Modulation of synaptic plasticity by short-term aerobic exercise in adult mice.

Physiological effects of different types, of continuous and interval aerobic training, have been largely described and studied in the adult man. It was previously indicated that interval training plays an important role in maximizing both peripheral muscle and central cardiorespiratory adaptations, permitting significant functional improvement even in healthy sedentary subjects. Since the outcome of different aerobic training trials on cognitive processes had never been evaluated, we compared, on an experimental mouse model, the effects of four training exercise protocols, named respectively C100, I100, C50 and I50 depending on the volume and on the type of training proposed, continuous or interval method. Therefore, to asses quantitative and qualitative functional changes, we analyzed several physical parameters before and after 6 weeks training in all four groups with respect to the control sedentary animals and we studied synaptic plasticity, by extracellular in vitro recordings, in hippocampal mouse slices, a region involved in learning and memory processes. We found that all four protocols of exercise applied in this study exerted positive effects on both physical and training parameters inducing weight augmentation, strength endurance and aerobic endurance increase, and potentiation of motor coordination. However, the improvement observed failed to induce an enhancement in synaptic plasticity in three out of four exercise protocols and only in the slices from mice trained with the interval 50% volume exercise the long term potentiation (LTP) increased with respect to the sedentary group. These findings suggest that motor activity exerts positive effects on cognitive processes provided that certain principles are respected, such as the training load and the elements of which it is composed, in order to plan the right quantitative and qualitative parameters and the appropriate recovery periods.

Miglustat Reverts the Impairment of Synaptic Plasticity in a Mouse Model of NPC Disease.

Niemann-Pick type C disease is an autosomal recessive storage disorder, characterized by abnormal sequestration of unesterified cholesterol within the late endolysosomal compartment of cells and accumulation of gangliosides and other sphingolipids. Progressive neurological deterioration and insurgence of symptoms like ataxia, seizure, and cognitive decline until severe dementia are pathognomonic features of the disease. Here, we studied synaptic plasticity phenomena and evaluated ERKs activation in the hippocampus of BALB/c NPC1-/- mice, a well described animal model of the disease. Our results demonstrated an impairment of both induction and maintenance of long term synaptic potentiation in NPC1-/- mouse slices, associated with the lack of ERKs phosphorylation. We then investigated the effects of Miglustat, a recent approved drug for the treatment of NPCD. We found that in vivo Miglustat administration in NPC1-/- mice was able to rescue synaptic plasticity deficits, to restore ERKs activation and to counteract hyperexcitability. Overall, these data indicate that Miglustat may be effective for treating the neurological deficits associated with NPCD, such as seizures and dementia.

Water polo throwing velocity and kinematics: differences between competitive levels in male players.

AIM: In water polo, throwing is one of the most important and frequently used technical skills for the player. There is no scientific literature that provides information about differences in throwing between elite and sub-elite water polo players. The aim of our study was to study differences in throwing velocities and kinematic variables in elite and sub-elite level male water polo players. METHODS: We considered the variables under standardized conditions during a typical motion, the five-meter shot (penalty). Thirty-four athletes from the Men's First Division Water Polo Championship and forty-two players participating in the National Fourth Division League, took part in the study. Video analysis measures were taken with high-speed digital cameras and the videos were analyzed offline with Dartfish 5.0 Pro. RESULTS: No correlation was found between body mass, height and throwing velocity. Elite players had higher values ​for ball speed (22.8±2.4 m/s for elite team and 18.4±1.7 m/s for sub-elite team; P=0.002) and greater elbow angle (157.5±10.3 degree for elite team versus 146.7±8.9 degree for sub-elite team; P=0.002). In elite team the throwing time was lower (165.6±22.2 and 188.6±23.9 ms, respectively; P=0.05) and the shoulder angle was smaller (115.1±10.3 and 123.8±12.4 degree, respectively; P=0.03) than in sub-elite team. Head height was significantly greater in elite players (elite players 71.1±8.7 cm, sub-elite players 65.6±6.2 cm; P=0.03). CONCLUSION: Differences in kinematic characteristics between elite and sub-elite players were showed. Differences in elbow and shoulder action must be considered both in training and injury prevention.

Detraining in young soccer players.

BACKGROUND: Two types of detraining can be described: short-term detraining with a period of less than 4 weeks, and long-term detraining (period longer than 4 weeks). The purpose of this study is to verify the presence and eventually the magnitude of physiological cardiorespiratory changes in young team sport players after a period of long-term detraining. METHODS: Fourteen young soccer players (15 ± 1 year) were studied with two incremental tests at the end of the regular season and after a six-week total break period from training activities. Physiological variables were evaluated: heart rate (HR), oxygen uptake (VO2), volume of ventilation (VE), aerobic (VA) and anaerobic (Van) running speed at thresholds and maximum effort were recorded. RESULTS: This study shows the magnitude of the physiological changes in young players after a period of long-term detraining. The results showed significant decreases at the end of the detraining period of VO2 at VA of 22.7% (44.54 ± 4.56 vs. 34.41 ± 4.57 mL/kg/min, P<0.05), of 25.8% of VO2 at VAn (54.60 ± 5.81 vs. 40.48 ± 5.07 mL/kg/min, P<0.05) and of 21.2% in VO2 max (62.83 ± 5.77 vs. 49.46 ± 6.51 mL/kg/min, P<0.05). Speed at VA (11.5 ± 0.96 vs. 10.7 ± 0.97 km/h; P<0.05), speed at VAn (15.3 ± 1.05 vs. 14.2 ± 1.48 km/h; P<0.05), peak running speed (18.8 ± 1.20 vs. 17.2 ± 1.1 km/h; P<0.05). CONCLUSION: It is likely that alteration of metabolic parameters may significantly affect the range of physical condition and especially, aerobic-anaerobic resistance and maintenance training would be advisable in young athletes during the transition period. Given the relevance of worsening demonstrated by our data, coaches should avoid very long periods of complete rest (no more than 15 days) at the end of the season.

Physiological profile of water polo players in different competitive levels.

AIM: The purpose of this study was to determine if there are different physiological characteristics in water polo players of three different competitive levels (national team, NT, junior national team, NJ, and amateur club, AC). METHODS: To better define the training levels of water polo players competing at different levels, we administered a shuttle swim test (SST, a specific test used by Italian coaches) and a classic speed-lactate test. The shuttle swim test is based on actions at maximum intensity followed by incomplete recoveries. To compare the athletes, we used their morphological characteristics, the speed during an incremental test associated with fixed blood lactate concentrations of 2 mmol*1-1 (Aerobic Threshold, AT) and 4 mmol*1-1 (Anaerobic Threshold, AnT), and the SST data (speed, heart rate and lactate concentration). RESULTS: The heart rate at the end of the SST was 164+/-12 beats*min-1 for NT, 166+/-10 beats*min-1 for NJ (no significant difference, P>0.05) and 179+/-9 beats*min-1 for AC (significantly different from NT and NJ, P<0.05). The AT and AnT speeds were significantly higher in NT than in AC and NJ (P<0.05). No significant differences were found in AT and AnT speeds between AC and NJ (P>0.05). The mean speed during the shuttle swim test was significantly higher in NT and NJ than in AC (P<0.05). Lactate values were similar in the NT, AC and NJ groups (P>0.05). The SST mean speed was significantly correlated with the AT (P<0.01) and AnT speeds (P<0.05) in three groups . In all groups no significant correlation was found between SST blood lactate and AT or AnT speeds (P>0.05). CONCLUSION: Some differences were found among the senior and junior professional and amateur water polo players in both SST performance and Aerobic and Anaerobic Thre-shold speeds. The shuttle swim test for water polo provides conditioning coaches and sport scientists with data on the sport-specific movement speed and the competition-specific fatigue resistance in each athlete.

Cholesterol depletion inhibits synaptic transmission and synaptic plasticity in rat hippocampus.

Several neurodegenerative disorders are associated with impaired cholesterol homeostasis in the nervous system where cholesterol is known to play a role in modulating synaptic activity and stabilizing membrane microdomains. In the present report, we investigated the effects of methyl-beta-cyclodextrin-induced cholesterol depletion on synaptic transmission and on the expression of 1) paired-pulse facilitation (PPF); 2) paired-pulse inhibition (PPI) and 3) long-term potentiation (LTP) in the CA1 hippocampal region. Results demonstrated that cyclodextrin strongly reduced synaptic transmission and blocked the expression of LTP, but did not affect PPF and PPI. The role of glutamatergic and GABAergic receptors in these cholesterol depletion-mediated effects was evaluated pharmacologically. Data indicate that, in cholesterol depleted neurons, modulation of synaptic transmission and synaptic plasticity phenomena are sustained by AMPA-, kainate-and NMDA-receptors but not by GABA-receptors. The involvement of AMPA-and kainate-receptors was confirmed by fluorimetric analysis of intracellular calcium concentrations in hippocampal cell cultures. These data suggest that modulation of receptor activity by manipulation of membrane lipids is a possible therapeutic strategy in neurodegenerative disease.

Reduced GABAB receptor subunit expression and paired-pulse depression in a genetic model of absence seizures.

Neocortical networks play a major role in the genesis of generalized spike-and-wave (SW) discharges associated with absence seizures in humans and in animal models, including genetically predisposed WAG/Rij rats. Here, we tested the hypothesis that alterations in GABA(B) receptors contribute to neocortical hyperexcitability in these animals. By using Real-Time PCR we found that mRNA levels for most GABA(B(1)) subunits are diminished in epileptic WAG/Rij neocortex as compared with age-matched non-epileptic controls (NEC), whereas GABA(B(2)) mRNA is unchanged. Next, we investigated the cellular distribution of GABA(B(1)) and GABA(B(2)) subunits by confocal microscopy and discovered that GABA(B(1)) subunits fail to localize in the distal dendrites of WAG/Rij neocortical pyramidal cells. Intracellular recordings from neocortical cells in an in vitro slice preparation demonstrated reduced paired-pulse depression of pharmacologically isolated excitatory and inhibitory responses in epileptic WAG/Rij rats as compared with NECs; moreover, paired-pulse depression in NEC slices was diminished by a GABA(B) receptor antagonist to a greater extent than in WAG/Rij rats further suggesting GABA(B) receptor dysfunction. In conclusion, our data identify changes in GABA(B) receptor subunit expression and distribution along with decreased paired-pulse depression in epileptic WAG/Rij rat neocortex. We propose that these alterations may contribute to neocortical hyperexcitability and thus to SW generation in absence epilepsy.

Synaptic hyperexcitability of deep layer neocortical cells in a genetic model of absence seizures.

We used sharp-electrode, intracellular recordings in an in vitro brain slice preparation to study the excitability of neocortical neurons located in the deep layers (>900 microm from the pia) of epileptic (180-210-days old) Wistar Albino Glaxo/Rijswijk (WAG/Rij) and age-matched, non-epileptic control (NEC) rats. Wistar Albino Glaxo/Rijswijk rats represent a genetic model of absence seizures associated with generalized spike and wave (SW) discharges in vivo. When filled with neurobiotin, these neurons had a typical pyramidal shape with extensive apical and basal dendritic trees; moreover, WAG/Rij and NEC cells had similar fundamental electrophysiological and repetitive firing properties. Sequences of excitatory postsynaptic potentials (EPSPs) and hyperpolarizing inhibitory postsynaptic potentials (IPSPs) were induced in both the strains by electrical stimuli delivered to the underlying white matter or within the neocortex; however, in 24 of 55 regularly firing WAG/Rij cells but only in 2 of 25 NEC neurons, we identified a late EPSP that (1) led to action potential discharge and (2) was abolished by the N-methyl-D-aspartate (NMDA) receptor antagonist 3,3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonate (20 microM; n = 8/8 WAG/Rij cells). Finally, we found that the fast and slow components of the stimulus-induced IPSPs recorded during the application of glutamatergic receptor antagonists had similar reversal potentials in the two strains, while the peak conductance of the fast IPSP was significantly reduced in WAG/Rij cells. These findings document an increase in synaptic excitability that is mediated by NMDA receptors, in epileptic WAG/Rij rat neurons located in neocortical deep layers. We propose that this mechanism may be instrumental for initiating and maintaining generalized SW discharges in vivo.

Repetitive low-frequency stimulation reduces epileptiform synchronization in limbic neuronal networks.

Deep-brain electrical or transcranial magnetic stimulation may represent a therapeutic tool for controlling seizures in patients presenting with epileptic disorders resistant to antiepileptic drugs. In keeping with this clinical evidence, we have reported that repetitive electrical stimuli delivered at approximately 1 Hz in mouse hippocampus-entorhinal cortex (EC) slices depress the EC ability to generate ictal activity induced by the application of 4-aminopyridine (4AP) or Mg(2+)-free medium (Barbarosie, M., Avoli, M., 1997. CA3-driven hippocampal-entorhinal loop controls rather than sustains in vitro limbic seizures. J. Neurosci. 17, 9308-9314.). Here, we confirmed a similar control mechanism in rat brain slices analyzed with field potential recordings during 4AP (50 microM) treatment. In addition, we used intrinsic optical signal (IOS) recordings to quantify the intensity and spatial characteristics of this inhibitory influence. IOSs reflect the changes in light transmittance throughout the entire extent of the slice, and are thus reliable markers of limbic network epileptiform synchronization. First, we found that in the presence of 4AP, the IOS increases, induced by a train of electrical stimuli (10 Hz for 1 s) or by recurrent, single-shock stimulation delivered at 0.05 Hz in the deep EC layers, are reduced in intensity and area size by low-frequency (1 Hz), repetitive stimulation of the subiculum; these effects were observed in all limbic areas contained in the slice. Second, by testing the effects induced by repetitive subicular stimulation at 0.2-10 Hz, we identified maximal efficacy when repetitive stimuli are delivered at 1 Hz. Finally, we discovered that similar, but slightly less pronounced, inhibitory effects occur when repetitive stimuli at 1 Hz are delivered in the EC, suggesting that the reduction of IOSs seen during repetitive stimulation is pathway dependent as well as activity dependent. Thus, the activation of limbic networks at low frequency reduces the intensity and spatial extent of the IOS changes that accompany ictal synchronization in an in vitro slice preparation. This conclusion supports the view that repetitive stimulation may represent a potential therapeutic tool for controlling seizures in patients with pharmaco-resistant epileptic disorders.

Intrinsic optical signals and electrographic seizures in the rat limbic system.

We measured the intrinsic optical signals (IOSs) generated by rat hippocampus-entorhinal cortex (EC) slices in response to single shock electrical stimuli delivered in the EC deep layers during application of the convulsant drug 4-aminopyridine (50 microM). With field potential recordings the stimulus-induced responses had duration = 35 +/- 6.3 s mean +/- SEM, n = 7 slices) and characteristics resembling electrographic seizures. IOS changes reflecting an increase in light transmittance occurred in the EC and hippocampus following similar stimuli (n = 45). IOSs increased progressively to reach peak values 20-30 s after the stimulus and returned slowly to prestimulus values within 100 s, thus outlasting the field potential discharge. IOS changes initiated in the medial EC, near to the stimulation site, and spread to the lateral EC, the dentate, and the CA3/CA1 areas. IOS spread from EC to hippocampus was not seen after perforant path cut (n = 5). Moreover, field potential and IOS responses were markedly decreased by excitatory amino acid receptor antagonists (n = 12). The antiepileptic drugs topiramate (10-100 microM, n = 16) or lamotrigine (100-400 microM, n = 12) reduced the IOS changes in the EC and their spread to distant areas. These effects were reversible and dose-dependent (IC50 = 48 microM and 210 microM for topiramate and lamotrigine, respectively). Thus, in 4AP-treated hippocampus-EC slices, IOS changes accompany and outlast the field potential epileptiform responses, depend on glutamatergic transmission and are characterized by temporal and spatial distributions consistent with propagation through established anatomical pathways. We also propose that IOSs may represent a reliable tool for screening the effects of neuroactive compounds such as antiepileptic drugs.

Electrophysiology of regular firing cells in the rat perirhinal cortex.

The electrophysiological properties of neurons in the rat perirhinal cortex were analyzed with intracellular recordings in an in vitro slice preparation. Cells included in this study (n = 59) had resting membrane potential (RMP) = -73.9 +/- 8.5 mV (mean +/- SD), action potential amplitude = 95.5 +/- 10.4 mV, input resistance = 36.1 +/- v 15.7 M omega, and time constant = 13.9 +/- 3.4 ms. When filled with neurobiotin (n = 27) they displayed a pyramidal shape with an apical dendrite and extensive basal dendritic tree. Injection of intracellular current pulses revealed: 1) a tetrodotoxin (TTX, 1 microM)-sensitive, inward rectification in the depolarizing direction (n = 6), and 2) a time- and voltage-dependent hyperpolarizing sag that was blocked by extracellular Cs+ (3 mM, n = 5) application. Prolonged (up to 3 s) depolarizing pulses made perirhinal cells discharge regular firing of fast action potentials that diminished over time in frequency and reached a steady level (i.e., adapted). Repetitive firing was followed by an afterhyperpolarization that was decreased, along with firing adaptation, by the Ca(2+)-channel blocker Co2+ (2 mM, n = 6). Action potential broadening became evident during repetitive firing. This behavior, which was more pronounced when larger pulses of depolarizing current were injected (and thus when repetitive firing attained higher rates), was markedly decreased by Co2+ application. Subthreshold membrane oscillations at 5-12 Hz became apparent when cells were depolarized by 10-20 mV from RMP, and action potential clusters appeared with further depolarization. Application of glutamatergic and GABAA receptor antagonists (n = 4), CO2+ (n = 6), or Cs+ (n = 5) did not prevent the occurrence of these oscillations that were abolished by TTX (n = 6). Our results show that pyramidal-like neurons in the perirhinal cortex are regular firing cells with electrophysiological features resembling those of other cortical pyramidal elements. The ability to generate subthreshold membrane oscillations may play a role in synaptic plasticity and thus in the mnemonic processes typical of this limbic structure.

Spindle-like thalamocortical synchronization in a rat brain slice preparation.

We obtained rat brain slices (550-650 microm) that contained part of the frontoparietal cortex along with a portion of the thalamic ventrobasal complex (VB) and of the reticular nucleus (RTN). Maintained reciprocal thalamocortical connectivity was demonstrated by VB stimulation, which elicited orthodromic and antidromic responses in the cortex, along with re-entry of thalamocortical firing originating in VB neurons excited by cortical output activity. In addition, orthodromic responses were recorded in VB and RTN following stimuli delivered in the cortex. Spontaneous and stimulus-induced coherent rhythmic oscillations (duration = 0.4-3.5 s; frequency = 9-16 Hz) occurred in cortex, VB, and RTN during application of medium containing low concentrations of the K(+) channel blocker 4-aminopyridine (0.5-1 microM). This activity, which resembled electroencephalograph (EEG) spindles recorded in vivo, disappeared in both cortex and thalamus during application of the excitatory amino acid receptor antagonist kynurenic acid in VB (n = 6). By contrast, cortical application of kynurenic acid (n = 4) abolished spindle-like oscillations at this site, but not those recorded in VB, where their frequency was higher than under control conditions. Our findings demonstrate the preservation of reciprocally interconnected cortical and thalamic neuron networks that generate thalamocortical spindle-like oscillations in an in vitro rat brain slice. As shown in intact animals, these oscillations originate in the thalamus where they are presumably caused by interactions between RTN and VB neurons. We propose that this preparation may help to analyze thalamocortical synchronization and to understand the physiopathogenesis of absence attacks.

The inhibitory effects of interleukin-6 on synaptic plasticity in the rat hippocampus are associated with an inhibition of mitogen-activated protein kinase ERK.

Several cytokines have short-term effects on synaptic transmission and plasticity that are thought to be mediated by the activation of intracellular protein kinases. We have studied the effects of interleukin-6 (IL-6) on the expression of paired pulse facilitation (PPF), posttetanic potentiation (PTP), and long-term potentiation (LTP) in the CA1 region of the hippocampus as well as on the activation of the signal transducer and activator of transcription-3 (STAT3), the mitogen-activated protein kinase ERK (MAPK/ERK), and the stress-activated protein kinase/c-Jun NH(2)-terminal kinase (SAPK/JNK). IL-6 induced a marked and dose-dependent decrease in the expression of PTP and LTP that could be counteracted by the simultaneous treatment with the tyrosine kinase inhibitor lavendustin A (LavA) but did not significantly affect PPF. The IL-6-induced inhibition of PTP and LTP was accompanied by a simulation of STAT3 tyrosine phosphorylation and an inhibition of MAPK/ERK dual phosphorylation, in the absence of changes in the state of activation of SAPK/JNK. Both effects of IL-6 on STAT3 and MAPK/ERK activation were effectively counteracted by LavA treatment. The results indicate the tyrosine kinases and MAPK/ERK are involved in hippocampal synaptic plasticity and may represent preferential intracellular targets for the actions of IL-6 in the adult nervous system.

Interleukin-6 inhibits neurotransmitter release and the spread of excitation in the rat cerebral cortex.

Cytokines are extracellular mediators that have been reported to affect neurotransmitter release and synaptic plasticity phenomena when applied in vitro. Most of these effects occur rapidly after the application of the cytokines and are presumably mediated through the activation of protein phosphorylation processes. While many cytokines have an inflammatory action, interleukin-6 (IL-6) has been found to have a neuroprotective effect against ischaemia lesions and glutamate excitotoxicity, and to increase neuronal survival in a variety of experimental conditions. In this paper, the functional effects of IL-6 on the spread of excitation visualized by dark-field/infrared videomicroscopy in rat cortical slices and on glutamate release from cortical synaptosomes were analysed and correlated with the activation of the STAT3, mitogen-activated protein kinase ERK (MAPK/ERK) and stress-activated protein kinase/cJun NH2-terminal kinase (SAPK/JNK) pathways. We have found that IL-6 depresses the spread of excitation and evoked glutamate release in the cerebral cortex, and that these effects are accompanied by a stimulation of STAT3 tyrosine phosphorylation, an inhibition of MAPK/ERK activity, a decreased phosphorylation of the presynaptic MAPK/ERK substrate synapsin I and no detectable effects on SAPK/JNK. The effects of IL-6 were effectively counteracted by treatment of the cortical slices with the tyrosine kinase inhibitor lavendustin A. The inhibitory effects of IL-6 on glutamate release and on the spread of excitation in the rat cerebral cortex indicate that the protective effect of IL-6 on neuronal survival could be mediated by a downregulation of neuronal activity, release of excitatory neurotransmitters and MAPK/ERK activity.

GABA(B) receptor activation promotes seizure activity in the juvenile rat hippocampus.

We analyzed how the GABA(B) receptor agonist baclofen (10-50 microM) influences the activity induced by 4-aminopyridine (4-AP, 50 microM) in the CA3 area of hippocampal slices obtained from 12- to 25-day-old rats. Interictal and ictal discharges along with synchronous GABA-mediated potentials occurred spontaneously in the presence of 4-AP. Baclofen abolished interictal activity (n = 29 slices) and either disclosed (n = 21/29) or prolonged ictal discharges (n = 8/29), whereas GABA-mediated potentials occurred at a decreased rate. The N-methyl-D-aspartate (NMDA) receptor antagonist 3,3-(2-carboxypiperazine-4-yl)-propyl-1-phosphate (CPP, 10 microM, n = 8) did not modify the GABA-mediated potentials or the ictal events recorded in 4-AP + baclofen. In contrast ictal, activity, but not GABA-mediated potentials, was blocked by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM, n = 5). Most baclofen effects were reversed by the GABA(B) receptor antagonist CGP 35348 (1 mM; n = 4). Baseline and transient increases in [K(+)](o) associated with the 4-AP-induced synchronous activity were unaffected by baclofen. Baclofen hyperpolarized CA3 pyramids (n = 8) recorded with K-acetate-filled electrodes by 4.8 +/- 1.3 mV and made spontaneous, asynchronous hyperpolarizing and depolarizing potentials disappear along with interictal depolarizations. GABA-mediated synchronous long-lasting depolarizations (LLDs) and asynchronous depolarizations were also studied with KCl-filled electrodes in 4-AP + CPP + CNQX (n = 6); under these conditions baclofen did not reduce LLD amplitude but abolished the asynchronous events. Dentate hilus stimulation at 0. 2-0.8 Hz suppressed the ictal activity recorded in 4-AP + baclofen (n = 8). Our data indicate that GABA(B) receptor activation by baclofen decreases transmitter release leading to disappearance of interictal activity along with asynchronous excitatory and inhibitory potentials. By contrast, GABA-mediated LLDs and ictal events, which reflect intense action potential firing invading presynaptic inhibitory and excitatory terminals respectively, are not abolished. We propose that the proconvulsant action of baclofen results from 1) block of asynchronous GABA-mediated potentials causing disinhibition and 2) activity-dependent changes in hippocampal network excitability.

Multiple actions of the novel anticonvulsant drug topiramate in the rat subiculum in vitro.

We used an in vitro slice preparation to study whether and how the anticonvulsant drug topiramate (TPM, 50-500 microM) modulates the excitability of rat subicular neurons that generate action potential bursts mainly caused by voltage-dependent, Na+-electrogenesis. Subiculum is a gating structure for outputs originating from the hippocampus proper, and thus it may play a role in limbic seizures. In 28/45 neurons, TPM induced a steady hyperpolarization of the resting membrane potential (RMP) that ranged between -2 and -16 mV and was associated with a 24-62% decrease of the apparent membrane input resistance. TPM also depressed the ability of these cells to generate action potential bursts in response to brief (5-150 ms) depolarizing pulses; such an effect was characterized by an increase in the amount of intracellular depolarizing current required for eliciting action potential bursts, and it also occurred when the TPM-induced steady hyperpolarization was compensated by injecting steady depolarizing current. In addition TPM reduced by approx. 50% the regular action potential firing elicited by prolonged (350-1000 ms) depolarizing pulses (n=15 of 27 neurons). Recovery of the TPM-induced changes was not seen during washout for periods of 20-80 min (n=7). Both the steady hyperpolarization of the RMP and the input resistance decrease elicited by TPM were markedly reduced by the GABAA receptor antagonists bicuculline methiodide (10 microM; n=6) or picrotoxin (100 microM; n=2); such an effect was associated with a reduction, but not with blockade of the depressant action exerted by TPM on burst generation. Our findings indicate that TPM reduces subicular cell excitability, and modifies bursting ability and repetitive firing properties. These effects may be ascribed to actions on voltage-gated, Na+ electrogenesis and GABAA receptors. We propose that these changes in excitability may all contribute to the anticonvulsant action of TPM in limbic seizures that occur in temporal lobe epilepsy patients.

Modulation of epileptiform activity by adenosine A1 receptor-mediated mechanisms in the juvenile rat hippocampus.

The modulatory role played by purinergic mechanisms on the epileptiform discharges induced by 4-aminopyridine (4AP, 50 microM) in juvenile (10 to 25-day-old) rat hippocampal slices was studied with field potential recordings in the CA3 stratum radiatum. 4AP-induced activity consisted of interictal and ictal discharges along with isolated gamma-aminobutyric acid-mediated potentials. The adenosine analogues 2-Cl-adenosine (10-200 microM) and N-ethylcarboxamido-adenosine (5-10 microM), the A1 receptor agonist N6-(L2-phenylisopropyl)-adenosine (2-10 microM), and the adenosine uptake inhibitor dipyridamole (1-40 microM) reduced and eventually abolished interictal and ictal discharges with IC50 values that were larger for ictal discharges as compared to interictal activity. These purinergic agents did not modify the rate of occurrence of the gamma-aminobutyric acidmediated potentials recorded during application of excitatory amino acid receptor antagonists. The changes induced by 2-Cl-adenosine, N6-(L2-phenylisopropyl)-adenosine, or dypiridamole were reversed by caffeine (500 microM) or 8-cyclopentyl-1,3-dipropylxantine (100 microM). However, these adenosine receptor antagonists did not alter the epileptiform discharges induced by 4AP. The depressant effects induced by N6-(L2-phenylisopropyl)-adenosine on the epileptiform activity were maintained in the presence of barium (2 mM), which blocks adenosine postsynaptic actions. These results demonstrate that activation of adenosine A1 receptors in the juvenile rat hippocampus leads to an anticonvulsant action that can be ascribed to a decreased release of glutamate from CA3 pyramidal cell terminals. We also propose that during the first weeks of postnatal life endogenous adenosine does not activate A1 receptors to a degree to control the ability of hippocampal neurons to generate epileptiform activity in the 4AP model.

Contribution of GABA(A)-mediated conductances to anoxia-induced depolarization.

CA1 pyramids were studied intracellularly in rat hippocampal slices to establish the contribution of excitatory amino acid (EAA) and GABA(A) receptors to the depolarizations induced by brief (< 10 min) anoxic episodes. An increase of the amplitude of the depolarizations evoked by successive anoxic episodes occurred with KCl (n=4 cells), not with K-acetate-filled (n=3) recording electrodes. Moreover, with K-acetate-filled electrodes the anoxic depolarization amplitude was reduced, but not abolished by EAA receptor antagonists (n=14). The residual anoxic depolarizations were blocked by a GABA(A) receptor antagonist (n=5) and decreased by the carbonic anhydrase inhibitor acetazolamide (n=4). We conclude that the anoxic depolarizations generated by CA1 pyramids are caused by the activation of EAA along with GABA(A) receptors leading to an increased membrane conductance to both Cl- and HCO3-.