bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic construction of a neural network from multiple pattern generators in the lobster stomatogastric nervous system
Authors: Meyrand P , Simmers J , Moulins M
Published: April 2018

In the stomatogastric nervous system (STNS) of the lobster Homarus gammarus, the rhythmic discharge of a pair of identified modulatory neurons (PS cells) is able to construct de novo a functional network from neurons otherwise belonging to other functional networks. The PS interneurons are electrically coupled and possess endogenous oscillatory properties that can be activated synaptically by stimulation of an identified sensory pathway. PS neurons themselves project synaptically onto the three major neural networks (esophageal, gastric mill, and pyloric) of the STNS. When a PS is rhythmically active in vitro, either spontaneously (rarely) or in response to direct stimulation, it dramatically restructures the otherwise independent activity patterns of all three target networks. This functional reconfiguration elicited by a single cell does not rely on changes in neuronal allegiance to pre-existing circuits, or on a simple merger of these different circuits. Rather, PS is responsible for the creation of an entirely new motor rhythm in that, via its widespread synaptic connections, the interneuron is able to subjugate the ongoing activity of the three STNS circuits and selectively appropriate individual elements to its own intrinsic rhythm. In addition, PS excites motor neurons that innervate dilator muscles of a valve situated between the esophagus and the stomach. The reorganization of the regional foregut motor rhythms by the interneuron is therefore coordinated to the opening of this valve, which itself carries sensory receptors that have been found to activate bursting in PS. Our data suggest that the role of PS in massively restructuring stomatogastric output is to generate a unique motor pattern appropriate for swallowing-like behavior. In a wider context, moreover, the results demonstrate that a neural network may not exist as a predefined entity within the CNS, but may be dynamically assembled according to changing behavioral circumstances.
Light and electron microscope distribution of the NMDA receptor subunit NMDAR1 in the rat nervous system using a selective anti-peptide antibody
Authors: Petralia RS , Yokotani N , Wenthold RJ
Published: April 2018

NMDA receptors play key roles in synaptic plasticity and neuronal development, and may be involved in learning, memory, and compensation following injury. A polyclonal antibody that recognizes four of seven splice variants of NMDAR1 was made using a C-terminus peptide (30 amino acid residues). NMDAR1 is the major NMDA receptor subunit, found in most or all NMDA receptor complexes. On immunoblots, this antibody labeled a single major band migrating at M(r) = 120,000. The antibody did not cross-react with extracts from transfected cells expressing other glutamate receptor subunits, nor did it label non-neuronal tissues. Immunostained vibratome sections of rat tissue showed labeling in many neurons in most structures in the brain, as well as in the cervical spinal cord, dorsal root and vestibular ganglia, and in pineal and pituitary glands. Staining was moderate to dense in the olfactory bulb, neocortex, striatum, some thalamic and hypothalamic nuclei, the colliculi, and many reticular, sensory, and motor neurons of the brainstem and spinal cord. The densest stained cells included the pyramidal and hilar neurons of the CA3 region of the hippocampus, Purkinje cells of the cerebellum, supraoptic and magnocellular paraventricular neurons of the hypothalamus, inferior olive, red nucleus, lateral reticular nucleus, peripheral dorsal cochlear nucleus, and motor nuclei of the lower brainstem and spinal cord. Ultrastructural localization of immunostaining was examined in the hippocampus, cerebral cortex, and cerebellar cortex. The major staining was in postsynaptic densities apposed by unstained presynaptic terminals with round or mainly round vesicles, and in associated dendrites. The pattern of staining matched that of previous in situ hybridization but differed somewhat from that of binding studies, implying that multiple types of NMDA receptors exist. Comparison with previous studies of localization of other glutamate receptor types revealed that NMDAR1 may colocalize with these other types in many neurons throughout the nervous system.
ATP-activated current and its interaction with acetylcholine-activated current in rat sympathetic neurons
Authors: Nakazawa K
Published: April 2018

Ionic current activated by extracellular ATP was characterized using whole-cell voltage clamp of rat sympathetic neurons isolated from superior cervical ganglia. ATP (10–1000 microM) activated an inward current (IATP) at negative holding potentials in almost all the cells (> 97%). The current was reversed near 0 mV in a quasi-physiological external solution, and the concentration dependence could be fitted by a curve with an EC50 value of 60 microM and a Hill coefficient of 1.8. The relationship between IATP and the current activated by ACh (IACh) was examined. ACh (100 microM) activated an inward current one- to fivefold larger than the current activated by 100 microM ATP. IATP and IACh were not additive; the current activated by simultaneous application of ATP and ACh was only as large as the current activated by ACh alone. During current activation by ATP or ACh, the current activated by the other agonist became smaller, suggesting that these agonists reciprocally inhibit their excitatory responses. The reciprocal inhibition appeared to depend on the extent of channel opening because the reduction of the current elicited by each agonist was relieved when the current elicited by the other agonist had been desensitized. Suramin (100 microM), a purinoceptor antagonist, selectively inhibited IATP whereas two open-channel blockers of nicotinic receptor channels, hexamethonium (10–100 microM) and d- tubocurarine (1–10 microM), inhibited IACh without affecting IATP. When 140 mM glucosamine was used as an external cation, only ATP but not ACh activated a considerable inward current at -150 mV. The ATP-induced glucosamine influx was reduced by simultaneous application of ACh. These results suggest that channel activation by ATP and that by ACh are not independent, and these two excitatory neurotransmitters negatively interact with each other at postsynaptic level in rat sympathetic neurons. The interaction between the ATP- and the ACh- induced conductances was hypothetically explained based upon our previous proposal of “channel overlap”; that is, ATP activates a subpopulation of the nicotinic receptor channels.
Synaptic physiology of horizontal afferents to layer I in slices of rat SI neocortex
Authors: Cauller LJ , Connors BW
Published: April 2018

Layer I is a dense synaptic zone ubiquitous in cerebral cortex. Here we describe a novel in vitro preparation of rat somatosensory (SI) neocortical slices that isolates the fibers that extend horizontally through layer I, and allows intracellular and extracellular analysis of synaptic input to dendrites in layer I. Current source-density analysis of this isolated horizontal layer I input reveals monophasic current sinks restricted to layer I and the most superficial part of layer II. The layer I synaptic response of each neuron was correlated with its morphology by filling penetrated cells with biocytin. All filled cells that responded to horizontal layer I inputs were pyramidal neurons in layers II, III, or V with distal apical dendrites in layer I. There was no evidence of antidromic activation from isolated layer I stimulation, and HRP injected into layer I was not transported via the isolated layer I pathway to cortical neurons within the slice. Therefore, this preparation provides a unique way to study an extrinsic synaptic input localized to the most distal apical dendrites of many pyramidal neurons. In contrast to the EPSP-IPSP sequence characteristically evoked by deep layer stimulation, horizontal layer I inputs evoked long- lasting EPSPs (approximately 50 msec); IPSPs were observed only rarely, in the most superficial neurons. Horizontal layer I-evoked EPSPs were blocked by the non-NMDA glutamate receptor antagonist 6-cyano-7- nitroquinoxaline-2,3-dione. Consistent with the very distal site of layer I inputs to layer V pyramidal neurons, the amplitudes of initial EPSPs were insensitive to manipulations of the somatic membrane potential. However, these distal EPSPs were greatly attenuated when combined with IPSPs evoked by deep layer stimulation, indicating that the proximal inputs may modulate distal EPSPs with shunting inhibition. In many layer V neurons, the initial EPSP evoked by horizontal layer I stimulation was followed by a variable late depolarization that was blocked by the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid. Since these late depolarizations were enhanced by somatic depolarization and abolished by hyperpolarization, they appeared to be generated postsynaptically at a site more proximal than the initial EPSP that was insensitive to these manipulations. Synaptic inputs to the distal tufts of pyramidal neurons may trigger active currents along the apical dendrites that amplify the EPSP on its way to the soma.
Extension of synaptic extracellular matrix during nerve terminal sprouting in living frog neuromuscular junctions
Authors: Chen L , Ko CP
Published: April 2018

Remodeling of the synaptic extracellular matrix (ECM) and its dynamic relationship with nerve terminal plasticity have been demonstrated in normal frog neuromuscular junctions (NMJs) in vivo (Chen et al., 1991). Our previous work has led to a hypothesis that extension of synaptic ECM precedes nerve terminal growth during synaptic remodeling. To test this hypothesis, the present study examined the changes of synaptic ECM in frog NMJs that were primarily undergoing nerve terminal growth and sprouting. Frog sartorius muscles were double stained with a fluorescent nerve terminal dye (4-Di-2-Asp) and rhodamine-tagged peanut agglutinin (PNA), which recognizes synaptic ECM. The double-labeled NMJs were visualized in vivo with video-enhanced fluorescence microscopy. Nerve sprouting was then induced in the muscle by grafting segments of the contralateral sciatic nerve. The identified NMJs were restrained and reexamined 2–3 months later. Extensive sprouting was observed in 46% of 167 identified NMJs. At junctional regions that showed extension or formation of new branches, synaptic ECM was commonly seen to have the same shape and distribution as the nerve terminal. However, extension of synaptic ECM beyond the corresponding nerve terminals, often by tens of microns, was observed in 29% of these newly formed junctional regions. This lack of correlation might be transient, as growth of nerve terminals following extended, PNA-stained ECM was seen. Examination with histological staining not only confirmed a lack of nerve terminal at the extended synaptic ECM region but also indicated an absence of AChE and postsynaptic junctional folds. The absence of these postsynaptic specializations at the extended, PNA- stained ECM region makes it unlikely that this region was previously occupied by nerve terminals that had retracted. Thus, the present study provides further findings consistent with the hypothesis that synaptic ECM precedes nerve terminal outgrowth and that the extension of synaptic ECM may play a role in synaptic remodeling.
Voltage-dependent effects of opioid peptides on hippocampal CA3 pyramidal neurons in vitro
Authors: Moore SD , Madamba SG , Schweitzer P , Siggins GR
Published: April 2018

Opioid peptides, and especially the dynorphins, have been localized to several circuits in the CA3 hippocampal region, yet electrophysiological studies often find mixed effects of opiates on the excitability of CA3 neurons. Reasoning that these mixed effects might involve voltage-dependent actions, we tested the effect of several opiates on CA3 pyramidal neurons using single-electrode voltage-clamp recording in a slice preparation of rat hippocampus. In most CA3 neurons, the voltage-dependent K+ current known as the M-current (IM) was uniquely sensitive to the opioid peptides, with the direction of response dependent upon the opiate type and concentration. Thus, an opiate selective for kappa receptors, U-50,488H, significantly augmented IM. The kappa-selective agonists dynorphin A and dynorphin B, which exist in mossy fiber afferents to CA3 pyramidal neurons, also markedly augmented IM at low concentrations (20–100 nM). By contrast, dynorphin A at higher concentrations (1–1.5 microM) often reduced IM. Similarly, several opiates [e.g., D-Ala2,D-Leu5-enkephalin: (DADL), [D- Pen2,5]-enkephalin (DPDPE)] known to act on the delta receptor subtypes reduced the M-current, with partial reversal of this effect by naloxone. Neither the selective mu-receptor agonist [D-Ala2, NMe-Phe4, Gly-ol]-enkephalin (DAMGO) nor the nonopioid fragment of dynorphin, des- Tyr-dynorphin, consistently altered IM. These opiate effects on IM were accompanied by changes in conductance and holding current consistent with their respective effects on IM. Dynorphin A did not measurably affect the Q-current, a conductance known to contribute to inward rectification in hippocampal pyramidal neurons. The opiate effects on IM were not altered by pretreatment with Cs+ (which blocks IQ) or Ca2+ channel blockers. The opposing effects of the dynorphins (both A and B) and DADL on IM were antagonized by naloxone (1–3 microM), and the dynorphin-induced augmentations of IM were usually reversed by the kappa receptor antagonist norbinaltorphimine. These results suggest that the opiates can have opposing effects on the same voltage- dependent K+ channel type (the M channel) in the rat CA3 pyramidal neuron, with the direction of the response depending on which receptor subtype is activated. These data not only help explain the mixed effects of opiates seen in other studies, but also suggest a potential postsynaptic function for the endogenous opiates contained in the CA3 mossy fibers.
Early postnatal development of thyrotropin-releasing hormone (TRH) expression, TRH receptor binding, and TRH responses in neurons of rat brainstem
Authors: Bayliss DA , Viana F , Kanter RK , Szymeczek-Seay CL , Berger AJ , Millhorn DE
Published: April 2018

We investigated the postnatal development of the thyrotropin-releasing hormone (TRH)-containing raphe system in the brainstem of neonatal rats. Postnatal changes in TRH expression in nucleus (n.) raphe obscurus (ROb) and n. raphe pallidus (RPa) were evaluated by in situ hybridization using an 35S-labeled oligonucleotide probe complementary to TRH precursor mRNA. TRH mRNA expression was low at birth [postnatal day 0 (P0)], but was clearly evident by P7 and increased from that time to reach sustained high levels from P14 to P28. Consistent with this postnatal increase in TRH expression, we found increases in the density of TRH-immunoreactive (IR) fibers, which are derived from ROb and RPa, in the hypoglossal nucleus (nXII). TRH-IR fibers in nXII were very sparse at P0, but increased markedly over the first 2 postnatal weeks. The change in TRH innervation of nXII was closely matched by concomitant increases in 3H-methyl-TRH binding in nXII; specific TRH binding increased from very low levels at birth to high levels of P14. Finally, we recorded intracellularly the electrophysiological responses to TRH of hypoglossal motoneurons (HMs; n = 42) of neonatal rats (P0- P21) in a brainstem slice preparation. The response of neonatal HMs to TRH, in contrast to adult HMs, was highly variable. In some neonatal HMs, even at P0, TRH caused a depolarization with a decrease in input conductance (GN) that was characteristic of the response of all adult HMs. However, in other neonatal HMs, TRH was either without effect or caused a slight depolarization with no apparent change in GN, responses that were unlike those of adult HMs. A response was considered typical (i.e., “adult-like”) if GN decreased to < 85% of control. The percentage of cells responding in a typical manner increased progressively from 25% at P0-P2 to 100% after P11. In addition, we found that the density of TRH-sensitive current (normalized to cell capacitance) increased with postnatal age in HMs that responded in a typical manner, suggesting that expression of the TRH-sensitive conductance is also developmentally regulated. Together, these data indicate that the TRH raphe neuronal system of the rat brainstem is not fully mature at the time of birth but develops over the first few postnatal weeks. This was true of levels of TRH mRNA in caudal raphe nuclei, density of TRH-IR fibers and 3H-methyl-TRH binding in nXII, and also the manner and magnitude of electrophysiological responses of HMs to exogenously applied TRH.
Reactive astrogliosis in the neonatal mouse brain and its modulation by cytokines
Authors: Balasingam V , Tejada-Berges T , Wright E , Bouckova R , Yong VW
Published: April 2018

Reactive astrogliosis is a characteristic response of astrocytes to inflammation and trauma of the adult CNS. To assess the hypothesis that cytokines from inflammatory mononuclear cells that accumulate around lesion sites have a role in modulating astrogliosis, this study sought to take advantage of the neonatal system in which astrogliosis is reported to be minimal following injury and in which the immune system is relatively immature compared to adult animals. A nitrocellulose membrane implant into the cortex of postnatal day 3 mice resulted in a tremendous astrogliotic response 4 d later, as measured by glial fibrillary acidic protein (GFAP) immunoreactivity and GFAP content. In contrast, a neonatal stab wound produced limited astroglial response when compared to the adult stab wound. Utilizing the neonatal stab wound model, cytokines were microinjected into the wound site at the time of injury. All cytokines tested (gamma-IFN, IL-1, IL-2, IL-6, TNF- alpha, and M-CSF) resulted in a significantly increased astrogliosis. The specificity of the cytokine response was demonstrated by the inability of human gamma-IFN, but not mouse gamma-IFN, in enhancing neonatal mouse astrogliosis, in accordance with reports that the interaction of gamma-IFN with its receptor occurs in a species-specific manner. We conclude that neonatal astrocytes can become reactive if an adequate injury stimulus is presented, and that the release of immunoregulatory cytokines by cells around lesion sites may be a mechanism that contributes to the production of gliosis.
Neural mechanisms underlying melodic perception and memory for pitch
Authors: Zatorre RJ , Evans AC , Meyer E
Published: April 2018

The neural correlates of music perception were studied by measuring cerebral blood flow (CBF) changes with positron emission tomography (PET). Twelve volunteers were scanned using the bolus water method under four separate conditions: (1) listening to a sequence of noise bursts, (2) listening to unfamiliar tonal melodies, (3) comparing the pitch of the first two notes of the same set of melodies, and (4) comparing the pitch of the first and last notes of the melodies. The latter two conditions were designed to investigate short-term pitch retention under low or high memory load, respectively. Subtraction of the obtained PET images, superimposed on matched MRI scans, provides anatomical localization of CBF changes associated with specific cognitive functions. Listening to melodies, relative to acoustically matched noise sequences, resulted in CBF increases in the right superior temporal and right occipital cortices. Pitch judgments of the first two notes of each melody, relative to passive listening to the same stimuli, resulted in right frontal-lobe activation. Analysis of the high memory load condition relative to passive listening revealed the participation of a number of cortical and subcortical regions, notably in the right frontal and right temporal lobes, as well as in parietal and insular cortex. Both pitch judgment conditions also revealed CBF decreases within the left primary auditory cortex. We conclude that specialized neural systems in the right superior temporal cortex participate in perceptual analysis of melodies; pitch comparisons are effected via a neural network that includes right prefrontal cortex, but active retention of pitch involves the interaction of right temporal and frontal cortices.
Mammalian homologs of Drosophila ELAV localized to a neuronal subset can bind in vitro to the 3' UTR of mRNA encoding the Id transcriptional repressor
Authors: King PH , Levine TD , Fremeau RT , Keene JD
Published: April 2018

Mammalian cDNAs encoding a rat (Rel-N1) and a human (Hel-N1) neuronal RNA-binding protein have been cloned and characterized with respect to tissue specificity, neuroanatomical localization, and RNA binding specificity. Both proteins are highly similar to the product of the Drosophila elav gene, which is expressed in all neurons of the fly and is required for development of the nervous system. However, in situ hybridization of rat tissues demonstrated more restricted expression of Rel-N1 mRNA within a subset of neurons of the hippocampus, cortex, and other regions of the gray matter, but not in glial cells or white matter. In vitro RNA binding experiments demonstrated that Hel-N1 can bind to the 3′ untranslated region (3′ UTR) of Id mRNA, a transcript that encodes a helix-loop-helix transcriptional repressor that is abundantly expressed in undifferentiated neural precursors. Sequences characterized for Hel-N1 binding were also abundantly present in the 3′ UTR of the Drosophila extramacrochaetae mRNA, which encodes an Id homolog. Thus, we have identified a potential link between a neuronal 3′ UTR RNA-binding protein and regulatory transcription factors involved in neural development. These findings are interpreted in light of recent studies in which mRNA 3′ UTRs were found to be important for the regulation of cell growth and differentiation.
Self-administration of morphine, DAMGO, and DPDPE into the ventral tegmental area of rats
Authors: Devine DP , Wise RA
Published: April 2018

Intracranial self-administration of mu- and delta-opioid agonists was demonstrated in male Long-Evans rats. Independent groups were allowed to lever-press for ventral tegmental area (VTA) microinfusions of morphine, the selective mu agonist [D-Ala2,N-Me-Phe4-Gly5-ol]- enkephalin (DAMGO), the selective delta-agonist [D-Pen2,D-Pen5]- enkephalin (DPDPE), or ineffective drug vehicle. Morphine, DAMGO, and DPDPE were each effective in establishing and maintaining lever- pressing habits. Lever-pressing responses were extinguished during a session when vehicle was substituted for drug, and reinstated when drug reinforcement was reestablished. Thus, it appears that VTA mu- and delta-opioid receptors are each involved in reinforcement of opiate self-administration. The effective dose of DAMGO--both for establishing and for maintaining the lever-press habit--was 100 times lower than the effective doses for DPDPE and morphine, suggesting that the major contribution of VTA mechanisms to intravenous heroin self- administration involves an action on mu-opioid receptors.
Neurotransmitter profile of saccadic omnipause neurons in nucleus raphe interpositus
Authors: Horn AK , Buttner-Ennever JA , Wahle P , Reichenberger I
Published: April 2018

Saccadic omnipause neurons (OPNs) are essential for the generation of saccadic eye movements. In primates OPNs are located near the midline within the nucleus raphe interpositus (rip). In the present study we used several different neuroanatomical methods to investigate the transmitters associated with OPNs in the monkey. Immunolabeling for the calcium-binding protein parvalbumin was employed to mark OPNs in the monkey and define the homologous cell group in cat and human. The use of antibodies against GABA, glycine (GLY), glutamate (GLU), serotonin (5-HT), and tyrosine hydroxylase revealed that the somata of OPNs are GLY immunoreactive, but they are devoid of GABA and 5-HT immunostaining. In situ hybridization with the GAD67 mRNA probe confirmed the negative GABA immunostaining of OPNs. 3H-GLY was injected into a projection field of OPNs, the rostral interstitial nucleus of the medial longitudinal fascicle (riMLF)--the vertical saccadic burst neuron area. This resulted in selective retrograde labeling of the OPNs in rip, while no labeling was found in the superior colliculus, which sends an excitatory projection to the riMLF. The somata and dendrites of putative burst neurons in the riMLF were contacted by numerous GLY- immunoreactive terminals. The quantitative analysis of immunoreactive terminal-like structures contacting OPNs revealed a strong input from GLY- and GABA-positive terminals on somata and dendrites, whereas GLU- positive puncta were mainly confined to the dendrites. Very few 5-HT and catecholaminergic terminals contacted OPN somata. Our findings suggest that OPNs use GLY as a neurotransmitter, and they receive numerous contacts from GABAergic, glycinergic, and glutaminergic afferents, and significantly fewer from monoaminergic inputs.
Enhanced activation of NMDA receptor responses at the immature retinogeniculate synapse
Authors: Ramoa AS , McCormick DA
Published: April 2018

The maturation of retinogeniculate excitatory transmission and intrathalamic inhibition was studied in slices of the dorsal LGN obtained from ferrets during the first 2 postnatal months. Response to optic tract stimulation at neonatal ages consisted of slow EPSPs lasting several hundred milliseconds. Application of the NMDA receptor antagonist D-(-)-2-amino-5-phosphonovaleric acid (D-APV) during the first 2 postnatal weeks resulted in EPSPs that were reduced in peak amplitude and dramatically curtailed in duration, indicating that NMDA receptors participate strongly in retinogeniculate transmission at the immature synapse. Gradually, EPSPs became shorter in duration such that after the second postnatal week, the retinogeniculate EPSPs were only a few milliseconds in duration. At this late stage of development responses were remarkably less affected by application of D-APV. These changes in contribution of NMDA receptors to retinogeniculate transmission were found to be due to the development of strong IPSPs, the result of gradual maturation of activation of GABAergic inhibition. Indeed, application of bicuculline methiodide to block GABAA receptor- mediated IPSPs strongly enhanced the NMDA component of the EPSPs in more mature cells. The voltage dependence and kinetics of NMDA-induced excitatory postsynaptic currents (NMDA EPSCs) were characterized by voltage-clamp recordings after blocking AMPA/kainate receptors with 6- cyano-7-nitroquinoxaline-2,3-dione and GABAA receptors wit' bicuculline methiodide. The voltage dependence of the NMDA EPSCs remained unaltered with age. During the first postnatal month the kinetic properties of the NMDA EPSCs also remained unaltered, but a reduction in EPSC duration was observed within the following weeks, well after the critical period of anatomical reorganization.(ABSTRACT TRUNCATED AT 250 WORDS)
Both open and closed NMDA receptor channels desensitize
Authors: Lin F , Stevens CF
Published: April 2018

Desensitization of NMDA receptors was studied at the single-channel level using outside-out patches taken from rat hippocampus CA neurons maintained short term in culture. The amount of desensitization that accumulated as a function of time during the application of NMDA (2.5 microM) was measured by the response to the rapid application of NMDA at a high concentration (100 microM). Records were sorted into two classes: those in which no openings were detected during the application of 2.5 microM NMDA, and those in which some channel openings occurred. Analysis of these data reveals that some desensitization accumulated when no channels opened, but that more desensitization developed when channels opened. The observations indicate that channels can pass from the closed state to the desensitized state, but that desensitization occurs more rapidly from the open state.
Cloning and characterization of the choline acetyltransferase structural gene (cha-1) from C. elegans
Authors: Alfonso A , Grundahl K , McManus JR , Rand JB
Published: April 2018

We have cloned the cha-1 gene from Caenorhabditis elegans using the method of transposon tagging, cha-1 is the structural gene for ChAT, the enzyme that synthesizes ACh. Sequence analysis of cDNAs predicts a protein of 71.5 kDa; comparison of the deduced amino acid sequence with ChAT sequences from other species confirms that cha-1 encodes ChAT. Comparison of cDNA and genomic sequences reveals that transcription is from right to left on the genetic map, and that some of the transcripts may result from trans-splicing of the 22-base spliced leader SL 1. The cha-1 gene is organized into 11 exons. The first exon contains only untranslated sequences, and is followed by an extremely long intron. The coding sequence of the cha-1 transcript is disrupted by mutations in the cha-1 gene. We have determined the sites of four transposon insertions and the end-points of two deletions that lead to the cha-1 mutant phenotype; one of the deletions appears to eliminate gene function completely. Comparison of the Drosophila, rat, and C. elegans genes reveals conserved motifs and conserved intron sites.
Thermal hyperalgesia in association with the development of morphine tolerance in rats: roles of excitatory amino acid receptors and protein kinase C
Authors: Mao J , Price DD , Mayer DJ
Published: April 2018

In a rat model of morphine tolerance, we examined the hypotheses that thermal hyperalgesia to radiant heat develops in association with the development of morphine tolerance and that both the development and expression of thermal hyperalgesia in morphine-tolerant rats are mediated by central NMDA and non-NMDA receptors and subsequent protein kinase C (PKC) activation. Tolerance to the analgesic effect of morphine was developed in rats utilizing an intrathecal repeated treatment regimen. The development of morphine tolerance and thermal hyperalgesia was examined by employing the tail-flick test and paw- withdrawal test, respectively. Intrathecal MK 801 (an NMDA receptor antagonist), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; a non-NMDA receptor antagonist), or GM1 ganglioside (an intracellular PKC inhibitor) treatment was given to examine the effects of these agents on the development and expression of thermal hyperalgesia in morphine- tolerant rats. Tolerance to the analgesic effect of morphine was reliably developed in rats following once daily intrathecal (onto the lumbosacral spinal cord) injection of 10 micrograms of morphine sulfate for 8 consecutive days as demonstrated by the decreased analgesia following morphine administration on day 8 as compared to that on day 1. In association with the development of morphine tolerance, thermal hyperalgesia to radiant heat developed in these same rats. Paw- withdrawal latencies were reliably decreased in morphine-tolerant rats as compared to nontolerant (saline) controls when tested on day 8 before the last morphine treatment and on day 10 (i.e., 48 hr after the last morphine treatment). The coincident development of morphine tolerance and thermal hyperalgesia was potently prevented by intrathecal coadministration of morphine with MK 801 (10 nmol) or GM1 (160 nmol), and partially by CNQX (80 nmol). MK 801 (5, 10 nmol, not 2.5 nmol) and CNQX (80, 160 nmol, not 40 nmol), but not GM1 (160 nmol), also reliably reversed thermal hyperalgesia in rats rendered tolerant to morphine when tested 30 min after each drug treatment on day 10 (48 hr after the last morphine treatment). The data indicate that thermal hyperalgesia develops in association with the development of morphine tolerance and that the coactivation of central NMDA and non-NMDA receptors is crucial for both the development and expression of thermal hyperalgesia in morphine-tolerant rats. Furthermore, intracellular PKC activation plays a critical role in the development of thermal hyperalgesia in morphine-tolerant rats.(ABSTRACT TRUNCATED AT 400 WORDS)
Spatial correlates of firing patterns of single cells in the subiculum of the freely moving rat
Authors: Sharp PE , Green C
Published: April 2018

Hippocampal lesions cause spatial learning deficits, and single hippocampal cells show location-specific firing patterns, known as place fields. This suggests the hippocampus plays a critical role in navigation by providing an ongoing indication of the animal's momentary spatial location. One question that has received little attention is how this locational signal is used by downstream brain regions to orchestrate actual navigational behavior. As a first step, we have examined the spatial firing correlates of cells in the dorsal subiculum as rats navigate in an open-field, pellet-searching task. The subiculum is one of the few major output zones for the hippocampus, and it, in turn, projects to numerous other brain areas, each thought to be involved in various learning and memory functions. Most subicular cells showed a robust locational signal. The patterns observed were different from those in the hippocampus, however, in that cells tended to fire throughout much of the environment, but showed graded, location-related rate modulation, such that there were some localized regions of high firing and other regions with relatively low firing. There were slight quantitative differences between the proximal (adjacent to the hippocampus) and distal (farther from the hippocampus) subicular regions, with distal cells showing slightly higher average firing rates, spatial signaling, and firing field size. This was of interest since these two regions have different efferent connections. Examination of spike trains allowed classification of cells into bursting, nonbursting, and theta (putative interneuron) categories, and this is similar to subicular cell types identified in vitro. Interestingly, the bursting and nonbursting types did not differ detectably in spatial firing properties, suggesting that differences in intrinsic membrane properties do not necessitate differences in coding of environmental inputs. The results suggest that the subiculum transmits a robust, highly distributed spatial signal to each of its projection areas, and that this signal is transmitted in both a bursting and nonbursting mode.
GABAA receptor subunit immunoreactivity in primate visual cortex: distribution in macaques and humans and regulation by visual input in adulthood
Authors: Hendry SH , Huntsman MM , Vinuela A , Mohler H , de Blas AL , Jones EG
Published: April 2018

Subunit proteins that make up functional GABAA receptors were localized immunocytochemistry in the primary visual cortex (area 17) of adult monkeys and humans. Immunoreactivity for the alpha 1, beta 2/3, and gamma 2 subunits is greatest in layers (II-III, IVA and IVC) of monkey area 17 that contain the highest density of GABA neurons and terminals. Immunostaining for each subunit is unevenly distributed in layers II and III, where patches of immunoreactivity correspond to regions of intense cytochrome oxidase (CO) staining, and in layer IVA, where intense immunoreactivity forms a honeycomb pattern identical to the CO staining pattern. Immunoreactivity for the subunits is localized principally within the neuropil, which, by simultaneous comparison with the distribution of microtubule-associated protein immunostaining, was found to include bundles of thin dendrites and zones of numerous dendritic segments. In addition, gamma 2 immunostaining surrounds the somata of a subpopulation of GABAergic neurons, immunoreactive for the calcium-binding protein parvalbumin. All three subunits are present in the somata and processes of neurons that occupy the white matter subjacent to monkey area 17. In human visual cortex, the alpha 1, beta 2/3, and gamma 2 subunits are distributed in a manner similar to that found in monkeys, with relatively intense immunostaining in layers IVC and IVA. In layer IVC, vertical stripes of intense receptor immunostaining (20–30 microns wide) alternate with wider stripes of pale immunostaining (30–60 microns wide). In the upper and lower halves of IVC beta, these stripes form lattices similar to those in layers IVC and IVA of monkeys. Following monocular deprivation by intravitreal injections of TTX in adult monkeys, immunoreactivity for each subunit in layer IVC consists of alternating intensely and lightly stained stripes. Comparison with the pattern of CO staining indicates that intense immunostaining for alpha 1, beta 2/3, and gamma 2 occurs in normal-eye stripes while abnormally light immunostaining is present in deprived-eye stripes. For all three subunits, immunoreactivity in deprived-eye stripes is reduced within 5 d of monocular deprivation and remains abnormally low for deprivations that extend to at least 30 d. These findings indicate that each of several GABAA receptor subunits adopt similar laminar and compartmental distributions in monkey and human area 17 and are likely to be expressed by the same neurons. The deprivation-dependent reduction in immunoreactivity for alpha 1, beta 2/3, and gamma 2 subunits suggests that all are regulated by visually driven activity.(ABSTRACT TRUNCATED AT 400 WORDS)
Component placement optimization in the brain
Authors: Cherniak C
Published: April 2018

This computational neuroanatomy study evaluates how well some formalisms derived from combinatorial network optimization theory fit as models for brain structure. At multiple hierarchical levels--brain, ganglion, individual cell--physical placement of neural components appears consistent with a single, simple goal: minimize cost of connections among the components. The most dramatic instance of this “save wire” organizing principle is reported for adjacencies among ganglia in the nematode nervous system; among about 40,000,000 alternative layout orderings, the actual ganglion placement in fact requires the least total connection length. In addition, evidence supports a component placement optimization hypothesis for positioning of individual neurons in the nematode, and also for positioning of mammalian cortical areas.
Calcium wave fronts that cross gap junctions may signal neuronal death during development
Authors: Wolszon LR , Rehder V , Kater SB , Macagno ER
Published: April 2018

Embryonic anterior pagoda (AP) neurons in the leech interact with their segmental homologs in adjacent ganglia through transient axons that overlap during a critical period of development and then retract. However, when an AP neuron is ablated mechanically or by irradiation during this period, an adjacent homolog responds by reinitiating growth of its overlapped axon and thereby taking over vacated territory (Gao and Macagno, 1987b; Gao, 1989). The death of an AP cell is therefore communicated to its homolog, but the mechanism underlying this signaling is presently unknown. Since it was recently found that AP homologs are electrically and dye coupled through their transient axons (Wolszon et al., 1994), we investigated the possibility that gap junctions may mediate the cell death signal that could occur between developing neurons. Among several candidate intercellular signals, we began by studying calcium dynamics in embryonic AP cells, in situ, since calcium is known to cross gap junctions and is implicated in cell death in many systems. We found that elements that usually increase [Ca2+]i in adult neurons, such as releasable internal stores or voltage- dependent calcium channels, were not present at the critical period. Instead, mechanisms that reduce free calcium, such as buffering and pumping, were the most robust. When a large, focal calcium rise was produced in an AP axon by making a lesion with a UV microbeam (leading to eventual death of these neurons), calcium did not rise quickly throughout the cell, but rather moved in a slow (0.05–0.25 micron/sec) wave front away from the lesion site, into other processes of the damaged cell. Furthermore, when a calcium wave front reached the growth cone of a transient axon, it crossed at the gap junctions into the coupled axon of the neighboring AP neuron, but went no further. Since it is known that an AP responds to a neighbor's death by reinitiating growth only in that axon that contacts the dying cell (Gao and Macagno, 1987b; Gao, 1989), these observations are consistent with calcium playing a role in the signaling of cell death to homologs that are coupled to a dying cell.
Intranigral fetal dopamine grafts induce behavioral compensation in the rat Parkinson model
Authors: Nikkhah G , Bentlage C , Cunningham MG , Bjorklund A
Published: April 2018

Neural transplantation in experimental Parkinsonism has so far focused on the ectopic placement of fetal ventral mesencephalic (VM) neurons into the dopamine-denervated caudate-putamen. VM grafts are effective in restoring dopamine neurotransmission in the grafted caudate-putamen and in partial amelioration of behavioral deficits. Recent pharmacological and physiological data have provided strong evidence that dopamine released from dendrites of the substantia nigra pars compacta (SNc) neurons within the pars reticulata (SNr) plays an important role in the regulation of the basal ganglia output pathways. Using a novel microtransplantation approach, multiple small cell suspension grafts (250 nl) derived from the VM of E14 rat embryos were implanted into the SNr of unilaterally 6-hydroxydopamine-lesioned rats. Behavioral changes in drug-induced rotation asymmetry were monitored for up to 14 weeks postgrafting, followed by a quantitative assessment and correlation of tyrosine hydroxylase (TH)-positive cell survival. The reduction in rotational asymmetry caused by the intranigral VM grafts was 64% for SKF 38393 (D1 agonist), 54% for apomorphine (mixed D1 and D2 agonist), and 67% for quinpirole (D2 agonist) when compared to a control spinal cord graft group. By contrast, amphetamine-induced rotation was completely unaffected. The correlation between number of TH-positive cells and behavioral compensation was highest for the D1 agonist (R = -0.729), though clear-cut also for the mixed D1/D2 agonist apomorphine (R = -0.664) and the D2 agonist quinpirole (R = -0.642). Favorable morphological features of the VM micrografts included extensive migration of the dopaminergic neurons into the host SNr and the formation of dense patches of dendrite-like TH-positive terminal networks within the SNr. The results demonstrate a novel pattern of behavioral recovery induced by intranigral VM transplants in the rat Parkinson model. This may have important implications for the understanding of how the nigrostriatal dopamine system influences motor control in the basal ganglia as well as for the development of optimal transplantation strategies in Parkinson's disease.
Fields in human motor areas involved in preparation for reaching, actual reaching, and visuomotor learning: a positron emission tomography study
Authors: Kawashima R , Roland PE , O'Sullivan BT
Published: April 2018

The purpose of this study was to examine the functional organization of motor cortices in the human brain involved in reaching and visuomotor learning. All subjects were asked to learn the positions of seven circular targets projected on a screen. Each time the targets were turned off, they were required to close their eyes and keep them closed, and, after a delay, to point to the center of the targets in a prescribed order using their right hand. The regional cerebral blood flow (rCBF) was measured with 15O-butanol and positron emission tomography in 20 subjects during a rest state, an initial learning stage, and a later learning stage. Ten subjects constituted the reaching group in which rCBF was measured during actual reaching; the 10 other subjects constituted the preparation group in which rCBF was measured in the delay period between target exposure and actual reaching. Individual subtraction images (each stage minus rest) were calculated and transformed into a standard size and shape brain image by the adjustable computerized brain atlas and averaged, after which significant changes of rCBF were identified. In all reaching and preparation for reaching phases, cortical fields were activated in the left primary motor area (M1) and the left premotor area (PMA). Within M1, fields active in the delay phases were adjacent to the fields active only during actual reaching movements. During the course of learning, additional fields of activity appeared in both M1 and PMA. The results indicate that three types of fields occur in M1 and PMA: (1) fields directly engaged in the efferent control of peripheral muscle contraction, (2) fields engaged in preparatory activity for reaching, and (3) fields appearing after learning of the task has taken place.
Combinatorial expression of three zebrafish genes related to distal- less: part of a homeobox gene code for the head
Authors: Akimenko MA , Ekker M , Wegner J , Lin W , Westerfield M
Published: April 2018

We describe analysis of zebrafish distal-less-related homeobox genes that may serve as specifiers of positional information in anterior regions of the CNS and in peripheral structures. We isolated three zebrafish genes, dlx2, dlx3, and dlx4, by screening embryonic cDNA libraries. Comparisons of the predicted sequences of the Dlx2, Dlx3, and Dlx4 proteins with distal-less proteins from other species suggest that vertebrate distal-less genes can be divided into four orthologous groups. We observed similarities but also unique features of the expression patterns of the zebrafish dlx genes. Among the three genes, dlx3 alone is expressed during gastrulation. Shortly after gastrulation, cells in the ventral forebrain rudiment express dlx2 and dlx4, but not dlx3, and hindbrain neural crest cells express only dlx2. Presumptive precursor cells of the olfactory placodes express dlx3 and dlx4 but not dlx2. Transcripts of dlx3 and dlx4 are present in overlapping subsets of cells in the auditory vesicle and in cells of the median fin fold, whereas dlx2 is never expressed in the auditory vesicle and only at low levels in localized regions of the median fin fold. Cells of the visceral arches and their primordia express all three dlx genes, but with different developmental time courses. We suggest that combinatorial expression of the dlx genes is part of a homeobox gene code specifying pattern formation or cell fate determination in the forebrain, in peripheral structures of the head, and in the fins.
Thalamocortical axons extend along a chondroitin sulfate proteoglycan- enriched pathway coincident with the neocortical subplate and distinct from the efferent path
Authors: Bicknese AR , Sheppard AM , O'Leary DD , Pearlman AL
Published: April 2018

The distinct axonal tracts of the mature nervous system are defined during development by sets of substrate-bound and diffusible molecular signals that promote or restrict axonal elongation. In the adult cerebral cortex, efferent and afferent axons are segregated within the white matter. To define the relationship of growing efferent and afferent axons in the developing murine cortex to chondroitin sulfate proteoglycans (CSPGs) in the pericellular and extracellular matrix, we used the fluorescent tracer Dil to determine axonal trajectories and immunolabeling to disclose the distribution of CSPGs. Axons of neurons in the preplate are the first to leave the cortex; they arise in the CSPG-rich preplate and extend obliquely across it to enter the CSPG- poor intermediate zone. Slightly later, axons of cortical plate neurons extend directly across the CSPG-rich subplate, and then turn abruptly to run in the upper intermediate zone. In contrast, once afferent axons from the thalamus reach the developing cortical wall, their intracortical trajectory is centered on the CSPG-rich subplate, above the path taken by efferent axons. Our findings demonstrate a molecular difference between the adjacent but distinct efferent and afferent pathways in developing neocortex. Early efferents cross the subplate and follow a pathway that contains very little CSPG, while afferents preferentially travel more superficially within the CSPG-rich subplate. Thus, CSPGs and associated extracellular matrix (ECM) components in the preplate/subplate do not form a barrier to axonal initiation or outgrowth in the neocortex as they may in other locations. Instead, their distribution suggests a role in defining discrete axonal pathways during early cortical development.