Effect of in vivo microdialysis of 1,2,3,4-tetrahydro-9-aminoacridine (THA) on the extracellular concentration of acetylcholine in the striatum of anesthetized rats.

1,2,3,4-Tetrahydro-9-aminoacridine (THA, tacrine) is a potent cholinesterase (ChE) inhibitor which is under consideration for the treatment of Alzheimer's disease. This paper examines the effect of in vivo microdialysis of THA, THB-013 (an analog of THA) and physostigmine on the extracellular concentration of acetylcholine (ACh) in the striatum of anesthetized rat, as well as their effects on in vitro striatal ChE activity. In addition, the interaction of THA and physostigmine with cholinergic receptors in rat striatum has been investigated. All three drugs inhibited ChE activity and increased the extracellular concentration of ACh in a concentration-dependent manner. In the presence of THA, atropine induced a smaller increase in extracellular ACh concentrations than it did in the presence of physostigmine, under experimental conditions in which THA (100 microM) and physostigmine (10 microM) produced an equivalent effect on ChE activity. THA bound significantly to both muscarinic and nicotinic receptors in rat striatum, whereas physostigmine did not show significant binding. THA (100 microM) and physostigmine (10 microM) produced an additive effect on the extracellular concentration of ACh, and the addition of THA (10 microM) to physostigmine (1 microM) produced further inhibition of in vitro ChE activity. 4-Aminopyridine (100 microM), a K+ channel blocker, showed no detectable effect by itself on the extracellular concentration of ACh, however, it significantly increased the extracellular concentration of ACh in the presence of physostigmine (10 microM).(ABSTRACT TRUNCATED AT 250 WORDS)