Recruitment of Reticulospinal Neurones and Steady Locomotion in Lamprey

Neural Networks : the Official Journal of the International Neural Network Society. Aug, 1998  |  Pubmed ID: 12662770

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.

Origins of Callosal Projections to the Supplementary Motor Area (SMA): a Direct Comparison Between Pre-SMA and SMA-proper in Macaque Monkeys

The Journal of Comparative Neurology. Jan, 2002  |  Pubmed ID: 11793348

The two subdivisions of the supplementary motor area (SMA), the pre-SMA (rostrally) and SMA-proper (caudally), exhibit distinct functional properties and clear differences with respect to their connectivity with the spinal cord, the thalamus, and other homolateral motor cortical areas. The goal of the present study was to establish in monkeys whether these subdivisions also differ with regard to their callosal connectivity. Two fluorescent retrograde tracers (Fast Blue and Diamidino Yellow) were injected in each animal, one in the pre-SMA and the second in the SMA-proper. Tracer injections in the pre-SMA or in SMA-proper resulted in significant numbers of labeled neurons in the opposite SMA, premotor cortex (PM), cingulate motor areas (CMA), and cingulate gyrus. Labeled neurons in M1 were rare, being observed only after injection in the SMA-proper. The two subdivisions of the SMA differed in the proportion of labeled neurons found across areas providing their callosal inputs. The SMA-proper receives about half of its callosal inputs from its counterpart in the other hemisphere (42-65% across monkeys). A comparable proportion of neurons was found in the pre-SMA after injection in the opposite pre-SMA (32-47%). The pre-SMA receives more callosal inputs from the rostral halves of the dorsal PM, the ventral PM, and the CMA than from their caudal halves. In addition, the pre-SMA, but not the SMA-proper, receives callosal inputs from the prefrontal cortex. The SMA-proper receives more callosal inputs from the caudal halves of the dorsal PM and ventral PM than from their rostral halves. The two subdivisions of the SMA receive callosal inputs from the same cortical areas (except the prefrontal cortex and M1), but they differ with respect to the quantitative contribution of each area of origin. In conclusion, quantitative data now support the notion that pre-SMA receives more transcallosal inputs than the SMA-proper.

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

Brain Research. Aug, 2004  |  Pubmed ID: 15261113

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.

Divergence and Convergence of Thalamocortical Projections to Premotor and Supplementary Motor Cortex: a Multiple Tracing Study in the Macaque Monkey

The European Journal of Neuroscience. Feb, 2005  |  Pubmed ID: 15787707

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.

Primate Adult Brain Cell Autotransplantation, a New Tool for Brain Repair?

Experimental Neurology. Nov, 2005  |  Pubmed ID: 15913609

If successful, autologous brain cell transplantation is an attractive approach to repair lesions and restore function of the central nervous system. We demonstrate that monkey adult brain cells obtained from cortical biopsy and kept in culture for 4 weeks exhibit neural progenitor characteristics. After reimplantation into a lesion area of the donor cerebral cortex, these cells can successfully survive and acquire neuronal characteristics over time. These results open new perspectives in the field of brain repair and may lead to future clinical applications.

Reduction of the Hand Representation in the Ipsilateral Primary Motor Cortex Following Unilateral Section of the Corticospinal Tract at Cervical Level in Monkeys

BMC Neuroscience. 2005  |  Pubmed ID: 16135243

After sub-total hemi-section of cervical cord at level C7/C8 in monkeys, the ipsilesional hand exhibited a paralysis for a couple of weeks, followed by incomplete recovery of manual dexterity, reaching a plateau after 40-50 days. Recently, we demonstrated that the level of the plateau was related to the size of the lesion and that progressive plastic changes of the motor map in the contralesional motor cortex, particularly the hand representation, took place following a comparable time course. The goal of the present study was to assess, in three macaque monkeys, whether the hand representation in the ipsilesional primary motor cortex (M1) was also affected by the cervical hemi-section.

Callosal Connections of Dorsal Versus Ventral Premotor Areas in the Macaque Monkey: a Multiple Retrograde Tracing Study

BMC Neuroscience. 2005  |  Pubmed ID: 16309550

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.

Intrathecally Infused Antibodies Against Nogo-A Penetrate the CNS and Downregulate the Endogenous Neurite Growth Inhibitor Nogo-A

Molecular and Cellular Neurosciences. May-Jun, 2006  |  Pubmed ID: 16697217

Neutralizing antibodies against the neurite growth inhibitory protein Nogo-A are known to induce regeneration, enhance compensatory growth, and enhance functional recovery. In intact adult rats and monkeys or spinal cord injured adult rats, antibodies reached the entire spinal cord and brain through the CSF circulation from intraventricular or intrathecal infusion sites. In the tissue, anti-Nogo antibodies were found inside Nogo-A expressing oligodendrocytes and neurons. Intracellularly, anti-Nogo-A antibodies were colocalized with endogenous Nogo-A in large organels, some of which containing the lysosomal marker cathepsin-D. This suggests antibody-induced internalization of cell surface Nogo-A. Total Nogo-A tissue levels in spinal cord were decreased in intact adult rats following 7 days of antibody infusion. This mechanism was confirmed in vitro; cultured oligodendrocytes and neurons had lower Nogo-A contents in the presence of anti-Nogo-A antibodies. These results demonstrate that antibodies against a CNS cell surface protein reach their antigen through the CSF and can induce its downregulation.

Nogo-A-specific Antibody Treatment Enhances Sprouting and Functional Recovery After Cervical Lesion in Adult Primates

Nature Medicine. Jul, 2006  |  Pubmed ID: 16819551

In rodents, after spinal lesion, neutralizing the neurite growth inhibitor Nogo-A promotes axonal sprouting and functional recovery. To evaluate this treatment in primates, 12 monkeys were subjected to cervical lesion. Recovery of manual dexterity and sprouting of corticospinal axons were enhanced in monkeys treated with Nogo-A-specific antibody as compared to monkeys treated with control antibody.

Anti-Nogo-A Antibody Treatment Enhances Sprouting of Corticospinal Axons Rostral to a Unilateral Cervical Spinal Cord Lesion in Adult Macaque Monkey

The Journal of Comparative Neurology. Jun, 2007  |  Pubmed ID: 17394135

After injury, regrowth of axons in mammalian adult central nervous system is highly limited. However, in monkeys subjected to unilateral cervical lesion (C7-C8 level), neutralization of an important neurite outgrowth inhibitor, Nogo-A, stimulated axonal sprouting caudal to the lesion, accompanied by enhanced functional recovery of manual dexterity, compared with lesioned monkeys treated with a control antibody (Freund et al. [2006] Nat. Med. 12:790-792). The present study aimed at comparing the same two groups of monkeys for axonal sprouting rostral to the cervical lesion. The corticospinal tract was labeled by injecting the anterograde tracer biotinylated dextran amine into the contralesional motor cortex. The corticospinal axons were interrupted at the level of the lesion, accompanied by retrograde axonal degeneration (axon dieback), reflected by the presence of terminal retraction bulbs. The number of terminal retraction bulbs was lower in anti-Nogo-A antibody treated monkeys, and, when present, they were found closer to the lesion than in control-antibody treated monkeys. Compared with control antibody treated monkeys, the anti-Nogo-A antibody treated monkeys exhibited an increased cumulated axon arbor length and a higher number of axon arbors going in the medial direction from the white to the gray matter. Higher in the cervical cord (at C5 level), the anti-Nogo-A treatment enhanced the number of corticospinal fibers crossing the midline, suggesting axonal sprouting. Thus, the anti-Nogo-A antibody treatment enhanced axonal sprouting rostral to the cervical lesion; some of these fibers grew around the lesion and into the caudal spinal segments. These processes paralleled the observed improved functional recovery.

Can Experiments in Nonhuman Primates Expedite the Translation of Treatments for Spinal Cord Injury in Humans?

Nature Medicine. May, 2007  |  Pubmed ID: 17479102

Anti-Nogo-A Antibody Treatment Does Not Prevent Cell Body Shrinkage in the Motor Cortex in Adult Monkeys Subjected to Unilateral Cervical Cord Lesion

BMC Neuroscience. 2008  |  Pubmed ID: 18194520

After unilateral cervical cord lesion at the C7/C8 border interrupting the dorsolateral funiculus in adult monkeys, neutralization of Nogo-A using a specific monoclonal antibody promoted sprouting of corticospinal (CS) axons rostral and caudal to the lesion and, in parallel, improved functional recovery. In monkeys lesioned but not treated with the anti-Nogo-A antibody, the CS neurons in the contralesional primary motor cortex (M1) survived to the axotomy, but their soma shrank. Because the anti-Nogo-A treatment induces regeneration and/or sprouting of CS axons, it may improve access to neurotrophic factors. The question therefore arises as to whether anti-Nogo-A treatment prevents the soma shrinkage observed in the contralesional M1?

Anti-Nogo-A Antibody Treatment Promotes Recovery of Manual Dexterity After Unilateral Cervical Lesion in Adult Primates--re-examination and Extension of Behavioral Data

The European Journal of Neuroscience. Mar, 2009  |  Pubmed ID: 19291225

In rodents and nonhuman primates subjected to spinal cord lesion, neutralizing the neurite growth inhibitor Nogo-A has been shown to promote regenerative axonal sprouting and functional recovery. The goal of the present report was to re-examine the data on the recovery of the primate manual dexterity using refined behavioral analyses and further statistical assessments, representing secondary outcome measures from the same manual dexterity test. Thirteen adult monkeys were studied; seven received an anti-Nogo-A antibody whereas a control antibody was infused into the other monkeys. Monkeys were trained to perform the modified Brinkman board task requiring opposition of index finger and thumb to grasp food pellets placed in vertically and horizontally oriented slots. Two parameters were quantified before and following spinal cord injury: (i) the standard 'score' as defined by the number of pellets retrieved within 30 s from the two types of slots; (ii) the newly introduced 'contact time' as defined by the duration of digit contact with the food pellet before successful retrieval. After lesion the hand was severely impaired in all monkeys; this was followed by progressive functional recovery. Remarkably, anti-Nogo-A antibody-treated monkeys recovered faster and significantly better than control antibody-treated monkeys, considering both the score for vertical and horizontal slots (Mann-Whitney test: P = 0.05 and 0.035, respectively) and the contact time (P = 0.008 and 0.005, respectively). Detailed analysis of the lesions excluded the possibility that this conclusion may have been caused by differences in lesion properties between the two groups of monkeys.

A Case of Polymicrogyria in Macaque Monkey: Impact on Anatomy and Function of the Motor System

BMC Neuroscience. 2009  |  Pubmed ID: 20030837

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).