Cholinergic innervation of the pancreas in the sheep

Antibodies raised against vesicular acetylcholine transporter (VAChT) were applied to study the cholinergic innervation pattern of the pancreas of the sheep. To determine whether the cholinergic pancreatic neuronal elements contain tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP) or substance P (SP) double immunocytochemistry was used. A moderate number of VAChT-immunoreactive (IR) nerve terminals were distributed between the acini, whereas only single cholinergic nerve fibres innervated the interlobular connective tissue. VAChT-positive nerve fibres supplying the endocrine pancreas were found only occasionally. The pancreatic blood vessels and ducts system were devoid of VAChT-containing nerve endings. All intrapancreatic neurons studied showed immunoreactivity to VAChT, but intrapancreatic ganglia were not innervated with cholinergic nerve fibres. The colocalization of VAChT and TH or VAChT and SP was detected in distinct populations of nerve fibres localized amongst the acini, but not within the islet nor in the connective tissue. Single VAChT-IR nerve terminals co-expressing NPY were distributed around the acini, islets as well as in the connective tissue septa. A moderate number of VAChT-IR/VIP-IR nerve endings were located in the exocrine pancreas, whereas the islets and connective tissue were innervated with VAChT/VIP-containing nerve fibres only occasionally. In the vast majority of VAChT-positive intrapancreatic perikarya the presence of TH was additionally found. A moderate number of VAChT-IR intrapancreatic perikarya co-expressed NPY, SP or VIP. The results of the present study demonstrate species-dependent cholinergic innervation pattern of the pancreas of the sheep. The co-localization of VAChT with the neuropeptides suggests the existence of functional interactions influencing the ovine pancreas (mainly exocrine) activity.