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Objective. The blue light-activated inhibitory opsin, stGtACR2, is gaining prominence as a neuromodulatory tool due its ability to shunt-inhibit neurons and is being frequently used in in vivo experimentation. However, experiments involving stGtACR2 use longer durations of blue light pulses, which inadvertently heat up the local brain tissue and confound experimental results. Therefore, the heating effects of illumination parameters used for in vivo optogenetic inhibition must be evaluated. Approach. To assess blue light (473 nm)-induced heating of the brain, we used a computational model as well as direct temperature measurements using a fiber Bragg grating (FBG). The effects of different light power densities (LPDs) and pulse durations on evoked potentials (EP) recorded from dentate gyrus were assessed. For opsin-negative rats, LPDs between 127 and 636 mW mm -2 and pulse durations between 20 and 5120 ms were tested while for stGtACR2 expressing rats, LPD of 127 mW mm -2 and pulse durations between 20 and 640 ms were tested. Main results. Increasing LPDs and pulse durations logarithmically increased the peak temperature and significantly decreased the population spike (PS) amplitude and latencies of EPs. For a pulse duration of 5120 ms, the tissue temperature increased by 0.6 °C-3.4 °C. All tested LPDs decreased the PS amplitude in opsin-negative rats, but 127 mW mm -2 had comparatively minimal effects and a significant effect of increasing light pulse duration was seen from 320 ms and beyond. This corresponded with an average temperature increase of 0.2 °C-1.1 °C at the recorded site. Compared to opsin-negative rats, illumination in stGtACR2-expressing rats resulted in much greater inhibition of EPs. Significance. Our study demonstrates that light-induced heating of the brain can be accurately measured in vivo using FBG sensors. Such light-induced heating alone can affect neuronal excitability. Useful neuromodulation by the activation of stGtACR2 is still possible while minimizing thermal effects., (© 2021 IOP Publishing Ltd.)

Neuropeptide Y's (NPY) anticonvulsant effect is generally attributed to its inhibitory effect on glutamate release from presynaptic nerve terminals, which is nicely demonstrated in in vitro settings. To date no study has attempted to investigate the effect of NPY in vivo on extracellular (EC) glutamate levels thus, via intracerebral microdialysis, we determined NPY's effect on hippocampal glutamate concentrations in vivo, and consequently the involvement of Y(1) receptors to this effect. NPY or the Y(1) agonist D-His26-NPY was intrahippocampally administered in rats for 2h, during which the hippocampal glutamate dialysate levels were monitored. Pilocarpine was subsequently co-administered with NPY or D-His26-NPY to determine their effect on pilocarpine-induced limbic seizures. Unexpectedly we noted that intrahippocampal administration of NPY or D-His26-NPY increased glutamate dialysate levels in a reproducible manner. NPY attenuated pilocarpine induced seizures, whereas D-His26-NPY did not. To clarify the role of Y(1) receptors in NPY's glutamatergic effect, NPY was co-administered with the selective Y(1) antagonist BVD10. Hippocampal Y(1) receptor blockade prevented the NPY-induced increase in hippocampal glutamate, proving that this induced glutamate increase is clearly Y(1) receptor mediated. This is the first evidence that NPY enhances hippocampal EC glutamate overflow in vivo via hippocampal Y(1) receptors without interfering with or contributing to NPY's anticonvulsant effect. Whilst this finding contrasts with the supposed glutamatergic hypothesis for NPY in the hippocampus, it is of significance to further assist in deciphering NPY's mechanisms of action in in vivo settings., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

The aim of this study was to examine the effects of amygdalohippocampal deep brain stimulation (AH-DBS) on cognitive functioning in patients with refractory temporal lobe epilepsy. The population consisted of 10 patients (7 men) who underwent ipsilateral (n=8) or bilateral (n=2) AH-DBS. Intellectual and neuropsychological evaluation was performed before and 6 months after initiation of AH-DBS. Group analyses revealed no overall pattern of change in cognitive measures, but improvement was seen in emotional well-being. Individual results varied over a broad spectrum ranging from no cognitive effects to negative effects on intelligence capacities, divided attention, and concept formation, to positive effects on speed of information processing and speed of finger movements. AH-DBS is a valuable treatment alternative for patients with refractory epilepsy that appears to have no major adverse neuropsychological consequences and enhances emotional well-being on the group level. Individual results are too diverse at this moment to allow viable interpretation. Additional studies are needed to confirm these preliminary results., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Vagus nerve stimulation (VNS) is an effective adjunctive treatment for medically refractory epilepsy. In this study, we measured VNS-induced changes in hippocampal neurotransmitter levels and determined their potential involvement in the anticonvulsive action of VNS, to elucidate the mechanism of action responsible for the seizure suppressing effect of VNS in an animal model for limbic seizures. We used in vivo intracerebral microdialysis to measure VNS-induced changes in hippocampal extracellular concentrations of noradrenaline, dopamine, serotonin and GABA in freely moving, male Wistar rats. During the same experiment, the effect of VNS on pilocarpine-induced limbic seizures was assessed using video-EEG monitoring. The involvement of VNS-induced increases in hippocampal noradrenaline in the mechanims of action of VNS was evaluated by blocking hippocampal α(2)-receptors. VNS produced a significant increase in hippocampal noradrenaline concentration (69 ± 16% above baseline levels). VNS also increased the latency between pilocarpine infusion and the onset of epileptiform discharges, and reduced the duration and severity of pilocarpine-induced limbic seizures. A strong positive correlation was found between the noradrenergic and anticonvulsive effects of VNS. Blockade of hippocampal α(2 -receptors reversed the seizure-suppressing effect of VNS. VNS induces increases in extracellular hippocampal noradrenaline, which are at least partly responsible for its seizure-suppressing effect in a model for limbic seizures, and constitute a potential biomarker for the efficacy of VNS in temporal lobe epilepsy., (© 2011 The Authors. Journal of Neurochemistry © 2011 International Society for Neurochemistry.)

Noradrenaline exerts inhibitory effects on seizure susceptibility. Subtype selective agonists and antagonists were used to identify the anticonvulsant hippocampal adrenoreceptors. Intrahippocampal dialysis was used for administration of all compounds, including pilocarpine for limbic seizure induction, and as the neurotransmitter sampling tool. The noradrenaline reuptake inhibitor maprotiline mediated anticonvulsant effects, associated with dose-dependent increases in extracellular hippocampal noradrenaline, dopamine and GABA levels. At high concentrations, maprotiline produced proconvulsant effects associated with high levels of noradrenaline, dopamine and glutamate. Maprotiline's anticonvulsant effect was blocked by administration of either a selective α(2) - and β(2) -antagonist. α(2) -Antagonist administration with maprotiline was associated with a further increase in noradrenaline and dopamine from maprotiline alone; whereas β(2) -antagonist administered with maprotiline inhibited the dopamine increases produced by maprotiline. α(1A) -Antagonism blocked the GABA-ergic but not the anticonvulsive effect of maprotiline. These results were confirmed as combined but not separate α(2) - and β(2) -adrenoreceptor stimulation, using selective agonists, inhibited limbic seizures. Interestingly, α(1A) -receptor stimulation and α(1D) -antagonism alone also inhibited seizures associated with respectively significant hippocampal GABA increases and glutamate decreases. The main findings of this study are that (i) increased hippocampal noradrenergic neurotransmission inhibits limbic seizures via combined α(2) - and β(2) -receptor activation and (ii) α(1A) - and α(1D) -adrenoreceptors mediate opposite effects on hippocampal excitability., (© 2010 The Authors. Journal of Neurochemistry © 2010 International Society for Neurochemistry.)

Purpose: Despite different treatment options for patients with refractory epilepsy such as epilepsy surgery and neurostimulation, many patients still have seizures and/or drug-related cerebral and systemic side effects. Local intracerebral delivery of antiepileptic compounds may represent a novel strategy with specific advantages such as the option of higher local doses and reduced side effects. In this study we evaluate the antiepileptic effect of local delivery of adenosine in the kainic acid rat model, a validated model for temporal lobe epilepsy., Methods: Fifteen rats, in which intraperitoneal kainic acid injection had induced spontaneous seizures, were implanted with a combination of depth electrodes and a cannula in both hippocampi. Cannulas were connected to osmotic minipumps to allow continuous hippocampal delivery. Rats were freely moving and permanently monitored by video-EEG (electroencephalography). Seizures were scored during 2 weeks of local hippocampal delivery of saline (baseline), followed by 2 weeks of local adenosine (6 mg/ml) (n = 10) or saline (n = 5) delivery (0.23 μl/h) (treatment). In 7 of 10 adenosine-treated rats, saline was also delivered during a washout period., Results: During the treatment period a mean daily seizure frequency reduction of 33% compared to the baseline rate was found in adenosine-treated rats (p < 0.01). Four rats had a seizure frequency reduction of at least 50%. Both nonconvulsive and convulsive seizures significantly decreased during the treatment period. In the saline-control group, mean daily seizure frequency increased with 35% during the treatment period., Conclusions: This study demonstrates the antiseizure effect of continuous adenosine delivery in the hippocampi in rats with spontaneous seizures.

The neurobiological relationships between epilepsy and depression are receiving increased experimental attention. A key role for limbic monoamines in depression has been established and we recently showed the importance of hippocampal monoamines in limbic seizure control. We here studied whether anticonvulsant compounds are antidepressant and can elevate hippocampal dopamine (DA) or serotonin (5-HT) levels determined by in vivo microdialysis in rats. We used assessment of seizure severity in the focal pilocarpine model, antidepressant-like activity within the rat forced swim and the mouse tail suspension tests, and locomotor activity in an open field as behavioural tests. We studied the tricyclic antidepressant imipramine, the selective 5-HT reuptake inhibitor citalopram and the selective DA reuptake blocker GBR-12909. These compounds with combined antidepressant-anticonvulsant properties all directly enhanced extracellular hippocampal DA or 5-HT levels. Since glutamate-mediated hyperexcitability in temporal lobe regions seems to be involved in disturbed emotional behaviour, we next investigated possible antidepressant effects and hippocampal DA or 5-HT modulations exerted by selective ionotropic and metabotropic glutamate receptor ligands with anticonvulsant properties. Combined anticonvulsant-antidepressant activities of the NMDA antagonist MK-801 and the mGluR group I antagonists (AIDA, MPEP) were also associated with locally elicited increases in hippocampal DA and/or 5-HT levels. This study highlights that the hippocampus is an important site of action of combined anticonvulsant-antidepressant and monoamine enhancing effects.

Increases in hippocampal extracellular neurotransmitter levels have consistently been observed during temporal lobe seizures in humans, but animal studies on this subject have yielded conflicting results. Our aim was to better characterise the relationship between seizure activity and changes in hippocampal glutamate, GABA, dopamine and serotonin by comparing three limbic seizure models which differ only in the pharmacological mechanism used to induce seizures. Seizures were evoked in freely moving rats by intrahippocampal microperfusion, via a microdialysis probe, of the muscarinic receptor agonist pilocarpine (10mM), GABA(A) receptor antagonist picrotoxin (100microM) or group I metabotropic glutamate receptor agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG) (1mM). Seizure-related behavioural changes were scored and hippocampal extracellular glutamate, GABA, dopamine and serotonin concentrations were monitored. Seizures were of comparable severity in all groups. During seizures, hippocampal glutamate, GABA and dopamine concentrations increased in all groups. Glutamate increases were significantly higher in the picrotoxin group. Hippocampal serotonin concentration increased following pilocarpine and picrotoxin, but not DHPG. Our results suggest a direct relationship between seizure activity and increased hippocampal extracellular concentrations of glutamate, GABA and dopamine, but not serotonin. The fact that picrotoxin induces seizures by disinhibition, rather than direct excitation, may account for the larger glutamate increases in this group.

The potent anticonvulsant properties of neuropeptide Y (NPY) are generally attributed to a Y2 receptor-mediated inhibition of glutamatergic synaptic transmission. Independent studies have shown that NPY increases brain dopamine content, possibly via interaction with sigma 1 receptors. Recently, we showed that increased extracellular hippocampal dopamine attenuates pilocarpine-induced limbic seizures via activation of hippocampal D2 receptors. Our aim in this study was to elucidate the role of increased hippocampal dopamine in the mechanism of the anticonvulsant action of NPY and to investigate the involvement of Y2 and sigma 1 receptors in this process. Limbic seizures were evoked in freely moving rats by intrahippocampal administration of pilocarpine via a microdialysis probe. NPY was administered intracerebroventricularly, intrahippocampally via the microdialysis probe, or coadministered intrahippocampally with the D2 receptor antagonist remoxipride, the Y2 receptor antagonist BIIE0246 or the sigma 1 receptor antagonist BD1047. Changes in hippocampal extracellular dopamine were monitored, and behavioural changes indicative of seizure activity were scored. Intracerebroventricular (10 nmol/3 microL) and intrahippocampal (20-50 microm) NPY administration increased hippocampal dopamine and attenuated pilocarpine-induced seizures. Hippocampal D2 receptor blockade (4 microm remoxipride) reversed the anticonvulsant effect of NPY. Y2 receptor blockade (1 microm BIIE0246) reversed the anticonvulsant effect of NPY but did not prevent NPY-induced increases in hippocampal dopamine. Sigma 1 receptor blockade (10 microm BD1047) abolished NPY-induced increases in hippocampal dopamine and reversed the anticonvulsant effect of NPY. Our results indicate that NPY-induced increases in hippocampal dopamine are mediated via sigma 1 receptors and contribute to the anticonvulsant effect of NPY via increased activation of hippocampal D2 receptors. This novel mechanism of anticonvulsant action of NPY is separate from, and may be complementary to, the well established Y2 receptor-mediated inhibition of hippocampal excitability.

We recently showed that dopamine (DA) and serotonin (5-HT) exert anticonvulsant effects against limbic seizures in rats mediated by hippocampal D(2) and 5-HT(1A) receptor stimulation. For exogenously administered monoamines, anticonvulsant activity was only observed following 70--400% and 80--350% increases in baseline levels for dopamine and serotonin, respectively. The aim of the present microdialysis study was to investigate whether oxcarbazepine and its active metabolite, 10,11-dihydro-10-hydroxycarbamazepine (MHD) promote the release of hippocampal monoamines. Initially, concentration-response experiments were performed. Different concentrations of both compounds were perfused into the hippocampus via the microdialysis probe and tested for their effects on extracellular monoamine levels and anticonvulsant properties against pilocarpine-evoked seizures in rats. Anticonvulsant activity was always accompanied by significant increases in dopamine and serotonin levels. The anticonvulsant threshold concentrations for oxcarbazepine (100 microM) and 10,11-dihydro-10-hydroxycarbamazepine (250 microM) were associated with, respectively, 140 and 205% increases in hippocampal dopamine and 288 and 176% increases in serotonin concentrations. Co-perfusion of these anticonvulsant threshold concentrations for both compounds either with a selective D(2) or 5-HT(1A) antagonist abolished all anticonvulsant effects. This study shows that oxcarbazepine and 10,11-dihydro-10-hydroxycarbamazepine exert important monoamine promoting effects that, at least partly, contribute to the anticonvulsant mechanism of action of these compounds. The effects on dopamine and serotonin levels are therefore proposed as pharmacodynamic markers for the anticonvulsant activity of these compounds. These pharmacodynamic markers are here shown to be useful for the selection of anticonvulsant threshold concentrations of oxcarbazepine and 10,11-dihydro-10-hydroxycarbamazepine.

Purpose: Our recent work (Clinckers et al., J Neurochem 2004;89:834-43) demonstrated that intrahippocampal perfusion of 2 nM dopamine or serotonin via a microdialysis probe offered complete protection against focal pilocarpine-induced limbic seizures and did not influence basal extracellular hippocampal glutamate levels. Ten nanomolar dopamine or serotonin perfusion, however, worsened seizures and was accompanied by significant extracellular glutamate increases to approximately 200%. The significance of these glutamate elevations in seizure generation remains unclear. The present microdialysis study investigated the modulatory role of extracellular hippocampal glutamate levels in these monoaminergic protective and proconvulsant effects., Methods: A first group of male Wistar albino rats was perfused intrahippocampally for 240 min with 6.25 microM glutamate alone to increase extracellular levels by 200%. Other animals were perfused with anticonvulsant concentrations of monoamines throughout the experiments while receiving continuous coperfusions of 6.25 microM glutamate either before, during, and after (240 min) or only after (100 min) pilocarpine perfusion (40 min). Rats were scored for epileptic behavior, and the mean scores were compared with those of the control group. Microdialysates were analyzed for monoamine and glutamate content with microbore liquid chromatography., Results: No convulsions occurred during glutamate perfusion alone. When monoamines and glutamate were coperfused before pilocarpine administration, the anticonvulsant effect of the monoamines was lost. Glutamate addition after pilocarpine administration did not affect monoaminergic seizure protection., Conclusions: These results indicate that extracellular glutamate increases per se do not necessarily induce seizures but that they can modulate the anticonvulsant effects exerted by hippocampal monoamines.

The present microdialysis study evaluated the anticonvulsant activity of extracellular hippocampal dopamine (DA) and serotonin (5-HT) with concomitant assessment of the possible mutual interactions between these monoamines. The anticonvulsant effects of intrahippocampally applied DA and 5-HT concentrations were evaluated against pilocarpine-induced seizures in conscious rats. DA or 5-HT perfusions protected the rats from limbic seizures as long as extracellular DA or 5-HT concentrations ranged, respectively, between 70-400% and 80-350% increases compared with the baseline levels. Co-perfusion with the selective D(2) blocker remoxipride or the selective 5-HT(1A) blocker WAY-100635 clearly abolished all anticonvulsant effects. These anticonvulsant effects were mediated independently since no mutual 5-HT and DA interactions were observed as long as extracellular DA and 5-HT levels remained within these protective ranges. Simultaneous D(2) and 5-HT(1A) receptor blockade significantly aggravated pilocarpine-induced seizures. High extracellular DA (> 1000% increases) or 5-HT (> 900% increases) concentrations also worsened seizure outcome. The latter proconvulsive effects were associated with significant increases in extracellular glutamate (Glu) and mutual increases in extracellular monoamines. Our results suggest that, within a certain concentration range, DA and 5-HT contribute independently to the prevention of hippocampal epileptogenesis via, respectively, D(2) and 5-HT(1A) receptor activation.

The effects of several metabotropic receptor (mGluR) ligands on baseline hippocampal glutamate and GABA overflow in conscious rats and the modulation of limbic seizure activity by these ligands were investigated. Intrahippocampal mGluR group I agonist perfusion via a microdialysis probe [1 mm (R,S)-3,5-dihydroxyphenylglycine] induced seizures and concomitant augmentations in amino acid dialysate levels. The mGlu1a receptor antagonist LY367385 (1 mm) decreased baseline glutamate but not GABA concentrations, suggesting that mGlu1a receptors, which regulate hippocampal glutamate levels, are tonically activated by endogenous glutamate. This decrease in glutamate may contribute to the reported LY367385-mediated anticonvulsant effect. The mGlu5 receptor antagonist 2-methyl-6-(phenylethynyl)-pyridine (50 mg/kg) also clearly abolished pilocarpine-induced seizures. Agonist-mediated actions at mGlu2/3 receptors by LY379268 (100 microm, 10 mg/kg intraperitoneally) decreased basal hippocampal GABA but not glutamate levels. This may partly explain the increased excitation following systemic LY379268 administration and the lack of complete anticonvulsant protection within our epilepsy model with the mGlu2/3 receptor agonist. Group II selective mGluR receptor blockade with LY341495 (1-10 microm) did not alter the rats' behaviour or hippocampal amino acid levels. These data provide a neurochemical basis for the full anticonvulsant effects of mGlu1a and mGlu5 antagonists and the partial effects observed with mGlu2/3 agonists in vivo.

Aims: The blue light‐sensitive chloride‐conducting opsin, stGtACR2, provides potent optogenetic silencing of neurons. The present study investigated whether activation of stGtACR2 in granule cells of the dentate gyrus (DG) inhibits epileptic afterdischarges in a rat model. Methods: Rats were bilaterally injected with 0.9 μl of AAV2/7‐CaMKIIα‐stGtACR2‐fusionred in the DG. Three weeks later, afterdischarges were recorded from the DG by placing an optrode at the injection site and a stimulation electrode in the perforant path (PP). Afterdischarges were evoked every 10 min by unilateral electrical stimulation of the PP (20 Hz, 10 s). During every other afterdischarge, the DG was illuminated for 5 or 30 s, first ipsilaterally and then bilaterally to the PP stimulation. The line length metric of the afterdischarges was compared between illumination conditions. Results: Ipsilateral stGtACR2 activation during afterdischarges decreased the local field potential line length only during illumination and specifically at the illuminated site but did not reduce afterdischarge duration. Bilateral illumination did not terminate the afterdischarges. Conclusion: Optogenetic inhibition of excitatory neurons using the blue‐light sensitive chloride channel stGtACR2 reduced the amplitude of electrically induced afterdischarges in the DG at the site of illumination, but this local inhibitory effect was insufficient to reduce the duration of the afterdischarge. [ABSTRACT FROM AUTHOR]

Aim: GtACR2, a light-activated chloride channel, is an attractive tool for neural inhibition as it can shunt membrane depolarizations. In this study, we assessed the effect of activating GtACR2 on in vivo hippocampal CA1 activity evoked by Schaffer collateral (SC) stimulation. Methods: Adult male Wistar rats were unilaterally injected with 0.5 μL of adeno associated viral vector for induction of GtACR2-mCherry (n = 10, GtACR2 group) or mCherry (n = 4, Sham group) expression in CA1 pyramidal neurons of the hippocampus. Three weeks later, evoked potentials (EPs) were recorded from the CA1 subfield placing an optrode (bipolar recording electrode attached to an optic fiber) at the injection site and a stimulation electrode targeting SCs. Effects of illumination parameters required to activate GtACR2 such as light power densities (LPDs), illumination delays, and light-pulse durations were tested on CA1 EP parameters [population spike (PS) amplitude and field excitatory postsynaptic potential (fEPSP) slope]. Results: In the GtACR2 group, delivery of a 10 ms light-pulse induced a negative deflection in the local field potential which increased with increasing LPD. When combined with electrical stimulation of the SCs, light-induced activation of GtACR2 had potent inhibitory effects on CA1 EPs. An LPD of 160 mW/mm2 was sufficient to obtain maximal inhibition CA1 EPs. To quantify the duration of the inhibitory effect, a 10 ms light-pulse of 160 mW/mm2 was delivered at increasing delays before the CA1 EPs. Inhibition of EPs was found to last up to 9 ms after the cessation of the light-pulse. Increasing light-pulse durations beyond 10 ms did not result in larger inhibitory effects. Conclusion: Precisely timed activation of GtACR2 potently blocks evoked activity of CA1 neurons. The strength of inhibition depends on LPD, lasts up to 9 ms after a light-pulse of 10 ms, and is independent of the duration of the light-pulse given. [ABSTRACT FROM AUTHOR]

Objective: More than one‐third of patients with temporal lobe epilepsy (TLE) continue to have seizures despite treatment with antiepileptic drugs, and many experience severe drug‐related side effects, illustrating the need for novel therapies. Selective expression of inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) allows cell‐type‐specific reduction of neuronal excitability. In this study, we evaluated the effect of chemogenetic suppression of excitatory pyramidal and granule cell neurons of the sclerotic hippocampus in the intrahippocampal mouse model (IHKA) for temporal lobe epilepsy. Methods: Intrahippocampal IHKA mice were injected with an adeno‐associated viral vector carrying the genes for an inhibitory DREADD hM4Di in the sclerotic hippocampus or control vector. Next, animals were treated systemically with different single doses of clozapine‐N‐oxide (CNO) (1, 3, and 10 mg/kg) and clozapine (0.03 and 0.1 mg/kg) and the effect on spontaneous hippocampal seizures, hippocampal electroencephalography (EEG) power, fast ripples (FRs) and behavior in the open field test was evaluated. Finally, animals received prolonged treatment with clozapine for 3 days and the effect on seizures was monitored. Results: Treatment with both CNO and clozapine resulted in a robust suppression of hippocampal seizures for at least 15 hours only in DREADD‐expressing animals. Moreover, total EEG power and the number of FRs were significantly reduced. CNO and/or clozapine had no effects on interictal hippocampal EEG, seizures, or locomotion/anxiety in the open field test in non‐DREADD epileptic IHKA mice. Repeated clozapine treatment every 8 hours for 3 days resulted in almost complete seizure suppression in DREADD animals. Significance: This study shows the potency of chemogenetics to robustly and sustainably suppress spontaneous epileptic seizures and pave the way for an epilepsy therapy in which a systemically administered exogenous drug selectively modulates specific cell types in a seizure network, leading to a potent seizure suppression devoid of the typical drug‐related side effects. [ABSTRACT FROM AUTHOR]

Abstract: Neuropeptide Y''s (NPY) anticonvulsant effect is generally attributed to its inhibitory effect on glutamate release from presynaptic nerve terminals, which is nicely demonstrated in in vitro settings. To date no study has attempted to investigate the effect of NPY in vivo on extracellular (EC) glutamate levels thus, via intracerebral microdialysis, we determined NPY''s effect on hippocampal glutamate concentrations in vivo, and consequently the involvement of Y1 receptors to this effect. NPY or the Y1 agonist D-His26-NPY was intrahippocampally administered in rats for 2h, during which the hippocampal glutamate dialysate levels were monitored. Pilocarpine was subsequently co-administered with NPY or D-His26-NPY to determine their effect on pilocarpine-induced limbic seizures. Unexpectedly we noted that intrahippocampal administration of NPY or D-His26-NPY increased glutamate dialysate levels in a reproducible manner. NPY attenuated pilocarpine induced seizures, whereas D-His26-NPY did not. To clarify the role of Y1 receptors in NPY''s glutamatergic effect, NPY was co-administered with the selective Y1 antagonist BVD10. Hippocampal Y1 receptor blockade prevented the NPY-induced increase in hippocampal glutamate, proving that this induced glutamate increase is clearly Y1 receptor mediated. This is the first evidence that NPY enhances hippocampal EC glutamate overflow in vivo via hippocampal Y1 receptors without interfering with or contributing to NPY''s anticonvulsant effect. Whilst this finding contrasts with the supposed glutamatergic hypothesis for NPY in the hippocampus, it is of significance to further assist in deciphering NPY''s mechanisms of action in in vivo settings. [Copyright &y& Elsevier]

The anti-convulsant properties of angiotensin IV (Ang IV), an inhibitor of insulin-regulated aminopeptidase (IRAP) and somatostatin-14, a substrate of IRAP, were evaluated in the acute pilocarpine rat seizure model. Simultaneously, the neurochemical changes in the hippocampus were monitored using in vivo microdialysis. Intracerebroventricularly (i.c.v.) administered Ang IV or somatostatin-14 caused a significant increase in the hippocampal extracellular dopamine and serotonin levels and protected rats against pilocarpine-induced seizures. These effects of Ang IV were both blocked by concomitant i.c.v. administration of the somatostatin receptor-2 antagonist cyanamid 154806. These results reveal a possible role for dopamine and serotonin in the anti-convulsant effect of Ang IV and somatostatin-14. Our study suggests that the ability of Ang IV to inhibit pilocarpine-induced convulsions is dependent on somatostatin receptor-2 activation, and is possibly mediated via the inhibition of IRAP resulting in an elevated concentration of somatostatin-14 in the brain. [ABSTRACT FROM AUTHOR]

The present microdialysis study evaluated the anticonvulsant activity of extracellular hippocampal dopamine (DA) and serotonin (5-HT) with concomitant assessment of the possible mutual interactions between these monoamines. The anticonvulsant effects of intrahippocampally applied DA and 5-HT concentrations were evaluated against pilocarpine-induced seizures in conscious rats. DA or 5-HT perfusions protected the rats from limbic seizures as long as extracellular DA or 5-HT concentrations ranged, respectively, between 70-400% and 80-350% increases compared with the baseline levels. Co-perfusion with the selective D2 blocker remoxipride or the selective 5-HT1A blocker WAY-100635 clearly abolished all anticonvulsant effects. These anticonvulsant effects were mediated independently since no mutual 5-HT and DA interactions were observed as long as extracellular DA and 5-HT levels remained within these protective ranges. Simultaneous D2 and 5-HT1A receptor blockade significantly aggravated pilocarpine-induced seizures. High extracellular DA (>1000% increases) or 5-HT (>900% increases) concentrations also worsened seizure outcome. The latter pro-convulsive effects were associated with significant increases in extracellular glutamate (Glu) and mutual increases in extracellular monoamines. Our results suggest that, within a certain concentration range, DA and 5-HT contribute independently to the prevention of hippocampal epileptogenesis via, respectively, D2 and 5-HT1A receptor activation. [ABSTRACT FROM AUTHOR]

We recently showed that intrahippocampally administered dopamine and serotonin exert concentration-dependent non-protective, protective and proconvulsant effects against limbic seizures in rats. Anticonvulsant action was mediated via, respectively, hippocampal D2 and 5-HT1A receptor stimulation, while proconvulsant effects were associated with concomitant hippocampal glutamate increases. We here examined whether increases in endogenous hippocampal dopamine and serotonin exert similar actions. Initially, dose-response experiments were performed with intrahippocampal perfusions of GBR-12909 and citalopram, respectively, selective dopamine and serotonin re-uptake blockers. Based on their effects on monoaminergic release, a potential non-protective, protective and proconvulsant concentration was selected. The predicted non-protective GBR-12909 (10 μM) and citalopram (0.5 μM) concentrations failed to prevent pilocarpine-induced seizures. The predicted protective GBR-12909 (100 μM) and citalopram (1 μM) perfusions resulted in complete anticonvulsant action, again mediated by D2 and 5-HT1A receptors. Unexpectedly, at predicted proconvulsant concentrations complete anticonvulsant action was obtained and hippocampal Glu remained unaltered. This study shows that selective monoamine re-uptake blockers have important anticonvulsant properties. Based on the previously established anticonvulsant monoamine ranges, anticonvulsant threshold concentrations can be predicted for compounds with endogenous dopamine or serotonin promoting effects. Non-selective actions curtailing glutamatergic activity may further be responsible for the unexpected anticonvulsant effects at predicted proconvulsant concentrations. [Copyright &y& Elsevier]