Optical determination of impulse conduction velocity during development of embryonic chick cervical vagus nerve bundles.
1. Employing an optical method for multiple-site simultaneous recording of electrical activity, we have determined the conduction velocity in cervical vagus nerve bundles isolated from 5- to 21-day-old chick embryos, and investigated its developmental changes. 2. The preparations were stained with a voltage-sensitive merocyanine-rhodanine dye (NK2761), and action potential- (impulse-) related optical signals were elicited by brief stimuli applied to the end of the vagus nerve bundle with a suction electrode. Optical signals were recorded simultaneously from many contiguous regions using a 12 x 12-element photodiode array. 3. The optical signals spread with small delay from the site of stimulation. From the relationship between the delay and distance from the current-applying electrode, conduction velocities were estimated in each tested preparation: the conduction velocity was very small and increased monotonically from about 0.1 m s-1 at 5 days embryonic age to about 0.4 m s-1 by hatching. The increase in the conduction velocity was closely related to a developmental increase in the diameter of the vagus nerve bundle. 4. In addition, we have examined the spread of electrotonic potentials. The space constant was very small (200-450 microns) and increased as development proceeded. 5. Compound optical action signals having two distinct components were also recorded. They often appeared to be concentrated in the preparations from 8- to 12-day-old embryos. The conduction velocity of the second component was slower than that of the first. We suggest that appearance of the second component reflects degeneration of a subset of axons resulting from 'neural cell death' during the development of the vagus nerve.
Sakai
T
T
Department of Physiology, Tokyo Medical and Dental University School of Medicine, Japan.
Komuro
H
H
Katoh
Y
Y
Sasaki
H
H
Momose-Sato
Y
Y
Kamino
K
K
D000200:Action Potentials / Q000187:drug effects; D000375:Aging / Q000502:physiology; D000818:Animals; D002642:Chick Embryo; D004553:Electric Conductivity / Q000502:physiology; D004558:Electric Stimulation; D008854:Microscopy, Electron; D009431:Neural Conduction / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D014630:Vagus Nerve / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure
D013779:Tetrodotoxin