LS-2-P-2500 Does adipokinetic hormone play a role in neuronal communication within the insect brain?

Adipokinetic hormones (AKHs) are a group of well-known insect metabolic neurohormones. Those hormones are responsible for activation of insect organism under stress conditions and for keeping the body homeostasis. AKHs are synthesized and released from an endocrine retrocerebral gland - the corpus cardiacum, however, small amounts of the hormone have been identified also in the brain. Interestingly, a role of AKH in the brain is not satisfactory elucidated. To contribute to solving of this problem we studied a subcellular localization of AKHs in the brain of the firebug Pyrrhocoris apterus (Heteroptera, Insecta), which possesses two AKHs: octapeptides Pyrap-AKH and Peram-CAH-II. Confocal and immunoelectron microscopy revealed that in brain neurones the hormones are synthesised in specialized secretory granules that are localized predominantly in neuronal bodies, from them they are probably transported into the axons, where the hormones might play a role in neuronal signalling. This was supported by recording of the positive AKH immunoreaction in axons unequivocally outside the granules. The neurotransmittor function of AKH in insect brain is assumed for a long time, nevertheless, the situation is far from clear and the direct proof is still missing.

For immunoelectron microscopy we have used 4% formaldehyde (EM Grade) fixation, embedding into Epon-araldite resin or into LR White resin, polyclonal rabbit anti-Pyrap-AKH as primary and anti-rabbit as secondary antibody conjugated with colloidal gold. Sections were stained with lead citrate, carbon coated and examined under the Jeol 1010 transmission electron microscope.