A specific taurine recognition site in the rabbit brain is responsible for taurine effects on thermoregulation

Abstract

1 Taurine and GABA are recognized as endogenous cryogens. In a previous study, some structural analogues of taurine, namely 6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine 1,1-dioxide (TAG), 2-aminoethylarsonic (AEA), 2-hydroxyethanesulfonic (ISE) and (7)cis-2-aminocyclohexane sulfonic acids (CAHS) have been shown to displace [ 3 H]taurine binding from rabbit brain synaptic membrane preparations, without interacting either with GABA-ergic systems, nor with taurine uptake mechanism, thus behaving like direct taurinergic agents. 2 To answer the question whether the role of taurine as an endogenous cryogen depends on the activation of GABA receptors or that of specific taurine receptor(s), taurine or the above structural analogues were injected intracerebroventricularly in conscious, restrained rabbits singularly or in combination and their effects on rectal (RT)-and ear -skin temperature and gross motor behavior (GMB) were monitored. 3 Taurine (1.2 Â 10 À6 -4.8 Â 10 À5 mol) induced a dose-related hypothermia, vasodilation at ear vascular bed and inhibition of GMB. CAHS, at the highest dose tested (4.8 Â 10À5 mol) induced a taurine-like effect either on RT or GMB. On the contrary ISE, injected at the same doses of taurine, induced a dose-related hyperthermia, vasoconstriction and excitation of GMB. AEA and TAG caused a dose-related hyperthermia, but at doses higher than 1.2 Â 10 À7 mol caused death within 24 h after treatment. 4 CAHS (4.8 Â 10 À5 mol) antagonized the hyperthermic effect induced by TAG (1.2 Â 10 À6 mol), AEA (1.2 Â 10 À8 mol) or ISE (4.8 Â 10 À5 mol). 5 In conclusion, these findings may indicate the existence of a recognition site specific for taurine, responsible for its effects on thermoregulation.

Neuroprotective Mechanisms of Taurine against Ischemic Stroke

“…In our previous studies [86], we demonstrated that the receptor is neither activated nor antagonized by structurally similar amino acids such as glutamate, GABA and glycine. These observations were later supported by Frosini and colleagues [87]. There is also a strong possibility of there being two types of taurine receptor; an ionotropic taurine receptor [88] and a metabotropic taurine receptor [60].…”

Possible Human Endogenous Cryogens

“…However, endogenous cryogenic substance contained in urine has not been identified so far. Recently, there are several reports showing possible cryogens, such as taurine, GABA, or leukotrienes [21][22][23]. However, they are rather small molecules and may produce anapyrexia as neurotransmitters, mediators or modulators in the central nervous system.…”

Modes of Action of Taurine and Granulocyte Colony-stimulating Factor in Neuroprotection

“…Definitive identification of taurine receptors is still emerging. 20,21 Further mechanistic studies are necessary to understand the direct role of taurine receptors on propagating neurotransmission. A summary schematic depicting the mode of action of taurine as a neuroprotective agent is shown in Figure 1.…”

“…20 Recently, an independent report further strengthened our findings that a specific recognition site exists that is used exclusively by taurine. 21 Taurine is known for its ability to neuromodularly inhibit postsynaptic taurine receptors and act as an indirect agonist of GABAA and glycine receptors, thereby increasing the duration of chloride channel conductance. 22 Apart from this, the presence of a sodium-dependent taurine transporter (TauT) has been confirmed, and TauT knockouts demonstrate retinal degeneration, reduced olfactory sensitivity, and the manifestation of clinically important age-dependent diseases.…”