Degeneration time for optimal staining by Nauta technique. A study on transected vagal fibers of the cat

A laser confocal microscopic study of vagal afferent innervation of rat aortic arch: chemoreceptors as well as baroreceptors

Although the aortic nerves contain vagal afferents that terminate in both the wall of the aortic arch (putative baroreceptors) and its associated glomus tissue (putative chemoreceptors) in most mammalian species, the aortic nerves of the rat have been widely assumed to contain only baro- or pressor afferents. The present study reconsidered this anomaly by characterizing vagal afferent endings and their targets in the aortic arch region of the rat, both qualitatively and quantitatively. Eight Sprague-Dawley rats received intracranial vagal motor rhizotomy unilaterally to eliminate efferents in the nerve and then, two weeks later, injections of the tracer DiI (1,1'-dioleyl-3,3,3',3'-tetramethylindocarbocyanine methanesulfonate) into the ipsilateral nodose ganglion. The aortic arch and its surrounding tissue, with the common carotid and subclavian arteries attached, were examined with both conventional epifluorescence and confocal microscopes. Consistent with earlier observations, vagal afferents formed both flower-spray and end-net terminals rather diffusely within the wall of the aortic arch. More interestingly, vagal afferents also innervated glomus or SIF (i.e., small intensely fluorescent) cell bodies at the junction areas of the common carotid and subclavian arteries. To identify the course of these fibers, six additional animals received DiI injection into the nodose unilaterally after a complete cervical vagotomy caudal to the nodose; in these animals, the aortic nerve had been separated from the vagal trunk and kept intact. There were no marked differences in innervation patterns between the nonvagotomized and the cervically vagotomized animals, indicating that the vagal axons innervating the walls of the blood vessels and the SIF cells in the aortic arch region travel through the aortic nerves. Using a stereological method, we estimated the relative number of chemo- and baroreceptor afferents innervating the aortic arch. About 16.4% (left) and 13.1% (right) of fibers in the aortic nerves innervate SIF cells. These findings challenge the general consensus that the aortic nerves of rats contain exclusively baroreceptor fibers.

Sequential events of degeneration and synaptic remodelling in the viper optic tectum following retinal ablation. A degeneration, radioautographic and immunocytochemical study

The ultrastructural changes taking place in the retino-recipient layers of the viper optic tectum were examined between 5 and 122 days after retinal ablation. The initial degeneration of retinotectal terminals proceeds at widely different rates and is characterized by a marked degree of polymorphism in which a number of different patterns can be discerned. In the final stages of degeneration, either both the degenerating bouton and the distal portion of the postsynaptic element are engulfed by reactive glia, or, more frequently, only the degenerating terminal is eliminated and the postsynaptic differentiation remains. The free postsynaptic differentiations are reoccupied predominantly by boutons containing pleiomorphic vesicles and which are for the most part gamma-aminobutyric acid (GABA)ergic, thus forming heterologous synapses; less frequently these sites are occupied by boutons of the ipsilateral visual contingent to form homologous synapses. These two processes, both of which depend on terminal axonal sprouting, take place within the first 3 postoperative months. They are followed by a decrease in the number of heterologous synapses and a concurrent increase in the number of homologous synapses newly formed by optic boutons generated by collateral preterminal sprouting of ipsilateral retinotectal fibres. The data suggest that partial deafferentation of the optic tectum induces a transitory GABAergic innervation of free postsynaptic sites prior to the restoration of new retinal synaptic contacts.

Segregation of coarse and fine glossopharyngeal axons in the visceral nucleus of the tractus solitarius of the cat

The projections of coarse and fine axons of the glossopharyngeal (IX) nerve upon the caudal two thirds of the nucleus of the tractus solitarius (NTS) were studied in the cat. These afferents convey the chemo- and baroreceptor activities from the carotid receptors. We applied the Fink-Heimer method on brainstem sections, at different survival times, after a petrosal ganglionectomy. A segregation of fine and coarse fibered components was observed. Degeneration of coarse axons was mostly found in the lateral NTS, while fine fiber degeneration was predominant in regions of the medial and commissural NTS. The injection of WGA-HRP in the different NTS divisions demonstrated that the lateral NTS was mainly innervated by the set of largest neurons of the petrosal ganglion and that the medial and the commissural NTS were innervated by the set of smaller neurons of the ganglia. These results were discussed in relation to cytoarchitecture, myeloarchitecture, distribution of normal axons, and known central connectivity of the different NTS divisions. We concluded that coarse and fine visceral afferents of the IX nerve, which includes the afferents of the carotid body and the carotid sinus, represent different afferent populations that project to particular divisions of the NTS and connect to different central pathways.

An electron microscope study of vagus nerve composition in the ferret

The total number of axons in the cervical and abdominal vagus nerves of the ferret was counted. The ratio of myelinated to non-myelinated, and afferent to efferent axons was determined. The fibre diameter spectrum of myelinated axons was measured. The total number of axons in the ferret cervical vagus is similar to other mammals (approximately 28,000); the majority of axons are afferent (approx. 24,000) and also the majority of axons are nonmyelinated (approx. 27,000). The dorsal abdominal trunk is about twice the size of the ventral trunk although both trunks have the same number of efferent axons. The abdominal vagal trunks are over 90% afferent.