bluuebunny/crossref_metadata_2025 huggingface dataset:
Retina-derived POU-domain factor-1: a complex POU-domain gene implicated in the development of retinal ganglion and amacrine cells
Authors: Zhou H , Yoshioka T , Nathans J
Published: April 2018

A novel POU-domain protein, retina-derived POU-domain factor-1 (RPF-1), has been identified through the isolation of cDNA and genomic DNA clones. In the adult, RPF-1 is expressed only within the CNS, where its expression is restricted to the medical habenulla, to a dispersed population of neurons in the dorsal hypothalamus, and to subsets of ganglion and amacrine cells in the retina. The human RPF-1 gene spans > 125 kb and gives rise to multiple differentially spliced transcripts. In the human retina, the most abundant mRNA isoforms are derived from an alternate splicing event that inserts an evolutionarily conserved peptide of 36 amino acids into the DNA recognition helix of the POU- specific domain. In vitro, the RPF-1 POU domain lacking the insert binds to a consensus Oct-1 binding site, whereas the alternately spliced POU domain does not. RPF-1 protein first appears in the developing mouse retina at e11, where it localizes to neuroblasts that have recently migrated from the mitotic zone to the future ganglion cell layer. These data suggest that RPF-1 is likely to be involved in early steps in the differentiation of amacrine and ganglion cells.
Inhibition of protein tyrosine kinases impairs axon extension in the embryonic optic tract
Authors: Worley T , Holt C
Published: April 2018

The role of protein tyrosine kinase (PTK) activity in the development of the retinal projection was examined in vivo by applying inhibitors of cytoplasmic PTKs, herbimycin A and lavendustin A, to intact brain preparations of Xenopus embryos. The inhibitors were present during the period when retinal ganglion cell axons first navigate through the optic tract to reach their target, the optic tectum. A majority of inhibitor-treated retinal axons stalled at the beginning of the optic tract, leading to an 80% reduction in projection length at the highest doses. All inhibitor-treated axons that did extend into the optic tract exhibited normal pathfinding behavior. Tyrosine kinase assays of inhibitor-treated brains demonstrated that at doses at which retinal axon extension was severely impaired, PTK activity, including that of src family proteins, was reduced by 50–60%. Consistent with the in vivo findings, PTK inhibitors reduced neurite outgrowth from cultured retinal neurons by 70–80%. This contrasts with the strong enhancement of outgrowth induced by the same inhibitors in cultured chick ciliary ganglion neurons and suggests that the mediation of outgrowth by PTK activity may vary in different neuronal types. Inhibitor-treated growth cones cultured on laminin were larger than normal, suggesting that tyrosine phosphorylation can modulate growth cone-substrate adhesive interactions. Our results in vivo and in vitro provide complementary evidence that retinal axon outgrowth is inhibited by pharmacological blockers of PTK activity and indicate that inhibitor-sensitive PTKs normally play a role in promoting retinal neurite extension.
Chronic hyponatremia reduces survival of magnocellular vasopressin and oxytocin neurons after axonal injury
Authors: Dohanics J , Hoffman GE , Verbalis JG
Published: April 2018

Axonal injury to hypothalamic magnocellular vasopressin (AVP) and oxytocin (OT) neurons causes degeneration of a substantial subpopulation of these neurons. In this study, we investigated the influence of osmolality on this injury-induced cell death. Normonatremic, chronically hypernatremic, and chronically hyponatremic rats received pituitary stalk compression (SC), which causes degeneration of AVP and OT terminals in the neurohypophysis. Twenty-one days after SC, rats were perfused and hypothalami were serially sectioned and alternately stained for AVP-neurophysin and OT- neurophysin immunoreactivities. Normonatremic and hypernatremic rats exhibited a triphasic pattern of water intake after SC, with peak intakes 3 times higher than those exhibited by sham-operated normonatremic rats. In contrast, hyponatremic SC rats exhibited peak water intakes of 600 ml/24 hr, approximately 9–10 times the water intakes of sham-operated normonatremic rats. In normonatremic rats, SC caused degeneration of 65% of the AVP neuron population in the SON and 73% in the PVN, but only 31% of the OT neuron population in the SON and 35% in the PVN. Similar results were found in hypernatremic rats after SC. However, in hyponatremic rats SC caused degeneration of 97% of the AVP neuron population in the SON and 93% in the PVN, and 90% of the OT neuron population in the SON and 84% in the PVN. Our results, therefore, demonstrate that injury-induced degeneration of magnocellular AVP and OT neurons is markedly exacerbated by chronic hypo-osmolar conditions, but neuronal survival is not enhanced by chronic hyperosmolar conditions.
Upregulation of GABAACurrent by Astrocytes in Cultured Embryonic Rat Hippocampal Neurons
Authors: Liu Qi-Ying , Schaffner Anne E. , Li Yong-Xin , Dunlap Veronica , Barker Jeffery L.
Published: April 2018

Embryonic rat hippocampal neurons were cultured on poly-d-lysine (PDL) or a monolayer of postnatal cortical astrocytes to reveal putative changes in neuronal physiology that involve astrocyte-derived signals during the first 4 d of culture. GABA-induced Cl−current (IGABA) was quantified using outside-out and whole-cell patch-clamp recordings beginning at 30 min, when cells had become adherent. The amplitude and density (current normalized to membrane capacitance) of IGABAin neurons grown on astrocytes became statistically greater than that recorded in neurons grown on PDL after 2 hr in culture (HIC). Although the current density remained unchanged in neurons on astrocytes, that in neurons on PDL decreased and became statistically lower beginning after 2 HIC. The differences in amplitude and density of IGABAin the two groups of neurons were maintained during the 4 d experiment. The upregulation effect of astrocytes on neuronal IGABArequired intimate contact between the neuronal cell body and underlying astrocytes. Suppression of spontaneous Cac2+elevations in astrocytes by bis(2-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid that was loaded intracellularly decreased their modulatory effects on IGABA. IGABAin all cells was blocked completely by bicuculline and exhibited virtually identical affinity constants, Hill coefficients, and potentiation by diazepam in the two groups. Outside-out patch recordings revealed identical unitary properties of IGABAin the two groups. More channels per unit of membrane area could explain the astrocyte enhancement of IGABA. The results reveal that cortical astrocytes potentiate IGABAin hippocampal neurons in a contact-dependent manner via a mechanism involving astrocyte Cac2+elevation.
Glutamate Responses of Bipolar Cells in a Slice Preparation of the Rat Retina
Authors: Euler Thomas , Schneider Horst , Wässle Heinz
Published: April 2018

Whole-cell currents from >70 voltage-clamped bipolar cells were recorded in a slice preparation of the rat retina. The recorded cells were identified and classified by intracellular staining with Lucifer yellow. Glutamate, the specific agonists (±)-2-amino-4-phosphonobutyric acid (AP-4) and kainate (KA), and the antagonist 6-cyanoquinoxaline-2,3-dione (CNQX) were applied. The cells could be isolated from presynaptic influences by the co-application of bicuculline, strychnine, and cobalt ions. Responses to AP-4 were elicited only from bipolar cells with axons stratifying in the inner part of the inner plexiform layer (IPL). AP-4 caused an outward current in these cells attributable to the closure of nonspecific cation channels. Responses to kainate representing a direct action of the drug on the recorded cells were observed only in bipolar cells with axons stratifying in the outer part of the IPL. KA caused a CNQX-sensitive inward current in these cells, associated with openings of nonspecific cation channels. The results predict that cone bipolar (CB) cells with axons terminating in the outer IPL are OFF-bipolars, whereas those with axons terminating in the inner IPL are ON-bipolars. Most of the cells expressed GABA-gated Cl−conductances. In rod bipolar and in some CB cells, only part of the GABA-induced currents could be blocked by the application of bicuculline, suggesting the presence of GABACreceptors in addition to GABAAreceptors.
Immunological Instability of Persistent Adenovirus Vectors in the Brain: Peripheral Exposure to Vector Leads to Renewed Inflammation, Reduced Gene Expression, and Demyelination
Authors: Byrnes Andrew P. , MacLaren Robert E. , Charlton Harry M.
Published: April 2018

Nonreplicating adenovirus vectors are being developed as vehicles for the delivery of therapeutic genesin vivo. Whereas in many organs an antiviral T cell response eliminates the vector and damages local tissue, when adenovirus vectors are injected into the brain the subsequent immune attack can be ineffective, allowing the vector to persist.

In the present study, E1-deleted human adenovirus vectors were injected into the caudate nucleus of rats. Two months later, expression of protein from the vector was still evident and little inflammation was seen. A subcutaneous injection of adenovirus vector at this time, however, led within 2 weeks to severe mononuclear inflammation and microglial activation in the caudate. This caused local demyelination and a decrease in detectable protein expression from the vector. Interestingly, intense microglial activation and numerous lymphocytes and monocytes were also seen in brain areas containing neurons capable of retrogradely transporting the adenovirus vector from the caudate. Control experiments established that this inflammation in distant brain areas was not a nonspecific consequence of degeneration.

These experiments demonstrate that although adenovirus vectors can persist in the brain without causing chronic inflammation, they remain the potential target of a damaging cell-mediated immune response brought about by a subsequent peripheral exposure to vector. The finding of lymphocytes in brain areas that project to the caudate further shows that viral antigens that are retrogradely transported by neurons can also be the target of a T cell attack.
Covert Orienting of Attention in the Rat and the Role of Striatal Dopamine
Authors: Ward Nick M. , Brown Verity J.
Published: April 2018

Attention can be directed to a location in the absence of overt signs of orienting, a phenomenon termed “covert orienting.” The ability to orient attention covertly has been well documented in humans, but recent progress has been made with the operational definition of the processes involved in covert orienting. Reaction times to visual targets are quickened when attention is drawn to the location of the subsequent target, and processes such as disengagement, maintenance, and movement of attention can be dissociated by using this method. The possible involvement of striatal dopamine in covert orienting is disputed, with conflicting reports of deficits in covert orienting in patients with Parkinson’s disease. To examine the significance of dopamine in the striatum in attentional processes, a test of covert orienting, analogous to that used in humans, was devised for the rat. Unilateral dopamine-depleting lesions of the striatum resulted in increases in mean reaction times contralateral to the side of the lesion, but reaction times did not change differentially as a function of the requirements to maintain, disengage, or shift attention. These findings add additional support to the hypothesis that the deficit that appears as hemineglect observed after striatal damage reflects a motor impairment rather than damage in neural systems underlying mechanisms for directing attention.
Conditioned and Unconditioned Stimuli Increase Frontal Cortical and Hippocampal Acetylcholine Release: Effects of Novelty, Habituation, and Fear
Authors: Acquas Elio , Wilson Catriona , Fibiger Hans C.
Published: April 2018

Recent evidence showing that basal forebrain cholinergic neurons with projections to the frontal cortex and hippocampus are activated by behaviorally salient stimuli suggests that these neurons are involved in arousal and/or attentional processes. We sought in the present experiments to test this hypothesis by examining whether unconditioned stimuli (a tone and flashing light) that normally increase cortical and hippocampal acetylcholine (ACh) release would fail to do so after habituation (i.e., repeated presentation with no programmed consequences). In addition, the extent to which presentation of these stimuli would continue to increase ACh release when they had previously been paired with an aversive stimulus was investigated. Three experimental groups were used: habituation, novel stimuli, and conditioned fear. Subjects in each of these groups were placed in a training apparatus for twelve 200 min sessions. While the habituation group received extensive exposure to the tone and light during the training sessions, subjects in the novel stimuli group were placed in the apparatus but were never exposed to the tone or light during these sessions. The conditioned fear group was treated identically to the habituation group, with the addition that the tone and light were paired with footshock. On completion of these training schedules, all animals were implanted with microdialysis probes in the frontal cortex and hippocampus. Two days later, they were placed in the apparatus and the tone and light were presented to all subjects during microdialysis. In the novel stimuli group, the tone and light (unconditioned stimuli) produced significant increases in frontal cortical and hippocampal ACh release. Similarly, in the conditioned fear group, presentation of the tone and light (conditioned stimuli) also significantly increased ACh release in frontal cortex and hippocampus. In contrast, in the habituation group the tone and light failed to significantly enhance ACh release in either structure. During the test session, the tone and light elicited a variety of arousal- and fear-related behaviors in the novel stimuli and conditioned fear groups. In contrast, subjects in the habituation group generally failed to respond to these stimuli.

These data indicate that cortically and hippocampally projecting basal forebrain cholinergic neurons are activated by conditioned and unconditioned stimuli that produce arousal in rats (novelty or conditioned fear). In contrast, presentation of these stimuli to habituated animals fails to enhance ACh release. These findings are consistent with a growing body of information indicating that ACh release in the cortex and hippocampus is reliably activated by behaviorally relevant stimuli. They also provide strong support for the hypothesis that cholinergic neurons in the basal forebrain are involved in arousal and/or attentional processes.
gp120-Induced Neurotoxicity in Hippocampal Pyramidal Neuron Cultures: Protective Action of TGF-β1
Authors: Meucci Olimpia , Miller Richard J.
Published: April 2018

We found that TGF-β1, a cytokine that previously has been reported to have neuroprotective effects, was able to prevent the toxicity induced by the HIV-1 coat protein gp120 in hippocampal pyramidal neuron cultures. In the presence of glia, gp120 induced time- and dose-dependent cell death, which was more pronounced in mature (7–19 d in culture) than in young neurons (2–7 d in culture). Staining with nuclear dyes (propidium iodide and Hoechst 33342),in situdetection of DNA fragments, and DNA analysis on agarose gels indicated that apoptosis was mainly responsible for the death caused by the viral protein. However, after several days of treatment, death-displaying necrotic features also occurred. Neurotoxicity induced by gp120 was dependent on the activation of NMDA receptors and required the presence of glia as well as new protein synthesis. Thus, the effect of gp120 was abolished by the NMDA receptor antagonist APV and partially reduced by cycloheximide. Only modest neurotoxicity was observed in pure neuronal cultures deprived of the glia feeder layer. Fura-2-based videoimaging showed that treatment with gp120 enhanced the ability of NMDA to increase neuronal [Ca2+]i. The impairment of neuronal Ca2+homeostasis was prevented completely by TGF-β1. Therefore, it is likely that the neuroprotective action of the cytokine is attributable to its ability to stabilize neuronal [Ca2+]i.
The Role of K+Currents in Frequency-Dependent Spike Broadening inAplysiaR20 Neurons: A Dynamic-Clamp Analysis
Authors: Ma Minghong , Koester John
Published: April 2018

The R20 neurons ofAplysiaexhibit frequency-dependent spike broadening. Previously, we had used two-electrode voltage clamp to examine the mechanisms of this spike broadening (Ma and Koester, 1995). We identified three K+currents that mediate action-potential repolarization: a transient A-type K+current (IAdepol), a delayed rectifier current (IK-V), and a Ca2+-sensitive K+current (IK-Ca). A major constraint in that study was the lack of completely selective blockers forIAdepolandIK-V, resulting in an inability to assess directly the effects of their activation and inactivation on spike broadening. In the present study, the dynamic-clamp technique, which employs computer simulation to inject biologically realistic currents into a cell under current-clamp conditions (Sharp et al., 1993a,b), was used either to blockIAdepolorIK-Vor to modify their inactivation properties.

The data in this paper, together with earlier results, lead to the following hypothesis for the mechanism of spike broadening in the R20 cells. As the spike train progresses, the primary responsibility for spike repolarization gradually shifts fromIAdepoltoIK-VtoIK-Ca. This sequence can be explained on the basis of the relative rates of activation and inactivation of each current with respect to the constantly changing spike durations, the cumulative inactivation ofIAdepolandIK-V, and the progressive potentiation ofIK-Ca. Positive feedback interactions between spike broadening and inactivation contribute to the cumulative inactivation of bothIAdepolandIK-V. The data also illustrate that when two or more currents have similar driving forces and partially overlapping activation characteristics, selectively blocking one current under current-clamp conditions can lead to a significant underestimate of its normal physiological importance.
Kinetics of NMDA Channel Opening
Authors: Dzubay Jeffrey A. , Jahr Craig E.
Published: April 2018

The period required for NMDA channels to open for the first time after agonist binding (the first latency) was estimated in outside-out patch recordings from rat hippocampal neurons using fast-application techniques and the open channel blocker MK-801. In the presence of MK-801, brief applications ofl-glutamate or the low-affinity agonistl-cysteate resulted in a similar amount of block despite the much shorter period of channel activation byl-cysteate. A brief coapplication ofl-glutamate and MK-801 resulted in a block similar to that found with an application ofl-glutamate in a background of MK-801. These results, along with our findings that MK-801 does not block desensitized receptors, indicate that NMDA channels have a mean first latency of ∼10 msec, consistent with a peak open probability near 0.3. If NMDA channels at synapses behave similarly, relatively few channels would be required to produce the postsynaptic calcium transient associated with synaptic plasticity and developmental regulation.
Stimulus Specificity of Phase-Locked and Non-Phase-Locked 40 Hz Visual Responses in Human
Authors: Tallon-Baudry Catherine , Bertrand Olivier , Delpuech Claude , Pernier Jacques
Published: April 2018

Considerable interest has been raised by non-phase-locked episodes of synchronization in the gamma-band (30–60 Hz). One of their putative roles in the visual modality is feature-binding. We tested the stimulus specificity of high-frequency oscillations in humans using three types of visual stimuli: two coherent stimuli (a Kanizsa and a real triangle) and a noncoherent stimulus (“no-triangle stimulus”). The task of the subject was to count the occurrences of a curved illusory triangle. A time–frequency analysis of single-trial EEG data recorded from eight human subjects was performed to characterize phase-locked as well as non-phase-locked high-frequency activities.

We found an early phase-locked 40 Hz component, maximal at electrodes Cz–C4, which does not vary with stimulation type. We describe a second 40 Hz component, appearing around 280 msec, that is not phase-locked to stimulus onset. This component is stronger in response to a coherent triangle, whether real or illusory: it could reflect, therefore, a mechanism of feature binding based on high-frequency synchronization. Because both the illusory and the real triangle are more target-like, it could also correspond to an oscillatory mechanism for testing the match between stimulus and target. At the same latencies, the low-frequency evoked response components phase-locked to stimulus onset behave differently, suggesting that low- and high-frequency activities have different functional roles.
Apical Dendritic Location of Slow Afterhyperpolarization Current in Hippocampal Pyramidal Neurons: Implications for the Integration of Long-Term Potentiation
Authors: Sah Pankaj , Bekkers John M.
Published: April 2018

Trains of action potentials in hippocampal pyramidal neurons are followed by a prolonged afterhyperpolarization (AHP) lasting several seconds, which is attributable to the activation of a slow calcium-activated potassium current (sIAHP). Here we examine the location of sIAHPon CA1 pyramidal neurons by comparing it with two GABAergic inhibitory postsynaptic currents (IPSCs) with known somatic and dendritic locations. Whole-cell patch-clamp recordings were made from CA1 pyramidal neurons in acute hippocampal slices. Stepping the membrane potential at the peak of sIAHPproduced a relaxation (“switchoff”) of the AHP current with a time constant of 7.4 ± 0.4 msec (mean ± SEM). The switchoff time constants for somatic and dendritic GABAAIPSCs were 3.5 ± 0.5 msec and 8.8 ± 0.3 msec, respectively. This data, together with cable modeling, indicates that active sIAHPchannels are distributed over the proximal dendrites within ∼200 μm of the soma. Excitatory postsynaptic potentials (EPSPs) evoked in stratum (s.) radiatum had their amplitudes shunted more by the AHP than did EPSPs evoked in s. oriens, suggesting that active AHP channels are restricted to the apical dendritic tree. Blockade of the AHP during a tetanus, which in control conditions elicited a decremental short-term potentiation (STP), converted STP to long-term potentiation (LTP). Thus, activation of the AHP increases the threshold for induction of LTP. These results suggest that in addition to its established role in spike frequency adaptation, the AHP works as an adjustable gain control, variably hyperpolarizing and shunting synaptic potentials arising in the apical dendrites.
The Fibroblast Growth Factor Receptor-1 Is Necessary for the Induction of Neurite Outgrowth in PC12 Cells by aFGF
Authors: Lin Hsien-Yi , Xu Jingsong , Ornitz David M. , Halegoua Simon , Hayman Michael J.
Published: April 2018

The PC12 subclone, fnr-PC12 cells, is defective in neurite outgrowth in response to acidic fibroblast growth factor (aFGF); however, its response to nerve growth factor (NGF) is normal. Examination of the expression of FGF receptors (FGFRs) revealed that although PC12 cells express FGFR-1, -3, and -4, fnr-PC12 cells have a reduced level of expression of FGFR-1 but not FGFR-3 and -4. Transfection of FGFR-1 into fnr-PC12 cells efficiently restored aFGF-induced neurite outgrowth, whereas transfection of FGFR-3 was much less efficient. Transfection of a chimeric receptor consisting of the extracellular domain of FGFR-3 fused to the transmembrane and intracellular domain of FGFR-1, termed FR31b, efficiently restored aFGF-induced neurite outgrowth. This demonstrates that the difference between these two receptors in their ability to induce neurite outgrowth is attributable to differences in the signaling capacity of their cytoplasmic domains. Activation of the chimeric receptor by aFGF induced a stronger and more persistent increase in the tyrosine phosphorylation of cellular proteins than did activation of FGFR-3 alone. In particular, the activation of MAP kinase by FR31b was more persistent than when activated by FGFR-3. This difference in signaling potential of FGFR-1 and -3 in fnr-PC12 cells may account for the difference in the potential for induction of neurite outgrowth. These results demonstrate that FGF-induced neurite outgrowth in PC12 cells occurs mainly via FGFR-1 and not via the other FGFRs expressed in these cells.
Divergent Projections from the Anterior Inferotemporal Area TE to the Perirhinal and Entorhinal Cortices in the Macaque Monkey
Authors: Saleem K. S. , Tanaka K.
Published: April 2018

Area TE is located at the latter part of the ventral visual cortical pathway, which is essential for visual recognition of objects. TE projects heavily to the perirhinal region, which is important for visual recognition memory of objects. To study the organization of projections from TE to the perirhinal (areas 35 and 36) and entorhinal (area 28) cortices, we made focal injections ofPhaseolus vulgarisleucoagglutinin (PHA-L) and large injections of biocytin or wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into anterior levels of TE in macaque monkeys. Injections of PHA-L into the ventral part of anterior TE (TEav) resulted in labeling of terminals distributed widely in area 36 (approximately one-half of its total extent), although the injection sites were limited to 0.7 mm in width. The labeled terminals tended to be denser in the medial part of area 36. There was less dense but definite labeling in area 35 and the lateral part of area 28. After a single injection of PHA-L or WGA-HRP into the dorsal part of anterior TE (TEad), labeled terminals were confined to a small region at the lateral part of area 36 (less than one-tenth of its total extent). The projections to areas 35 and 28 from TEad were much sparser than those from TEav.

The different patterns of projections to the perirhinal and entorhinal cortices, together with previously reported differences in their afferent and other efferent connections, suggest the functional differentiation between TEav and TEad. The divergent projection from TEav to the perirhinal cortex may facilitate the association of different visual features in the perirhinal cortex.
Protein Kinase and G-Protein Regulation of Ca2+Currents inHermissendaPhotoreceptors by 5-HT and GABA
Authors: Yamoah Ebenezer N. , Crow Terry
Published: April 2018

The effects of serotonin (5-HT) and GABA on two Ca2+currents, a transient low-voltage-activated current (tLVA) and a sustained high-voltage-activated current (sHVA) were examined in isolated photoreceptors ofHermissenda. The sHVA current was blocked by 5-HT and reduced by activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate. The effects of 5-HT were transiently reversed by staurosporine and partially blocked by the PKC inhibitor peptide [PKC(19–36)]. GABA enhanced both the tLVA and sHVA currents at low concentrations (5 nmto 5 μm) and reduced the sHVA current at high concentrations (>10 μm). The GABA-mediated enhancement of the Ca2+current at low concentrations was sensitive to block by picrotoxin. The protein kinase A (PKA) inhibitor peptide [PKI(6–22)amide] blocked enhancement of both Ca2+currents produced by cAMP analogs and GABA, suggesting that the effects at low concentrations may be PKA mediated. Caged GTP-γ-S released by flash photolysis reduced the sHVA current, and pretreatment of the photoreceptors with pertussis toxin blocked the effects of higher concentrations of GABA, indicating that at higher concentrations, the effects may be G-protein mediated.
GABABReceptors, Monoamine Receptors, and Postsynaptic Inositol Trisphosphate-Induced Ca2+Release Are Involved in the Induction of Long-Term Potentiation at Visual Cortical Inhibitory Synapses
Authors: Komatsu Yukio
Published: April 2018

γ-Aminobutyric acid (GABA)Areceptor-mediated inhibitory synaptic transmission in visual cortex undergoes long-term potentiation (LTP), which is input-specific and associative. The present study, conducted under a blockade of ionotropic glutamate receptors, demonstrates an induction mechanism of LTP considerably different from those of associative LTP at excitatory synapses. Inhibitory responses of layer V cells evoked by layer IV stimulation were studied in developing rat visual cortex slices by using intracellular and whole-cell recording methods. LTP induction was prevented by the application of an antagonist for GABABreceptors but not for GABAAor metabotropic glutamate receptors. Inhibition of postsynaptic G-proteins, phospholipase C, inositol trisphosphate (IP3) receptors, or Ca2+increase prevented the generation of LTP, as did the blockade of GABABreceptors.

In rat cerebral cortex, GABABreceptor activation is not known to affect the IP3level by itself. However, it facilitates IP3formation induced by the activation of α1adrenoceptors, which are believed to be located postsynaptically. Accordingly, I examined the involvement of these and other amine receptors, including histamine H1, muscarinic acetylcholine, and serotonin 5-HT2receptors, all of which are coupled to IP3formation. Only the blockade of α1adrenoceptors or serotonin 5-HT2receptors prevented LTP induction in most, but not all, of the cells. These results suggest that LTP induction requires the activation of postsynaptic GABABreceptors and that its effect is mediated at least partly by facilitation of the monoamine-induced IP3formation, which then causes Ca2+release from the internal stores in postsynaptic cells.
Peripheral Neuropathy in Mice Transgenic for a HumanMDR3 P-Glycoprotein Mini-Gene
Authors: Smit Jaap J. M. , Baas Frank , Hoogendijk Jessica E. , Jansen Gerard H. , van der Valk Martin A. , Schinkel Alfred H. , Berns Anton J. M. , Acton Dennis , Nooter Kees , Burger Herman , Smith Sander J. , Borst Piet
Published: April 2018

We have generated mice transgenic for a humanMDR3 mini-gene, under control of a hamstervimentinpromoter. Expression of theMDR3 transgene was found in mesenchymal tissues, peripheral nerves, and the eye lens. These MDR3 transgenic mice have a slowed motor nerve conduction and dysmyelination of their peripheral nerves. An extensive dysmyelination in some transgenic strains results in a severe peripheral neuropathy with paresis of the hind legs. How expression of theMDR3 transgene causes these abnormalities is unknown. TheMDR3 gene encodes a large glycosylated plasma membrane protein with multiple transmembrane spanning domains, which are involved in the translocation of the phospholipid phosphatidylcholine through the hepatocyte canalicular membrane. The ability of the MDR3 P-glycoprotein to alter phospholipid distribution in the plasma membrane of Schwann cells may cause the damage. It is also possible, however, that the presence of a large glycoprotein in the cell membrane may be sufficient to severely disturb myelination of peripheral nerves.
Trans-Synaptic Stimulation of Cortical Acetylcholine Release after Partial 192 IgG-Saporin-Induced Loss of Cortical Cholinergic Afferents
Authors: Fadel Jim , Moore Holly , Sarter Martin , Bruno John P.
Published: April 2018

Environmental and pharmacological stimulation of cortical acetylcholine (ACh) efflux was determined in rats sustaining partial deafferentation of cortical cholinergic inputs. Rats were bilaterally infused with the selective cholinotoxin 192 IgG-saporin (0.005 μg/0.5 μl/site) into the frontoparietal cortex. In the first experiment, animals were pretrained to associate the onset of darkness with presentation of a palatable fruit cereal reward. The ability of this stimulus to enhance frontoparietal ACh efflux alone, and with the benzodiazepine receptor (BZR) weak inverse agonist ZK 93,426 (1.0 or 5.0 mg/kg, i.p.), was determined in lesioned and sham-lesioned rats. Intracortical infusions of 192 IgG-saporin reduced basal cortical ACh efflux by 47% of sham-lesioned values, consistent with reductions in the density of AChE-positive fibers. In spite of this deafferentation, ZK 93,426 produced a transient potentiation of the cortical ACh efflux induced by the darkness/cereal stimulus similar to that observed in control animals. In the second experiment, the ability of the more efficacious BZR partial inverse agonist FG 7142 (8.0 mg/kg, i.p.) to enhance basal cortical ACh efflux was compared in lesioned and sham-lesioned rats. Again, lesioned rats exhibited an increase comparable to control animals after FG 7142. This drug-induced stimulation of cortical ACh efflux was comparably and completely blocked in both groups by co-perfusion with tetrodotoxin (1.0 μm). These results suggest similarities in the modulation of cortical ACh efflux in intact and partially deafferented rats and indicate the potential of BZR inverse agonists for restoring transmission in animals with partial loss of cortical cholinergic inputs.
An Opioidergic Cortical Antinociception Triggering Site in the Agranular Insular Cortex of the Rat that Contributes to Morphine Antinociception
Authors: Burkey Adam R. , Carstens Earl , Wenniger Julia J. , Tang Jinwen , Jasmin L.
Published: April 2018

We report an anatomically defined opioid-responsive site in the rostral agranular insular cortex (RAIC) of the rat and characterize the antinociception produced by morphine acting within this region. Immunohistochemistry for the μ-opioid receptor identified a discretely localized cluster of densely labeled dendrite-like processes in the agranular insular cortex. The antinociceptive effect of morphine microinjected unilaterally into this area was evaluated using the formalin test. Antinociception was observed in both ipsilateral and contralateral hindpaws. Local pretreatment with naltrexone in the RAIC blocked the antinociception of local morphine injection, confirming that morphine was acting at an opioid receptor. Unilateral injection of naloxone methiodide into the RAIC reversed the behavioral antinociception of systemic morphine bilaterally in the formalin test. Evidence for a descending inhibitory mechanism acting on spinal nociceptive neurons was obtained by monitoring noxious stimulus-inducedc-fosexpression in rats having undergone formalin testing and by electrophysiological recording of single units in the lumbar dorsal horn after localized application of morphine into the RAIC. A significant reduction in the number of Fos-like immunoreactive neurons was found ipsilateral to the formalin stimulus in nociresponsive areas of the dorsal horn after on-site injections of morphine into the RAIC. Electrophysiological recording of nociresponsive dorsal horn neurons demonstrated a naloxone-reversible reduction in noxious thermal stimulus-evoked firing after morphine injection into this same area. These results suggest that the RAIC contributes to opioid-receptor-mediated antinociception after either local or systemic morphine administration and that these effects may be associated with an increased descending inhibition of dorsal horn neurons.
Release of [3H]-d-Aspartate from Primary Astrocyte Cultures in Response to Raised External Potassium
Authors: Rutledge Eric M. , Kimelberg Harold K.
Published: April 2018

There are significant Ca2+-independent increases in extracellular glutamate and aspartate during various CNS insults such as ischemia and anoxia. However, the cellular sources of such presumed nonvesicular excitatory amino acid (EAA) release have not been established. To further explore potential mechanisms and sites for EAA release, we studied the release of preloaded [3H]-d-aspartate from primary cultured astrocytes prepared from the cerebral cortices of rat pups. Two phases of release were seen in response to raised KCl. The first phase was small and transient, and the second phase was slower and increased progressively. The initial phase of [3H]-d-aspartate release was greatly enhanced by ouabain pretreatment and was inhibited when astrocytes were preexposed to the EAA transport inhibitor threo-hydroxy β-aspartic acid (THBA). Neither of these manipulations affected the second release component. The second phase of release was inhibited by an anion channel blocker, L-644,711, which is known to inhibit hypotonic swelling-induced release of EAA. Ouabain also resulted in the first phase of release occurring at lower [K+]o. Omission of Ca2+had no effect on either phase of [3H]-d-aspartate release. These results support the hypothesis that the first component of release in cultured astrocytes is a reversal of the glutamate transporter, and the second component is a result of high KCl-induced swelling. Because marked increases in [K+]oare well established in CNS pathologies such as ischemia, such release may represent a significant source for the increased extracellular EAAs seen in such conditions.
Translocation of RNA Granules in Living Neurons
Authors: Knowles Roger B. , Sabry James H. , Martone Maryann E. , Deerinck Thomas J. , Ellisman Mark H. , Bassell Gary J. , Kosik Kenneth S.
Published: April 2018

Sorting of RNAs to specific subcellular loci occurs in diverse settings from fly oocytes to mammalian neurons. Using the membrane-permeable nucleic acid stain SYTO 14, we directly visualized the translocation of endogenous RNA in living cells. Labeled RNA was distributed nonrandomly as discrete granules in neuronal processes. The labeled granules colocalized with poly(A+) mRNA, with the 60S ribosomal subunit, and with elongation factor 1α, suggesting that granules represent a translational unit. A subset of labeled granules colocalized with β-actin mRNA. Correlative light and electron microscopy indicated that the fluorescent granules corresponded to clusters of ribosomes at the ultrastructural level. Poststaining of sections with heavy metals confirmed the presence of ribosomes within these granules. In living neurons, a subpopulation of RNA granules was motile during the observation period. They moved at an average rate of 0.1 μm/sec. In young cultures their movements were exclusively anterograde, but after 7 d in culture, one-half of the motile granules moved in the retrograde direction. Granules in neurites were delocalized after treatment with microtubule-disrupting drugs. These results raise the possibility of a cellular trafficking system for the targeting of RNA in neurons.
Dynamics of Mismatch Correction in the Hippocampal Ensemble Code for Space: Interaction between Path Integration and Environmental Cues
Authors: Gothard Katalin M. , Skaggs William E. , McNaughton Bruce L.
Published: April 2018

Populations of hippocampal neurons were recorded simultaneously in rats shuttling on a track between a fixed reward site at one end and a movable reward site, mounted in a sliding box, at the opposite end. While the rat ran toward the fixed site, the box was moved. The rat returned to the box in its new position. On the initial part of all journeys, cells fired at fixed distances from the origin, whereas on the final part, cells fired at fixed distances from the destination. Thus, on outward journeys from the box, with the box behind the rat, the position representation must have been updated by path integration. Farther along the journey, the place field map became aligned on the basis of external stimuli. The spatial representation was quantified in terms of population vectors. During shortened journeys, the vector shifted from an alignment with the origin to an alignment with the destination. The dynamics depended on the degree of mismatch with respect to the full-length journey. For small mismatches, the vector moved smoothly through intervening coordinates until the mismatch was corrected. For large mismatches, it jumped abruptly to the new coordinate. Thus, when mismatches occur, path integration and external cues interact competitively to control place-cell firing.

When the same box was used in a different environment, it controlled the alignment of a different set of place cells. These data suggest that although map alignment can be controlled by landmarks, hippocampal neurons do not explicitly represent objects or events.
Synaptic Inputs to ON Parasol Ganglion Cells in the Primate Retina
Authors: Jacoby Roy , Stafford Donna , Kouyama Nobuo , Marshak David
Published: April 2018

In primates, the retinal ganglion cells that project to the magnocellular layers of the lateral geniculate nucleus have distinctive responses to light, and one of these has been identified morphologically as the parasol ganglion cell. To investigate their synaptic connections, we injected parasol cells with Neurobiotin in lightly fixed baboon retinas. The five ON-center cells we analyzed by electron microscopy received ∼20% of their input from bipolar cells. The major synaptic input to parasol cells was from amacrine cells via conventional synapses and, in this respect, they resembled α ganglion cells of the cat retina. We also found the gap junctions between amacrine cells and parasol ganglion cells that had been predicted from tracer-coupling experiments. To identify the presynaptic amacrine cells, ON-center parasol cells were injected with Neurobiotin and Lucifer yellow in living macaque retinas, which were then fixed and labeled by immunofluorescence. Two kinds of amacrine cells were filled with Neurobiotin via gap junctions: a large, polyaxonal cell containing cholecystokinin and a smaller one without cholecystokinin. There were also appositions between cholecystokinin-containing amacrine cell processes and parasol cell dendrites. Cholinergic amacrine cell processes often followed parasol cell dendrites and made extensive contacts. In other mammals, the light responses of polyaxonal amacrine cells like these and cholinergic amacrine cells have been recorded, and the effects of acetylcholine and cholecystokinin on ganglion cells are known. Using this information, we developed a model of parasol cells that accounts for some properties of their light responses.
Costorage and Corelease of Modulatory Peptide Cotransmitters with Partially Antagonistic Actions on the Accessory Radula Closer Muscle ofAplysia californica
Authors: Vilim F. S. , Price D. A. , Lesser W. , Kupfermann I. , Weiss K. R.
Published: April 2018

Many neurons that contain a classical neurotransmitter also contain modulatory peptides, but it has been difficult to establish unequivocally that these peptides are functional cotransmitters. Here, we provide evidence for functional cotransmission in a neuromuscular system ofAplysia. Using immunocytochemical techniques, we localize members of two peptide families, the small cardioactive peptides (SCPs) and the buccalins (BUCs), to a single subset of dense-core vesicles in the terminals of the cholinergic motorneuron B15. We describe a new preparation and method for the direct detection of released peptides and show that the SCPs and BUCs are released when neuron B15 is intracellularly stimulated. Consistent with their subcellular localization, the SCPs and BUCs are released in a stoichiometric ratio that is constant across conditions that change the absolute amount of peptides released. Peptide release is calcium-dependent but does not require muscle contractions. Thus, the release cannot be attributed to a displacement of peptides that may be present in the extracellular space. In previous studies, we characterized the physiological firing patterns of neuron B15. Here, we simulate these firing patterns and show that peptide release occurs. Additionally, we find that significant quantities of material are released under behaviorally relevant conditions. We find that concentrations of released peptides in the muscle are in the concentration range in which exogenously applied peptides exert characterized modulatory actions on muscle contractions. Together, our findings provide strong support for the hypothesis that peptides contained in neuron B15 are functional cotransmitters.
Endogenous Activation of μ and δ-1 Opioid Receptors Is Required for Long-Term Potentiation Induction in the Lateral Perforant Path: Dependence on GABAergic Inhibition
Authors: Bramham Clive R. , Sarvey John M.
Published: April 2018

Opioid peptides costored with glutamate have emerged as powerful regulators of long-term potentiation (LTP) induction in several hippocampal pathways. The objectives of the present study were twofold: (1) to identify which opioid receptor types (μ, δ, or κ) regulate LTP induction at lateral perforant path–granule cell synapses and (2) to test the hypothesis that endogenous opioids regulate LTP induction via modulation of GABAergic inhibition. LTP of lateral perforant path-evoked field EPSPs was induced selectively by high-frequency stimulation applied to the outer third of the molecular layer of the dentate gyrus of rat hippocampal slices. No changes in medial perforant path responses occurred. LTP was blocked when high-frequency stimulation was applied in the presence of the μ receptor antagonist CTAP, the selective δ-1 receptor antagonist BNTX, or the δ-1 and δ-2 receptor antagonist naltrindole. By contrast, the κ-1 opioid receptor antagonist NBNI had no effect on LTP induction. The role of GABAergic inhibition was investigated by comparing the effect of naloxone on LTP induction in slices maintained in standard buffer and picrotoxin-containing buffer. Naloxone blocked LTP in standard buffer, whereas normal LTP was induced in picrotoxin-treated, disinhibited slices. Finally, NMDA receptor blockade completely inhibited LTP in both standard and disinhibited slices. The results show that μ and δ-1 opioid receptors regulate LTP induction and that this mechanism critically depends on GABAergic inhibition. A key issue then becomes how endogenous opioids fine-tune the activity of intact inhibitory networks in the dentate gyrus, effectively gating synaptic plasticity in specific dendritic strata.
The Influence of Auditory and Visual Distractors on Human Orienting Gaze Shifts
Authors: Corneil Brian D. , Munoz Douglas P.
Published: April 2018

We studied the influences of competing visual and auditory stimuli on horizontal gaze shifts in humans. Gaze shifts were made to visual or auditory targets in the presence of either an irrelevant visual or auditory cue. Within an experiment, the target and irrelevant cue were either aligned (enhancer condition) or misaligned (distractor condition) in space. The times of presentation of the target and irrelevant cue were varied so that the target could have been presented before the irrelevant cue, or the irrelevant cue before the target. We compared subject performance in the enhancer and distractor conditions, measuring reaction latencies and the frequency of incorrect gaze shifts. Performance differed the most when the irrelevant cue was presented before the target and differed the least when the target was presented before the irrelevant cue. Our results reveal that, in addition to the spatial and temporal register of the stimuli, the experimental context in which the stimuli are presented also influences multisensory integration: an irrelevant auditory cue influenced gaze shifts to visual targets differently than an irrelevant visual cue influenced gaze shifts to auditory targets. Furthermore, we observed patterns of influence unique to either visual or auditory irrelevant cues that occurred regardless of the modality of the target. We believe that subjects adopted a state of motor readiness that reflected the unique demands of target selection in each experiment and that this state modulated the influences of the irrelevant cue on the target.