bluuebunny/crossref_metadata_2025 huggingface dataset:
Neurofilament proteins and the mesolimbic dopamine system: common regulation by chronic morphine and chronic cocaine in the rat ventral tegmental area
Authors: Beitner-Johnson D , Guitart X , Nestler EJ
Published: March 2018

The ventral tegmental area (VTA) and its dopaminergic projections appear to mediate some of the rewarding properties of opiates, cocaine, and other drugs of abuse. In a previous study, we demonstrated that chronic morphine and cocaine exert common actions on tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, in this dopaminergic brain reward region (Beitner-Johnson and Nestler, 1991). In the present study, we investigated the effects of chronic morphine and cocaine on other phosphoproteins in the VTA by back phosphorylation and two-dimensional electrophoretic analysis. It was found that a number of phosphoproteins, in addition to tyrosine hydroxylase, were regulated similarly by the two drug treatments in this brain region. Several of these morphine- and cocaine-regulated phosphoproteins were identified as neurofilament (NF) proteins. Chronic, but not acute, administration of either morphine or cocaine was found to decrease levels of the three NF proteins, NF-200 (NF-H), NF-160 (NF-M), and NF-68 (NF-L), by between 15% and 50% in the VTA by back phosphorylation, immunolabeling, and Coomassie blue staining. Such regulation of NF proteins was selective, in that no detectable changes were observed in the levels of eight other major cytoskeletal or cytoskeletal-associated proteins analyzed. Furthermore, NF levels were not altered by chronic treatment with either imipramine or haloperidol, two psychotropic drugs without reinforcing properties, or by chronic stress. Morphine and cocaine regulation of NFs showed regional specificity, as NF levels were not altered in the substantia nigra, or other parts of the brain or spinal cord, by these drug treatments. NFs are thought to function as determinants of neuronal morphology and to be associated with axonal transport. Thus, decreased NF levels in the VTA in response to chronic morphine and chronic cocaine could lead to drug-induced alterations in the structural and functional properties of this brain region, which may represent, in turn, part of a common biochemical basis of morphine and cocaine addiction and craving.
Visual processing of motion-defined form: selective failure in patients with parietotemporal lesions
Authors: Regan D , Giaschi D , Sharpe JA , Hong XH
Published: March 2018

The following psychophysical data were obtained from 13 patients with unilateral cerebral hemispheric lesions and 20 control subjects: speed thresholds for detecting and for recognizing motion-defined letters, speed thresholds for detecting coherent motion and for discriminating its direction, and visual acuity for recognizing letters of 96% and 11% contrast. Acuity was between 6/6 and 6/3 for all patients. Four patients showed a selective loss of ability to recognize motion-defined letters, while the ability to detect those same letters was spared, as was the ability to detect coherent motion and discriminate its direction (type I loss). Three patients showed a loss of ability both to recognize and to detect motion-defined letters, while the ability to detect coherent motion and discriminate its direction was spared (type II loss). All seven patients who failed to recognize motion-defined letters had extensive lesions in parietotemporal white matter underlying Brodmann cortical areas 18, 19, 37, 39, 21, and 22. The lesion was in the left hemisphere for three patients and in the right hemisphere for the remaining four. The region of overlap in these seven patients was not invaded by the lesion in any of the other six patients, and none of these six patients showed a loss of ability to recognize motion-defined letters. Three patients showed selective loss of acuity for low-contrast letters with normal Snellen acuity. The lesions in these three patients extended more posteriorly than in any other patient, and their region of overlap was in white matter underlying areas 18 and 19. We conclude that (1) the loss of ability to recognize letters in seven patients was specific to motion-defined letters rather than being a general loss of letter-recognition ability, (2) this visual loss was specific to motion-defined form rather than being a general failure of motion processing, and (3) the visual loss was not produced by lesions that did not involve the localized cerebral region specified above. To explain the existence of type I and of type II loss with sparing of the detection and discrimination of coherent motion, we propose that motion information is processed hierarchically. We further suggest that homologs of the socalled motion and color/form pathways (i.e., areas V1/MT/MST/7a and areas V1/V4/IT) are interconnected to form a distributed system that is important for the recognition of motion-defined form.(ABSTRACT TRUNCATED AT 400 WORDS)
Multiple types of high-threshold calcium channels in rabbit sensory neurons: high-affinity block of neuronal L-type by nimodipine
Authors: McCarthy RT , TanPiengco PE
Published: March 2018

Whole-cell and cell-attached patch recording have been used to characterize multiple types of voltage-dependent calcium channels in neurons freshly dispersed from rabbit dorsal root ganglia. In whole- cell patch recordings, high-threshold current, strongly resistant to inactivation by depolarized holding potentials (L-type; V1/2 = -27.2 mV), was potently inhibited by nimodipine. Assuming 1:1 binding, the dissociation constant for nimodipine binding to the inactivated state of the L-type calcium channel (KI) was 5.3 nM (n = 8). In contrast, a second type of high-threshold current less resistant to inactivation by depolarized holding potentials (N-type; V1/2 = -56.9 mV) was not blocked by nimodipine. Nimodipine-resistant N-type calcium current was inhibited by omega-conotoxin (5 microM). Cell-attached patch recordings of single calcium channel currents demonstrated the existence of three different unitary conductances; 7.4 pS, 13.1 pS, and 24.1 pS. The 24.1 pS high-threshold channel was enhanced by (-) BAY K 8644 and inhibited by nimodipine in a concentration- and voltage-dependent manner. Hyperpolarization reversed this block. These results demonstrate that, as in cardiac and smooth muscle, there is a component of neuronal high- threshold current corresponding to the L-type calcium channel that can be blocked with high affinity by nimodipine.
Two pharmacologically and kinetically distinct transient potassium currents in cultured embryonic mouse hippocampal neurons
Authors: Wu RL , Barish ME
Published: March 2018

Transient potassium currents in mammalian central neurons influence both the repolarization of single action potentials and the timing of repetitive action potential generation. How these currents are integrated into neuronal function will depend on their specific properties: channel availability at the resting potential, activation threshold, inactivation rate, and current density. We here report on the voltage-gated transient potassium currents in embryonic mouse hippocampal neurons dissected at embryonic days 15–16 and grown in dissociated cell culture for up to 3 d. Two transient potassium currents, A-current and D-current, were isolated based on steady state inactivation and sensitivity to 4-aminopyridine (4-AP) and dendrotoxin (DTx). A-current had an activation threshold of approximately -50 mV and was half-inactivated at approximately -81 mV. A-current relaxations at voltages between -40 and +40 mV could be fit by single exponential functions with time constants of 20–25 msec; these time constants showed little sensitivity to voltage. In contrast, D-current had an activation threshold of between -40 and -30 mV and was half-inactivated at approximately -22 mV. D-current inactivation was voltage dependent; time constants of fitted exponential functions ranged from approximately 7 sec at -40 mV to 200 msec at +40 mV. A slower component of inactivation was also evident. D-current was preferentially blocked by 4-AP (100 microM) and DTx (1 microM). Operationally, A- and D- currents could be cleanly separated based on conditioning pulse potential and 4-AP sensitivity. Total transient potassium current amplitude increased during the time that neurons were in culture (recordings were made between 2 hr after dissociation and 3 d in culture). When normalized for cell capacitance (an index of membrane area), A-current density (pA/pF) decreased and D-current density increased, even during a period between days 1 and 3 when total transient current density remained constant. This observation suggests that A- and D-currents may be reciprocally modulated. Since blockade of D-current (with 100 microM 4-AP) increased both action potential duration and repetitive firing in response to constant current stimulation, long-term modulation of the A-current:D-current ratio may affect the excitability of hippocampal neurons.
Lesions of the central nucleus of the amygdala, but not the paraventricular nucleus of the hypothalamus, block the excitatory effects of corticotropin-releasing factor on the acoustic startle reflex
Authors: Liang KC , Melia KR , Campeau S , Falls WA , Miserendino MJ , Davis M
Published: March 2018

Intracerebroventricular (icv) infusion of corticotropin-releasing factor (CRF) was previously found to produce a long-lasting, dose- dependent (0.1–1.0 microgram) increase in the amplitude of the acoustic startle reflex. The present study sought to determine where in the CNS CRF acts to increase startle. Intracisternal infusion of CRF (0.1–1.0 microgram) increased startle with a time course and magnitude similar to that produced by icv CRF, unlike intrathecal infusion, which produced a small, more rapid enhancement of startle. While lesions of the paraventricular nucleus of the hypothalamus had no effect on icv CRF-enhanced startle, bilateral lesions of the central nucleus of the amygdala significantly attenuated the excitatory effect of icv CRF but had no effect on intrathecal CRF-enhanced startle. Even though lesions of the amygdala blocked icv CRF-enhanced startle, local infusion of CRF into the amygdala did not significantly elevate startle. The present data indicate that the amygdala is part of the neural circuitry required for icv CRF to elevate startle, but does not appear to be the primary receptor area where CRF acts. The involvement of the amygdala in icv CRF-enhanced startle is consistent with the hypothesis that both the amygdala and CRF are critically involved in fear and stress.
Retinal growth in foveated teleosts: nasotemporal asymmetry keeps the fovea in temporal retina
Authors: Easter SS
Published: March 2018

Fish retinas continue to grow throughout life by adding neurons at the margin, with the result that cells born at a peripheral site are steadily displaced toward the center of the enlarging retina. This presents a functional problem for fish with specialized temporal areas such as a fovea--how to reconcile continual growth with the maintenance of a temporal location for the fovea. One possibility is that the retina grows asymmetrically, with most new retina added nasally, relatively little temporally. I have tested this hypothesis by evaluating retinal growth in marine teleosts from 15 families, both foveated and unfoveated. The pattern of growth was revealed by exploiting the fact that each new generation of ganglion cells sends its axons into the optic nerve as a cohort; small grains of the carbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethyl- indocarbocyanine were applied to various sites in the cross section of the optic nerves of adults, and the retrogradely labeled cell bodies in the retina were visualized in whole-mounts. The labeled cells lay in annuli, each one a generation of ganglion cells. Representatives of seven of the families showed clearly asymmetric growth: the labeled annuli were close together on the temporal side and more distant nasally, the embryonic fissure curved from its ventral origin toward the temporal side, and in six of these families, labeled fibers from temporal retina skirted the fovea. Members of the other eight families, without specialized areas, had more symmetric retinal growth: labeled annuli were equally spaced on all sides, the embryonic fissure was vertical, and there were no skirting fibers. The following hypothesis is supported: the retina grows asymmetrically, and maintains the area for acute vision oriented toward the anterior field.
Variable membrane glycoproteins in different growth cone populations
Authors: Li HN , Quiroga S , Pfenninger KH
Published: March 2018

The question of whether growth cones generated by different neurons contain distinctive membrane glycoproteins was examined. Growth cone particles (GCPs) were isolated from specific regions of fetal or early postnatal brain, and their membrane proteins were analyzed by 2D gel electrophoresis and Western blotting, using WGA as a probe. These blots were compared to those generated by synaptosomes from adult brain. The patterns reveal a number of WGA-binding glycoproteins that are uniformly present in these subcellular fractions and others that are found in GCPs from selected brain regions only. The results indicate, therefore, substantial pattern diversity for the different, restricted growth cone populations. Some of the WGA-binding glycoproteins seen in GCPs disappear with increasing age and are absent from synaptosomes, while others seem to become more prominent. One of the glycoprotein complexes present in all GCP and synaptosome fractions analyzed is gp93. It has an apparent molecular weight of 90–97 kDa and exhibits unusually high heterogeneity in GCPs from whole fetal brain. The gp93 complex covers a pI range from about 4.9 to about 6.4 and consists of at least 12 different species, probably isoelectric variants. In GCPs from different brain regions, the sets of gp93 species observed are different and characteristic. Neuraminidase digestion shifts the gp93 pattern to a more neutral pI but simplifies it only partially, indicating that variable sialic acid content explains the molecular diversity to some extent. Thus, gp93 is a glycoprotein complex whose members are expressed and/or posttranslationally processed differentially in different growth cone populations. Such a glycoprotein family may be involved in selective cell-cell recognition.
Functional influence of interlaminar connections in the hamster's superior colliculus
Authors: Mooney RD , Huang X , Rhoades RW
Published: March 2018

The aim of this study was to determine the functional importance of intrinsic connections within the hamster's superior colliculus (SC) in the development of the visual responses of neurons in the deep layers of this nucleus. We used localized injections of lidocaine to block action potentials of fibers that passed through the superficial layers and injections of CoCl2 to block synaptic transmission in these layers. We also determined the morphology of a number of the deep layer cells recorded in these experiments by intracellular injection of HRP. Injection of lidocaine into the superficial layers completely abolished the visual- and/or optic chiasm-evoked responses of all 40 deep layer cells tested. Thus, fibers that either pass through or synapse in the superficial layers are necessary for the visual responses of deep layer neurons. Injections of CoCl2 restricted to the superficial layers significantly reduced the visual responsivity of 86% of 92 deep layer neurons tested and abolished the visual responses of 68% of these cells. Superficial layer injections of CoCl2 were equally effective in reducing the responses of neurons with dendrites that ascended into the superficial layers (all seven cells tested and recovered) and those of cells with dendrites restricted to the deep layers (six of seven cells tested and recovered). Injections of CoCl2 into the deep layers, in the region of the cell being recorded, significantly reduced the visual responses of 59% of 37 cells and abolished the visual responses of 40% of the neurons tested. Deep CoCl2 injections abolished the visual responses of three of four cells with dendrites restricted to the deep layers and only one of four cells with dendrites that ascended into the superficial layers. These results indicate that descending interlaminar axons from visually responsive superficial layer cells may be responsible for the visual responsivity of most neurons in the deep SC layers of hamster. Also, some deep layer neurons in this species may receive effective visual input through their dendrites that ascend into the superficial layers, where they are likely to be contacted by retinal axons or axon collaterals of superficial layer cells.
Synaptic basis for developmental plasticity in a birdsong nucleus
Authors: Mooney R
Published: March 2018

The development and adult production of birdsong are subserved by specialized brain nuclei, including the robust nucleus of the archistriatum (RA), and its afferents originating in the caudal nucleus of the ventral hyperstriatum (HVc) and the lateral portion of the magnocellular nucleus of the anterior neostriatum (L-MAN). An in vitro brain slice preparation was used to characterize the electrophysiological properties of L-MAN and HVc axonal synapses within RA and to examine how these synaptic connections change during the course of song development. Electrical stimulation of L-MAN and not HVc fibers evoked excitatory synaptic potentials from virtually all RA neurons in brain slices prepared from male and female zebra finches less than 25 d of age. These “L-MAN” EPSPs were blocked substantially by the NMDA receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-APV; 50–100 microM) and by hyperpolarization of the postsynaptic membrane. In contrast, when slices were prepared from male finches greater than 35 d of age, electrical stimulation of the L-MAN and the HVc fiber tracts evoked synaptic responses from over 70% of RA neurons. Although the L-MAN EPSPs resembled those seen in RA before day 25, the “HVc” EPSPs were relatively insensitive to D-APV, but almost completely abolished by 6-cyano-7-nitroquinoxaline-2,3-dione, a non-NMDA glutamate receptor antagonist. These experiments indicate that L-MAN and HVc axons make pharmacologically distinct synapses on the same RA neurons, and that these synapses first form at different stages during development.
Functional anatomy of human procedural learning determined with regional cerebral blood flow and PET
Authors: Grafton ST , Mazziotta JC , Presty S , Friston KJ , Frackowiak RS , Phelps ME
Published: March 2018

The functional anatomy of motor skill acquisition was investigated in six normal human subjects who learned to perform a pursuit rotor task with their dominant right hand during serial positron emission tomography (PET) imaging of relative cerebral blood flow (relCBF). The effect of motor execution, rather than learning, was identified by a comparison of four motor performance scans with two control scans (eye movements only). Motor execution was associated with activation of a distributed network involving cortical, striatonigral, and cerebellar sites. Second, the effect of early motor learning was examined. Performance improved from 17% to 66% mean time on target across the four PET scans obtained during pursuit rotor performance. Across the same scans, significant longitudinal increases of relCBF were located in the left primary motor cortex, the left supplementary motor area, and the left pulvinar thalamus. The results demonstrate that changes of regional cerebral activity associated with early learning of skilled movements occur in sites that are a subset of a more widely distributed network that is active during motor execution.
Gene regulation in an ascending nociceptive pathway: inflammation- induced increase in preprotachykinin mRNA in rat lamina I spinal projection neurons
Authors: Noguchi K , Ruda MA
Published: March 2018

Tachykinin peptides are distributed widely in the nervous system and have been shown to play a prominent role in nociceptive pathways in the spinal cord and dorsal root ganglia. This study investigated the inflammation-induced response of dorsal horn projection neurons and local circuit neurons expressing preprotachykinin (PPT) mRNA using RNA blot analysis and in situ hybridization histochemistry. To identify projection neurons, fluorogold was injected into the parabrachial area of the brainstem. In laminae I, II and V/VI ipsilateral to inflammation, there was a differential increase in the number of neurons exhibiting PPT mRNA. In lamina I, the number of spinal projection neurons containing PPT mRNA showed a greater than 200% increase. The identification of spinal projection neurons with inflammation-induced increases in PPT mRNA suggests that tachykinin peptides may act as neurotransmitters in nociceptive CNS projection pathways.
NGF induces the expression of the VGF gene through a cAMP response element
Authors: Hawley RJ , Scheibe RJ , Wagner JA
Published: March 2018

NGF is a peptide growth factor that plays a key role in the differentiation and survival of neurons in both the PNS and CNS. NGF acts through both transcription-dependent and transcription-independent mechanisms to regulate the differentiation of PC12 cells. To better understand the regulation of gene expression by NGF, we have defined a cis-acting sequence that is immediately upstream of the transcription start site of the VGF (a2/NGF33.1) gene that is required for induction by NGF. Within this sequence is a consensus cAMP response element (CRE) embedded in a 14 base pair palindrome. Mutations in this CRE eliminate induction of the VGF gene both by NGF and by agents that act via cAMP. Although this sequence confers transcriptional induction by both NGF and cAMP, it is not sufficient to allow induction by epidermal growth factor, acidic or basic fibroblast growth factor, or phorbol 12- myristate 13-acetate (PMA). Thus, this sequence defines an element that is selectively activated by NGF and cAMP. Promoter fragments from the VGF gene that include the core CRE efficiently bind the inducible transcription factor CREB, while fragments bearing mutations that eliminate NGF and cAMP inducibility fail to do so. Sequence comparisons and hybridization studies indicate that there are at least two alternatively spliced forms of VGF mRNA, and the accumulation of both of these forms is similarly regulated by NGF and cAMP.
Enduring memory impairment in monkeys after ischemic damage to the hippocampus
Authors: Zola-Morgan S , Squire LR , Rempel NL , Clower RP , Amaral DG
Published: March 2018

Patient RB became amnesic following an episode of global ischemia that resulted in a bilateral lesion of the CA1 field of the hippocampus. This finding suggested that damage restricted to the hippocampus is sufficient to produce clinically significant memory impairment. To evaluate further the effect of ischemic brain damage on memory, we have developed an animal model of cerebral ischemia in the monkey. Monkeys were subjected to 15 min of reversible ischemia, using a noninvasive technique involving carotid occlusion and pharmacologically induced hypotension. These monkeys sustained significant loss of pyramidal cells in the CA1 and CA2 fields of the hippocampus, as well as loss of somatostatin-immunoreactive cells in the hilar region of the dentate gyrus. Cell loss occurred bilaterally throughout the rostrocaudal extent of the hippocampus but was greater in the caudal portion. Except for patchy loss of cerebellar Purkinje cells, significant damage was not detected in areas outside the hippocampus, including adjacent cortical regions, that is, entorhinal, perirhinal, and parahippocampal cortex, and other regions that have been implicated in memory function. On behavioral tests, the ischemic monkeys exhibited significant and enduring memory impairment. On the delayed nonmatching to sample task, the ischemic monkeys were as impaired as monkeys with lesions of the hippocampal formation and adjacent parahippocampal cortex (the H+ lesion). On two other memory tasks, the ischemic monkeys were less impaired than monkeys with the H+ lesion. In neuropathological evaluations, it has always been difficult to rule out the possibility that significant areas of neuronal dysfunction have gone undetected. The finding that ischemic lesions produced overall less memory impairment than H+ lesions indicates that the ischemic monkeys (and by extension, patient RB) are unlikely to have widespread neuronal dysfunction affecting memory that was undetected by histological examination. These results provide additional evidence that the hippocampus is a focal site of pathological change in cerebral ischemia, and that damage limited to the hippocampus is sufficient to impair memory.
Regulation of somatodendritic dopamine release in the ventral tegmental area by opioids and GABA: an in vivo microdialysis study
Authors: Klitenick MA , DeWitte P , Kalivas PW
Published: March 2018

Microdialysis of the ventral tegmental area in conscious rats was used to evaluate the influence of opioids and GABA agonists on extracellular levels of GABA and somatodendritically released dopamine. The administration of morphine through the dialysis probe elicited significant, dose-dependent increases in the levels of extracellular dopamine and significantly reduced the extracellular concentration of GABA. In contrast, a dose-dependent decrease in somatodendritic extracellular dopamine was produced following the administration of the GABAB agonist baclofen. The increase in dopamine levels elicited by morphine (100 microM) was completely blocked by either baclofen (100 microM) coadministration or peripheral injection of naloxone (2 mg/kg, i.p.). Application of the GABAA agonist muscimol produced a significant increase in both extracellular levels of dopamine and locomotor activity. The present results, together with other electrophysiological, neurochemical, and behavioral data, support a hypothesis that stimulation of mu-opioid or GABAA receptors inhibits the activity of GABAergic afferents to dopamine neurons, thereby removing tonic inhibitory regulation, whereas stimulation of GABAB receptors directly inhibits dopamine neurons.
Differential effects of serotonin, FMRFamide, and small cardioactive peptide on multiple, distributed processes modulating sensorimotor synaptic transmission in Aplysia
Authors: Pieroni JP , Byrne JH
Published: March 2018

At least two processes contribute to the modulation by 5-HT of the connections between sensory neurons and motor neurons in Aplysia. The first involves broadening of the presynaptic spike through modulation of 5-HT-sensitive K+ channels that leads to elevated levels of intracellular Ca2+ and increased release of transmitter. A second process (or set of processes) apparently accounts for the amount of facilitation not produced by presynaptic spike broadening. This spike duration-independent (SDI) process is particularly prominent in depressed synapses. We used a protocol in which spikes were prebroadened into a range of durations in which further spike broadening by itself has little or no effect on facilitation of the EPSP.5-HT produced pronounced facilitation in depressed synapses under these conditions. Another modulatory agent, small cardioactive peptide (SCPb), also broadened spikes in sensory neurons but did not produce facilitation comparable to that produced by 5-HT. These results indicate that 5-HT activates the SDI process whereas SCPb fails to do the same. A 5 min preexposure to the modulatory peptide FMRFamide inhibited 5-HT-induced activation of the SDI process, whereas a 1 min preexposure did not. Another process(es) that may modulate synaptic efficacy in sensorimotor synapses involves changes in the properties of the motor (follower) neuron, such as input resistance. FMRFamide decreased the input resistance of postsynaptic neurons. This action could contribute to the effects of FMRFamide when administered alone, but it did not appear to be responsible for the inhibitory action of FMRFamide on 5-HT-induced facilitation. Neither 5-HT nor SCPb had a clear effect on input resistance. The actions of these three agents, therefore, seem to be differentially distributed among various pre- and postsynaptic processes involved in the modulation of synaptic transmission.
Three-dimensional structure of dendritic spines and synapses in rat hippocampus (CA1) at postnatal day 15 and adult ages: implications for the maturation of synaptic physiology and long-term potentiation [published erratum appears in J Neurosci 1992 Aug;12(8):following table of contents]
Authors: Harris KM , Jensen FE , Tsao B
Published: March 2018

It has long been hypothesized that changes in dendritic spine structure may modify the physiological properties of synapses located on them. Due to their small size, large number, and highly variable shapes, standard light microscopy of Golgi impregnations and electron microscopy (EM) of single thin sections have not proved adequate to identify most spines in a sample or to quantify their structural dimensions and composition. Here we describe a new approach, the series sample, that was developed to classify by shape and subcellular composition all of the spines and synapses in a sample of neuropil by viewing them through serial EM sections. Spines in each class are then randomly selected for serial reconstruction and measurement in three dimensions. This approach was used to assess whether structural changes in hippocampal CA1 spines could contribute to the enhanced synaptic transmission and the greater endurance of long-term potentiation (LTP) that occur with maturation. Our results show a near doubling in the total density of synapses in the neuropil and along reconstructed dendrites between postnatal day 15 (PND 15) and adult ages. However, this doubling does not occur uniformly across all spine and synapse morphologies. Thin spines, mushroom spines containing perforated postsynaptic densities (PSDs) and spine apparatuses, and branched spines increase by about four-fold in density between PND 15 and adult ages. In contrast, stubby spines decrease by more than half and no change occurs in mushroom spines with macular PSDs or in dendritic shaft synapses. The stubby spines that remain are smaller in adults than at PND 15 and the mushroom spines are larger, while no change occurs in the three-dimensional structure of thin spines. Only a few spine necks at either age are constricted or long enough to attenuate charge transfer; therefore, the doubling in synapses should mediate the enhancement of synaptic transmission that occurs with maturation. In addition, LTP is not likely to be mediated by widening of spine necks at either age. However, the constricted spine necks could serve to concentrate specific molecules at activated synapses, thereby enhancing the specificity and endurance of LTP with maturation. These results demonstrate that the new series sample method combined with three- dimensional reconstruction reveals quantitative changes in the frequency and structure of spines and synapses that are not discernable by other methods and are likely to have dramatic effects on synaptic physiology and plasticity.
Developmental changes in calcium conductances contribute to the physiological maturation of cerebellar Purkinje neurons in culture
Authors: Gruol DL , Deal CR , Yool AJ
Published: March 2018

The relationship between calcium conductances and developmental changes in the active and passive membrane properties of cerebellar Purkinje neurons from rats was studied in a culture model system by using current-clamp and voltage-clamp techniques. These cultures, at 6–21 d of age, represented the main period of morphological and physiological development of the Purkinje neuron. In the current-clamp studies, input resistance decreased and the current-voltage curve became more S-shaped as the neurons matured in culture. Spike-generating properties also changed. Immature Purkinje neurons without dendritic structure produced repetitive, fast TTX-sensitive simple spikes when stimulated electrically. The simple spike frequency increased with maturation. In older neurons (greater than or equal to 12 d in vitro) with well- developed dendritic structure, a burst event, the complex spike, preceded the repetitive simple spike firing. Magnesium (10 mM) and cadmium (50–100 microM), calcium channel blockers, antagonized the repetitive simple spike firing in both young and old neurons. The complex spike of the older neurons was also antagonized by magnesium (10 mM) but was resistant to cadmium (50–100 microM), suggesting that a pharmacologically distinct calcium conductance mediated this spike event. Whole-cell voltage-clamp recordings showed that the older Purkinje neurons expressed two calcium currents, a low-threshold rapidly inactivating calcium current resistant to cadmium (50–100 microM) and a high-threshold slowly inactivating calcium current antagonized by cadmium (50–100 microM). In young Purkinje neurons without dendritic structure (6–9 d in vitro), only the high-threshold calcium current was evident. The amplitude of this current increased approximately 50% during development. These results indicate that the developmental expression of calcium conductances plays a prominent role in the physiological maturation of the cultured Purkinje neurons, which closely simulate the physiologic cells they model. The high-threshold calcium conductance is expressed early in development and contributes to repetitive simple spike firing of both the young and old neurons. The low-threshold calcium conductance appears later in development, coincident with dendritic expression, and plays a major role in the generation of the complex spike.
Spontaneous locomotor hyperactivity in a mouse mutant with a deletion including the Snap gene on chromosome 2
Authors: Hess EJ , Jinnah HA , Kozak CA , Wilson MC
Published: March 2018

The gene encoding the synaptosomal-associated protein--25 kDa (SNAP-25) was mapped by analysis of somatic cell hybrids and an intersubspecies backcross to mouse Chromosome 2. To identify potential mutants for SNAP- 25, mice bearing mutations mapping to this region of Chromosome 2 were screened for Snap gene abnormalities. Mice heterozygous for the semidominant mutation coloboma (Cm/+) were identified that carried a deletion of Snap gene sequence. Analysis of genomic DNA revealed that the Snap gene dosage in Cm/+ mice was 50% lower than control littermates. Additionally, SNAP-25 mRNA and protein expression were 50% lower in coloboma mice than control littermates. The coloboma mouse phenotype is characterized by small eyes and head bobbing; in addition, we observed that these mice were extremely hyperactive with spontaneous locomotor activity exceeding three times control mouse activity. The localization of the genetic abnormality in coloboma mice using the Snap gene marker will provide a powerful tool for studying the biologic basis of locomotor hyperactivity.
Localization of adenylyl and guanylyl cyclase in rat brain by in situ hybridization: comparison with calmodulin mRNA distribution
Authors: Matsuoka I , Giuili G , Poyard M , Stengel D , Parma J , Guellaen G , Hanoune J
Published: March 2018

Cyclic nucleotides are major intracellular mediators in the signal transduction events in synaptic neurotransmission of the CNS. Intracellular Ca2+ is known to regulate adenylyl cyclase (AC) in a calmodulin (CaM)-dependent manner, and guanylyl cyclase (GC), in an indirect manner through CaM-sensitive nitric oxide synthase. To ascertain the physiological significance of cyclic nucleotide second messenger systems, we have localized the mRNAs encoding AC, GC, and CaM in the rat brain by in situ hybridization using 35S-labeled RNA probes. The AC mRNA is widely distributed throughout the brain; strong hybridization signal was observed in the granular layers of the cerebellum, in the pyramidal and granule cells of the hippocampus, and in the olfactory system. These AC mRNA localizations are compatible with the distribution of Ca2+/CaM-sensitive AC activities. In contrast to AC mRNA distribution, GC mRNA has a more limited distribution. Significant signals were observed in the striatum, in the pyramidal and granule cells of the hippocampus, in the olfactory system, in the inferior and superior colliculus, in the Purkinje cells of the cerebellum, in the locus coeruleus, and in many pyramidal cells in the layers II-III and V of the cerebral cortex, and mainly, in the occipital cortex. In some discrete brain regions, a close correlation was found between enzyme activity and mRNA hybridization signal of GC. The distinct distribution of AC and GC mRNAs suggests that different cyclic nucleotide second messenger systems have specialized functions. On the other hand, CaM mRNA was colocalized with the AC and GC mRNA, but its distribution was more abundant and specific for neuronal cells, since there was little hybridization signal with CaM probe in neuronal fiber regions such as the corpus callosum and the anterior commissure. The high expression of CaM mRNA in neuronal cells is in agreement with its biochemical role in the regulation of various enzymes. Results of the present study should help in analyzing the role of cyclic nucleotides and CaM in physiological and pathological situations in the CNS.
Metabolism of omega-conotoxin-sensitive voltage-operated calcium channels in human neuroblastoma cells: modulation by cell differentiation and anti-channel antibodies
Authors: Passafaro M , Clementi F , Sher E
Published: March 2018

The turnover of voltage-operated calcium channels was studied in two different human neuroblastoma cell lines (IMR32 and SH-SY5Y) using omega-conotoxin. The 125I-omega-conotoxin bound to surface channels was internalized and degraded by the cells in a time- and temperature- dependent manner. The radioactive degradation products released in the medium were all trichloroacetic acid soluble and no longer recognized by anti-omega-conotoxin antibodies. Altering the pH of intracellular organelles with chloroquine and inhibiting lysosomal proteases with leupeptin reduced 125I-omega-conotoxin degradation but had no effect on its internalization. Postlabeling measurements showed that the rates of 125I-omega-conotoxin internalization and degradation were equal to the rate of channel removal from the cell surface after protein synthesis inhibition. The rate of removal of omega-conotoxin binding sites was parallel to the rate of loss of functional channels, as measured by means of the fura-2 technique. Drug-induced differentiation of human neuroblastoma cells slowed down channel internalization and degradation rates, leading to the known increased expression of plasma membrane calcium channels in differentiated cells. On the other hand, both human (from Lambert-Eaton myasthenic patients) and murine (from immunized mice) anti-channel antibodies increased the rates of channel internalization and degradation, leading to channel downregulation. The activity of presynaptic calcium channels is already known to be acutely modulated by a number of different agents (e.g., hormones and neurotransmitters); our studies suggest that a different form of channel modulation (changes in the number of channels due to interference with channel turnover) may be active over a longer time scale in neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Subtype-selective cholecystokinin receptor antagonists block cholecystokinin modulation of dopamine-mediated behaviors in the rat mesolimbic pathway
Authors: Crawley JN
Published: March 2018

Subtype-selective antagonists of the peripheral-type (CCK-A) and the central-type (CCK-B) cholecystokinin (CCK) receptors were employed to determine the receptor subtype(s) mediating the modulatory actions of CCK on dopamine-induced changes in exploratory activity at three sites in the mesolimbic pathway of the rat. The CCK-A antagonist L-364,718 (10 ng) blocked CCK potentiation of dopamine-induced hyperlocomotion in the medial posterior nucleus accumbens. The CCK-B antagonist CI-988 (20 ng) blocked CCK inhibition of dopamine-induced hyperlocomotion in the anterior nucleus accumbens. The CCK-B antagonists CI-988 (20 ng) and L- 365,260 (10 ng) blocked CCK potentiation of dopamine-induced hypolocomotion in the ventral tegmental area. These data indicate a CCK- B pharmacology in the cell body and anterior terminal field, and a CCK- A pharmacology in the posterior terminal field, of the mesolimbic dopamine pathway. Behavioral analyses using the selective CCK antagonists did not detect a contribution of endogenous CCK to exploratory locomotion. L-364,718 (10 ng), L-365,260 (10 ng), and CI- 988 (20 ng or 2 micrograms), microinjected into the medial posterior nucleus accumbens, anterior nucleus accumbens, or ventral tegmental area, had no effect on baseline exploratory locomotion or on dopamine- induced changes in exploratory locomotion. Using a dark-induced hyperlocomotion paradigm, the CCK antagonists at these doses at these sites and intraperitoneally had no effect on the high levels of exploratory locomotor activity exhibited by the rats in the dark testing environment, or the lower levels of exploratory activity in the lighted environment. Endogenous CCK may not be released during dopamine- induced hyperlocomotion or dark-induced hyperlocomotion, or endogenous CCK may not contribute significantly to exploratory behaviors mediated through the mesolimbic dopamine pathway. Utilization of these potent, selective, nonpeptide CCK antagonists, with the doses, vehicles, and routes of administration developed in the present studies, will guide further investigations into the role of endogenous CCK in other facets of mesolimbic function.
Neural coding of tactile texture: comparison of spatial and temporal mechanisms for roughness perception
Authors: Connor CE , Johnson KO
Published: March 2018

A previous study showed that roughness perception may depend on either temporal or spatial variations in firing rate among cutaneous mechanoreceptive afferents. The present study was designed to distinguish between these hypotheses. Plastic surfaces embossed with patterns of dots designed to produce predictable alterations in temporal and spatial firing rate variation were used as stimuli in psychophysical and neurophysiological experiments. Subjective roughness magnitudes obtained from psychophysical experiments fitted the predictions of the spatial but not the temporal hypothesis. In the neurophysiological experiments, the stimuli were scanned across the receptive fields of cutaneous mechanoreceptive afferents. Firing rate variation in the neural responses was measured using a range of temporal and spatial filters. Temporal variation was not correlated with roughness magnitude. Spatial variation, on a scale of 1–2 mm (one to two receptor spacings), was closely correlated with roughness.
Changes in the cortical map of the hand following postnatal ulnar and radial nerve injury in monkeys: organization and modification of nerve dominance aggregates
Authors: Wall JT , Huerta MF , Kaas JH
Published: March 2018

The ulnar and radial nerves to the hands of 12–31-d-old marmoset monkeys were transected and ligated, and the monkeys were subsequently reared for periods of 1.4–1.6 years with only median nerve innervation to the hand. Features of organization in the cortical area 3b hand map were then assessed with neurophysiological mapping procedures, and compared to features in monkeys that had undergone either a normal postnatal development with three intact hand nerves, or an abnormal development with two intact nerves due to postnatal injury of the median nerve. A systematic comparison of cortical organization in these monkeys led to three main findings. First, some features of organization show little or no change when monkeys are reared with one, two, or three hand nerves. These features include receptive field size and the overall size of the hand map. Second, other features are, in contrast, clearly altered in an injury-dependent manner. These features include cortical neuronal thresholds to light tactile stimuli, and the spatial location, size, shape, continuity, and somatotopic interfacing of representations of the parts of the hand. Finally, estimates of the peripheral innervation territories of the hand nerves, and of the corresponding distributions of cortical neurons activated by inputs from these territories, indicate that the normal hand map contains bandlike aggregates of neurons that are dominantly activated by inputs from each nerve. Postnatal nerve injuries alter the size of these nerve dominance aggregates.
Restricted expression of N- and R-cadherin on neurites of the developing chicken CNS
Authors: Redies C , Inuzuka H , Takeichi M
Published: March 2018

The expression of two cadherins, N- and R-cadherin, was mapped in the CNS of chicken embryos of 6–11 d incubation, focusing on the sensory and motor fiber systems. In the spinal cord, the laterally located fibers of the dorsal funiculus express N-cadherin while the medially located fibers do not. These two fiber systems have a different course within the CNS but associate to form the spinal dorsal roots. In the hindbrain, N-cadherin is expressed by the descending trigeminal (general somatic sensory) tract, which is contiguous with the N- cadherin-positive zone of the dorsal funiculus of the spinal cord. R- cadherin is not expressed by sensory fibers, but is expressed by the visceral motor system of the vagus and glossopharyngeal nerves, which are N-cadherin negative. The motor neurites expressing R-cadherin have a different course within the brain than the sensory neurites expressing N-cadherin, although they form the common sensory/motor roots of the vagus nerve at the surface of the brain. The possibility that N-cadherin provides a guidance cue for sensory axon migration within the CNS by a homophilic adhesion mechanism was investigated in vitro. Explants from sensory spinal ganglia expressing N-cadherin were placed on N-cadherin-transfected neuroblastoma cells, and axon outgrowth was visualized. Results showed that the sensory axons defasciculate and closely follow the cell-cell boundaries between transfected cells where high levels of N-cadherin are expressed. These results show that the two cadherins, like members of the immunoglobulin superfamily of molecules, are expressed in a topographically restricted fashion during chick brain development. They furthermore suggest that N- cadherin expression by neurites may play a role in guiding these neurites along CNS paths that express the same molecule.
Adrenal hormones suppress cell division in the adult rat dentate gyrus
Authors: Gould E , Cameron HA , Daniels DC , Woolley CS , McEwen BS
Published: March 2018

The rat dentate gyrus is unusual among mammalian brain regions in that it shows cell birth well into adulthood. During development, dentate gyrus cell birth is regulated by adrenal steroids. However, it is presently unknown whether cell division in the adult is also mediated by these same factors. In order to determine whether this is the case, we combined adrenalectomy, with or without corticosterone (CORT) replacement, and 3H-thymidine autoradiography, Nissl staining, and immunohistochemistry for the glial cell markers vimentin and glial fibrillary acidic protein (GFAP) as well as for the neuronal marker neuron-specific enolase. Removal of circulating adrenal steroids resulted in a greater density of both GFAP-immunoreactive and vimentin- immunoreactive cells compared to sham-operated animals; CORT replacement prevented increases in both of these cell types. The increase in the density of vimentin-immunoreactive cells probably resulted from an increase in the birth of these cells, as adrenalectomized rats showed greater numbers of 3H-thymidine-labeled vimentin-positive cells compared to sham rats. In contrast, no changes in the number of 3H-thymidine-labeled GFAP-positive cells were observed with adrenalectomy, indicating that the increase in this cell type probably does not involve cell birth. In addition, the density of 3H- thymidine-labeled cells that were not immunoreactive for either glial cell marker and that showed neuronal characteristics was dramatically increased with adrenalectomy. These results suggest that adrenal hormones normally suppress the birth of both glia and neurons in the adult rat dentate gyrus.