Minor disturbances in central nervous system function in familial neurohypophysial diabetes insipidus.

Familial neurohypophysial diabetes insipidus (FNDI) is caused by a defect in vasopressin synthesis and release as a result of a heterozygous mutation in the gene for the vasopressin prohormone. The predominant characteristic of FNDI is excessive thirst and urine production. However, vasopressin not only has peripheral endocrine effects, but also regulates numerous brain functions. We investigated whether central functions are affected in FNDI, by studying neuropsychological functioning of 23 affected members (15 males, 8 females) of a large family carrying a T/G transition mutation at nucleotide 2110 (codon 116) of the vasopressin prohormone gene (Cys116Gly). The relatively large number of family members with FNDI made it possible to compare cognitive and other CNS effects in these subjects with those of family members without FNDI. Thirty-seven adult volunteers (20 males, 17 females) from the same family and 11 non-family members (2 males, 9 females) from northern part of The Netherlands were tested. The mean age of the subjects was 35+/-12 years. Of the 63 quantified neuropsychological parameters few were statistically different between the subjects with FDNI and control subjects. Memory retrieval processes and sustained attention were worse in the subjects with FDNI. Moreover, these individuals reported significantly fewer symptoms of agoraphobia and miscellaneous symptoms, and had significantly lower scores on a scale measuring anger. The performance of FNDI subjects on an auditory verbal learning test (the 15-word test learning trial) was worse, but not significantly so, than that of the subjects without FDNI. There were subjective complaints of forgetfulness and slow recalls and those were observed in daily life by non-affected family members. These moderate differences in neuropsychological performance indicate that in human FNDI parvocellular vasopressin systems that supply the brain may be less affected or give no such serious disabilities, than the magnocellular hypothalamo-neurohypophysial system that provides vasopressin for endocrine regulation of water homeostasis.

Neuropeptides, food intake and body weight regulation: a hypothalamic focus.

Energy homeostasis is controlled by a complex neuroendocrine system consisting of peripheral signals like leptin and central signals, in particular, neuropeptides. Several neuropeptides with anorexigenic (POMC, CART, and CRH) as well as orexigenic (NPY, AgRP, and MCH) actions are involved in this complex (partly redundant) controlling system. Starvation as well as overfeeding lead to changes in expression levels of these neuropeptides, which act downstream of leptin, resulting in a physiological response. In this review the role of several anorexigenic and orexigenic (hypothalamic) neuropeptides on food intake and body weight regulation is summarized.

Familial neurohypophysial diabetes insipidus in a large Dutch kindred: effect of the onset of diabetes on growth in children and cell biological defects of the mutant vasopressin prohormone.

Familial neurohypophysial diabetes insipidus (FNDI) is an autosomal dominant trait in which expression of a mutant vasopressin prohormone reduces vasopressin production. We investigated the NP85 Cys-->Gly mutant vasopressin prohormone in a large kindred in The Netherlands. We demonstrate that growth retardation is an important early sign in two children from this kindred, which recuperates by substitution therapy with 1-desamino-8-D-arginine vasopressin. To obtain clues about the basis for the dominant inheritance of FNDI, we analyzed the trafficking and processing of the mutant vasopressin prohormone in cell lines by metabolic labeling and immunoprecipitation. The mutant vasopressin prohormone was retained in the endoplasmic reticulum and thus was not processed to vasopressin. This defect was not caused by dimerization of the vasopressin prohormone via its unpaired cysteine residue. High level expression of the mutant vasopressin prohormone in cell lines resulted in strong accumulation in the endoplasmic reticulum and an altered morphology of this organelle. We hypothesize that disturbance of the endoplasmic reticulum results in dysfunction and ultimately cell death of the cells expressing the mutant prohormone. Our data support the hypothesis that FNDI is a progressive neurodegenerative disease with delayed onset of symptoms. Its treatment requires early detection of symptoms for which growth parameters are useful.

Weak 24-h periodicity of body temperature and increased plasma vasopressin in melancholic depression.

Earlier work has shown that plasma vasopressin levels of depressed patients were higher than those of healthy controls. The aim of the present study was to determine whether plasma vasopressin levels were correlated to parameters of the circadian rhythm. Forty-one patients with major depression and twenty-five controls participated in a case-control design under natural circumstances in a field study to investigate plasma vasopressin levels three times daily, circadian motor activity, and the 24-h periodicity of body temperature for five consecutive 24-h periods. Temperature measurements consisted of at least five, but mostly six or more measurements every 24 h. Twenty-two percent of the patients, but none of the controls lacked 24-h periodicity of body temperature. In melancholic patients increased vasopressin levels in plasma correlated with a weak 24-h periodicity of body temperature. The role of vasopressin is discussed in the light of the present findings.

CRH signalling in the bed nucleus of the stria terminalis is involved in stress-induced cardiac vagal activation in conscious rats.

The bed nucleus of the stria terminalis (BNST) is involved in autonomic and behavioral reactions to fearful stimuli and contains corticotropin-releasing hormone (CRH) fibers and terminals. The role of CRH in the medial part of the BNST in the regulation of heart rate (HR) and PQ interval of the electrocardiogram was studied under resting conditions and conditioned fear stress in freely moving rats. Microinfusion of CRH (0.2 microg/0.6 microl) in the medial BNST under resting conditions significantly enhanced HR as compared to saline treatment, but did not reduce the PQ interval, indicating that exogenous CRH in the medial BNST can activate both the sympathetic and parasympathetic cardiac outflow. In addition, CRH induced a slight increase in gross locomotor activity, an effect that succeeded the tachycardiac response, indicating that the HR response was not a consequence of increased locomotor activity, but likely a direct effect of CRH. CF was induced by 10-min forced exposure to a cage in which the rat had experienced footshocks (5 x 0.5 mA x 3s) the day before. alpha-helical CRH(9-41) (alphahCRH; 5 microg/0.6 microl), a non-selective CRH receptor antagonist, or saline was infused into the medial BNST of rats prior to CF. CF induced freezing behavior, associated with an increase in HR and PQ interval, indicating activation of sympathetic and vagal outflow to the heart. alphahCRH significantly reduced the PQ response, but enhanced the tachycardia, suggesting inhibition of vagal activity. In addition, alpha-helical CRH(9-41) reduced the freezing response. Taken together, the data provide first evidence that CRH, released in the medial BNST during stress, contributes to cardiac stress responses, particularly by activating vagal outflow.

The role of the CRH type 1 receptor in autonomic responses to corticotropin- releasing hormone in the rat.

The involvement of the corticotropin-releasing hormone (CRH) type 1 receptor in CRH-induced cardiac responses was studied in freely moving rats. Intracerebroventricular (icv) infusion of 2 microg CRH under resting conditions resulted in a significant increase in heart rate (HR), but did not significantly affect the PQ interval of the electrocardiogram. This effect involves sympathetic nervous system (SNS) activation, since CRH-treatment resulted in a marked increase in plasma norepinephrine (NE) and epinephrine (E), and sympathetic blockade by subcutaneously injected atenolol (1 mg/kg), a beta1-selective adrenergic antagonist, completely prevented the CRH-induced tachycardia. CRH infusion after sympathetic blockade resulted in an elongation of the PQ interval, indicating CRH-induced vagal activation. Gross locomotor activity (GA) was determined to study its possible indirect effects on cardiac activity. Although CRH induced a marked increase in GA, this effect followed the tachycardiac response, indicating that the HR response was not a consequence of increased locomotor activity, but was a direct effect of icv CRH. Treatment with CP-154,526 (icv, 10 or 25 microg), a selective CRH type 1 receptor antagonist, did not affect baseline HR, plasma NE and E, whereas it partially blocked the CRH-induced increase in HR, plasma NE and E levels. CP-154,526 treatment had no significant effects on baseline or CRH-induced changes in GA. These results indicate that CRH activates the sympathetic nervous system at least in part via the CRH type 1 receptor.

Endogenous corticotropin-releasing hormone inhibits conditioned-fear-induced vagal activation in the rat.

The role of the endogenous corticotropin-releasing hormone (CRH) system in the regulation of heart rate, PQ interval (a measure of vagal activity), gross activity and release of adrenocorticotropic hormone (ACTH), noradrenaline and adrenaline into the blood during conditioned fear was studied in freely moving rats. Intracerebroventricular (i.c.v.) infusion of alpha-helical CRH-(9-41) (10 microgram/3 microliter), a non-selective CRH receptor antagonist, under resting conditions had no significant effect on gross activity, heart rate and PQ interval, indicating that alpha-helical CRH at this dose was devoid of agonist effects. Conditioned fear was induced by 10 min forced exposure to a cage in which the rat had experienced footshocks (5x0.5 mAx3 s) 1 day before. Conditioned-fear rats showed freezing behaviour, associated with an increase in heart rate, PQ interval, noradrenaline and adrenaline, indicating that the conditioned-fear-induced cardiac effects were the result of coactivation of the sympathetic and parasympathetic nervous system. The i.c.v. pre-treatment of rats with alpha-helical CRH significantly reduced the conditioned-fear-induced tachycardiac and ACTH response, and enhanced the increase in PQ interval, without affecting the noradrenaline and adrenaline response. These results suggest that endogenous CRH reduces the vagal response to conditioned-fear stress in rats. To test this, rats were pre-treated with atropine methyl nitrate (0.3 mg/kg, subcutaneously; s.c.), a peripherally acting cholinergic receptor antagonist. This resulted in a complete blockade of the alpha-helical CRH-induced decrease in heart rate response and increase in PQ interval. From these findings, it is concluded that endogenous CRH in the brain inhibits vagal outflow induced by emotional stress.

Behavioral pharmacology of neuropeptides related to melanocortins and the neurohypophyseal hormones.

Neuropeptides are peptides which affect the nervous system. They are derived from large precursor molecules. These are converted to neurohormones, neuropeptides of the "first generation", which can be further converted to neuropeptides of the "second generation". This review is a brief survey of the nervous system effects of neuropeptides derived from pro-opiomelanocortin (POMC) and the neurohypophyseal hormones. Processing of these molecules results in neuropeptides of the first and second generation which have similar, different, more selective or even opposite effects. Among those are effects on learning and memory processes, grooming, stretching and yawning, social, sexual and rewarded behavior, aging and nerve regeneration, thermoregulation, pain, sensitivity to seizures, and cardiovascular control. Results of animal studies as well as those of clinical studies suggest that these neuropeptides may be beneficial in aging, neuropathy, memory disturbances and schizophrenia. Most of these nervous system effects in animal studies were found before receptors in the nervous system for the various neuropeptides were detected. G-protein-coupled receptors for the neuropeptides of the "first generation", i.e., melanocortin receptors, opioid receptors, and neurohypophyseal hormone receptors have been found, in contrast to the receptors for neuropeptides of the "second generation", although there are indications that G-protein coupled receptors for these may be present in the brain.

Conditioned fear-induced tachycardia in the rat: vagal involvement.

The effects of conditioned fear on gross activity, heart rate, PQ interval, noradrenaline and adrenaline were studied in freely moving rats. Subcutaneous (s.c.) injections of atropine methyl nitrate (0.5 mg/kg) during rest resulted in a significant shortening of the PQ interval, indicating that the PQ interval can be used as a measure of vagal activity. Conditioned fear was induced by 10-min forced exposure to a cage in which the rat had previously experienced footshocks (5 x 0.5 mA x 3 s). In non-shocked controls, an increase in gross activity was found and a pronounced tachycardia, without changes in PQ interval. Conditioned fear rats showed immobility behaviour, associated with a less pronounced tachycardia and an increase in PQ interval. Noradrenaline was similarly increased in both groups, whereas adrenaline was increased in conditioned fear rats only. To further evaluate the role of the vagus, rats were exposed to conditioned fear after pre-treatment with atropine methyl nitrate (0.5 mg/kg, s.c.). Again, immobility was observed with a concomitant tachycardia, but without an increase in PQ interval. These results indicate that the autonomic nervous system is differentially involved in heart rate regulation in conditioned fear rats and in non-shocked controls: in non-shocked controls a predominant sympathetic nervous system activation results in an increase in heart rate, whereas in conditioned fear rats the tachycardiac response is attenuated by a simultaneous activation of sympathetic nervous system and parasympathetic nervous system.

Neuropsychological performance and plasma cortisol, arginine vasopressin and oxytocin in patients with major depression.

BACKGROUND: The aim of the study was to search for the existence of, and define, a possible relationship between performance in neuropsychological tests and baseline concentrations of plasma cortisol, vasopressin and oxytocin in medication-free patients with a major depressive episode. METHODS: Measures of depression and anxiety were obtained and a neuropsychological battery was presented. Blood for neuropeptide analysis was drawn by venepuncture at 8.00, 16.00 and 23.00 h. RESULTS: The melancholic patients performed less well on the neuropsychological battery than did the non-melancholic patients, but these differences could be accounted for by the severity of the illness. Global intellectual functioning was negatively correlated with mean baseline plasma concentrations of cortisol. Patients with high mean plasma vasopressin concentrations remembered more auditory presented words in the delayed recall test and produced more intrusions in the visual word learning list than did patients with low or normal mean plasma vasopressin concentrations. No association was found between neuropsychological performance and plasma concentrations of oxytocin. CONCLUSIONS: Our findings support the hypothesis that elevated baseline plasma cortisol concentrations are related to cognitive impairment in depressed patients and the hypothesis that the neuropeptide vasopressin independently enhances memory, directly or indirectly through increasing arousal and attention.

Plasma arginine vasopressin and motor activity in major depression.

BACKGROUND: Previously, we found that mean plasma concentrations of arginine vasopressin (AVP), but not of oxytocin (OT), were higher in depressed patients than in healthy controls. Plasma AVP concentrations were positively correlated to clinically rated psychomotor retardation. To further explore this previously reported relation we studied psychomotor retardation by means of an activity monitor, which is a more fine-focused and more objective instrument to analyze motor retardation than a clinical rating scale. METHODS: Plasma AVP and OT concentrations, and day- and nighttime wrist activity were measured in 48 in- and outpatients with major depression and 30 healthy controls during a period of 5 consecutive days and nights. RESULTS: Principal components analysis revealed three components of motor activity: motor activity during wakefulness, motor activity during sleep, and the awake/sleep time ratio. In patients and controls an inverse relationship between plasma AVP concentrations and motor activity during wakefulness was found. Patients with elevated AVP plasma levels showed increased motor activity during sleep. CONCLUSIONS: These results suggest that high plasma AVP levels are related to the clinical picture of daytime psychomotor retardation and nighttime motor activity in major depression. Mean plasma OT concentrations were not related to measures of motor activity.

Vagal activation in novelty-induced tachycardia during the light phase in the rat.

The effects of repeated exposure to a novel test box on cardiac and behavioral activities (locomotion, rearing, grooming, scanning, and immobility) were studied in rats tested during the dark phase ("dark" rats) or the light phase ("light" rats) of the lighting cycle, using a telemetry system for registration of ECGs during the first and fifth tests. Heart rate (HR) was used to monitor sympathetic and parasympathetic activity; the PQ interval was used to monitor parasympathetic activity. Behavior was videotaped simultaneously. In light rats, the first and fifth exposures to the test box resulted in higher increases of active behavior and HR than in dark rats, whereas the duration of the PQ interval of the ECG was increased in light rats only. This indicates that in the light phase novelty induces active behavior associated with an increase in both sympathetic and vagal outflow, whereas in the dark phase behavioral activation is predominantly associated with increased sympathetic activity, without appreciable changes in vagal outflow. In addition, light rats showed less active behavior during the fifth than during the first exposure, indicating behavioral habituation. This behavioral habituation to the test box in the light phase coincided with vagal habituation (a diminution of the PQ interval). The increase of the tachycardiac response during the fifth exposure as compared to the first exposure suggests that it is not likely that sympathetic outflow was part of the habituation process. In dark rats no behavioral or cardiac habituation was found.

Vasopressin metabolites: a link between vasopressin and memory?

The effects of endogenous metabolites of the neuropeptide vasopressin (VP) in behavioural tests led to the hypothesis that VP metabolites have a more selective function than VP. In contrast to VP, no peripheral effects have been found thus far with VP metabolites and their function seems to be associated with memory-related behaviour. VP metabolites can improve both consolidation and retrieval of memory. Effects on autonomic and electrophysiological parameters and interactions with other neurotransmitter systems have provided some information about the processes that could underlie the effects of VP metabolites on memory-related behaviour. There is evidence that the effects of VP metabolites could be mediated by a VP metabolite receptor, which is different from the known VP receptors. The VP metabolite receptor could be a link between the neuropeptide VP and memory-related behaviour.

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.

Vasopressin fragment, AVP-(4-8), improves long-term and short-term memory in the hole board search task.

The hole board search task (HBST) measures long-term and short-term memory, operationally defined as reference memory and working memory. The HBST is an open-field spatial learning test. Previously, we have shown that desglycinamide(Arg8) vasopressin (DGAVP) modulated reference memory, working memory, spatial sequence memory, and learning in the HBST in a dose-dependent manner (Vawter MP, Van Ree JM. Effects of des-glycinamide-sup-9-(arginine-sup-8) vasopressin upon spatial memory in the hole-board search task. Psychobiology 1995; 23: 45-51). To examine the potential active site of the DGAVP molecule, the fragment of the vasopressin amino acid sequence, [pGlu4,Cyt6]AVP-(4-8) (AVP-(4-8)), was administered 1 h prior to training in the HBST. Three groups received either 0, 0.3 microgram, or 1 microgram AVP-(4-8). A repeated measures MANOVA showed the AVP-(4-8) pretreatment factor to be significant (P = 0.048) on the reference memory measure, but not the working memory or learning measures. Interactions between peptide x sessions for reference memory (P = 0.015), working memory (P = 0.003) and learning (P = 0.010) indicated differences in improvement over sessions between placebo- and peptide-treated groups. Post hoc comparisons revealed that the AVP-(4-8) fragment in a dose of 0.3 microgram increased reference memory on the fourth, fifth and sixth acquisition sessions compared with placebo or 1 microgram AVP-(4-8) pretreated groups. Working memory and errors were significantly lowered by 0.3 microgram AVP-(4-8) on the first acquisition session when compared with placebo pretreatment. Thus, AVP-(4-8) improves long-term and short-term memory scores in the HBST, similar to previous results with DGAVP. However, AVP-(4-8) appears twice as potent than DGAVP in improving long-term memory scores in the HBST. The data suggest that the memory modulating property of DGAVP is contained within the amino acid sequence of the AVP-(4-8) peptide.

Plasma levels of arginine vasopressin elevated in patients with major depression.

Mentally healthy subjects show increased plasma concentrations of the neuropeptides, arginine vasopressin (AVP) and oxytocin (OT), under conditions of stress, but data are lacking about plasma concentrations of AVP and OT in patients with major depression. We thus assessed plasma concentrations of AVP and OT in patients with major depression (n = 52) and healthy controls (n = 37). Mean plasma AVP concentrations were higher in the group of depressed patients than in controls. A subgroup of 16 patients showed very high levels of plasma AVP, but no other feature differentiating this subgroup from the other patients was found. In-patients showed higher plasma AVP levels than out-patients, and melancholic patients had higher plasma AVP levels than did nonmelancholic patients. Plasma AVP levels were slightly related to psychomotor retardation and significantly inversely to neuroticism. Patients' plasma OT concentrations had a wider range than in controls. AVP and AVP-mediated functions may be a factor in the clinical picture of depression, possibly by influencing the activity of the hypothalamic-pituitary-adrenal axis.

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.