Figure 6. Simplified scheme of mechanisms that control electrical and molecular coupling of SCN neurons.

Two adjacent SCN neurons with clock genes that comprise a transcriptional-translational feedback loop (TTL). Propagating action potentials are presented as yellow lightning bolts. Pink insets: circadian mPer2^Luc rhythms from cell 1 and cell 2. Yellow insets: short-term patterns of action potentials from cell 1 and cell 2, as shown in Long et al., 2005 and Wang et al., 2014. (A) In the presence of Cx36 gap junctions, electrical activity and clock gene rhythms of SCN neurons are both coupled between cells. Molecular rhythms of clock genes are presumably mainly synchronized by neurotransmitters like GABA and VIP. (B) In the absence of functional gap junctions, clock gene rhythms are still synchronized by GABA and VIP. However, electrical activity is no longer synchronized, and cells fire with different patterns.