Schnupp J W, King A J, Smith A L, Thompson I D
University Laboratory of Physiology, Oxford, United Kingdom.
J Neurosci. 1995 Feb;15(2):1516-31. doi: 10.1523/JNEUROSCI.15-02-01516.1995.
In the ferret (Mustela putorius) the map of auditory space in the deeper layers of the superior colliculus (SC) matures over a period of several postnatal weeks, a process known to be guided by both visual and auditory experience. The auditory responses are initially very broadly tuned, and gradually become more selective for specific sound locations that coincide with the visual receptive fields recorded in the same region of the SC. To investigate the possible involvement of NMDA-type glutamate receptors in the postnatal development of this auditory representation, we have reared ferrets in which 400 microns thick sheets of the slow-release polymer Elvax, containing the NMDA receptor antagonists MK801 or APV, were placed on the dorsal surface of the SC. The Elvax was implanted on postnatal day (P) 25-27, just before the onset of hearing, and removed 5-6 weeks later, just prior to recording from the SC on around P61-70. In vitro measurements with Elvax containing 3H-MK801 revealed that the amount of drug released declined sharply over the first 10 d and then stabilized at a fairly constant rate for the following 5 weeks. These in vitro data were found to parallel the in vivo release of MK801 from implanted Elvax slices. Diffusion of MK801 from the implant was measured and significant levels were found within 800 microns of the SC surface, suggesting that the action of MK801 was restricted to the superficial and intermediate layers of the nucleus. Extracellular recordings were made from visual and auditory units in the SC in response to free-field stimulation. The visual responses of units recorded in the superficial layers appeared to be unaffected by either of the drug treatments, and formed a normal, adult-like map of visual azimuth along the rostrocaudal axis of the SC in all animals. Most of the auditory single-unit responses recorded at this age in normal, unoperated controls were spatially tuned and topographically organized, although the map of sound azimuth was less precise than that in adult ferrets. Data from age-matched control animals that had been reared with drug-free Elvax implants were not statistically different from the unoperated juvenile ferrets. However, in animals reared with APV or MK801 Elvax implants, there was an increase in the relative numbers of auditory units that were ambiguously tuned to two or more locations.(ABSTRACT TRUNCATED AT 400 WORDS)
在雪貂（鼬属）中，上丘深层的听觉空间图谱在出生后的几周内逐渐成熟，这一过程已知受视觉和听觉经验的引导。听觉反应最初非常宽泛，逐渐对与在上丘同一区域记录的视觉感受野相重合的特定声音位置变得更具选择性。为了研究NMDA型谷氨酸受体在这种听觉表征出生后发育中的可能作用，我们饲养了雪貂，在其上丘背表面放置了含有NMDA受体拮抗剂MK801或APV的400微米厚的缓释聚合物Elvax片。Elvax在出生后第（P）25 - 27天植入，就在听力开始之前，5 - 6周后取出，就在大约P61 - 70从SC记录之前。用含有3H - MK801的Elvax进行的体外测量显示，药物释放量在最初10天内急剧下降，然后在接下来的5周内以相当恒定的速率稳定下来。发现这些体外数据与植入的Elvax切片中MK801的体内释放情况相似。测量了MK801从植入物中的扩散，发现在SC表面800微米范围内有显著水平，这表明MK801的作用仅限于该核的浅层和中层。对上丘中的视觉和听觉单元进行细胞外记录以响应自由场刺激。在浅层记录的单元的视觉反应似乎不受任何一种药物处理的影响，并且在所有动物中沿着SC的前后轴形成了正常的、类似成年动物的视觉方位图。在这个年龄的正常未手术对照动物中记录的大多数听觉单单元反应在空间上是调谐的并且具有拓扑结构，尽管声音方位图不如成年雪貂精确。来自用无药物Elvax植入物饲养的年龄匹配对照动物的数据与未手术的幼年雪貂没有统计学差异。然而，在用APV或MK801 Elvax植入物饲养的动物中，对两个或更多位置进行模糊调谐的听觉单元的相对数量增加。（摘要截于400字）
