Calbindin immunoreactivity of enteric neurons in the guinea-pig ileum

Previous studies have identified Dogiel type II neurons with cell bodies in the myenteric plexus of guinea-pig ileum to be intrinsic primary afferent neurons. These neurons also have distinctive electrophysiological character istics (they are AH neurons) and 82-84% are immunoreactive for calbindin. T hey are the only calbindin-immunoreactive neurons in the plexus. Neurons wi th analogous shape and electrophysiology are found in submucosal ganglia, b ut, with antibodies used in previous studies, they lack calbindin immunorea ctivity. An antiserum that is more effective in revealing calbindin in the guinea-pig enteric nervous system has been reported recently. In the presen t work, we found that this antiserum reveals the same population that was p reviously identified in myenteric ganglia, and does not reveal any further population of myenteric nerve cells. In submucosal ganglia, 9-10% of nerve cells were calbindin immunoreactive with this antiserum. The submucosal neu rons with calbindin immunoreactivity were also immunoreactive for choline a cetyltransferase, but not for neuropeptide Y (NPY) or vasoactive intestinal peptide (VIP). Small calbindin-immunoreactive neurons (average profile 130 mum(2)) were calretinin immunoreactive, whereas the large calbindin-immuno reactive neurons (average profile 330 mum(2)) had tachykinin (substance P) immunoreactivity. Calbindin immunoreactivity was seen in about 50% of the c alretinin neurons and 40% of the tachykinin-immunoreactive submucosal neuro ns. It is concluded that, in the guinea-pig ileum, only one class of myente ric neuron, the AH/Dogiel type II neuron, is calbindin immunoreactive, but, in the submucosal ganglia, calbindin immunoreactivity occurs in cholinergi c, calretinin-immunoreactive, secretornotor/vasodilator neurons and AH/Dogi el type II neurons.