bluuebunny/crossref_metadata_2025 huggingface dataset:
Do the relative mapping densities of the magno- and parvocellular systems vary with eccentricity?
Authors: Livingstone MS , Hubel DH
Published: March 2018

Two recent papers on the macaque visual system have concluded that in the lateral geniculate body the ratio of the number of cells in the magnocellular system to the number in the parvocellular system representing the same area of visual field increases by a factor of 20 between the fovea and the far periphery. In the primary visual cortex the relative cell densities of the 2 systems change little with eccentricity. These calculations therefore predict a 20-fold change in the relative densities of the inputs to the visual cortex from the 2 subdivisions of the lateral geniculate body. To test this prediction, we asked if the following vary with eccentricity: (1) the ratio of the number of magnocellular to parvocellular neurons innervating a given area of striate cortex and (2) the relative density, in the magno- and parvo-recipient sublaminae of layer 4C, of radioactivity transported from the eye to the cortex. Neither of these ratios showed any significant variation with eccentricity. These results seem to throw doubt on the contention that the ratio between the magnocellular and parvocellular layers of the number of cells per degree2 of visual field varies significantly with eccentricity.
Synaptic specificity in frog sympathetic ganglia during reinnervation, sprouting, and embryonic development
Authors: Feldman DH
Published: March 2018

B cells and C cells in frog lumbar sympathetic ganglia are specifically innervated by preganglionic B fibers and C fibers, respectively. To explore the mechanisms underlying the formation of these specific synapses, electrophysiological studies were made of sprouting and regenerating synaptic connections following interruption of the preganglionic pathways. Studies were also made of developing connections in tadpole ganglia. After partial denervation (by selective interruption of B fibers), the C fibers sprouted and innervated B cells. When B fibers regenerated, they reinnervated B cells only, and within several weeks, C fiber synapses on B cells were no longer found. After complete denervation (by interruption of both B and C fibers) specific synaptic connections were eventually restored. At least 2 experimentally separable processes underlie this specificity: First, there is a preference for appropriate connections from the outset of reinnervation, seen even in the absence of competition between the 2 groups of preganglionic fibers. Despite this preference, however, some inappropriate synapses are formed. Second, those inappropriate synapses that do arise are eliminated when appropriate synapses are allowed to reform, as a result of competitive interactions between the 2 preganglionic fiber groups. In normally developing tadpole ganglia, B and C cells were not readily distinguishable. The great majority of tadpole neurons were found to be innervated exclusively by either B or C fibers. Some neurons were innervated by both preganglionic fiber groups, a situation virtually never found in adult ganglia. It thus appears that in normal development, as in reinnervation, innervation is by and large selective; inappropriate synapses may form, but they are eliminated during maturation, presumably through competitive interactions.
Insect cardioactive neuropeptides: peptidergic modulation of the intrinsic rhythm of an insect heart is mediated by inositol 1,4,5- trisphosphate
Authors: Tublitz NJ
Published: March 2018

The beat frequency of the myogenic heart of the tobacco hawkmoth, Manduca sexta, markedly increases at adult emergence in response to 2 blood-borne peptide neurohormones, known as the cardioacceleratory peptides (CAP1 and CAP2). Three independent lines of evidence are presented supporting the hypothesis that the CAPs exert their cardiostimulatory effects on the insect myocardium through a change in the intracellular levels of inositol 1,4,5-trisphosphate (InsP3). I show that (1) InsP3 levels increase in response to CAP2 in a timely fashion, (2) exogenous application of InsP3 mimics the effects of CAP2 application, and (3) a blocker of InsP3 metabolism inhibits the effect of CAP2. These results provide strong support for the hypothesis that InsP3 is likely to be the second messenger in the regulation of heart beat activity by CAP2. Besides establishing the nature of the signaling system between CAP2 and the heart, these data also identify a novel role for InsP3, namely, the control of contraction frequency in a myogenic muscle. Given the widespread distribution of cellular systems employing InsP3 as a second messenger, it is suggested that InsP3 may also be involved in the long-term regulation of rhythmic activity in other spontaneously contractile muscles and endogenously active cells.
Conditional discrimination learning in Aplysia californica
Authors: Colwill RM , Absher RA , Roberts ML
Published: March 2018

Two experiments examined whether the relation between a conditioned stimulus (CS) and an unconditioned stimulus (US) might be brought under the control of contextual stimuli in the invertebrate Aplysia californica. Subjects received exposure to 2 different contexts. In both experiments, a tactile CS was paired with a shock US in one of those contexts. In the other context, that tactile CS was either nonreinforced (Experiment 1) or explicitly unpaired with the shock US (Experiment 2). Responding to the CS during a subsequent test was greater in the context in which that CS had been paired with the US compared with the context in which it had been nonreinforced or unpaired. These findings are discussed in terms of theories of conditional discrimination learning.
Two anatomically specific classes of candidate cholinoceptive neurons in the rat olfactory bulb
Authors: Nickell WT , Shipley MT
Published: March 2018

The pharmacohistochemical technique of Butcher (1978) and choline acetyltransferase (ChAT) immunocytochemistry were used to demonstrate the presence, morphology, and differential distribution of 2 classes of acetylcholinesterase (AChE)-positive, ChAT-negative neurons in the rat olfactory bulb. One population of these neurons is located preferentially in a stratum just deep to the mitral cell layer (mcl). These AChE-positive intramitral neurons are significantly larger than the predominant inframitral neuronal type, the granule cell. Inframitral AChE-positive neurons appear to send processes deeper into the granule cell layer and superficially into the external plexiform layer (epl), above the mcl. Neurophysiological experiments reported in a companion article are consistent with the existence of a population of cholinoceptive neurons with the location and characteristics of these large inframitral interneurons. A second class of AChE-positive, ChAT-negative neurons is found exclusively in the glomerular layer. These neurons are located primarily in the periglomerular region and the superficial third of the epl; they are somewhat larger than typical periglomerular cells. Juxtaglomerular AChE neurons are smaller than inframitral AChE neurons. Since there are no neurons in the olfactory bulb that produce ChAT, the synthetic enzyme for ACh, the AChE-positive cells reported here are hypothesized to be cholinoceptive neurons for the cholinergic projection from the basal forebrain to the olfactory bulb. Anatomical, physiological, and receptor-ligand binding data are consistent with this interpretation.
Retinotopic organization of the developing retinotectal projection in the zebrafish embryo
Authors: Stuermer CA
Published: March 2018

Developing retinal axons in the zebrafish embryo were stained with HRP or with the fluorescent dyes dil and diO to study the formation of the retinotectal projection. Retinal axons leave the eye at 34–36 hr postfertilization (PF), invade the tectum at 46–48 hr PF, and innervate the tectal neuropil at 70–72 hr PF. Dorsal and ventral axons occupy separate aspects of the optic nerve and tract and pass into their retinotopically appropriate ventral and dorsal hemitectum, respectively. Nasal and temporal axons are segregated in the nerve, mixed in the tract, and are coextensive over the rostral half of tectum until 56 hr PF. They then segregate again, due to the progression of nasal axons into the open caudal tectum. Thus, at 70–72 hr PF, dorsal and ventral as well as temporal and nasal axons occupy their retinotopically appropriate tectal quadrants. After ablation of the temporal retina prior to the time of axonal outgrowth, the nasal axons bypass the vacant rostral tectum to terminate in the caudal tectal half. Temporal axons in the absence of nasal axons remain restricted to their appropriate rostral tectal half, suggesting that nasal and temporal axons possess a preference for their retinotopically appropriate tectal domains. Measurements of individual terminal arbors and the tectal areas in embryos and in adult zebrafish showed that individual arbors are large with respect to the embryonic tectum but are about 14–15 times smaller than in the adult. However, the proportion of tectum covered by embryonic arbors is about 7 times larger than in the adult, suggesting that a higher precision of the adult projection is achieved as a result of a greater enlargement of the tectum than of the arbors.
Colocalization of taurine- and cysteine sulfinic acid decarboxylase- like immunoreactivity in the cerebellum of the rat with monoclonal antibodies against taurine
Authors: Magnusson KR , Madl JE , Clements JR , Wu JY , Larson AA , Beitz AJ
Published: March 2018

Two monoclonal antibodies against fixative-modified taurine, Tau1 and Tau2, were produced, characterized, and used in the present study to analyze the distribution of taurine in the cerebellum of the rat. In addition, immunohistochemical colocalization experiments were performed to determine whether cerebellar neurons contain both taurine and its synthesizing enzyme, cysteine sulfinic acid decarboxylase (CSADC). In ELISAs, both Tau1 and Tau2 displayed high affinities for taurine conjugated to various carrier proteins and possessed some cross- reactivity for other amino acids which are present in lower concentrations in the brain than taurine. Tau2 was found to recognize only taurine and hypotaurine when paraformaldehyde was used to fix the amino acids to carrier proteins. With the use of glutaraldehyde fixation, Tau1 cross-reacted with conjugates of beta-alanine and hypotaurine and Tau2 cross-reacted strongly with conjugates of cysteic acid and hypotaurine and weakly with cysteine sulfinic acid. Despite different cross-reactivities, Tau1 and Tau2 exhibited almost identical patterns of neuronal staining in bands of Purkinje cells in the cerebellum. Staining of Purkinje cell dendrites was more prominent than staining of the soma. Light immunoreactivity was present in Golgi, stellate, and basket cells. A scattered population of granule cells displayed taurine-like immunoreactivity at the electron microscopic level. Immunostaining was identified in some terminals in the Purkinje cell layer and in a limited number of mossy fibers. Tau2-like immunoreactivity was colocalized with CSADC-like immunoreactivity in the cerebellar neurons described above. These immunoreactive cells may represent a subpopulation of neurons that contain a higher concentration of taurine than neighboring cells due to their ability to synthesize taurine. The intense immunoreactive staining of Purkinje cell dendrites provides support for the hypothesis that calcium- dependent release of taurine in the cerebellum may originate primarily from dendritic rather than synaptic processes and suggests a neuromodulator role for taurine in the cerebellum.
The projection of individual axons from the parabrachial region of the brain stem to the dorsal lateral geniculate nucleus in the cat
Authors: Uhlrich DJ , Cucchiaro JB , Sherman SM
Published: March 2018

In mammals, the retinogeniculocortical pathway is the primary afferent route to visual cortex. The flow of information along this pathway can be modulated at the thalamic level (i.e., at the lateral geniculate nucleus) as a function of arousal, attention, and phenomena such as eye movements. Physiological studies indicate that an important source of this state-dependent influence on geniculate neuronal responsiveness is the parabrachial region of the brain stem. We used the anterograde tracer Phaseolus vulgaris leucoagglutinin to study the anatomical connections between the parabrachial region and the lateral geniculate nucleus. Labeled parabrachial axons are found throughout the thalamus, including all laminae of the lateral geniculate nucleus, the lateral posterior-pulvinar complex, the ventral lateral geniculate nucleus, the perigeniculate nucleus, and the reticular nucleus of the thalamus. Within these nuclei, the axons exhibit sporadically branched terminal arbors with boutons mostly en passant. Serial reconstructions indicate that individual parabrachial axons that innervate the lateral geniculate nucleus may terminate in other visual thalamic nuclei as well, but not in thalamic nuclei that subserve other modalities. Finally, the labeled parabrachial axons are morphologically heterogeneous; they differ in their innervation targets, terminal arbor shape, and the size spectrum of their boutons. These data suggest that this portion of the ascending parabrachial pathway, which may be functionally diverse, coordinates the responsiveness of the varied thalamic nuclei involved with vision.
Evidence that guanosine triphosphate (GTP)-binding proteins control a synaptic response in brain: effect of pertussis toxin and GTP gamma S on the late inhibitory postsynaptic potential of hippocampal CA3 neurons
Authors: Thalmann RH
Published: March 2018

These experiments show that a synaptic response in brain, namely, the late inhibitory postsynaptic potential (IPSP) of hippocampal CA3 neurons in the rat hippocampal slice, was blocked by 2 compounds affecting guanosine triphosphate (GTP)-binding proteins. The first of these compounds, pertussis toxin, an inactivator of several GTP-binding proteins (G-proteins), excluding the GTP-binding protein that stimulates adenylyl cyclase, was injected intrahippocampally. The second compound, GTP gamma S, a nonhydrolyzable analog of GTP, was injected directly into postsynaptic neurons via the recording electrode. An ADP-ribosylation assay verified that the pertussis toxin had modified a major portion of the hippocampal pertussis toxin substrates of approximately 40,000 apparent molecular weight. Each agent blocked the conductance associated with both the late IPSP and the response to baclofen, an agonist for a putative receptor mediating the late IPSP (GABAB). These compounds did not block the mossy fiber excitatory postsynaptic potential (EPSP), the GABAA-mediated early IPSP, or the response to the GABAA agonist 4,5,6,7-tetrahydroisoxazolo- (5,4-C)-pyridin-3-ol. It is possible that these measurements underestimated the degree of blockade of the specific potassium conductance of the late IPSP since at least a portion of the GTP-gamma S-insensitive response was not a potassium conductance at all. Rather, it was a response with a reversal potential some 30 mV positive to that of the late IPSP. On the basis of these experiments, I propose that the transmitter receptor of the late IPSP activates a potassium conductance via a G-protein that is sensitive to blockade by pertussis toxin and that GTP gamma S and baclofen activate a conductance that depends upon the same G-proteins and/or potassium channels as does the late IPSP.
Timing factors in the coordination of speech movements
Authors: Gracco VL
Published: March 2018

Speech movement coordination involves substantial timing adjustments among multiple degrees of muscles and movement freedom. The present investigation examined the kinematic and muscle timing adjustments associated with the production of select speech movements. For oral closing movements, the timing of the upper lip, lower lip, and jaw peak velocities were found to be tightly coupled, apparently reflecting a coordinative strategy. In contrast, oral opening movements demonstrated reduced temporal coupling and inconsistent sequencing across subjects. Overall, it appears that the temporal organization of speech movements varies with the specific movement goals. In order to evaluate the coordinative patterns for oral closing in detail, the temporal adjustments of multiple perioral muscles associated with the systematic closing peak velocity relations were examined. The relative timing of muscle onsets and peak EMG amplitudes was found to be predictably related to the peak velocity timing variations, suggesting that the motor commands are temporally scaled to generate changes in speaking conditions. It was also found that the mechanical properties of the speech articulators influence movement coordination and can be exploited to maximize movement efficiency. The systematic change in muscle timing characteristics for all synergistic muscles apparently reduces the degrees of freedom to control, thereby facilitating the coordination process.
Localization of a family of muscarinic receptor mRNAs in rat brain
Authors: Buckley NJ , Bonner TI , Brann MR
Published: March 2018

A family of 4 rat muscarinic receptors (m1, m2, m3, and m4) have recently been cloned and sequenced (Bonner et al., 1987). Since pharmacological probes that are presently available do not appear to distinguish among 3 of these muscarinic receptors, we constructed oligonucleotide probes corresponding to the N-terminal sequences of the muscarinic receptors and used them to specifically localize m1, m2, m3, and m4 mRNA in sections of rat brain using in situ hybridization histochemistry. Northern analysis demonstrated a 3.1 kilobase (kb) m 1 mRNA, a 4.5 kb m3 mRNA, and a 3.3 kb m4 mRNA in cerebral cortex, striatum, hippocampus, and cerebellum. In situ hybridization histochemistry indicated a prevalence of m1 mRNA in the pyramidal cell layer of the hippocampus, the granule cell layer of the dentate gyrus, the olfactory bulb, amygdala, olfactory tubercule, and piriform cortex. Caudate putamen and cerebral cortex showed moderate levels of labeling. m2 mRNA was detectable in the medial septum, diagonal band, olfactory bulb, and pontine nuclei. m3 and m4 mRNA were also prevalent in the olfactory bulb and pyramidal cell layer of the hippocampus but were present only in low levels in the dentate gyrus. m3 mRNA was present in superficial and deep layers of the cerebral cortex, whereas m4 mRNA was more evenly distributed with a slightly more intense labeling evident in the midcortical layer. In addition, m3 mRNA was present in a number of thalamic nuclei and brain-stem nuclei, while m4 mRNA predominated in the caudate putamen. These data offer a new basis on which to interpret the heterogeneity of muscarinic actions in the CNS.
A unique membrane protein is expressed on early developing limbic system axons and cortical targets
Authors: Horton HL , Levitt P
Published: March 2018

The limbic system-associated membrane protein (LAMP) is a 64 kDa protein that, in the adult brain, is present in cortical and subcortical regions comprising the limbic system (Levitt, 1984). The developmental expression of LAMP was studied in fetal rat brains to determine the specific patterns of distribution and the cellular elements that exhibit LAMP immunoreactivity. Light microscopic immunocytochemical analysis revealed that LAMP is expressed on neurons and their growing axons early in fetal development, at a time coincident with pathway formation and differentiation of limbic system nuclei. In the forebrain, where limbic system structures are heavily concentrated, immunoreactivity appears on subpopulations of axons in a temporal sequence that correlates with the time of formation of pathways carrying limbic system axons. Thus, staining is evident first at embryonic day (E) 15 on fibers within the internal capsule coursing from the diencephalon to cortex. LAMP immunoreactivity appears over the next 3 d in the anterior commissure, fornix, and corpus callosum. Ultrastructural immunocytochemical analysis reveals dense surface staining of fascicles of developing axons and growth cones. The axonal staining is transient, disappearing during the second postnatal week of development. In cerebral cortex, cells in presumptive limbic cortical regions such as lateral perirhinal sulcal cortex and prefrontal cortex are LAMP immunoreactive from the inception of the cortical plate. These cortical regions are clearly delineated from surrounding unstained nonlimbic areas as early as E15. Thus, LAMP expression in the cortex may represent one of the earliest markers of specific cytoarchitectonic areas.(ABSTRACT TRUNCATED AT 250 WORDS)
Activation of the hippocampus and dentate gyrus by working-memory: a 2- deoxyglucose study of behaving rhesus monkeys
Authors: Friedman HR , Goldman-Rakic PS
Published: March 2018

The 2-deoxyglucose method was used to examine metabolic activity in the hippocampus, dentate gyrus, and amygdala of rhesus monkeys performing working-memory and control tasks. A working-memory group was tested on 1 of 3 tasks requiring trial-by-trial updating of information: delayed spatial response, delayed spatial alternation, or delayed object alternation. A control group was tested either on an associative memory problem, visual pattern discrimination, or a sensory-motor task that did not have an explicit mnemonic component. Local cerebral glucose utilization (LCGU) in specific layers of the dentate gyrus and the CA1 and CA3 sectors of the hippocampus, as well as in 7 distinct nuclei of the amygdala, was measured and compared across groups. Metabolic rate in specific layers of the dentate gyrus and the CA3 and CA1 fields of the hippocampus was enhanced in the working-memory compared with the control group: LCGU was between 18 and 24% higher in the granule cell and molecular layers of the dentate gyrus and in the molecular and radiatum layers of CA1 and CA3 in the hippocampus. In contrast, no significant group differences in LCGU were found for any of the 7 amygdaloid nuclei examined: the lateral, lateral basal, medial basal, accessory basal, cortical, central, and medial nuclei. These results are consistent with previous evidence showing that lesions of the hippocampus affect memory selectively, producing deficits on some memory problems while sparing others. Our findings further suggest that working-memory may be a common denominator among those tasks that are sensitive to hippocampal damage in monkeys. The contribution of the amygdala to performance on memory tasks, on the other hand, appears to be independent of the specific type of memory process that is engaged.
Selection of postsynaptic serotonin receptors during reinnervation of an identified leech neuron in culture
Authors: Drapeau P , Sanchez-Armass S
Published: March 2018

Serotoninergic Retzius neurons reform an inhibitory synapse onto pressure-sensitive mechanosensory (P) neurons when the cells are removed from the nervous system of the leech and are juxtaposed in tissue culture. The somas of P cells in situ and single (uninnervated) P cells in culture have both a depolarizing and Cl-dependent hyperpolarizing response to application of the transmitter serotonin (5- HT). Synaptic release of 5-HT by a Retzius cell in situ and in culture evokes a Cl-dependent postsynaptic response but does not appear to activate the depolarizing receptors. We have characterized the ionic currents induced by synaptically released and applied 5-HT in voltage- clamped P cells in culture in order to determine the responses to transmitter and their modifications following innervation. When 5-HT was applied to single P cells, 2 types of channels were activated by 5- HT and could be distinguished by changing the ionic composition of the superfusion solution. In an impermeant cation (TrisCl) solution, a 5-HT- dependent Cl current was activated. When single P cells were superfused with a Cl-free solution (Cl replaced by impermeant SO4), 5-HT activated a monovalent cation current. Following innervation of a P cell by a cocultured Retzius cell, the reversal potential of the peak postsynaptic current depended on the Cl gradient and the synaptic response was blocked by the Cl channel blocker 9-anthracenecarboxylic acid. Thus, synaptic release of 5-HT activated solely the Cl channels and not the cationic channels. Pipette application of 5-HT onto innervated P cells activated a Cl conductance comparable in magnitude to the synaptic response. In contrast, the cationic conductance was reduced roughly 5-fold. It is concluded that innervation of a P cell by a Retzius cell resulted in clustering of the synaptic 5-HT receptors, which activate Cl channels and reduction of the nonsynaptic, cationic response. The result is a selection of receptors in the cultured P cell that mimics the pattern observed in vivo.
Neuroprotective effects of MK-801 in vivo: selectivity and evidence for delayed degeneration mediated by NMDA receptor activation
Authors: Foster AC , Gill R , Woodruff GN
Published: March 2018

The ability of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 to prevent neuronal degeneration in the rat striatum and hippocampus caused by intracerebral injection of excitotoxins has been examined. Excitotoxic damage was assessed after 7 d, using histological and biochemical [choline acetyltransferase (ChAT) glutamate decarboxylase (GAD)] measurements. Systemically administered MK-801 was found to protect against neurodegeneration caused by NMDA (200 nmol) and the naturally occurring NMDA receptor agonist quinolinate (120–600 nmol) but not against that induced by kainate (5 nmol) or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA; 50 nmol), indicating a selectivity for NMDA receptor-mediated neuronal loss. Neurotoxicity caused by NMDA (200 nmol) or quinolinate (200 nmol) was prevented by MK-801 (1–10 mg/kg, i.p.) administered in a single dose after excitotoxin injection. In the striatum, significant protection of cholinergic neurons (assessed by ChAT measurements) was observed when MK-801 was given up to 5 hr after injection of NMDA or quinolinate, whereas protection of GABAergic neurons (assessed by GAD measurements) was obtained up to 2 hr. The results suggest that GABAergic neurons degenerate more rapidly than cholinergic neurons. The competitive NMDA receptor antagonist 3-[(+/-)-2-carboxypiperazin-4-yl]- propyl-1-phosphonate (100 mg/kg, i.p.) gave partial protection of striatal neurons when administered 1 hr after quinolinate injection. In the rat hippocampus, administration of 10 mg/kg MK-801 i.p. 1 hr after quinolinate injection caused almost complete protection of pyramidal and granule neurons, whereas the degeneration of CA3/CA4 pyramidal neurons caused by kainate injection was unaffected. These observations indicate that neurons in rat striatum and hippocampus do not die as an immediate consequence of exposure to high concentrations of NMDA agonists but that a delayed process is involved that requires NMDA receptor activation. In this respect, intracerebral injections of NMDA agonists may mimic the pathological changes that are thought to occur in the brain following periods of cerebral ischemia, where delayed neuronal degeneration occurs.
Single-channel analysis of four distinct classes of potassium channels in Drosophila muscle
Authors: Zagotta WN , Brainard MS , Aldrich RW
Published: March 2018

A number of mutations have been shown to affect potassium channels in Drosophila muscle. Single-channel analysis of the effects of mutations will prove a powerful approach for studying the molecular mechanisms of ion channel gating. As an initial step towards studying the effects of mutations at the single-channel level, we have characterized wild-type potassium channels in cultured embryonic myotubes using whole-cell, cell-attached, inside-out, and outside-out configurations of the patch- clamp technique. The myotubes differentiate in vitro from primary cultures of late-gastrula stage embryos of Drosophila. The whole-cell outward currents develop in a characteristic sequence. At 8 hr after plating a small delayed outward current is present. Between 10 and 12 hr after plating an A-type outward current develops, followed, between 13 and 16 hr, by a large increase in the delayed current. The A-type current is absent at all developmental stages in myotubes homozygous for the mutant ShKS133. At least 4 different types of potassium channels contribute to the whole-cell outward currents: a fast transient 14 pS A-type potassium channel (A1), a slowly inactivating 14 pS potassium channel (KD), a 40 pS potassium channel that does not inactivate during voltage pulses up to 2.4 sec in duration (KO), and a 90 pS potassium channel that is strongly activated by membrane stretch (KST). Channels indistinguishable from the KD and KST channels were also observed in patch-clamp studies on larval body wall muscle fibers. A1 channels were also present in intact dorsal longitudinal flight muscles. The A1 channel underlies the rapidly inactivating component of the whole-cell current. It inactivates with a similar time course and voltage dependence to the A-current and is similarly blocked by 5 mM 4- aminopyridine. The KD channel underlies a large fraction of the delayed component of the whole-cell current. Ensemble averages of single KD channels inactivate with the same time course as the delayed current. The KO channel represents a smaller fraction of the whole-cell delayed outward current. Its increase in open probability with voltage is due primarily to a voltage dependence of its closed times. The KST channel is voltage and calcium independent and would therefore only contribute to the leak whole-cell current.
cDNA cloning and characterization of three genes uniquely expressed in cerebellum by Purkinje neurons
Authors: Nordquist DT , Kozak CA , Orr HT
Published: March 2018

The characteristics that distinguish the different neuronal cell types of an organism are believed to be primarily determined by unique patterns of cellular gene expression. The identification of cell-type specific molecules should therefore provide a good basis for understanding the biology of specific neuron types. In this paper, we describe the isolation of cDNA clones corresponding to mRNA uniquely expressed by Purkinje cells in mature mouse cerebellum. Three cDNA clones were selected from a library of normal mouse cerebellar cDNA by virtue of their failure to hybridize to mRNA sequences from the cerebella of Purkinje cell degeneration (pcd) mice. The cDNA clones were shown by in situ and Northern hybridization to correspond with mRNA present in Purkinje cells but absent or at low levels in other cell types of the cerebellum. By sequence analysis, clone PCD29 was determined to encode the calcium-binding protein calbindin-D28K. Clones PCD5 and PCD6 encode previously undescribed proteins of 99 and greater than 500 amino acids, respectively. All 3 PCD clones hybridized to mouse mRNA from sources other than cerebellum; clone PCD5 was found to have the most restricted expression, as it hybridized only to mRNA from cerebellum and eye. To define potential correlations between the PCD clones and mutations in the mouse genome known to affect Purkinje cells, clones PCD5, PCD6, and PCD29 were localized to mouse chromosomes 8, 6, and 4, respectively.
Determinants of patchy metabolic labeling in the somatosensory cortex of cats: a possible role for intrinsic inhibitory circuitry
Authors: Juliano SL , Whitsel BL , Tommerdahl M , Cheema SS
Published: March 2018

Despite repeated experimental demonstration that somatic stimulation leads to an intermittent, “column-like” pattern of 2-deoxyglucose (2DG) label in the somatosensory cortex, the functional significance of this pattern remains uncertain. A number of recent studies have suggested that the putative inhibitory neurotransmitter GABA may play an influential role in the cortical processing of sensory information. To test the possibility that GABA-mediated inhibitory processes might participate in the formation of the 2DG patches, the 2DG pattern obtained under “normal” experimental conditions was compared with the pattern observed when cortical inhibition was modified by topical application of the GABA antagonist, bicuculline methiodide (BIC). Under “normal” experimental conditions, we found that somatic stimulation led to an intermittent, patch like distribution of 2DG uptake in cat somatosensory cortex, which exhibited consistent features in animals studied using the same stimulus and experimental condition. Reconstructions of the stimulus-evoked activity patterns revealed that the label was confined to territories known to receive input from the stimulated body region and was organized into elongated strips. Topical application of BIC to the somatosensory cortex dramatically altered the dimension of the metabolic patches, which were often embedded in a field of elevated 2DG uptake. In BIC-treated hemispheres the average width of 2DG patches was 1266 microns, whereas the average width of patches in the opposite untreated hemisphere (elicited by identical stimuli) was 713 microns. Unfolded maps of the labeling pattern revealed that in the BIC-treated hemispheres adjacent “strips” of 2DG label tended to fuse, leading to a less intermittent distribution than that observed in the untreated hemispheres. An important role for GABA in the formation of the normal cortical response to somatic stimulation is suggested.
Structural and functional properties of reticulospinal neurons in the early-swimming stage Xenopus embryo
Authors: van Mier P , ten Donkelaar HJ
Published: March 2018

This study presents direct evidence that in Xenopus laevis embryos ipsi- and contralaterally descending reticulospinal fibers from the caudal brain stem project to the spinal cord, where they directly contact primary motoneurons. At stage 30, occasional contacts between primary motoneurons and descending axons are present. These contacts are possibly already functional since presynaptic vesicles were sometimes observed. Furthermore, the physiological data obtained in this study suggest that reticulospinal neurons in the caudal brain stem are involved in the central generation of early swimming. The first ingrowth of reticulospinal axons was observed in the rostral spinal cord after application of HRP to the caudal brain stem of stage 27/28 embryos. By stage 32, many supraspinal axons could be found in the spinal cord at the level of the 12/13th myotome, near the time of the first rhythmic swimming. Both lamellipodial and varicose growth cones were found. Intracellular recordings from the brain stem and extracellular recordings from the myotomal muscles in curarized embryos around stage 30 revealed neurons in the caudal brain stem which were active during early fictive swimming. After intracellular staining with Lucifer yellow neurons with descending axons were found in the brain- stem reticular formation. These reticulospinal neurons showed “motoneuron-like” phasic activity, producing one spike each swimming cycle. Rhythmically occurring spikes with swimming periodicity were superimposed on a sustained depolarization level of some 5–30 mV. Reticulospinal neurons in the brain stem resemble descending interneurons in the spinal cord by their morphology, projection pattern, and activity during early swimming. Reticulospinal neurons and descending interneurons might therefore form one continuous population of projecting interneurons with a different location but a similar function. In support of this we propose that the embryonic brain-stem reticular formation forms part of the swimming pattern generator.
Aplysia synaptosomes. II. Release of transmitters
Authors: Chin GJ , Shapiro E , Schwartz JH
Published: March 2018

A subcellular fraction (P3) from Aplysia is enriched in synaptosomes (Chin et al., 1988) and is capable of accumulating 5-HT and choline. At an external 3H-5-HT concentration of 1.8 microM, the P3 fraction took up 0.12 nmol/mg protein in 30 min. Uptake was dependent on external Na+. Electron microscopic autoradiography showed that much of the accumulated 3H-5-HT is localized to synaptosomes. At 0.5 microM 3H- choline, P3 took up 0.11 nmol/mg protein in 30 min and converted 40% to 3H-ACh. This synaptosomal fraction was also capable of releasing transmitter. After 3H-5-HT or 3H-choline was taken up, P3 released about 5% of the total radioactive transmitter in a Ca2+-dependent manner during a 30 sec exposure to a depolarizing concentration of K+ (100 mM). Identified, prelabeled synaptosomes were prepared by injecting 3H-choline into the large cholinergic neuron L10. The abdominal ganglia containing the injected cells were then fractionated, yielding synaptosomes containing radioactivity derived from L10. After this synaptosomal fraction was exposed to high K+, 2% of the radioactivity was released in a Ca2+-dependent manner. This release was completely blocked by 0.1 mM histamine, a modulatory transmitter that has previously been shown to cause presynaptic inhibition in L10.
Plasticity of process-bearing glial cell cultures from neonatal rat cerebral cortical tissue
Authors: Ingraham CA , McCarthy KD
Published: March 2018

The factors and cellular interactions that influence the commitment of cells to specific neural lineages are not well understood. We have used cultured non-neuronal process-bearing (PB) cells from neonatal rat cerebral cortices as a model to assess the influence of various culture conditions on the determination of cells as either astroglia or oligodendroglia. Increasing postseparation plating density was significantly associated (p less than 0.001) with decreasing percentages of glial fibrillary acidic protein (GFAP+) cells, increasing percentages of galactocerebroside (GC+) cells, and increasing percentages of nonstained cells. As the fetal calf serum content of growth medium was increased, the percentage of GFAP+ cells increased, and as the serum content was decreased, the percentage of GC+ cells increased. Evidence of minimal cell proliferation and the observation of PB cells that coexpressed GFAP and GC supported the conclusion that PB cells switched their phenotypic expression from GFAP+ in serum to GC+ in serum-free medium. PB cells exhibited plasticity in their phenotypic expression as cells grown for 9 d in serum-free medium were still responsive to the effects of serum, while cells grown for 6 d in serum were refractory to serum withdrawal. This research has demonstrated the plasticity of PB cells separated from polygonal astroglia as they expressed GFAP in the presence of serum and GC in serum-free medium.
Flow cytometric analysis of rat striatal nerve terminals
Authors: Wolf ME , Kapatos G
Published: March 2018

Methods were developed for the analysis and isolation of striatal nerve terminals (synaptosomes) using fluorescence-activated cell sorting (FACS). Comparison of the light-scattering properties of synaptosomal and mitochondrial fractions indicated that particles in the synaptosomal fraction were generally larger and more sensitive to hypotonic lysis, consistent with results obtained by other methods of analysis. FACS analysis using indirect immunofluorescence techniques indicated that approximately 84% of the synaptosomal fraction was labeled by monoclonal antibody (mAb) A2B5 and thus appeared to be of neuronal origin. After permeabilization, between 5 and 10% of the particles were labeled by a mAb to glial fibrillary acidic protein, suggesting that they were derived from astrocytes. A fluorescent voltage-sensitive dye (VSD) was used to distinguish intact synaptosomes from free mitochondria (only the former maintain a membrane potential under the present experimental conditions). Approximately 83% of the synaptosomal fraction exhibited increased fluorescence after incubation with the VSD; furthermore, the fluorescence signal decreased in response to depolarizing agents (elevated potassium and veratridine). A portion of the mitochondrial fraction responded similarly, consistent with the presence of contaminating synaptosomes. Analysis of synaptosomal labeling by 11 fluorescein-conjugated plant lectins indicated that striatal nerve terminals differ significantly in their cell surface glycoconjugates. Subpopulations of synaptosomes defined on the basis of lectin binding were collected by FACS onto filters and probed with a mAb to tyrosine hydroxylase (TH) using Western blot techniques. While subpopulations exhibited different amounts of TH immunoreactivity, none of the lectins appeared to recognize TH-positive (i.e., dopaminergic) synaptosomes exclusively. These findings demonstrate that synaptosomes can be characterized and isolated for further study based on FACS analysis of properties such as size, membrane potential, and the presence of intracellular or cell surface molecules.
Priming of D1-dopamine receptor responses: long-lasting behavioral supersensitivity to a D1-dopamine agonist following repeated administration to neonatal 6-OHDA-lesioned rats
Authors: Criswell H , Mueller RA , Breese GR
Published: March 2018

The present study demonstrates that repeated administration of SKF- 38393, a D1-dopamine agonist, is necessary for maximal behavioral supersensitivity of D1-dopamine receptor responses in neonatal 6-OHDA- lesioned rats, confirming earlier work. This repeated administration of SKF-38393, which is referred to as priming of D1-dopamine receptor responses, resulted in a progressive increase in locomotor activity, as well as several other behaviors. This priming phenomenon lasted at least 6 months. Repeated administration of the D2-dopamine agonist LY- 171555 also increased behavioral responses to the D1-dopamine agonist. However, previous administration of a D2-dopamine agonist was not necessary for priming of D1-dopamine receptor responses, because D1- dopamine receptor priming could be produced in the presence of a D2- dopamine receptor antagonist. Blockade of D1-dopamine receptors with SCH-23390 prior to injection of SKF-38393 prevented the increasing responsiveness following repeated administration of this D1-dopamine agonist. Selective neonatal destruction of dopamine-containing neurons produced the same result as did destruction of catecholamine-containing neurons, indicating that the noradrenergic system is not involved in this phenomenon. Priming of D1-dopamine receptor responses by repeated administration of SKF-38393 was not observed in unlesioned controls or in rats that received catecholamine-depleting lesions as adults. Repeated administration of scopolamine also was able to prime behavioral responses to SKF-38393 in neonatal 6-OHDA-lesioned rats, indicating that endogenous release of dopamine can prime D1-dopamine receptor responses in neonatally lesioned rats. In addition, responses to indirect-acting agonists were enhanced in rats that had been primed with a D1-dopamine agonist when compared wit responses in unprimed animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Ultrastructural analysis of substance P-immunoreactive nerve fibers in myenteric ganglia of guinea pig small intestine
Authors: Llewellyn-Smith IJ , Furness JB , Costa M
Published: March 2018

Electron microscopic immunocytochemistry has been used to study the distribution and synaptic relationships of substance P (SP)- immunoreactive nerve fibers in ultrathin sections from whole-mount preparations of myenteric ganglia from guinea pig small intestine. At the light microscopic level, myenteric ganglia stained for ultrastructural study contained dense arrays of SP-immunoreactive nerve fibers around and between the neuronal and glial cell bodies. At the electron microscopic level, SP-containing nerve fiber profiles occurred throughout the neuropil of the myenteric ganglia. Both vesicle- containing and nonvesiculated nerve fiber profiles were immunoreactive. The positive vesiculated profiles contained variable proportions of small clear and large granular vesicles. Two-thirds of the vesicle- containing nerve fiber profiles in myenteric ganglia were immunoreactive for SP. Many vesiculated SP-immunoreactive nerve fiber profiles were directly apposed to each myenteric neuron. However, only about 0.6% of these vesiculated profiles formed synapses that showed the ultrastructural specializations of vesicle clustering presynaptically and fuzzy electron-dense material on the postsynaptic membrane. On the other hand, morphologically identifiable synapses with SP-immunoreactivity comprised about half the total number of synapses in the ganglia. SP-immunoreactive synapses were observed on nonvesiculated nerve processes in the periphery of the ganglia and on nerve cell bodies. Most of the axosomatic SP synapses occurred on small neurons that lay either on the surfaces of the ganglia or near the fibers of the internodal strands where they traveled through the ganglia. Both SP-positive and SP-negative nerve cell bodies received SP synapses.(ABSTRACT TRUNCATED AT 250 WORDS)
The role of gonadal hormones in neuromuscular synapse elimination in rats. I. Androgen delays the loss of multiple innervation in the levator ani muscle
Authors: Jordan CL , Letinsky MS , Arnold AP
Published: March 2018

The normal period of synapse elimination in the androgen-sensitive levator ani (LA) muscle occurs between 2 and 4 weeks after birth, well after the period of synapse elimination for most other rat muscles. To evaluate whether gonadal androgen might be involved in the delayed development of single innervation in the LA, we compared the time course of synapse elimination in LA muscles that lacked endogenous gonadal androgen or were exposed to exogenous androgen. Tetranitroblue tetrazolium was used to stain neuromuscular connections. Our results suggest that both endogenous and exogenous androgen delay the normal process of synapse elimination. Removing endogenous androgen resulted in lower levels of multiple innervation in the LA, suggesting that androgen may normally influence synapse elimination. Moreover, androgen treatment prevented much of the normal loss of multiple innervation in the LA. Androgen treatment during the normal period of synapse elimination also increased the diameter of LA muscle fibers, enhanced the development of preterminal branching, and increased the number of junctional sites on some LA fibers. Because androgen did not appear to induce the formation of new synapses through sprouting, we conclude that androgen maintained multiple innervation in the LA by preventing the normal ontogenetic process of synapse elimination.
The role of gonadal hormones in neuromuscular synapse elimination in rats. II. Multiple innervation persists in the adult levator ani muscle after juvenile androgen treatment
Authors: Jordan CL , Letinsky MS , Arnold AP
Published: March 2018

In the previous study (Jordan et al., 1989), we demonstrated that androgen treatment of juvenile male rats inhibits the elimination of synapses in the levator ani (LA) muscle. In the present study, we asked whether synapse elimination would occur once this juvenile androgen treatment ended. Castrated male rats were given androgen during a juvenile treatment period (7–34 d) and were killed 4 or 8 weeks after the end of androgen treatment (at 9 or 13 weeks after birth). The adult pattern of innervation in the LA was assessed (1) anatomically by counting the number of stained motor axons innervating single muscle fibers and (2) electrophysiologically by counting the number of components in intracellularly recorded endplate potentials. Based on the number of stained motor axons, the LA from juvenile androgen- treated castrates had as much multiple innervation 1 and 2 months after the end of androgen treatment (at 9 and 13 weeks) as was present during androgen treatment at 4 weeks. This suggests that no further synapse loss occurred in the LA once androgen treatment ended. Based on electrophysiological measures, adult LA muscles previously exposed to androgen were found to contain significantly more polyneuronal innervation than normal adult LA muscles. Juvenile androgen treatment also increased the size but not the number of motoneurons in the spinal nucleus of the bulbocavernosus which contains LA motoneurons. Thus, the increased level of multiple innervation in the LA is not due to a higher than normal number of motoneurons innervating this muscle. Because multiple innervation persists in the LA in the absence of continued androgen treatment, androgen may have permanently prevented synapse elimination.(ABSTRACT TRUNCATED AT 250 WORDS)