Rapid nonisotopic assay of tryptophan-5-hydroxylase activity in tissues

Reversible and irreversible phases of serotonin depletion by 4-chloroamphetamine

Pretreatment of rats with an agent that inhibits uptake into serotoninergic neurons [Lilly 110140: 3-(p-trifluoromethylphenoxy)-N-methyl-3-phenylpropylamine hydrochloride] prevented the depletion of brain serotonin by 4-chloroamphetamine, presumably by preventing the entry of 4-chloroamphetamine into the serotonin neuron. When the uptake inhibitor was given after 4-chloroamphetamine, the lowering of both serotonin and tryptophan hydroxylase levels in brain was reversed. Serotonin levels returned to normal after 110140 administration to 4-chloroamphetamine-treated rats at a rate similar to the calculated rate of serotonin turnover in rats treated with 110140 alone. Progressively less reversibility of the 4-chloroamphetamine effect occurred when 110140 was injected at 8, 16 and 24 hr after 4-chloroamphetamine, and no reversibility was observed when 110140 was injected at 32 or 48 hr after 4-chloroamphetamine. These findings indicate that the depletion of brain serotonin by 4-chloroamphetamine is initially reversible but that there is a gradual transition into an irreversible effect between 24 and 48 hr after 4-chloroamphetamine injection. Apparently the prolonged presence of 4-chloroamphetamine inside the serotonin neuron produced by continual reuptake of 4-chloroamphetamine is required for the semi-permanent depletion of brain serotonin stores.

Abnormalities in grooming behavior and tryptophan hydroxylase activity in the superior colliculi in cats with pontile and frontal neocortical lesions

Cats with pontile or frontal neocortical lesions display a dissociation of the appetitive and consummatory components of grooming behavior when their body surface is tactually stimulated, an abnormal behavior that waxes and wanes with the seasons of the year. Tryptophan hydroxylase activity is significantly decreased in the superior colliculi of cats with pontile lesions and of cats with frontal neocortical lesions. The results suggest that the change in tryptophan hydroxylase activity is mediated neuronally and is a transneuronal effect on the serotonergic input to the superior colliculi. Pharmacological manipulations of the serotonergic system in normal cats failed to induce the abnormal behavior, indicating that other factors are involved in the genesis of the abnormal behavior.

Septal tryptophan-5-hydroxylase: divergent response to raphe lesions and parachlorophenylalanine

A soluble form of tryptophan-5-hydroxylase activity was found to be present in areas rich in serotonergic terminals (colliculi, hippocampus, septal area, and remaining telencephalon) as well as in brainstem, an area rich in cell bodies. The enzymatic activity in all brain regions, except the septal area, was inhibited to varying degrees following administration of parachlorophenylalanine. Destruction of the raphe nuclei in the midbrain led to a large and comparable decrease in both serotonin content and tryptophan hydroxylase activity of the hippocampus. In contrast, these lesions did not significantly affect the enzymatic activity of the septal area although the serotonin content was decreased by 72 percent. These findings suggest that the major portion of the tryptophan hydroxylase activity of the septal area is uniquely different from that found in other telencephalic areas in that it is not localized in serotonergic nerve terminals nor is it inhibited by parachlorophenylalanine.