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Functionally heterogeneous segmental oscillators generate swimming in the medical leech
C G Hocker1, X Yu, W O Friesen
1Department of Biology, NSF Center for Biological Timing, University of Virginia, Charlottesville, VA 22903-2477, USA.
Journal of Comparative Physiology. A, Sensory, Neural, and Behavioral Physiology
|November 21, 2000
Summary
Individual leech nerve cord ganglia can generate swim oscillations, but their function varies along the cord. Anterior and posterior ganglia show weaker, slower oscillations compared to mid-cord ganglia.
Area of Science:
- Neuroscience
- Animal Behavior
- Physiology
Background:
- Swimming in the medicinal leech (Hirudo medicinalis) is controlled by neuronal circuits in the ventral nerve cord.
- The ventral nerve cord consists of homologous segmental ganglia, but the functional equivalence of swim oscillator circuits within these ganglia is not fully understood.
Purpose of the Study:
- To investigate whether individual ganglia throughout the leech ventral nerve cord can generate swim oscillations.
- To measure the cycle periods of local swim oscillations in isolated ganglia.
- To determine the functional distribution of swim-generating capabilities along the nerve cord.
Main Methods:
- Isolated individual ganglia and short chains of ganglia from different regions of the leech ventral nerve cord.
- Recorded and analyzed swim-like oscillations.
- Measured the cycle periods of these oscillations.
Main Results:
- Swim-generating function is broadly distributed but not uniform across individual ganglia.
- Anterior ganglia exhibited less robust oscillations than mid-cord ganglia.
- Posterior ganglia showed even weaker activity, with no oscillations observed posterior to segment 12.
- Swim-cycle periods followed a U-shaped pattern, with longer periods in anterior (2.3 s) and posterior (up to 4.0 s) ganglia compared to mid-cord ganglia (approx. 1.0 s).
Conclusions:
- The leech swim system is composed of functionally heterogeneous local oscillator units.
- The distribution and properties of these units vary along the ventral nerve cord.