Neural control of circadian rhythmicity in the crayfish

Abstract

Gross locomotor activity, as well as the movements of single walking legs, were monitored in intact and surgically altered crayfish (Procambarus clarkii). Section of the circumesophageal connectives (CEC) abolished the circadian activity rhythm in both the first and fourth pair of walking legs (Figs. 1–3), while section of the nerve cord between the third and fourth thoracic ganglia abolished rhythmicity in only the fourth pair (Fig. 4). Bilateral ablation of the eyestalks led to a several fold increase in total daily activity and caused the animal to be continually active; however, quantitative measurements of the locomotor activity revealed that a circadian rhythm in the level of activity persists for 6–12 days following eyestalk removal (Figs. 7, 8, 13, 14). These results suggest that the circadian oscillation for the locomotor rhythm originates in the supraesophageal ganglion and is coupled to thoracic locomotor centers via axons in the CEC. The activity rhythm of eyestalkless animals could also be entrained to a light cycle even after ablation of the caudal photoreceptor; however, certain features of entrainment were altered (Figs. 9–12). Thus, although the eyestalks are not required for rhythmicity, eyestalk structures apparently do participate in entrainment.