Sulpiride increases and dopamine decreases intracranial temperature in rats when injected in the lateral hypothalamus: an animal model for the neuroleptic malignant syndrome?

Acute Dystonic Reaction and the Neuroleptic Malignant Syndrome

Up to 90% of patients on chronic antipsychotic therapy will experience adverse neurologic side effects, with many of these effects attributable to the dopamine-blocking properties of these drugs. Even the newer, “atypical” antipsychotics are increasingly associated with neurologic complications. In the acute care setting, these medications have broad application beyond the management of psychiatric illness. Given the extent of their use, clinicians should be familiar with the spectrum of neurological syndromes that can develop. Some are common, such as akathisia, acute dystonic reaction, tardive dyskinesia, and drug-induced parkinsonism. Others, such as the life-threatening neuroleptic malignant syndrome, are rare yet must be recognized early to affect survival and improve outcome. This discussion highlights 2 idiosyncratic syndromes, acute dystonic reaction and neuroleptic malignant syndrome. The differential diagnosis for both syndromes and their management is discussed.

Relationship between mean daily ambient temperature range and hospital admissions for schizophrenia: Results from a national cohort of psychiatric inpatients

Environmental temperature is known to correlate with schizophrenia, but little is known about the association with changes in temperature. This 12-year study aimed to evaluate the relationship between the mean daily range of ambient temperature and schizophrenia admissions in a national cohort of psychiatric inpatients in Taiwan. Meteorological data provided by the Central Weather Bureau of Taiwan were interpolated to create representative estimates. Psychiatric inpatient admissions in all hospitals with medical services enrolled in the current health care insurance system were retrieved from the 1996-2007 Psychiatric Inpatient Medical Claim dataset of the National Health Insurance Research Database. Generalized linear models with Poisson distributions were used to analyze the impact of mean diurnal change of temperature on schizophrenia admissions, controlling for internal correlations and demographic covariates. The daily temperature range varied between 1.7°C and 12.1°C (1st to 99th percentile). The relative risk of schizophrenia admission was significantly increased at a temperature range of 3.2°C (10th percentile), and the maximum was at 12.1°C (99th percentile); however, no such association was found with schizoaffective disorder. When restricted to the capital and largest city, the effects of temperature range were prominent and may correlate with temperature itself. The joint effect of temperature and temperature range was associated with elevated risk, particularly at cooler temperatures. A positive correlation was found between increasing temperature range and schizophrenia admissions. The increase in morbidity at high percentiles suggests that the increasing dynamics of temperature range are a valid reflection of risk, highlighting the need for precautionary action.

Neuroleptic malignant syndrome: mechanisms, interactions, and causality

This review focuses on new data from recent publications concerning how compounding interactions between different thermoregulatory pathways influence the development of hyperthermia and/or neuroleptic malignant syndrome (NMS), and the fundamental issue of the presumed causal role of antipsychotic drugs. The formal criteria for substantiating cause-effect relationships in medical science, established by Hill, are applied to NMS and, for comparison, also to malignant hyperthermia and serotonin toxicity. The risk of morbidities related to hyperthermia is reviewed from human and experimental data: temperatures in excess of 39.5°C cause physiological and cellular dysfunction and high mortality. The most temperature-sensitive elements of neural cells are mitochondrial and plasma membranes, in which irreversible changes occur around 40°C. Temperatures of up to 39°C are "normal" in mammals, so, the term hyperthermia should be reserved for temperatures of 39.5°C or greater. The implicitly accepted presumption that NMS is a hypermetabolic and hyperthermic syndrome is questionable and does not explain the extensive morbidity in the majority of cases, where the temperature is less than 39°C. The thermoregulatory effects of dopamine and acetylcholine are outlined, especially because they are probably the main pathways by which neuroleptic drugs might affect thermoregulation. It is notable that even potent antagonism of these mechanisms rarely causes temperature elevation and that multiple mechanisms, including the acute phase response, stress-induced hyperthermia, drugs effects, etc., involving compounding interactions, are required to precipitate hyperthermia. The application of the Hill criteria clearly supports causality for drugs inducing both MH and ST but do not support causality for NMS.

The discriminative stimulus effects of dopamine D2- and D3-preferring agonists in rats

RATIONALE

Previous research has found the stimulus effects of dopamine D2- and D3-preferring agonists difficult to distinguish in drug discrimination studies. Antagonism studies suggest that the stimulus effects of both types of agonists may be mediated primarily through D2 receptors.

OBJECTIVES

The current study was designed to further assess the receptors mediating the stimulus effects of these agonists and to attempt to train rats to discriminate directly between D2- and D3-preferring dopamine agonists.

MATERIALS AND METHODS

Four groups of eight rats were trained to discriminate either 0.1 mg/kg of the D3-preferring agonist pramipexole from saline, 1.0 mg/kg of the D2-preferring agonist sumanirole from saline, 0.1 mg/kg pramipexole from either saline or 1.0 mg/kg sumanirole, or 1.0 mg/kg sumanirole from either saline or 0.1 mg/kg pramipexole.

RESULTS

Three of eight rats in the 0.1 mg/kg pramipexole vs. 1.0 mg/kg sumanirole or saline failed to meet the training criteria, and the discrimination in this group was tenuous. The D2-preferring antagonist L-741,626 at 1.0 mg/kg was more effective at shifting to the right the pramipexole dose-response curve in pramipexole-trained rats, while 32 mg/kg of the selective D3 antagonist PG01037 had little effect. Quinpirole and 7-OH-DPAT fully or partially substituted for both pramipexole and sumanirole in each group tested, while cocaine did not substitute in any group.

CONCLUSIONS

Antagonist data along with the pattern of training and substitution data suggested that D2 receptor activation is primarily responsible for the stimulus effects of both sumanirole and pramipexole with D3 receptor activation playing little or no role.

Neuroleptic malignant syndrome and serotonin syndrome

This chapter is focused on drug-induced hyperthermia with special regard to use of antipsychotics and antidepressants for the treatment of schizophrenia and major depression, respectively. Neuroleptic malignant syndrome (NMS) develops during the use of neuroleptics, whereas serotonin syndrome is caused mainly by serotoninergic antidepressants. Although both syndromes show various symptoms, hyperthermia is the main clinical manifestation. In this review we describe the historical background, clinical manifestations, diagnosis, and differential diagnosis of these two syndromes based on our observations on the experimental and clinical data.

The distribution and morphological characteristics of catecholaminergic cells in the diencephalon and midbrain of the bottlenose dolphin (Tursiops truncatus)

The present study describes the distribution and cellular morphology of catecholaminergic neurons in the diencephalon and midbrain of the bottlenose dolphin (Tursiops truncatus). Tyrosine hydroxylase immunohistochemistry was used to visualize these putatively dopaminergic neurons. The standard A1-A17, C1-C3, nomenclature is used for expediency; however, the neuroanatomical names of the various nuclei have also been given. Dolphins exhibit certain tyrosine hydroxylase immunoreactive (TH-ir) catecholaminergic neuronal groups in the midbrain (A8, A9, A10) and diencephalon (A11, A12, A14), however, no neuronal clusters clearly corresponding to the A13 and A15 groups could be identified. The subdivisions of these neuronal groups are in general agreement with those of other mammals, but there is a high degree of species specificity. First, three TH-ir neuronal groups not identified in other species were found: in the ventral lateral peri-aqueductal gray matter, posterior dorsal hypothalamus, and rostral mesencephalic raphe. Second, the normal components of the substantia nigra (A9 or pars compacta, A9 lateral or pars lateralis, A9 ventral or pars reticulata) were extremely cell sparse, but there was a substantial expansion of the A9 medial and A10 lateral subdivisions forming an impressive 'ventral wing' in the posterior substantia nigra. The findings of this and previous studies suggest a distinct evolutionary trend occurring in the neuromodulatory systems in mammals. The results are discussed in relation to motor control, thermoregulation, unihemispheric sleep, and dolphin cognition.

Acute cardiac failure in neuroleptic malignant syndrome

We present a case of rapid onset acute cardiac failure developing as part of neuroleptic malignant syndrome in a 35-year-old woman following treatment with thioridazine and lithium. Post mortem histology of cardiac and skeletal muscle showed similar changes of focal cellular necrosis and vacuolation suggesting a common disease process.

Malignant syndrome in Parkinson's disease: concept and review of the literature

We reviewed literature on malignant syndrome occurring in patients with Parkinson's disease (PD) during the course of drug therapy. Clinical features were high fever, marked rigidity, consciousness disturbance, autonomic dysfunction, and elevation of serum creatine kinase. The clinical features were essentially similar to those of neuroleptic malignant syndrome. The immediate triggering event was, most often, discontinuation or reduction of anti-parkinsonian drugs, particularly of levodopa. But no anti-parkinsonian drug was the exception to the induction of malignant syndrome. Serious complications were severe pneumonia, disseminated intravascular coagulation, and acute renal failure. Early treatment with intravenous fluid infusion and external body cooling are essential for good recovery. Bromocriptine and dantrolene sodium were used frequently. It has been claimed that they are effective; however, randomized controlled studies are needed to explicitly prove the efficacy of these drugs in malignant syndrome associated with PD.

A collaborative study on the malignant syndrome in Parkinson's disease and related disorders

We report the results of a collaborative study on malignant syndrome (MS) that developed in patients being treated with levodopa and other anti-parkinsonian drugs. We analyzed clinical features, laboratory findings, precipitating events, and risk factors for poor outcome. The study was conducted in five centers in Japan. Patients who developed MS between January 1991 and December 1997 were included. The enrollment criteria used were the same as those for neuroleptic MS proposed by Levenson et al. (1985).A total of 99 episodes were encountered in 93 patients (72 with Parkinson's disease and 21 with secondary parkinsonism); one patient had four recurrences of MS and three patients had two recurrences. High fever was the most frequent clinical manifestation of MS followed by worsening of parkinsonism, and then altered levels of consciousness. Serum creatine kinase was abnormally elevated in all the patients studied. Life-threatening complications were rhabdomyolysis, disseminated intravascular coagulation, and acute renal failure. The most frequent precipitating event was discontinuation or dose reduction of anti-parkinsonian drugs, particularly levodopa. No drug was the exception in the precipitation of MS. Intercurrent infection was the next most common precipitating event. MS developed without drug withdrawal or infection in some patients. In five patients, severe "wearing off" phenomenon was the only event preceding the onset of MS. Hot weather and dehydration appeared to be the cause in three patients. Among the total of 99 episodes, patients recovered to the pre-MS state following 68 episodes (68.7%); in the remaining 31.3%, patients failed to recover to their previous state. Older age, higher Hoehn and Yahr stage during the symptomatic phase of MS, higher akinesia score, and the absence of wearing off phenomenon prior to developing MS were associated with poor outcome. The most frequently used treatments of MS were intravenous fluid, levodopa, dantrolene sodium, and intragastric bromocriptine. Early introduction of treatment is important. Any elevation of body temperature during the course of anti-parkinsonian drug treatment should be considered as MS until proved otherwise.

Abnormal thermoregulation in drug-free male schizophrenia patients

Schizophrenia patients may develop various thermoregulatory disturbances. We hypothesized that a standardized exercise-heat tolerance test [two 50-min bouts of walking a motor-driven treadmill at 40 degrees C (relative humidity=40%)] would reveal abnormal thermoregulation in drug-free schizophrenia patients. Six drug-free schizophrenia outpatients and seven healthy comparison subjects participated in this study. The schizophrenia patients exhibited significantly higher baseline and exertion-related rectal temperature. The relevance of these findings to the pathophysiology of schizophrenia-related thermoregulatory disorders is as yet unclear.

Dopamine-acetylcholine interaction in the rat lateral hypothalamus in the control of locomotion

Pharmacological, neurochemical, and behavioral techniques were used to characterize DA-ACh interaction within the lateral hypothalamus (LH) in the context of locomotion, feeding behavior, and reinforcement. In Experiment 1, the muscarinic agonist carbachol injected in the LH increased locomotor activity in proportion to dose. In Experiment 2, the same doses of carbachol proportionately increased exctracellular DA in the nucleus accumbens (Nac) as monitored by brain microdialysis. Dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) also increased. In Experiment 3, LH infusion by reverse microdialysis of the D(2) receptor blocker sulpiride released ACh in the LH in a dose-response manner. This suggested that sulpiride disinhibits ACh release via D(2) receptors in the LH and thereby facilitates behavior. Confirming this in Experiment 4, local LH atropine 5 min before sulpiride suppressed the locomotor response to sulpiride for about 20 min. These results suggest that sulpiride acts in the LH by disinhibiting a hypothalamic locomotor mechanism that is cholinergically driven and connected with the mesoaccumbens dopamine pathway. Given prior results that local sulpiride in the LH can induce hyperphagia and reward, this system may be involved in searching for food and rewarding feeding behavior. In conclusion, DA acts in the LH via D(2) receptors to inhibit cholinergic neurons or terminals that are part of an approach system for eating.

Characterization of D-fenfluramine-induced hypothermia: evidence for multiple sites of action

The effects of D-fenfluramine on core body temperature has been largely investigated under conditions of either high or low ambient temperature, whereas little research has focused on this response under normal environmental conditions. Moreover, there has been neglect in research on the mechanisms underlying changes in body temperature. In this study, we demonstrate that D-fenfluramine (5 and 10 mg/kg) induces a sustained decrease in body temperature in the rat under normal ambient temperatures. Pre-treatment with the selective serotonin reuptake inhibitor sertraline (5 mg/kg), the full 5-HT(1A) receptor antagonist 4-fluoro-N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-2-pyridinyl benzamide], WAY 100635 (0.15 mg/kg) and the 5-HT(2C) receptor antagonist benzofuran-2-carboxamidine, RO 43-0440 (2.5 mg/kg) blocked D-fenfluramine-induced hypothermia. Depletion of 5-hydroxytryptamine (5-HT) stores following treatment with the serotonergic neurotoxin parachlorophenylalanine reversed the initial hypothermic effects of D-fenfluramine but not the later effects, as D120 min post-challenge) in animals pre-treated with parachlorophenylalanine. Such findings are consistent with a requirement for D-fenfluramine uptake into 5-HT neurons followed by release of 5-HT from intracellular stores and stimulation of post-synaptic 5-HT receptors to reduce body temperature. The hypothermic response to D-fenfluramine was potentiated by ketanserin pre-treatment 30 min post-challenge but then antagonized at later time intervals. Pre-treatment with the dopamine, D(2) antagonist, haloperidol (1 mg/kg) and sulpiride (30 mg/kg) had a similar effect in blocking the hypothermia as WAY 100635, suggesting a role for dopamine D(2) receptors in the response. Pre-treatment with the alpha(2)-adrenoceptor antagonist yohimbine failed to block the hypothermic response. These results suggest multiple sites of action mediating D-fenfluramine-induced hypothermia and may be the result of a combined effect of D-fenfluramine and its active metabolite norfenfluramine affecting not only the release of 5-HT but also stimulation of post-synaptic receptors.

Physiologic and neuroendocrine responses to intravenous naloxone in subjects with Alzheimer's disease and age-matched controls

BACKGROUND

Prior work showed that administration of naloxone HCl had different behavioral effects in patients with Alzheimer's disease (AD) than controls. The aim of the present study was to contrast the physiologic and neuroendocrine responses to administration of a wide range of doses of intravenous naloxone of patients with probable Alzheimer's disease to aged-matched controls.

METHODS

This was a double-blind, placebo-controlled, study of 12 patients with probable Alzheimer's disease and 8 age-matched normal controls who each received intravenous infusions of naloxone HCl on 3 different days in doses of 0.1 mg/kg and 2.0 mg/kg preceded by test doses of 0.5 mcg/kg. Order of treatment condition was randomized. Vital signs and plasma cortisol and prolactin were obtained at regular intervals.

RESULTS

Both groups showed increased cortisol after naloxone 0.1 mg/kg and 2.0 mg/kg (p < .0001), but the increase was significantly greater and longer lived in controls than in patients. Patients, but not controls, also experienced a significant hypothermic response after naloxone 2.0 mg/kg (p < .05). Prolactin, heart rate, and blood pressure did not change following naloxone and did not differ between groups.

CONCLUSIONS

These findings support a growing body evidence that HPA axis activity is increased in AD, and further suggest that at least part of this may be due to decreased opiatergic tonic inhibition.

Drug-induced hyperthermia

Drug-related causes of hyperthermia can often be overlooked in the setting of elevated body temperature. This article reviews the pathophysiology, presentation, and treatment of several drug-induced hyperthermia syndromes: malignant hyperthermia, neuroleptic malignant syndrome, sympathomimetic poisoning, and anticholinergic toxicity. Although the general approach is similar, specific management strategies may be required for each syndrome.

Development of an animal model for neuroleptic malignant syndrome: heat-exposed rabbits with haloperidol and atropine administration exhibit increased muscle activity, hyperthermia, and high serum creatine phosphokinase level

The neuroleptic malignant syndrome (NMS) is a life-threatening complication of neuroleptic treatment. To elucidate the pathogenesis of NMS, an animal model has been developed. Experimental rabbits treated with haloperidol (1 mg/kg) by intramuscular injection, were studied for the diagnostic symptoms of increased muscle rigidity, elevated body temperature, and high serum creatine phosphokinase (CPK) level. Administration of haloperiodol (1 mg/kg) and atropine (0.4 mg/kg), and exposure to high ambient temperature (35 degrees C) induced a significant increase in electromyographic activity with muscle rigidity similar to that observed in patients with NMS. Such rabbits also showed elevated body temperature and serum CPK value. In addition to the similarity of the signs and symptoms, all parameters measured (muscle rigidity, body temperature, and serum CPK level) were normalized by dantrolene treatment. The effectiveness of dantrolene in the experimental animal partially confirms the validity of this animal model for NMS. This experimental animal model for NMS may be useful to elucidate the pathogenesis of NMS.

Prochlorperazine-induced neuroleptic malignant syndrome

Neuroleptic malignant syndrome can present in a variety of ways. In a review of the medical literature we could find few well-documented reports of prochlorperazine-induced neuroleptic malignant syndrome. We report such a case with its workup, recognition, and management.

Dipsogenic effect of pituitary adenylate cyclase activating polypeptide (PACAP38) injected into the lateral hypothalamus

PACAP38 bilaterally injected in the vicinity of the perifornical lateral hypothalamus (pfLH) induced drinking behavior in rats. The animals (n = 12) drank 19.7 +/- 4.1 ml of water during the hour following PACAP38 microinjections (1 nmol/0.5 microliter). In the same rat sulpiride microinjections (45 nmol/0.5 microliter) had relatively mild effects (7.8 +/- 1.4 ml/h). The dipsogenic effects of sulpiride and PACAP38 were well correlated suggesting that both substances trigger drinking behavior activating the same hypothalamic mechanisms. Neither sulpiride nor PACAP38 promoted drinking when injected just 1.3 mm behind the effective zone. This negative result is an evidence of the neuroanatomical specificity of the dipsogenic effects of both substances. These preliminary results suggest that PACAP38 in the pfLH could be a neuropeptide regulating drinking behavior and perhaps body fluid volume and osmolarity and arterial blood pressure.