The objective of this project is to correlate performance on memory-related behavioral tasks with neurotransmitter changes occurring in brain regions that process memory. Hormones released from the adrenals during emotionally arousing events influence cell groups in the lateral parabrachial nucleus (PB) and central amygdala (AMY) to encode new experiences more effectively. Since some adrenal hormones do not enter the brain, their effects on anatomical structures must be mediated by some intervening mechanism. Brainstem nuclei in the nucleus of the solitary tract (NTS) receive input regarding changes in peripheral autonomic and neuroendocrine states via the vagus nerve and convey this information to neurons in the PB and AMY. The proposed experiments are based on the hypothesis that the intervening mechanism by which epinephrine influences the AMY or PB during memory storage involves activation of catecholaminergic nuclei in the NTS. This hypothesis will be tested by determining if the reported effects of a peripheral injection of epinephrine on influencing amygdala neurotransmitter levels or facilitating memory storage processes are altered by removing the contribution of the NTS. In these experiments, the involvement of the NTS will be reduced by blocking noradrenergic receptors in this nucleus or interrupting neural transmission with the use of local anesthetics. The second set of experiments will test the hypothesis by examining whether stimulation of NTS noradrenergic neurons mimics, or produces comparable effects on memory and central amygdala norepinephrine activity as that produced by peripheral epinephrine. The final series of experiments will determine if there are corresponding increases in extracellular levels of norepinephrine in both the NTS and central amygdala after epinephrine injection, and if the changes are mediated by the PB. These findings are expected to have implications in the treatment of memory disorders by increasing understanding of the interactions between brain structures and neurotransmitter systems that regulate memory.
