Figure 4.

Acute DOP receptor antagonist injection suppressed the antiallodynic effect of nortryptiline treatment in KOP^+/+ and KOP^−/− mice. After at least 2 weeks of antidepressant or saline treatment, the animals received an injection of the DOP receptor antagonist naltrindole (5 mg·kg⁻¹, s.c.) or its control saline solution. The mechanical threshold was measured before and 30 min after injection. (A) While acute saline injection did not change the paw withdrawal threshold, naltrindole induced a relapse of mechanical allodynia in neuropathic KOP^+/+ mice treated with nortriptyline. No effect of naltrindole or saline was seen in sham mice or in saline-treated neuropathic animals. (B) Similar results were obtained in KOP^−/− mice. Data are expressed as mean ± SEM, n (number of animals) are given in parentheses.