Effect of Phe-Phe amide (2 pmol, i.t.) on the mechanical threshold in diabetic and non-diabetic mice. The nociceptive threshold was determined by a von Frey filament test 30 min after dipeptide injection. (+)-Pentazocine [(+)PTZ, 10 nmol, i.t] was administered 10 min prior to the injection of Phe-Phe amide. Each point represents the mean with S.E.M. for 7-11 mice. *P < 0.05 vs. respective before-treatment group; #P < 0.001 vs. vehicle-pretreated group (Bonferroni test).