Propriospinal neurons with ascending collaterals to the dorsal medulla,the thalamus and the tectum: a retrograde fluorescent double-labeling study of the cervical cord of the rat

Summary Branching neurons with descending propriospinal collaterals and ascending collaterals to the dorsal medulla, the thalamus and the tectum were studied in the rat's cervical spinal cord (C1–C8), using the retrograde fluorescent double-labeling technique: Diamidino Yellow Dihydrochloride (DY) was injected in the cord at T2, True Blue (TB) was injected in the brain stem. DY-labeled descending propriospinal neurons were present in all laminae, except lamina IX. They were concentrated in lamina I, laminae IV to VIII, and in the lateral spinal nucleus, LSN. TB-labeled neurons projecting to the dorsal medulla were concentrated in lamina IV and the medial parts of laminae V and VI (probably representing postsynaptic dorsal column — PSDC — neurons), but were also present in lamina I, the LSN, the lateral dorsal horn, and in laminae VII and VIII. DY-TB double-labeled neurons giving rise to both a descending propriospinal collateral and an ascending collateral to the dorsal medulla were intermingled with the TB single-labeled neurons. About 4% of the descending propriospinal neurons gave rise to an ascending collateral to the dorsal column nuclei; these double-labeled cells constitute a sizable fraction (10%) of the PSDC neurons. TB-labeled spinothalamic and spinotectal neurons were located in lamina I, the lateral cervical nucleus (LCN), the LSN, the lateral lamina V, lamina VII and VIII, lamina X and in the spinal extensions of the dorsal column nuclei, predominantly contralateral to the TB injections. DY-TB double-labeled neurons were present throughout C1–C8 in the LSN, lateral lamina V, lamina VIII, ventromedial lamina VII, and lamina X. Only very few were observed in lamina I and the LCN, and none in the spinal extensions of the dorsal column nuclei. The double-labeled neurons constituted only a minor fraction of all labeled neurons; 3–5% of the spinothalamic neurons and about 1–7% of the spinotectal neurons were double-labeled. Conversely, only about 1% of the labeled descending propriospinal neurons gave rise to an ascending spinothalamic collateral, and even fewer (0.1 to 0.6%) to a collateral to the dorsal midbrain. The LSN displayed the highest relative content of branching neurons. Up to 20% of its ascending spinothalamic and spinotectal neurons and up to 8% of its descending propriospinal neurons were found to be branching neurons, indicating that the LSN constitutes an unique cell-group in the rat spinal cord.     

Spinocerebellar neurons and propriospinal neurons in the cervical spinal cord: a fluorescent double-labeling study in the rat and the cat

Summary In the cervical spinal cord of the rat and the cat, the distributions of spinocerebellar and of descending propriospinal neurons were investigated using the retrograde fluorescent double-labeling technique. Moreover, a search was made for the presence of neurons with both ascending spinocerebellar and descending propriospinal axoncollaterals. Diamidino Yellow Dihydrochloride (DY) was injected at T2, while True Blue (TB) (in rats) or Fast Blue (FB) (in cats) was injected in the cerebellum. The distributions of labeled neurons were very similar in the rat and the cat. DY-labeled propriospinal neurons, projecting to T2 or below, were most numerous in lamina I and laminae IV to VIII. In the rat, such neurons were also present in the lateral spinal nucleus (LSN). TB- or FB-labeled spinocerebellar neurons were concentrated in the central cervical nucleus (CCN) at C1-C4, in the central part of lamina VII at C5-T1, in the medial part of lamina VI and the adjoining dorsomedial part of lamina VII at C2/C3-T1, and in Clarke's column. They were also found in lamina V at C1 and C7-T1, and in lamina VIII at all levels. In both species only very few DYTB/FB double-labeled neurons, representing neurons with branching axons, were observed; in C1-T1, only about 0,5% of all TB/FB-labeled Spinocerebellar neurons and about 0,05% of all DY-labeled descending propriospinal neurons were double-labeled. The double-labeled neurons were all located centrally in lamina VII at C5-T1, but even in that area they constituted not more than 1,5% (rat) and 4% (cat) of the labeled spinocerebellar neurons. These findings indicate that, in the cervical cord of the rat and the cat, descending propriospinal neurons and spinocerebellar neurons are to a large extent separate populations.     

神经示踪定位SD大鼠长下行脊髓固有神经元胞体及其轴突投射的解剖位置

目的 利用神经示踪技术探讨SD大鼠长下行脊髓固有神经元及其轴突投射的解剖位置.方法 将荧光金(FG)注射入第1腰髓(L1)节段逆行标记大鼠下行脊髓固有神经元(DPNs)胞体;将顺行神经示踪剂生物素葡聚糖胺(BDA)注射到脊髓第3和第4颈髓处标记此处的DPNs胞体及其长下行脊髓固有束(LDPT).固定取材与切片染色后,检...     

Morphophysiological study on the divergent projection of axon collaterals of medial vestibular nucleus neurons in the cat

(1) Spikes of single neurons were extracellularly recorded in the medial vestibular nucleus (MVN) in decerebrate cats and were functionally identified as secondary type I neurons by observing their responses to horizontal rotation and monosynaptic activation after stimulation of the ipsilateral vestibular nerve. Axonal projection of these neurons was examined by their antidromic responses to stimulation of the contralateral abducens nucleus, the spinal cord, and the ascending and descending MLF. (2) Almost all secondary type I vestibular neurons which sent their axon to the contralateral abducens nucleus were antidromically activated from the descending MLF at the level of the obex as well. Nearly half of these neurons sent their collateral axon to the level of C1 segment in the spinal cord and approximately one third to the ascending MLF close to the oculomotor complex. (3) The mean conduction velocity was 29 m/s for descending collateral axons and 30 m/s for ascending collateral axons. (4) Systematic tracking for antidromic microstimulation in the contralateral abducens nucleus and spinal gray matter at C2-C3 suggested that collateral axons of single type I vestibular neurons gave off local branches in the abducens nucleus and the motoneuron pool in the upper cervical gray matter. Existence of terminal branches in the neck motoneuron pool was confirmed by intraaxonal staining with horseradish peroxidase (HRP). (5) Neurons which projected to both the contralateral abducens nucleus and the spinal cord were located in a fairly localized region in the ventrolateral part of the rostral MVN. Neurons which projected to the contralateral abducens nucleus and not to the spinal cord were located in a rostrocaudally wider area in the ventrolateral MVN. Neurons projecting to the spinal cord and not to the contralateral abducens nucleus were located in the widest area in the rostrocaudal direction, covering almost the whole extent of the rostral half of the MVN.     

Observations on the development of ascending spinal pathways in the clawed toad, Xenopus laevis

Summary The development of ascending spinal pathways has been studied in the clawed toad, Xenopus laevis. From stage 35 (hatching) on, HRP was applied at the spinomedullary border or to the area of the developing dorsal column nucleus, to analyze the development of ascending spinal pathways to the brain stem, and the onset and development of spinal projections to the dorsal column nucleus, respectively. Several populations of spinal neurons with ascending projections at least as far as the spinomedullary border were successively labeled. In early stages ascending spinal projections arise from Rohon-Beard cells and ascending interneuron populations located at the margin of the gray and white matter, i.e., marginal neurons. The ascending interneuron populations could be characterized as dorsolateral commissural and commissural interneurons projecting contralaterally, and as ipsilaterally projecting ascending interneurons and distinguished by Roberts and co-workers. Such a subdivision could be made until about stage 57. Then these ascending and commissural interneuron populations become intermingled with other populations of ascending tract neurons. Rohon-Beard cells could be labeled, more or less shrunken, until stage 55. Around stage 48 (at the time of the appearance of the limb buds) spinal ganglion cells could be labeled from the spinomedullary border and the developing dorsal column nucleus. At stage 48 such ascending primary spinal afferents were found to arise only from non-limbbud-innervating dorsal root ganglia. Gradually also the limb-bud-innervating ganglia give rise to ascending collaterals, so that by stage 53 all spinal ganglia send ascending collaterals to the brain stem. The number of cells of origin of secondary spinal afferents to the brain stem increases during development, and their distribution becomes more extensive. Particularly impressive is a large population of neurons in the dorsal horn projecting ipsilaterally to the dorsal column nucleus. Part of the latter population represents non-primary spinal afferents to the dorsal column nucleus.     

Spinal branching of rubrospinal axons in the cat

Summary The branching patterns of rubrospinal (RS) axons projecting to the cervical spinal cord between C3 and C8 were studied in the cat. RS neurons were identified by their antidromic responses to microstimulation of local axon branches within the cervical gray matter. Twenty-six of 58 RS neurons projecting to the cervical gray matter also sent axon branches to the thoracic spinal cord. Two out of 40 of these RS neurons also sent axon branches to the lumbar spinal cord. Using a collision technique, it was demonstrated that stem axons of rubrospinal neurons commonly sent multiple collaterals to different cervical segments.Neurons projecting to the cervical spinal cord alone were located in the dorsal quadrants of the red nucleus. Those projecting to cervical, as well as to more caudal segments, were intermingled with the former, and in slightly more ventral portions of the red nucleus. The presence of RS neurons projecting to widely separate levels of the spinal cord suggests that individual RS neurons may be capable of ultimately influencing two or more different motoneuron pools.     

Morphology of vertical canal related second order vestibular neurons in the cat

Summary The morphology of vertical canal related second order vestibular neurons in the cat was studied with the intracellular horseradish peroxidase method. Neurons were identified by their monosynaptic potentials following electrical stimulation via bipolar electrodes implanted into individual semicircular canal ampullae. Anterior and posterior canal neurons projected primarily to contralateral or ipsilateral motoneuron pools (excitatory and inhibitory pathways, respectively). The axons of contralaterally projecting neurons crossed the midline at the level of the abducens nucleus and bifurcated into an ascending and a descending main branch which travelled in the medial longitudinal fasciculus (MLF). Two types of anterior canal neurons were observed, one with unilateral and one with bilateral oculomotor projection sites. For both neuron classes, the major termination sites were in the. contralateral superior rectus and inferior oblique subdivisions of the oculomotor nucleus. In neurons which terminated bilaterally, major collaterals recrossed the midline within the oculomotor nucleus to reach the ipsilateral superior rectus motoneuron pool. Other, less extensive, termination sites of both neuron classes were in the contralateral vestibular nuclear complex, the facial nucleus, the medullary and pontine reticular formation, midline areas within and neighboring the raphé nuclei, and the trochlear nucleus. The ascending main axons continued further rostrally to reach the interstitial nucleus of Cajal and areas around the fasciculus retroflexus. The descending branches proceeded further caudal in the medial vestibulo-spinal tract but were not followed to their spinal target areas. In addition to two previously described posterior canal related neuron types (Graf et al. 1983), we found neurons with bilateral oculomotor terminals and a spinal collateral. Typical for posterior canal neurons, the major termination sites were in the trochlear nucleus (superior oblique motoneurons) and in the inferior rectus subdivision of the oculomotor nucleus. Axon collaterals recrossed the midline to reach ipsilateral inferior rectus motoneurons. The axons of ipsilaterally projecting neurons ascended through the reticular formation to join the MLF caudal to the trochlear nucleus. The main target sites of anterior canal related neurons were in the trochlear nucleus and the inferior rectus subdivision of the oculomotor nucleus. Minor collaterals reached the pontine reticular formation and areas in between the fiber bundles of the ipsilateral MLF. In some cases, small collaterals crossed the midline within the oculomotor nucleus to terminate in the inferior rectus subdivision on the contralateral side. The axon proceeded further rostral to project to the interstitial nucleus of Cajal and beyond. The main termination sites of posterior canal neurons were in the superior rectus and inferior oblique subdivisions of the oculomotor nucleus. Minor collaterals were also observed to reach the midline area within the oculomotor nucleus, however, prospective contralateral termination sites could not be identified. More rostral projections were found in the interstitial nucleus of Cajal. The described axonal arborization of second order vestibular neurons reflects the organization of intrinsic coordinate systems as exemplified by the geometry of the semicircular canal and the extraocular muscle planes. These neurons are interpreted to provide a matrix for coordinate system transformation, i.e. from vestibular into oculomotor reference frames, and to play a role in gaze control and related reflexes by distributing their signals to multiple termination sites.Abbreviations DV descending vestibular nucleus - INC interstitial nucleus of Cajal - INT nucleus intercalatus - IQ inferior oblique subdivision - LV lateral vestibular nucleus - MLF medial longitudinal fasciculus - MRF medullary reticular formation - MV medial vestibular nucleus - nVII facial nerve - PH nucleus praepositus hypoglossi - PRF pontine reticular formation - RO nucleus Roller - SR superior rectus subdivision - SV superior vestibular nucleus - III oculomotor nucleus - IV trochlear nucleus - VI abducens nucleus - VII facial nucleus - XII hypoglossal nucleus Supported by NIH grants EY04613 and NS02619     

Neurones in the cervical enlargement of the cat spinal cord antidromically activated from sacral segments and the inferior cerebellar peduncle

The electrophysiological investigation of neurones located in the cervical enlargement of the spinal cord was performed in eight-chloralose anaesthetized cats. Neurones were recorded intracellularly or extracellularly and identified by antidromic stimulation. The main purpose of the study was to test whether these neurones give off collateral branches ascending to the inferior cerebellar peduncle and descending to the sacral segments (S1/S2). Recordings were made from 78 neurones located in medial and central parts of Rexed's laminae VII and VIII of C6/C7 segments. Four subpopulations could be distinguished from their patterns of propriospinal or supraspinal projections: (a) ascending/descending neurones with axons ascending to RB and descending to S1/S2 (23%); (b) ascending/descending neurones projecting to RB and the level of Th13 (14%); (c) propriospinal neurones descending to Th13 (15%); (d) propriospinal neurones descending to S1/S2 (48%). Within these groups, ipsilateral, contralateral and bilateral descending projections were observed. The mean axonal conduction velocities for descending and ascending collaterals of bidirectional neurones were 59 and 39 m/s, respectively. Results suggest that parallel transmission of information to supraspinal and spinal centres plays an important role in the process of movement coordination.     

Quantitative inter-segmental and inter-laminar comparison of corticospinal projections from the forelimb area of the primary motor cortex of macaque monkeys

Corticospinal projections from the forelimb area of the primary motor cortex to the C2-Th2 spinal cord segments were quantitatively analyzed using the high resolution anterograde tracer, biotinylated dextran amine (BDA), in rhesus monkeys (n=5). The majority of descending axons were located in the contralateral dorsolateral funiculus (DLF) (85-98%), but a minor portion was observed in the ipsilateral DLF (1-12%) and ventromedial funiculus (VMF) (1-7%). In the gray matter, axon collaterals and terminal buttons were found mainly in the contralateral laminae VI-VII and IX and ipsilateral lamina VIII. The majority of projections to the contralateral gray matter originated from the contralateral DLF, but a minority originated from the ipsilateral DLF. Axons from the ipsilateral DLF were not found to project collaterals on the ipsilateral side, but directly entered the contralateral side after crossing the midline. On the other hand, projections to the ipsilateral lamina VIII were from the ipsilateral VMF, and commissural axons were from the contralateral DLF. Terminal buttons in the motoneuron pool in the contralateral lamina IX were found mainly at the C7-Th1 spinal cord segments, whereas the projections to the contralateral laminae VI-VII, ipsilateral lamina VIII, and commissural axons were also found in more rostral segments, abundantly at the C4-C8 segments, 1-3 segments rostral to the motoneuronal projections. These results suggest that cortical control of contralateral forelimb motoneurons accompanies regulation of interneuronal systems in the contralateral laminae VI-VII and the ipsilateral lamina VIII located a few segments rostral to the motoneurons.     

Integration in descending motor pathways controlling the forelimb in the cat

Summary The morphology of single C3–C4 propriospinal neurones (PNs) including the cell body, dendritic tree, axonal trajectory and the pattern of projection and termination of axonal collaterals in the C3–C4 segments was investigated by intra-somatic or intra-axonal injection of horseradish peroxidase. All the C3–C4 PNs could be antidromically activated from the lateral funicle in C6 and the lateral reticular nucleus but not from Th13. Another criterion was that they received monosynaptic excitation from corticospinal fibres in the contralateral pyramid. Twenty-four C3–C4 PNs were successfully stained. They were located in the lateral part of laminae VI–VIII except for two neurones which were located in lamina V and two in lamina IX. Five to eleven dendrites originated from the cell bodies and extended throughout laminae IV–VIII and even into the white matter in the transverse plane and up to 3 mm rostro-caudally. The axonal trajectory from the cell body was usually curved before reaching the lateral funicle. The bifurcation of the stem axon into a descending and an ascending branch was mostly observed in the white matter close to or at the border between the white and grey matter at the level of the cell body. The ascending and descending axonal branches maintained their location in the same part of the lateral funicle. Sixteen out of 24 stem axons gave off collaterals in the grey matter and/or in the white matter. One to five collaterals were given off from the axons in the grey matter. Boutons were found in a restricted region in the intermediate zone from lamina VI to the border between laminae VII and VIII, in the lateral part of laminae V–IX, in the middle and medial parts of laminae VI–VIII. The termination in the vicinity of large neurones in lamina VIII suggests that long PNs receive collateral projections from the C3–C4 PNs. The finding that some collaterals terminated laterally in lamina IX is in agreement with electrophysiological observations that spinal accessory motoneurones receive disynaptic pyramidal excitation which is mediated via C3–C4 PNs. The collateral projection from the C3–C4 PNs to lateral and medial regions in laminae VI-VII is discussed in relation to feed-forward and feed-back inhibitory control of the C3–C4 PNs.     

Ascending and descending internuclear connections of the trigeminal sensory nuclei in the cat. A study with the retrograde and anterograde horseradish peroxidase technique

The distribution of cells of origin of ascending and descending internuclear connections in the trigeminal sensory nuclei was studied by the retrograde horseradish peroxidase technique in the cat. The termination of collaterals of these ascending axons was also studied by the anterograde transport of horseradish peroxidase. Following injections of horseradish peroxidase into the ventral part of the principal sensory nucleus and the adjacent reticular formation many small neurons were labeled ipsilaterally in the whole area of the caudal portion of the nucleus interpolaris and in laminae III and IV of the nucleus caudalis. Labeled neurons were also found in laminae I and V. Injections limited to either nucleus oralis, the ventral part of the principal sensory nucleus and the medial parabrachial nucleus labeled similar types of neurons in the above regions with a topographic relationship; neurons in the dorsal part of the nuclei caudalis and interpolaris project, dorsally, to rostral portions of the trigeminal sensory nuclei while those in the ventral part of the nuclei caudalis and interpolaris project ventrally. Anterograde labeling of axons arising from the nucleus caudalis demonstrates that the axons ascend in the intranuclear bundles and the adjacent reticular formation, and give off collaterals to the nuclei interpolaris and oralis, and the ventral part of the principal sensory nucleus. Injections limited to the nucleus caudalis labeled small neurons in the rostral portion of the nucleus oralis and the caudal portion of the nucleus interpolaris. The present study suggests that these ascending and descending internuclear connections of the trigeminal sensory nuclei may modulate transmission of afferent inputs to various projection sites, such as thalamus, superior colliculus, cerebellum and spinal cord.     

Differential input to dorsal horn dorsal spinocerebellar tract neurons in mid- and low-lumbar segments from upper cervical spinal cord in the cat

Previous studies showed that ipsilaterally projecting dorsal horn dorsal spinocerebellar tract (dh-DSCT) neurons located outside Clarke's column in mid- and caudal-lumbar segments of the spinal cord receive different afferent inputs. Here, we examined, using extracellular recordings in anaesthetized cats, whether there are also input differences to these populations of dh-DSCT neurons from: (a) the spinocervical tract (SCT), estimated by stimulation of the ipsilateral dorsolateral funiculus at cervical cord C3 and rostral C1, below and above the termination of SCT axons in the lateral cervical nucleus (LCN), and (b) descending/ascending fibres activated by electrical stimulation at rostral C1. Seventy percent (21/30) of the lower-lumbar (L6-L7) dh-DSCT neurons received significantly greater excitation from C3 than rostral C1, whereas only 17% (5/30) of the mid-lumbar (L5) dh-DSCT neurons had greater responses from C3 than rostral C1. Inhibition of background activity was seen in 30% of the lower-lumbar neurons, but only in 3% of mid-lumbar neurons. These findings suggest that lower-lumbar dh-DSCT neurons are much more likely, than mid-lumbar ones, to be influenced by the SCT and by systems descending from the brain, LCN and/or ascending systems. The experiments provide further evidence for differences in input to the subpopulations of dh-DSCT neurons.     

大鼠中脑导水管周围灰质向三叉神经脊束核尾侧亚核的5-羟色胺能投射

大鼠中脑导水管周围灰质(PAG)向三又神经脊束核尾侧亚核(Sp 5 C)投射的起源细胞在其吻、中、尾三个部分的分布不同,且由尾段向吻段有从腹侧向背侧移行的趋势。尾段的HRP逆标细胞主要位于PAG的腹外侧区、内侧区腹侧部;中段的标记细胞较多,主要见于腹外侧区、背侧区和背外侧区腹侧部,尚可见一些顺行标记的终末;吻段的标记细胞主要位于背外侧区,在上丘深层、Cajal氏中介核、Darkschewitsch氏核内,也可见标记细胞。标记细胞和终末均主要位于注射侧的PAG内。PAG向Sp 5 C投射的5-羟色胺(5-HT)样神经元主要位于PAG的中、尾段的腹外侧区和内侧区腹侧部。中段的双标细胞占全部双标细胞数的57％,尾段占41％,吻段占2％。在背中缝核(DR)内,亦可见到一些双标细胞。PAG内的双标细胞占其HRP标记细胞总数的37％,但仅占5-HT样阳性细胞总数的4.5％。标记细胞主要为中型(20—30μm)梭形及三角形,小型(<20μm)梭形和大型(>30μm)多角形细胞较少见。     

The red nucleus and the rubrospinal projection in the mouse

We studied the organization and spinal projection of the mouse red nucleus with a range of techniques (Nissl stain, immunofluorescence, retrograde tracer injections into the spinal cord, anterograde tracer injections into the red nucleus, and in situ hybridization) and counted the number of neurons in the red nucleus (3,200.9 ± 230.8). We found that the rubrospinal neurons were mainly located in the parvicellular region of the red nucleus, more lateral in the rostral part and more medial in the caudal part. Labeled neurons were least common in the rostral and caudal most parts of the red nucleus. Neurons projecting to the cervical cord were predominantly dorsomedially placed and neurons projecting to the lumbar cord were predominantly ventrolaterally placed. Immunofluorescence staining with SMI-32 antibody showed that ~60% of SMI-32-positive neurons were cervical cord-projecting neurons and 24% were lumbar cord-projecting neurons. SMI-32-positive neurons were mainly located in the caudomedial part of the red nucleus. A study of vGluT2 expression showed that the number and location of glutamatergic neurons matched with those of the rubrospinal neurons. In the anterograde tracing experiments, rubrospinal fibers travelled in the dorsal portion of the lateral funiculus, between the lateral spinal nucleus and the calretinin-positive fibers of the lateral funiculus. Rubrospinal fibers terminated in contralateral laminae 5, 6, and the dorsal part of lamina 7 at all spinal cord levels. A few fibers could be seen next to the neurons in the dorsolateral part of lamina 9 at levels of C8–T1 (hand motor neurons) and L5–L6 (foot motor neurons), which is consistent with a view that rubrospinal fibers may play a role in distal limb movement in rodents.     

Immunocytochemical identification of long ascending peptidergic neurons contributing to the spinoreticular tract in the rat

In the present study, we examined the peptidergic content of lumbar spinoreticular tract neurons in the colchicine-treated rat. This was accomplished by combining the retrograde transport of the fluorescent dye True Blue with the immunocytochemical labeling of neurons containing cholecystokinin-8, dynorphin A1-8, somatostatin, substance P or vasoactive intestinal polypeptide. After True Blue injections into the caudal bulbar reticular formation, separate populations of retrogradely labeled cells were identified as containing cholecystokinin-like, dynorphin-like, substance P-like or vasoactive intestinal polypeptide-like immunoreactivity. Retrogradely labeled somatostatin-like neurons were not identified in any of the animals examined. Each population of double-labeled cells showed a different distribution in the lumbar spinal cord. The highest yield of double-labeling occurred for cholecystokinin, with 16% of all intrinsic cholecystokinin-like neurons containing True Blue. These double labeled neurons were found predominantly at the border between lamina VII and the central canal region. About 11% of intrinsic vasoactive intestinal polypeptide-like neurons in the lumbar spinal cord were retrogradely labeled from the bulbar reticular formation. These neurons were found mostly in the lateral spinal nucleus, with only a few double-labeled cells located deep in the gray matter. Dynorphin-like double-labeled neurons were localized predominantly near the central canal; a smaller population was also seen in the lateral spinal nucleus. It was found that double-labeled dynorphin-like neurons made up 8% of all intrinsic dynorphin-like neurons. Retrogradely-labeled substance P-like neurons were rare; the few double-labeled neurons were found in the lateral spinal nucleus and lateral lamina V. These findings suggest a significant role for spinal cord peptides in long ascending systems beyond their involvement in local circuit physiology.     

Inputs from regularly and irregularly discharging vestibular nerve afferents to secondary neurons in squirrel monkey vestibular nuclei. III. Correlation with vestibulospinal and vestibuloocular output pathways.

1. A previous study measured the relative contributions made by regularly and irregularly discharging afferents to the monosynaptic vestibular nerve (Vi) input of individual secondary neurons located in and around the superior vestibular nucleus of barbiturate-anesthetized squirrel monkeys. Here, the analysis is extended to more caudal regions of the vestibular nuclei, which are a major source of both vestibuloocular and vestibulospinal pathways. As in the previous study, antidromic stimulation techniques are used to classify secondary neurons as oculomotor or spinal projecting. In addition, spinal-projecting neurons are distinguished by their descending pathways, their termination levels in the spinal cord, and their collateral projections to the IIIrd nucleus. 2. Monosynaptic excitatory postsynaptic potentials (EPSPs) were recorded intracellularly from secondary neurons as shocks of increasing strength were applied to Vi. Shocks were normalized in terms of the threshold (T) required to evoke field potentials in the vestibular nuclei. As shown previously, the relative contribution of irregular afferents to the total monosynaptic Vi input of each secondary neuron can be expressed as a %I index, the ratio (x100) of the relative sizes of the EPSPs evoked by shocks of 4 x T and 16 x T. 3. Antidromic stimulation was used to type secondary neurons as 1) medial vestibulospinal tract (MVST) cells projecting to spinal segments C1 or C6; 2) lateral vestibulospinal tract (LVST) cells projecting to C1, C6; or L1; 3) vestibulooculo-collic (VOC) cells projecting both to the IIIrd nucleus and by way of the MVST to C1 or C6; and 4) vestibuloocular (VOR) neurons projecting to the IIIrd nucleus but not to the spinal cord. Most of the neurons were located in the lateral vestibular nucleus (LV), including its dorsal (dLV) and ventral (vLV) divisions, and adjacent parts of the medial (MV) and descending nuclei (DV). Cells receiving quite different proportions of their direct inputs from regular and irregular afferents were intermingled in all regions explored. 4. LVST neurons are restricted to LV and DV and show a somatotopic organization. Those destined for the cervical and thoracic cord come from vLV, from a transition zone between vLV and DV, and to a lesser extent from dLV. Lumbar-projecting neurons are located more dorsally in dLV and more caudally in DV. MVST neurons reside in MV and in the vLV-DV transition zone.(ABSTRACT TRUNCATED AT 400 WORDS)     

Branching cortical neurons in cat which project to the colliculi and to the pons: a retrograde fluorescent double-labeling study

Summary The fluorescent double-labeling technique has been used to determine whether the corticopontine and the corticotectal fibers in the cat are derived from two different sets of neurons or whether they are derived from branching neurons which distribute collaterals to the pontine grey and the colliculi. After unilateral DY.2HCl injections in the pontine grey and FB injections in the ipsilateral colliculi, large numbers of FB-DY.2HCl double-labeled neurons were present in the cortex of the ipsilateral hemisphere. However, the labeled neurons in its rostral part may have represented pyramidal tract neurons which were labeled retrogradely because their fibers descended through the DY.2HCl injection area. Therefore, also DY.2HCl injections were made in the pyramid (i.e. caudal to the pons) and the cortical pyramidal tract area, containing the retrograde DY.2HCl-labeled neurons, was delineated. In the rest of the experiments only the DY.2HCl-labeled neurons in the caudal two thirds of the hemisphere (outside the pyramidal tract area) were taken into account because only these neurons could, with confidence, be regarded as corticopontine neurons. In some anterograde HRP transport experiments the trajectories of the corticotectal and the corticopontine fibers were visualized. On the basis of the findings the DY.2HCl injections in the pontine grey were placed such that they could not involve any of the corticotectal fibers passing from the cerebral peduncle to the colliculi. Thus artifactual doublelabeling of cortical neurons was avoided. However, also under these circumstances many double-labeled neurons were present in the caudal two thirds of the hemisphere. This led to the conclusion that in the cat a large proportion of the corticopontine neurons in the caudal two thirds of the hemisphere represent branching neurons which also distribute collaterals to the colliculi. The parietal (anterior part of the lateral gyrus, middle and posterior suprasylvian gyri) and the cingulate areas together contained three quarters of all labeled corticopontine neurons outside the pyramidal tract area. In the parietal areas roughly 25% of them were double-labeled and in the cingulate area 14%. However, in the visual areas 18 and 19 a much larger percentage (30–60%) was doublelabeled. In a recent study from our laboratory it was found that in the cat the pyramidal tract fibers distribute an abundance of collaterals to the pontine grey. Therefore, a large proportion of all corticopontine connections in this species appear to be established by branching neurons which also distribute fibers to other cell groups in the brain stem and the spinal cord.Abbreviations A.E. anterior ectosylvian sulcus - a.e.s. anterior ectosylvian sulcus - BC brachium conjunctivum - BCI brachium colliculus inferior - BP brachium pontis - cor. sulc. coronal sulcus - CP cerebral peduncle - CR. cruciate sulcus - CUN cuneiform nucleus - DBC decussation brachium conjunctivum - DLP dorsolateral pontine nucleus - IC inferior colliculus - inf. coll. inferior colliculus - INS. insula cortex - IO inferior olive - IP interpeduncular nucleus - LAT. lateral sulcus - l.s. lateral sulcus - MG medial geniculate body - LL lateral lemniscus - ML medial lemniscus - MLF medial longitudinal fascicle - NdG dorsal nucleus of Gudden - NLL nucleus lateral lemniscus - NRTP reticular tegmental pontine nucleus - ORB. orbital sulcus - P pyramid - PAG periaqueductal grey - P.E. posterior ectosylvian sulcus - RF reticular formation - PG pontine grey - RB restiform body - RN red nucleus - S. sylvian sulcus - SC superior colliculus - SN substantia nigra - SO superior olive - SPV spinal trigeminal complex - S.S. suprasylvian sulcus - s.syl.s. suprasylvian sulcus - S.SPL. suprasplenial sulcus - SPL. splenial sulcus - spl.s. splenial sulcus - sup. coll. superior colliculus - syl.s. sylvian sulcus - TB trapezoid body - VC vestibular complex - Vm trigeminal motor nucleus - Vs trigeminal principle nucleus - III oculomotor nucleus - IV trochlear nucleus - VI abducens nucleus - VII facial nerve - VIII vestibulo-trochlear nerve Supported in part by grant 13-46-91 of FUNGO/ZWO (Dutch Organization for Fundamental Research in Medicine)     

Origin and trajectory of the cerebello-olivary projection: an experimental study with radioactive and fluorescent tracers in the cat

It was demonstrated with autoradiographic methods that a tract of thin fibers, which is for the most part distinct from the brachium conjunctivum and its crossed descending limb, can be followed from the cerebellar nuclei to the inferior olive. Neurons from all regions of the interposed and dentate nuclei contribute to this tract. With two fluorescent tracers, Fast Blue and Diamidino Yellow Dihydrochloride, the perikarya of neurons in the cerebellar nuclei that project to the inferior olive or thalamus were identified and the possibility of collateral projections from single neurons to both regions was investigated. Numerous retrogradely labeled neurons were seen in the contralateral interposed and dentate nuclei but no double-labeled cells were ever encountered. The mean diameters of the cells projecting to the inferior olive were between 15 and 20 microns while the mean diameters for those projecting to the nucleus ventrolateralis of thalamus were between 25 and 35 microns. Differences in the morphology of the two cell populations were noted. It was also found that the fastigio-olivary projection is small, terminating mainly contralaterally, in the caudal medial accessory olive and subnucleus beta. It is concluded that cerebello-olivary fibers are not collaterals of the cerebellothalamic projection and that there are two different populations of neurons in the cerebellar nuclei that give rise to these distinct efferent projections.     

Axonal projections from Bötzinger expiratory neurons to contralateral ventral and dorsal respiratory groups in the cat

Summary We studied projection patterns of the augmenting expiratory neurons of the Bötzinger complex (BÖT) in the contralateral brainstem. Three experimental approaches were used: 1) electrophysiological analysis using antidromic microstimulation, and morphological analyses using 2) intraaxonal injection of HRP, and 3) application of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). Taken together, the three methods revealed morphological details of the axonal arborizations of the expiratory neurons in the BÖT and the ventral respiratory group (VRG). The majority of augmenting expiratory neurons of the BÖT had axonal collaterals in the contralateral brainstem. The stem axons to the contralateral side crossed the midline almost at the level of the cell somata. They descended dorsomedial to the ventral spinocerebellar tract and gave off collateral branches directed dorsomedially. Terminal boutons were distributed abundantly in the caudal part of the BÖT and in the more caudally situated VRG. Axon collaterals sometimes ran to the dorsal respiratory group (DRG) and distributed terminal boutons there. Together with the fact of extensive ipsilateral arborizations shown previously, the present results indicate that the augmenting expiratory neurons of the BÖT have wide bilateral influence on the BÖT, VRG, DRG, and spinal cord.Abbreviations VII facial nucleus - XII hypoglossal nucleus - AMB nucleus ambiguus - AP area postrema - CX external cuneate nucleus - D descending vestibular nucleus - DX dorsal-motor nucleus of the vagus - M medial vestibular nucleus - NTS nucleus of the solitary tract - R nucleus of Roller - S solitary tract - RFN retrofacial nucleus This paper is dedicated to Professor Hajime Mannen on the occasion of his 65th birthdaySupported by grants-in-aid for Scientific Research nos. 60304044, 62570068, 62770043, and 63570027 from the Japan Ministry of Education, Science and Culture