Differential inhibitory action of taurine between electrically evoked response and low Mg++/-induced spontaneous activity in the CA1 area of the rat hippocampal slices

Although one of the major physiological functions of taurine (2-aminoethanesulfonic acid) is the inhibitory action on the central nervous system (CNS), the mechanism of taurine in controlling the neuronal excitation in the CNS has been in controversy. Electrically evoked pEPSP and spontaneous activity induced by the perfusion of low Mg++/-ACSF were recorded in the CA1 pyramidal cell layer of the hippocampal slice. To test the inhibitory effect of taurine on spontaneous responses, taurine was treated for 2 min at various concentrations(1 mM-10 mM). Taurine reduced the spontaneous activity by 22.2% at 1 mM, and 100% at 2 mM in low Mg++/-ACSF. Evoked response was induced by electrical stimulation of Schaffer collateral-commissural fibers. Taurine reduced the evoked response by 11.68% at 3 mM, and 24.25% at 5 mM. Even 20 mM of taurine reduced the evoked response only by 24% after 5 min treatment. That is, the inhibitory efficacy was much higher in spontaneous activity than in evoked response. The GABAA receptor antagonist, 100 muM bicuculline, blocked the inhibitory action of taurine, while GABAB receptor antagonist, 700 muM phaclofen, did not. Taurine blocked the spontaneous activity in the presence of CNQX, and did not block the electrically evoked response in the presence of APV. The results suggest that taurine causes hyperpolarization in the cell by binding to GABAA receptor and preferentially attenuates NMDA receptor-mediated hyperexcitation, leaving synaptic transmission unmodified.

Effects of taurine on generalized seizure activity in the rat thalamocortical slice

Rat thalamocortical slices maintain synoptic connections between thalamus and cortex. When perfused with low Mg++-ACSF, thalamocortical slices exhibited two main types of spontaneous bursting activity. One is monotonic burst of 3-15 Hz and another is multiphasic bursts which have a tonic burst firing period and a late phase of clonic burst firing. These bursts are similar in frequency and during to EEG recordings from human generalized seizures. Exploiting the advantages of in vitro preparations, the electrophysiological action of taurine were studied. Exogeneous application of taurine profoundly decreased spontaneous bursting activities, which it caused only slight reduction of electrically evoked response in cortical layer. Taurine-induced current was blocked by 40 uM bicuculline, GABA receptor antagonist, in acutely isolated coritcal neurons. These results suggest that endogeneous taurine may regulate the hyperexcitablility through GABAa receptor.

Effects of taurine on generalized seizure activity in the rat thalamocortical slice

Rat thalamocortical slices maintain synoptic connections between thalamus and cortex. When perfused with low Mg++-ACSF, thalamocortical slices exhibited two main types of spontaneous bursting activity. One is monotonic burst of 3-15 Hz and another is multiphasic bursts which have a tonic burst firing period and a late phase of clonic burst firing. These bursts are similar in frequency and during to EEG recordings from human generalized seizures. Exploiting the advantages of in vitro preparations, the electrophysiological action of taurine were studied. Exogeneous application of taurine profoundly decreased spontaneous bursting activities, which it caused only slight reduction of electrically evoked response in cortical layer. Taurine-induced current was blocked by 40 uM bicuculline, GABA receptor antagonist, in acutely isolated coritcal neurons. These results suggest that endogeneous taurine may regulate the hyperexcitablility through GABAa receptor.