Previous evidence from electrophysiological experiments in anaesthetized cats with a chronic lateral lesion of the lower thoracic spinal cord indicated an expansion of the functional projections of expiratory bulbospinal neurones (EBSNs) in the segment above the lesion, measured at 16 weeks post-lesion. Here we investigate connections made by the same EBSNs to motoneurones in that segment, using cross-correlations between their discharges. The connections to the internal intercostal nerve motoneurones were found to be no different from controls. However, a significant increase was found in the number of connections between EBSNs and γ motoneurones of the external intercostal nerve (8/24, compared to 1/16) with possibly additional connections to the α motoneurones of the same nerve. Increased connections to the γ motoneurones of the internal intercostal nerve could not be ruled out. The expanded functional projections are thus likely to include new connections to γ motoneurones. We suggest that γ motoneurones may be inherently more receptive to new inputs. If so, the previously discounted role of abnormal fusimotor discharges in motor disorders would be worth reconsideration.

先前来自具有下胸脊髓慢性侧向病变的麻醉猫的电生理学实验的证据表明，在病变后 16 周测量，呼气球脊髓神经元 (EBSN) 在病变上方部分的功能投射扩大。在这里，我们研究了相同 EBSN 与该部分中运动神经元的连接，使用它们放电之间的互相关。发现与内部肋间神经运动神经元的连接与对照没有区别。然而，发现 EBSN 与肋间外神经的 γ 运动神经元之间的连接数量显着增加（8/24，与 1/16 相比），可能与同一神经的 α 运动神经元有额外的连接。不能排除与内肋间神经的 γ 运动神经元的连接增加。因此，扩展的功能预测可能包括与 γ 运动神经元的新连接。我们认为 γ 运动神经元可能天生更容易接受新的输入。如果是这样，先前被忽视的异常融合运动放电在运动障碍中的作用将值得重新考虑。