Shoykhet Michael, Shetty Pranav, Minnery Brandon S, Simons Daniel J
Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, 15261, USA.
J Neurophysiol. 2003 Sep;90(3):1432-7. doi: 10.1152/jn.00419.2003. Epub 2003 Jun 11.
The rodent whisker-to-barrel pathway constitutes a major model system for studying experience-dependent brain development. Yet little is known about responses of neurons to whisker stimulation in young animals. Response properties of trigeminal ganglion (NV) neurons in 2-, 3-, and 4-week-old and adult rats were examined using extracellular single-unit recordings and controlled whisker stimuli. We found that the receptive field size of NV neurons is mature in 2-week-old animals while response latencies, magnitudes, and angular tuning continue to develop between 2 weeks of age and adulthood. At the earliest time recorded, NV neurons respond to stimulation of only one whisker and can be characterized as slowly or rapidly adapting (SA, RA). The proportion of SA and RA neurons remains constant during development. Consistent with known on-going myelination of NV axons, response latencies decrease with age, becoming adult-like during the third and fourth postnatal weeks for RA and SA neurons, respectively. Unexpectedly, we found that evoked response magnitudes increase several-fold during development becoming adult-like only during the fourth postnatal week. In addition, RA neurons become less selective for whisker deflection angle with age. Maturation of response magnitude and angular tuning is consistent with developmental changes in the mechanical properties of the whisker, the whisker follicle, and the surrounding tissues. The findings indicate that whisker-derived tactile inputs mature during the first postnatal month when whisker-related cortical circuits are susceptible to long-term modification by sensory experience. Thus normal developmental changes in sensory input may influence functional development of cortical circuits.
啮齿动物的触须到桶状皮层通路是研究经验依赖性脑发育的主要模型系统。然而，对于幼小动物中神经元对触须刺激的反应知之甚少。使用细胞外单单位记录和可控的触须刺激，研究了2周龄、3周龄、4周龄和成年大鼠三叉神经节（NV）神经元的反应特性。我们发现，NV神经元的感受野大小在2周龄动物中已成熟，而反应潜伏期、幅度和角度调谐在2周龄至成年期之间持续发育。在最早记录的时间，NV神经元仅对一根触须的刺激做出反应，可分为慢适应或快适应（SA，RA）。SA和RA神经元的比例在发育过程中保持恒定。与已知的NV轴突持续髓鞘化一致，反应潜伏期随年龄减小，RA和SA神经元分别在出生后第三和第四周变得类似成年。出乎意料的是，我们发现诱发反应幅度在发育过程中增加了几倍，仅在出生后第四周才变得类似成年。此外，RA神经元对触须偏转角的选择性随年龄降低。反应幅度和角度调谐的成熟与触须、触须毛囊和周围组织力学特性的发育变化一致。这些发现表明，触须衍生的触觉输入在出生后第一个月成熟，此时与触须相关的皮层回路易受感觉经验的长期修饰。因此，感觉输入的正常发育变化可能影响皮层回路的功能发育。
