Is octopamine a transmitter mediating hormone release in insects?

Area of Science:

• Neurobiology
• Endocrinology
• Insect Physiology

Background:

• The corpus cardiacum (CC) in Locusta migratoria releases hyperlipemic hormone.
• This release is controlled by axons in nervus corpus cardiacum II (NCC II).
• The precise neurotransmitter involved in this synaptic control is not fully understood.

Purpose of the Study:

• To investigate the role of aminergic neurotransmitters in regulating hyperlipemic hormone release.
• To identify the specific neurotransmitter and receptor type involved in the NCC II-CC synapse.
• To explore the potential function of octopamine in insect hormone regulation.

Main Methods:

• Electrical stimulation of NCC II in isolated CC preparations.
• Application of aminergic agonists and antagonists (phenoxybenzamine, propranolol).
• Measurement of hormone release in response to stimulation and pharmacological agents.
• Quantification of octopamine levels in CC tissue.
• High-potassium saline was used as a control for non-synaptic release.

Main Results:

• Electrical stimulation of NCC II failed to induce hormone release in CC from reserpine-treated locusts.
• Alpha-adrenergic blocker phenoxybenzamine abolished electrically stimulated release, while beta-blocker propranolol potentiated it.
• Phenoxybenzamine did not affect high-potassium-induced release, suggesting postsynaptic receptor involvement.
• Octopamine was detected in CC, and its depletion by reserpine correlated with reduced hormone release.
• Exogenous octopamine induced hormone release, which was blocked by phenoxybenzamine.

Conclusions:

• The neurotransmitter controlling hyperlipemic hormone release is likely aminergic, possibly octopaminergic.
• Postsynaptic receptors on CC glandular cells resemble vertebrate alpha-adrenergic receptors.
• Octopamine is a potential neurotransmitter mediating hormone release in insects.