bluuebunny/crossref_metadata_2025 huggingface dataset:
Heparan sulfate proteoglycan and laminin immunoreactivity on cultured astrocytes: relationship to differentiation and neurite growth
Authors: Ard MD , Bunge RP
Published: March 2018

Extracellular matrix (ECM) produced by Schwann cells is known to promote growth of several types of neurites (Ard et al., 1987). Whether a similar material produced by astrocytes may be available to promote neurite growth during CNS development is now open to question. The present study was undertaken to define conditions under which cultured astrocytes deposit the ECM components laminin and heparan sulfate proteoglycan (HSPG), and to relate this deposition to the ability of astrocytes to support neurite growth. The use of 2 different culture media permitted the growth of astrocytes either with or without these ECM components. Neonatal rat cortical astrocytes were cultured by the method of McCarthy and de Vellis (1980) and studied by immunocytochemistry and electron microscopy. Astrocytes grown in serum- containing medium for 5 or 9 d after subculturing were shown to have fibrillar patches of ECM containing both HSPG and laminin immunoreactivity. Immunoreactivity for the 2 molecules was usually colocalized. In contrast, astrocytes subcultured for 5 d in defined medium showed no immunocytochemical staining for either laminin or HSPG and had no ECM visible in EM. Formation of stellate processes was increased when cells were grown in defined medium compared with that seen in serum-containing medium, and growth of the population was slower. In 3 other conditions, attainment of stellate morphological differentiation by the astrocytes was correlated with diminution in immunostaining for ECM components. (1) In older cultures (30–42 d after subculturing), stellate, mitotically quiescent cells showed relatively little HSPG or laminin immunoreactivity. (2) Cultures initially maintained in serum-containing medium and then converted to defined medium lost much of their immunoreactivity for ECM components and developed longer processes. (3) When neurites from fetal rat dorsal root ganglion explants grew across monolayers of astrocytes in serum- containing medium, diminution of ECM immunostaining and development of stellate processes were seen in areas directly contacted by the neurites. ECM-containing laminin and HSPG did not appear to be necessary for neurites to interact with astrocytes. In defined medium, in which no ECM was detected, dorsal root ganglion neurites were found in contact with astrocyte surfaces rather than on the rat tail collagen substratum on the culture dish.(ABSTRACT TRUNCATED AT 400 WORDS)
Primate motor cortex and free arm movements to visual targets in three- dimensional space. III. Positional gradients and population coding of movement direction from various movement origins
Authors: Kettner RE , Schwartz AB , Georgopoulos AP
Published: March 2018

In one experiment, we studied the relations between the frequency of discharge of 274 single cells in the arm area of the motor cortex of the monkey and the actively maintained position of the hand in space. We found that the frequency of discharge of 63.9% of the cells studied was a multilinear function of the position of the hand in space according to the following equation (multiple linear regression): d = f + fxsx + fysy + fzsz, where d is the discharge rate of a single cell, f, fx, fy, fz are regression coefficients, and sx, sy, sz are the coordinates of the position of the hand. The equation above defines a positional gradient which implies that the frequency of cell discharge will increase at a maximum rate when the position of the hand changes along a certain direction; we call this direction of orientation of the positional gradient, and the rate of change in discharge rate along this orientation, the magnitude of the gradient. The orientations of the positional gradients were distributed throughout three-dimensional (3-D) space and their magnitudes differed among different cells. In a different experiment, we studied the changes in activity of 289 cells in the arm area of the motor cortex when the monkeys made equal- amplitude movements that started from different points in space, were in the same direction, and traveled along parallel trajectories in 3-D space. Four pairs of such movement directions (i.e., a total of 8 movement directions) were studied for every cell, and the changes in cell activity associated with movements within each pair were compared. We found that these changes in cell activity did not differ statistically for 68.4% of the movement pairs studied but did differ for the remaining 31.6%. The data from the whole population of cells studied in this experiment were analyzed using the population vector analysis described in the preceding paper (Georgopoulos et al., 1988). Thus, 8 population vectors were calculated, 1 for each of the 8 movement directions studied. We found that the direction of the population vector was close to the direction of the corresponding movement. These results indicate that the population vector provides unique information concerning the direction of the movement even when the point of origin of the movement varies in 3-D space.
Relationships between segregated afferents and postsynaptic neurones in the optic tectum of three-eyed frogs
Authors: Katz LC , Constantine-Paton M
Published: March 2018

In 3-eyed frogs, afferents from 2 eyes converge on an optic tectum that normally receives input from only 1 eye. This produces an interdigitating series of stripes, resembling the ocular dominance columns in cats and monkeys. The consequences of this induced striping on the behavior of tectal dendrites was investigated in an in vitro preparation of the tectum. Stripes were labeled by anterograde transport of a fluorescent dye (rhodamine) and postsynaptic tectal cells labeled by intracellular injections of Lucifer yellow. The same types of cells were present in both normal and striped tecta, but dendritic arbors were altered in 2 ways. In normal tecta, dendrites were most frequently biased in a rostral direction. In striped tecta, dendrites were more frequently unbiased: fewer arbors had a strong rostral bias. The second effect of stripes was on the behaviors of individual dendrites of certain cell types. Some cells, primarily those with small, highly branched arbors, had dendrites that abruptly terminated at the borders between stripes. Other cells, with larger arbors, maintained “clumps” of dendrites in both eye's stripes. While these cells had portions of their dendritic arbor in more than one stripe, each individual dendrite was restricted to a single stripe. However, the processes of many cells, especially those with extensive, medial-laterally oriented dendrites, did not respect stripe boundaries in any obvious fashion. At the border between 2 stripes, there is an abrupt discontinuity in the patterns of activity in afferent axons. The dendritic alterations seen in striped tecta suggest that correlated activity can, in some cells, modulate the spatial arrangement of dendrites, such that an individual dendrite preferentially arborizes within such areas, but not between them. These cells as a whole can accommodate uncorrelated inputs, if these are segregated onto separate dendrites. This implies that local interactions between presynaptic terminals and postsynaptic dendrites, rather than action potentials in the postsynaptic cells, may furnish important signals for the modulation of dendritic arbor shape.
Phosphorylation of neurofilament proteins in intact neurons: demonstration of phosphorylation in cell bodies and axons
Authors: Black MM , Lee VM
Published: March 2018

The principal subunits of neurofilaments (NFs) of immature cultured sympathetic neurons have apparent Mr of 68,000 and 145,000; a 200,000 Mr subunit is also present, but at comparatively low levels. These subunits are referred to as the low (NFL), middle (NFM), and high (NFH) Mr subunits, respectively. We studied the phosphorylation of NFL and NFM in these neurons in order to characterize the NFL and NFM isoforms generated by this important posttranslational modification. NFL resolved into a single spot in 2-dimensional gels, although 2 spots were occasionally observed. NFM typically resolved into 3 variants, termed NFM a, b, and c, in order of increasing mobility, but as many as 6 variants were detected in some gels. NFL and, to a much greater degree, NFM became labeled following incubation of intact neurons with 32P-PO4. Although all 3 major NFM variants became labeled, NFM a was the most heavily labeled, followed by NFM b, and then NFM c. Two observations suggest that the generation of these 3 NFM variants is due to their phosphorylation. First, treatment of NFs with phosphatase prior to analysis reduced NFM to a single spot or band that comigrated with NFM c; NFM a and b were completely eliminated. However, NFM c was not fully dephosphorylated because it still reacted with a monoclonal antibody (mAb) specific for a phosphate-dependent epitope on NFM. Second, NFM was recognized by 4 mAbs to distinctly different phosphorylated epitopes of NFM, which suggested that at least 4 distinct sites on NFM can be phosphorylated in cultured neurons. Explant cultures were used to study the phosphorylation of NFL and NFM in cell bodies and axons. In these cultures, a central cell body mass (CBM) 0.5 mm in diameter contains all of the cell bodies, while peripheral to the CBM is a halo of pure axons that extends for 4–6 mm. These cultures were incubated with 32P-PO4 and CBM and axon regions were analyzed separately. NFL became phosphorylated to a greater extent in the CBM than in axons. NFM also became labeled in the CBM and axons, although the relative labeling of NFM a, b, and c in these regions differed considerably from each other and also from the pattern observed in whole neurons (cell bodies plus neurites, see above).(ABSTRACT TRUNCATED AT 400 WORDS)
Binding characteristics of brain-derived neurotrophic factor to its receptors on neurons from the chick embryo
Authors: Rodriguez-Tebar A , Barde YA
Published: March 2018

Brain-derived neurotrophic factor (BDNF), a protein known to support the survival of embryonic sensory neurons and retinal ganglion cells, was derivatized with 125I-Bolton-Hunter reagent and obtained in a biologically active, radioactive form (125I-BDNF). Using dorsal root ganglion neurons from chick embryos at 9 d of development, the basic physicochemical parameters of the binding of 125I-BDNF with its receptors were established. Two different classes of receptors were found, with dissociation constants of 1.7 x 10(-11) M (high-affinity receptors) and 1.3 x 10(-9) M (low-affinity receptors). Unlabeled BDNF competed with 125I-BDNF for binding to the high-affinity receptors with an inhibition constant essentially identical to the dissociation constant of the labeled protein: 1.2 x 10(-11) M. The association and dissociation rates from both types of receptors were also determined, and the dissociation constants calculated from these kinetic experiments were found to correspond to the results obtained from steady-state binding. The number of high-affinity receptors (a few hundred per cell soma) was 15 times lower than that of low-affinity receptors. No high-affinity receptors were found on sympathetic neurons, known not to respond to BDNF, although specific binding of 125I-BDNF to these cells was detected at a high concentration of the radioligand. These results are discussed and compared with those obtained with nerve growth factor on the same neuronal populations.
Dopaminergic and indoleamine-accumulating amacrine cells express GABA- like immunoreactivity in the cat retina
Authors: Wassle H , Chun MH
Published: March 2018

Colocalization of indoleamine uptake and GABA-like immunoreactivity was studied in the cat retina. Consecutive, semithin sections were incubated in antisera to either 5-HT (5-hydroxytryptamine) or GABA. More than 90% of all 5-HT-accumulating amacrine cells expressed GABA- like antigens. With the same approach, the colocalization of 5-HT uptake and GABA-like immunoreactivity was studied in rabbit and 75–80% of the 5-HT-accumulating amacrine cells expressed GABA-like immunoreactivity, thus confirming a previous study (Osborne and Beaton, 1986). Since, in both cat and rabbit, endogenous 5-HT could not be found by immunocytochemistry, one must consider the possibility that some GABAergic amacrine cells take up indoleamines. In the cat retina, antibodies against tyrosine hydroxylase (TH) label dopaminergic amacrine cells (Oyster et al., 1985). By incubating consecutive, semithin sections in antisera to either TH or GABA, it was found that 84% of the dopaminergic amacrine cells also expressed GABA-like immunoreactivity. GABA-like immunoreactivity and 3H-muscimol uptake were found to be colocalized in more than 90% of the amacrine cells labeled. However, dopaminergic amacrine cells did not accumulate 3H- muscimol. Evidence is presented from colocalization studies for 2 types of interplexiform cell in the cat retina. One is stained by GABA-like immunocytochemistry and by 3H-muscimol uptake. The other is the dopaminergic amacrine cell, which also expresses GABA-like immunoreactivity, but does not accumulate 3H-muscimol.
Characterization of bovine and human neuronal nicotinic acetylcholine receptors using monoclonal antibodies
Authors: Whiting PJ , Lindstrom JM
Published: March 2018

Neuronal acetylcholine receptors (AChRs), which bind nicotine with high affinity but do not bind alpha-bungarotoxin (alpha Bgt), have recently been immunoaffinity-purified from chicken (Whiting and Lindstrom, 1986a) and rat (Whiting and Lindstrom, 1987a) brain using monoclonal antibodies (mAbs). Here we report the characterization of nicotinic AChRs of bovine and human brain using as probes mAbs prepared to AChRs from rat brain. Both the human and bovine brain AChRs exhibit high affinity for L-nicotine (Ki = 16 nM for bovine AChR and Ki = 6.5 nM for human AChR) and other cholinergic agonists, relatively lower affinity for cholinergic antagonists, and do not bind alpha Bgt. These AChRs are affinity-labeled with bromoacetylcholine and 4-(N- maleimido)benzyltrimethylammonium iodide (MBTA) after reduction with dithiothreitol, indicating that amino acid residues homologous to cysteines 192 and 193 of alpha subunits of Torpedo electric organ AChRs are conserved. Immunoaffinity-purified bovine brain AChR consists of 2 types of subunit, Mr 50,600 and Mr 74,400. The Mr 74,400 subunit was affinity-labeled with 3H-MBTA, indicating that it contains the ACh binding site. Thus, mAbs have proven to be excellent probes for these proteins, and have been used to show that neuronal nicotinic AChRs of chickens, rats, and cattle are macromolecules approximately 10 S in size and composed of only 2 kinds of subunits: an ACh-binding subunit and a structural subunit.
Purification and characterization of an antigen that is spatially segregated in the primary olfactory projection
Authors: Schwob JE , Gottlieb DI
Published: March 2018

The monoclonal antibody RB-8 heavily labels axons from the ventrolateral olfactory epithelium and their terminals in the glomeruli of the ventrolateral olfactory bulb, but leaves the axons from the dorsomedial epithelium unstained or lightly stained. RB-8 reacts with a 125 kDa membrane protein in both olfactory nerve and other parts of the CNS (Schwob and Gottlieb, 1986). Here we report further characterization of the molecular nature and cellular localization of the RB-8 antigen. The RB-8 antigen is exposed on the surface of olfactory axons. Individual axons and axon bundles stain when explant cultures of the fetal olfactory epithelium are incubated with monoclonal RB-8 antibody while living. The cell membrane is demonstrably intact, and access to the cell interior is blocked under these conditions, since the living axons do not stain if exposed to an antibody against a known intracellular constituent. The RB-8 antigen is an integral membrane protein. When assayed by direct radioimmunoassay (RIA), the antigen remains associated with brain membranes after extraction at pH 11, which solubilizes numerous other protein bands. The 125 kDa RB-8 antigen was purified to homogeneity from whole rat brains by extracting membranes with sodium deoxycholate, immunoaffinity chromatography over an RB-8 antibody column, and preparative one- dimensional SDS-PAGE. The NH2-terminal amino acid sequence is apparently unique among neuron-specific proteins that have been sequenced and has only an insignificant degree of homology with other known proteins. Two polyclonal rabbit antisera raised against the purified antigen recognize only the 125 kDa protein on immunoblots. Immunohistochemical staining of the primary olfactory projection with the antisera exactly matches that seen with monoclonal RB-8 antibody. Thus, the RB-8 antigens in brain and in olfactory nerve are highly homologous, if not identical. Furthermore, the results with the antisera suggest that the expression of the entire 125 kDa protein is regulated differentially between ventral and dorsal zones of the olfactory epithelium. The additional characterization of the RB-8 antigen reported here places constraints on the potential functions of this protein. The availability of polyclonal antisera may prove useful in assessing the role of this spatially segregated antigen in the primary olfactory projection.
Voltage- and ligand-activated inwardly rectifying currents in dorsal raphe neurons in vitro
Authors: Williams JT , Colmers WF , Pan ZZ
Published: March 2018

Intracellular recordings were made from neurons in rat dorsal raphe in the slice preparation maintained at 37 degrees C. The single-electrode voltage-clamp method was used to measure membrane currents at potentials more negative than rest (-60 mV). Three types of inward rectification were observed: 2 in the absence of any drugs and the third induced by 5-HT 1 and GABA-B receptor agonists. In the absence of any drugs, an inward current activated over 1–2 sec when the membrane potential was stepped to potentials more negative than -70 mV. This current was blocked by cesium (2 mM) and resembles IQ or IH. A second inward current (IIR) occurred at membrane potentials near the potassium equilibrium potential (EK). This inward current activated within the settling time of the clamp and was abolished by both barium (10–100 microM) and cesium (2 mM). 5-HT 1 agonists activated a potassium conductance that hyperpolarized the cells at rest. This potassium conductance was about 2 nS at -60 mV and increased linearly with membrane hyperpolarization to about 4 nS at -120 mV. Baclofen activated a potassium conductance identical in amplitude and voltage dependence to that induced by 5-HT 1 agonists. Both the baclofen- and 5-HT-induced currents were nearly abolished in animals pretreated with pertussis toxin. The results indicate that a common potassium conductance is increased by 5-HT acting on 5-HT 1 receptors and baclofen acting on GABA-B receptors. This potassium conductance rectifies inwardly and is distinct from the Q-current. The ligand-activated potassium conductance also differs from the other form of inward rectification (IIR) in its voltage dependence and sensitivity to pertussis toxin.
NMDA- and non-NMDA-receptor components of excitatory synaptic potentials recorded from cells in layer V of rat visual cortex
Authors: Jones KA , Baughman RW
Published: March 2018

The pharmacological properties of excitatory synapses on pyramidal cells in layer V of rat visual cortex were investigated by recording EPSPs intracellularly in tissue slices. The EPSPs were evoked by electrically stimulating cells in layer II/III or axons in white matter. All of the layer V neurons were pyramidal in nature as determined by injections of Lucifer yellow or by electrophysiological criteria. Application of the broadly acting antagonists kynurenic acid and gamma-D-glutamylglycine reversibly antagonized the EPSPs from both presynaptic sources in a dose-dependent manner: 1 and 5 mM kynurenic acid produced 63 and 79% reductions, respectively, of control responses. The specific NMDA antagonist APV (50 microM) caused a small reduction in peak amplitude and a more significant reduction in the duration of the falling phase of EPSPs. When slices were bathed in Mg2+- free medium, the amplitude of the EPSP increased substantially. Under these conditions APV reduced the size of the EPSP to that observed with APV in the presence of 1 mM Mg2+. The voltage sensitivities of the APV- sensitive and APV-insensitive components of the layer II/III-evoked EPSPs were examined. The APV-insensitive component was not voltage dependent and had an extrapolated reversal potential of -10 mV. In contrast, the APV-sensitive component showed an NMDA-like voltage dependency; it was greatest at the most positive potentials tested (-45 mV) and nearly absent at membrane potentials below rest. At potentials near threshold, the APV-sensitive component contributed approximately half of the total response. Although the time to peak and decay were longer for the APV-sensitive component, the latency was the same as that of the APV-insensitive component. These results provide evidence that the layer II/III to V pathway, which comprises a major interlaminar circuit in cortex, is mediated directly through NMDA as well as non-NMDA receptors located on the layer V cells. This finding has implications for the role of this circuit in cortical visual plasticity.
Single neuron responses in amygdala of alert monkey during complex sensory stimulation with affective significance
Authors: Nishijo H , Ono T , Nishino H
Published: March 2018

Among other deficits, amygdalectomy impairs the ability of the animal to recognize the affective significance of a stimulus. In the present study, neuronal activity in the amygdala (AM) was recorded from alert monkeys while they performed tasks leading to the presentation of rewarding or aversive stimuli. Of 585 AM neurons tested, 312 (53.3%) responded to at least one stimulus in one or more of 5 major groups: 40 vision related, 26 audition related, 41 ingestion related, 117 multimodal, and 14 selective. Ingestion-related neurons were subdivided according to their responses to other stimuli: oral sensory, oral sensory plus vision, and oral sensory plus audition. Depending upon their responsiveness to the affective significance of the stimuli, neurons in the vision- and audition-related categories were divided into 2 subclasses: vis-I (26/40), vis-II (14/40), aud-I (8/26), and aud- II (18/26). All 4 subtypes usually responded to unfamiliar stimuli but seldom responded to neutral familiar stimuli. Types vis-I and aud-I responded to both positive and negative familiar stimuli. Types vis-II and aud-II responded to certain familiar negative stimuli but not to familiar positive stimuli. In vis-I neurons, responses were stronger for palatable foods than for less palatable foods. No neurons within vision-related, audition-related, and multimodal categories responded solely to positive or to negative stimuli. Of the 27 oral sensory neurons 9 were tested with saline or salted food, and 8 responded to normally aversive oral sensory stimuli in the same manner as they did to normal food or liquid (water or juice). In contrast to oral sensory neurons, all responses of 4 oral sensory-plus-vision and all of 4 selective neurons tested, as well as bar pressing behavior, were modulated by altering the affective significance of the food. These results suggest that the AM is one of the candidates for stimulus- affective association based on associative learning and memory.
The pattern of dendritic sprouting and retraction induced by axotomy of lamprey central neurons
Authors: Hall GF , Cohen MJ
Published: March 2018

We have investigated some of the factors controlling the distribution of axonal and dendritic sprouting following axotomy of a subset of Muller giant interneurons (anterior bulbar cells or ABCs) in the hindbrain of the larval sea lamprey (Petromyzon marinus). Sprouts originated from different sites in the cell depending on the distance of the axonal lesion from the soma. When the axon was cut close to the soma (within 500 microns), the dendritic tips sprouted profusely, whereas the proximal axon stump showed few sprouts and frequently disappeared entirely. Axotomy further from the soma (1000–1400 microns) resulted in less sprouting from the dendrites and more from the axon stump, with the total amount of dendritic plus axonal sprouting remaining constant. Axotomy at sites distant from the soma (1 cm or more) did not result in dendritic sprouting. No sprouts were ever observed emerging from the soma proper or from the axon stump except at the lesion site. Neuritic sprouts from dendrites and axon were similar in their gross morphology. Sprouts resembled axons rather than dendrites whatever their sites of origin; they followed linear, rostrocaudally oriented paths in the “basal plate” region of the hindbrain. Dendritic and axonal sprouts grew both rostrally and caudally within the brain. Either “close” or “distant” axotomy resulted in the retraction of the dendritic tree and of both dendritic and axonal sprouts by several months postaxotomy. Reaxotomy close to the soma 30 d after a distant axotomy accelerated the onset of this evoked dendritic retraction. Reaxotomy close to the soma also induced sprouting significantly sooner than did close axotomy alone. These results suggest that axotomy close to the soma causes axonal regeneration to be shunted into ectopic locations at the dendritic tips. The emerging sprouts then follow guidance cues appropriate for regenerating ABC axons.
L-glutamate increases internal free calcium levels in synaptoneurosomes from immature rat brain via quisqualate receptors
Authors: Benavides J , Claustre Y , Scatton B
Published: March 2018

Internal free calcium concentrations ([Ca2+]i) have been monitored in synaptoneurosomes from 8-d-old rat whole brain previously loaded with the calcium-sensitive fluorescent probe Fura 2. Under basal conditions, [Ca2+]i was around 200 nM, this concentration increasing only slowly during storage of the synaptoneurosomes at room temperature (40% increase 2 hr after loading). Opening of sodium channels with veratridine- (10 microM) or KCl- (30 mM) induced depolarization caused rapid increases in synaptoneurosomal [Ca2+]i. [Ca2+]i was also markedly increased by addition of the Ca2+ ionophore A23187 (10–100 nM). The effect of veratridine, but not of KCl was prevented by previous addition of TTX (1 microM). KCl-induced [Ca2+]i increase was dependent on external Ca2+ and was partially blocked by the dihydropyridine derivative PN 200–110 (IC50 0.15 microM, maximal inhibition 55% at 3 microM). L-Glutamate elicited a concentration-dependent fast increase in synaptoneurosomal [Ca2+]i in the 8-d-old (but not in the adult) rat brain (EC50 = 2 microM). The effect of glutamate was stereospecific, the EC50 of the D-isomer being 47 times higher than that of L-isomer. The magnitude of the L-glutamate response differed in several brain regions, being highest in the cerebral cortex and lowest in the cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)
Topological localization of a segment of the eel voltage-dependent sodium channel primary sequence (AA 927-938) that discriminates between models of tertiary structure
Authors: Gordon RD , Li Y , Fieles WE , Schotland DL , Barchi RL
Published: March 2018

Antibodies were raised against a synthetic peptide corresponding to residues 927–938 of the eel electroplax sodium channel primary sequence. This segment, lying between putative internal repeat domains II and III, is postulated to be exposed on the cytoplasmic surface of the membrane in several recent models of channel tertiary structure and on the external surface in another. The antiserum and affinity-purified IgG derived from it specifically recognize the peptide and the eel sodium channel in a solid-phase radioimmunoassay and bind to a single diffuse band of 260–280 kDa on Western blots of eel electroplax membrane proteins. All reactions are blocked by co-incubation of the antibodies with the synthetic peptide (1 microM). The antibody immunoprecipitates the solubilized channel in a form that retains its characteristic high-affinity binding of saxitoxin. In eel electroplax, the antibodies label only the innervated membrane known to contain sodium channels; at the ultrastructural level, this labeling is exclusively associated with the cytoplasmic surface of the membrane. Sodium channels containing the epitope are not seen in the postsynaptic membrane or in the membrane of the presynaptic nerve terminal. Segment 927–938 of the eel sodium channel is accessible on the surface of the protein in its solubilized form and is exposed in the cytoplasmic face of the innervated membrane of the electroplax in situ. This location is consistent with 3 models of channel structure but not with a fourth.
Electrophysiology of morphologically identified mossy cells of the dentate hilus recorded in guinea pig hippocampal slices
Authors: Scharfman HE , Schwartzkroin PA
Published: March 2018

A specific population of cells located in the hilus of the hippocampal fascia dentata was studied in guinea pig hippocampal slices using standard intracellular recording techniques. Twenty-one such cells were characterized using electrophysiological techniques and were identified morphologically as mossy cells following intracellular injection of the fluorescent dye Lucifer yellow. These cells had a resting membrane potential (mean, -64.6 mV), action potential amplitude (mean, 78.6 mV), action potential duration (mean, 2.2 msec), and time constant (mean, 24.2 msec) similar to those of hippocampal pyramidal cells of area CA3. Rectification seen in their I-V curves, and their ability to fire action potentials in accommodating trains or bursts in response to injected current pulses, were also similar to those of area CA3 pyramidal cells. However, these cells could be distinguished from area CA3 pyramidal cells by their higher input resistance (mean, 97.4 M omega) and higher level of spontaneous activity. The synaptic responses of mossy cells were also different from those of CA3 pyramidal cells. First, mossy cells responded to low levels of stimulation in all areas of the hippocampal slice that were tested, even areas as remote as area CA1. Second, the responses of mossy cells to stimulation consisted primarily of EPSPs. Hyperpolarizing IPSP-like events followed EPSPs in some cells, but the hyperpolarizations were small and monophasic, even after the cell was depolarized with current injection. This response contrasts with the smaller EPSP and the prominent, biphasic IPSP elicited by afferent stimulation of area CA3 pyramidal cells. The physiological and morphological characteristics of these cells suggest that they could play an important role in the integration of electrical activity in the hippocampus.
The distribution of acetylcholine receptors in chick ciliary ganglion neurons following disruption of ganglionic connections
Authors: Jacob MH , Berg DK
Published: March 2018

Chick ciliary ganglion neurons have nicotinic acetylcholine receptors (AChRs) that mediate primary chemical synaptic transmission through the ganglion. Previous studies have shown that preganglionic denervation reduces the total number of AChRs in the ganglion about 3-fold in 10 d, while postganglionic axotomy reduces AChR levels about 10-fold in 5 d. Since the neurons contain large numbers of intracellular AChRs in addition to the surface AChRs, the present studies were undertaken to determine whether either surface or internal AChR pools are changed selectively by the operations. An anti-AChR monoclonal antibody followed by an HRP-conjugated secondary antibody was used to visualize AChR distributions on neurons in ciliary ganglia 5 d after postganglionic axotomy and 10 d after preganglionic denervation. Ganglia were permeabilized by treatment with saponin to obtain access to intracellular receptors. The results show that the operations do not qualitatively change the subcellular localization of AChRs, but they do alter the levels relative to control ganglia. Axotomy produces substantial declines both in the number of synaptic AChRs and in the number of intracellular AChRs. Denervation produces a significant, though less extensive decline in the number of intracellular receptors while having no detectable effect on the number of synaptic AChRs. Small alterations in receptor distribution would have gone undetected by the present techniques. Regulation of neuronal AChRs differs in several respects from that described for muscle AChRs: presynaptic input appears to be less important for controlling neuronal AChRs, while signals from the postsynaptic target tissue may be essential for maintaining synaptic receptors on the neurons.
Distinct cellular expression of beta I- and beta II-subspecies of protein kinase C in rat cerebellum
Authors: Ase K , Saito N , Shearman MS , Kikkawa U , Ono Y , Igarashi K , Tanaka C , Nishizuka Y
Published: March 2018

Immunohistochemical and biochemical studies with subspecies-specific antibodies have revealed that beta I- and beta II-subspecies of protein kinase C, which result from alternative splicing of a single RNA transcript, show different regional expression in rat CNS. In the cerebellar cortex, beta I-subspecies is localized mainly in the granular layer, whereas beta II-subspecies is found predominantly in the molecular layer, most apparently in the presynaptic nerve endings that terminate at Purkinje cells. These distribution patterns are in sharp contrast to that of gamma-subspecies, which is most abundant within the Purkinje cells. The different patterns of expression imply that the multiple subspecies of protein kinase C may each have a specific function in modulating the neuronal activity of particular cell types.
Motor nerve terminal sprouting in formamide-treated inactive amphibian skeletal muscle
Authors: Wines MM , Letinsky MS
Published: March 2018

Motor axons can form sprouts from their terminal arborizations in response to partial denervation, and when exposed to pharmacological blocking agents like TTX, botulinum toxins alpha-bungarotoxin, or curare. Each of these experimental procedures has cessation of muscle contractile activity as a common feature. We tested the specific role of muscle fiber inactivity in regulating nerve terminal sprouting by chronically treating adult frog (Rana pipiens) cutaneous pectoris muscles with formamide. Exposure to formamide, unlike the other compounds used to study sprouting, selectively inhibits muscle contractions without blocking pre- or postsynaptic transmission or muscle fiber action potentials. Repeated formamide applications were used to achieve chronic block of muscle contractile activity in vivo for up to 6 weeks. Motor axons in formamide-treated inactive muscle sprouted only from their terminal arborizations, but not from nodes of Ranvier. The onset of this sprouting was protracted compared with that seen in pharmacologically blocked mammalian muscles, and sprouts in formamide-treated muscles were more complex and ornate. The frequency of sprouting terminals was less in these formamide-treated muscles than that seen after alternate methods of contractile block, and this suggests that contractile inactivity alone serves as only a moderate cue for sprouting. The possibility is discussed that the prolific sprouting seen following neurotoxin administration may, in fact, be due to perturbations in synaptic transmission or muscle electrical activity rather than muscle fiber inactivity.
Calcitonin gene-related peptide prevents disuse-induced sprouting of rat motor nerve terminals
Authors: Tsujimoto T , Kuno M
Published: March 2018

Calcitonin gene-related peptide (CGRP) coexists with acetylcholine (ACh) in motor nerve terminals. Externally applied CGRP has been shown to increase the synthesis of ACh receptors in cultured myotubes by a mechanism independent of muscle activity. Thus, CGRP is suggested to be a neurotrophic factor that may regulate the expression of several long- term events occurring at the neuromuscular junction. We have examined the effect of CGRP on the sprouting of motor nerve terminals induced by chronic block of nerve-muscle activity in adult rats. Daily treatment with CGRP suppressed the disuse-induced terminal sprouting in a dose- dependent manner, whereas the morphology of motor nerve terminals in active muscles was unaffected by CGRP. CGRP may be a possible candidate for an antisprouting agent which has been postulated to exist in nerve terminals. The disuse-induced outgrowth of terminal sprouts was accompanied by an increase in the mean quantum content of end-plate potentials, as well as in the frequency of spontaneous miniature end- plate potentials. This increased transmitter release was still maintained at the junctions in which disuse-induced terminal sprouting had been suppressed by CGRP. It is suggested that the formation of terminal sprouts per se is not responsible for the plastic change of transmitter release induced by prolonged disuse of the neuromuscular junction.
Nucleus basalis and thalamic control of neocortical activity in the freely moving rat
Authors: Buzsaki G , Bickford RG , Ponomareff G , Thal LJ , Mandel R , Gage FH
Published: March 2018

EEG and single-unit techniques have been used to study the EEG correlates of cellular firing in the neocortex, n. reticularis (RT) and “specific” thalamic nuclei, and the cholinergic forebrain area (nucleus basalis, NB). Neuronal firing was related to the ongoing behavior of the rat. In addition, using a 16-channel neocortical recording/mapping system, we studied the effects of ibotenic acid lesion of NB, RT, and other thalamic nuclei on the patterns and spatial distribution of neocortical electrical activity. The majority of neurons in neocortex, NB, and RT increased their firing rates during walking, as compared to during immobility, with concurrent decrease of delta power in the neocortical EEG. During immobility, high-voltage spindles (HVS; greater than 1 mV) were occasionally recorded from the neocortex. Depth profiles of HVS and slow delta waves were different in the neocortex. Neocortical cells decreased their discharge frequency during the positive portion of delta waves recorded in layers V and VI. All cells in the neocortex and specific thalamic nuclei fired rhythmically and phase-locked to the spike component of HVS. RT neurons showed an opposite phase relationship and fired mainly during the wave component of HVS. Half of the NB neurons also showed phasic modulation with HVS. Circumscribed lesion of RT and extensive damage of other thalamic regions, including the intralaminar nuclei, suppressed HVS but had no effect on the neocortical EEG correlates of behavior. In sharp contrast, damage to the NB resulted in a dramatic increase of slow delta waves on the side of the lesion, mimicking the effect of scopolamine administration. We suggest that the NB plays a key role in neocortical arousal by directly activating the neocortex and by suppressing the rhythm generation in the RT-thalamocortical circuitry. We further suggest that the NB system may serve as a structural basis for the concept of the generalized ascending activation of Moruzzi and Magoun (1949).
Characteristics of hippocampal primed burst potentiation in vitro and in the awake rat
Authors: Diamond DM , Dunwiddie TV , Rose GM
Published: March 2018

A pattern of electrical stimulation based on 2 prominent physiological features of the hippocampus, complex spike discharge and theta rhythm, was used to induce lasting increases in responses recorded in area CA1 of hippocampal slices maintained in vitro and from the hippocampus of behaving rats. This effect, termed primed burst (PB) potentiation, was elicited by as few as 3 stimuli delivered to the commissural/associational afferents to CA1. The patterns of stimulus presentation consisted of a single priming pulse followed either 140 or 170 msec later by a high-frequency burst of 2–10 pulses; control stimulation composed of unprimed high-frequency trains of up to 10 pulses had no enduring effect. Of all intervals tested, only 140 and 170 msec delays between the priming and burst stimuli were effective. PB potentiation could be induced both homo- and heterosynaptically. In the latter case, the priming pulse and burst stimuli were delivered to different dendritic fields; under these conditions, the PB effect was confined to the “burst” pathway. PB potentiation is not dependent on somal spiking; dendritic activation appears to be both necessary and sufficient for lasting changes to occur. Two findings indicate that PB potentiation and LTP have common mechanisms: (1) The effects of PB stimulation and LTP were not additive, in that saturation of the enhancement by PB stimulation eliminated any further increases in response with LTP stimulation; and (2) both PB potentiation and LTP were prevented if the N-methyl-D-aspartate antagonists 2-amino-5- phosphonovaleric acid or phencyclidine were added to the in vitro perfusion medium. Recordings from the hippocampus of awake rats demonstrated that PB potentiation of the CA1 population spike and slope of the EPSP are reliably induced under physiological conditions. This extensive characterization of PB stimulation provides novel information regarding the physiological and pharmacological basis of a possible role of endogenous rhythms in the processing and storage of information.
A selective mnemonic role for the hippocampus in monkeys: memory for the location of objects
Authors: Parkinson JK , Murray EA , Mishkin M
Published: March 2018

Monkeys were trained preoperatively on a one-trial learning task in which they were required to associate in memory a novel object and the place in which it had just appeared. After learning the task to a level of 80% correct responses, they received bilateral ablations of either the hippocampal formation or the amygdaloid complex. The monkeys with amygdalectomy showed a small drop in performance initially but then regained their preoperative level. By contrast, the monkeys with hippocampectomy dropped to near-chance levels of performance and remained there throughout postoperative testing. Both groups performed at better than 90% correct responses on a test of recognition memory. These results, taken together with earlier work, suggest that although the hippocampus and amygdala appear to participate equally in object recognition, only the hippocampus is critical for the rapid formation of object-place associations.
Ionic currents of Drosophila neurons in embryonic cultures
Authors: Byerly L , Leung HT
Published: March 2018

Drosophila offers a unique opportunity to determine how the genome codes for ionic channels in an organized nervous system. Considerable progress has already been made in studying the molecular biology of Drosophila K channels. In order for similar progress to be made on neuronal voltage-dependent Ca channels, a physiological preparation is needed in which the function of these channels can be directly studied. The patch-clamp studies reported here show that cultures of embryonic Drosophila cells (Seecof and Unanue, 1968) meet this need. These cultures provide the first opportunity to study with voltage-clamp techniques the Ca and Na currents of Drosophila neurons. The focus of these studies is on the Ca current; however, descriptions of the K and Na currents are also given since they help to characterize the cells studied and the quality of the voltage clamp. The voltage-dependent K, Na, and Ca currents of Drosophila neurons are very similar to those of molluscan neurons and other better studied neurons. The K currents are the largest currents in these neurons, averaging over 300 pA at +20 mV. There are 2 classes of Ca-independent K currents, inactivating currents that are 4-AP sensitive, and noninactivating currents that are insensitive to 4-AP. A large fraction of the K currents are located in the somal membrane. The Na currents are TTX sensitive and probably located in the processes. The peak amplitudes of the Ca currents vary from 0 to over 100 pA in these neurons, averaging 40 pA. With 5 mM external Ca2+ or Ba2+, the Ba currents are about twice as large as the Ca currents. Although 100 microM Cd2+ completely blocks the Ca current, organic blockers have very little effect. Variable inactivation characteristics and sensitivity to washout suggest the possibility of multiple types of Ca channels. A search for single-channel Ba currents in the somal membrane was unsuccessful.
Korsakoff's syndrome: radiological (CT) findings and neuropsychological correlates
Authors: Shimamura AP , Jernigan TL , Squire LR
Published: March 2018

Quantitative analyses were performed on computer tomography (CT) scans from 7 patients with Korsakoff's syndrome, 7 age-matched alcoholic subjects, and 7 age-matched healthy control subjects. CT values were used to estimate tissue density and fluid volume in specified brain areas. Tissue density was assessed by averaging CT values in small (5 x 5 mm) areas sampled bilaterally in 6 specified areas--thalamus, head of the caudate nucleus, putamen, anterior white matter, posterior white matter, and centrum semiovale. We assessed fluid volume using a semiautomated computer algorithm that estimated the proportion of fluid in 7 brain regions--total ventricular space, third ventricle, interventricular region, frontal sulci, peri-Sylvian region, medial cerebellum, and vertex. For the patients with Korsakoff's syndrome, we also assessed the correlation between CT measures and performance on 6 cognitive and 12 memory tests. Compared with alcoholic subjects and healthy control subjects, patients with Korsakoff's syndrome had lower CT density values bilaterally in the region of the thalamus and had greater estimated fluid bilaterally in the region of the third ventricle. Alcoholic and healthy control subjects did not differ on these measures. Significant cortical atrophy in frontal sulcal and peri- Sylvian areas was detected both in patients with Korsakoff's syndrome and in alcoholic subjects. For patients with Korsakoff's syndrome, impairment on behavioral tests, and on memory tests in particular, was correlated with low-density values in the thalamus and with high fluid values in the region of the frontal sulci. Damage to diencephalic and frontal areas may especially contribute to the memory and cognitive impairment exhibited by patients with Korsakoff's syndrome.
Dual effects of theophylline on spontaneous transmitter release from frog motor nerve terminals
Authors: Barry SR
Published: March 2018

Alkylxanthine drugs, such as theophylline, block adenosine receptors, inhibit phosphodiesterases and other enzymes, and cause the release of calcium from intracellular stores. Adenosine receptor blockade occurs at low micromolar concentrations of the drugs, while other effects occur in the millimolar concentration range. The effects of theophylline were tested on spontaneous transmitter release at the frog cutaneous-pectoris neuromuscular junction (NMJ). A change in the frequency, but not the amplitude, of miniature endplate potentials (mepps) was interpreted as a change in spontaneous transmitter release. In normal Ringer's, theophylline, at concentrations of 100 microM and 1 mM, theophylline had no consistent effect on spontaneous release. In contrast, theophylline produced dual effects on mepp frequency in hyperosmotic Ringer's. At 10 microM, theophylline depressed mepp frequency, while, at 100 microM and 1 mM, theophylline increased mepp rate. Since low micromolar concentrations of theophylline depressed spontaneous transmitter release, this action may result from adenosine receptor blockade and inhibition of a tonic, stimulatory effect of adenosine. This hypothesis was supported by the following experimental results: (1) Micromolar concentrations of theophylline reversed the effects of applied adenosine on neuromuscular transmission. (2) The inhibitory effect of theophylline was mimicked by 2 other alkylxanthines, 8-phenyltheophylline and 8-p-sulfophenyltheophylline. These drugs may be more specific adenosine receptor antagonists than theophylline. (3) The inhibitory effect of theophylline was mimicked by adenosine deaminase, an enzyme that breaks down and inactivates adenosine. (4) The depressant action of theophylline was masked by the addition of adenosine deaminase to the hyperosmotic Ringer's. Application of adenosine to the frog NMJ reduces spontaneous transmitter output.(ABSTRACT TRUNCATED AT 250 WORDS)