Detection of Neuropathic Pain in a Rat Model of Peripheral Nerve Injury

Abstract

Simple withdrawal from von Frey tactile stimulation, although frequently used, is not a valid measure of peripheral nerve injury pain in rats, whereas a complex hyperalgesic-type response is a specific neuropathy-induced behavior.

Opposing effects of spinal nerve ligation on calcium-activated potassium currents in axotomized and adjacent mammalian primary afferent neurons

“…Small cells were dissociated from rats with SNL (n=10) exhibiting 39.1±23.5% hyperalgesic response rates and sham-operated rats (n=4) with 0±0% hyperalgesic response rates (Mann Whitney U = 0, p=0.002). Hyperalgesic responses were sustained paw lifting, shaking and licking in response to nociceptive mechanical stimulation (application of the tip of a 22 gauge spinal needle) [33].…”

“…Selection of rats suitable for further tissue harvesting was performed after behavioral testing as previously described [33]. In order to become familiar with the testing procedures and environment, rats were brought to the testing area for 4 hours or more, at least one day after arrival at the animal care facility.…”

“…Only SNL rats with an ipsilateral hyperalgesic response (at least 20% averaged over 3 test days) and normal contralateral responses, as well as SS rats with normal bilateral responses were used for study. Hyperalgesic response rates were calculated as described previously [33], and compared between SNLoperated and skin sham operated rats that were included in the study by Mann-Whitney nonparametric test.…”

Painful Nerve Injury Shortens the Intracellular Ca2+ Signal in Axotomized Sensory Neurons of Rats

“…16 At least 1 day after arrival at the animal care facility, rats were brought to the testing area for 4 h of familiarization with handling and the environment. Hind paws were stimulated in random order with a 22-gauge spinal needle applied with pressure adequate to indent but not penetrate the plantar skin 2 days before surgery and on the 10th, 12th, and 14th postoperative days.…”

Mode of Action of Spinal Cord Stimulation in Neuropathic Pain

“…Only in rare cases of very pronounced hypersensitivity can shaking and lifting of the paw, without being peripherally stimulated, occasionally be observed, and this could be a sign of spontaneous pain. 17 Considering that in humans, injury to peripheral nerves only occasionally gives rise to evoked and/or spontaneous pain, it is not unexpected that experimental nerve injury in rats does not always result in painful hypersensitivity. Furthermore, chronic neuropathic pain due to nerve injury in patients is associated with cutaneous, mechanical hypersensitivity in only 20%--40% of cases.…”