Selective disturbance of pain sensitivity after social isolation

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Abstract

The effects of social isolation or NMDA-receptor antagonists on pain sensitivity have repeatedly been described. However, the mechanisms underlying the alterations of pain perception in these models still remain a matter of debate. Thus, we aimed to determine the long-lasting effects of subchronic ketamine treatment and social isolation on the C- and Aδ-fiber-mediated nociception. Wistar rats after weaning (21-23 days old) were either housed individually or grouped for 21 days. The animals were treated daily for 14 days with either ketamine (30 mg/kg) or saline. On the 21st day, tail-flick latency was determined at 48 °C (C-fiber activation) and 52 °C (affects mainly Aδ-fibers), and rats were rehoused. Tail-flick test was repeated 2 and 4 weeks later. On the 5th week, carrageenan-induced heat hyperalgesia was determined on paw-withdrawal test before and after morphine treatment (1, 2 or 3 mg/kg). Regarding tail-flick latencies at 48 °C, juvenile isolation, but not ketamine resulted in a significantly enhanced pain threshold (p < 0.001) throughout the investigation period, while the changes at 52 °C were not significant. In addition, both isolation and ketamine treatments enhanced the antihyperalgesic effect of 2 mg/kg morphine. In summary, juvenile isolation exerts a long-lasting effect on acute heat pain sensitivity, disturbing primarily the C-fiber-linked pain pathways, suggesting a selective disruption in the parallel sensory pathways. Since both social isolation and NMDA treatment are well-known animal models of schizophrenia, our results showed that juvenile isolation but not ketamine administration can simulate hypoalgesia associated with this disease.

Original languageEnglish
Pages (from-to)18-22
Number of pages5
JournalPhysiology and Behavior
Volume96
Issue number1
DOIs
Publication statusPublished - Jan 8 2009

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Keywords

  • C-fiber
  • Hyperalgesia
  • Isolation
  • Juvenile
  • NMDA-receptor
  • Nociception
  • Opioid
  • Pain
  • Rat
  • Schizophrenia

ASJC Scopus subject areas

  • Experimental and Cognitive Psychology
  • Behavioral Neuroscience

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