Aspects of Entrainment of CHH Cell Activity and Hemolymph Glucose Levels in Crayfis

¹ Zoölogisch Laboratorium, Faculteit der Wiskunde en Natuurwetenschappen, Katholieke Universiteit, Toernooiveld, 6525 ED Nijmegen, The Netherlands

We investigated the effects of several experimental conditions, such as constant darkness, light/dark phase-shift, covered eyes, eyestalks and rostral regions, and optic tract sectioning, on the entrainment of daily blood glucose rhythmicity in the crayfish. Hemolymph glucose determination over a 24 h period and a morphometrical study on the secretory activity of the Crustacean Hyperglycemic Hormone (CHH)-producing cells in the eyestalk using immunocytochemistry were carried out. Our results indicate that Astacus leptodactylus exhibits an endogenous circadian blood glucose rhythm entrained by the light/dark schedule.

The light stimuli that control the rhythm are not de tected by the compound eyes nor by the caudal photoreceptor but most probably by a photoreceptor located elsewhere in the eyestalk. After disruption of the neural connection between the optic lobes and the cerebral ganglion, blood glucose rhythmicity persists, which indicates that the biological clock of the blood glucose rhythm is located within the optic lobes.

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