bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuropeptide Y mRNA and immunoreactivity in hypothalamic neuroendocrine neurons: effects of adrenalectomy and chronic osmotic stimulation
Authors: Larsen PJ , Mikkelsen JD , Jessop DS , Lightman SL , Chowdrey HS
Published: March 2018

Neuropeptide Y (NPY) coexists with vasopressin or oxytocin in magnocellular neurons of the hypothalamo-neurohypophysial tract. Using quantitative in situ hybridization histochemistry and immunohistochemistry, we have studied the effects of adrenalectomy and chronic osmotic stimulation, either alone or in combination, on NPY mRNA expression and NPY immunoreactivity in magnocellular neurons of the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, and arcuate nucleus (Arc). Adrenalectomy and chronic osmotic stimulation each increased NPY mRNA levels in magnocellular neurons of the PVN and SON, while the combination of both treatments had an additive effect. In the Arc, only the combination of adrenalectomy and chronic osmotic stimulation increased NPY mRNA levels. Chronic osmotic stimulation also resulted in a marked increase of NPY-immunoreactive magnocellular perikarya in the PVN and SON. In contrast, adrenalectomy had only minor effects on the number of NPY-immunoreactive magnocellular PVN/SON perikarya. Neither chronic osmotic stimulation nor adrenalectomy affected the number of NPY-immunoreactive Arc perikarya. However, adrenalectomy decreased the number of NPY-immunoreactive nerve terminals in the external zone of the median eminence, while chronic osmotic stimulation increased the number of immunoreactive nerve fibers in the internal zone of the median eminence. The present study provides evidence that adrenalectomy and chronic osmotic stimulation can separately influence NPY gene transcription in magnocellular hypothalamo-neurohypophysial neurons, while only the combined effect of adrenalectomy and chronic osmotic stimulation increases NPY mRNA expression in neurons of the Arc.
A PET study of visuospatial attention
Authors: Corbetta M , Miezin FM , Shulman GL , Petersen SE
Published: March 2018

Positron emission tomography (PET) was used to identify the neural systems involved in shifting spatial attention to visual stimuli in the left or right visual field along foveofugal or foveocentric directions. Psychophysical evidence indicated that stimuli at validly cued locations were responded to faster than stimuli at invalidly cued locations. Reaction times to invalid probes were faster when they were presented in the same than in the opposite direction of an ongoing attention movement. PET evidence indicated that superior parietal and superior frontal cortex were more active when attention was shifted to peripheral locations than when maintained at the center of gaze. Both regions encoded the visual field and not the direction of an attention shift. In the right superior parietal lobe, two distinct responses were localized for attention to left and right visual field. Finally, the superior parietal region was active when peripheral locations were selected on the basis of cognitive or sensory cues independent of the execution of an overt response. The frontal region was active only when responses were made to stimuli at selected peripheral locations. These findings indicate that parietal and frontal regions control different aspects of spatial selection. The functional asymmetry in superior parietal cortex may be relevant for the pathophysiology of unilateral neglect.
Visuospatial versus visuomotor activity in the premotor and prefrontal cortex of a primate
Authors: di Pellegrino G , Wise SP
Published: March 2018

When visuospatial stimuli instruct a limb movement, the stimulus can be said to have both sensory and sensorimotor aspects. We studied the premotor and prefrontal areas of a rhesus monkey in order to identify neuronal activity related to the motor (or instructional) aspects of such stimuli. A rhesus monkey chose limb-movement targets according to one of two rules: (1) visuospatial stimuli instructed and triggered a limb movement toward their locations or (2) identical stimuli triggered a movement toward a predetermined target regardless of their location. Gaze and head fixation assured that each stimulus appeared at a constant location in both retinocentric and craniocentric coordinates, as well as in allocentric space. The task required that the spatial location cued by certain stimuli had to be either remembered or attended after stimulus presentation and before movement. Thus, the visuospatial information presented under one rule differed from that presented under the other only in its motor (instructional) significance and not in its attentional, spatial, mnemonic, or strictly sensory aspects. We could thereby test and confirm the hypothesis that the motor significance of visuospatial cues should commonly affect neuronal activity in the premotor cortex, but less commonly do so in the prefrontal cortex.
Multiple types of calcium channels in acutely isolated rat neostriatal neurons
Authors: Hoehn K , Watson TW , MacVicar BA
Published: March 2018

Voltage-activated high- and low-threshold Ca2+ currents were studied using whole-cell voltage-clamp techniques and fura-2 fluorescence measurements of intracellular Ca2+ in neurons acutely isolated from rat neostriatum. High-threshold Ca2+ currents activated around -40 mV and were present in at least 95% of neostriatal neurons. The maximum current, 736 +/- 44 pA (mean +/- SEM, n = 141), was observed around 0 mV. In 70% of neurons, high-threshold Ca2+ currents exhibited both inactivating and noninactivating components. The majority of the high- threshold Ca2+ currents appeared to belong neither to the “L-type” nor the “N-type” classification, since omega-conotoxin (5 microM) decreased this current by only 29% and nimodipine (10 microM) decreased the noninactivating component of this current by only 17%. A low-threshold transient (T-type) Ca2+ current was observed in 40% of neurons. When both T-type and high-threshold Ca2+ currents were present, their maximum amplitudes were 78 +/- 7 pA and 800 +/- 57 pA, respectively (mean +/- SEM, n = 58). At a holding potential of -100 mV, the T-type Ca2+ current activated around -60 mV, with maximum current near -40 mV. Steady-state inactivation of the T-type Ca2+ current was observed at holding potentials positive to -125 mV, and the current was half- inactivated at -88 mV. Recovery from inactivation to 90% of maximum occurred within 800 msec. Mn2+ or Co2+ (3 mM) blocked both high- threshold and T-type Ca2+ currents, whereas Cd2+ (25 microM) or verapamil (50 microM and 150 microM) preferentially blocked high- threshold over T-type Ca2+ currents. In response to depolarization by 50 mM K+, fura-2 fluorescence measurements showed increased intracellular Ca2+ in both the soma and the proximal dendrites of neostriatal neurons that was markedly reduced by 25 microM Cd2+. These findings suggest that high-threshold Ca channels are present in both the soma and proximal dendrites of neostriatal neurons.
Catecholaminergic cell lines from the brain and adrenal glands of tyrosine hydroxylase-SV40 T antigen transgenic mice
Authors: Suri C , Fung BP , Tischler AS , Chikaraishi DM
Published: March 2018

Brain (CATH.a) and adrenal (PATH.1 and PATH.2) cell lines have been established that synthesize abundant dopamine and norepinephrine and express the appropriate catecholaminergic biosynthetic enzymes, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase. The lines were derived from TH-positive tumors in transgenic mice carrying the SV40 T antigen oncogene under the transcriptional control of 773 base pairs of 5′ flanking sequences from the rat TH gene. Although the lines continue to express T antigen, they exhibit neuronal properties such as neurofilaments and synaptophysin and lack glial intermediate filaments. Although in vivo TH is only expressed in postmitotic neurons in the CNS, the CATH.a line demonstrates that TH expression and continued cell division are not incompatible after oncogenic transformation.
Calcium influx and protein phosphorylation mediate the metabolic stabilization of synaptic acetylcholine receptors in muscle
Authors: Caroni P , Rotzler S , Britt JC , Brenner HR
Published: March 2018

During neuromuscular synapse development, the degradation rate of ACh receptors (AChRs) accumulated in the synaptic portion of the muscle membrane is drastically reduced under neural control, their half-life t1/2 increasing from 1 d to about 12 d. Recent evidence suggests that the metabolic stability of synaptic AChRs is mediated by the muscle activity induced by the nerve. We have now investigated the pathway linking muscle activity and metabolic stabilization of synaptic AChRs in organ cultured rat muscle. Soleus and diaphragm muscles were denervated for 14-40 d, a procedure leading to the destabilization of synaptic AChRs, and conditions required to restabilize synaptic AChRs in the denervated muscle were analyzed. The activity-dependent stabilization of synaptic AChRs in chronically denervated endplates required calcium entry through dihydropyridine-sensitive Ca2+ channels activated by high-frequency stimulation for approximately 6 hr and was specific for synaptic AChRs. As in vivo, extrasynaptic AChRs were not stabilized, and their t1/2 remained 1 d. The stabilization process was not dependent on de novo protein synthesis, and it could also be brought about by elevated cAMP levels. Furthermore, it required shorter stimulation periods in the presence of the phosphatase inhibitors okadaic acid and calyculin A, whereas blockade of protein kinases with high doses of staurosporine blocked the stabilization. Activity- dependent, dihydropyridine-sensitive as well as cAMP-dependent phosphorylation of myosin light chain was observed. These findings are consistent with the notion that muscle activity initiates AChR stabilization via the activation of calcium-dependent protein phosphorylation reactions.
Aggregation of sodium channels during development and maturation of the neuromuscular junction
Authors: Lupa MT , Krzemien DM , Schaller KL , Caldwell JH
Published: March 2018

The voltage-activated Na channel (NaCh) is an integral membrane protein that is enriched at the neuromuscular end plate. Using loose-patch voltage-clamp and immunofluorescence, we have found that the aggregation of NaChs occurs late, during maturation of the neuromuscular junction. A decline in expression of embryonic NaCh mRNA and increase in adult NaCh mRNA precedes the onset of aggregation, and the appearance of functional adult NaChs coincides with NaCh aggregation. We tested the possibility that only the adult NaCh subtype could aggregate during development and found that both the embryonic and adult isoforms become concentrated at the synapse. The NaCh is the first postsynaptic membrane protein shown to become clustered postnatally, and the mechanism producing this aggregation appears to be different from the process producing aggregation of other synaptic proteins.
Clonal patterns of cell proliferation, migration, and dispersal in the brainstem of the chicken embryo
Authors: Hemond SG , Glover JC
Published: March 2018

Retroviral-mediated gene transfer was used to study clonal patterns of proliferation, migration, and dispersal in the brainstem of the chicken embryo. Clones were generated at stages 13–17 (Hamburger and Hamilton, 1951), a period of neurogenesis in the brainstem neural tube subsequent to the formation of rhombomeres. Clones were examined in separate experiments at stages 24–27, when many neurons migrate and differentiate; at stages 28–29, when brainstem nuclei begin to form; and at stages 34–35, when brainstem nuclei are fully formed. Stages 24– 29 are characterized by a general variability in proliferative kinetics and migratory behavior. Clone sizes range from 1 to 29 cells, and migration patterns range from strictly radial (i.e., normal to the ventricular surface) to combined radial and tangential (i.e., perpendicular to the radial component). There is, however, an underlying systematic variation: (1) clones exhibiting tangential migration contain on average more cells than clones exhibiting only radial migration, and (2) the proportion of tangentially migrating clones increases from medial to lateral. By stages 34–35 some individual clones have apparently dispersed to disparate neuronal groups. The regional diversity observed among clones suggests that position along the mediolateral axis may determine the proliferative potential of progenitors and the migratory behavior and subsequent dispersal of their descendants.
Assembly of GABAA receptor subunits: alpha 1 beta 1 and alpha 1 beta 1 gamma 2S subunits produce unique ion channels with dissimilar single- channel properties
Authors: Angelotti TP , Macdonald RL
Published: March 2018

Recent experimental evidence has led to the hypothesis that GABAA receptor channel (GABAR) heterogeneity or receptor channel subtypes may occur by differential assembly of a given set of subunits into various configurations. Alternatively, assembly of subunits into mature GABARs may arise from an ordered process to produce a preferred form of the receptor channel, as seen for nicotinic ACh receptors. In the preceding article, we demonstrated that transient expression of GABAR alpha 1 and beta 1 subunits in mouse L929 fibroblast cells produced two different types of GABARs, when coexpressed with and without the gamma 2S subunit. Not only did these GABARs differ in their GABA and diazepam pharmacology, but initial single-channel recordings suggested that the two types of GABARs (alpha 1 beta 1 and alpha 1 beta 1 gamma 2S) had different conductance and gating properties. It also appeared that alpha 1 beta 1 gamma 2S GABARs were preferentially formed over alpha 1 beta 1 GABARs, but it was not completely shown if both forms of GABARs were produced when a cell expressed all three subunits. To characterize further the assembly process and determine the preferred form, if it existed, it was necessary to obtain a kinetic “fingerprint” for both alpha 1 beta 1 and alpha 1 beta 1 gamma 2S GABARs. Thus, single-channel patch-clamp recording and kinetic analysis of receptor channel gating were performed. For both alpha 1 beta 1 and alpha 1 beta 1 gamma 2S GABARs, GABA evoked single-channel openings to both a main conductance (15 and 29 pS, respectively) and a subconductance level (10 and 21 pS, respectively) with greater than 90% of the total current through the main conductance level openings. The two GABAR populations were further differentiated by their open and burst properties. On average, alpha 1 beta 1 gamma 2S GABARs opened for almost three times the duration as alpha 1 beta 1 GABARs (6.0 vs 2.3 msec, respectively) and had three openings per burst. alpha 1 beta 1 GABARs opened predominantly as single opening bursts. Using the conductance and gating properties to differentiate the two GABAR populations, we determined that alpha 1 beta 1 GABARs were rarely, if ever, formed upon coexpression of all three subunits, suggesting that alpha 1 beta 1 gamma 2S GABARs were the preferred final form of the receptor channel. Also, the homogeneity of the conductance and gating properties of alpha 1 beta 1 gamma 2S GABARs among the different patches studied implied that a single preferred configuration of GABARs may exist.(ABSTRACT TRUNCATED AT 400 WORDS)
Dorsolateral prefrontal lesions and oculomotor delayed-response performance: evidence for mnemonic "scotomas"
Authors: Funahashi S , Bruce CJ , Goldman-Rakic PS
Published: March 2018

The spatial memory functions of the monkey's prefrontal cortex were examined with oculomotor delayed-response (ODR) paradigms that required the animal to remember the spatial location of peripheral visual cues, while maintaining fixation on a central visual target during the presentation of each cue and during a subsequent 1.5–8 sec delay period. Four rhesus monkeys received unilateral or serial prefrontal lesions in and around the principal sulcus after they reached criterion performance on the ODR tasks. Unilateral lesions disrupted the performance of memory-guided eye movements to spatial cues in the visual field contralateral to the hemisphere in which the lesion was placed. Memory-guided eye movements to ipsilateral cues were mildly affected by unilateral lesions, and these lesions had little or no effect on performance in visually guided control tasks. With addition of a second lesion in the opposite hemisphere, the deficit was extended to include the opposite hemifield. The impairment was characterized by eye movements of inappropriate direction, and, excepting the one lesion that extended into the frontal eye field region of the arcuate sulcus, saccadic reaction times and velocities were the same before and after the lesions. The effect of the lesions was delay dependent: performance was rarely altered at the shortest (1.5 sec) delay but became progressively worse as the delay period was lengthened. The present results strengthen the evidence that the delayed-response deficits of monkeys with prefrontal lesions are caused by failure to maintain a transient memory “trace” in working memory, and indicate for the first time that working memory mechanisms are lateralized: memories for visuo- spatial coordinates in each hemifield are processed primarily in the contralateral prefrontal cortex. These findings provide evidence for the concept of mnemonic hemianopias and mnemonic scotomas, that is, memory deficits for particular hemifields or visual field locations, unaccompanied by simple sensory or motor deficits.
Developmental expression of TERM-1 glycoprotein on growth cones and terminal arbors of individual identified neurons in the grasshopper
Authors: Meier T , Therianos S , Zacharias D , Reichert H
Published: March 2018

The chemoaffinity theory postulates the existence of cell-specific molecular signals that uniquely identify individual developing neurons. Such molecules are thought to promote both accurate axon outgrowth and the formation of correct synaptic connections. To identify candidates for such neuron-specific recognition molecules, we generated monoclonal antibodies that recognize surface-associated antigens expressed by individual identified neurons in the grasshopper embryo. Here we report on a molecular label that is expressed exclusively by two pairs of sibling interneurons in the developing CNS. Our experiments indicate that during axogenesis, this molecule is expressed at the surface of the growth cones of these cells, while during subsequent synaptogenesis, it becomes concentrated at the cells' developing terminal arbors. In both cases the molecule appears to be secreted by the labeled structures. This molecule, which we call TERM-1, is a glycoprotein with a molecular weight of approximately 48 kDa. The highly restricted spatiotemporal expression pattern of TERM-1 implies that individual developing neurons can acquire and retain unique molecular labels that may be important for neuron-specific outgrowth and target recognition.
Recoverable and nonrecoverable deficits in conditioned responses after cerebellar cortical lesions
Authors: Harvey JA , Welsh JP , Yeo CH , Romano AG
Published: March 2018

This study reexamined the effects of unilateral damage to cerebellar hemispheral lobule VI on the rabbit's conditioned nictitating membrane (NM) response. Extensive unilateral removal of hemispheral lobule VI in 11 rabbits impaired ipsilateral conditioned responses as reflected by reductions of 52% in mean frequency and 53% in mean amplitude during test trials on the first postoperative session. The decreases in the amplitude and frequency of conditioned responses were highly correlated (r = 0.82). The frequency of conditioned responses recovered to control levels but their amplitudes remained reduced such that the correlation between these two measures of responding was no longer significant by the 12th postoperative conditioning session. The decrease in the amplitude of conditioned responses was not accompanied by changes in onset latency or rise time. There was no significant impairment of conditioned responses in surgical controls and animals with only partial damage to hemispheral lobule VI. It was concluded that hemispheral lobule VI plays an important role in the regulation of motor centers in the brainstem so as to facilitate the initiation and optimum execution of the conditioned NM reflex. This cortical regulation of the conditioned NM response may contain learned elements; however, these cannot be resolved with lesion methods, nor has their existence been proven in this or other lesion studies. Nevertheless, the results of this study do demonstrate that the cerebellar cortex cannot be considered as the single locus necessary for NM conditioning.
Developmental cues modulate GABAA receptor subunit mRNA expression in cultured cerebellar granule neurons
Authors: Beattie CE , Siegel RE
Published: March 2018

The developmental expression of mRNAs encoding the GABAA receptor was analyzed in the rat cerebellar cortex and in cultured cerebellar granule neurons. Our studies in vivo reveal that the alpha 1-, beta 2-, and gamma 2-subunit mRNA levels in the cerebellar cortex rise dramatically during the second post-natal week, a period temporally correlated with extensive cerebellar maturation. To determine if these increases were preprogrammed or dependent on extrinsic factors, we examined subunit mRNA expression in granule cell cultures prepared at embryonic day 19 (E19) and postnatal day 10 (P10), immature and mature stages of cerebellar development, respectively. In E19 cultures, the alpha 1, beta 2, and gamma 2 GABAA receptor subunit mRNAs were present and their levels remained constant over the 21 d culture period. These results suggest that GABAA receptor gene expression is not intrinsic to the immature granule cells. A different pattern was found in P10 cultures where the three subunit mRNAs were initially present at levels approximately sixfold higher than those found at E19. The beta 2- and gamma 2-subunit mRNAs remained constant for 4 d and then increased sixfold between 4 and 7 d in culture. The magnitude and time course of these increases were similar to the developmental changes that occurred in vivo. Thus, our findings raise the possibility that signals encountered during development are necessary to induce GABAA receptor subunit mRNA expression. Moreover, these cues have been received by granule neurons prior to P10.(ABSTRACT TRUNCATED AT 250 WORDS)
Expression of AMPA-selective glutamate receptor subunits in morphologically defined neurons of the mammalian cochlear nucleus
Authors: Hunter C , Petralia RS , Vu T , Wenthold RJ
Published: March 2018

Glutamate and related amino acids mediate fast excitatory neurotransmission in the vertebrate CNS via ligand-gated cationic channels in the neuronal membrane. These channels are composed of different subunits that assemble into a functional receptor/channel complex. Although studies have shown that these subunits are differentially expressed in neurons, few studies have quantitatively addressed the cell-specific expression of glutamate subunits in relation to known glutamatergic pathways. In the vertebrate auditory system, glutamate is the proposed neurotransmitter of the auditory nerve and parallel fiber pathways. In situ hybridization histochemistry was used to localize AMPA-selective glutamate receptor subunit mRNAs in seven cell types of the rat cochlear nucleus. GluR1-GluR4 AMPA- selective subunits were all expressed in cochlear nucleus neurons; however, the subunits expressed in identified cells varied with the cell type. Granule cells, previously not known to receive glutamatergic input, expressed GluR2 and GluR4 subunits. Cartwheel and stellate interneurons in the dorsal cochlear nucleus, which receive parallel fiber input, expressed all four subunits. Neurons receiving synaptic input from the auditory nerve, including globular, round, spherical, and fusiform cells, expressed GluR2, GluR3, and GluR4 subunits. Furthermore, a subpopulation of round cells in the ventral cochlear nucleus, and fusiform cells in the dorsal cochlear nucleus, expressed the GluR3 subunit at greatly reduced levels compared to neighboring cells. The results confirm the auditory nerve and parallel fiber pathways as glutamatergic and identify a third synaptic population, projecting to granule cells, which is likely glutamatergic. The data suggest that the composition of GluR1-GluR4 subunits on neurons in the cochlear nucleus may be related to presynaptic input; moreover, heterogeneous patterns of expression of the GluR3 subunit, in addition, suggest that variability in mRNA levels within one population of morphologically defined cells is present.
Alpha-bungarotoxin binding to hippocampal interneurons: immunocytochemical characterization and effects on growth factor expression
Authors: Freedman R , Wetmore C , Stromberg I , Leonard S , Olson L
Published: March 2018

The nicotinic cholinergic antagonist alpha-bungarotoxin (alpha-BT) binds throughout the rat hippocampal formation. The binding is displaceable by d-tubocurarine. The most heavily labeled cells are GABA- containing interneurons in the dentate and in Ammon's horn. These neurons have several different morphologies and contain several neuropeptides. alpha-BT-labeled interneurons in the dentate are small cells between the granular and molecular layers that often contain neuropeptide Y. alpha-BT-labeled interneurons in CA1 are medium-sized interneurons, occasionally found in stratum pyramidale, but more often found in stratum radiatum and stratum lacunosum moleculare. These neurons often contain cholecystokinin. The largest alpha-BT-labeled interneurons are found in CA3, in both stratum radiatum and stratum lucidum. These neurons are multipolar and frequently are autofluorescent. They often contain somatostatin or cholecystokinin. These large interneurons have been found to receive medial septal innervation and may also have projections that provide inhibitory feedback directly to the medial septal nucleus. The cholinergic innervation of the hippocampus from the medial septal nucleus is under the trophic regulation of NGF and brain-derived neurotrophic factor, even in adult life. Expression of mRNA for both these factors is increased in CA3 and the dentate after intraventricular administration of alpha-BT, but not after administration of the muscarinic antagonist atropine. alpha-BT-sensitive cholinergic receptors on inhibitory interneurons may be critical to medial septal regulation of the hippocampal activity, including the habituation of response to sensory input.
Na+ channel immunolocalization in peripheral mammalian axons and changes following nerve injury and neuroma formation
Authors: Devor M , Govrin-Lippmann R , Angelides K
Published: March 2018

Nerve injury frequently triggers hyperexcitability and the ectopic initiation of impulses in primary afferent axons. An important consequence is neuropathic paresthesias and pain. Electrogenesis in normal afferents depends on appropriate Na+ channel concentrations. Therefore, we have asked whether injury might trigger changes in axolemmal Na+ channel distribution that could account for neuropathic hyperexcitability. We used an Na+ channel-specific antibody, 7493, to immunolocalize Na+ channels ultrastructurally in membranes of normal rat axons, and to assess remodeling following nerve section and neuroma formation. Selective labeling of nodal axolemma and, more weakly, of Schwann cell membrane, confirmed the efficacy of our immunolabeling protocol. In neuromas at postoperative times associated with peak ectopic activity, we found clear evidence of Na+ channel accumulation. Specifically, soon after myelin was stripped from large-diameter axons, the exposed, formerly internodal axolemma became immunopositive. Small- diameter unmyelinated axons and axon sprouts in the neuroma were also marked with 7493 IgG. Activated phagocytic macrophages and endothelial cells were 7493 negative. Both large- and small-diameter axons in neuromas end in swollen, organelle-packed “end bulbs.” Most, but not all, of these acquired Na+ channel immunolabeling. We propose that remodeling results from a modification of the normal process of Na+ channel turnover in neural membranes. Na+ channel protein accumulates in preterminal axolemma and neuroma end bulbs due to a combination of permissive factors (especially myelin removal) and promotional factors (removal of normal downstream targets). This accumulation is a likely precursor of afferent hyperexcitability in injured nerve.
Somatostatin inhibition of hippocampal CA1 pyramidal neurons: mediation by arachidonic acid and its metabolites
Authors: Schweitzer P , Madamba S , Champagnat J , Siggins GR
Published: March 2018

We used electrophysiological methods in a slice preparation to study the mechanisms of somatostatin (SS) effects on hippocampal pyramidal neurons. SS hyperpolarizes hippocampal pyramidal neurons in part by augmenting the time- and voltage-dependent M-current (IM), which has been shown to be reduced by muscarinic agonists. The SS effects are abolished by the phospholipase A2 inhibitors 4-bromophenacyl bromide and quinacrine. Arachidonic acid (AA) mimics all the effects of SS on hippocampal pyramidal neurons. The effects of AA and SS on IM are blocked by the lipoxygenase inhibitor nordihydroguaiaretic acid but not by the cyclooxygenase inhibitor indomethacin. Prostaglandins E2, F2 alpha, and I2 do not increase IM. However, the specific 5-lipoxygenase inhibitors 5,6-methanoleukotriene A4 methylester and 5,6- dehydroarachidonic acid both blocked the IM-augmenting action of either SS or AA. Leukotriene C4 (but not leukotriene B4) increases IM to the same extent as AA. IM was not altered by the 12-lipoxygenase product 12- hydroperoxyeicosatetraenoic acid, and SS effects were not altered by the 12-lipoxygenase inhibitor baicalein. These data implicate 5- lipoxygenase metabolite(s) (probably leukotriene C4) as a mediator for the IM-augmenting effect of SS. In addition, when the IM effect is blocked by lipoxygenase inhibitors, both SS and AA elicit another outward current that is not blocked by either lipoxygenase or cyclooxygenase inhibitors, suggesting a direct role of AA itself distinct from the IM effect. SS did not alter significantly Ca(2+)- dependent action potentials or, in whole-cell recordings, inward currents likely to represent high-threshold Ca2+ currents. The combined results of these studies suggest that SS hyperpolarizes hippocampal neurons by two mechanisms, both mediated through the AA system. However, one mechanism (IM) involves a metabolite of AA and is most effective at slightly depolarized potentials, whereas the other may involve AA itself and be more effective at membrane potentials near rest.
GABA shapes sensitivity to interaural intensity disparities in the mustache bat's inferior colliculus: implications for encoding sound location
Authors: Park TJ , Pollak GD
Published: March 2018

This study examined how GABAergic inhibition affected binaural properties of neurons in the mustache bat's inferior colliculus. Evaluations were made by documenting changes in acoustically evoked inhibition that occurred when GABAergic inputs were reversibly blocked by iontophoretic application of the GABAA antagonist bicuculline. We studied neurons sensitive to interaural intensity disparities (IIDs), since these are the principal cues animals use to localize high- frequency sounds. Neurons sensitive to these cues receive excitation from one ear and inhibition from the other ear, and are called EI neurons. Recordings focused on the EI region in the hypertrophied 60 kHz isofrequency contour, where the sensitivities of the EI cells to IIDs are systematically ordered, thereby creating a map of IID sensitivity. EI neurons were classified on the basis of their IID functions, of which there were two principal types. Seventy percent of the cells had conventional IID functions where the firing rate evoked by a fixed intensity at the contralateral (excitatory) ear remained constant with low intensities at the ipsilateral (inhibitory) ear and then declined progressively as the intensity at the ipsilateral ear increased. We refer to cells that had this type of IID function simply as EI neurons. The IID functions in the remaining 30% of the cells showed binaural facilitation and were classified as EI/f neurons. In these cells, increasing sound intensity at the ipsilateral (inhibitory) ear when the intensity at the contralateral (excitatory) ear was fixed, initially caused the firing rate to increase by at least 25% above the rate evoked by the sound at the contralateral ear alone. Additional intensity increases at the ipsilateral ear then resulted in a marked decline in response rate. We examined the effects of bicuculline on three binaural properties: (1) the degree of inhibition evoked by the ipsilateral ear (the maximum inhibition), (2) the IID at which the unit's discharge rate declined by 50% (the 50% point), and (3) binaural facilitation. There are three main findings. First, bicuculline substantially reduced or eliminated the inhibition evoked by the ipsilateral ear in about 40% of the cells. In the other 60% of the cells, bicuculline had little or no effect on the magnitude of the ipsilaterally evoked inhibition. The second finding is that in more than half of the cells in which there was little or no reduction in the magnitude of the ipsilaterally evoked inhibition, bicuculline changed the IID at which the ipsilaterally evoked inhibition caused the discharge rate to decline by 50%.(ABSTRACT TRUNCATED AT 400 WORDS)
The contribution of NMDA and non-NMDA receptors to fast and slow transmission of sensory information in the rat SI barrel cortex
Authors: Armstrong-James M , Welker E , Callahan CA
Published: March 2018

The main objective of this study was to establish the contribution of NMDA receptors to natural processing of somatosensory information within rat SI barrel cortex. Responses of 52 cells in layers I-IV of the rat barrel cortex were analyzed by PSTH (peristimulus histogram) analysis of evoked spikes in reply to brief deflections of the principal whisker in animals anesthetized with urethane. Short and longer peak latency responses within PSTHs were compared in the presence and absence of the specific NMDA and non-NMDA antagonists D(-)- 2-amino-5-phosphonovaleric acid and 6,7-dinitroquinoxaline-2,3-dione, which were administered locally to neurons by iontophoresis and additionally tested against their putative specific agonists, NMDA and quisqualate, respectively. The results suggest the following. (1) The generation of most spikes from cells in layers I-IV is dependent upon activation of NMDA receptors. However, NMDA receptors do not contribute to responses at very short latencies commensurate with monosynaptic thalamocortical relay for layer IV cells. These appear to be entirely mediated through non-NMDA receptors. (2) In the absence of transmission through NMDA receptors, non-NMDA receptors do not generate significant spike activity in later (10–100 msec latency) discharges. (3) NMDA receptor participation in first spike generation is directly dependent upon the latency of response of the cell to principal whisker deflection. (4) Latency of response, non-NMDA receptor-mediated spike generation and laminar location were powerfully covariant. (5) In addition, it was found that cells exhibiting short-duration spikes ( < 0.7 msec; “fast-spike units”) in layer IV responded powerfully at short latencies, first spikes being entirely dependent upon non-NMDA but not NMDA receptor action, later spikes (10–100 msec poststimulus) being > 80% dependent upon NMDA receptor action. It is concluded that most sensorially driven spike activity in layers I-IV is dependent upon NMDA receptor action. This appears to be enabled by contingent subthreshold depolarization largely through non-NMDA receptor action, whereas the earliest thalamocortical discharges are evoked solely through non-NMDA receptors.
Sites of microtubule stabilization for the axon
Authors: Baas PW , Ahmad FJ , Pienkowski TP , Brown A , Black MM
Published: March 2018

We have sought to determine the principal site(s) in the neuron where axonal microtubules (MTs) are stabilized. To accomplish this, we compared the proximal and distal regions of the axon and the axon shaft with regard to their content of newly stabilized MT polymer, using the following criteria. Stable polymer was identified by its resistance to nocodazole, and newly stabilized polymer was distinguished from older stable polymer by the staining of the former but not the latter for tyrosinated alpha-tubulin. Our results indicate that roughly 36.4%, 5.4%, and 2.4% of the total MT mass in the proximal and distal regions of the axon and the axon shaft is newly stabilized, respectively. Thus, while MT stabilization occurs throughout the axon, the proximal region is by far the most active with regard to this process.
Short-term changes in the numerical density of synapses in the intermediate and medial hyperstriatum ventrale following one-trial passive avoidance training in the chick
Authors: Doubell TP , Stewart MG
Published: March 2018

Previous ultrastructural studies using stereological counting techniques, based on assumptions regarding shape, size, and orientation of synapses, have suggested synaptic remodeling occurred at least 24 hr after one-trial passive avoidance training in day-old chicks. The present study estimates the mean synaptic density (Nv syn) in a region of the chick forebrain known to be involved in memory formation, the intermediate and medial hyperstriatum ventrale (IMHV), 1 and 24 hr following one-trial passive avoidance training. A stereological technique, the “disector,” that makes no assumptions about size, shape, and orientation of synapses was used in the synaptic analyses. The density of axospinous synapses increased by approximately 77% at 1 hr posttraining in the right IMHV of chicks (M-trained) that learned to avoid a bitter-tasting bead, compared to those (W-trained controls) that peck a water-coated bead. A measure of the postsynaptic density size, the mean projected height of synapses (H), was 57% smaller 1 hr posttraining in the right IMHV of M-trained chicks. These differences were not found at 24 hr posttraining. We suggest that structural modification of synapses may be a key part of the processes involved in short-term memory formation.
Cellular localizations of AMPA glutamate receptors within the basal forebrain magnocellular complex of rat and monkey
Authors: Martin LJ , Blackstone CD , Levey AI , Huganir RL , Price DL
Published: March 2018

The cellular distributions of alpha-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid (AMPA) receptors within the rodent and nonhuman primate basal forebrain magnocellular complex (BFMC) were demonstrated immunocytochemically using anti-peptide antibodies that recognize glutamate receptor (GluR) subunit proteins (i.e., GluR1, GluR4, and a conserved region of GluR2, GluR3, and GluR4c). In both species, many large GluR1-positive neuronal perikarya and aspiny dendrites are present within the medial septal nucleus, the nucleus of the diagonal band of Broca, and the nucleus basalis of Meynert. In this population of neurons in rat and monkey, GluR2/3/4c and GluR4 immunoreactivities are less abundant than GluR1 immunoreactivity. In rat, GluR1 does not colocalize with ChAT, but, within many neurons, GluR1 does colocalize with GABA, glutamic acid decarboxylase (GAD), and parvalbumin immunoreactivities. GluR1- and GABA/GAD-positive neurons intermingle extensively with ChAT-positive neurons. In monkey, however, most GluR1-immunoreactive neurons express ChAT and calbindin-D28 immunoreactivities. The results reveal that noncholinergic GABAergic neurons, within the BFMC of rat, express AMPA receptors, whereas cholinergic neurons in the BFMC of monkey express AMPA receptors. Thus, the cellular localizations of the AMPA subtype of GluR are different within the BFMC of rat and monkey, suggesting that excitatory synaptic regulation of distinct subsets of BFMC neurons may differ among species. We conclude that, in the rodent, BFMC GABAergic neurons receive glutamatergic inputs, whereas cholinergic neurons either do not receive glutamatergic synapses or utilize GluR subtypes other than AMPA receptors. In contrast, in primate, basal forebrain cholinergic neurons are innervated directly by glutamatergic afferents and utilize AMPA receptors.
Adult-type glycine receptors form clusters on embryonic rat spinal cord neurons developing in vitro
Authors: St John PA , Stephens SL
Published: March 2018

The time course of development and the cellular and subcellular distributions of adult-type, strychnine-binding glycine receptors (GlyRs) were examined on rat spinal cord neurons in vitro using both the GlyR antagonist strychnine and a specific antibody against the receptor. Spinal cord neurons in vivo had no detectable adult-type GlyRs at embryonic day 14, the age used to establish cell cultures. After being placed in culture, neurons continued for several days to show no expression of adult-type GlyRs. This contrasted with the observation that these neurons began to express receptors for substance P within 24 hr in culture. Beginning after 5–7 d in culture, however, neurons began to express adult-type GlyRs on their surfaces, and the number of such receptors increased abruptly thereafter. Ultimately, about 80% of the neurons in heterogeneous spinal cord cultures came to express adult-type GlyRs, with all of them beginning to express the GlyRs at approximately the same time. The subcellular distribution of adult-type GlyRs on neurons was observed by fluorescence microscopy using both anti-GlyR antibody and a fluorescent derivative of strychnine. On neurons that had been in culture for more than 10 d, GlyRs were localized in focal clusters, or aggregates, that were distributed over both cell bodies and neurites. The apparent location of these clusters on the cell surface was confirmed by the observation that GlyRs could be labeled with the antibody on living neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of neuromuscular transmission by conventional and peptide transmitters released from excitatory and inhibitory motor neurons in Aplysia
Authors: Church PJ , Whim MD , Lloyd PE
Published: March 2018

The anterior portion of intrinsic buccal muscle (I3a) is innervated by two excitatory motor neurons, B3 and B38, and the newly identified inhibitory motor neuron, B47. We show that B47 is cholinergic while B3 and B38 are not. B3 and B38 have previously been shown to express the neuropeptides FMRFamide and the small cardioactive peptides (SCPs) A and B, respectively. We present evidence here that B47 synthesizes the neuropeptide myomodulin A (Mma). When placed in culture, B3, B38, and B47 continued to synthesize their respective peptides. These peptides were released in a stimulation- and Ca(2+)-dependent manner, suggesting that they are transmitters in these neurons. By using B3-evoked excitatory junction potentials (EJPs) and muscle contractions as assays, we next examined the modulatory effects of superfusion of peptides and stimulation of motor neurons B38 and B47. Superfusing the muscle with low concentrations of the SCPs, FMRFamide, or Mma enhanced B3-evoked EJPs and contractions. Stimulation of B47 simultaneously with B3 reduced the amplitude of B3-evoked contractions. However, when either B47 or B38 was stimulated in extended bursts designed to release their peptide transmitters, subsequent B3-evoked EJPs and contractions were enhanced. We believe that this modulation is due at least in part to the release of peptides from the terminals of B38 and B47. The SCPs potently increase cAMP levels in I3a muscle fibers. Likewise, stimulation of B38 in extended bursts increased cAMP levels in the muscle. This provides independent evidence that the SCPs are released from B38 terminals in the muscle. Therefore, we have described a neuromuscular preparation amenable to the study of both excitatory and inhibitory motor neurons that utilize a variety of conventional and peptide transmitters. Our results suggest that these motor neurons can function in two states. When stimulated in single brief bursts, they primarily release conventional transmitters. When stimulated in a series of prolonged bursts, they release both conventional transmitters and peptide cotransmitters. These dual states are most pronounced in the case of B47, which, depending on the stimulation paradigm, can act selectively to inhibit or enhance the effects of a second motor neuron innervating the same muscle.
A heparan sulfate proteoglycan in developing avian axonal tracts
Authors: Halfter W
Published: March 2018

A neuronal heparan sulfate proteoglycan was identified by a panel of four monoclonal antibodies. The antibodies were generated from mice immunized with embryonic chick retina basal lamina (clones 3A12, 3A3, and 9E10) and embryonic chick optic tract (clone 6D2). Cross-reactivity of all four antibodies with the purified proteoglycan confirmed that the antibodies were directed to the same antigen. Antibodies to heparan sulfate proteoglycan from embryonic chick muscle or EHS mouse tumor (perlecan) did not cross-react with the neuronal heparan sulfate proteoglycan, suggesting that the two proteoglycans are not related. In Western blots, the proteoglycan had a molecular weight of 600 kDa that dropped to 250 kDa when the samples were treated with heparitinase or nitric acid. Immunocytochemistry showed that in early stages of chick and quail development, the proteoglycan was exclusively localized in basal laminae and had a distribution similar to that of laminin. During further development, a strong labeling was also found in the extracellular environment of nerve tracts, such as the optic nerve and white matter areas of the brain and spinal cord. The labeling of axonal tracts declined from embryonic day 10 onward, while labeling in basal laminae persisted. Antibodies to muscle heparan sulfate proteoglycan or to perlecan did not label nerve fibers. The data show that embryonic neuronal tissue expresses a new type of heparan sulfate proteoglycan.
Bidirectional long-term modification of synaptic effectiveness in the adult and immature hippocampus
Authors: Dudek SM , Bear MF
Published: March 2018

Previously we showed that delivering 900 pulses to the Schaffer collateral-CA1 pathway at 1–3 Hz causes a lasting depression of synaptic effectiveness that is input specific and dependent on NMDA receptor activation (Dudek and Bear, 1992a). Here we describe experiments aimed at further characterizing this homosynaptic long-term depression (LTD) and comparing it with long-term potentiation (LTP). To address the question of whether depressed synapses can still be potentiated and vice versa, LTP was saturated with repeated high- frequency tetani, and then LTD was induced with low-frequency stimulation (LFS). A second strong tetanus then restored the potentiation, indicating that the same synapses whose transmission had been depressed by LFS were capable of subsequently supporting potentiation. In a complementary experiment, LTD was induced first and then a strong high-frequency tetanus was delivered. We found that the resulting LTP achieved the same absolute magnitude as that observed in control slices that had received the high-frequency stimulation alone. Next, the postnatal development of LTD was investigated in slices prepared from rats at 6–35 d of age. The consequences of LFS were far more pronounced in slices from young rats. LTD following 900 pulses at 1 Hz measured -45 +/- 4% in CA1 of rats less than 2 weeks old as compared with -20 +/- 4 in animals at 5 weeks postnatal. It was also found that LTD precedes the developmental onset of LTP in CA1. Finally, we addressed the question of whether LTD could be saturated by repeated episodes of LFS in slices prepared from 3-week-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)