bluuebunny/crossref_metadata_2025 huggingface dataset:
Encoding of Visual Motion Information and Reliability in Spiking and Graded Potential Neurons
Authors: Haag Juergen , Borst Alexander
Published: April 2018

We investigated the information about stimulus velocity inherent in the membrane signals of two types of directionally selective, motion-sensitive interneurons in the fly visual system. One of the cells, the H1-cell, is a spiking neuron, whereas the other, the HS-cell, encodes sensory information mainly by a graded shift of its membrane potential. Using a pseudo-random velocity waveform by which a visual grating is moving along the horizontal axis of the eye, both cell types follow the stimulus velocity at higher precision than in response to a step-like velocity function. To measure how much information about the stimulus velocity is preserved in the cellular responses, we calculated the coherence between the stimulus and the neural signals as a function of stimulus frequency. At frequencies up to ∼10 Hz motion information is well contained in the electrical signals of HS- and H1-cells: For HS-cells the coherence value amounts to ∼70%, and for H1-cells this value is ∼60%. Comparing these values with the coherence expected from a linear encoding reveals that the fidelity of the original stimulus is deteriorated in the neural signal partly by neural noise and partly by the nonlinearity inherent in the process of visual motion detection. The degree to which this nonlinearity contributes to the decrease in coherence depends on the maximum velocity used in the experiments; the smaller the stimulus amplitude, the higher the coherence and, thus, the smaller the nonlinearity in encoding of stimulus motion. All these results are in agreement with model simulations in which visual motion is processed by an array of local motion detectors, the spatially integrated output of which is considered the equivalent of the neural signals of HS- and H1-cells.
Studies on Long-Term Depression in Area CA1 of the Anesthetized and Freely Moving Rat
Authors: Staubli Ursula , Scafidi Joey
Published: April 2018

Homosynaptic long-term depression (LTD) is reported to occur in field CA1 of hippocampal slices collected from immature brains. Because the effect has been postulated to be a memory storage mechanism, it is of interest to test for its presence in adult, awake animals. Unfortunately, not only has hippocampal LTD proved difficult to obtain reliablyin vivo, but the few successful studies vary with respect to protocols and evidence that the depression is input-specific. The present study tested for input-specific (homosynaptic) LTD in field CA1 after application of various stimulation protocols to the Schaffer collateral/commissural projections in freely moving, adult rats. The results indicate that although low-frequency trains do induce decrements in synaptic transmission lasting for hours to several days, the success rate of eliciting input-specific LTD in the awake rat is very modest compared with the ease with which stable potentiation is obtained in the same synapses. Moreover, it is questionable that the effective protocols represent patterns of activity likely to occur during behavior. The stronger the afferent activation during low-frequency stimulation, the greater was the probability of eliciting LTD accompanied by persistent heterosynaptic depression. Clear evidence for the occurrence of LTD, irrespective of stimulation protocol and current intensity, could not be obtained in rats under barbiturate anesthesia. In all, the results do not accord with the suggestion that LTD occurs routinely in the hippocampusin vivoas part of memory encoding.
Dual Ultrastructural Localization of μ-Opioid Receptors and NMDA-Type Glutamate Receptors in the Shell of the Rat Nucleus Accumbens
Authors: Gracy K. Noelle , Svingos Adena L. , Pickel Virginia M.
Published: April 2018

The effectiveness of NMDA antagonists in modulating the motor and motivational effects of opiates is attributed, in part, to functional associations involving NMDA receptors and μ-opioid receptors (MORs) in the shell of the nucleus accumbens (Acb). To determine the subcellular sites for potential functional interactions between opiate ligands and NMDA receptors in this region, we examined the ultrastructural localization of antipeptide antisera against MOR and the R1 subunit of the NMDA receptor in the Acb shell of the adult rat brain. MOR-like immunoreactivity (MOR-LI) was seen primarily in dendrites, whereas NMDAR1-like immunoreactivity (NMDAR1-LI) was detected more often in axon terminals forming asymmetric synapses. In these profiles, MOR labeling was localized mainly to extrasynaptic plasma membranes, whereas NMDAR1-LI was associated with both synaptic and extrasynaptic sites. Of 307 MOR-labeled processes, 17.9% of the dendrites and 9.4% of the axon terminals also contained NMDAR1-LI. In addition, 24.7% of the dendrites containing only MOR-LI were apposed to NMDAR1-labeled axons or terminals. We conclude that in the shell of the Acb, the output of single neurons can be dually modulated by (1) activation of MOR and NMDA receptors in the same dendrites or (2) combined activation of presynaptic NMDA receptors in afferents contacting dendrites containing MOR. In addition, the colocalization of MOR and NMDAR1 in certain axon terminals in the Acb suggests their dual involvement in the presynaptic release of neurotransmitters in this region.
Dynamic Changes in Nucleus Accumbens Dopamine Efflux During the Coolidge Effect in Male Rats
Authors: Fiorino Dennis F. , Coury Ariane , Phillips Anthony G.
Published: April 2018

The Coolidge effect describes the reinitiation of sexual behavior in a “sexually satiated” animal in response to a novel receptive mate. Given the role of the mesolimbic dopamine (DA) system in the initiation and maintenance of motivated behavior, microdialysis was used to monitor nucleus accumbens (NAC) DA transmission during copulation, sexual satiety, and the reinitiation of sexual behavior. In agreement with earlier reports, the presentation of an estrous female behind a screen and copulation were associated with significant increases in NAC DA efflux. Return of NAC DA concentrations to baseline values coincided with a period of sexual satiety, although concentrations of the DA metabolites, dihydroxyphenylacetic acid and homovanillic acid, remained elevated. The presentation of a novel receptive female behind a screen resulted in a slight increase in NAC DA, which was augmented significantly during renewed copulation with the novel female. The present data suggest that the stimulus properties of a novel receptive female may serve to increase NAC DA transmission in a sexually satiated male rat, and this, in turn, may be related to the reinitiation of sexual behavior.
Parallel Medullary Gustatospinal Pathways In a Catfish: Possible Neural Substrates for Taste-Mediated Food Search
Authors: Kanwal Jagmeet S. , Finger Thomas E.
Published: April 2018

Taste and tactile fibers in the facial nerve of catfish innervate extraoral taste buds and terminate somatotopically in the facial lobe (FL)—a medullary structure crucial for gustatory-mediated food search. The present study was performed to determine the neural linkages between the gustatory input and the spinal motor output. Spinal injections of horseradish peroxidase (HRP) label spinopetal cells in the octaval nuclei, the nucleus of the medial longitudinal fasciculus, and reticulospinal neurons (Rsps) in the brainstem medial reticular formation (RF), including the Mauthner cell. A somatotopically organized, direct faciospinal system originating from superficial cells scattered in the lateral lobule of the facial lobe (ll) is also labeled. The brainstem reticulospinal cells are segmentally organized into 14 clusters within eight segments of the reticular formation and includes one cluster (RS5) directly ventral to the FL. Injections of HRP or fluorescent tracers into the medial lobule of the FL label a facioreticular projection terminating around the Rsps of RS5. DiI injections into this area of the RF retrogradely label deeply situated bipolar neurons, especially in the medial and intermediate lobules of the FL. Electrophysiological recordings in and around RS5 show units with large receptive fields and with responses to chemical and tactile stimulation. The FL projects to the spinal cord via two pathways: (1) a topographically organized direct faciospinal pathway, and (2) an indirect facioreticulospinal pathway in which reticular neurons process and integrate gustatory information before influencing spinal circuitry for motor control during food search.
Microtubule Organization and Stability in the Oligodendrocyte
Authors: Lunn Katharine F. , Baas Peter W. , Duncan Ian D.
Published: April 2018

The oligodendrocyte is the glial cell responsible for the formation and maintenance of CNS myelin. Because the development of neuronal morphology is known to depend on the presence of highly organized microtubule arrays, it may be hypothesized that the properties of microtubules influence the form and function of oligodendrocytes. The goals of the present study were to define the physical attributes of microtubules in oligodendrocytes maintainedin vitro. The results of electron and confocal microscopy indicate that microtubules are present throughout the cell bodies and large and small processes of oligodendrocytes and are rarely associated with discrete microtubule-organizing centers. A modified “hooking” protocol demonstrated that the polarity orientation of microtubules is uniformly plus-end distal in small oligodendrocyte processes, compared with a nonuniform, predominantly plus-end distal orientation in large processes. Oligodendrocytes were exposed to the microtubule-depolymerizing drug nocodazole to examine microtubule stability in these cells. The results suggest that oligodendrocyte microtubules can be resolved into at least three distinct microtubule populations that differ in their kinetics of depolymerization in the presence of nocodazole. These findings suggest that the properties of the oligodendrocyte microtubule array reflect the functions of the different regions of this highly specialized cell.
Redox Modulation ofhsloCa2+-Activated K+Channels
Authors: DiChiara Timothy J. , Reinhart Peter H.
Published: April 2018

The modulation of ion channel proteins by cellular redox potential has emerged recently as a significant determinant of channel function. We have investigated the influence of sulfhydryl redox reagents on human brain Ca2+-activated K+channels (hslo) expressed in both human embryonic kidney 293 cells andXenopusoocytes using macropatch and single-channel analysis. Intracellular application of the reducing agent dithiothreitol (DTT): (1) shifts the voltage of half-maximal channel activation (V0.5) ≈18 mV to more negative potentials without affecting the maximal conductance or the slope of the voltage dependence; (2) slows by ≈10-fold a time-dependent right-shift inV0.5values (“run-down”); (3) speeds macroscopic current activation kinetics by ≈33%; and (4) increases the single-channel open probability without affecting the unitary conductance. In contrast to DTT treatment, oxidation with hydrogen peroxide shifts macropatchV0.5values to more positive potentials, increases the rate of channel run-down, and decreases the single-channel open probability. KCachannels cloned fromDrosophiladiffer fromhslochannels in that they show very little run-down and are not modulated by the addition of DTT. These data indicate thathsloCa2+-activated K+channels may be modulated by changes in the cellular redox potential as well as by the transmembrane voltage and the cytoplasmic Ca2+concentration.
Cholecystokinin Increases GABA Release by Inhibiting a Resting K+Conductance in Hippocampal Interneurons
Authors: Miller Karen K. , Hoffer Alan , Svoboda Kurt R. , Lupica Carl R.
Published: April 2018

Cholecystokinin (CCK) is found co-localized with the inhibitory neurotransmitter GABA in interneurons of the hippocampus. Also, CCK receptors are found in abundance in this brain region. The possibility that CCK alters interneuron activity was examined using whole-cell current- and voltage-clamp recordings from visualized interneurons in the stratum radiatum of area CA1 in rat hippocampal slices. The effect of CCK on GABA-mediated IPSCs was also determined in pyramidal neurons. The sulfated octapeptide CCK-8S increased action potential frequency or generated inward currents in the majority of interneurons. These effects of CCK persisted in the presence of tetrodotoxin and cadmium, suggesting that they were direct. Current–voltage plots revealed that CCK-8S inhibited a conductance that was linear across command potentials and reversed near the equilibrium potential for K+ions. The K+channel blocker tetraethylammonium (10 mm) generated inward currents similar to those initiated by CCK, and it occluded the effect of the peptide. BaCl2(1 mm) and 4-aminopyridine (2 mm) did not alter the effect of CCK. The CCKBreceptor antagonist PD-135,158 completely blocked the inward currents generated by CCK-8S. CCK also resulted in an increase in spontaneous action potential-dependent IPSC frequency, but no changes in action potential-independent miniature IPSCs or evoked IPSCs in pyramidal neurons. These results provide evidence that CCK can depolarize hippocampal interneurons through the inhibition of a resting K+conductance, leading to increased tonic inhibition of pyramidal neurons. This action of CCK may contribute to its anticonvulsant properties, as observed in limbic seizure models.
Tyrosine Phosphorylation of Nicotinic Acetylcholine Receptor Mediates Grb2 Binding
Authors: Colledge Marcie , Froehner Stanley C.
Published: April 2018

Tyrosine phosphorylation of the nicotinic acetylcholine receptor (AChR) is associated with an altered rate of receptor desensitization and also may play a role in agrin-induced receptor clustering. We have demonstrated a previously unsuspected interaction betweenTorpedoAChR and the adaptor protein Grb2. The binding is mediated by the Src homology 2 (SH2) domain of Grb2 and the tyrosine-phosphorylated δ subunit of the AChR. Dephosphorylation of the δ subunit abolishes Grb2 binding. A cytoplasmic domain of the δ subunit contains a binding motif (pYXNX) for the SH2 domain of Grb2. Indeed, a phosphopeptide corresponding to this region of the δ subunit binds to Grb2 SH2 fusion proteins with relatively high affinity, whereas a peptide lacking phosphorylation on tyrosine exhibits no binding. Grb2 is colocalized with the AChR on the innervated face ofTorpedoelectrocytes. Furthermore, Grb2 specifically copurifies with AChR solubilized from postsynaptic membranes. These data suggest a novel role for tyrosine phosphorylation of the AChR in the initiation of a Grb2-mediated signaling cascade at the postsynaptic membrane.
A Family of Delayed Rectifier Kv1 cDNAs Showing Cell Type-Specific Expression in the Squid Stellate Ganglion/Giant Fiber Lobe Complex
Authors: Rosenthal Joshua J. C. , Liu Taylor I. , Gilly William F.
Published: April 2018

Squid giant axons are formed by giant fiber lobe (GFL) neurons of the stellate ganglion (SG). Other large motoneurons in the SG form a parallel system. A small family of cDNAs (SqKv1A–D) encoding Kv1 α-subunits was identified in a squid (Loligo opalescens) SG/GFL library. Members have distinct 5′ untranslated regions (UTRs) and initial coding regions, but beyond a certain point (nucleotide 34 of SqKv1A) only nine differences exist. 3′ UTRs are identical. Predicted α-subunits are nearly identical, and only the N termini differ significantly, primarily in length. RNase protection assays that use RNA isolated from specific SG regions show that SqKv1A mRNA is expressed prominently in the GFL but not in the SG proper. SqKv1B yields the opposite pattern. SqKv1D also is expressed only in the SG. SqKv1C expression was not detectable.In situhybridizations confirm these results and reveal that SqKv1B mRNA is abundant in many large neurons of the SG, whereas SqKv1D expression is limited to small isolated clusters of neurons. SqKv1A and B are thus the predominant Kv1 mRNAs in the SG/GFL complex. Activation properties of SqKv1A and B channels expressed in oocytes are very similar to one another and compare favorably with properties of native delayed rectifier channels in GFL neurons and large SG neurons. The Kv1 complement in these squid neurons thus seems to be relatively simple. Several differences exist between cloned and native channels, however, and may reflect differences in the cellular environments of oocytes and neurons.
Neuronal Localization of Presenilin-1 and Association with Amyloid Plaques and Neurofibrillary Tangles in Alzheimer’s Disease
Authors: Busciglio Jorge , Hartmann Henrike , Lorenzo Alfredo , Wong Caine , Baumann Karlheinz , Sommer Bernd , Staufenbiel Matthias , Yankner Bruce A.
Published: April 2018

Mutations in the presenilin-1 (PS1) gene is a cause of early- onset familial Alzheimer’s disease (AD). Endogenous PS1 is associated with the endoplasmic reticulum in the cell body of undifferentiated SH-SY5Y neuroblastoma cells. At early stages of neuronal differentiation in rat hippocampal culture, PS1 appears in all neuritic processes and in growth cones. In mature differentiated neurons, PS1 is concentrated in the somatodendritic compartment but is also present at lower levels in axons. A similar localization of PS1 is observedin vivoin neurons of the adult human cerebral cortex. In sporadic AD, PS1 appears in the dystrophic neurites of mature amyloid plaques and co-localizes with a subset of intraneuronal neurofibrillary tangles (NFTs). About 30% of hippocampal NFTs are labeled with a highly specific antibody to the PS1 C-terminal loop domain but not with an antibody to the PS1 N terminus. This observation is consistent with a potential association of the PS1 C-terminal fragment with NFTs, because PS1 is constitutively cleaved to N- and C-terminal fragments in neurons. These results suggest that PS1 is highly expressed and broadly distributed during early stages of neuronal differentiation, consistent with a role for PS1 in neuronal differentiation. Furthermore, the co-localization of PS1 with NFTs and plaque dystrophic neurites implicates a role for PS1 in the diverse pathological manifestations of AD.
Brain Aging: Changes in the Nature of Information Coding by the Hippocampus
Authors: Tanila Heikki , Shapiro Matthew , Gallagher Michela , Eichenbaum Howard
Published: April 2018

Advanced age in rats is associated with a decline in spatial memory capacities dependent on hippocampal processing. As yet, however, little is known about the nature of age-related alterations in the information encoded by the hippocampus. Young rats and aged rats identified as intact or impaired in spatial learning capacity were trained on a radial arm maze task, and then multiple parameters of the environmental cues were manipulated to characterize the changes in firing patterns of hippocampal neurons corresponding to the presence of particular cues or the spatial relationships among them. The scope of information encoded by the hippocampus was reduced in memory-impaired aged subjects, even though the number of neurons responsive to salient environmental cues was not different from that in young rats. Furthermore, after repeated manipulations of the cues, memory-intact aged rats, like young rats, altered their spatial representations, whereas memory-impaired aged rats showed reduced plasticity of their representation throughout testing. Thus changes in hippocampal memory representation associated with aging and memory loss can be characterized as a rigid encoding of only part of the available information.
Mice Lacking Metabotropic Glutamate Receptor 5 Show Impaired Learning and Reduced CA1 Long-Term Potentiation (LTP) But Normal CA3 LTP
Authors: Lu You-Ming , Jia Zhengping , Janus Christopher , Henderson Jeffrey T. , Gerlai Robert , Wojtowicz J. Martin , Roder John C.
Published: April 2018

Class I metabotropic glutamate receptors (mGluRs) have been postulated to play a role in synaptic plasticity. To test the involvement of one member of this class, we have recently generated mutant mice that express no mGluR5 but normal levels of other glutamate receptors. The CNS revealed normal development of gross anatomical features. To examine synaptic functions we measured evoked field EPSPs in the hippocampal slice. Measures of presynaptic function, such as paired pulse facilitation in mutant CA1 neurons, were normal. The response of mutant CA1 neurons to low concentrations of (1S,3R)−1-amino-cyclopentane-1,3-dicarboxylic acid (ACPD) was missing, which suggests that mGluR5 may be the primary high affinity ACPD receptor in these neurons. Long-term potentiation (LTP) in mGluR5 mutants was significantly reduced in the NMDA receptor (NMDAR)-dependent pathways such as the CA1 region and dentate gyrus of the hippocampus, whereas LTP remained intact in the mossy fiber synapses on the CA3 region, an NMDAR-independent pathway. Some of the difference in CA1 LTP could lie at the level of expression, because the reduction of LTP in the mutants was no longer observed 20 min after tetanus in the presence of 2-amino-5-phosphonopentanoate. We propose that mGluR5 plays a key regulatory role in NMDAR-dependent LTP. These mutant mice were also impaired in the acquisition and use of spatial information in both the Morris water maze and contextual information in the fear-conditioning test. This is consistent with the hypothesis that LTP in the CA1 region may underlie spatial learning and memory.
Recovery of Neurofilament Expression Selectively in Regenerating Reticulospinal Neurons
Authors: Jacobs Alan J. , Swain Gary P. , Snedeker Joseph A. , Pijak Donald S. , Gladstone Laura J. , Selzer Michael E.
Published: April 2018

During regeneration of lamprey spinal axons, growth cones lack filopodia and lamellipodia, contain little actin, and elongate much more slowly than do typical growth cones of embryonic neurons. Moreover, these regenerating growth cones are densely packed with neurofilaments (NFs). Therefore, after spinal hemisection the time course of changes in NF mRNA expression was correlated with the probability of regeneration for each of 18 identified pairs of reticulospinal neurons and 12 cytoarchitectonic groups of spinal projecting neurons. During the first 4 weeks after operation, NF message levels were reduced dramatically in all axotomized reticulospinal neurons, on the basis of semiquantitativein situhybridization for the single lamprey NF subunit (NF-180). Thereafter, NF expression returned toward normal in neurons whose axons normally regenerate beyond the transection but remained depressed in poorly regenerating neurons. The recovery of NF expression in good regenerators was independent of axon growth across the lesion, because excision of a segment of spinal cord caudal to the transection site blocked regeneration but did not prevent the return of NF-180 mRNA. The early decrease in NF mRNA expression was not accompanied by a reduction in NF protein content. Thus the axotomy-induced loss of most of the axonal volume resulted in a reduced demand for NF rather than a reduction in volume-specific NF synthesis. We conclude that the secondary upregulation of NF message during axonal regeneration in the lamprey CNS may be part of an intrinsic growth program executed only in neurons with a strong propensity for regeneration.
Neurons Promote Macrophage Proliferation by Producing Transforming Growth Factor-β2
Authors: Dobbertin Alexandre , Schmid Peter , Gelman Michèle , Glowinski Jacques , Mallat Michel
Published: April 2018

The infiltration of bone marrow-derived macrophages into the CNS contributes to growth and reactions of microglia during development or after brain injury. The proliferation of microglial cells is stimulated by colony-stimulating factor 1 (CSF-1), an astrocyte-produced growth factor that acts on mononuclear phagocytes. In the present study, we have shown, using anin vitromodel system, that rodent neurons obtained from the developing cerebral cortex produce a soluble factor that strongly enhances the proliferation of macrophages cultured in the presence of CSF-1. Both macrophages isolated from the developing brain and those from the adult bone marrow were stimulated. Kinetic analyses of [3H]thymidine incorporation into macrophages indicated that their response to the neuron-derived factor involved a shortening of the cycle of proliferating cells. The effect of neurons on macrophages was blocked in the presence of antibodies neutralizing transforming growth factor-β2 (TGF-β2), whereas recombinant TGF-β2 stimulated macrophage proliferation in the presence of CSF-1. Neuronal secretion of TGF-β2 was confirmed by reverse transcription-PCR detection of TGF-β2 transcripts and immunodetection of the protein within neurons and in their culture medium.In situhybridization and immunohistochemical experiments showed neuronal expression of TGF-β2 in sections of cerebral cortex obtained from 6-d-old rats, an age at which extensive developmental recruitment of macrophages occurs in this cerebral region. Altogether, our results provide direct evidence that neurons have the capacity to promote brain macrophage proliferation and demonstrate the role of TGF-β2 in this neuronal function.
A Novel Type of GABAergic Interneuron Connecting the Input and the Output Regions of the Hippocampus
Authors: Ceranik Katja , Bender Roland , Geiger Jörg R. P. , Monyer Hannah , Jonas Peter , Frotscher Michael , Lübke Joachim
Published: April 2018

The main excitatory pathway of the hippocampal formation is controlled by a network of morphologically distinct populations of GABAergic interneurons. Here we describe a novel type of GABAergic interneuron located in the outer molecular layer (OML) of the rat dentate gyrus with a long-range forward projection from the dentate gyrus to the subiculum across the hippocampal fissure. OML interneurons were recorded in hippocampal slices by using the whole-cell patch-clamp configuration. During recording, cells were filled with biocytin for subsequent light and electron microscopic analysis. Neurons projecting to the subiculum were distributed throughout the entire OML. They had round or ovoid somata and a multipolar dendritic morphology. Two axonal domains could be distinguished: an extensive, tangential distribution within the OML and a long-range vertical and tangential projection to layer 1 and stratum pyramidale of the subiculum. Symmetric synaptic contacts were established by these interneurons on dendritic shafts in the OML and subiculum. OML interneurons were characterized physiologically by short action potential duration and marked afterhyperpolarization that followed the spike. On sustained current injection, they generated high-frequency (up to 130 Hz, 34°C) trains of action potentials with only little adaptation.In situhybridization and single-cell RT-PCR analysis for GAD67 mRNA confirmed the GABAergic nature of OML interneurons. GABAergic interneurons in the OML projecting to the subiculum connect the input and output regions of the hippocampus. Hence, they could mediate long-range feed-forward inhibition and may participate in an oscillating cross-regional interneuron network that may synchronize the activity of spatially distributed principal neurons in the dentate gyrus and the subiculum.
Absence of a Persistently Elevated 37 kDa Fos-Related Antigen and AP-1-Like DNA-Binding Activity in the Brains of Kainic Acid-TreatedfosB Null Mice
Authors: Mandelzys Allan , Gruda Mary Ann , Bravo Rodrigo , Morgan James I.
Published: April 2018

Chronic stimulation of the nervous system or acute administration of kainic acid results in a persistent increase in AP-1-like DNA-binding activity in the brain. However, the composition and function of these AP-1 complexes remain controversial. By comparing wild-type andfosB-null mice treated with kainic acid, we establish that the complexes comprise JunD in association with an ∼37 kDa Δ-FosB species. Δ-FosB was expressed persistently in neurons in many areas of the CNS, even thoughfosB mRNA only increased transiently. This implies that the 37 kDa protein is very stable.fosB−/− mice are predisposed to seizures. Therefore, the chronic expression of Δ-FosB elicited by kainic acid seizures may be indicative of a compensatory/protective role in the pathophysiology of epilepsy.
Visualization of the Distribution of Autophosphorylated Calcium/Calmodulin-Dependent Protein Kinase II after Tetanic Stimulation in the CA1 Area of the Hippocampus
Authors: Ouyang Yannan , Kantor David , Harris Kristen M. , Schuman Erin M. , Kennedy Mary B.
Published: April 2018

Autophosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) at threonine-286 produces Ca2+-independent kinase activity and has been proposed to be involved in induction of long-term potentiation by tetanic stimulation in the hippocampus. We have used an immunocytochemical method to visualize and quantify the pattern of autophosphorylation of CaMKII in hippocampal slices after tetanization of the Schaffer collateral pathway. Thirty minutes after tetanic stimulation, autophosphorylated CaM kinase II (P-CaMKII) is significantly increased in area CA1 both in apical dendrites and in pyramidal cell somas. In apical dendrites, this increase is accompanied by an equally significant increase in staining for nonphosphorylated CaM kinase II. Thus, the increase in P-CaMKII appears to be secondary to an increase in the total amount of CaMKII. In neuronal somas, however, the increase in P-CaMKII is not accompanied by an increase in the total amount of CaMKII. We suggest that tetanic stimulation of the Schaffer collateral pathway may induce new synthesis of CaMKII molecules in the apical dendrites, which contain mRNA encoding its α-subunit. In neuronal somas, however, tetanic stimulation appears to result in long-lasting increases in P-CaMKII independent of an increase in the total amount of CaMKII.

Our findings are consistent with a role for autophosphorylation of CaMKII in the induction and/or maintenance of long-term potentiation, but they indicate that the effects of tetanus on the kinase and its activity are not confined to synapses and may involve induction of new synthesis of kinase in dendrites as well as increases in the level of autophosphorylated kinase.
The trkA Receptor Mediates Growth Cone Turning toward a Localized Source of Nerve Growth Factor
Authors: Gallo Gianluca , Lefcort Frances B. , Letourneau Paul C.
Published: April 2018

We have developed anin vitrosystem for studying the interaction of chick dorsal root ganglion neuronal growth cones with a localized source of nerve growth factor (NGF) covalently conjugated to polystyrene beads. Growth cones rapidly turned and migrated under NGF-coated beads in a process that involved the initial formation of persistent contact with a bead, followed by directed flow of cytoplasm toward the point of contact. A role for the local activation of the high-affinity NGF receptor trkA was suggested by a strong inhibition of the turning response by (1) the addition of an antibody against the extracellular portion of trkA, (2) the elevation of the background concentration of NGF to saturate trkA, or (3) the presence of a concentration of the drug K252a that inhibits trkA activation. NGF binding to the pan-neurotrophin receptor p75 is also involved but is not required for turning. These data show a new role for both the trkA and the p75 receptors: the mediation of local events in the guidance of nerve growth cones.
Functional Specificity of Long-Range Intrinsic and Interhemispheric Connections in the Visual Cortex of Strabismic Cats
Authors: Schmidt Kerstin E. , Kim Dae-Shik , Singer Wolf , Bonhoeffer Tobias , Löwel Siegrid
Published: April 2018

The development of both long-range intracortical and interhemispheric connections depends on visual experience. Previous experiments showed that in strabismic but not in normal cats, clustered horizontal axon projections preferentially connect cell groups activated by the same eye. This indicates that there is selective stabilization of fibers between neurons exhibiting correlated activity. Extending these experiments, we investigated in strabismic cats: (1) whether tangential connections remain confined to columns of similar orientation preference within the subsystems of left and right eye domains; and (2) whether callosal connections also extend predominantly between neurons activated by the same eye and preferring similar orientations. To this end, we analyzed in strabismic cats the topographic relationships between orientation preference domains and both intrinsic and callosal connections of area 17. Red and green latex microspheres were injected into monocular iso-orientation domains identified by optical imaging of intrinsic signals. Additionally, domains sharing the ocular dominance and orientation preference of the neurons at the injection sites were visualized by 2-deoxyglucose (2-DG) autoradiography. Quantitative analysis revealed that 56% of the retrogradely labeled cells within the injected area 17 and 60% of the transcallosally labeled neurons were located in the 2-DG-labeled iso-orientation domains. This indicates: (1) that strabismus does not interfere with the tendency of long-range horizontal fibers to link predominantly neurons of similar orientation preference; and (2) that the selection mechanisms for the stabilization of callosal connections are similar to those that are responsible for the specification of the tangential intrinsic connections.
Cells in Laminae III and IV of the Rat Spinal Cord that Possess the Neurokinin-1 Receptor and Have Dorsally Directed Dendrites Receive a Major Synaptic Input from Tachykinin-Containing Primary Afferents
Authors: Naim Magda , Spike Rosemary C. , Watt Christine , Shehab Safa A. S. , Todd Andrew J.
Published: April 2018

Many neurons with cell bodies in laminae III or IV of the spinal dorsal horn possess the neurokinin 1 receptor and have dorsal dendrites that arborize in the superficial dorsal horn. We have performed a confocal microscopic study to determine whether these cells receive inputs from substance P-containing primary afferents. All neurons of this type received contacts from substance P-immunoreactive axons, and in most cases the contacts onto dorsal dendrites were very numerous. A great majority (90–100%) of substance P-immunoreactive varicosities in contact with these cells were also immunoreactive with antibody to calcitonin gene-related peptide, indicating that they were of primary afferent origin. The density of contacts from substance P-immunoreactive varicosities onto these cells was significantly higher than that seen on cholinergic neurons in lamina III (which do not possess the receptor). Electron microscopy revealed that synapses were present at points of contact between substance P-immunoreactive boutons and dorsal dendrites of cells with the neurokinin 1 receptor. Some cells of this type belong to the spinothalamic tract, and we therefore examined neurons with cell bodies in laminae III or IV that possessed the neurokinin 1 receptor and were labeled retrogradely after thalamic injection of cholera toxin B subunit. These cells also received contacts from substance P-immunoreactive axons on their dorsal dendrites. The results of this study indicate that neurons of this type are a major target for substance P-containing primary afferents.
Repeated Generalized Seizures Induce Time-Dependent Changes in the Behavioral Seizure Response Independent of Continued Seizure Induction
Authors: Samoriski Gary M. , Applegate Craig D.
Published: April 2018

This study examined both the acute and long-lasting changes in seizure susceptibility that occur in response to the repeated induction of generalized seizure activity. Daily flurothyl-induced generalized clonic seizures resulted in a progressive decrease in both the generalized seizure threshold and the latency to the first myoclonic jerk. The threshold reduction was significant as early as the second trial and was maximal by trial 5. However, a minimum of eight seizures was necessary for the maximal reduction to be long-lasting. The present study also examined the effects of the number of seizures and the duration of the stimulation-free interval on the type of generalized seizure expressed. During the induction phase of the experiment, only generalized clonic seizures (“forebrain seizures”) were expressed. If, however, the animal was retested after a 1, 2, 3, or 4 week stimulation-free interval, a progressive increase in both the proportion of animals expressing “brainstem seizure” behaviors and the median seizure score was observed. The progression of flurothyl-induced generalized seizure behaviors was significantly altered if (1) a minimum of eight generalized clonic seizures had been expressed, and (2) a minimum of a 2 week stimulation-free interval followed. Fewer generalized clonic seizures failed to reliably produce changes in seizure phenotype, even after extended stimulus-free intervals. These data indicate that specific kindling processes are initiated during the interval of repeated seizure induction and evolve in the absence of continued seizure induction. Furthermore, these mechanisms of epileptogenesis were found to be manifest predominantly as a change in the seizure phenotype expressed and to proceed independent of changes in the generalized seizure threshold.
Neonatal Nonhandling andIn UteroPrenatal Stress Reduce the Density of NADPH-Diaphorase-Reactive Neurons in the Fascia Dentata and Ammon’s Horn of Rats
Authors: Vaid R. R. , Yee B. K. , Shalev U. , Rawlins J. N. P. , Weiner I. , Feldon J. , Totterdell S.
Published: April 2018

The density of nitric oxide (NO)-producing neurons in the fascia dentata and Ammon’s horn was assessed in 6-month-old male rats using NADPH-diaphorase (NADPH-d) histochemistry. Two separate experiments investigated whether (1) the complete absence of neonatal handling or (2) the administration of periodic prenatal stress could affect the expression and distribution of NADPH-d reactivity in the hippocampus, when compared with rats raised in normal standard laboratory conditions. Experiment 1 demonstrated that adult rats that received no handling during neonatal development (from birth to postnatal day 22) showed a very substantial reduction in NADPH-d-positive neurons per unit area throughout the entire hippocampus when compared with rats that received regular daily handling in this period. Quantitative analysis further revealed that this effect was significantly more pronounced in Ammon’s horn than in the fascia dentata, and within Ammon’s horn the dorsal region was selectively more affected. Experiment 2 showed that prenatal stress, which involved the administration of daily restraint stress to pregnant dams throughout the gestation period, also led to a reduction in NADPH-d reactivity in the hippocampus of the offspring of these dam when they reached adulthood.

The present results suggest that behavioral manipulations in the early neonatal or prenatal period can significantly alter the neurodevelopment of the hippocampal NO system and these changes might be related to some of the behavioral abnormalities that emerge later in adulthood.
β-Adrenergic Stimulation Selectively Inhibits Long-Lasting L-Type Calcium Channel Facilitation in Hippocampal Pyramidal Neurons
Authors: Cloues Robin K. , Tavalin Steven J. , Marrion Neil V.
Published: April 2018

L-type calcium channels are abundant in hippocampal pyramidal neurons and are highly clustered at the base of the major dendrites. However, little is known of their function in these neurons. Single-channel recording using a low concentration of permeant ion reveals a long-lasting facilitation of L-type channel activity that is induced by a depolarizing prepulse or a train of action potential waveforms. This facilitation exhibits a slow rise, peaking 0.5–1 sec after the train and decaying over several seconds. We have termed this behavior “delayed facilitation,” because of the slow onset. Delayed facilitation results from an increase in opening frequency and the recruitment of longer duration openings. This behavior is observed at all membrane potentials between −20 and −60 mV, with the induction and magnitude of facilitation being insensitive to voltage. β-Adrenergic receptor activation blocks induction of delayed facilitation but does not significantly affect normal L-type channel activity. Delayed facilitation of L-type calcium channels provides a prolonged source of calcium entry at negative membrane potentials. This behavior may underlie calcium-dependent events that are inhibited by β-adrenergic receptor activation, such as the slow afterhyperpolarization in hippocampal neurons.
Differential Expression of α-Bungarotoxin-Sensitive Neuronal Nicotinic Receptors in Adrenergic Chromaffin Cells: A Role for Transcription Factor Egr-1
Authors: Criado Manuel , Domı́nguez del Toro Eduardo , Carrasco-Serrano Carmen , Smillie Frazer I. , Juı́z José M. , Viniegra Salvador , Ballesta Juan J.
Published: April 2018

Adrenomedullary chromaffin cells express at least two subtypes of acetylcholine nicotinic receptors, which differ in their sensitivity to the snake toxin α-bungarotoxin. One subtype is involved in the activation step of the catecholamine secretion process and is not blocked by the toxin. The other is α-bungarotoxin-sensitive, and its functional role has not yet been defined. The α7 subunit is a component of this subtype. Autoradiography of bovine adrenal gland slices with α-bungarotoxin indicates that these receptors are restricted to medullary areas adjacent to the adrenal cortex and colocalize with the enzyme phenylethanolamineN-methyl transferase (PNMT), which confers the adrenergic phenotype to chromaffin cells. Transcripts corresponding to the α7 subunit also are localized exclusively to adrenergic cells. To identify possible transcriptional regulatory elements of the α7 subunit gene involved in the restricted expression of nicotinic receptors, we isolated and characterized its 5′ flanking region, revealing putative binding sites for the immediate early gene transcription factor Egr-1, which is known to activate PNMT expression. In reporter gene transfection experiments, Egr-1 increased α7 promoter activity by up to sevenfold. Activation was abolished when the most promoter-proximal of the Egr-1 sites was mutated, whereas modification of a close upstream site produced a partial decrease of the Egr-1 response. Because Egr-1 was found to be expressed exclusively in adrenergic cells, we suggest that this transcription factor may be part of a common mechanism involved in the induction of the adrenergic phenotype and the differential expression of α-bungarotoxin-sensitive nicotinic receptors in the adrenal gland.
Quantitative Single-Cell-Reverse Transcription-PCR Demonstrates That A-Current Magnitude Varies as a Linear Function ofshalGene Expression in Identified Stomatogastric Neurons
Authors: Baro Deborah J. , Levini Robert M. , Kim Marshall T. , Willms Allan R. , Lanning Cathy Cole , Rodriguez Hilda E. , Harris-Warrick Ronald M.
Published: April 2018

DifferentShakerfamily α-subunit genes generate distinct voltage-dependent K+currents when expressed in heterologous expression systems. Thus it generally is believed that diverse neuronal K+current phenotypes arise, in part, from differences inShakerfamily gene expression among neurons. It is difficult to evaluate the extent to which differentialShakerfamily gene expression contributes to endogenous K+current diversity, because the specificShakerfamily gene or genes responsible for a given K+current are still unknown for nearly all adult neurons. In this paper we explore the role of differentialShakerfamily gene expression in creating transient K+current (IA) diversity in the 14-neuron pyloric network of the spiny lobster,Panulirus interruptus. We used two-electrode voltage clamp to characterize the somaticIAin each of the six different cell types of the pyloric network. The size, voltage-dependent properties, and kinetic properties of the somaticIAvary significantly among pyloric neurons such that the somaticIAis unique in each pyloric cell type. Comparing these currents with theIAs obtained from oocytes injected withPanulirus shakerandshalcRNA (lobsterIshakerand lobsterIshal, respectively) reveals that the pyloric cellIAs more closely resemble lobsterIshalthan lobsterIshaker. Using a novel, quantitative single-cell-reverse transcription-PCR method to count the number ofshaltranscripts in individual identified pyloric neurons, we found that the size of the somaticIAvaries linearly with the number of endogenousshaltranscripts. These data suggest that theshalgene contributes substantially to the peak somaticIAin all neurons of the pyloric network.
T-Type Ca2+Current Properties Are Not Modified by Ca2+Channel β Subunit Depletion in Nodosus Ganglion Neurons
Authors: Lambert Régis C. , Maulet Yves , Mouton Jérôme , Beattie Ruth , Volsen Steve , De Waard Michel , Feltz Anne
Published: April 2018

At the molecular level, our knowledge of the low voltage-activated Ca2+channel (T-type) has made little progress. Using an antisense strategy, we investigated the possibility that the T-type channels have a structure similar to high voltage-activated Ca2+channels. It is assumed that high voltage-activated channels are made of at least three components: a pore forming α1subunit combined with a cytoplasmic modulatory β subunit and a primarily extracellular α2δ subunit. We have examined the effect of transfecting cranial primary sensory neurons with generic anti-β antisense oligonucleotides. We show that in this cell type, blocking expression of all known β gene products does not affect T-type current, although it greatly decreases the current amplitude of high voltage-activated channels and modifies their voltage dependence. This suggests that β subunits are likely not constitutive of T-type Ca2+channels in this cell type.
Evidence That the Homeodomain Protein Gtx Is Involved in the Regulation of Oligodendrocyte Myelination
Authors: Awatramani Raj , Scherer Steven , Grinspan Judith , Collarini Ellen , Skoff Robert , O’Hagan David , Garbern James , Kamholz John
Published: April 2018

We have investigated the patterns of postnatal brain expression and DNA binding of Gtx, a homeodomain transcription factor. Gtx mRNA accumulates in parallel with the RNAs encoding the major structural proteins of myelin, myelin basic protein (MBP), and proteolipid protein (PLP) during postnatal brain development; Gtx mRNA decreases in parallel with MBP and PLP mRNAs in the brains of myelin-deficient rats, which have a point mutation in the PLP gene. Gtx mRNA is expressed in differentiated, postmitotic oligodendrocytes but is not found in oligodendrocyte precursors or astrocytes. These data thus demonstrate that Gtx is expressed uniquely in differentiated oligodendrocytes in postnatal rodent brain and that its expression is regulated in parallel with the major myelin protein mRNAs, encoding MBP and PLP, under a variety of physiologically relevant circumstances.

Using a Gtx fusion protein produced in bacteria, we have confirmed that Gtx is a sequence-specific DNA-binding protein, which binds DNA sequences containing a core AT-rich homeodomain binding site. Immunoprecipitation of labeled DNA fragments encoding either the MBP or PLP promoter regions with this fusion protein has identified several Gtx-binding fragments, and we have confirmed these data using an electrophoretic mobility shift assay. In this way we have identified four Gtx binding sites within the first 750 bp of the MBP promoter and four Gtx binding sites within the first 1.3 kb of the PLP promoter. In addition, inspection of the PLP promoter sequence demonstrates the presence of six additional Gtx binding sites. These data, taken together, strongly suggest that Gtx is important for the function of differentiated oligodendrocytes and may be involved in the regulation of myelin-specific gene expression.