Catnip and oestrous behaviour in the cat.

Wild animal hunters and photographers have long taken advantage of the attraction that catnip holds over members of the cat family, while domestic cat owners purchase dried catnip leaves for use as a rejuvenator and exerciser that will bring old cats to new life. Indeed, when cats have the leaves placed near them, they immediately approach, sniff, and shortly thereafter rub their faces into the leaves and roll back and forth over them. The first group to take any scientific interest in the phenomenon were chemists, who concentrated on isolating the aromatic component that causes the reaction. It had been assumed and was subsequently verified by Todd (1963), that the odour and not the taste of the catnip causes the response. Catnip (Nepeta cataria) or catmint, is a member of the mint family and grows wild over a large area of America and Europe. By distilling the crushed plant to obtain the volatile oil, fractionating this into its constituents and testing with both African lions and domestic cats, an unsaturated lactone, trans-cis nepetalatone, was identified as the active ingredient (McElvain, Bright & Johnson, 1941 ; McElvain, Walters & Bright, 1942; Bates & Sigel, 1963). This type of chemical analysis, however, does not explain why the substance elicits the reaction. A possible answer was not suggested until Todd (1962) studied the inheritance of the catnip response. He had observed that only a proportion of cats reacted to catnip, and through controlled breeding experiments found that the predisposition to respond was inherited as a dominant autosomaI gene. It was during the course of these investigations that he incidentally observed that the rolling pattern of the catnip reacting cat was strikingly similar to some aspects of female oestrous behaviour (Todd, 1963). On the strength of this observation Todd suggested that the catnip odour might be related to oestrus in some way, perhaps resembling a sex odour or pheromone.