Shaddock Palombi P, Backoff P M, Caspary D M
Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, IL 62702, USA.
Hear Res. 2001 Mar;153(1-2):174-80. doi: 10.1016/s0378-5955(00)00264-1.
The inferior colliculus (IC) is a processing center for monaural and binaural auditory signals. Many units in the central nucleus of the inferior colliculus (CIC) respond to amplitude and frequency modulated tones, features found in communication signals. The present study examined potential effects of age on responses to sinusoidally amplitude modulated (SAM) tones in CIC and external cortex of the inferior colliculus (ECIC) units in young and aged F344 rats. Extracellular recordings from 154 localized single units of aged (24 month) rats were compared to recordings from 135 IC units from young adult (3 month) animals. SAM tones were presented at 30 dB above threshold. Comparisons were made between CIC and ECIC regarding the percentage of units responding to SAM stimuli, the relationship between SAM responsiveness and temporal response patterns, maximum discharge rates and maximum modulation gains, shapes of rate transfer functions and synchronization modulation transfer functions (MTFs) in response to SAM tones. Sixty percent of units in young and aged rat IC were selectively responsive to SAM stimuli. Eighty-one percent of units classified as onset temporal response patterns were not tonically responsive to SAM stimuli. Median maximum discharge rate in response to SAM tones was 17.6/s in young F344 rats; median maximum modulation gain was 3.85 dB. These measurements did not change significantly with age. Thirty-seven percent of young rat units displayed bandpass MTFs and 53% had lowpass MTFs. There was a significant age-related shift in the distribution of MTF shapes in both the CIC and ECIC. Aged animals showed a lower percentage of bandpass functions and a higher percentage of lowpass functions. Age-related changes observed in SAM coding may reflect an altered balance between excitatory/inhibitory neurotransmitter efficacy in the aged rat IC, and/or possibly a change in the functional dynamic range of IC neurons.
下丘（IC）是单耳和双耳听觉信号的处理中心。下丘中央核（CIC）中的许多神经元对调幅和调频音调做出反应，这些特征存在于通信信号中。本研究考察了年龄对年轻和老年F344大鼠CIC以及下丘外侧皮质（ECIC）神经元对正弦调幅（SAM）音调反应的潜在影响。将154个老年（24个月）大鼠的局部单个神经元的细胞外记录与135个年轻成年（3个月）动物的IC神经元记录进行比较。SAM音调以高于阈值30 dB的强度呈现。比较了CIC和ECIC之间对SAM刺激有反应的神经元百分比、SAM反应性与时间反应模式之间的关系、最大放电率和最大调制增益、响应SAM音调的速率传递函数和同步调制传递函数（MTF）的形状。年轻和老年大鼠IC中60%的神经元对SAM刺激有选择性反应。81%归类为起始时间反应模式的神经元对SAM刺激无紧张性反应。年轻F344大鼠对SAM音调的中位数最大放电率为17.6次/秒；中位数最大调制增益为3.85 dB。这些测量结果随年龄没有显著变化。37%的年轻大鼠神经元显示带通MTF，53%具有低通MTF。CIC和ECIC中MTF形状的分布都有与年龄相关的显著变化。老年动物中带通函数的百分比更低，低通函数的百分比更高。在SAM编码中观察到的与年龄相关的变化可能反映了老年大鼠IC中兴奋性/抑制性神经递质效能之间平衡的改变，和/或可能反映了IC神经元功能动态范围的变化。
