EFFECTS OF ALTERED GRAVITY ON IDENTIFIED PEPTIDERGIC NEURONS OF THE CRICKET ACHETA DOMESTICUS.
The development of organisms requires a permanent interplay between genetic and environmental factors. Identified neurons that are common in insects are excellent models to determine the specific contribution of these factors for the development of the nervous system. The aim of the study was to investigate effects of altered gravity (AG) on identified peptidergic neurons in a cricket (Acheta domesticus), in particular, if embryos are exposed to AG during the period of neuronal proliferation. - Methods: Usually, AG started when embryos were one day old. The experiment CRISP-2 during the 10-days Italian Soyuz taxi flight ENEIDE to the ISS in April 2005 included inflight fertilization. After termination of the 10 to 16 days lasting AG exposures, the nervous system was taken from the embryo shortly before hatching or from the 1st instar larva to perform immunocytochemical stainings of allatostatin-(ASTA)-ir-, CCAP-ir-, and perisulfakinin-(PSK)-ir-neurons. - Results: Observations from exposures to 3g or simulated microgravity in a fast-rotating 2D-clinostat or the random positioning machine (RPM) revealed a low effect of AG on axonal and dendritic projection patterns as well as on the size of the cell soma of ASTA-, CCAP- and PSK-neurons. Only 1 out of 9 investigated neuron types, the C-BM1 CCAP neurons within the terminal ganglion, revealed a significant sensitivity; after 2D-clinorotation, their somata were smaller by about 20% (p<0.05) compared to the 1g-controls if the rotating axis was vertical to the longitudinal axis of the egg. The analysis of the CRISP-2 experiment is not yet completed. - Conclusions: Lack of significant differences between 1g- and AG-larvae does not exclude an AG sensitivity during early development. Compensatory mechanisms might be activated during on-going AG conditions to overcome transient deviations from normal neuronal development. The earlier hatching of 1st instar larvae after inflight fertilization compared to the 1g-ground controls as demonstrated for the space flight experiment CRISP-2 makes this hypothesis very likely.