[Formation of descending pathways to the spinal cord].
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Animals↗
Biomedical subjects
N Okado
Publications and source records attributed to N Okado.
The onset and development of descending pathways to the spinal cord in the chick embryo.
The ontogenetic development of afferent (supraspinal and propriospinal) as well as efferent (ascending) fiber connections of the spinal cord was examined following the injection of horseradish peroxidase (HRP) or wheat germ agglutinin HRP (WGA-HRP) into the cervical and lumbar spinal cords (or brains) of embryos ranging in age from 4 to 14 days of incubation. A few cells were first reliably retrogradely labelled in the pontine reticular formation on embryonic day (E) 4 and E5 following the injection of WGA-HRP into the cervical and lumbar spinal cord, respectively. Propriospinal projections to the lumbar spinal cord, originating from brachial spinal cord, were found by E5, and from the cervical spinal cord by E5.5. Ascending fibers arising from neurons in the lumbar spinal cord could be followed to rostral mesencephalic levels in E5 embryos. Thus, the earliest supraspinal, propriospinal, and ascending fiber connections appear to be formed almost simultaneously. Retrogradely labelled cells were found in the raphe, reticular, vestibular, interstitial, and hypothalamic nuclei in E5.5 embryos following lumbar injections of WGA-HRP. Except for neurons in cerebellar nuclei, all the cell groups of origin that project to the cervical spinal cord of posthatching chicks were also retrogradely labelled by E8. There was a delay in the time of appearance of the projections from various regions of the brain stem to the lumbar versus the cervical spinal cord, ranging from 0.5 to 7 days, but typically of about 3 days duration. A large number of cells located in the ventral hypothalamic region, just dorsal to the optic chiasma, were found to be labelled following cervical HRP injection between E6 and E10. These cells may represent transient projections that are present only during embryonic stages since no labelled cells were found in this region in the newly-hatched chick.
Animals↗
Behavioral analysis of opiate-mediated inhibition in the early chick embryo.
Morphine (opiate agonist) produced a dose-dependent decrease in the spontaneous motility of 5- and 9-day chick embryos. Naloxone (opiate antagonist) appeared to reverse competitively the inhibition of motility caused by morphine. The effects of morphine on spontaneous motility in 5-day embryos were also reversed stereospecifically by the opiate antagonist pairs WIN 44441-3/WIN 44441-2 and levallorphan/dextrallorphan. Levorphanol (opiate agonist) also produced a dose-dependent decrease in the motility of 5-day embryos while its inactive (+)-isomer, dextrophan, was not effective. Etorphine (opiate agonist) was more than 1000-fold more effective than morphine in inhibiting the motility of 5-day embryos. The effectiveness of several opiate agonists and antagonists on the spontaneous motility of 5-day embryos was similar to their effectiveness in radioligand-binding studies on isolated membrane receptors from either adult mammalian brain or ileum. Levorphanol was more effective than dextrophan and etorphine was substantially more effective than morphine in decreasing the spontaneous motility of 4-day embryos. WIN 44441-3 was more effective than WIN 44441-2 in reversing the inhibition of motility in 4-day embryos caused by morphine. Morphine inhibited spontaneous hind-limb motility in both thoracic spinal and sham-operated 7-day embryos; the inhibition of motility caused by morphine was reversed by WIN 44441-3 in both thoracic spinal and sham-operated 7-day embryos. [Leu5]enkephalin-like immunoreactivity in the lumbar spinal cord was concentrated in the superficial laminae of the dorsal horn and along the midline rostral to the central canal. A lesser concentration of immunoreactive processes occurred in the medial and lateral motor columns where labelled varicosities appeared to contact motoneurons. Opiate receptors appear to be present at least as early as day 5 (and perhaps as early as day 4) in the chick embryo. Opiate receptors appear to be present in the lumbar spinal cord of the chick embryo at least as early as day 7. The structural requirements for ligand binding to opiate receptors in the 5-day chick embryo are similar to the requirements for ligand binding to opiate receptors in the adult.
Age Factors↗
Development of retinohypothalamic projections in the chick embryo.
The retinal projection to the hypothalamus was investigated in embryonic as well as hatched chick using wheat germ agglutinin-conjugated horseradish peroxidase as an anterograde tracer. The presence of an aggregation of anterogradely labeled terminals in the hypothalamus was used to identify the suprachiasmatic nucleus (SCN). The first clear labeling of retinal fibers in the SCN was found on embryonic day 16, whereas labeling was found in the other primary visual projections, in the diencephalon and mesencephalon, several days earlier. Thus, the retinohypothalamic projection is the last primary visual pathway to develop in the chick embryo.
Animals↗
Cell death of motoneurons in the chick embryo spinal cord. IX. The loss of motoneurons following removal of afferent inputs.
The primary aim of this study was to clarify the role of supraspinal, propriospinal, and primary sensory afferents in motoneuron (MN) development in the lateral motor column (LMC) of the lumbar spinal cord of the chick embryo. For this purpose three types of operations were carried out on embryonic day (E) 2. (1) The spinal cord was transected at the cervical (C-gap) or at the thoracic (T-gap) level so as to eliminate supraspinal and/or propriospinal inputs to the lumbar cord. (2) The entire lumbar neural crest was removed (NCR) in order to eliminate primary sensory inputs arising from the dorsal root ganglia (DRG). (3) A combined operation of T-gap and lumbar NCR was performed. The numbers of MNs in the LMC of the lumbar spinal cord were counted in embryos sacrificed between E10 and E18. The number of MNs on E10, when naturally occurring neuron death is almost complete, was not changed following either operation 1 or 2 described above. However, by E16, when naturally occurring neuron death is over, these same deafferented groups had 20 to 25% fewer MNs than did controls. Thus, the removal of either descending or sensory (DRG) afferents results in a significant increased loss of MNs that appears to take place only during the final stages of natural neuronal death or later. By contrast, the removal of both sources of input (T-gap + NCR) results in an additional 37% loss of MNs by E10 compared to controls. Thus, in this group deafferentation significantly increases cell loss during the major period of naturally occurring MN death (E5 to E10). No further loss of MNs occurs in this group after E10. Chronic treatment of deafferented embryos with curare from E6 to E9 or from E10 to E14 prevented the naturally occurring MN loss during these stages but was without effect on the increased cell loss induced by deafferentation. These results imply that the cellular mechanisms involved in target- versus afferent-regulated cell death are different. Collectively, these results indicate that the regulation of MN numbers is more complicated than previously thought. Both targets and afferents appear to be involved in controlling the survival of this population of neurons during the period of naturally occurring MN death.
Animals↗
[Sensitivity of the recent bacterial isolates to cefotaxime and other cephem antibiotics].
Antimicrobial susceptibility of 703 nonselected strains of 14 different bacterial species to cefazolin, cefmetazole, cefotiam, cefoperazone latamoxef, and cefotaxime (CTX) was examined. CTX was the most active against E. coli, Klebsiella, Serratia, P. mirabilis, H. influenzae, beta-Streptococcus group A, beta-Streptococcus group B and S. pneumoniae. On the other hand, CTX-resistant (MIC greater than or equal to 50 micrograms/ml) strains were isolated at the following frequencies: Citrobacter, 21.7%; Enterobacter, 7.7%; Serratia, 4.6%; P. aeruginosa, 40.4% and B. fragilis, 28.6%. Of the 411 strains classified as very sensitive () or moderately sensitive (++) by disk method, 405 strains (98.5%) were inhibited by less than or equal to 12.5 micrograms/ml of CTX. Only 1 strain (0.2%) was falsely classified as moderately sensitive and no strains were falsely categorized as resistant.
Bacteria↗
[Chronological variations in blood isolates and their susceptibility to various antibiotics].
Chronological variation in blood isolates obtained from 1968 to 1982 was studied. Escherichia coli was the most frequent isolates followed by Klebsiella species, glucose-non-fermentative Gram-negative rods (excluding Pseudomonas aeruginosa), Enterobacter-Serratia group, and Staphylococcus aureus. The isolation of glucose-non-fermentative Gram-negative rods, about half of which being Achromobacter xylosoxidans, increased greatly in number from 1980. A total of 113 strains of blood isolates was examined for susceptibility to various antibiotics. Although there was a significant increase in S. aureus resistant to GM, these strains were susceptible to cephalosporins. In the 9 strains of GM-resistant aerobic Gram-negative rods (2 strains of Klebsiella, 2 strains of Enterobacter, 4 strains of Serratia and 1 strain of P. aeruginosa), 3 strains of Serratia species were also resistant to AMK. Two strains of LCM-resistant Bacteroides fragilis were susceptible to LMOX, but 1 strain was not inhibited by 100 micrograms/ml of CFX. Among the clinical specimens, differences were found in the rate of isolation of resistant strains, particularly in the case of Serratia and P. aeruginosa. Antibiotic resistant strains were isolated more frequently from urine and the least frequently from sputum. Since the frequency of isolation of resistant strains varied according to organism, clinical material and year of isolation, microbiological laboratories should develop their own data base from which clinicians can make rational therapeutic decisions.
Anti-Bacterial Agents↗
Axoglial synaptoid contacts in the neural lobe of the human fetus.
Axoglial synaptoid contacts as well as junctional specializations were examined in the neural lobe of five human fetuses ranging from 7.5 to 19 weeks of ovulation age. Because synapselike contacts (SLC), which have both presynaptic and postsynaptic densities, were observed only in the younger fetus (7.5 weeks), they may be transient structures. Axoglial SLC were also found in older fetuses, but their structural characteristics were different from those found in a 7.5-week fetus in that the cytoplasmic membrane density was found only on the presynaptic side and its extent was decreased. In the youngest fetus observed here (7.5 weeks), puncta adherentia were observed. In the fetuses older than 11 weeks, gap junctions, long adherentia-type junctions with thick filamentous structures, and mixed junctions with both types of contact were found between pituicytes.
Axons↗
Early myelin formation and glial cell development in the human spinal cord.
In order to identify the onset of myelination as well as to clarify the development of glial cells in human cervical spinal cord 21 embryos and fetuses ranging from 5 weeks of ovulation age (16 mm in crown-rump length) to 13 weeks (110 mm) were examined with the light the electron microscope. The first appearance of definite myelinated fibers occurred in the lateral portion of the ventral marginal layer of 66-mm (10-weeks) fetus. These nascent myelinated axons were always of larger diameter than unmyelinated axons. Although they occurred infrequently, there were, nevertheless, degenerative changes observed in some of these first myelinated axons in the 66-mm fetus. by this time glial cells in the marginal layer rapidly increased in number and substantial differentiation had occurred. Young oligodendrocytes are considered as the only myelin-forming cells in the human spinal cord.
Fetus↗
The cells of origin of the trigeminothalamic, trigeminospinal and trigeminocerebellar projections in the cat.
Using the retrograde horseradish peroxidase technique, we have examined the distribution of labeled thalamic-, spinal- and cerebellar-projecting neurons in the trigeminal sensory nuclei of the cat. Injections into the nucleus ventralis posterior of the thalamus resulted in labeling of neurons in lamina I (subnucleus zonalis), the deeper part of lamina IV (the subnucleus magnocellularis) of the nucleus caudalis and in lamina V (the lateral extension of the nucleus medullae oblongatae centralis) on the contralateral side. A very large number of labeled small neurons were observed mainly in the caudal part of the nucleus interpolaris and in the ventral division of the principal sensory nucleus on the contralateral side and in the dorsal division of the principal sensory nucleus on the ipsilateral side. Injections into the known projection areas of the cerebellar cortex labeled mainly ipsilaterally the trigeminocerebellar neurons in a restricted ventrolateral area of lamina IV of the nucleus caudalis at its rostral level and in lamina V. Many labeled neurons were also observed in the nucleus interpolaris. Although the distribution overlapped with that of the trigeminothalamic neurons, the greatest majority were concentrated in its rostral part where the trigeminothalamic neurons were very small in number. In addition, labeled neurons were observed in the rostral part of the nucleus oralis and the ventralmost part of the ventral division of the principal sensory nucleus. No labeled neurons were observed in the dorsal division of the principal sensory nucleus and the mesencephalic nucleus. The trigeminospinal neurons were labeled mainly ipsilaterally following injections into the upper cervical cord. They were located in laminae I and III, the deeper part of lamina IV of the nucleus caudalis and in lamina V. Only scattered labeled neurons were found in the nucleus interpolaris. The number of labeled neurons increased in the nucleus oralis at the level of the superior olive. They tended to be distributed around or dorsal to the group of the trigeminothalamic neurons at the caudal part of the principal sensory nucleus. No neurons of the principal sensory nucleus appeared to project to the spinal cord. Based on the large size and location, the trigeminospinal neurons could be differentiated from the other projection neurons in the nucleus oralis. The present study demonstrates that the trigeminal sensory nuclei are composed of groups of neurons with different projections, since the main aggregations are localized at different levels. However, it should be examined whether the neuronal groups, which are labeled from the different structures in similar locations, are composed of individual neurons projecting to more than one of these structures.
Animals↗
Onset of synapse formation in the human spinal cord.
The time of onset of synapse formation was examined in the cervical spinal cord of eight human embryos ranging from 4 (8 mm in crown-rump length) to 6 (22 mm) weeks of ovulation age. The first synapses were found in the motor nucleus of a 10-mm embryo (Streeter's horizon XV). They contained only a small number of synaptic vesicles and had asymmetrical membrane thickening, with thicker postsynaptic membranes than presynaptic ones. With the exception of an occasional axosomatic synapse, nearly all synapses found in a 10-mm embryo were axodendritic. In an 11-mm embryo (Streeter's horizon XVI), synapselike contacts (SLC) were found in the dorsal marginal layer. They contained a small number of synaptic vesicles and had "reversed membrane specialization" with prominent presynaptic membrane densities. The number of SLC decreased in older embryos. Judging from the morphological characteristics of membrane specializations and the temporal decrease in number, SLC are considered to be either transient synapses on the borderline cells or axoglial synapses. Synapses in the regions outside the motor nucleus first appeared in the dorsal marginal layer of a 14-mm embryo (Streeter's horizon XVII).
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Spinocerebellar projections to lobules I and II of the anterior lobe in the cat, as studied by retrograde transport of horseradish peroxidase.
Spinocerebellar tract (SCT) neurons projecting to lobules I and II of the cerebellar anterior lobe were identified by the retrograde horseradish peroxidase technique in the cat. Instead of a conventional stereotaxic approach, we removed ventral parts of the vermis of the posterior lobe and approached the posterior aspect of lobule I through the fourth ventricle. Under direct visual guidance, discrete injections were made into lobule I or II with a glass micropipette. Neurons projecting to lobule I were located mainly in the central cervical nucleus (CCN), the medial part of lamina VII of L6 to the causal segments, and in lamina VIII of S2 to the caudal segments (with crossed ascending axons). The latter two groups correspond to medial lamina VII group of the lumbar to the caudal segments and the ventral horn group of the sacral-caudal segments of our previous studies. A small number of Clarke column neurons (with uncrossed ascending axons) also projected to lobule I. All of these neuronal groups projected to lobule II. In addition, large neurons in lamina V and the border between laminae IV and V from S2 to the caudal segments projected to sublobule IIA, and more numerously to sublobule IIB (with crossed ascending axons). They belong to the dorsal horn group of the sacral-caudal segments of our previous studies. Spinal border cells (with crossed ascending axons) projected to sublobule IIB, and a small number, to sublobule IIA. It was suggested that the CCN neurons project more densely to the median region whereas Clark column neurons project to the lateral part of these lobules.
Afferent Pathways↗
Descending projections from the spinal and mesencephalic nuclei of the trigeminal nerve to the spinal cord in the cat. A study with the horseradish peroxidase technique.
Descending projections from the spinal (Vsp) and the mesencephalic nuclei (Vme) of the trigeminal nerve to the spinal cord were studied by means of the retrograde horseradish peroxidase technique in the cat. The number of labeled neurons was largest in the case of high cervical injections and decreased as the injections were placed caudally. Small laminae III and IV neurons of the nucleus caudalis (Vc) were labeled ipsilaterally following injections placed as caudally as the middle cervical segments (C4-C5). Lamina I (marginal) neurons of the Vc were labeled ipsilaterally after injections at the middle thoracic level (T6) but those of C1 were labeled after lumbar injections (L3). Lamina V neurons of C1 and the medullary counterparts were labeled bilaterally after injections placed caudally to thoracic segments. A few small neurons were labeled in the ipsilateral nucleus interpolaris (Vi) after injections placed as caudally as the middle cervical segments (C6). Among the subdivisions of the Vsp, the labeled neurons were most numerous in the nucleus oralis (Vo). They were medium-sized and large, and appeared bilaterally, with an ipsilateral predominance at the level of the superior olive. The great majority projected to the cervical segments but a few also projected to the lower cervical to the thoracic segments (C8-T9). Neurons of the Vme projected ipsilaterally to the upper cervical segments (C1-C3). No projections were found from the principal sensory nucleus. The present study suggests that the trigeminospinal projections of the Vsp and the Vme are composed of various cells of origin and thereby subserve not only the trigeminospinal reflex but other unknown functions.
Animals↗
Cells of origin of brainstem afferents to lobules I and II of the cerebellar anterior lobe in the cat.
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Afferent Pathways↗
An electron microscopic study on the structural development of the neural lobe in the human fetus.
Structural development of the neural lobe of the hypophysis was studied by light and electron microscopy in five human fetuses ranging from 7.5 to 19 weeks of ovulation age. Clusters of small clear vesicles were found occasionally in axon profiles in a fetus of 7.5 weeks. Granular vesicles in axon profiles first accumulated in a fetus of 8.5 weeks. Concurrently, fenestration of capillary walls and expansion of perivascular spaces were observed. After 8.5 weeks, three types of vesicle-containing axon profiles were found, which contained predominantly granular vesicles (GP), small clear vesicles (SP), and a mixed population of both granular and small clear vesicles (MX), respectively. Their numbers increased significantly during two periods, 7.5-8.5 weeks and 15.5-19 weeks. Ratios of GP, SP, and MX to the total number of the three types of axon were almost the same in all the fetuses studied, i.e., about 40%, 40%, and 20%, respectively. Developmental changes in the diameter of granular vesicles were examined in GP, SP, and MX of each fetus. Apart from a few exceptions, the mean diameter of granular vesicles was larger in GP than in MX, which was in turn larger than in SP. The diameters increased with development and those in GP reached almost the same value as in the adult by 19 weeks.
Axons↗
Development of the human cervical spinal cord with reference to synapse formation in the motor nucleus.
Synaptic development in the motor neuropil of the cervical spinal cord was quantitatively studied by light and electron microscopy in human embryos and fetuses ranging from five to 19 weeks of ovulation age. The numbers of axodendritic synapses increase substantially at the end of the eighth week. However, axosomatic cynapses rapidly proliferate between 10.5 and 13 weeks of ovulation age. The increases in both types of synapses generally coincide with the behavioral changes in human fetuses that have been reported by other investigators. Only synaptic boutons containing spherical vesicles (S-type synapses) were found in the motor neuropil throughout the stages examined; no synapses with flattened vesicles (F-type synapses) were encountered. The majority of these synaptic boutons contain only a small number of synaptic vesicles (fewer than 20), although the number tends to increase with maturation. There is no significant maturational change in the size of synaptic vesicles. The present study suggests that synapse formation in the motor neuropil of the human fetus cervical spinal cord may continue up to 19 weeks of ovulation age because immature types of synapse are found in all fetuses. Myelin formation probably begins by the 11th week.
Axons↗
Synaptogenesis in the cervical cord of the human embryo: sequence of synapse formation in a spinal reflex pathway.
Synaptogenesis in the cervical cord was studied by light and electron microscopy in human embryos ranging from four to seven weeks of ovulation age. The stage of embryonic development was estimated on the basis of external morphology of embryos and histology of the eye ball with reference to Streeter's horizon. No synapses were found in the cervical cord of the embryo at Streeter's horizon XIV (8 mm; estimated ovulation age, 28-30 days). A small number of axodendritic synapses appear in the motor neuropil of the cervical cord at Streeter's horizon XVII (14 mm; estimated ovulation age, 34-36 days). Since no primary afferents are demonstrated to reach the motor neuropil at this stage (the premotile period), these synapses are considered to be formed between interneurons and motor neurons. On the other hand, the formation of synapses outside the motor neuropil of the cervical cord was recognized at Streeter's horizon XX (22 mm; estimated ovulation age, 40-42 days), which corresponded to the period of onset of the precocious reflex, but not by horizon XIX (18 mm; estimated ovulation age, 38-40 days). The first axosomatic synapses were found in the motor neuropil at Streeter's horizon XVII (estimated ovulation age, 34-36 days). The present study suggests that the formation of synapses between interneurons and dendrites of spinal motor neurons precedes that of synapses between interneurons and collaterals of primary afferents. This sequence of synaptogenesis is in agreement with that reported in earlier studies with silver stain methods.
Gestational Age↗
A new technique of silver impregnation for oligodendrocytes with potassium dicyanoargentate by means of perfusion-fixation method.
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Animals↗