bluuebunny/crossref_metadata_2025 huggingface dataset:
The contribution of excitatory amino acids to central sensitization and persistent nociception after formalin-induced tissue injury
Authors: Coderre TJ , Melzack R
Published: March 2018

The contribution of excitatory amino acids (EAAs) to the development of central sensitization and persistent nociception in response to tissue injury in rats was examined following the subcutaneous injection of formalin into the hindpaw. Formalin-induced nociceptive behaviors were enhanced by intrathecal pretreatment with the EAAs L-glutamate and L- aspartate. An enhancement of the formalin nociceptive response was also produced by intrathecal pretreatment with the receptor-selective EAA agonists NMDA and trans-(+/- )-1-amino-1,3-cyclopentane dicarboxylic acid (ACPD), but not (R,S)-alpha-amino-3-hydroxy-5-methylisozazole-4- propionic acid hydrobromide (AMPA). The effect of NMDA was enhanced by a combined administration with AMPA or APCD. Formalin nociceptive responses were dose-dependently reduced by intrathecal pretreatment with the NMDA receptor antagonists 2-amino-5-phosphonovaleric acid (APV) and (+)-MK-801 hydrogen maleate, but not the selective AMPA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione or the selective metabotropic EAA receptor antagonist 2-amino-3-phosphonopropionic acid. The results suggest that EAAs acting at the NMDA receptor contribute to central sensitization and persistent nociception following subcutaneous formalin injection.
Kainic acid lesions of the dorsal nucleus of the lateral lemniscus: effects on binaural evoked responses in rat auditory cortex
Authors: Glenn SL , Kelly JB
Published: March 2018

The effects of unilateral lesions of the dorsal nucleus of the lateral lemniscus (DNLL) on binaural processing were examined by measuring the amplitude of auditory cortical evoked responses in the albino rat. Lesions were made by pressure injection of small quantities of kainic acid through a micropipette lowered into the lateral lemniscus. Comparisons were made between normal animals and animals with unilateral DNLL damage. In normal animals, the amplitude of evoked potentials recorded from left and right primary auditory cortex varied as a function of the time difference between clicks delivered to the two ears. Maximum responses were obtained from the hemisphere contralateral to the leading click, and response amplitude was progressively reduced as the interaural time difference (ITD) was shifted in favor of the ipsilateral ear over the range from +600 microseconds to -600 microseconds. The functions in the left and right hemisphere were symmetrical mirror images of one another. Destruction of the DNLL had no significant effect on the maximum response amplitude, evoked response threshold, or response latency in either hemisphere. On the other hand, the lesion did have the effect of greatly reducing the slope of the ITD function in the hemisphere contralateral to the lesion. The change in slope was attributed to a reduction in the strength of inhibition produced by stimulation of the ipsilateral ear. No effect was seen on the slope of the function in the ipsilateral hemisphere. Animals with lesions that spared DNLL but destroyed the intermediate and ventral nucleus of the lateral lemniscus had normal binaural response functions. These data show that the DNLL plays an important role in shaping binaural responses in the contralateral auditory pathway.
D1-like and D2-like dopamine receptors synergistically activate rotation and c-fos expression in the dopamine-depleted striatum in a rat model of Parkinson's disease
Authors: Paul ML , Graybiel AM , David JC , Robertson HA
Published: March 2018

Selective agonists for D1-like and D2-like dopamine receptors can interact synergistically to enhance each other's actions on locomotion and behavior in experimental animals. Clinically, the combination of the D2 agonist bromocriptine with L-dopa (which has pronounced D1 effects) is a highly effective treatment for Parkinson's disease. The mechanisms underlying this important receptor interaction are poorly understood and are the subject of intense study in vitro. In rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway, D1-selective (but not D2-selective) dopamine agonists produce a marked increase in expression of the immediate-early gene c-fos in the striatum ipsilateral to the 6-OHDA lesion. In the experiments reported here, we have used this in vivo model to explore the possibility that combinations of D1-selective and D2-selective agonists might have effects on c-fos transcription that are different from those exhibited by D1 or D2 agonists administered alone. We examined the effects of the D1-selective agonist SKF-38393 and the D2-selective agonist quinpirole (LY 171555) on the expression of Fos-like protein and c-fos mRNA in the caudoputamen and made parallel behavioral observations in the same animals. A low dose of SKF-38393 produced little contraversive rotation and little induction of Fos-like immunoreactivity in the striatum. A low dose of quinpirole elicited contralateral rotation but little or no induction of Fos-like immunoreactivity in the caudoputamen; there was, however, induction of Fos in the globus pallidus ipsilateral to the 6-OHDA lesion. Combination of the low dose of SKF-38393 and quinpirole produced a synergistic effect on rotation and elicited, in the dopamine-depleted caudoputamen, a striking pattern of Fos-like protein expression in which Fos-positive neurons were concentrated in striosomes and in the dorsolateral caudoputamen. Northern blot analysis showed that c-fos mRNA was expressed following combined agonist treatment but was not detectable after the single-agonist treatments. Both the contraversive rotation and the induction of Fos-like immunoreactivity were blocked by the preadministration of the D1-preferring antagonist SCH-23390 and the D2-selective antagonist raclopride in combination. Pretreatment with the glutamate NMDA receptor antagonist MK-801 also blocked the induction of Fos-like immunoreactivity, and it reversed the rotation. These findings suggest a D1/D2 synergistic mechanism that involves the participation of D1-responsive striatonigral and D2-responsive striatopallidal output pathways, and that is sensitive to glutamatergic modulation.
Immunogold quantification of glutamate in two types of excitatory synapse with different firing patterns
Authors: Shupliakov O , Brodin L , Cullheim S , Ottersen OP , Storm-Mathisen J
Published: March 2018

A quantitative immunocytochemical method was used to study the regional levels of glutamate in two types of lamprey (Ichtyomyzon unicuspis) axon, which both activate excitatory amino acid receptors, but which when active exhibit different firing patterns. Giant reticulospinal axons fire in brief bursts, while dorsal column axons, mainly belonging to cutaneous afferents, show a sustained firing at high frequency. In both types of axon, clusters of synaptic vesicles showed a strong accumulation of glutamate immunogold labeling, and the density of gold particles correlated strictly with the packing density of synaptic vesicles. The most densely packed vesicle areas had a particle density corresponding to a concentration of fixed glutamate of about 30 mM in coprocessed glutamate conjugates, suggesting an intravesicular glutamate concentration of at least 60 mM. The level of labeling in axoplasmic matrix was considerably lower, but differed significantly between the two types of axon. Dorsal column axons showed a particle density in axoplasmic matrix that was approximately four times higher than that in giant reticulospinal axons. The mitochondrial glutamate labeling was also significantly stronger in the dorsal column axons. In addition, the number of mitochondrial profiles surrounding vesicle clusters was about four times higher in dorsal column synapses than in reticulospinal synapses. Antisera to aspartate, GABA, glutamine, and homocysteate failed to produce a specific labeling of synaptic vesicle clusters in reticulospinal or dorsal column axons. In conjunction with previous demonstrations of a stimulus-induced vesicle depletion in giant reticulospinal synapses (Wickelgren et al., 1985), these results imply that glutamate is released from synaptic vesicles. The different extravesicular glutamate levels in reticulospinal axons and dorsal column axons may relate to different requirements for the refilling of synaptic vesicles in these functionally divergent neurons.
Early development of glycine- and GABA-mediated synapses in rat spinal cord
Authors: Wu WL , Ziskind-Conhaim L , Sweet MA
Published: March 2018

Motoneuron responses to the inhibitory amino acids glycine and GABA, and the contribution of inhibitory synapses to developing sensorimotor synapses were studied in rat spinal cords during the last week in utero. In differentiating motoneurons, glycine and GABA induced Cl(-)- dependent membrane depolarizations and large decreases in membrane resistance. These responses gradually decreased during embryonic development, and at birth they were significantly smaller than in embryos. In motoneurons of embryos and neonates, dorsal root stimulation produced only depolarizing potentials, some of which reversed at -50 mV membrane potential. Reduction of extracellular Cl- concentrations increased the amplitude of these potentials, suggesting that they are generated by Cl- current. Contribution of Cl(-)-dependent potentials to compound dorsal root-evoked potentials was studied by determining the effects of glycine and GABA antagonists on them. In motoneurons of embryos at days 16–17 of gestation (D16-D17), strychnine or bicuculline blocked dorsal root-evoked potentials. This suppression was neither the result of a decrease in neuronal excitability nor the inhibition of glutamate receptors. Strychnine-evoked depression was not blocked by atropine, indicating that it was not due to disinhibition of muscarinic synapses. By D19, strychnine and bicuculline significantly increased dorsal root-evoked potentials rather than blocking them. This reversed function did not result from an increase in neuronal excitability or changes in the specificity of strychnine and bicuculline antagonism. The number of glycine- and GABA-immunoreactive cells increased 20% between D17 and D19. The number of immunoreactive cells and fibers significantly increased in the motor nuclei and dorsal horn laminae. These morphological changes may contribute to establishment of new synaptic contacts on motoneurons, thus changing the actions of strychnine and bicuculline on dorsal root-evoked potentials.
Basic fibroblast growth factor: a potential regulator of proliferation and intermediate filament expression in the retina
Authors: Lewis GP , Erickson PA , Guerin CJ , Anderson DH , Fisher SK
Published: March 2018

Proliferation of astrocytes, and a concomitant increase of intermediate filaments in astrocytes are two fundamental responses of the CNS to injury. We have previously identified these two events in the retina's response to detachment of the neural retina from the adjoining monolayer of retinal pigmented epithelium. In order to analyze the potential role of basic fibroblast growth factor (bFGF) in these responses, we studied cellular proliferation and intermediate filament protein expression in the retinas of cats and rabbits 4 d and 4 weeks after a single intravitreal injection of 1 microgram of bFGF. Our results show that bFGF stimulates both of these processes in an otherwise normal eye. The eyes that received bFGF had significantly elevated numbers of 3H-thymidine-labeled Muller cells, astrocytes, vascular cells, retinal pigmented epithelial cells, microglia, and macrophages by comparison to control eyes. This proliferation was apparent at 4 d after the injection of bFGF but not after 4 weeks. In control eyes, antibodies to glial fibrillary acidic protein and vimentin labeled intermediate filaments only in the inner (vitread) portion of the Muller cells, the specialized radial astrocytes that span the width of the retina. In eyes that had been injected with bFGF, almost the entire Muller cell cytoplasm was labeled at 4 d after injection; after 4 weeks, the cytoplasmic labeling intensity had increased significantly. Release or activation of endogenous stores of bFGF after injury or disease may be involved in the control of cellular proliferation and intermediate filament expression in the retina and elsewhere in the CNS.
Calbindin and parvalbumin cells in monkey VPL thalamic nucleus: distribution, laminar cortical projections, and relations to spinothalamic terminations
Authors: Rausell E , Bae CS , Vinuela A , Huntley GW , Jones EG
Published: March 2018

The ventral posterior lateral nucleus (VPL) of the monkey thalamus was investigated by histochemical staining for cytochrome oxidase (CO) activity and by immunocytochemical staining for the calcium-binding proteins parvalbumin and 28 kDa calbindin. Anterograde and retrograde tracing experiments were used to correlate patterns of differential distribution of CO activity and of parvalbumin and calbindin cells with the terminations of spinothalamic tract fibers and with the types of cells projecting differentially to superficial and deeper layers of primary somatosensory cortex (SI). VPL is composed of CO-rich and CO- weak compartments. Cells are generally smaller in the CO-weak compartment. Parvalbumin-immunoreactive cells and parvalbumin- immunoreactive medial lemniscal fiber terminations are confined to the CO-rich compartment. Calbindin-immunoreactive cells are found in both the CO-rich and CO-weak compartments. The CO-weak compartment, containing only calbindin cells, forms isolated zones throughout VPL and expands as a cap covering the posterior surface of the ventral posterior medial nucleus (VPM). Spinothalamic tract terminations tend to be concentrated in the CO-weak compartment, especially in the posterior cap. Other CO-weak, parvalbumin-negative, calbindin-positive nuclei, including the posterior, ventral posterior inferior, and anterior pulvinar and the small-celled matrix of VPM are also associated with concentrations of spinothalamic and caudal trigeminothalamic terminations. Parvalbumin cells are consistently larger than calbindin cells and are retrogradely labeled only after injections of tracers in middle and deep layers of SI. The smaller calbindin cells are the only cells retrogradely labeled after placement of retrograde tracers that primarily involve layer I of SI. The compartmental organization of VPL is similar to but less rigid than that previously reported in VPM. VPL and VPM relay cells projecting to different layers of SI cortex can be distinguished by differential immunoreactivity for the two calcium-binding proteins. The small- celled, CO-weak, calbindin-positive zones of VPL and VPM appear to form part of a wider system of smaller thalamic neurons unconstrained by traditional nuclear boundaries that are preferentially the targets of spinothalamic and caudal trigeminal inputs, and that may have preferential access to layer I of SI.
Excitatory amino acid-mediated responses and synaptic potentials in medial pontine reticular formation neurons of the rat in vitro
Authors: Stevens DR , McCarley RW , Greene RW
Published: March 2018

Neurons of the medial pontine reticular formation (mPRF) are involved in the execution of numerous behaviors including initiation of locomotion, eye movements, startle responses, and rapid eye movement sleep phenomena. Approximately half of the afferent projections to mPRF neurons come from within the reticular formation (Shammah-Lagnado et al., 1987). In spite of the importance of reticulo-reticular connections, virtually nothing is known about transmitters mediating these synapses. In order to identify a candidate excitatory neurotransmitter, the actions of excitatory amino acids (EAAs) on the membrane properties of mPRF neurons recorded in rat brainstem slices in vitro were studied. Standard intracellular recording methods, including single-electrode voltage clamp, were used to examine the postsynaptic actions of EAAs. We also tested whether EAA antagonists block EPSPs evoked by stimulation of the contralateral reticular formation in the slices. mPRF neurons responded to both non-NMDA and NMDA agonists. NMDA- induced conductances were voltage dependent and depressed by physiological concentrations of magnesium. Stimulation of the contralateral reticular formation elicited EPSPs that were depressed by the general EAA antagonist kynurenate. Evoked EPSPs were partially depressed by 6,7-dinitroquinoxaline-2,3-dione. The evoked EPSP was further reduced by the NMDA antagonist (+/-)-2-amino-5- phosphonopentanoic acid in some cases. These results suggest that excitatory reticulo-reticular neurotransmission is mediated by an EAA. Both non-NMDA and NMDA receptors contribute to EAA neurotransmission in the mPRF formation and play an integral role in reticular formation function.
Identified postnatal mesolimbic dopamine neurons in culture: morphology and electrophysiology
Authors: Rayport S , Sulzer D , Shi WX , Sawasdikosol S , Monaco J , Batson D , Rajendran G
Published: March 2018

To examine the intrinsic properties of postnatal mesolimbic dopamine (DA) neurons, we dissociated the ventral tegmental area (VTA) from postnatal rats, enriched for DA neurons by microdissection or gradient purification, and grew the cells in culture. In these cultures, up to 50% of neurons were dopaminergic. DA neurons resembled their in vivo counterparts in soma shapes, and in showing two levels of tyrosine hydroxylase (TH) expression, axodendritic differentiation, two sizes of synaptic vesicles, nest-like synaptic arrangements with non-DA cells, and synaptic specializations. Electrophysiologically, however, they could not be distinguished from non-DA cells, which could be consistent with heterogeneity in cell properties. To examine a functional subset of VTA DA neurons, we retrogradely labeled VTA neurons projecting to the nucleus accumbens. These mesoaccumbens neurons were 86% TH positive, 56% cholecystokinin positive, and 0% neurotensin positive; they also displayed the soma shapes characteristic of DA neurons more generally and two levels of TH expression. Like their in vivo counterparts, mesoaccumbens cells generally fired single broad spikes that were triggered by slow depolarizations and had robust spike afterhyperpolarizations, low- and high-threshold Ca2+ spikes, rapid accommodation of firing, time-dependent anomalous rectification, and hyperpolarizing autoreceptor responses. Strikingly, the expression of these active properties did not change with time in culture. Mesoaccumbens DA cells could be identified by a distinctive subset of properties that made up an electrophysiological signature; however, unlike their in vivo counterparts, they were less often spontaneously active and never fired in bursts. These results suggest that most DA cell properties are intrinsic to the cells, including a significant heterogeneity that is maintained in postnatal culture; their level and mode of activity, however, appear to require afferent input. Culturing identified postnatal VTA DA neurons now makes possible examination of the impact of their individual properties on synaptic function.
Posttetanic potentiation at the crayfish neuromuscular junction is dependent on both intracellular calcium and sodium ion accumulation
Authors: Mulkey RM , Zucker RS
Published: March 2018

The fluorescent indicator fura-2 was used to measure cytoplasmic calcium in presynaptic terminals in the crayfish Procambarus clarkii under conditions that raise intracellular sodium to examine whether sodium can elevate intracellular calcium concentration ([Ca2+]i) or prolong its efflux and thus influence the magnitude and duration of posttetanic potentiation (PTP). Sodium was elevated in presynaptic terminals at rest by either (1) injection of sodium into the excitatory axon, (2) application of veratridine to open sodium channels, or (3) addition of ouabain to block Na/K exchange, with [Ca2+]i increasing by either 430, 400, or 180 nM, respectively. Intracellular calcium concentration increased only when external calcium was present, indicating that calcium influx occurred through Na/Ca exchange. Additionally, ouabain enhanced excitatory junctional potentials (EJPs) eightfold. Elevation of sodium using a high-frequency stimulation in zero-calcium Ringer's did not elevate [Ca2+]i during the train or immediately afterward when calcium-containing Ringer's was re- introduced. This indicates that a physiological sodium load does not release calcium from internal stores or reverse Na/Ca exchange to levels where [Ca2+]i accumulation is detectable. We examined the ability of sodium to interfere with calcium efflux from presynaptic terminals by loading boutons with both sodium and calcium or calcium alone using high-potassium depolarization. Elevation of internal sodium slowed calcium efflux from the terminal (12.3 min) compared to calcium removal without a sodium load (4.0 min). When sodium loading was increased during a tetanus by application of ouabain, the time constants for decay of EJP potentiation, 17.3 min, and for [Ca2+]i, 35 min, were longer than control values, 4.4 min and 5.8 min, respectively. In addition, using lithium to inhibit the efflux of calcium by Na/Ca exchange following a PTP-inducing train also lengthened the decay of [Ca2+]i to 15.7 min. Intracellular sodium accumulation in presynaptic terminals slows the efflux of calcium through Na/Ca exchange, and may therefore augment and prolong PTP.
Cell-specific expression of high levels of human S100 beta in transgenic mouse brain is dependent on gene dosage
Authors: Friend WC , Clapoff S , Landry C , Becker LE , O'Hanlon D , Allore RJ , Brown IR , Marks A , Roder J , Dunn RJ
Published: March 2018

The beta-subunit of S100 protein (S100 beta) is highly conserved in the mammalian brain. The gene coding for human S100 beta has been mapped to chromosome 21. In order to study the consequences of overexpression of the S100 beta gene, transgenic mice were generated by microinjection of a 17.3 kilobase human genomic fragment containing the three exons and the transcription control elements of the human S100 beta gene. Mice from four transgenic lines carried approximately 10–100 transgene copies. Northern blotting demonstrated a tissue-specific and gene dose- dependent expression of human S100 beta mRNA in mouse brain. Increased expression of S100 beta mRNA was correlated with an increased production of S100 beta protein. Examination of brain sections by in situ hybridization and immunocytochemistry indicated that S100 beta was localized globally to astrocytes, as well as to discrete neurons in the mesencephalic and motor trigeminal, facial, and lemniscus nuclei in both normal and transgenic mice. In peripheral tissues, human S100 beta was expressed at 10–50-fold lower levels than in brain. The strict gene dosage dependence and cell specificity of transgene expression suggest the presence of a locus control region (LCR) in the human S100 beta gene. The mice tolerated 10–100-fold higher than normal levels of S100 beta gene expression in brain without any gross physical or behavioral abnormalities. The high-level expression and cell specificity of the S100 beta promoter/LCR suggest that it may provide a valuable tool to direct the expression of other transgenic products to specific cell types in the CNS.
Increases in extracellular dopamine in the nucleus accumbens by cocaine are inversely related to basal levels: effects of acute and repeated administration
Authors: Weiss F , Paulus MP , Lorang MT , Koob GF
Published: March 2018

Repeated administration of cocaine enhances several of the behavioral and neurochemical responses to subsequent cocaine injections, an effect that has been attributed, in part, to decreased somatodendritic autoreceptor sensitivity of mesocorticolimbic dopamine (DA) neurons. Such changes in autoregulation may not only modify the direct effects of cocaine on extracellular DA levels but also result in tonically increased basal DA release in the terminal areas of the mesocorticolimbic DA system. The present study was therefore designed to investigate the effects of repeated cocaine administration on basal extracellular DA concentrations in the nucleus accumbens (NAC) using in vivo microdialysis procedures in halothane-anesthetized rats. We subsequently examined the relationship between basal DA levels and the increase in extracellular DA produced by an acute injection of cocaine, and determined whether this relationship was altered by prior, repeated exposure to cocaine. Rats received one daily intraperitoneal injection of cocaine (30 mg/kg) or its vehicle (saline) for 10 consecutive days. On days 1, 3, or 7 after termination of the repeated cocaine treatment, extracellular DA levels in the NAC were determined under basal conditions and following a single intraperitoneal cocaine challenge injection (10 mg/kg) in separate groups of rats. Repeated cocaine administration produced a substantial increase in basal DA release in the NAC that was most prominent on day 1 post-cocaine (mean +/- SEM: 10.7 +/- 2.55 nM vs 3.55 +/- 0.56 nM) but was no longer apparent on day 7 post-cocaine. Higher extracellular DA levels were also observed after cocaine challenge in rats that received repeated cocaine treatments. Similar to the increase in basal release, this effect was most pronounced on day 1 post-cocaine (23.6 +/- 4.36 nM vs 12.61 +/- 1.76 nM) but did not persist through day 7 post-cocaine.(ABSTRACT TRUNCATED AT 250 WORDS)
Distributed but convergent ordering of corticostriatal projections: analysis of the frontal eye field and the supplementary eye field in the macaque monkey
Authors: Parthasarathy HB , Schall JD , Graybiel AM
Published: March 2018

The degree of parallel processing in frontal cortex-basal ganglia circuits is a central and debated issue in research on the basal ganglia. To approach this issue directly, we analyzed and compared the corticostriatal projections of two principal oculomotor areas of the frontal lobes, the frontal eye field (FEF) and the supplementary eye field (SEF). We first identified cortical regions within or adjacent to each eye field by microstimulation in macaque monkeys and then injected each site with either 35S-methionine or WGA-HRP conjugate. We analyzed the corticostriatal projections and also the interconnections of the pairs of cortical areas. We observed major convergence of the projections of the FEF and the SEF within the striatum, principally in the caudate nucleus. In cross sections through the striatum, both projections were broken into a series of discontinuous input zones that seemed to be part of complex three-dimensional labyrinths. Where the FEF and SEF projection fields were both present, they overlapped patch for patch. Thus, both inputs were dispersed within the striatum but converged with one another. Striatal afferents from cortex adjacent to the FEF and the SEF did not show convergence with SEF and FEF inputs, but did, in part, converge with one another. For all pairs of cortical areas tested, the degree of overlap in the corticostriatal projections appeared to be directly correlated with the degree of cortical interconnectivity of the areas injected. All of the corticostriatal fiber projections observed primarily avoided immunohistochemically identified striosomes. We conclude that there is convergence of oculomotor information from two distinct regions of the frontal cortex to the striatal matrix, which is known to project into pallidonigral circuits including the striatonigrocollicular pathway of the saccadic eye movement system. Furthermore, functionally distinct premotor areas near the oculomotor fields often systematically projected to striatal zones adjacent to oculomotor field projections, suggesting an anatomical basis for potential interaction of these inputs within the striatum. We propose that parallel processing is not the exclusive principle of organization of forebrain circuits associated with the basal ganglia. Rather, patterns of both convergence and divergence are present and are likely to depend on multiple functional and developmental constraints.
Fos-defined activity in rat brainstem following centripetal acceleration
Authors: Kaufman GD , Anderson JH , Beitz AJ
Published: March 2018

To identify rat brainstem nuclei involved in the initial, short-term response to a change in gravito-inertial force, adult Long-Evans rats were rotated in the horizontal plane for 90 min in complete darkness after they were eccentrically positioned off the axis of rotation (off- axis) causing a centripetal acceleration of 2 g. Neural activation was defined by the brainstem distribution of the c-fos primary response gene protein, Fos, using immunohistochemistry. The Fos labeling in off- axis animals was compared with that of control animals who were rotated on the axis of rotation (on-axis) with no centripetal acceleration, or who were restrained but not rotated. In the off-axis animals there was a significant labeling of neurons: in the inferior, medial, and y-group subnuclei of the vestibular complex; in subnuclei of the inferior olive, especially the dorsomedial cell column; in midbrain nuclei, including the interstitial nucleus of Cajal, nucleus of Darkschewitsch, Edinger-Westphal nucleus, and dorsolateral periaqueductal gray; in autonomic centers including the solitary nucleus, area postrema, and locus coeruleus; and in reticular nuclei including the lateral reticular nucleus and the lateral parabrachial nucleus. Also, there was greater Fos expression in the dorsomedial cell column, the principal inferior olive subnuclei, inferior vestibular nucleus, the dorsolateral central gray, and the locus coeruleus in animals who had their heads restrained compared to animals whose heads were not restrained. As one control, the vestibular neuroepithelium was destroyed by injecting sodium arsanilate into the middle ear, bilaterally. This resulted in a complete lack of Fos labeling in the vestibular nuclei and the inferior olive, and a significant reduction in labeling in other nuclei in the off-axis condition, indicating that these nuclei have a significant labyrinth-sensitive component to their Fos labeling. The data indicate that several novel brainstem regions, including the dorsomedial cell column of the inferior olive and the periaqueductal gray, as well as more traditional brainstem nuclei including vestibular and oculomotor related nuclei, respond to otolith activation during a sustained centripetal acceleration.
Patterns of inter- and intralaminar GABAergic connections distinguish striate (V1) and extrastriate (V2, V4) visual cortices and their functionally specialized subdivisions in the rhesus monkey
Authors: Kritzer MF , Cowey A , Somogyi P
Published: March 2018

Local GABAergic connections are undoubtedly important for the operation of cerebral cortex, including the tuning of receptive field properties of visual cortical neurons. In order to begin to correlate specific configurations of GABAergic networks with particular receptive field properties, we examined the arrangement of GABAergic neurons projecting to foci in compartments of known functional specialization in striate (area V1) and extrastriate (areas V2, V4) cortices of rhesus monkeys. GABAergic cells were detected autoradiographically following microinjections into supragranular, granular, or infragranular layers of 5, 10, or 50 nl of 3H-nipecotic acid, which selectively exploits the GABA reuptake mechanism. These injections produced complex inter- and intralaminar distributions of retrograde perikaryal labeling that was selective for GABA-immunopositive neurons and glia. The pattern of retrograde labeling depended on both the laminar and cytoarchitectonic location of injection sites. In all cases, a high density of labeled neurons was present in the immediate vicinity of injection sites, with the density of labeled neurons decreasing for the most part uniformly with horizontal distance. Injections in supragranular layers produced relatively widespread labeling (up to 1.5–1.7 mm from the center of injections) in upper layers, whereas in granular and infragranular layers, labeling was confined to a radius of 0.25–0.5 mm. Conversely, injections in infragranular layers produced labeling that was widest (up to 1 mm) in lower layers, but more laterally restricted in supragranular layers. Injections in granular layers, on the other hand, produced an even distribution of labeling, 0.6–1.0 mm in diameter, throughout all layers. Comparably placed injections in V1, V2, and V4 resulted in patterns of labeling that were distinguished by features including stepwise increases in the lateral extent of labeling from striate to extrastriate areas, and the circular versus markedly elongated intralaminar distribution of labeled neurons in V1 and V4 versus V2. Further, for superficial injections, labeling was present in all layers in V1 and V2, but did not extent below the top layer V in area V4. These findings offer clear examples of organizational differences in the intrinsic inhibitory connections of visual cortices. The results also demonstrate that the number of GABAergic neurons projecting to any spot in cortex decreases systematically with horizontal distance from the spot, and that radiolabeled cells do not coalesce to form slabs, columns, or clusters. This relatively even distribution of retrogradely labeled cells in the tangential plane is consistent with recent computer simulations (Worgotter and Koch, 1991) that suggest that inhibitory neurons broadly tuned as a population can produce the specific response properties of cortical neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Myelin acquisition in the central nervous system of the mouse revealed by an MBP-Lac Z transgene
Authors: Foran DR , Peterson AC
Published: March 2018

Myelin has pronounced effects upon the morphology, function, and growth of axons in the mammalian CNS. Consequently, oligodendrocyte development and myelination have been investigated using a wide variety of histological, immunocytochemical, ultrastructural, and biochemical techniques. While many of the spatial and temporal features of myelin appearance have been characterized, for any one species only limited regions of the CNS have been investigated. To address this limitation, we have derived transgenic mice in which the bacterial Lac Z gene is regulated by promoter elements of the myelin basic protein gene. When differentiating oligodendrocytes begin to elaborate recognizable myelin, they initiate expression of the MBP-Lac Z transgene and accumulate readily detectable levels of beta-galactosidase. Here, we exploit the sensitivity, resolution, and ease of beta-galactosidase histochemical assays to characterize the temporal and spatial patterns of CNS myelination in the mouse. Many features of the myelination program revealed by this approach were predicted by the immunocytochemical and ultrastructural data derived from other species. Nonetheless, previously undocumented patterns were also encountered. beta-Galactosidase was expressed first by oligodendrocytes in the ventral spinal cord, 1 d prior to birth. There, myelination proceeded in a strictly rostral-caudal direction, whereas in the dorsal cord, myelination initiated in the cervical enlargement and proceeded in both rostral and caudal directions. In the cerebellum, deep regions myelinated first, and in the optic nerve, myelination initiated at the retinal end. In contrast, the lateral olfactory tracts, pons, and optic chiasm initiated myelination along their entire course.(ABSTRACT TRUNCATED AT 250 WORDS)
Presynaptic localization of sodium/calcium exchangers in neuromuscular preparations
Authors: Luther PW , Yip RK , Bloch RJ , Ambesi A , Lindenmayer GE , Blaustein MP
Published: March 2018

Calcium ions play a critical role in neurotransmitter release. The cytosolic Ca2+ concentration ([Ca2+]cyt) at nerve terminals must therefore be carefully controlled. Several different mechanisms, including a plasmalemmal Na/Ca exchanger, are involved in regulating [Ca2+]cyt. We employed immunofluorescence microscopy with polyclonal antiserum raised against dog cardiac sarcolemmal Na/Ca exchanger to determine the distribution of the exchanger in vertebrate neuromuscular preparations. Our data indicate that the Na/Ca exchanger is concentrated at the neuromuscular junctions of the rat diaphragm. The exchanger is also present in the nonjunctional sarcolemma, but at a much lower concentration than in the junctional regions. Denervation markedly lowers the concentration of the exchanger in the junctional regions; this implies that the Na/Ca exchanger is concentrated in the presynaptic nerve terminals. In Xenopus laevis nerve and muscle cell cocultures, high concentrations of the exchanger are observed along the neurites as well as at the nerve terminals. The high concentrations of Na/Ca exchanger at presynaptic nerve terminals in vertebrate neuromuscular preparations suggest that the exchanger may participate in the Ca-dependent regulation of neurotransmitter release. The Na/Ca exchanger is also abundant in developing neurites and growth cones, where it may also be important for Ca2+ homeostasis.
Comparative characterization and autoradiographic distribution of neuropeptide Y receptor subtypes in the rat brain
Authors: Dumont Y , Fournier A , St-Pierre S , Quirion R
Published: March 2018

Some evidence has suggested the existence and differential distribution of neuropeptide Y (NPY) receptor subtypes in the mammalian brain (Dumont et al., 1990; Aicher et al., 1991). We now report on the extensive characterization and visualization of at least two classes of NPY receptor sites using a highly selective Y1 analog, [Leu31,Pro34]- NPY or [Pro34]-NPY, and a relatively specific Y2 competitor, NPY13-36. Autoradiographic studies using 125I-peptide YY (125I-PYY) clearly reveal that the Y1 receptor subtype is most abundant in various cortical areas, the dentate gyrus of the hippocampal formation, the claustrum, and the reuniens nucleus of the thalamus. In most other regions, 125I-PYY binding is potently inhibited by increasing concentrations of either NPY2-36 or NPY13-36, suggesting a Y2-like profile. Furthermore, binding assays using homogenates from discrete brain regions clearly demonstrate that various NPY fragments and analogs compete for 125I-PYY labeling with profiles indicative of heterogeneity of NPY receptor subtypes, even in the presence of a selective Y1 blocker. Thus, it is likely that, in addition to the Y1 receptor, which is particularly concentrated in cortical areas, the rat brain is enriched with a receptor class (Y2) that can exist under high- or low-affinity states or with additional receptor subtypes that are recognized by 125I-PYY. These findings cannot be explained by the existence of the very recently reported Y3 receptor subtype, since PYY does not possess significant affinity to this site (Grundemar et al., 1991). Further experiments are currently in progress to determine the nature and functional significance of each of these NPY/PYY receptor sites.
Plasticity in the frequency representation of primary auditory cortex following discrimination training in adult owl monkeys
Authors: Recanzone GH , Schreiner CE , Merzenich MM
Published: March 2018

Previous studies have shown that the tonotopic organization of primary auditory cortex is altered subsequent to restricted cochlear lesions (Robertson and Irvine, 1989) and that the topographic reorganization of the primary somatosensory cortex is correlated with changes in the perceptual acuity of the animal (Recanzone et al., 1992a-d). Here we report an increase in the cortical area of representation of a restricted frequency range in primary auditory cortex of adult owl monkeys that is correlated with the animal's performance at a frequency discrimination task. Monkeys trained for several weeks to discriminate small differences in the frequency of sequentially presented tonal stimuli revealed a progressive improvement in performance with training. At the end of the training period, the tonotopic organization of Al was defined by recording multiple-unit responses at 70-258 cortical locations. These responses were compared to those derived from three normal monkeys and from two monkeys that received the same auditory stimuli but that were engaged in a tactile discrimination task. The cortical representation, the sharpness of tuning, and the latency of the response were greater for the behaviorally relevant frequencies of trained monkeys when compared to the same frequencies of control monkeys. The cortical area of representation was the only studied parameter that was correlated with behavioral performance. These results demonstrate that attended natural stimulation can modify the tonotopic organization of Al in the adult primate, and that this alteration is correlated with changes in perceptual acuity.
Growth cone dynamics during the migration of an identified commissural growth cone
Authors: Myers PZ , Bastiani MJ
Published: March 2018

We have used time-lapse video microscopy to study the behavior of a neuron, Q1, that pioneers the posterior commissure of the embryonic grasshopper. Our goal is to use time-lapse video as a tool to acquire a precise picture of normal development over time, and thereby identify stereotypic activities that might indicate important interactions necessary for proper formation of the commissure. We have identified specific and reproducible behaviors that suggest the presence of underlying cellular interactions that may play a role in pathfinding. In particular, the Q1 growth cone undergoes several morphological changes as it contacts the midline. As a commissural neuron, the midline may be a target in its outgrowth; Q1's typical response upon contacting the midline with its filopodia, however, is a rapid retraction. This inhibitory reaction can be overridden by contact with filopodia of its contralateral homolog. Q1's growth cone can translocate across the midline at an accelerated rate by a process resembling “filopodial dilation” (O'Connor et al., 1990) once the two Q1 growth cones meet. Ablation of the contralateral Q1 blocks Q1's advance across the midline. We have also analyzed in detail the behavior of individual filopodia to identify behavioral differences that could indicate differences in substrate adhesivity. Except for instances of filopodial dilation seen only at the midline, we found no significant asymmetries in rates of filopodial extension and retraction, or in the survival times of individual filopodia. We suggest that either the adhesive signal used by Q1 is relatively weak, requiring the integration of many adhesive interactions by many filopodia to be resolved, or the guidance cues may not be adhesive in nature.
Development of larval muscle properties in the embryonic myotubes of Drosophila melanogaster
Authors: Broadie KS , Bate M
Published: March 2018

The entire developmental history of muscle membrane electrogenesis can be observed in the embryonic myotubes of Drosophila. We have examined the development of ionic currents and muscle properties using whole- cell patch-clamp techniques throughout embryonic myogenesis. In the early stages of myogenesis, from myoblast fusion through to establishing epidermal insertions, the myotubes are electrically inert and are electrically and dye coupled to adjacent myotubes. Membrane electrogenesis begins in the mid-embryonic stages (early stage 16), when the myotubes abruptly uncouple, revealing the first of five prominent extrajunctional currents: a small, inward, voltage-gated calcium current (ICa). The uncoupling of the embryonic myotubes heralds the onset of extremely rapid electrogenesis; within several minutes both the fast, inactivating (IA; Shaker) and delayed, noninactivating (IK) outward potassium currents, the stretch-activated outward potassium current, and the junctional glutamate-gated inward current all appear and begin to develop in a current-specific manner. Very late in embryogenesis (late stage 17), the calcium-dependent, outward potassium currents [rapid, inactivating (ICF; slowpoke) then delayed, noninactivating (ICS)] develop, completing the complement of macroscopic currents in the mature larval muscle. Hence, the voltage- gated currents (ICa, IA, and IK, respectively) appear relatively early, and the calcium-dependent currents (ICF, ICS) appear only very late during myogenesis. This developmental progression of current maturation is reflected in dynamic changes in the voltage responses of the embryonic membrane, from wholly passive response to current injection in the early, coupled myotubes to regenerating, overshooting action potentials in the mature embryonic muscle. The earliest embryonic IA current has a midpoint of inactivation 40 mV more negative than the IA current in the mature embryo. As myogenesis proceeds, the inactivation curve develops a biphasic character, suggesting that a low-inactivation IA channel is present in early development and progressively replaced by the mature form as development proceeds. The current at all stages can be completely eliminated in Shaker mutants (ShKS133). These findings suggest that an embryonic form of the Shaker IA channel is present during early myogenesis. The prominent IA current present in early development is almost entirely inactivated at the physiological resting potential; the significance and mechanism of this developmental shift are unclear.
A large chondroitin sulfate proteoglycan has the characteristics of a general extracellular matrix component of adult brain
Authors: Iwata M , Carlson SS
Published: March 2018

Extracellular matrix (ECM) is a secreted extracellular network. Few components of adult brain ECM are known. We have identified a new, large chondroitin sulfate proteoglycan (T1 antigen) that acts like a general ECM protein of brain. First, it is present throughout the brain; second, it has the properties of an extracellular protein; and third, it is extracted only under denaturing conditions. Immunocytochemical localization of the T1 antigen by light microscope shows it to be present throughout the rat brain in both white and gray matter. The T1 antigen outlines Purkinje and other large cells. No antigenicity is seen inside these cells. Biochemical evidence suggests that the T1 antigen is extracellular rather than cytosolic or intravesicular. The T1 antigen is disulfide-linked to two other proteins. Disulfide bonds are found only in extracellular or intravesicular proteins, not in intracellular cytosolic proteins. Moreover, the T1 antigen is probably not intravesicular. Unlike intravesicular proteins, only a small amount of T1 antigen is solubilized by nondenaturing detergents. While nondenaturing detergents extract but a small amount of T1 antigen from rat brain, the majority is solubilized by denaturing conditions (6 M guanidine-HCl). This behavior is similar to that of ECM components in other tissues and is unlike that of membrane proteins, even those linked to the cytoskeleton. We hypothesize that the insolubility of the T1 antigen in brain is due to its presence in an extracellular aggregate. The T1 antigen is a proteoglycan with a highly glycosylated protein core of 300 kDa. It does not appear to be related to the large, heavily glycosylated chondroitin sulfate proteoglycans aggrecan and versican, which were discovered in non-neural tissues. Antibodies to a 15 residue peptide present in both aggrecan and versican do not react with the T1 antigen.