bluuebunny/crossref_metadata_2025 huggingface dataset:
Apparent age-related resistance of type II hippocampal corticosteroid receptors to down-regulation during chronic escape training
Authors: Eldridge JC , Brodish A , Kute TE , Landfield PW
Published: April 2018

Corticosteroids appear to modulate neuronal loss in the hippocampus during aging. However, there is a seeming paradox in the literature in that age-related neuronal loss develops more prominently during the later phases of the lifespan, whereas brain corticosterone receptors have been reported to decline with aging, an effect that might be anticipated to reduce the impact of corticosteroids on cell loss. In order to study the regulatory sensitivity of hippocampal corticosteroid receptors (HCSR) during aging, which could play a role in this apparent paradox, rats of 3 ages (4, 12, and 18 months old at the start of training) were given 6 months of chronic escape training using a mild footshock in a 2-way shuttle-escape task (4 hr/d, 5 d/week). Animals were killed either 1 d or 3 weeks following the 6 month training paradigm. Nontrained home cage controls also were maintained in parallel with each age group. Although previous studies have measured receptors in rats adrenalectomized 12 hr or more prior to death, rats intact at death were used in the present studies to avoid possible confounding effects from age differences in receptor up-regulation or response to surgery. Receptor capacity was analyzed with a saturation assay able to measure available type II HCSR in intact rats. Results showed that, in intact young-mature rats (10 months old at death), type II HCSR were down-regulated at 1 d, but not at 3 weeks, after the end of the 6 months of training. However, significant decreases in HCSR were not observed in late mid-aged (18-month-old) or aged (24-month- old) rats at the 1 d point, indicating apparent resistance to down- regulatory stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)
Second messengers involved in the mechanism of action of bradykinin in sensory neurons in culture
Authors: Burgess GM , Mullaney I , McNeill M , Dunn PM , Rang HP
Published: April 2018

Application of bradykinin to neonatal rat dorsal root ganglion neurons caused a depolarization associated with an inward current and an increase in membrane conductance that was probably due to the opening of sodium channels. No hyperpolarization or outward current was detected. In addition, bradykinin increased the rate of 45Ca uptake into the neurons by a mechanism that was blocked by the dihydropyridine calcium channel antagonist nifedipine. Direct activation of protein kinase C (PKC) with phorbol esters mimicked the ability of bradykinin to depolarize the neurons and to increase the rate of 45Ca uptake. Down- regulation of PKC by prolonged treatment with phorbol esters and treatment of the cells with staurosporine, which inhibits PKC, blocked both bradykinin- and phorbol ester-induced 45Ca influx, and substantially reduced the proportion of cells that gave electrophysiological responses to either agent. Bradykinin also activated polyphosphoinositidase C in the dorsal root ganglion neurons, elevating levels of inositol(1,4,5)-trisphosphate and 1,2- diacylglycerol, an endogenous activator of PKC. It is suggested, therefore, that PKC may mediate some of the effects of bradykinin in sensory neurons.
Expression of pheromone binding proteins during antennal development in the gypsy moth Lymantria dispar
Authors: Vogt RG , Kohne AC , Dubnau JT , Prestwich GD
Published: April 2018

We have identified 2 olfactory specific proteins in the gypsy moth Lymantria dispar that are uniquely associated with the male antennae, the principal olfactory organs of this animal. These proteins were the major soluble protein components of the olfactory sensilla, present in equivalent amounts. Both proteins comigrated on SDS-PAGE, showing an apparent molecular mass of 15,000 Da but migrated separately on non-SDS- PAGE, indicating differences in net charge. N-terminal amino acid sequence analysis showed that the 2 proteins share 50% identity, indicating that they are genetically distinct homologs. Both proteins bound the L. dispar sexpheromone, associated with antisera prepared against the previously identified phermone-binding protein (PBP) of the moth Antheraea polyphemus, and shared sequence identity with the A. polyphemus PBP. These 2 proteins are therefore identified as L. dispar PBPs and are termed PBP1 and PBP2 based on their migration differences on non-SDS-PAGE. It is estimated that PBP1 and PBP2 are present in the sensilla lumen at a combined concentration of 13.4 mM. The expression of the L. dispar PBPs was examined during the 11 d development of the adult antenna. PBP1 and PBP2 were first detected by non-SDS-PAGE analysis and Coomassie blue staining 3 d before adult eclosion, on day A-3. Levels increased, reaching a plateau on day A-1 that continued into adult life. In vivo labeling studies indicated that the rate of PBP synthesis increased from A-3 to a plateau on A-2, where it remained into adult life. In vitro translations of antennal mRNAs indicated that translatable PBP mRNA was available at a very low level on day A-4, increased slightly on A-3 and dramatically on A-2, and remained at a high level into adult life. PBP mRNA represented the major translatable mRNA in the antenna during this period. It was estimated that the PBPs undergo a combined steady-state turnover of 8 x 10(7) molecules/hr/sensillum. Cursory in vivo and in vitro translation studies of antennal mRNA from A. polyphemus and Manduca sexta showed similar temporal patterns of PBP expression, suggesting that the L. dispar observations are general.
Calcium-dependent depolarizations originating in lizard motor nerve terminals
Authors: Morita K , Barrett EF
Published: April 2018

Action potentials and afterpotentials were recorded via a microelectrode inserted into motor axons innervating the lizard ceratomandibularis muscle. Intra-axonal injection of Lucifer yellow dye indicated that these axons innervate multiple (at least 6–25) motor terminals. In 10 mM tetraethylammonium (TEA), the action potential was followed by a sequence of afterpotentials, whose amplitude and duration increased with increasing proximity to motor nerve terminals. In axons impaled within 1 mm of their most distal terminals, these afterpotentials included a depolarizing plateau (mean amplitude and duration: 32 mV, 24 msec) and a subsequent smaller depolarization that decayed over a time course of several hundred milliseconds. These depolarizing afterpotentials were Ca dependent: They increased with increasing bath [Ca] and were abolished by low [Ca]-high [Mg] solutions, by omega-conotoxin (GVIA, 1 microM), by addition of Cd (1 microM) or Mn (0.3–1 mM) to the bath, and by selective perfusion of Cd over the terminal region. In [Ca]-free solutions the afterpotentials were restored by selective perfusion of Ca over the terminal region but not by Ca applied to the more proximal nerve trunk. When Na influx was eliminated by 1–10 microM tetrodotoxin or by substitution of TEA for bath Na, passage of depolarizing current into the axon evoked prolonged depolarizing afterpotentials that were blocked by Mn. Bay K 8644 (0.1–1 microM), a dihydropyridine that prolongs the opening of certain calcium channels, enhanced mainly the slower component of the depolarizing afterpotential. Nimodipine (0.1–1 microM), a dihydropyridine that favors the closed state of some calcium channels, shortened the plateau phase of the depolarizing afterpotential. Another antagonist dihydropyridine, nitrendipine (0.1–1 microM), had little or no effect on the depolarizing afterpotential but did antagonize the actions of Bay K 8644. These results suggest that the intraaxonally recorded Ca- dependent afterpotentials are caused by electrotonic spread of depolarizations produced by calcium influx into that axon's terminals and that some motor nerve terminal calcium channels are sensitive to certain dihydropyridines.
Postmetamorphic cell death in the nervous and muscular systems of Drosophila melanogaster
Authors: Kimura KI , Truman JW
Published: April 2018

Programmed cell death occurs in the nervous and muscular system of newly emerged adult Drosophila melanogaster. Many of the abdominal muscles that were used for eclosion and wing-spreading behavior degenerate by 12 hr after eclosion. Related neurons in the ventral ganglion also die within the first 24 hr. Ligation experiments showed that the muscle breakdown is triggered by a signal from the anterior region, presumably the head, that occurs about 1 hr before adult emergence. The timing of this signal suggests that eclosion hormone may be involved. Although muscle death is triggered prior to ecdysis, it can be delayed, at least temporarily, by forcing the emerging flies to show a prolonged ecdysis behavior. In contrast to the muscles, the death of the neurons is triggered after emergence. The signal for neuronal degeneration is closely correlated with the initiation of wing inflation behavior. Ligation and digging experiments and behavioral manipulations that either blocked or delayed wing expansion behavior had a parallel effect in suppressing or delaying neuronal death.
Head-direction cells recorded from the postsubiculum in freely moving rats. II. Effects of environmental manipulations
Authors: Taube JS , Muller RU , Ranck JB
Published: April 2018

The discharge characteristics of postsubicular head-direction cells in a fixed environment were described in the previous paper (Taube et al., 1990). This paper reports changes in the firing properties of head- direction cells following changes in the animal's environment. Head- direction cells were recorded from rats as they moved freely in a 76-cm- diameter gray cylinder. A white card, occupying 100 degrees of arc, was taped to the inside wall of the cylinder and served as the major orienting spatial cue in the animal's environment. Rotation of the cue card produced near-equal rotation in the preferred firing direction of head-direction cells, with minimal changes in peak firing rate, directional firing range, or asymmetry of the firing-rate/head- direction function. Card removal had no effect on peak firing rate or range of firing, but in 8/13 cells the preferred direction rotated by at least 24 degrees. Similarly, changing the shape of the environment to a rectangular or square enclosure caused the preferred firing direction to rotate by at least 48 degrees for 8/10 cells in the rectangle and 3/8 cells in the square, with minimal changes in the peak firing rate or directional firing range. Hand holding the animals and moving them around the cylinder had no effect on the preferred direction or firing range of the cell, but decreased the maximal firing rate in 7/9 cells. On 2 occasions, 2 head-direction cells were recorded simultaneously. The rotation of the preferred firing direction for one cell was the same as the rotation of the preferred direction for the second cell after each environmental manipulation. These results demonstrate that specific visual cues in the environment can exert control over the preferred firing direction and indicate that head- direction cell firing is not a simple sensory response to visual cues, but rather represents more abstract information concerning the animal's spatial relationship with its environment. The constancy of the angle between the preferred firing directions of pairs of simultaneously recorded head-direction cells suggests that there is a fixed mapping of the population onto direction within the environment. Thus, environmental manipulations appear to cause only a change in the reference direction, but leave all other discharge characteristics of directional cells unchanged. In the discussion, comparisons are drawn between the responses of head-direction cells and hippocampal place cells to similar environmental manipulations (Muller and Kubie, 1987), and ways in which these 2 spatial systems interact in navigation are discussed.(ABSTRACT TRUNCATED AT 400 WORDS)
Enhanced behavioral conditioning to context and impaired behavioral and neuroendocrine responses to conditioned stimuli following ceruleocortical noradrenergic lesions: support for an attentional hypothesis of central noradrenergic function
Authors: Selden NR , Robbins TW , Everitt BJ
Published: April 2018

This study tested the hypothesis that cortical noradrenaline (NA) depletion induced by 6-hydroxydopamine (6-OHDA) widens attentional span, impairing the acquisition of conditioning to an explicit stimulus while enhancing conditioning to contextual stimuli. Sham-operated and NA-depleted rats were exposed to pairings of an auditory (clicker) CS and (footshock) US in a distinctive environment. Half of the lesioned and half of the control animals were trained with a short trace interval between presentations of clicker and shock, and half with a long trace. Associative learning theory predicts that a long trace interval should bias intact animals towards stronger contextual conditioning and, in contrast, a short trace interval should bias controls towards stronger CS conditioning. During testing, NA-depleted animals showed impaired fear conditioning to explicit cues, compared with controls, indicated by their reduced suppression of drinking when the CS was introduced into a separate, lick-operant chamber. In contrast, the same animals exhibited enhanced fear of contextual cues, as shown by their greater preference for a “safe” environment over the one in which they were shocked. The behavioral and plasma corticosterone responses of individual animals to the CS were positively correlated in both the lesion and sham groups. Corticosterone levels corroborated the impairment in CS conditioning caused by the lesion. In contrast, behavioral and corticosterone responses to contextual stimuli were not significantly correlated in either group, and there was no enhancement of the corticosterone response to contextual stimuli in the lesioned animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Retinal graft-mediated pupillary responses in rats: restoration of a reflex function in the mature mammalian brain
Authors: Klassen H , Lund RD
Published: April 2018

We have shown previously that fetal retinae transplanted to neonatal rat brains are capable of making the pretectal connections necessary for driving a pupillary reflex in response to light. At birth, the rat brain is still developing and presents a favorable environment for fiber outgrowth and synaptogenesis. A remaining question is whether such grafts will also establish functional connections within the less plastic mature brain. Fetal retinae taken from Sprague-Dawley rats at embryonic day 13 or 14 were implanted in the pretectal region of mature host rats ranging in age from 6 to 11 weeks. The contralateral host eye was removed to reduce afferent competition within the pretectum between the optic input of graft and host. The remaining host optic nerve was cut before testing to eliminate all remaining host visual input. Beginning 1 month after transplantation, the retinae were surgically exposed and illuminated. In 6 of 24 animals, illumination elicited an obvious pupilloconstriction response in the host eye. The magnitude of this graft-mediated response varied between animals. Two animals produced very brisk responses, comparable to the best results seen following transplantation into neonatal hosts. In these cases, the degree of constriction was clearly dependent on the level of graft illumination. The 4 other animals produced responses that were less brisk. All 6 animals with clear-cut graft-mediated pupillary responses had well-formed grafts containing numerous rosettes and ganglion cells. In addition to these 6 animals, 9 others showed extremely small or variable pupillary changes on graft illumination. The remaining 9 animals showed no stimulus-associated pupillary activity. Grafts in this group tended to be poorly formed or were located outside the pretectal area. These results show that transplanted retinae are capable of making specific functional connections with the mature brain, since an appropriate visual reflex can be elicited by illuminating the graft in the absence of host visual input.
Terminal sprouting is not responsible for enhanced transmitter release at disused neuromuscular junctions of the rat
Authors: Tsujimoto T , Umemiya M , Kuno M
Published: April 2018

Chronic block of nerve-muscle activity is known to induce sprouting of motor nerve terminals and to enhance transmitter release at the neuromuscular junction. Increased transmitter release has been assumed to be a physiological correlate of disuse-induced sprouting of nerve terminals. We examined this assumption in the rat extensor digitorum longus muscle following chronic conduction block of the sciatic nerve with TTX. The minimal period of nerve block required for the expression of terminal sprouting was 3 d, whereas transmitter release, measured by the quantal analysis of end-plate potentials, was already enhanced within 24 hr of nerve block. Following 6 d of nerve block, sprouting was observed in about 35% of the motor nerve terminals examined. Under this condition, the total length of individual terminals was significantly greater in the terminals with sprouts than those without sprouts. However, enhancement of transmitter release occurred uniformly at these junctions regardless of the presence or absence of terminal sprouts. Also, transmitter release enhanced by nerve block for 2 d remained elevated for at least 4 d even after resumption of nerve activity without the formation of terminal sprouts. It is concluded that terminal sprouting and increased transmitter release induced in disused neuromuscular junctions are not causally related and that the signals for inducing these 2 events are at least quantitatively different.
Aminergic modulation of graded synaptic transmission in the lobster stomatogastric ganglion
Authors: Johnson BR , Harris-Warrick RM
Published: April 2018

Graded chemical synaptic transmission is important for establishing the motor patterns produced by the pyloric central pattern generator (CPG) circuit of the lobster stomatogastric ganglion (Raper, 1979; Anderson and Barker, 1981; Graubard et al., 1983). We examined the modulatory effects of the amines dopamine (DA), serotonin (5-HT), and octopamine (Oct) on graded synaptic transmission at all the central chemical synapses made by the pyloric dilator (PD) neuron onto its follower cells, using synaptic input-output curves measured from cell somata. DA strongly reduced the graded synaptic strength at all the PD synapses. DA reduction of chemical synaptic strength from PD onto the inferior cardiac (IC) neuron could change the sign of synaptic interaction between these 2 cells from inhibitory to excitatory by uncovering a weak electrical connection. 5-HT had weaker and more variable effects, reducing graded synaptic strength from the PD onto the lateral pyloric and pyloric neurons and enhancing the weak synapse from the PD to the IC cell. Oct strongly enhanced the graded synaptic strength at all the PD central synapses. Oct enhancement of graded synaptic strength between the PD and IC cells could also change the sign of the interaction: weak, excitatory electrical coupling, which was sometimes dominant before Oct, was masked by the enhanced chemical inhibitory interaction during Oct application. Measurements of electrical coupling between 2 PD cells and between 2 postsynaptic cells suggest that Oct does not change the input resistance of these cells and may act directly at the PD synapses. The effects of DA and 5-HT are most easily explained by their general reductions in pre- and postsynaptic input resistance. DA, 5-HT, and Oct each produce a distinct pyloric motor pattern (Flamm and Harris-Warrick, 1986a). These amine-induced motor patterns may be explained by the unique actions of each amine on the intrinsic membrane properties of different pyloric CPG neurons (Flamm and Harris-Warrick, 1986b) and by modulation of graded synaptic transmission between the pyloric neurons.
Construction of a protoglomerular template by olfactory axons initiates the formation of olfactory glomeruli in the insect brain
Authors: Oland LA , Orr G , Tolbert LP
Published: April 2018

Olfactory glomeruli in insects share many features of organization with their vertebrate counterparts, and yet offer distinct advantages for study of neuronal development. Previous studies have revealed that the olfactory lobes of the brain of the moth Manduca sexta arise postembryonically and that glomeruli in the lobe are induced by olfactory afferent axons (Hildebrand et al., 1979; Oland and Tolbert, 1987). In the present study, we have used the Golgi method, intracellular labeling of neurons with Lucifer yellow, and electron microscopy to follow neuronal development in the antennal lobe through the period when glomeruli develop. Our results, taken together with other results from our laboratory, suggest that olfactory sensory axons have the intrinsic ability to form protoglomeruli, and that an interaction between these axons and glial cells (but not the majority of the neurons of the antennal lobe) causes the glial cells to surround the protoglomeruli. Ingrowth of the neurites of most antennal-lobe neurons into the protoglomeruli occurs after a small delay and appears to be constrained to glomerular units by the presence of the glial boundaries. Synapses, initially not detected in the protoglomeruli, begin to appear as soon as the neurites of antennal-lobe neurons appear in the glomeruli. Thus, antennal axons, instead of immediately seeking out postsynaptic targets, first form the template for organization of future glomeruli. The neurites of most of the neurons of the antennal lobe grow outward to meet the olfactory sensory axons, and in doing so, join with these axons to form glomeruli. Preliminary results concerning the development of a second class of neuron in the lobe, the projection neurons, indicate that at least some of these neurons may arborize in the region of the protoglomeruli very early and therefore participate with the afferent axons in laying the foundation for glomeruli.
Differential involvement of protein kinase C isozymes in Alzheimer's disease
Authors: Masliah E , Cole G , Shimohama S , Hansen L , DeTeresa R , Terry RD , Saitoh T
Published: April 2018

Decreased levels of protein kinase C (PKC) and a reduction in the in vitro phosphorylation of a Mr 86,000 protein (P86), the major PKC substrate, are biochemical characteristics of brain tissue from patients with Alzheimer's disease (AD) (Cole et al., 1988). In the current study, we utilized antibodies against individual isozymes of PKC to assess the degree of involvement of different PKC isoforms in AD. The concentration of PKC(beta II) was lower in particulate fractions prepared from AD hippocampal and cortical tissue than in controls and higher in AD cytosol fractions from the cortex than in controls. Immunohistochemical studies in AD neocortex revealed reduced numbers of anti-PKC(beta II)-immunopositive neurons and diminished staining intensity. In contrast, AD hippocampal neurons in CA3-CA4 were more intensely stained with anti-PKC(beta II) antiserum than were controls. The concentration of PKC(beta I) was lower in particulate fractions prepared from AD hippocampus than in controls and was higher in soluble fractions prepared from AD cortex than in controls. The concentration of PKC(alpha) was lower in AD particulate fractions than in controls in the hippocampus. Immunohistochemistry with PKC(alpha) antiserum revealed moderately intense neuron staining and an intense staining of glial cells in AD neocortex. The concentrations and histochemical distributions of PKC(gamma) were not altered in the disease. PKC immunoreactivity was also found in neuritic plaques. The staining patterns of neuritic plaques with different isoform antibodies varied considerably. Anti-PKC(alpha) faintly stained entire plaques and surrounding glial cells; anti-PKC(beta I) stained dystrophic plaque neurites; and anti-PKC(beta II) stained the amyloid-containing portions of plaques.
Glycine-insensitive NMDA-sensitive receptor expressed in Xenopus oocytes by guinea pig cerebellar mRNA
Authors: Sekiguchi M , Okamoto K , Sakai Y
Published: April 2018

The electrophysiological and pharmacological properties of N-methyl-D- aspartate (NMDA)-sensitive receptors expressed in Xenopus oocytes by injection of total poly(A)+RNAs (mRNAs) from the cerebellum and cerebrum of guinea pigs were compared. The inward current induced by NMDA under voltage-clamp in cerebellar mRNA-injected oocytes was depressed in a voltage-dependent fashion by Mg2+ to show a negative slope conductance and selectively antagonized by D-2-amino-5- phosphonovalerate (D-APV) and phencyclidine (PCP). Glycine (0.01–10 microM) did not potentiate NMDA-induced currents in cerebellar mRNA- injected oocytes, while it potentiated NMDA-induced currents in cerebral mRNA-injected oocytes in a dose-dependent fashion. 6-Cyano-7- nitroquinoxaline-2,3-dione and 7-chlorokynure-nate suppressed the NMDA response but significantly less potently in cerebellar mRNA-injected oocytes than in cerebral mRNA-injected oocytes. These results suggest that the NMDA-sensitive receptor expressed in Xenopus oocytes by guinea pig cerebellar mRNA resembles the cerebral NMDA receptor in its high sensitivities to Mg2+, PCP, and D-APV, but it is distinct from the cerebral NMDA receptor in responsiveness to glycine.
Docosahexaenoic acid utilization during rod photoreceptor cell renewal
Authors: Gordon WC , Bazan NG
Published: April 2018

The supply of docosahexaenoic acid (22:6) to the frog retina, and its subsequent use by retinal cells, was studied by autoradiography and biochemical methods. Different delivery routes of 3H-22:6 were evaluated. Predominant uptake by the neural retina, mainly in ganglion cell axons, outer synaptic layer, and Muller cells, was observed when the radiolabeled fatty acid was given intravitreally or by short-term incubations of eyecups. In short-term eyecup incubations, Muller cells preferentially labeled, suggesting their involvement as a transient storage site. After intravenous or dorsal lymph sac injections of 3H- 22:6, most of the retinal label was seen in rod photoreceptor cells. Two different labeling patterns were found in rod outer segments (ROS) as a function of postinjection time: an overall diffuse labeling pattern, as well as a dense-label region at the ROS base. This dense- label region expanded until it reached the apex of the ROS after about 30 d. HPLC analysis of fatty acid methyl esters from retinal lipid extracts showed that 3H-22:6 comprised essentially all of the label until after day 46, indicating lack of metabolic recycling of this molecule. Lipid-extracted retinal residue was devoid of radioactivity, demonstrating that protein did not contain significant covalently bound label. 3H-22:6 acylated to phospholipids in photoreceptor membranes moved apically, as evidenced by the expanding labeled region from the base of the ROS. Oil droplets in both the pigment epithelium and the cone photoreceptors labeled heavily, suggesting that 22:6 may be transiently stored. ROS tips that were phagocytosed by the pigment epithelium contained label similar in density to that of the outer segments, demonstrating that 22:6-phospholipids, at least in part, cycle through the pigment epithelial cells during visual cell renewal. In parallel experiments in frogs injected with 3H-leucine and maintained under the same experimental conditions, well-define, narrow protein bands were observed. Since the leading edge of the 3H-leucine- labeled band (rhodopsin), and that of the dense-label region of 3H-22:6 migrated at the same rate, reaching the rod tips at the same time, we suggest that the 3H-22:6-labeled phospholipids giving this profile are a unique molecular species noncovalently associated with rhodopsin.
Light-induced calcium release and re-uptake in toad rods
Authors: Fain GL , Schroder WH
Published: April 2018

Laser micromass analysis was used to investigate the effect of light on the Ca content of rod outer segments in the isolated retina and eyecup of the toad, Bufo marinus. Isolated retinas were incubated in Ringer for which most of the Ca (normally 97% 40Ca) was replaced with 44Ca, so that release of internal Ca (as 40Ca) could be distinguished from the uptake of 44Ca from the external medium. Continuous illumination produced a decline in outer segment 40Ca content. In bright light, the decrease in 40Ca was sigmoidal, beginning with a delay of at least 4 sec, reaching a maximal rate of 1–2 x 10(8) Ca/rod/sec after 8–16 sec, and declining to zero as the light-releasable pool of 40Ca was exhausted within 1–2 min. Decreases of similar magnitude and time course to those observed in isolated retina were also seen in an eyecup preparation. The rate of light-dependent release was reduced 20- to 60- fold by substitution of external Na with choline or Li. The rate of 44Ca uptake from the external medium into rods was little affected during continuous illumination. Uptake, however, was markedly increased in darkness following light exposure. This Ca re-uptake occurred at a rate approximately 2-fold greater in eyecups than in isolated retinas. We interpret our results to show that light causes an increase in the permeability or transport of Ca across the disk membrane and that the Ca is extruded from the rod via Na/Ca (or Na/Ca-K) exchange across the plasma membrane. Cessation of illumination stimulates the resequestration of Ca back into the disks, and this process is somehow enhanced by the presence of the pigment epithelium.
The role of GABAergic inhibition in processing of interaural time difference in the owl's auditory system
Authors: Fujita I , Konishi M
Published: April 2018

The barn owl uses interaural time differences (ITDs) to localize the azimuthal position of sound. ITDs are processed by an anatomically distinct pathway in the brainstem. Neuronal selectivity for ITD is generated in the nucleus laminaris (NL) and conveyed to both the anterior portion of the ventral nucleus of the lateral lemniscus (VLVa) and the central (ICc) and external (ICx) nuclei of the inferior colliculus. With tonal stimuli, neurons in all regions are found to respond maximally not only to the real ITD, but also to ITDs that differ by integer multiples of the tonal period. This phenomenon, phase ambiguity, does not occur when ICx neurons are stimulated with noise. The main aim of this study was to determine the role of GABAergic inhibition in the processing of ITDs. Selectivity for ITD is similar in the NL and VLVa and improves in the ICc and ICx. Iontophoresis of bicuculline methiodide (BMI), a selective GABAA antagonist, decreased the ITD selectivity of ICc and ICx neurons, but did not affect that of VLVa neurons. Responses of VLVa and ICc neurons to unfavorable ITDs were below the monaural response levels. BMI raised both binaural responses to unfavorable ITDs and monaural responses, though the former remained smaller than the latter. During BMI application, ICx neurons showed phase ambiguity to noise stimuli and no longer responded to a unique ITD. BMI increased the response magnitude and changed the temporal discharge patterns in the VLVa, ICc, and ICx. Iontophoretically applied GABA exerted effects opposite to those of BMI, and the effects could be antagonized with simultaneous application of BMI. These results suggest that GABAergic inhibition (1) sharpens ITD selectivity in the ICc and ICx, (2) contributes to the elimination of phase ambiguity in the ICx, and (3) controls response magnitude and temporal characteristics in the VLVa, ICc, and ICx. Through these actions, GABAergic inhibition shapes the horizontal dimension of the auditory receptive fields.
Both alpha- and beta-subunits contribute to the agonist sensitivity of neuronal nicotinic acetylcholine receptors
Authors: Luetje CW , Patrick J
Published: April 2018

A family of genes has been identified that encodes subunits of nicotinic acetylcholine receptors (nAChRs) and is expressed in the nervous system. Functional neuronal nAChRs can be expressed in Xenopus oocytes by injection of RNA encoding 1 of 2 different beta-subunits (beta 2, beta 4) in pairwise combination with RNA encoding 1 of 3 different alpha-subunits (alpha 2, alpha 3, alpha 4). We examined the sensitivity of these 6 different alpha- beta-subunit combinations to the nicotinic agonists ACh, nicotine, cytisine, and 1,1-dimethyl-4- phenylpiperazinium (DMPP). Each subunit combination displayed a distinct pattern of sensitivity to these 4 agonists. The alpha 2 beta 2 combination was 5-fold more sensitive to nicotine than to acetylcholine, while the alpha 3 beta 2 combination was 17-fold less sensitive to nicotine than to ACh, and the alpha 3 beta 4 combination was equally sensitive to both nicotine and ACh. nAChRs composed of alpha 2, alpha 3, or alpha 4 in combination with beta 2 were 14–100- fold less sensitive to cytisine than to ACh. In contrast, nAChRs composed of alpha 2, alpha 3, or alpha 4 in combination with beta 4 were 3–17-fold more sensitive to cytisine than to ACh. The alpha 2 beta 2, alpha 3 beta 2, and alpha 3 beta 4 combinations were each equally sensitive to DMPP and ACh, while the alpha 2 beta 4, alpha 4 beta 2, and alpha 4 beta 4 combinations were 4–24-fold less sensitive to DMPP than to ACh. We also demonstrated that these differences are neither a consequence of variation in the relative amounts of RNA injected nor an artifact of oocyte expression. The oocyte system can accurately express ligand-gated ion channels because mouse muscle nAChRs expressed in oocytes display pharmacological properties similar to those reported for these receptors expressed on BC3H-1 cells. We conclude that both the alpha- and the beta-subunits contribute to the pharmacological characteristics of neuronal nAChRs.
The temporal profile of 72-kDa heat-shock protein expression following global ischemia
Authors: Simon RP , Cho H , Gwinn R , Lowenstein DH
Published: April 2018

The potential role of the nonconstitutive 72-kDa heat-shock protein (HSP72) in selective neuronal vulnerability to ischemia was studied in rats subjected to graded global ischemia. Immunocytochemistry using a monoclonal antibody against HSP72 was performed on tissue collected after 24 hr of reperfusion. The appearance of HSP72 immunoreactivity correlated in a graded fashion with those regions known to be selectively vulnerable in ischemia. That is, HSP72 was induced in only hilar interneurons and CA1 pyramidal cells following brief ischemia. After intermediate durations of ischemia, HSP72 was expressed in the CA3 neurons and cortical layers 3 and 5, and after the longest intervals, HSP72 appeared in dentate granule cells. Heat-shock protein expression preceded cell death (assessed with acid fuchsin staining) in all regions. This temporal profile suggests that the capability of neurons to express HSP72 is unlikely to account for selective vulnerability of different brain regions following ischemia; its role in neuroprotection during ischemic injury in vivo remains unknown.
D2 dopamine receptor activation of potassium channels in identified rat lactotrophs: whole-cell and single-channel recording
Authors: Einhorn LC , Gregerson KA , Oxford GS
Published: April 2018

Dopamine (DA) is the major physiological regulator of prolactin secretion from the anterior pituitary, exerting a tonic inhibitory control that is mediated by D2 DA receptors. D2 receptors in both the anterior pituitary and CNS are thought to produce some of their inhibitory effects via a coupling to potassium (K+) channels to increase K+ conductance. Utilizing the reverse hemolytic plaque assay and patch-clamp techniques, we characterize the actions of DA on membrane potential and associated DA-activated whole-cell current, as well as the single K+ channels that underlie the response in primary rat lactotrophs. We demonstrate that DA (5 nM to 1 microM) or D2- selective agonists (RU24213 and quinpirole) evoke a hyperpolarization of membrane potential that was blocked by D2 antagonists and associated with an increased K+ conductance. Whole-cell current responses to ramp voltage commands revealed a DA-activated current whose reversal potential was near the calculated Nernst potential for K+, varied as a function of K+ concentration, exhibited some inward rectification, and was Ca2+ independent. The current was insensitive to tetraethylammonium (TEA; 10 mM), partially blocked by 4-aminopyridine (4-AP; 5 mM), and almost completely inhibited by quinine (100 microM). Cell-attached recordings in the presence of DA or a D2 agonist revealed the opening of a K+ channel that was not present in the absence of DA or when a D2 receptor antagonist was included with DA. Analysis of the single- channel current showed the current-voltage relationship to be linear at negative patch potentials and yielded a unitary conductance of 40.2 pS in the presence of 150 mM KCl. The channels were not blocked by TEA (10 mM), were slightly suppressed by 4-AP (5 mM), and were almost completely inhibited by quinine (100 microM). These experiments establish that in primary rat lactotrophs, DA acts at D2 receptors to activate the opening of single K+ channels, which results in an increase in K+ conductance and associated membrane hyperpolarization. This is the first characterization of single DA-activated K+ channels in an endocrine cell.
Fate of GAP-43 in ascending spinal axons of DRG neurons after peripheral nerve injury: delayed accumulation and correlation with regenerative potential
Authors: Schreyer DJ , Skene JH
Published: April 2018

Proteins characteristic of growing axons often fail to be induced or transported along axons that have been interrupted far from their cell bodies in the adult mammalian CNS. Here, we inquire whether long axons in the mammalian CNS can support efficient axonal transport and deposition of one such protein, GAP-43, when the protein is induced in neuron cell bodies. We have used immunocytochemistry to follow the fate of GAP-43 in dorsal column axons ascending the rat spinal cord from dorsal column axons ascending the rat spinal cord from dorsal root ganglion (DRG) neurons, after synthesis of the protein is induced in these cells by peripheral nerve injury. Sciatic nerve lesions do lead to an accumulation of GAP-43 in dorsal column axons derived from the lumbar DRG. However, in distal segments of these CNS axons, accumulation of GAP-43 is apparent only after a delay of 1-2 weeks, in contrast to its rapid accumulation in axon segments within the PNS environment, suggesting that deposition and stabilization of GAP-43 can be limited by local, posttranslational regulation. GAP-43 immunoreactivity subsides to control levels within 8 weeks after crush lesions that permit peripheral axon regeneration, but remains robust 8 weeks after resection lesions that prevent peripheral regeneration. Accumulation of GAP-43 in cervical dorsal column axons after peripheral nerve injury is closely correlated with the ability of these axons to respond to local cues capable of eliciting axon growth (Richardson and Verge, 1986).
The molecular and pharmacological properties of muscarinic cholinergic receptors expressed by rat sweat glands are unaltered by denervation
Authors: Grant MP , Landis SC , Siegel RE
Published: April 2018

Previous studies have indicated that denervation of adult rodent sweat glands results in the loss of secretory responsiveness to muscarinic agonists. To elucidate the molecular basis of this loss, we have characterized the muscarinic cholinergic receptor present in adult rat sweat glands and examined the effects of cholinergic denervation on its properties and expression. When homogenates of gland-rich tissue from adult animals were assayed with [N-methyl-3H]-scopolamine, a high- affinity muscarinic antagonist, the concentration of muscarinic receptors was 301 fmol/mg protein and the affinity was 131 pM. Autoradiographic analysis demonstrated that ligand binding sites were detectable only on glands. In competition studies with well- characterized muscarinic agents, the receptor exhibited typical muscarinic pharmacology. Further investigation with the selective muscarinic antagonists 4-diphenylacetoxy-N-methylpiperidine methiodide, pirenzepine, and AF DX-116 revealed that the sweat gland receptor belongs to the M2 glandular pharmacological subtype. In situ hybridization histochemistry with receptor subtype-specific oligonucleotide probes indicated that rat sweat glands express the m3 molecular receptor subtype. Seven days after sciatic nerve transection, when denervated glands were compared to those on the contralateral unoperated side, there was no significant difference either in the concentration or affinity of muscarinic binding sites or in receptor density or distribution. Furthermore, the molecular subtype and the level of its expression were unchanged. Thus, it appears that muscarinic binding sites and m3 receptor mRNA are present in denervated sweat glands that are unresponsive to muscarinic stimulation. These results suggest that the regulation of responsiveness occurs at a point distal to the expression of muscarinic receptors.
Processing of beta-amyloid precursor protein in microglia and astrocytes favors an internal localization over constitutive secretion
Authors: Haass C , Hung AY , Selkoe DJ
Published: April 2018

Microglial cells and astrocytes are closely associated with nearly all compact deposits of the amyloid beta-protein found in the senile plaques characteristic of Alzheimer's disease and trisomy 21. The biosynthesis and metabolic fate of the beta-amyloid precursor protein (beta APP) in astrocytes has not been characterized, and its identification in microglia has not been described. Here, we report the expression of beta APP by astrocytes and microglia in primary cultures of cerebral cortex from newborn rats. Using metabolic labeling followed by immunoprecipitation, we show that both astrocytes and microglia express substantial amounts of the major isoforms of beta APP. This is confirmed by PCR-mediated amplification of the corresponding mRNAs, showing that all three major transcripts (beta APP695, beta APP751, and beta APP770) are present in relatively equal amounts. Despite rapid turnover of the precursor, astrocytes and microglia show a reduced production of soluble fragments of beta APP compared to cells transfected with beta APP cDNAs. The relative amount of soluble beta APP molecules generated is both cell type and isoform specific. Immunocytochemistry reveals that full-length beta APP is located in internal membranous vesicles, with only very little insertion at the cell surface. The latter data are in agreement with the reduced ability of microglia and astrocytes to cleave the beta APP into soluble derivatives. Our findings indicate that both astrocytes and microglia strongly express all three major forms of beta APP but apparently process these molecules by an alternative pathway that generates very small amounts of soluble beta APP. The immunocytochemical localization and the biochemical data lead to the suggestion that beta APP may not function principally as a cell surface or secreted protein in vivo but may have an important intracellular function.
FMRFamide modulation of secretory machinery underlying presynaptic inhibition of synaptic transmission requires a pertussis toxin- sensitive G-protein
Authors: Haydon PG , Man-Son-Hing H , Doyle RT , Zoran M
Published: April 2018

The neuropeptide FMRFamide modulates synaptic transmission between identified neurons of the pond snail Helisoma trivolvis. FMRFamide causes a presynaptic inhibition of transmitter release by actions on ion channels and secretory machinery (Man-Son-Hing et al., 1989). The actions of FMRFamide on secretory machinery were studied using giant synapses that form between somata in culture. Using the calcium cage DM- nitrophen, synchronized, calcium-clamped release of neurotransmitter was promoted by UV photolysis. A series of UV flashes (15 msec duration) repeatedly promoted the transient synchronized release of neurotransmitter. Addition of FMRFamide reduced the magnitude of these flash-evoked inhibitory postsynaptic currents. Under conditions of synchronized transmitter release, FMRFamide modulates the secretory responsiveness to internal calcium. The release of neurotransmitter at somasoma synapses was determined to be quantal in nature. To test for the involvement of G-proteins in mediating the effects of FMRFamide on secretory machinery, the modulation of the frequency of miniature inhibitory postsynaptic currents (MIPSCs) was examined. Addition of FMRFamide reduced the frequency of MIPSCs without affecting intracellular free calcium measured with fura-2. Injection of a nonhydrolyzable analog of GTP, GTP gamma S, mimicked the effect of FMRFamide and reduced MIPSC frequency. Preinjection of the presynaptic soma with the A-protomer of pertussis toxin (PTX) prevented FMRFamide from reducing MIPSC frequency. Thus, a PTX-sensitive G-protein mediates the action of FMRFamide on secretory machinery. Similarly, preinjection of the presynaptic soma with PTX prevented FMRFamide from reducing the magnitude of action potential-evoked IPSC. Dose-response curves for the actions of FMRFamide on secretory machinery and calcium current were constructed and demonstrated that secretory machinery can be modulated at concentrations of FMRFamide (less than or equal to 10(-7) M) that do not affect calcium current magnitude. At a concentration of 10(-7) M FMRFamide, action potential-evoked synaptic transmission was reduced. Thus, synaptic transmission can be regulated by the modulation of secretory machinery, without a requirement for the modulation of ion channels.
Muscarinic agonists activate an inwardly rectifying potassium conductance in medial pontine reticular formation neurons of the rat in vitro
Authors: Gerber U , Stevens DR , McCarley RW , Greene RW
Published: April 2018

Intracellular recordings were obtained from neurons in pontine reticular formation slices of the rat to characterize a cholinergic- gated increase in conductance. The conductance increase was associated with a hyperpolarization of the membrane potential and with an outward current under voltage-clamp conditions. Current-voltage relations and potassium substitution experiments indicated mediation by a change in permeability, primarily to potassium. This potassium conductance exhibited inward rectification at membrane potentials negative to resting potential, a novel finding for cholinergic actions in CNS neurons. Further characterization of this inwardly rectifying potassium conductance revealed marked sensitivity to low concentrations of barium. Cholinergically evoked currents were relatively unaffected by the presence of extracellular cesium. Cholinergic effects persisted in TTX. The outward currents elicited by carbachol or methacholine were blocked only by high concentrations of pirenzepine, a selective antagonist of the M1 muscarinic receptor. The interaction between these agents is quantitatively consistent with cholinergic action at postsynaptic muscarinic receptors of the non-M1 subtype.