Neurochemical organization of the macaque striate cortex: correlation of cytochrome oxidase with Na+K+ATPase, NADPH-diaphorase, nitric oxide synthase, and N-methyl-D-aspartate receptor subunit 1

Fluoride affects memory by altering the transcriptional activity in the central nervous system of Lymnaea stagnalis

Fluoride (F^-), has been found to affect learning and memory in several species. In this study, we exposed an F^--naïve, inbred strain of Lymnaea stagnalis to a concentration of F^- similar to that naturally occurring in wild ponds. We found that the exposure to F^- before the configural learning procedure obstructs the memory formation and blocks the configural learning-induced upregulation of CREB1, GRIN1, and HSP70 in snails' central ring ganglia. Along with altering the mRNA levels of these key genes for memory formation, a single acute F^- exposure also upregulates Cytochrome c Oxidase, a major regulatory enzyme of the electron transport chain, which plays direct or indirect roles in reactive oxygen species production. As the central nervous system is sensitive to oxidative stress and consistent with previous studies from mammals, our results suggest a potential role of oxidative stress in memory impairment. To our knowledge, this is the first study investigating the neuronal mechanism of memory impairment in an invertebrate species that is exposed to natural F^- levels.

Effects of Nrf1 in Hypothalamic Paraventricular Nucleus on Regulating the Blood Pressure During Hypertension

The incidence rate and mortality of hypertension increase every year. Hypothalamic paraventricular nucleus (PVN) plays a critical role on the pathophysiology of hypertension. It has been demonstrated that the imbalance of neurotransmitters including norepinephrine (NE), glutamate (Glu) and γ-aminobutyric acid (GABA) are closely related to sympathetic overactivity and pathogenesis of hypertension. N-methyl-D-aspartate receptor (NMDAR), consisting of GluN1 and GluN2 subunits, is considered to be a glutamate-gated ion channel, which binds to Glu, and activates neuronal activity. Studies have found that the synthesis of respiratory chain enzyme complex was affected and mitochondrial function was impaired in spontaneously hypertensive rats (SHR), further indicating that mitochondria is associated with hypertension. Nuclear respiratory factor 1 (Nrf1) is a transcription factor that modulates mitochondrial respiratory chain and is related to GluN1, GluN2A, and GluN2B promoters. However, the brain mechanisms underlying PVN Nrf1 modulating sympathoexcitation and blood pressure during the development of hypertension remains unclear. In this study, an adeno-associated virus (AAV) vector carrying the shRNA targeting rat Nrf1 gene (shNrf1) was injected into bilateral PVN of male rats underwent two kidneys and one clip to explore the role of Nrf1 in mediating the development of hypertension and sympathoexcitation. Administration of shNrf1 knocked down the expression of Nrf1 and reduced the expression of excitatory neurotransmitters, increased the expression of inhibitory neurotransmitters, and reduced the production of reactive oxygen species (ROS), and attenuated sympathoexcitation and hypertension. The results indicate that knocking down Nrf1 suppresses sympathoexcitation in hypertension by reducing PVN transcription of NMDAR subunits (GluN1, GluN2A, and GluN2B), rebalancing PVN excitatory and inhibitory neurotransmitters, inhibiting PVN neuronal activity and oxidative stress, and attenuating sympathetic activity.

Nitrergic neurons of the forepaw representation in the rat somatosensory and motor cortices: A quantitative study

Nitrergic neurons (NNs) are inhibitory neurons capable of releasing nitric oxide (NO) that are labeled with nicotinamide adenine dinucleotide phosphate diaphorase histochemistry. The rat primary somatosensory (S1) and motor (M1) cortices are a favorable model to investigate NN populations by comparing their morphology, since these areas share the border of forepaw representation. The distribution of the Type I NN of the forepaw representation in the S1 and M1 cortices of the rat in different laminar compartments and the morphological parameters related to the cell body and dendritic arborization were measured and compared. We observed that the neuronal density in the S1 (130 NN/mm³ ) was higher than the neuronal density in the M1 (119 NN/mm³ ). Most NN neurons were multipolar (S1 with 58%; M1 with 69%), and a minority of the NN neurons were horizontal (S1 with 6%; M1 with 12%). NN found in S1 had a higher verticality index than NN found in M1, and no significant differences were observed for the other morphological parameters. We also demonstrated significant differences in most of the morphological parameters of the NN between different cortical compartments of S1 and M1. Our results indicate that the NN of the forepaw in S1 and M1 corresponds to a neuronal population, where the functionality is independent of the different types of sensory and motor processing. However, the morphological differences found between the cortical compartments of S1 and M1, as well as the higher density of NNs found in S1, indicate that the release of NO varies between the areas.

Ring models of binocular rivalry and fusion

When similar visual stimuli are presented binocularly to both eyes, one perceives a fused single image. However, when the two stimuli are distinct, one does not perceive a single image; instead, one perceives binocular rivalry. That is, one perceives one of the stimulated patterns for a few seconds, then the other for few seconds, and so on - with random transitions between the two percepts. Most theoretical studies focus on rivalry, with few considering the coexistence of fusion and rivalry. Here we develop three distinct computational neuronal network models which capture binocular rivalry with realistic stochastic properties, fusion, and the hysteretic transition between. Each is a conductance-based point neuron model, which is multi-layer with two ocular dominance columns (L & R) and with an idealized "ring" architecture where the orientation preference of each neuron labels its location on a ring. In each model, the primary mechanism initiating binocular rivalry is cross-column inhibition, with firing rate adaptation governing the temporal properties of the transitions between percepts. Under stimulation by similar visual patterns, each of three models uses its own mechanism to overcome cross-column inhibition, and thus to prevent rivalry and allow the fusion of similar images: The first model uses cross-column feedforward inhibition from the opposite eye to "shut off" the cross-column feedback inhibition; the second model "turns on" a second layer of monocular neurons as a parallel pathway to the binocular neurons, rivaling out of phase with the first layer, and together these two pathways represent fusion; and the third model uses cross-column excitation to overcome the cross-column inhibition and enable fusion. Thus, each of the idealized ring models depends upon a different mechanism for fusion that might emerge as an underlying mechanism present in real visual cortex.

Neurobiological substrates of persistent working memory deficits and cocaine-seeking in the prelimbic cortex of rats with a history of extended access to cocaine self-administration

Cocaine use disorder (CUD) is associated with prefrontal cortex dysfunction and cognitive deficits that may contribute to persistent relapse susceptibility. As the relationship between cognitive deficits, cortical abnormalities and drug seeking is poorly understood, development of relevant animal models is of high clinical importance. Here, we used an animal model to characterize working memory and reversal learning in rats with a history of extended access cocaine self-administration and prolonged abstinence. We also investigated immediate and long-term functional changes within the prelimbic cortex (PrL) in relation to cognitive performance and drug-seeking. Adult male rats underwent 6 days of short-access (1 h/day) followed by 12 days of long-access (6 h/day) cocaine self-administration, or received passive saline infusions. Next, rats were tested in delayed match-to-sample (DMS) and (non)match-to-sample (NMS) tasks, and finally in a single context + cue relapse test on day 90 of abstinence. We found that a history of chronic cocaine self-administration impaired working memory, though sparing reversal learning, and that the components of these cognitive measures correlated with later drug-seeking. Further, we found that dysregulated metabolic activity and mGlu5 receptor signaling in the PrL of cocaine rats correlated with past working memory performance and/or drug-seeking, as indicated by the analysis of cytochrome oxidase reactivity, mGlu5 and Homer 1b/c protein expression, as well as Arc mRNA expression in mGlu5-positive cells. These findings advocate for a persistent post-cocaine PrL dysfunction, rooted in ineffective compensatory changes and manifested as impaired working memory performance and hyperreactivity to cocaine cues. Considering the possible interplay between the neural correlates underlying post-cocaine cognitive deficits and drug-seeking, cognitive function should be evaluated and considered when developing neurobiologically-based treatments of cocaine relapse.

Expression of m1-type muscarinic acetylcholine receptors by parvalbumin-immunoreactive neurons in the primary visual cortex: a comparative study of rat, guinea pig, ferret, macaque, and human

Cholinergic neuromodulation is a candidate mechanism for aspects of arousal and attention in mammals. We have reported previously that cholinergic modulation in the primary visual cortex (V1) of the macaque monkey is strongly targeted toward GABAergic interneurons, and in particular that the vast majority of parvalbumin-immunoreactive (PV) neurons in macaque V1 express the m1-type (pirenzepine-sensitive, Gq-coupled) muscarinic ACh receptor (m1AChR). In contrast, previous physiological data indicates that PV neurons in rats rarely express pirenzepine-sensitive muscarinic AChRs. To examine further this apparent species difference in the cholinergic effectors for the primary visual cortex, we have conducted a comparative study of the expression of m1AChRs by PV neurons in V1 of rats, guinea pigs, ferrets, macaques, and humans. We visualize PV- and mAChR-immunoreactive somata by dual-immunofluorescence confocal microscopy and find that the species differences are profound; the vast majority (>75%) of PV-ir neurons in macaques, humans, and guinea pigs express m1AChRs. In contrast, in rats only ∼25% of the PV population is immunoreactive for m1AChRs. Our data reveal that while they do so much less frequently than in primates, PV neurons in rats do express Gq-coupled muscarinic AChRs, which appear to have gone undetected in the previous in vitro studies. Data such as these are critical in determining the species that represent adequate models for the capacity of the cholinergic system to modulate inhibition in the primate cortex.

Regulation of Na(+)/K(+)-ATPase by neuron-specific transcription factor Sp4: implication in the tight coupling of energy production, neuronal activity and energy consumption in neurons

A major source of energy demand in neurons is the Na(+)/K(+)-ATPase pump that restores the ionic gradient across the plasma membrane subsequent to depolarizing neuronal activity. The energy comes primarily from mitochondrial oxidative metabolism, of which cytochrome c oxidase (COX) is a key enzyme. Recently, we found that all 13 subunits of COX are regulated by specificity (Sp) factors, and that the neuron-specific Sp4, but not Sp1 or Sp3, regulates the expression of key glutamatergic receptor subunits as well. The present study sought to test our hypothesis that Sp4 also regulates Na(+)/K(+)-ATPase subunit genes in neurons. By means of multiple approaches, including in silico analysis, electrophoretic mobility shift and supershift assays, chromatin immunoprecipitation, promoter mutational analysis, over-expression, and RNA interference studies, we found that Sp4, with minor contributions from Sp1 and Sp3, functionally regulate the Atp1a1, Atp1a3, and Atp1b1 subunit genes of Na(+)/K(+)-ATPase in neurons. Transcripts of all three genes were up-regulated by depolarizing KCl stimulation and down-regulated by the impulse blocker tetrodotoxin (TTX), indicating that their expression was activity-dependent. Silencing of Sp4 blocked the up-regulation of these genes induced by KCl, whereas over-expression of Sp4 rescued them from TTX-induced suppression. The effect of silencing or over-expressing Sp4 on primary neurons was much greater than those of Sp1 or Sp3. The binding sites of Sp factors on these genes are conserved among mice, rats and humans. Thus, Sp4 plays an important role in the transcriptional coupling of energy generation and energy consumption in neurons.

Neuron-specific specificity protein 4 bigenomically regulates the transcription of all mitochondria- and nucleus-encoded cytochrome c oxidase subunit genes in neurons

Neurons are highly dependent on oxidative metabolism for their energy supply, and cytochrome c oxidase (COX) is a key energy-generating enzyme in the mitochondria. A unique feature of COX is that it is one of only four proteins in mammalian cells that are bigenomically regulated. Of its thirteen subunits, three are encoded in the mitochondrial genome and ten are nuclear-encoded on nine different chromosomes. The mechanism of regulating this multisubunit, bigenomic enzyme poses a distinct challenge. In recent years, we found that nuclear respiratory factors 1 and 2 (NRF-1 and NRF-2) mediate such bigenomic coordination. The latest candidate is the specificity factor (Sp) family of proteins. In N2a cells, we found that Sp1 regulates all 13 COX subunits. However, we discovered recently that in primary neurons, it is Sp4 and not Sp1 that regulates some of the key glutamatergic receptor subunit genes. The question naturally arises as to the role of Sp4 in regulating COX in primary neurons. The present study utilized multiple approaches, including chromatin immunoprecipitation, promoter mutational analysis, knockdown and over-expression of Sp4, as well as functional assays to document that Sp4 indeed functionally regulate all 13 subunits of COX as well as mitochondrial transcription factors A and B. The present study discovered that among the specificity family of transcription factors, it is the less known neuron-specific Sp4 that regulates the expression of all 13 subunits of mitochondrial cytochrome c oxidase (COX) enzyme in primary neurons. Sp4 also regulates the three mitochondrial transcription factors (TFAM, TFB1M, and TFB2M) and a COX assembly protein SURF-1 in primary neurons.

Distribution and morphology of nitrergic neurons across functional domains of the rat primary somatosensory cortex

The rat primary somatosensory cortex (S1) is remarkable for its conspicuous vertical compartmentalization in barrels and septal columns, which are additionally stratified in horizontal layers. Whereas excitatory neurons from each of these compartments perform different types of processing, the role of interneurons is much less clear. Among the numerous types of GABAergic interneurons, those producing nitric oxide (NO) are especially puzzling, since this gaseous messenger can modulate neural activity, synaptic plasticity, and neurovascular coupling. We used a quantitative morphological approach to investigate whether nitrergic interneurons, which might therefore be considered both as NO volume diffusers and as elements of local circuitry, display features that could relate to barrel cortex architecture. In fixed brain sections, nitrergic interneurons can be revealed by histochemical processing for NADPH-diaphorase (NADPHd). Here, the dendritic arbors of nitrergic neurons from different compartments of area S1 were 3D reconstructed from serial 200 μm thick sections, using 100x objective and the Neurolucida system. Standard morphological parameters were extracted for all individual arbors and compared across columns and layers. Wedge analysis was used to compute dendritic orientation indices. Supragranular (SG) layers displayed the highest density of nitrergic neurons, whereas layer IV contained nitrergic neurons with largest soma area. The highest nitrergic neuronal density was found in septa, where dendrites were previously characterized as more extense and ramified than in barrels. Dendritic arbors were not confined to the boundaries of the column nor layer of their respective soma, being mostly double-tufted and vertically oriented, except in SG layers. These data strongly suggest that nitrergic interneurons adapt their morphology to the dynamics of processing performed by cortical compartments.

Regulation of Na(+)/K(+)-ATPase by nuclear respiratory factor 1: implication in the tight coupling of neuronal activity, energy generation, and energy consumption

BACKGROUND

NRF-1 regulates mediators of neuronal activity and energy generation.

RESULTS

NRF-1 transcriptionally regulates Na(+)/K(+)-ATPase subunits α1 and β1.

CONCLUSION

NRF-1 functionally regulates mediators of energy consumption in neurons.

SIGNIFICANCE

NRF-1 mediates the tight coupling of neuronal activity, energy generation, and energy consumption at the molecular level. Energy generation and energy consumption are tightly coupled to neuronal activity at the cellular level. Na(+)/K(+)-ATPase, a major energy-consuming enzyme, is well expressed in neurons rich in cytochrome c oxidase, an important enzyme of the energy-generating machinery, and glutamatergic receptors that are mediators of neuronal activity. The present study sought to test our hypothesis that the coupling extends to the molecular level, whereby Na(+)/K(+)-ATPase subunits are regulated by the same transcription factor, nuclear respiratory factor 1 (NRF-1), found recently by our laboratory to regulate all cytochrome c oxidase subunit genes and some NMDA and AMPA receptor subunit genes. By means of multiple approaches, including in silico analysis, electrophoretic mobility shift and supershift assays, in vivo chromatin immunoprecipitation, promoter mutational analysis, and real-time quantitative PCR, NRF-1 was found to functionally bind to the promoters of Atp1a1 and Atp1b1 genes but not of the Atp1a3 gene in neurons. The transcripts of Atp1a1 and Atp1b1 subunit genes were up-regulated by KCl and down-regulated by tetrodotoxin. Atp1b1 is positively regulated by NRF-1, and silencing of NRF-1 with small interference RNA blocked the up-regulation of Atp1b1 induced by KCl, whereas overexpression of NRF-1 rescued these transcripts from being suppressed by tetrodotoxin. On the other hand, Atp1a1 is negatively regulated by NRF-1. The binding sites of NRF-1 on Atp1a1 and Atp1b1 are conserved among mice, rats, and humans. Thus, NRF-1 regulates key Na(+)/K(+)-ATPase subunits and plays an important role in mediating the tight coupling between energy consumption, energy generation, and neuronal activity at the molecular level.

Bigenomic regulation of cytochrome c oxidase in neurons and the tight coupling between neuronal activity and energy metabolism

Cytochrome c oxidase is the terminal enzyme of the mitochondrial electron transport chain, without which oxidative metabolism cannot be carried to completion. It is one of only four unique, bigenomic proteins in mammalian cells. The holoenzyme is made up of three mitochondrial-encoded and ten nuclear-encoded subunits in a 1:1 stoichiometry. The ten nuclear subunit genes are located in nine different chromosomes. The coordinated regulation of such a multisubunit, multichromosomal, bigenomic enzyme poses a challenge. It is especially so for neurons, whose mitochondria are widely distributed in extensive dendritic and axonal processes, resulting in the separation of the mitochondrial from the nuclear genome by great distances. Neuronal activity dictates COX activity that reflects protein amount, which, in turn, is regulated at the transcriptional level. All 13 COX transcripts are up- and downregulated by neuronal activity. The ten nuclear COX transcripts and those for Tfam and Tfbms important for mitochondrial COX transcripts are transcribed in the same transcription factory. Bigenomic regulation of all 13 transcripts is mediated by nuclear respiratory factors 1 and 2 (NRF-1 and NRF-2). NRF-1, in addition, also regulates critical neurochemicals of glutamatergic synaptic transmission, thereby ensuring the tight coupling of energy metabolism and neuronal activity at the molecular level in neurons.

Cholinergic suppression of visual responses in primate V1 is mediated by GABAergic inhibition

Acetylcholine (ACh) has been implicated in selective attention. To understand the local circuit action of ACh, we iontophoresed cholinergic agonists into the primate primary visual cortex (V1) while presenting optimal visual stimuli. Consistent with our previous anatomical studies showing that GABAergic neurons in V1 express ACh receptors to a greater extent than do excitatory neurons, we observed suppressed visual responses in 36% of recorded neurons outside V1's primary thalamorecipient layer (4c). This suppression is blocked by the GABA(A) receptor antagonist gabazine. Within layer 4c, ACh release produces a response gain enhancement (Disney AA, Aoki C, Hawken MJ. Neuron 56: 701-713, 2007); elsewhere, ACh suppresses response gain by strengthening inhibition. Our finding contrasts with the observation that the dominant mechanism of suppression in the neocortex of rats is reduced glutamate release. We propose that in primates, distinct cholinergic receptor subtypes are recruited on specific cell types and in specific lamina to yield opposing modulatory effects that together increase neurons' responsiveness to optimal stimuli without changing tuning width.

Morphometric variability of nicotinamide adenine dinucleotide phosphate diaphorase neurons in the primary sensory areas of the rat

Even though there is great regional variation in the distribution of inhibitory neurons in the mammalian isocortex, relatively little is known about their morphological differences across areal borders. To obtain a better understanding of particularities of inhibitory circuits in cortical areas that correspond to different sensory modalities, we investigated the morphometric differences of a subset of inhibitory neurons reactive to the enzyme nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) within the primary auditory (A1), somatosensory (S1), and visual (V1) areas of the rat. One hundred and twenty NADPH-d-reactive neurons from cortical layer IV (40 cells in each cortical area) were reconstructed using the Neurolucida system. We collected morphometric data on cell body area, dendritic field area, number of dendrites per branching order, total dendritic length, dendritic complexity (Sholl analysis), and fractal dimension. To characterize different cell groups based on morphology, we performed a cluster analysis based on the previously mentioned parameters and searched for correlations among these variables. Morphometric analysis of NADPH-d neurons allowed us to distinguish three groups of cells, corresponding to the three analyzed areas. S1 neurons have a higher morphological complexity than those found in both A1 and V1. The difference among these groups, based on cluster analysis, was mainly related to the size and complexity of dendritic branching. A principal component analysis (PCA) applied to the data showed that area of dendritic field and fractal dimension are the parameters mostly responsible for dataset variance among the three areas. Our results suggest that the nitrergic cortical circuitry of primary sensory areas of the rat is differentially specialized, probably reflecting peculiarities of both habit and behavior of the species.

Mesolimbic effects of the antidepressant fluoxetine in Holtzman rats, a genetic strain with increased vulnerability to stress

This is the first metabolic mapping study of the effects of fluoxetine after learned helplessness training. Antidepressants are the most commonly prescribed medications, but the regions underlying treatment effects in affectively disordered brains are poorly understood. We hypothesized the antidepressant action of fluoxetine would produce adaptations in mesolimbic regions after 2 weeks of treatment. We used Holtzman rats, a genetic strain showing susceptibility to novelty-evoked hyperactivity and stress-evoked helplessness, to map regional brain metabolic effects caused by fluoxetine treatment. Animals underwent learned helplessness, and subsequently immobility time was scored in the forced swim test (FST). On the next day, animals began receiving 2 weeks of fluoxetine (5mg/kg/day) or vehicle and were retested in the FST at the end of drug treatment. Antidepressant behavioral effects of fluoxetine were analyzed using a ratio of immobility during pre- and post-treatment FST sessions. Brains were analyzed for regional metabolic activity using quantitative cytochrome oxidase histochemistry as in our previous study using congenitally helpless rats. Fluoxetine exerted a protective effect against FST-induced immobility behavior in Holtzman rats. Fluoxetine also caused a significant reduction in the mean regional metabolism of the nucleus accumbens shell and the ventral hippocampus as compared to vehicle-treated subjects. Additional networks affected by fluoxetine treatment included the prefrontal-cingulate cortex and brainstem nuclei linked to depression (e.g., habenula, dorsal raphe and interpeduncular nucleus). We concluded that corticolimbic regions such as the prefrontal-cingulate cortex, nucleus accumbens, ventral hippocampus and key brainstem nuclei represent important contributors to the neural network mediating fluoxetine antidepressant action.

The kinesin superfamily protein KIF17 is regulated by the same transcription factor (NRF-1) as its cargo NR2B in neurons

The kinesin superfamily of motor proteins is known to be ATP-dependent transporters of various types of cargoes. In neurons, KIF17 is found to transport vesicles containing the N-methyl-D-aspartate receptor NR2B subunit from the cell body specifically to the dendrites. These subunits are intimately associated with glutamatergic neurotransmission as well as with learning and memory. Glutamatergic synapses are highly energy-dependent, and recently we found that the same transcription factor, nuclear respiratory factor 1 (NRF-1), co-regulates energy metabolism (via its regulation of cytochrome c oxidase and other mitochondrial enzymes) and neurochemicals of glutamatergic transmission (NR1, NR2B, GluR2, and nNOS). The present study tested our hypothesis that NRF-1 also transcriptionally regulates KIF17. By means of in silico analysis, electrophoretic mobility shift and supershift assays, in vivo chromatin immunoprecipitation assays, promoter mutations, and real-time quantitative PCR, we found that NRF-1 (but not NRF-2) functionally regulates Kif17, but not Kif1a, gene. NRF-1 binding sites on Kif17 gene are highly conserved among mice, rats, and humans. Silencing of NRF-1 with small interference RNA blocked the up-regulation of Kif17 mRNA and proteins (and of Grin1 and Grin2b) induced by KCl-mediated depolarization, whereas over-expressing NRF-1 rescued these transcripts and proteins from being suppressed by TTX. Thus, NRF-1 co-regulates oxidative enzymes that generate energy and neurochemicals that consume energy related to glutamatergic neurotransmission, such as KIF17, NR1, and NR2B, thereby ensuring that energy production matches energy utilization at the molecular and cellular levels.

Chromosome conformation capture of transcriptional interactions between cytochrome c oxidase genes and genes of glutamatergic synaptic transmission in neurons

Neuronal activity and energy metabolism are tightly coupled processes. Recently, we found that nuclear respiratory factor 1 co-regulates all subunits of cytochrome c oxidase (COX, representing oxidative energy metabolism) and glutamatergic neurochemicals, including NR1 (Grin1) and NR2B (Grin2b) of NMDA receptors, GluR2 (Gria2) of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, and neuronal nitric oxide synthase (Nos1). Moreover, all 10 nuclear-encoded COX subunit genes and three transcription factor genes for the three mitochondrial-encoded COX subunits are transcribed in the same transcription factory. The goal of the present study was to test our hypothesis that genomic loci for Grin1, Grin2b, Gria2, and Nos1 interact with those for COX at the transcriptional level. By means of chromosome conformation capture, interactions were found among all of these genes in neurons, but not in C2C12 muscle cells. COX subunit genes also did not interact with neurochemical genes not regulated by nuclear respiratory factor 1, nor with genes for calreticulin, a non-mitochondrial protein. Depolarizing stimulation up-regulated interaction frequencies between COX and neurochemical genes, whereas impulse blockade with tetrodotoxin or inhibition of COX with KCN down-regulated them in neurons. Thus, an efficient mechanism is in place for coordinating the transcriptional coupling of energy metabolism and glutamatergic neurotransmission at the molecular level in neurons.

Glutamate receptor ion channels: structure, regulation, and function

The mammalian ionotropic glutamate receptor family encodes 18 gene products that coassemble to form ligand-gated ion channels containing an agonist recognition site, a transmembrane ion permeation pathway, and gating elements that couple agonist-induced conformational changes to the opening or closing of the permeation pore. Glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system and are localized on neuronal and non-neuronal cells. These receptors regulate a broad spectrum of processes in the brain, spinal cord, retina, and peripheral nervous system. Glutamate receptors are postulated to play important roles in numerous neurological diseases and have attracted intense scrutiny. The description of glutamate receptor structure, including its transmembrane elements, reveals a complex assembly of multiple semiautonomous extracellular domains linked to a pore-forming element with striking resemblance to an inverted potassium channel. In this review we discuss International Union of Basic and Clinical Pharmacology glutamate receptor nomenclature, structure, assembly, accessory subunits, interacting proteins, gene expression and translation, post-translational modifications, agonist and antagonist pharmacology, allosteric modulation, mechanisms of gating and permeation, roles in normal physiological function, as well as the potential therapeutic use of pharmacological agents acting at glutamate receptors.

Energy metabolism of the visual system

The visual system is one of the most energetically demanding systems in the brain. The currency of energy is ATP, which is generated most efficiently from oxidative metabolism in the mitochondria. ATP supports multiple neuronal functions. Foremost is repolarization of the membrane potential after depolarization. Neuronal activity, ATP generation, blood flow, oxygen consumption, glucose utilization, and mitochondrial oxidative metabolism are all interrelated. In the retina, phototransduction, neurotransmitter utilization, and protein/organelle transport are energy-dependent, yet repolarization-after-depolarization consumes the bulk of the energy. Repolarization in photoreceptor inner segments maintains the dark current. Repolarization by all neurons along the visual pathway following depolarizing excitatory glutamatergic neurotransmission preserves cellular integrity and permits reactivation. The higher metabolic activity in the magno- versus the parvo-cellular pathway, the ON- versus the OFF-pathway in some (and the reverse in other) species, and in specialized functional representations in the visual cortex all reflect a greater emphasis on the processing of specific visual attributes. Neuronal activity and energy metabolism are tightly coupled processes at the cellular and even at the molecular levels. Deficiencies in energy metabolism, such as in diabetes, mitochondrial DNA mutation, mitochondrial protein malfunction, and oxidative stress can lead to retinopathy, visual deficits, neuronal degeneration, and eventual blindness.

Morphological variability of NADPH diaphorase neurons across areas V1, V2, and V3 of the common agouti

Previous studies have shown a noticeable phenotypic diversity for pyramidal cells among cortical areas in the cerebral cortex. Both the extent and systematic nature of this variation suggests a correlation with particular aspects of cortical processing. Nevertheless, regional variations in the morphology of inhibitory cells have not been evaluated with the same detail. In the present study we performed a 3D morphometric analysis of 120 NADPH diaphorase (NADPH-d) type I neurons in the visual cortex of a South American Hystricomorph rodent, the diurnal agouti (Dasyprocta sp.). We found significant differences in morphology of NADPH-d type I neurons among visual cortical areas: cells became progressively larger and more branched from V1 to V2 and V3. Presumably, the specialized morphology of these cells is correlated with different sampling geometry and function. The data suggest that area-specific specializations of cortical inhibitory circuitry are also present in rodents.

Increased vulnerability to depressive-like behavior of mice with decreased expression of VGLUT1

BACKGROUND

Many studies link depression to an increase in the excitatory-inhibitory ratio in the forebrain. Presynaptic alterations in a shared pathway of the glutamate/gamma-aminobutyric acid (GABA) cycle may account for this imbalance. Evidence suggests that decreased vesicular glutamate transporter 1 (VGLUT1) levels in the forebrain affect the glutamate/GABA cycle and induce helpless behavior. We studied decreased VGLUT1 as a potential factor enhancing a depressive-like phenotype in an animal model.

METHODS

Glutamate and GABA synthesis as well as oxidative metabolism were studied in heterozygous mice for the VGLUT1+/- and wildtype. The regulation of neurotransmitter levels, proteins involved in the glutamate/GABA cycle, and behavior by both genotype and chronic mild stress (CMS) were studied. Finally, the effect of chronic imipramine on VGLUT1 control and CMS mice was studied.

RESULTS

VGLUT1+/- mice showed increased neuronal synthesis of glutamate; decreased cortical and hippocampal GABA, VGLUT1, and excitatory amino acid transporter 1 (EAAT1) as well as helplessness and anhedonia. CMS induced an increase of glutamate and a decrease of GABA, the vesicular GABA transporter (VGAT), and glutamic acid decarboxylase 65 (GAD65) in both areas and led to upregulation of EAAT1 in the hippocampus. Moreover, CMS induced anhedonia, helplessness, anxiety, and impaired recognition memory. VGLUT1+/- CMS mice showed a combined phenotype (genotype plus stress) and specific alterations, such as an upregulation of VGLUT2 and hyperlocomotion. Moreover, an increased vulnerability to anhedonia and helplessness reversible by chronic imipramine was shown.

CONCLUSIONS

These studies highlight a crucial role for decreased VGLUT1 in the forebrain as a biological mediator of increased vulnerability to chronic mild stress.

Coupling of energy metabolism and synaptic transmission at the transcriptional level: role of nuclear respiratory factor 1 in regulating both cytochrome c oxidase and NMDA glutamate receptor subunit genes

Neuronal activity and energy metabolism are tightly coupled processes. Regions high in neuronal activity, especially of the glutamatergic type, have high levels of cytochrome c oxidase (COX). Perturbations in neuronal activity affect the expressions of COX and glutamatergic NMDA receptor subunit 1 (NR1). The present study sought to test our hypothesis that the coupling extends to the transcriptional level, whereby NR1 and possibly other NR subunits and COX are coregulated by the same transcription factor, nuclear respiratory factor 1 (NRF-1), which regulates all COX subunit genes. By means of multiple approaches, including in silico analysis, electrophoretic mobility shift and supershift assays, in vivo chromatin immunoprecipitation, promoter mutations, and real-time quantitative PCR, NRF-1 was found to functionally bind to the promoters of Grin 1 (NR1), Grin 2b (NR2b) and COX subunit genes, but not of Grin2a and Grin3a genes. These transcripts were upregulated by KCl and downregulated by tetrodotoxin (TTX) in cultured primary neurons. However, silencing of NRF-1 with small interference RNA blocked the upregulation of Grin1, Grin2b, and COX induced by KCl, and overexpression of NRF-1 rescued these transcripts that were suppressed by TTX. NRF-1 binding sites on Grin1 and Grin2b genes are also highly conserved among mice, rats, and humans. Thus, NRF-1 is an essential transcription factor critical in the coregulation of NR1, NR2b, and COX, and coupling exists at the transcriptional level to ensure coordinated expressions of proteins important for synaptic transmission and energy metabolism.

Differential regulation of the neuronal isoform of nitric oxide synthase in the superior colliculus and dorsal lateral geniculate nucleus of the adult rat brain following eye enucleation

Nitric oxide has been shown to play various physiological and pathological roles in the visual system. We studied here the expression of the neuronal isoform of nitric oxide synthase in the rat superior colliculus and in the dorsal lateral geniculate nucleus after unilateral enucleation, by means of immunohistochemistry, immunoblotting, and real-time PCR. Immunohistochemistry revealed an increase of nitric oxide synthase-positive neurons in specific layers of the superior colliculus and in the dorsal lateral geniculate nucleus between 1 and 30 days post-lesion. Immunoblotting analyses confirmed that the neuronal isoform of nitric oxide synthase is upregulated in the superior colliculus and in the dorsal lateral geniculate nucleus after retinal removal. Diaminofluorescein histochemistry suggested that nitric oxide production was increased in both deafferented retinorecipient areas. Our real-time PCR results indicated that nitric oxide synthase transcript levels in the superior colliculus were not significantly altered after monocular enucleation, although an upregulation of the enzyme transcription was detected into the deafferented dorsal lateral geniculate nucleus. These findings indicated that neuronal nitric oxide synthase may undergo different forms of regulation in the adult deafferented visual system.

Animal models of restricted repetitive behavior in autism

Restricted, repetitive behavior, along with deficits in social reciprocity and communication, is diagnostic of autism. Animal models relevant to this domain generally fall into three classes: repetitive behavior associated with targeted insults to the CNS; repetitive behavior induced by pharmacological agents; and repetitive behavior associated with restricted environments and experience. The extant literature provides potential models of the repetitive behavioral phenotype in autism rather than attempts to model the etiology or pathophysiology of restricted, repetitive behavior, as these are poorly understood. This review focuses on our work with deer mice which exhibit repetitive behaviors associated with environmental restriction. Repetitive behaviors are the most common category of abnormal behavior observed in confined animals and larger, more complex environments substantially reduce the development and expression of such behavior. Studies with this model, including environmental enrichment effects, suggest alterations in cortical-basal ganglia circuitry in the development and expression of repetitive behavior. Considerably more work needs to be done in this area, particularly in modeling the development of aberrant repetitive behavior. As mutant mouse models continue to proliferate, there should be a number of promising genetic models to pursue.

Neuropil reactivity, distribution and morphology of NADPH diaphorase type I neurons in the barrel cortex of the adult mouse

The mouse, like a few other rodent and marsupial species, displays a striking modular architecture in its primary somatosensory cortex (SI). These modules, known as barrels, are mostly defined by the peculiar arrangement of granule cells and thalamic axons in layer IV. In the present work, we studied both the distribution and morphology of neurons stained for NADPH diaphorase (NADPH-d) and neuropil reactivity in the posteromedial barrel subfield (PMBSF), which represents the mystacial whiskers. We then compared our results with previous descriptions of NADPH-d distribution in both neonatal and young mice. We found two types of neurons in the PMBSF: type I neurons, which have large cell bodies and are heavily stained by the NADPH-d reaction; and type II neurons, characterized by relatively small and poorly stained cell bodies. The distribution of type I cells in the PMBSF was not homogenous, with cells tending to concentrate in septa between barrels. Moreover, the cells found in septal region possess both a larger and more complex dendritic arborization than cells located inside barrels. Our findings are at variance with results from other groups that reported both an absence of type II cells and a homogeneous distribution of type I cells in the PMBSF of young animals. In addition, our results show a distribution of type I cells which is very similar to that previously described for the rat's barrel field.

Differential expression of muscarinic acetylcholine receptors across excitatory and inhibitory cells in visual cortical areas V1 and V2 of the macaque monkey

Cholinergic neuromodulation, a candidate mechanism for aspects of attention, is complex and is not well understood. Because structure constrains function, quantitative anatomy is an invaluable tool for reducing such a challenging problem. Our goal was to determine the extent to which m1 and m2 muscarinic acetylcholine receptors (mAChRs) are expressed by inhibitory vs. excitatory neurons in the early visual cortex. To this end, V1 and V2 of macaque monkeys were immunofluorescently labelled for gamma-aminobutyric acid (GABA) and either m1 or m2 mAChRs. Among the GABA-immunoreactive (ir) neurons, 61% in V1 and 63% in V2 were m1 AChR-ir, whereas 28% in V1 and 43% in V2 were m2 AChR-ir. In V1, both mAChRs were expressed by fewer than 10% of excitatory neurons. However, in V2, the population of mAChR-ir excitatory neurons was at least double that observed in V1. We also examined m1 and m2 AChR immunoreactivity in layers 2 and 3 of area V1 under the electron microscope and found evidence that GABAergic neurons localize mAChRs to the soma, whereas glutamatergic neurons expressed mAChRs more strongly in dendrites. Axon and terminal labelling was generally weak. These data represent the first quantitative anatomical study of m1 and m2 AChR expression in the cortex of any species. In addition, the increased expression in excitatory neurons across the V1/V2 border may provide a neural basis for the observation that attentional effects gain strength up through the visual pathway from area V1 through V2 to V4 and beyond.

Characteristics of cytochrome oxidase activity in visual system neurons in kittens reared in conditions of flashing illumination

The studies reported here addressed the effects of flashing (15 Hz) lights on the metabolic activity of visual system neurons in animals reared in condition of crepuscular illumination. Activity of the respiratory enzyme cytochrome oxidase was detected in the cortex of visual areas 17 and 18 and in the lateral geniculate body in kittens. The results showed that kittens subjected to this stimulation, unlike intact kittens and kittens reared in conditions of crepuscular illumination, showed a change in the pattern of cytochrome oxidase distribution in cortical field 17 consisting of the appearance of alternating areas of increased and decreased enzyme activity in layers III and IV. In cortical field 18 and the lateral geniculate body, experimental kittens showed no changes in the cytochrome oxidase activity distribution pattern. It is suggested that flashing illumination leads to disturbance of the balance in activity in the Y and X conducting channels of the visual system.

The cortical column: a structure without a function

This year, the field of neuroscience celebrates the 50th anniversary of Mountcastle's discovery of the cortical column. In this review, we summarize half a century of research and come to the disappointing realization that the column may have no function. Originally, it was described as a discrete structure, spanning the layers of the somatosensory cortex, which contains cells responsive to only a single modality, such as deep joint receptors or cutaneous receptors. Subsequently, examples of columns have been uncovered in numerous cortical areas, expanding the original concept to embrace a variety of different structures and principles. A "column" now refers to cells in any vertical cluster that share the same tuning for any given receptive field attribute. In striate cortex, for example, cells with the same eye preference are grouped into ocular dominance columns. Unaccountably, ocular dominance columns are present in some species, but not others. In principle, it should be possible to determine their function by searching for species differences in visual performance that correlate with their presence or absence. Unfortunately, this approach has been to no avail; no visual faculty has emerged that appears to require ocular dominance columns. Moreover, recent evidence has shown that the expression of ocular dominance columns can be highly variable among members of the same species, or even in different portions of the visual cortex in the same individual. These observations deal a fatal blow to the idea that ocular dominance columns serve a purpose. More broadly, the term "column" also denotes the periodic termination of anatomical projections within or between cortical areas. In many instances, periodic projections have a consistent relationship with some architectural feature, such as the cytochrome oxidase patches in V1 or the stripes in V2. These tissue compartments appear to divide cells with different receptive field properties into distinct processing streams. However, it is unclear what advantage, if any, is conveyed by this form of columnar segregation. Although the column is an attractive concept, it has failed as a unifying principle for understanding cortical function. Unravelling the organization of the cerebral cortex will require a painstaking description of the circuits, projections and response properties peculiar to cells in each of its various areas.

Regulation of mitochondrial gene expression by energy demand in neural cells

Mitochondrial DNA (mtDNA) encodes critical subunit proteins of the oxidative phosphorylation (OXPHOS) complex that generates ATP. This study tested the hypothesis that mitochondrial gene expression in neural cells is regulated by energy demand, as modified via stimulation of cellular sodium transport. Exposure of PC12S cells to the sodium ionophore monensin (250 nm) for 1-6 h caused a 13-60% decrease in cellular ATP (from 15 to 5 nmol per mg protein at 6 h). Levels of mitochondrial DNA-encoded mRNAs (mt-mRNAs) increased significantly (150%) within the first hour of exposure to monensin, and then decreased significantly (50%) at 3-4 h. Levels of mtDNA-encoded 12S rRNA and nuclear DNA-encoded OXPHOS subunit mRNAs were not significantly affected. Exposure of primary cerebellar neuronal cultures to the excitatory amino acid glutamate caused a similar rapid and significant increase followed by a significant decrease in cell mt-mRNA levels. The monensin-induced initial increase in mt-mRNA levels was abolished by pretreatment with actinomycin D or by reducing extracellular sodium ion concentration. The monensin-induced delayed reduction in mt-mRNA levels was accelerated in the presence of actinomycin D, and was accompanied by a 67% reduction in the half-life (from 3.6 to 1.2 h). Exposure of PC12S cells to 2-deoxy-d-glucose significantly decreased cellular ATP levels (from 14.2 to 7.1 nmol per mg protein at 8 h), and increased mt-mRNA levels. These results suggest a physiological transcriptional mechanism of regulation of mitochondrial gene expression by energy demand and a post-transcriptional regulation that is independent of energy status of the cell.

Quantitative immuno-electron microscopic analysis of nuclear respiratory factor 2 alpha and beta subunits: Normal distribution and activity-dependent regulation in mammalian visual cortex

The macaque visual cortex is exquisitely organized into columns, modules, and streams, much of which can be correlated with its metabolic organization revealed by cytochrome oxidase (CO). Plasticity in the adult primate visual system has also been documented by changes in CO activity. Yet, the molecular mechanism of regulating this enzyme remains not well understood. Being one of only four bigenomic enzymes in mammalian cells, the transcriptional regulation of this enzyme necessitates a potential bigenomic coordinator. Nuclear respiratory factor 2 (NRF-2) or GA-binding protein is a transcription factor that may serve such a critical role. The goal of the present study was to determine if the two major subunits of NRF-2, 2alpha and 2beta, had distinct subcellular distribution in neurons of the rat and monkey visual cortex, if major metabolic neuronal types in the macaque exhibited different levels of the two subunits, and if they would respond differently to monocular impulse blockade. Quantitative immuno-electron microscopy was used. In both rats and monkeys, nuclear labeling of alpha and beta subunits was mainly over euchromatin rather than heterochromatin, consistent with their active participation in transcriptional activity. Cytoplasmic labeling was over free ribosomes, the Golgi apparatus, and occasionally the nuclear envelope, signifying sites of synthesis and possible posttranslational modifications. The density of both subunits was much higher in the nucleus than in the cytoplasm for all neurons examined, again indicating that their major sites of cellular action is in the nucleus.

Behavioral correlates of differences in neural metabolic capacity

Cytochrome oxidase is a rate-limiting enzyme in oxidative phosphorylation, the major energy-synthesizing pathway used by the central nervous system, and cytochrome oxidase histochemistry has been extensively utilized to map changes in neural metabolism following experimental manipulations. However, the value of cytochrome oxidase activity in predicting behavior has not been analyzed. We argue that this endeavor is important because genetic composition and embryonic environment can engender differences in baseline neural metabolism in pertinent neural circuits, and these differences could represent differences in the degree to which specific behaviors are 'primed.' Here we review our studies in which differences in cytochrome oxidase activity and in behavior were studied in parallel. Using mammalian and reptilian models, we find that embryonic experiences that shape the propensity to display social behaviors also affect cytochrome oxidase activity in limbic brain areas, and elevated cytochrome oxidase activity in preoptic, hypothalamic, and amygdaloid nuclei correlates with heightened aggressive and sexual tendencies. Selective breeding regimes were used to create rodent genetic lines that differ in their susceptibility to display learned helplessness and in behavioral excitability. Differences in cytochrome oxidase activity in areas like the paraventricular hypothalamus, frontal cortex, habenula, septum, and hippocampus correlate with differences in susceptibility to display learned helplessness, and differences in activity in the dentate gyrus and perirhinal and posterior parietal cortex correlate with differences in hyperactivity. Thus, genetic and embryonic manipulations that engender specific behavioral differences produce specific neurometabolic profiles. We propose that knowledge of neurometabolic differences can yield valuable predictions about behavioral phenotype in other systems.

A periodic network of neurochemical modules in the inferior colliculus

A new organization has been found in shell nuclei of rat inferior colliculus. Chemically specific modules with a periodic distribution fill about half of layer 2 of external cortex and dorsal cortex. Modules contain clusters of small glutamic acid decarboxylase-positive neurons and large boutons at higher density than in other inferior colliculus subdivisions. The modules are also present in tissue stained for parvalbumin, cytochrome oxidase, nicotinamide adenine dinucleotide phosphate-diaphorase, and acetylcholinesterase. Six to seven bilaterally symmetrical modules extend from the caudal extremity of the external cortex of the inferior colliculus to its rostral pole. Modules are from approximately 800 to 2200 microm long and have areas between 5000 and 40,000 microm2. Modules alternate with immunonegative regions. Similar modules are found in inbred and outbred strains of rat, and in both males and females. They are absent in mouse, squirrel, cat, bat, macaque monkey, and barn owl. Modules are immunonegative for glycine, calbindin, serotonin, and choline acetyltransferase. The auditory cortex and ipsi- and contralateral inferior colliculi project to the external cortex. Somatic sensory influences from the dorsal column nuclei and spinal trigeminal nucleus are the primary ascending sensory input to the external cortex; ascending auditory input to layer 2 is sparse. If the immunopositive modular neurons receive this input, the external cortex could participate in spatial orientation and somatic motor control through its intrinsic and extrinsic projections.

A morphometric study of the progressive changes on NADPH diaphorase activity in the developing rat's barrel field

The distribution of NADPH diaphorase (NADPH-d)/nitric oxide synthase (NOS) neurons was evaluated during the postnatal development of the primary somatosensory cortex (SI) of the rat. Both cell counts and area measurements of barrel fields were carried out throughout cortical maturation. In addition, NADPH-d and cytochrome oxidase (CO) activities were also compared in both coronal and tangential sections of rat SI between postnatal days (P) 10 and 90. Throughout this period, the neuropil distributions of both enzymes presented a remarkable similarity and have not changed noticeably. Their distribution pattern show the PMBSF as a two-compartmented structure, displaying a highly reactive region (barrel hollows) flanked by less reactive regions (barrel septa). The number of NADPH-d neurons increased significantly in the barrel fields between P10 and P23, with peak at P23. The dendritic arborization of NADPH-d neurons became more elaborated during barrel development. In all ages evaluated, the number of NADPH-d cells was always higher in septa than in the barrel hollows. Both high neuropil reactivity and differential distribution of NADPH-d neurons during SI development suggest a role for nitric oxide throughout barrel field maturation.

The chemo- and somatotopic architecture of the Galago cuneate and gracile nuclei

The pattern of peripheral nerve inputs into the dorsal column nuclei, cuneate and gracile, was investigated in the prosimian Galago garnetti. The major findings were, that there is a greater segregation of the inputs from the fingers/hand within the cuneate compared with input form the toes/foot within the gracile. In both nuclei, cell clusters can be identified as cytochrome oxidase dense blotches, reactive also for the activity-dependent enzyme nitric oxide synthase. In the cuneate, cell clusters were apparent as six main cytochrome oxidase/nitric oxide synthase-reactive ovals arranged in a medial to lateral sequence. In contrast in the gracile, a higher degree of parcellation was noted and several cytochrome oxidase/nitric oxide synthase blotches were distributed along the rostrocaudal axis of the nucleus. This different architecture parallels differences in the organization of the inputs from the hand and from the foot. In the cuneate, cholera toxin B subunit conjugated to horseradish peroxydase labeled terminals from the glabrous and hairy skin of digits d1 to d5 segregated in each of the five most lateral cytochrome oxidase/nitric oxide synthase blotches. Afferents from the thenar, palmar pads and hypothenar overlapped with those from digit 1, digit 2 to digit 4 and digit 5, respectively. Inputs from wrist arm and shoulder were segregated in the most medial blotch. In the gracile, multiple foci of cholera toxin B subunit conjugated to horseradish peroxydase labeled terminals were observed upon injections of single sites in the toes or plantar pads. Although in multiple foci, inputs from different toes segregated from one another as well. Terminals from the plantar pads appeared to converge on the same cytochrome oxidase/nitric oxide synthase blotches targeted by inputs from the toes. In both the cuneate and the gracile, cytochrome oxidase/nitric oxide synthase blotches also presented intense immunoreactivity for GABA, calbindin, parvalbumin, and brain derived neurotrophic factor. Finally, in the cuneate the cell cluster region presented similarities in prosimian galagos and four species of New World monkeys, whereas it appeared more differentiated and complex in the Old Word macaque monkeys. In conclusion, the different pattern of segregation of the inputs from the hand and from the foot can be related to the different metabolic organization of the cuneate and of the gracile, respectively.

Upregulation of NMDA receptor and neuronal NADPH-d/NOS expression in the nodose ganglion of acute hypoxic rats

Nitric oxide may serve as a neuronal messenger in the regulation of cardiorespiratory function via the N-methyl-D-aspartate (NMDA) receptor-mediated neuronal nitric oxide synthase (nNOS) activation. Since hypoxic stress would drastically influence the cardiorespiratory function, the present study aimed to examine if the expression of nNOS and NMDA receptor subunit 1 (NMDAR1) in the nodose ganglion (NG) would alter under different extents of hypoxia treatment. The nicotinamine adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry, nNOS and NMDAR1 immunofluorescence were used to examine nNOS and NMDAR1 expression in the NG following exposing of adult rats in the altitude chamber (0.27 atm, PO(2)=43 torr) for 2 and 4 h. The present results showed that NADPH-d, nNOS and NMDAR1 reactivities were co-localized in the NG under normoxic and hypoxic environment. Quantitative evaluation revealed that about 43% of neurons in the NG showed positive response for NADPH-d/nNOS and NMDAR1 reactivities. However, in animals subjected to hypoxia, both the percentage and the staining intensity of NADPH-d/nNOS and NMDAR1 labeled neurons were drastically increased. The percentage of NADPH-d/nNOS and NMDAR1-immunoreactive neurons in the NG was raised to 68% as well as 77%, respectively, following 2 and 4 h of hypoxic exposure. The magnitude of up-regulation was positively correlated with the duration of hypoxic periods. No significant cell loss was observed under this experimental paradigm. These findings suggest that different extents of hypoxia might induce the higher expression of nNOS and NMDAR1 in the NG, which could contribute to the neuronal integration as responding to the different physiological demands under hypoxic stress.

How accurate is magnetic resonance imaging of brain function?

Since it was introduced a decade ago, functional magnetic resonance imaging (fMRI) has come to dominate research on the human brain. However, fMRI maps are based on secondary metabolic and hemodynamic events that follow neuronal activity, and not on the electrical activity itself. Therefore, the representation provided by fMRI cannot be assumed a priori to be exact. The accuracy of these maps depends on the spatial extent of the metabolic and hemodynamic changes induced by neuronal activity, and the role played by the vasculature in converting these changes to signals detected by magnetic resonance imaging. Significant progress has been made in both areas, suggesting that it is possible to obtain both spatially accurate and quantitative data on brain function from magnetic resonance methodologies.

Environmental enrichment: effects on stereotyped behavior and regional neuronal metabolic activity

The present study evaluated whether environmental enrichment-related effects on the development of stereotyped behavior in deer mice were associated with alterations in neuronal metabolic activity. Deer mice were reared under either enriched or standard housing conditions for 60 days following weaning. All mice were then placed in automated photocell detectors and classified as either stereotypic or non-stereotypic. Neuronal metabolic activity was then assessed using cytochrome oxidase (CO) histochemistry. The results demonstrated that environmental enrichment significantly increased neuronal metabolic activity in the motor cortex. Furthermore, non-stereotypic mice exhibited significantly more CO activity than stereotypic mice in the cortex, striatum, nucleus accumbens, thalamus, hippocampus and amygdala. This latter effect was due to the enriched mice as evidenced by a significant interaction between housing condition and behavioral status in the cortex, striatum, nucleus accumbens, thalamus and hippocampus. Thus, the observed increase in CO activity reflected increased neuronal metabolic activity in non-stereotypic enriched mice relative to stereotypic enriched mice. These results suggest that, in a developmental model of spontaneous stereotypy, the enrichment-related prevention of stereotyped behavior is associated with increased CO activity.

An energy budget for signaling in the grey matter of the brain

Anatomic and physiologic data are used to analyze the energy expenditure on different components of excitatory signaling in the grey matter of rodent brain. Action potentials and postsynaptic effects of glutamate are predicted to consume much of the energy (47% and 34%, respectively), with the resting potential consuming a smaller amount (13%), and glutamate recycling using only 3%. Energy usage depends strongly on action potential rate--an increase in activity of 1 action potential/cortical neuron/s will raise oxygen consumption by 145 mL/100 g grey matter/h. The energy expended on signaling is a large fraction of the total energy used by the brain; this favors the use of energy efficient neural codes and wiring patterns. Our estimates of energy usage predict the use of distributed codes, with <or=15% of neurons simultaneously active, to reduce energy consumption and allow greater computing power from a fixed number of neurons. Functional magnetic resonance imaging signals are likely to be dominated by changes in energy usage associated with synaptic currents and action potential propagation.

Nitrergic neurons make synapses on dual-input dendritic spines of neurons in the cerebral cortex and the striatum of the rat: implication for a postsynaptic action of nitric oxide

Pre-embedding electron microscopic immunocytochemistry was used to examine the ultrastructure of neurons containing nitric oxide synthase and to evaluate their synaptic relationships with target neurons in the striatum and sensorimotor cerebral cortex. Intense nitric oxide synthase immunoreactivity was found by light and electron microscopy in a type of aspiny neuron scattered in these two regions. The intensity of the labeling was uniform in the soma, dendrites and axon terminals of these neurons. In both forebrain regions, nitric oxide synthase-immunoreactive neurons received synaptic contacts from unlabeled terminals, which were mostly apposed to small-caliber dendrites. The unlabeled symmetric contacts were generally about four times as abundant as the unlabeled asymmetric contacts on the nitric oxide synthase-immunoreactive neurons. Terminals labeled for nitric oxide synthase were filled with synaptic vesicles and were observed to contact unlabeled neurons. Only 54% (in the cerebral cortex) and 44.3% (in the striatum) of the nitric oxide synthase-immunoreactive terminals making apposition with the target structures were observed to form synaptic membrane specializations within the plane of the randomly sampled sections. The most common targets of nitric oxide synthase-immunoreactive terminals were thin dendritic shafts (54% of the immunoreactive terminals in the cortex and 75.7% of the immunoreactive terminals in the striatum), while dendritic spines were a common secondary target (42% of the immunoreactive terminals in the cortex and 20.6% of the immunoreactive terminals in the striatum). The spines contacted by nitric oxide synthase-immunoreactive terminals typically also received an asymmetric synaptic contact from an unlabeled axon terminal. These findings suggest that: (i) nitric oxide synthase-immunoreactive neurons in the cortex and striatum preponderantly receive inhibitory input; (ii) nitric oxide synthase-containing terminals commonly make synaptic contact with target structures in the cortex and striatum; (iii) spines targeted by nitric oxide synthase-containing terminals in the cortex and striatum commonly receive an asymmetric contact as well, which may provide a basis for a synaptic interaction of nitric oxide with excitatory input to individual spines.

Maturation of NADPH-d activity in the rat's barrel-field cortex and its relationship to cytochrome oxidase activity

Histochemical detection of NADPH-d activity in rat barrel-field cortex reveals four types of distributions. (i) A transient, diffuse neuropil staining is visible in the cortical plate and in deeper layers until postnatal day (P) 4. Thereafter, until P15, it is segregated in whisker-specific patches in layer IV, then the pattern gradually disappears, becoming virtually indistinct by P21. This transient patterning of diffuse NADPH-d activity in layer IV disappears after cortical injections of kainic acid and is affected by neonatal damage to the contralateral snout. An intense labeling (ii) of scattered cells and (iii) of a plexus of fibers is present. With maturation, the cells become localized mostly in layers II/III, in the lower part of layer V, and in layer VI. They are sparse in layer I, in upper layer V, and in layer IV where their somata are located primarily in the interbarrel septa. (iv) Light staining of cortical neurons is detected mostly in layers II-IV but occasionally also in layers V-VI. Cytochrome c oxidase (CO)-positive patches associated with barrels are first detected in layer IV around P4-P5; their staining density increases with development, then stays high. In the adult, CO activity is moderate in supragranular layers, highest in the barrels in layer IV, low in upper layer V, medium dense in the deeper half of layer V, and low in lamina VI. Thus, NADPH-d and CO activities are not necessarily colocalized in the rodent barrel-field cortex. The varied (transient and long-lasting) distributions of NADPH-d activity indicate that the enzyme and its associated production of NO serve multiple roles in developing and adult barrel-field cortex.