The Journal of Neuroscience, September 15, 2000, 20(18):6950-6961
Remodeling of Membrane Properties and Dendritic Architecture
Accompanies the Postembryonic Conversion of a Slow into a
Fast Motoneuron
Carsten
Duch and
R. B.
Levine
Division of Neurobiology, University of Arizona, Tucson, Arizona
85721
The postembryonic acquisition of behavior requires alterations in
neuronal circuitry, which ultimately must be understood as specific
changes in neuronal structure, membrane properties, and synaptic
connectivity. This study addresses this goal by describing the
postembryonic remodeling of the excitability and dendritic morphology
of an identified motoneuron, MN5, which during the metamorphosis of
Manduca sexta (L.) changes from a slow motoneuron that
is involved in larval-crawling behavior into a fast adult flight
motoneuron. A fivefold lower input resistance, a higher firing
threshold, and an increase in voltage-activated K+
current contribute to a lower excitability of the adult MN5, which is a
prerequisite for its newly acquired behavioral role. In addition, the
adult MN5 displays larger Ca2+ currents. The
dendrites of MN5 undergo extensive remodeling. Drastic regression of
larval dendrites during early pupal stages is followed by rapid growth
of new dendrites. Critical changes in excitability take place during
the onset of adult dendrite formation. Larval Ca2+
currents are absent when dendritic remodeling is most dramatic but
increase markedly during later development. Changes in
Ca2+ and K+ currents follow
different time courses, allowing the transient occurrence of
Ca2+ spikes during pupal stages when new dendritic
branching ceases. The adult MN5 can produce prolonged
Ca2+ spikes after K+ currents are
reduced. We suggest that alterations in Ca2+ and
K+ currents are necessary for the participation of
MN5 in flight behavior and that the transient production of
Ca2+ spikes may influence postembryonic dendritic remodeling.
Key words:
postembryonic development; calcium current; potassium
current; neuronal differentiation; insect; Manduca sexta; CNS; flight behavior
Copyright © 2000 Society for Neuroscience 0270-6474/00/20186950-12$05.00/0