Lack of paclitaxel effects on intracranial self-stimulation in male and female rats: comparison to mechanical sensitivity.

Paclitaxel is a cancer chemotherapy with adverse effects that include peripheral neuropathy, neuropathic pain, and depression of behavior and mood. In rodents, hypersensitive paw-withdrawal reflexes from mechanical stimuli serve as one common measure of paclitaxel-induced pain-related behavior. This study tested the hypothesis that paclitaxel would also depress rates of positively reinforced operant responding as a measure of pain-related behavioral depression. Male and female Sprague-Dawley rats were equipped with electrodes targeting the medial forebrain bundle, trained to lever press for electrical brain stimulation in an assay of intracranial self-stimulation (ICSS), and treated with four injections of varying paclitaxel doses (0.67, 2.0, or 6.0 mg/kg/injection×4 injections on alternate days). Mechanical sensitivity, body weight, and ICSS were evaluated before, during, and for 3 weeks after paclitaxel treatment. Paclitaxel doses sufficient to produce mechanical hypersensitivity did not reliably depress ICSS in male or female rats. Moreover, the degree of behavioral suppression in individual rats did not correlate with mechanical sensitivity. Paclitaxel treatment regimens commonly used to model chemotherapy-induced neuropathic pain in rats are not sufficient to depress ICSS.