Journal of Neurophysiology, Vol 58, Issue 6 1420-1430, Copyright © 1987 by APS
Voltage spread in an identified interneuron of the barnacle's visual system
L. A. Oland, A. E. Stuart, J. H. Hayashi and J. C. Callaway
Department of Physiology, University of North Carolina, Chapel Hill 27514.
1. The interneuron that is postsynaptic to barnacle photoreceptors (the
inverting, or I-cell) receives similar synaptic input from the receptors
onto its two distinct and separate arbors. We compared the spread of
light-evoked synaptic potentials from the proximal and distal arbors with
the cell's soma in order to ascertain how well voltages spread in this
cell. 2. The proximal and distal arbors are connected by a commissural
process approximately 200 microns in length and 2 microns in diameter.
Voltages spreading from the distal arbor along this process were 20-60% of
their original value, and delayed 15-20 ms, when recorded at the cell's
soma. 3. The reversal potential of the receptor's input to the distal
arbor, determined by injecting current into the soma, appeared
substantially negative (-150 mV) to that of the identical input to the
proximal arbor (-80 mV). Assuming identical reversal potentials in the two
arbors, this difference indicates that more current must be injected into
the I-cell's soma to change the voltage of the distal arbor to a given
potential than to change that of the proximal arbor to the same potential.
4. Comparison of input from a lateral eye to the ipsilateral arbor with
that from the median eye to the same arbor indicates that these two inputs
are at an electrically equivalent distance from the soma. 5. Uneven
illumination of the eyes may, through local conductance changes, cause the
arbors to function independently, even to the point where one arbor may
depolarize when the other is hyperpolarized.
