Opioid peptides (enkephalins, dynorphins and endorphins) are proteins found mostly in the central nervous system of mammals. These proteins act like morphine and interact with the same opioid receptors as drugs like morphine. These morphine-like proteins and opioid receptors make up the naturally occurring Opioid Receptor System. This system plays an important role in several physiological functions including the adaptation to physical or psychological stress in mammals. They are evolved in fear and anxiety; and with human diseases such as depression and post-traumatic stress disorder (PTSD). Therefore, a focus of Dr. Franklin’s research is on understanding the mechanism(s) behind the regulation of the production of these proteins in the brain.
Dr. Franklin is also interested in how the Opioid Receptor System and the CB1 cannabinoid (marijuana) Receptor System interact. This is because both systems have a common effect on the dopaminergic brain reward system (the pleasure centers in the brain). Therefore, both the Opioid and CB1 cannabinoid Receptor Systems are implicated in mood control, motivation, pain and stress responses, and involve neurons containing different populations of dopamine (D1-Like and D2-Like) receptors. Dr. Franklin is addressing the following question: What are the functional/behavioral consequences of CB1 ablation (gene knock-out) on the brain reward system and is it relevant to neuropathology (e.g., depression, attention deficit hyperactive disorder [ADHD], drug addiction)?
1. Yoburn, B.C., Franklin, S.O., Calvano, S.E. and Inturrisi, C.E.: Regulation of rat adrenal medullary enkephalins by glucocorticoids. Life Sci. 40: 2495-2503, 1987.
2. Inturrisi, C.E., Franklin, S.O., Yoburn, B.C., Huang, T., Nip, T.J. and LaGamma, E.F.: Characterization of enkephalins in rat adrenal medullary explants. Brain Res. 448: 230-236, 1988.
3. Franklin, S.O., Yoburn, B.C., Zhu, Y-S., Branch, A.D., Robertson, H.D. and Inturrisi, C.E.: Preproenkephalin mRNA and enkephalin in normal and denervated adrenals in the Syrian hamster: Comparison with central nervous system tissues. Mol. Brain Res., 10: 241-250, 1991.
4. Franklin, S.O., Zhu, Y-S., Yoburn, B.C. and Inturrisi, C.E.: Transsynaptic activity regulates proenkephalin and tyrosine hydroxylase gene expression and the response to reserpine in the hamster adrenal. Mol. Pharmacol. 40: 515-522, 1991.
5. Franklin, S.O.: Changes in proenkephalin gene expression in the developing hamster. Dev. Brain Res. 101: 239-248 (1997).
6. Jimenez, R., Yoburn, B.C., Calvano, S.E. and Franklin, S.O.: Preproenkephalin mRNA and enkephalin levels in the adult Syrian hamster: the influence from glucocorticoids. Mol. Brain Res. 66: 179-183 (1999).
7. Franklin, S.O. and Jimenez, R.: Increases in preproenkephalin (PPenk) mRNA levels in the Syrian hamster: the influence from glucocorticoids is dependent on age and tissue. Brain Res. 1086: 65-75 (2006).
8. Gerald, T.M., Ward, G.R., Howlett, A.C. and Franklin, S.O.: CB1 knock-out mice display significant changes in striatal opioid peptide and D4 dopamine receptor gene expression. Brain Res. 1093:20-24 (2006)
9. Ward, G.R., Dempsey, K.T., Clodfelter, D.E., Gerald, T.M., Krissinger, D.J., Patel, K.M., Vrana, K.E., Franklin, S.O., and Howlett, A.C., Glucocorticoids plus opioids upregulate genes that influence synaptic plasticity, Cell. Mol. Neurobiol. 27:651-660 (2007)
10. Gerald, T.M., Howlett, A.C., Ward, G.R., Ho, C., and Franklin, S.O., Gene expression of opioid and dopamine systems in mouse striatum: Effects of CB1 receptors, age and sex, Psychopharmacology (Berl). 198:497–508 (2008) DOI 10.1007/s00213-008-1141-8
NIH PubMed Publications for Steven Franklin