ACTIONS OF STIMULATION TO MEDULLARY PYRAMID ON SINGLE NEURONS IN CAT'S MOTOR CORTEX By

Abstract

There is no doubt that it is extremely important to investigate on the reactions of various neurons in the motor cortex including the cortical neurons with descending pyramidal tract fibers to electrical stimulation, if one wishes really to understand the significance of activities of those neurons. As to the study on motor cortex of warm-blo3ded animal by means of microelectrode technique, not only extracellular recording, which has been quite fruitful, but also intracellular recording is technically possible though not without some difficulty ; and thanks lo this method the neuronal mechanisms in this region havz recently been more and more clearly elucidated. Particularly, since the cells of the cortical neurons with descending pyramidal tract fibers are large enough to be rather easily recorded intracellularly, and can be clearly identified through medullary pyramidal antidromic stimulation I Phillips, '55 a, '59 ' , the characteristics of those neurons have been better elucidated by investigating the effects of stimulation on the cortical surface 1 Phillips, '56 b, Byanch and Afavtin,'58 , specific relay nuclei of the thalamus Li, '56, '57, Branch and lWartiii, 18, .4sanz(nza, '59 I , callosal fibers 1 ilsanuina and Okanzoto, '59 I , peripheral nerves I Li, '59, A4saizuma '591, etc. Recently we have performed both electrical and chemical stimulation experiments on the unitary activities not only of the neurons with descending pyramidal tract fibers but also some other neurons in cat's motor cortex ' Sawu. nilamycznza, Hanai and Kaji, '59 a , and also attempted an elucidation on the neuronal mechanism of epileptic seizures as our special undertaking 'Sazcia, Maruyama. Hanai and Kaji, 'i9b1, the results of which will be reported in detail in separate papers. What we are to give here are some further contributory reports conzerning the nature of the neurons with descending pyramidal tract fibers and a few new findings concerning some other neurons to medullary pyramidal electrical stimulation. Furthermore, the above experiments helped us to have some insight in the analysis of the evoked potentials thereof. ' iMethods 15 adult ~x t ? n e r c USVCI.

Membrane potentials in isolated neurones in vitro from Deiters' nucleus of rabbit

“…The values of their membrane potentials at 230 C (Table 3) then fell within the range found at 370 C in cells identified by antidromic stimulation as pyramidal motoneurones (Phillips, 1956;Li, 1959;Sawa et al 1960). The gangliosides are n-acetyl-neuraminic acid H. HILLMAN AND H. HYDI@N containing fatty acids, which have a variety of biochemical properties, including that of restoring to cerebral slices their ability to respond biochemically to electrical stimulation, after it had been lost owing to the application of basic proteins (for review, see Mcllwain, 1963).…”

“…Recently, Ito, Hongo, Yoshida, Okada & Obata (1964) have recorded in Deiters' neurones of anaesthetized cats resting potentials of 50-70 mV. In mammalian pyramidal cells in vivo (Phillips, 1956;Sawa, Maruyama, Kaji & Hanai, 1960), and in cells which gave spike discharges in cerebral slices in vitro (Hillman, Campbell & McIlwain, 1963), the mean resting potentials were generally 50-55 mV, which is only 10-15 mV higher than those found here at the lower temperature. However, addition of a ganglioside preparation increased the resting potential to within the range found in vivo (Table 3).…”

“…Many amino acids and other agents applied iontophoretically to cerebral and spinal motoneurones depolarize them (Krnjevic & Phillis, 1963;Curtis, Perrin & Watkins, 1960;Curtis, Phillis & Watkins, 1960), but a ganglioside preparation here had the effect of increasing cellular polarization, as it did in cerebral slices (Hillman, 1961). The values of their membrane potentials at 230 C (Table 3) then fell within the range found at 370 C in cells identified by antidromic stimulation as pyramidal motoneurones (Phillips, 1956;Li, 1959;Sawa et al 1960). The gangliosides are n-acetyl-neuraminic acid H. HILLMAN AND H. HYDI@N containing fatty acids, which have a variety of biochemical properties, including that of restoring to cerebral slices their ability to respond biochemically to electrical stimulation, after it had been lost owing to the application of basic proteins (for review, see Mcllwain, 1963).…”

Action of Strychnine to Cortical Neurons

“…Depolarizing waves generated by single shocks to the medullary pyramid are considered to be excitatory post-synaptic potentials or EPSPs12, 15,17). In the course of strychninization, these elicited EPSPs become larger in amplitude and longer in duration, showing a similar pattern to the spontaneously occurring long-lasting depolarizing wave : Thus, it is quite reasonable to assume that the latter could also be summated EPSPs.…”

“…Hyperpolarizing waves elicited by the medullary pyramidal shocks are considered to be inhibitory post-synaptic potentials or IPSPs12, 15,17). Thus, by analogy in the cases of EPSPs above mentioned, hyperpolarizing waves.…”