Ganglionic and arterial release of neuropeptide Y by bullfrog sympathetic neurons

Sympathetic C neurons in lumbar paravertebral ganglia of the bullfrog have previously been shown to be vasomotor in function and to express neuropeptide Y (NPY). In the present experiments, a sensitive radioimmunoassay was used to measure the NPY content of ganglia and the descending abdominal aorta and to measure the overflow of NPY evoked by depolarizing concentrations of K⁺. Paravertebral ganglia 9 and 10 contain 3.1 pg NPY/μg protein and the aorta contains 0.18 pg NPY/μg protein. During 20-min depolarizations in high K⁺ (58 mM) Ringer, the ganglia released ∼ 5% of their NPY content and the aorta released ∼ 2% of its NPY content. Pretreatment of the tissues with Ringer containing 0.18 mM Ca²⁺, 8 mM Mg²⁺, and 1 mM Co²⁺ blocked the NPY release elicited by high K⁺. These findings provide further evidence that NPY is a postganglionic co-transmitter in sympathetic C neurons of the bullfrog.