bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrophysiological Characterization of Chemosensory Neurons from the Mouse Vomeronasal Organ
Authors: Liman Emily R. , Corey David P.
Published: April 2018

The mechanism of sensory transduction in chemosensory neurons of the vomeronasal organ (VNO) is not known. Based on molecular data, it is likely to be different from that mediating sensory transduction in the main olfactory system. To begin to understand this system, we have characterized the electrophysiological properties of dissociated mouse VNO neurons with patch-clamp recording. Sensory neurons were distinguished from nonsensory neurons by the presence of a dendrite, by immunoreactivity for olfactory marker protein, and by the firing of action potentials. The resting potential of VNO neurons was approximately −60 mV, and the average input resistance was 3 GΩ. Current injections as small as 1–2 pA elicited steady trains of action potentials that showed no sign of adaptation during a 2 sec stimulus duration. The voltage-gated conductances in VNO neurons are distinct from those in olfactory neurons. The Na+current is composed of two components; the major component was TTX-sensitive (Ki = 3.6 nm). The outward K+current activates at −30 mV with kinetics 10 times slower than for K+currents in olfactory neurons. The Ca2+current is composed of at least two components: an L-type current and a T-type current that activates at −60 mV and is not found in olfactory neurons. We find no evidence for cyclic nucleotide-gated channels in VNO neurons under a variety of experimental conditions, including those that produced large responses in mouse olfactory neurons, which is further evidence for a novel transduction pathway.
APPL, theDrosophilaMember of the APP-Family, Exhibits Differential Trafficking and Processing in CNS Neurons
Authors: Torroja Laura , Luo Liqun , White Kalpana
Published: April 2018

TheDrosophila Applgene encodes a transmembrane protein that is expressed exclusively in neurons. Amino acid comparisons show that APPL protein is a member of the amyloid precursor protein (APP)-like family of proteins. Similar to mammalian APP-family proteins, APPL is synthesized as a transmembrane holoprotein and cleaved to release a large secreted amino-terminal domain. Using immunocytochemical methods, we have analyzed the distribution of APPL in theDrosophilaCNS. Surprisingly, although APPL is present in all neuronal cell bodies, the neuropil shows stereotypic differential distribution. Double-labeling experiments with different neuronal markers were used to distinguish between APPL associated with neuronal processes or extracellular matrix. The distribution of APPL protein produced from transgenes encoding wild-type (APPL), secretion-defective (APPLsd), and constitutively secreted (APPLs) forms was analyzed in anAppl-deficient background to determine which APPL form is associated with different neuropil regions. We found that APPLsdprotein is enriched where APPL immunoreactivity coincides with neuronal processes. In contrast, APPLspreferentially localizes to those parts of the neuropil that show a diffuse APPL signal that rarely colocalizes with processes, and thus seems to be a component of the extracellular matrix. These data indicate that proteolytic cleavage and trafficking of APPL is differentially regulated in different neuronal populations. Through metamorphosis, APPL is especially abundant in growing axons and in areas where synapses are forming. Interestingly, in adult brains, APPL protein is enriched in the mushroom bodies and to a lesser extent in the central complex, structures involved in learning and memory.
Glial Growth Factor 2, a Soluble Neuregulin, Directly Increases Schwann Cell Motility and Indirectly Promotes Neurite Outgrowth
Authors: Mahanthappa Nagesh K. , Anton Eva S. , Matthew William D.
Published: April 2018

Schwann cells proliferate, migrate, and act as sources of neurotrophic support during development and regeneration of peripheral nerves. Recent studies have demonstrated that neuregulins, a family of growth factors secreted by developing motor and peripheral neurons, influence Schwann cell development. In this study, we use three distinct assays to show that glial growth factor 2 (GGF2), a secreted neuregulin, exerts multiple effects on mature Schwann cellsin vitro. At doses submaximal for proliferation, GGF2 increases the motility of Schwann cells cultured on peripheral nerve cryosections. Furthermore, in a novel bioassay, focal application of GGF2 causes directed migration in conventional monolayer cultures of Schwann cells. At higher doses, GGF2 causes proliferation, as described previously. In a new explant culture system designed to emulate entubulation repair of transected peripheral nerves, GGF2 concentrations greater than necessary to saturate the mitotic response induce the secretion by Schwann cells of activities that promote sympathetic neuron survival and outgrowth. These findings support a model in which neuregulins secreted by peripheral neurons are key components of reciprocal neuron–glia interactions that are important for peripheral nerve development and regeneration.
Regulation of ERK ( Extracellular Signal Regulated Kinase), Part of the Neurotrophin Signal Transduction Cascade, in the Rat Mesolimbic Dopamine System by Chronic Exposure to Morphine or Cocaine
Authors: Berhow Melissa T. , Hiroi Noboru , Nestler Eric J.
Published: April 2018

Local infusion of brain-derived neurotrophic factor (BDNF) into the ventral tegmental area (VTA) can prevent and reverse the ability of chronic morphine or cocaine exposure to induce tyrosine hydroxylase (TH) in this brain region. The present study examined a possible role for extracellular signal regulated kinases (ERKs), the major effector for BDNF and related neurotrophins, in morphine and cocaine action in the VTA. Chronic, but not acute, administration of morphine or cocaine increased ERK catalytic activity specifically in the VTA. This increase in ERK activity reflected an increase in the state of phosphorylation of ERK, with no change in levels of total ERK immunoreactivity. Chronic infusions of BDNF into the VTA reduced total ERK immunoreactivity with no change in ERK activity, and also blocked the morphine-induced increase in ERK activity. These results suggest that chronic BDNF elicits a compensatory increase in the phosphorylation of the remaining ERK molecules and thereby prevents any additional increase in response to drug exposure. Such a role for ERK in morphine action was demonstrated directly by chronically infusing antisense oligonucleotides to ERK1 into the VTA. This treatment selectively reduced levels of ERK1 immunoreactivity in a sequence-specific manner without detectable toxicity. Intra-VTA infusion of ERK1 antisense oligonucleotides mimicked the effects of chronic BDNF infusions on ERK immunoreactivity, ERK activity, and TH immunoreactivity in the VTA under both control and morphine-treated conditions. The chronic morphine-induced increases in ERK activity and TH expression in the VTA also were blocked by local infusion of NMDA glutamate receptor antagonists, suggesting a role for glutamate in mediating these drug effects. Together, these findings support a scheme whereby chronic, systemic administration of morphine or cocaine leads to a sustained increase in ERK phosphorylation state and activity in the VTA, which, in turn, contributes to drug-induced increases in TH, and perhaps other drug-induced adaptations, elicited selectively in this brain region.
The Analysis of Complex Motion Patterns by Form/Cue Invariant MSTd Neurons
Authors: Geesaman Bard J. , Andersen Richard A.
Published: April 2018

Several groups have proposed that area MSTd of the macaque monkey has a role in processing optical flow information used in the analysis of self motion, based on its neurons’ selectivity for large-field motion patterns such as expansion, contraction, and rotation. It has also been suggested that this cortical region may be important in analyzing the complex motions of objects. More generally, MSTd could be involved in the generic function of complex motion pattern representation, with its cells responsible for integrating local motion signals sent forward from area MT into a more unified representation. If MSTd is extracting generic motion pattern signals, it would be important that the preferred tuning of MSTd neurons not depend on the particular features and cues that allow these motions to be represented. To test this idea, we examined the diversity of stimulus features and cues over which MSTd cells can extract information about motion patterns such as expansion, contraction, rotation, and spirals. The different classes of stimuli included: coherently moving random dot patterns, solid squares, outlines of squares, a square aperture moving in front of an underlying stationary pattern of random dots, a square composed entirely of flicker, and a square of nonFourier motion. When a unit was tuned with respect to motion patterns across these stimulus classes, the motion pattern producing the most vigorous response in a neuron was nearly the same for each class. Although preferred tuning was invariant, the magnitude and width of the tuning curves often varied between classes. Thus, MSTd is form/cue invariant for complex motions, making it an appropriate candidate for analysis of object motion as well as motion introduced by observer translation.
Role of the Amygdala in the Coordination of Behavioral, Neuroendocrine, and Prefrontal Cortical Monoamine Responses to Psychological Stress in the Rat
Authors: Goldstein Lee E. , Rasmusson Ann M. , Bunney B. Steve , Roth Robert H.
Published: April 2018

Exposure to mild stress is known to activate dopamine (DA), serotonin (5-HT), and norepinephrine (NE) metabolism in the anteromedial prefrontal cortex (m-PFC). Neuroanatomical site(s) providing afferent control of the stress activation of the m-PFC monoaminergic systems is at present unknown. The present study used a conditioned stress model in which rats were trained to fear a substartle-threshold tone paired previously with footshock and assessed for behavioral, neuroendocrine, and neurochemical stress responses. Bilateral NMDA-induced excitotoxic lesioning of the basolateral and central nuclei of the amygdala was performed before or after training. Pretraining amygdala lesions blocked stress-induced freezing behavior, ultrasonic vocalizations, adrenocortical activation, and dopaminergic metabolic activation in the m-PFC. Post-training amygdala lesions blocked stress-induced m-PFC DA, 5-HT, and NE metabolic activation. Post-training amygdala lesions also blocked stress-induced freezing and defecation, and greatly attenuated adrenocortical activation. These data provide evidence of amygdalar control of stress-induced metabolic activation of the monoaminergic systems in the m-PFC, as well as amygdalar integration of behavioral and neuroendocrine components of the rat stress response. These results are discussed in terms of possible relevance to stress-induced exacerbation of schizophrenic symptoms and the pathophysiology of post-traumatic stress disorder.
Comparative Study of Pre- and Postsynaptic 5-HT1AReceptor Modulation of Anxiety in Two Ethological Animal Tests
Authors: File Sandra E. , Gonzalez Luis E. , Andrews Nick
Published: April 2018

The purpose of this study was to determine the roles of the presynaptic 5-hydroxytryptamine1A(5-HT1A) receptors in the median raphénucleus (MRN) and of the postsynaptic 5-HT1Areceptors in its projection area of the dorsal hippocampus in the social interaction and elevated plus-maze tests of anxiety. Direct administration of the 5-HT1Areceptor agonist (±)-8-hydroxy-dipropylaminotetralin (8-OH-DPAT, 200 ng) into the MRN had significant anxiolytic effects in all three test situations examined (social interaction, plus-maze trials 1 and 2). These anxiolytic effects were antagonized by a silent dose (200 ng) of the 5-HT1Areceptor antagonist WAY 100635, confirming that they were mediated by 5-HT1Areceptors. In contrast, after bilateral administration to the dorsal hippocampus, 8-OH-DPAT (100 ng) had significant anxiogenic effects in the social interaction test and in plus-maze trial 2. These anxiogenic effects were antagonized by silent doses of 5-HT1Areceptor antagonists [(+)WAY 100135, 10 mg/kg s.c., and intrahippocampal (±)tertatolol, 3 μg, respectively], confirming mediation by 5-HT1Areceptors. In rats naive to the plus-maze, neither 8-OH-DPAT (50, 100, or 200 ng) nor the 5-HT1Areceptor antagonist (±)tertatolol (3 μg) had any significant effect when administered to the dorsal hippocampus. This demonstrates that previous experience of a rat in the plus-maze has a major effect on the sensitivity of dorsal hippocampal 5-HT1Areceptors, as we have demonstrated previously for the 5-HT1Areceptors in the dorsal raphé nucleus. Overall, our results provide evidence that stimulation of the presynaptic 5-HT1Areceptors in the MRN results in an anxiolytic action, whereas stimulation of the post-synaptic 5-HT1Areceptors in its projection area results in an anxiogenic effect. These results are consistent with an overall reduction in 5-HT neurotransmission in the dorsal hippocampus having an anxiolytic effect, and they explain the relatively weak anxiolytic profile detected when 5-HT1Areceptor agonists are given systemically.
Functional Diversity of P-Type and R-Type Calcium Channels in Rat Cerebellar Neurons
Authors: Tottene Angelita , Moretti Alessandra , Pietrobon Daniela
Published: April 2018

By combining single-channel and whole-cell patch-clamp recordings, we have established the sensitivity to ω-agatoxin IVA and ω-conotoxin MVIIC (SNX-230) of G1, G2, and G3, the three novel non-L-, non-N-type Ca2+channels characterized previously in rat cerebellar granule cells. G1 channels were blocked irreversibly by both ω-conotoxin MVIIC and low doses of ω-agatoxin IVA (saturation at 50 nm). Thus, according to pharmacological criteria, G1 channels must be classified as P-type Ca2+channels. Being slowly inactivating during depolarizing pulses and completely inactivated at voltages in which steady-state inactivation of P-type channels in Purkinje cells is negligible, G1 represents a novel P subtype. Neither G2 nor G3 was blocked irreversibly by ω-conotoxin MVIIC, and therefore both are R-type Ca2+channels. G2 and G3 have some biophysical properties similar to those of low-voltage-activated (LVA) Ca2+channels (e.g., voltage range for steady-state inactivation,V1/2 = −90 mV), some properties similar to those of high-voltage-activated (HVA) Ca2+channels (e.g., high sensitivity to Cd2+block), and other properties intermediate between those of LVA and HVA Ca2+channels, with LVA properties prevailing in G2 and HVA properties prevailing in G3. The R-type whole-cell current was inhibited by Ni2+with a biphasic dose–response curve (IC50: 4 and 153 μm), suggesting that G2 and G3 may have a different sensitivity to Ni2+block. Our results uncover functional diversity of both native P-type and R-type Ca2+channels and show that R subtypes with distinct biophysical properties are coexpressed in rat cerebellar granule cells.
GABABReceptor-Activated Inwardly Rectifying Potassium Current in Dissociated Hippocampal CA3 Neurons
Authors: Sodickson Deborah L. , Bean Bruce P.
Published: April 2018

GABA and the GABABreceptor agonist baclofen activated a potassium conductance in acutely dissociated hippocampal CA3 neurons. Baclofen-activated current required internal GTP, was purely potassium selective, and showed strong inward rectification. As with acetylcholine-activated current in atrial myocytes, external Cs+blocked inward but not outward current in a highly voltage-dependent manner, whereas Ba2+blocked with no voltage dependence. Unlike the cardiac current, however, the baclofen-activated current showed no intrinsic voltage-dependent relaxation. With fast solution exchange, current was activated by baclofen or GABA with a lag of ∼50 msec followed by an exponential phase (time constant ∼225 msec at saturating agonist concentrations); deactivation was preceded by a lag of ∼150 msec and occurred with a time constant of ∼1 sec. GABA activated the potassium conductance with a half maximally effective concentration (EC50) of 1.6 μm, much lower than that for activation of GABAAreceptor-activated chloride current in the same cells (EC50∼25 μm). At low GABA concentrations, activation of the GABABcurrent had a Hill coefficient of 1.4–2.1, suggesting cooperativity in the receptor-to-channel pathway. Although the maximal conductance activated by GABABreceptors is much smaller than that activated by GABAAreceptors, its higher sensitivity to GABA and slower time course make it well suited to respond to low concentrations of extra-synaptic GABA.
Excitatory GABA Responses in Embryonic and Neonatal Cortical Slices Demonstrated by Gramicidin Perforated-Patch Recordings and Calcium Imaging
Authors: Owens David F. , Boyce Leslie H. , Davis Marion B. E. , Kriegstein Arnold R.
Published: April 2018

Gramicidin perforated-patch-clamp recordings in brain slices were used to obtain an accurate assessment of the developmental change in the GABAAreceptor reversal potential (EGABAA) in embryonic and early postnatal rat neocortical cells including neuroepithelial precursor cells, cortical plate neurons, and postnatal neocortical neurons. Our results demonstrate that there is a progressive negative shift inEGABAA, with the most positive values found in the youngest cortical precursor cells. At the early stages of neocortical development,EGABAAis determined by the chloride (Cl−) gradient, and the internal chloride concentration ([Cl−]i) decreases with development.EGABAAis positive to the resting potential, indicating that GABA serves to depolarize developing neocortical cells. Consistent with this conclusion, GABAAreceptor activation with muscimol was found to increase the internal calcium concentration ([Ca2+]i) in both embryonic and early postnatal neocortical cells through the activation of voltage-gated calcium channels (VGCCs). Postnatal cells exhibit spontaneous postsynaptic synaptic currents, which are eliminated by bicuculline methiodide (BMI) but not glutamate receptor antagonists and reverse at the Cl−equilibrium potential. Likewise, brief spontaneous increases in [Ca2+]i, sensitive to BMI and TTX, are observed at the same ages, suggesting that endogenous synaptic GABAAreceptor activation can depolarize cells and activate VGCCs. These results suggest that GABAAreceptor-mediated depolarization may influence early neocortical developmental events, including neurogenesis and synaptogenesis, through the activation of Ca2+-dependent signal transduction pathways.
Development of Orientation Preference Maps in Ferret Primary Visual Cortex
Authors: Chapman Barbara , Stryker Michael P. , Bonhoeffer Tobias
Published: April 2018

The development of orientation preference maps was studied in ferret primary visual cortex using chronic optical imaging of intrinsic signals. The emergence and maturation of the maps were examined over time in single animals. The earliest age at which cortical domains selectively responsive to particular stimulus orientations were observed varied considerably between individuals, from postnatal day 31 to 36. In all cases, the earliest maps seen were low-contrast, with regions of orientation-specific activity that were difficult to distinguish from noise. These early maps matured over a period of several days into the high-contrast, patchy maps typical of adult animals. The structure of the orientation maps was remarkably constant over time. The indistinct features in the earliest maps were always patches of the same sizes and shapes and at the same locations as in the maps obtained in subsequent recording sessions. Details of the more mature maps, including the relative intensities of individual iso-orientation domains, were also constant from one recording session to another over periods of several weeks. The patterning of iso-orientation domains in ferret primary visual cortex thus is established early in development and remains stable over time, unaffected by either normal visual experience or the anatomical rearrangements of geniculocortical afferents into eye-specific domains.
Sensory Organ Generation in the Chick Inner Ear
Authors: Wu Doris K. , Oh Seung-Ha
Published: April 2018

There are a total of eight sensory organs in the chick inner ear. Each sensory organ has a distinct structure tailored for its function, and its morphology is well characterized. However, the origin of these sensory organs and the lineage relationships among them are largely unknown. In this report, we show that BMP4 (bone morphogenetic protein), a secreted protein of the TGF-β gene family, is the earliest sensory marker identified to date for the chick inner ear. In addition to BMP4, we show that Msx-1 is a sensory marker for the three cristae, the lagena, and macula neglecta. P75NGFR (nerve growth factor receptor) is a marker for the three cristae only. Based on the expression pattern of these three genes—BMP4, Msx-1, and p75NGFR—it is estimated that the first sensory organs to be generated were the superior and posterior cristae at stage 19, followed by the macula sacculi at stage 20, the lateral crista at stage 22, the basilar papilla and lagena at stage 23, the macula utriculi at stage 24, and the macula neglecta at stage 29. The age of generation of each sensory organ as defined by the first appearance of these molecular markers is well in advance of the histological differentiation. In addition, the differential gene expressions in each presumptive sensory organ may contribute to the distinct structure of the mature organ.
μ-Opioid and δ-Opioid Receptors Are Expressed in Brainstem Antinociceptive Circuits: Studies Using Immunocytochemistry and Retrograde Tract-Tracing
Authors: Kalyuzhny Alexander E. , Arvidsson Ulf , Wu Wei , Wessendorf Martin W.
Published: April 2018

Opioid-produced antinociception in mammals seems to be mediated in part by pathways originating in the periaqueductal gray (PAG) and the rostroventral medulla (RVM), and these pathways may include serotonergic neurons. In the present study, we examined the relationship of the cloned μ- and δ-receptors (MOR1 and DOR1, respectively) to PAG neurons projecting to the RVM, and RVM neurons projecting to the dorsal spinal cord. This was carried out by combining immunocytochemical staining for MOR1, DOR1, and serotonin with fluorescent retrograde tract-tracing. Of 133 retrogradely labeled cells in the RVM, 31% were immunoreactive for MOR1. Of the double-labeled cells, 41% also were immunoreactive for 5HT. Fifty-three percent of retrogradely labeled cells were apposed by DOR1-ir varicosities; 29% of the apposed cells were immunoreactive for 5HT. In the mesencephalon, cells retrogradely labeled from the RVM were usually surrounded by MOR1-ir structures; however, retrogradely labeled cells were never observed to be immunoreactive for MOR1. Similarly, retrogradely labeled cells in the caudal midbrain were seldom, if ever, labeled for DOR1; however, they frequently were apposed by DOR1-ir varicosities. Of 156 retrogradely labeled profiles from three rats, 52 (33%) were apposed by DOR1-ir varicosities. We conclude that both μ- and δ-opioid receptors could be involved in the antinociception mediated by the PAG–RVM–spinal cord circuit. In addition, opioids seem likely to have both direct and indirect effects on spinally projecting RVM cells in general, and on serotonergic RVM cells in particular.
Spinal Cord Terminations of the Medial Wall Motor Areas in Macaque Monkeys
Authors: Dum Richard P. , Strick Peter L.
Published: April 2018

We used anterograde transport of wheat germ agglutinin-horseradish peroxidase to examine the pattern of spinal termination of efferents from the supplementary motor area (SMA) and the two caudal cingulate motor areas (CMAd and CMAv). Our analysis was limited to cervical segments of the macaque. For comparison, we also examined the pattern of termination of efferents from the primary motor cortex (M1).

The SMA, CMAd, CMAv, and M1 all terminate in the ventral horn (lamina IX). Thus, all of these motor areas appear to have direct connections with spinal motoneurons, particularly those innervating muscles of the fingers and wrist. All of the motor areas also terminate in the intermediate zone of the spinal cord (laminae V–VIII). Terminations from the SMA and M1 were densest in three regions: (1) dorsolaterally within laminae V–VII; (2) dorsomedially within lamina VI; and (3) ventromedially within lamina VII and adjacent lamina VIII. In contrast, efferents from the CMAd terminate most densely in the dorsolateral portion of the intermediate zone, whereas those from the CMAv were concentrated in the dorsomedial region. Thus, the CMAd and CMAv may innervate distinct sets of interneurons that project directly to motoneurons, and thereby influence specific aspects of segmental motor control.

These results suggest that corticospinal projections from the SMA, CMAd, and CMAv are in many respects similar to those of efferents from M1. Consequently, each of the motor areas on the medial wall has the potential to generate and control movement at the level of the spinal cord and may provide an anatomical substrate for the recovery of motor function that follows damage to M1.
Respiratory Neurons Mediating the Breuer–Hering Reflex Prolongation of Expiration in Rat
Authors: Hayashi Fumiaki , Coles Sharon K. , McCrimmon Donald R.
Published: April 2018

Afferent input from pulmonary stretch receptors is important in the control of the timing of inspiratory and expiratory phases of the respiratory cycle. The current study was undertaken to identify neurons within a column of respiratory neurons in the ventrolateral medulla (termed the ventral respiratory group, VRG) that, when activated by lung inflation, produce the Breuer–Hering (BH) reflex in which lung inflation causes inspiratory termination and expiratory prolongation. Intracellular recordings of VRG neurons revealed three groups of inspiratory (I) and two groups of expiratory (E) neurons similar to previous descriptions: I-augmenting (I-Aug), I-decrementing (I-Dec), I-plateau (I-All), E-augmenting (E-Aug), and E-decrementing (E-Dec) neurons. Low-intensity, low-frequency stimulation of a vagus nerve elicited paucisynaptic EPSPs in E-Dec, I-Aug, and I-All neurons that could be divided into two groups on the basis of latency (2.8 ± 0.1 msec,n = 10; 4.0 ± 0.1 msec,n = 17). IPSPs were elicited in I-Aug and I-All neurons (4.8 ± 0.1 msec,n = 12). However, only E-Dec neurons were depolarized when the BH reflex was activated by lung inflation (7.5 cm H2O) or mimicked by vagus nerve stimulation (50 Hz). All other neurons were hyperpolarized and ceased firing during BH reflex-mediated expiratory prolongation. A subset of E-Dec neurons (termed E-Decearly) discharged before inspiratory termination and could contribute to inspiratory termination. The findings are consistent with the hypothesis that a group of E-Dec neurons receives a paucisynaptic (probably disynaptic) input from pulmonary afferents and, in turn, inhibits inspiratory neurons, thereby lengthening expiration.
Neural Delays Shape Selectivity to Interaural Intensity Differences in the Lateral Superior Olive
Authors: Park Thomas J. , Grothe Benedikt , Pollak George D. , Schuller Gerd , Koch Ursula
Published: April 2018

Neurons in the lateral superior olive (LSO) respond selectively to interaural intensity differences (IIDs), one of the chief cues used to localize sounds in space. LSO cells are innervated in a characteristic pattern: they receive an excitatory input from the ipsilateral ear and an inhibitory input from the contralateral ear. Consistent with this pattern, LSO cells generally are excited by sounds that are more intense at the ipsilateral ear and inhibited by sounds that are more intense at the contralateral ear. Despite their relatively homogeneous pattern of innervation, IID selectivity varies substantially from cell to cell, such that selectivities are distributed over the range of IIDs that would be encountered in nature. For some time, researchers have speculated that the relative timing of the excitatory and inhibitory inputs to an LSO cell might shape IID selectivity. To test this hypothesis, we recorded from 50 LSO cells in the free-tailed bat while presenting stimuli that varied in interaural intensity and in interaural time of arrival. The results suggest that, for more than half of the cells, the latency of inhibition was several hundred microseconds longer than the latency of excitation. Increasing the intensity to the inhibitory ear shortened the latency of inhibition and brought the timing of the inputs from the two ears into register. Thus, a neural delay of the inhibition helped to define the IID selectivity of these cells, accounting for a significant part of the variation in selectivity among LSO cells.
Immunocytological and Biochemical Localization and Biological Activity of the Newly Sequenced Cerebral Peptide 2 inAplysia
Authors: Phares Gregg A. , Lloyd Philip E.
Published: April 2018

Cerebral peptide 2 (CP2), a 41 amino acid neuropeptide, was identified because it was transported from the cerebral ganglia ofAplysiato other central ganglia. Immunocytology indicates that CP2 is distributed widely in the CNS and peripheral tissues ofAplysia. Most CP2-immunoreactive neurons were found in the cerebral ganglia and extensively overlap with the distribution of cerebral peptide 1 (CP1). HPLC analyses confirm that individual cerebral neurons synthesize both CP1 and CP2. In other ganglia, CP1 and CP2 are localized predominantly to different neurons. CP2-immunoreactive fibers and varicosities are present in the neuropil of all ganglia but were found surrounding cell bodies and axon hillocks most often in the buccal and abdominal ganglia. Thus, the effects of CP2 on neurons in these ganglia were determined using intracellular recording. In the buccal ganglia, CP2 evokes rhythmic activity in many motor neurons that seems similar to that observed during ingestion; however, only one identified neuron was found to be depolarized directly. By contrast, in the abdominal ganglion, many neurons are depolarized directly by CP2. A number of these have been shown to be part of the circuit that regulates respiratory pumping. Injection of CP2 into freely behavingAplysiaincreases the rate of respiratory pumping and causes other changes in behavior. CP2 is stable in hemolymph, which raises the possibility that it may act as a hormone. Thus, CP2 is a bioactive neuropeptide that is present in many neurons and likely functions as a transmitter or a hormone.
Polygenic Disease and Retinitis Pigmentosa: Albinism Exacerbates Photoreceptor Degeneration Induced by the Expression of a Mutant Opsin in Transgenic Mice
Authors: Naash Muna I. , Ripps Harris , Li Shihong , Goto Yoshinobu , Peachey Neal S.
Published: April 2018

Expression of a mouse opsin transgene containing three point mutations (V20G, P23H, and P27L; termed VPP) causes a progressive photoreceptor degeneration that resembles in many important respects that seen in patients with autosomal dominant retinitis pigmentosa caused by a P23H point mutation. We have attempted to determine whether the degree of degeneration induced by expression of the transgene is influenced by albinism, a genetically mediated recessive trait that results in a deficiency in melanin formation in pigmented tissues throughout the body. Litters of albino and pigmented mice (normal as well as transgenic) were reared in either darkness or cyclic light. Retinal structure and function were evaluated by light microscopy, electroretinography (ERG), and retinal densitometry. The data were consistent in demonstrating that at similar ages, the extent of photoreceptor degeneration was greater in transgenic albino animals than in their pigmented counterparts. The albino VPP mice had significantly fewer cell bodies in the outer nuclear layer of the retina, a larger reduction in ERG amplitude, and a lower rhodopsin content in the rod photoreceptors. These structural and functional differences could not be attributed to the greater level of retinal illumination experienced by the albino retina under normal ambient conditions, because they persisted when pigmented and albino mice were reared in darkness from birth. Although the explanation remains unclear, our findings indicate that the rate of photoreceptor degeneration in VPP mice is adversely affected by the existence of the albino phenotype, a factor that may have implications for the counseling of human patients with retinitis pigmentosa and a familial history of other genetic disorders.
Motor Discoordination Results from Combined Gene Disruption of the NMDA Receptor NR2A and NR2C Subunits, But Not from Single Disruption of the NR2A or NR2C Subunit
Authors: Kadotani Hiroshi , Hirano Tomoo , Masugi Miwako , Nakamura Kenji , Nakao Kazuki , Katsuki Motoya , Nakanishi Shigetada
Published: April 2018

NMDA receptors consist of two distinct classes of subunits. The NR1 subunit possesses all properties of the NMDA receptor-channel complex, whereas four NR2 subunits (NR2A–2D) potentiate and differentiate NMDA receptor responses by heteromeric assemblies with NR1. The mRNAs for the five NMDA receptor subunits are expressed in the cerebellum in a distinct temporospatial manner. To study functions of the NMDA receptors in the cerebellum, we generated knockout mice deficient in either NR2A or NR2C or both of these subunits. All three mutant mice developed normally and showed normal overall morphology of the cerebellum. The NMDA receptor-mediated components of EPSCs in granule cells, as assessed by whole-cell recordings of cerebellar slices, were reduced in NR2A- and NR2C-deficient mice and nearly abolished in mice lacking both NR2A and NR2C. The NR2A- and NR2C-deficient granule cells were different in the current–voltage relationship and time course of NMDA receptor responses. The NR2A and NR2C subunits thus contribute to distinct NMDA receptor-mediated excitatory transmission in mossy fiber–granule cell synapses in the mature cerebellum. Both NR2A- and NR2C-deficient mice showed no impaired movements in the motor coordination tasks tested. The mutant mice deficient in both NR2A and NR2C could also manage simple coordinated tasks, such as staying on a stationary or a slowly rotating rod, but failed more challenging tasks such as staying on a quickly rotating rod. These data demonstrate that the NMDA receptors play an active role in motor coordination.
ADrosophilaCalcium Channel α1 Subunit Gene Maps to a Genetic Locus Associated with Behavioral and Visual Defects
Authors: Smith Lee A. , Wang XinJing , Peixoto Alexandre A. , Neumann Eric K. , Hall Linda M. , Hall Jeffrey C.
Published: April 2018

We have cloned cDNAs that encode a complete open reading frame for a calcium channel α1 subunit fromDrosophila melanogaster. The deduced 1851 amino acid protein belongs to the superfamily of voltage-gated sodium and calcium channels. Phylogenetic analysis shows that the sequence of this subunit is relatively distant from sodium channel α subunits and most similar to genes encoding the A, B, and E isoforms of calcium channel α1 subunits. To indicate its similarity to this subfamily of vertebrate isoforms, we name this protein Dmca1A, forDrosophila melanogastercalcium channel α1 subunit, type A. Northern blot analysis detected a single 10.5 kb transcript class that is regulated developmentally, with expression peaks in the first larval instar, midpupal, and late pupal stages. In late-stage embryos, Dmca1A is expressed preferentially in the nervous system. Variant transcripts are generated by alternative splicing. In addition, single nucleotide variations between cDNAs and genomic sequence are consistent with RNA editing. Dmca1A maps to a chromosomal region implicated in, and is the likely candidate for, the gene involved in the generation of behavioral, physiological, and lethal phenotypes of thecacophony, nightblind-A, andlethal(1)L13mutants.
Matrix Metalloproteinase-9 (MMP-9) Is Synthesized in Neurons of the Human Hippocampus and Is Capable of Degrading the Amyloid-β Peptide (1–40)
Authors: Backstrom Jon R. , Lim Giselle P. , Cullen Michael J. , Tökés Zoltán A.
Published: April 2018

We reported earlier that the levels of Ca2+-dependent metalloproteinases are increased in Alzheimer’s disease (AD) specimens, relative to control specimens. Here we show that these enzymes are forms of the matrix metalloproteinase MMP-9 (EC3.4.24.35) and are expressed in the human hippocampus. Affinity-purified antibodies to MMP-9 labeled pyramidal neurons, but not granular neurons or glial cells. MMP-9 mRNA is expressed in pyramidal neurons, as determined with digoxigenin-labeled MMP-9 riboprobes, and the presence of this mRNA is confirmed with reverse transcriptase PCR. The cellular distribution of MMP-9 is altered in AD because 76% of the total 100 kDa enzyme activity is found in the soluble fraction of control specimens, whereas only 51% is detectable in the same fraction from AD specimens. The accumulated 100 kDa enzyme from AD brain is latent and can be converted to an active form with aminophenylmercuric acetate.

MMP-9 also is detected in close proximity to extracellular amyloid plaques. Because a major constituent of plaques is the 4 kDa β-amyloid peptide, synthetic Aβ1–40was incubated with activated MMP-9. The enzyme cleaves the peptide at several sites, predominantly at Leu34-Met35within the membrane-spanning domain. These results establish that neurons have the capacity to synthesize MMP-9, which, on activation, may degrade extracellular substrates such as β-amyloid. Because the latent form of MMP-9 accumulates in AD brain, it is hypothesized that the lack of enzyme activation contributes to the accumulation of insoluble β-amyloid peptides in plaques.
Neural Cell Type-Specific Expression of QKI Proteins Is Altered inquakingviableMutant Mice
Authors: Hardy Rebecca J. , Loushin Carrie L. , Friedrich Jr. Victor L. , Chen Qi , Ebersole Thomas A. , Lazzarini Robert A. , Artzt Karen
Published: April 2018

qkI, a newly cloned gene lying immediately proximal to the deletion in thequakingviablemutation, is transcribed into three messages of 5, 6, and 7 kb. Antibodies raised to the unique carboxy peptides of the resulting QKI proteins reveal that, in the nervous system, all three QKI proteins are expressed strongly in myelin-forming cells and also in astrocytes. Interestingly, individual isoforms show distinct intracellular distributions: QKI-6 and QKI-7 are localized to perikaryal cytoplasm, whereas QKI-5 invariably is restricted to the nucleus, consistent with the predicted role of QKI as an RNA-binding protein. Inquakingviablemutants, which display severe dysmyelination, QKI-6 and QKI-7 are absent exclusively from myelin-forming cells. By contrast, QKI-5 is absent only in oligodendrocytes of severely affected tracts. These observations implicate QKI proteins as regulators of myelination and reveal key insights into the mechanisms of dysmyelination in thequakingviablemutant.
Endocytosis of Activated TrkA: Evidence that Nerve Growth Factor Induces Formation of Signaling Endosomes
Authors: Grimes Mark L. , Zhou Jie , Beattie Eric C. , Yuen Eric C. , Hall Deborah E. , Valletta Janice S. , Topp Kimberly S. , LaVail Jennifer H. , Bunnett Nigel W. , Mobley William C.
Published: April 2018

The survival, differentiation, and maintenance of responsive neurons are regulated by nerve growth factor (NGF), which is secreted by the target and interacts with receptors on the axon tip. It is uncertain how the NGF signal is communicated retrogradely from distal axons to neuron cell bodies. Retrograde transport of activated receptors in endocytic vesicles could convey the signal. However, little is known about endocytosis of NGF receptors, and there is no evidence that NGF receptors continue to signal after endocytosis. We have examined early events in the membrane traffic of NGF and its receptor, gp140TrkA(TrkA), in PC12 cells. NGF induced rapid and extensive endocytosis of TrkA in these cells, and the receptor subsequently moved into small organelles located near the plasma membrane. Some of these organelles contained clathrin and α-adaptin, which implies that TrkA is internalized by clathrin-mediated endocytosis. Using mechanical permeabilization and fractionation, intracellular organelles derived from endocytosis were separated from the plasma membrane. After NGF treatment, NGF was bound to TrkA in endocytic organelles, and TrkA was tyrosine-phosphorylated and bound to PLC-γ1, suggesting that these receptors were competent to initiate signal transduction. These studies raise the possibility that NGF induces formation of signaling endosomes containing activated TrkA. They are an important first step in elucidating the molecular mechanism of NGF retrograde signaling.
Changing Patterns of Expression and Subcellular Localization of TrkB in the Developing Visual System
Authors: Cabelli Robert J. , Allendoerfer Karen L. , Radeke Monte J. , Welcher Andrew A. , Feinstein Stuart C. , Shatz Carla J.
Published: April 2018

Neurotrophins play important roles in the survival, differentiation, and maintenance of CNS neurons. To begin to investigate specific roles for these factors in the mammalian visual system, we have examined the cellular localization of the neurotrophin receptor trkB within the developing cerebral cortex and thalamus of the ferret using extracellular domain-specific antibodies.

At prenatal ages (gestation is 41 d), trkB-immunostained fibers were observed in the internal capsule and as two distinct fascicles within the intermediate zone of the cerebral cortex. The staining of these fiber tracts declined with increasing age, whereas soma and dendrite staining of cortical neurons was first evident in early postnatal life and increased during subsequent development. Staining of subplate neurons [by prenatal day 5 (P5)] was followed by staining of cortical layer 5 neurons (at P10). By P31, trkB immunoreactivity was particularly prominent in layers 3 and 5 but was absent from subplate neurons. Staining included cells, especially pyramidal neurons, in all cortical layers by P45, and this pattern was maintained into adulthood. The optic tract and fibers within the lateral geniculate nucleus (LGN) were also strongly trkB immunoreactive at prenatal ages. Cellular staining of a subset of LGN neurons, those within the C-layers and perigeniculate nucleus, was apparent by P10 and maintained until P45, when the adult pattern of highly trkB-immunoreactive neurons in all layers of the LGN first appeared.

The pattern of trkB immunoreactivity suggests that specific subsets of cortical and thalamic neurons may respond to neurotrophins such as brain-derived neurotrophic factor and/or NT-4/5 at discrete developmental times and locations. The appearance of trkB on axon fibers early in development and then on cell bodies and dendritic processes later is consistent with roles for both long-range and local, including autocrine and/or paracrine, delivery of neurotrophins in cell survival and maturation.
A Role for Nitric Oxide in the Development of the Ferret Retinogeniculate Projection
Authors: Cramer Karina S. , Angelucci Alessandra , Hahm Jong-On , Bogdanov Mikhail B. , Sur Mriganka
Published: April 2018

The ferret retinogeniculate projection segregates into eye-specific layers during the first postnatal week and into ON/OFF sublaminae, which receive inputs from either on-center or off-center retinal ganglion cells, during the third and fourth postnatal weeks. The restriction of retinogeniculate axon arbors into eye-specific layers appears to depend on action potential activity (Shatz and Stryker, 1988) but does not require activation of NMDA receptors (Smetters et al., 1994). The formation of ON/OFF sublaminae is also activity-dependent and is disrupted byin vivoblockade of NMDA receptors (Hahm et al., 1991). To investigate a possible mechanism whereby blockade of postsynaptic NMDA receptors in the lateral geniculate nucleus (LGN) results in changes in the size and position of presynaptic axon arbors, we tested the role of the diffusible messenger nitric oxide (NO) in the development of the retinogeniculate pathway. We found previously that NO synthase (NOS) is transiently expressed in LGN cells during the refinement of retinogeniculate projections (Cramer et al., 1995). In this study, treatment with NG-nitro-l-arginine (l-NoArg), an arginine analog that inhibits NOS, during the third and fourth postnatal weeks resulted in an overall pattern of sublamination that was significantly reduced compared with normal and control animals. Single retinogeniculate axon arbors were located in the middle of eye-specific layers rather than toward the inner or outer half as in normal or control animals. The effect of NOS inhibition was not a consequence of the hypertensive effect ofl-NoArg. In contrast to the effect ofl-NoArg on the formation of ON/OFF sublaminae, treatment withl-NoArg during the first postnatal week did not disrupt the formation of eye-specific layers. Biochemical assays indicated significant inhibition of NOS during both treatment periods. These data suggest that NO acts together with NMDA receptors in activity-dependent refinement of connections during a specific phase of retinogeniculate development.
Influence of Cocaine on the JAK–STAT Pathway in the Mesolimbic Dopamine System
Authors: Berhow Melissa T. , Hiroi Noboru , Kobierski Linda A. , Hyman Steven E. , Nestler Eric J.
Published: April 2018

Chronic exposure to cocaine produces characteristic biochemical adaptations within the rat ventral tegmental area (VTA), a brain region rich in dopaminergic neurons implicated in the reinforcing and locomotor-activating properties of cocaine. Some of these changes are mimicked by chronic ciliary neurotrophic factor (CNTF) infusions into the same brain area. We show in this study that chronic cocaine treatment regulates the signal transduction pathway used by CNTF specifically in the VTA. There is an increase in immunoreactivity of Janus kinase (JAK2), a CNTF-regulated protein tyrosine kinase, in the VTA after chronic but not acute cocaine administration. This increase is not seen in the nearby substantia nigra or several other brain regions studied. Furthermore, this increase in JAK2 is not seen after chronic administration of other psychotropic drugs and was not observed for JAK1. The increase in JAK2 levels is associated with an increased responsiveness of the system to acute CNTF infusion into the VTA, as measured by induction in this brain region of signal transducers and activators of transcription (STAT) DNA binding activity and of Fos-like proteins, two known functional endpoints of JAK activation. Double-labeling immunohistochemical studies show that JAK2 immunoreactivity in the VTA is enriched in dopaminergic and nondopaminergic cells, both of which exhibit increased JAK2 immunoreactivity after chronic cocaine treatment. These findings suggest a scheme whereby some of the effects of chronic cocaine on VTA dopaminergic neurons are mediated directly by regulation of the JAK–STAT pathway in these cells, as well as perhaps indirectly by regulation of this pathway in nondopaminergic cells.