Müller C, Torrealba F
Departamento de Ciencias Fisiológicas, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Alameda 340, Casilla 114-D, Santiago, Chile.
Brain Res Dev Brain Res. 1998 Oct 1;110(2):203-13. doi: 10.1016/s0165-3806(98)00108-4.
We had previously found a ca. 30% cell death during the prenatal ontogeny of the suprachiasmatic nucleus (SCN) of lambs. The period of neuron death was preceded by the establishment of the retinohypothalamic connections, a major input to this nucleus that allows the entrainment to light of the circadian rhythms generated by the SCN. The present study determined the temporal relationship between the period of ontogenetic neuron death and the establishment of the principal afferent and efferent connections of the SCN in hamsters. We found that during the first 3 postnatal days the SCN volume increases mainly by the addition of cells. After a peak 6140 neurons on each side during the third postnatal day, the SCN underwent an acute decrease of about 40% in neuron number, which led to the final adult complement of neurons, estimated in 3400 neurons per nucleus. The connections of the SCN were studied by placing DiI crystals either into the optic nerve, or into the SCN of brains fixed at different ages. We found, in agreement with previous studies, that retinal axons can be detected after the fifth postnatal day, that is, after the large decrease in neuron number. As for the SCN efferents, they began to invade the appropriate targets during the second postnatal day, followed by a large increase in the density of these efferent projection in the subsequent days. In conclusion, the massive neuronal death in the SCN was preceded by the formation of efferent connections, and followed by the formation of the retinohypothalamic tract.
我们之前发现，在羔羊视交叉上核（SCN）的产前个体发育过程中，约有30%的细胞死亡。神经元死亡期之前是视网膜下丘脑连接的建立，这是该核的主要输入，使得SCN产生的昼夜节律能够与光照同步。本研究确定了仓鼠个体发育过程中神经元死亡期与SCN主要传入和传出连接建立之间的时间关系。我们发现，在出生后的前3天，SCN体积主要通过细胞增加而增大。在出生后第3天每侧达到6140个神经元的峰值后，SCN神经元数量急剧减少约40%，这导致了最终成年时的神经元数量，估计每个核为3400个神经元。通过将DiI晶体置于视神经或不同年龄固定大脑的SCN中来研究SCN的连接。我们发现，与之前的研究一致，视网膜轴突在出生后第5天之后即可检测到，即神经元数量大幅减少之后。至于SCN的传出纤维，它们在出生后第2天开始侵入适当的靶标，随后在接下来的几天里这些传出投射的密度大幅增加。总之，SCN中大量神经元死亡之前是传出连接的形成，之后是视网膜下丘脑束的形成。
