Abstract
Locomotor control requires functional flexibility to support an animal's
full behavioral repertoire. This flexibility is partly endowed by
neuromodulators, allowing neural networks to generate a range of motor
output configurations. In hatchling Xenopus tadpoles, before the
onset of free-swimming behavior, the gaseous modulator nitric oxide (NO)
inhibits locomotor output, shortening swim episodes and decreasing swim
cycle frequency. While populations of nitrergic neurons are already
present in the tadpole's brain stem at hatching, neurons positive for
the NO-synthetic enzyme, NO synthase, subsequently appear in the spinal
cord, suggesting additional as yet unidentified roles for NO during
larval development. Here, we first describe the expression of locomotor
behavior during the animal's change from an early sessile to a later
free-swimming lifestyle and then compare the effects of NO throughout
tadpole development. We identify a discrete switch in nitrergic
modulation from net inhibition to overall excitation, coincident with
the transition to free-swimming locomotion. Additionally, we show in
isolated brain stem-spinal cord preparations of older larvae that NO's
excitatory effects are manifested as an increase in the probability of
spontaneous swim episode occurrence, as found previously for the
neurotransmitter dopamine, but that these effects are mediated within
the brain stem. Moreover, while the effects of NO and dopamine are
similar, the two modulators act in parallel rather than NO operating
serially by modulating dopaminergic signaling. Finally, NO's activation
of neurons in the brain stem also leads to the release of NO in the
spinal cord that subsequently contributes to NO's facilitation of
swimming.
Original language | English |
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Pages (from-to) | 1446-1457 |
Journal | Journal of Neurophysiology |
Volume | 115 |
Issue number | 3 |
Early online date | 18 Mar 2016 |
DOIs | |
Publication status | Published - Mar 2016 |
Keywords
- Locomotion
- Tadpole
- Development
- Nitric oxide
- Modulation
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Keith Thomas Sillar
- School of Psychology and Neuroscience - Emeritus Professor
Person: Emeritus Professor