The development of spinal circuits underlying motor behaviors was examined in zebrafish. Zebrafish embryos showed three sequential, stereotyped behaviors: a transient period of spontaneous coiling contractions, followed by touch-evoked rapid coils, and swimming. Lesioning the hindbrain eliminated swimming and touch responses, but not the spontaneous contractions. / The first (spontaneous) behavior was chosen for further analysis in order to characterize the underlying circuit. In vivo patch clamp recordings were obtained from identified spinal neurons. These neurons showed periodic depolarizations that triggered rhythmic bursts of action potentials with a frequency and duration that were consistent with those of the spontaneous contractions. As with the behavior, transecting the spinal cord at the hindbrain border did not affect the rhythmic activity patterns of the neurons. Surprisingly the contractions and the periodic depolarizations were insensitive to both general and specific blockade of synaptic transmission. The periodic depolarizations were suppressed by heptanol and by intracellular acidification treatments that are known to uncouple gap junctions, indicating that electrotonic synapses could underlie network synchronization during the earliest motor behavior. / Paired recordings were obtained from identified spinal neurons. These showed that active ipsilateral neurons were electrically coupled in a simple network consisting initially of motoneurons and only three types of interneurons. Therefore, this early spinal circuit consists of rhythmically active and electrically coupled neurons. Furthermore, this circuit is also initially independent of the main neurotransmitter systems, sensory inputs, and descending hindbrain projections. The descending projections are required later in development for the onset of touch responses and swimming.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.37628 |
| Date | January 2001 |
| Creators | Saint-Amant, Louis. |
| Contributors | Drapeau, Pierre (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001845262, proquestno: NQ75680, Theses scanned by UMI/ProQuest. |
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