bluuebunny/crossref_metadata_2025 huggingface dataset:
The neural signal for skin indentation depth. II. Steady indentations
Authors: Mei J , Tuckett RP , Poulos DA , Horch KW , Wei JY , Burgess PR
Published: March 2018

The glabrous skin of the monkey's hand was stimulated with a waveform that indented the skin at a rate of 0.4 mm/sec, held the skin steadily or nearly steadily indented for 12 sec or longer, and then retracted back to the starting position. Recordings were made of activity in single afferent fibers in response to these stimuli. The average discharge frequency of 21 slowly adapting mechanoreceptors declined 38% during the first 12 sec of a steady indentation when the amplitude of the displacement was 0.65 mm and 36% when the displacement was 1.3 mm. When the plateau was not steady but the indentation depth gradually decreased by 15% during the 12-sec plateau period, the average decline was 47% for the 0.65-mm indentation and 46% for the 1.3-mm stimulus. When the indentation depth gradually increased by 15% during the 12-sec plateau, the discharge declined an average of 26% during the 0.65-mm indentation and 22% during the 1.3-mm displacement. To determine the effect of receptor adaptation on the perception of skin indentation depth, 13 human subjects had the skin of their fingertips indented 1 mm with similar trapezoidal waveform and were asked whether the indentation depth increased or decreased during the plateau portion of the stimulus. Ten of the 13 subjects thought that the indentation depth was increasing when the plateau was steady. The method of limits was then used to determine how much the stimulus had to change for the subject to feel the depth during the plateau as unchanging; i.e., a “perceptual zero.”(ABSTRACT TRUNCATED AT 250 WORDS)
Acetylcholine receptor clustering in rat myotubes: requirement for CA2+ and effects of drugs which depolymerize microtubules
Authors: Bloch RJ
Published: March 2018

The acetylcholine receptor (AChR) clusters which form in the plasma membranes of cultured rat myotubes disappear when the myotubes are exposed to medium depleted of Ca2+. This loss of receptor clusters is reversible and depends both on extracellular Ca2+ concentrations and on temperature. Other divalent cations (Mg2+, Ba2+, Sr2+, Co2+, Mn2+) do not maintain receptor clusters when Ca2+ is absent. Extracellular Na+, which promotes Ca2+ efflux from myotube cultures, is necessary for cluster loss to occur in Ca2+-depleted medium. Experiments using colchicine and other drugs which depolymerize microtubules suggest that the cytoskeleton is involved in AChR clustering. At submicromolar concentrations, these drugs afford partial protection against cluster loss caused by Ca2+ depletion. Colchicine also alters the organization of vinculin in the vicinity of AChR clusters. It is concluded that receptor clustering probably depends on intracellular Ca2+ and on a structure or mechanism indirectly affected by colchicine.
Regional innervation of rabbit ciliary ganglion cells by the terminals of preganglionic axons
Authors: Forehand CJ , Purves D
Published: March 2018

In the rabbit, ciliary ganglion neurons with dendrites maintain inputs from several different axons during the period of synaptic rearrangement that occurs in early postnatal life. Neurons without dendrites, on the other hand, lose the majority of their initial inputs and are innervated in maturity by the terminals of only one or two axons (Purves, D., and R.I. Hume (1981) J. Neurosci. 1: 441–452; Hume, R.I., and D. Purves (1981) Nature 293: 469–471). We have explored the basis of this phenomenon by individually marking preganglionic axons and the neurons they innervate with horseradish peroxidase. In general, the innervation of geometrically complex (multiply innervated) neurons by individual preganglionic axons is regional. That is, the synaptic contacts made by an axon on these neurons are limited to a portion of the postsynaptic surface that includes some, but not all, of the dendrites. This regional innervation of target neurons is consistent with the view that dendrites allow multiple innervation to persist by providing relatively separate postsynaptic domains for individual preganglionic axons. Such regional innervation may mitigate competitive interactions between the several axons which initially innervate the same neuron.
Mobility of extrajunctional acetylcholine receptors on denervated adult muscle fibers
Authors: Stya M , Axelrod D
Published: March 2018

We report the lateral mobility of extrajunctional acetylcholine receptors (AChR), marked with fluorescently labeled alpha-bungarotoxin, on rat flexor digitorum brevis single muscle fibers maintained in cell culture. Mobility is measured by a modification of the fluorescence photobleaching recovery technique. The denervated rat flexor digitorum brevis muscle fibers exhibit a nonuniform distribution of AChR on their sarcolemmas. Diffusely distributed AChR have an average diffusion coefficient of about 2.5 X 10(-11) cm2/sec, somewhat lower than that of diffusely distributed AChR on embryonic rat myotubes in culture. Extrajunctional AChR aggregated into small clusters (less than 20 microns) have an average diffusion coefficient of about 5 X 10(-12) cm2/sec. Both the clustered and nonclustered extrajunctional AChR have lateral mobilities several orders of magnitude greater than that of junctional AChR.
DARPP-32, a dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein enriched in dopamine-innervated brain regions. I. Regional and cellular distribution in the rat brain
Authors: Walaas SI , Greengard P
Published: March 2018

The present study documents the existence in mammalian brain of a phosphoprotein which may play a biological role in dopaminoceptive neurons. This protein has been designated DARPP-32 (dopamine- and adenosine 3′:5′-monophosphate-regulated phosphoprotein-32,000). The regional distribution of DARPP-32 in the rat brain follows the general pattern of dopaminergic innervation. DARPP-32 is present in dopaminoceptive rather than dopaminergic neurons. Moreover, it appears to be concentrated in a subpopulation of dopaminoceptive cells, namely those containing D-1 receptors (dopamine receptors coupled to adenylate cyclase activation), where it is localized in cell bodies, dendrites, axons, and nerve terminals. DARPP-32 is phosphorylated in intact cells from the caudatoputamen by dopamine and by 8-bromo-cyclic adenosine 3′:5′-monophosphate and in cell-free preparations by cyclic adenosine 3′:5′-monophosphate-dependent protein kinase. In two accompanying papers, we report the purification and biochemical characterization of DARPP-32 (Hemmings, H.C., Jr., A.C. Nairn, D.W. Aswad, and P. Greengard (1984) J. Neurosci. 4: 99–110) and the immunocytochemical localization of this phosphoprotein (Ouimet, C.C., P. Miller, H.C. Hemmings, Jr., S.I. Walaas, and P. Greengard (1984) J. Neurosci. 4: 111–124).
DARPP-32, a dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein enriched in dopamine-innervated brain regions. II. Purification and characterization of the phosphoprotein from bovine caudate nucleus
Authors: Hemmings HC , Nairn AC , Aswad DW , Greengard P
Published: March 2018

DARPP-32 is a neuronal phosphoprotein of Mr = 32,000, originally identified in rat brain (Walaas, S.I., D.W. Aswad, and P. Greengard (1983) Nature 301: 69–72). This protein has now been identified in bovine caudate nucleus cytosol and purified 435-fold to apparent homogeneity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purification procedure involved acid extraction at pH 2, CM-cellulose chromatography, DEAE-cellulose chromatography, hydroxylapatite chromatography, and gel filtration on Ultrogel AcA 44. The purified catalytic subunit of cAMP-dependent protein kinase catalyzed the incorporation of 0.96 mol of phosphate/mol of purified DARPP-32. Phosphorylation occurred exclusively on threonine. The isoelectric point of dephospho-DARPP-32 was 4.7, and that of phospho- DARPP-32 was 4.6. The amino acid composition showed a high content of glutamate/glutamine and proline, and a low content of hydrophobic amino acids. DARPP-32 was found to have a Stokes radius of 34 A and a sedimentation coefficient of 2.05 S, indicating that it exists as an elongated monomer.
Regulation of efficacy at central synapses
Authors: Korn H , Faber DS , Burnod Y , Triller A
Published: March 2018

The quantal nature of synaptic depression produced by high frequency stimulations has been analyzed at a central synapse for the first time. Simultaneous intracellular recordings were obtained from the Mauthner cell and adjacent identifiable inhibitory interneurons. The presynaptic cells were stimulated at frequencies from 2 to 33 Hz, and the corresponding release parameters were determined using a computational procedure described elsewhere (Korn, H., A. Triller, A. Mallet, and D. S. Faber (1981) Science 213: 898–901). As in our previous studies, these entities were correlated with histological features of the neurons following systematic horseradish peroxidase injections and reconstructions. Evidence was obtained that, in the range of physiological conditions used, the binomial parameter n (number of available quanta for release) remains constant; thus every synaptic bouton continues to function as an independent all-or-none releasing unit. The progressive reduction in amplitude of postsynaptic potentials can be attributed solely to a lower probability of release, as shown by the fall of the binomial parameter p. This evidence supports the concept that p is a critical variable for short-term modifications of synaptic efficacy and may provide insight for instances of synaptic plasticity underlying those behavioral changes which can be attributed to presynaptic loci. The present study also represents a necessary step toward linking mathematical variables of models for transmitter exocytosis with subcellular events.
The effect of spontaneous electromechanical activity on the metabolism of acetylcholinesterase in cultured embryonic rat myotubes
Authors: Brockman SK , Younkin LH , Younkin SG
Published: March 2018

We have investigated the effect of electromechanical activity on the molecular forms of acetylcholinesterase (AChE) in cultured embryonic rat myotubes. Both globular and asymmetric forms of AChE are present on the 5th day of culture when myotubes are just beginning to fibrillate. Between days 5 and 8, the 4 S (G1), 10 S (G4), and 16 S (A12) forms increase dramatically, and appreciable 12.5 S (A8) AChE appears. When fibrillation is prevented by adding tetrodotoxin on day 4, the increases in the A12 and A8 forms are prevented, and the increases in the G4 and G1 forms are significantly impaired. At 8 days, fibrillating myotubes have 19 times more A12 AChE and over 4 times more G1 and G4 enzyme than do nonfibrillating myotubes. The effect of tetrodotoxin is reversible. When tetrodotoxin is removed at 7 days, fibrillation resumes promptly, and globular and asymmetric forms recover. Light microscopic examination of fibrillating and nonfibrillating myotubes showed that tetrodotoxin does not affect the gross morphological development of the myotubes. Titration of AChE-active sites with O- ethyl-S2-diisopropyl methyl-phosphonothionate demonstrated that the increase in AChE activity associated with fibrillation is due to an increase in the number of AChE molecules present and not to an increase in the rate at which individual AChE molecules turn over acetylcholine. To evaluate AChE metabolism in fibrillating and nonfibrillating myotubes, we examined the enzyme after inactivating it with paraoxon. Paraoxon readily penetrates cells and diethylphosphorylates a serine in the active site of AChE, thereby inactivating it. The diethylphosphorylated enzyme is stable, but it can be reactivated rapidly and quantitatively with pyridine-2-aldoxime methiodide (2-PAM). After inactivating AChE with paraoxon, we simultaneously evaluated synthesis (by following the newly synthesized active AChE) and turnover (by following the 2-PAM-reactivatable AChE). Our results show that globular and asymmetric forms of AChE are both synthesized more rapidly in fibrillating than in nonfibrillating myotubes.
Connections made by transplants to the cerebral cortex of rat brains damaged in utero
Authors: Floeter MK , Jones EJ
Published: March 2018

Homografts consisting of pieces of neocortex or dissociated cortical cells were transplanted from fetal rats into the cortex of newborn, microcephalic hosts. The cortex of the hosts lacked cells of the superficial layers, as a result of prenatal administration of a cytotoxic drug methylazoxymethanol. Grafts exhibited an internal organization with a tendency to form a molecular layer, and alternating cell and fiber zones, although these were not consistently oriented with respect to the host cortex. Both pyramidal and nonpyramidal cells survived. Some grafts were shown to receive callosal connections. Axonal outgrowth from transplanted neurons to several host brain areas was demonstrated with retrograde tracers. Outgrowth occurred not only to the contralateral cortex, in which the host's own callosal projection was deficient, but also to the thalamus and spinal cord, in which the host projection was intact. Thus, grafted fetal cortex is capable of making connections in the methylazoxymethanol-damaged host, but the pattern of connections made is not influenced by host deficiencies.
Locus coeruleus activity in vitro: intrinsic regulation by a calcium- dependent potassium conductance but not alpha 2-adrenoceptors
Authors: Andrade R , Aghajanian GK
Published: March 2018

Locus coeruleus neurons recorded intracellularly in rat brainstem slices exhibited spontaneous activity and a marked afterhyperpolarization following a burst of spikes. This afterhyperpolarization was associated with an increase in membrane conductance and resulted in a marked postactivation inhibition of spontaneous activity. Since the reversal potential of the afterhyperpolarization was found to be virtually identical when recorded with KCl or potassium acetate-filled electrodes and shifted in the hyperpolarizing and depolarizing direction with decreases and increases in extracellular potassium concentrations, respectively, the afterhyperpolarization seen following a burst of spikes in this cell group appears to be mediated by an increase in potassium conductance. The afterhyperpolarization and postactivation inhibition were markedly attenuated by reducing calcium influx by either omitting extracellular calcium in the bathing medium or blocking calcium channels with manganese or cadmium. Thus, the afterhyperpolarization and the resulting postactivation inhibition appear to be largely mediated by the activation of a calcium-dependent potassium conductance. Previous reports in vivo have suggested that activation of alpha 2-adrenoceptors by norepinephrine release from recurrent axons or dendrites may mediate self-inhibition in the locus coeruleus. In this study, we examined the effect of blocking alpha 2-adrenoceptors on the afterhyperpolarization and postactivation inhibition. Administration of the alpha 2- adrenoceptor antagonist piperoxane failed to produce any changes in either of these parameters, suggesting that at least in vitro the afterhyperpolarization and postactivation inhibition seen in locus coeruleus neurons do not result from the activation of alpha 2- adrenoceptors.
Terminal patterns of single, physiologically characterized optic tract fibers in the cat's lateral geniculate nucleus
Authors: Bowling DB , Michael CR
Published: March 2018

We have examined the patterns of termination of single, physiologically identified optic tract fibers in the dorsal lateral geniculate nucleus (LGNd) of the cat. The axons were impaled with a recording micropipette and characterized by their responses to light and by their conduction latencies to electrical stimulation of the optic nerve. Horseradish peroxidase was then iontophoretically injected from the pipette into the single fibers. Subsequent histological processing and serial reconstruction revealed the fibers' destinations, patterns of arborization, and the spatial distributions of their terminal boutons. Axons classified as type X invariably projected to layer A or A1 of the LGNd and some sent a collateral into the medial interlaminar nucleus (MIN). Axons of the Y type terminated in layer A or A1 and the MIN. Those from the contralateral eye nearly always had an additional termination in the magnocellular C layer, whereas those from the ipsilateral eye occasionally terminated in layer C1. In the A layers axons distributed their terminal boutons in columns that spanned the widths of the layers. The columns differed in size, shape, and density depending on whether they were from X, Y-on, or Y-off axons. The columns from both X-on and X-off axons were narrow cylinders averaging about 150 micron in width. The columns usually contained fewer than a thousand boutons and about 60% of the boutons were concentrated in the upper halves of the layers. The Y columns were wider, averaging about 375 micron in width, and contained around 1500 boutons. About 70% of the Y boutons were concentrated in the lower halves of the layers. Y-on columns were often broader at the tops and the bottoms of the layers than near the centers, giving them an hourglass shape. The Y-off columns were broader at the bottoms of the layers than at the tops, giving them the shape of a cone or a truncated cone. These distinctive bouton distributions suggest the presence of a sublaminar organization in the A layers based on differences in the density and lateral spread of the terminations of X, Y-on, and Y-off afferents.
Receptive field properties in the cat's lateral geniculate nucleus in the absence of on-center retinal input
Authors: Horton JC , Sherk H
Published: March 2018

In the cat, lateral geniculate neurons and retinal ganglion cells can almost all be categorized as on-center (excited by light stimuli) or off-center (excited by dark stimuli). We have investigated how these cells are affected when a drug is applied to the retina that, in the mudpuppy, inactivates on-bipolar cells (Slaughter, M. M., and R. F. Miller (1981) Science 211: 182–185). This drug, D,L-2-amino-4- phosphonobutyric acid (APB), is an analogue of glutamate. After injecting APB into the vitreous of the eye, we could record in the optic tract from fibers of off-center retinal ganglion cells that appeared normal in their responses, but we could find no fibers from on- center cells in the injected eye. In the lateral geniculate nucleus (LGN), the outcome was similar. Of a sample of 144 cells studied quantitatively, 13 had extremely poor responses and could not be characterized as on-or off-center. The remaining 131 cells had off- centers and appeared largely normal. Their receptive field organization was unaltered: the field center was excited by dark (off) stimuli and inhibited by light, whereas the surround was inhibited by off stimulation. Of particular interest was the fact that the surrounds of many off-center cells could still be excited by light stimuli; thus, despite the probable inactivation of on-bipolar cells, not all on- responses in the LGN were abolished. As a group, off-center cells were somewhat less responsive then in control experiments. Except for this change, APB appeared to affect only on-center cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Alterations in the structure, function, and chemistry of C fibers following local application of vinblastine to the sciatic nerve of the rat
Authors: Fitzgerald M , Woolf CJ , Gibson SJ , Mallaburn PS
Published: March 2018

Vinblastine, a transport blocker, was applied locally to the sciatic nerve in rats. It was found to be a powerful neurotoxin with a dose- dependent action, destroying all afferents at doses of 5 X 10(-4)M, primarily C fibers at intermediate doses of 2.5 X 10(-4)M, and only at a critically low dose of 10(-4)M was a degeneration-free axon transport blockade, lasting for 4 to 5 days, produced. Such transport block failed to alter thermal responsiveness of the rats as measured behaviorally, by the flexor reflex, or by dorsal horn cell responses. It did, however, significantly reduce both the chemical sensitivity of the C afferents and their ability to produce neurogenic edema. This began 24 hr after treatment and lasted 4 to 5 days. Therefore, it is likely that these functions are dependent on the continuous transport of some compound to the axon terminals from the cell body. This low concentration of local vinblastine treatment also resulted in depletion of fluoride-resistant acid phosphatase from C fiber terminals in the dorsal horn of the spinal cord. Transmission from C fibers to second- order neurons in the spinal cord, however, was totally unaffected. Substance P levels in the spinal terminals was largely unaffected, although in 1 of 5 cases there was depletion. It appears, therefore, that some, but not all, retrograde changes in sensory neurons following peripheral nerve damage can be mimicked by blockade of axon transport. The effects following vinblastine treatment are compared to other peripheral nerve manipulations, such as cut, crush, and application of local capsaicin.
The Dunce gene of Drosophila: roles of Ca2+ and calmodulin in adenosine 3':5'-cyclic monophosphate-specific phosphodiesterase activity
Authors: Walter MF , Kiger JA
Published: March 2018

Two genetically distinct forms of cyclic nucleotide phosphodiesterases are present in adult Drosophila melanogaster. Form II, which specifically hydrolyzes adenosine 3′:5′-cyclic monophosphate (cAMP), is controlled by the dunce+ gene. Mutants of this gene either eliminate this enzyme form entirely or alter its kinetic and thermal properties, suggesting that dunce+ is the structural gene for this enzyme. These mutants are defective in memory formation, habituation, and sensitization and exhibit elevated cAMP levels, implicating cAMP in these neurological processes. The other phosphodiesterase, Form I, which hydrolyzes both cAMP and guanosine 3′:5′-cyclic monophosphate (cGMP), is not affected by dunce mutations. Because both cAMP and Ca2+ serve as intracellular second messengers in mediating the effects of neurotransmitters, the effects of Ca2+ on each form of phosphodiesterase have been investigated. Previous work has suggested that Form I is activated by calmodulin in a Ca2+-dependent manner. We confirm this activation and demonstrate that the activation involves the Ca2+-dependent association of two molecules of calmodulin with one Form I molecule. Under conditions permitting activation and association of Form I with calmodulin, we observe no interaction of Ca2+/calmodulin with Form II. Our studies suggest that the primary physiological defect, associated with a defective or absent Form II cAMP-specific phosphodiesterase and leading to the dunce neurological phenotype, is due to a direct failure to regulate the cAMP level in nerve cells rather than to a failure to mediate a signal resulting from a cAMP- induced Ca2+ influx, associated with presynaptic facilitation.
Mutations altering synaptic connectivity between identified neurons in Drosophila
Authors: Thomas JB , Wyman RJ
Published: March 2018

By studying the effects of mutations on a simple circuit of identified neurons in Drosophila, we have found genes whose proper functioning is necessary to produce normal synaptic connections between the neurons. These neurons comprise the giant fiber (GF) system; the GFs are command neurons activated by a light-off stimulus and evoke a stereotyped pattern of activity in the thoracic muscles producing an escape jump. Each GF monosynaptically drives a motor neuron innervating the tergotrochanteral muscle (jump muscle, TTM). Each GF also disynaptically drives the motor neurons innervating the dorsal longitudinal flight muscle (DLM) via the peripherally synapsing interneuron (PSI) (King, D. G., and R. J. Wyman (1980) J. Neurocytol. 9: 753–770; M. A. Tanouye and R. J. Wyman (1980) J. Neurophysiol. 44: 405–421). A search was made for mutations affecting these identified synapses. Fifty thousand mutagenized flies were screened for nonjumping behavior to the light-off stimulus. Fifty-seven nonjumping mutant lines were established from individuals selected in the screen. Members of the lines were then tested for abnormal GF motor output to the TTM and DLM. From these lines, four X-linked mutations (representing three complementation groups) were isolated which affect the circuit. The mutations differentially disrupt specific synapses within the GF system. One mutation, bendless, disrupts synaptic transmission between the GF and the TTM motor neuron. Another, gfA, disrupts the synaptic connections of the PSI, and a third mutation, passover, disrupts transmission in both pathways.
The origin of thalamic inputs to the arcuate premotor and supplementary motor areas
Authors: Schell GR , Strick PL
Published: March 2018

We have used retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase to examine the origin of thalamic input to the two premotor areas with the densest projections to the motor cortex: the arcuate premotor area (APA) and the supplementary motor area (SMA). Retrograde transport demonstrated that the two premotor areas and the motor cortex each receive thalamic input from separate, cytoarchitectonically well defined subdivisions of the ventrolateral thalamus. According to the nomenclature of Olszewski (Olszewski, J. (1952) The Thalamus of the Macaca mulatta. An Atlas for Use with the Stereotaxic Instrument, S. Karger, AG, Basel), input to the APA originates largely from area X, input to the SMA originates largely from the pars oralis subdivision of nucleus ventralis lateralis (VLo), and that to the motor cortex originates largely from the pars oralis subdivision of nucleus ventralis posterior lateralis (VPLo). These observations, when combined with prior studies on the termination of various subcortical efferents in the thalamus, lead to the following scheme of connections: (1) rostral portions of the deep cerebellar nuclei project to the motor cortex via VPLo; (2) caudal portions of the deep cerebellar nuclei project to the APA via area X; and (3) the globus pallidus projects to the SMA via VLo. Thus, each thalamocortical pathway is associated with a distinct subcortical input.
Development of somatostatin-like immunoreactivity in embryonic sympathetic ganglia
Authors: Maxwell GD , Sietz PD , Chenard PH
Published: March 2018

Neural crest cells are the embryonic progenitors of several adult cell types, including some neurons that contain the neuroactive peptide somatostatin. To begin to understand the control of peptide expression during neuronal ontogeny, we have investigated the development of somatostatin-like immunoreactivity (SLI) in embryonic quail paravertebral sympathetic ganglia in vivo. SLI was identified by immunohistochemistry in paraformaldehyde-fixed cryostat sections from the trunk region of quail embryos. SLI was first observed in the cells of the primary sympathetic trunks at stage 18 (Zacchei, A.M. (1961) Arch. Ital. Anat. Embriol. 66:36–62), which corresponds to embryonic day 4 (E4). The primary sympathetic trunks are the sites of the initial aggregation of neural crest cells to form the sympathetic ganglia. The SLI in these cells was located in the cytoplasm and was absent from the nucleus. SLI persisted in subsequent developmental stages as formation of the definitive sympathetic ganglia occurred. At stage 23 (E7), when the lumbosacral paravertebral sympathetic ganglia have reached their definitive location, some cells in the ganglia contained SLI, and they were often located adjacent to one another. During the later stages of embryogenesis, sympathetic ganglia can be dissected from the embryo and the SLI content determined by radioimmunoassay. The amount of SLI is several-fold higher in ganglia removed at stage 23–24 (E7–8) than in ganglia removed at stage 26–27 (E9–10) or stage 31–32 (E13–14). This decline in SLI content reflects an absolute decrease per ganglion and is not solely due to the growth of tissue devoid of SLI.(ABSTRACT TRUNCATED AT 250 WORDS)
Localization of phencyclidine binding sites on alpha and beta subunits of the nicotinic acetylcholine receptor from Torpedo ocellata electric organ using azido phencyclidine
Authors: Haring R , Kloog Y , Sokolovsky M
Published: March 2018

A photolabile derivative of phencycliding (PCP), azido phencyclidine (AZ-PCP), was synthesized and used to localize PCP binding sites on the acetylcholine receptor from Torpedo ocellata electric organ. In the dark, the binding of micromolar concentrations of [3H]AZ-PCP to a receptor-enriched membrane preparation fits a single dissociation constant (Kd = 2.65 microM) and is very similar to the binding of [3H]PCP. The agonist carbamylcholine increases the association rate (and the affinity) of these ligands to the receptor, but it does not alter the total number of available binding sites. Following UV irradiation and gel electrophoresis, [3H]AZ-PCP was found to label specifically the alpha and beta subunits of the receptor. The labeling of the alpha subunit band was heavier, and it was inhibited by tetracaine and PCP but not by alpha-bungarotoxin (alpha-Bgt). The addition of carbamylcholine enhanced the labeling of the beta subunit; this effect was diminished by alpha-Bgt. The labeling of the beta subunit was also inhibited by tetracaine and PCP. The effect of carbamylcholine, which binds to the alpha subunit, could be the result of an induced conformational change, which is propagated to the beta subunit and increases its labeling by [3H]AZ-PCP. A simple model which accommodates the binding and photoaffinity labeling data is described. According to the model, the high affinity PCP binding site is located between the alpha and beta receptor subunits, and the drug thus becomes attached simultaneously to both. Hypothetical overlapping recognition sites for PCP on these receptor subunits would allow binding (and labeling) with increased affinity in the presence of carbamylcholine with no increase in the number of available sites.
Subcortical efferent projections of the medial geniculate nucleus mediate emotional responses conditioned to acoustic stimuli
Authors: LeDoux JE , Sakaguchi A , Reis DJ
Published: March 2018

The purpose of this study was to identify the afferent link in the neural pathway which mediates emotional responses coupled to auditory stimuli. We evaluated whether autonomic and behavioral responses elicited by acoustic conditioned emotional stimuli are based on afferent information derived from the auditory cortex or from the auditory thalamic relay station, the medial geniculate nucleus (MG), in rats. The rat auditory cortex was defined through anterograde neuroanatomical tracing studies involving the injection of HRP into MG. Lesions were then placed in the auditory cortex or in MG. After 10 to 20 days the rats were subjected to classical fear conditioning trials involving the pairing of a pure tone with electric footshock. Changes in mean arterial pressure and heart rate and the duration of immobilization (“freezing”) and drink suppression elicited by presentation during extinction trials (no footshock) of the acoustic conditioned emotional stimulus were measured. Auditory cortex lesions did not affect the magnitude of the mean arterial pressure or heart rate conditioned responses nor the duration of freezing or drink suppression. In contrast, lesions of MG suppressed the magnitude of both the autonomic and somatomotor (behavioral) conditioned emotional responses but did not affect either autonomic or somatic responses elicited by the footshock unconditioned stimulus. Lesions of the inferior colliculus, the primary source of afferent input to MG, replicated the effects of MG lesions. These findings demonstrate that lesions of MG and lower auditory centers, but not lesions of the auditory cortex, block autonomic and behavioral conditioned emotional responses coupled to acoustic stimuli and indicate that subcortical rather than cortical efferents of MG sustain these responses. Our concurrent observation that MG projects to several subcortical areas (central and lateral amygdala; caudate-putamen; ventromedial hypothalamus) involved in emotional behavior and autonomic function suggests hypotheses concerning subsequent links in this emotional processing pathway.
Effects of iontophoretically released amino acids and amines on primate spinothalamic tract cells
Authors: Willcockson WS , Chung JM , Hori Y , Lee KH , Willis WD
Published: March 2018

The effects of glutamate (Glu), gamma-aminobutyric acid (GABA), glycine (Gly), serotonin (5-HT), norepinephrine (NE), dopamine (DA), and acetylcholine (ACh) were examined in this study by iontophoretic application onto primate spinothalamic tract (STT) neurons identified antidromically by stimulation in the contralateral thalamus. Drugs were tested for effects on background activity, Glu-induced firing, and activity evoked by pinching of the skin. Whereas Glu excited STT cells and was thus used for tests of the other compounds, the amino acids GABA and Gly inhibited Glu- and pinch-induced activity in all STT cells examined. STT cells were also inhibited by 5-HT, NE, and DA. Only two cases of excitation by 5-HT were seen (of 58 cells tested). ACh also had inhibitory actions on STT cells, although 3 of 21 cells exhibited some enhancement of activity. The effects of these compounds on identified STT cells resemble previous demonstrations of the effects of these drugs on dorsal horn interneurons. The results suggest that GABA, Gly, 5-HT, NE, and DA may be inhibitory neurotransmitters on nociceptive STT cells.
In vivo biosynthesis of [35S]- and [3H]substance P in the striatum of the rat and their axonal transport to the substantia nigra
Authors: Krause JE , Reiner AJ , Advis JP , McKelvy JF
Published: March 2018

The biosynthesis and axonal transport of the neuropeptide substance P (SP) in the striatonigral tract of the rat was examined using an in vivo radiolabeling of the rostral corpus striatum and a series of high performance liquid chromatography (HPLC) steps for the purification of radiolabeled SP. The corpus striatum of unrestrained rats was continuously infused via indwelling cannulae for 16 hr with [35S]methionine or a mix of [3H]leucine and [3H]proline. Radiolabeled SP was acid extracted from discrete regions of this striatonigral SP projection--corpus striatum (SP-immunopositive cell bodies), ansa lenticularis (striatonigral SP axons), and substantia nigra (striatonigral SP terminals)--and was purified to a constant specific activity by sequential HPLC. The radiochemical purity of SP was verified by chemical derivative formation (SP-Met11-sulfoxide) and further HPLC. The in vivo labeling procedure resulted in a high level of incorporation of the amino acids into tissue protein and peptide pools. [35S]SP and [3H]SP were positively identified in all three regions of this peptidergic projection. The amount of [35S]SP harvested in each region accounted for 0.0015%, 0.003%, and 0.071% of the total tissue 35S present in the striatum, striatonigral fibers, and substantia nigra, respectively. The amount of [3H]SP harvested in each region accounted for 0.0025%, 0.011%, and 0.27% of the total tissue 3H present in the three regions, respectively. The amount of radiolabeled SP in the striatonigral regions for both isotopic infusion studies was highly correlated with the immunoassayable SP content in those regions, suggesting rapid equilibration of de novo biosynthesized SP with striatonigral tissue pools of SP. Tritium autoradiography of the striatonigral projection after 3H-amino acid infusion provided further support for the specificity of the radiolabeling procedures. Heavily labeled fibers were seen leaving the striatal infusion site caudally, forming a distinct fiber bundle. This bundle projected caudoventrally and formed a dense terminal plexus primarily within the reticulata portion of the substantia nigra. These results demonstrate that SP biosynthesis in the corpus striatum and its transport to the substantia nigra can be studied in discrete striatonigral regions obtained from individual unrestrained rats. This preparation should allow for studies on the dynamics of SP biosynthesis, axonal transport, and turnover in the striatonigral projection.
Modification of synapses in androgen-sensitive muscle. I. Hormonal regulation of acetylcholine receptor number in the songbird syrinx
Authors: Bleisch W , Luine VN , Nottebohm F
Published: March 2018

The songbird syrinx is sexually dimorphic and responds to changes in blood testosterone levels with changes in muscle size and in activity of cholinergic enzymes (Luine, V., F. Nottebohm, C. Harding, and B.S. McEwen (1980) Brain Res. 192: 89–107). Here, we demonstrate that there is a sex difference in the number of acetylcholine receptors (AChRs) in the syrinx and that alterations in the levels of circulating testosterone can cause changes in AChR number in syringeal muscles. These results suggest that the size or number of endplates in the syringeal muscles may be increased by circulating testosterone. The time course of these effects was examined after increases in blood testosterone in females and decreases in males. We also examined the effect of increased testosterone in syrinx isolated from neural influences by denervation and found that denervated muscle responded to testosterone with an increase in acetylcholinesterase activity but not with increases in protein content or AChR number.
Neuropeptide modulation of photosensitivity. II. Physiological and anatomical effects of substance P on the lateral eye of Limulus
Authors: Mancillas JR , Selverston AI
Published: March 2018

A system of efferent substance P-like immunoreactive fibers innervates the ommatidia of the Limulus lateral eye. Thus, we tested the physiological effects of substance P on the lateral eye by measuring the electroretinogram, a population potential reflecting the photoreceptors' response to light, under different experimental conditions. Substance P had no direct effect on the photoreceptors, but it induced an increase in their responsiveness to test flashes of light. The latency, magnitude, and duration of this reversible modulatory effect was dose-dependent. The lateral eye displays an endogenous circadian rhythm in its responsiveness to light. Application of exogenous substance P in the daytime causes an immediate rise as well as an increase in the nocturnal peak, while injection of one of its antagonists (D-Pro2, D-Phe7, D-Trp9 substance P) in the afternoon retards the normal rise in sensitivity and reduces the nighttime levels. Passive incubation with substance P antibodies at midnight caused a drop to diurnal levels of photosensitivity. Short-term changes in photosensitivity, similar in their nature to the substance P-induced ones, were caused by arousing the subjects. Arousal had an effect on the ongoing circadian rhythm similar to that of substance P application. Thus, the substance P efferent system may regulate neural responsiveness in both a short-term, environmentally induced manner, as well as for level setting in a circadian fashion. The mechanism for substance P-induced increases in photosensitivity involves changes in ommatidial structure: contraction of distal pigment cells, resulting in an increased aperture, and contraction of the retinular cells and rhabdom, resulting in a wider diameter of the latter. These structural modifications result in a greater angle of acceptance and increased light quantum catch.
Olfactory marker protein: turnover and transport in normal and regenerating neurons
Authors: Kream RM , Margolis FL
Published: March 2018

A 19,000-dalton acidic protein designated olfactory marker protein (OMP) is a cell-specific marker of mature olfactory chemosensory neurons. Intranasal irrigation of mouse olfactory epithelium with [35S]methionine labeled OMP to high specific activity. Turnover and transport characteristics of 35S-labeled OMP were compared to those of 35S-labeled global cytosol protein in groups of young, adult, and Triton-treated adult mice. The latter contained primarily large numbers of regenerating olfactory neurons. In olfactory epithelium of young and Triton-treated mice, the specific activity of OMP was three times that of global cytosol protein, whereas in adults the two measures were equal. In all three groups, however, the rate of degradation of OMP was roughly equal to that of cytosol protein (T1/2 = 5 to 6 days). By contrast, differences in T1/2 for OMP decline in the bulb of adult, young, and Triton-treated adult mice were highly significant (T1/2′s of 9.3, 6.1, and 4 to 5 days, respectively; p = 0.001). The specific activity of [35S]methionine incorporated in OMP exceeded that of the free amino acid 5-fold, indicating minimal precursor reutilization during the course of our experiments. Turnover data indicate that increased isotope incorporation into OMP in the epithelium is matched by an accelerated rate of degradation in the bulb. This may be correlated with the physiological state or developmental age of the primary neurons since in young and Triton-treated adult mice, rapidly maturing “young” olfactory neurons represent a larger proportion of the total population than in adults. Thus, OMP behaves as a typical, relatively slowly transported soluble protein (v = 2 to 4 mm/day, slow component b).
The arousal of ingestive behaviors by chemical injection into the brain of the suckling rat
Authors: Ellis S , Axt K , Epstein AN
Published: March 2018

Three neurochemical agents known to arouse ingestion in adult rats were studied in milk-sated rat neonates ingesting fluids away from their dams. All were given intracerebroventricular (ICV) injection. Drinking of both milk and water by 2-day-olds injected with angiotensin II (Ang II) was confirmed. The characteristic adult dipsogenic response, intake of water greater than that of milk, appeared at 8 days. ICV carbachol (Carb), on the other hand, did not elicit drinking before 4 days, despite the fact that these dipsogens (Carb and Ang II) may both affect receptors in the subfornical organ. ICV norepinephrine (NE) increased milk intake beginning at 9 to 10 days, which coincides with the age at which central adrenergic receptors believed to mediate NE's orexigenic effect are appearing in the developing forebrain. NE had no effect on water intake at any age. The effects of all three agents on ingestive behaviors were dose-dependent. These data suggest that the neural systems utilized by Ang II, Carb, and NE are competent for mediation of specific ingestive behaviors before they reach full anatomical and biochemical maturity. Last, NE did not increase milk intake of pups suckling from their dam at any age. The noradrenergic system that is developing in the rat brain during the suckling period appears to be a nascent control of subsequent adult feeding rather than a functioning control of ongoing suckling.
Trans-striatal dialysis coupled to reverse phase high performance liquid chromatography with electrochemical detection: a new method for the study of the in vivo release of endogenous dopamine and metabolites
Authors: Imperato A , Di Chiara G
Published: March 2018

A method for the estimation in rats of the in vivo release and metabolism of dopamine (DA) is described. The method is based on the dialysis principle and consists of inserting transversally in the striatum a thin (0.2 mm) dialysis tube (Amicon Vitafiber) which is then perfused with Ringer. The Ringer, flowing at a constant rate of 2 microliters/min in the dialysis tube, extracts low molecular weight substances from the surrounding tissue by way of simple diffusion along a concentration gradient. At the distal end of the dialysis tube, the Ringer is collected every 10 to 20 min and directly injected into a high performance liquid chromatographer (HPLC) equipped with reverse phase octadecyl sulfate columns which separate DA and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). These substances are then quantitatively estimated by oxidative electrochemical detection. The basal output of DA is 0.3 pmol/20 min, whereas the outputs of DOPAC and HVA are 60 and 20 pmol/20 min, respectively. In basal conditions the output of DA, DOPAC, and HVA is stable over at least 10 hr. Histological examination of the track left by the dialysis probe in rats after 10 hr of continuous dialysis reveals very little damage and normal neuronal morphology in the vicinity of the dialysis tube. Increase of the K+ concentration in the Ringer to 30 mM produced a sharp, reversible increase of DA output. Both the basal and K+-stimulated release were Ca++ dependent, because omission of Ca++ abolished basal and K+-stimulated DA release. Electrical stimulation of the nigrostriatal DA neurons in the medial forebrain bundle sharply increased DA output. Amphetamine sulfate in low doses (1.0 mg/kg, i.v.) produced a 9-fold increase in DA release and decreased DOPAC and HVA output. alpha-Methyl tyrosine (150 mg/kg, i.v.) reduced within 2 hr DA release to 15% of basal values and in parallel also decreased the output of DOPAC and HVA. Reserpine (5 mg/kg, i.p.) reduced DA release but in a slower fashion than alpha- methyl tyrosine and increased DOPAC and HVA. Pargyline (75 mg/kg, i.p.) produced a 4-fold increase of DA release, while it rapidly brought to zero DOPAC and HVA output. gamma-Butyrolactone (700 mg/kg, i.p.) rapidly and lastingly reduced DA, DOPAC, and HVA output. The biochemical and histological results obtained indicate that the method is suitable to estimate in the rat the changes in the release o f endogenous DA and its metabolites which take place in vivo under administration of centrally acting drug.
Cholecystokinin receptors: biochemical demonstration and autoradiographical localization in rat brain and pancreas using [3H] cholecystokinin8 as radioligand
Authors: Van Dijk A , Richards JG , Trzeciak A , Gillessen D , Mohler H
Published: March 2018

Since cholecystokinin8 (CCK8) seems to be the physiological ligand of CCK receptors in the brain, it would be the most suitable probe for the characterization of CCK receptors in radioligand binding studies. [3H]CCK8 was synthetized with a specific radioactivity sufficient for the detection of high affinity binding sites. [3H]CCK8 binds saturably and reversibly to distinct sites in rat brain and pancreas with nanomolar affinity. While the C-terminal tetrapeptide of CCK is the minimal structure required for nanomolar affinity in the brain, the entire octapeptide sequence is required for binding affinity in pancreas. Desulfated CCK8 and several gastrin-I peptides, which are likewise unsulfated, show virtually no affinity to the binding sites in pancreas but high affinity in cerebral cortex. The ligand specificity of the CCK peptides corresponds to their electrophysiological potency in the brain and their stimulation of secretion in pancreas, respectively. Autoradiographically, high densities of [3H]CCK8 binding sites were found in cerebral cortex and olfactory bulb, medium levels in nucleus accumbens, hippocampus, dentate gyrus, and striatum with virtually no labeling in cerebellum. This pattern is similar to the distribution of CCK-like immunoreactivity in the brain. In pancreas, equally high levels of [3H]CCK8 labeling were found in the exocrine and endocrine region. [3H]CCK8 binding sites differ from those identified previously with [125I]Bolton-Hunter-CCK33 by their sensitivity to guanyl nucleotides in the brain, their ion dependency in the brain, and pancreas, and their different autoradiographical localization in some parts of the brain. The distribution of CCK binding sites labeled with [3H]CCK8 appears to correlate better with the CCK immunoreactivity than those labeled with [125I]Bolton-Hunter-CCK33. Thus, [3H]CCK8 appears to be the radioligand of choice for the investigation of CCK receptors.