NEURAL CONNECTION BETWEEN HYPOTHALAMIC VENTROMEDIAL NUCLEUS AND PARAMEDIAN MIDBRAIN AREA AND ITS ELECTROPHYSIOLOGICAL CHARACTERISTICS / 第二军医大学学报

ABSTRACT

AEPs were recorded at 1046 paramedian midbraih sites in 31 cats of both sexes when electrical stimulations were applied to 46 points within the HVMs after the cats had been anesthetized with nembutal and paralyzed with flaxedil. In the 103 responsive sites where AEPs were recorded, 151 fast wave responses were obtained. When the HVM was stimulated with electrical pulses of increasing intensity, two types of midbrain responses were recorded"graded" and "all or none". Responsiveness of AEPs was tested for using paired stimui (PST) of different frequencies. Of the 111 AEPs tested, 38 could follow PST above 500Hz, 27 between 200-499Hz, and 46 under 199Hz. In order to test the responsiveness of AEPs further, short trains of pulses were applied. The results suggested that there might be both transsynaptic and direct connections between the two brain regions. According to calculations,the conduction velocity over this path was about 0. 29-4. 1m/sec., similar to the conduction velocity in thin myelinated and nonmyelinated fibers of the peripheral nerve. On the basis of the electrophysiological and histological data, it is suggested that there might be a topographical organization between HVM and mesencephalic central gray in dorsal-dorsal ventral-ventral direction. Some characteristics of responses which may belong to central axons are described. Advantages of the method of combining PST test with short train test in the evaluation of responsveness of the neural tissues are discussed..