Changes in local cerebral glucose utilization induced by convulsants

Long-Term Study of Brain Lesions Following Soman, in Comparison to DFP and Metrazol Poisoning

The long-term histopathological effects of acute lethal (95 μg kg-1) and sublethal (56 μg kg-1) doses of soman were studied in rats and were compared to lesions caused by equipotent doses of either another cholinesterase (ChE) inhibitor, DFP (1.8 mg kg-1), or a non-organophosphorus convulsant, metrazol (100 mg kg-1). Severe toxic signs were noted following one LD50 dose administration of all the compounds, yet only soman induced brain lesions. Moreover, even when administered at a sublethal dose (0.5 LD50), soman induced some histological changes without any clinical signs of intoxication.

Soman-induced brain lesions were assessed quantitatively using a computerized image analyser. The analysis was carried out for up to 3 months following administration, and a dynamic pattern of pathology was shown. The cortical thickness and area of CA1 and CA3 cells declined significantly as early as 1 week post-exposure. No pathological findings were detected following DFP and metrazol administration. It is therefore suggested that brain lesions are not common for all ChE inhibitors and that convulsions per se are not the only factor leading to brain damage following the administration of soman. The degenerative process (found also with the sublethal dose of soman) might be due to a secondary effect, unrelated to soman's clinical toxicity, but leading to long-term brain injuries.

Cerebral metabolism of glucose and pyruvate in soman poisoning

Organophosphates, such as the nerve gas soman, cause inhibition of acetylcholine esterase, accumulation of acetylcholine in synaptic clefts, and excessive activation of cholinergic receptors, causing central nervous symptoms such as tremor and seizures. Soman-poisoned animals have low brain levels of ATP, indicating that energy demand is greater than energy supply. We investigated whether soman poisoning is accompanied by an increased brain metabolism of glucose, as can be inferred from the accumulation of radiolabeled 2-deoxyglucose found in previous studies, or whether soman poisoning entails impairment of cerebral energy metabolism. We performed 13C nuclear magnetic resonance spectroscopy on brain extracts from soman-poisoned mice (160 microg/kg; 1 LD50) that had been dosed with 13C-labeled glucose or pyruvate intravenously. Formation of 13C-labeled glutamate, GABA and glutamine from [1-(13)C]glucose was reduced by approximately 30% in awake, soman-intoxicated animals, but formation of these amino acids from [3-(13)C]pyruvate was not different in soman-intoxicated animals and controls. These results suggest that soman intoxication entails inhibition of glycolysis, but not of tricarboxylic acid cycle activity in the brain. However, when brain metabolism was depressed by a sedative dose of diazepam (5 mg/kg) soman intoxication caused increased metabolism of 13C-labeled glucose. The latter finding shows that the soman-poisoned brain has a high energy requirement even during anticonvulsant therapy. We conclude that metabolic inhibition, as seen in awake, soman-intoxicated animals, may lower seizure threshold and contribute to soman-related neurodegeneration and lethality.

Toxicogenomic studies of the rat brain at an early time point following acute sarin exposure

We have studied sarin-induced global gene expression patterns at an early time point (2 h: 0.5 x LD50) using Affymetrix Rat Neurobiology U34 chips and male Sprague-Dawley rats. A total of 46 genes showed statistically significant alterations from control levels. Three gene categories contained more of the altered genes than any other groups: ion channel (8 genes) and calcium channel and binding proteins (6 genes). Alterations were also found in the following gene groups: ATPases and ATP-based transporters (4), growth factors (4), G-protein-coupled receptor pathway-related molecules (3), neurotransmission and neurotransmitter transporters (3), cytoskeletal and cell adhesion molecules (2), hormones (2), mitochondria-associated proteins (2), myelin proteins (2), stress-activated molecules (2), cytokine (1), caspase (1), GABAnergic (1), glutamergic (1), immediate early gene (1), prostaglandin (1), transcription factor (1), and tyrosine phosphorylation molecule (1). Persistent alteration of the following genes also were noted: Arrb1, CaMKIIa, CaMKIId, Clcn5, IL-10, c-Kit, and Plp1, suggesting altered GPCR, kinase, channel, and cytokine pathways. Selected genes from the microarray data were further validated using relative RT-PCR. Some of those genes (GFAP, NF-H, CaMKIIa, Calm, and MBP) have been shown by other laboratories and ours, to be involved in the pathogenesis of sarin-induced pathology and organophosphate-induced delayed neurotoxicity (OPIDN). Induction of both proapoptotic (Bcl2l11, Casp6) and antiapoptotic (Bcl-X) genes, besides suppression of p21, suggest complex cell death/protection-related mechanisms operating early on. Principal component analysis (PCA) of the expression data confirmed that the changes in gene expression are a function of sarin exposure, since the control and treatment groups separated clearly. Our model (based on current and previous studies) indicates that both degenerative and regenerative pathways are activated early and contribute to the level of neurodegeneration at a later time, leading to neuro-pathological alterations.

Regional neural activity within the substantia nigra during peri-ictal flurothyl generalized seizure stages

Structures responsible for the onset, propagation, and cessation of generalized seizures are not known. Lesion and microinfusion studies suggest that the substantia nigra pars reticulata (SNR) seizure-controlling network could play a key role. However, the expression of neural activity within the SNR and its targets during discrete pre- and postictal periods has not been investigated. In rats, we used flurothyl to induce generalized seizures over a controlled time period and 2-deoxyglucose autoradiography mapping technique. Changes in neural activity within the SNR were region-specific. The SNRposterior was selectively active during the pre-clonic period and may represent an early gateway to seizure propagation. The SNRanterior and superior colliculus changed their activity during progression to tonic-clonic seizure, suggesting the involvement in coordinated regional activity that results in inhibitory effects on seizures. The postictal suppression state was correlated with changes in the SNR projection targets, specifically the pedunculopontine tegmental nucleus and superior colliculus.

Repeated contact with subtoxic soman leads to synaptic vulnerability in hippocampus

Soman, an anticholinesterase and dangerous nerve agent, produces convulsions, memory impairment, and cell loss in the brain, especially in the hippocampus. Soman-induced accumulation of acetylcholine initiates mechanisms responsible for the development of incapacitating seizures. The prolonged epileptiform nature of these seizures causes the release of another excitatory neurotransmitter, glutamate, which has been linked to the toxic action of the nerve agent. Here, we tested whether subtoxic soman exposures influence the brain's sensitivity to glutamate-based excitotoxicity. Over a 1-week period, hippocampal slice cultures were exposed daily to a transient level of soman that produced no evidence of synaptic deterioration. After the subtoxic soman treatments, however, the tissue became vulnerable to a brief episode of glutamate receptor overstimulation that normally resulted in little or no excitotoxic damage. In those slice cultures treated with subtoxic soman, a decline in synaptic markers as well as an increase in spectrin breakdown occurred 24 hr after the mild excitotoxic event. Exposure to high soman concentrations alone produced similar synaptic degeneration, but without evident cell death, suggesting that synaptic decline is an early neurotoxicological response to the nerve agent. Interestingly, enhanced excitotoxic sensitivity caused the brain tissue to become susceptible to disparate insults initiated before or after the soman contact. These findings indicate that seemingly innocuous soman exposures leave the hippocampus sensitive to the types of insults implicated in traumatic brain injury and stroke. They also warn that asymptomatic contact with soman may lead to progressive synaptopathogenesis and that early indicators of soman exposure are critical to prevent potential brain injury.

Early changes in MAP2 protein in the rat hippocampus following soman intoxication

We investigated the time course of both MAP2 (microtubule-associated protein 2) levels and its phosphorylation degree in the rat hippocampus during the first 90 min following the onset of soman-induced seizures. The quantitative immunoblot analysis of hippocampal extracts revealed that MAP2 increased significantly in response to a sustained epileptic activity (from 60 min of seizure duration). In addition, intense MAP2 dephosphorylation was also observed 60 to 90 min after the onset of seizures. The possible neuropathological consequences of these two early MAP2 changes are discussed in relation to the both excessive stimulation of glutamate receptors and subsequent dendritic spine alterations occurring in hippocampal neurons soon after soman intoxication.

Soman-induced seizures: limbic activity, oxidative stress and neuroprotective proteins

Soman, a potent acetylcholinesterase inhibitor, induces status epilepticus in rats followed by conspicuous neuropathology, most prominent in piriform cortex and the CA3 region of the hippocampus. Cholinergic seizures originate in striatal-nigral pathways and with fast-acting agents (soman) rapidly spread to limbic related areas and finally culminate in a full-blown status epilepticus. This leads to neurochemical changes, some of which may be neuroprotective whereas others may cause brain damage. Pretreatment with lithium sensitizes the brain to cholinergic seizures. Likewise, other agents that increase limbic hyperactivity may sensitize the brain to cholinergic agents. The hyperactivity associated with the seizure state leads to an increase in intracellular calcium, cellular edema and metal delocalization producing an oxidative stress. These changes induce the synthesis of stress-related proteins such as heat shock proteins, metallothioneins and heme oxygenases. We show that soman-induced seizures cause a depletion in tissue glutathione and an increase in tissue 'catalytic' iron, metallothioneins and heme oxygenase-1. The oxidative stress induces the synthesis of stress-related proteins, which are indicators of 'stress' and possibly provide neuroprotection. These findings suggest that delocalization of iron may catalyze Fenton-like reactions, causing progressive cellular damage via free radical products.

Regional brain activation by bicuculline visualized by functional magnetic resonance imaging. Time-resolved assessment of bicuculline-induced changes in local cerebral blood volume using an intravascular contrast agent

Functional magnetic resonance imaging (fMRI) has been applied to study rat focal brain activation induced by intravenous administration of the GABA(A) antagonist bicuculline. Using magnetite nanoparticles as a blood pool contrast agent, local changes in cerebral blood volume (CBV) were assessed with high temporal (10 s) and spatial (0.35 x 0.6 mm(2)) resolutions. Upon infusion of the bicuculline region-specific increases in CBV have been observed, suggesting CBV to reflect brain activity. During the first 2 min, the signal increases were predominant in the cortex, followed by increases in other brain areas, such as the caudate putamen, thalamus and cerebellum. Ten minutes after the start of infusion, a dominant response was observed in the thalamus, while in the caudate putamen a biphasic response pattern was seen. The magnitude of the signal responses in all brain regions was dependent on the dose of bicuculline and, in general, matched the known distribution of GABA(A) binding sites. This study suggests that pharmacological fMRI, displaying brain function at the highly specific level of drug-receptor interaction, should foster our understanding of normal and pathological brain function.

Alterations in local cerebral glucose utilization produced by D3 dopamine receptor-selective doses of 7-OH-DPAT and nafadotride

The D3 dopamine receptor, localized primarily in limbic brain areas, is a potential antipsychotic site. The effects of D3 receptor stimulation or blockade on neuronal activity were determined using the [14C]-2-deoxyglucose method. Freely-moving, adult, male, Sprague-Dawley rats were injected s.c. with saline, agonist 7-hydroxy-diphenylaminotetralin (7-OH-DPAT) (0.1 mg/kg), or antagonist l-nafadotride (1 mg/kg). These doses of 7-OH-DPAT and l-nafadotride are behaviorally active and are 10-fold lower than a dose producing significant in vivo occupancy of D2 receptors. The [14C]-2-deoxyglucose procedure was initiated 30 min after the administration of the test compound. The rate of local cerebral glucose utilization (LCGU) was determined by quantitative autoradiography. 7-OH-DPAT produced a significant increase in LCGU in the substantia nigra. l-Nafadotride produced significant increases in LCGU in several brain areas including the lateral preoptic area, lateral habenula, caudate, septal area, entorhinal cortex, and some thalamic and hypothalamic areas. These observations indicate that stimulation or blockade of D3 receptors alters LCGU and that produces a unique pattern of alterations in LCGU suggestive of potential antipsychotic activity.

Neuropharmacological mechanisms of nerve agent-induced seizure and neuropathology

This paper proposes a three phase "model" of the neuropharmacological processes responsible for the seizures and neuropathology produced by nerve agent intoxication. Initiation and early expression of the seizures are cholinergic phenomenon; anticholinergics readily terminate seizures at this stage and no neuropathology is evident. However, if not checked, a transition phase occurs during which the neuronal excitation of the seizure per se perturbs other neurotransmitter systems: excitatory amino acid (EAA) levels increase reinforcing the seizure activity; control with anticholinergics becomes less effective; mild neuropathology is occasionally observed. With prolonged epileptiform activity the seizure enters a predominantly non-cholinergic phase: it becomes refractory to some anticholinergics; benzodiazepines and N-methyl-D-aspartate (NMDA) antagonists remain effective as anticonvulsants, but require anticholinergic co-administration; mild neuropathology is evident in multiple brain regions. Excessive influx of calcium due to repeated seizure-induced depolarization and prolonged stimulation of NMDA receptors is proposed as the ultimate cause of neuropathology. The model and data indicate that rapid and aggressive management of seizures is essential to prevent neuropathology from nerve agent exposure.

Forebrain metabolic activation induced by the repetition of audiogenic seizures in Wistar rats

In Wistar rats susceptible to audiogenic seizures (Wistar AS) inbred in our laboratory, the exposure to an intense sound induces an epileptic seizure characterized by a running episode followed by a tonic phase showing the major involvement of brainstem structures. After 10-20 sound-induced seizures, development of facial and forelimb clonus and/or tonic-clonic seizures characterize the generalization from brainstem to the forebrain as a result of seizure repetition. In order to specify the anatomical substrates of repeated audiogenic seizures in Wistar AS, we used the 2-deoxyglucose (2DG) technique over a 5 min period to map the midbrain and forebrain structures activated by audiogenic seizures before and after seizure repetition. In naive Wistar AS, six of the 22 structures showed a significant 20-56% increase in relative optical densities compared to non-epileptic controls; these were central and medial amygdala nuclei, perirhinal cortex, medial septum, subthalamic and caudate nuclei. In kindled Wistar AS, 12 additional structures showed a significant 16-121% increase in 2DG labeling. These structures were the substantia nigra, all layers of the hippocampus, the basolateral amygdala, three thalamic nuclei, the frontal motor and prefrontal cortices. In conclusion, the metabolic activation of midbrain and forebrain areas in kindled versus naive Wistar AS rats reflects the changes in the nature of the seizures and the involvement of these structures in the spread of seizure activity from the brainstem to the forebrain during seizure repetition.

The model of pentylenetetrazol-induced status epilepticus in the immature rat: short- and long-term effects

In order to assess acute, short and long-term effects of seizures in the immature rat brain, we studied the metabolic, circulatory and histopathological changes induced by pentylenetetrazol (PTZ) given at postnatal day 10 (P10) or 21 (P21). Seizures were induced by repetitive subconvulsive injections of PTZ given as a first dose of 40 mg/kg followed 10 min later by 20 mg/kg. Thereafter, rats received every 10 min additional injections of PTZ 10 mg/kg until the onset of status epilepticus. Local cerebral metabolic rates for glucose (LCMRglc) were measured both during the seizures in P10 and P21 rats and in the young adult animal at P60 by means of the quantitative 2-deoxyglucose technique. Rates of local cerebral blood flow (LCBF) were determined during the seizures by the iodoantipyrine technique. Short-term histological changes were assessed by acid fuchsin and hematoxylin-eosin staining and by HSP72 immunohistochemistry. At P10, LCMRglcs uniformly increased (38-400%) over control values during seizures. At P21, metabolic increases (39-181%) occurred only in 20% of the structures while LCMRglcs decreased in most cortical, hippocampal and sensory areas as well as in mammillary body, discrete thalamic nuclei and white matter areas. At P10, LCBF rose (32-184%) in all brain structures whereas, at P21, LCBF decreased in cortical, hippocampal and sensory regions and increased in most other areas. At P60, in animals having seized at either age, significant long-term decreases in LCMRglcs were recorded in hippocampus, auditory and piriform cortex, medial geniculate body and mammillary body. In P60 animals exposed to PTZ at P10, LCMRglcs were also decreased in 3 other sensory areas. In P60 animals exposed to seizures at P21, LCMRglcs were additionally decreased in sensory regions, cortices, thalamic and hypothalamic regions. Neuronal cells were transiently stained with acid fuchsin, with a peak occurring at 24 h after the seizures. The stain was visible in all regions of cerebral cortex and hippocampus and in some thalamic and hypothalamic nuclei. This transient staining was not accompanied by cell degeneration as assessed by hematoxylin-eosin histology. No HSP72 expression could be detected 24 h after the seizures, neither at P10 nor at P21. The present study shows that the immature rat neurons undergo altered metabolic rates and local circulatory decreases in the acute phase, a change in the affinity of acid fuchsin as a short-term effect and long-term metabolic decreases. All these changes are located in the same regions, i.e., cerebral cortex, hippocampus, sensory regions as well as scattered thalamic and hypothalamic nuclei. Thus, short- and long-term metabolic changes induced by seizures can be used as an index of cell stress in the immature rat brain. Since all these changes occur in the absence of visible neuronal death, they might be related to changes in the final arborization and synaptic organization of the developing brain.

Early histopathologic and ultrastructural changes in the heart of Sprague-Dawley rats following administration of soman

Male Sprague-Dawley rats were given atropine methylnitrate (20 mg/kg) and HI-6 (125 mg/kg) ip 10 min before a single injection of 130 micrograms soman/kg sc, and the heart was examined by light and electron microscopy 10, 25, 45, 90, and 180 min after the onset of seizures. Seizures appeared within 6-11 min after treatment. Control rats were given saline sc in place of soman. Early myocardial lesions consisting of hypercontraction and hyperextension of sarcomeres, focal myocytolysis, and contraction bands were detected in individual or groups of myocardial fibers. Hypercontraction was characterized by shortening of the sarcomere length, disappearance of the I and H bands, and thickening of the Z line. In contrast, hyperextended sarcomeres had thickened I and H bands. Myocytolysis was characterized by a progressively severe focal dissolution of myofilaments and edema of the affected sarcoplasmic area. Contraction bands appeared to result from the breakdown of markedly hypercontracted myofibril bundles. Due to the presence of a number of surviving myofilaments and the preservation of the sarcolemmal tube, distortion of the overall myocytic structure was minimal. Changes in the mitochondria and other intracellular organelles were also minimal and nonspecific. The close resemblance of morphologic findings to those induced by catecholamines supports the view that soman-induced myocardial damage is secondary to a treatment-related release of unphysiologic amounts of endogenous catecholamines.

Involvement of non-muscarinic receptors in phosphoinositide signalling during soman-induced seizures

Previous investigations have indicated that soman-induced convulsions involve the inositol lipid signalling system. We previously reported that 10 min after the onset of seizures, inositol 1,4,5-triphosphate (IP3) build-up was coupled to activation of non-muscarinic receptor subtypes. In the present study, we demonstrate that (1) in addition to muscarinic receptors, histamine H1 subtypes and glutamate metabotropic receptors contribute to the first IP3 increase (first 10 min of seizures) and (2) the histamine H1 subtype and glutamate metabotropic receptors are also involved in the second step of inositol phosphate response (after 10 min of seizures). alpha 1-adrenoceptor and 5-HT2 receptors, known to be coupled to phosphoinositide turnover, did not participate in soman-induced IP3 response. Neurochemical interactions between cholinergic, histamine H1 and glutamate metabotropic systems, responsible of the phosphoinositide hydrolysis under soman are envisaged.

Malaoxon-induced brain phosphoinositide turnover and changes in brain calcium levels by female gender in pregnant and non-pregnant convulsing and non-convulsing rats

Alterations in malaoxon-(MO)-induced brain regional phosphoinositide (PI) turnover and in brain calcium levels were studied in female non-pregnant and pregnant rats, and in their offspring. The adult rats were followed for 1 or 4 h after MO for tonic-clonic convulsions. A dose of 8.2 mg kg-1 of MO caused similar convulsions in 74% of the pregnant rats as we have reported in young male rats with a dose of 39.2 mg kg-1. However, convulsions did not occur in non-pregnant female rats. Inositol and inositol monophosphate levels were similar in all control rats. MO decreased brain inositol both in pregnant and non-pregnant female rats, and in the cerebellum of the offspring. In contrast to the findings in male rats, MO only randomly increased brain inositol-1-phosphate in female rats, or in their offspring. However, cerebral inositol-4-phosphate levels were similarly increased both in the non-pregnant and the pregnant rats irrespectively of convulsions. MO did not elevate cerebral Ca2+ in female rats or their offspring, in contrast to the male rats. The present results suggest that female rats are more sensitive than male rats to MO-induced PI signalling, and during pregnancy, also to MO-induced overt convulsions, but not to changes in cerebral Ca2+.

Effect of pentylentetrazol-induced seizures on A1 adenosine receptor regional density in the mouse brain: a quantitative autoradiographic study

Adenosine has been shown to be a major regulator of neuronal activity in convulsive disorders, exerting its anticonvulsant effect through central A1 adenosine receptors. The aim of the present study was to investigate the effect of generalized tonic-clonic seizures induced by pentylentetrazol on regional changes in A1 adenosine receptor density and distribution in the mouse brain by in vitro quantitative autoradiography. As radioligand the specific agonist of A1 receptors [3H]cyclohexyladenosine was used. After two consecutive (once daily) pentylentetrazol-induced convulsions a widespread upregulation of A1 receptor density was detected with a marked enhancement in structures that mediate seizure activity like hippocampus, mamillary bodies, septum, substantia nigra, thalamic nuclei and cerebral cortices. On the contrary, in basal ganglia a significant downregulation of A1 receptors was observed. These results indicate that: (i) the observed increases or decreases in A1 receptor density are organized in selective anatomical structures related to seizure development rather than uniform in the brain; and (ii) since the upregulation of A1 receptors is sufficient to enhance the physiological depressive response of adenosine, the overall evoked increases seen here may lead to a stronger inhibitory tone and accordingly to a more efficient anticonvulsant effect of endogenous adenosine.

Neuroprotective activity of glutamate receptor antagonists against soman-induced hippocampal damage: quantification with an omega 3 site ligand

Previous investigations have indicated that the measurement of omega 3 (peripheral-type benzodiazepine) binding site densities could be of widespread applicability in the localization and quantification of neural tissue damage in the central nervous system. In the first step of the present study, the suitability of this approach for the assessment of soman-induced brain damage was validated. Autoradiographic study revealed marked increases of omega 3 site densities in several brain areas of convulsing rats 2 days after soman challenge. These increases were well-correlated with the pattern and the amplitude of neuropathological alterations due to soman and closely related to both glial reaction and macrophage invasion of the lesioned tissues. We then used this marker to assess, in mouse hippocampus, the neuroprotective activity against soman-induced brain damage of NBQX and TCP which are respective antagonists of non-NMDA and NMDA glutamatergic receptors. Injection of NBQX at 20 or 40 mg/kg 5 min prior to soman totally prevented the neuronal damage. Comparatively, TCP had neuroprotective efficacy when administered at 1 mg/kg 5 min prior to soman followed by a reinjection 1 h after. These results demonstrate that both NBQX and TCP afford a satisfactory neuroprotection against soman-induced brain damage. Since it is known that the neuropathology due to soman is closely seizure-related, the neuroprotective activities of NBQX and TCP are discussed in relation with the respective roles of non-NMDA and NMDA receptors in the onset and maintenance of soman-induced seizures.

Characterization of phosphoinositide hydrolysis products induced by hexachlorocyclohexane isomers in rat brain cortex

Water-soluble inositol metabolites were separated by anion-exchange chromatography in order to determine whether or not gamma-hexachlorocyclohexane (gamma-HCH, lindane) and related compounds affect phosphatidylinositol hydrolysis in rat brain cortex slices. Hydrolysis was increased by delta- and gamma-HCH, while alpha- and beta-HCH were inactive. Muscarinic receptor stimulation of rat cortical slices with carbachol increases inositol phosphates formation. The combined effect of carbachol and the hexachlorocyclohexane isomers together were approximately equal to the sum of the effect of each one separately. The results suggest that lindane stimulates phosphoinositide phospholipase C and/or inhibits the phosphatases implicated in dephosphorylation of inositol phosphates.

Second messengers in cholinergic-induced convulsions and neuronal injury

Acetylcholine (ACh) is a powerful excitatory neurotransmitter in the brain. Stimulation of brain cholinergic muscarinic receptors (mAChR) cause persistent tonic-clonic convulsions. mAChRs are coupled to G-protein which mediates the receptor stimulation to phospholipidase C (PLC). PLC hydrolyses phosphatidylinositol-4,5-bisphosphate (PI), a membrane phospholipid, into two second messengers, inositol-1,4,5-trisphosphate (Ins(1,4,5)P3), and diacylglycerol (DAG). Both messengers cause neuronal stimulation and when in excess, may contribute to neuronal injury. Indirect cholinergic agonists organophosphates (OPs) such as soman, paraoxon, and malaoxon, and direct cholinergic agonists, such as pilocarpine, are powerful convulsants. They stimulate brain mAChR-coupled to PI signalling as indicated by decreased brain inositol and increased brain inositol monophosphates, metabolites in PI turnover, and indirectly reflect the activity of the brain PI system. In rats, during cholinergic convulsions, brain inositol decreases, and inositol monophosphates increase prior to and during convulsions. Persistent convulsions cause neuronal injury especially in the hippocampus and cortex, and associated increase in brain Ca2+. The mechanisms of convulsions and associated neuronal have remained open, but both in vitro and in vivo data provide evidence that facilitated PI signalling and increases in free intracellular Ca2+ may have an important role in these events. Age and female sex amplify the effects of cholinergic brain stimulation and convulsions.

An experimental model of generalized seizures for the measurement of local cerebral glucose utilization in the immature rat. II. Mapping of brain metabolism using the quantitative [14C]2-deoxyglucose technique

The quantitative autoradiographic [14C]2-deoxyglucose technique (2DG) was applied to measure the effects of pentylenetetrazol (PTZ)-induced status epilepticus (SE) on local cerebral metabolic rates for glucose (LCMRglc) in 10 (P10)-, 14 (P14)-, 17 (P17)- and 21 (P21)-day-old rats. To produce long-lasting SE (55 min), the animals received repetitive, timed intraperitoneal injections of subconvulsive doses of PTZ until SE was reached. At P10 and P14, SE induced a marked increase in LCMRglc which affected 66 of the 76 structures studied. Increases were especially high (200-400%) in limbic and motor cortices at P10 and in some brainstem areas at these 2 ages. At P17 and P21, average brain glucose utilization was similar in seizing and control rats, but in PTZ-treated rats reflected a redistribution in local metabolic rates with increases in brainstem, midbrain, hypothalamus and septum, decreases in cortex, hippocampus, some sensory areas and white matter and no change in many motor and limbic structures. In a few cerebral regions, such as hippocampus, dentate gyrus and mammillary body, LCMRglc did not increase at P10 and P14 and decreased at P17 and P21 in PTZ- vs. saline-treated rats. The results of the present study show that the immature brain responds to sustained seizure activity in a specific way according to its maturational state. Moreover, these data allow the mapping of the vulnerability of cerebral structures to seizures, according to their metabolic response to convulsions.

Patterns of glucose use after bicuculline-induced convulsions in relationship to gamma-aminobutyric acid and mu-opioid receptors in the ventral pallidum--functional markers for the ventral pallidum

Bicuculline-induced convulsions increased glucose use throughout the brain and sharply demarcated the ventral pallidum and globus pallidus. Glucose use in the nucleus accumbens also increased after bicuculline-induced convulsions, except for a circumscribed region in the dorsomedial shell. Since the projection from the nucleus accumbens to the ventral pallidum contains gamma-aminobutyric acid (GABA) and the opioid peptide, enkephalin, the pattern of increased glucose use in the ventral pallidum and nucleus accumbens after bicuculline-induced convulsions was compared to the topography of GABAA and mu-opioid receptors. The pattern of glucose use in the nucleus accumbens and ventral pallidum resembled the topography of GABAA, but differed from that of mu-opioid receptors. Bicuculline may disinhibit GABAergic efferents to the ventral pallidum resulting in a dramatic increase in glucose use within striatopallidal synaptic terminals as well as in local terminals of the pallidal projection neurons.

Free radical generation in the brain precedes hyperbaric oxygen-induced convulsions

We tested the hypothesis that hyperbaric oxygenation (HBO) generates free radicals in the brain before the onset of neurological manifestations of central nervous system (CNS) oxygen poisoning. Chronically cannulated, conscious rats were individually placed in a transparent pressure chamber and exposed to (1) 5 atmospheres absolute (ATA) oxygen for 15 min (n = 4); (2) 5 ATA oxygen for 30 min (n = 5), during which no visible convulsions occurred; (3) 5 ATA oxygen for 30 min with recurrent convulsions (n = 6); (4) 5 ATA oxygen until the appearance of the first visible convulsions (n = 5); (5) 4 ATA oxygen for 60 min during which no convulsions occurred (n = 5); and (6) 5 ATA air for 30 min (n = 5, controls). Immediately before compression, 1 mL of 0.1 M of alpha-phenyl-N-tert-butyl nitrone (PBN) was administered intravenously (iv) for spin trapping. At the termination of each experiment, rats were euthanized by pentobarbital iv and decompressed within 1 min. Brains were rapidly removed for preparation of lipid extracts (Folch). The presence of PBN spin adducts in the lipid extracts was examined by electron spin resonance (ESR) spectroscopy. ESR spectra from unconvulsed rats exposed to 5 ATA oxygen for 30 min revealed both oxygen-centered and carbon-centered PBN spin adducts in three of the five brains. One of the five rats in this group showed an ascorbyl signal in the ESR spectrum.(ABSTRACT TRUNCATED AT 250 WORDS)

The osmotic/calcium stress theory of brain damage: are free radicals involved?

This overview presents data showing that glucose use increases and that excitatory amino acids (i.e., glutamate, aspartate), taurine and ascorbate increase in the extracellular fluid during seizures. During the cellular hyperactive state taurine appears to serve as an osmoregulator and ascorbate may serve as either an antioxidant or as a pro-oxidant. Finally, a unifying hypothesis is given for seizure-induced brain damage. This unifying hypothesis states that during seizures there is a release of excitatory amino acids which act on glutamatergic receptors, increasing neuronal activity and thereby increasing glucose use. This hyperactivity of cells causes an influx of calcium (i.e., calcium stress) and water movements (i.e., osmotic stress) into the cells that culminate in brain damage mediated by reactive oxygen species.

Effects of soman-induced seizures on different extracellular amino acid levels and on glutamate uptake in rat hippocampus

Extracellular amino acid levels in CA3 and CA1 fields of rat hippocampus, an area highly sensitive to seizures, were determined by intracranial microdialysis during seizures induced by systemic administration of soman (o-1,2,2-trimethylpropyl methylphosphonofluoridate), a potent inhibitor of acetylcholinesterase. The glutamate uptake level was determined on another series of animals in hippocampus homogenates. An early and transient increase in the extracellular glutamate level occurred in CA3 within 30 min of seizures, with correlated brief elevations of taurine, glycine and glutamine levels. The glutamate level increased early in CA1, declined and then became more sustained (after 50 min of seizures). Apparent elevations of taurine, glycine and glutamine levels in CA1 accompanied changes in glutamate concentrations. Changes of glutamate level correlated with an increase in the glutamate uptake which rapidly declined after 40 min of seizures. The role of the transient release of glutamate in CA3 and of the sustained release in CA1 in prolonged soman-induced seizures is considered. The correlation between glutamate and other amino acid release is studied.

Lithium modifies convulsions and brain phosphoinositide turnover induced by organophosphates

Inositol-1-phosphate (Ins1P), an index of phosphoinositide (PI) turnover, was measured in frontal and piriform cortices, caudate, thalamus, hippocampus and cerebellum in saline or LiCl (5 m Eq./kg) pretreated rats 60 min. after graded doses of DFP, paraoxon, or soman. DFP only produced bursts of convulsive activity whereas both paraoxon and soman produced prolonged tonic-clonic convulsions. All three organophosphates (OP) produced convulsions at a lower dose in LiCl than in saline pretreated rats. Regional Ins1P correlated better with the presence or absence of convulsions than with the dose of paraoxon or soman. This was true both in saline and LiCl pretreated rats. In saline pretreated non-convulsing rats, there was a cholinergic increase (1.5-2.0 X) in Ins1P in all brain regions except cerebellum after OP injection. In saline pretreated convulsing rats, there was a marked seizurogenic further increase in Ins1P; highest in caudate (8 X) and cortex (6 X). In LiCl pretreated nonconvulsing rats, the OP-induced cholinergic increase in Ins1P was significant only in caudate, thalamus and hippocampus. In LiCl pretreated convulsing rats, the further seizurogenic increase in Ins1P was less than in saline pretreated rats except in thalamus and hippocampus. Thus, OP produce both a cholinergic and a seizurogenic increase in PI turnover. These data suggest that increased PI turnover in the hippocampus may indicate a lithium-induced lowering of the seizure threshold for OP in limbic regions.

Metabolic anatomy of the focal epilepsy produced by cessation of chronic intracortical GABA infusion in the rat

Cessation of chronic (5 days), unilateral infusion of GABA into the somatomotor cortex of rats induces focal epileptic spikes which remain limited to the infused site and never evolve into generalized seizures. We have considered this finding as a new model of focal epilepsy and named it "GABA withdrawal syndrome". In the present study, we have measured local cerebral glucose utilization in order to map the cortical and subcortical regions involved in the GABA withdrawal syndrome. Local cerebral glucose utilization increased two- to three-fold in a 1-1.5 mm diameter area, involving all the cortical layers at the GABA-infusion site. This hypermetabolic area contained a central (1-2 mm diameter) hypometabolic zone showing neuronal depopulation in some animals. Except for the epileptic focus, the hemisphere ipsilateral to the infusion site was slightly hypometabolic. However, there was a large increase (three- to five-fold) in some ipsilateral thalamic nuclei (posterior oralis, ventralis postero-lateralis, centralis lateralis, ventralis lateralis and reticularis thalami nucleus). The local cerebral glucose utilization of the contralateral cortex and thalamus were unchanged. The present results confirm the focal nature of the epileptogenic syndrome produced by stopping chronic, intracortical GABA infusion. These results are markedly different from those described in the penicillin focal epilepsy model. Our data also show that specific ipsilateral thalamic relays may, by an as yet unknown mechanism, play a role in maintaining paroxysmal activity during the GABA withdrawal syndrome.

Alterations of A1 adenosine receptors in different mouse brain areas after pentylentetrazol-induced seizures, but not in the epileptic mutant mouse 'tottering'

Single and repeated Pentylentetrazol (PTZ)-induced convulsions are associated with significant changes of A1 adenosine receptors (detected using the radioligand [3H]cyclohexyladenosine, [3H]CHA) in 4 different brain areas of the mouse, namely cortex, hippocampus, cerebellum and striatum. In hippocampus and cerebellum, a rapid increase in [3H]CHA binding, by 26% and 30% respectively, was observed 1 h after a single PTZ convulsion. In striatum, on the contrary, a significant decrease by 30% in [3H]CHA binding was seen, whereas in cortex no significant change could be detected. After daily repeated PTZ convulsions, a significant increase of A1 receptors by 26% appeared also in cortex, while the changes of A1 receptors observed in the other brain areas after a single PTZ convulsion were maintained in almost the same range. All the alterations observed were due to changes of the total number of A1 receptors (Bmax) without changes in receptor affinity (Kd). A significant increase in the latency of PTZ seizure (time between the PTZ-injection and the beginning of the seizure) was also observed after repeated PTZ-induced convulsions at the time when the changes in A1 adenosine receptors were noted. Considered together, these results provide further evidence for an A1 receptor-mediated modulation of seizure susceptibility and indicate that specific brain areas may play different roles in this modulation. The binding of [3H]CHA to membranes from different cortical and subcortical areas of the epileptic mutant mouse 'tottering' was not different from that in control animals.

Characterization of GABAergic seizure regulation in the midline thalamus

This study characterized the role of GABA in the central medial intralaminar nucleus on seizures induced by pentylenetetrazol given systemically. Injections of the direct selective GABAA agonist, piperidine-4-sulfonic acid or the indirect GABAA agonists, flurazepam and pentobarbital, in this region depressed arousal and facilitated myoclonic and clonic seizures induced by pentylenetetrazol but only caused slight inhibition of tonic seizures. In contrast the GABAB agonist (-)baclofen facilitated all three types of seizures. Recording after injection of piperidine-4-sulfonic acid and (-)baclofen revealed marked suppression and slowing of thalamic and cortical electrical activity. Thalamic injections of the GABAA antagonist, bicuculline methiodide, had opposite behavioral effects, causing hyperactivity and episodes of violent running, not accompanied by EEG discharges. When pentylenetetrazol was infused concommitantly there was marked facilitation of the tonic seizures, which occurred without preceding myoclonic of clonic seizures, or EEG spikes. These results demonstrate that GABA-mediated neurotransmission in the central medial intralaminar nucleus can control the threshold of seizures and that GABA agonists and antagonists have opposite effects. It is suggested that the central medial intralaminar nucleus is not a site of origination or spread of seizures, but controls seizures indirectly by regulating the excitability of other structures and that different synaptic mechanisms and anatomical connections mediate effects on different types of seizures.

Effect of LiCl pretreatment on cholinomimetic-induced seizures and seizure-induced brain edema in rats

Male Sprague-Dawley rats received LiCl (5 mEq/kg; sc) or saline 24 h prior to injection of cholinomimetics. Physostigmine (PHY, 0.54-0.80 mg/kg), diisopropylfluorophosphate (DFP, 1.3-2.5 mg/kg), pilocarpine (PIL, 23-30 mg/kg), or saline was injected subcutaneously at time 0. Rats were observed for seizure activity for 2 h, survivors were killed 24 h later and edema was measured in samples from parietal and piriform cortices, dorsal thalmus, and hippocampus. None of the rats pretreated with saline had seizures when given doses of cholinomimetics alone. However, rats pretreated with LiCl had the following incidence of seizures: PHY 68%, DFP 71% and PIL 100%. Rats given cholinomimetic agents alone did not have brain edema. In contrast, all LiCl-pretreated rats that seized had pronounced brain edema which was greatest in the piriform cortex. Thus, these studies demonstrate that LiCl pretreatment potentiates cholinomimetic-induced seizures. Further, cholinomimetic-induced seizures produce brain changes resulting in edema.

Potentiation of malaoxon-induced convulsions by lithium: early neuronal injury, phosphoinositide signaling, and calcium

Convulsions, neuronal morphology, brain phosphoinositide (PI) signaling, and calcium levels were studied in rats 1, 4, and 72 hr after malaoxon (MO; 26.2 or 39.2 mg/kg ip) subsequent to pretreatment with saline or LiCl (10 meq/kg ip). The high dose of MO induced convulsions in 60% of the rats whereas the low dose was ineffective. In nonconvulsing rats, MO transiently increased cerebral inositol 1-phosphate (Ins1P), an intermediate in PI cycle, but consistently elevated brain Ins1P in convulsing rats. LiCl did not induce convulsions, but elevated the resting level of Ins1P and decreased that of inositol. Lithium also increased the potential of MO to cause convulsions but attenuated MO-induced elevations of Ins1P. Moreover, total Ca2+ in cortex increased in LiCl-pretreated convulsing and nonconvulsing rats after MO. Astrocytic edema and cytoplasmic vacuolation and/or shrinkage of neurons in cortical layers 2-3 and in the hippocampus as well as in some subcortical structures occurred only in convulsing rats. These results suggest that PI signaling may be involved in convulsions and contribute to the early neuronal injury. Cerebral Ca2+ elevations seemed to precede permanent neuronal injury. A target other than the inhibition of the hydrolysis of inositol phosphates may be the site of lithium's action in cholinergic convulsions.

Effects of lindane on the glucose metabolism in rat brain cortex cells

The influence of 0.5 mM gamma-hexachlorocyclohexane (gamma-HCH, lindane) on glucose transport has been investigated using the analog 3-O-methyl-D-(U-14C)glucose. The glucose uptake was lineal for at least 10 sec. Preincubation of dissociated brain cortex cells with lindane decreased the transport of glucose with respect to the controls. The treatment of brain cortex cells with other organochlorine compounds indicated that the alpha-, delta-HCH isomers and dieldrin reproduced the same inhibitory pattern, while beta-HCH and endrin were inactive. The total radioactivity incorporated into CO2 from (U-14C) glucose in the cerebral cortex is also inhibited by lindane in a time dependent manner.

Identification of a median thalamic system regulating seizures and arousal

This study better defines the way in which the thalamus controls expression of experimental generalized seizures. The effects of small intrathalamic injections of the direct GABA agonist muscimol on the thresholds of pentylenetetrazol (PTZ)-induced seizures and on spontaneous behavior were determined in the rat and compared with the effects of injections of gamma-vinyl-GABA (GVG), an irreversible inhibitor of GABA transaminase. Muscimol injections produced neuronal inhibition in a relatively small area of thalamus, whereas GVG injections produced inhibition in a much larger area. Muscimol injections in the midline thalamus in the vicinity of the paraventricular, paratenial, interanteromedial, intermediodorsal, and central medial nuclei facilitated PTZ myoclonic and clonic seizures and also produced sedation. These effects on seizure thresholds were attributable both to a lower PTZ threshold dose for initiation of electroencephalographic (EEG) seizure activity and to an increased probability of this EEG activity being expressed as behavioral seizures. Midline injections located more posteriorly in the thalamus also inhibited tonic seizures. Muscimol injections placed laterally, dorsally, or ventrally to this midline thalamic region had much less effect on behavior or seizures. In contrast, GVG injections in the anterior medial thalamus elevated the threshold for all PTZ seizure types and for associated EEG seizure activity but had little effect on spontaneous behavior. These findings demonstrate the existence of an important seizure regulatory system in the midline of the thalamus and a direct anatomic link between the mechanisms for regulating arousal and seizure production which may help explain the association between sleep and seizure facilitation in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of soman intoxication on the organization of rat brain ribosomes and the translational activity of mRNA in a cell-free system

The effect of soman on rat brain ribosomes organization and translational activity of mRNA in cell-free system was studied in rats exposed to 1.3 LD50 soman (120 micrograms/kg body weight) and in rats repeatedly injected with 0.4 LD50 soman (35 micrograms/kg). Fifteen minutes after the injection of 1.3 LD50 soman the heavy polyribosomal fraction from rat brain was found to be enriched and translational activity of mRNA was enhanced. In rats administered five injections of 0.4 LD50 soman at 24-h intervals, the low density ribosomes appeared as the predominant fraction whereas the activity of mRNA in all cell-free system was significantly impaired. It is concluded that soman intoxication expresses a stimulatory or inhibitory effect on the processes of protein synthesis in the rat brain, depending on the dose schedule of soman administration.

Restriction of enhanced [2-14C]deoxyglucose utilization to rhinencephalic structures in immature amygdala-kindled rats

Sixteen-day-old albino rat pups were kindled to varying degrees of seizure severity with amygdala stimulations spaced 15 to 20 min apart. Subsequently, each rat pup was injected (ip) with 10 microCi of [2-14C]-deoxyglucose, and received several additional kindled seizures at regular intervals throughout the following 80 min, at which time it was killed and processed for deoxyglucose autoradiography. Increased seizure severity was associated with correspondingly increased deoxyglucose utilization in many rhinencephalic limbic structures. However, unlike adults, rat pups did not show discernibly increased neocortical, thalamic, or substantia nigra utilization. We postulate that the apparent confinement of seizure activity to limbic structures in pups is related to their relative lack of postictal seizure refractoriness, as well as to other indices of increased seizure susceptibility in immature animals.

Time-course of malaoxon-induced alterations in brain regional inositol-1-phosphate levels in convulsing and nonconvulsing rats

The potential of a single dose of malaoxon (26.2 or 39.2 mg/kg i.p.) to produce convulsions and to increase cerebral levels of inositol-1-phosphate (Ins1P), an intermediate in phosphoinositide (PI) cycle, was followed for 1, 4, or 72 hr. The lower dose of malaoxon did not produce convulsions whereas the higher dose induced convulsions in 60% of the exposed rats. Malaoxon caused a dose-dependent, at most 2-fold, increase in brain regional Ins1P levels in nonconvulsing rats as compared to controls. At the higher dose of malaoxon, in convulsing rats, the Ins1P-levels increased 4-fold above the control Ins1P-levels. In nonconvulsing rats, the Ins1P-levels reached their maximum 1-4 hr after the administration of malaoxon, whereas in convulsing rats the levels increased for 72 hr. The results suggest that PI-signalling is associated with convulsions produced by malaoxon.

Review: cholinergic mechanisms and epileptogenesis. The seizures induced by pilocarpine: a novel experimental model of intractable epilepsy

High-dose treatment with pilocarpine hydrochloride, a cholinergic muscarinic agonist, induces seizures in rodents following systemic or intracerebral administration. Pilocarpine seizures are characterized by a sequential development of behavioral patterns and electrographic activity. Hypoactivity, tremor, scratching, head bobbing, and myoclonic movements of the limbs progress to recurrent myoclonic convulsions with rearing, salivation, and falling, and status epilepticus. The sustained convulsions induced by pilocarpine are followed by widespread damage to the forebrain. The amygdala, thalamus, olfactory cortex, hippocampus, neocortex, and substantia nigra are the most sensitive regions to epilepsy-related damage following convulsions produced by pilocarpine. Spontaneous seizures are observed in the long-term period following the administration of convulsant doses of pilocarpine. Developmental studies show age-dependent differences in the response of rats to pilocarpine. Seizures are first noted in 7-12 day-old rats, and the adult pattern of behavioral and electroencephalographic sequelae of pilocarpine is seen in 15-21-day-old rats. During the third week of life the rats show an increased susceptibility to the convulsant action of pilocarpine relative to older and younger animals. The developmental progress of the convulsive response to pilocarpine does not correlate with evolution of the brain damage. The adult pattern of the damage is seen after a delay of 1-2 weeks in comparison with the evolution of seizures and status epilepticus. The susceptibility to seizures induced by pilocarpine increases in rats aged over 4 months. The basal ganglia curtail the generation and spread of seizures induced by pilocarpine. The caudate putamen, the substantia nigra, and the entopeduncular nucleus govern the propagation of pilocarpine-induced seizures. The antiepileptic drugs diazepam, clonazepam, phenobarbital, valproate, and trimethadione protect against pilocarpine-induced convulsions, while diphenylhydantoin and carbamazepine are ineffective. Ethosuximide and acetazolamide increase the susceptibility to convulsant action of pilocarpine. Lithium, morphine, and aminophylline also increase the susceptibility of rats to pilocarpine seizures. The pilocarpine seizure model may be of value in designing new therapeutic approaches to epilepsy.

Substantia nigra lesions in mercaptopropionic acid induced status epilepticus: a light and electron microscopic study

Light microscopic and ultrastructural changes of substantia nigra were studied in paralyzed ventilated rats with status epilepticus induced by mercaptopropionic acid. Some rats were killed at the end of seizure activity and others were examined in varying intervals after the arrest of seizure. The earliest changes were reduction in the size of the neuronal nuclei and chromatin clumping followed by simultaneous distention of axons and dendrites. There was also enlargement of the neuronal perikarya associated with microvacuolation. This neuronal microvacuolation corresponded ultrastructurally to swollen mitochondria with disrupted cristae. These changes were followed by progressive neuronal shrinkage and astrocytic swelling. The swollen astrocytic processes together with swollen neurites gave a spongy appearance to the involved area. The lesion thereafter progressively enlarged and evolved into an area of frank necrosis containing abundant macrophages. This lesion is morphologically different from that produced in cortex and hippocampus by seizure activity or due to the direct effect of excitotoxins. The significance of substantia nigra pars reticularis changes and their pathogenesis are discussed.

The effects of FG 7142 upon local cerebral glucose utilization suggest overlap between limbic structures important in anxiety and convulsions

The effects of the beta-carboline benzodiazepine receptor ligand FG 7142 upon local cerebral glucose utilization have been examined in conscious rats using the quantitative [14C]2-deoxyglucose autoradiographic technique. FG 7142 (1-10 mg/kg i.v.) produced behavioural changes consistent with an anxiogenic action. At the largest dose of FG 7142 (10 mg/kg) 30% of the animals experienced overt convulsions. In the data analysis animals were divided according to the behavioural response elicited by the drug. In animals not expressing convulsions, FG 7142 (1-10 mg/kg) effected increases in glucose utilization in 33 of the 65 regions examined. The majority of changes were confined to limbic structures with pronounced effects occurring in the mammillary body, anterior thalamic nuclei, septal nuclei and the oriens and molecular layers of the hippocampus. Glucose use in other structures associated with auditory and visual processing, such as the medial and lateral geniculate body, and associated cortical areas, was also significantly increased. However, brain regions involved in motor control were minimally affected. The patterns of local cerebral glucose use in animals expressing FG 7142-induced convulsions were contrasted with those from an equivalent non-seizure group. Some limbic structures which were significantly affected by FG 7142 (non-seizure group) displayed a further increase in glucose utilization during convulsions. These included the mammillary body and septum. Many other limbic structures (anterior thalamic nuclei, CA fields of the hippocampus and basolateral amygdala) did not display this further rise in glucose utilization. In the cortical amygdala, lateral preoptic area of the hypothalamus, nucleus accumbens and lateral elevations in glucose utilization were restricted to those animals experiencing overt convulsions.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Soman-induced convulsions affect the inositol lipid signaling system: potentiation by lithium; attenuation by atropine and diazepam

Effects of atropine or diazepam pretreatment on soman-induced convulsions and brain phosphoinositide (PI) metabolism, as assessed by brain regional inositol-1-phosphate (IP1) levels, were studied in saline and LiCl-pretreated rats. IP1, an intermediate in PI turnover, was measured in cortex, caudate, thalamus, hippocampus, and cerebellum. Soman (100 micrograms/kg; sc) produced convulsions in 63% of the saline-pretreated rats, whereas with LiCl pretreatment all rats exposed to 100 micrograms/kg of soman had tonic-clonic convulsions. Thus, LiCl pretreatment potentiated soman-induced convulsions. Tissue IP1 increased severalfold in soman-exposed convulsing rats with the highest increases being in frontal cortex and caudate. In contrast, no marked increases of IP1 occurred in similarly treated nonconvulsing rats. LiCl treatment itself increased IP1 levels without causing convulsions. In LiCl-pretreated rats, soman again markedly elevated IP1 levels above LiCl alone in convulsing rats, whereas no such effect occurred in nonconvulsing rats. In LiCl-pretreated rats, the increased IP1 levels associated with soman-induced convulsions were greatest in hippocampus and piriform cortex. Thus, LiCl appears to lower the threshold for the spread of seizure activity through limbic structures, thereby potentiating cholinergic-induced convulsions. Diazepam and atropine both blocked soman-induced convulsions, and brain regional IP1 elevations were concomitantly abolished as well. These results indicate that soman-induced convulsions involve the inositol lipid signaling system. This involvement is potentiated by lithium but attenuated by atropine and diazepam.

Functional [14C]2-deoxyglucose mapping of progressive states of status epilepticus induced by amygdala stimulation in rat

Electrical stimulation of rat amygdala induced self-sustained steady-state seizures (status epilepticus (SE] within 60 min. These SE states varied in behavioral severity from mere alteration of motility to frank clonic convulsions. Four distinct behavioral states were observed: immobility, exploration, mastication and clonus. These SE states were associated with [14C]2-deoxyglucose (2-DG) autoradiography anatomic patterns that were correspondingly more extensive and complex. Four distinct 2-DG activation patterns were observed: a restricted pattern involving several discrete limbic nuclei, including amygdala; more extensive patterns involving numerous limbic areas, first unilaterally, then bilaterally; finally the most extensive pattern involving widespread areas of forebrain. These data imply a systematic progression of seizure activity: originating in the amygdala, then spreading to some direct amygdala projection areas, and from there to a restricted network of interconnected ipsilateral limbic nuclei. This restricted network then recruits most of the remaining limbic structures, first ipsilaterally, then contralaterally. Finally, most of the basal ganglia, thalamus and neocortex are recruited.

Progression and generalization of seizure discharge: anatomical and neurochemical substrates

Seizure activity is generated and propagated by specific subcortical circuits. The substantia nigra (SN) and the area tempestas (AT) have been identified as two exemplary substrates for the control of experimental seizures. In animal models, GABAergic transmission has been shown to protect against seizures of different origins and methods of induction. Neuroactive peptides and excitatory amino acids may work with GABA in the SN to control the propagation of a wide variety of seizure types. In contrast, inhibition of AT pons selectively protects against seizures associated with limbic circuits. The AT is also a site from which bilaterally synchronous convulsions can be triggered in response to manipulations of cholinergic, GABAergic, and excitatory amino acid receptors. Definition of other pathways of seizure development and the effects of pharmacologic treatments on discrete brain regions await further research efforts.

Effects of moderate ethanol sedation on brain regional 2-deoxyglucose uptake in alcohol-sensitive and alcohol-insensitive rat lines

Acute intraperitoneal ethanol administration (2 g/kg) decreased the accumulation of radioactivity after [14C]2-deoxy-D-glucose injection into grossly dissected brain regions of alcohol-sensitive (ANT) and alcohol-insensitive (AT) rat lines. In autoradiography, the balance of radioactivity uptake between different functional systems (as judged from relative optical density ratios) was changed after ethanol: especially in the ANT rats, areas associated with sensory input were damped but motor relay nuclei were relatively active, suggesting a tendency to motor overactivity relative to sensory input. The ANT rats furthermore showed slight relative damping of cortical associative areas and differences in limbic structures compared to the AT rats, which, provided that changes in the balance between brain regions with a decreased overall activity are meaningful, suggests that the higher level of ethanol-induced motor impairment of the ANT rats may be related to defects in their integration of sensory and motor processes.

Cerebral glucose uptake in lindane-treated rats

The pesticide and ectoparasiticide lindane, gamma-isomer of hexachlorocyclohexane, is a powerful CNS-stimulant inducing convulsions and other signs of hyperexcitability in mammals. The present work was carried out to investigate the effect of lindane on brain regional glucose uptake at convulsant and non-convulsant doses. Local glucose uptake was measured in male Wistar rats using a modification of the 2-deoxyglucose (2-DG) method. Animals received i.p. [3H]2-DG and the amount of label in different brain structures of control and lindane-treated animals was assayed by a liquid scintillation counting of 18 dissected regions. Lindane at single convulsant dose (150 mg/kg, p.o.) increased 2-DG uptake in olfactory tubercules, hypothalamus, hippocampus, parafloculi and hypophysis. The uptake was decreased in parietal cortex, thalamus and pons-medulla. The pattern of 2-DG uptake after a single non-convulsant dose of 30 mg/kg p.o. was not so modified. After 1 week of treatment with 10 mg/kg per day p.o., increased 2-DG uptake was observed in superior colliculi while it was decreased in parietal cortex. The increase of 2-DG uptake in limbic regions observed at the convulsive dose agrees with the experimental association between poisoning signs induced by lindane and damage in the limbic system.

Direct microinjection of soman or VX into the amygdala produces repetitive limbic convulsions and neuropathology

Rats were injected in the amygdala and other forebrain sites with nmolar amounts of the highly toxic organophosphate 'nerve agent' compounds soman or VX (O-ethyl-S-(2-diisopropylaminoethyl)-methylphosphonothioate) in an attempt to determine the mechanism(s) responsible for the permanent brain pathology that has been observed following systemic intoxication with these agents. Injections were performed using a stereotaxically guided microsyringe in animals maintained under halothane/oxygen anesthesia or using chronically implanted cannulae in conscious animals. Bilateral microsyringe injections of up to 11.0 nmol soman into the amygdala failed to evoke abnormal behavior or brain pathology. When rats were pretreated with lithium chloride, or when carbachol was coadministered, soman injections evoked repetitive clonic convulsions and neuropathology. Unilateral injections of 3.4 nmol of VX into the amygdala elicited convulsions and brain damage in 67% of the animals tested. Atropine pretreatment (15.0 mg/kg, i.p.) prevented the development of convulsions and brain damage. Neuropathology was observed only in animals that developed repetitive convulsions; the piriform and entorhinal cortex, amygdala, hippocampus and thalamus were the brain structures most consistently damaged. With unilateral injections, the damage was more severe on the side ipsilateral to the injection. The behavioral topography of the convulsions and the neuroanatomical distribution and nature of the subsequent pathology closely resemble that observed with systemic administration of these compounds. The results indicate that the nerve agents are not directly neurotoxic, that peripherally induced hypoxia or anoxia are unlikely mechanisms of the neuropathology, and that the brain damage produced by these compounds is primarily seizure-mediated.

Attenuation of cerebral glucose use in kainic acid-treated rats by diazepam

Diazepam's impact on kainic acid seizure-induced local cerebral glucose utilization (LCGU) was assessed by a quantitative [14C]2-deoxyglucose method. Male rats were injected i.p. with either kainic acid (12 mg/kg) or its vehicle, 3 or 48 h before LCGU determination. Diazepam (3.2 mg/kg) or its vehicle were injected i.m. 15 min before, 1 and 2.5 h after kainic acid. Diazepam blocked kainic acid-induced overt convulsions, attenuated LCGU increases at 3 h and prevented 48 h LCGU decreases in piriform cortex and amygdala. LCGU in (% of vehicle): CA3 (438%), CA4 (537%) and CA1-ventral (340%) of hippocampus, interpeduncular nucleus (200%) and lateral lemniscus (213%) were still significantly above vehicle levels in the 3 h diazepam-kainic acid group. These results suggest that diazepam suppresses the spread of kainic acid-induced seizure activity from the proposed CA3 epileptogenic focus. In addition, diazepam reduces, but does not abolish, hypermetabolic activity at the foci itself.

Changes in extracellular amino acids during soman- and kainic acid-induced seizures

Extracellular amino acid levels in the rat piriform cortex, an area highly susceptible to seizure-induced neuropathology, were determined by means of intracranial microdialysis. Seizures were induced by systemic administration of either soman (O-1,2,2-trimethylpropyl methylphosphonofluoridate), a potent inhibitor of acetylcholinesterase, or the excitotoxin kainic acid. Extracellular glutamate levels increased in animals with seizures shortly after administration of either convulsant, but this change was statistically significant only in the case of soman-treated animals. Extracellular taurine levels increased markedly, reaching two- and fourfold baseline levels during the second hour of soman- and kainic acid-induced seizures, respectively. Taurine levels did not increase in the subpopulation of soman-treated animals without seizures, a finding indicating that elevation of extracellular taurine level is seizure related. Thus, we propose that taurine efflux may be a physiological cellular response to neuronal changes produced by excitotoxic chemicals, either directly or as a consequence of seizures.