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Intrinsic and extrinsic modulation of a single central pattern generating circuit
P T Morgan1, R Perrins, P E Lloyd
1Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, New York 10029, USA.
Journal of Neurophysiology
|September 9, 2000
Summary
This study reveals how intrinsic and extrinsic neuromodulation control biting behaviors in Aplysia. Both systems enhance motor program frequency, but extrinsic modulation primes biting, while intrinsic modulation occurs during the act.
Area of Science:
- Neuroscience
- Behavioral Biology
- Computational Neuroscience
Background:
- Neural circuit flexibility, crucial for rhythmic behaviors, is attributed to intrinsic and extrinsic neuromodulation.
- Direct comparison of these modulatory forms has been challenging due to studies in disparate neural circuits.
- Understanding neuromodulation in central pattern generators (CPGs) is key to deciphering motor control.
Purpose of the Study:
- To investigate and compare intrinsic and extrinsic neuromodulation of the Aplysia biting central pattern generator (CPG).
- To elucidate the specific roles and temporal dynamics of extrinsic and intrinsic modulatory systems.
- To determine the mechanisms underlying the observed modulatory effects and their functional significance.
Main Methods:
- Electrophysiological recordings and pharmacological manipulations in Aplysia.
- Investigation of the roles of metacerebral cell (MCC) neurons and cerebral peptide-2 (CP-2) in modulating the biting CPG.
- Analysis of the temporal interplay between extrinsic (serotonergic MCC) and intrinsic (CP-2/CBI-2) modulatory systems.
Main Results:
- Both extrinsic and intrinsic neuromodulation increase biting motor program frequency and shorten protraction phase duration.
- Extrinsic modulation by MCC neurons (mimicked by serotonin) and intrinsic modulation by CBI-2 interneurons (via CP-2) were identified.
- MCC activity precedes biting initiation (appetitive phase), while CBI-2 activity coincides with biting (consummatory phase), indicating distinct temporal roles.
Conclusions:
- The Aplysia biting CPG is dually modulated by extrinsic (MCC) and intrinsic (CBI-2/CP-2) systems with distinct temporal patterns.
- Sequential activation allows for prefacilitation of biting during appetitive phases without disrupting ongoing behaviors.
- This temporal segregation of neuromodulation optimizes motor control by separating preparatory and execution-phase functions.
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