6-hydroxydopa during development of central adrenergic neurons produces different long-term changes in rat brain noradrenaline

6-hydroxydopa (6-OH-DOPA) administered to rats during their early development produces long-term modifications in the content of brain noradrenaline (NA) which have regional differences. An increase in brain stem NA is observed when the rats are exposed to the drug between the day 14 of gestation and the 9th postnatal day. When 6-OH-DOPA is injected subcutaneously on the 13th postnatal day or later, there is a decrease in brain stem NA. On the other hand, the content of NA in the telediencephalon is depleted for the first time in rats exposed to the drug during the day 16 of gestation, the decrease is more evident when the injection is done on days 17 or 18 and the effect is also marked when the drug is administered in the period between the day of birth and the 20th day of age. These results indicate that 6-OH-DOPA exerts different effects during the process of development and that the increase in brain stem NA is not solely dependent on the depletion produced in the forebrain because both phenomena are temporally dissociated. The adrenergic neurons injured by the drug, most probably respond in such a way that leads to an increase in brain stem NA only during the period in which they are under the influence of the factors controlling their physiologic development.

Stimulation of beta-adrenergic receptors in the pineal gland increases the noradrenaline stores of its sympathetic nerves

The administration of isoproterenol decreases the level of serotonin in the rat pineal gland and at the same time it increases pineal noradrenaline. These effects depend on the stimulation of a beta-adrenergic receptor because they are blocked by pretreatment of the animals with propranolol; this drug by itself does not modify either serotonin or noradrenaline levels in the pineal. The elevation of noradrenaline produced by isoproterenol is selective for the pineal because it is not observed in the salivary gland innervated by postganglionic adrenergic fibers from the same origin as pineal nerves. Pineal serotonin is stored in equilibrium in two compartments, i.e., the parenchymal cells and the adrenergic nerves and thus is most probably reduced in both sites. Since noradrenaline and serotonin are detected in pineal nerve vesicles and may coexist in them, the diminution of intravesicular serotonin, by making more storage sites available, probably determines the selective increase of pineal noradrenaline. A similar modification in the ratio of intravesicular amines as a result of the physiological stimulation of pineal beta-adrenergic receptors by the adrenergic neurotransmitter may explain some of the changes observed in the content of pineal amines.

Cytochemistry of 5-hydroxytryptamine at the electron microscope level. I. Study of the specificity of the reaction in isolated blood platelets

Blood platelets obtained from normal rabbits and those isolated from reserpine-treated animals and subsequently incubated in vitro with 5-hydroxytryptamine, norepinephrine and histamine were assayed for amine content or processed for examination under the electron microscope. With the glutaraldehyde-dichromate reaction for unsubstituted catechol- and indoleamines, reactive granules were observed in normal platelets. Formaldehyde fixation prior to the glutaraldehyde-dichromate reaction resulted in a similar image under the electron microscope. In platelets obtained from animals treated with reserpine a decrease of the amine content with a corresponding reduction in the number of dense granules was observed. Following incubation with 5-hydroxytryptamine the concentration of the amine increased markedly and the number of dense granules that reacted with both techniques became practically normal. In norepinephrine-incubated platelets dense granules were demonstrated with the glutaraldehyde-dichromate reaction, but no reactive products were observed using prefixation with formaldehyde. Histamine was also incorporated into depleted platelets but gave no reaction. It is concluded that prefixation with formaldehyde renders negative the reaction with catecholamines, leaving unaffected indoleamine-reactive sites. The previous assumption that the dense granules contain 5-hydroxytryptamine has been confirmed by such a cytochemical approach. The possibility that these organelles constitute a common storage site for different amines is discussed.