bluuebunny/crossref_metadata_2025 huggingface dataset:
Visual Control of Hand‐reaching Movement: Activity in Parietal Area 7m
Authors: Ferraina S. , Garasto M. R. , Battaglia‐Mayer A. , Ferraresi P. , Johnson P. B. , Lacquaniti F. , Carniniti R.
Published: April 2006

The activity of single neurons was studied in parietal area 7m while monkeys performed an instructed‐delay reaching task to visual targets under normal light conditions and in darkness. The task was aimed at assessing the influence of vision of hand position on the neural activity of 7m related either to static posture and movement of the hand or to eye position in the orbit. The results show the existence of preparatory, movement‐related and postural activity for the control of reaching, all of which are strongly modulated by vision. The activity of many 7m neurons, otherwise insensitive to pure visual stimuli, seems to reflect complex interactions between gaze angle and hand position in the visual field.
Cocaine‐induced Increase in Cortical Acetylcholine Release: Interaction with the Hypothalamo—Pituitary—Adrenal Axis
Authors: Day Jamie C. , Piazza Pier Vincenzo , Le Moal Michel , Maccari Stefania
Published: April 2006

An influence on drug‐taking behaviours of the stress‐related hypothalamo‐pituitary‐adrenal (HPA) axis and its final hormonal mediator, corticosterone, has previously been demonstrated. A role for cortically projecting cholinergic neurons in these behaviours can also be proposed. The experiments presented here examine the effect of the drug of abuse cocaine (15 mg/kg) on the release of acetylcholine (ACh) in the cortex of freely moving rats, using the technique of in vivo microdialysis. To assess a possible modulatory influence of the HPA axis via its final hormonal mediator corticosterone, the cocaine‐induced effect on cortical ACh release in intact rats was compared to that in adrenalectomized (ADX) rats, which thus lacked their endogenous source of corticosterone, and in ADX rats in which the cocaine‐induced corticosterone peak and/or the basal circadian concentrations of serum corticosterone were simulated by replacement treatments. The results reported here demonstrate that cortical ACh release is greatly increased by cocaine in intact rats; ADX prolongs the return to basal levels of cortical ACh, and the chronic replacement of circadian levels of corticosterone normalizes this effect. In contrast, during the plateau period of cocaine‐induced increased cortical ACh release, where no effect of ADX is evident, rats with chronic replacement of corticosterone show an attenuated cocaine‐induced cortical ACh release, and the acute replacement of the cocaine‐induced corticosterone secretion further attenuates this response. These results demonstrate that cocaine stimulates cortically projecting cholinergic neurons, and that the HPA hormone corticosterone modulates this interaction in a complex manner which merits further investigation.
Relative Changes in Regional Cerebral Blood Flow During Spinal Cord Stimulation in Patients with Refractory Angina Pectoris
Authors: Hautvast Raymond W. M. , Ter Horst Gert J. , DeJong Bauke M. , DeJongste Mike J. L. , Blanksma Paul K. , Paans Anne M. J. , Korf Jakob
Published: April 2006

Spinal cord stimulation applied at thoracic level 1 (T1) has a neurally mediated anti‐anginal effect based on anti‐ischaemic action in the myocardium. Positron emission tomography was used to study which higher brain centres are influenced by spinal cord stimulation. Nine patients with a spinal cord stimulator for angina pectoris were studied using H215O as a flow tracer. Relative changes in regional cerebral blood flow related to stimulation compared with non‐stimulation were assessed and analysed using the method of statistical parametric mapping. Increased regional cerebral blood flow was observed in the left ventrolateral periaqueductal grey, the medial prefrontal cortex [Brodmann area (BA) 9/10], the dorsomedial thalamus bilaterally, the left medial temporal gyrus (BA 21), the left pulvinar of the thalamus, bilaterally in the posterior caudate nucleus, and the posterior cingulate cortex (BA 30). Relative decreases in rCBF were noticed bilaterally in the insular cortex (BA 20/21 and BA 38), the right inferior temporal gyrus (BA 19/37), the right inferior frontal gyrus (BA 45), the left inferior parietal lobulus (BA 40), the medial temporal gyrus (BA 39) and the right anterior cingulate cortex (BA 24). It is concluded that spinal cord stimulation used as an additional treatment for angina applied at TI modulates regional cerebral blood flow in brain areas known to be associated with nociception and in areas associated with cardiovascular control.
α7 and α8 Nicotinic Receptor Subtypes Immunopurified from Chick Retina have Different Immunological, Pharmacological and Functional Properties
Authors: Gotti Cecilia , Moretti Milena , Maggi Roberto , Longhi Renato , Hanke Wolfang , Klinke Nicole , Clementi Francesco
Published: April 2006

Nicotinic receptors are present in the chick retina, but their structure and functional characteristics are still unclear. Using anti‐α7 and anti‐α8 subunit‐specific antibodies, we immunopurified the α7 and α8 subtypes of chick retina neuronal nicotinic receptors. When analysed by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis, the two purified subtypes consistently showed a similar peptide composition characterized by the presence of two major peptides of Mr 58 ± 1 and 54 ± 1 kDa, and two minor peptides of 67 and 61 ± 1 kDa. In the α7 subtype, the 58 kDa peptide was recognized by anti‐α7 but not by anti‐α8 antibodies; in the α8 subtype, the 58 kDa peptide was recognized only by anti‐α8 antibodies. The α7 subtype had a single class of [125]a‐bungarotoxin binding sites with a KD value of 1.2 nM, whereas the purified α8 subtype had two classes of binding sites, one with a KD of 5.5 nM and the other with very high affinity (KD 52 pM), but present in only 8% of the receptors. Competition binding experiments also showed the presence on the α8 subtype of highand low‐affinity classes of binding sites; the affinity for cholinergic drugs of the former was greater than that of the single class present on the α7 subtype. When reconstituted in planar lipid bilayers, both subtypes formed ligand‐gated cation channels with major conductance levels of 42 and 52 pS but with different lifetimes; the two channels were activated by agonists and blocked by d‐tubocurarine and the glycinergic antagonist strychnine. In line with the binding data, the reconstituted α8 subtype had greater agonist sensitivity than the α7 subtype.
Regulation of Rat Neuronal Voltage‐dependent Calcium Channels By Endogenous p21‐ras
Authors: Fitzgerald E. M. , Dolphin A. C.
Published: April 2006

Influx of calcium through voltage‐dependent calcium channels (VDCCs) has been implicated in the processes of cell growth and differentiation. Various signalling proteins, including nerve growth factor (NGF), p21–ras and src tyrosine kinases, have been suggested to have a role in the regulation of neuronal VDCCs. Using the whole‐cell patch‐clamp technique we have investigated the role of endogenous p21–ras in the regulation of VDCCs in primary cultured dorsal root ganglion (DRG) neurons obtained from neonatal rats. Neutralization of endogenous p21–ras by microinjection of p21–ras antibody (Y13–259) reduced the maximum peak barium current, Imax whereas microinjection of oncogenic p21–K‐ras increased the current. Thus, endogenous p21–ras is involved in the tonic regulation of calcium currents in these cells. lntracellular application of a phosphopeptide, Trk490, which prevents the binding of the adaptor protein shc to the activated NGF receptor, so blocking p21–ras activation, reduced Imax. Similarly, deprivation of NGF by overnight incubation in NGF‐free medium also reduced ImaX, Together, these results suggest that NGF receptor tyrosine kinase activation of p21–ras is likely to be involved in the tonic regulation of VDCCs in DRG neurons. Deprivation of NGF combined with microinjection of p21–ras antibody (Y13–259), however, caused an even greater reduction of Imax. Thus, NGF activation can only partially explain the regulation of these currents by endogenous p21–ras. Src tyrosine kinases have been suggested to activate p21–ras. In DRG neurons, microinjection of purified src tyrosine kinase, pp60c‐src, increased Imax in these cells. However, co‐microinjection of pp60c‐src with Y13–259 antibody prevented the increase in Imax, implying that pp60c‐src can also regulate calcium currents via the activation of endogenous p21–ras. Further support for the involvement of tyrosine kinases in VDCC regulation was provided by the application of the general tyrosine kinase inhibitor, genistein, which also reduced Imax, Thus, VDCCs in rat DRG neurons appear to be tonically up‐regulated by endogenous p21–ras. This effect appears largely to involve NGF receptor tyrosine kinase activation of p21–ras. In addition, src tyrosine kinase may also regulate VDCCs, possibly via p21–ras.
Neurotrophin‐3 Delivered Locally via Fibronectin Mats Enhances Peripheral Nerve Regeneration
Authors: Sterne G. D. , Brown R. A. , Green C. J. , Terenghi G.
Published: April 2006

A better understanding of the mechanisms of nerve regeneration could improve the outcome of surgical nerve repair. We have previously shown that axonal regeneration is increased by nerve growth factor. Neurotrophin‐3 (NT‐3) belongs to the same family as nerve growth factor but acts on a distinct neuron subpopulation. As little is known about its role following nerve injury, we have investigated the effect of NT‐3 delivered via fibronectin mats, previously shown to support nerve regeneration comparable to nerve grafts. NT‐3 stimulation (0.1–1000 ng/ml) of neurite extension from embryonic chick dorsal root ganglia in vitro has shown that fibronectin can bind and release bioactive NT‐3. Fibronectin mats impregnated with NT‐3 (500 ng/ml) were grafted into 1 cm sciatic nerve defects in adult Lewis rats. Plain mats were used as controls. Computerized quantification of penetration distance, volume of axonal regeneration and myelinated fibre counts was undertaken using immunostaining for axonal markers (growth‐associated protein 43, calcitonin gene‐related peptide, substance P, vasoactive intestinal peptide and neuropeptide tyrosine), or S100 orthionine blue staining up to 8 months postoperatively. The maximal effect of NT‐3 occurred at day 15, when for GAP43‐immunostained axons both penetration distance (NT‐3, 6.10 ± 0.42 mm; control, 4.11 ± 0.41 mm; P <0.01) and staining area (NT‐3, 0.137 ± 0.012 mm2; control, 0.077 ± 0.018 mm2; P < 0.05) were significantly increased. Similar results were found for each neuronal subpopulation investigated. By 8 months after repair, the NT‐3 group supported a significantly greater number of myelinated axons (NT‐3, 7003 ± 402; control, 4932 ± 725; P < 0.05) of similar diameter and g‐ratio to controls. These results demonstrate the contribution of NT‐3 to the increase of nerve regeneration promoted by growth factors.
Organization and Development of Facial Motor Neurons in the Kreisler Mutant Mouse
Authors: McKay Ian J. , Lewis Julian , Lumsden Andrew
Published: April 2006

The adult facial nerve contains the axons from two populations of efferent neurons. First, the branchiomotor efferent neurons that innervate the muscles of the second arch. These neurons project out of the hindbrain in the motor root and form the facial motor nuclei. Second, the preganglionic efferent neurons that innervate the submandibular and pterygopalatine ganglia. These neurons project from the hindbrain via the intermediate nerve and form the superior salivatory nucleus. The motor neurons of the facial nerve are known to originate within rhombomeres 4 and 5. In the kreisler mouse mutant there is a specific disruption of the hindbrain ‐rhombomeres 5 and 6 appear to be absent. To investigate changes in the organization of the facial motor neurons in this mutant, we have used lipophilic dyes to trace the facial motor components both retrogradely and anterogradely. As expected, facial motor neurons are missing from rhombomere 5 in this mutant. In addition, the loss of these neurons correlates with the specific loss of the superior salivatory nucleus. In contrast, the branchiomeric neurons, that originate in rhombomere 4, appear to develop normally. This includes the caudal migration of their cell bodies forming the genu of the facial nerve. Our studies confirm that rhombomeres are critical to hindbrain development and that they are the fundamental unit at which motor neurons are specified.
Temporo‐frontal Disconnection Impairs Visual‐visual Paired Association Learning but not Configural Learning in Macaca Monkeys
Authors: Gutnikov Sergei A. , Ma Yuan‐Ye , Gaffan David
Published: April 2006

Cynomolgus monkeys were tested in two computer‐controlled visual associative memory tasks. The monkeys chose between visual objects on a screen by touching one. In the configural learning task one correct object and one wrong object were presented in each trial. Each of these two objects was composed of two coloured alphanumeric characters abutted together. The designation of the objects as ‘correct’ or ‘wrong’ followed a configural rule: e.g. if AB and CD are correct objects then AD and CB are wrong. In the paired association learning task in each trial three spatially separate objects (single alphanumeric characters) were presented. The central object was an instruction cue and the designation of the side objects as ‘correct’ or ‘wrong’ choices followed a paired association rule: e.g. if A, C and B are presented (C in the centre) then A is correct and B is wrong: however, if A, D and C are presented then C is correct and A is wrong. Disrupting the direct cortico‐cortical interaction between the inferior temporal cortex and the prefrontal cortex by uncinate fascicle transection led to a learning deficit in the paired association task but not in the configural task. These results suggest that the uncinate fascicle facilitates visual‐visual associative learning only in the specific case where a visual object acts as an instruction cue to guide the conditional choice of another, spatially separate object, and they support the evidence for a specific role of the uncinate fascicle in the learning of conditional tasks with visual instruction cues.
Differential Display Reveals Transcriptional Up‐regulation of the Motor Molecules for Both Anteroarade and Retrograde Axonal Transport During Nerve Regeneration
Authors: Su Q. N. , Namikawa K. , Toki H. , Kiyama H.
Published: April 2006

RNA fingerprinting using an arbitrary primed polymerase chain reaction was carried out to compare differences in expression of mRNAs between axotomized and normal hypoglossal motoneurons in the mouse. In this survey, the kinesin light chain (KLC) was identified as a nerve injury‐associated molecule. This was also confirmed by in situ hybridization using hemihypoglossal nerve‐transected brain sections. In order to identify the exact species of molecules belonging to the KLC family, in situ hybridization was carried out with oligonucleotide probes specific to rat KLC A, KLC B and KLC C, using the rat hypoglossal nerve injury model. In addition, expression of both ubiquitous and neuron‐specific kinesin heavy chain and cytoplasmic dynein which is a retrograde motor, was also examined. Expression of all the members of the KLC (A‐C) family and dynein was up‐regulated during nerve regeneration, whereas the abundant expression of the neuron‐specific KHC mRNA was not changed. The present results indicate that the molecules associated with both anterograde and retrograde axonal transport are up‐regulated in their expression during efferent motor nerve regeneration, suggesting that the retrograde transport of growth factors and anterograde transport of vesicles, providing membrane material, could be increased during motor nerve regeneration.
The Copper Chelator d‐Penicillamine Delays Onset of Disease and Extends Survival in a Transgenic Mouse Model of Familial Amyotrophic Lateral Sclerosis
Authors: Hottinger Andreas F. , Fine Eric G. , Gurney Mark E. , Zurn Anne D. , Aebischer Patrick
Published: April 2006

A subpopulation of familial cases of amyotrophic lateral sclerosis has been linked to mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). There is in vitro evidence that certain SOD1 mutants, in addition to their normal dismutation function, show increased ability of the enzyme to act as a peroxidase. This reaction is sensitive to inhibition by copper chelators. To test this hypothesis in vivo, we administered the copper chelator d‐penicillamine to a transgenic mouse model of familial amyotrophic lateral sclerosis overexpressing a mutated form of human SOD1. We demonstrate that oral administration of d‐penicillamine is able to delay the onset of the disease and extend the survival of these mice. Histological studies also showed a decreased loss of facial motor neurons in d‐penicillamine‐treated transgenic mice, corroborating the slower evolution of the disease in these animals. These results suggest that copper chelators may benefit patients with familial amyotrophic lateral sclerosis linked to mutations in the SOD1 gene.
Overexpression of Nerve Growth Factor in Skin Increases Sensory Neuron Size and Modulates Trk Receptor Expression
Authors: Goodness Thomas P. , Albers Kathryn M. , Davis Frankie E. , Davis Brian M.
Published: April 2006

Sensory neuron development and differentiation is dependent on a family of growth factors known as neurotrophins. Neurotrophins modulate neuron development via trk tyrosine kinase receptor proteins trkA, trkB and trkC. To determine how elevated levels of a target‐derived neurotrophin might affect neuronal differentiation, we analysed trk expression in the trigeminal ganglion of transgenic mice that overexpressed nerve growth factor (NGF) in the skin. increased levels of NGF caused a five‐fold increase in neurons expressing trkA mRNA and a two‐fold increase in neurons expressing trkC. In control mice, cell size distributions of neuronal subpopulations expressing each trk mRNA showed the three subpopulations distributed over a narrow, overlapping range. In contrast, cell size distribution in NGF‐transgenic mice was significantly divergent due in large part to hypertrophy of trkA neurons and, to a lesser extent, trkC neurons. In addition, we examined neurons that bound the isolectin B4 from Bandeiraea simplicifolia (BS‐IB4) because most of these neurons do not express any trk receptor in the adult. There was a significant increase in the size of BS‐IB4–positive neurons in transgenic mice; however, there was no increase in their number. These studies indicate that an increased level of target‐derived NGF affects the development of sensory neurons that in the adult express trkA or trkC, as well as neurons that do not express trk receptors.
Postnatal Changes in Electrophysiological Properties of Rat Nucleus Tractus Solitarii Neurons
Authors: Vincent Anne , Tell Fabien
Published: April 2006

Whole‐cell recordings in brainstem slices revealed postnatal changes in passive and firing properties in the rat caudal nucleus tractus solitarii (cNTS) neurons. Membrane potential, threshold for Na+ spike and degree of sag were unchanged during development. In the adult, the rheobase was twice that found at birth. The input resistance decreased over the period studied, while time constants declined markedly after the third postnatal week. At all postnatal ages, Na+‐dependent action potentials (APs) were elicited in response to depolarization. Nevertheless, AP duration gradually decreased by 40% over the developmental period studied. Spike amplitude was smaller at birth than at any other ages and reached a peak two weeks after birth. At all ages, Na+‐dependent APs were blocked by application of tetrodotoxin. Full APs were replaced by an initial slow oscillation in young cells and by oscillations in older cells. The TTX‐resistant oscillations were altered by cobalt (2 mM) and cadmium (100 μM). The spike afterhyperpolarization (AHP) was not altered during development, but was observed in less neurons in adult cells when measured at a holding potential of ‐60 mV. Neurons were subdivided into one of three classes based on their responses to a hyperpolarizing prepulse: 1) post‐inhibitory rebound (PIR) cells, 2) delayed excitation (DE) cells and 3) NON cells expressing neither PIR nor DE. The relative proportions of different cell types varied with age. The mean maximum duration of DE increased three times. Voltage‐clamp experiments revealed that the DE was due to the activation of an A‐current. In addition, a three‐fold increase in its inactivation rate was observed postnatally. The physiological significance of these results is discussed.
Relations Between Long‐term Synaptic Modifications and Paired‐pulse Interactions in the Rat Neocortex
Authors: Volgushe Maxim , Voronin Leon L. , Chistiakova Marina , Singer Wolf
Published: April 2006

The phenomenon of paired‐pulse facilitation (PPF) was exploited to investigate the role of presynaptic mechanisms in the induction and maintenance of long‐term synaptic plasticity in the neocortex. Long‐term potentiation (LTP) and depression (LTD) were induced without afferent activation by applying tetani of intracellular pulses. Our results show that synaptic modifications closely resembling LTP and LTD can be induced by postsynaptic activation alone. The polarity of these synaptic modifications depends on initial properties of the input, as indicated by a correlation between initial PPF ratio and post‐tetanic amplitude changes: inputs exhibiting strong PPF, which might be associated with low release probability tend to be potentiated, while inputs with small PPF are more likely to show depression. Maintenance of both LTP and LTD involve presynaptic mechanisms, as indicated by changes in PPF ratios and in failure rate after LTP or LTD induction. Presynaptic mechanisms could include changes in release probability and/or in the number of active release sites. Because induction was postsynaptic, this supports the notion of a retrograde signal. The relative contribution of pre‐ and postsynaptic mechanisms in the maintenance of long‐term synaptic modifications depends on the initial state of the synaptic input and on LTP magnitude. PPF changes were especially pronounced in inputs which had initially high PPF and underwent strong potentiation. Since LTP and LTD are associated with changes of PPF ratios these synaptic modifications do not only alter the gain but also the temporal properties of synaptic transmission. Because of the LTP associated reduction of PPF, potentiated inputs profit less from temporal summation, favouring transmission of synchronized, low frequency activity.
Glutamatergic Modulation of Cortical Acetylcholine Release in the Rat: A CombinedIn VivoMicrodialysis, Retrograde Tracing and lmmunohistochemical Study
Authors: Giovannini M. G. , Giovannelli L. , Bianchi L. , Kalfin R. , Pepeu G.
Published: April 2006

The microdialysis technique with one or two probes was used to investigate the modulation of cortically projecting cholinergic neurons by glutamatergic input in the ratin vivo. Male albino Wistar rats (250–300 g) were used. Under chloral hydrate anaesthesia microdialysis membranes were positioned in the parietal cortex, nucleus basalis magnocellularis (NBM) or medial septum. Acetylcholine was assayed using high‐performance liquid chromatography (HPLC) with electrochemical detection while GABA was detected using HPLC with fluorimetric detection after derivatization of the amino acid with ephthalaldehyde. Septo‐cortical neurons were retrogradely labelled with fluoro‐gold. Double labelling with choline acetyltransferase (ChAT) immunoreactivity was performed to identify these neurons. Our main findings were that: (i) icv. administration of the NMDA antagonist 3–((R)‐2‐carboxypiperazin‐4‐yl)‐propyl‐1‐phosphonic acid (CPP, 1–5 nmol) increased cortical acetylcholine outflow; (ii) local administration of CPP (100 μM) to the cortex had no effect on cortical acetylcholine outflow: (iii) local administration of CPP (100 μM) to the NBM decreased cortical acetylcholine outflow; (iv) local administration of CPP (100–200 μM) to the septum increased cortical GABA and acetylcholine outflow; (v) administration of muscimol to the septum prevented the effect of CPP on cortical acetylcholine outflow: (vi) retrograde tracing with fluoro‐gold labelled cell bodies in the medial septum; (vii) septal fluoro‐gold‐positive neurons were not ChAT‐immunoreactive. Ourin vivoneurochemical results, in combination with retrograde tracing and immunohistochemistry, indicate that the cortically projecting cholinergic system is indirectly regulated by a glutamatergic input via a polysynaptic GABAergic circuitry located in the septum.
Antidepressant Drugs Inhibit a Gial 5‐Hydroxytryptamine Transporter in Rat Brain
Authors: Bel Nuria , Figueras Gloria , Vilaró M. Teresa , Suñol Cristina , Artigas Francesc
Published: April 2006

We assessed the role of glial cells in the uptake of serotonin (5‐hydroxytryptamine, 5‐HT). Primary cultures of rat and mouse cortical astrocytes took up and deaminated 5‐HT. The antidepressants citalopram, clomipramine, fluoxetine, fluvoxamine, paroxetine and sertraline inhibited this process. The presence of the mRNAs for the 5‐HT transporter and monoamine oxidase‐A (MOA‐A) was established in cultured astrocytes and in adult rat brain areas with (midbrain and brainstem) and without (frontal cortex) serotonergic cell bodies after reverse transcription‐polymerase chain reaction and hybridization with probes complementary to the cloned neuronal 5‐HT transporter and MAO‐A. To examine in vivo the role of astrocytes in the elimination of 5‐HT from the extracellular brain space, 5‐HT was perfused through dialysis probes implanted in the frontal cortex of conscious rats and its concentration was measured at the probe outlet. Tissue 5‐HT recovery was dose‐dependently inhibited by the concurrent perfusion of citalopram, fluoxetine and paroxetine, showing that it essentially measured uptake through the high‐affinity 5‐HT transporter. Rats lesioned with 5,7‐dihydroxytryptamine (5,7‐DHT; 88% reduction of tissue 5‐HT) displayed tissue 5‐HT recovery slightly higher than sham‐operated rats (55 ± 2 vs. 46 ± 3%, P < 0.001), a finding perhaps attributable to the astrogliosis induced by 5,7‐DHT denervation. Rats lesioned with 6‐hydroxydopamine showed tissue 5‐HT uptake similar to controls, suggesting negligible reuptake of 5‐HT by catecholaminergic terminals. These results are consistent with the presence of a glial component of 5‐HT uptake in the rodent brain, sensitive to antidepressants, which takes place through a 5‐HT transporter very similar or identical to that present in neurons.
Neurites of Period‐expressing PDH Cells in the Fly's Optic Lobe Exhibit Circadian Oscillations in Morphology
Authors: Pyza E. , Meinertzhagen I. A.
Published: April 2006

Circadian rhythms have been shown both in the expression of the period (per) gene in ‘lateral neurons’ and in cells of the outermost neuropil, or lamina, of the fly's optic lobe. Some lateral neurons also exhibit PDH peptide‐like immunoreactivity, arborizing widely throughout the optic lobe. Using confocal microscopy in the housefly, we analysed the size and spacing of PDH neurite varicosities, sites of possible peptide release exhibiting circadian rhythmicity. During the subjective day in constant darkness, there were fewer, larger varicosities than during subjective night. The endogenous rhythm was masked by the light exposure that occurred under a day‐night cycle and continuous light conditions. Our findings indicate that PDH neurites convey circadian information out from the pacemaker, where they could regulate the circadian rhythms that have been described in the lamina, possibly via cyclical release of their peptide.
Functional Properties of Neuronal Nicotinic Acetylcholine Receptor Channels Expressed in Transfected Human Cells
Authors: Ragozzino D. , Fucile S. , Giovannelli A. , Grassi F. , Mileo A. M. , Ballivet M. , Alemà S. , Eusebi F.
Published: April 2006

To study how subunit composition affects the functional properties of neuronal nicotinic acetylcholine receptors (nAChRs), we examined the behaviour of acetylcholine (ACh)‐induced single‐channel currents in human BOSC 23 cells transiently transfected with various subunit cDNA combinations. For all nAChRs examined (chick and rat α3β4, chick α<3/β2, α4β2, α4β4, α7and α8, expression levels were high enough to allow measurements of acetylcholine‐evoked whole‐cell currents and nicotine‐elicited Ca2+ transients as well as the functional characterization of nAChR channels. Unitary acetylcholine‐evoked events of α8 nAChR had a slope conductance of 23 pS, whereas two conductance classes (19–23 and 32–45 pS) were identified for all other nAChR channels. The mean channel open times were significantly longer for homomeric α7 and α8 nAChRs (6–7 ms) than for heteromeric nAChRs (1–3 ms), with the exception of α3α4nAChRs (8.4 ms for rat, 7 ms for chick). At least two species of heterologously expressed nAChRs (α3α4and α3α2) exhibited single‐channel characteristics similar to those reported for native receptors. The variety of nAChRs channel conductance and kinetic properties encountered in human cells transfected with nAChR subunits contributes to the functional diversity of nAChRs in nerve cells.
Release of Serotonin in the Rat Locus Coeruleus: Effects of Cardiovascular, Stressful and Noxious Stimuli
Authors: Singewald Nicolas , Kaehler Stefan , Hemeida Ramadan , Philippu Athineos
Published: April 2006

To investigate the function of serotonergic neurons within the locus coeruleus, this brain nucleus of conscious, freely moving rats was superfused with artificial cerebrospinal fluid through a push‐pull cannula and the extracellular concentration of serotonin was determined in the superfusate. Serotonin release was increased by depolarization with veratridine (5 μM) or 80 mM K+, while superfusion with tetrodotoxin (1 μM) or systemic administration of 8–hydroxy‐2–(di‐n‐propylamino)tetralin substantially diminished the release rate of serotonin in the locus coeruleus. The pressor response to intravenous infusion of noradrenaline (4 μg/kg/min) was associated with a pronounced increase in the release rate of serotonin. Superfusion of the locus coeruleus with tetrodotoxin (1 μM) abolished the increase in serotonin release evoked by the pressor response. A fall of blood pressure produced by intravenous administration of nitroprusside (150 μg/kg/min) or chlorisondamine (3 mg/kg) diminished the release rate of serotonin. Immobilization, noise (95 dB) or tail pinch increased the release of serotonin in the locus coeruleus and slightly elevated blood pressure. Chlorisondamine abolished the rise in blood pressure elicited by tail pinch without influencing the increased serotonin release. Tail pinch‐induced serotonin release was abolished by superfusion with tetrodotoxin. The findings demonstrate that neuronal serotonin release in the locus coeruleus responds to cardiovascular and sensory stimuli, suggesting a function of serotonergic neurons in central blood pressure regulation, as well as in the modulation of locus coeruleus activity by stress and noxious stimuli.
Electrophysiological Effects of Temporary Deafferentation on Two Characterized Cell Types in the Nucleus Gracilis of the Rat
Authors: Panetsos Fivos , Nuñez Angel , Avendaño Carlos
Published: April 2006

Single‐ and multiunit recordings were made in the nucleus gracilis of anaesthetized rats in order to study the characteristics of the responses to natural cutaneous stimulation before and during local anaesthetic‐induced deafferentation. Two types of cells were found which exhibited different electrophysiological features at rest and in response to stimulation of their receptive fields (RFs). Low‐frequency (LF) neurons (77%) had very low spontaneous activity, and most could be antidromically activated from the medial lemniscus. High‐frequency (HF) cells (23%) had a much higher spontaneous discharge rate, with shorter spike duration, and did not project through the lemniscus. Both cell types generated phasic responses with similar latencies following cutaneous stimulation. Recordings of lemniscal axons had similar characteristics to those of LF neurons. Within minutes after anaesthetizing the functional centre of the RF, the LF and HF cells displayed new RFs, and enhanced responses to stimuli delivered at the periphery of the original fields. Firing rates increased during anaesthesia, but only in LF cells. Using a paired‐stimulation paradigm, many LF neurons displayed during anaesthesia a decrease of the normal inhibition that the conditioning stimulus evoked on the responses to the test stimulus; the opposite effect was observed in all HF cells. These results suggest that (i) LF neurons correspond to thalamic projection cells, and HF neurons may be inhibitory interneurons; (ii) by disinhibiting LF (but not HF) cells, temporary deafferentation may increase neuronal responsiveness to peripheral stimulation, and thus contribute to reveal new RFs, and (iii) these changes in the nucleus gracilis may partly account for the reorganization of representational maps at higher levels of the somatosensory pathways.
Interneurons in the Hippocampal Dentate Gyrus: an In Vivo intracellular Study
Authors: Sik Attila , Penttonen Markku , Buzsáki György
Published: April 2006

Interneurons in the dentate area were characterized physiologically and filled with biocytin in urethane‐anaesthetized rats. On the basis of axonal targets the following groups could be distinguished. (i) Large multipolar interneurons with spiny dendrites in the deep hilar region densely innervated the outer molecular layer and contacted both granule cells and parvalbumin‐positive neurons (hilar interneuron with perforant pathway‐associated axon terminals; HIPP cells). (ii) A pyramidal‐shaped neuron with a cell body located in the subgranular layer innervated mostly the inner molecular layer and the granule cell layer (hilar interneuron with commissural‐associational pathway‐associated axon terminals; HICAP cell). It contacted both granule cells and interneurons. Axon collaterals of HIPP and HICAP neurons covered virtually the entire Septo‐temporal extent of the dorsal dentate gyrus. (iii) Calbindin‐immunoreactive neurons with horizontal dendrites in stratum oriens of the CA3c region gave rise to a rich axon arbor in strata oriens, pyramidale and radiatum and innervated almost the entire extent of the dorsal hippocampus, with some collaterals entering the subicular area (putative trilaminar cell). (iv) Hilar basket cells innervated mostly the granule cell layer and to some extent the inner molecular layer and the CA3c pyramidal layer. HIPP and trilaminar interneurons could be antidromically activated by stimulation of the fimbria. Only the HICAP cells could be monosynaptically discharged by the perforant path input. All interneurons examined showed phase‐locked activity to the extracellularly recorded theta/gamma oscillations or to irregular dentate electroencephalogram spikes. These observations indicate that the interconnected interneuronal system plays a critical role in coordinating population activity of the dentate gyrus and Ammon's horn.
Effects of a Cognition‐enhancer, Linopirdine (DuP 996), on M‐type Potassium Currents (IK(M)) Some Other Voltage‐ and Ligand‐gated Membrane Currents in Rat Sympathetic Neurons
Authors: Lamas J. Antonio , Selyanko A. A. , Brown D. A.
Published: April 2006

Linopirdine is a cognition enhancer which augments depolarization‐induced transmitter release in the cortex and which is under consideration for potential treatment of Alzheimer's disease. It has previously been reported to inhibit M‐type K+ currents in rat hippocampal neurons. In the present experiments we have tested its effect on whole‐cell M‐currents and single M‐channels, and on a range of other membrane currents, in dissociated rat superior cervical sympathetic ganglion cells. Linopirdine inhibited the whole‐cell M‐current with an IC50 of 3.4 μM and blocked M‐channels recorded in excised outside‐out membrane patches but not in inside‐out patches. This suggests that linopirdine directly blocks M‐channels from the outside. It was much less effective in inhibiting other voltage‐gated potassium currents [delayed rectifier (IK(v)), IC50 63 μM; transient (IA) current, IC50 69 μM] and produced no detectable inhibition of the fast and slow Ca2+‐activated K+ currents Ic and IAHP or of a hyperpolarization‐activated cation current (IQ/Ih), at 10–30 μM. However, it reduced acetylcholine‐activated nicotinic currents and GABA‐activated Cl‐ currents with IC50 values of 7.6 and 26 μM respectively. It is concluded that linopirdine shows some 20–fold selectivity for M‐channels among different K+ channels but can also block some transmitter‐gated channels. The relationship between M‐channel block and the central actions of linopirdine are discussed.
Pharmacological and Physiological Characterization of Murine Homomeric β3 GABAA Receptors
Authors: Wooltorton Julian R. A. , Moss Stephen J. , Smart Trevor G.
Published: April 2006

γ‐Aminobutyric acid (GABAa) receptor β3 subunits were expressed in Xenopus laevis oocytes and studied using two‐electrode voltage clamp. Injected oocytes exhibited an increased resting membrane conductance and more depolarized membrane potentials compared to uninjected control cells. Oocytes expressing β3 subunits were insensitive to GABA and muscimol, but pentobarbitone increased the membrane conductance in a concentration‐dependent manner. The membrane current response to pentobarbitone reversed at the Cl−equilibrium potential and at relatively high concentrations (>500 μM), a rebound CI− current was induced following the removal of pentobarbitone. In transfected human embryonic kidney (HEK) cells, the rebound current amplitude was reduced by desensitizing the β3 receptor with increased durations of ligand application. Both picrotoxin (0.5 nM to 10 μM) and Zn2+ (10 nM to 100 μM) reduced the resting membrane conductance for β3 cDNA‐injected oocytes. These oocytes were insensitive to flurazepam (5 μM) and alphaxalone (10 μM), but responded with increased membrane conductance to propofol (10 μM) and pregnanolone (50 nM to 5 μM). The antagonists, bicuculline (10 μM) and strychnine (50 nM to 100 μM), also induced conductance increases in a concentration dependent manner; however, glycine (1 mM) was inactive. It was concluded that β3 subunits form spontaneously opening ion channels that can be up‐regulated by some allosteric modulators, principally by pentobarbitone and propofol and, surprisingly, by bicuculline and strychnine, whilst picrotoxin and Zn2+ acted as antagonists. Computer modelling of some kinetic schemes was used to describe the rebound current observed in transfected HEK cells. This indicated that pentobarbitone, after modulation of the conductance, is potentially capable of further binding to the β3 receptor complex ‘driving’ the receptor into one or more desensitized states. This phenomenon may be of some importance for native neuronal GABAA receptors, where pentobarbitone can also evoke rebound current activation.
Neurosteroids: Expression of Functional 3β‐Hydroxysteroid Dehydrogenase by Rat Sensory Neurons and Schwann Cells
Authors: Guennoun R. , Schumacher M. , Robert F. , Delespierre B. , Gouézou M. , Eychenne B. , Akwa Y. , Robel P , Baulieu E. E.
Published: April 2006

Steroids which are synthesized within the nervous system, such as progesterone, have been termed ‘neurosteroids’. Levels of progesterone are much larger in peripheral nerves of rats and mice than in plasma, and persist after removal of the steroidogenic endocrine glands. Schwann cells are a source of progesterone: when isolated from embryonic dorsal root ganglia, they can synthesize progesterone from pregnenolone, the obligate precursor of all steroids. Locally produced progesterone has been shown to play an important role in myelination of peripheral nerve. We show here that sensory neurons from embryonic dorsal root ganglia also express 3β‐hydroxysteroid dehydrogenase and can convert [3H]pregnenolone to [3H]progesterone. Moreover, when cultured under different conditions and incubated for 24 h in the presence of 100 nM [3H]pregnenolone, they produce 5–10 times more [3H]progesterone than Schwann cells. The conversion of pregnenolone to progesterone by neurons is further increased by a diffusible factor produced by Schwann cells. Sensory neurons can also metabolize progesterone to 5α‐dihydroprogesterone, but unlike Schwann cells, they do not produce 3α,5α‐tetrahydroprogesterone, a potent positive allosteric modulator of γ‐aminobutyric acid type A receptors. We also show that cells isolated from the adult nervous system still have the capacity to convert [3H]pregnenolone to progesterone and its 5α‐reduced metabolites: neurons and Schwann cells purified from dorsal root ganglia of 6 week old male rats show a similar pattern of pregnenolone metabolism to cells isolated from 18 day old embryos. These findings further support the important role of progesterone in the development and regeneration of the peripheral nervous system.
Interneurons Immunoreactive for Vasoactive Intestinal Polypeptide (VIP) are Extensively Innervated by Parvalbumin‐Containing Boutons in Rat Primary Somatosensory Cortex
Authors: Staiger Jochen F. , Freund Tamás F. , Zilles Karl
Published: April 2006

Sensory perception results from the synchronized action of large ensembles of cortical neurons. Receptive field properties of such neurons in sensory areas strongly depend on circuits utilizing the inhibitory amino acid transmitter γ‐aminobutyric acid (GABA). GABAergic neurons often co‐localize neuropeptides and/or calcium‐binding proteins in a cell‐type specific manner. We have taken advantage of this fact to study the synaptic circuitry involving presynaptic parvalbumin‐containing boutons (originating from horizontally extensive basket cells) and postsynaptic VlP‐immunoreactive GABAergic targets which mostly have a vertically oriented axonal field. Abundant appositions between parvalbumin‐immunoreactive boutons and all VIP‐stained neurons were observed at the light microscopic level. The numbers of contacts ranged between three and well over 20 for single VIP cells. The higher numbers were especially frequent in the supragranular and granular layers contacting the numerous bipolar, as well as multipolar VIP cells located there; but the VlP‐immunoreactive neurons in the infragranular layers were also targeted by parvalbumin‐immunoreactive boutons without exception, albeit in more variable, mostly lower numbers. Correlated electron microscopic investigations revealed that virtually all of these light microscopically observed appositions resembled symmetric synaptic specializations. The vast majority were located on the soma or proximal dendrites of the VIP‐positive neurons. Since pyramidal cells, in turn, represent a major target for the parvalbumin and VIP synapses, the activation of these synapses may lead to coherent oscillations providing the necessary clock function to synchronize pyramidal cell discharges, both across and within cortical columns.
Evidence That Agrin directly Influences Presynaptic Differentiation at Neuromuscular Junctions In Vitro
Authors: Campagna Jason A. , Ruegg Markus A. , Bixby John L.
Published: April 2006

The synaptic protein agrin is required for aspects of both pre‐ and postsynaptic differentiation at neuromuscular junctions. Although a direct effect of agrin on postsynaptic differentiation, presumably through the MuSK receptor, is established, it is not clear whether agrin directly affects the presynaptic nerve. To provide evidence on this point, we used anti‐agrin IgG to disrupt agrin function in chick ciliary ganglion (CG) neuron/myotube cocultures. In cocultures grown in the presence of 200 μg/ml anti‐agrin IgG, clustering of acetylcholine receptors (AChRs), extracellular matrix proteins, and the synaptic vesicle protein synaptotagmin (syt) at nerve‐muscle contacts was inhibited. Syt clustering was still inhibited in the presence of 100 μg/ml blocking antibody, while the postsynaptic clustering of AChRs, heparan sulphate proteoglycan, and s‐laminin was retained. Additionally, in CG neurons cultured with COS cells expressing agrin A0B0, which lacks the ability to signal postsynaptic differentiation, syt clustering was induced and this clustering was also blocked by anti‐agrin IgG. Our results demonstrate that agrin function is acutely required for pre‐ and postsynaptic differentiation in vitro, and strongly suggest that agrin is directly involved in the induction of presynaptic differentiation.
Spatial Learning Deficits in Mice with a Targeted Glucocorticoid Receptor Gene Disruption
Authors: Oitzl Melly S. , de Kloet E. Ron , Joëls Marian , Schmid Wolfgang , Cole Timothy J.
Published: April 2006

Previous studies in rats using the Morris water maze suggested that the processing of spatial information is modulated by corticosteroid hormones through mineralocorticoid and glucocorticoid receptors in the hippocampus. Mineralocorticoid receptors appear to be involved in the modulation of explorative behaviour, while additional activation of glucocorticoid receptors facilitates the storage of information. In the present study we used the water maze task to examine spatial learning and memory in mice homozygous and heterozygous for a targeted disruption of the glucocorticoid receptor gene. Compared with wild‐type controls, homozygous and heterozygous mice were impaired in the processing of spatial but not visual information. Homozygous mutants performed variably during training, without specific platform‐directed search strategies. The spatial learning disability was partly compensated for by increased motor activity. The deficits were indicative of a dysfunction of glucocorticoid receptors as well as of mineralocorticoid receptors. Although the heterozygous mice performed similarly to wild‐type mice with respect to latency to find the platform, their strategy was more similar to that of the homozygous mice. Glucocorticoid receptor‐related long‐term spatial memory was impaired. The increased behavioural reactivity of the heterozygous mice in the open field points to a more prominent mineralocorticoid receptor‐mediated function. The findings indicate that (i) the glucocorticoid receptor is of critical importance for the control of spatial behavioural functions, and (ii) mineralocorticoid receptor‐mediated effects on this behaviour require interaction with functional glucocorticoid receptors. Until the development of site‐specific, inducible glucocorticoid receptor mutants, glucocorticoid receptor‐knockout mice present the only animal model for the study of corticosteroid‐mediated effects in the complete absence of a functional receptor.