The Role of Norepinephrine in a Learning-Relevant Neural System

95 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.There is much evidence to suggest that norepinephrine (NE) is an important factor in many physiological and psychological functions. However, clear demonstrations of the behavioral relevance of the effects NE has on the activity of single neurons have been lacking. In this experiment, the neural effects of NE were studied in the context of a neural system with a known functional relevance. Discriminative avoidance training was given to rabbits occupying a rotating-wheel conditioning apparatus. Positive (CS+) and negative (CS$-$) conditional stimuli (1 and 8 kHz tones) were each presented for 60 trials in daily conditioning sessions. The unconditional stimulus was a footshock delivered five seconds following the onset of the CS+ on trials in which no avoidance response occurred. Localized depletions of NE were accomplished by the injection of 6-hydroxydopamine into either the cingulate cortex (Brodmann's Area 29) or the anteroventral nucleus of the thalamus (AVN). Neural activity was monitored through electrodes chronically implanted in the AVN and Area 29. Depletions of NE in Area 29 decreased the rate of conditioned avoidance responding, in comparison with control subjects. In conjunction with this, rabbits with lower natural levels of NE in area 29 were found to respond less often than those with a higher natural NE concentration. The depletion of NE in Area 29 resulted in a reduced magnitude of CS-elicited neuronal responding in Area 29 and an increased magnitude in the AVN, when compared to control subjects. Depletions of NE in the thalamus resulted in more frequent conditioned avoidance responding, enhanced neuronal responding in the AVN and decreased neuronal responding in Area 29. Rabbits with higher natural levels of NE in the AVN, and the hippocampus, made significantly more avoidance responses than those with lower natural NE concentrations. These results are interpreted in the context of a model (Gabriel, Sparenborg & Stolar, 1986, 1987) which explains functional relationships between behavior and neural activity in the AVN, Area 29, and the hippocampus. The results suggest that NE, in the AVN and Area 29, is critically involved both in processes which limit, and which drive, neuronal activity and behavior.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD