Activity of monoamine oxidase in the medial preoptic area and median eminence of female rats of different ages

Total monoamine oxidase activity in the medial preoptic area and median eminence (with surrounding tissue) has been studied in female rats of three age groups, viz., those aged 1.5–2 months (peripubertal), 4–5 months (mature), and over 12 months (aging). Monoamine oxidase activity was measured using kynuramine as a substrate and changes in the concentration of product (4-hydroxyquinoline) were recorded at 327 nm. In the medial preoptic area, the lowest activity (nmole kynuramine/min/mg protein, M ± m) was found during the peripubertal period (1.55 ± 0.11), while in mature and aging rats the activities were similar (1.93 ± 0.12 and 2.01 ± 0.15, respectively). In the median eminence, the greatest activity of monoamine oxidase was found in the aging rats (6.61± 0.56), whereas in the rats of peripubertal and mature age the activities were similar (4.79 ± 0.57 and 4.36 ± 0.25, respectively). In animals aged 4–5 months, we found a tendency toward a negative correlation between the activity of monoamine oxidase in the medial preoptic area and the activity in the median eminence. Our results suggest that opposing changes in enzyme activity are necessary for the coordinated work of the monoaminergic systems in the areas studied.