This chapter discusses the possible alteration of neuropeptidergic systems in schizophrenia. The neuropeptides vastly outnumber the conventional amine and amino acid transmitters, and several forms of potent interaction with conventional neurotransmitters are demonstrated. If neurochemical disturbance underlies schizophrenic phenomena, then it is reasonable to assume that one or more of the neuropeptides will eventually turn out to be implicated—although at present, there is no marker to point the way as in the case of the neuroleptics and dopamine. It is revealed that neuropeptides are present in the brain in extremely low concentrations; in the picomolar and femtomolar range, while the “classical neurotransmitters,” such as glutamate and the monoamines, are in contrast, present in nanomolar and millimolar concentrations. The low concentrations of neuropeptides necessitate the use of sensitive measurement techniques, such as radioimmunoassay (RIA).
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