bluuebunny/crossref_metadata_2025 huggingface dataset:
B-50/GAP43 is localized at the cytoplasmic side of the plasma membrane in developing and adult rat pyramidal tract
Authors: Gorgels TG , Van Lookeren Campagne M , Oestreicher AB , Gribnau AA , Gispen WH
Published: March 2018

The neuron-specific phosphoprotein B-50/GAP43 has been implicated in axonal outgrowth, since high levels of B-50/GAP43 are found in growth cones and during development of the nervous system. In adult brain, the B-50 levels are decreased. B-50 is primarily found in axons and presynaptic terminals. It is phosphorylated by protein kinase C, and this process has been implicated in the modulation of membrane signal transduction. During the outgrowth of the pyramidal tract, high levels of B-50 have been reported, whereas a low amount of B-50 persists into the adult stage. By immunoelectron microscopy, using immunogold labeling on cryosections and pre-embedding peroxidase labeling, we examined the distribution of B-50 in the pyramidal tract at the third cervical segment in developing 2-d-old and adult 90-d-old rats. B-50 immunoreactivity was found in axons and growth cones of the outgrowing tract. In the adult pyramidal tract, both unmyelinated and myelinated axons contained B-50 immunoreactivity. The immunogold label was predominantly located at the plasma membrane. Since the peroxidase reaction product was observed exclusively intracellularly, we conclude that the B-50 immunoreactivity is predominantly located at the cytoplasmic side of the plasma membrane of axons and growth cones. The high immunoreactivity in growth cones and axons of the outgrowing pyramidal tract further supports the hypothesis that B-50 plays a role in neurite outgrowth. The presence of B-50 in the adult pyramidal tract cannot merely be attributed to transport to the synapse. Therefore, it is suggested that B-50 plays, in addition, a local, growth-associated role in the adult tract.
Gamma-interferon-like immunoreactivity in axotomized rat motor neurons
Authors: Olsson T , Kristensson K , Ljungdahl A , Maehlen J , Holmdahl R , Klareskog L
Published: March 2018

Major histocompatibility complex (MHC) encoded antigens, absent or present at only low levels in normal brain tissue, are induced locally around axotomized motor neurons. We here report that immunoreactivity for the potent MHC-inducing factor, gamma-interferon (IFN-gamma), appears in the cytoplasm of such neurons. Rat facial nerves were interrupted (crushed or cut), and later, at various intervals, cryosections from the facial nuclei were subjected to immunohistochemistry with monoclonal antibodies reacting with IFN-gamma and MHC antigens. IFN-gamma-like immunoreactivity appeared briskly in the cytoplasm of the axotomized motor neurons. The immunoreactivity subsided after a nerve crush as the target muscles were reinnervated, but persisted when nerve regeneration was prevented after a nerve cut. These results point to a role for nerve cell-derived IFN-gamma-like molecules in eliciting the neural cell responses to axotomy.
Penetrating head injury in young adulthood exacerbates cognitive decline in later years
Authors: Corkin S , Rosen TJ , Sullivan EV , Clegg RA
Published: March 2018

Few investigators have studied whether the behavioral effects of brain insult in adulthood are stable after the period of maximum recovery. We addressed this issue in a 30-year longitudinal study of 84 veterans of World War II, 57 with penetrating head injury (HI) and 27 with peripheral nerve injury (PNI), matched with respect to age, premorbid intelligence, and premorbid education. Each subject was examined during the 1950s and during the 1980s; each examination included the largely verbal Army General Classification Test (AGCT) (with Vocabulary, Arithmetic, and Block Counting subscales) and the Hidden Figures Test (which measures figure-ground discrimination). HI exacerbated decline in performance over time, irrespective of lesion site or cognitive test. HI and PNI subjects differed significantly (p less than 0.05) in AGCT Total and Arithmetic change scores, and means were in the same direction for all other measures. In analyses contrasting subjects in each of the eight lesion groups to PNI subjects, those with left parietal lobe injuries showed significantly greater decline from the 1950s to the 1980s on the Vocabulary and Arithmetic subscales of the AGCT, as did those with left temporal lobe injuries on the Arithmetic subscale, whereas subjects with right parietal lobe injuries showed significantly greater decline on the Hidden Figures Test. We hypothesize that the observed reduction of cognitive capacities late in life was due to some combination of HI in young adulthood, secondary effects of the injury occurring with time, effects of stress on remaining brain tissue caused by functioning for decades in a compromised state, and changes in the brain occurring with age. Although the HI subjects were not demented, follow-up studies must assess whether exacerbated decline is a harbinger of dementia.
Brain cytochrome oxidase: purification, antibody production, and immunohistochemical/histochemical correlations in the CNS
Authors: Hevner RF , Wong-Riley MT
Published: March 2018

Cytochrome oxidase (CO) is a mitochondrial energy-generating enzyme used in brain studies as a marker of neural functional activity. The activity of CO in different brain regions, revealed histochemically, is distributed nonhomogeneously but in distinct patterns. Localized differences in CO activity could arise from localized differences in enzyme amount or from localized regulation of enzyme turnover number (molecular activity). To distinguish between these alternatives, we used antibodies against purified calf brain CO to assess the immunohistochemical distribution of CO amount (protein immunoreactivity) in several brain regions. Calf brain mitochondria (synaptic and nonsynaptic populations) were isolated from gray matter homogenates by differential centrifugation. CO was purified from detergent extracts of the mitochondria by cytochrome c-Sepharose 4B affinity chromatography. Antisera against the purified CO were raised in rabbits. The antibodies reacted specifically with CO, predominantly subunit IV, in SDS immunoblots. The antibodies did not react in SDS immunoblots with any other proteins solubilized from mitochondria or caudate nucleus but did cross-react with brain CO from other mammalian species and with bovine heart CO. The immunohistochemical distribution of CO amount matched the histochemical distribution of CO activity in all regions tested, including the monkey hippocampus and the mouse olfactory bulb, somatosensory (barrel) cortex, and cerebellum. Thus, the amount of CO in neural tissue is distributed in the same nonhomogeneous pattern as the histochemical activity of CO. The results suggest that mechanisms exist by which CO molecules are selectively distributed within neurons to meet local metabolic demands posed by neural functional activity.
Postischemic synaptic physiology in area CA1 of the gerbil hippocampus studied in vitro
Authors: Urban L , Neill KH , Crain BJ , Nadler JV , Somjen GG
Published: March 2018

After transient forebrain ischemia in the Mongolian gerbil, CA1b hippocampal pyramidal cells degenerate during a period of 2–4 d. We tested the hypothesis that this delayed neuronal death is preceded by excessive synaptic excitation. Hippocampal slices were prepared from gerbils that had been subjected to a 5 min occlusion of both common carotid arteries. Input/output curves demonstrated enhancement of the initial slope of the Schaffer collateral-commissural focally recorded EPSP at all stimulus currents between 5 and 10 hr after the ischemic insult. The duration of the focally recorded EPSP also increased. At the same time, the excitability of the CA1b pyramidal cells decreased. Thus, the EPSP brought fewer pyramidal cells to threshold than the same size EPSP in control slices. During the first 14 hr after ischemia, the antidromic population spike remained unaffected. By 24 hr after ischemia, however, the focally recorded EPSP and both orthodromic and antidromic population spikes were markedly depressed, and they declined further over the next 2 d. No recovery was detected. In the same slices, transient ischemia only mildly and reversibly affected the response of dentate granule cells to perforant path stimulation and did not affect their response to antidromic stimulation. Hippocampal slices adjacent to those used for electrophysiological recording were analyzed histologically. Examination of somatic argyrophilia confirmed that CA1b pyramidal cells suffered delayed neuronal death, whereas dentate granule cells remained intact. Pyramidal cell argyrophilia was, however, not detected until 2 d after these neurons had become virtually inexcitable. We conclude that CA1b pyramidal cells begin to lose electrophysiological function well before definite morphological signs of degeneration become visible. The observation of enhanced excitatory transmission 5–10 hr after reperfusion is consistent with the idea that delayed ischemic neuronal death results, at least in part, from excessive excitation.
Regulation of ionic currents in pheochromocytoma cells by nerve growth factor and dexamethasone
Authors: Garber SS , Hoshi T , Aldrich RW
Published: March 2018

Growth factors and hormones induce differentiation of clonal pheochromocytoma (PC12) cells, which are derived from rat adrenal medulla chromaffin cells. On application of nerve growth factor (NGF), PC12 cells extend neurites and express properties characteristic of autonomic ganglion cells. In contrast, incubation of PC12 cells with a corticosteroid, dexamethasone (DEX), does not induce neurite formation but causes an increase in tyrosine hydroxylase activity, suggesting that the cells become chromaffin cell-like. The ability of NGF and DEX to regulate ionic currents has been less well studied. Therefore, we examined how long-term NGF and DEX treatments affected voltage- dependent Na, Ca, and K currents in PC12 cells. Voltage-dependent Na currents were observed only in a small fraction of the PC12 cells in the absence of NGF or DEX. Virtually all NGF-treated cells expressed Na currents within 7 d. DEX increased the number of cells expressing voltage-dependent Na current slowly over 3 weeks, but, unlike NGF, DEX did not change Na current density. Both NGF and DEX also affected the expression of voltage-dependent Ca currents. Most of the untreated cells had only sustained, high-threshold voltage-dependent Ca currents. Chronic application of NGF or DEX increased the fractions of the cells that showed transient, low-threshold T-type Ca currents in addition to the high-threshold currents. The T-type Ca current density, however, increased significantly only in NGF-treated cells. Neither DEX nor NGF affected the voltage-dependent K currents. These results suggest that the expression of voltage-dependent Na and Ca currents are differentially regulated by NGF and DEX. The distinction between treated and untreated cells decreased after 3 weeks in culture as older untreated cells showed increases in the fraction of cells expressing both Na and low-threshold Ca currents. A PC12 subline selected for adherence to uncoated plastic also showed increased fraction of cells expressing these currents, suggesting that interactions with substrate may also influence ionic current expression.
Diversity of the transient outward potassium current in somata of identified molluscan neurons
Authors: Serrano EE , Getting PA
Published: March 2018

We have undertaken a quantitative study of the differences in the properties of the fast transient outward current (A-current) between identified neurons of 2 species of nudibranch mollusc. Somata from identifiable neurons of Archidoris montereyensis and Anisodoris nobilis were isolated and voltage-clamped with a 2-microelectrode voltage clamp at 11 degrees C. We examined diversity in the expression of the time- and voltage-dependent properties of A-current by measuring the following parameters: (1) current magnitude, (2) current density, (3) inactivation kinetics, (4) the voltage dependence of steady-state activation and inactivation. We first characterized A-current in each cell type by measuring these parameters for each identified neuron in a series of animals of a given species. The results of these measurements were used to describe the A-current properties of an identified neuron in terms of a mean and SD. The SD measured diversity within the animal population for any given cell type, while the mean values could be compared to measure diversity in the expression of A-current between identified neurons. When we compared mean values for A-current properties between identified neurons of a given species, we did not detect statistically significant differences in the steady-state voltage dependence of activation and inactivation. However, there were statistically significant differences in peak A-current magnitude, density, and inactivation kinetics between identified neurons. We examined differences between the species by comparing the A-current properties of homologous neurons. The major difference between the species was that outward current magnitude and density were significantly greater in Anisodoris than in Archidoris. We conclude that the magnitude and density of A-current differ between identified nudibranch neurons. The neurons also differentially express A-current inactivation kinetics in a cell-specific manner.
Regenerated retinal ganglion cell axons can form well-differentiated synapses in the superior colliculus of adult hamsters
Authors: Carter DA , Bray GM , Aguayo AJ
Published: March 2018

To investigate in adult animals the distribution and differentiation of the synapses made by axotomized CNS neurons whose regenerating axons are guided back to their natural targets in the brain, we attached an autologous peripheral nerve (PN) graft 2–3 cm in length to the ocular stump of a transected optic nerve (ON) in adult hamsters, inserted the distal end of the graft into the superior colliculus (SC), and, 6–8 weeks later, labeled the retinal ganglion cell (RGC) axons that entered the SC with HRP orthogradely transported from the eye. By light microscopy, regenerated RGC axons extended from the graft into the retinorecipient layers of the SC for up to 500 microns, distances that approximate the lengths of normal RGC arbors. We compared 698 control and 758 regenerated HRP-labeled axon terminals from 4 intact and 4 experimental animals by electron microscopy. The structure of the regenerated RGC terminals, the type of synaptic contacts formed, the ratios of contacts to terminal perimeter, and the domains of the postsynaptic neurons contacted were similar to those of controls. These results indicate that regenerated RGC axons can form well- differentiated synapses in the SC. Morphological differences between the regenerated and control synapses were the larger size of some regenerated terminals, the greater mean length of the regenerated synapses, and the higher proportion of contacts with dendrites that contained vesicles. The synaptic differentiation attained by these reformed retinocollicular projections suggests that regenerating CNS axons and their target neurons in the adult mammalian brain may retain or reexpress certain molecular determinants of normal connectivity.(ABSTRACT TRUNCATED AT 250 WORDS)
Partial injury to central noradrenergic neurons: reduction of tissue norepinephrine content is greater than reduction of extracellular norepinephrine measured by microdialysis
Authors: Abercrombie ED , Zigmond MJ
Published: March 2018

We have examined the impact of partial injury to central noradrenergic terminals on whole tissue norepinephrine (NE) content in hippocampus and on the concentration of NE and 3,4-dihydroxyphenylacetic acid in extracellular fluid of that structure (using microdialysis perfusion). Partial unilateral depletions of hippocampal tissue NE content were produced by administration of 6-hydroxydopamine (2–10 micrograms) into the dorsal noradrenergic bundle, and 2 weeks later microdialysis probes were placed in hippocampus ipsilateral to the lesion. The resting concentration of NE in hippocampal dialysates was unaffected by the lesion unless the reduction of tissue NE content exceeded 50%. In contrast, the basal concentration of 3,4-dihydroxyphenylacetic acid in hippocampal dialysates declined in proportion to tissue NE content. Tail shock or local perfusion with excess K+ increased NE in dialysates from sham-lesioned animals and produced equivalent changes in NE in dialysates from animals with moderate (less than or equal to 50%) depletions of tissue NE content. No significant increases of NE in dialysates were observed in response to these stimuli in animals with depletions of tissue NE content greater than 50%. To the degree that transmitter level in dialysates is representative of extracellular transmitter concentration, the results suggest that compensatory processes exist by which a normal extracellular concentration of transmitter can be maintained under both basal and stimulated conditions despite the loss of up to one half of a neuronal population. (ABSTRACT TRUNCATED AT 250 WORDS)
Clustered distribution and variability in kinetics of transient K channels in molluscan neuron cell bodies
Authors: Premack BA , Thompson S , Coombs-Hahn J
Published: March 2018

The spatial distribution of transient K current, IA, was studied using a combination of patch-clamp and whole-cell voltage-clamp techniques. The average IA current density in somatic patches is 0.64 times the current density in the entire axotomized cell body, a finding which suggests that the axon hillock or initial segment of the axon has a higher concentration of IA channels than much of soma. The highest density of active channels during the peak IA is 1/micron2 at a membrane voltage of -20 mV. There is no evidence for a gradient in the distribution of IA channels in the cell body, but the channels are not evenly distributed. The variability in the number of channels per patch for multiple patches on the same neuron is much higher than expected for a random distribution. Statistical analysis of the data yields a coefficient of dispersion of 8.1, a value indicating a high degree of clustering. The utility of this statistic for evaluating channel distributions is discussed. Several lines of evidence suggest that the upper limit for the area of IA channel clusters is approximately 250 micron2. Single-channel currents attributed to IA were recorded in the cell-attached configuration. The voltage dependence of channel opening and inactivation are the same as measured in whole-cell voltage-clamp experiments. The single-channel conductance is about 9 pS in normal saline. Patches 9–30 micron2 in areas that contain IA channels are often devoid of other K channel types, suggesting that IA channels can occur in isochannel clusters. IA inactivation follows an exponential time course in all of the neurons examined, but the time constant of inactivation ranges from 25 to 560 msec in different cells. The voltage dependence of activation and inactivation and the reversal potential of the current are approximately the same in all cells. When multiple patches on the same neuron are studied, it is found that IA inactivates exponentially with approximately the same time constant in each patch, regardless of patch area. The data suggest that each neuron expresses predominantly, and perhaps exclusively, a single type of IA channel with distinct kinetic properties. The wide range of IA inactivation time constants observed in different cell suggests that a large number of channel types are available for expression. Possible mechanisms for generating diversity in channel types are discussed.
The firing of hippocampal place cells predicts the future position of freely moving rats
Authors: Muller RU , Kubie JL
Published: March 2018

Direct observation and automatic, video-based methods reveal that a large fraction of hippocampal pyramidal neurons recorded from freely moving rats behave as “place cells”; the firing of each place cell occurs almost exclusively when the rat is in a restricted part of its current environment. In earlier work, 2-dimensional firing distributions for place cells over the apparatus area were made under the assumption that the correct location for each spike was the animal's position at the instant that the spike was fired. Spatial firing distributions generated in this way often have a very simple structure, in which the single region of intense activity has a just one maximum, and where the rate decreases monotonically in all directions away from the maximum. We will refer to patterns of this sort as “ideal.” We describe how the spatial firing pattern is altered by assigning spikes to positions earlier or later than the instant at which they were fired. Spatial firing distributions were generated for a range of constant displacements of the spike time-series against the position time series. Three quantitative measures were used to estimate the extent to which the spatial firing pattern at different “spike/position shifts” approximated the ideal pattern. The 3 measures are in agreement that spikes must precede the animal's position by about 120 msec for the spatial firing pattern to be closest to the ideal. These results suggest that hippocampal unit activity predicts the animal's future location on a short time scale.
Ultrastructural localization of molecular subtypes of immunoreactive neural cell adhesion molecule (NCAM) in the adult rodent striatum
Authors: DiFiglia M , Marshall P , Covault J , Yamamoto M
Published: March 2018

Neural cell adhesion molecule (NCAM) is a plasma membrane glycoprotein that is thought to mediate adhesion between neuronal elements and play an important role in neural development. Although NCAM has been found in the adult brain, as well as the developing brain, little is known about its function or ultrastructural distribution. A monoclonal antibody which was directed against embryonic (E15-E17) mouse brain and identified 180 and 140 kDa molecular weight forms of NCAM was used to examine the immunohistochemical localization of NCAM in the rodent striatum. Light microscopic results in the adult mouse and rat showed that most NCAM180,140 immunoreactivity was localized to the relatively small population of medium and large-sized aspiny interneurons of the caudate nucleus and to the majority of neurons in the globus pallidus. Ultrastructural analysis revealed that reaction product in aspiny somata was present in discrete, closely spaced patches of cytoplasm along the inner face of the plasma membrane and was also prominent in somatic protrusions which were frequently apposed to synapsing axons. Distal aspiny and pallidal dendrites containing NCAM180,140 received numerous synaptic inputs. Within caudate neuropil NCAM180,140 was also present in spines with thin necks and small spine heads which were postsynaptic to unlabeled axon terminals and in preterminal (unmyelinated) axons and terminal boutons that issued from myelinated bundles and formed asymmetric synapses with unlabeled dendritic spines. This study provides the first evidence in adult brain that NCAM180,140 varies in extent and location within neurons. The heterogeneous distribution of NCAM180,140 in neurons of the basal ganglia may be related to a number of functions such as maintaining or modulating the density and distribution of synaptic inputs and the formation of new contacts on dendritic spines.
Neuronal plasminogen activators: cell surface binding sites and involvement in neurite outgrowth
Authors: Pittman RN , Ivins JK , Buettner HM
Published: March 2018

Sympathetic neurons release both urokinase plasminogen activator (uPA) and tissue plasminogen activator (tPA). A number of inhibitors of serine proteases have been tested to determine their effects on neurite outgrowth from rat sympathetic neurons. Some inhibitors increase neurite outgrowth while others have little or no effect on outgrowth. Inhibition of plasminogen activator (PA) activity but not other serine protease activity correlates with the increase in neurite outgrowth (uPA, r = 0.89; tPA, r = 0.86; plasmin, r = 0.015; thrombin, r = 0.025). Antibodies that inhibit uPA activity increase neurite outgrowth, while antibodies that bind to uPA but do not inhibit activity do not alter outgrowth. Time-lapse videomicroscopy of neurite outgrowth indicates that about 85% of the neurites increase their rate of outgrowth following exposure to inhibitors of PA. Routinely, 1–2 min after exposure of a growth cone to an inhibitor, there is an increase in lamellipodial activity at the leading edge of the growth cone and a decrease in lamellipodial activity on the sides and base of the growth cone. The increase in the rate of outgrowth combined with the decrease in lamellipodial activity on the sides of the growth cones results in neurites being very long and straight in the presence of inhibitors (persistence time P = 3.7 and 15.3 hr for controls and in the presence of inhibitors of PA, respectively). PAs released from sympathetic neurons and PC12 cells interact with 3 different binding sites on the cell surface: (1) an inhibitor of serine proteases (including uPA and tPA) is bound to the surface via a heparinase-sensitive site; (2) a uPA- selective binding site is present in patches on the bottom surface of PC12 cells; and (3) a tPA-selective binding site with high affinity (KD = 23 +/- 10 nM) and high capacity (340,000 +/- 130,000 sites/neuron) for 125I-tPA is homogeneously distributed over the entire surface. Data in the present study are consistent with PA being involved in neurite outgrowth and open the possibility of other PA-dependent functions occurring when tPA and/or uPA interacts with cell surface binding sites.
Identification of proteins that are developmentally regulated during early cerebral corticogenesis in the rat
Authors: Geschwind DH , Hockfield S
Published: March 2018

Between embryonic day 14 (E14) and embryonic day 21 (E21), the rat neopallium develops from a relatively homogeneous band of mitotic precursor cells into a complex laminated structure containing diverse classes of neurons. In order to identify some of the molecular components underlying this process, 2-dimensional PAGE was used to compare proteins expressed before cortical neurons are born (E14) with those expressed during neurogenesis and neuronal migration (E17 and E21). This approach has permitted the identification of 15 proteins that show greater than 3-fold changes in their rate of accumulation between E14 and E21. Six proteins show consistent up-regulation, ranging from 3.2- to 10.7-fold. Five proteins show consistent down- regulation ranging from 9- to 22-fold. Four proteins that appear at E21 are not detectable on fluorograms of E14 cortex, even after long exposures, and thus are up-regulated more than 200-fold from E14 to E21 and may be considered to appear de novo. The molecular weights and isoelectric points of most of these 15 suggest that they are previously unreported, developmentally regulated proteins. Comparisons of gels of cortex to gels of lung and heart suggest that several of these proteins are enriched in brain relative to non-neural tissues. This analysis also indicates that, despite the large morphogenic changes observed during this developmental period, few proteins (less than 3%) among the total spectrum analyzed show large changes in their rates of synthesis.
Lesions of perirhinal and parahippocampal cortex that spare the amygdala and hippocampal formation produce severe memory impairment
Authors: Zola-Morgan S , Squire LR , Amaral DG , Suzuki WA
Published: March 2018

In monkeys, bilateral damage to the medial temporal region produces severe memory impairment. This lesion, which includes the hippocampal formation, amygdala, and adjacent cortex, including the parahippocampal gyrus (the H+A+ lesion), appears to constitute an animal model of human medial temporal lobe amnesia. Reexamination of histological material from previously studied monkeys with H+A+ lesions indicated that the perirhinal cortex had also sustained significant damage. Furthermore, recent neuroanatomical studies show that the perirhinal cortex and the closely associated parahippocampal cortex provide the major source of cortical input to the hippocampal formation. Based on these 2 findings, we evaluated the severity of memory impairment in a group of monkeys that received bilateral lesions limited to the perirhinal cortex and parahippocampal gyrus (the PRPH lesion). The performance of the PRPH group was compared with that of monkeys with H+A+ lesions, who had been studied previously, and with a group of normal monkeys. Monkeys with PRPH lesions were severely impaired on 3 amnesia-sensitive tasks: delayed nonmatching to sample, object retention, and 8-pair concurrent discrimination. On pattern discrimination, a task analogous to ones that amnesic patients perform well, monkeys in the PRPH group performed normally. Overall, monkeys with PRPH lesions were as impaired or more impaired than the comparison group of monkeys with H+A+ lesions. These and other recent findings (Zola-Morgan et al., 1989b) suggest that the severe memory impairment in monkeys and humans associated with bilateral medial temporal lesions results from damage to the hippocampal formation and adjacent, anatomically related cortex, not from conjoint hippocampus-amygdala damage.
Identification of morphine- and cyclic AMP-regulated phosphoproteins (MARPPs) in the locus coeruleus and other regions of rat brain: regulation by acute and chronic morphine
Authors: Guitart X , Nestler EJ
Published: March 2018

Regulation of cAMP-dependent protein phosphorylation by acute and chronic morphine was studied in the rat locus coeruleus (LC), a brain region that appears to play an important role in mediating morphine action in animals, including humans. Rats were treated chronically with morphine under conditions known to induce states of tolerance and dependence. Protein phosphorylation was then studied in extracts of LC and other brain regions with back-phosphorylation assays under different conditions and with 1- and 2-dimensional electrophoretic procedures. Evidence was obtained to suggest that chronic morphine increased the phosphorylation state of proteins of 165, 55, and 14–20 kDa and increased the total amount of proteins of 145, 71, 62, 58, and 51 kDa in the LC. Concomitant treatment of rats with naltrexone, an opiate receptor antagonist, blocked the ability of morphine to influence each of these proteins, indicating that morphine regulation of protein phosphorylation occurred through the specific activation of opiate receptors. Regulation of 165, 71, 62, 58, 55, and 51 kDa by chronic morphine was specific to the LC among the brain regions studied, whereas regulation of 145 and 14–20 kDa was also observed in the frontal cortex, neostriatum, and dorsal raphe. Most of the phosphoproteins whose phosphorylation state or total amount was increased by chronic morphine treatment in the LC in vivo were also shown to have their phosphorylation state decreased by acute morphine treatment in isolated LC nuclei ex vivo. In addition, the phosphorylation state of most of these morphine-regulated phosphoproteins was stimulated by forskolin or cAMP analogs in isolated LC and by cAMP in broken cell preparations of this brain region, supporting the view that these proteins are physiological substrates for cAMP-dependent protein kinase in the LC. Phosphoproteins regulated by morphine and cAMP were designated “MARPPs,” morphine- and cAMP- regulated phosphoproteins, whereas those regulated by morphine but not by cAMP were designated “MRPPs.” Taken together, the results of this study indicate that chronic morphine produces specific alterations in cAMP-dependent protein phosphorylation in the LC and raise the possibility that regulation of these specific phosphoproteins contributes to the development of tolerance and/or dependence in these neurons.
ATP-activated channels in rat and bullfrog sensory neurons: concentration dependence and kinetics
Authors: Bean BP
Published: March 2018

The concentration dependence and kinetics of ionic currents activated by extracellular adenosine 5′-triphosphate (ATP) were studied in voltage-clamped dorsal root ganglion neurons from rats and bullfrogs. About 40% of neurons of both species responded to ATP with an increase in membrane conductance. The ATP-activated currents were similar in the 2 species, except that currents in rat neurons desensitized faster. In bullfrog neurons, the conductance was half-maximally activated by about 3 microM ATP; at low concentrations, the conductance increased 3- to 7- fold for a doubling in [ATP], suggesting that several ATP molecules must bind in order to activate the current. A steeper concentration- response relationship than expected from 1:1 binding was also seen in rat neurons. The current activated quickly upon application of ATP and decayed quickly when ATP was removed. Activation kinetics were faster at higher [ATP], with time constants decreasing from about 200 msec at 0.3 microM ATP to about 10 msec at 100 microM ATP. Deactivation kinetics (tau approximately 100–200 msec) were independent of the ATP concentration. The rapid activation and deactivation make it seem likely that the ATP-activated current is mediated by direct ligand binding rather than by a second-messenger system. The experimental observations can be mimicked by a simple model in which ATP must bind to 3 identical, noninteracting sites in order to activate a channel. The potency and kinetics of ATP action were voltage-dependent, with hyperpolarization slowing deactivation and increasing ATP's potency. Deactivation kinetics were also sensitive to the concentration of external Ca, becoming faster in higher Ca.
ATP-activated channels in rat and bullfrog sensory neurons: current- voltage relation and single-channel behavior
Authors: Bean BP , Williams CA , Ceelen PW
Published: March 2018

Ionic currents activated by extracellular adenosine 5′-triphosphate (ATP) were studied in voltage-clamped dorsal root ganglion neurons from rats and bullfrogs. Under quasiphysiological ionic conditions, ATP- activated current reversed near 0 mV and showed strong inward rectification. Strong inward rectification was maintained even in symmetric solutions of divalent-free Cs glutamate. Examined with a resolution of 10s of microseconds, the rectification was instantaneous. Inward current was greatly reduced when N-methyl-D-glucamine was substituted for external Na. ATP-activated inward currents could be recorded with Ca as the only external cation; estimated from reversal potentials, the ratio of Ca to Na permeability is about 0.3. Unitary channel activity could be recorded when ATP was applied to outside-out patches. When activated, a single channel flickered rapidly, with a mean current of about 0.5 pA at -100 mV. Large concentrations of ATP put the channel in the activated, flickery condition virtually all the time, while at lower concentrations, periods of flickering were interspersed with closures. Analysis of whole-cell current fluctuations showed precisely the characteristics expected if such channels underlie the macroscopic currents.
An identified motoneuron with variable fates in embryonic zebrafish
Authors: Eisen JS , Pike SH , Romancier B
Published: March 2018

Every trunk hemisegment of the zebrafish is innervated by 3 identified primary motoneurons whose development can be observed directly in living embryos. In this paper, we describe another identified neuron that is part of this system. Unlike the other primary motoneurons which are present in all trunk hemisegments, this cell is present in slightly less than half of the trunk hemisegments. Additionally, this cell has at least 2 different fates: it may become a primary motoneuron and arborize in an exclusive muscle territory, or it may die during embryonic development. We have named this cell VaP, for variable primary. We show that the presence of VaP does not affect the early development of the other primary motoneurons in the same hemisegment. Moreover, we show that ablation of both VaP and caudal primary does not alter pathfinding by another identified primary motoneuron.
Noradrenergic modulation of the masseteric reflex in behaving cats. I. Pharmacological studies
Authors: Stafford IL , Jacobs BL
Published: March 2018

The masseteric (jaw closure) reflex was utilized as a model system for assessing functional changes in central norepinephrine (NE) neurotransmission. This monosynaptic reflex was chosen because of its simple and well-defined circuitry, and because its motor component receives a dense NE innervation. Previous experiments in our laboratory described NE modulation of this reflex in the anesthetized rat. The present experiments examine the effects of NE on this response in the unanesthetized, behaving cat. The masseteric reflex was elicited by electrical stimulation of the mesencephalic trigeminal nucleus, and the response was recorded via electrodes permanently implanted in the masseter muscle. The amplitude of the reflex response was measured before and at various intervals following microinfusion (0.5 microliters) of NE or of various NE agonists directly into the motor trigeminal nucleus (MoV). Microinfusions of NE (0.125–5.0 micrograms) produced dose-dependent increases in the amplitude of the elicited reflex response. These effects were evident within 1 min postinfusion and lasted up to 30 min; in all cases, the response amplitude returned to baseline levels. The increase seen in response to 0.5 micrograms NE was blocked by pretreatment with the alpha-1-adrenergic antagonist prazosin, but not by pretreatment with the serotonin (5-HT) antagonist methysergide. Methysergide did, however, completely block the increase in the amplitude seen in response to microinfusion of 5-HT. Infusion of the alpha-1-adrenergic agonist phenylephrine also increased the amplitude of the reflex response. By contrast, infusion of the beta- adrenergic agonist isoproterenol had no effect, whereas clonidine, a presynaptic alpha-2-adrenergic agonist, decreased its amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)
Locomotion evoked by stimulation of the brain stem in the Atlantic stingray, Dasyatis sabina
Authors: Livingston CA , Leonard RB
Published: March 2018

The primary pathway descending to the spinal cord to initiate locomotion in the stingray is located in the intermediate to ventral portion of the lateral funiculus; a second pathway is located in the dorsolateral funiculus. The goal of this study was to identify the origins of these pathways in the rhombencephalic reticular formation (RF). To do this we used microstimulation of the RF in conjunction with selective lesions of the brain stem and spinal cord. In some animals microinjections of excitatory amino acids were used to avoid stimulating axons of passage. Locomotion in the contralateral pectoral fin was evoked by microstimulation of the dorsal and ventral reticular nuclei, the middle and superior RF, and the ventral portion of the lateral RF. The regions from which locomotion was evoked by chemical stimulation were more restricted and included the rostral dorsal reticular nucleus, the middle RF, and the adjacent ventral lateral RF. This area encompasses the magnocellular RF and coincides with the distribution of numerous reticulospinal cells that project ipsilaterally into the ventral half of the lateral funiculus. Our results indicate, then, that locomotion in the stingray is mediated primarily by a pathway originating in the magnocellular RF that descends ipsilaterally in the ventral half of the lateral funiculus to elicit swimming in the contralateral pectoral fin. We suggest that this primary pathway is specifically associated with the control of locomotion. We also demonstrated that locomotion can be evoked independently from the lateral RF, but is probably mediated by an indirect pathway relaying near the spinomedullary junction or in the rostral spinal cord.
Sensitive and critical periods for visual calibration of sound localization by barn owls
Authors: Knudsen EI , Knudsen PF
Published: March 2018

This study describes developmental changes in the capacity of owls to adjust sound localization in response to chronic prismatic displacement of the visual field and to recover accurate sound localization following the restoration of normal vision. Matched, binocular displacing prisms were mounted over the eyes of 19 barn owls (Tyto alba) beginning at ages ranging from 10 to 272 d. In nearly all cases, the visual field was shifted 23 degrees to the right. Sound localization was assessed on the basis of head orientations to sound sources, measured in a darkened sound chamber with a search coil system. Chronic exposure to a displaced visual field caused the owls to alter sound localization in the direction of the visual field displacement, thereby inducing a sound-localization error. The size of the sound-localization error that resulted depended on the age of the animal when prism experience began. Maximal errors of about 20 degrees were induced only when prism experience began by 21 d of age. As prism experience began at later ages, the magnitude of induced errors decreased. A bird that wore prisms beginning at 102 d of age, altered sound localization by only 6 degrees. An adult owl, when exposed chronically to a displaced visual field, altered sound localization by about 3 degrees. We refer to the early period in life when displaced vision induces exceptionally large sound-localization errors (relative to those induced in the adult) as a sensitive period. The capacity to recover accurate sound localization following restoration of normal vision was tested in 7 owls that had been raised wearing prisms. Four owls that had prisms removed by 182 d of age recovered accurate localization rapidly (over a period of weeks), whereas 3 owls that were older when the prisms were removed did not recover accurate localization when tested for up to 7 months after prism removal. Adjustment of sound localization slowed greatly or ceased at about 200 days of age, referred to here as the critical period for visual calibration of sound localization. Three owls were subjected repetitively to displacement of the visual field. An owl that adjusted sound localization to the left of normal during the sensitive period retained the capacity to adjust again to the left, but not to the right of normal, later in the critical period. The converse was true for an owl that adjusted sound localization to the right of normal during the sensitive period.(ABSTRACT TRUNCATED AT 400 WORDS)
Long-term potentiation and activity-dependent retinotopic sharpening in the regenerating retinotectal projection of goldfish: common sensitive period and sensitivity to NMDA blockers
Authors: Schmidt JT
Published: March 2018

The regenerating retinotectal projection in goldfish goes through an activity-driven refinement that appears to involve the elimination of inappropriate branches from early arbors. Retinotopically appropriate branches may be stabilized because the normally correlated firing of neighboring ganglion cells causes summation of their postsynaptic responses and increases their effectiveness by a Hebbian mechanism. In this study, I report that the regenerating projection has an increased capacity for long-term potentiation (LTP) that may be related to the activity-driven sharpening. In the normal projection, field potentials, reflecting currents from EPSPs elicited by optic nerve shock, are large (greater than 4 mV) and very stable. In newly regenerated projections, field potentials are initially small (less than 1 mV), but a train of 20 stimuli at 0.1 Hz results in a large (100–200%) increase in amplitude that is stable for at least 8 hr, and in 3 cases overnight. The capacity for potentiation is greatest from 20 to 40 d postcrush, the time just after arrival of the optic fibers, and during the period of retinotopic sharpening. A greater-than-normal capacity for potentiation persists for many months. Topical application of NMDA receptor blockers AP5 or AP7 at 25 microM prevents potentiation without decrementing ongoing responses. The closely related agent AP6, which is not an NMDA receptor blocker, does not prevent potentiation. In addition, infusion of the NMDA receptor blockers AP5 or AP7 into the tectal ventricle (4 microliters/d of 500 microM solution) for 2–3 weeks during regeneration prevented retinotopic sharpening, as assessed by electrophysiological mapping. At each tectal point, responsive areas in the visual field were enlarged to 28 degrees vs 11–12 degrees in control regenerates and normals. This was comparable to data from fish regenerating with activity blocked with intraocular tetrodotoxin or synchronized by stroboscopic illumination and indicates uncorrected errors in targeting of regenerated arbors (Schmidt, 1985). The results support the involvement of NMDA receptors in sharpening and suggest that the initial step in stabilizing appropriate branches may be a long- lasting increase in synaptic gain.
Local accumulation of acetylcholine receptors is neither necessary nor sufficient to induce cluster formation
Authors: Stollberg J , Fraser SE
Published: March 2018

Acetylcholine receptors (AChRs) accumulate at developing neuromuscular junctions in part via lateral migration of diffusely expressed receptors. Using a model system--cultured Xenopus muscle cells exposed to electric fields--we have shown that AChRs, concentrated at the cathode-facing cell pole, continue to aggregate there after the field is terminated (Stollberg and Fraser, 1988). These observations are consistent with the possibility that the field-induced increase in receptor concentration triggers the aggregation event. Only 2 other molecular events could initiate the electric field-induced receptor aggregation: (1) a local increase in the density of some other molecules, or (2) a voltage-sensitive mechanism. Treatment of muscle cell cultures with neuraminidase changes the cell surface charge and has been reported to reverse the direction of electromigration for AChRs and concanavalin A binding sites (Orida and Poo, 1978). Using digitally analyzed fluorescence videomicroscopy, we find that AChRs in neuraminidase-treated cultures accumulate at both cell poles in an electric field. After termination of the field, the AChR continues to aggregate at the cathode-facing pole, as in cells not treated with neuraminidase. However, receptor density decreases at the anode-facing pole, indicating that elevated AChR density does not initiate receptor aggregation. Cells pretreated with neuraminidase and trypsin (which blocks receptor aggregation) display reversed receptor distributions compared to untreated controls, indicating that electromigration has indeed been reversed. The rate at which neuraminidase- and trypsin- treated cells approach steady-state distributions indicates a receptor diffusion constant of approximately 1.2 x 10(-9) cm2/sec, consistent with a diffusion trap mechanism of receptor aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)
Lectin binding identifies a subpopulation of neurons in chick dorsal root ganglia
Authors: Scott SA , Patel N , Levine JM
Published: March 2018

We screened a variety of lectins with different sugar specificates to determine whether subpopulations of dorsal root ganglion (DRG) neurons in the chick can be distinguished by the carbohydrates they express. Of the 15 lectins tested only those that recognize N-acetylgalactosamine (galNac) residues labeled a subset of DRG neurons. For example, Dolichos biflorus (DBA) labeled a population of small-diameter neurons in the dorsomedial DRG and their terminals in the dorsal horn in hatchling chicks. Staining of live neurons in vitro demonstrated that DBA was binding to the cell surface. Labeling first appeared in sensory neurons at about St.38 (E12) and in dorsal horn laminae 1 and 2 at about St.42 (E16). Fainter labeling appeared somewhat later in lamina 3, after hatching. Labeling of the tissue sections was eliminated by chloroform: methanol extraction and reduced by alpha-N- acetylgalactosaminidase digestion, but survived trypsinization. Together these results suggest that a subset of DRG neurons in the chick can be identified by the presence of a cell surface glycoconjugate, perhaps a glycolipid, containing terminal alpha-linked galNac residues.