bluuebunny/crossref_metadata_2025 huggingface dataset:
Interval between the synthesis and assembly of cytoskeletal proteins in cultured neurons
Authors: Black MM , Keyser P , Sobel E
Published: March 2018

We have used pulse-chase experiments to study the time interval between the synthesis and assembly of tubulin and neurofilament proteins (NFP) in sympathetic neurons grown in tissue culture. After varying pulse- chase times, cultures were extracted with Triton X-100 such that polymerized tubulin and NFP were insoluble, while unassembled tubulin and NFP were quantitatively solubilized. The partitioning of labeled tubulin and NFP between Triton X-100-soluble and insoluble, or cytoskeletal, fractions was determined with an isoelectric focusing X SDS gel electrophoresis assay. Labeled tubulin and NFP in cultures pulse-labeled for 5–10 min partitions primarily with the soluble fraction. When pulse-labeled cultures were chased for increasing periods of time, relatively more of the total labeled tubulin and NFP partitioned with the cytoskeleton, attaining maximal values after chase times of 60–120 and 15–30 min, respectively. The maximal values for the relative levels of labeled tubulin and NFP in polymer were 70–75 and greater than 90%, respectively. The levels of labeled tubulin and NFP synthesized during a short pulse-label remained constant for at least 2 hr, indicating that selective turnover of soluble tubulin and NFP does not detectably contribute to the changes in solubility properties of these proteins observed in the pulse-chase experiments. These results indicate that newly synthesized tubulin and NFP are rapidly assembled from soluble precursors. The lag between the synthesis and assembly of the 145,000-molecular-weight NFP is not related to its phosphorylation because its initial incorporation into the cytoskeleton occurs prior to its phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)
A role for action-potential activity in the development of neuronal connections in the kitten retinogeniculate pathway
Authors: Dubin MW , Stark LA , Archer SM
Published: March 2018

The role of action potentials in the development of proper synaptic connections in the mammalian CNS was studied in the kitten retinogeniculate pathway. Our basic finding is that there is improper segregation of retinal inputs onto LGN cells after prolonged retinal action-potential blockade. Retinal ganglion cell firing was silenced from birth by repeated monocular injections of TTX. The resulting ganglion cell connections in the LGN were studied electrophysiologically after the action-potential blockade was ended. Most cells in the deprived LGN layers received excitatory input from both ON-center and OFF-center type ganglion cells, whereas LGN cells normally receive inputs only from ON-center or OFF-center ganglion cells, but not from both types. Improper segregation of ON and OFF inputs has never been reported after other types of visual deprivation that do not block ganglion cell activity. Control experiments showed that receptive fields in the nondeprived LGN layers were normal, that ganglion cell responses remained normal, and that there was no obvious ganglion cell loss. We also showed that individual LGN cells with ON and OFF excitatory inputs were not present in normal neonatal kittens. Two other types of improper input segregation in response to action- potential blockade were also found in the deprived LGN layers. (1) A greater than normal number of LGN cells received both X- and Y-type ganglion cell input. (2) Almost half of the cells at LGN layer borders were excited binocularly. Recovery of LGN normality was rapid and complete after blockade that lasted for only 3 weeks from birth, but little recovery was seen after about 11 weeks of blockade. The susceptibility to action-potential blockade decreased during the first 3 postnatal weeks. These findings may result from axon-terminal sprouting or from the failure of axon terminals to retract. The results are consistent with the idea that normally synchronous activity of neighboring ganglion cells of like center-type may be used in the refinement of retinogeniculate synaptic connections.
Dynamic changes in the dendritic geometry of individual neurons visualized over periods of up to three months in the superior cervical ganglion of living mice
Authors: Purves D , Hadley RD , Voyvodic JT
Published: March 2018

We describe a means of visualizing the same neuron in the superior cervical ganglion of young adult mice over intervals of up to 3 months. The dendrites of these neurons change during this interval; some branches retract, others elongate, and still others appear to form de novo. Thus, neuronal dendrites in this part of the nervous system are subject to continual change beyond what is usually considered the developmental period. The remodeling of postsynaptic processes further implies that the synaptic connections made onto these cells undergo substantial rearrangement well into adulthood.
Determination of the molecular weight of neuronectin, a conditioned medium-derived, substrate-binding neurite-extension factor: comparison with laminin using radiation-inactivation analysis
Authors: Coughlin MD , Grover AK , Jung CY
Published: March 2018

Neurite outgrowth from a wide variety of peripheral neurons is stimulated and may be directed in culture by a substrate-binding factor(s) derived from medium conditioned over numerous types of cells. This factor, or family of factors, which we shall call neuronectin by reason of its ability to serve as an attachment molecule for neurons, has been studied by target-size analysis using radiation inactivation. The radiation-inactivation method has the unique advantage of providing a means for determining the actual functional size of a biologically active molecule irrespective of its state of purification. By this method, the functional size of the major neurite outgrowth-promoting activity (neuronectin) from mouse heart cell conditioned medium has been found to be 350,000 Da. While neuronectin has not yet been purified, determination of the actual functional size provides a framework within which possible models must fit. Thus, although neurite outgrowth-promoting activity in this system is found to be associated with a complex containing laminin, fibronectin, heparan sulfate proteoglycan, and other extracellular matrix molecules, the total size of the functional molecule or molecular complex serving as the major source of activity is limited to 350,000 Da. Consequently, our results suggest that neuronectin from mouse heart cell-conditioned medium is different from laminin (Mr approximately 900,000), a molecule that also exhibits neurite-promoting activity. In addition to the difference in molecular size, neuronectin and laminin differ in that laminin, unlike neuronectin, gives rise to toxic or inhibitory products when exposed to high-energy radiation.
Preference for autogenous song by auditory neurons in a song system nucleus of the white-crowned sparrow
Authors: Margoliash D
Published: March 2018

Neuronal activity in the hyperstriatum ventrale, pars caudale (HVc) is associated with and necessary for the production of song by songbirds. HVc neurons also respond to acoustic stimuli. The present investigation assessed the auditory response properties of neurons in HVc by testing with the individual bird's own (autogenous) song and the songs of conspecific birds. Throughout HVc, multiunit clusters preferentially responded to autogenous song. Selectivity for autogenous song was apparent even when compared to similar intradialect songs, and neuronal clusters preferred autogenous song over the (tutor) song model that birds heard during the impressionable phase early in life. The responses to autogenous song were stable in the adult. HVc neurons were sensitive to the acoustic parameters of autogenous song and consistently exhibited a diminished response to modified song. In contrast, field L neurons, which are presumed to be a source of auditory input to HVc, did not exhibit selectivity for autogenous song and showed no special sensitivity to the acoustic parameters of autogenous song. These observations implicate song (motor) learning in shaping the response properties of HVc, but not field L, auditory neurons. It is proposed that HVc auditory neurons may contribute to a bird's ability to discriminate among conspecific songs by acting as an “autogenous reference” during perception of those songs.
Central projections of identified Drosophila sensory neurons in relation to their time of development
Authors: Palka J , Malone MA , Ellison RL , Wigston DJ
Published: March 2018

Eight sensory structures (campaniform sensilla), appearing identical in the light and scanning electron microscopes, are found in specific locations on the wings of Drosophila. Their axons enter one of 2 central tracts, a medial one or a lateral one. The topographic arrangement of the sensilla on the wing is not reflected in this central projection pattern. There is, however, a strict correlation between the time when a sensillum develops and the path its axon follows: The 4 sensilla whose axons form the medial projection are born and differentiate early during the development of the wing, while the other 4 sensilla, all of which project laterally, arise during a second wave of differentiation. This time-related projection pattern remains stable in the face of a variety of genetically induced alterations in the precise number and location of sensilla.
Astrocytes, oligodendrocytes, and Schwann cells share a common antigenic determinant that cross-reacts with myelin basic protein: identification with monoclonal antibody
Authors: Brenner T , Lisak RP , Rostami A , Pleasure DE , Silberberg DH
Published: March 2018

We have produced a monoclonal antibody against myelin basic protein that reacts with astrocytes, oligodendrocytes, and Schwann cells. This antibody was generated by fusion of mouse myeloma cells with spleen cells from BALB/c mice immunized with delipidated white matter from adult rat corpus callosum. The antibody was characterized via solid- phase radioimmunoassay, immunoblot of SDS-PAGE, and by indirect immunofluorescence staining of monolayer cultures containing oligodendrocytes, astrocytes, and Schwann cells. Myelin basic protein (MBP) was shown previously to be present only in myelin producing cells in CNS and PNS (oligodendroglia and Schwann cells) and not in astrocytes. The binding of this monoclonal antibody to all 3 cell types suggests that these cells share a common epitope. This epitope may be related to a common progenitor cell.
Electrophysiological and anatomical identification of the peripheral axons and target tissues of Aplysia neurons R3-14 and their status as multifunctional, multimessenger neurons
Authors: Rittenhouse AR , Price CH
Published: March 2018

The giant neurons R3–14 in the parietovisceral ganglion of Aplysia, originally proposed to be a homogeneous group of neuroendocrine cells, are likely candidates for a multifunctional and multiple messenger status. The studies reported here suggest that individual R3–14 giant neurons not only innervate specific target tissues but appear to operate more autonomously than previously thought. Identified members of the group were traced into peripheral tissues by electrophysiological, autoradiographic, and intracellular cobalt staining techniques. Five neurons (numbered R6, R7, R8, R11, and R14) were identified on the basis of their unique patterns of axonal projections. R6 innervates the ganglionic artery and pericardial area; R7 and R8, the heart; R11, the kidney; and R14, a large number of vascular tissues. The wide distribution of R3–14 terminals innervating a variety of vascular tissues indicates that several general and local aspects of circulatory physiology are likely to be regulated by these neurons. R3–14 contain the free amino acid glycine, a putative neuromodulator that potentiates cardiac and vascular smooth muscle contraction and several small peptides of unknown, but probably neurohormonal, function. A model is proposed in which R3–14 release glycine to modulate local (e.g., hemolymph pressure and distribution) cardiovascular performance and, indirectly, metabolic homeostasis as well.
Isolated frog olfactory cilia: a preparation of dendritic membranes from chemosensory neurons
Authors: Chen Z , Pace U , Heldman J , Shapira A , Lancet D
Published: March 2018

The recently introduced frog olfactory cilia preparation (Chen and Lancet, 1984; Pace et al., 1985) has been useful for studies of molecular chemosensory mechanisms. Here we describe in detail the properties of this cilia preparation. The “calcium shock” procedure leads to a complete removal of the cilia from the olfactory epithelial surface. Isolated cilia constitute segments of proximal regions with 9 X 2 + 2 microtubular arrangement and a large proportion of membrane vesicles, probably derived from the ciliary distal segments. Polypeptides unique to the olfactory cilia preparation, compared to a control preparation of palate respiratory cilia, are identified by Coomassie brilliant blue staining, silver staining, and radiolabeled lectin overlays, as well as by biosynthetic labeling with 35S- methionine in epithelial explants and protein phosphorylation in isolated cilia. The olfactory cilia preparation contains odorant- sensitive adenylate cyclase, which is absent in control membranes from deciliated epithelium. High activities of tyrosine and serine/threonine protein kinases are also present. The olfactory cilia preparation described should be instrumental in the further elucidation of the biochemistry and molecular biology of vertebrate olfaction.
Characterization of ameboid microglia isolated from developing mammalian brain
Authors: Giulian D , Baker TJ
Published: March 2018

Ameboid microglia are isolated from the cerebral tissue of neonatal rat by selective cell adhesion to plastic. Histochemical markers show that the microglial preparations are homogeneous (95 +/- 3%) and represent a 10% yield from starting cultures. Isolated ameboid microglia contain nonspecific esterase activity, the macrophage surface antigens MAC-1 and MAC-3, and acetylated low-density lipoprotein receptors. Ameboid cells have functional properties similar to those of macrophages, including the ability to engulf 5 micron latex beads, to secrete Interleukin-1 (IL-1) and to release superoxide anion. Unlike monocytes and adherent spleen cells, ameboid microglia do not show peroxidase activity by histochemical stain. Unlike resident peritoneal macrophages, ameboid microglia proliferate in vitro. Scanning electron microscopy shows that ameboid cells have short, spinous processes that can be distinguished from the ruffled surfaces of body macrophages. Our observations suggest that ameboid microglia are a distinct class of mononuclear phagocytic cells. Retinoic acid and dimethyl sulfoxide, agents known to accelerate differentiation in vitro, stimulate ameboid cells to develop thin processes several hundred microns in length. These “process-bearing” microglia eventually lose the capacity to engulf latex beads and to proliferate. They also show reductions in nonspecific esterase activity and in the binding of acetylated low- density lipoprotein. We suggest that in vitro ameboid microglia differentiate into nonphagocytic cells similar to ramified microglia found in normal adult brain. The isolation techniques described here provide the opportunity to study the composition and function of different microglial subpopulations during the development of the CNS.
Processing of color, form and disparity information in visual areas VP and V2 of ventral extrastriate cortex in the macaque monkey
Authors: Burkhalter A , Van Essen DC
Published: March 2018

The responses of single cells to light bars of different orientation, direction of motion, speed, binocular disparity, and wavelength were systematically analyzed in areas V2 and VP of ventral extrastriate visual cortex in the macaque monkey. Selectivity for each of these parameters was assessed quantitatively using computer-controlled procedures. In both VP and V2 (both representing the superior contralateral quadrant), more than half of the cells studied were selective for stimulus color and more than half for stimulus orientation. In contrast, only a small minority of the VP and V2 cells were selective for the direction of stimulus motion. Comparison with reports of single-unit properties in dorsal extrastriate cortex suggests there are no major differences in the incidence of orientation, direction, and color selectivity between ventral and dorsal subdivisions of V2. Between V3 and VP, though, there are marked differences: Color-selective cells are much less common in V3 than VP, whereas direction-selective cells are more common in V3. This dorsoventral difference in the distribution of neuronal response properties suggests a significant asymmetry in the way visual information is processed in upper and lower parts of the visual field. The properties of cells in VP suggest that it plays an important role in both form and color vision, similar to that attributed to area V4.
D-1 dopamine receptors in the rat brain: a quantitative autoradiographic analysis
Authors: Dawson TM , Gehlert DR , McCabe RT , Barnett A , Wamsley JK
Published: March 2018

The distribution of dopamine D-1 receptors has been determined in the rat brain by a quantitative in vitro light-microscopic autoradiographic method. The binding of [N-methyl-3H]-SCH 23390 to slide-mounted tissue sections takes place with characteristics expected of a substance that recognizes D-1 receptors. The binding is saturable, has high affinity, and exhibits an appropriate pharmacology and stereospecificity in several discrete microscopic brain regions as determined by quantitative autoradiography. The highest density of D-1 receptors occurs in the caudate-putamen, accumbens nucleus, olfactory tubercle, and the substantia nigra pars reticulata. High concentrations of D-1 receptors were associated with the intercalated and medial nuclei of the amygdala, entopeduncular nucleus, and major island of Calleja. Furthermore, moderate to low concentrations were observed in several other structures, such as the frontal cortex, subthalamic nucleus, and several thalamic, hypothalamic, and hippocampal areas. The distribution of D-1 receptors correlates very well with projection areas of dopaminergic pathways. This technique furnishes a powerful assay for the accumulation of detailed pharmacologic and anatomical data about D- 1 receptors, and the results suggest possible CNS sites of action of D- 1 dopamine receptor selective compounds.
Facilitation and delayed release at single frog neuromuscular junctions
Authors: Cohen IS , Van der Kloot W
Published: March 2018

Facilitation and delayed spontaneous release were recorded from neuromuscular junctions at 2 temperatures. In some experiments, Sr2+ substituted for Ca2+. We measured the ratio of delayed release to resting spontaneous release (D), and the ratio of the second end-plate potential amplitude to the first (F). An extension of the model of Barton et al. (1983) relating Ca2+ to evoked and spontaneous release is presented. If residual Ca2+ accounts for facilitation and delayed release, then D must be greater than F. In all of our experiments, D was greater than F. We conclude that residual Ca2+ is sufficient to account for facilitation and delayed release at the frog neuromuscular junction. However, D falls abruptly at a time when F is almost unaltered, which raises serious difficulties in accepting the residual calcium hypothesis.
Maldevelopment of visual motion processing in humans who had strabismus with onset in infancy
Authors: Tychsen L , Lisberger SG
Published: March 2018

Binocular experience in infancy is necessary for the normal development of the visual cortex. However, it is not known whether binocular experience also affects the processing of specific kinds of visual information such as motion. We now report deficits in visual motion processing in 7 adult humans who lacked binocularity in infancy because of strabismus. As probes for assessing visual motion processing, we used the initiation of smooth pursuit eye movements and the judgment of target velocity independent of eye movement. Monocular viewing was essential to reveal the deficits. For horizontal pursuit, strabismic subjects showed nasal-temporal asymmetries, such that nasally directed target motion evoked more vigorous pursuit. For vertical pursuit, strabismics showed up-down asymmetries, such that upward target motion evoked more vigorous pursuit. In addition, strabismics had abnormalities in the relative effectiveness of different parts of the visual field for initiating both horizontal and vertical pursuit. Psychophysical judgements of horizontal target velocity revealed deficits analogous motion was perceived as faster than temporally directed motion, even when the 2 directions of motion were actually presented at the same speed. The magnitude of the motion processing deficits in each subject was correlated with the severity of the clinical signs of the strabismus. Our results suggest 2 possible interpretations. Maldevelopments of visual motion processing may cause strabismus in infancy, or alternatively, strabismus in the critical period for visual development may cause a maldevelopment of visual motion processing.
Oligodendroglia development in cell culture as monitored with a monoclonal antibody
Authors: Collins JM , Seeds NW
Published: March 2018

A new marker for young oligodendrocytes has been identified by a monoclonal antibody (mOg-1, IgM isotype) prepared from cerebellar plasma membrane stimulated mouse lymphocytes. mOg-1 reactive cells in the mouse cerebellum first appear at day 19 of gestation. Future white matter layers of fixed sections of neonatal rat cerebellum were labeled with mOg-1. Although EM analysis has shown cell-surface binding by presumptive oligodendroglia in neonatal cerebellum, the antibody does not bind to compact myelin. In cell cultures prepared from 6-d-old mice, 1.1% of the cells bound mOg-1 after 3 d in culture, but up to 5% of the cells bound mOg-1 after 2 weeks in culture. Of these same Og-1- positive cells, 69% bound anti-galactocerebroside and 65% bound anti- myelin basic protein. After a week in culture Og-1-positive cells often produced lamellar sheets extending a millimeter over the polylysine substratum in the absence of normal myelin formation. mOg-1 recognizes a cell-surface determinant distinct from well-characterized oligodendroglial molecules (galactocerebroside, sulfatide and myelin basic protein) that is expressed early in oligodendrocyte development. The antibody has been used to follow the maturation of oligodendrocytes in cultures of both normal and jimpy mouse cerebellum.
Inhibitory circuitry in the ventral cochlear nucleus is probably mediated by glycine
Authors: Wu SH , Oertel D
Published: March 2018

Intracellular recordings from brain slice preparations of the ventral cochlear nuclei (VCN) of mice have shown that both the major cell types, stellate and bushy cells, distinguishable by their responses to intracellularly injected current (Oertel, 1983; Wu and Oertel, 1984), receive late inhibitory as well as early excitatory inputs when the auditory nerve is stimulated electrically. When the extracellular Cl- concentration was lowered or when the intracellular Cl- was raised, the reversal potential of IPSPs became more positive; the reversal potentials were independent of the extracellular K+ concentration. Therefore, IPSPs result from increases in Cl- permeability. To determine whether either or both GABA or glycine might mediate the inhibition, the sensitivity of cells to bath-applied putative neurotransmitters was tested. All cells responded to applications of 0.1–10 mM GABA and glycine with large drops in input resistance; these drops were Cl- dependent. To determine which of these 2 substances was more likely to mediate the IPSPs, antagonists specific to GABA and glycine were tested for their ability to block the IPSPs. All IPSPs were eliminated by 1 microM strychnine, a blocker of glycine-mediated inhibition; they were not consistently blocked by 100 microM bicuculline or by 100 microM picrotoxin, blockers of GABA-mediated inhibition. These results indicate that the inhibition is likely to be mediated by glycine. A simple interpretation of the finding that IPSPs have latencies (1.2–4 msec) at least 2X as long as EPSPs (0.6–0.9 msec) is that cells in the VCN are excited monosynaptically by auditory nerve fibers, and that they are inhibited disynaptically through interneurons within the VCN. To test physiologically whether EPSPs and IPSPs are, respectively, monosynaptic and polysynaptic, 500–700 microM sodium pentobarbital was applied to the preparation. Pentobarbital raised the thresholds of all impaled cells and their synaptic inputs. EPSPs could be evoked in the presence of pentobarbital by raising the stimulus strength, as expected when thresholds are raised in a monosynaptic circuit; even if the thresholds of IPSPs were lower than those of EPSPs in normal saline, they were raised above those of EPSPs in the presence of pentobarbital. The finding that the thresholds of IPSPs are raised more than those of EPSPs supports the interpretation that IPSPs are mediated through a polysynaptic pathway, and this may explain why inhibition has been detected inconsistently in vivo.
Interspecific comparisons of the size of neural song control regions and song complexity in duetting birds: evolutionary implications
Authors: Brenowitz EA , Arnold AP
Published: March 2018

Previous studies have demonstrated a correlation between song repertoire size and volume of song control regions (SCRs) in the brains of songbirds. In the present study we demonstrate that 2 congeneric species of tropical duetting wrens, the rufous-and-white wren (Thryothorus rufalbus) and the bay wren (T. nigricapillus), share the same relationship between SCR volume and vocal complexity. In each species, females sing in elaborate duets with males. Males of these species have similar song repertoire sizes; there is no significant difference between heterospecific males in the volumes of SCRs. Female rufous-and-white wrens have less than half as large a song repertoire as female bay wrens, and all of their SCRs measured are significantly smaller than those of bay wren females. This interspecific equivalence of the relationship between SCR volume and repertoire size suggests that the neural system regulating vocal behavior in songbirds is evolutionarily conservative in the manner in which it encodes song complexity.
Sustained transmitter output by increased transmitter turnover in limb muscles of old mice
Authors: Kelly SS , Robbins N
Published: March 2018

The ability of neuromuscular junctions in old animals to maintain tetanic output was tested in phasic and tonic limb muscles and the physiologic mechanism of maintenance was elucidated by analysis of the turnover of a false transmitter during prolonged tetani. Transmitter release during and after tetani was compared in limb muscles of young (8–9 month) and old (28–30 month) male CBF-1 mice. Amplitudes of end- plate potentials (epp's) in curarized preparations and of spontaneous miniature end-plate potentials (mepp's) were measured in vitro at 30 degrees C in soleus and extensor digitorum longus (edl) muscles. In both young and old soleus muscles, epp amplitude was maintained at about 45% of resting level during the latter part of trains of 1,200 stimuli at 10 Hz but recovered to about 90% control within a few seconds after stimulation ceased. In edl muscles of young mice, epp amplitudes during a 20 Hz train of 1,200 impulses steadily declined to about 20% of control and gradually recovered over 2 min after the tetanus. In old edl muscles, tetanic decay of the epp's was greater and recovery slower than in young muscles, but absolute epp amplitudes were invariably greater. During trains of 6,000 impulses at 10 Hz, plateau epp amplitude decayed to 40–50% in young soleus muscle and 30–40% control in old muscle, but recovery was similar and absolute epp amplitudes were greater in old soleus muscle. A false transmitter precursor, homocholine (HoCh), was used to investigate the mechanism of this prolonged output, and, therefore, the use of HoCh in this system was first validated.(ABSTRACT TRUNCATED AT 250 WORDS)
Anatomical evidence for direct projections from the entorhinal area to the entire cortical mantle in the rat
Authors: Swanson LW , Kohler C
Published: March 2018

The entorhinal area is the most highly differentiated cortical field of the hippocampal formation from an anatomical point of view, and is best known as the origin of the perforant pathway, a massive association projection to the molecular layer of the dentate gyrus and Ammon's horn. This pathway is important as the first link in the so-called “trisynaptic circuit,” which is thought to form the basic unit of information processing in the hippocampal formation and has been implicated in the elaboration of short-term memory and the more permanent storage of selected events in other parts of the cortical mantle. We have reexamined the efferent projections of the lateral entorhinal area with a sensitive new method that utilizes the anterograde axonal transport of a lectin, Phaseolus vulgaris leukoagglutinin (PHA-L), that is not internalized by fibers of passage, and displays labeled axons with the clarity of Golgi impregnations. The results of 5 experiments with injections confined entirely to the lateral entorhinal area suggest that this area sends fibers to innervate the entire cortical mantle, as well as to a longitudinal zone extending the length of the striatum (nucleus accumbens and medial caudoputamen) and the basolateral complex of the amygdala. In an additional series of experiments, injections of the fluorescent retrograde tracer fast blue that were centered in medial prefrontal, somatosensory, auditory, and motor areas of the cortex invariably labeled many neurons in layer IV of the lateral entorhinal area, as well as in other layers, depending on the site of injection. Finally, the results of double retrograde tracer experiments indicated that the 2 densest projections from the lateral entorhinal area--to the medial prefrontal region and to the dentate gyrus and Ammon's horn--arise from essentially separate populations of neurons. These findings serve to clarify the neural mechanisms underlying the role of the hippocampal formation in learning and memory, as well as in locomotor activity associated with goal-oriented behavior.
Schwann cells stimulated to proliferate in the absence of neurons retain full functional capability
Authors: Porter S , Clark MB , Glaser L , Bunge RP
Published: March 2018

Schwann cells from neonatal rat sciatic nerve can be maintained and grown in culture in the absence of neurons. We are interested in substantially expanding such cultures for use in the study of Schwann cells, their growth responses, and their interactions with neurons. However, it was important to determine if expanded cell populations retained their distinguishing biological properties and their ability to differentiate when recombined with neurons. Therefore, we have compared the functional properties of extensively expanded populations of sciatic nerve Schwann cells to those of embryonic dorsal root ganglion (DRG) Schwann cells that had been briefly expanded in vitro in the continuous presence of ganglion neurons. Sciatic nerve Schwann cells were cultured and purified according to the methods of Brockes et al. (1979). A combination of crude glial growth factor and forskolin was found to act synergistically in providing maximal stimulation of Schwann cell proliferation. Sciatic nerve Schwann cells that were continuously expanded for at least 2 months were compared to Schwann cells derived from fetal dorsal root ganglia. The results indicate that the complement of secreted proteins from both cell populations, either in isolation or recombined with neurons, was essentially identical; both cell populations expressed the cell-surface antigens laminin and Ran 1 (217C antibody); after seeding onto DRG neurons, both cell populations associated with neuronal processes with the same time course; and under identical nutrient conditions, both cell populations were observed to exhibit a comparable capacity for myelination of DRG axons in vitro. Thus, methods used to establish primary cultures of rat sciatic nerve Schwann cells and to expand secondary cultures in vitro in the absence of neurons preserve basic Schwann cell functions.
Kainic acid alters the metabolism of Met5-enkephalin and the level of dynorphin A in the rat hippocampus
Authors: Kanamatsu T , Obie J , Grimes L , McGinty JF , Yoshikawa K , Sabol S , Hong JS
Published: March 2018

Male Fischer-344 rats were given a single intrastriatal injection of kainic acid (KA; 1 microgram/rat), which caused recurrent motor seizures lasting 3–6 hr. During the convulsive period, native Met5- enkephalin-like (ME-LI) and dynorphin A (1–8)-like (DYN-LI) immunoreactivities in hippocampus decreased by 31 and 63%, respectively. By 24 hr after dosing, the hippocampal opioid peptides had returned to control levels, and by 48 hr ME-LI had increased 270% and DYN-LI 150%. Immunocytochemical analysis revealed that ME-LI and Leu5-enkephalin-like (LE-LI) immunostaining in the mossy fibers of dentate granule cells and the perforant-temporoammonic pathway had decreased visibly by 6 hr and had increased markedly by 48 hr following KA. A visible decrease in DYN-LI in mossy fiber axons within 6 hr was followed by a substantial increase by 48 hr. To determine whether the increases in hippocampal ME-LI reflected changes in ME biosynthesis, levels of mRNA coding for preproenkephalin (mRNAenk) and cryptic ME-LI cleaved by enzyme digestion from preproenkephalin were measured. Following the convulsive period (6 hr), mRNAenk was 400% of control, and by 24 hr, cryptic ME-LI was 300% of control. Increases in native and cryptic ME-LI and in mRNAenk were also noted in entorhinal cortex, but not in hypothalamus or uninjected striatum. Our data suggest that KA-induced seizures cause an increase in ME release, followed by a compensatory increase in ME biosynthesis in the hippocampus and entorhinal cortex.
Effects of ischemia-like conditions on cultured neurons: protection by low Na+, low Ca2+ solutions
Authors: Goldberg WJ , Kadingo RM , Barrett JN
Published: March 2018

An in vitro system was used to mimic several aspects of ischemia, including low oxygen pressure, low nutrient levels, and the accumulation of cellular products thought to contribute to damage during ischemia. We replaced normal culture medium from 3-week-old basal ganglia cultures with oxygen-depleted, nutrient-deficient medium. After incubation in an atmosphere of 94% N2, 6% CO2 for 5 hr at 37 degrees C, the cultures were returned to normal medium. After a 24 hr recovery period, cell viability was assessed in terms of cell number, electrophysiological properties, and immunohistochemical markers. When the medium used during the ischemic period was a normal balanced salt solution, more than 70% of the cells were damaged by the low-oxygen, low-glucose stress. Loss of cell processes and cell swelling were the most evident signs of damage. The majority of the cells remaining viable were astrocytes. Neuronal damage was observed only when both glucose and oxygen were deficient. Some damage was evident even at oxygen tensions of 60 mm Hg when glucose was absent from the medium; much more extensive damage was observed at tensions below 1.0 mm Hg. Lowering both extracellular sodium and calcium resulted in more than a 2-fold increase in survival (70 vs 28%). These results indicate that damage to neurons during conditions of extreme energy deprivation such as ischemia may be mediated by the influx of calcium and/or sodium.
Quantitative correlation between barrel-field size and the sensory innervation of the whiskerpad: a comparative study in six strains of mice bred for different patterns of mystacial vibrissae
Authors: Welker E , Van der Loos H
Published: March 2018

In mice from 6 strains bred for different patterns of mystacial vibrissae, we studied the consequences of the presence of supernumerary whiskers for the sensory innervation of the vibrissal follicles and their cortical representation in the barrel field. The parameters were number of axons innervating individual vibrissal follicles, tangential area of individual barrels, and thickness of the layers in the barrel cortex. These parameters are highly constant for animals within a strain but may differ greatly between strains. For all strains, the innervation of a follicle depends on its position on the whiskerpad, the highest innervation density being at the posterolateral corner. This matches the wave of development that travels over this part of the face during embryogenesis. Although large differences exist between strains in the number of axons innervating the whiskerpad, the relative number of axons innervating the “standard” follicles of 1 row is remarkably constant. The thickness of the barrel cortex increases from posteromedial to anterolateral for all strains. This increase is due to variations in thickness of the cortical output layers (II and III, V and VI). For individual barrel-follicle pairs, we calculated the ratio between cortical barrel area and axon number. The major findings were that supernumerary follicles are innervated and, given a threshold number of axons, represented by barrels; barrel area per peripheral axon differs between follicles within a row and is highest for the supernumerary elements; and for each strain there is a direct, linear correlation between axon number and barrel size, which differs significantly among certain, but not all, strains. The data allowed us tentatively to define some of the factors that play a role in the formation of brain maps and pointed to the existence of major genetic differences between mouse strains with respect to these factors.
A GABAergic inhibitory component within the hippocampal commissural pathway
Authors: Ribak CE , Seress L , Peterson GM , Seroogy KB , Fallon JH , Schmued LC
Published: March 2018

Previous results from immunocytochemical and retrograde transport studies indicated that some GABAergic neurons in the hilus of the dentate gyrus may have axonal projections through the hippocampal commissure. This study has utilized a combined immunocytochemical and retrograde transport method as well as 2 anterograde electron- microscopic methods to determine the existence of this projection in rats. Combined tracer and immunofluorescence studies showed several double-labeled GABAergic neurons in the hilus contralateral to the injection site. The electron-microscopic studies revealed both degenerating and HRP-labeled commissural axons that formed symmetric synapses, the type shown to be formed by GABAergic terminals in the hippocampus. These data demonstrate a GABAergic component within the hippocampal commissural pathway and add further evidence that cortical GABAergic terminals are not derived exclusively from intrinsic neurons.
Guidance of neuronal growth cones in the grasshopper embryo. III. Recognition of specific glial pathways
Authors: Bastiani MJ , Goodman CS
Published: March 2018

In the previous 2 papers, we focused on the selective affinities that growth cones display for specific axonal pathways. Little is known, however, about how this orthogonal scaffold of axonal pathways in the CNS is established in the first place, and what, if any, role glia might play in these events. Here we show an important relationship between pioneering growth cones and primitive glial cells in the developing longitudinal connectives and peripheral nerve roots of the grasshopper embryo. We describe a preformed glial pathway for the formation of the intersegmental nerve, one of the major roots exiting the CNS. The growth cones that pioneer this nerve display a selective affinity for the segment boundary cell (SBC), a primitive glial cell that establishes the location of this nerve root. Similar glial cells are also found along the pathway where the longitudinal connectives form, and they too may play an important role in the formation of the first longitudinal axonal pathways. Experimental analysis shows that when the SBC is ablated, the growth cones that normally turn laterally to pioneer the intersegmental nerve do not do so, thus confirming the importance of the guiding role of this glial cell. We postulate that a simple orthogonal scaffold of primitive glia is involved in the initial patterning of axonal pathways within and exiting the insect CNS; this concept is remarkably similar to the blueprint hypothesis proposed by Singer et al. (1979) to explain the development of axon pathways in vertebrates.
Phosphoprotein F1: purification and characterization of a brain kinase C substrate related to plasticity
Authors: Chan SY , Murakami K , Routtenberg A
Published: March 2018

To study the role of protein kinase C (PKC) and its substrates in neuronal function, we have investigated the in vitro endogenous phosphorylation of the neuronal phosphoprotein F1 after induction of synaptic plasticity by long-term potentiation (LTP). The protein F1 phosphorylation was found to increase 5 min (Routtenberg et al., 1985), 1 hr (Lovinger et al., 1986) and 3 d (Lovinger et al., 1985) after LTP. The characteristics of this protein bear close similarities to a number of proteins characterized in various neuronal systems, such as B50 (brain specific, synaptosome-enriched protein), pp46 (a growth cone protein), and GAP 43 (nerve growth and regeneration-associated protein). A positive identification of the purified protein F1 with these proteins would link protein F1 to the developmental growth of axons, nerve regeneration, and polyphosphoinositide metabolism, as well as adult plasticity. We have therefore purified and partially characterized native protein F1 so that a meaningful comparison among the properties of these proteins can be made. Using synaptosomal plasma membrane (P2′) as starting material, subsequent purification involved pH extraction, 40–80% ammonium sulfate precipitation, hydroxylapatite, and phenyl-Sepharose column chromatography. This procedure achieved greater than 800-fold purification and about 45% yield relative to P2′. Purified protein F1 (Mr = 47,000, pI = 4.5) was found to be a hydrophilic molecule and was phosphorylated by 1000-fold purified PKC in the presence of phosphatidylserine (PS) and Ca2+. The Ka of PS activation is about 15 micrograms/ml (approximately 20 microM), and that of Ca2+ is about 25 microM. Diolein and DiC:8 (a synthetic diacylglycerol) lowered the requirement of Ca2+ for maximal stimulation from 100 to 5 microM. Ca2+-calmodulin kinases type I and II did not phosphorylate protein F1. The phosphoamino acid analysis showed that 97% of the total incorporated 32P-phosphate was on the serine residue. Phosphopeptide mapping using V8-protease generated 2 phospho-fragments having apparent Mr of 13,000 and 11,000. Calmodulin at 3.6 microM inhibited 95% of protein F1 phosphorylation by PKC. The availability of purified native protein F1 should facilitate investigation of the physiological role of this protein in the nervous system and its functional regulation by PKC.
Topographic targeting errors in the retinocollicular projection and their elimination by selective ganglion cell death
Authors: O'Leary DD , Fawcett JW , Cowan WM
Published: March 2018

In adult rats, as in other rodents, the retinocollicular projection is topographically organized in a very precise manner. Experiments involving the use of the retrogradely transported fluorescent dye fast blue as either a short- or long-term marker in neonatal rats indicate that the precision of this retinotopic projection does not arise ab initio, but rather is brought about by the preferential elimination of those ganglion cells whose axons project to topographically inappropriate regions of the colliculus. Such topographic targeting errors have been identified along both the rostrocaudal and mediolateral axes of the colliculus, and their elimination occurs during the period of naturally occurring ganglion cell death, which is completed by about postnatal day 10. When impulse activity in the retinal ganglion cell axons is blocked by repeated intraocular injections of the sodium channel-blocking agent tetrodotoxin (TTX) throughout the postnatal period of ganglion cell death, the preferential loss of the incorrectly projecting ganglion cells does not occur in the activity-blocked eye, although, as reported elsewhere, the overall loss of ganglion cells is comparable to that seen in normal animals. This supports the notion that the mechanism for selecting against incorrectly projecting ganglion cells is based on impulse activity among the competing ganglion cell axons. However, under activity-block conditions, the aberrantly projecting axons appear to retract from the caudal margin of the colliculus. The death of retinal ganglion cells during development thus seems to serve 2 purposes: It provides for the quantitative matching of the ganglion cell population to the needs of its central projection fields, and, at the same time, it serves to selectively eliminate those cells whose axons project to inappropriate targets or to inappropriate regions within the correct target fields.
Neuronal control of bird song production
Authors: McCasland JS
Published: March 2018

Bird song represents a powerful model system for many of the important problems in behavioral neurobiology, offering both easily measured sensory and motor patterns and a discrete neural effector system. Methods were developed to record the discharge of neurons in singing birds to examine the functions of nuclei in the song control pathway previously implicated anatomically. In several cases, lesions and other techniques were employed to test predictions derived from electrode recordings. Four major findings emerge from these studies. Single-unit recordings from telencephalic nucleus hyperstriatum ventrale, pars caudale (HVc) show several classes of neurons with apparently specialized roles in song production and/or sensorimotor interaction. The nucleus interfacialis (Nlf; Nottebohm, 1980), which provides an input to HVc and is anatomically the “highest” nucleus in the descending motor pathway, is uniquely placed among vocal control nuclei to be a generator of timing cues for song. Consistent with the unidirectional connections between nuclei of the descending pathway, Nlf, HVc, and nucleus robustus archistriatalis (RA) are activated sequentially prior to sound onset. Three other nuclei with connections to or from the descending tract do not show song-related activity in the adult. Bilateral HVc recordings and peripheral disruptions of the vocal apparatus suggest that both hemispheres and syringeal halves normally make similar contributions to most if not all song syllables. The latter finding casts doubt on the analogy between neural lateralization in bird song and in human speech.