at the spinal level , nociception is relayed in the dorsal horn , where opioid peptides as well as all types of opioid receptors are abundant . mu-opioid receptor-mediated anti-nociceptive processes appear to be most important in this region , but sigma-opioid receptors may also be involved .
C0034801
opioid receptors
C0074504
sigma-opioid receptors