Adaptation of the layer V supraspinal motor corticofugal projections from the primary (M1) and premotor (PM) cortices after CNS motor disorders in non-human primates: A survey

Translational Neuroscience, 2024 · DOI: https://doi.org/10.1515/tnsci-2022-0342 · Published: April 25, 2024

Simple Explanation

Motor commands travel from the brain's motor areas to muscles, primarily through the corticospinal projection. Other brain structures also help control movement, influenced by motor areas via corticofugal projections. These pathways adapt after motor trauma or disease. After injuries or diseases affecting movement, the corticorubral projection decreases, and the corticoreticular projection usually decreases except after spinal cord injury, where it increases. Treatments like anti-NogoA antibodies can enhance these effects. While the corticospinal tract remains key, these other corticofugal projections also adapt and may support motor recovery. They could be targets for treatments like electrical neurostimulation.

Study Duration

3-6 months postinjury or MPTP infusion

Participants

Adult macaque monkeys divided into four groups: Intact, SCI, MCI, and PD (2-3 animals within each subgroup)

Evidence Level

Review Article

Key Findings

1
Corticorubral projections significantly decreased after motor trauma or disease, irrespective of treatment.
2
Corticoreticular projections decreased in MCI and PD groups, but increased significantly after spinal cord injury, especially with anti-NogoA antibody treatment.
3
Corticosubthalamic projections increased in the PD group, potentially compensating for the loss of dopaminergic neurons.

Research Summary

This review summarizes the complex adaptations of supraspinal motor corticofugal projections after motor trauma or disease in non-human primates. The study analyzes changes in corticoreticular, corticotectal, corticorubral, and corticosubthalamic projections following spinal cord injury, motor cortex injury, and Parkinson's disease. The most consistent finding was a downregulation of corticorubral projections, while corticoreticular projections showed variable responses depending on the type of injury. Anti-NogoA antibody treatment often amplified these changes, suggesting a role in promoting functional recovery. The study suggests that these supraspinal motor corticofugal projections, in addition to the corticospinal tract, play a role in motor adaptation and recovery. Future therapies could target these pathways to enhance functional outcomes.

Practical Implications

Therapeutic Targets

Supraspinal corticofugal projections are potential targets for clinical strategies, such as selective electrical neurostimulations, to enhance motor functional recovery.

Treatment Combinations

Electrical neurostimulation may be combined with axonal re-growth enhancement strategies and/or cellular therapies for more effective motor rehabilitation.

Personalized Rehabilitation

Therapeutic strategies should consider individual differences in spared connections and brain areas to optimize treatment approaches and promote adaptive synergy across corticofugal projection systems.

Study Limitations

1
Incomplete data for certain subgroups (e.g., untreated PD monkeys, corticofugal projections from PM in SCI monkeys)
2
Low number of animals (2–3) within each subgroup
3
Ethical constraints inherent to non-human primate studies

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