Acute effect of anticonvulsants on amygdaloid kindled seizures induced with low-frequency stimulations

Melanoma with in-frame deletion of MAP2K1: a distinct molecular subtype of cutaneous melanoma mutually exclusive from BRAF, NRAS, and NF1 mutations

While the genomics of BRAF, NRAS, and other key genes influencing MAP kinase (MAPK) activity have been thoroughly characterized in melanoma, mutations in MAP2K1 (MEK1) have received significantly less attention and have consisted almost entirely of missense mutations considered secondary oncogenic drivers of melanoma. Here, we investigated melanomas with in-frame deletions of MAP2K1, alterations characterized as MAPK-activating in recent experimental models. Our case archive of clinical melanoma samples with comprehensive genomic profiling by a hybrid capture-based DNA sequencing platform was searched for MAP2K1 genetic alterations. Clinical data, pathology reports, and histopathology were reviewed for each case. From a cohort of 7119 advanced melanomas, 37 unique cases (0.5%) featured small in-frame deletions in MAP2K1. These included E102_I103del (n = 11 cases), P105_A106del (n = 8), Q58_E62del (n = 6), I103_K104del (n = 5), I99_K104del (n = 3), L98_I103del (n = 3), and E41_F53del (n = 1). All 37 were wild type for BRAF, NRAS, and NF1 genomic alterations ("triple wild-type"), representing 2.0% of triple wild-type melanomas overall (37/1882). Median age was 66 years and 49% were male. The majority arose from primary cutaneous sites (35/37; 95%) and demonstrated a UV signature when available (21/25; 84%). Tumor mutational burden was typical for cutaneous melanoma (median = 9.6 mut/Mb, range 0-35.7), and frequently mutated genes included TERTp (63%), CDKN2A (46%), TP53 (11%), PTEN (8%), APC (8%), and CTNNB1 (5%). Histopathology revealed a spectrum of appearances typical of melanoma. For comparison, we evaluated 221 cases with pathogenic missense single nucleotide variants in MAP2K1. The vast majority of melanomas with missense SNVs in MAP2K1 showed co-mutations in BRAF (58%), NF1 (23%), or NRAS (18%). In-frame deletions in MAP2K1, previously shown in experimental models to be strongly MAPK-activating, characterized a significant subset of triple wild-type melanoma (2.0%), suggesting a primary oncogenic role for these mutations. Comprehensive genomic profiling of melanomas enables detection of this alteration, which may have implications for potential therapeutic options.

Acute effects of various GABA receptor agonists and glutamate antagonists on focal hippocampal seizures in freely moving rats elicited by low-frequency stimulation

In this study, we examined the acute anticonvulsant spectrum of (1) dizocilpine (0.03-3 mg/kg), CGS 19755 (1-10 mg/kg), and 7-chlorokynurenic acid (1-100 nmol) (NMDA receptor/ionophore complex antagonists); (2) muscimol (0.1-10 nmol; direct GABA(A) agonist); (3) YM90K (3-10 mg/kg; AMPA receptor antagonist); and (4) diazepam (2 and 5 mg/kg) and carbamazepine (5 and 20 mg/kg), two standard anticonvulsants, using the partially-kindled hippocampal model for epileptic seizures in freely moving rats. The anticonvulsant effect of these compounds were assessed by determining (1) the afterdischarge (AD), which is indicative of the severity of the seizure and related to seizure maintenance, and (2) the pulse number threshold (PNT), which is indicative of the seizure threshold or initiation. In addition, ataxia, a measure of CNS dysfunction, was assessed for each compound. Overall, our results indicated that the anticonvulsant compounds examined could be classified into three categories based on effects on the AD and PNT: (1) elevation of PNT (carbamazepine, dizocilpine, CGS 19755 and 7-chlorokynurenic acid); (2) reduction of AD (diazepam and muscimol); and (3) mixed action, i.e., increased PNT and decreased AD (YM90K). Behavioral data indicated that all compounds, except carbamazepine, produced a dose- or concentration-dependent ataxia. Overall, our results suggest that NMDA receptors play a role in seizure initiation, whereas the GABA(A) receptors appear to be involved in seizure maintenance and AMPA receptors may be involved in both phenomena.

Acute effect of c-fos antisense oligodeoxynucleotide on hippocampal partial seizures elicited by electrical stimulation in rats

We examined the effects of antisense oligodeoxynucleotides (ODNs) to c-fos mRNA on hippocampal partial seizures in rats. As control, sense and scrambled control ODNs were also tested. Each ODN (10 nmol/10 microliters) was injected into the lateral ventricles for 2 consecutive days. Fifteen hours after the last injection, electrical stimulation was delivered to assess the effects on after discharge threshold and afterdischarge duration (ADD). One hour after seizures, c-Fos and Jun-B immunocytochemistries were performed. Antisense ODNs significantly decreased ADD and control ODNs failed to change any parameters. In the antisense ODNs group, c-Fos expression occurred ipsilateral to the stimulation site in dentate granule cells, while Jun-B expression was seen bilaterally. In the majority of control ODNs animals, c-Fos and Jun-B expression in dentate granule cells occurred bilaterally. These findings suggest that the injection of antisense ODNs selectively inhibit contralateral c-Fos expression and that c-fos plays a key role in hippocampal excitability and seizure expression during hippocampal partial seizures.

Antiepileptic effects of MK-801, a noncompetitive NMDA-receptor antagonist, in the low-frequency kindling model of epilepsy

We assessed the acute effect of MK-801 (0.05-0.7 mg/kg), a noncompetitive NMDA-receptor antagonist, on hippocampus-kindled seizures induced with low-frequency (2 Hz) electrical stimulations. MK-801 dose-dependently increased the seizure threshold (PNT, the number of stimulating pulses required for the triggering of epileptic after discharge), whereas most of the previous studies which assessed the effect of MK-801 on kindled seizures could not detect the elevation of seizure threshold by MK-801. In addition MK-801 decreased the severity of induced seizures at low doses at which previous studies could not detect the antiepileptic effect of MK-801, suggesting that the low-frequency kindling technique might be a more sensitive and reliable model of epilepsy than the conventional high-frequency kindling technique.

Tolerance to the anticonvulsant effects of phenobarbital, trimethadione, and clonazepam in kindled rats: cross tolerance to carbamazepine

The kindled-convulsion model was used to assess the development of tolerance and cross tolerance to the anticonvulsant effects of antiepileptic drugs. In Experiment 1, tolerance developed to the anticonvulsant effects of bidaily (one every 48 h) IP injections of phenobarbital, trimethadione, and clonazepam on convulsions elicited 1 h after each injection in kindled rats by amygdala stimulation. In Experiment 2, kindled rats that were tolerant to the anticonvulsant effects of phenobarbital, trimethadione, or clonazepam received bidaily IP injections of carbamazepine, each followed 1 h later by a convulsive amygdala stimulation. There was a statistically significant transfer of tolerance from phenobarbital to carbamazepine, but not from either trimethadione or clonazepam to carbamazepine. Apparently, tolerance to anticonvulsant drugs is most likely to transfer between drugs that are effective against similar kinds of clinical and experimental seizures and have similar putative mechanisms of action.

Effects of anticonvulsants on hippocampus-generating seizures

Acute effects of 4 anticonvulsants on hippocampal kindled seizures induced with about 3 Hz electrical stimulations were assessed in cats. The number of stimulating pulses required for the triggering of epileptic afterdischarge (pulse-number threshold, PNT) was used as the indicator for the seizure threshold. Duration of afterdischarge (ADD), ictal and interictal behaviors and serum drug levels were also recorded. PB produced a PNT-increase more prominently than an ADD-decrease with seizure stage regression. PHT produced only a proconvulsive effect by decreasing PNT. CBZ also produced a proconvulsive effect by decreasing PNT at a low dose, and decreased PNT and ADD simultaneously at a high dose. Conversely VPA increased PNT and ADD simultaneously. These results were discussed comparing mainly with a previous study of amygdala-generating seizures.

Effects of chronic treatment of methamphetamine and imipramine on amygdaloid seizure's generation

We assessed the effects of chronic treatment of methamphetamine (1-2 mg/kg/day, i.p., 17 days) and imipramine (2-8 mg/kg/day, p.o., 17 days) on amygdala-generating seizures using the kindling method induced by low-frequency electrical stimulations. The number of stimulating pulses required for the triggering of epileptic afterdischarge (pulse-number threshold: PNT) is the indicator of seizure generating threshold. A PNT elevation followed by its reduction occurred, compared to the pretreatment level, during a 2 mg/kg/day chronic methamphetamine treatment. A reduction in the PNT and triggered afterdischarge durations occurred during a chronic imipramine treatment. These results indicate that both methamphetamine and imipramine reduced the seizure generating threshold by repeated applications. It is suggested that this finding might be related to the psychoactive potency and associated neurochemical changes which are known to be caused by these drugs.

Effects of chronic lithium treatment on limbic seizure generation in the cat

The effect of chronic lithium administration (2.2-8.7 mEq/kg/day, 17 days) to the cat on seizure initiation in the amygdala and hippocampus was assessed by the low-frequency kindling technique. Lithium 4.3 mEq/kg/day PO, producing a serum lithium level between 1.2 and 1.6 mEq/l, caused an elevation of the amygdala seizure threshold on treatment days 5-9. In contrast, the same dosage caused a transient reduction of the hippocampus seizure threshold on treatment days 13-17 and on withdrawal days 21-25. Lithium 2.2 mEq/kg/day PO caused no significant effect on the parameters of the two types of seizure. Lithium 8.7 mEq/kg/day PO caused severe behavioral changes and did not permit chronic treatment. These results indicate that the effect of chronic lithium treatment on limbic seizures is dependent on the location of epileptic focus.

Acute effect of TRH, flunarizine, lithium and zotepine on amygdaloid kindled seizures induced with low-frequency stimulation

We assessed the acute effects of various drugs on amygdaloid kindled seizures induced with low-frequency stimulations. We used the number of stimulating pulses required for the induction of epileptic afterdischarge (pulse-number threshold; PNT) as an indicator of the seizure generating threshold and the duration of induced seizures (AD duration; ADD) as an indicator of the seizures. TRH increased the PNT without affecting the ADD at a high dose (1.2 mg/kg). Flunarizine decreased the PNT and ADD simultaneously at a high dose (50 mg/kg). Lithium increased the PNT without affecting the ADD at two doses (100 mg/kg, 200 mg/kg). Zotepine decreased the PNT without affecting the ADD at two doses (8 mg/kg, 16 mg/kg). We propose that the technique of low-frequency kindling is a useful experimental model in assessing the effects of antipsychotic or antiepileptic drugs on the excitability of the limbic regions.