bluuebunny/crossref_metadata_2025 huggingface dataset:
Optokinetic reflex in squirrel monkeys after long‐term monocular deprivation
Authors: Hoffmann K‐P. , Distler C. , Grüsser O‐J.
Published: March 2003

Horizontal optokinetic nystagmus (OKN) as well as neuronal response properties in the nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system (NOT‐DTN) were investigated in three monocularly deprived squirrel monkeys. In two monkeys occlusion of one eye was performed at birth (early) and in the third after 7 weeks (late). In adulthood, in early deprived monkeys monocular horizontal OKN tested through the non‐deprived eye was symmetrical and in no way different from normal, i.e. stimulation in the temporonasal and nasotemporal direction elicited equal and robust responses. OKN through the early occluded eye, however, was grossly abnormal with low gain and great variability in the consistency of nasotemporal and temporonasal slow phase eye movements. When in the late deprived monkey the non‐deprived eye was occluded a strong spontaneous nystagmus developed despite the deprived eye viewing a stationary pattern. The slow phases were directed from nasal to temporal for the deprived eye. When tested through the non‐deprived eye all neuronal responses of the NOT‐DTN were normal. The deprived eye's influence on NOT‐DTN neurons was extremely weak. No neuron with a moderate or even dominant input from the deprived eye was found after early deprivation. In the late deprived case the deficit was not as severe but still the non‐deprived eye was clearly dominating the responses in all neurons tested. Velocity tuning of neurons tested through the non‐deprived eye was normal and qualitatively corresponded well to slow phase eye velocity in response to equivalent retinal slip during OKN. Through the early deprived eye, however, velocity tuning was extremely poor. It was somewhat better through the late deprived eye. We suggest that the dramatic deterioration in the optokinetic reflex found after long‐term monocular deprivation for the amblyopic eye is probably caused by the almost complete loss of retinal and cortical input driven by that eye to the NOT‐DTN. These results are discussed in relation to our previous results in cats and reports in the literature for humans with occlusion amblyopia.
Differential patterns of semaphorin expression in the developing rat brain
Authors: Skaliora Irini , Singer Wolf , Betz Heinrich , Püschel Andreas W.
Published: March 2003

Semaphorins are a large family of cell‐surface and secreted proteins that have been shown to function as chemorepellents or inhibitors of growth cones of peripheral neurons, yet little is known about their role in patterning central pathways. In order to examine whether semaphorins may be involved in guiding the formation of the reciprocal thalamocortical connections in the rat, we have analysed the spatial and temporal expression of five recently identified rodent semaphorins (semB, C, D, F and G) using in situ hybridization. Transcripts of all five genes were present throughout the period examined (E15–P7) and displayed highly specific spatiotemporal distributions. We have based our discussion of putative semaphorin effects on their known functions as chemorepellents and found their spatiotemporal expression patterns compatible with such a role in several developmental events. Specifically, semaphorins are in the position to: (i) prevent neurite extension into the ventricular neuroepithelium throughout the brain; (ii) confer non‐permissive properties to the embryonic cortical plate, hence regulating the radial invasion of corticopetal afferents; (iii) confine axonal extension to the intermediate zone and subplate; (iv) maintain the fasciculated state of thalamocortical and corticothalamic axons, and prevent them from branching while they grow through the striatum; and (v) restrict the terminal arborizations of thalamic afferents to layer IV. The evidence that different semaphorin genes are often co‐expressed further suggests that the various molecules might interact in synergistic ways. Taken together, our results support the hypothesis that semaphorins could act as guidance signals in the development of the thalamocortical projections and suggest that innervation specificity is achieved through the combined action of multiple guidance cues. Furthermore, these data provide a basis for the design of functional assays and the study of mice carrying knockouts in specific semaphorin genes.
Immortalized gonadotropin‐releasing hormone neurons secrete γ‐aminobutyric acid – evidence for an autocrine regulation
Authors: Ahnert‐Hilger G. , John M. , Kistner U. , Wiedenmann B. , Jarry H.
Published: March 2003

The immortalized hypothalamic neuronal cell lines GT1‐1 and GT1‐7 represent unique model systems to investigate the physiological control of gonadotropin‐releasing hormone (GnRH) secretion.

Using immunofluorescence microscopy, key proteins of regulated exocytosis, e.g. synaptotagmin, synaptobrevin and SNAP‐25 (synaptosomal associated protein of 25 kDa) were found in GT1 neurons. In addition, GT1 neurons contained synaptophysin, a marker protein for small synaptic vesicles (SSVs) which are responsible for the storage of neurotransmitters such as γ‐aminobutyric acid (GABA). Upon subcellular fractionation, a lighter vesicle population characterized by synaptophysin separated from a denser vesicle population containing GnRH. Both vesicle populations contained synaptobrevin and synaptotagmin. Besides GnRH, GT1 neurons expressed glutamic acid decarboxylase at the mRNA‐level and synthesized GABA. More importantly, GT1 neurons took up and stored 3H‐GABA. The stored GABA was released after stimulation with increasing K+ concentrations and by α‐latrotoxin. Reducing the extracellular Ca2+‐concentration abolished stimulated secretion, indicating that GABA was released by regulated exocytosis. Hormone secretion from GT1 neurons is controlled by GABA via GABAA and GABAB receptors reflecting the situation in vivo.

Our data provide the first evidence that GT1 neurons possess a second regulated secretory pathway sustained by SSVs storing and releasing GABA. The released GABA influences GnRH secretion by an auto‐ or paracrine loop.
Brain Ac39/physophilin: cloning, coexpression and colocalization with synaptophysin
Authors: Carrión‐Vázquez Mariano , Fernández Ana María , Chowen Julie , Nieto‐Sampedro Manuel
Published: March 2003

Physophilin is an oligomeric protein that binds the synaptic vesicle protein synaptophysin constituting a complex that has been hypothesized to form the exocytotic fusion pore. Microsequencing of several physophilin peptides putatively identified this protein as the Ac39 subunit of the V‐ATPase. Ac39 has recently been shown to be present in a synaptosomal complex which, in addition to synaptophysin, includes the bulk of synaptobrevin II, and subunits c and Ac115 of the V0 sector of the V‐ATPase. We have cloned physophilin from mouse brain and found a differential region of 12 amino acids when compared with the previously reported sequence of Ac39 from bovine adrenal medulla. RT‐PCR cloning from the bovine adrenal medulla demonstrates that sequencing errors occurred in the previous cloning study, and shows that the amino acid sequences of physophilin and Ac39 are completely identical. In situ hybridization in rat brain reveals a largely neuronal distribution of Ac39/physophilin mRNA which spatio‐temporally correlates with those of subunit c and synaptophysin. Immunohistochemical analysis shows that Ac39/physophilin is mostly concentrated in the neuropil with a pattern identical to subunit A and very similar to synaptophysin. Double‐labelling immunofluorescence shows a complete colocalization of Ac39/physophilin with subunit A and a partial colocalization with synaptophysin in the neuropil. Our findings bring anatomical support for the in vivo occurrence of the synaptophysin‐Ac39/physophilin interaction and further suggest a coordinated transcription of V‐ATPase and synaptophysin genes. A putative role of Ac39/physophilin in the inactivation of the V‐ATPase by disassembly of its V1 sector is also discussed.
Scalp recorded direct current brain potentials during human sleep
Authors: Marshall Lisa , Mölle Matthias , Fehm Horst L. , Born Jan
Published: March 2003

The direct current (DC) potential recorded from the scalp of awake humans has been considered a reflection of general changes in cortical excitability. This study examined DC potential shifts in humans during a night of continuous sleep. Standard polysomnographic recordings and skin temperature were measured simultaneously. Contrary to expectations, average DC potential level indicated higher negativity during nonrapid eye movement (NREM) sleep than REM sleep and wakefulness. Moreover, a dynamic regulation of the DC potential level was revealed in association with the NREM–REM sleep cycle comprising four successive phases: (i) a steep ‘NREM‐transition‐negative shift’ during the initial 10–15 min of the NREM sleep period; (ii) a more subtle ‘NREM‐positive slope’ during the subsequent NREM sleep period; (iii) a steep ‘REM‐transition‐positive shift’ starting shortly prior to the REM sleep period, and (iv) a ‘REM‐negative slope’, characterizing the remaining greater part of the REM sleep period. DC potential changes were only weakly related to changes in slow‐wave activity (r2 < 0.18). The NREM‐negative slope and REM‐positive slope could reflect, respectively, gradually increasing and decreasing cortical excitability resulting from widespread changes in the depolarization of apical dendrites. In contrast, the NREM‐transition‐negative shift and the REM‐transition‐positive shift may reflect the progression and retrogression, respectively, of a long‐lasting hyperpolarization in deeply lying neurons.
Intraventricular galanin modulates a 5‐HT1A receptor‐mediated behavioural response in the rat
Authors: Misane Ilga , Razani Haleh , Jansson Fu‐Hua Wang anders , Fuxe Kjell , Ögren Sven Ove
Published: March 2003

The present studies have examined whether the neuropeptide galanin can modulate brain serotoninergic (5‐HT) neurotransmission in vivo and, particularly, 5‐HT1A receptor‐mediated transmission. For that purpose, we studied the ability of galanin (given bilaterally into the lateral ventricle, i.c.v.) to modify the impairment of passive avoidance retention induced by the selective 5‐HT1A agonist 8‐hydroxy‐2‐(di‐n‐propyloamino)tetralin (8‐OH‐DPAT) when injected prior to training. This impairment appears to be mainly related to activation of 5‐HT1A receptors in the CNS. Galanin dose‐dependently (significant at 3.0 nmol/rat) attenuated the passive avoidance impairment (examined 24 h after training) induced by the 0.2 mg/kg dose of 8‐OH‐DPAT. This 8‐OH‐DPAT dose produced signs of the 5‐HT syndrome indicating a postsynaptic 5‐HT1A receptor activation. Furthermore, both the impairment of passive avoidance and the 5‐HT syndrome were completely blocked by the 5‐HT1A receptor antagonist WAY 100635 (0.1 mg/kg). Galanin (0.3 or 3.0 nmol) or WAY 100635 (0.1 mg/kg) failed by themselves to affect passive avoidance retention. 8‐OH‐DPAT given at a low dose 0.03 mg/kg, which presumably stimulates somatodendritic 5‐HT1A autoreceptors in vivo, did not alter passive avoidance retention or induce any visually detectable signs of the 5‐HT syndrome. Galanin (0.3 or 3.0 nmol) given i.c.v. in combination with the 0.03 mg/kg dose of 8‐OH‐DPAT, did not modify passive avoidance. The immunohistochemical study of the distribution of i.c.v. administered galanin (10 min after infusion) showed a strong diffuse labelling in the periventricular zone (100–200 μm) of the lateral ventricle. Furthermore, in the dorsal and ventral hippocampus galanin‐immunoreactive nerve cells appeared both in the dentate gyrus and the CA1, CA2 and CA3 layers of the hippocampus. In the septum only endogenous fibres could be seen while in the caudal amygdala also galanin‐immunoreactive nerve cells were visualized far away from the labelled periventricular zone. At the level of the dorsal raphe nucleus a thin periventricular zone of galanin immunoreactivity was seen but no labelling of cells. These results suggest that galanin can modulate postsynaptic 5‐HT1A receptor transmission in vivo in discrete cell populations in forebrain regions such as the dorsal and ventral hippocampus and parts of the amygdala. The indication that galanin administered intracerebroventrically may be taken up in certain populations of nerve terminals in the periventricular zone for retrograde transport suggests that this peptide may also affect intracellular events.
Association Basolateral amygdala stimulation evokes glutamate receptor‐dependent dopamine efflux in the nucleus accumbens of the anaesthetized rat
Authors: Floresco Stan B. , Yang Charles R. , Phillips Anthony G. , Blaha Charles D.
Published: March 2003

Afferents from the basolateral amygdala and dopamine projections from the ventral tegmental area to the nucleus accumbens have both been implicated in reward‐related processes. The present study used in vivo chronoamperometry with stearate‐graphite paste electrodes in urethane‐anaesthetized rats to determine how basolateral amygdala efferents to the nucleus accumbens synaptically regulate dopamine efflux. Repetitive‐pulse (20 Hz for 10 s) electrical stimulation of the basolateral amygdala evoked a complex pattern of changes in monitored dopamine oxidation currents in the nucleus accumbens related to dopamine efflux. These changes were characterized by an initial increase that was time‐locked to stimulation, a secondary decrease below baseline, followed by a prolonged increase in the dopamine signal above baseline. The effects of burst‐patterned stimulation (100 Hz, 5 pulses/burst, 1‐s interburst interval, 40 s) of the basolateral amygdala on the basal accumbens dopamine signal were similar to those evoked by 20 Hz stimulation, with the lack of a secondary suppressive component. Infusions of the ionotropic glutamate receptor antagonists (±)‐2‐amino‐5‐phosphonopentanoic acid (APV) or 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX) into the nucleus accumbens dose‐dependently blocked or attenuated the initial and prolonged increases in the dopamine signal following 20 Hz or burst‐patterned basolateral amygdala stimulation. Infusions of the metabotropic glutamate receptor antagonist (+)‐α‐methyl‐4‐carboxyphenylglycine selectively blocked the intermediate suppressive effect of 20 Hz basolateral amygdala stimulation on dopamine oxidation currents. Blockade of glutamate receptors or inhibition of dopamine neuronal activity via infusions of either APV + DNQX, lidocaine or γ‐hydroxybutyric acid, respectively, into the ventral tegmental area did not effect the pattern of changes in the accumbens dopamine signal evoked by basolateral amygdala stimulation. These data suggest that the glutamatergic basolateral amygdala inputs to nucleus accumbens dopamine terminals synaptically facilitate or depress dopamine efflux, and these effects are independent of dopamine neuronal firing activity. Moreover, these results imply that changes in nucleus accumbens dopamine levels following presentation of reward‐related stimuli may be mediated, in part, by the basolateral amygdala.
Potentiation of murine astrocyte antioxidant defence by bcl‐2: protection in part reflects elevated glutathione levels
Authors: Papadopoulos Marios C. , Koumenis Iphigenia L. , Xu Lijun , Giffard Rona G.
Published: March 2003

Overexpression of the proto‐oncogene bcl‐2 has been shown to protect a variety of cell types from oxidative and non‐oxidative injury, blocking apoptotic and necrotic types of cell death. Retroviral vectors were used to stably overexpress bcl‐2 in primary murine astrocyte cultures with more than 95% efficiency. Compared to β‐galactosidase‐expressing and uninfected control cells, bcl‐2 overexpressing astrocytes suffered < 40% injury after 24 h glucose deprivation, while controls were essentially completely injured. After exposure to 0.2 mm hydrogen peroxide, the bcl‐2 overexpressing astrocytes suffered < 40% the injury seen in controls. In contrast, when the cultures were injured by combined oxygen–glucose deprivation, no difference in the extent or time course of injury was found between cells overexpressing bcl‐2 and those expressing β‐galactosidase. To investigate one possible mechanism of bcl‐2 protection, we measured the levels of glutathione and three antioxidant enzymes. Astrocytes overexpressing bcl‐2 had elevated glutathione levels (130–200%), increased superoxide dismutase (170%) and glutathione peroxidase (140%) activities compared with β‐galactosidase‐expressing controls. Bcl‐2 overexpressing astrocytes suffered less lipid peroxidation after glucose deprivation, as assessed by cis‐parinaric acid fluorescence, and demonstrated more rapid removal of hydrogen peroxide from the medium. When glutathione levels were decreased 80% by pretreatment with buthionine sulfoximine, the extent of protection from glucose deprivation of bcl‐2 overexpressing cells was decreased by about half. Increased antioxidant defence contributes to protection from glucose deprivation in bcl‐2 overexpressing astrocytes.
A dopamine‐μ1 opioid link in the rat ventral tegmentum shared by palatable food (Fonzies) and non‐psychostimulant drugs of abuse
Authors: Tanda Gianluigi , Di Chiara Gaetano
Published: March 2003

The role of μ1 opioid receptors in the stimulation of dopamine transmission in the rat nucleus accumbens by an unusual palatable food (Fonzies) and non‐psychostimulant drugs of abuse was investigated by the use of naloxonazine, a pseudo‐irreversible antagonist of μ1 opioid receptors. Feeding of Fonzies stimulated dopamine release in the medial prefrontal cortex and in the shell, but not in the core of the nucleus accumbens. Pretreatment with naloxonazine given systemically (15 mg/kg i.p. 20 h before) completely prevented the stimulation of dopamine release in the shell of the nucleus accumbens by Fonzies without affecting that in the prefrontal cortex. Systemic pretreatment with naloxonazine reduced or, depending on the dose, abolished, the stimulation of dopamine release in the nucleus accumbens shell by morphine, nicotine and ethanol, but did not affect that by haloperidol. Naloxonazine also prevented the stimulatory effects of Fonzies, nicotine and morphine on nucleus accumbens dopamine transmission when infused bilaterally in the ventral tegmental area. The results indicate that μ1 opioid receptors in the ventral tegmentum play a major role in the stimulant effects of food and drugs of abuse on mesolimbic dopamine transmission.
Interleukin‐1β and the interleukin‐1 receptor antagonist act in the striatum to modify excitotoxic brain damage in the rat
Authors: Lawrence Catherine B. , Allan Stuart M. , Rothwell Nancy J.
Published: March 2003

The cytokine interleukin‐1 (IL‐1) has been implicated in ischaemic, traumatic and excitotoxic brain damage. The results presented here reveal novel actions of IL‐1 in the striatum which markedly exacerbate cortical neuronal damage elicited by local excitotoxins in the striatum or cortex.

Intrastriatal infusion of IL‐1 receptor antagonist, IL‐1ra, markedly inhibited striatal neuronal damage caused by N‐methyl‐d‐aspartate (NMDA) or α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) receptor activation in the rat. In contrast, intracortical infusion of IL‐1ra failed to inhibit NMDA or AMPA receptor‐induced damage in the cortex.

Intrastriatal co‐infusion of IL‐1β with the NMDA or AMPA receptor agonist did not affect local striatal damage induced by activation of either glutamate receptor subtype, but caused extensive cortical damage when administered into the striatum with AMPA. This secondary damage was significantly reduced by pretreatment with the NMDA receptor antagonist (MK‐801), which did not affect local (striatal) damage caused by AMPA. Infusion of IL‐1β into the striatum (but not the cortex) markedly enhanced cortical damage caused by infusion of an NMDA or AMPA receptor agonist into the cortex.

These data reveal selective actions of IL‐1 and IL‐1ra in the striatum, which influence cortical neuronal loss and suggest that IL‐1 selectively enhances damage caused by AMPA receptor activation.
Layer‐specific dendritic regression of pyramidal cells with ageing in the human prefrontal cortex
Authors: de Brabander  , Kramers  , Uylings
Published: March 2003

The dendritic field of pyramidal neurons in cortical layers IIIc and V of the prefrontal cortex in ageing humans was studied. The three‐dimensional branching pattern of the basilar dendrites of Golgi–Cox impregnated neurons was analysed in the middle frontal gyrus (areas 9 and 46) in eight subjects between the ages of 49 and 90 years, all without a neurological or psychiatric disorder.

The results revealed a significant regression of the layer V dendritic pattern with increasing age, but the layer IIIc neurons did not show any age‐related changes. Together with our earlier data on the postnatal development of the same cell types in the prefrontal cortex, we hypothesize that the layer V neurons in the prefrontal cortex start to regress from the fifth decade onwards, in contrast to the layer IIIc neurons which remain stable from puberty on.

We conclude that pyramidal cells in layer IIIc and V in a similar cortical region undergo a differential ageing effect.
Differentiation of rat hypothalamic dopaminergic neurons is stimulated in vitro by target cells: the melanotrophs
Authors: Egles  , René  , Varon  , Louis  , Félix  , Schimchowitsch
Published: March 2003

We have investigated in vitro the influence of pituitary intermediate lobe melanotrophs on the differentiation of their afferent hypothalamic dopaminergic neurons. The presence of melanotrophs in primary cultures of foetal hypothalamic neurons induces an increase of the number of dopaminergic neurons (while the total neuronal population remains unchanged) and induces a stimulation of their neuritic outgrowth. These effects are mediated by diffusible factors since they are reproduced by application of conditioned medium issued from co‐cultures with intermediate lobe cells from newborn rats. Moreover, by immunoneutralization of α‐melanocyte‐stimulating hormone (αMSH) in the co‐culture or conditioned medium, or by application of the peptide itself, we demonstrate that the neuritotrophic effect on dopaminergic neurons is mediated by αMSH, the main secretory product of melanotrophs, whereas the inductive effect on the number of dopaminergic neurons is attributable to another diffusible neurotrophic factor(s) present in foetal, but not adult, adenohypophysis. Similar effects are observed on cultures of newborn hypothalamic neurons. However, at this stage of neuronal development, αMSH also increases the number of dopaminergic neurons, which could be due to a change of neuronal receptivity. We show that the neuritotrophic influence of αMSH is restricted to the dopaminergic neurons connected to the melanotrophs, and that in addition, these neurons systematically co‐express the tyrosine hydroxylase and glutamate decarboxylase as the neurons innervating the melanotrophs in situ. These findings indicate that the differentiation of dopaminergic hypothalamic neurons is influenced by the target cells, melanotrophs, and that this trophic influence implicates αMSH.
Endogenous nerve growth factor regulates the sensitivity of nociceptors in the adult rat
Authors: Bennett David L. H. , Koltzenburg Martin , Priestley John V. , Shelton David L. , McMahon Stephen B.
Published: March 2003

Nerve growth factor (NGF) has a well characterized role in the development of the nervous system and there is evidence that it interacts with nociceptive primary afferent fibres. Here we applied a synthetic tyrosine kinase A IgG (trkA‐IgG) fusion molecule for 10–12 days to the innervation territory of the purely cutaneous saphenous nerve in order to bind, and thereby neutralize endogenous NGF in adult rats. Using neurophysiological analysis of 152 nociceptors we now show that sequestration of NGF results in specific changes of their receptive field properties. The percentage of nociceptors responding to heat dropped significantly from a normal 57% to 32%. This was accompanied by a rightward shift and a reduced slope of the stimulus response function relating the intracutaneous temperature to the neural response. The number of nociceptors responding to application of bradykinin was also significantly reduced from a normal of 28% to 8%. In contrast, the threshold for mechanical stimuli and the response to suprathreshold stimuli remained unaltered, as did the percentage of nociceptors responding to noxious cold. The reduced sensitivity of primary afferent nociceptors was accompanied by a reduction in the innervation density of the epidermis by 44% as assessed with quantitative immunocytochemical analysis of the panaxonal marker PGP 9.5. This demonstrates that endogenous NGF in the adult specifically modulates the terminal arborization of unmyelinated fibres and the sensitivity of primary afferent nociceptors to thermal and chemical stimuli in vivo.
Small sensory neurons in the rat dorsal root ganglia express functional NK‐1 tachykinin receptor
Authors: Li Hong‐Sheng , Zhao Zhi‐Qi
Published: March 2003

The tachykinins substance P (SP) and neurokinin A, released by the C‐type primary afferent fibre terminals of the small dorsal root ganglion (DRG) neurons, play important roles in spinal nociception. By means of non‐radioactive in situ hybridization and whole‐cell recording, we showed that the small rat DRG neurons also express the NK‐1 tachykinin receptor. In situ hybridization demonstrated that the positive neurons in rat DRG sections were mainly small cells (85.9%) with diameters less than 25 μm. The remaining positive neurons (14.1%) were cells with medium diameters between 26 and 40 μm. No positive large neurons (diameters > 40 μm) were observed. Expression in small DRG neurons (diameter < 21 μm) was confirmed by in situ hybridization of isolated cells, which were demonstrated to express NK‐1 receptor mRNA at a very high frequency (> 90% of small DRG neurons) and therefore were subjected to whole‐cell recording. In 57 of 61 cells recorded, SP or the selective NK‐1 receptor agonist [Sar9, Met(O2)11]SP (Sar‐SP, 1 or 2 μm) produced a delayed vibrating inward current (50–300 nA) with a long duration of 0.5–2 h. These currents were blocked by co‐application of the NK‐1 receptor antagonist L‐668, 169 (1 μm), but were not affected by the NK‐2 antagonist

L‐659, 877 (2 μm). Both current‐clamp recording and cell‐attached single‐channel recording demonstrated that the long‐lasting response was due to the opening of a channel with an inward current. Employment of non‐Ca2+ and Ca2+ + choline solutions revealed that this channel might be a Ca2+‐permeable, non‐selective cation channel. The prolonged NK‐1 tachykinin response exhibited extreme desensitization. This work suggests that presynaptic NK‐1 autoreceptors may be present on the primary afferent terminals in the spinal cord, where they could contribute to the chronic pain and hyperalgesia.
Chemosensitivity of nociceptive, mechanosensitive afferent nerve fibres in the guinea‐pig ureter
Authors: Sann Holger
Published: March 2003

The mechanosensitivity and chemosensitivity of afferent fibres were investigated in an in vitro preparation of the guinea‐pig ureter. Electrophysiological recordings were obtained from 5 U‐1 (low mechanical threshold, contraction‐sensitive) and 74 U‐2 units (high threshold). U‐2 units had significant higher levels of spontaneous activity, lower conduction velocities, higher mechanical thresholds (U‐1: 7 mmHg; U‐2: 39 mmHg), less pronounced phasic responses and longer latencies in the response to distensions than the U‐1 units. For chemical stimulation, guinea‐pig urine (> 800 mosmol/L), bradykinin and capsaicin were applied intraluminally. The responses of U‐1 units mainly corresponded to the contractions induced by the chemical stimulation. The vast majority of the U‐2 units were excited by urine, bradykinin (threshold: 0.1–1 μm) and capsaicin (threshold: 0.03–0.3 μm). The responses to urine could be mimicked by high concentrations of potassium ions (> 200 mm), but not by an equiosmolar solution of NaCl, urea and mannitol. Chemical stimulation could also result in a transient sensitization of the U‐2 units to mechanical stimuli. In the anaesthetized guinea‐pig, pseudo‐affective responses could be evoked by ureteric distension (threshold: 30–60 mmHg) and serosal application of capsaicin. Intraluminal application of urine in vivo did not evoke any reactions, suggesting that the responses of the U‐2 units to urine might be due to an impaired barrier function of the urothelium in vitro. The data are in agreement with the hypothesis that U‐2 units are visceral polymodal nociceptors. Since the U‐1 units were also able to encode at least noxious mechanical stimuli, their involvement in visceral nociception cannot be excluded.
Modulation of the voltage‐gated sodium current in rat striatal neurons by DARPP‐32, an inhibitor of protein phosphatase
Authors: Schiffmann  , Desdouits  , Menu  , Greengard  , Vincent J‐D. , Vanderhaeghen J‐J. , Girault J‐A.
Published: March 2003

DARPP‐32 is a cyclic adenosine monophosphate‐regulated inhibitor of protein phosphatase 1, highly enriched in striatonigral neurons. Stimulation of dopamine D1 receptors increases phosphorylation of DARPP‐32, whereas glutamate acting on N‐methyl‐d‐aspartate receptors induces its dephosphorylation. Yet, to date, there is little direct evidence for the function of DARPP‐32 in striatal neurons. Using a whole cell patch‐clamp technique, we have studied the role of DARPP‐32 in the regulation of voltage‐gated sodium channels in rat striatal neurons maintained in primary culture. Injection of phospho‐DARPP‐32, but not of the unphosphorylated form, reduced the sodium current amplitude. This effect was similar to those induced by okadaic acid, with which there was no additivity and by tautomycin. Our results indicate that, in striatal neurons, sodium channels are under dynamic control by phosphorylation/dephosphorylation, and that phospho‐DARPP‐32 reduces sodium current by stabilizing a phosphorylated state of the channel or an associated regulatory protein. We propose that the DARPP‐32‐mediated modulation of sodium channels, via inhibition of phosphatase 1, contributes to the regulation of these channels by D1 receptors and other neurotransmitters which influence the state of phosphorylation of DARPP‐32.
Cytoskeletal and nuclear localization of myelin oligodendrocytic basic protein isoforms
Authors: Montague  , Barrie  , Thomson  , Kirkham  , McCallion  , Davies  , Kennedy  , Griffths>
Published: March 2003

The recently described single copy Myelin‐associated Oligodendrocytic Basic Protein (Mobp) gene is expressed exclusively in the central nervous system (CNS). The gene encodes a family of small highly basic polypeptides with predicted amino acid lengths of 69, 71, 81, 99 and 170, all of which share a 68 residue amino terminal. Here we report on the subcellular distribution of two of these polypeptides termed MOBP81 and MOBP170 in transiently transfected Cos7 cells using an antibody raised against a region common to all isoforms of MOBP. Additionally, we describe MOBP trafficking in cultured mouse spinal cord oligodendrocytes. Immunostaining for MOBP81 is intense in the perinuclear region and extends throughout the cytoplasm colocalizing with the microtubular cytoskeletal network. Consistent with this we demonstrate that MOBP partitions with the cytoskeletal fraction prepared from myelin. In contrast, although MOBP170 is present in the cytoplasm it does not colocalize with the cytoskeleton and displays a greater variation in distribution. In the majority of transfectants immunostaining is present throughout the karyoplasm but with increased intensity around the nucleolus. Within mouse primary oligodendrocytes endogenous MOBP is present in the cell body and processes colocalizing with the microtubular network. Immunoreactivity is not detectable in the nucleus in these mature oligodendrocytes. These significant differences in MOBP81 and MOBP170 protein kinesis coupled to different expression profiles of their respective message populations may be indicative of both myelin structural and cellular/regulatory functions, respectively, for these polypeptides.
A role for slow NMDA receptor‐mediated, intrinsic neuronal oscillations in the control of fast fictive swimming in Xenopus laevis larvae
Authors: Reith Carolyn A. , Sillar Keith T.
Published: March 2003

In larvae of the amphibian, Xenopus laevis, spinal neurons which are active during fictive swimming also display tetrodotoxin‐resistant membrane potential oscillations following the coactivation of N‐methyl‐dl‐aspartate (NMDA) and 5‐hydroxytryptamine (serotonin or 5‐HT) receptors (Scrymgeour‐Wedderburn et al. 1997;Eur. J. Neurosci., 9, 1473–1482). The oscillations are slow (≈0.5 Hz) compared with swimming (≈7–35 Hz) raising doubt over their contribution to the cycle by cycle depolarizations occurring during swimming. We investigated an alternative: that the intrinsic oscillations modulate swimming activity over many consecutive cycles. Bath application of NMDA induced continuous fictive swimming that differed between embryonic and larval preparations. In 81% of larval preparations (n = 36), there was a slow (approximately every 2 s) rhythmic modulation of ventral root activity in which burst durations and intensities increased as cycle periods decreased. This pattern of activity was enhanced rather than abolished following blockade of glycine and γ‐aminobutyric acid (GABA) A receptors and presumably therefore resulted from a periodic increase in the excitation of motor neurons. To determine whether this slow rhythm resulted from intrinsic, 5‐HT‐dependent membrane potential oscillations, larvae were spinalized to prevent the release of 5‐HT from brainstem raphe neurons. The resulting pattern of NMDA‐induced activity lacked any slow modulation. The slow modulation could also be enhanced by the bath application of a 5‐HT receptor agonist (5‐carboxamidotryptamine) and abolished either by the addition of an antagonist (pindobind‐5‐HT1A) or by removal of magnesium ions, providing more direct evidence for a contribution of intrinsic oscillations. Thus, the 5‐HT‐dependent intrinsic oscillations modulate NMDA‐induced swimming activity over several consecutive cycles.
Reduction of noradrenaline impairs attention and dopamine depletion slows responses in Parkinson's disease
Authors: Riekkinen Minna , Kejonen Kosti , Jäkälä Pekka , Soininen Hilkka , Riekkinen Paavo
Published: March 2003

We investigated the role dopamine and noradrenaline in the modulation of attention in Parkinson's disease (PD) patients. We observed that PD patients with mild and moderate motor disability did not differ in their attentional accuracy in easy tests, but the severe PD group was slightly disrupted in a more arduous test of attention. Attentional accuracy was not affected by withdrawal of dopaminergic drugs in mild or severe PD patients. The movements of severe PD patients were slower, and withdrawal of dopaminergic drugs aggravated motor slowing more in severe PD patients. Clonidine (0.5 and 2 μg/kg) retarded accuracy of performance in the most difficult attention test in mild PD patients, but had no effect in the severe PD group. Clonidine had no effect on movement times. These data suggest that a defect in noradrenaline release may contribute to the impaired accuracy of attention in severe PD patients and that dopamine may be important for maintaining rapid motor responding.
Visual activity is required to maintain the phenotype of supragranular NPY neurons in rat area 17
Authors: Obst Kirstin , Bronzel Margit , Wahle Petra
Published: March 2003

Visual activity governs the functional maturation of the mammalian visual cortex. We report here, that visual experience is required for stabilizing the phenotype of a subset of cortical interneurons. Neurons expressing neuropeptide Y mRNA (NPY neurons) display a transiently higher expression in the early postnatal visual areas 18a and 17 that is followed by a phenotype restriction during the second postnatal month: about 50% of the NPY neurons in supragranular and infragranular layers of area 18a, and in infragranular layers of area 17 gradually stop the NPY expression. In contrast, the expression remains unchanged in supragranular layers of area 17. Dark rearing rats from birth to up to 100 days does neither prevent the developmental onset of NPY mRNA expression, nor does it prevent the phenotype restriction from occurring. In contrast, in dark reared animals NPY neurons in supragranular layers of area 17 now also undergo a phenotype restriction. Returning animals to light after variable periods of darkness results in an upregulation of NPY mRNA expression selectively in neurons in supragranular layers of area 17. These neurons acquire a constitutive expression during the second postnatal month. This suggests that the phenotypic specification of a distinct subset of cortical interneurons is regulated by visual experience which thus influences on the maturation of the neurochemical architecture of area 17.
Basic fibroblast growth factor promotes the generation and differentiation of calretinin neurons in the rat cerebral cortex in vitro
Authors: Pappas Ioannis S. , Parnavelas John G.
Published: March 2003

Calretinin‐expressing neurons are some of the earliest postmitotic cells to appear in the developing cerebral cortex. Lineage studies have shown that the expression of this calcium‐binding protein in cortical neurons is not genetically programmed and is likely to be induced by external factors. A number of studies have clearly shown that basic fibroblast growth factor (bFGF) and a number of neurotrophins promote the proliferation and differentiation of cortical progenitor cells to a particular lineage. Here, using a culture system of dissociated rat cortical cells, we found that brain‐derived neurotrophic factor and neurotrophin‐3 promoted the morphological differentiation of one of the calretinin‐containing neuronal subpopulations, the Cajal–Retzius cells. Another subpopulation of calretinin‐expressing cells of smaller size and bipolar form was generated when cultures were treated with bFGF. The progenitors of these neurons were stimulated by bFGF to divide a number of times before initiating their differentiation programme. The number of calretinin‐expressing neurons increased further when cultures were treated with a combination of bFGF and retinoic acid.
Death‐signalling cascade in mouse cerebellar granule neurons
Authors: Tanabe Hiroki , Eguchi Yutaka , Shimizu Shigeomi , Martinou Jean‐Claude , Tsujimoto Yoshihide
Published: March 2003

Molecular mechanisms of neuronal cell death are still largely unknown. In the present study, the signal transduction pathway of cell death in cerebellar granule neurons was examined by employing various death‐preventative agents. When death was induced by the depletion of serum and a depolarizing level of potassium, transient increase in active c‐Jun, mitochondrial membrane potential (Δψ) loss, activation of caspase‐3 (‐like) proteases, and nuclear condensation and fragmentation were observed. The protein synthesis inhibitor cycloheximide blocked all these phenomena, whereas RNA synthesis inhibitor actinomycin‐D, survival factor such as insulin‐like growth factor‐1, brain‐derived neurotrophic factor, high K+(25 mm) and overproduced antiapoptotic protein Bcl‐2, prevented Δψ loss, caspase activation, and nuclear change, but not an increase in active c‐Jun. The caspase inhibitor z‐Asp‐CH2‐DCB (carbobenzoxy‐l‐aspartyl‐α‐[(2,6‐dichlorobenzoyl) oxy]methane) only inhibited activation of caspases and nuclear change. These results suggest that the death signal in cerebellar granule neurons is sequentially transduced in the order of c‐Jun activation,de novoRNA synthesis, mitochondrial Δψ loss, activation of caspase‐3 (‐like) proteases and nuclear change.
Reduced after‐hyperpolarization in rat piriform cortex pyramidal neurons is associated with increased learning capability during operant conditioning
Authors: Saar Drorit , Grossman Yoram , Barkai Edi
Published: March 2003

Learning‐related cellular modifications were studied in the rat piriform cortex. Water‐deprived rats were divided to three groups: ‘trained’ rats were trained in a four‐arm maze to discriminate positive cues in pairs of odours, ‘control’ rats were ‘pseudo‐trained’ by random water rewarding, and ‘naive’ rats were water‐deprived only. In one experimental paradigm, the trained group was exposed to extensive training with rats learning to discriminate between 35 and 50 pairs of odours. Piriform cortex pyramidal neurons from ‘trained’, ‘control’ and ‘naive’ rats did not differ in their passive membrane properties and single spike characteristics. However, the after‐hyperpolarizations (AHPs) that follow six‐spike trains were reduced after ‘extensive training’ by 43% and 36% compared with ‘control’ and ‘naive’, respectively. This effect was not observed in the piriform cortex of another group of rats, in which hyperexcitability was induced by chemical kindling. In another experimental paradigm rats were trained only until they demonstrated ‘rule learning’, usually after discriminating between one and two pairs of odours (‘mild training’). In this experiment, a smaller, yet significant, reduction (20%) in AHPs was observed. AHP reduction was apparent in most of the sampled neurons. AHP remained reduced up to 3 days after the last training session. 5 days or more after the last training session, AHP amplitude recovered to pre‐training value and did not differ between ‘trained’ rats and the others. Accordingly, training suspension for 5 days or more resulted in slower learning of novel odours. We suggest that increased neuronal excitability, manifested as reduced AHP, is related to the ability of the cortical network to enter a ‘learning mode’ which creates favourable conditions for enhanced learning capability.
Rewarding effects elicited by the microinjection of either AMPA or NMDA glutamatergic antagonists into the ventral tegmental area revealed by an intracranial self‐administration paradigm in mice
Authors: David Vincent , Durkin Thomas P. , Cazala Pierre
Published: March 2003

In order to study the functional role of the trans‐synaptic neuronal interaction between glutamatergic afferents and mesolimbic dopaminergic neurons in internal reward processes, BALB/c male mice were unilaterally implanted with a guide‐cannula, the tip of which was positioned 1.5 mm above the ventral tegmental area (VTA). On each day of the following experimental period, a stainless steel injection cannula was inserted into the VTA in order to study the eventual self‐administration behaviour of either the competitive N‐methyl‐ d‐aspartate antagonist, d(–)‐2‐amino‐7‐phosphonoheptanoic acid (AP‐7) or the α‐amino‐3‐hydroxy‐5‐methyl‐isoxazole‐4‐propionic acid antagonist, 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX) (3 ng/50 nL) using a spatial discrimination task in a Y maze. Mice rapidly discriminated between the arm enabling a microinjection of either of these glutamatergic antagonists and the neutral arm of the maze, and a robust self‐administration of either of these compounds was observed from the first session of acquisition. These data provide strong evidence that the intra‐VTA microinjection of either of these subclasses of glutamatergic antagonist produces an effect which is interpreted centrally by the experimental subjects as being highly rewarding. Once the self‐administration response had been fully acquired by the experimental subjects, preinjection of the dopaminergic D2 antagonist, sulpiride (50 mg/kg i.p.), 30 min before the test, produced a rapid extinction of the self‐administration response. This latter result demonstrates the dopaminergic D2 receptor dependence of this intra‐VTA self‐administration of both of these subclasses of glutamatergic antagonist. We conclude that the different glutamatergic afferent neuronal inputs to the VTA globally exert, in vivo, via the mediation of interposed endogenous GABAergic interneurons, a tonic trans‐synaptic inhibitory regulation of neuronal activity in the mesolimbic dopaminergic pathway and that this complex neuronal interaction in the VTA plays a significant functional part in the modulation of internal reward processes.
Inositol 1,4,5‐trisphosphate activates non‐selective cation conductance via intracellular Ca2+ increase in isolated frog taste cells
Authors: Okada Yukio , Fujiyama Rie , Miyamoto Takenori , Sato Toshihide
Published: March 2003

The effect of intracellular Ca2+ increase was analysed in isolated frog taste cells under the whole‐cell patch clamp. External application of a Ca2+‐ionophore, ionomycin (3 μm) induced the sustained inward current of −200 ± 17 pA (mean ± SE, n = 23) at – 50 mV in taste cells. The ionomycin‐induced response was observed in most of the cells exposed in the drug, but not when 10 mm BAPTA (1,2‐bis (o‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid) was included in the pipette (eight cells). Steady‐state I–V relationships of ionomycin‐induced currents were almost linear and reversed at – 8 ± 1 mV (n = 23). The simultaneous removal of Na+ and Ca2+ from the external solution eliminated the response completely (three cells). Intracellular dialysis with 1 mm Ca2+ or 50 μm inositol 1,4,5‐trisphosphate (IP3) in K+‐internal solution also induced an inward current in the taste cells. The Ca2+‐induced and IP3‐induced responses were observed in 82% and 36% of the cells dialysed with the drugs, respectively. The Ca2+‐induced and IP3‐induced currents were inhibited by external Cd2+ (1–2 mm). The reversal potentials of the inward currents were – 15 ± 3 mV (n = 9) in Ca2+ dialysis and – 11 ± 3 mV (n = 13) in IP3 dialysis. The half‐maximal Ca2+ concentration in the pipette to induce the inward current was ≈ 170 μm. The results suggest that IP3 can depolarize the taste cell with mediation by intracellular Ca2+.
Differential expression of voltage‐gated K+ and Ca2+ currents in bipolar cells in the zebrafish retinal slice
Authors: Connaughton  , Maguire
Published: March 2003

Whole‐cell voltage‐gated currents were recorded from bipolar cells in the zebrafish retinal slice. Two physiological populations of bipolar cells were identified. In the first, depolarizing voltage steps elicited a rapidly activating A‐current that reached peak amplitude ≤ 5 ms of step onset. IA was antagonized by external tetraethylammonium or 4‐aminopyridine, and by intracellular caesium. The second population expressed a delayed rectifying potassium current (IK) that reached peak amplitude ≥ 10 ms after step onset and did not inactivate. IK was antagonized by internal caesium and external tetraethylammonium. Bipolar cells expressing IK also expressed a time‐dependent h‐current at membrane potentials < – 50 mV. Ih was sensitive to external caesium and barium, and was also reduced by Na+‐free Ringer. In both groups, a calcium current (ICa) and a calcium‐dependent potassium current (IK(Ca)) were identified. Depolarizing voltage steps > – 50 mV activated ICa, which reached peak amplitude between – 20 and – 10 mV. ICa was eliminated in Ca+2‐free Ringer and blocked by cadmium and cobalt, but not tetrodotoxin. In most cells, ICa was transient, activating rapidly at – 50 mV. This current was antagonized by nickel. The remaining bipolar cells expressed a nifedipine‐sensitive sustained current that activated between – 40 and – 30 mV, with both slower kinetics and smaller amplitude than transient ICa. IK(Ca) was elicited by membrane depolarizations > – 20 mV. Bipolar cells in the zebrafish retinal slice preparation express an array of voltage‐gated currents which contribute to non‐linear I–V characteristics. The zebrafish retinal slice preparation is well‐suited to patch clamp analyses of membrane mechanisms and provides a suitable model for studying genetic defects in visual system development.