In vivo imaging of brain incorporation of fatty acids and of 2-deoxy-D-glucose demonstrates functional and structural neuroplastic effects of chronic unilateral visual deprivation in rats

Regional cerebral 'incorporation coefficients' k* of each of 3 labeled long-chain fatty acids -[9,10-3H]palmitate ([3H]PA), [1-14C]arachidonate ([14C]AA) and [1-14C]docosahexaenoate ([14C]DHA)-were measured using quantitative autoradiography in 11 bilateral brain visual areas of 3.5-month-old awake, hooded, Long-Evans rats, and were compared with regional cerebral metabolic rates for glucose (rCMRglc). The rats, which had undergone unilateral orbital enucleation at 15 days of age, were studied either in the dark with eyelids of the intact eye sutured, or when stimulated in a light box with the intact eye open. rCMRglc did not differ between homologous contralateral and ipsilateral visual areas in the dark or during stimulation, but was elevated bilaterally by 25% or more in many visual areas during stimulation compared with dark. Contralateral compared with ipsilateral k* was lower for each fatty acid tracer in superficial gray of the superior colliculus (in dark and during stimulation) and dorsal nucleus of lateral geniculate body (during stimulation). In the dark, k* for [3H]PA was correlated significantly with rCMRglc for the 22 visual areas studied, whereas during stimulation k* for [14C]AA was correlated with rCMRglc. These results suggest that central neuroplastic changes following chronic unilateral enucleation are accompanied by reduced incorporation of [3H]PA, [14C]AA and [14C]DHA into contralateral brain ares that normally receive crossed retinofugal fibers, and by symmetry of rCMRglc in the dark but increased bilateral symmetrical responsiveness of rCMRglc to visual stimulation of the intact eye.     

Fatty acid incorporation depicts brain activity in a rat model of Parkinson's disease

Following pulse labeling with [3H]arachidonic acid ([3H]AA), its incorporation pattern in brain reflects regional changes in neurotransmitter signal transduction using phospholipase A2, that is, functional activity. In a rat model of Parkinson's disease, unilateral 6-hydroxydopamine lesion in the substantia nigra, [3H]AA acid incorporation from blood was increased in cerebral cortex, caudate putamen, globus pallidus, entopeduncular nucleus, subthalamic nucleus and substantia nigra pars reticulata ipsilateral to the lesion. This increased [3H]AA incorporation likely reflects disinhibition of basal ganglia and cortical circuits secondary to absent inhibitory nigrostriatal dopaminergic input.     

Differential effects of buprenorphine and pentazocine on the regional cerebral metabolic rate for glucose in the conscious rat

The effects of buprenorphine (BNP, 10-200 micrograms/kg, i.v.) and pentazocine (PTZ, 2.5-10 mg/kg, i.v.) on the regional cerebral metabolic rate for glucose (rCMRglc) were analyzed in nine anatomically discrete areas of the conscious rat brain by the simultaneous use of [14C]2-deoxyglucose, the glucose analogue that can be phosphorylated in the brain, and [3H]3-O-methylglucose, a nonmetabolizable glucose analogue. Originally, this method was developed by Gjedde and Diemer in the rat and in humans. The rCMRglc was significantly decreased by BNP (100 or 200 micrograms/kg) in most of the brain regions investigated, except the cerebellum. In contrast, PTZ (10 mg/kg) significantly increased rCMRglc in the cerebral cortex and medulla. In the cerebral cortex and medulla, the direction of the effect on rCMRglc was opposite for BNP (22% decrease at the dose of 200 micrograms/kg) and PTZ (22% increase at the dose of 10 mg/kg). These findings strongly suggest that the discrepancies between the marked effects of BNP (a partial mu agonist and kappa antagonist) and PTZ (a mu antagonist and kappa agonist) on rCMRglc reflect the selectivity of agonist action at the different types of opioid receptors, mu and kappa receptors, in the rat brain.     

Regulation of cerebral microvessels by glutamatergic mechanisms

We studied changes in glutamate receptors, expression of immediate early genes, and AP-1 DNA binding activity in the brains of phenobarbital (PB)-dependent and -withdrawn rats to investigate the possible involvement of activation of glutamate receptors in PB withdrawal syndrome. PB-dependent rats were prepared by feeding drug-admixed food for 5 weeks. Autoradiographic analysis showed that binding of [3H(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imin e (MK-801), an antagonist of N-methyl-D-aspartic acid (NMDA) receptors, increased significantly in the cerebral cortices of PB-dependent and 24-h-withdrawn rats. However, [3H]MK-801 binding in the hippocampus and [3H]6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and [3H]kainic acid binding in the hippocampus and cerebral cortex were essentially unchanged in both groups. PB withdrawal seizures were followed by increased expression of c-fos mRNA in the hippocampus and cerebral cortex and of c-jun mRNA in the cerebral cortex. The induction of c-fos and c-jun mRNA was suppressed by administration of MK-801. Furthermore, PB withdrawal enhanced AP-1 DNA binding activity in the brain. The present findings suggest functional enhancement of glutamatergic neurotransmission during the development of PB withdrawal syndrome.     

Neurotoxin domoic acid produces cytotoxicity via kainate- and AMPA-sensitive receptors in cultured cortical neurones

Domoic acid, a naturally occurring kainoid, has been responsible for several outbreaks of fatal poisoning after shellfish ingestion, and we examined its neurotoxic mechanism in cultured murine cortical neurones. Using observations of neuronal viability and morphology, exposure to domoic acid for 24 h was found to induce substantial concentration-dependent neuronal cell death. Domoic acid-mediated neuronal death was attenuated by the non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitro-quinoxaline-2,3-dione and the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-selective antagonist LY293558 ((3S,4aR,6R,8aR)-6-[2-(1H-tetrazol-5-yl)-ethyl]-1,2,3, 4,4a,5,6,7,8,8a-decahydroisoquinoline-3-carboxylic acid), but unaffected by NS-102 (5-nitro-6,7,8,9-tetrahydrobenzo[g]indole-2, 3-dione-3-oxime)--a low-affinity kainate receptor antagonist. Domoic acid was equipotent with (S)-AMPA (EC50 values 3.8 and 3.4 microM respectively); however, (S)-AMPA induced only 50% cell death compared to > 80% cell death induced by domoic acid. Kainate also killed > 80% of cortical neurones; however, domoic acid was about 19 times more potent than kainate (EC50 75 microM). We show the potent neurotoxicity of domoic acid for the first time in a pure neuronal model and indicate that domoic acid acts via high-affinity AMPA- and kainate-sensitive glutamate receptors to produce excitotoxic cell death.     

Modification of [3H]MK801 binding to rat brain NMDA receptors after the administration of a convulsant drug and an adenosine analogue: a quantitative autoradiographic study

Specific [3H]MK801 binding to rat brain NMDA receptors after the administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) was studied by means of a quantitative autoradiographic method. MP administration (150 mg/kg, i.p.) caused significant decreases in [3H]MK801 binding in several hippocampus subareas and layers, mainly in CA1 and CA3 at seizure (11-27%) and postseizure (8-16%) and in cerebral occipital cortex at seizure (18-22%). In nucleus accumbens, a rise was observed at postseizure (44%) and a tendency to increase at seizure (24%). CPA (2mg/kg, i.p.) decreased ligand binding in hippocampus (CAI, CA2, CA3) (17-22%) and in occipital cerebral cortex (18-24%). When CPA was administered 30 minutes before MP (which delayed seizure onset) and rats were sacrificed at seizure, decreases in [3H]MK801 binding in several layers of CA1 and CA3 of hippocampus (11-27%) and in CA1, CA2, CA3 (24-35%) after CPA+MP postseizure, and an increase in CA2 after CPA and CPA+MP postseizure (20-34%), were observed. A drop was found in the occipital subarea (18-24%) after CPA and in the frontal and occipital subarea after CPA+MP postseizure (24-34%) while no changes were observed in any treatment involving the other cerebral cortex regions, thalamic nuclei, caudate putamen and olfactory tubercle. These results show that [3H]MK801 binding changes according to drug treatment and the area being studied, thus indicating a different role in seizure activity.     

Role of P-450 arachidonic acid epoxygenase in the response of cerebral blood flow to glutamate in rats

BACKGROUND AND PURPOSE: Glutamate, a major excitatory neurotransmitter in the brain, has been implicated in the hyperemic response to increases in the activity of neurons, but the mechanism of glutamate-induced dilation of cerebral blood vessels is unknown. Glutamate has been shown to enhance the release of arachidonic acid (AA) in brain tissue and cultured astrocytes. We have previously shown that astrocytes metabolize AA to vasodilator products, epoxyeicostrienoic acids (EETs), and express a P-450 AA epoxygenase, P-450 2C11. We tested the hypothesis that glutamate-induced dilation of cerebral arterioles is mediated in part by changes in the formation and release of EETs by perivascular astrocytes. METHODS: Primary astrocyte cultures were prepared from 3-day-old rat pups. The cells were labeled with [14C]AA, and the effect of glutamate on the formation of EETs from [14C]AA by cultured astrocytes was studied. The expression of P-450 2C11 protein in the microsomal fractions of cultured astrocytes was assessed by Western blot. In vivo cerebral blood flow measurements were made in adult rats by laser-Doppler flowmetry after administration of glutamate into the subdural space of the rat before and after treatment with miconazole. RESULTS: Glutamate treatment (100 mumol/L for 30 minutes) induced a threefold increase in the formation of EETs from [14C]AA by cultured astrocytes, and the increase was inhibited by miconazole (20 mumol/L), an inhibitor of P-450 AA epoxygenase. Treatment with glutamate (100 mumol/L) for 12 hours increased the expression of P-450 2C11 protein in the microsomal fraction of cultured astrocytes. The response of laser-Doppler cerebral blood flow to administration of glutamate (500 mumol/L) into the subdural space of the rat was significantly attenuated after treatment with miconazole (20 mumol/L for 30 minutes). CONCLUSIONS: These findings suggest a role for a P-450 AA epoxygenase in astrocytes in the coupling between the metabolic activity of neurons and regional blood flow in the brain.     

Neural and behavioural effects of domoic acid, an amnesic shellfish toxin, in the rat.

Two experiments with 38 rats examined the neurotoxic effects of domoic acid. In Exp 1, iv injection of 0.5–2.0 mg/kg or intraventricular (ivc) injection of 0.04–0.08 μg of domoic acid caused seizures in the hippocampus, tonic-clonic convulsions, and death within a few days. Convulsions and ensuing death were prevented by diazepam. Ss pretreated with intraperitoneal/ly (ip) diazepam (5 mg/kg) tolerated an ivc dose of domoic acid of 0.4 μg, but showed a loss of pyramidal neurons mainly in the CA3, the CA4, and a part of the CA1 areas of the dorsal hippocampus. In Exp 2, learning of a radial maze task was severely impaired in naive Ss after ivc injection of domoic acid (and diazepam, ip). In Ss previously trained on the maze task, domoic acid interfered with relearning of the same task. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Release of dopamine, GABA and EAA in rats during intrastriatal perfusion with kainic acid, NMDA and soman: a comparative microdialysis study

There is an increasing amount of experimental evidence that excitatory amino acids (EAAs) are involved in the brain lesions observed after severe intoxication with the highly toxic organophosphorus compound soman. This study was undertaken to compare the acute actions of soman, and the glutamatergic receptor agonists kainic acid and N-methyl-D-aspartate (NMDA) on striatal release of dopamine and amino acids. The neurotoxic compounds were administered in high (10 mM) concentrations by unilateral intrastriatal microdialysis perfusion in freely moving rats. During the microdialysis the animals were observed for toxic signs related to convulsion. The glial fibrillary acidic protein (GFAP) was monitored as a marker of neurotoxicity in parts of prefrontal cortex, hippocampus, striatum and cerebellum. Acetylcholinesterase (AChE) inhibition in six brain regions was measured after soman perfusion in order to assess its cerebral distribution. We found that soman perfusion induced a major release of dopamine, GABA and aspartate in the striatum. Kainic acid also induced a release of dopamine and aspartate. NMDA was not as potent an inducer of striatal neurotransmitter release as soman and kainic acid. Soman and kainic acid perfusion produced convulsive behaviour in the rats. The main neurochemical event in the striatum during soman- and kainate-induced convulsions is the release of dopamine. We suggest that this major dopamine release might be as important as an increase in EAA in the cascade of pathological events leading to the brain damage in the striatum observed after soman intoxication.     

Intravenously injected radiolabelled fatty acids image brain tumour phospholipids in vivo: differential uptakes of palmitate, arachidonate and docosahexaenoate

This paper investigates the incorporation of intravenously (i.v.) administered radiolabelled fatty acids--[9,10(3)-H]palmitate (3H-PA), [1-14C]arachidonate (14C-AA) and [1-14C]docosahexaenoate (14C-DHA)--into intracerebrally implanted tumours in awake Fischer-344 rats. A suspension of Walker 256 carcinosarcoma tumour cells (1 x 10(6) cells) was implanted into the right cerebral hemisphere of 8- to 9-week-old rats. Seven days after implantation, the awake rat was infused i.v. for 5 min with 3H-PA (6.4 mCi/kg), 14C-AA (170 microCi/kg) or 14C-DHA (100 microCi/kg). Twenty minutes after the start of infusion, the rat was killed and coronal brain sections were obtained for quantitative autoradiography and histology. Each fatty acid showed well-demarcated incorporation into tumour tissue. Areas of necrosis or haemorrhage showed no or small levels of incorporation. The ratios of incorporation into the tumour to incorporation into contralateral brain regions were 2.8-5.5 for 3H-PA, 2.1-3.3 for 14C-AA and 1.5-2.2 for 14C-DHA. The mean ratios differed significantly between the fatty acids (P < 0.01). 3H-PA was not incorporated into necrotic tumours despite the presence of an open blood-tumour barrier, indicated by extravasated horseradish peroxidase. The incorporation rate constant of 3H-PA was similar for small intracerebral and large extracerebral tumours. The results show that 3H-PA, 14C-AA and 14C-DHA are incorporated more readily into tumour tissue than into brain, and that the increase is primarily due to increased utilization of fatty acids by tumour cells and not due to a high blood-tumour permeability. The relative increases in rates of incorporation for the different fatty acids may be related to lipid composition of the tumour and to the requirement of and specific role of these fatty acids in tumour cell growth and division.     

"Acquisition of a complex place task in rats with selective ibotenate lesions of hippocampal formation: Combined lesions of subiculum and entorthinal cortex versus hippocampus": Correction.

Reports an error in "Acquisition of a complex place task in rats with selective ibotenate lesions of hippocampal formation: Combined lesions of subiculum and entorhinal cortex versus hippocampus" by John-Paul Bouffard and Leonard E. Jarrard (Behavioral Neuroscience, 1988[Dec], Vol 102[6], 828-834). This article's corresponding plate appears on page 995. The information should read, "Plate A. Photomicrographs of horizontal, cresyl violet stained sections at dorsal, middle, and ventral levels of the brain for an unoperated control rat (left), an animal from the Subiculum + Entorhinal lesion group (middle), and a rat from the hippocampus group (right)." (The following abstract of the original article appeared in record 1989-28756-001.) The effects of isolating the hippocampus from its neocortical inputs and outputs by damaging the deep layers of entorhinal cortex and subiculum were compared with direct removal of the hippocampus using acquisition of a complex radial maze task. A series of eight problems (four out of eight arms being correct) were learned under either massed (45 s) or distributed (10 min) practice conditions, thus varying contextual information. Performance of rats with subiculum/entorhinal cortex lesions was similar to that of controls in all aspects of the radial maze task; whereas animals with hippocampal lesions were impaired on nearly all dependent measures. Although the effects of varying the intertrial interval were generally small, distributed practice did serve to facilitate the performance of hippocampal rats in terms of working memory. These findings are discussed as they related to recent theorizing in the area. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In vivo uptake of [3H]nimodipine in focal cerebral ischemia: modulation by hyperglycemia

Cell membrane depolarization and tissue acidosis occur rapidly in severely ischemic brain. Preischemic hyperglycemia is recognized to increase ischemic tissue acidosis and the present studies were undertaken to correlate depolarization and tissue acidosis during acute focal cerebral ischemia and hyperglycemia. We used a dual-label autoradiography method to simultaneously measure the in vivo distribution of [3H]nimodipine and [14C]DMO (5,5-dimethyl-2,4-oxazolidinedione) in brain to identify regions of ischemic depolarization and measure regional net tissue pH. Regional cerebral blood flow (CBF) was measured in separate studies. Measurements were made 30 minutes after combined middle cerebral artery and ipsilateral common carotid artery occlusion in normoglycemic and hyperglycemic rats. Tissue pH in the ischemic cortex was depressed to 6.76 +/- 0.11 in normoglycemic rats (n = 12) and 6.57 +/- 0.13 in hyperglycemic rats (n = 12), with significantly greater acidosis in the hyperglycemic group (P < 0.001). In contrast the ratio of [3H]nimodipine uptake in the ischemic cortex relative to the contralateral nonischemic cortex was significantly greater in normoglycemic (1.83 +/- 0.45) than hyperglycemic (1.40 +/- 0.50) rats (P < 0.05). Within this region of ischemic cortex CBF was 31 +/- 22 mL/100 g in normoglycemic rats (n = 8) and 33 +/- 22 mL/100 g/min in hyperglycemic rats (n = 9). Cerebral blood flow did not differ between these two groups in any region. Thus hyperglycemia reduced the extent of ischemic depolarization within the cortex during the first 30 minutes of focal cerebral ischemia. This effect may be related to the increased tissue acidosis or to other factors that may lessen calcium influx and preserve cellular energy stores in the ischemic cortex of the hyperglycemic rats.     

Research on factors affecting neonatal tetanus and its prevention through immunization

This study examined [3H]MK-801 binding to the N-methyl-D-aspartate (NMDA) receptor in membranes prepared from cerebral cortex, hippocampus and corpus striatum of 3 week old rats exposed to 10 weeks of intermittent hypobaric hypoxia (4300 m; 450 Torr) and compared results with those of normoxic controls. The cortex, hippocampus and striatum of hypoxic animals had a 36, 35 and 31% reduction in binding sites (Bmax) and a 29, 32 and 17% decrease (reflecting increased affinity) in the dissociation constant (Kd) when compared to controls. In the cerebral cortex, both glutamate (100 microM) and glycine (10 microM) enhanced 3[H]MK-801 binding by two to 3-fold. Coagonist glutamate, however, had a higher EC50 (0.44 microM) in the hypoxic cortical membranes when compared to controls (0.28 microM). No significant differences were found in the EC50 of glycine. The results show that the NMDA receptor is altered in several brain regions of rats developing in a hypoxic environment.     

C-Fos, Jun D and HSP72 immunoreactivity, and neuronal injury following lithium-pilocarpine induced status epilepticus in immature and adult rats

In order to follow the maturation-related evolution of neuronal damage, cellular activation and stress response subsequent to Li-Pilo seizures in the 10- (P10), 21-day-old (P21) and adult rat, we analyzed the expression of the c-Fos protein as a marker of cellular activation, HSP72 immunoreactivity as the stress response and silver staining for the assessment of neuronal damage in 20 selected brain regions. The early wave of c-Fos measured at 2 h after the onset of seizures was present in most structures of the animals at the three ages studied and particularly strong in the cerebral cortex, hippocampus and amygdala. The late wave of c-Fos measured at 24 h after the onset of seizures and that was shown to correlate to neuronal damage was absent from the P10 rat brain, and present mainly in the cerebral cortex and hippocampus of P21 and adult rats. The expression of the stress response, assessed by the immunoreactivity of HSP72 at 24 h after the seizures was absent from the P10 rat brain and present in the entorhinal cortex, amygdala, hippocampus and thalamus of P21 and adult rats. The expression of Jun D at 24 h after the seizures was discrete and present in most brain regions at all ages. Neuronal injury assessed by silver staining at 6 h after the onset of seizures was very discrete in the brain of the P10 rat and limited to a few neurons in the piriform and entorhinal cortices. In older animals, marked neuronal degeneration occurred in the cerebral cortex, amygdala, hippocampus, lateral septum and thalamus. Thus the immediate cell activation induced by lithium-pilocarpine seizures which is present at all ages translates only into a late wave of c-Fos and the expression of HSP72 in P21 and adult animals in which there will be extensive cell damage.     

Effects of antisense oligodeoxynucleotides to NR1 on suppression of seizures and protection of cortical neurons from excitotoxicity in vivo and in vitro

OBJECTIVE: To investigate the effects of NR1 subunit on the initiation and development of seizures and protection of cortical neurons from excitotoxicity by using antisense oligodeoxynucleotides (ODN) to NR1 in vivo and in vitro. METHODS: Intracerebroventricular injection, temporal cortex slices discharge, cerebral cortical neuronal culture, induction of neurotoxicity and [3H]MK-801 binding were used in this study. RESULTS: After an antisense ODN for NR1 was administered intracerebroventricularly (i.c.v. 100 micrograms in 10 microliters) once daily, for three days in genetically epilepsy-prone rats (GEPR, P77PMC), the animals did not develop any clonic and tonic convulsions and their seizure scores were significantly lower compared to the control groups. The frequency and amplitude of early seizure-like events (SLEs) and late recurrent discharges (LRD), induced by lowering Mg2+, were reduced in entorhinal cortex (EC) of the temporal slice treated by antisense ODNs. Pretreatment with antisense ODN (2 microM) protected more than 52% of glutamate-sensitive neurons and reduced the [3H]MK-801 binding to 50% in cultured cerebral cortical neurons. CONCLUSIONS: N-methy-D-aspartate-receptors (NMDAR), specifically the NR1 subunit, may participate and play important roles in the initiation and propagation of epilepsy in the P77PMC rat.     

Subchronic intraventricular infusion of quinolinic acid produces working memory impairment--a model of progressive excitotoxicity

It has been proposed by Yamada et al. [Neurosci. Lett. 118: 128-131 (1990); J. Pharmacobiodyn. 14: 351-355 (1991)] that subchronic i.c.v. infusion of the NMDA receptor agonist quinolinic acid may serve as a model for some aspects of neurodegenerative dementia. In the present study, quinolinic acid (9 mM) was infused i.c.v. by ALZET osmotic minipumps for 2 weeks. This treatment produced a short-term working memory deficit in the T-maze (alternation) but no change in reversal learning in the same test. The working memory deficit in the T-maze was progressive i.e. seen after 14, but not 3 days of infusion and persisted for at least for 3 weeks after the termination of the infusion. Histological examination revealed a modest decrease in the number of cells in the nucleus basalis magnocellularis but not in the striatum, entorhinal cortex, or hippocampus. However, in most of the structures studied, morphological changes such as swollen somata and irregular shape were observed indicative of alterations in neuronal function. Autoradiography in the hippocampus revealed a decrease in [3H]hemicholinium and [3H]quinuclidinyl benzilate (QNB) binding to choline uptake sites and muscarinic receptors respectively. Surprisingly no change was observed in [3H]MK-801 binding to NMDA receptor channels in the hippocampus and cortex. The subchronic infusion of quinolinic acid may serve as a model of progressive deterioration of cognitive functions.     

Anatomical localization and time course of Fos expression following soman-induced seizures

Soman (pinacolymethylphosphonofluoridate), a highly potent, irreversible inhibitor of cholinesterase, causes intense convulsions, neuropathology and, ultimately, death. There is evidence that certain brain structures are selectively vulnerable to the pathological consequences of soman-induced seizures. A working hypothesis is that central nervous system (CNS) structures with the earliest and most severe signs of neuropathology may be key sites for the initiation of the seizures. Fos, the immediate-early gene product, increases rapidly in several animal seizure models. Thus, we reasoned that the earliest brain regions to express Fos might be involved in the initiation and maintenance of soman-induced convulsions. To assess this, rats were injected with a single, convulsive dose of soman (77.7 micrograms/kg, i.m.). The animals were euthanized and processed for immunocytochemical analysis at several time points. Robust Fos expression was seen in layer II of the piriform cortex and the noradrenergic nucleus locus coeruleus within 30-45 minutes. One hour following soman injection, staining was more intense in the piriform cortex layer II and in the locus coeruleus. In addition, Fos was evident in the piriform cortex layer III, the entorhinal cortex, the endopiriform nucleus, the olfactory tubercle, the anterior olfactory nucleus and the main olfactory bulb. By 2 hours, Fos staining was present throughout the cerebral cortex, thalamus, caudate-putamen and the hippocampus. At 8 hours and beyond, Fos expression returned to control levels throughout the CNS except for the piriform cortex and the locus coeruleus which still had robust labeling. By 24 hours, neuropathology was evident throughout the rostral-caudal extent of layer II of the piriform cortex. The rapid induction of Fos in the piriform cortex and the locus coeruleus, taken together with previous anatomical, eletrophysiological and neurochemical studies, suggests that prolonged, excessive exposure to synaptically released acetylcholine and norepinephrine triggers the production of soman-induced seizures initially in the piriform cortex and subsequently in other cortical and subcortical structures.     

Experimental brain injury induces expression of amyloid precursor protein, which may be related to neuronal loss in the hippocampus

Previous reports have demonstrated that some focal brain injuries increase amyloid precursor protein (APP) immunoreactivity in the region surrounding the injury where it was localized, in damaged axons and in pre-alpha 2 cells of the entorhinal cortex. However, to date, APP expression in the hippocampus remote from the impact site has not been comprehensively studied. Therefore, we have evaluated APP expression not only in the locally injured cerebral cortex but also in the hippocampus remote from the impact site. In the present paper, diffuse axonal injury was induced in rats in midline fluid percussion injury. APP expression was examined post injury using Western blot analysis and immunohistochemistry. Western blot analysis demonstrated that the expression of 100-kd APP was increased in both the cerebral cortex and hippocampus 24 h after injury. It then decreased in the hippocampus, but did not change in the cerebral cortex, 7 days after injury. Immunohistochemical studies showed increased immunoreactivity of APP in the neuronal perikarya and reactive astrocytes near the region of injury in the cerebral cortex 24 h to 7 days after injury. In the hippocampus, APP accumulated in the CA3 neurons 24 h and 3 days after injury, although no hemorrhagic lesions were seen at that site. The APP positive neurons in CA3 showed shrunken cell bodies and pyknotic nuclei 3 days after injury, and some of the neurons in CA3 had disappeared by 7 days postinjury. The results of present study suggest that traumatic brain injury induces overexpression and accumulation of APP in neuronal perikarya and that these events are followed by degeneration of CA3 neurons. Further, the decline in APP expression in the hippocampus is thought to be due to neuronal loss in CA3 subsector.     

Chronic changes in synaptic responses of entorhinal and hippocampal neurons after amino-oxyacetic acid (AOAA)-induced entorhinal cortical neuron loss

Chronic changes in synaptic responses of entorhinal and hippocampal neurons after amino-oxyacetic acid (AOAA)-induced entorhinal neuron loss. J. Neurophysiol. 80: 3031-3046, 1998. Synaptic responses of entorhinal cortical and hippocampal neurons were examined in vivo and in vitro, 1 mo to 1.5 yr after a unilateral entorhinal lesion caused by a focal injection of amino-oxyacetic acid (AOAA). It has been shown previously that injection of AOAA into the medial entorhinal cortex produces cell loss in layer III preferentially. Although behavioral seizures stopped approximately 2 h after AOAA treatment, abnormal evoked responses were recorded as long as 1.5 yr later in the entorhinal cortex and hippocampus. In the majority of slices from AOAA-treated rats, responses recorded in the superficial layers of the medial entorhinal cortex to white matter, presubiculum, or parasubiculum stimulation were abnormal. Extracellularly recorded responses to white matter stimulation were prolonged and repetitive in the superficial layers. Intracellular recordings showed that residual principal cells in superficial layers produced prolonged, repetitive excitatory postsynaptic potentials (EPSPs) and discharges in response to white matter stimulation compared with brief EPSPs and a single discharge in controls. Responses of deep layer neurons of AOAA-treated rats did not differ from controls in their initial synaptic response. However, in a some of these neurons, additional periods of excitatory activity occurred after a delay. Abnormal responses were recorded from slices ipsilateral as well as contralateral to the lesioned hemisphere. Recordings from the entorhinal cortex in vivo were abnormal also, as demonstrated by prolonged and repetitive responses to stimulation of the area CA1/subiculum border. Evoked responses of hippocampal neurons, recorded in vitro or in vivo, demonstrated abnormalities in selected pathways, such as responses of CA3 neurons to hilar stimulation in vitro. There was a deficit in the duration of potentiation of CA1 population spikes in response to repetitive CA3 stimulation in AOAA-treated rats. Theta activity was reduced in amplitude in area CA1 and the dentate gyrus of AOAA-treated rats, although evoked responses to angular bundle stimulation could not be distinguished from controls. The results demonstrate that a preferential lesion of layer III of the entorhinal cortex produces a long-lasting change in evoked and spontaneous activity in parts of the entorhinal cortex and hippocampus. Given the similarity of the lesion produced by AOAA and entorhinal lesions in temporal lobe epileptics, these data support the hypothesis that preferential damage to the entorhinal cortex contributes to long-lasting changes in excitability, which could be relevant to the etiology of temporal lobe epilepsy.     

Imaging the induction and spread of seizure activity in the isolated brain of the guinea pig: the roles of GABA and glutamate receptors

1. The induction and spread of seizure activity was studied using imaging and electrophysiological techniques in the isolated whole brain of the guinea pig. We examined the role of GABA and glutamate receptor subtypes in controlling the spread of seizure activity across the olfactory cortex from a focus in the entorhinal cortex. Seizure spread was monitored by video imaging of intrinsic optical signals (reflectance changes) combined with multiple extracellular recordings. Both the unilateral and bilateral spread of seizure activity was monitored in different experiments. 2. Electrical stimulation of the lateral entorhinal cortex (10-15 V, 5 Hz, 5-10 s) evoked seizure activity that originated in the entorhinal cortex/hippocampus and later spread preferentially toward the posteromedial cortical amygdaloid nucleus ipsilaterally and bilaterally. The pattern of seizure spread in a given brain was highly reproducible. 3. The influence of gamma-aminobutyric acid (GABA) receptors on the spread of seizure activity was monitored at higher resolution on one side of the brain. Perfusion of a low concentration of the GABAA antagonist bicuculline methiodide (20 microM) resulted in spontaneous seizures that spread to the posteromedial cortical amygdaloid nucleus more rapidly than electrically evoked seizures [spread times: 5.5 +/- 3.7 s vs. 15.5 +/- 2.7 s, respectively (means +/- SE)]. Seizure spread was also more extensive in the presence of bicuculline involving the posterior perirhinal cortex and larger areas over the medial amygdala. Higher concentrations of bicuculline (100 microM) resulted in even more widespread propagation of spontaneous seizure activity throughout the olfactory cortex as well as to the perirhinal, insular, and occipital cortices. This concentration of bicuculline also further reduced the time required for seizure activity to spread from the entorhinal cortex to the posteromedial cortical amygdaloid nucleus (spread time = 2.3 +/- 1.7 s). The GABAB antagonist, CGP 35348 (200 microM), in contrast, had no significant effect of seizure induction or propagation. 4. The role of glutamate receptor subtypes in seizure propagation was studied by examining the bilateral spread of seizures. Perfusion of the kainate/alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (K/A) receptor antagonist (6-cyano-7-nitroquinoxaline-2,3-dione, CNQX, 20 microM) completely and reversibly suppressed stimulus-evoked seizure activity as detected electrophysiologically and optically. CNQX also reduced the magnitudes of field potentials recorded in the isolated brain in a reversible manner by an average of 70.8 +/- 2.21% of control. The N-methyl-D-aspartate (NMDA) receptor antagonist dibenzocyclohepteneimine (MK-801) did not significantly alter the magnitudes or shapes of field potentials recorded in the isolated brain nor did it significantly alter seizure activity measured optically or electrophysiologically. 5. Perfusion of the metabotropic glutamate receptor agonist [trans-1-amino-(IS,3R)-cyclopentanedicarboxylic acid (trans-ACPD), 150 microM] completely and reversibly suppressed stimulus-evoked seizure activity as detected electrophysiologically and optically. The magnitudes of field potentials recorded in the isolated brain also were reduced by trans-ACPD an average of 75.4 +/- 5.39% of control values. 6. These results demonstrate that GABAA-mediated transmission is functionally present and may play an important role in epileptic tissue in limiting the spread of seizure activity from the entorhinal cortex to the posteromedial cortical amygdaloid nucleus and in creating functional pathways or preferential routes of seizure spread. GABAB-mediated postsynaptic inhibition played no significant role in the induction or spread of seizure activity in this study. K/A receptors but not NMDA receptors are necessary for the induction and subsequent spread of seizure activity originating in the entorhinal cortex/hippocampus.