Peruzzi D, Bartlett E, Smith P H, Oliver D L
Department of Anatomy, University of Connecticut Health Center, Farmington, Connecticut, 06030-3405, USA.
J Neurosci. 1997 May 15;17(10):3766-77. doi: 10.1523/JNEUROSCI.17-10-03766.1997.
The goal was to investigate possible monosynaptic GABAergic projections from the inferior colliculus (IC) to thalamocortical neurons of the medial geniculate body (MGB) in the rat. Although there is little evidence for such a projection in other sensory thalamic nuclei, a GABAergic, ascending auditory projection was reported recently in the cat. In the present study, immunohistochemical and tract-tracing methods were used to identify neurons in the IC that contain GABA and project to the MGB. GABA-positive projection neurons were most numerous in the central nucleus and less so in the dorsal and lateral cortex. They were rare in the lateral tegmental system and brachium of the IC. The dorsal nucleus of the lateral lemniscus also contained GABA-positive projection neurons. In brain slices, stimulation of the brachium produced monosynaptic inhibitory postsynaptic potentials in morphologically identified thalamocortical relay neurons. The inhibitory potentials cannot originate locally, because they persisted when ionotropic glutamatergic transmission was blocked. Typically, brachium stimulation elicited a GABAA-mediated inhibitory potential followed by an excitatory potential and a longer latency GABAB-mediated inhibitory potential. We conclude that the GABA-containing neurons of the IC make short-latency, monosynaptic inputs to the thalamocortical projection neurons in the MGB. Such inputs may distinguish the main auditory pathway from indirect or tegmental auditory pathways as well as from other sensory systems. Monosynaptic inhibitory inputs to the medial geniculate may be important for the regulation of firing patterns in thalamocortical neurons.
目的是研究大鼠中从下丘（IC）到内侧膝状体（MGB）的丘脑皮质神经元可能存在的单突触GABA能投射。尽管在其他感觉丘脑核中几乎没有证据支持这种投射，但最近在猫中报道了一种GABA能的、上行听觉投射。在本研究中，采用免疫组织化学和示踪方法来鉴定IC中含有GABA并投射到MGB的神经元。GABA阳性投射神经元在中央核中最多，在背侧和外侧皮质中较少。它们在外侧被盖系统和IC的臂中很少见。外侧丘系背核也含有GABA阳性投射神经元。在脑片中，刺激IC臂在形态学上鉴定的丘脑皮质中继神经元中产生单突触抑制性突触后电位。这些抑制性电位不能起源于局部，因为当离子型谷氨酸能传递被阻断时它们仍然存在。通常，刺激IC臂会引发一个GABAA介导的抑制性电位，随后是一个兴奋性电位和一个潜伏期更长的GABAB介导的抑制性电位。我们得出结论，IC中含GABA的神经元对MGB中的丘脑皮质投射神经元进行短潜伏期的单突触输入。这种输入可能将主要听觉通路与间接或被盖听觉通路以及其他感觉系统区分开来。对内侧膝状体的单突触抑制性输入可能对丘脑皮质神经元放电模式的调节很重要。
