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The potential efficacy of indomethacin (a potent inhibitor of endogenous prostaglandin synthesis) on spinal cord-evoked potentials and edema formation occurring after a focal trauma to the spinal cord was examined in a rat model. The spinal cord evoked potentials were recorded in urethane-anesthetized male rats using monopolar electrodes placed epidurally over the T9 (rostral) and T12 (caudal) segments after stimulation of the ipsilateral right tibial and sural nerves. Reference electrodes were placed in the corresponding paravertebral muscles. The spinal cord evoked potential consisted of a small positive peak followed by a broad and high negative peak. Amplitudes and latencies of the maximal positive peak and the maximal negative peak were measured. The latencies and amplitudes 30 min before injury were used as references (100%). A complete loss was denoted as 0%. All the potentials were quite stable during 30 min of recording before injury. Infliction of trauma to the T10-T11 segments of the spinal cord with a sterile scalpel blade (about 5 mm longitudinal and 2 mm deep incision into the right dorsal horn extending to Rexed's laminae VII) in untreated animals resulted in an immediate depression of the rostral maximal negative peak amplitude (60-100%) which persisted during 5 h of recording. The latencies of the rostral as well as caudal maximal negative and positive peaks increased successively from 2 h post-trauma. In this group of animals, 5 h after injury the spinal cord water content in the traumatized segments was increased by more than 6% as compared with a group of uninjured animals. Pretreatment with indomethacin (10 mg/kg body weight i.p. 30 min before injury) markedly attenuated the immediate decrease in the maximal negative peak amplitude after injury, but did not influence the successive latency increase. However, the increase in the water content of the traumatized cord after 5 h was less pronounced compared with untreated injured rats. Our results show a beneficial effect of indomethacin on trauma-induced spinal cord evoked potential changes and edema formation. Prostaglandins may thus influence early bioelectrical changes occurring in traumatized spinal cord not reported earlier. The findings support the view that early recording of spinal cord evoked potential may be useful to predict the outcome in some forms of spinal cord injuries.

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.

The potential neuroprotective efficacy of dynorphin A antiserum on BBB dysfunction, edema formation and brain pathology was examined in a closed head injury (CHI) model in the rat. The CHI was produced by an impact of 0.224 N on the right parietal bone under anesthesia by dropping a weight of 114.6 g on the skull from a height of 20 cm through a guide tube. This concussive brain injury resulted in profound BBB disruption as evidenced by leakage of Evans blue and radioiodine in the brain. Edema formation and swelling at 5 h were most pronounced in the contralateral cerebral hemisphere. Pretreatment with dynorphin A antiserum (1:20, monoclonal) infused into the left lateral cerebral ventricle (30 microL in PBS) either 30 min before or 30 min after CHI significantly attenuated BBB dysfunction, brain edema formation, volume swelling and brain pathology. However, no reduction in brain edema, BBB permeability or improved brain pathology was seen when the antiserum was given 60 min post-CHI. These observations are the first to suggest that antiserum to dynorphin when administered into the CSF during early phase of CHI is neuroprotective. Our work further indicates that dynorphin is actively involved in the cellular and molecular mechanisms of edema formation and BBB breakdown in CHI.

The permeability of blood vessels in rat spinal nerve roots was investigated with Evans blue-albumin as an in vivo macromolecular tracer and lanthanum nitrate as an electron microscopic ionic marker added to a fixative. Rats injected intravenously with Evans blue, showed macroscopic distinct staining of dorsal root ganglia, whereas spinal nerve roots remained unstained. Fluorescence microscopy, however, revealed clear extravascular fluorescence both in ventral and dorsal roots 2 or 18 h after tracer administration. Two different types of blood vessels exists in spinal nerve roots; large extrinsic (radicular) in the root sheath and minute intrinsic vessels in the parenchyma. Lanthanum added to a fixative, perfused through the vessels was detected in the lumen of both types of vessels, usually adhering to the luminal plasma membrane and in many invaginations from that membrane. Lanthanum also entered the clefts between endothelial cells but was always stopped at the junctions which are, thus, of the tight type. Diffuse penetration of the compound into the cytoplasm was seen in one endothelial cell, but no fenestrations were detected. Junctions between the endothelial cells of vessels in rat spinal nerve roots are impermeable to lanthanum and most likely also to other large molecular substances like albumin. Thus, probable routes for serum albumin to enter the nerve roots, where it normally is present, must be either by centripetal extracellular diffusion from the ganglia and the peripheral nerve or by vascular leakage in the roots, caused by for instance pinocytosis across endothelial cells.

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 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. The neuronal and glial cell changes were also markedly reduced in the drugtreated rats. The disruption of myelin and the vacuolation of the gray matter were much less severe. Our results show that p-CPA can markedly modify the edema and the cellular changes occurring in the traumatic spinal injury and indicate that serotonin is somehow involved in the production of the early, and thus important, pathological events.

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.

The role of heme oxygenase (HO) in closed head injury (CHI) was examined using a potent HO and guanylyl cyclase inhibitor, zinc protoporphyrin (Zn-PP) in the rat. Blood-brain barrier (BBB) permeability to Evans blue and radioiodine, edema formation, and plasma and brain levels of serotonin were measured in control, CHI, and Zn-PP-treated CHI rats. CHI was produced by an impact of 0.224 N on the right parietal bone by dropping 114.6 g weight from a height of 20 cm in anesthetized rats. This concussive injury resulted in edema formation and brain swelling 5 hours after insult that was most pronounced in the contralateral hemisphere. The whole brain was edematous and remained in a semi-fluid state. Microvascular permeability disturbances to protein tracers were prominent in both cerebral hemispheres and the underlying cerebral structures. Plasma and brain serotonin showed pronounced increases and correlated with edema formation. Pretreatment with Zn-PP (10 mg/ kg, i.p) 30 minutes before or after CHI attenuated edema formation, brain swelling, plasma and brain serotonin levels, and microvascular permeability at 5 hours. Brain edema, BBB permeability, and serotonin levels were not attenuated when the compound was administered 60 minutes post-CHI suggesting that HO is involved in cellular and molecular mechanisms of edema formation and BBB breakdown early after CHI.

The role of histamine in edema formation, blood-spinal cord barrier (BSCB) permeability, and spinal cord blood flow (SCBF) following spinal cord injury (SCI) was examined using modulation of histamine H1, H2, and H3 receptors in the rat. Focal trauma to the spinal cord at the T10-11 level significantly increased spinal cord edema formation, BSCB permeability to protein tracers and SCBF reduction in the T9 and T12 segments. Pretreatment with histamine H1 receptor antagonist mepyramine (1 mg, 5 mg, and 10 mg/kg, i.p.) did not attenuate spinal pathophysiology following SCI. Blockade of histamine H2 receptors with cimetidine or ranitidine (1 mg, 5 mg, or 10 mg/kg 30 minutes before injury) significantly reduced early pathophysiological events in a dose dependent manner. The effects of ranitidine were far superior to cimetidine in identical doses. Pretreatment with a histamine H3 receptor agonist alpha-methylhistamine (1 mg and 2 mg/kg/i.p.), that inhibits histamine synthesis and release in the CNS, thwarted edema formation, BSCB breakdown, and SCBF disturbances after SCI. The lowest dose of histamine H3 agonist was most effective. Blockade of histamine H3 receptors with thioperamide (1 mg, 5 mg/kg, i.p.) exacerbated spinal cord pathology. These observations suggest that stimulation of histamine H3 receptors and blockade of histamine H2 receptors is neuroprotective in SCI.

The possibility that a chronic nerve ligation impairs the spinal cord cellular microenvironment was examined using leakage of endogenous albumin, reaction of astrocytes, and structural changes in a rat model. Rats subjected to 8 weeks of unilateral L4/L5 nerve ligation (a model of neuropathic pain) showed leakage of albumin, up-regulation of glial fibrillary acidic protein (GFAP) immunoreaction, and abnormal cell reaction. Distortion and loss of nerve cells as well as general sponginess of the gray matter was clearly evident. Cell changes were present in both dorsal and ventral horns and were most marked on the ipsilateral side compared to the contralateral cord. Nerve cell and glial cell changes are normally present in the regions showing intense albumin immunoreactivity, indicating disruption of the blood-spinal cord barrier (BSCB). Our observations indicate that a chronic nerve lesion has the capacity to induce selective breakdown of the BSCB that could be responsible for activation of astrocytes and abnormal cell reaction. These findings enhance our understanding of the pathophysiology of neuropathic pain and/or other spinal cord disorders.

Previous investigations from our laboratory show that up-regulation of neuronal nitric oxide synthase (NOS) following spinal cord injury (SCI) is injurious to the cord. Antiserum to dynorphin A (1-17) induces marked neuroprotection in our model of SCI, indicating an interaction between dynorphin and NOS regulation. The present investigation was undertaken to find out whether topical application of dynorphin A (1-17) antiserum has some influence on neuronal NOS up-regulation in the traumatized spinal cord. SCI was produced in anesthetized animals by making a unilateral incision into the right dorsal horn of the T10-11 segments. The antiserum to dynorphin A (1-17) was applied (1 : 20, 20 microL in 10 seconds) 5 minutes after trauma over the injured spinal cord and the rats were allowed to survive 5 hours after SCI. Topical application of dynorphin A (1-17) antiserum significantly attenuated neuronal NOS up-regulation in the adjacent T9 and T12 segments. In the antiserum-treated group, spinal cord edema and cell injury were also less marked. These observations provide new evidence that the opioid active peptide dynorphin A may be involved in the mechanisms underlying NOS regulation in the spinal cord after injury, and confirms our hypothesis that up-regulation of neuronal NOS is injurious to the cord.

We examined the potential efficacy of brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF) applied over traumatized spinal cord, alone or in combination, for attenuating motor dysfunction, blood-spinal cord barrier (BSCB) breakdown, edema formation, and cell injury in a rat model. Under Equithesin anesthesia, spinal cord injury (SCI) was performed by making a unilateral incision into the right dorsal horn of the T10-11 segment. The rats were allowed to survive 5 hours after trauma. The BDNF or GDNF was applied (0.1 to 1 microg/10 microl in phosphate buffer saline) 30, 60, or 90 minutes after SCI. Topical application of BDNF or GDNF 30 minutes after SCI in high concentration (0.5 microg and 1 microg) significantly improved motor function and reduced BSCB breakdown, edema formation, and cell injury at 5 hours. These beneficial effects of neurotrophins were markedly absent when administered separately either 60 or 90 minutes after injury. However, combined application of BDNF and GDNF at 60 or 90 minutes after SCI resulted in a significant reduction in motor dysfunction and spinal cord pathology. These novel observations suggest that neurotrophins in combination have potential therapeutic value for the treatment of SCI in clinical situations.

The neuroprotective efficacy of post-injury treatment with the antioxidant compound H-290/51 (10, 30, and 60 minutes after trauma) on immediate early gene expression (c-fos), blood-spinal cord barrier (BSCB) permeability, edema formation, and motor dysfunction was examined in a rat model of spinal cord injury (SCI). SCI was produced by a longitudinal incision into the right dorsal horn of the T10-11 segment under Equithesin anesthesia. Focal SCI in control rats resulted in profound up-regulation of c-fos expression, BSCB dysfunction, edema formation, and cell damage in the adjacent T9 and T12 segments at 5 hours. Pronounced motor dysfunction was present at this time as assessed using the Tarlov scale and the inclined plane test. Treatment with H-290/51 (50 mg/kg, p.o.) 10 and 30 minutes after SCI (but not after 60 minutes) markedly attenuated c-fos expression and motor dysfunction. In these groups, BSCB permeability, edema formation, and cell injuries were mildly but significantly reduced. These observations suggest that (i) antioxidants are capable of attenuating cellular and molecular events following trauma, and (ii) have the capacity to induce neuroprotection and improve motor function if administered during the early phase of SCI, a novel finding.

The possibility that the upregulation of hemeoxygenase (HO) enzyme responsible for carbon monoxide (CO) formation in the spinal cord following trauma is involved in edema formation and cell damage was examined in a rat model. A focal trauma to the rat spinal cord by making an incision into the right dorsal horn of the T10-11 segment resulted in profound upregulation of HO-2 (the constitutive isoform of the enzyme) expression in the T9 and T12 segments 5 h after injury. In these segments a marked increase in edema formation, nerve cell damage, and expression of heat shock protein (HSP 72) were observed. Pretreatment with p-chlorophenylalanine (p-CPA, a serotonin synthesis inhibitor) significantly attenuated the trauma induced edema formation, cell injury, and HSP expression. Upregulation of HO-2 in p-CPA treated traumatised rats was considerably reduced. These observations suggest that (i) spinal cord injury has the capacity to induce an upregulation of HO-2 and HSP expression, (ii) abnormal production of CO as reflected by HO-2 expression is injurious to the cord, and (iii) that endogenous serotonin is involved in HO-2 expression in the cord.

The influence of the potent L-type Ca[2+] channel antagonist Nimodipine on spinal cord evoked potentials (SCEP) and axonal injury following trauma to the spinal cord was examined in a rat model. Spinal cord injury (SCI) was produced by an incision into the right dorsal horn of the T10-11 segments under urethane anaesthesia (1.5 g/kg, i.p.). SCEPs were recorded by epidural electrodes placed over the T9 (rostral) and T12 (caudal) segments after stimulation of the right tibial and sural nerves. SCI induced a pronounced decrease of the SCEP negative amplitude in the rostral (T9) recordings immediately after trauma. Axonal injury seen as degradation of myelin basic protein (MBP) immunostaining and myelin vesiculation at the ultrastructural level was most pronounced at 5 h. Continuous administration of Nimodipine (2 microg/kg/min, i.v.) from 30 min prior to injury until sacrifice markedly attenuated the changes in SCEP amplitude and latency. Axonal damage, loss of MBP, and myelin vesiculation were much less evident in the nimodipine treated traumatised rats. These observations suggest that Ca[2+] channels play an important role in the trauma induced alterations in SCEP and axonal injury, and indicate a therapeutic value of Ca[2+] blockers in SCI.

The possibility that antiserum to tumour necrosis factor-alpha (TNF-alpha) is neuroprotective in spinal cord injury (SCI) was examined in a rat model. SCI was produced by making an incision into the right dorsal horn at the T10-11 segments. Top TNF-alpha antiserum at three concentrations (1:10; 1:50 and 1:100) given 30 min before or 2 min, 5 min or 10 min after trauma resulted in marked reduction in visible swelling, edema formation, and leakage of radiolabelled iodine tracer within the T9 and T12 segments at 5 h in a dose dependent manner. This neuroprotective effect was most pronounced when the antiserum at the highest dose level (1:10) was applied 10 min after SCI. The TNF-alpha antiserum also reduced the SCI induced upregulation of neuronal nitric oxide synthase (nNOS) immunoreactivity in a concentration dependent manner. Taken together, these results suggest that local application of TNF-alpha antiserum is neuroprotective in SCI and that this effect is mediated through NOS regulation.

The role of oxidative stress in spinal cord injury (SCI) induced upregulation of constitutive or inducible isoforms of nitric oxide synthase (cNOS or iNOS) is not well known. The present investigation was undertaken to examine the influence of an antioxidant compound H-290/51 (Astra-Zeneca, Mölndal, Sweden) on SCI induced cNOS and iNOS upregulation in a rat model. SCI induced by incision into the right dorsal horn of the T10-11 segment resulted in marked NOS upregulation. Upregulation of cNOS was most prominent in the uninjured T9 and T12 segments. On the other hand, iNOS expression was most marked in the injured T10-11 segments. These NOS immunoreactivities were mainly confined to the injured cells located in the edematous regions of the cord exhibiting profound leakage of Evans blue and [131]Iodine-sodium tracers. Pre-treatment with H-290/51 markedly attenuated the trauma-induced cNOS and iNOS expression along with the microvascular permeability disturbances, edema formation and cell injury. These results suggest that (i) oxidative stress is involved in SCI induced induction of cNOS and iNOS, (ii) NO plays an important role in the cord pathology, and (iii) that the compound H-290/51 has a potential therapeutic value in SCI.

The possibility that five new low molecular weight compounds with varying affinity and selectivity to the melanocortin receptors will exert neuroprotective effects in the spinal cord injury (SCI) induced edema formation and cell damage was examined in a rat model. A focal trauma of the rat spinal cord made by an incision into the right dorsal horn (T10-11) resulted in profound edema formation, leakage of Evans blue albumin and cell injury of the T9 segment at 5 h. Topical application of the Melacure compound ME10501 in high doses (10 microg in 10 microl) given 5 min after SCI resulted in most significant neuroprotection of the T9 segment of the cord compared to other compounds. Thus, marked reduction in water content, leakage of Evans blue albumin, and cell injury were observed in ME10501 treated traumatised rats. These observations suggest that the non-peptide compound ME10501 with affinity to the melanocortin receptor MC4 is capable to induce neuroprotection in the spinal cord following trauma not reported earlier.

Alterations of the blood-spinal cord barrier (BSCB) following spinal cord injury (SCI) and leakage of serum proteins induce vasogenic edema and cell damage. The possibility that two members of the neurotrophin family, BDNF or IGF-1 induce neuroprotection by attenuating the BSCB permeability following trauma was examined in a rat model. Repeated topical application of BDNF or IGF-1 (0.1 1microg, 0.5 microg or 1 microg in 10 microl) onto the spinal cord 30 min before SCI or 2, 5, 10 or 30 min thereafter significantly attenuated BSCB permeability to Evans blue and iodine. In the neurotrophin treated rats. edema formation, degradation of MBP, and myelin vesiculation were much less frequent compared to the untreated traumatised rats. The protective effect of BDNF and IGF-1 was most pronounced at the high dose (1 microg in 10 microl) given either 30 min before or within 10 min after SCI. The observations suggest that early intervention with neurotrophins in high doses following trauma (within 10 min) attenuates disturbances of the fluid microenvironment of the spinal cord. This indicates that BSCB opening plays an important role in SCI induced myelin vesiculation and cord pathology.

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.

The neuroprotective efficacy of growth hormone on a focal spinal cord trauma induced alteration in the blood-spinal cord barrier (BSCB) and edema formation was examined in a rat model. Under Equithesin anaesthesia, one segment laminectomy was done over the T10-11 segments. Spinal cord injury was produced by making an incision into the right dorsal horn of the T10-11 segments (2 mm deep and 4 mm long). The animals were allowed to survive 5 h after injury. Highly purified rat growth hormone [rGH, 25 microl of a 1microg/ml solution) was applied over 10 sec topically on the exposed surface of the spinal cord 30 min before injury. The identical doses of the rGH were repeated 0 min, 30 min, 60 min, 120 min, 180 min and 240 min following injury. Saline (0.9% NaCl) treated traumatised rats at identical intervals served as controls. Traumatised rats treated with saline exhibited marked edema formation and extravasation of Evans blue and ([125])Iodine tracers in the spinal cord. At the ultrastructural level, perivascular edema and exudation of lanthanum across the endothelial cells was quite frequent in the spinal cord. Pretreatment with rGH significantly attenuated the edema formation and the extravasation of tracers in the spinal cord. In these rats, perivascular edema and infiltration of lanthanum across the endothelial cells was not much evident. These observations show that the rGH has the capacity to reduce the early manifestations of microvascular permeability disturbances and edema formation following trauma and further suggest a possible therapeutic potential of the hormone for the treatment of spinal cord injuries.

Dynorphin is a neuropeptide that is present in high quantities in the dorsal horn of the spinal cord. The peptide is actively involved in pain processing pathways. However, its involvement in spinal cord injury is not well known. Alteration in dynorphin immunoreactivity occurs following a focal trauma to the rat spinal cord. Infusion of dynorphin into the intrathecal space of the cord results in ischemia, cell damage and abnormal motor function. Antibodies to dynorphin when injected into the intrathecal space of the spinal cord following trauma improve motor recovery, reduce edema and cell changes. However, influence of dynorphin on trauma induced alteration in spinal cord bioelectrical activity is still not known. Spinal cord evoked potentials (SCEP) are good indicator of spinal cord pathology following trauma. Therefore, in present investigation, influence of dynorphin antibodies on trauma induced changes in SCEP were examined in our rat model. In addition, spinal cord edema formation, microvascular permeability disturbances and cell injury were also investigated. Our results show that topical application of dynorphin antiserum (1 : 200) two min before injury markedly attenuated the SCEP changes immediately after injury. In the antiserum treated animals, a significant reduction in the microvascular permeability, edema formation and cell injury was observed in the traumatised spinal cord. These observations suggest that (i). dynorphin is involved in the altered bioelectrical activity of the spinal cord following trauma, (ii). the peptide actively participates in the pathophysiological processes of cell injury in the spinal cord trauma, and (iii). the dynorphin antiserum has potential therapeutic value for the treatment of spinal cord injuries.

Endothelin-1 (ET-1), a 21 amino acid peptide exerts a wide range of biological activities including vasoconstriction, mitogenesis and inotropic effects on the heart. In this study, we examined whether endocardial endothelial cells express ET-1 and evaluated its functional properties. Using immunofluorescence localization method, we demonstrated cytoplasmic staining of ET-1 in the human endocardial endothelial cells from the right atrium and left ventricle. Employing reverse transcriptase polymerase chain reaction (RT-PCR) expression of ET-1 mRNA and its receptors ET(A) and ET(B) mRNAs were found in human myocardial as well as in endocardial endothelial cells. Biological activity of endocardial endothelial cells derived ET-1 was established as the conditioned media obtained from cultured porcine endocardial endothelial cells induced a slowly developing, strong and long-lasting contraction of circular rat aortic segments, with similar characteristics to that obtained with exogenous ET-1. Furthermore, the selective endothelin-A receptor antagonist, FR 139317, blocked the conditioned media induced contractions. Our results suggest that endocardial endothelial cells express and release biologically active ET-1 which could play a pivotal role in the regulation of myocardial contractility as well as a circulatory peptide may further act in other peripheral target organs.

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.

Influence of serotonin on upregulation of cellular-fos (c-fos) following a focal spinal cord injury was examined using immunohistochemistry in a rat model. Spinal cord injury was produced by making a unilateral longitudinal incision of the dorsal horn of the T10-11 segments. A focal lesion to the cord markedly upregulated c-fos immunohistochemistry at 5 h which was mainly located in the edematous regions of the cord in the injured as well as in the perifocal T9 and T12 segments. Pretreatment with p-CPA, a serotonin synthesis inhibitor, significantly attenuated the c-fos upregulation along with the edematous expansion of the cord. These results for the first time suggest that trauma induced release of serotonin and edema formation are important biological signals inducing c-fos expression.

Influence of brain derived neurotrophic factor (BDNF) and insulin like growth factor-1 (IGF-1) on spinal cord injury induced disturbances in spinal cord conduction, edema formation and cellular stress response was examined in a rat model. Pretreatment with BDNF or IGF-1 significantly attenuated the loss of SCEP negative amplitude seen immediately after spinal cord injury. In these neurotrophins treated rats, upregulation of heat shock protein (HSP 72 kD) immunoreactivity, a measure of cellular stress response and spinal cord edema formation were considerably reduced 5 h after injury. These results suggest that neurotrophic factors improve spinal cord conduction after trauma and this beneficial effect of growth factors may be related with their ability to attenuate trauma induced cellular stress response, not reported earlier.

Influence of brain derived neurotrophic factor (BDNF) on carbon monoxide (CO) production following spinal cord injury was examined using expression of the constitutive isoform of the enzyme hemeoxygenase-2 (HO-2) in a rat model. A longitudinal incision of the right dorsal horn on the T10-11 segment markedly increased the HO-2 immunostaining in the cord at 5 h. At this time period, breakdown of the blood-spinal cord barrier (BSCB) and edema formation were quite prominent. Repeated topical application of BDNF (20 microliters of a 1 microgram/ml solution) over the exposed surface of the cord significantly attenuated the edematous expansion of the cord and the disturbances in the BSCB permeability. In BDNF-treated rats, expression of HO-2 immunoreactivity was considerably reduced. These results strongly suggest that BDNF is neuroprotective in spinal trauma and this growth factor has the capacity to attenuate CO production by downregulating HO-2 expression.

Influence of a new antioxidant compound H-290/51 on carbon monoxide (CO) production following spinal cord injury was examined using immunohistochemistry of the constitutive isoform of heme oxygenase-2 (HO-2) in a rat model. Subjection of rats to 5 h spinal cord injury by making an incision into the right dorsal horn of the T10-11 segments resulted in upregulation of HO-2 in the injured and adjacent T9 and T12 segments. At this time, disruption of the blood-spinal cord barrier (BSCB) permeability, edema formation and cell injury were more pronounced. Pretreatment with H-290/51 (50 mg/kg, p.o., 30 min before trauma) significantly attenuated the HO-2 immunoreactivity along with breakdown of the BSCB permeability, edema and cell injury. These results for the first time demonstrate that the antioxidant compound H-290/51 is capable of attenuating HO-2 expression and thereby influencing CO production. Furthermore, our observations indicate that oxidative stress is involved in CO production, as reflected by HO-2 expression, which is injurious to the cord and H-290/51 exerts powerful neuroprotective effects in spinal cord injury.

The role of bradykinin in breakdown of the blood-spinal cord barrier (BSCB) permeability following a focal lesion to the cord was examined using a potent bradykinin BK2 receptor antagonist, HOE-140 in a rat model. Spinal cord injury was produced by an incision into the right dorsal horn of the T10-11 segment. In a separate group of rats HOE-140 (1 mg/kg) was administered intravenously 30 min before injury. A focal trauma to the cord markedly increased the extravasation of Evans blue and [131]I-sodium tracers in the cord at 5 h. Pretreatment with HOE-140 significantly attenuated the extravasation of these tracers in the spinal cord. At ultrastructural level, lanthanum was seen within the endothelial cell cytoplasm, in vesicular profiles as well as in the basal lamina in the untreated traumatised rats. In HOE-140 treated rats, the lanthanum was mainly confined within the lumen. These observations strongly suggest that bradykinin is involved in the breakdown of the BSCB permeability probably via bradykinin BK2 receptors, not reported earlier.

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.

The role of serotonin in trauma induced alterations in blood-brain barrier (BBB) permeability, cerebral blood flow (CBF), brain edema and cell changes were examined in a new model of cortical injury in the rat using a pharmacological approach. A longitudinal incision into the right parietal cerebral cortex (about 3 mm deep and 5 mm long) was associated with a profound increase in the BBB permeability to Evans blue and [131]I-sodium, brain water content, and a reduction in the CBF in both the ipsilateral and contralateral hemispheres 5 h after trauma. Nissl staining showed a profound nerve cell reaction in the parietal cerebral cortex of both hemispheres. The intensity of these pathological changes was most pronounced in the traumatised hemisphere. Pretreatment with p-CPA, a serotonin synthesis inhibitor, significantly attenuated breakdown of the BBB permeability, brain edema and the CBF disturbances. Damaged and distorted nerve cells were markedly less frequent in p-CPA treated rats. This effect of the drug was most pronounced in the contralateral hemisphere. The observations strongly suggest that serotonin is one of the important neurochemical mediators of BBB permeability disturbances and brain edema formation in the trauma induced brain damage.

The influence of carbon monoxide (CO) on chronic spinal nerve lesion induced spinal cord neurodegeneration was examined using immunohistochemical expression of the constitutive isoform of its synthesising enzyme, hemeoxygenase-2 (HO-2) in a rat model. Spinal nerve lesion at L-5 and L-6 level was produced according to the Chung model of neuropathic pain and rats were allowed to survive for 8 weeks. Sham operated rats, in which the spinal nerves were exposed but not ligated, served as controls. Ligation of spinal nerves in rats resulted in an upregulation of HO-2 expression which was most pronounced in the ipsilateral gray matter of the spinal cord compared to the contralateral side. In these rats, morphological investigations showed distorted neurons, membrane disruption, synaptic damage and myelin vesiculation. Sham operated rats did not show an upregulation of HO-2 expression and the structural changes in the spinal cord were absent. These observations strongly suggest that spinal nerve lesion is associated with an increased production of CO which is somehow contributing to the neurodegenerative changes in the spinal cord, not reported earlier.

Influence of a new anti-oxidant compound H-290/51 on expression of nitric oxide synthase (NOS) and heme oxygenase (HO) enzymes responsible for nitric oxide (NO) and carbon monoxide (CO) production, respectively was examined in the CNS following heat stress in relation to cell injury. Exposure of rats to 4h heat stress at 38 degrees C in a biological oxygen demand (BOD) incubator (relative humidity 50-55%, wind velocity 20-25cm/sec) resulted in profound edema and cell injury in many parts of the cerebral cortex, hippocampus, cerebellum, thalamus, hypothalamus and brain stem. Immunostaining of constitutive isoforms of neuronal NOS (nNOS) and HO-2 revealed marked upregulation in damaged and distorted neurons located within the edematous brain regions. Pretreatment with H-290/51 (50 mg/kg, p.o., 30 min before heat stress) significantly reduced the edematous swelling and cell injury and resulted in a marked attenuation of nNOS and HO-2 expression. These observations suggest that upregulation of NOS and HO is associated with cell injury, and the antioxidant compound H-290/51 is neuroprotective in heat stress.

The influence of exogenous rat growth hormone on spinal cord injury induced alterations in spinal cord evoked potentials (SCEP) and edema formation was examined in a rat model. Repeated topical application of rat growth hormone (20microl of 1microg/ml solution) applied 30min before injury and at 0min (at the time of injury), 10min, 30min, 60min, 120min, 180min, and 240min, resulted in a marked preservation of SCEP amplitude after injury. In addition, the treated traumatised cord showed significantly less edema and cell changes. These observations suggest that growth hormone has the capacity to improve spinal cord conduction and attenuate edema formation and cell injury in the cord indicating a potential therapeutic implication of this peptide in spinal cord injuries.

The influence of brain derived neurotrophic factor (BDNF) or insulin like growth factor-1 (IGF-1) on spinal cord trauma induced carbon monoxide (CO) production and cellular stress response was examined using immunostaining of the constitutive isoform of the hemeoxygenase (HO-2) enzyme and the heat shock protein (HSP 72kD) expression in a rat model. Subjection of rats to a 5 h spinal trauma inflicted by an incision into the right dorsal horn at T10-11 segment markedly upregulated the HO-2 and HSP expression in the adjacent spinal cord segments (T9 and T12). Pretreatment with BDNF or IGF-1 significantly attenuated the trauma induced HSP expression. The upregulation of HO-2 was also considerably reduced. These results show that BDNF and IGF-1 attenuate cellular stress response and production of CO following spinal cord injury which seems to be the key factors in neurotrophins induced neuroprotection.

Influence of the extract of Gingko biloba (EGB-761) and one of its constituent Gingkolide B (BN-52021) on hyperthermia induced cellular damage and heat shock protein (HSP 72kD) response was examined in a rat model. Rats subjected to 4h heat stress at 38 degrees C in a biological oxygen demand (BOD) incubator (relative humidity 50-55%, wind velocity 20-25cm/sec) resulted in profound edema and cell injury in many parts of the cerebral cortex, hippocampus, cerebellum, thalamus, hypothalamus and brain stem. Immunostaining of HSP 72 kD showed marked upregulation in the damaged and distorted neurons located within the edematous area. Pretreatment with EGB-761 (50mg/kg/day, p.o.) and BN-520 21 (2mg/kg, p.o.) per day for 5 days significantly reduced HSP expression and attenuated cell damage. Our results show that EGB-761 and its component Gingkolide B (BN-52021) has the capacity to reduce edema and cell injury following hyperthermia and this effect of the compound is somehow associated with a reduction in cellular stress response as evidenced with a reduction in HSP expression.

The influence of the new antioxidant compound H-290/51 was examined on the substance P endopeptidase (SPE) activity in a rat model of spinal cord injury. This compound (H-290/51) has neuro-protective effects on edema and cell changes in this model. Infliction of trauma to the cord by making an incision into the right dorsal horn of the T10-11 segment resulted in a marked upregulation of SPE in the segments rostral to the lesion. On the other hand, the injured and adjacent caudal segments exhibited a marked down-regulation of the enzyme activity. Pretreatment with H 290/51 increased the SPE activity in the T9 segment but downregulated the enzyme activity in the T10-11 and T12 segments. The drug induced enzyme activity change was not further influenced by the trauma of the cord. The results indicate that a focal trauma induces widespread alterations in spinal cord SPE activity which can be influenced by the anti-oxidant drug H 290/51, suggesting that SPE is somehow involved in cell injury.

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.

Involvement of serotonin in the early microvascular reactions and cell changes following trauma of the spinal cord was examined using topical application of serotonin antibodies to the traumatised cord in a rat model. A focal trauma of the spinal cord was produced by making an incision into the right dorsal horn of the T10-11 segments (about 2 mm deep and 5 mm long); the animals were allowed to survive 5 h after injury. Monoclonal 5-HT antibodies (1:20) were applied (25 microliters in 10 sec) to the traumatised spinal cord 2 min after injury. There was a significant reduction in the breakdown of the blood-spinal cord barrier, edema formation, and cell changes in the traumatised rats which received 5-HT antiserum compared to the injured rats given saline. These results show that 5-HT is an important mediator involved in the early pathophysiological responses of spinal cord injury.

The possibility that diazepam will influence spinal cord evoked potentials (SCEP), edema formation and cell changes following spinal cord injury (SCI) was examined in a rat model. The SCI was produced in equithesin anaesthetised animals by making a longitudinal incision (about 2 mm deep and 5 mm long) in the right dorsal horn of the T10-11 segments. The SCEP were recorded from the epidural space of the T9 segment after stimulation of the right tibial and sural nerves. The SCEP consisted of a small positive peak followed by a broad and high negative peak. Infliction of trauma to the rats resulted in an immediate and pronounced decrease of the maximal negative peak (MNP) amplitude. The spinal cord edema and cell changes were markedly pronounced 5 h after injury. Pretreatment with diazepam attenuated the early SCEP changes induced by the trauma and reduced the later development of edema and cell injury. These results suggest that benzodiazepine receptors are involved in trauma induced alterations in SCEP changes, edema formation and cell injury, not reported earlier.

The neuroprotective effects of insulin like growth factor-1 (IGF-1) on spinal cord injury induced edema formation, cell changes and profound upregulation of constitutive isoform of neuronal nitric oxide synthase (cNOS) was examined in a rat model. A focal spinal cord injury produced by making a lesion (about 2 mm deep and 5 mm long) of the right dorsal horn of the T10-11 segment resulted in a marked edema formation, cell injury and upregulation of cNOS following 5 h after trauma. In separate groups application of IGF-1 (0.1 microgram/microliter) topically on the exposed spinal cord (T10-11) starting from 30 min before injury (20 microliter), immediately before injury followed by 30 min, 60 min and thereafter every 1 h after injury until sacrifice resulted in significant attenuation of edema formation and cell changes. Immunohistochemistry showed a less pronounced expression of cNOS in the T9 and T12 segments of the cord in IGF treated rats compared to untreated traumatised controls. These results for the first time show that IGF treatment is neuroprotective and this effects of the IGF appears to be mediated via inhibition of NOS upregulation.

The possibility that endogenous serotonin (5-hydroxytryptamine, 5-HT) participates in alteration of the blood-brain barrier (BBB) following short-term forced swimming (FS) exercise was examined in a rat model. Subjection of conscious young (age 8-9 weeks, 80-90 g) animals to continuous FS (at a water temperature of 30 +/- 1 degrees C) for 30 min, increased the permeability of the BBB to Evans blue albumin (EBA) and 131I-sodium in six and nine brain regions, respectively. The EBA staining was noted in posterior cingulate cortex, parietal, occipital cortices, cerebellar vermis, medial lateral cerebellar cortices and dorsal surface of hippocampus. In addition to these brain regions, the BBB permeability to 131I-sodium was further extended to caudate nucleus, thalamus and hypothalamus. This effect of FS on the BBB permeability was absent in adult (age 24-30 weeks, 300-400 g) animals. Measurement of 5-HT showed a profound increase of plasma and brain in young rats by 180% and 250%, respectively, from the control group. Adult animals showed only a minor increase in brain and plasma 5-HT levels. In young animals, pretreatment with p-CPA (a 5-HT synthesis inhibitor) and indomethacin (a prostaglandin synthesis inhibitor) prevented the FS induced increase in BBB permeability and 5-HT levels. Destruction of serotonergic neurons with 5,7-dihydroxytryptamine (5,7-DHT) reduced the breakdown of the BBB and attenuated the brain 5-HT level without affecting the plasma 5-HT. Cyproheptadine, ketanserin (5-HT2 receptor antagonists) and vinblastine (a vesicular transport inhibitor) prevented the increased permeability of the BBB alone. The plasma and brain 5-HT continued to remain high. These observations suggest that (i) 5-HT plays an important role in the breakdown of BBB permeability in FS, (ii) this effect of 5-HT on BBB permeability is mediated by 5-HT2 receptors, and (iii) FS induced increase in BBB permeability is age dependent.

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 μg/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 serotonin 2 receptor antagonist) prevented the serotonin-induced decrease of the electroencephalogram amplitude. The blood-brain barrier permeability to Evans Blue and [ 131 I]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 serotonin 2 receptors.

The possibility that serotonin and prostaglandins participate in edema formation following heat stress (HS) was examined in young rats. Exposure of conscious young animals (8-9 weeks old) to heat at 38 degrees C in a biological oxygen demand (BOD) incubator (relative humidity 50-55%; wind velocity 20-25 cm/s) for 4 h resulted in marked increase in the whole brain water content (about 3%) as compared to animals kept at room temperature (21 degrees C). A marked extravasation of Evans blue and 131I-sodium occurred in the brain of heat exposed animals as compared to normal animals. Morphological examination using electron microscopy of selected brain regions of heat stressed animals showed profound cell changes. Thus perivascular edema, swollen neuronal and glial cells, membrane damage, vesiculation of myelin, axonal swelling and synaptic damage was frequent in this group of untreated animals. Pretreatment with ketanserin (a selective serotonin2 receptor antagonist) or indomethacin (an inhibitor of prostaglandin synthesis) markedly reduced edema formation after 4 h HS in young animals. These heat stressed animals had considerably less extravasation of protein tracers as compared to the untreated group. Cell changes and edema at the ultrastructural level were mainly absent. Our results suggest that serotonin and prostaglandins are involved in heat stress induced breakdown of the BBB permeability, edema formation, and cell damage.

The influence of naloxone (an opioid receptor antagonist) on spinal cord conduction and edema formation as a result of trauma to the cord was investigated in a rat model. The spinal cord injury (SCI) was inflicted in urethane anesthetized animals by a longitudinal incision into the right dorsal horn of the T10-11 segments, about 2 mm deep and 5 mm long. Spinal cord evoked potentials (SCEP) were recorded epidurally from the T9 (rostral) and T12 (caudal) segments after stimulation of the ipsilateral tibial and sural nerves at the ankle. The edema was measured by determining water content of the cord at s h after injury. In rats not given naloxone SCI resulted in an immediate long-lasting depression of the rostral maximal negative peak (MNP) amplitude (about 60%) and a significant increase in the latency of the rostral maximal positive peak (MPP). Pretreatment with naloxone inhibited the immediate post-injury decrease of the rostral MNP and some of the increase of MPP latency. The water content in the traumatized spinal cord was reduced by 3% in naloxone treated animals compared with untreated injured controls. Our results indicate that endogenous opioid peptides participate in changes of spinal cord conduction after trauma and influence edema formation probably via multiple opioid receptors.

The metabolic alteration of 5-HT in four different regions of rat brain and plasma was studied under acute and chronic heat stress. A generalised elevation of 5-HT in all the brain regions along with high plasma level was observed in animals subjected to 4 hour heat stress at 38 degrees C. Such elevation of brain 5-HT may be due to entry of plasma 5-HT into the brain owing to breakdown of blood-brain barrier (BBB). In heat adapted rats, where BBB remained unaffected, no increase in brain 5-HT was observed, rather a significantly low level was maintained both in plasma and brain tissue.

The possibility that serotonin may play a role in heat adaptation was examined in a rat model of heat stress (HS). Subjection of animals to acute 4 h HS (but not to 1 h and 2 h duration) in a biological oxygen demand (BOD) incubator (relative humidity 50-55%, wind velocity 20-25 cm/s) resulted in profound hyperthermia (41.68 +/- 0.25 degrees C) associated with behavioural salivation and prostration. This experimental condition simulates the out door environmental conditions of Varanasi, India during the month of June. Measurement of serotonin (5-hydroxytryptamine, 5-HT) content in the plasma and brain showed a profound increase of the amine by 462% and 187% respectively from the control group. Morphological examination in these animals revealed marked cell changes in the brain at both light and electron microscopic level. Thus chromatolysis, shrunken and dark neurons along with a general sponginess of the gray and white matter was quite frequent in all the brain regions. At ultrastructural level, perivascular edema, damage to pre- and postsynaptic terminals, swollen neurons and glial cells, splitting of myelin and vacuolation was very common throughout the whole brain. The microvessels were mainly collapsed and a diffuse infiltration of lanthanum ion within the endothelium was common. Occasionally, lanthanum could also be seen within the basement membrane. However, the tight junctions were mainly intact. On the other hand, when animals exposed to chronic heat stress of 1 h duration at the same intensity for 7 days and then subjected to a 4 h HS on the 8th day, resulted in only minor symptoms. Thus these 4 h heat stressed animals did not exhibit hyperthermia or increased serotonin levels in plasma and brain as compared to the animals exposed to chronic HS of 1 h duration until alone 7th day. These heat adapted animals did not show any marked cell changes in the brain. However, the values of circulating 5-HT level and rectal temperature of these chronically heat stressed animals (for 1 h daily) were mild but significantly elevated on the 7th day as compared to the intact control animals. These results show that: 1. chronic HS of short duration induces heat tolerance; 2. the circulating 5-HT level some how appears to play an important role in the pathophysiology of HS; hand in the physiological mechanism(s) of secondary heat adaptation.

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.

The distribution of dynorphin A in the spinal cord and brain of normal rats and of rats subjected to a focal injury of the spinal cord was examined in a rat model using a radioimmunoassay (RIA) technique. The validity of RIA was checked by high performance liquid chromatography (HPLC). Furthermore, the possibility that the peptide is somehow functionally related with endogenous 5-hydroxytryptamine (5-HT, serotonin), was also evaluated using a pharmacological approach. In normal animals, the peptide content was very similar in the spinal cord segments (T9, T10-11, and T12) examined whereas, the dynorphin content of the whole brain was about two-fold higher compared with that in the spinal cord. A focal injury to the spinal cord in the right dorsal horn (about 1.5 mm deep, 2.5 mm long and 1.5 mm to the right of the midline) of the lower thoracic cord (T10-11) in urethane anaesthetised animals significantly altered the peptide content in the whole brain as well as in the spinal cord. Thus, a decrease in the peptide level in whole brain, T10-11 and in the T12 segments of the spinal cord was observed 1 and 2 h after trauma. At 5 h, the peptide had accumulated markedly in the T9 segment (about a two-fold increase) as compared with the controls. At this time, the peptide content had been restored in the T10-11 and T12 segments. On the other hand, the whole brain dynorphin level continued to remain low (by 55%) as compared to the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

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)