Redies H, Brandner S, Creutzfeldt O D
Department of Neurobiology, Max-Planck-Institute of Biophysical Chemistry, Göttingen, Federal Republic of Germany.
J Comp Neurol. 1989 Apr 22;282(4):489-511. doi: 10.1002/cne.902820403.
We investigated the projection from the medial geniculate body (MG) to the tonotopic fields (the anterior field A, the dorsocaudal field DC, the small field S) and to the nontonotopic ventrocaudal belt in the auditory cortex of the guinea pig. The auditory fields were first delimited in electrophysiological experiments with microelectrode mapping techniques. Then, small quantities of horseradish peroxidase (HRP) and/or fluorescent retrograde tracers were injected into the sites of interest, and the thalamus was checked for labeled cells. The anterior field A receives its main thalamic input from the ventral nucleus of the MG (MGv). The projection is topographically organized. Roughly, the caudal part of the MGv innervates the rostral part of field A and vice versa. After injection of tracer into low or medium best-frequency sites in A, we also found a topographic gradient along the isofrequency contours: the dorsal (ventral) part of a cortical isofrequency strip receives afferents from the rostral (caudal) portions of the corresponding thalamic isofrequency band. However, it is not so obvious whether such a gradient exists also in the high-frequency part of the projection. A second, weaker projection to field A originates in a magnocellular nucleus that is situated caudomedially in the MG and was therefore named the caudomedial nucleus. The dorsocaudal field DC receives input from the same nuclei as the anterior field, but the location of the labeled cells in the MGv is different. This was demonstrated by injection of different tracers into sites with like best frequencies in fields A and DC, respectively. After injection of HRP into the 1-2-kHz isofrequency strip in field A and injection of Nuclear Yellow (NY) into the 1-2-kHz site in field DC, the labeled cells in the MGv form one continuous array that runs from caudal to rostral over the whole extent of the MGv. The anterior part of this array consists of NY-labeled cells; i.e., it projects to field DC. The caudal part is formed by HRP-labeled cells; i.e., it innervates field A. These findings indicate that there is only one continuous tonotopic map in the MGv. This map is split when projected onto the cortex so that two adjacent tonotopic fields (A and DC) result. The cortical maps are rotated relative to the thalamic map in that rostral portions of the MGv project to caudal parts of the tonotopic cortex and vice versa.(ABSTRACT TRUNCATED AT 400 WORDS)
我们研究了豚鼠内侧膝状体（MG）向听觉皮层的音频拓扑区域（前区A、背尾区DC、小区S）以及非音频拓扑腹尾带的投射。首先通过微电极图谱技术在电生理实验中划定听觉区域。然后，将少量辣根过氧化物酶（HRP）和/或荧光逆行示踪剂注入感兴趣的部位，并检查丘脑有无标记细胞。前区A主要从MG的腹侧核（MGv）接收丘脑输入。这种投射是按拓扑结构组织的。大致来说，MGv的尾侧部分支配A区的头侧部分，反之亦然。在将示踪剂注入A区低频或中频最佳频率部位后，我们还在等频率轮廓上发现了一种拓扑梯度：皮层等频率带的背侧（腹侧）部分接收来自相应丘脑等频率带头侧（尾侧）部分的传入纤维。然而，在投射的高频部分是否也存在这样的梯度并不那么明显。对A区的第二种较弱投射起源于位于MG尾内侧的一个大细胞核，因此被命名为尾内侧核。背尾区DC与前区接收来自相同核的输入，但MGv中标记细胞的位置不同。分别将不同的示踪剂注入A区和DC区具有相同最佳频率的部位，证明了这一点。在将HRP注入A区1 - 2千赫兹等频率带并将核黄（NY）注入DC区1 - 2千赫兹部位后，MGv中的标记细胞形成一个连续的阵列，在MGv的整个范围内从尾侧延伸到头侧。这个阵列的前部由NY标记的细胞组成；即它投射到DC区。尾部由HRP标记的细胞形成；即它支配A区。这些发现表明MGv中只有一个连续的音频拓扑图谱。当投射到皮层上时，这个图谱会分开，从而产生两个相邻的音频拓扑区域（A和DC）。皮层图谱相对于丘脑图谱发生了旋转，因为MGv的头侧部分投射到音频拓扑皮层的尾侧部分，反之亦然。（摘要截取自400字）
