bluuebunny/crossref_metadata_2025 huggingface dataset:
Developmental Switch in the Short-Term Modification of Unitary EPSPs Evoked in Layer 2/3 and Layer 5 Pyramidal Neurons of Rat Neocortex
Authors: Reyes Alex , Sakmann Bert
Published: April 2018

Amplitudes of EPSPs evoked by repetitive presynaptic action potentials can either decrease (synaptic depression) or increase (synaptic facilitation). To determine whether facilitation and depression in the connections between neocortical pyramidal cells varied with the identity of the pre- or the postsynaptic cell and whether they changed during postnatal development, whole-cell voltage recordings were made simultaneously from two or three pyramidal cells in layers 2/3 and 5 of the rat sensorimotor cortex. Unitary EPSPs were evoked when pre- and postsynaptic neurons were in the same and in different layers. In young [postnatal day 14 (P14)] cortex, EPSPs evoked in all connected neurons depressed. The degree of depression was layer specific and was determined by the identity of the presynaptic cell. EPSPs evoked by stimulation of presynaptic layer 5 neurons depressed significantly more than did those evoked by stimulation of layer 2/3 neurons. In mature cortex (P28), however, the EPSPs evoked in these connected neurons facilitated to a comparable degree regardless of the layer in which pre- and postsynaptic neurons were located. The results suggest that in young cortex the degree of synaptic depression in connected pyramidal cells is determined primarily by whether the presynaptic cell was in layer 2/3 or 5 and that maturation of the cortex involves a developmental switch from depression to facilitation between P14 and P28 that eliminates the layer-specific differences. A functional consequence of this switch is that in mature cortex the spread of excitation between neocortical pyramidal neurons is enhanced when action potentials occur in bursts.
Different Contributions of Microtubule Dynamics and Transport to the Growth of Axons and Collateral Sprouts
Authors: Gallo Gianluca , Letourneau Paul C.
Published: April 2018

Axonal growth is believed to depend on microtubule transport and microtubule dynamic instability. We now report that the growth of axon collateral branches can occur independent of microtubule dynamic instability and can rely mostly on the transport of preassembled polymer. Raising embryonic sensory neurons in concentrations of either taxol or nocodazole (NOC) that largely inhibit microtubule dynamics significantly inhibited growth of main axonal shafts but had only minor effects on collateral branch growth. The collaterals of axons raised in taxol or nocodazole often contained single microtubules with both ends clearly visible within the collateral branch (“floating” microtubules), which we interpret as microtubules undergoing transport. Furthermore, in these collaterals there was a distoproximal gradient in microtubule mass, indicating the distal accumulation of transported polymer. Treatment of cultures with a high dose of nocodazole to deplete microtubules from collaterals, followed by treatment with 4–20 nmvinblastine to inhibit microtubule repolymerization, resulted in the time-dependent reappearance and subsequent distal accumulation of floating microtubules in collaterals, providing further evidence for microtubule transport into collateral branches. Our data show that, surprisingly, the contribution of microtubule dynamics to collateral branch growth is minor compared with the important role of microtubule dynamics in growth cone migration, and they indicate that the transport of microtubules may provide sufficient cytoskeletal material for the initial growth of collateral branches.
DSD-1-Proteoglycan Is the Mouse Homolog of Phosphacan and Displays Opposing Effects on Neurite Outgrowth Dependent on Neuronal Lineage
Authors: Garwood Jeremy , Schnädelbach Oliver , Clement Albrecht , Schütte Katrin , Bach Alfred , Faissner Andreas
Published: April 2018

DSD-1-PG is a chondroitin sulfate proteoglycan (CSPG) expressed by glial cells that can promote neurite outgrowth from rat embryonic mesencephalic (E14) and hippocampal (E18) neurons, an activity that is associated with the CS glycosaminoglycans (GAGs). Further characterization of DSD-1-PG has included sequencing of peptides from the core protein and the cloning of the corresponding cDNA using polyclonal antisera against DSD-1-PG to screen phage expression libraries. On the basis of these studies we have identified DSD-1-PG as the mouse homolog of phosphacan, a neural rat CSPG. Monoclonal antibodies 3H1 and 3F8 against carbohydrate residues on rat phosphacan recognize these epitopes on DSD-1-PG. The epitopes of the antibodies, L2/HNK-1 and L5/Lewis-X, which have been implicated in functional interactions, are also found on DSD-1-PG. Although DSD-1-PG has previously been shown to promote neurite outgrowth, its upregulation after stab wounding of the CNS and its localization in regions that are considered boundaries to axonal extension suggested that it may also have inhibitory functions. Neonatal dorsal root ganglion (DRG) explants grown on a rich supportive substrate (laminin) with and without DSD-1-PG were strikingly inhibited by the proteoglycan. The inhibitory effects of DSD-1-PG on the DRG explants were not relieved by removal of the CS GAGs, indicating that this activity is associated with the core glycoprotein. The neurite outgrowth from embryonic hippocampal neurons on laminin was not affected by the addition of DSD-1-PG. This indicates that DSD-1-PG/mouse phosphacan can have opposing effects on the process of neurite outgrowth dependent on neuronal lineage.
Change in the Shape of Dendritic Spines Caused by Overexpression of Drebrin in Cultured Cortical Neurons
Authors: Hayashi Kensuke , Shirao Tomoaki
Published: April 2018

Dendritic spines are known to be extremely motile, providing a structural mechanism for synaptic plasticity. Actin filaments are thought to be responsible for the changes in the shape of spines. We tested our hypothesis that drebrin, an actin-binding protein, is a regulator of spine shape. In high-density long-term primary cultures of rat cerebral cortex neurons, drebrin was colocalized with actin filaments at spines. We introduced drebrin tagged with green fluorescent protein (GFP) into these neurons to test the ability of exogenous drebrin to localize at spines and the effect of overexpression of drebrin on spine shape. We observed that exogenous drebrin indeed accumulated in spines. But when the actin-binding domain of drebrin was deleted, the protein was distributed in both spines and dendritic shafts, indicating that accumulation of drebrin in the spines required its actin-binding activity. Statistical analysis of the lengths of spines as determined from confocal laser microscopic images revealed that the spines were significantly longer in GFP-drebrin-expressing neurons than in GFP-expressing neurons. The longer spines labeled with GFP-drebrin were demonstrated to be postsynaptic by double labeling of the presynaptic terminals with antibody against synaptophysin. These results directly indicate that drebrin binds to actin filaments at dendritic spines and alters spine shape.
Contributions of the Brain Angiotensin IV–AT4Receptor Subtype System to Spatial Learning
Authors: Wright John W. , Stubley LeighAnn , Pederson Eric S. , Kramár Enikö A. , Hanesworth Jodi M. , Harding Joseph W.
Published: April 2018

The development of navigational strategies to solve spatial problems appears to be dependent on an intact hippocampal formation. The circular water maze task requires the animal to use extramaze spatial cues to locate a pedestal positioned just below the surface of the water. Presently, we investigated the role of a recently discovered brain angiotensin receptor subtype (AT4) in the acquisition of this spatial learning task. The AT4receptor subtype is activated by angiotensin IV (AngIV) rather than angiotensins II or III, as documented for the AT1and AT2receptor subtypes, and is heavily distributed in the CA1–CA3fields of the hippocampus. Chronic intracerebroventricular infusion of a newly synthesized AT4agonist (Norleucine1-AngIV) via osmotic pump facilitated the rate of acquisition to solve this task, whereas treatment with an AT4receptor antagonist (Divalinal) significantly interfered with the acquisition of successful search strategies. Animals prepared with bilateral knife cuts of the perforant path, a major afferent hippocampal fiber bundle originating in the entorhinal cortex, displayed deficits in solving this task. This performance deficit could be reversed with acute intracerebroventricular infusion of a second AT4receptor agonist (Norleucinal). These results suggest that the brain AngIV–AT4system plays a role in the formation of spatial search strategies and memories. Further, application of an AT4receptor agonist compensated for spatial memory deficits in performance accompanying perforant path knife cuts. Possible mechanisms underlying this compensatory effect are discussed.
Recollection and Familiarity in Recognition Memory: An Event-Related Functional Magnetic Resonance Imaging Study
Authors: Henson R. N. A. , Rugg M. D. , Shallice T. , Josephs O. , Dolan R. J.
Published: April 2018

The question of whether recognition memory judgments with and without recollection reflect dissociable patterns of brain activity is unresolved. We used event-related, functional magnetic resonance imaging (fMRI) of 12 healthy volunteers to measure hemodynamic responses associated with both studying and recognizing words. Volunteers made one of three judgments to each word during recognition: whether they recollected seeing it during study (R judgments), whether they experienced a feeling of familiarity in the absence of recollection (K judgments), or whether they did not remember seeing it during study (N judgments). Both R and K judgments for studied words were associated with enhanced responses in left prefrontal and left parietal cortices relative to N judgments for unstudied words. The opposite pattern was observed in bilateral temporoccipital regions and amygdalae. R judgments for studied words were associated with enhanced responses in anterior left prefrontal, left parietal, and posterior cingulate regions relative to K judgments. At study, a posterior left prefrontal region exhibited an enhanced response to words subsequently given R versus K judgments, but the response of this region during recognition did not differentiate R and K judgments. K judgments for studied words were associated with enhanced responses in right lateral and medial prefrontal cortex relative to both R judgments for studied words and N judgments for unstudied words, a difference we attribute to greater monitoring demands when memory judgments are less certain. These results suggest that the responses of different brain regions do dissociate according to the phenomenology associated with memory retrieval.
Nuclear Factor κB Nuclear Translocation Upregulates c-Myc and p53 Expression during NMDA Receptor-Mediated Apoptosis in Rat Striatum
Authors: Qin Zheng-Hong , Chen Ren-Wu , Wang Yumei , Nakai Masami , Chuang De-Maw , Chase Thomas N.
Published: April 2018

Nuclear factor κB (NF-κB) appears to participate in the excitotoxin-induced apoptosis of striatal medium spiny neurons. To elucidate molecular mechanisms by which this transcription factor contributes to NMDA receptor-triggered apoptotic cascadesin vivo, rats were given the NMDA receptor agonist quinolinic acid (QA) by intrastriatal infusion, and the role of NF-κB in the induction of apoptosis-related genes and gene products was evaluated. QA administration induced time-dependent NF-κB nuclear translocation. The nuclear NF-κB protein after QA treatment was comprised mainly of p65 and c-Rel subunits as detected by gel supershift assay. Levels of c-Myc and p53 mRNA and protein were markedly increased at the time of QA-induced NF-κB nuclear translocation. Immunohistochemical analysis showed that c-Myc and p53 induction occurred in the excitotoxin-sensitive medium-sized striatal neurons. NF-κB nuclear translocation was blocked in a dose-dependent manner by the cell-permeable recombinant peptide NF-κB SN50, but not by the NF-κB SN50 control peptide. NF-κB SN50 significantly inhibited the QA-induced elevation in levels of c-Myc and p53 mRNA and protein. Pretreatment or posttreatment with NF-κB SN50, but not the control peptide, also substantially reduced the intensity of QA-induced internucleosomal DNA fragmentation. The results suggest that NF-κB may promote an apoptotic response in striatal medium-sized neurons to excitotoxic insult through upregulation of c-Myc and p53. This study also provides evidence indicating an unique signaling pathway from the cytoplasm to the nucleus, which regulates p53 and c-Myc levels in these neurons during apoptosis.
5-HT1BReceptor–Mediated Presynaptic Inhibition of Retinal Input to the Suprachiasmatic Nucleus
Authors: Pickard Gary E. , Smith Bret N. , Belenky Michael , Rea Michael A. , Dudek F. Edward , Sollars Patricia J.
Published: April 2018

The suprachiasmatic nucleus (SCN) receives glutamatergic afferents from the retina and serotonergic afferents from the midbrain, and serotonin (5-HT) can modify the response of the SCN circadian oscillator to light. 5-HT1Breceptor-mediated presynaptic inhibition has been proposed as one mechanism by which 5-HT modifies retinal input to the SCN (Pickard et al., 1996). This hypothesis was tested by examining the subcellular localization of 5-HT1Breceptors in the mouse SCN using electron microscopic immunocytochemical analysis with 5-HT1Breceptor antibodies and whole-cell patch-clamp recordings from SCN neurons in hamster hypothalamic slices. 5-HT1Breceptor immunostaining was observed associated with the plasma membrane of retinal terminals in the SCN. 1-[3-(Trifluoromethyl)phenyl]-piperazine HCl (TFMPP), a 5-HT1Breceptor agonist, reduced in a dose-related manner the amplitude of glutamatergic EPSCs evoked by stimulating selectively the optic nerve. Selective 5-HT1Aor 5-HT7receptor antagonists did not block this effect. Moreover, in cells demonstrating an evoked EPSC in response to optic nerve stimulation, TFMPP had no effect on the amplitude of inward currents generated by local application of glutamate. The effect of TFMPP on light-induced phase shifts was also examined using 5-HT1Breceptor knock-out mice. TFMPP inhibited behavioral responses to light in wild-type mice but was ineffective in inhibiting light-induced phase shifts in 5-HT1Breceptor knock-out mice. The results indicate that 5-HT can reduce retinal input to the circadian system by acting at presynaptic 5-HT1Breceptors located on retinal axons in the SCN.
Sex Differences in Brain Gray and White Matter in Healthy Young Adults: Correlations with Cognitive Performance
Authors: Gur Ruben C. , Turetsky Bruce I. , Matsui Mie , Yan Michelle , Bilker Warren , Hughett Paul , Gur Raquel E.
Published: April 2018

Sex-related differences in behavior are extensive, but their neuroanatomic substrate is unclear. Indirect perfusion data have suggested a higher percentage of gray matter (GM) in left hemisphere cortex and in women, but differences in volumes of the major cranial compartments have not been examined for the entire brain in association with cognitive performance. We used volumetric segmentation of dual echo (proton density and T2-weighted) magnetic resonance imaging (MRI) scans in healthy volunteers (40 men, 40 women) age 18–45. Supertentorial volume was segmented into GM, white matter (WM), and CSF. We confirmed that women have a higher percentage of GM, whereas men have a higher percentage of WM and of CSF. These differences sustained a correction for total intracranial volume. In men the slope of the relation between cranial volume and GM paralleled that for WM, whereas in women the increase in WM as a function of cranial volume was at a lower rate. In men the percentage of GM was higher in the left hemisphere, the percentage of WM was symmetric, and the percentage of CSF was higher in the right. Women showed no asymmetries. Both GM and WM volumes correlated moderately with global, verbal, and spatial performance across groups. However, the regression of cognitive performance and WM volume was significantly steeper in women. Because GM consists of the somatodendritic tissue of neurons whereas WM comprises myelinated connecting axons, the higher percentage of GM makes more tissue available for computation relative to transfer across distant regions. This could compensate for smaller intracranial space in women. Sex difference in the percentage and asymmetry of the principal cranial tissue volumes may contribute to differences in cognitive functioning.
Sex Steroid Regulation of the Inflammatory Response: Sympathoadrenal Dependence in the Female Rat
Authors: Green Paul G. , Dahlqvist Solbritt Rantapää , Isenberg William M. , Strausbaugh Holly J. , Miao Frederick J.-P. , Levine Jon D.
Published: April 2018

To investigate the role of sex steroids in sex differences in the response of rats to the potent inflammatory mediator bradykinin (BK), we evaluated the effect of sex steroid manipulation on the magnitude of BK-induced synovial plasma extravasation (PE). The magnitude of BK-induced PE is markedly less in females. Ovariectomy of female rats increased BK-induced PE, and administration of 17β-estradiol to ovariectomized female rats reconstituted the female phenotype. Castration in male rats decreased BK-induced PE, and administration of testosterone or its nonmetabolizable analog dihydrotestosterone reconstituted the male phenotype. The results of these experiments strongly support the role of both male and female sex steroids in sex differences in the inflammatory response.

Because the stress axes are sexually dimorphic and are important in the regulation of the inflammatory response, we evaluated the contribution of the hypothalamic–pituitary–adrenal and the sympathoadrenal axes to sex differences in BK-induced PE. Neither hypophysectomy nor inhibition of corticosteroid synthesis affected BK-induced PE in female or male rats. Adrenal denervation in females produced the same magnitude increase in BK-induced PE as adrenalectomy or ovariectomy, suggesting that the adrenal medullary factor(s) in females may account for the female sex steroid effect on BK-induced PE. Furthermore, we have demonstrated that in female but not male rats, estrogen receptor α immunoreactivity is present on medullary but not cortical cells in the adrenal gland. These data suggest that regulation of the inflammatory response by female sex steroids is strongly dependent on the sympathoadrenal axis, possibly by its action on estrogen receptors on adrenal medullary cells.
Reactivation of Hippocampal Cell Assemblies: Effects of Behavioral State, Experience, and EEG Dynamics
Authors: Kudrimoti Hemant S. , Barnes Carol A. , McNaughton Bruce L.
Published: April 2018

During slow wave sleep (SWS), traces of neuronal activity patterns from preceding behavior can be observed in rat hippocampus and neocortex. The spontaneous reactivation of these patterns is manifested as the reinstatement of the distribution of pairwise firing-rate correlations within a population of simultaneously recorded neurons. The effects of behavioral state [quiet wakefulness, SWS, and rapid eye movement (REM)], interactions between two successive spatial experiences, and global modulation during 200 Hz electroencephalographic (EEG) “ripples” on pattern reinstatement were studied in CA1 pyramidal cell population recordings. Pairwise firing-rate correlations during often repeated experiences accounted for a significant proportion of the variance in these interactions in subsequent SWS or quiet wakefulness and, to a lesser degree, during SWS before the experience on a given day. The latter effect was absent for novel experiences, suggesting that a persistent memory trace develops with experience. Pattern reinstatement was strongest during sharp wave–ripple oscillations, suggesting that these events may reflect system convergence onto attractor states corresponding to previous experiences. When two different experiences occurred in succession, the statistically independent effects of both were evident in subsequent SWS. Thus, the patterns of neural activity reemerge spontaneously, and in an interleaved manner, and do not necessarily reflect persistence of an active memory (i.e., reverberation). Firing-rate correlations during REM sleep were not related to the preceding familiar experience, possibly as a consequence of trace decay during the intervening SWS. REM episodes also did not detectably influence the correlation structure in subsequent SWS, suggesting a lack of strengthening of memory traces during REM sleep, at least in the case of familiar experiences.
Enhancement of Locomotor Activity and Conditioned Reward to Cocaine by Brain-Derived Neurotrophic Factor
Authors: Horger Brian A. , Iyasere Christiana A. , Berhow Melissa T. , Messer Chad J. , Nestler Eric J. , Taylor Jane R.
Published: April 2018

The mesolimbic dopamine (DA) system has been implicated in drug reward, locomotor sensitization, and responding for reward-related stimuli [termed conditioned reinforcers (CR)]. Here, we investigated the effect of brain-derived neurotrophic factor (BDNF), which enhances the survival and function of dopaminergic neurons, on stimulant-induced locomotor sensitization and responding for CR. In experiment 1, BDNF was infused into the nucleus accumbens (NAc) or ventral tegmental area over 2 weeks via chronically implanted minipumps (1–2.5 μg/d), and the psychomotor stimulant effects of cocaine (5–15 mg/kg, i.p.) were studied. We found that BDNF enhanced the initial stimulant effects of cocaine and seemed to facilitate the development of sensitization to repeated cocaine doses. In experiment 2, we studied the effects of intra-NAc BDNF infusions on responding for CR. BDNF-treated rats showed twice as many CR responses compared with controls when saline was first administered. BDNF enhanced responding on the CR lever more than four times that seen in control animals after a cocaine injection (10 mg/kg, i.p.). The enhanced response to cocaine in BDNF-treated animals persisted for more than a month after the BDNF infusions had stopped, indicating long-lasting changes in the mesolimbic DA system caused by BDNF administration. In experiment 3, we examined locomotor sensitization to cocaine in heterozygous BDNF knock-out mice and found that the development of sensitization was delayed compared with wild-type littermates. These results demonstrate the profound effects of BDNF on the enhancement of both cocaine-induced locomotion and facilitation of CR and suggest a possible role for BDNF in long-term adaptations of the brain to cocaine.
Intrinsic Neurons of Fastigial Nucleus Mediate Neurogenic Neuroprotection against Excitotoxic and Ischemic Neuronal Injury in Rat
Authors: Glickstein Sara B. , Golanov Eugene V. , Reis Donald J.
Published: April 2018

Electrical stimulation of the cerebellar fastigial nucleus (FN) elevates regional cerebral blood flow (rCBF) and arterial pressure (AP) and provides long-lasting protection against focal and global ischemic infarctions. We investigated which neuronal element in FN, perikarya or axons, mediates this central neurogenic neuroprotection and whether it also protects against excitotoxicity. In anesthetized rats, the FN was stimulated for 1 hr, and ibotenic acid (IBO) was microinjected unilaterally into the striatum. In unstimulated controls, the excitotoxic lesions averaged ∼40 mm3. Stimulation of FN, but not dentate nucleus (DN), significantly reduced lesion volumes up to 80% when IBO was injected 15 min, 72 hr, or 10 d, but not 30 d, thereafter. In other rats, intrinsic neurons of FN or DN were destroyed by pretreatment with IBO. Five days later, the FN was stimulated, and 72 hr later, IBO was microinjected into the striatum. Lesions of FN, but not DN, abolished neuroprotection but not the elevations of rCBF and AP elicited from FN stimulation. Excitotoxic lesions of FN, but not DN, also abolished the 37% reduction in focal ischemic infarctions produced by middle cerebral artery occlusion. Excitation of intrinsic FN neurons provides long-lasting, substantial, and reversible protection of central neurons from excitotoxicity, as well as focal ischemia, whereas axons in the nucleus, probably collaterals of ramified brainstem neurons, mediate the elevations in rCBF, which do not contribute to neuroprotection. Long-lived protection against a range of injuries is an unrecognized function of FN neurons transmitted over pathways distinct from those regulating rCBF.
Enhanced Neurotrophin-Induced Axon Growth in Myelinated Portions of the CNS in Mice Lacking the p75 Neurotrophin Receptor
Authors: Walsh Gregory S. , Krol Karmen M. , Crutcher Keith A. , Kawaja Michael D.
Published: April 2018

Axonal growth in the adult mammalian CNS is limited because of inhibitory influences of the glial environment and/or a lack of growth-promoting molecules. Here, we investigate whether supplementation of nerve growth factor (NGF) to the CNS during postnatal development and into adulthood can support the growth of sympathetic axons within myelinated portions of the maturing brain. We have also asked whether p75NTRplays a role in this NGF-induced axon growth. To address these questions we used two lines of transgenic mice overexpressing NGF centrally, with or without functional expression of p75NTR(NGF/p75+/+and NGF/p75−/−mice, respectively). Sympathetic axons invade the myelinated portions of the cerebellum, beginning shortly before the second week of postnatal life, in both lines of NGF transgenic mice. Despite the presence of central myelin, these sympathetic axons continue to sprout and increase in density between postnatal days 14 and 100, resulting in a dense plexus of sympathetic fibers within this myelinated environment. Surprisingly, the growth response of sympathetic fibers into the cerebellar white matter of NGF/p75−/−mice is enhanced, such that both the density and extent of axon ingrowth are increased, compared with age-matched NGF/p75+/+mice. These dissimilar growth responses cannot be attributed to differences in cerebellar levels of NGF protein or sympathetic neuron numbers between NGF/p75+/+and NGF/p75−/−mice. Our data provide evidence demonstrating that growth factors are capable of overcoming the inhibitory influences of central myelin in the adult CNS and that neutralization of the p75NTRmay further enhance this growth response.
Mitogenic Signaling by ATP/P2Y Purinergic Receptors in Astrocytes: Involvement of a Calcium-Independent Protein Kinase C, Extracellular Signal-Regulated Protein Kinase Pathway Distinct from the Phosphatidylinositol-Specific Phospholipase C/Calcium Pathway
Authors: Neary Joseph T. , Kang Yuan , Bu Yurong , Yu Esther , Akong Katherine , Peters Christopher M.
Published: April 2018

Activation of ATP/P2Y purinergic receptors stimulates proliferation of astrocytes, but the mitogenic signaling pathway linked to these G-protein-coupled receptors is unknown. We have investigated the role of extracellular signal-regulated protein kinase (ERK) in P2Y receptor-stimulated mitogenic signaling as well as the pathway that couples P2Y receptors to ERK. Downregulation of protein kinase C (PKC) in primary cultures of rat cerebral cortical astrocytes greatly reduced the ability of extracellular ATP to stimulate ERK. Because occupancy of P2Y receptors also leads to inositol phosphate formation, calcium mobilization, and PKC activation, we explored the possibility that signaling from P2Y receptors to ERK is mediated by a phosphatidylinositol-specific phospholipase C (PI-PLC)/calcium pathway. However, neither inhibition of PI-PLC nor chelation of calcium significantly reduced ATP-stimulated ERK activity. Moreover, a preferential inhibitor of calcium-dependent PKC isoforms, Gö6976, was significantly less effective in blocking ATP-stimulated ERK activity than GF102903X, an inhibitor of both calcium-dependent and -independent PKC isoforms. Furthermore, ATP stimulated a rapid translocation of PKCδ, a calcium-independent PKC isoform, but not PKCγ, a calcium-dependent PKC isoform. ATP also stimulated a rapid increase in choline, and inhibition of phosphatidylcholine hydrolysis blocked ATP-evoked ERK activation. These results indicate that P2Y receptors in astrocytes are coupled independently to PI-PLC/calcium and ERK pathways and suggest that signaling from P2Y receptors to ERK involves a calcium-independent PKC isoform and hydrolysis of phosphatidylcholine by phospholipase D. In addition, we found that inhibition of ERK activation blocked extracellular ATP-stimulated DNA synthesis, thereby indicating that the ERK pathway mediates mitogenic signaling by P2Y receptors.
Presenilin 1 Facilitates the Constitutive Turnover of β-Catenin: Differential Activity of Alzheimer’s Disease–Linked PS1 Mutants in the β-Catenin–Signaling Pathway
Authors: Kang David E. , Soriano Salvador , Frosch Matthew P. , Collins Tucker , Naruse Satoshi , Sisodia Sangram S. , Leibowitz Gil , Levine Fred , Koo Edward H.
Published: April 2018

Although an association between the product of the familial Alzheimer’s disease (FAD) gene, presenilin 1 (PS1), and β-catenin has been reported recently, the cellular consequences of this interaction are unknown. Here, we show that both the full length and the C-terminal fragment of wild-type or FAD mutant PS1 interact with β-catenin from transfected cells and brains of transgenic mice, whereas E-cadherin and adenomatous polyposis coli (APC) are not detected in this complex. Inducible overexpression of PS1 led to increased association of β-catenin with glycogen synthase kinase-3β (GSK-3β), a negative regulator of β-catenin, and accelerated the turnover of endogenous β-catenin. In support of this finding, the β-catenin half-life was dramatically longer in fibroblasts deficient inPS1, and this phenotype was completely rescued by replacement of PS1, demonstrating that PS1 normally stimulates the degradation of β-catenin. In contrast, overexpression of FAD-linked PS1 mutants (M146L and ΔX9) failed to enhance the association between GSK-3β and β-catenin and interfered with the constitutive turnover of β-catenin.In vivoconfirmation was demonstrated in the brains of transgenic mice in which the expression of the M146L mutant PS1 was correlated with increased steady-state levels of endogenous β-catenin. Thus, our results indicate that PS1 normally promotes the turnover of β-catenin, whereas PS1 mutants partially interfere with this process, possibly by failing to recruit GSK-3β into the PS1–β-catenin complex. These findings raise the intriguing possibility that PS1–β-catenin interactions and subsequent activities may be consequential for the pathogenesis of AD.
Differential Depression at Excitatory and Inhibitory Synapses in Visual Cortex
Authors: Varela Juan A. , Song Sen , Turrigiano Gina G. , Nelson Sacha B.
Published: April 2018

The function of cortical circuits depends critically on the balance between excitation and inhibition. This balance reflects not only the relative numbers of excitatory and inhibitory synapses but also their relative strengths. Recent studies of excitatory synapses in visual and somatosensory cortices have emphasized that synaptic strength is not a fixed quantity but is a dynamic variable that reflects recent presynaptic activity. Here, we compare the dynamics of synaptic transmission at excitatory and inhibitory synapses onto visual cortical pyramidal neurons. We find that inhibitory synapses show less overall depression than excitatory synapses and that the kinetics of recovery from depression also differ between the two classes of synapse. When excitatory and inhibitory synapses are stimulated concurrently, this differential depression produces a time- and frequency-dependent shift in the reversal potential of the composite postsynaptic current. These results indicate that the balance between excitation and inhibition can change dynamically as a function of activity.
A Role of Actin Filament in Synaptic Transmission and Long-Term Potentiation
Authors: Kim Chong-Hyun , Lisman John E.
Published: April 2018

The role of actin filaments in synaptic function has been studied in the CA1 region of the rat hippocampal slice. Bath application (2 hr) of the actin polymerization inhibitor latrunculin B did not substantially affect the shape of dendrites or spines. However, this and other drugs that affect actin did affect synaptic function. Bath-applied latrunculin B reduced the synaptic response. Several lines of evidence indicate that a component of this effect is presynaptic. To specifically test for a postsynaptic role for actin, latrunculin B or phalloidin, an actin filament stabilizer, was perfused into the postsynaptic neuron. The magnitude of long-term potentiation (LTP) was decreased at times when baseline transmission was not yet affected. Longer applications produced a decrease in baseline AMPA receptor (AMPAR)-mediated transmission. The magnitude of the NMDA receptor-mediated transmission was unaffected, indicating a specific effect on the AMPAR. These results suggest that postsynaptic actin filaments are involved in a dynamic process required to maintain AMPAR-mediated transmission and to enhance it during LTP.
Calcium-Induced Calcium Release Contributes to Action Potential-Evoked Calcium Transients in Hippocampal CA1 Pyramidal Neurons
Authors: Sandler Vladislav M. , Barbara Jean-Gaël
Published: April 2018

Calcium-induced calcium release (CICR) is a mechanism by which local elevations of intracellular calcium (Ca2+) are amplified by Ca2+release from ryanodine-sensitive Ca2+stores. CICR is known to be coupled to Ca2+entry in skeletal muscle, cardiac muscle, and peripheral neurons, but no evidence suggests that such coupling occurs in central neurons during the firing of action potentials. Using fast Ca2+imaging in CA1 neurons from hippocampal slices, we found evidence for CICR during action potential-evoked Ca2+transients. A low concentration of caffeine enhanced Ca2+transient amplitude, whereas a higher concentration reduced it. Simultaneous Ca2+imaging and whole-cell recordings showed that membrane potential, action potential amplitude, and waveform were unchanged during caffeine application. The enhancement of Ca2+transients by caffeine was not affected by the L-type channel blocker nifedipine, the phosphodiesterase inhibitor IBMX, the adenylyl cyclase activator forskolin, or the PKA antagonist H-89. However, thapsigargin or ryanodine, which both empty intracellular Ca2+stores, occluded this effect. In addition, thapsigargin, ryanodine, and cyclopiazonic acid reduced action potential-evoked Ca2+transients in the absence of caffeine. These results suggest that Ca2+release from ryanodine-sensitive stores contributes to Ca2+signals triggered by action potentials in CA1 neurons.
The Mitogen-Activated Protein Kinase Cascade Couples PKA and PKC to cAMP Response Element Binding Protein Phosphorylation in Area CA1 of Hippocampus
Authors: Roberson Erik D. , English Joey D. , Adams J. Paige , Selcher Joel C. , Kondratick Christine , Sweatt J. David
Published: April 2018

Activation of the mitogen-activated protein kinase (MAPK) cascade recently was discovered to play an important role in synaptic plasticity in area CA1 of rat hippocampus. However, the upstream mechanisms regulating MAPK activity and the downstream effectors of MAPK in the hippocampus are uncharacterized. In the present studies we observed that hippocampal MAPK activation is regulated by both the PKA and PKC systems; moreover, we found that a wide variety of neuromodulatory neurotransmitter receptors (metabotropic glutamate receptors, muscarinic acetylcholine receptors, dopamine receptors, and β-adrenergic receptors) couple to MAPK activation via these two cascades. In additional studies we observed that PKC is a powerful regulator of CREB phosphorylation in area CA1. MAPK plays a critical role in transcriptional regulation by PKC, because MAPK activation is a necessary component for increased CREB phosphorylation in response to the activation of this kinase. Surprisingly, we also observed that MAPK activation is necessary for PKA coupling to CREB phosphorylation in area CA1. Overall, these studies indicate an unexpected richness of diversity in the regulation of MAPK in the hippocampus and suggest the possibility of a broad role for the MAPK cascade in regulating gene expression in long-term forms of hippocampal synaptic plasticity.
Neuroprotection atDrosophilaSynapses Conferred by Prior Heat Shock
Authors: Karunanithi Shanker , Barclay Jeffrey W. , Robertson R. Meldrum , Brown Ian R. , Atwood Harold L.
Published: April 2018

Synapses are critical sites of information transfer in the nervous system, and it is important that their functionality be maintained under stressful conditions to prevent communication breakdown. Here we show that synaptic transmission at theDrosophilalarval neuromuscular junction is protected by prior exposure to heat shock that strongly induces expression of heat shock proteins, in particular hsp70. Using a macropatch electrode to record synaptic activity at individual, visualized boutons, we found that prior heat shock sustains synaptic performance at high test temperatures through pre- and postsynaptic alterations. After heat shock, nerve impulses release more quantal units at high temperatures and exhibit fewer failures of release (presynaptic modification), whereas the amplitude of quantal currents remains more constant than does that in nonheat-shocked controls (postsynaptic modification). The time course of these physiological changes is similar to that of elevated hsp70. Thus, stress-induced neuroprotective mechanisms maintain function at synapses by modifying their properties.
Dendritic DynamicsIn VivoChange during Neuronal Maturation
Authors: Wu Gang Yi , Zou Dong Jing , Rajan Indrani , Cline Hollis
Published: April 2018

In vivo imaging of optic tectal neurons in the intactXenopustadpole permits direct observation of the structural dynamics that occur during dendritic arbor formation. Based on images of single DiI-labeled neurons collected at daily intervals over a period of 6 d, we divided tectal cell development into three phases according to the total length of the dendritic arbor. During phase 1, the cell differentiates from a neuroepithelial cell type and extends an axon out of the tectum. The total dendritic branch length (TDBL) is <100 μm. During phase 2, when TDBL is 100–400 μm, the dendritic arbor grows rapidly. During phase 3, when TDBL is >400 μm, the dendritic arbor grows slowly and appears stable. Neurons at different positions along the rostrocaudal developmental axis of the tectum were imaged at 2 hr intervals over 6 hr and at 24 hr intervals over several days. Images collected at 2 hr intervals were analyzed to determine rates of branch additions and retractions. Morphologically complex, phase 3 neurons show half the rate of branch additions and retractions as phase 2 neurons. Therefore, rapidly growing neurons have dynamic dendritic arbors, and slower-growing neurons are structurally stable. The change in growth rate and dendritic arbor dynamics from phase 2 to phase 3 correlates with the developmental increase in synaptic strength in neurons located along the rostrocaudal tectal axis. The data are consistent with the idea that strong synaptic inputs stabilize dendritic arbor structures and that weaker synaptic inputs are permissive for a greater degree of dynamic rearrangements and a faster growth rate in the dendritic arbor.
Inhibition of Dentate Granule Cell Neurogenesis with Brain Irradiation Does Not Prevent Seizure-Induced Mossy Fiber Synaptic Reorganization in the Rat
Authors: Parent Jack M. , Tada Eiji , Fike John R. , Lowenstein Daniel H.
Published: April 2018

Aberrant reorganization of dentate granule cell axons, the mossy fibers, occurs in human temporal lobe epilepsy and rodent epilepsy models. Whether this plasticity results from the remodeling of preexisting mossy fibers or instead reflects an abnormality of developing dentate granule cells is unknown. Because these neurons continue to be generated in the adult rodent and their production increases after seizures, mossy fibers that arise from either developing or mature granule cells are potential substrates for this network plasticity. Therefore, to determine whether seizure-induced, mossy fiber synaptic reorganization arises from either developing or mature granule cell populations, we used low-dose, whole-brain x-irradiation to eliminate proliferating dentate granule cell progenitors in adult rats. A single dose of 5 Gy irradiation blocked cell proliferation and eliminated putative progenitor cells in the dentate subgranular proliferative zone. Irradiation 1 d before pilocarpine-induced status epilepticus significantly attenuated dentate granule cell neurogenesis after seizures. Two irradiations, 1 d before and 4 d after status epilepticus, essentially abolished dentate granule cell neurogenesis but failed to prevent mossy fiber reorganization in the dentate molecular layer. These results indicate that dentate granule cell neurogenesis in the mature hippocampal formation is vulnerable to the effects of low-dose ionizing irradiation. Furthermore, the development of aberrant mossy fiber remodeling in the absence of neurogenesis suggests that mature dentate granule cells contribute substantially to seizure-induced network reorganization.
Presynaptically Located CB1 Cannabinoid Receptors Regulate GABA Release from Axon Terminals of Specific Hippocampal Interneurons
Authors: Katona István , Sperlágh Beáta , Sı́k Attila , Käfalvi Attila , Vizi E. Sylvester , Mackie Ken , Freund Tamás F.
Published: April 2018

To understand the functional significance and mechanisms of action in the CNS of endogenous and exogenous cannabinoids, it is crucial to identify the neural elements that serve as the structural substrate of these actions. We used a recently developed antibody against the CB1 cannabinoid receptor to study this question in hippocampal networks. Interneurons with features typical of basket cells showed a selective, intense staining for CB1 in all hippocampal subfields and layers. Most of them (85.6%) contained cholecystokinin (CCK), which corresponded to 96.9% of all CCK-positive interneurons, whereas only 4.6% of the parvalbumin (PV)-containing basket cells expressed CB1. Accordingly, electron microscopy revealed that CB1-immunoreactive axon terminals of CCK-containing basket cells surrounded the somata and proximal dendrites of pyramidal neurons, whereas PV-positive basket cell terminals in similar locations were negative for CB1. The synthetic cannabinoid agonist WIN 55,212-2 (0.01–3 μm) reduced dose-dependently the electrical field stimulation-induced [3H]GABA release from superfused hippocampal slices, with an EC50value of 0.041 μm. Inhibition of GABA release by WIN 55,212-2 was not mediated by inhibition of glutamatergic transmission because the WIN 55,212-2 effect was not reduced by the glutamate blockers AP5 and CNQX. In contrast, the CB1 cannabinoid receptor antagonist SR 141716A (1 μm) prevented this effect, whereas by itself it did not change the outflow of [3H]GABA.

These results suggest that cannabinoid-mediated modulation of hippocampal interneuron networks operate largely via presynaptic receptors on CCK-immunoreactive basket cell terminals. Reduction of GABA release from these terminals is the likely mechanism by which both endogenous and exogenous CB1 ligands interfere with hippocampal network oscillations and associated cognitive functions.
Spatiotemporal Analysis of Local Field Potentials and Unit Discharges in Cat Cerebral Cortex during Natural Wake and Sleep States
Authors: Destexhe Alain , Contreras Diego , Steriade Mircea
Published: April 2018

The electroencephalogram displays various oscillation patterns during wake and sleep states, but their spatiotemporal distribution is not completely known. Local field potentials (LFPs) and multiunits were recorded simultaneously in the cerebral cortex (areas 5–7) of naturally sleeping and awake cats. Slow-wave sleep (SWS) was characterized by oscillations in the slow (<1 Hz) and delta (1–4 Hz) frequency range. The high-amplitude slow-wave complexes consisted in a positivity of depth LFP, associated with neuronal silence, followed by a sharp LFP negativity, correlated with an increase of firing. This pattern was of remarkable spatiotemporal coherence, because silences and increased firing occurred simultaneously in units recorded within a 7 mm distance in the cortex. During wake and rapid-eye-movement (REM) sleep, single units fired tonically, whereas LFPs displayed low-amplitude fast activities with increased power in fast frequencies (15–75 Hz). In contrast with the widespread synchronization during SWS, fast oscillations during REM and wake periods were synchronized only within neighboring electrodes and small time windows (100–500 msec). This local synchrony occurred in an apparent irregular manner, both spatially and temporally. Brief periods (<1 sec) of fast oscillations were also present during SWS in between slow-wave complexes. During these brief periods, the spatial and temporal coherence, as well as the relation between units and LFPs, was identical to that of fast oscillations of wake or REM sleep. These results show that natural SWS in cats is characterized by slow-wave complexes, synchronized over large cortical territories, interleaved with brief periods of fast oscillations, characterized by local synchrony, and of characteristics similar to that of the sustained fast oscillations of activated states.
Immunohistochemical Evidence of Seizure-Induced Activation of trk Receptors in the Mossy Fiber Pathway of Adult Rat Hippocampus
Authors: Binder Devin K. , Routbort Mark J. , McNamara James O.
Published: April 2018

Recent work suggests that limiting the activation of the trkB subtype of neurotrophin receptor inhibits epileptogenesis, but whether or where neurotrophin receptor activation occurs during epileptogenesis is unclear. Because the activation of trk receptors involves the phosphorylation of specific tyrosine residues, the availability of antibodies that selectively recognize the phosphorylated form of trk receptors permits a histochemical assessment of trk receptor activation. In this study the anatomy and time course of trk receptor activation during epileptogenesis were assessed with immunohistochemistry, using a phospho-specific trk antibody. In contrast to the low level of phosphotrk immunoreactivity constitutively expressed in the hippocampus of adult rats, a striking induction of phosphotrk immunoreactivity was evident in the distribution of the mossy fibers after partial kindling or kainate-induced seizures. The anatomic distribution, time course, and threshold for seizure-induced phosphotrk immunoreactivity correspond to the demonstrated pattern of regulation of BDNF expression by seizure activity. These results provide immunohistochemical evidence that trk receptors undergo activation during epileptogenesis and suggest that the mossy fiber pathway is particularly important in the pro-epileptogenic effects of the neurotrophins.