The effect of seizures on recovery of function following cortical contusion in the rat

Tongxinluo promotes axonal plasticity and functional recovery after stroke

Background

The aim of this study was to investigate the neural plasticity in contralesional cortex and the effects of tongxinluo (TXL) in cerebral ischemic rats.

Methodology

We used stroke-prone renovascular hypertensive (RHRSP) cerebral ischemia rat models to study the effect of TXL and the underlying mechanisms. We performed foot-fault and beam-walking tests to evaluate the motor function of rats after cortical infarction. Biotinylated dextran amine (BDA) was used to track axonal sprouting and neural connections.

Results

TXL enhanced the recovery of motor function in cerebral infarction rats. TXL increased axonal sprouting in the peri-infarcted area but not in the corpus callosum, indicating in situ origination instead of crossing between cortical hemispheres through the corpus callosum. TXL promoted the sprouting of corticospinal axons into the denervated side of spinal gray matter. The synaptophysin (SYN)-positive intensity in the peri-infarcted area of TXL-treated group was greater than that in the vehicle group. We observed co-localization of SYN with BDA-positive fibers in the denervated spinal cord gray matter in the TXL group, suggesting that axonal remodeling and synaptic connections were promoted by TXL.

Conclusion

TXL may promote the recovery of neurological function by promoting the axonal remodeling and synapse formation of motor neuronal fibers after focal cortical infarction in hypertensive rats.

A working model for hypothermic neuroprotection

Therapeutic hypothermia significantly improves survival without disability in near-term and full-term newborns with moderate to severe hypoxic-ischaemic encephalopathy. However, hypothermic neuroprotection is incomplete. The challenge now is to find ways to further improve outcomes. One major limitation to progress is that the specific mechanisms of hypothermia are only partly understood. Evidence supports the concept that therapeutic cooling suppresses multiple extracellular death signals, including intracellular pathways of apoptotic and necrotic cell death and inappropriate microglial activation. Thus, the optimal depth of induced hypothermia is that which effectively suppresses the cell death pathways after hypoxia-ischaemia, but without inhibiting recovery of the cellular environment. Thus mild hypothermia needs to be continued until the cell environment has recovered until it can actively support cell survival. This review highlights that key survival cues likely include the inter-related restoration of neuronal activity and growth factor release. This working model suggests that interventions that target overlapping mechanisms, such as anticonvulsants, are unlikely to materially augment hypothermic neuroprotection. We suggest that further improvements are most likely to be achieved with late interventions that maximise restoration of the normal cell environment after therapeutic hypothermia, such as recombinant human erythropoietin or stem cell therapy.

Effects of total saponins from Trillium tschonoskii rhizome on grey and white matter injury evaluated by quantitative multiparametric MRI in a rat model of ischemic stroke

ETHNOPHARMACOLOGICAL RELEVANCE

Trillium tschonoskii rhizome (TTR), a medicinal herb, has been traditionally used to treat traumatic brain injury and headache in China. Although the potential neuroprotective efficacy of TTR has gained increasing interest, the pharmacological mechanism remains unclear. Steroid saponins are the main bioactive components of the herb.

AIM OF THE STUDY

To investigate the protective and repair-promoting effects of the total saponins from TTR (TSTT) on grey and white matter damages in a rat model of middle cerebral artery occlusion (MCAO) using magnetic resonance imaging (MRI) assay.

MATERIALS AND METHODS

Ischemic stroke was induced by MCAO. TSTT and Ginaton (positive control) were administered orally to rats 6h after stroke and daily thereafter. After 15 days of treatment, the survival rate of each group was calculated. We then conducted neurological deficit scores and beam walking test to access the neurological function after ischemic stroke. Subsequently, T2-weighted imaging (T2WI) and T2 relaxometry mapping were performed to measure infarct volume and grey and white matter integrity, respectively. Moreover, diffusion tensor imaging (DTI) was carried out to evaluate the grey and white matter microstructural damage. Additionally, arterial spin labelling (ASL) - cerebral blood flow (CBF) and magnetic resonance angiography (MRA) images provided dynamic information about vascular hemodynamic dysfunction after ischemic stroke. Finally, haematoxylin and eosin (HE) staining was carried out to evaluate the stroke-induced pathological changes in the brain.

RESULTS

The survival rate and neurological behavioural outcomes (Bederson scores and beam walking tests) were markedly ameliorated by TSTT (65mg/kg) treatment within 15 days after ischemic stroke. Moreover, T2WI and T2 relaxometry mapping showed that TSTT (65mg/kg) significantly reduced infarct volume and attenuated grey and white matter injury, respectively, which was confirmed by histopathological evaluation of brain tissue. The results obtained from DTI showed that TSTT (65mg/kg) not only significantly alleviated axonal damage and demyelination, but also promoted axonal remodelling and re-myelination. In addition, TSTT treatment also enhanced vascular signal density and increased CBF in rats after MCAO.

CONCLUSION

Our results suggested the potential protective and repair-promoting effects of TSTT on grey and white matter from damage induced by ischemia. This study provides a modern pharmacological basis for the application of TSTT in managing ischemic stroke.

Predicting and preventing psychopathology following temporal lobe epilepsy surgery

Less than 3% of temporal lobe epilepsy (TLE) surgical outcome studies have investigated the psychiatric sequelae and morbidity associated with surgery. This is disproportionate to the extent of the problem. Variable prevalence rates have been reported for post-surgical depression, anxiety, and interictal psychosis. Until recently, very few studies distinguished de novo postoperative presentations from pre-existing conditions, making it difficult to accurately assess the impact of TLE surgery on psychiatric morbidity. Predictors of de novo postoperative presentations have proved elusive. This current review summarizes the findings from a systematic literature review of the psychiatric morbidity associated with TLE surgery including newly published follow-up data from our own series of 280 surgical patients. A framework for future research, possible pathophysiological mechanisms, and translational models are also discussed.

Acute neuroprotective effects of extremely low-frequency electromagnetic fields after traumatic brain injury in rats

Traumatic brain injury commonly has a result of a short window of opportunity between the period of initial brain injury and secondary brain injury, which provides protective strategies and can reduce damages of brain due to secondary brain injury. Previous studies have reported neuroprotective effects of extremely low-frequency electromagnetic fields. However, the effects of extremely low-frequency electromagnetic fields on neural damage after traumatic brain injury have not been reported yet. The present study aims to investigate effects of extremely low-frequency electromagnetic fields on neuroprotection after traumatic brain injury. Male Sprague-Dawley rats were used for the model of lateral fluid percussion injury, which were placed in non-electromagnetic fields and 15 Hz (Hertz) electromagnetic fields with intensities of 1 G (Gauss), 3 G and 5 G. At various time points (ranging from 0.5 to 30 h) after lateral fluid percussion injury, rats were treated with kainic acid (administered by intraperitoneal injection) to induce apoptosis in hippocampal cells. The results were as follows: (1) the expression of hypoxia-inducible factor-1α was dramatically decreased during the neuroprotective time window. (2) The kainic acid-induced apoptosis in the hippocampus was significantly decreased in rats exposed to electromagnetic fields. (3) Electromagnetic fields exposure shortened the escape time in water maze test. (4) Electromagnetic fields exposure accelerated the recovery of the blood-brain barrier after brain injury. These findings revealed that extremely low-frequency electromagnetic fields significantly prolong the window of opportunity for brain protection and enhance the intensity of neuroprotection after traumatic brain injury.

Strain-related differences after experimental traumatic brain injury in rats

The present study directly compares the effects of experimental brain injury in two commonly used rat strains: Fisher 344 and Sprague-Dawley. We previously found that Fisher rats have a higher mortality rate and more frequent seizure attacks at the same injury level than Sprague-Dawley rats. Although strain differences in rats are commonly accepted as contributing to variability among studies, there is a paucity of literature addressing strain influence in experimental neurotrauma. Therefore this study compares outcome measures in two rat strains following lateral fluid percussion injury. Fisher 344 and Sprague-Dawley rats were monitored for changes in physiological measurements, intracranial pressure, and electroencephalographic activity. We further analyzed neuronal degeneration and cell death in the injured brain using Fluoro-Jade-B (FJB) histochemistry and caspase-3 immunostaining. Behavioral studies using the beam walk and Morris water maze were conducted to characterize strain differences in both motor and cognitive functional recovery following injury. We found that Fisher rats had significantly higher intracranial pressure, prolonged seizure activity, increased FJB-positive staining in the injured cortex and thalamus, and increased caspase-3 expression than Sprague-Dawley rats. On average, Fisher rats displayed a greater amount of total recording time in seizure activity and had longer ictal durations. The Fisher rats also had increased motor deficits, correlating with the above results. In spite of these results, Fisher rats performed better on cognitive tests following injury. The results demonstrate that different rat strains respond to injury differently, and thus in preclinical neurotrauma studies strain influence is an important consideration when evaluating outcomes.

Anti-epileptogenesis in rodent post-traumatic epilepsy models

Post-traumatic epilepsy (PTE) accounts for 10-20% of symptomatic epilepsies. The urgency to understand the process of post-traumatic epileptogenesis and search for antiepileptogenic treatments is emphasized by a recent increase in traumatic brain injury (TBI) related to military combat or accidents in the aging population. Recent developments in modeling of PTE in rodents have provided tools for identification of novel drug targets for antiepileptogenesis and biomarkers for predicting the risk of epileptogenesis and treatment efficacy after TBI. Here we review the available data on endophenotypes of humans and rodents with TBI associated with epilepsy. Also, current understanding of the mechanisms and biomarkers for PTE as well as factors associated with preclinical study designs are discussed. Finally, we summarize the attempts to prevent PTE in experimental models.

Acute neuroprotection to pilocarpine-induced seizures is not sustained after traumatic brain injury in the developing rat

Following CNS injury there is a period of vulnerability when cells will not easily tolerate a secondary insult. However recent studies have shown that following traumatic brain injury (TBI), as well as hypoxic-ischemic injuries, the CNS may experience a period of protection termed "preconditioning." While there is literature characterizing the properties of vulnerability and preconditioning in the adult rodent, there is an absence of comparable literature in the developing rat. To determine if there is a window of vulnerability in the developing rat, post-natal day 19 animals were subjected to a severe lateral fluid percussion injury followed by pilocarpine (Pc)-induced status epilepticus at 1, 6 or 24 h post TBI. During the first 24 h after TBI, the dorsal hippocampus exhibited less status epilepticus-induced cell death than that normally seen following Pc administration alone. Instead of producing a state of hippocampal vulnerability to activation, TBI produced a state of neuroprotection. However, in a second group of animals evaluated 20 weeks post injury, double-injured animals were statistically indistinguishable in terms of seizure threshold, mossy fiber sprouting and cell survival when compared to those treated with Pc alone. TBI, therefore, produced a temporary state of neuroprotection from seizure-induced cell death in the developing rat; however, this ultimately conferred no long-term protection from altered hippocampal circuit rearrangements, enhanced excitability or later convulsive seizures.

A long-term video-EEG and behavioral follow-up after endothelin-1 induced middle cerebral artery occlusion in rats

The aim was to test the hypothesis that occlusion of the middle cerebral artery (MCA) results in the development of epilepsy in rats. Further, we investigated whether lesion volume, hippocampal pathology, early seizures, or severity of behavioral impairment is associated with the development and severity of epilepsy or interictal spiking. MCA occlusion was induced by intracerebral injection of endothelin-1 (ET; 120 pmol). One group of ET-injected rats were followed-up for 6 months (n = 15) and another for 12 months (n = 20). Sham-operated animals were injected with saline (n = 12). Occurrence of early and late seizures was monitored by intermittent video-electroencephalography. Sensorimotor function was tested with the running wheel and tapered beam-walking tests. Emotional learning and memory were assessed with the fear conditioning test and spatial learning and memory with the Morris water maze. Finally, brains were processed for histology. Only one rat developed late spontaneous seizures (i.e., epilepsy). Epileptiform interictal spiking was detected in 9 of 26 animals. Early seizures did not predict the development of epilepsy, spiking activity, or severity of behavioral impairment. Production of MCA stroke by intracerebral injection of ET was not a strong trigger of epileptogenesis in adult rats. Further studies are needed to investigate the effect of age, genetic background, and location of ET-injection on the development of hyperexcitability and the risk of post-stroke epileptogenesis.

Post-Traumatic Neural Depression and Neurobehavioral Recovery after Brain Injury

There are an estimated 2 million traumatic brain injuries (TBIs) each year in the United States, making the yearly incidence eight times greater than that of breast cancer and 34 times greater than HIV/AIDS. Still, it remains a "silent epidemic" because TBI results in persistent neurobehavioral impairment, without necessarily imparting a physical scar. The present review is a comparative analysis of TBI research, both basic and applied, outlining the evidence that at least one component of the brain's innate response to insult (e.g., post-traumatic neural depression) is sufficiently well understood to be the target of additional clinical studies and therapeutic strategy development.

Seizure heralding functional recovery in a patient with apallic syndrome: A case report with retrospective-prospective observation

BACKGROUND

It has been suggested that there exists a close relationship between seizure discharges and functional recovery from brain injury, and that paroxysmal bombardment in late seizures may herald functional recovery or may "kick-start" recovery.

CASE REPORT

We report the case of a 52-year-old patient who, following a subarachnoid hemorrhage and multiple surgeries, experienced discernible apallic syndrome of long duration. His hospitalization is well documented. The patient underwent protracted, intense rehabilitation, but he remained in this prolonged state of loss of consciousness and behavioral passivity until he experienced a series of periodic seizures. Widespread improvement in his cognitive and functional abilities coincided closely with the seizure activity. The literature on this topic is reviewed.

CONCLUSION

This case confirms the close relationship between seizure discharges and functional recovery reported in preclinical literature.

Seizures and Epilepsy After Ischemic Stroke

Background— Although a long-recognized clinical phenomenon, there remain many questions regarding the epidemiology of seizures and epilepsy after ischemic stroke, their effect on outcome, and their treatment.

Summary of Review— Interpretation of the various studies that have been conducted of postischemic stroke seizures and epilepsy are complicated by their heterogeneous designs, inconsistent uses of terminology, small sample sizes, different periods of follow-up, and ambiguities in seizure identification and classification. Estimates of the rate of early postischemic stroke seizures range from 2% to 33%. The rates of late seizures vary from 3% to 67%. The rate of postischemic stroke epilepsy is ≈2% to 4% and is higher in those who have a late seizure. Data reflecting seizure subtypes are limited. Aside from cortical location and, possibly, stroke severity, no other risk factors for postischemic stroke seizures have been consistently demonstrated. Results regarding the impact of postischemic stroke seizures on outcome are inconsistent.

Conclusions— Much additional work is needed to better understand the epidemiology and social impact of postischemic stroke seizures and epilepsy, their prevention, and optimal management.

Experimental focal ischemic injury: behavior-brain interactions and issues of animal handling and housing

In experimental neurological models of brain injury, behavioral manipulations before and after the insult can have a major impact on molecular, anatomical, and functional outcome. Investigators using animals for preclinical research should keep in mind that people with brain injury have lived in, and will continue to live in, an environment that is far more complex than that of the typical laboratory rodent. To yield more reliable and relevant behavioral assessment, it may be appropriate in some cases to house animals in environments that allow for motor enrichment and to handle animals in ways that promote tameness. Experience can affect mechanisms of plasticity and degeneration beneficially or adversely. Behavioral interventions that have been found to modulate postinjury brain events are reviewed. The timing and interaction of biological and motor therapies and the potential contribution of experience-dependent and drug-induced trophic factor expression are discussed.

The effects of repeated minimal electroconvulsive shock exposure on levels of mRNA encoding fibroblast growth factor-2 and nerve growth factor in limbic regions

Chronic, but not acute, exposure to minimal electroconvulsive shock (ECS) has been shown to decrease vulnerability to neuronal cell death, without itself causing neuronal damage. One potential mechanism for the neuroprotective effect of ECS is the increase in fibroblast growth factor-2 (FGF-2) which occurs after chronic, but not acute, ECS exposure. This raises the possibility that repeated seizures over a period of several days may alter the transcriptional regulation of FGF-2. To test this hypothesis, the present study compared the effect of acute (1 day) vs. chronic (7 days) ECS treatment on levels of mRNA for FGF-2 in rhinal and frontal cortices, hippocampus, and olfactory bulbs. In addition, mRNA for another prominent neurotrophic factor, nerve growth factor (NGF), was assayed concurrently. At 8 h after acute ECS, mRNA levels increased by 60% for FGF-2 and 136% for NGF in rhinal cortex, 32% for FGF-2 and 36% for NGF in frontal cortex, and by 13% for NGF in hippocampus. After 7 days of ECS treatment the respective increases were 72% and 80%, 53% and 38%, and 28%. No increases were observed in olfactory bulbs after either treatment regimen. The peak increases in FGF-2 mRNA were consistently greater after chronic treatment, but the differences from those seen acutely reached significance in frontal cortex only. However, the duration over which mRNA for FGF-2 was elevated did not differ between the acute and chronic ECS groups. NGF mRNA induction was neither enhanced nor prolonged as a result of chronic ECS as compared to acute ECS treatment. These results suggest that chronic ECS treatment may lead to an enhanced rate of transcription of message for FGF-2 but not for NGF, in selected brain regions. At the same time, the results indicate that chronic ECS treatment induces FGF-2 and NGF mRNA expression in a tissue-specific manner and that this induction is maintained over the 7-day treatment period. The sustained increases in mRNAs for these trophic factors may contribute to the neuroprotective actions of chronic ECS treatment.

Administration of adenosine receptor agonists or antagonists after controlled cortical impact in mice: effects on function and histopathology

Adenosine is an endogenous neuroprotectant via anti-excitotoxic effects at A(1) receptors, and blood flow promoting and anti-inflammatory effects at A(2a) receptors. Previous studies showed improved motor function after fluid percussion injury (FPI) in rats treated with the broad-spectrum adenosine receptor agonist 2-chloroadenosine (2-CA). We studied the effects of 2-CA, a specific A(1) agonist (2-chloro-N(6)-cyclopentyladenosine, CCPA), and a specific A(1) antagonist (8-cyclopentyl-1,3-dipropylxanthine, DPCPX) on motor task and Morris water maze (MWM) performance, and histopathology (contusion volume, hippocampal cell counts) after controlled cortical impact (CCI) in mice. Each agent (12 nmol), or respective vehicle (saline or DMSO) was injected into dorsal hippocampus beneath the contusion immediately after CCI or craniotomy (sham). 2-CA treatment attenuated wire grip deficits after CCI (P<0.05 versus other treatments). DPCPX treatment exacerbated deficits on beam balance (P<0.05 versus sham). No treatment effect was seen on MWM performance, although there was a deleterious effect of the DMSO vehicle used for DPCPX. Contusion volume tended to be attenuated by 2-CA (P=0.08 versus saline) and increased after either DMSO or DPCPX (P<0.05 versus all groups). CA1 and CA3 counts were decreased in all groups versus sham. However, treatment with the selective A(1) agonist CCPA attenuated the CA3 cell loss (P<0.05 versus other treatment). We suggest that the beneficial effect of the broad spectrum adenosine receptor agonist 2-CA on motor function after CCI is not mediated solely by effects at the A(1) receptor.

Cortical and subcortical lesions impair skilled walking in the ladder rung walking test: a new task to evaluate fore- and hindlimb stepping, placing, and co-ordination

The ladder rung walking test is a new task to assess skilled walking and measure both forelimb and hindlimb placing, stepping, and inter-limb co-ordination. Rats spontaneously walk from a starting location to a goal along a horizontal ladder. The spacing between the rungs of the ladder is variable and can be changed to prevent the animal from learning either the absolute or relative location of the rungs. The testing procedure requires minimal training and allows detailed quantitative and qualitative analysis using video recording. The utility of the test is described with postoperative data obtained from animals with unilateral neocortical strokes produced by pial stripping over the motor cortex, neonatal and adult unilateral corticospinal tract lesions produced by tract section at the pyramids, and unilateral dopamine depletions produced by injection of 6-hydroxydopamine into the nigrostriatal bundle. In addition, a group of aged rats was examined. Deficits in limb placing, stepping and co-ordination displayed by the animals demonstrate that this test can discriminate between lesions of the motor system or age-associated impairments. The test is useful for assessing loss and recovery of function due to brain or spinal cord injury, the effectiveness of treatment therapies, as well as compensatory processes through which animals adapt to nervous system injury.

Vigabatrin directed against kindled seizures following cortical insult: impact on epileptogenesis and somatosensory recovery

The anticonvulsant drug vigabatrin has not been found to be detrimental to the recovery process when administered following focal cortical insult. This finding is in contrast to the negative postinjury consequences of other anticonvulsant drugs (e.g., phenobarbital and diazepam) with more direct activation of the GABA/benzodiazepine receptor complex. Moreover, phenobarbital directed against kindled seizures affects functional recovery more adversely than either the drug or subconvulsive seizures alone. The purpose of the present study was to determine whether vigabatrin (150, 200, and 250 mg/kg) directed against kindled seizures would impact recovery from lesion-induced somatosensory deficits. Vigabatrin was coupled with daily electrical kindling of the amygdala during the first week after a unilateral anteromedial cortex (AMC) lesion. Somatosensory recovery was assessed using bilateral tactile stimulation tests. Animals receiving the highest dose of vigabatrin prior to electrical kindling (250 mg/kg vigabatrin/kindled) remained significantly impaired even after two months of testing relative to vehicle/kindled, kindled/250 mg/kg vigabatrin, which received vigabatrin after electrical kindling, and the 150, 200, and 250 mg/kg vigabatrin/nonkindled groups (p < 0.0001). In contrast, neither vigabatrin (at any of the doses tested) nor subconvulsive kindled seizures impacted the recovery process (p > 0.05) when administered alone (i.e., without the drug + seizure interaction). These data add to the accumulating experimental and clinical evidence suggesting that the neurobehavioral consequences of the interaction between anticonvulsant drugs and subclinical seizures after brain insult are detrimental to functional recovery.

Distinctive amygdala kindled seizures differentially affect neurobehavioral recovery and lesion-induced basic fibroblast growth factor (bFGF) expression

The differing effects of partial seizures on neurobehavioral recovery following anteromedial cortex (AMC) injury in rats have previously been reported. Specifically, convulsive Stage 1 seizures evoked ipsilateral to the lesion during the 6-day post-lesion critical period delayed recovery, while non-convulsive Stage 0 seizures were neutral. The present study was designed to elaborate on that research by examining several potential mechanisms for the seizure-associated difference observed in functional outcome. Anesthetized rats sustained unilateral AMC lesions followed by implantation of a stimulating electrode in the amygdala ipsilateral (Expt. 1) or contralateral (Expt. 2) to the lesion. Beginning 48 h after surgery, animals were kindled to evoke Stage 0 or Stage 1 seizure activity during the critical period. Kindling trials and afterdischarge (AD) were controlled to ascertain their role in functional outcome. Recovery from somatosensory deficits was assessed over a two-month period. The results revealed that (i) Stage 0 seizures did not impact recovery regardless of whether initiated ipsilateral or contralateral to the lesion, (ii) Stage 1 seizures prevented recovery only when initiated in the ipsilateral hemisphere during the post-lesion critical period, and (iii) the detrimental effect of Stage 1 seizures appears to be independent of the number of kindling trials provided and cumulative AD. Thus, to determine why Stage 1 seizures evoked in the hemisphere ipsilateral to the lesion impeded recovery, a separate group of animals (Expt. 3) were kindled accordingly and processed for c-Fos and basic fibroblast growth factor (bFGF) immunohistochemistry. It was hypothesized that Stage 1 seizures evoked in the injured hemisphere prevent recovery by blocking lesion-induced bFGF expression in structures shown to be important for recovery after cortex lesions (e.g., striatum). The results confirmed our hypothesis and suggest that the seizure-associated inhibition of lesion-induced bFGF may alter the growth factor-mediated plasticity necessary for functional recovery.

Phenobarbital administration directed against kindled seizures delays functional recovery following brain insult

Anti-convulsant drug administration or recurrent seizures can impact functional recovery following brain insult. The nature of that impact depends on a variety of factors, including timing of drug administration and drug mechanism of action, as well as seizure number, timing, and severity. The objective of this study was to determine the functional consequences of anti-convulsant administration directed against seizure activity in brain-damaged animals. To this end, phenobarbital was coupled with daily electrical kindling of the amygdala beginning 48 h after a unilateral anteromedial cortex lesion. Recovery from somatosensory deficits was assessed, as was regional atrophy and basic fibroblast growth factor (bFGF) expression. Animals receiving phenobarbital prior to daily kindling failed to recover within 2 months of testing. In contrast, animals receiving saline prior to kindling as well as phenobarbital-treated non-kindled animals recovered within 2 months after the lesion. Though the exact mechanisms underlying these behavioral phenomena remain uncertain, patterns of bFGF expression among the groups provide some insight. Taken together, results from the present study suggest that anti-convulsant drug administration directed against subclinical seizure activity can be more detrimental to functional recovery than seizures alone or anti-convulsant drug treatment after seizure activity has occurred.

Kindled seizures during a critical post-lesion period exert a lasting impact on behavioral recovery

The present study was undertaken to assess the effects of amygdala kindling on behavioral recovery following unilateral frontal cortex damage in rats. Daily electrical stimulation of the amygdala began 48 h after lesion and continued until all animals had a single Stage 5 seizure. When amygdala kindled seizure activity ratable as Stage 0 occurred within the first 6 days after lesion, animals recovered from somatosensory asymmetries in approximately 3 weeks. In contrast, kindled animals that experienced Stage 1 seizure activity within the first 6 days after lesion failed to recover from somatosensory deficits in 4 months of testing. Differences in rate of recovery could not be accounted for by lesion size or placement. These data support the notion that not only is there a 'critical period' after brain damage during which the recovery process is vulnerable to seizure activity, but the type of kindled seizure that is experienced during that time ultimately determines how recovery is affected.

Hyperbaric oxygen tolerance in newborn mammals--hypothesis on mechanisms and outcome

Newborn mammals, compared to adults, are extremely resistant to the CNS effects of hyperbaric oxygenation (HBO) induced by excessive generation of reactive oxygen species. This tolerance to HBO may be related to either physiological responses or the chemical characteristics of the immature brain, including a low cerebral blood flow and energy metabolism, and a low concentration of polyunsaturated fatty acids. In adult mammals the main protective mechanism against CNS oxygen toxicity, besides endogenous antioxidants, is a transient HBO-induced cerebral vasoconstriction. How cerebral vasculature reacts to HBO in the immature brain is not known. We present indirect evidence suggesting that HBO in newborn rats induces a persistent cerebral vasoconstriction concurrently with a severe and maintained reduction in ventilation. It is speculated that the outcome of these physiologic responses to hyperoxic exposures may be: (a) extension of tolerance to both CNS and pulmonary oxygen poisoning; (b) creation of a profound hypoxic-ischemic condition in vulnerable neural structures; and (c) impairment of the circulatory and ventilatory responses to hypoxic stimuli on return to air with consequent development of a secondary hypoxic-ischemic condition. These hypothetical pre- and post-HBO events may set the stage for the development of some delayed neurological disorders, including the retinopathy of prematurity and the retardation of brain development in fetuses or prematurely-born infants subjected to oxygen therapy.

Seizures and recovery from experimental brain damage

The effects of the gamma-aminobutyric acid antagonist, pentylenetetrazol (PTZ), on recovery from somatosensory and motor asymmetries after unilateral sensorimotor cortex lesions were investigated. Behavior was assessed using a bilateral tactile stimulation test and a measure of forelimb motor coordination. Immediately after surgery, the PTZ-treated and saline (SAL) control groups both exhibited severe ipsilateral behavioral asymmetries. Rats receiving PTZ recovered significantly faster from somatosensory asymmetry than those receiving SAL. Recovery was complete in the PTZ group within 3 postoperative weeks, while the SAL group failed to reach a comparable level until 2 months after surgery. There was no difference between PTZ and SAL groups on recovery of forelimb motor coordination. No difference in lesion size between the SAL and the PTZ groups could be found. These data are consistent with the hypothesis that post-traumatic neuronal depression may contribute to the severity of sensorimotor deficits observed after brain damage.