Lacosamide (LCM) is a new antiepileptic drug with a previously unknown mode of action. Using electrophysiological recording techniques in a range of in vitro preparations I have determined a mechanism of action of the new drug. In a 4-aminopyridine model of tonic-clonic seizures in rat visual cortex in vitro, LCM stereoselectively reduced maximal frequency and duration of tonic activity with EC[50�s] of 71 and 41 [mu]M respectively. LCM (100 [mu]M) significantly reduced excitability in whole cell patch clamped neurons producing non-selective reduction in the incidence of excitatory/inhibitory postsynaptic currents (EPSCs; LCM: 46.1 � 15.5 %, P <0.01, n = 4, IPSCs; LCM: 24.9 � 9.6 %, P <0.01, n = 4) and block of spontaneous action potentials (EC₅₀ 61 [mu]M). The inhibitory effects of LCM did not result from changes in passive membrane properties (including resting membrane potential or input resistance) as assessed by application of voltage ramps between -70 to +20 mV. LCM did not mimic the effects of diazepam as an allosteric modulator of GABA[A] receptor currents, nor did it inhibit evoked excitatory currents mediated by AMPA or NMDA receptors. Unlike phenytoin (DPH), carbamazepine (CBZ) or lamotrigine (LTG) that blocked sustained action potential firing evoked by brief depolarising steps (750 ms) or ramps (-70 to 20 mV, 90 mV.sec⁻�), LCM could weakly reduce the frequency of action potentials evoked by brief depolarisation suggesting a potential interaction with VGSCs. In accordance with this, the effect of LCM upon neurotransmission was negated in the presence of tetrodotoxin (200 nM, TTX). The frequency of miniature EPSCs was not altered by the drug (100 [mu]M). These results discounted some crucial potential anticonvulsant targets for LCM but implied a potential interaction with electrogenic VGSCs. When SRF duration was prolonged (10 s) LCM produced significant (P <0.01, n = 4-10, EC₅₀: 48 [mu]M) inhibition, but not within the first second of the burst EC₅₀: 640 [mu]M). Evoked TTX sensitive sodium currents in N1E-115 neuroblastoma cells were significantly reduced by LCM, CBZ, LTG and DPH when V[h]: -60 mV. Hyperpolarizing pulses (500 ms) to -100 mV could reverse block by CBZ, LTG and DPH but not LCM. The V₅₀ for steady state fast inactivation was more hyperpolarized by CBZ (-79.45 � 2.64 mV, n = 5, P < 0.001), LTG (-72.30 � 1.70 mV, n = 6, P <0.05) and DPH (-77.17 � 2.32 mV, n = 6, P <0.05) but not by LCM (-65.02 � 1.75 mV, n = 6, CONTROL: -65.84 � 0.86 mV). In contrast to CBZ, LCM did not slow recovery from fast inactivation or produce frequency dependent facilitation of block of a 3 s, 10 Hz pulse train. LCM (100 [mu]M) did produce a (V₅₀: CONTROL ~64 mV, LCM -57.47 � 4.53 mV, P <0.001, n = 4-8) hyperpolarizing shift in the voltage dependence of slow sodium channel inactivation and promoted channel entry into the slow inactivated state (P <0.001, n = 6) but did not alter the rate of recovery. I therefore conclude that LCM produces inhibition of epileptiform cellular activity, at least in part, via enhancement of voltage gated sodium channel slow inactivation and represents a molecule possessing a unique anticonvulsant mechanism of action.

Carisbamate (CRS) and lamotrigine (LTG) are anticonvulsants which act mainly on neuronal voltage-gated sodium channels, that have been shown to have antidepressant-like effects in animal models of depression. In vivo electrophysiological recordings were carried out following 2 and 14 days of CRS or LTG administration. Overall firing activity in the dorsal raphe, locus coeruleus and ventral tegmental area were decreased with CRS. Similarly, a decrease in the dorsal raphe was also observed with LTG. Despite these presynaptic decreases in firing activity, both anticonvulsants exhibited significant enhancement of serotonergic transmission in the hippocampus as demonstrated by increased tonic activation of postsynaptic 5-HT1A receptors. This may be attributed to the observed desensitization of the terminal 5-HT1B autoreceptors. This study suggests that the enhanced serotonergic effect may be associated with an antiglutamatergic effect, and may contribute to the antidepressant-like effect of CRS in the forced swim test and the antidepressant properties of LTG.

Graduation date: 1993

The purpose of this study was to determine how early seizure blockade with ethosuximide (ESX) would influence ion channel expression and long-term spike-wave discharge (SWD) activity in epileptic WAG/Rij rats. The goal was to elucidate the question Do seizures beget seizures? in a genetically prone model and if so, to attempt to interrupt this cycle by early intervention. In our first experiment, we used immunocytochemistry to determine the effect of ESX on cortical expression of ion channels in treated and untreated WAG/Rij rats and age-matched Wistar controls. This experiment revealed that treatment with ESX blocked the upregulation of Nav1.1 and Nav1.6 as well as the downregulation of HCN1 that is associated with epileptic activity in rats (p < .05). In a second experiment, WAG/Rij rats were divided into 3 groups: untreated (H2O), temporary early treatment (ESX 4 month), and continuous early treatment (ESX continuous), and SWD activity was measured by electroencephalogram (EEG) at various timepoints. This second experiment revealed that animals in the ESX 4 month group spent less percent time in SWD (0.242 ± .068 SEM) than animals in the H2O group (0.769 ± .060 SEM, p < .001), although they spent slightly more percent time in SWD than animals in the ESX continuous group (0.020 ± .065 SEM, p = .003). This effect was predominantly due to seizure number, and average seizure duration did not vary among the three groups. Additionally, power spectrum analysis revealed a significant correlation when the difference between power spectra for H2O and ESX 4 month rats was compared to the power spectrum of a seizure (Pearson correlation equals 0.955, 2-tailed significance < .000000001), suggesting quantitatively that seizures were reduced by temporary early treatment. This suggests that early prevention of SWD may reduce the burden of seizures later in life, and that possibilities for prevention of genetic absence epilepsy should be further investigated.

published_or_final_version / Community Medicine / Master / Master of Public Health

Lacosamide (LCM) is a new antiepileptic drug with a previously unknown mode of action. Using electrophysiological recording techniques in a range of in vitro preparations I have determined a mechanism of action of the new drug. In a 4-aminopyridine model of tonic-clonic seizures in rat visual cortex in vitro, LCM stereoselectively reduced maximal frequency and duration of tonic activity with EC[50�s] of 71 and 41 [mu]M respectively. LCM (100 [mu]M) significantly reduced excitability in whole cell patch clamped neurons producing non-selective reduction in the incidence of excitatory/inhibitory postsynaptic currents (EPSCs; LCM: 46.1 � 15.5 %, P <0.01, n = 4, IPSCs; LCM: 24.9 � 9.6 %, P <0.01, n = 4) and block of spontaneous action potentials (EC₅₀ 61 [mu]M). The inhibitory effects of LCM did not result from changes in passive membrane properties (including resting membrane potential or input resistance) as assessed by application of voltage ramps between -70 to +20 mV. LCM did not mimic the effects of diazepam as an allosteric modulator of GABA[A] receptor currents, nor did it inhibit evoked excitatory currents mediated by AMPA or NMDA receptors. Unlike phenytoin (DPH), carbamazepine (CBZ) or lamotrigine (LTG) that blocked sustained action potential firing evoked by brief depolarising steps (750 ms) or ramps (-70 to 20 mV, 90 mV.sec⁻�), LCM could weakly reduce the frequency of action potentials evoked by brief depolarisation suggesting a potential interaction with VGSCs. In accordance with this, the effect of LCM upon neurotransmission was negated in the presence of tetrodotoxin (200 nM, TTX). The frequency of miniature EPSCs was not altered by the drug (100 [mu]M). These results discounted some crucial potential anticonvulsant targets for LCM but implied a potential interaction with electrogenic VGSCs. When SRF duration was prolonged (10 s) LCM produced significant (P <0.01, n = 4-10, EC₅₀: 48 [mu]M) inhibition, but not within the first second of the burst EC₅₀: 640 [mu]M). Evoked TTX sensitive sodium currents in N1E-115 neuroblastoma cells were significantly reduced by LCM, CBZ, LTG and DPH when V[h]: -60 mV. Hyperpolarizing pulses (500 ms) to -100 mV could reverse block by CBZ, LTG and DPH but not LCM. The V₅₀ for steady state fast inactivation was more hyperpolarized by CBZ (-79.45 � 2.64 mV, n = 5, P < 0.001), LTG (-72.30 � 1.70 mV, n = 6, P <0.05) and DPH (-77.17 � 2.32 mV, n = 6, P <0.05) but not by LCM (-65.02 � 1.75 mV, n = 6, CONTROL: -65.84 � 0.86 mV). In contrast to CBZ, LCM did not slow recovery from fast inactivation or produce frequency dependent facilitation of block of a 3 s, 10 Hz pulse train. LCM (100 [mu]M) did produce a (V₅₀: CONTROL ~64 mV, LCM -57.47 � 4.53 mV, P <0.001, n = 4-8) hyperpolarizing shift in the voltage dependence of slow sodium channel inactivation and promoted channel entry into the slow inactivated state (P <0.001, n = 6) but did not alter the rate of recovery. I therefore conclude that LCM produces inhibition of epileptiform cellular activity, at least in part, via enhancement of voltage gated sodium channel slow inactivation and represents a molecule possessing a unique anticonvulsant mechanism of action.

Thesis (MAppSc in Pharm) -- University of South Australia, 1993

Thesis (Ph. D.)--Virginia Commonwealth University, 2006. / Prepared for: Dept. of Neurology. Bibliography: leaves 180-205. Also available online.

Carisbamate (CRS) and lamotrigine (LTG) are anticonvulsants which act mainly on neuronal voltage-gated sodium channels, that have been shown to have antidepressant-like effects in animal models of depression. In vivo electrophysiological recordings were carried out following 2 and 14 days of CRS or LTG administration. Overall firing activity in the dorsal raphe, locus coeruleus and ventral tegmental area were decreased with CRS. Similarly, a decrease in the dorsal raphe was also observed with LTG. Despite these presynaptic decreases in firing activity, both anticonvulsants exhibited significant enhancement of serotonergic transmission in the hippocampus as demonstrated by increased tonic activation of postsynaptic 5-HT1A receptors. This may be attributed to the observed desensitization of the terminal 5-HT1B autoreceptors. This study suggests that the enhanced serotonergic effect may be associated with an antiglutamatergic effect, and may contribute to the antidepressant-like effect of CRS in the forced swim test and the antidepressant properties of LTG.

The study herein described represents a continuation of the work on 5-(2-thienyl)-5-substituted hydantoins which has been in progress in the laboratories of the North Texas State College for the past several years. It has for its purpose the study of the effect of lengthening the carbon chain connecting a cyclohexyl radical to 5-(2-thienyl)hydantoin in the 5- position.