Systemic and nigral application of amphetamine both cause an increase in extracellular concentration of ascorbate in the caudate nucleus of the rat.

Unmodified microvoltammetric electrodes and electrochemically modified cylindrical electrodes, both constructed from carbon fibers, were used to determine changes in ascorbate concentration in the caudate nucleus of the anesthetized rat following administration of amphetamine. The increased ascorbate levels with systemic amphetamine originate from a CNS source, since the response is not eliminated in adrenalectomized animals, and does not occur when p-hydroxyamphetamine, an agent with peripheral actions similar to amphetamine, is used as a stimulus. Local application of amphetamine in the caudate nucleus results in an increase in catechols. However, this procedure results in a decrease of the extracellular concentration of ascorbate. Unilateral nigral infusion of dopamine or amphetamine leads to a significant increase in the concentrations of ascorbate detected bilaterally in the caudate nuclei with in vivo electrochemistry. In contrast, the paradigm causes a decrease in extracellular catechols on the ipsilateral side and an increase on the contralateral side. These experiments demonstrate that the extracellular level of ascorbate is not correlated with dopamine secretion. Furthermore, the data show that the action of amphetamine on ascorbate concentration in the caudate nucleus is in part mediated by the nigral actions of amphetamine.