Influence of long-term acute heat exposure on regional blood-brain barrier permeability, cerebral blood flow and 5-HT level in conscious normotensive young rats

Heat stroke and cytokines

Heat stroke is a life-threatening illness that affects all segments of society, including the young, aged, sick, and healthy. The recent high death toll in France (Dorozynski, 2003) and the death of high-profile athletes has increased public awareness of the adverse effects of heat injury. However, the etiology of the long-term consequences of this syndrome remains poorly understood such that preventive/treatment strategies are needed to mitigate its debilitating effects. Cytokines are important modulators of the acute phase response (APR) to stress, infection, and inflammation. Current data implicating cytokines in heat stroke responses are mainly from correlation studies showing elevated plasma levels in heat stroke patients and experimental animal models. Correlation data fall far short of revealing the mechanisms of cytokine actions such that additional research to determine the role of these endogenous substances in the heat stroke syndrome is required. Furthermore, cytokine determinations have occurred mainly at end-stage heat stroke, such that the role of these substances in progression and long-term recovery is poorly understood. Despite several studies implicating cytokines in heat stroke pathophysiology, few studies have examined the protective effect(s) of cytokine antagonism on the morbidity and mortality of heat stroke. This is particularly surprising since heat stroke responses resemble those observed in the endotoxemic syndrome, for which a role for endogenous cytokines has been strongly implicated. The implication of cytokines as mediators of endotoxemia and the presence of circulating endotoxin in heat stroke patients suggests that much knowledge can be gained from applying our current understanding of endotoxemic pathophysiology to the study of heat stroke. Heat shock proteins (HSPs) are highly conserved proteins that function as molecular chaperones for denatured proteins and reciprocally modulate cytokine production in response to stressful stimuli. HSPs have been shown repeatedly to confer protection in heat stroke and injury models. Interactions between HSPs and cytokines have received considerable attention in the literature within the last decade such that a complex pathway of interactions between cytokines, HSPs, and endotoxin is thought to be occurring in vivo in the orchestration of the APR to heat injury. These data suggest that much of the pathophysiologic changes observed with heat stroke are not a consequence of heat exposure, per se, but are representative of interactions among these three (and presumably additional) components of the innate immune response. This chapter will provide an overview of current knowledge regarding cytokine, HSP, and endotoxin interactions in heat stroke pathophysiology. Insight is provided into the potential therapeutic benefit of cytokine neutralization for mitigation of heat stroke morbidity and mortality based on our current understanding of their role in this syndrome.

Alterations in blood-brain barrier function by morphine and methamphetamine

The possibility that stress associated with morphine and amphetamine administration or withdrawal will influence the blood-brain barrier (BBB) and brain dysfunction was examined in a rodent model. Repeated daily administration of morphine (10 mg/kg, i.p.) resulted in drug dependence in rats on the sixth day and onwards. Measurement of the BBB permeability to large molecule tracers normally bound to proteins, e.g., Evans blue albumin and radioiodine (([131])Iodine) did not show any leakage on the 12th day of drug dependence. On the other hand, spontaneous withdrawal of morphine on day 1 resulted in profound stress symptoms. These symptoms were much more intense on the second day of morphine withdrawal. Alterations in the BBB to protein tracers were seen in several regions of the brain. This increase in BBB to protein tracers was most pronounced on the second day of morphine withdrawal. These rats also exhibited abnormal neuronal, glial and stress protein, the heat-shock protein 72 kD (HSP-72 kD) response. On the other hand, acute administration of methamphetamine (40 mg/kg, i.p.) in mice resulted in marked extravasation of endogenous serum protein as seen with increased expression of albumin immunohistochemistry. These observations suggest that psychostimulants and associated stress are capable to influence the brain function, probably through modifying the BBB function, not reported earlier.

Methods to produce hyperthermia-induced brain dysfunction

The recent increase in the frequency and intensity of killer heat waves across the globe has aroused worldwide medical attention to exploring therapeutic strategies to attenuate heat-related morbidity and/or mortality. Death due to heat-related illnesses often exceeds >50% of heat victims. Those who survive are crippled with lifetime disabilities and exhibit profound cognitive, sensory, and motor dysfunction akin to premature neurodegeneration. Although more than 50% of the world populations are exposed to summer heat waves; our understanding of detailed underlying mechanisms and the suitable therapeutic strategies have still not been worked out. One of the basic reasons behind this is the lack of a reliable experimental model to simulate clinical hyperthermia. This chapter describes a suitable animal model to induce hyperthermia in rats (or mice) comparable to the clinical situation. The model appears to be useful for studying the effects of heat-related illnesses on changes in various organs and systems, including the central nervous system (CNS). Since hyperthermia is often associated with profound brain dysfunction, additional methods to examine some crucial parameters of brain injury, e.g., blood-brain barrier (BBB) breakdown and brain edema formation, are also described.

Blood-cerebrospinal fluid barrier in hyperthermia

The blood-CSF barrier (BCSFB) in choroid plexus works with the blood-brain barrier (BBB) in cerebral capillaries to stabilize the fluid environment of neurons. Dysfunction of either transport interface, i.e., BCSFB or BBB, causes augmented fluxes of ions, water and proteins into the CNS. These barrier disruptions lead to problems with edema and other compromised homeostatic mechanisms. Hyperthermic effects on BCSFB permeability and transport are not as well known as for BBB. However, it is becoming increasingly appreciated that elevated prostaglandin synthesis from fever/heat activation of cyclooxygenases (COXs) in the BCSFB promotes water and ion transfer from plasma to the ventricles; this harmful fluid movement into the CSF-brain interior can be attenuated by agents that inhibit the COXs. Moreover, new functional data from our laboratory animal model indicate that the BCSFB (choroidal epithelium) and the CSF-bordering ependymal cells are vulnerable to whole body hyperthermia (WBH). This is evidenced from the fact that rats subjected to 4h of heat stress (38 degrees C) showed a significant increase in the translocation of Evans blue and (131)Iodine from plasma to cisternal CSF, and manifested blue staining of the dorsal surface of the hippocampus and caudate nucleus. Degeneration of choroidal epithelial cells and underlying ependyma, a dilated ventricular space and damage to the underlying neuropil were frequent. A disrupted BCSFB is associated with a marked increase in edema formation in the hippocampus, caudate nucleus, thalamus and hypothalamus. Taken together, these findings suggest that the breaching of the BCSFB in hyperthermia significantly contributes to cell and tissue injuries in the CNS.

A Potent Serotonin-Modulating Compound AP-267 Attenuates Morphine Withdrawal-Induced Blood-Brain Barrier Dysfunction in Rats

The possibility that a serotonin 5-HT2c receptor-modulating compound, AP-267, will influence spontaneous morphine withdrawal symptoms and the alterations in the brain fluid microenvironment was examined in a rat model. Daily administration of morphine (10 mg/kg, i.p.) for 10 days resulted in dependence of rats as seen by loss of analgesic response. On the 11th day, no morphine administration was given. This resulted in profound withdrawal symptoms 24 h after morphine withdrawal. The magnitude and severity of these symptoms were increased further 48 h after withdrawal. Measurement of the blood-brain barrier (BBB) permeability, a measure of perturbed brain fluid microenvironment showed leakage of Evans blue and radioiodine tracers in several parts of the brain in rats showing withdrawal symptoms. Whereas, rats treated with AP-267 either on the 1st day or 2nd day morphine withdrawal showed much less symptoms and leakage of the BBB. Taken together, these observations suggest that (a) stress associated with the withdrawal symptoms are sufficient enough to induce breakdown of the BBB function, and (b) modulation of serotonin 5-HT2c receptors may have some protective influence on the stress symptoms and the BBB disruption.

Spinal nerve lesion alters blood-spinal cord barrier function and activates astrocytes in the rat

Alterations in the spinal cord microenvironment in a neuropathic pain model in rats comprising right L-4 spinal nerve lesion were examined following 1, 2, 4 and 10 weeks using albumin and glial fibrillary acidic protein (GFAP) immunoreactivity. Rats subjected to nerve lesion showed pronounced activation of GFAP indicating astrocyte activation, and exhibited marked leakage of albumin, suggesting defects of the blood-spinal cord barrier (BSCB) function in the corresponding spinal cord segment. The intensities of these changes were most prominent in the gray matter of the lesioned side compared to the contralateral cord in both the dorsal and ventral horns. The most marked changes in albumin and GFAP immunoreaction were seen after 2 weeks and persisted with mild intensities even after 10 weeks. Distortion of nerve cells, loss of neurons and general sponginess were evident in the gray matter of the spinal cord corresponding to the lesion side. These nerve cell and glial cell changes was mainly evident in the areas showing leakage of endogenous albumin in the spinal cord. These novel observations indicate that chronic nerve lesion has the capacity to induce a selective increase in local BSCB permeability that could be instrumental in nerve cell and glial cell activation. These findings may be relevant to our current understanding on the pathophysiology of neuropathic pain.

Whole-body hyperthermia in the rat disrupts the blood-cerebrospinal fluid barrier and induces brain edema

The present investigation was undertaken to find out whether whole-body hyperthermia (WBH) alters blood-cerebrospinal fluid barrier (BCSFB) permeability to exogenously-administered tracers and whether choroid plexus and ependymal cells exhibit morphological alterations in hyperthermia. Rats subjected to 4 hours of heat stress at 38 degrees C in a biological oxygen demand (BOD) incubator exhibited a profound increase in the BCSFB to Evans blue and radioiodine. Blue staining of the dorsal surface of the hippocampus and caudate nucleus and a significant increase in Evans blue and [131]Iodine in cisternal cerebrospinal fluid were seen following 4-hour heat stress compared to control. Degeneration of choroidal epithelial cells and underlying ependyma, a dilated ventricular space, and degenerative changes in the underlying neuropil were frequent. Hippocampus, caudate nucleus, thalamus, and hypothalamus exhibited profound increases in water content after 4 hours of heat stress. These observations suggest that hyperthermia induced by WBH is capable of breaking down the BCSFB and contributing to cell and tissue injury in the central nervous system.

Branched-chain amino acid supplementation and human performance when hypohydrated in the heat

The serotonin system may contribute to reduced human performance when hypohydrated in the heat. This study determined whether branched-chain amino acid (BCAA) supplementation could sustain exercise and cognitive performance in the heat (40 degrees C dry bulb, 20% relative humidity) when hypohydrated by 4% of body mass. Seven heat-acclimated men completed two experimental trials, each consisting of one preparation and one test day. On day 1, a low-carbohydrate diet was eaten and subjects performed exhaustive cycling (morning) and treadmill exercise in the heat (afternoon) to lower muscle glycogen and achieve the desired hypohydration level. On day 2, subjects consumed an isocaloric BCAA and carbohydrate (BC) or carbohydrate-only drink during exercise. Experimental trials included 60 min of cycle ergometry (50% peak oxygen uptake) followed by a 30-min time trial in the heat. A cognitive test battery was completed before and after exercise, and blood samples were taken. BC produced a 2.5-fold increase (P < 0.05) in plasma BCAA and lowered (P < 0.05) the ratios of total tryptophan to BCAA and large neutral amino acid. Blood prolactin, glucose, lactate, and osmolality were not different between trials but increased over time. Cardiovascular and thermoregulatory data were also similar between trials. BC did not alter time-trial performance, cognitive performance, mood, perceived exertion, or perceived thermal comfort. We conclude that BCAA does not alter exercise or cognitive performance in the heat when subjects are hypohydrated.

Blood-brain barrier integrity may be threatened by exercise in a warm environment

Seven active men were recruited to examine changes in the serum concentration of S100beta, a proposed peripheral marker of blood-brain barrier permeability, following prolonged exercise in temperate (T) and warm (W) conditions. Subjects were seated immersed to the neck in water at 35.0 (0.1) degrees C (T) or 39.0 (0.1) degrees C (W) for 30 min. Subjects then entered a room maintained at either 18.3 (1.8) degrees C (T) or 35.0 (0.3) degrees C (W) and completed 60 min of cycle exercise at 60% peak oxygen uptake. Serum S100beta concentration was elevated after exercise in the W trial (+0.12 (0.10) microg/l; P = 0.02) but not after the T trial (P = 0.238). Water immersion and exercise elevated core temperature by 2.1 (0.5) degrees C to 39.5 (0.3) degrees C at the end of exercise in the W trial compared with a 0.9 (0.2) degrees C increase during the T trial (P < 0.001). Weighted mean skin temperature was higher throughout the W trial compared with the T trial (P < 0.001). Heart rate (P < 0.001) and blood glucose (P < 0.001) and lactate (P < 0.001) concentrations were elevated to a greater extent during exercise in the W trial than in the T trial. Ratings of perceived exertion (P < 0.001) and thermal comfort (P < 0.001) were markedly higher throughout the W trial than in the T trial. The results of this study demonstrate that serum S100beta was elevated after water immersion and prolonged exercise in a warm environment, suggesting that blood-brain barrier permeability may be altered.

Antioxidant compounds EGB-761 and BN-52021 attenuate brain edema formation and hemeoxygenase expression following hyperthermic brain injury in the rat

Role of carbon monoxide (CO) in hyperthermic brain injury induced brain pathology was examined in a rat model using immunohistochemistry of the hemeoxygenase-2 (HO-2) enzyme. Exposure of rats to 4 h heat stress at 38 degrees C resulted in profound hyperthermia, breakdown of the blood-brain barrier (BBB), brain edema formation, cell damage and expression of HO-2 in several brain regions. Pretreatment with potent antioxidant compounds EGB-761 and BN-52021 markedly reduced the HO-2 expression, BBB breakdown, brain edema formation and cell damage without attenuating the hyperthermic response. This effect was most marked in animals treated with EGB-761. These observations suggest that upregulation of HO-2 representing generation of CO plays important roles in hyperthermic brain injury, and oxidative stress seems to be one of the most important signals in inducing HO-2 expression in hyperthermia, not reported earlier.

Selective alteration of calcitonin gene related peptide in hyperthermic brain injury. An experimental study in the rat brain using immunohistochemistry

The possibility that calcitonin gene related peptide (CGRP) participates in the pathophysiology of hyperthermic brain injury was examined in a rat model. The CGRP immunoreactivity was examined in several brain regions of control and 4 h heat stressed rats using immunohistochemistry. Subjection of animals to heat stress in a biological oxygen demand (BOD) incubator at 38 degrees C for 4 h resulted in a marked redistribution of CGRP immunoreactivity. Thus, in cerebral cortex, hippocampus, cerebellum, medulla and spinal cord the CGRP immunoreactivity was profoundly increased following heat stress. On the other hand in brain stem and pons, the CGRP activity is downregulated. These observations suggest that heat stress has the capacity to influence CGRP immunoreactivity and this redistribution of the peptide is somehow associated with the molecular mechanisms of thermal information processing system of the CNS in heat stress, not reported earlier.

Role of nitric oxide in blood-brain barrier permeability, brain edema and cell damage following hyperthermic brain injury. An experimental study using EGB-761 and Gingkolide B pretreatment in the rat

The role of oxidative stress in hyperthermia induced upregulation of constitutive and inducible isoforms of nitric oxide synthase (NOS) in the central nervous system (CNS) was investigated using immunohistochemistry in a rat model. Exposure of rats to heat stress at 38 degrees C for 4 h resulted in marked upregulation of constitutive NOS (cNOS) and a mild but significant expression of inducible NOS (iNOS) in several brain regions exhibiting leakage of the blood-brain barrier (BBB), brain edema formation and cell injury. Pretreatment with the potent antioxidative compound EGB-761 or its constituent, Ginkgolide B significantly attenuated upregulation of cNOS and iNOS in the brain and also reduced the BBB permeability disturbances, brain edema and cell injury. These neuroprotective effects were most marked in the EGB-761 pretreated rats. Our observations strongly suggest that (i) EGB-761 and Ginkgolide B pretreatment offer significant neuroprotection in hyperthermic brain injury, (ii) upregulation of cNOS and iNOS are injurious to the cell and, (iii) oxidative stress plays an important role in NOS expression and cell injury.

Chronic fatigue syndrome: neurological findings may be related to blood--brain barrier permeability

Despite volumes of international research, the etiology of chronic fatigue syndrome (CFS) remains elusive. There is, however, considerable evidence that CFS is a disorder involving the central nervous system (CNS). It is our hypothesis that altered permeability of the blood-brain barrier (BBB) may contribute to ongoing signs and symptoms found in CFS. To support this hypothesis we have examined agents that can increase the blood-brain barrier permeability (BBBP) and those that may be involved in CFS. The factors which can compromise the normal BBBP in CFS include viruses, cytokines, 5-hydroxytryptamine, peroxynitrite, nitric oxide, stress, glutathione depletion, essential fatty acid deficiency, and N-methyl-D-aspartate overactivity. It is possible that breakdown of normal BBBP leads to CNS cellular dysfunction and disruptions of neuronal transmission in CFS. Abnormal changes in BBBP have been linked to a number of disorders involving the CNS; based on review of the literature we conclude that the BBB integrity in CFS warrants investigation.

Ritanserin as add-on medication to neuroleptic therapy for patients with chronic or subchronic schizophrenia

The effect of ritanserin, a potent 5HT 2A/2C receptor antagonist, used as an add-on medication to neuroleptic treatment in patients with schizophrenia, was compared with that of placebo, in an international, double-blind, parallel-group study. Previously established neuroleptic therapy was maintained, and ritanserin 10 mg or placebo was given once daily for 8 weeks. Psychopathology was assessed with the Positive and Negative Syndrome Scale (PANSS) and the Clinical Global Impression (CGI) cale. Safety assessments included the Extrapyramidal Symptom Rating Scale (ESRS), and the requirement for antiparkinsonian medication was monitored. About 70 per cent of patients completed the treatment. There was no difference between the two groups in the numbers of patients with clinical improvement at endpoint on the PANSS negative subscale and total PANSS. The CGIs of overall severity of schizophrenia were better under placebo. The overall prevalence of side effects and the requirements for antiparkinsonism medication were comparable in the two groups. Copyright 2000 John Wiley & Sons, Ltd.

Exposure to prenatal carbon monoxide and postnatal hyperthermia: short and long-term effects on neurochemicals and neuroglia in the developing brain

The effects of prenatal exposure to carbon monoxide (CO), a major component of cigarette smoke, was studied alone or in combination with postnatal hyperthermia, on the structural and neurochemical development of the postnatal brain at 1 and 8 weeks. Pregnant guinea pigs (n = 11) were exposed to 200 p.p.m CO for 10 h/day from midgestation until term (68 days), whereas control mothers (n = 10) breathed room air. On postnatal day 4, neonates from the control and CO-exposed pregnancies were exposed to hyperthermia (35 degrees C) for 75 min or remained at ambient (23 degrees C) temperature. Using semiquantitative immunohistochemical techniques the following neurotransmitter alterations were found in the medulla at 1 week: a decrease in met-enkephalin-immunoreactivity (IR) following postnatal hyperthermia and an increase in 5-hydroxytryptamine-IR following a combination of CO and hyperthermia. No alterations were observed in substance P- or tyrosine-hydroxylase-IR in any paradigm. At 8 weeks of age the combination of prenatal CO exposure followed by a brief hyperthermic stress postnatally resulted in lesions throughout the brain and an increase in glial fibrillary acidic protein-IR in the medulla. Such effects on brain development could be of relevance in cardiorespiratory control in the neonate and could have implications for the etiology of Sudden Infant Death Syndrome, where smoking and hyperthermia are major risk factors.

Nitric oxide in the pathophysiology of hyperthermic brain injury. Influence of a new anti-oxidant compound H-290/51. A pharmacological study using immunohistochemistry in the rat

The possibility that nitric oxide (NO) is involved in the pathophysiology of brain injury caused by heat stress (HS) was examined using neuronal nitric oxide synthase (NOS) immunohistochemistry in a rat model. In addition, to find out a role of oxidative stress in NOS upregulation and cell injury, the effect of a new antioxidant compound H-290/51 (Astra Hässle, Mölndal, Sweden) was examined in this model. Subjection of conscious young rats to 4 h HS in a biological oxygen demand (BOD) incubator at 38 degrees C resulted in a marked upregulation of NOS in many brain regions compared to control rats kept at room temperature (21 +/- 1 degree C). This NOS immunoreactivity was found mainly in distorted neurons located in the edematous regions not normally showing NOS activity. Breakdown of the blood-brain barrier (BBB) permeability, increase in brain water content and marked neuronal, glial and myelin reaction were common findings in several brain regions exhibiting upregulation of NOS activity. Pretreatment with H-290/51 significantly attenuated the upregulation of NOS in rats subjected to HS. In these animals breakdown of the BBB permeability, edema and cell changes were considerably reduced. Our results suggest that hyperthermic brain injury is associated with a marked upregulation of NOS activity in the CNS and this upregulation of NOS and concomitant cell injury can be reduced by prior treatment with an antioxidant compound H 290/51. These observations indicate that oxidative stress seems to be an important endogenous signals for NOS upregulation and cell reaction in hyperthermic brain injury.

Central analgesic actions of loperamide following transient permeation of the blood brain barrier with Cereport (RMP-7)

The bradykinin analog, Cereport (RMP-7), was designed to increase permeability of the blood brain barrier (BBB). Over the past several years it has been developed primarily as a means of increasing permeability of the blood brain tumor barrier, where early evidence indicated a particularly robust and reliable effect. The present series of experiments were intended to determine whether Cereport might also be used to increase delivery of pharmacological agents across the normal (i.e., non-tumor) BBB. This was accomplished by testing the ability of Cereport to enhance delivery of the peripherally acting opiate agonist, loperamide, to the brain, as evidenced by induction of a centrally mediated analgesic effect. Intravenous administration of a combination of Cereport and loperamide produced a significant analgesic effect (2-fold increase in response times) when animals were tested on a hotplate apparatus. Loperamide alone did not produce analgesia. An analysis of the time course of analgesia revealed a graded onset of analgesia which peaked at 30 min, maintained asymptote at 60 min, and began to diminish by 120 min following Cereport and loperamide administration. Finally, the analgesic effects of combining Cereport and loperamide were completely blocked when animals were pre-treated with the opiate antagonist naloxone, demonstrating that the analgesia was mediated through opiate receptors. Collectively, these results suggest that Cereport was able to increase delivery of loperamide across the BBB, allowing it to gain access to opiate receptors in the CNS to produce a centrally mediated analgesic effect. They therefore provide clear evidence that safe and well-tolerated doses of Cereport can increase permeability of the normal (i.e., non-tumor) BBB. Moreover, they provide the first evidence of a pharmacological effect specifically enabled by controlled (i.e., receptor-mediated) modulation of the BBB.

Reversible blood-brain barrier dysfunction after intracarotid hyperthermic saline infusion

An animal model for reversible blood-brain barrier disruption has been developed. Retrograde infusion of hyperthermic saline solution 43 degrees C into the left external carotid artery of normothermic, Wistar rats, reversibly increases cerebrovascular permeability to Evans-blue albumin in the left cerebral hemisphere. Isotonic saline solutions at 37 degrees C for group I and 43 degrees C for group II were infused for 30-s at a constant rate of 0.12 ml/s into the left external carotid artery. Evans-blue, the barrier tracer was administered intravenously either prior to or at intervals of 5, 30, 180, 360 min after the hyperthermic saline infusion under pentobarbital anesthesia. All animals receiving hyperthermic saline perfusion had disturbed blood-brain barrier permeability. Based on visual inspection, disruption grade in the left hemispheres of six of 11 animals was grade 3+. Mean values for Evans-blue dye were found to be 0.28 +/- 0.06 mg/g of tissue in left hemisphere after normothermic saline infusion (group I), and 2.41 +/- 0.5 mg/g of tissue in the same hemisphere after hyperthermic saline infusion (group II). The difference was found to be significant between group I and group II (p < 0.01). The increase in cerebrovascular permeability was temporary, even though Evans-blue albumin extravasation remained slightly elevated 3 h after infusion and was normal 6 h after infusion.

Acute heat stress induces edema and nitric oxide synthase upregulation and down-regulates mRNA levels of the NMDAR1, NMDAR2A and NMDAR2B subunits in the rat hippocampus

The influence of heat stress on constitutive isoform of neuronal nitric oxide synthase (cNOS) and NMDA receptor gene expression in hippocampus was examined in a rat model. Subjection of animals to 4 h heat stress at 38 degrees C resulted in a marked upregulation of cNOS in the hippocampus accompanied with a marked general expansion and edematous cell changes. On the other hand NMDA receptor messenger RNA encoding NMDAR1, NMDAR2A and NMDAR2B subunits showed a marked downregulation in the hippocampus of heat stressed rats compared to the controls. Our results show that upregulation of cNOS is instrumental in heat stress associated edema and cell injury. Furthermore, an increased production of NO as evident with upregulation of cNOS appears to be a key factor in the downregulation of NMDA receptor gene expression in heat stress.

Role of neurochemicals in brain edema and cell changes following hyperthermic brain injury in the rat

The involvement of three potent neurochemical mediators of the edema formation such as serotonin, prostaglandins and opioids in the pathophysiology of hyperthermic brain injury was examined in a rat model using a pharmacological approach. Hyperthermic brain injury was induced in conscious young rats by exposing them to heat stress at 38 degrees C for 4 h. In these rats the blood-brain barrier (BBB) permeability, brain edema, cerebral blood flow (CBF), heat shock protein 72 kD (HSP) response and cell changes were examined. Pretreatment with ketanserin (a serotonin-2 receptor antagonist), indomethacin (prostaglandin synthesis inhibitor) and naloxone (opioid receptor antagonist) in separate groups of rats reduced hyperthermia and HSP response following heat stress and significantly attenuated changes in the BBB permeability, brain edema, CBF and cell reaction. These results suggest that the pathophysiology of hyperthermic brain injury is a complex mechanisms and several neurochemicals are involved in the brain pathology caused by heat stress.

Influence of acute exposure to heat on the blood-brain barrier permeability during acute hypertension

In mild hyperthermic rats with acute hypertension induced by intravenous injection of adrenaline, changes in blood-brain barrier permeability to macromolecules were investigated using Evans blue as indicator. Evans blue albumin extravasation was determined macroscopically, and a quantitative estimation with spectrophotometer using homogenized brain to release the dye was also performed to evaluate the macroscopic findings. Four groups of rats were studied: group I: control normothermia; group II: acute exposure to heat; group III: normothermia + acute hypertension; group IV: acute exposure to heat + acute hypertension. The rats were anesthetized with diethyl-ether. Body temperature was increased by elevating ambient temperature in the vented box covered with a 3 mm thick black copper plate. The colonic temperature was increased to 39 +/- 0.5 degrees C. During adrenaline-induced acute hypertension the mean arterial blood pressure increased in both normothermic and mild hyperthermic animals. Mean values for Evans blue dye were found to be 0.20 +/- 0.04 mg% whole brain in normothermic control rats and 0.30 +/- 0.1 mg% in hyperthermic rats (p < 0.05). Mean values for Evans blue dye in the whole brain were found to be 0.63 +/- 0. 2 mg% in the normothermic rats and 0.40 +/- 0.2 mg% in the mild hyperthermic rats during adrenaline-induced hypertension (p < 0.05). Our results show that the extravasation of Evans blue albumin was less pronounced in the brains of mild hyperthermic rats compared to normothermic rats after adrenaline-induced acute hypertension.

Impairment of blood-brain barrier function by serotonin induces desynchronization of spontaneous cerebral cortical activity: experimental observations in the anaesthetized rat

The possibility that elevation of serotonin in the circulation, which is found in various pathological states, influences the spontaneous cerebral cortical activity was examined in a rat model. The electroencephalogram was recorded using bipolar epidural electrodes placed over the frontal and parietal cerebral cortex. Intravenous infusion of serotonin (10 micrograms/kg per min for 10 min) decreased the electroencephalogram amplitude in both frontal and parietal recordings within 4 min of infusion. This decrease in amplitude was reversible, Pretreatment with cyproheptadine (a potent serotonin2 receptor antagonist) prevented the serotonin-induced decrease of the electroencephalogram amplitude. The blood-brain barrier permeability to Evans Blue and [131I]sodium was increased in frontal and parietal cortex. This increase in blood-brain barrier permeability was absent in animals pretreated with cyproheptadine. These results provide direct evidence that an elevated level of serotonin in blood has the capacity to influence spontaneous cortical electrical activity. This effect of serotonin on electroencephalogram appears to be due to its ability to enter into the brain parenchyma by inducing a short-term breakdown of the blood-brain barrier, probably via serotonin2 receptors.

Vascular permeability to growth hormone in the rat central nervous system after focal spinal cord injury. Influence of a new anti-oxidant H 290/51 and age

Vascular permeability to the growth hormone (GH) across the blood-brain barrier (BBB) is unknown. This investigation was undertaken to examine vascular permeability to 125I-labelled rat growth hormone (rGH) in the central nervous system (CNS) of normal animals. Since age and spinal cord injury influences the metabolism of GH, these factors were also included. No statistically significant difference was seen regarding rGH permeability between young (aged 19-21 weeks) and old (age 38-42 weeks) animals. A focal trauma to the cord, produced by an incision into the right dorsal horn of the T10-11 segments in young animals, increased rGH permeability in several spinal cord segments at 0.5-5.0 h after injury. This permeability increase progressed over time. Similar trauma to old rats resulted in a significantly less increase in rGH permeability in the spinal cord 5 h after the trauma. This indicates that trauma-induced increased permeability of rGH is age-dependent. Pretreatment of normal young animals with a new antioxidant (H 290/51) did not influence the rGH permeability. However the drug prevented the trauma-induced increase of rGH permeability at 5 h after injury. This indicates that inhibition of lipid peroxidation has some protective effect on trauma-induced increase in rGH permeability.

Regional specificity of the long-term variation of tyrosine hydroxylase protein in rat catecholaminergic cell groups after chronic heat exposure

The present study was carried out to investigate the effect of chronic heat exposure on tyrosine hydroxylase (TH) protein content in catecholaminergic rat brain-stem areas such as the anterior (LCA) and posterior (LCP) locus coeruleus, the substantia nigra (SN), the ventral tegmental area, and the dorsomedial (DMM) and the ventrolateral medulla and in the adrenal gland (AG). Male Sprague-Dawley rats were exposed to 34 degrees C during 3, 7, or 14 days. Controls were kept at 25 degrees C for the same period. In the LCA, TH content was decreased on day 7 (-34%) and 14 (-37%) of heat exposure. In the SN, TH protein content was decreased on day 7 (-25%) and 14 (-20%) after 34 degrees C. In the DMM cell group, 14 days at 34 degrees C produced a decrease (-20%) of TH content. In all of these structures, TH content variations were correlated with body temperature variations. In the AG, TH content increased progressively to peak (+31%) after 14 days of chronic heat exposure. This increase was also associated with body temperature modification. The selective and body temperature-related response to long-term TH protein content variations following chronic heat exposure observed in the LCA, SN, DMM, and AG could represent an adaptive physiological response of these catecholaminergic cells.

Heat stress affects blood-brain barrier permeability to horseradish peroxidase in mice

The blood-brain barrier of mice subjected to hyperthermia for 0-135 min was examined using horseradish peroxidase (HRP) and Evans blue dye tracers by light, fluorescence and electron microscopy. Neither control nor heat-stressed mice exhibited extravasation of the Evans blue dye-albumin complex from the brain microvasculature. Gross examination of vibratome sections processed to reveal HRP reaction product exhibited multiple microfoci of HRP extravasation. Electron microscopic observations of the heat-stressed tissues revealed HRP reaction product within pinocytotic vesicles, tubulo-vesicular complexes, transendothelial channels and occasionally flooded within the cytoplasm of endothelial cells. HRP reaction product could clearly be seen in the basal laminae of the capillaries and in the surrounding neuropil. This study demonstrates that blood-brain barrier permeability to HRP is increased in response to heat stress and introduces a new, reproducible model of blood-brain barrier disruption.

Histamine modulates heat stress-induced changes in blood-brain barrier permeability, cerebral blood flow, brain oedema and serotonin levels: an experimental study in conscious young rats

The possibility that endogenous histamine plays an important role in modulating the pathophysiology of heat stress was examined in young rats using a pharmacological approach. Subjection of young animals (six to seven weeks old) to heat stress at 38 degrees C for 4 h in a biological oxygen demand incubator (relative humidity 47-50%, wind velocity 20-25 cm/s) resulted in a profound increase in blood-brain barrier permeability to Evans Blue albumin (whole brain 375%) and [131I]sodium (whole brain 478%) along with a significant reduction in the cerebral blood flow (mean 34%). The water content of the whole brain was elevated by 4.5% (about 19% volume swelling) from the control. At this time-period, the plasma and whole brain 5-hydroxytryptamine levels were elevated by 656% and 328%, respectively, from the control group. Pretreatment with cimetidine (a histamine H2 receptor antagonist) significantly thwarted the increases in the brain water content and the blood-brain barrier permeability. In cimetidine-pretreated animals, the cerebral blood flow was significantly elevated and the plasma and brain 5-hydroxytryptamine (serotonin) levels were slightly but significantly reduced as compared with the untreated stressed group. However, prior treatment with mepyramine (a histamine H1 receptor antagonist) neither attenuated the changes in water content and the blood-brain barrier permeability nor altered the cerebral blood flow and 5-hydroxytryptamine levels. In fact, there was a significantly higher permeation of the tracers across the cerebral vessels in these drug-treated animals along with a greater accumulation of the brain water content as compared with the untreated stressed group. The cerebral blood flow and 5-hydroxytryptamine levels showed only minor changes from the untreated stressed group. These results show, probably for the first time, that (i) the endogenous histamine plays an important role in the pathophysiology of heat stress, and (ii) this effect appears to be mediated via specific histamine H2 receptors.

Acute systemic heat stress increases glial fibrillary acidic protein immunoreactivity in brain: experimental observations in conscious normotensive young rats

The possibility that astrocytes participate in the pathophysiology of thermal brain injury caused by systemic heat exposure was examined in conscious young rats. The temporal and regional pattern of the astrocytic response to thermal injury was characterized by demonstrating the immunoreactivity of glial fibrillary acidic protein (GFAP) using monoclonal antibody and avidin-biotin complex technique. Exposure of conscious young animals to heat at 38 degrees C for 4 h in a biological oxygen demand incubator resulted in a marked increase of the GFAP immunoreactivity in specific brain regions as compared with the intact controls. The intensity of the increased GFAP immunoreactivity was mainly noted in pons, medulla and cerebellum, followed by thalamus, hypothalamus, hippocampus and caudate nucleus. The cerebral cortex of heat-exposed animals showed only a mild increase in GFAP immunoreactivity which was predominantly concentrated in cingulate, parietal and pyriform cortices. The immunostaining in general was seen in the perivascular glia, within the neuropil and the glia limitans. This increase in GFAP immunoreactivity was absent in animals exposed to the same ambient temperature (38 degrees C) for 1 h and 2 h, or at a lower temperature (36 degrees C) for 4 h. These results show that (i) astrocytes actively participate in the pathophysiology of heat stress, (ii) endogenous thermal brain injury elicits activation and hypertrophy of astrocytes ("reactive gliosis") depending on the magnitude and duration of the ambient heat stimulus, and (iii) the astrocytic reaction (observed as increased GFAP immunostaining) could be induced much more rapidly within a very short survival period of 4 h, not reported earlier.

Age-related pathophysiology of the blood-brain barrier in heat stress

The possibility that the blood-brain barrier (BBB) might play an important role in the pathophysiology of heat stress (HS) has been examined in young (age 8-9 weeks) and adult (age 24-32 weeks) rats. Exposure of young rats to 4 h HS at 38 degrees C in a biological oxygen demand (BOD) incubator (relative humidity 47-50%, wind velocity 20-26 cm/sec, simulating the environmental conditions of Varanasi, India, during the month of June) resulted in a marked hyperthermia (41.7 +/- 0.23 degrees C) and behavioral symptoms. In these animals there was a profound increase in the permeability of the BBB to Evans blue-albumin (EBA) (464%) and to 131I-sodium iodide (515%), accompanied by a marked increase in the brain water content (4%), of the levels of serotonin (5-hydroxytryptamine, 5-HT) in plasma (687%) and in brain (267%) and a pronounced reduction (30%) in cerebral blood flow (CBF). Morphological examination using light- and electron-microscopy revealed profound neuronal changes associated with a marked increase in glial fibrillary acidic protein (GFAP) and in vimentin immunoreactivities, together with a substantial reduction in myelin basic protein (MBP) immunostaining in the brain. These changes were more pronounced in the brain-stem reticular formation, pons and medulla region. On the other hand, exposure of adult animals to the same intensity of HS resulted in mild or no changes in BBB permeability, content of brain water and 5-HT in the plasma and brain, CBF or other cellular changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of traumatic spinal cord edema using evoked potentials recorded from the spinal epidural space. An experimental study in the rat

Spinal cord evoked potentials (SCEP) elicited by simultaneous distal tibial and sural nerve stimulation were continuously recorded from the epidural space at the T9 and T12 levels of urethane anaesthetized rats before and after a unilateral incision (about 3 mm deep and 5 mm long) in the right dorsal horn of the T10-11 segments. The changes in SCEP were correlated with the increase in spinal cord water content measured 5 h after injury. In addition, the influence of serotonin (5-HT) in mediating such changes was explored using a pharmacological approach. The changes in SCEP immediately after injury correlated well with development of spinal cord edema measured 5 h after injury. Thus, the maximal negative peak (MNP) amplitude of SCEP decreased by an average of 64.0% immediately after injury and the water content of the spinal cord was increased from 71.6% (controls) to 77.6% 5 h after injury. Pretreatment with p-CPA (a serotonin synthesis inhibitor) prevented the initial decrease of the MNP amplitude and also the increase of water content (72.5%). On the other hand, pretreatment with cyproheptadine (a 5-HT2 receptor antagonist) enhanced both the initial decrease of the MNP amplitude as well as the increase of water content (81.3%). The results show a good correlation between changes of SCEP immediately after injury and the magnitude of spinal cord edema (r = 0.9) measured 5 h after injury. The findings reveal a major role of serotonin in mediating early changes of SCEP and later development of spinal cord edema and demonstrate a prognostic value of early SCEP recordings in predicting the final outcome of traumatic spinal cord injuries.

Role of histamine in pathophysiology of heat stress in rats

Role of histamine in pathophysiology of heat stress (HS) was examined using a pharmacological approach. Subjection of young animals (6-7 wks old) to HS at 38 degrees C for 4 in a B.O.D. incubator resulted in a profound increase in blood-brain barrier (BBB) permeability to Evans blue albumin (EBA) and 131I-sodium by 375% and 478% from the control values respectively. At this time period, the brain water content showed a 3.6% increase from the control. Pretreatment with histamine H2 receptor antagonist cimetidine significantly reduced the extravasation of both the tracers and thwarted the increase of brain water content as compared to the untreated group. On the other hand, pretreatment with histamine H1 antagonist mepyramine failed to reduce these parameters. On the contrary, there was a significantly higher permeation of the tracers in brain along with a greater accumulation of brain water content as compared to the untreated group. These results point out a beneficial effect of histamine H2 receptor antagonists in the pathophysiology of HS.

Changes in blood-brain barrier and cerebral blood flow following elevation of circulating serotonin level in anesthetized rats

Plasma serotonin (5-HT) was elevated by an intravenous infusion of this amine into urethane-anaesthetized rats and the concentration approximated that present in various neurological diseases and mental abnormalities. An infusion of 10 micrograms per kg body weight for 10 min significantly increased blood-brain barrier (BBB) permeability to Evans blue and 131I-sodium measured in whole brain. Regional BBB determinations with labelled 131I-sodium showed that the permeability to this compound was increased in the cerebral cortex, hippocampus, caudate nucleus, hypothalamus, colliculus and the cerebellum but not in the pons and the medulla oblongata. Regional blood flow was reduced in the same parts which showed BBB abnormality tested with 125I-labeled microspheres. Pretreatment with cyproheptadine, a 5-HT2 receptor antagonist, prevented the BBB increase and the regional blood flow was near normal values. Similar effects were obtained with indomethacin, a prostaglandin synthesis inhibitor. Vinblastine, known to influence vesicular transport, eliminated extravasation of the tracers but the regional blood flow remained depressed. A hypothesis is put forward that serotonin after binding to its receptor in the cerebral vessels stimulates prostaglandin which either directly or by means of cyclic adenosine monophosphate causes an increased vesicular transport across the endothelial cells and thus an extravasation of tracer substances in the brain. Obviously, this form of exudation can be influenced by pharmacological means.

Effects of p-chlorophenylalanine on microvascular permeability changes in spinal cord trauma. An experimental study in the rat using 131I-sodium and lanthanum tracers

The possibility that serotonin can take part in the initiation of the increased microvascular permeability occurring in a spinal cord trauma was investigated in a rat model with 131I-sodium and lanthanum as tracers. We influenced the serotonin content in the tissue pharmacologically by treating animals with a serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA), before the production of the injury and compared the results with injured, untreated controls. A small incision was made in the dorsal horn of the lower thoracic cord. It caused a progressive extravasation of 131I-sodium in the damaged segment, measured after 1, 2 and 5 h. Rostral and caudal segments also showed a significant but lower accumulation of 131I-sodium. Lanthanum added to the fixative was used as an ionic tracer detectable by electron microscopy. The endothelial cells of microvessels removed from the perifocal region after 5 h showed a marked increase in the number of lanthanum-filled vesicles. Many endothelial cells had a diffuse penetration of the tracer into the cytoplasm and the basement membrane. However, the tight junctions usually remained closed to lanthanum. Pretreatment with p-CPA markedly reduced the extravasation of 131I-sodium measured at 5 h in the traumatized cord. At the cellular level, the endothelial vesicles filled with lanthanum approached the condition of uninjured animals. The diffuse infiltration of lanthanum into endothelial cells and its spread into the basement membrane of the vascular wall were usually absent. Our results indicate that serotonin plays a role in the initiation of the increased microvascular permeability which occurs in spinal cord injuries.

Edema formation and cellular alterations following spinal cord injury in the rat and their modification with p-chlorophenylalanine

The possibility that serotonin can modify the early pathological sequences occurring in spinal cord trauma was investigated in a rat model. To that end we took advantage of the possibility of influencing serotonin pharmacologically by treating animals with a serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA) before the production of the injury and compared the results with injured, untreated controls. A unilateral incision was made into the dorsal horn of the lower thoracic cord (about 2.5 mm deep, 4.5 mm long) and the rats were allowed to survive up to 5 h after the trauma. The injured region from untreated animals showed macroscopically at that time a pronounced swelling and the water content had increased by 3.5% as compared to intact controls. The segments rostral and caudal to the lesion also exhibited a profound increase in water content. Light microscopy revealed a significant expansion of the spinal cord as compared to controls. The swelling was most pronounced in the gray matter on the injured side. Electron microscopy showed distorted neurons, swollen astrocytes and extracellular edema in the gray matter in and around the primary lesion. There was also a sponginess in the surrounding white matter with disruption of myelin, collapsed axons and widened periaxonal spaces. Pretreatment of the rats with p-CPA significantly reduced the swelling of the injured spinal cord and there was no visible expansion. The ipsilateral edema in the central gray matter was considerable less pronounced as compared to that in untreated animals. The increase in water content was less than 1% in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain oedema and cellular changes induced by acute heat stress in young rats

Exposure of young animals (70-80 g, Age 6-7 weeks) to heat stress (HS) at 38 degrees C for 4 h in a B.O.D. incubator (rel humid 50-55%, wind vel 28.6 cm/sec) resulted in a 4.41% increased brain water content from the control value. Morphological studies in parietal cerebral cortex at light microscopical level revealed chromatolysis and appearance of dark neurons. Electron microscopy of similar regions showed perivascular oedema, vacuolation and collapsed microvessels. The swelling of astrocytes and of postsynaptic membranes was frequent. A diffuse infiltration of lanthanum (La[NO3]3) in endothelial cell cytoplasm and in the vesicles was very common. Occasionally, the lanthanum was seen in the basement membrane but the tight junctions were mainly intact. At this time period, a significant increase in blood-brain barrier (BBB) permeability as well as 5-HT levels in brain and plasma were observed. Pretreatment with p-CPA (a 5-HT synthesis inhibitor) prevented the increase of brain water content. BBB permeability and 5-HT levels in brain and plasma. Cyproheptadine (a 5-HT2 receptor antagonist) treatment significantly reduced the occurrence of increased brain water content and the BBB permeability. The 5-HT level continued to remain high. These results point out a probable role of 5-HT in pathophysiology of HS via 5-HT2 receptors.

Early accumulation of serotonin in rat spinal cord subjected to traumatic injury. Relation to edema and blood flow changes

Changes in the concentration of serotonin (5-hydroxytryptamine) in the early period after a focal traumatic injury to rat spinal cord were determined and related to the formation of edema and alterations in blood flow. A unilateral, 5-mm-long and 3-mm-deep traumatic injury located 2 mm from the midline was created in the T10-11 segment of the cord. Five hours after the injury the serotonin concentration in the traumatized segment had increased more than 100% compared with controls. There was also a progressive increase in water content of the traumatized segment measured 1-5 h after the injury. On the other hand, the spinal cord blood flow showed a progressive decrease to about 35% of its initial value at 5 h. Pretreatment with p-chlorophenylalanine, a serotonin synthesis inhibitor, impeded the elevation in water content measured 5 h after the trauma. The spinal cord blood flow remained close to normal values and the increase in serotonin was absent. Our results show that trauma to the rat spinal cord will induce changes in the serotonin concentration of the tissue and that the associated formation of edema and blood flow alterations can be alleviated in serotonin depleted rats. Obviously, serotonin plays a significant role in the pathophysiology of traumatic injury of rat spinal cord.

Role of histamine in traumatic brain edema. An experimental study in the rat

The possibility that histamine plays a role in the formation of traumatic brain edema was investigated in the rat. A 3 mm deep and 3 mm long stab injury was performed in the right parietal cortex under urethane anaesthesia. The brain water content and histamine levels in plasma and brain were measured at the end of 1, 2 and 5 h periods after trauma. There was a 3.46% increase in brain water content in the traumatized hemisphere from the value in the control group at 5 h. The histamine content was increased by 107% in plasma and 51% in the traumatized brain hemisphere from the control value at this time period. The increased brain water content as well as the elevated plasma and brain histamine levels were prevented by prior treatment with the histamine H2-receptor antagonist cimetidine. Mepyramine (a histamine H1-receptor antagonist) failed to reduce the increased brain water content and the histamine levels in plasma and brain remained high. The results strongly indicate that histamine has a role in the formation of early traumatic brain edema and that this reaction can be influenced by pharmacological procedures.