Interaction of taurine and related compounds with GABAergic neurones in the nucleus raphe dorsalis

Potential protective effect of taurine against dibromoacetonitrile-induced neurotoxicity in rats

Dibromoacetonitrile (DBAN) is a disinfection by-product of water chlorination. Epidemiological studies indicate that it might present a potential hazard to human health. The present study aimed to investigate the possible neurotoxicity of DBAN in rats and possible protection by taurine. Based on initial dose-response experiment, DBAN (60 mg/kg) was administrated orally for 7 days. DBAN administration significantly impaired behavior of rats. Further, DBAN produced significant decrease of monoamines, γ-aminobutyric acid (GABA), glutamate contents, acetylcholinestrase (AChE) and aspartate aminotransferase (AST) activities, in rat brain. On the other hand, a significant increase in malondialdehyde (MDA), nitric oxide (NO) contents and lactic dehydrogenase (LDH) activity was observed. Co-administration of taurine (200mg/kg, i.p.) with DBAN mitigated most tested parameters. In conclusion, the present study indicates that DBAN has the propensity to cause significant oxidative damage in rat brain. However, taurine has a promising role in attenuating the obtained hazardous effects of DBAN.

Effects of taurine on rat behaviors in three anxiety models

In our previous studies using an elevated plus-maze test in mice, taurine was shown to present an anxiolytic-like effect after single and repeated administration. The aim of the present study was to investigate the anxiolytic and behavioral effects of taurine on rats in the open field, hole-board, and social interaction test compared to the positive control diazepam. Taurine (14, 42, and 126 mg/kg, i.p.) was administered 30 min before the tests. In the social interaction and hole-board tests, taurine (42 mg/kg) significantly increased social interaction time and the number and duration of head-dipping. In the open field test, taurine (126 mg/kg, i.p.) presented anxiolytic-like effects by increasing the number of center entries, time spent in the central area and the anti-thigmotactic score while having no effect on the locomotor activity. Results from these experiments suggest that taurine produces an anxiolytic-like effect in these animal models and may act as a modulator or anti-anxiety agent in the central nervous system.

Neuroprotective effect of taurine in 3-nitropropionic acid-induced experimental animal model of Huntington's disease phenotype

An experimental animal model of Huntington's disease (HD) phenotype was induced using the mycotoxin 3-nitropropionic acid (3-NP) and was well characterized behaviorally, neurochemically, morphometrically and histologically. Administration of 3-NP caused a reduction in prepulse inhibition (PPI) of acoustic startle response, locomotor hyper- and/or hypoactivity, bilateral striatal lesions, brain oxidative stress, and decreased striatal gamma-aminobutyric acid (GABA) levels. Taurine is a semi-essential beta-amino acid that was demonstrated to have both antioxidant and GABA-A agonistic activity. In this study, treatment with taurine (200 mg/kg daily for 3 days) prior to 3-NP administration reversed both reduced PPI response and locomotor hypoactivity caused by 3-NP injection. Taurine pretreatment also caused about 2-fold increase in GABA concentration compared to 3-NP-treated animals. In addition, taurine demonstrated antioxidant activity against oxidative stress induced by 3-NP administration as evidenced by the reduced striatal malondialdehyde (MDA) and elevated striatal glutathione (GSH) levels. Histochemical examination of striatal tissue showed that prior administration of taurine ahead of 3-NP challenge significantly increased succinate dehydrogenase (SDH) activity compared to 3-NP-treated animals. Histopathological examination further affirmed the neuroprotective effect of taurine in 3-NP-induced HD in rats. Taken together, one may conclude that taurine has neuroprotective role in the current HD paradigm due, at least partly, to its indirect antioxidant effect and GABA agonistic action.

Differential increase in taurine levels by low-dose ethanol in the dorsal and ventral striatum revealed by microdialysis with on-line capillary electrophoresis

Ethanol increases taurine efflux in the nucleus accumbens or ventral striatum (VS), a dopaminergic terminal region involved in positive reinforcement. However, this has been found only at ethanol doses above 1 g/kg intraperitoneally, which is higher than what most rats will self-administer. We used a sensitive on-line assay of microdialysate content to test whether lower doses of ethanol selectively increase taurine efflux in VS as opposed to other dopaminergic regions not involved in reinforcement (e.g., dorsal striatum; DS). Adult male rats with microdialysis probes in VS or DS were injected with ethanol (0, 0.5, 1, and 2 g/kg intraperitoneally), and the amino acid content of the dialysate was measured every 11 sec using capillary electrophoresis and laser-induced fluorescence detection. In VS, 0.5 g/kg ethanol significantly increased taurine levels by 20% for 10 min. A similar increase was seen after 1 g/kg ethanol, which lasted for about 20 min after injection. A two-phased taurine efflux was observed with the 2.0 g/kg dose, where taurine was increased by 2-fold after 5 min but it remained elevated by 30% for at least 60 min. In contrast, DS exhibited much smaller dose-related increases in taurine. Glycine, glutamate, serine, and gamma-aminobutyric acid were not systematically affected by lower doses of ethanol; however, 2 g/kg slowly decreased these amino acids in both brain regions during the hour after injection. These data implicate a possible role of taurine in the mechanism of action of ethanol in the VS. The high sensitivity and time resolution afforded by capillary electrophoresis and laser-induced fluorescence detection will be useful for detecting subtle changes of neuronally active amino acids levels due to low doses of ethanol.

Leptin uptake by serotonergic neurones of the dorsal raphe

The effects of leptin on food intake, metabolism, sleep patterns and reproduction may be mediated, in part, by the midbrain serotonergic systems. Here, we report on the distribution of neurones that accumulate leptin in the raphe nuclei of male and female rats after intracerebroventricular administration of mouse recombinant leptin labelled with digoxigenin. Direct leptin-targeted cells were present in the periventricular grey, pontine and raphe nuclei. Confocal microscopy revealed that raphe neurones which accumulated leptin were predominantly serotonergic. The temporal pattern of leptin accumulation by raphe neurones showed a marked gender difference: 6 h after leptin administration, all male and female rats showed massive leptin binding in the dorsal raphe, while 30 min after leptin treatment, only 10% of male rats exhibited leptin-labelled cells in contrast to 50% of females. The present observations reveal that leptin can be selectively accumulated by serotonergic neurones in the raphe nuclei and that this mechanism is gender specific. These findings support the idea that the midbrain serotonergic system is an important mediator of the effects of leptin on brain function and may provide an explanation for gender differences in metabolism regulation and its coordination with higher functions of the brain.

Acamprosate decreases the hypermotility during repeated ethanol withdrawal

One of the known behavioral actions of acamprosate is to prevent relapse in weaned alcoholics. However, the mechanism underlying this effect remains unclear. In this study, the motility of Wistar male rats, which were either alcoholized by ethanol inhalation or simultaneously alcoholized and treated orally by acamprosate (400 mg/kg/ day) for 4 weeks, was measured during four episodes of the ethanol withdrawal. The concentrations of excitatory and inhibitory amino acids were also assayed by the microdialysis technique with OPA/BME precolumn derivatisation and electrochemical detection in the nucleus accumbens. Acamprosate reduces both the motility and the glutamate microdialysate content during the first 12 h of ethanol withdrawal in comparison to the alcoholized untreated group. The basal concentration of the sulfonated amino acid taurine increased significantly in alcoholized acamprosate-treated rats compared to alcoholized untreated rats. These results suggest that acamprosate is able to reduce the hypermotility during ethanol withdrawal syndrome directly by reducing the nucleus accumbens glutamate concentration or indirectly by increasing the taurine and GABA brain level.

Changes in female cognitive performance after energetic drink consumption: a preliminary study

1. A group of males and a group of females consumed either no drink, a placebo or a caffeine-containing energy drink. Subjects were requested to perform a simple reaction times task and a go-no-go reaction times task. 2. Males responded significantly faster than females. The effect of drink was apparent only for females performing the go-no-go task, while it was undetectable in female simple reaction times and in males. 3. A mild effect due to the drink, but not to the placebo, appears only when the task requires a certain degree of cognitive processing and is evident only in subjects possibly adopting a cognitive strategy that allows an improvement of performance.

Central effects of acamprosate: part 1. Acamprosate blocks the glutamate increase in the nucleus accumbens microdialysate in ethanol withdrawn rats

One of the known behavioral actions of acamprosate is to decrease hypermotility during alcohol withdrawal. However, the mechanism of this effect remains unclear. In this study, the concentrations of excitatory and inhibitory amino acids were assayed by the microdialysis technique with OPA/BME precolumn derivatization and electrochemical detection in the nucleus accumbens of male Wistar rats which were either alcoholized by ethanol inhalation or simultaneously alcoholized and treated orally by acamprosate (400 mg/kg/day) for 4 weeks. Without treatment, extracellular glutamate increased during the withdrawal phase, while other amino acids tested (aspartate, arginine, taurine, alanine and GABA) remained stable. In contrast, the alcoholized rats treated with acamprosate failed to present the increase in glutamate during ethanol withdrawal, while other amino acids tested also remained stable. The observed glutamate increase could be responsible for the hyperexcitability observed during episodes of ethanol withdrawal. These results suggest that acamprosate is able to reduce the ethanol withdrawal syndrome by reducing the concentration of glutamate in the nucleus accumbens.

Taurine increases in the nucleus accumbens microdialysate after acute ethanol administration to naive and chronically alcoholised rats

The extracellular changes of amino acids (glutamate, taurine and GABA) in the nucleus accumbens of freely moving rats were estimated using the microdialysis technique following acute and chronic ethanol injections (1, 2, and 3 g/kg body weight). Compared to baseline values, taurine increased by 154% +/- 73%, 142% +/- 40% and 162% +/- 75% 20 min after the acute injection of respectively, 1, 2, and 3 g/kg body weight ethanol, while 40 min after ethanol injection, taurine had increased by 124% +/- 36%, 146% +/- 54% and 168% +/- 98%. No changes in either glutamate or GABA were detected at any time points assayed. In the rats which had received chronic ethanol administration prior to a further acute ethanol injection (1, 2, and 3 g/kg body weight), taurine increased by 138% +/- 73%. 144% +/- 39% and 180% +/- 85% 20 min after the ethanol injection at 40 min post ethanol injection taurine had increased by 134% +/- 44%, 160% +/- 56% and 158% +/- 45%, compared to the basal baseline value. No significant changes were observed in either glutamate or GABA microdialysate content in these chronic studies. The biological role played by taurine after acute ethanol injection in the nucleus accumbens remains unclear but may be associated with a yet, undefined mechanism, in reducing the cytotoxicity of ethanol.

Neurochemical bases of locomotion and ethanol stimulant effects

The locomotor stimulant effect produced by alcohol (ethanol) is one of a large number of measurable ethanol effects. Ethanol-induced euphoria in humans and locomotor stimulation in rodents, a potential animal model of human euphoria, have long been recognized and the latter has been extensively characterized. Since the euphoria produced by ethanol may influence the development of uncontrolled or excessive alcohol use, a solid understanding of the neurochemical substrates underlying such effects is important. Such an understanding for spontaneous locomotion and for ethanol's stimulant effects is beginning to emerge. Herein we review what is known about three neurochemical substrates of locomotion and of ethanol's locomotor stimulant effects. Several lines of research have implicated dopaminergic, GABAergic, and glutamatergic neurotransmitter systems in determining these behaviors. A large collection of work is cited, which strongly implicates the above-mentioned neurotransmitter substances in the control of spontaneous locomotion. A smaller, but persuasive, body of evidence suggests that central nervous system processes utilizing these transmitters are involved in determining the effects of ethanol on locomotion. Particular emphasis has been placed on the mesolimbic ventral tegmental area to nucleus accumbens dopaminergic pathway, and on the ventral pallidum/substantia innominata, where GABA and glutamate have been found to play a role in altering the activity of this dopaminergic pathway. Research on ethanol and drug locomotor sensitization, increased responsiveness to the substance with repeated administration, is also reviewed as a process that may be important in the development of drug addiction.

Intraperitoneal administration of baclofen increases consumption of both solid and liquid diets in rats

It has previously been demonstrated that systemic administration of the GABAB receptor agonist baclofen increases food intake but decreases water intake in rats. In the present study, the effects of baclofen (2-4 mg/kg i.p.) were investigated on food intake in non-deprived rats given access to either pelleted food (n = 8) or a palatable liquid diet (n = 8). Baclofen (2-4 mg/kg i.p.) significantly increased the consumption of both the pelleted and the liquid foods. The increased intake of the liquid diet (i) argues against the involvement of non-specific gnawing in the increased consumption of the solid food by baclofen, and (ii) suggests that the inhibition of water intake produced by baclofen is not due to interference with the mechanical aspects of drinking, such as licking on a drinking spout, or the swallowing of liquid.