The effect of tranylcypromine on noradrenergic nerve terminals in different brain regions

Synaptosomes were prepared from cerebellum, cortex, hypothalamus and hippocampus of rat brain. The noradrenaline content of synaptosomes and vesicles was assayed; the latter was measured after washing the synaptosomes with osmolizing solution. Incubating synaptosomes with [(3)H]noradrenaline under saturating conditions led to the uptake and retention in the vesicles of additional noradrenaline. Vesicular noradrenaline content and uptake were measured and from these vesicular storage capacity and saturation were calculated. These parameters were compared in control rats and in rats pretreated with the monoamine oxidase inhibitor tranylcypromine. Tranylcypromine pretreatment caused a rise in vesicular noradrenaline in all four brain regions, but only in the hypothalamus was this accompanied by a statistically significant reduction in both vesicular noradrenaline uptake and storage capacity.