Branching neurons in the cervical spinal cord: a retrograde fluorescent double-labeling study in the rat

Summary Branching neurons giving rise to ascending and descending collaterals were studied in the cervical spinal cord of the rat. After unilateral injection of two retrograde fluorescent tracers, i.e. DY.2HCl at T2 or more caudal levels and TB at C1 or more rostral levels, many DY-TB double-labeled neurons were found in C3 to C8. These neurons were located bilaterally throughout the spinal grey matter, as well as in the lateral spinal nucleus (LSN). However, no double-labeled neurons could be detected in the laminae I and II on either side. The double-labeled neurons must represent branching neurons giving rise to a collateral ascending to the rostral injection-site or above, and another collateral descending to the caudal injection-site or below. The descending collaterals were found to extend to various spinal levels, including the lumbosacral cord. However, most of them terminated at shorter distances from their parent cell bodies; thus 20% of the C3–C8 neurons projecting to C1 or above had a descending collateral reaching T2, 8% had a collateral reaching T9, and 3% a collateral reaching L2/L3. The ascending collaterals of the majority of the branching neurons passed into the most caudal part of the medulla oblongata, and about half of these collaterals reached the level of the rostral part of the inferior olive. In regard to the neurons located in the segments C5–C8, about 13% of those projecting to T2 or below distribute an ascending collateral restricted to C2–C4, while 29% of those had an ascending collateral to C1 or above.     

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.     

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...     

An electrophysiological investigation of propriospinal inspiratory neurons in the upper cervical cord of the cat

Summary This study was performed in order to describe the location, axonal projection and possible synaptic action of the inspiratory neurons recently described in the upper cervical cord. In 26 cats anaesthetized with Nembutal, extracellular recordings were made from 224 cervical inspiratory units which were found near the lateral border of lamina VII and formed a column extending from the caudal end of the nucleus retroambigualis at the C₁ segment to the rostral half of the C₃ segment. Most of the units (approximately 85%) could be excited antidromically from the thoracic cord. Antidromic mapping showed collateral branches to the C₅ segment in the vicinity of the phrenic nucleus, occasionally crossing the midline. No synaptic connections with phrenic motoneurones could be revealed either by cross-correlation of the activity of the cervical units with the discharge of C₅ phrenic root, or by spike-triggered averaging (STA) of the post-synaptic noise recorded intracellularly from phrenic motoneurons. Extensive branching was found in the examined T₃–T₅ segments with arborizations near the ipsilateral intercostal motor nuclei and often extending across the midline. Cross-correlation experiments did not show clear monosynaptic connections to the inspiratory intercostal motoneurons. Intracellular recording from intercostal motoneurons and STA resulted in a few (2 out of 37) small, probably disynaptic, e.p.s.p.s. It is concluded that the upper cervical neurons are involved in the control of phrenic and intercostal motoneurons, probably through a disynaptic pathway involving segmental interneurons.     

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)     

Pyramidal excitation in long propriospinal neurones in the cervical segments of the cat

Summary 1. The effect of stimulating the contralateral pyramid has been investigated with intracellular recording from 128 long propriospinal neurones (long PNs) in the C3-Th1 segments of the cat. Long PNs were identified by the antidromic activation from the Th13 segment. They were located in laminae VII–VIII of Rexed. Single pyramidal stimulation evoked monosynaptic EPSPs in 15/40 of the long PNs in cats with intact pyramid. In 15 other long PNs, a train of three to four pyramidal stimuli evoked EPSPs with latencies indicating a minimal disynaptic linkage. The remaining 25% of the long PNs lacked mono- or disynaptic pyramidal EPSPs. In a few cases longer latency excitation was observed. 2. The location of the intercalated neurones which mediate the disynaptic pyramidal EPSPs was investigated by making four different lesions of the corticofugal fibres: 1) at the border of the C5 and C6 segments, 2) at the border of the C2 and C3 segments, 3) at the caudal part of the pyramid; three mm rostral to the decussation and 4) at the level of the trapezoid body. Stimulation of the corticofugal fibres was made either rostral to lesion 3 (rPyr) in order to activate neurones in a cortico-bulbospinal pathway or caudal to lesion 3 (cPyr) to activate neurones in a corticospinal pathway. In the former case, in one experiment, stimulation was made in the pyramid between lesions 3 and 4 (double pyramidal lesion). In case of cPyr stimulation, lesions 1 and 2 were added sequentially in order to investigate if the corticospinal excitation was mediated via C3–C4 PNs. All lesions were made mechanically, except lesion 2 which in some of the experiments was performed by reversible cooling. 3. Stimulation in the pyramid rostral to lesion 3 and in between lesions 3 and 4 evoked disynaptic EPSPs in the long PNs, which shows that they were mediated via reticulospinal neurones. Stimulation in cPyr after lesion 3 elicited disynaptic EPSPs, which remained after lesion 1 but were abolished after adding lesion 2. It is concluded that the disynaptic cPyr EPSPs were mediated via intercalated neurones in the C3–C4 segments. 4. When the disynaptic cPyr EPSP was conditioned with a single volley in nucleus ruber and/or in tectum, it was markedly facilitated, especially when the conditioned volley was applied simultaneously with the effective cPyr volley. The results show that the intercalated neurones in the C3–C4 segments receive monosynaptic convergence from cortico-, rubro- and tectospinal] fibres. Stimulation in the lateral reticular nucleus (LRN) evoked monosynaptic EPSPs. These EPSPs had similar latencies and shapes as those previously recorded in forelimb motoneurones and which have been shown to be due to activation of ascending branches of the C3–C4 PNs. This finding in addition to the striking similarity of the descending input pattern of long PNs as compared to the forelimb motoneurones strongly suggest that short C3–C4 PNs project both to long PNs as well as to forelimb motoneurones. 5. Spatial facilitation of disynaptic EPSPs in long PNs was also observed between rPyr volleys and tectal volleys. The results suggest that common reticulospinal neurones which project to the long PNs receive monosynaptic convergence from corticofugal and tectofugal fibres but in some of the reticulospinal neurones the main input is cortical and in others tectal. Monosynaptic EPSPs were evoked from the medial part of the reticular formation, from 2 mm caudal to 6 mm rostral of the obex level. These EPSPs were presumably due to direct activation of reticulospinal neurones. 6. Convergence of disynaptic excitation mediated by cortico-propriospinal and cortico-reticulospinal routes was observed in about 12% of the long PNs. Convergence of monosynaptic corticospinal and disynaptic corticoreticulospinal and/or cortico-propriospinal input was observed in about 15% of the long PNs. 7. The role of the monosynaptic pyramidal input and disynaptic corticoreticulospinal and cortico-propriospinal (mediated by short C3–C4 PNs) inputs to long PNs is discussed in relation to postural control during movements of head and forelimb.     

Lumbar dorsal root projections to spinocerebellar cell groups in the rat spinal cord: a double labeling study

Summary The aim of this study has been to investigate projections to spinocerebellar cell groups from lumbar dorsal root ganglia (DRGs) in the rat. The binding subunit of cholera toxin conjugated to horseradish peroxidase (B-HRP) was used to label primary afferent fibers. Spinocerebellar neurons were labeled retrogradely by Fluoro-Gold (FG). To determine the orientation of dendrites, retrogradely labeled spinocerebellar neurons were studied, following injections of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) into cerebellum. FG or WGA-HRP labeled neurons were found mainly in laminae V and VII, in the lateral group of lamina IX, in Clarke's column (CC) and in the dorsal funiculus. B-HRP labeled primary afferent fibers overlapping with FG labeled cells were observed at all these locations after injections of B-HRP into different DRGs. The overlap in lamina V was found mainly medially and dorsolaterally. CC was found to receive dense projections from DRGs L1–6. In the lumbar part of CC, labeling from DRGs L4–5 overlapped and was distributed over the entire mediolateral extent of the CC, whereas labeling from DRGs L1–3 was somatotopically organized and projected to successively more dorsomedial areas. The central area of lamina VII showed moderate labeling from DRGs L3–5. The lateral group of lamina IX received only smaller amounts of labeled fibers from DRGs L3–5.     

Identification of phrenic afferents to the external cuneate nucleus: a fluorescent double-labeling study in the cat

In the cat, C5-C6 dorsal root ganglion cells related to phrenic afferents projecting directly to the ipsilateral external cuneate nucleus (ECN) were submitted to a double-labeling procedure using anterogradely transported Fast Blue and retrogradely transported Nuclear yellow. These afferents, certainly related to muscle spindles and/or Golgi tendon organs, are very few and terminate preferentially in the intermediate and rostral parts of the ECN. Our results confirm previous electrophysiological and histological studies on the participation of phrenic afferents to the spino-cuneo-cerebellar pathway ascending through the dorsal columns.     

Cervical cord neurons labeled by horseradish peroxidase application to the sciatic nerve in the rat

After horseradish peroxidase (HRP) application to the proximal cut end of the sciatic nerve in rats aged 3-10 days, HRP-labeled neuronal cell bodies were found ipsilaterally in the ventrolateral region of the ventral horn in the cervical enlargements of the spinal cord. Such labeled neurons were occasionally seen in rats aged 15 days, but not seen at all in rats aged 60-90 days. The labeling was presumably the result of a retrograde transneuronal axonal transport of HRP applied to the sciatic nerve.     

Neurogenesis of cuneothalamic neurons and NO-containing neurons in the cuneate nucleus of the rat

The genesis of the cuneothalamic neurons (CTNs) in the rat cuneate nucleus was determined by a double-labeling method using 5'-bromodeoxyuridine (BrdU), the thymidine analogue, and Fluoro-Gold (FG), a retrograde fluorescent tracer. BrdU-positive cells were observed in the cuneate nucleus in all rats receiving BrdU injection at embryonic days (E) E13--E16; none was detected in rats given BrdU injection at E12. At E13 and E14, BrdU-positive cells were randomly distributed. However, at E15, the number of BrdU-positive cells was clearly reduced and the majority of them was located at the dorsolateral or peripheral region of the nucleus. FG/BrdU double-labeling study showed the existence of BrdU-labeled CTNs when the mother rat received BrdU injection at E13 and E14, being more numerous at E13 in which the neurons were scattered throughout the nucleus. At E14, however, the majority of the BrdU-labeled CTNs were located superficially in the nucleus. Double-labeled cells were undetected in rats that had been exposed to BrdU at E15 and E16. Quantitative data showed that the majority (ca 70-80%) of the CTNs were generated at E13, and were markedly decreased at E14 (ca 4-6%). Using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry coupled with BrdU immunohistochemistry, we have shown the NADPH-d/BrdU double-labeled neurons in the nucleus between E13 and E15, with the majority of them occurring at E14, but absent at E16. The present results suggest that the CTNs are generated prior to the NO-containing neurons in the cuneate nucleus.     

Nerve cell bodies in the dorsal funiculus of the rat spinal cord

Summary Nerve cell bodies located within the white matter of the dorsal funiculus (DF neurons) have been previously observed but not described in detail. The present study examines the morphology, ontogeny, and projection of DF neurons utilizing Fluoro-Gold as a retrograde tracer, alone, and in combination with tritiated thymidine autoradiography in the spinal cord of the rat. DF neurons were consistently labelled in spinal segments T13 through L2 following injections of Fluoro-Gold into the cerebellum. The cell bodies of DF neurons were small to medium in size, fusiform to multipolar in shape, and were located on the side ipsilateral to the injection site. Cell counts revealed approximately five labelled cells per millimeter along the longitudinal axis. An examination of neurogenesis using tritiated thymidine combined with Fluoro-Gold showed that DF neurons have relatively late birthdates as do other spinocerebellar neurons of the dorsal horn. Retrograde axon tracing studies in the spinal cord using Fluoro-Gold showed that DF neurons project rostrally via the ipsilateral lateral funiculus. The significance of the presence of nerve cells in the dorsal funiculus is unclear, but judging from their location, ontogeny, and projection, DF neurons are probably derived from the same pool of neurons as those in the Nucleus dorsalis.     

Projection patterns of lamina VIII commissural neurons in the lumbar spinal cord of the adult cat: an anterograde neural tracing study

This study was designed to characterize the morphology of commissural axons, with the goal of revealing some of the organizing principles of their projections in the lumbosacral cord. Axons were labeled anterogradely with biotinylated-dextran amine which was injected in the left lamina VIII and the adjoining parts of lamina VII in the lumbar segments L5-L6 in seven cats. After 3-4 weeks, commissural axons were well labeled throughout lumbosacral segments L1-S2. After crossing the midline at the injection level, labeled axons traveled rostrally and/or caudally in the contralateral ventral and lateral funiculi giving off multiple axon collaterals. The trajectories of 34 single axons were traced in their entirety from their points of origin to their distal ends. Most of these axons were thin (proximal diameter <3.5 microm) and short (<30 mm), and gave off 6 to 32 axon collaterals at short intercollateral distances (mean <2 mm) in the lumbosacral enlargement. Some thicker axons (diameter >3.5 microm) ascended as far as the thoracic level; these supplied only four to six collaterals at long intercollateral intervals ( approximately 6.5 mm). All of the axons except one projected unilaterally. The axons as a whole terminated throughout the contralateral ventral horn. However, axons that traveled in different parts of the white matter had different characteristic terminal arborizations. The collaterals of axons that traveled in the ventral funiculus terminated preferentially in laminae VII-VIII, while those in the lateral funiculus terminated in lamina IX. Although the collateral branching patterns differed from one axon to another, collaterals arising from a particular axon usually exhibited similar patterns at different rostrocaudal levels. These uniform collateral termination patterns indicate that the morphology of each neuron might be specifically related to its function. This may allow future studies to identify different functional types of commissural neurons on the basis of much less extensive reconstructions.     

Cerebellar and spinal projections of the coeruleus complex in the duck: A fluorescent retrograde double-labeling study

The double fluorescent retrograde tracing technique was used to identify, within the coeruleus complex (Co complex) of the duck, the nerve cells projecting to the cerebellar cortex and to the spinal cord. This technique was also used to investigate the possibility that the cerebellar and spinal projections of the Co complex are collaterals of the same axons. In the same animal, nuclear Diamidino yellow dihydrochloride (DY) fluorescent tracer was placed into the cerebellar cortex of folia V–VII, and cytoplasmic fluorescent Fast blue (FB) dye was injected into C₃–C₄ spinal cord segments. FB labeled multipolar somata and DY fluorescent nuclei were intermingled within the dorsal caudal region of the locus coeruleus (LCo) and within the dorsal division of the nucleus subcoeruleus (dSCo). Moreover, in the LCo, a low proportion of double-labeled neurons (about 3–4% of labelings) was evidenced among single-labeled neurons. In the ventral division of the nucleus subcoeruleus (vSCo), occasional DY labeled nuclei were found, whereas FB-labeled cells were frequently present. The present findings reveal the location of the coeruleocerebellar and coeruleospinal projecting neurons within the Co complex of the duck. They are intermingled in the caudal portion of the LCo and along the rostrocaudal extent of the subjacent dSco. The LCo and the dSCo are the major source of the projections to the folia V–VII, whereas the vSCo contributes very slightly to the innervation of the cerebellar injected areas. Moreover, the double-labeling study demonstrates that in the duck a low percentage of neurons within the ventrolateral portion of the caudal region of the LCo projects both to the cerebellar cortex of folia V–VII and to C₃–C₄ spinal cord segments via collaterals. Therefore, these neurons simultaneously influence the cerebellar cortex and spinal cord. The possibility that the projections studied are noradrenergic and that they play a role in feeding is discussed. Anat. Rec. 251:392–397, 1998. © 1998 Wiley-Liss, Inc.     

The C3-C4 propriospinal system in the cat and monkey: a spinal pre-motoneuronal centre for voluntary motor control

This review deals with a spinal interneuronal system, denoted the C3-C4 propriospinal system, which is unique in the sense that it so far represents the only spinal interneuronal system for which it has been possible to demonstrate a command mediating role for voluntary movements. The C3-C4 propriospinal neurones govern target reaching and can update the descending cortical command when a fast correction is required of the movement trajectory and also integrate signals generated from the forelimb to control deceleration and termination of reaching.     

Electrophysiological properties of sympathetic preganglionic neurons in the cat spinal cord in vitro

Intracellular recordings were obtained from sympathetic preganglionic neurons of the intermedio-lateral nucleus of the adult cat in slices of upper thoracic spinal cord maintained in vitro. The neurons were identified by their antidromic responses to stimulation of various ipsilateral sites. Sites from which antidromic responses could be evoked were the white ramus, the ventral root, the ventral root exit zone, the white matter between the latter and the outer edge of the tip of the ventral horn, the lateral edge of the ventral horn. Resting membrane potential was –61.3±1.6 mV (mean±SEM), input resistance 67.5±3.7 M, time constant 11.5±1.2 ms. The amplitude of the action potential generated by antidromic or direct stimulation was 77.4±2.3 mV. Threshold for direct spikes was 18.2±1.8 mV. The action potential had an average duration of 3.03±0.16 ms. It showed a prominent hump on the falling phase. The action potential had a tetrodotoxin (TTX)-sensitive and a TTX-resistant component. The latter was abolished by cobalt.Tetraethylammonium, cesium and barium prolonged the action potential duration which acquired a plateau-shape. A prolonged after-hyperpolarization (AHP) followed the sympathetic preganglionic neuron spike. Following a single spike, AHP duration and peak amplitude were 2.8±0.3 s and 16.6±0.7 mV, respectively. The AHP was abolished by cesium or barium, but enhanced by tetraethylammonium. An AHP followed the TTX-resistant spike. EPSPs and IPSPs could be generated by focal stimulation. The EPSP triggered spikes when threshold (15.0±2.0 mV) was reached. The slice of the thoracic spinal cord provides a useful experimental preparation for analysis of cellular properties and synaptic mechanisms of the sympathetic preganglionic neuron.     

Collateral projections of neurons from the lower part of the spinal cord to anterior and posterior cerebellar termination areas

Summary The collateral projections of spinocerebellar neurons located in the L 2 to Ca 1 spinal segments in the cat were investigated by retrograde fluorescent double labeling technique. Rhodamine labeled latex microspheres (Rm) and Fast Blue (FB) were used for injections into the cerebellum in 8 cats. Two additional cats, with injections of Fluoro-Gold (FG) combined with Rm were excluded because lipofuchsin autofluorescence obscured the labeling. After injections with one tracer unilaterally in the paramedian lobule and another tracer bilaterally in the anterior lobe, double labeled neurons were found on the side of the paramedian lobule injection in the column of Clarke at L 2–L 4, laminae IV–VI at L 2–L 5 and the dorsolateral nucleus at L 2–L 6. After bilateral injections of one tracer in lobule VIII B and another in the anterior lobe, double labeled neurons were found bilaterally in the column of Clarke at L 2–L 4, laminae IV–VI at L 2–L 5, the medial part of lamina VII at L 6–L 7 and in certain cell groups at sacro-coccygeal levels. Neurons in the lateral part of lamina VII at L 3–L 5 and the ventrolateral nucleus of L 4–L 5 were labeled exclusively from injections in the anterior lobe. The findings indicate that spinocerebellar neurons at lumbar and more caudal levels of the cat spinal cord have different projection patterns in the cerebellum. A certain number of neurons which project to the anterior lobe have divergent axon collaterals supplying also the posterior vermis and/or the paramedian lobule. Other neurons project to the anterior or to the posterior lobe only.Abbreviations CC column of Clarke - DL dorsolateral nucleus - FB Fast Blue - lam. lamina - lat. lateral - med. medial - N. f. fastigial nucleus - p. copul. pars copularis (paramedian lobule) - pfl.d. dorsal paraflocculus - pmd paramedian lobule - p.post pars posterior (paramedian lobule) - pyr. pyramis - Rm Rhodamine labeled latex microspheres - VL ventrolateral nucleus - I–IX (on cerebellar diagrams) cerebellar lobules, according to Larsell (1953) - A, B (following Roman numeral VIII) sublobules VIII A and VIII B - IV–IX (on spinal cord diagrams) laminae according to Rexed (1954) On leave from Capital Institute of Medicine, Beijing, The People's Republic of China     

Projections from the interstitial nucleus of cajal to the inferior olive and to the spinal cord in cat: A retrograde fluorescent double-labeling study

Injections of the fluorescent dyes Fast Blue (FB) and Nuclear Yellow (NY) were placed in the inferior olive and cervical spinal cord respectively in three experimental animals. Results showed that the interstitial nucleus of Cajal (INC) projected mainly to the spinal cord, with only a modest termination within the inferior olive. The nucleus of Darkschewitsch and the rostromedial portion of the red nucleus projected heavily to the inferior olive but not to the spinal cord. Very few INC neurons were double-labeled with FB and NY, suggesting that only a small minority of spinal projecting neurons in the INC give rise to collaterals which terminate within the inferior olive.     

Electrophysiological characteristics of vasomotor preganglionic neurons and related neurons in the thoracic spinal cord of the rat: an intracellular study in vivo

Sympathetic preganglionic neurons (SPN) represent the final central neurons in the sympathetic pathways which regulate vasomotor tone; they therefore play a pivotal role in the re-distribution of cardiac output to different vascular beds in response to environmental challenges. While the consensus view is that activity in these neurons is due mainly to supraspinal inputs, the possibility that some activity may be generated intrinsically and modified by synaptic inputs cannot be excluded. Therefore, in order to distinguish between these two possibilities, the electrophysiological properties of cardiovascular-like SPN in the upper thoracic spinal cord of the anesthetized rat were examined and their response to activation of vasodepressor inputs was investigated. Intracellular recordings were made from 22 antidromically identified SPN of which 17 displayed irregular, but maintained, spontaneous activity; no evidence of bursting behavior or pacemaker-like activity was observed. Stimulation of the aortic depressor nerve or a vasodepressor site within the nucleus tractus solitarius (NTS) resulted in a membrane hyperpolarization, decrease in cell input resistance and long-lasting cessation of neuronal firing in SPN including a sub-population which had cardiac-modulated patterns of activity patterns. Recordings were also undertaken from 80 non-antidromically-activated neurons located in the vicinity of SPN; 23% of which fired in phase with the cardiac cycle, with this peak of activity occurring before similar increases in cardiac-modulated SPN. Stimulation of vasodepressor regions of the NTS evoked a membrane hyperpolarization and decrease in cell input resistance in cardiac-modulated but not non-modulated interneurons. These studies show that activity patterns in SPN in vivo are determined principally by synaptic inputs. They also demonstrate that spinal interneurons which exhibit cardiac-modulated patterns of activity are postsynaptically inhibited following activation of baroreceptor pathways. However, the question as to whether these inhibitory pathways and/or disfacilitation of tonic excitatory drive underlies the baroreceptor-mediated inhibition of SPN remains to be determined.     

Intersegmental synchronization of spontaneous activity of dorsal horn neurons in the cat spinal cord

Extracellular recordings of neuronal activity made in the lumbosacral spinal segments of the anesthetized cat have disclosed the existence of a set of neurons in Rexed's laminae III–VI that discharged in a highly synchronized manner during the occurrence of spontaneous negative cord dorsum potentials (nCDPs) and responded to stimulation of low-threshold cutaneous fibers (<1.5×T) with mono- and polysynaptic latencies. The cross-correlation between the spontaneous discharges of pairs of synchronic neurons was highest when they were close to each other, and decreased with increasing longitudinal separation. Simultaneous recordings of nCDPs from several segments in preparations with the peripheral nerves intact have disclosed the existence of synchronized spontaneous nCDPs in segments S1–L4. These potentials lasted between 25 and 70 ms and were usually larger in segments L7–L5, where they attained amplitudes between 50 and 150 μV. The transection of the intact ipsilateral hindlimb cutaneous and muscle nerves, or the section of the dorsal columns between the L5 and L6, or between the L6 and L7 segments in preparations with already transected nerves, had very small effects on the intersegmental synchronization of the spontaneous nCDPs and on the power spectra of the cord dorsum potentials recorded in the lumbosacral enlargement. In contrast, sectioning the ipsilateral dorsal horn and the dorsolateral funiculus at these segmental levels strongly decoupled the spontaneous nCDPs generated rostrally from those generated caudally to the lesion and reduced the magnitude of the power spectra throughout the whole frequency range. These results indicate that the lumbosacral intersegmental synchronization between the spontaneous nCDPs does not require sensory inputs and is most likely mediated by intra- and intersegmental connections. It is suggested that the occurrence of spontaneous synchronized nCDPs is due to the activation of tightly coupled arrays of neurons, each comprising one or several spinal segments. This system of neurons could be involved in the modulation of the information transmitted by cutaneous and muscle afferents to functionally related, but rostrocaudally distributed spinal interneurons and motoneurons, as well as in the selection of sensory inputs during the execution of voluntary movements or during locomotion. Electronic Publication