Neuropeptide Y-like immunoreactivity in bullfrog sympathetic ganglia is restricted to C cells.

Staining the entire chain of paravertebral sympathetic ganglia in the bullfrog with an antiserum against porcine neuropeptide Y (NPY) revealed that, in each ganglion, a subpopulation of neurons expresses NPY-like immunoreactivity. Chromaffin cells in the sympathetic ganglia and in the adrenal gland were not stained by the anti-NPY serum. Since neurons in ganglia 9 and 10 of the sympathetic chain can be classified into 3 distinct groups on the basis of established electrophysiological criteria, we sought to identify the neurons in these ganglia that contain the NPY-like immunoreactivity. Accordingly, a series of cells was impaled with intracellular recording electrodes, identified as either fast B-, slow B-, or C-type neurons, filled with Lucifer yellow, and then processed with the anti-NPY serum for indirect immunofluorescence. These double-label experiments revealed that NPY-like immunoreactivity is expressed selectively by C-type sympathetic neurons. Counts of immunoreactive cells indicate that 55% of the neurons in ganglia 9 and 10 are C cells. A major target of the C cells appears to be the vasculature. In 3 different tissues innervated by sympathetic neurons, namely, the adrenal gland, the sartorius muscle, and the skin of the hindlimb, axons containing NPY-like immunoreactivity were found primarily within or near blood vessels. Within 14-60 d after extirpation of sympathetic ganglia 9 and 10, most immunoreactive axons in the sartorius muscle and nearby skin disappeared. In conjunction with other evidence, the possibility arises that sympathetic C cells function as vasomotor neurons that use an NPY-like substance and epinephrine as cotransmitters.