MRC Institute of Hearing Research, University Park Nottingham, UK.
Front Syst Neurosci. 2011 Jun 21;5:53. doi: 10.3389/fnsys.2011.00053. eCollection 2011.
Reversible inactivation of the cortex by surface cooling is a powerful method for studying the function of a particular area. Implanted cooling cryoloops have been used to study the role of individual cortical areas in auditory processing of awake-behaving cats. Cryoloops have also been used in rodents for reversible inactivation of the cortex, but recently there has been a concern that the cryoloop may also cool non-cortical structures either directly or via the perfusion of blood, cooled as it passed close to the cooling loop. In this study we have confirmed that the loop can inactivate most of the auditory cortex without causing a significant reduction in temperature of the auditory thalamus or other subcortical structures. We placed a cryoloop on the surface of the guinea pig cortex, cooled it to 2°C and measured thermal gradients across the neocortical surface. We found that the temperature dropped to 20-24°C among cells within a radius of about 2.5 mm away from the loop. This temperature drop was sufficient to reduce activity of most cortical cells and led to the inactivation of almost the entire auditory region. When the temperature of thalamus, midbrain, and middle ear were measured directly during cortical cooling, there was a small drop in temperature (about 4°C) but this was not sufficient to directly reduce neural activity. In an effort to visualize the extent of neural inactivation we measured the uptake of thallium ions following an intravenous injection. This confirmed that there was a large reduction of activity across much of the ipsilateral cortex and only a small reduction in subcortical structures.
通过表面冷却使皮层可逆失活是研究特定区域功能的强大方法。已将植入式冷却冷冻环用于研究清醒行为猫的听觉处理中单个皮质区域的作用。冷冻环也已用于啮齿动物的皮层可逆失活，但最近有人担心冷冻环可能会直接或通过接近冷却环的血液冷却而冷却非皮质结构。在这项研究中，我们证实，冷冻环可以在不显着降低听觉丘脑或其他皮质下结构温度的情况下失活大部分听觉皮层。我们将冷冻环放置在豚鼠皮层表面，将其冷却至 2°C，并测量新皮层表面的热梯度。我们发现，温度在距环路半径约 2.5mm 的范围内下降到 20-24°C。这种温度下降足以降低大多数皮质细胞的活性，并导致几乎整个听觉区域失活。当直接在皮层冷却期间测量丘脑、中脑和中耳的温度时，温度略有下降（约 4°C），但不足以直接降低神经活动。为了可视化神经失活的程度，我们测量了静脉注射后铊离子的摄取。这证实了同侧皮层的大部分区域的活性有很大降低，而皮质下结构的活性仅略有降低。
