Stojic A S, Lane R D, Killackey H P, Qadri B A, Rhoades R W
Department of Anatomy and Neurobiology, Medical College of Ohio, Toledo 43699, USA.
J Comp Neurol. 1998 Nov 16;401(2):187-204.
We previously reported the abnormal expression of hindlimb receptive fields in the stump representation of the primary somatosensory cortex (SI) in rats that sustained neonatal forelimb removal when cortical gamma-aminobutyric acid (GABA) receptors were pharmacologically blocked (Lane et al. [1997] J. Neurophysiol. 77:2723-2735). In this study, we attempted to identify the substrate for this functional modification. Three potential substrates were examined: 1) changes in intracortical connections within SI; 2) alterations in the projection pattern of thalamocortical afferents from the ventroposterior lateral (VPL) nucleus to SI; and 3) changes in the receptive fields of thalamocortical neurons. We used biotinylated dextran amine and Phaseolus vulgaris leucoagglutinin to examine the intracortical projections associated with the stump and hindlimb representations of SI. True Blue and Diamidino Yellow were used to study the organization of the VPL projections to SI. Finally, single-unit recordings from VPL neurons were made to examine the functional organization of this nucleus in neonatally amputated adult rats. Tracer studies demonstrated no significant change in the intracortical connections or VPL projections associated with the stump and hindlimb SI in neonatally amputated rats. Recordings from VPL of neonatally manipulated rats revealed a small, but significant, population of cells (19.0%) within the stump representation that had dual stump and hindlimb receptive fields. Thus, the data suggest that the functional reorganization observed in SI of neonatally amputated rats may reflect functional alterations occurring in its thalamic inputs.
我们之前报道过，在新生大鼠前肢被切除后，当对皮质γ-氨基丁酸（GABA）受体进行药理学阻断时，大鼠初级体感皮层（SI）残端代表区的后肢感受野会出现异常表达（Lane等人，[1997]《神经生理学杂志》77:2723 - 2735）。在本研究中，我们试图确定这种功能改变的底物。研究了三种潜在的底物：1）SI内皮质内连接的变化；2）从腹后外侧（VPL）核到SI的丘脑皮质传入投射模式的改变；3）丘脑皮质神经元感受野的变化。我们使用生物素化葡聚糖胺和菜豆白细胞凝集素检查与SI的残端和后肢代表区相关的皮质内投射。使用真蓝和双脒基黄研究VPL到SI的投射组织。最后，对VPL神经元进行单单位记录，以检查新生期截肢成年大鼠中该核的功能组织。示踪研究表明，新生期截肢大鼠中与SI的残端和后肢相关的皮质内连接或VPL投射没有显著变化。对新生期进行处理的大鼠的VPL记录显示，在残端代表区内有一小部分但数量可观的细胞（19.0%）具有残端和后肢双重感受野。因此，数据表明，在新生期截肢大鼠的SI中观察到的功能重组可能反映了其丘脑输入中发生的功能改变。
