bluuebunny/crossref_metadata_2025 huggingface dataset:
Anatomy and physiology of supernumerary cercal afferents in crickets: implications for pattern formation
Authors: Murphey RK , Johnson SE , Sakaguchi DS
Published: March 2018

The afferent projection of supernumerary sensory neurons was examined in the cricket cercal sensory system. When a right cercus was exchanged for a left cercus the growth of supernumerary cerci was induced. The supernumerary cerci which formed tended to appear medial and/or lateral in a simple left leads to right exchange and were always right handed. Distal to the region where transplant and supernumerary meet, receptors on the supernumerary structure appear in a recognizable pattern typical of control cerci, and individual receptors homologous in position to control receptors could be identified. The supernumerary neurons associated with these identified receptors projected to the same area of neuropil as their homologs and thus uniquely identified neurons by all of the usual criteria were produced by the regeneration process. When the response properties of one postsynaptic neuron were examined it was shown that supernumerary afferents innervated it in a normal manner. The supernumerary neurons provide tests of various hypotheses for the assembly of ordered afferent projections. First, their axon trajectories are often atypical, but the terminal arbors grow into their proper areas in spite of this. Thus axon trajectory can be uncoupled from target area and is therefore unlikely to be a decisive factor in growth of the arbor. Second, supernumerary neurons are born later in development than their control homologs but their aroborizations are completely normal, adding to the existing evidence against a timing mechanism in the assembly of this afferent projection. Third, supernumerary neurons share target regions with their homologs, indicating a lack of competitive interactions. The most economical hypothesis to explain the precise mapping between the cercus and CNS holds that one step in the differentiation of insect sensory neurons is position dependent and that this step determines the choice of a target region within the CNS.
Three-dimensional structure of dendritic spines in the rat neostriatum
Authors: Wilson CJ , Groves PM , Kitai ST , Linder JC
Published: March 2018

Dendritic spines of rat neostriatal neurons were examined by light microscopy and high voltage stereo electron microscopy (HVEM) following selective staining by intracellular microinjection of horseradish peroxidase. Conventionally prepared material also was used for quantitative analysis of dendritic spines from serial thin sections of neostriatum. Stereo electron microscopy of semithin sections from rat neostriatum fixed using a protocol designed to preserve cytoskeletal integrity was employed to examine the organization of the dendritic spine cytoplasm. Light microscopic and HVEM examination of spiny dendrites and quantitative analysis of serial thin sections from normal material revealed no distinct spine types but rather continuous and independent variation of spine head diameter, stalk diameter, and stalk length. Likewise, there was no systematic relationship between any of these spine dimensions and dendritic diameter. Spine head membrane surface area was directly related to the area of the synaptic junctional membrane of the spine head. In semithin sections, the cytoplasm of the spine contained membranous saccules of spine apparatus and a delicate cytoskeletal network composed of microfilaments and a set of finer and more variable cytoskeletal filaments. It is proposed that this cytoskeletal network together with the spine apparatus is responsible for the maintenance and alteration of spine shape and in this way controls the effectiveness of axospinous synapses.
Hormonal control of a developing neuromuscular system. II. Sensitive periods for the androgen-induced masculinization of the rat spinal nucleus of the bulbocavernosus
Authors: Breedlove SM , Arnold AP
Published: March 2018

The spinal nucleus of the bulbocavernosus (SNB) and its target muscles are reduced or absent in normal female rats (Breedlove, S. M., and A. P. Arnold (1980) Science 210: 564–566). We now report that prenatal treatment of females with testosterone propionate (TP) significantly increases the number of SNB neurons found in adulthood. Dihydrotesterone propionate (DHTP) treatment just after but not before birth also masculinizes the number of SNB neurons in females. SNB soma size is significantly masculinized, i.e., enlarged, by administration of androgen prenatally or as late as 7 to 11 days after birth, even though this late postnatal treatment has no effect on the number of SNB cells. Following TP treatment in adulthood, the androgenized females did not display the postural correlates of male copulatory behavior more often than did control females. From these results we infer the following. (1) Androgens act both before and after birth to influence the sexually dimorphic development of the SNB system. (2) There are different sensitive periods for the masculinization of SNB neuronal number and neuronal size, indicating that these two dimorphic characteristics of the SNB are masculinized by somewhat independent mechanisms. (3) TP and DHTP may act via separate mechanisms to alter the number of SNB neurons. (4) Aromatized metabolites of testosterone are not necessary for masculinization of the SNB system. (5) Virilization of the SNB system does not ensure the masculinization of the traditionally defined measures of male copulatory behavior in rodents.
The prenatal development of the cat's retinogeniculate pathway
Authors: Shatz CJ
Published: March 2018

The prenatal development of connections between the retina and the lateral geniculate nucleus (LGN) was studied by means of the anterograde axonal transport of 3H-amino acids or horseradish peroxidase injected intraocularly in fetal cats older than embryonic day 27 (E27) and in newborn cats. (Gestation is 65 days.) A retinothalamic pathway exists as early as E28, when label can be seen in both ipsilateral and contralateral optic tracts. Afferents from the contralateral eye are the first to invade the anlage of the LGN by E32 with those from the ipsilateral eye following about 3 days later. Initially, the pattern of labeling within the nucleus is uniform, suggesting that the two sets of afferents must share a good deal of territory at early ages. By E47, however, gaps appear in the labeling pattern contralaterally, indicating that afferents from the two eyes are beginning to segregate from each other. Segregation continues so that by E54 it is possible to identify unambiguously regions of the LGN destined to comprise ipsilateral and contralateral eye layers. By birth, afferent input appears adult-like in organization, with the two sets of afferents almost completely segregated from each other into their appropriate layers. Cellular lamination of the nucleus has just commenced, however, thereby lagging the onset of afferent segregation by about 2 weeks. Prenatal development could be followed much more easily in the horizontal than in the coronal plane of section due to the finding here that the LGN is displaced approximately 90 degrees in the horizontal plane between E40 and E60. Measurements of the area occupied by the ipsilateral and contralateral afferents within the LGN indicated that even prior to segregation, the two sets of afferents are not completely intermixed within the LGN. On the contrary, those from the contralateral eye retain almost exclusive control of some territory throughout development. This detail contrasts with development in primates, in which intermixing of afferents from the two eyes is thought to be complete early on (Rakic, P. (1976) Nature 261: 467–471). Nevertheless, in the cat, as in other mammals, development of the retinogeniculate pathway is broadly characterized by an initial period of overlap followed by a period of segregation that gives rise to the adult pattern of afferent input.
Exclusive potassium dependence of the membrane potential in cultured mouse oligodendrocytes
Authors: Kettenmann H , Sonnhof U , Schachner M
Published: March 2018

Membrane potential, conductance, and intracellular potassium concentration were measured in oligodendrocytes in 3- to 10-week-old cultures of embryonic mouse spinal cord. After intracellular recording the cells were first injected with Lucifer Yellow and then stained by immunofluorescence using rhodamine-labeled monoclonal antibody 01 specific for oligodendrocyte cell surfaces. The membrane potential of these identified oligodendrocytes was in mV -66 +/- 4.3 SD; it could be reversibly reduced almost to zero by the addition of ouabain. Changes in external K+ but not Na+, Ca++, or Cl- changed the membrane potential. A 10-fold increase in extracellular potassium concentration ([K+]0) depolarized the cell by about 52 mV. This is less than the 61 mV predicted by the Nernst equation for a K+ electrode assuming a constant intracellular potassium concentration ([K+]i). However, when [K+]i was measured with an ion-selective electrode during the increase in [K+]0 it was found to rise. The Nernst equation for K+ accurately predicts the oligodendrocyte membrane potential when the increase in [K+]i is taken into account. Oligodendrocytes may be described as accurate K+ electrodes with a variable reference solution.
Cyclic adenosine 3':5'-monophosphate phosphodiesterase and its role in learning in Drosophila
Authors: Shotwell SL
Published: March 2018

Drosophila carrying the X-linked mutation dunce (dnc) showed poor learning in a negative reinforcement olfactory conditioning paradigm (Dudai, Y., Y.-N. Jan, D. Byers, W.G. Quinn, and S. Benzer (1976) Proc. Natl. Acad. Sci. U.S.A. 73: 1684–1688). More recently, dnc flies were shown to have reduced activity for one of two cAMP phosphodiesterases (PDEs) present in normal flies, PDE II, whereas PDE form I was unaffected (Byers, D., R. L. Davis, and J. A. Kiger, Jr. (1981) Nature 289: 79–81). A micro-assay technique is described that allows the separate measurement of PDE I and PDE II in crude extracts, based on specific inhibition of PDE I [3H]cAMP hydrolysis by cGMP. Using this technique, PDE II is shown to occur normally at high specific activity in the nervous system, consistent with the hypothesis that this enzyme plays a role in neuronal function. Reduced PDE II activity correlates with poor learning in dnc flies at three developmental stages (first and third instar larva and adult), as well as in response to genetic modification of dnc gene activity. Biochemical and genetic experiments fail to reveal any abnormal regulation of PDE II in dnc. The specific activity of PDE II is shown to correlate in a one to one fashion with the level of normal dnc gene (dnc+) activity at five different doses of dnc+. These results support the hypothesis that PDE II represents the primary product of the dnc gene, indicating a role for this enzyme in Drosophila learning.
Effects of neonatal capsaicin treatment on nociceptive thresholds in the rat
Authors: Nagy JI , van der Kooy D
Published: March 2018

The responsiveness to noxious thermal, mechanical, and chemical stimuli was examined in adult rats that had been treated neonatally with capsaicin. A range of capsaicin doses was employed to determine whether the neurotoxicity of capsaicin to primary afferent fibers would be manifested behaviorally in a selective effect on nociceptive thresholds to specific stimuli. Animals were given 5 to 100 mg/kg of capsaicin at 2 days of age and were examined 2 to 4 months later using the tail flick and hot plate tests to determine thermal thresholds, the paw pressure test to determine mechanical thresholds, and the formalin test to determine chemical thresholds. Significant impairments of treated animals' responses to all three types of stimuli were found at high doses of capsaicin and at doses which seem to lead to the depletion of only unmyelinated primary afferent fibers. Slightly higher doses of capsaicin were required to increase thermal nociceptive thresholds in the tail flick test as compared with the other tests, and mechanical nociception seemed to be the most sensitive to the effects of capsaicin. At any particular dose of capsaicin, considerable variability was found in the responsiveness of animals to noxious stimuli. This may partly explain the inconsistencies in studies of nociceptive thresholds in capsaicin-treated animals. The results also demonstrate the difficulty of correlating the degree of analgesia exhibited by these animals with the extent of loss of primary afferent fibers or with the depletion of afferent putative peptide transmitters.
Fast axonal transport in permeabilized lobster giant axons is inhibited by vanadate
Authors: Forman DS , Brown KJ , Livengood DR
Published: March 2018

We have developed a method for permeabilizing axons and reactivating the fast transport of microscopically visible organelles. Saltatory movements of organelles in motor axons isolated from lobster walking legs were observed using Nomarski optics and time-lapse video microscopy. In the center of the axon most of the particles and mitochondria moved in the retrograde direction, but immediately below the axolemma the majority moved in the anterograde direction. When axons were permeabilized with 0.02% saponin in an adenosine 5′- triphosphate (ATP)-free “internal” medium, all organelle movement ceased. Saltatory movements resembling those in intact axons immediately reappeared upon the addition of MgATP. Very slight movement could be detected with ATP concentrations as low as 10 microM, and movement appeared to be maximal with 1 to 5 mM ATP. Vanadate, which does not affect axonal transport in intact axons, inhibited the reactivated organelle movements in permeabilized axons. Movement was rapidly and reversibly inhibited by 50 to 100 microM sodium orthovanadate. The effects of vanadate, including the time course of inhibition, its reversibility, and its concentration dependence, are consistent with the hypothesis that a dyneinlike like molecule may play a role in the mechanism of fast axonal transport.
Complex somatosensory receptive fields of cells in the deep laminae of the hamster's superior colliculus
Authors: Rhoades RW , Mooney RD , Jacquin MF
Published: March 2018

Responses to separate and simultaneous application of noxious and innocuous tactile stimuli were examined for neurons recorded from the deep layers of the hamster's superior colliculus. Forty-four percent of the units isolated were responsive only to innocuous, primarily cutaneous, stimuli; 10% were activated only by noxious stimulation; and 15% were characterized as having a wide dynamic range. The remaining 31% of the somatosensory cells recorded had complex receptive field properties which have not heretofore been described for tectal neurons in any species. Ten percent of all somatosensory cells had no excitatory receptive fields, but their spontaneous discharges could be suppressed by low threshold and/or noxious stimulation of discrete portions of the body. In 18% of the units which we recorded, innocuous and noxious stimuli had opposing effects upon cellular activity. Most of these neurons had small receptive fields in which innocuous tactile stimuli yielded excitation and larger fields, often including most of the body surface, where noxious stimulation suppressed both spontaneous activity and the responses normally elicited by appropriate tactile stimulation. Finally, a very small number of units (3% of all somatosensory cells recorded) had multiple receptive fields in which low threshold stimulation produced opposing effects on spontaneous activity. Somatosensory units were recorded in all of the deep laminae, but cells with complex response characteristics were isolated primarily in stratum griseum profundum.
Corticotropin-releasing factor immunoreactivity is widely distributed within the central nervous system of the rat: an immunohistochemical study
Authors: Cummings S , Elde R , Ells J , Lindall A
Published: March 2018

The discovery of a 41-amino acid peptide with potent corticotropin- releasing factor properties has prompted a search for neurons that contain this substance and potentially utilize it in intercellular communication. The present study utilized immunohistochemical methods and an antiserum directed against a synthetic replica of ovine corticotropin-releasing factor. The rat hypothalamus was found to contain striking immunoreactive groups of neuronal perikarya within the paraventricular, periventricular, and anterior hypothalamic nuclei, some of which are likely to project to the external layer of the median eminence and thereby comprise a hypophysiotropic system. Certain other hypothalamic nuclei, as well as many other regions of the central nervous system, were found to contain corticotropin-releasing factor- immunoreactive neurons. Among the most prominent of these were neurons in the bed nucleus of stria terminalis, the central nucleus of the amygdala, the region of the dorsal raphe, locus ceruleus, the external cuneate nucleus, and the medullary reticular formation. Thus, corticotropin-releasing factor, like many other neurohormones and peptides, may participate in neuroendocrine regulation as well as play a role as a neurotransmitter-like substance in numerous extrahypothalamic circuits.
Muscle activity and the loss of electrical coupling between striated muscle cells in Xenopus embryos
Authors: Armstrong DL , Turin L , Warner AE
Published: March 2018

The gap junctions between embryonic striated muscle cells are lost during development. The time course of their elimination has been examined with electrophysiological techniques in myotomes of Xenopus laevis embryos. Gap junctions were detected by the passage of electronic current or the fluorescent dye, Lucifer Yellow, from one muscle cell to another. These tracers only spread to neighboring cells when injected intracellularly. All the muscle cells are electrically coupled at stage 24 when neuromuscular transmission begins, but normally many cells become uncoupled during the next 48 hr. In contrast, the muscle cells remain electrically coupled if neuromuscular transmission is blocked during that period with tricaine or alpha- bungarotoxin. When muscle activity recovers, the loss of coupling resumes. Once the coupling has disappeared, neuromuscular blockade does not restore it. Muscle contraction is blocked during development in a mutant of Xenopus, even though the muscle cells remain electrically excitable. After stage 32 in these immobile embryos, the muscle cells are stimulated repeatedly by regular bursts of neural activity. Although they never contract, the mutant muscle cells become uncoupled at the same time as the muscle cells in normal embryos. The results suggest that some consequence of repeated cholinergic activation, other than contraction, stimulates the loss of gap junctions between striated muscle cells during development. The elimination of gap junctions may be required for neural control of subsequent muscle differentiation.
Postsynaptic effects of magnesium and calcium at the mouse neuromuscular junction
Authors: McLarnon JG , Quastel DM
Published: March 2018

The effects of elevated magnesium and calcium concentrations on height and time course of miniature endplate currents (MEPCs) at the mouse neuromuscular junction were studied. With both ions, MEPC height was decreased; the rate of decay of MEPCs was reduced in high magnesium and was unchanged in high calcium. Raised Mg2+ or Ca2+ both acted to modify the effects on MEPC time course of procaine, scopolamine, atropine, lidocaine, and quinidine, all of which act to cause biphasic decay of MEPCs in a manner consistent with reversible “plugging” of endplate channels, with rate constants for blocking and unblocking that are sensitive to postsynaptic transmembrane potential. Both the blocking and unblocking rate constants were decreased by increasing divalent ion concentration. No such reduction of rate constants was observed using menthol or pentobarbital, which appear to block channels in a voltage- independent manner. It is concluded that the divalent ions act to alter the channel environment via interactions with charged groups in or near the endplate channels.
The role of excitatory amino acid transmitters in the mudpuppy retina: an analysis with kainic acid and N-methyl aspartate
Authors: Slaughter MM , Miller RF
Published: March 2018

A variety of glutamate and aspartate analogues were used to characterize the excitatory amino acid receptors in the mudpuppy retina. This approach revealed two general classes of receptors which were represented by the agonists kainic acid and N-methyl aspartic acid. Kainic acid was found to be a potent photoreceptor transmitter agonist on all three types of second-order neurons, and it was a powerful excitant of amacrine and ganglion cells. N-Methyl aspartate had little effect in the outer retina, but it had potent stimulatory effects on inner retinal neurons. N-Methyl aspartate antagonists selectively blocked light responses in some sustained OFF ganglion cells. These results suggest that both photoreceptors and bipolar neurons may use glutamate Or an analogue, whereas aspartate may be utilized by a class of sustained ON amacrine cells.
Dopamine elicits feeding motor program in Limax maximus
Authors: Wieland SJ , Gelperin A
Published: March 2018

A neural system within the cerebral and buccal ganglia of the terrestrial mollusc Limax maximus responds to lip chemostimulation by emitting a feeding motor program (FMP) in vivo and in vitro. We have analyzed chemically the cerebral and buccal ganglia of Limax for neurotransmitters involved in controlling expression of FMP. Dopamine was found in clusters of cells in and the neuropil of the cerebral ganglia at a concentration of 62 pmol/ganglion; a large proportion of such dopamine-containing cells projected to the lips. The buccal ganglia contained several small dopaminergic cells and large amounts of dopamine in the neuropil; the measured concentration was 10 pmol/ganglion. Exogenous dopamine applied to the cerebral and buccal ganglia in vitro between 10(-7) M and 3 X 10(-6) M excited an autoactive salivary duct motor neuron (FB) and inhibited an autoactive secretomotor neuron (BSN). Concentrations of dopamine between 3 X 10(- 6) M and 3 X 10(-5) M triggered FMP output, with an increased probability of triggering at higher concentrations of dopamine. ADTN and SK&F38393 were potent agonists in this system, whereas ergonovine was the only potent antagonist found; none of the neuroleptics tested was effective. Thus, the Limax system shows agonist responses similar to the vertebrate D1 receptors, but its antagonist-binding properties appear to have requirements quite different from vertebrate receptors. The effects of exogenous serotonin differed from dopamine's effects; serotonin excited BSN and several buccal motor neurons, could not elicit synchronized motor program cycling, and was not efficiently blocked by ergonovine. These data suggest that dopamine is a good candidate as an endogenous triggering and sustaining transmitter for the Limax feeding motor program.
The expression of antigens by embryonic neurons and glia in segmental ganglia of the leech Haemopis marmorata
Authors: Macagno ER , Stewart RR , Zipser B
Published: March 2018

Monoclonal antibodies (mAbs) raised against adult leech nervous systems were screened on embryos of the leech Haemopis marmorata in order to determine when in development specific antigens are first expressed and the order in which they are expressed by different cells or tissues. Three of the mAbs produced by Zipser and McKay (Zipser, B., and R. McKay (1981) Nature 289: 549-554) were screened: Lan3-1, Lan3-5, and Lan3-6. Each mAb shows a different pattern of labeling in the adult leech nerve cord (Zipser, B. (1982) J. Neurosci. 2: 1453–1464). The embryonic stages studied were from 5 days after egg deposition to 30 days (emergence from the cocoon). The pattern of labeling was assayed in whole mounts using horseradish peroxidase-conjugated second antibodies. The principal results are as follows. (1) Antigens recognized by Lan3-5 are first expressed by the glia of the roots of the anterior segmental ganglia at 6 to 7 days, several days later by the interganglionic connective glia, and near the end of embryonic development by ganglionic neurons. An anterior to posterior temporal gradient is observed in the expression of these antigens. In addition, Lan3-5 also labels the protonephridia and nephridia from early development onward. (2) Antigens recognized by Lan3-6 are first expressed by a pair of neurons in each segmental ganglion and later in development by additional neurons. By the time of emergence, however, only about half of the neurons that label in the adult have done so, implying that some neurons express these antigens postembryonically. Labeling with Lan3-6 is first seen in neuronal somata and only later in neuronal processes. (3) Antigens recognized by Lan3-1 and expressed by segmentally specific neurons in ganglia 5 and 6 are not detectable during embryonic development, but are so at early postembryonic stages. Thus, these three mAbs provide an approach to study different aspects of the development of the leech nervous system, specifically the relation between glial and neuronal differentiation and the genesis of segmentally specific phenotypes.
Expression of the capacity to release [3H]norepinephrine by neural crest cultures
Authors: Maxwell GD , Sietz PD
Published: March 2018

Cultures of trunk neural crest cells from quail embryos were tested for their ability to release [3H]norepinephrine [( 3H]NE) in response to depolarization. After 7 days in vitro, exposure of the cultures to either the alkaloid veratridine or 40 mM K+ results in the evoked release of [3H]NE. The release evoked by veratridine is blocked in the presence of tetrodotoxin. The release evoked by increased K+ is blocked by the calcium antagonist cobalt. Release in response to the nicotinic cholinergic agonist 1,1-dimethyl-4-phenylpiperazine was also observed. The amount of evoked release is highly correlated with the number of histochemically demonstrable catecholamine-containing cells in a given culture. Autoradiography reveals that the radioactivity taken up by these cultures is located in a subpopulation of cells whose morphology resembles that of the histochemically detectable catecholamine- containing cell population. Whereas capacity for the release of [3H] NE is readily detectable after 7 days in vitro, it is detectable only with difficulty after 4 days in vitro. There is a greater than 6-fold increase in uptake capacity over the period of 4 to 7 days in vitro. These results demonstrate that neural crest cultures grown without their normal synaptic inputs or targets can exhibit the capacity for stimulus secretion coupling characteristic of synaptic neurotransmitter release.
Sprouting and regeneration of sensory axons after destruction of ensheathing glial cells in the leech central nervous system
Authors: Elliott EJ , Muller KJ
Published: March 2018

To test the importance of glia during regeneration of mechanosensory neuron axons in the leech central nervous system, individual glial cells that ensheathed the axons were destroyed by intracellular protease injection. Recordings with intracellular microelectrodes showed that glial-desheathed axons re-established synaptic connections with their appropriate target cell, a motor neuron, as frequently and as selectively as control, glial-ensheathed axons. Intracellular staining with horseradish peroxidase showed that desheathed regenerating axons sprouted more than controls, and loss of the glial cell in some cases caused uninjured (intact) axons to sprout. Successful, accurate regeneration could occur whether axons grew along normal or along aberrant pathways. The distal stumps of some sensory axons severed from cell bodies and maintained in organ culture survived without their glial sheath for up to 3 weeks. These experiments show that, although loss of the glial cell affects sensory axon growth, the glial cell is not required for accurate axonal regeneration in the leech central nervous system.
Concentration dependence of rapid axonal transport: a study of the transport kinetics of [35S]methionine-labeled protein in postganglionic sympathetic fibers of the bullfrog
Authors: Litchy WJ , Brimijoin S
Published: March 2018

The kinetics of transport of radiolabeled proteins in sympathetic axons of the bullfrog sciatic nerve were examined after injection of [35S]methionine into the S9 sympathetic ganglion. Under resting conditions at 20 degrees C, the fastest moving material was carried distally at 5.7 +/- 0.3 mm/hr. Various manipulations of temperature in the proximal part of the nerve were used to alter the amount of protein transported into the distal region, which was always kept at 20 degrees C. The velocity in this test region was found to increase to over 9 mm/hr when material that had accumulated at a cold block for 4 hr was released by rewarming. This acceleration was transient, and base line velocity was regained after 2 hr. In order to increase the local concentration of transported protein by a second method, the proximal part of several nerves was warmed to 28 degrees C. Maximal transport velocity in the 20 degrees C test region rose to 6.2 +/- 0.12 mm/hr. To decrease the local concentration of transported protein, the proximal part of other nerves was cooled to 15 degrees C. Maximal transport velocity in the 20 degrees C test region fell to 4.7 +/- 0.7 mm/hr. We conclude that there is a small but real tendency for the velocity of rapid axonal transport in this neural system to be positively related to the availability of material suitable for transport.
Synaptic plasticity within the interpeduncular nucleus after unilateral lesions of the habenula in neonatal rats
Authors: Hamill GS , Lenn NJ
Published: March 2018

In rats, synaptic terminations of the medial habenular (MH) afferents to the interpeduncular nucleus (IPN) are just beginning to form at the time of birth. The alterations in synaptogenesis resulting from unilateral MH lesions placed in neonatal rats were demonstrated with the autoradiographic and degeneration methods after the operated animals had reached maturity. The distribution of S synapses, en passant MH afferents to the central IPN, is normally 95% ipsilateral to their MH of origin in spite of the fact that their axons cross through the contralateral half of the IPN one or more times. The lesions result in a symmetrical distribution of S synapses from the remaining MH. The density of this projection on each side is equal to the normal ipsilateral density of termination. Crest synapses, present in intermediolateral IPN bilaterally, consist of two endings which contact a narrow dendritic process. Normally, the two endings arise one from each MH at 90% of crest synapses, and two from the same MH at 10%. After unilateral MH lesions in neonates, approximately 96% of crest synapses are formed by two axons from the one remaining MH. At only 4% of crest synapses one or both processes is heterologous, that is, of non-MH origin. These findings demonstrate that synapse formation on IPN neurons preferentially favors MH afferents, both normally and when left- right interaction is precluded by a neonatal unilateral lesion. Left- right interactions normally occur at both the level of the left and right sides of the IPN with regard to S synapses and individual left and right habenular afferents at crest synapses. Plasticity at crest synapses is considerably greater in neonates compared to adult rats. Control of these phenomena can be understood as the interaction of multiple factors. These may include specific determinants localized to the presynaptic axons, particularly prior to synaptogenesis and competition for synaptic space, especially with regard to S synapses and perhaps involving synapse elimination. There is also evidence for postsynaptic determinants both in the separation of synaptic types into separate subnuclei and in the formation of crest synapses in the IPN regardless of the presence of normal or reduced numbers of MH afferents, or their total absence.
Preferential immunohistochemical localization of vasoactive intestinal polypeptide (VIP) in the sacral spinal cord of the cat: light and electron microscopic observations
Authors: Honda CN , Rethelyi M , Petrusz P
Published: March 2018

In the present study we have employed immunoperoxidase techniques to investigate the distribution of vasoactive intestinal polypeptide (VIP)- like immunoreactivity in the spinal cord and sensory ganglia of the cat. The spinal distribution of VIP-containing neuronal processes was also compared with that of substance P (SP), somatostatin (SOM), and cholecystokinin-8 (CCK) at lumbar, sacral, and coccygeal levels. At sacral levels, VIP was found to be contained in small and medium-sized primary sensory neurons and in dorsal rootlets. Deafferentation, by either ganglionectomy or dorsal rhizotomy, resulted in a nearly complete loss of VIP immunoreactivity in the spinal cord. The spinal distribution of VIP fibers and terminals was most dense and extensive in sacral segments. Forming a thin shell around the dorsal horn, collaterals, apparently originating from Lissauer's tract, projected either medially or laterally through lamina I. Laterally, many VIP axons terminated in lateral laminae V to VII. Others projected further through the neck of the dorsal horn to medial lamina V and the gray matter near the central canal. Medially, VIP axons descended through lamina I to expand into terminal fields in the posterior commissure and medial lamina V. At the ultrastructural level, VIP-like immunoreactivity was found in dense core vesicles within axonal enlargements containing both large dense core and smaller clear round vesicles. Synaptic connections were infrequently observed but, when encountered, were of the simple axodendritic type. The spinal distribution of VIP-containing fibers was remarkably similar to that reported for pelvic nerve visceral afferents, both in termination patterns within the spinal gray matter and in localization to the sacral cord. The density of SP-, SOM-, and CCK-containing fibers and terminals was constant at all levels examined (L4 to Co4). In marked contrast, the distribution of VIP fibers, much like that of pelvic nerve afferents, was mostly confined to sacral segments. Thus, although SP, SOM, and CCK may be contained within a population of sacral visceral afferents, they must be common to afferent systems in other segments as well. VIP, however, appears to be preferentially contained within pelvic visceral afferent fibers confined mostly to sacral segments.
Calcium entry causes a prolonged refractory period in peptidergic neurons of Aplysia
Authors: Kaczmarek LK , Kauer JA
Published: March 2018

A brief train of electrical stimuli to the pleuroabdominal connective of Aplysia produces a cumulative depolarization in the peptidergic bag cell neurons within the abdominal ganglion. This response is followed by an afterdischarge which lasts for about 30 min, and then by a prolonged refractory period lasting for several hours. During the refractory period the cumulative depolarization in response to stimulation is attenuated, and stimulation either fails to initiate afterdischarges or produces discharges of much shorter duration. We have used the cationophore X537A to test the hypothesis that the prolonged refractory period is caused by calcium entry into the bag cell neurons during the afterdischarge. Exposure of intact bag cell clusters to X537A at concentrations from 1 to 10 microM for a period of 20 min in calcium-containing media produced no change in their resting potentials or in their ability to generate action potentials, but induced a state resembling natural refractoriness in response to subsequent stimulation. Both natural refractoriness and that induced by X537A could be overcome by extracellular tetraethylammonium ions (90 mM). Dose response data showed that concentrations of ionophore of 2.5 to 5.0 microM produce an attenuation of afterdischarge that is similar to that following a stimulated afterdischarge. These concentrations of X537A also produced an enhancement of 3H-labeled peptide release from these cells that is comparable to that observed on stimulation of an afterdischarge. Moreover, the time course of recovery from exposure to 5.0 microM X537A parallels that of natural refractoriness, recovery being essentially complete about 20 hr after X537A exposure or stimulation. The ionophore did not affect the mean duration of afterdischarge when applied in calcium-deficient media. The electrical effects of X537A were investigated using isolated bag cell neurons in cell culture. After treatment with the adenylate cyclase activator, forskolin, and theophylline, such isolated cells show many of the electrical changes occurring in intact bag cell clusters at the onset of afterdischarge, including the enhancement of action potentials, as well as increased input resistance and the emergence of oscillations in membrane potential. None of these parameters was significantly affected by concentrations of ionophore that induce refractoriness. In response to repetitive intracellular stimulation, however, some forskolin- treated cells undergo a cumulative depolarization which is similar to that seen at the onset of afterdischarge in intact clusters. This cumulative depolarization was found to be attenuated or abolished by 5.0 microM X537A.(ABSTRACT TRUNCATED AT 400 WORDS)
Immunochemical properties and cytochemical localization of the voltage- sensitive sodium channel from the electroplax of the eel (Electrophorus electricus)
Authors: Fritz LC , Brockes JP
Published: March 2018

Immunochemical methods have been used to investigate questions concerning the relatedness of sodium channels from different sources and their distribution in the eel electroplax. The reagents employed were two monoclonal antibodies, 5D10 (Moore, H. -P. H., L. C. Fritz, M. A. Raftery, and J. P. Brockes (1982) Proc. Natl. Acad. Sci. U.S.A. 79: 1673–1677) and 5F3, and a rabbit antiserum; all three were directed against determinants present on the 250,000-dalton component of the eel sodium channel. In quantitative adsorption assays, the three reagents were effectively adsorbed by eel electroplax membranes but not by brain membranes from rat, frog, or chick. The rabbit antiserum bound to immobilized membranes of rat brain at a level only approximately 0.1% of that seen with electroplax membranes. The reactivity of the three reagents with the eel electroplax was further investigated by indirect immunofluorescence on frozen sections. Whereas 5D10 showed no detectable reactivity, the rabbit antiserum and, especially, 5F3 stained the electrically excitable caudal face of the electrocytes but not the inexcitable rostral face. The reactivity of 5F3 was examined in greater detail and showed occasional abrupt discontinuities where the membrane was not stained. The presence of positive 5F3 immunoreactivity appeared to be correlated with extracellular filamentous material.
Differential regulation of acetylcholine sensitivity and alpha- bungarotoxin-binding sites on ciliary ganglion neurons in cell culture
Authors: Smith MA , Margiotta JF , Berg DK
Published: March 2018

Levels of acetylcholine (ACh) sensitivity and numbers of alpha- bungarotoxin (alpha-Bgt)-binding sites have been measured for chick ciliary ganglion neurons grown in cell culture under various conditions. The two properties were found not to change in parallel. Neurons maintained in culture medium supplemented with embryonic eye extract developed high levels of ACh sensitivity and low numbers of alpha-Bgt-binding sites, whereas neurons grown in medium containing elevated K+ concentrations displayed the reverse. Neurons from media containing both eye extract and elevated K+ concentrations had both low levels of sensitivity and low numbers of toxin sites. The growth conditions do not alter the basic binding properties of the ACh receptors and alpha-Bgt-binding sites. Both the ACh receptor dose- response characteristics and the pharmacological properties of the toxin-binding sites were similar for neurons grown in media containing eye extract or elevated K+ concentrations. The inhibitory effects of eye extract on development of alpha-Bgt-binding sites appeared to be specific: eye extract had previously been shown to stimulate neuronal growth and cholinergic development, and in the present study eye extract enhanced development of ACh sensitivity and had no effect on mechanisms responsible for binding and accumulation of tetanus toxin. Eye extract did not block alpha-Bgt binding in competition binding experiments and did not cause redistribution of toxin sites away from the neuronal soma. These results demonstrate that ACh sensitivity and alpha-Bgt-binding sites can be independently regulated on the neurons and suggest that the two membrane properties are associated with separate membrane components.
Neurite regeneration by Aplysia neurons in dissociated cell culture: modulation by Aplysia hemolymph and the presence of the initial axonal segment
Authors: Schacher S , Proshansky E
Published: March 2018

Neurons from the abdominal ganglion of the mollusc Aplysia californica regenerate neurite processes in dissociated cell culture. Both the nature of neurite outgrowth and the morphology of the cells are influenced by the presence of adult Aplysia hemolymph in the growth medium and the presence of a portion of a cell's original axonal process. Aplysia hemolymph enhances cell survival, the initiation of neurite outgrowth from multiple sites on the cell body surface, the linear growth of the processes, and the amount of branching by those processes. Hemolymph also decreases the diameter of the outgrowing neurite fascicles and the diameter of the individual neurites within the fascicles. The presence of a cell's original axon reduces the time required for the initiation of neurite outgrowth and restricts the formation of multipolar processes. In addition, the presence of an initial axonal segment is essential for neurite regeneration from large adult neurons.
Biochemical properties of the nerve growth factor-inducible large external (NILE) glycoprotein
Authors: Salton SR , Shelanski ML , Greene LA
Published: March 2018

In the presence of nerve growth factor (NGF), PC12 pheochromocytoma cells undergo neuronal differentiation with a concomitant 3- to 5-fold increase in the specific level of an Mr = 230,000 cell surface component named the NGF-inducible large external, or NILE, glycoprotein. Antisera raised against NILE glycoprotein (NILE GP) purified from PC12 cells have been found to recognize most, if not all, neurons derived from the peripheral and central nervous systems. In the current studies several of the biochemical properties of NILE GP were investigated. NILE GP was found to be phosphorylated in NGF-treated and -untreated PC12 cells and in cultured rat sympathetic neurons. The phosphate moiety of NILE GP is almost completely alkali labile, suggesting that phosphoserine groups predominate. Immunoprecipitation experiments revealed that incorporation of [32P]phosphate into NILE GP relative to total PC12 cell phosphoprotein was not significantly altered at 12 and 24 hr of NGF treatment but was enhanced 3-fold after 7 days and up to 5-fold after 2 to 3 weeks of NGF exposure. These changes in phosphorylated NILE GP paralleled, and therefore appeared to be mainly a consequence of, the NGF-induced increase in total cellular levels of NILE GP. By two-dimensional gel analysis, anti-NILE GP selectively immunoprecipitated two NGF-inducible spots (apparent Mr = 230,000; pI = 6.4 to 6.6) from PC12 cells labeled with either [3H] fucose, [35S]methionine, or [32P]phosphate. Anti-NILE GP immunoprecipitated a single band (apparent Mr = 205,000) from extracts of rat brain labeled with [3H] glucosamine. This confirms the previously established apparent molecular weight difference between central and peripheral NILE GP cross-reactive material. When PC12 cells, cerebellar cultures, and cultured cerebral cortex were treated with tunicamycin and labeled with [35S]methionine, nonglycosylated bands each with Mr = 160,000 were immunoprecipitated, implying that the differences in the mobilities on sodium dodecyl sulfate gels of cross- reactive NILE GP from different tissues is due to variation in glycosylation rather than to large differences in apoprotein structure. Prolonged treatment of PC12 cells with trypsin produced an immunoreactive fragment of NILE GP of apparent Mr = 28,000 that was phosphorylated but not glycosylated, and that remained in the membrane. NILE GP remained predominantly membrane associated under a variety of aqueous extraction conditions, suggesting that it is an integral membrane protein.
Activators of cyclic adenosine 3':5'-monophosphate accumulation in rat hippocampal slices: action of vasoactive intestinal peptide (VIP)
Authors: Etgen AM , Browning ET
Published: March 2018

The present experiments tested the ability of putative neurotransmitters and neuromodulators to regulate cyclic adenosine 3′:5′-monophosphate (cAMP) levels in rat hippocampal slices. Slices from ovariectomized adult female rats were equilibrated for 1 hr and incubated for 20 min with various test compounds, and cAMP was extracted and quantified using a competitive protein-binding assay. Norepinephrine, adenosine, histamine, and prostaglandins E1 and E2 alpha, induced moderate (1.5- to 5-fold) increases in cellular cAMP, whereas dopamine, serotonin, prostaglandin F2 alpha, and glutamate were relatively ineffective. Most striking was the observation that vasoactive intestinal peptide (VIP) produced marked elevation (approximately 80-fold at 6 microM) of hippocampal slice cAMP content. In contrast, other peptides produced only 2-fold increased (glucagon, somatostatin) or no change in cellular cAMP levels (enkephalins, LHRH, ACTH analogue, arginine vasopressin). Significant elevations in cAMP were seen with VIP concentrations as low as 20 nM; the cAMP response was half-maximal at 1 microM VIP and maximized between 10 and 20 microM. At maximally effective concentrations, VIP was 86% as effective in increasing cAMP as maximal concentrations of forskolin, a compound which activates adenylate cyclase in most cell types. The cAMP response to 10 microM VIP was pronounced after a 1-min incubation (16-fold elevations) and was maximal at 30 min (140-fold elevation). When slices from other brain areas were compared, it was found that regions known to contain high levels of VIP (cerebral cortex) also responded to VIP treatment with 30- to 50-fold elevations in cAMP.(ABSTRACT TRUNCATED AT 400 WORDS)
Size, shape, and solubility of a class of releasable cell surface proteins of sympathetic neurons
Authors: Sweadner KJ
Published: March 2018

Exposed on the cell surface of sympathetic neurons in culture is a family of high molecular weight glycoproteins (B1, B2, B3, and B4, related to the NILE protein) which undergoes post-translational modification (Sweadner, K. J. (1983) J. Neurosci. 3: 2504–2517). B1 and B3 are converted to B2 and B4 by what might be limited proteolysis. These proteins normally require detergents to release them from the cells. When neurotransmitter release is evoked chemically, however, derivatives of the proteins (S2 and S4) are released into the medium. A hydrodynamic analysis of the structure of the released proteins and their membrane-associated precursors was undertaken to determine whether the proteins are released as membrane fragments, aggregates, or monomers in solution, and to give information on the structure and disposition of the proteins on the cell surface. Measurements of the Stokes radii, sedimentation coefficients, partial specific volumes, and frictional coefficients of the proteins indicate that they are released into the medium as soluble monomers. The hydrodynamic analysis also indicates that they are nonglobular (probably fibrous) in shape, both before and after post-translational modification and release. Their true molecular weights are calculated to be approximately 130,000 to 170,000. Although B1, B2, B3, and B4 are probably intrinsic membrane proteins, their releasability suggests that most of their mass is exposed to the aqueous extracellular medium.