Each animal was initially sedated with an i.m. injection of 12 mg kga??1 alfaxalone (Alfaxan; Jurox Pty Ltd, Rutherford, NSW, Australia) and 3 mg kga??1 diazepam (Mayne Pharma, Mulgrave, VIC, Australia). We then gave preoperative intramuscular injections of 0.2 mg kga??1 atropine (AstraZeneca, NorthRyde, NSW, Australia), to reduce lung secretions, and dexamethasone (0.3 mg kga??1; Mayne Pharma), to reduce inflammation. Subsequent surgery was performed under supplemental local anaesthesia (lignocaine 2 ; AstraZeneca). A femoral vein was cannulated, the trachea exposed and an endotracheal tube inserted, and the head was placed in a stereotaxic frame.