CONTROL OF ALTERNATIVE BEHAVIORAL STATES BY SEROTONIN IN CAENORHABDITIS-ELEGANS

Serotonin has been implicated in the regulation of a wide range of bra in functions involving alternative behavioral states, including the co ntrol of mood, aggression, sex, and sleep. Here, we report that in the nematode Caenorhabditis elegans, serotonin controls a switch between two distinct, on/off states of egg-laying behavior. Through quantitati ve analysis of the temporal pattern of egg-laying events, we determine d that egg laying can be modeled as a novel random process, in which a nimals fluctuate between discrete behavioral states: an active state, during which eggs are laid in clusters, and an inactive state, during which eggs are retained. Single-cell ablation experiments indicate tha t two pairs of motor neurons, HSNL/HSNR and VC4/VC5, can induce the ac tive phase by releasing serotonin. These neurons also release acetylch oline, which appears to trigger individual egg-laying events within th e active phase. Genetic experiments suggest that determination of the behavioral states observed for C. elegans egg laying may be mediated t hrough protein kinase C-dependent (PKC-dependent) modulation of voltag e-gated calcium channels.