SUMMARY Galanin, a newly discovered peptide, was found throughout the gastrointestinal tract of man, pig, and rat, exclusively in nerves. The concentrations of immunoreactive galanin ranged from 3-7±0-7 (mean±SEM) pmollg in rat antrum to 76-5±14-3 pmol/g in pig colon. The predominantly intrinsic origin of the galanin nerves was shown by the finding of the peptide in submucosal ganglion cells, the majority of which also contained VIP. Furthermore, neither extrinsic denervation of the gut nor administration of capsaicin, which selectively destroys extrinsic afferent fibres, had any significant effect on the galanin innervation. The caudal projection of galanin-immunoreactive fibres was demonstrated by complete transection of the gut, which led to their reduction in the 1 to 2 cm distal to the cut. The abundance of galanin in the innervation of the mammalian gut and its reported action on smooth muscle contractility suggest this peptide to be a novel regulatory factor in the control of bowel function.The system of mammalian regulatory peptides continues to expand with the discovery of new active molecules. One of the latest peptides to be isolated and characterised has been termed galanin.' The name of this 29 amino acid peptide was derived from the fact that its N-and C-terminal residues are glycine and alanine, respectively. Galanin has been reported to occur in rat brain and in the intestinal tract of mice, rats, guinea pigs, and pigs.2 3 As yet, little is known about the actions of galanin but preliminary pharmacological experiments have shown that it causes smooth muscle contraction in rat gut and induces mild hyperglycaemia.' 4 In the present study, the techniques of immunocytochemistry and radioimmunoassay were used in combination to determine the distribution of galanin in the human, porcine and rodent gastrointestinal tracts and, using surgical and pharmacological manipulations, to examine the origin, projections and nature of galanin-containing nerves in the gut of the rat. Fresh specimens of human bowel (fundus, n=8; antrum, n=11; duodenum, n=10; jejunum, n=4; ileum, n=3 (for immunocytochemistry only) and colon, n=10) were obtained at surgery from segments of bowel resected for carcinoma or duodenal ulcer. From each specimen, full thickness samples were taken from macroscopically and histologically normal areas at least 8 cm from the tumour margin. In addition, specimens of antrum, fundus, duodenum, jejunum, ileum and colon were obtained from five rats and nine pigs. All normal tissues were processed for immunocytochemistry and radioimmunoassay.
SURGICAL PROCEDURES (a) Extrinsic denervationIn order to determine whether enteric galaninimmunoreactive nerves have an intrinsic and/or extrinsic origin, portions of rat gut were extrinsically denervated. Six rats (Sprague-Dawley) were anaesthetised with sodium pentabarbitone (20 mg/kg ip). The abdomen was opened and the terminal ileum 849 on 9 May 2018 by guest. Protected by copyright.