bluuebunny/crossref_metadata_2025 huggingface dataset:
Distinct Contributions of High- and Low-Voltage-Activated Calcium Currents to Afterhyperpolarizations in Cholinergic Nucleus Basalis Neurons of the Guinea Pig
Authors: Williams Sylvain , Serafin Mauro , Mühlethaler Michel , Bernheim Laurent
Published: April 2018

The contributions made by low- (LVA) and high-voltage-activated (HVA) calcium currents to afterhyperpolarizations (AHPs) of nucleus basalis (NB) cholinergic neurons were investigated in dissociated cells. Neurons with somata >25 μmwere studied because 80% of them stained positively for choline acetyltransferase and had electrophysiological characteristics identical to those of cholinergic NB neurons previously recorded in basal forebrain slices. Calcium currents of cholinergic NB neurons first were dissected pharmacologically into an amiloride-sensitive LVA and at least five subtypes of HVA currents. Approximately 17% of the total HVA current was sensitive to nifedipine (3 μm), 35% to ω-conotoxin-GVIA (200–400 nm), 10% to ω-Agatoxin-IVA (100 nm), and 20% to ω-Agatoxin-IVA (300–500 nm), suggesting the presence of L-, N-, P-, and Q-type channels, respectively. A remaining current (R-type) resistant to these antagonists was blocked by cadmium (100–200 μm). We then assessed pharmacologically the role that LVA and HVA currents had in activating the apamin-insensitive AHP elicited by a long train of action potentials (sAHP) and the AHP evoked either by a short burst of action potentials or by a single action potential (mAHP) that is known to be apamin-sensitive. During sAHPs, ∼60% of the hyperpolarization was activated by calcium flowing through N-type channels and ∼20% through P-type channels, whereas T-, L-, and Q-type channels were not involved significantly. In contrast, during mAHPs, N- and T-type channels played key roles (∼60 and 30%, respectively), whereas L-, P-, and Q-type channels were not implicated significantly. It is concluded that in cholinergic NB neurons various subtypes of calcium channels can differentially activate the apamin-sensitive mAHP and the apamin-insensitive sAHP.
Electrophysiological Changes That Accompany Reactive GliosisIn Vitro
Authors: MacFarlane Stacey Nee , Sontheimer Harald
Published: April 2018

Anin vitroinjury model was used to examine the electrophysiological changes that accompany reactive gliosis. Mechanical scarring of confluent spinal cord astrocytes led to a threefold increase in the proliferation of scar-associated astrocytes, as judged by bromodeoxyuridine (BrdU) labeling. Whole-cell patch-clamp recordings demonstrated that current profiles differed absolutely between nonproliferating (BrdU−) and proliferating (BrdU+) astrocytes. The predominant current type expressed in BrdU−cells was an inwardly rectifying K+current (KIR; 1.3 pS/pF). BrdU−cells also expressed transient outward K+currents, accounting for less than one-third of total K+conductance (G). In contrast, proliferating BrdU+astrocytes exhibited a dramatic, approximately threefold reduction in KIR(0.45 pS/pF) but showed a twofold increase in the conductance of both transient (KA) (0.67–1.32 pS/pF) and sustained (KD) (0.42–1.10 pS/pF) outwardly rectifying K+currents, with aGKIR:GKDratio of 0.4. Relative expression ofGKIR:GKDled to more negative resting potentials in nonproliferating (−60 mV) versus proliferating astrocytes (−53 mV;p= 0.015). Although 45% of the nonproliferating astrocytes expressed Na+currents (0.47 pS/pF), the majority of proliferating cells expressed prominent Na+currents (0.94 pS/pF). Injury-induced electrophysiological changes are rapid and transient, appearing within 4 hr postinjury and, with the exception of KIR, returning to control conductances within 24 hr. These differences between proliferating and nonproliferating astrocytes are reminiscent of electrophysiological changes observed during gliogenesis, suggesting that astrocytes undergoing secondary, injury-induced proliferation recapitulate the properties of immature glial cells. The switch in predominance from KIRto KDappears to be essential for proliferation and scar repair, because both processes were inhibited by blockade of KD.
Activation of CPP32-Like Caspases Contributes to Neuronal Apoptosis and Neurological Dysfunction after Traumatic Brain Injury
Authors: Yakovlev Alexander G. , Knoblach Susan M. , Fan Lei , Fox Gerard B. , Goodnight Randyll , Faden Alan I.
Published: April 2018

We examined the temporal profile of apoptosis after fluid percussion-induced traumatic brain injury (TBI) in rats and investigated the potential pathophysiological role of caspase-3-like proteases in this process. DNA fragmentation was observed in samples from injured cortex and hippocampus, but not from contralateral tissue, beginning 4 hr after TBI and continuing for at least 3 d. Double labeling of brain with terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) and an antibody directed to neuronal nuclear protein identified apoptotic neurons with high frequency in both traumatized rat cortex and hippocampus. Cytosolic extracts from injured cortex and hippocampus, but not from contralateral or control tissue, induced internucleosomal DNA fragmentation in isolated nuclei with temporal profiles consistent with those of DNA fragmentation observedin vivo. Caspase-3 mRNA levels, estimated by semiquantitative RT-PCR, were elevated fivefold in ipsilateral cortex and twofold in hippocampus by 24 hr after TBI. Caspase-1 mRNA content also was increased after trauma, but to a lesser extent in cortex. Increased caspase-3-like, but not caspase-1-like, enzymatic activity was found in cytosolic extracts from injured cortex. Intracerebroventricular administration of z-DEVD-fmk—a specific tetrapeptide inhibitor of caspase-3—before and after injury markedly reduced post-traumatic apoptosis, as demonstrated by DNA electrophoresis and TUNEL staining, and significantly improved neurological recovery. Together, these results implicate caspase-3-like proteases in neuronal apoptosis induced by TBI and suggest that the blockade of such caspases can reduce post-traumatic apoptosis and associated neurological dysfunction.
Developmental Expression Pattern of Phototransduction Components in Mammalian Pineal Implies a Light-Sensing Function
Authors: Blackshaw Seth , Snyder Solomon H.
Published: April 2018

Whereas the pineal organs of lower vertebrates have been shown to be photosensitive, photic regulation of pineal function in adult mammals is thought be mediated entirely by retinal photoreceptors. Extraretinal regulation of pineal function has been reported in neonatal rodents, although both the site and molecular basis of extraretinal photoreception have remained obscure. In this study we examine the developmental expression pattern of all of the principal components of retinal phototransduction in rat pineal via cRNAin situhybridization. All of the components needed to reconstitute a functional phototransduction pathway are expressed in the majority of neonatal pinealocytes, although the expression levels of many of these genes decline dramatically during development. These findings strongly support the theory that the neonatal rat pineal itself is photosensitive. In addition, we observe in neonatal pinealocytes the expression of both rod-specific and cone-specific phototransduction components, implying the existence of functionally different subtypes of pinealocytes that express varying combinations of phototransduction enzymes.
Amyloid β-Protein (Aβ) 1–40 But Not Aβ1–42 Contributes to the Experimental Formation of Alzheimer Disease Amyloid Fibrils in Rat Brain
Authors: Shin Ryong-Woon , Ogino Koichi , Kondo Akira , Saido Takaomi C. , Trojanowski John Q. , Kitamoto Tetsuyuki , Tateishi Jun
Published: April 2018

Two major C-terminal variants ending at Val40 and Ala42 constitute the majority of amyloid β-protein (Aβ), which undergoes postsecretory aggregation and deposition in the Alzheimer disease (AD) brain. To probe the differential pathobiology of the two Aβ variants, we used anin vivoparadigm in which freshly solubilized Aβ1–40 or Aβ1–42 was injected into rat brains, followed by examination using Congo red birefringence, Aβ immunohistochemistry, and electron microscopy. In the rat brain, soluble Aβ 1–40 and Aβ1–42 formed aggregates, and the Aβ1–40 but not the Aβ1–42 aggregates showed Congo red birefringence. Electron microscopy revealed that the Aβ1–40 aggregates contained fibrillar structures similar to the amyloid fibrils of AD, whereas the Aβ1–42 aggregates contained nonfibrillar amorphous material. Preincubation of Aβ1–42 solutionin vitroled to the formation of birefringent aggregates, and after injection of the preincubated Aβ1–42, the aggregates remained birefringent in the rat brain. Thus, a factor or factors might exist in the rat brain that inhibit the fibrillar assembly of soluble Aβ1–42. To analyze the postsecretory processing of Aβ, we used the samein vivoparadigm and showed that Aβ1–40 and Aβ1–42 were processed at their N termini to yield variants starting at pyroglutamate, and at their C termini to yield variants ending at Val40 and at Val39. Thus the normal rat brain could produce enzymes that mediate the conversion of Aβ 1–40/1–42 into processed variants similar to those in AD. This experimental paradigm may facilitate efforts to elucidate mechanisms of Aβ deposition evolving into amyloid plaques in AD.
A Role for Collapsin-1 in Olfactory and Cranial Sensory Axon Guidance
Authors: Kobayashi Hiroaki , Koppel Adam M. , Luo Yuling , Raper Jonathan A.
Published: April 2018

Collapsin-1 is a member of the semaphorin family of signaling molecules that acts as a repellent for growing spinal sensory axons. We have constructed a chimeric collapsin-1/alkaline phosphatase probe to visualize putative collapsin-1 receptorsin vitroandin situ. As predicted by the activity profile of collapsin-1, the probe binds spinal sensory tracts, ventral spinal roots, and the sympathetic chain but does not bind retinal axons. In addition, we find that the probe binds sensory axons arising from the olfactory epithelium and some, but not all, cranial sensory nerves. As predicted by these binding studies,in vitroassays demonstrate that primary olfactory sensory, trigeminal, and jugular ganglion growth cones collapse in the presence of soluble collapsin-1. Comparing the expression pattern of collapsin-1 with the trajectories of collapsin-1 responsive axons suggests that in both the spinal cord and the olfactory bulb, collapsin-1 prevents premature entry of sensory axons into their target and helps determine the final location of sensory terminations.
Glutamate Transporter Protein Subtypes Are Expressed Differentially during Rat CNS Development
Authors: Furuta Akiko , Rothstein Jeffrey D. , Martin Lee J.
Published: April 2018

Extracellular glutamate concentrations are regulated by glial and neuronal transporter proteins. Four glutamate transporter subtypes have been identified in rat brain; GLAST and GLT-1 are primarily astrocytic, whereas EAAC1 and EAAT4 are neuronal. Using immunoblotting and immunohistochemistry with subtype-specific antipeptide antibodies, we examined the protein expression and regional and cellular localization of each glutamate transporter subtype in embryonic and postnatal rat CNS. Each transporter had a specific pattern of expression. GLAST immunoreactivity was low prenatally but became enriched in cerebellar Bergmann glia early postnatally and then was also present in forebrain later postnatally. The post-translational modification of GLAST was unique among the subtypes; glycosylated GLAST increased with maturation, whereas nonglycosylated protein decreased in abundance postnatally. GLT-1 was present in fetal brain and spinal cord, with expression progressively increasing to adult levels throughout the neuraxis by postnatal day 26. Transient expression of GLT-1 immunoreactivity along axonal pathways was observed prenatally, in contrast to the exclusive localization of GLT-1 to astrocytes in the adult CNS. EAAC1, localized to neurons, was enriched in forebrain, diencephalon, and hindbrain during prenatal and postnatal development. EAAC1 expression was greater in newborn brain compared with adult brain. EAAT4 had a region-specific distribution; EAAT4 was mainly in cerebellum, localized to Purkinje cells, with much lower levels in forebrain. EAAT4 levels increased in cerebellum with age. We conclude that during CNS development the expression of glutamate transporter subtypes is differentially regulated, regionally segregated, and coordinated.
Reduced Levels of Norepinephrine Transporters in the Locus Coeruleus in Major Depression
Authors: Klimek Violetta , Stockmeier Craig , Overholser James , Meltzer Herbert Y. , Kalka Sheila , Dilley Ginny , Ordway Gregory A.
Published: April 2018

The norepinephrine transporter (NET) is a membrane protein responsible for termination of the action of synaptic norepinephrine and is a site of action of many drugs used to treat major depression. The present study determined whether the binding of [3H]nisoxetine to the NET is altered in the locus coeruleus (LC) in major depression, using brain tissue collected postmortem from subjects diagnosed with major depression and from age-matched normal control subjects. Thirteen of the 15 major depressive subjects studied died by suicide. The distribution of [3H]nisoxetine binding along the rostro-caudal axis of the nucleus was uneven and was paralleled by a similar uneven distribution of neuromelanin-containing cells in both major depressives and psychiatrically normal control subjects. The binding of [3H]nisoxetine to NETs in the midcaudal portion of the LC from major depressive subjects was significantly lower than that from age-matched, normal control subjects. The binding of [3H]nisoxetine to NETs in other regions of the LC was similar in major depressives and control subjects. In contrast to reductions in binding to NETs, there were no significant differences in the number of noradrenergic cells at any particular level of the LC between major depressives and normal control subjects. The decreased binding of [3H]nisoxetine to NETs in the LC in major depression may reflect a compensatory downregulation of this transporter protein in response to an insufficient availability of its substrate (norepinephrine) at the synapse.
Response Properties of Corticotectal and Corticostriatal Neurons in the Posterior Lateral Suprasylvian Cortex of the Cat
Authors: Niida Takahiro , Stein Barry E. , McHaffie John G.
Published: April 2018

Lateral suprasylvian cortex (LS) is an important source of visual projections to both the striatum and superior colliculus. Although these two LS efferent systems are likely to be involved in different aspects of visual processing, little is known about their functional properties. In the present experiments, 86 neurons in halothane-anesthetized, paralyzed cats were recorded along the posterior aspects of the medial and lateral banks of LS (PMLS and PLLS). Neurons were selected for analysis on the basis of antidromic activation from electrodes chronically implanted in the superior colliculus and caudate nucleus. The segregated nature of corticostriatal and corticotectal neurons was apparent; in no instance could a neuron be antidromically activated from both the superior colliculus and the caudate nucleus. Many common features were revealed between corticotectal and corticostriatal neurons; the majority of neurons in both populations were binocular and contralaterally dominant, showed similar responses to stationary flashed light, and expressed within-field spatial summation and surround inhibition. However, a number of information-processing features distinguished between corticotectal and corticostriatal neurons; the former were generally tuned to lower velocities than were the latter, and, for a given eccentricity in visual space, corticotectal neurons had smaller receptive fields than did corticostriatal neurons. Moreover, most corticotectal neurons displayed a marked preference for movements toward temporal visual space, whereas corticostriatal neurons revealed no specialization for a particular direction of movement. In addition, whereas corticotectal neurons were selective for receding stimuli, corticostriatal neurons were selective for approaching stimuli. The presence of these two corticofugal pathways is discussed in relation to their presumptive functional roles in the facilitation of attentive and orientation behaviors.
The Murine P84 Neural Adhesion Molecule Is SHPS-1, a Member of the Phosphatase-Binding Protein Family
Authors: Comu S. , Weng W. , Olinsky S. , Ishwad P. , Mi Z. , Hempel J. , Watkins S. , Lagenaur C. F. , Narayanan V.
Published: April 2018

P84 is a neuronal membrane glycoprotein that promotes the attachment and neurite outgrowth of cultured murine cerebellar cells. The heterophilic adhesive properties of P84 and its localization at sites of synaptogenesis suggest that it may be involved in regulation of synapse formation or maintenance. P84 is expressed in subsets of neurons throughout the CNS. By cloning the cDNA encoding murine P84, we have discovered that this molecule is a member of a family of phosphatase-binding proteins and is identical to the murine SHPS-1 cDNA. Here we report the cloning of two alternatively spliced forms of P84 and describe its localization within the CNS byin situhybridization.
Preferential Termination of Corticorubral Axons on Spine-Like Dendritic Protrusions in Developing Cat
Authors: Saito Yasuhiko , Song Wen-Jie , Murakami Fujio
Published: April 2018

The formation of synaptic contacts is a crucial event during neural development and is thought to be achieved by complex interactions between incoming axons and the neurons in the target. We have focused on spine-like dendritic protrusions (SLDPs), which are transient pleomorphic protrusive structures seen in developing brains. Although the functional significance of SLDPs remains unknown, accumulatingin vitroevidence suggests that the SLDP plays an important role in synaptogenetic interactions with axons. As a test of this idea, the present study was performed to examine whether the SLDPs are the preferential sites of synapse formationin vivo.

The ultrastructure of biocytin-labeled corticorubral (CR) terminals was examined in serial thin sections during the period of synaptogenesis in newborn cats. We found that a major proportion (86%) of the CR synapses was formed on SLDPs. The presynaptic terminals were often invaginated by fine processes extending from the tips of SLDPs. Synaptic structures presumably of cortical origin were also found on SLDPs of HRP-labeled rubrospinal cells, suggesting that SLDPs postsynaptic to labeled CR terminals originate at least in part from rubrospinal cells. Taken together, these results indicate that SLDPs may represent preferred sites of synapse formation and support the notion that SLDPs play a role in synaptogenic interactions during brain development.
The Olivocerebellar Projection Mediates Ibogaine-Induced Degeneration of Purkinje Cells: A Model of Indirect, Trans-Synaptic Excitotoxicity
Authors: O’Hearn Elizabeth , Molliver Mark E.
Published: April 2018

Ibogaine, an indole alkaloid that causes hallucinations, tremor, and ataxia, produces cerebellar neurotoxicity in rats, manifested by degeneration of Purkinje cells aligned in narrow parasagittal bands that are coextensive with activated glial cells. Harmaline, a closely related alkaloid that excites inferior olivary neurons, causes the same pattern of Purkinje cell degeneration, providing a clue to the mechanism of toxicity. We have proposed that ibogaine, like harmaline, excites neurons in the inferior olive, leading to sustained release of glutamate at climbing fiber synapses on Purkinje cells. The objective of this study was to test the hypothesis that increased climbing fiber activity induced by ibogaine mediates excitotoxic Purkinje cell degeneration. The inferior olive was pharmacologically ablated in rats by a neurotoxic drug regimen using 3-acetylpyridine, and cerebellar damage attributed to subsequent administration of ibogaine was analyzed using immunocytochemical markers for neurons and glial cells. The results show that ibogaine administered after inferior olive ablation produced little or no Purkinje cell degeneration or glial activation. That a lesion of the inferior olive almost completely prevents the neurotoxicity demonstrates that ibogaine is not directly toxic to Purkinje cells, but that the toxicity is indirect and dependent on integrity of the olivocerebellar projection. We postulate that ibogaine-induced activation of inferior olivary neurons leads to release of glutamate simultaneously at hundreds of climbing fiber terminals distributed widely over the surface of each Purkinje cell. The unique circuitry of the olivocerebellar projection provides this system with maximum synaptic security, a feature that confers on Purkinje cells a high degree of vulnerability to excitotoxic injury.
An Initial, Three-Day-Long Treatment with Alcohol Induces a Long-Lasting Phenomenon of Selective Tolerance in the Activity of the Rat Hypothalamic–Pituitary–Adrenal Axis
Authors: Lee Soon , Rivier Catherine
Published: April 2018

We determined whether an initial alcohol challenge induced long-lasting changes in the activity of the hypothalamic–pituitary–adrenal (HPA) axis. Adult male rats received intragastric injections of the vehicle or a moderately intoxicating dose of alcohol (3.0 gm/kg) daily for 3 d. When animals were acutely challenged with alcohol 3–12 d later, their ACTH and corticosterone responses were significantly blunted, compared with that of vehicle-pretreated rats. In contrast, exposure to mild electric foot shocks induced a pattern of ACTH secretion that was comparable in animals administered alcohol or the vehicle previously, indicating a lack of cross-tolerance. No significant differences were observed in pituitary responsiveness to corticotropin-releasing factor or vasopressin in rats pretreated with the vehicle or alcohol. The influence of the initial drug treatment was not mimicked by exposure to foot shocks, nor was it prevented by administering a potent corticotropin-releasing factor antagonist to block the elevations in plasma ACTH and corticosterone induced by this initial treatment. Finally, we found that rats injected initially with the vehicle and challenged subsequently with alcohol exhibited the expected increased neuronal activation (measured by the upregulation of steady-state mRNA and protein levels of immediate early genes) in the paraventricular nucleus of their hypothalamus. In contrast, this response was markedly decreased in animals exposed previously to the drug.

To our knowledge, this is the first report that exposure to a stress (i.e., alcohol), although not immediately altering the response of the HPA axis to this particular signal, induces a selective tolerance that is both slow to develop and long-lasting. The primary mechanism mediating the ability of an initial drug treatment to decrease subsequent responses of the HPA axis to a second drug challenge seems to be the inability of hypothalamic neurons to respond adequately to this second challenge.
Expression of Voltage-Gated Potassium Channels Decreases Cellular Protein Tyrosine Phosphorylation
Authors: Holmes Todd C. , Berman Kevin , Swartz Jill E. , Dagan Daniel , Levitan Irwin B.
Published: April 2018

Protein tyrosine phosphorylation by endogenous and expressed tyrosine kinases is reduced markedly by the expression of functional voltage-gated potassium (Kv) channels. The levels of tyrosine kinase protein and cellular protein substrates are unaffected, consistent with a reduction in tyrosine phosphorylation that results from inhibition of protein tyrosine kinase activity. The attenuation of protein tyrosine phosphorylation is correlated with the gating properties of expressed wild-type and mutant Kv channels. Furthermore, cellular protein tyrosine phosphorylation is reduced within minutes by acute treatment with the electrogenic potassium ionophore valinomycin. Because tyrosine phosphorylation in turn influences Kv channel activity, these results suggest that reciprocal modulatory interactions occur between Kv channel and protein tyrosine phosphorylation signaling pathways.
Cyclin Dependent Kinase Inhibitors and Dominant Negative Cyclin Dependent Kinase 4 and 6 Promote Survival of NGF-Deprived Sympathetic Neurons
Authors: Park David S. , Levine Beth , Ferrari Giovanna , Greene Lloyd A.
Published: April 2018

Neuronal apoptosis plays a critical role in both normal development and disease. However, the precise molecular events controlling neuronal apoptosis are not well understood. Previously, we hypothesized that cell cycle regulatory molecules function in controlling the apoptotic pathways of trophic factor-deprived neurons. To test this hypothesis, we used the RNA alphavirus Sindbis to express three known cyclin dependent kinase inhibitors (CKIs), p16ink4, p21waf/cip, and p27kip1, and dominant negative mutant forms of four known G1cyclin dependent kinases (CDKs), Cdk2, Cdk3, Cdk4, and Cdk6, in primary cultured rat superior cervical ganglion sympathetic neurons. We demonstrate that expression of each of the CKIs protects the postmitotic cultured neurons from apoptotic death evoked by withdrawal of NGF. In addition, we show that expression of dominant negative forms of Cdk4 or Cdk6, but not Cdk2 or Cdk3, protects NGF-deprived sympathetic neurons from death. Such findings suggest the participation of several CDKs and their cognate cyclins in a neuronal apoptotic pathway.
Expression of Neuroserpin, an Inhibitor of Tissue Plasminogen Activator, in the Developing and Adult Nervous System of the Mouse
Authors: Krueger Stefan R. , Ghisu Gian-Piero , Cinelli Paolo , Gschwend Thomas P. , Osterwalder Thomas , Wolfer David P. , Sonderegger Peter
Published: April 2018

Neuroserpin is a serine protease inhibitor of the serpin family that has been identified as an axonally secreted glycoprotein in neuronal cultures of chicken dorsal root ganglia. To obtain an indication for possible functions of neuroserpin, we analyzed its expression in the developing and the adult CNS of the mouse. In the adult CNS, neuroserpin was most strongly expressed in the neocortex, the hippocampal formation, the olfactory bulb, and the amygdala. In contrast, most thalamic nuclei, the caudate putamen, and the cerebellar granule cells were devoid of neuroserpin mRNA. During embryonic development, neuroserpin mRNA was not detectable in neuroepithelia, but it was expressed in the differentiating fields of most CNS regions concurrent with their appearance. In the cerebellum, the granule cells and a subgroup of Purkinje cells were neuroserpin-positive during postnatal development. As a further step toward the elucidation of neuroserpin function, we performed a study to identify potential target proteases.In vitro, neuroserpin formed SDS-stable complexes and inhibited the amidolytic activity of tissue plasminogen activator, urokinase, and plasmin. In contrast, no complex formation with or inhibition of thrombin was found. Expression pattern and inhibitory specificity implicate neuroserpin as a candidate regulator of plasminogen activators, which have been suggested to participate in the modulation or reorganization of synaptic connections in the adult. During development, neuroserpin may attenuate extracellular proteolysis related to processes such as neuronal migration, axogenesis, or the formation of mature synaptic connections.
Mechanism and Kinetics of Heterosynaptic Depression at a Cerebellar Synapse
Authors: Dittman Jeremy S. , Regehr Wade G.
Published: April 2018

High levels of activity at a synapse can lead to spillover of neurotransmitter from the synaptic cleft. This extrasynaptic neurotransmitter can diffuse to neighboring synapses and modulate transmission via presynaptic receptors. We studied such modulation at the synapse between granule cells and Purkinje cells in rat cerebellar slices. Brief tetanic stimulation of granule cell parallel fibers activated inhibitory neurons, leading to a transient elevation of extracellular GABA, which in turn caused a short-lived heterosynaptic depression of the parallel fiber to Purkinje cell EPSC. Fluorometric calcium measurements revealed that this synaptic inhibition was associated with a decrease in presynaptic calcium influx. Heterosynaptic inhibition of synaptic currents and calcium influx was eliminated by antagonists of the GABABreceptor. The magnitude and time course of the depression of calcium influx were mimicked by the rapid release of an estimated 10 μmGABA using the technique of flash photolysis. We found that inhibition of presynaptic calcium influx peaked within 300 msec and decayed in <3 sec at 32°C. These results indicate that presynaptic GABABreceptors can sense extrasynaptic GABA increases of several micromolar and that they rapidly regulate the release of neurotransmitter primarily by modulating voltage-gated calcium channels.
Phosphodiesterase I, A Novel Adhesion Molecule and/or Cytokine Involved in Oligodendrocyte Function
Authors: Fuss Babette , Baba Hiroko , Phan Tom , Tuohy Vincent K. , Macklin Wendy B.
Published: April 2018

One of the more complex developmental processes occurring postnatally in the CNS is the formation of the myelin sheath by oligodendrocytes. To examine the molecular events that take place during myelination, we isolated oligodendrocyte-derived cDNA clones, one of which (p421.HB) represents a putative alternatively spliced isoform of rat brain-specific phosphodiesterase I (PD-Iα) and a species homolog of the human cytokine autotaxin. Analysis of the structural composition of the p421.HB/PD-Iα protein suggests a transmembrane-bound ectoenzyme, which, in addition to the phosphodiesterase-active site contains presumed cell recognition and Ca2+-binding domains. Consequently, it may be involved in extracellular signaling events. Expression of p421.HB/PD-Iα is enriched in brain and spinal cord, where its mRNA can be detected in oligodendrocytes and in cells of the choroid plexus. Expression in the brain increases during development with an intermediate peak of expression around the time of active myelination and maximal expression in the adult. We have identified four presumably alternatively spliced isoforms, two of which appear to be CNS-specific. Decreased levels of p421.HB/PD-Iα mRNA in the dysmyelinating mouse mutantjimpy, but notshiverer, suggest a role for p421.HB/PD-Iα during active myelination and/or late stages of oligodendrocyte differentiation. Furthermore, p421.HB/PD-Iα mRNA levels were reduced in the CNS at onset of clinical symptoms in experimental autoimmune encephalomyelitis. These data together implicate the importance of p421.HB/PD-Iα in oligodendrocyte function, possibly through cell–cell and/or cell–extracellular matrix recognition.
Absence of Sensory Neurons before Target Innervation in Brain-Derived Neurotrophic Factor-, Neurotrophin 3-, and TrkC-Deficient Embryonic Mice
Authors: Liebl Daniel J. , Tessarollo Lino , Palko Mary Ellen , Parada Luis F.
Published: April 2018

Gene-targeting experiments of Trk receptors and neurotrophins has confirmed the expectation that embryonic sensory and sympathetic neurons require neurotrophin function for survival. They have further revealed correlation between a specific neurotrophin requirement and eventual sensory modality. We have analyzed embryonic and neonatal mice with mutations in the BDNF, neurotrophin 3 (NT-3), and TrkC genes. Our data confirm an unexpectedly high proportion of sensory neuron losses in NT-3 (>70%), BDNF (>20%), and TrkC (>30%) mutants, which encompass populations thought to be NGF-dependent. Direct comparison of TrkC and NT-3 mutants indicates that only a subset of the NT-3-dependent neurons also requires TrkC. The observed losses in our TrkC mutant, which is null for all proteins encoded by the gene, are more severe than those previously reported for the kinase-negative TrkC mutation, implicating additional and important functions for the truncated receptors. Our data further indicate that mature NGF-requiring neurons undergo precocious and transitory requirements for NT-3 and/or BDNF. We suggest that neurotrophins may function in creating early heterogeneity that would enable ganglia to compensate for diverse modality requirements before the period of naturally occurring death.
Spatial Relationships among Three Columnar Systems in Cat Area 17
Authors: Hübener Mark , Shoham Doron , Grinvald Amiram , Bonhoeffer Tobias
Published: April 2018

In the primary visual cortex, neurons with similar response properties are arranged in columns. As more and more columnar systems are discovered it becomes increasingly important to establish the rules that govern the geometric relationships between different columns. As a first step to examine this issue we investigated the spatial relationships between the orientation, ocular dominance, and spatial frequency domains in cat area 17. Using optical imaging of intrinsic signals we obtained high resolution maps for each of these stimulus features from the same cortical regions. We found clear relationships between orientation and ocular dominance columns: many iso-orientation lines intersected the borders between ocular dominance borders at right angles, and orientation singularities were concentrated in the center regions of the ocular dominance columns. Similar, albeit weaker geometric relationships were observed between the orientation and spatial frequency domains. The ocular dominance and spatial frequency maps were also found to be spatially related: there was a tendency for the low spatial frequency domains to avoid the border regions of the ocular dominance columns. This specific arrangement of the different columnar systems might ensure that all possible combinations of stimulus features are represented at least once in any given region of the visual cortex, thus avoiding the occurrence of functional blind spots for a particular stimulus attribute in the visual field.
CA3-Driven Hippocampal-Entorhinal Loop Controls Rather than SustainsIn VitroLimbic Seizures
Authors: Barbarosie Michaela , Avoli Massimo
Published: April 2018

Continuous application of 4-aminopyridine (4-AP, 50 μm) to combined slices of hippocampus–entorhinal cortex obtained from adult mice induces (1) interictal discharges that initiate in the CA3 area and propagate via the hippocampal regions CA1 and subiculum to the entorhinal cortex and return to the hippocampus through the dentate gyrus; and (2) ictal discharges that originate in the entorhinal cortex and propagate via the dentate gyrus to the hippocampus proper. Ictal discharges disappear over time, whereas synchronous interictal discharges continue to occur throughout the experiment. Lesioning the Schaffer collaterals abolishes interictal discharges in CA1, entorhinal cortex, and dentate gyrus and discloses entorhinal ictal discharges that propagate, via the dentate gyrus, to the CA3 subfield. Interictal discharges originating in CA3 also prevent the occurrence of ictal events generated in the entorhinal cortex during application of Mg2+-free medium. In both models, ictal discharge generation recorded in the entorhinal cortex after Schaffer collateral cut is prevented by mimicking CA3 neuronal activity through rhythmic electrical stimulation (0.25–1.5 Hz) of the CA1 hippocampal output region. Our findings demonstrate that interictal discharges of hippocampal origin control the expression of ictal epileptiform activity in the entorhinal cortex. Sectioning the Schaffer collaterals may model the chronic epileptic condition in which cell damage in the CA3 subfield results in loss of CA3 control over the entorhinal cortex. Hence, we propose that the functional integrity of hippocampal output neurons may represent a critical control point in temporal lobe epileptogenesis.
Interaction of GABA and Excitatory Amino Acids in the Basolateral Amygdala: Role in Cardiovascular Regulation
Authors: Soltis Robert P. , Cook Jennifer C. , Gregg Adam E. , Sanders Brian J.
Published: April 2018

Activation of the amygdala in rats produces cardiovascular changes that include increases in heart rate and arterial pressure as well as behavioral changes characteristic of emotional arousal. The objective of the present study was to examine the interaction of GABA and excitatory amino acid (EAA) receptors in the basolateral amygdala (BLA) in regulating cardiovascular function. Microinjection of the GABAAreceptor antagonist bicuculline methiodide (BMI) or the E A A receptor agonists NMDA or AMPA into the same region of the BLA of conscious rats produced dose-related increases in heart rate and arterial pressure. Injection of the nonselective EAA receptor antagonist kynurenic acid into the BLA prevented or reversed the cardiovascular changes caused by local injection of BMI or the noncompetitive GABA antagonist picrotoxin. Conversely, local pretreatment with the glutamate reuptake inhibitorl-trans-pyrrolidine-2,4-dicarboxylic acid enhanced the effects of intra-amygdalar injection of BMI. The cardiovascular effects of BMI were also attenuated by injection of either the NMDA antagonist 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) or the AMPA receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX). When these two EAA receptor antagonists were combined, their ability to suppress BMI-induced tachycardic and pressor responses was additive. These findings indicate that the cardiovascular effects caused by blockade of GABAergic inhibition in the BLA of the rat are dependent on activation of local NMDA and AMPA receptors.
Crossed Rhythmic Synaptic Input to Motoneurons during Selective Activation of the Contralateral Spinal Locomotor Network
Authors: Kjaerulff Ole , Kiehn Ole
Published: April 2018

To investigate the cellular mechanisms underlying locomotor-related left–right coordination, we monitored the crossed synaptic input to lumbar motoneurons during contralateral ventral root rhythmicity in the neonatal rat spinal cordin vitro. Using a longitudinal split-bath setup, one hemicord was kept in normal solution, whereas the contralateral hemicord was exposed to 5-HT and NMDA. With this approach, rhythmic bursting could be induced in the ventral roots on the agonist-exposed side, whereas the ventral roots on the agonist-free side remained silent. Intracellular recordings were made from L1–L3 motoneurons on the silent agonist-free side during rhythmic activity in the contralateral ventral roots. At the resting membrane potential, the typical crossed synaptic input was a rhythmic barrage of depolarizing IPSPs. This input modulated the frequency of spikes induced with depolarizing direct current by inhibiting firing in phase with the contralateral bursts. Intracellular chloride loading increased the amplitude of the IPSPs, suggesting that they were chloride-dependent. Strychnine but not bicuculline generally blocked the rhythmic inhibitory input when added to the agonist-free side during contralateral rhythmicity. APV and CNQX on the agonist-free side abolished the rhythmic inhibitory input in most motoneurons but not in all.

We suggest that rat spinal motoneurons receive a mainly glycinergic rhythmic inhibition from the contralateral half of the locomotor network. Unlike in simpler vertebrates, the crossed inhibition often appears to be at least disynaptic, involving inhibitory premotor neurons located on the same side as the receiving motoneurons. These premotor neurons are rhythmically excited via a crossed pathway that depends on glutamatergic transmission.
Modulation of Hypothalamic–Pituitary–Adrenal Function by Transgenic Expression of Interleukin-6 in the CNS of Mice
Authors: Raber Jacob , O’Shea Ross D. , Bloom Floyd E. , Campbell Iain L.
Published: April 2018

Interleukin-6 (IL-6) and IL-6 receptor mRNA and protein have been reported in different brain regions under normal and pathophysiological conditions. Although much is known about the hypothalamic–pituitary–adrenal (HPA) axis stimulation after acute administration, less is known about the chronic effects of IL-6 on the function of the HPA axis. In the present study, we examined the function of the HPA axis in transgenic mice in which constitutive expression of IL-6 under the control of the glial fibrillary acidic protein (GFAP) promoter was targeted to astrocytes in the CNS. GFAP-IL6 mice heterozygous or homozygous for the IL-6 transgene had normal basal plasma corticosterone levels but, after restraint stress, showed abnormally increased levels in a gene dose-dependent manner. The increased plasma corticosterone levels in the IL-6 transgenic mice were associated with increased adrenal corticosterone content and hyperplasia of both adrenal cortex and medulla. Notably, plasma adrenocorticotrophic hormone (ACTH) levels and pituitary ACTH content were either not changed or decreased in these mice, whereas plasma arginine vasopressin (AVP) was increased, supporting a role for AVP in response to acute immobilization stress. The reduced ACTH response together with the adrenal hyperplasia in the IL-6 transgenic mice suggests direct activation at the level of the adrenal gland that may be directly activated by AVP or sensitized to ACTH. A similar mechanism may play a role in the blunted ACTH response and elevated corticosterone levels under pathophysiological conditions observed in humans with high brain levels of IL-6.
Sublethal Oxygen–Glucose Deprivation Alters Hippocampal Neuronal AMPA Receptor Expression and Vulnerability to Kainate-Induced Death
Authors: Ying Howard S. , Weishaupt Jochen H. , Grabb Margaret , Canzoniero Lorella M. T. , Sensi Stefano L. , Sheline Christian T. , Monyer Hannah , Choi Dennis W.
Published: April 2018

Recent studies have suggested that rats subjected to transient global brain ischemia develop depressed expression of GluR-B in CA1 hippocampal neurons. The present study was performed to determine whether a similar change in AMPA receptor expression could be triggeredin vitroby sublethal oxygen–glucose deprivation in rat hippocampal neuronal cultures. mRNA was extracted from individual hippocampal neurons via patch electrodes and amplified by RT-PCR 24–48 hr after sublethal oxygen–glucose deprivation. Compared with controls, insulted neurons expressed increased levels of GluR-D flop. As an indication that this change in receptor expression was functionally significant, insulted cultures exhibited increased AMPA- or kainate-induced45Ca2+accumulation sensitive toJorospider toxin and increased vulnerability to kainate-induced death. These data support the hypothesis that exposure to ischemia may enhance subsequent hippocampal neuronal vulnerability to AMPA receptor-mediated excitotoxicity by modifying the relative expression of AMPA receptor subunits in a manner that promotes Ca2+permeability.
Analysis of the Mechanism of Loss of Trophic Factor Dependence Associated with Neuronal Maturation: A Phenotype Indistinguishable fromBaxDeletion
Authors: Easton Rachael M. , Deckwerth Thomas L. , Parsadanian Alexander Sh. , Johnson Eugene M.
Published: April 2018

During development, sympathetic neurons are critically dependent on nerve growth factor (NGF) for survival. Neurons isolated from the superior cervical ganglia (SCG) of embryonic rodents and maintained for 1 weekin vitroundergo programmed cell death in response to NGF deprivation. As the cells maturein vitroandin vivo, however, these neurons develop a resistance to NGF deprivation and become much less acutely dependent on NGF for survival. Using anin vitromodel of neuronal maturation, we confirmed that SCG neurons maintained in culture for 3–4 weeks did not experience a dramatic loss in viability after NGF removal, yet they did undergo the initial biochemical and genetic changes elicited by NGF deprivation of young neurons. NGF deprivation of mature neurons produced rapid decreases in glucose uptake and protein and RNA synthesis rates, increased phosphorylation of c-Jun, and an increase in c-junmRNA. Mature neurons, however, experienced a block in the cell death program before the final stages of the pathway activated in young neurons, which includes the induction of c-fosmRNA and characteristic apoptotic nuclear changes. This maturation-induced block was indistinguishable by these criteria from the block produced byBaxdeficiency. Expression ofBaxin mature neurons restored the apoptotic pathway, such that after NGF removal,Bax-overexpressing mature neurons resumed the apoptotic program, including the induction of c-Fos and passage through a caspase checkpoint. Thus, a block in the apoptotic program at or near the BAX checkpoint accounts for the decreased dependence of mature neurons on neurotrophic factor to maintain survival.
A Neural Model of Multimodal Adaptive Saccadic Eye Movement Control by Superior Colliculus
Authors: Grossberg Stephen , Roberts Karen , Aguilar Mario , Bullock Daniel
Published: April 2018

How does the saccadic movement system select a target when visual, auditory, and planned movement commands differ? How do retinal, head-centered, and motor error coordinates interact during the selection process? Recent data on superior colliculus (SC) reveal a spreading wave of activation across buildup cells the peak activity of which covaries with the current gaze error. In contrast, the locus of peak activity remains constant at burst cells, whereas their activity level decays with residual gaze error. A neural model answers these questions and simulates burst and buildup responses in visual, overlap, memory, and gap tasks. The model also simulates data on multimodal enhancement and suppression of activity in the deeper SC layers and suggests a functional role for NMDA receptors in this region. In particular, the model suggests how auditory and planned saccadic target positions become aligned and compete with visually reactive target positions to select a movement command. For this to occur, a transformation between auditory and planned head-centered representations and a retinotopic target representation is learned. Burst cells in the model generate teaching signals to the spreading wave layer. Spreading waves are produced by corollary discharges that render planned and visually reactive targets dimensionally consistent and enable them to compete for attention to generate a movement command in motor error coordinates. The attentional selection process also helps to stabilize the map-learning process. The model functionally interprets cells in the superior colliculus, frontal eye field, parietal cortex, mesencephalic reticular formation, paramedian pontine reticular formation, and substantia nigra pars reticulata.
Fluorescence-Imaged Microdeformation of the Outer Hair Cell Lateral Wall
Authors: Oghalai John S. , Patel Alpen A. , Nakagawa Takashi , Brownell William E.
Published: April 2018

Outer hair cell (OHC) electromotility appears to be central to mammalian hearing and originates within its lateral wall. The OHC lateral wall is a unique trilaminate structure consisting of the plasma membrane (PM), the cortical lattice (CL), and the subsurface cisternae (SSC). We selectively labeled and imaged the lateral wall components in the isolated guinea pig OHC under confocal microscopy. The PM was labeled with a voltage-sensitive dye, di-8-ANEPPS; the SSC was labeled with the sphingomyelin precursor, NBD-C6-ceramide; and F-actin in the CL was labeled with conjugates of phalloidin. Interactions among the three layers were evaluated with the micropipette aspiration technique. The PM was tethered to the CL and SSC until, at a critical deformation pressure, the PM separated, allowing visualization of the extracisternal space, and ultimately formed a vesicle. After detaching, the stiffness parameter of the PM was 22% of that of the intact lateral wall. We conclude that the lateral wall PM is more compliant than the CL/SSC complex. The data clarify the structural basis for electromotile force coupling in the OHC lateral wall.