Thermosensitivity of rat's scrotum.

与其他皮肤感觉相比，温度感觉在神经生理学上没有很好的记录。这是因为传递皮肤温度信息的神经元数量很少。这种倾向在这种感觉的中继站越高越强烈；也就是脊髓，丘脑和大脑皮层。1973年，Hellon发现，在大鼠的脊髓背角和其他中枢神经系统中，对阴囊的热刺激有反应的神经元密度很高。此后，该系统作为热传入途径的模型被许多研究者研究。然而，最近Kanosue et al.（1984, 1985）发现这些神经元对阴囊温度变化本身没有反应，而且这种反应是非特异性的，伴随着脑电图唤醒。因此，在本研究中，我通过分析操作行为来检验大鼠是否真的“感觉”到了阴囊温度的变化，并将阴囊热刺激作为一种非条件刺激。一只老鼠被关在一个小笼子里。将Pertier装置（5 x 5 cm）连接到阴囊上，并在尾部周围设置一对用于施加电击的电极。初始阴囊温度（T_<src>）设定在正常32‰。然后逐步升高至42ºC， 10秒后对机尾进行电击，使T_<scr>恢复到原来的低电平。如果大鼠按下设置在动物前面的杠杆，大鼠可以避免电击，T_<scr>减小。我在11只老鼠身上测试了这种操作性条件反射。不幸的是，没有老鼠学会这个任务。然而，不能仅仅从这个结果得出结论说，大鼠感觉不到阴囊温度的变化，因为刺激可能比非条件刺激时间长，即使它感觉到了。

Temperature sensation is not well documented neurophysiologically as compared with other skin sensation. This is because number of neurons that convey informations of skin temperature is small. This tendency becomes stronger at higher relay station of this sensation; that is, spinal cord, thalamus, and cerebral cortex. In 1973 Hellon found that there are a high density of neurons in the spinal dorsal horn and other central nervous system that responded to thermal stimulation of the scrotum in rats. From later on, this system was studied by many investigators as a model of thermal afferent pathway. Recently, however, Kanosue et al. (1984, 1985) found that these neurons do not respond to scrotal temperature change itself and that the responses are nonspecific one which accompany EEG arousal. Therefore, in the present study I examined if rats really "feel" scrotal temperature change by analyzing operant behavior, in which scrotal thermal stimulation was used as an unconditioned stimulus. A rat was placed in a small cage. A Pertier device (5 x 5 cm) was attached to the scrotum and a pair of electrodes for applying an electrical shock were set around the tail. At first scrotal temperature (T_<src>) was set at normal level of 32ﾟC. Then, it was raised stepwisely to 42ﾟC and 10 sec later electrical shock was applied to the tail and T_<scr> was returned to the original low level. If the rat pressed a lever, setting in front of the animal, he could avoid the shock and T_<scr> was decreased. I tested this operant conditioning in eleven rats. Unfortunately, no rat learned this task. It can not be concluded only from this result, however, that the rat does not sense scrotal temperature change, because the stimulus might have been too week as an unconditioned stimulus, even though he sensed it.