Cognitive, Behavioral, and Systems NeuroscienceResearch PaperQuantitative inter-segmental and inter-laminar comparison of corticospinal projections from the forelimb area of the primary motor cortex of macaque monkeys
Research Highlights
▶Primate M1 controls spinal motoneurons and rostrally located interneurons in parallel. ▶Commissural corticospinal axons are abundant in C4–C8 segments. ▶Uncrossed corticospinal fibers mostly cross the midline at the spinal level.
Section snippets
Animals
Five rhesus monkeys (Macaca mulatta; Mo1: male, 4.15 kg, 3 y 4 mon; Mo2: female, 4.35 kg, 4 y 6 mon; Mo3: female, 3.4 kg, 3 y 2 mon; Mo4: female 3.4 kg, 3 y 1 mon; Mo5: male 4.3 kg, 4 y 5 mon, all at the time of BDA injection) were used in the present study. The experiments were subjected to prior reviews by the ethical committee of the National Institutes of Natural Science and were performed in accordance with the guideline of the Ministry of Education, Culture, Sports, Science and Technology
Injection site
The core of the injection site was determined by the distribution of the bulk of the BDA reaction product and by the needle tracks. Closed circles on the brain sections shown in Fig. 1A–E indicate the identified core of the injection sites in Mo1–5, respectively. The injection sites in Mo1, 2 and 5 were distributed both in the anterior bank of the CS and the convexity, while those in Mo3 and 4 were distributed more medially and more rostrally, mainly in the convexity and partly extended into
Discussion
In this study, we performed a systematic quantitative analysis of the axon branching and distribution of terminal buttons of corticospinal fibers originating from the restricted forelimb area of M1 in the individual laminae of the gray matter from the C2 to Th2 segments of the spinal cord of the macaque monkey. Using a similar method, a recent study by Rosenzweig et al. (2009) showed corticospinal projection to the cervical segments in monkeys by using BDA as an anterograde tracer. In their
Conclusion
In addition to the direct cortico-motoneuronal connection to the lateral motor nuclei at the C7–Th1 segments, the corticospinal neurons in the forelimb area of the primary motor cortex project to the spinal cord interneuronal population in the contralateral intermediate zone and ipsilateral lamina VIII distributed a few segments rostral to the motoneuronal projections.
Acknowledgments
We are grateful to Drs. Noriyuki Higo and Yumi Murata for their contribution to the experiments and helpful discussions, to Drs. Kazuhiko Seki and Tomohiko Takei for valuable comments on an earlier version of the manuscript and to Dr. Y. Abe and Dr. S. Goto (Institute of Wild Animals) for care of the animals. We also thank Kaoru Isa for assistance in histological processing. This study was supported by the Core Research for Evolutionary Science and Technology (CREST) of Japanese Science and
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Present address: Department of Physiology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.