Introduction: Of approximately 200 peptides that are known to exist in the body, 80 carry out functions as neurotransmitters and about 20 have been linked to Alzheimer's disease (AD).
Development: In this article we review the most salient studies that have been conducted on neuropeptides such as corticotropin-releasing hormone, thyrotropin-releasing hormone, somatostatin, neuropeptide Y, oxytocin, arginine vasopressin, galanin and insulin, as well as the insulin-like growth factors, the glucagon-like peptides, vasoactive intestinal peptide, cholecystokinin, substance P, opioid peptides and the neuropeptide NAP. Although attempts are made to find a causal association with AD, in many cases the findings are contradictory or not very conclusive.
Conclusions: The most notable points could be the reduction in substance P in the cerebral cortex, hippocampus, basal ganglia and cephalospinal fluid; the diminished levels of somatostatin in the same structures except for the basal ganglia; the reduction in the amount of vasopressin except in the temporal lobe; and the increased levels of dynorphin and leucine enkephalin.