Study Of Relations Between Visual Adaptations Of Insect Visual System And 5-HT Content In Optic Lobe

Although light intensity in an animal's environment may vary by eleven orders of magnitude, visually driven behaviors can still deal with such changing environment. Adaptation allows the visual system to be functional in such large spectrum and significantly sensitive to match with the surrounding. We define the adaptation of the visual system to the light environment by adjusting its sensitivity as visual adaptation.Neural network adaptations to the light and darkness are thought to be controlled by light-dependent changes in 5-HT levels. In other words, 5-HT may modulate the visual adaptation state of insect visual system. This modulation is recognized to have two mechanisms. First, neurotransmitters related to visual adaptation may only release when light and darkness change. The transmitters need not to be released, when light intensity doesn't change. Second, dark adaptation and light adaptation of the related neurons in the retinal network are in a dynamic push-and-pull equilibrium, which is modulated by the levels of two kinds of transmitters. One kind of transmitters may shift the balance in favor of dark adaptation, however, the other one displayed contrary function. The state of visual system is determined by their relative contents that two kinds of transmitters released. When light adaptation transmitters work more active than dark adaptation, visual system will shift to light adaption. This experiment was designed according to these two possible mechanisms.Under same immunochemistry staining conditions, different species of insects were compared with each other by 5-HT content in their brain. We report different insects have significant difference in 5-HT content in their brain. The 5-HT content of insects that lived in darkness (such as Culex pipiens pallens) or cave insect (such as Camponotus japonicus) are higher than those (such as Mimathyma schrenckii) that live in lightness and slight-changing light intensity. We analyzed, because of the light intensity in environment of ants always changed sharply, the insect need frequent and strong visual adaptation, and thus need more modulate transmitter. We hypothesized that 5-HT was related with the visual adaptation of insect. To test this hypothesis, we divided the insect (Camponotus japonicus) into four groups for light stimulation. First group was stimulated by constant light for 9 days. The second group was kept in darkness for 9 days. The third group was treated by the alternative light and darkness for 9 days. The fourth group was retained in the natural light also for 9 ?days. Then we applied the immunochemical methods to compare those four groups in their 5-HT contents. By the image pro plus technique, we measured the grey values in the positive region of the four groups, which were statistically analyzed by the ANOVA. It was demonstrated that the difference between the grey values among the four groups was not significant. The result of this light stimulation was not consistent with our expectation. We believed that this was caused by the improper stimulation condition, which did not cause any significant difference in 5-HT content. What's more, the combination of the immunochemistry and image analysis was not sensitive and accurate. Thus it can not detect the slight difference in 5-HT content caused by the light stimulation.