In summary, the DA hypothesis is intriguing and there seem to be many indications that dopamine is involved in schizophrenia. However, the mechanisms of DA dysfunction are complex and for the most part unknown and clearly cannot be explained by a simple overactivity hypothesis. It would be most interesting to know something about DA activity in the limbic cortical area of schizophrenics, since these appear more likely to be involved in the bizarre thought process and cognitive dysfunction observed in schizophrenia. Finally, it must be re-emphasized that even if dopamine plays a critical role in this mental disorder, long-term compensatory changes in other neural systems are undoubtedly implicated in the overall picture of the disease.
Concluding Statement. We have presented a brief overview of hypotheses concerning the relation between the neurochemistry of the brain and disturbances of affect. At present, although we have some idea of the neural basis of mental illness, little can be said with certainty. Clearly the aminergic systems have been the primary focus of research in this domain, mainly because of their predominance in the limbic system and their role in the control of behavior. There is indeed much evidence that the amines are somehow involved in affective states, but knowledge of precise mechanisms is still lacking. Further, the functional importance of a whole new class of substances in the brain, the neuropeptides, is becoming apparent. Knowledge of how peptides act in the brain may aid the development of new and better therapeutic agents in the treatment of mental illness. Moreover, future research on the functional interactions between neuropeptides and amines may be of great importance in elucidating the neural code of behavior.
We extend our warmest thanks to Mrs. Bea Bradley for typing the manuscript. The writing of this chapter was supported in part by a NATO Postdoctoral Fellowship in Science ( National Science Foundation) awarded to A.E.K.
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