Stimulation of AChE activity in relation to changes in electronmicroscopic structure of adult rat cerebrocortical synaptosomes pretreated with 3-5-3'-triiodo-L-thyronine.

Triiodothyronine (T3) stimulated AChE activity in depolarization-induced intact synaptosomes (isolated from adult rat cerebral cortex) suspended in calcium-supplemented choline chloride buffer in a time-dependent manner maximally 45-60 s after T3 administration and in a dose-dependent manner with an optimum at 10-100 nM. T3 (100 nM) had no such effects on AChE activity in synaptosomes at non-depolarized conditions. There was no direct effect of T3 on AChE activity of lysed synaptosomal suspension in the physiological range (nM) of T3. The experiments suggest that T3 might have a role in the calcium-dependent release/co-release of acetylcholine from intact synaptosomes concomitant with the acceleration of choline uptake mechanisms that has been reported to accompany elevation of AChE activity. Additionally, electron microscopic structures showed condensation of the cytosolic content with increase in electron density, formation of intrasynaptosomal coarse vesicles and appearance of vesicular fusion like structures (meandering) at the periphery in depolarization-induced T3-treated (60 s) intact synaptosomes, indicating the occurrence of the release of neurotransmitters. The present investigation indicates a definite role of T3 on Ca2+-dependent cholinergic neurotransmission.