Abstract
Our previous study has shown that chronic morphine exposure induces neuronal apoptosis within the spinal cord dorsal horn; however, the mechanisms of morphine-induced apoptosis remain unclear. Here we examined whether adenylyl cyclase (AC) and protein kinase A (PKA) would play a role in this process. Intrathecal morphine regimen (10 microg, twice daily x 7 days) that resulted in antinociceptive tolerance induced spinal apoptosis as revealed by in situ terminal deoxynucleotidyl transferase (TdT)-UTP-biotin nick end labeling (TUNEL). The TUNEL-positive cells were detected primarily in the superficial laminae of the spinal cord dorsal horn, which was associated with an increase in the expression of activated caspase-3 and mitogen-activated protein kinase (MAPK) within the same spinal region. Co-administration of morphine with a broad AC inhibitor (ddA), a PKA inhibitor (H89), or a MAPK inhibitor (PD98059) substantially reduced the number of TUNEL-positive cells, as compared with the morphine alone group. The results indicate that the spinal AC and PKA pathway through intracellular MAPK may be contributory to the cellular mechanisms of morphine-induced apoptosis.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adenylyl Cyclases / drug effects*
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Adenylyl Cyclases / metabolism
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Animals
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Apoptosis / drug effects*
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Apoptosis / physiology
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Caspase 3
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Caspases / drug effects
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Caspases / metabolism
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Cyclic AMP / biosynthesis
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Cyclic AMP-Dependent Protein Kinases / drug effects*
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Cyclic AMP-Dependent Protein Kinases / metabolism
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Drug Interactions / physiology
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Drug Tolerance / physiology
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Enzyme Activation / drug effects
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Enzyme Activation / physiology
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Enzyme Inhibitors / pharmacology
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MAP Kinase Signaling System / drug effects
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MAP Kinase Signaling System / physiology
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Male
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Mitogen-Activated Protein Kinase 1 / drug effects
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Mitogen-Activated Protein Kinase 1 / metabolism
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Morphine / toxicity*
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Nerve Degeneration / chemically induced*
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Nerve Degeneration / enzymology
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Neuronal Plasticity / drug effects
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Neuronal Plasticity / physiology
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Neurotoxins / toxicity
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Posterior Horn Cells / drug effects*
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Posterior Horn Cells / enzymology
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Rats
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Rats, Sprague-Dawley
Substances
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Enzyme Inhibitors
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Neurotoxins
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Morphine
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Cyclic AMP
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Cyclic AMP-Dependent Protein Kinases
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Mitogen-Activated Protein Kinase 1
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Casp3 protein, rat
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Caspase 3
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Caspases
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Adenylyl Cyclases