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.     

Aminergic and cholinergic afferents to REM sleep induction regions of the pontine reticular formation in the rat

Microinjection of cholinergic agonists in a dorsolateral part of the mesopontine tegmentum has been shown to induce a rapid eye movement (REM) sleep-like state. Physiological evidence indicates that not only acetylcholine but also various amine transmitters, including those implicated in behavioral state regulation, affect neuronal activity in this region of the pontine reticular formation. In the present study, sources of select aminergic and cholinergic inputs to this REM sleep induction zone were identified and quantitatively analyzed by using fluorescence retrograde tracing combined with immunofluorescence in the rat. In addition to previously demonstrated cholinergic projections from the pedunculopontine and laterodorsal tegmental nuclei, the REM sleep induction zone received various aminergic inputs that originated in widely distributed regions of the brainstem and hypothalamus. Serotoninergic afferents represented a mean of 44% of all aminergic/cholinergic source neurons projecting to the REM sleep induction zone, which was comparable to the mean percentage of 39% represented by cholinergic afferent neurons. The serotoninergic afferents originated from the raphe nuclei at all brainstem levels, with heavier projections from the pontine than from the medullary raphe nuclei. Unexpectedly, an additional major serotoninergic input was provided by serotoninergic neurons in the nucleus prosupralemniscus (B9). Noradrenergic afferent neurons represented a mean of 14% of all aminergic/cholinergic source neurons, which was only about one-third of the mean percentage of either cholinergic or serotoninergic source neurons. These noradrenergic projection neurons were located not only in the locus ceruleus (8%) but also in the lateral tegmentum, including the A5 (4%) and A7 (2%) cell groups. Histaminergic neurons in the tuberomammillary hypothalamic nucleus represented a minor group of afferent neurons (3%), and a still smaller input came from adrenegic C1 neurons. The pattern of these transmitter-specific afferent connections appeared to be similar regardless of the longitudinal level within the REM sleep induction zone. The present results are consistent with previous behavioral and physiological evidence for a role of the pontine REM sleep induction zone in triggering REM sleep. The regulation of REM sleep induction would be best understood in terms of a state-dependent interplay of cholinergic, serotoninergic, and other inputs all acting convergently upon neurons in the REM sleep-inducing region of the pontine reticular formation.     

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.     

中指近节背侧岛状皮瓣

介绍中指近节背侧岛状皮瓣的应用解剖,该皮瓣的营养动脉为第2掌背动脉,位置表浅,解剖容易,安全可靠。自1990年11月以来,应用该皮瓣修复手部软组织缺损共6例,均获成功。     

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.     

Spinal cord transplants enhance the recovery of locomotor function after spinal cord injury at birth

Summary Fetal spinal cord transplants placed into the site of a neonatal spinal cord lesion alter the response of immature CNS neurons to injury. The transplants prevent the retrograde cell death of immature axotomized neurons and support the growth of axons into and through the site of injury. In the present experiments we used a battery of locomotor tasks to determine if these transplants are also capable of promoting the recovery of motor function after spinal cord injury at birth. Embryonic (E14) spinal cord transplants were placed into the site of a spinal cord over-hemisection in rat pups. Three groups of animals were used: 1) normal control animals, 2) animals with a spinal cord hemisection only, and 3) animals with a spinal cord transplant at the site of the hemisection. Eight to twelve weeks later, the animals were trained and videotaped while crossing runways requiring accurate foot placement and footprinted while walking on a treadmill. The videotapes and footprints were analyzed to obtain quantitative measures of locomotor function. Footprint analysis revealed that the animals' base of support during locomotion was increased by a neonatal hemisection. The base of support in animals with transplants was similar to control values. Animals with a hemisection rotated their hindlimbs further laterally than did control animals during locomotion. A transplant at the site of injury modified this response. Normal animals were able to cross a grid runway quickly with only a few errors. In contrast, animals with a hemisection took a longer time and made more errors while crossing. The presence of a transplant at the site of injury enabled the animals to cross the grid more quickly and to make fewer errors than the animals with a hemisection only. Animals that received the transplants demonstrated qualitative and quantitative improvements in several parameters of locomotion. Spinal cord transplants at the site of neonatal spinal cord injury result in enhanced sparing or recovery of motor function. We suggest that this transplant induced recovery of function is a consequence of the anatomical plasticity elicited by the transplants.     

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)