Negative components of the direct cortical response

Dendritic (DPs) and slow negative potentials (SNPs) arising in response to direct electrical stimulation of the cortex in cats under deep Nembutal anesthesia were studied. Monosynaptic DPs reflect EPSPs of apical dendrites; they develop in response to impulses arriving from fibers in layer I. DPs are strengthened by application of eserine and by Ca⁺⁺, and weakened by the action of Mg⁺⁺, Br^–, and caffeine. Analysis of changes in DPs evoked by paired stimuli indicates that Ca⁺⁺, Mg⁺⁺, and Br^– influence the presynaptic elements of axo-dendritic synapses, while caffeine acts on their postsynaptic elements. DPs are abolished by application of GABA; strychnine does not affect them. From these and other facts it can be concluded that there are no inhibitory synapses on apical dendrites. Evidence of the participation of the neuroglia in SNP genesis is analyzed. SNPs are selectively depressed by x-rays, strengthened by Ca⁺⁺, and weakened by Mg⁺⁺. Against the background of SNPs, DPs are inhibited and the ratio between amplitudes of DPs evoked by paired stimuli is changed. It is concluded that during SNPs the dendrites and presynaptic terminals of axo-dendritic synapses are deploarized.Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 339–348, July–August, 1970.     

Effect of cortical extracellular GABA on motor response

Journal of Computational Neuroscience - To elucidate how the flattening of sensory tuning due to a deficit in tonic inhibition slows motor responses, we simulated a neural network model in which a...     

Origin of slow negative potential of direct cortical response in cats

To investigate mechanisms of formation of the electrocorticographic slow negative potential (SNP) evoked by direct electrical stimulation of the cortical surface, poststimulus single unit activity in the stimulated area was studied in anesthetized cats and changes in SNP in the depth of the cortex were analyzed. The results showed that membrane hyperpolarization, accompanied by cessation of action potential generation, develops parallel with SNP in neuron bodies in the stimulated area. Investigation of the nature of this hyperpolarization showed that during its development excitability of the neuron and resistance of the postsynaptic membrane fall. It is concluded from the results that this membrane hyperpolarization is an indicator of IPSP development in the neuron bodies. The results of laminar recording showed that SNP may diminish or even disappear in the depth of the cortex without subsequent reversal. Determination of dipoles formed along an axis perpendicular to the cortical surface showed that SNP has one source and two sinks, which are located symmetrically relative to it. The presence of two symmetrical sinks must indicate an active source, formed as a result of hyperpolarization of the neuron membrane. On the basis of the results SNP can be regarded as a field potential formed on the cortical surface as a result of IPSP development in the neuron bodies.Institute of Clinical and Experimental Neurology, Ministry of Health of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 15, No. 3, pp. 314–320, May–June, 1983.     

Effect of psychotropic drugs on somatosensory evoked cortical potentials]

The effects of some typical clinically tested psychotropic drugs were studied in acute experiments on awake rats. Potentials in somatosensory cortex were evoked by peripheral stimulation. Haloperidol, diazepam, medazepam, desipramin and a new substance, the MPP-sulton, caused significant modification in latency and amplitude of some components of the potentials. Between the effects of psychotropic drugs exist differences which, in turn, were clearly distinguishable from the modification of these evoked responses by unspecific narcotic effects of hexobarbital.     

Effect of pefloxacin on immune response]

The influence on cellular immune response of different doses of the pefloxacin was studied in vivo as well as in vitro experiments. The pefloxacin in super bactericidal concentrations (2.0 mg/ml and 0.4 mg/ml) possess pronounced supressing effect the T-lymphocyte proliferation in blast transformation reaction. While in concentration 0.08 mg/ml pefloxacin does not show such activity. The pefloxacin in maximal effective concentration (200 mg/kg) suppressed activity in delayed hypersensitivity skin reaction of intact mice towards sheep erythrocytes on 20.3 percent only.     

Effect of temperature on impulse activity of cortical neurons in guinea pigs

The temperature change of incubating fluid from 37 to 24 degrees C results in significant decrease of neuronal spontaneous firing rate in parietal cortex slices. Evoked spike responses to microiontophoretic application of glutamate practically did not change.     

Effect of high local temperature on reflex cutaneous vasodilation

We examined the effect of high local forearm skin temperature (Tloc) on reflex cutaneous vasodilator responses to elevated whole-body skin (Tsk) and internal temperatures. One forearm was locally warmed to 42 degrees C while the other was left at ambient conditions to determine if a high Tloc could attenuate or abolish reflex vasodilation. Forearm blood flow (FBF) was monitored in both arms, increases being indicative of increases in skin blood flow (SkBF). In one protocol, Tsk was raised to 39-40 degrees C 30 min after Tloc in one arm had been raised to 42 degrees C. In a second protocol, Tsk and Tloc were elevated simultaneously. In protocol 1, the locally warmed arm showed little or no change in blood flow in response to increasing Tsk and esophageal temperature (average rise = 0.76 +/- 1.18 ml X 100 ml-1 X min-1), whereas FBF in the normothermic arm rose by an average of 8.84 +/- 3.85 ml X 100 ml-1 X min-1. In protocol 2, FBF in the normothermic arm converged with that in the warmed arm in three of four cases but did not surpass it. We conclude that local warming to 42 degrees C for 35-55 min prevents reflex forearm cutaneous vasodilator responses to whole-body heat stress. The data strongly suggest that this attenuation is via reduction or abolition of basal tone in the cutaneous arteriolar smooth muscle and that at a Tloc of 42 degrees C a maximum forearm SkBF has been achieved. Implicit in this conclusion is that local warming has been applied for a duration sufficient to achieve a plateau in FBF.     

The effect of a high external temperature on cellular immunity]

The study was made of spleen cells proliferative response to mitogens PHA, Con A or alloantigens in relation to hyperthermia effects. Acute hyperthermia (rectal temperature 42 degrees) enhanced lymphocyte function, proliferative responses to allo-antigens, PHA and Con A increased. Thermal shock was associated with suppression of the spleen cell response. Mice suffering from hyperthermia for 20 min (43-44 degrees) daily during 10, 20 and 30 days showed suppressed T-cell immune response. Normal splenocyte proliferation recovered 40 days after hyperthermia induction.     

Effect of degree of uniformity on predicted visual cortical response tuning curves

 The different cortical visual cells exhibit a large repertoire of responses to sinusoidal gratings, depending on their receptive field structure and the stimulation parameters. It has been shown previously that the tuning curves and histogram shapes of cell responses are affected by subunit distances. One receptive field model (Spitzer and Hochstein 1985b) incorporated subunit distance but assigned it as a constant parameter, for ease of calculation. Here we investigate different tuning curve properties of various primary cortical cell types during testing of 10 deg of nonuniform distances of the receptive fields’ subunits. The effect of nonuniformity was compared for average responses, tuning curve shapes, maximum peak responses, and bandwidths across four cell types of different sizes. The shapes and other properties of tuning curves are usually found to be retained also when the degree of uniformity is not very high for most of the cell types. In addition, the effect of uniformity is compared across these different response properties. The maximum peak responses of the tuning curve are found to display a lower coefficient of variation than the bandwidth, for all cell types, for most degrees of uniformity. Received: 15 June 1993/Accepted in revised form: 5 August 1994     

Glial origin of the slow negative potential of the direct cortical response: Microelectrode study and mathematical analysis

The slow negative potential of the direct cortical response is similar in its shape, time course, and relationship to repetitive stimulation to depolarization of cortical glial cells but differs from the IPSP of cortical neurons. According to the results of digital spectral (frequency) analysis, the basis of the slow negative potential is the glial component formed by summation of components which coincide with glial depolarization processes with an accuracy determined by a constant factor. The much smaller component (as regards relative contribution) is the indirect result of the development of an IPSP in the neurons.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 76–84, January–February, 1982.     

Effect of repeated serotonin injections on temperature regulation in the rat]

The effect of repeated serotonine injections was investigated in thirty Wistar rats tested under normo-, hypo- und hyperthermic conditions. 7 mul of a 0.5% serotonine solution (5HT) were injected into the third ventricle at 1-hr intervals. Temperature responses such as oxygen consumption and rectal temperature were measured and the heat loss was calculated. Intraventricular serotonine produced cooling in all animals. The central mechanisms of heat production were inhibited and those of heat loss were activated. The serotonine responses were most pronounced in hypothermic rats and least effective in hyperthermic animals.