ABSTRACT
This chapter examines whether there are technical reasons, conceptual reasons, or biological reasons for the lack of definitely established physiological roles for gut peptides despite the explosion of scientific interest. It considers that the present state of insight may be merely a normal stage in development of understanding the control functions of neuropeptides. Inability to localize receptors in relation to release sites is clearly a serious limitation, especially in light of the understanding that there are several loci of receptors to most peptides; they may be presynaptic or postsynaptic in the plexuses and pre-junctional or post-junctional in the muscles. The existence of multiple related peptides and receptor subtypes for nearly all neuropeptides is a further technical complication, since in most cases each of the subtypes can recognize several related peptides. The chapter also presents some closing thoughts on the key concepts discussed in the preceding chapters of this book.
