Enaminones and norepinephrine employ convergent mechanisms to depress excitatory synaptic transmission in the rat nucleus accumbens in vitro

We recently reported that anticonvulsant anilino enaminones depress excitatory postsynaptic currents (EPSCs) in the nucleus accumbens (NAc) indirectly via gamma-aminobutyric acid (GABA) acting on GABA(B) receptors [S.B. Kombian et al. (2005)Br. J. Pharmacol., 145, 945-953]. Norepinephrine (NE) and dopamine (DA), both known to be involved in seizure disorders, also depress EPSCs in this nucleus. The current study explored a possible interaction between enaminones and adrenergic and/or dopaminergic mechanisms that may contribute to their synaptic depression and anticonvulsant effect. Using whole-cell recording in rat forebrain slices containing the NAc, we show that NE-induced, but not DA-induced, EPSC depression occludes E139-induced EPSC depressant effect. UK14,304, a selective alpha(2) receptor agonist, mimicked the synaptic effect of NE and also occluded E139 effects. Phentolamine, a non-selective alpha-adrenergic antagonist that blocked NE-induced EPSC depression, also blocked the E139-induced EPSC depression. Furthermore, yohimbine, an alpha(2)-adrenoceptor antagonist, also blocked the E139-induced EPSC depression, while prazosin, a selective alpha(1)-adrenergic antagonist, and propranolol, a non-selective beta-adrenoceptor antagonist, did not block the E139 effect. Similar to the E139-induced EPSC depression, the NE-induced EPSC depression was also blocked by the GABA(B) receptor antagonist, CGP55845. By contrast, however, neither SCH23390 nor sulpiride, D1-like and D2-like DA receptor antagonists, respectively, blocked the E139-induced synaptic depression. These results suggest that NE and E139, but not DA, employ a similar mechanism to depress EPSCs in the NAc, and support the hypothesis that E139, like NE, may act on alpha(2)-adrenoceptors to cause the release of GABA, which then mediates synaptic depression via GABA(B) receptors.     

Cholecystokinin inhibits evoked inhibitory postsynaptic currents in the rat nucleus accumbens indirectly through gamma-aminobutyric acid and gamma-aminobutyric acid type B receptors

We recently reported that cholecystokinin (CCK) excited nucleus accumbens (NAc) cells and depressed excitatory synaptic transmission indirectly through gamma-aminobutyric acid (GABA), acting on presynaptic GABAB receptors (Kombian et al. [2004] J. Physiol. 555:71-84). The present study tested the hypothesis that CCK modulates inhibitory synaptic transmission in the NAc. Using in vitro forebrain slices containing the NAc and whole-cell patch recording, we examined the effects of CCK on evoked inhibitory postsynaptic currents (IPSCs) recorded at a holding potential of -80 mV throughout CCK-8S caused a reversible inward current accompanied by a concentration-dependent decrease in evoked IPSC amplitude. Maximum IPSC depression was approximately 25% at 10 microM, with an estimated EC50 of 0.1 microM. At 1 microM, CCK-8S induced an inward current of 28.3 +/- 4.8 pA (n=6) accompanied by an IPSC depression of -18.8% +/- 1.6% (n=6). This CCK-induced IPSC depression was blocked by pretreatment with proglumide (100 microM; -3.7% +/- 6.9%; n=4) and by LY225910 (100 nM), a selective CCKB receptor antagonist (4.4% +/- 2.6%; n=4). It was not blocked by SCH23390 (10 microM; -23.5% +/- 1.3%; P < 0.05; n=7) or sulpiride (10 microM; -21.8% +/- 5.1%; P <0.05; n=4), dopamine receptor antagonists. By contrast, it was blocked by CGP55845 (1 microM; -0.4% +/- 3.4%; n=5) a potent GABAB receptor antagonist, and by forskolin (50 microM; 9.9% +/- 5.2%; n=4), an adenylyl cyclase activator, and H-89 (1 microM; 6.9% +/- 3.9%; n=4), a protein kinase A (PKA) inhibitor. These results indicate that CCK acts on CCKB receptors to increase extracellular levels of GABA, which then acts on GABAB receptors to decrease IPSC amplitude.     

Activation of SK channels inhibits epileptiform bursting in hippocampal CA3 neurons

The role of calcium-activated potassium channels in the regulation of neuronal hyperexcitability, as in epilepsy, is unclear. To examine this issue, we have used the acute hippocampal slice model of epileptiform activity to investigate the effects of an enhancer of SK channel activity, 1-ethyl-benzimidazolinone (EBIO). That EBIO is an SK channel modulator was confirmed by its potentiation of hSK1, hSK2, hSK3 and hIK currents (EC(50) values in the range of 130-870 microM) and its apamin (1 microM) sensitive reduction of the number of action potentials fired in CA3 pyramidal neurons in response to a depolarizing current step. In addition, while EBIO did not significantly affect electrically evoked glutamatergic synaptic transmission, it did inhibit epileptiform activity (IC(50) values in the range of 150-325 microM) induced by (1) modifying the extracellular ionic environment by removing extracellular Mg(2+) or elevating extracellular K(+) from 3.0 to 8.5 mM and (2) disinhibiting the slice using 3 mM pentylenetetrazol or combined application of 10 microM gabazine and 10 microM CGP55845. Furthermore, its inhibitory effect in the full disinhibition model of epileptiform activity (10 microM gabazine + 10 microM CGP55845) was occluded by the SK channel blocker apamin (300 nM-1 microM) which in its own right increased the duration and reduced the frequency of individual epileptiform bursts. In conclusion, compounds that enhance the activation of small conductance Ca(2+) -activated K(+) channels are effective inhibitors of epileptiform activity in vitro.     

Anticonvulsant action of GABA(B) receptor positive modulator CGP7930 in immature rats

GABA(B) receptors mediate inhibition at early stages of development but mixed anti-and proconvulsant action of their agonists affecting all receptors was found in immature rats. Positive allosteric modulators of GABA(B) receptors potentiate only already active GABA(B) receptors and therefore more specific action is expected. Possible anticonvulsant action of CGP7930 was studied in a model of pentetrazol-induced seizures previously used for studies with agonists baclofen and SKF97541. Pentetrazol (100mg/kg) was administered subcutaneously in male rats 7, 12, 18, 25 and 90 days old pretreated with CGP7930 in doses 1-40 mg/kg i.p. High doses of CGP7930 suppressed generalized tonic-clonic seizures in all five age groups. Animals 18 and less days old exhibited a specific suppression of the tonic phase after lower doses of CGP7930. Twelve-day-old rats were the most sensitive to anticonvulsant effect of CGP7930 (even the 2-mg/kg dose suppressed the tonic phase whereas 20-mg/kg dose was active in other age groups). Minimal clonic seizures (mS) were moderately potentiated by low doses of CGP7930 in 18-day-old but suppressed by the highest dose in 25-day-old rats. The 60-mg/kg dose of PTZ induced only mS in 4 out of 9 25-day-old rats; the 40-mg/kg dose of CGP7930 combined with this lower dose of PTZ resulted in the only proconvulsant effect--generalized tonic-clonic seizures appeared in two rats. Results from 12-day-old rats suggest a possibility to find an age-specific anticonvulsant among positive allosteric modulators of GABA(B) receptors.     

Inhibitory postsynaptic currents of rat substantia nigra pars reticulata neurons: role of GABA receptors and GABA uptake.

Whole-cell patch-clamp recordings were made from substantia nigra pars reticulata neurons in midbrain slices of young rats to study the characteristics of spontaneous and evoked inhibitory postsynaptic currents and factors which govern their decay kinetics. In the presence of the glutamate receptor antagonists D, L-2-amino-5-phosphonopentanoic acid (20 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (20 microM), bicuculline-sensitive spontaneous inward inhibitory postsynaptic currents were often observed using high Cl(-) electrodes. Application of the selective GABA(B) receptor antagonist CGP55845A (2 microM) did not alter the half decay time of these inhibitory postsynaptic currents, which however was prolonged by the potent GABA uptake blocker tiagabine (1 microM). In addition, the frequencies and amplitudes of the inhibitory postsynaptic currents were significantly reduced by tiagabine but these effects were prevented by CGP55845A. Inhibitory postsynaptic currents with similar sensitivity to bicuculline could also be evoked intranigrally. Similar to the spontaneous currents, the decay time of evoked inhibitory postsynaptic currents was not affected by 2 microM CGP55845A. However, in the absence of CGP55845A, tiagabine shortened the IPSC decay time but had an opposite effect if CGP55845A was present. These data suggest that the spontaneous and evoked inhibitory postsynaptic currents recorded from substantia nigra pars reticulata neurons are mediated mainly by GABA(A) receptors. Uptake of GABA helps to terminate these currents. When the uptake mechanism is blocked, accumulation of GABA would lead to activation of presynaptic GABA(B) receptors and reduction in GABA release. The role of postsynaptic GABA(B) receptors in substantia nigra pars reticulata of young rats seems to be minimal.     

High frequency deep brain stimulation in the hippocampus modifies seizure characteristics in kindled rats

PURPOSE: This experimental animal study evaluates the effect of high frequency deep brain stimulation (HFS DBS) on seizures in the Alternate Day Rapid Kindling model for temporal lobe epilepsy (TLE). The target for HFS is the hippocampus, as this structure is often presumed to be the seizure focus in human TLE. METHODS: Rats (n = 12) were fully kindled in the hippocampus according to the Alternate Day Rapid Kindling protocol. Characteristics of the evoked afterdischarges (AD) were determined in the baseline period using AD threshold, AD latency, and AD duration as parameters. Rats were divided into a treated group (n = 7) that received 130 Hz HFS for 1 week, and a control group (n = 5) that did not receive HFS. Rats were retested in the following week. After 1 additional week of rest, the HFS group was continuously stimulated again for 1 week, during which AD evoked by kindling stimuli were characterized again. RESULTS: HFS had a direct effect on evoked AD: during HFS, it increased AD threshold to 203 +/- 13% of controls (p < 0.01) and increased AD latency to 191 +/- 19% (p < 0.05). It decreased AD duration to 71 +/- 9% (p < 0.05) of controls. The effect outlasted the HFS stimulation as in the week following HFS similar differences, but smaller in size, could still be established. CONCLUSION: Continuous HFS (130 Hz) in the hippocampus of epileptic rats modulates the characteristics of evoked AD in a way that reflects a reduction in excitability of the target region.     

Calcium-dependent and ouabain-resistant oxygen consumption in the rat neurohypophysis

To analyze rapid changes in energy metabolism in the neurohypophysis, pO2 was measured in the tissue in vitro with a miniature O2 electrode (tip diameter less than 100 microns, 90% response time less than 3 s). Electrical stimulation (20 Hz, 5 s) evoked immediate pO2 decreases by 93.4 +/- 10.5 mm Hg (mean +/- S.E.M., n = 12) which lasted for about 1 min and were blocked by tetrodotoxin (1 microM) or sodium cyanide (1 mM). Replacement of Ca2+ in the perifusing medium with Mn2+ reduced the pO2 decreases to 23.1 +/- 4.9% (n = 5) of the value before the replacement. In normal medium, ouabain application (1 mM, 3 min) suppressed the electrically evoked pO2 decreases only slightly to 82.6 +/- 6.5% (n = 5). In the Mn2+ medium, the same ouabain application suppressed the pO2 changes to 28.8 +/- 1.4%. High K+ (70 mM) evoked pO2 decreases by 175.8 +/- 14.9 mm Hg (n = 5) within 1-2 min. These pO2 changes were reduced to 35.6 +/- 3.8% in an Mn2+ medium. Veratridine (100 microM) evoked pO2 decreases by 204.8 +/- 36.3 mm Hg (n = 5). During the pO2 decreases, the effects of electrical or high K+ stimulation on pO2 were blocked. These results indicate that O2 consumption was evoked by electrical stimulation, and probably that high K+ or veratridine application in the neurohypophysis is mainly dependent on extracellular calcium and resistant to ouabain. The relationship between O2 consumption and exocytotic release is discussed.     

Partial hippocampal kindling increases GABAB receptor-mediated postsynaptic currents in CA1 pyramidal cells

In previous studies, we showed that partial hippocampal kindling decreased the efficacy of the presynaptic GABAB receptors on both GABAergic and glutamatergic terminals of CA1 neurons in hippocampal slices in vitro. In this study, GABAB receptor-mediated inhibitory postsynaptic currents (GABAB-IPSCs) were assessed by whole-cell recordings in CA1 pyramidal neurons in hippocampal slices of male Long-Evans rats. The peak GABAB-IPSC evoked by a brief train of supramaximal stratum radiatum stimuli (20 pulses of 300 Hz) in the presence of picrotoxin (0.1 mM) and kynurenic acid (1 mM) was larger in neurons of kindled (65.9 +/- 5.2 pA, N=42 cells) than control (45.8 +/- 4.8 pA, N=32 cells) rats (P<0.01). Adding GABA uptake blocker nipecotic acid (1 mM) or GABAB receptor agonist baclofen (0.01 mM) in the perfusate induced outward currents that were blocked by GABAB receptor antagonist CGP 55845A (1 microM). The peak outward current induced by nipecotic acid was larger in neurons of the kindled (55.4 +/- 5.7 pA, N=30) than the control group (39.8 +/- 4.5 pA, N=28) (P<0.05). However, the magnitude of the baclofen-induced current was not different between kindled (90.8 +/- 6.9 pA, N=29) and control (87.2 +/- 5.9 pA, N=21) groups (P>0.05). We concluded that partial hippocampal kindling increased GABAB-IPSCs in hippocampal CA1 pyramidal cells via multiple presynaptic mechanisms.     

Opposite effects of alpha 1- and beta-adrenoceptor stimulation on both glutamate- and gamma-aminobutyric acid-mediated spontaneous transmission in cultured rat hippocampal neurons

The effects of adrenergic receptor stimulation on spontaneous synaptic transmission were investigated in cultured rat hippocampal neurons by recording spontaneous excitatory and inhibitory postsynaptic currents (sEPSC and sIPSC). Noradrenaline (NA) inhibited sEPSC in a concentration-dependent manner, with maximal effect at 10 microM. The alpha(1)- and alpha(2)-adrenoceptor-selective agonists cirazoline and clonidine induced an inhibition of sEPSC appearance, whereas the beta-adrenoceptor agonist isoproterenol elicited an increase. The inhibitory effect of NA was reversed by alpha(1)-adrenoceptor blockade. The participation of gamma-aminobutyric acid (GABA)(B)-receptor stimulation in the inhibitory effect of NA was further examined. GABA(B)-receptor stimulation with baclofen induced a strong inhibition of bursting activity, which was fully reversed by the GABA(B) antagonist CGP 55845. By itself, CGP 55845 exerted a stimulatory effect on sEPSC frequency. In the presence of CGP 55845, the inhibitory effects of cirazoline and clonidine were maintained. NA (1, 10, and 100 microM) and alpha-adrenoceptor agonists decreased miniature EPSC and IPSC occurrence, whereas beta-adrenergic stimulation increased it. In 50% of the cells examined, NA (1, 10 microM) had a stimulatory effect on sIPSC, whereas, in the remaining 50% of cells, NA (1, 10 microM) had an inhibitory effect. In all the cells, 100 microM NA induced an inhibition of sIPSC. The inhibitory effect of NA was due to alpha(1)-receptor stimulation, whereas the excitatory effect was due to beta-receptor stimulation. In cultured hippocampal neurons, spontaneous excitatory and inhibitory synaptic transmissions are both similarly altered by adrenoceptor stimulation. However, in a subset of cells, low concentrations of NA mediate an increase of sIPSC via beta-adrenoceptor activation.     

Gamma-vinyl GABA reduces paired pulse inhibition in the rat dentate gyrus in vivo and in vitro

Gamma vinyl GABA (GVG), an irreversible GABA transaminase inhibitor, has anticonvulsant effects. GVG increases GABA levels in the brain by blocking its degradation, and is presumed to enhance GABAergic inhibition, however, in some cases it exacerbates seizures. We investigated the effects of GVG in vivo and in vitro on paired pulse inhibition (PPI) recorded in the rat dentate gyrus (DG) evoked by perforant path stimulation. At 2.5 h and 24 h after administration of GVG (1 g/kg, i.p.), there was a loss of PPI at both 15- and 25-ms interpulse intervals (IPI). Activation of presynaptic GABA(B) autoreceptors could explain this in vivo effect. We therefore further investigated the effects of co-application of GVG with the GABA(B) antagonists 2-OH saclofen (saclofen) or CGP 35348 (CGP) on PPI in hippocampal slices by in vitro study. Bath application of GVG (400 and 500 microM) not only resulted in a loss of perforant path evoked PPI at a 15-ms IPI, but produced facilitation of the second population spike relative to the first. Co-application of saclofen (250 microM) with GVG (500 microM) prevented facilitation of the second response of a paired-pulse. The facilitation of the second stimulation response produced by GVG (400 microM) was converted to inhibition by bath application of CGP 35348 (400 microM). These results suggest that activation of presynaptic GABA(B) receptors by increased extracellular GABA may be one of the contributing factors to the apparent paradoxical effect of GVG on PPI in the DG.     

Role of GABAB receptors in GABA and baclofen-induced inhibition of adult rat cerebellar interpositus nucleus neurons in vitro

Previous studies suggested that the postsynaptic GABA(B) receptors of deep cerebellar nuclear neurons of adult rats were not activated by selective GABA(B) receptor agonist baclofen or endogenous GABA released by cerebellar cortical Purkinje cells, although the receptors have been demonstrated to exist in the deep cerebellar nuclei. In this study, cerebellar slices of adult rats were prepared for testing effects of GABA, baclofen and muscimol (selective GABA(A) receptor agonist) on cerebellar interpositus nucleus (IN) neurons. Perfusing slices with GABA (10-1000 microM), baclofen (1-30 microM) and muscimol (1-100 microM) respectively produced a dose-dependent inhibitory response on the IN neurons (n = 39, 62 and 50), which was not blocked by low-Ca(2+)/high-Mg(2+) medium (n = 5, 6 and 6), supporting a direct postsynaptic action of these GABAergic agonists. Moreover, both selective GABA(B) receptor antagonist CGP35348 and selective GABA(A) receptor antagonist bicuculline were capable of partially blocking the inhibitory response of IN neurons to GABA (n = 14 and 11), suggesting that the GABA-induced inhibition may contain two components, a GABA(B) receptors-mediated component and a GABA(A) receptors-mediated one. Further experiments revealed that not only muscimol (n = 50) but also baclofen (n = 62) suppressed IN cells' activity. The baclofen-induced inhibition was selectively blocked by CGP35348 (n = 12) but not by bicuculline (n = 8), whereas the muscimol-induced inhibition was selectively antagonized by bicuculline (n = 8) instead of CGP35348 (n = 9). These results indicate that GABA(B) receptors in the IN neurons can be activated not only by GABA but also by baclofen, suggesting that besides GABA(A) receptors, GABA(B) receptors may also be involved in mediating the inhibitory effect of GABA on cerebellar IN neurons of adult rats.     

Zinc,magnesium and copper profiles in three experimental models of epilepsy

Trace metals are involved in the mechanisms of CNS excitability, including epilepsy. In this study, atomic absorption spectrophotometry was used to determine concentrations of Mg(2+), Cu(2+) and Zn(2+) in plasma (microg/ml) and hair (microg/g) samples. Differential profiles of trace metals were detected in rats displaying three different kinds of seizures, i.e. acute audiogenic seizures (generalized tonic-clonic type GTC) and audiogenic kindling (limbic type; LS) in Wistar Audiogenic Rats (WARs) and electroshock-induced seizures (ES) in Wistar non-epileptic rats (resistant). Significantly lower Zn(2+) concentrations were observed in the plasma of WARs (0.80+/-0.02) compared with resistants (0.89+/-0.03) in the basal (non-seizing) condition. After GTC, WARs showed lower Zn(2+) levels (0.64+/-0.12) while both Mg(2+) (12.56+/-1.51) and Cu(2+) (0.81+/-0.14) were higher than in non-seizing WARs. After ES-induced seizures only Mg(2+) changed, being higher than in the basal condition (11.78+/-2.25 and 8.90+/-0.95). In hair, basal levels of Mg(2+) and Cu(2+) (192.49+/-36.73 and 13.33+/-1.76) were higher whereas Zn(2+) (136.53+/-15.67) was lower in WARs than in resistants. WARs submitted to 0, 3 and 25 stimuli presented higher Mg(2+) concentrations as the number of stimuli increased. In animals receiving the same number of stimuli, Zn(2+) levels were higher for animals displaying GTC (151.09+/-5.53) than those displaying LS (128.07+/-8.51). In conclusion, seizure type (limbic or generalized tonic-clonic) and number of stimuli seem to be the determinant factors for changes in Zn(2+) and Mg(2+) levels, respectively.     

Evidence for the presence of N-methyl-D-aspartate receptors in the ventral tegmental area of the rat: an electrophysiological in vitro study

Extracellular recordings were obtained from spontaneously active, presumed dopaminergic neurons of the ventral tegmental area (VTA) of the rat in a slice preparation. Bath-applied N-methyl-D-aspartate (NMDA) (1-20 microM) activated all neurons tested (n = 36). This effect was clearly concentration-dependent (n = 14), quickly reversible and reproducible. No bursting type of discharge was observed during NMDA infusion. The NMDA receptor blocker DL-2-amino-5-phosphonovaleric acid (50 microM) reversibly antagonized the increase in cell firing produced with 10 microM NMDA by 83.5 +/- 3% (mean +/- S.E.M.) (n = 8, P less than 0.05). Lowering the Mg2+ concentration of the perfusion fluid to one-third of its normal value significantly enhanced the excitatory effect of 5 microM NMDA (n = 7, P less than 0.05), but not of 500 nM carbachol (n = 6). Finally, NMDA did not modify the sensitivity of dopaminergic autoreceptors of VTA neurons (n = 8), when compared to controls (n = 10). These observations strongly support the presence of specific NMDA receptors in the VTA.     

Chlormethiazole inhibits epileptiform activity by potentiating GABA(A) receptor function

Chlormethiazole has sedative, hypnotic, anticonvulsant and neuroprotective properties. Using in vitro grease-gap recordings, we show that it inhibits epileptiform activity in neocortical slices superfused with Mg(2+)-free medium (IC(50) approximately 200 microM). At an antiepileptic concentration (300 microM), chlormethiazole potentiated the action of exogenously applied GABA (1 mM) but did not affect responses to the glutamate receptor agonists N-methyl-D-aspartate (10 microM) or L-quisqualic acid (3 microM). The GABA(A) receptor antagonist N-methyl-bicuculline (50 microM) reduced chlormethiazole's potency to inhibit the epileptiform activity. These results indicate that chlormethiazole's anticonvulsant action is likely mediated by potentiating GABA(A)ergic inhibition rather than by antagonising glutamatergic excitation.     

Anticonvulsant activity of two orally active competitive N-methyl-D-aspartate antagonists, CGP 37849 and CGP 39551, against sound-induced seizures in DBA/2 mice and photically induced myoclonus in Papio papio.

Two novel N-methyl-D-aspartate (NMDA) antagonists, DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid CPG 37849 and the corresponding 1-ethyl ester CGP 39551, were tested as anticonvulsants in DBA/2 mice and photosensitive Senegalese baboons, Papio papio. In DBA/2 mice, CGP 37849 is more potent than CGP 39551 when administered intracerebroventricularly (i.c.v.) or intraperitoneally (i.p.) (ED50 for suppression of clonic seizures at 60 min: i.c.v. 0.038 and 0.21 nmol; i.p. 3.40 and 19.1 mumol/kg, respectively). When administered orally in mice, the two compounds are approximately equipotent (ED50 CGP 37849, 35.2 mumol/kg; ED50 CGP 39551, 28.1 mumol/kg). The time course of action of CGP 39551 is exceptionally prolonged: 42 mumol/kg i.p. protects against clonic seizures for 48 h. Protection provided by other NMDA antagonists in mice is of much shorter duration: 2-amino-5-phosphono-pentanoic acid (AP5) 1 h, 2-amino-7-phosphono-heptanoic acid (AP7) 4 h, 2-amino-7-phosphono-heptanoic acid 1-ethyl ester 3 h, 4-(3-phosphonopropyl)-2-piperazine carboxylic acid (CPP) 2 h, cis-4-(phosphonomethyl)-2-piperidine-carboxylic acid (CGS 19755) 4 h, and CGP 37849 4 h. After oral administration of the drugs, the therapeutic index (TI = ratio of the ED50 values for rotorod performance and anticonvulsant protection) remains relatively constant at 5.9-7.2 for 3 h (CGP 37849) and 4.0-6.1 for 24 h (CGP 39551). After i.p. administration, the TI values are CGP 37849 at 1 h 2.4, and at 3 h 20.0, CGP 39551 at 1 h 2.3, at 3 h 7.1, and at 24 h 3.6. In baboons, acute administration of CGP 37849 at doses of 48-191 mumol/kg intravenously (i.v.) suppresses photically induced myoclonus for at least 285 min, with severe side effects at the highest dose tested. CGP 39551 at doses of 169-675 mumol/kg i.v. shows weak anticonvulsant activity only at the highest dose tested (accompanied by severe side effects). CGP 37849 at 48-96 mumol/kg orally (p.o.) fails to protect against photically induced myoclonus up to 4 h after administration, but 191 mumol/kg (40 mg/kg) p.o. produces complete suppression of seizures after 24 h. On the other hand, CGP 39551 at 169 mumol/kg (40 mg/kg) p.o. produces total suppression of seizure activity at 4 h with a longer duration of anticonvulsant action (2-3 days).(ABSTRACT TRUNCATED AT 400 WORDS)     

Efficacy of lamotrigine in institutionalized, developmentally disabled patients with epilepsy: a retrospective evaluation.

The paper evaluates the efficacy of the newer anticonvulsant lamotrigine in a developmentally disabled patient population. A retrospective evaluation was done at two institutional centres to assess adjunctive lamotrigine (Lamictal) efficacy in a developmentally disabled population. Mean seizure frequency was compared between a 2-month pre-lamotrigine baseline period and a 2-month treatment period. A 3-month lamotrigine titration phase occurred between baseline and treatment periods. Seizure frequency data was obtained from standardized, daily seizure records. Adverse effect data was obtained from medical and nursing notes. An intent to treat analysis was performed. Data were analysed using Student's t-test for paired data. We evaluated 44 centre residents (25 male, 19 female, average age 33 +/- 11 years). Mean lamotrigine dose was 272 +/- 133 mg per day. A significant reduction in seizure frequency was noted. Seizure frequency (all seizures) was 10.1 +/- 11.2 during the baseline period vs. 5.8 +/- 7.9 seizures per month during the treatment period (P = 0.002). Thirty-two percent of patients (n = 14) had greater than a 75% reduction in seizure frequency. Twenty-three percent of patients (n = 10) had a 50-74% seizure reduction. Twenty-five percent of patients (n = 11) had less than a 50% reduction in seizures, while 20% (n = 9) had an increase in seizures. A significant reduction of 48% in generalized seizures (9.5 +/- 11.6 vs. 4.9 +/- 6.5 seizures per month, P = 0.013) was noted. Reductions in partial seizure frequency of 48% (7.9 +/- 10 vs. 4 +/- 6.6 seizures per month, P = 0.16) as well as in mixed-type seizures (19.9 +/- 9.3 was vs. 15 +/- 12.1 seizures per month, P = 0.11) were also seen; however, these changes did not reach significance. Overall, lamotrigine was well tolerated by the subject population. Adjunctive treatment with lamotrigine appears to be an efficacious and well-tolerated treatment for seizures in a significant percentage of developmentally disabled patients with epilepsy.     

Substance P inhibits potassium and calcium currents in inner ear spiral ganglion neurons

Substance P (SP), a member of the tachykinin family of neurotransmitters and neuromodulators, has been identified on spiral ganglion neurons (SGNs) in the inner ear; however, its high affinity receptor, neurokinin-1 (NK1), has not been identified and the physiological effects of SP on SGNs are not well understood. To address these issues, immunolabeling, RT-PCR, Western blots and whole-cell patch-clamp recordings were made from SGNs in P0-P5 mouse cochlear organotypic cultures. The NK1 receptor was detected on SGNs by immunocytochemistry, the protein was detected in cochlear tissues by Western blots, and the mRNA for the NK1 receptor was also found in cochlear tissues of postnatal mice (P2) by RT-PCR. Application of SP (1 to 25 microM) significantly increased the latency of SGN action potentials (APs) (mean increase 7.8 +/- 4 ms; 25 microM of SP), prolonged the duration of the action potential and made the resting potential (RP) more positive (mean 9.0 +/- 7 mV) relative to normal values (-54 +/- 6 mV). SP (1 to 25 microM) also suppressed voltage-activated potassium currents (IK+) and calcium currents (ICa2+). Puffing 25 microM of SP onto SGNs suppressed IK+ by 43 +/- 9% (n = 7) and ICa2+ by 40.6 +/- 5.6% (n = 7); both currents recovered when SP was washed out. A SP antagonist blocked the SP-induced suppression of IK+ and ICa2+. These results indicate that SP acting through NK1 receptors can have direct neuromodulatory effects on SGNs.     

Vasopressin reverses aluminum-induced impairment of synaptic plasticity in the rat dentate gyrus in vivo

Aluminum (Al), an important neurotoxin, contributes to a variety of cognitive dysfunction and mental diseases. Previous studies have demonstrated that Al impairs hippocampal long-term potentiation (LTP) in vitro and in vivo. In the present study, both LTP and LTD (long-term depression) were recorded in the same animal to investigate the Al-induced impairment of synaptic plasticity. Another aim of the present research was to verify whether the impairment of synaptic plasticity induced by Al could be reversed by vasopressin (VP) treatment. Neonatal Wistar rats were exposed to Al from parturition through adulthood (pre- and post-weaning) by the drinking of 0.3% aluminum chloride (AlCl(3)) solution. The input-output (I/O) function, paired-pulse reaction (PPR), excitatory postsynaptic potential (EPSP) and population spike (PS) amplitude were measured in the dentate gyrus (DG) of adult rats (60-90 days) in response to stimulation applied to the lateral perforant path. The results showed: (1) Al reduced the amplitudes of both EPSP LTP (control: 132+/-7%, n=7; Al-exposed: 115+/-10%, n=8, P<0.05) and PS LTP (control: 242+/-18%, n=7; Al-exposed: 136+/-7%, n=8, P<0.01) significantly. The amplitudes of EPSP LTD (control: 82+/-6%, n=7; Al-exposed: 92+/-7%, n=8, P<0.05) and PS LTD (control: 81+/-4%, n=7; Al-exposed: 98+/-5%, n=8, P<0.05) were also decreased by Al treatment. The Al-induced impairments of PS LTP and PS LTD were more serious than that of EPSP LTP and EPSP LTD. (2) In control rats, VP had an increase in the PS LTP amplitude (control: 242+/-18%, n=7; control+VP: 358+/-23%, n=6, P<0.01), while it had no significant effects on PS LTD (control: 81+/-4%, n=7; control+VP: 76+/-7%, n=6, P>0.05). (3) In Al-exposed rats, VP had a significant increase in the amplitudes of both PS LTP (Al-exposed: 136+/-7%, n=8, Al-exposed+VP: 255+/-16%, n=6, P<0.01) and PS LTD (Al-exposed: 98+/-5%, n=8; Al-exposed+VP: 81+/-6%, n=6, P<0.05). After the application of VP, the range of synaptic plasticity (PS LTP+PS LTD) in Al-exposed rats increased from 38% to 174%, which surpassed that in control rats (161%). It was suggested that VP could reverse Al-induced impairment of synaptic plasticity and might be an effective medicine to cure Al-induced neurological disorders.     

Metabolic GHB precursor succinate binds to gamma-hydroxybutyrate receptors: characterization of human basal ganglia areas nucleus accumbens and globus pallidus

Binding of the metabolic gamma-hydroxybutyrate (GHB) precursor succinate to NCS-382-sensitive [3H]GHB-labeled sites in crude synaptosomal or purified synaptic membrane fractions prepared from the human nucleus accumbens (NA), globus pallidus (GP) and rat forebrain has been shown. This site can be characterized by binding of ethyl hemisuccinate and gap-junction blockers, including carbenoxolone hemisuccinate and beta-GRA. There was no significant binding interaction between GABAB receptor ligands (CGP 55845, (R)-baclofen) and these [3H]GHB-labeled sites. GHB, NCS-382 and succinate binding profile of [3H]GHB-labeled sites in rat forebrain, human NA or GP synaptic membranes were similar. The synaptic fraction isolated from the rat forebrain was characterized by GHB binding inhibition constants: Ki,NCS-382 = 1.2 +/- 0.2 microM, Ki,GHB = 1.6 +/- 0.3 microM and Ki,SUCCINATE = 212 +/- 66 microM. In crude membranes containing mainly extrasynaptic membranes, distinct GHB and GABAB receptor sites were found in the NA. By contrast, extrasynaptic GABAB receptor sites of rat forebrain and GP were GHB- and succinate-sensitive, respectively. The heterogeneity of GABAB sites found in native membranes indicates GABAB receptor-dependent differences in GHB action. Based on these findings, we suggest that succinate (and possibly drugs available as succinate salt derivatives) can mimic some of the actions of GHB.     

Effects of retigabine on rhythmic synchronous activity of human neocortical slices

The antiepileptic effects of the novel antiepileptic drug retigabine (D-23129) [N-(2-amino-4-(4-flurobenzylamino)phenyl) carbamid acid ethyl ester] were tested in neocortical slice preparations (n=23) from 17 patients (age, 3-42 years) who underwent surgery for the treatment of intractable epilepsy. Epileptiform events consisted of spontaneously occurring rhythmic sharp waves, as well as of epileptiform field potentials (EFP) elicited by superfusion with Mg(2+)-free solution without or with addition of 10 micromol/l bicuculline. (1) Spontaneous rhythmic sharp waves (n=6), with retigabine application, the repetition rate was decreased down to 12-47% of initial value (10 micromol/l, n=3) after 180 min or suppressed completely within 12 min (50 micromol/l, n=3). (2) Low Mg(2+) EFP (n=9), with retigabine application, the repetition rate was decreased down to 50 and 65% of initial value (10 micromol/l; n=2) after 180 min or suppressed completely after 9-55 min (10, 50 and 100 micromol/l; n=2 in each case). In one slice only a transient reduction of the repetition rate was seen with 10 micromol/l retigabine. (3) Low Mg(2+) EFP with addition of bicuculline (n=8), with retigabine application, the repetition rate was decreased down to 12-55% of initial value (10 micromol/l; n=4) after 180 min or suppressed completely after 6-30 min (50 and 100 micromol/l; n=2 in each case). The depressive effect of retigabine was reversible in all but one slice. The results show a clear antiepileptic effect of retigabine in human neocortical slices on spontaneously occurring rhythmic sharp waves and different types of induced seizure activity.