Varying Expression of Mu and Kappa Opioid Receptors in Cockatiels () and Domestic Pigeons (.

UNLABELLED

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.

OBJECTIVES

The objectives of this study were to determine the relative gene expression and polymorphisms present for mu and kappa opioid receptors ( and ) in the cerebrum, brainstem, spinal cord, and footpad of cockatiels and pigeons.

METHODS

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 and relative to a reference gene phosphoglycerate kinase 1 ( using the ΔΔCt method. Sanger sequencing was performed to identify polymorphisms, if present.

RESULTS

There were higher expression levels of compared to in all tissues examined regardless of species ( < 0.001, FDR < 0.001) Cockatiels had less expression in the cerebrum compared to pigeons ( = 0.005, FDR = 0.004). Cockatiels had more expression in the brainstem ( = 0.045, FDR = 0.029), but less expression in the footpad compared to pigeons ( = 0.029, FDR = 0.021). No other significant differences in or expression were identified across species. Two missense polymorphisms were identified in none were found in

CONCLUSION

The differential expression of opioid receptors between cockatiels and pigeons could have implications for variability in analgesic response between these two species.