Diversity and development of circadian rhythms in the European rabbit

Three main concerns underlie this review: 1)The need to draw together the w idely dispersed information available on the circadian biology of the rabbi t. Although the rabbit is a classic laboratory mammal, this extensive body of information is often overlooked by chronobiologists, and despite several advantages of this species. In terms of its general biology the rabbit is the best studied laboratory mammal in the wild, it demonstrates a wide vari ety of robust circadian functions, and being a lagomorph, it provides a use ful comparison with more commonly studied rodent species. 2) The need to mo re fully exploit a developmental approach to understanding circadian functi on, and the particular suitability of the rabbit for this. Female rabbits o nly visit their altricial young for a few minutes once every 24 h to nurse, and survival of the young depends on the tight circadian-controlled synchr onization in behavior and physiology of the two parties. Patterns of circad ian rhythmicity in neonatal pups associated with nursing do not form a smoo th continuum into weaning and adult life, and may reflect the action of sep arate mechanisms operating in their own right. 3) Using information from th e first two points, to emphasize the diversity and complexity of circadian rhythms underlying behavioral and physiological functions in adult and deve loping mammals. Information accruing on circadian functions in the rabbit m akes it increasingly difficult to account for these in terms of one or two regulatory mechanisms or "oscillators." Thus, it is argued that in addition to the reductionist, molecular approaches currently dominating much of chr onobiology, the study of circadian systems as emergent characteristics of w hole organisms operating in complex environments merits special attention.