Erkert Hans G, Gburek Viola, Scheideler Angelika
Institute for Zoology/Animal Physiology, University of Tuebingen, Morgenstelle 28, D-72076 Tuebingen, Germany.
Physiol Behav. 2006 Jun 15;88(1-2):39-46. doi: 10.1016/j.physbeh.2006.03.003. Epub 2006 Apr 19.
Besides rods the retina of the nocturnal greater bushbaby, genus Otolemur, also contains small cones which, however, do not allow color vision. In order to find out whether these cones might be involved in circadian photoreception in the Garnet's galago Otolemur garnettii we determined the threshold for photic entrainment. Activity recordings revealed a short circadian period of 22.6+/-0.7 h subjected to pronounced long-lasting aftereffects. The animals had a relatively high threshold for photic entrainment at about 3-30 lux. This indicates that the cones and/or other, as yet unidentified photoreceptive retinal cells may be involved in circadian photoreception. The galagos' threshold for photic entrainment also depended on the luminosity during the dark phase of the light dark cycles. Results furthermore showed that in Otolemur aftereffects may play a crucial role for circadian entrainment. Light time luminosities just below the individuals' threshold for photic entrainment strongly inhibited the galagos' locomotor activity and, thus, produced pronounced negative masking effects on their free-running circadian activity rhythm. From this it may be inferred that masking direct effects of light are not induced or mediated via the circadian system, i.e. via the circadian pacemaker in the hypothalamic suprachiasmatic nuclei, but at a higher central nervous integrational stage.
除了视杆细胞外，夜行动物大婴猴属（Otolemur）的视网膜中还含有小的视锥细胞，然而，这些视锥细胞并不能实现色觉。为了弄清楚这些视锥细胞是否可能参与了加氏婴猴（Otolemur garnettii）的昼夜节律光感受，我们测定了光致同步的阈值。活动记录显示，其昼夜节律周期较短，为22.6±0.7小时，并伴有明显的长期后效应。这些动物的光致同步阈值相对较高，约为3 - 30勒克斯。这表明视锥细胞和/或其他尚未确定的视网膜光感受细胞可能参与了昼夜节律光感受。婴猴的光致同步阈值还取决于明暗周期黑暗阶段的光照度。此外，结果表明，在大婴猴属中，后效应可能对昼夜节律同步起着关键作用。略低于个体光致同步阈值的光照时间强度会强烈抑制婴猴的运动活动，从而对其自由运行的昼夜活动节律产生明显的负掩蔽效应。由此可以推断，光的掩蔽直接效应不是通过昼夜节律系统，即下丘脑视交叉上核中的昼夜节律起搏器诱导或介导的，而是在更高的中枢神经整合阶段产生的。
