Vasopressin: a homeostatic effector in the febrile process

Vasopressin-induced cytoplasmic and nuclear calcium signaling in embryonic cortical astrocytes: dynamics of calcium and calcium-dependent kinase translocation

The present study sought to determine the downstream consequences of V1a vasopressin receptor (V1aR) activation of Ca2+ signaling in cortical astrocytes. Results of these analyses demonstrated that V1aR activation led to a marked increase in both cytoplasmic and nuclear Ca2+. We also investigated V1aR activation of Ca2+-activated signaling kinases, protein kinase C (PKC), Ca2+/calmodulin-dependent protein kinase II (CaMKII), and the mitogen-activated protein (MAP) kinases [MAPK and extracellular signal-regulated kinases 1 and 2 (ERK1/2)], their localization within cytoplasmic and nuclear compartments, and activation of their downstream nuclear target, the transcription factor cAMP response element-binding protein (CREB). Results of these analyses demonstrated that V1aR activation led to a significant rise in PKC, CaMKII, and ERK1/2 activation, with CaMKII and ERK1/2 demonstrating dynamic transport between cytoplasmic and nuclear compartments. Although no evidence of PKC translocation was apparent, PKC and CaMKs were required for activation and nuclear translocation of ERK1/2. Subsequent to CaMKII and ERK1/2 translocation to the nucleus, CREB activation occurred and was found to be dependent on upstream activation of ERK1/2 and CaMKs. These data provide the first systematic analysis of the V1aR-induced Ca2+ signaling cascade in cortical astrocytes. In addition, results of this study introduce a heretofore unknown effect of vasopressin, dynamic Ca2+ signaling between the cytoplasm and nucleus that leads to comparable dynamics of kinase activation and shuttling between cytoplasmic and nuclear compartments. Implications for development and regeneration induced by V1aR activation of CREB-regulated gene expression in cortical astrocytes are discussed.

Regulation and mechanism of L-type calcium channel activation via V1a vasopressin receptor activation in cultured cortical neurons

We have sought to elucidate the biochemical mechanisms that underlie the memory enhancing properties of the neural peptide vasopressin. Toward that goal we have investigated vasopressin induction of calcium signaling cascades, long held to be involved in long-term memory function, in neurons derived from the cerebral cortex, a brain region associated with long-term memory. Our previous studies demonstrated that in cultured cortical neurons, V1a vasopressin receptor (V1aR) activation resulted in a sustained rise in intracellular calcium concentration that was dependent on calcium influx (Son & Brinton, 1998). To investigate the mechanism of V1aR-induced calcium influx, we investigated V1aR activation of the calcium channel subtype(s) in cortical neurons cultured from Sprague-Dawley rat embryonic day 18 fetuses. The results of these analyses demonstrated that the L-type calcium channel blocker nifedipine blocked 250 nM V1 vasopressin receptor agonist (V1 agonist)-induced calcium influx. Intracellular calcium imaging analyses using fura-2AM demonstrated that blockade of L-type calcium channels prevented the 250 nM V1 agonist-induced rise in intracellular calcium concentration. These results indicate that the influx of extracellular calcium via L-type calcium channels is an essential step in the initiation of the V1 agonist-induced rise in intracellular calcium concentration. To determine the mechanism of V1aR activation of L-type calcium channels, regulatory components of the phosphatidylinositol signaling pathway were investigated. The results of these analyses demonstrated that V1 agonist-induced calcium influx was blocked by both a phospholipase C inhibitor (U-73122) and a protein kinase C inhibitor (bisindolylmaleimide I). Further analysis of V1aR activation of protein kinase C (PKC) demonstrated that V1 agonist induced PKC activity within 1 min of exposure in cultured cortical neurons. These data indicate that in cultured cortical neurons, V1aR activation regulates the influx of extracellular calcium via L-type calcium channel activation through a protein kinase-C-dependent mechanism. The results of these studies provide biochemical mechanisms by which vasopressin could enhance memory function. Those mechanisms include a complex cascade that is initiated by activation of the phosphatidylinositol pathway, activation of protein kinase C, followed by phosphorylation of L-type calcium channels to initiate the influx of extracellular calcium to activate a cascade of calcium-dependent release of intracellular calcium.

Effects of hydration on febrile temperature patterns in rabbits

Patients with fever have a predisposition to experience dehydration, which may alter their thermoregulatory responses to elevated body temperature. In view of the recent discovery of the antipyretic activity of arginine vasopressin (AVP), it is possible that dehydration has a beneficial role during fever. Dehydration may enhance endogenous antipyresis by stimulating AVP release, making aggressive fluid replacement, which may inhibit AVP release, undesirable during fever. This study addressed the effects of manipulation of hydration status on temperature and cardiovascular responses in endotoxin-injected rabbits. Eight unanesthetized chronically instrumented rabbits were exposed to lipopolysaccharide (LPS) while in euhydrated state, after furosemide (5 mg/kg) and 24 hours of water deprivation (dehydrated), after infusion of saline (30 mL/kg) while in euhydrated state (hyperhydrated), and after saline (mL/per overnight body weight loss in grams) while in dehydrated state (rehydrated). Dehydrated rabbits display higher fevers that are biphasic in nature and are accompanied by increased vasoconstriction and duration of mean arterial pressure increases, indicating that activation of antipyretic mechanisms in dehydrated rabbits was not sufficient to reduce body core temperature. In addition, fluid supplementation in euhydrated rabbits did not alter the febrile response; however, a marked decrease in heart rate was noted. Furthermore, fluid supplementation in dehydrated rabbits significantly attenuates the rectal temperature and heart rate response to LPS injection, indicating the possibility that activation of antipyretic mechanisms of AVP in rehydrated rabbits was sufficient to reduce body core temperature. The results suggest that fluid supplementation has a beneficial role in keeping body temperature lower .

Vasopressin-induced calcium signaling in cultured cortical neurons

Earlier autoradiographic studies from our laboratory detected vasopressin recognition sites in the mammalian cerebral cortex [R.E. Brinton, K.W. Gee, J.K. Wamsley, T.P. Davis, H.I. Yamamura, Regional distribution of putative vasopressin receptors in rat brain and pituitary by quantitative autoradiography, Proc. Natl. Acad. Sci. U. S.A., 81 (1984) 7248-7252; C. Chen, R.D. Brinton, T.J. Shors, R.F. Thompson, Vasopressin induction of long-lasting potentiation of synaptic transmission in the dentate gyrus, Hippocampus, 3 (1993) 193-204]. More recently, we have detected mRNA for the V1a vasopressin receptors (V1aRs) in cultured cortical neurons [R.S. Yamazaki, Q. Chen, S.S. Schreiber, R.D. Brinton, V1a Vasopressin receptor mRNA expression in cultured neurons, astroglia, and oligodendroglia of rat cerebral cortex, Mol. Brain Res., 45 (1996) 138-140]. To determine whether these recognition sites are functional receptors, we have pursued the signal transduction mechanism associated with the V1a vasopressin receptor in enriched cultures of cortical neurons. Results of these studies demonstrate that exposure of cortical neurons to the selective V1 vasopressin receptor agonist, [Phe2,Orn8]-vasotocin, (V1 agonist) induced a significant accumulation of [3H]inositol-1-phosphate ([3H]IP1). V1 agonist-induced accumulation of [3H]IP1 was concentration dependent and exhibited a linear dose response curve. Time course analysis of V1 agonist-induced accumulation of [3H]IP1 revealed a significant increase by 20 min which then decreased gradually over the remaining 60 min observation period. V1 agonist-induced accumulation of [3H]IP1 was blocked by a selective V1a vasopressin receptor antagonist, (Phenylac1, D-Tyr(Me)2, Arg6,8, Lys-NH29)-vasopressin. Results of calcium fluorometry studies indicated that V1 agonist exposure induced a marked and sustained rise in intracellular calcium which was abolished in the absence of extracellular calcium. The loss of the rise in intracellular calcium was not due to a failure to induce PIP2 hydrolysis since activation of the phosphatidylinositol pathway occurred in the absence of extracellular calcium. V1 agonist activation of calcium influx was then investigated. V1 agonist-induced 45Ca2+ uptake was concentration dependent with a biphasic time course at 250 nM. Preincubation with the L-type calcium channel blocker, nifedipine, blocked V1 agonist-induced calcium influx suggesting V1 agonist-induced L-type calcium channel activation in cortical neurons. Furthermore, V1 agonist-induced calcium influx was blocked by both bisindolyleimide I (PKC inhibitor) and U-73122 (PLC inhibitor) suggesting a modulation of V1 agonist-induced L-type calcium channel activation by downstream components of the phosphatidylinositol signaling pathway such as protein kinase C. These results indicate that in cultured cortical neurons, V1a vasopressin receptor activation leads to induction of the phosphatidylinositol signaling pathway, influx of extracellular calcium via L-type calcium channel activation, and a rise in intracellular calcium which is dependent on V1a receptor activated influx of extracellular calcium. These data are the first to demonstrate an effector mechanism for the V1 vasopressin receptor in the cerebral cortex and provide a potential biochemical mechanism that may underlie vasopressin enhancement of memory function.

Anatomic patterns of Fos immunostaining in rat brain following systemic endotoxin administration

To identify brain neurons that participate in the acute phase response, rat brains were examined immunocytochemically for Fos protein following the intravenous administration of bacterial endotoxin (lipopolysaccharide, LPS). Two to three hours after the injection of LPS, 150 micrograms/kg body weight, to adult male Long-Evans rats, a consistent anatomic pattern of Fos immunostained cell nuclei is seen. In the brain stem, prominant Fos immunostaining is induced in tyrosine hydroxylase immunoreactive neurons of the caudal ventral-lateral medulla (the A1 cell group), in both tyrosine hydroxylase positive and negative neurons of nu. tractus solitarius, in the parabrachial nu., and in a few neurons of the locus ceruleus. In the hypothalamus, endotoxin induces Fos expression in magnocellular neurons of the paraventricular and supraoptic nuclei and internuclear cell groups. A higher percentage of oxytocin-immunoreactive cells is double labeled for Fos nuclear immunostaining than vasopressin-immunoreactive cells. A minority of somatostatin immunoreactive periventricular hypothalamic neurons are Fos positive. Other hypothalamic nuclei that contain endotoxin-induced Fos nuclear immunostaining include the parvocellular neurons of the paraventricular nu., the dorsomedial and arcuate nuclei, the lateral hypothalamus, the dorsal hypothalamic area (zona incerta), and the median nucleus of the preoptic area. LPS induces numerous Fos-positive neurons in regions known to respond to a variety of stressful stimuli; these regions include the preoptic area, bed nucleus of the stria terminalis, lateral septum, and the central and medial nuclei of the amygdala. Moreover, Fos nuclear immunostaining is seen in neurons of circumventricular organs: the organum vasculosum of the lamina terminalis, the subfornical organ, and the area postrema. The maximum intensity of Fos nuclear immunostaining occurs 2-3 h after endotoxin administration and declines thereafter. It is attenuated by pretreatment with indomethacin, 25 mg/kg body weight Sc, or dexamethasone, 1 mg/kg IP. These observations are consistent with the participation of a variety of brain neuronal systems in the acute phase response and elucidate the functional neuroanatomy of that response at the cellular level.

Central effects of interleukin-1 on blood pressure, thermogenesis, and the release of vasopressin, ACTH, and atrial natriuretic peptide

To assess the central role of interleukin 1-beta (IL-1 beta) in the release of ACTH, vasopressin (AVP) and atrial natriuretic peptide (ANP) and in the regulation of blood pressure and thermogenesis, 3 ng (0.173 pM) x 100-1 x BW-1 (LIL), 30 ng (1.73 pM) x 100g-1 x BW-1 (MIL), and 150 ng (8.63 pM) x 100g-1 x BW-1 (HIL) of human IL-1 beta dissolved in sterile saline were injected intracerebroventricularly to conscious rats. In the control rats, saline alone (5 microliters) was administered. In three other groups, rats were pretreated with indomethacin, a cyclooxygenase inhibitor, given i.v. (1 mg x 100g-1 x BW-1); medium and high doses of IL-1 beta or its vehicle were given. In the LIL group, IL-1 beta increased blood pressure, body temperature and plasma AVP and ANP without any changes in heart rate (HR) and plasma ACTH. In the MIL group, plasma ACTH was increased, and changes in the other parameters were similar to those in the LIL group. In the HIL group, however, the pressor and thermogenetic responses were attenuated; plasma AVP, ACTH, and ANP were increased; and HR was unchanged. In the control (CON) group, none of these parameters was changed throughout the studies. Indomethacin abolished the AVP and ACTH responses to IL-1 beta, but potentiated the pressor and hypothermic responses and increased plasma ANP. These data suggest that the actions of IL-1 beta on AVP and ACTH release and thermogenesis, but not on blood pressure and the release of ANP, are modulated by the stimulated central production of prostaglandins.

Comparison of the effects of bacterial lipopolysaccharide and muramyl dipeptide on food intake

For further characterization of the mechanism involved in the anorexia during bacterial infection, we investigated whether muramyl dipeptide (MDP), the minimal immunologically active structure of gram-positive bacterial cell walls, affects rats' food intake in the same way as lipopolysaccharide (LPS) from E. coli. MDP (1.6 mg/kg body weight = b.wt.) injected intraperitoneally (IP) reduced food intake by decreasing meal frequency without affecting meal size. Indomethacin (2.5 mg/kg b.wt., IP) but not verapamil (5 mg/kg b.wt., IP) attenuated the hypophagic effect of MDP. In further experiments, MDP and LPS (100 micrograms/kg b.wt., IP) both inhibited gastric emptying and indomethacin failed to block this effect of LPS. Hepatic vagotomy did not attenuate the hypophagic effects of MDP or LPS. LPS reduced water intake only when food was available, but reduced food intake also during water deprivation. MDP did not affect water intake. MDP and LPS both had an aversive effect, but LiCl, which was also aversive, failed to reduce feeding under the conditions tested. This questions the role of a conditioned taste aversion in the hypophagia induced by MDP or LPS. The results suggest that a stimulation of eicosanoid synthesis contributes to MDP-induced hypophagia and may therefore also contribute to the anorexia during infection. In contrast, an inhibition of gastric emptying, an activation of hepatic satiety signals or a reduction of water intake, does not seem to be crucial for the hypophagic effects of MDP or LPS.

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.

Effects of urethane, ambient temperature and injection route on rat body temperature and metabolism due to endotoxins

1. We have investigated the influence of environmental temperature, anaesthesia and route of administration on rectal temperature and other metabolic responses to two preparations of bacterial endotoxin in male adult Wistar rats. 2. Urethane anaesthesia, environmental temperatures of 20 and 28 degrees C, subcutaneous (S.C.) and intraperitoneal (I.P.) routes of administration and butanol and trichloroacetic acid (TCA) extracts of E. coli endotoxin (1.2 mg/kg) were used. 3. In addition to rectal temperature, serum zinc, albumin and urea concentrations and liver protein, RNA and zinc contents were measured. 4. Fevers were produced by injections of both endotoxins, by either route at 28 degrees C. Butanol-extracted endotoxin produced a more rapid response than the TCA extract via the I.P. route whereas the TCA extract produced a higher temperature than the butanol extract when the S.C. route was used. 5. Fevers were inhibited at an environmental temperature of 20 degrees C and by anaesthesia, while the former had no effect on compositional changes the latter inhibited the fall in serum zinc in response to subcutaneous doses of either endotoxin and the increase in liver zinc content in response to the butanol extract of endotoxin. 6. At 20 degrees C a marked fall in rectal temperature occurred in conscious rats 2 h after receiving the TCA but not the butanol extract of endotoxin. Temperature depression was more severe when endotoxin was administered by the I.P. route. 7. Serum urea was elevated in conscious rats by the TCA extract of endotoxin via both routes but only by the I.P. route for the butanol extract of endotoxin. In anaesthetized animals only the TCA extract of endotoxin raised serum urea concentration when given intraperitoneally. 8. Serum albumin and liver protein and RNA were unaffected by endotoxin injections over the 7 h time course of the study. 9. Rectal temperature responses to endotoxins were influenced in direction and magnitude by all variables employed in the study, while compositional changes were unaffected by environmental temperature but influenced to varying degrees by urethane anaesthesia and the route of administration employed.

Stimulation of vasopressin release in the ventral septum of the rat brain suppresses prostaglandin E1 fever

1. Infusion of prostaglandin E1 (PGE1) into a lateral cerebral ventricle of the rat evoked a rise in core temperature which could be attenuated by electrical stimulation of the bed nucleus of the stria terminalis (BST). Electrical stimulation of the BST in the absence of PGE1 did not alter body temperature in the afebrile rat. 2. When the intracerebroventricular (I.C.V.) infusion of PGE1 was preceded by a bilateral injection of saline or vasopressin V2 antagonist d(CH2)5D-ValVAVP into the ventral septal area (VSA), electrical stimulation of the BST suppressed the PGE1 hyperthermia. However, when the vasopressin V1 antagonist d(CH2)5Tyr(Me)AVP was injected into the VSA prior to I.C.V. infusion of PGE1, electrical stimulation of the BST did not alter the hyperthermic response to PGE1. 3. These actions were site specific in that the suppression of PGE1 hyperthermia was observed only when the electrode tips were located in the area of the BST. Similarly, the V1 antagonist only blocked the effect of electrical stimulation when injected into the VSA. 4. When the vasopressin V1 antagonist was injected into the VSA, the PGE1 fever was prolonged when compared to the controls with saline. 5. Injection of saline, vasopressin V1 and V2 antagonist into the VSA, without PGE1 or BST stimulation, did not evoke any significant change in the core temperature of the rats. 6. These data are consistent with the hypothesis that vasopressin may function within the brain as an endogenous antipyretic and that vasopressin may act in a BST-VSA neuronal pathway concerned with endogenous antipyresis.

Adaptive changes in thermoregulation and their neuropharmacological basis

Adaptive changes of the thermoregulatory system include morphological and functional modifications. The morphological modifications such as changes in body shape and insulation need time periods of months to years to develop, unless they are genetically fixed and appear seasonally. In general, they are preceded by functional modifications, including changes in capacity of the effector systems and changes in regulatory characteristics, which need much less time to develop. These early changes in regulatory characteristics, which can be defined as deviations in threshold and gain of the thermoregulatory responses, have been described and subdivided into short-term (minutes) and long-term (weeks) modifications. Evidence for the participation of monoaminergic brain stem systems in these modifications has been reviewed. On the basis of recent insights into the organization of the thermoregulatory system, and of evaluation of experimental evidence from electrophysiological, neuropharmacological, and neuroanatomical studies it can be concluded that these systems are involved in adaptive modifications. Receiving information from several sensory systems they seem to deliver additional modulatory signals, which may interfere with the processing of specific thermal information at several sites. Theoretically, the central monoamines may participate in the control of thermal input, in the central integration of thermal signals, and in modification of output signals to thermoregulatory effectors. Best documented is their modulatory action on thermosensitive and thermointegrative hypothalamic neurons. There, the monoamines 5-hydroxytryptamine and noradrenaline act as antagonists, which enhance or diminish the effects of thermal afferents mediated by other transmitters. Moreover, the antagonistic monoaminergic systems are interconnected and can influence each other at the level of lower brain stem. The activity in central monoaminergic systems can also be modified by neurohumoral feedback mechanisms from the periphery. By means of these interrelations the vegetative responses of the organism can be corrected and optimized. These interrelations can explain also some cross-adaptive changes in the thermoregulatory threshold for shivering evoked by nonthermal factors such as food intake or long-distance running.

alpha-Melanocyte-stimulating hormone infused ICV fails to affect body temperature or endotoxin fever in the cat

Permanent cannulae for intracerebroventricular (ICV) infusion were implanted bilaterally in cats following stereotaxic procedures. After colonic temperature was recorded for a one-hour baseline, a 300 microliter ICV infusion was given of CSF control vehicle, 1:100 dilution of W3110 E. coli endotoxin (10(8) organisms/ml) or alpha-melanocyte-stimulating hormone (alpha-MSH) in one of seven doses ranging from 50.0 ng to 50.0 micrograms. Whereas ICV E. coli always induced an intense and prolonged fever of rapid onset, alpha-MSH infused similarly was essentially without effect on the deep body temperature of the normothermic cat. When each of the doses of alpha-MSH was infused ICV, either during the rising phase of an E. coli fever or after the febrile response had reached its asymptote, the core temperature of the cat was unaffected. Similarly, a mixture of E. coli combined with alpha-MSH given ICV failed to alter the characteristics of the rapidly developing fever produced in the cat by this endotoxin. On the other hand, either excess Ca++ ions (50 mM) given ICV or the antipyretic drug. Dipyrone, administered systematically during the course of an endotoxin fever effectively attenuated the animal's elevated body temperature. These results demonstrate that alpha-MSH is apparently neither involved in the central mechanisms underlying normal thermoregulation, nor does it act as an endogenous antipyretic in the cat as has been postulated in another species.

Effects of preoptic and hypothalamic thermal stimulation on electrical activity of neurosecretory cells in the supraoptic nucleus

In anesthetized rats, the effect of preoptic-hypothalamic thermal stimulation was studied on supraoptic neurosecretory cells identified antidromically. More than 70% of the supraoptic neurons responded to preoptic-hypothalamic thermal stimulation in two different manners. Forty-five percent of these responding neurons increased and decreased their firing activities during rise and fall in preoptic temperature, respectively, and did not show any transient alteration in the activities. The remaining 55% transiently altered firing activities during change in temperature, but the activity depended on level of the temperature in the steady state. In almost all neurons of either type, averaged firing rates were minimal at preoptic-hypothalamic temperatures below 36 degrees C and maximal at temperatures above 39 degrees C. In 73% of the thermally responsive neurons, firing rate changed simultaneously with arterial blood pressure. In the remaining 27%, however, neuronal responses were observed without any fluctuation in the blood pressure. These results suggest that activities of the supraoptic neurosecretory cells are influenced by brain temperature.

Perfusion of vasopressin within the rat brain suppresses prostaglandin E-hyperthermia

These experiments were undertaken to determine whether arginine vasopressin (AVP) could suppress a prostaglandin hyperthermia and to localize sites of these actions in the rat. Prostaglandin E2 (PGE2) sensitive sites were localized in the ventral-septal area by microinjecting 200 ng/0.5 microliter of prostaglandin E2. During perfusion with an artificial CSF, PGE2 injected into the lateral cerebral ventricle evoked a hyperthermia of more than 1 degree C. Perfusion of 6.5 micrograms/ml of AVP markedly attenuated the PGE2-induced hyperthermia. These results suggest that AVP suppresses PGE2-induced hyperthermia in sites in which PGE2 evokes an increase in core temperature.

The effects of neurohypophyseal hormones on tolerance to the hypothermic effect of ethanol

Mice were made tolerant to the hypothermic effect of ethanol by repeated administration of ethanol (4 g/kg, 25% v/v, IP) on three consecutive days. The colonic temperature was measured in individually-housed animals immediately before and 45 min after ethanol treatment. Peptide treatments with various schedules were made SC 2 hr before the first ethanol challenge. The decrease in hypothermic response was accepted as a tolerance phenomenon, which developed in control animals by day 2. A single injection of oxytocin (OXT) or lysine vasopressin (LVP [0.1 or 1 IU peptide] animal) before the first ethanol injection did not change the initial sensitivity to ethanol. This absence of acute interactions is also reflected in the sleep onset and sleep duration after 5 g/kg ethanol (IP). In contrast, both OXT and LVP affected the development of tolerance. Repeated treatments with graded doses of OXT (0.5-2 IU) or LVP (0.25-1 IU) every day for 3 days blocked the development of tolerance. 0.002 IU LVP facilitated the development of hypothermic tolerance. The remaining doses of the peptides were ineffective. A high dose of LVP (1 IU) facilitated hypothermic tolerance if the peptide was injected when tolerance to ethanol had developed fully without previous peptide treatment. OXT, on the other hand, was ineffective in this particular experimental model. The data suggest that both neurohypophyseal hormones (LVP and OXT) block the early developmental phase of tolerance to ethanol. On the other hand, LVP facilitated the expression of tolerance if the peptide was given to mice with fully developed tolerance.

Vasopressin and vasotocin facilitate reversal of a brightness discrimination

Male albino rats received vasopressin, vasotocin, pressinoic acid or placebo and were tested on an aversively motivated brightness discrimination task. Treatment with both vasopressin and vasotocin had no effect on acquisition but facilitated the reversal of the discrimination. Pressinoic acid had an inconsistent effect. The results are interpreted to show that the C terminal of the peptides vasopressin and vasotocin influence potency of these peptides. Furthermore, the results are interpreted as showing that both vasotocin and vasopressin influence selective attention during aversively motivated tasks.

Comparison of the development of experimental pyelonephritis in homozygous brattleboro diabetes insipidus rats, heterozygous control rats and normal Wistar rats

A comparative study was performed on haematogenous experimental pyelonephritis by injecting a Staphylococcus aureus suspension i.v. to homozygous and heterozygous Brattleboro and Wistar rats. The numbers of viable bacteria in blood, urine and kidney homogenates and the pathomorphological scores determined on the tenth day of infection were significantly lower in Brattleboro diabetes insipidus rats than in heterozygous Brattleboro and normal Wistar rats. The results suggest that homozygous Brattleboro rats are much more resistant to experimental pyelonephritis.

Vasopressin: its role in antipyresis and febrile convulsion

When pyrogenic substances are injected intravenously into experimental animals, a sequence of events is set in motion which involves the hypothalamus and perhaps other portions of the diencephalon to produce a febrile response. We now present evidence that the brain produces its own endogenous antipyretic which may serve as a means of controlling the extent of the fever. When arginine vasopressin is perfused through the lateral septal area of the hypothalamus of the sheep, fever is suppressed. Vasopressin alone does not lower normal body temperature when perfused through this region of the brain. In addition, evidence is provided to indicate that vasopressin is released within the lateral septal area during the febrile response. It is concluded that, in fever, arginine vasopressin may be released in the lateral septal area of the brain and serve as an endogenous antipyretic. Results indicate that, following an initial application of vasopressin into the brain itself, a subsequent similar administration of vasopressin produces seizure-like activity. Therefore, it is suggested that this release of arginine vasopressin may contribute to the production of febrile convulsion.

Implications of neuropeptides in neurological diseases

Neuropeptides are sufficiently stable to allow valid radioimmunoassay of peptide concentrations in post-mortem human nervous tissue and in human cerebrospinal fluid. Studies have now documented abnormalities of peptide concentrations in degenerative diseases of the brain. Somatostatin concentration is reduced in the hippocampus and neocortex of patients dying with Alzheimer's type dementia. In Huntington's disease, there are reduced concentrations of substance P, met-enkephalin and cholecystokinin in the basal ganglia; in contrast the concentrations of somatostatin and TRH are increased. Immunocytochemical and experimental lesion studies are underway in an attempt to localize the peptide-containing cells affected by these disorders; and the potential role of alterations in neuropeptide function in the pathogenesis, clinical manifestations and therapy of these illnesses is of great interest. Although alterations of CSF peptide concentrations have been reported in a variety of human diseases, interpretation of these results requires knowledge of the origin and disposition of CSF peptides. Future research into the pathology of peptidergic systems will depend on the development of specific peptide antagonists to probe dynamic aspects of peptide function and on the application of the tools of molecular biology, such as specific mRNA assays, to human material.

Thermoregulatory, behavioral and seizure modulatory effects of AVP in the gerbil

Recent reports suggest that arginine vasopressin (AVP) may be an endogenous antipyretic peptide and a mediator of febrile convulsions [10,12]. The spontaneously seizing Mongolian gerbil was used to investigate the thermoregulatory, behavioral and seizure modulatory effects of AVP. Injection of AVP (1.0 and 5.0 micrograms IV and 0.01-1.0 mg/kg SC) caused dose-related falls in body temperature. Stereotypic scratching, terminated by a body shake, was observed after AVP (1.0-5.0 micrograms IV). However, such behavior was not observed after subcutaneous injection of AVP. AVP did not potentiate seizure induction in the gerbils but rather reduced the seizure incidence. The data demonstrate that AVP can reduce body temperature and cause specific behaviors, but it does not appear to play a role in the pathogenesis of seizures in the seizure sensitive strain of Mongolian gerbil.

The vasopressin receptor antagonist dPTyr (Me) AVP does not prevent stress-induced ACTH and corticosterone release

Most of the experimental evidence for a role of arginine-vasopressin (AVP) in adrenocorticotropic hormone (ACTH) release comes from in vitro studies. The multimolecular nature of the hypothalamic factor responsible for corticotropin (CRF) release has long been recognized, but the importance of AVP as a cofactor is controversial. The recently characterized 41-residue peptide fulfills the criteria for a physiological role in ACTH release and it is potentiated in vitro by AVP. In vivo, AVP is able to stimulate ACTH secretion, and Brattleboro rats, deficient in AVP, show a reduced activity of the hypothalamo-hypophysial-adrenocortical system (HHCS) (see ref. 13 for references). Direct evidence for involvement of AVP in the physiological release of ACTH is, however, still lacking. The recent development of AVP receptor antagonists provides the opportunity to test this hypothesis directly. I report here that pretreatment by 1-deaminopenicillamine, 2-(O-methyl)tyrosine arginine-vasopressin (dPTyr(Me)AVP), a potent antagonist of the vasopressor, behavioural and ACTH-releasing properties of AVP, does not modify the ACTH and corticosterone secretion induced by exposure to a novel environment, but totally inhibits the increase of ACTH and corticosterone levels induced by AVP. The results do not support the hypothesis for a physiological involvement of AVP in ACTH release.

Altered release of growth hormone and thyrotropin induced by endotoxin in the rat

Plasma growth hormone (GH) and thyrotropin (TSH) levels were measured in freely behaving rats for 6 h on three consecutive days. On the 1st and 3rd days there was no treatment, and on the 2nd day endotoxin (150 mg/kg) was administered intravenously. Endotoxin causes a biphasic temperature response: an initial hypothermia persisting for 1 h, followed by hyperthermia evident from 5 to 8 h after injection. Normal pulsatile GH release observed on the 1st day was abolished on the 2nd day by the endotoxin treatment. On the 3rd day, however, GH secretion was greater than on the initial control day. TSH release was also suppressed by endotoxin and showed a rebound release on the subsequent day. The suppression of GH secretion by endotoxin was reversed in all animals by antisomatostatin serum, and the suppression of TSH secretion by endotoxin was reversed in some animals. These results suggest that endotoxin is a potent stimulus for hypothalamic somatostatin release in the rat. Endotoxin profoundly alters adenohypophyseal hormone release.