Increase of brain taurine contents of E1 mice by physiological stimulation

Possible anxiolytic effects of taurine in the mouse elevated plus-maze

The effects of taurine, an inhibitory amino acid, on the behavior of male mice were examined in the elevated plus-maze test of anxiety. Acute taurine treatment (60 mg/kg, PO) significantly increased the percentage of time spent in the open arms. Moreover, when taurine was administered daily for seven days and the plus-maze test was conducted 40 minutes after the last administration, a significant increase of the percentage of time in the open arms was observed even at dose of 2.5 mg/kg, however the open arm entries and the total entries were unaffected at any dose tested. In order to get a comprehensive profile of drug action, detailed behavioral analyses were further exerted. Single administration of 60 mg/kg taurine can significantly reduce the total rears. The results suggest that taurine have some anxiolytic-like properties, although its effects seem more limited and are not consistent with those presented by classic anxiolytics, such as diazepam.

New seizure frequency QTL and the complex genetics of epilepsy in EL mice

EL/Suz (EL) mice experience recurrent seizures that are similar to common partial complex epilepsy in humans. In the mice, seizures occur naturally at 90-100 days of age, but can be induced in younger mice and analyzed as a semi-quantitative trait after gentle rhythmic stimulation. A previous genetic mapping study of EL backcrosses to the strains ABP/LeJ or DBA/2J showed two quantitative trait loci (QTL) with large effects on seizure frequency (El1, Chr 9; El2, Chr 2) and implied the existence of other QTL with lesser effects. To further the understanding of EL-derived seizure alleles, we examined intercross progeny of EL and the strains ABP/LeJ and DDY/Jcl, and also a backcross of (EL x DDY)F1 hybrids to DDY. A new large-effect seizure frequency QTL was found (El5, Chr 14), a more minor QTL confirmed (El3, Chr 10), and two additional QTL proposed (El4, Chr 9; El6, Chr 11). The serotonin receptor gene, Htr2a, maps near and is a candidate for El5, and linkages of other serotonin receptor genes to seizure frequency QTL are noted. In addition, a strong gender effect was revealed, and epistasis was found between Chr 9 and Chr 14 markers. Despite this progress, however, our results revealed a more complex determinism of epilepsy in EL mice than previously described. In particular, no single El locus or pair was essential for frequent seizures, as QTL with large effects, such as El5, El2, and El1, were highly dependent on genetic context. Our studies highlight the importance of gene interaction in some complex mammalian traits defined by natural variation.

The anticonvulsant effect of citalopram on El mice, and the levels of tryptophan and tyrosine and their metabolites in the brain

Serotonin(5-HT) plays an important role in the seizures of El mice since the seizure threshold of El mice correlates with the 5-HT concentration in the central nervous system. In this study, the anticonvulsant effect of a 5-HT reuptake blocker, citalopram, was evaluated behaviorally and biochemically. El mouse convulsions were inhibited by oral administration of citalopram for 2 weeks. Citalopram increased tryptophan and tyrosine amounts, and decreased the 5-HT, 5-hydroxyindoleacetic acid, kynurenine, and dopamine amounts in the brain. These findings show that citalopram depresses monoaminergic metabolism. Given the known convulsant effect of kynurenine, it is suggested that its decrease by citalopram may involve attenuation of El mice seizures.

Regional distribution of tyrosine, tryptophan, and their metabolites in the brain of epileptic El mice

Tyrosine, tryptophan, and their metabolites in the brain of ddY, non-stimulated El (El (-)), and stimulated El (El (+)) mice were measured using the three dimensional HPLC. The tryptophan content was lower in El (+) than ddY and El (-) mice. The 5-hydroxytryptophan content was much higher in both El groups. The serotonin content of El (+) was higher than that of ddY and El (-) mice. The kynurenine content was remarkably high in the El mice. The dopamine content was lower in El (-) than in ddY mice, whereas it was greater in El (+) than in El (-) mice. The norepinephrine showed higher levels in El (+) mice. These facts suggest that El mice possess congenital metabolic abnormalities of tryptophan and tyrosine and that kynurenine may play an important role as convulsant in El mice seizures along with changes in serotonin, dopamine, and norepinephrine that are inhibitory agents and responded to the repetitive convulsions.

Regional excitatory and inhibitory amino acid levels in epileptic El mouse brain

Inbred mutant El mice are highly susceptible to convulsive seizures upon "tossing" stimulation. The levels of excitatory (e.g. glutamate and aspartate) and inhibitory amino acids [e.g. gamma-amino-butyrate (GABA)] were examined in discrete regions of stimulated El mice [El(+)], non-stimulated El mice [El(-)] and ddY mice, which do not have convulsive disposition. In comparison with ddY, a general increased levels of aspartate, glutamate, glutamine, and taurine were detected in brain regions of El(-). The levels of GABA and glycine were almost the same in ddY and El(-). Compared to El(+), the levels of aspartate, glutamate, glutamine, and GABA in El(-) were either the same or higher. In the case of taurine and glycine, the levels in El(-) were either the same or lower than El(+). Alanine is special in that El(-) have a higher level than El(+) in hippocampus but lower in cerebellum. Furthermore, while marked changes were registered in several brain regions, none of the amino acids investigated showed any significant differences in the hypothalamus of three different groups of mice.

Increased seizure susceptibility induced by guanidinoethane sulfonate in E1 mice and its relation to glutamatergic neurons

Convulsions and brain levels of amino acids and 5-hydroxytryptamine (5-HT) in E1 mice were examined after oral administration of a 1% guanidinoethane sulfonate (GES) solution. The incidence of convulsions increased 3 days after starting GES administration, and this effect continued throughout the 6 months of drug administration. Glutamate levels were increased in the cerebrum, and glutamine levels were increased in the cerebellum three days after starting GES administration. Brain 5-HT levels were not changed at that time. These results suggest that increased seizure susceptibility induced by GES in E1 mice is related to glutamatergic neurons.

Distribution of Calbindin-D28K 1 (CaBP) in the cerebral cortex and hippocampus of the epileptic (El) mouse

The distribution of Calbindin-D28K (CaBP), a calcium-binding protein that binds Ca2+ with high affinity, was measured by radioimmunoassay in various cortical regions of the epileptic strain of mice El. The El strain, in which seizures are induced by repeated vestibular stimulation, had significantly lower levels of CaBP in the hippocampus and dorsal occipital cortical areas than the control CF-1 strain. Following induction of seizures in the El strain, a further decrease in CaBP levels was observed in the hippocampal formation and ventral temporal cortical regions, areas where paroxysmal activity is generated in this strain. Considering the role of CaBP as an intraneuronal calcium buffer, the present findings indicate that neuronal calcium regulation is genetically altered in the El strain and is further disturbed during the events that lead to induction of seizures.

Reduced uptake and release of 5-hydroxytryptamine and taurine in the cerebral cortex of epileptic El mice

Inbred mutant El mice are highly susceptible to convulsive seizures upon 'throwing' stimulation, and the inhibition of 5-hydroxytryptamine (5-HT) and taurine activities appears to be involved in the El mouse seizures. Uptake and release of [3H]5-HT and [3H]taurine into and from cerebral neurocortical slices using a superfusion system were investigated in both non-stimulated and stimulated El mice [El(-), El(+)] and in ddY mice, which do not have a convulsive disposition. Release was defined as 40 mM K+-stimulated release. 5-HT and taurine uptake in El(+) was lower than El(-) but no difference in either uptake was found between ddY and El(-). Release of 5-HT and taurine in El(-) was higher than in ddY whereas their release in El(+) was lower than in El(-). The taurine level in the cerebral neocortex of El(-) and El(+) was higher than in ddY. These results suggest that the synaptic function of the 5-HT and taurine containing neurons is suppressed and that dysfunction of these inhibitory neurons is involved in the seizure susceptibility in the El mice.

Effect of taurine on a benzodiazepine-GABA-chloride ionophore receptor complex in rat brain membranes

Taurine at 10 mM had no effect on basal binding of [3H]diazepam to the membranes, while it significantly inhibited a GABA-stimulated binding of [3H]diazepam in cerebral cortex, hippocampus, but not in cerebellum. The inhibition by taurine in the presence of GABA (1 microM to 1 mM) was not competitive. At low concentrations (0.04 to 0.2 nM) the binding of [3H]propyl-beta-carboline-3-carboxylate, a ligand exhibiting higher affinity for type I than type II benzodiazepine receptors, was not enhanced by GABA, while the binding of higher concentrations (0.5 nM) was. This GABA enhancement of [3H]propyl-beta-carboline-3-carboxylate binding was also selectively blocked by taurine. Pentobarbital increased the binding of [3H]diazepam in a medium containing chloride and this effect was potentiated by taurine at 1-10 mM. These findings may be relevant to the modulatory role of taurine in the central nervous system.

Brain monoamine levels and E1 mouse convulsions

E1 mice had higher levels of brain dopamine (DA) and serotonin (5-HT) and a lower level of brain norepinephrine (NE) compared with the other strains of inbred mice. In the interictal stage of "stimulated" E1 mouse, the brain DA, NE and 5-HT levels were significantly lower compared with the non-stimulated E1 mouse. The administration of 5-hydroxytryptophan with MK486 markedly depressed the incidence of seizures in the E1 mouse. Evidence of abnormal DA, NE and 5-HT metabolism was found at the development age when the seizures became frequent. These results show that 5-HT may be closely related to the E1 mouse seizure susceptibility.