Binding sites for [3H]AF-DX 116 and effect of AF-DX 116 on endogenous acetylcholine release from rat brain slices

Brain Res. 1989 Sep 4;496(1-2):285-94. doi: 10.1016/0006-8993(89)91075-5.


The present study shows that the putative M2 ligand, [3H]AF-DX 116, binds to two classes of muscarinic sites in homogenates of rat hippocampus, striatum and cerebral cortex: one with a high affinity (Kd less than 5 nM)/low capacity (Bmax = 30-63 fmol/mg protein), and a second of lower affinity (Kd greater than 65 nM) and higher capacity (Bmax greater than 190 fmol/mg protein). In experiments which tested the effects of the muscarinic antagonists on acetylcholine (ACh) release from brain slices, the non-selective antagonist (-)-quinuclidinyl benzylate and atropine significantly enhanced the potassium (25 mM)-evoked release of ACh. This effect was mimicked by the M2 ligand AF-DX 116, but neither the M1-selective antagonist pirenzepine, nor the putative M3-muscarinic antagonist, 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), altered ACh release. Also, the muscarinic agonist, oxotremorine, significantly depressed evoked ACh release from brain slices, an effect that was completely antagonized by atropine or by AF-DX 116, but not by pirenzepine or 4-DAMP. Thus, it appears that presynaptic muscarinic autoreceptors in the rat hippocampus, striatum and cerebral cortex belong to the M2 subtype of muscarinic receptors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcholine / metabolism*
  • Animals
  • Brain / drug effects
  • Brain / metabolism*
  • In Vitro Techniques
  • Male
  • Oxotremorine / pharmacology
  • Parasympathomimetics / metabolism*
  • Parasympathomimetics / pharmacology
  • Pirenzepine / analogs & derivatives*
  • Pirenzepine / metabolism
  • Pirenzepine / pharmacology
  • Rats
  • Rats, Inbred Strains
  • Receptors, Muscarinic / classification
  • Receptors, Muscarinic / drug effects*


  • Parasympathomimetics
  • Receptors, Muscarinic
  • Pirenzepine
  • Oxotremorine
  • Acetylcholine
  • otenzepad