From the labs
Collect CSF for microbiology and cytology first. Obtain samples of cerebrospinal fluid by needle puncture of the dura mater at the foramen magnum before removing the brain from the cranium. Take additional swabs and fresh samples of tissue for microbiology and molecular tests once the brain and spinal cord is exposed before collecting the samples to be fixed.
Collect tissue of a size suitable for histopathology. Ideally pieces should be at least 2-3cm long/wide and no more than 0.5-1cm thick to allow adequate fixative penetration. (Applies to all organs, not just brain). When there are gross lesions, take the sample from the margin so both normal and affected tissue are submitted.
Fix tissues without distortion. The rule of thumb is a volume of formalin 10x the volume of the samples. Don’t put the formalin pots in the fridge or freezer.
If fixing a whole brain, use enough 10% buffered formalin and a sufficiently large histology pot to enable the brain to ‘float’ with the cerebrum resting below – so that the caudal brainstem is not bent or twisted. For cattle use at a least a 2L pot filled to the top with formalin. Fix in formalin at room temperature for at least 3 days.
Packing samples for transport. If tissue wedges have been in formalin for 24 hours before dispatch, the formalin can be drained off and all samples sent in one container (this reduces weight and bulk for safe postage). Don’t let the samples dry out on the bench: wrap them in formalin-soaked gauze and put them into a sturdy screw top container sealed with parafilm or electrical tape. Place the container in a zip-lock bag to contain any spillage that might occur during transport. Then pack in your esky along with the other samples on the core sampling list.
When sending a whole fixed brain, take extra care to ensure the fixed brain can’t be damaged during handling and transport.
Take care with formalin. Use commercial premixed neutral buffered formalin where possible to reduce handling (the mixing of stock solutions) and avoid inadequate fixation of tissues (understrength solutions) or excessive shrinkage and pigment deposits (overstrength solutions).
Formaldehyde is regarded as carcinogenic in humans. Take extreme care with its use and storage. Only use 10% NBF in a well-ventilated area, and wear protective gloves, safety glasses and protective clothing. Minimise your exposure, and that of others, by careful handling and secure packaging of fixed samples.