bluuebunny/crossref_metadata_2025 huggingface dataset:
Single mossy fiber axonal systems of human dentate granule cells studied in hippocampal slices from patients with temporal lobe epilepsy [published erratum appears in J Neurosci 1993 Jun;13(6):following table of contents]
Authors: Isokawa M , Levesque MF , Babb TL , Engel J
Published: March 2018

Previous histological and immunocytochemical studies suggest that reorganization of the dentate granule cell axons, the mossy fibers, can occur in epileptic human hippocampus (Sutula et al., 1989; Houser et al., 1990; Babb et al., 1991) and in animal models of epilepsy (Tauck and Nadler, 1985; Sutula et al., 1988; Cronin et al., 1992). However, neuroanatomical analyses of the trajectory and morphology of reorganized axons are not yet available. The present study was conducted to investigate single dentate granule cell axonal systems in human epileptic hippocampus. Individual mossy fibers were directly visualized by injecting a tracer (biocytin or Lucifer yellow) intracellularly in hippocampal slices prepared from temporal lobes that were surgically removed from patients for treatment of intractable epilepsy. Two major arborization patterns were identified: (1) the parent axons extended to and coursed through the hilus toward CA3, leaving collaterals along their paths in the hilus (N = 19 neurons); (2) in addition to the aforementioned axonal system, collateral(s) branched from the parent axon near the soma and projected to the granule cell layer and molecular layer, forming an aberrant axonal pathway (N = 9 neurons). These aberrant collaterals bore large boutons similar to those of the hilar axons and formed extensive plexuses in the granule cell layer and/or in the molecular layer. The summed length of collaterals in the granular/molecular layers was 1110.8 microns on average, which was one-fourth of the total summed length of the mossy fibers (3698.5 microns on average). The size of the somata in neurons that had aberrant collaterals was significantly larger than that of neurons without such collaterals (p < 0.025). In four cases, filopodium- like fine processes were present near the axon hillock and proximal parts of the parent axon, suggesting that the aberrant collateral formation might be an ongoing process in these tissues. The lack of control slices from normal living human hippocampus makes it difficult to assess to what extent the present findings are epilepsy associated. However, the presence of aberrant mossy fiber collaterals in the hippocampi used in the present study has been confirmed by Timm's staining and/or dynorphin immunohistochemistry in comparison with nonepileptic autopsy material, indicating its relation to epilepsy (Babb et al., 1991, 1992). At present, there seems to be a consensus that the projection of mossy fiber collaterals to the supragranular layer is a rare occurrence in normal rats (Lorento de No, 1934; Claiborne et al., 1986; Seress et al., 1991; present study), normal monkeys (Seress et al., 1991), and normal humans (Houser et al., 1990).(ABSTRACT TRUNCATED AT 400 WORDS)
Testosterone enhancement of the nerve cell body response to injury: evidence using in situ hybridization and ribosomal DNA probes
Authors: Kinderman NB , Jones KJ
Published: March 2018

In axotomized peripheral motoneurons capable of successful regeneration, one of the earliest morphological indicators of the injury response occurs within the nucleolus. In the initial part of this investigation, we mapped the nucleolar response of injured adult hamster facial motoneurons from a molecular perspective, utilizing in situ hybridization and ribosomal DNA probes complementary to stable rRNA. Recently, we have discovered that the gonadal steroid, testosterone propionate (TP), accelerates recovery from facial paralysis in the hamster by increasing the rate of regeneration of the fastest regrowing axons. In the second part of this study, the hypothesis that TP accomplishes these effects on facial nerve regeneration through an enhancement of the nerve cell body response to injury was tested using in situ hybridization and rDNA probes. Adult intact male hamsters were subjected to right facial nerve axotomies at the stylomastoid foramen. One-half of the axotomized animals received subcutaneous implants of TP, with the remainder sham implanted. In situ hybridization with tritiated rDNA probes was accomplished and levels of hybridizable rRNA assessed both qualitatively and quantitatively. Axotomy alone induced an upregulation in rRNA levels, with peak changes occurring by 24 hr postoperative and continuing through postoperative day 4. These molecular changes in the nucleolar response preceded, by a full day, any morphological signs of the nucleolar reactive pattern previously found in this cell type, and, as such, point to the usefulness of in situ hybridization as a tool to identify the earliest events associated with the axon reaction. A secondary smaller increase in rRNA levels was observed during the later stages of regeneration. TP significantly augmented the ribosomal response to injury, with levels of rRNA increased as early as 6 hr and the magnitude of the response greater than that occurring following axotomy alone. These results provide the first mechanistic step in the identification of the cellular processes underlying gonadal steroid augmentation of neuronal reparative processes. We conclude that TP accelerates the “switch” from a normal to a reparative state and suggest that this priming effect may be causally related to the differential effects of TP on the regenerative properties of this cell type.
Nerve growth factor is a potent inducer of proliferation and neuronal differentiation for adult rat chromaffin cells in vitro
Authors: Tischler AS , Riseberg JC , Hardenbrook MA , Cherington V
Published: March 2018

Adult rat chromaffin cells in vitro show a large proliferative response to NGF, followed by neuronal differentiation. Infection of replicating chromaffin cells with a retrovirus carrying the Escherichia coli beta- galactosidase (beta-gal) gene demonstrates beta-gal expression in cells that continue to multiply, that differentiate into neurons, and that become static. The effects of NGF on proliferation and differentiation are abolished by the protein kinase inhibitors K252a and staurosporine, and by cholera toxin, an activator of adenylate cyclase. They are diminished, but not abolished, by high concentrations of dexamethasone. Both cholera toxin alone and phorbol myristate acetate (PMA), an activator of protein kinase C, elicit small and inconsistent mitogenic responses. The responses to PMA cannot be shown to be additive with the effects of NGF. NGF is a known mitogen and neuritogen for chromaffin cells from neonatal rats, but has not previously been believed to affect similarly chromaffin cells from adults. The present findings suggest that portions of NGF signaling pathways might continue to be involved in regulating proliferation of adult rat chromaffin cells in vivo, and might be constitutively activated in PC12 cells and other adrenal medullary tumors. They further suggest that rat chromaffin cells might be propagated in vitro to obtain large numbers of sympathetic neurons expressing normal or exogenous genes.
Contrasting immunohistochemical localizations in rat brain of two novel K+ channels of the Shab subfamily
Authors: Hwang PM , Fotuhi M , Bredt DS , Cunningham AM , Snyder SH
Published: March 2018

We have localized CDRK and DRK1, two novel K+ channels of the Shab subfamily by immunohistochemistry. The two channels are closely related in structure with about 90% amino acid identity in the N-terminal and middle portions and 60% identity in the C-terminal region. We observe striking differences in cellular localizations of the two channels. DRK1 tends to localize to cell bodies and proximal dendrites discretely, while CDRK is diffusely present in cell bodies and is also found on fibers in specific brain areas. In the cerebral cortex DRK1 is localized to pyramidal cells, whereas CDRK occurs in small cells, presumably interneurons. These localizations may reflect specialized delayed rectifier functions and targeting properties manifested differentially by K+ channel subfamily members.
Developmental regulation of segment-specific cholinergic receptors on Retzius neurons in the medicinal leech
Authors: Kristan WB , French KA , Szczupak L
Published: March 2018

Retzius (Rz) neurons in the midbody ganglia of medicinal leeches responded to ACh, applied to their somata, in a manner that depended upon the neuron's segmental location: Rz neurons in ganglia from midbody segments 5 and 6 [Rz(5,6)] hyperpolarized, whereas Rz neurons from all other segments [Rz(X)] depolarized. Midbody segments 5 and 6 are notable because they contain the male and female reproductive organs. Both types of Rz neurons responded to ACh in a complex way, but the initial phase of each response appeared to be nicotinic because nicotinic agonists evoked the responses and nicotinic antagonists blocked them. The reversal potentials of the responses and the effects of changing the internal and external Cl- concentration indicated that the hyperpolarizing response of Rz(5,6) neurons depended upon Cl- whereas the depolarizing response of Rz(X) neurons did not. The segmentally characteristic responses of Rz neurons arose during embryonic development. Removing the reproductive ducts [the peripheral targets of Rz(5,6)] early in embryogenesis caused the Rz(5,6) neurons to depolarize in response to ACh rather than to hyperpolarize. This result indicates that development of the characteristic response of Rz neurons to ACh is strongly influenced by interactions between the neurons and their appropriate target tissues.
Neurofibromin is enriched in the endoplasmic reticulum of CNS neurons
Authors: Nordlund M , Gu X , Shipley MT , Ratner N
Published: March 2018

NF1 patients display CNS abnormalities including learning disabilities, clumsiness, astrocytomas, and abnormalities on magnetic resonance imaging exams. To determine whether the cellular and neuroanatomical distribution of neurofibromin reveals possible function for neurofibromin in the brain, we stained rat brain tissue sections with anti-neurofibromin antibodies. Neurofibromin is highly enriched in large projection neurons, such as cortical and hippocampal pyramidal cells and cerebellar Purkinje cells. Neurofibromin is present in cell bodies and in axons, but is highly enriched in dendrites. Immunoelectron microscopic analysis demonstrates that NF1 is associated with smooth vesiculotubular elements and cisternal stacks and with multivesicular bodies in the cell body and dendrites, but not with the plasma membrane, nucleus, nuclear envelope, Golgi apparatus, mitochondria, or rough endoplasmic reticulum. The preferential localization of neurofibromin to the smooth endoplasmic reticulum, together with evidence that neurofibromin modulates ras GTPase activity, suggests that some, if not all, of the CNS manifestations of NF1 might result from the altered expression of neurofibromin in neurons, perhaps through disruption of Ca2+ signaling, translocation of organelles, or endocytic pathways.
Thalamocortical response transformations in simulated whisker barrels
Authors: Kyriazi HT , Simons DJ
Published: March 2018

Layer IV of rodent somatosensory cortex contains identifiable networks of neurons, called “barrels,” that are related one-to-one to individual whiskers on the face. A previous study (Simons and Carvell, 1989) described differences between the response properties of thalamic and cortical vibrissa neurons and proposed that these transformations can be explained by several features of barrel anatomy and physiology: nonlinear neuronal properties, strongly responsive inhibitory and less responsive excitatory neurons, convergent thalamic inputs to cells of both types, and interconnections among barrel neurons. In the present study these features were incorporated into a computational model in order to test their explanatory power quantitatively. The relative numbers of excitatory and inhibitory cells and the relative numbers of synapses of thalamic and intrabarrel origin were chosen to be consistent with available light and electron microscopic data. Known functional differences between excitatory and inhibitory barrel neurons were simulated through differences in spike activation functions, refractory periods, postsynaptic potential decay rates, and synaptic strengths. The model network was activated by spike trains recorded previously from thalamic neurons in response to three different whisker deflection protocols, and output, which consisted of spikes generated by the simulated neurons, was compared to data from our previous neurophysiological experiments. For each type of whisker stimulus, the same set of parameter values yielded accurate simulations of the cortical response. Realistic output was obtained under conditions where each barrel cell integrated excitatory and inhibitory synaptic inputs from a number of thalamic and other barrel neurons and where the ratios between network excitation, network inhibition, and thalamic excitation were approximately constant. Several quantities are defined that may be generally useful in characterizing neuronal networks. One important implication of the results is that thalamic relay neurons not only provide essential drive to the cortex but could, by changing their tonic activities, also directly regulate the tonic inhibition present in the cortex and thereby modulate cortical receptive field properties.
Activation of metabotropic glutamate receptors produces reciprocal regulation of ionotropic glutamate and GABA responses in the nucleus of the tractus solitarius of the rat
Authors: Glaum SR , Miller RJ
Published: March 2018

Whole-cell voltage-clamp recordings were made in thin transverse slices from neurons of the dorsomedial subdivision of the nucleus of the tractus solitarius (NTS) of the rat. Cells were exposed to either the ionotropic glutamate receptor agonist (R, S)-alpha-amino-3-hydroxy-5- methylisoxazole-4-propionate (AMPA) or the GABAA receptor agonist muscimol via pressure ejection directed at the cell soma. The metabotropic glutamate receptor agonist 1S,3R-1-aminocyclopentane-1,3- dicarboxylate (1S,3R-ACPD; 2–100 microM) reversibly depressed muscimol- evoked currents. Conversely, 1S,3R-ACPD reversibly potentiated AMPA- evoked currents. High-frequency stimulation of the tractus solitarius in the presence of 6,7-dinitroquinoxaline-2,3-dione and D-2-amino-5- phosphonopentanoic acid also produced a reversible depression of muscimol-evoked currents that was occluded in the presence of 100 microM 1S,3R-ACPD. 8-Br-cGMP or brain-derived natriuretic peptide mimicked the effects of 1S,3R-ACPD on AMPA and muscimol currents. However, agents that mimicked the actions of cAMP or diacylglycerol did not. These findings indicate that metabotropic glutamate receptors may mediate multiple components of excitatory transmission in the NTS including modulation of glutamate and GABA-activated ion channels.
Phenotypic plasticity in adult sympathetic ganglia in vivo: effects of deafferentation and axotomy on the expression of vasoactive intestinal peptide
Authors: Hyatt-Sachs H , Schreiber RC , Bennett TA , Zigmond RE
Published: March 2018

The expression of neurotransmitters/neuromodulators in sympathetic neurons is regulated by anterograde and retrograde mechanisms. We have examined the role of such mechanisms in the regulation of the neuropeptide vasoactive intestinal peptide (VIP). The adult rat superior cervical ganglion (SCG) contains low levels of peptide-like immunoreactivity (IR) and mRNA for VIP. Some VIP-IR nerve processes, but only a few VIP-IR cell bodies, are detectable. Previous evidence demonstrates, however, that after the SCG is placed in organ culture for 48 hr, the level of VIP-IR and VIP mRNA and the number of VIP-IR cell bodies and fibers increase considerably. Two of the possible causes for these changes in peptide expression in sympathetic neurons are deafferentation and axotomy, both of which occur when the SCG is placed in culture. To determine the importance of deafferentation, the preganglionic cervical sympathetic trunk was cut and the ganglion left in situ. Forty-eight hours later, VIP-IR increased twofold. A corresponding increase in the number of VIP-IR nerve processes was seen, but there was no detectable change in the number of VIP-IR cell bodies. The content of VIP/PHI mRNA also increased by 1.8-fold. The effect of axotomy on VIP-IR was examined by cutting the postganglionic internal and external carotid nerves and leaving the ganglion in situ. Forty-eight hours later, the level of VIP-IR increased 22-fold, many immunostained neurons were found, and the content of VIP mRNA increased over fivefold. After either deafferentation or axotomy, changes in VIP- IR were accompanied by comparable changes in the related molecule peptide histidine isoleucine amide (PHI)-IR. Neuropeptide Y-IR, on the other hand, decreased after deafferentation and increased only twofold after axotomy. The results indicate plasticity in the expression of VIP- and PHI-IR in adult sympathetic neurons in vivo, and suggest that the changes previously seen in organ culture were primarily a response to axotomy.
Direct evidence for loss and replacement of projection neurons in adult canary brain
Authors: Kirn JR , Nottebohm F
Published: March 2018

Normally occurring projection neuron loss and replacement were quantified over a 6 month period in the pathway from the high vocal center (HVC) to the robust nucleus of the archistriatum (RA) in adult male canaries. Fluorescent latex microspheres were injected into RA in April--a procedure resulting in long-term retrograde labeling of RA- projecting HVC neurons. Labeled cell densities were then obtained 4 and 20 d later in April and 195 d later in October. We found that 41–49% of the RA-projecting HVC neurons present the previous April were no longer present in October. Fluorogold injections in RA 3 d prior to death in April and October retrogradely labeled similar overall densities of RA- projecting HVC neurons, indicating that cells lost over this 6 month period were replaced by new RA-projecting HVC neurons. Newer cells were larger than older cells, suggesting that an age-dependent reduction in size might precede death. Over the same time interval, no loss was observed for neurons projecting from the lateral magnocellular nucleus of the anterior neostriatum to RA. Thus, loss was specific to the input from HVC to RA. These findings raise the possibility that much if not all of the pathway from HVC to RA is replaced within a year. The time period examined encompasses the yearly transition from stable song to song learning in the canary (Nottebohm et al., 1986, 1987). A pronounced loss and replacement of neurons implicated in vocal control during this period may relate to the canary's ability to modify song in adulthood.
Expression of glutamate receptor genes in white matter: developing and adult rat optic nerve
Authors: Jensen AM , Chiu SY
Published: March 2018

We have identified the glutamate receptor genes expressed by developing and adult rat optic nerve. Results from PCR suggested that of the ionotropic glutamate receptor (GluR) gene family, only GluR1 and GluR3 subunits are expressed by optic nerve. However, Northern blot analysis demonstrated that only the GluR1 subtype is expressed at appreciable levels. In situ hybridization histochemistry of GluR1 was performed and a diffuse pattern of expression was observed in both postnatal day 15 and adult optic nerve. Restriction mapping of the GluR1 PCR product indicated the expression of the flip alternative splice version in optic nerve. The detected GluR1 message was not due to axons because no loss of expression was observed after the degeneration of axons. PCR analysis also revealed the presence of a metabotropic glutamate receptor in optic nerve.
Neurodegeneration induced by beta-amyloid peptides in vitro: the role of peptide assembly state
Authors: Pike CJ , Burdick D , Walencewicz AJ , Glabe CG , Cotman CW
Published: March 2018

The progressive neurodegeneration of Alzheimer's disease has been hypothesized to be mediated, at least in part, by beta-amyloid protein. A relationship between the aggregation state of beta-amyloid protein and its ability to promote degeneration in vitro has been previously suggested. To evaluate this hypothesis and to define a structure- activity relationship for beta-amyloid, aggregation properties of an overlapping series of synthetic beta-amyloid peptides (beta APs) were investigated and compared with beta AP neurotoxic properties in vitro. Using light microscopy, electrophoresis, and ultracentrifugation assays, we found that few beta APs assembled into aggregates immediately after solubilization, but that over time peptides containing the highly hydrophobic beta 29–35 region formed stable aggregations. In short-term neuronal cultures, toxicity was associated specifically with those beta APs that also exhibited significant aggregation. Further, upon the partial reversal of beta 1–42 aggregation, a concomitant loss of toxicity was observed. A synthetic peptide derived from a different amyloidogenic protein, islet amyloid polypeptide, exhibited aggregation but not toxicity, suggesting that beta AP-induced neurotoxicity in vitro is not a nonspecific reaction to aggregated protein. The correlation between beta AP aggregation and neurotoxicity was also observed in long-term neuronal cultures but not in astrocyte cultures. These data are consistent with the hypothesis that beta-amyloid protein contributes to neurodegeneration in Alzheimer's disease.
Bag cell extract inhibits tail-siphon withdrawal reflex, suppresses long-term but not short-term sensitization, and attenuates sensory-to- motor neuron synapses in Aplysia
Authors: Goldsmith JR , Byrne JH
Published: March 2018

The peptides released from the bag cells (bag cell peptides, BCPs) in Aplysia californica are responsible for eliciting or modulating a repertoire of behaviors preceding and accompanying egg laying. Our interest was in determining to what extent behaviors that can occur simultaneously with egg laying are modulated. To address this issue, we examined the effects of an extract (bag cell extract, BCE) that contained BCPs, as well as egg-laying hormone (ELH), an identified BCP, on both the tail-siphon withdrawal reflex and the ability of that reflex to exhibit sensitization, a simple form of nonassociative learning. In addition, we examined the ability of BCE, as well as the individual BCPs, to modulate a component of the circuitry of the reflex. Behavioral experiments indicated that BCE inhibited the baseline withdrawal reflex and suppressed long-term sensitization of the reflex while leaving short-term sensitization unaffected. These effects were not observed in animals receiving an extract of a control ganglion or in animals receiving ELH, and therefore may be attributed to the actions of one or more BCPs, but presumably not to ELH alone. Electrophysiological experiments revealed that BCE also attenuated the monosynaptic EPSP elicited in tail motor neurons by tail sensory neurons. In subsequent experiments in which the BCPs were individually applied, only one BCP, beta-BCP, significantly attenuated the EPSPs. This effect was independent of narrowing of the presynaptic action potential. Taken together, these results suggest a novel behavioral modification attributed to BCPs, inhibition of the tail-siphon withdrawal reflex, and suggest a possible locus of action and peptide candidate for this effect. In addition, these experiments raise the possibility that BCPs may exert a long-lasting effect (> 24 hr), selectively blocking a simple form of long-term memory.
Casein kinase II phosphorylates the synaptic vesicle protein p65
Authors: Bennett MK , Miller KG , Scheller RH
Published: March 2018

p65 (synaptotagmin), an abundant synaptic vesicle protein, has been implicated in the processes of vesicle docking and fusion. To characterize further the properties of this important neuronal protein, we have investigated its phosphorylation in vitro. Immunoprecipitation of p65 results in coprecipitation of a protein kinase that phosphorylates p65 as well as syntaxin, a plasma membrane protein that interacts with p65. p65 is phosphorylated on a threonine residue (Thr- 128) within the cytoplasmic domain near the transmembrane region. The coprecipitating protein kinase was identified as casein kinase II based on its catalytic properties, the sequence surrounding Thr-128, and Western blot analysis of the anti-p65 immunoprecipitates. Affinity chromatography utilizing bacterially expressed fragments of p65 demonstrated that casein kinase II interacts with a domain of p65 distinct from the phosphorylation site. In a synaptic vesicle fraction, the phosphorylation of p65 is stimulated by sphingosine and by detergent solubilization, suggesting that p65 phosphorylation may be subject to regulatory processes.
Microstimulation in visual area MT: effects of varying pulse amplitude and frequency
Authors: Murasugi CM , Salzman CD , Newsome WT
Published: March 2018

We have previously shown that perceptual judgements of motion direction are based in part on the activity of direction selective neurons in extrastriate visual area MT (Salzman et al., 1990, 1992). In those experiments, we applied low-amplitude microstimulation pulses (10 microA, 200 Hz) to clusters of MT neurons whose preferred directions were similar. The effect of microstimulation was to bias the monkeys' choices on a direction discrimination task toward the preferred direction of neurons at the stimulation site. The results suggest that microstimulation generated a directionally specific cortical signal by activating selectively neurons near the electrode tip. To test this notion more directly, we have now examined the behavioral effects of varying current amplitude, current frequency, and electrode position. In the majority of experiments, the directional bias in the monkeys' choices was reduced or eliminated as current amplitude increased to 80 microA. In addition, 80 microA stimulating pulses frequently impaired overall performance as measured by the percentage of correct responses. This decrement in performance indicated that 80 microA pulses introduced “noise” into the neural circuitry encoding motion direction, presumably by increasing current spread to activate a larger population of neurons representing all directions of motion. In contrast, increasing current frequency to 500 Hz (10 microA pulses) preserved the directional specificity of microstimulation effects. The precise position of the stimulating electrode also influenced the magnitude of microstimulation effects; in some cases, differences in position on the order of 100 microns determined whether an experiment yielded a very large effect or no effect at all. Thus, directionally specific activation of cortical circuitry within MT can be disrupted by increases in current spread or by small changes in electrode position. These observations suggest that the effects of low-amplitude microstimulation depend upon direct activation of a well-localized population of neurons.
Neurons, astrocytes, and oligodendrocytes of the rat cerebral cortex originate from separate progenitor cells: an ultrastructural analysis of clonally related cells
Authors: Luskin MB , Parnavelas JG , Barfield JA
Published: March 2018

The diverse array of neurons and glia in the mammalian cerebral cortex arises from proliferating cells of the ventricular zone that surrounds the lateral ventricles of the developing brain. A fundamental but unresolved question is whether the individual cells of the ventricular zone are committed to producing progeny of only one particular phenotype or whether they generate progeny of more than one phenotype. We have begun to address this question by asking if individual cells of the ventricular zone generate exclusively neurons or glia at the onset of cortical neurogenesis in the rat. To assess the phenotypes of cells derived from a common progenitor cell, retroviral-mediated gene transfer was used to introduce the reporter gene, Escherichia coli beta- galactosidase, into ventricular zone cells at embryonic day 15 or 16. We used histochemistry to reveal beta-galactosidase-expressing cells in the mature rat cerebral cortex. Isolated clusters of beta-galactosidase- expressing cells, presumably clones, were identified in serial sections. Since the histochemical reaction product is electron dense, each cell could be examined at the ultrastructural level and assigned definitively to one of the major classes of cells in the cerebral cortex on the basis of well-established morphological criteria. This approach overcomes the problems of cell type identification encountered with light microscopy, where it is not always possible to distinguish between different cell phenotypes. We found that virtually all clones contained cells of exclusively one type: either all astrocytes, all oligodendrocytes, or all neurons. Furthermore, each particular cell type exhibited a different pattern and intensity of staining. The neuronal clones, with one exception, were composed of either all pyramidal cells (projection neurons), or all nonpyramidal cells (interneurons). The size and composition of neuronal clones did not seem related to their position in the cerebral cortex. Collectively, our observations indicate that separate progenitor cells exist for pyramidal neurons, nonpyramidal neurons, astrocytes, and oligodendrocytes. The striking phenotypic homogeneity in the clones arising from individual progenitor cells suggests that by the onset of cortical neurogenesis, at least some lineage restrictions have already occurred among the precursor cell population. Thus, our results suggest that lineage may play a pivotal role in determining some of the functionally important phenotypic attributes of cells in the cerebral cortex.
Extended temporal gradient for the retrograde and anterograde amnesia produced by ibotenate entorhinal cortex lesions in mice
Authors: Cho YH , Beracochea D , Jaffard R
Published: March 2018

Effects of ibotenic entorhinal cortex (EC) lesions on both retrograde and anterograde amnesia in mice were assessed using two-choice discrimination tasks learned at different intervals before surgery in two eight-arm radial mazes. The results indicated that EC-lesioned mice were severely impaired in postoperative retention of discrimination problems learned 3 d or 2 weeks prior to surgery, but showed no deficit on problems learned between 4, and up to 6 weeks before surgery, as compared to sham-operated controls. When trained on a novel two-choice discrimination problem (not acquired preoperatively), experimental subjects demonstrated quite normal rates of acquisition, but were impaired in learning its reversal. Furthermore, they exhibited a faster rate of forgetting (anterograde amnesia) relative to controls over a 2- week retention interval. These results indicate that approximately 4 weeks is required before memory for a two-choice spatial discrimination problem no longer depends on the integrity of the entorhinal cortex, and suggests that, beyond this time, an EC-independent memory storage system is capable of supporting the retrieval of information. The data, together with complementary behavioral results, are discussed in the context of current theories of memory storage.
Electrical resonance of isolated hair cells does not account for acoustic tuning in the free-standing region of the alligator lizard's cochlea
Authors: Eatock RA , Saeki M , Hutzler MJ
Published: March 2018

The cochlea of the alligator lizard is divided into two morphologically and physiologically distinct regions. In the “tectorial region,” hair bundles of hair cells are draped by a tectorial membrane, whereas in the “free-standing region,” hair bundles are said to be free-standing because there are no overlying tectorial structures. The acoustic tuning of the free-standing region depends at least in part on mechanical resonances of the hair bundles. In the turtle cochlea, in contrast, acoustic tuning depends in large part upon the electrical properties of the hair cells. We have investigated the electrical properties of hair cells isolated from the free-standing region of the alligator lizard's cochlea. When injected with steps of depolarizing current, these “free-standing hair cells” exhibited electrical resonances that were comparable in frequency and quality to electrical resonances in cochlear hair cells from turtles, chicks, and alligators, and in saccular hair cells from frogs and fish. In the lizard's free- standing hair cells, however, the electrical resonance frequencies (< 300 Hz) were a decade below the cells' acoustic characteristic frequencies (between 1 and 4 kHz), showing that the electrical resonance is not likely to contribute to acoustic tuning. The electrical resonances were not apparent at rest. The cells' resting potentials were significantly more negative than the activation voltage (approximately -40 mV) of the Ca(2+)-dependent K+ current upon which the electrical resonance has been shown to depend in other hair cells. At potentials more negative than -50 mV, an inwardly rectifying K+ conductance dominated. Because we observed no electrical tuning above 300 Hz, our results indirectly support a mechanical origin for acoustic tuning in the free-standing region of the alligator lizard cochlea. These results further show that acoustic tuning cannot be inferred solely from the electrical resonances of isolated hair cells.
Mitochondrial and nuclear gene expression for cytochrome oxidase subunits are disproportionately regulated by functional activity in neurons
Authors: Hevner RF , Wong-Riley MT
Published: March 2018

Mitochondrial respiratory complexes such as cytochrome oxidase (CO) contain both mitochondrial- and nuclear-encoded subunits. To determine whether mitochondrial and nuclear gene expression are regulated proportionately in neurons, we analyzed CO subunit mRNA and mitochondrial DNA (mtDNA) levels by in situ hybridization and grain counting in the visual system of normal and monocular TTX-treated monkeys. We compared the regulation of these molecules with the regulation of CO activity and CO protein, analyzed by histochemistry and immunohistochemistry, respectively. In normal animals, CO activity was in general related more closely to mtDNA and CO subunit I (COI) (mitochondrial-encoded) mRNA levels than to COIV or COVIII (nuclear- encoded) mRNA levels. For example, puffs (also known as blobs) of high CO activity in striate cortex were enriched in mtDNA and COI mRNA, but not COIV or COVIII mRNA. In 3–7 d TTX-treated animals, proportionate decreases in CO activity and CO protein were observed in specific visual centers; these changes were accompanied by disproportionate decreases in COI, COIV, and COVIII mRNA levels. After 7 d of TTX, COI mRNA fell by 49 +/- 3% (mean +/- SEM) in LGN neurons, while COIV and COVIII mRNAs fell by only 18 +/- 3% and 29 +/- 3%, respectively. In comparison, CO activity decreased by 23 +/- 2%, and mtDNA by 26 +/- 4%. Qualitative observations in striate cortex also indicated that COI mRNA changed more than COIV mRNA, COVIII mRNA, mtDNA, or CO activity. Our results suggest that the local distribution of CO within neurons, and acute regulatory changes in CO activity occurring over periods of days are controlled mainly by regulation of the mitochondrial genes that encode the catalytic subunits of the enzyme.
Stress-induced inhibition of protein synthesis initiation: modulation of initiation factor 2 and guanine nucleotide exchange factor activities following transient cerebral ischemia in the rat
Authors: Hu BR , Wieloch T
Published: March 2018

Neuronal protein synthesis is severely depressed following stress such as heat-shock, hypoxia, and hypoglycemia. Following reversible cerebral ischemia, protein synthesis is transiently inhibited in ischemia- resistant areas, but persistently depressed in vulnerable brain regions. Eukaryotic initiation factor 2 (eIF-2) activity, that is, the formation of the ternary complex eIF-2.GTP.initiator 35S-Met-tRNA, a rate-limiting step in the initiation of cellular protein synthesis, was studied in the rat brain during and following 15 min of transient global cerebral ischemia. At 30 min and 1 hr of reperfusion, a general decrease of eIF-2 activity by approximately 50% was seen in the postmitochondrial supernatant (PMS). In the relatively resistant neocortex and CA3 region of the hippocampus, the eIF-2 activity returns to control levels at 6 hr of reperfusion, but remains depressed in the vulnerable striatum and the CA1 region. Similarly, the activity of the guanine nucleotide exchange factor (GEF), which catalyzes the exchange of GTP for GDP bound to eIF-2, a crucial step for the continued formation of the ternary complex, is transiently reduced in neocortex but persistently depressed in striatum. The postischemic decrease in eIF-2 activity is further attenuated by agarose-bound alkaline phosphatase, and mixing experiments revealed that a vanadate-sensitive phosphatase may be responsible for the depression. Addition of partially purified GEF to PMS from postischemic neocortex restored eIF- 2 activity to control levels. We conclude that ischemia alters the balance between phosphorylation and dephosphorylation reactions, leading to an inhibition of GEF and a depression of ternary complex formation.(ABSTRACT TRUNCATED AT 250 WORDS)
The contributions of protein kinase A and protein kinase C to the actions of 5-HT on the L-type Ca2+ current of the sensory neurons in Aplysia
Authors: Braha O , Edmonds B , Sacktor T , Kandel ER , Klein M
Published: March 2018

In the sensory neurons of Aplysia, 5-HT acts through cAMP to reduce current flow through two classes of K+ channels, the S-K + channel and a transient K+ channel (Ikv). In addition, 5-HT increases a voltage- dependent, nifedipine-sensitive Ca2+ current. In this article we show that, while the effect on the S-K+ channel is mediated exclusively by cAMP, the effect on the Ca2+ current can be mimicked by phorbol 12,13- dibutyrate (PDBu) as well as by intracellular injection of cAMP. We then use specific blockers of protein kinase C (PKC) and the cAMP- dependent protein kinase A (PKA) to examine the roles of PKC and PKA in mediating the effect of 5-HT on the nifedipine-sensitive Ca2+ current. We find that H-7, a kinase inhibitor that appears to inhibit PKC more effectively than PKA in intact Aplysia neurons, reverses the increase in the Ca2+ current produced by PDBu. Moreover, H-7 partially blocks the effect of 5-HT on the Ca2+ current without affecting the decrease in the S-K+ current. A more specific PKC inhibitor (the 19–31 pseudosubstrate of PKC) also partially blocks the increase in the Ca2+ current produced by 5-HT, suggesting that this increase is mediated by PKC. Rp-cAMPS, a specific blocker of PKA, did not block the increase in the Ca2+ current produced by 5-HT, suggesting that the effect of 5-HT on this current may be mediated to only a small extent by PKA. The effect of 5-HT on the S-K+ current and the Ca2+ current can also be separated on basis of the time course of their appearance. The fact that the decrease in the S-K+ current precedes the increase in Ca2+ current suggests that there may be a temporal difference in the activation of the two kinase systems.
A higher control center of locomotor behavior in the Drosophila brain
Authors: Strauss R , Heisenberg M
Published: March 2018

In order to elucidate the behavioral significance of the central complex (CC), we have examined walking in 15 Drosophila mutant strains belonging to eight independent X-linked genes that affect the structure of the CC. Compared to four different wild-type strains, all are impaired either in a general or in a paradigm-dependent manner. Behavioral deficits concern walking activity, walking speed, or “straightness of walking” as measured in an object fixation task, in fast phototaxis, and in negative geotaxis. Behavioral deficits of three strains with mutations in different genes were studied in detail using mosaic analysis and high-speed cinematography. In all cases the focus for declining walking activity is located in the brain and is fully correlated with the respective defect of the CC. A high correlation between the degree of the behavioral impairment and the severity of the structural defect in two strains further adds to the evidence. Declining walking activity is not an unspecific side effect of structural brain defects, as steady walking is observed in structural mutants of the visual system and mushroom bodies. In mutant flies no- bridgeKS49 (nob), step size as a function of the stepping period is reduced. The focus of the resulting reduced average and maximum walking speeds resides in the brain and, again, the behavioral impairment fully correlates with the structural defects of the CC. While no indication is found for a role of the CC in setting up the basic stepping rhythm in straight walking (a respective phenotype in mutant central- complexKS181 flies resides in the ventral ganglion), a role in turning and start/stop maneuvers is suggested by aberrations in the stepping pattern of nob flies during such episodes.
The jamming avoidance response in Eigenmannia is controlled by two separate motor pathways
Authors: Metzner W
Published: March 2018

The gymnotiform fish Eigenmannia generates weakly electric signals for electrolocation and communication. The signals are produced by electric organ discharges (EODs) that are driven by a medullary pacemaker nucleus. To avoid jamming by neighboring conspecifics with similar frequencies, a fish raises its own EOD frequency if the neighbor's frequency is lower, and it lowers its EOD frequency if the neighbor's frequency is higher (Watanabe and Takeda, 1963). Both the raising and lowering of EOD frequency of this jamming avoidance response (JAR; Bullock et al., 1972) are thought to be controlled by feature- extracting neurons in the diencephalic prepacemaker nucleus (PPn-G) that discriminate the sign of the frequency difference between the jamming signal and the fish's EOD (Kawasaki et al., 1988a; Rose et al., 1988; for review, see Heiligenberg, 1991). These prepacemaker neurons are excited in response to lower jamming frequencies, thereby raising the frequency, and inhibited by higher jamming frequencies, producing a discharge deceleration. The results of experiments presented here, however, suggest a mechanism for the motor control of the JAR that is different from the one described previously (see, e.g., Heiligenberg, 1991). Two prepacemaker nuclei, one PPn-G and one sublemniscal prepacemaker nucleus (SPPn) (Keller et al., 1991 a,b), which provide the only known inputs to the pacemaker, were lesioned selectively. This article explores the effects of these lesions on the JAR. Pharmacological experiments were used to elucidate the transmitter types involved. The results suggest that the JAR is controlled by two separate motor pathways. One controls frequency rises and originates in the dorsal substructure of the nucleus electrosensorius (Keller, 1988). It sends excitatory connections to the diencephalic prepacemaker and finally to the pacemaker nucleus, where AMPA-type receptors mediate the synaptic transmission. The second pathway controls frequency decreases and originates in the ventral substructure of the nucleus electrosensorius. It provides GABAergic input to the SPPn. The SPPn is tonically active and also controls the EOD frequency even in the absence of jamming signals. Its projection to the pacemaker nucleus is mediated by NMDA-type receptors. The results of this study suggest that there is no single population of final, feature-extracting elements or “recognition units” that controls JAR-related shifts of the pacemaker frequency. Instead, the motor control of the JAR consists of an interaction of two independent pathways according to a “push-pull” principle.
Gangliosides rescue neuronal cells from death after trophic factor deprivation
Authors: Ferrari G , Batistatou A , Greene LA
Published: March 2018

Serum-free cultures of PC 12 cells have been used as a model system for studying neuronal death occurring after neurotrophic factor deprivation. In this system, NGF rescues cells from death and prevents apoptotic DNA fragmentation. We report here that GM1 also promotes long- term survival of naive and NGF-pretreated PC 12 cells in serum-free medium and prevents internucleosomal cleavage of PC 12 cell DNA. In contrast to NGF, GM1 does not promote neurite outgrowth or somatic hypertrophy. The survival effects of GM1 are concentration dependent, with maximal activity at 30–50 microM. Optimal promotion of survival is obtained with multiple additions of GM1. Asialo-GM1 and sialic acid do not mimic these actions, indicating a requirement for the intact GM1 molecule. Prevention of serum-free PC 12 cell death is also obtained with di-, tri-, and tetrasialogangliosides. The ganglioside effects on survival and DNA fragmentation appear to be independent of macromolecular synthesis. GM1 is also effective under conditions in which cellular protein kinase C activity is downregulated by preexposure to high concentration of 12-O-tetradecanoylphorbol-13- acetate. Furthermore, GM1 promotes long-term survival of cultured rat sympathetic neurons after withdrawal of NGF. These findings complement prior observations that gangliosides protect cerebellar granule neurons from neurotoxicity caused by exposure to excitatory amino acids and extend the actions of gangliosides to rescue of neuronal cells deprived of neurotrophic factor support.
Expression of glutamate receptor genes in the mammalian retina: the localization of GluR1 through GluR7 mRNAs
Authors: Hamassaki-Britto DE , Hermans-Borgmeyer I , Heinemann S , Hughes TE
Published: March 2018

Seven distinct cDNAs encoding functional subunits of the AMPA/kainate- type glutamate receptors have been recently cloned. This in situ hybridization study was done to determine which subunits are expressed in the retina and, where possible, which neurons express them. Hybridization of 35S-UTP-labeled cRNA probes with transverse sections revealed that mRNAs for all seven receptor subunits (GluR1-GluR7) are expressed in both cat and rat retinas. GluR1 and GluR2 produced labeling over the entire inner nuclear layer (INL) and ganglion cell layer (GCL). GluR3-GluR7 have more limited distributions, indicative of expression by only a subset of neurons. All of the subunits are expressed by the cells at the inner edge of the INL, where amacrine cells reside, yet the layers with the horizontal, bipolar, and ganglion cells contain different subsets of subunits. These findings suggest that these glutamate receptor subunits are employed at many of the retinal synapses, including the photoreceptor input to the outer plexiform layer and the bipolar cell's contacts with the processes at the INL. It is also possible that some glial cells in the INL express some of the subunits. Since different combinations of GluR1-GluR3 have been shown to play an important role in the calcium permeability in response to glutamate, we investigated whether single cells coexpressed those subunits. By hybridizing adjacent semithin (1 micron) sections of the cat retina with probes for GluR1-GluR3, it was possible to observe coexpression of all three subunits, or of pairs of these subunits, in cells within the INL and GCL.