Age-related differences in the effects of some muscarinic agents on acetylcholine release from rat neostriatal slices.

The purpose of this study was to investigate whether the muscarinic modulation of neostriatal acetylcholine release changes with senescence. Neostriatal slices from Fischer 344 rats aged 3, 10 and 28 months were prepared and incubated in Krebs-Ringer bicarbonate buffer oxygenated with 95% O2/5% CO2. Acetylcholine release from slices of each age group was monitored in the presence or absence of muscarinic agents, and the release in the presence of the drug was compared to the release from slices of age-matched controls in the absence of drug. The muscarinic agonist, oxotremorine, and two muscarinic antagonists, atropine and pirenzepine, were tested for their effects on acetylcholine release. Pirenzepine is selective in its interaction with the M1 muscarinic receptor subtype; atropine and oxotremorine are nonselective in their actions. Of the three drugs tested, pirenzepine displayed a significant age-related difference in its effects on acetylcholine release. Whereas the effects of pirenzepine (50 microM) on acetylcholine release modulation in slices from the 3-month rats were negligible, the M1-selective antagonist increased the release of acetylcholine from slices of 10- and 28-month rats by another 42 and 192% (P less than .05), respectively. Atropine (1 microM) was also tested, and an increase in acetylcholine release by another 64, 104 and 218% (all P less than .05) was observed in slices from the 3-, 10- and 28-month rats, respectively. In the presence of oxotremorine (50 microM), acetylcholine release decreased in slices from the 3-month rats by 35% (P less than .1), but changed by only 7 and 15% in the 10- and 28-month slices, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)