NEUROANATOMY AND SEROTONIN IMMUNOREACTIVITY IN THE BRAIN AND SUBOESOPHAGEAL GANGLION OF THREE BEETLES / 神经解剖学杂志

ABSTRACT

The structure and 5-HT immunoreactivity in the brain and suboesophageal ganglion of three beetles, Ambrostoma quadriimpressum, Henosepilachna vigintioctomaculata and Oxycetonia jucunda, were first studied by means of colophony-paraffin embedding serial section technique and strepteavidin-peroxidase immunohistochemical method. The results showed that the brains of these three taxonomically closely related beetles were remarkably different in composition and size. Mushroom bodies and antennal lobes in Oxycetonia jucunda were conspicuous. Calyces and lobes of the mushroom bodies.were much developed. In contrast, calyces of Ambrostoma quadriimpressum and Henosepilachna vigintioctomaculata were extremely undeveloped. However, the postretinal fibres and circumpharyngeal nerves of Ambrostoma quadriimpressum were highly developed. In the three beetles, 5-HT immunoreactivity was present in all neuropils of the brain and the suboesophageal ganglion. The pattern of 5-HT immunoreactivity and the localization of immunoreactive somata which often clustered into groups were similar among these beetles, while the immunoreactivity intensity was distinct, especially in the lamina. The results suggest that the three beetles have given rise to adaptive radiation under the evolutionary pressure because of the long-term different life styles and living environments in which the taxonomic status of Ambrostoma quadriimpressum is relatively low. The similarity of the pattern of 5-HT immunoreactivity and localization of some positive somata among the three beetles raise the possibility that 5-HT seemes to serve similar physiological function in different insects. Furthermore, 5-HT might be involved in modulating the ingestion by regulating muscular activity and visual sensitivity.