About Our Lab

Research in the Smale lab is aimed at understanding how the neural mechanisms governing behavior are transformed as natural selection shapes the behavior patterns exhibited by animals. The focus is specifically on determining how the neural mechanisms controlling daily, or “circadian,” rhythms changed as day-active animals evolved from their night-active ancestors. When this happened the mechanisms controlling the temporal organization of a coordinated suite of behavioral and physiological variables were dramatically transformed. However, relatively little is known about this issue because most research into the neural substrates controlling circadian rhythms has been done with nocturnal rodents. One reason is that there has been no suitable diurnal rodent model with which to examine these questions. Although some of our work focuses on ground squirrels and degus, we are working primarily with the Nile grass rat Arvicanthis niloticus, a diurnal rodent recently imported to the United States from Africa. We are currently examining the grass rat with respect to its circadian rhythms and the neural structures controlling them. At the center of these structures within the mammalian brain is the suprachiasmatic nucleus (SCN). This tightly packed cluster of cells functions as a “master clock”. It generates circadian rhythms, and it coordinates rhythms generated in a host of subsidiary oscillators. We are using a variety of techniques to determine if there are differences in some aspect of SCN function that might contribute to differences between diurnal and nocturnal mammals. We are also evaluating the ways in which downstream targets of the SCN function differently in day- and night-active species. In addition to these issues of differences between-species, we are examining differences in daily activity patterns among individuals within species. Specifically, we are looking at grass rats that vary with respect to when they are most active, and the neural bases of those differences.

Recent Publications

Nixon, J.P. and Smale, L. 2007. A comparative analysis of the distribution of immunoreactive orexin A and B in the brains of nocturnal and diurnal rodents. Behavioral and Brain Functions, 3:28 (13 Jun 2007).

Ramanathan, C., Nuñez, A.A., Schwartz, M.D., Martinez, G. and Smale, L. 2006. Temporal and spatial distribution of immunoreactive PER1 and PER2 proteins in the suprachiasmatic nucleus and peri-suprachiasmatic region of the diurnal grass rat (Arvicanthis niloticus). Brain Research, 1073-1074: 348-358.

Smale, L., Heideman, P.D., and French, J.A. 2005. Behavioral Neuroendocrinology in Nontraditional Species of Mammals: Things the “Knockout” Mouse CAN’T Tell Us. Hormones and Behavior 48: 474-483.

Schwartz, M.D., and Smale, L. 2005. Individual differences in rhythms of behavioral sleep and its neural substrates in Nile grass rats. Journal of Biological Rhythms, in press.

Nixon, J.P. and Smale, L. 2005. Orexin fibers form appositions with Fos expressing neuropeptide-Y cells in the grass rat intergeniculate leaflet. Brain Research 1053: 33-37.

Mahoney, M.M. and Smale, L. 2005. Arginine vasopressin and vasoactive intestinal polypeptide fibers make appositions with gonadotropin-releasing hormone and estrogen receptor cells in the diurnal rodent Arvicanthis niloticus. Brain Research 1049(2): 156-164.

Mahoney, M.M. and Smale, L. 2005. A daily rhythm in mating behavior in a diurnal murid rodent Arvicanthis niloticus. Hormones and Behavior, 47: 8-13.

Lambert, C.M., Machida, K.K., Smale, L., Nuñez, A.A .and Weaver, D.R. 2005. Analysis of the Prokineticin 2 system in a diurnal rodent, the unstriped Nile grass rat (Arvicanthis niloticus), Journal of Biological Rhythms 20: 206-218.

Schwartz, M.D., Nuñez, A.A. and Smale, L. 2004. Differences in the suprachiasmatic nucleus and lower subparaventricular zone of diurnal and nocturnal rodents. Neuroscience 127: 13-23.

Nixon, J.P. and Smale, L. 2004. Individual differences in wheel-running rhythms are related to temporal and spatial patterns of activation of orexin A and B cells in a diurnal rodent (Arvicanthis niloticus). Neuroscience 127: 25-34.

Mahoney, M.M., Sisk, C., Ross, H.E. and Smale, L. 2004. Circadian regulation of gonadotropin-releasing hormone neurons and the preovulatory surge in luteinizing hormone in the diurnal rodent, Arvicanthis niloticus, and in a nocturnal rodent, Rattus norvegicus. Biology of Reproduction 70: 1049-1054.

Smale, L., Lee, T. and Nuñez, A.A. 2003. Mammalian diurnality: Some facts and gaps. Journal of Biological Rhythms 18: 356-366.

Nunes, S., McElhinny, T.L., Mahoney, M.M. and Smale, L. 2002. Effects of photoperiod on the reproductive condition of Nile grass rats (Arvicanthis niloticus) from an equatorial population. African Journal of Ecology 40: 295-302.

Martinez, G.S., Smale, L. and Nuñez, A.A. 2002. Diurnal and nocturnal rodents show rhythms in orexinergic neurons. Brain Research 955: 1-7.

Smale, L., Castleberry, C. and Nuñez, A.A. 2001. Fos rhythms in the hypothalamus of Rattus and Arvicanthis that exhibit nocturnal and diurnal patterns of rhythmicity. Brain Research 899(1-2): 101-105.

Mahoney, M., Bult, A. and Smale, L. 2001. Phase response curve in light-induced Fos expression in the suprachiasmatic nucleus and adjacent hypothalamus of Arvicanthis niloticus. Journal of Biological Rhythms 16(2): 149-162.

Smale, L., McElhinny, T., Nixon, J., Gubik, B., and Rose, S. 2001. Patterns of wheel running are related to Fos expression in neuropeptide-Y-containing neurons in the intergeniculate leaflet of Arvicanthis niloticus. Journal of Biological Rhythms 16(2): 163-172.

Novak, C.M., Harris, J., Smale, L., and Nuñez, A.A. 2000. Suprachiasmatic nucleus projections to the paraventricular thalamic nucleus in nocturnal rats (Rattus norvegicus) and diurnal Nile grass rats (Arvicanthis niloticus). Brain Research 874(2): 147-157.

Mahoney, M.M., Nuñez, A.A. and Smale, L. 2000. Calbindin and Fos within the suprachiasmatic nucleus and adjacent hypothalamus of Arvicanthis niloticus and Rattus norvegicus. Neuroscience 99: 565-575.

Novak, C.M., Smale, L., and Nuñez, A.A. 2000. Rhythms in Fos expression in brain areas related to the sleep-wake cycle in the diurnal Arvicanthis niloticus. American Journal of Physiology 278: R1267-R1274.

Blanchong, J.B. and Smale, L. 2000. Temporal patterns of activity in the unstriped Nile rat, Arvicanthis niloticus in its natural habitat. Journal of Mammalogy. 81: 595-599.