Related Experiment Video
Updated: Oct 9, 2025
Early Pathological and Magnetic Resonance Detection of Cerebral Injury Using a Rat Model of Neonatal Hypoxic Ischemic Encephalopathy
Published on: October 28, 2022
Deleterious Effect of Crossfostering in Rat Pups on Hypoxic-Ischaemic Injury Tolerance and Hypothermic
Julia K Gundersen1, David A Menassa1,2, Thomas R Wood1,3
1Institute of Basic Medical Sciences, Department of Physiology, University of Oslo, Oslo, Norway.
Insights
Crossfostering rat pups significantly increased brain injury and reduced the effectiveness of hypothermia (HT) neuroprotection. This common practice may invalidate research findings if not accounted for, impacting animal research principles.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Animal Models
Background:
- Hypothermia (HT) is a neuroprotective treatment for hypoxic-ischaemic (HI) brain injury.
- Crossfostering is a common practice in animal breeding facilities.
- The impact of crossfostering on HI injury models and HT neuroprotection is not well understood.
Purpose of the Study:
- To investigate the effect of crossfostering on injury susceptibility in a rat model of HI brain injury.
- To determine if crossfostering influences the efficacy of hypothermia-induced neuroprotection.
Main Methods:
- Analyzed 219 postnatal day 7 (P7) rat pups from experiments conducted between 2013-2015.
- Compared outcomes between crossfostered and non-crossfostered pups subjected to HI insult and randomized to normothermia or HT.
- Assessed brain injury via hemisphere area loss and histopathology; microglial reactivity was also examined.
Main Results:
- Crossfostered pups exhibited double the brain injury compared to non-crossfostered pups.
- Hypothermic neuroprotection was less effective and less consistent in crossfostered pups (16% vs. 31% relative neuroprotection).
- No significant difference in microglial reactivity was observed between groups.
Conclusions:
- Crossfostering significantly alters outcomes in HI brain injury models, increasing injury and reducing neuroprotection efficacy.
- This common breeding practice is an unexplored variable that can lead to invalid research conclusions.
- Crossfostering may conflict with the principles of replacement, reduction, and refinement in animal research.
Abstract:
We study the effect of hypothermia (HT) following hypoxic-ischaemic (HI) brain injury in postnatal day 7 (P7) rats. In 2015, new European Union animal transport regulations prompted a change in practice at the breeding facility, which henceforth crossfostered P3 litters to P8 older lactating dams prior to transportation. It is generally assumed that crossfostering does not significantly affect the experimental results. The aim of this study was to examine whether crossfostering affects our model consistency by modifying injury susceptibility and hypothermic neuroprotection. We analysed 219 pups from 11 experiments conducted between 2013 and 2015: 73 non-crossfostered and 146 crossfostered pups. At P7, all pups underwent unilateral common carotid artery ligation followed by 50 min of hypoxia (8% O2, 36°C). Immediately after this mild insult, the pups were randomized to post-insult normothermia or HT treatment. Pups were culled at P14. Injury was assessed by area loss of the ipsilateral hemisphere and histopathology scoring of the hippocampus, cortex, thalamus, and basal ganglia. Crossfostered pups had double the injury compared to non-crossfostered pups irrespective of the treatment group. Hypothermic neuroprotection was statistically significant, but with a smaller and less consistent effect in crossfostered pups (relative neuroprotection 16% vs. 31% in non-crossfostered). These results demonstrate hypothermic neuroprotection following a mild HI insult. A representative subset of 41 animals was also assessed for evidence of microglial reactivity; however, no detectable difference in microglial reactivity was observed between any of the groups. In conclusion, crossfostering alters outcomes in our established model through reduced insult tolerance and variable neuroprotection. Crossfostering as a common breeding practice is a largely unexplored variable in animal research that may result in invalid research conclusions if inadequately adjusted for by larger group sizes. As a result, crossfostering is likely to be inconsistent with the principles of replacement, reduction, and refinement.
