Autonomic ganglionic neurones in rabbits with differing resistance to emotional stress

The aim of the present study was to evaluate the reactions of autonomic neurones of the nodose ganglion of the vagus nerve, and the stellate and superior cervical ganglia in rabbits under emotional stress, and to correlate these reactions with the individual variations in responses to the stressor. Emotional stress was induced in immobilized adult male Chinchilla rabbits by electrical stimulation of the ventromedial hypothalamus and skin. During the experiment (3 hours) arterial blood pressure (BP) was recorded. Metabolic activities of the stellate and superior cervical sympathetic ganglia and nodose ganglion were measured as contents of biogenic amines and their synthesizing and degrading enzymes, neuronal size and dry mass and total RNA; these corresponded to the changes in BP. One group of rabbits showed small fluctuations of BP throughout the experiment and were defined as resistant to stress, whereas in the other group (predisposed to stress) BP progressively decreased. In the former, there was a smaller increase of sympathetic and nodose ganglia metabolic activity than in the latter, in which changes included reduced neuronal dry mass, increased RNA content compared with controls, and reduced tyrosine hydroxylase activity and increased norepinephrine content compare with controls and stress- resistant rabbits. The predisposed rabbits showed earlier and greater increases in circulating norepinephrine concentrations than the resistant rabbits, indicating sustained sympathetic activation. The data indicate that the ganglia of the sympathetic nervous system are part of a major mechanism of BP regulation under acute experimental emotional/painful stress. The nodose ganglion participates in the maintenance of stable cardiovascular function in extreme conditions.