Pattern of neuronal activity associated with conscious and unconscious processing of visual signals

Following striate cortex damage in monkeys and humans there can be residual function mediated by parallel visual pathways. In humans this can sometimes be associated with a “feeling” that something has happened, especially with rapid movement or abrupt onset. For less transient events, discriminative performance may still be well above chance even when the subject reports no conscious awareness of the stimulus. In a previous study we examined parameters that yield good residual visual performance in the “blind” hemifield of a subject with unilateral damage to the primary visual cortex. With appropriate parameters we demonstrated good discriminative performance, both with and without conscious awareness of a visual event. These observations raise the possibility of imaging the brain activity generated in the “aware” and the “unaware” modes, with matched levels of discrimination performance, and hence of revealing patterns of brain activation associated with visual awareness. The intact hemifield also allows a comparison with normal vision. Here we report the results of a functional magnetic resonance imaging study on the same subject carried out under aware and unaware stimulus conditions. The results point to a shift in the pattern of activity from neocortex in the aware mode, to subcortical structures in the unaware mode. In the aware mode prestriate and dorsolateral prefrontal cortices (area 46) are active. In the unaware mode the superior colliculus is active, together with medial and orbital prefrontal cortical sites.

Induction of inhibitory factor κBα mRNA in the central nervous system after peripheral lipopolysaccharide administration: An in situ hybridization histochemistry study in the rat

In this study we investigate the mRNA expression of inhibitory factor κBα (IκBα) in cells of the rat brain induced by an intraperitoneal (i.p.) injection of lipopolysaccharide (LPS). IκB controls the activity of nuclear factor κB, which regulates the transcription of many immune signal molecules. The detection of IκB induction, therefore, would reveal the extent and the cellular location of brain-derived immune molecules in response to peripheral immune challenges. Low levels of IκBα mRNA were found in the large blood vessels and in circumventricular organs (CVOs) of saline-injected control animals. After an i.p. LPS injection (2.5 mg/kg), dramatic induction of IκBα mRNA occurred in four spatio-temporal patterns. Induced signals were first detected at 0.5 hr in the lumen of large blood vessels and in blood vessels of the choroid plexus and CVOs. Second, at 1–2 hr, labeling dramatically increased in the CVOs and choroid plexus and spread to small vascular and glial cells throughout the entire brain; these responses peaked at 2 hr and declined thereafter. Third, cells of the meninges became activated at 2 hr and persisted until 12 hr after the LPS injection. Finally, only at 12 hr, induced signals were present in ventricular ependyma. Thus, IκBα mRNA is induced in brain after peripheral LPS injection, beginning in cells lining the blood side of the blood–brain barrier and progressing to cells inside brain. The spatiotemporal patterns suggest that cells of the blood–brain barrier synthesize immune signal molecules to activate cells inside the central nervous system in response to peripheral LPS. The cerebrospinal fluid appears to be a conduit for these signal molecules.

A sensory brain map for each behavior?

Multiple brain maps are commonly found in virtually every vertebrate sensory system. Although their functional significance is generally relatively little understood, they seem to specialize in processing distinct sensory parameters. Nevertheless, to yield the stimulus features that ultimately elicit the adaptive behavior, it appears that information streams have to be combined across maps. Results from current lesion experiments in the electrosensory system, however, suggest an alternative possibility. Inactivations of different maps of the first-order electrosensory nucleus in electric fish, the electrosensory lateral line lobe, resulted in markedly different behavioral deficits. The centromedial map is both necessary and sufficient for a particular electrolocation behavior, the jamming avoidance response, whereas it does not affect the communicative response to external electric signals. Conversely, the lateral map does not affect the jamming avoidance response but is necessary and sufficient to evoke communication behavior. Because the premotor pathways controlling the two behaviors in these fish appear to be separated as well, this system illustrates that sensory–motor control of different behaviors can occur in strictly segregated channels from the sensory input of the brain all through to its motor output. This might reflect an early evolutionary stage where multiplication of brain maps can satisfy the demand on processing a wider range of sensory signals ensuing from an enlarged behavioral repertoire, and bridging across maps is not yet required.

Chs6p-dependent Anterograde Transport of Chs3p from the Chitosome to the Plasma Membrane in Saccharomyces cerevisiae

Chitin synthase III (CSIII), an enzyme required to form a chitin ring in the nascent division septum of Saccharomyces cerevisiae, may be transported to the cell surface in a regulated manner. Chs3p, the catalytic subunit of CSIII, requires the product of CHS6 to be transported to or activated at the cell surface. We find that chs6Δ strains have morphological abnormalities similar to those of chs3 mutants. Subcellular fractionation and indirect immunofluorescence indicate that Chs3p distribution is altered in chs6 mutant cells. Order-of-function experiments using end4–1 (endocytosis-defective) and chs6 mutants indicate that Chs6p is required for anterograde transport of Chs3p from an internal endosome-like membrane compartment, the chitosome, to the plasma membrane. As a result, chs6 strains accumulate Chs3p in chitosomes. Chs1p, a distinct chitin synthase that acts during or after cell separation, is transported normally in chs6 mutants, suggesting that Chs1p and Chs3p are independently packaged during protein transport through the late secretory pathway.

Description of microcolumnar ensembles in association cortex and their disruption in Alzheimer and Lewy body dementias

The cortex of the brain is organized into clear horizontal layers, laminae, which subserve much of the connectional anatomy of the brain. We hypothesize that there is also a vertical anatomical organization that might subserve local interactions of neuronal functional units, in accord with longstanding electrophysiological observations. We develop and apply a general quantitative method, inspired by analogous methods in condensed matter physics, to examine the anatomical organization of the cortex in human brain. We find, in addition to obvious laminae, anatomical evidence for tightly packed microcolumnar ensembles containing approximately 11 neurons, with a periodicity of about 80 μm. We examine the structural integrity of this new architectural feature in two common dementing illnesses, Alzheimer disease and dementia with Lewy bodies. In Alzheimer disease, there is a dramatic, nearly complete loss of microcolumnar ensemble organization. The relative degree of loss of microcolumnar ensembles is directly proportional to the number of neurofibrillary tangles, but not related to the amount of amyloid-β deposition. In dementia with Lewy bodies, a similar disruption of microcolumnar ensemble architecture occurs despite minimal neuronal loss. These observations show that quantitative analysis of complex cortical architecture can be applied to analyze the anatomical basis of brain disorders.

A universal scaling law between gray matter and white matter of cerebral cortex

Neocortex, a new and rapidly evolving brain structure in mammals, has a similar layered architecture in species over a wide range of brain sizes. Larger brains require longer fibers to communicate between distant cortical areas; the volume of the white matter that contains long axons increases disproportionally faster than the volume of the gray matter that contains cell bodies, dendrites, and axons for local information processing, according to a power law. The theoretical analysis presented here shows how this remarkable anatomical regularity might arise naturally as a consequence of the local uniformity of the cortex and the requirement for compact arrangement of long axonal fibers. The predicted power law with an exponent of 4/3 minus a small correction for the thickness of the cortex accurately accounts for empirical data spanning several orders of magnitude in brain sizes for various mammalian species, including human and nonhuman primates.

Peptides containing glutamine repeats as substrates for transglutaminase-catalyzed cross-linking: Relevance to diseases of the nervous system

Many proteins contain reiterated glutamine residues, but polyglutamine of excessive length may result in human disease by conferring new properties on the protein containing it. One established property of a glutamine residue, depending on the nature of the flanking residues, is its ability to act as an amine acceptor in a transglutaminase-catalyzed reaction and to make a glutamyl–lysine cross-link with a neighboring polypeptide. To learn whether glutamine repeats can act as amine acceptors, we have made peptides with variable lengths of polyglutamine flanked by the adjacent amino acid residues in the proteins associated with spinocerebellar ataxia type 1 (SCA1), Machado–Joseph disease (SCA3), or dentato-rubral pallido-luysian atrophy (DRPLA) or those residues adjacent to the preferred cross-linking site of involucrin, or solely by arginine residues. The polyglutamine was found to confer excellent substrate properties on any soluble peptide; under optimal conditions, virtually all the glutamine residues acted as amine acceptors in the reaction with glycine ethyl-ester, and lengthening the sequence of polyglutamine increased the reactivity of each glutamine residue. In the presence of transglutaminase, peptides containing polyglutamine formed insoluble aggregates with the proteins of brain extracts and these aggregates contained glutamyl–lysine cross-links. Repeated glutamine residues exposed on the surface of a neuronal protein should form cross-linked aggregates in the presence of any transglutaminase activated by the presence of Ca2+.

N-Methyl-d-aspartate antagonists and apoptotic cell death triggered by head trauma in developing rat brain

Morbidity and mortality from head trauma is highest among children. No animal model mimicking traumatic brain injury in children has yet been established, and the mechanisms of neuronal degeneration after traumatic injury to the developing brain are not understood. In infant rats subjected to percussion head trauma, two types of brain damage could be characterized. The first type or primary damage evolved within 4 hr and occurred by an excitotoxic mechanism. The second type or secondary damage evolved within 6–24 hr and occurred by an apoptotic mechanism. Primary damage remained localized to the parietal cortex at the site of impact. Secondary damage affected distant sites such as the cingulate/retrosplenial cortex, subiculum, frontal cortex, thalamus and striatum. Secondary apoptotic damage was more severe than primary excitotoxic damage. Morphometric analysis demonstrated that the N-methyl-d-aspartate receptor antagonists 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonate and dizocilpine protected against primary excitotoxic damage but increased severity of secondary apoptotic damage. 2-Sulfo-α-phenyl-N-tert-butyl-nitrone, a free radical scavenger, did not affect primary excitotoxic damage but mitigated apoptotic damage. These observations demonstrate that apoptosis and not excitotoxicity determine neuropathologic outcome after traumatic injury to the developing brain. Whereas free radical scavengers may prove useful in therapy of head trauma in children, N-methyl-d-aspartate antagonists should be avoided because of their propensity to increase severity of apoptotic damage.

Changes in brain cell shape create residual extracellular space volume and explain tortuosity behavior during osmotic challenge

Diffusion of molecules in brain extracellular space is constrained by two macroscopic parameters, tortuosity factor λ and volume fraction α. Recent studies in brain slices show that when osmolarity is reduced, λ increases while α decreases. In contrast, with increased osmolarity, α increases, but λ attains a plateau. Using homogenization theory and a variety of lattice models, we found that the plateau behavior of λ can be explained if the shape of brain cells changes nonuniformly during the shrinking or swelling induced by osmotic challenge. The nonuniform cellular shrinkage creates residual extracellular space that temporarily traps diffusing molecules, thus impeding the macroscopic diffusion. The paper also discusses the definition of tortuosity and its independence of the measurement frame of reference.

Remodeling of α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor subunit composition in hippocampal neurons after global ischemia

Transient global ischemia induces selective delayed cell death, primarily of principal neurons in the hippocampal CA1. However, the molecular mechanisms underlying ischemia-induced cell death are as yet unclear. The present study shows that global ischemia triggers a pronounced and cell-specific reduction in GluR2 [the subunit that limits Ca2+ permeability of α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors] in vulnerable CA1 neurons, as evidenced by immunofluorescence of brain sections and Western blot analysis of microdissected hippocampal subfields. At 72 h after ischemia (a time before cell death), virtually all CA1 pyramidal neurons exhibited greatly reduced GluR2 immunolabeling throughout their somata and dendritic processes. GluR2 immunolabeling was unchanged in pyramidal cells of the CA3 and granule cells of the dentate gyrus, regions resistant to ischemia-induced damage. Immunolabeling of the AMPA receptor subunit GluR1 was unchanged in CA1, CA3, and dentate gyrus. Western analysis indicated that GluR2 subunit abundance was markedly reduced in CA1 at 60 and 72 h after the ischemic insult; GluR1 abundance was unchanged in all subfields at all times examined. These findings, together with the previous observation of enhanced AMPA-elicited Ca2+ influx in postischemic CA1 neurons, show that functional GluR2-lacking, Ca2+-permeable AMPA receptors are expressed in vulnerable neurons before cell death. Thus, the present study provides an important link in the postulated causal chain between global ischemia and delayed death of CA1 pyramidal neurons.

Nonneuronal isoforms of STOP protein are responsible for microtubule cold stability in mammalian fibroblasts

A number of cycling mammalian cells, such as NIH 3T3, contain abundant subsets of cold-stable microtubules. The origin of such microtubule stabilization in nonneuronal cells is unknown. We have previously described a neuronal protein, stable tubule-only polypeptide (STOP), that binds to microtubules and induces cold stability. We find that NIH 3T3 fibroblasts contain a major 42-kDa isoform of STOP (fibroblastic STOP, F-STOP). F-STOP contains the central repeats characteristic of brain STOP but shows extensive deletions of N- and C-terminal protein domains that are present in brain STOP. These deletions arise from differences in STOP RNA splicing. Despite such deletions, F-STOP has full microtubule stabilizing activity. F-STOP accumulates on cold-stable microtubules of interphase arrays and is present on stable microtubules within the mitotic spindle of NIH 3T3 cells. STOP inhibition by microinjection of affinity-purified STOP central repeat antibodies into NIH 3T3 cells abolishes both interphase and spindle microtubule cold stability. Similar results were obtained with Rat2 cells. These results show that STOP proteins have nonneuronal isoforms that are responsible for the microtubule cold stability observed in mammalian fibroblasts.

Diagnosis of Creutzfeldt-Jakob disease by measurement of S100 protein in serum: prospective case-control study

Objective: To analyse serum concentrations of brain specific S100 protein in patients with Creutzfeldt-Jakob disease and in controls.

Molecular Cloning and Characterization of Phocein, a Protein Found from the Golgi Complex to Dendritic Spines

Phocein is a widely expressed, highly conserved intracellular protein of 225 amino acids, the sequence of which has limited homology to the ς subunits from clathrin adaptor complexes and contains an additional stretch bearing a putative SH3-binding domain. This sequence is evolutionarily very conserved (80% identity between Drosophila melanogaster and human). Phocein was discovered by a yeast two-hybrid screen using striatin as a bait. Striatin, SG2NA, and zinedin, the three mammalian members of the striatin family, are multimodular, WD-repeat, and calmodulin-binding proteins. The interaction of phocein with striatin, SG2NA, and zinedin was validated in vitro by coimmunoprecipitation and pull-down experiments. Fractionation of brain and HeLa cells showed that phocein is associated with membranes, as well as present in the cytosol where it behaves as a protein complex. The molecular interaction between SG2NA and phocein was confirmed by their in vivo colocalization, as observed in HeLa cells where antibodies directed against either phocein or SG2NA immunostained the Golgi complex. A 2-min brefeldin A treatment of HeLa cells induced the redistribution of both proteins. Immunocytochemical studies of adult rat brain sections showed that phocein reactivity, present in many types of neurons, is strictly somato-dendritic and extends down to spines, just as do striatin and SG2NA.

Cerebral energetics and the glycogen shunt: Neurochemical basis of functional imaging

Positron-emission tomography and functional MRS imaging signals can be analyzed to derive neurophysiological values of cerebral blood flow or volume and cerebral metabolic consumption rates of glucose (CMRGlc) or oxygen (CMRO2). Under basal physiological conditions in the adult mammalian brain, glucose oxidation is nearly complete so that the oxygen-to-glucose index (OGI), given by the ratio of CMRO2/CMRGlc, is close to the stoichiometric value of 6. However, a survey of functional imaging data suggests that the OGI is activity dependent, moving further below the oxidative value of 6 as activity is increased. Brain lactate concentrations also increase with stimulation. These results had led to the concept that brain activation is supported by anaerobic glucose metabolism, which was inconsistent with basal glucose oxidation. These differences are resolved here by a proposed model of glucose energetics, in which a fraction of glucose is cycled through the cerebral glycogen pool, a fraction that increases with degree of brain activation. The “glycogen shunt,” although energetically less efficient than glycolysis, is followed because of its ability to supply glial energy in milliseconds for rapid neurotransmitter clearance, as a consequence of which OGI is lowered and lactate is increased. The value of OGI observed is consistent with passive lactate efflux, driven by the observed lactate concentration, for the few experiments with complete data. Although the OGI changes during activation, the energies required per neurotransmitter release (neuronal) and clearance (glial) are constant over a wide range of brain activity.

Functional neuroimaging studies of encoding, priming, and explicit memory retrieval

Human functional neuroimaging techniques provide a powerful means of linking neural level descriptions of brain function and cognition. The exploration of the functional anatomy underlying human memory comprises a prime example. Three highly reliable findings linking memory-related cognitive processes to brain activity are discussed. First, priming is accompanied by reductions in the amount of neural activation relative to naive or unprimed task performance. These reductions can be shown to be both anatomically and functionally specific and are found for both perceptual and conceptual task components. Second, verbal encoding, allowing subsequent conscious retrieval, is associated with activation of higher order brain regions including areas within the left inferior and dorsal prefrontal cortex. These areas also are activated by working memory and effortful word generation tasks, suggesting that these tasks, often discussed as separable, might rely on interdependent processes. Finally, explicit (intentional) retrieval shares much of the same functional anatomy as the encoding and word generation tasks but is associated with the recruitment of additional brain areas, including the anterior prefrontal cortex (right > left). These findings illustrate how neuroimaging techniques can be used to study memory processes and can both complement and extend data derived through other means. More recently developed methods, such as event-related functional MRI, will continue this progress and may provide additional new directions for research.