Circadian changes in homovanillic acid and ascorbate levels in the rat striatum using microprocessor-controlled voltammetry.

Circadian variations in the extracellular concentration of ascorbate and homovanillic acid in the striatum of unrestrained rats were measured simultaneously at 12 min intervals over periods of up to 48 h using carbon paste electrodes and microprocessor-controlled linear sweep voltammetry. Both compounds show a similar time course over a 24 h period, reaching a peak at 04.00 h and falling to a minimum at around 16.00 h. The changes in homovanillic acid probably reflect changes in dopamine release associated with circadian variations in the level of motor activity, while the origin and function of the ascorbate changes are unknown.