Anatomical demonstration of gamma motoneurons in the cat's spinal cord

The modified Gudden method of Brodal was used in an attempt to localize anatomically the γ-motoneurons of the spinal gray matter. In thirty kittens, aged 3–12 days, various limb nerves were sectioned. The kittens were killed 2–10 days after operation and representative segments of the cord were fixed in alcohol, embedded in paraffin and subsequently cut in serial transverse sections and stained with thionine. Typically, small nerve cells with retrograde changes were found intermingled with similarly affected large α-motoneurons in Rexed's lamina IX. Since the γ-fibers of peripheral nerves are thin (< 8 μ), and based on the very likely assumption that small neurons have thin axons, it is concluded that the small neurons exhibiting retrograde changes in the present investigation were γ-motoneurons. They composed 10–15 per cent of all nerve cells in the spinal gray matter showing retrograde changes following section of limb nerves. Other small cells in lamina IX, which did not react to nerve section, were presumably interneurons.