Digitalis-like biological activity in rat cerebellum

The cytosolic fraction of rat cerebellum possesses a factor(s) which is capable of inhibiting synaptosomal Na,K-ATPase activity, competing with [3H]ouabain binding to rat brain synaptosomes, and inducing positive inotropy in guinea pig atrial strips. These results demonstrate the existence of a ouabain-like principle in rat cerebella. The inhibitory activity of the factor was found to be partially thermolabile and diminished by a proteolytic agent, and the activity could be augmented by increasing concentrations of Mg2+, suggesting a regulatory mechanism for the endogenous digitalis-like principle.     

Hydroxyurea inhibits thymidine kinase activity in developing rat cerebellum

Hydroxyurea when injected intraperitoneally into rats either as a single dose or as three consecutive daily doses, markedly inhibited thymidine kinase activity in cerebellum on 7th day. The inhibitory effect of the drug was found to be both dose and time dependent. The drug has however, failed to exert any inhibitory action when added to the reaction mixture in vitro. It is concluded that the well established inhibition on DNA synthesis by hydroxyurea may not be solely due to its action on ribonucleotide reductase (EC 1.17.4.1) but probably due to its interference at several other sites including thymidine kinase.     

Estimation of structural changes in the cataractous rat lens using Raman spectroscopy.

For quantitative evaluation of cataract-related changes in lens proteins and lens water, the relative contents of water and SH residues and changes in the microenvironments of aromatic amino acid residues were quantitatively examined in cataract of the rat lens which had been induced by sodium selenite. Using Raman spectroscopy, results were compared with those of age-matched control lenses. The relative contents of water and SH residues decreased with increasing age in normal lenses from 3 to 8 weeks of age. In the cataractous lens, the relative water content increased constantly as compared with that of age-matched controls. The relative SH residue content continued to decline in the cataractous lenses of animals at every age. The microenvironments of tyrosine residues in cataractous lenses also changed progressively.     

Post-translational changes of chromosomal proteins in rat cerebellum during postnatal development

Acetylation, phosphorylation and methylation of nuclear proteins in rat cerebellum at 10 and 30 days of age were investigated in vitro. Isolated nuclei were incubated in the presence of [1-14C]acetyl CoA, S-adenosyl [methyl-3H]methionine and [gamma-32P]ATP and then separated into histones and non histone proteins (NHP), which were further fractionated by polyacrylamide gel electrophoresis. The results obtained indicate that acetylation, phosphorylation and methylation of both basic and acidic proteins decrease from 10 to 30 days of age. Electrophoretic analysis of histones shows that the decrease mainly concerns H1, H3, and H2b fractions. The H3 fraction is always more labeled than the other fractions and shows the major changes during postnatal development. Phosphorylation of H2a and H4 fractions increases from 10 to 30 days of age, whereas acetylation and methylation of these fractions do not show significant changes from 10 to 30 days. The densitometric and radioactive patterns of NHP show considerable changes between 10 and 30 days, especially in the high molecular weight region. The incorporation of 14C-acetyl and 3H-methyl groups and of 32P phosphate appears to be generalized throughout the molecular weight range and decreases from 10 to 30 days of age. The methylation of an as yet unidentified protein with a molecular weight of approximately 110,000 daltons occurred at both ages.     

Differential acetylcholinesterase activity in rat cerebrum, cerebellum and hypothalamus

Acetylcholinesterase (AChE) has been purified from three different regions of rat brain using Sephadex G 200 column. SDS PAGE (6%) showed single band for the purified AChE fractions. Purified and lyophilized AChE from different (NH4)2SO4 precipitated fractions of three brain parts were utilized for in vitro enzyme kinetics using Dimethoate (Dmt) as inhibitor. K(m) values for cerebellum and hypothalamus were almost similar whereas cerebrum showed a different K(m) value compared to other two regions. With the drug Rivastigmine it was found that % G1 and G4 forms of AChE in three different parts of brain are different.     

Accuracy in estimating motor commands using neuronal population coding

We consider the problem of estimating motor commands from an ensemble of neuronal activities. The population vector algorithm proposed by Georgopoulos provides largely biased estimations when preferred directions of neurons are non-uniformly distributed. To improve this, various decoding methods have been proposed. However, dependence of decoding accuracy on the motor command and other features of neural activities, such as baseline firing rates or amplitudes of tuning curves, have not been quantitatively discussed. In this study, we propose a new method to estimate the motor command in the maximum likelihood estimation framework, which is analytically tractable. We find that the estimation accuracy is independent of the motor command. Using our estimation method, we can estimate the motor command with equal accuracy in all directions.     

A model for evoked activity of hippocampal neuronal population

A system of equations governing the activity of hippocampal neuron populations is proposed. This continual firing-rate model is aimed to simulate evoked potentials and synchronous wave activity of the neural tissue. The populations of excitatory and inhibitory neurons and the types of synaptic receptors are distinguished. The model is based on the idea of control and averaging of Hodgkin-Huxley equations, a simple model of a threshold elicitation of population action potential bursts, approximations of synaptic currents by the second-order differential equations, and hyperbolic partial derivative equation of axonal excitation propagation. The model was fitted to intracellular cordings of postsynaptic potentials and postsynaptic currents in CA1 of rat hippocampal slices.     

Uptake of GABA by neuronal and nonneuronal cells in dispersed cell cultures of postnatal rat cerebellum

A study was made of the time course and kinetics of [³H]GABA uptake by dispersed cell cultures of postnatal rat cerebellum with and without neuronal cells. The properties of GABA neurons were calculated from the biochemical difference between the two types of cultures. It was found that for any given concentration of [³H]GABA, or any time up to 20 min, GABA neurons in cultures 21 days in vitro had an average velocity of uptake several orders of magnitude greater than that of nonneuronal cells. In addition, the apparent K_m values for GABA neurons for high and low affinity uptake were 0.33 × 10⁻⁶ M and 41.8 × 10⁻⁴ M, respectively. For nonneuronal cells, the apparent K_m for high affinity uptake was 0.29 × 10⁻⁶ M. The apparent V_max values for GABA neurons for high and low affinity uptake were 28.7 × 10⁻⁶ mol/g DNA/min and 151.5 mmol/g DNA/min, respectively. For nonneuronal cells, the apparent V_max for high affinity uptake was 0.06 × 10⁻⁶ mol/g DNA/min. No low affinity uptake system for nonneuronal cells could be detected after correcting the data for binding and diffusion. By substituting the apparent kinetic constants in the Michaelis-Menten equation, it was determined that for GABA concentrations of 5 × 10⁻⁹ M to 1 mM or higher over 99% of the GABA should be accumulated by GABA neurons, given equal access of all cells to the label. In addition, high affinity uptake of [³H]GABA by GABA neurons was completely blocked by treatment with 0.2 mM ouabain, whereas that by nonneuronal cells was only slightly decreased. Most (75–85%) of the [³H]GABA (4.4 × 10⁻⁶ M) uptake by both GABA neurons and nonneuronal cells was sodium and temperature dependent.     

Uptake and metabolism of glutamate and aspartate by astroglial and neuronal preparations of rat cerebellum

Astrocytes, neuronal perikarya and synaptosomes were prepared from rat cerebellum. Kinetics of high and low affinity uptake systems of glutamate and aspartate, nominal rates of¹⁴CO₂ production from [U–¹⁴C]glutamate, [U–¹⁴C]aspartate and [1–¹⁴C]glutamate and activities of enzymes of glutamate metabolism were studied in these preparations. The rate of uptake and the nomial rate of production of¹⁴CO₂ from these amino acids was higher in the astroglia than neuronal perikarya and synaptosomes. Activities of glutamine synthetase and glutamate dehydrogenase were higher in astrocytes than in neuronal perikarya and synaptosomes. Activities of glutaminase and glutamic acid decarboxylase were observed to be highest in neuronal perikarya and synaptosomes respectively. These results are in agreement with the postulates of theory of metabolic compartmentation of glutamate while others (presence of glutaminase in astrocytes and glutamine synthetase in synaptosomes) are not. Results of this study also indicated that (i) at high extracellular concentrations, glutamate/aspartate uptake may be predominantly into astrocytes while at low extracellular concentrations, it would be into neurons (ii) production of -ketoglutarate from glutamate is chiefly by way of transamination but not by oxidative deamination in these three preparations and (iii) there are topographical differences glutamate metabolism within the neurons.     

Background impulse activity of neurons of the fastigial nucleus in the rat cerebellum

Background impulse activity (BIA) of neuronal elements of the fastigial nucleus (FN) of rat cerebellum were investigated for the first time with the aid of various methods of statistical analysis. A clear predominance of stationary impulse flows (IFs) was discovered, along with irregularities in such flows, variously expressed and including a significant number of realizations of a regular component of impulse activity. Nonstationary IFs constituted a special variety of BIA; they were found in 15% of the total number of neurons investigated. Serial correlation analysis of the durations of interspike intervals (ISIs), both of stationary and nonstationary IFs, allowed us to identify six main varieties of ISI dynamics in the BIA of neurons of the fastigial nucleus. The patterns of recorded IFs and variations in IFs can serve as an adequate indices of the state of cellular activity during intracellular recording from cells of the central nervous system.L. A. Orbeli Institute of Physiology, Armenian Academy of Sciences, Yerevan. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 441–450, July–August, 1991.     

Immunocytochemical localization of microtubule-associated protein 1 in rat cerebellum using monoclonal antibodies

Immunohistochemical staining with monoclonal antibodies showed that microtubule-associated protein 1 (MAP1) has a restricted cellular distribution in the rat cerebellum. Anti-MAP1 staining was found only in neurons, where it was much stronger in dendrites than in axons. There were striking variations in the apparent concentration of MAP1 in different classes of neurons. Purkinje cells were the most strongly labeled, while granule cell neurons gave a faint, threshold-level reaction with the antibody. The reaction of Golgi neurons was intermediate between these two extremes. Equivalent results were obtained using two different methods of tissue preparation. Thus MAP1 appears to be a neuron-specific protein that is highly concentrated in dendrites and occurs at markedly different levels in different types of neurons. These observations provide further indications of heterogeneity among brain microtubules.     

Uptake of GABA by neuronal and nonneuronal cells in dispersed cell cultures of postnatal rat cerebellum.

A study was made of the time course and kinetics of [3H]GABA uptake by dispersed cell cultures of postnatal rat cerebellum with and without neuronal cells. The properties of GABA neurons were calculated from the biochemical difference between the two types of cultures. It was found that for any given concentration of [3H]GABA, or any time up to 20 min, GABA neurons in cultures 21 days in vitro had an average velocity of uptake several orders of magnitude greater than that of nonneuronal cells. In addition, the apparent Kmvalues for GABA neurons for high and low affinity uptake were 0.33 X 10(-6) M and 41.8 X 10(-4) M, respectively. For nonneuronal cells, the apparent Km for high affinity uptake was 0.29 X 10(-6) M. The apparent Vmax values for GABA neurons for high and low affinity uptake were 28.7 X 10(-6) mol/g DNA/min and 151.5 mmol/g DNA/min, respectively. For nonneuronal cells, the apparent Vmax for high affinity uptake was 0.06 X 10(-6) mol/g DNA/min. No low affinity uptake system for nonneuronal cells could be detected after correcting the data for binding and diffusion. By substituting the apparent kinetic constants in the Michaelis-Menten equation, it was determined that for GABA concentrations of 5 X 10(-9) M to 1 mM or higher over 99% of the GABA should be accumulated by GABA neurons, given equal access of all cells to the label. In addition, high affinity uptake of [3H]GABA by GABA neurons was completely blocked by treatment with 0.2 mM ouabain, whereas that by noneuronal cells was only slightly decreased. Most (75-85%) of the [3H]GABA (4.4 X 10(-6) M) uptake by both GABA neurons and nonneuronal cells was sodium and temperature dependent.     

Estimation of population firing rates and current source densities from laminar electrode recordings

This model study investigates the validity of methods used to interpret linear (laminar) multielectrode recordings. In computer experiments extracellular potentials from a synaptically activated population of about 1,000 pyramidal neurons are calculated using biologically realistic compartmental neuron models combined with electrostatic forward modeling. The somas of the pyramidal neurons are located in a 0.4 mm high and wide columnar cylinder, mimicking a stimulus-evoked layer-5 population in a neocortical column. Current-source density (CSD) analysis of the low-frequency part (<500 Hz) of the calculated potentials (local field potentials, LFP) based on the ‘inverse’ CSD method is, in contrast to the ‘standard’ CSD method, seen to give excellent estimates of the true underlying CSD. The high-frequency part (>750 Hz) of the potentials (multi-unit activity, MUA) is found to scale approximately as the population firing rate to the power 3/4 and to give excellent estimates of the underlying population firing rate for trial-averaged data. The MUA signal is found to decay much more sharply outside the columnar populations than the LFP.     

Uncovering spatial topology represented by rat hippocampal population neuronal codes

Hippocampal population codes play an important role in representation of spatial environment and spatial navigation. Uncovering the internal representation of hippocampal population codes will help understand neural mechanisms of the hippocampus. For instance, uncovering the patterns represented by rat hippocampus (CA1) pyramidal cells during periods of either navigation or sleep has been an active research topic over the past decades. However, previous approaches to analyze or decode firing patterns of population neurons all assume the knowledge of the place fields, which are estimated from training data a priori. The question still remains unclear how can we extract information from population neuronal responses either without a priori knowledge or in the presence of finite sampling constraint. Finding the answer to this question would leverage our ability to examine the population neuronal codes under different experimental conditions. Using rat hippocampus as a model system, we attempt to uncover the hidden "spatial topology" represented by the hippocampal population codes. We develop a hidden Markov model (HMM) and a variational Bayesian (VB) inference algorithm to achieve this computational goal, and we apply the analysis to extensive simulation and experimental data. Our empirical results show promising direction for discovering structural patterns of ensemble spike activity during periods of active navigation. This study would also provide useful insights for future exploratory data analysis of population neuronal codes during periods of sleep.     

Intranasal epitalon infusion modulates neuronal activity in the rat neocortex

Properties of tetrapeptide epitalon (Ala-Glu-Asp-Gly) constructed on the basis of pineal peptide extract, have been studied. The intranasal infusions: a noninvasive way to deliver this peptide to CNS hypassing the blood-brain barrier, was used. The aim of the study is to estimate epitalon action on rat motor cortex spontaneous activity. Wistar male rats were anesthetized with urethane (1 g/kg). Extracellular unit recording was made using glass microelectrodes (1-2 MOhm). After recording of spontaneous activity (10-15 min), epitalon intranasal infusion (2 ng) was followed by 30-minute recording. Within a few minutes after the infusion, significant activation of neural activity was observed (2-2.5-fold higher frequency of neuronal spikes). Complex response consisting of several phases was identified in some recordings. The spikes frequency growth during 5 to 7 min (first phase) after the infusion was followed by the second (11-12 min) and the third (17-18 min) phases. An increase of neuronal spontaneous activity was conditioned by the higher frequency of already active units and by the involvement of previously silent cells. At least the first phase of epitalon action can be explained by direct action of the peptide on the cells of the motor cortex.     

Modulating neuronal activity produces specific and long-lasting changes in numerical competence

Around 20% of the population exhibits moderate to severe numerical disabilities [1-3], and a further percentage loses its numerical competence during the lifespan as a result of stroke or degenerative diseases [4]. In this work, we investigated the feasibility of using noninvasive stimulation to the parietal lobe during numerical learning to selectively improve numerical abilities. We used transcranial direct current stimulation (TDCS), a method that can selectively inhibit or excitate neuronal populations by modulating GABAergic (anodal stimulation) and glutamatergic (cathodal stimulation) activity [5, 6]. We trained subjects for 6 days with artificial numerical symbols, during which we applied concurrent TDCS to the parietal lobes. The polarity of the brain stimulation specifically enhanced or impaired the acquisition of automatic number processing and the mapping of number into space, both important indices of numerical proficiency [7-9]. The improvement was still present 6 months after the training. Control tasks revealed that the effect of brain stimulation was specific to the representation of artificial numerical symbols. The specificity and longevity of TDCS on numerical abilities establishes TDCS as a realistic tool for intervention in cases of atypical numerical development or loss of numerical abilities because of stroke or degenerative illnesses.     

Effects of extremely-low-frequency electric fields on neuronal activity in rat brain

The effects of 50-, 30-, and 15-Hz electric field exposure on the activity of spontaneously firing neurons in the brain of anaesthetized rats were studied. Exposure to fields of 100 V/m (peak-to-peak, in air) produced no effect on the overall rate of neuronal firing, but some synchronicity with the period of the exposure waveform was seen with 15- and 30-Hz electric fields.