Spinal ERK2 activation through δ 2-opioid receptors contributes to nociceptive behavior induced by intrathecal injection of leucine-enkephalin.

Highlights: [•] Nociceptive behavior was not observed in mice treated with i.t. Leu-ENK alone. [•] Leu-ENK co-injected with peptidase inhibitors evoked nociceptive behaviors. [•] Leu-ENK co-injected with peptidase inhibitors evoked activation of spinal ERK2. [•] The nociceptive behavioral response was evoked through spinal δ 2-opioid receptor. [Copyright &y& Elsevier]