Involvement of L-triiodothyronine in acetylcholine metabolism in adult rat cerebrocortical synaptosomes

Despite the recently emerging notion of thyroid-hormone involvement in neurotransmission in the adult mammalian brain, adequate evidence for a cellular basis of the process is still lacking. The present study indicates the involvement of thyroid hormones in cholinergic system of the adult rat cerebral cortex. Administration of L-triiodothyronine (T-3, 0.025 to 4 mug/g) in single doses increased the synaptosomal acetylcholinesterase (AchE) and Mg2+-ATPase activity maximally at 24 hours in a dose-dependent way. Propylthiouracil (PTU)-treated hypothyroid rats showed a significant increase in AchE and Mg2+-ATPase activity compared to euthyroid rats. T-3-treatment on hypothyroid rats decreased AchE activity in synaptosomes compared to the hypothyroid synaptosomal values. Mg2+-ATPase activity found in (PTU+T-3)-treated group and T-3-treated group remained high. These results predict that T-3 stimulates acetylcholine (Ach) metabolism by increasing AchE activity as well as uptake of the released Ach through an increase in synaptosomal Mg2+-ATPase activity. This indicates a positive impact of T-3 on the cholinergic system in the adult mammalian brain.