Valproate treatment induces age- and sex-dependent neuronal activity changes according to a patch clamp study.

Autism spectrum disorder is a heterogeneous neurodevelopmental disorder characterized by impaired social interactions, restricted, and stereotyped behaviors. The valproic acid model is one of the most recognized and broadly used models in rats to induce core symptoms of this disorder. Comorbidity of epilepsy and autism occurs frequently, due to similar background mechanisms that include the imbalance of excitation and inhibition. In this series of experiments, treatment was performed on rat dams with a single 500 mg/kg dose i.p. valproate injection on embryonic day 12.5. Intracellular whole-cell patch clamp recordings were performed on brain slices prepared from adolescent and adult offspring of both sexes on pyramidal neurons of the medial prefrontal cortex and entorhinal cortex. Current clamp stimulation utilizing conventional current step protocols and dynamic clamp stimulation were applied to assess neuronal excitability. Membrane properties and spiking characteristics of layer II-III pyramidal cells were analyzed in both cortical regions. Significant sex-dependent and age-dependent differences were found in several parameters in the control groups. Considering membrane resistance, rheobase, voltage sag slope, and afterdepolarization slope, we observed notable changes mainly in the female groups. Valproate treatment seemed to enhance these differences and increase network excitability. However, it is possible that compensatory mechanisms took place during the maturation of the network while reaching the age-group of 3 months. Based on the results, the expression of the hyperpolarization-activated cyclic nucleotide-gated channels may be appreciably affected by the valproate treatment, which influences fundamental electrophysiological properties of the neurons such as the voltage sag. Remarkable changes appeared in the prefrontal cortex; however, also the entorhinal cortex shows similar tendencies.

Anti-glutamatergic Effects of Three Lignan Compounds: Arctigenin, Matairesinol and Trachelogenin - An ex vivo Study on Rat Brain Slices.

Arctigenin is a bioactive dibenzylbutyrolactone-type lignan exhibiting various pharmacological activities. The neuroprotective effects of arctigenin were demonstrated to be mediated via inhibition of AMPA and KA type glutamate receptors in the somatosensory cortex of the rat brain. The aim of this study was to compare the effects of arctigenin with matairesinol and trachelogenin on synaptic activity in ex vivo rat brain slices. Arctigenin, matairesinol and trachelogenin were isolated from Arctium lappa, Centaurea scabiosa and Cirsium arvense, respectively, and applied on brain slices via perfusion medium at the concentration range of 0.5 - 40 µM. The effects of the lignans were examined in the CA1 hippocampus and the somatosensory cortex by recording electrically evoked field potentials. Arctigenin and trachelogenin caused a significant dose-dependent decrease in the amplitude of hippocampal population spikes (POPS) and the slope of excitatory postsynaptic potentials (EPSPs), whereas matairesinol (1 µM and 10 µM) decreased EPSP slope but had no effect on POPS amplitude. Trachelogenin effect (0.5 µM, 10 µM, 20 µM) was comparable to arctigenin (1 µM, 20 µM, 40 µM) (p > 0.05). In the neocortex, arctigenin (10 µM, 20 µM) and trachelogenin (10 µM) significantly decreased the amplitude of evoked potential early component, while matairesinol (1 µM and 10 µM) had no significant effect (p > 0.05). The results suggest that trachelogenin and arctigenin act via inhibition of AMPA and KA receptors in the brain and trachelogenin has a higher potency than arctigenin. Thus, trachelogenin and arctigenin could serve as lead compounds in the development of neuroprotective drugs.

Epileptiform Events and Kainate Receptor Activity Changes Considerably during Entorhinal Cortex Development: An ex vivo Study.

Epilepsy is a commonly diagnosed neurological disease, which often develops already in childhood. The prominent feature of this dysfunction is the strong, unprovoked hypersynchronous neuronal activity of the brain, especially in the cortex, which appears in recurrent seizures. Previous studies indicated a potential modulatory role of kainate types of glutamate receptors in this mechanism. In our experiments, we used combined hippocampal-entorhinal rat brain slices of different ages. Developing (2-, 3-, and 4-week-old), adolescent (6-week-old), and adult (3-month-old) groups were investigated. During the experiments, first, we provoked convulsions with magnesium-free perfusion solution; then, to investigate the role of kainate receptors, seizure-like events (SLEs) were suppressed by applying a specific GluK1/2 antagonist (UBP-296). Neuronal network activity was recorded by a multi-electrode array chip, and temporal features of field potentials and single-cell activity were analyzed in the different age-groups. The frequency, duration of spontaneous events, the overall seizure characteristics, and spike activities were compared. Spontaneous events were categorized into interictal epileptiform discharges (IEDs) and SLEs on the basis of the temporal structure of activities. In 3- and 4-week-old animals, IEDs were observable, which entirely disappeared after the 4th week. The structure and the length of SLEs varied in the younger animals (3- and 4-week-old animals); however, after the 6th week, these events became more stabilized. In most groups, the count of detected spikes was significantly higher in layer II/III than in layer V. The neuronal networks started to behave like adult ones at 4 weeks of age. The length of events decreased in adult animals due to the maturation of the network, and the inhibition becomes stronger. The IEDs disappeared completely, and the SLEs became stable and stereotypic in 6-week-old animals. UBP-296 administration reduced the number of IEDs; however, this had no substantial effect on the SLEs.

Alterations of the Hippocampal Networks in Valproic Acid-Induced Rat Autism Model.

Autism Spectrum Disorder (ASD) is one of the most frequently diagnosed neurodevelopmental disorders, characterized among others by impairments in social interactions and repetitive behavior. According to one of the leading hypotheses about its origin, ASD is caused by the imbalance of excitatory and inhibitory circuit activity. ASD-related morphological and functional changes can be observed in several brain regions i.e., in the prefrontal cortex and the hippocampus. It is well-established that prenatal valproic-acid (VPA) exposure of rats on day 12.5 leads to neurodevelopmental alterations with autism-like clinical and behavioral symptoms. The aim of this study was to investigate potential changes in the excitability of neuronal networks and individual neurons of the hippocampus elicited by prenatal VPA treatment. As there are marked sex differences in ASD, offspring of both sexes were systematically tested, using two different age groups, to elucidate eventual differences in neurodevelopment after VPA treatment. Excitatory connections and long-term synaptic plasticity as well as intrinsic excitability of CA1 pyramidal cells were examined. Pregnant female Wistar rats received saline or 500 mg/kg VPA i. p. on gestation day 12.5. Brain slices of 6-week-old and 3-month-old offspring were investigated using extra- and intracellular electrophysiological techniques. Field potential- and whole-cell patch clamp recordings were carried out to measure network excitability and single cell activity in the CA1 region hippocampus. Enhanced excitability of hippocampal networks was detected in the 6-week-old VPA-treated male rats; however, this change could not be observed in 3-month-old males. Intrinsic excitability of single neurons, however, was increased in 3-month-old males. In 6-week-old treated females, the most prominent effect of VPA was an increase in voltage sag, to a similar degree to the neurons of the older age group. In 3-month-old females, a network excitability increase could be demonstrated, in a lesser degree than in younger males. It can be concluded, that VPA treatment had diverse effects on hippocampal excitability depending on the sex and the age of the animals. We found that certain alterations manifested in 6-week-old rats were compensated later, on the other hand, other changes persisted until the age of 3 months.

Zearalenone alters the excitability of rat neuronal networks after acute in vitro exposure.

Zearalenone (ZEA) is a mycotoxin produced by Fusarium species, detectable in various cereals and processed food products worldwide. ZEA displays a significant estrogenic activity, thus its main health risk is the interference with sexual maturation and reproduction processes. However, in addition to being key hormonal regulators of reproductive function, estrogenic compounds have a widespread role in brain, as neurotrophic and neuroprotective factors, and they may influence the activity of several brain areas not directly linked to reproduction, as well. Therefore, in the present study, acute effects of ZEA were studied on certain neuronal functions in rats. Experiments were performed on rat brain slices or live rats. Slices were incubated in ZEA-containing (10-100 µM) solution for 30 min. Electrically evoked and spontaneous field potentials were studied in the neocortex and in the hippocampus. At higher concentrations, ZEA incubation of the slices altered excitability and the pattern of epileptiform activity in neocortex and inhibited the development of LTP in hippocampus. For the verification of these in vitro results, in vivo electrophysiological and immunohistochemical investigations were also performed. ZEA was administered systemically (5 mg/kg, i.p.) to male rats and somatosensory evoked potentials and neuronal activation studied by c-fos expression were analyzed. No neuronal activation could be demonstrated in the hippocampus within 2 h of the injection. In the somatosensory cortex, ZEA did not change in vivo evoked potential parameters, but the activation of a small neuronal population could be demonstrated with the c-fos technique in this brain area. This result could be associated with the ZEA-induced alteration of epileptiform activity observed in vitro. Altogether, the toxin altered the excitability and plasticity of neuronal networks after direct treatment in slices, but the effects were less prominent on the given brain areas after systemic treatment in vivo. A probable explanation for the partial lack of in vivo effects may be that after a single injection, ZEA did not cross the blood-brain barrier at sufficient rate to allow the build-up of comparable concentrations in the investigated brain areas. However, in case of compromised blood-brain barrier functions or long-term repeated exposure, alterations in cortical and hippocampal functions cannot be ruled out.

Short-term neuronal effects of fumonisin B1 on neuronal activity in rodents.

Fumonisin B1 (FB1) is a mycotoxin produced by microscopic fungi (mostly Fusarium species), which may infect our major crops. The toxin inhibits the development of these plants and may also have harmful effects on animals and humans consuming the infected crops. FB1 inhibits sphingolipid biosynthesis which leads to altered membrane characteristics and consequently, altered cellular functions. There are some indications that the toxin has inhibitory effects on neuronal activity in case of repeated consumption, presumably due to sphingolipid depletion. However, according to new literature data, FB1 may have acute excitatory neural effects, too, via different mechanisms of action. Therefore, in the present study, we addressed the neuronal network effects of FB1 following acute treatment, using different electrophysiological techniques in vitro and in vivo. Acute treatments with FB1 (10-100 µM) were carried out on brain slices, tissue cultures and live animals. After direct treatment of samples, electrically evoked or spontaneous field potentials were examined in the hippocampus and the neocortex of rat brain slices and in hippocampal cell cultures. In the hippocampus, a short-term increase in the excitability of neuronal networks and individual cells was observed in response to FB1 treatment. In some cases, the initially enhanced excitation was reversed presumably due to overactivation of neuronal networks. Normal spontaneous activity was found to be stimulated in hippocampal cell cultures. Seizure susceptibility was not affected in the neocortex of brain slices. For the verification of the results caused by direct treatment, effects of systemic administration of FB1 (7.5 mg/kg, i.p.) were also examined. Evoked field potentials recorded in vivo from the somatosensory cortex and cell activation measured by the c-fos technique in hippocampus and somatosensory cortex were analyzed. However, the hippocampal and cortical stimulatory effect detected in vitro could not be demonstrated by these in vivo assays. Altogether, the toxin enhanced the basic excitability of neurons and neuronal networks after direct treatment but there were no effects on the given brain areas after systemic treatment in vivo. Based on the observed in vitro FB1 effects and the lack of data on the penetration of FB1 across the blood-brain barrier, we assume that in vivo consequences of FB1 administration can be more prominent in case of perturbed blood-brain barrier functions.

The mycotoxin deoxynivalenol activates GABAergic neurons in the reward system and inhibits feeding and maternal behaviours.

Deoxynivalenol (DON) or vomitoxin, is a trichothecene mycotoxin produced mainly by Fusarium graminearum and culmorum. Mycotoxins or secondary metabolic products of mold fungi are micro-pollutants, which may affect human and animal health. The neuronal and behavioural actions of DON were analysed in the present study. To address, which neurons can be affected by DON, the neuronal activation pattern following intraperitoneal injection of DON (1 mg/kg) was investigated in adult male rats and the results were confirmed in mice, too. DON-induced neuronal activation was assessed by c-Fos immunohistochemistry. DON injection resulted in profound c-Fos activation in only the elements of the reward system, such as the accumbens nucleus, the medial prefrontal cortex, and the ventral tegmental area. Further double labelling studies suggested that GABAergic neurons were activated by DON treatment. To study the behavioural relevance of this activation, we examined the effect of DON on feed intake as an example of reward-driven behaviours. Following DON injection, feed consumption was markedly reduced but returned to normal the following day suggesting an inhibitory action of DON on feed intake without forming taste-aversion. To further test how general the effect of DON on goal-directed behaviours is, its actions on maternal behaviour was also examined. Pup retrieval latencies were markedly increased by DON administration, and DON-treated mother rats spent less time with nursing suggesting reduced maternal motivation. In a supplementary control experiment, DON did not induce conditioned place preference arguing against its addictive or aversive actions. The results imply that acute uptake of the mycotoxin DON can influence the reward circuit of the brain and exert inhibitory actions on goal-directed, reward-driven behaviours. In addition, the results also suggest that DON exposure of mothers may have specific implications.

Kainate receptors have different modulatory effect in seizure-like events and slow rhythmic activity in entorhinal cortex ex vivo.

In the neocortex, neurons form functional networks, the members of which exhibit a variable degree of synchronization. Slow rhythmic activity may be regarded as a balanced interplay of excitatory and inhibitory neuronal network activity, which is essential in learning and memory consolidation. On the other hand, seizures may be considered as hypersynchronized network states occurring in epileptic diseases. The brain slice method and multi-electrode array (MEA) systems offer a good opportunity for the modelling of cortical spontaneous activities by examining their initiation and propagation. Our main goals were to characterise and compare spontaneous activities developing in different conditions and cortical network states. The role of kainate receptors in these processes was also tested. According to our results, there are demonstrable dissimilarities between slow rhythmic activities vs. seizure-like events developing in the rat entorhinal cortex ex vivo in normal vs. epileptic conditions. Propagation velocity, time scale, activity pattern and pharmacological sensitivity are all different. Kainate receptors play a role in network activity in entorhinal cortex, they are capable to prolong the duration of the events of epileptiform activity. Their regulatory effect is more prominent under epileptic than under normal conditions.

Analysis of Propagation of Slow Rhythmic Activity Induced in Ex Vivo Rat Brain Slices.

Slow wave oscillation is a synchronous oscillatory mechanism that is a characteristic wave type of the cerebral cortex during physiological deep sleep or anesthesia. It may play an important role in cortical analysis of sensory input. Our goal was (1) to develop optimal conditions for the induction of this slow rhythmic activity in adult rat cortical slices, (2) to identify connections through which the activity propagates between coupled cortical regions, and (3) to study the pattern of horizontal and vertical flow of activity developed spontaneously in cortical slices. Experiments were performed on intact or differently incised rat cortical slices. According to our results, spontaneous cortical activity develops reliably in slightly modified artificial cerebrospinal fluid, first in the entorhinal cortical region of horizontally cut slices and then it spreads directly to the perirhinal (PRh) cortex. The activity readily generated in layer 2/3 of the entorhinal cortex then quickly spreads vertically to upper layer 2-3 in the same area and to the neighboring regions, that is, to the PRh cortex. Synchronization of activity in neighboring cortical areas occurs through both callosal connections and layer 2-3 intrinsic network, which are important in the propagation of spontaneous, inherent cortical slow wave activity.

Causal relationship between local field potential and intrinsic optical signal in epileptiform activity in vitro.

The directed causal relationship were examined between the local field potential (LFP) and the intrinsic optical signal (IOS) during induced epileptiform activity in in vitro cortical slices by the convergent cross-mapping causality analysis method. Two components of the IOS signal have been distinguished: a faster, activity dependent component (IOSh) which changes its sign between transmitted and reflected measurement, thus it is related to the reflectance or the scattering of the tissue and a slower component (IOSl), which is negative in both cases, thus it is resulted by the increase of the absorption of the tissue. We have found a strong, unidirectional, delayed causal effect from LFP to IOSh with 0.5-1s delay, without signs of feedback from the IOSh to the LFP, while the correlation was small and the peaks of the cross correlation function did not reflect the actual causal dependency. Based on these observations, a model has been set up to describe the dependency of the IOSh on the LFP power and IOSh was reconstructed, based on the LFP signal. This study demonstrates that causality analysis can lead to better understanding the physiological interactions, even in case of two data series with drastically different time scales.

T-2 mycotoxin treatment of newborn rat pups does not significantly affect nervous system functions in adulthood.

T-2 toxin is primarily produced by Fusarium sp. abundant under temperate climatic conditions. Its main harmful effect is the inhibition of protein synthesis. Causing oxidative stress, it also promotes lipid peroxidation and changes plasma membrane phospholipid composition; this may lead to nervous system alterations. The aim of the present study was to examine whether a single dose of T-2 toxin administered at newborn age has any long-lasting effects on nervous system functions. Rat pups were treated on the first postnatal day with a single intraperitoneal dose of T-2 toxin (0.2 mg/bwkg). Body weight of treated pups was lower during the second and third week of life, compared to littermates; later, weight gain was recovered. At young adulthood, behavior was tested in the open field, and no difference was observed between treated and control rats. Field potential recordings from somatosensory cortex and hippocampus slices did not reveal any significant difference in neuronal network functions. In case of neocortical field EPSP, the shape was slightly different in treated pups. Long-term synaptic plasticity was also comparable in both groups. Seizure susceptibility of the slices was not different, either. In conclusion, T-2 toxin did not significantly affect basic nervous system functions at this dose.

Sleep deprivation decreases neuronal excitability and responsiveness in rats both in vivo and ex vivo.

Sleep deprivation has severe consequences for higher nervous functions. Its effects on neuronal excitability may be one of the most important factors underlying functional deterioration caused by sleep loss. In the present work, excitability changes were studied using two complementary in vivo and ex vivo models. Auditory evoked potentials were recorded from freely-moving animals in vivo. Amplitude of evoked responses showed a near-continuous decrease during deprivation. Prevention of sleep also reduced synaptic efficacy ex vivo, measured from brain slices derived from rats that underwent sleep deprivation. While seizure susceptibility was not affected significantly by sleep deprivation in these preparations, the pattern of spontaneous seizure activity was altered. If seizures developed, they lasted longer and tended to contain more spikes in slices obtained from sleep-deprived than from control rats. Current-source density analysis revealed that location and sequence of activation of local cortical networks recruited by seizures did not change by sleep deprivation. Moderate differences seen in the amplitude of individual sinks and sources might be explained by smaller net transmembrane currents as a consequence of decreased excitability. These findings contradict the widely accepted conception of synaptic homeostasis suggesting gradual increase of excitability during wakefulness. Our results also indicate that decreased neuronal excitability caused by sleep deprivation is preserved in slices prepared from rats immediately after deprivation. This observation might mean new opportunities to explore the effects of sleep deprivation in ex vivo preparations that allow a wider range of experimental manipulations and more sophisticated methods of analysis than in vivo preparations.

The insecticide esfenvalerate modulates neuronal excitability in mammalian central nervous system in vitro.

Pyrethroids are neurotoxic insecticides showing significant selective toxicity on insects over mammals, but effects on mammalian nervous system are not negligible. These substances act on the voltage-gated sodium channel, prolonging the duration of the open state. The present study focused on the effect of the pyrethroid esfenvalerate on the excitability of neuronal networks in vitro. From isolated rat brain slices, neocortical and hippocampal evoked field potentials were recorded; four concentrations (5-40µM) of esfenvalerate were tested using in vitro administration of the commercial product Sumi-Alpha 5 EC®. Basic excitability and short- and long-term synaptic plasticity were studied. Application of the lowest concentration elicited epileptiform discharges in neocortex, while the highest concentration exerted a strong inhibitory effect on the excitability of both brain areas. The amplitude of population spikes in hippocampal slices was decreased by all applied concentrations. Significant decrease in basic excitability was accompanied by increase of paired-pulse facilitation in hippocampus and decreased efficacy of the development of long-term potentiation in both regions. Pyrethroids have been scarcely studied on brain slices so far, but our results are in concordance with literary data obtained on other in vitro neuronal test systems. It has been described previously that lower concentrations of pyrethroids lead to overexcitation of neurons and repetitive firing (which is in the background of hyperexcitatory symptoms occurring in case of in vivo exposure). Higher concentrations, however, may lead to depolarization block and to inhibition of neuronal firing.

Arctigenin reduces neuronal responses in the somatosensory cortex via the inhibition of non-NMDA glutamate receptors.

Lignans are biologically active phenolic compounds related to lignin, produced in different plants. Arctigenin, a dibenzylbutyrolactone-type lignan, has been used as a neuroprotective agent for the treatment of encephalitis. Previous studies of cultured rat cerebral cortical neurones raised the possibility that arctigenin inhibits kainate-induced excitotoxicity. The aims of the present study were: 1) to analyse the effect of arctigenin on normal synaptic activity in ex vivo brain slices, 2) to determine its receptor binding properties and test the effect of arctigenin on AMPA/kainate receptor activation and 3) to establish its effects on neuronal activity in vivo. Arctigenin inhibited glutamatergic transmission and reduced the evoked field responses. The inhibitory effect of arctigenin on the evoked field responses proved to be substantially dose dependent. Our results indicate that arctigenin exerts its effects under physiological conditions and not only on hyper-excited neurons. Furthermore, arctigenin can cross the blood-brain barrier and in the brain it interacts with kainate sensitive ionotropic glutamate receptors. These results indicate that arctigenin is a potentially useful new pharmacological tool for the inhibition of glutamate-evoked responses in the central nervous system in vivo.

Repeated application of 4-aminopyridine provoke an increase in entorhinal cortex excitability and rearrange AMPA and kainate receptors.

Entorhinal cortex is a highly epilepsy-prone brain region. Effects of repetitive seizures on ionotropic glutamate receptors (iGluRs) were investigated in rat entorhinal cortex slices. Seizures were induced by daily administration of 4-aminopyridine (4-AP). Electrophysiological, pharmacological and histological investigations were carried out to determine changes in synaptic efficacy and in sensitivity of iGluRs due to recurring seizures. Repeated 4-AP-induced seizures increased the amplitude of evoked synaptic field responses in rat entorhinal cortical slices. While vulnerability to inhibition of AMPA receptors by the specific antagonist GYKI 52466 was slightly reduced, responsiveness to NMDA receptor antagonist APV remained unaffected. Testing of bivalent cation permeability of iGluRs revealed reduced Ca(2+)-influx through non-NMDA receptors. According to the semi-quantitative histoblot analysis GluA1-4, GluA1, GluA2, GluK5, GluN1 and GluN2A subunit protein expression differently altered. While there was a marked decrease in the level of GluA1-4, GluA2 and GluK5 receptor subunits, GluA1 and GluN2A protein levels moderately increased. The results indicate that brief convulsions, repeated daily for 10 days can increase overall entorhinal cortex excitability despite a reduction in AMPA/kainate receptor activity, probably through the alteration of local network susceptibility.

In vitro intrinsic optical imaging can be used for source determination in cortical slices.

In the last decades intrinsic optical imaging has become a widely used technique for monitoring activity in vivo and in vitro. It is assumed that in brain slices the source of intrinsic optical signals (IOSs) is the change in light scattering caused by cell swelling or shrinkage. The aim of the present study was to find a correlation between electrical activity and parallel optical characteristics, elicited by 4-aminopyridine-containing or Mg(2+) -free medium in rat cortical brain slices. Electrophysiological signals and reflected light alterations were recorded during spontaneous seizure activity. Current source density (CSD) analysis was performed on the electrophysiological records. Direct correlation analysis of IOS to CSD was made, and source distribution provided by IOS and CSD methods was compared by determining Matthews correlation coefficient. The gradual development of seizure-like activity elicited the reduction of light reflectance. The main findings of our experiments are that long-term epileptiform activity resulted in persistent alteration in IOSs of brain slices. The observed IOS pattern remained stable after 1 h incubation in convulsants. The pattern of IOS shows good correlation with the data obtained from the CSD analysis. Persistent IOS changes provide information about the area-specific changes of basic excitability, which can serve as a background for ictal and interictal-like epileptiform activity. We can conclude that changes in IOSs correlate well with electrophysiological recordings under different conditions. Our experiments provide evidence that underlying synchronised neuronal processes produce parallel alterations in IOSs and electrophysiological activity.

Changes in synaptic efficacy in rat brain slices following extremely low-frequency magnetic field exposure at embryonic and early postnatal age.

An earlier study demonstrated changes in synaptic efficacy and seizure susceptibility in adult rat brain slices following extremely low-frequency magnetic field (ELF-MF) exposure. The developing embryonic and early postnatal brain may be even more sensitive to MF exposure. The aim of the present study was to determine the effects of a long-term ELF-MF (0.5 and 3 mT, 50 Hz) exposure on synaptic functions in the developing brain. Rats were treated with chronic exposure to MF during two critical periods of brain development, i.e. in utero during the second gestation week or as newborns for 7 days starting 3 days after birth, respectively. Excitability and plasticity of neocortical and hippocampal areas were tested on brain slices by analyzing extracellular evoked field potentials. We demonstrated that the basic excitability of hippocampal slices (measured as amplitude of population spikes) was increased by both types of treatment (fetal 0.5 mT, newborn 3 mT). Neocortical slices seemed to be responsive mostly to the newborn treatment, the amplitude of excitatory postsynaptic potentials was increased. Fetal ELF-MF exposure significantly inhibited the paired-pulse depression (PPD) and there was a significant decrease in the efficacy of LTP (long-term potentiation induction) in neocortex, but not in hippocampus. On the other hand, neonatal treatment had no significant effect on plasticity phenomena. Results demonstrated that ELF-MF has significant effects on basic neuronal functions and synaptic plasticity in brain slice preparations originating from rats exposed either in fetal or in newborn period.

Carbon nanotubes exert basic excitatory enhancement in rat brain slices.

Carbon nanotubes are promising new tools in biomedicine but they may have yet some unknown influences on the organism. In the present study, the acute effect of solubilized, multi-walled carbon nanotubes (MWCNTs) on basic neuronal functions was examined. Rat brain slices were treated in vitro with nanotube-containing colloid solutions at concentrations of 100-800 µg/ml and evoked field potentials were recorded from the somatosensory cortex and hippocampus. Basic excitability of the treated slices was characterized by the amplitude of field excitatory postsynaptic potentials (fEPSPs) and population spikes. Experimental results indicated significantly higher excitability of treated samples than that of controls. Multiple components in evoked potentials were observed, which is in accordance with the increased excitability of investigated brain areas. Tests of short- and long-term plasticity were also performed, which revealed no difference between control and treated slices. Experimental results suggest an interaction between nanotubes and brain tissue. MWCNTs seem to act on the basic membrane potential of neurons by changing membrane properties or via a mechanism linked to voltage-gated ion channels, rather than influencing specific synaptic transmission. Further investigation is needed to clarify the nature of interactions between nanotubes and brain tissue.

Changes in synaptic efficacy and seizure susceptibility in rat brain slices following extremely low-frequency electromagnetic field exposure.

The effects of electromagnetic fields (EMFs) on living organisms are recently a focus of scientific interest, as they may influence everyday life in several ways. Although the neural effects of EMFs have been subject to a considerable number of investigations, the results are difficult to compare since dissimilar exposure protocols have been applied on different preparations or animals. In the present series of experiments, whole rats or excised rat brain slices were exposed to a reference level-intensity (250-500 microT, 50 Hz) EMF in order to examine the effects on the synaptic efficacy in the central nervous system. Electrophysiological investigation was carried out ex vivo, on neocortical and hippocampal slices; basic synaptic functions, short- and long-term plasticity and seizure susceptibility were tested. The most pronounced effect was a decrease in basic synaptic activity in slices treated directly ex vivo observed as a diminution in amplitude of evoked potentials. On the other hand, following whole-body exposure an enhanced short- and long-term synaptic facilitation in hippocampal slices and increased seizure susceptibility in neocortical slices was also observed. However, these effects seem to be transient. We can conclude that ELF-EMF exposure exerts significant effects on synaptic activity, but the overall changes may strongly depend on the synaptic structure and neuronal network of the affected region together with the specific spatial parameters and constancy of EMF.

In vitro effects of fipronil on neuronal excitability in mammalian and molluscan nervous systems.

The effect of the insecticide fipronil on non-target organisms was studied on rat brain slices and identified giant neurons of the pond snail Lymnaea stagnalis. This compound acts as an antagonist on GABA(A) receptors. Although fipronil has moderate mammalian toxicity, our experiments confirmed that it modifies neuronal excitability in the rat somatosensory cortex. The amplitudes of evoked field potentials increased significantly after 30 min fipronil treatment. Short-term plasticity was examined with paired-pulse stimulation, this phenomenon was not affected by fipronil. On the other hand, the efficacy of LTP-induction was enhanced in the treated slices. Fipronil is highly toxic to freshwater invertebrates, especially molluscs. In Lymnaea stagnalis, the firing pattern of a GABA receptor- containing neuron (RPeD1) was studied. On this neuron, GABA has an excitatory, hypopolarizing effect. Fipronil treatment decreased the action potential frequency in a concentration-dependent manner. On the membrane potential of the cell, it had a slightly hyperpolarizing effect. These experiments confirmed that fipronil toxicity is mediated by GABA receptors in the nervous system of invertebrates as well as vertebrates. These types of experiments may help in establishing tolerance levels of pesticide residues and in finding proper treatment in case of eventual poisonings.