Sex Differences in Behavioral Circadian Rhythms in Laboratory Rodents

Abstract

There is a strong bias in basic research on circadian rhythms toward the use of only male animals in studies. Furthermore, of the studies that use female subjects, many use only females and do not compare results between males and females. This review focuses on behavioral aspects of circadian rhythms that differ between the sexes. Differences exist in the timing of daily onset of activity, responses to both photic and non-photic stimuli, and in changes across the lifespan. These differences may reflect biologically important traits that are ecologically relevant and impact on a variety of responses to behavioral and physiological challenges. Overall, more work needs to be done to investigate differences between males and females as well as differences that are the result of hormonal changes across the lifespan.

Neuroendocrine underpinnings of sex differences in circadian timing systems

“…A review of sex differences in rodent circadian behaviors, including period, responses to external stimuli, and anticipatory behaviors, indicates that the most apparent sex difference in behavior is in the timing of activity onset [66]. Daily variation of activity onset is closely related to the phase of estrous cycle in females; males are similarly variable in activity onset when tested on 4 consecutive days though the causes of male variability are not known [67].…”

How does sex matter? Behavior, stress and animal models of neurobehavioral disorders

“…Indeed, the analysis of non reproductive behavior of several mammalian species show sex differences in infant play, aggression, learning, exploration, activity level, behavioral circadian rythms, food intake and preference, novelty seeking, impulsivity, emotional behavior, cognitive ability and many more (Archer, 1975;Brain et al, 1991;Palanza, 2001;Alexander and Hines, 2002;Dalla and Shors, 2009;ter Horst et al, 2012;Lonsdorf et al, 2014;Argue and McCarthy, 2015;Krizo and Mintz, 2014;Fukushima et al, 2015;Carroll and Smethells, 2015) However, sex differences are not identical across species, as they depends upon specific, socio-ecological selective pressures that had acted during evolution. For example in laboratory rats and mice, females are more active and less anxious in several tests than males, but such a sex difference varies depending upon context, strain and age (Johnson and File, 1991;Palanza et al, 2001;An et al, 2011;ter Horst et al, 2012;Gioiosa et al, 2007Gioiosa et al, , 2013, while in other species of rodents, such as meadow voles, males are more active than females (Perrot-Sinal et al, 2000).…”

Oestradiol Exposure Early in Life Programs Daily and Circadian Activity Rhythms in Adult Mice

“…Gonadal hormones modify the timekeeping system during development and in adulthood. There are sex differences in chronobiology in humans, as well as laboratory animals and insects , including the free‐running period , the time of activity onset , the quantity of total activity and the response to photic cues , as well as altered daily and circadian rhythm activity after oestrogen receptor modification . These sex differences are modulated, in part, by the circulating hormones in sexually mature animals.…”

“…These sex differences are modulated, in part, by the circulating hormones in sexually mature animals. However, most studies examining the effects of gonadal hormones on the timekeeping system have focused on the activational effects of oestradiol in adult females . There is a paucity of literature concerning how oestrogens organise the adult circadian system during development .…”