Relationship between heterosynaptic reflex facilitation and acquisition of the nictitating membrane response in control and scopolamine- injected rabbits

Abstract

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)

Oscillatory brain states and learning: Impact of hippocampal theta-contingent training

“…Previous work has shown that manipulations capable of disrupting hippocampal theta (e.g., medial septal lesions and cholinergic antagonists) have a deleterious effect on acquisition of this task (16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Animals are capable of learning the task, albeit at a slower rate (but see ref.…”

“…Spectral analysis of these samples revealed that rabbits exhibiting a large proportion of slow-wave frequencies in the theta range (2-8 Hz) learned at a faster rate than those that had higher frequencies (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). The correlation between a ratio index of hippocampal frequencies (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) Hz͞2-8 Hz) and trials to criterion was 0.72. These findings indicate that an important determinant of eyeblink acquisition rate is a preexisting brain state that can be assessed by differences in hippocampal slow waves.…”

Trace Eyeblink Conditioning Increases CA1 Excitability in a Transient and Learning-Specific Manner

“…Postsynaptic alterations of both the postburst AHP and accommodation have been implicated in these models. These are particularly intriguing because the cholinergic antagonist scopolamine impairs acquisition of delay conditioning (Solomon, 1983;Harvey et al, 1985) and prevents acquisition of trace conditioning in rabbits (Kaneko and Thompson, 1995) and because acetylcholine application decreases the AHP and blocks accommodation in hippocampal neurons in vitro (Cole and Nicoll, 1983;Cole and Nicoll, 1984;Knöpfel et al, 1990). An interesting speculation is that scopolamine could compete and interfere with acetylcholine's modulation of postsynaptic excitability of CA1 neurons, thus impairing learning.…”

Hippocampal Ripple-Contingent Training Accelerates Trace Eyeblink Conditioning and Retards Extinction in Rabbits

“…To further examine early associative changes, CS-mediated reflex facilitation (Harvey et al, 1985;Weisz and LoTurco, 1988;Weisz and McInerney, 1990;Wikgren and Korhonen, 2001;Wikgren et al, 2002) was assessed by comparing unconditioned response (UR) magnitudes in the very first five trials to those in the last five trials in the first session. For this, the mean response amplitude during the 300 ms period following the US onset was determined.…”