Castro-Alamancos M A, Calcagnotto M E
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.
J Neurophysiol. 2001 Apr;85(4):1489-97. doi: 10.1152/jn.2001.85.4.1489.
The thalamus is the principal relay station of sensory information to the neocortex. In return, the neocortex sends a massive feedback projection back to the thalamus. The thalamus also receives neuromodulatory inputs from the brain stem reticular formation, which is vigorously activated during arousal. We investigated the effects of two neuromodulators, acetylcholine and norepinephrine, on corticothalamic responses in vitro and in vivo. Results from rodent slices in vitro showed that acetylcholine and norepinephrine depress the efficacy of corticothalamic synapses while enhancing their frequency-dependent facilitation. This produces a stronger depression of low-frequency responses than of high-frequency responses. The effects of acetylcholine and norepinephrine were mimicked by muscarinic and alpha(2)-adrenergic receptor agonists and blocked by muscarinic and alpha-adrenergic antagonists, respectively. Stimulation of the brain stem reticular formation in vivo also strongly depressed corticothalamic responses. The suppression was very strong for low-frequency responses, which do not produce synaptic facilitation, but absent for high-frequency corticothalamic responses. As in vitro, application of muscarinic and alpha-adrenergic antagonists into the thalamus in vivo abolished the suppression of corticothalamic responses induced by stimulating the reticular formation. In conclusion, cholinergic and noradrenergic activation during arousal high-pass filters corticothalamic activity. Thus, during arousal only high-frequency inputs from the neocortex are allowed to reach the thalamus. Neuromodulators acting on corticothalamic synapses gate the flow of cortical activity to the thalamus as dictated by behavioral state.
丘脑是感觉信息向新皮层传递的主要中继站。作为回报，新皮层向丘脑发出大量反馈投射。丘脑还接收来自脑干网状结构的神经调节输入，在觉醒过程中该结构会被强烈激活。我们研究了两种神经调节剂乙酰胆碱和去甲肾上腺素对体外和体内皮质丘脑反应的影响。体外啮齿动物脑片的结果表明，乙酰胆碱和去甲肾上腺素会降低皮质丘脑突触的效能，同时增强其频率依赖性易化作用。这导致低频反应比高频反应受到更强的抑制。乙酰胆碱和去甲肾上腺素的作用分别被毒蕈碱和α₂ - 肾上腺素能受体激动剂模拟，并分别被毒蕈碱和α - 肾上腺素能拮抗剂阻断。体内刺激脑干网状结构也会强烈抑制皮质丘脑反应。对于不产生突触易化的低频反应，这种抑制非常强烈，但对于高频皮质丘脑反应则不存在。与体外情况一样，在体内向丘脑应用毒蕈碱和α - 肾上腺素能拮抗剂可消除刺激网状结构所诱导的皮质丘脑反应抑制。总之，觉醒期间胆碱能和去甲肾上腺素能激活对皮质丘脑活动进行高通滤波。因此，在觉醒期间，只有来自新皮层的高频输入能够到达丘脑。作用于皮质丘脑突触的神经调节剂根据行为状态控制皮质活动向丘脑的传递。
