Not all 'predator odours' are equal: cat odour but not 2,4,5 trimethylthiazoline (TMT; fox odour) elicits specific defensive behaviours in rats.

The behavioural responses to two commonly used 'predator odours' were assessed in male Wistar rats. Cat odour was presented to rats in the form of a piece of collar that had been worn by a domestic cat. Fox odour was presented in an equivalent piece of (unworn) collar that had been impregnated with 2,4,5 Trimethylthiazoline (TMT)-an extract of fox faeces. Other rats were exposed to collars containing Triethylamine (TEA), a putrid fishy smell, or formaldehyde, which has an acrid irritating smell. Experiment 1 showed that rats approached cat odour, TMT and TEA significantly less than they did an unworn collar. However, only cat odour increased retreat to the hide box, reduced locomotor activity and elicited 'head out' behaviour. When tested immediately after odour exposure, only cat odour exposed rats showed increased anxiety in the elevated plus maze and suppressed activity in a 90-min general activity test. When returned to the odour-paired environment 24 h later in the absence of test odours, only rats that had previously received cat odour showed evidence of conditioned fear. Experiment 2 showed that rats given the benzodiazepine drug midazolam (0.5 mg/kg) display increased approach and decreased defensiveness towards a cat odour impregnated collar. In contrast, midazolam accentuated the avoidance of TMT and formaldehyde containing collars. Experiment 3 showed that when cat odour was presented in a small, enclosed environment, rats display increased body immobility, decreased grooming and increased orientation towards the odour-exuding stimulus. These responses were not seen with TMT or TEA containing collars. Taken together, these results suggest that while cat odour strongly elicits specific defensive behaviours in rats, TMT has effects that are more characteristic of an aversive odour. We suggest that the results of some previous studies using TMT may need to be reassessed.