A primate model for the study of tonic pain, pain tolerance and diffuse noxious inhibitory controls

Pharmacological comparison of a nonhuman primate and a rat model of oxaliplatin-induced neuropathic cold hypersensitivity

Oxaliplatin is a first‐line treatment for colorectal cancer. However, shortly following treatment, cold‐evoked hypersensitivity appears in the extremities and over time, the pain is such that oxaliplatin dosing may need to be markedly reduced or even terminated. There is currently a lack of efficacious treatments for oxaliplatin‐induced peripheral neuropathy, which is due in part to the difficulty in translating findings obtained from preclinical rodent models of chemotherapy‐induced peripheral neuropathy. Nonhuman primates (NHP) are phylogenetically closer to humans than rodents and may show drug responses that parallel those of humans. A significant decrease in tail withdrawal latency to 10°C water (“cold hypersensitivity”) was observed beginning 3 days after intravenous infusion of oxaliplatin (5 mg/kg) in Macaca fascicularis. A single treatment of duloxetine (30 mg/kg, p.o.) ameliorated oxaliplatin‐induced cold hypersensitivity, whereas pregabalin (30 mg/kg, p.o.) and tramadol (30 mg/kg, p.o.) did not. By contrast, in rats, no significant cold hypersensitivity, or increased responsiveness to acetone applied to the hind paws, was observed 3 days after the first injection of oxaliplatin (5 mg/kg, i.p., once per day, two injections). Therefore, rats were tested after six treatments of oxaliplatin, 17 days after the first treatment. All analgesics (30 mg/kg, p.o.) significantly ameliorated cold hypersensitivity in rats. The activity of analgesics in the oxaliplatin‐treated macaques parallel clinical findings. The current results indicate that the NHP could serve as a bridge species to improve translatability of preclinical findings into clinically useful treatments for oxaliplatin‐induced peripheral neuropathy.

Effects of noxious cooling of the skin on pain perception in man

By means of somatosensory evoked brain potentials following painful CO2 laser stimulation (pain SEPs) and a pain visual analogue scale (VAS), we investigated changes in pain perception caused by noxious cooling of the skin in normal subjects. Pain SEPs were recorded from scalp electrodes following laser stimulation applied to the leg under various conditions as follows: (1) control (without any interference); (2) 46 degrees C foot (dipping the foot ipsilateral to the stimulated leg in hot water at 46 degrees C); (3) 0 degrees C foot (dipping the foot ipsilateral to the stimulated leg in ice water at 0 degrees C); and (4) 0 degrees C hand (dipping the hand contralateral to the stimulated leg in ice water at 0 degrees C). Marked decreases in amplitude of pain SEPs and VAS were observed under all conditions as compared with the control (P < 0.001); the degree of pain relief was significantly correlated with changes in pain SEPs. These changes were greatest in the '0 degrees C hand' condition, followed in decreasing order by '0 degrees C foot' and '46 degrees C foot', and there was a significant difference between '0 degrees C hand' and the '46 degrees C foot' condition. We considered that the decrease in pain is due to the diffuse noxious inhibitory control (DNIC). The reason why the degree of pain relief in '0 degrees C foot' condition was less than that in '0 degrees C hand' condition is unclear, but some particular spatial summation of two kinds of nociceptive impulses mediated by the same pathway might take place.

Diffuse noxious inhibitory control. Reappraisal by pain-related somatosensory evoked potentials following CO2 laser stimulation

The effects of DNIC (diffuse noxious inhibitory control) in humans were evaluated by means of pain SEPs (somatosensory evoked potentials) and pain visual analogue scale (VAS) following CO2 laser stimulation applied to the left knee while conditioning stimuli (non-noxious and noxious thermal stimuli) applied to the right hand. Pain SEPs were recorded from scalp electrodes following laser stimulation applied to the left knee during various conditions as follows: (1) control (without any interference), (2) non-noxious (dipping the right hand in water at 41 degrees C for 3 min), (3) noxious (dipping the right hand in water at 46 degrees C for 3 min), and (4) after-effect (3-6 min after taking the hand from the water at 46 degrees C). The present pain SEPs findings confirmed the presence of DNIC in humans, and indicates: (1) degree of pain relief was significantly correlated with changes in pain SEPs, particularly a marked decrease in amplitude, and a decrease in VAS; (2) DNIC was more effective on the second pain than the first pain; (3) the effect of DNIC gradually increased over time, but it rapidly disappeared after the conditioning stimuli ceased; and (4) DNIC was not due merely to changes of attention. I propose that the site responsible for DNIC is the brainstem or the spinal cord rather than the cerebral hemisphere.

Deep brain stimulation: a review of basic research and clinical studies

Deep brain stimulation for pain control in humans was first used almost 30 years ago and has continued to receive considerable attention. Despite the large number of clinical reports describing pain relief, numerous studies have indicated that the results of these procedures vary considerably. In addition, many neurosurgeons find the procedures unpredictable, and considerable disagreement still exists regarding important issues related to the technique itself. This review gives an historical overview of the relevant basic and clinical literature and provides a critical examination of the clinical efficacy, choice of stimulation sites, parameters of stimulation, and effects on experimental pain. Finally, we give suggestions for future research that could more definitively determine the usefulness of deep brain stimulation for pain control.