Figure 5.

Hypothesis of endogenous circadian rhythms in baseline levels of intracellular Ca²⁺- and cyclic nucleotide-levels at different Zeitgeber times controlling spontaneous activity in the absence of odor stimulation. During the activity phase at night baseline levels of intracellular Ca²⁺ are low, of cGMP are low, and of cAMP are high. At the rest phase during the day elevated baseline levels in intracellular Ca²⁺-concentration are maintained, as well as high cGMP-, and low cAMP-concentrations. The endogenous rhythms are not gated by light, but anticipate light–dark rhythms. While our preliminary experiments support cyclic nucleotide-rhythms, it remains to be examined whether rhythms in intracellular baseline Ca²⁺ concentration phase-lead or phase-lag the other rhythms.