bluuebunny/crossref_metadata_2025 huggingface dataset:
Inward current responses to urinary substances in rat vomeronasal sensory neurons
Authors: Inamura Kouhei , Kashiwayanagi Makoto
Published: March 2003

No study has yet demonstrated an inward current in response to pheromonal substances in vomeronasal sensory neurons. Using female rat vomeronasal sensory neurons, we here successfully recorded inward currents in response to urine from various sources. Of the neurons that responded to urine, 77% responded to only one type of urine. Male Wistar urine induced responses preferentially in the apical layer of the sensory epithelium, whilst male Donryu and female Wistar urine induced responses mainly in the basal layer of the epithelium. The amplitude of inward currents induced by application of male Wistar urine was voltage‐dependent with average amplitude of −47.1 ± 6.2 pA at −74 mV. The average reversal potential for male Wistar urine was −9.3 ± 6.1 mV, which was not apparently different from the reversal potentials for urine from different species. It is likely that the urine‐induced inward currents in response to different types of urine are mediated via a similar channel. The simultaneous removal of Na+ and Ca2+ from extracellular solution eliminated the response. The magnitude of the urine‐induced inward current in Cl–‐free external solution was similar to that in normal solution, suggesting that the urine‐induced current is cation selective. Removal of external Ca2+ enhanced the amplitude of the urine‐induced current and prolonged the response. Application of the constant‐field equation indicated a very high permeability coefficient for Ca2+. This study first demonstrated that substances contained in urine elicited inward currents, which induce an excitatory response in vomeronasal sensory neurons, through cation‐selective channels.
Excitable properties in astrocytes derived from human embryonic CNS stem cells
Authors: Gritti Angela , Rosati Barbara , Lecchi Marzia , Vescovi Angelo L. , Wanke Enzo
Published: March 2003

Although it is widely believed that astrocytes lack excitability in adult tissue, primitive action potential‐like responses have been elicited from holding potentials negative to −80 mV, in cultured and injury‐induced gliotic rodent astrocytes and in human glia under pathological conditions such as glioblastomas and temporal lobe epilepsy. The present study was designed to investigate the properties of astrocytes (identified by immunoreactivity for glial fibrillary acidic protein) derived from multipotent human embryonic CNS stem cells and cultured for 12–25 days in differentiating conditions. We describe here for the first time that brief (1 ms) current pulses elicit spikes from a resting potential (VREST) of ≈ −37 mV and, more interestingly, that spontaneous firing can be occasionally recorded in human astrocytes. A voltage‐clamp study revealed that in these cells: (i) the half‐inactivation of the tetrodotoxin (TTX)‐sensitive Na+ channels is around VREST; (ii) the delayed rectifier K+ current is very small; (iii) the ever‐present transient outward A‐type K+ channels are paradoxically capable of inhibiting the action potentials elicited from a negative membrane potential (−55 to −60 mV); and (iv) inwardly rectifying currents are not present. The responses predicted from a simulation model are in agreement with the experiments. As suggested by recent studies, the decrease of Na+ channel expression and the changes of the electrophysiological properties during the postnatal maturation of the CNS seem to exclude the possibility that astrocytes may play an excitable role in adult tissue. Our data show that excitability and firing should be considered an intrinsic attribute of human astrocytes during CNS development. This is likely to have physiological importance because the role of astrocytes during development is different from the [K+]o‐buffering role played in adult CNS, namely the glutamate release and/or the guiding of migrating neurons.
Differential modulation of rod and cone calcium currents in tiger salamander retina by D2 dopamine receptors and cAMP
Authors: Stella Salvatore L. , Thoreson Wallace B.
Published: March 2003

Synaptic transmission from vertebrate photoreceptors involves activation of L‐type calcium currents (ICa). Dopamine is an important circadian neuromodulator in the retina and photoreceptors possess D2 dopamine receptors. We examined modulation of ICa by dopamine and cAMP in retinal slices and isolated cells of larval tiger salamander. Results show that dopamine and a D2 agonist, quinpirole, enhanced ICa in rods and red‐, blue‐ and UV‐sensitive small single cones but inhibited ICa in red‐sensitive large single cones. A D1 agonist, SKF‐38393, was without effect. Quinpirole effects were blocked by pertussis toxin (PTx) pretreatment indicating involvement of PTx‐sensitive G‐proteins. Like dopamine, inhibition of cAMP‐dependent protein kinase (PKA) by Rp‐cAMPS enhanced ICa in rods and small single cones, but inhibited ICa in large single cones. In contrast, forskolin and Sp‐cAMPS, which stimulate PKA, inhibited ICa in rods and small single cones but enhanced ICa in large single cones. Sp‐cAMPS also occluded effects of quinpirole. These results suggest that D2 receptors modulate ICa via inhibition of cAMP. Differences among the responses of photoreceptors to cAMP are consistent with the possibility that small single cones and rods may possess different Ca2+ channel subtypes than large single cones. The results with dopamine and quinpirole showing inhibition of ICa in large single cones and enhancement of rod ICa were unexpected because previous studies have shown that dopamine suppresses rod inputs and enhances cone inputs into second‐order neurons. The present results therefore indicate that the dopaminergic enhancement of cone inputs does not arise from modulation of photoreceptor ICa.
Experience‐dependent plasticity of visual acuity in rats
Authors: Prusky Glen T. , West Paul W. R. , Douglas Robert M.
Published: March 2003

Rats have become a popular model for investigating the mechanisms underlying ocular dominance plasticity; however, no quantitative assessment of the effects of visual deprivation on behavioural acuity has been reported in this species. We measured the spatial acuity of monocularly and binocularly deprived rats with a visual discrimination task. The average spatial acuity of normal rats and rats deprived of vision after postnatal day 40 was ≈ 1 cycle/degree. Monocular deprivation up to postnatal day 40 resulted in a 30% decrease in acuity and there was no recovery after 8 months. Identical binocular deprivation produced a comparable but significantly smaller reduction in acuity. The deleterious effects of monocular and binocular deprivation on visual acuity indicate that the development of cortical receptive field properties related to spatial tuning are affected by both monocular and binocular deprivation. The similarities in the effects of visual deprivation on visual acuity between rats and other mammals confirm that rats are a good model system for studying the cellular and molecular mechanisms underlying experience‐dependent visual plasticity.
GABAB receptor protein and mRNA distribution in rat spinal cord and dorsal root ganglia
Authors: Towers S. , Princivalle A. , Billinton A. , Edmunds M. , Bettler B. , Urban L. , Castro‐Lopes J. , Bowery N. G.
Published: March 2003

The presence of metabotropic receptors for GABA, GABAB, on primary afferent terminals in mammalian spinal cord has been previously reported. In this study we provide further evidence to support this in the rat and show that the GABAB receptor subunits GABAB1 and GABAB2 mRNA and the corresponding subunit proteins are present in the spinal cord and dorsal root ganglion. We also show that the predominant GABAB1 receptor subunit mRNA present in the afferent fibre cell body appears to be the 1a form. In frozen sections of lumbar spinal cord and dorsal root ganglia (DRG) GABAB receptors were labelled with [3H]CGP 62349 or the sections postfixed with paraformaldehyde and subjected to in situ hybridization using oligonucleotides designed to selectively hybridize with the mRNA for GABAB(1a), GABAB(1b) or GABAB2. For immunocytochemistry (ICC), sections were obtained from rats anaesthetized and perfused‐fixed with paraformaldehyde. The distribution of binding sites for [3H]CGP 62349 mirrored that previously observed with [3H]GABA at GABAB sites. The density of binding sites was high in the dorsal horn but much lower in the ventral regions. By contrast, the density of mRNA (pan) was more evenly distributed across the laminae of the spinal cord. The density of mRNA detected with the pan probe was high in the DRG and distributed over the neuron cell bodies. This would accord with GABAB receptor protein being formed in the sensory neurons and transported to the primary afferent terminals. Of the GABAB1 mRNA in the DRG, ≈ 90% was of the GABAB(1a) form and ≈ 10% in the GABAB(1b) form. This would suggest that GABAB(1a) mRNA may be responsible for encoding presynaptic GABAB receptors on primary afferent terminals in a manner similar to that we have previously observed in the cerebellar cortex. GABAB2 mRNA was also evenly distributed across the spinal cord laminae at densities equivalent to those of GABAB1 in the dorsal horn. GABAB2 mRNA was also detected to the same degree within the DRG. Immunocytochemical analysis revealed that GABAB(1a), GABAB(1b) and GABAB2 were all present in the spinal cord. GABAB(1a) labelling appeared to be more dense than GABAB(1b) and within the superficial dorsal horn GABAB(1a) was present in the neuropil whereas GABAB(1b) was associated with cell bodies in this region. Both 1a and 1b immunoreactivity was expressed in motor neurons in lamina IX. GABAB2 immunoreactivity was expressed throughout the spinal cord and was evident within the neuropil of the superficial laminae.
Deficit in conditional visuomotor learning by local infusion of bicuculline into the ventral prefrontal cortex in monkeys
Authors: Wang Min , Zhang Hui , Li Bao‐Ming
Published: March 2003

To explore the role of the ventral prefrontal cortex (PFv) in conditional visuomotor learning, we infused locally bicuculline, a GABAergic antagonist, into the PFv of two monkeys, well trained on a two‐problem visuomotor task. The task required the monkeys to execute one of two motor actions (moving a handle to the left or to the right) in response to one of two familiar visual patterns (circle or triangle). The two patterns mapped 1 : 1 onto the two motor actions: for each pattern one and only one motor action was scored, correct and reinforced. In contrast to these sessions with familiar patterns, in the learning sessions the monkeys were presented with one or two novel patterns and required to learn the arbitrarily determined associations between these patterns and the two motor actions. We found that bilateral infusion of bicuculline into PFv dramatically impaired the monkeys' ability to learn novel pattern–response associations: the trials and errors to criterion (90% correct) increased significantly. The errors were mainly an inability to apply ‘Win‐Stay’, ‘Lose‐Shift’ and ‘Change‐Shift’ strategies. There was no effect on the monkeys' performance in responding to familiar patterns. Similar infusion of bicuculline into the dorsal prefrontal cortex was without effect on either novel‐pattern learning or familiar‐pattern performance. We conclude that the ventral prefrontal cortex is necessary for learning new visuomotor associations, but has less importance, if any, for performing pre‐established ones.
Inhibition of brain‐derived neurotrophic factor and glial cell line‐derived neurotrophic factor expression reduces dopaminergic sprouting in the injured striatum
Authors: Batchelor P. E. , Liberatore G. T. , Porritt M. J. , Donnan G. A. , Howells D. W.
Published: March 2003

After striatal injury, sprouting dopaminergic fibres grow towards and intimately surround wound macrophages which, together with microglia, express the dopaminergic neurotrophic factors glial cell line‐derived neurotrophic factor (GDNF) and brain derived neurotrophic factor (BDNF). To evaluate the importance of these endogenously secreted neurotrophic factors in generating striatal peri‐wound dopaminergic sprouting, the peri‐wound expression of BDNF or GDNF was inhibited by intrastriatal infusion of antisense oligonucleotides for 2 weeks in mice. Knock‐down of both BDNF and GDNF mRNA and protein levels in the wounded striatum were confirmed by in situ hybridization and enzyme‐linked immunosorbent assay, respectively. Dopamine transporter immunohisto‐chemistry revealed that inhibition of either BDNF or GDNF expression resulted in a marked decrease in the intensity of peri‐wound sprouting. Quantification of this effect using [H3]‐mazindol autoradiography confirmed that peri‐wound sprouting was significantly reduced in mice receiving BDNF or GDNF antisense infusions whilst control infusions of buffered saline or sense oligonucleotides resulted in the pronounced peri‐wound sprouting response normally associated with striatal injury. BDNF and GDNF thus appear to be important neurotrophic factors inducing dopaminergic sprouting after striatal injury.
Soluble TNF receptors partially protect injured motoneurons in the postnatal CNS
Authors: Terrado José , Monnier Dominique , Perrelet Daniel , Vesin Dominique , Jemelin Stéphane , Buurman Wim A. , Mattenberger Louise , King Béatrice , Kato Ann C. , Garcia Irene
Published: March 2003

There is accumulating evidence that cytokines are involved in the functioning of the brain and the spinal cord. However, it has been controversial whether they exert a neurotoxic or a neuroprotective effect. To address this question in vivo, we have examined the survival of injured motoneurons in a line of transgenic mice that overexpress the soluble form of tumour necrosis factor receptor‐1 (sTNFR1). In these animals, all of the circulating TNF and lymphotoxin‐α are neutralized by the continuous expression of the soluble receptor. Following axotomy of the facial nerve in 7‐day‐old control mice, we observed a loss of approximately 90% of the motoneurons at two weeks survival. In the transgenic mice under the same conditions, the percentage of motoneuron survival was increased two‐fold (515 vs. 224) and varied as a function of the level of the circulating receptor. These results indicate that neutralization of endogenous TNF and lymphotoxin‐α by means of overexpression of the soluble receptor can decrease cell death of injured motoneurons and suggest that these cytokines may play an important role in neuronal degeneration in the CNS following a lesion.
Caspase‐3 is activated following axotomy of neonatal facial motoneurons and caspase‐3 gene deletion delays axotomy‐induced cell death in rodents
Authors: Vanderluit Jacqueline L. , McPhail Lowell T. , Fernandes Karl J. L. , McBride Christopher B. , Huguenot Claire , Roy Sophie , Robertson George S. , Nicholson Donald W. , Tetzlaff Wolfram
Published: March 2003

In this report, we examined the possible functions of the cell death protease, caspase‐3, in the axotomy‐induced apoptosis of facial motoneurons in newborn rodents. Using in situ hybridization and Western blot, we found higher levels of caspase‐3 mRNA and pro‐caspase‐3 protein expression in motoneurons of neonatal and 2‐week‐old rats than adult rats. Following facial motoneuron axotomy, caspase‐3 mRNA and protein expression increased in motoneurons of both neonatal and adult rats. However, using an antibody directed to the activated form of the caspase‐3 protease, we found that catalytically active caspase‐3 was present only in axotomized neonatal motoneurons. As motoneurons in neonatal but not adult rodents are susceptible to axotomy‐induced apoptosis, we hypothesized that caspase‐3 may play a role in their demise. To determine the necessity of caspase‐3 activation in axotomy‐induced apoptosis, we counted the number of surviving motoneurons at 4 and 7 days following axotomy in wild type mice and caspase‐3 gene‐deleted mice. There were nearly three times more surviving motoneurons in caspase‐3 gene‐deleted mice than in wild type mice at both 4 days (mean 1074 vs. 464, P < 0.005) and 7 days (mean 469 vs. 190, P < 0.005) following injury, indicating a slower rate of death. Examination of the dying motoneurons using TUNEL staining (for fragmented DNA) and bisbenzimide staining (for nuclear morphology) revealed incomplete nuclear condensation in caspase‐3‐deficient motoneurons. These results demonstrate that caspase‐3 activation plays important roles in the rapid demise of axotomized neonatal motoneurons.
Riluzole inhibits the persistent sodium current in mammalian CNS neurons
Authors: Urbani Andrea , Belluzzi Ottorino
Published: March 2003

The effects of 0.1–100 μm riluzole, a neuroprotective agent with anticonvulsant properties, were studied on neurons from rat brain cortex. Patch‐clamp whole‐cell recordings in voltage‐clamp mode were performed on thin slices to examine the effects of the drug on a noninactivating (persistent) Na+ current (INa,p). INa,p was selected because it enhances neuronal excitability near firing threshold, which makes it a potential target for anticonvulsant drugs. When added to the external solution, riluzole dose‐dependently inhibited INa,p up to a complete blocking of the current (EC50 2 μm), showing a significant effect at therapeutic drug concentrations. A comparative dose‐effect study was carried out in the same cells for the other main known action of riluzole, the inhibitory effect on the fast transient sodium current. This effect was confirmed in our experiments, but we found that it was achieved at levels much higher than putative therapeutic concentrations. Only the effect on INa,p, and not that on fast sodium current, can account for the reduction in neuronal excitability observed in cortical neurons following riluzole treatment at therapeutic concentrations, and this might represent a novel mechanism accounting for the anticonvulsant and neuroprotective properties of riluzole.
Acute transcranial magnetic stimulation of frontal brain regions selectively modulates the release of vasopressin, biogenic amines and amino acids in the rat brain
Authors: Keck Martin E. , Sillaber Inge , Ebner Karl , Welt Tobias , Toschi Nicola , Kaehler Stefan T. , Singewald Nicolas , Philippu Athineos , Elbel Gregor K. , Wotjak Carsten T. , Holsboer Florian , Landgraf Rainer , Engelmann Mario
Published: March 2003

Using intracerebral microdialysis in urethane‐anaesthetized adult male Wistar rats, we monitored the effects of acute repetitive transcranial magnetic stimulation (rTMS; 20 trains of 20 Hz, 2.5 s) on the intrahypothalamic release of arginine vasopressin (AVP) and selected amino acids (glutamate, glutamine, aspartate, serine, arginine, taurine, γ‐aminobutyric acid) and the intrahippocampal release of monoamines (dopamine, noradrenaline, serotonin) and their metabolites (homovanillic acid, 3,4‐dihydroxyphenylacetic acid, 5‐hydroxyindoleacetic acid). The stimulation parameters were adjusted according to the results of accurate computer reconstructions of the current density distributions induced by rTMS in the rat and human brains, ensuring similar stimulation patterns in both cases. There was a continuous reduction in AVP release of up to 50% within the hypothalamic paraventricular nucleus in response to rTMS. In contrast, the release of taurine, aspartate and serine was selectively stimulated within this nucleus by rTMS. Furthermore, in the dorsal hippocampus the extracellular concentration of dopamine was elevated in response to rTMS. Taken together, these data provide the first in vivo evidence that acute rTMS of frontal brain regions has a differentiated modulatory effect on selected neurotransmitter/neuromodulator systems in distinct brain areas.
Regional and cellular expression of the parkin gene in the rat cerebral cortex
Authors: D'agata Velia , Grimaldi Maurizio , Pascale Alessia , Cavallaro Sebastiano
Published: March 2003

A mutation in the parkin gene has been identified as the cause for an autosomal recessively inherited form of early onset Parkinson's disease. We have recently isolated the mRNA coding for the rat homologue of parkin and showed its widespread expression in the central nervous system (CNS) by in situ hybridization. In the present study we investigated the distribution of parkin in the rat cerebral cortex with a polyclonal antibody that reacts with a single ∼ 52‐kDa protein, corresponding to the predicted molecular mass of parkin. Conventional light microscopic studies revealed intense parkin immunoreactivity (IR) throughout the cortex. Examination of mixed cortical neuro‐glial cultures by indirect immunofluorescence technique coupled to traditional epifluorescence and confocal microscopy analysis demonstrated the expression of parkin in the cytoplasm and neurites of neurons, and its absence in glial fibrillary acidic protein (GFAP)‐positive astrocytes. The predominant neuronal parkin‐IR and ‐mRNA expression was confirmed by Western blot analysis and reverse transcription‐polymerase chain reaction (RT‐PCR), respectively, performed on highly enriched neuronal and type I astrocytes cultures. The information gathered in our study about the cellular and subcellular distribution of parkin should facilitate further research on its physiological role in the nervous system.
Functional connections are established in the deafferented rat spinal cord by peripherally transplanted human embryonic sensory neurons
Authors: Levinsson Anders , Holmberg Hans , Schouenborg Jens , Seiger Åke , Aldskogius Håkan , Kozlova Elena N.
Published: March 2003

Functionally useful repair of the mature spinal cord following injury requires axon growth and the re‐establishment of specific synaptic connections. We have shown previously that axons from peripherally grafted human embryonic dorsal root ganglion cells grow for long distances in adult host rat dorsal roots, traverse the interface between the peripheral and central nervous system, and enter the spinal cord to arborize in the dorsal horn. Here we show that these transplants mediate synaptic activity in the host spinal cord. Dorsal root ganglia from human embryonic donors were transplanted in place of native adult rat ganglia. Two to three months after transplantation the recipient rats were examined anatomically and physiologically. Human fibres labelled with a human‐specific axon marker were distributed in superficial as well as deep laminae of the recipient rat spinal cord. About 36% of the grafted neurons were double labelled following injections of the fluorescent tracers MiniRuby into the sciatic and Fluoro‐Gold into the lower lumbar spinal cord, indicating that some of the grafted neurons had grown processes into the spinal cord as well as towards the denervated peripheral targets. Electrophysiological recordings demonstrated that the transplanted human dorsal roots conducted impulses that evoked postsynaptic activity in dorsal horn neurons and polysynaptic reflexes in ipsilateral ventral roots. The time course of the synaptic activation indicated that the human fibres were non‐myelinated or thinly myelinated. Our findings show that growing human sensory nerve fibres which enter the adult deafferentated rat spinal cord become anatomically and physiologically integrated into functional spinal circuits.
The role of 5‐HT1A receptors in mediating the anxiogenic effects of nicotine following lateral septal administration
Authors: Cheeta Survjit , Kenny Paul J. , File Sandra E.
Published: March 2003

The purpose of the present study was to determine the role of the 5‐HT1A receptors in the lateral septum in the mediation of the anxiogenic effects of nicotine in the social interaction and elevated plus maze tests of anxiety in the rat. Bilateral infusion of (–)‐nicotine (4 and 8 μg) and of the 5‐HT1A receptor agonist 8‐OH‐DPAT (200 and 500 ng) into the lateral septum decreased the time spent in social interaction, indicating anxiogenic effects. The anxiogenic effect of 8‐OH‐DPAT (500 ng) was completely reversed by coadministration of a behaviourally inactive dose of the 5‐HT1A receptor antagonist, WAY 100635 (200 ng). The anxiogenic effect of the lower dose of (–)‐nicotine (4 μg) was completely reversed by WAY 100635 (200 ng), but the reversal was only partial following administration of 8 μg nicotine. In a second test of anxiety, the elevated plus maze, lateral septal administration of 8‐OH‐DPAT (500 ng) and nicotine (4 μg) induced anxiogenic effects. In this test, the anxiogenic effect of nicotine (4 μg) was completely reversed by coadministration of WAY 100635 (200 ng). The effects of 8‐OH‐DPAT demonstrate that stimulation of 5‐HT1A receptors in the lateral septum has anxiogenic effects in two animal tests and that the anxiogenic effects of nicotine are mediated at least in part by these 5‐HT1A receptors.
Expression of GABAC receptor ρ1 and ρ2 subunits during development of the mouse retina
Authors: Greka Anna , Lipton Stuart A. , Zhang Dongxian
Published: March 2003

Retinal γ‐aminobutyric acid type C (GABAC) receptors consist of ρ subunits. Here we report our results from a competitive PCR and patch‐clamp electrophysiology study quantifying ρ subunit message and characterizing GABAC receptor‐mediated currents at different stages of mouse retinal development. Mouse ρ1 message is first detected at postnatal day 6 (P6), increases significantly until P9 and remains at this level through adulthood, whereas mouse ρ2 message does not appear until P9, peaks at P15 and remains at this level through adulthood. There is an approximate twofold excess of ρ1 compared to ρ2 message at most stages of development, which persists in adulthood. Functional GABAC receptors are detected in acutely dissociated bipolar cells of P9 or older mouse retina. Early in development (P9–10), GABAC receptors are composed solely of ρ1 subunits, but subsequently contain ρ1 and/or ρ2 subunits (by P11 and later). These findings are intriguing because the onset and rapid increase in ρ subunit transcription and functional expression match the initiation and active period of bipolar cell differentiation in retinal development as well as the stage of eye opening and initial visual experience in the rodent. The investigation of mouse ρ subunits here forms a basis for future studies on the role of GABAC receptors in retinal development.
Presynaptic inhibition by muscimol through GABAB receptors
Authors: Yamauchi Tatsuhito , Hori Tetsuya , Takahashi Tomoyuki
Published: March 2003

The γ‐aminobutyric acid type A (GABAA) receptor agonist muscimol is widely used as a tool for reducing neuronal activities particularly in experiments in vivo. At the synapse formed by the calyx of Held in the rat brainstem slice, the GABAA receptor agonist muscimol (> 10 μm) attenuated the amplitude of excitatory post synaptic currents (EPSCs) accompanied by an increase in the coefficient of variation of EPSCs, suggesting its presynaptic inhibitory effect. This muscimol effect was not affected by bicuculline but occluded the presynaptic inhibitory effect of the GABAB receptor agonist baclofen and was abolished by the type B GABA (GABAB) receptor‐specific antagonist (+)‐5,5‐dimethyl‐2‐morpholineacetic acid (SCH 50911; 20 μm). We conclude that muscimol activates presynaptic GABAB receptors thereby attenuating synaptic transmission.
Involvement of sst2 somatostatin receptor in locomotor, exploratory activity and emotional reactivity in mice
Authors: Viollet C. , Vaillend C. , Videau C. , Bluet‐Pajot M. T. , Ungerer A. , L'héritier A. , Kopp C. , Potier B. , Billard J. ‐M. , Schaeffer J. , Smith R. G. , Rohrer S. P. , Wilkinson H. , Zheng H. , Epelbaum J.
Published: March 2003

Somatostatin (SRIF) controls many physiological and pathological processes in the central nervous system but the respective roles of the five receptor isotypes (sst1–5) that mediate its effects are yet to be defined. In the present study, we attempted to identify functions of the sst2 receptor using mice with no functional copy of this gene (sst2 KO mice). In contrast with control 129Sv/C57Bl6 mice, sst2 mRNA was no longer detectable in the brain of sst2 KO mice; 125I‐labeled Tyr0DTrp8‐SRIF14 binding was also greatly reduced in almost all brain structures except for the hippocampal CA1 area, demonstrating that sst2 accounts for most SRIF binding in mouse brain. Invalidation of this subtype generated an increased anxiety‐related behaviour in a number of behavioural paradigms, while locomotor and exploratory activity was decreased in stress‐inducing situations. No major motor defects could be detected. sst2 KO mice also displayed increased release of pituitary ACTH, a main regulator of the stress response. Thus, somatostatin, via sst2 receptor isotype pathways, appears involved in the modulation of locomotor, exploratory and emotional reactivity in mice.
Laterodorsal tegmental stimulation elicits dopamine efflux in the rat nucleus accumbens by activation of acetylcholine and glutamate receptors in the ventral tegmental area
Authors: Forster Gina L. , Blaha Charles D.
Published: March 2003

Cholinergic and glutamatergic neurons in the laterodorsal tegmentum (LDT) and neighbouring mesopontine nuclei are thought to influence mesolimbic dopaminergic neuronal activity involved in goal‐directed behaviours. We measured the changes in dopamine oxidation current (corresponding with dopamine efflux) in the nucleus accumbens (NAc) in response to electrical stimulation of the LDT using in vivo chronoamperometry in urethane‐anaesthetized rats. LDT stimulation (35 Hz pulse trains for 60 s, 1 s intertrain interval) evoked a three‐component change in dopamine efflux in the NAc: (i) an initial stimulation time‐locked increase in the dopamine signal above baseline, followed by (ii) an immediate decrease below baseline, and thereafter by (iii) a prolonged increase in the dopamine signal above baseline. Intra‐VTA infusion of the nicotinic receptor antagonist mecamylamine (5 μg/0.5 μL) or the ionotropic glutamate receptor antagonist kynurenate (10 μg/μL) attenuated the first LDT‐elicited component. The second suppressive component was abolished by intra‐LDT infusions of either the nonselective or the M2‐selective muscarinic receptor antagonists scopolamine (100 μg/μL) and methoctramine (50 μg/μL), respectively. In contrast, intra‐VTA infusions of scopolamine (200 μg/μL) resulted in a selective attenuation of the third facilitatory component, whereas both second and third components were abolished by systemic injections of scopolamine (5 mg/kg). These results suggest that the initial increase, subsequent decrease, and final prolonged increase in extracellular dopamine levels in the NAc are selectively mediated by LDT‐elicited activation of (i) nicotinic and glutamatergic receptors in the VTA, (ii) muscarinic M2 autoreceptors on LDT cell bodies, and (iii) muscarinic receptors in the VTA, respectively.
Graded expression of EphA3 in the retina and ephrin‐A2 in the superior colliculus during initial development of coarse topography in the wallaby retinocollicular projection
Authors: Stubbs Janine , Palmer Ann , Vidovic Maria , Marotte Lauren R.
Published: March 2003

We describe the expression of EphA3 and EphA7 receptors and ephrin‐A2 ligand in the retina and the superior colliculus during the development of the retinocollicular projection in the marsupial wallaby (Macropus eugenii), using immunoblotting and immunohistochemistry. EphA3 in the retina was in a striking, low central to high peripheral gradient, superimposed on which was a high temporal to low nasal level of expression. This distribution was evident from postnatal day 30, when axons are growing into the colliculus and forming a coarsely organized topographic projection, to postnatal day 65, when axons have arborized in their correct retinotopic positions. EphA7 showed a shallow centroperipheral gradient with no nasotemporal differences in expression. In the superior colliculus no rostrocaudal differences in distribution were detected for either of these receptors. Ephrin‐A2 was distributed in a gradient increasing from the rostral to the caudal pole in the superficial layers of the superior colliculus only up to postnatal day 30. Ephrin‐A2 was evenly distributed in the retina throughout development of the projection. Expression of EphA3 in the retina increased, while the expression of ephrin‐A2 in the colliculus was downregulated over time. The graded expression of EphA3 and ephrin‐A2 early in the development of the projection suggests that they play a role in establishment of coarse topography of retinal axons along the rostrocaudal axis of the superior colliculus. However, the gradients were not complementary, meaning that EphA3 alone cannot mediate the repulsive interactions with ephrin‐A2 that have been postulated to underlie formation of the topographic map.
Early and delayed induction of immediate early gene expression in a novel focal cerebral ischemia model in the rat
Authors: Johansson Inga‐Maj , Wester Per , Háková Michaela , Gu WeiGang , Seckl Jonathan R. , Olsson Tommy
Published: March 2003

This study aimed at evaluating changes in expression of immediate early genes in a new photothrombotic focal ischemia model that exhibits late spontaneous reperfusion and morphological restoration in the region‐at‐risk within the cerebral cortex. Gene expression was studied with Northern blots, in situ hybridization and immunohistochemistry. At early time points (1–4 h), nerve growth factor‐induced gene A and B, and c‐fos mRNAs, were quickly induced throughout the ipsilateral cortex, with no obvious differences between the region‐at‐risk and remote cortical areas. High concentrations of nerve growth factor‐induced gene A and c‐Fos proteins were present within the region‐at‐risk even when cortical cerebral blood flow was as low as 40% of control values. At 4 h the nerve growth factor‐induced gene A mRNA and protein expression was significantly decreased in the hippocampus vs. naive controls. However, a small decrease was also found in sham‐operated and anaesthetized controls. A late induction, at 5 days, of c‐fos and nerve growth factor‐induced gene B mRNAs was seen bilaterally in the hippocampus and also, in the case of nerve growth factor induced‐gene B, in the contralateral cortex. A complex pattern of changes in immediate early gene expression occurs after reversible focal cortical ischemia. This may be important for tissue recovery as well as neuropsychiatric symptoms after stroke.
Functional connections and epileptic spread between hippocampus, entorhinal cortex and amygdala in a modified horizontal slice preparation of the rat brain
Authors: Stoop Ron , Pralong Etienne
Published: March 2003

The hippocampus, the entorhinal cortex and the amygdala are interconnected structures of the limbic system that are implicated in memory and emotional behaviour. They demonstrate synaptic plasticity and are susceptible to development of temporal lobe epilepsy, which may lead to emotional and psychological disturbances. Their relative anatomical disposition has limited the study of neurotransmission and epileptic spread between these three regions in previous in vitro preparations. Here we describe a novel, modified‐horizontal slice preparation that includes in the same plane the hippocampus, entorhinal cortex and amygdala. We found that, following application of bicuculline, each region in our preparation could generate spontaneous bursts that resembled epileptic interictal spikes. This spontaneous activity initiated in the hippocampal CA3/2 region, from where it propagated and controlled the activity in the entorhinal cortex and the amygdala. We found that this spontaneous bursting activity could spread via two different pathways. The first pathway comprises the well‐known subiculum–entorhinal cortex–perirhinal cortex–amygdala route. The second pathway consists of a direct connection between the CA1 region and perirhinal cortex, through which the hippocampal bursting activity can spread to the amygdala while bypassing the entorhinal cortex. Thus, our experiments provide a new in vitro model of initiation and spread of epileptic‐like activity in the ventral part of the limbic system, which includes a novel, fast and functional connection between the CA1 region and perirhinal cortex.
Tone‐evoked oscillations in the rat auditory cortex result from interactions between the thalamus and reticular nucleus
Authors: Cotillon N. , Edeline J. ‐M.
Published: March 2003

This study investigates the origins of tone‐evoked oscillations (5–13 Hz) in the thalamo‐cortical auditory system of anaesthetized rats. In three separate experiments, the auditory sector of the reticular nucleus (RE), the auditory cortex and the auditory thalamus were inactivated by local applications of muscimol (1 mg/mL). To assess the efficacy of this procedure, recordings were performed in the inactivated structure in each experiment; and to determine the extent of the drug diffusion autoradiographic experiments were carried out. The evolution of the strength of the oscillations was followed using power spectra during the whole recording session. In the first experiment, muscimol injection in the auditory RE totally suppressed the tone‐evoked oscillations in the auditory thalamus and cortex. In the second experiment, inactivation of the auditory cortex did not interfere with the presence of tone‐evoked oscillations in the auditory RE. In the third experiment, inactivation of the auditory thalamus impaired the oscillations produced by cortical stimulation in the auditory RE. From these results, it appears that both the auditory thalamus and the auditory sector of the RE, but not the auditory cortex, are involved in the generation of stimulus‐evoked oscillations in the thalamo‐cortical auditory system.
Adenoviral gene transfer to the injured spinal cord of the adult rat
Authors: Huber Andrea B. , Ehrengruber Markus U. , Schwab Martin E. , Brösamle Christian
Published: March 2003

We have investigated gene transfer to the injured adult rat spinal cord by the use of a recombinant adenovirus. 105 or 5 × 106 plaque‐forming units (pfu) of a replication‐defective adenoviral vector carrying the green fluorescent protein (GFP) reporter gene were injected into a dorsal hemisection lesion at spinal level T8. Gene expression and inflammatory responses were studied 4, 8 and 21 days after surgery. Numerous cells within 3 mm on each side of the lesion were found to express high levels of GFP at 4 days after infection as shown by GFP fluorescence and immunohistochemistry. At 8 days, expression was still strong although weaker than at 4 days. After 21 days, transgene expression had almost ceased. Expression was neither higher nor more prolonged in animals that had received the higher vector dose. Delayed injection 1 week after spinal injury also did not increase transgene expression. Infected cell types were identified immunohistochemically. The most prominent transduced cells were spinal motoneurons. Additionally, we could identify other neurons, astrocytes, oligodendrocytes and peripheral cells infiltrating the lesion site. The glial and inflammatory reaction at and around the lesion was studied by cresyl violet histology, α‐GFAP, OX42 and α‐CD‐8 immunohistochemistry. No significant differences from controls were found in the low virus group; in the high virus group a strong invasion of CD‐8‐positive lymphocytes was found. Open‐field locomotion analysis showed virus‐infected animals performing as well as control animals. Adenoviral gene transfer may be an efficient way to introduce factors to the injured spinal cord in paradigms of research or therapy.
SAP97 concentrates at the postsynaptic density in cerebral cortex
Authors: Valtschanoff Juli G. , Burette Alain , Davare Monika A. , Leonard A. Soren , Hell Johannes W. , Weinberg Richard J.
Published: March 2003

SAP97, a PDZ‐containing protein, is reported to concentrate in axon terminals, where its function remains unknown. Using highly specific new antibodies, we show that SAP97 in rat cerebral cortex is associated with heteromeric AMPA receptors via a selective biochemical interaction between SAP97 and the GluR1 subunit. Using light and electron microscopic immunocytochemistry, we demonstrate cellular and synaptic colocalization of SAP97 and GluR1, and show that SAP97 concentrates at synapses that contain GluR1 but not necessarily GluR2 or GluR3. Using quantitative postembedding immunogold electron microscopy, we find that SAP97 is at highest concentration within the postsynaptic density of asymmetric synapses. These data suggest that SAP97 may help to anchor GluR1‐containing AMPA receptors at the synapse. As a multifunctional scaffolding protein, SAP97 may organize components of AMPA‐related intracellular signalling pathways, including those associated with calcium‐permeable homomeric GluR1 channels.
Differential learning‐stage dependent patterns of c‐Fos protein expression in brain regions during the acquisition and memory consolidation of an operant task in mice
Authors: Bertaina‐Anglade Valérie , Tramu Gérard , Destrade Claude
Published: March 2003

The present study analysed the effects of the stage of learning of an appetitive operant conditioning task on the spatial and temporal patterns of c‐Fos protein levels in the brain of BALB/c mice. c‐Fos levels were assessed by immunohistochemistry at either 60, 120 or 180 min after either the first, the second or the fifth daily training session and compared to sham animals. The results show an increase of c‐Fos‐positive nuclei in several subcortical and cortical brain regions, 60‐min post‐acquisition. Because these activations were a function of task mastery, the data indicate that they were specifically related to learning. Following the first acquisition session, significant increases in c‐Fos‐positive neurons were observed in the dorsal hippocampus (CA3), anterior cingulate, occipital and parietal cortices. Following the second daily training session, c‐Fos was highly expressed in some subcortical regions, the hippocampus, the subiculum, the entorhinal, and posterior cingulate areas. Moreover, a significant correlation was found between the progression of performance from day 1 to day 2 and c‐Fos expression on the hippocampal CA1 subfield. Following complete acquisition, no further task‐dependent increases in c‐Fos‐labelled nuclei was observed in any brain region sampled, suggesting that the intervention of c‐Fos‐induced mechanisms in the consolidation process were terminated. The training stage‐dependent changes in regional post‐training c‐Fos expression in the hippocampus and the connected limbic regions suggest that this neuronal network is actively engaged in memory consolidation processes.
Activation of nicotinic acetylcholine receptors induces long‐term potentiation in vivo in the intact mouse dentate gyrus
Authors: Matsuyama Shogo , Matsumoto Akira , Enomoto Taira , Nishizaki Tomoyuki
Published: March 2003

The present study was conducted to clarify the role of nicotinic ACh receptors (nAChRs) on long‐term potentiation (LTP) in vivo in the intact mouse dentate gyrus using extracellular recording techniques. Intraperitoneal application of nicotine at a dose of 3.0 mg/kg but not 0.03 or 0.3 mg/kg produced a gradually developing, long‐lasting increase for 120 min similar to tetanic LTP. Nicotine at a dose of 9.0 mg/kg caused a temporary increase followed by depression. The long‐lasting potentiation induced by nicotine at 3.0 mg/kg, which was named nicotinic long‐term potentiation (LTPn), and tetanic LTP were significantly suppressed by pretreatment with mecamylamine (0.5 mg/kg i.p.), a nonselective nicotinic antagonist, but not affected by postapplication of mecamylamine. Interestingly, choline, a selective α7 nAChR agonist, at 3.0–90 mg/kg, induced the long‐lasting potentiation similar to LTPn in a dose‐dependent manner in vivo in the intact mouse dentate gyrus. The long‐lasting potentiation induced by choline (30 mg/kg i.p.) was additionally increased by postapplication of nicotine (3.0 mg/kg i.p.) or tetanic stimulation. The present study revealed that systemic application of nicotine or choline induced the long‐lasting potentiation in vivo in the intact mouse dentate gyrus, suggesting that α7 nAChRs may contribute to the induction of LTP by nicotine, and supporting in vivo animal studies that nicotine improves learning and memory performance.
Expression of c‐Met in developing rat hippocampus: evidence for HGF as a neurotrophic factor for calbindin D‐expressing neurons
Authors: Korhonen Laura , Sjöholm Ulrika , Takei Nobuyuki , Kern Michael A. , Schirmacher Peter , Castrén Eero , Lindholm Dan
Published: March 2003

Hepatocyte growth factor‐scatter factor (HGF) is expressed in different parts of the nervous system, and has been shown to exhibit neurotrophic activity. Here we show that c‐Met, the receptor for HGF, is expressed in developing rat hippocampus, with the highest levels during the first postnatal weeks. To study the function of HGF, hippocampal neurons were prepared from embryonic rats and treated with different HGF concentrations. In these cultures, HGF increased the number of neurons expressing the 28‐kDa calcium‐binding protein (calbindin D) in a dose‐dependent manner. The effect of HGF was larger than that observed with either brain‐derived neurotrophic factor (BDNF) or neurotrophin‐3 (NT‐3), and cotreatment of the cultures with HGF and the neurotrophins was additive with respect to calbindin D neurons. Besides affecting the number of neurons, HGF significantly increased the degree of sprouting of calbindin D‐positive neurons, suggesting an influence on neuronal maturation. BDNF and NT‐3 stimulated neurite outgrowth of calbindin D neurons to a much smaller degree. In contrast to calbindin D neurons, HGF did not significantly increase the number of neurons immunoreactive with the neurotransmitter γ‐aminobutyric acid (GABA) in the hippocampal cultures. Immunohistochemical studies showed that c‐Met‐, calbindin D‐ and HGF‐immunoreactive cells are all present in the dentate gyrus and partly colocalize within neurons. These results show that HGF acts on calbindin D‐containing hippocampal neurons and increases their neurite outgrowth, suggesting that HGF plays an important role for the maturation and function of these neurons in the hippocampus.
Late postnatal reorganization of GABAA receptor signalling in native GnRH neurons
Authors: Sim Joan A. , Skynner Michael J. , Pape Jean‐Rémi , Herbison Allan E.
Published: March 2003

The molecular and cellular characteristics of the gonadotropin‐releasing hormone (GnRH) neurons have been difficult to ascertain due to their scattered distribution within the basal forebrain. Using morphological criteria coupled with single cell RT‐PCR postidentification, we have developed a method for investigating native GnRH neurons in the mouse brain and used it to examine the development of GABAA receptor signalling in this phenotype. Following the harvesting of the cytoplasmic contents of individual GnRH neurons, single cell multiplex RT‐PCR experiments demonstrated that GABAA receptor α1–5, β1–3 and γ2 & 3 subunit transcripts were expressed by both neonatal (postnatal day 5) and juvenile (day 15–20) GnRH neurons in a heterogeneous manner. Following puberty, this profile was reduced to a predominant α1, α5, β1, γ2 subunit complement in rostral preoptic area GnRH neurons of the adult female. Whole‐cell patch‐clamp recordings revealed little difference between juvenile and adult GnRH neurons in their resting membrane potential and spontaneous firing rates. All GnRH neurons were found to be subjected to a tetrodotoxin‐insensitive, tonic GABAergic barrage signalling through the GABAA receptor. However, marked heterogeneity in the sensitivity of individual juvenile GnRH neurons to GABA was revealed and, in parallel with the change in subunit mRNA profile, this was dramatically reduced in the reproductively competent adult GnRH neurons. These findings provide the first electrical and molecular characterization of the GnRH phenotype and demonstrate a novel pattern of late postnatal reorganization of native GABAA receptor gene expression and signalling in the GnRH neuronal population.