Fig. 6.

Male Sprague Dawley rats received intrathecal infusions of saline or of DAMGO (1 nmol · μl⁻¹ · hr⁻¹) for 7 d. Antinociceptive dose–response functions for intrathecal morphine were generated in the 52°C water tail-flick test 10 min after treatment. The saline- or DAMGO-infused rats received either intrathecal morphine alone or morphine 10 min after intrathecal pretreatment with antiserum to dynorphin A(1–17) (i.e., dynorphin antiserum given 20 min before the test). The following groups were used: naive rats (○), rats infused with saline and challenged with morphine (■), rats infused with saline and challenged with morphine after pretreatment with dynorphin antiserum (▵), rats infused with DAMGO and challenged with morphine (●), and rats infused with DAMGO and challenged with morphine after pretreatment with dynorphin antiserum (▪). Five to 10 separate animals were used for eachpoint on the dose–response curve. i.th., Intrathecal.