Changes in the extracellular potassium concentration and the slow negative cortical potential

Changes in the extracellular potassium ion concentration ([K⁺]₀) of the suprasylvian gyrus of the cat cortex were recorded by potassium-selective microelectrodes; the electric field potential was recorded at the same time. Under deep anesthesia one electrical stimulus, of sufficient intensity to induce a slow negative potential when applied to the cortical surface, evoked a local increase in [K⁺]₀ by 0.1–1.5 mM. The time course of this rise was very similar to that of the slow negative potential. It is suggested that this potential reflects glial depolarization under the influence of K⁺ ions.I.S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Institute of Physiology, Czechoslovak Academy of Sciences, Prague. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 459–463, September–October, 1980.     

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.     

The slow negative wave of the evoked potential of the frog midbrain tectum

A surface-negative slow wave (SW) with a latent period of 50–60 ms, an amplitude of up to 3 mV, and a duration of 0.5–1.5 sec follows the postsynaptic components in the potential of the midbrain tectum (MBT) of a curarized frog (Rana temporaria L.) evoked by electrical stimulation of the optic nerve. The SW develops as a result of the arrival of a synchronous afferent volley along amyelinic fibers; it is generated as a result of depolarization of radially oriented cellular elements; the periventricularly located parts of these structures serve as the source of the current. In the case of rhythmical stimulation, the SW is summed to a value exceeding 10 mV, while at the beginning of stimulation with a frequency of 10–40/sec, the SW is facilitated. After the injection of picrotoxin, selective sensitivity of the SW to this substance was not found. An SW also develops from direct stimulation of the MBT. Comparison of the results of recording neuronal activity shows that the SW is connected with direct afferent inhibition. It is assumed that the SW is generated by elements of the ependymoglia.A. N. Severtsov Institute of Evolutionary Animal Morphology and Ecology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 145–153, March–April, 1971.     

The relationship between a conditioned slow negative potential and focused attention]

A conditioned slow negative vertex potential (CSNP) was studied in the interval between two stimuli: anticipatory and trigger, under different experimental conditions, namely; in response to a trigger stimulus the subject was to press an operating key; or to memorize the number of trigger stimuli; or to respond to the trigger stimulus by pressing the key and memorizing the number of anticipatory stimuli. A sound, geomatrical figures and separate words flashing up on a screen were used as stimuli. All of them were presented both as anticipatory and trigger signals. If a sound was used as an anticipatory stimulus, and a word as trigger one, the recorded CSNP was at its maximum in the case of a simple motor reaction, and at its lowest during retention. When the stimuli interchanged, was drawn to the anticipatory verbal stimulus, the CSNP amplitude diminished and the latency became shorter. The dependence of SCNP parameters on the subject's attention drawn to the anticipatory resp. trigger stimuli is discussed.     

Midpoint potential of signal II (slow) in Tris-washed photosystem-II particles

In Tris-washed Photosystem-II particles we are able to induce an EPR signal in the dark by addition of an iridium salt (K₂IrCl₆). This signal is attributed to signal II_s (slow) (D⁺) and the redox titration gives an E_m value of 760 mV for the couple $\text{D}{}^{\mathrm{+}}\text{D}$. On the basis of our previous studies on the equilibrium between D⁺Z and DZ⁺ (K = 10⁴) (Boussac, A. and Etienne, A.L. (1982) Biochem. Biophys. Res. Commun. 109, 1200–1205), we therefore attribute a value of 1 V for the E_m of the $\text{Z}{}^{\mathrm{+}}\text{Z}$ couple. A second effect of K₂IrCl₆ is to modify the spectral characteristics of signal II. We conclude that K₂IrCl₆ is able to change the environment of the species from which signal II_s and signal II_f originate.     

An allotype linked gene that is associated with a negative or very low anti-phosphorylcholine response (PC) phenotype in wild mice (CNV)

In contrast to most inbred and wild mice, a population of wild mice recently isolated from a farm in Centreville, MD, and designated CNV produced no anti-phosphorylcholine (PC) antibodies (less than 1 microgram/ml) in response to immunization with the PC antigen Streptococcus pneumoniae (R36A) and gave 9 to 36 micrograms/ml anti-PC response to PC-KLH at 14 days after immunization. When another carbohydrate antigen, namely, bacterial levan, was used, CNV mice all gave high antibody titers. When CNV (PC-) mice were bred to inbred C.B20 (PC+) mice, 82% of the F1 and 76% of the F2 hybrids were surprisingly non-responders (PC-), which suggested that PC- gene(s) of CNV origin dominated the response to these antigens. The 18% PC+ phenotype in the F1 hybrids indicated possible heterozygosity of the PC genes controlling the PC- response in the CNV mice. Genetic studies on CNV mouse No. 378 supported this possibility. Analysis of the F2 data strongly suggest that two genes determined the PC- response, one of which was closely linked to the Igh-C allotype locus (chromosome 12). Hypothetically, we propose that CNV mice have two genes that cooperate but that sometimes act independently to express the PC- phenotype. Surprisingly, when F1 mice giving PC- phenotypes were back-crossed to C.B20, very few mice (18%) were PC-. This indicated that the PC- determining genes of CNV origin were not able to dominate immune responses in the presence of a larger number of C.B20 genes. This kind of expression may be regulated by other factors, such as clonotype competition and clonal dominance.     

An easy method to record slow potential shifts (SPS) in rabbits using the oddball paradigm

Rabbits with chronically implanted Ag-AgCl electrodes over somatosensory and visual cortex were trained to a modified 'oddball' paradigm with visual stimulation. Event related potentials (ERP) and slow potential shifts (SPS) were recorded. By means of a computer controlled stimulator 'frequent' and 'rare' LED flashes were administered to the eyes of the rabbit. If 'rare' stimuli were reinforced by a weak electrical footshock, negative SPS rose steeper and reached significantly higher amplitudes than in 'frequent' conditions without reinforcement. Different kinds of the follow-up of 'frequent' and 'rare' series were tested. Best effects were obtained, if a session was divided into 3 blocks (3 srs. 'frequent'--5 srs. 'rare' reinforced--2 srs. 'frequent' and probability of 'rare' flashes was 20%. Our present data formed a basis for investigations on the neuronal and glial sources of SPS in rabbits.     

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.     

Reproduction in the slow loris (Nycticebus coucang)

The reproductive biology of the slow loris (Nycticebus coucang) is poorly documented because of infrequent captive breeding success and the absence of field studies of this species. Reproductive data were collected from a breeding colony of slow lorises held at the Duke University Primate Center for the past 10 years. Nineteen infants were born, with a sex ratio of 1:1 and a neonatal mortality rate of 15.8%. In all cases, litter size was one. Females born in the colony copulated for the first time between 18 and 24 months of age. A male that reached sexual maturity in the colony sired his first offspring at the age of 17 months. Estrous cycles ranged in duration from 29–45 days, with copulations usually occurring for 1 day of estrus. Gestation length averaged 192.2 days. Although a postpartum estrus was observed in three cases of infant death, no conceptions resulted. Lactation lasted approximately 6 months. A clear birth peak was observed, with 12 out of 19 births occurring in March, April, and May. The comparatively low basal metabolic rate of this species may account for the unusually low reproductive rate of the slow loris in comparison with other prosimian primates.     

Genetic association analysis of copy-number variation (CNV) in human disease pathogenesis

Structural genetic variation, including copy-number variation (CNV), constitutes a substantial fraction of total genetic variability and the importance of structural genetic variants in modulating human disease is increasingly being recognized. Early successes in identifying disease-associated CNVs via a candidate gene approach mandate that future disease association studies need to include structural genetic variation. Such analyses should not rely on previously developed methodologies that were designed to evaluate single nucleotide polymorphisms (SNPs). Instead, development of novel technical, statistical, and epidemiologic methods will be necessary to optimally capture this newly-appreciated form of genetic variation in a meaningful manner.     

Crystal structure of DsbDgamma reveals the mechanism of redox potential shift and substrate specificity(1)

The Escherichia coli transmembrane protein DsbD transfers electrons from the cytoplasm to the periplasm through a cascade of thiol-disulfide exchange reactions. In this process, the C-terminal periplasmic domain of DsbD (DsbDgamma) shuttles the reducing potential from the membrane domain (DsbDbeta) to the N-terminal periplasmic domain (DsbDalpha). The crystal structure of DsbDgamma determined at 1.9 A resolution reveals that the domain has a thioredoxin fold with an extended N-terminal stretch. In comparison to thioredoxin, the DsbDgamma structure exhibits the stabilized active site conformation and the extended active site alpha2 helix that explain the domain's substrate specificity and the redox potential shift, respectively. The hypothetical model of the DsbDgamma:DsbDalpha complex based on the DsbDgamma structure and previous structural studies indicates that the conserved hydrophobic residue in the C-X-X-C motif of DsbDgamma may be important in the specific recognition of DsbDalpha.     

The thalamus in the motor system.

The ventrolateral (VL) and anterior (VA) are the main thalamic relay for cerebellar and pallidal efferents going to the motor cortex. Four aspects of the function of these nuclei are briefly considered. (1) It is well known that these thalamic structures are not a simple relay on the way to the motor cortex, but that they have a gating function for the cerebellar afferents. The gating mechanism is active during slow-wave sleep, with deafferentation and with the use of various anesthetics. Possibly, it might play a role in the central organization of movement. (2) The organization at the unitary level of the projections between VL and motor cortex is examined and their role in the command of motor synergies through the motor cortex is strongly suggested. (3). It appears that unitary activity of VL neurons is not only related to movement but also to postural changes associated with movement. (4) The sensory input to VL nucleus is briefly analyzed. The inefficacy of exteroceptive stimulation in awake animals, in contrast with the effect of the same stimulation in anesthetized preparations, is discussed.     

Fluorescence emission spectral shift measurements of membrane potential in single cells.

Previous measurements of transmembrane potential using the electrochromic probe di-8-ANEPPS have used the excitation spectral shift response by alternating excitation between two wavelengths centered at voltage-sensitive portions of the excitation spectrum and recording at a single wavelength near the peak of the emission spectrum. Recently, the emission spectral shift associated with the change in transmembrane potential has been used for continuous membrane potential monitoring. To characterize this form of the electrochromic response from di-8-ANEPPS, we have obtained fluorescence signals from single cells in response to step changes in transmembrane potentials set with a patch electrode, using single wavelength excitation near the peak of the dye absorption spectrum. Fluorescence changes at two wavelengths near voltage-sensitive portions of the emission spectrum and shifts in the complete emission spectrum were determined for emission from plasma membrane and internal membrane. We found that the fluorescence ratio from either dual-wavelength recordings, or from opposite sides of the emission spectrum, varied linearly with the amplitude of the transmembrane potential step between -80 and +60 mV. Voltage dependence of difference spectra exhibit a crossover point near the peak of the emission spectra with approximately equal gain and loss of fluorescence intensity on each side of the spectrum and equal response amplitude for depolarization and hyperpolarization. These results are consistent with an electrochromic mechanism of action and demonstrate how the emission spectral shift response can be used to measure the transmembrane potential in single cells.     

Activation parameters of the blue shift (Shibata shift) subsequent to protochlorophyllide phototransformation

The Shibata shift was analyzed in flash irradiated wheat (Triticum aestivum, L., cult. MV17) leaf homogenates in the pressure range of 0.1 to 500 MPa, at temperatures of 20, 30 and 40 degrees C. The kinetics of the blue shift (called Shibata shift in case of intact leaves) was followed by repeated recording of fluorescence emission spectra after phototransformation. At 20 degrees C, above 100 MPa, the blue shift slowed down remarkably. Two components of the blue shift could be distinguished, one was pressure-dependent and the other was almost pressure-independent. The pressure-independent component can be associated with minor conformational changes of the NADPH:protochlorophyllide oxidoreductase (POR) enzyme, followed by molecular movements of the newly formed chlorophyllide molecules. The calculated activation volume of the pressure-dependent component was 43+/-11 cm(3) mol(-1) at 20 degrees C. This value reflects major molecular reorganizations in the lipid system of the membrane and in the chlorophyllide-protein complexes, and corresponds to changes of the tertiary structure of proteins which can proceed directly or indirectly via structural changes of the membrane lipids. The process was inhibited by 300 and 400 MPa at 30 and 40 degrees C, respectively. The activation volume reduced to 35+/-1.5 cm(3) mol(-1) at 40 degrees C. The decrease of the activation volume with increasing temperature indicates that the blue shift requires loosened lipid structures. The activation energy of the blue shift (measured between 10 and 40 degrees C at atmospheric pressure) was 100+/-20 kJ/mol, indicating that the structural change involves rearrangement of strong molecular interactions.     

Territorial shift in the yellow-handed titi monkey (Callicebus torquatus)

In this study, the ranging pattern of a single group of monogamous and territorial Callicebus torquatus was recorded over a 7-year period from 1974 to 1980. Data on ranging pattern were recorded by direct observation; daily movement patterns were plotted on an accurate, scaled map of the territory. Data were obtained during 1–3-month studies each year from 1974 to 1978 and in 1980, as well as during a 12-month study in 1979-1980. These studies show that the exclusive territory maintained by the group was not spatially stable over the 7-year period. The group gradually moved its territory to the northeast, to the extent that the territory used in 1980 was completely noncoincident with the territory used in 1974 by the same group. Analysis of the ranging pattern from the 12-month study indicates that the group did not exhibit seasonal preferences for different parts of its range. Seasonal ranging patterns, therefore, are not likely to account for the observed territorial shift. It is suggested that territorial shifting may be related to the need for monogamous groups to find new territories for their offspring.