[Hypothetical concept: the physiopathological entity of monoaminergic psychoses]

The importance of amino acid transport across the blood-brain barrier as the limiting factor in the metabolism of monoamines has been emphasized by many recent publications. Particularly critical is the transport of tryptophan, since tryptophan hydroxylase is not saturated. This transport is regulated by complex mechanisms, both at the periphery (total and free plasmatic levels and levels of the other essential amino acids) and centraly (by feedback mechanism initiated at the pre- and post-synaptic levels). The hydroxylated derivatives of tryptophan and tyrosine, i.e. 5-HTP and L-DOPA, most probably share the same transport mechanism as these amino acids themselves. In manic-depressive patients, the uptake of L-5-HTP is increased during the depressive phase, while the uptake of L-DOPA, is increased during the manic phase. We suggest that an increase in the uptake of tryptophan may set off oscillations in all the monoaminergic systems, thus providing a biochemical model of manic-depressive psychosis. In terms of this model, melancholy would be due to a hyperserotoninergic syndrome together with a relative hypocatecholaminergic syndrome. Mania would be due to a homogeneous hypercatecholaminergic syndrome together with a relative hyposerotoninergic syndrome. Such a model is compatible with present knowledge of the physiology of monoamines, of the semeiology and biological disturbances of manic-depressive psychosis, and of the treatment of this disease. It reconciles the monoaminergic and ionic theories of the disease better than other existing hypotheses. A reduced transport of tryptophan with a secondary increase in the transport ot tyrosine provides a conceivable model for schizophrenia. Indeed, a serotoninergic hypoactivity coupled with a dopaminergic hyperactivity, with or without a noradrenergic deficiency, would account for the semeiology quite adequately. This model too would be compatible with present knowledge of monoamine physiology, of the biochemical disturbances underlying schizophrenia and of the mode of action of anti-psychotic drugs. This unitarian heuristic concept of the monoaminergic psychoses would be in better agreement with the classic clinical data concerning this disease (typology intermediate syndromes and crossed heredity).