Calretinin-containing preganglionic nerve terminals in the rat superior cervical ganglion surround neurons projecting to the submandibular salivary gland

Abstract

The distribution and targets of calretinin-immunoreactive preganglionic nerve terminals in the superior cervical ganglion of the rat were examined using immunohistochemistry and retrograde neuronal tracing. Calretinin-immunoreactive nerve terminals were found throughout the ganglion, forming distinct pericellular baskets around a sub-population of postganglionic neurons. The targets of postganglionic neurons surrounded by calretinin-immunoreactive nerve terminals were determined after injection of tracer into the submandibular salivary gland, the extra-orbital lacrimal gland, the thyroid gland, the anterior chamber of the eye or the skin of the forehead. Only when tracer was injected into the submandibular gland were neurons labelled that were surrounded by calretinin-immunoreactive nerve terminals. When immunohistochemistry using antisera to neuropeptide Y was combined with retrograde tracing, only submandibular gland projecting neurons lacking neuropeptide Y were surrounded by calretinin-immunoreactive terminals. When retrograde neuronal tracer was injected into the superior cervical ganglion, a proportion of retrogradely-labelled neurons in the upper thoracic spinal cord showed relatively weak calretinin-immunoreactivity. All calretinin-immunoreactive terminals in the superior cervical ganglion disappeared following section of the sympathetic chain distal to the superior cervical ganglion. Thus, calretinin is present in a population of preganglionic neurons projecting exclusively to neuropeptide Y non-immunoreactive (presumably secretomotor) neurons innervating the submandibular salivary gland of the rat.