GABA-from Inhibition to Cognition: Emerging Concepts

Neural functioning and plasticity can be studied on different levels of organization and complexity ranging from the molecular and synaptic level to neural circuitry of whole brain networks. Across neuroscience different methods are being applied to better understand the role of various neurotransmitter systems in the evolution of perception and cognition. GABA is the main inhibitory neurotransmitter in the adult mammalian brain and, depending on the brain region, up to 25% of the total number of cortical neurons are GABAergic interneurons. At the one end of the spectrum, GABAergic neurons have been accurately described with regard to cell morphological, molecular, and electrophysiological properties; at the other end researchers try to link GABA concentrations in specific brain regions to human behavior using magnetic resonance spectroscopy. One of the main challenges of modern neuroscience currently is to integrate knowledge from highly specialized subfields at distinct biological scales into a coherent picture that bridges the gap between molecules and behavior. In the current review, recent findings from different fields of GABA research are summarized delineating a potential strategy to develop a more holistic picture of the function and role of GABA.

High-Frequency Conductivity Plateau and Ionic Hopping Processes in a Ternary Lithium Borate Glass

Complete conductivity spectra of a lithium ion conducting glass of composition B2O3-0.56Li2O - 0.45 LiBr have been taken at twelve temperatures from 173 K to 573 K, covering the frequency range from a few Hertz up to about 50 THz. For the first time, a separation of the hopping and vibrational contributions to the spectra has been performed. The resulting frequency dependent hopping conductivity displays a high-frequency plateau similar to those known to exist in crystalline solid electrolytes like RbAg4I5 and Na-β-alumina. In the dispersive regime of the conductivity, there is an increase of the apparent power-law exponent from p = 0.6 to q = 1.3. The spectra are evaluated by combined application of the jump relaxation model and the dynamic structure model. Besides the translational hopping of the lithium ions via the preferred Ā sites, more localized kinds of motion are also detected, viz., hops into the less favoured C̄ sites (and mostly back again) as well as smaller displacements of the ions within their local environment.

Creation and Recombination of Frenkel Defects in AgBr

Complete ionic conductivity spectra as well as quasielastic and inelastic neutron scattering spectra have been taken of solid silver bromide at various temperatures. High-amplitude vibrational move­ments, essentially of the silver ions, contribute to both kinds of spectra. In particular, a conductivity maximum, located at about 500 GHz, reflects oscillations of individual silver ions along directions. -The microwave and millimetre-wave conductivities are dominated by a thermally activated Debye-type relaxation process. The effect is consistently explained by the frequent hopping of silver ions from regular octahedral lattice sites into tetrahedral interstitial sites and back again, i.e., by the frequent creation and recombination of Frenkel pairs. -The effect is also responsible for the existence of thermally activated quasielastic components in the neutron scattering spectra. The width of the coherent quasielastic scattering shows that the forward-backward hopping of a silver ion is accompanied by fast correlated movements of ions in its immediate neighbourhood.

Low Frequency Lattice Absorption in RbAg4I5 Solid Electrolyte

Far infrared transmission and reflexion measurements were performed on polycrystalline samples of α-RbAg4I5 solid electrolyte. As in α-AgI, an anomalous broad low frequency ab­sorption band centred at 5 · 1011 Hz is found in addition to the lattice absorption at ca. 3 · 1012 Hz. Since it is rather tempera­ture insensitive, the low frequency band indicates the exis­tence of very slow high amplitude lattice vibrations in this material.

The Barmer study: impact of standardized warming of the injection site to enhance insulin absorption and reduce prandial insulin requirements and hypoglycemia in obese patients with diabetes mellitus

BACKGROUND

The primary objective of this prospective controlled study was to investigate the impact of standardized injection-site warming on prandial rapid acting insulin dose and glycemic control when studied under real-world conditions.

METHODS

All 145 participating patients (51 female, 94 male, 13 type 1 and 132 type 2 patients, age: 61.6 ± 8.4 yrs, HbA1c: 7.19 ± 0.50%) were treated with intensive insulin glargine and short-acting insulin analog therapy. After a 4 week treatment optimization run-in period, patients were randomized to continue therapy for three months without (control) or with a local injection-site warming device (InsuPad * ). Observation parameters included HbA1c, insulin dose, frequency of hypoglycemia, body weight and adverse events.

RESULTS

HbA1c improved in both arms until study end (control group: 6.3 ± 0.5%; injection-site warming device: 6.3 ± 0.5%; both p < 0.001 vs. baseline). To achieve this good control, patients in the control group needed to increase the daily prandial insulin dose by 8.1% (from 66 ± 31 U to 71 ± 38 U, p < 0.05) with stable basal insulin requirements. Patients who used the injection-site warming device required less prandial insulin (70 ± 43 U to 55 ± 34 U; -19%, p < 0.001) and slightly more basal insulin (+3.9%). Total daily insulin dose increased in the control group (+3.7%) and decreased with warming device use (-8.6%, p < 0.001). The number of hypoglycemic events (<63 mg/dL) during the observation period was higher in the control group (6.2 ± 9.9/patient vs. injection-site warming device: 3.3 ± 4.8/patient, p < 0.05). Main study limitations can be seen in the open label design reliability of the collected dose information and the very obese patient cohort.

CONCLUSION

When treating obese patients to target with insulin therapy, use of an injection-site warming device for 3 months resulted in a lower frequency of hypoglycemic events and a reduction in prandial insulin analog requirements. If these results are confirmed in other patient populations, an injection-site warming device may be useful in achieving treatment targets with a safer and more efficient basal bolus therapy in insulin-treated patients with type 1 and type 2 diabetes.

The Migration Concept for Ionic Motion in Materials With Disordered Structures

The dynamics of the mobile ions in materials with disordered structures are a challengingly complicated many-particle process. In this paper, we consider characteristic frequency-dependent conductivities and permittivities of such materials and show that they can be well reproduced within the framework of the MIGRATION concept. The meaning of the acronym is MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. In the MIGRATION concept, we attempt to grasp the essence of the ion dynamics in a simple set of rules which convey a physical picture of the most relevant elementary processes. The rules are expressed in terms of three coupled rate equations which then form the basis for deriving frequency-dependent model conductivities and permittivities.

Concept of Mismatch and Relaxation Derived from Conductivity Spectra of Solid Electrolytes

Crystalline ion conductors like RbAg4I5 and others display a characteristic shape of their dispersive conductivities at frequencies below the microwave regime. As the temperature is decreased, the onset of the dispersion is shifted to lower frequencies and thus the characteristic shape of the dispersion becomes visible in an increasingly broad frequency range. In a log-log plot of the frequency-dependent conductivity, the slope is found to increase continuously, but not to surpass unity. For the first time, this behavior is now consistently explained. The particular shape of the dispersion is shown to be equivalent to a proportionality of the rates of relaxation via the singleand many-particle routes. This is the essence of the concept of mismatch and relaxation (CMR). Model conductivity spectra based on the CMR include the UDR (universal dynamic response) as well as the NCL (nearly constant loss) behavior. Both universalities are thus traced back to a common dynamic origin.

First and Second Universalities: Expeditions Towards and Beyond

Understanding the mechanisms of translational and localised ionic movements in disordered materials has seen intense activity spanning several decades. This article attempts to convey a concise overview of our contribution to this field over the period from 2005 to 2010 and to place it in its broad context.

From Ostwald′s Times to Solid State Ionics: Migration and Localised Hopping of Silver Ions in Crystalline Rubidium Silver Iodide

Since Ostwald′s times, the concepts of ionic motion in condensed matter have been extended to comprise systems with increasingly complex dynamic properties. Today, one of the central problems in the field of SOLID STATE IONICS consists in finding simple, yet relevant rules for the correlated hopping motion of the mobile ions in structurally disordered ionic materials. Rubidium silver iodide, RbAg4I5, belongs to this class of materials. To analyse the hopping dynamics of the mobile silver ions in the three phases of RbAg4I5, we have taken conductivity spectra at frequencies up to the far infrared. Also, a simple set of rules for the development of the ion dynamics with time has been provided by the MIGRATION concept, the acronym standing for MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. In the phases α and β, an increasing tendency for correlated forward-backward hopping is observed as the temperature is decreased from 298K to 129K. At the first-order β-γ phase transition at 121.8K, the number of translationally mobile silver ions is found to be markedly reduced. The conductivity spectra of the different phases of RbAg4I5 are well explained by the MIGRATION concept as long as the angular frequency does not exceed the elementary hopping rate of the mobile silver ions. At higher frequencies, an additional dynamic feature is encountered, which is superimposed onto the MIGRATION-type conductivity. This feature, which shows a nearly constant loss (NCL) behaviour, becomes increasingly pronounced as the temperature is lowered. It is caused by a strictly localised motion of interacting silver ions. In our model treatment for the MIGRATION and NCL parts of the dynamic conductivity, the potentially translational and the strictly localised ionic hopping motion are best described with a single elementary hopping rate. Consequently, this rate marks the beginning of the NCL behaviour on the angular frequency scale. This observation is in agreement with earlier results obtained by Leon et al. on solid lithium-ion conductors.

Pressure-Dependent Diffusion Coefficients and Haven Ratios in Cation-Conducting Glasses

The influence of hydrostatic pressure on diffusion and ionic conduction is providing deeper insights into the atomistic mechanisms of ionic motion in glasses. We have studied the tracer diffusion of 22Na in a sodium borate glass and of 86Rb in a rubidium borate glass as functions of hydrostatic pressures. The activation volumes of tracer diffusion are DeltaVD(Rb) = 33.5 cm3 mol-1 and DeltaVD(Na) = 6.1 cm3 mol-1. In comparison, the activation volumes of charge diffusion obtained recently from the pressure dependence of conductivity are smaller: DeltaVsigma(Rb) = 7.2 cm3 mol(-1) and DeltaVsigma(Na) = 2.8 cm3 mol(-1). These differences, where (DeltaVD - DeltaVsigma) > 0, imply that the Haven ratios decrease with pressure. This effect is particularly significant for the rubidium borate glass. Starting from basic equations of linear response theory for mass and charge transport, we develop a model that accounts for these experimental findings. The difference between the activation volumes, DeltaVD and DeltaVsigma, and the pressure-dependent Haven ratios are consequences of collective movements of ions in glass, implying a concerted motion of ions in a chain- or caterpillar-like fashion. In our treatment, it is a vacant site (with ions jumping into it successively) that moves along an extended pathway. Hence, we regard vacant sites as the carriers of charge and ions as the carriers of diffusing matter. The decrease of the Haven ratio with pressure is attributed to the influence of pressure on the topology of the conduction pathways, which are progressively straightened out with increasing pressure.

Patientenklassifikation und Risikoprofilanalysen bei Typ-2-Diabetikern in der Schwerpunktpraxis

BACKGROUND AND OBJECTIVE

Disease management programs (DMP) e. g. for diabetes mellitus, should be the clinical and economic basis for a structured treatment. This article shows results of specialized outpatient treatment using a risk factor depending patient classification.

PATIENTS AND METHODS

Diabetes associated co-morbidities, micro- and macrovascular complications, the results and findings of blood pressure and metabolism of glucose and lipids, as well as all treatment-associated costs of 5245 type 2 diabetics were collected for a period of 12 months, accompanied by different measures of quality control. For documentation in the centres, all available original data were used as local data sources.

RESULTS

The patient classification system, on which diabetic risk profiles are based, covered 74.3 % of all type 2 diabetic patients. Daily direct costs for all treatment measures ranged between EUR 4.79 (primary prevention) and EUR 8.96 for patients suffering from advanced diabetic foot syndrome. Most of the treatment costs arose from prescriptions of pharmaceuticals, other remedies and aids. Specific strategies of therapy were both related to the severity of co-morbidities and the time since manifestation of diabetes (r = 0.486; p < 0.01, two-sided). The share of patients receiving diet and exercise only decreased from 22.8 % (primary prevention) to below 10 % of patients suffering from microvascular complications. Simultaneously, the share of patients receiving insulin increased up to 81.8 % of patients suffering from advanced diabetic retinopathy.

CONCLUSION

The risk profile specific variation in the results clearly shows the need of a risk factor depending classification system for type 2 diabetes, which could be useful to reform and focus the system of compensating payments between health insurance companies more and more on morbidity, or on risk profiles.

The dynamic spatio-temporal behavior of visual responses in thalamus and cortex

Due to eye and object movements the visual world changes on a rather fast time scale and the neuronal network of the primary visual pathway has to immediately react to these changes. Accordingly the neuronal activity patterns in the visual thalamus and cortex show a pronounced dynamic behavior which reenters the circuitry such that the actual cell responses are also guided by the activation history of the network. Thus, spatial and temporal aspects of visual receptive fields change not only by means of the actual visual stimulation hut also as a consequence of the state of the network. In this short review we summarize the different aspects which can influence the temporal firing patterns of cells in the visual thalamus (lateral geniculate nucleus, LGN) mainly by demonstrating how their inter-spike interval distributions will change. We then show that these firing patterns are able to change the spatial shape of receptive fields in the visual cortex (see Fig. 12 for a summary diagram). Finally, by means of a biophysical model, we will argue that the observed changes could serve to adjust the temporal and spatial resolution within the primary visual pathway to the different demands for information processing in an attentive as compared to a non-attentive state.

Changes of contrast gain in cat dorsal lateral geniculate nucleus by dopamine receptor agonists

The modulatory effects of dopamine (DA) on the contrast gain of retino-geniculate transmission were tested with local micro-iontophoretical application of DA and the DA receptor agonists SKF38393 (SKF, D1/D5) and quinpirole (QUIN, D2/D3/D4) while recording visually induced spike activity of relay cells of the dorsal aspect of cat lateral geniculate nucleus (dLGN) in the anesthetised and paralyzed preparation. DA and QUIN could either facilitate or inhibit visual activity in a dose-dependent fashion: small amounts caused a facilitation while larger quantities resulted in a more (DA) or less (QUIN) strong inhibition. The effect of SKF was almost always suppressive and increased with the amount of drug applied. The absolute change in activity was depending on stimulus contrast and the strength of the elicited response: facilitation and inhibition of activity was proportional to stimulus contrast and response strength and thus resulted in a changed contrast gain. The results indicate that the visual deficits found in Parkinson's disease patients my be not solely related to retinal dysfunctions.

Changes in response modulation of cat perigeniculate neurons related to EEG state and application of neuromodulators

Spike activity of single perigeniculate (PGN) neurons was recorded in the anaesthetized (N2O/halothane) and paralysed cat during presentation of moving gratings of optimal spatial frequency. Typically, the ongoing (tonic, spontaneous) activity of PGN cells increased during a rise in EEG delta power accompanied by a reduction and often a total loss of spike rate modulation by the moving grating. The opposite behaviour was found when the EEG delta power vanished. Micro-iontophoretically applied acetylcholine (ACh) had an effect similar to a decrease in EEG delta power, decreasing ongoing activity but increasing the response modulation depth. The opposite effect could be achieved with the excitatory action of serotonin (5-HT), mimicking a strengthened EEG delta power. These data support previous data indicating that PGN neurons contribute to spatio-temporal tuning of subcortical visual activity in a state-dependent way.

High-frequency (300-800 Hz) components in cat geniculate (dLGN) early visual responses

We analysed the early visual responses of relay cells of the dorsal part of cat lateral geniculate nucleus (dLGN) for the occurrence and characteristics of high-frequency (>300 Hz) spike patterns comparable to the high-frequency oscillations (HFO) found in the human somatosensory system. By using a special algorithm for correcting response latency, we can show that the vast majority of dLGN visual responses which were elicited by a sudden change in contrast show HFOs in the range of 300 to more than 800 Hz. After response time correction these HFOs are clearly visible in summed responses, indicating that these patterns are highly reproducible by identical stimuli. On this basis we analysed the HFOs in more detail. We found the oscillation frequency to increase with stimulus contrast and the area of the receptive field centre covered by an excitatory stimulus. Inhibition reduces the oscillation frequency as demonstrated with additional stimulation of the antagonistic surround of the receptive field and by blocking inhibition with micro-iontophoretical application of bicuculline methiodide. The HFO was almost independent of the state of the system as estimated from the EEG pattern. Based on these findings we discuss whether bursts of action potentials triggered by the low-threshold calcium spike (LTS) can contribute to this pattern of visual thalamic activity.