Neuroendocrine responses to a cold pressor stimulus in polydipsic hyponatremic and in matched schizophrenic patients

Association of Postural Blood Pressure Response With Disease Severity in Primary Open Angle Glaucoma

PRCIS

Patients with primary open angle glaucoma (POAG) demonstrated exaggerated postural blood pressure dip in recumbency that was positively correlated with the severity of glaucomatous optic neuropathy (GON). Postural dip testing can be used clinically as a marker of systemic vascular dysregulation in GON risk assessment.

OBJECTIVE

To investigate whether patients with POAG demonstrated abnormal postural blood pressure response to recumbency and whether such abnormal postural response correlated with GON severity.

PATIENTS AND METHODS

This is a prospective observational study where 47 patients with POAG underwent intraocular pressure and systemic arterial blood pressure, systolic blood pressure (SBP) and diastolic blood pressure (DBP), measurement in seated and after 20-minute recumbency positions. Mean arterial blood pressure (MABP) was calculated for seated and recumbent positions. The percentage difference between seated and recumbent SBP, DBP, and MABP was calculated according to which participants were divided into 3 groups, that is, nondippers, normal dippers, and exaggerated dippers with percentage dips of <10%, ≥10%≤20%, >20%, respectively. Participants underwent optical coherence tomography of optic nerve head to measure retinal nerve fiber layer thickness (RNFLT) which was used as a structural biomarker of GON.

RESULTS

RNFLT was lower in exaggerated dippers than in nondippers and normal dippers. There was a negative correlation between postural dip and average RNFLT. Linear regression showed that postural dip was associated with lower RNFLT independent of age and intraocular pressure. The χ 2 independence test demonstrated a strong relation among corresponding dip groups for SBP, DBP, and MABP. However, it showed no significant relation between hypertension and postural dip. Fisher exact test showed no relation between antihypertensive medication and postural dip.

CONCLUSIONS

Patients with POAG demonstrated abnormal postural blood pressure response comprising exaggerated recumbent dip which was positively correlated with disease severity. Postural dip assessment may serve as a simple clinic-based test of systemic vascular dysregulation as part of GON risk evaluation.

Altered physical pain processing in different psychiatric conditions

Several reports indicate either increased or decreased pain sensitivity associated with psychiatric disorders. Chronic pain is highly prevalent in many of these conditions. We reviewed the literature regarding experimental pain sensitivity in patients with major depression, bipolar disorder, posttraumatic stress disorder (PTSD), generalized anxiety disorder, panic disorder, obsessive-compulsive disorder and schizophrenia. Electronic searches were performed to identify studies comparing experimental pain in patients with these conditions and controls. Across 31 depression studies, reduced pain threshold was noted except for ischemic stimuli, where increased pain tolerance and elevated sensitivity to ischemic pain was observed. A more pervasive pattern of low pain sensitivity was found across 20 schizophrenia studies. The majority of PTSD studies (n = 20) showed no significant differences compared with controls. The limited number of bipolar disorder (n = 4) and anxiety (n = 9) studies precluded identification of clear trends. Wide data variability was observed. Awareness of psychiatric patients' pain perception abnormalities is needed for active screening and addressing physical comorbidities, in order to enhance quality of life, life expectancy and mental health.

Psychophysiological stress-reactivity in clinical and non-clinical voice-hearers

BACKGROUND

Psychosis is associated with dysregulation of psychophysiological stress-reactivity, including in subjective, autonomic nervous system (ANS) and hypothalamic-pituitary-adrenal (HPA) parameters.

AIMS

This study investigated whether dysregulated psychophysiological stress-reactivity is specifically associated with auditory verbal hallucinations (AVHs) or psychosis more generally by comparing voice-hearers with and without a need for care.

METHOD

Clinical (n = 20) and non-clinical voice-hearers (n = 23), as well as a healthy control group with no voices (n = 23), were compared on HPA and ANS responses, and subjective reactivity, to a psychophysiological stress paradigm, the socially evaluative cold pressor test.

RESULTS

Measures of HPA function in both clinical and non-clinical voice-hearers diverged from non-voice-hearing controls. Clinical participants showed a blunted peak response compared to both non-clinical groups (p = 0.02), whilst non-clinical voice-hearers showed, at trend-level, reduced cortisol levels during stress exposure compared to both clinical voice-hearers (p = 0.07) and healthy controls (p = 0.07), who unexpectedly did not differ from each other (p = 0.97). Clinical participants showed greater subjective stress levels than both non-clinical groups (p < 0.001), as well as greater anticipatory stress (p = 0.001) and less recovery. There were no differences between groups on parameters of the ANS (all p > 0.05).

CONCLUSIONS

Dysregulated psychophysiological stress-function is present in clinical voice-hearers, and partially discriminates them from non-clinical voice-hearers. Overall, the present findings identified specific potential psychophysiological markers of risk and resilience in auditory verbal hallucinations and need for care.

Primary polydipsia: Update

In primary polydipsia pathologically high levels of water intake physiologically lower arginine vasopressin (AVP) secretion, and in this way mirror the secondary polydipsia in diabetes insipidus in which pathologically low levels of AVP (or renal responsiveness to AVP) physiologically increase water intake. Primary polydipsia covers several disorders whose clinical features and significance, risk factors, pathophysiology and treatment are reviewed here. While groupings may appear somewhat arbitrary, they are associated with distinct alterations in physiologic parameters of water balance. The polydipsia is typically unrelated to homeostatic regulation of water intake, but instead reflects non-homeostatic influences. Recent technological advances, summarized here, have disentangled functional neurocircuits underlying both homeostatic and non-homeostatic physiologic influences, which provides an opportunity to better define the mechanisms of the disorders. We summarize this recent literature, highlighting hypothalamic circuitry that appears most clearly positioned to contribute to primary polydipsia. The life-threatening water imbalance in psychotic disorders is caused by an anterior hippocampal induced stress-diathesis that can be reproduced in animal models, and involves phylogenetically preserved pathways that appear likely to include one or more of these circuits. Ongoing translational neuroscience studies in these animal models may potentially localize reversible pathological changes which contribute to both the water imbalance and psychotic disorder.

Expression of vasopressin mRNA in the hypothalamus of individuals with a diagnosis of schizophrenia

OBJECTIVE

This study investigates the expression of mRNA encoding vasopressin in the hypothalamus of autopsy brains of individuals diagnosed with schizophrenia.

METHODS

Ten brains of individuals with schizophrenia and 10 brains from individuals without any disease were examined during autopsy. The hypothalamic block was dissected and immersion fixed in paraformaldehyde, sucrose substituted, frozen, and cut into 20-µm-thick coronal cryostat sections. The sections were hybridized with an S-35-labeled DNA antisense oligo probe and after washing covered by an X-ray film. The hybridization signals on the films were transferred to a computer and densitometrically quantified.

RESULTS

The densitometry signals showed a statistically significant lower mRNA expression (53% decrease; p = 0.014) in the paraventricular nucleus of the individuals with schizophrenia compared to the controls. In the supraoptic nucleus, the decrease in the group with schizophrenia was 39% compared to the controls, but this decrease was not statistically significant (p = 0.194).

CONCLUSIONS

Our results show a low expression of mRNA encoding vasopressin in the paraventricular nucleus of the individuals with schizophrenia. We suggest that vasopressin is not directly involved in the pathogenesis of schizophrenia, but might influence schizophrenic symptoms via vasopressin receptors located in the social behavioral neural network in the forebrain.

Haloperidol affects bones while clozapine alters metabolic parameters - sex specific effects in rats perinatally treated with phencyclidine

Background

The presentation of schizophrenia (SCH) symptoms differs between the sexes. Long-term treatment with antipsychotics is frequently associated with decreased bone mineral density, increased fracture risk and metabolic side effects. Perinatal phencyclidine (PCP) administration to rodents represents an animal model of SCH. The aim of this study was to assess the effects of chronic haloperidol and clozapine treatment on bone mass, body composition, corticosterone, IL-6 and TNF-α concentrations and metabolic parameters in male and female rats perinatally treated with PCP.

Methods

Six groups of male and six groups of female rats (n = 6-12 per group) were subcutaneously treated on 2nd, 6th, 9th and 12th postnatal day (PN), with either PCP (10 mg/kg) or saline. At PN35, one NaCl and PCP group (NaCl-H and PCP-H) started receiving haloperidol (1 mg/kg/day) and one NaCl and PCP group (NaCl-C and PCP-C) started receiving clozapine (20 mg/kg/day) dissolved in drinking water. The remaining NaCl and PCP groups received water. Dual X-ray absorptiometry measurements were performed on PN60 and PN98. Animals were sacrificed on PN100. Femur was analysed by light microscopy. Concentrations of corticosterone, TNF-α and IL-6 were measured in serum samples using enzyme-linked immunosorbent assay (ELISA) commercially available kits. Glucose, cholesterol and triacylglycerol concentrations were measured in serum spectrophotometrically.

Results

Our results showed that perinatal PCP administration causes a significant decrease in bone mass and deterioration in bone quality in male and female rats. Haloperidol had deleterious, while clozapine had protective effect on bones. The effects of haloperidol on bones were more pronounced in male rats. It seems that the observed changes are not the consequence of the alterations of corticosterone, IL-6 and TNF-α concentration since no change of these factors was observed. Clozapine induced increase of body weight and retroperitoneal fat in male rats regardless of perinatal treatment. Furthermore, clozapine treatment caused sex specific increase in pro-inflammatory cytokines.

Conclusion

Taken together our findings confirm that antipsychotics have complex influence on bone and metabolism. Evaluation of potential markers for individual risk of antipsychotics induced adverse effects could be valuable for improvement of therapy of this life-long lasting disease.

Electronic supplementary material

The online version of this article (10.1186/s40360-017-0171-4) contains supplementary material, which is available to authorized users.

Impact of reward on pain threshold and tolerance to experimental pain (Cold Pressor Task) in healthy subjects and patients with schizophrenia

Reduced pain sensitivity is considered as a potential endophenotype of schizophrenia. Patient's motivation in pain experimental studies was neither assessed nor controlled. This study aimed to assess the effect of reward on pain in patients with schizophrenia compared to controls. Rewarded subjects showed higher pain threshold and tolerance compared to unrewarded subjects. Pain tolerance was significantly lower in patients than in controls when they were not rewarded. Reward resulted in an increase of pain tolerance with a higher manner in patients. This study suggests that better control of motivational aspects could improve assessment of pain sensitivity in schizophrenia.

Hiponatremia in the practice of a psychiatrist. Part 2: psychogenic polydipsia

Objective. The study is the second part of the literature review on hyponatremia in patients with diagnosed mental disorders. This article focuses on psychogenic polydipsia as, along with the SIADH, one of the two most common causes of hyponatremia in the mentioned group of patients.

Method: The literature review was based on searching the Medline, the Google Scholar and the Ebsco databases in Polish and English by entering the following phrases: psychogenic polydipsia, the psychosis – intermittent hyponatremia – polydipsia syndrome, water intoxication.

Discussion: Psychogenic polydipsia occurs in up to 25% of patients treated for mental disorders. It most frequently concerns patients with schizophrenia. 30% of patients with psychogenic polydipsia suffer from hyponatremia with or without symptoms of water intoxication. In the etiology of psychogenic polydipsia, the influence of dopaminergic and noradrenergic neurotransmission has been considered, as well as angiotensin, which is claimed to have dipsogenic properties. In order to reduce the severity of the disorder, attempts have been made to administer the following groups of medications: β-blockers, opioid receptor antagonists, angiotensin convertase inhibitors and angiotensin receptor antagonists. Other methods include replacing classic antipsychotic drugs with clozapine. There are also reports of a reduced severity of polydipsia with hyponatremia after introducing risperidone and olanzapine. Preventing episodes of water intoxication in patients with psychogenic polydipsia requires the monitoring of their body weight and a suitable reduction of fluid intake by them.

Results: Mentally ill patients, especially those with chronic schizophrenia, should be monitored for psychogenic polydipsia and the concomitant hyponatremia.

Fulminant crural compartment syndrome preceded by psychogenic polydipsia

We report a case of bilateral anterolateral crural compartment syndrome elicited by hyponatraemia and psychogenic polydipsia. The unusual constellation of clinical findings and diminished pain expression made initial diagnostic procedures challenging. The possible pathogenesis and treatment options are discussed. Impairment of lower extremity function at follow-up was serious and permanent.

Brain circuit dysfunction in a distinct subset of chronic psychotic patients

OBJECTIVE

To identify the mechanism of unexplained hyponatremia and primary polydipsia in schizophrenia and its relationship to the underlying psychiatric illness.

METHODS

Briefly review previous studies that led to the conclusion the hyponatremia reflects altered hippocampal inhibition of peripheral neuroendocrine secretion. In greater detail, present the evidence supporting the hypothesis that circuit dysfunction associated with the hyponatremia and the polydipsia contributes to the underlying mental disorder.

RESULTS

Polydipsic patients with and without hyponatremia exhibit enhanced neuroendocrine responses to psychological stress in proportion to structural deformations on their anterior hippocampus, amygdala and anterior hypothalamus. Nonpolydipsic patients exhibit blunted responses and deformations on other hippocampal and amygdala surfaces. The deformations in polydipsic patients are also proportional to diminished peripheral oxytocin levels and impaired facial affect recognition that is reversed by intranasal oxytocin. The anterior hippocampus is at the hub of a circuit that modulates neuroendocrine and other responses to psychological stress and is implicated in schizophrenia. Preliminary data indicate that other measures of stress reactivity are also enhanced in polydipsics and that the functional connectivity of the hippocampus with the other structures in this circuitry differs in schizophrenia patients with and without polydipsia.

CONCLUSION

Polydipsia may identify a subset of schizophrenia patients whose enhanced stress reactivity contributes to their mental illness. Stress reactivity may be a symptom dimension of chronic psychosis that arises from circuit dysfunction that can be modeled in animals. Hence polydipsia could be a biomarker that helps to clarify the pathophysiology and heterogeneity of psychosis as well as identify novel therapies. Clinical investigators should consider obtaining indices of water balance, as these may help them unravel and more concisely interpret their findings. Basic researchers should assess if the polydipsic subset is a patient group particularly suitable to test hypotheses arising from their translational studies.

A systematic review of the ability of urine concentration to distinguish antipsychotic- from psychosis-induced hyponatremia

Life-threatening hyponatremia in psychotic patients is common and typically is attributable to either antipsychotic medication or to acute psychosis in those with the polydipsia-hyponatremia syndrome. The preferred treatment for one situation may worsen the hyponatremia if caused by the other situation. Hence it is critical to distinguish between these two possibilities. Case reports and series were identified through electronic databases. Fifty-four cases of hyponatremia without recognized causes in psychotic patients were divided into those with dilute (<plasma osmolality) or concentrated (>plasma osmolality) urine. The distribution of urine concentration and measures likely to be associated with psychotic illness and its treatment were compared in both groups. Naranjo׳s scale was utilized to determine the probability hyponatremia was drug-induced. Urine osmolality fit a bimodal distribution (intersection 219mOsm/kg) better than a unimodal distribution. 'Probable' drug-induced cases occurred 6.8 (95%CI=1.6-28.9) times more often in those with concentrated urine. Acute psychotic exacerbations occurred 4.5 (95%CI=0.4-54.1) times more often in those with dilute urine. These findings, as well as several other trends in the data, indicate that measures of urine concentration can help distinguish between antipsychotic-induced and psychosis-induced hyponatremia.

Schedule-induced polydipsia as a model of compulsive behavior: neuropharmacological and neuroendocrine bases

BACKGROUND

Schedule-induced polydipsia (SIP), characterized by the development of excessive drinking under intermittent food-reinforcement schedules, has been proposed as a successful model for obsessive-compulsive disorder (OCD), schizophrenia, and alcohol abuse.

OBJECTIVES

The purpose of this study was to review the main findings and current thinking regarding the use of SIP for compulsivity assessment and evaluate its contribution to improving our knowledge of the neurobehavioral mechanisms underlying the excessive behavior manifested in SIP relevant to compulsive behavior disorders.

METHODS

The literature reviews SIP procedure and surveys main findings about its neurobehavioral basis and pharmacology relevant to its possible status as a model for compulsive disorders. Specifically, we reviewed effects of antipsychotics and serotoninergic drugs used in the treatment of OCD and schizophrenia. We also considered individual differences in SIP and its relevance as a possible compulsivity endophenotype.

CONCLUSIONS

SIP represents an animal model of non-regulatory and excessive drinking that may be valid for studying the psychopharmacology of the compulsive phenotype and modeling different psychopathologies from compulsivity spectrum disorders.

Divergent effects of two different doses of intranasal oxytocin on facial affect discrimination in schizophrenic patients with and without polydipsia

RATIONALE

Hyponatremia and dexamethasone resistance in polydipsic schizophrenic patients are attributable to changes in hippocampal-modulated antidiuretic and stress hormone activity, respectively. The relationship of the neuroendocrine findings to the psychiatric illness, however, is unknown. An impaired ability to identify facial emotions has been linked to core features of schizophrenia and to diminished levels of the closely related hormone, oxytocin, in the polydipsic subset. Intranasal oxytocin enhances facial affect discrimination in healthy subjects.

OBJECTIVE

The aim of this study is to explore if oxytocin reverses impaired facial affect discrimination in schizophrenic patients with, relative to that in patients without, polydipsia.

METHODS

Intranasal oxytocin (10 or 20 IU) and placebo were administered on three occasions to five polydipsic schizophrenic patients, eight nonpolydipsic patients, and 11 healthy controls. Subsequently, subjects rated the presence and intensity of six facial emotions.

RESULTS

Emotion recognition fell in both patient groups following 10 IU of oxytocin due to an increased propensity to identify all emotions regardless of whether they were displayed. By contrast, emotion recognition improved following 20 IU in polydipsic relative to nonpolydipsic patients due primarily to divergent effects on the bias to identify fear in nonfearful faces.

CONCLUSION

The effects of 20 IU oxytocin support the hypothesis that altered neuroendocrine function in polydipsic patients contributes to their psychiatric illness. Further studies are warranted to confirm these findings and assess if oxytocin treatment improves social functioning in this subset. This is the first psychopharmacologic study to compare different doses of oxytocin in the same subject, thus the significance of the opposing responses is unclear.

Cortisol rapidly disrupts prepulse inhibition in healthy men

Stress is known to affect sensorimotor gating (measured with prepulse inhibition of startle, or PPI), possibly improving perception of threat signals at the expense of other input during states of arousal. Stress also induces a variety of autonomic nervous system and endocrine responses, such as an activation of the hypothalamic-pituitary-adrenal axis. The latter will result in the release of the stress hormone cortisol which is known to exert rapid and sustained action on several CNS processes. Since previous studies have not clarified whether and which stress response components may mediate effects on sensorimotor gating, this study asked whether a link may exist between cortisol and sensorimotor gating. We tested whether cortisol may affect PPI by assessing PPI before, during, and after non-stressful, covert 1mg IV cortisol infusions in 27 healthy men in a single-blind and placebo-controlled within-subject design. Cortisol induced a rapid reduction of PPI, with its maximum at 20 min after administration, and PPI returned to baseline after another 20 min. Startle magnitude in the absence of a prepulse was not affected. This rapid effect of the IV cortisol infusions is probably mediated by a non-genomic mechanism. We conclude that stress effects on sensorimotor gating may be mediated by glucocorticoids. The disruption of sensorimotor gating by the stress hormone cortisol may serve the processing of intense and potentially dangerous startling stimuli.

Increased schedule-induced polydipsia in the rat following subchronic treatment with MK-801

Primary polydipsia, defined as excessive fluid intake not explained by medical causes, has been reported to occur in over 20% of chronically ill psychiatric inpatients and is especially common in schizophrenic populations. We tested the hypothesis that in an animal model of schizophrenia-like symptoms (subchronic injections of MK-801, 0.5 mg/kg twice daily for 7 days) an increase in the acquisition of schedule-induced polydipsia (SIP) will occur. Young adult, male rats acquired SIP when food-restricted and placed on a non-contingent fixed-time 1-min food schedule. In comparison with saline-treated control animals, subchronic MK-801 treatment significantly increased SIP. These findings suggest an animal model of polydipsia associated with schizophrenia in humans.

Structural pathology underlying neuroendocrine dysfunction in schizophrenia

Polydipsic hyponatremic schizophrenic (PHS) patients exhibit altered neuroendocrine activity that has been linked to their life-threatening water imbalance, as well as to impaired function and reduced volume of the anterior hippocampus. Polydipsic patients without hyponatremia (polydipsic normonatremic schizophrenics: PNS) exhibit similar, albeit less marked, changes in neuroendocrine activity and anterior hippocampal function, but not reduced anterior hippocampal volume. Indeed, reduced anterior hippocampal volume is seen in patients with normal water balance (nonpolydipsic normonatremic schizophrenics: NNS) whose neuroendocrine activity and anterior hippocampal function differ markedly from those with polydipsia. In an effort to reconcile these findings we measured hippocampal, amygdala and 3rd ventricle shapes in 26 schizophrenic patients (10 PNS, 7 PHS, 9 NNS) and 12 healthy controls matched for age and gender. Bilateral inward deformations were localized to the anterior lateral hippocampal surface (part of a neurocircuit which modulates neuroendocrine responses to psychological stimuli) in PHS and to a lesser extent in PNS, while deformations in NNS were restricted to the medial surface. Proportional deformations of the right medial amygdala, a key segment of this neurocircuit, were seen in both polydipsic groups, and correlated with the volume of the 3rd ventricle, which lies adjacent to the neuroendocrine nuclei. Finally, these structural findings were most marked in those with impaired hippocampal-mediated stress responses. These results reconcile previously conflicting data, and support the view that anterior lateral hippocampal pathology disrupts neuroendocrine function in polydipsic patients with and without hyponatremia. The relationship of these findings to the underlying mental illness remains to be established.

A randomised controlled study of risperidone and olanzapine for schizophrenic patients with neuroleptic-induced acute dystonia or parkinsonism

The objective of this study was to compare the effects of risperidone and olanzapine in schizophrenic patients with intolerant extrapyramidal side effects (EPS) on first generation antipsychotics. We conducted an 8-week, rater-blinded, flexible dose study. Seventy patients with schizophrenia, who met the DSM-IV research criteria of having neuroleptic-induced acute dystonia or parkinsonism, were randomly assigned to risperidone or olanzapine group. The primary outcome was a comparison of the incidence of concomitant anticholinergic drugs usage between the groups to manage their acute dystonia and parkinsonism. The average doses of risperidone and olanzapine from baseline to study end point were 1.8-3.5 mg/day and 7.7-11.7 mg/day, respectively. There were no significant differences in demographic data, severity of EPS or psychotic symptoms between the groups at baseline assessment. Patients taking risperidone had significantly higher incidence of using anticholinergic drugs to manage acute dystonia or parkinsonism overall during the study (OR = 5.17, 95%CI = 1.49-17.88, P = 0.013). There was no significant between-group difference in the changing of rating scales of EPS and psychotic symptoms. The results of our study favour olanzapine as a better choice in schizophrenic patients with intolerant EPS. Double-blinded, fixed dose and different ethnical study for EPS-intolerant schizophrenic patients is needed to confirm the results of our study.

A systematic review of hypothalamic-pituitary-adrenal axis function in schizophrenia: implications for mortality

There is convincing evidence that environmental stress plays a significant role in modifying both mental and physical health. The biological mechanisms linking stress to ill health are not fully understood, but significant evidence points to a central role of the stress axes; the hypothalamic- pituitary-adrenal (HPA) axis and the sympathetic nervous system. Together these two systems link the brain and the body and are crucial in maintaining homeostasis as well as improving an organism's survival chances in the face of environmental challenge. There is evidence of altered HPA axis function in people with a range of mental disorders, and this may in part explain the poor physical health of people with psychotic, mood and anxiety disorders. This paper systematically reviews HPA axis function in people with schizophrenia and relates this to the pattern of physical health seen in this disease. In summary, the evidence suggests people with schizophrenia can experience both hyper- and hypo-function of the HPA axis. It is likely that this contributes to the pattern of poor physical health and premature mortality suffered by people with schizophrenia, in particular the high rates of cardiovascular and metabolic disturbance.

The mechanism of life-threatening water imbalance in schizophrenia and its relationship to the underlying psychiatric illness

Impaired water excretion was noted to coincide with psychotic exacerbations in the first decades of the past century. In the ensuing decades, life-threatening water intoxication and elevated plasma levels of the antidiuretic hormone, arginine vasopressin (AVP) were reported in a subset of persons with schizophrenia. Subsequent studies demonstrated that the osmotic set point for AVP secretion was transiently reset in these patients by an unknown process and that this was further exacerbated by acute psychosis. More recent studies indicate that the AVP dysfunction is a manifestation of a hippocampal-mediated impairment in the regulation of both AVP and HPA axis responses to psychological, but not other types of, stimuli. Of potential significance, is that schizophrenic patients without water imbalance exhibit the opposite pattern of responses. Preliminary data indicate those with water imbalance also demonstrate a closely linked deficit in central oxytocin activity which may account for their diminished social function. These latter behavioral deficits are perhaps the most disabling and treatment resistant features of schizophrenia, which recent studies suggest, may respond to oxytocin agonists. Together these findings support the view that schizophrenia is a heterogeneous disorder, and provide novel biomarkers and approaches for exploring the pathophysiology and treatment of severe mental illness.

Diminished plasma oxytocin in schizophrenic patients with neuroendocrine dysfunction and emotional deficits

Polydipsic hyponatremic schizophrenic patients (PHS) exhibit enhanced plasma arginine vasopressin (pAVP) and hypothalamic pituitary adrenal (HPA) axis responses to stress that appear attributable to anterior hippocampal dysfunction. Neuroanatomic and electrophysiologic studies indicate oxytocin activity in PHS patients should also be affected. Furthermore, oxytocin normally diminishes HPA responses to stress and facilitates cognitive and behavioral functions impaired in schizophrenia, suggesting that diminished oxytocin activity could contribute to this subsets' neuropsychiatric disorder. In the present study, we measured plasma oxytocin levels at intervals before and after stress induction in six polydipsic hyponatremic (PHS), four polydipsic normonatremic (PNS), five nonpolydipsic normonatremic schizophrenic (NNS) patients and seven healthy controls. Most of these subjects also completed studies measuring their medial temporal lobe volumes, their hippocampal-mediated HPA feedback and their ability to discriminate different facial emotions (an oxytocin-sensitive measure which is markedly impaired in schizophrenia). Results demonstrated that 1) plasma oxytocin levels were lower (p=.006) in hyponatremic patients relative to the other three groups, whose levels were similar and did not change. Oxytocin levels across all subjects were 2) inversely correlated with anterior hippocampal (p=.004) (but not posterior hippocampal or amygdala volumes), and 3) directly correlated with the integrity of hippocampal-mediated HPA feedback (p=.039). Finally, 4) oxytocin levels predicted schizophrenic patients' ability to correctly identify facial emotions (p=.004). These preliminary data provide further evidence that neuroendocrine dysfunction in PHS reflects anterior hippocampal pathology and contributes to a characteristic neuropsychiatric syndrome.

Hypoalgesia in schizophrenia is independent of antipsychotic drugs: a systematic quantitative review of experimental studies

Diminished sensitivity to pain in schizophrenia has been reported since the early works of Bleuler [Bleuler E. Textbook of psychiatry (trans. Brill HA, 1951). New York: Dover Publications; 1911] and Kraepelin [Kraepelin E. Dementia praecox and paraphrenia. Edinburgh, Scotland: E and S Livingstone; 1919]. Over the last decade, experimental studies have measured pain perception in schizophrenia and produced mixed results. This meta-analysis sought to determine if the scientific literature confirms the hypothesized hypoalgesia in schizophrenia. The search was performed with computerised literature databases. A study was retained in the meta-analysis if: (i) it comprised a group of schizophrenia patients, compared to a control group of healthy volunteers; and (ii) pain was measured via experimental procedures (e.g. thermal, electrical, or mechanical stimuli). Using Comprehensive Meta-Analysis-2, effect size estimates of the differences in pain scores (all pain scores derived from all pain tests) between schizophrenia patients and healthy volunteers were calculated. Eleven studies were included in the meta-analysis. For the composite analysis, a positive, moderate, and significant effect size estimate emerged (N=497; Hedges's g=0.437; p=0.005), suggesting that patients with schizophrenia show a diminished response to experimentally-induced pain. Secondary analyses showed that: (i) drug-free patients also have hypoalgesic responses; and that (ii) sensory thresholds are increased in schizophrenia patients. This meta-analysis substantiates the hypothesis of a diminished pain response in schizophrenia. The study also suggests that hypoalgesia in schizophrenia cannot be solely explained by the effects of antipsychotic drugs, and that it may not be a pain-specific blunted response. Further studies are warranted to determine the clinical and biological correlates, and the social and health consequences, of hypoalgesia in schizophrenia.