Table 1. Primer set sequences for RT-PCR used in this study.
| Gene | Forward primer (5´ to 3´) | Reverse primer (5´ to 3´) | Product size (bp) | GeneBank accession ID |
| Pdyn | GTTCCCTGTGTGCAGTGAGGAC | TAGCGTTTGGCCTGTTTTCTCA | 418 | NM_019374.3 |
| Oprk1 | GATGTCATTGAATGCTCCTTGC | CAGGATCATCAGGGTGTAGCAG | 138 | NM_017167.2 |
| Actb | TGTCACCAACTGGGACGATA | GGGGTGTTGAAGGTCTTCAAA | 165 | NM_031144.3 |