GABA and serotonin immunoreactivity during postembryonic brain development in the beetle Tenebrio molitor.

Analysis of the serotonin immunoreactive neurons in the central brain of the beetle Tenebrio molitor during postembryonic development shows that the basic structural characteristics of larval brain resemble those of the adult. Most, if not all, serotonin immunoreactive central brain neurons persist with metamorphosis. Their fate can be followed during development. GABA immunoreactivity occurs in about 360 neurons assembled in ten different clusters of somata in the larval midbrain. During metamorphosis no additional clusters are formed. However, the number of immunoreactive neurons increases to 450. Their morphological analysis is restricted to location of the somata and the distribution of arborizations within neuropil areas. Metamorphic transition of glomerular sub-units in the antennal lobes as well as ellipsoid body development can be followed by GABA immunohistochemistry. Furthermore, the study of these transitions proved useful in displaying changes during metamorphic pattern formation induced by sublethal application of the pyrethroid insecticide fenvalerate.