THE AEPS OF THE PARAMEDIAN MIDBRAIN AREA ELICITED BY STIMULATING THE HDM, HP AND HL AREAS IN THE CAT / 第二军医大学学报

ABSTRACT

In 23 cats of either sex anesthetized with nembutal, the AEPs(Averaged evoked potentials) were recorded in the paramedian midbrain area which either the HDM (Hypothalamic dorsomedial nucleus) or HP (Posterior hypothalamic nucleus) or HL (Lateral hypothalamic nucleus) and nearby structures were being stimulated. The responsive characteristics of the AEPs were tested with PST (Paired Stimuli) of defferent frequenencies. It was found that there are "spike-like" responses and "slow wave" in the cat's midbrain during hypothalamic stimulation . According to its responsiveness to electrical stimuli of increasing strength, the AEPs could be classified into two types: "graded" and "all or none" like. Of 75 AEPs elicited by stimulating the HDM, 24 could follow a PST with a freqency of more than 500Hz, 31 a PST with a frequency of 200-499Hz and 20 a PST with a frequency of less 199Hz. The midbrain responsive loci were mainly distributed in an area including central gray and adjacent tegmentum,but seldom in the tectum. On the basis of calculation of the conduction distance between the stimulating and recording sites and that of ahe latency of the response which could follow a PST with more than 500Hz, the conduction velocity over the path was estimated to be about 0.65-8.18m/sec., which was in the range of conduction velocity of thin myelinated and nonmyelinated fibers in the peripharal nerve. Results of the similar kind were obtained with HP or HL stimulations.But HL-MFB(medial forebrain bundle) stimulations elicited a AEP with a longer duration. These results were in agreement with those abtained in the rat, they showed some responsive characteristics belonging to the cat's brain, i.e. the wider spectrum of conduction velocity, the more restricted area for the appearance of a given midbrain response, and the predominant distribution of responsive loci within the central gray and ventral tegmentum adjacent to it.