Journal of Neuroscience, Vol 5, 596-602, Copyright © 1985 by Society for Neuroscience
Relationship between heterosynaptic reflex facilitation and acquisition of the nictitating membrane response in control and scopolamine- injected rabbits
JA Harvey, I Gormezano and VA Cool-Hauser
Classical conditioning of the rabbit nictitating membrane response was
accomplished by presenting a 100-msec tone conditioned stimulus at
intervals of 0, 100, 200, 400, and 800 msec before the presentation of a
100-msec shock unconditioned stimulus. In addition, tone-alone and
shock-alone trials were interspersed during conditioning. On the first day
of conditioning, during which there was no evidence of acquisition of
conditioned responses to the tone conditioned stimulus, the amplitudes of
the nictitating membrane response evoked on paired tone- shock trials were
compared with the amplitudes obtained on shock-alone trials to provide a
measure of reflex facilitation. There was a significant correlation (+0.86)
in control animals between the degree of reflex facilitation and the degree
of learning demonstrated at the various tone-shock intervals. Both reflex
facilitation and learning were absent at the 0-msec tone-shock interval,
increased at the 100- msec interval, reached a maximum at the 200-msec
interval, and then declined at the longer intervals. Scopolamine (0.4
mg/kg) did not affect the amplitude of the nictitating membrane response
elicited on shock-alone trials but eliminated any evidence of reflex
facilitation or learning at the 100- and 800-msec intervals and
significantly reduced both reflex facilitation and learning at the 200- and
400-msec intervals. The comparable effects of scopolamine on both reflex
facilitation and learning were reflected by a significant correlation
(+0.95) between these two measures.(ABSTRACT TRUNCATED AT 250 WORDS)