bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential expression of preproenkephalin and preprodynorphin mRNAs in striatal neurons: high levels of preproenkephalin expression depend on cerebral cortical afferents
Authors: Uhl GR , Navia B , Douglas J
Published: March 2018

Preproenkephalin and preprodynorphin mRNAs can be detected by in situ hybridization in medium-sized striatal neurons in normal rats and in rats with unilateral cerebral cortical lesions. Hybridization of 35S- labeled oligonucleotide cDNAs complementary to specific regions of each mRNA reveals that preproenkephalin-expressing neurons are more numerous than cells expressing preprodynorphin. Hybridization densities above enkephalin-positive neurons are also more than twice those noted above preprodynorphin-expressing cells. Northern analyses of mRNA extracted from the striatum are consistent with these relationships. The striatal preproenkephalin hybridization densities are decreased ipsilateral to cerebral cortical lesions; this change evolves largely between 1 and 5 d following the lesion. Striatal preproenkephalin mRNA is thus more prominent than preprodynorphin mRNA and depends on cerebral cortical inputs for its full expression.
Medullary regions mediating atonia
Authors: Lai YY , Siegel JM
Published: March 2018

Electrical stimulation studies have implicated the medial medulla in the inhibition of muscle tone. In the present report we present evidence for suppression of muscle tone by chemical activation of the medial medulla. We find 2 distinct zones within the classically defined medial medullary inhibitory area. A rostral region corresponding to the nucleus magnocellularis (NMC) is sensitive to glutamate. Atonia produced by activation of this region is mediated by non-NMDA receptors. A caudal region, corresponding to the nucleus paramedianus (NPM) is sensitive to ACh. Atonia produced by activation of this region is mediated by muscarinic receptors. Activation of these regions both in acute decerebrate and intact cats suppresses muscle tone. We find that the cholinoceptive dorsolateral pontine region, previously implicated in atonia control, can be activated by glutamate-sensitive non-NMDA receptors. Microinjection of atropine into the NPM or of glutamylglycine into the NMC blocks atonia elicited by pontine carbachol injection. The medullary regions identified here are hypothesized to mediate the suppression of muscle tone that occurs in rapid eye movement sleep and in cataplexy and may have a role in postural control in waking.
Separation of quisqualate- and kainate-selective glutamate receptors in cultured neurons from the rat superior colliculus
Authors: Perouansky M , Grantyn R
Published: March 2018

The aim of the present study was to identify and characterize the receptors and ionic channels mediating the compound response of tectal neurons to exogenous L-glutamate (Glu). Particular attention was paid to the question of whether separate receptors and channels exist for quisqualate (QA) and kainate (KA) and, if so, whether binding to one of these receptors would modify the response elicited through the other. Neurons were dissociated from the superficial gray layer of the superior colliculus from E21 or P1 rats. Between days 14 and 21 in vitro, responsiveness of tectal neurons to Glu and related substances was tested by recording the whole-cell currents induced by rapid superfusion with drug-containing salt solutions. Our experiments showed that tectal neurons express at least 3 distinct types of receptors for acidic amino acids. KA-activated currents (I(KA)) differ from QA- activated currents (I(QA)) in their dose-response characteristics, desensitization patterns, selective blockade with kynurenic acid and suppression by elevated [Ca2+]o, I(KA), but not I(QA), is significantly reduced by low levels of [Cl-]o, and the [Cl-]o-dependent shift of the reversal potential for I(KA) suggests that KA promotes a conductance decrease for Cl-. Such an effect has been ascribed to APB-receptors, but L-2-amino-4-phosphonobutyrate (APB) itself failed to induce current responses in tectal neurons. KA was without effect when administered together, and in equimolar concentrations, with QA. The block of I(KA) was, however, surmounted by applying KA at considerably higher concentrations. It is concluded that QA acts as a low-affinity competitive antagonist at the KA site and as a high-affinity agonist at its own receptor. The response to the endogenous ligand Glu reflects properties of all receptors. QA and KA receptors account for 20–30% (QA) and 49–82% (KA) of the compound current elicited with 100 microM Glu. These results indicate that binding of Glu does not, in contrast to QA, produce any significant suppression of the KA-receptor-mediated current component.
The role of preparation in tuning anticipatory and reflex responses during catching
Authors: Lacquaniti F , Maioli C
Published: March 2018

The pattern of muscle responses associated with catching a ball in the presence of vision was investigated by independently varying the height of the drop and the mass of the ball. It was found that the anticipatory EMG responses comprised early and late components. The early components were produced at a roughly constant latency (about 130 msec) from the time of ball release. Their mean amplitude decreased with increasing height of fall. Late components represented the major build-up of muscle activity preceding the ball's impact and were accompanied by limb flexion. Their onset time was roughly constant (about 100 msec) with respect to the time of impact (except in wrist extensors). This indicates that the timing of these responses was based on an accurate estimate of the instantaneous values of the time-to- contact (time remaining before impact). The mean amplitude of the late anticipatory responses increased linearly with the expected momentum of the ball at impact. The reflex responses evoked by the ball's impact consisted in a short-latency coactivation of flexor and extensor muscles at the elbow and wrist joints. Their mean amplitude generally increased with the intensity of the perturbation both in the stretched muscles and in the shortening muscles. We argue that both the anticipatory and the reflex coactivation are centrally preset in preparation for catching and are instrumental for stabilizing limb posture after impact. A model with linear, time-varying viscoelastic coefficients was used to assess the neural and mechanical contributions to the damping of limb oscillations induced by the ball's impact. The model demonstrates that (1) anticipatory muscle stiffening and anticipatory flexion of the limb are synergistic in building up resistance of the hand to vertical displacement and (2) the reflex coactivation produces a further increment of hand stiffness and viscosity which tends to offset the decrement which would result from the limb extension produced by the impact.
Secretin and vasoactive intestinal peptide activate tyrosine hydroxylase in sympathetic nerve endings
Authors: Schwarzschild MA , Zigmond RE
Published: March 2018

Secretin and vasoactive intestinal peptide (VIP) are known to stimulate tyrosine hydroxylase (TH) activity acutely in the rat superior cervical ganglion (SCG). Because TH-containing neurons in the SCG innervate the iris, submaxillary gland, and pineal gland, we examined the effects of secretin and VIP in these 3 autonomic end organs in vitro. Both peptides stimulated TH activity in each tissue. These stimulations resembled those in the SCG in that (1) secretin displayed a higher potency than VIP in all 3 end organs, (2) the peptide effects were unchanged when calcium was excluded from the incubation medium, and (3) they were mimicked by activators of the cyclic adenosine monophosphate (cAMP) pathway. These findings indicate that secretin and VIP can regulate transmitter metabolism in both the cell bodies and axon terminals of neurons originating in the SCG. Furthermore, the data raise the possibility that catecholamine synthesis in sympathetic nerve terminals is modulated by peptides released by other, nearby nerve endings.
Expression of nerve-muscle topography during development
Authors: Laskowski MB , High JA
Published: March 2018

Previous studies have indicated that in 2 muscles of the adult rat, the anterior serratus and the diaphragm, the rostrocaudal axis of the motoneuron pool projects topographically onto the rostrocaudal axis of the muscle. In the present work we have asked whether this orderly topography emerges as a function of postnatal synaptic rearrangement or whether this pattern is already established at birth. The anterior serratus muscle was studied over the period ranging from embryonic day 17 through postnatal day 30. Using 2 criteria of topography, average segmental innervation and average target field of cervical roots C6 and C7, we found that a topographic distribution of the motoneuron pool is already present prior to birth and maintained throughout the postnatal period. Moreover, both C6 and C7 form an orderly map over the surface of the serratus in the embryo, and the topography is sharpened during postnatal periods. The diaphragm also is topographically innervated at birth and undergoes a comparable sharpening of the projection map postnatally. We conclude that the topographic projection of motoneurons is established prior to birth in these muscles, and postnatal synaptic rearrangement serves to sharpen the topographic map toward the adult pattern. These results also suggest that the pursuit of basic mechanisms underlying topography should be directed toward initial embryonic nerve-muscle contacts.
Lipopolysaccharide-free conditions in primary astrocyte cultures allow growth and isolation of microglial cells
Authors: Gebicke-Haerter PJ , Bauer J , Schobert A , Northoff H
Published: March 2018

Primary rat astrocyte cultures were used to isolate a macrophage population that does not adhere to the confluent glial cells. The cells multiplied vigorously in coculture with astrocytes during the 14 d culture period, provided that functionally active lipopolysaccharide (LPS) was either absent or present in very low concentrations. Based on morphological, immunocytochemical, and pharmacological data, it was concluded that the isolated cells were microglia, the resident macrophages of the brain. The findings characterized them as a distinct cell population that shares features both of peritoneal macrophages and of astroglial cells. Like peritoneal macrophages, the isolated cells were able to phagocytize as shown by their ingestion of latex beads and uptake of L-leucyl methylester. Furthermore, they were immunocytochemically stainable by a specific monoclonal antibody (ED 1) against a macrophage-specific antigen (Dijkstra et al., 1985). They also synthesized prostaglandin E2 (PGE2) and secreted interleukin 1 (IL- 1) upon stimulation with LPS. Upon stimulation with the ionophore A23187, PGD2, the predominant prostaglandin of the brain, was the major PG metabolite released by these cells. In contrast to peritoneal macrophages, microglial cells were able to multiply. Proliferation of microglial cells in coculture with astrocytes was suppressed when 2 ng LPS/ml or higher concentrations were added to astroglial culture media. These astrocyte cultures, which contained approximately 1% microglia, were used to investigate the influence of LPS on prostaglandin and IL-1 secretion in order to compare astroglial and microglial features. Increasing LPS concentrations induced increased PGE2 secretion, whereas PGD2 secretion was essentially unaffected by LPS. The critical influence of LPS contaminations in most of the commercially available animal sera used for astrocyte cultures on cellular composition in general and on metabolism of hormones and growth factors in particular is discussed.
Autoradiographic localization and characterization of tachykinin receptor binding sites in the rat brain and peripheral tissues
Authors: Mantyh PW , Gates T , Mantyh CR , Maggio JE
Published: March 2018

Quantitative receptor autoradiography using several radiolabeled tachykinins was used to localize and characterize tachykinin peptide receptor binding sites in rat CNS and peripheral tissues. Autoradiographic localization and displacement experiments using several radiolabeled tachykinins indicate that in the rat there are at least 3 distinct tachykinin receptor binding sites. One of these is present in both the CNS and peripheral tissues, one is present only in the CNS, and one is present only in peripheral tissues. The first tachykinin receptor binding site, which is detectable in both the CNS and peripheral tissues, appears to prefer substance P (SP) as an endogenous ligand. Areas expressing high concentrations of this binding site include the medial septum, superior colliculus, inferior olive, inner plexiform layer of the retina, external muscle of the bladder, and the muscularis externa of the esophagus. The second type of tachykinin receptor binding site, which is detectable only in the CNS appears to prefer either neuromedin K (NK) and/or substance K (SK) as the endogenous ligand. This receptor binding site is labeled by Bolton- Hunter conjugates of NK, SK, eledoisin, or kassinin and is found in high concentrations in laminae 4 and 5 of the cerebral cortex, the ventral tegmental area, laminae 1 and 2 of the spinal cord, and the inner plexiform layer of the retina. The third type of tachykinin receptor binding site is detectable only in peripheral tissues and appears to prefer SK as the endogenous ligand. This receptor binding site is labeled by SK, eledoisin, or kassinin radioligands and tissues that express high concentrations include the muscularis mucosae of the esophagus, the circular muscle of the colon, and the external muscle of the bladder. These data suggest that SP receptors are expressed in the brain and peripheral tissues, NK receptors are expressed in the CNS, and SK receptors are expressed in peripheral tissue. These data fit well with radioimmunoassay data that suggest that, whereas in the CNS SP, SK and NK are present in high concentrations, in peripheral tissues only SP and SK are present in detectable concentrations. The present classification of tachykinin receptors places a lower limit on the number of mammalian tachykinin receptor types and provides a functional/morphological framework for exploring the diverse actions of tachykinin peptides in both the CNS and peripheral tissues.
Cerebellar lesions and the nictitating membrane reflex: performance deficits of the conditioned and unconditioned response
Authors: Welsh JP , Harvey JA
Published: March 2018

Unilateral cerebellar lesions abolished the occurrence of ipsilateral conditioned nictitating membrane responses during the 285 msec interval between onset of the conditioned and unconditioned stimuli on paired trials. This effect was obtained in 15 animals sustaining damage to the dorsolateral aspects of the interpositus nucleus and the adjoining white matter. However, conditioned responses did occur during the 800 msec observation interval employed on tone-alone test trials, and these responses exhibited the classic performance deficits normally associated with cerebellar damage: a low frequency of occurrence (14%, as compared with 96% before the lesion); a 3.1 mm decrease in amplitude; a 236 msec increase in onset latency; a 563 msec increase in latency of peak amplitude; and a 327 msec increase in rise time. Four of the 15 animals failed to demonstrate greater than 5% responding during the test trials. These performance deficits were not specific to the learned, conditioned response. Unconditioned responses were also reduced in frequency and increased in latency of peak amplitude and rise time, especially when elicited at lower air-puff intensities. These deficits in the unconditioned response were observed in animals that failed to exhibit conditioned responses on either paired or test trials, as well as in animals demonstrating conditioned responses only during test trials. We conclude that the cerebellum has a general role in regulating the nictitating membrane reflex so that deficits in learned responses observed after cerebellar lesions are secondary to a broader deficit in performance. The performance deficits appear to consist of a sensory component, as reflected by an increase in stimulus threshold for elicitation of the nictitating membrane reflex, and a motor component, as reflected by the altered topography of the evoked response. The results of this study thus reaffirm the role of the cerebellum in regulating the sensorimotor processes necessary for the optimal performance of both conditioned and unconditioned responses and extends this role to the expression of a simple cranial nerve reflex.
Cyclic AMP only partially mediates the actions of serotonin at lobster neuromuscular junctions
Authors: Goy MF , Kravitz EA
Published: March 2018

Serotonin (5-HT) has multiple physiological actions at lobster neuromuscular junctions, including facilitation of transmitter release from nerve terminals and an increase in the tone and excitability of muscle fibers. These physiological effects of 5-HT are accompanied by a rise in intracellular levels of cAMP. We have used combined biochemical and physiological approaches to investigate whether cAMP directly mediates the physiological actions of the hormone. Based on the following lines of evidence, we conclude that the postsynaptic increase in muscle tone occurs independently of cAMP and that while the cyclic nucleotide does play a role in the facilitation of transmitter release by 5-HT, there is also a cAMP-independent component to this facilitation. (1) Agents that mimic the action of 5-HT on cAMP levels (forskolin, IBMX, SQ20009, 8-bromo cAMP) fail to mimic the postsynaptic actions of the amine. These agents do facilitate transmitter release, although none of them has as large an effect as does 5-HT. (2) When 5- HT is removed, presynaptic facilitation decays as the sum of 2 exponentials with very different time courses. The rate of the slower process is similar to the rate of breakdown of cAMP, while the faster process and the postsynaptic response decay significantly more rapidly. (3) IBMX retards the breakdown of cAMP and simultaneously retards the decay of the slower presynaptic process, with little or no effect on the other responses. (4) IBMX and forskolin potentiate the effect of 5- HT on cAMP levels and selectively enhance the slowly decaying presynaptic component with little or no effect on the other responses.
Selective modulation of spike duration by serotonin and the neuropeptides, FMRFamide, SCPB, buccalin and myomodulin in different classes of mechanoafferent neurons in the cerebral ganglion of Aplysia
Authors: Rosen SC , Susswein AJ , Cropper EC , Weiss KR , Kupfermann I
Published: March 2018

An examination of the cellular properties and synaptic outputs of mechanoafferent neurons found on the ventrocaudal surface of the cerebral ganglion of Aplysia indicated that the cerebral mechanoafferent (CM) neurons are a heterogeneous population of cells. Based on changes in action potential duration in response to bath applications of 5-HT in the presence of TEA, CM neurons could be divided into 2 broad classes: mechanoafferents whose spikes broaden in response to 5-HT (CM-SB neurons) and mechanoafferents whose spikes narrow in response to 5-HT (CM-SN neurons). Morphological and electrophysiological studies of the CM-SN neurons indicated that they were comprised of previously identified interganglionic cerebral-buccal mechanoafferent (ICBM) neurons and a novel set of sensory neurons that send an axon into the LLAB cerebral nerve and have perioral zone receptive fields that are similar to those of ICBM neurons. Changes in spike width due to 5-HT were correlated with changes in synaptic output as indicated by the magnitudes of EPSPs evoked in postsynaptic neurons. Electrical stimulation of cerebral nerves and connectives also produced spike narrowing or broadening, and the sign of the effect was a function of the parameters of stimulation. Both heterosynaptic facilitation and heterosynaptic depression of EPSPs evoked in follower cells could be demonstrated. A variety of putative neuromodulators other than 5-HT were also found to affect the duration of action potentials in both classes of CM neurons. FMRFamide had effects opposite to that of 5-HT. SCPB and a recently characterized Aplysia neuropeptide, buccalin, broadened the spikes of both CM classes. Another neuropeptide, myomodulin, decreased the duration of CM-SB neuron spikes but had no effect on CM-SN spikes. Since the CM neurons appear to mediate a variety of competing behaviors, including feeding, locomotion, and defensive withdrawal, the various neuromodulator actions may contribute to the mechanisms whereby behaviors are selected and modified.
Inhibitors of protein kinase C prevent enhancement of calcium current and action potentials in peptidergic neurons of Aplysia
Authors: Conn PJ , Strong JA , Kaczmarek LK
Published: March 2018

Following brief stimulation of an afferent pathway, the bag cell neurons of Aplysia undergo a dramatic change in excitability, resulting in a prolonged discharge of spontaneous action potentials. During the discharge, the action potentials of the bag cell neurons become enhanced in height and width. The afterdischarge triggers release of neuroactive peptides that initiate egg-laying behavior in this animal. Evidence suggests that changes in excitability of the bag cell neurons may be mediated by activation of protein kinase C (PKC) and cAMP- dependent protein kinase (cAMP-PK). PKC activators, such as the phorbol ester TPA (12-O-tetradecanoyl-13-phorbol acetate), enhance the amplitude of action potentials in isolated bag cell neurons in cell culture. These agents act by unmasking a previously covert species of voltage-dependent calcium channel resulting in an increase in calcium current. In the accompanying paper (Conn et al., 1989), we showed that H-7, a protein kinase inhibitor, inhibits the effect of TPA, and is a selective inhibitor of PKC relative to cAMP-PK in these cells. We now report that another PKC inhibitor, sphinganine, also inhibits the effect of TPA on action potential height and calcium current in cultured bag cell neurons, and that N-acetylsphinganine, an inactive sphinganine analog, fails to inhibit the effects of PKC activators. Although both H-7 and sphinganine prevent the effects of TPA when added prior to TPA addition, neither compound reverses the effects of TPA when added after the action potentials have already become enhanced by TPA.(ABSTRACT TRUNCATED AT 250 WORDS)
Two sexually dimorphic cell groups in the human brain
Authors: Allen LS , Hines M , Shryne JE , Gorski RA
Published: March 2018

A quantitative analysis of the volume of 4 cell groups in the preoptic- anterior hypothalamic area (PO-AHA) and of the supraoptic nucleus (SON) of the human brain was performed in 22 age-matched male and female individuals. We suggest the term Interstitial Nuclei of the Anterior Hypothalamus (INAH 1–4) to identify these 4 previously undescribed cell groups in the PO-AHA. While 2 INAH and the SON were not sexually dimorphic, gender-related differences were found in the other 2 cell groups. One nucleus (INAH-3) was 2.8 times larger in the male brain than in the female brain irrespective of age. The other cell group (INAH-2) was twice as large in the male brain, but also appeared to be related in women to circulating steroid hormone levels. Since the PO- AHA influences gonadotropin secretion, maternal behavior, and sexual behavior in several mammalian species, these results suggest that functional sex differences in the hypothalamus may be related to sex differences in neural structure.
Nicotinic and muscarinic agonists stimulate rapid protein kinase C translocation in PC12 cells
Authors: Messing RO , Stevens AM , Kiyasu E , Sneade AB
Published: March 2018

Phosphoinositide hydrolysis, a major mechanism for signal transduction in neural cells, generates diacylglycerol, which can in turn activate protein kinase C (PKC). Although cholinergic agonists elicit phosphoinositide hydrolysis in neural tissues, little is known about activation of PKC by cholinergic agonists. PKC requires phosphatidylserine for activation, and in intact cells this lipid requirement is satisfied by binding of the enzyme to cell membranes. Therefore, in intact cells, activation of PKC is often associated with a decrease in cytosolic PKC activity accompanied by an increase in membrane-associated activity. We studied cholinergic-induced activation of PKC by examining changes in the subcellular distribution of the enzyme in PC12 cells treated with cholinergic drugs. Carbachol (1 mM) induced large and rapid increases in membrane-associated PKC activity; a maximal increase of 460% occurred after 5 sec of incubation. Carbachol-induced PKC translocation was concentration-dependent, with a biphasic dose-response curve yielding approximate EC50 values of 10(-6) M and 10(-4) M for the high- and low-affinity components, respectively. Experiments with selective cholinergic agents demonstrated that both muscarinic and nicotinic receptors are involved in carbachol-induced PKC translocation, but the response is predominantly mediated by nicotinic receptor stimulation. Muscarinic-induced association of PKC with cell membrane fractions was resistant to extraction by chelators, whereas nicotinic-mediated membrane binding was partially reduced by homogenization of cells in the presence of EGTA. Omission of calcium from the incubation medium or chelation of calcium with EGTA completely blocked muscarinic- and nicotinic-induced translocation. In addition, the calcium channel blocker nifedipine reduced the nicotinic response by 60%. (ABSTRACT TRUNCATED AT 250 WORDS)
Differentiation increases type II calmodulin-dependent protein kinase in the neuroblastoma/glioma cell line 108CC15 (NG108-15)
Authors: Vallano ML , Beaman-Hall CM
Published: March 2018

A type II calcium/calmodulin-dependent protein kinase (CaM kinase II) was purified approximately 300-fold from cultured neuroblastoma/glioma (NG108) cell homogenate. The purification of the kinase, which used a combination of differential centrifugation and chromatography on cation- exchange, calmodulin-affinity, and gel-filtration resins, was monitored by the ability of the kinase to phosphorylate the high-molecular-weight microtubule-associated protein 2 (MAP-2). The kinase was compared with authentic CaM kinase II purified from rat brain cytosol. Based upon holoenzyme molecular weight, subunit composition and molecular weight, calcium-dependent calmodulin-binding to subunits, calcium/calmodulin- dependent autophosphorylation of subunits, substrate specificity, apparent km's for ATP and calmodulin, phosphopeptide maps of subunits, time course, and heat lability, the kinase was identified as a type II calcium/calmodulin-dependent protein kinase. When cellular differentiation was induced under specific conditions of cell culture, a significant increase in the apparent activity and amount of the kinase per mg protein was observed relative to control cells. These studies suggest that there is an increase in CaM kinase II expression during cellular differentiation, which may relate to the concurrent development of electrical excitability, synaptogenesis, and elaboration of cytoskeletal elements. Thus, the NG108 cell should provide a useful model to study the physiological functions of CaM kinase II.
Sprouts emerging from the dendrites of axotomized lamprey central neurons have axonlike ultrastructure
Authors: Hall GF , Poulos A , Cohen MJ
Published: March 2018

We have examined the dendritic and axonal ultrastructure of intact anterior bulbar reticulospinal neurons (ABCs) in the CNS of the larval sea lamprey and compared it with that of the dendrites and neuritic sprouts from ABCs examined 2 months following axotomy. Dendrites and axons of intact ABCs are distinguishable from one another by several ultrastructural criteria: (1) the predominance of microtubules in the dendritic cytoskeleton and neurofilaments in that of the axon, (2) the exclusively postsynaptic status of the dendrites versus the presynaptic status of the axon, and (3) the presence of polyribosomes and large numbers of mitochondria in the dendrites and their respective absence and scarcity in the axon. The ultrastructure of axonal sprouts evoked by axotomy of ABCs 1–1.5 mm from their somata (“intermediate axotomy”) in many ways resembled that of intact axons. Axonal sprouts were presynaptic to other neurons, and their cytoskeletons consisted mainly of neurofilaments. They also exhibited some features not seen in either axons or dendrites, such as numerous clusters of small vesicles that were not associated with synapses and, in some cases, close associations with glial elements. We also examined sprouts emerging from the dendrites of ABCs following axotomy within 500 microns of their somata (“close axotomy”) and found that such “dendritic” sprouts closely resembled axonal sprouts; they possessed neurofilament- dominated cytoskeletons, were presynaptic to other neurons, and were often associated with glial elements. The dendrites of ABCs undergoing dendritic sprouting retained their normal gross morphology but possessed a mixture of “axonal” and “dendritic” ultrastructural characteristics, exhibiting neurofilament-dominated cytoskeletons while remaining entirely postsynaptic to other neurons. However, there were significantly fewer synapses on the dendrites of axotomized cells than were found on the dendrites of intact ABCs. We conclude that sprouts evoked by axotomy are intrinsically axonal in character whether they originate from the axon stump or from the dendritic tree. Our results also suggest that the materials necessary for axonal regeneration may displace elements of the dendritic cytoskeleton as they are transported through the dendrites to the emerging “dendritic” sprouts following close axotomy.
The expression of the growth associated protein B50/GAP43 in the olfactory system of neonatal and adult rats
Authors: Verhaagen J , Oestreicher AB , Gispen WH , Margolis FL
Published: March 2018

B50/GAP43 is a neuron-specific phosphoprotein whose expression is associated with neural development and synaptic plasticity. Its postnatal ontogeny was investigated in the primary olfactory pathway of the rat using immunohistochemical methods. The unique ability of the olfactory neuroepithelium to generate new neurons from a population of precursor cells present in the basal cell layer of this tissue makes it a valuable model in the study of neural development. In newborn rats B50/GAP43 is present throughout the entire population of olfactory receptor neurons. These cells are stained throughout, from the ciliated dendritic knob to their axon terminals in the bulb. This appears to be the first example of unambiguous B50/GAP43 expression in dendritic processes. With increasing age the distribution of this protein becomes progressively restricted to a subpopulation of olfactory neurons. Comparison of the expression of B50/GAP43 and the olfactory marker protein (OMP), a polypeptide only present in mature olfactory neurons, revealed that during postnatal development of the olfactory system these 2 proteins are expressed in a nearly reciprocal fashion. In adult animals (3.5 months-6 months of age), B50/GAP43-positive cells are exclusively present adjacent to the basal cell layer of the neuroepithelium. Basal cells appear to be unstained. The region of the epithelium containing the B50/GAP43-positive cells is virtually devoid of OMP-positive neurons. A significant fraction of these B50/GAP43- containing cells bear dendritic and neuritic processes. However, these cells do not express olfactory cilia. It is probable that the olfactory neurons expressing the growth-associated B50/GAP43 protein may correspond to a particular subset of olfactory neurons at an intermediate state of maturation.
Effects of background illumination on the horizontal cell responses in the tiger salamander retina
Authors: Yang XL , Wu SM
Published: March 2018

Synaptic transmission between photoreceptors and horizontal cells (HCs) was studied in the flat-mounted isolated retinas of the tiger salamander. Background illumination expedited the rise time of the HC light response, and the HC response rise time (HCRRT) reached steady state about 2 sec after the onset of the background illumination. The change in HCRRT is probably responsible for the background-induced enhancement of the HC responses to short light stimuli. The amplitude of the HC responses to 100 msec light steps in the presence of background illumination was 2–5 times larger than that measured under dark-adapted conditions. Background illumination exerted little effect on the response rise time in cones and bipolar cells, and thus it caused no significant response enhancement in those cells. The background-induced change in HCRRT correlated closely with the rod voltage but not with the HC voltage. These results suggest that the background-induced change in HCRRT is probably mediated by postsynaptic events in HCs because no significant time course change is observed in photoreceptors and bipolar cells (which share the same synapses with the HCs). A suppressive rod action on the cone inputs in HCs may be responsible for modulating the HCRRT. By shortening the HCRRT, background illumination regulates the frequency response of the photoreceptor-HC synapse and alters the capacity of spatial resolution of retinal bipolar cells.
Lesions of the hippocampal formation but not lesions of the fornix or the mammillary nuclei produce long-lasting memory impairment in monkeys
Authors: Zola-Morgan S , Squire LR , Amaral DG
Published: March 2018

A group of tasks sensitive to human amnesia were used to characterize the severity and duration of memory impairment in monkeys following bilateral damage to the hippocampal formation, fornix, or mammillary nuclei. Monkeys with hippocampal formation lesions (which included the hippocampus proper, dentate gyrus, subiculum, posterior entorhinal cortex, and much of the parahippocampal gyrus) exhibited a substantial and lasting memory impairment. Monkeys with fornix transection or bilateral damage to the mammillary nuclei were impaired on the first task administered after surgery (delayed nonmatching to sample). However, they performed all the other tasks normally and were unimpaired when the delayed nonmatching to sample task was re- administered 18 months after surgery. The findings are consistent with reports that damage limited to the human hippocampus can produce a clinically significant and permanent amnesia. Because fornix transection or mammillary lesions produced only transient memory impairment, it seems unlikely that similar damage in humans can cause a severe or permanent amnesia.
Membrane proteins of the nerve growth cone and their developmental regulation
Authors: Simkowitz P , Ellis L , Pfenninger KH
Published: March 2018

The membrane polypeptides of growth cone fragments (“growth cone particles,” GCPs) isolated from fetal rat brain by subcellular fractionation have been analyzed in further detail. The major polypeptides of salt-washed GCP membranes detected by 1-dimensional gel electrophoresis (Ellis et al., 1985b) resolve in 2-dimensional gels as a spot of 52 kDa that comigrates with beta-tubulin and reacts with anti- beta-tubulin; a 46 kDa, pl 4.3, polypeptide (pp46) that has no equivalent in the soluble fraction and is identical to one of the GCP's major phosphoproteins (Katz et al., 1985) and to GAP43 (Willard et al., 1985); a spot of 42 kDa that comigrates with actin; and a species of 34 kDa (p34) without soluble equivalent. The prominent 38 kDa doublet identified in 1-dimensional gels is difficult to resolve in 2- dimensional gels. The major phosphoproteins pp80ac, pp46, and pp40 (Katz et al., 1985), as well as p34 partition into the oil phase of Triton X-114 extracts, suggesting that they are integral membrane proteins, at least in our experimental conditions. The properties of pp46 reported here are in conflict with the highly hydrophilic amino acid sequence predicted for GAP43/B50/F1 (Basi et al., 1987; Karns et al., 1987). Growth-cone and presynaptic membrane proteins are compared as follows. After eye injection of 35S-methionine, GCPs and synaptosomes are isolated from the target areas of optic nerve of fetal and adult rats, respectively. Polypeptides are separated by 1- and 2- dimensional gel electrophoresis and the radiolabeled species identified fluorographically. The comparison of labeled GCP and synaptosome polypeptides shows that all 5 major Coomassie blue-stained polypeptides of GCP membranes (52, 46, 42, 38, 34 kDa) are intensely labeled after eye injection. However, in synaptosomes, these polypeptides are weakly labeled if at all; instead, an intensely labeled polypeptide of 28 kDa, and several additional species not seen in GCPs, have appeared. Therefore, the major growth cone membrane proteins are developmentally regulated, and the rates of synthesis and transport into the axonal ending of neuronal polypeptides change dramatically at the time of synaptogenesis.
In vivo development of nicotinic acetylcholine receptor channels in Xenopus myotomal muscle
Authors: Owens JL , Kullberg R
Published: March 2018

The development of acetylcholine receptor (AChR) channel function in Xenopus myotomal muscle was studied by single-channel recordings from cell-attached patches of nonjunctional membrane in vivo. AChR channels were studied from the time of their first appearance on the muscle membrane until the time of full maturity of the muscle. Two predominant amplitude classes of AChR channels were observed with slope conductances of about 40 and 60 pS. During the first day after their initial appearance on the membrane, the small-conductance channels were the most numerous class on the muscle membrane. The large-conductance channels then began to be expressed in significant numbers and, over the next 2 d, became the predominant channel type. The large- conductance class had an apparent mean open time of approximately 0.7 msec at resting potential, which remained constant throughout development. The small channel initially had an apparent open time of approximately 3 msec at resting potential, which decreased during development by about 50%. The decrease in open time of the small channel was correlated in time with the increased expression of the large-conductance channels. Openings of the large-conductance channels were generally separated by closed intervals of more than 1 msec, whereas openings of the small-conductance channels were commonly interrupted by brief gaps of about 0.2 msec duration. The duration of the brief gaps did not change during development.
Expansion of the central arborizations of persistent sensory neurons during insect metamorphosis: the role of the steroid hormone, 20- hydroxyecdysone
Authors: Levine RB
Published: March 2018

During insect metamorphosis many larval neurons persist but are modified to serve new behavioral roles at later stages of life. For example, certain larval mechanosensory neurons expand their central arborizations during pupal development and evoke a different behavioral response, the gin trap reflex. The role of the insect steroid hormone, 20-hydroxyecdysone (20-HE) in this developmental change was investigated by removing the normal source of the hormone, followed by topical application of 20-HE to the peripheral somata of the sensory neurons. In prepupal animals that were ligated between the abdomen and thorax to remove the source of ecdysteroids the sensory neurons retained a larval arborization pattern. Topical application of 20-HE to the peripheral sensory neuron somata caused the treated neurons to undergo terminal arbor expansion within the CNS. The treated sensory neurons were not able to evoke the normal pupal behavioral response, but instead caused a larval-like reflex response. In a previous study, sensory neurons that were treated peripherally with a juvenile hormone analog during the commitment peak of ecdysteroids were shown to retain a larval arborization pattern at pupation and to not evoke the gin trap reflex (Levine et al., 1986). Within 4 d of pupation, however, these neurons belatedly developed expanded terminal arbors and evoked the pupal reflex. In the present study, similarly treated animals were ligated at pupation to block the surge in ecdysteroids that normally occurs at this time. This treatment prevented both the delayed expansion and the reflex, whereas topical 20-HE application induced growth and allowed the treated sensory neurons to evoke the gin trap reflex. It is concluded that both 20-HE and juvenile hormone act directly on the cell bodies of the sensory neurons to regulate the growth of their central processes. This growth is necessary but not sufficient for the development of the gin trap reflex, suggesting that other steroid-dependent changes must also occur within the CNS. Thus, as in the vertebrates, steroid hormones direct important developmental events within the insect nervous system.
Acetylcholine receptor-like molecules are found in both synaptic and extrasynaptic clusters on the surface of neurons in the frog cardiac ganglion
Authors: Sargent PB , Pang DZ
Published: March 2018

Sixty monoclonal antibodies (mAbs) made against nicotinic acetylcholine receptors (AChRs) from electric organ were tested for their ability to cross-react at synaptic sites in the frog cardiac ganglion, where transmission is mediated by ACh via nicotinic receptors. Forty-one of the mAbs tested were known to bind to AChRs in frog skeletal muscle (Sargent et al., 1984). As determined by double-label immunofluorescence microscopy, 8 of the 60 mAbs bound to small, punctate sites that lay within areas of synaptic contact, marked by an anti-synaptic vesicle antibody. One of the 8 cross-reacting antibodies that produced particularly intense staining (mAb 22) was chosen for further study and was found to bind to the postsynaptic membrane beneath active zones, as determined by peroxidase immunocytochemistry and electron microscopy. This suggests that mAb 22 crossreacts with AChRs on the ganglion cell surface. While most mAb 22 immunoreactivity was located in the postsynaptic membrane, about 20% of the peroxidase- stained patches were extrasynaptic (327 patches analyzed from 8 ganglia). Virtually no peroxidase-stained patches were observed when an isotype-matched control mAb was used in place of mAb 22. In frog skeletal muscle peroxidase-stained patches obtained with mAb 22 were found exclusively at synaptic sites (179 patches examined from 6 muscles). These results suggest that extrasynaptic patches of AChRs are present in innervated autonomic neurons but not in innervated skeletal muscle.
A muscle acetylcholine receptor is expressed in the human cerebellar medulloblastoma cell line TE671
Authors: Luther MA , Schoepfer R , Whiting P , Casey B , Blatt Y , Montal MS , Montal M , Linstrom J
Published: March 2018

The human neuromedulloblastoma cell line TE671 is shown by single- channel recordings to express nicotinic acetylcholine receptors (AChRs) that are blocked by alpha-bungarotoxin (alpha Bgt). These AChRs do not react with antisera to the alpha Bgt-binding protein of brain or with monoclonal antibodies (mAbs) to brain nicotinic AChRs that do not bind alpha Bgt. TE671 AChRs do react with autoantibodies to muscle AChRs from myasthenia gravis patients and with mAbs to muscle AChRs, including mAbs specific for extrajunctional AChRs. AChRs. AChRs purified from TE671 cells are composed of 4 kinds of subunits corresponding to those of muscle AChR. Sequences of cDNAs for the ACh- binding alpha subunit and the delta subunit of this AChR further identify it as muscle AChR. Expression of TE671 AChR can be up- regulated by nicotine and dexamethasone, and down-regulated by forskolin.
Hippocampal place cells: stereotypy and plasticity
Authors: Breese CR , Hampson RE , Deadwyler SA
Published: March 2018

Hippocampal complex spike cells were recorded during exploration for water delivered to cups located in various regions of an elevated platform. Place fields were recorded with a video monitoring system that recorded movements as the animal explored each of the 5 cup locations where water was delivered on the platform. Plasticity of place cell firing as a function of selective water delivery to specific cup locations on the platform was also examined. Several characteristics of place cell firing were studied that indicated a high degree of control by factors such as relative direction of movement and trajectory through the field. Time-shift analyses indicated cell firing was most representative of the place field at the time of spike occurrence. It was demonstrated that place fields possess borders in which firing was increased or decreased upon entering or leaving a particular region of the platform. The most important finding from this investigation was the pronounced degree of plasticity exhibited by place cells. Selective delivery of water to a single location on the platform was sufficient in most of the cases tested to shift the location of the field to the location where water was available. These findings suggest hippocampal place cell firing, although highly influenced by spatial and directional features of the environment, can readily change under conditions in which significant stimuli are added or removed from those locations.
Receptor specificity of a glucocorticoid- and stress-induced hippocampal protein
Authors: Schlatter LK , Dokas LA
Published: March 2018

Following treatment of rats with a subcutaneous injection of 5 mg of corticosterone, hippocampal slices in vitro show increased labeling from 35S-methionine of a protein with an apparent molecular weight (Mr) of 35,000. Increased protein labeling is seen in response to corticosterone, dexamethasone, and aldosterone, steroids that associate with glucocorticoid receptors. Little or no response occurs after administration of progesterone or estradiol. Because the injected dose of steroids is high and responses to an injection of this magnitude may be pharmacological, several experiments have been done to determine whether stimuli that increase endogenous levels of corticosterone have the same effect on labeling of the 35,000 Mr protein. One hour after various stresses (immobilization, cold, ether, and sham-injection), when plasma levels of corticosterone are elevated, labeling of the 35,000 Mr protein is increased. Injection of ACTH also stimulates the synthesis of this protein in intact animals in a manner analogous to that seen with corticosterone injections. In addition, a dose-response curve for corticosterone with adrenalectomized rats shows that synthesis of the protein is maximally increased when the injected dosage causes serum levels of corticosterone to increase to the levels seen during stress. The increase in labeling of the 35,000 Mr protein in adrenalectomized animals is only half as great as that observed in intact animals. Injections of the type II glucocorticoid (GR) receptor agonist, RU 28362, into adrenalectomized rats differentially stimulates the synthesis of the 35,000 Mr protein compared with the mineralocorticoid aldosterone, which has a higher affinity for the type I (CR) receptor.(ABSTRACT TRUNCATED AT 250 WORDS)