The Study On Circadian Rhythm And Phototaxis Mechanism Of Gryllus Bimaculatus Compound Eyes

Objective In order to investigate the changes of circadian rhythm and central nervous mechanism of visual signal processing in compound eyes of insect mircobrian, we studied the histology inside the Gryllus bimaculatus compound eyes and the different changes produced by the forebrain corpora pedunculata area reacting to different light intensity. This study revealed that the forebrain corpora pedunculata area was involved in visual regulation, and was the central structure for the adjustment of light intensity.Methods We observed the external characteristics of compound eyes with entity dissecting microscope. With the methods of conventional paraffin section, HE staining, neuronal markers, we observed the changes in characteristics of the inner microscopic structure of the compound eye under the condition of diurnal variation and the location of optic nerve in the brain. With the application of electrophysiological microelectrode technique and RM6240-based multi-channel analysis system for physiological signal acquisition and processing, we electrically stimulated the forebrain corpora pedunculata area with different light intensities, recording its electrical activities, and use the system for statistical analysis.Results The compound eyes of Gryllus bimaculatus were in front of the their heads, oval and convex outside, there were about 3,400 small hexagonal eyes on the surface, tightly packed into a honeycomb-like to each other, the mechanoreceptors were distributed in the small gaps between the small eyes.Every small eyes of Gryllus bimaculatus compound eyes consisted of cornea, crystalline cone, rhabdom, retinal cells and the base film from the inside to the outside. The primary pigment cells were distributed around the crystalline cone, the secondary pigment cells were distributed around the retinal cells. Microstructure within the compound eye (the crystalline cone, pigment granules, retinal cell nucleus) will change as the light and dark conditions change, the pigment granules were more evenly distributed on the rod in the light, but the pigment granules are mainly located in the upper section of the rod under dark-adapted condition. The crystalline cone and rod bundle showed a circadian rhythm. Electrophysiologically, the discharge volume, amplitude and frequency of the forebrain corpora pedunculata area regularly changed as the light intensity changed; when the light intensity LogI<2, the discharge volume, amplitude and frequency of the forebrain corpora pedunculata area increased as the light intensity increased; when the light intensity LogI>2, the discharge volume, amplitude and frequency of the forebrain corpora pedunculata area decreased as the light intensity increased.Conclusion The compound eyes of Gryllus bimaculatus were the primary structure of visual processing, with circadian rhythm. Under light and dark conditions, the internal histological structure changed. The optic lobes transmitted the visual information through the projecting of nerve fibers to the mushroom body, central complex, pons and so on, these parts of crickets may be related to high-level visual information processing center. Electrophysiologically, the discharge volume, amplitude and frequency of the forebrain corpora pedunculata area regularly changed as the light intensity changed. According to the regular changes of neuronal electrical activities changing with the variation of light intensity, we conferred the forebrain corpora pedunculata area was involved in cricket visual regulation.