AUTHOR=Fousse Samantha L. , Golsen Bryce M. , Sanchez-Migallon Guzman David , Paul-Murphy Joanne R. , Stern Joshua A. 

TITLE=Varying Expression of Mu and Kappa Opioid Receptors in Cockatiels (Nymphicus hollandicus) and Domestic Pigeons (Columba livia domestica)

JOURNAL=Frontiers in Genetics

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2020.549558

DOI=10.3389/fgene.2020.549558

ISSN=1664-8021

ABSTRACT=<p>Avian species have varying analgesic responses to opioid drugs. Some of this variability could be due to extrinsic factors such as administration route or dose. However, intrinsic factors such as gene expression or polymorphic differences in opioid receptors may be important components.</p><sec><title>Objectives</title><p>The objectives of this study were to determine the relative gene expression and polymorphisms present for mu and kappa opioid receptors (<italic>OPRM1</italic> and <italic>OPRK1</italic>) in the cerebrum, brainstem, spinal cord, and footpad of cockatiels and pigeons.</p></sec><sec><title>Methods</title><p>Tissue biopsies were obtained from 11 adult cockatiels (6 male and 5 female) and 11 adult pigeons (6 male and 5 female). RNA was extracted and qPCR was performed to determine the level of gene expression for <italic>OPRM1</italic> and <italic>OPRK1</italic> relative to a reference gene phosphoglycerate kinase 1 (<italic>PGK1)</italic> using the ΔΔCt method. Sanger sequencing was performed to identify polymorphisms, if present.</p></sec><sec><title>Results</title><p>There were higher expression levels of <italic>OPRM1</italic> compared to <italic>OPRK1</italic> in all tissues examined regardless of species (<italic>p</italic> &lt; 0.001, FDR <italic>p</italic> &lt; 0.001) Cockatiels had less <italic>OPRK1</italic> expression in the cerebrum compared to pigeons (<italic>p</italic> = 0.005, FDR <italic>p</italic> = 0.004). Cockatiels had more <italic>OPRM1</italic> expression in the brainstem (<italic>p</italic> = 0.045, FDR <italic>p</italic> = 0.029), but less <italic>OPRM1</italic> expression in the footpad compared to pigeons (<italic>p</italic> = 0.029, FDR <italic>p</italic> = 0.021). No other significant differences in <italic>OPRM1</italic> or <italic>OPRK1</italic> expression were identified across species. Two missense polymorphisms were identified in <italic>OPRK1;</italic> none were found in <italic>OPRM1.</italic></p></sec><sec><title>Conclusion</title><p>The differential expression of opioid receptors between cockatiels and pigeons could have implications for variability in analgesic response between these two species.</p></sec>