Colocalized neuropeptides activate a central pattern generator by acting on different circuit targets

Area of Science:

• Neuroscience
• Neurobiology
• Crustacean neurophysiology

Background:

• The lobster stomatogastric ganglion (STG) generates the pyloric rhythm, a triphasic motor pattern crucial for digestion.
• Descending modulatory inputs normally regulate STG activity.
• Red pigment-concentrating hormone (RPCH) and Cancer borealis tachykinin-related peptide (CabTRP) are co-localized in STG-projecting fibers.

Purpose of the Study:

• To investigate the roles of RPCH and CabTRP in modulating the STG's pyloric rhythm.
• To determine if these neuropeptides act directly on specific STG neurons.
• To understand how co-released neuropeptides cooperate to restore network function.

Main Methods:

• Isolated lobster STG preparation.
• Electrophysiological recordings of neuronal activity.
• Application of exogenous RPCH and CabTRP.
• Removal of rhythmic drive from anterior bursting neurons.

Main Results:

• Isolated STG without modulatory inputs showed silent LP and PY neurons, with AB and PD neurons active at low frequency.
• RPCH (10^-6 M) selectively activated the lateral pyloric (LP) neuron.
• CabTRP (10^-6 M) selectively activated the pyloric (PY) neurons.
• The effects of RPCH and CabTRP persisted even when rhythmic drive was removed, indicating direct neuronal targets.
• Co-application of RPCH and CabTRP restored triphasic pyloric motor patterns with phase relationships similar to intact preparations.

Conclusions:

• RPCH and CabTRP act as cotransmitters that cooperatively activate the STG pyloric circuit.
• RPCH directly targets LP neurons, while CabTRP directly targets PY neurons.
• Cooperative action of neuropeptides on distinct network components is essential for generating complex motor patterns.