Vasopressin may mediate febrile convulsions

Analysis of the expression patterns of AVP, IGF-1, and TNF-α, APP, CD44, IFN-β IFN A β-6, α-syn, and NFL and CLU genes in generalized and focal seizures

Objective

The aim of our study was to investigate the relationship between clinical indicators and gene dysregulation in different types of epilepsy, while also seeking to identify a diagnostic model capable of distinguishing between focal and generalized seizures. This highlights the critical importance of understanding clinical indicators and gene dysregulation for targeted therapeutic interventions to effectively address the specific seizure types effectively.

Materials and methods

In this study, we conducted a comprehensive analysis of the peripheral blood of epilepsy patients (n = 100) and a control group (n = 51) to determine the differential gene expression. Our analysis involved a range of statistical approaches, including correlation analysis to establish the association between clinical indicators and gene dysregulation, and principal component analysis to highlight distinct disease group from control group. Furthermore, we developed diagnostic models using logistic regression to aid in the accurate diagnosis of epilepsy.

Results

Among several selected genes in this study such as AVP (AUC = 0.832, p < 0.0001), IGF-1 (AUC = 0.658, p = 0.0015), TNF-α (AUC = 0.8970, p < 0.0001), APP (AUC = 0.742, p < 0.0001), CD44 (AUC = 0.614, p = 0.021) and NfL (AUC = 0.937, p < 0.0001), and CLU (AUC = 0.923, p < 0.0001) have shown the outstanding discrimination. In addition to this, when all genes were included in the model, the overall diagnostic power increased significantly (AUC = 0.9968). A differential diagnostic model for focal and generalized seizures was established which discloses AUC = 0.7027, (95 % CL, 0.5765 to 0.8289, p = 0.0019).

Conclusion

The conclusions drawn from these findings represented that this is the first study to highlight the distinctive gene patterns of both focal and generalized seizures, implying that peripheral blood can serve as a diagnostic source to distinguish between these seizures types, aiding in the accurate classification of epilepsy. The findings from this study indicate a promising direction for investigating more targeted pharmacological interventions directed to address the distinct needs of both focal and generalized epilepsy, which offers advancements in treatment strategies for distinctive seizure types.

Serum Neurofilament Levels in Children With Febrile Seizures and in Controls

Objective

Neuroaxonal damage is reflected by serum neurofilament light chain (sNfL) values in a variety of acute and degenerative diseases of the brain. The aim of this study was to investigate the impact of febrile and epileptic seizures on sNfL, serum copeptin, and prolactin levels in children compared with children with febrile infections without convulsions.

Methods

A prospective cross-sectional study was performed in children aging 6 months to 5 years presenting with fever (controls, n = 61), febrile seizures (FS, n = 78), or epileptic seizures (ES, n = 16) at our emergency department. sNfL, copeptin, and prolactin were measured within a few hours after the event in addition to standard clinical, neurophysiological, and laboratory assessment. All children were followed up for at least 1 year after presentation concerning recurrent seizures.

Results

Serum copeptin values were on average 4.1-fold higher in FS and 3.2-fold higher in ES compared with controls (both p < 0.01). Serum prolactin values were on average 1.3-fold higher in FS compared with controls ( p < 0.01) and without difference between ES and controls. There was no significant difference of mean sNfL values (95% CI) between all three groups, FS 21.7 pg/ml (19.6–23.9), ES 17.7 pg/ml (13.8–21.6), and controls 23.4 pg/ml (19.2–27.4). In multivariable analysis, age was the most important predictor of sNfL, followed by sex and C reactive protein. Neither the duration of seizures nor the time elapsed from seizure onset to blood sampling had an impact on sNfL. None of the three biomarkers were related to recurrent seizures.

Significance

Serum neurofilament light is not elevated during short recovery time after FS when compared with children presenting febrile infections without seizures. We demonstrate an age-dependent decrease of sNfL from early childhood until school age. In contrast to sNfL levels, copeptin and prolactin serum levels are elevated after FS.

Copeptin as a serum biomarker of febrile seizures

Background and Objectives

Accurate diagnosis of febrile seizures in children presenting after paroxysmal episodes associated with fever, is hampered by the lack of objective postictal biomarkers. The aim of our study was to investigate whether FS are associated with increased levels of serum copeptin, a robust marker of arginine vasopressin secretion.

Methods

This was a prospective emergency-setting cross-sectional study of 161 children between six months and five years of age. Of these, 83 were diagnosed with febrile seizures, 69 had a febrile infection without seizures and nine had epileptic seizures not triggered by infection. Serum copeptin and prolactin levels were measured in addition to standard clinical, neurophysiological, and laboratory assessment. Clinical Trial Registration: NCT01884766.

Results

Circulating copeptin was significantly higher in children with febrile seizures (median [interquartile range] 18.9 pmol/L [8.5-36.6]) compared to febrile controls (5.6 pmol/L [4.1-9.4]; p <0.001), with no differences between febrile and epileptic seizures (21.4 pmol/L [16.1-46.6]; p = 0.728). In a multivariable regression model, seizures were the major determinant of serum copeptin (beta 0.509; p <0.001), independently of clinical and baseline laboratory indices. The area under the receiver operating curve for copeptin was 0.824 (95% CI 0.753-0.881), significantly higher compared to prolactin (0.667 [0.585-0.742]; p <0.001). The diagnostic accuracy of copeptin increased with decreasing time elapsed since the convulsive event (at 120 min: 0.879 [0.806-0.932] and at <60 min: 0.975 [0.913-0.997]).

Conclusions

Circulating copeptin has high diagnostic accuracy in febrile seizures and may be a useful adjunct for accurately diagnosing postictal states in the emergency setting.

Neuropeptides as targets for the development of anticonvulsant drugs

Epilepsy is a common neurological disorder characterized by recurrent seizures. These seizures are due to abnormal excessive and synchronous neuronal activity in the brain caused by a disruption of the delicate balance between excitation and inhibition. Neuropeptides can contribute to such misbalance by modulating the effect of classical excitatory and inhibitory neurotransmitters. In this review, we discuss 21 different neuropeptides that have been linked to seizure disorders. These neuropeptides show an aberrant expression and/or release in animal seizure models and/or epilepsy patients. Many of these endogenous peptides, like adrenocorticotropic hormone, angiotensin, cholecystokinin, cortistatin, dynorphin, galanin, ghrelin, neuropeptide Y, neurotensin, somatostatin, and thyrotropin-releasing hormone, are able to suppress seizures in the brain. Other neuropeptides, such as arginine-vasopressine peptide, corticotropin-releasing hormone, enkephalin, β-endorphin, pituitary adenylate cyclase-activating polypeptide, and tachykinins have proconvulsive properties. For oxytocin and melanin-concentrating hormone both pro- and anticonvulsive effects have been reported, and this seems to be dose or time dependent. All these neuropeptides and their receptors are interesting targets for the development of new antiepileptic drugs. Other neuropeptides such as nesfatin-1 and vasoactive intestinal peptide have been less studied in this field; however, as nesfatin-1 levels change over the course of epilepsy, this can be considered as an interesting marker to diagnose patients who have suffered a recent epileptic seizure.

Reduced immunoreactivity of tyrosine hydroxylase in the hypothalamic paraventricular nucleus of the seizure sensitive gerbil

We compared the immunoreactivity and numbers of tyrosine hydroxylase (TH) immunoreactive neurons and neuropil in the paraventricular nucleus (PVN) of the hypothalamus between the seizure sensitive (SS) and seizure resistant (SR) gerbils. The distributional pattern of TH immunoreactivity was similar in both groups: TH immunoreactivity was seen mainly in magnocellular neurons of the PVN. However, total TH immunoreactivity in the neurons and neuropil in the SS gerbils was significantly lower than that in the SR gerbils. In addition, the number of TH immunoreactive neurons in the SS gerbils was also much lower than those in the SR gerbils. These results indicate that SS gerbils have a low TH immunoreactivity in the hypothalamic PVN compared with that in SR gerbils.

Arginine vasopressin does not contribute to seizures induced by intracerebroventricularly-injected pilocarpine

Arginine vasopressin (AVP) has been shown to contribute to the production of seizures. Here, we aimed to investigate the effects of AVP on seizures induced by intracerebroventricular (i.c.v.) injection of pilocarpine. Rats were treated with 0.2-2.4 mg/5 microl pilocarpine intracerebroventricularly, to obtain the dose-response relationship for behavioural seizures. 2.4 mg/5 microl pilocarpine induced status epilepticus in all rats and 0. 2 mg/5 microl pilocarpine did not produce any sign of seizure in any of the rats. In the second step, AVP (0.01-1000 ng/2 microl; i.c.v.) was injected 5 min before i.c.v. injection of a low dose pilocarpine (0.4 mg/5 microl) and rats were observed for percentage of status epilepticus, status epilepticus latency and behavioural seizure scores. None of the applied doses of AVP had any significant effect on seizures induced by 0.4 mg/5 microl i.c.v. pilocarpine. Subcutaneous injection of 1000 ng AVP 1h before 0.4 mg i.c.v. pilocarpine also did not produce significant difference with respect to the 0.4 mg pilocarpine group. Finally, pretreatment with neither an AVP V(1) receptor antagonist (25, 125, 250 ng/5 microl; i.c.v.) nor an AVP V(2) receptor antagonist (25, 125, 250 ng/5 microl; i.c.v.) prevented status epilepticus, induced by 2.4 mg/5 microl i.c.v. pilocarpine. We conclude that AVP does not act as a convulsant agent in centrally-induced pilocarpine seizures.

Arginine vasopressin in the pathogenesis of febrile convulsion and temporal lobe epilepsy

We aimed to investigate the possible convulsant action of arginine vasopressin (AVP) in both a febrile convulsion model in rat pups and a temporal lobe epilepsy model in adult rats and to define the receptor type which mediates this effect. In rat pups, 125 ng V2 receptor antagonist significantly prevented hyperthermic seizures, but did not affect seizure latency. In adult rats, the only effective dose and agent was 125 ng V2 receptor antagonist, which prevented pilocarpine-induced status epilepticus, extended the status epilepticus latency and improved the 24 h survival rate. These data suggest that AVP has a convulsant activity in febrile convulsions and also in seizures independent of fever, and this effect is mediated by V2 receptors.

Peptidergic mechanisms of hyperthermia-evoked convulsions in rats in early postnatal ontogenesis

This report addresses the verification of the hypothesis that arginine-vasopressin affects the formation of hyperthermia-evoked convulsions in early ontogenesis in rats on days 3, 5, 7, and 9 of postnatal life. The modification of experimental febrile convulsions by PACAP (pituitary adenylate cyclase-activating peptide) was investigated; PACAP is a physiological regulator of the neurosecretion of arginine-vasopressin. Arginine-vasopressin (10 microg/rat) and PACAP (0.01 microg/rat) decreased the latency of generalized tonic-clonic convulsions and the time of truncal generalization of convulsive activity on days 3 and 5 of rat development. Animals given arginine-vasopressin (0.1-10 microg/rat) sowed significant increases in the duration of generalized convulsions to the level of status epilepticus on day 9 of life. Conversely, administration of higher doses of PACAP (0.1 microg/rat) increased the threshold of tonic-clonic convulsions on days 3 and 5 and decreased it on days 7 and 9 of postnatal development. The indirect involvement of PACAP in the mechanisms of experimental febrile convulsions is suggested to act via changes in arginine-vasopressin neurosecretion.

Circadian rhythms: interactions with seizures and epilepsy

Circadian rhythms are endogenously-mediated 24 h cycles of behavioral or physiological activity. The interactions among the mammalian circadian clock, acute seizures, and chronic epilepsy are not well-characterized. Evidence suggests that seizures are susceptible to circadian modulation, and that this modulation varies with epilepsy syndrome and location of seizure foci. The circadian timing system and secondary circadian cycles of hormone secretion, sleep and wakefulness, and recurrent environmental factors are discussed as potential systems that effect spontaneous seizure recurrence. Experimental designs should take into account time-of-day effects on seizure threshold and occurrence. Further work is required to determine what mechanisms account for daily variation in seizure susceptibility.

The vasopressin deficient Brattleboro rats: a natural knockout model used in the search for CNS effects of vasopressin

Behavioral neuroscience is using more and more gene knockout techniques to produce animals with a specific deletion. These studies have their precedent in nature. A mutation may result in a limited genetic defect, as seen in the vasopressin (VP) deficiency in the Brattleboro rat. The mutation is in a single pair of autosomal loci, and the sequences of VP gene from wild-type and homozygous Brattleboro rats are identical except for a single nucleotide deletion in the second exon. The deletion results in the synthesis of an altered VP precursor that is unable to enter the secretory pathway. The genetic disturbance results in a central diabetes insipidus comparable to that found in humans. Starting with our work during the early 1970s we found that the genetic defect in the availability of VP causes deficits in central nervous system (CNS) functions. Behavioral processes from cognition to drug tolerance appeared to be disturbed by the absence of VP, but not all behaviors are affected. The specificity of the absence of VP in causing behavioral deficits is shown in many cases. However, certain deficits are due to genetic factors other than the deletion of the VP gene. The picture is further complicated by differences in testing conditions, the absence of proper controls, i.e. heterozygous and wild-type Brattleboro rats, sex, compensation phenomena, and the absence of neuropeptides co-localized with VP. Interestingly, an age dependent spontaneous shunt to a heterozygous phenotype in vasopressinergic neurons might also compensate for the disturbance. Accordingly, findings in knockout animals should be interpreted with caution. One should realize that brain functions are modulated by multiple neuropeptides and that neuropeptides possess multiple CNS effects.

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.

Proconvulsive effect of vasopressin; mediation by a putative V2 receptor subtype in the central nervous system

Subcutaneously (s.c.) administered [Arg8]vasopressin (AVP) potentiated seizures induced by intracerebroventricular (i.c.v.) injection of 1.95 mg pilocarpine (a muscarinic cholinergic agonist). A bell-shaped relation between dose and effect was found. I.c.v. pretreatment with a V1, V2 or oxytocin receptor antagonist was performed to determine whether and what type of receptor is involved in this proconvulsive effect of vasopressin. For these experiments a higher dose of pilocarpine (2.4 mg i.c.v.) was injected. This caused seizures in a slightly but not significantly higher percentage of the rats. A dose-dependent protective action of the V2 receptor antagonist d(CH2),[D-Ile2,Ile4]AVP (effective doses were 25 and 125 ng) on seizures was found. A reduction was observed in the number of animals that developed tonic-clonic convulsions. Neither the V1 receptor antagonist d(CH2)5[Tyr(Me)2]AVP nor the oxytocin receptor antagonist desGly(NH2)9d(CH2)5[Tyr(Me)2Thr4]OVT possessed anti-convulsive activity. Subsequently the type of receptor was studied in detail with fragments of AVP with either V1 or V2 activity. AVP (with V1 and V2 affinity) (1 and 3 microg s.c.) potentiated pilocarpine (1.95 mg) induced seizures. Vasotocin and oxytocin were without effect. Interestingly neither s.c. nor i.c.v. administration of the selective kidney type vasopressin receptor (V2) agonist dDAVP potentiated pilocarpine induced seizures. Several selective antidiuretic agonists (V2), such as d[Val4]AVP, d[Phe2,Val4,D-Arg8]vasopressin (3 microg), [Val4,D-Arg8]vasopressin (3 microg) and d[Val4,D-Arg8]vasopressin (3 microg) were active. Other selective antidiuretic compounds, such as [Val4]AVP, dAVP, d[Tyr(Me)2]AVP and HO[D-Arg8]vasopressin (3 microg) did not influence seizures. These results demonstrate that a combination of substitution of aminoacid 4 (Gln) by Val and to a lesser extent deamination and the D-arginine form yield an active molecule, which can potentiate pilocarpine induced seizures and suggest the existence of a V2 receptor subtype in the brain.

The role of vasopressin, somatostatin and GABA in febrile convulsion in rat pups

In order to further elucidate a possible role of neuropeptides and GABA in the pathogenesis of febrile convulsions, we studied changes of immunoreactive-arginine vasopressin (IR-AVP), IR-somatostatin (IR-SRIF) and gamma-aminobutyric acid (GABA) in the rat brain after febrile convulsions induced by ultra-red light (UR). Male Wistar rats at 16 days of age irradiated with UR developed generalized convulsions after 4.9 +/- 0.5 min irradiation. Six rats were killed by microwave irradiation 3 min after UR irradiation prior to convulsion development, and 29 rats were killed either 0 min, 2 h, 6 h, 24 h or 48 h after febrile convulsions. Non-irradiated rats served as controls. The rat brain was dissected into 4 regions; amygdala, hypothalamus, cortex and hippocampus, and subjected to radioimmunoassays. IR-AVP levels in hypothalamus were increased 3 min after UR and decreased at 2 h and 6 h after the convulsions. IR-SRIF levels were increased in cortex and hippocampus at 3 min after UR and 0 min after the convulsions. The GABA content increased in all regions tested at 2 h and 6 h after the convulsions. These results suggest that AVP, SRIF and GABA may be involved in the pathogenesis of febrile convulsions in different ways.

Vasopressin in the cerebrospinal fluid of febrile children with or without seizures

Immaturity in water and electrolyte balance in the brain has been considered to increase the susceptibility of young animals and children to febrile convulsions (FCs). Arginine-vasopressin (AVP) is involved in the regulation of several centrally mediated events such as modulation of fever and the ease with which water permeates into and out of the brain. To evaluate the possible role of AVP in the control of water balance and susceptibility to convulsions during fever we measured the AVP concentration in the cerebrospinal fluid (CSF) and plasma of febrile children with or without convulsions. The febrile population consisted of 47 children, of whom 29 experienced seizures during fever. Seven children with epileptic symptoms and 18 children without seizures were included as nonfebrile controls. The CSF AVP concentration in febrile children without seizures and in nonfebrile convulsive children was significantly lower (0.60 +/- 0.07 pmol/l, mean +/- SEM, P < 0.01 and 0.65 +/- 0.19 pmol/l, P < 0.05, respectively) than in nonfebrile children without convulsions (0.83 +/- 0.06 pmol/l). However, the levels of CSF AVP were not significantly different in children with FCs (0.71 +/- 0.06 pmol/l) compared with other groups. CSF AVP correlated with the CSF osmolality (r = 0.33, P = 0.02). No statistical differences in plasma AVP levels between the groups could be found. The present data provide support for the hypothesis of synchronous regulation of osmolality and AVP concentration in CSF. During fever the concentration of CSF AVP was lower in nonconvulsive children compared with nonfebrile nonconvulsive children. CSF AVP levels were not affected in febrile children by convulsions.

Osmolality and electrolytes in cerebrospinal fluid and serum of febrile children with and without seizures

During acute febrile diseases mild disturbances of water and electrolyte balance occur frequently. It has been suggested that changes in electrolyte balance, in particular hyponatraemia, might predispose a child to convulsions during febrile illness; however, the changes of electrolytes in the CSF are not known. We have studied the effects of fever and convulsions on water and electrolyte balance in CSF and serum by measuring osmolality and electrolyte concentrations in children. The febrile population consisted of 60 children, 36 of whom had seizures during fever. Twenty-one children without convulsions and nine children with epileptic symptoms were nonfebrile controls. We noticed that CSF is subject to changes in osmolality and electrolyte concentration during fever, while convulsions do not exhibit such changes. CSF osmolality and sodium concentrations were lower in febrile children than in nonfebrile controls. The osmolality in febrile children with convulsions was 3.8% (P < 0.01) and without seizures 3.5% (P < 0.01) lower than in nonfebrile nonconvulsive children. The changes in CSF sodium concentration, and to a lesser extent potassium and chloride concentrations, paralleled those of CSF osmolality. A positive correlation was observed between the CSF and serum osmolatities (r = 0.73, P < 0.0001), and sodium concentrations (r = 0.63, P < 0.0001). A negative correlation between the body temperature and both CSF osmolality (r = -0.66, P < 0.0001) and sodium concentration (r = -0.59, P < 0.0001) exhibits also the important regulative role of increased body temperature.

CONCLUSION

Fever is an important factor for disturbances in fluid and electrolyte balance. The alterations in CSF osmolality and sodium concentration do not, however, give an unambiguous explanation for the susceptibility to simple febrile seizures.

Barrel rotation induced by central arginine8-vasopressin treatment: involvement of neurohypophyseal peptide receptors

Two series of experiments were done to investigate the mechanism underlying arginine8-vasopressin (AVP)-induced barrel rotation in rats. In the first series, the effect of intracerebroventricular (ICV) administration of various neurohypophyseal hormone antagonists on AVP-induced barrel rotation was studied. The more vasopressin was given, the more the rats exhibited barrel rotation. ICV pretreatment with a V1 vasopressin receptor antagonist, d(CH2)5[Tyr(Me)2]AVP, prevented barrel rotation, while similar treatment with a V2-antagonist, d(CH2)5[dIle2Ile4]AVP, did not affect vasopressin-induced barrel rotation. However, Des-Gly,NH2d(CH2)5[Tyr)Me2)Thr4Orn8]-vasotocin, a specific oxytocin antagonist, potentiated the effect of AVP on barrel rotation. The second experiment was performed in rats equipped with a telemetry system to measure heart rate (HR), core temperature (CT), and gross locomotor activity. Also, in this experiment the incidence of AVP-induced barrel rotation was dose-dependent, as was the number of rats that died. Barrel rotation was accompanied by a significant decrease in CT and HR, while rats that did not develop hypothermia did not show barrel rotation. These results suggest that a V1 receptor is involved in barrel rotation. Since AVP-induced hypothermia is also mediated by a V1 receptor, it is postulated that hypothermia is a prerequisite for barrel rotation to occur. Further experiments are needed to substantiate this hypothesis.

Plasma and cerebrospinal fluid arginine vasopressin in patients with and without fever

Hyponatraemia has been described in association with a number of acute infectious diseases, mainly bacterial and tuberculous meningitis and pneumonia, and has been attributed to inappropriate secretion of arginine vasopressin (AVP). The mechanism of inappropriate AVP production is uncertain, but there is experimental evidence to suggest that fever may stimulate secretion of AVP into plasma and cerebrospinal fluid. In this study, AVP concentrations in plasma and cerebrospinal fluid from 37 febrile children with infections have been compared with those from 27 afebrile control subjects. Ten of the febrile children had meningitis (eight bacterial, two viral) and the remainder a variety of other infectious diseases. Seventy four per cent of febrile infected children were hyponatraemic (serum sodium less than 135 mmol/l) compared with only 8% of the afebrile controls. Plasma AVP concentrations were significantly higher in the febrile patients (median 2.92 pmol/l, range 1.0-23.25, n = 28) than in controls (median 1.67 pmol/l, range 0.57-6.0, n = 14) but there was no significant difference in cerebrospinal fluid AVP concentrations. There was no difference in plasma AVP concentrations between patients with meningitis and those with infections not involving the central nervous system. Careful attention should be paid to fluid and electrolyte balance in all children with acute infections.

Thermal biology of the laboratory rat

The purpose of this paper is to thoroughly review the literature and present a data base of the basic thermoregulatory parameters of the laboratory rat. This review surveys the pertinent papers dealing with various aspects of the thermal biology of the laboratory rat, including: metabolism, thermoneutrality, core and brain temperature, thermal tolerance, thermal conductance and insulation, thermoregulatory effectors (i.e., thermogenesis, peripheral vasomotor tone, evaporation, and behavior), thermal acclimation, growth and reproduction, ontogeny, aging, motor activity and exercise, circadian rhythm and sleep, gender differences, and other parameters. It is shown that many facets of the thermoregulatory system of the laboratory rat are typical to that of most homeothermic species. However, is several instances the rat exhibits unique thermoregulatory responses which are not comparable to other species.

Kindling in spontaneous hypertensive rats

Vasopressin is a neurohormone and neuromodulator with many effects on behavior. Rats lacking vasopressin have been found to develop kindled seizures more slowly with amygdala stimulation. In the present study the spontaneous hypertensive (SH) rat and rats from the parent strain, the Wistar-Kyoto (WKY) rat received amygdala and pyriform kindling. The SH rat has been reported to have increased plasma vasopressin and increased brain vasopressin release. Plasma vasopressin, osmolality and hematocrit were also measured in blood samples obtained through chronic, indwelling catheters implanted in SH, WKY normal and Sprague-Dawley rats. SH rats were found to kindle with fewer afterdischarges than WKY normal rats with both amygdala and pyriform cortex stimulation. The total afterdischarge duration required to reach each kindling stage was significantly shorter in the SH rat. Plasma osmolality and vasopressin were significantly higher in the SH rats compared to WKY normal rats and Sprague-Dawley rats. These findings provide additional evidence that vasopressin may influence the establishment of enduring behaviors such as kindled seizures.

Protection by GABA agonists, gamma-hydroxybutyric acid, and valproic acid against seizures evoked in epileptic chicks by hyperthermia

With microwave diathermy, febrile seizures were produced in epileptic chicks aged 2-5 days. Drugs that enhance GABAergic activity (i.e., GABA, muscimol, and progabide), as well as valproic acid and gamma-hydroxybutyric acid, produced dose-dependent increases in latency to onset of seizures.

Anterior neocortical kindling in vasopressin-deficient rats

Kindling of seizures with stimulation of anterior neocortex was examined in control rats and in Brattleboro rats deficient in arginine-vasopressin (AVP). There were no significant differences between control rats, homozygous Brattleboro rats, and heterozygous Brattleboro rats in the rate and pattern of kindling of generalized seizures. Thus AVP is not critically involved in anterior neocortical kindling.

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.

Ontogeny of susceptibility to experimental febrile seizures in rats

Two experiments were conducted using microwave hyperthermia (MHT) to induce seizures among limited numbers of Long-Evans rat pups. The MHT model of febrile seizures eliminates several methodological complications inherent in previous animal models of the disorder. In Experiment 1, rat pups were rendered hyperthermic with MHT or were sham-irradiated on Days 11, 13, 15 or 17 postpartum. The results indicate a statistically significant decline in seizure susceptibility with age. In Experiment 2, rats were subjected to either single or multiple hyperthermic episodes on Days 11, 13, 15, or 17 postpartum. The results indicate an increase in susceptibility to seizures attributable to prior seizure history. In both experiments, seizures were induced with increases in rectal temperature of 1 to 3 degrees C. The results parallel many clinical features of febrile seizures and argue the efficacy of the MHT model.

Subcellular localization and characterization of vasopressin binding sites in the ventral septal area, lateral septum, and hippocampus of the rat brain

[Arg8]-Vasopressin (AVP) has been shown to exert characteristic central physiological actions in the ventral septal area of the rat brain. This study reports the characterization of receptors for AVP in synaptic plasma membranes prepared from the ventral septal area, the lateral septum, and the hippocampus. Binding of [3H]AVP was temperature and time dependent, linearly related to protein concentration, saturable, and specific. Scatchard plot analysis suggested the presence of a population of binding sites in the three brain areas with dissociation constants and maximal binding capacities, respectively, of 1.06 +/- 0.39 nM and 24.0 +/- 7.01 fmol/mg of protein (mean +/- SEM; n = 3 for the ventral septal area, 0.92 +/- 0.13 nM and 47.0 +/- 4.96 fmol/mg of protein (n = 3) for the lateral septum, and 0.91 +/- 0.14 nM and 25 +/- 5.02 fmol/mg of protein (n = 3) for the hippocampus. In all three brain regions, the rank order of potencies of several vasopressin analogs, unrelated peptides, and other compounds for competitive displacement of ligand indicated a receptor with properties resembling those of the V1-like receptor for AVP. These data document the presence of a high-affinity, V1-like vasopressin receptor in the rat ventral septal area for which the pharmacological properties are similar to those previously reported in physiological studies.

Serotonin reduction in the mouse neostriatum during hyperthermia-induced convulsions studied by immunohistochemistry

Changes occurring in serotonin neurons during hyperthermia-induced convulsions were examined by means of a modified immunohistochemical method. All mice (8-12 weeks of age) exposed to the temperature of 50 degrees C had convulsions, showing a generalized tonic and/or clonic pattern. Immediately after the convulsions, the animals were perfused transcardially with a fixative. A significant reduction in serotonin immunoreactivity was observed in the neostriatum (caudate-putamen complex) of the mice which had hyperthermia-induced seizures, while the serotonin immunoreactivity remained unchanged in the neocortex and paleostriatum. These results suggest that serotonin may be an important mediator in the mechanism of hyperthermia-induced convulsions or that the susceptibility of serotonin neurons to a convulsive state is greatest in the neostriatum.

Barrel rotation evoked by intracerebroventricular vasopressin injections in conscious rats. I. Description and general pharmacology

Intracerebroventricular (i.c.v.) arginine-vasopressin (AVP) injections in rats evoke an unusual motor response termed 'barrel rotation' (BR). This report documents several aspects of BR after i.c.v. AVP in conscious, adult male Sprague-Dawley rats: single i.c.v. AVP injections (100-1000 ng/5 microliters) evoke BR in about 50% of naive rats with no relationship to dose and 20% mortality; no directional preference exists for BR, and sensitivity to BR does not vary over a weight range of 301-475 g; continuous i.c.v. AVP infusions at doses of 50-2500 ng/h evoked BR in 13 and 50% of rats tested at the extreme ranges; latency to BR was always within 3-6 min in infusion experiments; a protocol where rats received a single i.c.v. AVP injection (1 microgram) on day 1 followed on day 3 by 0.5 micrograms, increased the proportion of rats with BR from 51% to 83% (P less than 0.05), indicating a sensitization phenomenon; latency to BR after single i.c.v. injections did not fit the assumption of single underlying normal distribution; a novel method to analyze these data, hazard plotting, revealed two phases to the BR latency under ambient illumination. The following paper presents evidence of visual/vestibular involvement and the efficacy of anti-seizure drugs. Collectively, the data are compatible with the hypothesis that brain vasopressin pathways are involved in some abnormalities of motor output.

Kindling of the hippocampus and septum in vasopressin-deficient rats (Brattleboro strain)

Homozygous and heterozygous Brattleboro rats deficient in central vasopressin and Long-Evans control rats were electrically kindled in the ventral hippocampus or lateral septum. The homozygous and heterozygous Brattleboro groups stimulated in the ventral hippocampus or lateral septum kindled significantly faster than the respective Long-Evans control groups. The accelerated kindling rate of the Brattleboro groups is attributed to faster seizure development during the early seizure stages. These results suggest that vasopressin may be involved in the kindling of convulsions from limbic structures where it is normally found.

The role of arginine vasopressin in alcohol dependence and withdrawal

The development and maintenance of tolerance to the physiological and behavioral effects of repeated exposure to ethanol can be altered markedly by the presence of arginine vasopressin (AVP). In addition, AVP has been implicated in the etiology of convulsions, including those induced by exposure to high ambient temperatures. In light of these findings, experiments were conducted to determine the role, if any, that AVP might play in the pathogenesis of alcohol-withdrawal convulsions. Thirty-two male Long Evans (LE) rats and 32 age-matched male homozygous Brattleboro (DI) rats (genetically deficient in AVP) were exposed to ethanol vapor concentrations adjusted to maintain blood alcohol levels of each rat at 150-350 mg/dl. Following at least 5 days of ethanol exposure, the animals were withdrawn. From 3-24 hr after cessation of ethanol administration, withdrawal severity was assessed by observing the response of each animal to a 60-120 sec period of auditory stimulation. No significant differences were observed in either latency to onset or severity of the convulsions in LE and DI rats upon ethanol withdrawal. Thus, alcohol-withdrawal convulsions, unlike hyperthermia-induced convulsions, may be mediated by a neurochemical substrate other than AVP.

Experimental febrile convulsions in epileptic chickens: the anticonvulsant effect of elevated gamma-aminobutyric acid concentrations

The high seizure susceptibility in epileptic chickens is due to an autosomal recessive mutation. In 3-day-old chicks homozygous for the epilepsy gene (epileptics), elevation of body temperature using microwave diathermy evoked an initial febrile seizure resembling the clonic seizures evoked in epileptic chicks by photic stimulation. After complete recovery, this was followed by a clonic-tonic seizure. In nonepileptic heterozygote hatchmates (carriers) of the same age, only the latter seizure pattern was observed. In 16- to 17-day-old chicks of either phenotype, both seizure patterns were observed during hyperthermia. In all cases, the temperature at which seizures occurred was significantly lower in epileptic than in nonepileptic chicks, indicating a lower threshold for febrile seizures when there is an inherited predisposition to convulse. The occurrence of seizures was dependent on the body temperature and not on the rate of rise of temperature. Elevation of the brain gamma-aminobutyric acid (GABA) concentrations by administration of the GABA transaminase inhibitor gamma-vinyl GABA reduced the incidence of the initial febrile seizures and increased the latency in those birds that were not fully protected.

Endotoxin increases vasopressin release independently of known physiological stimuli

Plasma vasopressin (AVP) increases after endotoxin administration in freely behaving unanesthetized rats. The present experiments sought to determine the factors that mediate this vasopressin response. Endotoxin (150 micrograms/kg iv) elicited a significant increase in plasma AVP concentration. This response was accompanied by unchanged plasma osmolality, hypotension, increased hematocrit (reflecting decreased plasma volume), hypothermia, and hyperglycemia. Pretreatment with the prostaglandin synthesis inhibitor, indomethacin (5 mg/kg sc), had no effect on the vasopressin response to endotoxin but abolished or significantly attenuated the changes in blood pressure, hematocrit, temperature, and plasma glucose while leaving plasma osmolality unaltered. These investigations indicate that endotoxin stimulates vasopressin secretion into plasma independently of changes in plasma osmolality, systemic blood pressure, plasma volume, body temperature, or plasma glucose. The results also suggest that vasopressin responses to endotoxin are not mediated by prostaglandins, whereas prostaglandins do play a role in endotoxin's effects on blood pressure, plasma volume, temperature, and plasma glucose.

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.

Neuropeptides: a role as endogenous mediators or modulators of epileptic phenomena

As more small peptidergic components of the central nervous system are isolated, their role in disease states is being investigated. Several of these neuropeptides, especially the opioidlike peptides, adrenocorticotropic hormone, and some hypothalamic releasing factors, have been found to alter neuronal excitability. This finding has led to the proposal that these peptides may play a role in the pathogenesis of the epilepsies. We tested this hypothesis in a genetic model of epilepsy. At nontoxic doses, several exogenously administered peptides had anticonvulsant properties, while others were proconvulsant. The most potent anticonvulsant was the opioidlike peptide beta-endorphin. Its effect was similar to that of the opioid alkaloids. Using the potent antagonist naloxone hydrochloride to block possible endogenous opioid-like peptides, we found no effects on seizures in naive animals. Naloxone did alter postictal events, however, by partially blocking the postictal refractoriness to further seizures. We speculate that one possible role for the endogenous opioid peptides may be to limit the spread of seizures or to modulate postictal susceptibility to further seizures. Naloxone was effective in this model only after stressful situations occurred that modified the seizures and presumably induced a release of endogenous opioidlike peptides. Support for this hypothesis from other epilepsy models is discussed. Other peptidergic systems may also be active in various epileptic models, and the current understanding of their roles is reviewed.

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.

Amygdala and pyriform cortex kindling in vasopressin deficient rats (Brattleboro strain)

Homozygous and heterozygous Brattleboro rats and Long--Evans control rats were subjected to repeated electrical stimulation of the amygdala or pyriform cortex in a kindling paradigm. The homozygous Brattleboro group stimulated in the amygdala was retarded in its kindling rate relative to heterozygous Brattleboros and Long--Evans controls. The retarded kindling rate of the homozygous Brattleboros stimulated in the amygdala is attributed to a delay in seizure development at stages 1 and 2 which suggests that vasopressin may be necessary for normal kindling from the amygdala to take place.

Centrally mediated effects of neurohypophyseal hormones

The neurohypophyseal hormones oxytocin and vasopressin cause a variety of biological effects in animals which are mediated by central nervous system mechanisms. Among the best studied of these effects is the modulation of both memory processes and the development of drug tolerance and dependence. Neurohypophyseal hormones have also been shown to alter various physiological parameters such as heart rate and body temperature following central administration. In addition, these peptides can profoundly alter spontaneous, unlearned behavior in several rodent species. Many of the centrally mediated effects of neurohypophyseal hormones have been shown to be elicited at sites within the brain stem and the limbic system where vasopressin and oxytocin occur in cell bodies, axons and nerve terminals, suggesting a physiological role for these peptide effects. The various central effects of neurohypophyseal hormones involve different mechanisms which can be distinguished from one another on the basis of required dose, time-course of action, and structure-activity relationships. Thus, alterations of spontaneous behavior are mediated by putative receptors closely related to vasopressin receptors in blood vessels responsible for the peripheral pressor response while the effects on memory processes are mediated by a mechanism which is not closely related to those involved in the peripheral hormonal effects of the peptides. The influence of neurohypophyseal hormones on memory and attention may be useful clinically. A potential role for these peptides in mental disorders is discussed.

Febrile seizures in epileptic chicks: the effects of phenobarbital, phenytoin and valproate

Epileptic seizures can be evoked in chicks homozygous for the epileptic seizure gene (epi, epi) by elevating their body temperature using microwave diathermy. These seizures precede and differ in motor seizure pattern from a second clonic-tonic seizure produced by hyperthermia in both epileptic and carrier (heterozygote, Epi, epi) chicks. Hyperthermia did not evoke seizures in adult epileptic chickens. Phenobarbital delayed the onset of epileptiform seizures whereas phenytoin and valproate had no effect. These data suggest that epileptic chicks may provide a suitable model for studies on febrile convulsions.

The effects of vasopressin on electrical activity in the guinea-pig supraoptic nucleus in vitro

Brain slices of the guinea-pig hypothalamus were used to determine the effects of vasopressin on intracellular potentials in neurones of the supraoptic nucleus. Vasopressin (0.05-1 i.u./ml.) depolarized the membrane without apparent change in the input resistance and decreased the spontaneous firing rate. This action of vasopressin was retained in the medium containing 0 mM-Ca2+, 12 mM-Mg2+ and 0.3 mM-EGTA. Amplitude of the vasopressin-induced depolarization was voltage-independent. Ion-substitution experiments showed that the changes in [K+]o, [Cl-]o and [Ca2+]o had little effect upon the amplitude of vasopressin-induced depolarization, whereas the depletion of [Na+]o slightly reduced the amplitude. The vasopressin-induced depolarization was blocked at a temperature of 15 degrees C and by ouabain in a dose of 10(-4) M. Dibutyryl cyclic AMP (2 mM) produced electrophysiological effects similar to those seen with vasopressin, and actions of both agents were potentiated by either papaverine (10(-4) M) or theophylline (10(-2) M). Contents of cyclic AMP in tissues incubated with vasopressin were significantly higher than in cases of incubation with normal Krebs solution. We conclude that vasopressin directly modulates the activity of supraoptic neurones, possibly through activation of adenylate cyclase.

Central neurohypophyseal peptide pathways: interactions with endocrine and other autonomic functions

Electrophysiological and pharmacological studies have been carried out in rats and rabbits to attempt to identify possible functional roles for neurohypophyseal peptides in brain. In anesthetized rats, single unit recordings and antidromic activation criteria were utilized to identify projections of the paraventricular nucleus (PVN) to neurohypophysis and to extrahypothalamic areas (amygdala or nucleus tractus solitarius). None of the cells tested innervated more than one of these areas and, when tested for their responses to haemorrhage, increased body osmolarity, or suckling of pups, only the osmotic stimulus caused increased activity in some cells projecting to amygdala or nucleus tractus solitarius. Indirect evidence as well as direct measurement by radioimmunoassay of arginine vasopressin (AVP) in brain perfusates revealed probable central release of AVP in response to stimuli known to activate pituitary secretion of this peptide. These observations raise the possibility that certain brain and pituitary peptidergic systems may function in a co-ordinated manner.