bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Cell Migration from the Lateral Ganglionic Eminence in the Rat
Authors: De Carlos J. A. , López-Mascaraque L. , Valverde F.
Published: April 2018

From previous developmental studies, it has been proposed that the neurons of the ventrolateral cortex, including the primary olfactory cortex, differentiate from progenitor cells in the lateral ganglionic eminence. The objective of the present study was to test this hypothesis. The cells first generated in the forebrain of the rat migrate to the surface of the telencephalic vesicle by embryonic day (E) 12. Using [3H]thymidine, we found that most of these cells contributed to the formation of the deep layer III of the primary olfactory cortex. To study the migratory routes of these cells, we made localized injections of the carbocyanine fluorescent tracers DiI and DiA into various parts of the lateral ganglionic eminence in living embryos at E12–E14 and subsequently maintained the embryos in a culture device for 17–48 hr. After fixation, most migrating cells were located at the surface of the telencephalic vesicle, whereas others were seen coursing tangentially into the preplate. Injections made at E13 and in fixed tissue at E15 showed that migrating cells follow radial glial fibers extending from the ventricular zone of the lateral ganglionic eminence to the ventrolateral surface of the telencephalic vesicle. The spatial distribution of radial glial fibers was studied in Golgi preparations, and these observations provided further evidence of the existence of long glial fibers extending from the ventricular zone of the lateral ganglionic eminence to the ventrolateral cortex. We conclude that cells of the primary olfactory cortex derive from the lateral ganglionic eminence and that some early generated cells migrating from the lateral ganglionic eminence transgress the cortico-striatal boundary entering the preplate of the neocortical primordium.
Neuronal Activity in the Medial Prefrontal Cortex during Pavlovian Eyeblink and Nictitating Membrane Conditioning
Authors: Powell Donald A. , Maxwell Brian , Penney James
Published: April 2018

The present study assessed Pavlovian eyeblink (EB) conditioning, using tones and periorbital shock as the conditioned and unconditioned stimuli (CS and US), and nictitating membrane (NM) conditioning, using tones and airpuffs as the CS and US. During each experiment, CS-evoked changes in multiple-unit activity (MUA) in the medial prefrontal cortex (mPFC) were recorded. Concomitant heart rate (HR) conditioned responses (CRs) were also recorded. A nonassociative control group received explicitly unpaired presentations of the CS and US in each experiment. Increases in both NM and EB CRs occurred over sessions in the paired, but not the unpaired, groups. Decelerative HR CRs also occurred in the eyeshock, but not the airpuff, group. Although tone-evoked increases in neuronal activity were obtained during 10 initial tone-alone presentations in all groups, this activity habituated over trials. CS-evoked increases in neuronal activity also occurred, but this activity was considerably greater in the group that received periorbital shock as the US. During subsequent extinction trials, decreases in tone-evoked neuronal activity occurred in this group, compared with the previous CS/US paired trials. CS-evoked MUA increases were minimal during all except the pretraining phase of the study in the CS/US unpaired control groups and in the paired airpuff group. These findings show that neuronal activity during associative learning occurs in the mPFC during Pavlovian EB, as well as HR conditioning, but this activity apparently reflects an affective component to learning that is only indirectly related to skeletal conditioning.
Activation of Locus Coeruleus Enhances the Responses of Olfactory Bulb Mitral Cells to Weak Olfactory Nerve Input
Authors: Jiang Maorong , Griff Edwin R. , Ennis Matthew , Zimmer Lee A. , Shipley Michael T.
Published: April 2018

The main olfactory bulb (MOB) receives a dense projection from the pontine nucleus locus coeruleus (LC), the largest collection of norepinephrine (NE)-containing cells in the brain. LC is the sole source of NE innervation of MOB. Previous studies of the actions of exogenously applied NE on mitral cells, the principal output neurons of MOB, are contradictory. The effect of synaptically released NE on mitral cell activity is not known, nor is the influence of NE on responses of mitral cells to olfactory nerve inputs. The goal of the present study was to assess the influence of LC activation on spontaneous and olfactory nerve-evoked activity of mitral cells.

In methoxyflurane-anesthetized rats, intracoerulear microinfusions of acetylcholine (ACh) (200 mm; 90–120 nl) evoked a four- to fivefold increase in LC neuronal discharge, and a transient EEG desynchronization and decrease in mitral cell discharge. LC activation increased excitatory responses of mitral cells evoked by weak (i.e., perithreshold) nasal epithelium shocks (1.0 Hz) in 17/18 cells (mean increase = 67%). The discharge rate of mitral cells at the time that epithelium-evoked responses were increased did not differ significantly from pre-LC activation baseline values. Thus, changes in mitral baseline activity do not account for the increased response to epithelium stimulation. These findings suggest that increased activity in LC–NE projections to MOB may enhance detection of relatively weak odors.
Modulatory Role of Drebrin on the Cytoskeleton within Dendritic Spines in the Rat Cerebral Cortex
Authors: Hayashi Kensuke , Ishikawa Ryoki , Ye Li-Hong , He Xiao-Ling , Takata Kuniaki , Kohama Kazuhiro , Shirao Tomoaki
Published: April 2018

Morphological changes in the dendritic spines have been postulated to participate in the expression of synaptic plasticity. The cytoskeleton is likely to play a key role in regulating spine structure. Here we examine the molecular mechanisms responsible for the changes in spine morphology, focusing on drebrin, an actin-binding protein that is known to change the properties of actin filaments. We found that adult-type drebrin is localized in the dendritic spines of rat forebrain neurons, where it binds to the cytoskeleton. To identify the cytoskeletal proteins that associated with drebrin, we isolated drebrin-containing cytoskeletons using immunoprecipitation with a drebrin antibody. Drebrin, actin, myosin, and gelsolin were co-precipitated. We next examined the effect of drebrin on actomyosin interaction.In vitro, drebrin reduced the sliding velocity of actin filaments on immobilized myosin and inhibited the actin-activated ATPase activity of myosin. These results suggest that drebrin may modulate the actomyosin interaction within spines and may play a role in the structure-based plasticity of synapses.
Organization of Octopus Arm Movements: A Model System for Studying the Control of Flexible Arms
Authors: Gutfreund Yoram , Flash Tamar , Yarom Yosef , Fiorito Graziano , Segev Idan , Hochner Binyamin
Published: April 2018

Octopus arm movements provide an extreme example of controlled movements of a flexible arm with virtually unlimited degrees of freedom. This study aims to identify general principles in the organization of these movements. Video records of the movements ofOctopus vulgarisperforming the task of reaching toward a target were studied. The octopus extends its arm toward the target by a wave-like propagation of a bend that travels from the base of the arm toward the tip. Similar bend propagation is seen in other octopus arm movements, such as locomotion and searching. The kinematics (position and velocity) of the midpoint of the bend in three-dimensional space were extracted using the direct linear transformation algorithm. This showed that the bend tends to move within a single linear plane in a simple, slightly curved path connecting the center of the animal’s body with the target location. Approximately 70% of the reaching movements demonstrated a stereotyped tangential velocity profile. An invariant profile was observed when movements were normalized for velocity and distance. Two arms, extended together in the same behavioral context, demonstrated identical velocity profiles. The stereotyped features of the movements were also observed in spontaneous arm extensions (not toward an external target). The simple and stereotypic appearance of the bend trajectory suggests that the position of the bend in space and time is the controlled variable. We propose that this strategy reduces the immense redundancy of the octopus arm movements and hence simplifies motor control.
Contribution of the Dorsal Nucleus of the Lateral Lemniscus to Binaural Responses in the Inferior Colliculus of the Rat: Interaural Time Delays
Authors: Kidd Sean A. , Kelly Jack B.
Published: April 2018

The contribution of the dorsal nucleus of the lateral lemniscus (DNLL) to binaural responses in the inferior colliculus of the rat was determined for a wide range of interaural time differences (ITDs). Single-unit action potentials were recorded from the inferior colliculus before and after local injection of the excitatory amino acid antagonist kynurenic acid into the DNLL. Binaural properties were determined by manipulating the time difference between paired clicks delivered to the ears ipsilateral and contralateral to the recording site. The probability of an action potential decreased as contralateral stimulation was delayed, relative to ipsilateral stimulation. These data generated a sigmoidal ITD curve for delays between −1.0 and +1.0 msec. By extending the time intervals beyond 1 msec, it was possible to determine the trailing edge of the inhibition produced by ipsilateral stimulation. The duration of the inhibitory effect varied from cell to cell but lasted as long as 20 msec in some cases. Injection of kynurenic acid into the DNLL contralateral to the recording site reduced the extent of both short (0–1 msec) and long-lasting (1–20 msec) inhibition in the inferior colliculus. No effect was seen after injections ipsilateral to the recording site. The data demonstrate that the DNLL plays an important role in shaping ITD responses in the inferior colliculus and contributes to both the short and long-lasting inhibition produced by stimulation of the ipsilateral ear.
Two Alternatively Spliced Forms of the cGMP-Gated Channel α-Subunit from Cone Photoreceptor Are Expressed in the Chick Pineal Organ
Authors: Bönigk Wolfgang , Müller Frank , Middendorff Ralf , Weyand Ingo , Kaupp U. Benjamin
Published: April 2018

Light sensitivity of the pineal has been retained in most vertebrates, except mammals. Retinal photoreceptors and pinealocytes share common components of light-dependent signaling pathways. In particular, an ion channel gated by cGMP has been electrophysiologically identified in chick pinealocytes; however, the physiological function of a light-sensitive enzyme cascade is not known, and primary structures of only a few pineal components have been determined. By PCR analysis and cloning of the respective cDNA, we show that the chick pineal expresses the α-subunit of the cyclic nucleotide-gated (CNG) channel of rod photoreceptors and two short forms of the cone CNG channel. Analysis of the chick cone CNG channel gene reveals that these forms are produced by alternative splicing, which removes either one or two exons from the transcript. The shorter splice variant is functional when heterologously expressed, and it is approximately twofold more sensitive to activation by cGMP than the cone CNG channel. The chick cone CNG channel and the pineal splice form are both modulated by Ca2+/calmodulin (CaM). The CaM sensitivity might be mediated by a putative CaM-binding site in an N-terminal segment encoded by exon 4. This exon is missing in the gene for the rod CNG channel α-subunit. Pineal CNG channels are candidates for receptor-mediated Ca2+entry into pinealocytes and may be an important element of signaling pathways that control the light response and secretion of the pineal hormone melatonin.
Maternal Cocaine Treatment Alters Dynorphin and Enkephalin mRNA Expression in Brains of Fetal Rhesus Macaques
Authors: Chai Lin , Choi Wan S. , Rönnekleiv Oline K.
Published: April 2018

Cocaine exposurein uterois known to cause a variety of behavioral and motor deficits that may be attributable to alterations in the dopamine neurocircuitry. To ascertain cocaine effects in the fetus, we developed a nonhuman primate model in which pregnant monkeys were administered cocaine from day 20 through day 60 or 70 of gestation. Fetuses from these pregnancies develop a repertoire of neural deficiencies, including decreased mRNA expression of tyrosine hydroxylase in the midbrain and increased mRNA expression of dopamine receptor subtypes in the rostral forebrain. Presently, we studied the effects of maternal cocaine treatment on the mRNA expression of the endogenous opioids preprodynorphin (PPD) and preproenkephalin (PPE) in fetal monkey brains. Fetuses exposed to saline (0.9%) or cocaine (3 mg/kg) were delivered by Caesarean section, the fetal brains were dissected, and tissue RNA was extracted and quantified using ribonuclease protection assay analysis. The opioid peptides PPD and PPE were expressed in the fetal monkey brain by day 60, and even higher levels were found in day 70 fetuses. Maternal exposure to cocaine increased gene expression of PPD and PPE in the fetus at both day 60 and day 70 of gestation. Dynorphin mRNA levels were significantly elevated in the striatum, whereas enkephalin mRNA was elevated in both the frontal cortex and the striatal area of fetuses whose mothers received cocaine. Changes in the expression of these opioid peptides in presumed dopamine target neurons, which mediate motivation and reward, as well as motor control, provide further evidence for profound consequences ofin uterococaine exposure on the developing dopamine neurocircuitry.
AMPA and NMDA Glutamate Receptor Subunits in Midbrain Dopaminergic Neurons in the Squirrel Monkey: An Immunohistochemical andIn SituHybridization Study
Authors: Paquet Maryse , Tremblay Martine , Soghomonian Jean-Jacques , Smith Yoland
Published: April 2018

The objective of the present study was to analyze the cellular and subcellular localization of ionotropic glutamate receptor subunits in midbrain dopaminergic neurons in the squirrel monkey. This was achieved by means of immunohistochemistry at light and electron microscopic levels andin situhybridization histochemistry.

Colocalization studies show that nearly all dopaminergic neurons in both the ventral and dorsal tiers of the substantia nigra compacta (SNc-v, SNc-d) and the ventral tegmental area (VTA) are immunoreactive for AMPA (GluR1, GluR2/3, and GluR4) and NMDAR1 receptor subunits, but not for NMDAR2A/B subunits. The immunoreactivity of the receptor subunits is associated mainly with perikarya and dendritic shafts. Apart from the intensity of immunolabeling for the GluR4 subunit, which is quite similar for the different groups of midbrain dopaminergic neurons, the overall intensity of immunostaining for the other subunits is higher in the SNc-v and SNc-d than in the VTA. In line with these observations,in situhybridization shows that the average level of labeling for the GluR2 and NMDAR1 subunit mRNAs is significantly higher in the SNc-v than in the VTA, and for the NMDAR1 subunit, higher in the SNc-v than in the SNc-d. In contrast, no significant difference was found for the level of GluR1 mRNA labeling among the three groups of midbrain dopaminergic neurons. At the subcellular level in the SNc-v, AMPA (GluR1 and GluR2/3) and NMDAR1 receptor subunit immunoreactivity is preferentially associated with the postsynaptic densities of asymmetric synapses, but occasionally some immunoreactivity is found along nonsynaptic portions of plasma membranes of dendrites. A small number of preterminal axons, axon terminals, and glial cell processes are also immunoreactive.

Our observations indicate that the different groups of midbrain dopaminergic neurons in primates exhibit a certain degree of heterogeneity with regard to the level of expression of some ionotropic glutamate receptor subunits. The widespread neuronal and glial localization of glutamate receptor subunits suggests that excitatory amino acids may act at different levels to control the basal activity and, possibly, to participate in the degeneration of midbrain dopaminergic neurons in Parkinson’s disease.
Control of Neurotransmitter Release by Presynaptic Waveform at the Granule Cell to Purkinje Cell Synapse
Authors: Sabatini Bernardo L. , Regehr Wade G.
Published: April 2018

The effect of changes in the shape of the presynaptic action potential on neurotransmission was examined at synapses between granule and Purkinje cells in slices from the rat cerebellum. Low concentrations of tetraethylammonium were used to broaden the presynaptic action potential. The presynaptic waveform was monitored with voltage-sensitive dyes, the time course and amplitude of presynaptic calcium entry were determined with fluorescent calcium indicators, and EPSCs were measured with a whole-cell voltage clamp. Spike broadening increased calcium influx primarily by prolonging calcium entry without greatly affecting peak presynaptic calcium currents, indicating that the majority of calcium channels reach maximal probability of opening in response to a single action potential and that spike broadening increases the open time of these channels. EPSCs were exquisitely sensitive to elevations of calcium influx produced by spike broadening; there was a high power relationship between calcium influx and release such that a 23% increase in spike width led to a 25% increase in total calcium influx, which in turn doubled synaptic strength.

The finding that even small changes in spike width influence neurotransmitter release suggests that altering the presynaptic waveform may be an important means of modifying the strength of this synapse. Waveform changes do not, however, contribute significantly to presynaptic modulation via activation of adenosine A1or GABABreceptors. Furthermore, greatly reducing presynaptic calcium influx did not alter the presynaptic waveform, indicating that calcium channels and calcium-activated channels do not participate in shaping the presynaptic waveform.
Localized and Transient Elevations of Intracellular Ca2+Induce the Dedifferentiation of Axonal Segments into Growth Cones
Authors: Ziv Noam E. , Spira Micha E.
Published: April 2018

The formation of a growth cone at the tip of a severed axon is a key step in its successful regeneration. This process involves major structural and functional alterations in the formerly differentiated axonal segment. Here we examined the hypothesis that the large, localized, and transient elevation in the free intracellular calcium concentration ([Ca2+]i) that follows axotomy provides a signal sufficient to trigger the dedifferentiation of the axonal segment into a growth cone. Ratiometric fluorescence microscopy and electron microscopy were used to study the relations among spatiotemporal changes in [Ca2+]i, growth cone formation, and ultrastructural alterations in axotomized and intactAplysia californicaneurons in culture. We report that, in neurons primed to grow, a growth cone forms within 10 min of axotomy near the tip of the transected axon. The nascent growth cone extends initially from a region in which peak intracellular Ca2+concentrations of 300–500 μmare recorded after axotomy. Similar [Ca2+]itransients, produced inintactaxons by focal applications of ionomycin, induce the formation of ectopic growth cones and subsequent neuritogenesis. Electron microscopy analysis reveals that the ultrastructural alterations associated with axotomy and ionomycin-induced growth cone formation are practically identical. In both cases, growth cones extend from regions in which sharp transitions are observed between axoplasm with major ultrastructural alterations and axoplasm in which the ultrastructure is unaltered. These findings suggest that transient elevations of [Ca2+]ito 300–500 μm, such as those caused by mechanical injury, may be sufficient to induce the transformation of differentiated axonal segments into growth cones.
Purkinje Cell Survival and Axonal Regeneration Are Age Dependent: AnIn VitroStudy
Authors: Dusart Isabelle , Airaksinen Matti S. , Sotelo Constantino
Published: April 2018

Purkinje cells are among the most resistant neurons to axotomy and the most refractory to axonal regeneration. By using organotypic cultures, we have studied age- and environment-related factors implicated in Purkinje cell survival and axonal regeneration. Most Purkinje cells taken from 1- to 5-d-old rats, the period in which these neurons are engaged in intense synaptogenesis and dendritic remodeling, die 1 week after plating, whereas if cultured before or after this period, Purkinje cells survive, even in the absence of deep nuclear neurons, their postsynaptic targets. Cerebellar slices taken from 10-d-old rats and keptin vitrofor 1 week acquire a cellular composition resembling mature cerebellum. Their Purkinje cells are resistant to axotomy, but even when confronted with permissive environments (sciatic nerves or fetal cerebellar slices), their axons do not regenerate. In contrast, fetal rat and mouse Purkinje cells are able to regenerate their axons on mature cerebellar slices. This regeneration is massive, and the regrowing axons invade all cerebellar regions of the apposed mature slices, including white matter. These results show that Purkinje cell survival and axonal regeneration are age-related and independent from environmental constraints. Moreover, our observations suggest strongly that the onset of synaptogenesis of Purkinje cell axons could provide a signal to turn off their growth program and that, thereafter, permissive microenvironment alone is unable to reestablish such a program.
Quantitative Trait Loci Involved in Genetic Predisposition to Acute Alcohol Withdrawal in Mice
Authors: Buck Kari Johnson , Metten Pamela , Belknap John K. , Crabbe John C.
Published: April 2018

Alcohol dependence (alcoholism) is accompanied by evidence of tolerance, withdrawal (physiological dependence), or compulsive behavior related to alcohol use. Studies of strain and individual differences using animal models for acute physiological dependence liability are useful means to identify potential genetic determinants of liability in humans. Behavioral and quantitative trait analyses were conducted using animal models for high risk versus resistance to acute physiological dependence. Using a two-step genetic mapping strategy, loci on mouse chromosomes 1, 4, and 11 were mapped that contain genes that influence alcohol withdrawal severity. In the aggregate, these three risk markers accounted for 68% of the genetic variability in alcohol withdrawal. Candidate genes in proximity to the chromosome 11 locus include genes encoding the α1, α6, and γ2subunits of type-A receptors for the inhibitory neurotransmitter, GABA. In addition, suggestive linkage is indicated for two loci on mouse chromosome 2, one nearGad1encoding glutamic acid decarboxylase, and the other near theEl2locus which influences the seizure phenotype in the neurological mutant strain El. The present analyses detect and map some of the loci that increase risk to develop physiological dependence and may facilitate identification of genes related to the development of alcoholism. Syntenic conservation between human and mouse chromosomes suggests that human homologs of genes that increase risk for physiological dependence may localize to 1q21–q32, 2q24–q37/11p13, 9p21–p23/1p32–p22.1, and 5q32–q35.
Diminished Inflammation and Nociceptive Pain with Preservation of Neuropathic Pain in Mice with a Targeted Mutation of the Type I Regulatory Subunit of cAMP-Dependent Protein Kinase
Authors: Malmberg Annika B. , Brandon Eugene P. , Idzerda Rejean L. , Liu Hantao , McKnight G. Stanley , Basbaum Allan I.
Published: April 2018

To assess the contribution of PKA to injury-induced inflammation and pain, we evaluated nociceptive responses in mice that carry a null mutation in the gene that encodes the neuronal-specific isoform of the type I regulatory subunit (RIβ) of PKA. Acute pain indices did not differ in the RIβ PKA mutant mice compared with wild-type controls. However, tissue injury-evoked persistent pain behavior, inflammation of the hindpaw, and ipsilateral dorsal horn Fos immunoreactivity was significantly reduced in the mutant mice, as was plasma extravasation induced by intradermal injection of capsaicin into the paw. The enhanced thermal sensitivity observed in wild-type mice after intraplantar or intrathecal (spinal) administration of prostaglandin E2was also reduced in mutant mice. In contrast, indices of pain behavior produced by nerve injury were not altered in the mutant mice. Thus, RIβ PKA is necessary for the full expression of tissue injury-evoked (nociceptive) pain but is not required for nerve injury-evoked (neuropathic) pain. Because the RIβ subunit is only present in the nervous system, including small diameter trkA receptor-positive dorsal root ganglion cells, we suggest that in inflammatory conditions, RIβ PKA is specifically required for nociceptive processing in the terminals of small-diameter primary afferent fibers.
Serotonin at the Laterodorsal Tegmental Nucleus Suppresses Rapid-Eye-Movement Sleep in Freely Behaving Rats
Authors: Horner Richard L. , Sanford Larry D. , Annis Douglas , Pack Allan I. , Morrison Adrian R.
Published: April 2018

Serotonin [5-hydroxytryptamine (5-HT)] is believed to play an important inhibitory role in the regulation of rapid-eye-movement (REM) sleep. 5-HT may exert this effect on neurons of the laterodorsal tegmental (LDT) nuclei that are implicated as important in the generation of REM sleep and phasic REM events such as ponto-geniculo-occipital (PGO) waves and respiratory variability. In rat brainstemin vitro, 5-HT hyperpolarizes and inhibits the bursting properties of LDT neurons assumed to be involved in generating REM sleep and PGO waves. This study tests the hypothesis thatin vivo5-HT at the LDT nuclei suppresses REM sleep and phasic REM events. Ten rats were implanted with bilateral cannulae aimed at the LDT and with electrodes for recording the electroencephalogram, neck electromyogram, PGO waves, and diaphragm electromyogram. During REM sleep, 5-HT (100 nl; 1–1.5 mm), saline, or sham microinjections were performed; repeated microinjections were separated by ∼1 hr. After the first microinjection, REM sleep as a percent of the total sleep time was reduced with 5-HT (mean percent REM, 19.9 ± 2.5% for 5-HT vs 26.8 ± 2.4% for saline;p= 0.02). REM duration was reduced by 37% with 5-HT (p= 0.01), but REM episode frequency was changed less consistently (p= 0.21), suggesting that 5-HT mainly disrupted REM sleep maintenance. Per unit time of REM sleep, 5-HT had no effect on the amount or variability of REM PGO activity (p> 0.740) or on the mean or coefficient of variation of REM respiratory rate (p> 0.11). With subsequent microinjections, the effects of 5-HT on REM sleep were similar. A dose-dependent REM sleep suppression with 5-HT was observed in five rats tested. These data suggest thatin vivo5-HT at the LDT nuclei suppresses REM sleep expression. Although 5-HT did not disproportionately reduce the occurrence of phasic events within REM, total REM phasic activity was reduced because of less REM sleep after 5-HT.
Temporal Coding of Concurrent Acoustic Signals in Auditory Midbrain
Authors: Bodnar Deana A. , Bass Andrew H.
Published: April 2018

A fundamental problem faced by the auditory system of humans and other vertebrates is the segregation of concurrent vocal signals. To discriminate between individual vocalizations, the auditory system must extract information about each signal from the single temporal waveform that results from the summation of the simultaneous acoustic signals. Here, we present the first report of midbrain coding of simultaneous acoustic signals in a vocal species, the plainfin midshipman fish, that routinely encounters concurrent vocalizations. During the breeding season, nesting males congregate and produce long-duration, multiharmonic mate calls that overlap, producing beat waveforms. Neurophysiological responses to two simultaneous tones near the fundamental frequencies of natural calls reveal that midbrain units temporally code the difference frequency (dF). Many neurons are tuned to a specific dF; their selectivity overlaps the range of dFs for naturally occurring acoustic beats. Beats and amplitude-modulated (AM) signals are also coded differently by most units. Although some neurons exhibit differential tuning for beat dFs and the modulation frequencies (modFs) of AM signals, others exhibit similar temporal selectivity but differ in their degree of synchronization to dFs and modFs. The extraction of dF information, together with other auditory cues, could enable the detection and segregation of concurrent vocalizations, whereas differential responses to beats and AM signals could permit discrimination of beats from other AM-like signals produced by midshipman. A central code of beat dFs may be a general vertebrate mechanism used for coding concurrent acoustic signals, including human vowels.
Nociceptin Inhibits T-Type Ca2+Channel Current in Rat Sensory Neurons by a G-Protein-Independent Mechanism
Authors: Abdulla Fuad A. , Smith Peter A.
Published: April 2018

Nociceptin (orphanin FQ) is a novel, opioid-like, heptadecapeptide that is an endogenous ligand for the opioid receptor-like (ORL1) receptor. Unlike classical opioids, nociceptin can produce hyperalgesia when injected intracerebroventricularly into mice. Despite this, nociceptin has been reported to decrease transmitter release, activate an inwardly rectifying K+conductance, and suppress high-voltage-activated Ca2+channel conductances (HVAgCa) in much the same way as μ-, δ-, and κ-opioids. We report an action of nociceptin that is not shared by morphine: the suppression of low-voltage-activated, transient calcium (barium) current (IBa,T) in acutely dissociated rat dorsal root ganglion (DRG) neurons (EC50= 100 nm). This effect was reflected as inhibition of bursts of action potentials that can be evoked in “medium-sized” DRG neurons. Experiments with GTP-γ-S (100 μm), GDP-β-S (2 mm), or aluminum fluoride (AlF3) (100 μm) in the patch pipette failed to provide evidence for G-protein involvement in nociceptin-inducedIBa,Tsuppression. By contrast, both morphine and nociceptin suppressed HVAgCa, and the latter response was affected by intracellular GTP-γ-S, GDP-β-S, and AlF3in ways that confirmed G-protein involvement. The selective effect of nociceptin onIBa,Tmay therefore be relevant to understanding why its behavioral actions differ from those of other opioids. This G-protein-independent effect of the action of nociceptin may reflect a new general mechanism of action for opioid peptides within the nervous system.
Targeted Overexpression of the Neurite Growth-Associated Protein B-50/GAP-43 in Cerebellar Purkinje Cells Induces Sprouting after Axotomy But Not Axon Regeneration into Growth-Permissive Transplants
Authors: Buffo Annalisa , Holtmaat Anthony J. D. G. , Savio Tiziana , Verbeek J. Sjef , Oberdick John , Oestreicher A. Beate , Gispen Wilhelm Hendrik , Verhaagen Joost , Rossi Ferdinando , Strata Piergiorgio
Published: April 2018

B-50/GAP-43 is a nervous tissue-specific protein, the expression of which is associated with axon growth and regeneration. Its overexpression in transgenic mice produces spontaneous axonal sprouting and enhances induced remodeling in several neuron populations (Aigner et al., 1995; Holtmaat et al., 1995). We examined the capacity of this protein to increase the regenerative potential of injured adult central axons, by inducing targeted B-50/GAP-43 overexpression in Purkinje cells, which normally show poor regenerative capabilities. Thus, transgenic mice were produced in which B-50/GAP-43 overexpression was driven by the Purkinje cell-specific L7 promoter. Uninjured transgenic Purkinje cells displayed normal morphology, indicating that transgene expression does not modify the normal phenotype of these neurons. By contrast, after axotomy numerous transgenic Purkinje cells exhibited profuse sprouting along the axon and at its severed end. Nevertheless, despite these growth phenomena, which never occurred in wild-type mice, the severed transgenic axons were not able to regenerate, either spontaneously or into embryonic neural or Schwann cell grafts placed into the lesion site. Finally, although only a moderate Purkinje cell loss occurred in wild-type cerebella after axotomy, a considerable number of injured transgenic neurons degenerated, but they could be partially rescued by the different transplants placed into the lesion site. Thus, B-50/GAP-43 overexpression substantially modifies Purkinje cell response to axotomy, by inducing growth processes and decreasing their resistance to injury. However, the presence of this protein is not sufficient to enable these neurons to accomplish a full program of axon regeneration.
ε Subunit-Containing Acetylcholine Receptors in Myotubes Belong to the Slowly Degrading Population
Authors: Sala Carlo , O’Malley James , Xu Rufeng , Fumagalli Guido , Salpeter Miriam M.
Published: April 2018

Two types of muscle acetylcholine receptors (AChRs) can be distinguished on the basis of their degradation rates and sensitivities to innervation, muscle activity, and agents elevating intracellular cAMP. The first type (Rs), is present in a stable form (degradationt½= ∼10 d) at the adult innervated neuromuscular junctions (NMJs). Rs can also exist in a less stable form (called accelerated Rs;t½= ∼3–5 d) at denervated NMJs and in aneurally cultured myotubes; agents that increase intracellular cAMP reversibly modulate Rs stability. The second type of AChR is a rapidly degrading receptor (Rr) expressed only in embryonic and noninnervated muscles. Rr can be stabilized by ATP and not by cAMP. This study tested the hypothesis that the degradation properties unique to the Rs are attributable to the presence of the ε subunit.

Immunoprecipitation and Western blot analysis of AChRs extracted from rat muscle cells in tissue culture showed that AChRs recognized by antibodies against the ε subunit degraded as a single population with a half-life similar to that of the slow component, Rs, in these cells. In addition, as for Rs receptors in denervated NMJs and cultured muscle cell, the degradation rate of these ε-containing AChRs was stabilized by dibutyryl-cAMP. The data indicate that the ε-containing AChRs behave like Rs. Thus, the presence of the ε subunit is sufficient for selecting an AChR molecule to the Rs pool.
Metabotropic Glutamate Receptor-Mediated Suppression of an Inward Rectifier Current Is Linked via a cGMP Cascade.
Authors: Dixon Don B. , Copenhagen David R.
Published: April 2018

Glutamate, the neurotransmitter released by photoreceptors, excites horizontal cells and OFF-type bipolar cells by activating ionotropic receptors. This study investigated an additional action of glutamate in which it modulates a voltage-gated ion channel in horizontal cells. We find that glutamate and APB (2-amino-4-phosphonobutyrate) produce a delayed and moderately prolonged suppression of an inward rectifier current (IRK+). This effect is proposed to occur via an APB-sensitive metabotropic glutamate receptor (mGluR) because common agonists for the ionotropic or APB-insensitive mGluRs are ineffective and the APB-insensitive receptor antagonist α-methyl-4-carboxyphenylglycine (MCPG) does not block the actions of glutamate or APB. 8-Br-cGMP, 1-methyl-3-isobutylxanthine (IBMX), and atrial natriuretic peptide (ANP) but not 8-Br-cAMP mimic the suppression of IRK+. The effects of glutamate and APB are blocked by protein kinase inhibitors including Rp-8-pCPT-cGMPS, H-8, and H-7 as well as by ATPγS. We hypothesize that the APB receptor suppresses IRK+via upregulation of cGMP and subsequent activation of a cGMP-dependent protein kinase. This pathway is likely regulated by an ATP-dependent phosphorylation. This is a novel signaling pathway for mGluRs and indicates that at least two distinct APB-activated pathways exist in the retina. Functionally, this APB receptor-mediated action found in horizontal cells would provide a means by which spatially restricted changes of glutamate, produced by local illumination of photoreceptors, could regulate IRK+and consequently the response properties of these neurons. This would serve to adapt selectively retinal regions stimulated by small regions of the visual world.
In VitroIschemia Promotes Glutamate-Mediated Free Radical Generation and Intracellular Calcium Accumulation in Hippocampal Pyramidal Neurons
Authors: Perez Velazquez Jose L. , Frantseva Marina V. , Carlen Peter L.
Published: April 2018

Ischemia-induced cell damage studies have revealed a complex mechanism that is thought to involve glutamate excitotoxicity, intracellular calcium increase, and free radical production. We provide direct evidence that free radical generation occurs in rat CA1 pyramidal neurons of organotypic slices subjected to a hypoxic–hypoglycemic insult. The production of free radicals is temporally correlated with intracellular calcium elevation, as measured by injection of fluo-3 in individual pyramidal cells, using patch electrodes. Free radical production (measured as changes in the fluorescence emission of dihydrorhodamine 123) peaked during reoxygenation and paralleled rising intracellular calcium. Electrophysiological whole-cell recordings revealed membrane potential depolarization and decreased input resistance during the ischemic insult. Glutamate receptor blockade resulted in decreased free radical production and markedly diminished intracellular calcium accumulation, and prevented neuronal depolarization and input resistance decrease during the ischemic episode. These results provide evidence for a direct involvement of glutamate in oxidative damage resulting from ischemic episodes.
Developmental Regulation of Basket/Stellate Cell→Purkinje Cell Synapses in the Cerebellum
Authors: Pouzat Christophe , Hestrin Shaul
Published: April 2018

We used paired recordings to study the development of synaptic transmission between inhibitory interneurons of the molecular layer and Purkinje cells in the cerebellar cortex of the rat. The electrophysiological data were combined with a morphological study of the recorded cells using biocytin or Lucifer yellow staining. Thirty-one interneuron–Purkinje cell pairs were obtained, and 11 of them were recovered morphologically. The age of the rats ranged from 11 to 31 d after birth. During this period synaptic maturation resulted in an 11-fold decrease in the average current evoked in a Purkinje cell by a spike in a presynaptic interneuron. Unitary IPSCs in younger animals exhibited paired-pulse depression, whereas paired-pulse facilitation was found in more mature animals. These data suggest that reduction in transmitter release probability contributed to the developmental decrease of unitary IPSCs. However, additional mechanisms at both presynaptic and postsynaptic loci should also be considered. The decrease of the average synaptic current evoked in a Purkinje cell by an action potential in a single interneuron suggests that as development proceeds interneuron activities must be coordinated to inhibit efficiently Purkinje cells.
Release Sites and Calcium Channels in Hair Cells of the Chick’s Cochlea
Authors: Martinez-Dunst C. , Michaels R. L. , Fuchs P. A.
Published: April 2018

Rapid transmitter release at synapses depends on the close proximity of voltage-gated calcium channels (VGCCs). In mechanosensory hair cells of the vertebrate inner ear, dihydropyridine-sensitive VGCCs may be preferentially expressed at release sites to support transmitter release. In support of this hypothesis we have found that whole-cell current through VGCCs covaried with afferent innervation density among hair cells of the chick’s basilar papilla (the avian analog of the mammalian Organ of Corti). The size as well as number of presynaptic dense bodies (PDBs) around which transmitter vesicles cluster varied systematically among equivalent populations of hair cells examined with electron microscopy. The total number of VGCCs was correlated with total release area (PDB cross-sectional area × the number of PDBs) among neurally located (tall) hair cells. Abneural, short hair cells with little or no afferent contact expressed a low number of VGCCs independent of release area. The implication is that hair cells augment calcium channel expression by adding release sites and by making release sites larger. This suggests further that aspects of hair cell excitability, such as electrical tuning, could depend on the synaptic architecture of each cell.
Developmental Regulation of thecm2Muscarinic Acetylcholine Receptor Gene: Selective Induction by a Secreted Factor Produced by Embryonic Chick Retinal Cells
Authors: McKinnon Lise A. , Gunther Erik C. , Nathanson Neil M.
Published: April 2018

The expression of thecm2muscarinic acetylcholine receptor gene increases dramatically in chick retina during embryonic developmentin vivo. A similar developmental increase incm2expression occurs in embryonic chick retinal cells in culture. Conditioned medium from mature, but not young, retinal cultures contains a secreted factor that causes a selective increase in expression of cm2, but not cm3 or cm4, receptors. The secreted factor has been partially purified from serum-free medium, is protease-sensitive, and has a molecular weight >10 kDa. The cm2-inducing factor stimulates expression of acm2promoter/luciferase reporter gene, demonstrating that the increase incm2expression is attributable to increased gene transcription. Incubation of retinal cells with 14 identified neurotrophic and growth factors did not increasecm2expression, suggesting that a novel developmentally regulated secreted factor mediates the subtype-specific induction of thecm2receptor gene in retina.
Neurons Produce a Neuronal Cell Surface-Associated Chondroitin Sulfate Proteoglycan
Authors: Lander Cynthia , Zhang Hong , Hockfield Susan
Published: April 2018

Monoclonal antibody Cat-315 recognizes a chondroitin sulfate proteoglycan (CSPG) expressed on the surface of subsets of neurons in many areas of the mammalian CNS (Lander et al., 1997). The cell type-specific expression exhibited by the Cat-315 CSPG and other perineuronal net CSPGs imparts a distinct molecular surface identity to a neuron (Celio and Blumcke, 1994; Lander et al., 1997). The cell type(s) producing these surface-associated proteins and yielding this cellular diversity has remained in question. The expression of the Cat-315 CSPG in primary rat cortical cultures has permitted an examination of the cellular source of the Cat-315 antigen, as well as a determination of its spatial relationship to the neuronal surface.

Live-cell labeling of primary neuronal cultures demonstrates that the Cat-315 CSPG is on the extracellular surface of neurons. Furthermore, extraction experiments demonstrate that the Cat-315 CSPG lacks a transmembrane domain and that the entire molecule is extracellular and, therefore, can be considered a constituent of brain extracellular matrix. Several lines of evidence indicate that neurons with cell surface staining produce the Cat-315 CSPG. First, neurons with cell surface staining also show intracellular Cat-315 immunoreactivity. Second, β-xyloside or monensin, reagents that inhibit the synthesis and transport of CSPGs, increase intracellular Cat-315 immunoreactivity within neurons that express cell surface Cat-315 immunoreactivity. Third, double labeling with Cat-315 and a polyclonal antibody for the Golgi complex demonstrates a precise colocalization of the intracellular Cat-315 immunoreactivity with the Golgi. Together, these observations demonstrate that neurons contribute to the extracellular matrix of brain and that the Cat-315 CSPG is produced by the neurons that carry Cat-315 cell surface immunoreactivity.
Spatiotemporal Tuning of Low-Frequency Cells in the Anteroventral Cochlear Nucleus
Authors: Carney Laurel H. , Friedman Michele
Published: April 2018

Low-frequency cells in the anteroventral cochlear nucleus (AVCN) can be sensitive to changes in the spatiotemporal pattern of discharges across their auditory nerve (AN) inputs (Carney, 1990). This sensitivity suggests that these cells may be tuned to particular spatiotemporal patterns, or features, in the discharge patterns of populations of AN fibers. To evaluate and characterize this sensitivity, we developed a technique whereby the physiological responses of AVCN cells to wide-band noise were analyzed using the simulated response of a population of AN fibers to the same noise stimulus. By averaging the simulated two-dimensional spatiotemporal pattern of AN activity that preceded each AVCN discharge, it was possible to derive a two-dimensional reverse-correlation function that characterized the spatiotemporal tuning of each AVCN cell. The derived spatiotemporal tuning pattern represented a feature in the AN population response that was most likely to precede discharges of the AVCN cell. To test the spatiotemporal tuning characterizations, we used these patterns to predict the responses of cells to noise stimuli statistically independent from the stimuli used to characterize the cells. This technique provides a general tool for the study of any neural system that involves the analysis of spatiotemporal input patterns.
Variability and Correlated Noise in the Discharge of Neurons in Motor and Parietal Areas of the Primate Cortex
Authors: Lee Daeyeol , Port Nicholas L. , Kruse Wolfgang , Georgopoulos Apostolos P.
Published: April 2018

We analyzed the magnitude and interneuronal correlation of the variability in the activity of single neurons that were recorded simultaneously using a multielectrode array in the primary motor cortex and parietal areas 2/5 in rhesus monkeys. The animals were trained to move their arms in one of eight directions as instructed by a visual target. The relationship between variability (SD) and mean of the discharge rate was described by a power function with a similar exponent (∼0.57), regardless of the cortical area or the behavioral condition. We examined whether the deviation from mean activity between target onset and the end of the movement was correlated on a trial-by-trial basis with variability in activity during the hold period before target onset. In both cortical areas, for about a quarter of the neurons, the neuronal noise of these two periods was positively correlated, whereas significant negative correlations were seldom observed. Overall, neurons with higher signal correlation (i.e., similar directional pattern) showed higher noise correlation in both cortical areas. On the other hand, when the data were divided according to the distance between the electrode tips from which the neurons were recorded, a consistent relationship between the signal and noise correlations was found only for pairs of neurons recorded through the same electrode. These results suggest that nearby neurons with similar directional tuning carry primarily redundant messages, whereas neurons in separate cortical columns perform more independent processing.
D1/D5 Dopamine Receptors Inhibit Depotentiation at CA1 Synapses via cAMP-Dependent Mechanism
Authors: Otmakhova Nonna A. , Lisman John E.
Published: April 2018

Recent work has shown that D1/D5 dopamine receptors can enhance long-term potentiation (LTP). We investigated whether D1/D5 receptors also affect depotentiation, the reversal of LTP by low-frequency stimulation. D1/D5 agonists greatly reduced depotentiation, an effect that was inhibited by a D1/D5 antagonist. The D1/D5 effect appears to be mediated by adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA), because it was mimicked by the AC activator forskolin and was inhibited by the AC and PKA inhibitors.In vivostudies show that dopamine is released when a reward occurs. Our results raise the possibility that the memory of events before reward might be retained selectively, because dopamine blocks their erasure.