Glutamate induces different neuronal conditioned responses than ACPD when used as a locally ionophoresed unconditioned stimulus in the cat motor cortex.
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.
Woody
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Department of Neurobiology, UCLA Center for Health Sciences, Mental Retardation Research Center, Brain Research Institute, NPI, 760 Westwood Plaza, Los Angeles, CA 90024, USA.
D000161:Acoustic Stimulation / Q000379:methods; D000287:Administration, Topical; D000818:Animals; D003213:Conditioning, Psychological / Q000187:drug effects*; D003515:Cycloleucine / Q000008:administration & dosage* / Q000031:analogs & derivatives*; D004192:Discrimination, Psychological; D018698:Glutamic Acid / Q000008:administration & dosage*; D006801:Humans; D007478:Iontophoresis; D009044:Motor Cortex / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists
D018094:Receptors, Metabotropic Glutamate; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D018698:Glutamic Acid