added 45 minutes after ROSC until hypothermia (T=4°C below baseline) was attained. Esophageal (core) temperature, shivering, cardiopulmonary parameters, and time to hypothermia after ROSC were monitored. sNSE and csfNSE were measured 180 minutes after ROSC. HBN-1 induced hypothermia significantly lowered temperature compared to FH 5-45 minutes after ROSC (p<0.0001). Time to hypothermia was reduced by HBN-1 (93±6 minutes) compared to FH (177±10 minutes) (p<0.0001). HBN-1 sNSE (0.7±1.9 ng/mL) and csfNSE (17.3±1.9 ng/mL) were lower compared to FH (6±1.6 ng/mL) and (49.7±32.0 ng/mL) (p<0.0001, p=0.022, respectively). There was no shivering with HBN-1 cooling while all FH cooled swine shivered (p<0.0001). The time to reach target hypothermia after cardiac arrest was reduced by nearly 50% with HBN-1 compared to the FH method of inducing hypothermia. Moreover, surrogate biomarkers of brain injury were significantly reduced with HBN-1 as compared to FH. While HBN-1-induced hypothermia shows promise for being neuroprotective, survival studies are needed to confirm these preliminary findings.

Induction of a prolonged hypothermic state by drug-induced reduction in the thermoregulatory set-point

BACKGROUND

The marked improvement in outcome following induction of hypothermia after cardiac arrest has spurred the search for better methods to induce cooling. A regulated decrease in core temperature mediated by a drug-induced reduction in the set point for thermoregulation may be an ideal means of inducing hypothermia. To this end, the exploratory drug HBN-1 was assessed as a means to induce mild and prolonged hypothermia.

METHODS

Free moving rats were infused i.v. for 12 hours with: a vehicle at room temperature (normothermia), a vehicle chilled to 4°C (forced hypothermia), or HBN-1 (mixture of ethanol, lidocaine, and vasopressin) at room temperature. Core (intra-abdominal) temperature (Tc) was measured telemetrically, tail skin temperature (Ttail) by infrared thermography, metabolic rate (MR) was estimated with indirect calorimetery, and shivering was scored visually.

RESULTS

HBN-1 elicited a reduction in Tc from 37.5°C to 34°C within 80 minutes after initiation of the infusion; Tc was maintained between 33°C and 34°C for more than 13 hours. HBN-1 infusion was associated with a reduction in MR (p=0.0006), a slight reduction in Ttail, and no evidence of shivering (p<0.001). The forced hypothermia group displayed shivering (p<0.001), a significant increase in MR, and a decrease in Ttail, indicative of peripheral vasoconstriction to reduce heat loss.

CONCLUSION

HBN-1 infusion induced a mild and prolonged hypothermia in free moving, unanesthetized rats characterized by modulation of thermoeffectors to reduce heat gain and increase heat loss. HBN-1 thus appears to elicit regulated hypothermia and may provide a new method for achieving a prolonged state of therapeutic hypothermia.

Deconstructing sociality, social evolution and relevant nonapeptide functions

Although behavioral neuroendocrinologists often discuss "sociality" as a unitary variable, the term encompasses a wide diversity of behaviors that do not evolve in a linked fashion across species. Thus grouping, monogamy, paternal care, cooperative breeding/alloparental care, and various other forms of social contact are evolutionarily labile and evolve in an almost cafeteria-like fashion, indicating that relevant neural mechanisms are at least partially dissociable. This poses a challenge for the study of the nonapeptides (vasopressin, oxytocin, and homologous neuropeptides), because nonapeptides are known to modulate all of these aspects of sociality in one species or another. Hence, we may expect substantial diversity in the behavioral functions of nonapeptides across species, and indeed this is the case. Further compounding this complexity is the fact that the pleiotropic contributions of nonapeptides to social behavior are matched by pleiotropic contributions to physiology. Given these considerations, single "model systems" approaches to nonapeptide function will likely not have strong predictive validity for humans or other species. Rather, if we are to achieve predictive validity, we must sample a wide diversity of species in an attempt to derive general principles. In the present review, I discuss what is known about functional evolution of nonapeptide systems, and critically evaluate general assumptions about bonding and other functions that are based on the model systems approach. From this analysis I attempt to summarize what can and cannot be generalized across species, and highlight critical gaps in our knowledge about the functional evolution of nonapeptide systems as it relates to dimensions of sociality.

Vasopressin innervation of the mouse (Mus musculus) brain and spinal cord

The neuropeptide vasopressin (AVP) has been implicated in the regulation of numerous physiological and behavioral processes. Although mice have become an important model for studying this regulation, there is no comprehensive description of AVP distribution in the mouse brain and spinal cord. With C57BL/6 mice, we used immunohistochemistry to corroborate the location of AVP-containing cells and to define the location of AVP-containing fibers throughout the mouse central nervous system. We describe AVP-immunoreactive (-ir) fibers in midbrain, hindbrain, and spinal cord areas, which have not previously been reported in mice, including innervation of the ventral tegmental area, dorsal and median raphe, lateral and medial parabrachial, solitary, ventrolateral periaqueductal gray, and interfascicular nuclei. We also provide a detailed description of AVP-ir innervation in heterogenous regions such as the amygdala, bed nucleus of the stria terminalis, and ventral forebrain. In general, our results suggest that, compared with other species, the mouse has a particularly robust and widespread distribution of AVP-ir fibers, which, as in other species, originates from a number of different cell groups in the telencephalon and diencephalon. Our data also highlight the robust nature of AVP innervation in specific regulatory nuclei, such as the ventral tegmental area and dorsal raphe nucleus among others, that are implicated in the regulation of many behaviors.

Central actions of arginine vasopressin and a V1a receptor antagonist on maternal aggression, maternal behavior, and grooming in lactating rats

Maternal aggression is a robust type of aggression displayed by lactating female rats. Although arginine vasopressin (AVP) has been implicated in the control of male aggression, its involvement in maternal aggression has not been thoroughly investigated. Previous neuroanatomical studies suggest that AVP may mediate the display of aggression during lactation. In the current study, AVP and an AVP V1a receptor antagonist were centrally administered to primiparous rats on days 5 and 15 of lactation, and aggression, maternal behavior, and grooming were recorded. Although AVP did not affect the number of attacks or duration of aggression, it increased the latency to initiate aggression on day 5, in addition to decreasing maternal behavior and increasing grooming. Conversely, V1a antagonist treatment increased maternal aggression on both days of lactation, decreased maternal behavior on day 15, and decreased grooming on day 5. Thus, it appears that central AVP activity modulates maternal aggression, as well as maternal behavior and grooming behavior during lactation.

Social behavior functions and related anatomical characteristics of vasotocin/vasopressin systems in vertebrates

The neuropeptide arginine vasotocin (AVT; non-mammals) and its mammalian homologue, arginine vasopressin (AVP) influence a variety of sex-typical and species-specific behaviors, and provide an integrational neural substrate for the dynamic modulation of those behaviors by endocrine and sensory stimuli. Although AVT/AVP behavioral functions and related anatomical features are increasingly well-known for individual species, ubiquitous species-specificity presents ever increasing challenges for identifying consistent structure-function patterns that are broadly meaningful. Towards this end, we provide a comprehensive review of the available literature on social behavior functions of AVT/AVP and related anatomical characteristics, inclusive of seasonal plasticity, sexual dimorphism, and steroid sensitivity. Based on this foundation, we then advance three major questions which are fundamental to a broad conceptualization of AVT/AVP social behavior functions: (1) Are there sufficient data to suggest that certain peptide functions or anatomical characteristics (neuron, fiber, and receptor distributions) are conserved across the vertebrate classes? (2) Are independently-evolved but similar behavior patterns (e.g. similar social structures) supported by convergent modifications of neuropeptide mechanisms, and if so, what mechanisms? (3) How does AVT/AVP influence behavior - by modulation of sensorimotor processes, motivational processes, or both? Hypotheses based upon these questions, rather than those based on individual organisms, should generate comparative data that will foster cross-class comparisons which are at present underrepresented in the available literature.

Microinjection of arginine vasopressin into the central nucleus of amygdala suppressed nociceptive jaw opening reflex in freely moving rats

This study was performed to examine the antinociceptive effect after microinjection of arginine vasopressin (AVP) into the central nucleus of amygdala. We recorded the jaw opening reflex in freely moving rats. After injection of 0.2 or 0.4 nM AVP into the central nucleus of amygdala, digastric electromyogram (dEMG) was suppressed to 55 +/- 5% or 88 +/- 3 of the control. Artificial cerebrospinal fluid had no effects on the basal dEMG activity. V(1) vasopressin receptor antagonist blocked the suppressive effect produced by microinjection of 0.4 nM AVP from 53 +/- 3 to 81 +/- 3% of the control. However, V(2) vasopressin receptor antagonist did not affect changes in dEMG. We observed dEMG activity after intracerebroventricular injection of naloxone, methysergide, or phentolamine. All drugs did not affect the basal dEMG activity at our dose. Naloxone blocked the suppressive effect of 0.4 nM AVP from 42 +/- 4 to 79 +/- 5% of the control. Methysergide also inhibited the suppression of dEMG from 44 +/- 3 to 83 +/- 6% of the control. However, phentolamine, an alpha-adrenergic receptor antagonist, did not affect the suppression of dEMG. These results indicate AVP in the central nucleus of amygdala has potent analgesic effects in the orofacial area. The antinociception of central AVP seems to be mediated by opioid and serotonergic pathways.

Neuropeptide expression in rat paraventricular hypothalamic neurons that project to the spinal cord

The paraventricular hypothalamic nucleus (PVH) exerts many of its regulatory functions through projections to spinal cord neurons that control autonomic and sensory functions. By using in situ hybridization histochemistry in combination with retrograde tract tracing, we analyzed the peptide expression among neurons in the rat PVH that send axons to the spinal cord. Projection neurons were labeled by immunohistochemical detection of retrogradely transported cholera toxin subunit B, and radiolabeled long riboprobes were used to identify neurons containing dynorphin, enkephalin, or oxytocin mRNA. Of the spinally projecting neurons in the PVH, approximately 40% expressed dynorphin mRNA, 40% expressed oxytocin mRNA, and 20% expressed enkephalin mRNA. Taken together with our previous findings on the distribution of vasopressin-expressing neurons in the PVH (Hallbeck and Blomqvist [1999] J. Comp. Neurol. 411:201-211), the results demonstrated that the different PVH subdivisions display distinct peptide expression patterns among the spinal cord-projecting neurons. Thus, the lateral parvocellular subdivision contained large numbers of spinal cord-projecting neurons that express any of the four investigated peptides, whereas the ventral part of the medial parvocellular subdivision displayed a strong preponderance for dynorphin- and vasopressin-expressing cells. The dorsal parvocellular subdivision almost exclusively contained dynorphin- and oxytocin-expressing spinal cord-projecting neurons. This parcellation of the peptide-expressing neurons suggested a functional diversity among the spinal cord-projecting subdivisions of the PVH that provide an anatomic basis for its various and distinct influences on autonomic and sensory processing at the spinal level.

Arginine vasopressin, fever and temperature regulation

While central administration of arginine vasopressin (VP) to the non-febrile rat at high doses can cause hypothermia, there is little evidence for a role for endogenous VP in normal thermoregulation. In contrast, VP arising from cell bodies in the bed nucleus of the stria terminalis and innervating the ventral septal areas and possibly the amygdala appears to be an endogenous antipyretic, i.e. a substance capable of reducing fever. As the synthesis of VP in bed nucleus neurons is dependent upon circulating androgens, female rats have much less VP in these cells and their projections than do male rats. In keeping with this, females may make use of VP to a lesser extent than do males to bring about antipyresis. The phenomenon whereby the VP receptor can become sensitized by previous exposure to VP may be responsible for some states of endogenous antipyresis, in which fevers are suppressed through overactivity of the vasopressinergic system. States of endogenous antipyresis can be revealed around the time of parturition in both the neonate and the mother.

Effect of intraseptal vasotocin and vasoactive intestinal polypeptide infusions on courtship song and aggression in the male zebra finch (Taeniopygia guttata)

The present experiments were conducted to test the hypothesis that septal arginine vasotocin (AVT) and vasoactive intestinal polypeptide (VIP) modulate directed song (a courtship behaviour) and aggression in male zebra finches (Taeniopygia guttata). Subjects were surgically fitted with a guide cannula directed at the septum. Following recovery they were tested for aggression and directed song following infusions of AVT, its antagonist (anti-vasopressin, AVP), and saline volume control. Infusion of the AVT antagonist significantly reduced all three aggressive behaviours measured (pecks, beak fences and chases); and AVT infusion significantly facilitated beak fencing. Vasoactive intestinal polypeptide treatment significantly reduced pecking. No treatment produced a change in directed song. Comparison with findings in mammals suggests that modulation of aggression by septal AVT (or AVP) is evolutionarily conserved in vertebrates, but modulation of aggression by VIP has not previously been reported for any vertebrate.

Vasotocin and vasoactive intestinal polypeptide modulate aggression in a territorial songbird, the violet-eared waxbill (Estrildidae: Uraeginthus granatina)

Previous research demonstrates that intraseptal administrations of arginine vasotocin (AVT) inhibit male aggression in the territorial field sparrow (Emberizidae: Spizella pusilla) but facilitate aggression in the colonial zebra finch (Estrildidae: Taeniopygia guttata). In order to determine whether this difference may be related to the territorial and colonial social organizations of these two species, the effect of AVT infusions was examined in a territorial Estrildid species, the violet-eared waxbill (Uraeginthus granatina). This species is more closely related to the zebra finch than to the field sparrow and shares most critical features of breeding ecology in common with zebra finches, but differs in social organization. AVT infusions administered via chronic guide cannulae directed at the septum significantly inhibited aggressive behavior, consistent with results in the territorial field sparrow, supporting the hypothesis that social organization is correlated with AVT function. Similar experiments with mesotocin and substance P produced no effects on any of the behaviors measured, but infusions of vasoactive intestinal polypeptide (VIP) significantly facilitated aggression. This result contrasts with the inhibitory effect of septal VIP obtained in the colonial zebra finch, suggesting that VIP function may be correlated with social organization as well.

Effects of vasopressin and involvement of receptor subtypes in the rat central amygdaloid nucleus in vitro

Effects of arginine-vasopressin (AVP) on neurons in the central amygdaloid nucleus (ACe) were investigated with rat brain slice preparations using extracellular recording methods. Of 160 ACe neurons tested, 70 cells (44%) were excited and 9 cells (6%) were inhibited by bath application of AVP at 3 x 10(-7) M. The excitatory effects of AVP were dose-dependent and the threshold concentration was approximately 10(-10) to 10(-9) M. The excitatory effects of AVP persisted under blockade of synaptic transmission by perfusing with Ca2+-free and high-Mg2+ medium, whereas the inhibitory effects were abolished by synaptic blockade. AVP-induced effects were mimicked by a V1-receptor agonist and completely blocked by a selective V1-antagonist. V2-agonist produced no effects on ACe neurons and V2-antagonist had no effect on AVP-induced excitation. These results showed that the excitatory effect of AVP on ACe neurons was produced by a direct action through the V1-receptors, whereas the inhibitory response of ACe neurons to AVP seemed to be produced by an indirect action. The results of this study suggest that AVP is involved in the amygdala-relevant functions as a neurotransmitter or a neuromodulator.

Inhibition of the vasopressin-enhancing effect on memory retrieval and relearning by a vasopressin V1 receptor antagonist in mice

We have previously shown that [Arg8]vasopressin bilaterally administered into the ventral hippocampus of mice at a dose of 0.025 ng/animal 10 min prior to the retention session, improved long-term retrieval processes and relearning of a Go-No-Go visual discrimination task. The purpose of the present study was to determine whether the vasopressin V1 receptor antagonist, -beta-mercapto-beta,beta-cyclopentamethylenepropionyl1, O-Me-Tyr2,Arg8]vasopressin, d(CH2)5Tyr(Me)vasopressin), is able to block the behavioral effect of arginine-vasopressin in the ventral hippocampus. We first tested the effect of three doses of d(CH2)5Tyr(Me)vasopressin (0.025, 1, and 6.3 ng/animal) in the same experimental conditions as used for arginine-vasopressin. The results showed a dose-dependent deleterious effect of the vasopressin V1 receptor antagonist on retrieval and relearning, suggesting the involvement of endogenous arginine-vasopressin in the ventral hippocampus for these memory processes. Second, we tested the ability of d(CH2)5Tyr(Me)vasopressin to block the enhancing effect of experimentally administered arginine-vasopressin. The antagonist was injected at a dose of 0.025 ng, which had no intrinsic effect on behavior, or at a dose of 1 ng, which had a weak deleterious effect on behavior, followed by administration of 0.025 ng of arginine-vasopressin. The results showed that even at the weakest dose (0.025 ng), d(CH2)5Tyr(Me)vasopressin blocked the enhancing effect of arginine-vasopressin on retrieval and relearning. Thus, as for other behaviors and structures, the antagonist microinjected into the ventral hippocampus prevents the enhancing effect of arginine-vasopressin on long-term retrieval and relearning. However, the exclusive involvement of the vasopressin V1 receptors remain to demonstrate vis-a-vis oxytocin receptors.

Vasopressin in the brain of a desert hibernator, the jerboa (Jaculus orientalis): presence of sexual dimorphism and seasonal variation

The distribution of vasopressin innervation in the brain of the jerboa (Jaculus orientalis) was investigated, with special attention to sex differences and seasonal variations. Vasopressin perikarya were observed in the paraventricular and supraoptic nuclei, the suprachiasmatic nucleus, the periventricular nucleus, the medial preoptic area, the bed nucleus of the stria terminalis, and the medial amygdaloid nucleus. In addition, vasopressin cell bodies were observed in the ventral retrochiasmatic area. After treatment with colchicine, vasopressin perikarya were also observed around the organum vasculosum laminae terminalis, in the medial diagonal band of Broca, and in the dorsal medial preoptic nucleus. Vasopressin fibers were also found to be more widespread in the jerboa brain than in other rodents. Fibers were observed in the medial diagonal band of Broca, the stria medullaris, the tuber cinerum, the area postrema, the medial vestibular nucleus, and the dorsal motor nucleus of the vagus. Sexual dimorphism and seasonal variation in vasopressin immunoreactivity were observed in areas that not only showed a testosterone-dependent vasopressin innervation in other rodents but also in the paratenial and mediodorsal thalamic nuclei, the tuber cinerum, the supramammillary complex, the zona incerta, the interpeduncular complex, and the dorsal and medial raphe nuclei. A denser vasopressin innervation was observed in spring/summer (sexual active period) than in autumn. Numerous brain structures contained vasopressin receptors (cerebral cortex, hypothalamus, substantia nigra, dentate gyrus, thalamic nuclei, superior colliculus, dorsal cochlear nucleus, and cerebellum); no sex- or season-related differences were observed. These data indicate a high level of vasopressin in the jerboa brain, which may reflect an adaptation to its harsh bioclimatic environment.

Induction of arousal in hibernating European hamsters (Cricetus cricetus L.) by vasopressin infusion in the lateral septum

Vasopressin immunostaining in the lateral septum of the European hamster (Cricetus cricetus L.) disappears in autumn, at the time of the first appearance of hypothermic periods characteristic to hibernation. Previous results have shown that chronic administration of vasopressin in the lateral septum during winter prevents the expression of hypothermic periods, suggesting a role for this peptide in hibernation. It is now observed that acute infusion of vasopressin, and in 50% of the cases, of a specific vasopressin V1 receptor agonist, during a hypothermic period results in an immediate termination of hypothermia. Infusion of oxytocin or a vasopressin V2 receptor agonist were without effect. The results indicate that the seasonal variation in central vasopressin activity, possibly through an interaction with V1 receptors, may play an important role in the expression of hibernation in the European hamster.

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.

Vasopressin-induced motor effects: localization of a sensitive site in the amygdala

Arginine vasopressin (AVP) induces motor effects when administered into the cerebral ventricles, the ventral septal area (VSA), or the vestibular cerebellum of the rat brain. Because AVP-like immunoreactivity and AVP-binding sites exist in the central medial amygdala (cmeA), and because the amygdala can be kindled to produce motor effects, we hypothesized that the amygdala might play a role in AVP-induced motor effects. This hypothesis was tested by observing motor behavior in response to injection of AVP into the central medial region of the amygdala. Our results demonstrate that an initial injection of AVP into the cmeA caused minor motor effects, including immobility, prostration and ataxia, whereas a similar injection, given 24 h later, caused severe motor effects including barrel rotations and myoclonic/myotonic-like convulsive behavior. A potential receptor basis for the AVP-induced motor and sensitization effects in the cmeA was investigated using AVP analogues. A V1 antagonist, d(CH2)5Tyr(Me)AVP, blocked both the motor and sensitization effects produced by cmeA AVP injection. A V2 receptor agonist, DDAVP, did not affect motor activity upon cmeA injection, but did, however, sensitize animals to subsequent cmeA AVP injection. These results suggest that the cmeA is a sensitive site for AVP-induced motor effects and that these motor effects are sensitized by prior exposure to AVP. While the motor effects observed after cmeA AVP injection are mediated via AVP receptors that resemble the V1 type, the sensitization effect may be mediated via multiple receptor systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Ingestive behaviors of the rat deficient in vasopressin synthesis (Brattleboro strain). Effect of chronic treatment by dDAVP

Spontaneous manipulator and locomotor activities, food and fluid intake have been recorded from rats suffering from a genetic lack of central vasopressin (VP) synthesis (Brattleboro strain, DI), their heterozygous litter mates (HZ) or Long Evans (LE) rats. The daily patterns of activities did not differ, except for their drinking behavior. This was mainly associated with food intake during the dark period with LE rats but was distributed equally during light and dark periods with DI rats. HZ rats showed a behavioral heterogeneity, some of them following the daily pattern of LE rats, and others, that of DI rats. The daily feeding pattern was identical in the three genotypes but the selection between two isocaloric contrasted diets was different. When they were fed ad lib, HZ and DI rats consumed less carbohydrate than LE rats, the protein intake being unchanged. On the contrary, when the DI rats were only fed during the dark period, they ate more carbohydrate than LE rats. The peripheral infusion of a V2 AVP agonist (dDAVP) restored a normal hydric balance in DI rats but failed to modify the diet selection. These data show that in the rats, the lack of central VP synthesis disturbs both the selection of diets and the efficiency of the satiety signals. These disturbances were unchanged by the peripheral VP treatment which suggested the direct involvement of the central release of the neuropeptide.

Depletion of brain alpha-MSH alters prostaglandin and interleukin fever in rats

Alpha-melanocyte stimulating hormone (alpha-MSH), a putative endogenous antipyretic agent, is synthesized largely within neurons in the arcuate nucleus. To test the hypothesis that destruction of this area would increase the febrile response, male Wistar rats, treated as neonates with intraperitoneal injections of monosodium glutamate (MSG) or saline, were given intracerebroventricular (i.c.v.) injections of prostaglandin E1 (20 ng; 200 ng) or purified interleukin-1 (20 U) and body temperature was monitored. The fevers displayed by the MSG-treated animals were significantly greater (P less than 0.05) than those of the controls for the lower dose of PGE1 at 10-30 min and for IL-1 at 3-6 h after the injections. MSG-treated rats showed significant reduction (P less than 0.01) in alpha-MSH content of the medial basal hypothalamus and lateral septum when compared to saline controls. Body temperature response of non-febrile animals to high ambient temperature was not affected by the MSG treatment. These data support the hypothesis that alpha-MSH is an endogenous antipyretic in the rat.

Central vasopressin infusion prevents hibernation in the European hamster (Cricetus cricetus)

The amount of immunocytochemically detectable vasopressin in the brain of the European hamster (Cricetus cricetus) shows a seasonal variation; i.e., dense vasopressin immunoreactivity is present in the lateral septum during summer but is absent in autumn and winter [Buijs, R. M., Pévet, P., Masson-Pévet, M., Pool, C. W., De Vries, G. J., Canguilhem, B. & Vivien-Roels, B. (1986) Brain Res. 371, 193-196]. In the winter period the European hamster hibernates. Since vasopressin in the lateral septum is known to be involved in the control of body temperature, we investigated whether infusion of vasopressin in the lateral septum during autumn-winter could influence hypothermic patterns normally seen in hibernating animals. Hamsters whose lateral septum was infused with vasopressin showed almost no periods of hypothermia, whereas hamsters treated with control infusions displayed a normal hibernation pattern. The results indicate that persistence of vasopressin release in the lateral septum of the European hamster during winter can prevent hibernation.

Physiological effects of arginine vasotocin and mesotocin in cockerels

1. The effects of continuous infusion of 0.1, 1.0 and 10.0 mU/min/kg body weight of arginine vasotocin (AVT) or mesotocin (MT) on cardiovascular and thermoregulatory responses, on plasma osmolality and ionic composition and on plasma concentrations of AVT, MT, prolactin and aldosterone, were investigated in conscious White Leghorn cockerels. 2. Neither of the peptides, at any dose, affected cardiovascular functions, plasma ions and osmolality. Infusion of MT at the rate of 10 mU/min/kg body weight increased respiratory rate. Both peptides at doses of 1 and 10 mU/min/kg reduced the temperatures of the comb and shank but had no effect on the skin and cloaca. 3. Doses of 0.1 and 1.0 mU MT/min/kg reduced plasma aldosterone and at 10 mU/min/kg increased plasma AVT. At any given dose MT had no effect on plasma prolactin. AVT at 0.1 and 1.0 mU/min/kg of AVT reduced plasma MT. AVT at 1.0 mU/min/kg increased plasma prolactin and at 10 mU/min/kg reduced plasma aldosterone. 4. During saline infusion, plasma MT was positively correlated with plasma AVT and negatively correlated with respiratory rate and cloacal temperature. Plasma AVT showed a positive correlation with plasma MT and aldosterone and a negative correlation with respiratory rate and skin temperature. 5. During saline infusion, there was no significant correlation between cardiovascular functions, or plasma osmolality and ionic composition and plasma MT or AVT. 6. The present study suggests that interrelationships between circulating concentrations of AVT and MT do exist and that AVT affects aldosterone secretion. These neurohypophysical peptides are involved in thermoregulation.

Prostaglandin fever in rats is altered by kainic acid lesions of the ventral septal area

The ventral septal area (VSA) has been shown to be a region within the rat brain where arginine vasopressin (AVP) acts to reduce fever. To test the hypothesis that destruction of this area would affect the magnitude of the febrile response, body temperature was monitored in male, Wistar rats given intracerebroventricular injections of prostaglandin E1 (200 ng) and saline (10 microliter) before and after bilateral injections of kainic acid (KA) or of saline vehicle into the VSA. While fever heights were unaffected by the lesion, fever in the KA-lesioned animals remained significantly elevated (P less than 0.05) for 1 h after the peak response. There was no significant difference in the fever responses displayed by sham-lesioned animals. The body temperature response of non-febrile animals to high or low ambient temperature was unaffected by the lesions. The enhanced fever following the KA lesion, but not sham lesions of the VSA would support the hypothesis that this region is involved in endogenous suppression of fever.

The role of vasopressin as an antipyretic in the ventral septal area and its possible involvement in convulsive disorders

Perfusion of the peptide, arginine vasopressin (AVP), within the ventral septal area (VSA) of the brain of a number of species reduces fever but not normal body temperature. This antipyretic response appears to be mediated by AVP receptors of the V1 subtype. Lesions of the VSA with kainic acid are associated with prolonged and enhanced fevers in rats. A role for endogenous AVP in fever suppression within the VSA comes from several types of experiments: (1) AVP release within the VSA is inversely correlated to fever height; (2) AVP antagonists or antiserum injected into the VSA prolong fever; (3) animals lacking endogenous AVP in the VSA (Brattleboro rat, long-term castrated rat) develop enhanced fevers. Electrical stimulation of the AVP-containing cell bodies of the bed nucleus of the stria terminalis (BST) orthodromically inhibits VSA neurons and also suppresses fever; the latter effect can be abolished with application of a V1 antagonist to the VSA. Iontophoretic studies indicate that AVP inhibits glutamate-stimulated activity of thermoresponsive and other VSA neurons. AVP can also act in the VSA to cause severe motor disturbances; this action is receptor mediated and increases in severity upon sequential exposure to AVP. Because sites of action of the antipyretic and convulsive action of AVP are similar, and because animals lacking brain AVP display reduced convulsive activity, it is possible that AVP, released during fever, could be involved in the genesis of convulsive activity.

Prostaglandin E1 hyperthermia in water or food deprived rats

The effect of 48 hours of water deprivation on the colonic temperature response to intrahypothalamic injection of prostaglandin E1 (PGE1) was investigated in adult male rats. Water deprivation did not alter colonic temperature of rats at a neutral ambient temperature. Administration of PGE1 at doses of 50, 200 and 400 ng gave rise to a short latency dose dependent hyperthermia in both control and water deprived rats. Water deprived rats had significantly greater increases in colonic temperature following the two higher doses of PGE1. Control rats and water deprived rats exposed to the cold (5 degrees C) had decreases in colonic temperature which were not significantly different. Water deprivation, which should increase the plasma levels of the putative endogenous antipyretic vasopressin, does not attenuate PGE1 hyperthermia but has a slight enhancing effect. Following food deprivation for 48 hours rats had a slight but significantly greater increase in colonic temperature following intrahypothalamic injection of 200 ng PGE1. Thus the water deprivation induced change in responsiveness to PGE1 may be due to the decrease in food intake which accompanies water deprivation. The mechanism by which rats exhibit an enhanced febrile response to PGE1 administration following food or water deprivation is not yet known.

Long-term cold adaptation in the rat

1. To determine whether long-term cold exposure induces insulative adaptation in the rat, two groups of eight adult animals each were exposed to 4 and 25 degrees C, respectively, for 18 months. 2. At any ambient temperature between -5 and 30 degrees C, the cold adapted animals had a higher rate of oxygen uptake, and higher unfurred skin temperatures than the controls. 3. At ambient temperatures below thermoneutrality, whole body thermal resistance increased continuously in both groups of animals. 4. It is concluded that long-term exposure does not induce insulative adaptation, and that thermal resistance is not maximal at the lower critical temperature.

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.

The antipyretic effects of centrally administered vasopressin at different ambient temperatures

The antipyretic response to arginine vasopressin (AVP) was investigated at 3 ambient temperatures using unanesthetized freely behaving male rats. Responses of non-febrile and febrile rats to intracerebroventricular (i.c.v.) injections of AVP and s.c. injection of indomethacin were observed at cold (4 degrees C), thermoneutral (25 degrees C) and warm (32 degrees C) ambient temperatures. In agreement with previous reports i.c.v. AVP at 25 degrees C decreased brain temperature of febrile but not non-febrile rats. This antipyretic effect was also observed at the warm ambient temperature and during cold exposure. Responses to s.c. indomethacin were qualitatively similar to i.c.v. AVP at neutral and warm temperatures. In the cold, however, indomethacin decreased the brain temperature of both non-febrile and febrile animals, although unlike AVP, brain temperature of non-febrile animals were decreased somewhat more than that of febrile animals. These data show that AVP decreases brain temperature of febrile more than non-febrile rats at all ambient temperatures and may therefore be acting partially on febrile set point. It is likewise clear that AVP affects specific effector mechanisms since antipyretic effects were of different magnitudes at different ambient temperatures. The observation that AVP and indomethacin have qualitatively similar effects on fever at the 3 ambient temperatures suggest that they may act via a common neural pathway.

Perfusion of the septum of the rabbit with vasopressin antiserum enhances endotoxin fever

The septal region of the brains of conscious, adult, male New Zealand White rabbits were perfused by means of a push-pull system before and after an intravenous administration of bacterial pyrogen extracted from Salmonella abortus equi. Perfusion of the septal area with sucrose solution (260 mM) had no significant effect on the resulting fever (1.13 +/- 0.09 degrees C) when compared to a control fever without the push-pull perfusion (1.06 +/- 0.12 degrees C). Arginine vasopressin (AVP) added to the perfusing solution (20 micrograms/ml) caused a significant attenuation of the fever (0.81 +/- 0.20 degrees C). An antiserum specific to AVP when added to the perfusing solution resulted in a fever which was significantly greater (2.38 +/- 0.13 degrees C) than the control. Radioimmunoassay of perfusates collected from the control perfusions before and during fever showed that, as the body temperature rose in response to the pyrogen, the level of AVP in the perfusate collected from the septal area decreased. These results provide further evidence that AVP may act in the septal area of the brain to modulate the febrile response.

Effects of treadmill running and swimming on plasma and brain vasopressin levels in rats

The influence of treadmill or swimming exercise on resting values of plasma and brain arginine vasopressin (AVP), and plasma sodium, potassium, osmolality and proteins was studied after 5 weeks of training using female Wistar rats. The duration of daily training sessions was progressively increased to reach 6 h/day for swim training (S) and 3 h/day for treadmill running (T). Compared to their untrained controls, treadmill and swim training were respectively associated with: a significant lower body weight; a decreased plasma AVP (36.4% for T and 47.4% for S) and hypothalamic AVP (20% for T and 16% for S); a higher hypophyseal AVP (145% for T and 36.3 for S); a decreased plasma osmolality (6.7% for T and 6.1% for S), sodium (1.2% for both) and potassium (15% for T and 22.4% for S); and no change in protein concentration. For T, rectal temperature increased (38.5 +/- 0.20 to 39.7 +/- 0.5) and for S rectal temperature decreased from 38.6 +/- 0.12 to 37.74 +/- 0.10). The differences observed in AVP contents of the pineal and Harderian glands (enhanced only in the treadmill groups) could be explained by the supposed role of these glands in thermoregulation. Two conclusions could be drawn from this study: there are no parallel changes in the hypothalamo-hypophyseal system (where AVP plays its endocrine role) and the brain (where AVP is a neurotransmitter); plasma changes could be explained by an extracellular fluid expansion with Na and K loss leading to a decrease in AVP secretion.