Light Scattering Changes Follow Evoked Potentials from Hippocampal
Schaeffer's Collateral Stimulation
David M. Rector, Gina R. Poe, Morten P. Kristensen and Ronald M. Harper*
Brain Research Institute, University of California at Los Angeles, Los
Angeles, CA 90095-1761, Tel: 310-825-5303, FAX: 310-206-5855, e-mail:
harper@aunix.loni.ucla.edu
APStracts 4:0072, 1997.
ABSTRACT
We assessed relationships of evoked electrical and light scattering changes
from cat dorsal hippocampus following Schaeffer's collateral stimulation.
Under anesthesia, eight stimulating electrodes were placed in the left
hippocampal CA1 field, and an optic probe, coupled to a photodiode or a CCD
camera to detect scattered light changes, was lowered to the contralateral
dorsal hippocampal surface. Light at 660ñ10 nm illuminated the tissue through
optic fibers surrounding the optic probe. An attached bipolar electrode
recorded evoked right hippocampal commissural potentials. Electrode recording
s and photodiode output were simultaneously acquired at 2.4 kHz during single
biphasic pulse stimuli of 0.5 ms duration, 0.1 Hz intervals. Camera images
were digitized at 100 Hz. An average of 150 responses was calculated for each
of six stimulating current levels. Stimuli elicited a complex population
synaptic potential which lasted 100 to 200 ms, depending on stimulus intensity
and electrode position. Light scattering changes peaked 20 ms after stimuli,
and occurred simultaneously with population spikes. A long-lasting light
scattering component peaked 100 to 500 ms after the stimulus, concurrently
with larger population post synaptic potentials. Optical signals occurred over
a similar time course as electrical signals, and increased with larger
stimulation amplitude to a maximum, then decreased with further increases in
stimulation current. Camera images revealed a topographical response pattern
which paralleled the photodiode measurements, and depended on stimulation
electrode position. Light scattering changes accompanied fast electrical
responses, occurred too rapidly for perfusion, and showed a stimulus intensity
relationship not consistent with glial changes.
Received 1997 January 24,; accepted in final form 1997 May 14.
APS Manuscript Number J0066-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 11 June 1997