Significance of biogenic amines in functional disturbances resulting from brain injury

The Diagnosis and Management of Concussion in Children and Adolescents

BACKGROUND

Concussion is a complex brain injury that results in more than 100,000 emergency department visits for school-aged children each year in the United States. All 50 US states have passed concussion legislation designed to promote safety in youth sports. Most of these laws require medical clearance by a licensed health care provider before returning to sport, which may have contributed to an increase in pediatric subspecialty referrals, particularly referrals to the child neurologist.

METHODS

We reviewed the literature on pediatric concussion.

RESULTS

This review summarizes the current knowledge and recommendations for concussion diagnosis and management in children and adolescents, athletes and nonathletes. It highlights concussion epidemiology, pathophysiology, advances in neuroimaging, and potential health risks including second impact syndrome and chronic traumatic encephalopathy. It also underscores clinical areas where evidence is lacking.

CONCLUSIONS

The diagnosis and management of concussion requires specific considerations in children. Further concussion research must be done to minimize injury risk and to optimize medical care for this common problem.

Dissociation of cerebral glucose metabolism and level of consciousness during the period of metabolic depression following human traumatic brain injury

Utilizing [18F]fluorodeoxyglucose positron emission tomography (FDG-PET), we studied the correlation between CMRglc and the level of consciousness within the first month following human traumatic brain injury. Forty-three FDG-PET scans obtained on 42 mild to severely head-injured patients were quantitatively analyzed for the determination of regional cerebral metabolic rate of glucose (CMRglc). Reduction of cerebral glucose utilization, defined as a CMRglc of < or =4.9 mg/100 g/min, was present regionally in 88% of the studies. The prevalence of global cortical CMRglc reduction was higher in severely head-injured patients (86% versus 67% mild-moderate), although the absolute magnitude was similar across the injury severity spectrum (mean CMRglc 3.9 +/- 0.6 mg/100 g/min). The level of consciousness, as measured by the Glasgow Coma Scale, correlated poorly with the global cortical CMRglc value (r = 0.08; p = 0.63). With regards to severity of head injury, this correlation was worst for the severely injured (r = -0.11; p = 0.58) and better for the mildly injured patients (r = 0.50; p = 0.07). In most cases, intraparenchymal hemorrhagic lesions were associated with either focal CMRglc reduction or elevation. It is concluded that the etiologies of CMRglc reduction are likely multifactorial given the complex nature of traumatic brain injury and that the reduction of CMRglc represents a fundamental pathobiologic state following head injury that is not tightly coupled to level of consciousness.

Effects of a restricted unilateral neocortical lesion upon cerebral glucose and oxidative metabolisms in fetal and neonatal cats

The present study was designed to measure cerebral glucose and oxidative metabolisms and to assess relationships with previously identified morphological changes in adult cats with a unilateral, restricted neocortical lesion sustained either during fetal life or neonatally. Local cerebral metabolic rates for glucose (LCMR(glc)) were measured using the [14C]2-deoxy-D-glucose (2 DG) autoradiography method and oxidative capacity was determined using cytochrome oxidase histochemistry (C.O.). Only glucose metabolism in the fetal-lesioned cats was affected substantially. There was a global decrease (31.0% relative to controls) of the LCMR(glc) for both cerebral hemispheres while focal decreases were seen mainly in thalamic and neostriatal nuclei (and reaching declines of over 50%). Cats with a neonatal lesion showed only a tendency to such declines (19.5% and 22.0% for the right and left hemispheres, respectively). C.O. values were not affected significantly either globally or locally in any of the age-at-lesion groups. In previous work using fetal animals with similar lesions, morphological evidence of subcortical neuropile degeneration was not observed; instead, a marked decrease in size of the ipsilateral remaining neocortex and a pronounced distortion of gyri and sulci patterns bilaterally were found. In this context, we propose that in the fetal-lesioned cats, there was a widespread lesion-induced decrease in corticofugal (and transcortical) synaptic inputs which was responsible for a decline in functional (synaptic) activities, and that this, in turn, caused a downturn in glucose utilization. In the neonatal cats minor degeneration, coupled with lack of reinnervation, would account for the tendency to 2 DG declines. These results indicate that the long-term metabolic response of the fetal brain to injury is also less adaptive than that of the neonatal brain. Since standard methods are available to measure cerebral metabolism in humans, our studies in animal models may help understanding the long term physiological consequences of developmental focal brain damage in patients as well as to predict the relationships between cerebral metabolism and the underlying long-term morphological effects of such lesions.

Alpha 1-adrenoceptor blockade increases behavioral deficits in traumatic brain injury

Experimental enhancement of noradrenergic activity following traumatic brain injury (TBI) accelerates behavioral recovery if performed at a time when brain norepinephrine (NE) turnover is decreased. But, since NE turnover is markedely increased immediately after TBI, the present study was undertaken to evaluate the effect of modulating these early changes in NE metabolism on recovery of function. Rats were pretrained on a modified beam walking task. Thirty minutes prior to unilateral somatosensory cortex contusion they were treated with a NE reuptake blocker [desmethy-limipramine (DMI); 10 mg/kg, ip, n = 6] or an alpha 1-adrenoreceptor antagonist [prazosin (PRZ); 3 mg/kg, ip, n = 6]. PRZ pretreatment markedly worsened beam walking performance throughout the 3 weeks following injury, whilst DMI pretreatment did not affect performance compared to injured controls (n = 4). Despite the marked behavioral deficits, PRZ-treated animals showed no apparent worsening of histological damage (n = 11 per group) and lesion size was the same in all groups. In separate experiments (n = 4 per group), PRZ lowered basal blood pressure and prevented the rise in pressure immediately following TBI. However, blood pressures in the three groups came to the same level within 20 sec following TBI. This suggest that the action of PRZ was not simply due to hypotension-induced ischemia. It is possible that blockade of alpha 1-adrenoreceptors in the immediate posttrauma period leads to enhancement of excitatory neurotransmission, which exacerbates behavioral deficits.

Focal traumatic brain injury causes widespread reductions in rat brain norepinephrine turnover from 6 to 24 h

The effect of right sensorimotor traumatic brain injury (TBI) in male Sprague-Dawley rats on brain norepinephrine (NE) turnover was assessed by measuring the decline of endogenous NE levels following tyrosine hydroxylase inhibition produced with alpha-methyl-p-tyrosine. Right sensorimotor cortex contusions were produced by a pneumatically driven piston which depressed the dural surface by 2 mm at 3.2 m/s. TBI rats were compared to uninjured, anesthetized controls at 6 h and 24 h after surgery. While NE turnover was not affected at the lesion site at 6 h after TBI, it was either abolished or decreased by 33-75% bilaterally in the hypothalamus and in the cerebral cortex surrounding and rostral to the lesion site. In the cortex caudal to the lesion site, NE turnover was completely abolished. NE turnover in cerebral cortex opposite the lesion site and in the contralateral cerebellum was decreased by 51 and 43%, respectively, at 6 h. At 24 h, NE turnover was either abolished or decreased bilaterally by 45-92% in all cortical areas, in the hypothalamus, cerebellum, locus coeruleus and medulla. Thus, right sensorimotor cortex contusion causes a marked, early and widespread depression of brain NE turnover. Since amphetamine increases NE turnover, this may explain the dramatic improvement in behavioral deficits which occurs following amphetamine administration at 24 h after such lesions.

Ischemia as an excitotoxic lesion: protection against hippocampal nerve cell loss by denervation

There are several indications for an involvement of neuroexcitatory mechanisms in ischemic neuron damage. Since we forwarded the hypothesis in 1982 that the transmitter glutamate is playing a key role, several lines of evidence have substantiated this: there is a pronounced transmitter release induced by ischemia and there is uptake of Ca++ via NMDA-operated calcium channels. Under certain circumstances postischemic neuron death can be impaired by administration of either NMDA-antagonists or calcium blockers. Further proof for the induction of harmful excitatory mechanisms by ischemia has been obtained by preischemic denervation of the vulnerable nerve cells. After transient cerebral ischemia in rats or gerbils, there are signs of irreversible damage (eosinophilia) of neurons in the dentate hilus (somatostatin-positive cells) after 2-3 hours and of hippocampal pyramidal neurons after 2-3 days (delayed neuron death). In the first case, removal of the (main) input to hilus cells by degranulation (colchicine selectively eliminates granule cells) protects these. In the case of pyramidal neurons removal of Schaffer collaterals/commisurals or input from the entorhinal cortex have a protective effect. Recently, we have measured glutamate and calcium in CA1 of denervated rats during 10 min of ischemia, and it turns out that there is almost no extracellular glutamate release or lowering of calcium in contrast to ischemic animals with intact innervation. Also in the postischemic period there are indications of a continuation of the damaging processes induced by ischemia. Besides the well known postischemic hypoperfusion, a prolonged release of glutamate has been reported, as well as burst firing in some models.(ABSTRACT TRUNCATED AT 250 WORDS)

Hippocampal CA3 lesion prevents postconcussive metabolic dysfunction in CA1

Immediately following fluid-percussion (F-P) brain injury, the hippocampus exhibits a marked increase in its local CMRglc (LCMRglc; mumol/100 g/min) as determined using [14C]2-deoxy-D-glucose autoradiography. This injury-induced increase in metabolism is followed in 6 h by a subsequent decrease in LCMRglc. These two postinjury metabolic states may be the result of ionic disruptions following trauma via stimulation of glutamate-gated ion channels. To determine if endogenous glutamate innervation to the CA1 region of the hippocampus can provide an anatomical basis for this proposed mechanism, it was removed by kainic-acid-induced destruction of CA3, and the effect on CA1 metabolism following concussive injury was studied. Five days before a lateral F-P injury (3.5-4.5 atm), kainic acid (0.5 microgram) or vehicle was stereotaxically injected into the left ventricle of 65 rats. Histological inspection indicated that kainic acid produced severe cell loss primarily in the CA3 region of the hippocampus ipsilateral to the injection. The metabolic results indicated that immediately following injury, animals with an intact hippocampus exhibited an increase in LCMRglc to 84.6 +/- 5 within the CA1 region, representing a 81.5% increase over controls. However, in the CA3-lesioned animals, CA1 showed no evidence of an injury-induced hypermetabolism, with LCMRglc remaining at control levels (51.4 +/- 3.9). At 6 h postinjury, the intact hippocampus exhibited a reduction of LCMRglc to rates of 40.7 +/- 4.7 within the CA1 region, representing a 17.9% reduction compared with controls. In contrast, CA3-lesioned animals exhibited less of an injury-induced decrease in LCMRglc within the CA1 region, exhibiting a mean rate of 43.4 +/- 4.5, representing only a 12.5% reduction compared with controls. These results indicate that the removal of the CA3 projection to CA1 protects the CA1 cells from the metabolic dysfunction typically seen following injury. This supports our previous work indicating the important role glutamate plays in the ionic flux and subsequent metabolic changes that follow traumatic brain injury.

Diffuse prolonged depression of cerebral oxidative metabolism following concussive brain injury in the rat: a cytochrome oxidase histochemistry study

Utilizing a lateral fluid percussion injury as a model of cerebral concussion, rats were studied histochemically measuring the degree of cytochrome oxidase activity present within different structures at different times following injury. After concussion, the cerebral cortex ipsilateral to the site of injury exhibited a diffuse decrease in its level of chromotome oxidase (CO) activity beginning at as soon as one day and lasting for up to 10 days after the insult. The ipsilateral dorsal hippocampus also exhibited an injury-induced decrease in CO activity, however, it was not as severe as in the cortex. These results indicate that oxidative metabolism is depressed primarily within the cerebral cortex and hippocampus for several days following a cerebral concussion. We propose that this period of metabolic depression may delineate a period of time during which the injured brain is unable to function normally and thus would be vulnerable to a second insult.

Dynamic changes in local cerebral glucose utilization following cerebral conclusion in rats: evidence of a hyper- and subsequent hypometabolic state

Following cerebral concussion, in which there is no evidence of direct morphological damage, cells are exposed to an increase in extracellular potassium as well as an accumulation of calcium. This concussion-induced ionic flux most likely alters the cellular energy demands thereby modifying metabolic processes. To investigate the metabolic changes after cerebral concussion, local cerebral metabolic rates for glucose (lCMRglc) utilizing [14C]2-deoxy-D-glucose were studied in rats (n = 98; 250-300 g) immediately, 30 min, 6 h, 1, 2, 3, 5 and 10 days following a unilateral frontoparietal fluid percussion (F-P) injury (3.7-4.3 atm). Compared to sham controls, animals exhibited bilateral hypermetabolism immediately following brain injury. However, this effect was more pronounced in structures ipsilateral to the site of F-P and was especially marked for the cerebral cortex (46.6-30.1% higher than control) and hippocampus (90.1-84.4% higher than control). By 30 min post-trauma many ipsilateral regions still showed evidence of hypermetabolism, although their lCMRglc had subsided. Beginning as early as 6 h following injury many regions within the ipsilateral cortex and hippocampus went into a state of metabolic depression (16.4-33.7% of control) which lasted for as long as 5 days. These results indicate that, although not mechanically damaged from the insult, cells exposed to concussive injury dramatically alter their metabolic functioning. This period of post-concussive metabolic dysfunction may delineate a period of time, following injury, during which cells are functionally compromised.

Postischemic glucose metabolism is modified in the hippocampal CA1 region depleted of excitatory input or pyramidal cells

During early postischemic reperfusion, the vulnerable brain regions (e.g., hippocampal CA1) show a relatively high deoxyglucose accumulation. To investigate if this accumulation is a marker for the later-occurring regional cell death and to determine its cellular localization, we studied the glucose metabolism in the CA1 region post ischemia after removal of its pre- or postsynaptic components. A 20-min period of cerebral ischemia was used for selective removal of the main postsynaptic component in CA1 pyramidal cells, and a bilateral intraventricular injection of kainic acid for removal of the majority of presynaptic axon terminals in this region (and postsynaptic terminals and cell bodies in CA3). The glucose metabolism was studied in these two lesion types and in sham-operated animals before and after a period of ischemia. There was a 60% reduction of metabolism after ischemia in the nonvulnerable regions, whereas CA1 and sometimes CA3 showed a columnar pattern of high and low metabolism. CA1 and CA3 devoid of the postsynaptic component showed increased postischemic metabolism. The latter was due to the presence of macrophages, as demonstrated by an enzyme histochemical stain for nonspecific esterase. CA1 with no presynaptic component showed a postischemic depression of the glucose metabolism similar to the rest of the brain. It is suggested that the level of the postischemic glucose metabolism in the ischemia-vulnerable regions is determined by the presence of both synaptic components. The presence of macrophages in a region gives rise to apparently normal values of glucose metabolism.

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.

Delayed hypometabolism induced by bilateral ischemia in the gerbil: regional metabolic thresholds

The common carotid arteries were occluded in gerbils for 5 min and the metabolic rate was estimated by measuring the loss of high-energy phosphate equivalents at 4 days of reperfusion in the cerebral cortex, hippocampus, and striatum. Metabolites values at 4 days of reperfusion were not different from those of controls with the exception of glycogen, which was significantly elevated in the hippocampus. The metabolic rate, as determined by the "closed-box" method at 4 days of reflow, was decreased by more than 50% in all three regions after 5 min of bilateral ischemia. The ischemic time necessary to elicit the hypometabolic response at 4 days of reflow was 2, 3 and 4 min for the striatum, hippocampus, and cortex, respectively. It is suggested that delayed postischemic hypometabolism may be a component of an adaptive process which counteracts, to varying degrees, the deleterious effects of ischemia depending on the region examined.