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

Abstract

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.

Introduction

Taurine, 2-aminoethane-sulphonic acid, is one of the few sulfur-containing amino acids that is found in relatively high concentrations in the central nervous system of mammals. This amino acid has been shown to be essential for the development, survival, growth of vertebrate neurons (Hayes et al., 1975). Taurine deficiency has been confirmed in many neuropathological conditions, such as epilepsy Barbeau et al., 1975, Joseph and Emson, 1976, mental depression (Perry, 1976), and the alcohol withdrawal syndrome (Ikeda, 1977). It has been reported that taurine contents in brain increased significantly at the onset of convulsions, as induced by tossing the animals up many times. On the other hand, taurine administration increased the threshold of convulsion by the stimulation in E1 mice (Iwata et al., 1979). Taurine (2 g/kg, PO) can significantly prolong the latency of convulsion induced by strychnine (Fonnum, 1978) and the pentobarbital sleeping time in mice (Zhang et al., 1981). In open-field test, Sanberg et al. reported that increasing doses of taurine significantly decreased ambulation levels, increased latency scores, and increased thigmotaxis (Sanberg and Ossenkopp, 1977).

In the past ten years, more and more researches were focused on the interaction of taurine with GABA system. Taurine competitively inhibited [³H]muscimol binding to purified GABA_A receptors with an IC₅₀ value of 50 μM, it showed notably a higher affinity for β₅₅ polypeptide (Bureau and Olsen, 1991). Moreover, it has been found that taurine interacted with GABA_A receptor-linked benzodiazepine receptor binding sites (Medina and DeRobertis, 1984). An inhibition of GABA_B binding sites at 1–5 μM taurine also was observed (Kontro and Oja, 1990). Since the fact of Gabaergic-Benzodiazepine system involved in the aetiology of anxiety has been widely accepted, taurine is a chemical analogue and imitates the action of GABA, it might be also concerned with anxiety. So we are interested in the relationship between taurine and anxiety. The main purpose of this study is to examine the effects of taurine on the behavior of mice in the elevated plus-maze, a most commonly used animal models of anxiety. Besides the conventional methods to index the level of anxiety and general activity on the plus-maze (Lister, 1987), some other ethological measures have been developed to improve the sensitivity of the model (Cole and Rodgers, 1994). In our present study, both traditional and novel measures were adopted to observe the drug effects.