Persistent hyperalgesia in the cisplatin-treated mouse as defined by threshold measures, the conditioned place preference paradigm, and changes in dorsal root ganglia activated transcription factor 3: the effects of gabapentin, ketorolac, and etanercept

Abstract

Background: Painful neuropathy is a dose-limiting side effect in cancer chemotherapy. To characterize this phenomenon, we examined pain behavior and analgesic actions in a mouse model of cisplatin polyneuropathy.

Methods: Male C57BL/6 mice received intraperitoneal cisplatin or saline (2.3 mg/kg/d) every other day 6 times over 2 weeks for a total dose of 13.8 mg/kg. Thermal escape latencies, mechanical allodynia using von Frey hairs, and observation of behavior/morbidity and body weights were assessed. After onset of allodynia, we examined the actions of intraperitoneal gabapentin (100 mg/kg), etanercept (20 and 40 mg/kg), ketorolac (15 mg/kg), and morphine (1, 3, and 10 mg/kg). Additionally, using the conditioned place preference (CPP) paradigm, we examined the effects of gabapentin and ketorolac on the presumed pain state initiated by cisplatin. Additionally, we examined the spinal cord and dorsal root ganglia (DRG) of cisplatin-treated mice.

Results: Cisplatin, but not saline treatment, produced persistent hindpaw tactile allodynia, which persisted 46 days with no effect on thermal escape. Gabapentin and morphine, but neither etanercept nor ketorolac, produced a complete but transient (2-hour) reversal of the allodynia. Etanercept (40 mg/kg) pretreatment resulted in a delay in onset of mechanical allodynia. Using CPP, gabapentin, but not ketorolac, in cisplatin animals resulted in a significant preference for the drug-associated treatment compartment. There was no place preference in non-cisplatin-treated (nonallodynic) mice after gabapentin injection. Immunohistochemistry in cisplatin-treated mice showed no change in glial fibrillary acidic protein (astrocyte) or Iba1 (ionized calcium binding adaptor molecule 1) (microglia) activation states, but a significant increase in activated transcription factor 3 was observed in the DRG.

Conclusions: Cisplatintreated mice display allodynia and an activation of DRG activated transcription factor 3, which is paralleled by its effects on behavior in the CPP system, wherein gabapentin, but not ketorolac, in the presence of the cisplatin polyneuropathy, is positively rewarding, confirming that this neuropathy is an aversive (painful) state that is ameliorated by gabapentin.

Fig. 1

A. Figure presents the tactile threshold plotted vs. time after the initiation of cisplatin or saline treatment (six i.p. injections, one every other day). B. Thermal escape latencies measured before and at 29 days after the initiation of cisplatin or vehicle treatment. C. Changes in body weight of cisplatin-injected mice and vehicles plotted vs. time after the initiation of cisplatin or vehicle treatment. Results are presented as mean ± standard error (n = 6 in each group) (^*P < .05, ^****P < .0001).

Fig. 2

Figure plots tactile thresholds in the cisplatin-induced neuropathic mice before and after injection of gabapentin (100 mg/kg, A), ketorolac (15 mg/kg, B), and morphine (1, 3, and 10 mg/kg, C). Results are presented as mean ± standard error (n = 4–6 per group) (^*P < .05, ^**P < .01, ^****P < .0001).

Fig. 3

Figure plots effects of etanercept for posttreatment on tactile thresholds in the cisplatin-induced neuropathic mouse. A. Mouse received posttreatment etanercept (20 or 40 mg/kg, i.p.) or vehicle 15 days after initiation of cisplatin. B. Mouse received pretreatment with etanercept (40 mg/kg, i.p.) immediately before the initiation of cisplatin injections. Results are presented as mean ± standard error (n = 4–6 per group) (^*P < .05, ^**P < .01, ^****P < .0001).

Fig. 4

Figure presents time spent in the drug (saline-control, gabapentin or ketorolac) paired chamber in the conditioned place preference (CPP) paradigm. (A) Animals that were cisplatin-treated (allodynic) underwent CPP with gabapentin (100 mg/kg, i.p.) or ketorolac (15 mg/kg, i.p.). (B) Animals that were noncisplatin-treated (nonallodynic) underwent CPP with gabapentin (100 mg/kg, i.p.). Results are presented as mean ± standard error (n = 5–7 per group) (^*P < .05)

Fig. 5

Figure presents spinal immunohistochemistry of A, B: microglia (Iba1) or C,D: astrocyte (GFAP) in spinal dorsal horn of saline (control) or cisplatin-treated mice harvested 30 days after initiation of treatment. E,F: Quantification of immune-staining intensity for Iba1 and GFAP staining in dorsal horn of cisplatin mice. As indicated intensity was numerically increased slightly, but change was not statistically significant as compared to control group (n = 6–7 per group). Scale bars represent 100 μm.

Fig. 6

Figure presents immunohistochemistry for Activated Transcription Factor 3 (ATF3) (+) cell in the dorsal root ganglia (DRG) of control and cisplatin-treated mice at 30 days after initiation of treatment. A: In control animals ATF3(+) cells were few if not absent. B: In contrast, ATF3 staining was increased markedly in cisplatin-treated mice. C: In animals harvested 30 days after initiation of cisplatin treatment showed significant activation of neuronal ATF3 as compared to control group (n = 4–5 per group) (*P < .05). Scale bars represent 100 μm. Arrows indicate ATF3 (+) cells.