The effect of amobarbital sodium on conditioned fear as measured by the potentiated startle response in rats.

Abstract

The startle response in rats to a sudden sound was increased when the startle was elicited in the presence of a flashing light (CS) which had previously been paired with electric shock. The magnitude of this potentiated startle was used as a measure of the conditioned fear elicited by the CS. The effects of different doses of amobarbital sodium on the potentiated startle, the startle in the presence of a flashing light which had not been paired with shock, and the startle to electric shock were tested. It was found that the drug reduced the magnitude of the potentiated startle response and reduced even more the startle to electric shock, but apparently had little, if any, effect on the startle to loud sound in the presence of a neutral CS. The effects lasted for at least 90 min after i.p. injections of the drug. The action of amobarbital was interpreted in terms of a selective reduction in the strength of the fear drive, but other interpretations were not ruled out. The fact that this drug produced differential effects on startle responses elicited in different ways, suggests that such responses may be useful measures of differential psychopharmacological effects.