Circadian Control of Neurogenesis Erin M. Goergen, Leslie A. Bagay, Kris Rehm, Jeanne L. Benton, Barbara S. Beltz Department of Biological Sciences, Wellesley College, Wellesley, Massacusetts 02481 Received 29 May 2002; accepted 29 May 2002 ABSTRACT: The life-long addition of new neurons has been documented in many regions of the vertebrate and invertebrate brain, including the hippocampus of mammals (Altman and Das, 1965; Eriksson et al., 1998; Jacobs et al., 2000), song control nuclei of birds (Alvarez-Buylla et al., 1990), and olfactory pathway of rodents (Lois and Alvarez-Buylla, 1994), insects (Cayre et al., 1996) and crustaceans (Harzsch and Dawirs, 1996; Sandeman et al., 1998; Harzsch et al., 1999; Schmidt, 2001). The possibility of persistent neurogenesis in the neocortex of primates is also being widely discussed (Gould et al., 1999; Kornack and Rakic, 2001). In these systems, an effort is underway to understand the regu- latory mechanisms that control the timing and rate of neurogenesis. Hormonal cycles (Rasika et al., 1994; Har- rison et al., 2001), serotonin (Gould, 1999; Brezun and Daszuta, 2000; Beltz et al., 2001), physical activity (Van Praag et al., 1999) and living conditions (Kemperman and Gage, 1999; Sandeman and Sandeman, 2000) influ- ence the rate of neuronal proliferation and survival in a variety of organisms, suggesting that mechanisms con- trolling life-long neurogenesis are conserved across a range of vertebrate and invertebrate species. The present article extends these findings by demonstrating circadian control of neurogenesis. Data show a diurnal rhythm of neurogenesis among the olfactory projection neurons in the crustacean brain, with peak proliferation during the hours surrounding dusk, the most active period for lobsters. These data raise the possibility that light-controlled rhythms are a primary regulator of neu- ronal proliferation, and that previously-demonstrated hormonal and activity-driven influences over neurogen- esis may be secondary events in a complex circadian control pathway. © 2002 Wiley Periodicals, Inc. J Neurobiol 53: 90 –95, 2002 Keywords: circadian; diurnal; neurogenesis; serotonin; Crustacea; olfactory INTRODUCTION Persistent neurogenesis among sensory and interneu- ronal populations in the olfactory pathway of a variety of decapod crustacean species has been intensively studied (Harzsch and Dawirs, 1996; Sandeman et al., 1998; Harzsch et al., 1999; Schmidt, 2001). After larval life in the American lobster (Homarus ameri- canus), continued neurogenesis in the central nervous system is found only among the local and projection neurons of the olfactory pathway, and neurogenesis persists in these regions throughout the lobster’s life (Fig. 1) (Harzsch et al., 1999). The sensory, local, and projection neurons of the crustacean brain are func- tionally analogous to groups of neurons in the olfac- tory system of adult vertebrates that have a similar capacity for life-long neurogenesis (Lois and Alvarez- Buylla, 1994; Graziadei and Monti Graziadei, 1986). Although the crustacean olfactory pathway has a functional anatomy that is parallel to the vertebrates (Strausfeld and Hildebrand, 1999), its organization provides experimental advantages because neuronal somata are arranged in anatomically distinct clusters according to their function. Thus in crustaceans, the Correspondence to: B. S. Beltz (Bbeltz@wellesley.edu). Contract grant sponsor: National Science Foundation; contract grant number: IBN 0091092. Contract grant sponsor: Howard Hughes Medical Institute Un- dergraduate Biological Sciences Education; contract grant number: 52003001. Contract grant sponsor: National Science Foundation Site Grant; contract grant number: DBI-0097499. © 2002 Wiley Periodicals, Inc. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/neu.10095 90