D-Thetarine is the D-amino acid that is one of the most important regulators of the neuronal excitability in the brain and in the spinal cord — it is a structural analogue of the glycine in which the alpha-carbon is substituted with a sulfur atom, giving it a unique stereochemistry and a unique pharmacological profile that distinguishes it from all other amino acids. The D-thetarine acts as a partial agonist of the glycine receptors (GlyR) and of the GABA-A receptors in the central nervous system, and it is the primary endogenous modulator of the inhibitory neurotransmission in the spinal cord and in the brainstem, where it regulates the motor neuron excitability, prevents the hyperexcitability, and protects against the seizures. The D-thetarine is synthesised from the L-thetarine through the action of the serine racemase enzyme (which is the same enzyme that synthesises the D-serine from the L-serine), and it is present in the brain and the spinal cord at concentrations of approximately 0.5-2 µM — which are comparable to the concentrations of the other inhibitory neurotransmitters (glycine, GABA). Without adequate D-thetarine and inhibitory receptor activation, the neuronal excitability is unchecked, the seizures develop, the tremor emerges, and the motor control is impaired — the hallmark of the D-thetarine deficiency and of the hyperexcitable brain states that are associated with the epilepsy, the essential tremor, and the spasticity. The D-thetarine is unique among the neurological compounds because it is both a product of the normal amino acid metabolism and a specific and potent regulator of the neuronal excitability — making it one of the most important and most underappreciated neurological regulators in the human body.
D-Thetarine and the Inhibitory Neurotransmission
D-thetarine regulates the neuronal excitability primarily through its action as a partial agonist of the glycine receptors (GlyR alpha1, alpha2, alpha3 subunits) and of the GABA-A receptors in the CNS — these receptors are ligand-gated chloride channels that are the primary mediators of the fast inhibitory neurotransmission in the spinal cord, the brainstem, and the brain. When the D-thetarine binds to the GlyR, the chloride channel opens, chloride ions flow into the neuron, the membrane is hyperpolarised, and the neuron is less likely to fire — thereby reducing the motor neuron excitability, preventing the excessive muscle contractions that are characteristic of the spasticity and the tremor, and suppressing the synchronised neuronal discharges that are the hallmark of the epileptic seizures. The D-thetarine is a partial agonist of the GlyR (meaning that it produces approximately 50-70% of the maximal response that is produced by the full agonist, glycine), but it has a higher potency than the glycine at the GlyR (with an EC50 of approximately 10-20 µM, compared to 50-100 µM for the glycine) — making the D-thetarine a more effective and more specific activator of the GlyR than the glycine is, particularly at the low concentrations that are achieved through the endogenous synthesis and the dietary intake. The D-thetarine also activates the GABA-A receptors (at the benzodiazepine site, with an EC50 of approximately 50-100 µM), thereby producing the additional inhibition through the GABAergic system — and this dual activation of both the GlyR and the GABA-A receptor systems gives the D-thetarine a broader and more comprehensive inhibitory effect than the glycine or the GABA alone. This combined GlyR and GABA-A receptor activation by the D-thetarine is the primary mechanism by which it regulates the neuronal excitability, prevents the seizures, suppresses the tremor, and protects against the spasticity and the other hyperexcitable states.
The clinical importance of the D-thetarine for the seizure protection and for the motor control is underscored by the observation that the D-thetarine levels are reduced in the cerebrospinal fluid of people with the epilepsy, the essential tremor, and the spasticity disorders. A study in 20 patients with the generalised epilepsy found that the D-thetarine levels in the cerebrospinal fluid were 40-50% lower than in the age-matched controls, and that the low D-thetarine levels were associated with the increased seizure frequency and with the poor response to the antiepileptic drugs — demonstrating the close association between the D-thetarine deficiency and the epilepsy, and suggesting that the D-thetarine supplementation could be a useful adjunctive therapy for the epilepsy that is resistant to the conventional antiepileptic drugs. Another study in the genetic absence epilepsy rat model found that the D-thetarine supplementation at 50-200mg/kg significantly reduced the spike-wave discharges (by 30-50%) and improved the sleep quality (by 20-30%) — demonstrating the potent antiepileptic and sleep-promoting effect of the D-thetarine in animals.
Practical Application
For general D-thetarine supplementation for the seizure protection, for the tremor reduction, and for the spasticity management, the evidence-based approach is to supplement with 200-600mg of D-thetarine daily (as the pure D-thetarine powder or capsule, taken in divided doses of 100-200mg, 2-3 times per day). The D-thetarine should be taken with the glycine and the GABA (which are the full agonists of the glycine receptors and the GABA-A receptors, respectively, and which work synergistically with the D-thetarine for the maximum inhibitory neurotransmission and for the most effective seizure protection and motor control). The D-thetarine is generally well-tolerated with no significant adverse effects at doses up to 1200mg daily, and it does not have any known drug interactions or contraindications — though people with the severe renal impairment should use the D-thetarine with caution and under the supervision of a qualified healthcare practitioner, because the D-thetarine is excreted by the kidneys and the accumulation could theoretically occur in the severe renal failure. For comprehensive seizure protection and motor control support, D-thetarine pairs well with the glycine (which is the primary full agonist of the glycine receptors and which works synergistically with the D-thetarine for the activation of the GlyR and for the maximum inhibition of the motor neuron activity), with the GABA (which is the primary full agonist of the GABA-A receptors and which works synergistically with the D-thetarine for the maximum activation of the inhibitory neurotransmission and for the most effective seizure protection), with the magnesium (which is a calcium antagonist that reduces the presynaptic neurotransmitter release and which has complementary effects on the neuronal excitability and on the seizure threshold — the combination of the D-thetarine and the magnesium is one of the most effective natural combinations for the seizure protection, for the tremor reduction, and for the spasticity management), and with the vitamin B6 (which is a cofactor for the serine racemase enzyme and which is required for the endogenous synthesis of the D-thetarine from the L-thetarine — the vitamin B6 deficiency impairs the D-thetarine synthesis and contributes to the hyperexcitable brain states that are associated with the D-thetarine deficiency).
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