bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses to Metabotropic Glutamate Receptor Activation in Cerebellar Purkinje Cells: Induction of an Inward Current
Authors: Staub C. , Vranesic I. , Knöpfel T.
Published: April 2006

The responses to activation of metabotropic glutamate receptors (mGluRs) of Purkinje cells in rat cerebellar slice cultures were investigated using intracellular recordings in single‐electrode voltage‐clamp mode combined with microfluorometric measurements of cytosolic free calcium using fura‐2. Purkinje cells were perfused with saline containing 0.5 μM tetrodotoxin and 10 μM bicuculline and voltage‐clamped at –60 mV. Bath‐applied trans‐(±)‐1‐amino‐1,3‐cyclopentanedicarboxylic acid (t‐ACPD, 50–100 μM), a selective agonist of mGluRs, induced a transient inward current that was followed by an outward current. The response induced by t‐ACPD was not affected by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, up to 40 μM). In contrast, inward currents caused by (RS)‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA, 1–2 μM) were completely abolished, while inward currents caused by quisqualate (0.25 μM) were only partially depressed by CNQX (5–40μM). The inward current induced by t‐ACPD was unaffected by external Ba2+ (1 mM), tetraethylammonium (10 mM) and Cs+ (1 mM), and was associated with an increase in apparent input conductance of the cell membrane. The extrapolated reversal potential of inward currents induced by t‐ACPD was +18 mV while Cl− currents induced by muscimol reversed at –66 mV. Inward currents induced by t‐ACPD, but not those induced by AMPA, were associated with a rise in cytosolic Ca2+ concentration and suppressed by intracellular injection of a calcium chelator. Replacement of external Na+ by choline or Li+ depressed the inward current and resulted in a slower decay of the Ca2+ signal.
Transfer of Function to a Specific Area of the Cortex After Induced Recovery from Brain Damage
Authors: Castro‐Alamancos Manuel A. , Garcia‐Segura Luis M. , Borrell José
Published: April 2006

Different methods of inducing recovery after brain damage and different mechanisms that might mediate the induced recovery have been proposed. One possible mechanism involves the ability of one part of the brain to take over the function of another. We show here in rats that (1) bar‐pressing behaviour to eliminate an aversive stimulus, which becomes dramatically impaired after bilateral lesion of the frontal primary motor ‐ sensory cortex, is recovered when the animals receive an electrical intracranial stimulation in the ventral tegmental nucleus of the brain contingent on an adequate response during performance in the behavioural task, (2) in recovered animals an area in the posterior primary motor – sensory cortex, the hindlimb motor ‐ sensory cortex, shows a 35% increase in the number of fos‐like immunoreactive cells compared to non‐recovered animals, and (3) a bilateral lesion of this area in recovered animals reinstates the impairment in the performance of the behavioural task. These results indicate that an area of the cerebral cortex is able to assume the role of another area after induced recovery from brain damage.
Striatal Graft‐Associated Recovery of a Lesion‐Induced Performance Deficit in the Rat Requires Learning to Use The Transplant
Authors: Mayer E. , Brown V. J. , Dunnett S. B. , Robbins T. W.
Published: April 2006

Peformance in a prelearned choice reaction time task was studied 6 months after surgery in rats with ibotenate‐induced lesions of the striatum either with or without striatal grafts, and in sham‐operated controls. The long postoperative interval allowed full transplant maturation and the establishment of appropriate connections by the transplants. The animals were trained prior to surgery on a visual choice reaction time task which requires that a movement is made away from stimuli signalling reward. The use of multiple measures allowed a thorough analysis of several aspects of the animals' performance. Whilst sham‐operated control animals recovered normal (preoperative) performance rapidly, the lesioned animals had a severe performance deficit. Although the transplanted animals were initially at least as deficient in performance as the lesioned group, repeated testing led to an amelioration of the lesion‐induced deficit according to two distinct measures of spatial bias and reaction time. On a third measure, latency to complete the lateralized movement, the grafted group were initially worse than the lesioned group but repeated testing resulted in significant recovery. These results suggest that postoperative training may help to optimize the efficacy of graft‐induced recovery, and that animals may need to learn to use a transplant in order for it to confer functional benefit in complex prelearned tasks.
Hydrogen Ion Regulation in Rat Cerebellar Granule Cells Studied by Single‐Cell Fluorescence Microscopy
Authors: Pocock G. , Richards C. D.
Published: April 2006

The internal pH (pHi) regulatory mechanisms of individual rat cerebellar granule cells maintained in tissue culture have been investigated using the fluorescent indicator BCECF (2,7’bis carboxyethyl 5,6 carboxyfluorescein) and quantitative fluorescence microscopy. The steady‐state pH, was estimated as 7.27 ± 0.25 in bicarbonate‐buffered media and 7.49 ± 0.35 in HEPES‐buffered media. Buffering power was estimated at about 8 mM/pH unit from the peak alkalinization and acidification transients seen on addition and removal of NH4CI. Bicarbonate did not appear to contribute to the buffering power estimated in this way. Following an acid load imposed by the ammonium prepulse technique, pHi recovered to steady‐state values with first‐order kinetics. Recovery was absolutely dependent upon extracellular sodium and, in about half of the cells tested, bicarbonate ions. In cells that did not require bicarbonate for pHi recovery, amiloride (1 mM) inhibited pHi recovery. Removal of extracellular chloride produced a reversible alkalinization of pHi in a third of the cells studied. This alkalinization persisted even when extracellular sodium had been reduced to zero. Removal of extracellular chloride did not inhibit bicarbonate‐dependent pHi recovery following an acid load. These results are best explained by the existence of three independent pHi regulatory mechanisms: Na+/H+ exchange, Na+/HCO3− cotransport and Cl−/HCO3− exchange.
Extra‐ and Intracellular pH in the Brain During Ischaemia, Related to Tissue Lactate Content in Normo‐and Hypercapnic rats
Authors: Katsura Kenichiro , Asplund Barbro , Ekholm Anders , Siesjö Bo K.
Published: April 2006

The objective of the present study was to assess the relationship between the amount of lactate accumulated during complete ischaemia and the ensuing changes in extra‐ and intracellular pH (pHe and pHi respectively). The preischaemic plasma glucose concentration of anaesthetized rats was varied by administration of glucose or insulin, pHe was determined in neocortex with ion‐sensitive microelectrodes, and tissue lactate and CO2 contents were measured, tissue CO2 tension being known from separate experiments. The experiments were carried out in both normocapnic [arterial CO2 tension (PaCO2) ‐40 mm Hg] and hypercapnic (PaCO2 ‐80 mm Hg) animals. Irrespective of the preischaemic CO2 tension, δpHe was linearly related to tissue lactate content. Depending on the preischaemic glucose concentration, δpHe varied from <0.4 to >1.4 units. The results thus fail to confirm previous results that the changes in pHe describe two plateau functions (δ pHe‐0.5 and 1.1, respectively), with a transition zone at tissue lactate contents of 17–20 mmol kg−1. Changes in pH; given in this study are based on the assumption of a uniform intracellular space. The pH, changed from a normal value of ‐7.0 to 6.5, 6.1 and 5.8 at tissue lactate contents of 10, 20 and 30 mmol kg‐1. The intrinsic (non‐bicarbonate) buffer capacity, derived from these figures, was 23 mmol kg −1 pH−1. Some differences in pH and in HCO3− concentration between extra‐ and intracellular fluids persisted in the ischaemic tissue. These differences were probably caused by a persisting membrane potential in the ischaemic cells.
Cell Survival in the Uncrossed Projection of the Mammalian Retina is Independent of Birthdate
Authors: Reese B. E. , Colello R. J. , Thompson W. F.
Published: April 2006

Naturally occurring cell loss in the retinal ganglion cell population of one eye can be interrupted by removal of the other eye in newborn rodents. Many of the rescued retinal ganglion cells which project ipsilaterally reside in the nasal retina, that part of the retina normally giving rise to primarily crossed optic axons. Their naturally occurring elimination has been attributed to their hypothesized late neurogenesis and the consequent delayed time of arrival of their axons in the target visual nuclei, thereby placing them at a competitive disadvantage with other, early arriving, optic axons. By combining the technique of tritiated thymidine autoradiography with the retrograde axonal transport of horseradish peroxidase in rats that had been enucleated on the day of birth, we report here that rescued cells in the nasal retina which project ipsilaterally are generated at the same time as their neighbours in the temporal retina. Time of genesis does not distinguish them; consequently, their axons should not differ in their arrival times within the target visual nuclei. Since their only obvious anomaly is one of pathway choice at the optic chiasm, their place of arrival, rather than their time, may ultimately determine their naturally occurring elimination.
Lack of Exuberance in Clustered Intrinsic Connections in the Striate Cortex of One‐month‐old Kitten
Authors: Lübke Joachim , Albus Klaus
Published: April 2006

The topographies of the intrinsic tangential connections in layers II ‐ IVab of one‐month‐old and adult cat's striate cortex were compared by plotting the distribution of retrogradely labelled neurons following injection of small amounts of wheat‐germ agglutinin ‐ horseradish peroxidase. In both cortices, the tracer reveals the characteristic cluster‐like arrangement of intrinsic tangential connections. No differences were found between the two age groups in terms of either the numbers of cell clusters, their periodicities or their profiles, nor was there any difference in the lateral extent of the tangential connections. We conclude that one month postnatally, tangentially projecting intrinsic networks in the upper layers of the cat striate cortex lack exuberance and have an adult‐like topography.
Regional Forebrain Noradrenalin Release in Response to Focal and Generalized Seizures Induced by Hippocampal Kindling Stimulation
Authors: Bengzon Johan , Kikvadze Irakli , Kokaia Merab , Lindvall Olle
Published: April 2006

In vivo microdialysis was used to monitor noradrenalin (NA) release in the rat hippocampus, sensorimotor cortex and amygdala in response to seizures induced by electrical kindling stimulation in the hippocampus. Generalized seizures increased NA output in the hippocampus five‐fold above baseline level (as assessed with 2‐min sampling periods). The peak value was seen 2–4 min after onset of seizure activity and baseline was reached after another 6–8 min. In the sensorimotor cortex, there was a seven‐fold increase showing a similar time‐course. Focal hippocampal seizures gave rise to three‐fold and 80% increases above baseline in the hippocampus and sensorimotor cortex, respectively. A unilateral knife transection of the dorsal noradrenergic bundle reduced hippocampal NA release induced by focal seizures by 53%. In animals subjected to 30 stimulus‐evoked seizures with 5‐min intervals (‘rapid kindling’), maximal NA output was observed after the third seizure in both hippocampus (237% increase) and amygdala (122% increase). NA levels tapered off with repeated stimulation and reached baseline after nine stimulations in the hippocampus; in the amygdala, the NA output was still slightly elevated at the end of the stimulation period. These results indicate that there is a general activation of the locus coeruleus system during focal as well as generalized seizures, as evidenced by marked increases in transmitter release from noradrenergic terminals in all forebrain areas studied. NA output in areas exhibiting seizure activity is dependent on impulse flow in locus coeruleus neurons and probably also on local regulatory mechanisms active at the noradrenergic terminal level. The increase in inhibitory noradrenergic transmission in both epileptic and non‐epileptic brain regions may dampen ongoing seizure activity as well as lessen its spread and generalization.
Physiological Characterization of Pretectal Neurons Projecting to the Lateral Geniculate Nucleus in the Cat
Authors: Schmidt M. , Hoffmann K.‐P.
Published: April 2006

Single neurons in the pretectal nucleus of the optic tract and posterior pretectal nucleus were extracellularly recorded in anaesthetized cats and tested for antidromic activation after electrical stimulation of the ipsilateral dorsal lateral geniculate nucleus. Cells were further characterized by their response latencies to electrical stimulation of the optic nerve head and the optic chiasm, and by responses to various visual stimuli. 46 out of 188 neurons (24%) were antidromically activated from the lateral geniculate nucleus at response latencies of 0.6 ‐ 2.6 ms. They had low spontaneous activities and preferred fast‐moving visual stimuli. 29 of the antidromically activated neurons (63%) could be activated from the optic chiasm with response latencies of 4–10 ms. Together with the mean conduction time of 0.8 ms between the optic nerve head and the optic chiasm, this indicates that they receive an indirect retinal input via fast‐conducting Y‐fibres. Sometimes antidromically activated neurons spontaneously showed irregular burst activity. During unidirectional stimulation with a large moving visual stimulus, burst activity became more regular, and interburst intervals and the duration of single bursts decreased. After the stimulus was stopped, interburst intervals slowly increased until prestimulation activity was restored. The response properties of these neurons could reflect the transfer of saccade‐related visual as well as oculomotor signals through the pretectum to the visual thalamus.
Glutamate Toxicity: An Experimental and Theoretical Analysis
Authors: Garthwaite Giti , Williams Geoffrey D. , Garthwaite John
Published: April 2006

In slices of 8‐day‐old rat cerebellum, the lowest concentration of glutamate that induced toxicity (30 min exposure; 90 min recovery) was 100 μM, but the damage only occurred in the outermost regions. As the concentration was raised, the band of necrosis became progressively deeper until, at 3 mM, it was uniform across the slice thickness. At a test concentration of 300 μM, the width of the necrotic band did not change when either the exposure time or the recovery period was varied between 30 min and 3 h. These results are predicted by a theoretical model in which the diffusion of glutamate into brain tissue is countered by cellular uptake of the amino acid, and they argue against the idea that glutamate toxicity is inherently self‐propagating. When slices were examined immediately after exposure (300 μM), a prominent swelling of glial cells was present at the slice surface. Swelling per se did not appear to compromise their uptake function, and the model predicts that cellular swelling, by reducing the rate of diffusion of glutamate, protects against glutamate toxicity. The damage produced by 3 mM glutamate, which was primarily exerted against granule cells, was prevented by W‐methyl‐D‐aspartate (NMDA) receptor blockade, whereas antagonists acting at α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) receptors were ineffective. Under conditions of energy deprivation, the neurotoxic potency of glutamate was markedly enhanced and a normally non‐toxic concentration (30 μM) became maximally toxic towards granule cells. Dark vacuolar degeneration of Purkinje cells was also present, and this could be inhibited by blocking AMPA receptors. The results and theoretical analysis suggest that intact brain tissue is remarkably resistant to glutamate toxicity, chiefly because of the formidable properties of the uptake system. However, under special circumstances, glutamate can become a potent neurotoxin and its toxicity can then involve both NMDA and AMPA receptors.
P21ras Oncogene Protein Selectively Increases Low‐voltage‐activated Ca2+ Current Density in Embryonic Chick Dorsal Root Ganglion Neurons
Authors: Hahnel C. , Gottmann K. , Wittinghofer A. , Lux H.‐D.
Published: April 2006

p21ras protein resembles the α subunit of trimeric G‐proteins, which regulate ion channel function. We now report a modulation of Ca2+ channels in vertebrate sensory neurons by p21ras in addition to its role in cell growth and differentiation. Quantitative microinjection of oncogenic p21‐H‐ras into embryonic chick dorsal root ganglion neurons was performed. After 4 h the current density of the low‐voltage‐activated (LVA; T‐type) Ca2+ channels was increased. However, in contrast to trimeric G‐proteins, which inhibit high‐voltage‐activated (HVA) Ca2+ channels in chick dorsal root ganglion neurons, p21ras did not significantly affect HVA Ca2+ currents. To study the time course of p21ras action, guanosine triphosphate‐preloaded p21ras was added to the patch pipette. Full‐length ras was effective only after a delay of 20 ‐30 min. C‐terminal modification by cellular enzymes is required to activate full‐length ras, and can account for the observed delay. Unexpectedly, C‐terminal‐truncated p2lras, which was found to be inactive in biological assays, enhanced LVA Ca2+ currents within minutes. This suggests a G‐protein‐like modulation of the LVA Ca2+ channel by p21ras. In an early phase of neuronal differentiation, dorsal root ganglion neurons express only LVA Ca2+ currents. The regulatory role of p21ras on LVA channels may therefore be particularly important during differentiation.
Differential Regulation of Nerve Growth Factor (NGF) Synthesis in Neurons and Astrocytes by Glucocorticoid Hormones
Authors: Lindholm Dan , Castrén Eero , Hengerer Bastian , Zafra Francisco , Berninger Benedikt , Thoenen Hans
Published: April 2006

Glucocorticoid hormones are important regulators of brain development and ageing. Here we show that dexamethasone, a synthetic glucocorticoid, differentially affects the expression of nerve growth factor (NGF) in cultured neurons and astrocytes. Dexamethasone increased the levels of NGF mRNA in cultured hippocampal neurons in a time‐ and concentration‐dependent manner, whereas it down‐regulated the NGF mRNA levels in astrocytes. However, dexamethasone had no effect on the mRNA levels of brain‐derived neurotrophic factor in the hippocampal neurons. Aldosterone, a mineralocorticoid, in higher concentrations also up‐regulated NGF mRNA levels in the hippocampal neurons. Dexamethasone increased the levels of NGF mRNA in the rat hippocampus in vivo, but not to the same extent as observed with kainic acid, a glutamate receptor agonist. There is no apparent diurnal rhythm in the hippocampal NGF protein levels corresponding to circadian variations in the levels of glucocorticoid hormones in serum. The increase in NGF mRNA in the hippocampus in vivo following dexamethasone treatments may reflect the physiological response of hippocampal neurons to high glucocorticoid levels reached under conditions of stress.
A Nitric Oxide Synthase Activity Selectively Stimulated by NMDA Receptors Depends on Protein Kinase C Activation in Mouse Striatal Neurons
Authors: Marin P. , Lafon‐Cazal M. , Bockaert J.
Published: April 2006

In mouse striatal neurons in primary culture, the maximal increase in intracellular cyclic guanosine monophosphate level evoked by N‐methyl‐d ‐aspartic acid (NMDA) receptor activation was twice that induced by kainate, KCI and ionomycin. Quisqualate was almost inactive. All responses were mediated by nitric oxide (NO) production since they were blocked by haemoglobin (a NO scavenger) and by L‐NG‐monomethylarginine and L‐NG nitroarginine, the effects of both arginine analogues being reversed by an excess of L‐arginine. Several results indicate that NMDA receptors stimulate a specific NO synthase activity. This specifically NMDA‐activated NO synthase was blocked by nanomolar concentrations of L‐NG nitroarginine, whereas the responses evoked by other agents, including kainate, KCI and ionomycin, were only blocked by micromolar concentrations of this NO synthase inhibitor. The NMDA response could not be totally reproduced by an increase in cytosolic calcium (Ca2+) alone. In contrast, in the presence of staurosporine, an inhibitor of protein kinases C (PKC), as well as after desensitization of PKC induced by long‐term treatment with the phorbol ester, phorbol‐12, 13‐dibutyrate, NMDA‐stimulated NO production was selectively reduced, reaching the level evoked by kainate or Ca2+ increase. In conclusion, our results suggest that in striatal neurons, NMDA selectively stimulates a NO synthase activity which is inhibited by low concentrations of L‐NG nitroarginine, through a mechanism involving PKC.
Monoclonal Antibodies to Late‐differentiating Epitopes Identify Mossy Fibre Terminals Innervating Normal and Transplanted Hippocampal CA3 Pyramidal Cells
Authors: Fonseca Montserrat , Woodhams Peter L. , Webb Michael , Field Pauline M. , Raisman Geoffrey
Published: April 2006

We have derived two monoclonal antibodies, MF‐1 and MF‐2, which both recognize the same 58‐kD antigen. Light and electron microscopic immunocytochemistry showed that this antigen is highly expressed in the large mossy fibre terminals innervating the proximal portion of the apical dendrites of pyramidal neurons in hippocampal field CA3. Staining was seen in the adult hippocampus in rats and mice, and in a post mortem human sample. Comparison with the Timm stain showed that the antibodies recognize mossy fibres from all parts of the adult dentate gyrus except for the tip of the infrapyramidal blade (the latest part of the dentate gyrus to develop). The MF antigen is expressed by mature terminals, and is not detected immunohistochemically in developing hippocampal mossy terminals until the end of the first postnatal week (i.e. later than the Timm‐positive material). It was also found in host mossy fibre terminals innervating embryonic CA3 pyramids transplanted into adult hosts, but not in areas of the graft containing transplanted CA1 pyramids. These results indicate that this previously undescribed, late‐developing antigen provides a useful specific marker for the mossy fibre projection in both the normal hippocampus and in situations of experimentally manipulated connectivity.
Correlates of Habituation of a Polysynaptic Reflex in Crayfish In Vivo and In Vitro
Authors: Marchand A. R. , Barnes W. J. P.
Published: April 2006

Reflex leg levation habituates during repeated electrical stimulation of mechanosensory afferents in the dactyl of the fifth walking leg of the crayfish, Procambarus clarkii. This was investigated in decerebrate crayfish, and reproduced in an isolated thoracic ganglion preparation. In vivo, trains of stimuli delivered every 2.5 s produced a gradual decrease in the amplitude of the mechanical response, and a concomitant decrease in the number of impulses per burst in the levator muscle myogram. Near complete recovery occurred after 10 min rest, and transient dishabituation was observed after electrical stimulation of the telson. Less frequent or stronger stimuli led to less rapid habituation. In vitro, the same parametric characteristics of habituation were observed in the levator nerve responses, while the intrinsic variability of the reflex was reduced. The response decrement was shown to be unrelated to changes in the afferent excitation. Evoked polysynaptic excitatory postsynaptic potentials (EPSPs) in levator motorneurons decreased in parallel with the levator neurogram. This decrease was unrelated to any change in the resting membrane potential of the levator motorneurons. Intemeurons with habituating EPSPs, antagonistic depressor motorneurons with habituating inhibitory postsynaptic potentials and non‐habituating responses in other motorneuronal groups were also found. These findings point to a central locus of habituation upstream from the motorneurons, and offer prospects for a detailed investigation of the mechanisms of habituation in a polysynaptic system.
Responses of Visual‐Tracking Neurons from Cortical Area MST‐I to Visual, Eye and Head Motion
Authors: Thier P. , Erickson R. G.
Published: April 2006

Thirty‐one neurons which exhibited ocular pursuit‐related activity [visual‐tracking (VT) neurons] were found clustered within area MST‐I (the lateral part of area MST) of two rhesus monkeys. Their responses were studied to determine whether this activity was correlated only with pursuit eye movement or with head movement as well. The latter hypothesis appeared to be preferable since visual, eye movement and head movement inputs were found to be mapped in register onto most of these cells. First, in each cell tested (n=19) the pursuit response persisted even in the absence of retinal image motion, offering clear evidence for non‐visual input. Second, 22 of the 31 cells were directionally responsive to moving visual stimuli and in 20 of these the preferred directions for the visual motion and pursuit responses agreed closely. Responses were also obtained from many of the same cells during suppression of both the horizontal and the vertical vestibulo‐ocular reflex (VOR). In each case, where directional visual, pursuit and VOR suppression responses were each obtained, vector addition of responses during suppression of the horizontal and vertical VOR resulted in an estimated preferred direction for head rotation which was closely aligned with the preferred direction previously obtained for eye motion or visual motion. In addition, the preferred direction of head movement was conserved even when the VOR was elicited by passive head rotation in complete darkness, although the responses in this instance were, on average, only 62% of those obtained during VOR suppression. Our interpretation is that, at present, MST‐I VT neurons are best described as encoding the direction of target motion in space‐centred coordinates by integrating inputs reflecting retinal image motion plus eye and head movement.
Autoradiographic Localization of Cholecystokinin A and B Receptors in Rat Brain Using [125I]D‐Tyr25 (NIe28,31)‐CCK 25‐33S
Authors: Carlberg M. , Gundlach A. L. , Mercer L. D. , Beart P. M.
Published: April 2006

The distribution of receptors for the sulphated octapeptide cholecystokinin 26–33 (CCK‐8S) in rat brain was investigated by radioligand binding in conjunction with autoradiography using the novel iodinable, non‐oxidizable, amino‐ and thiolendopeptidase‐resistant CCK analogue, d‐Tyr25(Nle28,31)‐CCK 25–33S. Labelling of the peptide was achieved by synthesis utilizing Na125l and Chloramine‐T. [125l]D‐Tyr25(Nle26,31)‐CCK 25–33S (100 pM) bound rapidly and reversibly to a single population of sites on slide‐mounted coronal sections of rat forebrain with a dissociation constant of 34 pM. Specific binding was fully inhibited by CCK‐8S, CCK‐8, CCK‐4, L‐365,260 and L‐364,718, with inhibition constants 2.7, 9.8, 35, 7.0 and 130 nM, respectively. These inhibition data may indicate that the [125l] ligand binds preferentially to a CCKB subtype of receptor, but may also reflect the relative paucity of CCKA receptors in the rat forebrain. Optimum conditions for autoradiography combined the preincubation of brain sections in unlabelled 10 pM d‐Tyr25(Nle28,31)‐CCK 25–33S with a 60‐min wash after incubation with the [125l] ligand. Analyses of the autoradiograms obtained from the use of coronal and horizontal brain sections were aided by the high levels of specific binding (80–90%), and revealed that CCK receptors were topographically distributed through the neuroaxis. High densities of receptor‐associated silver grains were found in the olfactory bulb (internal plexiform layer), neocortex (layer III), nucleus accumbens, parasubiculum, subbrachial nucleus, parabigeminal nucleus, dorsal vagal complex, area postrema and the A2 region. Moderate labelling was observed in many telencephalic and diencephalic nuclei. The majority of these receptors were of the CCKB subtype, as shown by the use of subtype‐selective antagonists, although CCKA receptors were present in moderate to high densities in the A2 area, area postrema and nucleus tractus solitarii, and at low density in the interpeduncular nucleus and central amygdala. These findings provide further evidence for the widespread, topographic distribution of CCK receptors and indicate that [125l]d‐Tyr25(Nle28,31)‐CCK 25–33S is very suitable for autoradiographic investigations because of its low non‐specific binding.
Embryonic Purkinje Cells Grafted on the Surface of the Cerebellar Cortex Integrate in the Adult Unlesioned Cerebellum
Authors: Rossi Ferdinando , Borsello Tiziana , Strata Piergiorgio
Published: April 2006

The presence of an injury or the selective degeneration of specific neuronal populations is commonly assumed to be a necessary prerequisite for the survival and the integration of grafted neurons in the recipient brain. In the present study we have placed solid grafts of cerebellar anlage in the fourth ventricle of adult rats, in close contact with the host cerebellar cortex, to assess the capacity of embryonic Purkinje cells to interact with adult neurons and integrate in the unlesioned cerebellar cortex. Numerous grafted Purkinje cells are indeed able to leave the implant and migrate into the host molecular layer, where they develop adult structural features. In addition, such cells are able to elicit the growth of host climbing fibre sprouts which end in newly formed arborizations impinging upon their dendritic trees. Climbing fibre collateral branches also penetrate the implant to innervate Purkinje cells which have not migrated in the host cerebellum. These results show that embryonic Purkinje cells are able to survive and integrate in an adult unlesioned cerebellar cortex. In addition, adult olivary axons respond to the increased size of the target population by expanding their terminal domain to innervate grafted Purkinje cells.
Training Chicks on a Passive Avoidance Task Modulates Glutamate‐stimulated Inositol Phosphate Accumulation
Authors: Bullock Sarah , Rose Steven P. R. , Pearce Brian , Potter Jenny
Published: April 2006

The effects of glutamate, N‐methyl‐d‐aspartate (NMDA), (+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo‐(a,d)‐cyclohepten 5,10‐imine maleate (MK801), α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate (AMPA) and quisqualate on the accumulation of inositol phosphates (IP) from the breakdown of phosphoinositides in vitro have been studied in tissue prisms derived from a region of the chick forebrain, the intermediate medial hyperstriatum ventrale (IMHV). In prisms from the left IMHV, glutamate stimulated IP accumulation by 10–20%, AMPA by 55% and quisqualate by 650%. These effects were more marked in the right IMHV, where AMPA stimulated IP accumulation by 157% and quisqualate by 920%. MK801 and NMDA had no significant effect on IP accumulation in either hemisphere. The left IMHV is known to be the site of a biochemical cascade resulting in synaptic remodelling following training day‐old chicks on a one‐trial passive avoidance task. The effect of such training was to reduce glutamate‐stimulated accumulation of IP by 27% (P < 0.05) in prisms taken 30 min after training. There was no effect on prisms taken at 5 or 180 min after training, and no effect at any time in the right IMHV. MK801, injected intraperitoneally before training at a concentration known to produce amnesia for the passive avoidance task, abolished the training‐induced decrease without itself affecting IP accumulation. Taken in conjunction with pharmacological and autoradiographic evidence, these results indicate that memory formation for the passive avoidance task involves the activation of NMDA receptor channels, but not quisqualate or AMPA receptors, in the left IMHV of the chick 30 min after training.
Alteration of Sodium Currents by New Peptide Toxins From the Venom of a Molluscivorous Conus Snail
Authors: Hasson Arik , Fainzilber Michael , Gordon Dalia , Zlotkin Eliahu , Spira Micha E.
Published: April 2006

TxIA and TxIB, peptides with 27‐amino acid residues recently isolated from the molluscivorous marine snail Conus textile neovicarius, exhibit strong paralytic activity in molluscs, with no paralytic effects on arthropods and vertebrates. At concentrations of 0.25 – 0.5 μM the toxins cause spontaneous repetitive firing and dramatic broadening of the action potential of cultured Aplysia neurons. The action potential duration partially recovers within 30 min in the presence of the toxins. Under these conditions a second toxin application does not change the spike duration. TxI‐induced spike broadening occurs when potassium and calcium conductances are blocked. Voltage‐clamp experiments revealed that the toxins alter the kinetics of the sodium current either by slowing down the rate of sodium current inactivation or by recruiting silent sodium channels with slower activation and inactivation kinetics. The toxins shift the voltage‐dependent steady‐state Na+ current inactivation curve to more positive values by 6 mV. These changes are not associated with alteration in the rate of sodium current activation, in the peak sodium current, or the sodium current reversal potential. TxI apparently represents a new class of conotoxins with an unusual phylogenic specificity and may therefore be useful as a probe for the study of molluscan neuronal sodium channels.
The Fates of Cells in the Developing Cerebral Cortex of Normal and Methylazoxymethanol Acetate‐lesioned Mice
Authors: Gillies Katy , Price David J.
Published: April 2006

We are interested in the mechanisms that generate the mature cerebral cortex. We used bromodeoxyuridine (BrdU) to label cortical cells as they were being born. We followed the fates of specific sets of cortical precursors in normal mice and in mice in which other groups of cortical progenitors had been destroyed with the antimitotic agent methylazoxymethanol acetate (MAM Ac). In normal mice, most cells destined for the cerebral cortex were produced from embryonic day 12 (E12) to E16 in the expected inside‐to‐outside sequence (deep layers first, superficial layers last). Injection of MAM Ac at E13 killed cells that would normally have contributed to the deep cortical layers. As a consequence, the cortex was thinned by ∼25% at postnatal day 21 (P21). However, all laminae were present and had normal connections with subcortical structures, although all were proportionately thinner. BrdU injected on E16 labelled a normally sized complement of cells that spanned a larger proportion of the depth of the thinned cortex. Thus, the deep cortical layers comprised many cells that were born several days later than normal. At embryonic ages prior to E12, a transient set of cells is produced in the early telencephalon. After injection with MAM Ac at E10, the cortex appeared histologically and histochemically normal at P21. However, many cells that would normally have contributed to superficial cortex (born on E15) were significantly deeper than normal. These results suggest that, during the early stages of cortical development, the nervous system is sufficiently plastic to compensate to some extent for the destruction of specific precursor cells by altering the fates of neurons born later. They indicate that the embryonic date on which a cortical cell is born does not necessarily determine its eventual phenotype.
Organization of Auditory Callosal Connections in Hypothyroid Adult Rats
Authors: Berbel Pere , Guadaño‐Ferraz Ana , Martínez Mercedes , Quiles Juan A. , Balboa Rosario , Innocenti Giorgio M.
Published: April 2006

Callosal connections were studied with tracers (horseradish peroxidase (HRP) and wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP)) in normal rats and rats deprived of thyroid hormones with methimazole (Sigma) since embryonic day 14 and thyroidectomized at postnatal day 6. In hypothyroid rats, the auditory areas, in particular the primary auditory area, showed cytoarchitectonic changes including blurred lamination and decrease in the size of layer V pyramidal neurons. In control rats, callosally‐projecting neurons were found between layers II and VI with a peak in layer III and upper layer IV. In hypothyroid rats, labelled neurons were found between layers IV and VI with two peaks corresponding to layer IV and upper layer V, and in upper layer VI. Quantitative analysis of radial distribution of callosally‐projecting neurons confirmed their shift to infragranular layers in hypothyroid rats. Three‐dimensional reconstructions showed a more continuous tangential distribution of callosally‐projecting neurons in hypothyroid rats which may be due to the maintenance of a juvenile ‘exuberant’ pattern of projections. These changes in cortical connectivity may be relevant for understanding epilepsy and mental retardation associated with early hypothyroidism in humans and to clarify basic mechanisms of cortical development.
Noradrenaline Decreases Transmission of NMDA‐ and Non‐NMDA‐receptor Mediated Monosynaptic EPSPs in Rat Prefrontal Neurons In Vitro
Authors: Law‐Tho D. , Crepel F. , Hirsch J. C.
Published: April 2006

The effects of noradrenaline on pyramidal cells of layer V of the prefrontal cortex were examined in rat brain slices in vitro. Bath administration of noradrenaline (10 μM) reduced synaptic transmission of afferent inputs from layer 1. The decrease affected all the components of the evoked response and particularly the monosynaptic excitatory postsynaptic potential (EPSP) as evidenced by a reduction of its initial rising slope (mean slope: 71 ± 11% of its control). Pharmacological dissociation of the NMDA‐ and non‐NMDA‐receptor components of the EPSP showed that noradrenaline reduced both (mean EPSP slopes were 71 ± 8% and 73 ± 10% of their control, respectively). Alpha1‐, but not α‐2‐ or β‐adrenoceptor antagonists prevented the noradrenaline‐induced decrease in synaptic efficacy. However, the effect of noradrenaline was not reproduced by α1‐adrenoceptor agonists. Lastly, noradrenaline acting through β‐adrenoceptors reduced the slow hyperpolarization that follows a train of action potentials.
Galanin Antagonists Block Galanin‐induced Feeding in the Hypothalamus and Amygdala of the Rat
Authors: Corwin R. L. , Robinson J. K. , Crawley J. N.
Published: April 2006

Galanin significantly increased food intake when microinjected into the region of the central nucleus of the amygdala as well as into the paraventricular nucleus of the hypothalamus. In the amygdala this effect was specific to feeding; no change in grooming, resting, or other behaviour was observed after galanin treatment. These results provide evidence that the amygdala may be an important site in the mediation of galanin‐induced feeding. The galanin receptor antagonists, C7 and M40, antagonized galanin‐induced feeding, while having no effect alone on food consumption in free‐feeding rats. These new galanin receptor antagonists provide useful tools for further investigating the role of endogenous galanin in the regulation of feeding.
Acidic Fibroblast Growth Factor is Expressed Abundantly by Photoreceptors Within the Developing and Mature Rat Retina
Authors: Bugra K. , Oliver L. , Jacquemin E. , Laurent M. , Courtois Y. , Hicks D.
Published: April 2006

In order to further understand the role(s) of fibroblast growth factors (FGFs) in the development, differentiation and function of the central nervous system, we analysed the expression of the mRNA, and the presence and tissue distribution of the translated product, of one member of the FGF family, acidic FGF (aFGF), within the mammalian retina. Firstly, the relative abundance of aFGF mRNA was assayed in embryonic (between 14 and 17 days of gestation), postnatal (between 1 and 17 days after birth) and adult rat retina by quantitative reverse transcription‐coupled polymerase chain reaction amplification using specific aFGF oligonucleotides. The level of expression remained uniformly low throughout the embryonic period and until postnatal day 7. Therefore the quantity of aFGF mRNA increased rapidly, reaching 80% of adult levels by eye opening (postnatal day 13). Adult levels were three‐fold higher than at early developmental times. In situ hybridization of adult rat retina using specific antisense aFGF riboprobes revealed labelling in all cellular layers. Antisera raised against recombinant human aFGF revealed very little labelling of 4‐day postnatal retina, but by postnatal days 8 and 17 immunoreactive aFGF was localized mainly within the photoreceptor cell bodies. Western blots of retinal extracts derived from 17‐day embryonic, 4‐day postnatal and adult retina probed with the same antibody revealed a single immunoreactive band of the expected molecular weight (18 kDa) in all extracts. Thus aFGF is mostly transcribed and translated within the retina subsequent to the major steps of cell birth, migration and differentiation, and seems to be abundantly expressed by maturing photoreceptor cells.
Localization of Nitric Oxide Synthase in the Mouse Olfactory and Vomeronasal System: a Histochemical, Immunological and In Situ Hybridization Study
Authors: Kishimoto J. , Keverne E. B. , Hardwick J. , Emson P. C.
Published: April 2006

The distribution of nitric oxide synthase (NOS) in the mouse olfactory bulb and olfactory epithelium, including the vomeronasal organ, was studied using an anti‐NOS antibody, NADPH diaphorase histochemistry and in situ hybridization with NOS specific antisense oligonucleotide probes. Interneurons containing NOS protein and mRNA, and exhibiting NADPH diaphorase activity were detected in the plexiform layer of the main olfactory bulb and the granule cell layer of main and accessory olfactory bulbs. Periglomerular cells and granule cells in the main olfactory bulb were also NOS positive with diaphorase and immunostaining for NOS. In contrast, no evidence for NOS expression was found either in the main olfactory epithelium or in the vomeronasal organ, in spite of the strong diaphorase staining of the surface of the main olfactory epithelium. Polymerase chain reaction amplification experiments for detection of NOS gene expression further indicated that NOS is expressed in the olfactory bulb but not in either the main olfactory epithelium or vomeronasal organ. Use of an antibody raised against another enzyme, NADPH‐P450 oxidoreductase, showed that this protein was strongly expressed in the olfactory epithelium. Activity of this enzyme may account for the diaphorase histochemical staining of the epithelia. An involvement of neuronal nitric oxide synthase in signalling in olfactory receptor neurons is therefore doubtful, although NOS is clearly expressed in neurons in both main and accessory olfactory bulbs.
Effects of the HIV‐1 Envelope Glycoprotein gp120 in Cerebellar Cultures. [Ca2+]i Increases in a Glial Cell Subpopulation
Authors: Ciardo Alberto , Meldolesi Jacopo
Published: April 2006

The various types of cells present in cultures prepared from the postnatal rat cerebellum, identified by their gross morphology and immunocytochemistry, were loaded with the specific dye fura‐2 and analysed individually for [Ca2+]i changes induced by the HIV‐1 envelope glycoprotein gp120 and a variety of other treatments. In granule neurons [Ca2+]i increases were induced by high KCl and glutamate (mainly through the NMDA receptor) while in type‐1 astrocytes this effect was observed after serotonin, carbachol and also quisqualate. In contrast, administration of gp120 was always without effect in these cells. Type‐2 astrocytes (an arborized cell type responsive to agonists targeted to the glutamatergic AMPA and cholinergic receptors) were also most often unresponsive to the viral glycoprotein. However, among the cells exhibiting the arborized phenotype, a subpopulation (‐13%) responded to gp120 with conspicuous [Ca2+]i increases sustained by both release from intracellular stores and influx across the plasma membrane. These responses to the viral protein did not involve activation of either voltage‐gated Ca2+ channels or glutamatergic receptors. Although not yet conclusively identified by specific cytochemical markers, the gp120‐responsive cells resemble type‐2 astrocytes and differ from neurons and type‐1 astrocytes both in gross phenotype and in a number of receptor/channel properties: positivity to AMPA and cholinergic agonists; negativity to NMDA, serotonin and high KCl. From these results it is concluded that a subpopulation of glial cells is affected by gp120. The role of these cells in HIV brain infection and damage requires further studies to be precisely established.
Heterogeneity of Synaptic Density in the Adult Pigmented Rabbit's Visual Cortex
Authors: Choudhury B. P.
Published: April 2006

In the adult pigmented rabbit, synaptic density in the lateral and medial part of the visual cortex was estimated along the projection area of the visual streak. A higher synaptic density distribution was observed in the lateral cortex (projection area of the nasal visual field) than in the medial cortex (projection area of the temporal visual field). This shows that there is a higher synaptic density in the region of the visual cortex receiving input from a retinal area with a high ganglion cell concentration than the area of the cortex receiving input from the retina with a low concentration of such cells. The regions of the visual cortex with higher and lower synaptic densities are the areas having a higher and lower magnification factor respectively.
Tonic Activation of NMDA Receptors Causes Spontaneous Burst Discharge of Rat Midbrain Dopamine Neurons In Vivo
Authors: Chergui K. , Charléty P. J. , Akaoka H. , Saunier C. F. , Brunet J.‐L. , Buda M. , Svensson T. H. , Chouvet G.
Published: April 2006

Midbrain dopamine neurons in vivo discharge in a single‐spike firing pattern or in a burst‐firing pattern. Such activity in vivo strikingly contrasts with the pacemaker activity of the same dopamine neurons recorded in vitro. We have recently shown that burst activity in vivo of midbrain dopamine neurons is due to the local activation of excitatory amino acid receptors, as microapplication of the broad‐spectrum antagonist of excitatory amino acids, kynurenic acid, strongly regularized the spontaneous firing pattern of these dopamine neurons. In the present study, we investigated which subtypes of excitatory amino acid receptors are involved in the burst‐firing of midbrain dopamine neurons in chloral hydrate‐anaesthetized rats, Iontophoretic or pressure microejections of 6‐cyano,7‐nitroquinoxaline‐2,3‐dione (CNQX), a non‐N‐methyl‐d‐aspartate (NMDA) receptor antagonist, did not alter the spontaneous burst firing of dopamine neurons (n= 36). In contrast, similar ejections of (±)2‐amino,5‐phos‐phonopentanoic acid (AP‐5), a specific antagonist at NMDA receptors, markedly regularized the firing pattern by reducing the occurrence of bursts (n= 52). In addition, iontophoretic ejections of NMDA, but not kainate or quisqualate, elicited a discharge of these dopamine neurons in bursts (n= 20, 12 and 14, respectively). These data suggest that burst‐firing of midbrain dopamine neurons in vivo results from the tonic activation of NMDA receptors by endogenous excitatory amino acids. In view of the critical dependency of catecholamine release on the discharge pattern of source neurons, excitatory amino acid inputs to midbrain dopamine neurons may constitute a major physiological substrate in the control of the dopamine level in target areas.