Diurnal patterns of electrical activity in crayfish neurosecretory cells

The electrical activity of single neurons in the X ogan-sinus gland system of the crayfish was continuously recorded from isolated eyestalks kept in d arkness over periods of time up to 96 h. Ample diurnal variations were dete cted in the spontaneous firing rate of single units in the sinus gland and the X organ-sinus gland tract. Some units displayed a nocturnal peak of act ivity; others were more active at day-time. Intracellular recordings from X organ somata showed similar diurnal pattern s of activity. During the silent periods, the neurons could be activated by intracellular stimulation through the recording electrode. The transition from resting to activity phases was concurrent with a slow depolarization a nd increase of membrane conductance. No correlation could be documented wit h the pattern of synaptic input.