Figure 3.

Models of integrating circadian clock information. In a hypothetical neuronal circuit of three neurons, information from the first neuron is communicated to the third neuron. In metabotropic communication (solid red arrow), the circadian clock from neuron 1 regulates the release of neurotransmitters that communicate to the transcription machinery in neuron 2. In turn, neuron 2 integrates information from its own circadian clock to the signal and communicates to neuron 3. In ionotropic communication (dashed red arrow), the circadian clock from neuron 1 communicates to neuron 3 by bypassing the circadian clock in neuron 2, using neuron 2 as a communications cable. Sinusoidal line in nucleus represents the circadian clock. White circles represent vesicles. Red circles represent neurotransmitters. Thick arrows represent direction of changing action potential (⁺⁺⁺⁺⁺). Small arrows represent steps of communication within and across neurons.