Role of the cholinergic system of the neostriatum in regulating several forms of defensive behavior

Studies were carried out on the effects of microinjection of carbacholine, a choline receptor agonist, into the dorsal striatum on the discrimination of sensory signals in chronic experiments on dogs with an operant defensive reflex involving maintenance of a flexor pose and in rats trained to a conditioned active escape reflex (CAER) in a T-maze; the sensory signals involved were important in the behavioral situations used. Carbacholine microinjection improved the process of discrimination, with an increase in the number of correct responses in rats in the T-maze discrimination-requiring CAER, and with improvements in responses to differentiation stimuli in the operant defensive reflex requiring maintenance of a defined pose in dogs. The efficiency of the effect depended on the level of training. There were two situations in which responses did not improve: when there was no signal discrimination in background conditions before microinjection, and in conditions of complete differentiation of the signals, i.e., complete training. It would appear that the neostriatum is not involved in the behavioral reactions in either of these situations, and this may result primarily from low levels of neuronal activity in response to these signals.