Localization of the main noradrenergic neuron groups in the pons and medulla of the rabbit and the importance of cathodal lesions for prolonged survival.

Methods for stereotaxically localizing the major noradrenergic (NA) cell groups (i.e. A1, A2, A5 and A6 + A7) in the rabbit are described. Using a modified Kopf head holder we used surface landmarks including the obex for making lesions of the A1 and A2 cells in the medulla. Localization of the pontine cell groups was done by mapping intracerebral structures including the facial nerve for A5 and the motor nucleus of the trigeminal nerve for A6 + A7. In the initial experiments we made A1 lesions by passing anodal currents through stainless steel electrodes, which was associated with pulmonary oedema, neurological complications and a high mortality. This syndrome was probably related to toxic effects of ferric ion deposition, and disappeared when cathodal currents were employed. We have now made 106 bilateral cathodal lesions in the different groups, with a 20% intraoperative mortality. But virtually all survivors remained indefinitely in clinically good condition for the 2-4 weeks duration of our experiments. In 65 of these rabbits we achieved greater than 75% of NA cell destruction (average 84%). From the cardiovascular viewpoint 'non-specific' damage by the lesions was relatively small, except after A2 lesions where there was some impairment in the baroreceptor-heart rate reflex, though a considerable amount of residual function remained.