Rosario Pasaro

Brainstem connections of the rat ventral respiratory subgroups: afferent projections

Propriobulbar neurons having axonal projections to the Ventral Respiratory Group (VRG) were retrogradely labeled after discrete injections of Fast blue into one of the three physiologically identified subdivisions (Bötzinger Complex, rostral inspiratory and caudal expiratory regions). Neurons that project to these regions were found throughout the rostrocaudal extent of the medulla and the pons in a variety of areas known to have cardio-respiratory function. Labeled somata were located within the nuclei of the solitary tract (commissural, intermediate and ventrolateral), other subdivisions of VRG, parabrachial nuclei (medial, dorsolateral and central lateral), Kölliker-Fuse nucleus, retrotrapezoid nucleus, lateral paragigantocellular nucleus and lateral tegmental field of the pons. Within the nuclei of the solitary tract and the Kölliker-Fuse nucleus, there was a topographical organization with respect to the three subdivisions of the VRG.

Connections of the rostral ventral respiratory neuronal cell group: an anterograde and retrograde tracing study in the rat

The connections of the rostral ventral respiratory cell group (VRG) were retrogradely and anterogradely determined after discrete injections of a mixture of the fluorescent tracers Fast Blue (FB) and Fluoro Ruby (FR) into the physiologically identified rostral inspiratory cell group. Retrogradely FB-labeled neurons and/or anterogradely FR-labeled fibers and terminal fields were located bilaterally in a variety of brain areas. Both retrograde and anterograde labelings were mainly found in: 1) the deep cerebellar nuclei; 2) the lateral lemniscus and paralemniscal nuclei, deep gray, and white intermediate layers of the superior colliculus, tegmental (laterodorsal and microcellular) nuclei, and central gray; and 3) the septohypothalamic nucleus, and lateral and posterior hypothalamic areas. The FR-labeled terminal-like elements were found in: 1) Crus 2 of the ansiform lobule, and the simple, 2, and 3 cerebellar lobules; 2) the subcoeruleus, deep mesencephalic, and Edinger-Westphal nuclei; and 3) the premammillary, lateral, and medial mammillary nuclei, retrochiasmatic part of the supraoptic nucleus, and the zona incerta. The FB-labeled neurons were found in: 1) the parapedunculopontine tegmental and cuneiform nuclei, caudal linear nucleus of the raphe, and adjacent area of the cerebral peduncle; 2) the thalamic posterior nuclear group and subparafascicular, parafascicular, and gelatinosus thalamic nuclei; 3) the parastrial amygdaloid and subthalamic nuclei; and 4) the olfactory tubercle, granular, and agranular insular cortex, parietal and lateral orbital cortices. The connections of the rostral VRG with several cerebellar, midbrain, diencephalic, and telencephalic regions could provide an anatomical substrate for a role of these regions in the control of respiratory-related functions.

A morphological study of ambiguus nucleus motoneurons innervating the laryngeal muscles in the rat and cat

The location and axonal projections of laryngeal motoneurons (LMn) have been studied in rats and cats using horseradish peroxidase as a retrograde tracer. LMn are located in the caudal part of the ambiguus nucleus in both species. In the cat, LMn are organized in two groups with a specific orientation of their dendritic trees. LMn axonal projections are ipsilateral in cats and bilateral in rats.

Pontomedullary Efferent Projections of the Ventral Respiratory Neuronal Subsets of the Rat

The pontomedullary trajectories of projections efferent from the ventral respiratory cell group were anterogradely labelled after discrete injections of Fluoro Ruby into three morphophysiologically identified subdivisions (Bötzinger complex, rostral inspiratory, and caudal expiratory cell groups). The anterogradely labelled varicosities were located in a variety of areas involved in cardiorespiratory function: other subdivisions of the ventral respiratory cell group, the parabrachial (medial, central, and external lateral), Kölliker-Fuse, and lateral paragigantocellular nuclei, A5, and perifacial areas. Although the target areas were similar for the three studied subdivisions, some differences of the location and densities of labelled varicosities were found. Anterogradely labelled fibre bundles were found bilaterally after all of the tracer injections. Three caudally efferent bundles passed through the ventral respiratory cell group, dorsal medullary, and paramedian reticular nuclei. A labelled fibre bundle also took an ascending route through the ventral respiratory cell group: it surrounded the facial nucleus, and then followed two different pathways, one coursing towards forebrain areas and the other to the parabrachial and Kölliker-Fuse complex. Bundles of efferent axons decussated mainly at medullary levels and to a lesser extent in the pons. In the contralateral medulla and pons these labelled fibre bundles followed pathways similar to those observed ipsilaterally. The three ventral respiratory neuronal subsets sent axonal projections through similar tracts, but within them they were topographically organized. The present data are discussed with respect to the circuitry involved in the mechanisms of cardiorespiratory and other visceral functions.

Localization of respiratory bulbospinal and propriobulbar neurons in the region of the nucleus ambiguus of the rat

The location of neurons within the ventral respiratory group (VRG) of rat was mapped following injections of 3 different fluorochrome tracers into different sites known to receive projections from VRG neurons. Injection sites included muscles innervated by the vagus (X) and glossopharyngeal (IX) nerves, and the sites of expiratory activity in the caudal medulla and of inspiratory activity in the spinal cord at the C4 level. Labeling of vagal motoneurons resulting from fluorochrome injections into muscles innervated by X and IX nerves was always ipsilateral to the site of injection. Both propriobulbar and bulbospinal neurons had primarily ipsilateral projections. No double-labeled cell bodies were observed. The cell bodies of the 3 types of neurons, propriobulbar, bulbospinal and vagal/glossopharyngeal, were unevenly distributed along the rostrocaudal axis of the VRG, suggesting a complex mosaic of neurons which regulate respiratory-related functions such as swallowing and vocalization.

Location of motoneurons supplying the intrinsic laryngeal muscles of rats. Horseradish peroxidase and fluorescence double-labeling study

This paper describes a qualitative and quantitative investigation of the location of the motoneurons innervating the intrinsic laryngeal muscles of rats. Injections of horseradish peroxidase, Diamidino Yellow and True Blue were made either in one or, simultaneously, in three laryngeal muscles. Unlike those in cats and rabbits, the motoneurons that make up the nucleus ambiguus (NA) in rats are not arranged in two separate subgroups, that is one belonging to the cricothyroid (CT) motoneurons and the other to the rest of the intrinsic laryngeal motoneurons. Instead, a superimposition of CT and posterior cricoarytenoid (PCA) motoneurons was observed in the rostral third of the NA. Motoneurons innervating the PCA, thyroarytenoid (TA) and lateral cricoarytenoid (LCA) muscle overlap in the medial third of the NA. Finally, in the region of the NA caudal to the obex, the TA and LCA motoneurons also overlap. Labeled motoneurons were located in the ipsilateral side to the injected muscle in all cases.

Identification of central nervous system neurons innervating the respiratory muscles of the mouse: a transneuronal tracing study.

In recent years, the central control of breathing in mammals has been the subject of numerous studies. The aim of the present one was to characterize the neuronal network projecting to the main respiratory motoneurons, in adult mice. To this end, the morphology and location of the respiratory motoneurons and their sequential connections with other neurons were revealed using a transneuronal tracing technique by means of the rabies virus infection. The injections of the rabies virus in the respiratory muscles resulted in labeling the motoneurons and their serially connected interneurons at multiple levels of the mouse central nervous system: spinal cord, pons and medulla, cerebellum, mesencephalon, diencephalon, and telencephalon. Most of these labeled areas have been previously identified in the control of cardiorespiratory regulation, as well as in other autonomic functions. These anatomical data provide support for the integration of respiratory-related activities in complex behavioral responses. Furthermore, these data suggest similarities in the evolution of central respiratory networks in mammals.

Study of the topographical distribution of different populations of motoneurons within rat's nucleus ambiguus, by means of four different fluorochromes.

The topographical neuronal distribution within the rat nucleus ambiguus has been studied with the simultaneous retrograde labeling technique by means of four different fluorochromes injected within the various muscles and/or nerves of the oro-pharyngeal region. This technique has permitted the identification of several types of neurons along the same coronal plane. Most were motoneurons innervating the various muscles of the upper airway, including pharyngeal constrictor, stylopharyngeal, intrinsic laryngeal and the upper portion of the esophagus. Some neurons may have been preganglionic parasympathetic neurons. No evidence of axonal branching of any of the labeled motoneurons or parasympathetic neurons was found.

Location of motoneurons and internuclear neurons within the rat abducens nucleus by means of horseradish peroxidase and fluorescent double labeling.

The distribution of abducens motoneurons and internuclear neurons was determined in the rat by injections of horseradish peroxidase or fluorochromes into the ipsilateral lateral rectus muscle and the contralateral oculomotor nucleus either separately or simultaneously. The labeled somata of abducens internuclear neurons were intermingled with the labeled motoneurons at the medial third of the nucleus, but they were more segregated at the rostral third, where the labeled interneurons were more numerous. Internuclear neurons were preferentially located around and ventral to the central part of the facial genu, while motoneurons were located more dorsomedially, closer to the midline than in other species of mammals. The evolutionary trend of the location of both populations of neurons is also discussed.

Cytoarchitectonic organization of laryngeal motoneurons within the nucleus ambiguus of the cat.

The central distribution of laryngeal motoneurons was studied in the cat by retrograde axonal transport of horseradish peroxidase. The enzyme was injected selectively into the cricothyroid (CT), lateral cricoarytenoid and thyroarytenoid (LCA-TA), and posterior cricoarytenoid (PCA) muscles of the larynx with or without the previous sectioning of the left laryngeal recurrent nerve (LR) or the left superior laryngeal nerve (SL). The CT motoneurons appeared as a compact group of medium-size cells located in the rostral one-third of the nucleus ambiguus (nA). The LCA-TA motoneurons were found in the caudal two-thirds of the nA, constituting a loose group of large motoneurons. The PCA motoneurons were located throughout the whole extend of the nA, the cells being large in the caudal pole and smaller in the rostral one-third of nA. Laryngeal muscle innervation was exclusively of ipsilateral origin. Axonal projections in the brain stem were different depending on the nerve (LR or SL) by which the efferent fibers were sent.