Burrows M
Department of Zoology, University of Cambridge, England.
J Neurosci. 1992 Apr;12(4):1477-89. doi: 10.1523/JNEUROSCI.12-04-01477.1992.
Mechanosensory information from exteroceptive hairs on the legs of a locust is first processed in a segmental ganglion by a midline population of spiking local interneurons for use in adjustments of posture and locomotion. Each interneuron receives excitatory inputs from a characteristic array of these receptors so that the surface of a leg is mapped onto the whole population of interneurons as a series of overlapping receptive fields. The properties of this first synaptic connection, and the contributions of individual afferents forming the receptive fields of the interneurons are examined. The gain of the excitatory synaptic connection between the hair afferents and the interneurons is often high, so that a single afferent spike can lead directly to a spike in the interneuron. Repetitive spikes in a hair afferent evoke EPSPs in an interneuron that decline in amplitude but that may summate. The first EPSP in any sequence is always the largest. The high frequencies of afferent spikes that are evoked by a normal deflection of a hair saturate the synaptic connection so that the amplitude of depolarization is no greater than to a single spike. The EPSPs from two hairs in a receptive field can summate but lead to no heterosynaptic facilitation. High-frequency bursts of spikes in one afferent can reduce the postsynaptic effect of another afferent. The amplitude of the EPSPs and the gain of the synaptic connections differ markedly between the hairs that comprise the receptive field of an interneuron. There are gradients of effectiveness, generally according to the axes of the leg, with one group of adjacent hairs producing the largest-amplitude EPSPs and having the highest gains. Individual hairs may contribute to the receptive field of more than one interneuron, and the gain of these connections may differ. The complexity of a receptive field is further accentuated by the specificity of connections made by the different physiological types of hair receptors. High-threshold hairs may make synaptic connections with an interneuron, but adjacent low-threshold hairs may not. This organization of the receptive fields means that the interneurons are sensitive to certain inputs and can reliably pass on a signal from one hair. It also implies that greater weighting is given to inputs from certain regions.
来自蝗虫腿部外感受毛的机械感觉信息首先在节段神经节中由一群中线发放的局部中间神经元进行处理，以用于姿势和运动的调整。每个中间神经元从这些感受器的特定阵列接收兴奋性输入，这样腿部表面就作为一系列重叠的感受野映射到整个中间神经元群体上。我们研究了这第一个突触连接的特性，以及构成中间神经元感受野的各个传入纤维的贡献。毛传入纤维与中间神经元之间兴奋性突触连接的增益通常很高，以至于单个传入纤维的一个冲动可以直接导致中间神经元产生一个冲动。毛传入纤维的重复冲动在中间神经元中诱发兴奋性突触后电位（EPSP），其幅度会下降但可能会总和。任何序列中的第一个EPSP总是最大的。毛发正常偏转诱发的传入纤维高频冲动会使突触连接饱和，以至于去极化幅度不会大于单个冲动所产生的幅度。感受野中两根毛发产生的EPSP可以总和，但不会导致异突触易化。一根传入纤维中的高频冲动爆发可以降低另一根传入纤维的突触后效应。构成中间神经元感受野的毛发之间，EPSP的幅度和突触连接的增益明显不同。通常沿着腿部轴线存在有效性梯度，一组相邻毛发产生幅度最大的EPSP且增益最高。单个毛发可能对不止一个中间神经元的感受野有贡献，并且这些连接的增益可能不同。不同生理类型的毛感受器所建立连接的特异性进一步加剧了感受野的复杂性。高阈值毛发可能与中间神经元建立突触连接，但相邻的低阈值毛发可能不会。感受野的这种组织方式意味着中间神经元对某些输入敏感，并且能够可靠地传递来自一根毛发的信号。这也意味着对来自某些区域的输入给予了更大的权重。
