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.

The goal of the present neuroanatomical study in macaque monkeys was twofold: (1) to clarify whether the hand representation of the primary motor cortex (M1) has a transcallosal projection to M1 of the opposite hemisphere; (2) to compare the topography and density of transcallosal connections for the hand representations of M1 and the supplementary motor area (SMA). The hand areas of M1 and the SMA were identified by intracortical microstimulation and then injected either with retrograde tracer substances in order to label the neurons of origin in the contralateral motor cortical areas (four monkeys) or, with an anterograde tracer, to establish the regional distribution and density of terminal fields in the opposite motor cortical areas (two monkeys). The main results were: (1) The hand representation of M1 exhibited a modest homotopic callosal projection, as judged by the small number of labeled neurons within the region corresponding to the contralateral injection. A modest heterotopic callosal projection originated from the opposite supplementary, premotor, and cingulate motor areas. (2) In contrast, the SMA hand representation showed a dense callosal projection to the opposite SMA. The SMA was found to receive also dense heterotopic callosal projections from the contralateral rostral and caudal cingulate motor areas, moderate projections from the lateral premotor cortex, and sparse projections from M1. (3) After injection of an anterograde tracer (biotinylated dextran amine) in the hand representation of M1, only a few small patches of axonal label were found in the corresponding region of M1, as well as in the lateral premotor cortex; virtually no label was found in the SMA or in cingulate motor areas. Injections of the same anterograde tracer in the hand representation of the SMA, however, resulted in dense and widely distributed axonal terminal fields in the opposite SMA, premotor cortex, and cingulate motor areas, while labeled terminals were clearly less dense in M1. It is concluded that the hand representations of the SMA and M1 strongly differ with respect to the strength and distribution of callosal connectivity with the former having more powerful and widespread callosal connections with a number of motor fields of the opposite cortex than the latter. These anatomical results support the proposition of the SMA being a bilaterally organized system, possibly contributing to bimanual coordination.

Progress continues in the development of reparative interventions to enhance recovery after experimental spinal cord injury (SCI). Here we discuss to what extent rodent models of SCI have limitations for ensuring the efficacy and safety of treatments for humans, and under what circumstances it would be advantageous or necessary to test treatments in nonhuman primates before clinical trials. We discuss crucial differences in the organization of the motor systems and behaviors among rodents, nonhuman primates and humans, and argue that studies in nonhuman primates are critical for the translation of some potential interventions to treat SCI in humans.Traumatic SCI has long-term health, economic and social consequences worldwide 1,2 , giving a sense of the urgency to the development of ways to treat it. Treatments that lead to at least partial functional recovery after SCI can substantially improve the quality of life of affected individuals. Consequently, there is considerable need to take to the clinic those interventions that have shown effectiveness in promoting functional improvement in laboratory animals.Progress continues in the identification of interventions that augment plasticity after injury by promoting axonal regeneration and sprouting in rodents [3][4][5][6] . Some of these treatments may be efficacious in patients with SCI, and have or are entering phase 1 clinical trials. Important differences exist, however, between the nervous systems of rodents and humans,

The mechanisms of recovery of manual dexterity after unilateral lesion of the sensorimotor cortex in adult primates remain a matter of debate. It has been proposed that the cortical zone adjacent to the lesion may take over part of the function of the damaged cortex. To investigate further this possibility, two adult (4-5 years old) macaque monkeys were trained to perform a natural precision-grip task to assess hand dexterity. Intracortical microstimulations (ICMS) were used to map the hand area in M1 on both hemispheres. Ibotenic acid was then injected intracortically to damage the representation in M1 of the preferred hand. Subsequent histological analysis indicated that the hand representation in M1 was indeed lesioned, but, due to a spread of ibotenic acid, the lesion encroached a significant extent of the hand representation in the primary somatosensory cortex. A few minutes after infusion of ibotenic acid, there was a complete loss of dexterity of the preferred hand, which lasted for 1-2 months. Later, a progressive functional recovery of the affected hand took place over a 3- to 4-month period, reaching a stable level corresponding to 30% of the pre-lesion behavioral score. ICMS remapping, conducted nine months after the lesion, revealed that stimulation of the intact or lesioned M1 did not induce any visible movement of the recovered hand. The M1 hand representation on the intact hemisphere was similar to that observed before the lesion. Transient inactivation of the M1 hand/arm areas or of the dorsal and ventral premotor cortical areas (PM) on both hemispheres was undertaken by using microinjections of the GABA-agonist muscimol. Inactivations of M1 had no effect. Inhibition of PM in the damaged hemisphere suppressed the recovered manual dexterity of the affected hand. These results suggest that PM plays a significant role in the incomplete functional recovery of hand dexterity following unilateral damage of the sensorimotor cortex in adult monkeys.

Multisensory and sensorimotor integrations are usually considered to occur in superior colliculus and cerebral cortex, but few studies proposed the thalamus as being involved in these integrative processes. We investigated whether the organization of the thalamocortical (TC) systems for different modalities partly overlap, representing an anatomical support for multisensory and sensorimotor interplay in thalamus. In 2 macaque monkeys, 6 neuroanatomical tracers were injected in the rostral and caudal auditory cortex, posterior parietal cortex (PE/PEa in area 5), and dorsal and ventral premotor cortical areas (PMd, PMv), demonstrating the existence of overlapping territories of thalamic projections to areas of different modalities (sensory and motor). TC projections, distinct from the ones arising from specific unimodal sensory nuclei, were observed from motor thalamus to PE/PEa or auditory cortex and from sensory thalamus to PMd/PMv. The central lateral nucleus and the mediodorsal nucleus project to all injected areas, but the most significant overlap across modalities was found in the medial pulvinar nucleus. The present results demonstrate the presence of thalamic territories integrating different sensory modalities with motor attributes. Based on the divergent/convergent pattern of TC and corticothalamic projections, 4 distinct mechanisms of multisensory and sensorimotor interplay are proposed.