Synaptic connections of central carotid sinus afferents in the nucleus of the tractus solitarius of the rat. I. An electron microscopic study.
A transganglionic transport technique was used to study the synaptic connections of the central carotid sinus afferents in the nucleus of the tractus solitarius of the rat by electron microscopy. The caudal part of the nucleus was profusely innervated. Labelled fibres extended to the contralateral nucleus, and to the ipsilateral dorsal motor nucleus of the vagus nerve, nucleus ambiguus, spinal nucleus of the trigeminal nerve and the area postrema. The labelled terminals were densely packed with clear, predominantly spherical vesicles about 50 nm in diameter and a few often swollen mitochondria. The terminals synapsed on dendrites of various calibres, spindle- or pear-shaped somal profiles with short axes lesser than 8 microns, and axon terminals. In axo-axonal synapses, most labelled terminals appeared to be presynaptic. Frequently, profiles of labelled terminals were in direct apposition with one another. The latter may represent the morphological substrate of the interaction between baro- and chemoreceptor inputs in the nucleus of the tractus solitarius and warrants further study. The present results indicate that in addition to direct inputs, the carotid sinus afferents are able to influence second-order neurons in the nucleus of the tractus solitarius indirectly through presynaptic modulation.
Chen
I L
IL
Department of Anatomy, Tulane Medical School, New Orleans, LA 70112.
Weber
J T
JT
Rieck
R W
RW
Yates
R D
RD
D000344:Afferent Pathways / Q000033:anatomy & histology; D000818:Animals; D002346:Carotid Sinus / Q000294:innervation*; D005154:Facial Nerve / Q000648:ultrastructure; D005260:Female; D005930:Glossopharyngeal Nerve / Q000648:ultrastructure; D008526:Medulla Oblongata / Q000648:ultrastructure*; D008854:Microscopy, Electron; D009475:Neurons, Afferent / Q000648:ultrastructure*; D051381:Rats; D011921:Rats, Inbred WKY; D013569:Synapses / Q000648:ultrastructure; D014630:Vagus Nerve / Q000648:ultrastructure