**1. Introduction**

"Oh dear! Oh dear! I shall be too late". The White Rabbit in Alice's Adventures in Wonderland, Lewis Carroll (1865) [1].

### **1.1 The rabbit as a model species in mammalian chronobiology**

Timing is clearly of the essence in many aspects of the European rabbit's behavioural biology and contributes importantly to this species' proverbial reproductive success. The European rabbit *Oryctolagus cuniculus*, the ancestor of all domestic breeds, has been widely used in the study of mammalian chronobiology. Consistent with various well-studied rodent models, such as the white rat (*Rattus norvegicus*) and the golden hamster (*Mesocricetus auratus*), the rabbit shows circadian (or at least diurnal) rhythmicity in several important behavioural and physiological functions. These include

motor activity, feeding, drinking, urination, and defecation, as well as haematological parameters, serotonin concentration in the brainstem, content and absorption of volatile fatty acids in the alimentary tract, visual evoked potentials, and intraocular pressure (review in [2]). In addition, due to the rabbit's abundance, size, and importance as an agricultural pest, it is one of the best-studied laboratory mammals in the wild.

Under natural conditions, the rabbit is a primarily nocturnal or crepuscular species, which is most active during the night with peaks in activity levels at dawn and dusk (in nature: [3–5]; in the laboratory: [6, 7]). Aschoff's rule states that the endogenous free-running circadian period observed in complete darkness (DD) will shorten for diurnal animals and lengthen for nocturnal animals when they are exposed to constant light [8]. Rabbits typically show free-running rhythms in several functions that lengthen in accordance with Aschoff's rule when they are transferred from DD to LL [9]. Furthermore, the phase-response curve of the rabbit's daily pattern of wheel-running activity in response to brief 1-hour light pulses [10] conforms to classic phase-response curves reported for nocturnal rodents [11].
