Grosse J, Davis F C
Department of Biology, Northeastern University, Boston, MA 02115, USA.
Brain Res Bull. 1999 Jan 15;48(2):185-94. doi: 10.1016/s0361-9230(98)00162-2.
Maternal cues entrain a circadian pacemaker in fetal Syrian hamsters. These cues may act through dopaminergic activation of the fetal suprachiasmatic nucleus (SCN); injection of the dopamine D1 agonist SKF38393 to pregnant hamsters entrains activity rhythms of their pups and induces expression of c-fos in the fetal SCN. The aim of this study was to examine the ability of SKF38393 to entrain neonatal Syrian hamsters and to determine the age at which this effect is lost. SKF38393 injections given to two groups of pups at opposite times of day on postnatal days (PN) 1-5 entrained the pups' activity rhythms to average phases that differed by 9.25 h. SKF38393 failed to establish different average phases when given on PN 6-10. Injection of SKF38393 on PN 1, but not PN 6, induced expression of Fos. These results demonstrate that dopaminergic activation is a potent entraining stimulus in neonatal hamsters and that its entraining effects, as well as its ability to induce Fos, are lost by PN 6. The phase established by dopaminergic activation was approximately opposite to that previously shown to be established by melatonin injections. Dopaminergic activation and melatonin may mimic separate but complementary maternal entraining signals which represent day and night.
母体线索可使叙利亚仓鼠胎儿的昼夜节律起搏器同步化。这些线索可能通过胎儿视交叉上核（SCN）的多巴胺能激活起作用；给怀孕的仓鼠注射多巴胺D1激动剂SKF38393可使它们幼崽的活动节律同步化，并诱导胎儿SCN中c-fos的表达。本研究的目的是检测SKF38393使新生叙利亚仓鼠同步化的能力，并确定这种效应消失的年龄。在出生后第1 - 5天的不同时间给两组幼崽注射SKF38393，可使幼崽的活动节律同步到平均相差9.25小时的相位。在出生后第6 - 10天给予SKF38393时，未能建立不同的平均相位。在出生后第1天而非第6天注射SKF38393可诱导Fos表达。这些结果表明，多巴胺能激活是新生仓鼠中一种有效的同步刺激，并且其同步效应以及诱导Fos的能力在出生后第6天消失。多巴胺能激活所建立的相位与先前显示的褪黑素注射所建立的相位大致相反。多巴胺能激活和褪黑素可能模拟了分别但互补的母体同步信号，分别代表白天和黑夜。
