Djouhri L, Jankowska E
Department of Preclinical Veterinary Sciences, University of Edinburgh, Summerhall, UK.
Exp Brain Res. 1998 Mar;119(1):39-46. doi: 10.1007/s002210050317.
The possibility of collateral segmental actions of spinocervical tract (SCT) neurones upon interneurones with input from cutaneous and group II muscle afferents was investigated in deeply anaesthetized cats. To this end, intracellular and/or extracellular recordings were made from 35 dorsal horn and 15 intermediate zone interneurones in midlumbar segments of the spinal cord and effects of stimulation of the ipsilateral dorso-lateral funiculus (DLF) at C3 and C1 levels, i.e. below and above the lateral cervical nucleus where axons of SCT cells terminate, were compared. The stimuli applied at the C3 segment were within the range of stimuli (50-100 microA) required for antidromic activation of SCT neurones in the same experiment. Those applied at the C segment (200-500 microA) were at least 3 times stronger than C3 stimuli. Under the same experimental conditions, long ascending and descending tract neurones (dorsal spino-cerebellar and rubro-spinal tract neurones) with axons in the DLF were activated at similar thresholds from the C and C3 segments. Intracellular recordings were made from 29 interneurones of which 19 (65%) were dorsal horn and 10 (35%) were intermediate zone interneurones. Excitatory postsynaptic potentials (EPSPs) evoked by single stimuli applied at the C3 segment, but not the C segment, were found in 14 (48%) of those interneurones; their latencies (3.0-5.7 ms) and frequency following with only minimal temporal facilitation were as required for potentials being evoked monosynaptically by the fastest conducting SCT neurones. Extracellular recordings were made from 30 interneurones (24 dorsal horn and 6 intermediate zone interneurones), and in these neurones spike potentials induced from the C3, but not from the C segment, were evoked only by short trains of stimuli. However, their latencies from the first effective stimulus (4.3-5.4 ms) were compatible with mono- or oligosynaptically mediated collateral actions of SCT neurones. They were found in 10 (33%) of the 30 investigated interneurones. Similar effects of C3 stimuli were found in similar proportions of dorsal horn interneurones and intermediate zone interneurones. Indications were also found for synaptic actions evoked by C3 stimuli that could not be attributed to direct collateral actions of SCT neurones. In some intracellularly recorded dorsal horn interneurones, short-latency EPSPs were evoked from the C3 segment by the 2nd or 3rd stimulus in the train, but not by single stimuli. In other dorsal horn and intermediate zone interneurones, inhibitory postsynaptic potentials (IPSPs) were evoked from the C3 segment at minimal latencies (2.7-3.2 ms), which might be too short to allow their mediation via SCT neurones. We conclude that SCT neurones might be used to forward information from muscle group II and cutaneous afferents not only to neurones in the lateral cervical nucleus and via them to thalamus and cerebral cortex but also to interneurones in spinal reflex pathways. Thereby reflex actions evoked from group II and cutaneous afferents might be co-ordinated with responses mediated by supraspinal neurones. We conclude also that dorsal horn and intermediate zone mid-lumbar interneurones might contribute to the previously reported di-and poly-synaptic excitation or inhibition of postsynaptic dorsal column (PSDC), spinothalamic tract (STT) and spinomesencephalic tract (SMT) neurones by collateral actions of SCT cells. Thereby these interneurones might contribute to the co-ordination of responses mediated by various populations of supraspinal neurones.
在深度麻醉的猫身上，研究了脊髓颈段（SCT）神经元对来自皮肤和II类肌传入纤维的中间神经元的侧支节段性作用的可能性。为此，在脊髓腰段中部的35个背角中间神经元和15个中间带中间神经元进行了细胞内和/或细胞外记录，并比较了在C3和C1水平刺激同侧背外侧索（DLF）的效果，即SCT细胞轴突终止的外侧颈核下方和上方。在同一实验中，在C3节段施加的刺激在SCT神经元逆向激活所需的刺激范围内（50 - 100微安）。在C节段施加的刺激（200 - 500微安）比C3刺激至少强3倍。在相同的实验条件下，轴突位于DLF的长的升、降束神经元（背脊髓小脑束和红核脊髓束神经元）从C和C3节段以相似的阈值被激活。对29个中间神经元进行了细胞内记录，其中19个（65%）是背角中间神经元，10个（35%）是中间带中间神经元。在这些中间神经元中的14个（48%）中发现了由C3节段而非C节段施加的单个刺激诱发的兴奋性突触后电位（EPSP）；它们的潜伏期（3.0 - 5.7毫秒）和跟随频率仅伴有最小的时间易化，符合由传导最快的SCT神经元单突触诱发电位的要求。对30个中间神经元进行了细胞外记录（24个背角中间神经元和6个中间带中间神经元），在这些神经元中，仅由短串刺激诱发了来自C3节段而非C节段的锋电位。然而，它们从第一个有效刺激开始的潜伏期（4.3 - 5.4毫秒）与SCT神经元单突触或寡突触介导的侧支作用相符。在30个被研究的中间神经元中的10个（33%）中发现了这种情况。在背角中间神经元和中间带中间神经元中，以相似比例发现了C3刺激的类似效果。还发现了一些由C3刺激诱发的、不能归因于SCT神经元直接侧支作用的突触作用迹象。在一些细胞内记录的背角中间神经元中，串刺激中的第二个或第三个刺激从C3节段诱发了短潜伏期的EPSP，但单个刺激未诱发。在其他背角和中间带中间神经元中，从C3节段以最小潜伏期（2.7 - 3.2毫秒）诱发了抑制性突触后电位（IPSP），其潜伏期可能太短，无法通过SCT神经元介导。我们得出结论，SCT神经元可能不仅用于将来自II类肌和皮肤传入纤维的信息传递给外侧颈核中的神经元，并通过它们传递给丘脑和大脑皮层，还用于传递给脊髓反射通路中的中间神经元。因此，由II类肌和皮肤传入纤维诱发的反射作用可能与脊髓上神经元介导的反应相协调。我们还得出结论，背角和腰段中间带中间神经元可能通过SCT细胞的侧支作用，对先前报道的突触后背柱（PSDC）、脊髓丘脑束（STT）和脊髓中脑束（SMT）神经元的双突触和多突触兴奋或抑制起作用。因此，这些中间神经元可能有助于协调由各种脊髓上神经元群体介导的反应。
