Distribution of P2Y6 and P2Y12 receptor: their colocalization with calbindin, calretinin and nitric oxide synthase in the guinea pig enteric nervous system

The distribution of P2Y6 and P2Y12 receptor-immunoreactive (ir) neurons and fibers and their coexistence with calbindin, calretinin and nitric oxide synthase (NOS) has been investigated with single and double labeling immunostaining methods. The results showed that 30–36% of the ganglion cells in the myenteric plexus are strongly P2Y6 receptor-ir neurons; they are distributed widely in the myenteric plexus of stomach, jejunum, ileum and colon, but not in the submucosal plexus, with a typical morphology of multipolar neurons with a long axon-like process. About 42–46% of ganglion cells in both the myenteric and submucosal plexuses show P2Y12 receptor-ir. About 28–35% of P2Y6 receptor-ir neurons were found to coexist with NOS and 41–47% of them coexist with calretinin, but there was no coexistence of P2Y6 receptor-ir with calbindin. In contrast, all P2Y12 receptor-ir neurons were immunopositive for calbindin, although occasionally P2Y12 receptor-ir neurons without calbindin immunoreactivity were found, while none of the P2Y12 receptor-ir neurons were found to coexist with calretinin or NOS in the gastrointestinal system of guinea pig. The P2Y12 receptor-ir neurons coexpressing calbindin-ir in the small intestine are Dogiel type II/AH, intrinsic primary afferent neurons.