Photic regulation of c-Fos expression in the protocerebrum of crayfish

Abstract

In various species of crayfish it has been proposed that different extra-retinal photoreceptors and pacemakers could be involved in the photo entrainment mechanisms. The identity of the neural structures responsible for this phenomenon is not known. The objective of this work was to contribute to the knowledge of the neurophysiological mechanisms and structures underlying the biological clock of crayfish by studying c-fos induction in one of the neural structures proposed as a pacemaker, the brain. Using qualitative – quantitative immunohistochemical and image methods we identified light-induced c-Fos immunoreactivity in cells located in the median protocerebrum of the supraesophagic ganglion. The immunoreaction varied with circadian time. The protocerebrum showed a statistically significant c-Fos induction, especially in neurons of the dorsal anterior region and the protocerebral bridge. A statistically significant difference between the control and the experimental conditions indicated a differential sensitivity in the early subjective night. This is the first report on c-Fos expression in crayfish and indicates that this marker may be a useful tool for studying the circadian clock in this organism.