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更高中继站变得更强，即脊髓，丘脑和大脑皮层。1973年，Hellon发现大鼠的脊髓背角和其他中枢神经系统中有高密度的神经元对阴囊的热刺激做出反应。后来，许多研究者将该系统作为热传入通路的模型进行了研究。然而，最近Kanosue等（1984，1985）发现这些神经元本身对阴囊温度变化不作出反应，并且这些反应是伴随EEG唤醒的非特异性反应。因此，在本研究中，我检查，如果大鼠真的“感觉”阴囊温度变化，通过分析操作行为，其中阴囊热刺激被用作一个无条件刺激。一只老鼠被关在一个小笼子里。将Pertier装置（5x 5cm）附接到阴囊，并将用于施加电击的一对电极设置在尾部周围。首先将阴囊温度（T_<src>）设定在正常水平32 ℃。然后，逐步升高至42 ℃，10秒后对尾部施加电击，T_<scr>恢复到原来的低水平。如果大鼠按下一个杠杆，设置在动物的前面，他可以避免电击和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，没有老鼠学会这项任务。然而，不能仅仅从这个结果得出结论，大鼠感觉不到阴囊温度的变化，因为刺激可能太弱，作为一个无条件刺激，即使他感觉到了。

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.