![]() In addition, light is known to initiate a mitogen-activated protein kinase signaling cascade that induces transcription of both per and mkp1 phosphatase. Employing Leloup-Goldbeter mammalian clock neurons we model the ventrolateral SCN network and show that light acting weakly upon a strongly rhythmic vasoactive intestinal polypeptide oscillation can explain the observed light-dark cycle memory. ![]() ![]() We entrained Siberian hamsters to various light-dark cycles and then tracked their activity into constant darkness to show that they retain a memory of the previous light-dark cycle before returning to their own free-running period. In complete darkness, this network synchronizes through the exchange of action potentials that release vasoactive intestinal polypeptide, striking a compromise, free-running period close to 24 h long. The mammalian circadian oscillator, or suprachiasmatic nucleus (SCN), contains several thousand clock neurons in its ventrolateral division, many of which are spontaneous oscillators with period lengths that range from 22 to 28 h.
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