Excitotoxic damage of retinal glial cells depends upon normal neuron-glial interactions

BACKGROUND: It is unclear whether the serum prolactin (PRL) surge following electroconvulsive therapy (ECT) is a marker of optimal ECT administration. We investigated the relations among PRL surge, stimulus parameters, and outcome in major depressive disorder (MDD). METHODS: Seventy-nine patients with MDD were randomized in a double-blind trial to right unilateral (RUL) or bilateral (BL), and to low-dose (just above seizure threshold) or high-dose (2.5 x threshold) ECT. RESULTS: Change in PRL (delta PRL) varied among treatment groups, with significant effects of electrode placement (BL > RUL, p < .006), electrical dosage (high > low, p < .04), and gender (female > male, p < .005). There was no evidence that clinical improvement was associated with greater PRL surge. CONCLUSIONS: Although delta PRL varied with parameters impacting on response rates, these data indicate the PRL surge cannot serve as a useful index of clinically effective treatment. This finding does not support the view that diencephalic seizure propagation is necessary for ECT to exert therapeutic effects.     

Electroconvulsive therapy of acute manic episodes: a review of 50 years' experience

OBJECTIVE: The most common indication for electroconvulsive therapy (ECT) is major depression. It is less recognized that ECT is effective also in the treatment of acute mania. This article aims to provide a comprehensive and critical review of the literature on the use of ECT for manic patients. METHOD: All published papers in the English language on the use of ECT in acute mania that could be found were reviewed with regard to efficacy, frequency and number of treatments, bilateral versus unilateral electrode placement, predictors of antimanic response, stability of therapeutic response, cognitive consequences, and other relevant issues. RESULTS: The evidence indicates that ECT is associated with remission or marked clinical improvement in 80% of manic patients and that it is an effective treatment for patients whose manic episodes have responded poorly to pharmacotherapy. Manic patients do not require a high frequency or prolonged course of treatments to respond to ECT. The seizure threshold appears to be lower in manic patients than in depressed patients. The issues of relapse following response to ECT, cognitive consequences of ECT, and the relative merits of unilateral versus bilateral ECT in manic patients require further study. CONCLUSIONS: ECT is an effective and safe treatment for acute mania. Remission of mania following ECT reflects a primary therapeutic effect rather than a secondary consequence of an ECT-induced organic brain syndrome.     

Analysis of the association of a heat shock protein70-1 gene promoter polymorphism with myocardial infarction and coronary risk traits

In 12 depressed inpatients referred for bilateral electroconvulsive therapy (ECT), each patient was titrated at the first treatment session by using an ascending method-of-limits procedure with a step-wise increase in pulse frequency (frequency titration) or train duration (duration titration). At the second treatment session, seizure threshold was redetermined by using the method (frequency or duration titration) not used at the first treatment. Frequency or duration was maintained at the lowest level when the other parameter was titrated. Seizure threshold was significantly lower with duration titration (mean, 90 mC; SD, 27.3) than frequency titration (mean, 114 mC; SD, 35.6; p = 0.03). On average, patients in the duration-titration group required 1.2 (SD, 0.6) subconvulsive stimulations before a seizure was elicited, and patients in the frequency-titration group required 1.7 (SD, 0.9) subconvulsive stimulations before a seizure was elicited, a nonsignificant difference. These findings suggest that to elicit a seizure during ECT, increasing train duration may be slightly more efficient than increasing frequency. Basic and other clinical research findings indicate that increasing pulse width may be an inefficient way to elicit a seizure. Therefore the following sequence in the determination of seizure threshold is worth considering when using dose-titration or related techniques: the train duration should be increased first before increasing pulse frequency, and the decision to increase pulse width should be reserved for patients who do not seize at the maximal duration and frequency settings. Further empiric research is needed to establish the utility of this approach.     

Dexmedetomidine failed to block the acute hyperdynamic response to electroconvulsive therapy

BACKGROUND: Orally administered clonidine (0.2-0.3 mg) has been reported to decrease the acute hypertensive response to electroconvulsive therapy (ECT) without prolonging early recovery. This preliminary study was designed to evaluate the acute hemodynamic effects of the investigational alpha2-adrenergic agonist, dexmedetomidine, in patients undergoing a series of ECT treatments. METHODS: Six patients undergoing a series of three to six consecutive ECT treatments were studied according to a randomized, double-blind, placebo-controlled protocol All patients received either saline or dexmedetomidine, 0.5 or 1.0 microg/kg intravenously, 10-30 min before induction of anesthesia for ECT using a standardized anesthesia protocol. In addition to assessing the cardiovascular variables, the duration of seizure activity, degree of sedation, and time to discharge from the Phase I recovery unit were assessed. RESULTS: Although dexmedetomidine produced dose-related increases in the level of sedation before the ECT procedure, it failed to decrease the peak blood pressure and heart rate responses after the ECT treatment. The 0.5 and 1.0 microg/kg doses of dexmedetomidine prolonged the times to orientation and to discharge from the Phase I unit. CONCLUSIONS: The results of this pilot study suggest that dexmedetomidine (0.5-1.0 microg/kg given intravenously) is not beneficial in controlling the acute hyperdynamic response after ECT.     

Fitting the treatment to the patient: recent advances in the practice of electroconvulsive therapy

Traditionally it has been thought that a grand mal seizure is both necessary and sufficient for the maximum efficacy of ECT. Recent important research, however, has demonstrated that both the electrical dosage above the seizure threshold, i.e. the suprathreshold dosage, and the electrode placement (unilateral or bilateral) determine the efficacy of this treatment, as well as the degree of cognitive impairment. This article reviews the development of these significant concepts and suggests specific practical recommendations for incorporating these into contemporary ECT practice.     

Enteropathy associated T cell lymphoma presenting as an isolated CNS lymphoma three years after diagnosis of coeliac disease: T cell receptor polymerase chain reaction studies failed to show the original enteropathy to be a clonal disorder

We have studied the effects of methohexitone and propofol with and without alfentanil on seizure duration and recovery in this observer-blinded, prospective, randomized, crossover study involving 24 patients undergoing electroconvulsive therapy (ECT). Each patient had four treatment sessions, and received the following four i.v. regimens in random order: methohexitone 0.75 mg kg-1, methohexitone 0.50 mg kg-1 and alfentanil 10 micrograms kg-1, propofol 0.75 mg kg-1, propofol 0.50 mg kg-1 and alfentanil 10 micrograms kg-1. Additional methohexitone or propofol was given as needed in 10-20-mg increments until loss of consciousness. Suxamethonium 1.0 mg kg-1 i.v. was given for muscular paralysis. Mean motor and EEG seizure durations were longer with methohexitone-alfentanil (44.7 (SD 15.0) and 70.5 (29.7) s) than with methohexitone (37.6 (12.6) and 52.6 (15.3) s) and similarly, seizures were longer with propofol-alfentanil (36.8 (15.2) and 54.5 (20.9) s) than with propofol alone (27.2 (11.9) and 39.2 (3.9) s). Seizures were longest with methohexitone-alfentanil and shortest with propofol. Recovery time was statistically shorter in patients receiving propofol compared with methohexitone-alfentanil and methohexitone alone. Alfentanil with a reduced dose of methohexitone or propofol provided unconsciousness and increased seizure duration in patients undergoing ECT. We conclude that the combination of methohexitone with alfentanil is a good regimen for ECT, especially for patients with short seizure duration.     

Regulation of hypothalamic arginine vasopressin messenger ribonucleic acid and pituitary arginine vasopressin content in fetal sheep: effects of acute tonicity alterations and fetal maturation

OBJECTIVE: Fetal arginine vasopressin contributes to fetal and amniotic fluid homeostasis by increasing water resorption in the kidney and, at higher plasma levels, circulatory homeostasis by vasopressor effects. In utero and neonatal exposure of rat pups to prolonged alterations in plasma osmolality may permanently alter (imprint) pituitary arginine vasopressin content and adult responses to osmotic challenges. Our objective was to investigate fetal developmental changes and the impact of maternal dehydration and maternal hyponatremia on fetal pituitary arginine vasopressin content and hypothalamic arginine vasopressin messenger ribonucleic acid expression. STUDY DESIGN: Ten pregnant ewes with singleton fetuses (135 +/- 1 day) were chronically prepared with maternal vascular catheters. Ewes were assigned to receive water deprivation (n = 4) [desamino, D-Arg8]-arginine vasopressin-induced plasma hyponatremia (n = 3), or 4 days of observation (n = 3). Three additional pregnant ewes with preterm (110 +/- 1 day) singleton fetuses were also included for a study of maturational effects. Daily maternal blood samples were analyzed for determination of plasma arginine vasopressin, electrolytes, and osmolality. After the study protocol, fetuses were operatively delivered, umbilical blood samples obtained, and fetuses put to death for pituitary and hypothalamic tissues. Pituitary arginine vasopressin content was determined by radioimmunoassay, and hypothalamus arginine vasopressin messenger ribonucleic acid expression was detected by Northern blotting. RESULTS: Dehydration significantly (P < .05) increased, and hyponatremia significantly decreased maternal plasma sodium concentration compared with controls. Fetal plasma sodium concentration significantly changed in parallel with maternal values (dehydration: 139 +/- 1 to 150 +/- 1 mEq/L; hyponatremia: 138 +/- 1 to 128 +/- 5 mEq/L). Fetal hypothalamic arginine vasopressin messenger ribonucleic acid expression and pituitary content did not change in relation to these relatively acute alterations in plasma tonicity. However, among all animals, arginine vasopressin messenger ribonucleic acid expression was significantly negatively correlated with pituitary arginine vasopressin content (r2 = 0.563; P = .02). Arginine vasopressin messenger ribonucleic acid expression was significantly lower in both preterm and near-term fetuses (P < .05) than that in the maternal ewe, although pituitary arginine vasopressin content (in micrograms per milligram of protein) was significantly greater in preterm fetuses (P < .01, vs maternal; P < .05, vs near term). CONCLUSIONS: The significant inverse relation between arginine vasopressin content and arginine vasopressin messenger ribonucleic acid suggests a dynamic arginine vasopressin synthesis-content feedback relationship is functional in the near-term fetus. Although relatively acute periods of maternal hypertonicity or hypotonicity do not alter fetal pituitary arginine vasopressin content or hypothalamic arginine vasopressin messenger ribonucleic acid expression, longer-term plasma tonicity alterations may potentially have an impact on the fetal arginine vasopressin hypothalamic-pituitary axis.     

The ictal electroencephalogram as a marker for the efficacy of electroconvulsive therapy

The question of how to define a therapeutically adequate electroconvulsive therapy (ECT) has been under discussion since the early days of ECT. Although convention has asserted a demand for minimum seizure times, the complex electrophysiological conditions involved in developing a generalized seizure make it problematic for therapeutic efficacy of ECT to be linked only with seizure duration. Within the framework of an open clinical study of 40 patients, selected parameters of the ictal electroencephalogram (EEG) have now been examined with respect to differentiation between therapeutically effective and ineffective treatments. For this purpose a rating scale covering both quantitative and qualitative features of the ictal EEG was used. Although this study recorded no correlations between seizure duration and clinical improvement, correlations were established between clinical improvement, on the one hand, and the frequency of epileptic discharges and their slowing during the spike-wave phase as well as the stereotypy of the discharge or a "stable" pattern of rhythmic spike-wave or sharp wave complexes, on the other. The results suggest that several of these EEG parameters might be combined to form a marker for therapeutically adequate ECT, and that treatment might be controlled accordingly.     

Benefits of a clinical pharmacokinetic service in optimising phenytoin use in the western Cape

OBJECTIVES: To study the benefits of a clinical pharmacokinetic service in optimising phenytoin use in the Western Cape. DESIGN: Assessment of the response to treatment was based on the number of seizures during the 3 months before entering the study (first baseline period), 3 months after entering the study (second baseline period) and 3 months before the termination of the study (test period). Patients kept a seizure diary throughout the study. The Michaelis-Menten model was used to calculate doses and predict steady-state serum concentrations. SETTING: Nine epilepsy clinics. SUBJECTS: One hundred and ninety-five (113 black and 82 coloured) compliant people with epilepsy receiving generic phenytoin monotherapy. OUTCOME MEASURES: Reduction in seizure frequency and adverse effects. RESULTS: A reduction in seizure frequency (64.8% compared with pre-optimisation) was experienced by 64.9% of patients. Mean seizure frequency was reduced from 3.39 to 1.18 per month. Reductions in seizure frequency of 100% and more than 50% were reported by 39.2% and 58.7% of patients, respectively. Adverse effects of phenytoin were reduced from 20.5% at the first visit to 3.2% at the last visit. CONCLUSION: The clinical pharmacokinetic dosing service for phenytoin applied in this study contributed significantly to the success of epilepsy management.     

Temporary results only in electroconvulsive therapy in therapy-resistant depression; retrospective study

OBJECTIVE: To evaluate the use and efficacy of electroconvulsive therapy (ECT) in refractory major depression according to DSM-III-R criteria, and to look for factors predicting response in the acute phase and the occurrence of relapse or recurrence after recovery. DESIGN: Retrospective. SETTING: University Hospital Rotterdam, The Netherlands. METHODS: Of all patients who received ECT between January 1988 and July 1993 data were collected by study of clinical records and of information by treating physicians after discharge. Every patient was visited once, or received an outpatient department appointment, to obtain informed consent, take a follow-up history and evaluate social functioning by scoring Global Assessment of Functioning and Sickness Impact Profile rating scales. RESULTS: 35 patients received ECT. In clinical practice, the guidelines of the Netherlands Psychiatric Association were not violated; most patients had received adequate pharmacological pretreatment before the decision to start ECT was made. Two patients died in hospital (not from ECT). In the acute phase 25 of the 33 patients still alive upon discharge showed good recovery. Seven of these suffered relapse within six months. The number of patients with a return of depressive symptoms rose to 12 by the end of the first year of follow-up. Sociodemographic variables and treatment characteristics did not appear to influence the result of treatment in the acute phase, nor the occurrence of relapse or recurrence. With less intensive pre- and post-ECT drug treatment the chances of relapse were increased. CONCLUSIONS: ECT is an effective treatment in the acute phase of a depression. Results after a longer period of follow-up are less satisfactory.     

Cardiovascular morbidity in high-risk patients during ECT

OBJECTIVE: Cardiovascular events are the principal cause of medical morbidity in patients receiving ECT. To assess the risks of ECT for individuals with preexisting cardiovascular disease, the authors examined medical complications in older patients treated with ECT during a 1-year period. METHOD: A case-control design was used in a review of the charts of 80 consecutive patients who received ECT from August 1990 to August 1991. On the basis of accepted clinical criteria, patients over 50 years of age were divided into two groups: one at increased risk for cardiac complications (N = 26) and one at standard cardiac risk (N = 27). Outcome was measured with a scale designed to assess clinically relevant medical complications. RESULTS: The risk group was older and had received more medical consultations before ECT than the nonrisk group. Although patients in the risk group were more likely to develop minor complications during ECT, they did not differ significantly from the comparison group in the rate of major complications. No patients died or sustained permanent cardiac morbidity during ECT. CONCLUSIONS: In contrast to a similar study at the same site 15 years earlier, the current study found ECT to be relatively safe in an unselected study group of elderly patients with preexisting cardiac risk factors. The findings underscore the advances in ECT technique over the past 15 years and the importance of identifying and carefully managing patients with cardiac risk factors before and during ECT.     

Oxytocin acts at V1 receptors to excite sympathetic preganglionic neurones in neonate rat spinal cord in vitro

Intracellular recordings were made from sympathetic preganglionic neurones (SPNs) in transverse slices of thoraco-lumbar spinal cord of young rats (12-20 days old). A small group of SPNs generally having higher membrane potentials (-70 mV) compared to a remaining group (-66 mV) showed spontaneous oscillations of their membrane potential. Oxytocin superfused in concentrations of 0.1-30 microM had four effects on SPNs, inducing slow depolarisation, EPSPs, IPSPs and brief rhythmic oscillations. The slow depolarisation was unaffected by TTX whereas this abolished the other changes. The oxytocin-induced depolarisation was associated with a slow inward current and was not reversed at membrane potentials negative to EK, it increased at more positive potentials and was still present in low Ca2+ and high Mg2+ solutions. These features of the oxytocin induced current are similar to those of the TTX resistant voltage dependent Na+ current described in brainstem autonomic neurones. Vasopressin superfused at concentrations of 0.1 microM to 30 microM had similar effects on SPNs to those of oxytocin. A comparison of the effects of oxytocin and vasopressin on the same neurones revealed that oxytocin was almost 10 times less potent than vasopressin. The effects of oxytocin were not mimicked by a selective oxytocin agonist but were mimicked by a selective vasopressin V1a agonist and blocked by a selective V1a antagonist. Therefore it is concluded that the effects of oxytocin on SPNs are mediated by the vasopressin V1a receptor. It is suggested that oxytocin and vasopressin terminals in the lateral horn are part of a descending system controlling oscillating networks of SPNs in the spinal cord.     

Phenotype of the tomato high pigment-2 mutant is caused by a mutation in the tomato homolog of DEETIOLATED1

Autism is a poorly understood developmental disorder characterized by social impairment, communication deficits, and compulsive behavior. The authors review evidence from animal studies demonstrating that the nonapeptides, oxytocin and vasopressin, have unique effects on the normal expression of species-typical social behavior, communication, and rituals. Based on this evidence, they hypothesize that an abnormality in oxytocin or vasopressin neurotransmission may account for several features of autism. As autism appears to be a genetic disorder, mutations in the various peptide, peptide receptor, or lineage-specific developmental genes could lead to altered oxytocin or vasopressin neurotransmission. Many of these genes have been cloned and sequenced, and several polymorphisms have been identified. Recent gene targeting studies that alter expression of either the peptides or their receptors in the rodent brain partially support the autism hypothesis. While previous experience suggests caution in hypothesizing a cause or suggesting a treatment for autism, the available preclinical evidence with oxytocin and vasopressin recommends the need for clinical studies using gene scanning, pharmacological and neurobiological approaches.     

Fractioning of Cu, Mn, Zn, and Pb in mineral soils along an oak forest vegetation gradient in Mexico City

PURPOSE: The purpose of this study was to test the hypothesis that a ketogenic diet would increase the resistance of rats to pentylenetetrazole (PTZ)-induced seizures and to understand the relation of ketonemia to seizure resistance. METHODS: A freely consumed, high-fat (ketogenic) diet was administered to male Sprague-Dawley rats for 5-10 weeks, while control animals were fed either rodent chow or a high-carbohydrate diet. Ketonemia was measured as plasma levels of beta-hydroxybutyric acid (beta-OHB). Seizures were induced by tail-vein infusion of pentylenetetrazole. RESULTS: The ketogenic diet produced a highly significant (p<0.01) increase in beta-OHB levels within 5 days. Induction of seizures by PTZ 35 days after animals were placed on their respective diets showed that ketogenic animals had a significantly (p<0.01) increased threshold for seizure induction compared with those fed an isocaloric diet of either high-carbohydrate or normal rodent chow. Ketogenic animals did not exhibit increased seizure severity relative to controls, despite receiving consistently higher doses of PTZ. CONCLUSIONS: The ketogenic diet resulted in an increased seizure threshold, confirming the hypothesis, and seizure threshold was found to be a direct function of the level of ketonemia.     

Characterization of natriuretic activity from posterior pituitary lobes

Previous studies have indicated the existence of natriuretic factors of hormonal nature with the posterior pituitary gland as a possible site of origin. It was in this light that a series of experiments was designed to examine the posterior pituitary for such factors. Acetic acid extracts of porcine and bovine posterior pituitary lobe tissue were subjected to gel filtration on Sephadex G-25. Several fractions in the molecular size range of 1000 were obtained which possessed potent natriuretic activity as assayed in rats. The activity of these fractions maximally increased sodium excretion to 6-8 muequiv./min, a 10- to 40-fold increase above control, when administered intraperitoneally to hydropenic, conscious rats. However, oxytocin and vasopressin, present in the posterior pituitary are natriuretic. These hormones were measured by radioimmunoassay, and invariably only those fractions which contained vasopressin and (or) oxytocin possessed natriuretic activity. Moreover, the extent of the natriuresis could be accounted for by the vasopressin and (or) oxytocin content of the test fractions. The natriuretic property of this material was abolished by treatment with thioglycollate. Further purification of natriuretic fractions by ion exchange resins, thin-layer chromatography and isoelectric focusing failed to resolve natriuretic activity from vasopressin and oxytocin. Similar results were observed following analysis of fractions isolated by gel filtration of acetic acid extracts of ventral hypothalamus tissue. The natriuretic fractions isolated from hypothalamic tissue were indistinguishable from oxytocin and vasopressin. These experiments suggest that the natriuretic activity in neurohypophyseal extracts can be attributed to oxytocin and vasopressin.     

2D 1H and 13C NMR evidence for stereoselective formation of a new bond C-N, C-S or C-C in the reaction of ivalin acetate with substituted pyrimidines

OBJECTIVE: This review examines the evidence supporting the proposition that a threshold clozapine plasma level can predict clinical response. In addition, it provides a brief overview of the pharmacokinetics, side effects, drug interactions and assay methodology of clozapine. METHOD: A comprehensive search of relevant literature was made with respect to the above criteria. The findings were collated and analysed to produce an overview of the usefulness of using clozapine levels in clinical practice. RESULTS: Most researchers find that, although the correlation between dose of clozapine and clinical effect is not high, a threshold plasma level of 350-420 ng mL-1 of clozapine is associated with an increased probability of a good clinical response to the drug. Results vary, however, with the study design. CONCLUSIONS: The data reviewed present a case for increasing the dose of clozapine in non-responsive patients to achieve a plasma level of at least 350-420 ng mL-1. Non-response at these levels, however, should not preclude a further upward titration of dose. This should occur unless (i) clinical response is obtained at a lower dose, (ii) intolerable side effects occur, or (iii) a daily dose of 900 mg is reached.     

Comparison of the biodistribution and the efficacy of monoclonal antibody 323/A3 labeled with either 131I or 186Re in human ovarian cancer xenografts

The effects of arginine vasopressin (AVP) and oxytocin (OT) upon thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) release were studied in euthyroid rats. Intracerebroventricular (i.c.v.) infusion of AVP in doses of 0.5 ng or 5 ng led to significant increases in plasma levels of TSH as well as FT4 and FT3. The effects of OT injected i.c.v. in similar doses were not consistent (there was no parallel between the changes of respective hormones plasma levels). It may be concluded that vasopressin modulate the pituitary-thyroid system function; AVP is probably a physiological stimulator of TSH and thyroid hormones secretion.     

Etiopathogenesis of rheumatoid arthritis

We studied osmoregulation of plasma vasopressin in 5 patients with newly diagnosed diabetes mellitus. All patients showed typical symptoms of uncontrolled diabetes mellitus such as marked hyperglycemia, polyuria, and polydipsia, but did not have advanced diabetic complications. Vasopressin release was studied using 5% hypertonic saline infusion test twice: before treatment when the patient was hyperglycemic, and after treatment 1 to 2 months later when the patient was euglycemic. Plasma vasopressin was measured by a sensitive and specific radioimmunoassay. The mean basal plasma vasopressin value in the patients was significantly higher in the hyperglycemic compared with the euglycemic state (3.75 +/- 0.70 vs 1.18 +/- 0.46 pmol/l, respectively; P < 0.05). The relationship of plasma vasopressin with serum sodium, but not plasma osmolality, during hyperglycemia showed an apparent hypersecretion of vasopressin. In both cases, the sensitivity of the vasopressin response to osmotic stimuli was significantly decreased. During euglycemia, the sensitivity of vasopressin secretion to either sodium or osmolality was almost normal, although a slight rise in the osmostat was observed compared with normal subjects. Together, we found that the positive correlation of vasopressin with sodium or osmolality is maintained but significantly altered in patients with untreated diabetes mellitus. Especially noteworthy is the lowered threshold and decreased sensitivity of osmotically-induced vasopressin secretion during hyperglycemia, which may be caused by multiple factors such as diabetes-associated hypovolemia, osmogenic effects of glucose and other osmoles, depletion of the pool of vasopressin available for release, and the metabolic derangement of osmoreceptor/magnocellular neurons.     

AVPR2 variants and V2 vasopressin receptor function in nephrogenic diabetes insipidus

BACKGROUND: The AVPR2 gene encodes the type 2 vasopressin receptor, a member of the vasopressin/oxytocin receptor subfamily of G protein-coupled receptors. Disruption of AVPR2 causes X-linked congenital nephrogenic diabetes insipidus (NDI), yet the functional significance of most gene sequence variations found in association with NDI has not been proven. The large number of naturally occurring AVPR2 mutations constitutes a model system for studying the structure-function relationship of G protein-coupled receptors. This analysis can be aided by examining amino acid sequence variation and conservation among evolutionarily disparate members of the subfamily. METHODS: Twenty-five new NDI patients were evaluated by DNA sequencing for mutations in AVPR2. Receptors encoded by eighteen NDI alleles were tested for physiologic signaling activity in response to varying concentrations of arginine vasopressin (AVP) in a sensitive cell culture assay. Seventeen amino acid sequences from the vasopressin/oxytocin receptor subfamily were aligned and conserved residues were identified and correlated with the locations of NDI associated variations. RESULTS: Twenty-four variant alleles were found among the 25 new patients. Thirteen had no prior family history of expressed NDI. All 18 of the NDI-associated AVPR2 alleles tested for function demonstrated diminished response to stimulation with AVP. Twelve failed to respond at all, whereas six signaled only at high AVP concentrations. Evolutionarily conserved residues clustered in the transmembrane domains and in the first and second extracellular loops, and NDI-associated missense mutations appeared mostly in the conserved domains. CONCLUSIONS: Sporadic cases are frequent and they usually represent the X-linked rather than the autosomal form of NDI. Genetic and functional testing can confirm this in individual cases. Mutations in this study affecting ligand binding domains tend to retain partial signaling in vitro, whereas those that introduce a charged residue in a transmembrane domain are inactive. The minimal partial signaling observed in cultured cells is unlikely to correlate with clinically significant urine concentrating ability. Other AVPR2 mutations with milder effects on receptor function probably exist, but may not be expressed clinically as typical NDI.     

Naloxone-induced supersensitivity of oxytocin neurones to opioid antagonists

Here we report that a single administration of naloxone to conscious rats produces no significant increase in oxytocin release, but when repeated 3-4 days later results in a large release of oxytocin. Plasma oxytocin concentrations were measured in conscious and urethane-anaesthetized rats pretreated with naloxone or isotonic saline on Day 1. On Days 2, 3 or 4, a second dose of naloxone was given, producing an increase in oxytocin secretion in naloxone-pretreated groups (P < 0.05 vs. controls) on Day 3 and 4, but not on Day 2. The specificity of the opioid antagonist supersensitivity was determined by injection of the kappa-antagonist nor-binaltorphimine (nor-BNI). Pretreated rats (naloxone, saline or nor-BNI, Day 1) received an additional acute nor-BNI injection (Day 4) which increased plasma oxytocin concentration in the three groups. However, this increase was higher in naloxone-pretreated rats with no differences between the nor-BNI- and saline-pretreated animals. Measurements of electrical activity of single supraoptic nucleus oxytocin neurons and of plasma oxytocin concentration (Day 4) showed that naloxone modestly enhanced the responsiveness of oxytocin neurons to cholecystokinin (CCK) in naloxone-pretreated rats (by comparison with saline-pretreated rats), but had only a small effect on basal firing rate that did not differ between naloxone-pretreated rats and saline-pretreated rats. To investigate whether naloxone-pretreatment modified the effect of morphine on CCK-induced oxytocin release, on Day 4 CCK was injected i.v. with or without morphine. Morphine at a dose of 0.1 mg/kg did not affect CCK-induced oxytocin release, whereas 1 mg/kg of morphine blocked this release in both saline- and naloxone-pretreated rats. The results suggest that naloxone induces opioid antagonist supersensitivity on oxytocin secretion, mainly by up-regulating kappa-opioid mechanisms on oxytocin nerve terminals in the posterior pituitary.