Alterations in Hippocampal Neurogenesis and Pain Behavior in Mice: An Experimental Study

Abstract

As living condition has been shown to affect rates of neurogenesis, the current study was designed to examine the relationship between neurogenesis and pain behavior, particularly stress-induced analgesia (SIA) and tonic pain. Mice received daily injection stress and were placed in group or isolated housing conditions, with or without access to a running wheel in order to differentially manipulate neurogenesis. Both males and females were used in this study to investigate sex differences involved. Animals were tested with hotplate and tail withdrawal tests before and after restraint stress to examine SIA (experiment 1), and with a subcutaneous formalin injection to assess changes in tonic pain—particularly in the late phase (experiment 2). Group housed runners were expected to have increased neurogenesis, decreased SIA and increased late phase formalin pain; however, findings did not support this hypothesis. In experiment 1, significant differences in overall acute pain were observed, depending on housing and running. In experiment 2, overall formalin pain behavior was influenced by housing, while running differentially influenced pain behaviors in each phase. Significant changes in neurogenesis were not observed, which--along with a number of confounding variables--may have influenced inconsistent findings.