bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitric Oxide via cGMP-Dependent Mechanisms Increases Dye Coupling and Excitability of Rat Supraoptic Nucleus Neurons
Authors: Yang Qin Z. , Hatton Glenn I.
Published: April 2018

Unlike many neuron populations, supraoptic nucleus (SON) neurons are rich in both nitric oxide synthase (NOS) and the NO receptor-soluble guanylyl cyclase (GC), the activation of which leads to cGMP accumulation. Elevations in cGMP result in increased coupling among SON neurons. We investigated the effect of NO on dye coupling in SONs from male, proestrus virgin female, and lactating rats. In 167 slices 263 SON neurons were recorded; 210 of these neurons were injected intracellularly (one neuron per SON) with Lucifer yellow (LY). The typically minimal coupling seen in virgin females was increased nearly fourfold by the NO precursor,l-arginine, or the NO donor, sodium nitroprusside (SNP).l-Arginine-induced coupling was abolished by a NOS inhibitor. In slices from male and lactating rats who have a higher basal incidence of coupling, SNP increased coupling by approximately twofold over control (p< 0.03). SNP effects were prevented by the NO scavenger hemoglobin (20 μm) and by the selective blocker of NO-activated GC, ODQ (10 μm). These results suggest that NO released from cells within the SON can expand the coupled network of neurons and that this action occurs via cGMP-dependent processes. Because increased coupling is associated with elevated SON neuronal excitability, we also studied the effects of 8-bromo-cGMP on excitability. In both phasically and continuously firing neurons 8-bromo-cGMP (1–2 mm), but not cGMP, produced membrane depolarizations accompanied by membrane conductance increases. Conductance increases remained when depolarizations were eliminated by current-clamping the membrane potential. Thus, NO-induced cGMP increases SON neuronal coupling and excitability.
Odor Coding in a Model Olfactory Organ: TheDrosophilaMaxillary Palp
Authors: de Bruyne Marien , Clyne Peter J. , Carlson John R.
Published: April 2018

Odor coding relies on the activity of different classes of receptor neurons, each with distinct response characteristics. We have examined odor coding in a model olfactory organ, the maxillary palp ofDrosophila. This organ contains only 120 olfactory receptor neurons, compartmentalized in sensory hairs called sensilla, and provides an opportunity to characterize all neurons in an entire olfactory organ. Extensive extracellular recordings from single sensilla reveal that the neurons fall into six functional classes. Each of the 60 sensilla houses two neurons, which observe a pairing rule: each sensillum combines neurons of two particular classes, thereby yielding three sensillum types. The sensillum types are intermingled on the surface of the palp, but their distribution is not random. The neurons exhibit diverse response characteristics, providing the basis for an olfactory code. A particular odor can excite one neuron and inhibit another, and a particular neuron can be excited by one odor and inhibited by another. Some excitatory responses continue beyond the end of odor delivery, but responses to most odors terminate abruptly after the end of odor delivery, with some followed by a period of poststimulus quiescence. The specificity of odor response is examined in detail for the neurons of one sensillum, which were found to differ in their relative responses to a homologous series of esters. Adaptation and cross-adaptation are documented, and cross-adaptation experiments demonstrate that the two neurons within one type of sensillum can function independently. The analysis of all neuronal types in this model olfactory organ is discussed in terms of its functional organization and the mechanisms by which it encodes olfactory information.
Transmembrane Domain I Contributes to the Permeation Pathway for Serotonin and Ions in the Serotonin Transporter
Authors: Barker Eric L. , Moore Kimberly R. , Rakhshan Fariborz , Blakely Randy D.
Published: April 2018

Mutation of a conserved Asp (D98) in the rat serotonin (5HT) transporter (rSERT) to Glu (D98E) led to decreased 5HT transport capacity, diminished coupling to extracellular Na+and Cl−, and a selective loss of antagonist potencies (cocaine, imipramine, and citalopram but not paroxetine or mazindol) with no change in 5HTKmvalue. D98E, which extends the acidic side chain by one carbon, affected the rank-order potency of substrate analogs for inhibition of 5HT transport, selectively increasing the potency of two analogs with shorter alkylamine side chains, gramine, and dihydroxybenzylamine. D98E also increased the efficacy of gramine relative to 5HT for inducing substrate-activated currents inXenopus laevisoocytes, but these currents were noticeably dependent on extracellular medium acidification.I–Vprofiles for substrate-independent and -dependent currents indicated that the mutation selectively impacts ion permeation coupled to 5HT occupancy. The ability of the D98E mutant to modulate selective aspects of substrate recognition, to perturb ion dependence as well as modify substrate-induced currents, suggests that transmembrane domain I plays a critical role in defining the permeation pathway of biogenic amine transporters.
Activation of Caspase-3 in the Retina of Transgenic Rats with the Rhodopsin Mutation S334ter during Photoreceptor Degeneration
Authors: Liu Changdong , Li Yiwen , Peng Min , Laties Alan M. , Wen Rong
Published: April 2018

The role of caspase-3 in photoreceptor degeneration was examined in a line of transgenic rats that carry a rhodopsin mutation S334ter. Photoreceptor degeneration in these animals is rapid. It is detected as early as postnatal day (PD) 8, and by PD 20, only one of the original 12 rows of nuclei remain in the outer nuclear layer. At PD 11 and 12, the number of photoreceptors dying per day reaches a peak of ∼30% of the total photoreceptors in the retina. Coincident with this rapid degeneration is an increase in caspase-3-like activity as assessed by the cleavage of a fluorescent substrateN-acetyl-Asp-Glu-Val-Asp-aminomethylcoumarin and an increase in activated caspase-3 as determined by Western blot analysis for its 12 kDa subunit. Intraocular injection of an irreversible caspase-3 inhibitorN-benzyloxycarbonal-Asp(OMe)-Glu(OMe)-Val-Asp(Ome)-fluoromethyketone partially protected photoreceptors from degeneration. These findings indicate that a caspase-3-dependent mechanism is operative in photoreceptor death in the transgenic rats under investigation.
Expression of Human Apolipoprotein E3 or E4 in the Brains ofApoe−/−Mice: Isoform-Specific Effects on Neurodegeneration
Authors: Buttini Manuel , Orth Matthias , Bellosta Stefano , Akeefe Hassibullah , Pitas Robert E. , Wyss-Coray Tony , Mucke Lennart , Mahley Robert W.
Published: April 2018

Apolipoprotein (apo) E isoforms are key determinants of susceptibility to Alzheimer’s disease. The apoE4 isoform is the major known genetic risk factor for this disease and is also associated with poor outcome after acute head trauma or stroke. To test the hypothesis that apoE3, but not apoE4, protects against age-related and excitotoxin-induced neurodegeneration, we analyzed apoE knockout (Apoe−/−) mice expressing similar levels of human apoE3 or apoE4 in the brain under control of the neuron-specific enolase promoter. Neuronal apoE expression was widespread in the brains of these mice. Kainic acid-challenged wild-type orApoe−/−mice had a significant loss of synaptophysin-positive presynaptic terminals and microtubule-associated protein 2-positive neuronal dendrites in the neocortex and hippocampus, and a disruption of neurofilament-positive axons in the hippocampus. Expression of apoE3, but not of apoE4, protected against this excitotoxin-induced neuronal damage. ApoE3, but not apoE4, also protected against the age-dependent neurodegeneration seen inApoe−/−mice. These differences in the effects of apoE isoforms on neuronal integrity may relate to the increased risk of Alzheimer’s disease and to the poor outcome after head trauma and stroke associated with apoE4 in humans.
Abnormalities in Neuronal Process Extension, Hippocampal Development, and the Ventricular System of L1 Knockout Mice
Authors: Demyanenko Galina P. , Tsai Amy Y. , Maness Patricia F.
Published: April 2018

In humans, mutations in the L1 cell adhesion molecule are associated with a neurological syndrome termed CRASH, which includes corpus callosum agenesis, mental retardation, adducted thumbs, spasticity, and hydrocephalus. A mouse model with a null mutation in the L1 gene (Cohen et al., 1997) was analyzed for brain abnormalities by Nissl and Golgi staining and immunocytochemistry. In the motor, somatosensory, and visual cortex, many pyramidal neurons in layer V exhibited undulating apical dendrites that did not reach layer I. The hippocampus of L1 mutant mice was smaller than normal, with fewer pyramidal and granule cells. The corpus callosum of L1-minus mice was reduced in size because of the failure of many callosal axons to cross the midline. Enlarged ventricles and septal abnormalities were also features of the mutant mouse brain. Immunoperoxidase staining showed that L1 was abundant in developing neurons at embryonic day 18 (E18) in wild-type cerebral cortex, hippocampus, and corpus callosum and then declined to low levels with maturation. In the E18 cortex, L1 colocalized with microtubule-associated protein 2, a marker of dendrites and somata. These new findings suggest new roles for L1 in the mechanism of cortical dendrite differentiation, as well as in guidance of callosal axons and regulation of hippocampal development. The phenotype of the L1 mutant mouse indicates that it is a potentially valuable model for the human CRASH syndrome.
Spatiotemporal Expression Patterns of Metalloproteinases and Their Inhibitors in the Postnatal Developing Rat Cerebellum
Authors: Vaillant Catherine , Didier-Bazès Marianne , Hutter Agnès , Belin Marie-Francoise , Thomasset Nicole
Published: April 2018

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade the components of the extracellular matrix (ECM). The balance between MMPs and their inhibitors [tissue inhibitors of metalloproteinases (TIMPs)] in the pericellular environment determines the most significant proteolytic events in tissue remodeling.In vitroevidence is accumulating that these molecules may be crucial in the maturation of neural cells. Here, we investigated thein vivoexpression of MMPs 2, 3, and 9 and TIMPs 1, 2, and 3 in the developing and adult rat cerebellum using immunohistochemistry andin situhybridization. During postnatal development, all Purkinje (PK) cell somata expressed all the MMPs and TIMPs studied, whereas their growing dendritic trees expressed only MMP 3 and TIMP 3. In the adult, MMP 3 was confined to PK cell bodies, whereas TIMP 3 was expressed in PK cell somata and processes. Irrespective of the developmental stage, Bergmann glial processes contained only MMP 9, but their somata contained both TIMP 1 and MMP 9. In granular cells, MMPs 3 and 9 and TIMPs 1, 2, and 3 were chiefly detected at a time when migration is known to be maximal; except for that of TIMP 1, their expression persisted in the internal granular layer in the adult. The functional relevance of MMP expression was verified by gelatin zymography. MMP 9 activity was maximal on postnatal day 10 (P10) and was detectable at a low level on P15 and in the adult, whereas MMP 2 activity remained similar throughout postnatal development. Regional and cell-specific expression of MMPs and TIMPs closely reflects the successive stages of cerebellar development, thereby suggesting a pivotal role for ECM proteolysis in brain development and plasticity.
Attenuation of Ischemia-Induced Cellular and Behavioral Deficits by X Chromosome-Linked Inhibitor of Apoptosis Protein Overexpression in the Rat Hippocampus
Authors: Xu Daigen , Bureau Yves , McIntyre Dan C. , Nicholson Donald W. , Liston Peter , Zhu Yanxia , Fong Wei Gin , Crocker Stephen J. , Korneluk Robert G. , Robertson George S.
Published: April 2018

Transient forebrain ischemia produced by four-vessel occlusion (4-VO) triggers the delayed death of CA1 neurons in the hippocampus, resulting in behavioral deficits of spatial learning performance. We demonstrate that CA1 neuronal loss induced by 4-VO (12 min) is preceded by a selective and marked elevation of catalytically active caspase-3 in these neurons, indicative of apoptosis. Virally mediated overexpression of the anti-apoptotic gene X chromosome-linked inhibitor of apoptosis protein (XIAP) prevented both the production of catalytically active caspase-3 and degeneration of CA1 neurons after transient forebrain ischemia. CA1 neurons protected in this manner appeared to function normally, as assessed by immunohistochemical detection of the neuronal activity marker nerve growth factor inducible-A and by spatial learning performance in the Morris water maze. These findings indicate that caspase-3 activation is a key event in ischemic neuronal death and that blockade of this event by XIAP overexpression permits CA1 neurons to survive and operate properly after an ischemic insult.
Differential Neural Responses during Performance of Matching and Nonmatching to Sample Tasks at Two Delay Intervals
Authors: Elliott Rebecca , Dolan Raymond J.
Published: April 2018

Visual short-term memory in humans and animals is frequently assessed using delayed matching to sample (DMTS) and delayed nonmatching to sample (DNMTS) tasks across variable delay intervals. Although these tasks depend on certain common mechanisms, there are behavioral differences between them, and neuroimaging provides a means of assessing explicitly whether this is underpinned by differences at a neural level. Findings of delay-dependent deficits, after lesions in humans and animals, suggest that the neural implementation of these tasks may also critically depend on the delay interval. In this study we determined whether there were differential neural responses associated with DMTS and DNMTS tasks at two different delay intervals using functional magnetic resonance imaging. Ten healthy volunteers were studied under four test conditions: DMTS and DNMTS at 5 and 15 sec delay. The main effect of DMTS compared with DNMTS across both delay intervals was associated with significant activation in bilateral head of caudate and medial orbitofrontal cortex. By contrast, DNMTS compared with DMTS was associated with significant activation in mediodorsal thalamus, bilateral lateral orbitofrontal cortex, and left premotor cortex. The main effect of short compared with long delay, across both tasks, was associated with significantly greater activity in occipital and parietal cortices. By contrast, long compared with short delay was associated with significantly greater activity in temporal and ventrolateral frontal cortices. We conclude that DMTS and DNMTS are not equivalent and furthermore that the precise neural implementation of these tasks is a dynamic function of delay interval.
Vibrissae-Evoked Behavior and Conditioning before Functional Ontogeny of the Somatosensory Vibrissae Cortex
Authors: Landers Margo S. , Sullivan Regina M.
Published: April 2018

The following experiments determined that the somatosensory whisker system is functional and capable of experience-dependent behavioral plasticity in the neonate before functional maturation of the somatosensory whisker cortex. First, unilateral whisker stimulation caused increased behavioral activity in both postnatal day (P) 3–4 and P8 pups, whereas stimulation-evoked cortical activity (14C 2-deoxyglucose autoradiography) was detectable only in P8 pups. Second, neonatal rat pups are capable of forming associations between whisker stimulation and a reinforcer. A classical conditioning paradigm (P3–P4) showed that the learning groups (paired whisker stimulation–shock or paired whisker stimulation–warm air stream) exhibited significantly higher behavioral responsiveness to whisker stimulation than controls. Finally, stimulus-evoked somatosensory cortical activity during testing [P8; using14C 2-deoxyglucose (2-DG) autoradiography] was assessed after somatosensory conditioning from P1–P8. No learning-associated differences in stimulus-evoked cortical activity were detected between learning and nonlearning control groups. Together, these experiments demonstrate that the whisker system is functional in neonates and capable of experience-dependent behavioral plasticity. Furthermore, in contrast to adult somatosensory classical conditioning, these data suggest that the cortex is not required for associative somatosensory learning in neonates.
The Alzheimer's Disease Amyloid Precursor Protein Modulates Copper-Induced Toxicity and Oxidative Stress in Primary Neuronal Cultures
Authors: White Anthony R. , Multhaup Gerd , Maher Fran , Bellingham Shayne , Camakaris James , Zheng Hui , Bush Ashley I. , Beyreuther Konrad , Masters Colin L. , Cappai Roberto
Published: April 2018

The amyloid precursor protein (APP) of Alzheimer's disease can reduce copper (II) to copper (I) in a cell-free system potentially leading to increased oxidative stress in neurons. We used neuronal cultures derived from APP knock-out (APP−/−) and wild-type (WT) mice to examine the role of APP in copper neurotoxicity. WT cortical, cerebellar, and hippocampal neurons were significantly more susceptible than their respective APP−/−neurons to toxicity induced by physiological concentrations of copper but not by zinc or iron. There was no difference in copper toxicity between APLP2−/−and WT neurons, demonstrating specificity for APP-associated copper toxicity. Copper uptake was the same in WT and APP−/−neurons, suggesting APP may interact with copper to induce a localized increase in oxidative stress through copper (I) production. This was supported by significantly higher levels of copper-induced lipid peroxidation in WT neurons. Treatment of neuronal cultures with a peptide corresponding to the human APP copper-binding domain (APP142–166) potentiated copper but not iron or zinc toxicity. Incubation of APP142–166 with low-density lipoprotein (LDL) and copper resulted in significantly increased lipid peroxidation compared to copper and LDL alone. Substitution of the copper coordinating histidine residues with asparagines (APP142–166H147N, H149N, H151N) abrogated the toxic effects. A peptide corresponding to the zinc-binding domain (APP181–208) failed to induce copper or zinc toxicity in neuronal cultures. These data support a role for the APP copper-binding domain in APP-mediated copper (I) generation and toxicity in primary neurons, a process that has important implications for Alzheimer's disease and other neurodegenerative disorders.
Multiple and Opposing Roles of Cholinergic Transmission in the Main Olfactory Bulb
Authors: Castillo Pablo E. , Carleton Alan , Vincent Jean-Didier , Lledo Pierre-Marie
Published: April 2018

The main olfactory bulb is a critical relay step between the olfactory epithelium and the olfactory cortex. A marked feature of the bulb is its massive innervation by cholinergic inputs from the basal forebrain. In this study, we addressed the functional interaction between cholinergic inputs and intrinsic bulbar circuitry. Determining the roles of acetylcholine (ACh) requires the characterization of cholinergic effects on both neural excitability and synaptic transmission. For this purpose, we used electrophysiological techniques to localize and characterize the diverse roles of ACh in mouse olfactory bulb slices. We found that cholinergic inputs have a surprising number of target receptor populations that are expressed on three different neuronal types in the bulb. Specifically, nicotinic acetylcholine receptors excite both the output neurons of the bulb, i.e., the mitral cells, as well as interneurons located in the periglomerular regions. These nicotine-induced responses in interneurons are short lasting, whereas responses in mitral cells are long lasting. In contrast, muscarinic receptors have an inhibitory effect on the firing rate of interneurons from a deeper layer, granule cells, while at the same time they increase the degree of activity-independent transmitter release from these cells onto mitral cells.

Cholinergic signaling thus was found to have multiple and opposing roles in the olfactory bulb. These dual cholinergic effects on mitral cells and interneurons may be important in modulating olfactory bulb output to central structures required for driven behaviors and may be relevant to understanding mechanisms underlying the perturbations of cholinergic inputs to cortex that occur in Alzheimer's disease.
Loss of Synaptic Depression in Mammalian Anterior Cingulate Cortex after Amputation
Authors: Wei Feng , Li Ping , Zhuo Min
Published: April 2018

Two forms of activity-dependent long-term depression (LTD) in the CNS, as defined by their sensitivity to the blockade of NMDA receptors, are thought to be important in learning, memory, and development. Here, we report that NMDA receptor-independent LTD is the major form of long-term plasticity in the anterior cingulate cortex (ACC). Both L-type voltage-gated calcium channels and metabotropic glutamate receptors are required for inducing LTD. Amputation of a third hindpaw digit in an adult rat induced rapid expression of immediate early genes in the ACC bilaterally and caused a loss of LTD that persisted for at least 2 weeks. Our results suggest that synaptic LTD in the ACC may contribute to enhanced neuronal responses to subsequent somatosensory stimuli after amputation.
Neuralization of theXenopusEmbryo by Inhibition of p300/ CREB-Binding Protein Function
Authors: Kato Yoichi , Shi Yang , He Xi
Published: April 2018

p300/ CREB-binding protein (CBP) is a transcriptional coactivator for a plethora of transcription factors and plays critical roles in signal transduction pathways. We report that the inhibition of p300/CBP function in theXenopusembryo abolishes non-neural tissue formation and, strikingly, initiates neural induction and primary neurogenesis in the entire embryo. The observed neuralization is achieved in the absence of anterior or posterior gene expression, suggesting that neural fate activation and anterior patterning may represent distinct molecular events. We further demonstrate that the neuralizing and anteriorizing activities of chordin and noggin are separable properties of these neural inducers. This study reveals that all embryonic cells possess intrinsic neuralizing capability and that p300/CBP function is essential for embryonic germ layer formation and neural fate suppression during vertebrate embryogenesis.
Areas Involved in Encoding and Applying Directional Expectations to Moving Objects
Authors: Shulman Gordon L. , Ollinger John M. , Akbudak Erbil , Conturo Thomas E. , Snyder Abraham Z. , Petersen Steven E. , Corbetta Maurizio
Published: April 2018

Two experiments used functional magnetic resonance imaging (fMRI) to examine the cortical areas involved in establishing an expectation about the direction of motion of an upcoming object and applying that expectation to the analysis of the object. In Experiment 1, subjects saw a stationary cue that either indicated the direction of motion of a subsequent test stimulus (directional cue) or provided no directional information (neutral cue). Their task was to detect the presence of coherent motion in the test stimulus. The stationary directional cue produced larger modulations than the neutral cue, with respect to a passive viewing baseline, both in motion-sensitive areas such as left MT+ and the anterior intraparietal sulcus, as well as motion-insensitive areas such as the posterior intraparietal sulcus and the junction of the left medial precentral sulcus and superior frontal sulcus. Experiment 2 used an event-related fMRI technique to separate signals during the cue period, in which the expectation was encoded and maintained, from signals during the subsequent test period, in which the expectation was applied to the test object. Cue period activations from a stationary, directional cue included many of the same motion-sensitive and -insensitive areas from Experiment 1 that produced directionally specific modulations. Prefrontal activations were not observed during the cue period, even though the stationary cue information had to be translated into a format appropriate for influencing motion detection, and this format was maintained for the duration of the cue period (∼5 sec).
Replay and Time Compression of Recurring Spike Sequences in the Hippocampus
Authors: Nádasdy Zoltán , Hirase Hajime , Czurkó András , Csicsvari Jozsef , Buzsáki György
Published: April 2018

Information in neuronal networks may be represented by the spatiotemporal patterns of spikes. Here we examined the temporal coordination of pyramidal cell spikes in the rat hippocampus during slow-wave sleep. In addition, rats were trained to run in a defined position in space (running wheel) to activate a selected group of pyramidal cells. A template-matching method and a joint probability map method were used for sequence search. Repeating spike sequences in excess of chance occurrence were examined by comparing the number of repeating sequences in the original spike trains and in surrogate trains after Monte Carlo shuffling of the spikes. Four different shuffling procedures were used to control for the population dynamics of hippocampal neurons. Repeating spike sequences in the recorded cell assemblies were present in both the awake and sleeping animal in excess of what might be predicted by random variations. Spike sequences observed during wheel running were “replayed” at a faster timescale during single sharp-wave bursts of slow-wave sleep. We hypothesize that the endogenously expressed spike sequences during sleep reflect reactivation of the circuitry modified by previous experience. Reactivation of acquired sequences may serve to consolidate information.
Learning Induces a CDC2-Related Protein Kinase, KKIAMRE
Authors: Gomi Hiroshi , Sun William , Finch Caleb E. , Itohara Shigeyoshi , Yoshimi Kenji , Thompson Richard F.
Published: April 2018

To elucidate molecular mechanisms in learning and memory, we analyzed expression of mRNAs in brains of rabbits undergoing eyeblink conditioning. Infusion of the transcription inhibitor actinomycin D into the cerebellar interpositus nucleus reversibly blocked learning but not performance of the conditioned response. Differential display PCR analysis of cerebellar interpositus RNAs from trained and pseudotrained rabbits identified a 207 bp band that was induced with learning. The fragment was used to isolate a cDNA from a λgt11 rabbit brain library containing a 1698 bp open reading frame. The deduced amino acid sequence contains the KKIAMRE motif, which is conserved among cell division cycle 2 (cdc2)-related kinases. These results suggest that there is a new category of cdc2-related kinases in the brain whose function may be important in learning and memory.
Involvement of Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) and p53 in Neuronal Apoptosis: Evidence That GAPDH Is Upregulated by p53
Authors: Chen Ren-Wu , Saunders Paul A. , Wei Huafeng , Li Zhuangwu , Seth Prem , Chuang De-Maw
Published: April 2018

We recently reported that cytosine arabinoside (AraC)-induced apoptosis of cerebellar neurons involves the overexpression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The present study was undertaken to investigate whether p53 and/or Bax overexpression participates in the AraC-induced apoptosis of cerebellar granule cells and, if so, the relationship between p53 induction and GAPDH overexpression in these cells.

AraC-induced apoptosis of cerebellar granule cells was preceded by an increase in levels of p53 mRNA and protein detected between 1 and 8 hr after treatment. The mRNA level for a p53 target gene, Bax, was also increased. The increase in GAPDH mRNA lasted longer than that of either p53 or Bax, and the level of GAPDH protein in the particulate fraction increased after induction of GAPDH mRNA. The antisense oligonucleotide to p53 protected granule cells from AraC-induced chromatin condensation, internucleosomal cleavage, and apoptotic death. The inhibition of p53 expression by the p53 antisense oligonucleotide not only blocked the expression of Bax but also partially suppressed the increased GAPDH mRNA and protein levels. Conversely, the suppression of GAPDH expression and subsequent attenuation of apoptosis of granule cells by GAPDH antisense oligonucleotide did not influence the expression of p53 or Bax. Cerebellar granule cells prepared from p53 knock-out mice were resistant to AraC toxicity, and the p53 gene knock-out suppressed AraC-upregulated GAPDH expression. Moreover, infection of PC12 cells with an adenoviral vector containing p53 gene dramatically increased GAPDH expression and triggered cell apoptosis. These results suggest that AraC-induced apoptosis of cerebellar granule cells involves the expression of both GAPDH and p53 and that, similar to Bax, GAPDH is upregulated by p53 after exposure to the apoptotic insult.
Control of GluR1 AMPA Receptor Function by cAMP-Dependent Protein Kinase
Authors: Banke T. G. , Bowie D. , Lee H.-K. , Huganir R. L. , Schousboe A. , Traynelis S. F.
Published: April 2018

Modulation of postsynaptic AMPA receptors in the brain by phosphorylation may play a role in the expression of synaptic plasticity at central excitatory synapses. It is known from biochemical studies that GluR1 AMPA receptor subunits can be phosphorylated within their C terminal by cAMP-dependent protein kinase A (PKA), which is colocalized with the phosphatase calcineurin (i.e., phosphatase 2B). We have examined the effect of PKA and calcineurin on the time course, peak open probability (PO,PEAK), and single-channel properties of glutamateevoked responses for neuronal AMPA receptors and homomeric GluR1(flip) receptors recorded in outside-out patches. Inclusion of purified catalytic subunit Cα-PKA in the pipette solution increased neuronal AMPA receptorPO,PEAK(0.92) compared with recordings made with calcineurin included in the pipette (PO,PEAK0.39). Similarly, Cα-PKA increasedPO,PEAKfor recombinant GluR1 receptors (0.78) compared with patches excised from cells cotransfected with a cDNA encoding the PKA peptide inhibitor PKI (PO,PEAK0.50) or patches with calcineurin included in the pipette (PO,PEAK0.42). Neither PKA nor calcineurin altered the amplitude of single-channel subconductance levels, weighted mean unitary current, mean channel open period, burst length, or macroscopic response waveform for recombinant GluR1 receptors. Substitution of an amino acid at the PKA phosphorylation site (S845A) on GluR1 eliminated the PKA-induced increase inPO,PEAK, whereas the mutation of a Ca2+,calmodulin-dependent kinase II and PKC phosphorylation site (S831A) was without effect. These results suggest that AMPA receptor peak response open probability can be increased by PKA through phosphorylation of GluR1 Ser845.
GluR5 and GluR6 Kainate Receptor Subunits Coexist in Hippocampal Neurons and Coassemble to Form Functional Receptors
Authors: Paternain Ana V. , Herrera Marı́a T. , Nieto M. Angela , Lerma Juan
Published: April 2018

We have performed nonradioactive doublein situhybridization to study the expression of glutamic acid decarboxylase and GluR6 or GluR5 subunits in hippocampal slices. Our results indicate that althoughGluR6is primarily expressed by pyramidal cells and dentate granule neurons andGluR5is prominently expressed in nonpyramidal cells, there is a significant population of GABAergic interneurons that coexpress the two glutamate receptor subunits. To assess whether the two subunits could coassemble to form heteromeric receptors, we studied the electrophysiological responses when both subunits were coexpressed in HEK293 cells. Responses evoked by rapid application of either glutamate, (RS)-α-amino-3-hydroxy-5-tert-butyl-4-isoxazolepropionic acid (ATPA) the selective agonist of GluR5 receptors), and AMPA in cells cotransfected with GluR6(R) and GluR5(Q) presented a similar degree of outward rectification. This can only be attributed to the fact that all receptors have at least one GluR6(R) subunit in their structure, conferring outward rectification, and at least one GluR5(Q) subunit to confer sensitivity to ATPA and AMPA. More than 80% of the receptors expressed by a single cell were found to be GluR5/R6 heteromers, presenting different desensitization and gating properties to homomeric R6 receptors. These results lead us to believe that a population of interneurons in the hippocampus express receptors made up of both GluR5 and GluR6 subunits and provide evidence for a greater diversity of kainate receptors in the brain than previously thought, that may account for a higher functional complexity.
Selective Innervation of Retinorecipient Brainstem Nuclei by Retinal Ganglion Cell Axons Regenerating through Peripheral Nerve Grafts in Adult Rats
Authors: Avilés-Trigueros Marcelino , Sauvé Yves , Lund Raymond D. , Vidal-Sanz Manuel
Published: April 2018

The pattern of axonal regeneration, specificity of reinnervation, and terminal arborization in the brainstem by axotomized retinal ganglion cell axons was studied in rats with peripheral nerve grafts linking the retina with ipsilateral regions of the brainstem, including dorsal and lateral aspects of the diencephalon and lateral aspect of the superior colliculus. Four to 13 months later, regenerated retinal projections were traced using intraocular injection of cholera toxin B subunit. In approximately one-third of the animals, regenerated retinal axons extended into the brainstem for distances of up to 6 mm. Although axons followed different patterns of ingrowth depending on their site of entry to the brainstem, within the pretectum, they innervated preferentially the nucleus of the optic tract and the olivary pretectal nucleus in which they formed two types of terminal arbors. Within the superior colliculus, axons extended laterally and formed a different terminal arbor type within the stratum griseum superficiale. In the remaining two-thirds of the animals, retinal fibers formed a neuroma-like structure at the site of entry into the brainstem, or a few fibers extended for very short distances within the neighboring neuropil. These experiments suggest that regenerated retinal axons are capable of a highly selective reinnervation pattern within adult denervated retinorecipient nuclei in which they form well defined terminal arbors that may persist for long periods of time. In addition, these studies provide the anatomical correlate for our previous functional study on the re-establishment of the pupillary light reflex in this experimental paradigm.
Dependence of GABAergic Synaptic Areas on the Interneuron Type and Target Size
Authors: Kubota Yoshiyuki , Kawaguchi Yasuo
Published: April 2018

In the neostriatum, several types of interneuron with distinct firing patterns and expression of neuroactive substances are known to exist. We found two types of neostriatal interneurons, parvalbumin-containing fast-spiking (FS) cells and somatostatin-containing low-threshold spike (LTS) cells to both be immunoreactive for GABA at their axon terminals in immersion-fixed brain slices from rat. To reveal the differences in synaptic connections between these two types of GABAergic interneurons, the postsynaptic target and their synaptic structure were compared by three-dimensional reconstructions from electron microscopic images of intracellularly stained axon terminals. FS cells made a greater proportion of synaptic contacts onto somata than LTS cells. Although terminal boutons of FS and LTS cells were similar in volume, their synaptic junctional areas differed in size distribution and relation to the dimensions of postsynaptic dendritic shafts or spines. Whereas the synaptic junctional areas of FS cells (0.024–0.435 μm2;n= 28) sharply and linearly increased with the circumference of the postsynaptic dendrites or spines (0.939–5.146 μm), the slope for the junctional area of LTS cells (0.02–0.103 μm2;n= 29) against circumference (0.844–4.252 μm) was less steep, and a much weaker correlation was seen. In addition to the differences in firing patterns, expressed molecules, axonal arborizations, and postsynaptic targets, this variation in dependency of the synaptic area on the target size suggests functional differentiation of GABAergic interneurons.
Differential Activation in Somatosensory Cortex for Different Discrimination Tasks
Authors: Braun Christoph , Schweizer Renate , Elbert Thomas , Birbaumer Niels , Taub Edward
Published: April 2018

Maps of the body surface in somatosensory cortex have been shown to be highly plastic, altering their configuration in response to changes in use of body parts. The current study investigated alterations in the functional organization of the human somatosensory cortex resulting from massed practice. Over a period of 4 weeks, subjects were given synchronous tactile stimulation of thumb (D1) and little finger (D5) for 1 hr/d. They had to identify the orientation of the stimuli. Neuroelectric source localization based on high-resolution EEG revealed that, when subjects received passive tactile stimulation of D1 or D5, the representations of the fingers in primary somatosensory cortex were closer together after training than before. There was also an apparently correlative tendency to anomalously mislocalize near-threshold tactile stimuli equally to the distant finger costimulated during training rather than preferentially to the finger nearest to the finger stimulated in a post-training test. However, when the stimulus discrimination had to be made, neuroelectric source imaging revealed that the digital representations of D1 and D5 were further apart after training than before. Thus, the same series of prolonged repetitive stimulations produced two different opposite effects on the spatial relationship of the cortical representations of the digits, suggesting that differential activation in the same region of somatosensory cortex is specific to different tasks.
A Model of High-Frequency Ripples in the Hippocampus Based on Synaptic Coupling Plus Axon–Axon Gap Junctions between Pyramidal Neurons
Authors: Traub Roger D. , Bibbig Andrea
Published: April 2018

So-called 200 Hz ripples occur as transient EEG oscillations superimposed on physiological sharp waves in a number of limbic regions of the rat, either awake or anesthetized. In CA1, ripples have maximum amplitude in stratum pyramidale. Many pyramidal cells fail to fire during a ripple, or fire infrequently, superimposed on the sharp wave-associated depolarization, whereas interneurons can fire at high frequencies, possibly as fast as the ripple itself. Recently, we have predicted that networks of pyramidal cells, interconnected by axon–axon gap junctions and without interconnecting chemical synapses, can generate coherent population oscillations at >100 Hz. Here, we show that such networks, to which interneurons have been added along with chemical synaptic interactions between respective cell types, can generate population ripples superimposed on afferent input-induced intracellular depolarizations. During simulated ripples, interneurons fire at high rates, whereas pyramidal cells fire at lower rates. The model oscillation is generated by the electrically coupled pyramidal cell axons, which then phasically excite interneurons at ripple frequency. The oscillation occurs transiently because rippling can express itself only when axons and cells are sufficiently depolarized. Our model predicts the occurrence of spikelets (fast prepotentials) in some pyramidal cells during sharp waves.
Presynaptic P2X Receptors Facilitate Inhibitory GABAergic Transmission between Cultured Rat Spinal Cord Dorsal Horn Neurons
Authors: Hugel Sylvain , Schlichter Rémy
Published: April 2018

The superficial layers of the spinal cord dorsal horn (DH) express P2X2, P2X4, and P2X6 subunits entering into the formation of ionotropic (P2X) receptors for ATP. Using a culture system of laminae I–III from neonatal rat DH, we show that ATP induced a fast nonselective cation current in 38% of the neurons (postsynaptic effect). ATP also increased the frequency of miniature IPSCs (mIPSCs) mediated by GABAAreceptors or by glycine receptors in 22 and 9%, respectively, of the neurons tested (presynaptic effect) but had no effect on glutamatergic transmission. The presynaptic effect of ATP on GABAergic transmission was not significantly affected by thapsigargin (1 μm) but was completely dependent on Ca2+influx. Presynaptic and postsynaptic effects were inhibited by suramin, pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid, and reactive blue and were not reproduced by uridine 5′-triphosphate (UTP) or adenosine 5′-O-(2-thiodiphosphate) (ADP-β-S), suggesting the implication of ionotropic P2X rather than of metabotropic P2Y receptors. αβ-methylene-ATP (100 μm) did not reproduce the effects of ATP. ATP reversibly increased the amplitude of electrically evoked GABAergic IPSCs and reduced paired-pulse inhibition or facilitation without affecting IPSC kinetics. This effect was preferentially, but not exclusively, observed in neurons coreleasing ATP and GABA. We conclude that in cultured DH neurons, the effects of ATP are mediated by P2X receptors having a pharmacological profile dominated by the P2X2 subunit. The presynaptic receptors might underlie a modulatory action of ATP on a subset of GABAergic interneurons involved in the spinal processing of nociceptive information.
Expression of Bcl-2 Protects against Photoreceptor Degeneration inretinal degeneration slow(rds) Mice
Authors: Nir Izhak , Kedzierski Wojciech , Chen Jeannie , Travis Gabriel H.
Published: April 2018

Theretinal degeneration sloworrdsgene encodes rds/peripherin, an integral membrane glycoprotein in the outer segments of rod and cone photoreceptors. Mice homozygous for a null mutation inrdsfail to develop outer segments and undergo subsequent degeneration of photoreceptors by the apoptotic pathway. Mutations in the humanRDSgene are responsible for several forms of inherited blindness including autosomal-dominant retinitis pigmentosa and macular degeneration. Here, we examined the effects of ectopic Bcl-2 expression in transgenic photoreceptors on the rate of retinal degeneration inrdsmutant mice. We observed an approximately twofold preservation of photoreceptors compared with nontransgenicrdsmutant mice at 3 months. Immunoblot analysis showed similar levels of Bcl-2 in 2-, 3-, and 4-week-old transgenic mice. Expression of Bcl-2 in therdsmouse did not lead to outer segment formation and did not induce cell death. These results suggest that Bcl-2 expression may be an effective therapeutic strategy in humans with mutations inRDSor other genes that affect the integrity of photoreceptor outer segments.
Effects of Neurotrophins on Cortical Plasticity: Same or Different?
Authors: Lodovichi Claudia , Berardi Nicoletta , Pizzorusso Tommaso , Maffei Lamberto
Published: April 2018

Neurotrophins are important regulators of visual cortical plasticity. It is still unclear, however, whether they play similar or different roles and which are their effects on the electrical activity of cortical neuronsin vivo. We therefore compared the effects of all neurotrophins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT-4), and neurotrophin-3 (NT-3) on visual cortical plasticity and on cell spontaneous and visually evoked activity. Rats were monocularly deprived for 1 week at the peak of the critical period, and neurotrophins were infused intracortically. The main finding is that, with the exception of NT-3, all neurotrophins affect the outcome of monocular deprivation, but there are clear differences in their mechanisms of action. In particular, NT-4 and NGF counteract monocular deprivation effects without causing detectable alterations either in spontaneous or visually evoked neuronal activity. BDNF is less effective on ocular dominance plasticity and, in addition, strongly affects spontaneous and visually evoked activity in cortical neurons.
Organization of Ionotropic Glutamate Receptors at Dendrodendritic Synapses in the Rat Olfactory Bulb
Authors: Sassoè-Pognetto Marco , Ottersen Ole P.
Published: April 2018

Dendrodendritic synapses between mitral (or tufted) and granule cells of the olfactory bulb play a major role in the processes of odor discrimination and olfactory learning. Release of glutamate at these synapses activates postsynaptic receptors on the dendritic spines of granule cells, as well as presynaptic NMDA receptors in the mitral cell membrane. However, immunocytochemical studies have failed to demonstrate the presence of ionotropic glutamate receptors in granule cell dendrites. By using a postembedding immunogold procedure, we describe here the precise organization of neurotransmitter receptors at dendrodendritic synapses. We show that there is a selective localization of glutamate and GABA receptors at asymmetric and symmetric synaptic junctions, respectively. In addition, we demonstrate that NMDA and AMPA receptors are clustered at postsynaptic specializations on granule cell spines and that they are extensively colocalized. Conversely, glutamate receptors do not appear to be concentrated in clusters on mitral cell dendrites, suggesting that the presynaptic effects of glutamate are mediated by a small complement of extrasynaptic receptors. By analyzing the subsynaptic distribution of the NR1 and GluR2/3 subunits, we show that they are distributed along the entire extent of the postsynaptic specialization, indicating that both NMDA and AMPA receptors are available for dendrodendritic signaling between mitral and granule cells. These results indicate that the principles recently found to underlie the organization of glutamate receptors at axospinous synapses also apply to dendrodendritic synapses.
Mice Lacking G-Protein Receptor Kinase 1 Have Profoundly Slowed Recovery of Cone-Driven Retinal Responses
Authors: Lyubarsky A. L. , Chen C.-K. , Simon M. I. , Pugh E. N.
Published: April 2018

G-Protein receptor kinase 1 (GRK1) (“rhodopsin kinase”) is necessary for the inactivation of photoactivated rhodopsin, the light receptor of the G-protein transduction cascade of rod photoreceptors. GRK1 has also been reported to be present in retinal cones in which its function is unknown. To examine the role of GRK1 in retinal cone signaling pathways, we measured in mice having null mutations of GRK1 (GRK1 −/−) cone-driven electroretinographic (ERG) responses, including an a-wave component identified as the field potential generated by suppression of the circulating current of the cone photoreceptors. Dark-adapted GRK1 −/− animals generated cone-driven ERGs having saturating amplitudes and sensitivities in both visible and UV spectral regions similar to those of wild-type (WT) mice. However, after exposure to a bright conditioning flash, the cone-driven ERGs of GRK1 −/− animals recovered 30–50 times more slowly than those of WT mice and similarly slower than the cone-driven ERGs of mice homozygously null for arrestin (Arrestin −/−), whose cone (but not rod) response recoveries were found to be as rapid as those of WT. Our observations argue that GRK1 is essential for normal deactivation of murine cone phototransduction and provide the first functional evidence for a major role of a specific GRK in the inactivation of vertebrate cone phototransduction.