Histological observations on circadian changes in the neurosecretory cells of cockroach sub-oesophageal ganglia

Abstract

Six pairs of neurosecretory cells in the sub-oesophageal ganglion of Periplaneta americana stain intensely with paraldehyde fuchsin; their morphology is described. These cells were subjected to a detailed histological study throughout the 24 hr. No clear evidence of a circadian cycle in the movement of neurosecretory material was detected in any of them. The nuclei of one pair of neurosecretory cells believed to be concerned in the control of the circadian rhythm of locomotion were significantly larger during the period of maximum locomotor activity than at other times, but no sharp change in their nuclear volume was detected at the onset of activity. Possible errors in the estimation of nuclear volume are discussed. The results are considered in relation to those of other workers and in relation to the possibility that circadian metabolic changes in the organism as a whole may be reflected in synchronous changes in many of its cells.