Vasomotor, pilomotor and secretomotor neurons distinguished by size and neuropeptide content in superior cervical ganglia of mice

Populations of postganglionic sympathetic neurons projecting to cranial targets from the superior cervical ganglia of mice were identified by retrograde axonal tracing with Fast blue combined with double-labelling immunofluorescence to detect immunoreactivity to tyrosine hydroxylase and neuropeptide Y. Nearly all neurons in the ganglion contained tyrosine hydroxylase immunoreactivity, but only about 50% of them also contained immunoreactivity to neuropeptide Y. The maximum diameter of cells with immunoreactivity to neuropeptide Y was significantly smaller than that of cells without it. Terminal axons containing immunoreactivity to both neuropeptide Y and tyrosine hydroxylase occurred around blood vessels supplying most cranial tissues, including the skin. Axons with immunoreactivity to tyrosine hydroxylase but not to neuropeptide Y innervated the piloerector muscles and the acini of the salivary glands. After injection of Fast blue into the skin or the submandibular salivary gland, populations of vasomotor, pilomotor and secretomotor neurons could be distinguished by soma size and by neuropeptide Y immunoreactivity. Neurons projecting to the salivary glands were the largest (mean diameter: 32 μm) and lacked immunoreactivity to neuropeptide Y; neurons projecting to cutaneous blood vessels were the smallest (mean diameter: 19 μm) and contained immunoreactivity to neuropeptide Y; neurons projecting to piloerector muscles were intermediate in size (mean diameter: 23 μm) and lacked neuropeptide Y immunoreactivity. A cluster analysis procedure confirmed that soma size and peptide content together identify major functional populations of neurons in the superior cervical ganglia of mice.