Immunohistochemical localization of circadian oscillators in the brain and prothoracic glands of the insect Rhodnius prolixus

In the insect Rhodnius prolizus, both moulting hormones (ecdysteroids) and the brain neuropeptide prothoracicotropic hormone (PTTH) that regulates them are released with a circadian rhythm. The synthesis of ecdysteroids by the prothoracic glands (PGs) remains rhythmic in the absence of PTTH. Circadian rhythms are driven by underlying circadian oscillators. The present study localizes the circadian oscillators that regulate these hormones. The PERIOD and TIMELESS proteins (PER and TIM) are critical components of circadian oscillators. PER and TIM were localized by immunohistochemistry using confocal microscopy.

The present study reports that neurons in the brain containing PER and TIM are found in only two paired locations. One group of neurons is adjacent to the single paired PTTH-producing cells in the dorsal protocerebrum (“dorsal neurons”). The second group, “lateral neurons”, is located at the base of each optic lobe.

The findings confirm the presence of multiple circadian oscillators in the neuroendocrine axis that regulates development. They reveal that analogs of the “dorsal neurons”, described in Drosophila with unknown function, regulate neuropeptide releases (Abstract shortened by UMI.)