ABSTRACT
Signaling between nerve cells and between nerve cells and different organs is effected by neuroactive substances such as amino acids, monoamines, acetylcholine, purines, and neuropeptides. This chemical language forms the basis of life for multicellular organisms and is a major player in diverse functions such as mood, memory, circadian rhythm, sexual behavior, brain development, and degeneration. The neuropeptides are evolutionarily very old and constitute a plethora of compounds in contrast to the relatively few so-called classical transmitters [1]. Neuropeptides are typically localized together with a nonpeptide transmitter, which suggests that the role of the peptides is modulation of the basic chemical transmission exerted by classical transmitters. The diversity of neuropeptides is exemplified in a “simple” organism such as the nematode C. elegans, which has 41 genes that encode neuropeptide precursors despite there being only about 1000 somatic cells in the whole animal [2]. In humans, neuropeptides are involved in regulation of the release of hormones from the pituitary, probably in pain and analgesia, and in regulation of food intake [1]. A neuropeptide antagonist has also recently been used in treatment of depression. The finding that many neuropeptides show a plastic expression and are upregulated following dif-ferent forms of injury implies longterm trophic effects that make this signaling system interesting from a future therapeutic point of view [1].
