The Journal of Pain
(272) Peripheral nociceptors contribute to oxaliplatin-induced neuropathy J Du, Z Ding, and S Carlton; University of Texas Medical Branch, Galveston, TX A chemotherapeutic agent, oxaliplatin (OXALI), has neurotoxic effects on the peripheral nervous system and treatment in humans causes peripheral neuropathy. Using an animal model, we analyzed changes in peripheral nociceptors to understand their contributions to sensory abnormalities in OXALI-induced neuropathy. Male rats were habituated, baselined for von Frey thresholds and injected (i.p.) with OXALI (or vehicle) once every other day for a total of 4 injections. Two weeks following the first injection, rats were retested for mechanical sensitivity and used to record nociceptors in a skin-nerve preparation. Nociceptors were isolated from the hindpaw plantar nerve, their receptive fields identified and responses to mechanical, heat and cold recorded. The data demonstrated that post-injection, weight gain in OXALI rats was slower compared to vehicle: mean weight gain on 14D was 13.2 6 2.3% above baseline for vehicle-treated but only 8.7 6 2.0% for OXALI-treated. OXALI rats developed mechanical sensitivity evidence by a 75% decrease from baseline in von Frey threshold compared to a 25% decrease in the vehicle group on 14D. Nociceptor recordings showed that spontaneous activity was increased (0.0860.02 imp/s vs 0.7260.11 imp/s, p<0.001). Thermal discharge rate was increased (1.3660.16 imp/s vs 2.4860.29 imp/s, p<0.05), but threshold was not changed (40.5960.56 vs 41.7660.49 Co). Nociceptors developed mechanical sensitivity evidenced by a decreased threshold (108.44 6 18.08 mN vs 85.07 613.57 mN) and increased discharge rate (2.0860.45 imp/s vs 2.3660.36 imp/s) but these did not reach significance. OXALI treatment induced hypersensitivity to cold stimuli evidenced by increased discharge rate to 5 C (1.0660.16 imp/s vs 4.3160.66 imp/s, p<0.001). Thus, the data demonstrate that cold sensitivity reported in humans and rats following OXALI treatment is due, at least in part, to sensitization of peripheral nociceptors. The mechanical sensitivity that develops may be due to neuroplasticity in the CNS with minor contributions from peripheral nociceptors.
(273) The antinociceptive and tolerance effects of methamphetamine and morphine in rats with chronic inflammatory pain M Mehalick, M Cyr, and M Morgan; Washington State University, Vancouver, WA Chronic administration of psychostimulants such as methylphenidate or methamphetamine produce long term changes in response to opioids. For example, newborn rats treated with psychostimulants show enhanced opioid antinociception and tolerance when they become adults. In contrast, adult rats treated with psychostimulants show reduced opioid antinociception and tolerance. These effects in adult rats may be further reduced in chronic pain states because chronic pain causes a reduction in DA receptors and in the antinociceptive effects of psychostimulants. Therefore, the goal of this study was to test the hypothesis that chronic pain blocks the enhanced morphine antinociception and tolerance caused by pretreating rats with psychostimulants. Adult male rats received daily injections of methamphetamine (3 mg/kg, s.c.) or saline for 10 days. Following a two-week wash out period, an i.pl. injection of Freund’s Complete Adjuvant (CFA) or saline was given in the hind paw. Rats were pretreated with morphine (5 mg/kg) or saline twice daily for 2 days to induce tolerance. Cumulative doses of morphine (1.8, 3.2, 5.6, 10, 22 mg/kg) were administered one day later to assess for tolerance development. Pretreatment with methamphetamine had no effect on nociception whether assessed with a mechanical (von Frey) or thermal (hot plate) test. Morphine produced comparable antinociception whether rats were pretreated with methamphetamine and saline. Tolerance was enhanced in non-CFA rats treated with methamphetamine F(3, 152) = 10.43, p < 0.05. In contrast, no tolerance developed in CFA rats treated with methamphetamine F(3, 147) = 0.59, p < 0.05. These results show that morphine tolerance is reduced in rats with chronic pain despite prior methamphetamine exposure. This investigation was supported by NIH grant DA027625. (Cyr & Morgan, Neuropharmacology, 2009.)
Abstracts (274) Diversification of biogenic amines, substance P and neurotrophic factor produces chronic muscular pain and tactile allodynia accompanied by depression – A putative animal model of pain-depression dyad V Arora, A Kuhad, and K Chopra; University Institute of Pharmaceutical Sciences, Panjab University, Chandigarh, India Numerous studies point to the frequent co-morbidity between pain and depression. In clinical practice, depression is often associated with an increased incidence of clinical pain complaints and thus, the co-morbidity of pain and depression has been suggested to be a common phenomenon. This complex interaction is often labeled as Depression-Pain syndrome or Pain-Depression dyad, implying that the condition often coexist and respond to similar treatments, exacerbate one another, and share biological pathways. The biochemical theory of depression-pain dyad posits a neurochemical imbalance of key neurotransmitters: serotonin, norepinephrine, and dopamine along with the disruption in the levels of substance P and nerve growth factor. Thus, the present study was designed to investigate the effect of para-chlorophenylalanine on diversification of biogenic amines (Serotonin, Nor-Epinephrine and Dopamine), Substance P and nerve growth factor on the pain-depression dyad to establish a new rodent model and support the possibility of a relationship and specifically address the neurogenic mechanism that might be involved. The study demonstrates that Pregabalin and duloxetine significantly attenuated the pCPA-induced decrease in mechanical hyperalgesia and mechanical allodynia but not by diclofenac. The validity of the use of this pCPA animal as a Pain-depression model is demonstrated from three different aspects, i.e., face validity (manifestation of chronic pain and depression), construct validity (dysfunction of biogenic amine Substance P and nerve growth factor-mediated central nervous system pain control is involved), and predictive validity (similar responses to treatments used in patients with pain and depression). Conclusively, this rodent model gives an important consideration to 1) an understanding of various neurobiological substrates such as neurotransmitter alterations and different pathways such as Substance P, nerve growth factor to address the common mechanism that resulted in neurophysiologcal overlap between pain and depression; and 2) the proposed model will serve as a screening platform for the mechanism-driven therapeutic interventions.
(275) Intrathecal mesenchymal stem cells reduce the reactive oxygen species and pain behavior in neuropathic rat W Lee, Y Ko, C Song, and E Jang; Chungnam National University Hospital, Daejeon, Chungnam National University, South Korea Neuropathic pain induced by spinal or peripheral nerve injury seldom responds to usual pain killer, nerve block, and other pain managements. Recently several studies using stem cells in animal models suggested the new way to control this refractory and devastating disease. In this study, we have used the spinal nerve ligation model to investigate if intrathecal mesenchymal stem cells (MSCs) were able to decrease the pain behavior in rats and how these cells relate to the reactive oxygen species (ROS). Unilateral L5 ligation method was used to induce pain in left hind paws of rats. Pain behavior (allodynia) was tested on 3, 7, 10, 12, 14, 17, and 24 days after the ligation surgery. MSCs (10ul, 1x105, n=10) or phosphate buffer saline (PBS, 10ul) was injected intrathecally using a micropump into the L5-L6 interspace on 7 days after the surgery. Dihydroethidium, an oxidative fluorescent dye, was used to detect ROS on 24 days after ligation. The overall experimental procedures were performed in accordance with the animal care guideline of the Korean Academy of Medical Science. Results The tight ligation of L5 spinal nerve in the left hind paws of rats induced allodynia after the 3 days of the surgery. Injection of Intrathecal MSCs significantly alleviated the allodynia than intrathecal PBS from 14 days after the surgery (intrathecal post-injection 7 days). ROS expression in the gray matter of lumbar spinal cord was significantly increased on 24 days after surgery. Intrathecal MSCs reduce significantly ROS expression than intrathecal PBS. These results suggest that MSCs may modulate neuropathic pain generation through ROS expression after spinal nerve ligation.