Original Articles

Dualistic action of scopolamine on avoidance conditioned response in dogs

Xin-yi Niu, Wei-jun Wang, Yin-chang Jin


Six mongrel dogs were trained to respond conditionally to an electric stimulus on the skin when a bell-ringing served as the positive conditional stimulus to which the dogs responded by raising the right foreleg to switch off the subsequent electric stimulus. The dogs were also trained to discriminate a buzzer-ringing, the negative conditional stimulus, from the bell.
Scopolamine administered singly in these dogs produced a stimulating effect at 0.1 mg/kg as shown by failure of the dogs to discriminate the signals, and a depressive effect at 0.5 mg/kg as shown by their failure to respond to positive conditional stimuli. The dogs showed a “tolerance” to repeated doses of the drug. Scopolamine synergized with chlorpromazine in depressive effect and with amphetamine in stimulating effect. The present results confirmed the previous reports on the dualistic central action of scopolamine not only at different doses but also at an identical dose.
In view of the development of surgical anesthesis with scopolamine and chlorpromazine on the basis of the synergism in their central depressive effect, further studies on the mechanism of their actions, alone or in combination, are desirable.

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