bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of an Amygdalo-Nigrostriatal Pathway in Associative Learning
Authors: Han Jung-Soo , McMahan Robert W. , Holland Peter , Gallagher Michela
Published: April 2018

The present study examined the role of an amygdalo-nigrostriatal pathway in associative learning. An asymmetrical lesion model was used to test whether a circuit from the amygdala central nucleus to the dorsolateral striatum, via the substantia nigra, is critical for mediating conditioned orienting responses. Rats with an asymmetrical lesion, consisting of neurotoxic removal of central nucleus neurons in one hemisphere and depletion of the dopamine innervation of the dorsolateral striatum in the contralateral hemisphere, failed to acquire conditioned orienting responses. In contrast, the asymmetrical lesion had no effect on spontaneous orienting or learning another response directed to the source of the food unconditioned stimulus in the same task. A second experiment tested the effect of reversible inactivation of the dorsolateral striatum contralateral to a neurotoxic central nucleus lesion on acquisition of the conditioned orienting response. Although inactivation did not affect spontaneous orienting, rats failed to acquire the conditioned orienting response during sessions in which inactivation occurred. Immediately after the inactivation procedure was terminated, however, a significant increase in orienting to the conditioned stimulus was evident. These data support the interpretation that the dorsolateral striatum provides a route for the expression of the conditioned orienting response but is not essential for acquisition of this learned behavior.
H. M.’s Medial Temporal Lobe Lesion: Findings from Magnetic Resonance Imaging
Authors: Corkin Suzanne , Amaral David G. , González R. Gilberto , Johnson Keith A. , Hyman Bradley T.
Published: April 2018

Although neuropsychological studies of the amnesic patient H. M. provide compelling evidence that normal memory function depends on the medial temporal lobe, the full extent of his surgical resection has not been elucidated. We conducted magnetic resonance imaging studies to specify precisely the extent of his bilateral resection and to document any other brain abnormalities. The MRI studies indicated that the lesion was bilaterally symmetrical and included the medial temporal polar cortex, most of the amygdaloid complex, most or all of the entorhinal cortex, and approximately half of the rostrocaudal extent of the intraventricular portion of the hippocampal formation (dentate gyrus, hippocampus, and subicular complex). The collateral sulcus was visible throughout much of the temporal lobe, indicating that portions of the ventral perirhinal cortex, located on the banks of the sulcus, were spared; the parahippocampal cortex (areas TF and TH) was largely intact. The rostrocaudal extent of the ablation was ∼5.4 cm (left) and 5.1 cm (right). The caudal 2 cm, approximately, of the hippocampus body (normal length, ∼4 cm) was intact, although atrophic. The temporal stem was intact. Outside the temporal lobes, the cerebellum demonstrated marked atrophy, and the mammillary nuclei were shrunken. The lateral temporal, frontal, parietal, and occipital lobe cortices appeared normal for age 66 years. The mediodorsal thalamic nuclei showed no obvious radiological changes. These findings reinforce the view that lesions of the hippocampal formation and adjacent cortical structures can produce global and enduring amnesia and can exacerbate amnesia beyond that seen after more selective hippocampal lesions.
Phenotypic Alteration of Astrocytes Induced by Ciliary Neurotrophic Factor in the Intact Adult Brain, As Revealed by Adenovirus-Mediated Gene Transfer
Authors: Lisovoski Fabrice , Akli Said , Peltekian Elise , Vigne Emmanuelle , Haase Georg , Perricaudet Michel , Dreyfus Patrick A. , Kahn Axel , Peschanski Marc
Published: April 2018

Synthesis of the ciliary neurotrophic factor (CNTF) and its specific receptor (CNTFRα) is widespread in the intact CNS, but potential biological roles for this system remain elusive. Contradictory results have been obtained concerning a possible effect on the morphological and biochemical phenotype of astrocytes. To reassess this question, we have taken advantage of adenovirus-mediated gene transfer into the rat brain to obtain the local release of CNTF. Stereotaxic administration of CNTF recombinant adenovirus vectors into the striatum led to phenotypic changes in astrocytes located in regions that were related axonally to striatal neurons at the injection site. Astrocytes appeared hypertrophied and displayed an increase in both GFAP and CNTF immunoreactivity. This response was observed up to 5 weeks after injection, the longest time studied. It was not observed after the administration of a control vector. The methodology used in the present study, allowing us to analyze the effect of the factor in areas remote from the injection site, has provided conclusive evidence that CNTF affects the astroglial phenotype in the intact CNS. The characteristics of these effects may explain why contradictory results have been obtained previously, because this signaling system seems to have a low efficiency and therefore requires a high local concentration of the factor close to the target cells. One might speculate as to the involvement of a CNTF astroglio–astroglial signaling system in the organized response of a population of astrocytes to changes in CNS homeostasis detected locally, even by a single cell.
Action Potential-Dependent Regulation of Gene Expression: Temporal Specificity in Ca2+, cAMP-Responsive Element Binding Proteins, and Mitogen-Activated Protein Kinase Signaling
Authors: Fields R. Douglas , Eshete Feleke , Stevens Beth , Itoh Kouichi
Published: April 2018

Specific patterns of neural impulses regulate genes controlling nervous system development and plasticity, but it is not known how intracellular signaling cascades and transcriptional activation mechanisms can regulate specific genes in response to specific patterns of action potentials. Studies using electrical stimulation of mouse dorsal root ganglion neurons in culture show that the temporal dynamics of intracellular signaling pathways are an important factor. Expression ofc-fosvaried inversely with the interval between repeated bursts of action potentials. Transcription was not dependent on a large or sustained increase in intracellular Ca2+, and high Ca2+levels separated by long interburst intervals (5 min) produced minimal increases inc-fosexpression. Levels of the transcription factor cAMP-responsive element binding protein (CREB), phosphorylated at Ser-133, increased rapidly in response to brief action potential stimulation but remained at high levels several minutes after an action potential burst. These kinetics limited the fidelity with which P-CREB could follow different patterns of action potentials, and P-CREB levels were not well correlated withc-fosexpression. The extracellular-regulated kinase (ERK) mitogen-activated protein kinases (MAPK) also were stimulated by action potentials of appropriate temporal patterns. Bursts of action potentials separated by long intervals (5 min) did not activate MAPK effectively, but they did increase CREB phosphorylation. This was a consequence of the more rapid dephosphorylation of MAPK in comparison to CREB. High expression ofc-foswas dependent on the combined activation of the MAPK pathway and phosphorylation of CREB. These observations show that temporal features of action potentials (and associated Ca2+transients) regulate expression of neuronal genes by activating specific intracellular signaling pathways with appropriate temporal dynamics.
Gain of Rod to Horizontal Cell Synaptic Transfer: Relation to Glutamate Release and a Dihydropyridine-Sensitive Calcium Current
Authors: Witkovsky Paul , Schmitz Yvonne , Akopian Abram , Krizaj David , Tranchina Daniel
Published: April 2018

We related rod to horizontal cell synaptic transfer to glutamate release by rods. Simultaneous intracellular records were obtained from dark-adapted rod–horizontal cell pairs. Steady-state synaptic gain (defined as the ratio of horizontal cell voltage to rod voltage evoked by the same light stimulus) was 3.35 ± 0.60 for dim flashes and 1.50 ± 0.03 for bright flashes. Under conditions of maintained illumination, there was a measurable increment of horizontal cell hyperpolarization for each light-induced increment of rod hyperpolarization over the full range of rod voltages.

In separate experiments we studied glutamate release from an intact, light-responsive photoreceptor layer, from which inner retinal layers were removed. Steady light reduced glutamate release as a monotonic function of intensity; spectral sensitivity measures indicated that we monitored glutamate release from rods. The dependence of glutamate release on rod voltage was well fit by the activation function for a high-voltage-activated, dihydropyridine-sensitive L-type calcium current, suggesting a linear dependence of glutamate release on [Ca]iin the synaptic terminal. A simple model incorporating this assumption accounts for the steady-state gain of the rod to horizontal cell synapse.
Deafferentation Causes Apoptosis in Cortical Sensory Neurons in the Adult Rat
Authors: Capurso Sabrina A. , Calhoun Michael E. , Sukhov Renat R. , Mouton Peter R. , Price Donald L. , Koliatsos Vassilis E.
Published: April 2018

The present study provides an experimental model of the apoptotic death of pyramidal neurons in rat olfactory cortex after total bulbectomy. Terminal transferase (TdT)-mediated deoxyuridine triphosphate (d-UTP)-biotin nick end labeling (TUNEL), DNA electrophoresis, and neuronal ultrastructure were used to provide evidence of apoptosis; neurons in olfactory cortex were counted by stereology. Maximal TUNEL staining occurred in the piriform cortex between 18 and 26 hr postbulbectomy. Within the survival times used in the present study (up to 48 hr postlesion), cell death was observed exclusively in the piriform cortex; there was no evidence of cell death in any other areas connected with the olfactory bulb. Neurons undergoing apoptosis were pyramidal cells receiving inputs from, but not projecting to, the olfactory bulb. The apical dendrites of these neurons were contacted by large numbers of degenerating axonal terminals. Gel electrophoresis of DNA purified from lesioned olfactory cortex showed a ladder pattern of fragmentation. Inflammatory cells or phagocytes were absent in the environment of degenerating neurons in the early stages of the apoptotic process. The present model suggests that deafferentation injury in sensory systems can cause apoptosis. In addition, olfactory bulbectomy can be used for investigating molecular mechanisms that underlie apoptosis in mature mammalian cortical neurons and for evaluating strategies to prevent the degeneration of cortical neurons.
Olfactory Bulb Recovery after Early Sensory Deprivation
Authors: Cummings D. M. , Henning H. E. , Brunjes P. C.
Published: April 2018

Olfactory bulbs retain the ability to acquire new neurons throughout life. Unilateral olfactory deprivation during the first postnatal month in rats results in a dramatic reduction in the size of the experimental olfactory bulb. Part of this reduction is attributable to the death of neurons and glia. To examine the regenerative capacity of the juvenile olfactory bulb, we developed a technique for reversible olfactory deprivation. Reversible blockade from postnatal day 1 (P1) to P20 or P30 results in reduced bulb volume and tyrosine hydroxylase immunostaining, and decreased depth in the olfactory mucosa. In another experiment, normal stimulation was restored for varying periods of time, and experimental and control bulb volumes were measured. Recovery of bulb size occurs after 40 d of normal stimulation. Rats injected with a thymidine analog to label dividing cells during the recovery period revealed that rescue results at least in part from the addition of new neurons and glia. Thus, cells born after the return of normal levels of environmental stimulation can replace some of the neurons and glia that are lost during olfactory deprivation. This system can be used to study mechanisms that underlie neuronal regeneration in the maturing mammalian brain.
Presynaptic Versus Postsynaptic Localization of μ and δ Opioid Receptors in Dorsal and Ventral Striatopallidal Pathways
Authors: Olive M. Foster , Anton Benito , Micevych Paul , Evans Christopher J. , Maidment Nigel T.
Published: April 2018

Parallel studies have demonstrated that enkephalin release from nerve terminals in the pallidum (globus pallidus and ventral pallidum) can be modulated by locally applied opioid drugs. To investigate further the mechanisms underlying these opioid effects, the present study examined the presynaptic and postsynaptic localization of δ (DOR1) and μ (MOR1) opioid receptors in the dorsal and ventral striatopallidal enkephalinergic system using fluorescence immunohistochemistry combined with anterograde and retrograde neuronal tracing techniques. DOR1 immunostaining patterns revealed primarily a postsynaptic localization of the receptor in pallidal cell bodies adjacent to enkephalin- or synaptophysin-positive fiber terminals. MOR1 immunostaining in the pallidum revealed both a presynaptic localization, as evidenced by punctate staining that co-localized with enkephalin and synaptophysin, and a postsynaptic localization, as evidenced by cytoplasmic staining of cells that were adjacent to enkephalin and synaptophysin immunoreactivities. Injections of the anterograde tracerPhaseolus vulgarisleucoagglutinin (PHA-L) or the retrograde tracer Texas Red-conjugated dextran amine (TRD) into the dorsal and ventral striatum resulted in labeling of striatopallidal fibers and pallidostriatal cell bodies, respectively. DOR1 immunostaining in the pallidum co-localized only with TRD and not PHA-L, whereas pallidal MOR1 immunostaining co-localized with PHA-L and not TRD. These results suggest that pallidal enkephalin release may be modulated by μ opioid receptors located presynaptically on striatopallidal enkephalinergic neurons and by δ opioid receptors located postsynaptically on pallidostriatal feedback neurons.
Intracellular Recordings in Response to Monaural and Binaural Stimulation of Neurons in the Inferior Colliculus of the Cat
Authors: Kuwada Shigeyuki , Batra Ranjan , Yin Tom C. T. , Oliver Douglas L. , Haberly Lewis B. , Stanford Terrence R.
Published: April 2018

The inferior colliculus (IC) is a major auditory structure that integrates synaptic inputs from ascending, descending, and intrinsic sources. Intracellular recordingin situallows direct examination of synaptic inputs to the IC in response to acoustic stimulation. Using this technique and monaural or binaural stimulation, responses in the IC that reflect input from a lower center can be distinguished from responses that reflect synaptic integration within the IC. Our results indicate that many IC neurons receive synaptic inputs from multiple sources. Few, if any, IC neurons acted as simple relay cells. Responses often displayed complex interactions between excitatory and inhibitory sources, such that different synaptic mechanisms could underlie similar response patterns. Thus, it may be an oversimplification to classify the responses of IC neurons as simply excitatory or inhibitory, as is done in many studies. In addition, inhibition and intrinsic membrane properties appeared to play key roles in creatingde novotemporal response patterns in the IC.
Caenorhabditis elegans rab-3Mutant Synapses Exhibit Impaired Function and Are Partially Depleted of Vesicles
Authors: Nonet Michael L. , Staunton Jane E. , Kilgard Michael P. , Fergestad Tim , Hartwieg Erika , Horvitz H. Robert , Jorgensen Erik M. , Meyer Barbara J.
Published: April 2018

Rab molecules regulate vesicular trafficking in many different exocytic and endocytic transport pathways in eukaryotic cells. In neurons, rab3 has been proposed to play a crucial role in regulating synaptic vesicle release. To elucidate the role of rab3 in synaptic transmission, we isolated and characterizedCaenorhabditis elegans rab-3mutants. Similar to the mouse rab3A mutants, these mutants survived and exhibited only mild behavioral abnormalities. In contrast to the mouse mutants, synaptic transmission was perturbed in these animals. Extracellular electrophysiological recordings revealed that synaptic transmission in the pharyngeal nervous system was impaired. Furthermore,rab-3animals were resistant to the acetylcholinesterase inhibitor aldicarb, suggesting that cholinergic transmission was generally depressed. Last, synaptic vesicle populations were redistributed inrab-3mutants. In motor neurons, vesicle populations at synapses were depleted to 40% of normal levels, whereas in intersynaptic regions of the axon, vesicle populations were elevated. On the basis of the morphological defects at neuromuscular junctions, we postulate that RAB-3 may regulate recruitment of vesicles to the active zone or sequestration of vesicles near release sites.
Contingent-Dependent Enhancement of Rhythmic Motor Patterns: AnIn VitroAnalog of Operant Conditioning
Authors: Nargeot Romuald , Baxter Douglas A. , Byrne John H.
Published: April 2018

Operant conditioning is characterized by the contingent reinforcement of a designated behavior. Previously, feeding behavior inAplysiahas been demonstrated to be modified by operant conditioning, and a neural pathway (esophageal nerve; E n.) that mediates some aspects of reinforcement has been identified. As a first step toward a cellular analysis of operant conditioning, we developed anin vitrobuccal ganglia preparation that expressed the essential features of operant conditioning. Motor patterns that represented at least two different aspects of fictive feeding (i.e., ingestion-like and rejection-like motor patterns) were elicited by tonic stimulation of a peripheral buccal nerve (n.2,3). Three groups of preparations were examined. In a contingent-reinforcement group, stimulation of E n. was contingent on the expression of a specific type of motor pattern (i.e., either ingestion-like or rejection-like). In a yoke-control group, stimulation of E n. was not contingent on any specific pattern. In a control group, E n. was not stimulated. The frequency of the reinforced pattern increased significantly only in the contingent-reinforcement group. No changes were observed in nonreinforced patterns or in the motor patterns of the control and yoke-control groups. Contingent reinforcement of the ingestion-like pattern was associated with an enhancement of activity in motor neuron B8, and this enhancement was specific to the reinforced pattern. These results suggest that the isolated buccal ganglia expressed an essential feature of operant conditioning (i.e., contingent reinforcement modified a designated operant) and that this analog of operant conditioning is accessible to cellular analysis.
Neurokinin 1 Receptor Internalization in Spinal Cord Slices Induced by Dorsal Root Stimulation Is Mediated by NMDA Receptors
Authors: Marvizón Juan Carlos G. , Martı́nez Vicente , Grady Eileen F. , Bunnett Nigel W. , Mayer Emeran A.
Published: April 2018

The excitability of spinal neurons that transmit pain is modulated by glutamate and substance P (SP). Glutamate is an excitatory neurotransmitter in the dorsal horn, and its effects are enhanced by SP acting on neurokinin 1 receptors (NK1Rs). We assessed activation of NK1Rs by studying their internalization in spinal cord slices. NK1Rs were localized in sections from the slices by using immunohistochemistry combined with fluorescence and confocal microscopy. Incubating the slices with SP induced internalization in most NK1R-positive neurons in laminae I, IIo, and X and in half of NK1R-positive neurons in laminae III–V. SP-induced internalization was abolished by the specific NK1R antagonist L-703,606 (1 μm). Stimulating the dorsal root with long-duration (0.4 msec) pulses evoked EPSPs in dorsal horn neurons with latencies consistent with the conduction speed of A∂- and C-fibers. High-frequency (100 Hz) stimulation of the dorsal root with these pulses induced NK1R internalization in neurons in laminae I–IIoof the stimulated side of the slice but not in the contralateral side or in other laminae. Stimulation at lower frequencies (1 and 10 Hz) failed to elicit significant internalization, suggesting that the release of SP is frequency-dependent. Internalization produced by the 100 Hz tetanus was mimicked by NMDA and blocked by an NMDA antagonist, 2-amino-5-phosphonopentanoic acid, but not by the AMPA and kainate antagonist CNQX. The NK1R antagonist L-703,606 abolished the internalization produced by 100 Hz stimulation or NMDA. Therefore, the release of SP in the dorsal horn appears to be controlled by NMDA receptors.
κ2Opioid Receptors in Limbic Areas of the Human Brain Are Upregulated by Cocaine in Fatal Overdose Victims
Authors: Staley Julie K. , Rothman Richard B. , Rice Kenner C. , Partilla John , Mash Deborah C.
Published: April 2018

Cocaine is thought to be addictive because chronic use leads to molecular adaptations within the mesolimbic dopamine (DA) circuitry that affect motivated behavior and emotion. Although the reinforcing effects of cocaine are mediated primarily by blocking DA reuptake into the presynaptic nerve terminal, reciprocal signaling between DA and endogenous opioids has important implications for cocaine dependence. The present study used the opioid antagonist 6 β-[125iodo]-3,14-dihydroxy-17-cyclopropylmethyl-4,5 α-epoxymorphinan ([125I]IOXY) after pretreatment with the site-directed acylating agents 2-(p-ethoxybenzyl)-1-diethylaminoethyl-5-isothiocyanatobenzimidiazole-HCl (μ-selective) andN-phenyl-N-[1-(2-(4-isothiocyanato)-phenethyl)-4-piperidinyl]-propanamide-HCl (δ-selective) to examine the effect of cocaine exposure on the distribution and density of κ2receptors in autopsy studies of human cocaine fatalities. The selective labeling of the κ2receptor subtype was demonstrated by competition binding studies, which gave a pharmacological signature (IOXY ≥ (+)-bremazocine ≫ U50,488 ≥ U69,593) distinct from either the κ1or κ3receptor subtypes. Visualization of [125I]IOXY labeling revealed that κ2receptors localize to mesocortical and subcortical limbic areas, including the cingulate, entorhinal, insular, and orbitofrontal cortices and the nucleus accumbens and amygdala. The number of κ2receptors in the nucleus accumbens and other limbic brain regions from cocaine fatalities was increased twofold as compared with age-matched and drug-free control subjects. Cocaine overdose victims, who experienced paranoia and marked agitation before death, also had elevated densities of κ2receptors in the amygdala. These findings demonstrate for the first time that κ2receptor numbers are upregulated by cocaine exposure. The molecular adaptation of κ2receptor numbers may play a role in the motivational incentive associated with episodes of binge cocaine use and in the dysphoria that follows abrupt cocaine withdrawal.
Substantia Nigra D1Receptors and Stimulation of Striatal Cholinergic Interneurons by Dopamine: A Proposed Circuit Mechanism
Authors: Abercrombie Elizabeth D. , DeBoer Peter
Published: April 2018

Dopamine release can regulate striatal acetylcholine effluxin vivothrough at least two receptor mechanisms: (1) direct inhibition by dopamine D2receptors on the cholinergic neurons, and (2) excitation initiated by dopamine D1receptors. The neuroanatomical locus of the latter population of D1receptors and the pathway(s) involved in the expression of their influence are controversial issues. We have tested the hypothesis that D1receptors in substantia nigra pars reticulata are involved in the excitatory component of dopaminergic actions on striatal acetylcholine output.In vivomicrodialysis was used in awake rats. Infusion of the selective D1receptor agonistR(+)-1-Phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 38393) hydrochloride into pars reticulata of substantia nigra elicited a significant increase in striatal acetylcholine efflux. Likewise,d-amphetamine applied into pars reticulata of substantia nigra by reverse dialysis produced an elevation in acetylcholine output measured at a second microdialysis probe in the striatum. Application ofd-amphetamine in the striatum by reverse dialysis elicited a decrease in striatal acetylcholine efflux that could be reversed subsequently by local application ofd-amphetamine in substantia nigra pars reticulata. A 2 mg/kg intraperitoneal dose ofd-amphetamine, which has no net effect on striatal acetylcholine output under control conditions, elicited a significant decrease in acetylcholine efflux when the D1receptor antagonistR(+)-7-Chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390) hydrochloride was applied simultaneously via a second microdialysis probe in substantia nigra pars reticulata. Thus, an excitatory D1-mediated influence on striatal acetylcholine output is initiated in substantia nigra pars reticulata, and this influence contributes to the effects of indirect dopaminergic agonists such asd-amphetamine on striatal acetylcholine efflux. These results indicate an important role of somatodendritic dopamine release, in addition to nerve terminal dopamine release, in the regulation of activity in basal ganglia circuits.
Decreased Frequency But Not Amplitude of Quantal Synaptic Responses Associated with Expression of Corticostriatal Long-Term Depression
Authors: Choi Sukwoo , Lovinger David M.
Published: April 2018

We have investigated the site of expression of striatal long-term synaptic depression (LTD) using analysis of Sr2+-induced asynchronous release of quanta from stimulated synapses. The cumulative amplitude distribution of Sr2+-induced asynchronous synaptic responses overlaps with that of miniature EPSCs (mEPSCs), suggesting that Sr2+-induced asynchronous responses are quantal. Quantal amplitude at stimulated synapses is not significantly altered after LTD induction, whereas quantal frequency decreases after LTD induction. The decrease in quantal frequency is prevented when LTD expression is blocked by dialyzing 10 mmEGTA into the postsynaptic neuron. Our findings are most consistent with the idea that expression of striatal LTD involves decreased neurotransmitter release with no change in quantal amplitude, despite the fact that induction of striatal LTD involves postsynaptic mechanisms.
Ca2+Influx Amplifies Protein Kinase C Potentiation of Recombinant NMDA Receptors
Authors: Zheng Xin , Zhang Ling , Wang Alice P. , Bennett Michael V. L. , Zukin R. Suzanne
Published: April 2018

Protein kinase C (PKC) potentiates NMDA receptors in hippocampal, trigeminal, and spinal neurons. Although PKC phosphorylates the NMDA receptor subunit NR1 at four residues within the C terminal splice cassetteC1, the molecular mechanisms underlying PKC potentiation of NMDA responses are not yet known. The present study examined the role of Ca2+in PKC potentiation of recombinant NMDA receptors expressed inXenopusoocytes. We found that Ca2+influx through PKC-potentiated NMDA receptors can further increase the NMDA response (“Ca2+amplification”). Ca2+amplification required a rise in intracellular Ca2+concentration at or near the intracellular end of the channel and was independent of Ca2+-activated Cl−current. Ca2+amplification depended on extracellular Ca2+concentration during NMDA application and not during PKC activation. Ca2+amplification was reduced by the membrane-permeant Ca2+-chelating agent BAPTA-AM. Mutant receptors with greatly reduced Ca2+permeability did not exhibit Ca2+amplification. Receptors containing the NR1 N-terminal splice cassette showed more Ca2+amplification, possibly because of their larger basal current and therefore greater Ca2+influx. Contrary to expectation, splicing out the two C-terminal splice cassettes of NR1 enhanced PKC potentiation in a manner independent of extracellular Ca2+. This observation indicates that PKC potentiation does not require phosphorylation of theC1cassette of the NR1 subunit. PKC potentiation of NMDA receptorsin vivois likely to be affected by Ca2+amplification of the potentiated signal; the degree of amplification will depend in part on alternative splicing of the NR1 subunit, which is regulated developmentally and in a cell-specific manner.
Mutant Superoxide Dismutase-1-Linked Familial Amyotrophic Lateral Sclerosis: Molecular Mechanisms of Neuronal Death and Protection
Authors: Ghadge G. D. , Lee J. P. , Bindokas V. P. , Jordan J. , Ma L. , Miller R. J. , Roos R. P.
Published: April 2018

Mutations in human Cu/Zn superoxide dismutase-1 (SOD) cause ∼20% of cases of familial amyotrophic lateral sclerosis (FALS). We investigated the mechanism of mutant SOD-induced neuronal degeneration by expressing wild-type and mutant SODs in neuronal cells by means of infection with replication-deficient recombinant adenoviruses. Expression of two FALS-related mutant SODs (A4V and V148G) caused death of differentiated PC12 cells, superior cervical ganglion neurons, and hippocampal pyramidal neurons. Cell death included many features typical of apoptosis. Death could be prevented by copper (Cu2+) chelators, Bcl-2, glutathione, vitamin E, and inhibitors of caspases. Mutant SOD-expressing PC12 cells had higher rates of superoxide (O2−) production under a variety of conditions. The results support the hypothesis that mutant SOD induced-neurodegeneration is associated with disturbances of neuronal free radical homeostasis.
Postexcitatory Inhibition of the Crayfish Lateral Giant Neuron: A Mechanism for Sensory Temporal Filtering
Authors: Vu Eric T. , Berkowitz Ari , Krasne Franklin B.
Published: April 2018

Crayfish escape from threats by either giant neuron-mediated “reflex” tail flexions that occur with very little delay but do not allow for much sensory guidance of trajectory or by “nongiant” tail flexion responses that allow for sensory guidance but occur much less promptly. Thus, when a stimulus occurs, the nervous system must make a rapid assessment of whether to use the faster reflex system or the slower nongiant one. It does this on the basis of the abruptness of stimulus onset; only stimuli of very abrupt onset trigger giant-mediated responses. We report here that stimuli which excite the lateral giant (LG) command neurons for one form of reflex escape also produce a slightly delayedpostexcitatory inhibition(PEI) of the command neurons. As a result, only stimuli that become strong enough to excite the command neurons to firing threshold before the onset of PEI, within a few milliseconds of stimulus onset, can cause giant-mediated responses. This inhibition is directed to distal dendrites of the LG neurons, which allows for some location specificity of PEI within the sensory field of a single hemisegment.
Inhibition of Axonal Growth by Brefeldin A in Hippocampal Neurons in Culture
Authors: Jareb Mark , Banker Gary
Published: April 2018

The outgrowth of neuronal processes involves a great increase in the surface area of the cell. The supply of membrane material necessarily must be coordinated with the demands for neurite growth. The selective growth of only one or two neurites at any given time during the development of polarity raises the possibility that the production of materials by the soma is limiting for growth (Dotti and Banker, 1987; Dotti et al., 1988; Goslin and Banker, 1990). To examine the role of the availability of membrane components during the development of polarity and axonal elongation, we treated neurons with brefeldin A, an antibiotic that disrupts the trafficking of vesicles from the Golgi complex to the plasma membrane. Treatment with brefeldin A (1 μg/ml) inhibited axonal growth within 0.5 hr; in unpolarized cells it prevented the formation of an axon. These results indicate that the availability of membrane components of Golgi-derived vesicles is required for axonal growth and hence the development of polarity. Inhibitors of protein and RNA synthesis also blocked axonal growth and the development of polarity, but over a much slower time course. This suggests that the full complement of proteins and mRNAs required for the initial development of polarity is present for several hours before polarity is actually established.
Extracellular Serotonin in the Lateral Hypothalamic Area Is Increased during the Postejaculatory Interval and Impairs Copulation in Male Rats
Authors: Lorrain Daniel S. , Matuszewich Leslie , Friedman Ross D. , Hull Elaine M.
Published: April 2018

Serotonin (5-HT) is generally inhibitory to masculine sexual behavior. It has been suggested that 5-HT released after ejaculation may promote the sexual quiescence of the postejaculatory interval (PEI). The following experiments were conducted to test (1) whether extracellular 5-HT increases in either the anterior lateral hypothalamic area (LHAA) or the medial preoptic area (MPOA) of male rats after ejaculation; (2) whether increasing 5-HT in these sites, by microinjecting the selective serotonin reuptake inhibitor alaproclate, could inhibit copulatory abilities; and (3) whether copulation deficits produced by alaproclate were attributable to locomotor impairments. The effects of local application of alaproclate on extracellular 5-HT levels in the LHAAand the MPOA were also tested. Extracellular serotonin was measured in all experiments usingin vivomicrodialysis.

Ejaculation was correlated with enhanced 5-HT release from the LHAA; no 5-HT increases were observed before ejaculation, and levels were decreased toward basal values during a subsequent copulatory series. Elevating 5-HT in the LHAAby microinjecting alaproclate inhibited copulation by increasing the latency to mount, intromit, and ejaculate. This inhibition did not result from nonspecific locomotor impairments. In the MPOA, 5-HT release remained stable throughout copulation, and microinjecting alaproclate into this site did not significantly alter sexual behavior.

These data support the large body of evidence suggesting that 5-HT is inhibitory to masculine sexual behavior. Furthermore, the LHAA, but not the MPOA, may be one site responsible for serotonergic inhibition of copulation during the PEI.
Identification of Two Nervous System-Specific Members of theergPotassium Channel Gene Family
Authors: Shi Wenmei , Wymore Randy S. , Wang Hong-Sheng , Pan Zongming , Cohen Ira S. , McKinnon David , Dixon Jane E.
Published: April 2018

Two new potassium channel genes,erg2 anderg3, that are expressed in the nervous system of the rat were identified. These two genes form a small gene family with the previously describederg1 (HERG) gene. Theerg2 anderg3 genes are expressed exclusively in the nervous system, in marked contrast toerg1, which is expressed in both neural and non-neural tissues. All three genes are expressed in peripheral sympathetic ganglia. Theerg3 channel produces a current that has a large transient component at positive potentials, whereas the other two channels are slowly activating delayed rectifiers. Expression of theerg1 gene in the sympathetic nervous system has potential implications for the etiology of the LQT2 form of the human genetic disease long QT syndrome.
Study of Proline-Directed Protein Kinases Involved in Phosphorylation of the Heavy Neurofilament Subunit
Authors: Giasson Benoit I. , Mushynski Walter E.
Published: April 2018

The high-molecular-mass neurofilament subunit (NFH) is normally hypophosphorylated in the neuronal perikaryon and undergoes extensive phosphorylation after entering the initial axon segment. Aberrant hyperphosphorylation of perikaryal NFH is a common feature of many neurological diseases. In a previous study (Giasson and Mushynski, 1996), we demonstrated a correlation between phosphorylation of perikaryal NFH and induction of stress-activated protein kinase (SAPK)-γ. In this report, we present direct evidence showing that thein vivoactivation of SAPKs by an upstream activator (MEKK-1) caused extensive NFH phosphorylation. We also show that stress-activated p38 kinases were not involved in the phosphorylation of perikaryal NFH in cultured dorsal root ganglion neurons and that this process was reversible. SAPKγ was shown to be located in both the cell body and the neurites of the cultured neurons, suggesting that it is likely to be involved in the phosphorylation of cytoplasmic substrates. These could include neuritic NFH, which is highly phosphorylated despite the demonstrated lack of cyclin-dependent kinase-5 activity in these neurons. Neuritic NFH was also highly phosphorylated in neuronal cultures devoid of Schwann cells, indicating that this form of post-translational modification does not require cues stemming from Schwann cell–axon contacts. Collectively, these findings provide significant new insights into mechanisms involved in NFH phosphorylation in normal neurons and in disease states characterized by aberrant phosphorylation of neurofilaments.
Luteinizing Hormone-Releasing Hormone (LHRH) Neurons Maintained in Hypothalamic Slice Explant Cultures Exhibit a Rapid LHRH mRNA Turnover Rate
Authors: Maurer Jennifer A. , Wray Susan
Published: April 2018

Evidence indicates that neuropeptide gene expression is tightly coupled to biosynthesis and secretion. Moreover, rhythmic gene expression often accompanies rhythmic secretion. Luteinizing hormone-releasing hormone (LHRH) neurosecretion, which regulates gonadal function, is pulsatile, with interpulse intervals of ∼1 hr and pulse decays of <30 min in rats. As a basis for a rapid fall in peptide secretion, we hypothesize that LHRH mRNA levels rapidly decay. To address this hypothesis, we examined LHRH mRNA turnover in primary postnatal LHRH neurons maintained in long-term hypothalamic/preoptic area slice explant cultures, usingin situhybridization histochemistry (ISHH). Relative LHRH mRNA content per cell was quantitated by single-cell analysis after transcription inhibition with 5,6-dichloro-1-d-ribofuranosyl-benzimidazole (DRB) or actinomycin D. Cultures were maintained in serum-free medium with tetrodotoxin to suppress spontaneous electrical activity and hence assess only intrinsic cellular activity. A plot of LHRH mRNA level per cell versus DRB treatment time showed a rapid initial decay of LHRH mRNA (t½, 5–13 min), followed by a slower decay rate (t½, 329–344 hr). LHRH cell number after drug treatment as determined by immunocytochemistry did not change. Comparison of mammalian LHRH mRNA 3′-untranslated regions showed two conserved regions. These data indicate that, in primary LHRH neurons, LHRH mRNA has an intrinsically high rate of turnover and a mRNA stabilization component. Foremost, decay of LHRH mRNA, the fastest reported for a neuropeptide to date, corresponds to the decay of LHRH peptide pulses.
Identification of Caveolin and Caveolin-Related Proteins in the Brain
Authors: Cameron Patricia L. , Ruffin Johnna W. , Bollag Roni , Rasmussen Howard , Cameron Richard S.
Published: April 2018

Caveolae are 50–100 nm, nonclathrin-coated, flask-shaped plasma membrane microdomains that have been identified in most mammalian cell types, except lymphocytes and neurons. To date, multiple functions have been ascribed to caveolae, including the compartmentalization of lipid and protein components that function in transmembrane signaling events, biosynthetic transport functions, endocytosis, potocytosis, and transcytosis. Caveolin, a 21–24 kDa integral membrane protein, is the principal structural component of caveolae. We have initiated studies to examine the relationship of detergent-insoluble complexes identified in astrocytes to the caveolin–caveolae compartment detected in cells of peripheral tissues. Immunolocalization studies performed in astrocytes reveal caveolin immunoreactivity in regions that correlate well to the distribution of caveolae and caveolin determined in other cell types, and electron microscopic studies reveal multiple clusters of flask-shaped invaginations aligned along the plasma membrane. Immunoblot analyses demonstrate that detergent-insoluble complexes isolated from astrocytes are composed of caveolin-1α, an identification verified by Northern blot analyses and by the cloning of a cDNA using reverse transcriptase-PCR amplification from total astrocyte RNA. Using a full-length caveolin-1 probe, Northern blot analyses suggest that the expression of caveolin-1 may be regulated during brain development. Immunoblot analyses of detergent-insoluble complexes isolated from cerebral cortex and cerebellum identify two immunoreactive polypeptides with apparent molecular weight and isoelectric points appropriate for caveolin. The identification of caveolae microdomains and caveolin-1 in astrocytes and brain, as well as the apparent regulation of caveolin-1 expression during brain development, identifies a cell compartment not detected previously in brain.
Sexual Dimorphism in the Spinal Cord Is Absent in Mice Lacking the Ciliary Neurotrophic Factor Receptor
Authors: Forger Nancy G. , Howell Michelle L. , Bengston Lynn , MacKenzie Laura , DeChiara Thomas M. , Yancopoulos George D.
Published: April 2018

Ciliary neurotrophic factor (CNTF) has potent survival-promoting effects on motoneuronsin vitroandin vivo. We examined knockout mice with null mutations of the gene for either CNTF itself or the α-subunit of the CNTF receptor (CNTFRα) to assess whether CNTF and/or its receptors are involved in the development of a sexually dimorphic neuromuscular system. Male rodents have many more motoneurons in the spinal nucleus of the bulbocavernosus (SNB) than do females. This sex difference is caused by hormone-regulated death of SNB motoneurons and their target muscles. Sexual dimorphism of SNB motoneuron number developed completely normally in CNTF knockout (CNTF −/−) mice. In contrast, a sex difference in the SNB was absent in CNTFRα −/− animals: male mice lacking a functional CNTF α-receptor had fewer than half as many SNB motoneurons than did wild-type males and no more than did their female counterparts. Size of the bulbocavernosus and levator ani muscles, the main targets of SNB motoneurons, was not affected in either CNTF or CNTFRα knockout males. These observations suggest that signaling through the CNTF receptor is involved in sexually dimorphic development of SNB motoneuron number and that target muscle survival per se is not sufficient to ensure motoneuron survival in this system. In addition, our observations are consistent with the suggestion that CNTF itself is not the only endogenous ligand for the CNTF receptor. A second, as yet unknown, ligand may be important for neural development, including sexually dimorphic motoneuron development.
Insular Cortical Projections to Functional Regions of the Striatum Correlate with Cortical Cytoarchitectonic Organization in the Primate
Authors: Chikama Masanori , McFarland Nikolaus R. , Amaral David G. , Haber Suzanne N.
Published: April 2018

We examined the striatal projections from different cytoarchitectonic regions of the insular cortex using anterograde and retrograde techniques. The shell and medial ventral striatum receive inputs primarily from the agranular and ventral dysgranular insula. The central ventral striatum receives inputs primarily from the dorsal agranular and dysgranular insula. Projections to the central ventral striatum originate from more posterior and dorsal insular regions than projections to the medial ventral striatum. The dorsolateral striatum receives projections primarily from the dorsal dysgranular and granular insula.

These results show that cytoarchitectonically less differentiated (agranular) insular regions project to the ventromedial “limbic” part of the ventral striatum, whereas more differentiated (granular) insular regions project to the dorsolateral “sensorimotor” part of the striatum. The finding that the ventral “limbic” striatum receives inputs from less differentiated regions of the insula is consistent with the general principle that less differentiated cortical regions project primarily to the “limbic” striatum. Functionally, the ventral striatum receives insular projections primarily related to integrating feeding behavior with rewards and memory, whereas the dorsolateral striatum receives insular inputs related to the somatosensation. Information regarding food acquisition in the insula may be sent to the intermediate area of the striatum.
Effects of Sleep on Wake-Induced c-fosExpression
Authors: Basheer Radhika , Sherin Jonathan E. , Saper Clifford B. , Morgan James I. , McCarley Robert W. , Shiromani Priyattam J.
Published: April 2018

We investigated the effects of sleep on wake-induced c-fosexpression in the cerebral cortex of rats and c-fos-lacZtransgenic mice. In the cortex of rats, the levels of c-Fos, detected both by immunocytochemistry and Western blot, remained high during 6 or 12 hr of enforced wakefulness but declined rapidly (within 1 hr) with increasing time of recovery sleep. Similarly, in the transgenic mice in whichlacZexpression is driven from the c-fospromoter, β-galactosidase activity was high after enforced wakefulness and declined with increasing amounts of sleep. These results suggest that the decrease in c-Fos protein in cortical neurons during sleep may be attributable to cessation of c-fosexpression, activation of a process that degrades the wake-induced c-Fos, or both.
Effects of the Metabotropic Glutamate Receptor Antagonist MCPG on Phosphoinositide Turnover and Synaptic Plasticity in Visual Cortex
Authors: Huber Kimberly M. , Sawtell Nathaniel B. , Bear Mark F.
Published: April 2018

The neurotransmitter glutamate, in addition to activating ligand-gated ion channels, also stimulates phosphoinositide (PI) hydrolysis in neurons by activating a group of G-protein-coupled metabotropic glutamate receptors (mGluRs). A role for mGluRs in synaptic plasticity originally was hypothesized based on the observation that the developmental decline in glutamate-stimulated PI turnover is well correlated with the decline in experience-dependent synaptic plasticity in visual cortex. Over the past few years, the compound α-methyl-4-carboxyphenylglycine (MCPG) has been widely used to test the role of PI-coupled mGluRs in a number of types of synaptic plasticity, including long-term potentiation (LTP), long-term depression (LTD), ocular dominance plasticity in visual cortex, and the neural plasticity underlying learning and memory. The conclusions of most of these studies were based on the assumption that MCPG blocks the actions of glutamate at PI-coupled mGluRs in the cerebral cortex. Here we show that this assumption is not valid in visual cortex. Although MCPG does antagonize the actions of the synthetic mGluR agonist 1S,3R-aminocyclopentane-1,3-dicarboxylic acid, it fails to block PI turnover and changes in spike adaptation stimulated by glutamate, the endogenous mGluR ligand. In addition, we find that MCPG fails to block the NMDA receptor-dependent forms of LTP, LTD, and depotentiation in visual cortex.