The activities of the A and B forms of the
enzyme monoamine oxidase (
MAO, E.C. 1.4.3.4) have been assessed with the substrates
5-hydroxytryptamine and
benzylamine respectively in seven areas of the brains of 39 patients with
schizophrenia and 44 control subjects. Whereas previous studies have found the
enzyme unchanged in brain in
schizophrenia, in this study there was a modest but significant decrease in the activity of
MAO-B in frontal and temporal cortices and in amygdala. This decrease could not be accounted for by
neuroleptic medication, age, sex or post-mortem variables. In a series of 22 patients who had been assessed in life, the reduction in
MAO-B activity was found to be associated specifically with the presence of negative symptoms (flattening of affect and paucity of speech). The findings are therefore consistent with other evidence for structural and neurochemical change in the temporal lobe that have been associated with the type II (defect state) syndrome of
schizophrenia. The change in
enzyme activity is unlikely to be related to a change in monoamine metabolism but may reflect a disturbance in glial function. The change in
MAO-B activity in brain in this study is confined to particular areas of brain and a subgroup of patients; it is thought to be entirely unrelated to earlier reports of reductions of
enzyme activity in platelets, which are probably attributable to prolonged
neuroleptic medication.