Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 50, Issue 2 B90-B96, Copyright © 1995 by The Gerontological Society of America
Effects of chlordiazepoxide and scopolamine, but not aging, on the detection and identification of conditional visual stimuli
J McGaughy and M Sarter
Department of Psychology, Ohio State University.
Our previous studies revealed impairments in the ability of aged rats to
detect brief, rarely and unpredictably occurring stimuli. The failure of
these impairments to interact with the effects of benzodiazepine receptor
(BZR) ligands was attributed to low demands on stimulus-related information
processing. Thus, in the present experiment, rats of different ages were
trained to detect visual stimuli that were flashing at 20 Hz, or were
constantly illuminated, for 8, 3, or 5 sec. Additionally, selection of the
correct lever to report detection required the processing of propositional
rules (e.g., flashing-go left; constant-go right), i.e., the identification
of the stimulus. All measures of performance varied with stimulus duration.
Subsedative doses of the BZR agonist chlordiazepoxide (CDP; 3.13, 4.69
mg/kg), similar to the effects of the muscarinic antagonist scopolamine
(.025, 0.1 mg/kg), impaired response accuracy, increased the number of
errors of omission and decreased response latencies. Animals aged 28 months
omitted more trials following the administration of CDP than 12- month-old
rats. Age did not produce main effects and did not interact with the
effects of the drugs on response accuracy. It is speculated that, as
stimuli had to be presented for relatively long periods of time (to
maintain above chance-level discrimination performance), demands on
detection remained too low to replicate previously documented effects of
age. The demonstration of interactions between the effects of age and of
BZR-ligands appears to depend on combined demands for stimulus detection
and identification.
