bluuebunny/crossref_metadata_2025 huggingface dataset:
Lambert-Eaton Antibodies Inhibit Ca2+Currents But Paradoxically Increase Exocytosis during Stimulus Trains in Bovine Adrenal Chromaffin Cells
Authors: Engisch Kathrin L. , Rich Mark M. , Cook Noah , Nowycky Martha C.
Published: April 2018

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease that affects neurotransmitter release at peripheral synapses. LEMS antibodies inhibit Ca2+currents in excitable cells, but it is not known whether there are additional effects on stimulus-secretion coupling. The effect of LEMS antibodies on Ca2+currents and exocytosis was studied in bovine adrenal chromaffin cells using whole-cell voltage clamp in perforated-patch recordings. Purified LEMS IgGs from five patients inhibited N- and P/Q-type Ca2+current components to different extents. The reduction in Ca2+current resulted in smaller exocytotic responses to single depolarizing pulses, but the normal relationship between integrated Ca2+entry and exocytosis (Engisch and Nowycky, 1996) was preserved. The hallmark of LEMS is a large potentiation of neuromuscular transmission after high-frequency stimulation. In chromaffin cells, stimulus trains can induce activity-dependent enhancement of the Ca2+–exocytosis relationship. Enhancement during trains occurs most frequently when pulses are brief and evoke very small amounts of Ca2+entry (Engisch et al., 1997). LEMS antibody treatment increased the percentage of trains eliciting enhancement through two mechanisms: (1) by reducing Ca2+entry and (2) through a Ca2+-independent effect on the process of enhancement. This leads to a paradoxical increase in the amount of exocytosis during stimulus trains, despite inhibition of Ca2+currents.
Expression of Type 2 Iodothyronine Deiodinase in Hypothyroid Rat Brain Indicates an Important Role of Thyroid Hormone in the Development of Specific Primary Sensory Systems
Authors: Guadaño-Ferraz Ana , Escámez Maria José , Rausell Estrella , Bernal Juan
Published: April 2018

Thyroid hormone is an important epigenetic factor in brain development, acting by modulating rates of gene expression. The active form of thyroid hormone, 3,5,3′-triiodothyronine (T3) is produced in part by the thyroid gland but also after 5′-deiodination of thyroxine (T4) in target tissues. In brain, ∼80% of T3 is formed locally from T4 through the activity of the 5′-deiodinase type 2 (D2), an enzyme that is expressed mostly by glial cells, tanycytes in the third ventricle, and astrocytes throughout the brain. D2 activity is an important point of control of thyroid hormone action because it increases in situations of low T4, thus preserving brain T3 concentrations. In this work, we have studied the expression of D2 by quantitativein situhybridization in hypothyroid animals during postnatal development. Our hypothesis was that those regions that are most dependent on thyroid hormone should present selective increases of D2 as a protection against hypothyroidism. D2 mRNA concentration was increased severalfold over normal levels in relay nuclei and cortical targets of the primary somatosensory and auditory pathways. The results suggest that these pathways are specifically protected against thyroid failure and that T3 has a role in the development of these structures. At the cellular level, expression was observed mainly in glial cells, although some interneurons of the cerebral cortex were also labeled. Therefore, the T3 target cells, mostly neurons, are dependent on local astrocytes for T3 supply.
Catecholamine Synthesis is Mediated by Tyrosinase in the Absence of Tyrosine Hydroxylase
Authors: Rios Maribel , Habecker Beth , Sasaoka Toshikuni , Eisenhofer Graeme , Tian Hua , Landis Story , Chikaraishi Dona , Roffler-Tarlov Suzanne
Published: April 2018

Catecholamine neurotransmitters are synthesized by hydroxylation of tyrosine tol-dihydroxyphenylalanine (l-Dopa) by tyrosine hydroxylase (TH). The elimination of TH in both pigmented and albino mice described here, like pigmented TH-null mice reported previously (Kobayashi et al., 1995; Zhou et al., 1995), demonstrates the unequivocal requirement for catecholamines during embryonic development. Although the lack of TH is fatal, TH-null embryos can be rescued by administration of catecholamine precursors to pregnant dams. Once born, TH-null pups can survive without further treatment until weaning. Given the relatively rapid half-life of catecholamines, we expected to find none in postnatal TH-null pups. Despite the fact that the TH-null pups lack TH and have not been supplemented with catecholamine precursers, catecholamines are readily detected in our pigmented line of TH-null mice by glyoxylic acid-induced histofluorescence at postnatal day 7 (P7) and P15 and quantitatively at P15 in sympathetically innervated peripheral organs, in sympathetic ganglia, in adrenal glands, and in brains. Between 2 and 22% of wild-type catecholamine concentrations are found in these tissues in mutant pigmented mice. To ascertain the source of the catecholamine, we examined postnatal TH-null albino mice that lack tyrosinase, another enzyme that converts tyrosine tol-Dopa but does so during melanin synthesis. In contrast to the pigmented TH-null mice, catecholamine histofluorescence is undetectable in postnatal albino mutants, and the catecholamine content of TH-null pups lacking tyrosinase is 18% or less than that of TH-null mice with tyrosinase. Thus, these extraordinary circumstances reveal that tyrosinase serves as an alternative pathway to supply catecholamines.
Striatal Neuronal Activity and Responsiveness to Dopamine and Glutamate after Selective Blockade of D1 and D2 Dopamine Receptors in Freely Moving Rats
Authors: Kiyatkin Eugene A. , Rebec George V.
Published: April 2018

Although striatal neurons receive continuous dopamine (DA) input, little information is available on the role of such input in regulating normal striatal functions. To clarify this issue, we assessed how systemic administration of selective D1 and D2 receptor blockers or their combination alters striatal neuronal processing in freely moving rats. Single-unit recording was combined with iontophoresis to monitor basal impulse activity of dorsal and ventral striatal neurons and their responses to glutamate (GLU), a major source of excitatory striatal drive, and DA. SCH-23390 (0.2 mg/kg), a D1 antagonist, strongly elevated basal activity and attenuated neuronal responses to DA compared with control conditions, but GLU-induced excitations were enhanced relative to control as indicated by a reduction in response threshold, an increase in response magnitude, and a more frequent appearance of apparent depolarization inactivation. In contrast, the D2 antagonist eticlopride (0.2 mg/kg) had a weak depressing effect on basal activity and was completely ineffective in blocking the neuronal response to DA. Although eticlopride reduced the magnitude of the GLU response, the response threshold was lower, and depolarization inactivation occurred more often relative to control. The combined administration of these drugs resembled the effects of SCH-23390, but whereas the change in basal activity and the GLU response was weaker, the DA blocking effect was stronger than SCH-23390 alone. Our data support evidence for DA as a modulator of striatal function and suggest that under behaviorally relevant conditions tonically released DA acts mainly via D1 receptors to provide a continuous inhibiting or restraining effect on both basal activity and responsiveness of striatal neurons to GLU-mediated excitatory input.
Motor Pattern Specification by Dual Descending Pathways to a Lobster Rhythm-Generating Network
Authors: Combes Denis , Meyrand Pierre , Simmers John
Published: April 2018

In the European lobsterHomarus gammarus, rhythmic masticatory movements of the three foregut gastric mill teeth are generated by antagonistic sets of striated muscles that are driven by a neural network in the stomatogastric ganglion.In vitro, this circuit can spontaneously generate a single (type I) motor program, unlikein vivoin which gastric mill patterns with different phase relationships are found. By using paired intrasomatic recordings, all elements of the gastric mill network, which consists mainly of motoneurons, have been identified and their synaptic relationships established. The gastric mill circuit ofHomarusis similar to that of other decapod crustaceans, although some differences in neuron number and synaptic connectivity were found. Moreover, specific members of the lobster network receive input from two identified interneurons, one excitatory and one inhibitory, that project from each rostral commissural ganglion. Integration of input from these projection elements is mediated by synaptic interactions within the gastric mill network itself. In arrhythmic preparations, direct phasic stimulation of the previously identified commissural gastric (CG) interneuron evokes gastric mill output similar to the type I pattern spontaneously expressedin vitroandin vivo. The newly identified gastric inhibitor interneuron makes inhibitory synapses onto a different subset of gastric mill neurons and, when activated with the CG neuron, drives gastric mill output similar to the type II pattern that is only observed in the intact animal. Thus, two distinct phenotypes of gastric mill network activity can be specified by the concerted actions of parallel input pathways and synaptic connectivity within a target central pattern generator.
Dynamic Restructuring of a Rhythmic Motor Program by a Single Mechanoreceptor Neuron in Lobster
Authors: Combes Denis , Meyrand Pierre , Simmers John
Published: April 2018

We have explored the synaptic and cellular mechanisms by which a single primary mechanosensory neuron, the anterior gastric receptor (AGR), reconfigures motor output of the gastric mill central pattern generator (CPG) in the stomatogastric nervous system (STNS) of the lobsterHomarus gammarus. AGR is activatedin vivoby contraction of the medial tooth protractor muscle gm1 and accesses the gastric CPG via excitation of two in-parallel interneurons, the excitatory commissural gastric (CG) and the inhibitory gastric inhibitor (GI). In the spontaneously active STNSin vitro, weak firing of AGR in time with gastric mill motoneurons (GM) reinforces an ongoing type I gastric mill rhythm in which all gastric teeth power-stroke motoneurons are synchronously active. With strong AGR firing, these phase relationships switch abruptly to a type II pattern in which lateral and medial teeth power-stroke motoneurons fire in antiphase. Our results suggest that these bimodal actions on the gastric mill rhythm depend on the balance of firing of the CG and GI interneurons and that selection of the pathway resides in their different postsynaptic sensitivities to AGR. Whereas high intrinsic firing rates of the CG neuron ensure that the excitatory pathway predominates during low levels of sensory input, strong synaptic facilitation in the GI neuron favors the inhibitory pathway during high levels of receptor activity. Feedback from a single mechanosensory neuron is thus able, in an activity-dependent manner, to specify different motor programs from a single central pattern-generating network.
Somatotopic Activation of Opioid Systems by Target-Directed Expectations of Analgesia
Authors: Benedetti Fabrizio , Arduino Claudia , Amanzio Martina
Published: April 2018

We induced specific expectations of analgesia on four different parts of the body to understand how endogenous opioid systems are activated by expectancies. The left hand, right hand, left foot, and right foot were simultaneously stimulated by means of a subcutaneous injection of capsaicin, which produces a painful burning sensation. Specific expectations of analgesia were induced by applying a placebo cream on one of these body parts and by telling the subjects that it was a powerful local anesthetic. In such a way, expectancy of the anesthetic effect was directed only toward the part on which the placebo cream was applied. We found that a placebo analgesic response occurred only on the treated part, whereas no variation in pain sensitivity was found on the untreated parts. If the same experiment was performed after an intravenous infusion of the opioid antagonist naloxone, this highly spatial-specific placebo response was totally abolished, indicating that it was completely mediated by endogenous opioid systems. These findings show that a spatially directed expectation of pain reduction is capable of inducing a specific effect only on the part of the body which is the target of the expectation. Most important, this specific effect is mediated by endogenous opioids, indicating that placebo-activated opioids do not act on the entire body but only on the part where expectancy is directed. This suggests that a highly organized and somatotopic network of endogenous opioids links expectation, attention, and body schema.
Upregulation of Tumor Necrosis Factor α Transport across the Blood–Brain Barrier after Acute Compressive Spinal Cord Injury
Authors: Pan Weihong , Kastin Abba J. , Bell Richard L. , Olson Richard D.
Published: April 2018

Tumor necrosis factor α (TNF) is a cytokine that is involved in the inflammatory process after CNS injury and is implicated in neuroregeneration. A saturable transport system for TNF located at the blood–brain barrier (BBB) is responsible for the limited entry of TNF from blood to the CNS in normal mice.

After partial disruption of the BBB by compression of the lumbar spinal cord, permeability to TNF was increased not only in the lumbar spinal cord but also in brain and distal spinal cord segments, where the BBB remained intact. The increase in the entry of TNF to the CNS followed a biphasic temporal pattern, with a first peak immediately after injury and a second peak starting on day 3; these changes lasted longer than the mere disruption of the BBB. The increased entry of TNF was abolished by addition of excess unlabeled TNF, showing that the transport system for TNF remained saturable after spinal cord injury (SCI) and providing evidence that the enhanced entry of TNF could not be explained by diffusion or leakage.

This study adds strong support for our concept that the saturable transport system for TNF across the BBB can be upregulated in the diseased state, and it suggests that the BBB is actively involved in the modulation of the processes of degeneration and regeneration after SCI.
Cellular Defects and Altered Gene Expression in PC12 Cells Stably Expressing Mutant Huntingtin
Authors: Li Shi-Hua , Cheng Anna L. , Li He , Li Xiao-Jiang
Published: April 2018

Expanded polyglutamine tracts cause huntingtin and other proteins to accumulate and aggregate in neuronal nuclei. Whether the intranuclear aggregation or localization of a polyglutamine protein initiates cellular pathology remains controversial. We established stably transfected pheochromocytoma PC12 cells that express the N-terminal fragment of huntingtin containing 20 (20Q) or 150 (150Q) glutamine residues. The 150Q protein is predominantly present in the nuclei, whereas the 20Q protein is distributed throughout the cytoplasm. Electron microscopic examination confirmed that most of the 150Q protein is diffuse in the nucleus with very few microscopic aggregates observed. Compared with parental PC12 cells and cells expressing 20Q, cells expressing 150Q display abnormal morphology, lack normal neurite development, die more rapidly, and are more susceptible to apoptotic stimulation. The extent of these cellular defects in 150Q cells is correlated with the expression level of the 150Q protein. Differential display PCR and expression studies show that cells expressing 150Q have altered expression of multiple genes, including those that are important for neurite outgrowth. Our study suggests that mutant huntingtin in the nucleus is able to induce multiple cellular defects by interfering with gene expression even in the absence of aggregation.
The Native Rat Olfactory Cyclic Nucleotide-Gated Channel Is Composed of Three Distinct Subunits
Authors: Bönigk Wolfgang , Bradley Jonathan , Müller Frank , Sesti Federico , Boekhoff Ingrid , Ronnett Gabriele V. , Kaupp U. Benjamin , Frings Stephan
Published: April 2018

Cyclic nucleotide-gated (CNG) channels play central roles in visual and olfactory signal transduction. In the retina, rod photoreceptors express the subunits CNCα1 and CNCβ1a. In cone photoreceptors, only CNCα2 expression has been demonstrated so far. Rat olfactory sensory neurons (OSNs) express two homologous subunits, here designated CNCα3 and CNCα4. This paper describes the characterization of CNCβ1b, a third subunit expressed in OSNs and establishes it as a component of the native channel. CNCβ1b is an alternate splice form of the rod photoreceptor CNCβ1a subunit. Analysis of mRNA and protein expression together suggest co-expression of all three subunits in sensory cilia of OSNs. From single-channel analyses of native rat olfactory channels and of channels expressed heterologously from all possible combinations of the CNCα3, -α4, and -β1b subunits, we conclude that the native CNG channel in OSNs is composed of all three subunits. Thus, CNG channels in both rod photoreceptors and olfactory sensory neurons result from coassembly of specific α subunits with various forms of an alternatively spliced β subunit.
Developmental Requirement of gp130 Signaling in Neuronal Survival and Astrocyte Differentiation
Authors: Nakashima Kinichi , Wiese Stefan , Yanagisawa Makoto , Arakawa Hirokazu , Kimura Naoki , Hisatsune Tatsuhiro , Yoshida Kanji , Kishimoto Tadamitsu , Sendtner Michael , Taga Tetsuya
Published: April 2018

gp130 is a signal-transducing receptor component used in common by the interleukin-6 (IL-6) family of hematopoietic and neurotrophic cytokines, including IL-6, IL-11, leukemia-inhibitory factor, ciliary neurotrophic factor, oncostatin-M, and cardiotrophin-1. We have examined in this study a role of gp130 in the nervous system by analyzing developmental cell death of several neuronal populations and the differentiation of astrocytes in gp130-deficient mice. A significant reduction was observed in the number of sensory neurons in L5 dorsal root ganglia and motoneurons in the facial nucleus, the nucleus ambiguus, and the lumbar spinal cord in gp130 −/− mice on embryonic day 18.5. On the other hand, no significant neuronal loss was detectable on day 14.5, suggesting a physiological role of gp130 in supporting newly generated neurons during the late phase of development when naturally occurring cell death takes place. Moreover, expression of an astrocyte marker, GFAP, was severely reduced in the brain of gp130 −/− mice. Our data demonstrate that gp130 expression is essential for survival of subgroups of differentiated motor and sensory neurons and for the differentiation of major populations of astrocytesin vivo.
Chronic Pain is Associated with Increased TrkA Immunoreactivity in Spinoreticular Neurons
Authors: Pezet Sophie , Onténiente Brigitte , Grannec Gaël , Calvino Bernard
Published: April 2018

Repetitive noxious stimulation leads to permanent adaptive changes of central pathways involved in the genesis and integration of nociception. Several classes of neurotrophic factors that affect brain plasticity are also involved in the regulation of sensory functions in adulthood. To investigate a putative role of nerve growth factor (NGF) in central plasticity linked to chronic pain, modifications in immunoreactivity (IR) for the high-affinity NGF receptor, TrkA, were studied at spinal levels in a rat model of inflammatory chronic pain, adjuvant-induced arthritis (AIA). We report a specific increase in the number of TrkA-IR profiles in laminae V–VI at lumbar levels L3 and L4 in arthritic rats. Tract tracing using FluoroGold injections in the ventrobasal complex of the thalamus and in the brainstem showed that these increased TrkA-IR profiles are spinoreticular neurons. Dual labeling with calcitonin gene-related peptide or substance P showed that TrkA-IR neurons were mainly located in projection fields of small- to medium-sized primary afferent fibers, which convey nociceptive inputs. These results suggest that TrkA-containing neurons of the spinal dorsal horn participate in the first central relay of transmission of nociceptive information to supraspinal centers. Enhanced numbers of TrkA-IR neurons during AIA strongly support the hypothesis of a participation of NGF in adaptive mechanisms of central nociceptive pathways observed in chronic pain states.
Prospective Coding for Objects in Primate Prefrontal Cortex
Authors: Rainer Gregor , Rao S. Chenchal , Miller Earl K.
Published: April 2018

We examined neural activity in prefrontal (PF) cortex of monkeys performing a delayed paired associate task. Monkeys were cued with a sample object. Then, after a delay, a test object was presented. If the test object was the object associated with the sample during training (i.e., its target), they had to release a lever. Monkeys could bridge the delay by remembering the sample (a sensory-related code) and/or thinking ahead to the expected target (a prospective code). Examination of the monkeys’ behavior suggested that they were relying on a prospective code. During and shortly after sample presentation, neural activity in the lateral PF cortex primarily reflected the sample. Toward the end of the delay, however, PF activity began to reflect the anticipated target, which indicated a prospective code. These results provide further confirmation that PF cortex does not simply buffer incoming visual inputs, but instead selectively processes information relevant to current behavioral demands, even when this information must be recalled from long-term memory.
Optic Flow Input to the Hippocampal Formation from the Accessory Optic System
Authors: Wylie Douglas R. W. , Glover Randal G. , Aitchison John D.
Published: April 2018

Recent studies in rodents have implicated the hippocampal formation in “path integration”: the ability to use self-motion cues (ideothesis) to guide spatial behavior. Such models of hippocampal function assume that self-motion information arises from the vestibular system. In the present study we used the retrograde tracer cholera toxin subunit B, the anterograde tracer biotinylated dextran amine, and standard extracellular recording techniques to investigate whether the hippocampal formation [which consists of the hippocampus proper and the area parahippocampalis (Hp/APH) in pigeons] receives information from the accessory optic system (AOS). The AOS is a visual pathway dedicated to the analysis of the “optic flow fields” that result from self-motion. Optic flow constitutes a rich source of ideothetic information that could be used for navigation. Both the nucleus of the basal optic root (nBOR) and nucleus lentiformis mesencephali of the AOS were shown to project to the area ventralis of Tsai (AVT), which in turn was shown to project to the Hp/APH. A smaller direct projection from the nBOR pars dorsalis to the hippocampus was also revealed. During extracellular recording experiments, about half of the cells within the AVT responded to optic flow stimuli. Together these results illustrate that the Hp/APH receives information about self-motion from the AOS. We postulate that this optic flow information is used for path integration. A review of the current literature suggests that an analogous neuronal circuit exists in mammals, but it has simply been overlooked.
Differential Distribution of Intracellular Glutamate Receptors in Dendrites
Authors: Rubio Maria E. , Wenthold Robert J.
Published: April 2018

Glutamate receptors are synthesized in the cell body and transported in intracellular compartments to the target synapse. The objective of the present study was to analyze the intracellular pool of glutamate receptors and determine whether the intracellular pool was related to the synaptic distribution of the receptors. As a model system, we chose the fusiform cell of the dorsal cochlear nucleus for which we have previously demonstrated that receptors are selectively targeted to synapses on apical and basal dendrites. A combination of retrograde tracing and postembedding immunogold labeling was used to quantify intracellular receptors in segments of apical and basal dendrites. Immunolabeling for GluR4 and mGluR1α is present at synapses on basal dendrites but not on apical dendrites, whereas immunolabeling for GluR2/3 is present at both populations of synapses. In the analysis of intracellular pools, we find that GluR2/3 is equally distributed in apical and basal dendrites, whereas GluR4 and mGluR1α are more concentrated in basal dendrites than in apical dendrites. These findings indicate that the distribution of intracellular receptors is related to that of synaptic receptors and suggest that a mechanism exists in neurons to target proteins to dendritic domains soon after synthesis. We found no evidence for the existence of a pool of intracellular receptors, which could represent a receptor reserve, near the postsynaptic density. Receptors were often found in clusters associated with tubulovesicular membranes of the endoplasmic reticulum, identified with immunoglobulin binding protein (BIP) or calnexin, suggesting that this organelle is involved in receptor transport in dendrites.
Diminished Viability, Growth, and Behavioral Efficacy of Fetal Dopamine Neuron Grafts in Aging Rats with Long-Term Dopamine Depletion: An Argument for Neurotrophic Supplementation
Authors: Collier Timothy J. , Sortwell Caryl E. , Daley Brian F.
Published: April 2018

We examined the behavioral and morphological correlates of the response to a single intrastriatal dispersed cell graft of fetal rat ventral mesencephalic tissue in male Fischer-344 rats of varying age (4, 17, and 24–26 months old) and history of mesostriatal dopamine (DA) depletion (1 or 14 months). Our goal was to determine the impact of advancing age and duration of DA depletion in the host on DA graft viability and function. The findings can be summarized as follows. (1) Fetal DA neuron grafts that were effective in completely ameliorating amphetamine-induced rotational behavior in young rats with short-term lesions were virtually without effect in aged rats with long-term lesions. Middle-aged rats with long-term lesions responded to these grafts with partial behavioral recovery. (2) Age of the host at the time of transplantation, and not duration of DA depletion, was the primary determinant of response to DA grafts. (3) Diminished efficacy of grafts in lesioned aging rats was related to decreased survival and neurite extension of transplanted DA neurons. (4) Co-grafts of DA neurons with Schwann cells as a source of neurotrophic support improved the behavioral outcome of grafts in aged lesioned rats. These findings support the view that the DA-depleted striatum of aged rats is an impoverished environment for survival, growth, and function of DA grafts. Consistent with this view, local supplementation of the neurotrophic environment of grafted DA neurons with products of co-grafted Schwann cells, a demonstrated source of neurotrophic activity for embryonic DA neurons, improved graft outcome.
Coordinated Transcriptional Regulation of theunc-25Glutamic Acid Decarboxylase and theunc-47GABA Vesicular Transporter by theCaenorhabditis elegansUNC-30 Homeodomain Protein
Authors: Eastman Catharine , Horvitz H. Robert , Jin Yishi
Published: April 2018

An important aspect of the specification of neuronal fate is the choice of neurotransmitter. InCaenorhabditis elegansthe neurotransmitter GABA is synthesized by the UNC-25 glutamic acid decarboxylase (GAD) and packaged into synaptic vesicles by the UNC-47 transporter. Bothunc-25andunc-47are expressed in 26 GABAergic neurons of five different types. Previously, we have identified that theunc-30homeobox gene controls the fate of 19 type D GABAergic neurons. We report here that the UNC-30 homeodomain protein transcriptionally regulates the expression ofunc-25andunc-47in the 19 type D neurons. UNC-30 bound to theunc-25andunc-47promoters sequence-specifically. Mutations in the UNC-30 binding sites of theunc-25andunc-47promoters abolished the expression of reporter genes in the D neurons. The ectopic expression of UNC-30 induced the ectopic expression of reporter genes driven by the wild-typeunc-25andunc-47promoters. Our data establish a mechanism for cell type-specific transcriptional coregulation of genes required for the synthesis and packaging of the neurotransmitter GABA.
Nicotinic Receptor Assembly Requires Multiple Regions throughout the γ Subunit
Authors: Eertmoed Alison L. , Green William N.
Published: April 2018

Assembly of ionotropic neurotransmitter receptors typified by acetylcholine receptors (AChRs) is thought to be directed by an N-terminal extracellular domain of a subunit. Consistent with this hypothesis, chimeras with the δ subunit N-terminal domain fused to the rest of the γ subunit can substitute for δ, but not γ, subunits during AChR assembly. However, chimeras with the γ subunit N-terminal domain fused to the rest of the δ subunit cannot substitute for γ or δ subunits during assembly. Furthermore, expression of this chimera with the four wild-type subunits prevents the formation of α-bungarotoxin (Bgt) binding sites. Instead of AChR pentamers, complexes are assembled containing only the chimera and either α or β subunits. Based on the results of additional γ-δ chimeras, there are at least two different regions within the C-terminal half of the chimera required for the dominant-negative effect. Our results indicate that the N-terminal domain of the γ subunit mediates the initial subunit associations, whereas signals in the C-terminal half of the subunit are required for subsequent subunit interactions.
Estradiol Modulates bcl-2 in Cerebral Ischemia: A Potential Role for Estrogen Receptors
Authors: Dubal Dena B. , Shughrue Paul J. , Wilson Melinda E. , Merchenthaler Istvan , Wise Phyllis M.
Published: April 2018

We have shown that physiological levels of estradiol exert profound protective effects on the cerebral cortex in ischemia induced by permanent middle cerebral artery occlusion. The major goal of this study was to begin to elucidate potential mechanisms of estradiol action in injury. Bcl-2 is a proto-oncogene that promotes cell survival in a variety of tissues including the brain. Because estradiol is known to promote cell survival via Bcl-2 in non-neural tissues, we tested the hypothesis that estradiol decreases cell death by influencingbcl-2expression in ischemic brain injury. Furthermore, because estradiol may protect the brain through estrogen receptor-mediated mechanisms, we examined expression of both receptor subtypesERαandERβin the normal and injured brain. We analyzed gene expression by RT-PCR in microdissected regions of the cerebral cortex obtained from injured and sham female rats treated with estradiol or oil. We found that estradiol prevented the injury-induced downregulation ofbcl-2expression. This effect was specific tobcl-2, as expression of other members of thebcl-2family (bax, bcl-xL, bcl-xS, andbad) was unaffected by estradiol treatment. We also found that estrogen receptors were differentially modulated in injury, withERβexpression parallelingbcl-2expression. Finally, we provide the first evidence of functional ERβ protein that is capable of binding ligand within the region of the cortex where estradiol-mediated neuroprotection was observed in cerebral ischemia. These findings indicate that estradiol modulates the expression ofbcl-2in ischemic injury. Furthermore, our data suggest that estrogen receptors may be involved in hormone-mediated neuroprotection.
Delayed Rectifier Currents in Rat Globus Pallidus Neurons Are Attributable to Kv2.1 and Kv3.1/3.2 K+Channels
Authors: Baranauskas Gytis , Tkatch Tatiana , Surmeier D. James
Published: April 2018

The symptoms of Parkinson disease are thought to result in part from increased burst activity in globus pallidus neurons. To gain a better understanding of the factors governing this activity, we studied delayed rectifier K+conductances in acutely isolated rat globus pallidus (GP) neurons, using whole-cell voltage-clamp and single-cell RT-PCR techniques. From a holding potential of −40 mV, depolarizing voltage steps in identified GP neurons evoked slowly inactivating K+currents. Analysis of the tail currents revealed rapidly and slowly deactivating currents of similar amplitude. The fast component of the current deactivated with a time constant of 11.1 ± 0.8 msec at −40 mV and was blocked by micromolar concentrations of 4-AP and TEA (KD∼140 μm). The slow component of the current deactivated with a time constant of 89 ± 10 msec at −40 mV and was less sensitive to TEA (KD= 0.8 mm) and 4-AP (KD∼6 mm). Organic antagonists of Kv1 family channels had little or no effect on somatic currents. These properties are consistent with the hypothesis that the rapidly deactivating current is attributable to Kv3.1/3.2 channels and the slowly deactivating current to Kv2.1-containing channels. Semiquantitative single-cell RT-PCR analysis of Kv3 and Kv2 family mRNAs supported this conclusion. An alteration in the balance of these two channel types could underlie the emergence of burst firing after dopamine-depleting lesions.
Local Presentation of Substrate Molecules Directs Axon Specification by Cultured Hippocampal Neurons
Authors: Esch Teresa , Lemmon Vance , Banker Gary
Published: April 2018

Axon specification is a crucial, early step in neuronal development, but little is known about how this event is controlledin vivo. To test the hypothesis that local presentation of growth-promoting molecules can direct axon specification, we cultured hippocampal neurons on substrates patterned with stripes of poly-l-lysine and either laminin (LN) or the neuron–glia cell adhesion molecule (NgCAM). Although undifferentiated neurites contacted both substrates equally, axons formed preferentially on LN or NgCAM. Time-lapse studies revealed that changes in the growth pattern of a cell indicative of axon specification began almost immediately after the growth cone of one of the neurites of the cell contacted LN or NgCAM. When cells were plated on alternating stripes of LN and NgCAM, cells with their somata on LN usually formed axons on NgCAM, whereas those with somata on NgCAM preferentially formed axons on LN. This suggests that the change from one axon-promoting substrate to another also provides a signal sufficient to specify the axon. These results demonstrate that contact with preferred substrate molecules can govern which neurite becomes the axon and thus direct the development of neuronal polarity.
Glutamate Release through Volume-Activated Channels during Spreading Depression
Authors: Basarsky Trent A. , Feighan Denise , MacVicar Brian A.
Published: April 2018

Volume-sensitive organic anion channels (VSOACs) in astrocytes are activated by cell swelling and are permeable to organic anions, such as glutamate and taurine. We have examined the release of glutamate through VSOACs during the propagation of spreading depression (SD). SD was induced by bath application of ouabain in hippocampal brain slices and was monitored by imaging intrinsic optical signals, a technique that provides a measure of cellular swelling. The onset of SD was associated with increased light transmittance, confirming previous studies that cellular swelling occurs during SD. NMDA receptor antagonists, either noncompetitive (MK-801, 10–50 μm) or competitive (CGS-17355, 100 μm), reduced the rate of propagation of SD, indicating that glutamate release contributes to SD onset. SD still occurred in zero Ca2+–EGTA (0-Ca2+–EGTA) solution, a manipulation that depresses synaptic transmission. HPLC measurements indicated that, even in this solution, there was significant glutamate release. Two lines of experiments indicated that glutamate was released through VSOACs during SD. First, 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), a blocker of VSOACs, depressed the rate of propagation of SD in a manner similar to NMDA antagonists. Second, NPPB inhibited the release of glutamate during SD in 0-Ca2+–EGTA external solution. These results indicate that cellular swelling during SD causes the activation of VSOACs and the release of glutamate by permeation through this channel. Cellular swelling is a result of neuronal activity and is observed during excitotoxicity. Therefore, glutamate release from VSOAC activation could occur under conditions of cell swelling and contribute to excitotoxic damage.
Bcl-2 Overexpression Does Not Protect Neurons from Mutant Neurofilament-Mediated Motor Neuron Degeneration
Authors: Houseweart Megan K. , Cleveland Don W.
Published: April 2018

Transgenic mice with a point mutation in the light neurofilament gene develop amyotrophic lateral sclerosis–like motor neuron disease characterized by selective spinal motor neuron loss, neurofilamentous accumulations, and severe muscle atrophy. To test whether the large motor neurons at risk in this disease could be protected from mutant neurofilament-mediated killing, these mice were bred to mice overexpressing the humanBcl-2proto-oncogene. Elevated levels of Bcl-2 increased the numbers of motor and sensory axons surviving after the developmental period of naturally occurring cell death but did not greatly reduce the number of degenerating axons or protect the large motor neurons from mutant neurofilament-mediated death.
Proline-Rich Synapse-Associated Protein-1/Cortactin Binding Protein 1 (ProSAP1/CortBP1) Is a PDZ-Domain Protein Highly Enriched in the Postsynaptic Density
Authors: Boeckers Tobias M. , Kreutz Michael R. , Winter Carsten , Zuschratter Werner , Smalla Karl-Heinz , Sanmarti-Vila Lydia , Wex Heike , Langnaese Kristina , Bockmann Juergen , Garner Craig C. , Gundelfinger Eckart D.
Published: April 2018

The postsynaptic density (PSD) is crucially involved in the structural and functional organization of the postsynaptic neurotransmitter reception apparatus. Using antisera against rat brain synaptic junctional protein preparations, we isolated cDNAs coding for proline-rich synapse-associated protein-1 (ProSAP1), a PDZ-domain protein. This protein was found to be identical to the recently described cortactin-binding protein-1 (CortBP1). Homology screening identified a related protein, ProSAP2. Specific antisera raised against a C-terminal fusion construct and a central part of ProSAP1 detect a cluster of immunoreactive bands of 180 kDa in the particulate fraction of rat brain homogenates that copurify with the PSD fraction. Transcripts and immunoreactivity are widely distributed in the brain and are upregulated during the period of synapse formation in the brain. In addition, two short N-terminal insertions are detected; they are differentially regulated during brain development. Confocal microscopy of hippocampal neurons showed that ProSAP1 is predominantly localized in synapses, and immunoelectron microscopyin siturevealed a strong association with PSDs of hippocampal excitatory synapses. The accumulation of ProSAP1 at synaptic structures was analyzed in the developing cerebral cortex. During early postnatal development, strong immunoreactivity is detectable in neurites and somata, whereas from postnatal day 10 (P10) onward a punctate staining is observed. At the ultrastructural level, the immunoreactivity accumulates at developing PSDs starting from P8. Both interaction with the actin-binding protein cortactin and early appearance at postsynaptic sites suggest that ProSAP1/CortBP1 may be involved in the assembly of the PSD during neuronal differentiation.
Evidence for Tonic Activation of NK-1 Receptors during the Second Phase of the Formalin Test in the Rat
Authors: Henry J. L. , Yashpal K. , Pitcher G. M. , Chabot J.-G. , Coderre T. J.
Published: April 2018

Behavioral, electrophysiological, and autoradiographic experiments were done to study the second nociceptive phase in the formalin test. In initial experiments, this second phase was attenuated by 1–10 mg of the NK-1 receptor antagonist CP-99,994, given subcutaneously 10, 30, or 60 min before formalin (n= 8–10) and by 20 μg given intrathecally 20 min after formalin (n= 13); the inactive isomer CP-100,263 was ineffective. In electrophysiological experiments on single dorsal horn neuronsin vivo, the excitatory responses to subcutaneous formalin injection (50 μl, 2.5%) were attenuated by subsequent intravenously administration of the NK-1 receptor antagonist CP-96,345 (0.5 mg/kg;n= 8), given 35–40 min after formalin, but not by the inactive enantiomer CP-96,344 (0.5 mg/kg;n= 9). Finally, autoradiographic binding of exogenous [125I]BH-substance P in the lumbar cord was reduced at 5 and 25 min after formalin (50 μl, 1 or 5%), with an intermediate level of reduction at 12 min. These data are interpreted as evidence that the second phase of nociceptive scores in the formalin test is attributable at least partially to tonic activation of NK-1 receptors at the spinal level, whether because of a temporally limited release of substance P, for example only during the first phase, but a slow removal or breakdown of substance P, or, more likely, because of tonic release from primary afferents throughout the second phase. Irrespective of the mechanism, it can be concluded that at least some of the persistent nociceptive effects associated with peripheral inflammation, or at least those provoked by subcutaneous injection of formalin, are mediated via continuous activation of NK-1 receptors at the level of the spinal dorsal horn; this may relate directly to mechanisms underlying prolonged nociceptive pains in humans.
Smell and Taste Perception inDrosophila melanogasterLarva: Toxin Expression Studies in Chemosensory Neurons
Authors: Heimbeck Gertrud , Bugnon Véronique , Gendre Nanaë , Häberlin Corinne , Stocker Reinhard F.
Published: April 2018

GAL4-driven targeted expression of tetanus toxin light chain (UAS-TeTxLC) in a subset of chemosensory neurons of the larval antennomaxillary complex (AMC) and pharynx causes abnormal chemosensory behavior inDrosophila melanogaster. Consistent with strongest staining in the dorsal organ (DO), the presumed olfactory organ of the AMC, tetanus toxin-expressing larvae subjected to an olfactory preference assay show anosmic behavior to most volatile substances tested. Furthermore, we observed reduced responses to sodium chloride, fructose, and sucrose in gustatory plate assays. Surprisingly, the entire subset of labeled sensory neurons from the terminal (maxillary) organ (TO) of the AMC was found to project via the antennal nerve to the larval antennal lobe region. The maxillary nerve remained completely unstained. Hence, a subset of neurons from the TO builds an anatomical entity with projections from the DO. Our results suggest that the AMC contains both olfactory and gustatory sensilla, and that the DO is the main olfactory organ in larvae.
Attenuation of Emotional and Nonemotional Memories after their Reactivation: Role of β Adrenergic Receptors
Authors: Przybyslawski Jean , Roullet Pascal , Sara Susan J.
Published: April 2018

A memory trace in its active state is susceptible to interference by amnesic agents, such as hypothermia and electroconvulsive shock, and by NMDA receptor antagonists, suggesting that a time-dependent consolidation process occurs each time a memory is reactivated. The role of β noradrenergic receptors in reconsolidation in rats was examined in both a positively reinforced radial maze task and a footshock-reinforced conditioned emotional response task. For the former, rats were trained over several days in a spatial reference memory task and received a single reactivation trial followed by propranolol. A temporally graded impairment was observed when propranolol treatment occurred after the memory reactivation trial. In the emotional task, memory impairing effects of propranolol were greater when the drug was administered after a reactivation trial than when administered immediately after the initial training. These results suggest that reactivation of memory triggers a β receptor-dependent cascade of intracellular events, recapitulating that which occurs during initial postacquisition consolidation, thus permitting reorganization of the existing memory as a function of new information in the retrieval environment. This remarkable lability of an active memory trace provides a new basis for pharmacotherapeutic intervention in such syndromes as Posttraumatic Stress Disorder. β adrenoreceptor antagonists may be promising pharmacological agents for attenuating debilitating memories at the time of their controlled reactivation.
Coordination of Fast and Slow Rhythmic Neuronal Circuits
Authors: Bartos Marlene , Manor Yair , Nadim Farzan , Marder Eve , Nusbaum Michael P.
Published: April 2018

Interactions among rhythmically active neuronal circuits that oscillate at different frequencies are important for generating complex behaviors, yet little is known about the underlying cellular mechanisms. We addressed this issue in the crab stomatogastric ganglion (STG), which contains two distinct but interacting circuits. These circuits generate the gastric mill rhythm (cycle period, ∼10 sec) and the pyloric rhythm (cycle period, ∼1 sec). When the identified modulatory projection neuron named modulatory commissural neuron 1 (MCN1) is activated, the gastric mill motor pattern is generated by interactions among MCN1 and two STG neurons [the lateral gastric (LG) neuron and interneuron 1]. We show that, during MCN1 stimulation, an identified synapse from the pyloric circuit onto the gastric mill circuit is pivotal for determining the gastric mill cycle period and the gastric–pyloric rhythm coordination. To examine the role of this intercircuit synapse, we replaced it with a computational equivalent via the dynamic-clamp technique. This enabled us to manipulate better the timing and strength of this synapse. We found this synapse to be necessary for production of the normal gastric mill cycle period. The synapse acts, during each LG neuron interburst, to boost rhythmically the influence of the modulatory input from MCN1 to LG and thereby to hasten LG neuron burst onset. The two rhythms become coordinated because LG burst onset occurs with a constant latency after the onset of the triggering pyloric input. These results indicate that intercircuit synapses can enable an oscillatory circuit to control the speed of a slower oscillatory circuit, as well as provide a mechanism for intercircuit coordination.
Excitotoxic Septal Lesions Result in Spatial Memory Deficits and Altered Flexibility of Hippocampal Single-Unit Representations
Authors: Leutgeb Stefan , Mizumori Sheri J. Y.
Published: April 2018

The septal nuclei are reciprocally connected with the hippocampal formation and contribute importantly to spatial and memory processing. Using excitotoxic lesions of the septal area, we investigated whether neurodegeneration in subcortical projections to hippocampus can compromise flexible information processing by hippocampal single units. In agreement with the mild effects of excitotoxic septal lesions on hippocampal physiology compared with fimbria-fornix lesions and septal inactivation, we observed limited lesion effects on single-unit activity. The location specificity of hippocampal complex spike cells remained unchanged, but a less reliable location-dependent discharge was observed in experimental animals with a pronounced postoperative working memory deficit. Testing in the absence of ambient illumination and in a new environment revealed that the spatial correlates of complex spike cells in lesioned animals may rely on a more limited set of sensory cues. Altered sensory cues resulted in a significantly different response pattern between the control and lesion group in the new environment, a situation that normally results in place field reorganization. Such a group difference was not observed during dark testing, a condition in which place field reorganization is less prominent. A contribution of hippocampal interneurons to the observed alterations in the spatial properties of the principal cells was suggested by decreased theta modulation in the lesioned group. Because excitotoxic lesions result in memory deficits that resemble age-related memory problems in the absence of age-related degenerative processes, we suggest that septal neurodegeneration could directly contribute to those behavioral changes with advanced age that correlate with functional alterations in the hippocampal formation.