bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Ca2+Stores in Metabotropicl-Glutamate Receptor-Mediated Supralinear Ca2+Signaling in Rat Hippocampal Neurons
Authors: Rae Mark G. , Martin Duncan J. , Collingridge Graham L. , Irving Andrew J.
Published: April 2018

The role of metabotropicl-glutamate (mGlu) receptors in supralinear Ca2+signaling was investigated in cultured hippocampal cells using Ca2+imaging techniques and whole-cell voltage-clamp recording. In neurons, but not glia, global supralinear Ca2+release from intracellular stores was observed when the mGlu receptor agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) was combined with elevated extracellular K+levels (10.8 mm), moderate depolarization (15–30 mV), or NMDA (3 μm). There was a delay (2–8 min) before the stores were fully charged, and the enhancement persisted for a short period (up to 10 min) after removal of the store-loading stimulus. Studies with the mGlu receptor antagonist 2-methyl-6-(phenylethynyl)-pyridine demonstrated that these effects were mediated by activation of the mGlu5receptor subtype. The L-type voltage-gated Ca2+channel antagonist nifedipine (10 μm) substantially reduced responses to DHPG obtained in the presence of elevated extracellular K+but not NMDA. This suggests that the Ca2+that is required to load the stores can enter either through L-type voltage-gated Ca2+channels or directly through NMDA receptors. The findings that both depolarization and NMDA receptor activation can facilitate mGlu receptor Ca2+signaling adds considerable flexibility to the processes that underlie activity-dependent changes in synaptic strength. In particular, a temporal separation between the store-loading stimulus and the activation of mGlu receptors could be used as a recency detector in neurons.
GABACReceptor Sensitivity Is Modulated by Interaction with MAP1B
Authors: Billups Daniela , Hanley Jonathan G. , Orme Mariam , Attwell David , Moss Stephen J.
Published: April 2018

GABACreceptors contain ρ subunits and mediate feedback inhibition from retinal amacrine cells to bipolar cells. We previously identified the cytoskeletal protein MAP1B as a ρ1 subunit anchoring protein. Here, we analyze the structural basis and functional significance of the MAP1B-ρ1 interaction. Twelve amino acids at the C terminus of the large intracellular loop of ρ1 (and also ρ2) are sufficient for interaction with MAP1B. Disruption of the MAP1B-ρ interaction in bipolar cells in retinal slices decreased the EC50of their GABACreceptors, doubling the receptors' current at low GABA concentrations without affecting their maximum current at high concentrations. Thus, anchoring to the cytoskeleton lowers the sensitivity of GABACreceptors and provides a likely site for functional modulation of GABACreceptor-mediated inhibition.
Decreases in Endogenous Opioid Peptides in the Rat Medullo-Coerulear Pathway after Chronic Morphine Treatment
Authors: Van Bockstaele Elisabeth J. , Peoples James , Menko A. Sue , McHugh Kirk , Drolet Guy
Published: April 2018

Several biochemical changes have been described in noradrenergic neurons of the locus coeruleus (LC) after chronic morphine treatment. Changes in neurochemical expression in opioid afferent projections to the LC may be equally important in modulating noradrenergic neurons during chronic opiate exposure. To test the hypothesis that opioid peptides in LC afferents are altered after chronic opiate administration, we exposed adult male rats to either morphine or placebo pellets for 5 d. Tissue sections through the LC were processed for peroxidase or gold–silver labeling of methionine5-enkephalin (met-ENK) and analyzed using light or electron microscopy, respectively. Light level densitometry and ultrastructural analysis showed that there was a significant decrease in immunolabeling for ENK in LC-afferent terminals of morphine-treated rats. Western immunoblot analysis confirmed that protein levels for both leucine5- and methionine5-ENK were significantly decreased in tissue samples containing the LC after chronic morphine treatment. To test whether decreases in ENK protein expression were mirrored by decreases in gene expression, Northern blot analysis of preproenkephalin (PPE) mRNA was conducted in tissue samples obtained through the medulla, a brainstem area that contains the major opioid afferents to the LC. PPE mRNA was reduced in samples obtained from morphine-treated rats. Finally,in situhybridization experiments confirmed significant decreases in PPE mRNA expression in the nucleus paragigantocellularis, a region known to provide a robust opioid input to the LC. These data suggest that there is a decrease in the synthesis of the opioid peptide mRNA and protein in the medullo-coerulear pathway after chronic exposure to morphine. Such alterations in opioid peptide levels during opiate dependence may contribute to the observed hyperactivity of LC neurons during opiate withdrawal.
A Conserved Clathrin Assembly Motif Essential for Synaptic Vesicle Endocytosis
Authors: Morgan Jennifer R. , Prasad Kondury , Hao Weihua , Augustine George J. , Lafer Eileen M.
Published: April 2018

Although clathrin assembly by adaptor proteins (APs) plays a major role in the recycling of synaptic vesicles, the molecular mechanism that allows APs to assemble clathrin is poorly understood. Here we demonstrate that AP180, like AP-2 and AP-3, binds to the N-terminal domain of clathrin. Sequence analysis reveals a motif, containing the sequence DLL, that exists in multiple copies in many clathrin APs. Progressive deletion of these motifs caused a gradual reduction in the ability of AP180 to assemble clathrinin vitro. Peptides from AP180 or AP-2 containing this motif also competitively inhibited clathrin assembly by either protein. Microinjection of these peptides into squid giant presynaptic terminals reversibly blocked synaptic transmission and inhibited synaptic vesicle endocytosis by preventing coated pit formation at the plasma membrane. These results indicate that the DLL motif confers clathrin assembly properties to AP180 and AP-2 and, perhaps, to other APs. We propose that APs promote clathrin assembly by cross-linking clathrin triskelia via multivalent interactions between repeated DLL motifs in the APs and complementary binding sites on the N-terminal domain of clathrin. These results reveal the structural basis for clathrin assembly and provide novel insights into the molecular mechanism of clathrin-mediated synaptic vesicle endocytosis.
α-Latrotoxin Releases Calcium in Frog Motor Nerve Terminals
Authors: Tsang Christopher W. , Elrick Donald B. , Charlton Milton P.
Published: April 2018

α-Latrotoxin (α-LTX) is a neurotoxin that accelerates spontaneous exocytosis independently of extracellular Ca2+. Although α-LTX increases spontaneous transmitter release at synapses, the mechanism is unknown. We tested the hypothesis that α-LTX causes transmitter release by mobilizing intracellular Ca2+in frog motor nerve terminals. Transmitter release was measured electrophysiologically and with the vesicle marker FM1-43; presynaptic ion concentration dynamics were measured with fluorescent ion-imaging techniques. We report that α-LTX increases transmitter release after release of a physiologically relevant concentration of intracellular Ca2+. Neither the blockade of Ca2+release nor the depletion of Ca2+from endoplasmic reticulum affected Ca2+signals produced by α-LTX. The Ca2+source is likely to be mitochondria, because the effects on Ca2+mobilization of CCCP (which depletes mitochondrial Ca2+) and of α-LTX are mutually occlusive. The release of mitochondrial Ca2+is partially attributable to an increase in intracellular Na+, suggesting that the mitochondrial Na+/Ca2+exchanger is activated. Effects of α-LTX were not blocked when Ca2+increases were reduced greatly in saline lacking both Na+and Ca2+and by application of intracellular Ca2+chelators. Therefore, although increases in intracellular Ca2+may facilitate the effects of α-LTX on transmitter release, these increases do not appear to be necessary. The results show that investigations of Ca2+-independent α-LTX mechanisms or uses of α-LTX to probe exocytosis mechanisms would be complicated by the release of intracellular Ca2+, which itself can trigger exocytosis.
Involvement of the Extracellular Signal-Regulated Kinase Cascade for Cocaine-Rewarding Properties
Authors: Valjent Emmanuel , Corvol Jean-Christophe , Pagès Christiane , Besson Marie-Jo , Maldonado Rafael , Caboche Jocelyne
Published: April 2018

A central feature of drugs of abuse is to induce gene expression in discrete brain structures that are critically involved in behavioral responses related to addictive processes. Although extracellular signal-regulated kinase (ERK) has been implicated in several neurobiological processes, including neuronal plasticity, its role in drug addiction remains poorly understood. This study was designed to analyze the activation of ERK by cocaine, its involvement in cocaine-induced early and long-term behavioral effects, as well as in gene expression. We show, by immunocytochemistry, that acute cocaine administration activates ERK throughout the striatum, rapidly but transiently. This activation was blocked when SCH 23390 [a specific dopamine (DA)-D1 antagonist] but not raclopride (a DA-D2 antagonist) was injected before cocaine. Glutamate receptors of NMDA subtypes also participated in ERK activation, as shown after injection of the NMDA receptor antagonist MK 801. The systemic injection of SL327, a selective inhibitor of the ERK kinase MEK, before cocaine, abolished the cocaine-induced ERK activation and decreased cocaine-induced hyperlocomotion, indicating a role of this pathway in events underlying early behavioral responses. Moreover, the rewarding effects of cocaine were abolished by SL327 in the place-conditioning paradigm. Because SL327 antagonized cocaine-induced c-fos expression and Elk-1 hyperphosphorylation, we suggest that the ERK intracellular signaling cascade is also involved in the prime burst of gene expression underlying long-term behavioral changes induced by cocaine. Altogether, these results reveal a new mechanism to explain behavioral responses of cocaine related to its addictive properties.
Adult Spinal Cord Stem Cells Generate Neurons after Transplantation in the Adult Dentate Gyrus
Authors: Shihabuddin Lamya S. , Horner Philip J. , Ray Jasodhara , Gage Fred H.
Published: April 2018

The adult rat spinal cord contains cells that can proliferate and differentiate into astrocytes and oligodendrogliain situ. Using clonal and subclonal analyses we demonstrate that, in contrast to progenitors isolated from the adult mouse spinal cord with a combination of growth factors, progenitors isolated from the adult rat spinal cord using basic fibroblast growth factor alone display stem cell properties as defined by their multipotentiality and self-renewal. Clonal cultures derived from single founder cells generate neurons, astrocytes, and oligodendrocytes, confirming the multipotent nature of the parent cell. Subcloning analysis showed that after serial passaging, recloning, and expansion, these cells retained multipotentiality, indicating that they are self-renewing. Transplantation of anin vitro-expanded clonal population of cells into the adult rat spinal cord resulted in their differentiation into glial cells only. However, after heterotopic transplantation into the hippocampus, transplanted cells that integrated in the granular cell layer differentiated into cells characteristic of this region, whereas engraftment into other hippocampal regions resulted in the differentiation of cells with astroglial and oligodendroglial phenotypes. The data indicate that clonally expanded, multipotent adult progenitor cells from a non-neurogenic region are not lineage-restricted to their developmental origin but can generate region-specific neuronsin vivowhen exposed to the appropriate environmental cues.
Differential Postnatal Development of Catecholamine and Serotonin Inputs to Identified Neurons in Prefrontal Cortex of Rhesus Monkey
Authors: Lambe Evelyn K. , Krimer Leonid S. , Goldman-Rakic Patricia S.
Published: April 2018

The monoaminergic innervation of cerebral cortex has long been implicated in its development. Methods now exist to examine catecholamine and serotonin inputs to identified neurons in the cerebral cortex. We have quantified such inputs on pyramidal and nonpyramidal cells in prefrontal cortex of rhesus monkeys ranging in age from 2 weeks to 10 years. Individual layer III neurons were filled with Lucifer yellow and double-immunostained with axons containing either tyrosine hydroxylase (TH) or 5-hydroxytryptamine (5-HT). The filled cells were reconstructed, and putative appositions between the axons and dendritic spines and shafts were quantified at high magnification using light microscopy.

The density of catecholamine appositions on pyramidal neurons matures slowly, reaching only half the adult level by 6 months of age and thereafter rising gradually to adult levels by 2 years of age. By contrast, the density of serotonin appositions on pyramidal cells reaches the adult level before the second week after birth. The average adult pyramidal neuron in layer III of area 9m receives three times stronger input from catecholaminergic than from serotoninergic axons. The overall density of both inputs to interneurons does not appear to change during postnatal development. Selective changes in the TH innervation of pyramidal cells against a backdrop of constant TH innervation of interneurons suggest that the balance between excitation and inhibition may change developmentally in the prefrontal cortex. By contrast, 5-HT innervation of both types of neurons remains relatively constant over the age range studied.
Stable Hebbian Learning from Spike Timing-Dependent Plasticity
Authors: van Rossum M. C. W. , Bi G. Q. , Turrigiano G. G.
Published: April 2018

We explore a synaptic plasticity model that incorporates recent findings that potentiation and depression can be induced by precisely timed pairs of synaptic events and postsynaptic spikes. In addition we include the observation that strong synapses undergo relatively less potentiation than weak synapses, whereas depression is independent of synaptic strength. After random stimulation, the synaptic weights reach an equilibrium distribution which is stable, unimodal, and has positive skew. This weight distribution compares favorably to the distributions of quantal amplitudes and of receptor number observed experimentally in central neurons and contrasts to the distribution found in plasticity models without size-dependent potentiation. Also in contrast to those models, which show strong competition between the synapses, stable plasticity is achieved with little competition. Instead, competition can be introduced by including a separate mechanism that scales synaptic strengths multiplicatively as a function of postsynaptic activity. In this model, synaptic weights change in proportion to how correlated they are with other inputs onto the same postsynaptic neuron. These results indicate that stable correlation-based plasticity can be achieved without introducing competition, suggesting that plasticity and competition need not coexist in all circuits or at all developmental stages.
Purinergic and Adrenergic Agonists Synergize in Stimulating Vasopressin and Oxytocin Release
Authors: Kapoor John R. , Sladek Celia D.
Published: April 2018

The A1 catecholamine neurons of the caudal ventrolateral medulla transmit hemodynamic information to the vasopressin (VP) neurons in the hypothalamus. These neurons corelease ATP with norepinephrine. Perifused explants of the hypothalamoneurohypophyseal system were used to investigate the role of these substances on VP release. ATP (100 μm) increased VP release 1.5-fold (p= 0.027). The response was rapid but unsustained. It was blocked by the P2receptor antagonist pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS). The α1-adrenergic agonist phenylephrine (PE; 100 μm) also increased VP release by 1.5-fold (p= 0.014). Again, the response was rapid and unsustained. However, simultaneous perifusion of explants with ATP (100 μm) and PE (100 μm) resulted in a threefold to fourfold increase in VP release, which was sustained for as long as 4 hr. There was a similar synergistic effect of ATP and PE on oxytocin release. Interestingly, the synergistic response was delayed ∼40 min relative to the response to either agent alone. Several experiments were performed to elucidate the cellular mechanisms of this synergism. The effect was blocked by PPADS, a protein kinase C inhibitor (bisindolylmaleimide I HCl), and actinomycin, an inhibitor of gene transcription. These data suggest that P2Xreceptor activation, PKC-mediated phosphorylation, and gene transcription are required for the synergistic response. The marked synergism of these coreleased agents is probably important to achieve sustained increases in plasma VP in response to prolonged hypotension. These observations may also have broad applications to CNS function, because ATP may be coreleased at noradrenergic synapses throughout the CNS.
Thalamic Reticular Nucleus Activation Reflects Attentional Gating during Classical Conditioning
Authors: McAlonan Kerry , Brown Verity J. , Bowman Eric M.
Published: April 2018

All senses, except olfaction, are routed through the thalamus to cerebral cortex. Thus, the thalamus is often referred to as the sensory gateway to cortex. Located between thalamus and cortex is a thin lamina of neurons called the thalamic reticular nucleus, which may function as an attentional gate. The phenomenon of blocking in classical conditioning provides an opportunity to test whether an attended stimulus activates the thalamic reticular nucleus more than an unattended stimulus: when a second stimulus is presented together with a previously conditioned stimulus, conditioned responding to the second stimulus is inhibited.

Different groups of rats were given conditioning sessions with a single stimulus, a light or a tone, and then given conditioning sessions with compound (light and tone) stimuli. Blocking was confirmed using probe trials of single stimulus presentations. After a final test session of compound stimulus presentations, the brains were processed for the presence of Fos protein. Here we show that Fos-positive neurons were more numerous in the sector of the thalamic reticular nucleus associated with the attended conditioned stimulus than in the sector associated with the unattended stimulus. Thus, we provide evidence for an involvement of the thalamic reticular nucleus in selective attention.
Prenatal Cocaine Exposure Increases Sensitivity to the Attentional Effects of the Dopamine D1 Agonist SKF81297
Authors: Bayer Lorna E. , Brown Alison , Mactutus Charles F. , Booze Rose M. , Strupp Barbara J.
Published: April 2018

Sensitivity to the attentional effects of SKF81297, a selective full agonist at dopamine D1receptors, was assessed in adult rats exposed to cocaine prenatally (via intravenous injections) and controls. The task assessed the ability of the subjects to monitor an unpredictable light cue of either 300 or 700 msec duration and to maintain performance when presented with olfactory distractors. SKF81297 decreased nose pokes before cue presentation and increased latencies and response biases (the tendency to respond to the same port used on the previous trial), suggesting an effect of SKF81297 on the dopamine (DA) systems responsible for response initiation and selection. The cocaine-exposed (COC) and control animals did not differ in sensitivity to the effects of SKF81297 on these measures. In contrast, the COC animals were significantly more sensitive than were controls to the impairing effect of SKF81297 on omission errors, a measure of sustained attention. This pattern of results provides evidence that prenatal cocaine exposure produces lasting changes in the DA system(s) subserving sustained attention but does not alter the DA system(s) underlying response selection and initiation. These findings also provide support for the role of D1receptor activation in attentional functioning.
Putative Cortical and Thalamic Inputs Elicit Convergent Excitation in a Population of GABAergic Interneurons of the Lateral Amygdala
Authors: Szinyei Csaba , Heinbockel Thomas , Montagne Julia , Pape Hans-Christian
Published: April 2018

Synaptic circuitry in the rat lateral amygdala (AL) was studied in brain slices using electrophysiological recordings. Electrical stimulation of external and internal capsules evoked an EPSC followed by a sequence of GABAAand GABABreceptor-mediated IPSC in principal neurons. Paired stimulation of either afferents resulted in a significant reduction (∼45%) of the second GABAAreceptor-mediated IPSC. A priming stimulation, consisting of a priming pulse to one pathway followed by a pulse to the other pathway, resulted in a strong depression of the second IPSC basically identical to that during paired stimulation. Paired- and primed-pulse depressions were largely relieved by 10 μmCGP 55845A, indicating regulation through presynaptic GABABreceptors. Furthermore, putative interneurons responded with EPSCs of constant latencies to minimal stimulation of both cortical and thalamic fibers, indicating convergent monosynaptic input. At higher stimulation strength, an ∼15% reduction of EPSCs occurred in interneurons after paired and primed stimulation, which was not sensitive to CGP 55845A. These findings indicate that a rather homogeneous population of interneurons exists in the AL with respect to their afferent connectivity, in that they receive convergent input through putative thalamic and cortical fibers, both directly and indirectly (through principal neurons), and mediate inhibitory control of postsynaptic principal neurons. This symmetrically built GABAergic circuitry can be of functional significance, given the distinctive role of the two afferent input systems for the mediation of different components of fear responses and the importance of GABAergic mechanisms for limitation of excessive neuronal activity.
Reduced Inhibition in an Animal Model of Cortical Dysplasia
Authors: Zhu Wei Jian , Roper Steven N.
Published: April 2018

Cortical dysplasia has a strong association with epilepsy in humans, but the underlying mechanisms for this are poorly understood.In uteroirradiation of rats produces diffuse cortical dysplasia and neuronal heterotopia in the neocortex and hippocampus. Usingin vitroneocortical slices, whole-cell patch-clamp recordings were obtained from pyramidal neurons in dysplastic cortex and control neocortex. Spontaneous IPSCs were reduced in amplitude (35%) and frequency (70%) in pyramidal cells from dysplastic cortex. Miniature IPSCs were reduced in frequency (66%) in dysplastic cortex. Two additional measures of cortical inhibition, monosynaptic evoked IPSCs and paired pulse depression of evoked EPSCs, were also impaired in dysplastic cortex. Spontaneous EPSCs were increased in amplitude (42%) and frequency (77%) in dysplastic cortex, but miniature EPSCs were not different between the two groups. These data demonstrate significant physiological impairment in inhibitory synaptic transmission in experimental cortical dysplasia. This supports previous immunohistochemical findings in this model and observations in humans of a reduction in the density of inhibitory interneurons in dysplastic cortex.
Cannabinoids Reveal the Necessity of Hippocampal Neural Encoding for Short-Term Memory in Rats
Authors: Hampson Robert E. , Deadwyler Sam A.
Published: April 2018

The memory-disruptive effects of Δ9-tetrahydrocannabinol (Δ9-THC) and the synthetic cannabinoid WIN 55,212-2 (WIN-2) were assessed in rats exposed to varying doses of each drug (Δ9-THC, 0.5–2.0 mg/kg; WIN-2, 0.25–0.75 mg/kg) during performance of a delayed nonmatch to sample (DNMS) task. Cannabinoids affected performance in a dose × delay-dependent manner, with WIN-2 showing a potency more than four times that of Δ9-THC. These effects on DNMS performance were eliminated if the cannabinoid CB1 receptor antagonist SR141617A (Sanofi Research Inc.) was preadministered, but doses of the antagonist alone had no effect on performance. Simultaneous recording from ensembles of hippocampal neurons revealed that both WIN-2 and Δ9-THC produced dose-dependent reductions in the frequency (i.e.,“strength”) of ensemble firing during the sample phase of the task to the extent that performance was at risk for errors on >70% of trials as a function of delay. This decrease in ensemble firing in the Sample phase resulted from selective interference with the activity of differentiated hippocampal functional cell types, which conjunctively encoded different combinations of task events. A reduction in ensemble firing strength did not occur in the nonmatch phase of the task. The findings indicate that activation of CB1 receptors renders animals at risk for retention of item-specific information in much the same manner as hippocampal removal.
A Calcium-Dependent Feedback Mechanism Participates in Shaping Single NMDA Miniature EPSCs
Authors: Umemiya Masashi , Chen Nansheng , Raymond Lynn A. , Murphy Timothy H.
Published: April 2018

NMDA receptors (NMDARs) are highly calcium-permeable and are negatively regulated by intracellular calcium during prolonged exposure to agonist. We have investigated whether calcium-mediated feedback occurs during transient exposure to glutamate during single synaptic events. Examination of miniature EPSCs (mEPSCs) indicated that the decay kinetics of the NMDAR component was markedly slowed by the intracellular perfusion of exogenous calcium buffers (BAPTA or Fluo-3). In contrast, the AMPA receptor component of the miniature EPSC was unaffected. Slow on-rate calcium buffers, such as EGTA, did not alter kinetics of the NMDAR component of the mEPSC. Addition of exogenous fast calcium buffers did not slow the decay kinetics of glutamate-evoked currents mediated by NR1/NR2A heteromers expressed in HEK 293 cells, suggesting that the effect we observed in neurons may be specific to processes associated with synaptically activated receptors. Trial-to-trial amplitude variability of miniature calcium transients mediated by NMDARs increased with the injection of exogenous calcium buffers, suggesting that the amplitude of synaptic calcium transients are maintained at a rather constant level by a calcium-mediated feedback mechanism.
Characterization of Extracellular Dopamine Clearance in the Medial Prefrontal Cortex: Role of Monoamine Uptake and Monoamine Oxidase Inhibition
Authors: Wayment Hollie K. , Schenk James O. , Sorg Barbara A.
Published: April 2018

In vitrorotating disk electrode (RDE) voltammetry andin vivomicrodialysis were used to characterize dopamine clearance in the rat medial prefrontal cortex (mPFC). RDE studies indicate that inhibition by cocaine, specific inhibitors of the dopamine transporter (DAT) and norepinephrine transporter (NET), and low Na+produced a 50–70% decrease in the velocity of dopamine clearance. Addition of the monoamine (MAO) inhibitors,l-deprenyl, clorgyline, pargyline, orin vivonialamide produced 30–50% inhibition. Combined effects of uptake inhibitors withl-deprenyl on dopamine clearance were additive (up to 99% inhibition), suggesting that at least two mechanisms may contribute to dopamine clearance. Dopamine measured extracellularly 5 min after exogenous dopamine addition to incubation mixtures revealed that most conditions of DAT/NET inhibition did not produce elevated dopamine levels above controls. Inhibition of MAO produced elevated dopamine levels only after long-term, but not short-term, incubationin vitro. Short-term incubation ofl-deprenyl combined with DAT and NET uptake inhibitors increased dopamine above control levels, consistent with more than one mechanism of dopamine clearance. Local infusion of pargyline (100 or 300 μm) into the mPFC or striatum via microdialysis produced more pronounced and immediate increases in mPFC dopamine levels compared with striatum. Furthermore, dopamine elevation in the mPFC was not accompanied by a decrease in the dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, as found in the striatum. These findings may have revealed a unique mechanism of mPFC dopamine clearance and therefore contribute to the understanding of multiple behaviors that involve mPFC dopamine transmission, such as schizophrenia, drug abuse, and working memory function.
Glucocorticoid Receptor-Mediated Suppression of Activator Protein-1 Activation and Matrix Metalloproteinase Expression after Spinal Cord Injury
Authors: Xu Jan , Kim Gyeong-Moon , Ahmed S. Hinan , Xu Jinming , Yan Ping , Xu Xiao Ming , Hsu Chung Y.
Published: April 2018

Post-traumatic inflammatory reaction may contribute to progressive tissue damage after spinal cord injury (SCI). Two key transcription factors, nuclear factor κB (NF-κB) and activator protein-1 (AP-1), are activated in inflammation. An increase in NF-κB binding activity has been shown in the injured spinal cord. We report activation of AP-1 after SCI. Electrophoretic mobility shift assay showed that AP-1 binding activity increased after SCI, starting at 1 hr, peaking at 8 hr, and declining to basal levels by 7 d. Methylprednisolone (MP) is the only therapeutic agent approved by the Food and Drug Administration for treating patients with acute traumatic SCI. MP reduced post-traumatic AP-1 activation. RU486, a glucocorticoid receptor (GR) antagonist, reversed MP inhibition of AP-1 activation. Immunostaining showed an increase in the expression of the Fos-B and c-Jun components of AP-1 in the injured cord. Ac-fosantisense oligodeoxynucleotide (ODN) inhibited AP-1, but not NF-κB, activation after SCI. AP-1 and NF-κB can transactivate genes encoding matrix metalloproteinase-1 (MMP-1) and MMP-9. Western blotting and immunostaining show increased expression of MMP-1 and MMP-9 in the injured cord. MP inhibited MMP-1 and MMP-9 expression after SCI. RU486 reversed this MP effect. Thec-fosantisense ODN, however, failed to suppress MMP-1 or MMP-9 expression. These findings demonstrate that MP may suppress post-traumatic inflammatory reaction by inhibiting both the AP-1 and NF-κB transcription cascades via a GR mechanism. Expression of inflammatory genes such as MMP-1 and MMP-9 that are transactivated jointly by AP-1 and NF-κB may not be suppressed by inhibiting only AP-1 activity.
Expression of Brain-Derived Neurotrophic Factor in Cortical Neurons Is Regulated by Striatal Target Area
Authors: Canals Josep M. , Checa Núria , Marco Sònia , Åkerud Peter , Michels Alice , Pérez-Navarro Esther , Tolosa Eduard , Arenas Ernest , Alberch Jordi
Published: April 2018

Changes in BDNF expression after different types of brain insults are related to neuroprotection, stimulation of sprouting, and synaptic reorganization. In the cerebral cortex, an autocrine–paracrine mechanism for BDNF has been proposed because the distribution patterns of BDNF and TrkB expression are almost identical. Moreover, cortical BDNF is anterogradely transported to the striatum, suggesting a role of BDNF in the functional interaction between the two brain regions. Here we have examined the expression of this neurotrophin in the cerebral cortex after various striatal lesions. Intrastriatal injection of quinolinate, kainate, 3-nitropropionic acid, or colchicine increased BDNF mRNA levels in cerebral cortex. In contrast, stimulation of neuronal activity in the striatum did not change cortical BDNF expression. Both excitatory amino acids increased BDNF expression in neurons of cortical layers II/III, V, and VI that project to the striatum. Moreover, grafting a BDNF-secreting cell line prevented both the loss of striatal neurons and the cortical upregulation of BDNF induced by excitotoxins. Because retrograde transport in the corticostriatal pathway was intact after striatal lesions, our results suggest that striatal damage upregulates endogenous BDNF in corticostriatal neurons by a transneuronal mechanism, which may constitute a protective mechanism for striatal and/or cortical cells.
The External Granule Layer of the Developing Chick Cerebellum Generates Granule Cells and Cells of the Isthmus and Rostral Hindbrain
Authors: Lin John C. , Cai Li , Cepko Constance L.
Published: April 2018

The external granule layer (EGL) on the dorsal surface of the developing cerebellum consists of neural progenitors originating from the rostral rhombic lip (RRL). The RRL and the EGL were thought to give rise exclusively to the granule neurons of the cerebellum (Alder et al., 1996). To study the fate of individual RRL cells, we used a retroviral library to mark clones in the chick embryo at Hamberger–Hamilton stages 10–12. RRL clones comprised the EGL and cerebellar granule cells, as expected. Surprisingly, however, as many as 50% of the RRL clones also contained cells ventral to the cerebellum proper. Ventral derivatives were found in clones with a medial origin, as well as in those with a lateral origin along the RRL. Some of the ventral progeny appeared to be in the process of migration, whereas others appeared to be differentiating neurons in the isthmus and the rostral hindbrain region, including the locus coeruleus (LC) and pontine reticular formation. Furthermore, the Phox2a marker of LC precursors was detected in the EGL within the anterior aspect of the cerebellum. A stream of cells originating in the EGL and expressing Phox2a was observed to terminate ventrally in the LC. These data demonstrate that single RRL progenitor cells are not restricted to producing only cerebellar granule cells; they produce both cerebellar granule cells and ventral derivatives, some of which become hindbrain neurons. They also suggest that some progeny of the EGL escape the cerebellum via the anterior aspect of the cerebellar peduncles, to contribute to the generation of ventral structures such as the LC.
Cell-Cycle Kinetics of Neocortical Precursors Are Influenced by Embryonic Thalamic Axons
Authors: Dehay Colette , Savatier Pierre , Cortay Véronique , Kennedy Henry
Published: April 2018

Thalamic afferents are known to exert a control over the differentiation of cortical areas at late stages of development. Here, we show that thalamic afferents also influence early stages of corticogenesis at the level of the ventricular zone. Using anin vitroapproach, we show that embryonic day 14 mouse thalamic axons release a diffusable factor that promotes the proliferation of cortical precursors over a restricted developmental window. The thalamic mitogenic effect on cortical precursors (1) shortens the total cell-cycle duration via a reduction of the G1phase; (2) facilitates the G1/S transition leading to an increase in proliferative divisions; (3) is significantly reduced by antibodies directed against bFGF; and (4) influences the proliferation of both glial and neuronal precursors and does not preclude the action of signals that induce differentiation in these two lineages. We have related thesein vitrofindings to thein vivocondition: the organotypic culture of cortical explants in which anatomical thalamocortical innervation is preserved shows significantly increased proliferation rates compared with cortical explants devoid of subcortical afferents. These results are in line with a number of studies at subcortical levels showing the control of neurogenesis via afferent fibers in both vertebrates and invertebrates. Specifically, they indicate the mechanisms whereby embryonic thalamic afferents contribute to the known early regionalization of the ventricular zone, which plays a major role in the specification of neocortical areas.
Developmental Expression of Retinal Cone cGMP-Gated Channels: Evidence for Rapid Turnover and Trophic Regulation
Authors: Ko Gladys Y.-P. , Ko Michael L. , Dryer Stuart E.
Published: April 2018

The cyclic GMP-gated cationic channels of vertebrate photoreceptors are essential for visual phototransduction. We have examined the developmental regulation of cGMP-gated channels in morphologically identified cones in the chick retina. Expression of cone-type cGMP-gated channel mRNA can be detected at embryonic day 6 (E6), but expression of functional channels, as accessed by patch-clamp recordings, cannot be detected until E8. Plasma membrane channels in embryonic cones have a high turnover rate because inhibition of protein synthesis or disruption of the Golgi apparatus causes an almost complete loss of functional cGMP-gated channels within 12 hr. Different subpopulations of cones begin to express functional channels at different developmental stages, but all cones express channels by E10. Expression of cGMP-gated channels in at least one cone subpopulation appears to require one or more soluble differentiation factors, which are presumably present in the normal microenvironment of the developing retina. Application of chick embryo extract (CEE), a rich source of trophic factors, causes marked stimulation of cGMP-gated channel expression in chick cones at E8, but not at E6. Inhibition of MAP kinase (Erk) signaling using PD98059, or inhibition of PI3 kinase signaling by LY294002, blocked the stimulatory effects of CEE on E8 cones. Several recombinant trophic factors were also tested, but none could mimic the stimulatory effects of CEE on channel expression. In summary, the developmental expression of cGMP-gated cationic channels in embryonic cones appears to be regulated by epigenetic factors. The ability of cones to respond to these epigenetic factors is also developmentally regulated.
Temporal Contrast Adaptation in the Input and Output Signals of Salamander Retinal Ganglion Cells
Authors: Kim Kerry J. , Rieke Fred
Published: April 2018

We investigated how the light-evoked input and output signals of salamander retinal ganglion cells adapt to changes in temporal contrast, i.e., changes in the depth of the temporal fluctuations in the light intensity about the mean. Increasing the temporal contrast sped the kinetics and reduced the sensitivity of both the light-evoked input currents measured at the ganglion cell soma and the output spike trains of the cell. The decline in sensitivity of the input currents after an increase in contrast had two distinct kinetic components with fast (<2 sec) and slow (>10 sec) time constants. The recovery of sensitivity after a decrease in contrast was dominated by a single component with an intermediate (4–18 sec) time constant. Contrast adaptation differed foronandoffcells, with both the kinetics and amplitude of the light-evoked currents ofoffcells adapting more strongly than those ofoncells. Contrast adaptation in the input currents of a ganglion cell, however, was unable to account for the extent of adaptation in the output spike trains of the cell, indicating that mechanisms intrinsic to the ganglion cell contributed. Indeed, when fluctuating currents were injected into a ganglion cell, the sensitivity of spike generation decreased with increased current variance. Pharmacological experiments indicated that adaptation of spike generation to the current variance was attributable to properties of tetrodotoxin-sensitive Na+channels.
Invariance of Angular Threshold Computation in a Wide-Field Looming-Sensitive Neuron
Authors: Gabbiani Fabrizio , Mo Chunhui , Laurent Gilles
Published: April 2018

The lobula giant motion detector (LGMD) is a wide-field bilateral visual interneuron in North American locusts that acts as an angular threshold detector during the approach of a solid square along a trajectory perpendicular to the long axis of the animal (Gabbiani et al., 1999a). We investigated the dependence of this angular threshold computation on several stimulus parameters that alter the spatial and temporal activation patterns of inputs onto the dendritic tree of the LGMD, across three locust species. The same angular threshold computation was implemented by LGMD in all three species. The angular threshold computation was invariant to changes in target shape (from solid squares to solid discs) and to changes in target texture (checkerboard and concentric patterns). Finally, the angular threshold computation did not depend on object approach angle, over at least 135° in the horizontal plane. A two-dimensional model of the responses of the LGMD based on linear summation of motion-related excitatory and size-dependent inhibitory inputs successfully reproduced the experimental results for squares and discs approaching perpendicular to the long axis of the animal. Linear summation, however, was unable to account for invariance to object texture or approach angle. These results indicate that LGMD is a reliable neuron with which to study the biophysical mechanisms underlying the generation of complex but invariant visual responses by dendritic integration. They also suggest that invariance arises in part from non-linear integration of excitatory inputs within the dendritic tree of the LGMD.
Regulation by the Medial Amygdala of Copulation and Medial Preoptic Dopamine Release
Authors: Dominguez Juan , Riolo Jon V. , Xu Zhujian , Hull Elaine M.
Published: April 2018

The medial preoptic area (MPOA) is a critical integrative site for male copulatory behavior in most vertebrate species. Extracellular dopamine (DA) is increased in the MPOA of male rats immediately before and during copulation. DA agonists microinjected into the MPOA of male rats facilitate and DA antagonists inhibit sexual behavior. A major source of input to the MPOA is the medial amygdala (MeA), which processes and relays olfactory information to the MPOA. We now report that microinjections of a DA agonist into the MPOA of animals with excitotoxic lesions of the amygdala restored copulatory ability that was lost after the lesions. Moreover, radio-frequency lesions of the MeA impaired copulation and blocked the increases in extracellular DA seen in animals with sham lesions during exposure to a receptive female and during copulation. Thus, both copulatory ability and the MPOA DA response, during exposure to a receptive female and during copulation, are facilitated by input from the MeA to the MPOA.
Membrane Lipid Rafts Are Necessary for the Maintenance of the α7 Nicotinic Acetylcholine Receptor in Somatic Spines of Ciliary Neurons
Authors: Brusés Juan L. , Chauvet Norbert , Rutishauser Urs
Published: April 2018

Calcium-permeable neurotransmitter receptors are concentrated into structurally and biochemically isolated cellular compartments to localize calcium-mediated events during neurotransmission. The cytoplasmic membrane contains lipid microdomains called lipid rafts, which can gather into microscopically visible clusters, and thus the association of a particular protein with lipid rafts can result in its redistribution on the cell surface. The present study asks whether lipid rafts participate in the formation and maintenance of the calcium-permeable α7-subunit nicotinic acetylcholine receptor (α7nAChR) clusters found in somatic spines of ciliary neurons. Lipid rafts and α7nAChR become progressively colocalized within somatic spines during synaptogenesis. To determine whether these rafts are required for the maintenance of α7nAChR aggregates, cholesterol was extracted from dissociated ciliary neurons by treatment with methyl-β-cyclodextrin. This treatment caused the dispersion of lipid rafts and the redistribution of α7nAChR into small clusters over the cell surface, suggesting that the integrity of lipid rafts is required to maintain the receptor clustering. However, lipid raft dispersion also caused the depolymerization of the F-actin cytoskeleton, which can also tether the receptor at specific sites. To assess whether interaction between rafts and α7nAChR is independent of F-actin filaments, the lipid raft patches were stabilized with a combination of the cholera toxin B subunit (CTX), which specifically binds to the raft component ganglioside GM1, and an antibody against CTX. The stabilized rafts were then treated with latrunculin-A to depolymerize F-actin. Under these conditions, large patches of CTX persisted and were colocalized with α7nAChR, indicating that the aggregates of receptors can be maintained independently of the underlying F-actin cytoskeleton. Moreover, it was found that the α7nAChR is resistant to detergent extraction at 4°C and floats with the caveolin-containing lipid-rich fraction during density gradient centrifugation, properties that are consistent with a direct association between the receptor and the membrane microdomains.
Mode and Tempo of Tangential Cell Migration in the Cerebellar External Granular Layer
Authors: Komuro Hitoshi , Yacubova Ellada , Yacubova Elina , Rakic Pasko
Published: April 2018

After their final mitosis, cerebellar granule cells remain in the external granular layer (EGL) for 20–48 hr before initiating their radial migration across the molecular layer (ML), but the significance of this latent period is not well understood. In the present study, we used a confocal microscope to examine morphogenetic changes and behavior of postmitotic granule cells restricted to the EGL in slice preparations of the postnatal mouse cerebellum. We found that, coincident with the extension of two uneven horizontal processes oriented parallel to the longitudinal axis of the folium, postmitotic granule cells start to migrate tangentially in the direction of the larger process. Interestingly, their morphology and the speed of cell movement change systematically with their position within the EGL. The rate of tangential cell movement is fastest (∼14.8 μm/hr) in the middle of the EGL, when cells have two short horizontal processes. As granule cells elongate their somata and extend longer horizontal processes at the bottom of the EGL, they move at a reduced rate (∼12.6 μm/hr). At the interface of the EGL and ML where cells migrate tangentially at the slowest rate (∼4.1 μm/hr), their somata round and then begin to extend couples of the descending processes into the ML. After the stationary period, granule cells abruptly extend a single vertical process and initiate the transition from tangential to radial migration, reshaping their rounded somata into a vertically elongated spindle. These observations suggest that tangential migration of granule cells within the EGL may provide the developmental mechanisms for their appropriate allocation across parasagittal compartments of the expanding cerebellar cortex.
Defects in Sensory Axon Growth Precede Neuronal Death in Brn3a-Deficient Mice
Authors: Eng S. Raisa , Gratwick Kevin , Rhee Jerry M. , Fedtsova Natalia , Gan Lin , Turner Eric E.
Published: April 2018

Brn3a/Brn-3.0 is a POU-domain transcription factor expressed in primary sensory neurons of the cranial and dorsal root ganglia and in specific neurons in the caudal CNS. Mice lacking Brn3a undergo extensive sensory neural death late in gestation and die at birth. To further examine Brn3a expression and the abnormalities that accompany its absence, we constructed a transgene containing 11 kb of Brn3a upstream regulatory sequence linked to a LacZ reporter. Here we show that these regulatory sequences direct transgene expression specifically to Brn3a peripheral sensory neurons of the cranial and dorsal root ganglia. Furthermore, expression of the 11 kb/LacZ reporter in the sensory neurons of the mesencephalic trigeminal, but not other Brn3a midbrain neurons, demonstrates that cell-specific transgene expression is targeted to a functional class of neurons rather than to an anatomical region. We then interbred the 11 kb/LacZ reporter strain with mice carrying a null mutant allele of Brn3a to generate 11 kb/LacZ, Brn3a knock-out mice. β-Galactosidase expression in these mice reveals significant axonal growth defects, including excessive and premature branching of the major divisions of the trigeminal nerve and a failure to correctly innervate whisker follicles, all of which precede sensory neural death in these mice. These defects in Brn3a−/−mice resemble strongly those seen in mice lacking the mediators of sensory pathfinding semaphorin 3A and neuropilin-1. Here we show, however, that sensory neurons are able to express neuropilin-1 in the absence of Brn3a.