Studies in vivo with dynorphin-(1-9): Analgesia but not gastrointestinal effects following intrathecal administration to mice

Direct administration of dynorphin-(1-9) (10-100 μg) into the spinal subarachnoid space of mice produced a dose-related analgesic effect at 5 and 10, but not 35 min, in the tail-flick test using hot water as the nociceptive stimulus. By contrast, the same doses did not affect gastrointestinal transit at 5, 10, 15 or 35 min after injection. These results suggest that dynorphin-(1-9) is similar in this endpoint to ketazocine-type κ opioid agonists in naive animals while confirming that intrathecal administration of dynorphin is analgesic in mice.