Contributions of the amygdaloid central nucleus to the modulation of the nictitating membrane reflex in the rabbit.

The contributions of the amygdaloid central nucleus (ACe) to the modulation of the amplitude of the nictitating membrane reflex (NMR) were determined. Experiment 1 demonstrated that low-level electrical stimulation of the ACe enhances the amplitude of the NMR when administered immediately preceding the elicitation of the reflex by an eyelid stimulus. In Experiment 2 the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase determined that the ACe projects to the entire rostrocaudal extent of the lateral tegmental field (LTF), the brainstem area in which the multisynaptic component of the unconditioned NMR pathway is believed to be located. These results are consistent with the hypothesis that the ACe, via its projections to the LTF, modulates reflex sensitivity during conditioned arousal and may contribute to the associative enhancement of the unconditioned NMR that occurs early during Pavlovian nictitating membrane conditioning.