Glutamate Induces Different Neuronal
Conditioned Responses than ACPD When Used As a Locally
Ionophoresed Unconditioned Stimulus in the Cat Motor Cortex
CH. D. WOODY
Departments of Neurobiology, Psychiatry and Biobehavioral
Science, UCLA Center for Health Sciences, Mental Retardation
Research Center, Brain Research Institute, Los Angeles, U.S.A.
Summary
Single unit recordings were made from the motor cortex of
conscious cats with glass micropipettes that allowed
ionophoretic application of 0.5 M glutamate in 2 M NaCl or 0.5 M
ACPD (1S,3R-1-amino-cyclopentane-1,3-dicarboxylic acid, a mGluR
agonist) in 2 M NaCl. Activity in response to a 70 dB click (1
ms rectangular pulse to loudspeaker) was studied before, during,
and immediately after applying each agent locally as a paired US
(90 nA current 570 ms after click for 300 ms in combination with
glabella tap). A 70 dB hiss sound was presented 4.4 sec after
the click as a discriminative stimulus (DS). CS and DS were
presented 10 times initially (adaptation); then CS, US plus tap,
and DS (approximately 10 times as conditioning); and then CS and
DS (2-10 times to test post-conditioning). Glutamate potentiated
the mean, early, 8-16 ms response to the click after
conditioning (t=18.2, p<0.0001), but not the baseline activity
which decreased from a mean of 17 spk/sec to 7 spk/sec (t=3.71,
p<0.001). Baseline activity increased to 31 spk/sec when
glutamate was applied during conditioning (t=3.30, p<0.005).
ACPD reduced the intermediate, 64-72 ms response to the click
after conditioning (t=8.18, p<0.0001), and potentiated the late
104-112 ms response (t=15.4, p<0.0001). Baseline activity was
slightly increased after conditioning with ACPD. Saline did not
potentiate the response to click. The results indicate that
glutamate agonists that differ in their receptor affinities can
induce different CRs when used as locally applied USs to
condition neuronal responses to a click CS in the motor cortex
of cats.
Key
words
Conditioning • Learning • Pavlov • Metabotropic receptors •
Excitatory amino acids
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Dr. C.D. Woody, UCLA Center for Health Sciences, NPI, 760
Westwood Plaza, Los Angeles, CA 90024, USA
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