Increases in NPY in non-sympathetic nerve fibres supplying rat mesenteric vessels after immunosympathectomy

The effect of nerve growth factor (NGF) deprivation on developing peripheral peptide-containing nerves has been examined in Wistar rats. Animals were treated from birth for 7 days with antibodies to NGF (10 μl/g body weight) and killed at 4 or 8 weeks of age. The nerves of the mesenteric and femoral blood vessels, vas deferens and bladder were viewed with histochemical and immunohistochemical techniques. The effectiveness of anti-NGF treatment was monitored by viewing catecholamine (CA)-containing nerves, which were virtually absent from the blood vessels, but were little affected in the vas deferens and bladder in both age groups. Immunoreactivity for substance P and calcitonin gene-related peptide was slightly reduced in the blood vessels. Immunoreactivity for neuropeptide Y (NPY) was reduced in the femoral blood vessels by 88% at both ages, but reductions in NPY immunoreactivity (NPY-IR) in the mesenteric vessels varied with age. In the mesenteric artery at 4 weeks, NPY-IR was reduced by 96% from control values, but at 8 weeks it was reduced by only 37%. Acute sympathectomy with 6-OHDA treatment reduced NPY-IR in the mesenteric artery by 98% at 4 weeks and 93% at 8 weeks. It is proposed that the increase in NPY-IR but not CA-containing nerves in the mesenteric artery between 4 and 8 weeks after immunosympathectomy is due to compensatory innervation from a non-sympathetic source (probably enteric neurons) that is available to mesenteric, but not to femoral blood vessels.