Lavialle M, Servière J
Laboratoire de Physiologie Sensorielle, INRA, Jouy-en-Josas, France.
Brain Res Dev Brain Res. 1995 May 26;86(1-2):275-82. doi: 10.1016/0165-3806(95)00039-g.
The hypothalamic suprachiasmatic nuclei (SCN) house the circadian clock in the mammalian brain. A glial fibrillary acidic protein immunoreactivity (GFAP-ir) distribution rhythm has been observed in the SCN of adult Syrian hamster. The implication of astrocytes in photic entrainment was analyzed through developmental studies of the photic pathway and of SCN astrocytes appearance. Using anterograde tracing we studied the timing of penetration of the retinohypothalamic tract (RHT) fibers into the SCN. Using c-fos induction by light we followed the maturation of RHT synapses in the SCN. When RHT terminals reach the SCN, c-fos induction can be obtained. Using GFAP immunoreactivity we demonstrated that the number of astrocytes increased in parallel with RHT development from PN5 to PN15. At PN15, a time when pups can shift from maternal to photic entrainment, RHT terminals and GFAP-ir exhibit an adult-like pattern. One demonstrated role of astrocytes is to control extracellular glutamate concentration. Glutamate is the neurotransmitter released at RHT terminals; its content fluctuates according to a circadian rhythm within the SCN. Thus the present data tend to indicate that SCN astrocytes are participating in the circadian rhythm of SCN glutamate content.
下丘脑视交叉上核（SCN）是哺乳动物大脑中的昼夜节律时钟所在部位。在成年叙利亚仓鼠的SCN中观察到了胶质纤维酸性蛋白免疫反应性（GFAP-ir）分布节律。通过对视路和SCN星形胶质细胞出现的发育研究，分析了星形胶质细胞在光诱导同步化中的作用。我们利用顺行示踪研究了视网膜下丘脑束（RHT）纤维进入SCN的时间。利用光诱导c-fos表达，我们追踪了SCN中RHT突触的成熟过程。当RHT终末到达SCN时，可诱导c-fos表达。利用GFAP免疫反应性，我们证明从出生后第5天（PN5）到PN15，星形胶质细胞数量随着RHT的发育而平行增加。在PN15时，幼崽能够从母源性同步化转变为光诱导同步化，此时RHT终末和GFAP-ir呈现出类似成年动物的模式。星形胶质细胞的一个已被证实的作用是控制细胞外谷氨酸浓度。谷氨酸是RHT终末释放的神经递质；其含量在SCN内随昼夜节律波动。因此，目前的数据倾向于表明SCN星形胶质细胞参与了SCN谷氨酸含量的昼夜节律。
