Increased Expression of Galanin in the Rat Superior Cervical Ganglion after Pre- and Postganglionic Nerve Lesions

Abstract

Using immunohistochemistry the expression of galanin (GAL) and galanin message-associated peptide (GMAP) in the superior cervical ganglion (SCG) was investigated 2, 4, 7, and 14 days after unilateral transection of the cervical sympathetic trunk (decentralization) or after cutting the external and internal carotid nerves (axotomy), as well as 7 days after removal of parotid gland tissue. In control SCGs including the sympathetic trunk and the carotid nerves, very few neurons and fibers were GAL/GMAP-positive. Two and 7 days after decentralization, about 5% of all counted neuron profiles in the ipsilateral SCG were GAL/GMAP immunoreactive. Immunoreactive cell bodies were distributed throughout the SCG, with a greater number in the most caudal portion of the ganglion. Many GAL/GMAP-positive nerve fibers were observed in the whole SCG, with strongly fluorescent bundles of immunoreactive fibers accumulated at the caudal end of the SCG. Several GAL /GMAP-immunoreactive nerve fibers were seen ipsilaterally in the external carotid nerve, whereas only a few positive fibers could be observed in the internal carotid nerve. About 2% of all counted neuron profiles in SCGs ipsilateral to decentralization still contained GAL/GMAP-immunoreactivity 14 days after the operation. The number of GAL/GMAP-positive cell bodies was at least doubled in the contralateral SCGs after decentralization compared to controls. After axotomy, about 50% of all counted neuron profiles were GAL/GMAP-positive in the ipsilateral SCG and distributed throughout the SCG. A strong accumulation of immunoreactive nerve fibers was observed in both the internal and external carotid nerves. The number of GAL/GMAP-positive cell bodies was slightly increased in the contralateral SCGs. After unilateral removal of parotid gland tissue, many GAL/GMAP-positive cell bodies and some fibers were observed in the caudal half of the ipsilateral SCG. The number of immunoreactive nerve fibers was increased also in the external carotid nerve, but not in the internal carotid nerve. In situ hybridization revealed prepro GAL mRNA in about 5% of all SCG neuron profiles in decentralized SCGs, paralleling the increase seen in GAL/GMAP peptide content. There was also a small increase in prepro VIP mRNA-positive cells in the caudal part of the SCG. The present results indicate that both pre- and postganglionic lesions increase the content of GAL/GMAP in the SCG, with a much more pronounced increase after transection of the carotid nerves.