Ascending and descending projections to medullary reticular formation sites which activate deep lumbar hack muscles in the rat

Summary The purpose of this study was to determine ascending and descending afferents to a medullary reticular formation (MRF) site that, when electrically stimulated, evoked EMG activity in lumbar deep back muscles. In anesthetized female rats, the MRF was explored with electrical stimulation, using currents less than 50 A, while EMG activity was recorded from the ipsilateral lateral longissimus (LL) and medial longissimus (ML). MRF sites that evoked muscle activity were located in the gigantocellular nucleus (Gi). At the effective stimulation site, the retrograde fluorescent tracer, Fluoro-Gold (FG), was deposited via a cannula attached to the stimulating electrode. In matched-pair control experiments, FG was deposited at MRF sites that were ineffective in producing EMG activity in LL and ML, for comparison of afferent projections to effective versus ineffective sites. Labeled cells rostral to FG deposition at effective MRF sites were located in the preoptic area, hypothalamus, limbic forebrain and midbrain, with particularly high numbers in the ipsilateral midbrain central gray, tegmentum, paraventricular nucleus and amygdala. At medullary levels, there was a heavy projection from the contralateral Gi. FG labeled cells were also located in the contralateral parvocellular reticular nucleus, and lateral, medial and spinal vestibular nuclei. Labeled cells with ascending projections were observed in greatest number in the rostral cervical spinal cord, with fewer cells at mid cervical levels and even fewer in the lumbar spinal cord. These labeled cells were located primarily in lamina V, VII, VIII and X. Locations of labeled cells following FG deposition at ineffective MRF sites were similar. However, there was a striking difference in the number of cells retrogradely labeled from the effective MRF sites compared to ineffective MRF sites. Significantly greater numbers of labeled cells were observed in the contralateral MRF, the midbrain, and the cervical spinal cord from the FG deposition at effective stimulation sites. These results suggest that one characteristic of MRF sites that activate epaxial muscles is a larger amount of afferent input, from the midbrain central gray and from contralateral Gi, compared to ineffective MRF sites. Ascending and descending inputs converge at the effective MRF sites, and the larger number of descending projections suggests a more powerful contribution of these afferents to deep lumbar back muscle activation.Abbreviations Amyg amygdala - Aq Aqueduct - C Cervical spinal cord - CC Central canal - ECu External cuneate - F Fornix - FG Fluoro-Gold - Gi Gigantocellular reticular nucleus - GiA Gigantocellular reticular nucleus, alpha - GiV Gigantocellular reticular nucleus, ventral - icp inferior cerebellar peduncle - IO Inferior olive - L Lumbar spinal cord - LL Lateral longissimus - LVN Lateral vestibular nucleus - MCG Midbrain central gray - ML Medial longissimus - ml medial lemniscus - MRF Medullary reticular formation - MVN Medial vestibular nucleus - OT Optic tract - PCRt Parvocellular reticular nucleus - Pn Pontine nuclei - PnO Pontine reticular nucleus, oral - PPT Pedunculopontine tegmental nucleus - PVN Paraventricular nucleus - py pyramidal tract - Sol nucleus of the solitary tract - Sp5 Spinal trigeminal nucleus - VMN Ventromedial nucleus - 3v third ventricle - 7 Facial nucleus - 12 hypoglossal nucleus     

Reticulospinal and reticuloreticular pathways for activating the lumbar back muscles in the rat

Erratum

Reticulospinal and reticuloreticular pathways for activating the lumbar back muscles in the rat     

Spinal projections to the lateral reticular nucleus in the rat

Summary The synaptic relationships and the distribution of the afferent terminals of the spinal pathway to the lateral reticular nucleus (LRN) of the rat were examined following induced degeneration. After high cervical hemisections, the spino-LRN projection was first examined with the Fink-Heimer silver impregnation method. Degeneration was confined primarily to the ipsilateral LRN and all three divisions of the nucleus were involved. Maximum degeneration was observed in the caudal regions of the parvocellular division. The magnocellular division, except for the extreme dorsomedial area, showed substantial degeneration as well. The subtrigeminal division throughout its entire length contained only sparse degeneration.Electron microscopic examination following spinal cord lesions revealed both round and pleomorphic-vesicle terminals in various stages of electron dense degeneration. The majority of the degenerating terminals were of the round-vesicle variety. Both types of terminals contacting somata were also observed to degenerate but their number was small in comparison to those on dendritic profiles. Terminals in synaptic contact with two dendritic profiles were also observed to degenerate. Some of the large terminals belonging to synaptic configurations (glomeruli) underwent degeneration and were therefore of spinal origin as well.     

An ultrastructural study of the lateral reticular nucleus in the rat

Summary A systematic study of the normal synaptic patterns within the lateral reticular nucleus (LRN) of the rat revealed various synaptic relationships. Two types of axon terminals were identified according to the morphology of the synaptic vesicles contained within them. Axon terminals with round vesicles established asymmetrical synaptic contacts with the somata and all areas of the dendritic trees including somatic and dendritic appendages. Pleomorphic-vesicle terminals established symmetrical synaptic contacts on somata and their appendages and on all sizes of dendrites and their appendages. Both round and pleomorphicvesicle terminals were infrequently seen to synapse upon the somata and proximal dendrites. The round-vesicle terminals outnumbered the pleomorphic-vesicle terminals on the dendritic trees. Terminals of the en passant type were also common throughout the LRN. Both round and pleomorphic-vesicle terminals were observed simultaneously contacting the soma and one or more dendritic profiles, or two different dendritic profiles. Synaptic configurations (glomeruli) were also observed in all three divisions of the nucleus. They consisted of a large, central, round-vesicle terminal contacting a number of small-calibre dendritic processes. This arrangement was surrounded by one or more sheets of glial lamellae. Puncta adherentia were observed on the apposed membranes of adjacent cells, adjacent dendrites and adjacent axon terminals.     

A Golgi study of the lateral reticular nucleus in the rat

Summary The organization of the lateral reticular nucleus (LRN) of the rat was investigated by using the Golgi technique. Golgi-Cox preparations revealed neurons with shapes similar to those observed in Nissl-stained preparations. Fusiform cells possess rectilinear dendrites with secondary dendrites which are longer than the parent stem. The remaining cell types have short dendrites which branch for three or four generations and follow a tortuous course. These two types of neurons are similar to the isodendritic and allodendritic neurons which have been reported in the reticular formation. The neurons throughout the LRN form cell clusters. In Golgi preparations five to ten cells are seen in each cluster but counterstaining reveals that the clusters are made up of many more cells than the Golgi preparations suggest. Many cells lie in close apposition and the dendrites of the cells in each cluster intertwine to form dendritic plexuses. Dendritic input from both neighbouring and distant cell clusters also contributes to the plexus formations within each cell cluster. Under high magnification, the dendrites show irregularities in their contours, including warty excrescenses, bumps and an array of spines, some of which are pedunculated. The appendages are confined primarily to distal portions of the dendrites, with few spines observed on the somata and proximal dendrites. Varicosed dendrites are also in common occurrence throughout the nucleus.     

Origin and fine structure of substance P-containing nerve terminals in the facial nucleus of the rat: an immunohistochemical study

Summary The distribution, origin and fine structure of substance P-like immunoreactive (SPI) nerve terminals in the facial nucleus of the rat were investigated by means of immunocytochemistry. SPI-terminals were concentrated in the intermediate and dorsal subnuclei of the facial nucleus. Hemi-transection of the brainstem just rostral to the facial nucleus or at the most caudal level of the medulla oblongata did not cause any change of SPI-terminals in the facial nucleus. Electrical destruction of the various parts of the medulla oblongata clearly demonstrated that SPI-terminals in the intermediate subnucleus were supplied contralaterally from the SPI-neurons in the dorsomedial part of the medullary reticular formation. Most of the SPI-terminals (85%) in the intermediate subnucleus of the facial nucleus were observed to make asymmetric synaptic contacts with large dendrites (mean diameter; 1.26 m). It was supposed that the contact sites are located on proximal parts of the dendrite. A few SPI-terminals (6%) formed axo-somatic contacts with large perikarya filled with numerous cytoplasmic organelles.Abbreviations used in Figures A n. ambiguus - AP area postrema - C n. cuneatus - Cod n. cochlearis dorsalis - Cov n. cochlearis ventralis - CU n. cuneiformis - FLM fasciculus longitudinalis medialis - G n. gracilis - MRF midbrain reticular formation - nts n. tractus solitarius - nVsp n. tractus spinalis nervi trigemini - nVII n. originis nervi facialis - nX n. originis dorsalis vagi - nXII n. originis nervi hypoglossi - OI n. olivaris inferior - rfl the ventro-lateral part of the caudal medullary reticular formation - rfm the dorso-medial part of the medullary reticular formation - RL n. reticularis lateralis - RM n. raphe magnus - rmg n. reticularis magnocellularis - RO n. raphe obscurus - sgc substantia grisea centralis - Vl n. vestibularis lateralis - Vm n. vestibularis medialis - Vsp n. vestibularis spinalis     

Arrangement of neurons in the medullary reticular formation and raphe nuclei projecting to thoracic, lumbar and sacral segments of the spinal cord in the cat

Summary The distribution of neurons in the medullary reticular formation and raphe nuclei projecting to thoracic, lumbar and sacral spinal segments was studied, using the technique of retrograde transport of horseradish peroxidase (HRP), alone or in combination with nuclear yellow (NY). Retrogradely labeled cells were observed in the lateral tegmental field (FTL), paramedian reticular nucleus, magnocellular reticular nucleus (Mc), in the gigantocellular nucleus (Gc), lateral reticular nucleus (LR), lateral paragigantocellular nucleus (PGL), rostral ventrolateral medullary reticular formation (RVR), as well as in the medullary raphe nuclei following the injection of the tracer substance(s) into various levels of the spinal cord. The FTL, the ventral portion of the paramedian reticular nucleus (PRv), Mc, LR, PGL and the raphe nuclei were found to project to thoracic, lumbar and sacral spinal segments. This projection was bilateral; the contralaterally projecting fibers crossed the midline at or near their termination site. The dorsal portion of the paramedian reticular nucleus (PRd), Gc and the RVR projected mainly to thoracic segments. This projection was unilateral. Experiments in which the HRP-injection was combined with lesion of the spinal cord showed that some descending raphe-spinal axons coursed presumably alongside the central canal. Experiments with two tracer substances suggested that some reticulo and raphe-spinal neurons had axon collaterals terminating both in thoracic and sacral spinal segments.Abbreviations CC Central Canal - FTL Lateral Tegmental Field - Gc Gigantocellular Nucleus - IO Inferior Olive - LR Lateral Reticular Nucleus - Mc Magnocellular Reticular Nucleus - Nc Cunetae Nucleus - Ng Gracile Nucleus - P Pyramidal Tract - PGL Lateral Paragigantocellular Nucleus - PRd Paramedian Reticular Nucleus,dorsal portion - PRv Paramedian Reticular Nucleus, ventral portion - RB Restiform Body - Ro Nucleus Raphe Obscurus - Rm Nucleus Raphe Magnus - Rpa Nucleus Raphe Pallidus - RVR Rostral Ventrolateral Medullary Reticular Formation - TSp5 Tractus Spinalis Nervi Trigemini - V4 Fourth Ventricle - 12N Hypoglossal Nerve - A B C D E and F correspond to levels Fr 16.0 Fr 14.7 Fr 12.7 Fr 11.6 Fr 10.0 and Fr 9.2 posterior to the frontal zero     

Ipsilateral and contralateral projections from upper cervical segments to the vestibular nuclei in the rat

The present study examined uncrossed and crossed projections from upper cervical segments to the vestibular nuclei, and the relationship between the afferents and vestibulospinal neurons in the rat. Afferent axons were labeled following unilateral injections of biotinylated dextran into the C2 and C3 segments, while vestibulospinal neurons were labeled following unilateral injections of cholera toxin subunit B into the same segments. The terminals of uncrossed afferents were distributed in the entire area of the rostrocaudal extent of the lateral vestibular nucleus (LV). In the magnocellular part (MVmc) of the medial vestibular nucleus (MV), they were seen near the parvocellular part (MVpc) of the MV at caudal levels. In the MVpc, terminals were seen laterally and ventromedially, close to the border of the MVmc. At caudal levels of the caudal part (MVc) of the MV, they were distributed within the groups of labeled neurons in the middle and lateral areas. In the descending vestibular nucleus (DV), terminals were abundant dorsally and laterally in the rostral two-thirds. The distribution of contralateral cervical afferents was similar to that of ipsilateral afferents. The terminals of ipsilateral and contralateral cervical afferents were seen in contact with vestibulospinal neurons in the DV. The present study demonstrates bilateral input from upper cervical segments to the LV, DV, and all subdivisions of the MV. The input to the LV would contribute to the tonic neck reflex or cervicovestibulospinal reflex.     

Cytoarchitecture and cytology of the lateral reticular nucleus in the rat

Summary The cytoarchitecture and cytology of the rat lateral reticular nucleus (LRN) was studied in serial sections of paraffin embedded tissue stained with cresyl violet. Cell outlines and nuclear outlines were drawn in the transverse plane and the nucleus was serially reconstructed. The LRN in the rat begins at a point just caudal to the caudal limit of the inferior olivary nucleus and extends to the mid-olivary level. The nucleus can be subdivided into a predominantly small-celled parvocellular division ventrally, a predominantly large-celled magnocellular division dorsomedially, and a subtrigeminal division dorsolaterally containing predominantly medium-sized cells. At rostral levels the nucleus comprises two parts, a medial principal portion and a lateral subtrigeminal division. Measurements of neuronal diameters yielded size distributions which confirmed the predominance of large cells in the magnocellular division, small cells in the parvocellular division and medium-sized cells in the subtrigeminal division. The neurons display multipolar, triangular, piriform and fusiform somata. All types show a range in size from small to large. The larger cells have abundant Nissl bodies which are coarse in nature and voluminous cytoplasm. The smaller cells have poorly developed Nissl bodies and scant amounts of cytoplasm.     

The inhibitory role of the visually responsive region of the thalamic reticular nucleus in the rat

Summary Two-shock inhibition, a feature of 98 of 100 P cells recorded in the dorsal lateral geniculate nucleus of the normal rat, was not observed in 91 of 140 geniculate cells after an electrolytic lesion had been made in the adjacent visually responsive thalamic reticular nucleus. Nine geniculate cells recorded both before and after a reticular lesion had their initial inhibition abolished or substantially reduced after the lesion. The reticular lesion eliminated the bursts of spikes which normally terminate periods of inhibition following electrical or photic stimulation but caused no other changes in receptive field organization of geniculate cells. We conclude that the visually responsive region of the thalamic reticular nucleus in the rat is responsible for the profound two-shock inhibition and for the post-inhibitory bursts which are normal properties of relay cells of the dorsal lateral geniculate nucleus.     

Neuropeptide FF in the lateral spinal and lateral cervical nuclei: Evidence of contacts on spinothalamic neurons

Neuropeptide FF (NPFF, F8Famide) is best known for its modulating effect on opioid analgesia and morphine tolerance. However, the exact mode of action of NPFF in sensory transmission is not known. We compared the distribution of NPFF-immunoreactive (ir) fibers and terminal-like thickenings with the retrograde, tracer-filled spinothalamic (ST) neurons in the lateral spinal nucleus (LSN) and lateral cervical nucleus (LCN) of rat, areas where NPFF-containing nerve terminals are abundant. We injected fluorescent latex microspheres into the ventroposterolateral thalamic nucleus and more medial thalamic nuclei, which are innervated by ST neurons. We found NPFF-ir terminal-like thickenings and fibers apposing the tracer-filled neurons in the LSN and LCN. ST neurons filled with the retrograde tracer making contacts with NPFF-ir terminal-like thickenings, were found to terminate not only in the ventroposterolateral thalamic nucleus but also in more medial thalamic nuclei. The highest number of tracer-filled ST neurons having NPFF-ir terminal-like thickenings and fibers in apposition were found at the cervical level. Our results suggest that NPFF-containing systems in the spinal cord of rat are not limited to the substantia gelatinosa, and the sensory functions of NPFF may be mediated at least partly through the modulation of the ST system. NPFF-ir contacts in the LSN and LCN might play an important role in the somatic sensory transmission system. This study shows evidence for the first time that the spinal NPFF-containing system may be involved in mechanisms that control sensory input to the supraspinal levels. Received: 11 March 1997 / Accepted: 10 September 1997     

Distribution of Fos-like immunoreactivity in the caudal medullary reticular formation following noxious facial stimulation in the rat

To investigate the topographic organization of nociceptive neurons in the caudal medullary reticular formation, the distribution of cells that exhibit c-fos expression was examined following a unilateral noxious facial stimulus: subcutaneous injection of formalin into the vibrissal pad of awake rats. Labelling for Fos-like immunoreactivity was present in a somatotopic distribution in a region of the lateral reticular formation adjacent to trigeminal nucleus caudalis, which corresponds approximately to lamina V of the medullary dorsal horn. Labelling in adjacent regions of the reticular formation showed no somatotopy but was predominantly ipsilateral. Contralateral labelling was concentrated ventrolaterally around the lateral reticular nucleus and dorsally near the nucleus of the solitary tract.     

Vestibulospinal and reticulospinal interactions in the activation of back muscle EMG in the rat

Summary The effects of electrical stimulation of the lateral vestibular nucleus (LVN) and medullary reticular formation (RF) on electromyographic activity in axial muscles medial longissimus (ML) and lateral longissimus (LL) in the rat were studied. Long trains (150–500 ms) at 200–330 Hz and 20–100 A were sufficient to activate ML and LL at latencies of 20–100 ms from the beginning of the train. Results of stimulation at 200–330 Hz to RF or LVN showed that muscle units were activated at a fixed latency from any effective pulse in the stimulus train. Using high frequency (1 kHz) trains of 3–6 pulses to LVN, EMG activity was detected at minimum latencies of 3.5–6 ms. When conduction times from the medulla to the spinal cord, and the spinal cord to the muscle are subtracted, this latency range is consistent with monosynaptic activation. In many cases, muscle units were recruited in order of size, with both RF and LVN stimulation. Combined stimulation of LVN and RF sites in n. gigantocellularis led to EMG activity in ML and LL at currents which were insufficient to evoke activity when presented singly. When stimulation of one site (300–400 ms train) was just sufficient to evoke a response, a shorter, overlapping train (100–150 ms) to the other site led to a higher rate of muscle activity that continued through the end of the long train, even after the short train had ended. In all cases, the effect of RF facilitating LVN was similar to the effect of LVN facilitating RF. The evidence for convergence between these two systems in the medulla and the spinal cord is discussed.     

A double-labelling study of reticular collaterals to the spinal cord and cerebellum of the North American opossum

Injections of horseradish peroxidase into either the spinal cord or cerebellum label neurons in the gigantocellular and lateral reticular nuclei of the North American opossum. In order to determine if neurons which project to the spinal cord and cerebellum are intermingled in these two nuclei and if single neurons provide collaterals to both areas, we have employed fluorescent markers in double-labelling experiments. Our results show that reticular neurons innervating either the spinal cord or cerebellum are often close together and that a few provide collaterals to both areas. Neurons providing such collaterals are rare, however, comprising 2% or less of those innervating either target alone.     

The distribution and origin of the ipsilateral descending limb of the brachium conjunctivum. An autoradiographic and horseradish peroxidase study in the rat

Summary The distribution, organization and origin of the ipsilateral descending limb of the Brachium Conjunctivum (B.C.), have been studied in the rat by using anterograde and retrograde tracing techniques. After injections of tritiated leucine/proline into the lateral cerebellar nucleus, covering both its medial part, corresponding to the dorsolateral hump (DLH) of Goodman et al. (1963) and its lateral part, (designated here as the lateral dentate, LD), and the neighboring interposed nucleus (NI), emerging fibres are numerous and leave laterally from the B.C. On the contrary, injections restricted to LD reveal very few such fibers. Within the lateral parvocellular reticular formation (LPRF) terminal labelling is heavy, and moderate to sparse within the adjacent trigeminal complex. Rostro-caudally, silver grain accumulation within the LPRF extends from the level of the motor trigeminal nucleus (VM) to the pyramidal decussation, exhibiting a cephalocaudal decrease of grain density. Within the trigeminal complex, labelling occurs in the caudal VM, the dorsal portion of the principal sensory nucleus, and within and around the trigeminal spinalis oralis. In addition, the area surrounding the VM (in part corresponding to the supratrigeminal region of Lorente de Nó 1922, 1933) is moderately labelled. After injections of HRP into various levels of the ipsilateral descending B.C.'s projection field, retrogradely labelled cells are numerous within the DLH. A slightly lesser amount of labelled cells are found in the lateral half of the NI, primarily concerning the nucleus interpositus posterior. Within the LD, only a few labelled cells are observed: these are mainly restricted to the dorsal portion at rostral levels of the nucleus. The results obtained by both the anterograde and retrograde studies suggest an absence of a topographic organization within this descending B.C. component. The possible functional meaning of these results is discussed.Abbreviations B.C. Brachium conjunctivum - DLH Dorsolateral hump - FTN Fibers of the trigeminal nerve - IO Inferior olive - LD Lateral dentate - LPRF Lateral parvocellular reticular formation - NI Interposed nucleus - NIA Nucleus interpositus anterior - NIP Nucleus interpositus posterior - NVII Facial nerve - PD Pyramidal decussation - TB Trapezoid body - VM Trigeminal motor nucleus - VPS Trigeminal principal sensory nucleus - VSC Trigeminal spinalis caudalis subnucleus - VSI Trigeminal spinalis interpolaris subnucleus - VSO Trigeminal spinalis oralis subnucleus - VII Facial nucleus - XII Hypoglossal nucleus This work was submitted as partial fulfillment for the degree of Doctorat de 3ème cycle at the Université Pierre et Marie Curie     

Evidence that dopamine‐beta‐hydroxylase immunoreactive neurons in the lateral reticular nucleus project to the spinal cord in the rat

The existence of noradrenergic projections from the lateral reticular nucleus (LRt) to the dorsal quadrant of cervical, thoracic, or lumbar spinal cord was investigated using a combined method of WGA‐apo‐HRP‐gold retrograde tracing and dopamine‐beta‐hydroxylase (DBH) immunocytochemistry. Preliminary retrograde tracing studies indicated that LRt neurons projecting to cervical, thoracic, or lumbar spinal cord were characteristically located near the perimeter of the LRt. Double‐labeling experiments demonstrated that a portion of these peripherally‐located, spinal‐projecting neurons were DBH‐immunoreactive. Double‐labeled neurons were also located at the parvocellular division of the contralateral LRt in the thoracic injection cases. Double‐labeled neurons were not observed at the subtrigeminal division in cervical, thoracic, or lumbar injection case. The results suggest the possibility that the noradrenergic LRt‐spinal pathway might be involved in a variety of pain processing and cardiovascular regulatory functions in the rat. Anat Rec 263:269–279, 2001. © 2001 Wiley‐Liss, Inc.     

Afferent organization of the lateral reticular nucleus in the rat: An anterograde tracing study

Summary The organization of the afferent projections to the lateral reticular nucleus of the rat was investigated following placement of horseradish peroxidase-conjugated wheatgerm agglutinin into the red nucleus, fastigial nucleus, various levels of the spinal cord or the sensorimotor area of the cerebral cortex. The pattern of distribution of anterogradely labelled profiles visualized with tetramethylbenzidine revealed that the caudal three-fourths of the lateral reticular nucleus received a large, topographically organized projection from the entire length of the contralateral spinal cord. The lateral part of the rostral half of the lateral reticular nucleus received a small projection from the contralateral red nucleus, the dorsal part of the middle third of the nucleus received a diffuse projection from the contralateral fastigial nucleus, and the extreme rostromedial part of the nucleus received a sparse projection from the contralateral cerebral cortex. The dorsal part of the middle third of the lateral reticular nucleus also received a small projection from the ipsilateral cervical spinal cord. The distribution of afferent fibres from different levels of the spinal cord, red nucleus, and fastigial nucleus overlapped substantially in the middle third of the lateral reticular nucleus, whereas the cerebral cortical receiving area was separate. These data suggest that the middle third of the lateral reticular nucleus integrates spinal and supraspinal impulses to the cerebellum, while the rostral part of the nucleus is involved in a separate cerebral cortico-cerebellar pathway.Abbreviations DSC dorsal spinocerebellar - ECN external cuneatus nucleus - F fastigial nucleus - FRA flexor reflex afferents - HRP horseradish peroxidase - IO inferior olivary nucleus - IP interpositus nucleus - LRN lateral reticular nucleus - MCP magnocellular portion - M-LRN magnocellular LRN - NA nucleus ambiguus - NSTT nucleus of the spinal tract of the trigeminal nerve - PCP parvicellular portion - R red nucleus - STP subtrigeminal portion - STT spinal tract of the trigeminal nerve - TMB tetramethylbenzidine - VSC ventral spinocerebellar - WGA wheatgerm agglutinin - b-VFRT bilateral ventral flexor reflex tract - c-VFRT contralateral ventral flexor reflex tract - i-FT ipsilateral forelimb tract     

Excitatory input to burst neurons from the labyrinth and its mediating pathway in the cat: location and functional characteristics of burster-driving neurons

Summary 1. Spikes of single neurons were recorded extracellularly in the cat prepositus hypoglossi nucleus and the underlying reticular formation and were identified as type II neurons by horizontal rotation. Among these neurons, those activated by contralateral vestibular nerve stimulation with short latencies (1.5–3.0 ms) were selected for further study. 2. A class of these identified neurons was antidromically activated from the contralateral excitatory burst neuron (EBN) area immediately rostral to the abducens nucleus. Systematic tracking for antidromic stimulation revealed a wide distribution of effective spots in and near the EBN area, with varied latencies and thresholds, suggesting terminal branching in that area. The same neurons were also antidromically activated from the contralateral inhibitory burst neuron (IBN) area, the region near the midline, and the nucleus reticularis tegmenti pontis. 3. These neurons exhibited a characteristic firing pattern related to nystagmus: with contralateral rotation the firing rate gradually increased during the slow phase (type II response) and further steeply increased in a burst fashion before and during the contraversive quick phase. Since the time of occurrence of burst activity in these neurons was similar to that of contralateral ENBs and IBNs that received their axonal projection, it is suggested that they send excitatory input to burst neurons, and can thus be called burster-driving neurons (BDNs). 4. Intracellular study revealed that stimulation of the BDN area produced monosynaptic EPSPs in contralateral EBNs. The monosynaptic connection of BDNs with EBNs was confirmed by detecting unitary extracellular synaptic currents of EBNs with the spike-triggered averaging technique. 5. In contrast to BDNs, another class of nystagmus-related type II neurons in the prepositus hypoglossi and medullary reticular formation showed a discharge pattern similar to that of abducens motoneurons on the same side. None of them was antidromically activated from the contralateral pontine reticular formation including the EBN area. Some neurons responded anti-dromically to stimulation of the ipsilateral dorsomedial pontine reticular formation. 6. In conclusion, the input from the horizontal canal during rotation reaches the contralateral prepositus hypoglossi nucleus and the underlying reticular formation through the vestibular nuclei, and a class of neurons in these structures (BDNs) responds to the canal input in a burst fashion following a tonic type II activity. The axons of BDNs cross the midline and monosynaptically excite EBNs on the side of the canal stimulated. The burst activity of BDNs at the quick phase is suggested to contribute to generation of spike burst of EBNs and IBNs.     

Sexual differences in the topographical distribution of serotonergic fibers in the anterior column of rat lumbar spinal cord

Summary Sexual dimorphism in the topographical organization of immunoreactive serotonergic fibers has been shown for the first time in the anterior column of the rat lumbar cord. A characteristic preferential arrangement of serotonergic fibers on the small cell column composed of anterior horn motoneurons, which have been proved to send their axons to the cremaster muscle, was demonstrated at the lumbar segments (L1–L2) of male rats, using the immunoperoxidase technique with antiserum against serotonin. A similar finding was also observed in female rats, but was less prominent than in males. Comparative analysis of the cell numbers and the size of neuronal somata of the aforementioned nucleus, done using retrograde transport of fluorescent dye (DAPI) via axonal fibers coursing down the genitofemoral nerve to the cremaster muscle, gave significantly larger values in males.The sexual difference in the serotonergic innervation pattern was, in consequence, surmised to be caused by the cytoarchitectonic contrast ascertained in the lumbar anterior column. Furthermore, there may be a striated muscle endowed with some active functions homologous to those of the male cremaster muscle in the female rat.     

大鼠前庭神经核群向腰髓投射特征——BDA法逆行研究

目的　研究大鼠前庭神经核群向脊髓的投射纤维特征。方法　在 7例SD大鼠采用结合生物素的葡聚糖胺(BDA)逆行法观察大鼠前庭核群向脊髓的投射。结果　除前庭神经上核 (SVN)外的其余各前庭核均有向大鼠腰髓的投射 ,单侧注射的实验动物中 ,前庭神经内侧核 (MVN)、外侧核 (LVN)和降核 (DVN)的标记神经元可见于双侧 ,其中MVN和LVN的标记神经元以注射同侧占优势 ,而DVN标记神经元两侧数量基本一致。结论　大鼠前庭脊髓尾侧束发出纤维投向脊髓腰段