Wheel-running and rest activity pattern interaction in two octodontids (Octodon degus, Octodon bridgesi)

Abstract

Wheel-running and other non-photic stimuli influence the rest-activity pattern of diurnal and nocturnal mammals. A day to night inversion of phase preference of activity was described among Octodon degus, when exposed to ad-libitum wheel running. We have studied the rest-activity pattern response in presence of ad libitum wheel-running in wild-captured male individuals from two species of genus Octodon: O. degus (n=9, crepuscular-diurnal) and O. bridgesi (n=3, nocturnal). After two months of habituation to laboratory conditions, recordings were performed in isolation chambers under a 12:12 light-dark schedule with or without access to a running wheel. Actograms were constructed from data obtained by an automated acquisition system. O. bridgesi were also recorded under constant darkness, with or without access to wheelrunning. Entrained to the light-dark schedule, a crepuscular pattern of activity was evident for O. degus, whereas O. bridgesi displayed a robust nocturnal chronotype. The activity of O. degus observed during the dark phase was enhanced when wheel-running was allowed. No significant change in phase preference was observed for O. bridgesi when wheel-running was allowed. A lengthening of endogenous period was observed in O. bridgesi after wheel-running exposure under constant darkness. Nocturnal and diurnal octodontids exhibit different masking responses to wheel-running.

Circadian organization of the diurnal Caviomorph rodent,Octodon degus

“…This wheelinduced phase-switch was replicated in two other experiments with laboratory-born animals (Kas & Edgar 1998, as well as in one experiment examining wild-caught degus (Ocampo-Garces et al 2005), suggesting that it is not an isolated phenomenon caused by inbreeding. However, it is certainly caused by laboratory conditions.…”

“…Other investigators have found that the degu shows diurnal rhythms in temperature and locomotor activity in the laboratory using methods of biotelemetry (Refinetti 1996;Kas & Edgar 1998;Kas & Edgar 1999). However, when the degus were given access to a running wheel, the observed rhythms frequently became crepuscular or nocturnal (Kas & Edgar 1998, 1999Garcia-Allegue et al 1999;Ocampo-Garces et al 2005; Figure 1). Kas and Edgar (1999) closely observed this phase-switching phenomenon in response to ad libitum wheel access.…”

“…Although many experiments have examined degu circadian rhythms while the animals were displaying unimodal, day-active behavior (e.g., Refinetti 1996;Jechura et al 2000;Hummer et al 2007;Vivanco et al 2007), other studies have focused on conditions which induced bimodal, crepuscular, or even nocturnal activity patterns (Kas & Edgar 1998, 1999Garcia-Allegue et al 1999;Ocampo-Garces et al 2005;Ocampo-Garces et al 2006;Refinetti 2006). These studies are complementary for developing an understanding of the underlying mechanisms determining phase-preference in this species.…”

Diurnally active rodents for laboratory research

“…40 Similar to observations on Mongolian gerbils, at least two investigations have reported degus to become nocturnal in the laboratory simply upon gaining access to a running wheel. 41,42 However, approximately half of the degus in two other studies were diurnal and half were nocturnal regardless of the presence or absence of running wheels, apparently as a matter of individual peculiarity. 30,41 Thus, although degus appear to be more diurnal than Mongolian gerbils, they do not seem to be reliably and consistently diurnal under laboratory conditions.…”

Chronotype changes during puberty depend on gonadal hormones in the slow-developing rodent, Octodon degus

“…More exaggerated chronotype flexibility is reported in the laboratory due to housing and lighting variables ( e.g ,. Kas and Edgar, 1999; Ocampo-Garces, 2005; Hagenauer and Lee, 2008). …”