Reaction of the mutant mouse nude to axonal injuries of the central nervous system.

The effects of unilateral forebrain and spinal cord hemisections were examined in the mutant athymic mouse nude. The activities of tyrosine hydroxylase and glutamic acid decarboxylase within the striatum and olfactory tubercle and within the midbrain ventral tegmentum, terminal fields of dopaminergic and GABA-ergic neurons, respectively, were measured to characterize the anterograde reaction of these neurons to axonal injuries. After forebrain hemisections a rapid (within 2 days) and permanent decrease was observed for all enzymes, indicating a permanent degeneration of axons with no recovery. Unilateral spinal cord hemisections resulted in a flaccid paralysis of the ipsilateral hind limb which subsided within 2 to 3 days after the lesion, and thereafter a permanent spasticity ensued. When spinal cord hemisection was repeated the initial flaccid paralysis did not occur and spasticity of the ipsilateral hind limb was immediately evident. The results indicate that regeneration of cut axons or even an improved motor recovery does not occur in the central nervous system of the nude mouse.     

'Juvenile' myasthenia gravis in early infancy

A previously well infant developed severe muscle weakness and hypotonia at 6 months of age. This was reversed by anticholinesterase medication. However, she had subsequent further weakness and died at 10 months after an acute respiratory arrest. The clinical pattern was that of the 'juvenile' form of myasthenia gravis rather than the 'congenital' forms which have previously been described in early infancy.     

Induction of dopamine-beta-hydroxylase in superior cervical ganglia in organ culture.

Dopamine-β-hydroxylase activity was increased in superior cervical ganglia maintained in vitro in media containing elevated levels of potassium. The addition of dibutyryl adenosine 3',5'-monophosphate (cyclic AMP) to normokalemic media also increased dopamine-β-hydroxylase activity. These effects were blocked by cycloheximide. The effect of raised potassium levels on dopamine-β-hydroxylase activity was potentiated by theophylline. In addition, elevated potassium activated the ganglion adenyl cyclase system. These results suggest that the depolarization-related induction of dopamine-β-hydroxylase in ganglia is mediated by cyclic AMP.     

On the mechanism of tachyphylaxis to tyramine in the isolated rat heart

Tyramine was shown to release [³H]-catecholamines from an isolated rat heart previously perfused with [³H]-noradrenaline. With successive injections of tyramine the amount of [³H]-catecholamine released fell progressively and there was a parallel decrease in the increment of amplitude and rate of contraction of the heart. Reserpinized hearts were shown to take up less [³H]-noradrenaline than normal hearts. Release of radioactivity and loss of responsiveness to tyramine occurred more rapidly in the reserpinized heart. In the same preparation the uptake of [¹⁴C]-tyramine exceeded the quantity of the noradrenaline released.