This project seeks to specify the neuroendocrine bases for circannual rhythms in behavior and physiology of mammals. The model species is the golden-mantled ground squirrel Spermophilus lateralis. The great majority of prior studies of seasonality has focused on rhythms that are not completely endogenous (Type I rhythms). This project is concerned with completely endogenous circannual rhythms that persist for many cycles in the absence of environmental input (Type II rhythms). The mechanisms that generate and synchronize Type II rhythms differ from those that mediate Type I rhythms. Type II rhythms are common in long-lived mammals, including primates; perhaps the most accessible route to gaining insight into the neuroendocrine bases of Type II rhythms in human behavior and physiology is to study relevant animal model systems.
Specific aims of the present project include: 1) characterization of the role of the suprachiasmatic nucleus in gating circannual rhythms of body mass, reproduction and hibernation to specific phases of each circannual cycle and determining whether a single circannual clock generates the several rhythms, 2) assessment of the effects of prolonged hypothermia on circannual rhythms: are the clock(s) that gate the body mass and reproduction rhythms arrested in squirrels that hibernate continuously for two or more years? 3) determination of the role of the suprachiasmatic nucleus in sex differences in circannual organization, 4) establishing whether changes in tissue temperature are necessary for the striking circannual modulation of circadian rhythms in locomotor activity, and 5) completion of an ongoing analysis of the neural sites at which melatonin phase shifts circannual rhythms. This research may provide insight into the proximate neural bases for human rhythms and aid in the development of hormone and light therapies for treatment of seasonal affective disorders and other seasonal disturbances.

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Research Project (R01)
Project #
Application #
Study Section
Psychobiology, Behavior, and Neuroscience Review Committee (PBN)
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Berkeley
Schools of Arts and Sciences
United States
Zip Code
Bittman, E L; Thomas, E M; Zucker, I (1994) Melatonin binding sites in sciurid and hystricomorph rodents: studies on ground squirrels and guinea pigs. Brain Res 648:73-9
Ruby, N F; Zucker, I; Licht, P et al. (1993) Olfactory bulb removal lengthens the period of circannual rhythms and disrupts hibernation in golden-mantled ground squirrels. Brain Res 608:1-6
Lee, T M; Zucker, I (1992) Estradiol phase-shifts circannual rhythms of golden-mantled ground squirrels. Am J Physiol 262:R1096-9
Dark, J; Ruby, N F; Wade, G N et al. (1992) Accelerated reproductive development in juvenile male ground squirrels fed a high-fat diet. Am J Physiol 262:R644-50
Lee, T M; Zucker, I (1991) Suprachiasmatic nucleus and photic entrainment of circannual rhythms in ground squirrels. J Biol Rhythms 6:315-30
Lee, T M; Holmes, W G; Zucker, I (1990) Temperature dependence of circadian rhythms in golden-mantled ground squirrels. J Biol Rhythms 5:25-34
Lee, T M; Pelz, K; Licht, P et al. (1990) Testosterone influences hibernation in golden-mantled ground squirrels. Am J Physiol 259:R760-7
Dark, J; Kilduff, T S; Heller, H C et al. (1990) Suprachiasmatic nuclei influence hibernation rhythms of golden-mantled ground squirrels. Brain Res 509:111-8
Dark, J; Stern, J S; Zucker, I (1989) Adipose tissue dynamics during cyclic weight loss and weight gain of ground squirrels. Am J Physiol 256:R1286-92
Forger, N G; Dark, J; Stern, J S et al. (1988) Lipectomy influences white adipose tissue lipoprotein lipase activity and plasma triglyceride levels in ground squirrels. Metabolism 37:782-6

Showing the most recent 10 out of 23 publications