Group housing of rodents is normally considered best practice, but a number of practical problems arise when rodents are fitted with cranial implants for measurements of neuronal activity in the brain. There are at present few guidelines available on how to house such animals. Norecopa collected anecdotal evidence from members of the international discussion forum CompMed in March 2019. The comments below are not necessarily the views of all CompMed members, nor are they necessarily best practice, but they are presented here in the hope that they will stimulate further refinement (and publication) of methods of housing these rodents:

• 'We have many implanted mice in our facility. We have several times attempted to group house animals which knew each other, but after some unfortunate incidents we decided to give up. The scientists did not want to take the risk of having to interrupt chronic studies, since we could not guarantee that the group housing would be successful. The same applies to rats, but some scientists have from time to time attempted to house implanted sibling rats in pairs. They have to watch them closely for the first few hours. This has worked well sometimes, but not always. To try and avoid complications, either for single-housed or group-house mice, we do the following:
  • We use cages without grids: UNO-cages with high plastic lids, or Tecniplast Blueline cages without grids.
  • The food is placed on the floor, we change it twice a week.
  • The UNO cages are not ventilated, so they are placed on shelves behind sliding curtains.
  • The Blueline cages are a bit too narrow for exercise wheels. We are on the lookout for better cage systems, but we have had problems finding one that is optimal both for the mice and the technicians.
  • We put exercise wheels in all cages. We use Datesand's polycarbonate igloos with a "saucer-wheel" on the top. The mice use them a lot. To avoid the implants getting stuck in the igloo, we block the entrance by putting an upside-down saucer inside.
  • We avoid using houses in the cage, but give them lots of nesting material. They have no problems making somewhere to hide out of this material.
  • We are testing different nesting materials. Cottonwool tampons seem to function well, since the implants do not get entangled in them as much as in other materials. The only problem is that the material is not compatible with our bedding handling equipment, so we have to remove it manually when we change cages.
  • We avoid using hammocks or "balconies" in the cages when housing implanted mice.'
• 'We've started to do that here with very few problems. The tricks seem to be to pair animals first to determine compatibility, to do the surgery on both animals at the same time, and to provide lots of nesting material. Our animals don't seem to be interfering with each other's implants at all.'
• 'I haven’t seen literature on the subject, but here’s something on epilepsy models (section 3.7 specifically addresses social housing).'
• 'We’re also venturing into rats, which worried me at first, but again, I think the instant feedback from the buddy ("don't do that, it hurts") makes it go better than one would expect with socially grooming animals.'
• 'I do not have literature references but we do have a fair amount of experience successfully co-housing implanted mice. You have to take it on a case by case basis. Some implants lend themselves better to co-housing than others. We have investigators who routinely co-house animals with simple headbars as well as fibre implants. Some take care to include outer caps or wraps to avoid there being anything that can easily catch on other implants or items in the cage. We are careful to include enrichment and housing items that also won’t interfere with the implants. We have not had animals chew on or disrupt each other’s implants, though I know that is a concern. The worst we have seen is the arm of an implant get caught in an ear tag of a cagemate. They were separated and no further concerns arose, but that could have been a problem. Overall, we encourage folks to at least explore the feasibility for their individual hardware.'

Do you have advice or publications of relevance to this subject? Please send them to Norecopa and we will add them to this page.

Literature

• Assessing the safety and suitability of nesting material for singly housed mice with surgically fitted head plates (Windsor & Bate, 2019)