bluuebunny/crossref_metadata_2025 huggingface dataset:
Differentiation and central projections of peripheral sensory cells with action-potential block in Drosophila mosaics
Authors: Burg MG , Wu CF
Published: March 2018

The ultrastructural differentiation and central projection of identified bristle mechanosensory neurons were examined in Drosophila mutants lacking action potentials. Two mutations, parats1 and napts, are known to block axonal conduction in centrally located neurons at high temperatures. Their effects on epithelial sensory cells, which are derived from imaginal disks during pupation, have not been determined. Furthermore, the parats1 napts double-mutant flies are lethal at all temperatures; thus the synergistic effect of these mutations on neurons has not yet been studied. It is possible to examine the above questions in genetic mosaics. By monitoring a reflex response involving identified bristle sensory cells, we found that the 2 mutations exert similar effects on these epithelial sensory cells as seen in central neurons. This also indicates that the action potential mechanisms in both epithelial sensory cells and central neurons are under similar genetic control. The parats1 napts double-mutant sensory cells in mosaics are nonfunctional at all temperatures, providing an opportunity to examine, at the single cell level, the development of neurons with activity block. Ultrastructural specializations typical of epithelial sensory cells were found in the double-mutant cells. Cobalt backfilling experiments showed that central projections of these nonfunctional sensory cells were not altered, as compared with the active contralateral sensory cells. Therefore, blockage of the action potential mechanism in individual sensory cells has no effect on their pathfinding and arborization.
Spectrin subtypes in mammalian brain: an immunoelectron microscopic study
Authors: Zagon IS , Higbee R , Riederer BM , Goodman SR
Published: March 2018

Spectrin is a major cytoskeletal component of the brain. At least 2 distinct spectrin subtypes are found in mammalian brain: brain spectrin(240/235) and brain spectrin(240/235E). In the present study spectrin subtypes were localized in the adult mouse brain by immunoelectron microscopy using antibodies that recognize each subtype. Brain spectrin(240/235E) was concentrated in neuronal cell bodies, dendrites, and postsynaptic terminals. It was also prominently associated with the plasma membrane, microtubules, filaments, mitochondria, endoplasmic reticulum, and nuclear envelope, and it appeared to interconnect structural elements within the cell. Brain spectrin(240/235E) also was localized to the plasma membrane, nuclear envelope, and cytoplasmic organelles of glial cell bodies. Brain spectrin(240/235) was detected in axons and presynaptic elements, where it was associated with the plasma membrane, microtubules, filaments, synaptic vesicles, and mitochondria. These results show that spectrin is distributed throughout the cytoplasm of neural cells, the location of spectrin is dependent on subtype, and the cytoplasmic surface of plasma membrane and organelles contains an extensive and intricate spectrin meshwork.
Activation of substantia nigra neurons: role in the propagation of seizures in kindled rats
Authors: Bonhaus DW , Walters JR , McNamara JO
Published: March 2018

The substantia nigra (SN) is crucial to the propagation of seizures in kindled rats and in other experimental seizure models. However, the mechanisms by which the SN acts to facilitate the propagation of seizures are unknown. To investigate these mechanisms we quantified the activity of SN neurons during seizures in kindled and naive rats in a paralyzed, ventilated state and examined the relationship between activity of neurons in the SN and the seizure-facilitating action of this structure. Our principal findings were that the majority of both SN dopamine and SN pars reticulata neurons, in kindled rats, fired in bursts temporally correlated to EEG waveforms recorded outside the SN during seizures; this response was only rarely found in SN neurons of naive rats during seizures elicited by stimulation of the amygdala; unlike kindled rats, lesions of the SN in naive rats did not suppress seizures. The finding that SN neurons fired in bursts during seizures in kindled, but not naive, rats indicates that seizure activity propagated into SN only in kindled rats. The correlation between seizure-suppressant effects of lesions and SN activation during seizures leads us to propose that one mechanism by which the SN promotes seizure propagation involves SN activation and transmission of seizure activity to targets of SN.
Brain-derived neurotrophic factor supports the survival of cultured rat retinal ganglion cells
Authors: Johnson JE , Barde YA , Schwab M , Thoenen H
Published: March 2018

Brain-derived neurotrophic factor (BDNF) is a small, basic protein purified from the mammalian brain that has been shown previously to support the survival of cultured spinal sensory neurons (Barde et al., 1982). In current studies, BDNF was tested for its ability to support the survival of cultured CNS cells isolated from the perinatal rat retina. Both immunofluorescent labeling of Thy-1 and prior retrograde labeling with HRP were used as retinal ganglion cell markers in vitro. With embryonic day (E) 17 retinas, it was found that BDNF allowed the survival of a small subpopulation of neurons (about 7% of the cells plated at this age) identified by the immunofluorescent labeling of Thy- 1. No detectable effects were seen when either the total number of cells or the number of tetanus toxin-positive neurons was measured. BDNF also had an effect on cultured neurons retrogradely labeled after HRP injections in the superior colliculi of neonatal rats. The BDNF- responsive population was therefore detected only in retinal cultures with specific markers and identified as consisting of retinal ganglion cells. These cells could be enriched about 80-fold by density gradient centrifugation, and purified ganglion cell cultures were shown to be responsive to BDNF. Whereas with E17 retinas, the number of surviving Thy-1 positive neurons could be kept constant for at least 4 d, the survival of postnatal neurons was only transiently increased by BDNF. We conclude that in the retina, BDNF affects only the survival of ganglion cells in vitro by a direct action on these cells. The results are discussed in terms of target-derived neurotrophic support during development.
Polyribosomes associated with synaptic specializations on axon initial segments: localization of protein-synthetic machinery at inhibitory synapses
Authors: Steward O , Ribak CE
Published: March 2018

Previous studies have revealed a selective association between polyribosomes and axospinous synapses in a variety of brain regions. The present study evaluates whether polyribosomes are also associated with the symmetrical and presumably inhibitory synaptic connections found on the initial segment of axons of some neurons in the CNS. The initial segments of pyramidal neurons in the sensorimotor cortex of the monkey and of granule cells in the hippocampus of the rat were examined. The initial segments of these cell types are contacted by GABAergic terminals that form symmetrical synaptic connections. In the present study, these initial segments were found to contain polyribosomes that tended to be selectively localized beneath the synaptic specializations. Both the synaptic connections and the polyribosomes were localized to the initial segment; after the point at which the axon became myelinated, neither synapses nor polyribosomes were found. The association between polyribosomes and synapses was also suggested by the position of the polyribosomes with respect to the synapse. In each cell type, the majority of the polyribosomes that were present in the initial segments appeared to be localized preferentially beneath synaptic sites, although some polyribosomes were also present in the core of the axon. These data reveal that polyribosomes are not peculiar to spine synapses, but rather are ubiquitous components of the subsynaptic region of many types of synapses. We propose that neurons may regulate their innervation by positioning protein-synthetic machinery (and appropriate mRNA molecules) at particular locations in order to construct particular types of synapses at defined positions on the postsynaptic cells' receptive surface.
Distribution of calpains I and II in rat brain
Authors: Hamakubo T , Kannagi R , Murachi T , Matus A
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.
An acetylcholinesterase-mediated density shift technique demonstrates that coated vesicles from chick myotubes may contain both newly synthesized acetylcholinesterase and acetylcholine receptors
Authors: Porter-Jordan K , Benson RJ , Buoniconti P , Fine RE
Published: March 2018

Coated vesicles isolated from 17 d chick embryo skeletal muscle contain acetylcholine receptors (AChRs) as shown by the presence of specific, latent binding sites for 125I-alpha bungarotoxin (125I-alpha-BTX). Since these coated vesicles also contain AChE (Benson et al., 1985), we hypothesized that a coated vesicle could carry both molecules: one an integral membrane protein, the other a secreted protein. An AChE- mediated density shift technique was used to obtain data that indicate that most isolated coated vesicles contain AChE and that some contain AChRs as well. Similar results were obtained with coated vesicles isolated from cultured chick embryo myotubes treated briefly with diisopropylfluorophosphate (DFP) to inactivate all preexisting AChE and allowed to synthesize AChE for 2 1/2 hr. These data are compatible with the hypothesis that both an integral plasma membrane protein, AChR, and a secretory protein, AChE, traverse the identical pathway after synthesis, as proposed by Rotundo and Fambrough (1980a). We suggest that coated vesicles are important intermediates in the exocytotic pathway, and that the large percentage of coated vesicles utilized for exocytotic transport can explain the rapid net increase in surface area achieved during myotube development. We also discuss the potential utility of the AChE-mediated density shift in studying the exocytotic and endocytotic pathways in other cell types, and possible pitfalls associated with its use.
Facilitatory action of etomidate and pentobarbital on recurrent inhibition in rat hippocampal pyramidal neurons
Authors: Proctor WR , Mynlieff M , Dunwiddie TV
Published: March 2018

Biochemical studies have shown that the non-barbiturate anesthetic etomidate can interact in a stereoselective, barbiturate-like fashion with the GABA/benzodiazepine receptor complex, enhancing both benzodiazepine and GABA binding, but its electrophysiological effects upon the mammalian CNS are largely unknown. The present investigations were designed to characterize the electrophysiological effects of etomidate on the recurrent GABAergic inhibitory pathway in the CA1 region of the rat in vitro hippocampal slice and to compare the actions of etomidate to those of pentobarbital. Electrical stimulation of the alveus elicited a biphasic hyperpolarizing response, consisting of an initial bicuculline-sensitive GABAergic IPSP. This was followed by a second component, termed the late hyperpolarizing potential (LHP), which is thought to reflect an increase in potassium conductance. Both pentobarbital (100 microM) and (+)-etomidate (10 microM) markedly increased the duration of the initial GABA-mediated IPSP, and frequently increased its amplitude as well. However, no significant effects of either of these drugs were observed on the LHP. Together with previous biochemical findings, our data suggest that the depressant effects of etomidate and barbiturates on the nervous system may reflect a common action upon a stereoselective receptor site intimately associated with bicuculline-sensitive GABA receptors and the chloride ion channel.
Quantitative autoradiographic localization of the D1 and D2 subtypes of dopamine receptors in rat brain
Authors: Boyson SJ , McGonigle P , Molinoff PB
Published: March 2018

The distribution of D1 and D2 receptors was studied in coronal sections of rat brain, using quantitative autoradiography. D1 receptors were labeled with 1.8 nM 3H-SKF-83566 (a brominated analog of 3H-SCH-23390), while D2 receptors were labeled with 1.0 nM 3H-spiroperidol (3H-SPD). The binding of both ligands to sections from brain and from a homogenate of caudate putamen (CPu mash) reached equilibrium within 80 min at 37 degrees C. CPu mash provided a virtually unlimited number of homogeneous sections that contained a high density of both D1 and D2 receptors. Sections of CPu mash were used in competition studies that confirmed that the specific binding of 3H-SKF-83566 was selective for D1 receptors, and that the binding of 3H-SPD was selective for D2 receptors. Scatchard analysis of equilibrium binding of the 2 ligands in the CPu in horizontal sections of rat brain revealed Kd values of 1.1 +/- 0.07 nM for 3H-SKF-83566 and 0.7 +/- 0.09 nM for 3H-SPD. Studies of the distribution of D1 and D2 receptors were carried out in coronal sections of brains from 5 rats. D1 receptors were found throughout the forebrain and were present in greater density than were D2 receptors in all regions examined except the olfactory nerve layer. In the CPu, nucleus accumbens, and olfactory tubercle, the densities of D1 and D2 receptors were, respectively, approximately 2,500 and 600–800 fmol/mg protein. In the substantia nigra, the density of D1 receptors was approximately 2,500 fmol/mg protein in both the compacta and the reticulata, but the density of D2 receptors was 230 fmol/mg protein in the compacta and 70 fmol/mg protein in the reticulata. The ventral tegmental area contained only 90 fmol/mg protein of D1 receptors, and D2 receptors were undetectable. The entopeduncular nucleus, zona incerta, and region of the ventral internal capsule had densities of D1 receptors of 550–950 fmol/mg protein and D2 receptor densities of less than 100 fmol/mg protein. Densities of D1 and D2 receptors were, respectively, 2,700 and 900 fmol/mg protein in the choroid plexus. Knowledge of the differences in the relative distributions of D1 and D2 receptors in various brain regions may increase our understanding of the functions of brain dopaminergic systems and may aid in the development of new therapeutic approaches for neuropsychiatric disorders.
Spatial buffering of K+ by the retinal pigment epithelium in frog
Authors: Immel J , Steinberg RH
Published: March 2018

Using K+-specific microelectrodes in the isolated retinal pigment epithelium preparation from frog eye, we have examined changes in extracellular K+ in the unstirred layer between the choroid and basal membrane. We found, using agents to depolarize apical and basal membranes, that membrane potential modulates K+ efflux from the basal membrane into the choroid. [K+] in the choroid was found to be higher than in the bathing medium. From the basal (scleral) surface of the choroid to the basal membrane of the retinal pigment epithelium, [K+] increased from 2 mM (bath concentration) to an average of 2.84 mM near the basal membrane. When [K+] was increased on the apical side, epithelial membranes depolarized and produced [K+] efflux from the basal membrane that led to an increase in choroidal [K+]. Ba2+, 2 mM, ouabain, 0.1 mM, also evoked increases in choroidal [K+] concomitant with membrane depolarization. Thus, apical Na+/K+ pump transport and K+ leakage due to tissue damage were eliminated as possible sources of observed increases in choroidal [K+] since apical Ba2+ and ouabain depolarize epithelial membranes without increasing apical [K+]. The effects of depolarizing agents were blocked by basal Ba2+, demonstrating the requirement for a large K+ conductance at the basal membrane. Theoretical analysis shows that shunt resistance and isolation of apical and basal compartments are limiting factors in the transfer of K+. In the retinal pigment epithelium, shunt resistance favors the transfer of electrical potentials between membranes while the paracellular pathway selectively impedes movement of K+ between compartments.(ABSTRACT TRUNCATED AT 250 WORDS)
Isolation of embryonic chick motoneurons and their survival in vitro
Authors: O'Brien RJ , Fischbach GD
Published: March 2018

This is the first of a series of 4 papers in which we describe the regulation of excitatory amino acid receptors on embryonic chick motoneurons dissociated from the lateral motor column and maintained in cell culture. Techniques are described for labeling embryonic chick motoneurons in vivo with Lucifer Yellow or fluorescein isothiocyanate conjugates of wheat germ agglutinin (Fl-WGA). We estimate that 65–95% of the motoneurons in the lateral motor column survive tissue dissociation and settle on an appropriate culture surface. The number of fluorescent motoneurons observed in heterogeneous spinal cord cell cultures decreases with a half-life of 2 d. The decline is due to fading of the fluorescent tracer rather than to loss of cells. Techniques are also described for separating motoneurons from other spinal cord cells with a fluorescence-activated cell sorter. Approximately 24% of the motoneurons in the lateral motor column can be isolated, and motoneurons comprise more than 90% of the population in cultures seeded with sorted cells. The survival of sorted and unsorted motoneurons in vitro is enhanced in the presence of skeletal myotubes or muscle conditioned medium, but the survival of non-motoneurons is not influenced by muscle. Electrophysiologic properties of sorted and unsorted motoneurons determined with patch-clamp techniques are similar. Both differ from mature motoneurons in their lower resting membrane potential (-50 mV), larger input resistance (450 M omega), and longer time constant (39 msec). Also they do not exhibit anomalous rectification or a calcium-activated potassium after hyperpolarization. Motoneurons grown in the absence of interneurons differ from motoneurons in heterogeneous spinal cord cell cultures in that their neurites (dendrites) are shorter and they branch less often.
Modulation of embryonic chick motoneuron glutamate sensitivity by interneurons and agonists
Authors: O'Brien RJ , Fischbach GD
Published: March 2018

Embryonic chick motoneurons grown in culture together with other spinal cord cells are more sensitive to L-glutamate than are sorted motoneurons grown in isolation. After 6 d in vitro, the difference in peak sensitivity reached 6-fold. Comparable increases in aspartate and kainate currents were observed, indicating that both G1 and G2 amino acid receptors were affected. Elimination of proliferating non-neuronal cells from mixed spinal cord cell cultures by addition of cytosine arabinoside (ara C) did not prevent the increase in motoneuron chemosensitivity, so the induction is probably due to the presence of interneurons. In contrast to their effect on glutamate response, interneurons did not affect the sensitivity of motoneurons to the inhibitory neurotransmitters GABA and glycine. Glutamate receptors expressed by sorted and unsorted motoneurons are identical in terms of their ED50, reversal potential, mean channel open time, and conductance, implying that the increased sensitivity of motoneurons in mixed cultures is due to an increase in the number of open channels. In addition to an increase in the number of channels, the distribution of glutamate sensitivity over the surface of individual motoneurons was altered in interneuron-containing cultures. The sensitivity of isolated motoneurons was greatest at the soma and decreased with distance along major processes, but the sites of highest sensitivity on motoneurons in mixed cultures occurred along their processes. Sharp peaks identified by focal iontophoresis of glutamate were separated by areas of lower sensitivity. The inductive effect of interneurons cannot be due to glutamate, the most likely excitatory interneuron-motoneuron transmitter in 6 d chick cultures.(ABSTRACT TRUNCATED AT 250 WORDS)
Step-tracking movements of the wrist in humans. I. Kinematic analysis
Authors: Hoffman DS , Strick PL
Published: March 2018

We have examined the kinematics of the initial trajectory of step- tracking movements performed by human subjects. Each subject tracked a target that required 5–30 degrees of radial or ulnar deviation of the wrist. All movements were to be performed as accurately as possible. Speed instructions were given before each trial. When subjects performed different amplitude movements following the same speed instruction, the peaks of velocity, acceleration, and jerk were linearly related to peak displacement. The peaks of velocity, acceleration, and jerk also changed when the speed instruction was altered. Thus, for any given movement, the peak values of the derivatives of displacement were dependent on both movement amplitude and intended speed. As a result, the peak values of the derivatives cannot be used by themselves to control or monitor peak displacement. When subjects performed different amplitude movements following the same speed instruction, movement duration tended to remain constant. In contrast, movement duration changed when the speed instruction was altered. Movements performed when subjects intended to move slowly had longer durations than when subjects intended to move quickly. These results suggest that subjects volitionally alter intended speed by selecting different movement durations. When both movement amplitude and intended speed were varied, the peak displacement of a step- tracking movement was linearly related to the product of 2 kinematic variables: the initial peak of a derivative of displacement (either velocity, acceleration, or jerk) and movement duration. On the basis of our observations, we propose that central commands generate step- tracking movements of different amplitudes and intended speeds by adjusting both the magnitude and duration of a derivative of displacement.
Oligodendrocyte cell adhesion molecules are related to neural cell adhesion molecule (N-CAM)
Authors: Bhat S , Silberberg DH
Published: March 2018

The glycoproteins responsible for calcium-dependent oligodendrocyte aggregation were purified and characterized. Using detergent extraction, lentil-lectin-Sepharose 4B affinity chromatography, and preparative gel electrophoresis, 3 proteins were purified to apparent homogeneity, with relative Mrs of 120,000, 140,000, and 180,000. The aggregation assay showed that all 3 proteins had the ability to block antibody-mediated inhibition of oligodendrocyte aggregation. The 120,000 protein was the most active of the three. Antisera were raised in rabbits to these 3 individual proteins. Western blot analyses showed that all three antisera recognized 120,000, 140,000, and 180,000 proteins, which indicated that the proteins were related. Western-blot analyses of cultured oligodendrocytes and purified rat myelin showed only the 120,000 protein. Immunoprecipitation of iodinated membrane proteins of cultured oligodendrocytes also indicated the presence of only the 120,000 Mr protein. Deglycosylation of the 120,000 protein by N-glycanase resulted in a 110,000 protein. The immunoblot pattern suggested some similarities between oligodendrocyte adhesion molecules and the neural cell adhesion molecule (N-CAM). Therefore, the 120,000, 140,000, and 180,000 Mr proteins were compared to N-CAM by Western-blot analysis, immunofluorescence staining, and by immunoprecipitation. The results suggest that oligodendrocytes contain a 120,000 membrane glycoprotein that is related to N-CAM.
High concentrations of N-acetylaspartylglutamate (NAAG) selectively activate NMDA receptors on mouse spinal cord neurons in cell culture
Authors: Westbrook GL , Mayer ML , Namboodiri MA , Neale JH
Published: March 2018

We examined the membrane action of the endogenous dipeptide and putative neurotransmitter N-acetylaspartylglutamate (NAAG) on the excitatory amino acid receptors of cultured mouse spinal cord neurons using electrophysiological methods. Responses to NAAG (1 microM-5 mM) were compared to those elicited by N-methyl-D-aspartate (1 microM-1 mM) and L-glutamate (0.5–500 microM). Under voltage clamp, concentration- response curves of agonist-evoked currents demonstrated that NAAG was much less potent than either L-glutamate or N-methyl-D-aspartate (NMDA), so that inward currents could be evoked only at NAAG concentrations above 300 microM. Analysis of the dipeptide by high- pressure liquid chromatography showed no evidence of contamination by excitatory amino acids, suggesting that NAAG has an intrinsic, although weak, neuroexcitatory action on spinal neurons. Previous studies have shown that activation of NMDA receptors produces a voltage-dependent response. The current-voltage relationship of responses evoked by NAAG was also voltage-dependent. The peptide-activated conductance decreased with hyperpolarization in the presence of extracellular Mg2+, such that little inward current could be evoked at a membrane potential of -80 mV. In addition, responses to NAAG were completely antagonized by 250 microM DL-2-amino-5-phosphonovaleric acid, a specific NMDA-receptor antagonist. Application of NAAG in Mg2+-free medium resulted in an inward current with a large increase in membrane current noise. The spectral density function of this current noise could be fitted with a single Lorentzian with a decay time constant near 5 msec and a calculated single-channel conductance of 50–60 pS.(ABSTRACT TRUNCATED AT 250 WORDS)
Mosaic architecture of the somatic sensory-recipient sector of the cat's striatum
Authors: Malach R , Graybiel AM
Published: March 2018

The striatum is known to have a compartmental organization in which histochemically defined zones called striosomes form branched 3- dimensional labyrinths embedded within the surrounding matrix. We explored how fiber projections from cortical somatic sensory areas representing cutaneous and deep-receptor inputs are organized in relation to this striatal architecture. Areas SI and 3a were mapped electrophysiologically, and distinguishable anterograde tracers (wheat germ agglutinin-HRP and 35S-methionine) were injected into physiologically identified loci. Primary somatic sensory corticostriatal projections were confined to a small, well-defined sector in the dorsolateral corner of the ipsilateral striatum. The somatic sensory afferents were arranged according to a coherent global body map in which rostral body parts were represented more laterally than caudal body parts. Single cortical loci innervated branched and clustered striatal zones that were reminiscent of the striosomes in their range of sizes and shapes yet lay strictly within the extrastriosomal matrix. In contrast to the global orderliness of the striatal body map, there were clear examples of locally complex patterns in which functionally distinct inputs interdigitated with each other. These patterns were often, but not always, produced when corticostriatal afferents carrying different submodality types were labeled. These findings demonstrate the existence of striosome-like striatal compartments within the seemingly uniform extrastriosomal matrix. The principle of mosaic organization thus holds throughout the tissue of the somatic sensory striatum. The striatal architecture delineated here could provide the anatomical substrate for computations requiring cross-modality comparisons within the framework of an overall somatotopy. If a similar multicompartmental architecture also characterizes other striatal regions, as seems likely, it may set general constraints on the nature of associative processing within the striatum as a whole.
Quantitative autoradiography of multiple 5-HT1 receptor subtypes in the brain of control or 5,7-dihydroxytryptamine-treated rats
Authors: Verge D , Daval G , Marcinkiewicz M , Patey A , el Mestikawy S , Gozlan H , Hamon M
Published: March 2018

The distribution of the 2 main types (A and B) of 5-HT1 binding sites in the rat brain was studied by light-microscopic quantitative autoradiography. The 5-HT1A sites were identified using 3H-8-hydroxy-2- (N-dipropylamino)tetralin (3H-8-OH-DPAT) or 3H-5-HT as the ligand. In the latter case, it was shown that 3H-5-HT binding to 5-HT1A sites corresponded to that displaceable by 0.1 microM 8-OH-DPAT or 1 microM spiperone. The “non-5-HT1A” sites labeled by 3H-5-HT in the presence of 0.1 microM 8-OH-DPAT corresponded mainly to 5-HT1B sites. 5-HT1A binding was notably high in limbic regions (dentate gyrus, CA1 and CA3 hippocampal regions, lateral septum, frontal cortex), whereas 5-HT1B binding was particularly concentrated in extrapyramidal areas (caudate nucleus, globus pallidus, substantia nigra). Except in the latter regions, where only one class of 5-HT1 sites was found, both 5-HT1A and 5-HT1B sites existed in all areas examined. The selective degeneration of serotoninergic neurons produced by an intracerebral injection of 5,7- dihydroxytryptamine was associated only with a significant loss of 5- HT1A binding to the dorsal raphe nucleus (-60%) and of 5-HT1B binding to the substantia nigra (-37%). These results are discussed in relation to the possible identity of 5-HT1A and/or 5-HT1B sites with the presynaptic 5-HT autoreceptors controlling nerve impulse flow and neurotransmitter release in serotoninergic neurons.
Guidance of neuronal growth cones in the grasshopper embryo. IV. Temporal delay experiments
Authors: Doe CQ , Bastiani MJ , Goodman CS
Published: March 2018

In the previous 3 papers, we demonstrated that neuronal growth cones display selective affinities for both specific axonal and glial pathways in the grasshopper embryo; for example, the pCC growth cone selectively recognizes the MP1/dMP2 axons, while the aCC growth cone selectively recognizes the U axons and a specific glial cell (the segment boundary cell). We were interested in further testing the temporal specificity of these affinities. To address this issue, we performed specific temporal transplant experiments by using a laser microbeam in ovo to ablate the neuronal precursor cell, neuroblast (NB) 1–1, that generates the aCC and pCC neurons. Neighboring ectodermal cells regulate and replace the ablated NB 1–1; the new NB 1–1 then generates the aCC and pCC neurons with a temporal delay of 10–20 hr (2– 4% of development), depending upon the experimental paradigm. The results of these temporal delay experiments further demonstrate the selective affinities of the aCC and pCC growth cones for specific axonal and glial surfaces and confirm that these specificities are absolute and not hierarchical. Furthermore, they suggest that precise timing is not important; both the pCC and aCC growth cones are able to selectively recognize their appropriate axonal and glial pathways after delays of 10–20 hr despite being confronted with the surfaces of many additional axons and pathways.
Bilateral syringeal coupling during phonation of a songbird
Authors: Nowicki S , Capranica RR
Published: March 2018

The syrinx of oscine birds (“true songbirds”) is a double vocal organ, and each side has generally been presumed to function independently under separate neural control during phonation. A significant counterexample is demonstrated here in the production of a common vocalization by the black-capped chickadee (Parus atricapillus), in which the 2 acoustic sources of the syrinx interact in a nonlinear fashion. The chickadee produces a sound with multiple frequency components that superficially resemble harmonics. An analysis of vocal production after unilateral and bilateral syringeal denervation shows instead that these frequency components are sum and difference frequencies, or heterodyne frequencies, resulting from cross-modulation between the 2 syringeal sides. A limited form of this bilateral coupling may be achieved after unilateral denervation of either syringeal side but not after bilateral denervation. Unilaterally denervated birds are capable of significant improvement in coupling after 10 d, too short a period for neural regrowth. These results suggest that coupling arises from a passive physical interaction between the 2 syringeal sources which is activated or regulated in some fashion by neural control from either side.
Plasticity of expression of a synaptic vesicle antigen in adult rat superior cervical ganglion
Authors: Greif KF
Published: March 2018

The effects of deafferentation and alterations of synaptic activity on levels of a synaptic vesicle-specific membrane protein (SV) were studied in the adult rat superior cervical ganglion (SCG) in vivo, using a monoclonal antibody directed against the protein. Levels of SV were quantified by radioimmunoassay. Deafferentation of the SCG results in a transient increase in SV levels in the SCG on days 7 and 10 after surgery, with levels then dropping below control levels on days 14, 21, and 30 after surgery. Immunohistochemical labeling of deafferented ganglia indicates that the increase is confined to the perikarya of principal ganglionic neurons. Levels of SV in an SCG target tissue, the iris, do not differ from control levels on day 7 after deafferentation, but are elevated at days 10, 14, and 30 after surgery. After reinnervation of the SCG, levels of SV in the SCG are elevated above control values, but do not differ from control values in the iris. Treatment with chlorisondamine, which blocks synaptic transmission in sympathetic ganglia, produces a significant increase in SV levels in the SCG after 7 d of treatment. Long-term chlorisondamine treatment results in reductions in SV in the SCG after 14 and 28 d. Treatment with phenoxybenzamine for 6 d, which reflexly increases synaptic activity, produces a marked decrease in SV in the SCG. These results suggest that activity, mediated by transsynaptic factors, contributes to the regulation of synthesis of a synaptic vesicle protein in the SCG. The results further suggest that accumulation of synaptic vesicles in terminals of the principal ganglion neurons may help regulate the maintenance of normal synaptic vesicle pools within sympathetic neurons.
Regulation of serotonin-stimulated phosphoinositide hydrolysis: relation to the serotonin 5-HT-2 binding site
Authors: Conn PJ , Sanders-Bush E
Published: March 2018

The hypothesis that serotonin (5-HT)-stimulated phosphoinositide hydrolysis is mediated by the 5-HT-2 binding site in cerebral cortex was tested by comparing antagonist Kd values determined by Schild analyses with Ki values at the 5-HT-2 binding site. A significant correlation was found between Kd values and Ki values at competing for 3H-ketanserin binding (R = 0.98), suggesting that the phosphoinositide- linked receptor and the 5-HT-2 site are identical. The 5-HT-2-mediated phosphoinositide response was then used as a measure of 5-HT-2 receptor sensitivity after in vivo treatments that alter the availability of 5- HT. Chronic treatment with the 5-HT-2 antagonist mianserin resulted in a significant decrease (52%) in the density of 5-HT-2 binding sites and a significant decrease (49%) in the maximal phosphoinositide hydrolysis response to 5-HT. Depletion of 5-HT levels with para- chlorophenylalanine or chemical denervation of serotonergic neurons with 5,7-dihydroxytryptamine had no significant effect upon 5-HT-2 receptor density or upon the phosphoinositide response to 5-HT. These data suggest that changes or lack of changes in 5-HT-2 receptor density following in vivo manipulations reflect the functional state of the receptor.
Synthesis of a growth-associated protein by embryonic rat cerebrocortical neurons in vitro
Authors: Perrone-Bizzozero NI , Finklestein SP , Benowitz LI
Published: March 2018

Proteins synthesized by embryonic rat cortical cultures were studied under conditions that were either permissive or nonpermissive to neurite outgrowth. Freshly dissected cortex from embryonic day 17 rat pups was mechanically dissociated and plated on poly(L-lysine) substrate in the presence of (1) serum-free media, which allowed neuronal survival but no outgrowth; (2) serum, which allowed survival of both neurons and glia as well as neurite outgrowth; or (3) a hormone- supplemented defined media, which allowed preferential survival and outgrowth of neurons. In addition, postnatal tissue was cultured as a source of glia. Cultures were pulse-labeled with 35S-methionine 48 hr after plating and the protein synthesis patterns examined by 2- dimensional gel electrophoresis followed by fluorography. The expression of an acidic 50 kDa protein, associated with the particulate fraction of cells, was found to be a prominent correlate of neurite outgrowth. This protein was synthesized in serum- or hormone-treated embryonic cultures showing neurite outgrowth but was undetectable in embryonic cultures without outgrowth or in postnatal glial cultures. By virtue of its migration position on 2-dimensional gels, its presence in a light membrane fraction, and its cleavage products after Staphylococcus aureus protease treatment, the 50 kDa protein appears to be identical to an acidic 43–49 kDa protein that has been identified in several developing and regenerating neural pathways, as well as to the B-50 phosphoprotein. These findings lend support for a critical role of this protein in neural development and demonstrate the feasibility of using primary CNS cell cultures to study its biosynthesis and function.
Migration and myelination by adult glial cells: reconstructive analysis of tissue culture experiments
Authors: Wolf MK , Brandenberg MC , Billings-Gagliardi S
Published: March 2018

Adult glia are capable of at least limited myelination of CNS axons. However, it is difficult to quantitate their myelination or migratory capacities and to examine contributions of the CNS environment or exogenous factors that might promote or inhibit this process in situ. We have therefore developed a mouse tissue culture system in which optic nerve glia (in the form of appropriately handled optic nerve) are added to chemically demyelinated cerebellar axons. Optic nerve up to postnatal day 411 (P411) contains cells that can migrate out of the nerve into the cerebellar explant and form myelin around its axons. The success rate for myelin formation in these cultures is 57% for immature (P7–11) glia and 55% for adult (P50–411) glia. Computer-generated reconstructions of cultures containing immature (P8) and adult (P89 and P139) nerves demonstrate that in all 3 cases the glia may migrate more than 0.6 mm before myelinating axons, assuming the shortest possible track. Both the age limit for myelination and distance limit for migration, if any, remain to be determined for these adult glia. In successful cultures, myelin always directly abuts the optic nerve surface, whether or not it also extends further, suggesting that migrating glia may depend upon contact guidance by myelin-receptive axons. We conclude that this culture system is a useful model of adult CNS myelin regeneration, in which one can examine the influence of potential trophic or toxic factors on specific aspects of myelinating glial cell behavior.
Excitatory amino acid receptors coupled with guanylate cyclase in primary cultures of cerebellar granule cells
Authors: Novelli A , Nicoletti F , Wroblewski JT , Alho H , Costa E , Guidotti A
Published: March 2018

Primary cultures of cerebellar granule cells have been used in pharmacologically and functionally characterizing excitatory amino acid recognition sites coupled with guanylate cyclase. When granule cells were incubated in physiological culture conditions (Locke's solution, pH 7.4), only kainate and, to a lesser extent, L-glutamate increased cyclic GMP (cGMP) levels. Under these conditions, L-aspartate, N-methyl- D-aspartate (NMDA), and quisqualate were inactive. When granule cells were incubated in the absence of extracellular Mg2+ or in the presence of the depolarizing agent veratrine, L-glutamate, L-aspartate, and NMDA became as effective as kainate in enhancing cGMP formation. The action of kainate was preferentially antagonized by 2,3-cis- piperidindicarboxylate, whereas the action of L-glutamate was preferentially antagonized by (+/-)2-amino-5-phosphonovalerate. These data suggest that 2 different excitatory amino acid recognition sites (activated by kainate or by L-glutamate, L-aspartate, and NMDA, respectively) are coupled with guanylate cyclase in primary cultures of cerebellar granule cells: While the coupling of the recognition site for kainate with guanylate cyclase operates under resting conditions and in the presence of Mg2+, the coupling of the recognition site for L- glutamate, L-aspartate, and NMDA with guanylate cyclase requires depolarizing conditions or the absence of extracellular Mg2+.
Development of learning and memory in Aplysia. I. Functional assembly of gill and siphon withdrawal
Authors: Rankin CH , Stopfer M , Marcus EA , Carew TJ
Published: March 2018

The marine mollusc Aplysia californica provides an excellent preparation with which to examine the development of the neuronal control of behavior for 2 reasons: first, adult Aplysia exhibit a variety of behaviors that are well understood in cellular terms; and second, the development of Aplysia from embryo to adult has been studied in considerable detail. Among the best understood behaviors in Aplysia are the withdrawal responses of the mantle organs (the gill, siphon, and mantle shelf), which exhibit 2 different kinds of behaviors: “spontaneous” contractions that are part of a fixed action pattern, a respiratory pumping sequence of the mantle organs, and reflex contractions in response to tactile stimuli. We have examined the development of both of these withdrawal behaviors in juvenile stages 9–12 and found that they are functionally assembled according to different ontogenetic timetables. Spontaneous contractions. As soon as the siphon and gill emerge, in stages 9 and 10, respectively, they each show a high rate of spontaneous contraction that gradually diminishes throughout subsequent stages until it reaches the low rate typical of adults (stage 13). Since the siphon emerges first, it already exhibits a significant decline in its spontaneous activity (e.g., in stage 11) when the gill's spontaneous activity is at its highest. In addition to a developmental trend in the rate of contractions, there was also a clear developmental progression in the degree of cocontraction of the siphon and gill during spontaneous contractions. In adults, the siphon and gill show a very high degree of cocontraction during spontaneous pumping. However, in juvenile animals, there was a very low degree. Thus, it appears that the siphon and gill withdrawal components of the fixed action pattern become progressively more functionally coupled during juvenile development. Reflex contractions. As soon as the siphon and gill emerge in their respective developmental stages, they exhibit a brisk withdrawal reflex to tactile stimulation of the siphon. Moreover, at each developmental stage, reflex siphon contractions were graded as a function of stimulus intensity, as they are in the adult. Finally, throughout development tactile stimulation of the siphon invariably evoked coincident contractions of both the siphon and the gill, which is characteristic of the adult reflex. Thus, unlike the fixed action pattern that takes several weeks to mature, the defensive withdrawal reflex closely resembles the adult form as soon as the effector organs emerge during juvenile development.(ABSTRACT TRUNCATED AT 400 WORDS)
Development of learning and memory in Aplysia. II. Habituation and dishabituation
Authors: Rankin CH , Carew TJ
Published: March 2018

The defensive withdrawal reflex of the mantle organs of Aplysia californica exhibits a variety of forms of both nonassociative and associative learning, which can exist in both short- and long-term forms. In addition, the reflex can be readily elicited and quantified as soon as the effector organs (siphon and gill) emerge at their respective developmental stages. Thus, this reflex system provides a useful preparation in which to study the development of learning and memory. In the present series of experiments we investigated the development of 2 forms of nonassociative learning, habituation and dishabituation, in the siphon withdrawal component of the reflex. This reflex response could be examined throughout the juvenile life of the animal (stages 9–12) since the reflex is functionally intact as soon as the siphon emerges in stage 9 (Rankin et al., 1987). We studied the development of habituation in stages 9–12 using tactile stimuli to the siphon delivered at interstimulus intervals (ISIs) of 1, 5, 10, and 30 sec. Habituation of siphon withdrawal was evident as early as juvenile stage 9. However, it existed in an immature form: Significant habituation was produced only with a very short (1 sec) ISI. No significant habituation occurred in response to 5 or 10 sec ISIs. Approximately 4 d later, in stage 10, significant habituation occurred to both 1 and 5 sec ISIs but not to a 10 sec ISI. Finally, approximately 1–2 weeks later, in stage 11, significant habituation occurred to 1, 5, and 10 sec ISIs but not to a 30 sec ISI, whereas stage 12 juveniles and adults (stage 13) readily habituated to a 30 sec ISI. Thus, there was a systematic developmental trend in the ability of the animals to habituate: Progressively older animals were capable of habituation to stimuli presented at progressively longer intervals. The systematic development of habituation was also evident by examining the amount of habituation exhibited to comparable ISIs by animals at different developmental stages. For all 4 ISIs examined, older animals showed significantly greater habituation than younger animals. Thus, our results show that habituation is present as soon as the siphon response system emerges and that it develops progressively throughout the juvenile life of the animal. Whereas habituation was present in the earliest developmental stage we examined (stage 9), dishabituation (in response to tail shock) did not emerge until 4–7 d later, in stage 10.(ABSTRACT TRUNCATED AT 400 WORDS)