Light Urethane Anesthesia Research Articles

Excitation, inhibition and rhythmical activity in hippocampal pyramidal cells in rabbits.

AbstractEuler, C. V. and J. D. Green. Excitation, inhibition and rhythmical activity in hippocampal pyramidal cells in rabbit.The activity pattern of single hippocampal pyramidal cells has been studied in rabbit under light urethane anaesthesia and with encéphale isoléin response to various stimuli. Deep depolarization leading to initial excitation followed by in‐activation of spike generation has been found to be a commonly operating mechanism in the hippocampal pyramids. Such ‘inactivation processes’ have appeared spontaneously as well as in response to various stimuli. They may be driven with great precision as well as appearing rhythmically in after discharges. The ‘inactivation process’ was commonly followed by a hyper‐polarization. Thus two different mechanisms of inhibition followed each other. Prolonged septal stimulation provoked trains of rhythmically recurring inactivation processes with bursts of declining spikes at the rising phase of each depolarizing wave.Close similarities between the theta rhythm and rhythmically recurring inactivation processes are described and it is suggested that the former is built up by the latter synchronously occurring in several neurones. The inactivation process was also found to be a commonly occurring cellular event during seizure activity.

Activity in Single Hippocampal Pyramids

AbstractEuler, C. V. and J. D. Green. Activity in single hippocampal Pyramids.Activity from single pyramidal cells of dorsal hippocampus has been studied in rabbits under light urethane anaesthesia or with encéphale isolé. Capillary microelectrodes were used for recording. Respiratory and cardiovascular movements of the brain were reduced by using a ‘closed system’. Extracellular biphasic positive‐negative spikes of large amplitude were frequently recorded. The shape of the extracellular spikes indicate that the soma spikes are usually not followed by excitation of the dendritic membrane. However, occasionally spikes with negative‐positive potential sequence indicating somatofugal excitation of the dendrites, have been recorded after a burst of positive‐negative spikes. This occurred in response to prolonged repetitive stimulation and in after‐discharges. Spikes were normally not recorded in the dendritic layer. Repetitive stimulation, however, elicited sharp spikes in the apical dendrites increasing in number and amplitude with increasing stimulus strength and duration.Action potentials and slow changes in membrane potential were commonly recorded with big attenuation but without other signs of serious injury.Polarizing hippocampal neurones with minute currents in the order of 2 × 10‐9A through the recording microelectrode stimulated or inhibited that cell from which the activity was extracellularly recorded.The hippocampus is an uncomplicated cortical structure with a relative uniform and simple lamination. These and other features make the Ammon's horn a suitable site for studies of cortical properties (see e. g. Euler, Green and Ricci 1958). This paper presents an analysis of the spontaneous activity in single hippocampal pyramids and a component analysis of spike potentials recorded extracellularly. A subsequent paper (Euler and Green 1960) deals with the activity patterns which can be elicited through afferent stimulation. A ‘positive’ wave with rapidly declining ‘positive’ spikes proved to be a pattern entity of possible significance for the ‘brain waves’ of the hippocampus. Although no successful intracellular records of this phenomenon were obtained, the experimental data presented in the present paper lend themselves to the conclusion that the spikes and the wave originate in the same neurone and that the phenomenon thus may be identified as the ‘inactivating process’ of Granit and Phillips (1956).

Influence of Oxygen Deficiency on Reflex Dilatation of the Pupil

The purpose of the studies reported in this paper is twofold: 1. To extend the systematic observations of Gellhorn and collaborators on the effect of oxygen deficiency on the central nervous system to the autonomic nervous system. 2. To choose a reaction which is determined exclusively or to a large extent by a central inhibitory process in order to study the influence of oxygen deficiency on such processes. Although the literature on the problem of reflex dilatation is still controversial a number of authors have shown that this reaction is largely due to an inhibition of the parasympathetic tonus of the Edinger-Westphal nucleus. This is particularly clear from the work of Bain, Irving and McSwiney, who find that the stimulation of the central end of the splanchnic fails to elicit pupillary dilatation after sectioning of the third nerve, although “section of the cervical sympathetic nerves has not been found to alter either the rate or the degree of the reaction to stimulation of somatic or visceral afferent fibers.” The experiments were carried out repeatedly on 12 rabbits, half of which had the cervical sympathetic cut on one side. The sciatic was exposed under light urethane anesthesia and 2-3 hours later the experiment was begun. The threshold reaction for pupillary dilatation was determined with faradic stimulation (Harvard inductorium, shielded electrode) while the animals inhaled air or a known O2-N2-mixture from Douglas bags. Very weak currents (coil distance 11-12 cm. or at an angle) were used for 1-3 seconds and the pupillary reaction was measured with a telescope. The results were uniform and showed that under the influence of 643% O2 the threshold for pupillary dilatation was raised.