Journal of Neuroscience, Vol 4, 3120-3127, Copyright © 1984 by Society for Neuroscience
Characterization of the cholinergic stimulation of phosphoinositide hydrolysis in rat brain slices
RA Gonzales and FT Crews
The stimulation of the formation of inositol phosphates by various
cholinergic agonists and antagonists was studied in rat brain cortical
slices. Incubation of the slices with [3H]inositol led to the incorporation
of radioactivity into inositol lipids. The accumulation of inositol
phosphates was then followed in the presence of 8 mM lithium which blocks
the hydrolysis of inositol phosphate. The release of inositol phosphate was
linear up to 15 min when stimulated by 1 mM carbachol. Acetylcholine,
muscarine, and methacholine also stimulated the release of inositol
phosphates with about the same efficacy as carbachol. Oxotremorine,
arecoline, pilocarpine, and bethanechol were not as effective as carbachol
at stimulating the accumulation of inositol phosphates. Indicative of
partial agonist activity, oxotremorine and pilocarpine inhibited the
maximal response induced by carbachol. Muscarinic antagonists atropine,
scopolamine, and pirenzepine blocked the stimulation by acetylcholine in
contrast to nicotinic antagonists, which had no effect. The brain regional
response to carbachol-stimulated inositol phosphate release varied widely
with large responses observed in the striatum, cerebral cortex, and
hippocampus. Smaller responses were seen in the brainstem, hypothalamus,
and cerebellum. Although carbachol stimulated inositol phosphate release in
cortical slices in the absence of added calcium, EGTA completely blocked
the response. These results suggest that the previously characterized
stimulation of the incorporation of 32Pi into phosphatidylinositol by
cholinergic agonists in synaptosomes (Fisher, S. K., P. D. Klinger, and B.
W. Agranoff (1983) J. Biol. Chem. 258: 7358-7363) is due to the initial
hydrolysis of inositol lipids.(ABSTRACT TRUNCATED AT 250 WORDS)