bluuebunny/crossref_metadata_2025 huggingface dataset:
Olfactory Neurons Expressing Closely Linked and Homologous Odorant Receptor Genes Tend to Project Their Axons to Neighboring Glomeruli on the Olfactory Bulb
Authors: Tsuboi Akio , Yoshihara Sei-ichi , Yamazaki Nika , Kasai Hiroaki , Asai-Tsuboi Hisae , Komatsu Madoka , Serizawa Shou , Ishii Tomohiro , Matsuda Yoichi , Nagawa Fumikiyo , Sakano Hitoshi
Published: April 2018

We have characterized two separate odorant receptor (OR) gene clusters to examine how olfactory neurons expressing closely linked and homologous OR genes project their axons to the olfactory bulb. Murine OR genes, MOR28, MOR10, and MOR83, share 75–95% similarities in the amino acid sequences and are tightly linked on chromosome 14.In situhybridization has demonstrated that the three genes are expressed in the same zone, at the most dorsolateral and ventromedial portions of the olfactory epithelium, and are rarely expressed simultaneously in individual neurons. Furthermore, we have found that olfactory neurons expressing MOR28, MOR10, or MOR83 project their axons to very close but distinct subsets of glomeruli on the medial and lateral sides of the olfactory bulb. Similar results have been obtained with another murine OR gene cluster for A16 and MOR18 on chromosome 2, sharing 91% similarity in the amino acid sequences. These results may indicate an intriguing possibility that olfactory neurons expressing homologous OR genes within a cluster tend to converge their axons to proximal but distinct subsets of glomeruli. These lines of study will shed light on the molecular basis of topographical projection of olfactory neurons to the olfactory bulb.
Essential Roles of c-JUN and c-JUN N-Terminal Kinase (JNK) in Neuregulin-Increased Expression of the Acetylcholine Receptor ε-Subunit
Authors: Si Jutong , Wang Qi , Mei Lin
Published: April 2018

Neuregulin is a neural factor implicated in upregulation of acetylcholine receptor (AChR) synthesis at the neuromuscular junction. Previous studies have demonstrated that the extracellular signal–regulated kinase (ERK) subgroup of MAP kinases is required for neuregulin-induced AChR gene expression. We report here that the neuregulin-mediated increase in AChR ε-subunit mRNA was a delayed response in C2C12 muscle cells. Neuregulin induced expression of immediate early genesc-junandc-fos, which followed and depended on the ERK activation. Treatment of muscle cells with cycloheximide to inhibit c-JUN synthesis at the protein level and suppression of c-JUN function by a dominant-negative mutant blocked neuregulin-induced expression of the ε-subunit gene, indicating an essential role of c-JUN in neuregulin signaling. Furthermore, neuregulin activated c-JUN N-terminal kinase (JNK) in C2C12 muscle cells. Blockade of JNK activation by overexpressing dominant-negative MKK4 inhibited ε-promoter activation. Moreover, overexpression of the JNK dominant-negative mutant inhibited neuregulin-mediated expression of the εtransgene and endogenous ε-mRNA. Taken together, our results demonstrate important roles of c-JUN and JNK in neuregulin-mediated expression of the AChR ε-subunit gene and suggest that neuregulin activates multiple signaling cascades that converge to regulate AChR ε-subunit gene expression.
Both the Neuronal and Inducible Isoforms Contribute to Upregulation of Retinal Nitric Oxide Synthase Activity by Brain-Derived Neurotrophic Factor
Authors: Klöcker Nikolaj , Kermer Pawel , Gleichmann Marc , Weller Michael , Bähr Mathias
Published: April 2018

Although neurotrophins are best known for their trophic functions, growing evidence suggests that neurotrophins can also be neurotoxic, for instance by enhancing excitotoxic insults. We have shown recently that brain-derived neurotrophic factor (BDNF) limits its neuroprotective action on axotomized rat retinal ganglion cells (RGCs) by upregulating nitric oxide synthase (NOS) activity (Klöcker et al., 1998). The aim of the present study was to investigate this interaction of BDNF and NOS in the lesioned adult rat retina in more detail. We used NOS immunohistochemistry and NADPH-diaphorase (NADPH-d) reaction to characterize morphologically retinal NOS expression and activity. Using reverse transcription-PCR and Western blot analysis, we were able to identify the NOS isoforms being regulated. Six days after optic nerve lesion, we observed an increase in neuronal NOS (NOS-I) mRNA and protein expression in the inner retina. This did not lead to a marked increase in overall retinal NOS activity. Only RGC axons displayed strongde novoNADPH-d reactivity. In contrast, intraocular injection of BDNF resulted in a marked upregulation of NOS activity in NOS-I-immunoreactive structures, leaving the level of NOS-I expression unchanged. In addition, an induction of inducible NOS (NOS-II) was found after BDNF treatment. We identified microglial cells increasing in number and being activated by BDNF, which could serve as the cellular source of NOS-II. In summary, our data suggest that BDNF upregulates retinal NOS activity by both a post-translational regulation of NOS-I activity and an induction of NOS-II. These findings might be useful for developing pharmacological strategies to improve BDNF-mediated neuroprotection.
Ovariectomy of Adult Rats Leads to Increased Expression of Astrocytic Basic Fibroblast Growth Factor in the Ventral Tegmental Area and in Dopaminergic Projection Regions of the Entorhinal and Prefrontal Cortex
Authors: Flores Cecilia , Salmaso Natalina , Cain Sean , Rodaros Demetra , Stewart Jane
Published: April 2018

Changes in astrocytic function may underlie the neurochemical and morphological alterations in limbic and cortical areas after estrogen loss in adult females. We assessed whether increased expression of basic fibroblast growth factor (bFGF), an astrocytic response involved in injury-induced neuronal plasticity, occurs after ovariectomy. We examined bFGF immunoreactivity (IR) in ovariectomized rats with oil or estradiol benzoate (5 μg every 4 d; Experiment 1) and in ovariectomized and intact animals (Experiment 2). In the ventral tegmental area (VTA), bFGF-IR and glial fibrillary acidic protein (GFAP)-IR were greater in ovariectomized animals than in animals with estrogen replacement. bFGF-IR in the VTA was greater in ovariectomized than in intact females. In the dorsal raphe, no differences between groups were found in GFAP-IR or bFGF-IR. In mesolimbic dopaminergic target areas within entorhinal cortex (Ent), prefrontal cortex, and nucleus accumbens, bFGF-IR was higher in Ent of ovariectomized animals 4 weeks after surgery in both experiments, but no differences were seen in nucleus accumbens or in an occipital cortical, control, area in either study. In Experiment 2, small increases in bFGF-IR were seen in the prefrontal cortex after ovariectomy. In the VTA and Ent, changes in bFGF-IR developed gradually, peaking at 4 weeks and waning at 40 weeks. Furthermore, increased dendritic arbor of Ent layer II/III pyramidal cells was found in ovariectomized females with the use of a modified Golgi–Cox staining procedure. These findings suggest that, within specific regions, ovariectomy induces astrocytic responses similar to those observed after injury that may affect neuronal chemistry and morphology.
Decreased G-Protein-Mediated Regulation and Shift in Calcium Channel Types with Age in Hippocampal Cultures
Authors: Blalock Eric M. , Porter Nada M. , Landfield Philip W.
Published: April 2018

The membrane density of L-type voltage-sensitive Ca2+channels (L-VSCCs) of rat hippocampal neurons increases over age [daysin vitro(DIV)] in long-term primary cultures, apparently contributing both to spontaneous cell death and to enhanced excitotoxic vulnerability. Similar increases in L-VSCCs occur during brain agingin vivoin rat and rabbit hippocampal neurons. However, unraveling both the molecular basis and the functional implications of these age changes in VSCC density will require determining whether the other types of high-threshold VSCCs (e.g., N, P/Q, and R) also exhibit altered density and/or changes in regulation, for example, by the important G-protein-coupled, membrane-delimited inhibitory pathway. These possibilities were tested here in long-term hippocampal cultures.

Pharmacologically defined whole-cell currents were corrected for cell size differences over age by normalization with whole-cell capacitance. The Ca2+channel current density (picoamperes per picofarad), mediated by each Ca2+channel type studied here (L, N, and a combined P/Q + R component), increased through 7 DIV. Thereafter, however, only L-type current density continued to increase, at least through 21 DIV. Concurrently, pertussis toxin-sensitive G-protein-coupled inhibition of non-L-type Ca2+channel current induced by the GABABreceptor agonist baclofen or by guanosine 5′-3-O-(thio)triphosphate declined dramatically with age in culture. Thus, the present studies identify selective and novel parallel mechanisms for the time-dependent alteration of Ca2+influx, which could importantly influence function and vulnerability during development and/or aging.
Metabotropic Glutamate Receptors Trigger Homosynaptic Protein Synthesis to Prolong Long-Term Potentiation
Authors: Raymond Clarke R. , Thompson Vida L. , Tate Warren P. , Abraham Wickliffe C.
Published: April 2018

We investigated the mechanisms by which previous “priming” activation of group I metabotropic glutamate receptors (mGluRs) facilitates the persistence of long-term potentiation (LTP) in area CA1 of rat hippocampal slices. Priming of LTP was elicited by either pharmacological or synaptic activation of mGluRs before a weak tetanic stimulus that normally produced only a rapidly decaying phase of LTP that did not involve protein synthesis or mGluRs. Pharmacological priming of LTP persistence by a selective group I mGluR agonist was blocked by an inhibitor of group I mGluRs and by inhibitors of translation, but not by a transcriptional inhibitor. The same mGluR agonist increased35S-methionine incorporation into slice proteins. LTP could also be facilitated using a synaptic stimulation priming protocol, and this effect was similarly blocked by group I mGluR and protein synthesis inhibitors. Furthermore, using a two-pathway protocol, the synaptic priming of LTP was found to be input-specific. To test for the contribution of group I mGluRs and protein synthesis to LTP in nonprimed slices, a longer duration control tetanization protocol was used to elicit a more slowly decaying form of LTP than did the weak tetanus used in the previous experiments. The persistence of the LTP induced by this stronger tetanus was dependent on mGluR activation and protein synthesis but not on transcription. Together, these results suggest that mGluRs couple to nearby protein synthesis machinery to homosynaptically regulate an intermediate phase of LTP dependent on new proteins made from pre-existing mRNA.
Septamer Element-Binding Proteins in Neuronal and Glial Differentiation
Authors: Dobi Albert , Palkovits Miklos , Palkovits Christina G. , Ring Mary A. , v. Agoston Denes
Published: April 2018

Differentiation of progenitors into neurons and glia is regulated by interactions between regulatory DNA elements of neuron- and glia-specific genes and transcription factors that are differentially expressed by progenitors at progressive stages of neural development. We have identified a novel DNA regulatory element (TTTGCAT = septamer) present on the enkephalin (ENK), neuronal cell adhesion molecule, neurofilament of 68 kDa (NF68), growth-associated protein of 43 kDa, glial high-affinity glutamine transporter, tyrosine hydroxylase, etc., genes. When septamer function was blocked by introducing septamer competitor DNA into primary differentiating neural cultures, mRNA levels of ENK, NF68, and glial fibrillary acidic protein decreased by 50–80%, whereas no effect was seen using a control DNA. Septamer elements serve as binding sites for lineage-specific multimeric complexes assembled from three distinct nuclear proteins. Progenitors express a 16 kDa protein (p-sept) which binds to DNA as a homodimer (detected as the 32 kDa P-band). Cells that entered the neuronal lineage express an additional 29 kDa protein (n-sept) that binds to the homodimerizedp-sept, and together they form a 62 kDa multimer (detected as N-band). Cells that entered the glial lineage express a distinct 23 kDa protein (g-sept), which along with the homodimerizedp-septform a 56 kDa multimer (observed as G-band). The binding of the distinct protein complexes (P, G, and N) to the septamer site causes a lineage-specific DNA bending (P = 53°; G = 72°; and N = 90°), which may contribute to the regulatory effect of the septamer interaction. In summary, septamer and its binding proteins represent novel protein–DNA interactions that may contribute to the regulation of neuroglial differentiation in the developing mammalian CNS.
The Lack ofEmx2Causes Impairment ofReelinSignaling and Defects of Neuronal Migration in the Developing Cerebral Cortex
Authors: Mallamaci Antonello , Mercurio Sara , Muzio Luca , Cecchi Chiara , Pardini Celia Leonor , Gruss Peter , Boncinelli Edoardo
Published: April 2018

Neocorticogenesis in mice homozygous for anEmx2null allele is the topic of this article. The development of both main components of neocortex, primordial plexiform layer derivatives and cortical plate, was analyzed, paying special attention to radial migration of neurons forming the cortical plate. The products of theReelingene, normally playing a key role in orchestrating radial migration of these neurons, display normal distribution at the beginning of the cortical neuronogenesis but are absent in the neocortical marginal zone of the mutant mice at the time when the cortical plate is laid down. As a consequence, the development of radial glia is impaired, and neurons making up the cortical plate display abnormal migration patterns. In addition, restricted defects along the rostrocaudal and the mediolateral axes are present in the subplate, suggesting anEmx2-specific role in priming the proper development of this layer.
The Analgesic Effects of Supraspinal μ and δ Opioid Receptor Agonists Are Potentiated during Persistent Inflammation
Authors: Hurley Robert W. , Hammond Donna L.
Published: April 2018

This study examined the antihyperalgesic and antinociceptive effects of opioid receptor agonists microinjected in the rostral ventromedial medulla (RVM) of rats 4 hr, 4 d, and 2 weeks after the induction of an inflammatory injury by injection of complete Freund's adjuvant (CFA) in one hindpaw. Nociceptive sensitivity of the ipsilateral, inflamed and the contralateral, uninflamed hindpaws was determined by the radiant-heat paw withdrawal test. The antihyperalgesic potency of the μ opioid receptor agonist [d-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO), determined for the inflamed hindpaw, was enhanced 4 d and 2 weeks after injury. The antinociceptive potency of DAMGO, determined for the contralateral, uninflamed hindpaw, was also progressively enhanced 4 hr, 4 d, and 2 weeks after injury. The magnitude of enhancement paralleled the chronicity of the injury. The greatest potentiation occurred 2 weeks after injury when the ED50value of DAMGO in CFA-treated rats was one-tenth that in saline-treated rats. The antihyperalgesic and antinociceptive effects of the δ opioid receptor agonist [d-Ala2,Glu4]deltorphin were also increased 2 weeks after injury. These results indicate that peripheral inflammatory injury alters the pharmacology of excitatory and inhibitory inputs that modulate the activity of RVM neurons in such a manner as to enhance the effects of opioid agonists in this region. These changes have ramifications not only for the alleviation of hyperalgesia at the site of injury but also for opioid-induced antinociception at sites remote to the injury as revealed by increases in the potency of opioid agonists to suppress nociceptive responses of the contralateral, uninflamed hindpaw.
Limitations of Cyclosporin A Inhibition of the Permeability Transition in CNS Mitochondria
Authors: Brustovetsky Nickolay , Dubinsky Janet M.
Published: April 2018

Activation of the mitochondrial permeability transition may contribute to excitotoxic neuronal death (Ankarcrona et al., 1996;Dubinsky and Levi, 1998). However, cyclosporin A (CsA), a potent inhibitor of the permeability transition in liver mitochondria, only protects against neuronal injury by limited doses of glutamate and selected ischemic paradigms. The lack of consistent CsA inhibition of the mitochondrial permeability transition was analyzed with the use of isolated brain mitochondria. Changes in the permeability of the inner mitochondrial membrane were evaluated by monitoring mitochondrial membrane potential (Δψ), using the distribution of tetraphenylphosphonium, and by monitoring mitochondrial swelling, using light absorbance measurements. Metabolic impairments, large Ca2+loads, omission of external Mg2+, or low doses of palmitic acid or the protonophore FCCP exacerbated Ca2+-induced sustained depolarizations and swelling and eliminated CsA inhibition. BSA restored CsA inhibition in mitochondria challenged with 50 μmCa2+,but not with 100 μmCa2+. CsA failed to prevent Ca2+-induced depolarization or to repolarize mitochondria when mitochondria were depolarized excessively. Similarly, CsA failed to prevent mitochondrial swelling or PEG-induced shrinkage after swelling when the Ca2+challenge produced a strong, sustained depolarization. Thus in brain mitochondria CsA may be effective only as an inhibitor of the permeability transition and the Ca2+-activated low permeability state under conditions of partial depolarization. In contrast, ADP plus oligomycin inhibited both permeabilities under all of the conditions that were tested.In situ, the neuroprotective action of CsA may be limited to glutamate challenges sufficiently toxic to induce the permeability transition but not so severe that mitochondrial depolarization exceeds threshold.
Contactin-Associated Protein (Caspr) and Contactin Form a Complex That Is Targeted to the Paranodal Junctions during Myelination
Authors: Rios Jose C. , Melendez-Vasquez Carmen V. , Einheber Steven , Lustig Marc , Grumet Martin , Hemperly John , Peles Elior , Salzer James L.
Published: April 2018

Specialized paranodal junctions form between the axon and the closely apposed paranodal loops of myelinating glia. They are interposed between sodium channels at the nodes of Ranvier and potassium channels in the juxtaparanodal regions; their precise function and molecular composition have been elusive. We previously reported that Caspr (contactin-associated protein) is a major axonal constituent of these junctions (Einheber et al., 1997). We now report that contactin colocalizes and forms aciscomplex with Caspr in the paranodes and juxtamesaxon. These proteins coextract and coprecipitate from neurons, myelinating cultures, and myelin preparations enriched in junctional markers; they fractionate on sucrose gradients as a high-molecular-weight complex, suggesting that other proteins may also be associated with this complex. Neurons express two contactin isoforms that differ in their extent of glycosylation: a lower-molecular-weight phosphatidylinositol phospholipase C (PI-PLC)-resistant form is associated specifically with Caspr in the paranodes, whereas a higher-molecular-weight form of contactin, not associated with Caspr, is present in central nodes of Ranvier. These results suggest that the targeting of contactin to different axonal domains may be determined, in part, via its association with Caspr. Treatment of myelinating cocultures of Schwann cells and neurons with RPTPβ–Fc, a soluble construct containing the carbonic anhydrase domain of the receptor protein tyrosine phosphatase β (RPTPβ), a potential glial receptor for contactin, blocks the localization of the Caspr/contactin complex to the paranodes. These results strongly suggest that a preformed complex of Caspr and contactin is targeted to the paranodal junctions via extracellular interactions with myelinating glia.
Corticolimbic Interactions Associated with Performance on a Short-Term Memory Task Are Modified by Age
Authors: Della-Maggiore Valeria , Sekuler Allison B. , Grady Cheryl L. , Bennett Patrick J. , Sekuler Robert , McIntosh Anthony R.
Published: April 2018

Aging has been associated with a decline in memory abilities dependent on hippocampal processing. We investigated whether the functional interactions between the hippocampus and related cortical areas were modified by age. Young and old subjects' brain activity was measured using positron emission tomography (PET) while they performed a short-term memory task (delayed visual discrimination) in which they determined which of two successively presented sine-wave gratings had the highest spatial frequency. Behavioral performance was equal for the two groups. Partial least squares (PLS) analysis of PET images identified a hippocampal voxel whose activity was similarly correlated with performance across groups. Using this voxel as a seed, a second PLS analysis identified cortical regions functionally connected to the hippocampus. Quantification of the neural interactions with structural equation modeling suggested that a different hippocampal network supported performance in the elderly. Unlike the neural network engaged by the young, which included prefrontal cortex Brodmann's area (BA) 10, fusiform gyrus, and posterior cingulate gyrus, the network recruited by the old included more anterior areas, i.e., dorsolateral prefrontal cortex (BA 9/46), middle cingulate gyrus, and caudate nucleus. Recruitment of a distinct corticolimbic network for visual memory in the elderly suggests that age-related neurobiological deterioration not only results in focal changes but also in the modification of large-scale network operations.
Involvement of the 5-HT1AReceptors in Classical Fear Conditioning in C57BL/6J Mice
Authors: Stiedl Oliver , Misane Ilga , Spiess Joachim , Ögren Sven Ove
Published: April 2018

The present study examined the involvement of the 5-HT1Areceptors in classical fear conditioning using the 5-HT1Aagonist 8-hydroxy-2-(di-n-propyloamino)tetralin hydrobromide (8-OH-DPAT) and the selective “silent” 5-HT1Areceptor antagonist (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclo-hexane carboxamide trihydrochloride (WAY 100635). The drugs were administered both subcutaneously and bilaterally into the dorsal hippocampus of male C57BL/6J mice. The training was performed in a single trial in which a tone was followed by a footshock. The retention of context- and tone-dependent fear was examined in separate tests conducted either 1 or 24 hr after training. Subcutaneous 8-OH-DPAT (0.1–1.0 mg/kg), when injected before but not after training, caused a dose-dependent impairment of contextual fear in both 1 and 24 hr tests, whereas tone-dependent fear was less affected. Pretraining intrahippocampal injections of 5.0 μg but not 1.0 μg 8-OH-DPAT caused a severe deficit in contextual fear when tested 24 hr after training. When injected both subcutaneously and intrahippocampally, 8-OH-DPAT induced the 5-HT syndrome, indicative of postsynaptic 5-HT1Areceptor activation at the dose ranges that impaired fear conditioning. However, the behavioral changes induced by 8-OH-DPAT at the time of training could not account for inhibitory effects of 8-OH-DPAT on fear conditioning. Neither subcutaneous (0.03 mg/kg) nor intrahippocampal (0.5 μg per mouse) WAY 100635 altered context- or tone-dependent fear. However, subcutaneous WAY 100635 blocked both the 5-HT syndrome and the impairment of fear conditioning induced by subcutaneous or intrahippocampal 8-OH-DPAT. In contrast, intrahippocampal WAY 100635 blocked the impairment caused by intrahippocampal but not subcutaneous 8-OH-DPAT, indicating the involvement of extrahippocampal 5-HT1Areceptors in fear conditioning. It is concluded that the deficits in fear conditioning induced by 8-OH-DPAT are a result of postsynaptic 5-HT1Areceptor activation that interferes with learning processes operating at acquisition but not consolidation. Furthermore, the dorsohippocampal 5-HT1Areceptors play an important but not exclusive role in the limbic circuitry subserving contextual fear conditioning.
Firing Patterns and Correlations of Spontaneous Discharge of Pallidal Neurons in the Normal and the Tremulous 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Vervet Model of Parkinsonism
Authors: Raz Aeyal , Vaadia Eilon , Bergman Hagai
Published: April 2018

To investigate the role of the basal ganglia in parkinsonian tremor, we recorded hand tremor and simultaneous activity of several neurons in the external and internal segments of the globus pallidus (GPe and GPi) in two vervet monkeys, before and after systemic treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and development of parkinsonism with tremor of 5 and 11 Hz.

In healthy monkeys, only 11% (20/174) of the GPe cells and 3% (1/29) of the GPi cells displayed significant 3–19 Hz oscillations. After MPTP treatment, 39% (107/271) of the GPe cells and 43% (26/61) of the GPi cells developed significant oscillations. Oscillation frequencies of single cells after MPTP treatment were bimodally distributed around 7 and 13 Hz. For 10% of the oscillatory cells that were recorded during tremor periods, there was a significant tendency for the tremor and neuronal oscillations to appear simultaneously.

Cross-correlation analysis revealed a very low level of correlated activity between pallidal neurons in the normal state; 95.6% (477/499) of the pairs were not correlated, and oscillatory cross-correlograms were found in only 1% (5/499) of the pairs. After MPTP treatment, the correlations increased dramatically, and 40% (432/1080) of the cross-correlograms had significant oscillations, centered around 13–14 Hz. Phase shifts of the cross-correlograms of GPe pairs, but not of GPi, were clustered around 0°.

The results illustrate that MPTP treatment changes the pattern of activity and synchronization in the GPe and GPi. These changes are related to the symptoms of Parkinson's disease and especially to the parkinsonian tremor.
A Series of Biotinylated Tracers Distinguishes Three Types of Gap Junction in Retina
Authors: Mills Stephen L. , Massey Stephen C.
Published: April 2018

Gap junctions serve many important roles in various tissues, but their abundance and diversity in neurons is only beginning to be understood. The tracer Neurobiotin has revealed many different networks interconnected by gap junctions in retina. We compared the relative permeabilities of five different retinal gap junctions by measuring their permeabilities to a series of structurally related tracers. When large tracers were injected, the staining of coupled cells fell off more rapidly in some networks than others relative to Neurobiotin controls. Three distinctly different permeability profiles were found, suggesting that multiple neuronal connexin types were present. The most permeant to large molecules were gap junctions from A-type horizontal cells. The permeability of gap junctions of two types of amacrine cell were not distinguishable from those from B-type horizontal cells. The lowest permeability was found for gap junctions between cone bipolar cells and the AII amacrine cells to which they are coupled. Because only a single neural connexin type has been identified in retina, our results suggest more types remain to be found.

To determine whether the unitary permeability of channels is altered by channel modulators, we reduced permeability with octanol and a cAMP analog. Although net permeability was substantially diminished, the proportion by which it declined was constant across tracer size. This suggests that these agents act only to close channels rather than alter individual channel permeabilities. This tracer series can therefore be used to contrast permeability properties of gap junctions in intact circuits, even at the level of individual channels.
Bistable Behavior of Inhibitory Neurons Controlling Impulse Traffic through the Amygdala: Role of a Slowly Deinactivating K+Current
Authors: Royer Sébastien , Martina Marzia , Paré Denis
Published: April 2018

The intercalated cell masses of the amygdala are clusters of GABAergic neurons located strategically to influence behavioral responsiveness. Indeed, they receive glutamatergic sensory inputs from the basolateral amygdaloid complex and generate feedforward inhibition in neurons of the central amygdala that mediate important components of fear responses. In the present study, using whole-cell recording methods in coronal slices of the guinea pig amygdala, we show that the activity of intercalated neurons is a function of their recent firing history because they express an unusual voltage-dependent K+conductance (termedISDfor slowly deinactivating). This conductance activates in the subthreshold regime, inactivates in response to suprathreshold depolarizations, and deinactivates very slowly upon return to rest. As a result, after bouts of suprathreshold activity, these cells enter a self-sustaining state of heightened excitability associated with an increased input resistance and a membrane depolarization. In turn, these changes increase the likelihood that ongoing synaptic activity will trigger orthodromic action potentials. However, because each orthodromic spike “renews” the inactivation ofISD, intercalated cells can remain hyperexcitable for a long time and, via the central amygdaloid nucleus, exert a lasting influence on behavior.
Potentiated Opioid Analgesia in Norepinephrine Transporter Knock-Out Mice
Authors: Bohn Laura M. , Xu Fei , Gainetdinov Raul R. , Caron Marc G.
Published: April 2018

Several studies have shown that activation of α2-adrenergic receptors (α2ARs) leads to mild analgesic effects. Tricyclic antidepressants (TCAs), such as desipramine (DMI), which block norepinephrine transporters (NETs), also produce mild antinociception. The coadministration of either α2AR agonists or TCAs with opiates produces synergistically potentiated antinociception. It has been postulated that the analgesic effects of TCAs are determined by their ability to inhibit norepinephrine reuptake via interactions with the NET. To test this idea, we studied mice lacking a functional NET in spontaneous and morphine-induced antinociceptive paradigms. Morphine (10 mg/kg, s.c.) treatment produced greater analgesia, as assayed in the warm water tail-flick assay, in NET-knock-out (-KO) mice than in wild-type (WT) mice. As anticipated, yohimbine, an inhibitor of α2ARs, blocked this potentiation. Moreover, a warm water swim-stress paradigm, which is known to induce the release of endogenous opioids, produced greater antinociception in NET-KO than in the WT mice. Naloxone, an inhibitor of opioid receptors, blocked the development of the swim-evoked analgesia in both WT and NET-KO mice, confirming the involvement of the endogenous opioid system. In the NET-KO mice, DMI did not further enhance analgesia but was still able to produce inhibitory effects on the locomotor activity of these mutants, suggesting that the effects of this TCA are not exclusively via interactions with the NET. In summary, these results demonstrate in a genetic model that both endogenous and exogenous opiate-mediated analgesia can be enhanced by elimination of the NET, indicating that the interaction of TCAs with NET mediates these effects.
The Light Response of ON Bipolar Neurons Requires Gαo
Authors: Dhingra Anuradha , Lyubarsky Arkady , Jiang Meisheng , Pugh Edward N. , Birnbaumer Lutz , Sterling Peter , Vardi Noga
Published: April 2018

ON bipolar neurons in retina detect the glutamate released by rods and cones via metabotropic glutamate receptor 6 (mGluR6), whose cascade is unknown. The trimeric G-protein Gomight mediate this cascade because it colocalizes with mGluR6. To test this, we studied the retina in mice negative for the α subunit of Go(Gαo−/−). Retinal layering, key cell types, synaptic structure, and mGluR6 expression were all normal, as was the a-wave of the electroretinogram, which represents the rod and cone photocurrents. However, the b-wave of the electroretinogram, both rod- and cone-driven components, was entirely missing. Because the b-wave represents the massed response of ON bipolar cells, its loss in the Gαonull mouse establishes that the light response of the ON bipolar cell requires Go. This represents the first function to be definedin vivofor the α subunit of the most abundant G-protein of the brain .
Co-Induction of p75NTRand p75NTR-Associated Death Executor in Neurons After Zinc Exposure in Cortical Culture or Transient Ischemia in the Rat
Authors: Park Jeong Ae , Lee Joo-Yong , Sato Taka-Aki , Koh Jae-Young
Published: April 2018

Recently, a 22 kDa protein termed p75NTR-associated death executor (NADE) was discovered to be a necessary factor for p75NTR-mediated apoptosis in certain cells. However, the possible role for p75NTR/NADE in pathological neuronal death has yet been undetermined. In the present study, we have examined this possibilityin vivoandin vitro. Exposure of cortical cultures to zinc induced both p75NTRand NADE in neurons, whereas exposure to NMDA, ionomycin, iron, or H2O2induced neither. In addition, zinc exposure increased neuronal NGF expression and its release into the medium. A function-blocking antibody of p75NTR(REX) inhibited association between p75NTRand NADE as well as neuronal death induced by zinc. Conversely, NGF augmented zinc-induced neuronal death. Caspase inhibitors reduced zinc-induced neuronal death, indicating that caspases were involved. Because reduction of NADE expression with cycloheximide orNADEantisense oligonucleotides attenuated zinc-induced neuronal death, NADE appears to contribute to p75NTR-induced cortical neuronal death as shown in other cells. Because zinc neurotoxicity may be a key mechanism of neuronal death after transient forebrain ischemia, we next examined this model. After ischemia, p75NTRand NADE were induced in degenerating rat hippocampal CA1 neurons. There was a close correlation between zinc accumulation and p75NTR/NADE induction. Suggesting the role of zinc here, injection of a metal chelator, CaEDTA, into the lateral ventricle completely blocked the induction of p75NTRand NADE. Our results suggest that co-induction of p75NTRand NADE plays a role in zinc-triggered neuronal deathin vitroandin vivo.
Dynamics of Hippocampal Ensemble Activity Realignment: Time versus Space
Authors: Redish A. David , Rosenzweig Ephron S. , Bohanick J. D. , McNaughton B. L. , Barnes C. A.
Published: April 2018

Whether hippocampal map realignment is coupled more strongly to position or time was studied in rats trained to shuttle on a linear track. The rats were required to run from a start box and to pause at a goal location at a fixed location relative to stable distal cues (room-aligned coordinate frame). The origin of each lap was varied by shifting the start box and track as a unit (box-aligned coordinate frame) along the direction of travel. As observed by Gothard et al. (1996a), on each lap the hippocampal activity realigned from a representation that was box-aligned to one that was room-aligned. We studied the dynamics of this transition using a measure of how well the moment-by-moment ensemble activity matched the expected activity given the location of the animal in each coordinate frame. The coherency ratio, defined as the ratio of the matches for the two coordinate systems, provides a quantitative measure of the ensemble activity alignment and was used to compare four possible descriptions of the realignment process. The elapsed time since leaving the box provided a better predictor of the occurrence of the transition than any of the three spatial parameters investigated, suggesting that the shift between coordinate systems is at least partially governed by a stochastic, time-dependent process.
DNA Replication Precedes Neuronal Cell Death in Alzheimer's Disease
Authors: Yang Yan , Geldmacher David S. , Herrup Karl
Published: April 2018

Alzheimer's disease (AD) is a devastating dementia of late life that is correlated with a region-specific neuronal cell loss. Despite progress in uncovering many of the factors that contribute to the etiology of the disease, the cause of the nerve cell death remains unknown. One promising theory is that the neurons degenerate because they reenter a lethal cell cycle. This theory receives support from immunocytochemical evidence for the reexpression of several cell cycle-related proteins. Direct proof for DNA replication, however, has been lacking. We report here the use of fluorescentin situhybridization to examine the chromosomal complement of interphase neuronal nuclei in the adult human brain. We demonstrate that a significant fraction of the hippocampal pyramidal and basal forebrain neurons in AD have fully or partially replicated four separate genetic loci on three different chromosomes. Cells in unaffected regions of the AD brain or in the hippocampus of nondemented age-matched controls show no such anomalies. We conclude that the AD neurons complete a nearly full S phase, but because mitosis is not initiated, the cells remain tetraploid. Quantitative analysis indicates that the genetic imbalance persists for many months before the cells die, and we propose that this imbalance is the direct cause of the neuronal loss in Alzheimer's disease.
Cortical Axon Guidance by the Glial Wedge during the Development of the Corpus Callosum
Authors: Shu Tianzhi , Richards Linda J.
Published: April 2018

Growing axons are often guided to their final destination by intermediate targets. In the developing spinal cord and optic nerve, specialized cells at the embryonic midline act as intermediate targets for guiding commissural axons. Here we investigate whether similar intermediate targets may play a role in guiding cortical axons in the developing brain. During the development of the corpus callosum, cortical axons from one cerebral hemisphere cross the midline to reach their targets in the opposite cortical hemisphere. We have identified two early differentiating populations of midline glial cells that may act as intermediate guideposts for callosal axons. The first differentiates directly below the corpus callosum forming a wedge shaped structure (the glial wedge) and the second differentiates directly above the corpus callosum within the indusium griseum. Axons of the corpus callosum avoid both of these populationsin vivo. This finding is recapitulatedin vitroin three-dimensional collagen gels. In addition, experimental manipulations in organotypic slices show that callosal axons require the presence and correct orientation of these populations to turn toward the midline. We have also identified one possible candidate for this activity because both glial populations express the chemorepellent moleculeslit-2, and cortical axons express theslit-2receptorsrobo-1androbo-2. Furthermore,slit-2repels–suppresses cortical axon growth in three-dimensional collagen gel cocultures.
Consistent Features in the Forelimb Representation of Primary Motor Cortex in Rhesus Macaques
Authors: Park Michael C. , Belhaj-Saı̈f Abderraouf , Gordon Michael , Cheney Paul D.
Published: April 2018

The purpose of this study was to systematically map the forelimb area of primary motor cortex (M1) in rhesus macaques in an effort to investigate further the organization of motor output to distal and proximal muscles. We used stimulus-triggered averaging (StTAing) of electromyographic activity to map the cortical representation of 24 simultaneously recorded forelimb muscles. StTAs were obtained by applying 15 μA stimuli to M1 sites while the monkey performed a reach and prehension task. Motor output to body regions other than the forelimb (e.g., face, trunk, and hindlimb) was identified using repetitive intracortical microstimulation to evoke movements. Detailed, muscle-based maps of M1 revealed a central core of distal (wrist, digit, and intrinsic hand) muscle representation surrounded by a “horseshoe”-shaped zone of proximal (shoulder and elbow) muscle representation. The core distal and proximal zones were separated by a relatively large region representing combinations of both distal and proximal muscles. On the basis of its size and characteristics, we argue that this zone is not simply the result of stimulus-current spread, but rather a distinct zone within the forelimb representation containing cells that specify functional synergies of distal and proximal muscles. Electrode tracks extending medially from the medial arm of the proximal muscle representation evoked trunk and hindlimb responses. No distal or proximal muscle poststimulus effects were found in this region. These results argue against the existence of a second, major noncontiguous distal or proximal forelimb representation located medially within the macaque M1 representation.
Propagation of Neocortical Inputs in the Perirhinal Cortex
Authors: Martina Marzia , Royer Sébastien , Paré Denis
Published: April 2018

The perirhinal area is a rostrocaudally oriented strip of cortex in which lesions produce memory and perceptual impairments. It receives topographically organized transverse projections from associative neocortical areas and is endowed with intrinsic longitudinal connections that could distribute neocortical inputs in the rostrocaudal axis. In search of distinguishing network properties that might support perirhinal involvement in memory, we have performed whole-cell recordings in horizontal perirhinal slices with preserved transverse neocortical links and intrinsic longitudinal connections. Neocortical stimulation sites in rostrocaudal register with regular spiking perirhinal neurons elicited a sequence of excitatory and inhibitory synaptic potentials. In contrast, apparently pure excitatory responses were observed when the stimulating and recording sites were separated by ≥1 mm in the rostrocaudal axis. This suggested that adjacent and distant neocortical stimuli influence regular spiking perirhinal neurons by pathways that respectively form and do not form synapses with inhibitory interneurons. In keeping with this, presumed interneurons did not respond to distant neocortical stimuli. These results suggest that neocortical inputs recruit perirhinal inhibitory interneurons located at the same transverse level, limiting the depolarization of principal perirhinal cells. In contrast, distant neocortical inputs only evoke excitation because longitudinal perirhinal pathways do not engage inhibitory interneurons. This leads us to suggest that the perirhinal network is biased to favor Hebbian-like associative interactions between coincident and spatially distributed inputs.
Multiple Types of Control by Identified Interneurons in a Sensory-Activated Rhythmic Motor Pattern
Authors: Kemenes György , Staras Kevin , Benjamin Paul R.
Published: April 2018

Modulatory interneurons that can drive central pattern generators (CPGs) are considered as good candidates for decision-making roles in rhythmic behaviors. Although the mechanisms by which such neurons activate their target CPGs are known in detail in many systems, their role in the sensory activation of CPG-driven behaviors is poorly understood. In the feeding system of the molluscLymnaea, one of the best-studied rhythmical networks, intracellular stimulation of either of two types of neuron, the cerebral ventral 1a (CV1a) and the slow oscillator (SO) cells, leads to robust CPG-driven fictive feeding patterns, suggesting that they might make an important contribution to natural food-activated behavior. In this paper we investigated this contribution using a lip–CNS preparation in which feeding was elicited with a natural chemostimulant rather than intracellular stimulation. We found that despite their CPG-driving capabilities, neither CV1a nor SO were involved in the initial activation of sucrose-evoked fictive feeding, whereas a CPG interneuron, N1M, was active first in almost all preparations. Instead, the two interneurons play important and distinct roles in determining the characteristics of the rhythmic motor output; CV1a by modulating motoneuron burst duration and SO by setting the frequency of the ongoing rhythm. This is an example of a distributed system in which (1) interneurons that drive similar motor patterns when activated artificially contribute differently to the shaping of the motor output when it is evoked by the relevant sensory input, and (2) a CPG rather than a modulatory interneuron type plays the most critical role in initiation of sensory-evoked rhythmic activity.
GABAAReceptor α1 Subunit Deletion Prevents Developmental Changes of Inhibitory Synaptic Currents in Cerebellar Neurons
Authors: Vicini Stefano , Ferguson Carolyn , Prybylowski Kate , Kralic Jason , Morrow A. Leslie , Homanics Gregg E.
Published: April 2018

Developmental changes in miniature IPSC (mIPSC) kinetics have been demonstrated previously in cerebellar neurons in rodents. We report that these kinetic changes in mice are determined primarily by developmental changes in GABAAreceptor subunit expression. mIPSCs were studied by whole-cell recordings in cerebellar slices, prepared from postnatal day 11 (P11) and P35 mice. Similar to reports in granule neurons, wild-type cerebellar stellate neuron mIPSCs at P11 had slow decay kinetics, whereas P35 mIPSCs decayed five times faster. When mIPSCs in cerebellar stellate neurons were compared between wild-type (+/+) and GABAAreceptor α1 subunit-deficient (−/−) littermates at P35, we observed dramatically slower mIPSC decay rates in −/− animals. We took advantage of the greater potency of imidazopyridines for GABA current potentiation with α1 subunit-containing receptors to characterize the relative contribution of α1 subunits in native receptors on inhibitory synapses of cerebellar granule neurons. Zolpidem-induced prolongation of mIPSC decay was variable among distinct cells, but it increased during development in wild-type mice. Similarly, Zolpidem prolongation of mIPSC decay rate was significantly greater in adult +/+ mice than in knock-outs. We propose that an increased α1 subunit assembly in postsynaptic receptors of cerebellar inhibitory synapses is responsible for the fast inhibitory synaptic currents that are normally observed during postnatal development.
An NMDA Receptor ER Retention Signal Regulated by Phosphorylation and Alternative Splicing
Authors: Scott Derek B. , Blanpied Thomas A. , Swanson Geoffrey T. , Zhang Chi , Ehlers Michael D.
Published: April 2018

Formation of mature excitatory synapses requires the assembly and delivery of NMDA receptors to the neuronal plasma membrane. A key step in the trafficking of NMDA receptors to synapses is the exit of newly assembled receptors from the endoplasmic reticulum (ER). Here we report the identification of an RXR-type ER retention/retrieval motif in the C-terminal tail of the NMDA receptor subunit NR1 that regulates receptor surface expression in heterologous cells and in neurons. In addition, we show that PKC phosphorylation and an alternatively spliced consensus type I PDZ-binding domain suppress ER retention. These results demonstrate a novel quality control function for alternatively spliced C-terminal domains of NR1 and implicate both phosphorylation and potential PDZ-mediated interactions in the trafficking of NMDA receptors through early stages of the secretory pathway.