Hirata Akio, Aguilar Juan, Castro-Alamancos Manuel A
Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, USA.
J Neurosci. 2006 Apr 19;26(16):4426-36. doi: 10.1523/JNEUROSCI.5298-05.2006.
Thalamocortical cells receive sensory signals via primary sensory afferents and cortical signals via corticothalamic afferents. These signals are influenced by a variety of neuromodulators that are released in the thalamus during specific behavioral states. Hence, different neuromodulators may set different thalamic modes of sensory information processing. We found that noradrenergic activation affects sensory and corticothalamic signals in the whisker thalamus differently than cholinergic activation. Whereas cholinergic activation increases the spontaneous firing (noise) and enlarges the receptive fields of ventroposterior medial thalamus (VPM) cells, noradrenergic activation decreases spontaneous firing and focuses receptive fields. Consequently, for sensory signals, noradrenergic activation sets bottom-up thalamic processing to a focused and noise-free excitatory receptive field, which contrasts with the broad and noisy excitatory receptive field characteristic of cholinergic activation. For corticothalamic signals, noradrenergic activation sets top-down processing to a noise-free high-frequency signal detection mode, whereas cholinergic activation produces a noisy broadband signal detection mode. The effects of noradrenergic activation on signal-to-noise ratios of VPM cells were found to be mediated by nucleus reticularis thalamic (nRt) cells. Hence, a major role of nRt cells is to regulate the noise level of thalamocortical cells during sensory processing. In conclusion, different modulators establish distinct modes of bottom-up and top-down information processing in the sensory thalamus.
丘脑皮质细胞通过初级感觉传入纤维接收感觉信号，并通过皮质丘脑传入纤维接收皮质信号。这些信号受到多种神经调质的影响，这些神经调质在特定行为状态下于丘脑中释放。因此，不同的神经调质可能会设定不同的丘脑感觉信息处理模式。我们发现，去甲肾上腺素能激活对触须丘脑的感觉和皮质丘脑信号的影响与胆碱能激活不同。胆碱能激活会增加自发放电（噪声）并扩大腹后内侧丘脑（VPM）细胞的感受野，而去甲肾上腺素能激活则会减少自发放电并使感受野集中。因此，对于感觉信号，去甲肾上腺素能激活将自下而上的丘脑处理设置为聚焦且无噪声的兴奋性感受野，这与胆碱能激活所特有的广泛且有噪声的兴奋性感受野形成对比。对于皮质丘脑信号，去甲肾上腺素能激活将自上而下的处理设置为无噪声的高频信号检测模式，而胆碱能激活则产生有噪声的宽带信号检测模式。发现去甲肾上腺素能激活对VPM细胞信噪比的影响是由丘脑网状核（nRt）细胞介导的。因此，nRt细胞的一个主要作用是在感觉处理过程中调节丘脑皮质细胞的噪声水平。总之，不同的调质在感觉丘脑中建立了不同的自下而上和自上而下信息处理模式。
