Modulation of the Central Pattern Generator by the Neuropeptide GnRH, in the Snail Helisoma trivolvis.

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Presentation or Lecture

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Conference or Event

Society for Neuroscience




Central pattern generators (CPGs) are independent circuits that control behaviors, which involve a repetitive pattern of muscle activity. Often one CPG can generate a number of motor patterns. The multifunctional CPG for feeding and regurgitation in snails has been extensively studied. This CPG is located in the buccal ganglia and controls the movements of the buccal mass. The snail orchestrates a very specific reproductive behavior during egg laying, which involves cleaning up of the substrate, making use of the same musculature involved in its feeding and regurgitation activities. While the motor output of the buccal CPG has been well characterized, less is known about the integration of sensory inputs, and the modulation of the CPG. The neuropeptide, Gonadotropin releasing hormone (GnRH), is known to regulate reproductive behaviors in vertebrates. New evidence indicates that this peptide has similar functions in invertebrates too. GnRH immunoreactivity (ir) has been found in the snail Helisoma trivolis both in the neurons in the cerebral and buccal ganglia and in nerves connecting them. GnRHir was also present in the intestinal nerve, which innervates the reproductive structures. If this nerve is severed, it prevents the occurrence of egg-laying behavior. Stimulation of the intestinal nerve causes long-term rhythmic activity in neurons of the buccal ganglia, which is very similar to the pattern induced in them on bath application of GnRH. Specifically we can see a marked reduction in Phase 3 firing in the motor neuron B19 and an increase in Phase 1 motor neuron activity. This pattern of activity is hypothesized to underlie substrate-cleaning behavior.