Beierlein Michael, Connors Barry W
Department of Neuroscience, Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA.
J Neurophysiol. 2002 Oct;88(4):1924-32. doi: 10.1152/jn.2002.88.4.1924.
Layer 6 is the main source of neocortical connections back to specific thalamic nuclei. Corticothalamic (CT) systems play an important role in shaping sensory input, but little is known about the functional circuitry that generates CT activity. We recorded from the two main types of neurons in layer 6, regular-spiking (RS; pyramidal neurons) and fast-spiking (FS; inhibitory interneurons) cells and compared the physiological properties of different excitatory inputs. Thalamic stimulation evoked two monosynaptic inputs with distinct properties: suspected thalamocortical (TC) synaptic events had short latencies, short-term synaptic depression, and paired-pulse responses that suggested subnormal axonal conduction. A second group of synaptic responses likely originated from intracortical collaterals of CT cells that were antidromically activated from the thalamus. These intracortical responses had longer latencies, short-term synaptic facilitation, and were transmitted by axons with supernormal conduction. Suspected TC inputs to FS cells had significantly larger amplitudes than those onto RS cells. Dual recordings from neighboring neurons in layer 6 revealed both facilitating and depressing synaptic connections; the depressing synapses were probably formed by layer 6 cells that do not project to the thalamus, and thus were not sampled by thalamic stimulation. We conclude that layer 6 neurons integrate a variety of inputs with distinct temporal dynamics that are determined by the presynaptic cell type.
第6层是新皮质与特定丘脑核团之间反向连接的主要来源。皮质丘脑(CT)系统在塑造感觉输入方面发挥着重要作用,但对于产生CT活动的功能回路却知之甚少。我们记录了第6层中两种主要类型的神经元,即规则发放(RS;锥体神经元)和快速发放(FS;抑制性中间神经元)细胞,并比较了不同兴奋性输入的生理特性。丘脑刺激诱发了两种具有不同特性的单突触输入:疑似丘脑皮质(TC)突触事件具有短潜伏期、短期突触抑制以及提示轴突传导异常的成对脉冲反应。第二组突触反应可能源自CT细胞的皮质内侧支,这些侧支从丘脑被逆向激活。这些皮质内反应具有更长的潜伏期、短期突触易化,并且由具有超常传导的轴突传递。疑似TC对FS细胞的输入幅度明显大于对RS细胞的输入幅度。对第6层相邻神经元的双记录显示了既有易化性又有抑制性的突触连接;抑制性突触可能由不投射到丘脑的第6层细胞形成,因此未被丘脑刺激采样。我们得出结论,第6层神经元整合了多种具有不同时间动态的输入,这些动态由突触前细胞类型决定。