Dopamine and serotonin in rat striatum during in vivo hypoxic-hypoxia

A Retrospective Analysis of Guanfacine for the Pharmacological Management of Delirium

Background Delirium is a syndrome of acute brain failure that represents a change from an individual's baseline cognitive functioning characterized by deficits in attention and multiple aspects of cognition that fluctuate in severity over time. The symptomatic management of delirium's behavioral manifestations remains difficult. The alpha-2 agonists, dexmedetomidine and clonidine, are efficacious, but their potential cardiovascular adverse effects limit their utilization. Guanfacine is an oral alpha-2 agonist with a lower potential for such adverse outcomes; however, its use in delirium has not been studied. Methods A retrospective descriptive analysis of guanfacine for managing hyperactive or mixed delirium at Tampa General Hospital from January 2020 to October 2020 was conducted. The primary outcome was the time reduction in acute sedative administration. Secondary outcomes included renewed participation in physical therapy or occupational therapy (PT/OT), decreased opioid use, and an incidence of cardiovascular adverse effects. Results One hundred forty-nine patients were identified as having received guanfacine for managing delirium during the study period. All experienced a reduction in acute sedative use after the initiation of guanfacine. In 93 patients receiving PT/OT and no longer participating due to behavioral agitation, 74% had a documented renewal of services within four days. Of 112 patients on opioids, 70% experienced a 25% reduction in opioid administration within four days. No patients experienced consecutive episodes of hypotension that required a change in their clinical care. Two patients experienced a single episode of consecutive bradycardia that led to the discontinuation of guanfacine.  Conclusions Based on our retrospective study, guanfacine is a well-tolerated medication for the management of delirium. Even in medically and critically ill patients, cardiovascular adverse events were rare with guanfacine. Patients treated with guanfacine experienced decreased acute sedative use for behavioral agitation. Additionally, patients treated with guanfacine received fewer opioids and were better able to participate in PT/OT. Future studies with prospective, randomized, placebo-controlled designs are warranted to evaluate this promising intervention for delirium further.

Multiple N-of-1 trials to investigate hypoxia therapy in Parkinson's disease: study rationale and protocol

Background

Parkinson’s disease (PD) is a neurodegenerative disease, for which no disease-modifying therapies exist. Preclinical and clinical evidence suggest that hypoxia-based therapy might have short- and long-term benefits in PD. We present the contours of the first study to assess the safety, feasibility and physiological and symptomatic impact of hypoxia-based therapy in individuals with PD.

Methods/Design

In 20 individuals with PD, we will investigate the safety, tolerability and short-term symptomatic efficacy of continuous and intermittent hypoxia using individual, double-blind, randomized placebo-controlled N-of-1 trials. This design allows for dose finding and for including more individualized outcomes, as each individual serves as its own control. A wide range of exploratory outcomes is deployed, including the Movement Disorders Society Unified Parkinson’s Disease Rating scale (MDS-UPDRS) part III, Timed Up & Go Test, Mini Balance Evaluation Systems (MiniBES) test and wrist accelerometry. Also, self-reported impression of overall symptoms, motor and non-motor symptoms and urge to take dopaminergic medication will be assessed on a 10-point Likert scale. As part of a hypothesis-generating part of the study, we also deploy several exploratory outcomes to probe possible underlying mechanisms of action, including cortisol, erythropoietin and platelet-derived growth factor β. Efficacy will be assessed primarily by a Bayesian analysis.

Discussion

This evaluation of hypoxia therapy could provide insight in novel pathways that may be pursued for PD treatment. This trial also serves as a proof of concept for deploying an N-of-1 design and for including individualized outcomes in PD research, as a basis for personalized treatment approaches.

Trial registration

ClinicalTrials.gov Identifier: NCT05214287 (registered January 28, 2022).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02770-7.

Tandem Mass Tagging-Based Quantitative Proteomics Analysis Reveals Damage to the Liver and Brain of Hypophthalmichthys molitrix Exposed to Acute Hypoxia and Reoxygenation

Aquaculture environments frequently experience hypoxia and subsequent reoxygenation conditions, which have significant effects on hypoxia-sensitive fish populations. In this study, hepatic biochemical activity indices in serum and the content of major neurotransmitters in the brain were altered markedly after acute hypoxia and reoxygenation exposure in silver carp (Hypophthalmichthys molitrix). Proteomics analysis of the liver showed that a number of immune-related and cytoskeletal organization-related proteins were downregulated, the ferroptosis pathway was activated, and several antioxidant molecules and detoxifying enzymes were upregulated. Proteomics analysis of the brain showed that somatostatin-1A (SST1A) was upregulated, dopamine-degrading enzyme catechol O methyltransferase (COMT) and ferritin, heavy subunit (FerH) were downregulated, and the levels of proteins involved in the nervous system were changed in different ways. In conclusion, these findings highlight that hypoxia–reoxygenation has potential adverse effects on growth, locomotion, immunity, and reproduction of silver carp, and represents a serious threat to liver and brain function, possibly via ferroptosis, oxidative stress, and cytoskeleton destruction in the liver, and abnormal expression of susceptibility genes for neurodegenerative disorders in the brain. Our present findings provide clues to the mechanisms of hypoxia and reoxygenation damage in the brain and liver of hypoxia-sensitive fish. They could also be used to develop methods to reduce hypoxia or reoxygenation injury to fish.

Delirium pathophysiology: An updated hypothesis of the etiology of acute brain failure

BACKGROUND

Delirium is the most common neuropsychiatric syndrome encountered by clinicians dealing with older adults and the medically ill and is best characterized by 5 core domains: cognitive deficits, attentional deficits, circadian rhythm dysregulation, emotional dysregulation, and alteration in psychomotor functioning.

DESIGN

An extensive literature review and consolidation of published data into a novel interpretation of known pathophysiological causes of delirium.

RESULTS

Available data suggest that numerous pathological factors may serve as precipitants for delirium, each having differential effects depending on patient-specific patient physiological characteristics (substrate). On the basis of an extensive literature search, a newly proposed theory, the systems integration failure hypothesis, was developed to bring together the most salient previously described theories, by describing the various contributions from each into a complex web of pathways-highlighting areas of intersection and commonalities and explaining how the variable contribution of these may lead to the development of various cognitive and behavioral dysfunctions characteristic of delirium. The specific cognitive and behavioral manifestations of the specific delirium picture result from a combination of neurotransmitter function and availability, variability in integration and processing of sensory information, motor responses to both external and internal cues, and the degree of breakdown in neuronal network connectivity, hence the term acute brain failure.

CONCLUSIONS

The systems integration failure hypothesis attempts to explain how the various proposed delirium pathophysiologic theories interact with each other, causing various clinically observed delirium phenotypes. A better understanding of the underlying pathophysiology of delirium may eventually assist in designing better prevention and management approaches.

Isolated psychosis during exposure to very high and extreme altitude - characterisation of a new medical entity

BACKGROUND

Psychotic episodes during exposure to very high or extreme altitude have been frequently reported in mountain literature, but not systematically analysed and acknowledged as a distinct clinical entity.

METHODS

Episodes reported above 3500 m altitude with possible psychosis were collected from the lay literature and provide the basis for this observational study. Dimensional criteria of the Diagnostic and Statistical Manual of Mental Disorders were used for psychosis, and the Lake Louise Scoring criteria for acute mountain sickness and high-altitude cerebral oedema (HACE). Eighty-three of the episodes collected underwent a cluster analysis to identify similar groups. Ratings were done by two independent, trained researchers (κ values 0.6-1).FindingsCluster 1 included 51% (42/83) episodes without psychosis; cluster 2 22% (18/83) cases with psychosis, plus symptoms of HACE or mental status change from other origins; and cluster 3 28% (23/83) episodes with isolated psychosis. Possible risk factors of psychosis and associated somatic symptoms were analysed between the three clusters and revealed differences regarding the factors 'starvation' (χ2 test, p = 0.002), 'frostbite' (p = 0.024) and 'supplemental oxygen' (p = 0.046). Episodes with psychosis were reversible but associated with near accidents and accidents (p = 0.007, odds ratio 4.44).

CONCLUSIONS

Episodes of psychosis during exposure to high altitude are frequently reported, but have not been specifically examined or assigned to medical diagnoses. In addition to the risk of suffering from somatic mountain illnesses, climbers and workers at high altitude should be aware of the potential occurrence of psychotic episodes, the associated risks and respective coping strategies.

Ventricular fibrillation cardiac arrest produces a chronic striatal hyperdopaminergic state that is worsened by methylphenidate treatment

Cardiac arrest survival rates have improved with modern resuscitation techniques, but many survivors experience impairments associated with hypoxic-ischemic brain injury (HIBI). Currently, little is understood about chronic changes in striatal dopamine (DA) systems after HIBI. Given the common empiric clinical use of DA enhancing agents in neurorehabilitation, investigation evaluating dopaminergic alterations after cardiac arrest (CA) is necessary to optimize rehabilitation approaches. We hypothesized that striatal DA neurotransmission would be altered chronically after ventricular fibrillation cardiac arrest (VF-CA). Fast-scan cyclic voltammetry was used with median forebrain bundle (MFB) maximal electrical stimulations (60Hz, 10s) in rats to characterize presynaptic components of DA neurotransmission in the dorsal striatum (D-Str) and nucleus accumbens 14 days after a 5-min VF-CA when compared to Sham or Naïve. VF-CA increased D-Str-evoked overflow [DA], total [DA] released, and initial DA release rate versus controls, despite also increasing maximal velocity of DA reuptake (V_max ). Methylphenidate (10 mg/kg), a DA transporter inhibitor, was administered to VF-CA and Shams after establishing a baseline, pre-drug 60 Hz, 5 s stimulation response. Methylphenidate increased initial evoked overflow [DA] more-so in VF-CA versus Sham and reduced D-Str V_max in VF-CA but not Shams; these findings are consistent with upregulated striatal DA transporter in VF-CA versus Sham. Our work demonstrates that 5-min VF-CA increases electrically stimulated DA release with concomitant upregulation of DA reuptake 2 weeks after brief VF-CA insult. Future work should elucidate how CA insult duration, time after insult, and insult type influence striatal DA neurotransmission and related cognitive and motor functions.

Neuropathogenesis of delirium: review of current etiologic theories and common pathways

Delirium is a neurobehavioral syndrome caused by dysregulation of neuronal activity secondary to systemic disturbances. Over time, a number of theories have been proposed in an attempt to explain the processes leading to the development of delirium. Each proposed theory has focused on a specific mechanism or pathologic process (e.g., dopamine excess or acetylcholine deficiency theories), observational and experiential evidence (e.g., sleep deprivation, aging), or empirical data (e.g., specific pharmacologic agents' association with postoperative delirium, intraoperative hypoxia). This article represents a review of published literature and summarizes the top seven proposed theories and their interrelation. This review includes the "neuroinflammatory," "neuronal aging," "oxidative stress," "neurotransmitter deficiency," "neuroendocrine," "diurnal dysregulation," and "network disconnectivity" hypotheses. Most of these theories are complementary, rather than competing, with many areas of intersection and reciprocal influence. The literature suggests that many factors or mechanisms included in these theories lead to a final common outcome associated with an alteration in neurotransmitter synthesis, function, and/or availability that mediates the complex behavioral and cognitive changes observed in delirium. In general, the most commonly described neurotransmitter changes associated with delirium include deficiencies in acetylcholine and/or melatonin availability; excess in dopamine, norepinephrine, and/or glutamate release; and variable alterations (e.g., either a decreased or increased activity, depending on delirium presentation and cause) in serotonin, histamine, and/or γ-aminobutyric acid. In the end, it is unlikely that any one of these theories is fully capable of explaining the etiology or phenomenologic manifestations of delirium but rather that two or more of these, if not all, act together to lead to the biochemical derangement and, ultimately, to the complex cognitive and behavioral changes characteristic of delirium.

Cocaine use in the past year is associated with altitude of residence

OBJECTIVES

Recently, increased rates of suicide in US counties at higher altitudes have been noted. Because of the documented association between cocaine use and suicide, we hypothesized that there would be a correlation between incidence of cocaine use and altitude of residence.

METHODS

Cocaine use data were obtained from the Substate Substance Abuse Estimates from the 1999-2001 National Surveys on Drug Use and Health. Data related to the percentages of people 12 years or older who used cocaine in the past year. Average elevation for US counties was calculated using the Shuttle Radar Topography Mission elevation data set, and subject region elevation was calculated by averaging the weighted elevations of each region's relevant counties. The correlation between elevation of a substate region and incidence of cocaine use in that region was calculated using Pearson correlation coefficients.

RESULTS

A significant correlation exists between mean altitude of a substate region and incidence of cocaine use in that region (r = 0.34; P < 0.0001). Regression analysis controlling for age, sex, race, education level, income, unemployment, and population density was performed. Altitude remained a significant factor (P = 0.007), whereas male sex (P = 0.008) and possessing less than a college education (P < 0.0001) were also significant predictors of self-reported cocaine use in the past year. It is important to note that cocaine use was assessed in isolation of other drugs of abuse, an additional confounding variable.

CONCLUSIONS

This study demonstrates a significant correlation between altitude of substate region of residence and incidence of cocaine use. It is possible that stress response due to hypoxia is responsible; however, this requires further investigation. However, because other substance use was not assessed, specificity of this association is unknown. In addition, this correlation may help explain the increased rate of suicide in areas of higher elevation.

Pathophysiology of perinatal asphyxia: can we predict and improve individual outcomes?

Perinatal asphyxia occurs still with great incidence whenever delivery is prolonged, despite improvements in perinatal care. After asphyxia, infants can suffer from short- to long-term neurological sequelae, their severity depend upon the extent of the insult, the metabolic imbalance during the re-oxygenation period and the developmental state of the affected regions. Significant progresses in understanding of perinatal asphyxia pathophysiology have achieved. However, predictive diagnostics and personalised therapeutic interventions are still under initial development. Now the emphasis is on early non-invasive diagnosis approach, as well as, in identifying new therapeutic targets to improve individual outcomes. In this review we discuss (i) specific biomarkers for early prediction of perinatal asphyxia outcome; (ii) short and long term sequelae; (iii) neurocircuitries involved; (iv) molecular pathways; (v) neuroinflammation systems; (vi) endogenous brain rescue systems, including activation of sentinel proteins and neurogenesis; and (vii) therapeutic targets for preventing or mitigating the effects produced by asphyxia.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

Cholinergic deficiency hypothesis in delirium: a synthesis of current evidence

Deficits in cholinergic function have been postulated to cause delirium and cognitive decline. This review examines current understanding of the cholinergic deficiency hypothesis in delirium by synthesizing evidence on potential pathophysiological pathways. Acetylcholine synthesis involves various precursors, enzymes, and receptors, and dysfunction in these components can lead to delirium. Insults to the brain, like ischemia and immunological stressors, can precipitously alter acetylcholine levels. Imbalances between cholinergic and other neurotransmitter pathways may result in delirium. Furthermore, genetic, enzymatic, and immunological overlaps exist between delirium and dementia related to the cholinergic pathway. Important areas for future research include identifying biomarkers, determining genetic contributions, and evaluating response to cholinergic drugs in delirium. Understanding how the cholinergic pathway relates to delirium may yield innovative approaches in the diagnosis, prevention, and treatment of this common, costly, and morbid condition.

Cerebrometabolic abnormalities in Alzheimer's disease

Extensive, replicated evidence in patients in vivo and in Alzheimer (AD) tissues in vitro indicates that impaired brain metabolism is one of the cardinal and essentially invariable events in AD. The degree of impairment in brain metabolism is proportional to the degree of clinical disability, both in vivo and in vitro. The 'cerebrometabolic lesion' cannot be attributed to 'slower thinking' or 'brain atrophy', because of quantitative considerations and because the metabolic lesion precedes the development of neuropsychological abnormalities or decreases in brain mass detectable by modern imaging techniques. The causes of the cerebrometabolic lesion in AD are not well defined. Free radicals seem likely to be involved, including free radicals generated from Alzheimer amyloid. Thus, the importance of the cerebrometabolic lesion is entirely compatible with most versions of the widely accepted 'amyloid cascade hypothesis' of AD. A variety of plausible, redundantly documented mechanisms are compatible with the proposal that the cerebrometabolic lesion is a proximate cause of the clinical disability in AD. In agreement with these findings, recent attempts to treat the cerebrometabolic lesion in AD have given encouraging preliminary results. The cerebrometabolic lesion in AD deserves further study.

Delirium

BACKGROUND

Delirium is a serious and often undetected neuropsychiatric syndrome. Failure to recognize and manage delirium can lead to longer hospital stays and increased morbidity and mortality, especially among the elderly.

REVIEW SUMMARY

This article reviews definitions and diagnosis. The Diagnostic and Statistical Manual of Mental Disorders, 4th edition, and the International Statistical Classification of Diseases and Related Health Problems, 10th edition, criteria are quite similar in their diagnostic criteria. Risk factors include advanced age, preexisting brain disease or cognitive impairment, multiple medications, and severe medical problems. Delirium in the elderly can be more subtle and recovery more prolonged. Diagnosis is more complex if there is already an underlying dementia. An organized approach should be used to discover etiology and in ordering appropriate laboratory studies. At the cellular level, delirium is considered to be a reversible disregulation of neuronal membrane function. This involves a selective vulnerability of certain populations of neurons and neurotransmitter dysfunction. Practical treatment issues are reviewed.

CONCLUSIONS

Despite advances, delirium is usually still diagnosed at the bedside. Having an organized approach to diagnosis and understanding the underlying pathophysiology should help with overall evaluation and treatment.

Axotomy along with hypoxia enhances the neuronal NADPH-d/NOS expression in lower brain stem motor neurons of adult rats

This study was aimed to determine whether axotomy coupled with hypoxia would exert a more profound effect on injury-induced neuronal nitric oxide synthase (NOS) expression. In this connection, the vagus and the hypoglossal nerves of adult rats were transected unilaterally in the same animal, and half of the operated animals were subjected to hypoxia treatment. Both the neuronal NOS immunohistochemistry and the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry were used to assess the neuronal NOS expression. The present results have shown that the number of NADPH-d/NOS-positive [NADPH-d/NOS(1)] neurons in the hypoglossal nucleus (HN) peaked at 14 days after axotomy, while that in dorsal motor nucleus of vagus (DMN) and nucleus ambiguus (NA) was progressively increased up to 60 days. The up-regulation of NADPH-d/NOS in HN and DMN was more pronounced in hypoxic than in normoxic animals, a feature that was not evident in the NA. Quantitative analysis showed that the number of surviving motoneurons in normoxic animals was significantly higher than those subjected to hypoxia at 14 days postaxotomy in HN and at all postaxotomy time points in DMN. The difference may be attributed to their different functional components. Since O2 deprivation leads to poor cellular function, the stronger expression of NADPH-d/NOS and the more drastic neuronal loss following nerve transection in the hypoxic animals compared with the controls suggest that hypoxia plays an important role in peripheral neuropathies in which NO is implicated.

Monoamine neurotransmitters in resected hippocampal subparcellations from neocortical and mesial temporal lobe epilepsy patients: in situ microvoltammetric studies

It is known that epilepsy patients diagnosed with neocortical temporal lobe epilepsy (NTLE), differ from those diagnosed with mesial temporal lobe epilepsy (MTLE), e.g., in hippocampal (HPC) pathology. In the present studies, we tested the hypothesis that NTLE and MTLE subtypes of human epilepsy might differ in regards to their HPC monoamine neurochemistry. Monoamine neurotransmitters were studied in separate signals and within s with semiderivative microvoltammetry, used in combination with stearate indicator, Ag-AgCl reference and stainless steel auxiliary microelectrodes. Anterior HPC specimens from the patients' epileptogenic zone, defined by electrocorticography, were resected neurosurgically from 13 consecutive patients with intractable temporal lobe epilepsy. Four patients were diagnosed with NTLE and nine with MTLE. The criteria for the diagnosis of NTLE versus MTLE was absence versus presence of HPC sclerosis, respectively, based on MRI examination of resected tissue. In addition, NTLE patients demonstrated seizure onset in anterolateral temporal neocortex on electroencephalography (EEG). HPC subparcellations studied were: (a) Granular Cells of the Dentate Gyrus (DG), (b) Polymorphic Layer of DG and (c) Pyramidal Layer: subfields, CA1 and CA2. Dopamine (DA), serotonin (5-HT), norepinephrine (NE) and ascorbic acid (AA) (co-factor in DA to NE synthesis), exhibited separate and characteristic half-wave potentials in millivolts. Each half-wave potential, i.e., the potential at which maximum current was generated, was experimentally established in vitro. Concentrations of neurotransmitters found in HPC subparcellations were interpolated from calibration curves derived in vitro from electrochemical detection of monoamines and AA in saline phosphate buffer. Significant differences between subtypes in concentration of monoamines were analyzed by the Mann Whitney rank sum test and those differences in probability distribution of monoamines were analyzed by the Fisher Exact test; in each case, P<0.01 was the criteria selected for determining statistical significance. DA concentrations were higher in NTLE compared with MTLE in each HPC subparcellation [P=0.037, 0.024 and 0.007, respectively (P<0.01)] and DA occurred more frequently in NTLE in the Pyramidal Layer [P=0.077 (P<0.01)]. AA was present in one NTLE patient. NE concentrations were higher in MTLE vs. NTLE in each subparcellation [P=0.012, 0.067 and 0.07, respectively (P<0.01)] and NE occurred more frequently in MTLE in Granular Cells of DG and Pyramidal Layer [P=0.052 and 0.014, respectively (P<0.01)]. In MTLE, NE concentrations in the CA1 subfield of the Pyramidal Layer were decreased vs. the CA2 subfield [P=0.063 (P<0.01)]. Serotonin was found in every HPC subparcellation of each subtype but 5-HT concentrations were higher in NTLE vs. MTLE in the Granular Cells of DG and the Pyramidal Layer (CA1 subfield) [P=0.076 and 0.095, respectively (P<0.01)]. Thus, this preliminary study showed that marked differences in HPC monoamine neurochemistry occurred in NTLE patients as compared with MTLE patients.

Lactic acid-induced increase of extracellular dopamine measured by microdialysis in rat striatum: evidence for glutamatergic and oxidative mechanisms

Striatal lactacidosis was induced by direct lactic acid perfusion to obtain a local pH as close as possible to that observed in ischemia. In a previous study we showed that such lactacidosis produces a diphasic increase in extracellular dopamine (DA). The present work investigated whether DA accumulation is related to a glutamatergic mechanism and/or production of reactive oxygen species (ROS) in the striatum. Concentrations of extracellular DA, glutamate and hydroxyl radicals ((.)OH) were measured in the presence or absence of an N-methyl-D-aspartate (NMDA) receptor blocker (dizocilpine, MK-801) or an antioxidant (Trolox). Measurements were performed using high-performance liquid chromatography (HPLC) with electrochemical and fluorimetric detection on samples obtained by an in vivo microdialysis perfusion technique and stored at -80 degrees C. The increase in lactic acid-induced DA was entirely suppressed by MK-801 and Trolox. Lactacidosis also induced an increase in extracellular glutamate and (.)OH concentrations at the same time as the first DA accumulation, as well as another (.)OH accumulation which preceded and accompanied the second DA concentration peak. Glutamate release was totally inhibited by MK-801 or Trolox. The first peak of (.)OH production was completely suppressed by MK-801 and Trolox, but the second one was only suppressed by Trolox. These data showed that the increase in DA induced by lactic acid was related to glutamatergic excitotoxicity and ROS production, suggested that the kinetic of events was different for the two DA accumulations.

Effects of carbon monoxide exposure on serotonergic neuronal systems in rat brain

It is well known that some psychiatric sequelae exist after CO poisoning, but few animal studies on serotonergic neuronal function after CO exposure have been carried out. We investigated the effects of successive carbon monoxide (CO) exposure (6000 ppm, 10 min, 3 repetitions) on serotonergic neuronal systems in rat brain. Serotonin (5-HT) concentrations were significantly decreased only in the frontal cortex from 1 hr to 7 days after CO exposure. 5-Hydroxyindoleacetic acid (5-HIAA) concentrations were significantly increased at 1 hr in all six brain regions measured (frontal cortex, striatum, hypothalamus, hippocampus, midbrain, and pons). 5-HT synthesis, measured by the accumulation of 5-hydroxytryptophan (5-HTP) after the administration of m-hydroxybenzylhydrazine (NSD-1015), was significantly decreased in all regions from 1 hr to 7 days after CO exposure. [3H]Ketanserin (5-HT2A) binding sites in the frontal cortex were not affected by CO exposure. DOI-induced head shakes, a 5-HT2A receptor mediated behavior, were not changed after CO exposure. These findings indicated that CO exposure caused presynaptic serotonergic neuronal dysfunctions that consisted mainly of decreased concentration of 5-HT in the frontal cortex or a decrease of 5-HT synthesis in all six regions, without compensatory hyperfunction of 5-HT2A receptors.

Effect of hemorrhagic hypotension on cortical oxygen pressure and striatal extracellular dopamine in cat brain

This study investigated the relationships between blood pressure, cortical oxygen pressure, and extracellular striatal dopamine in the brain of adult cats during hemorrhagic hypotension and retransfusion. Oxygen pressure in the blood of the cortex was measured by the oxygen dependent quenching of phosphorescence and extracellular dopamine, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) by in vivo microdialysis. Following a 2 h stabilization period after implantation of the microdialysis probe in the striatum, the mean arterial blood pressure (MAP) was decreased in a stepwise manner from 132 +/- 2 Torr (control) to 90 Torr, 70 Torr and 50 Torr, holding the pressure at each level for 15 min. The whole blood was then retransfused and measurements were continued for 90 min. As the MAP was lowered there was a decrease in arterial pH, from a control value of 7.37 +/- 0.05 to 7.26 +/- 0.06. The PaCO2 decreased during bleeding from 32.3 +/- 4.8 Torr to 19.6 +/- 3.6 Torr and returned to 30.9 +/- 3.9 Torr after retransfusion. The PaO2 was 125.9 +/- 15 Torr during control conditions and did not significantly change during bleeding. Cortical oxygen pressure decreased with decrease in MAP, from 50 +/- 2 Torr (control) to 42 +/- 1 Torr, 31 +/- 2 Torr and 22 +/- 2 Torr, respectively. A statistically significant increase in striatal extracellular dopamine, to 2,580 +/- 714% of control was observed when MAP decreased to below 70 Torr and cortical oxygen pressure decreased to below 31 Torr. When the MAP reached 50 Torr, the concentration of extracellular dopamine increased to 18,359 +/- 2,764% of the control value. A statistically significant decrease in DOPAC and HVA were observed during the last step of bleeding. The data show that decreases in systemic blood pressure result in decrease in oxygen pressure in the microvasculature of the cortex, suggesting vascular dilation is not sufficient to result in a full compensation for the decreased MAP. The decrease in cortical oxygen pressure to below 32 Torr is accompanied by a marked increase in extracellular dopamine in the striatum, indicating that even such mild hypoxia can induce significant disturbance in brain metabolism.

Effects of chronic episodic hypoxia on monoamine metabolism and motor activity

Chronic episodic hypoxia produces a wide array of cardiovascular dysfunctions in rats, including increases in blood pressure, heart rate, and sympathetic nerve activity. The action of episodic hypoxia might be related to low oxygen itself (hypoxemia) and/or combined with low CO2 (hypocapnia) resulting from hyperventilation. It is unknown whether or not the cardiovascular abnormalities are related to alterations in the central nervous system (CNS) that may be manifested as neurotransmitter and/or behavioral changes. In this study, we investigated effects of episodic eucapnic and hypocapnic hypoxia on monoamine metabolism in both CNS and adrenal glands, and on motor behavioral activity. Thirty-five male rats were divided into 3 groups. Experimental rats were exposed 8 h daily to varying fractional concentrations of inspired oxygen (FiO2) and carbon dioxide (FiCO2) for 35 days. These consisted of brief exposures (3-6s) of episodic (twice every min) eucapnic (3.5% FiO2 and 10% FiCO2, n = 6) or hypocapnic (3.5% FiO2 and 0% FiCO2, n = 14) hypoxia, or room air (21% FiO2 and 0.03% FiCO2, n = 15). Norepinephrine, dopamine, serotonin, and their metabolites in the hypothalamus, hippocampus, and adrenal glands were measured by high-performance liquid chromatography (HPLC). Spontaneous behavioral activity was assessed for 30 min by automated activity monitors. Episodic hypocapnic hypoxia produced a decrease in dopamine turnover and eucapnic hypoxia increased norepinephrine levels in the hypothalamus. Animals exposed to hypocapnic hypoxia also exhibited a consistent increase in horizontal (walking) and vertical (rearing) activity, as well as in total activity time. From these results, it is concluded that episodic eucapnic and hypocapnic hypoxia may affect metabolism of different neurotransmitters in the CNS.

Delirium. Advances in diagnosis, pathophysiology, and treatment

This article discusses research in the areas of morbidity and mortality, epidemiologic risk factors, phenomenology, pathophysiology, and treatment of delirium. Delirium assessment instruments are reviewed. The neuropathophysiologic understanding of delirium is discussed in the context of important CNS neural circuitry. Pharmacologic treatments of delirium in adults and children are outlined, with particular emphasis on intravenous use of butyrophenone neuroleptics.

Effect of various stressors on the level of lipid peroxide, antioxidants and Na+, K(+)-ATPase activity in rat brain

The level of malondialdehyde (MDA), an index of lipid peroxidation, and the antioxidants superoxide dismutase (SOD) and glutathione (GSH), as well as the activity of Na+, K(+)-ATPase, were assessed in whole rat brain after immobilization, anemic hypoxia (NaNO2) and 72 h starvation. The effect of these stressors on plasma glucose and corticosterone levels was also observed. Hypoxia and starvation stimulated the lipid peroxide formation in brain as indicated by an increase in the level of MDA, being higher after starvation than hypoxia. Brain SOD activity was also increased in response to hypoxia and starvation while GSH content was only diminished in hypoxia. However, neither MDA nor antioxidants were affected by immobilization. On the other hand, the activity of brain Na+, K(+)-ATPase was significantly increased by immobilization and hypoxia but decreased in starvation. A similar pattern of change was also observed in plasma glucose and corticosterone levels in response to these stressors. These results elucidate differences in the biochemical response of animals towards various types of stress, with increased lipid peroxide formation in hypoxia and starvation.

Alterations in striatal dopamine release and reuptake under conditions of mild, moderate, and severe cerebral ischemia

Cerebral ischemia can result in varying degrees of tissue damage. Conditions of severe ischemia can produce extensive areas of irreversible injury, whereas in conditions of moderate ischemia, tissue damage may be reversible, as in the region of the ischemic penumbra. The reversibility of tissue damage in the penumbral region is of clinical interest, because the characterization of conditions underlying this reversible state may provide information needed for the development of new therapeutic approaches for treatment. Our previous studies demonstrated neurochemical alterations in the levels of dopamine (DA) within the striatum after cerebral ischemia. In the present study, we postulate that these changes may be caused, in part, by alterations in transmitter release and reuptake. To test this hypothesis, forebrain ischemia was induced in Sprague-Dawley rats (Harlan, Indianapolis, IN) by means of bilateral common carotid artery occlusion and hemorrhagic hypotension. Cerebral blood flow (CBF) in the striatum was measured by the method of hydrogen clearance, and the extracellular DA ([DA]e) levels were measured by in vivo microdialysis. Varied reductions of CBF were induced and maintained for 5 hours. Three subgroups were established retrospectively according to the degree of CBF reduction: 67.7, 35.6, and 13.2% of normal CBF in the mild, moderate, and severe ischemic groups, respectively. The induction of ischemia resulted in 1.9-, 9.3-, and 122.3-fold increases in [DA]e above baseline in the mild, moderate, and severe ischemia groups, respectively. At 3 hours after the induction of ischemia, high potassium (100 mmol/L) or Nomifensin (Sigma, St. Louis, MO) (10 mmol/L), a DA uptake blocker, was administrated via a microdialysis probe to stimulate DA release while reductions in CBF were maintained continuously. Thirteen rats were used in the study of the release of DA by potassium or Nomifensin in nonischemic conditions. The administration of high potassium or Nomifensin stimulated DA release in conditions of mild and moderate ischemia. The increase in DA release by potassium stimulation was higher in rats with mild ischemia (106.6-fold) than that in normal rats (22.3-fold). This suggests a hyperexcitability of DA terminals under mild ischemia, as compared with nonischemic conditions. On the other hand, Nomifensin increased [DA]e levels more in moderately ischemic brains than in control brains, suggesting that DA uptake is up-regulated in the former case. The increased release of DA by potassium and Nomifensin was sustained after stimulation in conditions of mild and moderate ischemia. The high level of [DA]e with severe ischemia after ischemic induction was sustained throughout the period of study and was not stimulated by potassium or Nomifensin. We conclude that under conditions of mild and moderate ischemia, DA terminals become highly excitable and reuptake mechanisms are compromised. These changes of DA metabolism during mild and moderate ischemia may explain the sustainability of neurons in the "penumbra" condition of cerebral ischemia and the transformation of the ischemic penumbra to a necrotic core.

Ketamine antagonizes hypoxia-induced dopamine release in rat striatum

The purpose of this study is to investigate the hypothesis that ketamine, a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, attenuates hypoxia-induced striatal dopamine release in vivo. High-speed chronoamperometric recording techniques, using Nafion-coated carbon fiber electrodes, were used to evaluate extracellular dopamine (DA) concentration in the striatum. KCl and DA were locally applied directly to the striatum of urethane-anesthetized Sprague-Dawley rats, in order to measure release and clearance, respectively, of DA. These anesthetized animals were paralyzed with D-tubocurarine and connected to a respirator to allow controlled respiration. Systemic concentrations of oxygen and carbon dioxide were altered by changing the partial pressure of O2, CO2, N2 of inspired air and the rate of the respirator. Our data indicate that lowering the respiratory rate from 90 to 20 times/min for 5 min, in room air, caused a decrease in blood O2 while increasing the CO2 concentration. These changes in blood gas concentration were reversible and reproducible. We also found that lowering the respiratory rates potentiated K(+)-induced DA release but not DA clearance in the striatum. In an attempt to induce hypercapnia, the room air was replaced with high CO2-containing air (15% CO2 + 20% O2 + 65% N2), and this change resulted in increased blood CO2 levels without lowering O2 concentration. The hypercapnia did not alter K(+)-induced DA release in the striatum. Next, we attempted to simulate anoxic hypoxia in the absence of hypercapnia. Respiration with pure N2 for 30 s resulted in lowering blood O2 without increasing CO2 levels. Both basal and K(+)-evoked DA releases were increased during N2-induced anoxic hypoxia. These data suggested that transient hypoxia facilitates DA release in the striatum. It has been suggested that NMDA is involved in many hypoxia-mediated responses. We also found that systemic application of ketamine, which itself did not affect blood O2 or CO2 levels, antagonized hypoxia-induced electrochemical responses. These data suggest that the increase in DA release in vivo during short-term hypoxia may probably be mediated through NMDA receptors.

Effect of neonatal hypoxia-ischemia on nigro-striatal dopamine receptors and on striatal neuropeptide Y, dynorphin A and substance P concentrations in rats

Perinatal hypoxic-ischemic brain injury was induced in 7- to 8-day-old rats by ligating the left carotid artery with subsequent exposure to 9% oxygen atmosphere for 2.5 h. The animals were killed 7 days later and grouped according to the degree of brain injury sustained after hypoxia-ischemia. Total protein content measured in striatum ipsilateral to the ligation, and dissected from brains showing extensive damage, was reduced to 64% of contralateral tissue. The protein content was not altered in other groups including control animals exposed to air and in sham-operated animals exposed to hypoxic conditions. The concentration of (pg/mg protein) and total (pg/striatum) striatal dynorphin A-like immunoreactivity (DLI) from brains with extensive damage were increased to 481% and 285% of the contralateral side, respectively. Hypoxia-ischemia increased striatal neuropeptide Y-like immunoreactivity (NPYLI) concentration from brains with extensive damage to 157% of contralateral side, but when the results were expressed as total NPYLI content per striatum, NPYLI content in striatum with extensive damage remained unaltered. Substance P-like immunoreactivity (SPLI) concentration and total content per striatum from brains with extensive damage were reduced to 66% and 43% of the contralateral side, respectively. D1 and D2 receptor density in animals killed 10 days after injury was reduced by 24% and 22% of control, respectively, in striatum from brains with extensive damage. These results indicate complex changes in brain neuropeptides following neonatal hypoxia-ischemia. Damage in the substance P system could have functional effects on dopaminergic transmission while the increase in NPYLI and in DLI concentrations may respectively reflect the relative preservation from neuronal damage and possibly an increase in neuropeptide synthesis or decrease in release. The decrease in SPLI concentration and the increase DLI concentration induced by hypoxia-ischemia suggests that these peptides may be present in separate neurons.

Ibogaine modulates cocaine responses which are altered due to environmental habituation: in vivo microvoltammetric and behavioral studies

Ibogaine, a serotonergic (5-HTergic) indole alkaloid, was studied for cocaine modulatory effects on four parameters of behavior by computerized infrared photocell beam detection. The behavioral parameters were: a) locomotor activity (ambulations), b) rearing, c) stereotypy (fine movements, primarily grooming), and d) agoraphobia [(thigmotaxis) a natural tendency to avoid the center of the behavioral chamber]. With each behavioral data point, dopamine (DA) release, and serotonin (5-HT) release were detected within seconds in nucleus accumbens (NAcc) of the same behaving male Sprague-Dawley rats, using in vivo electrochemistry (voltammetry). Ibogaine was administered (40 mg/kg IP) for 4 consecutive days. Importantly, the DAergic and the 5-HTergic responses to (SC) cocaine and two behavioral responses, ambulations and central ambulations, were reduced in intensity due to extended time spent in the novel behavioral chamber (habituated). Rearing and fine movement patterns were not habituated. The results show that ibogaine downmodulated the (SC) cocaine-induced increase in NAcc DA release (p < 0.0001) and potentiated the (SC) cocaine-induced decrease in NAcc 5-HT release (p < 0.0001). Concurrently, ibogaine downmodulated cocaine-induced ambulation (p < 0.0001) and central ambulation behavior (p < 0.0001). On the other hand, the behavioral parameters that did not exhibit habituation, i.e., rearing behavior and fine movement behavior, were not downmodulated by ibogaine (p < 0.1558) (p < 0.3763), respectively. Furthermore, ibogaine itself did not significantly alter NAcc DA release over the 2-h period studied (p < 0.9113) although individual time points were significantly affected bidirectionally. Concurrently ibogaine significantly increased 5-HT release (p < 0.0155). Behaviorally, ibogaine appears to be a weak psychostimulant. The data show a critical modulatory role for 5-HT in ibogaine-cocaine interactions. Also elucidated as critical is the efficacy of ibogaine when the response to (SC) cocaine is decreased due to the habituation of the animals to their environment.

Evaluation of monoaminergic neurotransmitters in the rat striatum during varied global cerebral ischemia

Neurotransmitter release during cerebral ischemia has been extensively studied and is thought to play a key role in excitotoxic neuronal death. The changes in neurotransmitter release and its metabolism may reflect changes in cellular metabolism during ischemia. The purpose of this study is to assess alterations in extracellular dopamine and serotonin and their metabolites under varied degrees of ischemia in rat striatum to elucidate the pathophysiology of cerebral ischemia. Twenty rats were used to induce varied forebrain ischemia by means of bilateral common carotid artery occlusion along with hemorrhagic hypotension. Cerebral blood flow (CBF) in the striatum was measured every 40 minutes by methods of hydrogen clearance and maintained within certain ranges for 6 hours. Dopamine, serotonin, and their metabolites were measured every 20 minutes by in vivo microdialysis. Varying degrees of ischemia were obtained, ranging from 9.4 to 81.3% of control CBF. The animals were divided into three groups according to CBF levels measured 20 minutes after the induction of ischemia. In the mild ischemia group (n = 5), CBF ranged from 65 to 88% of baseline levels and resulted in only a slight increase of dopamine. In the moderate ischemia group (n = 10), CBF ranged from 21 to 48% of baseline levels and resulted in transient increases of dopamine (24-fold) and serotonin (5-fold). In the severe ischemia group (n = 5), CBF was below 14% of baseline levels and resulted in marked increases in dopamine (462-fold) and serotonin (225-fold). These alterations remained elevated for 3 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

The neuropathogenesis of delirium. A need to focus our research

Delirium symptoms suggest dysfunction of multiple brain regions. However, little is known about delirium's underlying neuropathogenesis. This article addresses the need for research on neuroanatomic and neuropathophysiologic underpinnings of delirium, analogous to that of schizophrenia and affective disorders. Electrophysiologic tests, structural and functional brain imaging, and neurotransmitter studies in delirium are critically reviewed. The importance of both cerebral cortical and subcortical areas is noted, with emphasis on frontal, right-hemisphere, and subcortical regions, including caudate and anteromedial thalamus. Each symptom of delirium can be viewed from a neuroanatomic and neurochemical perspective. Recommendations for research are made throughout the article.

Hypoxia induces different responses of striatal high- and low- affinity dopamine uptake sites

The dopamine (DA) uptake over a concentration range from 0.03 to 100 microM was studied in S1 fractions of the rat striatum prepared from control rats and those exposed for 14 h to hypobaric hypoxia. The uptake exhibited non-Michaelis-Menten kinetics, which were evaluated by applying an equation assuming two transport sites. The high-affinity uptake site was characterized by an apparent Michaelis-Menten constant of 0.47 microM and an apparent maximal transport rate of 113 pmol/mg protein/30 s. The respective constants of the low-affinity uptake site were 52.8 microM and 1490 pmol/mg protein/30 s. One hour after hypoxia kinetic constants of the high-affinity uptake were unchanged but the maximal transport rate of the low-affinity uptake was increased by 50%. The elevated low-affinity uptake capacity may represent a means of adaptation to hypoxia allowing a faster removal of high extracellular concentrations of DA.

Multiple methamphetamine injections induce marked increases in extracellular striatal dopamine which correlate with subsequent neurotoxicity

Acutely, methamphetamine (m-AMPH) is known to stimulate a net efflux of dopamine (DA) in the striatum while inhibiting DA uptake, thus producing high extracellular concentrations of DA. Repeated administration of m-AMPH has been shown to damage DA terminals in the striatum. However, little direct information exists about the relationship between m-AMPH-induced DA overflow and neurotoxicity. In the present study, we used in vivo microdialysis to explore this topic. Four, but not 3, injections of m-AMPH (4 mg/kg, sc, at 2 h intervals) damaged striatal DA terminals as measured by a 43-51% decrease in post mortem striatal DA content 1 week later. Striatal microdialysis in awake animals during the course of m-AMPH treatment showed that DA overflow increased after each m-AMPH injection, but that approximately 1.5 h after the fourth m-AMPH injection, a striking increase in DA overflow occurred that was significantly larger than that seen after any of the previous 3 injections. Additionally, in animals receiving 4 injections of m-AMPH, cumulative DA overflow was negatively correlated with striatal DA content 1 week later (r = -0.74, P less than 0.05), suggesting that the substantial DA overflow seen after the fourth m-AMPH injection is especially important in m-AMPH neurotoxicity.