5-Hydroxytryptamine-immunoreactive neurons and nerve fibers in the superior cervical ganglion of the rat

Abstract

Indirect immunofluorescence method was used to localize 5-hydroxytryptamine-inimunoreactive structures in the superior cervical ganglion of adult rats. In the ganglia of normal rats. 5-hydroxytryptamine immunoreactivity was localized in the small intensely fluorescent cells, but not in principal nerve cells. In the superior cervical ganglion of rats, pretreated with nialamide. a monoamine oxidase inhibitor. 150 mg/kg i.p., and the 5-hydroxytryptamine precursor, l-tryptophan, 45 mg/kg i.p. a large number of 5-hydroxytryptamine-immunoreactivc principal nerve cells and small intensely fluorescent cells were detected. The immunoreactive principal nerve cells had long processes, and 5-hydroxytryptamincimmunoreactive nerve fibers were observed traversing the ganglion. In ganglia of rats pretreated with colchicine, occasional 5-hydroxytryptaminc-immunoreactive principal nerve cells and several small intensely fluorescent cells were detected. Ligation of the main postganglionic nerve trunks of the superior cervical ganglion of normal rats resulted in the appearance of several 5-hydroxytryptamincimmunorcactivc principal nerve cells and nerve fibers in the ganglion. To study whether the 5-hydroxytryptamine immunoreactivity in the superior cervical ganglion represented uptake or synthesis of 5-hydroxytryptamine. rats were injected with a specific 5-hydroxytryptamine uptake inhibitor. Huoxetine. 10 mg/kg i.p. twice a day for 5 days, and then they were treated with nialamide and l-tryptophan. as described above. In the superior cervical ganglion of fluoxetinc-treatcd rats, a few 5-hydroxytryptamine-immunoreactive principal nerve and small intensely fluorescent cells, as well as some nerve Obers, were detected. Colocalization studies on the same section or on consecutive sections of the superior cervical ganglion, demonstrated that the 5-hydroxytryptaminc-immunoreactive principal nerve cells and small intensely fluorescent cells were also immunoreactive for the catecholamine-synthcsizing enzyme, tyrosine hydroxylase. The results of the present study demonstrate that the superior cervical ganglion of the rat contains 5-hydroxytryptaminc-immunoreactive principal neurons, which arc not detectable in control animals, but can be visualized after ligation of the postganglionic nerve trunks, after colchicine treatment or after prctrcatment of nialamide and l-tryptophan. The 5-hydroxytryptamine immunoreactivity is present in a subpopulation of principal nerve and small intensely fluorescent cells also after fluoxctine prctrcatment. raising the possibility that some principal nerve and small intensely fluorescent cells of the rat superior cervical ganglion not only take up but may also synthesize 5-hydroxytryptamine. in vivo. It is suggested that a subpopulation of sympathetic principal neurons in the rat superior cervical ganglion contain 5-hydroxytryptamine which may modulate neurotransmission in the superior cervical ganglion and or in the sympathetic target organs.