bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of calcium currents in sprouting PC12 cells
Authors: Streit J , Lux HD
Published: March 2018

Whole-cell calcium and barium currents were recorded from PC12 cell bodies and growth cones during nerve growth factor (NGF)-induced neurite outgrowth. Depolarizing voltage steps were applied to activate the currents, and pharmacological agents were used to separate them from other ionic currents. In recordings from growth cones still attached to neurites, current flow from central parts of the cell could be distinguished from the growth cone currents. On the other hand, currents from neuritic shafts and growth cones contributed to whole- cell currents recorded in the soma. Such currents were isolated by alternatively comparing recordings of whole-cell calcium currents with recordings in which calcium currents of defined parts of the cell were suppressed by exposing these regions to laminar streams of solutions with low calcium. The boundary between such streams and the bath solution was shown to be sharp using a calcium-selective microelectrode. The current deficits recorded when the growth cones were exposed to solutions with low calcium (growth cone currents) were within 10–50% of the total cell currents and similar to the currents recorded when the whole cell except the growth cone was exposed to low calcium. The current densities in the growth cones during initial sprouting were 5.4 times higher than those in the somata. Growth cone currents showed more inactivation than currents originating from the soma during pulses of 200 msec. In most experiments no calcium currents could be resolved in the neuritic shaft during initial neurite growth (1–10 d of NGF application), indicating low current density. In proximal segments of the neurites, however, a somatofugal decrease of the current density was observed. It is concluded from these results, that in outgrowing neurites of PC12 cells high densities of calcium channels are maintained in the growth cones, whereas in the neuritic shaft calcium channel density is initially low and later increases during consolidation of the neurites.
Neuropeptide Y in the cerebral cortex and the caudate-putamen nuclei: ultrastructural basis for interactions with GABAergic and non-GABAergic neurons
Authors: Aoki C , Pickel VM
Published: March 2018

In the cerebral cortex and caudate-putamen (CP) nuclei, neuropeptide Y (NPY) immunoreactivity is detectable within 1–2% of all neurons. The NPY-immunoreactive neurons are interneuronal and are believed to be mostly GABAergic in the cerebral cortex but not in the CP nuclei. Thus NPY and GABA may play different roles in the circuitry within these 2 regions. We tested this possibility by comparing the ultrastructure of NPY-containing neurons between (1) cortex (somatosensory and anterior cingulate areas) versus dorsolateral CP; and (2) GABAergic versus non- GABAergic NPY neurons within each area. Single coronal sections through the rat forebrain were dually labeled for GABA and NPY by combining immunoautoradiography with the immunoperoxidase method. NPY-containing neurons with or without GABA occurred throughout the rostrocaudal portions of CP and all laminae of somatosensory and anterior cingulate cortex. Comparisons between the areas confirmed that somata and terminals dually labeled for GABA and NPY were more prevalent in the cortex. NPY terminals lacking detectable GABA immunoreactivity also were found within the cortex, thus suggesting additional heterogeneity in cortical NPY innervation. The ultrastructural features of NPY perikarya in both regions were morphologically similar regardless of whether the cells also contained GABA. Most synaptic inputs to NPY neurons occurred at distal dendrites. In comparison to neighboring neurons, synaptic inputs to proximal dendrites and somata of NPY neurons of cortex and CP were rare, suggesting that fewer and weaker inputs may modulate the excitability of NPY-containing neurons. In both regions, nearly all NPY- and NPY-GABA-labeled terminals formed symmetric junctions suggestive of inhibitory action. The majority of these junctions were with dendrites containing neither NPY nor GABA. NPY terminals formed few contacts on proximal dendrites and somata of GABAergic neurons (8% of 179 contacts in cortex; 12% of 73 contacts in CP) which, unlike most singly-labeled GABAergic neurons, were sparsely innervated. Thus, NPY may play a more prominent role in modulation of certain GABAergic neurons than would be predicted by the observed frequency of NPY-to-GABA contacts in the two regions. One notable regional difference was the greater prevalence in cortex of axoaxonic associations between NPY-immunoreactive terminals and other terminals, some of which also contained NPY. These nonsynaptic associations may be involved in the modulation of (1) the release of NPY by another transmitter or (2) NPY's modulation of release of other transmitters in cortex.
Multiple electrosensory maps in the medulla of weakly electric gymnotiform fish. I. Physiological differences
Authors: Shumway CA
Published: March 2018

The electrosensory lateral line lobe in the weakly electric gymnotiform fish Eigenmannia contains 3 topographic maps of high-frequency (tuberous) electroreceptive information from the body surface. The maps receive identical primary afferent input since axonal collaterals of both amplitude- and phase-coding afferents project to all 3 maps (Heiligenberg and Dye, 1982). Response properties of the amplitude- coding pyramidal neurons in the multiple maps were investigated in order to determine whether the maps differ physiologically. Units in the lateral map have larger receptive fields and are more sensitive than units in the centromedial map. The former units respond more phasically and with shorter latencies to step changes in stimulus amplitude (measured from the stimulus onset to the maximum response). Although 75% of pyramidal cells in all maps show a center-surround receptive-field organization, the strength of the inhibitory surround varies among maps, tending to be weakest for units in the lateral map and strongest for units in the centromedial map. Pyramidal neurons also differ in their responses with respect to the temporal frequency of amplitude modulations; the majority of units in the lateral map prefer high temporal frequencies, while those in the centromedial map prefer low frequencies. These results suggest that the multiple electrosensory maps could provide the initial separation of spatial and temporal processing of sensory information, much as has been suggested for X and Y ganglion cells in the cat retina (Shapley and Perry, 1986). The centromedial map could provide high spatial contrast with correspondingly poor temporal resolution, while the more sensitive units in the lateral map could best provide information about temporal changes in stimulus amplitude.
Noradrenergic modulation of the masseteric reflex in behaving cats. II. Physiological studies
Authors: Stafford IL , Jacobs BL
Published: March 2018

Studies in the preceding paper demonstrated that the amplitude of the masseteric reflex in behaving cats is augmented by pharmacological manipulations that increase norepinephrine (NE) tone in the motor trigeminal nucleus (MoV) through exogenous means. The present studies examine whether such a relationship also exists under physiological conditions, i.e., whether physiological increases in NE synaptic activity are correlated with increases in the reflex amplitude. The masseteric reflex was elicited in behaving cats by electrical stimulation of the mesencephalic trigeminal nucleus (MesV) and the response recorded via electrodes permanently placed in the masseter muscle. Following baseline measures of the reflex amplitude, the reflex was gain elicited while cats were exposed to various environmental stimuli known to activate NE neurons: 15 min of 100-dB white noise, confrontation with a dog, or auditory clicks presented repetitively at various intervals prior to MesV stimulation. Presentation of the white noise or the dog significantly facilitated the reflex response for the duration of the exposure. The clicks produced reflex facilitation at 100 and 150 msec following their presentation and reflex suppression at 20 msec. Two approaches were then employed to determine whether NE mediated, at least in part, augmentation of the reflex produced by these environmental conditions. In the first, cats were given either the alpha-1-noradrenergic antagonist prazosin (5 mg/kg, i.p.) or the serotonin antagonist methysergide (0.5 mg/kg, i.p.). In all cases, prazosin blocked the reflex augmentation whereas methysergide was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Multiple GTP-binding proteins from cholinergic synaptic vesicles
Authors: Ngsee JK , Miller K , Wendland B , Scheller RH
Published: March 2018

Cholinergic synaptic vesicles purified from the electric organ of the marine ray, Discopyge ommata, contain 2 different size classes of GTP- binding proteins: one or more with an apparent molecular weight (MW) between 37 and 41 kDa, and 3 major and at least 2 minor proteins with MW between 20 and 29 kDa. These GTP-binding proteins were detectable using the alpha 32P-GTP overlay technique and covalent modification with bacterial toxins. The higher MW GTP-binding proteins are ADP- ribosylated by pertussis toxin and 2 of the lower MW GTP-binding proteins are sensitive to botulinum toxin.
Synaptic localization and neural regulation of an N- acetylgalactosaminyl transferase in skeletal muscle
Authors: Scott LJ , Balsamo J , Sanes JR , Lilien J
Published: March 2018

We have previously documented the properties of a approximately 220-kDa cell surface glycosyltransferase that transfers N-acetylgalactosamine to oligosaccharide chains (Balsamo et al., 1986b). Because N- acetylgalactosamine-terminated carbohydrates are concentrated at the neuromuscular junction (Scott et al., 1988), we assayed skeletal muscle for the presence of the N-acetylgalactosaminyl transferase. Using immunohistochemical methods, we found that the enzyme is localized at neuromuscular junctions on normal adult rat muscle fibers. Biochemical assays confirm that junctional areas are highly enriched in the approximately 220-kDa immunoreactive species as well as in enzyme activity associated with the approximately 220-kDa species. This restricted distribution is dependent on synaptic integrity, as the enzyme appears extrasynaptically on denervation. These results provide a plausible metabolic basis for the localization of a synapse-specific carbohydrate and demonstrate that the expression of a glycosyltransferase is regulated by synaptic interactions.
Neural circuits mediating visual flight control in flies. II. Separation of two control systems by microsurgical brain lesions
Authors: Hausen K , Wehrhahn C
Published: March 2018

The role of 2 sets of interneurons in the optic lobes of blowflies in visual course control was studied by means of brain lesions. The first set comprises the cells HS and H2, which respond to global horizontal motion. The second set are the FD-cells, which respond selectively to local horizontal motion. All these cells are output neurons of the third optic ganglion of flies and are thought to be coupled via descending neurons to the flight motor system. In 2 series of experiments specific cells of these 2 sets were inactivated by microsurgical brain lesions L1 and L2 respectively. The effects of the lesions on visual course control were tested by measuring the yaw torque responses of the animals in restrained flight before and after the operation. The flies were stimulated in these tests with monocular and binocular motion of periodic gratings moving in either the horizontal or the vertical direction. Lesion L1 in the right side of the brain inactivates the right HS-cells and the left H2- and FD-cells. This leads to a complete block of the response to binocular clockwise horizontal motion and a reduction of the response to monocular motion from front to back on the right side of the animal. Application of L1 also leads to a pronounced response to binocular motion from front to back not observed in normal animals. The response to monocular vertical motion is unaffected. Lesion L2 reduces all responses to monocular and binocular horizontal motion present in normal animals. The behavioral effects of the lesions are highly specific and consistent with predictions based on the well-known anatomical and physiological properties of the neural circuitry investigated. The results demonstrate directly that the HS-, H2-, and FD-cells control motion- induced steering maneuvers in flight.
Patterns of cell and fiber vulnerability in the mesostriatal system of the mutant mouse weaver. II. High affinity uptake sites for dopamine
Authors: Roffler-Tarlov S , Pugatch D , Graybiel AM
Published: March 2018

Weaver (gene symbol wv) is an autosomal recessive mutation in the mouse that causes the death of neurons in the cerebellum and of dopamine- containing neurons in the mid-brain. In the accompanying paper and in previous reports, the selective nature of the deficit produced by the gene in the dopamine-containing systems has been described after analysis of the patterns of the residual innervation in the striatum and the patterns of cell death in the midbrain. In the present report, we describe deficits in the terminals of the mesostriatal system occurring prior to a detectable dopamine deficiency in the striatum and prior to the onset of cell death in the mesencephalic dopamine- containing neurons during development. We have also found deficits in the remaining terminals of the adult weaver's striatum after the weaver pattern of innervation has been permanently established. Axonal terminals in the caudoputamen are impaired in weaver mice at postnatal day 7, before the onset of dopamine depletion in the caudoputamen and cell death in the midbrain. The impairment was revealed by a markedly deficient high-affinity uptake for 3H-dopamine by synaptosomes prepared from the caudoputamen. Throughout the remainder of development and in adulthood, the extent of the deficit in 3H-dopamine uptake was always greater than that for dopamine content. No striatal region was completely spared the effects of the gene. In the nucleus accumbens of the weavers, where dopamine content is normal, 3H-dopamine uptake was reduced by 35% in the synaptosomal preparations. In the olfactory tubercle, dopamine levels were reduced by 44% but 3H-dopamine uptake was reduced by 60%.(ABSTRACT TRUNCATED AT 250 WORDS)
Local cerebral glucose utilization in monkeys with hemiparkinsonism induced by intracarotid infusion of the neurotoxin MPTP
Authors: Palombo E , Porrino LJ , Bankiewicz KS , Crane AM , Sokoloff L , Kopin IJ
Published: March 2018

Quantitative 2-[14C]deoxyglucose autoradiography was used to map the pattern of alterations in local cerebral glucose utilization associated with unilateral lesions of the substantia nigra pars compacta produced by the infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into one internal carotid artery of rhesus monkeys. These monkeys become hemiparkinsonian, displaying rigidity, bradykinesia, and tremor of the limbs contralateral to the side of MPTP infusion; during spontaneous activity they turn toward the side of the lesion. Eighty- two brain areas were examined, and statistically significant metabolic changes were confined mainly to basal ganglia structures ipsilateral to the side of the lesion. Glucose utilization was reduced in the substantia nigra pars compacta and ventral tegmental area, i.e., in the areas of cell loss. Increases in glucose utilization in regions normally innervated by the lesioned area were observed in the post- commissural portions of the putamen and dorsolateral caudate. Other structures showing statistically significant metabolic changes were the external segment of the globus pallidus (+40%), subthalamic nucleus (- 17%), and pedunculopontine nucleus (+15%). There were also smaller changes in portions of the thalamus (ventral anterior nucleus, parafascicular nucleus) and premotor cortex. All significant metabolic changes were confined to the side of the substantia nigra lesion and were essentially restricted to regions involved in the production of movement or maintenance of posture.
Androgen regulation of dendritic growth and retraction in the development of a sexually dimorphic spinal nucleus
Authors: Goldstein LA , Kurz EM , Sengelaub DR
Published: March 2018

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic group of motoneurons whose development and maintenance are under androgenic control. Exposure to androgens early in development permanently alters SNB motoneuron number and soma size; in adulthood, androgens regulate dendritic and synaptic architecture. The present set of experiments investigates the influence of androgens on the development of SNB dendritic morphology. In normal males, SNB dendritic growth is biphasic, reaching exuberant lengths by the fourth postnatal week and then retracting to adult lengths by 7 weeks of age. This dendritic growth is androgen dependent--males castrated on postnatal day (P) 7 and given daily injections of testosterone propionate (TP) had exuberant dendritic lengths similar to those of normal males; dendritic length in oil-treated males remained at P7 levels. The early exuberant dendritic length was retained in TP-treated males through P49. The retraction of SNB dendrites after P28 is also influenced by androgens. Males castrated at P28 and given testosterone implants retained exuberant dendritic length at P49; blank-implanted males had significantly shorter dendritic lengths by P70. These results suggest that androgens are necessary for the early exuberant growth of SNB dendrites. Furthermore, the subsequent retraction of SNB dendrites may be halted when testosterone titers reach a critical level during puberty, stabilizing their adult length.
Serotonin immunoreactive boutons make synapses with feline phrenic motoneurons
Authors: Pilowsky PM , de Castro D , Llewellyn-Smith I , Lipski J , Voss MD
Published: March 2018

In anesthetized cats, phrenic motoneurons were intracellularly labeled with HRP. Immunohistochemistry was used to localize serotonin-like immunoreactivity that was present in numerous boutons and nerve fibers within the ventral horn of the C5 spinal segment. Immunoreactive boutons were frequently found in apposition to phrenic motoneurons, but these close contacts were more common on the dendrites than the cell body. At the electron microscope level, serotonin-immunoreactive boutons were found to make synapses with well-defined postsynaptic densities on proximal and distal dendrites of phrenic motoneurons. These results suggest that serotonin-containing neurons may directly affect the excitability of phrenic motoneurons, mainly through an input onto their extensive dendritic trees.
NMDA receptor agonist and antagonists alter retinal ganglion cell arbor structure in the developing frog retinotectal projection
Authors: Cline HT , Constantine-Paton M
Published: March 2018

The development of sensory maps is thought to require an activity- dependent structural rearrangement of afferent terminal arbors within the CNS which recreates the topographic relations of sensory somata present in the periphery. In the frog retinotectal projection, activation of the NMDA receptor plays a role in this structural plasticity. Exposure of the optic tectum of tadpoles to NMDA receptor antagonists results in a rearrangement of retinal ganglion cell arbors so that their organization into a topographic projection and eye- specific stripes is disrupted (Cline et al., 1987; Cline and Constantine-Paton, 1989). Exposure of the optic tectum to the receptor agonist, NMDA, increases the eye-specific segregation of these arbors (Cline et al., 1987). We examined the projection of the supernumerary retina and the morphology of individual retinal afferent arbors of untreated, NMDA-treated, APV-treated, MK801-treated, and MK801/NMDA- treated 3-eyed tadpoles and young postmetamorphic frogs in an effort to understand how NMDA receptor activation is involved in the growth and ordering of retinal arbors. Treatments with MK801 in combination with NMDA resulted in a desegregation of eye-specific stripes, whereas treatments with MK801 or NMDA alone did not. As reported previously, APV treatment resulted in stripe desegregation without increasing the tangential area (measured from 2-dimensional drawings) of the terminal arbors. However, a detailed analysis revealed that the APV-treated tadpole arbors have 35% reduction in branch density (branch tips/area) compared to untreated 3-eyed tadpole arbors. We treated the optic tectum with a range of concentrations of NMDA prepared in the slow- release plastic Elvax. NMDA at 10(-4) M in Elvax was the optimal concentration to produce the sharpening of stripe borders. Exposure of the tectum to NMDA at 10(-6) M in Elvax produced no change in the stripe pattern, while 10(-2) M NMDA in Elvax resulted in beading of the arbors. At the optimal concentration NMDA treatment results in a 75% reduction in the number of axons crossing from a stripe to an interstripe zone. Drawings of individual HRP-labeled, NMDA-treated arbors demonstrate that they have fewer branch points and fewer branch tips. NMDA treatment reduced arbor density by approximately 50%. Arbors drawn from untreated postmetamorphic frogs have twice the branch density of arbors from untreated tadpoles. NMDA treatment in these animals reduced the branch density by 55%, comparable to the reduction seen in tadpole branch density. Our data support a specific hypothesis for NMDA receptor involvement in the activity-dependent structural refinement process within the developing retinotectal projection.(ABSTRACT TRUNCATED AT 400 WORDS)
Neuron-glia interactions of rat hippocampal cells in vitro: glial- guided neuronal migration and neuronal regulation of glial differentiation
Authors: Gasser UE , Hatten ME
Published: March 2018

To examine neuron-glia interactions of hippocampal cells, including glial-guided neuronal migration, glial organization of neuronal positioning and neuronal regulation of astroglial differentiation, rat hippocampal tissue, harvested between embryonic day 16 (E16) and postnatal day 3 (P3), was dissociated into a single cell suspension and plated in glass coverslip microcultures (Hatten and Liem, 1981; Hatten et al., 1984). Immunostaining the cells with antibodies against the glial filament protein (AbGFP) revealed developmental stage-specific changes in the number and extent of morphological differentiation of hippocampal astroglial cells. At E16-E18, fewer than 5% of the cells were AbGFP-positive; stained cells were immature, bearing very short processes. By E19-E20, the number of stained cells increased to 15% of the total cell population. Three forms of differentiated glial cells predominated, a bipolar form bearing processes 30–50 microns, an elongated form which resembled the radial glia of hippocampus, bearing processes 120 microns in length, and a stellate form with 3 or more processes 30–50 microns in length. At P0-P3, glial morphological differentiation varied with the culture substratum; differentiated forms resembling those seen at E20 occurred on Matrigel, but not on polylysine. Quantitation of the distribution of neurons relative to AbGFP-stained glial processes revealed developmental stage-specific changes in glial organization of neuronal positioning in the cultures. In cultures of E16-E18 hippocampal cells, the neurons did not preferentially associate with astroglial cells. By E19-E20, extensive neuron-glia interactions occurred, with 80–90% of the neurons being located within 5–10 microns of a glial process. In addition to their organization of neuronal positioning, E20 hippocampal astroglial cells supported extensive neuronal migration. Migrating hippocampal neurons displayed a cytology and neuron-glia cell apposition identical to that described for migrating cerebellar granule cells in vitro (Edmondson and Hatten, 1987), closely apposing their cell soma against the hippocampal glial process and moving along the glial arm by extending a thickened, leading process. Migration was seen only along highly elongated glial profiles resembling radial glial seen in vivo. The morphological differentiation of hippocampal glial cells in vitro was dependent on cell-cell interactions with neurons. In the absence of neurons, purified hippocampal astroglia had flat, undifferentiated profiles and proliferated rapidly. The addition of hippocampal neurons rapidly arrested glial growth and induced glial process extension.
Immunocytochemical localization of the GABA transporter in rat brain
Authors: Radian R , Ottersen OP , Storm-Mathisen J , Castel M , Kanner BI
Published: March 2018

Polyclonal antibodies were raised against the GABA transporter (GABA- Tp) purified from rat brain tissue (Radian et al., 1986) and used for immunocytochemical localization of the antigen in several rat brain areas, including the cerebellum, hippocampus, substantia nigra, and cerebral cortex. Light microscopic studies with the peroxidase- antiperoxidase and biotin-avidin-peroxidase techniques suggested that GABA-Tp is localized in the same types of axons and terminals that contain endogenous GABA, as judged by comparison with parallel sections incubated with antibodies against glutaraldehyde-conjugated GABA. However, as expected from biochemical results, different neurons differed in their relative contents of GABA-Tp and GABA; thus, GABA-Tp was relatively low in striatonigral and Purkinje axon terminals and relatively high in nerve plexus around the bases of cerebellar Purkinje cells and hippocampal pyramidal and granule cells. The GABA-Tp antiserum did not produce detectable labeling of nerve cell bodies. Electron microscopic studies supported the light microscopic observations and provided direct evidence of cellular co-localization of GABA-Tp and GABA (as visualized by the peroxidase-antiperoxidase technique and postembedding immunogold labeling, respectively). The ultrastructural studies indicated the presence of GABA-Tp also in glial processes but not in glial cell bodies. The relative intensity of the neuronal and glial staining varied among regions: glial staining predominated over neuronal staining in the substantia nigra, whereas the converse was true in the cerebellum and hippocampus. The present immunocytochemical data demonstrate directly what has previously been inferred from biochemical and autoradiographic evidence: that the mechanisms for high-affinity GABA uptake is selectively and differentially localized in GABAergic neurons and in glial cells.
Subunit composition of nicotinic acetylcholine receptors from chick ciliary ganglia
Authors: Halvorsen SW , Berg DK
Published: March 2018

Nicotinic ACh receptors were immunoaffinity-purified from chick ciliary ganglia, radioiodinated, and examined by SDS-PAGE. Components with Mr's of 49, 52, and 60 kDa were obtained. Limited proteolysis produced different peptide maps from the components, confirming the 3 as distinct species. All are glycoproteins since treatment with glycopeptidase F altered their migration during electrophoresis. The 60 kDa component appears to be encoded by the AChR alpha 3 gene since it was selectively immunoprecipitated by an antiserum to a fusion protein containing a putative cytoplasmic region of the predicted alpha 3 gene product. The 49 kDa component selectively cross-reacted on immunoblots with 4 monoclonal antibodies that recognize a component of similar size in AChR preparations from chicken brain. The 52 kDa component is a novel species not previously identified in preparations of brain AChRs. If all 3 components represent integral AChR subunits, they may compose 2 receptor subtypes in the ganglion, e.g., one containing 49 and 60 kDa subunits and another containing 52 and 60 kDa subunits. This is supported by the finding that a receptor preparation can be obtained containing only the 49 and 60 kDa components and is consistent with reports of brain AChRs having only 2 types of subunits. Alternatively, ganglionic AChRs may contain 3 or more types of subunits, with at least one being selectively lost under certain conditions.
Physiological regulation of the picrotoxin receptor by gamma- butyrolactones and gamma-thiobutyrolactones in cultured hippocampal neurons
Authors: Holland KD , Ferrendelli JA , Covey DF , Rothman SM
Published: March 2018

We examined the effects of alkyl-substituted gamma-butyrolactones (GBLs), and gamma-thiobutyrolactones (TBLs) on GABA currents in cultured, voltage-clamped rat hippocampal neurons. Convulsant GBLs and TBLs reversiby diminished GABA responses in a concentration-dependent manner. beta-Ethyl-beta-methyl GBL (beta-EMGBL) completely abolished GABA responses at 3 mM (IC(50)390 microM), while TBL and beta-ethyl- beta-methyl TBL (beta-EMTBL)-induced inhibition of GABA currents was incomplete, saturating at about 50% of control at 300 microM and 10 mM for beta-EMTBL and TBL, respectively. beta-EMGBL and beta-EMTBL both increased the rate of decay of inhibitory post-synaptic currents (IPSCs) and beta-EMGBL also decreased IPSC peak amplitude. In contrast, the anticonvulsant alpha-ethyl-alpha-methyl TBL (alpha-EMTBL) potentiated GABA currents at all GABA concentrations tested; maximal potentiation was 190% of control at 1 mM alpha-EMTBL (EC50 102 microM). Another anticonvulsant alpha-ethyl-alpha-methyl GBL (alpha-EMGBL), potentiated responses to low (0.5 microM) but not high (greater than or equal to 10 microM) GABA. It also blocked the inhibitory effects of picrotoxin and beta-EMGBL and the facilitative effect of alpha-EMTBL on responses to 30 microM GABA. alpha-EMGBL did not interfere with other agents which augment GABA currents. Both alpha-EMTBL and alpha-EMGBL decreased the rate of IPSC decay without altering IPSC peak amplitude. None of these compounds had any direct membrane effects. We propose that beta-alkyl GBLs diminish GABA currents, and therefore, we hypothesize that these compounds are picrotoxin receptor agonists. beta- Alkyl TBLs partially diminish GABA currents and may be partial agonists.(ABSTRACT TRUNCATED AT 250 WORDS)
Cerebral white matter contains PDGF-responsive precursors to O2A cells
Authors: Grinspan JB , Stern JL , Pustilnik SM , Pleasure D
Published: March 2018

Cells dissociated from the cerebral white matter of immature rats were maintained in monolayer culture. Treatment with platelet-derived growth factor (PDGF) caused a large increase in the numbers of “O2A” oligodendroglial precursor cells (which bind the monoclonal antibody A2B5) and subsequently in the numbers of galactocerebroside (galC)- positive oligodendroglia. A2B5-negative “pre-O2A cells” in cerebral white matter cultures in which O2A cells and oligodendroglia had been killed by antibody-dependent complement-mediated cytolysis were induced by PDGF to proliferate and to differentiate into O2A cells and subsequently into oligodendroglia and type 2 astroglia. The most mature pre-O2A phenotype in these cultures was a small, round, process-bearing cell which expressed vimentin but not glial fibrillary acidic protein or galC. Cells of this phenotype were not observed upon PDGF treatment of immature rat optic nerve monolayer cultures from which O2A cells and oligodendrocytes had been depleted, and PDGF also failed to elicit the accumulation of O2A cells and oligodendroglia in such cultures.
Growth cones of chick sympathetic preganglionic neurons in vitro interact with other neurons in a cell-specific manner
Authors: Moorman SJ , Hume RI
Published: March 2018

The ability of the growth cones of sympathetic preganglionic neurons to recognize the neurons they encounter during their outgrowth and to react to them in a cell-type-specific manner may play a role in guiding them to appropriate targets during development in vivo. In this study, we examined the in vitro growth of sympathetic preganglionic neurons as they interacted with motor neurons, dorsal root ganglion neurons, and sympathetic ganglion neurons. All of these cell types might potentially be encountered by a growing preganglionic axon. The interaction of sympathetic preganglionic growth cones with each cell type was distinct. Sympathetic preganglionic growth cones fasciculated on motor- neuron neurites, collapsed after contact with the cell bodies and neurites of dorsal root ganglion neurons, and grew across the cell bodies and neurites of sympathetic ganglion neurons. These cell-type- specific responses stand in contrast to the collapse and retraction reported to be the most common growth-cone behaviors that result from contact between central and peripheral neurons in vitro and suggest that contact-mediated recognition might be sufficient for growth to and interaction with appropriate targets.
Cyclic AMP-induced slow inward current in depolarized neurons of Aplysia californica
Authors: Kehoe J
Published: March 2018

Cyclic nucleotides have been implicated in many long-lasting transmitter-induced effects on membrane conductance. One previously observed effect of cAMP on molluscan neurons is to induce a slow inward current, which has been further evaluated here in depolarized anterior and medial cells of the pleural ganglion of Aplysia californica in order to understand better its underlying ionic mechanisms and its sensitivity to a variety of pharmacological agents. This current, which appears to be the only cAMP-induced current seen in the anterior cells, was shown to invert at about +25 mV, that is, approximately 25-30 mV inferior to ENa. This reversal potential was lowered by about 15-16 mV when half of the extracellular Na was replaced by either mannitol or N- methyl-D-glucamine, whereas it was unaffected by changes in extracellular Cl, Ca, or Mg. The response persisted in seawater in which the Na had been totally replaced by K, and its reversal potential shifted towards more negative values. These data are consistent with the hypothesis that both Na and K ions permeate the channel, with a Na/K permeability ratio of approximately 2. Ca ions do not appear to permeate the channel, but they do have a marked inhibitory effect on the response amplitude, as do Mg ions when Ca is not present. Caffeine, intracellular acidification, and phosphodiesterase inhibitors enhance and prolong the response without changing its reversal potential. Previous studies have shown that both caffeine and intracellular acidification inhibit phosphodiesterase, and it is assumed that the common effect of these manipulations on the cAMP-induced inward current is mediated, at least partially, by the inhibition of that enzyme. In the medial cells of the pleural ganglion, this slow inward current is present, but is dominated in the depolarized cell by a cAMP-induced diminution in a Ca-activated K conductance (Kehoe, 1985b). This K conductance and, consequently, the noninverting, cAMP-induced inward current that reflects its diminution, were shown to disappear in Ca- free solutions, in the presence of isobutyl-1-methylxanthine (IBMX) or caffeine, and upon acidification of the cytoplasm. When this cAMP- sensitive K conductance is blocked, the presence of the inverting cAMP- induced cationic current is unmasked. The cAMP-induced cationic current is shown to have many properties in common with cyclic nucleotide- induced currents described in photoreceptors, olfactory receptor cilia, and cardiac myocytes, all of which have been shown to be outwardly rectifying cationic currents that are inhibited by divalent cations and do not involve the activation of a cAMP-dependent kinase.
Carboxypeptidase H in the hypothalamo-neurohypophysial system: evidence for processing and activation of a prohormone-processing enzyme during axonal transport
Authors: Hook VY , Affolter HU , Palkovits M
Published: March 2018

Investigations of peptide precursor processing in nerve cells, including studies on prooxytocin and provasopressin processing in the rat hypothalamo-neurohypophysial system, show that prohormone processing occurs during axonal transport of maturing secretory vesicles. Recent studies (Fricker et al., 1989; Rodriguez et al., 1989) show that carboxypeptidase H (CPH), one of several proteases required for prohormone processing, is synthesized as a proenzyme that presumably requires activation. To determine if pro-CPH, like prohormone precursors, is processed and activated during axonal transport, we have analyzed the molecular forms of CPH present at several levels in the rat hypothalamo-neurohypophysial system. These biochemical and immunochemical studies showed that the supraoptic nucleus (SON), a region enriched in neuronal cell bodies, possesses primarily an inactive 65-kDa species of CPH. The median eminence and pituitary stalk regions that are enriched in axons possess both the inactive 65-kDa and the active 55-kDa forms of CPH, and nerve terminals of the posterior pituitary contain primarily the active 55-kDa CPH. These results support the hypothesis that pro-CPH is processed and activated during axonal transport from neuronal perikarya of SON to nerve terminals of the posterior pituitary. Furthermore, analysis of immunoreactive CPH in the rat and bovine pituitary showed that each tissue possessed different relative amounts of zymogen compared to mature forms of CPH, suggesting that tissue-specific processing of pro- CPH occurs. Thus, the biosynthesis of active peptide hormones requires the simultaneous processing of proenzyme and prohormone.
Alz-50 recognizes a phosphorylated epitope of tau protein
Authors: Ueda K , Masliah E , Saitoh T , Bakalis SL , Scoble H , Kosik KS
Published: March 2018

Alz-50 is a monoclonal antibody that detects antigens enriched in the brain tissue of Alzheimer's disease (AD) patients. Although Alz-50 recognizes tau, an identified integral constituent of the AD paired helical filament (PHF), the exact nature of the antigenic site is unknown. An immunoblot analysis demonstrated that the antigenic sites to Alz-50 are diminished by acid phosphatase treatment. Consistent with this finding, Alz-50 antigens were more concentrated in brain homogenates prepared with phosphatase inhibitors. The epitope in tau with which Alz-50 reacts is located in the carboxy terminus within a 14- amino acid region from just beyond the microtubule-binding repeats to the carboxy terminus. An isolated carboxy-terminal chymotryptic peptide from bovine brain tau reactive with Alz-50 was analyzed by fast-atom- bombardment mass spectroscopy (FAB-MS) and was found to be present as both a monophosphopeptide and a nonphosphorylated peptide. The immunohistological analysis has demonstrated that Alz-50 staining of neurofibrillary tangles (NFTs) is sensitive to acid phosphatase but not to alkaline phosphatase. Furthermore, Alz-50 staining of NFTs was effectively adsorbed by a high concentration of phosphoserine but not by serine or phosphothreonine. These results strongly suggest that Alz- 50 recognizes a phosphorylated epitope in the carboxy terminus of tau which has not been previously detected by using alkaline phosphatase. The strong Alz-50 staining in AD samples may represent another association between a phosphorylation state and neurofibrillary lesions. As a marker of the inchoate tangle-bearing neuron, the characterization of the Alz-50 epitope in tau offers a partial molecular basis for the modifications that contribute to the assembly of PHFs.
Expression of neuropeptide-Y-like immunoreactivity begins after adrenergic differentiation and ganglionic synaptogenesis in developing bullfrog sympathetic neurons
Authors: Stofer WD , Horn JP
Published: March 2018

Immunoreactivities for tyrosine hydroxylase (TH) and neuropeptide Y (NPY) were studied in developing sympathetic neurons of bullfrog tadpoles and adults. At stage III, nearly all ganglion cells are positive for TH. This suggests early commitment to an adrenergic phenotype, the timing of which is analogous to that reported for sympathetic neurons in birds and mammals. During metamorphic stages and in juvenile bullfrogs, the expression of TH becomes transiently bimodal: many neurons are intensely positive; the remainder are faintly positive. In adult sympathetic neurons, TH expression is more uniform. NPY first appears in a few principal neurons (less than 1%) of paravertebral ganglia 9 and 10 at stage XI. The percentage of ganglion cells containing NPY then increases gradually, reaches adult levels (approximately 55%) by stage XX, and persists at these levels through metamorphosis. The development of NPY expression follows a similar time course in paravertebral ganglion 6. Double-label experiments in late- stage tadpoles and juvenile bullfrogs revealed that the intensely TH- positive neurons are negative for NPY. Taken together with recent electrophysiological data (Horn and Stofer, 1990), these results demonstrate that the development of NPY expression begins long after the onset of adrenergic differentiation and ganglionic synapse formation. The present findings also show that cellular levels of TH and NPY can be independently altered, and they suggest that the onset of NPY expression is not linked to maturation of peripheral targets, but rather to some more global event operating synchronously along the rostro-caudal axis.
Inhibition of protein kinase C blocks two components of LTP persistence, leaving initial potentiation intact
Authors: Colley PA , Sheu FS , Routtenberg A
Published: March 2018

Protein kinase C (PKC) activity is increased following hippocampal long- term potentiation (LTP; Akers et al., 1986). A similar increase in PKC activity is measured following the induction of a long-lasting potentiation with abbreviated high-frequency stimulation (HFS) in combination with PKC-activating phorbol esters (Colley et al., 1989). Because phorbol esters have no effect on the initial potentiation produced with HFS, and because PKC activity appears to be related to the persistence of LTP and not to the initial change, we concluded that PKC regulates a post-initiation component of LTP. To define the time domain in which PKC activation is necessary for LTP, we studied the effect of the PKC inhibitors polymyxin B (PMXB) and 1-(5- isoquinolinesulfonyl)-2-methylpiperazine (H-7) micropressure ejected at different time points before and after the induction of LTP. LTP was produced in intact rats with HFS of the perforant path, and inhibitor ejections were made in the molecular layer of the dentate gyrus. PMXB, which at lower doses is a selective inhibitor of PKC, had no effect on initial potentiation, yet caused decay of the potentiated response to baseline within 2 hr. Decay occurred when PMXB was ejected 15 min before and 15 and 30 min after HFS. PMXB, at either low or high doses, was ineffective in blocking LTP persistence at time points greater than 30 min after HFS. Low doses of H-7 produced similar effects to those of PMXB. However, in contrast to a high dose of PMXB, a high dose of H-7 inhibited the persistence of LTP when delivered 240 min after HFS.(ABSTRACT TRUNCATED AT 250 WORDS)
Interaction of forskolin with voltage-gated K+ channels in PC12 cells
Authors: Garber SS , Hoshi T , Aldrich RW
Published: March 2018

Forskolin (FSK) directly blocks a distinct class of voltage-dependent K+ channels in pheochromocytoma cells. We have studied the biophysical mechanism of FSK action on these channels. The mean open duration decreased linearly with [FSK], indicating that a single molecule of FSK interacts with a single open K+ channel. FSK did not alter the voltage dependence of activation or the latency to first opening. Whole-cell currents in the presence of FSK did not show a rising phase in tail currents, suggesting that FSK-bound channels can close. We used a kinetic scheme in which FSK binds preferentially to the open state of the channel to describe its interaction with the K+ channel. This scheme is analogous to the modulated receptor hypothesis used to describe the interaction of local anesthetics with voltage-dependent Na+ channels.
An in vitro analysis of sound localization mechanisms in the gerbil lateral superior olive
Authors: Sanes DH
Published: March 2018

One way in which animals localize sounds along the horizon is by detecting the level differences at the 2 ears. Neurons in the lateral superior olive (LSO) encode this cue by integrating the synaptic drive from ipsilateral excitatory and contralateral inhibitory connections. This synaptic integration was analyzed in 400–500-microns brain slices through the gerbil superior olive. Intracellular recordings from LSO neurons were obtained during the application of independent or conjoint electrical stimuli to the excitatory afferent and inhibitory afferent pathways. Stimulation of ascending fibers from the ipsilateral cochlear nucleus reliably evoked EPSPs and action potentials. Stimulation of the medial nucleus of the trapezoid body (MNTB) consistently evoked IPSPs. The evoked postsynaptic potentials differed in that IPSPs were 2 times the duration of EPSPs. An electrophysiological estimate of convergence indicated approximately 10 excitatory and 8 inhibitory afferents per LSO neuron. MNTB stimulation suppressed synaptically evoked action potentials. When stimulus amplitude was increased to the excitatory pathway, it was generally found that a greater MNTB stimulus was necessary to suppress the action potential. A similar commensurate rise in ipsilateral and contralateral acoustic stimulation was also found to be necessary to give the same criterion response. These results confirm that the LSO can integrate evoked action potentials and IPSPs to encode interaural level. Increasing stimulus voltage was found to decrease both action potential and IPSP latency, suggesting that intensity information may be encoded with temporal cues in the nervous system. It was also found that an evoked burst of action potentials could be inhibited in such a way as to yield intermediate discharge rates, dependent on contralateral stimulus level. Taken together, these results suggest that certain properties related to level-difference coding may be available for intracellular analysis using the brain- slice preparation. Several temporal characteristics of the synaptic potentials, including latency and duration, may play a critical role in this simple computation.
Opiate antagonist nalmefene improves intracellular free Mg2+, bioenergetic state, and neurologic outcome following traumatic brain injury in rats
Authors: Vink R , McIntosh TK , Rhomhanyi R , Faden AI
Published: March 2018

Treatment of CNS trauma with the opiate antagonist naloxone improves outcome, though the mechanisms of action remain speculative. Nalmefene is another opiate-receptor antagonist, but it has substantially greater potency and duration of action than naloxone. It also has increased activity at kappa opiate receptors and has recently been shown to limit histological changes and neurological dysfunction after traumatic spinal cord injury. The present study examined the effects of treatment with nalmefene on outcome after fluid-percussion-induced traumatic brain injury in rats, using magnetic resonance spectroscopy to monitor acute metabolic changes and behavioral tests to determine chronic neurological recovery. Single-dose treatment with nalmefene (100 micrograms/kg, i.v.) at 30 min after trauma significantly improved (p less than 0.05) neurological outcome (up to 4 weeks) as compared to saline-treated controls. Early changes in intracellular free-magnesium concentration, adenosine diphosphate concentration, and cytosolic phosphorylation potential were all significantly improved by nalmefene treatment, reflecting improved bioenergetic state. We suggest that the ability of nalmefene to improve cellular bioenergetics after trauma may in part account for the neuroprotective effects of this and related compounds.