Callosal connections of dorsal versus ventral premotor areas in the macaque monkey: a multiple retrograde tracing study

BACKGROUND: The lateral premotor cortex plays a crucial role in visually guided limb movements. It is divided into two main regions, the dorsal (PMd) and ventral (PMv) areas, which are in turn subdivided into functionally and anatomically distinct rostral (PMd-r and PMv-r) and caudal (PMd-c and PMv-c) sub-regions. We analyzed the callosal inputs to these premotor subdivisions following 23 injections of retrograde tracers in eight macaque monkeys. In each monkey, 2–4 distinct tracers were injected in different areas allowing direct comparisons of callosal connectivity in the same brain. RESULTS: Based on large injections covering the entire extent of the corresponding PM area, we found that each area is strongly connected with its counterpart in the opposite hemisphere. Callosal connectivity with the other premotor areas, the primary motor cortex, prefrontal cortex and somatosensory cortex varied from one area to another. The most extensive callosal inputs terminate in PMd-r and PMd-c, with PMd-r strongly connected with prefrontal cortex. Callosal inputs to PMv-c are more extensive than those to PMv-r, whose connections are restricted to its counterpart area. Quantitative analysis of labelled cells confirms these general findings, and allows an assessment of the relative strength of callosal inputs. CONCLUSION: PMd-r and PMv-r receive their strongest callosal inputs from their respective counterpart areas, whereas PMd-c and PMv-c receive strong inputs from heterotopic areas as well (namely from PMd-r and PMv-r, respectively). Finally, PMd-r stands out as the lateral premotor area with the strongest inputs from the prefrontal cortex, and only the PMd-c and PMv-c receive weak callosal inputs from M1

A case of polymicrogyria in macaque monkey: impact on anatomy and function of the motor system

Background: Polymicrogyria is a malformation of the cerebral cortex often resulting in epilepsy or mental retardation. It remains unclear whether this pathology affects the structure and function of the corticospinal (CS) system. The anatomy and histology of the brain of one macaque monkey exhibiting a spontaneous polymicrogyria (PMG monkey) were examined and compared to the brain of normal monkeys. The CS tract was labelled by injecting a neuronal tracer (BDA) unilaterally in a region where low intensity electrical microstimulation elicited contralateral hand movements (presumably the primary motor cortex in the PMG monkey). Results: The examination of the brain showed a large number of microgyri at macro- and microscopic levels, covering mainly the frontoparietal regions. The layered cortical organization was locally disrupted and the number of SMI-32 stained pyramidal neurons in the cortical layer III of the presumed motor cortex was reduced. We compared the distribution of labelled CS axons in the PMG monkey at spinal cervical level C5. The cumulated length of CS axon arbors in the spinal grey matter was not significantly different in the PMG monkey. In the red nucleus, numerous neurons presented large vesicles. We also assessed its motor performances by comparing its capacity to execute a complex reach and grasp behavioral task. The PMG monkey exhibited an increase of reaction time without any modification of other motor parameters, an observation in line with a normal CS tract organisation. Conclusion: In spite of substantial cortical malformations in the frontal and parietal lobes, the PMG monkey exhibits surprisingly normal structure and function of the corticospinal system

Behavioral Assessment of Manual Dexterity in Non-Human Primates

The corticospinal (CS) tract is the anatomical support of the exquisite motor ability to skillfully manipulate small objects, a prerogative mainly of primates1. In case of lesion affecting the CS projection system at its origin (lesion of motor cortical areas) or along its trajectory (cervical cord lesion), there is a dramatic loss of manual dexterity (hand paralysis), as seen in some tetraplegic or hemiplegic patients. Although there is some spontaneous functional recovery after such lesion, it remains very limited in the adult. Various therapeutic strategies are presently proposed (e.g. cell therapy, neutralization of inhibitory axonal growth molecules, application of growth factors, etc), which are mostly developed in rodents. However, before clinical application, it is often recommended to test the feasibility, efficacy, and security of the treatment in non-human primates. This is especially true when the goal is to restore manual dexterity after a lesion of the central nervous system, as the organization of the motor system of rodents is different from that of primates1,2. Macaque monkeys are illustrated here as a suitable behavioral model to quantify manual dexterity in primates, to reflect the deficits resulting from lesion of the motor cortex or cervical cord for instance, measure the extent of spontaneous functional recovery and, when a treatment is applied, evaluate how much it can enhance the functional recovery

From the Square Lattice to the Checkerboard Lattice : Spin Wave and Large-n Analysis

Within a spin wave analysis and a fermionic large-n limit, it is shown that the antiferromagnetic Heisenberg model on the checkerboard lattice may have different ground states, depending on the spin size $S$. Through an additional exchange interaction that corresponds to an inter-tetrahedra coupling, the stability of the N\'eel state has been explored for all cases from the square lattice to the isotropic checkerboard lattice. Away from the isotropic limit and within the linear spin wave approximation, it is shown that there exists a critical coupling for which the local magnetization of the N\'eel state vanishes for any value of the spin $S$. One the other hand, using the Dyson-Maleev approximation, this result is valid only in the case $S= \frac12$ and the limit between a stable and an unstable N\'eel state is at S=1. For $S= \frac12$, the fermionic large-n limit suggests that the ground state is a valence bond solid build with disconnected 4-spins singlets. This analysis indicates that for low spin and in the isotropic limit, the checkerboard antiferromagnet may be close to an instability between an ordered S=0 ground state and a magnetized ground state.Comment: 9 pages (revtex two column), 11 figures. Higher quality figures are available at http://benjamin.canals.free.fr/ukpublications.html Version to be published in Phys. Rev.

A unilateral section of the corticospinal tract at cervical level in Primate does not lead to measurable cell loss in Motor cortex

The effects of a unilateral interruption of the dorsolateral funiculus at cervical level on the survival of neurons in the motor cortex were investigated in macaque monkeys. The lesion was made on the left side at the transition region between the 7th and 8th cervical segments, above the motoneurons controlling hand muscles. As a result, the homolateral hand became paretic, although an incomplete recovery of manual dexterity took place during 2 months post-lesion. A quantitative anatomical assessment of pyramidal neurons in layer V was performed in the hindlimb area of the primary motor cortex and in the supplementary motor area (SMA proper). The pyramidal neurons were visualized using the marker SMI-32 and thus included the subpopulation of corticospinal neurons. These quantitative data demonstrated that the vast majority of the axotomized corticospinal (CS) neurons did not degenerate. Rather, their somata shrank, compared to the opposite hemisphere or to intact monkeys. This conclusion is in contrast to some previous studies in monkeys that argued for a substantial degeneration of motor cortex neurons as a result of transection of the corticospinal tract; yet in agreement with others that concluded the survival of most CS neurons. The survival of the majority of CS axotomized neurons is also consistent with the observation of numerous CS axons 1 mm above the cervical hemisection

Recruitment of reticulospinal neurones and steady locomotion in lamprey

In lamprey, the supraspinal control of velocity is mainly accomplished by the reticulospinal (RS) system. During locomotion, RS neurones are rhythmically active with a cycle duration corresponding to the duration of the swim cycle. While the velocity of the muscular contraction wave changes as swimming velocity changes, the conduction velocity of RS axons remains constant. Thus, an action potential generated during a specific phase of the swim cycle will, depending on swimming velocity, provide input to a particular downstream segment during different phases of its rhythmic activity. In order to investigate the importance of this effect for the control of locomotion, the temporal and spatial characteristics of the propagation of the population of action potentials along RS axons in the spinal cord were investigated. The results suggest that if RS neurones are recruited independently of their sizes and conduction velocities, a phasic wave of action potentials in these fibers will reach some segments during the inhibited phase of their rhythmic activity. Such an input could hinder a smooth propagation of the contraction wave and disrupt swimming. In contrast, by recruiting successively larger and hence more rapidly conducting neurones for successively more rapid swimming, the phasic wave of action potentials may propagate with the same velocity as that of the muscular contraction wave. Under such conditions, reticulospinal activity would support and stabilise locomotion

Progressive plastic changes in the hand representation of the primary motor cortex parallel incomplete recovery from a unilateral section of the corticospinal tract at cervical level in monkeys

After a sub-total hemisection of the cervical cord at level C7/C8 in monkeys, a paralysis of the homolateral hand is rapidly followed by an incomplete recovery of manual dexterity, reaching a plateau after about 40–50 days, whose extent appears related to the size of the lesion. During a few days after the lesion, the hand representation in the contralateral motor cortex disappeared, replaced by representations of either face or more proximal body parts. Later, however, following a time course (about 40 days) consistent with the functional recovery, progressive plastic changes in the contralateral motor cortex took place, as demonstrated by a progressive reappearance of digit movements elicited by intracortical microstimulation. These progressive plastic changes, which parallel the functional recovery, correspond to a reinstallation of a hand representation, though substantially diminished in size as compared to pre-lesion. Regarding the functional recovery, the motor cortex (including the reestablished hand area) contralateral to the unilateral cervical cord lesion played a crucial role in reestablishing control on finger movements, as assessed by reversible inactivation experiments. In contrast, the motor cortex ipsilateral to the cervical cord lesion, with largely intact projections to the spinal cord, did not contribute significantly to the recovered movements by the affected hand. These observations indicate that the CS fibers spared by the lesion are not sufficient, at least in their pre-lesion condition, to control the motoneurones innervating the digit muscles and that the pathways conveying signals from the contralateral M1 underwent reorganization

Anti-Nogo-A antibody treatment enhances functional recovery and sprouting of the corticospinal tract after spinal cord injury in adult primates

Eine vollständige Rückenmarksdurchtrennung führt zu einem totalen funktionellen Verlust jeglicher willentlicher Kontrolle unterhalb der Läsion. Die Ursache für diesen Verlust ist der limitierten Zellernneuerung und der ausbleibenen axonalen Regeneration zu zuschreiben. Erste Hinweise deuten daraufhin, dass die Präsenz von Myelin-assozierten inhibitorischen Wachstumsfaktoren, wie zum Beispiel Nogo-A, dafür verantworlich sind. Eine therapeutische Massnahme um diesen inhibitorischen Effekt entgegen zu wirken, ist die Applikation von Antikörpern welche diese Stoffe neutralisieren. Am Rattenmodel wurde erfolgreich gezeigt das nach einer Rückenmarksverletzung und einer zweiwöchigen Applikation eines neutralisierendes Antikörpers gegen das Protein Nogo-A, Nervenzellen dazu stimulierten wieder auszuwachsen und funktionelle Verknüpfungen herzustellen. Diese neuen Verbindungen ermöglichten den anti-Nogo-A behandelten Tieren im Vergleich zu Unbehandelten zu einer verbesserte Motorik. Das Ziel dieser These war es zu prüfen, ob die Translation dieser therapeutischen Anwendung am Primaten bevor es zur ersten klinischen Anwendung an querschnittsgelähmten Patienten gelangt. Der Translationschritt ist in sofern unumgänglich, da er zum einen erlaubt zu prüfen, ob die Neutralsierung und die folgliche Stimulierung von Nervenwachstum nicht irrtürmlicher Weise zu falschen Verbindungen führen könnte mit heftigen Nebenwirkung als Folge und zum anderen ob die Applizierung des Antikörpers am Primaten zu wessen Gruppe der Mensch zählt, funktioniert. Insgesamt wurden 13 adulten Makaken einer unilateralen zervikalen Läsion ausgesetzt. Sieben Tiere erhielten den neutralieserendem Antikörper gegen Nogo-A während vier Wochen und die Anderen sechs Tiere erhielten eine Kontrollantikörper Behandelung. Kontrollantikörper behandelte Tiere wiesen eine läsionsgrössen-abhängige motorische Genesung für einen Dexteritätstest auf mit sehr limitertem axonalen Wachstum des Kortikospinalen Tractes kaudal der Läsion. Im scharfen Gegensatz wiesen behandelte Tiere vermehrtes axonales Wachstum und eine vollständige funktionelle Erholung für diesen spezifischen Dexteritätstest auf (Kapitel 1, 2 und 3). Desweiteren führte die Neutrilaztion von Nogo-A zu einer verstärkten Reorganization des Kortikospinalen Trakt rostral der Läsion (Kapitel 4). Auf dem Nivieau des Kortex und des Pons wurden retrograde degenerative Veränderungen gemessen anhand der Zellgrösee und Anzal von Neuronen im motrischen Kortex und im Rotem Nucleus. In beiden untersuchten Arealen kam es zu eienr deutlichen vermindureung der Zellsomagrösse auf der lädierten Seite. Im Gegensatzt zum motorischen Kortex wo kein signifikanter Unterschied von Zell Anzahl gefunden wurde gab es zudem im Roten Nucleus eine deutlich Reduzierung der Anzahl von Neuronen auf der lädierten Seite. Diese degenerativen Vorgängen wurden nicht durch die anti-Nogo-A Behandlung vermindert (Kapitel 5 und 6). Zusammengefasst zeigen die Resultate dieser These dass eine Neutralization von einem Myelin-assoziertem Protein Nogo-A nach einer Rückenmarksverletzung zu einer verbesserten Motorik und vermehrtem axonalen Wachstum auf der Höhe der Läsion im adulten Primaten fürht, in Abwesenheit von Nebenwirkungen.After injury to the adult central nervous system (CNS), permanent deficits remain to a large part due to limited cell renewal, axonal regeneration and reestablishment of functional connectivity. Evidence indicate that the lack of axonal regeneration is partly due to the myelin-associated inhibitory factor Nogo-A. A therapeutical strategy to overcome this inhibition is to prevent the neurite outgrowth inhibitor Nogo-A from interacting with its neural receptors by using antibodies specifically binding to Nogo-A, thereby neutralizing its action. Experiences in the rodent model subjected to spinal cord injury have shown that neutralizing Nogo-A, by using specific antibodies not only promotes axonal regeneration but also leads to significant functional recovery. The aim of this thesis was to investigate whether this treatment strategy also leads to axonal regeneration and functional recovery in non-human adult primates subjected to a partial section of the spinal cord. This assessment is a crucial step towards a safe clinical application. Thirteen macaque monkeys were subjected to a unilateral cervical lesion at the border between the C7 and C8 segments. A group received intrathecal injections of a control antibody whereas the other animals received a monoclonal antibody recognizing Nogo- A. Functional recovery was tested using several motor tasks mainly focusing on manual dexterity. Control antibody treated monkeys showed a recovery that depends on lesion size. In contrast, anti-Nogo-A antibody treated monkeys recovered better and even returned to pre-lesion score levels in a manual dexterity task (Chapters 2 and 3). We further investigated, using light-microscopy, if the process of functional recovery is paralleled by an anatomical reorganization of the injured corticospinal tract (CST). At the spinal level, the area rostral and caudal to injury was analyzed for axonal regeneration. Compared to control antibody treated monkeys, an enhanced number of fibers presumably due to regenerative sprouting was observed rostral to the lesion in anti-Nogo-A antibody treated monkeys. Caudal to injury, a higher cumulated axonal arbor length and a higher number of axonal swellings were observed in anti-Nogo-A treated animals (Chapters 2 and 4). We also investigated the consequences of the lesion on corticospinal (CS) and rubrospinal (RS) neurons and whether the anti-Nogo-A antibody treatment had an influence on these effects. For this purpose the number and size of CS and RS neurons were measured in both sides of the brain using light-microscopy in intact, in control antibody as well as in anti-Nogo-A antibody treated monkeys. At the level of the motor cortex the number of pyramidal neurons remains similar on both hemispheres, but their somata shrunk on the side opposite to the lesion. In this case, the neutralization of Nogo-A did not protect the cells from shrinkage. In the red nucleus, the lesion also induced shrinkage of the soma of the neurons detected in the contralesional magnocellular part of the red nucleus (RNm). In contrast to cortical level, here, the number of cells detected in the contralesional RNm was consistently lower to that in the ipsilesional RNm, suggesting either cell loss or shrinkage beyond detection. Thus, the neutralization of Nogo-A by antibody infusion at the lesion side did not prevent the phenomena of cell somata shrinkage nor cell disappearance (Chapters 5 and 6). In summary the results reported in this thesis demonstrate that the neutralization of the neurite outgrowth inhibitor Nogo-A promotes axonal regeneration on the level of the spinal cord in adult monkeys subjected to a unilateral spinal cord lesion. This effect is paralleled by significant functional recovery. However, histological changes in the red nucleus and motor cortex were not prevented or attenuated by the anti-Nogo-A antibody treatment

Divergence and convergence of thalamocortical projections to premotor and supplementary motor cortex: a multiple tracing study in the macaque monkey

The premotor cortex of macaque monkeys is currently subdivided into at least six different subareas on the basis of structural, hodological and physiological criteria. To determine the degree of divergence/convergence of thalamocortical projections to mesial [supplementary motor area (SMA)-proper and pre-SMA] and lateral (PMd-c, PMd-r, PMv-c and PMv-r) premotor (PM) subareas, quantitative analyses were performed on the distribution of retrograde labelling after multiple tracer injections in the same animal. The results demonstrate that all PM and SMA subareas receive common inputs from several thalamic nuclei, but the relative contribution of these nuclei to thalamocortical projections differs. The largest difference occurs between subareas of SMA, with much greater contribution from the mediodorsal (MD) and area X, and a smaller contribution from the ventral lateral anterior (VLa) and ventral part of the ventral lateral posterior (VLpv) to pre-SMA than to SMA-proper. In PM, differences between subareas are less pronounced; in particular, all receive a significant contribution from MD, the ventral anterior (VApc) and area X. However, there are clear gradients, such as increasing projections from MD to rostral, from VLa and VLpv to caudal, and from dorsal VLp (VLpd) to dorsal premotor subareas. Intralaminar nuclei provide widespread projections to all premotor subareas. The degree of overlap between thalamocortical projections varies among different PM and SMA subareas and different sectors of the thalamus. These variations, which correspond to different origin and topography of thalamocortical projections, are discussed in relation to functional organizations at thalamic and cortical levels