Canady R A, Burd G D, DeVoogd T J, Nottebohm F
Rockefeller University, New York, New York 10021.
J Neurosci. 1988 Oct;8(10):3770-84. doi: 10.1523/JNEUROSCI.08-10-03770.1988.
Combinations of the Golgi stain, anterograde degeneration, and electron microscopy are used to further characterize the hormone-sensitive "type IV" neuron of the forebrain nucleus robustus archistriatalis (RA) of adult female canaries. Anterograde degeneration was used to "stain," at the electron-microscopic level, the axon terminals of neurons projecting to RA from hyperstriatum ventralis, pars caudalis (HVc) and from the lateral magnocellular nucleus of the anterior neostriatum (L-MAN). The HVc neurons projecting to RA type IV cells form synapses predominantly on the dendritic spines of those cells, while L-MAN neurons that project to RA type IV cells form a 2.5:1 mixture of shaft and spine synapses. There were about 1000 synapses from HVc neurons (about 30% of all spine synapses) on typical type IV cells and about 50 synapses from L-MAN neurons. Earlier work had shown that in female canaries the dendrites of type IV neurons of the avian song control nucleus RA increase in total length after systemic testosterone treatment, and that this increase in dendritic length was accompanied by the development of malelike song. We now show that testosterone treatment also increases the number of dendritic spines present in type IV neurons. Presumably this is accompanied by an increase in the number of synaptic inputs received by type IV cells. Earlier evidence suggested that the testosterone-induced addition of extra dendritic length to type IV cells occurred at existing dendritic tips. We tested the hypothesis that these added peripheral ends received a special subset of inputs, which might then account for the change in behavior, and found it to be false. Mapping and counts of degenerating synapses resulting from lesion of HVc and L-MAN suggest that under the influence of hormone, new synapses are added throughout the dendritic tree, with no special distribution or change in ratio of inputs occurring at the tip of dendrites. Under the influence of testosterone, each type IV cell may receive only "more of the same" inputs it received before onset of treatment. We speculate on how such changes in circuitry may relate to song stability and learning.
运用高尔基染色法、顺行性变性法和电子显微镜技术相结合，进一步对成年雌性金丝雀前脑古纹状体粗核（RA）中对激素敏感的“IV型”神经元进行特征描述。顺行性变性法用于在电子显微镜水平“标记”从腹侧尾状高纹状体（HVc）和新纹状体前部外侧大细胞核（L-MAN）投射到RA的神经元的轴突终末。投射到RA IV型细胞的HVc神经元主要在这些细胞的树突棘上形成突触，而投射到RA IV型细胞的L-MAN神经元形成轴突和树突棘突触比例为2.5:1的混合突触。典型的IV型细胞上有大约1000个来自HVc神经元的突触（约占所有树突棘突触的30%）以及大约50个来自L-MAN神经元的突触。早期研究表明，在雌性金丝雀中，鸟类鸣叫控制核RA的IV型神经元的树突总长度在全身注射睾酮后会增加，并且这种树突长度的增加伴随着雄鸟样鸣叫的发展。我们现在表明，睾酮处理还会增加IV型神经元中树突棘的数量。据推测，这伴随着IV型细胞接收的突触输入数量的增加。早期证据表明，睾酮诱导IV型细胞额外增加的树突长度出现在现有的树突末端。我们测试了这样一个假设，即这些新增的外周末端接收了一个特殊的输入子集，这可能解释了行为的变化，但发现该假设不成立。对HVc和L-MAN损伤导致的退化突触进行映射和计数表明，在激素的影响下，整个树突树都添加了新的突触，在树突末端没有出现特殊的分布或输入比例的变化。在睾酮的影响下，每个IV型细胞可能只接收其在治疗开始前接收的“更多相同”的输入。我们推测这种神经回路的变化可能与鸣叫的稳定性和学习有怎样的关系。
