Injections Of Wheat Germ Agglutinin-horseradish Peroxidase Research Articles

Evidence for corticocortical connections between areas 7 and 17 in cerebral cortex of the cat

This study provides the first evidence of direct corticocortical connections between areas 7 and 17 of the cat. Wheat germ agglutinin horseradish peroxidase (WGA-HRP) was administrated by micro-electrophoresis and micro-injection, respectively, into area 17 and area 7 in different hemispheres in eight cats. WGA-HRP labeled pyramidal neurons were observed primarily in layer 5 of areas 7 and 17 indicating that there are reciprocal connections between these areas. Optical imaging was used to guide WGA-HRP injections to single orientation columns in area 17. After such restricted injections labeled pyramidal cells were observed in layer 5 of area 7. These pyramidal cells were arranged as discontinuous patches extending across a broad region of area 7. These results suggest that feedback from area 7 to area 17 may arise from specific functional columns in area 7.

Projections of somatosensory cortex and frontal eye fields onto incertotectal neurons in the cat

The goal of this study was to determine whether the input-output characteristics of the zona incerta (ZI) are appropriate for it to serve as a conduit for cortical control over saccade-related activity in the superior colliculus. The study utilized the neuronal tracers wheat germ agglutinin-horseradish peroxidase (WGA-HRP) and biotinylated dextran amine (BDA) in the cat. Injections of WGA-HRP into primary somatosensory cortex (SI) revealed sparse, widespread nontopographic projections throughout ZI. In addition, region-specific areas of more intense termination were present in ventral ZI, although strict topography was not observed. In comparison, the frontal eye fields (FEF) also projected sparsely throughout ZI, but terminated more heavily, medially, along the border between the two sublaminae. Furthermore, retrogradely labeled incertocortical neurons were observed in both experiments. The relationship of these two cortical projections to incertotectal cells was also directly examined by retrogradely labeling incertotectal cells with WGA-HRP in animals that had also received cortical BDA injections. Labeled axonal arbors from both SI and FEF had thin, sparsely branched axons with numerous en passant boutons. They formed numerous close associations with the somata and dendrites of WGA-HRP-labeled incertotectal cells. In summary, these results indicate that both sensory and motor cortical inputs to ZI display similar morphologies and distributions. In addition, both display close associations with incertotectal cells, suggesting direct synaptic contact. From these data, we conclude that inputs from somatosensory and FEF cortex both play a role in controlling gaze-related activity in the superior colliculus by way of the inhibitory incertotectal projection.

Periparabigeminal and adjoining mesencephalic tegmental field projections to the dorsolateral periaqueductal grey in cat – a possible role for oculomotor input in the defensive system

The dorsolateral column of the mesencephalic periaqueductal grey (PAGdl) differs from its adjacent columns in terms of afferent and efferent connections and the distribution pattern of different histochemical substances. Functionally, PAGdl is associated with aversive and defensive behaviours, but in an earlier study of this laboratory [E.M. Klop et al. (2005) J. Comp. Neurol., 492, 303-322], it was found that PAGdl specifically receives input from the nucleus prepositus hypoglossi, which plays a role in oculomotor control. In search for other oculomotor-related brainstem structures projecting to PAGdl we studied the projections from the parabigeminal nucleus (PBGN) and its medially adjoining periparabigeminal area (PPBGA). In three cats, injections of wheatgerm agglutinin-horseradish peroxidase involving PAGdl did not, or to only a very limited extent, result in retrogradely labelled neurons in PBGN. When the peripheral parts of PAGdl were involved in the injection site, labelled neurons were located in PPBGA, while after an injection involving only the more central parts of PAGdl they were located in the tegmentum medial to the PPBGA. An anterograde tracing study using [3H]-leucine and biotinylated dextran amine affirmed that neurons in PPBGA project to more peripheral parts of PAGdl, while neurons located in the tegmentum medial to PPBGA project mainly to its central parts. These results provide further evidence for the existence of two different subdivisions of PAGdl. We hypothesize that PAGdl is alerted by sudden changes in the visual field, and that the PAGdl defensive system is inhibited when these changes are caused by eye movements.

Projection of the Magnocellular Red Nucleus to the Region of the Accessory Abducens Nucleus in the Rabbit

The projection of the magnocellular red nucleus (RNm) to the region of the accessory abducens nucleus (AABD) was traced in rabbit using the bidirectional tracer wheat germ agglutinin-horseradish peroxidase (WGA-HRP). In one set of animals, recordings of antidromic responses from RNm neurons elicited by electrical stimulation of the rubrospinal tract were used to localize injections of WGA-HRP for orthograde labeling of RNm terminals. In a different set of animals, horseradish peroxidase was injected into the retractor bulbi muscle to retrogradely label motoneurons of the AABD. The positions of RNm fibers and terminals were examined and compared to the locations and distribution of AABD cell bodies and labeled dendrites. Analyses revealed that along the entire rostrocaudal extent of the AABD, RNm efferents terminate primarily lateral to, or in the lateral aspects of, labeled motoneurons. For the rostral AABD, RNm efferents terminate only lateral to the nucleus. Although the terminals are not positioned to contact cell bodies of the AABD, they could overlap with dendrites that extend in the lateral direction. RNm efferents terminate more extensively within the posterior AABD, overlapping within both dendritic and cell body regions of the nucleus. Even in this posterior region, however, RNm efferents were distributed primarily over the lateral half of the nucleus. These data show that RNm can monosynaptically influence the AABD, through primarily its lateral and posterior aspects. Our findings also show that a major target of RNm efferents is the reticular cell population located lateral to the AABD, suggesting that the RNm also may affect AABD motoneuronal output indirectly through its projection to reticular cells.

Morphological Evidence for Secondary Vestibular Afferent Connections to the Dorsal Cochlear Nucleus in the Rabbit

An analysis of central afferent projections to the dorsal cochlear nucleus (dCo), one of the three target nuclei of the auditory nerve, was made using retrograde axonal tracer, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in the rabbit. The findings showed that, in addition to its afferents from the brainstem auditory nuclei (they are not described herein), the dCo received sparse bilateral connections from the caudal three quarters of the vestibular nuclear complex (VNC). Following selective iontophoretic injections of WGA-HRP into the dCo, a small number of labelled neurones (from 2 to 28 per case) was found in the rostral and caudal portions of the medial vestibular nucleus and in the inferior vestibular nucleus. These neurones were observed mainly in the lateral regions of the nuclei. No labelling appeared in other nuclei which belonged to the VNC. The secondary vestibulocochlear connections have not been reported before in any species. With the anatomical method used, however, their functional role is difficult to explain. Further study is necessary to identify the type of neurotransmitter as well as the physiological properties of vestibular neurones projecting to the dCo, in terms of their responses to a change of the head position and to sound.

Monosynaptic projections from the nucleus retroambiguus to motoneurons supplying the abdominal wall, axial, hindlimb, and pelvic floor muscles in the female rhesus monkey.

The nucleus retroambiguus (NRA) consists of premotor neurons in the caudal medulla. It is involved in expiration, vomiting, vocalization, and probably reproductive behavior by means of projections to distinct motoneuronal cell groups. Because no information is available about the NRA and its efferent pathways in primates, the present study examines NRA projections to the lumbosacral spinal cord in female rhesus monkeys. To identify the NRA, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into the lumbosacral cord in three monkeys. To study the distribution of NRA axons in the lumbosacral cord, WGA-HRP injections were made into the NRA in seven monkeys. To identify motoneuronal cell groups receiving input from the NRA, the same seven monkeys also received cholera toxin subunit b (CTb) injections into different hindlimb, axial, and pelvic floor muscles. The results show that NRA neurons projecting to the lumbosacral cord are mainly located between 1 to 4 mm caudal to the obex. They send numerous axons to external oblique and pelvic floor motoneurons, whereas projections to iliopsoas and axial motoneurons are less numerous. The projections are bilateral, but show a clear contralateral predominance in the iliopsoas, axial, and pelvic floor motoneuronal cell groups. At the ultrastructural level, NRA-terminal profiles make asymmetrical contacts with labeled and unlabeled dendrites in these motoneuronal cell groups and contain large amounts of spherical and a few dense core vesicles. It is concluded that the NRA is well developed in the monkey and that there exists a direct pathway from the NRA to lumbosacral motoneurons in this species. The finding that the NRA projects to a somewhat different set of motoneuronal cell groups compared with other species fits the concept that it is not only involved in expiration-related activities but also in species specific receptive and submissive behavior.

Spinal projections of cat primary afferent fibers innervating caudal facet joints.

The spinal projections of afferent fibers innervating the facet joints between caudal vertebrae were examined by the use of anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP). Experiments were performed on 5 adult cats in which spinal dorsal roots below the 2nd sacral segment (S2) on the right side were cut. Injections of WGA-HRP into the caudal facet joints gave rise to extensive cranio-caudal distribution of WGA-HRP positive products along the spinal cord, indicating that many afferent fibers innervating unilateral facet joints terminate bilaterally in laminae I-II, V-VI and X of the thoracic, lumbar, sacral and caudal spinal cord. These afferent fibers may convey a series of sensory information from the caudal facet joints to the spinal cord.

The organization of preoptic–medullary circuits in the male rat: evidence for interconnectivity of neural structures involved in reproductive behavior, antinociception and cardiovascular regulation

The present studies used anatomical tract-tracing techniques to delineate the organization of pathways linking the medial preoptic area and the ventral medulla, two key regions involved in neuroendocrine, autonomic and sensory regulation. Wheatgerm agglutinin–horseradish peroxidase injections into the ventromedial medulla retrogradely labeled a large number of neurons in the medial preoptic area, including both the median and medial preoptic nuclei. The termination pattern of preoptic projections to the medulla was mapped using the anterograde tracers Phaseolus vulgaris leucoagglutinin and biotinylated dextran amine. Tracer injections into the preoptic area produced a dense plexus of labeled fibers and terminals in the ventromedial and ventrolateral pons and medulla. Within the caudal pons/rostral medulla, medial preoptic projections terminated heavily in the nucleus raphe magnus; strong anterograde labeling was also present in the pontine reticular field. At mid-medullary levels, labeled fibers focally targeted the nucleus paragigantocellularis, in addition to the heavy fiber labeling present in the midline raphe nuclei. By contrast, very little labeling was observed in the caudal third of the medulla. Experiments were also conducted to map the distribution of ventral pontine and medullary neurons that project to the medial preoptic area. Wheatgerm agglutinin–horseradish peroxidase injections in the preoptic area retrogradely labeled a significant population of neurons in the ventromedial and ventrolateral medulla. Ascending projections from the medulla to the preoptic area were organized along rostral–caudal, medial–lateral gradients. In the caudal pons/rostral medulla, retrogradely labeled cells were aggregated along the midline raphe nuclei; no retrograde labeling was present laterally at this level. By contrast, in the caudal half of the medulla, cells retrogradely labeled from the medial preoptic area were concentrated as a discrete zone dorsal to the lateral reticular nucleus; labeled cells were not present in the ventromedial medulla at this level. The present findings suggest that the medial preoptic area and ventral midline raphe nuclei share reciprocal connections that are organized in a highly symmetrical fashion. By contrast, preoptic–lateral medullary pathways are not reciprocal. These preoptic–brainstem circuits may participate in antinociceptive, autonomic and reproductive behaviors.

Descending projections from the nucleus retroambiguus to the iliopsoas motoneuronal cell groups in the female golden hamster: possible role in reproductive behavior.

In the cat, the nucleus retroambiguus (NRA) projects to expiratory motoneurons in the brainstem and spinal cord. Recently, it has been demonstrated that the NRA sends fibers to a specific set of motoneurons in the lumbosacral cord, which pathway is thought to play a crucial role in mating behavior. The question is whether such projections exist in the hamster, because the female of this species displays a very distinctive receptive behavior. In the hamster, lumbosacral cord injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) combined with hemisection 1 or 2 segments rostral to injection sites in three of the five cases demonstrated retrogradely labeled neurons in the NRA at levels 1.0-2.25 mm caudal to the obex, contralateral to the injection sites. Injections of WGA-HRP into the NRA and adjoining reticular formation revealed that NRA fibers crossed the midline in the caudal medulla and descended in the contralateral lateral and ventrolateral funiculi to terminate bilaterally, but mainly contralaterally, in the motoneuronal cell groups of the abdominal wall and iliopsoas muscles. NRA projections to levels caudal to lumbar segment 5 were virtually absent. Electron microscopic examination revealed that, of the 162 labeled NRA terminal profiles found in the ultrathin sections, 144 (89%) made monosynaptic contacts with retrogradely labeled dendrites of iliopsoas motoneurons. These NRA terminals formed asymmetrical synapses and contained spherical vesicles indicative of an excitatory function. The results indicate that, in the hamster, direct contralateral NRA projections exist to iliopsoas motoneurons. A concept is discussed in which this pathway plays a crucial role in mating behavior.

Morphological characteristics of primary sensory and post-synaptic sympathetic neurones supplying the temporomandibular joint in the cat

The cells of origin of peripheral nerves that supply the temporomandibular joint were investigated by examining the centripetal transport of wheat germ agglutinin–horseradish peroxidase (WGA-HRP). Following WGA-HRP injection into the temporomandibular joint capsule of the cat, a large number of labelled neurones were observed in the trigeminal and superior cervical ganglia ipsilateral to the injection site, while no labelled neurones were detected in the cervical dorsal-root ganglia. Only one labelled neurone was seen in the stellate ganglion. Labelled neurones were primarily located in the posterolateral and dorsal regions of the trigeminal ganglion, but their distribution in the superior cervical ganglion was not localized to specific regions. The labelled neurones in the trigeminal ganglion were significantly larger than those in the superior cervical ganglion but the sizes of smaller neurones overlapped, suggesting that trigeminal ganglion neurones send both myelinated and unmyelinated fibres to the temporomandibular joint. The innervation of the temporomandibular joint by somatosensory and sympathetic fibres suggests that sympathetic nerves could be responsible for allodynia or neuropathic pain caused by temporomandibular disorders.

Nucleus retroambiguus projections to lumbosacral motoneuronal cell groups in the male cat.

Recently, in the female cat, nucleus retroambiguus (NRA) projections have been described as distinct motoneuronal cell groups in the lumbar enlargement, possibly involved in lordosis behavior. The present study deals with the NRA-lumbosacral pathway in the male cat. Lumbosacral injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were made to localize and quantify retrogradely labeled neurons in the caudal medulla. These injections were preceded by spinal hemisections to distinguish between neurons with ipsi- and contralaterally descending axons. The NRA-lumbosacral fibers descended almost exclusively contralaterally, but neurons in areas surrounding the NRA projected mainly ipsilaterally. Injections of WGA-HRP were made in the region of the NRA to determine its targets in the lumbosacral cord. To distinguish between the contralateral NRA pathways and the ipsilateral projections from neurons in the adjoining lateral tegmentum, the injections were preceded by ipsilateral hemisections in C2. A new scaling method was used to compare the results of the different cases, despite variations in size and segmental organization. The results show that the distribution pattern of anterogradely labeled fibers in the lumbosacral cord matched precisely the location of certain motoneuronal cell groups. The NRA projected densely to the abdominal wall and pelvic floor motoneurons in Onuf's nucleus, moderately to adductor longus, semimembranosus, and biceps femoris anterior motoneuronal cell groups, and only sparsely to iliopsoas and semitendinosus motoneuronal cell groups. Compared with the findings in the female, the NRA in the male cat projects more heavily to the biceps anterior and adductor longus and only sparsely to the iliopsoas and semitendinosus motoneuronal cell groups. These male-female differences are discussed.

Functional Demarcation of a Border Between Areas V6 and V6A in the Superior Parietal Gyrus of the Macaque Monkey

We have compared physiological data recorded from three alert macaque monkeys with separate observations of local connectivity, to locate and characterize the functional border between two related but distinct visual areas on the caudal face of the superior parietal gyrus. We refer to these areas as V6 and V6A. The occupy almost the entire extent of the anterior bank of the parieto-occipital sulcus, V6A being the more dorsal. These two areas are strongly interconnected. Anatomically, we have defined the border as the point at which labelled axon terminals first adopt a recognizably 'descending' pattern in their laminar characteristics, after injections of wheatgerm agglutinin-horseradish peroxidase into the dorsal half of the gyrus (in presumptive V6A). A similar principle was used to recognize the same border by the pattern of input from area V5, except that in this case the relevant transition in laminar characteristics is that between an 'intermediate' pattern (in V6) and an 'ascending' pattern (in V6A). V6A was found to be distinct from V6 in a number of its physiological properties. Unlike V6, it contains visually unresponsive cells as well as units with craniotopic receptive fields ('real-position' cells), units tuned to very slow stimulus speeds, units with complex visual selectivities and units with activity related to attention. V6A was also found to have a larger mean receptive field size and scatter than V6. By contrast, response properties related to the basic orientation and direction of moving bar stimuli were indistinguishable between V6 and V6A, as was the influence of gaze direction on cell activity in the two areas. Two-dimensional maps of the recording sites allowed reconstruction of the V6/V6A border. For comparison, the anatomical results were rendered on two-dimensional maps of identical format to those used to summarize the physiological data. After normalizing for relative size, the physiological and connectional estimates of the border between V6 and V6A were found to coincide, at least within the range of individual variation between hemispheres. An architectonic map in the same format was also made from a hemisphere stained for myelin and Nissl substance. Area PO, defined by its general density of myelination was not distinct in this material, but several architectural features were traceable and one of these was also found to approximate the V6/V6A border. The particular criteria that distinguish V6 from V6A differ from a recent description of areas PO and POd in the Cebus monkey; we believe it most likely that PO and POd together may correspond to V6.

Patterns of transmitter labelling and connectivity of the cat's nucleus of Darkschewitsch: A wheat germ agglutinin‐horseradish peroxidase and immunocytochemical study at light and electron microscopical levels

Immunocytochemical studies using antibodies raised against a number of probable synaptic transmitters of the mesodiencephalic area, and fibre-tracing studies using wheat germ agglutinin-horseradish peroxidase (WGA-HRP), have been performed in adult cats. Glutamate and aspartate immunoreactivity produced a strong labelling of many cell bodies and terminals in the nucleus of Darkschewitsch (ND). gamma-Aminobutyrate (GABA) immunoreactivity in the ND appeared as a moderate label in some small neurones, and as a strong label in a few glial-like cells, in addition to being present in high levels to produce strong labelling in many GABA-immunopositive terminals that possessed pleomorphic vesicles. Some choline acetyltransferase-positive terminals and dendrites and a few substance P-positive fine fibres possessing varicosities also were observed in the ND. Following WGA-HRP injection in the ND, dense terminal labelling was seen ipsilaterally in the rostral half of the medial accessory olive, suggesting that there may be a certain degree of mediolateral and dorsoventral topographic correspondance within the ND-olive projection. In the same cases, many cell bodies containing HRP reaction product also were found 1) ipsilaterally in the motor cortex, anterior pretectal nucleus, and a restricted area of the caudal part of the substantia nigra pars reticulata; 2) contralaterally in the anterior and posterior interposed cerebellar nuclei as well as in a portion of the lateral cerebellar nucleus; and 3) bilaterally in the zona incerta, the posterior pretectal nucleus, the pedunculopontine tegmental nuclei, the spinal trigeminal nucleus, the dorsal column nuclei, and the spinal cord. Details of the interrelationships and functional considerations amongst the ND, adjacent nuclei, and longitudinal zones of the cerebellum are discussed.

Caudal medullary pathways to lumbosacral motoneuronal cell groups in the cat: evidence for direct projections possibly representing the final common pathway for lordosis.

The nucleus retroambiguus (NRA) projects to distinct brainstem and cervical and thoracic cord motoneuronal cell groups. The present paper describes NRA projections to distinct motoneuronal cell groups in the lumbar enlargement. Lumbosacral injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were made to localize and quantify the retrogradely labeled neurons in the caudal medullary lateral tegmentum. These injections were combined with spinal hemisections to distinguish between neurons having ipsi-or contralaterally descending axons. The NRA-lumbosacral fibers descend almost exclusively contralaterally, but neurons in areas surrounding the NRA project mainly ipsilaterally. In an anterograde tracing study, injections of WGA-HRP or tritiated leucine were made in the region of the NRA to determine the NRA targets in the lumbosarcral cord. Hemisections in C2 made it possible to distinguish between NRA projections and projections from neurons in the adjoining lateral tegmentum. The results show delicate NRA projections to distinct lumbosacral motoneuronal cell groups innervating specific hindlimb muscles (iliopsoas, adductors, and hamstrings) as well as axial muscles (medial longissimus and proximal tail muscles). The projection is bilateral, with a contralateral predominance. Ipsilaterally terminating fibers are derived from NRA neurons whose axons cross the midline at the level of the obex, descend through the contralateral spinal white matter, and recross at the level of termination. A conceptual description is presented in which the periaqueductal gray-NRA-lumbosacral projections form the final common pathway for lordosis in the cat.

Ultrastructural evidence for a paucity of projections from the lumbosacral cord to the pontine micturition center or M-region in the cat: a new concept for the organization of the micturition reflex with the periaqueductal gray as central relay.

Information concerning the rate of bladder filling is determined by receptors in the bladder wall and conveyed via afferent fibers in the pelvic nerve to sensory neurons in the lumbosacral cord. It was assumed that this information is relayed from the lumbosacral cord to a medial cell group in the dorsolateral pontine tegmentum, called the M-region, the pontine micturition center, or Barrington's nucleus. The M-region, in turn, projects via long descending pathways to the sacral parasympathetic motoneurons. In the present electron microscopic study, it was investigated in cats whether monosynaptic projections from lumbosacral neurons to the M-region indeed exist. Wheat-germ agglutinin-horseradish peroxidase injections were made into the lumbosacral cord. Many retrogradely labeled dendrites and somata were found in the M-region, but no labeled terminals were found on retrogradely labeled dendrites or somata. Only a small number of anterogradely labeled terminals, which were filled with mainly round vesicles, contacted unlabeled dendrites in the M-region. In contrast, many more anterogradely labeled terminals, which were filled with mainly round and, to a limited extent, dense core vesicles and with asymmetrical synapses, were found on dendrites in the lateral part of the periaqueductal gray (PAG). Previously (Blok and Holstege [1994] Neurosci. Lett. 166:93-96), it was demonstrated that the lateral part of the PAG contains neurons projecting to the M-region. A concept for the central organization of the micturition reflex is presented in which ascending projections from the lumbosacral cord convey information on bladder filling to the PAG.(ABSTRACT TRUNCATED AT 250 WORDS)

Zonal organization of the climbing fiber projection to the flocculus and nodulus of the rabbit: a combined axonal tracing and acetylcholinesterase histochemical study.

The localization and termination of olivocerebellar fibers in the flocculus and nodulus of the rabbit were studied with anterograde axonal transport methods [wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) and tritiated leucine] and correlated with the compartments in the white matter of these lobules delineated with acetylcholinesterase histochemistry (Tan et al. J. Comp. Neurol., 1995, this issue). Olivocerebellar fibers originating from the caudal dorsal cap travel through floccular compartments FC2 and FC4 to terminate as climbing fibers in floccular zones FZII and FZIV. Fibers from the rostral dorsal cap and the ventrolateral outgrowth traverse compartments FC1 and FC3, which are interleaved with compartments FC2 and FC4, and terminate in zones FZI and FZIII. Fibers from the rostral pole of the medial accessory olive traverse the C2 compartment and terminate in the C2 zone. FZI-III extend into the adjoining folium (folium p) of the ventral paraflocculus. The C2 zone continues across folium p into other folia of the ventral paraflocculus and into the dorsal paraflocculus. Four compartments and five zones were distinguished in the nodulus. Medial compartment XC1 contains olivocerebellar fibers from the caudal dorsal cap and subnucleus beta that terminate in the XZI zone. Olivocerebellar fibers from the rostral dorsal cap and the ventrolateral outgrowth occupy XC2 and terminate in XZII. The XC4 compartment contains fibers from both the caudal dorsal cap and from the rostral dorsal cap and the ventrolateral outgrowth. The latter terminate in a central portion of the XZIV zone. The dorsomedial cell column projects to the XZIII zone, which is present only in the dorsal part of the nodulus. The rostral medial accessory olive projects to the XZV zone, which occupies the lateral border of the nodulus. These results confirm and extend the conclusions of Katayama and Nisimaru ([1988] Neurosci. Res. 5:424-438) on the zonal pattern in the olivo-nodular projection in the rabbit. Additional observations were made on the presence of a lateral A zone (Buisseret-Delmas [1988] Neurosci. Res. 5:475-493) in the hemisphere of lobules VI and VII. Retrograde labeling of the nucleo-olivary tract of Legendre and Courville ([1987] Neuroscience 21:877-891) was observed after WGA-HRP injections into the inferior olive including the rostral dorsal cap and the ventrolateral outgrowth. The anatomical and functional implications of these observations are discussed.

The suprachiasmatic nucleus in the sheep: retinal projections and cytoarchitectural organization.

The retinal innervation, cytoarchitectural, and immunohistochemical organization of the suprachiasmatic nucleus (SCN) was studied in the domestic sheep. The SCN is a large elongated nucleus extending rostrocaudally for roughly 3 mm in the hypothalamus. The morphology is unusual in that the rostral part of the nucleus extends out of the main mass of the hypothalamus onto the dorsal aspect of the optic chiasm. Following intraocular injection of wheat-germ agglutinin-horseradish peroxidase or tritiated amino acids, anterograde label is distributed throughout the SCN. Retinal innervation of the SCN is bilaterally symmetric or predominantly ipsilateral. Quantitative image analysis demonstrates that, although the amount of autoradiographic label is greatest in the ventral and central parts of the nucleus, density varies progressively between different regions. In addition to the SCN, retinal fibers are also seen in the medial preoptic area, the anterior and lateral hypothalamic area, the dorsomedial hypothalamus, the retrochiasmatic area, and the basal telencephalon. Whereas the SCN can be identified using several techniques, complete delineation of the nucleus requires combined tract tracing, cytoarchitectural, and histochemical criteria. Compared with the surrounding hypothalamic regions, the SCN contains smaller, more densely packed neurons, and is largely devoid of myelinated fibers. Cell soma sizes are smaller in the ventral SCN than in the dorsal or lateral parts, but an obvious regional transition is lacking. Using Nissl, myelin, acetylcholinesterase, and cytochrome oxidase staining, the SCN can be clearly distinguished in the rostral and medial regions, but is less differentiated toward the caudal pole. Immunohistochemical demonstration of several neuropeptides shows that the neurochemical organization of the sheep SCN is heterogeneous, but that it lacks a distinct compartmental organization. Populations of different neuropeptide-containing cells are found throughout the nucleus, although perikarya positive for vasoactive intestinal polypeptide and fibers labeled for methionine-enkephalin are predominant ventrally; neurophysin-immunoreactive cells are more prominent in the dorsal region and toward the caudal pole. The results suggest that the intrinsic organization of the sheep SCN is characterized by gradual regional transitions between different zones.

Innervation of laryngeal nerve paraganglia: an anterograde tracing and immunohistochemical study in the rat.

Carotid body-like organs, paraganglia, frequently occur in the superior and recurrent laryngeal nerves. The paraganglia are supplied with a rich innervation of unknown origin. In the present study, the origin of the innervation of the paraganglia of the rat was studied with two different techniques. One approach was anterograde tracing of wheat-germ agglutinin-horseradish peroxidase after injection into the nodose and jugular ganglia of the vagus and the superior cervical ganglion. The other approach was immunohistochemical staining for neuropeptides after excision of the superior cervical ganglion, or vagotomy. Antisera against neuropeptide Y, vasoactive intestinal polypeptide, and calcitonin gene-related peptide were utilized. Both the tracing method and calcitonin gene-related peptide immunohistochemistry after vagotomy showed that the paraganglia receive sensory innervation from the vagal ganglia. No labeling was detected in the paraganglia after injection of wheat-germ agglutinin-horseradish peroxidase in the superior cervical ganglion. Excision of this ganglion did not lead to a decrease in the neuropeptide-Y innervation in the paraganglia, but most of this innervation in the surrounding blood vessels disappeared. The observations show that the superior cervical ganglion does not contribute to the innervation in the paraganglia and that the neuropeptide-Y innervation of the blood vessels originates from the superior cervical ganglion whereas that of the paraganglia has another origin, most likely local ganglionic cells. The results also suggest that the vasoactive intestinal polypeptide innervation in the paraganglia arises from local ganglionic cells. The two approaches complemented each other in mapping the afferent and efferent nerve supply of the paraganglia.

Nucleus Z: a somatosensory relay to motor thalamus.

1. It was the aim of this study to show that nucleus Z of the cat medulla acts as a relay between the spinal cord and the ventral lateral (VL) nucleus of the motor thalamus. For this purpose, extracellular recordings were made from neurons that were antidromically identified by stimulation in the rostral thalamus, particularly VL, and orthodromically activated by electrical stimulation of the spinal cord and/or natural stimulation of the hindlimb. The electrophysiological work was complemented by anatomic work. Here, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into nucleus Z and the termination sites of bulbothalamic projections were anterogradely labeled. 2. A total of 120 neurons were antidromically identified as projecting to thalamus: 101 to VL and 19 outside VL. The recording sites in nucleus Z were marked by dye injection or by electrolytic lesion. They were confined to a small region (roughly 1 mm in diameter), 2.8-3.7 mm rostral to obex, 2.9-3.8 mm lateral from the midline, and from the surface of the medulla to a depth of 1 mm. The antidromic latencies ranged between 0.8 and 3.2 ms, with no difference in latencies associated with location of neurons in nucleus Z or thalamic projection sites. 3. Injection of WGA-HRP labeled fibers and axon terminals in the contralateral thalamus. Terminal labeling was densest in the lateral parts of the mid- and caudal region of the VL nucleus and, to a lesser extent, in the adjacent rostrodorsal part of the ventro-posterior lateral (VPL) nucleus. The sites of terminal labeling in VL corresponded with location of antidromic stimulation sites. 4. Orthodromic activation of nucleus Z neurons was tested in response to electrical stimulation of the ipsilateral dorsolateral funiculus (which includes the dorsal spinocerebellar tract) and/or the dorsal columns. All neurons responded to stimulation of the dorsolateral funiculus (45/45). The responsiveness of 44 neurons was tested to stimulation of the dorsal columns. Only 8 of 44 tested responded with a discharge. The orthodromic latencies of unitary discharges ranged from 1.1 to 4.4 ms to stimulation of the dorsolateral funiculus, and from 1.1 to 4.9 ms to stimulation of the dorsal columns. Most responses are likely to be monosynaptic. Differences in latencies were not associated with location of recording sites or thalamic projection sites of nucleus Z neurons. 5. The responsiveness of many neurons (n = 84) was tested to natural stimulation of the ipsilateral hindlimb (which provides the sensory input to nucleus Z).(ABSTRACT TRUNCATED AT 400 WORDS)

Zonal Organization Within the Projection from the Inferior Olive to the Rostral Paramedian Lobule of the Cat Cerebellum

The projection from the inferior olivary nucleus to the forelimb-related regions of the c1, c2 and c3 zones within rostral folia of the paramedian lobule of the cat cerebellum was studied using a combined electrophysiological and neuroanatomical tracing technique. In each experiment, the cerebellar cortical zones were identified by their receipt of spino-olivocerebellar input evoked by percutaneous electrical stimulation of the limbs. A small (15-30 nl) injection of wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) was then made into the centre of one of the zones. The olivary regions projecting to each zone were compared with the regions within the olive that have previously been shown to project to the corresponding cortical zones within lobule V of the anterior lobe. The results show that some (but not all) of the paravermal zones in the anterior lobe are also represented in the paramedian lobule (PML). The most medial (c1) zone in rostral PML receives climbing fibre input from an area in the rostral dorsal accessory olive which overlaps partially with the area that projects to the medial half of the c1 zone in lobule V. A zone equivalent to the lateral half of the c1 zone (the cx zone) in lobule V does not appear to be present within rostral PML. A middle (c2) zone within rostral PML receives olivary input from a region within the rostral medial accessory olive that overlaps partially with the area that projects to the c2 zone in lobule V. The presence of a c3 zone within rostral PML was found to be variable between animals and it could be identified electrophysiologically in only two out of a possible nine cases. In summary, the results demonstrate that, although a number of similarities exist between the olivocerebellar projections to corresponding cortical zones in the two forelimb-receiving regions of the cat paravermal cortex, the differences in olivocerebellar connectivity between the two regions suggest that functional differences between them may also exist.