Department of Psychology
Phone: (360) 546-9726
Neural Mechanisms of Pain Modulation and Morphine Tolerance
Opiates such as morphine are the most effective treatment for pain.
Unfortunately, the ability of opioids to relieve pain is reduced with
repeated administration because of the development of tolerance. The
primary goal of our research is to determine the mechanism for tolerance
so long lasting and effective pain treatments can be developed. Our
research has shown that tolerance occurs by a change in opioid sensitive
GABAergic neurons in the ventrolateral region of the periaqueductal gray
(PAG). Injection of opioids into this brain region produces analgesia
and repeated injections results in tolerance. We are currently examining
the role of mu-opioid receptor internalization in morphine tolerance.
These studies indicate that repeated administration of morphine causes
tolerance by increasing the likelihood that the mu-opioid receptor will
internalize and thereby terminate membrane signaling.
This work is supported by the National Institute on Drug Abuse.
More information is available on Dr. Morgan's Psychology Web Page. See:
Michael Morgan was an undergraduate and graduate student at the
University, California at Los Angeles (UCLA) earning B.A. (1984) and
Ph.D. (1989) degrees in Psychology (Physiological Psychology emphasis).
He continued his education as a postdoctoral fellow in the Department of
Neurology at the University of California, San Francisco from 1989 to
1993. Dr. Morgan has been in the Department of Psychology at Washington
State University Vancouver since 1993. He is the only member of the
Vancouver faculty to receive both the Students Award for Teaching
Excellence and the Chancellors Award for Research Excellence
T. A., Ingram, S. L., Bobeck, . N., Hegarty, D. M., Aicher, S. A.,
S. & Morgan, M. M. (2010). Opioid receptor
internalization contributes to dermorphin-mediated antinociception.
Bobeck, E.N., McNeal, A.L. & Morgan, M.M. (2009) Drug
dependent sex differences in periaqueducatal gray mediated
antinociception in the rat. Pain,
Macey, T.A., Bobeck, E.N., Hegarty, D.H., Aicher, S.A., Ingram,S.L., &
Morgan, M.M. (2009).
Extracellular signal-regulated kinase 1/2
activation counteracts morphine tolerance in the periaqueductal gray of
the rat. The Journal of Pharmacology and Experimental Therapeutics,
331:412-8. PMID: 19684256
Morgan, M. M.
Bobeck, E. N., & Ingram, S. L. (2009). Glutamate Modulation of
Antinociception, but not Tolerance Produced by Morphine Microinjection
into the Periaqueductal Gray of the Rat. Brain Research, 1295:
59-66. PMID: 19664608
Cyr, M.C. & Morgan, M.M. (2009). Early Methylphenidate
Exposure Enhances Morphine Antinociception and Tolerance in Adult Rats.
7:673-677. PMID: 19646456
Meyer, P.J., Morgan, M.M., Kozell, L.B., & Ingram, S.L.
(2009). Contribution of dopamine receptors to periaqueductal
gray-mediated antinociception. Psychopharmacology,
204(3):531-40. PMID: 19225762
Morgan, M. M., Ashley, M. D., Ingram, S. L., &
Christie, M. (2009). Behavioral consequences
of chronic morphine-induced delta receptor upregulation in the
periaqueductal gray of the rat. Neural Plasticity,
2009:516328. PMID: 19266049
Morgan, M. M., Whittier, K. L., Hegarty, D. M., &
Aicher, S. A. (2008). Periaqueductal gray
neurons project to spinally projecting GABAergic neurons in the rostral
ventromedial medulla. Pain, 140(2):376-86. PMID:
Wilson, A. R., Maher, L., & Morgan, M. M. (2008).
Repeated Cannabinoid Injections into the Rat
Periaqueductal Gray Enhances Subsequent Morphine Antinociception.
Neuropharmacology, 55:1219-25. PMID: 18723035
Fossum, E. N., Lisowski, M. J., Macey, T. A., Ingram, S. L., &
Morgan, M. M. (2008). Microinjection of the vehicle dimethyl
sulfoxide (DMSO) into the periaqueductal gray modulates morphine
antinociception. Brain Research, 1204:53-58. PMID: 18342296
Loyd, D., Morgan, M.M., & Murphy,
A.Z. (2008). Sexually dimorphic activation of the periaqueductal
gray-rostral ventromedial medullary circuit during the development of
tolerance to morphine in the rat. European Journal of Neuroscience,
27(6):1517-24. PMID: 18364026
Ingram, S.L., Macey, T.A., Fossum, E.N., &
Morgan, M.M. (2008). Tolerance to
repeated morphine administration is associated with increased potency of
opioid agonists. Neuropsychopharmacology, 33:2494-2504.