ABSTRACT

Several studies have reported activity patterns of various diurnal species from the order Rodentia, in which most of the species are nocturnal. Most of these studies have been performed under controlled laboratory conditions. These studies found that most of these species change their activity patterns when held under laboratory conditions, have a diverse masking response to light, and their activity pattern is influenced by the presence of a running wheel. Squirrels are reported to be strictly diurnal both in the field as well as in laboratory settings, and, therefore, form an interesting species to study to better understand the switch to diurnality. The aim of the current study is to characterize the masking response and temporal organization of wheel-running activity rhythms in the palm squirrel, Funambulus pennantii, under semi-natural (NLD) and controlled laboratory conditions using different lighting schedules. Squirrels were housed individually in a resting cage with running wheel under NLD (n = 10) and squared 12:12 h of light-dark cycle (LD) (n = 20). After stable entrainment under the LD condition, squirrels were divided into two groups. One group was housed under constant darkness (DD) (n = 10) and another group under constant light (LL) (n = 10). Following the stable free-running rhythm under DD and LL, the LD condition was reinforced. The kinetics of the endogenous pacemaker was studied following a 6 h phase advance or delay of LD cycle. Further, palm squirrels were subjected to a 3.5: 3.5 h LD cycle to evaluate the masking response to light and dark. Squirrels demonstrated stable, clear, robust, and strict diurnal activity rhythm during NLD and LD. In DD and LL, F. pennantii free-ran from the phase of the previous LD cycle, and the free-running period was longer in LL than in DD. The percentage of activity during the light phase was significantly higher in NLD and LD (above 96%) compared to activity during the subjective day in the DD and LL conditions (above 91%). The alpha/rho ratio was significantly higher in the LL compared to other lighting schedules. Further, all ten squirrels re-entrained to both 6 h advance and delay shifts within 11 days. In the ultradian cycle, significant positive masking of light was evident in nine of ten squirrels. These results suggest that the: (i) circadian system of F. pennantii is stable and functional under various lighting conditions; (ii) basic temporal organization in activity pattern remained unaltered even in the presence of a running wheel; (iii) diurnality is the inherent trait of F. pennantii, and (iv) behavioral activity rhythms are governed by both the circadian clock and external masking. Thus, palm squirrels can be used as a suitable diurnal model in circadian biology to study the underlying mechanisms of diurnality and effects of different light schedules, wavelengths, and non-photic cues on physiological and behavioral parameters.

摘要

数项研究报告了来自啮齿类动物的各种昼夜物种的活动模式，其中大多数物种是夜间活动的。这些研究大多数是在受控实验室条件下进行的。这些研究发现，这些物种中的大多数在实验室条件下保持活动时会改变其活动模式，对光具有多种掩蔽响应，并且它们的活动模式会受到跑轮的影响。据报道，在野外和实验室环境中，松鼠都是严格昼夜的，因此，松鼠形成了一个有趣的物种，需要研究以更好地了解转向昼夜性。本研究的目的是表征棕松鼠Funambulus pennantii的轮转活动节奏的掩蔽反应和时间组织，在半自然（NLD）和受控实验室条件下使用不同的照明时间表。松鼠分别被安置在一个带有NLD（n = 10）下的行走轮的静止笼中，并在12:12 h的明暗循环（LD）（n = 20）下平方。在LD条件下稳定夹带后，将松鼠分为两组。一组居住在恒定黑暗（DD）下（n = 10），另一组居住在恒定光照（LL）下（n = 10）。遵循DD和LL下稳定的自由运动节奏，LD条件得到了加强。研究了内源性起搏器的动力学，该运动是在LD周期提前或延迟6 h后进行的。此外，对棕榈松鼠进行3.5：3.5 h LD循环以评估对明暗的掩盖响应。松鼠在NLD和LD期间表现出稳定，清晰，健壮和严格的昼夜活动节律。F. pennantii从上一个LD周期的阶段开始自由运行，LL的自由运行期比DD更长。与DD和LL条件下的主观活动期间（91％以上）相比，NLD和LD的轻度阶段活动百分比显着更高（96％以上）。与其他照明时间表相比，LL中的alpha / rho比明显更高。此外，所有十只松鼠在11天内重新夹带了6小时的进退和延迟班次。在超周期中，十只松鼠中有九只明显遮盖了光。这些结果表明：（i）F. pennantii的昼夜节律系统在各种照明条件下稳定且功能正常；（ii）即使在有跑轮的情况下，活动方式的基本时间安排仍保持不变；（iii）昼夜性是彭氏葡萄球菌（F. pennantii）的固有特征，并且（iv）行为活动节律受昼夜节律和外部掩蔽的支配。因此，棕榈松鼠可以用作昼夜节律生物学中合适的昼夜模型，以研究昼夜性的潜在机制以及不同光程，波长和非光线索对生理和行为参数的影响。