bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of Cell Death Induced by the Mitochondrial Toxin 3-Nitropropionic Acid: Acute Excitotoxic Necrosis and Delayed Apoptosis
Authors: Pang Zhen , Geddes James W.
Published: April 2018

Impaired energy metabolism may play an important role in neuronal cell death after brain ischemia and in late-onset neurodegenerative diseases. Both excitotoxic necrosis and apoptosis have been implicated in cell death induced by metabolic impairment. However, the factors that determine whether cells undergo apoptosis or necrosis are not known. In the present study, metabolic impairment was induced by 3-nitropropionic acid (3-NP), a suicide inhibitor of succinate dehydrogenase. Treatment of cultured rat hippocampal neurons with 3-NP resulted in two types of cell death with distinct morphological, pharmacological, and biochemical features. A rapid necrotic cell death, characterized by cell swelling and nuclear shrinkage, could be completely prevented by the NMDA receptor antagonist MK-801 (10 μm) and dose-dependently potentiated by low micromolar levels of extracellular glutamate. A slowly evolving apoptotic death, characterized by nuclear fragmentation, was not attenuated by MK-801 but was prevented by cycloheximide (1 μg/ml). The combination of MK-801 and cycloheximide resulted in an almost complete protection against 3-NP-induced cell death. DNA fragmentation, detected by the terminal deoxynucleotidyl transferase-mediated dUTP-X 3′ nick end-labeling technique, was a late event in apoptosis and also occurred after necrotic cell death. ATP depletion was an early event in the 3-NP-induced neuronal degeneration, and the decline in ATP was exacerbated by glutamate. We conclude that 3-NP triggers two separate cell death pathways: an excitotoxic necrosis as a result of NMDA receptor activation and a delayed apoptosis that is NMDA receptor-independent. Mildly elevated levels of extracellular glutamate shift the cell death mechanism from apoptosis to necrosis.
Dynamic Microtubule Ends Are Required for Growth Cone Turning to Avoid an Inhibitory Guidance Cue
Authors: Challacombe Jean F. , Snow Diane M. , Letourneau Paul C.
Published: April 2018

Growth cone turning is an important mechanism for changing the direction of neurite elongation during development of the nervous system. Our previous study indicated that actin filament bundles at the leading margin direct the distal microtubular cytoskeleton as growth cones turn to avoid substratum-bound chondroitin sulfate proteoglycan. Here, we investigated the role of microtubule dynamics in growth cone turning by using low doses of vinblastine and taxol, treatments that reduce dynamic growth and shrinkage of microtubule ends. We used time-lapse phase-contrast videomicroscopy to observe embryonic chick dorsal root ganglion neuronal growth cones as they encountered a border between fibronectin and chondroitin sulfate proteoglycan in the presence and absence of 4 nmvinblastine or 7 nmtaxol. Growth cones were fixed and immunocytochemically labeled to identify actin filaments and microtubules containing tyrosinated and detyrosinated α-tubulin.

Our results show that after contact with substratum-bound chondroitin sulfate proteoglycan, vinblastine- and taxol-treated growth cones did not turn, as did controls; instead, they stopped or sidestepped. Even before drug-treated growth cones contacted a chondroitin sulfate proteoglycan border, they were narrower than controls, and the distal tyrosinated microtubules were less splayed and were closer to the leading edges of the growth cones. We conclude that the splayed dynamic distal ends of microtubules play a key role in the actin filament-mediated steering of growth cone microtubules to produce growth cone turning.
The 5-HT3Receptor Is Present in Different Subpopulations of GABAergic Neurons in the Rat Telencephalon
Authors: Morales Marisela , Bloom Floyd E.
Published: April 2018

The type 3 serotonin receptor (5-HT3R) is a ligand-gated ion channel whose presence in the CNS has been established by radioligand binding,in situhybridization, and immunohistochemical analysis. To analyze further the role of the 5-HT3R in the CNS, we usedin situhybridization and immunocytochemistry to determine that 5-HT3R-expressing neurons are mainly GABA-containing cells in the rat telencephalon. We determined that 5-HT3R/GABA-containing neurons do not exhibit somatostatin immunoreactivity but often contain cholecystokinin (CCK) immunoreactivity. 5-HT3R-expressing cells with CCK immunoreactivity were observed in the neocortex, olfactory cortex, hippocampus, and amygdala. The 5-HT3R/CCK interneurons represent between 35 and 66% of the total population of CCK-containing cells in the neocortex.

Further characterization of the 5-HT3R/GABAergic neurons was based on their calcium-binding protein immunoreactivity and showed that these neurons lack parvalbumin (PV) and represent a subpopulation of calbindin (CB)-containing interneurons that were preferentially present in the CA1–CA3 subfield of the hippocampus. Although some 5-HT3R/GABAergic neurons with calretinin (CR) were found in the neocortex, olfactory cortex, hippocampus, and amygdala, these neurons were more often present in the agranular insular and piriform cortices.

We conclude that the neuronal expression of the 5-HT3R is selective within the GABA neuron population in the rat telencephalon. These 5-HT3R-expressing interneurons might contain CCK, CB, and CR. We suggest that serotonin through the 5-HT3R may regulate GABA and CCK neurotransmission in the telencephalon.
Dendrodendritic and Axoaxonic Synapses in the Thalamic Reticular Nucleus of the Adult Rat
Authors: Pinault Didier , Smith Yoland , Deschênes Martin
Published: April 2018

Currently, it is believed that cell–cell communications occur in the thalamic reticular nucleus (RT) during thalamocortical operations, but the anatomical substrate underlying these intrinsic interactions has not been characterized fully in the rat yet. To further our knowledge on this issue, we stained juxtacellularly rat RT neurons with biocytin or Neurobiotin and examined their intrinsic axon collaterals and “axon-like processes” at both light and electron microscopic levels. Of 111 tracer-filled RT cells for which the axon could be followed from its origin up to the thalamus, 12 displayed short-range, poorly ramifying varicose local axon collaterals, which remained undistinguishable from parent distal dendrites, raising the question as to whether their varicosities were presynaptic terminals. Correlated light and electron microscopic observations of the proximal part of these intrinsic varicose axonal segments revealed that their varicosities and intervaricose segments were, in fact, postsynaptic structures contacted by a large number of boutons that, for the most, formed asymmetric synapses and were nonimmunoreactive for GABA. Similarly, the so-called “axon-like processes” stemming from the soma or dendrites also were identified as postsynaptic structures. Two unexpected observations were made in the course of this analysis. First, the hillock and initial segment of some RT axons were found to receive asymmetric synaptic inputs from GABA-negative terminals. Second, examination of serial ultrathin sections of dendritic bundles cut in their longitudinal plane revealed the existence of several short symmetric dendrodendritic synapses and numerous puncta adhaerentia between component dendrites. In conclusion, dendrodendritic junctions might be a prominent anatomical substrate underlying interneuronal communications in the RT of the adult rat. Furthermore, excitatory axoaxonic synapses on the axon hillock, initial segment, and local axon collaterals might represent a powerful synaptic drive for synchronizing the firing of RT neurons. Future studies are essential to verify whether excitatory axoaxonic synapses with the axon hillock are a general feature in the RT.
Role of the Midbrain Periaqueductal Gray in Maternal Nurturance and Aggression:c-fosand Electrolytic Lesion Studies in Lactating Rats
Authors: Lonstein Joseph S. , Stern Judith M.
Published: April 2018

The upright crouched, or kyphotic, nursing posture of lactating rats is dependent on suckling stimulation from pups. Because of the neuroanatomical connections of the periaqueductal gray (PAG) and its sensorimotor integration of the analogous lordosis posture displayed by sexually receptive female rats, the possible role of the PAG in kyphosis was investigated usingc-fosimmunocytochemistry and electrolytic lesions. Lactating rats interacting with and nursing a litter of suckling pups showed greater Fos-immunoreactive nuclei in the lateral and ventrolateral caudal PAG (cPAGl,vl) compared with dams receiving nonsuckling somatosensory, distal, or no stimulation from pups. In contrast, this pattern was not evident in the rostral PAG, where the highest Fos levels occurred in nonsuckled dams, or in five other brainstem sites with either no group differences (peripeduncular, dorsal raphe, and pontine nuclei) or negligible Fos (ventral tegmental area, spinal trigeminal nuclei). After bilateral electrolytic lesions of the cPAGl,vlduring gestation or on day 7 postpartum, active maternal behaviors, such as retrieval and licking of pups, and total nursing time were essentially normal. Kyphotic nursing, however, was reduced by 85%, nursing in prone and supine postures increased substantially, and 24 hr litter weight gains were reduced, particularly early in lactation (by 26%). Furthermore, lesioned rats attacked a strange male twice as often as controls did, which is suggestive of reduced fearfulness. These results extend the known roles of the PAG in reproductive and defensive behaviors to the postural control of suckling-induced kyphotic nursing and the modulation of maternal aggression.
Identification of Estrogen-Responsive Genes in Neuroblastoma SK-ER3 Cells
Authors: Garnier M. , Di Lorenzo D. , Albertini A. , Maggi A.
Published: April 2018

To evaluate the role of estrogen receptor in the differentiation of cells of neural origin, we developed a molecular approach aimed at the identification of estrogen target genes by mRNA differential display PCR (ddPCR) in human neuroblastoma SK-ER3 cells. More than 3000 RNAs were examined, a few of which displayed a differential regulation pattern in response to 17β-estradiol (E2). Sequence analysis of three differentially amplified ddPCR products showed homology with the growth-associated nuclear protein prothymosin-α (PTMA), the Bcl2-interacting protein Nip2, and one mRNA previously described by others in fetal human brain. Two ddPCR products, referred to as P4 and P10, corresponded to new DNA sequences. Northern analysis confirmed that estrogen treatment of SK-ER3 cells resulted in the upregulation and downregulation of expression of these messages. In particular, PTMA was found to accumulate at both 1 and 17 hr after E2treatment, whereas P10 product accumulated only at 1 hr. Conversely, P4, Nip2, and the fetal brain-related mRNAs were significantly decreased by the treatment. Further time course analysis of PTMA and Nip2 mRNAs levels indicated that the hormone exerted a marked biphasic regulatory effect on expression of both messages during the course of cell differentiation. In the present study we report for the first time the identification of a panel of estrogen target genes in neural cells that provide new insights in the molecular mechanism of action of E2in cells of neural origin.
Postsynaptic Calcineurin Activity Downregulates Synaptic Transmission by Weakening Intracellular Ca2+Signaling Mechanisms in Hippocampal CA1 Neurons
Authors: Wang Jin-Hui , Kelly Paul T.
Published: April 2018

Protein phosphorylation and dephosphorylation are believed to functionally couple neuronal activity and synaptic plasticity. Our previous results indicated that postsynaptic Ca2+/calmodulin (CaM) signaling pathways play an important role in setting synaptic strength, and calcineurin (CaN) activity limits synaptic responses during basal synaptic transmission and long-term potentiation expression. The inhibition of postsynaptic CaN activity by FK-506 or an autoinhibitory peptide induced synaptic potentiation in hippocampal slices, which occludes tetanus-induced LTP. FK-506-induced synaptic potentiation was expressed in adult but not young rats. To elucidate mechanisms underlying CaN-inhibited synaptic potentiation, we co-injected certain agents affecting Ca2+signaling pathways with CaN inhibitors into CA1 neurons. Synaptic potentiation induced by FK-506 was significantly attenuated by co-injecting BAPTA, heparin/dantrolene (inhibitors of intracellular Ca2+release), a CaM-binding peptide, or CaM-KII/PKC pseudosubstrate peptides. These results indicate that postsynaptic CaN activity can downregulate evoked synaptic transmission by weakening intracellular Ca2+signals and downstream protein kinase activities.
Calcium Homeostasis and Reactive Oxygen Species Production in Cells Transformed by Mitochondria from Individuals with Sporadic Alzheimer’s Disease
Authors: Sheehan Jason P. , Swerdlow Russel H. , Miller Scott W. , Davis Robert E. , Parks Jan K. , Parker W. Davis , Tuttle Jeremy B.
Published: April 2018

Alzheimer’s disease (AD) is associated with defects in mitochondrial function. Mitochondrial-based disturbances in calcium homeostasis, reactive oxygen species (ROS) generation, and amyloid metabolism have been implicated in the pathophysiology of sporadic AD. The cellular consequences of mitochondrial dysfunction, however, are not known. To examine these consequences, mitochondrially transformed cells (cybrids) were created from AD patients or disease-free controls. Mitochondria from platelets were fused to ρ0cells created by depleting the human neuroblastoma line SH-SY5Y of its mitochondrial DNA (mtDNA). AD cybrids demonstrated a 52% decrease in electron transport chain (ETC) complex IV activity but no difference in complex I activity compared with control cybrids or SH-SY5Y cells. This mitochondrial dysfunction suggests a transferable mtDNA defect associated with AD. ROS generation was elevated in the AD cybrids. AD cybrids also displayed an increased basal cytosolic calcium concentration and enhanced sensitivity to inositol-1,4,5-triphosphate (InsP3)-mediated release. Furthermore, they recovered more slowly from an elevation in cytosolic calcium induced by the InsP3agonist carbachol. Mitochondrial calcium buffering plays a major role after this type of perturbation. β-amyloid (25–35) peptide delayed the initiation of calcium recovery to a carbachol challenge and slowed the recovery rate. Nerve growth factor reduced the carbachol-induced maximum and moderated the recovery kinetics. Succinate increased ETC activity and partially restored the AD cybrid recovery rate. These subtle alterations in calcium homeostasis and ROS generation might lead to increased susceptibility to cell death under circumstances not ordinarily toxic.
Expression of Specific Tubulin Isotypes Increases during Regeneration of Injured CNS Neurons, But Not after the Application of Brain-Derived Neurotrophic Factor (BDNF)
Authors: Fournier Alyson E. , McKerracher Lisa
Published: April 2018

Axonal regrowth after injury is accompanied by changes in the expression of tubulin, but the contributions of substrate molecules and neurotrophic factors in regulating these changesin vivoare not known. Adult rat retinal ganglion cells (RGCs) were examined after intraorbital axotomy, after application of a peripheral nerve (PN) graft to stimulate regeneration, and after axotomy and treatment with brain-derived neurotrophic factor (BDNF). After these treatments we usedin situhybridization to study mRNA levels for βI, βII, βIII, βIVa, and Tα1 tubulin isotypes. Levels of mRNA for all isotypes were downregulated after intraorbital axotomy. During regrowth of injured RGC axons, mRNA levels for βII, βIII, and Tα1 isotypes were upregulated specifically and dramatically, suggesting that elevated expression of these isotypes is correlated specifically with axonal regrowth. A corresponding increase in βIII protein levels was detected by immunocytochemistry. The βI and βIVamRNAs were not increased during regeneration. BDNF did not elicit a specific increase in the mRNA levels for the βIII and Tα1 isotypes and had only a small effect on mRNA levels for the βII isotype. Therefore, despite the ability of BDNF to support the survival of injured RGCs and to enhance neurite outgrowth of retinal neuronsin vitro, thein vivoapplication of BDNF alone is unable to induce the program of changes in growth-associated tubulins that accompany regeneration of RGC axons into PN grafts. We speculate that, in addition to BDNF, cooperative signaling with substrate molecules is required to allow RGCs to regenerate and exhibit tubulin isotype switching.
Endogenous Serine Protease Inhibitor Modulates Epileptic Activity and Hippocampal Long-Term Potentiation
Authors: Lüthi Andreas , Putten Herman van der , Botteri Florence M. , Mansuy Isabelle M. , Meins Marita , Frey Uwe , Sansig Gilles , Portet Chantal , Schmutz Markus , Schröder Markus , Nitsch Cordula , Laurent Jean-Paul , Monard Denis
Published: April 2018

Protease nexin-1 (PN-1), a member of the serpin superfamily, controls the activity of extracellular serine proteases and is expressed in the brain. Mutant mice overexpressing PN-1 in brain under the control of the Thy-1 promoter (Thy 1/PN-1) or lacking PN-1 (PN-1−/−) were found to develop epileptic activityin vivoandin vitro. Theta burst-induced long-term potentiation (LTP) and NMDA receptor-mediated synaptic transmission in the CA1 field of hippocampal slices were augmented in Thy 1/PN-1 mice and reduced in PN-1−/− mice. Compensatory changes in GABA-mediated inhibition in Thy 1/PN-1 mice suggest that altered brain PN-1 levels lead to an imbalance between excitatory and inhibitory synaptic transmission.
Inhibition of Stress-Induced Neuroendocrine and Behavioral Responses in the Rat by Prepro-Thyrotropin-Releasing Hormone 178–199
Authors: McGivern Robert F. , Rittenhouse Peter , Aird Fraser , Van de Kar Louis D. , Redei Eva
Published: April 2018

A corticotropin release-inhibiting factor (CRIF) in brain has been postulated for several decades, based on increased plasma levels of ACTH and corticosterone after hypothalamic–pituitary disconnection. Recentin vitrostudies indicate that prepro-TRH178–199 may function as an endogenous CRIF, prompting us to examine stress-related neuroendocrine and behavioral responses afterin vivoadministration to the adult male rat. Animals that were administered prepro-TRH178–199 intravenously 5 min before restraint stress exhibited a significant attenuation of stress-induced elevations of ACTH, corticosterone, and prolactin, as compared with controls infused with vehicle, whereas thyroid-stimulating hormone (TSH) secretion was not changed.

In behavioral studies of stress responsiveness, either the vehicle or prepro-TRH178–199 was administered intracerebroventricularly (ICV) 5 min before testing. In the open field, prepro-TRH178–199 significantly increased grooming, locomotor activity, rearing, and sniffing behaviors. In the light/dark box, it significantly increased the time animals spent in the light compartment and increased the number of crossings between the light/dark compartments. In the plus maze, the peptide significantly increased the amount of time animals spent in the open arms. The same dose of peptide, administered ICV, had no effect on peripheral hormone release in response to restraint stress. Overall, these results support a role for prepro-TRH178–199 in the inhibition of the neuroendocrine responses to stress at the level of the pituitary and indicate that it has central modulatory influences over stress-related behaviors.
Chronic Social Stress Alters Levels of Corticotropin-Releasing Factor and Arginine Vasopressin mRNA in Rat Brain
Authors: Albeck David S. , McKittrick Christina R. , Blanchard D. Caroline , Blanchard Robert J. , Nikulina Julia , McEwen Bruce S. , Sakai Randall R.
Published: April 2018

In the visible burrow system model of chronic social stress, male rats housed in mixed-sex groups quickly form a dominance hierarchy in which the subordinates appear to be severely stressed. A subgroup of subordinates have an impaired corticosterone response after presentation of a novel restraint stressor, leading to their designation as nonresponsive subordinates. To examine the mechanism underlying the blunted corticosterone response in these animals,in situhybridization histochemistry was used to quantify corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) mRNA expression in the brain. In two separate visible burrow system experiments, the nonresponsive subordinates expressed a significantly lower average number of CRF mRNA grains per cell in the paraventricular hypothalamic nucleus compared with stress-responsive subordinates, dominants (DOM), or cage-housed control (CON) rats. The number of CRF mRNA labeled cells was also significantly lower in nonresponders than in responsive subordinates or DOM. In the central amygdala, CRF mRNA levels were increased in both groups of subordinates compared with CON rats, whereas responsive subordinates exhibited higher levels than the DOM rats as well. AVP mRNA levels did not vary with behavioral rank in any subdivision of the paraventricular hypothalamic nucleus. In the medial amygdala, the number of cells expressing AVP mRNA was significantly greater in CON rats compared with both groups of subordinates, although the average number of AVP mRNA grains per cell did not vary with rank. In addition, the number of AVP-positive cells significantly correlated with plasma testosterone level.
Site-Specific and Sensory Neuron-Dependent Increases in Postsynaptic Glutamate Sensitivity Accompany Serotonin-Induced Long-Term Facilitation atAplysiaSensorimotor Synapses
Authors: Zhu Hui , Wu Fang , Schacher Samuel
Published: April 2018

Long-term changes in the efficacy ofAplysiasensory neuron (SN) connections accompany behavioral training or applications with 5-HT. The changes evoked by training or 5-HT include formation of new SN varicosities and transmitter release sites. Because new synapse formation requires proper alignment of presynaptic structures with postsynaptic zones containing a high density of transmitter receptors, we examined whether changes in postsynaptic sensitivity to the presumed SN transmitter (glutamate) were correlated with formation and distribution of new SN varicosities in contact with motor cell L7 in cell culture. The formation of stable SN connections after 4 d in culture did not significantly change overall responses to focal applications of glutamate. However, specific sites along L7’s axon apposed to SN varicosities expressed larger responses to glutamate compared with adjacent sites with few SN varicosities. After treatments with 5-HT that evoked long-term changes in both the structure and the function of SN–L7 synaptic interaction, glutamate responses increased selectively at sites along the surface of L7’s axon with preexisting or new SN varicosities. Increases in postsynaptic response to glutamate 24 hr after 5-HT treatment required interaction with an SN. These results suggest that new synapse formation between neurons, either with regeneration or after external stimuli that evoke increases in synaptic efficacy, involves site-specific changes in expression of functional neurotransmitter receptors on the postsynaptic cell that is regulated by interaction with the presynaptic neuron.
Modulation of GABAAReceptor Function by Tyrosine Phosphorylation of β Subunits
Authors: Wan Qi , Man Heng Ye , Braunton Jodi , Wang Wei , Salter M. W. , Becker L. , Wang Yu Tian
Published: April 2018

Protein tyrosine phosphorylation is a key event in diverse intracellular signaling pathways and has been implicated in modification of neuronal functioning. We investigated the role of tyrosine phosphorylation in regulating type A GABA (GABAA) receptors in cultured CNS neurons. Extracellular application of genistein (50 μm), a membrane-permeable inhibitor of protein tyrosine kinases (PTKs), produced a reversible reduction in the amplitude of GABAAreceptor-mediated whole-cell currents, and this effect was not reproduced by daidzein (50 μm), an inactive analog of genistein. In contrast, intracellular application of the PTK pp60c-src(30 U/ml) resulted in a progressive increase in current amplitude, and this potentiation was prevented by pretreatment of the neurons with genistein. Immunoprecipitation and immunoblotting of cultured neuronal homogenates indicated that the β2/β3 subunit(s) of the GABAAreceptor are tyrosine phosphorylatedin situ. Moreover, genistein (50 μm) was found to be capable of decreasing GABAAcurrents in human embryonic kidney 293 cells transiently expressing functional GABAAreceptors containing the β2 subunit. Thus, the present work provides the first evidence that native GABAAreceptors are phosphorylated and modulatedin situby endogenous PTKs in cultured CNS neurons and that phosphorylation of the β subunits may be sufficient to support such a modulation. Given the prominent role of GABAAreceptors in mediating many brain functions and dysfunctions, modulation of these receptors by PTKs may be important in a wide range of physiological and pathological processes in the CNS.
Evidence that 4-Hydroxynonenal Mediates Oxidative Stress-Induced Neuronal Apoptosis
Authors: Kruman Inna , Bruce-Keller Annadora J. , Bredesen Dale , Waeg Georg , Mattson Mark P.
Published: April 2018

Oxidative stress is believed to play important roles in neuronal cell death associated with many different neurodegenerative conditions (e.g., Alzheimer’s disease, Parkinson’s disease, and cerebral ischemia), and it is believed also that apoptosis is an important mode of cell death in these disorders. Membrane lipid peroxidation has been documented in the brain regions affected in these disorders as well as in cell culture andin vivomodels. We now provide evidence that 4-hydroxynonenal (HNE), an aldehydic product of membrane lipid peroxidation, is a key mediator of neuronal apoptosis induced by oxidative stress. HNE induced apoptosis in PC12 cells and primary rat hippocampal neurons. Oxidative insults (FeSO4and amyloid β-peptide) induced lipid peroxidation, cellular accumulation of HNE, and apoptosis. Bcl-2 prevented apoptosis of PC12 cells induced by oxidative stress and HNE. Antioxidants that suppress lipid peroxidation protected against apoptosis induced by oxidative insults, but not that induced by HNE. Glutathione, which binds HNE, protected neurons against apoptosis induced by oxidative stress and HNE. PC12 cells expressing Bcl-2 exhibited higher levels of glutathione and lower levels of HNE after oxidative stress. Collectively, the data identify that HNE is a novel nonprotein mediator of oxidative stress-induced neuronal apoptosis and suggest that the antiapoptotic action of glutathione may involve detoxification of HNE.
Disruption of Decrements in Conditioned Stimulus Processing by Selective Removal of Hippocampal Cholinergic Input
Authors: Baxter Mark G. , Holland Peter C. , Gallagher Michela
Published: April 2018

The attention directed to environmental stimuli can be modified by experience. For example, preexposure of a conditioned stimulus (CS) in the absence of reinforcement can retard subsequent conditioning of that stimulus when it is paired directly with an unconditioned stimulus, a phenomenon referred to as latent inhibition. Similarly, consistent pairings of a CS with another event can slow the acquisition of new information about that CS. Such phenomena suggest that reductions in the processing of CSs occur when they are made behaviorally irrelevant or consistent predictors of other events. On the basis of the observation that hippocampal lesions prevented such reductions in CS processing, we hypothesized that damage to basal forebrain cholinergic neurons that project to the hippocampus, using microinjections of the selective immunotoxin 192 IgG-saporin into the medial septum/vertical limb of the diagonal band (MS/VDB), also would disrupt normal reductions in CS processing. Lesions of hippocampal cholinergic input disrupted decreases in CS processing, manifested in both an absence of latent inhibition and a lack of reduced processing of a CS that had been a consistent predictor of another CS. These results indicate that cholinergic neurons in the MS/VDB play a role in the regulation of CS processing. Furthermore, these findings (in conjunction with previous findings) implicatebothrostral (hippocampal-projecting) and caudal (cortical-projecting) regions of the basal forebrain cholinergic system in the modulation of attention.
cAMP-Dependent Enhancement of Dihydropyridine-Sensitive Calcium Channel Availability in Hippocampal Neurons
Authors: Kavalali Ege T. , Hwang Katherine S. , Plummer Mark R.
Published: April 2018

Dihydropyridine-sensitive calcium channels can be strongly modulated by cAMP-dependent phosphorylation. This modulation takes the form of increased channel availability in cardiac myocytes (for review, see McDonald et al., 1994) and has been suggested to be essential for voltage-dependent facilitation in adrenal chromaffin cells (Artalejo et al., 1992) and skeletal muscle (Sculptoreanu et al., 1993b). To determine the role of cAMP-dependent phosphorylation on dihydropyridine-sensitive calcium channels in hippocampal neurons, we have used both single-channel and whole-cell recording techniques and have examined the effects of the membrane-permeable cAMP analog 8-(4-chlorophenylthio) (CPT)-cAMP and the protein kinase inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) andN-[2-(p-bromocinnamyl-amino)ethyl]-5-isoquinolinesulfonamide (H-89).

Hippocampal neurons contain two kinds of dihydropyridine-sensitive calcium channel activity: Ls and Lp (Kavalali and Plummer, 1994). The Ls channel closely resembles the cardiac L-type channel, whereas the Lp channel shows a novel low-voltage form of voltage-dependent potentiation (Kavalali and Plummer, 1996). 8-CPT-cAMP increased the availability of both the Ls and Lp channels and caused a parallel increase in Lp channel reopenings at the repolarization potential that result from voltage-dependent potentiation. This effect was completely blocked by the broad spectrum kinase inhibitor H-7 and by the protein kinase A-specific inhibitor H-89. The two inhibitors, however, did not disrupt baseline potentiation of the Lp channel, suggesting that cAMP-dependent protein kinase activity can enhance Ls and Lp channel activity but is not required for voltage-dependent potentiation in hippocampal neurons.
Phasic and Long-Term Depression in Brainstem Nucleus Tractus Solitarius Neurons: Differing Roles of AMPA Receptor Desensitization
Authors: Zhou Zhongren , Champagnat Jean , Poon Chi-Sang
Published: April 2018

One important question concerning the homeostatic regulation of many physiological processes is whether the control mechanisms are purely reflexogenic or whether they may involve neural adaptation in the form of learning and memory in the brainstem. Using a brainstem slice preparation in the rat, we studied the modifiability of neural transmission in the first-order synapses of the medial and commissural nucleus tractus solitarius of the medulla. Sustained low-frequency stimulation (5 Hz) of primary afferent fibers in the tractus solitarius resulted in a phasic depression (accommodation) of synaptic strength as reflected by a concomitant decrease in the evoked excitatory postsynaptic potentials. In one group of neurons (type I), synaptic strength recovered rapidly after low-frequency stimulation, whereas in another group of neurons (type II), synaptic strength remained depressed for >30 min, i.e., manifesting long-term depression (LTD). The latter was switched into a short-term depression lasting 15–25 min after pharmacological blockade of NMDA receptor channels withd-APV or chelation of intracellular calcium ions with EGTA, whereas the accommodation phase was unaffected. Application of an AMPA receptor anti-desensitization agent cyclothiazide abolished the LTD, but not the accommodation response. These results suggest the presence of separate postsynaptic sites for the induction of LTD and accommodation, one being sensitive to cyclothiazide, whereas the other is not. Moreover, the maintenance of LTD is dependent on the level of intracellular Ca2+. These phasic and long-term synaptic plasticity in the nucleus tractus solitarius may play a role in the homeostatic regulation of cardiorespiratory functions.
A Long-Lasting Calcium-Activated Nonselective Cationic Current Is Generated by Synaptic Stimulation or Exogenous Activation of Group I Metabotropic Glutamate Receptors in CA1 Pyramidal Neurons
Authors: Congar Patrice , Leinekugel Xavier , Ben-Ari Yehezkel , Crépel Valérie
Published: April 2018

We have shown previously that a selective metabotropic glutamate receptor (mGluR) agonist, 1S,3R-1-aminocyclo-pentane-1,3-dicarboxylate (1S,3R-ACPD), evokes an inward current in CA1 pyramidal neurons of rat hippocampal slices in the presence of K+channel blockers (Crépel et al., 1994). This current has been characterized as a Ca2+-activated nonselective cationic (CAN) current. Using whole-cell patch-clamp recordings and intracellular dialysis, we now have identified the mGluR subtype and the mechanisms underlying the CAN current (ICAN) and report for the first time the presence of a synapticICANin the mammalian CNS. First, we have shown pharmacologically that activation ofICANby 1S,3R-ACPD involves the group I mGluRs (and not the groups II and III) and a G-protein-dependent process. We also report thatICANis modulated by the divalent cations (Mg2+, Cd2+, and Zn2+). Second, we have isolated a slow synaptic inward current evoked by a high-frequency stimulation in the presence of K+channel blockers, ionotropic glutamate, and GABAAreceptor antagonists. This current shows similar properties to the exogenously evokedICAN: its reversal potential is close to the reversal potential of the 1S,3R-ACPD-evokedICAN, and it is G-protein- and Ca2+-dependent. Because the amplitude and duration ofICANincreased in the presence of a glutamate uptake blocker, we suggest that this synaptic current is generated via the activation of mGluRs. We propose that the synapticICAN, activated by a brief tetanic stimulation and leading to a long-lasting inward current, may be involved in neuronal plasticity and synchronized network-driven oscillations.
Postnatal Development of Membrane Properties and δ Oscillations in Thalamocortical Neurons of the Cat Dorsal Lateral Geniculate Nucleus
Authors: Pirchio M. , Turner J. P. , Williams S. R. , Asprodini E. , Crunelli V.
Published: April 2018

The development of membrane properties, firing patterns, and δ oscillations in neurons of the cat dorsal lateral geniculate nucleus (dLGN) was investigatedin vitroduring the first 7 postnatal weeks. Compared with adult neurons, the resting membrane potential was more depolarized at postnatal days 1–9 (P1–P9), the input resistance was higher at P1–P7, and action potentials had a higher threshold and a smaller amplitude at P1–P3 and a longer duration at P1–P9. At P1–P3 trains longer than 200 msec were rarely observed, and trains with more than three action potentials were only present in 41% of the neurons, whereas at P1–P7 the normalized slope of the instantaneous frequencies at the first five interspike intervals was smaller than in the adult. A long-lasting (up to 6 sec) afterhyperpolarization followed a short train of action potentials in 88 and 30% of neurons at P1–P3 and P30–P32, respectively, but it was rarely observed in the adult. The low-threshold Ca2+potential could evoke a burst of action potentials since P1. However, at P1–P7 the number of action potentials per burst was smaller (range, one to five), and at P1–P9 their maximum instantaneous frequency was lower (<190 Hz) than in the adult (range, six to eight, and 344 Hz, respectively). No δ oscillations were observed until P17, and their frequency (0.36 Hz) was lower than that in the adult (1.8 Hz). The percentage of neurons displaying δ oscillations and their frequency reached adult values by the end of the seventh postnatal week, i.e., well after the maturation of the membrane properties and firing patterns (second postnatal week). In conclusion, the maturation of the electrophysiological properties of thalamocortical neurons in the cat dLGN is completed later than the retinogeniculate axon segregation (Shatz CJ, 1983), and the immaturity of the oscillatory, and not of the burst-firing, activity is a limiting factor in the development of δ waves (Jouvet-Mounier et al., 1970).
Immunohistochemical Localization of Netrin-1 in the Embryonic Chick Nervous System
Authors: MacLennan A. John , McLaurin Diana L. , Marks Lianne , Vinson Emily N. , Pfeifer Marylynn , Szulc Susan V. , Heaton Marieta B. , Lee Nancy
Published: April 2018

Netrin-1 has profoundin vitroeffects on the growth properties of vertebrate embryonic axons. In addition,netrin-1mRNA is found in the floor plate of the embryonic nervous system, an intermediate target of many axons, including commissural axons that are affected by netrin-1in vitro. Moreover, genetic studies of netrin-1 homologs inCaenorhabditis elegansandDrosophilaimplicate these proteins in commissure formation. We raised polyclonal antisera that recognize chick netrin-1 in fixed tissue sections. The antisera were used to immunohistochemically map netrin-1 in the embryonic spinal cord, brain, and retina. The relationship between netrin-1 localization and the growth of pioneering axons suggests roles for netrin-1 in the regulation of circumferential, commissural, and longitudinal axon growth in the spinal cord and brain. The data also suggest that the primary or sole effect of netrin-1 on pioneering spinal cord commissural axons is haptotactic. Furthermore, the pattern of netrin-1 localization raises the possibility that this protein helps mediate neuronal migration in the spinal cord, brain, and retina.
HNMP-1: A Novel Hematopoietic and Neural Membrane Protein Differentially Regulated in Neural Development and Injury
Authors: Bolin Laurel M. , McNeil Tom , Lucian Linda A. , DeVaux Brigitte , Franz-Bacon Karin , Gorman Daniel M. , Zurawski Sandra , Murray Richard , McClanahan Terrill K.
Published: April 2018

Thehnmp-1(hematopoietic neural membrane protein) gene encodes a protein with striking similarity to the tetra-transmembrane-spanning protein encoded bypmp22.hnmp-1was cloned from an elutriated human monocyte library and is expressed in various human hematopoietic and lymphoid lineages as well as adult mouse spleen and thymus. In the mouse nervous system, HNMP-1 mRNA is temporally expressed by Schwann cells during sciatic nerve myelination. Dorsal root ganglia sensory and spinal cord α-motoneurons acquire HNMP-1 protein selectively throughout development. In the fiber tracts of the spinal cord and in sciatic nerve, HNMP-1 protein is axon-associated. Additionally a rapid and sustained level of HNMP-1 expression is observed in response to acute PNS injury. HNMP-1 is constituitively induced in sciatic nerve of Trembler J mice, which are mutant forpmp22and have a demyelinating/hypomyelinating phenotype. The expression pattern of HNMP-1 suggests a possible role for this molecule during active myelination.
Distributed Neural Systems Underlying the Timing of Movements
Authors: Rao Stephen M. , Harrington Deborah L. , Haaland Kathleen Y. , Bobholz Julie A. , Cox Robert W. , Binder Jeffrey R.
Published: April 2018

Timing is essential to the execution of skilled movements, yet our knowledge of the neural systems underlying timekeeping operations is limited. Using whole-brain functional magnetic resonance imaging, subjects were imaged while tapping with their right index finger in synchrony with tones that were separated by constant intervals [Synchronization (S)], followed by tapping without the benefit of an auditory cue [Continuation (C)]. Two control conditions followed in which subjects listened to tones and then made pitch discriminations (D). Both the S and the C conditions produced equivalent activation within the left sensorimotor cortex, the right cerebellum (dorsal dentate nucleus), and the right superior temporal gyrus (STG). Only the C condition produced activation of a medial premotor system, including the caudal supplementary motor area (SMA), the left putamen, and the left ventrolateral thalamus. The C condition also activated a region within the right inferior frontal gyrus (IFG), which is functionally interconnected with auditory cortex. Both control conditions produced bilateral activation of the STG, and the D condition also activated the rostral SMA. These results suggest that the internal generation of precisely timed movements is dependent on three interrelated neural systems, one that is involved in explicit timing (putamen, ventrolateral thalamus, SMA), one that mediates auditory sensory memory (IFG, STG), and another that is involved in sensorimotor processing (dorsal dentate nucleus, sensorimotor cortex).
Baculovirus Expression Provides Direct Evidence for Heteromeric Assembly of P2X2and P2X3Receptors
Authors: Radford Kathryn M. , Virginio Caterina , Surprenant Annmarie , North R. Alan , Kawashima Eric
Published: April 2018

P2X2and P2X3are subunits of P2X receptors, cation channels opened by binding extracellular ATP. cDNAs encoding P2X2and P2X3receptor subunits, each with one of two C-terminal epitope tags, were cloned into baculovirus. Virally infected insect cells (Spodoptera frugiperda) expressed moderate to high levels of the corresponding proteins, as detected by Western blotting, by the specific binding of [35S]ATP and by whole-cell recordings of membrane current evoked by ATP or αβmethylene-ATP. In cells infected at the same time with two viruses encoding P2X2and P2X3receptors, the two proteins could be cross-immunoprecipitated with antibodies specific for either of the epitope tags. Whole-cell recordings from these cells showed that ATP and αβmethylene-ATP evoked currents with agonist sensitivity and desensitization quite distinct from those observed when P2X2or P2X3receptors were expressed alone. The results offer a method to express large amounts of P2X receptor protein, and they provide direct evidence that P2X2and P2X3subunits assemble to form heteromeric channels having distinct properties from those formed as homomers.
Muscarinic Induction of Synchronous Population Activity in the Entorhinal Cortex
Authors: Dickson Clayton T. , Alonso Angel
Published: April 2018

Oscillation and synchronization of neural activity is important in normal brain function but is also relevant to epileptogenesis. One of the most frequent forms of epilepsy originates in temporal lobe circuitry of which the entorhinal cortex (EC) is crucial. Because muscarinic receptor activation promotes oscillatory dynamics in EC neurons, we investigated in a brain slice preparation the effects of carbachol (CCh) on oscillatory population activity in the EC. We found that CCh produced epileptiform activity in EC, which according to field profile and current source density analysis was usually driven by layer V. In addition, localized CCh application and surgical isolation experiments demonstrated that EC layer II, but not layer III, can also independently generate synchronous population activity.

Intracellular recordings from EC principal cells during epileptiform activity demonstrated large-amplitude, synaptically driven depolarizing events and bursts of action potentials synchronized to the field spikes. In layer II neurons, the depolarizing events had a multiphasic reversal potential that suggested concurrent glutamatergic and GABAergic synaptic input. Interestingly, although the epileptiform activity required activation of AMPA but not NMDA receptors, small-amplitude field spikes persisted during block of fast excitatory neurotransmission. These field spikes were correlated to large-amplitude IPSPs in layer II neurons, and both activities were abolished by GABAA-receptor antagonism. Thus, in response to muscarinic activation, pools of EC interneurons discharge synchronously by a mechanism not necessarily involving principal cell activation.

Given the differential projection pattern of EC layers V and II toward the neocortex and hippocampus, respectively, their robust epileptogenic character may be of major importance in temporal lobe epilepsy.
The Effect of Aging on Experience-Dependent Plasticity of Hippocampal Place Cells
Authors: Shen Jiemin , Barnes Carol A. , McNaughton Bruce L. , Skaggs William E. , Weaver Karen L.
Published: April 2018

The firing characteristics of 1437 CA1 pyramidal neurons were studied in relation to both spatial location and the phase of the theta rhythm in healthy young and old rats performing a simple spatial task on a rectangular track. The old rats had previously been found to be deficient on the Morris spatial learning task. Age effects on the theta rhythm per se were minimal. Theta amplitude and frequency during rapid eye movement sleep were virtually identical. During behavior, theta frequency was slightly reduced with age. In both groups, cell firing occurred at progressively earlier phases of the theta rhythm as the rat traversed the place field of the cell (i.e., there was “phase precession,” as reported by others). The net phase shift did not differ between age groups. The main finding of the study was a loss of experience-dependent plasticity in the place fields of old rats. During the first lap around the track on each day, the initial sizes of the place fields were the same between ages; however, place fields of young rats, but not old, expanded significantly during the first few laps around the track in a given recording session. As the place fields expanded, the rate of change of firing with phase slowed accordingly, so that the net phase change remained constant. Thus changes in field size and phase precession are coupled. A deficit in plasticity of place fields in old rats may lead to a less accurate population code for spatial location.
An Anatomical Basis for Visual Calibration of the Auditory Space Map in the Barn Owl’s Midbrain
Authors: Feldman Daniel E. , Knudsen Eric I.
Published: April 2018

The map of auditory space in the external nucleus of the inferior colliculus (ICX) of the barn owl is calibrated by visual experience during development. ICX neurons are tuned for interaural time difference (ITD), the owl’s primary cue for sound source azimuth, and are arranged into a map of ITD. When vision is altered by rearing owls with prismatic spectacles that shift the visual field in azimuth, ITD tuning in the ICX shifts adaptively. In contrast, ITD tuning remains unchanged in the lateral shell of the central nucleus of the inferior colliculus (ICCls), which provides the principal auditory input to the ICX, suggesting that the projection from the ICCls to the ICX is altered by prism-rearing.

In this study, the topography of the ICCls–ICX projection was assessed in normal and prism-reared owls by retrograde labeling using biotinylated dextran amine. In juvenile owls at the age before prism attachment, and in normal adults, labeling patterns were consistent with a topographic projection, with each ICX site receiving input from a restricted region of the ICCls with similar ITD tuning. In prism-reared owls, labeling patterns were systematically altered: each ICX site received additional, abnormal input from a region of the ICCls where ITD tuning matched the shifted ITD tuning of the ICX neurons. These results indicate that anatomical reorganization of the ICCls–ICX projection contributes to the visual calibration of the ICX auditory space map.