Genetic deletion of the norepinephrine transporter decreases vulnerability to seizures

Abstract

Norepinephrine (NE) has been reported to modulate neuronal excitability and act as endogenous anticonvulsant. In the present study we used NE transporter knock-out mice (NET-KO), which are characterized by high levels of extracellular NE, to investigate the role of endogenous NE in seizure susceptibility. Seizure thresholds for cocaine (i.p.), pentylenetetrazol (i.v.) and kainic acid (i.v.) were compared in NET-KO, heterozygous (NET-HT) and wild type (NET-WT) female mice. The doseresponse curve for cocaine-induced convulsions was significantly shifted to the right in NET-KO mice, indicating higher seizure thresholds. The threshold doses of pentylenetetrazol that induced clonic and tonic seizures were also significantly higher in NET-KO when compared to NET-WT mice. Similarly, NET-KO mice displayed higher resistance to convulsions engendered by kainic acid. For all drugs tested, the response of NET-HT mice was always intermediate. These data provide further support for a role of endogenous NE in the control of seizure susceptibility. KeywordsPentylenetetrazol; Kainic acid; Cocaine; Norepinephrine transporter; Seizures; Knock-out mice Norepinephrine (NE), released from neurons in the CNS, has been implicated in the modulation of seizure susceptibility. Inhibition of NE neurotransmission was reported to exacerbate seizures [5,21], while enhancement of NE neurotransmission appears to have anticonvulsant effects [18]. More recently, studies in mice lacking NE due to the genetic deletion of the enzyme dopamine beta-hydroxylase showed an increased susceptibility to seizures in the mutants [27] further supporting the hypothesis that NE might act as an endogenous modulator of convulsive seizures (for reviews see [28,7]). However, a fundamental question remains as to whether an elevation of extracellular levels of endogenous NE has an opposite effect. The recent generation of mice lacking the NE transporter (NET-KO), offered the opportunity to explore this question since extracellular NE levels are 100% higher in these animals compared to wild-type litter mates (NET-WT) [32]. Therefore, in the present study we have compared the susceptibility of NET-KO, heterozygous (NET-HT) and NET-WT mice to seizures induced by three distinct convulsant agents, i.e. cocaine, pentylenetetrazol and kainic acid.

Loss of System xc−Does Not Induce Oxidative Stress But Decreases Extracellular Glutamate in Hippocampus and Influences Spatial Working Memory and Limbic Seizure Susceptibility

“…The threshold for different phases of pilocarpine-or kainic acidinduced seizure activity was determined by intravenous infusion of pilocarpine (24 mg/ml) or kainic acid (7.5 mg/ml) in the lateral tail vein at a constant rate of 150 l/min (Kaminski et al, 2005). Methylscopolamine (1 mg/kg, s.c.) was injected 30 min before pilocarpine infusion to prevent peripheral cholinergic symptoms.…”

Effects of disulfiram and dopamine beta-hydroxylase knockout on cocaine-induced seizures

“…Enhancement of noradrenergic transmission suppresses seizure activity (Lindvall, et al, 1988;Weinshenker et al, 2001;Kaminski et al, 2005), whereas norepinephrine depletion with 6-hydroxydopamine or disulfiram exacerbates seizures and facilitates seizure kindling (Corcoran, et al, 1974;Callaghan and Schwark, 1979;McIntyre, 1980;Abed, 1994;Amabeoku and Syce, 1997), and Dbh -/-mice have increased susceptibility to seizure induced by flurothyl, pentylenetetrazole, kainic acid, and sound (Szot et al, 1999).…”

Seizure risk in patients with attention‐deficit‐hyperactivity disorder treated with atomoxetine

“…19 In addition, the presence of increased levels of norepinephrine has been shown to increase the threshold for drug-induced seizures in mice. 20 Thus, toxicology studies do not suggest that atomoxetine would lower seizure threshold in humans. …”