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NEUROPHARMACOLOGY
Department of Biochemistry, Universidad Central del Caribe, Bayamon, Puerto Rico (P.A.F., D.P., V.A.E.); and Mental Retardation Research Center, University of California-Los Angeles, Los Angeles, California (J.d.V.)
Although in neuronal cultures nicotine was reported to prevent early and
delayed excitotoxic death, no studies with nicotinic drugs have been done with
acute hippocampal slices. We investigated the effect of nicotine and
methyllycaconitine (MLA) on the toxicity of
N-methyl-D-aspartate (NMDA) in the CA1 area of hippocampal
slices. The excitotoxic effect of NMDA was assessed as decreased recovery of
the capability to produce synaptically evoked population spikes (PSs).
Application of nicotine or MLA before NMDA application increased the recovery
of PSs. This electrophysiological recovery was used as a measure of the early
neuroprotective events. The neuroprotection conferred by both nicotine and MLA
was inhibited by dihydro-
-erythroidine, showing mediation of
neuroprotection by
4
2 neuronal nicotinic receptors (nAChRs).
Because nicotine activates
4
2 and other nAChR subtypes, whereas
10 nM MLA inhibits the
7 subtype, we propose the involvement of a
neuronal circuitry-dependent mechanism for nicotinic neuroprotection. The
effect of nicotine downstream from the receptors was investigated using
inhibitors of cell signaling. The results suggest that the effect of nicotine
is mediated by tyrosine receptor kinases, 1,2-phosphatidylinositol-3 kinase,
and the mitogen-activated extracellular signal-regulated kinases. Although
nicotine neuroprotection is Ca2+-dependent, neither
L-type Ca2+ channels nor calmodulin-dependent protein
kinase is involved in the effect of nicotine. In summary, these results
suggest that in acute slices nicotinic protection is initiated either by
direct activation of
4
2 or indirectly by inhibition of
7
followed by signal transduction involving tyrosine kinases,
phospholipid-dependent kinases, and mitogen-activated kinases.
Address correspondence to: P. A. Ferchmin, Department of Biochemistry, Universidad Central Del Caribe, P.O. Box 60-327, Bayamon, Puerto Rico 00960-6032. E-mail: ferchmin{at}coqui.net or ferchmin{at}uccaribe.edu
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