Cerebral Slices Research Articles

MRS studies on cerebral metabolism in intact tissues

Use of combinations of multiply-labelled precursors ([1-13C] glucose, [2-13C] glucose, [2-13C] acetate and [1,2-13C] acetate), with analyses of isotopomers of resonances in 13C-MR spectra, is proving to be a promising approach to investigating metabolic trafficking betweeen neurones and glia in intact brain preparations. Parallel measurements of the energy state, [Ca2+]i and [Zn2+]i in superfused cerebral slices are performed using 31P- and 19F-MRS. The isotopomer analyses provided evidence for lactate production from glutamate in glia under normal conditions, and changes in the balance between neuronal and glial metabolism during depolarization. Deprivation of glucose and/or O2 gave evidence of metabolic adaptation, and hypoxia caused a diversion of glycolysis to glycerol 3-phosphate, thought to occur in glia. Exposure to excitotoxins resulted in less severe changes in [Ca2+]i and PCr than fuel deprivation or complete ischaemia, and caused release of zinc (possibly neuroprotective). The NMDA receptor blocker (MK801) reversed all of the effects of NMDA but not of glutamate or the other insults.

MRS studies on cerebral metabolism in intact tissues

Use of combinations of multiply-labelled precursors ([1-13C] glucose, [2-13C] glucose, [2-13C] acetate and [1,2-13C] acetate), with analyses of isotopomers of resonances in 13C-MR spectra, is proving to be a promising approach to investigating metabolic trafficking betweeen neurones and glia in intact brain preparations. Parallel measurements of the energy state, [Ca2+]i and [Zn2+]i in superfused cerebral slices are performed using 31P- and 19F-MRS. The isotopomer analyses provided evidence for lactate production from glutamate in glia under normal conditions, and changes in the balance between neuronal and glial metabolism during depolarization. Deprivation of glucose and/or O2 gave evidence of metabolic adaptation, and hypoxia caused a diversion of glycolysis to glycerol 3-phosphate, thought to occur in glia. Exposure to excitotoxins resulted in less severe changes in [Ca2+]i and PCr than fuel deprivation or complete ischaemia, and caused release of zinc (possibly neuroprotective). The NMDA receptor blocker (MK801) reversed all of the effects of NMDA but not of glutamate or the other insults.

Role of neuron-glial junctional domain proteins in the maintenance and termination of neuronal migration across the embryonic cerebral wall

To identify glial membrane proteins that contribute to the process of neuronal migration in the developing brain, we developed a polyclonal antiserum (D4) and a monoclonal antibody (NJPA1: neuron-glial junctional polypeptide antibody) that recognize membrane proteins localized to the plasmalemmal junction between migrating neurons and adjacent radial glial fibers (Cameron and Rakic, 1994). Here, we show that in the developing cerebral cortex, immunoreactivity for these junctional polypeptides is present throughout the neuronal migratory pathway but becomes minimal or absent where radial glial cell processes enter the marginal zone region, the barrier at which newly arrived neurons normally stop their migration and detach from their glial fiber substrate. We thus tested, using imprints of embryonic cerebral wall and slice preparations, whether the junctional membrane proteins detected by our antibodies contribute to the regulation of neuronal migration in the cerebral cortex. The rate of neuronal migration on glial cell substrates was reduced significantly in the presence of D4 or NJPA1 antibodies. Antibody exposure typically led to the withdrawal of leading processes, changes in microtubular organization and, in some instances, to detachment of neurons from their glial cell substrates. These results suggest that the polypeptides recognized by the D4 and NJPA1 antibodies are essential for the maintenance of normal neuronal migration. Dismantling of neuron-glial cell junctional domains formed by these membrane proteins may underlie neuronal cell detachment from glial migratory substrates at the interface between cortical plate and marginal zone in the developing cerebral wall.

Neuropharmacology of nicotine: effects on the autoregulation of acetylcholine release by substance P and methionine enkephalin in rodent cerebral slices and toxicological implications.

1. The neuronal release of acetylcholine (ACh) and its autoregulation by neuromodulators, substance P (SP) and methionine enkephalin (MEK), have been studied using superfused rodent cerebral slices. Nicotine exerts significant effects on autoregulation of ACh release, which may have toxicological implications. 2. Positive and negative feedback systems have been postulated for autoregulation of ACh release. The components of the positive feedback system include a muscarinic (Ms) receptor, SP, and activation of Ca2+ influx. Low levels of ACh in the biophase of the cholinergic synaptic gap may trigger the positive feedback system, and high levels of ACh may trigger the negative feedback system. 3. There are also neuronal pathways for direct reciprocal regulations of SP and MEK. 4. Low concentrations of nicotine triggers the release of ACh followed by MEK and SP. Release of SP causes neurogenic inflammation. 5. Nicotine and its metabolite, cotinine, activate platelet activating factor (PAF)-hydrolase and thereby enhance the turnover rate of PAF. This effect may contribute to tobacco-induced arterial thrombosis in peripheral and central nervous systems.

Acute hypoxia induces elevation of ornithine decarboxylase activity in neonatal rat brain slices.

Recent studies in vivo have demonstrated that ornithine decarboxylase (ODC) activity in the fetal rat brain is elevated 4-5-fold by acute maternal hypoxia. This hypoxic-associated increase is seen in the rat brain in both the newborn and the adult. Because of the intimate involvement of ODC in transcription and translation, as well as in growth and development, it is imperative that the manner in which hypoxia affects the regulation of this enzyme be better understood. In order to achieve this, a brain preparation in vitro was required to eliminate the confounding effects of the dam on the fetal and newborn brain ODC activity in vivo. Therefore, brain slices from 3-4-day-old (P-3) newborn rats were utilized to test the hypothesis that ODC activity increases in response to hypoxia in vitro. Cerebral slices from the P-3 rat pups were allowed to equilibrate and recover in artificial cerebrospinal fluid (ACSF) continuously bubbled with a mixture of 95% O2 and 5% CO2 for 1 h before beginning hypoxic exposures. Higher basal ODC activities were obtained by treating the slices with 0.03% fetal bovine serum (FBS) and 0.003% bovine serum albumin (BSA), rather than with ACSF alone. Hypoxia was induced in the slices by replacing the gas with 40%, 21%, 10%, or 5% O2, all with 5% CO2 and balance N2. With FBS and BSA treatment, ODC activity was maintained at about 0.15-0.11 nM CO2 mg-1 protein h-1 throughout the experiment, which was 2-3-fold higher than that without FBS and BSA. ODC activity increased significantly and peaked between 1 h and 2 h after initiation of hypoxia. For instance, with 21% O2, ODC activity increased approximately 1.5-fold at 1 h and approximately 2-fold at 2 h. These studies demonstrate that: (1) the hypoxic-induced increases observed in vivo in the fetal and newborn rat brain ODC activity can be approximated in a newborn rat brain slice preparation in vitro; (2) newborn rat brain slice preparations may provide an alternative to methods in vivo or cell culture methods for studying the regulation of acute hypoxic-induced enzymes; and (3) high, stable baseline ODC activities in brain slices suggest that the cells in the slice are capable of active metabolism if FBS and BSA are available to mimic conditions in vivo.

Regulatory sites and effectors ofd-[3H]aspartate release from rat cerebral cortex

To study the effect of agents interfering with the biosynthesis and/or the K(+)-evoked Ca(2+)-dependent release of neurotransmitter glutamate, rat cerebral slices were preincubated with Krebs-Ringer-HEPES-glucose-glutamine buffer (KRH buffer), loaded with D-[3H]aspartate and superfused with the preincubation medium in the presence or in the absence of Ca2+. The difference in radioactivity release divided by the basal release per min under the two conditions represented the K(+)-evoked Ca(2+)-dependent release. The agents used were: 1) Aminooxyacetic acid (AOAA), the inhibitor of transaminases, 2) Leucine (Leu), the inhibitor of phosphate activated glutaminase (PAG), 3) NH4+, the inhibitor of PAG, 4) Phenylsuccinic acid (Phs), the inhibitor of the mitochondrial ketodicarboxylate carrier, 5) ketone bodies, the inhibitors of glycolysis, 6) the absence of glutamine, the substrate of PAG. The results show that Leu, NH4+, Phs and the absence of Gln significantly increase the K(+)-evoked Ca(2+)-dependent release of radioactivity by 64%, 200%, 95% and 147% respectively, indicating that these agents are inhibitors of the K(+)-evoked Ca(2+)-dependent release of glutamate. Ketone bodies and AOAA had no effect. These results indicate that the major if not the exclusive biosynthetic pathway of neurotransmitter glutamate in rat cerebral cortex is through the PAG reaction and support a model for the pathway followed by neurotransmitter glutamate i.e. glutamate formed outside the inner mitochondrial membrane has to enter the mitochondrial matrix or is formed within it from where it can be extruded to supply the transmitter pool in exchange of GABA.

MRS studies on calcium and zinc in metabolizing cerebral slices exposed to glutamate and NMDA

The19F-NMR calcium indicator 5FBAPTA has been used to measure changes in free intracellular calcium, [Ca2+],, in superfused guinea pig cerebral cortical slices. Increases in [Ca2+], have been observed with depolarization and the combined insult of hypoxia and hypoglycemia. These increases in [Ca2+]i, can be explained by the excitotoxic hypothesis which proposes a central role for the neurotransmitter glutamate and the NMDA receptor in cell death. We, therefore, investigated the effects of glutamate and NMDA directly on [Ca2+]i, in cerebral cortical slices with31P-NMR to monitor the energy state. In the presence of glutamate (±Mg) a new resonance was observed in the19F spectra and was attributed to the Zn-5FBAPTA complex. The zinc peak appears with or just following an increase in [Ca2+]i, and with a drop in PCr. Similar results were obtained on exposing the tissues to NMDA. Zinc has been reported to be enriched in various parts of the brain and have a multiplicity of possible roles. This is the first time zinc has been shown in actively metabolizing tissue. The observation that the zinc resonance does not appear with depolarization or hypoxia and hypoglycemia suggests that the mechanisms of damage in these latter insults are not solely attributable to the release of excitotoxins.

Pretreatment of rat brain slices with ouabain decreases chloride-dependent l-glutamate transport in synaptic membrane

Possible roles of (Na(+)-K+)-ATPase on regulation of Cl(-)-dependent L-glutamate (L-Glu) transport in rat synaptic membrane were examined. Pretreatment of rat cerebral slices with 20 micrograms/ml veratrine, 56 mM K+ and 20 microM monensin increased Cl(-)-dependent L-[3H]-Glu uptake into membrane vesicles prepared from the slices. Pretreatment with (Na(+)-K+)-ATPase inhibitors, 100 microM ouabain, 100 microM strophanthidin, 100 microM vanadate and K(+)-free medium, decreased the uptake by 25-30%, while 5 microM A23187 and 10 microM ruthenium red had no effect. Ouabain (100 microM) caused the maximal effect in 10-20 min of incubation. The effect of (Na(+)-K+)-ATPase inhibitors was reversible and characterized by a decrease in Vmax of the uptake. Addition of 5 microM ouabain abolished the increases in the uptake induced by either veratrine, 56 mM K+ or monensin. Dose-inhibition curve of ouabain on the increased Cl(-)-dependent L-[3H]-Glu uptake was bi-phasic; ouabain at 0.5-5 microM selectively diminished the stimulatory effect of veratrine and inhibited the basal uptake at higher concentrations. Veratrine had no effect on L-[3H]-Glu uptake in 5 microM strophanthidin containing or K(+)-free medium. These results suggest the involvement of (Na(+)-K+)-ATPase in the veratrine-induced increase in Cl(-)-dependent L-Glu transport in rat brain synaptic membranes.

Improving effect of acetylcholine receptor agonists on a deficit of 2-deoxyglucose uptake in cerebral cortical and hippocampal slices in aged and AF64A-treated rats

The aim of the present study was to determine whether the facilitation of 2-deoxyglucose (2-DG) uptake in the cerebral and hippocampal slices by nicotinic and muscarinic receptor agonists is compromised in the aged rat brain. For this, the effects of the nicotinic receptor agonist nicotine, the muscarinic receptor agonists oxotremorine and McN-A-343, and the ACh esterase inhibitors physostigmine and NK247 on 2-DG uptake in the brain slices of young (2-month-old) and aged (24–26-month-old) rats were tested. The decrements of 2-DG uptake in the cortical slices of aged rats were significantly attenuated by treatment with oxotremorine, nicotine and amiridine. In contrast, the metabolic responsivity of hippocampal slices to these drugs was reduced. To assess whether age-related changes in 2-DG uptake may be due to deficits in cholinergic function, we tested these drugs on the decrements of 2-DG uptake in ethylcholine aziridinium (a neurotoxic analog of choline) injected rats. The reductions of 2-DG uptake by injection of ethylcholine aziridinium was attenuated by oxotremorine but not by physostigmine. The present results reveal that metabolic decrements in the cerebral cortex from aged or ethylcholine aziridinium-injected rats were attenuated by muscarinic and nicotinic receptor agonists, suggesting that the muscarinic and nicotinic receptor mechanism in the cerebral cortex may be involved in cholinergic drug-induced functional recovery in aged rats.

Age-related changes in glucose uptake of cerebral hemisphere slices of male garden lizards in response to starvation stress

In the male garden lizard, the glucose uptake of cerebral hemisphere slices did not change during maturation (young to middle-aged) but declined during ageing (middle-aged to old). Short-term starvation (3 days) did not cause a significant change in glucose uptake of cerebral hemisphere of young lizards but led to an increase in the parameter in both the middle-aged and old.

A novel protein induced in cortical epileptic focus of rat cerebrum: A possible linkage to epileptogenesis

To precisely evaluate a protein-related mechanism of epileptogenesis, we quantitatively analyzed the 70-kDa protein (namely, P70), a specific protein found in the cobalt-induced epileptic focus, and examined its effect on the electrocorticogram (ECoG) and cortical neurons in cerebral slices and its immunocytochemical localization in rats. Cobalt-induced cortical epileptogenic cortex exhibited a marked induction of P70. Its initiation time was ahead of the generation of epileptogenic activities. The anticonvulsant phenytoin (PHT) attenuated the cobalt-induced epileptogenic activities, but failed to suppress protein induction. Injection of this protein into the motor region of normal rat cerebral cortex elicited an epileptic ECoG and behavioral seizures. It also caused epileptiform activity with paroxysmal depolarization shifts in cortical neurons. These epileptogenic phenomena elicited by P70 were abolished by prior treatment with PHT or phenobarbital. Immunocytochemical analysis with an antiserum against P70 revealed that the reactivity was confined to pyramidal cells only in the region of the focus and was mainly localized on somatic, dendritic, and nuclear membranes and microtubles. These findings suggest that P70 may be linked to epileptogenesis.

Ion and autoreceptor regulation of purine release from rat cerebral slices

Ion and autoreceptor regulation of purine release from rat cerebral slices

Quantitation of cerebral atrophy in preclinical and end-stage Alzheimer's disease.

Morphometric analysis of standardized gross cerebral slices from 16 patients with end-stage Alzheimer's disease (AD), 14 controls without neuropathological lesions or neurological disease, and 4 neurologically intact nondemented patients with histopathological lesions of AD was used to measure cross-sectional areas of cerebral cortex, white matter, subcortical nuclei, and the ventricular system. In AD, there was global cerebral atrophy of both cortex and white matter, selective atrophy of the amygdala and hippocampus, and ex vacuo hydrocephalus. In addition, in half the cases of AD, white matter atrophy was associated with overt histopathological evidence of patchy rarefaction of fibers and gliosis. Patients with preclinical AD had prominent and selective shrinkage of white matter comparable to that observed in AD, yet their cortical areas were normal. These observations suggest that white matter degeneration is an intrinsic component of AD. Moreover, its presence in preclinical AD where cortical atrophy is not evident indicates that cytoskeletal abnormalities associated with axonal degeneration may precede and perhaps cause the cortical atrophy observed in clinically manifested AD.

The effects of bilirubin on brain energy metabolism during normoxia and hypoxia: an in vitro study using 31P nuclear magnetic resonance spectroscopy.

Available evidence from in vitro studies suggests that the neurotoxic effects of bilirubin may be exacerbated by, or even require, additional factors such as hypoxia or asphyxia. The aim herein was to use 31P nuclear magnetic resonance spectroscopy to study the effects of bilirubin on brain energy metabolism in vitro under conditions of normoxia and hypoxia. 31P nuclear magnetic resonance spectra were acquired from guinea pig cerebral hemisphere slices during superfusion with solutions containing bilirubin and albumin in 5:1 molar ratio. The effects of bilirubin at concentrations between 400 nmol/liter and 120 mumol/liter were studied under normoxic conditions. Bilirubin caused no apparent disruption in brain energy metabolism during normoxia. The combined effects of bilirubin (40 mumol/liter) and hypoxia were studied. Hypoxia alone led to a steady state reduction in the phosphocreatine to inorganic phosphate peak-height ratio to 0.30 (0.27-0.32) [mean (range) n = 3]. Bilirubin (40 mumol/liter) in the presence of hypoxia caused a further reduction in the phosphocreatine to inorganic phosphate ratio to 0.18 (0.17-0.20) [mean (range) n = 3, p less than 0.01, analysis of variance] which was rapidly reversed on returning to normoxia. These results demonstrate that bilirubin at the concentration studied requires hypoxia, in addition, to cause a measurable disturbance of brain energy metabolism. The nature of this interaction is unknown, but it may reflect the effect of intracellular acidosis on bilirubin solubility or the oxygen dependence of brain mitochondrial bilirubin oxidase.

Effects of arsenic on cholinergic parameters in brain in vitro

The effects of sodium arsenite (arsenite) on the cholinergic system in the brain of the mouse were investigated in vitro and compared with those of N-ethylmaleimide (NEM) and iodoacetate, both of which are alkylating sulfhydryl reagents. Arsenite, at concentrations greater than 10 −4M, inhibited depolarized and nondepolarized release of acetylcholine (ACh) from cerebral slices, the synthesis of ACh in the slices, high-affinity uptake of choline into synaptosomes and activity of acetylcholinesterase (AChE). On the other hand, arsenite potentiated dose-dependently the activity of choline acetyltransferase (ChAT). N-Ethylmaleimide and iodoacetate showed inhibitory effects similar to those of arsenite. However, some exceptions were that N-ethylmaleimide did not have any effect on the nondepolarized release of ACh while iodoacetate had no effect on high affinity uptake of choline and activity of AChE. In contrast to arsenite, N-ethylmaleimide and iodoacetate inhibited the activity of ChAT. Neither of arsenite, N-ethylmaleimide nor iodoacetate showed any effect on the binding of [ 3H]quinuclidinyl benzilate to muscarinic ACh receptors. Although arsenite is thought to inhibit the cholinergic system in brain in vivo, its potentiating effect on ChAT and inhibition of AChE may reduce this harmful effect.

Serotonin innervation in adult rat neostriatum. I. Quantified regional distribution

The distributional features of the serotonin (5-HT) innervation in adult rat neostriatum were examined and quantified using two complementary chemoanatomical methods: 5-HT-immunohistochemistry on serial histological sections and radioautography after [ 3H]5-HT uptake in whole cerebral hemisphere slices. As visualized and measured after peroxidase-antiperoxidase immunostaining, the neostriatal 5-HT fiber network pervading the entire neostriatum was 2–3 times denser in its ventral than dorsal parts, and showed a slight rostrocaudal increase in density. Its axonal length ranged from 1.06 to 4.18 m per mm 3 of striatal tissue. Radioautographic counts of the [ 3H]5-HT-labeled axon varicosities within comparable sectors of the neostriatum showed good correlation with this distribution pattern. As extrapolated after appropriate corrections for incomplete detection at the chosen exposure time and from the thickness of sections examined, the number of neostriatal 5-HT varicosities (innervation density) ranged from 1.5 to 4.8 millions and averaged 2.6 millions per mm 3 of tissue. These quantitative results provided new insights into the topographical organization of the dorsal raphe-neostriatal 5-HT projection system. They already allow for meaningful correlations with currently available microchemical data on intrastriatal 5-HT levels and should also be of considerable significance when as precise information becomes available on the number and localization of different 5-HT receptors and uptake carriers within rat neostriatum.

Autoinhibition of histamine synthesis mediated by presynaptic H 3-receptors

The regulation of histamine synthesis was studied on rat brain slices or synaptosomes labeled with l-[ 3H]histidine. Depolarization by increased extracellular K + concentration enhanced by about twofold the [ 3H]histamine formation in slices of cerebral cortex. This stimulation was also observed, although to a lesser extent, in synaptosomes from cerebral cortex and slices from the posterior hypothalamus where most histaminergic cell-bodies are located, suggesting that it may occur in nerve endings as well as in perikarya. In the presence of exogenous histamine in increasing concentrations the K +-induced stimulation was progressively reduced by up to 60–70%. The effect of exogenous histamine appears to be receptor-mediated as shown by its saturable character, high pharmacological specificity and competitive reversai by histamine antagonists. The ec 50 value of histamine for synthesis reduction (0.34 ± 0.03 μM) was similar to its ec 50 value for release inhibition known to be mediated by H 3-receptors. In addition, whereas mepyramine and tiotidine, two potent antagonists at H 1- and H 2-receptors, respectively, were poorly effective, the H 3-receptor antagonists burimamide and impromidine reversed the histamine effect in an apparently competitive manner. These effects were observed in slices of cerebral cortex or posterior hypothalamus as well as in cortical synaptosomes. Furthermore, even in the absence of added histamine, H 3-receptor antagonists enhanced the depolarization-induced stimulation of [ 3H]histamine synthesis, indicating a participation of released endogenous histamine in the synthesis control process. The potencies of H 3-receptor antagonists were similar to those of these agents at presynaptic autoreceptors controlling [ 3H]histamine release. It is concluded that H 3-receptors control not only release but also synthesis of histamine at the Ievel of nerve endings and also, presumably, of perikarya. A relationship between the two regulatory processes, possibly via intracellular calcium, seems likely but remains to be investigated at the molecular Ievel.

Regional and laminar density of the dopamine innervation in adult rat cerebral cortex

The topographie distribution and density of the dopamine innervation in adult rat cerebral cortex were investigated by means of a recently improved radioautographic procedure for the light microscopic visualization and counting of monoamine axonal varicosities. Dopamine terminals were specifically labeled by high-affinity uptake in whole cerebral hemisphere slices incubated for 15 min at 35°C with 10 −6M tritiated dopamine in the presence of 10 −4M pargyline and 5 × 10 −6M desipramine. The slices were subsequently fixed, embedded in Epon and processed for light microscope radioautography as large 4-μm-thick (whole hemisphere) or smaller, semi-thin sections (selected areas). In radioautographs of serial semi-thin sections exposed for various periods of time, the number of labeled axonal varicosities reached a plateau after 12–14 days of exposure. Counts on such sections of increasing thickness allowed to calculate a correcting factor to transform numbers obtained from 4-μm-thick sections into their equivalent for a tissue thickness of 0.5 μm from which all varicosities were detected. The number of labeled varicosities could then be expressed per mm 3 of tissue after measuring their mean caliper diameter in electron microscope radioautographs. As visualized at 3 transverse levels representing most of the major cytoarchitectonic divisions of cerebral cortex, two novel aspects were recognized in the topographic distribution of dopamine terminals: (1) the presence of a dopamine innervation in layer VIb of the frontal, parietal, temporal and occipital neocortex, and (2) a significant contingent of dopamine varicosities within the deep and not only upper layers of supragenual cingulate cortex. A fair number of dopamine varicosities were also detected in the upper layers of the dorsomedial frontal area, in the retrosplenial and adjacent occipital cortex as well as in the ventral subiculum and field CA1 of the hippocampus. As measured in 10 sectors representing different cortical regions, the highest density of dopamine innervation was found in the supragenual cingulate cortex (1.7 × 10 6) and particularly in its layers II and III (3.1 × 10 6). A slightly lower density was measured in the anteromedian “prefrontal” cortex (1.0 × 10 6). The rostrorhinal and the perirhinal cortex showed moderate dopamine innervation (3.0 and 5.5 × 10 5) with varicosities in every layer. The piriform and the posterior entorhinal cortex were also moderately and ubiquitously innervated (2.5 and 3.0 × 10 5). In the dorsofrontal, parietal and temporal neocortex, overall dopamine innervation was of low density (5.0−6.0 × 10 4) and concentrated in layer VI(2 × 10 5 varicosities/mm 3). The primary visual and the lateral occipital neocortex had the lowest density, with terminals also confined to layer VI(4.0 × 10 4). Together with recent immunocytochemical observations on developing or adult rat cortex, these results justify some revision of current views regarding the organizational features of the mesocortical dopamine system.

Effect of Amplitude-Modulated 147 MHz Radiofrequency Radiation on Calcium Ion Efflux from Avian Brain Tissue

Cerebral cortex tissue slices and cerebral hemispheres prepared from Gallus domesticus chicks were exposed to 147 MHz radiofrequency radiation, amplitude modulated at 16 Hz and applied at a power density of 0.75 mW/cm2, to determine the effect of such exposure of 45Ca2+ efflux from the avian brain tissue. Statistical analysis of these data demonstrates that such exposure has no significant effect on 45Ca2+ efflux.

Reduced uptake and release of 5-hydroxytryptamine and taurine in the cerebral cortex of epileptic E1 mice

Inbred mutant E1 mice are highly susceptible to convulsive seizures upon ‘throwing’ stimulation, and the inhibition of 5-hydroxytryptamine (5-HT) and taurine activities appears to be involved in the E1 mouse seizures. Uptake and release of [ 3H]5-HT and [ 3H]taurine into and from cerebral neurocortical slices using a superfusion system were investigated in both non-stimulated and stimulated E1 mice [E1(−), E1(+)] and in ddY mice, which do not have a convulsive disposition. Release was defined as 40 mM K +-stimulated release. 5-HT and taurine uptake in E1(+) was lower than E1 (−) but no difference in either uptake was found between ddY and E1 (−). Release of 5-HT and taurine in E1(−) was higher than in ddY whereas their release in E1(+) was lower than in E1(−). The taurine level in the cerebral neocortex of E1(−) and E1(+) was higher than in ddY. These results suggest that the synaptic function of the 5-HT and taurine containing neurons is suppressed and that dysfunction of these inhibitory neurons is involved in the seizure susceptibility in the E1 mice.