On a Simple General Principle of Brain Organization.

A possible framework to characterize nervous system dynamics and its organization in conscious and unconscious states is introduced, derived from a high level perspective on the coordinated activity of brain cell ensembles. Some questions are best addressable in a global framework and here we build on past observations about the structure of configurations of brain networks in conscious and unconscious states and about neurophysiological results. Aiming to bind some results together into some sort of coherence with a central theme, the scenario that emerges underscores the crucial importance of the creation and dissipation of energy gradients in brain cellular ensembles resulting in maximization of the configurations in the functional connectivity among those networks that favor conscious awareness and healthy conditions. These considerations are then applied to indicate approaches that can be used to improve neuropathological syndromes.

Dynamiceuticals: The Next Stage in Personalized Medicine.

The surge in the interest in personalized medicine necessitates a corresponding rational approach for implementing such individualized therapies. Dynamiceuticals represents a natural extension of the Pharmaceutical and Electroceutical fields, where the precise determination of the dynamical regimes of the pathophysiology will guide to devise therapies that ameliorate the pathology in a well-controlled manner, thus being precisely tailored toward the implementation of individualized medicine. This approach foretells to lessen side-effects and achieve superior efficacy as compared with current trial-and-error or open-loop strategies. But does the current state of knowledge and technology allow this scheme to offer what it claims?

Rapid brief feedback intracerebral stimulation based on real-time desynchronization detection preceding seizures stops the generation of convulsive paroxysms.

OBJECTIVE: To investigate the abortion of seizure generation using "minimal" intervention in hippocampi using two rat models of human temporal lobe epilepsy. METHODS: The recording or stimulation electrodes were implanted into both hippocampi (CA1 area). Using the kainic acid (chronic: experiment duration 24 days) and the 4-aminopyridine (acute: experiment duration 2 h) models of paroxysms in rats, a real-time feedback stimulation paradigm was implemented, which triggered a short periodic electrical stimulus (5 Hz for 5 s) upon detecting a seizure precursor. Our seizure precursor detection algorithm relied on the monitoring of the real-time phase synchronization analysis, and detected/anticipated electrographic seizures as early as a few seconds to a few minutes before the behavioral and electrographic seizure onset, with a very low false-positive rate of the detection. RESULTS: The baseline mean seizure frequencies were 5.39 seizures per day (chronic) and 13.2 seizures per hour (acute). The phase synchrony analysis detected 88% (434 of 494) of seizures with a mean false alarm of 0.67 per day (chronic) and 83% (86 of 104) of seizures with a mean false alarm of 0.47 per hour (acute). The feedback stimulation reduced the seizure frequencies to 0.41 seizures per day (chronic) and 2.4 seizures per hour (acute). Overall, the feedback stimulation paradigm reduced seizure frequency by a minimum of 80% to a maximum of 100% in 10 rats, with 83% of the animals rendered seizure-free. SIGNIFICANCE: This approach represents a simple and efficient manner for stopping seizure development. Because of the short on-demand stimuli, few or no associated side effects are expected in clinical application in patients with epilepsy. Abnormal synchrony patterns are common features in epilepsy and other neurologic and psychiatric syndromes; therefore, this type of feedback stimulation paradigm could be a novel therapeutic modality for use in various neurologic and psychiatric disorders.

Information gain in the brain's resting state: A new perspective on autism.

Along with the study of brain activity evoked by external stimuli, an increased interest in the research of background, "noisy" brain activity is fast developing in current neuroscience. It is becoming apparent that this "resting-state" activity is a major factor determining other, more particular, responses to stimuli and hence it can be argued that background activity carries important information used by the nervous systems for adaptive behaviors. In this context, we investigated the generation of information in ongoing brain activity recorded with magnetoencephalography (MEG) in children with autism spectrum disorder (ASD) and non-autistic children. Using a stochastic dynamical model of brain dynamics, we were able to resolve not only the deterministic interactions between brain regions, i.e., the brain's functional connectivity, but also the stochastic inputs to the brain in the resting state; an important component of large-scale neural dynamics that no other method can resolve to date. We then computed the Kullback-Leibler (KLD) divergence, also known as information gain or relative entropy, between the stochastic inputs and the brain activity at different locations (outputs) in children with ASD compared to controls. The divergence between the input noise and the brain's ongoing activity extracted from our stochastic model was significantly higher in autistic relative to non-autistic children. This suggests that brains of subjects with autism create more information at rest. We propose that the excessive production of information in the absence of relevant sensory stimuli or attention to external cues underlies the cognitive differences between individuals with and without autism. We conclude that the information gain in the brain's resting state provides quantitative evidence for perhaps the most typical characteristic in autism: withdrawal into one's inner world.

The biophysical bases of will-less behaviors.

Are there distinctions at the neurophysiological level that correlate with voluntary and involuntary actions? Whereas the wide variety of involuntary behaviors (and here mostly the deviant or pathological ones will be considered) will necessarily be represented at some biophysical level in nervous system activity-for after all those cellular activity patterns manifest themselves as behaviors and thus there will be a multiplicity of them-there could be some general tendencies to be discerned amongst that assortment. Collecting observations derived from neurophysiological activity associated with several pathological conditions characterized by presenting will-less actions such as Parkinson's disease, seizures, alien hand syndrome and tics, it is proposed that a general neurophysiologic tendency of brain activity that correlates with involuntary actions is higher than normal synchrony in specific brain cell networks, depending upon the behavior in question. Wilful, considered normal behavior, depends on precise coordination of the collective activity in cell ensembles that may be lost, or diminished, when there are tendencies toward more than normal or aberrant synchronization of cellular activity. Hence, rapid fluctuations in synchrony is associated with normal actions and cognition while less variability in brain recordings particularly with regards to synchronization could be a signature of unconscious and deviant behaviors in general.

Patterns of brain activity distinguishing free and forced actions: contribution from sensory cortices.

The neural basis of decision-making is extremely complex due to the large number of factors that contribute to the outcome of even the most basic actions as well as the range of appropriate responses within many behavioral contexts. To better understand the neural processes underlying basic forms of decision-making, this study utilized an experiment that required a choice about whether to press a button with the right or left hand. These instances of decision-making were compared to identical button presses that were experimentally specified rather than selected by the subject. Magnetoencephalography (MEG) was used to record neural activity during these-what are being termed-free and forced actions and differences in the MEG signal between these two conditions were attributed to the distinct forms of neural activity required to carry out the two types of actions. To produce instances of free and forced behavior, cued button-pressing experiments were performed that use visual, aural, and memorized cues to instruct experimental subjects of the expected outcome of individual trials. Classification analysis of the trials revealed that cortical regions that allowed for the most accurate classification of free and forced actions primarily handle sensory input for the modality used to cue the trials: occipital cortex for visually cued trials, temporal cortex for aurally cued trials, and minor non-localized differences in MEG activity for trials initiated from memory. The differential roles of visual and auditory sensory cortices during free and forced actions provided insight into the neural processing steps that were engaged to initiate cued actions. Specifically, it suggested that detectable differences exist in the activity of sensory cortices and their target sites when subjects performed free and forced actions in response to sensory cues.

Distinct dynamical patterns that distinguish willed and forced actions.

The neural pathways for generating willed actions have been increasingly investigated since the famous pioneering work by Benjamin Libet on the nature of free will. To better understand what differentiates the brain states underlying willed and forced behaviours, we performed a study of chosen and forced actions over a binary choice scenario. Magnetoencephalography recordings were obtained from six subjects during a simple task in which the subject presses a button with the left or right finger in response to a cue that either (1) specifies the finger with which the button should be pressed or (2) instructs the subject to press a button with a finger of their own choosing. Three independent analyses were performed to investigate the dynamical patterns of neural activity supporting willed and forced behaviours during the preparatory period preceding a button press. Each analysis offered similar findings in the temporal and spatial domains and in particular, a high accuracy in the classification of single trials was obtained around 200 ms after cue presentation with an overall average of 82%. During this period, the majority of the discriminatory power comes from differential neural processes observed bilaterally in the parietal lobes, as well as some differences in occipital and temporal lobes, suggesting a contribution of these regions to willed and forced behaviours.

Finding simplicity in complexity: general principles of biological and nonbiological organization.

What differentiates the living from the nonliving? What is life? These are perennial questions that have occupied minds since the beginning of cultures. The search for a clear demarcation between animate and inanimate is a reflection of the human tendency to create borders, not only physical but also conceptual. It is obvious that what we call a living creature, either bacteria or organism, has distinct properties from those of the normally called nonliving. However, searching beyond dichotomies and from a global, more abstract, perspective on natural laws, a clear partition of matter into animate and inanimate becomes fuzzy. Based on concepts from a variety of fields of research, the emerging notion is that common principles of biological and nonbiological organization indicate that natural phenomena arise and evolve from a central theme captured by the process of information exchange. Thus, a relatively simple universal logic that rules the evolution of natural phenomena can be unveiled from the apparent complexity of the natural world.

Severity of atypical absence phenotype in GABAB transgenic mice is subunit specific.

Overexpression of GABA(B)R1a receptors in mice (R1a(+)) results in an atypical absence seizure phenotype characterized by 3- to 6-Hz slow spike-and-wave discharges (SSWDs), reduced synaptic plasticity, and cognitive impairment. Here we tested the hypothesis that increased R1 expression causes atypical absence epilepsy and is not subunit specific. GABA(B)R1b receptors were overexpressed in mouse forebrain (R1b(+)) and confirmed by immunoblot and (3)H-CGP54626A autoradiography. The R1b(+) mice showed a reduction in hippocampal long-term potentiation and GABA(A) receptor-mediated inhibitory postsynaptic currents. R1b(+) mice manifested an electrographic, pharmacological, and behavioral phenotype consistent with atypical absence seizures, though less robust than R1a(+) in terms of SSWD duration and severity of cognitive impairment. These results suggest that abnormal GABA(B)R1b function plays a lesser role in the development of atypical absence epilepsy.

Succinic semialdehyde dehydrogenase deficiency: GABAB receptor-mediated function.

The succinic semialdehyde dehydrogenase (SSADH) null mouse (SSADH(-/-)) represents a viable animal model for human SSADH deficiency and is characterized by markedly elevated levels of both gamma-hydroxybutyric acid (GHB) and gamma-aminobutyric acid (GABA) in brain, blood, and urine. In physiological concentrations, GHB acts at the GHB receptor (GHBR), but in high concentrations such as those observed in the brains of children with SSADH deficiency, GHB is thought to be a direct agonist at the GABABR receptor (GABABR). We tested the hypothesis that both GHBR and GABABR-mediated function are perturbed in SSADH deficiency. Therefore, we examined the high affinity binding site for GHB as well as the expression and function of the GABABR in mutant mice made deficient in SSADH (SSADH(-/-)). There was a significant decrease in binding of the specific GABABR antagonist, [3H]CGP-54626A at postnatal day (PN)7 and PN14 in SSADH(-/-) when compared to wild type control animals (SSADH(+/+)), particularly in hippocampus. GABABR-mediated synaptic potentials were decreased in SSADH(-/-). Immunoblot analysis of GABABR1a, R1b, and R2 in SSADH(-/-) indicated a trend towards a region-specific and time-dependent decrease of GABABR subunit protein expression. There was no difference between SSADH(-/-) and wild type in binding of either [3H]GHB or a specific GHBR antagonist to the GHBR. These data suggest that the elevated levels of GABA and GHB that occur in SSADH(-/-) lead to a use-dependent decrease in GABABR-mediated function and raise the possibility that this GHB- and GABA-induced perturbation of GABABR could play a role in the pathogenesis of the seizures and mental retardation observed in SSADH deficiency.

Carbenoxolone does not cross the blood brain barrier: an HPLC study.

BACKGROUND: Carbenoxolone (CBX) is a widely used gap junctional blocker. Considering several reports indicating that transient gap junctional blockade could be a favourable intervention following injuries to central nervous tissue, and some current enthusiasm in studies using systemic injections of CBX, it is imperative to consider the penetration of CBX into central nervous tissue after systemic administrations. So far, only very indirect evidence suggests that CBX penetrates into the central nervous system after systemic administrations. We thus determined the amounts of CBX present in the blood and the cerebrospinal fluid of rats after intraperitoneal administration, using high performance liquid chromatography. RESULTS: CBX was found in the blood of the animals, up to 90 minutes post-injection. However, the cerebrospinal fluid concentration of CBX was negligible. CONCLUSION: Thus, we conclude that, most likely, CBX does not penetrate the blood brain barrier and therefore recommend careful consideration in the manner of administration, when a central effect is desired.

Role of gap junctional coupling in astrocytic networks in the determination of global ischaemia-induced oxidative stress and hippocampal damage.

While there is evidence that gap junctions play important roles in the determination of cell injuries, there is not much known about mechanisms by which gap junctional communication may exert these functions. Using a global model of transient ischaemia in rats, we found that pretreatment with the gap junctional blockers carbenoxolone, 18alpha-glycyrrhetinic acid and endothelin, applied via cannulae implanted into the hippocampus in one hemisphere, resulted in decreased numbers of TUNEL-positive neurons, as compared with the contralateral hippocampus that received saline injection. Post-treatment with carbenoxolone for up to 30 min after the stroke injury still resulted in decreased cell death, but post-treatment at 90 min after the ischaemic insult did not result in differences in cell death. However, quinine, an inhibitor of Cx36-mediated gap junctional coupling, did not result in appreciable neuroprotection. Searching for a possible mechanism for the observed protective effects, possible actions of the gap junctional blockers in the electrical activity of the hippocampus during the ischaemic insult were assessed using intracerebral recordings, with no differences observed between the saline-injected and the contralateral drug-injected hippocampus. However, a significant reduction in lipid peroxides, a measure of free radical formation, in the hippocampus treated with carbenoxolone, revealed that the actions of gap junctional coupling during injuries may be causally related to oxidative stress. These observations suggest that coupling in glial networks may be functionally important in determining neuronal vulnerability to oxidative injuries.

Functional contribution of specific brain areas to absence seizures: role of thalamic gap-junctional coupling.

The synchronized discharges typical of seizures have a multifactorial origin at molecular, cellular and network levels. During recent years, the functional role of gap-junctional coupling has received increased attention as a mechanism that may participate in seizure generation. We have investigated the possible functional roles of thalamic and hippocampal gap-junctional communication (GJC) in the generation of spike-and-wave discharges in a rodent model of atypical absence seizures. Seizures in this model spread throughout limbic, thalamic and neocortical areas. Rats were chronically implanted with cannulae to deliver drugs or saline, and local field potentials recordings were performed using intracerebral electrodes positioned in distinct brain areas. Initially, the effects on synaptic transmission of the gap-junctional blockers used in this study were determined. Neither carbenoxolone (CBX) nor 18-alpha-glycyrrhetinic acid altered chemical synaptic transmission at the concentrations tested. These two compounds, when injected via cannulae into the reticular nucleus of the thalamus (NRT), decreased significantly the duration of seizures as compared with saline injections or injections of the CBX inactive derivative glycyrrhizic acid. CBX injections into the hippocampus resulted in diminished seizure activity as well. NRT injections of trimethylamine, which presumably causes intracellular alkalinization (thereby promoting gap-junctional opening), enhanced seizures and spindle activity. These observations suggest that, in this rodent model, thalamic and limbic areas are involved in the synchronous paroxysmal activity and that GJC contributes to the spike-and-wave discharges.

A subharmonic dynamical bifurcation during in vitro epileptiform activity.

Epileptic seizures are considered to result from a sudden change in the synchronization of firing neurons in brain neural networks. We have used an in vitro model of status epilepticus (SE) to characterize dynamical regimes underlying the observed seizure-like activity. Time intervals between spikes or bursts were used as the variable to construct first-return interpeak or interburst interval plots, for studying neuronal population activity during the transition to seizure, as well as within seizures. Return maps constructed for a brief epoch before seizures were used for approximating the local system dynamics during that time window. Analysis of the first-return maps suggests that intermittency is a dynamical regime underlying the observed epileptic activity. This type of analysis may be useful for understanding the collective dynamics of neuronal populations in the normal and pathological brain.

Bicarbonate-dependent depolarizing potentials in pyramidal cells and interneurons during epileptiform activity.

Experimental and theoretical evidence indicates that GABAergic neurotransmission is fundamental for the synchronization of neuronal activity. In particular, the role of GABA in epileptiform activity has received increased attention due to, among others, the fact that the GABA-mediated potentials can be depolarizing, and hence excitatory, in some circumstances. Evidence is presented here that bicarbonate efflux via GABAA receptors in interneurons and pyramidal cells of the CA1 hippocampal area contribute to depolarizing GABAA-mediated potentials in an in vitro nonpharmacological seizure-like model of status epilepticus. Seizure-like and interictal activity was evoked in rat horizontal hippocampal slices using a superfusing solution with low magnesium concentration (0.5-0.9 mm). Whole-cell recordings from stratum oriens-alveus interneurons and CA1 pyramidal cells revealed that, during epileptiform activity, some GABAA-mediated potentials were depolarizing, and were suppressed by the carbonic anhydrase inhibitor ethoxyzolamide as well as by the GABAA-receptor antagonist bicuculline. These observations indicate that the depolarizing potentials observed during epileptiform activity reflect both glutamatergic and GABAA-receptor-mediated activity, and adds further support for the important role of GABAergic interneurons in promoting long-range synchronization.

Anti-porin antibodies prevent excitotoxic and ischemic damage to brain tissue.

The mitochondrial permeability transition (MPT) is a converging event for different molecular routes leading to cellular death after excitotoxic/oxidative stress, and is considered to represent the opening of a pore in the mitochondrial membrane. There is evidence that the outer mitochondrial membrane protein porin is involved in the MPT and apoptosis. We present here a proof-of-principle study to address the hypothesis that anti-porin antibodies can prevent excitotoxic/ischemia-induced cell death. We generated anti-porin antibodies and show that the F(ab)(2) fragments penetrate living cells, reduce Ca(2+)-induced mitochondrial swelling as other MPT blockers do, and decrease neuronal death in dissociated and organotypic brain slice cultures exposed to excitotoxic and ischemic episodes. These observations present direct evidence that anti-porin antibody fragments prevent cell damage in brain tissue, that porin is a crucial protein involved in mitochondrial and cell dysfunction, and that it is conceivable that antibodies can be used as therapeutic agents.

Mathematics and the gap junctions: in-phase synchronization of identical neurons.

A close consideration of some mathematical results with regards to neuronal synchronization mechanisms are examined. It is well known that intercellular coupling via gap junctions normally occurs between identical neurons, such as the coupling between inhibitory interneurons belonging to the same class. It is unknown why this should happen. The theory of coupled oscillators offers some explanations to answer the questions of the functional role of electrical interactions mediated by gap junctions and the necessity to couple identical neurons. The inference presented here from the mathematical results is that only if the cells are identical will their firing synchronize in-phase. Thus, we propose the concept that the functional role of gap junctional electrical coupling is to synchronize neurons in-phase and therefore this type of coupling will be found between neurons belonging to the same class.

Gap junctions and neuronal injury: protectants or executioners?

The authors review concepts and recent experimental observations that relate gap junctional communication to the pathophysiology of neuronal injury, specifically ischemic or traumatic damage. The role played by this type of direct intercellular communication during the progression of the injuries can be conceived to be either detrimental or beneficial, depending on the arguments employed. The data indicate that, far from being a simple matter of judgment, the contribution of gap junctions to cell injury is a complicated phenomenon that depends on the specific insult and network in which it operates.

Ischemia-induced brain damage depends on specific gap-junctional coupling.

Ischemic brain injury results in neuronal loss and associated neurologic deficits. Although there is some evidence that intercellular communication via gap junctions can spread oxidative cell injury, the possible role of gap-junctional communication in ischemia-induced cell death is the object of debate. Because gap junctions directly connect the cytoplasms of coupled cells, they offer a way to propagate stress signals from cell to cell. The authors investigated the contribution of gap-junctional communication to cell death using an in vitro ischemia model, which was reproduced by submersion of organotypic hippocampal slices into glucose-free deoxygenated medium. The gap-junctional blocker carbenoxolone significantly decreased the spread of cell death, as measured by propidium iodide staining, over a 48-hour period after the ischemic episode. Carbenoxolone ameliorated the hypoxia-induced impairment of the intrinsic neuronal electrophysiologic characteristics, as measured by whole-cell patch clamp recordings. To determine whether specific connexins were involved in the spread of postischemic cell death, the authors partially reduced the synthesis of specific connexins using antisense oligodeoxynucleotides. Simultaneous knockdown of two connexins localized mostly in neurons, connexins 32 and 26, resulted in significant neuroprotection 48 hours after the hypoxic-hypoglycemic episode. Similarly, partial reduction of the predominant glial connexin 43 significantly decreased cell death. These results indicate that gap-junctional communication contributes to the propagation of hypoxic injury and that specific gap junctions could be a novel target to reduce brain damage.