ABSTRACT. The distribution and ontogeny of the galanin-like immunoreactive (Gal-IR) neural structures in the pancreas of cattle, sheep and goat were investigated immunohistochemically. The present study confirmed the previous findings on the immunolocalization of galanin both in the neural elements and endocrine cells of cattle, and reported for the first time its exclusive localization in the neural elements of sheep and goat. The frequency of Gal-IR nerve fibers and nerve cell bodies was high in cattle and low in sheep and goat. Their first detection was at the first fetal trimester in cattle and third trimester in sheep and goat. In cattle, a marked increase in the frequency of Gal-IR nerve fibers was observed from the third trimester to early neonatal stage followed by a decrease after three months postnatal. In contrast to the non-preferential distribution pattern in sheep, the Gal-IR nerve fibers in cattle and goat pancreas were predominantly associated with the acini, excretory ducts and blood vessels, but rarely detected in the pancreatic islets. The Gal-IR nerve cell bodies were observed as isolated bodies in the intra-and interlobular connective tissues and as a group within the intrapancreatic ganglia. At the vicinity of the nerve cell bodies, Gal-IR nerve fibers were observed. The present findings may suggest that: (1) galanin regulates pancreatic function as neurotransmitter/neuromodulator in ruminants; (2) galanin plays a more important role in large than in small ruminants; and (3) Galanin, a 29-amino acid peptide, was first isolated from the pig upper intestine [22]. One of the extensively studied biological effect of galanin is its ability to regulate insulin secretion in pig [16], dog [5,9,15], rat [8,12,18], mouse [11] and human [1,3]. This physiological action of galanin coupled with its effect on pancreatic exocrine secretion [18,23] and release of other pancreatic hormones such as pancreatic polypeptide [3,20], glucagon [3,5,9,11,12,16] and somatostatin [3,5,9,16] [1,14,19]. Recently, we have reported striking findings on the presence of galanin-like immunoreactivity not only in the neural elements but also in the endocrine cells of the large islets of cattle, a large ruminant species [2,17]. Large islet is one of the two distinct types of pancreatic islets in cattle [4]. Compared to the small islets, the islets of Langerhans, which are embedded in the exocrine tissue, and present in the fetus, young and adult, the large islets are enmeshed in the interlobular connective tissue, and prominent in the fetus and neonate but negligible in the adult [4]. Such type of islet, which has also been reported in sheep [23] and goat [unpublished observation], may be speculated as a characteristic feature of ruminants. Whether the peculiarity in the distribution of galanin-like immunoreactive (Gal-IR) structures in the cattle pancreas is also true to all ruminants or not remains to be clarified.The present study was, therefore, conducted to investigate and compare the distribution and ontogeny of the Ga...