Intracellular Recordings from the Motor Cortex during EEG Arousal in Unanaesthetized Brain Preparations of the Cat

Abstract

1. Intracellular recordings were made from 92 neurones in the precruciate cortex of encephale isole and midpontine pretrigeminal preparations of the cat. 2. All but only one of these cells showed appreciable changes in the membrane potential during the transition from the cortical slow wave phase to the EEG arousal occurring spontaneously or induced by stimulating the midbrain reticular formation. Thus, 38 cells were depolarized (D-type cells), 48 cells hyperpolarized (H-type cells) and 5 cells showed an early hyperpolarization and a later depolarization (mixed type). 3. The latency of intracellular responses to reticular stimulation was shorter in the D-type cells than the H-type or mixed-type cells, and shorter for each of the D-and H-types in the cells of the superficial layers than those of the deep layers. 4. The D-type cells were distributed widely through laminae I to V, but the majority was sampled in lamina II. The H-type cells were located in laminae III-VI with the mode at the upper half of lamina III. The mixed-type cells were mostly located in laminae V and VI. 5. Antidromically identified slow pyramidal tract (PT) cells (n =9) all belonged to the D-type, and fast PT cells either to the H-(n=11) or the mixed type (n 4) . 6. These results suggest that the EEG arousal is a state composed of both excitatory and inhibitory responses of cortical cells which are processed from the superficial to the deep layers.EEG arousal (MORUZZI and MAGOUN, 1949) has been ascribed to one of the main manifestations of arousal of the brain, and may accompany the orienting or investigatory response which provides a turning point in animal behaviour (PAVLOV, 1927 ;MORUZZI, 1962 ;MAGOUN, 1963 ;SOKOLOV, 1963). Recent electrophysiological studies of EEG, extracellular units or field potentials recorded from various neocortical regions have revealed that neuronal responses on the EEG arousal

Vertical spread of neuronal activity within the cat motor cortex investigated with epicortical stimulation and intracellular recording.

“…The head of the animal was fixed atraumatically on the semi-chronic stereotaxic frame (Narishige SN-3, SA-8) by two metal bars that were anchored to the skull. As pointed out earlier (INUBUsHI et al, 1978a), general care was important to maintain the preparation in a sound condition. No signs of discomfort of the animal or disturbance on the electrocorticogram (ECoG) were observed during the experiments, in which a spontaneous alternation of sleep and waking patterns occurred.…”

“…As previously described (INUBUsHI et a!., 1978a), the surgery was performed under ether anesthesia. The preparation was immobilized afterwards, had all wounds infiltrated with procaine, and was carefully maintained under artificial respiration in a sound-attenuated and electrically shielded room.…”

“…The microelectrode was filled with 2 M KCH3SO4 solution, and those with electrical resistances of 30-80 MSS were selected for the intracellular recording. After setting all the recording and stimulating electrodes, the cortex was covered with wax as described previously (INUBUsHI et al, 1978a).…”

“…1, 2, 4, 9, 10, 13) were reproduced on an X -Y recorder (Watanabe WX4401) through the memory devices or signal averagers (Nihon Kohden DAT-1100; Digitimer NL-750 and PDP-11). Care was taken to select the frequency characteristics of potential reproduction in a sufficiently wide range (INUBUSHI et al, 1978a).…”

“…When the vertical direction of microelectrode tracking was verified within the error of 10°, the location of recorded cells was determined by the depth reading on an electronic micromanipulator (Narishige ME-71, cf. INUBUSHI et al, 1978a). Correction of the depth reading was not necessary except for a few tracks, in which the site of penetration was too close to the cruciate sulcus.…”