Effects of injury on the indoleamines in cerebral cortex

Serotonin 5-HT1A receptors modulate depression-related symptoms following mild traumatic brain injury in male adult mice

Traumatic brain injury is a complex phenomenon leading to neurological diseases and persistent disability that currently affects millions of people worldwide. Increasing evidence shows that a wide range of patients with mild traumatic brain injury (mTBI) suffer from depression during the initial stages of injury and the post-acute stages of recovery. However, the underlying mechanisms involved in depression following mTBI are still not fully understood. The aim of this study was to determine whether serotonin 5-hydroxytryptamine-1A (5-HT1A) receptor is involved in the regulation of depression-related behaviors following mild traumatic brain injury in mice. Mice with or without mTBI received intracerebroventricular injections of 5-HT1A receptor agonist (8-OH-DPAT) or antagonist (WAY-100635) for 5 days, then animals were subjected to behavioral tests. Four behavioral tests including novelty-suppressed feeding test, forced swim test, sucrose preference test and tail suspension test were used to evaluate depression-related symptoms in animals. Our results indicated that mTBI induction increased depression-like symptoms through altering serotonin 5-HT1A receptor activity in the brain. Activation of 5-HT1A receptor by a subthreshold dose of 8-OH-DPAT led to a significant decrease in depression-like behaviors, whereas blockade of 5-HT1A receptor by a subthreshold dose of WAY-100635 resulted in a considerable increase in depression-like phenotypes in mTBI-induced mice. The major strength of the present study is that depression-related symptoms were assessed in four behavioral tests. The present study supports the idea that disturbances in the function of serotonergic system in the brain following mTBI can play an important role in the regulation of depression-related behaviors.

Neurotransmitter Systems in a Mild Blast Traumatic Brain Injury Model: Catecholamines and Serotonin

Exposure to improvised explosive devices can result in a unique form of traumatic brain injury--blast-induced traumatic brain injury (bTBI). At the mild end of the spectrum (mild bTBI [mbTBI]), there are cognitive and mood disturbances. Similar symptoms have been observed in post-traumatic stress disorder caused by exposure to extreme psychological stress without physical injury. A role of the monoaminergic system in mood regulation and stress is well established but its involvement in mbTBI is not well understood. To address this gap, we used a rodent model of mbTBI and detected a decrease in immobility behavior in the forced swim test at 1 d post-exposure, coupled with an increase in climbing behavior, but not after 14 d or later, possibly indicating a transient increase in anxiety-like behavior. Using in situ hybridization, we found elevated messenger ribonucleic acid levels of both tyrosine hydroxylase and tryptophan hydroxylase 2 in the locus coeruleus and the dorsal raphe nucleus, respectively, as early as 2 h post-exposure. High-performance liquid chromatography analysis 1 d post-exposure primarily showed elevated noradrenaline levels in several forebrain regions. Taken together, we report that exposure to mild blast results in transient changes in both anxiety-like behavior and brain region-specific molecular changes, implicating the monoaminergic system in the pathobiology of mbTBI.

Head injury therapies

The results of clinical trials in traumatic brain injury have to date been disappointing, despite promising results with animal models. Some of the agents which have been tested in clinical trials and some which are currently under evaluation are reviewed, and possible reasons for the lack of clinical benefit are discussed.

Effects of fluoxetine on the 5-HT1A receptor and recovery of cognitive function after traumatic brain injury in rats

OBJECTIVE

This study examined the effects of chronic administration of fluoxetine, a selective serotonin reuptake inhibitor, on cognitive performance and 5-HT1A receptor immunoreactivity following traumatic brain injury.

DESIGN

Rats received a moderate severity of lateral fluid percussive injury or sham injury 24 hr after surgical preparation. Fluoxetine or vehicle was administered chronically on postinjury days 1-15. Motor performance and Morris water maze performance were assessed on postinjury days 1-5 and 11-15, respectively.

RESULTS

Results indicated that chronic fluoxetine treatment did not affect motor or maze performance. Injured groups showed significantly higher 5-HT1A receptor immunoreactivity on postinjury day 15 than sham-injured rats, and fluoxetine treatment did not alter 5-HT1A receptor immunoreactivity.

CONCLUSIONS

These results indicate that chronic postinjury fluoxetine administration did not influence the recovery of motor or Morris water maze performance following lateral fluid percussive injury. They also indicate that injury-induced changes in the 5-HT1A receptor may contribute to traumatic brain injury-induced cognitive deficits.

Neurotrauma care in the new millennium

The next millennium will see an explosion of neuromonitoring technology that will provide a more detailed understanding of brain-injured patients. This understanding will allow an individualized and intelligent application of the wide range of therapies that will become available. The measure of success for all of these endeavors will be individual patients and physicians' ability to return them to their normal lives.

Extracellular release of serotonin following fluid-percussion brain injury in rats

Serotonin has been implicated in the pathobiology of central nervous system trauma. Using microdialysis techniques, we performed measurements of extracellular serotonin release within the traumatized cerebral cortex of rats subjected to moderate fluid-percussion (F-P) brain injury. Twenty-four hours prior to TBI, a F-P interface was positioned parasagitally over the right cerebral cortex. On the second day, fasted rats were anesthetized with 70% nitrous oxide, 1% halothane and 30% oxygen. Under controlled physiological conditions and normothermic brain temperature (37-37.5 degrees C), rats were injured (n = 6) with a F-P pulse ranging from 1.8 to 2.0 atm. Following trauma, brain temperature was maintained for 4 h at 37 degrees C. Sham trauma animals (n = 7) were treated in an identical manner. Brain trauma induced acute elevations in the extracellular levels of serotonin (p < 0.01, ANOVA) compared to sham-operated controls. For example, serotonin levels increased from 18.85 +/- 7.12 pm/mL (mean +/- SD) in baseline samples to 65.78 +/- 11.36 in the first 10 min after trauma. The levels of serotonin remained significantly higher than control for the first 90-min sampling period. In parallel to the increase in serotonin levels after TBI, a significant 71.1% decrease (i.e., 182.29 +/- 30.08 vs 52.75 +/- 16.92) in extracellular 5-hydroxyindoleacetic acid (5-HIAA) levels was observed during the first 10 min after TBI. These data indicate that TBI is followed by a prompt increase in the extracellular levels of serotonin in cortical regions adjacent to the impact site. These neurochemical findings indicate that serotonin may play a significant role in the pathophysiology of TBI.

Cortical hypometabolism in injured brain: new correlations with the noradrenergic and serotonergic systems and with behavioral deficits

Changes with time after injury in behavioral deficits, as determined by the Morris swim test, and the in vivo specific binding of HEAT, a selective alpha 1-adrenoreceptor ligand, were compared with the time-course of development of cortical hypometabolism in rats with focal freezing lesions. In our trauma model, cortical hypometabolism was detectable in the lesioned hemisphere at 4 hr, became maximal (50% of normal) at 3 days and diminished towards normal on days 5 and 10 post-injury. Progressive impairment of acquisition of the Morris water maze task was demonstrated up to day 3 post-lesion with improvement thereafter. On day 3 the latency to reach criterion was 60% longer in lesioned animals than in corresponding sham-operated ones. An increase in the volume of distribution of HEAT, limited to cortical areas of the lesioned hemisphere, was demonstrable at 4 hr post-lesion and reached its maximum on day 3 (200% of normal) with subsequent return toward normal on days 5 and 10. Several types of drugs were shown previously to modify the cortical hypometabolism associated with cerebral injury. The present data indicate that the same drugs also modify the in vivo binding of HEAT and the behavioral deficits induced by brain lesions. Ibuprofen, a non-steroidal anti-inflammatory drug, p-chlorophenylalanine, an inhibitor of serotonin synthesis, ketanserin, a specific 5HT2-receptor antagonist, and prazosin, an alpha 1-adrenergic receptor blocker all normalized the in vivo binding of HEAT in the cortical areas of the lesioned hemisphere. All groups of animals treated with these drugs also showed subtle, but statistically highly significant improvements in latency to locate the platform in the Morris water maze. Taken together these results show good correlation between behavioral deficits, changes in alpha 1-noradrenergic receptor binding and cortical hypometabolism in injured brain. This supports the hypothesis that post-injury cortical hypometabolism is a reflection of cortical functional depression in which both the serotonergic and noradrenergic neurotransmitter systems play a role, compatible with their inhibitory effects in the cortex and their postulated involvement in cortical information processing.

Effect of injury on the bi-affinity alpha 1-adrenoreceptor binding in rat brain in vivo

Focal freezing lesions in rats cause a widespread decrease of cortical glucose utilization in the lesioned hemisphere, probably as a reflection of depressed cortical activity. The noradrenergic neurotransmitter system was implicated in these alterations when it was demonstrated that prazosin, a specific norepinephrine (NE) antagonist at alpha 1-adrenergic receptors, prevented their development. In normal rat brain, specific binding of [125I]HEAT [(+/-)2-(3-[125I]iodo-4-hydroxyphenyl)-ethyl-aminomethyl-tetralone], another selective alpha 1-adrenoreceptor ligand, was demonstrated in vivo at sites consistent with the alpha 1A- and alpha 1B-adrenoreceptor subtypes. In the present study, the effect of a freezing lesion on specific binding of [125I]HEAT in rat brain in vivo was determined three days after traumatization when cortical glucose use suggested the greatest degree of functional depression. The steady-state volumes of distribution of [125I]HEAT three days after injury were significantly increased in all the cortical areas of the lesioned hemisphere, but not in the subcortical structures. Injury did not modify the binding affinities for HEAT. However, a statistically significant increase in the number of low-affinity binding sites for this ligand was demonstrated in all cortical areas of the lesioned hemisphere, but not in subcortical structures. The traumatization did not modify Bmax estimates for the high-affinity binding of HEAT. The results support the hypothesis that changes in the noradrenergic system are of functional importance in brain injury and that at least some effects of injury are mediated by alpha 1B-adrenergic receptors.

Mediators of vascular and parenchymal mechanisms in secondary brain damage

Several putative mediators of vasogenic brain edema will be considered with respect to the following criteria: 1) their effect on blood-brain barrier (BBB) permeability, 2) their vasomotor actions which may increase driving forces for transmural bulk flow, 3) their influence on edema formation, 4) their actual tissue concentration in pathological states, and 5) the therapeutic results after specific treatment. Bradykinin (BK) can induce brain edema by increasing BBB permeability to small solutes and enhancing blood pressure in the microcirculation due to arterial dilatation and venous constriction. Its interstitial concentration is enhanced after experimental trauma. Since kallikrein inhibitors reduce brain swelling all criteria favour BK as a mediator of vasogenic edema. Arachidonic acid (AA) opens BBB also for large tracers but exerts only small vasomotor effects. The edema formation is associated with an increase of the AA concentration in the interstitial space. However, convincing therapeutic results on inhibition of AA are still lacking. In addition to the formation of vasogenic edema AA has been found to induce cytotoxic edema. From experiments dealing with the vasomotor effects Ellis et al. (Am J Physiol 255: H397-H400, 1988) concluded an interaction of BK and AA in brain injury. However, our own results do not favour this hypothesis since we found divergent vasomotor and permeability effects of BK and AA. Histamine (HA) opens BBB unspecifically and dilates cerebral vessels, mechanisms by which edema formation can be explained.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel pharmacologic therapies in the treatment of experimental traumatic brain injury: a review

Delayed or secondary neuronal damage following traumatic injury to the central nervous system (CNS) may result from pathologic changes in the brain's endogenous neurochemical systems. Although the precise mechanisms mediating secondary damage are poorly understood, posttraumatic neurochemical changes may include overactivation of neurotransmitter release or re-uptake, changes in presynaptic or postsynaptic receptor binding, or the pathologic release or synthesis of endogenous "autodestructive" factors. The identification and characterization of these factors and the timing of the neurochemical cascade after CNS injury provides a window of opportunity for treatment with pharmacologic agents that modify synthesis, release, receptor binding, or physiologic activity with subsequent attenuation of neuronal damage and improvement in outcome. Over the past decade, a number of studies have suggested that modification of postinjury events through pharmacologic intervention can promote functional recovery in both a variety of animal models and clinical CNS injury. This article summarizes recent work suggesting that pharmacologic manipulation of endogenous systems by such diverse pharmacologic agents as anticholinergics, excitatory amino acid antagonists, endogenous opioid antagonists, catecholamines, serotonin antagonists, modulators of arachidonic acid, antioxidants and free radical scavengers, steroid and lipid peroxidation inhibitors, platelet activating factor antagonists, anion exchange inhibitors, magnesium, gangliosides, and calcium channel antagonists may improve functional outcome after brain injury.

CSF neurotransmitter metabolites and short-term outcome of patients in coma after head injury

The main metabolites of the neurotransmitters noradrenaline, dopamine, and serotonin, methoxy-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5HIAA) respectively, were estimated by HPLC with electrochemical detection in CSF samples from 24 patients in coma after head injury, 1 to 12 (mean 3.0) days from accident, and from 24 age- and sex-matched subjects undergoing myelography for possible herniated disk. Analysis of variance with age as covariate, revealed significantly elevated levels of all three metabolites in the patients group. The concentrations of 5HIAA were negatively correlated to the score in the Glasgow Coma Scale. Fourteen patients who recovered with no or minor neurological deficits, had significantly lower CSF 5HIAA levels compared to the ten patients who had a bad outcome (death), while there were no differences regarding HVA or MHPG concentrations. The possibility of a connection of the high neurotransmitter turnover during coma to the development of post-traumatic depression is discussed.

Brain injury: new insights into neurotransmitter and receptor mechanisms

The studies reviewed here represent a continuing search for mechanisms which play a role in neurological disturbances resulting from brain injury. Focal cortical freezing lesions in rats were shown to cause a widespread decrease in local cerebral glucose utilization (LCGU) in cortical areas of the lesioned hemisphere and this was interpreted as reflecting a depression of cortical activity. Such an interpretation was supported by the finding that in lesioned brain reduction of cerebral metabolism by pentobarbital and isoflurane was limited by the metabolic depression that has already occurred as a result of injury and by the demonstration that the energy status and substrate (glucose) supply in the cortical areas in the injured brain have not been compromised at the time when LCGU was decreased. Both the serotonergic and the noradrenergic neurotransmitter systems were implicated in functional alterations associated with injury. Cortical serotonin (5-HT) metabolism was increased throughout the lesioned hemisphere and complete inhibition of 5-HT synthesis with p-chlorophenylalanine ameliorated the decrease in cortical LCGU, interpreted as reflecting cortical functional depression. Cortical norepinephrine metabolism was bilaterally increased in focally injured brain, while prazosin, a selective alpha 1-noradrenergic receptor blocker, normalized cortical LCGU in the lesioned hemisphere. Low-affinity in vivo binding of [125I]HEAT, another selective alpha 1-receptor ligand, was specifically increased in cortical areas of the lesioned hemisphere at the time of the greatest depression in LCGU, suggesting that alpha 1-adrenoreceptors may be of functional importance in injured brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of focal cortical freezing lesion on regional energy metabolism

Freezing lesions have been shown to cause a depression in glucose use, particularly in cortical areas of the brain ipsilateral to the lesion, and this effect was interpreted to be caused by a depressed functional activity in these regions. The metabolic status of the affected areas has not been previously examined and could be a factor in the observed changes in local CMRglc. In frozen-cut and dried sections taken from brains 3 days after freeze lesioning, discrete pieces of the median and lateral parietal cortex, striatum, hippocampus, and hypothalamus were dissected and analyzed for ATP, P-creatine, glucose, and lactate. CMRglc measurements were also made in the same animals. The concentrations of the four metabolites were significantly increased in the lesioned hemisphere, with the most predominant effects observed in the cortical areas that exhibited the greatest depression in CMRglc. The enriched metabolite profile, particularly in the cortical areas, is consistent with the hypothesis that decreased glucose use in the traumatized brain is caused by diminished need rather than by decreased supply of energy. Because the lumped constant in the operational equation of the deoxyglucose method for determination of CMRglc is a function of brain glucose content and decreases gradually in hyperglycemia, the degree of metabolic depression in cortical areas of lesioned hemisphere probably have been somewhat overestimated in this and previous publications. However, provisionally recalculated local CMRglc in the lesioned hemisphere remain significantly lower than in the contralateral hemisphere and in the normal brain.

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.

The effect of alpha-adrenergic receptor blockers prazosin and yohimbine on cerebral metabolism and biogenic amine content of traumatized brain

Widespread decrease in local cerebral glucose utilization (LCGU) previously shown to occur 3 days after a local freezing lesion was interpreted as reflecting a depression of functional activity in the affected areas. In parallel experiments, cortical norepinephrine (NE) content of traumatized brain was found to be decreased. The effects of prazosin (PZ), an alpha 1-adrenergic receptor blocker, and yohimbine (YOH), an alpha 2-blocker, on glucose use and biogenic amine content of lesioned rat brain were studied to determine if the changes in the noradrenergic system associated with injury are of functional importance, to identify the receptors that may be involved in mediating the action of NE in injured brain, and to look for evidence of interaction between the noradrenergic and the serotonergic systems in traumatized brain. PZ (1 mg/kg) given 30 min before the lesion ameliorated the subsequent metabolic cortical depression seen in untreated animals. PZ given for 3 days starting before the lesion (3 mg/kg/day) was also effective in normalizing LCGU in areas where it was depressed by lesioning, despite the fact that this regimen induced significant global decrease in LCGU in normal animals. Once cortical metabolic depression had developed 3 days after the lesion, it could not be modified by PZ. YOH was less effective than PZ and was so only when given for 3 days (22.5 mg/kg/day in three divided doses). PZ (3 mg/kg/day in three divided doses) slightly but significantly decreased the accumulation of the serotonin (5-HT) metabolite 5-hydroxyindoleacetic acid in the traumatized hemisphere. These results provide evidence that blockage of alpha 1-adrenergic receptors prevents the development of cortical dysfunction associated with brain trauma. This implies that the noradrenergic system plays a role in the functional consequences of injury and that this effect is, at least in part, mediated by alpha 1-adrenergic receptors. Furthermore, alpha 1-adrenergic receptor blockage appears to modulate cortical turnover of 5-HT, previously also implicated in functional consequences of brain injury. The data are compatible with inhibitory effects of NE in the cortex and suggest a potential of alpha 1-adrenergic blockage in development of novel therapeutic approaches to brain injury.

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.

Increased 5-hydroxytryptamine immunoreactivity in traumatized spinal cord. An experimental study in the rat

The possibility that serotonin (5-hydroxytryptamine, 5-HT) is involved in the early tissue reactions occurring in spinal cord trauma was examined in a rat model using an immunocytochemical technique. The injury was made in the form of a 5-mm long and 2.5-mm wide lesion of the right dorsal horn at the level of T10-11. Injured rats, pretreated with the 5-HT synthesis blocking agent, p-chlorophenyl alanine (p-CPA) were compared with untreated injured controls and the animals were allowed to survive for 5 h. The distribution of 5-HT was examined in proximal and distal cross- sections of the cord, located 2 and 5 mm away from the injury. Normal rats showed immunoreactive material in nerve cell processes and in a few nerve cell bodies of the ventral horns. The trauma to the spinal cord caused a marked increase in 5-HT immunoreactivity in the segments located 2 mm proximal and distal to the injury, particularly in the ipsilateral ventral horn. The segment located 5 mm distal to the lesion showed a similar increase in immunoreactivity but it was apparently less pronounced in the corresponding proximal segment. Treatment with p-CPA markedly reduced the trauma-induced increase in 5-HT immunoreactivity in all the segments. These immunohistochemical findings were in line with the changes in the contents of 5-HT measured biochemically in corresponding spinal cord segments. At the onset of the trauma to the spinal cord 5-HT is thus present in the tissue, mainly in the form of 5-HT-containing nerve cell processes.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

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.

Neurochemical approaches to the amelioration of brain injury

The studies reported here represent a continuing search for mechanisms which may play a role in neurological disturbances resulting from brain injury. In particular, they are part of an effort to elucidate the involvement of both the serotonergic and noradrenergic neurotransmitter systems in the wide-spread decrease in cortical glucose utilization, interpreted as reflecting a functional depression, associated with a focal cortical lesion in the rat. Quinolinic acid, an endogenous metabolite of L-tryptophan, a neurotoxin and an N-methyl-D-aspartate (NMDA) receptor agonist was found to accumulate in cortical areas of a traumatized rat hemisphere in parallel with a previously demonstrated increase of 5-hydroxyindoleacetic acid. Ketanserin (20 mg/kg/day), a 5-HT2 receptor blocker ameliorated the depression of glucose utilization in traumatized brain while MK-801 (3 mg/kg, before and after lesion), an NMDA receptor blocker, had no effect. Alpha 1-adrenergic receptors, quantitated in vivo with [125I]-HEAT (iodo-2-[beta-(4-hydroxyphenyl)-ethyl-aminomethyl]tetralone), were found to be elevated in cortical areas of the lesioned hemisphere, but not in other structures.

Effect of the serotonin antagonist ketanserin on the hemodynamic and morphological consequences of thrombotic infarction

The effect of the serotonin (5-hydroxytryptamine, 5-HT) antagonist ketanserin on the remote hemodynamic consequences of thrombotic brain infarction was studied in rats. Treated rats received an injection of 1 mg/kg ketanserin 30 min before and 1 h following photochemically induced cortical infarction. Local CBF (LCBF) was assessed autoradiographically with [14C]iodoantipyrine 4 h following infarction, and chronic infarct size was documented at 5 days. Thrombotic infarction led to significant decreases in LCBF within noninfarcted cortical regions. For example, mean LCBF was decreased to 63, 55, and 65% of control (nontreated normal rats) in ipsilateral frontal, lateral, and auditory cortices, respectively. In rats treated with ketanserin, significant decreases in LCBF were not documented within remote cortical areas compared with controls. In contrast to these hemodynamic effects, morphological analysis of chronic infarct size demonstrated no differences in infarct volume between treated (27 +/- 3 mm3) and nontreated (27 +/- 6 mm3) rats. These data are consistent with the hypothesis that 5-HT is involved in the widespread hemodynamic consequences of experimentally induced thrombotic infarction. Remote hemodynamic consequences of acute infarction can be inhibited without altering final infarct size.

Acute thrombotic infarction suppresses metabolic activation of ipsilateral somatosensory cortex: evidence for functional diaschisis

To study the effects of focal infarction on the capacity for functional activation of an ipsilateral somatosensory system remote from the lesion, we produced a small thrombotic infarct in the left frontal pole of male Wistar rats by a photochemical method. Five days later, the awake, restrained rats received tactile stimulation of the large whiskers (vibrissae) of the right side of the face, while a double-label 14C-autoradiographic study of local CMRglc (lCMRglc) and local CBF (lCBF) was performed. Unlesioned and unstimulated animals served as controls. In rats without frontal infarct, vibrissae stimulation led to activation of lCMRglc in the three synaptic relay stations of the barrel-field pathway (ipsilateral trigeminal medullary nucleus, contralateral ventrobasal thalamus, and contralateral barrel-field cortex). The mean increment in lCMRglc was 42% in lamina IV of barrel-field cortex and 49% in ventrobasal thalamus. Normalized lCBF tended to increase in superficial cortical laminae. In unstimulated animals with frontal infarct, lCMRglc was reduced by 20-30% throughout the ipsilateral barrel-field cortex as well as other ipsilateral cortical regions, but not in ventrobasal thalamus or other subcortical areas. In animals with frontal infarct subjected to contralateral vibrissae stimulation, a remarkable suppression of activation was observed throughout the barrel-field cortex so that left-less-than-right hemispheral lCMRglc asymmetry persisted despite stimulation. The ventrobasal thalamus, similarly, failed to increment its lCMRglc with vibrissae stimulation, whereas activation of the trigeminal nucleus was not suppressed. Similar trends were observed in the normalized lCBF data. These observations, which establish that a small frontal infarct is capable of suppressing normal physiological activation in remote ipsilateral brain structures, may have important implications with respect to suppression and recovery of function in human ischemic stroke.

Regional monoamine and metabolite levels in a feline brain tumor model

The presence of a brain tumor alters regional cerebral blood flow, oxygen consumption, and glucose utilization in adjacent and remote brain tissue, but its effect on brain neurotransmitter levels is unclear. In the present report, the levels of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in tumor tissue and gray and white matter obtained from cats with induced brain tumors were measured. Glioma cells (9L) were xenotransplanted into the central white matter of the right hemisphere, and 15 d later the brains were frozen in vivo. Samples of tumor, parietal (peritumor), temporal, and frontal gray and white matter were divided for analysis of water content and quantification of amines and their metabolites. The water content of white matter, but not gray matter, adjacent to the tumor was increased. Neurotransmitter amine and metabolite levels were much lower in the tumor than in brain tissue. In gray matter adjacent to the tumor, concentrations of DA and its metabolites HVA and DOPAC were significantly decreased from control, whereas 5-HIAA was increased. The NA, DA, HVA, and DOPAC levels were decreased in temporal gray matter, whereas all amine and metabolite levels were unchanged in frontal gray matter. These results indicate that altered neurotransmitter metabolism is one of the effects of the presence of a brain tumor.

Involvement of indoleamines in functional disturbances after brain injury

1. Focal cortical freezing lesions in rats caused a widespread decrease in local cerebral glucose utilization (LCGU) in cortical areas of the lesioned hemisphere and this was interpreted as reflecting a depression of cortical activity (Pappius 1981). Cortical serotonin (5-HT) metabolism was increased throughout the lesioned hemisphere (Pappius and Dadoun 1987). To find if these changes in the serotonergic system are of functional importance and mediate the observed changes in LCGU, the effects of inhibition of 5-HT synthesis with p-chlorophenylalanine (PCPA) on cerebral metabolism and indoleamine content in injured brain were studied (Pappius et al. 1988). PCPA decreased 5-HT levels in the cortical and raphe areas of both intact and injured brain in a dose dependent manner. At doses of PCPA ineffective on LCGU (50 and 100 mg/kg) brain trauma still resulted in increased 5-HT metabolism. PCPA at doses which selectively ameliorated the depression of cortical LCGU in the lesioned hemisphere (200 and 300 mg/kg) completely prevented changes in 5-HT and 5-hydroxyindoleacetic acid seen following traumatization in untreated animals. These results provide evidence that decreased LCGU in lesioned brain is due to an activation of the serotonergic system. The data are thus in agreement with a postulated inhibitory role of serotonin in the cerebral cortex, and its involvement in functional alterations associated with injury.

Significance of biogenic amines in functional disturbances resulting from brain injury

Focal cortical freezing lesions in rats caused a widespread decrease in local cerebral glucose utilization (LCGU) in cortical areas of the lesioned hemisphere and this was interpreted as reflecting a depression of cortical activity (Pappius, 1981). Cortical serotonin (5-HT) metabolism was increased throughout the lesioned hemisphere (Pappius and Dadoun, 1987). In contrast, norepinephrine (NE) was decreased bilaterally, while levels of dopamine and its metabolites were not affected (Pappius and Dadoun, 1986). To determine if the changes in these neurotransmitters are of functional importance and mediate the observed changes in LCGU, the effects of inhibition of 5-HT synthesis with p-chlorophenylalanine (PCPA) and alpha 1-adrenergic blockage with prazosin (PZ) on cerebral metabolism and biogenic amine content in injured brain were studied. At doses of PCPA ineffective on LCGU (50 and 100 mg/kg) brain trauma still resulted in increased 5-HT metabolism. PCPA at doses which selectively ameliorated the depression of cortical LCGU in the lesioned hemisphere (200 and 300 mg/kg) completely prevented changes in 5-HT and 5-hydroxyindoleacetic acid seen following traumatization in untreated animals. These results provide evidence that decreased LCGU in lesioned brain is due to an activation of the serotonergic system. Prazosin (1 mg/kg) given 30 min before the lesion significantly increased cortical glucose utilization in the injured hemisphere and was even more effective when the treatment was continued for 3 days. Prazosin did not modify changes in cortical biogenic amines seen in untreated animals. The data are in agreement with a postulated inhibitory role of serotonin and norepinephrine in the cerebral cortex and implicate both neurotransmitters in functional alterations associated with injury.

The effect of p-chlorophenylalanine on cerebral metabolism and biogenic amine content of traumatized brain

It was shown previously that focal cortical freezing lesions in rats cause widespread decrease in local cerebral glucose utilization (LCGU) in cortical areas of the lesioned hemisphere. This was interpreted as reflecting a depression of cortical activity. It was then demonstrated that cortical serotonin (5-HT) metabolism was increased throughout the lesioned hemisphere of a focally injured brain. To find out if the changes in the serotonergic system are of functional importance and mediate the observed changes in LCGU, the effects of the inhibition of 5-HT synthesis with p-chlorophenylalanine (PCPA) on cerebral metabolism and biogenic amine content in injured brain were studied. PCPA in doses up to 300 mg/kg had little, if any, effect on LCGU in intact brain and in doses up to 100 mg/kg did not modify the depressed LCGU in injured brain. In doses of 200 and 300 mg/kg, PCPA selectively increased cortical glucose utilization in the lesioned hemisphere where it was depressed following injury. PCPA decreased 5-HT levels in the cortical and raphe areas of both intact and injured brain in a dose-dependent manner. However, at doses of PCPA ineffective on LCGU (50 and 100 mg/kg), traumatization still resulted in increased 5-HT metabolism. Doses of PCPA that ameliorated the depression of LCGU in injured brain completely prevented increases in both 5-HT and its metabolite 5-hydroxyindoleacetic acid seen following traumatization in untreated animals. These results provide evidence that decreased LCGU in lesioned brain is due to an activation of the serotonergic system by traumatization. The data are in agreement with the postulated inhibitory role of serotonin in the cortex and its involvement in functional alterations associated with injury. They suggest that blockage of this neurotransmitter system may have a potential in the development of novel therapeutic approaches to brain injury.