bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective and nonselective stimulation of central cholinergic and dopaminergic development in vitro by nerve growth factor, basic fibroblast growth factor, epidermal growth factor, insulin and the insulin-like growth factors I and II
Authors: Knusel B , Michel PP , Schwaber JS , Hefti F
Published: April 2018

To study the selectivity of neurotrophic actions in the brain, we analyzed the actions of several known growth factors on septal cholinergic, pontine cholinergic, and mesencephalic dopaminergic neurons in culture. Similar to nerve growth factor (NGF), basic fibroblast growth factor (bFGF) stimulated choline acetyltransferase activity in septal cultures. In contrast to NGF, bFGF also enhanced dopamine uptake in mesencephalic cultures and stimulated cell proliferation in all 3 culture types. Insulin and the insulin-like growth factors I and II stimulated transmitter-specific differentiation and cell proliferation in all culture types. Epidermal growth factor (EGF) produced a small increase in dopamine uptake by mesencephalic cells and stimulated cell proliferation in all culture types. In septal cultures, bFGF was most effective when given at early culture times, NGF at later times. The stimulatory actions of bFGF and insulin did not require the presence of glial cells and were not mediated by NGF. In mesencephalic cultures, the stimulation of dopamine uptake by bFGF and EGF was dependent on glial proliferation. The results suggest different degrees of selectivity of the neurotrophic molecules. NGF and, very similarly, bFGF seem to influence septal cholinergic neurons directly and rather selectively, whereas the neurotrophic actions of insulin and the insulin-like growth factors appear to be more general.
The role of osmotic pressure and membrane potential in K(+)-stimulated taurine release from cultured astrocytes and LRM55 cells
Authors: Martin DL , Madelian V , Seligmann B , Shain W
Published: April 2018

The effects of [K+]o on taurine release from glial cells were studied with primary cultures of cerebellar astrocytes and with LRM55 cells, a continuous glial cell line. The characteristics of K(+)-stimulated taurine release were virtually identical in the 2 cell types. Both cerebellar astrocytes and LRM55 cells released taurine when stimulated with high-K+ medium prepared by isosmotically substituting KCl for NaCl, but neither cell type released taurine when stimulated with hyperosmotic high-K+ medium prepared by adding solid KCl to control medium. The membrane potential of LRM55 cells was measured by intracellular recording and was insensitive to changes in [K+]o below 20 mM. LRM55 cells released taurine when stimulated with nondepolarizing concentrations of K+ (13–22 mM) if the isosmotically prepared high-K+ medium was used, but the cells did not release taurine when treated with a depolarizing concentration of K+ (50 mM) if hyperosmotic high-K+ medium was used. The time course of K(+)- stimulated taurine release was quite slow, having a time to peak of 10– 15 min. Small changes (2.5–10%) in the osmolarity of the medium strongly affected taurine release by cerebellar astrocytes and LRM55 cells. K(+)-stimulated taurine release from both cell types was inhibited when the osmolarity was increased with sucrose or NaCl and was enhanced when the osmolarity was reduced. Similarly, baseline taurine release was suppressed by small elevations in osmolarity and increased by reduced osmolarity.(ABSTRACT TRUNCATED AT 250 WORDS)
Changes in the distribution of GAP-43 during the development of neuronal polarity
Authors: Goslin K , Schreyer DJ , Skene JH , Banker G
Published: April 2018

GAP-43, a neuron specific growth-associated protein, is selectively distributed to the axonal domain in developing neurons; it is absent from dendrites and their growth cones. Using immunofluorescence microscopy, we have further examined the distribution of GAP-43 during the development of hippocampal neurons in culture, in order to determine when this polarized distribution arises. Cultured hippocampal neurons initially extend several short processes which have the potential to become either axons or dendrites. At this stage, before the morphological expression of polarity, GAP-43 is concentrated in the growth cones of these processes but is distributed more or less equally among them. Polarity becomes established when one of these processes elongates to become the axon. At the earliest stage when the emerging axon can be identified, GAP-43 is preferentially concentrated in its growth cone. During the next few days, as the remaining processes take on dendritic properties, they lose their residual GAP-43 immunoreactivity. Throughout development, GAP-43 remains highly concentrated in the axonal growth cone, but the concentration of GAP-43 in the axon shaft increases, beginning near the growth cone and progressing proximally until GAP-43 is uniformly distributed along the entire axon. At all stages of development, GAP-43 is also concentrated in the region of the Golgi apparatus. These results suggest that the selective sorting of at least one membrane protein into the axon coincides with the morphological expression of polarity. These results also raise the possibility that GAP-43 may play an important role in the early phases of axonal outgrowth, by which the functional polarity of neurons is established.
Slow transport rates of cytoskeletal proteins change during regeneration of axotomized retinal neurons in adult rats
Authors: McKerracher L , Vidal-Sanz M , Aguayo AJ
Published: April 2018

To investigate cytoskeletal changes associated with axonal regrowth from damaged nerve cells in the mammalian CNS, we examined the slow transport of axonal proteins during the regeneration of adult rat retinal ganglion cell (RGC) axons. Although normally such RGC axons do not regrow after injury in the CNS, they can extend several centimeters when their nonneuronal environment is changed by replacing the optic nerve (ON) with a grafted segment of peripheral nerve (PN). Proteins transported in axons of RGCs from intact control and PN-grafted animals were labeled by an intraocular injection of 35S-methionine and examined 4–60 days later by SDS PAGE. During RGC regeneration into PN grafts, the transport rate of tubulin and neurofilament increased twofold, whereas that of actin decreased to nearly one third of its normal rate. Thus, in these regenerating RGC axons, all three major cytoskeletal proteins were largely transported within a single rate component rather than in the two separate components (SCa and SCb) normally observed in the intact ON. Furthermore, the 200 kDa neurofilament protein (NF-H) was persistently detected in Western blots during periods of active regeneration, a finding that contrasts with the late appearance of the NF-H during the developmental growth of retinal axons. The changes in slow transport observed during RGC regeneration in adult rats may reflect growth-associated responses of mature CNS neurons during periods of active axonal extension.
Chromatic mechanisms in striate cortex of macaque
Authors: Lennie P , Krauskopf J , Sclar G
Published: April 2018

We measured the responses of 305 neurons in striate cortex to moving sinusoidal gratings modulated in chromaticity and luminance about a fixed white point. Stimuli were represented in a 3-dimensional color space defined by 2 chromatic axes and a third along which luminance varied. With rare exceptions the chromatic properties of cortical neurons were well described by a linear model in which the response of a cell is proportional to the sum (for complex cells, the rectified sum) of the signals from the 3 classes of cones. For each cell there is a vector passing through the white point along which modulation gives rise to a maximal response. The elevation (theta m) and azimuth (phi m) of this vector fully describe the chromatic properties of the cell. The linear model also describes neurons in l.g.n. (Derrington et al., 1984), so most neurons in striate cortex have the same chromatic selectivity as do neurons in l.g.n. However, the distributions of preferred vectors differed in cortex and l.g.n.: Most cortical neurons preferred modulation along vectors lying close to the achromatic axis and those showing overt chromatic opponency did not fall into the clearly defined chromatic groups seen in l.g.n. The neurons most responsive to chromatic modulation (found mainly in layers IVA, IVC beta, and VI) had poor orientation selectivity, and responded to chromatic modulation of a spatially uniform field at least as well as they did to any grating. We encountered neurons with band-pass spatial selectivity for chromatically modulated stimuli in layers II/III and VI. Most had complex receptive fields. Neurons in layer II/III did not fall into distinct groups according to their chromatic sensitivities, and the chromatic properties of neurons known to lie within regions rich in cytochrome oxidase appeared no different from those of neurons in the interstices. Six neurons, all of which resembled simple cells, showed unusually sharp chromatic selectivity.
Cortical radial glia: identification in tissue culture and evidence for their transformation to astrocytes
Authors: Culican SM , Baumrind NL , Yamamoto M , Pearlman AL
Published: April 2018

Radial glia are transiently present in the developing cerebral cortex, where they are thought to guide the migration of neurons from the proliferative zone to the forming cortical plate. To provide a framework for experimental studies of radial glia, we have defined morphological and immunocytochemical criteria to identify them in primary cultures of cortical cells obtained at embryonic day 13 in the mouse. Cortical radial glia in culture for 1–2 d resemble radial glia in vivo: they have a long, thin, unbranched process extending from one or both ends of the elongated cell body and are labeled with the monoclonal antibody RC1 but not with antibodies to glial fibrillary acidic protein (abGFAP). We tested the specificity of RC1 by double- labeling with a panel of cell-type specific antibodies, and found that it labels radial glia, astrocytes, and fibroblast-like cells, but not neurons. Fibroblasts are easily distinguished from glia by morphology and by labeling with antibodies to fibronectin. To test the hypothesis that radial glia become astrocytes when their developmental role is complete, we examined their morphological and immunocytochemical development in culture. After 3–4 d in vitro radial glia develop several branched processes; in this transitional stage they are labeled by both RC1 and abGFAP. Many radial glia lose RC1 immunoreactivity as they become increasingly branched and immunoreactive to abGFAP. In areas of the cultures that have few neurons and in cultures depleted of neurons by washing, flat, nonprocess-bearing glia predominate. These cells do not lose immunoreactivity to RC1 during the 9-d period of observation even though they acquire GFAP.(ABSTRACT TRUNCATED AT 250 WORDS)
Long-term changes in purposive and reflexive responses to nociceptive stimulation following anterolateral chordotomy
Authors: Vierck CJ , Greenspan JD , Ritz LA
Published: April 2018

Macaca nemestrina monkeys received unilateral interruption of the spinothalamic tract, producing contralateral hypalgesia and a bilateral decrease in amplitude of the flexion reflex. These effects on operant escape and reflex responses to electrocutaneous stimulation (ES) were monitored for months to evaluate relationships between the extent of each lesion and the presence or absence of recovery from the early postoperative deficits. Before surgery, the animals were trained to perform an operant response that terminated ES to the lateral calf of either leg. The durations of ES tolerated by each monkey were inversely related to stimulus intensities within the pain sensitivity range of human subjects. The vigor of operant escape responses and the frequency of intertrial pulls of the manipulandum were directly related to stimulus intensity. Following anterolateral chordotomy at an upper thoracic level, these measures revealed a contralateral hypalgesia for each animal. Operant responsivity to stimulation contralateral to the lesion recovered to control levels for 7 animals (group R). Sustained contralateral recovery of operant reactivity was not observed for 8 monkeys (group U). Most of the lesions in groups R and U were similar in extent and location, involving the classical distribution of the spinothalamic tract (in the anterolateral and ventral columns). Thus, recovery was not determined solely by lesion configuration. However, when recovery did occur, it was associated with medially extensive lesions. A subgroup of 3 unrecovered animals received superficial lesions that did not substantially involve the gray matter or the ventral columns. For all animals, reflex magnitudes were initially diminished bilaterally and then increased over months of testing. Reflex recovery was greater for the animals that demonstrated recovery of intentional reactions to nociception (group R). An ipsilateral hyperreflexia became apparent for group R. Contralateral recovery to normal levels was observed for group R but not for group U. The time course of recovery for operant and reflex responses clearly differed, indicating that different processes determined changes in these spinal and supraspinal reactions to nociceptive stimulation.
Overlap of dopaminergic, adrenergic, and serotoninergic receptors and complementarity of their subtypes in primate prefrontal cortex
Authors: Goldman-Rakic PS , Lidow MS , Gallager DW
Published: April 2018

Quantitative in vitro autoradiography was used to determine and compare the areal and laminar distribution of the major dopaminergic, adrenergic, and serotonergic neurotransmitter receptors in 4 cytoarchitectonic regions of the prefrontal cortex (Walker's areas 12, 46, 9, and 25) in adult rhesus monkeys. The selective ligands, 3H-SCH- 23390, 3H-raclopride, 3H-prazosin, and 3H-clonidine were used to label the D1 and D2 dopamine receptor subtypes and the alpha 1- and alpha 2- adrenergic receptors, respectively, while 125I-iodopindolol was used to detect beta-adrenergic receptors. The radioligands, 3H-5- hydroxytryptamine and 3H-ketanserin labeled, respectively, the 5-HT1 and 5-HT2 receptors. Densitometry was performed on all cortical layers and sublayers for each of the 7 ligands to allow quantitative as well as qualitative comparison among them in each cytoarchitectonic area. Although each monoamine receptor was distributed in a distinctive laminar-specific pattern that was remarkably similar from area to area, there was considerable overlap among the dopaminergic, adrenergic, and serotoninergic receptors, while subtypes of the same receptor class tended to have complementary laminar profiles and different concentrations. Thus, the D1 dopamine, the alpha 1- and alpha 2- adrenergic, and the 5-HT1 receptors were present in highest relative concentration in superficial layers I, II, and IIIa (the “S” group). In contrast, the beta 1- and beta 2-adrenergic subtypes and the 5-HT2 receptor had their highest concentrations in the intermediate layers, IIIb and IV (the “I” group), while the D2 receptor was distinguished by relatively high concentrations in the deep layer V compared to all other layers (the “D” class). Consequently, clear laminar differences were observed in the D1 vs D2 dopaminergic, the alpha- vs beta- adrenergic, and the 5-HT1 vs 5-HT2 serotoninergic receptor subtypes in all 4 areas examined. The anatomical overlap of different monoaminergic receptors in the same cortical strata suggests that there may be families of receptors linked by localization on common targets, while the complementary laminar distribution of the D1 vs D2, the 5-HT1 vs 5- HT2 and the alpha- vs beta-adrenergic receptors raises the possibility that different subtypes within a given class may have distinctive actions in cortex by virtue of their localization on different cells or possibly different portions of the same cell. Understanding the anatomical arrangement of receptors within the cortical layers may aid in the analysis of monoaminergic modulation of higher cortical function.
Pseudorabies virus: a highly specific transneuronal cell body marker in the sympathetic nervous system
Authors: Strack AM , Loewy AD
Published: April 2018

The present report presents a series of experiments using Bartha's K strain of pseudorabies virus (PRV) designed to test the specificity of this virus as a retrograde transneuronal marker in the sympathetic nervous system of rats. Three experiments were performed. First, an injection of PRV was made in the anterior chamber of the eye, followed 24 hr later by an injection of WGA-HRP. PRV infected neurons in the superior cervical ganglion (SCG) always contained WGA-HRP. This dual labeling of SCG neurons suggests that the PRV cell body labeling does not nonspecifically infect nearby neurons. Second, after PRV injections into the pinna or eye, a specific segmental distribution of the transneuronal cell body labeling occurred in the intermediolateral cell column and related spinal areas. After eye injections, the majority of transneuronally labeled neurons were in the T1-T3 segments. After pinna injections, the majority of labeled cells were in the T2-T5 segments. Since the SCG cells innervating these 2 end organs lie in close proximity to each other within the ganglion, these results suggest that a specific transfer of the virus to the preganglionic neurons occurred, possibly via a transsynaptic mechanism. Third, virally infected glial cells were rarely found in the SCG or spinal cord. In summary, Bartha's K strain of PRV is a specific transneuronal retrograde grader marker in the sympathetic nervous system.
Structure, expression, and some regulatory mechanisms of the rat preprotachykinin gene encoding substance P, neurokinin A, neuropeptide K, and neuropeptide gamma
Authors: Carter MS , Krause JE
Published: April 2018

The rat preprotachykinin (PPT) gene encoding the neuropeptides substance P (SP), neurokinin A (NKA), neuropeptide K (NPK), and neuropeptide gamma was isolated from a lambda Charon 4A genomic library. Two overlapping clones contained all of the exons present in beta-PPT, including some 7 and 9 kb 5′ and 3′ flanking sequence, respectively. The presence of 1 major and 2 minor transcription initiation sites was determined from primer extension and nuclease protection experiments. Analysis of the nucleotide sequence homology between the rat and bovine revealed the presence of highly conserved regions throughout the entire coding region and within the 5′ flanking sequences. Primer extension and nuclease protection experiments demonstrated that the primary transcript is differentially spliced primarily into gamma- and beta-PPT mRNA in all tissues examined in the adult rat where the gene is expressed. beta-PPT mRNA contains all of the exons, whereas gamma-PPT mRNA lacks exon 4, which encodes part of the N-terminus of NPK. The alpha-PPT mRNA, which lacks exon 6 (the sequence encoding NKA and processing sites), comprises about 1% of the total PPT mRNA. An RNA secondary structure model is proposed to account for these specific exon exclusion events in the RNA splicing process. These results are discussed with regard to the mechanisms regulating SP gene expression and the functional significance of differential RNA splicing in the rat.
The formation of specific synaptic connections between muscle sensory and motor neurons in the absence of coordinated patterns of muscle activity
Authors: Frank E
Published: April 2018

The influence of patterned neuronal activity on the formation of specific monosynaptic connections between muscle sensory and motor neurons was studied in the developing spinal cord of the bullfrog. Motor innervation of the forelimb was disrupted in tadpoles by resection of the brachial ventral root before these synaptic connections began to form in the spinal cord. In those frogs accepted for analysis, motor reinnervation of the forelimb was nonspecific and there was no coordinated movement of the limb. Synaptic connections therefore developed in the absence of temporal correlations of activity in muscle spindle afferents and motoneurons. Despite this disruption, afferent fibers supplying the triceps brachii muscles selectively innervated a restricted subpopulation of brachial motoneurons. Those motoneurons that received large synaptic inputs from afferents in one branch of the triceps nerve also received large inputs from afferents in the other triceps branches. Inputs from afferents supplying other muscles were not correlated with those from triceps afferents, suggesting the existence of a property common to all triceps afferents causing them to innervate a common subpopulation of motoneurons. These results show that in the absence of normal patterned sensory activity, sufficient cues still exist to permit the formation of specific sets of synaptic connections, and they argue indirectly for the existence of chemical labels that can determine the pattern of these connections.
Lesions of the nigrostriatal dopamine projection increase the inhibitory effects of D1 and D2 dopamine agonists on caudate-putamen neurons and relieve D2 receptors from the necessity of D1 receptor stimulation
Authors: Hu XT , Wachtel SR , Galloway MP , White FJ
Published: April 2018

Extracellular single unit recording and microiontophoretic techniques were used to determine the sensitivities and interactions of D1 and D2 dopamine (DA) receptors in the caudate putamen (CPu) of rats that were denervated of DA by intraventricular injections of the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA). Seven to 10 d after the 6-OHDA injection, DA levels in the ipsilateral CPu were reduced to 11.8% of control. Current-response curves revealed that the inhibitory responses of CPu neurons to microiontophoretic administration of both the selective D1 receptor agonist SKF-38393 and the selective D2 receptor agonist quinpirole were significantly increased in 6-OHDA-pretreated rats, suggesting up-regulation of both receptor subtypes. Although our previous studies have established that D1 receptor activation is normally required for (enables) the inhibitory effects of selective D2 agonists in the CPu, this requirement was no longer evident in 6-OHDA- denervated rats. Whereas acute DA depletion [produced by the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine (AMPT)] attenuated the inhibitory effects of quinpirole on CPu neurons, long-term DA denervation (produced by 6-OHDA) enhanced the inhibitory effects of the D2 agonist. The enhanced effects of quinpirole in 6-OHDA-lesioned rats were not due to residual DA stimulating supersensitive D1 receptors (i.e., enabling) since further DA depletion (99.7%), produced by acute administration of AMPT in 6-OHDA-lesioned rats, failed to diminish the inhibitory efficacy of quinpirole. In addition to relieving D2 receptors from the need for D1 receptor-mediated enabling, 6-OHDA lesions also abolished the normal synergistic relationship between the receptor subtypes since low (subinhibitory) currents of SKF-38393 (4 nA) failed to potentiate the inhibitory effects of quinpirole on CPu neurons in lesioned rats. Similar findings (i.e., supersensitivity and loss of synergistic effects) were obtained from rats that had received repeated pretreatment with reserpine (2.5 mg/kg) for 4 d, indicating that these effects of 6-OHDA lesions were due to the depletion of synaptic DA rather than to the structural loss of DA terminals. Therefore, both the quantitative (potentiation) and the qualitative (enabling) synergistic effects between D1 and D2 receptors in the rat CPu were abolished when these receptors were functionally supersensitive. The present study provides electrophysiological support for previous behavioral studies indicating that the requirement of D1 receptor stimulation for D2 receptor-mediated functional effects (enabling) is not maintained in rats chronically depleted of DA by either 6-OHDA lesions or repeated reserpine.
Immunocytochemical and neurochemical evidence for age-related loss of GABA in the inferior colliculus: implications for neural presbycusis
Authors: Caspary DM , Raza A , Lawhorn Armour BA , Pippin J , Arneric SP
Published: April 2018

The present study describes substantial, selective, age-related loss of the putative inhibitory neurotransmitter GABA in the central nucleus of the inferior colliculus (CIC) of rat based on immunocytochemical and neurochemical data. For immunocytochemistry, neurons in the CIC were immunolabeled using an antibody against a GABA conjugate in young adult (2- to 7-month-old) and aged (18- to 29-month-old) Fischer-344 rats. Computer-assisted morphometry was then used to generate maps of GABA- immunoreactive neurons in the CIC. The number of GABA-positive neurons was reduced 36% in the ventrolateral portion of the CIC of aged animals (93 neurons/mm2) compared to their matched young adult cohorts (145 neurons/mm2; p less than 0.01). For neurochemistry, basal and K(+)- evoked release of the endogenous amino acids GABA, glutamate (Glu), aspartate (Asp), and tyrosine (Tyr) from micropunches of the CIC were measured in 8 age-paired animals from the 2 age groups using high- performance liquid chromatography. Overflow of radiolabeled acetylcholine (3H-ACh) was also determined. In both age groups, K(+)- evoked release of GABA, Glu, Asp, and 3H-ACh from CIC punches was significantly enhanced above basal efflux (+200, +215, +163, and +309%, respectively), while Tyr release was unchanged. Evoked release of 3H- ACh and all amino acids except Tyr showed substantial Ca2+ dependence. A significant (p less than 0.05) age-related reduction in both basal (- 35%) and K(+)-stimulated (-42%) efflux of GABA from the CIC was observed. A corresponding decrease in postrelease tissue content of GABA in CIC of aged rats was observed (-30%, p less than 0.05). In contrast, tissue content as well as basal and evoked release of Glu, Asp, Tyr, and 3H-ACh was similar between the 2 age groups. Age-related GABA neurochemical changes described in the CIC were not observed in the release of the other amino acids or 3H-ACh from either the rostral ventrolateral medulla or the somatosensory cortex, 2 brain regions involved in processing non-auditory sensory input. These data support previous findings that GABA, Glu, Asp, and ACh may subserve neurotransmission in the CIC. Additionally, these data provide clear evidence for a pronounced, region- and neurotransmitter-selective, age- related reduction of GABA in the CIC. These findings support the hypothesis that impairment of inhibitory GABAergic neurotransmission in the CIC may contribute to abnormal auditory perception and processing seen in neural presbycusis.
Structure-activity relationships for amino acid transmitter candidates acting at N-methyl-D-aspartate and quisqualate receptors
Authors: Patneau DK , Mayer ML
Published: April 2018

Dose-response curves for activation of excitatory amino acid receptors on mouse embryonic hippocampal neurons in culture were recorded for 15 excitatory amino acids, including the L-isomers of glutamate, aspartate, and a family of endogenous sulfur amino acids. In the presence of 3 microM glycine, with no extracellular Mg, micromolar concentrations of 11 of these amino acids produced selective activation of N-methyl-D-aspartate (NMDA) receptors. L-Glutamate was the most potent NMDA agonist (EC50 2.3 microM) and quinolinic acid the least potent (EC50 2.3 mM). Dose-response curves were well fit by the logistic equation, or by a model with 2 independent agonist binding sites. The mean limiting slope of log-log plots of NMDA receptor current versus agonist concentration (1.93) suggests that a 2-site model is appropriate. There was excellent correlation between agonist EC50S determined in voltage clamp experiments and KdS determined for NMDA receptor binding (Olverman et al., 1988). With no added glycine, and 1 mM extracellular Mg, responses to NMDA were completely blocked; responses to kainate and quisqualate were unchanged. Under these conditions, glutamate and the sulfur amino acids activated a rapidly desensitizing response, similar to that evoked by micromolar concentrations of quisqualate and AMPA, but mM concentrations of L- aspartate, homoquinolinic acid, and quinolinic acid failed to elicit a non-NMDA receptor-mediated response. Except for L-glutamate (EC50 480 microM), the low potency of the sulfur amino acids prevented the study of complete dose-response curves for the rapidly desensitizing response at quisqualate receptors. Small-amplitude nondesensitizing quisqualate receptor responses were activated by much lower concentrations of all quisqualate receptor agonists. Full dose-response curves for the nondesensitizing response were obtained for 9 amino acids; L-glutamate was the most potent endogenous agonist (EC50 19 microM). Domoate (EC50 13 microM) and kainate (EC50 143 microM) activated large-amplitude, nondesensitizing responses.
Proteolytic processing of beta-amyloid precursor by calpain I
Authors: Siman R , Card JP , Davis LG
Published: April 2018

The beta-amyloid peptide is a core component of the neuritic plaques that accumulate in Alzheimer's disease. Since the beta-peptide resides within a family of precursor proteins (APPs), proteolytic processing of APP is required for beta-amyloid deposition into plaques. Here, we have examined the role played by the calcium-dependent cysteine protease calpain I in APP processing. Immunoblotting with a specific APP antiserum was used to assess the in vitro degradation of rat brain APP, which appears as a triplet of polypeptides of Mr 110–130 kDa. Both soluble and membrane-bound APP were extraordinarily sensitive to activated calpain I. APP contains at least 3 distinct calpain I cleavage sites. The most protease-sensitive site was located within the highly acidic structural motif called the PEST domain, a second site was upstream of the putative N-linked glycosylation sites, and a third generated a 16 kDa carboxy-terminal fragment that contains the beta- peptide. Based on light microscopic immunohistochemistry, APP and calpain I were extensively colocalized within large numbers of neurons distributed throughout the rat brain, with especially high levels of each in neocortical layer 5, subiculum, globus pallidus, entopeduncular nucleus, anterodorsal and reticular thalamic nuclei, motor trigeminal nucleus, deep cerebellar nuclei, and Purkinje cells. Both antigens were most prevalent within neuronal perikarya. Intraventricular kainate infusion, which is known to cause rapid activation of hippocampal calpain I, produced a 32% decline in APP levels after 24 hr, suggestive of in vivo degradation of APP by calpain I. Following kainate-induced neuronal loss, both APP and calpain I immunoreactivities appeared in the surrounding reactive astroglia. These results indicate that calpain I may be involved in the normal and, perhaps, pathological processing of APP, and that this processing could occur in either neurons or reactive astrocytes. Calcium influx and calpain I activation may provide a mechanism by which excitatory neurotransmission regulates APP metabolism.
Nerve growth factor regulates sympathetic ganglion cell morphology and survival in the adult mouse
Authors: Ruit KG , Osborne PA , Schmidt RE , Johnson EM , Snider WD
Published: April 2018

We have investigated the effects of prolonged systemic injections of nerve growth factor (NGF) and its antiserum on the survival and morphology of sympathetic ganglion cells in adult mice. Using intracellular injections of Lucifer yellow in lightly fixed superior cervical ganglia, we show that total dendritic lengths of ganglion cells are increased 29% after 2 weeks of NGF treatment. The increased dendritic length is characterized by increased branching within the dendritic arborization and not by the addition of new primary dendrites. In addition, cell soma cross-sectional area was increased 45%. Conversely, administration of NGF antiserum for 1 month decreased total dendritic length by 33%, decreased ganglion cell body size by 26%, and reduced the number of neurons in the ganglion by 25%. After 3 months of NGF antiserum treatment, the number of neurons in the ganglion was reduced a total of 41%. NGF antiserum treatment for 1 month in aged (22 months old) animals reduced ganglion cell body size by 21% and cell number by 22%, decreases that are comparable to those observed in young adult animals. Our results indicate that, even in maturity, sympathetic ganglion cells remain dependent on NGF for survival and maintenance of dendritic geometry, and this dependence continues into old age.
Parcellation of sensorimotor transformations for arm movements
Authors: Flanders M , Soechting JF
Published: April 2018

Pointing to a visual target in 3-dimensional space requires a neural transformation from a visually derived representation of target location to an appropriate pattern of activity in arm muscles. Previous results suggested that 1 step in this process involves a transformation from a representation of target location to a representation of intended arm orientation, and that the neural implementation of this transformation involves a linear approximation to the mathematically exact, nonlinear solution. These results led to the hypothesis that the transformation is parceled into 2 separate channels. In 1 channel a representation of target azimuth is transformed into a representation of arm yaw angles, while in the other channel representations of target distance and target elevation are transformed into a representation of arm elevation angles. The present experiments tested this hypothesis by measuring the errors made by human subjects as they pointed to various parameters of the remembered location of a target in space. The results show that subjects can use the 2 hypothesized channels separately. For example, subjects can accurately point to the target's azimuth while ignoring the target's elevation and distance. The results also show that subjects are unable to point to the target's elevation while ignoring the target's distance, consistent with the hypothesis that information about target elevation and target distance is tied together in the same channel. The parcellation demonstrated in this study is compared to reports of parceled sensorimotor transformation in other vertebrate species.
Distribution and plasticity of immunocytochemically localized GABAA receptors in adult monkey visual cortex
Authors: Hendry SH , Fuchs J , deBlas AL , Jones EG
Published: April 2018

Immunocytochemical methods were used to reveal new details of the distribution and plasticity of GABAA receptors in the visual cortex of adult monkeys; the findings were compared with those of autoradiographic experiments involving the binding of 3H-muscimol and 3H-flunitrazepam. In both areas 17 and 18, a monoclonal antibody to the purified GABAA complex (deBlas et al., 1988) produced staining of punctate profiles in the neuropil and around cell bodies and large processes in layers I-VI. The receptor immunostaining was relatively intense in layers II-III, IVA, IVC beta, and VI; these alternated with lightly stained layers I, IVB, IVC alpha, and V. In area 18, the laminar pattern was similar except that layer IV was split into a superficial, lightly stained half and a deep, intensely stained half. In sections cut parallel to the pial surface, receptor distribution in most layers was found to be uniform. There were 3 exceptions in area 17: (1) patches of intense receptor staining were present in layers II and III; (2) a widely spaced, irregular lattice of intense staining was found in layer IVA; and (3) a much finer, regular lattice was present in layer IVC. The patches in layers II-III and the lattice in layer IVA coincided precisely with regions of intense cytochrome oxidase (CO) staining. The binding of 3H-muscimol and 3H-flunitrazepam revealed a laminar pattern that was similar in most respects, including greater ligand binding in layer IVA of area 17, but showed no evidence of the sublaminar organization in layers IVA and IVC beta. Inhomogeneities in receptor immunostaining but not ligand binding were also seen in layer III of area 18. Following a 5 or 10 d period in which intravitreal injections of TTX had silenced ganglion cell activity in one retina, GABAA receptor immunostaining in layer IVC beta was distributed in intensely stained stripes, 450–550 microns wide, that alternated with narrower, lightly stained stripes. Stripes were also seen with receptor immunostaining and with the binding of the 2 radioligands in layer IVC beta of monocularly enucleated monkeys. Comparison with CO staining revealed that the stripes of reduced immunostaining or ligand binding corresponded to columns dominated by the TTX-injected or enucleated eye. Quantitatively, the binding in the deprived eye columns was reduced by 25%.(ABSTRACT TRUNCATED AT 400 WORDS)
14C-2-deoxyglucose uptake in the ground squirrel brain during entrance to and arousal from hibernation
Authors: Kilduff TS , Miller JD , Radeke CM , Sharp FR , Heller HC
Published: April 2018

Neuronal activity underlying various phases of the mammalian hibernation cycle was investigated using the 14C-2-deoxyglucose (2DG) method. Relative 2DG uptake (R2DGU) values were computed for 96 brain regions across 7 phases of the hibernation cycle: euthermia, 3 body temperature (Tb) intervals during entrance into hibernation, stable deep hibernation, and 2 Tb intervals during arousal from hibernation. Multivariate statistical techniques were employed to identify objectively groups of brain regions whose R2DGU values showed a similar pattern across all phases of hibernation. Factor analysis revealed that most of the variability in R2DGU values for the 96 brain regions across the entire cycle could be accounted for by 3 principal factors. These factors could accurately discriminate the various phases of hibernation on the basis of the R2DGU values alone. Three hypothalamic and 3 cortical regions were identified as possibly mediating the entrance into hibernation because they underwent a change in R2DGU early in entrance into hibernation and loaded strongly on one of the principal factors. Another 4 hypothalamic regions were similarly identified as possibly causally involved in the arousal from hibernation. These results, coupled with characteristic changes in ordinal rank of the 96 brain regions in each phase of hibernation, support the concept that mammalian hibernation is an active, integrated orchestration of neurophysiological events rather than a state entered through a passive process.
Differential regulation of corticotropin-releasing factor mRNA in rat brain regions by glucocorticoids and stress
Authors: Imaki T , Nahan JL , Rivier C , Sawchenko PE , Vale W
Published: April 2018

The regulation of corticotropin-releasing factor (CRF) mRNA expression in the rat brain by glucocorticoids and stress was examined by Northern blot analysis and in situ hybridization histochemistry. Rats either were exposed to a single electrical footshock session and killed 2, 4, 12, or 24 hr later (acute stress), or were subjected to the same regimen twice daily for 3 or 7 d and killed on the day following the last session (chronic stress). Rats placed in the experimental chamber but not administered shock comprised a “sham-handling” group. Chronic (7 d) intermittent footshock stress resulted in an 84 +/- 26% (P less than 0.05) increase in CRF mRNA levels in the whole hypothalamus as detected by Northern blot analysis and a 97 +/- 29% (P less than 0.05) increase in the paraventricular nucleus (PVN) as detected using in situ hybridization. No significant change in CRF mRNA levels was observed in the hypothalamus at any time up to 24 hr after a single exposure to footshock stress. A different pattern of results was obtained in other CRF-expressing cell groups. In Barrington's nucleus (a pontine micturition center), both acute and chronic stress produced significant increases in CRF mRNA, while in the olfactory bulb, both paradigms resulted in decreased levels. By Northern blot analysis, CRF mRNA in the olfactory bulb declined steadily, beginning at 4 hr after acute stress, and reached significance at 24 hr (69.2 +/- 1.9% of control, P less than 0.05). Levels from chronically (7 d) stressed animals declined to 54.1 +/- 5.1% of control value (P less than 0.05). Analysis of hybridization histochemical material revealed that both the number of positively hybridized cells and the number of silver grains per cell in the mitral and external plexiform layers of the bulb decreased following acute and chronic stress. However, CRF mRNA levels in the olfactory bulb were decreased to a comparable extent in the sham- handling group, suggesting that exposure to a novel environment can effect a decrease in CRF mRNA levels in the olfactory bulb. To provide comparisons with the effects of manipulation of glucocorticoid status, comparable analyses were carried out in separate groups of animals following adrenalectomy (ADX) with and without corticosteroid replacement. After ADX, CRF mRNA levels in the whole hypothalamus increased 60 +/- 5% (P less than 0.05) and were normalized following dexamethasone replacement. In contrast to the hypothalamus, no effects of steroid manipulation on CRF mRNA levels in the olfactory bulb, midbrain, cerebral cortex, or brain stem were detected.(ABSTRACT TRUNCATED AT 400 WORDS)
Expression of diverse neuropeptide cotransmitters by identified motor neurons in Aplysia
Authors: Church PJ , Lloyd PE
Published: April 2018

Neuropeptide synthesis was determined for individual identified ventral- cluster neurons in the buccal ganglia of Aplysia. Each of these cells was shown to be a motor neuron that innervates buccal muscles that generate biting and swallowing movements during feeding. Individual neurons were identified by a battery of physiological criteria and stained with intracellular injection of a vital dye, and the ganglia were incubated in 35S-methionine. Peptide synthesis was determined by measuring labeled peptides in extracts from individually dissected neuronal cell bodies analyzed by HPLC. Previously characterized peptides found to be synthesized included buccalin, FMRFamide, myomodulin, and the 2 small cardioactive peptides (SCPs). Each of these neuropeptides has been shown to modulate buccal muscle responses to motor neuron stimulation. Two other peptides were found to be synthesized in individual motor neurons. One peptide, which was consistently observed in neurons that also synthesized myomodulin, is likely to be the recently sequenced myomodulin B. The other peptide was observed in a subset of the neurons that synthesize FMRFamide. While identified motor neurons consistently synthesized the same peptide(s), neurons that innervate the same muscle often express different peptides. Neurons that synthesized the SCPs also contained SCP-like activity, as determined by snail heart bioassay. Our results indicate that every identified motor neuron synthesizes a subset of these methionine-containing peptides, and that several neurons consistently synthesize peptides that are likely to be processed from multiple precursors.
Growth of regenerating goldfish axons is inhibited by rat oligodendrocytes and CNS myelin but not but not by goldfish optic nerve tract oligodendrocytelike cells and fish CNS myelin
Authors: Bastmeyer M , Beckmann M , Schwab ME , Stuermer CA
Published: April 2018

Encounters of regenerating goldfish retinal axons with oligodendrocytes and CNS myelin of mammals and fish were monitored in in vitro assays. Upon contact with highly branched rat oligodendrocytes, goldfish axons collapsed or grew around but never crossed these cells. However, in the presence of the antibody IN-1 against the oligodendrocyte-associated growth-inhibitory proteins, axons did grow over highly branched oligodencrocytes. In contrast to the mammalian oligodendrocytes, goldfish optic nerve/tract-derived oligodendrocytelike cells allowed the growth of axons across their surface and even along their processes. The fish growth cones avoided entering the region of rat CNS myelin applied to polylysine/laminin-coated coverslips or failed to elongate on this substrate. They were, however, able to pass over CNS myelin of fish. When exposed to rat CNS myelin as the sole substrate, axonal outgrowth from fish retinal explants was inhibited almost entirely. However, outgrowth on fish CNS myelin was substantial, but many more axons extended on fish or rat brain membranes that were depleted of myelin. Thus, goldfish retinal axons are sensitive to the axon-growth-inhibiting cell-surface molecules of mammalian oligodendrocytes as well as CNS myelin. Fish optic nerve oligodendrocytelike cells and fish CNS myelin lack these inhibitory properties and are growth permissive. These in vitro experiments suggest that the success of axonal regeneration in the fish optic nerve is causally related to the presence of growth-permissive properties and to the absence of growth inhibitors on fish optic nerve/tract oligodendrocytelike cells.
A direct demonstration of functional specialization in human visual cortex
Authors: Zeki S , Watson JD , Lueck CJ , Friston KJ , Kennard C , Frackowiak RS
Published: April 2018

We have used positron emission tomography (PET), which measures regional cerebral blood flow (rCBF), to demonstrate directly the specialization of function in the normal human visual cortex. A novel technique, statistical parametric mapping, was used to detect foci of significant change in cerebral blood flow within the prestriate cortex, in order to localize those parts involved in the perception of color and visual motion. For color, we stimulated the subjects with a multicolored abstract display containing no recognizable objects (Land color Mondrian) and contrasted the resulting blood flow maps with those obtained when subjects viewed an identical display consisting of equiluminous shades of gray. The comparison identified a unique area (area V4) located in the lingual and fusiform gyri of the prestriate cortex. For motion, blood flow maps when subjects viewed moving or stationary black and white random-square patterns were contrasted. The comparison identified a unique area located in the region of the temporo-parieto-occipital junction (area V5). We thus provide direct evidence to show that, just as in the macaque monkey, different areas of the human prestriate visual cortex are specialized for different attributes of vision. The striate cortex (V1) and the contiguous visual area (V2), which in the monkey brain feed both the homologous areas, were active in all 4 conditions. This pattern of activity allowed us to use an extension of the approach to assess the functional relationship between the 3 areas during color and motion stimulation. This is based on an hypothesis-led analysis of the covariance structure of the blood flow maps and promises to be a powerful tool for inferring anatomical pathways in the normal human brain.(ABSTRACT TRUNCATED AT 250 WORDS)