Connections of the parabrachial nucleus with the nucleus of the solitary tract and the medullary reticular formation in the rat.

We examined the subnuclear organization of projections to the parabrachial nucleus (PB) from the nucleus of the solitary tract (NTS), area postrema, and medullary reticular formation in the rat by using the anterograde and retrograde transport of wheat germ agglutinin-horseradish peroxidase conjugate and anterograde tracing with Phaseolus vulgaris-leucoagglutinin. Different functional regions of the NTS/area postrema complex and medullary reticular formation were found to innervate largely nonoverlapping zones in the PB. The general visceral part of the NTS, including the medial, parvicellular, intermediate, and commissural NTS subnuclei and the core of the area postrema, projects to restricted terminal zones in the inner portion of the external lateral PB, the central and dorsal lateral PB subnuclei, and the "waist" area. The dorsomedial NTS subnucleus and the rim of the area postrema specifically innervate the outer portion of the external lateral PB subnucleus. In addition, the medial NTS innervates the caudal lateral part of the external medial PB subnucleus. The respiratory part of the NTS, comprising the ventrolateral, intermediate, and caudal commissural subnuclei, is reciprocally connected with the K?lliker-Fuse nucleus, and with the far lateral parts of the dorsal and central lateral PB subnuclei. There is also a patchy projection to the caudal lateral part of the external medial PB subnucleus from the ventrolateral NTS. The rostral, gustatory part of the NTS projects mainly to the caudal medial parts of the PB complex, including the "waist" area, as well as more rostrally to parts of the medial, external medial, ventral, and central lateral PB subnuclei. The connections of different portions of the medullary reticular formation with the PB complex reflect the same patterns of organization, but are reciprocal. The periambiguus region is reciprocally connected with the same PB subnuclei as the ventrolateral NTS; the rostral ventrolateral reticular nucleus with the same PB subnuclei as both the ventrolateral (respiratory) and medial (general visceral) NTS; and the parvicellular reticular area, adjacent to the rostral NTS, with parts of the central and ventral lateral and the medial PB subnuclei that also receive rostral (gustatory) NTS input. In addition, the rostral ventrolateral reticular nucleus and the parvicellular reticular formation have more extensive connections with parts of the rostral PB and the subjacent reticular formation that receive little if any NTS input. The PB contains a series of topographically complex terminal domains reflecting the functional organization of its afferent sources in the NTS and medullary reticular formation.     

Afferent projections to the interpeduncular nucleus in the rat, as studied by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase

We examined the afferent projections to the subnuclei of the interpeduncular nucleus (IPN) in the rat by means of retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). We observed locations of retrogradely labeled cells following injections of WGA-HRP into the IPN, and distributions of anterogradely labeled fibers and terminals within the IPN following injections into the areas that contain cells of origin of afferents. Results of the retrograde and anterograde experiments have clarified the detailed organization of the IPN afferents. A part of the nucleus incertus, located dorsomedial to the dorsal tegmental nucleus, projects to the contralateral half of the rostral subnucleus of the IPN; the pars caudalis of the dorsal tegmental nucleus projects sparsely to the rostral lateral, dorsal lateral, lateral, caudal, and apical subnuclei predominantly contralaterally; the laterodorsal tegmental nucleus, to most of the subnuclei predominantly contralaterally; the ventromedial central gray rostral to the dorsal tegmental nucleus and lateral to the dorsal raphe nucleus projects to the rostral lateral and dorsal lateral subnuclei predominantly contralaterally; the median raphe nucleus, substantially to all subnuclei; the medial habenular nucleus, in a topographic manner, to the rostral, central, and intermediate subnuclei, to the rostral lateral and lateral subnuclei predominantly ipsilaterally, and to the dorsal lateral subnucleus predominantly contralaterally; the supramammillary nucleus and areas around the origin of the mammillothalamic tract and near the third ventricle project sparsely to the ventral part of the rostral subnucleus and to the central, lateral, caudal and apical subnuclei; the nucleus of the diagonal band, sparsely to the rostral, central, dorsal lateral, caudal, and apical subnuclei. These differential projections of the afferents to the subnuclei of the IPN may reflect its complex functions within the limbic midbrain circuit.     

Dendritic domains of nociceptive-responsive parabrachial neurons match terminal fields of lamina I neurons in the rat

This study investigates, in the anesthetized rat, the dendritic extent of parabrachial (PB) neurons whose nociceptive response to noxious stimuli has been previously recorded with an extracellular micropipette. The PB neurons were then injected with biocytin through the recording micropipette, via a juxtacellular technique. The dendritic arborization of individual PB neurons was carefully compared with the projections of medullary (trigeminal) and spinal lamina I neurons. The latter projections were labeled in separate animals that received injections of Phaseolus vulgaris-leucoagglutinin restricted to the superficial layers of spinal or medullary dorsal horn. We report here that: 1) PB neurons excited chiefly by noxious stimulation of the face have their dendritic tree located primarily within the field of lamina I trigeminal projections, i.e., in the caudal portion of PB area, around the external medial and the caudal part of the external lateral subnuclei; and 2) PB neurons excited chiefly by noxious stimulation of the paw or the tail have their dendritic tree located primarily within the field of lamina I spinal projections, i.e., in PB mid-extent, around the borderline between the external lateral and both the lateral crescent and the superior lateral subnuclei. Our results suggest the presence of an extensive excitatory axodendritic link between lamina I projections and PB nociceptive neurons around the lateral crescent and the external medial subnuclei. These findings strengthen the possibility of involvement of a subgroup of PB neurons in nociceptive processes.     

Trigeminal and dorsal column nuclei projections to the anterior pretectal nucleus in the rat

The projections of the trigeminal (V) sensory nuclei (VSN) and the dorsal column nuclei (DCN) to the anterior pretectal nucleus (APT) of the rat were investigated by the use of anterograde and retrograde transport of wheat-germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Injections of WGA-HRP into the APT retrogradely labeled neurons in the contralateral VSN and DCN. The labeled neurons in the VSN were most concentrated in the rostral V subnucleus interpolaris (Vi), but were also found in caudal V subnucleus oralis (Vo). No labeled neurons were seen in V subnucleus caudalis. In the DCN, retrogradely labeled neurons were observed in rostral portions of both the cuneate (Cu) and gracile (Gr) nuclei. Injections of WGA-HRP into the rostral Vi or caudal Vo resulted in dense anterograde terminal labeling in the ventral two-thirds of the APT; the labeling was maximal in the ventromedial part of the caudal half of the APT and did not extend into its most rostral portion. Labeling resulting from injections of tracer into Cu or Gr was located primarily in the ventral half of the APT, was maximal in the mid-levels of the nucleus and extended into its rostral portions. These results indicate the existence of prominent somatosensory projections to the APT and are consistent with recent findings suggesting a role for the APT in sensorimotor integration.     

Central distribution of trigeminal and upper cervical primary afferents in the rat studied by anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin

Injections of WGA-HRP were made in the rat trigeminal ganglion and C1-3 dorsal root ganglia (DRGs) to study the central projection patterns and their relations to each other. Trigeminal ganglion injections resulted in heavy terminal labeling in all trigeminal sensory nuclei. Prominent labeling was also observed in the solitary tract nucleus and in the medial parts of the dorsal horn at C1-3 levels, but labeling could be followed caudally to the C7 segment. Contralateral trigeminal projections were found in the nucleus caudalis and in the dorsal horn at C1-3 levels. The C1 DRG was found to be inconstant in the rat. When it was present, small amounts of terminal labeling were found in the external cuneate nucleus (ECN) and the central cervical nucleus (CCN). No dorsal horn projections were seen from the C1 DRG. Injections in the C2 DRG resulted in heavy labeling in the ECN, nucleus X, CCN, and dorsal horn, where it was mainly located in lateral areas. Labeling could be followed caudally to the Th 7 segment. C2 DRG projections also appeared in the cuneate nucleus (Cun), in all the trigeminal sensory nuclei, and in the spinal, medial, and lateral vestibular nuclei. A small C2 DRG projection was observed in the ventral cochlear nucleus. C3 DRG injections resulted in heavy labeling in both medial middle and lateral parts of the dorsal horn, in the ECN, and in nucleus X, whereas the labeling in the CCN was somewhat weaker. Smaller projections were seen to trigeminal nuclei, Cun, and the column of Clarke. Comparisons of the central projection fields of trigeminal and upper cervical primary afferents indicated a somatotopic organization but with a certain degree of overlap.     

Cholecystokinin-, galanin-, and corticotropin-releasing factor-like immunoreactive projections from the nucleus of the solitary tract to the parabrachial nucleus in the rat.

The parabrachial nucleus (PB) is the main relay for ascending visceral afferent information from the nucleus of the solitary tract (NTS) to the forebrain. We examined the chemical organization of solitary-parabrachial afferents by using combined retrograde transport of fluorescent tracers and immunohistochemistry for galanin (GAL), cholecystokinin (CCK), and corticotropin-releasing factor (CRF). Each peptide demonstrated a unique pattern of immunoreactive staining. GAL-like immunoreactive (-ir) fibers were most prominent in the "waist" area, the inner portion of external lateral PB, and the central and dorsal lateral PB subnuclei. Additional GAL-ir innervation was seen in the medial and external medial PB subnuclei. GAL-ir perikarya were observed mainly rostrally in the dorsal lateral, superior lateral, and extreme lateral PB. CCK-ir fibers and terminals were most prominent in the outer portion of the external lateral PB; some weaker labeling was also present in the central lateral PB. CCK-ir cell bodies were almost exclusively confined to the superior lateral PB and the "waist" area, although a few cells were seen in the K?lliker-Fuse nucleus. The distribution of CRF-ir terminal fibers in general resembled that of GAL, but showed considerably less terminal labeling in the lateral parts of the dorsal and central lateral PB, and the external medial and K?lliker-Fuse subnuclei. The CRF-ir cells were most numerous in the dorsal lateral PB and the outer portion of the external lateral PB; rostrally, scattered CRF-ir neurons were seen mainly in the central lateral PB. After injecting the fluorescent tracer Fast Blue into the PB, the distribution of double-labeled neurons in the NTS was mapped. GAL-ir cells were mainly located in the medial NTS subnucleus; 34% of GAL-ir cells were double-labeled ipsilaterally and 7% contralaterally. Conversely, 17% of the retrogradely labeled cells ipsilaterally and 16% contralaterally were GAL-ir. CCK-ir neurons were most numerous in the dorsomedial subnucleus of the NTS and the outer rim of the area postrema. Of the CCK-ir cells, 68% in the ipsilateral and 10% in the contralateral NTS were double-labeled, whereas 15% and 10%, respectively, of retrogradely labeled cells were CCK-ir. In the area postrema, 36% of the CCK-ir cells and 9% of the Fast Blue cells were double-labeled. CRF-ir neurons were more widely distributed in the medial, dorsomedial, and ventrolateral NTS subnuclei, but double-labeled cells were mainly seen in the medial NTS.(ABSTRACT TRUNCATED AT 400 WORDS)     

Primary afferent projections from the upper respiratory tract in the muskrat.

The central projections of the ethmoidal, glossopharyngeal, and superior laryngeal nerves were determined in the muskrat by use of the transganglionic transport of a mixture of horseradish peroxidase (HRP) and wheat germ agglutinin (WGA)-HRP. The ethmoidal nerve projected to discrete areas in all subdivisions of the ipsilateral trigeminal sensory complex. Reaction product was focused in ventromedial portions of the principal nucleus, subnucleus oralis, and subnucleus interpolaris. The subnucleus oralis also contained sparse reaction product in its dorsomedial part. Projections were dense to ventrolateral parts of laminae I and II of the rostral medullary dorsal horn, with sparser projections to lamina V. Label in laminae I and V extended into the cervical dorsal horn. A few labeled fibers were followed to the contralateral dorsal horn. The interstitial neuropil of the ventral paratrigeminal nucleus was densely labeled. Extratrigeminal primary afferent projections in ethmoidal nerve cases involved the K?lliker-Fuse nucleus and ventrolateral part of the parabrachial nucleus, the reticular formation surrounding the rostral ambiguous complex, and the dorsal reticular formation of the closed medulla. Retrograde labeling in the brain was observed in only the mesencephalic trigeminal nucleus in these cases. The cervical trunk of the glossopharyngeal and superior laryngeal nerves also projected to the trigeminal sensory complex, but almost exclusively to its caudal parts. These nerves terminated in the dorsal and ventral paratrigeminal nuclei as well as lamina I of the medullary and cervical dorsal horns. Lamina V received sparse projections. The glossopharyngeal and superior laryngeal nerves projected to the ipsilateral solitary complex at all levels extending from the caudal facial nucleus to the cervical spinal cord. At the level of the obex, these nerves projected densely to ipsilateral areas ventral and ventromedial to the solitary tract. Additional ipsilateral projections were observed along the dorsolateral border of the solitary complex. Near the obex and caudally, the commissural area was labeled bilaterally. Labeled fibers from the solitary tract projected into the caudal reticular formation bilaterally, especially when the cervical trunk of the glossopharyngeal nerve received tracer. Labeled fibers descending further in the solitary tract gradually shifted toward the base of the cervical dorsal horn. The labeled fibers left the solitary tract and entered the spinal trigeminal tract at these levels. Retrogradely labeled cells were observed in the ambiguous complex, especially rostrally, and in the rostral dorsal vagal nucleus after application of HRP and WGA-HRP to either the glossopharyngeal or superior laryngeal nerves. In glossopharyngeal nerve cases, retrogradely labeled neurons also were seen in the inferior salivatory nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Central distribution of cervical primary afferents in the rat, with emphasis on proprioceptive projections to vestibular, perihypoglossal, and upper thoracic spinal nuclei

The projections of primary afferents from rostral cervical segments to the brainstem and the spinal cord of the rat were investigated by using anterograde and transganglionic transport techniques. Projections from whole spinal ganglia were compared with those from single nerves carrying only exteroceptive or proprioceptive fibers. Injections of horseradish peroxidase (HRP) or wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) were performed into dorsal root ganglia C2, C3, and C4. Free HRP was applied to the cut dorsal rami C2 and C3, greater occipital nerve, sternomastoid nerve, and to the C1/2 anastomosis, which contains afferents from suboccipital muscles and the atlanto-occipital joint. WGA-HRP injections into ganglia C7 and L5 were performed for comparative purposes. Injections of WGA-HRP or free HRP into rostral cervical dorsal root ganglia and HRP application to C2 and C3 dorsal rami produced labeling in dorsal and ventral horns at the level of entrance, the central cervical nucleus, and in external and main cuneate nuclei. From axons ascending to pontine and descending to upper thoracic spinal levels, medial collaterals were distributed to medial and descending vestibular, perihypoglossal and solitary nuclei, and the intermediate zone and Clarke's nucleus dorsalis in the spinal cord. Lateral collaterals projected mainly to the trigeminal subnucleus interpolaris and to lateral spinal laminae IV and V. Results from HRP application to single peripheral nerves indicated that medial collaterals were almost exclusively proprioceptive, whereas lateral collaterals were largely exteroceptive with a contribution from suboccipital proprioceptive fibers. WGA-HRP injections into dorsal root ganglia C7 and L5 failed to produce significant labeling within vestibular and periphypoglossal nuclei, although they demonstrated classical projection sites within the brainstem and spinal cord. The consistent collateralisation pattern of rostral cervical afferents along their whole rostrocaudal course enables them to contact a variety of precerebellar, vestibulospinal, and preoculomotor neurons. These connections reflect the well-known significance of proprioceptive neck afferents for the control of posture, head position, and eye movements.     

Topographic organization of the projections from the interstitial system of the spinal trigeminal tract to the parabrachial nucleus in the rat

Neurons in the paratrigeminal nucleus are known to project to the parabrachial region, but both these areas are heterogeneous, and the subnuclei that account for these connections are not known. To characterize better these projections, we injected small amounts of fluorogold or latex beads labeled with rhodamine or fluorescein into the parabrachial area in the rat and evaluated the retrograde transport of tracer to the paratrigeminal nucleus and neighboring regions. The results show that the rostral part of the paratrigeminal nucleus projects to the medial subnucleus of the parabrachial nucleus. The intermediary part of the paratrigeminal nucleus projects to both the external lateral and to the external medial subnuclei of the parabrachial nucleus. The caudal part of the paratrigeminal nucleus projects to the ventral lateral subnucleus of the parabrachial nucleus. The dorsal paramarginal nucleus projects to the external lateral and the extreme lateral subnuclei of the parabrachial nucleus. Lamina I and II of the spinal trigeminal nucleus also project to the external lateral and the extreme lateral subnuclei of the parabrachial nucleus. In conclusion, the rostral, intermediate, and caudal parts of the paratrigeminal nucleus and the dorsal paramarginal nucleus each have clearly different projection patterns and presumably have different functions.     

Difference in central projection of primary afferents innervating facial and intraoral structures in the rat

Transganglionic transport of horseradish peroxidase-wheat germ agglutinin conjugate was used to study the central projection of primary afferent neurons innervating facial and intraoral structures. The examined primary neurons innervating the facial structures were those comprising the frontal and zygomaticofacial nerves and those innervating the cornea, while the primary neurons innervating the intraoral structures included those innervating the mandibular incisor and molar tooth pulps and those comprising the palatine nerve. The primary afferents innervating the facial structures project to the lateral or ventral parts of the trigeminal principal, oral and interpolar subnuclei, and to the rostral cervical spinal dorsal horn across laminae I through V, with a greater proportion being directed to the spinal dorsal horn. The primary afferents innervating the intraoral structures terminate in the dorsomedial subdivisions of the trigeminal principal, oral and interpolar subnuclei, and in laminae I, II, and V of the medial medullary dorsal horn, with a much denser projection being distributed to the rostral subnuclei. In addition to the above brain stem trigeminal sensory nuclear complex, they project to the supratrigeminal nucleus, caudal solitary tract nucleus, and paratrigeminal nucleus. These observations agree with previously reported data that the central projection of trigeminal nerve is organized in different manners for the facial and intraoral structures. Furthermore, the present findings in conjunction with our previous studies clarify that the central projection of primary afferents from the facial skin is organized in a clear somatotopic fashion and that the terminal fields of primary afferents from the intraoral structures extensively overlap in the brain stem trigeminal nuclear complex particularly in its rostral subdivisions. The central mechanism of trigeminal nociception is discussed with particular respect to its difference between the facial and intraoral structures.     

Organization of parabrachial projections from the spinal trigeminal nucleus oralis: an anterograde tracing study in the rat

In recent years, we have accumulated data showing that the spinal trigeminal nucleus oralis (Sp5O) contributes to the processing of somatosensory inputs from the orofacial region. Although the parabrachial area (PB) represents the main brainstem relay for autonomic, nociceptive, and gustatory afferents, few data are available regarding the topographical distribution of the efferent projections from the Sp5O to the PB. We have addressed this question with the rat, by using the anterograde tracer Phaseolus vulgaris leucoagglutinin. A dense trigeminoparabrachial pathway from the Sp5O toward, predominantly, the ipsilateral PB was revealed. Projections come mainly from the dorsal part of the Sp5O that was found to innervate densely the medial, external medial, and ventral lateral subnuclei. In contrast, the ventral part of the Sp5O projected almost exclusively to an as yet not formally described region, located dorsally and laterally to the lateral tip of the brachium conjunctivum, close to the K?lliker-Fuse nucleus. These results suggest that distinct regions within the Sp5O may be involved in the processing of gustatory and nociceptive information.     

Central projections of C4-C8 dorsal root ganglia in the rat studied by anterograde transport of WGA-HRP.

Injections of WGA-HRP were made in the rat C4-C8 dorsal root ganglia (DRGs) individually to study the central projections and their relations to each other. The main dorsal horn projections from these DRGs to the dorsal horn lamina II extended for about two segments rostrally and caudally to the injected DRG, whereas the projections to laminae I, III, and IV were less restricted rostrocaudally. Comparisons of the dorsal horn projections from the DRGs investigated indicated a tendency for a somatotopic organization, which was most prominent in lamina II. Labeled central branches from the C4-8 DRGs could be traced in the dorsal column as far caudally as 12-17 segments caudal to the level of entrance. Most of these fibers appeared to end in the medial dorsal horn base, including the column of Clarke. Labeling of primary afferents in the ventral horn generally extended for at least 3-4 segments rostral and caudal to the level of the injected DRG. Projections to the central cervical nucleus were most prominent from the C4 DRG and gradually became less prominent from the more caudal DRGs. Heavy projections to the cuneate nucleus (Cun) originated from the C7 and C8 DRG, whereas those from the C4-C6 DRGs were less extensive. The Cun projections from the different DRGs appeared to overlap, and the same was true for the projections to the external cuneate nucleus. Projections to the gracile nucleus, the vestibular nuclear complex, including nucleus X, and to trigeminal sensory nuclei were seen from all DRGs investigated.     

Retrograde labeling of rat dorsolateral septal nucleus neurons following intraseptal injections of WGA-HRP

Projection neurons in the rat dorsolateral septal nucleus (DLSN) were retrogradely labeled following intraseptal injection of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP). Injections of WGA-HRP centered in the medial septum (MS) and parts of the intermediate and ventrolateral subdivisions of the lateral septum retrogradely labeled only a few centrally scattered multipolar-shaped neurons. In contrast, injections placed in the nucleus of the diagonal band of Broca (DBB) consistently resulted in labeling of DLSN neurons of all sizes and shapes. Large injections in rostral DBB appeared to retrogradely label every DLSN neuron, while similar injections in caudal DBB only labeled neurons in restricted regions of the nucleus. A collection of small cells forming the ventricular border of caudal DLSN and a group of larger cells situated in the dorsolateral tip of rostral DLSN were consistently labeled following each DBB injection. The pattern of retrogradely labeled neurons in the DLSN appeared in a complementary fashion to that seen in the other lateral septal nuclei. Our findings support the conclusion that the DLSN is a morphologically heterogeneous nucleus consisting almost entirely of projection neurons. The pattern of retrograde labeling in the lateral septum suggests that these projection neurons may be topographically organized since distinct subpopulations of cells were labeled following different injections in the MS/DBB complex. © 1996 Wiley-Liss, Inc.     

Afferent connections and spinal projections of the pressor region in the rostral ventrolateral medulla of the cat

Following microinjection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the pressor region of the rostral ventrolateral medulla of the cat, the medulla, pons and hypothalamus were examined for retrogradely labelled cell bodies, while the thoracolumbar segments of the spinal cord were examined for anterogradely labelled axons. Dense groups of labelled cells were found in the following areas: (1) the nucleus of the solitary tract, particularly the medial, ventrolateral and commissural subnuclei; (2) the ambiguous complex and immediately surrounding area; (3) the K?lliker-Fuse nucleus in the pons; (4) the paraventricular nucleus and lateral hypothalamic area. In the spinal cord, labelled axons formed a band extending throughout the dorsolateral and ventrolateral funiculi at thoracic segments, while terminal labelling was observed in the intermediolateral nucleus and to a lesser extent the central autonomic area, but not in other parts of the grey matter. The findings are discussed in relation to the role of the rostral ventrolateral medulla in cardiovascular regulation, particularly the baroreceptor reflex.     

Nucleus of the solitary tract in the C57BL/6J mouse: Subnuclear parcellation,chorda tympani nerve projections,and brainstem connections

The nucleus of the solitary tract (NST) processes gustatory and related somatosensory information rostrally and general viscerosensory information caudally. To compare its connections with those of other rodents, this study in the C57BL/6J mouse provides a subnuclear cytoarchitectonic parcellation (Nissl stain) of the NST into rostral, intermediate, and caudal divisions. Subnuclei are further characterized by NADPH staining and P2X₂ immunoreactivity (IR). Cholera toxin subunit B (CTb) labeling revealed those NST subnuclei receiving chorda tympani nerve (CT) afferents, those connecting with the parabrachial nucleus (PBN) and reticular formation (RF), and those interconnecting NST subnuclei. CT terminals are densest in the rostral central (RC) and medial (M) subnuclei; less dense in the rostral lateral (RL) subnucleus; and sparse in the ventral (V), ventral lateral (VL), and central lateral (CL) subnuclei. CTb injection into the PBN retrogradely labels cells in the aforementioned subnuclei; RC and M providing the largest source of PBN projection neurons. Pontine efferent axons terminate mainly in V and rostral medial (RM) subnuclei. CTb injection into the medullary RF labels cells and axonal endings predominantly in V at rostral and intermediate NST levels. Small CTb injections within the NST label extensive projections from the rostral division to caudal subnuclei. Projections from the caudal division primarily interconnect subnuclei confined to the caudal division of the NST; they also connect with the area postrema. P2X₂‐IR identifies probable vagal nerve terminals in the central (Ce) subnucleus in the intermediate/caudal NST. Ce also shows intense NADPH staining and does not project to the PBN. J. Comp. Neurol. 522:1565–1596, 2014. © 2013 Wiley Periodicals, Inc.     

Projections from the parabrachial nucleus to the vestibular nuclei: potential substrates for autonomic and limbic influences on vestibular responses

Previous anatomical studies in rabbits and rats have shown that the superior vestibular nucleus (SVN), medial vestibular nucleus (MVN) and inferior vestibular nucleus (IVN) project to the parabrachial nucleus (PBN) and K?lliker-Fuse (KF) nucleus. Adult male albino rabbits and Long-Evans rats received iontophoretic injections of biotinylated dextran amine, Phaseolus vulgaris leucoagglutinin, Fluoro-Gold or tetramethylrhodamine dextran amine into either the vestibular nuclei or the PBN and KF nuclei. The results were similar in both rats and rabbits. Injections of retrograde tracers into the vestibular nuclei produced retrogradely labeled neurons bilaterally in caudal third of the medial, external medial, and external lateral PBN in both species, with more variable labeling in KF. Rats also had consistent bilateral (predominantly contralateral) labeling in the ventrolateral PBN. The most prominent labeling was produced from injections that included the SVN, with fewer labeled neurons observed from injections in the caudal MVN and the IVN. Anterograde transport of BDA from injections into the PBN and KF nuclei of rabbits revealed prominent projections to the SVN, dorsal aspect of the rostral MVN, caudal MVN, pars beta of the LVN and IVN. These connections appear to contain a component that is reciprocal to the vestibulo-parabrachial pathway and a non-reciprocal component to regions connected with the vestibulocerebellum and vestibulo-motor reflex pathways. These connections support the concept that a synthesis of autonomic, vestibular and limbic information is an integral property of pathways related to balance control in both the brain stem and forebrain. It is suggested that these projections may contribute broadly to both performance tradeoffs in vestibular-related pathways during variations in the behavioral context and affective state and the close association between anxiety and balance function.     

Mesodiencephalic projections to the vestibular complex in the cat

The distribution of cells in the rostral medial mesencephalon and caudal diencephalon which project to the vestibular complex was mapped in the cat by using retrograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Subsequent experiments using anterograde transport of WGA-HRP clarified the position of the terminations of the mesodiencephalic-derived afferents in the vestibular complex. After large injections which involved the entire vestibular complex, retrogradely labeled cells were seen in both the ipsilateral and contralateral interstitial nucleus of Cajal (INC) and were more numerous in its rostral pole. Labeled cells also occurred in the perifascicular region, both immediately adjacent to the fasciculus retroflexus and rostroventral to it. Fusiform midline cells of the Edinger-Westphal nucleus were also labeled, as well as a number of cells in the adjacent somatic portion of the oculomotor complex (OMC). Another group of labeled cells was observed within the contralateral medial terminal nucleus of the accessory optic tract (MTN) and in the posterior hypothalamic nucleus. Injections limited to subregions of the vestibular complex resulted in similar but slightly varying distributions and numbers of retrogradely labeled cells. After injections covering the caudal half of the medial vestibular nucleus (MVN) and descending vestibular nucleus (DVN), labeled cells in the INC and tegmentum dorsal to it were especially prominent, but none was seen in the MTN or OMC. Injections placed in the rostral MVN, lateral vestibular nucleus, y group, and superior vestibular nucleus resulted in a distribution of labeled cells similar to that seen following global vestibular injections, but these cells were fewer in number. After an injection confined to the y group, a small number of retrogradely labeled cells were seen in the rostral pole of the INC and immediately ventral to the fasciculus retroflexus. Projections from the rostral medial mesencephalon and caudal diencephalon to the MVN, DVN, and y group were confirmed by using anterograde transport of WGA-HRP. Direct projections from the INC-perifascicular regions and somatic neurons of the OMC to the caudal vestibular complex could play a role in eye-head coordination. Those projections from the rostral INC and MTN to the rostral vestibular complex may play a role in vertical eye movements and responses to visual stimuli which move in the vertical plane.     

Trigemino-autonomic connections in the muskrat: the neural substrate for the diving response

Stimulation of the anterior ethmoidal nerve of the muskrat produces a cardiorespiratory depression similar to the diving response. This includes an apnea, a parasympathetic bradycardia, and a selective increase in sympathetic vascular tone. However, the brainstem circuitry that links the afferent stimulus to the efferent autonomic responses is unknown. We used the anterograde transneuronal transport of the herpes simplex virus (HSV-1), strain 129, after its injection into the anterior ethmoidal nerve to determine the primary, secondary, and tertiary brainstem relays responsible for this cardiorespiratory response. In an effort to check the validity of this relatively untested tracer, we also injected the medullary dorsal horn with biotinylated dextran amine to determine the secondary trigemino-autonomic projections. Approximately 1 microl (6x10(6) PFU) of the HSV-1 virus was injected directly into the anterior ethmoidal nerve of muskrats. After 2-6 days, their trigeminal ganglions, spinal cords and brainstems were cut and immunohistologically processed for HSV-1. Initially (2 days), HSV-1 was observed only in the trigeminal ganglion. After approximately 3 days, HSV-1 was observed first in many brainstem areas optimally labeled between 4 and 4.5 days. In these cases, the ventrolateral superficial medullary dorsal horn, the ventral paratrigeminal nucleus and the interface between the interpolar and caudal subnuclei were labeled ipsilaterally. The nucleus tractus solitarius (NTS), especially its ventrolateral, dorsolateral, and commissural subnuclei were labeled as well as the caudal, intermediate and rostral ventrolateral medulla. Within the pons, the superior salivatory nucleus, the A5 area, the ventrolateral part of the parabrachial nucleus and the K?lliker-Fuse nucleus were labeled. Only after a survival of 4 days or more, the locus coeruleus, the nucleus raphe magnus, the nucleus paragigantocellularis, pars alpha, and the pontine raphe nucleus were labeled. Injections of biotinylated dextran amine were made into the medullary dorsal horn (MDH) in a location similar to that labeled after the viral injections. Fine fibers and terminals were labeled in the same brainstem areas labeled after injections of HSV-1 into the anterior ethmoidal nerve. This study outlines the potential brainstem circuit for the diving response, the most powerful autonomic reflex known. It also confirms the efficacy for using HSV-1, strain 129, as an anterograde transneuronal transport method.     

The Central Distribution of Primary Afferents from the External Eyelids, Conjunctiva, and Cornea in the Rabbit, Studied Using WGA-HRP and B-HRP as Transganglionic Tracers

We have analyzed the afferent limb of the eyeblink and nictitating membrane response of the rabbit by tracing the central distribution of primary afferents from the periorbital skin, conjunctiva, and cornea using horseradish peroxidase agglutinated to wheat germ (WGA-HRP) or conjugated to choleragenoid (B-HRP) as transganglionic tracers. Afferents in the periorbital skin and conjunctiva distribute most heavily to pars caudalis of the spinal trigeminal nucleus (Vc) and to the dorsal horn of spinal segment C1 (dhC1). These afferents terminate predominantly in laminae IIo and IIi and more weakly to the adjacent laminae I and III. There are much weaker projections to spinal segment C2, rostral Vc, and adjacent reticular formation (laminae IV and V) and to the lateral part of pars interpolaris of the spinal trigeminal nucleus (Vi). No conjunctival primary afferents were seen in the rostral divisions of the trigeminal system. Weak afferent inputs from the periorbital skin are present ventrally in pars oralis of the spinal trigeminal nucleus (Vo) and in the principal trigeminal nucleus (Vp). Corneal afferents distribute most densely in the ventral part of Vi and in islands of neuropil within the trigeminal tract at the level of Vi. They also project to caudal Vc and the adjacent dhC1 in laminae I, II, and III. There are sparse projections to the ventral and dorsal parts of Vp and to the ventral part of Vo. Reticular areas adjacent to ventral Vi also receive a few corneal afferents. WGA-HRP- and B-HRP-labeled terminals were distributed similarly in most areas, but lamina I of Vc received terminals labeled with WGA-HRP and Vp and Vo received cutaneous afferents labeled with B-HRP only. Since all subdivisions of the trigeminal system receive periocular and corneal afferent inputs, we suggest that all these subdivisions may be involved in reflex eyeblinks in the rabbit.     

Subregions of the periaqueductal gray topographically innervate the rostral ventral medulla in the rat.

Previous anatomical and physiological studies have revealed a substantial projection from the periaqueductal gray (PAG) to the nucleus paragigantocellularis (PGi). In addition, physiological studies have indicated that the PAG is composed of functionally distinct subregions. However, projections from PAG subregions to PGi have not been comprehensively examined. In the present study, we sought to examine possible topographic specificity for projections from subregions of the PAG to PGi. Pressure or iontophoretic injections of wheat germ agglutinin-conjugated horseradish peroxidase, or of Fluoro-Gold, placed into the PGi of the rat retrogradely labeled a substantial number of neurons in the PAG from the level of the Edinger-Westphal nucleus to the caudal midbrain. Retrogradely labeled neurons were preferentially aggregated in distinct subregions of the PAG. Rostrally, at the level of the oculomotor nucleus, labeled neurons were i) compactly aggregated in the ventromedial portion of the PAG corresponding closely to the supraoculomotor nucleus of the central gray, ii) in the lateral and ventrolateral PAG, and iii) in medial dorsal PAG. More caudally, retrogradely labeled neurons became less numerous in the dorsomedial PAG but were more widely scattered throughout the lateral and ventrolateral parts of the PAG. Only few retrogradely labeled neurons were found in the ventromedial part of the PAG at caudal levels. Injections of retrograde tracers restricted to subregions of the PGi suggested topography for afferents from the PAG. Injections into the lateral portion of the PGi yielded the greatest number of labeled neurons within the rostral ventromedial PAG. Medially placed injections yielded numerous retrogradely labeled neurons in the lateral and ventrolateral PAG. Injections placed in the rostral pole of the PGi (medial to the facial nucleus) produced the greatest number of retrogradely labeled neurons in the dorsal PAG. To examine the pathways taken by fibers projecting from PAG neurons to the medulla, and to further specify the topography for the terminations of these afferents in the PGi, the anterograde tracer Phaseolus vulgaris-leucoagglutinin was iontophoretically deposited into subregions of the PAG that contained retrogradely labeled neurons in the above experiments. These results revealed distinct fiber pathways to the rostral medulla that arise from the dorsal, lateral/ventrolateral, and ventromedial parts of the PAG. These injections also showed that there are differential but overlapping innervation patterns within the PGi. Consistent with the retrograde tracing results, injections into the rostral ventromedial PAG near the supraoculomotor nucleus yielded anterograde labeling immediately ventral to the nucleus ambiguus in the ventrolateral medulla, within the retrofacial portion of the PGi.(ABSTRACT TRUNCATED AT 400 WORDS)