bluuebunny/crossref_metadata_2025 huggingface dataset:
Glutamate receptors in the nucleus accumbens shell control feeding behavior via the lateral hypothalamus
Authors: Maldonado-Irizarry CS , Swanson CJ , Kelley AE
Published: April 2018

The nucleus accumbens in a brain region considered to be important in the regulation of appetitive behavior and reinforcement. The accumbens receives afferent input from corticolimbic and thalamic structures, which is primarily coded by excitatory amino acids (EAAs). The present studies investigated the role of EAA input to the nucleus accumbens in feeding behavior in rats, in two recently characterized subregions of the accumbens, the “core#x201D; and #x201C;shell#x201D;. In the first series of experiments, it was shown that blockade of alpha-amino-3-hydroxy-5- methylisoxazole-4-propionic acid (AMPA) and kainate glutamate receptors in the medial part of the accumbens, corresponding to the medial shell subregion, resulted in a pronounced feeding response. Bilateral microinfusion of 6,7-dinitroquinoxaline-2,3-dione (DNQX, 0.25–0.75 micrograms/0.5 microliters), 6-cyano-7-nitroquinoxaline (CNQX, 0.75–1.5 micrograms), and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo-(F) quinoxaline (NBQX, 0.2-1.0 micrograms) markedly stimulated food intake immediately following infusion, in a dose-dependent manner. Infusion of DNQX into the central accumbens region, corresponding to the core, did not elicit feeding. Infusion of the NMDA antagonists 2-amino-5-phosphonopentanoic acid (AP-5) and MK-801 (dizocilpine maleate) did not elicit feeding in either region. The feeding response to DNQX was blocked by local coinfusion of AMPA. Systemic pretreatment with naltrexone (5 mg/kg) had no effect on the DNQX-feeding response; however, prior systemic administration of both D-1 and D-2 antagonists reduced the response by half, suggesting a modulatory role for dopamine in the response. Moreover, the feeding response was completely inhibited by concurrent infusion of the GABAA agonist muscimol (10, 25 ng) into the lateral hypothalamus, a major projection area of the accumbens shell. These findings demonstrate a selective role for non-NMDA receptors in the nucleus accumbens shell in ingestive behavior, and suggest an important functional link between two major brain regions involved in reward, the nucleus accumbens and lateral hypothalamus.
Developmental and regional expression of multifunctional Ca2+/calmodulin-dependent protein kinase isoforms in rat brain
Authors: Brocke L , Srinivasan M , Schulman H
Published: April 2018

Multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) participates in diverse calcium signaling pathways in neurons. The alpha- and beta-CaM kinase isoforms are neuron-specific and highly abundant in rat brain. The variable domain of CaM kinase is a potential site for the generation of isoform diversity by alternative spicing of its N- and/or C-terminal segments. We used specific PCR primers which span the variable domain of either alpha- or beta-CaM kinase and isolated three new isoforms from rat brain, namely alpha B-, beta e- and beta'e-CaM kinase. alpha beta-CaM kinase contains 11 amino acids, likely inserted by alternative splicing, at the C-terminal segment of the variable domain. This insertion introduces a nuclear localization signal (NLS) that targets alpha B-CaM kinase to the nucleus of transfected cells; alpha-CaM kinase is excluded from the nucleus. The mRNA and the protein corresponding to this isoform are detected only in the diencephalon/midbrain regions. We have also identified two alternatively spliced isoforms of beta-CaM kinase that lack the 24 amino acid sequence at the N-terminal segment of the variable domain. Alternative splicing of these two isoforms occurs with a three base pair shift of the 3′-splice site. Our analysis shows that these new beta-CaM kinase isoforms are expressed primarily in early developmental stages, and we therefore term them beta e - (embryonic) and beta' e-CaM kinase. Recombinant alpha B-, beta e and beta' e-CaM kinase expressed in COS-7 cells exhibit characteristic Ca2+/calmodulin-dependent protein kinase activity and autophosphorylation.
The growth of the axon is not dependent upon net microtubule assembly at its distal tip
Authors: Yu W , Baas PW
Published: April 2018

Although there is agreement that the net addition of new microtubule polymer to the axon is required for its growth, controversy exists concerning the principal site in the neuron where this occurs. Some models hold that microtubule polymer is assembled within the cell body and translocated down the axon, while others hold that the net addition of polymer occurs at the distal tip of the axon. The foundation for the latter idea was a study in which anti-microtubule drugs were applied topically for 30 min to discrete regions of cultured sensory neurons (Bamburg et al., 1986). The axon continued to grow when the drugs were applied to the cell body, but stopped growing when the drugs were applied to the distal tip of the axon. Assuming that the sole action of the drug was to inhibit microtubule assembly, many workers have interpreted these findings as indicating that the growth of the axon requires net microtubule assembly at its distal tip. We repeated these experiments using a broader range of drug treatments, and evaluated using electron microscopy the effects of these treatments on microtubule levels. Our results indicate that the previous drug treatments went beyond inhibiting microtubule assembly, and also caused substantial microtubule disassembly. When the drug regime was altered so as to induce lower levels of microtubule disassembly in the distal region of the axon, the axon continued to grow. These results indicate that the growth of the axon is not dependent upon net microtubule assembly at its distal tip.
Impaired fear conditioning following unilateral temporal lobectomy in humans
Authors: LaBar KS , LeDoux JE , Spencer DD , Phelps EA
Published: April 2018

Classical fear conditioning was used in the present study as a model for investigating emotional learning and memory in human subjects with lesions to the medial temporal lobe. Animal studies have revealed a critical role for medial temporal lobe structures, particularly the amygdala, in simple and complex associative emotional responding. Whether these structures perform similar functions in humans is unknown. On both simple and conditional discrimination tasks, unilateral temporal lobectomy subjects showed impaired conditioned response acquisition relative to control subjects. This impairment could not be accounted for by deficits in nonassociative sensory or autonomic performance factors, or by differences in declarative memory for the experimental parameters. These results show that temporal lobe structures in humans, as in other mammals, are important components in an emotional memory network.
Development of glycinergic and glutamatergic synaptic transmission in the auditory brainstem of perinatal rats
Authors: Kandler K , Friauf E
Published: April 2018

In contrast to our knowledge about the anatomical development of the mammalian central auditory system, the development of its physiological properties is still poorly understood. In order to better understand the physiological properties of the developing mammalian auditory brainstem, we made intracellular recordings in brainstem slices from perinatal rats to examine synaptic transmission in the superior olivary complex, the first binaural station in the ascending auditory pathway. We concentrated on neurons in the lateral superior olive (LSO), which in adults, are excited from the ipsilateral side and inhibited from the contralateral side. Already at embryonic day (E) 18, when axon collaterals begin to invade the LSO anlage, synaptic potentials could be evoked from ipsilateral, as well as from contralateral inputs. Ipsilaterally elicited PSPs were always depolarizing, regardless of age. They had a positive reversal potential and could be completely blocked by the non-NMDA glutamate receptor antagonist CNQX. In contrast, contralaterally elicited PSPs were depolarizing from E18-P4, yet they turned into “adult-like,#x201D; hyperpolarizing PSPs after P8. Their reversal potential shifted dramatically from -21.6 +/- 17.7 mV (E18-P0) to -73.0 +/- 7.1 mV (P10). Regardless of their polarity, contralaterally elicited PSPs were reversibly blocked by the glycine receptor antagonist strychnine. Bath application of glycine and its agonist beta-alanine further confirmed the transitory depolarizing action of glycine in the auditory brainstem. Since the transient excitatory behavior of glycine occurs during a period during which glycinergic synaptic connections in the LSO are refined by activity- dependent mechanisms, glycinergic excitation might be a mechanism by which synaptic rearrangement in the contralateral inhibitory pathway is accomplished.
Repeated exposure to one song leads to a rapid and persistent decline in an immediate early gene's response to that song in zebra finch telencephalon
Authors: Mello C , Nottebohm F , Clayton D
Published: April 2018

Conspecific song induces a prompt increase in the expression of the zenk gene in the caudo-medial neostriatum (NCM), a part of the auditory telencephalon of songbirds. To test the hypothesis that zenk gene induction in NCM is related to the acquisition of new song-related memories, we presented adult male zebra finches with repeated playbacks of one song. In response, zenk mRNA levels in NCM increased for the first 30 min, but then declined back to baseline levels despite continued stimulation with the same song. When a novel song was then introduced, however, a full zenk response was triggered once again. Even when a full day had passed between the last exposure to a song and the testing period, the song that had been rendered “familiar#x201D; by repetition caused no zenk response, whereas a novel song caused a full response. Quantitative analysis indicates that individual cells in NCM must have undergone a selective loss in their zenk responsiveness to the repeated song, while still maintaining their ability to respond to the novel song. These results support the hypothesis that the induction of zenk is related to the formation of long-term memories. Analysis of the stimulus-specific modulation of zenk responses, coupled with appropriate behavioral assays, should provide insight into neural mechanisms responsible for the discrimination and storage of complex perceptual information.
Pronounced cellular diversity and extrasynaptic location of nicotinic acetylcholine receptor subunit immunoreactivities in the chicken pretectum
Authors: Ullian EM , Sargent PB
Published: April 2018

The diversity of nicotinic ACh receptor (AChR) expression in the chick lateral spiriform nucleus (SpL) was assessed using subunit-specific monoclonal antibodies (mAbs) and laser scanning confocal microscopy. The late embryonic SpL was immunoreactive for mAbs against the alpha 2, alpha 5, alpha 7, alpha 8, and beta 2 AChR subunits. Distinct neuronal cell classes were determined using pair-wise staining of mAbs. Approximately 90% of the neurons in the SpL contained both alpha 5-like immunoreactivity (LI) and beta 2-LI, with no neurons having only one of these subunit-LIs. Approximately 70% of the neurons contained alpha 2- LI. All alpha 2-LI neurons contained alpha 5/beta 2-LI; thus, neurons having alpha 2-LI are a subset of those having alpha 5- and beta 2-LI. Fewer neurons, approximately 20%, contained alpha 7-LI. A subset of alpha 7-positive neurons were immunoreactive for other subunits; for example, some alpha 7-positive neurons also contained alpha 2-LI. Fewer than 15% of the neurons contained alpha 8-LI. Some of the alpha 8-LI- containing neurons contained alpha 7-LI. The 14 week post-hatch SpL resembles the late embryonic nucleus in the percentage of neurons immunoreactive for alpha 2, alpha 5, alpha 7, alpha 8, and beta 2 AChR subunits, and in the presence of multiple classes based on AChR subunit immunoreactivity. In addition, alpha 4-LI was found in about 20% of the 14 week SpL neurons. Double-label immunofluorescence experiments with mAbs to AChRs and to synaptic vesicle antigens showed that most clusters of alpha 5-LI and beta 2-LI are extrasynaptic. The pronounced diversity of AChR subunit expression and the extrasynaptic location of AChR-LI suggest that AChR-like molecules in the SpL do not function solely to respond to transmitter focally released from presynaptic terminals.
Repeated treatment with haloperidol and clozapine exerts differential effects on dye coupling between neurons in subregions of striatum and nucleus accumbens
Authors: Onn SP , Grace AA
Published: April 2018

The delayed onset of action of antipsychotic drugs (APDs) during the treatment of schizophrenia has been hypothesized to temporally correlate with the induction of depolarization block in rat mesencephalic dopamine (DA) cell groups. Nevertheless, it is unknown whether these drugs also exert a delayed action on the dopaminoceptive postsynaptic target cells in the striatal complex. Using in vivo intracellular recording and dye labeling techniques, the effects of APDs on dye coupling were examined in subregions of the striatal complex defined by double staining for calbindin immunoreactivity. Rats treated repeatedly with APDs were found to exhibit a 66–71% higher incidence of coupling that occurred in a drug- and a region-specific manner, that is, both drug treatments increased dye coupling in the limbic-associated accumbens shell region whereas only haloperidol increased dye coupling in the motor-related striatal matrix and accumbens core regions. In addition, cells located in regions in which dye coupling was altered also showed significantly higher input resistance. These changes were not observed in response to DA receptor blockade by acute drug administration or when haloperidol was administered for a period sufficient to induce DA receptor supersensitivity but not DA cell depolarization block (i.e., 2 weeks). Therefore, alteration in dye coupling appears to be correlated temporally with the induction of DA cell depolarization block. The finding that both APDs exert a common action on neurons in the accumbens shell region is consistent with its identification as the site of therapeutic drug actions, whereas the capacity of haloperidol to also affect cells in the motor-related matrix and core regions correlates with its high propensity to induce extrapyramidal side effects.
Stress-induced sensitization and glucocorticoids. II. Sensitization of the increase in extracellular dopamine induced by cocaine depends on stress-induced corticosterone secretion
Authors: Rouge-Pont F , Marinelli M , Le Moal M , Simon H , Piazza PV
Published: April 2018

Secretion of glucocorticoids seems to control stress-induced sensitization of the behavioral effects of drugs of abuse by acting on the mesencephalic dopaminergic transmission, the principal neural substrate of sensitization. In order to investigate the mechanisms of this interaction between glucocorticoids and dopamine, we studied the sensitization of the increase in extracellular concentration of dopamine induced by cocaine in male rats in which corticosterone secretion was either intact or blocked. Extracellular concentrations of dopamine were evaluated in the nucleus accumbens of freely moving animals by means of microdialysis. Metyrapone, an inhibitor of corticosterone synthesis, was used to block stress-induced corticosterone secretion. Food-restriction (90% of the initial body weight) was the stressor used to induce sensitization. It was found that metyrapone (100 mg/kg s.c. twice a day for 8 d) suppressed stress- induced sensitization of the increase in accumbens dopamine induced by cocaine (10 mg/kg, i.p.) and sensitization of cocaine-induced locomotion Metyrapone suppressed both the development and the expression of sensitization. Thus, sensitization was equally blocked when the metyrapone treatment started either 1 d before the start of food-restriction or 8 d later, that is, when food-restriction-induced sensitization to cocaine was already established. In conclusion, our results suggest that glucocorticoids modify sensitization of the behavioral effects of cocaine by acting on extracellular concentrations of dopamine. Since addictive properties of psychostimulants seem mediated by the increase in extracellular concentrations of dopamine they induce, these findings may have implications for the development of new therapeutic strategies of addiction.
Delayed postischemic hypothermia: a six month survival study using behavioral and histological assessments of neuroprotection
Authors: Colbourne F , Corbett D
Published: April 2018

In the gerbil, brief global forebrain ischemia induces profound habituation and working memory impairments that stem from delayed hippocampal CA1 death. Short duration postischemic hypothermia has been shown to reduce CA1 loss, but such reports are controversial, as it is thought that protection may be transient. The purpose of this study was to investigate whether prolonged postischemic hypothermia provided long- term CA1 and functional neuroprotection. Previously, 90% of anterior CA1 neurons were rescued (30 d survival) when 24 hr of hypothermia (32 degrees C) was induced 1 hr following a 5 min occlusion that otherwise produced more than 95% loss (Colbourne and Corbett, 1994). We now find about 70% CA1 savings with this same hypothermic treatment in gerbils that survived for 6 months postischemia. While this is a significant reduction from 30 day survival (medial CA1 only), it nonetheless shows, for the first time, persistent, if not permanent neuroprotection, especially in middle and lateral CA1. In addition, in non-treated animals, ischemia impaired learning in an open field and T-maze for up to 6 months. Postischemic hypothermia significantly reduced these deficits. Hypothermia (32 degrees), when initiated 4 hr after ischemia, rescued approximately 12% of CA1 neurons at 6 months with a slight behavioral benefit. Milder hypothermia (34 degrees C, 1–25 hr postischemia, 30 d survival) also reduced habituation impairments and saved approximately 60% of CA1 neurons. Similar trends were found at more caudal CA1 levels. These results clearly show that postischemic hypothermia provides effective and long-lasting neuroprotection, which depends upon the delay to initiation, duration, and degree of cooling and survival time. The protracted functional and histological benefit observed justifies further basic and clinical investigation.
Neural network of structures in which GABAB receptors regulate absence seizures in the lethargic (lh/lh) mouse model
Authors: Hosford DA , Lin FH , Kraemer DL , Cao Z , Wang Y , Wilson JT
Published: April 2018

In previous work we have shown that GABAB receptors are required for expression of absence seizures in the lethargic (lh/lh) mouse model; that lh/lh mice have increased numbers of GABAB binding sites compared to nonepileptic littermates (designated +/+); and that the magnitude of the increased number of GABAB receptors in lh/lh mice correlated positively with the frequency of absence seizures. We performed this study to delineate the neural network in which GABAB receptors regulate absence seizures in lh/lh mice. We designed three successive screens which had to be passed by a candidate neuronal population before it could be considered a member of the neural network in which GABAB receptors regulate absence seizures. First, the neuronal populations in lh/lh mice had to have enriched GABAB binding sites compared to homologous populations in matched nonepileptic controls; baclofen- displaceable 3H-GABA binding was measured in autoradiograms for this screen. Second, the candidate populations had to generate spike-wave discharges (SWDs) during absence seizures in lh/lh mice; bipolar recording electrodes implanted into candidate neuronal structures were used in this screen. Third, the candidate populations had to demonstrate GABAB receptor-mediated regulation of absence seizures in lh/lh mice; microinjections of a GABAB agonist [(-)-baclofen] and antagonist (CGP 35348) were used for this screen. In this study we found that anterior ventral lateral thalamic nucleus (VLa), nucleus reticularis thalami (NRT), nucleus reuniens (RE) passed all three screens, and hence are members of the neural network in which GABAB receptors regulate absence seizures in lh/lh mice.
Injury-induced upregulation of bFGF and CNTF mRNAS in the rat retina
Authors: Wen R , Song Y , Cheng T , Matthes MT , Yasumura D , LaVail MM , Steinberg RH
Published: April 2018

Focal mechanical injury to the retina has been shown to slow or prevent photoreceptor degeneration near the lesion site in two animal models of retinal degeneration, inherited retinal dystrophy in the Royal College of Surgeons (RCS) and light damage in albino rats. Thus, when injured, the rat retina activates a self-protective mechanism to minimize damage. To identify injury responsive factors and cells, we examined the mRNAs for the following factors and some of their receptors: basic and acidic fibroblast growth factors (bFGF, aFGF) and FGF receptor-1 (FGFR1); ciliary neurotrophic factor (CNTF) and CNTF receptor alpha (CNTFR alpha); brain-derived neurotrophic factor (BDNF) and its receptor trkB; and insulin-like growth factor-1 (IGF-1) and IGFR-1 receptor (IGF-1R). After a single mechanical lesion to the subretinal space and retina, there was a substantial increase in bFGF and CNTF expression that persisted for the entire 10 d period of study. The increase in bFGF mRNA after injury was prompt and great in amplitude, while the elevation of CNTF mRNA was relatively slower. In addition, there was a transient increase in FGFR1 mRNA. In situ hybridizations showed that the elevation of bFGF and CNTF was localized to the vicinity of the lesion. The expression of GFAP (glial fibrillary acidic protein) mRNA also increased in response to injury. These findings strongly suggest that increases in endogenous bFGF and/or CNTF play key roles in injury-induced photoreceptor rescue.
Dye coupling between pyramidal neurons in developing rat prefrontal and frontal cortex is reduced by protein kinase A activation and dopamine
Authors: Rorig B , Klausa G , Sutor B
Published: April 2018

During early postnatal development, lamina II/III pyramidal cells in rat neocortex are extensively coupled via gap junctions. The factors regulating gap junction permeability, as well as the mechanisms underlying the developmental uncoupling process are not understood. To investigate the influence of protein kinase A-mediated phosphorylation on dye coupling in the developing neocortex, pyramidal cells in slices of rat frontal and prefrontal cortex were injected intracellularly with the tracer neurobiotin. Control injections revealed clusters of about 30 dye-coupled neurons. Preincubation with forskolin or direct activation of protein kinase A with Sp-cAMPS reduced the number of coupled cells by about 70%. A significant reduction in dye coupling was also observed following incubation with dopamine. Application of receptor selective agonists and antagonists revealed that the uncoupling was mediated by both dopamine D1 and D2 receptors. The protein kinase A inhibitor Rp-cAMPS reduced the effect of dopamine, suggesting that the neurotransmitter regulates gap junction permeability via protein kinase A activation. In the presence of either forskolin, Sp-cAMPS, or dopamine, neurons displayed a significantly higher input resistance compared to control conditions. During the second postnatal week, transient application of forskolin to single neurons reversibly increased input resistance. At later developmental stages when coupling incidence had declined, this action of forskolin was no longer observed. Our data demonstrate a dependence of gap junction permeability on protein kinase A activity and on dopamine receptor activation in developing rat neocortical neurons. These mechanisms may modulate junctional permeability during the period of circuit formation.
Reevaluation of the growth-permissive substrate properties of goldfish optic nerve myelin and myelin proteins
Authors: Wanner M , Lang DM , Bandtlow CE , Schwab ME , Bastmeyer M , Stuermer CA
Published: April 2018

To determine whether optic nerve myelin of goldfish carries mammalian- like neurite growth inhibitory proteins which can be neutralized by the antibody IN-1, myelin fractions of fish optic nerves were used as substrates for fish retinal ganglion cell axons and rat dorsal root ganglia (DRG). Axonal growth was monitored and compared with that of IN- 1 treated preparations. Growth of fish retinal axons and rat DRG neurites was substantial on goldfish optic nerve myelin and no improvement was observed with IN-1. In contrast, rat CNS myelin allowed only poor growth, and number of axons and length of DRG neurites increased significantly with IN-1. In addition, proteins of fish optic nerve myelin and bovine CNS myelin were extracted, reconstituted in liposomes and applied to growth cones. When goldfish myelin proteins in liposomes were seeded onto growth cones, 77% of fish and 89% of rat DRG growth cones continued to elongate, and the proportion of elongating fish growth cones (80%) did not significantly change when liposomes were pretreated with IN-1. But 73% of fish and 93% of rat growth cones collapsed with liposomes containing proteins from bovine CNS myelin. Upon IN-1 treatment, only 24% of fish growth cones collapsed. Thus, axon growth in vitro indicates that goldfish optic nerves, which permit successful axon regeneration in vivo, lack mammalian-like neurite growth inhibitors which are neutralized by IN-1.
Long-term potentiation of glutamatergic pathways in the lamprey brainstem
Authors: Alford S , Zompa I , Dubuc R
Published: April 2018

Plasticity of synaptic transmission has been investigated in the lamprey brainstem. In this preparation, neurons of the vestibular nuclei make monosynaptic connections to reticulospinal neurons of the posterior (PRRN) and middle (MRRN) rhombencephalic reticular nuclei. This glutamatergic projection shows a long-lasting enhancement in efficacy following a brief high frequency (50 Hz) train of stimuli (tetanus). Enhancement was found on the inputs from the octavomotorius intermediate (nOMI) and octavomotorius posterior (nOMP) nuclei to the reticulospinal neurons of the PRRN and MRRN, and persisted for the entire duration of the recordings. The enhancement was limited to the pathway that received tetanic stimulation for the inputs to any given reticulospinal neuron. It depended upon the activation of postsynaptic processes at least in part; dialysis of the reticulospinal neuron by recording with a whole-cell patch pipette prevented its induction. This dialysis-dependent abolition of enhancement was shown to be dependent on a change in Ca2+ concentration in the postsynaptic neuron. The enhancement was not affected by blockade of NMDA receptors with D,L-2- amino-5-phosphonopentanoate (AP5) but was prevented by the metabotropic glutamate receptor (mGluR) antagonist (R,S)-alpha-methyl-4- carboxyphenylglycine (MCPG). In conclusion, this study demonstrates that vestibular inputs to reticulospinal neurons are capable of undergoing long-term potentiation (LTP) and that this LTP shows synapse specificity. Furthermore, this LTP is activated by synaptic stimulation of a subtype of the m-GluR family and its induction is mediated by changing Ca2+ concentrations in the postsynaptic neuron.
Sympathetic axons pathfind successfully in the absence of target
Authors: Guidry G , Landis SC
Published: April 2018

To determine whether sympathetic axons require the presence of a peripheral target to grow to the correct destination, we examined the developing footpad innervation in tabby mutant mice which lack sweat glands. Despite the absence of sweat glands, noradrenergic sympathetic axons are transiently present in the presumptive target area and avoid the more distal epidermal/dermal domain occupied by sensory axons. Since sympathetic axon pathfinding was not dependent upon the target tissue, we compared the subsequent development of sweat gland axons in tabby footpads with that in control footpads. In wild-type mice, the gland-associated axonal plexus expands considerably as the secretory tubule enlarges and coils. This expansion, however, does not occur in tabby mice. The sweat gland innervation of wild-type mice loses catecholamines and acquires AChE activity and vasoactive intestinal peptide immunoreactivity. In tabby mutant mice, catecholaminergic fibers remain in the glandless footpads for 2 weeks and fail to acquire AChE or vasoactive intestinal peptide. In contrast to the altered development of gland innervation in tabby, the development of the innervation of footpad blood vessels was unaffected. Our observations indicate that the target is not required to direct sympathetic axons to the presumptive gland region of the footpad. In the absence of the target tissue, however, gland-targeted sympathetic axons retain an immature morphology and transmitter phenotype and then disappear.
Persistent activation of cAMP-dependent protein kinase by regulated proteolysis suggests a neuron-specific function of the ubiquitin system in Aplysia
Authors: Chain DG , Hegde AN , Yamamoto N , Liu-Marsh B , Schwartz JH
Published: April 2018

In response to the facilitating neurotransmitter serotonin (5-HT), the cAMP-dependent protein kinase (PKA) acquires a special mnemonic characteristic in Aplysia sensory neurons. PKA becomes persistently activated at basal cAMP concentrations owing to a decreased regulatory (R) to catalytic (C) subunit ratio. We previously implicated ubiquitin- mediated proteolysis in this selective loss of R. Here we show that ubiquitin (Ub), Ub-conjugates and proteasomes are present in cell bodies, axon, neuropil and nerve terminals of Aplysia neurons. Because R subunits are not decreased in muscle exposed to 5-HT, comparison of the two tissues provides a tractable approach to determine how the Ub pathway is regulated. We compared the structure of M1, the muscle- specific R isoform, to that of N4, a major neuronal R isoform, to rule out the possibility that the differences in their stability result from differences in structure. We present evidence that N4 and M1 are encoded by identical transcripts; they also behave similarly as protein substrates for the Ub pathway in extracts of the two tissues. Nervous tissue contains 20-times more free Ub, but we present evidence that the susceptibility of R subunits to degradation in neurons relative to muscle results from the greater capacity of neurons to degrade ubiquitinated proteins through the proteasome. Thus, factors that regulate the activity of proteasomes could underlie the enhanced degradation of R subunits in long-term sensitization.
Biphasic changes in locomotor behavior and in expression of mRNA for NGFI-A and NGFI-B in rat striatum following acute caffeine administration
Authors: Svenningsson P , Nomikos GG , Fredholm BB
Published: April 2018

The time course of expression of mRNA for NGFI-A and NGFI-B after a single intraperitoneal injection of saline or caffeine was examined using in situ hybridization. Administration of a high dose of caffeine (100 mg/kg) decreased locomotor behavior and increased NGFI-A and NGFI- B mRNA in the entire striatum. A lower dose of caffeine (50 mg/kg) caused a weak enhancement of both messages, which was confined to the lateral part of caudate-putamen. This dose increased horizontal, but not vertical, movement. In rats treated with the lowest dose of caffeine (25 mg/kg), the expression of both investigated genes tended to be lower than for saline-treated rats and both horizontal and vertical locomotor activity increased markedly. The reduction in the number of labeled neurons seemed to occur predominantly in enkephalin- containing neurons, which coexpress adenosine A2A receptors and dopamine D2 receptors. The decrease of mRNA for NGFI-A, NGFI-B, and jun B caused by caffeine (25 mg/kg) could be mimicked by the D2 agonist quinpirole (1 and 3 mg/kg). Moreover, caffeine could significantly decrease the expression seen following treatment with the D2 antagonist raclopride (2 mg/kg). In addition, in the parietal cortex, 25 mg/kg of caffeine caused a significant elevation of both examined immediate early genes. Thus, biphasic changes in locomotion induced by caffeine are paralleled by biphasic changes in mRNA for NGFI-A, NGFI-B, and jun B. The results also provide additional support for a functionally important interaction between adenosine and dopamine D2 receptors.
Junctional and extrajunctional glutamate receptor channels in Drosophila embryos and larvae
Authors: Nishikawa K , Kidokoro Y
Published: April 2018

Glutamate receptor channels in Drosophila embryos and larvae were examined with the patch-clamp technique in various configurations. In the cell-attached mode, only one type of channel was observed in the extrajunctional region at any stages. The burst duration histogram was fit with three exponentials. The burst duration of long component lengthened with increasing glutamate concentration. In excised outside- out patches the unitary channel current was 7.1 pA at -60 mV and direction of current reversed at zero membrane potential. In contrast, junctional receptor channels had different properties. In the whole- cell configuration, spontaneous synaptic currents with steps on the falling phase were observed. The step amplitudes had two discrete values of 9.4 and 18.5 pA at -60 mV, due to openings of junctional glutamate receptor channels. Synaptic currents changed amplitudes linearly with the membrane potential in the negative potential range but nonlinearly above zero. With 1 mM glutamate in the bath, synaptic currents were no longer observed. Instead, there were single channel events with the current amplitude varying between 8 and 12 pA at -60 mV. Their long burst duration depended on glutamate concentration indicating that they are glutamate receptor channel events. The extrapolated reversal potential of these channel currents was around +12 mV. These junctional receptor channels were strictly localized at the junction. Our findings suggest that the channel conversion mechanism in Drosophila is different from that observed in vertebrates. Further close examination of other intermediate steps during neuromuscular junction formation is needed.
Transiently selective activation of phosphoinositide turnover in layer V pyramidal neurons after specific mGluRs stimulation in rat somatosensory cortex during early postnatal development
Authors: Bevilacqua JA , Downes CP , Lowenstein PR
Published: April 2018

Biochemical analysis of muscarinic- and metabotropic-glutamate receptor stimulated phosphoinositide (PI) turnover in rat cortical preparations during the first three weeks of postnatal development indicates the existence of a transiently increased accumulation of labeled inositol polyphosphates during the first postnatal week (Gonzales and Crews, 1985; Dudek et al., 1989). We now report for first time the visualization of those neurons responding with increased PI turnover to glutamatergic or cholinergic-receptor stimulation in rat somatosensory cortex during early postnatal development utilizing a recently described method (Bevilacqua et al, 1994). Three, 7, 10, 14, and 21 d old rats were studied. Carbachol in the presence of lithium stimulates 3H-CMP-PA accumulation throughout the cortex at all ages studied. In comparison labeled neurons responding to t-ACPD in the presence of lithium were located exclusively in layer V at P3 and P7, but were found labeled throughout the cortex at P10. Given that glutamate and cholinergic agonist stimulation are both necessary but not sufficient for cortical plasticity to occur, and that muscarinic and mGluRs stimulation both induce a peak in PI turnover response during the same period of experience-dependent neocortical plasticity, PI derived second messengers signals might be involved in the regulation of the molecular mechanisms of neuronal plasticity. Furthermore, our results show the anatomical correlate of receptor-specific PI turnover activation, and indicate that specific agonist induced PI responses are age, and layer specific.
Directed expression of the growth-associated protein B-50/GAP-43 to olfactory neurons in transgenic mice results in changes in axon morphology and extraglomerular fiber growth
Authors: Holtmaat AJ , Dijkhuizen PA , Oestreicher AB , Romijn HJ , Van der Lugt NM , Berns A , Margolis FL , Gispen WH , Verhaagen J
Published: April 2018

B-50/GAP-43, a neural growth-associated phosphoprotein, is thought to play a role in neuronal plasticity and nerve fiber formation since it is expressed at high levels in developing and regenerating neurons and in growth cones. Using a construct containing the coding sequence of B- 50/GAP-43 under the control of regulatory elements of the olfactory marker protein (OMP) gene, transgenic mice were generated to study the effect of directed expression of B-50/GAP-43 in a class of neurons that does not normally express B-50/GAP-43, namely, mature OMP-positive olfactory neurons. Olfactory neurons have a limited lifespan and are replaced throughout adulthood by new neurons that migrate into the upper compartment of the epithelium following their formation from stem cells in the basal portion of this neuroepithelium. Thus, the primary olfactory pathway is exquisitely suited to examine a role of B-50/GAP- 43 in neuronal migration, lifespan, and nerve fiber growth. We find that B-50/GAP-43 expression in adult olfactory neurons results in numerous primary olfactory axons with enlarged endings preferentially located at the rim of individual glomeruli. Furthermore, ectopic olfactory nerve fibers in between the juxtaglomerular neurons or in close approximation to blood vessels were frequently observed. This suggests that expression of B-50/GAP-43 in mature olfactory neurons alters their response to signals in the bulb. Other parameters examined, that is, migration and lifespan of olfactory neurons are normal in B-50/GAP-43 transgenic mice. These observations provide direct in vivo evidence for a role of B-50/GAP-43 in nerve fiber formation and in the determination of the morphology of axons.
Multiple Shaker potassium channels in a primitive metazoan
Authors: Jegla T , Grigoriev N , Gallin WJ , Salkoff L , Spencer AN
Published: April 2018

Voltage-gated potassium channels are critical elements in providing functional diversity in nervous systems. The diversity of voltage-gated K+ channels in modern triploblastic metazoans (such as mollusks, arthropods and vertebrates) is provided primarily by four gene subfamilies (Shaker, Shal, Shab, and Shaw), but there has been no data from the ancient diploblastic metazoans until now. Diploblasts, represented by jellyfish and other coelenterates, arose during the first major metazoan radiation and are the most structurally primitive animals to have true nervous systems. By comparing the K+ channels of diploblasts and triploblasts, we may determine the fundamental set of K+ channels present in the first nervous systems. We now report the isolation of two Shaker subfamily cDNA clones, jShak1 and jShak2, from the hydrozoan jellyfish Polyorchis penicillatus (Phylum Cnidaria). JShak1 and jShak2 express transient outward currents in Xenopus oocytes most similar to Shaker currents from Drosophila in their rates of inactivation and recovery from inactivation. The finding of multiple Shaker subfamily genes is significant in that multiple Shaker genes also exist in mammals. In Drosophila, multiple Shaker channels are also produced, but by a mechanism of alternative splicing. Thus, the Shaker K+ channel subfamily had an established functional identity prior to the first major radiation of metazoans, and multiple forms of Shaker channels have been independently selected for in a wide range of metazoans.
A homeodomain protein selectively expressed in noradrenergic tissue regulates transcription of neurotransmitter biosynthetic genes
Authors: Zellmer E , Zhang Z , Greco D , Rhodes J , Cassel S , Lewis EJ
Published: April 2018

In order to characterize the specificity of expression of the neurotransmitter biosynthetic gene dopamine beta-hydroxylase (DBH), the identification of proteins that interact with the DB1 enhancer was initiated. A homeobox-containing cDNA was isolated from a PC12 expression cDNA library screened with the DB1 enhancer. The homeodomain is a member of the paired-like class, and is encoded by several nonidentical cDNAs. The cDNAs contain the same sequence in the homeodomain and 3′ coding and noncoding sequences, but diverge in sequence 5′ to the homeodomain. This family of homeobox-containing cDNAs is named Arix. Arix mRNA transcripts are found only in noradrenergic, DBH-positive tissues, and in cell lines derived from those tissue. The DB1 enhancer contains two binding sites for the Arix homeodomain, and both sites contribute to basal activity of the DBH promoter. When introduced into tissue culture, Arix regulates the transcriptional activity from the DBH promoter, and also from the promoter of the tyrosine hydroxylase gene, encoding the initial enzyme of the catecholamine biosynthetic pathway. The pattern of expression of the Arix transcripts, the presence of the homeodomain, and the transcriptional regulatory properties suggest that this family of proteins may be involved in the specificity of expression of the catecholamine biosynthetic genes.
Uncoupling of GABAA/benzodiazepine receptor alpha 1, beta 2, and gamma 2 subunit mRNA expression in cerebellar Purkinje cells of staggerer mutant mice
Authors: Luntz-Leybman V , Rotter A , Zdilar D , Frostholm A
Published: April 2018

The mammalian GABAA/benzodiazepine (GABAA/BZ) receptor is comprised of several subunit isoforms: alpha 1–6, beta 1–13, gamma 1–3 and delta. In the present studies, the expression of alpha 1, beta 2, and gamma 2 subunit mRNAs was examined in cerebellar Purkinje cells and deep cerebellar neurons of staggerer mutant mice during postnatal development. In control animals, the three subunit mRNAs were present at high density in Purkinje cells which, in adult animals, form a monolayer at the interface of the granule cell and molecular layers. The number of Purkinje cells in the staggerer cerebellar cortex is reduced; the majority of those that remain are retained within the granule cell layer and are unable to receive normal afferent synapses from granule cells. The three subunit mRNAs were ex pressed at similar levels in both staggerer and control Purkinje cells until postnatal day 9. After this time, although the alpha 1 subunit mRNA was maintained at control levels in staggerer Purkinje cells, the expression of beta 2 and gamma 2 subunit mRNAs decreased, and was largely absent by postnatal day 20. The loss of beta 2 and gamma 2 mRNA expression in staggerer was specific to Purkinje cells, since all three mRNAs were present throughout postnatal development in other brain regions, including the deep cerebellar nuclei. The present studies indicate that in cerebellar Purkinje cells, the GABAA/BZ receptor alpha 1, and beta 2, and gamma 2, subunit mRNAs are regulated by distinct mechanisms which are differentially affected by the staggerer mutation.
Peripheral target specification of synaptic connectivity of muscle spindle sensory neurons with spinal motoneurons
Authors: Wenner P , Frank E
Published: April 2018

The source of environmental cues determining the central connections of muscle sensory neurons was investigated by manipulating chick embryos so that sensory neurons supplied a duplicate set of dorsal thigh muscles. These neurons projected out ventral nerve pathways and along motor axons that normally project to ventral muscles but their ultimate target tissue was the duplicate set of dorsal muscles. The central connections of these sensory neurons to motoneurons supplying normal dorsal muscles were then determined with intracellular recordings in isolated spinal cord preparations. Sensory neurons supplying individual duplicate dorsal muscles made the same connections as those supplying the corresponding normal dorsal muscles; the pattern of these connections was different than that made by afferents supplying ventral muscles. Sensory neurons thus made synaptic connections appropriate for their target muscle rather than for their more proximal ventral environment. These findings suggest that the target muscle is the source of cues that determine the central connections of the sensory neurons projecting to it. Motoneurons forced to innervate novel muscle received many of the same sensory inputs they would normally receive, suggesting that motoneurons are less influenced by their target tissue than sensory neurons.
Axonal sprouting in layer V pyramidal neurons of chronically injured cerebral cortex
Authors: Salin P , Tseng GF , Hoffman S , Parada I , Prince DA
Published: April 2018

We performed experiments to determine whether axonal sprouting occurs in neurons of chronic neocortical epileptogenic lesions. Partially isolated somatosensory cortical islands with intact pial blood supply were prepared in mature rats. Neocortical slices from these lesions, studied 6–39 d later, generated spontaneous and/or evoked epileptiform field potentials (Prince and Tseng, 1993) during which neurons displayed prolonged polyphasic excitatory and inhibitory synaptic potentials/currents. Single electrophysiologically characterized layer V pyramidal neurons in control and epileptogenic slices were filled with biocytin using sharp and patch-electrode techniques, their axonal arbors reconstructed and compared quantitatively. Neurons in injured cortex had a 56% increase in total axonal length, a 64% increase in the number of axonal collaterals and more than a doubling (115% increase) of the number of axonal swellings. The presumed boutons were smaller and more closely spaced than those of control cells. In some neurons the main descending axon had hypertrophic segments from which branches arose. These highly significant changes were most marked in the perisomatic region of layer V. The axonal sprouting was associated with a decrease in somatic area but no significant change in dendritic arbors. Results suggest that a significant degree of axonal reorganization takes place in the chronically injured cortex where it might be an adaptive mechanism for recovery of function after injury, or might be maladaptive and play an important role in the generation of epileptiform events by increasing the numbers and density of synaptic contacts between neurons.
Expression and characterization of Aplysia protein kinase C: a negative regulatory role for the E region
Authors: Sossin WS , Fan X , Saberi F
Published: April 2018

The Aplysia nervous system contains two phorbol ester-activated protein kinase C isoforms, the Ca(2+)-activated Apl I and the Ca(2+)- independent Apl II. Short-term applications of the facilitatory transmitter serotonin (5-HT) activates Apl I, but not Apl II. In contrast, Apl II, but not Apl I, can form an autonomous kinase. To investigate the biochemical characteristics of the Aplysia kinases that might underlie their differential activation, we expressed Apl I, Apl II, and two derivatives of Apl II with deletions in the amino-terminal 150 amino acid E region in insect cells using the baculovirus system. Similar to nervous system extracts, expressed Apl II has more autonomous activity than Apl I. Removal of the E region lowered the amount of phosphatidylserine required for activation of Apl II, but did not remove the autonomous kinase activity. In addition, phosphatidylserine vesicles could sediment fusion proteins containing the E region, consistent with a role for the E region in lipid interactions. A partial deletion of the E region modifies activation of Apl II by phorbol esters and oleic acid, suggesting that in the intact enzyme the E region interacts with the phorbol ester-binding domain of the kinase. These results introduce a model whereby the E region acts as a negative regulator of Apl II activation and suggest that this inhibition may explain the inability of short-term applications of 5-HT to activate Apl II.