The Effect of Vincristine Sulphate on the Axoplasmic Flow of Proteins in Cultured Sympathetic Neurons

The effect of vincristine sulphate on the axoplasmic flow of labelled proteins in neurites of chick embryo sympathetic neurons growing in tissue culture was studied by autoradiography. In control neurons most of the 3H-proteins synthesized during a 90-min pulse with a 3H-amino acid were localized in cell bodies. There was a diminishing gradient of labelled proteins in the neurites which was highest in portions adjacent to the cell bodies and lowest at the periphery. During a physiological chase there was a gradual increase in the amount of label in the neurites, so that after a 15-h chase even the most peripheral portions were well labelled. This indicates that a portion of the labelled proteins synthesized in the cell bodies are transported peripherally into the neurites.

The centrifugal movement of labelled proteins in neurites was markedly decreased when cells were grown in medium containing 10 µg/ml vincristine sulphate. After a 15-h chase in the presence of drug only a small amount of label was in the peripheral portion of the neurites. Treatment with vincristine did not decrease the rate of amino acid incorporation or alter the rate of protein turnover during the course of the experiment. Thus an explanation of the results based on an altered rate of total cell protein synthesis or degradation is unlikely.

The capacity of sympathetic neurons to take up and concentrate exogenous [3H]norepinephrine in their neurites was only slightly reduced by vincristine. This indicates that at least some cellular activities requiring metabolic energy are relatively unaffected by the interruption in axoplasmic flow caused by vincristine and that the mechanism by which vincristine interferes with axoplasmic flow does not involve general cellular toxicity.

The major morphological differences between control and vincristine-treated neurons were the absence of microtubules and the presence of crystal-like structures within the cells. The relationship between the effect of vincristine on the axoplasmic flow of proteins and the arrangement of the microtubule system is discussed.

Selective in situ parasympathetic control of the canine sinoatrial and atrioventricular nodes

Methods were devised for the selective alteration of parasympathetic control over the sinoatrial (SA) or the atrioventricular (AV) node in anesthetized, thoracotomized mongrel dogs. Two epicardial sites were located at which parasympathetic nerve fibers enroute to the SA or the AV node could be stimulated or blocked. Selective nerve stimulation was accomplished with brief pulses (0.05 msec), and blockade was accomplished with topically applied lidocaine. At the intercaval site, only the SA node was affected. At the site near the coronary sinus ostium, only the AV node was affected in terms of parasympathetic control, but sometimes there were modest sympathetic effects on the SA node. The effects of stimulation at these sites, except for the SA speeding produced by stimulation at the site near the coronary sinus, were blocked by atropine. The effects were also blocked by ganglionic blockade. Probably, preganglionic parasympathetic fibers to the nodes are concentrated at these sites.

Sound-withdrawal hypertension in rats--a new form of experimental hypertension

Females of an inbred strain of Wistar rats, initially 160–180 g, develop hypertension when transferred from the stock (normal rat) room (NRR) to a sound-proofed semi-anechoic room (SPR). No hypertension develops when sounds in the NRR are relayed unchanged into the SPR. The hypertension reaches maximum at 4 weeks then decreases slightly to stabilize at a level approximately 30 mm Hg above normal before, and 20 mm Hg above normal after, pentolinium blockade. Histological changes are demonstrable in small arteries after 12 weeks in the SPR. Augmented pressor responses to fixed doses of noradrenaline and of tyramine, but not of angiotensin II and of vasopressin, and a general increase in organ/body wt ratios were evident in weeks 3–5 after entry to the SPR, but had reversed by week 12. These findings contrast with those made on salt-DOCA hypertensives.