Photometric assessment of glyoxylic acid-induced fluorescence of dopamine in the caudate nucleus.

New procedure for quantitative photometric assessment of glyoxylic acid-induced fluorescence of dopamine in the caudate nucleus are presented. A recently published cryostat method was used to process a series of 24 micrometer sections taken from the caudate nucleus of each animal. Fluorescent light contained within a circular field (0.8 mm diameter) was measured photometrically. Several defined positions within the caudate nucleus on each tissue section were selected for measurement. Thus, a grid of measurements taken throughout the caudate nucleus provided a three-dimensional description of fluorescence intensity within this structure on both sides of the brain. Several experiments were performed to evaluate both the reliability and validity of these procedures as an index of the relative regional content of dopamine within the caudate: (1) the relative distribution of fluorescence intensity within the mouse striatum was in good agreement with previously reported distributions based on biochemical determination of regional dopamine levels within the rodent brain; (2) pharmacological manipulation of dopamine levels with gamma-butyrolactone and alpha-methyl-p-tyrosine combined with amphetamine produced predictable changes in the fluorescence intensity measurements of mouse caudate relative to untreated controls; (3) in rats pre-treated with alpha-methyl-p-tyrosine, unilateral electrical stimulation of the substantia nigra caused overall differences in fluorescence intensity between the caudate nucleus on each side of the brain, which were a function of both the duration of stimulation and the stimulating pulse frequency; (4) local injections of 6-hydroxydopamine unilaterally into the ventral tegmentum of animals pretreated with desmethylimipramine caused significant reductions in the intensity of fluorescence recorded from the ipsilateral striatum. It is concluded that the photometric procedures presented in this report constitute a significant improvement in the description of regional variations in the intensity of dopamine-related fluorescence in the caudate nucleus.