Eliminating afferent impulse activity does not alter the dendritic branching of the amphibian Mauthner cell.
In the developing amphibian, the formation of extra vestibular contacts on the Mauthner cell (M-cell) enhances dendritic branching, while deprivation reduces it (Goodman and Model, 1988a). The mechanism underlying the interaction between afferent fibers and developing dendritic branches is not known; neural activity may be an essential component of the stimulating effect. We examined the role of afferent impulse activity in the regulation of M-cell dendritic branching in the axolotl (Ambystoma mexicanum) embryo. M-cells occur as a pair of large, uniquely identifiable neurons in the axolotl medulla. Synapses from the ipsilateral vestibular nerve (nVIII) are restricted to a highly branched region of the M-cell lateral dendrite. We varied the amount of nVIII innervation and eliminated neural activity. First, unilateral transplantation of a vestibular primordium deprived some M-cells of nVIII innervation and superinnervated others. Second, surgical fusion of axolotls to TTX-harboring California newt (Taricha torosa) embryos paralyzed the Ambystoma twin: voltage-sensitive Na+ channel blockade by TTX eliminated action potential propagation. Reconstruction of M-cells in 18 mm larvae revealed that dendritic growth was influenced by in-growing axons even in the absence of incoming impulses: impulse blockade had no effect on the stimulation of dendritic growth by the afferent fibers.
Goodman
L A
LA
Department of Neuroscience, Rose F. Kennedy Center for Research in Mental Retardation and Human Development, Albert Einstein College of Medicine, Bronx, New York 10461.
Model
P G
PG
D000200:Action Potentials / Q000187:drug effects; D000557:Ambystoma / Q000196:embryology; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology; D003712:Dendrites / Q000502:physiology*; D008526:Medulla Oblongata / Q000196:embryology / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D012455:Salamandridae / Q000196:embryology; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D014725:Vestibular Nerve / Q000187:drug effects / Q000196:embryology / Q000502:physiology
D013779:Tetrodotoxin