AF102B [(+-)-cis-2-methyl-spiro(1,3-oxathiolane-5,3')
quinuclidine], a structurally rigid analog of
acetylcholine, was investigated in a number of neurochemical, pharmacological and behavioral tests related to
cholinergic functions.
AF102B induced
atropine-sensitive contractions of isolated guinea pig ilea and trachea preparations with EC50 values of 3.5 and 3 microM being 87- and 1.3-fold less potent than
acetylcholine, respectively. Binding studies using the radioligands
pirenzepine, cis-
dioxolane and
quinuclidinyl benzilate in rat cerebral cortex and
quinuclidinyl benzilate in cerebellar homogenates indicated that
AF102B was a potent and highly selective M1-type
muscarinic probe, being more selective for M1 receptors than
oxotremorine,
carbachol and AF102A (the trans-isomer of
AF102B).
AF102B had a 3-fold higher apparent affinity for M1 receptors than the prototype M1 agonist,
McN-A-343, cis- and trans-AF30 (other rigid analogs of
acetylcholine). Treatment of rat cortical homogenates with Cu++
ions did not modify the affinity observed for the
muscarinic antagonists atropine,
scopolamine and
pirenzepine, whereas increasing the proportion of high affinity sites for the agonists
oxotremorine-M,
carbachol and
McN-A-343. The apparent affinity of
AF102B also increased by Cu++ treatment suggesting that this compound interacts with rat cerebral cortex
muscarinic receptors as an agonist.
AF102B did not affect high affinity
choline transport,
choline acetyltransferase and
acetylcholinesterase activities in rat brain preparations. In rats treated with
AF64A (the cholinotoxin
ethylcholine aziridinium ion; 3 nmol/2 microliters/side i.c.v.),
AF102B (1 mg/kg p.o. or i.p.), AF102A (1 mg/kg i.p.), cis-AF30 (1 mg/kg, i.p.) and
physostigmine (0.06 mg/kg i.p.), each reversed
cognitive impairments in a step-through passive avoidance task. Both
AF102B and AF102A (1 mg/kg i.p.), but not
physostigmine (0.1 mg/kg i.p.), were effective also in reversing reference memory impairments in a Morris water maze test. Repetitive administrations of
AF102B (0.2 mg/kg/day i.p.) improved AF64A-induced working memory deficits in the Morris water maze test, but did not affect open field behavior. The data show that the selective M1 agonist
AF102B can restore AF64A-induced
cognitive impairments, without producing adverse central and peripheral side effects at the effective doses and this can indicate its potential use for the treatment of
Alzheimer's disease.