THE TEMPORARY INACTIVATION OF THE RED NUCLEUS AFFECTS PERFORMANCE OF BOTH CONDITIONED AND UNCONDITIONED NICTITATING-MEMBRANE RESPONSES IN THE RABBIT

These experiments are part of a series of studies examining the role o f the red nucleus in the performance of the conditioned and unconditio ned nictitating membrane reflexes in the rabbit. Specifically, the exp eriments test the hypothesis that the temporary inactivation of the re d nucleus selectively affects the performance of the conditioned refle x. The experiments were designed to assess the effects of lidocaine an d control saline microinjections on conditioned as well as uncondition ed responses in both paired and unpaired trials. Rabbits were chronica lly implanted with cannulae through which small injecting tubes were p assed stereotaxically to the red nucleus. The animals were conditioned using a delay paradigm in which a 1 kHz tone and an air puff applied to the cornea were used as the unconditioned and conditioned stimulus, respectively. Once conditioned, the effects of either lidocaine or sa line injection were evaluated while alternating paired trials with unp aired trials in which only the air puff was applied. The principal fin ding of this study was that the amplitudes of both the conditioned and unconditioned responses were reduced following lidocaine injection in to the red nucleus. The effect on the unconditioned response amplitude could not be ascribed to any interaction between the conditioned and unconditioned responses, since it also was present in the unpaired tri als. The reduction in amplitude of the conditioned and unconditioned r esponses was shown to be correlated with changes in other characterist ics of the same responses. The data suggest that the red nucleus contr ibutes to the performance of both the conditioned and unconditioned ni ctitating membrane reflexes and consequently is not likely to be invol ved only in pathways responsible for mediating and/or storing the engr am for the conditioned reflex.