Despite the spectacular pace of molecular studies of opioids and their receptors, we do not yet know why opiates are analgesic -- that is, how do opiates selectively inhibit pain without affecting other sensations? Moreover, the puzzling ability of opiates to inhibit aching, persistent pain (""""""""2nd pain"""""""") without inhibiting sharp, transient pain (""""""""1st pain"""""""") is largely unaddressed in the literature, even though this underlies the clinical use of opiates for post-operative pain. The research in this proposal should explain the role of primary sensory neurons in the specificity of opiates for 2nd pain; that goal is possible because we are the first lab that can identify nociceptors in tissue culture. Nociceptors, the sensors for pain, are peripheral neurons that are specialized to detect noxious stimuli, stimuli so strong that they threaten or cause tissue damage. Because their cell bodies sit in ganglia along with neurons that sense the various other somatic sensations, nociceptors could never be identified in primary tissue culture. We have solved this problem, creating a primary tissue culture system that contains fluorescently labelled nociceptors along with other, un=labelled sensory neurons. The novel system should propel several avenues of research, including he role of nociceptors in the specificity of opiates for pain. Our research focuses on the inhibition of Ca2+ channels by the mu opioid receptor, the binding site for morphine, because Ca2+ channel inhibition directly suppresses neurotransmitter release from presynaptic terminals. Such presynaptic inhibition is widely recognized as a key element of opioid action. Methods will include patch clamp recording of Ca2+ channel activity, single cell PCR for opioid receptors, and antisense oligonucleotide suppression of genes for G protein subunits. Our most relevant prior research convinces us; (1) that we can distinguish nociceptors that subserve 1st pain from those that subserve 2nd pain and; (2) that we know the key functional properties of the signalling path between mu receptors and Ca2+ channels. The proposed experiments target three working hypotheses: (1) Ca2+ channels on non-nonciceptive sensory neurons are not inhibited by opioids; (2) Selective opiate suppression of Ca2+ channels on small, unmyelinated nociceptors contributes to selective opiate inhibition of 2nd pain; (3) Different subtypes of G proteins couple different presynaptic inhibitors to Ca2+ channels in nociceptors. Correlations between our data and existing clinical and psychophysical observations may suggest novel strategies for analgesia by explaining the basis of known analgesics. By fully describing the molecular details of the signal linking mu receptors to Ca2+channels, we expect to contribute to the search for biochemical differences between acute and chronic actions of opiates.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
5R01DA007415-07
Application #
2856544
Study Section
Special Emphasis Panel (SRCD (22))
Program Officer
Thomas, David Dale
Project Start
1991-09-30
Project End
2000-12-31
Budget Start
1999-02-15
Budget End
1999-12-31
Support Year
7
Fiscal Year
1999
Total Cost
Indirect Cost
Name
Oregon Health and Science University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
009584210
City
Portland
State
OR
Country
United States
Zip Code
97239
Benson, C J; Sutherland, S P (2001) Toward an understanding of the molecules that sense myocardial ischemia. Ann N Y Acad Sci 940:96-109
Benson, C J; Eckert, S P; McCleskey, E W (1999) Acid-evoked currents in cardiac sensory neurons: A possible mediator of myocardial ischemic sensation. Circ Res 84:921-8
Cook, S P; McCleskey, E W (1997) Desensitization, recovery and Ca(2+)-dependent modulation of ATP-gated P2X receptors in nociceptors. Neuropharmacology 36:1303-8
Ingram, S; Wilding, T J; McCleskey, E W et al. (1997) Efficacy and kinetics of opioid action on acutely dissociated neurons. Mol Pharmacol 52:136-43
Wilding, T J; Womack, M D; McCleskey, E W (1995) Fast, local signal transduction between the mu opioid receptor and Ca2+ channels. J Neurosci 15:4124-32
Nah, S Y; Park, H J; McCleskey, E W (1995) A trace component of ginseng that inhibits Ca2+ channels through a pertussis toxin-sensitive G protein. Proc Natl Acad Sci U S A 92:8739-43
Womack, M D; McCleskey, E W (1995) Interaction of opioids and membrane potential to modulate Ca2+ channels in rat dorsal root ganglion neurons. J Neurophysiol 73:1793-8
Nah, S Y; McCleskey, E W (1994) Ginseng root extract inhibits calcium channels in rat sensory neurons through a similar path, but different receptor, as mu-type opioids. J Ethnopharmacol 42:45-51
McCleskey, E W (1994) Calcium channels: cellular roles and molecular mechanisms. Curr Opin Neurobiol 4:304-12
Fieber, L A; McCleskey, E W (1993) L-type calcium channels in type I cells of the rat carotid body. J Neurophysiol 70:1378-84

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