Differential receptor activation by cockroach adipokinetic hormones produces differential effects on ion currents, neuronal activity, and locomotion.
Adipokinetic hormone (AKH) peptides in insects serve the endocrine control of energy supply. They also produce, however, neuronal, vegetative, and motor effects, suggesting that AKHs orchestrate adaptive behavior by multiple actions. We have cloned, for Periplaneta americana, the AKH receptor to determine its localization and, based on current measurements in neurons and heterologous expression systems, the mechanisms of AKH actions. Apart from fat body, various neurons express the AKH receptor, among them abdominal dorsal unpaired median (DUM) neurons, which release the biogenic amine octopamine. They are part of the arousal system and are involved in the control of circulation and respiration. Both the two Periplaneta AKHs activate the Gs pathway, and AKH I also potently activates Gq. AKH I and--with much less efficacy--AKH II accelerate spiking of DUM neurons through an increase of the pacemaking Ca2+ current. Because the AKHs are released from the corpora cardiaca into the hemolymph, they must penetrate the blood-brain barrier for acting on neurons. That this happens was shown electrophysiologically by applying AKH I to an intact ganglion. Systemically injected AKH I stimulates locomotion potently in striking contrast to AKH II. This behavioral difference can be traced back conclusively to the different effectiveness of the AKHs on the level of G proteins. Our findings also show that AKHs act through the same basic mechanisms on neuronal and nonneuronal cells, and they support an integration of metabolic and neuronal effects in homoeostatic mechanisms.
Wicher
Dieter
D
Department of Neurohormones,Saxon Academy of Sciences, Jena, Germany. dwicher@ice.mpg.de
Agricola
Hans-Jürgen
HJ
Söhler
Sandra
S
Gundel
Matthias
M
Heinemann
Stefan H
SH
Wollweber
Leo
L
Stengl
Monika
M
Derst
Christian
C
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000502:physiology; D006706:Homeostasis; D006801:Humans; D007150:Immunohistochemistry; D007301:Insect Hormones / Q000494:pharmacology* / Q000502:physiology; D008124:Locomotion / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D009655:Octopamine / Q000502:physiology; D009842:Oligopeptides / Q000494:pharmacology* / Q000502:physiology; D010526:Periplaneta / Q000502:physiology*; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D018010:Receptors, Invertebrate Peptide / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology
D007301:Insect Hormones; D009842:Oligopeptides; D018010:Receptors, Invertebrate Peptide; D015222:Sodium Channels; C044833:adipokinetic hormone; D009655:Octopamine; D019204:GTP-Binding Proteins; D002118:Calcium; D011761:Pyrrolidonecarboxylic Acid