Central adrenergic neurons in DOCA-salt hypertension

The effects of various doses of 6-hydroxydopamine (6-OHDA) injected into the hypothalamus on DOCA-salt-induced hypertension were studied. The development of hypertension was prevented in the group treated with the highest dose of 6-OHDA, and the onset of hypertension was delayed in a dose-dependent fashion in the groups treated with the lower doses of 6-OHDA. Catecholamine histofluorescence observations showed that the cannula tips placed the drug lateral to the third ventricle. The most prominent change observed was a marked unilateral reduction in the fluorescence of the dopaminergic nerves of the caudate-putamen and in the number of cell bodies in the substantia nigra. These results suggest possible sites of central aminergic control of blood pressure.

Cholinergic innervation of the canine and human ventricular conducting system. Anatomic and electrophysiologic correlations

Augmentation of vagal tone increases ventricular fibrillation threshold (VFT) under nonischemic and ischemic conditions and protects against spontaneous ventricular fibrillation during experimental myocardial infarction. The purpose of this study was to identify the anatomic pathways responsible for this cholinergically-mediated enhanced electrical stability and to determine whether or not these pathways are present in human hearts. Rich cholinergic innervation of the sinoatrial node, atrioventricular node, and atrial myocardium was confirmed in both canine and human hearts. Although sparse cholinergic innervation was present in ventricular myocardium, numerous cholinergic nerve fibers were present in ventricular conduction tissue of both canine and human hearts. To determine whether these cholinergic fibers mediate the protective effects of vagal stimulation, cholinergic fibers to the ventricular conducting system were ablated in dogs. The ablation procedures used resulted in histologic absence of cholinergic nerves in the ventricular conducting system; innervation of the atrium, however, was histologically intact. In these animals vagal stimulation no longer increased VFT but still caused slowing of the sinus rate. The effect of vagal stimulation on VFT was shown to be independent of adrenergic innervation in a group of catecholamine depleted animals (6-hydroxydopamine). We conclude that 1) the enhanced ventricular electrical stability produced by vagal stimulation in dogs is mediated by cholinergic nerve fibers which supply the ventricular conduction system, and 2) this anatomic pathway is present in human hearts.

Effects of vinblastine on noradrenergic axons

1 The effects of vinblastine and 6-hydroxydopamine (6-OHDA) on various parameters of adrenergic neurone functions in the rat were examined and compared.2 During the first 12 h after injection of vinblastine, although the concentration of cardiac noradrenaline was unaltered, the turnover rate of the catecholamine in the heart was reduced to 40 ng g(-1) h(-1) compared to a rate of 66 ng g(-1) h(-1) in the hearts of animals treated with 0.9% w/v NaCl solution.3 The uptake of noradrenaline by rat atria in vitro was inhibited by vinblastine (2.5 x 10(-4) M) or 6-OHDA (5 x 10(-5) M), but only the inhibitory effect of vinblastine was readily reversible. The in vitro uptake of noradrenaline by atria of vinblastine- or 6-OHDA-treated rats was found to be impaired two days after injection of the drugs. After 14 days, however, the noradrenaline uptake was 71% of control values after vinblastine and 91% after 6-OHDA.4 In addition to intensely fluorescent nerve trunks in epicardial connective tissue septa, a decrease in the number of fluorescent adrenergic terminals in the atria and ventricles could be observed two days after vinblastine injection. It is suggested that intravenous vinblastine treatment, like 6-OHDA, results in the destruction of adrenergic nerve terminals.

Sympathetic reinnervation of the rat iris in organ culture

Reinnervation of sympathetically denervated rat iris by superior cervical ganglion cells has been demonstrated to occur in vitro. Return of [(3)H]norepinephrine uptake by irises incubated in contact with ganglia was associated with the reappearance of nerve fibers containing catecholamines that were demonstrable by fluorescent histochemistry. The reinnervating neurons appeared to follow the same general pattern of innervation seen in the normal iris, but the density of the neural plexus was much greater. Nerve growth factor influenced the rate and extent of innervation of the iris but not of neuronal growth within the ganglion.