Journal of Neuroscience, Vol 3, 1014-1018, Copyright © 1983 by Society for Neuroscience
Enkephalin reduces calcium action potentials in Rohon-Beard neurons in vivo
JL Bixby and NC Spitzer
Rohon-Beard neurons of the Xenopus spinal cord develop somatic Ca++-
dependent action potentials at early embryonic stages. Because many
Ca++-dependent events are blocked or reduced by enkephalin in other
neuronal systems, we tested the effect of met-enkephalin on the Ca++ spikes
of Rohon-Beard cells. Our results indicate that met-enkephalin, which has
no effect on the resting membrane potential or conductance in these cells,
reversibly and specifically shortens their Ca++ action potentials, probably
by decreasing the Ca++ conductance. Enkephalin has a similar effect on
Xenopus dorsal root ganglion cells in vivo. Examination of Rohon-Beard
cells at various stages of development shows that enkephalin shortens Ca++
spikes from the earliest times that the spikes appear (approximately 21 hr
after fertilization) to the latest times they are detectable (7 to 9 days).
This very early response suggests either that enkephalin binds directly to
the Ca++ channels or that an "enkephalin receptor" is among the earliest
neuronal phenotypes to appear in these cells.