On the role of taurine in the cerebellar cortex: a reappraisal.

Certain amino acids are now widely accepted as constituting one of the major groups of neurotransmitters in the mammalian central nervous system. However, although the available data suggest that taurine may well be involved in central synaptic transmission, its precise neurohumoral role in many areas is still poorly understood. Some of the prerequisites for the identification of chemical transmitters have been fulfilled by taurine in various central structures, including the cerebellum, but data are still inconclusive concerning its possible role either as a classical neurotransmitter or as a modulator of neuronal excitability. The synaptic role of taurine in the cerebellum is supported by: 1) its high levels associate with the synaptic fraction, 2) the identification of a high-affinity uptake mechanism, 3) its inhibitory effects exerted upon Purkinje cells, and 4) the calcium-dependence of its stimulus-induced release. However, the criterion of identity of action has not been demonstrated and a specific taurine receptor has not yet been identified. Furthermore, the observed calcium-dependence of taurine efflux may be explained as a secondary result of the release of endogenous glutamate by an inhibitory feed-back mechanism acting through autoreceptors. Therefore, although the present data support a possible involvement of taurine in central neurotransmission, its precise synaptic role remains to be established.