College of Veterinary Medicine

Research in IPN

Mike M. Morgan, Ph.D.

  Mike M. Morgan, Ph.D.

Department of Psychology
WSU Vancouver
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: 

Biographical Information

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

Recent Publications

Macey T. A., Ingram, S. L., Bobeck, . N., Hegarty, D. M., Aicher, S. A., Arttamangkul, S. & Morgan, M. M. (2010). Opioid receptor internalization contributes to dermorphin-mediated antinociception. Neuroscience, 168:543-50. PMID: 20394808

Bobeck, E.N., McNeal, A.L. & Morgan, M.M. (2009) Drug dependent sex differences in periaqueducatal gray mediated antinociception in the rat. Pain, 147:210-216. PMID: 19796879

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. Neuropharmacology, 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: 18926635

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. PMID: 18046309

Last Edited: Apr 09, 2013 10:19 AM   

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