Effects of pars intercerebralis removal on circatidal rhythm in the mangrove cricket, Apteronemobius asahinai

The adverse effects of injected functionalized multi-walled carbon nanotube (f-MWCNT) on in vivo neurosecretory brain cells of Jamaican field cricket, Gryllus assimilis

Carbon nanotubes (CNTs) have been increasingly more prevalent due to their use in product technology owing to their exceptional electrical and thermal conductivity and tensile strength because of their nanostructure and strength of the bonds among carbon atoms. The potential increase of CNTs in the environment is a concern, and studies to assess the toxic effects of these nanomaterials (NMs) are needed. However, so far, most of the studies are focused on aquatic species and much less is understood about the effects of NM in terrestrial organisms. This investigation used a functionalized multi-walled carbon nanotube (f-MWCNT) and the Jamaican cricket Gryllus assimilis to assess the effects of this NM. Cricket nymphs were injected with f-MWCNT suspension-at three different concentrations. The insecticide Fipronil was used as a positive control. Survival was monitored, and histological analysis was made in the brains. Pyknotic cells were quantified in two brain regions, a neurosecretory called Pars intercerebralis (PI), and an associative region called mushroom body (MB). No mortality was observed in any f-MWCNT concentration tested. A significant increase in pyknotic cells was observed as sub-lethal effect for the intermediate concentration of f-MWCNT, at PI, while any significant change was observed at the Kenyon cells of the MB. These results are discussed in the context of agglomeration and dispersion of the f-MWCNT at different concentrations, and availability of the f-MWCNT on the circulatory system, as well as the natural decay of pyknotic cells with time and different patterns of adult cricket neurogenesis. Our results showed that f-MWCNT had negative effects in the neurosecretory region of the brain.

The optic lobe-pars intercerebralis axis is involved in circa'bi'dian rhythm of the large black chafer Holotrichia parallela

The large black chafer Holotrichia parallela exhibits ~ 48-h circa'bi'dian rhythm. Although circabidian rhythm is suggested to involve the circadian clock, no physiological studies have been conducted to verify this involvement. We examined the effects of optic lobe or pars intercerebralis removal on the circabidian rhythm. After removing both optic lobes, all beetles lost their circabidian rhythms (N = 25), but all beetles exhibited circabidian rhythm after removing unilateral optic lobe (N = 18). However, 22% of the latter group exhibited day switching. After removal of the pars intercerebralis, 26.3% beetles showed arrhythmic patterns (N = 19). The number of paraldehyde fuchsin-stained pars intercerebralis cells in the arrhythmic group was significantly reduced compared to in the intact and sham-operated groups. The activity in the pars intercerebralis-removed beetles was significantly higher than that in the control groups. The results show that the optic lobe and at least part of the pars intercerebralis are necessary for circabidian rhythm, and bilateral optic lobes are necessary to maintain regularity of the two-day rhythm in H. parallela. This suggests that a neural circuit of circadian clock cells in the optic lobe to pars lateralis might be evolutionally conserved and used also for the generation of circabidian rhythm.