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)

The periaqueductal gray in the cat projects to lamina VIII and the medial part of lamina VII throughout the length of the spinal cord

The periaqueductal gray (PAG) plays an important role in analgesia as well as in motor activities, such as vocalization, cardiovascular changes, and movements of the neck, back, and hind limbs. Although the anatomical pathways for vocalization and cardiovascular control are rather well understood, this is not the case for the pathways controlling the neck, back, and hind limb movements. This led us to study the direct projections from the PAG to the spinal cord in the cat. In a retrograde tracing study horseradish peroxidase (HRP) was injected into different spinal levels, which resulted in large HRP-labeled neurons in the lateral and ventrolateral PAG and the adjacent mesencephalic tegmentum. Even after an injection in the S2 spinal segment a few of these large neurons were found in the PAG. Wheat germ agglutinin-conjugated HRP injections in the ventrolateral and lateral PAG resulted in anterogradely labeled fibers descending through the ventromedial, ventral, and lateral funiculi. These fibers terminated in lamina VIII and the medial part of lamina VII of the caudal cervical, thoracic, lumbar, and sacral spinal cord. Interneurons in these laminae have been demonstrated to project to axial and proximal muscle motoneurons. The strongest PAG-spinal projections were to the upper cervical cord, where the fibers terminated in the lateral parts of the intermediate zone (laminae V, VII, and the dorsal part of lamina VIII). These laminae contain the premotor interneurons of the neck muscles. This distribution pattern suggests that the PAG-spinal pathway is involved in the control of neck and back movements. Comparing the location of the PAG-spinal neurons with the results of stimulation experiments leads to the supposition that the PAG-spinal neurons play a role in the control of the axial musculature during threat display.

Direct projections from the periaqueductal gray to the pontine micturition center (M-region). An anterograde and retrograde tracing study in the cat

Micturition is a spino-bulbo-spinal reflex. The bulbospinal part of this reflex is formed by the projections from the M-region, also called the pontine micturition center or Barrington's nucleus, to the preganglionic parasympathetic motoneurons in the sacral cord innervating the bladder. In respect to the spino-bulbar part of the micturition reflex, our group recently showed that the sacral cord projections to the brainstem terminate mainly in the periaqueductal gray (PAG). In this study it was investigated whether the PAG might serve as a link between the sacral cord and the M-region, by examining the possible connections using the tracers wheat germ-agglutin horseradish peroxidase and tritiated leucine. The results demonstrate that a specific circumscribed rostrocaudally oriented cell group within the ventrolateral PAG and parts of the dorsomedial PAG project specifically to the M-region. A concept is put forward in which specific parts of the PAG are involved in the control of micturition and that information concerning bladder filling is conveyed via the PAG to the M-region.

A new subdivision of the rat midbrain periaqueductal gray based on its myeloarchitecture

A new subdivision of the periaqueductal gray (PAG) based on its myelin content is described. Using a methacrylate-resin embedding technique for high resolution light microscopy, a myeloarchitectonic map of the normal rat PAG was made. Six main columns were distinguished. Column I is the central thin subependymal layer, in which myelinated axons are virtually absent. This layer is surrounded by column II with many rostrocaudally oriented fibers. Lateral and dorsolateral to column II lies column III, which contains rostrocaudally as well as tangentially oriented fibers. Column III is divided into a ventral and a dorsal part by column IV. This column is located in the dorsolateral part of the PAG and contains very few, mostly tangentially oriented fibers. Column V is located ventrally and contains a mixture of rostrocaudally and tangentially oriented fibers. Column VI is only present in the most caudal part of the PAG and contains mainly tangential fibers.

Staining myelin and myelin-like degradation products in the spinal cords of chronic experimental allergic encephalomyelitis (Cr-EAE) rats using Sudan black B staining of glycol methacrylate-embedded material

A high-resolution light-microscopical (HRLM) technique is described to visualize myelin, and macrophages containing degradation products of myelin, in the spinal cords of chronic relapsing experimental allergic encephalomyelitis (Cr-EAE) rats. This HRLM technique was developed to optimalize the correlation between nuclear magnetic resonance (NMR) characteristics and histopathological images in this well-established animal model for multiple sclerosis (MS). Spinal cords were fixed by perfusion with a combination of cacodylate-buffered glutaraldehyde and formaldehyde, post-fixed in Dalton's fixative (containing osmium tetroxide), rinsed in water, processed in ethanol, acetone, and embedded in glycol methacrylate resin (Technovit 7100/HistoResin). Semi-thin sections were stained with Sudan Black B and counterstained with Cresyl Fast Violet, resulting in black staining of myelin and its degradation products, with blue/violet staining of demyelinated axons and other tissue elements. These dyes were selected with the aid of a numerical model of staining, which took both access and lipophilicity into account. The staining procedure is simple and highly reproducible. The resulting images are contrast rich, and combine excellent morphology with a high degree of lipid retention.

Dorsal mesencephalic projections to pons, medulla, and spinal cord in the cat: limbic and non-limbic components

The vertebrate dorsal mesencephalon consists of the superior colliculus, the dorsal portion of the periaqueductal gray, and the mesencephalic trigeminal neurons in between. These structures, via their descending pathways, take part in various behavioral responses to environmental stimuli. This study was undertaken to compare the origins and trajectories of these pathways in the cat. Injections of horseradish peroxidase into the cervical spinal cord and upper medullary medial tegmentum retrogradely labeled cells mainly in the contralateral intermediate and deep superior colliculus, and in the ipsilateral dorsal and lateral periaqueductal gray and adjacent tegmentum. Only injections in the medullary lateral tegmental field labeled mesencephalic trigeminal neurons ipsilaterally. Autoradiographic tracing results, based on injections across the dorsal mesencephalon, revealed three efferent fiberstreams. A massive first fiberstream (limbic pathway), consisting of thin fibers, descended ipsilaterally from the dorsal and lateral periaqueductal gray and adjacent superior colliculus through the mesencephalic and pontine lateral tegmentum, terminating in these areas as well as in the ventral third of the caudal pontine and medullary medial tegmentum. A few fibers from the dorsal periaqueductal gray matter (PAG) were distributed bilaterally to the dorsal vagal, solitary, and retroambiguus nuclei. The second fiberstream (the predorsal bundle) descended contralaterally from the superior colliculus (SC) and consisted of both thick and thin labeled fibers. The thin fibers terminated bilaterally in the dorsomedial nucleus reticularis tegmenti pontis and the medial half of the caudal medial accessory inferior olive. The thick fibers targeted the contralateral dorsal two thirds of the caudal pontine and medullary medial tegmental fields, and the facial, abducens, lateral reticular, subtrigeminal, and prepositus hypoglossi nuclei. A few fibers recrossed the midline to terminate in the ipsilateral medial tegmentum. Caudal to the obex, fibers terminated laterally in the tegmentum and upper cervical intermediate zone. From the lateral SC, fibers terminated bilaterally in the lateral tegmental fields of the pons and medulla and lateral facial subnuclei. The third fiberstream (mesencephalic trigeminal or Probst tract) terminated in the supratrigeminal and motor trigeminal nuclei, and laterally in the tegmentum and upper cervical intermediate zone. In summary, neurons in the PAG and in the deep layers of the SC give rise to a massive ipsilateral descending pathway, in which a medial-to-lateral organization exists. A similar topographical pattern occurs in the crossed SC projections. The possibility that these completely different descending systems cooperate in producing specific defensive behaviors is discussed.

Descending pathways to the cutaneous trunci muscle motoneuronal cell group in the cat

1. The cutaneus trunci muscle (CTM) is a thin broad sheet of skeletal muscle just beneath the skin. It does not contain muscle spindles and receives its afferents from the overlying skin. Contraction of the muscle can easily be triggered by pinching the skin or, in the cat, by gentle displacement of the fur (CTM reflex). The afferent information of this reflex is conveyed via the cutaneous nerves, which are segmentally organized. In the cat, the CTM motoneurons are located in a circumscribed cell group in the ventrolateral part of the ventral horn of the C8 and T1 spinal segments. The CTM motor nucleus corresponds with "nucleus X" of Giovanelli Barilari and Kuypers and with "ventral motor nucleus" of Matsushita and Ueyama. 2. Relatively long ascending propriospinal pathways, originating in the thoracolumbar cord, exist between the cutaneous afferents and the CTM motor nucleus. Such pathways have been described physiologically, as well as anatomically. Our results, based on anterograde autoradiographic experiments with [3H]leucine injections in the C1, C2, C6, and C8 segments, suggest that propriospinal pathways to the CTM motor nucleus originating in the cervical cord do not exist, although these propriospinal projections are very strong to all other motoneuronal cell groups surrounding the CTM motor nucleus. 3. The present results also demonstrate specific supraspinal projections to the CTM motor nucleus originating in 1) the contralateral nucleus retroambiguous (NRA) and 2) the ipsilateral dorsolateral pontine tegmentum. These projections suggest that the CTM motor nucleus is not only involved in spinal reflexes, but also in other functions such as abdominal straining.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomical study of the final common pathway for vocalization in the cat

Vocalization, the nonverbal production of sound, can be elicited in many vertebrates by stimulation in several regions of the limbic system but most easily in the caudal periaqueductal gray (PAG). This study shows that a specific cell group in the lateral part of the caudal PAG and in the tegmentum just lateral to it projects bilaterally to the nucleus retroambiguus (NRA) in the caudal medulla oblongata. Similar but much weaker projections are derived from the dorsal PAG. Neurons in the NRA in turn project via a contralateral pathway through the ventral funiculus of the spinal cord to motoneuronal cell groups, innervating intercostal and abdominal muscles. These projections are stronger on the contralateral side, although at lower thoracic and upper lumbar levels, many fibers recross to terminate in the ipsilateral motoneuronal cell groups. In the brainstem NRA neurons project to the motoneuronal cell groups innervating mouth-opening and perioral muscles as well as to motoneurons innervating the pharynx, soft palate, and tongue, and probably to the larynx. All these muscles are active in vocalization. The present anatomical results, combined with the physiological results of others, indicate that the projections from PAG via NRA to vocalization motoneurons form the final common pathway in vocalization. The role of this pathway in the total framework of emotional behavior is discussed.

Afferent and efferent connections of the cholinoceptive medial pontine reticular formation (region of the ventral tegmental nucleus) in the cat

Following minor concussive brain injury when there is an otherwise general suppression of CNS activity, the ventral tegmental nucleus of Gudden (VTN) demonstrates increased functional activity (32). Electrical or pharmacological activation of a cholinoceptive region in this same general area of the medial pontine tegmentum contributes to certain components of reversible traumatic unconsciousness, including postural atonia (31, 32, 45). Therefore, in an effort to examine the neuroanatomical basis of the behavioral suppression associated with a reversible traumatic unconsciousness, the afferent and efferent connections of the VTN and putative cholinoceptive medial pontine reticular formation (cmPRF) were studied in the cat using the retrograde horseradish peroxidase (HRP), HRP/choline acetyltransferase (ChAT) double-labeling immunohistochemistry, and anterograde HRP and autoradiographic techniques. Based upon retrograde HRP labeling, the principal afferents to the VTN region of the cmPRF originated from the medial and lateral mammillary nuclei, and lateral habenular nucleus, and to a lesser extent from the interpeduncular nucleus, lateral hypothalamus, dorsal tegmental nucleus, superior central nucleus, and contralateral nucleus reticularis pontis caudalis. Other afferents, which were thought to have been labeled through spread of HRP into the medial longitudinal fasciculus (MLF), adjacent paramedian pontine reticular formation, or uptake by transected fibers descending to the inferior olive, included the nucleus of Darkschewitsch, interstitial nucleus of Cajal, zona incerta, prerubral fields of Forel, deep superior colliculus, nucleus of the posterior commissure, nucleus cuneiformis, ventral periaqueductal gray, vestibular complex, perihypoglossal complex, and deep cerebellar nuclei. In HRP/ChAT double labeling studies, only a very small number of cholinergic VTN afferent neurons were found in the medial parabrachial region of the dorsolateral pontine tegmentum, although the pedunculopontine and laterodorsal tegmental nuclei contained numerous single-labeled ChAT-positive cells. Anterograde HRP and autoradiographic findings demonstrated that the VTN gave rise almost exclusively to ascending projections, which largely followed the course of the mammillary peduncle (16,21) and medial forebrain bundle, or the tegmentopeduncular tract (4). The majority of fibers ascended to terminate in the medial and lateral mammillary nuclei, interpeduncular complex (especially paramedian subnucleus), ventral tegmental area, lateral hypothalamus, and the medial septum in the basal forebrain. Labeling that joined the mammillothalamic tract to terminate in the anterior nuclear complex of the thalamus was thought to occur transneuronally. Some projections were also observed to nucleus reticularis pontis oralis and caudalis, superior central nucleus, and dorsal tegmental nucleus adjacent to the VTN...

Projections from the rostral mesencephalic reticular formation to the spinal cord. An HRP and autoradiographical tracing study in the cat

Eye and head movements are strongly interconnected, because they both play an important role in accurately determining the direction of the visual field. The rostral brainstem includes two areas which contain neurons that participate in the control of both movement and position of the head and eyes. These regions are the caudal third of Field H of Forel, including the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and the interstitial nucleus of Cajal with adjacent reticular formation (INC-RF). Lesions in the caudal Field H of Forel in monkey and man result in vertical gaze paralysis. Head tilt to the opposite side and inability to maintain vertical eye position follow lesions in the INC-RF in cat and monkey. Projections from these areas to extraocular motoneurons has previously been observed. We reported a study of the location of neurons in Field H of Forel and INC-RF that project to spinal cord in cat. The distribution of these fiber projections to the spinal cord are described. The results indicate that: 1. Unlike the neurons projecting to the extra-ocular muscle motoneurons, the major portion of the spinally projecting neurons are not located in the riMLF or INC proper but in adjacent areas, i.e. the ventral and lateral parts of the caudal third of the Field H of Forel and in the INC-RF. A few neurons were also found in the nucleus of the posterior commissure and ventrally adjoining reticular formation. 2. Neurons in caudal Field H of Forel project, via the ventral part of the ventral funiculus, to the lateral part of the upper cervical ventral horn. This area includes the laterally located motoneuronal cell groups, innervating cleidomastoid, clavotrapezius and splenius motoneurons. At lower cervical levels labeled fibers are distributed to the medial part of the ventral horn. Projections from the caudal Field H of Forel to thoracic or more caudal spinal levels are sparse. 3. Neurons in the INC-RF, together with a few neurons in the area of the nucleus of the posterior commissure, project bilaterally to the medial part of the upper cervical ventral horn, via the dorsal part of the ventral funiculus. This area includes motoneurons innervating prevertebral flexor muscles and some of the motoneurons of the biventer cervicis and complexus muscles. Further caudally, labeled fibers are distributed to the medial part of the ventral horn (laminae VIII and adjoining VII) similar to the projections of Field H of Forel. A few INC-RF projections were observed to low thoracic and lumbosacral levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural evidence for direct monosynaptic rubrospinal connections to motoneurons in Macaca mulatta

The magnocellularis division of the red nucleus of the Macaca mulatta, a midbrain structure involved in processing motor information, is known by light microscopic analysis to project, via the rubrospinal tract, to the contralateral intermediate horn of the spinal cord. Physiological studies, however, provide additional evidence for direct monosynaptic connections to motoneurons subserving distal musculature. This electron microscopic study demonstrates, by analyzing the anterograde transport of 5% wheatgerm agglutinin-horseradish peroxidase injected into the red nucleus, the presence of labeled terminals synapsing upon somata and proximal dendrites of motoneurons in the lateral portion of the ventral horn of the cervical enlargement of the spinal cord. We conclude that this anatomical evidence confirms the presence of direct monosynaptic connections to spinal motoneurons in the primate.

Anatomical evidence for red nucleus projections to motoneuronal cell groups in the spinal cord of the monkey

In 4 rhesus monkeys wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injections were made in the mesencephalic tegmentum. In 3 cases with injections involving the red nucleus (RN), rubrospinal fibers descended mainly contralaterally to terminate in laminae V, VI and dorsal VII of the spinal cord and in the lateral motoneuronal cell groups at the level of the cervical and lumbosacral enlargements. In all 4 cases the area of the interstitial nucleus of Cajal (INC) was injected, which resulted in labeled interstitiospinal fibers in the medial part of the ipsilateral ventral funiculus of the spinal cord. The results indicate that there is no major qualitative difference between the mesencephalic (RN and INC) and motor cortical projections to the spinal cord.

Anatomical evidence for a strong ventral parabrachial projection to nucleus raphe magnus and adjacent tegmental field

Injections with [3H]leucine in the ventral parabrachial nuclei and nucleus Kölliker-Fuse of the cat revealed strong projections to the nucleus raphe magnus (NRM) and adjacent tegmentum, while similar injections in the adjacent nucleus subcoeruleus produced diffuse projections to large parts of the tegmentum, but not specifically to the NRM. Horseradish peroxidase (HRP) injections in the area of the NRM and adjacent tegmentum demonstrated many labeled neurons in the ventral parabrachial nuclei, nucleus Kölliker-Fuse and nucleus subcoeruleus. These results suggest that the inhibition of nociception induced by stimulation in the ventral parabrachial nuclei may be based on the projections of this area to NRM and adjacent tegmentum.

Projections from the red nucleus and surrounding areas to the brainstem and spinal cord in the cat. An HRP and autoradiographical tracing study

HRP injections at the C2, T1 and S1 spinal levels and in the medullary lateral tegmental field revealed that the contralaterally projecting rubro-bulbospinal neurons are located not only in the caudal but also to a certain extent in the rostral red nucleus (RN). These RN projections are somatotopically organized. Neurons projecting to the sacral cord are located in the ventrolateral RN, those projecting to the upper part of the spinal cord lie in the dorsomedial RN and those projecting to the medullary lateral tegmentum were found in the dorsal portions of the RN. These last neurons are smaller than many of the other RN neurons. The HRP results also revealed that the RN does not project to the caudal raphe nuclei. The autoradiographical results confirmed the HRP findings. They further indicated that the contralateral RN projections to the caudal brainstem precerebellar nuclei (nucleus corporis pontobulbaris, lateral reticular nucleus, lateral cuneate nucleus) and the dorsal column nuclei are also somatotopically organized. This was also true for the RN projections to the dorsomedial and intermediate facial subnuclei and the caudal pontine and medullary lateral tegmental field. These areas receive afferents from mainly the dorsal portions of the RN. Regarding the RN projections to the spinal cord, the autoradiographical tracing results revealed somatotopically organized contralateral RN projections to laminae V, VI and VII. Moreover, a small but distinct RN projection to a dorsolaterally located group of motoneurons at the C8-T1 level was demonstrated. Ipsilaterally a minor projection to the cervical and upper thoracic lateral intermediate zone was observed. Finally, strong ipsilateral projections from the rostral mesencephalon to the inferior olive were seen. These projections were derived from various rostral mesencephalic areas, including the nucleus of Darkschewitsch, the nucleus accessorius medialis of Bechterew, the interstitial nucleus of Cajal and the area of the rostral interstitial nucleus of the medial longitudinal fasciculus. In the cat it was difficult to define which of the mesencephalic areas projecting to the inferior olive represented the parvocellular RN. A new subdivision of the RN is proposed based on its projections and not on the size of its cells. In this concept the first group is formed by the RN neurons projecting contralaterally to the caudal brainstem and spinal cord. The second group consists of RN neurons projecting to the inferior olive.(ABSTRACT TRUNCATED AT 400 WORDS)

Supraspinal control of motoneurons innervating the striated muscles of the pelvic floor including urethral and anal sphincters in the cat

The nucleus of Onuf (ON) in mammals contains motoneurons innervating the pelvic floor muscles including the external urethral and anal sphincters. Recently, direct pathways from the dorsolateral pons to the ON, probably involved in supraspinal micturition control, have been reported (Holstege et al., 1986). Since the pelvic floor muscles are involved not only in micturition but also in various other functions (e.g., coughing, vomiting, defaecation, parturition), an attempt has been made to establish whether, in the cat, there exist other direct brainstem pathways to the ON motoneurons. Our results indicate that specific projections to the ON are derived from 3 different areas: (1) the ipsilateral paraventricular hypothalamic nucleus; (2) the ipsilateral caudal pontine lateral reticular formation; and (3) the contralateral caudal nucleus retroambiguus. More diffuse projections (to all motoneuronal cell groups in the spinal cord including the ON) are derived from (1) neurons in the area of the nucleus subcoeruleus in the dorsolateral pontine reticular formation, (2) the nucleus raphe pallidus, and (3) the ventral part of the medullary medial reticular formation. Possible functional implications of these pathways are discussed.

Some anatomical observations on the projections from the hypothalamus to brainstem and spinal cord: an HRP and autoradiographic tracing study in the cat

The hypothalamus is closely involved in a wide variety of behavioral, autonomic, visceral, and endocrine functions. To find out which descending pathways are involved in these functions, we investigated them by horseradish peroxidase (HRP) and autoradiographic tracing techniques. HRP injections at various levels of the spinal cord resulted in a nearly uniform distribution of HRP-labeled neurons in most areas of the hypothalamus except for the anterior part. After HRP injections in the raphe magnus (NRM) and adjoining tegmentum the distribution of labeled neurons was again uniform, but many were found in the anterior hypothalamus as well. Injections of 3H-leucine in the hypothalamus demonstrated that: The anterior hypothalamic area sent many fibers through the medial forebrain bundle (MFB) to terminate in the ventral tegmental area of Tsai (VTA), the rostral raphe nuclei, the nucleus Edinger-Westphal, the dorsal part of the substantia nigra, the periaqueductal gray (PAG), and the interpeduncular nuclei. Further caudally a lateral fiber stream (mainly derived from the lateral parts of the anterior hypothalamic area) distributed fibers to the parabrachial nuclei, nucleus subcoeruleus, locus coeruleus, the micturition-coordinating region, the caudal brainstem lateral tegmentum, and the solitary and dorsal vagal nucleus. Furthermore, a medial fiber stream (mainly derived from the medial parts of the anterior hypothalamic area) distributed fibers to the superior central and dorsal raphe nucleus and to the NRM, nucleus raphe pallidus (NRP), and adjoining tegmentum. The medial and posterior hypothalamic area including the paraventricular hypothalamic nucleus (PVN) sent fibers to approximately the same mesencephalic structures as the anterior hypothalamic area. Further caudally two different fiber bundles were observed. A medial stream distributed labeled fibers to the NRM, rostral NRP, the upper thoracic intermediolateral cell group, and spinal lamina X. A second and well-defined fiber stream, probably derived from the PVN, distributed many fibers to specific parts of the lateral tegmental field, to the solitary and dorsal vagal nuclei, and, in the spinal cord, to lamina I and X, to the thoracolumbar and sacral intermediolateral cell column, and to the nucleus of Onuf. The lateral hypothalamic area sent many labeled fibers to the lateral part of the brainstem and many terminated in the caudal brainstem lateral tegmentum, including the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus, and the solitary and dorsal vagal nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Spinal cord location of the motoneurons innervating the abdominal, cutaneous maximus, latissimus dorsi and longissimus dorsi muscles in the cat

Horseradish peroxidase (HRP) injections were made in the rectus abdominis, obliquus externus, obliquus internus, transversus abdominis, cutaneous maximus, latissimus dorsi and the longissimus dorsi muscles in the cat. The results showed that motoneurons innervating the obliquus externus, obliquus internus and transversus abdominis muscles were located in greatly overlapping areas of midthoracic, caudal thoracic and upper lumbar spinal segments. These motoneuronal cell groups were present laterally in the ventral horn and at caudal thoracic and upper lumbar levels they bordered on the white matter. The location of the rectus motoneurons differed somewhat from the location of the other motoneuronal cell groups because they were also present at low cervical and upper thoracic levels and in the segments T12 to L3 they were found in the ventral horn medial to the other abdominal muscle motoneuronal cell group. At mid-thoracic levels rectus motoneurons were located in the same area as the other abdominal muscle motoneurons. Latissimus dorsi motoneurons were observed in a large cell group in the ventrolateral part of the ventral horn at the levels caudal C6 to rostral C8. Furthermore they were found in the segments T9 to L3 laterally in the ventral horn which is the same area in which the other abdominal muscle motoneurons except the rectus ones are located. Longissimus dorsi motoneurons were located in the most ventral portion of the ventral horn in all thoracic and upper 4 lumbar segments. The cutaneous maximus motoneurons were found in a cell group, located ventrolaterally in the ventral horn at the edge of the gray and white matter at the level caudal C8-rostral T1. This cell group corresponds to the caudal part of the ventral motor nucleus (VMN) of Matsushita and Ueyama (1973). Interestingly, labeled motoneurons were also present in the VMN after injecting HRP in the abdominal muscles as well as in the caudal (but not in the rostral) parts of the latissimus dorsi muscle but not in the longissimus dorsi injected cases. The possibility whether these motoneurons are labeled because of leakage of HRP to abdominal and caudal latissimus dorsi muscles is discussed. If leakage would not be the case, motoneurons in the VMN may be involved in specific functions of the abdominal muscles, such as the so-called steady state contractions.

Anatomical evidence for an ipsilateral rubrospinal pathway and for direct rubrospinal projections to motoneurons in the cat

In 11 cases [3H]leucine injections were made in various parts of the red nucleus (NR) and surrounding area. The autoradiographical tracing results confirmed the existence of a somatotopic organization in the location of the rubrospinal neurons. Moreover the results demonstrated direct NR projections to the most dorsolaterally located motoneuronal cell group in the C8 and upper T1 spinal segments and some ipsilaterally descending rubrospinal fibers terminating in the lateral part of the cervical intermediate zone.

Anatomical and physiological observations on supraspinal control of bladder and urethral sphincter muscles in the cat

In 15 cats injections of 3H-leucine were made in the pontine tegmentum. Injections in the medial part of the dorsolateral pontine tegmentum (M-region) resulted in specific projections to the sacral intermediomedial and intermediolateral cell groups. The intermediolateral cell group contains preganglionic parasympathetic neurons that form the motor supply of the detrusor muscle of the bladder. Injections in the lateral part of the pontine tegmental field (L-region) produced labeled fibers in the nucleus of Onuf, which contains motoneurons innervating the pelvic floor including the anal and urethral sphincters. L-region projections to the sacral preganglionic parasympathetic neurons and M-region projections to the nucleus of Onuf were very limited or absent. In 12 cats physiological experiments were performed. Electrical stimulation in the L-region elicited a prompt increase in the pelvic floor EMG and urethral pressure but had little influence on the intravesical pressure. Stimulation in the M-region elicited a prompt decrease in the pelvic floor EMG and urethral pressure followed, after a delay of 2 seconds, by an increase in the intravesical pressure, so simulating normal micturition.

Afferent projections to the orbicularis oculi motoneuronal cell group. An autoradiographical tracing study in the cat

The motoneurons innervating the orbicularis oculi muscle from a subgroup within the facial nucleus, called the intermediate facial subnucleus. This makes it possible to study afferents to these motoneurons by means of autoradiographical tracing techniques. Many different injections were made in the brainstem and diencephalon and the afferent projections to the intermediate facial subnucleus were studied. The results indicated that these afferents were derived from the following brainstem areas: the dorsal red nucleus and the mesencephalic tegmentum dorsal to it; the olivary pretectal nucleus and/or the nucleus of the optic tract; the dorsolateral pontine tegmentum (parabrachial nuclei and nucleus of Kölliker-Fuse) and principal trigeminal nucleus; the ventrolateral pontine tegmentum at the level of the motor trigeminal nucleus; the caudal medullary medial tegmentum; the lateral tegmentum at the level of the rostral pole of the hypoglossal nucleus and the ventral part of the trigeminal nucleus and the nucleus raphe pallidus and caudal raphe magnus including the adjoining medullary tegmentum. These latter projections probably belong to a general motoneuronal control system. The mesencephalic projections are mainly contralateral, the caudal pontine and upper medullary lateral tegmental projections are mainly ipsilateral and the caudal medullary projections are bilateral. It is suggested that the different afferent pathways subserve different functions of the orbicularis oculi motoneurons. Interneurons in the dorsolateral pontine and lateral medullary tegmentum may serve as relay for cortical and limbic influences on the orbicularis oculi musculature, while interneurons in the ventrolateral pontine and caudal medullary tegmentum may take part in the neuronal organization of the blink reflex.

Anatomical observations on the afferent projections to the retractor bulbi motoneuronal cell group and other pathways possibly related to the blink reflex in the cat

In the cat retractor bulbi (RB) muscle reflexively retracts the eye ball into the orbit. This reflex action is called the nictitating membrane response which, together with the reflex contraction of the orbicularis oculi muscle, constitutes the blink reflex. The retractor bulbi (RB) motoneuronal nucleus is a small cell group located in the lateral tegmentum of the caudal pons, just dorsal to the superior olivary complex. The nucleus is identical to the accessory abducens nucleus and sends its fibers through the abducens nerve. Autoradiographical tracing results indicate that the RB nucleus receives some fibers from the principal and rostral spinal trigeminal nuclei and from the dorsal red nucleus and dorsally adjoining tegmentum. The same areas project to the intermediate facial subnucleus, containing motoneurons innervating the orbicularis oculi muscle. It is suggested that the trigeminal projections take part in the anatomical framework for the R1 component of the blink reflex. Two other brainstem areas i.e.: a portion of the caudal pontine ventrolateral tegmental field and the medullary medial tegmentum at the level of the hypoglossal nucleus were also found to project to the RB motoneuronal cell group and to the intermediate facial subnucleus. These projections were much stronger than those derived from the trigeminal nuclei and red nucleus. Moreover, the medullary premotor area projects not only to the blink motoneuronal cell groups but also to the pontine premotor area. It is suggested that both areas are involved in the R2 blink reflex component. The medullary blink premotor area receives afferents especially from oculomotor control structures in the reticular formation of the brainstem while the pontine blink premotor area receives afferents from the olivary pretectal nucleus and/or the nucleus of the optic tract and from the dorsal red nucleus and its dorsally adjoining area. Because the oculomotor control structures in the reticular formation (by way of the superior colliculus) and the red nucleus receive afferents from trigeminal nuclei, they may play an important role in tactually induced reflex blinking, while the pretectum could take part in the neuronal framework of the visually induced blink reflex.

Anatomical evidence that the pontine lateral tegmental field projects to lamina I of the caudal spinal trigeminal nucleus and spinal cord and to the Edinger-Westphal nucleus in the cat

Autoradiographical tracing results in the cat indicate that the lateral pontine tegmental field projects mainly contralaterally to the marginal layer of the spinal trigeminal nucleus, to laminae I and II and the lateral part of laminae V and VI of the spinal cord and the Edinger-Westphal nucleus. It is pointed out that the projections from the lateral pontine tegmentum are very similar to the ones derived from the Edinger-Westphal nucleus and that these two areas are reciprocally connected. It is postulated that both areas may play a role in supraspinal pain control.

Differential corticospinal projections in the cat. An autoradiographic tracing study

An autoradiographic study of the corticospinal projections from different parts of the cat sensorimotor cortex produced the following findings. The lateral part of area 4 projects contralaterally to the lateral intermediate zone of the cervical enlargement only. The intermediate part of area 4 projects throughout the spinal cord, contralaterally to the lateral part of the intermediate zone and bilaterally to its ventromedial part. The lateral and medial part of area 3 project contralaterally to the cervical and lumbosacral dorsal horn (including laminae I and II), respectively.

Projections of the bed nucleus of the stria terminalis to the mesencephalon, pons, and medulla oblongata in the cat

Injections of HRP in the nucleus raphe magnus and adjoining medial reticular formation in the cat resulted in many labeled neurons in the lateral part of the bed nucleus of the stria terminalis (BNST) but not in the medial part of this nucleus. HRP injections in the nucleus raphe pallidus and in the C2-segment of the spinal cord did not result in labeled neurons in the BNST. Injections of 3H-leucine in the BNST resulted in many labeled fibers in the brain stem. Labeled fiber bundles descended by way of the medial forebrain bundle and the central tegmental field to the lateral tegmental field of pons and medulla. Dense BNST projections could be observed to the substantia nigra pars compacta, the ventral tegmental area, the nucleus of the posterior commissure, the PAG (except its dorsolateral part), the cuneiform nucleus, the nucleus raphe dorsalis, the locus coeruleus, the nucleus subcoeruleus, the medial and lateral parabrachial nuclei, the lateral tegmental field of caudal pons and medulla and the nucleus raphe magnus and adjoining medial reticular formation. Furthermore many labeled fibers were present in the solitary nucleus, and in especially the peripheral parts of the dorsal vagal nucleus. Finally some fibers could be traced in the marginal layer of the rostral part of the caudal spinal trigeminal nucleus. These projections appear to be virtually identical to the ones derived from the medial part of the central nucleus of the amygdala (Hopkins and Holstege 1978). The possibility that the BNST and the medial and central amygdaloid nuclei must be considered as one anatomical entity is discussed.

Mesencephalic projections to the facial nucleus in the cat. An autoradiographical tracing study

In 33 cats the projections of different parts of the mesencephalon to the facial nucleus were studied with the aid of the autoradiographical tracing method. The results indicate the existence of many different mesencephalo-facial pathways. The dorsomedial facial subnucleus, containing motoneurons innervating ear muscles, receives afferents from 4 different mesencephalic areas: a, the most rostral mesencephalic reticular formation; b, the nucleus of Darkschewitsch and/or the ventral part of the rostral PAG; c, the interstitial nucleus of Cajal and/or the mesencephalic tegmentum dorsomedial to the red nucleus. These areas project bilaterally by way of an ipsilateral medial tegmental pathway. The medial part of the deep tectum. This area projects bilaterally by way of the tecto-spinal tract. The lateral mesencephalic tegmentum close to the parabigeminal nucleus. This area projects mainly contralaterally by way of a separate contralateral lateral tegmental fiber bundle. The mesencephalic tegmentum just dorsolateral to the red nucleus and perhaps from the dorsolateral red nucleus itself. This area projects contralaterally by way of the rubrospinal tract. The intermediate facial subnucleus containing motoneurons innervating the muscle around the eye, receives afferents from two different mesencephalic areas: The dorsal part of the rostral as well as caudal red nucleus (but not from its caudal pole) and from the dorsally adjoining mesencephalic tegmentum including the area of the nucleus of Darkschewitsch and the interstitial nucleus of Cajal. These areas project contralaterally by way of the contralateral rubrospinal tract. The nucleus of the optic tract and/or the olivary pretectal nucleus. This area projects contralaterally by way of a contralateral medial tegmental pathway. The lateral and ventrolateral facial subnuclei containing motoneurons innervating the muscles around the mouth receive afferents from two different mesencephalic areas: The lateral part of the deep tectal layers. This area projects contralaterally by way of the tecto-spinal tract. The nucleus raphe dorsalis and perhaps the nucleus centralis superior. This area projects by way of the lateral tegmentum of caudal pons and medulla.

Effects of neonatal and late unilateral enucleation on optokinetic responses and optic nerve projections in the rabbit

Rabbits were unilaterally enucleated at the age of 0 or 21 days or at adult age. After survival times of 6-21 months optokinetic nystagmus (OKN) was measured and retinofugal connections were traced with anterograde transport of horseradish peroxidase or 3H leucine, injected into the eye. Non-enucleated animals served as controls. The asymmetry of monocular OKN in normal rabbits, characterized by a strong preference for pursuit of motion in the nasal (anterior) direction, was only slightly alleviated after enucleation. Responses to stimulation in the nasal direction were unchanged; responses to stimulation in the temporal direction showed modest improvements especially after enucleation at adult age and to a smaller degree after enucleation at 0 or 21 days. Redistribution of retinofugal fibers from the eye remaining after enucleation was very limited. Contralateral connections, including those to the lateral geniculate nucleus, showed a normal distribution. Of the ipsilateral connections, those to the lateral geniculate nucleus were normal in extent and density, while those to the superior colliculus were enhanced, in agreement with previous workers (Chow et al. 1973, 1981). Changes in ipsilateral pretectal projections were extremely small; particularly no connections to the nucleus of the optic tract were developed in any of the normal or enucleated animals. Of the accessory optic nuclei, the medial terminal nucleus received a very small ipsilateral projection in normal rabbits, which was markedly enhanced after enucleation especially at 0 and 21 days, but even at adult age. It is concluded that functional and anatomical plasticity of OKN circuits in the rabbit is very limited from the time of birth.

Location of motoneurons innervating soft palate, pharynx and upper esophagus. Anatomical evidence for a possible swallowing center in the pontine reticular formation. An HRP and autoradiographical tracing study

Retrograde HRP studies indicated that motoneurons innervating soft palate and pharynx are located in especially the dorsal group of the nucleus ambiguus, while motoneurons innervating upper esophagus and cricothyroid muscles are located in the retrofacial nucleus, the most rostral part of the nucleus ambiguus. Autoradiographic tracing techniques revealed that in the caudal pontine tegmentum an area is located just dorsal to the superior olivary complex, that projects contralaterally to the ventral part of the trigeminal motor nucleus, the dorsal group of the nucleus ambiguus and the ventral part of the hypoglossal nucleus. In these areas motoneurons are located innervating the mylohyoid, soft palate, pharynx and geniohyoid muscles respectively. Since these muscles are all involved in swallowing, a possible involvement of this pontine tegmental area in swallowing is discussed.

The efferent connections of the nucleus of the optic tract and the superior colliculus in the rabbit

3H-leucine injections were made in tectal and pretectal areas in the rabbit. After injections in the nucleus of the optic tract (NOT) labeled fibers were distributed bilaterally to the superior colliculus, the dorsal part of the medial geniculate nucleus (MGd), and the pulvinar nucleus, and ipsilaterally to the external layer of the ventral lateral geniculate nucleus (LGv), the dorsal geniculate nucleus (LGd) pars beta, the reticular thalamic nucleus, and the lateral and medial terminal nucleus (LTN, MTN). Many labeled fibers were distributed to the lateral and some to the medial parts of the pontine nuclei. more caudally, coarse labeled fiber bundles descended ipsilaterally, distributing fibers to the prepositus hypoglossi and abducens nucleus and to the caudally adjoining medial reticular formation. Many labeled fibers were also present in the inferior olive, especially ipsilaterally in the dorsal cap and the ventrally adjoining pars beta, and a few in the contralateral dorsal cap area. Contralaterally, some descending fibers terminated in the dorsal part of the facial nucleus, in which motoneurons are located innervating the orbicularis oculi muscle. The superficial layers of superior colliculus distributed fibers bilaterally to the internal layer in the ventral lateral geniculate nucleus (LGv), the LGd alpha (lateral part), the MGd, the pulvinar, and more caudally to the ipsilateral parabigeminal and lateral pontine nuclei. The deep collicular layers distributed fibers ipsilaterally to MG (internal division), pulvinar, and the internal layer of LGv. Furthermore, ascending connections were found to the suprageniculate nucleus, the zona incerta, the mediodorsal nucleus, and some intralaminar and midline nuclei. Descending fibers terminated in the mesencephalic lateral tegmentum, pontine nuclei, and ventrally in the pontine and high medullary reticular formation. Contralaterally fibers were distributed to the nucleus reticularis tegmenti pontis (NRTP), the medial reticular formation, and the inferior olive just lateral to the nucleus beta. In one case fibers were also distributed to the lateral part of the contralateral facial nucleus in which motoneurons are located innervating the upper lip muscles.

Amygdaloid projections to the mesencephalon, pons and medulla oblongata in the cat

Amygdalotegmental projections were studied in 26 cats after injections of horseradish peroxidase (HRP) in the diencephalon, midbrain and lower brain stem and in 6 cats after injection of 3H-leucine in the amygdala. Following HRP injections in the posterior hypothalamus, periaqueductal gray (PAG) and tegmentum many retrogradely labeled neurons were present in the central nucleus (CE) of the amygdala, primarily ipsilaterally. Injections of HRP in the posterior hypothalamus and mesencephalon also resulted in the labeling of neurons in the basal nucleus, pars magnocellularis. Following 3H-leucine injections in CE and adjacent structures autoradiographically labeled fibers were present in the stria terminalis and ventral amygdalofugal pathways. In the mesencephalon heavily labeled fiber bundles were located lateral to the red nucleus. Labeled fibers and terminals were distributed to the mesencephalic reticular formation, substantia nigra, ventral tegmental area and PAG. In the pontine and medullary tegmentum the bulk of passing fibers was located laterally in the reticular formation. Many labeled fibers and terminals were distributed to the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus and lateral tegmental fields. Many terminals were also present in the solitary nucleus and dorsal motor nucleus of the vagus nerve. The location of the cells of origin and the distribution of the terminals of the amygdalotegmental projection suggest that this pathway plays an important role in the integration of somatic and autonomic responses associated with affective defense.

The organization of the bulbar fibre connections to the trigeminal, facial and hypoglossal motor nuclei. II. An autoradiographic tracing study in cat

In 34 cats 3H-leucine was injected in the pontine and medullary tegmentum. The location of the labelled neurons and the distribution of the labelled fibres and terminals were studied autoradiographically. The findings indicate that the neurons in the bulbar lateral tegmental field (Berman, 1968) represent the main source of the propriobulbar projections to the hypoglossal, facial and motor V nuclei, while those in the medial tegmental field distribute their fibres mainly to the spinal cord. The neurons in the lateral part of the lateral tegmental field give rise to ascending and descending fibres which compose the lateral propriobulbar system, and distribute fibres mainly to ipsilateral bulbar motor nuclei. The neurons in the medial part of the lateral tegmental field compose the medial propriobulbar system, which is organized bilaterally and tends to distribute fibres to the motor nuclei bilaterally. The various neuronal cell groups which project through the medial propriobulbar system to the different motor nuclei bilaterally show relatively less spatial segregation than those which project through the lateral system to these motor nuclei.

Propriobulbar fibre connections to the trigeminal, facial and hypoglossal motor nuclei. I. An anterograde degeneration study in the cat

The local bulbar connections to the V, VII and XII motor nuclei in the cat have been studied by means of the anterograde fibre degeneration technique in combination with the Fink-Heimer silver impregnation procedure. For this purpose electrolytic lesions were made mainly in the reticular formation of the medulla oblongata and the pons. For control purposes also, extrabulbar lesions were made in the cervical cord and the upper brain-stem and in addition, primary afferent fibres were interrupted by section of the upper cervical and trigeminal roots. The findings indicated the existence of a lateral and a medial propriobulbar fibre system, the former of which projects to the motor nuclei mainly ipsilaterally, while the latter tends to project bilaterally. Since the cells of origin of the propriobulbar fibre systems are difficult to determine by means of the anterograde degeneration technique these systems have also been investigated by means of the labelled amino-acid tracing technique. The findings thus obtained are reported in the adjoining paper.