bluuebunny/crossref_metadata_2025 huggingface dataset:
Postural Dependence of Muscle Actions: Implications for Neural Control
Authors: Buneo Christopher A. , Soechting John F. , Flanders Martha
Published: April 2018

The neural control of reaching entails the specification of a precise pattern of muscle activation distributed across the many muscles of the arm. Musculoskeletal geometry limits the possible solutions to this problem. Insight into the nature of this constraint was obtained by quantifying the postural variation in the mechanical actions of six human shoulder muscles. Estimates of muscle mechanical actions were obtained by electrically stimulating muscles to the point of contraction and recording the resulting forces and torques with a six-degree-of-freedom force–torque transducer. In a given experiment, data were obtained for up to 29 different arm postures. The mechanical actions of each muscle varied systematically with arm posture, regardless of the frame of reference used to define these actions. The nature of this dependence suggests that a relatively simple strategy can be used by the nervous system to account for the changing mechanical actions of arm muscles.
α-MSH Modulates Local and Circulating Tumor Necrosis Factor-α in Experimental Brain Inflammation
Authors: Rajora Nilum , Boccoli Giovanni , Burns Dennis , Sharma Sarita , Catania Anna P. , Lipton James M.
Published: April 2018

Tumor necrosis factor (TNF-α) underlies pathological processes and functional disturbances in acute and chronic neurological disease and injury. The neuroimmunomodulatory peptide α-MSH modulates actions and production of proinflammatory cytokines including TNF-α, but there is no prior evidence that it alters TNF-α induced within the brain. To test for this potential influence of the peptide, TNF-α was induced centrally by local injection of bacterial lipopolysaccharide (LPS). α-MSH given once i.c.v. with LPS challenge, twice daily intraperitoneally (i.p.) for 5 d between central LPS injections, or both i.p. and centrally, inhibited production of TNF-α within brain tissue. Inhibition of TNF-α protein formation by α-MSH was confirmed by inhibition of TNF-α mRNA. Plasma TNF-α concentration was elevated markedly after central LPS, indicative of an augmented peripheral host response induced by the CNS signal. The increase was inhibited by α-MSH treatments, in relation to inhibition of central TNF-α. Presence within normal mouse brain of mRNA for the α-MSH receptor MC-1 suggests that the inhibitory effects of α-MSH on brain and plasma TNF-α might be mediated by this receptor subtype. The inhibitory effect of α-MSH on brain TNF-α did not depend on circulating factors because the effect also occurred in brain tissuein vitro. This indicates that α-MSH can act directly on brain cells to inhibit their production of TNF-α. If central TNF-α contributes to pathology in CNS disease and injury, and promotes inflammation in the periphery, agents that act on brain α-MSH receptors should decrease the pathological TNF-α reaction and promote tissue survival.
Acetylcholine, Outer Hair Cell Electromotility, and the Cochlear Amplifier
Authors: Dallos Peter , He David Z. Z. , Lin Xi , Sziklai István , Mehta Samir , Evans Burt N.
Published: April 2018

The dominant efferent innervation of the cochlea terminates on outer hair cells (OHCs), with acetylcholine (ACh) being its principal neurotransmitter. OHCs respond with a somatic shape change to alterations in their membrane potential, and this electromotile response is believed to provide mechanical feedback to the basilar membrane. We examine the effects of ACh on electromotile responses in isolated OHCs and attempt to deduce the mechanism of ACh action. Axial electromotile amplitude and cell compliance increase in the presence of the ligand. This response occurs with a significantly greater latency than membrane current and potential changes attributable to ACh and is contemporaneous with Ca2+release from intracellular stores. It is likely that increased axial compliance largely accounts for the increase in motility. The mechanical responses are probably related to a recently demonstrated slow efferent effect. The implications of the present findings related to commonly assumed efferent behaviorin vivoare considered.
Dynamics of Single Neuron Activity in Monkey Primary Motor Cortex Related to Sensorimotor Transformation
Authors: Zhang Jun , Riehle Alexa , Requin Jean , Kornblum Sylvan
Published: April 2018

We investigated the dynamics of neuronal activity related to sensorimotor transformation during single experimental trials of a given stimulus–response (S-R) association task. A monkey was trained to perform wrist extension/flexion movements in the horizontal plane to align a pointer with a visual target while single unit activity in the primary motor cortex (MI) was being recorded. The stimulus was a colored light-emitting diode (LED) presented to either the left or right of a central reference point. The monkey had to point directly at the target (“compatible” S-R mapping) or point to the opposite side of the target position (“incompatible” S-R mapping), with the mapping rule specified by the color of the LED. Single neuron activities on the four correct trials (left/right stimulus × compatible/incompatible S-R mapping) were compared to determine whether such activities were more related to stimulus encoding and representation, to response preparation and execution, or to the “decision” processes translating the stimulus representation into a response representation. A novel mathematical technique, called LOCUS ANALYSIS, has been developed to quantitatively analyze and visualize the contribution of neuronal activity toward the sensory, motor, or sensorimotor (i.e., decisional) aspects of the task. Our data show that as a trial evolves, neuronal activity in MI, at a population level, is first correlated with the representation of the specific stimulus (the side of LED), then with the representation of the S-R mapping rule (the color of LED) as well as trial-specific S-R association (the conjunction of stimulus side and stimulus color), and finally with the representation of the behavioral response (extension or flexion wrist movement). Immediately after the issuance of the movement command, the populational activity in MI remains correlated with the trial-specific stimulus-response conjunctions, i.e., the context of the motor decision that the monkey has just made. Cells recorded successively in a single penetration tend to resemble each other in their pattern of firing on the four correct trials, suggesting a modular organization of neurons based on their functional role in the processing of the S-R association task. Our results indicate that MI belongs to a distributed network such that its neuronal activity reflects the underlying network dynamics that translate a stimulus representation into a response representation via the activation and application of appropriate S-R mapping rule.
Monoamine Oxidase Inhibition Causes a Long-Term Prolongation of the Dopamine-Induced Responses in Rat Midbrain Dopaminergic Cells
Authors: Mercuri Nicola B. , Scarponi Mariangela , Bonci Antonello , Siniscalchi Antonio , Bernardi Giorgio
Published: April 2018

The way monoamine oxidase (MAO) modulates the depression of the firing rate and the hyperpolarization of the membrane caused by dopamine (DA) on rat midbrain dopaminergic cells was investigated by means of intracellular recordingsin vitro. The cellular responses to DA, attributable to the activation of somatodendritic D2/3 autoreceptors, were prolonged and did not completely wash out after pharmacological blockade of both types (A and B) of MAO. On the contrary, depression of the firing rate and membrane hyperpolarization induced by quinpirole (a direct D2 receptor agonist) were not affected by MAO inhibition. Furthermore, although the inhibition of DA reuptake by cocaine and nomifensine caused a short-term prolongation of DA responses, the combined inhibition of MAO A and B enzymes caused a long-term prolongation of DA effects. Moreover, the effects of DA were not largely prolonged during the simultaneous inhibition of MAO and the DA reuptake system. Interestingly, the actions of amphetamine were not clearly augmented by MAO inhibition.

From the present data it is concluded that the termination of DA action in the brain is controlled mainly by MAO enzymes. This long-term prolongation of the dopaminergic responses suggests a substitutive therapeutic approach that uses MAO inhibitors and DA precursors in DA-deficient disorders in which continuous stimulation of the dopaminergic receptors is preferable.
Post-Transcriptional Regulation of Synaptic Vesicle Protein Expression and the Developmental Control of Synaptic Vesicle Formation
Authors: Daly Christopher , Ziff Edward B.
Published: April 2018

The regulated expression of synaptic vesicle (SV) proteins during development and the assembly of these proteins into functional SVs are critical aspects of nervous system maturation. We have examined the expression patterns of four SV proteins in embryonic hippocampal neurons developing in culture and have found that increases in the levels of these proteins result primarily from post-transcriptional regulation. Synaptotagmin I, vamp 2, and synapsin I proteins are synthesized at nearly constant rates as the neurons develop. However, these proteins are relatively unstable at early times in culture and undergo a progressive increase in half-life with time, possibly as a result of an increase in the efficiency with which they are incorporated into SVs. In contrast, synaptophysin is synthesized at a very low rate at early times in culture, and its rate of synthesis increases dramatically with time. The increase in synaptophysin synthesis is not simply the result of an increase in mRNA level, but is largely attributable to an increase in the rate of translational initiation. Despite the nearly constant rates of synthesis of synaptotagmin I, vamp 2, and synapsin I, we show that the number of SVs in these developing neurons increases, and that SV proteins are more efficiently targeted to SVs at later times in culture. Our results suggest that SV production during development is not limited by the rates of transcription of genes encoding the component proteins, thus allowing control of this process by cytoplasmic mechanisms, without signaling to the nucleus.
Ammonium and Glutamate Released by Neurons Are Signals Regulating the Nutritive Function of a Glial Cell
Authors: Tsacopoulos Marcos , Poitry-Yamate Carol L. , Poitry Serge
Published: April 2018

Glial cells transform glucose to a fuel substrate taken up and used by neurons. In the honeybee retina, photoreceptor neurons consume both alanine supplied by glial cells and exogenous proline. Ammonium (NH4+) and glutamate, produced and released in a stimulus-dependent manner by photoreceptor neurons, contribute to the biosynthesis of alanine in glia. Here we report that NH4+and glutamate are transported into glia and that a transient rise in the intraglial concentration of NH4+or of glutamate causes a net increase in the level of reduced nicotinamide adenine dinucleotides [NAD(P)H]. Biochemical measurements indicate that this is attributable to activation of glycolysis in glial cells by the direct action of NH4+and glutamate on at least two enzymatic reactions: those catalyzed by phosphofructokinase (PFK; ATP:d-fructose-6-phosphotransferase, EC2.7.1.11) and glutamate dehydrogenase (GDH;l-glutamate:NAD oxidoreductase, deaminating; EC1.4.1.3). This activation leads to an increase in the production and release of alanine by glia. This signaling, which depends on the rate of conversion of NH4+and glutamate to alanine and α-ketoglutarate, respectively, in the glial cells, raises the novel possibility of a tight regulation of the nutritive function of glia.
NR2A Subunit Expression Shortens NMDA Receptor Synaptic Currents in Developing Neocortex
Authors: Flint Alexander C. , Maisch Ulrike S. , Weishaupt Jochen H. , Kriegstein Arnold R. , Monyer Hannah
Published: April 2018

NMDA receptors play important roles in learning and memory and in sculpting neural connections during development. After the period of peak cortical plasticity, NMDA receptor-mediated EPSCs (NMDAR EPSCs) decrease in duration. A likely mechanism for this change in NMDA receptor properties is the molecular alteration of NMDA receptor structure by regulation of NMDA receptor subunit gene expression. The four modulatory NMDAR2A–D (NR2A–D) NMDA receptor subunits are known to alter NMDA receptor properties, and the expression of these subunits is regulated developmentally. It is unclear, however, how the four NR2 subunits are expressed in individual neurons and which NR2 subunits are important to the regulation of NMDA receptor properties during developmentin vivo. Analysis of NR2 subunit gene expression in single characterized neurons of postnatal neocortex revealed that cells expressing NR2A subunit mRNA had faster NMDAR EPSCs than cells not expressing this subunit, regardless of postnatal age. Expression of NR2A subunit mRNA in cortical neurons at even low levels seemed sufficient to alter the NMDA receptor time course. The proportion of cells expressing NR2A and displaying fast NMDAR EPSCs increased developmentally, thus providing a molecular basis for the developmental change in mean NMDAR EPSC duration.
Neurogenesis in the Dentate Gyrus of the Adult Tree Shrew Is Regulated by Psychosocial Stress and NMDA Receptor Activation
Authors: Gould Elizabeth , McEwen Bruce S. , Tanapat Patima , Galea Liisa A. M. , Fuchs Eberhard
Published: April 2018

These studies were designed to determine whether adult neurogenesis occurs in the dentate gyrus of the tree shrew, an animal phylogenetically between insectivores and primates, and to explore the possibility that this process is regulated by stressful experiences and NMDA receptor activation. We performed immunohistochemistry for cell-specific markers and the thymidine analog bromodeoxyuridine (BrdU), a marker of DNA synthesis that labels proliferating cells and their progeny, on the brains of adult tree shrews subjected to psychosocial stress or NMDA receptor antagonist treatment. Cells that incorporated BrdU in the dentate gyrus of adult tree shrews were primarily located in the subgranular zone, had morphological characteristics of granule neuron precursors, and appeared to divide within 24 hr after BrdU injection. Three weeks after BrdU injection, BrdU-labeled cells had neuronal morphology, expressed the neuronal marker neuron specific enolase, and were incorporated into the granule cell layer. Vimentin-immunoreactive radial glia were observed in the dentate gyrus with cell bodies in the subgranular zone and processes extending into the granule cell layer.

Exposure to acute psychosocial stress resulted in a rapid decrease in the number of BrdU-labeled cells in the dentate gyrus. In contrast, blockade of NMDA receptors, with the NMDA receptor antagonist MK-801, resulted in an increase in the number of BrdU-labeled cells in the dentate gyrus. These results indicate that adult neurogenesis occurs in the tree shrew dentate gyrus and is regulated by a stressful experience and NMDA receptor activation. Furthermore, we suggest that these characteristics may be common to most mammalian species.
Endogenous FGF-2 Is Important for Cholinergic Sprouting in the Denervated Hippocampus
Authors: Fagan Anne M. , Suhr Steven T. , Lucidi-Phillipi Carrie A. , Peterson Daniel A. , Holtzman David M. , Gage Fred H.
Published: April 2018

To investigate the molecular mechanisms of cholinergic sprouting in the hippocampus after removal of entorhinal cortical inputs, we evaluated trophic factor gene expression in the denervated hippocampus. Despite the proposed role for nerve growth factor (NGF) in this sprouting, we observed no change in NGF mRNA or protein at several postlesion time points. In contrast, FGF-2 mRNA was increased within 16 hr. FGF-2 immunoreactivity was localized within GFAP-positive hypertrophic astrocytes distributed specifically within the denervated outer molecular layer after the lesion. To address the functional significance of this increase in FGF-2, we assessed the magnitude of cholinergic sprouting in animals receiving chronic intracerebroventricular infusions of neutralizing antibodies specific for FGF-2 and compared it with that observed in lesioned animals receiving infusate controls. Animals given FGF-2 antibodies displayed a marked reduction in cholinergic sprouting as compared with controls. In fact, many of these animals exhibited virtually no sprouting at all despite histological verification of complete lesions. These results suggest that endogenous FGF-2 promotes cholinergic axonal sprouting in the injured adult brain. Furthermore, immunocytochemical localization of receptors for FGF-2 (i.e., FGFR1) on projecting basal forebrain cholinergic neurons suggests that FGF-2 acts directly on these neurons to induce the lesion-induced sprouting response.
Environmental Knowledge Is Subserved by Separable Dorsal/Ventral Neural Areas
Authors: Aguirre Geoffrey K. , D’Esposito Mark
Published: April 2018

Environmental psychology models propose that knowledge of large-scale space is stored as distinct landmark (place appearance) and survey (place position) information. Studies of brain-damaged patients suffering from “topographical disorientation” tentatively support this proposal. In order to determine if the components of psychologically derived models of environmental representation are realized as distinct functional, neuroanatomical regions, a functional magnetic resonance imaging (fMRI) study of environmental knowledge was performed. During scanning, subjects made judgments regarding the appearance and position of familiar locations within a virtual reality environment. The fMRI data were analyzed in a manner that has been empirically demonstrated to rigorously control type I error and provide optimum sensitivity, allowing meaningful results in the single subject. A direct comparison of the survey position and landmark appearance conditions revealed a dorsal/ventral dissociation in three of four subjects. These results are discussed in the context of the observed forms of topographical disorientation and are found to be in good agreement with the human lesion studies. This experiment confirms that environmental knowledge is not represented by a unitary system but is instead functionally distributed across the neocortex.
Failure of Centrally Placed Objects to Control the Firing Fields of Hippocampal Place Cells
Authors: Cressant Arnaud , Muller Robert U. , Poucet Bruno
Published: April 2018

Previous work has shown that the angular position of hippocampal place cell firing fields is accurately controlled by the position of a single white cue card attached to the wall of a recording cylinder: when the card is rotated, fields rotate equally. In this study, we asked whether similar control could be exerted by three-dimensional objects placed directly in the recording arena. In each of several conditions, the locations of the objects relative to each other and their distances from the cylinder wall were fixed. In Experiment 1, the objects were all near the center of the cylinder. In this condition, the angular position of firing fields could, in general, not be predicted from the angular position of the object set. When a white wall card was added to the object arrangement, the stimulus ensemble exerted nearly ideal control over angular firing position. Nevertheless, when the card was withdrawn, the objects still did not control field position. In Experiment 2, place cells were recorded in the presence of two new arrangements of the same objects used in Experiment 1. In the “clustered objects” condition, the objects were placed next to each other, 10 cm from the wall. In the “objects-at-periphery” condition, the objects were put against the cylinder wall by equally increasing the distances among the objects. In both conditions, we found virtually ideal control by the objects over angular field position. These results indicate that the failure of stimulus control in Experiment 1 must be attributable to the arrangement of the objects and not to the nature of the objects themselves. Overall, the results are in line with behavioral studies that show that it is very difficult to teach rats to locate food relative to landmarks inside the behavioral arena.
Effect of Alcohol on the Proestrous Surge of Luteinizing Hormone (LH) and the Activation of LH-Releasing Hormone (LHRH) Neurons in the Female Rat
Authors: Ogilvie Kathleen M. , Rivier Catherine
Published: April 2018

Reproduction is adversely affected by alcohol abuse in humans and laboratory animals. In rats, alcohol exposure suppresses both luteinizing hormone (LH) and sex steroid secretion, although consensus is lacking as to which level of the hypothalamic-pituitary-gonadal (HPG) axis is primarily affected. We tested the hypothesis that acute alcohol treatment inhibits the HPG axis by blunting release of LH-releasing hormone (LHRH) in female rats, by examining the effect of this drug on the central reproductive endocrine event; i.e., the proestrous surge of gonadotropins, which triggers ovulation. In a first series of experiments, we injected alcohol at 8 A.M. and 12 P.M. on proestrus and measured plasma levels of LH, estradiol (E2), and progesterone during the afternoons of proestrus and estrus. Alcohol administration blocked the proestrous surge of LH and ovulation. In subsequent experiments, alcohol inhibited the surge of LHRH (measured by push–pull cannulation) and LHRH neuronal activation (measured by Fos labeling in LHRH neurons). Because alcohol also decreased E2levels, we reasoned that it might have prevented positive feedback; however, alcohol retained its ability to inhibit the LH surge evoked by E2implantation in ovariectomized females, disproving this hypothesis. Additionally, alcohol does not act via increased corticosteroid secretion, because alcohol also blocked the proestrous surge in adrenalectomized females. Last, exogenous administration of LHRH to alcohol-blocked animals evoked LH secretion and ovulation, indicating that pituitary and/or ovarian function could be restored by mimicking the hypothalamic signal. Collectively, these data indicate that in female rats, alcohol inhibits the gonadotropin surge primarily by decreasing LHRH secretion.
Corticotropin-Releasing Factor, But Not Corticosterone, Is Involved in Stress-Induced Relapse to Heroin-Seeking in Rats
Authors: Shaham Yavin , Funk Douglas , Erb Suzanne , Brown Theodore J. , Walker Claire-Dominique , Stewart Jane
Published: April 2018

We showed previously that brief footshock stress and priming injections of heroin reinstate heroin-seeking after prolonged drug-free periods. Here, we examined whether the adrenal hormone, corticosterone, and brain corticotropin-releasing factor (CRF) were involved in such reinstatement. We tested the effects of adrenalectomy, chronic exposure to the corticosterone synthesis inhibitor metyrapone (100 mg/kg, s.c., twice daily), acute exposure to metyrapone, acute intracerebroventricular injections of CRF (0.3 and 1.0 μg), and intracerebroventricular injections of the CRF antagonist α-helical CRF (3 and 10 μg). Rats were trained to self-administer heroin (100 μg/kg/infusion, i.v.) for 12–14 d. Extinction sessions were given for 4–8 d (saline substituted for heroin). Tests for reinstatement were given after priming injections of saline and of heroin (0.25 mg/kg, s.c.), and after intermittent footshock (15 or 30 min, 0.5 mA). Adrenalectomy (performed after training) did not affect reinstatement by heroin but appeared to potentiate the reinstatement by footshock. Chronic exposure to metyrapone (from the beginning of extinction) or an acute injection of metyrapone (3 hr before testing) did not alter the reinstatement of heroin-seeking induced by footshock or heroin. Acute exposure to metyrapone alone potently reinstated heroin-seeking. In addition, acute exposure to CRF reinstated heroin-seeking, and the CRF antagonist α-helical CRF attenuated stress-induced relapse. The effect of the CRF antagonist on reinstatement by heroin was less consistent. These results suggest that CRF, a major brain peptide involved in stress, contributes to relapse to heroin-seeking induced by stressors.
Pituitary Adenylate Cyclase-Activating Peptide (PACAP) in the Retinohypothalamic Tract: A Potential Daytime Regulator of the Biological Clock
Authors: Hannibal Jens , Ding Jian M. , Chen Dong , Fahrenkrug Jan , Larsen Philip J. , Gillette Martha U. , Mikkelsen Jens D.
Published: April 2018

The retinohypothalamic tract (RHT) relays photic information from the eyes to the suprachiasmatic nucleus (SCN). Activation of this pathway by light plays a role in adjusting circadian timing via a glutamatergic pathway at night. Here we report a new signaling pathway by which the RHT may regulate circadian timing in the daytime as well. We used dual immunocytochemistry for pituitary adenylate cyclase-activating peptide (PACAP) and thein vivotracer cholera toxin subunit B and observed intense PACAP-immunoreactivity (PACAP-IR) in retinal afferents in the rat SCN as well as in the intergeniculate leaflet (IGL) of the thalamus. This PACAP-IR in the SCN as well as in the IGL was nearly lost after bilateral eye enucleation. PACAP afferents originated from small ganglion cells distributed throughout the retina. The phase of circadian rhythm measured as SCN neuronal activityin vitrowas significantly advanced (3.5 ± 0.4 hr) by application of 1 × 10−6mPACAP-38 during the subjective day [circadian time (CT)-6] but not at night (CT14 and CT19). The phase-shifting effect is channeled to the clock via a PACAP-R1 receptor, because mRNA from this receptor was demonstrated in the ventral SCN byin situhybridization. Furthermore, vasoactive intestinal peptide was nearly 1000-fold less potent in stimulating a phase advance at CT6. The signaling mechanism was through a cAMP-dependent pathway, which could be blocked by a specific cAMP antagonist, Rp-cAMPS. Thus, in addition to its role in nocturnal regulation by glutamatergic neurotransmission, the RHT may adjust the biological clock by a PACAP/cAMP-dependent mechanism during the daytime.
Widespread Peroxynitrite-Mediated Damage in Alzheimer’s Disease
Authors: Smith Mark A. , Richey Harris Peggy L. , Sayre Lawrence M. , Beckman Joseph S. , Perry George
Published: April 2018

Increasing evidence suggests that oxidative damage to proteins and other macromolecules is a salient feature of the pathology of Alzheimer’s disease. Establishing the source of oxidants is key to understanding what role they play in the pathogenesis of Alzheimer’s disease, and one way to examine this issue is to determine which oxidants are involved in damage.

In this study, we examine whether peroxynitrite, a powerful oxidant produced from the reaction of superoxide with nitric oxide, is involved in Alzheimer’s disease. Peroxynitrite is a source of hydroxyl radical-like reactivity, and it directly oxidizes proteins and other macromolecules with resultant carbonyl formation from side-chain and peptide-bond cleavage. Although carbonyl formation is a major oxidative modification induced by peroxynitrite, nitration of tyrosine residues is an indicator of peroxynitrite involvement. In brain tissue from cases of Alzheimer’s disease, we found increased protein nitration in neurons, including but certainly not restricted to those containing neurofibrillary tangles (NFTs). Conversely, nitrotyrosine was undetectable in the cerebral cortex of age-matched control brains. This distribution is essentially identical to that of free carbonyls.

These findings provide strong evidence that peroxynitrite is involved in oxidative damage of Alzheimer’s disease. Moreover, the widespread occurrence of nitrotyrosine in neurons suggests that oxidative damage is not restricted to long-lived polymers such as NFTs, but instead reflects a generalized oxidative stress that is important in disease pathogenesis.
Identification of a Long-Lasting Form of Odor Adaptation that Depends on the Carbon Monoxide/cGMP SecondMessenger System
Authors: Zufall Frank , Leinders-Zufall Trese
Published: April 2018

The diffusible messenger carbon monoxide (CO) has been proposed to mediate endogenous cyclic guanosine 3′,5′-monophosphate (cGMP) formation and sensory adaptation in vertebrate olfactory receptor neurons (ORNs). We have identified and characterized a long-lasting form of odor response adaptation (LLA) that operates at the level of isolated salamander ORNs and does not require any interactions from other cells. Manifestations of LLA are seen in reduced amplitude and prolonged kinetics of the cAMP-mediated excitatory odor response and the generation of a persistent current component that lasts for several minutes and is attributable to cyclic nucleotide-gated (CNG) channel activation by cGMP. Because these effects can be mimicked by micromolar amounts of exogenous cGMP or CO, we applied various inhibitors of cGMP formation. LLA is abolished selectively by heme oxygenase inhibitors known to prevent CO release and cGMP formation in ORNs, whereas odor excitation remains unaffected. In contrast, blockers of nitric oxide synthase are unable to eliminate LLA. Several controls rule out a contribution of nonspecific actions to the effects of CO inhibitors. The results indicate that endogenous CO/cGMP signals contribute to olfactory adaptation and underlie the control of gain and sensitivity of odor transduction. The findings offer a mechanism by which a single, brief odor stimulus can be translated into long-lasting intracellular changes that could play an important role in the perceptual adaptation to odors, and explain the longstanding puzzle that the olfactory CNG channels can be gated by both cAMP and cGMP.
Activation and Desensitization of Hippocampal Kainate Receptors
Authors: Wilding Timothy J. , Huettner James E.
Published: April 2018

We have used whole-cell recordings and rapid agonist applications to characterize the physiological properties of kainate receptors expressed by rat hippocampal neurons in dissociated cell culture. Activation of NMDA and AMPA receptors was prevented by inclusion of the noncompetitive antagonists MK-801 (2 μm) and GYKI 53655 (100 μm), respectively. In the presence of these inhibitors, both kainate (EC50= 23 μm) and glutamate (EC50= 310 μm) evoked desensitizing currents. Maximal peak currents for kainate with GYKI 53655 were 15 ± 3% as large as in control solutions without GYKI. In contrast to currents mediated by AMPA receptors, kainate currents recorded in GYKI were blocked potently by lanthanum (IC50= 2 μm) and were desensitized by 1 μm2S,4R-4-methylglutamate (SYM 2081). Coapplication of either 5 μmAMPA or 500 μmaspartate had little effect on responses to kainate, although AMPA alone elicited current at 1 mm. In most cells, the currents evoked by kainate, glutamate, and SYM 2081 varied linearly with membrane potential and reversed near 0 mV. Kainate elicited substantial current at steady state (∼30% of peak), whereas responses to glutamate and SYM 2081 desensitized almost completely within 0.2–2 sec. Inhibition produced by a 10 sec desensitizing prepulse was half-maximal at 0.22 μmfor SYM 2081 and 13 μmfor glutamate. Recovery from desensitization to kainate and glutamate was >80% complete within 60 sec but was three- to fourfold slower after exposure to SYM 2081. Exposure to Concanavalin A blocked desensitization of the currents but also reduced the peak current amplitudes. Collectively, these results confirm that kainate-preferring receptors underlie the currents evoked by kainate, glutamate, or SYM-2081 in the presence of GYKI 53655; they are not mediated by electrogenic transport or by AMPA-preferring receptors that are insensitive to GYKI. In contrast to previous work on embryonic hippocampal neurons, our results show that the properties of kainate receptors expressed by cells from older animals are distinct from those displayed by homomeric assemblies of the GluR6 subunit.
Cysteine String Proteins Associated with Secretory Granules of the Rat Neurohypophysis
Authors: Pupier Sandrine , Leveque Christian , Marqueze Beatrice , Kataoka Masakazu , Takahashi Masami , Seagar Michael J.
Published: April 2018

The properties and subcellular distribution of cysteine string proteins (csps) were analyzed in peptidergic nerve terminals of the rat neurohypophysis. Polyclonal antibodies raised against recombinant rat brain csp recognized a 36 kDa protein in isolated neurosecretosomes from the post-pituitary. After chemical deacylation, a single 27 kDa form was detected that displayed identical properties to csps in a whole-brain synaptosomal fraction. Immunoisolation demonstrated that synaptophysin and csps were located in the same vesicles. Density gradient centrifugation of postsynaptosomal supernatants of neurohypophysial homogenates revealed that csps and VAMP were present in two distinct vesicle populations. Synaptophysin was only detected in the slowly migrating population corresponding to small synaptic vesicles, whereas arginine vasopressin was present in the more rapidly sedimenting population indicating that it contains large dense core vesicles (LDCVs). Immobilized antibodies against csp, synaptotagmin, or VAMP captured vesicular arginine vasopressin confirming the association of these proteins with LDCVs. Co-immunoprecipitation assays with proteins solubilized from neurohypophysial or whole-brain nerve terminals failed to reveal complexes containing csp and [125I]ωGVIA receptors. These results indicate that csps in the CNS are associated with both small synaptic vesicles and LDCVs. However, they do not provide support for the hypothesis that protein complexes implicated in exocytosis, which interact with presynaptic N-type calcium channels, contain csps.
Stoichiometry and Assembly of a Recombinant GABAAReceptor Subtype
Authors: Tretter Verena , Ehya Noosha , Fuchs Karoline , Sieghart Werner
Published: April 2018

GABAAreceptors are ligand-gated chloride ion channels that are presumed to be pentamers composed of α, β, and γ subunits. The subunit stoichiometry, however, is controversial, and the subunit arrangement presently is not known. In this study the ratio of subunits in recombinant α1β3γ2 receptors was determined in Western blots from the relative signal intensities of antibodies directed against the N terminus or the cytoplasmic loop of different subunits after the relative reactivity of these antibodies had been determined with GABAAreceptor subunit chimeras composed of the N-terminal domain of one and the remaining part of the other subunit. Via this method a subunit stoichiometry of two α subunits, two β subunits, and one γ subunit was derived. Similar experiments investigating the composition of α1β3 receptors expressed on the surface of human embryonic kidney (HEK) 293 cells cotransfected with α1 and β3 subunits resulted in a stoichiometry of two α and three β subunits. Density gradient centrifugation studies indicated that combinations of α1β3γ2 or α1β3 subunits expressed in HEK 293 cells are able to form pentamers, whereas combinations of α1γ2 or β3γ2 subunits predominantly form heterodimers. These results provide valuable information on the mechanism of GABAAreceptor assembly and support the conclusion that GABAAreceptors are pentamers in which a total of four alternating α and β subunits are connected by a γ subunit.
5-HT2AReceptor-Mediated Regulation of Brain-Derived Neurotrophic Factor mRNA in the Hippocampus and the Neocortex
Authors: Vaidya Vidita A. , Marek Gerard J. , Aghajanian George K. , Duman Ronald S.
Published: April 2018

The influence of 5-HT receptor agonists on the expression of BDNF in brain was determined. Administration of a hallucinogenic 5-HT2A /2Creceptor agonist, but not a 5-HT1Areceptor agonist, resulted in a significant but differential regulation of BDNF mRNA levels in hippocampus and neocortex. In the hippocampus, the 5-HT2A /2Creceptor agonist significantly decreased BDNF mRNA expression in the dentate gyrus granule cell layer but did not influence expression of the neurotrophin in the CA subfields. In parietal cortex and other neocortical areas, but not piriform cortex, the 5-HT2A /2Creceptor agonist dramatically increased the expression of BDNF mRNA. The effect of the 5-HT2A /2Creceptor agonist on BDNF mRNA in both the hippocampus and the neocortex was blocked by pretreatment with a selective 5-HT2A, but not 5-HT2C, receptor antagonist. The expression of BDNF mRNA in the hippocampus is reported to be decreased by stress, raising the possibility that the 5-HT2Areceptor mediates this effect. Pretreatment with ketanserin, a 5-HT2A /2Creceptor antagonist, significantly blocked the stress-induced downregulation of BDNF mRNA in hippocampus, in support of this hypothesis. The results of this study raise the possibility that regulation of BDNF expression by hallucinogenic 5-HT2Areceptor agonists leads to adaptations of synaptic strength in the hippocampus and the neocortex that may mediate some of the acute and long-term behavioral effects of these agents.
Direct Measurements of Presynaptic Calcium and Calcium-Activated Potassium Currents Regulating Neurotransmitter Release at CulturedXenopusNerve–Muscle Synapses
Authors: Yazejian Bruce , DiGregorio David A. , Vergara Julio L. , Poage Robert E. , Meriney Stephen D. , Grinnell Alan D.
Published: April 2018

The understanding of neurotransmitter release at vertebrate synapses has been hampered by the paucity of preparations in which presynaptic ionic currents and postsynaptic responses can be monitored directly. We used cultured embryonicXenopusneuromuscular junctions and simultaneous pre- and postsynaptic patch-clamp current-recording procedures to identify the major presynaptic conductances underlying the initiation of neurotransmitter release. Step depolarizations and action potential waveforms elicited Na and K currents along with Ca and Ca-activated K (KCa) currents. The onset ofKCacurrent preceded the peak of the action potential. The predominantly ω-CgTX GVIA-sensitive Ca current occurred primarily during the falling phase, but there was also significant Ca2+entry during the rising phase of the action potential. The postsynaptic current began a mean of 0.7 msec after the time of maximum rate of rise of the Ca current. ω-CgTX also blockedKCacurrents and transmitter release during an action potential, suggesting that Ca andKCachannels are colocalized at presynaptic active zones. In double-ramp voltage-clamp experiments,KCachannel activation is enhanced during the second ramp. The 1 msec time constant of decay of enhancement with increasing interpulse interval may reflect the time course of either the deactivation ofKCachannels or the diffusion/removal of Ca2+from sites of neurotransmitter release after an action potential.
In VitroGeneration of Adult Rat Olfactory Sensory Neurons and Regulation of Maturation by Coculture with CNS Tissues
Authors: Grill Raymond J. , Pixley Sarah K.
Published: April 2018

Olfactory sensory neurons (OSNs) are continually generated throughout life. Although previous studies have examined neurogenesis in olfactory cell cultures derived from embryonic or newborn rodents, we demonstrate neurogenesis in cell cultures derived from adult rat tissues. Dissociated cells taken from adult rat nasal mucosal tissues (ANM cells) were plated onto a feeder layer of newborn rat cortical glia (astrocytes) in serum-free conditions. Immature OSNs (stained for neuron-specific tubulin, NST) increased in number between 1 and 5 din vitro(DIV) and in mass thereafter. Mature OSN (stained for olfactory marker protein, OMP) numbers decreased between 1 and 5 DIV, then increased over 5 DIV values by 12 and 15 DIV. Pulse labeling with [3H]thymidine confirmedin vitroneurogenesis. To determine whether the target cells for OSNs, olfactory bulb (OB) neurons, provide trophic support, dissociated newborn rat OB cells were cocultured with ANM cells on glia. This resulted in greater numbers of OMP-positive (OMP+) neurons after 9 DIV than ANM-alone cultures. This neurotrophic effect was not OB specific. Addition of newborn rat cerebellar and embryonic rat ventral mesencephalic cells to ANM cells also increased OMP+ neurons, whereas addition of newborn rat cortical cells or controls (purified glia or fibroblasts) did not. Changes in numbers of dopaminergic neurons (stained for tyrosine hydroxylase), present in OB and VM cultures, did not correlate with OMP+ neuronal increases. Thus, cultures of adult rat OSNs demonstrate neurogenesis, and trophic/maturation support is variably provided by CNS neurons (and not glia).
Maternally Derived Immunoglobulin Light Chain Is Present in the Fetal Mammalian CNS
Authors: Weiner Joshua A. , Chun Jerold
Published: April 2018

Toward identifying molecules involved in cell–cell interactions during cerebral cortical development, we have investigated the nature of immunoglobulin-like immunoreactivity (Ig-ir) in the murine cortex. Immunohistochemistry using several antisera recognizing IgG revealed intense immunoreactivity in the subplate and marginal zone of embryonic day 16 cortex, as well as in the hindbrain and spinal cord, particularly within ventral fiber tracts. In three independently derived mouse strains lacking the recombination activating genes RAG-1 or RAG-2, which are essential for Ig production, Ig-ir was absent from the fetal CNS. Western blot analyses of wild-type brains from embryonic day 12 through birth identified a 25 kDa protein that co-migrated with Ig light chain and was absent from RAG-1 or RAG-2 −/− brain samples. This result could be replicated with an antiserum specific for Ig κ light chain, but not with antisera specific for Ig γ or μ heavy chain. No Ig-ir was detected in the brains of RAG-1 +/− embryos carried by a −/− female, suggesting a maternal source of the immunoreactive molecule. In confirmation of this, Ig-ir could be partially reproduced by intraperitoneal injection of pregnant RAG-1 −/− females with normal mouse serum. We conclude that maternally derived Ig light chain is present in the fetal murine CNS. This may represent a novel maternal contribution to fetal neural development and implicates Ig molecules as potential mediators of cortical developmental events.
PET Measurement of Dopamine D2Receptor-Mediated Changes in Striatopallidal Function
Authors: Black Kevin J. , Gado Mokhtar H. , Perlmutter Joel S.
Published: April 2018

This study was designed to validate anin vivomeasurement of the functional sensitivity of basal ganglia neuronal circuits containing dopamine D2receptors. We hypothesized that a D2agonist would decrease striatopallidal neuronal activity, and hence regional cerebral blood flow (rCBF) over the axon terminals in the globus pallidus. Quantitative pallidal blood flow was measured using positron emission tomography (PET) with bolus injections of H215O and arterial sampling in six baboons before and after intravenous administration of the selective D2agonist U91356a. We also tested whether the response to U91356a was modified by previous acute administration of various antagonists. Another baboon had serial measurements of blood flow under identical conditions, but received no dopaminergic drugs. In all animals that received U91356a, pallidal flow decreased in a dose-related manner. Global CBF had a similar response, but the decline in pallidal flow was greater in magnitude and remained significant after accounting for the global effect. A D2antagonist, but not antagonists of D1, serotonin-2, or peripheral D2receptors, prevented this decrease. This work demonstrates and validates anin vivomeasure of the sensitivity of D2-mediated basal ganglia pathways. It also supports the hypothesis that activation of the indirect striatopallidal pathway, previously demonstrated using nonselective D2-like agonists, can be mediated specifically by D2receptors. We speculate that the U91356a-PET technique may prove useful in detecting functional abnormalities of D2-mediated dopaminergic function in diseases such as parkinsonism, dystonia, Tourette syndrome, or schizophrenia.
Modular Organization of Occipito-Temporal Pathways: Cortical Connections between Visual Area 4 and Visual Area 2 and Posterior Inferotemporal Ventral Area in Macaque Monkeys
Authors: Felleman Daniel J. , Xiao Youping , McClendon Evelyn
Published: April 2018

The modular organization of cortical pathways linking visual area 4 (V4) with occipital visual area 2 (V2) and inferotemporal posterior inferotemporal ventral area (PITv) was investigated through an analysis of the patterns of retrogradely labeled cell bodies after injections of tracers into V4 and PITv. Although cytochrome oxidase or other stains have failed to yield reliable independent anatomical markers for cortical modules beyond V1 and V2, V4 and PITv seem to have modular compartments with specific patterns of cortico-cortical connectivity. Tracer injections of V4 labeled cells in V2 (1) thin stripes exclusively, (2) interstripes exclusively, or (3) specific combinations of interstripe and thin stripe subcompartments. These labeling patterns suggest (1) that there is a complicated organization of inputs to V4, (2) that projections from V2 to V4 display a submodular selectivity, and (3) that projections from V2 to V4 display some degree of cross-stream convergence. Consistent with this framework, extensive regions of PITv provide feedback projections to interstripe-recipient portions of V4, whereas more restricted portions of PITv provide feedback to thin stripe-recipient portions of V4. Similarly, the feedforward projection from V4 to PITv often arose from multiple cell clusters across a wide expanse of V4. When distinguishable fluorescent tracers were injected into two PITv sites separated by 3–5 mm, a variety of projection patterns was observed in V4. In most cases, labeled cells were found in multiple, interdigitating, nonoverlapping clusters of 1–3 mm width, whereas in other cases the two labeled fields were highly intermixed. These results suggest that V4 and PITv contain functional modules that can be characterized by the specific patterns of segregated and convergent projections they receive from lower cortical areas. These specific patterns of intercortical input, in conjunction with intrinsic cortical circuitry, may endow extrastriate cortical neurons with new and more complex receptive field properties.
Group 1 and 2 Metabotropic Glutamate Receptors Play Differential Roles in Hippocampal Long-Term Depression and Long-Term Potentiation in Freely Moving Rats
Authors: Manahan-Vaughan Denise
Published: April 2018

This study examined the role of metabotropic glutamate receptors (mGluRs) in hippocampal long-term depression (LTD)in vivo. The group 1 mGluR antagonist (S)4-carboxyphenylglycine (4CPG), group 1/2 antagonist (RS)-α-methyl-4-carboxyphenylglycine (MCPG), and group 2 antagonists (RS)-α-methylserine-O-phos-phate monophenyl ester (MSOPPE) and (2S)-α-ethylglutamic acid (EGLU) were used. The NMDA receptor antagonistd(−)-2-amino-5-phosphonopentanoic acid (AP5) was used to examine the NMDA receptor contribution to the observed LTD. Adult male Wistar rats underwent implantation of stimulating and recording electrodes into the Schaffer collaterals and CA1 stratum radiatum, respectively. After recovery of 5–7 d, the field EPSP was measured from freely moving animals. Drugs were applied either before or after 1 Hz low-frequency train (LFT) or 100 Hz stimulation via a cannula implanted in the lateral cerebral ventricle. Nine hundred pulses at 1 Hz produced an LTD that was marked and long-lasting. This LTD was completely inhibited by pre-LFT application of AP5. MCPG inhibited LTD from 2 hr post-LFT. 4CPG partially impaired LTD. MSOPPE and EGLU completely blocked induction of LTD, although short-term depression remained intact. MSOPPE did not block long-term potentiation (LTP) induced by 100 Hz stimulation, whereas 4CPG produced a significant inhibition. When MSOPPE was present, LTD could not be induced either before or after LTP induction, whereas LTD could be induced in an identical protocol in vehicle-injected animals.

These results suggest a differential role for mGluRs in NMDA receptor-dependent hippocampal LTDin vivo. Group 1 mGluRs may play a role in both LTD and LTP, whereas group 2 mGluRs may be critically involved only in LTD induction.