Peptidergic modulation of a multi-functional central pattern generator in the pulmonate snail

Area of Science:

• Neurobiology
• Reproductive Behavior
• Invertebrate Zoology

Background:

• Egg laying in pulmonate snails involves substrate preparation via rhythmic rasping.
• The neurohormonal control of initiating egg laying is understood, but signals modulating buccal motor patterns for substrate cleaning are unknown.
• Invertebrate gonadotropin-releasing hormone/corazonin (invGnRH/CRZ) family neuropeptides are implicated in reproduction across species.

Purpose of the Study:

• To investigate the neurochemical signals modulating buccal central pattern generator (CPG) activity for substrate cleaning during egg laying in pulmonate snails.
• To determine the role of vertebrate gonadotropin-releasing hormone (GnRH) and invGnRH/CRZ neuropeptides in regulating egg-laying behaviors.

Main Methods:

• Immunohistochemistry
• Intracellular electrophysiology
• Extracellular nerve stimulation
• Pharmacological manipulation using vertebrate GnRH agonist and antagonist

Main Results:

• Vertebrate GnRH agonist altered the buccal motor pattern underlying substrate cleaning.
• Vertebrate GnRH antagonist blocked signals from the intestinal nerve, which are crucial for egg-laying behaviors.
• GnRH-triggered responses induced specific rhythmic buccal activity (phase 2 and non-phase 2) with phase 3 shutdown, mimicking rasping without swallowing.
• A member of the invGnRH/CRZ family was identified as a potential signal for switching the buccal CPG to a rasping rhythm.

Conclusions:

• Vertebrate GnRH signaling influences snail buccal motor patterns related to egg-laying substrate preparation.
• Neuropeptides from the invGnRH/CRZ family are likely involved in coordinating reproductive behaviors, specifically substrate cleaning, in pulmonate snails.
• This study reveals a novel role for invGnRH/CRZ neuropeptides in modulating complex motor patterns for specific reproductive actions.