Nociception and conditioned fear in rats: strains matter

PLoS One. 2013 Dec 23;8(12):e83339. doi: 10.1371/journal.pone.0083339. eCollection 2013.

Abstract

When using rats in pain research, strain-related differences in outcomes of tests for pain and nociception are acknowledged. However, very little is known about the specific characteristics of these strain differences. In this study four phylogenetically distant inbred rat strains, i.e. Wistar Kyoto (WKY), Fawn Hooded (FH), Brown Norway (BN) and Lewis (LE), were investigated in different tests related to pain and nociception. During Pavlovian fear conditioning, the LE and WKY showed a significantly longer duration of freezing behaviour than the FH and BN. Additionally, differences in c-Fos expression in subregions of the prefrontal cortex and amygdala between rat strains during retrieval and expression of conditioned fear were found. For example, the BN did not show recruitment of the basolateral amygdala, whereas the WKY, FH and LE did. During the hot plate test, the WKY and LE showed a lower thermal threshold compared to the BN and FH. In a follow-up experiment, the two most contrasting strains regarding behaviour during the hot plate test and Pavlovian fear conditioning (i.e. FH and WKY) were selected and the hot plate test, Von Frey test and somatosensory-evoked potential (SEP) were investigated. During the Von Frey test, the WKY showed a lower mechanical threshold compared to the FH. When measuring the SEP, the FH appeared to be less reactive to increasing stimulus intensities when considering both peak amplitudes and latencies. Altogether, the combined results indicate various differences between rat strains in Pavlovian fear conditioning, nociception related behaviours and nociceptive processing. These findings demonstrate the necessity of using multiple rat strains when using tests including noxious stimuli and suggest that the choice of rat strains should be considered. When selecting a strain for a particular study it should be considered how this strain behaves during the tests used in that study.

MeSH terms

  • Amygdala / physiology
  • Animals
  • Conditioning, Psychological
  • Evoked Potentials, Somatosensory / physiology*
  • Fear / physiology*
  • Fear / psychology
  • Freezing Reaction, Cataleptic / physiology
  • Gene Expression
  • Male
  • Nociception / physiology*
  • Pain Threshold / physiology*
  • Pain Threshold / psychology
  • Prefrontal Cortex / physiology
  • Proto-Oncogene Proteins c-fos / genetics
  • Rats
  • Rats, Inbred BN
  • Rats, Inbred Lew
  • Rats, Inbred WKY
  • Species Specificity

Substances

  • Proto-Oncogene Proteins c-fos

Grants and funding

The authors have no support or funding to report.