Direct evidence for the link between monoaminergic descending pathways and motor activity:: II. A study with microdialysis probes implanted in the ventral horn of the spinal cord

In order to define precisely the relation between descending monoaminergic systems and the motor system, we measured in the ventral horn of spinal cord of adult rats the variations of extracellular concentrations of 5-HT, 5-HIAA, DA and MHPG. Measurements were performed during rest, endurance running on a treadmill, and a post-exercise period, with microdialysis probes implanted permanently for 45 days. We found a slight decrease in both 5-HT and 5-HIAA during locomotion with a more marked decrease during the post-exercise period compared to the mean of rest values. In contrast, the concentration of DA and MHPG increased slightly during the exercise and decreased thereafter. These results, when compared with those of a previous study, which measured monoamines in the spinal cord white matter [C. Gerin, D. Bécquet, A. Privat, Direct evidence for the link between monoaminergic descending pathways and motor activity: I. A study with microdialysis probes implanted in the ventral funiculus of the spinal cord, Brain Res. 704 (1995) 191–201], highlight the complex regulation of the release of monoamines that occurs in the ventral horn.     

Crossed inhibition of the soleus H reflex during passive pedalling movement

We hypothesized that sensory input from the moving leg induces presynaptic inhibition of the soleus H reflex pathway in the contralateral stationary leg. The results showed a crossed inhibition during passive pedalling movement of the leg, which was not removed by low levels of tonic contraction of soleus in the stationary leg. The inhibition was correlated exponentially to the rate of the movement (R²=0.934, P<0.05) and was not dependent on the quadrants through which the moving leg was passing. Static flexion of the stationary leg caused ipsilateral inhibition of the reflexes (t=5.590, P<0.05), independent of the orientations of the other leg. We concluded that sensory inflow from the moving leg induces presynaptic inhibition in the stationary leg, that a complex transformation of the sensory input in the spinal cord or brain underlies the tonic crossed inhibition and phasic ipsilateral inhibition, and that descending motor commands exert a powerful control over these sensorimotor modulatory mechanisms.     

High resolution nuclear magnetic resonance imaging of the spinal cord in experimental demyelinating disease

Summary Chronic recurrent experimental allergic encephalomyelitis was induced in a strain 13 guinea pig by inoculation of isologous spinal cord homogenate. The spinal cord was obtained after perfusion with 4% paraformaldehyde and examined with nuclear magnetic resonance (NMR) imaging. Proton NMR spin echo images (repetition time: 3 s; echo times: 20 and 60 ms) were obtained from intact, isolated spinal cord in a 4.7 Tesla, 50 mm bore magnet. The slice thickness of the images was 380 m and the inplane resolution was 40×40 m. The images showed superficial areas of low signal intensity in the lateroventral regions of the white matter, in some instances with a seam of higher signal intensity. Neuropathologically, these abnormalities corresponded exactly to areas of demyelination. Control images did not show these abnormalities. The present high resolution imaging allowed a correlation between demyelination and abnormal NMR signals in a small laboratory animal with an inflammatory demyelinating disease.Supported by the Belgian Foundation of Medical Scientific Research (FGWO, grant 3.0096.86 and grant 3.0019.86), by the Institute for the promotion of Scientific Research in Industry and Agriculture (IWONL) and by the Scientic Research Planning Office of the Belgian Government (DPWB), contract no. 87/92-120     

Development of the rat thalamus: II. Time and site of origin and settling pattern of neurons derived from the anterior lobule of the thalamic neuroepithelium

Short-survival, sequential, and long-survival thymidine radiograms of rat embryos, fetuses, and young pups were analyzed in order to examine the time of origin, settling pattern, and neuroepithelial site of origin of the anterior thalamic nuclei--the lateral dorsal (lateral anterior), anterodorsal, anteroventral and anteromedial nuclei--and of two rostral midline structures--the anterior paraventricular and paratenial nuclei. The neurons of the lateral dorsal nucleus are generated over a 3-day period between days E14-E16 and their settling pattern displays a combined lateral-to-medial and dorsal-to-ventral neurogenetic gradient. The bulk of the neurons of the anteroventral nucleus are generated over a 3-day period between days E15-E17 and settle with an oblique lateral-to-medial and ventral-to-dorsal neurogenetic gradient. The bulk of the neurons of the anteromedial nucleus are generated over a 2-day period between days E16-E17 and show the same settling pattern as the anteroventral nucleus. The neurons of the anterodorsal nucleus are generated over a 3-day period between days E15-E17 and show a lateral-to-medial neurogenetic gradient. The bulk of the neurons of the central part and lateral part of the paraventricular nucleus are generated over a 2-day period (E16-E17 and E17-E18, respectively) and each part displays a ventral-to-dorsal neurogenetic gradient. Finally, the bulk of the neurons of the paratenial nucleus are generated over a 4-day period between days E15-E18 and settle with a lateral-to-medial neurogenetic gradient. Observations are presented that the anterior thalamic nuclei, constituting the distinct "limbic thalamus," derive from a discrete neuroepithelial source. This is the crescent-shaped germinal matrix lining the diencephalic (medial) wall of the hitherto unrecognized anterior transitional promontory, which we call the anterior thalamic neuroepithelial lobule. On day E16 three migratory streams leave the anterior neuroepithelial lobule and, on the basis of their labeling pattern in relation to the neurogenetic gradients of the anterior thalamic nuclei, they are identified, from dorsal to ventral, as the putative migratory streams of the anterodorsal, anteroventral, and lateral dorsal nuclei. On day E17 the putative migratory stream of the anteromedial nucleus appears to leave the same neuroepithelial region that on the previous days was the source of the anteroventral nucleus. Dorsally, two neuroepithelial patches persist after day E17 and these are identified as the putative cell lines of the anterior paraventricular and paratenial nuclei.     

Ultrastructural synaptology of Clarke's column

Summary An electron microscopic analysis of the synapses in Clarke's column of the cat, using fresh short term degeneration, long term degeneration for detection of the persisting elements, and a newly devised two-step degeneration technique using fresh short term degeneration for further analysis of the persisting synaptic elements in chronic degeneration cases. — Three kinds of synaptic terminals can be identified in the lower part (L₃ segmental level) of Clarke's column: (1) very large (so-called giant) axon terminals with spheric vesicles of primary muscle afferents establishing multiple (climbing-type) contacts mainly with the large dorsal spinocerebellar tract neurons; (2) small bouton-type terminals having spheric synaptic vesicles and originating mainly from spinal interneurons, localized below L₄ in the lumbar enlargement and contacting small distal dendrites and cell bodies of small cells; (3) two types of nerve terminals, originating from local neurons, and characterized by flattened vesicles. One type of (3) contacts mainly the large Clarke neurons directly, whereas the other establishes axo-axonic synapses with the giant terminals (1) of primary muscle affer ents. The possible functional significance of these findings is discussed.     

H-reflexes are smaller in dancers from The Royal Danish Ballet than in well-trained athletes

Summary The size of the maximalH-reflex (H _max) was measured at rest and expressed as a percentage of the maximalM-response (M _max) in 17 untrained subjects, 27 moderately trained subjects, 19 well-trained subjects and 7 dancers from the Royal Danish Ballet. TheH _max/M _max was significantly larger in the moderately and well-trained subjects than in the untrained subjects but smaller in the ballet dancers. It is therefore suggested that both the amount and the type of habitual activity may influence the excitability of spinal reflexes.     

Time course and effective sites for inhibition from midbrain periaqueductal gray of spinal dorsal horn neuronal responses to cutaneous stimuli in the cat

Summary Inhibition of spinal dorsal horn neuronal responses to noxious (50 °C) skin heating by stimulation of the midbrain periaqueductal gray (PAG) was quantitatively investigated in cats anesthetized with sodium pentobarbital and nitrous oxide. Systematic variation of the interval between onset of PAG stimulation (PAGS) and onset of noxious skin heating revealed that a marked reduction of spinal unit heat-evoked discharges occured immediately upon onset of PAGS, and ceased immediately at offset of PAGS with a post-stimulation excitatory rebound. Stimulation at sites in both ventral and dorsal PAG produced inhibition, the strength of which increased sometimes in a linear manner with increasing strength of PAGS. Thresholds for the generation of descending inhibition were higher in dorsal than ventral PAG. PAGS also inhibited spinal unit responses to non-noxious skin stimulation (brushing of hairs). Descending inhibition from PAG is considered as a possible mechanism for analgesia produced by stimulation of PAG and other brainstem structures.The work was supported by a grant from the Deutsche Forschungsgemeinschaft (Zi 110)     

Somatotopic termination of the spino-olivary fibers in the cat,studied with the wheat germ agglutinin-horseradish peroxidase technique

Summary Terminal sites of the spino-olivary fibers (SOFs) were examined by the anterograde transport of wheat germ agglutinin-horseradish peroxidase in the cat. The tracer was injected at various spinal cord levels from the first cervical to the caudal segments. The SOFs derived from the C1-T1 segments terminated medially in the caudal half (levels II–VIII of Brodal) of the medial accessory olive (MAO), which projects to the A zone of the cerebellar cortex, whereas the SOFs derived from the L6-S1 segments terminated laterally in the caudal half (levels I–VIII) of the MAO. No projections were found from the T2-L5 segments to the MAO. In the dorsal accessory olive (DAO), the SOFs terminated at levels III–XIV; the DAO projects to the B zone and the C1 and C3 zones of the cerebellar cortex. The SOFs derived from the C1-C4 segments terminated in the most medial part of the DAO (levels III–XIV), followed laterally by those from the C5-T1 segments. Further laterally, the SOFs derived from the T2-L5 and the L6-S1 segments terminated in the mediolateral order at levels V–XIV. The SOFs from the L6-S1 segments occupied the most lateral part of the DAO. The present study demonstrates that there is a distinct somatotopic termination of the SOFs in the mediolateral order in the caudal MAO and the DAO.     

The intra-cortical trajectory of the coeruleo-cortical projection in the rat: A tangentially organized cortical afferent

Cortical and sub-cortical lesions in the rat were used to analyze the intracortical trajectory of the noradrenergic axons, which were visualized by aldehyde-induced catecholamine histofluorescence and by immunohistochemistry using an antibody directed against rat dopamine-β-hydroxylase. Following subcortical lesions there is a slowly progressive reduction in the density of cortical noradrenergic axons, indicating that they undergo asynchronous anterograde degeneration. By 2 weeks after transection of the dorsal noradrenergic bundle, no dopamine β-hydroxylase-immunoreactive fibers are detectable in the ipsilateral cortex. Neither transection of the cingulum bundle, nor parasagittal incisions through the dorsal cortex lateral to the cingulum, diminished the noradrenergic innervation of medial or dorso-lateral cortex. A cortical lesion medial to the cingulum bundle markedly reduced the density of noradrenergic fibers in cingulate cortex caudal to the lesion, but did not affect the innervation of dorso-lateral cortex. In contrast, dorso-lateral frontal incisions and decortication (frontal lobotomy) produced a marked ipsilateral decrease in the noradrenergic fiber density throughout the remaining dorso-lateral cortex, while sparing the innervation of cingulate and infra-rhinal cortex.These results demonstrate that the dorso-lateral cortex is innervated by noradrenergic fibers in the medial forebrain bundle that reach the frontal pole, turn dorsally over the anterior portion of the forceps minor and continue caudally within the deep layers of frontal and dorso-lateral cortex, supplying the noradrenergic innervation throughout their trajectory. The medial cortex is innervated by a separate group of noradrenergic fibers that ascend through the septum, curve over the genu of the corpus callosum, and run caudally in the supracallosal stria.The present results show that the cingulum bundle is not a major intra-cortical noradrenergic pathway and does not provide branches that contribute significantly to the innervation of dorsal or lateral cortex. Thus the medial and lateral cortex can be selectively and differentially denervated of noradrenergic fibers and a coarse topographic order exists in the noradrenergic innervation of cortex. Since noradrenergic fibers travel long distances within the cortical grey matter, a small lesion of frontal cortex can have far-reaching effects on the innervation of distant, more caudal regions of cortex. The coeruleocortical projection has properties that differ from those of the best characterized cortical afferents and may be a useful model for the study of other ascending monoamine systems. The tangential, intracortical trajectory of the noradrenergic fibers would confer upon the coeruleo-cortical system the capacity to modulate neuronal activity simultaneously through a vast expanse of neocortex. A formulation of cortical organization is presented which integrates the tangential organization of the coeruleo-cortical projection with the concept of columnar organization of cortex.     

腰骶部SPR术中脊神经前后根定位的应用解剖

目的：为ＳＰＲ提供可靠的术中脊神经前、后根鉴别的解剖学依据。方法：在２０例成人脊柱标本上,去除后部结构,暴露整个马尾神经,对Ｌ１～Ｓ２节段的前后根进行形态学观察和测量。结果：脊神经后根位于马尾的后半部,前根则位于前半部。脊神经后根较相应的前根粗大,后根从Ｌ１～Ｓ１逐渐增大,以Ｓ１为最粗大;前根则以Ｌ３最粗大。相应前后根出硬脊膜前,有一段相互贴附并紧贴硬脊膜侧壁。结论：在多椎板切除ＳＰＲ术中前、后根的定位及鉴别,暴露时可根据前、后根出硬脊膜前的相互贴附;在限制性椎板切除时则可通过脊髓外侧索和Ｌ１前、后根之间的最下端的齿状韧带加以鉴别