bluuebunny/crossref_metadata_2025 huggingface dataset:
Microtubule-associated protein 2 (MAP2) is present in astrocytes of the optic nerve but absent from astrocytes of the optic tract
Authors: Papasozomenos SC , Binder LI
Published: March 2018

Using the peroxidase-antiperoxidase staining technique at the light- and electron-microscope levels and two monoclonal antibodies against microtubule-associated protein 2 (MAP2), we found that astrocytes located at the periphery of the rat optic nerve were strongly stained, while those in the central region were very weakly stained. MAP2 immunoreactivity was present in astrocytes of the optic chiasm, but was absent from astrocytes in the optic tract. Inside astrocytes, MAP2 immunoreactivity was excluded from bundles of glial filaments. Treatment of animals with beta,beta'-iminodipropionitrile (IDPN), which caused axonal atrophy, enhanced the staining intensity of all optic nerve astrocytes. Axons and oligodendrocytes remained unstained. Using PAGE and Western immunoblots, we found that extracts from bovine optic nerve contained MAP2. Astrocytes in any other region of the nervous system were negative for MAP2 immunoreactivity, except of the pituicytes and the astrocytes of the fimbria of hippocampus. The optic nerve, neurohypophysis, and hippocampal fimbria are white matter tracts that travel unsupported and free of surrounding nervous tissue. These findings suggest that MAP2 is expressed in astrocytes that are under excessive mechanical stress and further indicate that MAP2 may function as a cytoskeletal rigidifying agent in certain cells.
Factors affecting release of 3H-dopamine from perfused carp retina
Authors: O'Connor P , Dorison SJ , Watling KJ , Dowling JE
Published: March 2018

The effects of putative retinal neurotransmitters and several neuropeptides on 3H-dopamine release from isolated perfused carp (Cyprinus carpio) retinas were studied. Of the transmitter candidates tested, only serotonin (5-HT) and the 5-HT agonist tryptamine released 3H-dopamine. However, the release evoked by these agents was calcium (Ca2+) independent and not blockable by the 5-HT antagonist methysergide. We also investigated the antagonism of inhibitory inputs as a potential regulatory mechanism for dopamine release and found that the GABA antagonists, bicuculline and picrotoxin, stimulated a dose- dependent release of 3H-dopamine. The effects of the GABA antagonists were dependent on extracellular Ca2+ and could be inhibited by perfusion of the retina with GABA. Bicuculline and picrotoxin also stimulated an increase in cAMP accumulation, which was inhibited by the dopamine antagonist haloperidol. Our results support the hypothesis that the dopaminergic interplexiform cells of the teleost retina are under GABAergic inhibitory control.
The response of chick sensory neurons to brain-derived neurotrophic factor
Authors: Davies AM , Thoenen H , Barde YA
Published: March 2018

To determine the spectrum of activity of brain-derived neurotrophic factor (BDNF) among first-order sensory neurons, explants of the nine distinct populations of sensory neurons from embryonic chicks of 3–14 d incubation (E3-E14) were grown in collagen gels with and without BDNF in the culture medium. The explants responded to BDNF with profuse neurite outgrowth and comprised those in which neurons are derived from neural crest (the dorsomedial part of the trigeminal ganglion, rostromedial part of the trigeminal mesencephalic nucleus, jugular ganglion, and lumbosacral dorsal root ganglia) and from epibranchial placodes (the ventrolateral part of the trigeminal ganglion and the geniculate, petrosal, and nodose ganglia). This response was first clearly observed in the ventrolateral trigeminal and nodose ganglia as early as E4, but did not appear until later in other explants. The dorsomedial trigeminal, jugular, and geniculate ganglia were the latest to develop a response, which was not apparent until E8. In all explants the response was maximal between E10 and E12, and there was a decline in the magnitude of the response from E12 to E14. Although explants of the vestibular ganglion failed to respond to BDNF, the survival and growth of vestibular neurons in dissociated neuron-enriched cultures were promoted by BDNF. To investigate whether all first-order sensory neurons respond to BDNF or whether BDNF-responsive neurons comprise a distinct subset, we studied the influence of BDNF and NGF on the survival and growth of the placode-derived and the neural crest-derived neurons of the trigeminal ganglion in dissociated neuron-enriched culture.(ABSTRACT TRUNCATED AT 250 WORDS)
The sensitive period for auditory localization in barn owls is limited by age, not by experience
Authors: Knudsen EI , Knudsen PF
Published: March 2018

Early in life, the barn owl passes through a sensitive period during which it can interpret and make use of abnormal auditory cues for accurate sound localization. This capacity is lost at about 8 weeks of age, just after the head and ears reach adult size (knudsen et al. 1984a). The end of the sensitive period could be triggered either by an age-dependent process or by the exposure of the auditory system to stable or adult-like cues. To distinguish between these alternatives, we subjected baby owls to constant abnormal cues (chronic monaural occlusion) or to frequently changing abnormal cues (alternating monaural occlusion) throughout the sensitive period. In the first group of animals (n = 2), one ear was plugged continuously until 73 or 79 d of age, respectively, and then the earplug was switched to the opposite ear. Although these animals adjusted sound localization accuracy during the initial chronic monaural occlusion, they could not localize sounds at all after the earplug was switched to the opposite ear, and they remained unable to localize sounds as long as the opposite ear remained occluded (7 and 27 weeks, respectively). When the second monaural occlusion was finally removed, both birds localized sounds with errors that were similar to the errors they exhibited immediately after removal of the first monaural occlusion. One bird that was 127-d-old at the time the second earplug was removed corrected its localization error; the other bird, 250-d-old when the second earplug was removed, did not.(ABSTRACT TRUNCATED AT 250 WORDS)
Autoradiographic localization and characterization of atrial natriuretic peptide binding sites in the rat central nervous system and adrenal gland
Authors: Gibson TR , Wildey GM , Manaker S , Glembotski CC
Published: March 2018

Atrial natriuretic peptides (ANP) have recently been identified in both heart and CNS. These peptides possess potent natriuretic, diuretic, and vasorelaxant activities, and are all apparently derived from a single prohormone. Specific ANP binding sites have been characterized in the adrenal zona glomerulosa and kidney cortex, and one study reported ANP binding sites in the CNS. However, a detailed examination of the localization of ANP binding sites throughout the brain has not been reported. In this study, quantitative autoradiography was employed to examine the distribution of ANP receptors in the rat CNS. The binding of (3-125I-iodotyrosyl28) rat ANP-28 to binding sites in the rat CNS was saturable, specific for ANP-related peptides, and displayed high affinity (Kd = 600 pM). When the relative concentrations of ANP binding sites were determined throughout the rat brain, the highest levels of ANP binding were localized to the circumventricular organs, including the area postrema and subfornical organ, and the olfactory apparatus. Moderate levels of ANP binding sites were present throughout the midbrain and brain stem, while low levels were found in the forebrain, diencephalon, basal ganglia, cortex, and cerebellum. The presence of ANP binding sites in the subfornical organ and the area postrema, regions considered to be outside the blood-brain barrier, suggests that peripheral ANP levels may regulate some aspects of CNS control of salt and water balance. The possible functions of ANP binding sites in other regions of the rat brain are not known, but, like many other peptides, ANP may act as a neurotransmitter or neuromodulator at these loci.
Effects of nerve growth factor on the survival and synaptic function of Ia sensory neurons axotomized in neonatal rats
Authors: Miyata Y , Kashihara Y , Homma S , Kuno M
Published: March 2018

Sensory neurons with small diameters (A delta and C cells) are known to be responsive to exogenous NGF even at postnatal stages. We have examined whether large Group Ia sensory neurons (A alpha cells) arising from muscle spindles are also responsive to NGF in neonatal rats. For this purpose, monosynaptic excitatory postsynaptic potentials (EPSPs) were evoked in spinal motoneurons by Group Ia muscle afferent volleys. When a muscle nerve was crushed on the day after birth, the monosynaptic EPSPs elicited by afferent volleys from the muscle were depressed within several weeks. This synaptic depression was partially reversed by daily treatment with NGF. NGF treatment also enhanced the EPSPs evoked by stimulation of intact muscle nerves, but this effect was less marked than that on the EPSPs produced by stimulation of the previously crushed muscle nerve. Exogenous NGF was effective for the EPSPs when the treatment began on the day after birth but not when the treatment began 4 d after birth. Following crush of a muscle nerve on the day after birth, about 45% of the sensory neurons derived from the muscle were lost. The cell death of small sensory neurons was prevented by daily treatment with NGF, whereas the NGF treatment was ineffective in preventing the cell death of large sensory neurons. The results indicate that Group Ia sensory neurons are responsive to NGF during early postnatal life.
Bilateral augmentation of dopaminergic and serotonergic activity in the striatum and nucleus accumbens induced by conditioned circling
Authors: Szostak C , Jakubovic A , Phillips AG , Fibiger HC
Published: March 2018

The involvement of dopaminergic (DA) and serotonergic (5-HT) systems in circling was assessed by determining the neurochemical correlates of circling induced and maintained by two different schedules of water reinforcement. The conditioned circling paradigm was employed in an attempt to replicate reports that levels of DA and 3,4- dihydroxyphenylacetic acid (DOPAC) were increased in the striatum and nucleus accumbens septi (NAS) contralateral to the direction of circling. Rats trained to circle using a continuous schedule of reinforcement did not exhibit any changes in concentrations of DA, DOPAC, or homovanillic acid (HVA). Bilateral increases in 5-HT concentrations were observed in the striatum. Use of an intermittent schedule of reinforcement (FR-2) produced higher rates of circling. In rats maintained on the FR-2 schedule, no changes in DA or its metabolites were observed in the striatum. The ratio of HVA to DA was, however, increased bilaterally, suggesting a bilateral augmentation of DA utilization. Concentrations of DA were lower in the NAS contralateral to direction of turning. While NAS levels of HVA were elevated bilaterally when compared to non-circling controls, HVA was lower in the NAS contralateral to the direction of circling. DA utilization, as estimated by HVA: DA ratios, was increased bilaterally in the NAS. None of the measures of DA activity within the olfactory tubercle (OT) were influenced by circling. Turnover of 5-HT, as estimated by the ratio of 5-HT to 5-hydroxyindoleacetic acid (5-HIAA), was increased bilaterally in the striatum, NAS, and OT.(ABSTRACT TRUNCATED AT 250 WORDS)
A V1-like receptor mediates vasopressin-induced flank marking behavior in hamster hypothalamus
Authors: Albers HE , Pollock J , Simmons WH , Ferris CF
Published: March 2018

A vasopressin-sensitive mechanism within the medial preoptic area- anterior hypothalamus (MPOA-AH) appears to be essential for expression of a complex behavior involved in olfactory communication in Golden hamsters called flank marking. The present study investigated whether the induction of flank marking by arginine-vasopressin (AVP) within the MPOA-AH is mediated by a receptor that is more similar to the vasopressor (V1) or the antidiurectic (V2) AVP receptor. Adult male hamsters were anesthetized and implanted with a 26 gauge guide cannula stereotaxically aimed at the MPOA-AH and then microinjected with analogs of vasopressin, oxytocin, and selective V1 and V2 antagonists. Hamsters were tested for flank-marking behavior during a 5 or 10 min observation period following the injection of peptide in a vehicle of 100 nl of saline. None of the 15 analogs of AVP and oxytocin produced more flank marking than the 50.8 +/- 16.2 and 76.8 +/- 4.4 (mean +/- SEM; n = 4) flank marks observed following injection of AVP at the 1 or 10 ng dose, respectively. The number of flank marks produced by each analog was found to be highly related to the pressor activity of that analog at both the 1 ng (rho = +0.74, p less than 0.01) and 10 ng (rho = +0.82, p less than 0.01) doses. In contrast, no statistically reliable relationship between flank marking and the antidiuretic activity of these analogs was found at either dose (1 ng: rho = +0.07, p greater than 0.05; 10 ng: rho = +0.10, p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Structural similarities and differences between neurofilament proteins from five different species as revealed using monoclonal antibodies
Authors: Lee VM , Carden MJ , Schlaepfer WW
Published: March 2018

Neurofilament (NF) proteins isolated from human, rabbit, rat, and chicken spinal cord white matter were immunoblotted with monoclonal antibodies (MAbs) raised to bovine NF immunogens. The aim of these experiments was to test the degree of epitope conservation among NF proteins from different vertebrate species. In so doing, the validity of using antibodies raised to NF from one species (cow) for detecting NF proteins of other species was also tested. The MAbs used for these experiments were characterized using bovine NFs to define polypeptide specificity, the approximate location of epitopes within each NF polypeptide, and the effects on antibody recognition of the presence or absence of phosphorylated residues in these polypeptides (see Carden et al., 1985). Our findings indicate that epitopes located in the alpha- helical core domains of NF-H, NF-M, and NF-L are distinct from each other, yet are strongly conserved among the different species. Epitopes located in the noncore or peripheral domains of the NF polypeptides show variable degrees of cross-species preservation. For example, all epitopes in the peripheral domains of bovine NF-H that require the presence of phosphate groups for recognition (phosphorylation dependent) are widely expressed in all species studied. Many phosphorylation-dependent epitopes of bovine NF-H are also present in bovine NF-M, as well as in NF-H of non-bovine species. In addition, epitopes in the peripheral domain of NF-H that require dephosphorylation of NF polypeptides for recognition (dephosphorylation dependent) are also found in NF-H of other mammalian species but not in NF-H of chicken.(ABSTRACT TRUNCATED AT 250 WORDS)
Heterogeneity in migrating neural crest cells revealed by a monoclonal antibody
Authors: Barbu M , Ziller C , Rong PM , Le Douarin NM
Published: March 2018

A monoclonal antibody, GlN1, obtained by immunization with extracts of the 14 d embryonic quail nodose ganglion, is described. GlN1 recognizes an antigenic determinant present in virtually all the satellite cells of the peripheral ganglia, all Schwann cells of the peripheral nerves, and in subpopulations of sensory and autonomic neurons of embryonic and adult quails and chickens. The molecular weight of the antigen(s) revealed by GlN1 in embryonic day 12 quail dorsal root ganglion (DRG) cultures is around 80 kDa. In the neural crest, GlN1 determinant is found as soon as the crest cells leave the neural primordium. Only a proportion (25%) of the migrating neural crest cells carry the antigen. This demonstrates that the neural crest is composed of a heterogeneous population of cells from its early migratory stages. Being selectively distributed on neural crest cells and its derivatives, the GlN1 determinant may be considered as a “differentiation antigen” that will be useful in further studies on cell-line segregation during the ontogeny of the PNS.
Blockade of D-2 dopamine receptors strongly enhances the potency of enkephalins to inhibit dopamine-sensitive adenylate cyclase in rat neostriatum: involvement of delta- and mu-opioid receptors
Authors: Schoffelmeer AN , Hansen HA , Stoof JC , Mulder AH
Published: March 2018

The interactions between dopamine receptors and opioid receptors coupled to adenylate cyclase in rat neostriatum were investigated. cAMP efflux from neostriatal slices induced by simultaneous activation of (stimulatory) D-1 and (inhibitory) D-2 dopamine receptors with 30 microM dopamine was inhibited by the preferential delta-opioid receptor agonist [D-Ala2-D-Leu5] enkephalin (DADLE) and the mu-opioid receptor agonist morphine with an EC50 of 100 and 800 nM, respectively. On selective D-1 receptor activation (i.e., with D-2 receptors blocked by 10 microM (-)sulpiride), the EC50 of DADLE was strongly reduced to 3 nM, whereas that of morphine was unaffected. When D-1 and D-2 receptors were activated simultaneously, the inhibitory effects of DADLE (0.3 microM) and morphine (3 microM) on cAMP efflux were antagonized equally well by naloxone, a mu-opioid receptor antagonist. In contrast, on selective D-1 receptor activation, naloxone was about 20 times more potent in antagonizing the inhibitory effect of morphine than DADLE. Moreover, the delta-opioid receptor antagonist ICI 174864 (0.75 microM) did not affect the inhibitory effect of morphine but antagonized that of DADLE, provided that D-2 receptors were blocked. The highly selective delta-opioid receptor agonist [D-Pen2-D-Pen5] enkephalin (DPDPE) inhibited dopamine-stimulated cAMP efflux only when D-2 receptors were blocked. Similar results were obtained when the agonists SKF 38393 and LY 141865 were used to activate D-1 and D-2 receptors, respectively. These data indicate that blockade of D-2 receptors in the neostriatum elicits the coupling of delta-opioid receptors to dopamine- sensitive adenylate cyclase, thereby making it considerably more sensitive to inhibition by the enkephalins.
Glucocorticoid toxicity in the hippocampus: reversal by supplementation with brain fuels
Authors: Sapolsky RM
Published: March 2018

Glucocorticoids (GCs) can damage neurons of the hippocampus, the principal target tissue in the brain for the hormone. Hippocampal neuron loss during aging in the rat is accelerated by prolonged GC exposure and decelerated by adrenalectomy. GCs appear to damage these neurons indirectly by inducing a state of vulnerability and thus impairing their capacity to survive a variety of metabolic challenges. As such, high physiological concentrations of the steroid increase hippocampal damage induced by an antimetabolite toxin, an excitotoxin, or hypoxia-ischemia. Conversely, adrenalectomy attenuates the damage caused by these insults. This study suggests that GCs endanger hippocampal neurons by impairing their energy metabolism. Neurons are extremely vulnerable to such disruption, all the insults potentiated by GCs either impair energy production or pathologically increase energy consumption, and GCs inhibit glucose utilization in the hippocampus. Administration of different brain fuels--glucose, mannose, fructose, or the ketone beta-hydroxybutyrate--reduced hippocampal damage induced by coadministration of GCs and either of 2 different neurotoxins (kainic acid and 3-acetylpyridine). This appeared to be due to a reduction in the damaging synergy between GCs and the toxin; as evidence, a dose of mannose that attenuated damage induced by kainic acid plus GCs failed to reduce damage induced by the same dose of kainic acid alone. Glucose (whose utilization is noncompetitively inhibited by GCs) and fructose (which does not readily penetrate the blood-brain barrier) were less effective at reducing damage than the other 2 fuels.
Identified motoneurons and their innervation of axial muscles in the zebrafish
Authors: Westerfield M , McMurray JV , Eisen JS
Published: March 2018

The organization of spinal cord motoneurons and their innervation of axial (white) muscles in the zebrafish were studied. Motoneurons can be divided into 2 classes, primary and secondary, on the basis of their cell-body sizes and positions. Each side of each spinal segment contains 3 primary motoneurons that are uniquely identifiable as individuals by their stereotyped cell-body positions and peripheral branching patterns. Moreover, these motoneurons precisely innervate cell-specific subsets of contiguous muscle fibers in mutually exclusive regions of their own body segment. Individual muscle fibers receive inputs from a single primary motoneuron and, in addition, from up to 3 secondary motoneurons. The results demonstrate that the precision of innervation previously described in invertebrates is also present in some vertebrates.
Development and axonal outgrowth of identified motoneurons in the zebrafish
Authors: Myers PZ , Eisen JS , Westerfield M
Published: March 2018

We have observed the development of live, fluorescently labeled motoneurons in the spinal cord of embryonic and larval zebrafish. There are 2 classes of motoneurons: primary and secondary. On each side of each spinal segment there are 3 individually identifiable primary motoneurons, named CaP, MiP, and RoP. The motoneurons of the embryo and larva are similar in morphology and projection pattern to those of the adult. During initial development, axons of primary motoneurons make cell-specific, divergent pathway choices and grow without error to targets appropriate for their adult functions. We observed no period of cell death, and except for one consistently observed case, there was no remodeling of peripheral arbors. We have observed a consistent temporal sequence of axonal outgrowth within each spinal segment. The CaP motor axon is the first to leave the spinal cord, followed by the axons of the other primary motoneurons. The Mauthner growth cone enters the spinal cord after all the primary motoneurons of the trunk spinal cord have begun axonal outgrowth. Secondary motor growth cones appear only after the Mauthner growth cone has passed by. Our results suggest that this stereotyped temporal sequence of axonal outgrowth may play a role in defining the contacts between the Mauthner axon and the motoneurons; the behavior of growth cones in the periphery suggests that interactions with the environment, not timing, may determine path- finding and peripheral connectivity of the motoneurons.
Actions of pentobarbital on rat brain receptors expressed in Xenopus oocytes
Authors: Parker I , Gundersen CB , Miledi R
Published: March 2018

Functional receptor channels activated by GABA and other neurotransmitters were “transplanted” from rat brain to Xenopus oocytes by injecting the oocytes with total poly(A)+ mRNA isolated from rat or chick brain. Membrane currents elicited in the oocyte by GABA inverted polarity at about the chloride equilibrium potential (ca. -25 mV). Pentobarbital potentiated the GABA-activated currents, without appreciably changing the reversal potential or form of the current- voltage relationship. At low (less than 10(-5) M) concentrations of GABA, pentobarbital (100 microM) potentiated the responses by a factor of 10 or more, but responses to high (ca. 1 mM) concentrations of GABA were almost unchanged. Half-maximal activation of the response was obtained with about 3 X 10(-5) M GABA when applied alone and with about 4 X 10(-6) M GABA when applied together with 100 microM pentobarbital. At low doses of GABA, the size of the current increased as the 1.4th power of GABA concentration, but this relationship became nearly linear in the presence of pentobarbital. The potentiation of the GABA response increased linearly with concentrations of pentobarbital up to about 300 microM, reaching a maximum of about 50-fold. At higher concentrations of pentobarbital, the response to GABA declined. Relaxations of GABA- activated currents following voltage steps became slower in the presence of pentobarbital, suggesting that the open life-time of the channels was prolonged. In addition to actions on GABA-activated currents, pentobarbital itself elicited a small membrane current that inverted polarity at a potential (-10 mV) more positive than the GABA- activated current.(ABSTRACT TRUNCATED AT 250 WORDS)
An identified histaminergic neuron modulates feeding motor circuitry in Aplysia
Authors: Chiel HJ , Weiss KR , Kupfermann I
Published: March 2018

An identified histaminergic neuron, C2, in the marine mollusk Aplysia is a complex mechanoafferent which appears to contribute to the maintenance of food arousal by means of its synaptic connections to the metacerebral cell (MCC). Because C2 also has extensive synaptic outputs to neurons other than the MCC, we studied its possible motor functions. We identified several synaptic followers of C2 and found that some were excitatory motor neurons for extrinsic muscles of the buccal mass, while others were modulatory motor neurons that inhibited contractions. In addition, we found that these neurons and other synaptic followers of C2 received powerful inputs during feeding motor programs. In order to determine the functional significance of the synaptic outputs of C2, we studied extrinsic buccal muscles (E4 and E5) whose motor neuron (C6) is excited by C2. Extracellular recordings from these muscles indicated that they receive input during swallowing and rejection, but not during biting movements. Lesions of these muscles, or of all extrinsic muscles, did not prevent animals from feeding, but decreased feeding efficiency, that is, the amount of seaweed an animal could ingest with each swallow. The data suggest that C2 is an integrative proprioceptive cell that functions as a premotor neuron. The non-MCC synaptic outputs of C2 may reinforce the actions of the central feeding motor program. Specifically, C2 appears to aid the functioning of muscles that produce fine adjustments of the buccal mass and contribute to the efficiency of feeding behavior, rather than in producing gross movements.
Movement of retinal terminals in goldfish optic tectum predicted by analysis of neuronal proliferation
Authors: Raymond PA
Published: March 2018

Quantitative, computer-assisted autoradiography was used to assess the relative rate and pattern of growth of retina and tectum in larval and early juvenile goldfish. 3H-thymidine was used to mark the boundary of retina and tectum, and the location of this boundary was charted as the eye and brain grew and added more cells. The pattern of growth is at all times discordant. The original (larval) retina becomes surrounded by annuli of new tissue, whereas the larval tectum remains adjacent to the rostral edge as crescents of new tissue are added to the caudal end. After 2 years of growth, more than 95% of the total surface area of retina and tectum in goldfish derives from cells born after larval stages. Computer-aided reconstructions of 3H-thymidine labeled retina and tecta were used to predict the direction and magnitude of displacement of the retinotopic map. It was estimated that retinal terminals can shift 1.5–1.8 mm caudally at a rate of 5 micron/d during the first 2 years of growth. The terminals that move the farthest are those from temporal retina that project to rostral tectum. The magnitude and direction of the predicted movements matches certain features of HRP-filled retinal axons that others have assumed represented the history of displacements of the terminal arbors.
Cytosolic calcium elevation and cGMP production induced by serotonin in a clonal cell of glial origin
Authors: Ogura A , Ozaki K , Kudo Y , Amano T
Published: March 2018

It has been shown recently that astroglial cells of the mammalian CNS possess receptors for neurotransmitters. In order to analyze what sequences of cellular events occur upon activation of these glial receptors, we utilized a 5-HT receptor in a rat clonal cell of glial origin as a model system. When the C6BU-1 glioma cells were exposed to 5-HT, the cytosolic Ca2+ concentration ([Ca2+]i) was elevated and the cellular content of cGMP was increased in a dose-dependent manner. 5-HT receptor antagonists and a Ca2+ entry blocker suppressed the increases in both [Ca2+]i and cGMP. The magnitude of the cGMP increment depended on the environmental Ca2+ concentration and was totally blocked by Ca2+ depletion. Application of a Ca2+ ionophore increased [Ca2+]i and cGMP. There was a tendency for extremely high [Ca2+]i to suppress the cGMP increment. On the contrary, membrane-permeable cyclic nucleotide analogs failed to increase [Ca2+]i. These results suggest that the following sequence of events occurs in 5-HT-induced C6BU-1 cells: activation of 5-HT receptors, Ca2+ influx, a rise in [Ca2+]i, activation of guanylate cyclase, and, finally, activation of cyclic nucleotide phosphodiesterase.
Comparison of the light-sensitive and cyclic GMP-sensitive conductances of the rod photoreceptor: noise characteristics
Authors: Matthews G
Published: March 2018

Patch-clamp recordings were made from outer segments of single rod photoreceptors isolated from toad retina. Cyclic GMP (cGMP) and its hydrolysis-resistant analog, 8-bromo-cGMP, increased the conductance of excised membrane patches when applied to the intracellular face of the membrane but not when applied to the extracellular face. The rectification properties of the cGMP-dependent conductance depended on the concentration of divalent cations bathing the intra- and extracellular membrane faces. Current flow was favored from the side of the membrane, either internal or external, that was exposed to bathing fluid free of divalent cations. The power spectral density of cGMP- induced noise was fitted by a sum of 2 Lorentzian components, with corner frequencies differing approximately 15-fold on average. This suggests that channel gating is controlled by 2 kinetic components. To compare the cGMP-sensitive conductance with the light-sensitive conductance of the rod, cell-attached patch-clamp recordings were made from intact, dark-adapted rods, and noise arising from the light- sensitive conductance was analyzed. The power spectrum of the light- sensitive noise also exhibited 2 Lorentzian components similar to those of the cGMP-sensitive conductance in excised patches. These results are consistent with the idea that cGMP opens the light-sensitive channel of the rod outer segment.
Nerve growth factor receptors on chick embryo sympathetic ganglion cells: binding characteristics and development
Authors: Godfrey EW , Shooter EM
Published: March 2018

NGF is essential for the development and maintenance of sympathetic and certain sensory neurons. The NGF receptors on the surface of sympathetic ganglion cells from chick embryos were characterized; they consist of high-affinity receptors with a dissociation constant of about 10(-11) M, and low-affinity receptors with a dissociation constant of about 10(-9) M. There are more than 10 times as many low- affinity as high-affinity receptors per cell. The heterogeneity of NGF binding is not due to negatively cooperative interactions among the receptors. The high- and low-affinity components of NGF binding defined at steady state correspond to slowly and rapidly dissociating components of bound NGF seen in kinetic experiments. In addition, a very slowly dissociating component of bound NGF was observed; this component was a small fraction of binding at low concentrations of NGF but increased to 20–60% of bound NGF at the highest NGF concentrations examined. This very slowly dissociating component of bound NGF accounts for several peculiarities in the binding data not accounted for by steady-state binding of NGF to its high- and low-affinity receptors. Developmental studies showed that both high- and low-affinity NGF receptors were present on chick embryo sympathetic ganglion cells from 6.5 to 20 d in ovo. No significant differences in the numbers or affinities of the receptors were seen with cells from ganglia at 9, 11, or 15 d of development. Cultured non-neuronal cells from sympathetic ganglia had only low-affinity NGF receptors.
Adenosine stimulates glycogenolysis in mouse cerebral cortex: a possible coupling mechanism between neuronal activity and energy metabolism
Authors: Magistretti PJ , Hof PR , Martin JL
Published: March 2018

Adenosine promotes a concentration-dependent hydrolysis of 3H-glycogen newly synthesized from 3H-glucose by mouse cerebral cortical slices. The EC50 for this effect is 7 microM. Theophylline antagonizes the glycogenolysis induced by adenosine with an EC50 of 80 microM. The rank- order of potencies of adenosine agonists is adenosine 5′-cyclopropyl- carboxamide greater than 2-chloroadenosine much greater than N6- cyclohexyladenosine = adenosine, suggesting that adenosine promotes glycogenolysis via receptors of the A2 type. This contention is substantiated by the weak stereospecificity observed for the glycogenolytic action of D- and L-(phenylisopropyl)-adenosine. The glycogenolysis elicited by adenosine at 10 and 100 microM is inhibited by ouabain at 10 microM, a concentration of the cardiac glycoside not significantly affecting 3H-glycogen levels per se. Interestingly, the previously demonstrated glycogenolytic action of vasoactive intestinal peptide (Magistretti et al., 1981, 1984) and of norepinephrine (Quach et al., 1978) is also antagonized by ouabain. These results demonstrate the existence of a metabolic action of adenosine, which is sensitive to ouabain and appears to be mediated by A2 receptors. The concentrations at which adenosine promotes glycogenolysis are of the same order of magnitude as those reached extracellularly by the nucleoside during neuronal depolarization (Pull and McIlwain, 1972). This set of observations therefore supports the notion that adenosine plays a modulatory role in the coupling between neuronal activity and energy metabolism in the CNS.
Excitatory synaptic drive for swimming mediated by amino acid receptors in the lamprey
Authors: Dale N
Published: March 2018

In order to investigate the properties and pharmacology of the excitatory synaptic drive received by motoneurons during swimming in the lamprey, propriospinal excitatory interneurons were activated as a population by the regional application of N-methyl-D,L-aspartate (NMA) to either the 6–8 rostral-most or the 6–8 caudal-most segments of lengths of isolated spinal cord. This caused a rhythmic motor output to be generated in these regions. Synaptic potentials that were phase- locked to, and dependent on, the rhythmic motor activity of the segments exposed to the agonist could be recorded in motoneurons lying outside the activated regions. The synaptic drive to motoneurons located rostral or caudal to the activated regions was studied. Motoneurons received both descending and ascending synaptic input, which consisted of alternating excitatory and inhibitory phases. The inhibition could be reversed by chloride injection and blocked by strychnine, leaving an oscillating excitatory phase. The descending excitatory drive could extend 1–9 segments from the active region, while the ascending excitatory drive was recorded only in motoneurons that were 1–3 segments rostral to the active region. Both types of drive occurred in phase with the ipsilateral ventral root discharge: The peak depolarization of the descending drive occurred at the same point in the swimming cycle as that of the depolarizing phase seen during fictive swimming, while that of the ascending drive occurred significantly later. Both ascending and descending drives were partially reduced in amplitude by 2-amino-5-phosphonovaleric acid or Mg2+. The blocking action of Mg2+ was, in both cases, voltage dependent. Cis-2,3-piperidine dicarboxylic acid or kynurenic acid caused a much greater reduction in the amplitude of the oscillations. These results suggest that a major part of the excitatory drive for swimming in lamprey motoneurons is generated by populations of propriospinal interneurons with relatively long descending and/or short ascending axons, which fire rhythmically during swimming and release an amino acid transmitter that excites motoneurons through N-methyl-D- aspartate (NMDA) and non-NMDA receptors. This information will allow these important neurons to be identified in future experiments.
Maternal suprachiasmatic nuclei are necessary for maternal coordination of the developing circadian system
Authors: Reppert SM , Schwartz WJ
Published: March 2018

During late fetal and early neonatal life, the maternal circadian system coordinates the timing of a circadian clock in the hypothalamic suprachiasmatic nuclei (SCN) to the prevailing light-dark cycle. The role of the maternal SCN in the process of maternal coordination was investigated in rats. Complete lesions of the maternal SCN on day 7 of gestation disrupted rhythms of SCN glucose utilization in fetuses and pineal N-acetyltransferase activity in 10-d-old pups. This disruption was probably due to the desynchronization of individually oscillating fetal SCN, because individual pups born to and reared by SCN-lesioned dams under constant conditions exhibited normal circadian rhythms in drinking behavior. Cross-foster studies showed that the maternal circadian system can coordinate developing circadian rhythmicity during either the pre- or postnatal period. The results indicate that the maternal SCN are a necessary component of the mechanism of maternal coordination during both the pre- and postnatal periods.
Cloning and sequence analysis of cDNAs encoding precursors of urotensin II-alpha and -gamma
Authors: Ohsako S , Ishida I , Ichikawa T , Deguchi T
Published: March 2018

The primary structures of the precursors of urotensin II (UII)-alpha and -gamma, neuropeptide hormones of the caudal neurosecretory system of the carp, Cyprinus carpio, have been determined by analyzing the nucleotide sequences of cloned DNAs complementary to the mRNAs encoding them. A cDNA library, constructed with poly(A)+RNA in the preterminal spinal cord, was screened using 32P-labeled synthetic oligonucleotides representing all possible cDNA sequences corresponding to the pentapeptide common to all forms of carp UII (UII-alpha, -beta, and - gamma). Twenty out of 39 positive clones were analyzed with the restriction endonucleases, HindIII and PvuII, and classified into 4 groups. Nucleotide sequence analysis of 4 clones representing each group revealed that 2 clones encode the precursor of UII-alpha and the other 2 that of UII-gamma. Both precursors consist of 125 amino acid residues, and UII-alpha and -gamma exist at the carboxyl-termini preceded by Arg-Lys-Arg. The homology in both nucleotide and amino acid sequences between the precursors of UII-alpha and -gamma is more than 90%, suggesting that the genes were generated from a common ancestral gene by duplication. There is no sequence homology between the precursors of UII and urotensin I, another peptide hormone of the caudal neurosecretory system, nor between the precursors of UII and somatostatin-14. RNA transfer blot analysis indicated that mRNAs encoding the precursors of UII-alpha and -gamma are present in the spinal cord but not in the brain, intestine, liver, or kidney of the carp.(ABSTRACT TRUNCATED AT 250 WORDS)
Regional distribution of flunitrazepam binding constants: visualizing Kd and Bmax by digital image analysis
Authors: Toga AW , Santori EM , Samaie M
Published: March 2018

We demonstrate direct visualization of benzodiazepine binding parameters collected in a 3H-flunitrazepam saturation study. In this way the relationship between anatomy and specific binding, Kd and Bmax, can be appreciated. These experiments have resulted in image representations of specific flunitrazepam binding, Kd and Bmax. The images retain the anatomic localization inherent in the original autoradiogram and hence make these parameters amenable to visual survey. Binding constants were consistent with data presented elsewhere in the literature. The image of Bmax showed regional heterogeneity. Kd, on the other hand, was relatively homogeneous. These results demonstrate a means by which autoradiographic binding experiments can be extended to saturation studies without significant loss of data.
The blood-retinal barrier: leucine transport by the retinal pigment epithelium
Authors: Sellner PA
Published: March 2018

The transport of leucine across the isolated bullfrog pigment epithelium-choroid was studied in a modified Ussing chamber. With the same concentration of leucine on both sides of the tissue, there was a net flux in the apical-to-basal (retina-to-choroid) direction. The concentration dependence of the apical-to-basal flux comprised at least 2 components: a carrier-mediated flux, with an apparent Km of 0.76 mM and a Vmax of 298 nmol/cm2/hr, and a linear component with a slope of 33.4 cm/hr. The basal-to-apical flux was linear to 10 mM leucine, with a slope of 60 cm/hr. In the absence of Na+, the apical-to-basal flux was inhibited 20%, while the basal-to-apical flux was unaffected. The apical-to-basal flux could be inhibited to the level of the basal-to- apical flux by removing glucose from the solution and adding KCN. Otherwise both fluxes were relatively unaltered by metabolic poisons. There appear to be 3 contributors to the apical-to-basal flux: a weakly Na+-dependent carrier, a linear component (diffusion), and a countertransport mechanism. The basal-to-apical flux must have 2 linear mechanisms, diffusion to the same extent as the opposite flux, and possibly pinocytosis.
Cholinergic septal grafts into the hippocampal formation improve spatial learning and memory in aged rats by an atropine-sensitive mechanism
Authors: Gage FH , Bjorklund A
Published: March 2018

Behaviorally impaired old rats were selected from a population of 75 21- to 23-month-old rats on the basis of the place-investigated abilities in the Morris' water-maze task. After the pretransplant test, half of the old impaired rats received bilateral intrahippocampal cell suspension grafts prepared from the fetal septal-diagonal band region, which is rich in developing cholinergic neurons; the other half were left as sham-operated controls. Twelve weeks after grafting, the rats were retested in the water-maze using alternating cue-navigation and place-navigation trials (i.e., with visible or nonvisible escape platform). While the old impaired controls had deteriorated further between the 2 tests and showed poor retention of the pretransplant performance level, the grafted rats were significantly improved in comparison with both their pretransplant performance and the performance of the old impaired controls in the posttransplant test. The graft-induced effect was due both to an improved retention of the performance level acquired in the test performed prior to transplantation surgery, and to an improved acquisition of spatial memory of the escape platform site during the posttransplant test week (measured as an improved focusing of search over the platform site after platform removal). The acetylcholine esterase inhibitor physostigmine had no or only marginal effects on the performance of any of the young or aged rat groups. By contrast, the recovered navigational abilities and spatial memory in the grafted animals were completely abolished after administration of the muscarinic receptor antagonist atropine. A similar atropine-sensitivity was seen in behaviorally nonimpaired aged rats but not in the well-trained young control rats. The results show that cholinergic septal grafts, implanted into the hippocampal formation, improved spatial learning in the impaired aged rats primarily, or perhaps exclusively, by a recovery of the rats' ability to use spatial cues for place-navigation in the water-maze, while other aspects of the performance deficits in the water-maze task in the aged rats were left unaffected by the septal grafts. On the basis of parallel morphological studies, it is proposed that the effects of the septal grafts on the spatial learning impairments in the aged rats are critically dependent on the direct action of cholinergic neurons in the grafts via synapses formed onto neuronal elements in the host by their ingrowing axons.
Alterations in corticotropin-releasing factor-like immunoreactivity in discrete rat brain regions after acute and chronic stress
Authors: Chappell PB , Smith MA , Kilts CD , Bissette G , Ritchie J , Anderson C , Nemeroff CB
Published: March 2018

Corticotropin releasing factor (CRF) may regulate endocrine, autonomic, and behavioral responses to stress. Evidence indicates that CRF-like immunoreactivity (CRF-LI) is widely distributed throughout the CNS. In this study, the distribution of CRF-LI was determined in 36 rat brain regions by combined radioimmunoassay-micropunch dissection techniques and the effect of stress on CRF-LI was investigated, using a chronic stress model that induces endocrine changes in rats similar to those seen in depressed humans. A control group of rats was handled daily. An acute stress group was subjected to 3 hr of immobilization at 4 degrees C, while a chronic stress group was exposed to unpredictable stressors. Thirty-six brain regions were microdissected by the technique of Palkovits and assayed for CRF-LI, using a specific antiserum to ovine CRF. CRF-LI was detected in most regions. In controls, the highest concentrations were found in the arcuate nucleus/median eminence, the hypothalamic paraventricular (PVN) nucleus, and the periventricular nucleus. The next highest levels were found in the raphe nuclei and dorsal vagal complex. CRF-LI was well represented in the locus coeruleus (LC); in the central, cortical, and medial amygdaloid nuclei; and in the bed nucleus of the stria terminalis. Low concentrations occurred in the hippocampus and cerebrocortical regions. Appreciable concentrations were detected in midbrain and brain stem regions. Acute stress reduced CRF-LI in the arcuate nucleus/median eminence (ME) (by 52%) and in the median preoptic (MPO) nucleus (by 32%) and doubled its concentration in the locus coeruleus.(ABSTRACT TRUNCATED AT 250 WORDS)
Human amnesia and the medial temporal region: enduring memory impairment following a bilateral lesion limited to field CA1 of the hippocampus
Authors: Zola-Morgan S , Squire LR , Amaral DG
Published: March 2018

During the past 100 years clinical studies of amnesia have linked memory impairment to damage of the hippocampus. Yet the damage in these cases has not usually been confined to the hippocampus, and the status of memory functions has often been based on incomplete neuropsychological information. Thus, the human cases have until now left some uncertainty as to whether lesions limited to the hippocampus are sufficient to cause amnesia. Here we report a case of amnesia in a patient (R.B.) who developed memory impairment following an ischemic episode. During the 5 years until his death, R.B. exhibited marked anterograde amnesia, little if any retrograde amnesia, and showed no signs of cognitive impairment other than memory. Thorough histological examination revealed a circumscribed bilateral lesion involving the entire CA1 field of the hippocampus. Minor pathology was found elsewhere in the brain (e.g., left globus pallidus, right postcentral gyrus, left internal capsule), but the only damage that could be reasonably associated with the memory defect was the lesion in the hippocampus. To our knowledge, this is the first reported case of amnesia following a lesion limited to the hippocampus in which extensive neuropsychological and neuropathological analyses have been carried out.