Neuropeptide Y-immunoreactive neurons of the rat large intestine during development

Neuropeptide Y (NPY) is expressed in the enteric ganglia of the small and large intestines, where it inhibits gut secretion and motility. However, no data exist on changes in NPY expression or the colocalisation of this peptide with other neurochemical substances in the large intestine during postnatal development. To address this, immunohistochemistry was performed to determine the location of NPY and its colocalisation with choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS) and somatostatin (SOM) in the large intestine of male Wistar rats on postnatal days (P) 1, 10, 20, 30, 60, and at 24 months (24 M). NPY-immunoreactive (IR) neurons were identified in the myenteric (MG) and submucosal (SG) ganglia of the large intestine in newborns and older rats until senescence. In the MG, the percentage of NPY-IR neurons was low and decreased from 6.8 ± 0.8 in P1 rats to 4.2 ± 0.8 in P10 rats without further changes in postnatal development. In the SG, the proportion of NPY-IR neurons decreased from 75.4 ± 7.4% in P1-52.2 ± 5.2% in P30 rats. 100% of NPY-IR neurons colocalised with ChAT in the MG and SG of all rats. In the SG, NPY/ChAT-IR neurons innervating vessels were identified. The percentage of NPY/nNOS-IR neurons in the MG varied from 69.2 ± 4.20-76.8 ± 9.9. In the SG, the percentage of NPY/nNOS-IR neurons decreased 3.6-fold within the first 20 days of life. Only single cells were NPY/nNOS-IR in P30 and P60 rats, and their proportion increased again to 71.4 ± 5.8 in 24 M aged rats. The percentage of NPY/SOM-IR neurons fluctuated from 43.4 ± 12.8-56.4 ± 14.3 in the MG and from 41.4 ± 10.7-60.6 ± 10.3 in the SG, with no significant differences observed between age groups. The cross-sectional area of NPY-IR neurons was small in P1 and P10 rats and increased twofold between days 10 and 30 of life. No statistically significant differences were found between NPY+ and NPY- neurons, as well as between MG and SG, in rats of different ages. In conclusion, changes in the expression and colocalisation of NPY and nNOS are observed in the enteric ganglia of the large intestine during postnatal development. We suggest that these shifts in NPY expression may be associated with communications between NPY-IR neurons and their target cells at different stages of postnatal development.