THE LOCALIZATION OF NEURONS INNERVATING THE CAROTID-SINUS IN THE DOG

The localization of neurons innervating the carotid sinus of the dog w as studied by horseradish peroxidase histochemistry following microinj ection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) under the adventitia of the carotid sinus. Labeled cell bodies were found i n the petrosal (198 +/- 108; mean +/- S.D.) and superior cervical gang lia (SCG) (890 +/- 354 mean +/- S.D.) supporting the existence of both a sensory afferent and a sympathetic efferent innervation of the caro tid sinus. Labeled neurons in the petrosal ganglion were round pseudou nipolar neurons of variable size. Labeled neurons in the SCG were mult ipolar and appeared distributed over the whole ganglion, but with a hi gher density toward its caudal half. No labeled perikarya appeared eit her in the brainstem or in the nodose or jugular ganglia, suggesting t hat in the dog a vagal pathway for carotid sinus baroreceptor afferent s does not exist.