Fig. 14.

Schematic diagram of a hypothetical pattern of a coupled SCN neuronal network (A), and examples of weak synchrony during spontaneous activity of SCN neurons after active chemical synaptic transmission was blocked with low-calcium solutions (B). (A) Thick lines between neurons indicate strong coupling via large gap junctions; thin lines indicate weak coupling from small gap junctions. White circles show neurons without gap junctions, which do not show coupling or spikelets. Gray circles are neurons linked by “mini” gap junctions (thin connecting lines), which would be detected as weak coupling only if both coupled cells were recorded, but even then, would show small spikelets only when one of the weakly coupled neurons fires an action potential during the recording period. Black circles indicate the small fraction of SCN neurons that are more strongly coupled by larger gap junctions (thick connecting lines). Simultaneous recording from two SCN neurons more strongly coupled by larger gap junctions would show coupling coefficients of >0.1 and larger spikelets if the coupled neuron fired an action potential. (A, substantially modified from Dudek et al., 1983; B, modified from Bouskila and Dudek, 1993).