Carstens E, Trevino D L
J Comp Neurol. 1978 Nov 1;182(1):167-84. doi: 10.1002/cne.901820111.
Anatomical and electrophysiological methods were used to investigate the projections and response properties of neurons in the second cervical (C2) spinal segment of the cat giving origin to a previously undescribed projection to the ipsilateral thalamus. The method of retrograde axonal transport of horseradish peroxidase (HRP) was used to identify neurons in C2 giving rise to thalamic projections. Following large (3.0 microliter) thalamic HRP injections, a large number of labeled neurons was observed in lateral laminae VII-VIII of C2 ipsilateral to the injections. They occurred as small clusters of cells along the longitudinal axis of C2. Labeled neurons were also observed contralaterally in the lateral cervical nucleus, dorsal horn (especially medial lamina VI), and loosely distributed in the ventral horn. The ipsilaterally projecting neurons were also labeled following small (0.2--0.5 microliter) HRP injections restricted to individual spinothalamic terminal zones (intralaminar nuclei, ventrobasal complex-nucleus ventralis lateralis border zone, medial division of the posterior nuclei), indicating that as a group they project widely throughout the thalamus. Single unit recording methods were used to obtain complementary information on the functional properties of these neurons. The antidromic stimulation method was applied to identify units in C2 projecting to the ipsilateral thalamus in anesthetized, paralyzed cats. Three categories of ipsilaterally projecting C2 units were identified: (1) units not driven by any type of natural stimulation; (2) units having large cutaneous receptive fields (RFs) and wide dynamic response ranges ("widefield"), and (3) units with smaller RFs and varied properties ("other"). Widefield units with bilaterally symmetrical and asymmetrical RFs were observed. Co-stimulation of different portions of an excitatory RF produced summation of the unit response. Inhibitory RF components were identified in one-third of the widefield units. Unit recordings after spinal tract lesions revealed that the afferent input passed via the ipsilateral lateral and/or ventral funiculi. Widefield unit responses to somatosensory stimuli could be inhibited by dorsal column conditioning stimulation. Several "other" units resembled widefield units, while a second group had small RFs restricted to the C2 dermatome. Possible functional roles of the projecting C2 neurons in somatosensory and non-specific systems are discussed.
采用解剖学和电生理学方法，研究猫第二颈髓（C2）节段中发出至同侧丘脑的一种先前未描述投射的神经元的投射和反应特性。运用辣根过氧化物酶（HRP）逆行轴突运输法来识别C2节段中发出丘脑投射的神经元。在丘脑大量（3.0微升）注射HRP后，在注射同侧的C2节段VII - VIII层外侧观察到大量标记神经元。它们沿C2节段的纵轴呈小细胞簇状分布。在对侧的外侧颈核、背角（尤其是内侧VI层）也观察到标记神经元，并且在腹角呈散在分布。当将小剂量（0.2 - 0.5微升）HRP注射局限于各个脊髓丘脑终末区（板内核、腹侧基底复合体 - 腹外侧核边界区、后核内侧部）时，同侧投射的神经元也被标记，这表明它们作为一个群体广泛投射至整个丘脑。采用单单位记录方法获取关于这些神经元功能特性的补充信息。在麻醉、麻痹的猫中，应用逆向刺激法识别C2节段中投射至同侧丘脑的单位。识别出三类同侧投射的C2单位：（1）不受任何类型自然刺激驱动的单位；（2）具有大的皮肤感受野（RFs）和宽动态反应范围的单位（“宽野”单位），以及（3）具有较小RFs且特性各异的单位（“其他”单位）。观察到具有双侧对称和不对称RFs的宽野单位。对兴奋性RF的不同部分进行联合刺激可使单位反应总和。在三分之一的宽野单位中识别出抑制性RF成分。脊髓束损伤后的单位记录显示，传入输入通过同侧外侧和/或腹侧索。宽野单位对体感刺激的反应可被背柱条件刺激所抑制。一些“其他”单位类似于宽野单位，而另一组单位具有局限于C2皮节的小RFs。讨论了投射的C2神经元在体感和非特异性系统中的可能功能作用。
