Steady-state concentrations of choline and acetylcholine in rat brain parts during a constant rate infusion of deuterated choline

Abstract

An intravenous infusion of deuterated choline at constant rate for 6 min (5 or 25 μmoles kg⁻¹ min⁻¹) significantly increases the concentration of choline in plasma, occipital cortex and striatum. Both 5 and 25 μmoles kg⁻¹ min⁻¹ increase the concentration of acetylcholine in cortex but only 25 μmoles kg⁻¹ min⁻¹ increases the acetylcholine content in striatum. In contrast, 1 μmole kg⁻¹ min⁻¹ does not change the choline or acetylcholine content in cortex or striatum. A single pulse injection of choline (200 μmoles kg⁻¹) causes a significant increase in the concentration of choline in striatum 30 sec following injection. The choline content returns to normal values within 2 min. These studies show that when a pulse injection of a non-tracer dose of radioactive choline is used to measure brain acetylcholine turnover rate the maintenance of steady state must be verified within seconds after the pulse injection of radioactive choline. When constant infusion of deuterated choline is used to measure turnover rate of acetylcholine in the brain of rats, a dose of 1 μmole kg⁻¹ min⁻¹ appears to be a maximal infusion rate.