Choh-Luh Li

The effects of 5-minute ischemia in Mongolian gerbils: II. Changes of spontaneous neuronal activity in cerebral cortex and CA1 sector of hippocampus

SummarySpontaneous neuronal activity was recorded in the cerebral cortex and the CA1 sector of the hippocampus in gerbils during and after 5-min ischemia, produced by bilateral clamping of the common carotid arteries. It was found that spontaneous activity in both cortical and CA1 neurons ceased within 60 s after the onset of ischemia and that it began to reappear 10–20 min after the recirculation. During the next 24 h most CA1 neurons which were recorded showed hyperactivity. This was evident primarily by an increase in spike discharges, whereas recordings from the cerebral cortex were within the preocclusion ranges. On the 2nd day after ischemia, functioning CA1 neurons could not be found, as if they were in a state of functional death, although histological sections showed a general preservation of their cellular structure at that time.

Microelectrode studies of the electrical activity of the cerebral cortex in the cat.

After over twenty years of study, the neurophysiological basis of the rhythmic oscillations in electrical potential which can be recorded from the cerebral cortex remains poorly understood. The most direct approach to this problem, and the only one which will eventually give a definite answer, is by means of microelectrodes which will record the discharge of single nerve cells simultaneously with the slower potential oscillations as well as the direct-current potential field in which the single units lie. The original studies of Renshaw, Forbes & Morrison (1940) on the hippocampus of the cat showed that unitary discharge of the pyramidal cells could be recorded with the microelectrodes when they were placed within the stratum pyramidale. Only slow waves were seen when recording from the surface and there was no suggestion that the slow waves were made up of envelopes of spike discharge. In fact there seemed to be no clear relationship between the slow wave oscillations and the unitary spike potentials obtained from the pyramidal cells. Similar results have recently been obtained by Brookhart, Moruzzi & Snider (1950) in the cerebellum, who concluded that the 200-300 per sec rhythmic activity of the cerebellum did not correspond to unitary discharge of cells within the cortex of cerebellum as recorded with microelectrodes. Woldring & Dirken (1950) have, however, recently reported rapid spike activity from the surface of the cerebral cortex obtained with electrodes made with platinum wires of 30, gauge, and which was most prominent in the waking animal, with grouped spike potentials related to slow waves in light narcosis. In the present report we wish to present the results of microelectrode studies of unit activity within the cerebral cortex of the cat in relation to slow potential oscillations under different excitatory states as affected by barbiturate

The effect of acute arterial hypertension on the blood-brain barrier to protein tracers

SummaryA study was made on the effect of acute hypertension on the blood-brain barrier to proteins. The arterial blood pressure was raised by intravenous injections of metaraminol bitartrate (Aramine) and Evans Blue was used as protein tracer.Multiple foci Evans Blue extravasation became evident in the gray matter of the brain as early as 10 min after the sudden increase of blood pressure by 90 mm Hg or higher. As observed under the fluorescence microscope, the tracer had penetrated the walls of intracerebral vessels and accumulated in numerous adjacent neurons. EEG recordings from blue stained areas of the cerebral cortex showed changes in neuronal activity.ZusammenfassungDie Wirkung akuter Hypertension auf die Blut-Hirnschranke für Proteine wurde untersucht. Die arterielle Blutdrucksteigerung wurde durch. i.v. Verabreichung von Metaraminol-bitartrat (Aramine®) erzeugt. Als Schrankenindikator wurde Evansblau verwendet.Multiple Herde von Evansblau-Extravasaten fanden sich in der grauen Hirnsubstanz frühestens 10 min nach plötzlicher Steigerung des Blutdruckes um 90 mm Hg oder höher. Fluorescenzoptische Untersuchungen ergaben, daß der Indicator durch die Wand der intracerebralen Gefäße ausgetreten war und sich in zahlreichen benachbarten Nervenzellen angesammelt hatte. EEG-Ableitungen der blau angefärbten Rindenareale ergaben Veränderungen der neuronalen Aktivität.

Maintenance of resting membrane potentials in slices of mammalian cerebral cortex and other tissues in vitro

Investigation of the mammalian brain would be greatly furthered if portions from it could be studied by electrophysiological methods while they were completely isolated from the body, as the peripheral nerves and spinal ganglia can be studied. Spontaneous potentials were observed in an isolated portion of the frog brain by Libet & Gerard (1939). Burns (1950, 1951) made observations on responses to electrical stimulation of cortical slabs of the cat which were connected to the brain only through pial vessels. With completely isolated mammalian cerebral tissue adequate supply of metabolites for maintenance requires sections less than 0 35 mm in thickness, and electrical activity in such sections has not previously been recorded. It could be pictured as lost through damage to cells in preparation of the sections. However, such tissue under good metabolic conditions has proved to be remarkably autonomous, and has also shown metabolic responses to applied electrical impulses (McIlwain, 1951, 1956). With a variety of recording electrodes (but not intracellular electrodes), transmission of impulses could not be detected in such tissue. A reasonable explanation of the metabolic response is that polarized cell elements were maintained in the tissue and depolarized by the applied impulses. In this series of experiments evidence was sought for such polarized intracortical elements with the use of micropipette electrodes. Most observations were made on the cerebral cortex of guinea-pigs and cats. Slices from the liver, kidney and skeletal muscles were also examined.

Excitability characteristics of the A- and C-fibers in a peripheral nerve

Abstract The saphenous nerve of the cat was stimulated with square pulses, triangle waves, sine waves, and haversine waves of varying intensities and durations. We found that haversine waves, with the anode proximal to the cathode in relation to the recording electrode, were most effective in producing “break” responses. At a given intensity and duration of the haversine waves for stimulation, only the response of C-fibers in the nerve was recorded. The strength/duration curves show that the rheobase of the C-fibers was 0.033 ma; and of the A-fibers, 0.0166 ma. The C-fibers had a chronaxy of 1.5 msec; the A-delta fibers, 0.45 msec; and the A-beta fibers, 0.020 msec. The average conduction velocity of the C-fibers was 0.92 m/sec; of the A-delta fibers, 11.2 meters per second; and of the A-beta fibers, 85.8 m/sec. The temperature of the nerves in the experiment was 29–30 C.

Electrical analogues for tissues

Abstract The equations of Maxwell and Reyleigh for the electrical resistance of suspensions of spheres and cylinders have been widely used to calculate the volume concentration of nonconducting cells in several tissues. The assumptions made in the derivations of these equations are not valid over at least part of the concentration range from 50 to 100% so that such calculations are without analytical basis. Approximations for uniform, uniformly separated, space filling figures and for randomly oriented, uniform and uniformly distributed, conducting planes show that each of the equations is correct for volume concentrations approaching 100%. Analogue measurements were made with conducting paper for circular cylinders in square and hexagonal arrays and with an electrolytic tank for spheres in simple and face centered cubic arrays. The available theories are not entirely satisfactory. Similar measurements were made for a square array of square cylinders and a hexagonal array of hexagonal cylinders and for a cubic array of cubes and a hexagonal array of tetrakaidecahedra. In all cases it was found that the measured volume concentrations agreed with those given by the simple Rayleigh and Maxwell equations, to within the experimental accuracies of about 1%, over all of the concentration ranges measured from 30% or less to 90% or more. These analogue calculations thus provide a basis for the use of the equations over the entire range.

Extracellular space of the cerebral cortex of normothermic and hypothermic cats

Abstract The extracellular space (ECS) of the cerebral cortex in the cat was estimated by methods of electrical impedance measurements and concentration profiles of radioactively labeled compounds following subarchnoid (SA) perfusion. Taking various factors into consideration the space was found to be between 15 and 20% and unchanged when the temperature of the cortex was decreased from 37 to 15C. However, the rate of cerebrospinal fluid (CSF) formation, as determined by SA and ventriculocisternal (VC) perfusion, was found to be markedly reduced by hypothermia.

Specific resistivity of the cerebral cortex and white matter

Abstract Electrical resistance of the cortex and white matter of the cat was investigated by comparing the resistivity with that measured from solutions of known conductivities. At 36 C it was found that the specific resistance of the cortex is 556 ± 45 (SD) ohm cm and of the white matter, 580 ± 53 (SD) ohm cm.

Some properties of mammalian skeletal muscle fibres with particular reference to fibrillation potentials

Fibrillation potentials recorded from denervated muscle are generally believed to originate in single muscle fibres (Denny-Brown & Pennybacker, 1938). Eccles (1941) suggested that some of the fibrillation potentials recorded from denervated skeletal muscles of the cat may arise at any point along the muscle fibre, whereas Hayes & Woolsey (1942) concluded from their experiments on denervated rat diaphragm that all fibrillation potentials take origin from the end-plate zone. These views were based on observations by means of relatively large extracellular recording electrodes, and the origin of the potentials could not be determined with absolute certainty. With intracellular electrodes Nicholls (1956) measured the resting potentials and membrane resistance of denervated muscles of the frog, but no account was given of spontaneous fibrillation potentials, probably because fibrillation is infrequent in amphibia (Fatt & Katz, 1952). Membrane resting potentials of denervated mammalian skeletal muscles were also studied with intracellular electrodes by Ware, Bennett & McIntyre (1954). These authors likewise made no report on the spontaneous fibrillation potentials. The experiments described below were designed primarily to study the fibrillation potentials recorded with intracellular electrodes from denervated muscle fibres. This study also permitted observations on the responses to motor nerve stimulation in mammalian skeletal muscles in vivo.

The inhibitory effect of stimulation of a thalamic nucleus on neuronal activity in the motor cortex.

It is well known that the motor cortex receives thalamic projections from the nucleus ventralis lateralis (Polyak, 1932; Walker, 1936, 1938). This nucleus in turn derives its most important afferent supply from the rostral end of the parvocellular portion of the red nucleus (von Monakow, 1895), and more directly from the cerebellum by crossed fibres in the brachium conjunctivum (Crouch & Thompson, 1938; Walker, 1938). A postulated cortico-pontocerebello-dentato-rubro-thalamo-cortical circuit has been emphasized in relation to motor function (Bucy, 1944). The present study presents a series of experiments in which the effect of the discharge from the nucleus ventralis lateralis (VL) upon the activity of the motor cortical neurones was investigated, revealing that the neuronal activity can be inhibited by an afferent volley from this thalamic nucleus.