bluuebunny/crossref_metadata_2025 huggingface dataset:
L‐DOPA‐induced dyskinesia in the rat is associated with striatal overexpression of prodynorphin‐ and glutamic acid decarboxylase mRNA
Authors: Cenci M. A. , Lee C. S. , Björklund A.
Published: March 2003

Rats sustaining unilateral near‐complete 6‐hydroxydopamine lesions of the mesostriatal dopamine pathway received daily injections of 3,4 dihydroxyphenyl‐l‐alanine (L‐DOPA, 8 mg/kg plus 15 mg/kg benserazide) for 3 weeks. During this period, about 50% of the rats gradually developed abnormal involuntary movements, lasting for 2–3 h following each L‐DOPA dose. Rats were killed 3 days after the last L‐DOPA injection, and sections through the striatum were processed for in situ hybridization histochemistry.

  Within the L‐DOPA‐treated group, levels of preproenkephalin (PPE) mRNA, glutamic acid decarboxylase (GAD67) mRNA, and prodynorphin (PDyn) mRNA in the dopamine‐denervated caudate‐putamen, as well as GAD67 mRNA expression in the globus pallidus ipsilateral to the 6‐hydroxydopamine (6‐OHDA) lesion, were higher in dyskinetic than non‐dyskinetic animals, and positively correlated with the rats' dyskinesia scores. By contrast, striatal preprotachykinin mRNA expression and D2 receptor‐radioligand binding were not significantly associated with dyskinesia. Among all these markers, PDyn mRNA levels showed the most pronounced treatment‐dependence (three times higher in the L‐DOPA‐treated group than in saline‐injected lesion‐only controls), and the strongest correlation with the rats' dyskinesia scores (r2 = 0.82). However, a multiple regression equation including the three factors, GAD67 mRNA levels in the GP, GAD67 mRNA in the lateral CPu, and striatal PDyn mRNA, gave a better fit for dyskinesia scores than PDyn mRNA alone (r2 = 0.92).

  The results show that L‐DOPA‐induced dyskinesia is associated with overexpression of PDyn and GAD67 mRNA in the striatal projection neurons, and GAD67 mRNA levels in the globus pallidus. Due to its treatment‐dependent expression, and strong correlation with the associated dyskinetic symptoms, striatal PDyn mRNA, in particular, may play a role in the mechanisms of behavioural sensitization brought about by the drug.
Influence of handedness on peripheral auditory asymmetry
Authors: Khalfa S. , Veuillet E. , Collet L.
Published: March 2003

It is well established that in humans many differences between right‐ and left‐handers, anatomical, physiological and functional, exist. Left‐ and mixed‐handedness is associated with greater bihemispheric representation of cognitive functions than in right‐handers. Several studies indicate a left–right asymmetry in the function of hearing pathways between cochlea and auditory cortex, and furthermore, that this asymmetry is associated with handedness. Our investigation focuses on the medial olivo‐cochlear system, which has been demonstrated to be more effective in the right than left ear in right‐handers. The aim of the study was to investigate this auditory efferent system asymmetry according to handedness, gender, eyedness, footedness and the presence of spontaneous otoacoustic emissions. The medial efferent system has been found to be more effective in the right than left ear in right‐handers, while functioning symmetrically in left‐handers. Furthermore, the olivo‐cochlear system, assumed to be involved in basic language processing, shows an asymmetrical pattern of functioning influenced by handedness as well as by hemispheric language representation. Reverse medial efferent system asymmetry was observed in left‐handers compared to that in right‐handers, on condition that only left‐handed males were considered, or that the left‐handers were also left‐eyed, or that spontaneous otoacoustic emissions were present in the left ear of the left‐handers, or when only left‐handers without mixed‐handers were considered.
Evidence for functional native NMDA receptors activated by glycine or d‐serine alone in the absence of glutamatergic coagonist
Authors: Paudice Paolo , Gemignani Anita , Raiteri Maurizio
Published: March 2003

In this study we have examined the effects of N‐methyl‐d‐aspartate (NMDA) receptor activation on the release of cholecystokinin and somatostatin from rat neocortical nerve endings. The release of cholecystokinin‐like immunoreactivity (CCK‐LI) and of somatostatin‐like immunoreactivity (SRIF‐LI) elicited by 12 mm K+ from superfused synaptosomes, but not the spontaneous release, was increased by NMDA in a concentration‐dependent manner. The effects of NMDA could be prevented by antagonists selective for the glutamate recognition site, the receptor channel and the glycine site of the NMDA receptor. In the absence of NMDA, glycine increased on its own and in a concentration‐dependent manner the depolarization‐evoked release of both CCK‐LI and SRIF‐LI. This effect of glycine was strychnine‐insensitive and could be mimicked by d‐serine, a stereoselective agonist at the NMDA receptor glycine site. Antagonists selective for the glycine site or for the NMDA receptor channel prevented the effects of glycine/d‐serine; these effects were, however, insensitive to blockade of the glutamate recognition site of the NMDA receptor, suggesting that glutamate released from synaptosomes or present as contaminant was not involved. The neuropeptide release elicited by d‐serine was strongly inhibited by ifenprodil (0.3 μm) and by Zn2+ ions (50 nm), selective ligands at the NR2B and NR2A subunits of NMDA receptors, respectively. It is concluded that nerve terminals of CCK‐ and SRIF‐releasing neurons possess non‐conventional NMDA receptors whose channels can be operated by glycine or d‐serine without apparent activation of the glutamatergic coagonist site. These receptors may display the triple subunit combination NR1/NR2A/NR2B.
Classical conditioning modifies cytochrome oxidase activity in the auditory system
Authors: Poremba Amy , Jones Dirk , Gonzalez‐Lima F.
Published: March 2003

The effects of excitatory classical conditioning on cytochrome oxidase activity in the central auditory system were investigated using quantitative histochemistry. Rats in the conditioned group were trained with consistent pairings of a compound conditional stimulus (a tone and a light) with a mild footshock, to elicit conditioned suppression of drinking. Rats in the pseudorandom group were exposed to pseudorandom presentations of the same tone, light and shock stimuli without consistent pairings. Untrained rats in a naive group did not receive presentations of the experimental stimuli.

 The findings demonstrated that auditory fear conditioning modifies the metabolic neuronal responses of the auditory system, supporting the hypothesis that sensory neurons are responsive to behavioural stimulus properties acquired by learning. There was a clear distinction between thalamocortical and lower divisions of the auditory system based on the differences in metabolic activity evoked by classical conditioning, which lead to an overt learned behavioural response versus pseudorandom stimulus presentations, which lead to behavioural habituation. Increases in cytochrome oxidase activity indicated that tone processing is enhanced during associative conditioning at upper auditory structures (medial geniculate nucleus and secondary auditory cortices). In contrast, metabolic activation of lower auditory structures (cochlear nuclei and inferior colliculus) in response to the pseudorandom presentation of the experimental stimuli suggest that these areas may be activated during habituation to tone stimuli. Together these findings show that mapping the metabolic activity of cytochrome oxidase with quantitative histochemistry can be successfully used to map regional long‐lasting effects of learning on brain systems.
Interaction of frontal and perirhinal cortices in visual object recognition memory in monkeys
Authors: Parker Amanda , Gaffan David
Published: March 2003

Monkeys were trained preoperatively in visual object recognition memory. The task was delayed matching‐to‐sample with lists of trial‐unique randomly generated visual stimuli in an automated apparatus, and the stimuli were 2D visual objects made from randomly generated coloured shapes. We then examined the effect of either: (i) disconnecting the frontal cortex in one hemisphere from the perirhinal cortex in the contralateral hemisphere by crossed unilateral ablations; (ii) disconnecting the magnocellular portion of the mediodorsal (MDmc) thalamic nucleus in one hemisphere from the perirhinal cortex in the contralateral hemisphere; or (iii) bilaterally ablating first the amygdala, then adding fornix transection, then finally perirhinal cortex ablation. We found that both frontal/perirhinal and MDmc/perirhinal disconnection had a large effect on visual object recognition memory, whereas both amygdalectomy and the addition of fornix transection had only a mild effect. We conclude that the frontal lobe needs to interact with the perirhinal cortex within the same hemisphere for visual object recognition memory, but that routes through the amygdala and hippocampus are not of primary importance.
NT‐3, but not BDNF, prevents atrophy and death of axotomized spinal cord projection neurons
Authors: Bradbury Elizabeth J. , King Von R. , Simmons Lucinda J. , Priestley John V. , McMahon Stephen B.
Published: March 2003

Following spinal cord injury, projection neurons are frequently axotomized and many of the cells subsequently die. One goal in spinal injury research is to preserve damaged neurons so that ultimately they are accessible to regeneration‐promoting strategies. Here we ask if neurotrophin treatment can prevent atrophy and death of axotomized sensory projection neurons. In adult rats, a hemisection was made in the thoracic spinal cord and axotomized neurons were retrogradely labelled with Fluoro‐Gold. Four distinct populations of cells were identified in the lumbar spinal cord, and both numbers and sizes of labelled cells were assessed at different time points postlesion. A progressive and significant degeneration was observed over time with severe atrophy apparent in all cell populations and significant cell loss evident by 4 weeks postlesion. This time point was used to assess neurotrophin effects. Hemisected rats were treated with either neurotrophin 3 (NT‐3) or brain‐derived neurotrophic factor (BDNF, 12 μg/day for each), or a vehicle solution, delivered continuously to the lesion site via an osmotic minipump. Treatment with NT‐3, but not BDNF, completely reversed cell atrophy in three of the four cell populations and also induced a significant increase in the number of surviving cells. In situ hybridization experiments showed trkB and trkC mRNA to be expressed in the majority of ascending spinal projection neurons, suggesting that these cells should be responsive to both BDNF and NT‐3. However, only NT‐3 treatment was neuroprotective, indicating that BDNF may not have reached the cell bodies of injured neurons. These results demonstrate that NT‐3 may be of benefit in preventing the secondary cell loss that occurs following spinal injury.
Excitatory convergence of Y and non‐Y channels onto single neurons in the anterior ectosylvian visual area of the cat
Authors: Wang C. , Dreher B. , Assaad N. , Ptito M. , Burke W.
Published: March 2003

Numerous functional and hodological studies of the anterior ectosylvian visual area (AEV) of the cerebral cortex of the cat suggest that this area plays an important role in processing information about visual motion. In the present study, in cats with selective conduction block of Y fibres in one optic nerve, we have examined the extent of the excitatory convergence of Y (presumed ‘motion channel’) and non‐Y information channels on single neurons in AEV, as well as the contribution of the Y channel to the receptive field properties of AEV neurons. While in normal cats all neurons recorded from AEV were binocular, i.e. could be photically activated via either eye, in cats with selective conduction block of Y fibres in one optic nerve, a significant proportion (about 15%) of AEV cells could be photically activated only via the normal eye. In comparison to those in normal cats, the peak discharge rates of AEV neurons in the Y‐blocked cats were drastically reduced not only when photic stimuli were presented via the Y‐blocked eye, but also when they were presented via the normal eye. Selective block of Y input also resulted in a significant shift in velocity preferences towards the lower velocities. However, the direction selectivity indices of AEV neurons were not affected by selective Y block.

 Thus: (i) the responses of AEV neurons to a high velocity of motion are dependent on the integrity of the Y input; (ii) the ‘spontaneous’ (i.e. not photically evoked) discharges of Y retinal ganglion cells exert a facilitatory influence on the responses of AEV cells to photic stimuli; (iii) although the responses of AEV neurons are dominated by the Y inputs, AEV neurons also receive significant non‐Y excitatory inputs; and (iv) the strong direction selectivity revealed in most AEV neurons does not dependent on the integrity of Y input.
Long‐term depression of C‐fibre‐evoked spinal field potentials by stimulation of primary afferent Aδ‐fibres in the adult rat
Authors: Liu X. ‐G. , Morton C. R. , Azkue J. J. , Zimmermann M. , Sandkühler J.
Published: March 2003

Long‐term potentiation (LTP) of spinal C‐fibre‐evoked field potentials can be induced by brief electrical stimulation of afferent C‐fibres, by natural noxious stimulation of skin or by acute nerve injury. Here, we report that in urethane anaesthetized, adult rats prolonged high frequency burst stimulation of the sciatic nerve at Aδ‐fibre strength produced long‐term depression (LTD) of C‐fibre‐evoked field potentials, and also depressed the increased amplitudes of C‐fibre‐evoked field potentials recorded after LTP had been established (depotentiation). Electrical stimulation of Aβ‐fibres failed to induce LTD or depotentiation. In spinalized rats, prolonged Aδ‐fibre conditioning stimulation induced LTP rather than LTD of C‐fibre‐evoked field potentials. Thus, tonic descending inhibition may determine the direction of plastic changes in C‐fibre‐mediated synaptic transmission. Spinal application of the N‐methyl‐d‐aspartic acid receptor antagonist D‐APV blocked induction of LTD in intact rats and LTP in spinalized rats. The presently described LTD and the depotentiation of established LTP of C‐fibre‐evoked field potentials in spinal dorsal horn may underlie some forms of prolonged analgesia induced by peripheral nerve stimulation procedures.
Characterization of neuronal migration disorders in neocortical structures: extracellular in vitro recordings
Authors: Luhmann Heiko J. , Raabe Kristin , Qü Meishu , Zilles Karl
Published: March 2003

The majority of patients showing neuronal migration disorders in cortical structures suffer from pharmaco‐resistant epilepsy. In order to study the molecular and cellular mechanisms underlying this pronounced hyperexcitability, we used an animal model of focal cortical dysplasia demonstrating structural malformations which resemble the human pathology of microgyria. Neocortical slices prepared from adult rats, which at the day of birth received a cortical freeze lesion, were analysed in vitro with an array of eight extracellular recording electrodes to investigate the pattern and pharmacology of propagating epileptiform activity in microgyric cortex. In cortical slices exhibiting neuronal migration disorders, orthodromic synaptic stimulation elicited late recurrent activity and early epileptiform responses that spread with 0.06 m/s over ≥ 3.5 mm across the cortex. Application of a N‐methyl‐d‐aspartate (NMDA) antagonist blocked the late recurrent activity, but not the propagation of the early epileptiform responses. The latter were blocked by an (±)‐α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) antagonist, indicating that the spread of this activity was predominantly mediated by activation of AMPA receptors. A very similar response pattern could be observed in neocortical slices obtained from untreated age‐matched control rats, when the slice was partially disinhibited by bath‐application of 5 μm bicuculline methiodide. Stimulus‐evoked epileptiform signals recorded in disinhibited slices propagated with 0.08 m/s across the cortex and showed the same sensitivity to ionotropic glutamate antagonists as in dysplastic cortex. Our results indicate that widespread structural and/or functional modifications of the AMPA receptor and possibly also of the γ‐amino‐butyric acid type A receptor contribute to the pronounced hyperexcitability in dysplastic cortex.
Hippocampal neuronal activity and imprinting in the behaving domestic chick
Authors: Nicol A. U. , Brown M. W. , Horn G.
Published: March 2003

The hippocampus of the chick projects to the intermediate and medial part of the hyperstriatum ventrale (IMHV) which stores information acquired through the learning process of imprinting. We have investigated whether the response properties of hippocampal neurons are similar to those of IMHV neurons. Chicks were imprinted by exposure, one group (n = 7) to a rotating red box (RB), the other (n = 5) to a rotating blue cylinder (BC). Four chicks were untrained. The following day, when the chicks were ∼ 48 h old, neuronal activity was recorded in the left hippocampus. The proportion of neurons responding to the RB and that to the BC in untrained chicks were compared with the proportions in trained birds. (i) In RB‐trained chicks both the proportion responding to the RB and that to the BC were significantly increased. (ii) In BC‐trained chicks no significant effect on these proportions was found. Of the responsive neurons some were colour (red or blue) sensitive and others were shape (box or cylinder) sensitive; the proportions so responsive were not influenced by training condition. Certain neurons responded significantly differently when a stimulus was 0.5 m or 2 m from the chick (35%;d‐sensitive); very few neurons were equivalently responsive to a stimulus at both distances (3%;d‐invariant). These proportions were not significantly affected by training condition. Hippocampal responses are compared with those in the left IMHV. It is concluded that IMHV responses do not passively reflect those of hippocampal neurons.
The effects of anti‐nerve growth factor monoclonal antibodies on developing basal forebrain neurons are transient and reversible
Authors: Molnar Margherita , Tongiorgi Enrico , Avignone Elena , Gonfloni Stefania , Ruberti Francesca , Domenici Luciano , Cattaneo Antonino
Published: March 2003

In order to reassess the role of nerve growth factor (NGF) on rat basal forebrain cholinergic neurons (BFCNs) survival and/or phenotype maturation during the early postnatal life, we immunoneutralized NGF in vivo. Hybridoma cells producing the neutralizing anti‐NGF monoclonal antibody αD11 were implanted in the lateral ventricle of the rat at different postnatal ages (P2, P8 and P15) and the effects on the number and the soma size of cholinacetyltransferase (ChAT) positive neurons were analysed 1, 2 or 3 weeks after the injection. A marked decrease in the number and in the soma size of BFCNs was observed implanting hybridoma cells at P2 and performing the analysis 1 week later. These effects are reversed 3 weeks after the implant of hybridoma cells at P2. At this time point, the levels of αD11 antibodies in the brain parenchyma are still in a vast molar excess over endogenous NGF. No effects on BFCNs were observed implanting αD11 cells at P15 while LGN neurons showed marked shrinkage. Our results demonstrate that the reduction in the number of ChAT‐positive neurons during the first two postnatal weeks of anti‐NGF treatment is not due to cell death. We conclude that NGF is not a survival factor for BFCNs, and that the influence of NGF on BFCNs cell maturation during the first 2 postnatal weeks is transient and reversible. Our results on tyrosine kinase (Trk) coexpression, suggest that NGF may cooperate with other factors in the cholinergic phenotype differentiation and maintenance after the second postnatal week.
Complex regulation of the expression of the polysialylated form of the neuronal cell adhesion molecule by glucocorticoids in the rat hippocampus
Authors: Rodriguez J. J. , Montaron M. F. , Petry K. G. , Aurousseau C. , Marinelli M. , Premier S. , Rougon G. , Moal M. Le , Abrous D. N.
Published: March 2003

The gyrus dentatus is one of the few areas of the brain that continues to produce neurons after birth. The newborn cells differentiate into granule cells which project axons to their postsynaptic targets. This step is accompanied by the transient expression of the polysialylated isoforms of neuronal cell adhesion molecules (PSA‐NCAM) by the developing neurons. Glucocorticoid hormones have been shown to inhibit neurogenesis. We noted a functional correlation between PSA‐NCAM expression and glucocorticoid action after manipulation of corticosterone levels in the adrenalectomized rat. Adrenalectomy increased neurogenesis, evaluated from the incorporation of 5‐bromo‐2′‐deoxyuridine in neuronal precursors, as well as PSA‐NCAM expression. The increase in PSA‐NCAM‐immunoreactive (IR) cells in the gyrus dentatus, evidenced 72 h following adrenalectomy, persisted for at least a month. It was accompanied by enhanced dendritic arborization of PSA‐NCAM‐IR cells in the gyrus dentatus and by an increase in number of PSA‐NCAM‐IR fibres in the CA3 subfield. Neurogenesis was normalized by restitution of diurnal or nocturnal levels of corticosterone, whereas normalization of PSA‐NCAM expression was only observed after simulation of the complete circadian fluctuation of the hormone. Our findings reveal the complex action of corticosterone in modulating the expression of PSA‐NCAM in the gyrus dentatus of the hippocampal formation. They also highlight the importance of corticosterone fluctuations in the control of neurogenesis and plasticity in this structure.
The neuronal death induced by endotoxic shock but not that induced by excitatory amino acids requires TNF‐α
Authors: De Bock Frédéric , Derijard Benoît , Dornand Jacques , Bockaert Joël , Rondouin Gérard
Published: March 2003

We studied, using organotypic hippocampal slices in culture, the role of pro‐inflammatory cytokines, oxygen radicals and nitric oxide in neuronal death induced either by endotoxic insult [interferon (IFN) γ, 24 h followed by lipopolysaccharide, 24 h] or by glutamate receptor‐mediated excitotoxic insult. We demonstrated that neuronal death induced by endotoxic insult was absolutely dependent on the synthesis of tumour necrosis factor alpha (TNF‐α). Indeed, TNF‐α antibodies and SB203580, an inhibitor of p38 stress kinase known to block TNF‐α and other cytokine synthesis, completely protected neurons from the endotoxic insult. Inhibiting oxygen radical and nitric oxide productions also reduced the endotoxic shock. We also showed that after priming the cultures with IFN‐γ, TNF‐α was unable to induce neuronal death unless oxygen‐free radicals were exogenously provided. In contrast, although glutamate receptor‐induced excitotoxicity was associated with a low TNF‐α synthesis and a modest activation of p38 stress kinase, neither TNF‐α antibodies nor SB203580 were able to decrease excitotoxic neuronal insult. We did not reduce glutamate receptor‐induced neuronal death with superoxide dismutase plus catalase. In conclusion, although inflammation follows glutamate receptor‐mediated neurotoxicity, the mechanisms by which an endotoxic insult triggers neuronal death are different from those involved in excitotoxicity.
Modulation by substance P of synaptic transmission in the mouse hippocampal slice
Authors: Kouznetsova Maria , Nistri Andrea
Published: March 2003

The modulatory action of substance P on synaptic transmission of CA1 neurons was studied using intra‐ or extracellular recording from the mouse hippocampal slice preparation. Bath‐applied substance P (2–4 μm) or the selective NK1 receptor agonist substance P methylester (SPME, 10 nm–5 μm) depressed field potentials (recorded from stratum pyramidale) evoked by focal stimulation of Schaffer collaterals. This effect was apparently mediated via NK1 receptors since it was completely blocked by the selective NK1 antagonist SR 140333. The field potential depression by SPME was significantly reduced in the presence of bicuculline. Intracellular recording from CA1 pyramidal neurons showed that evoked excitatory postsynaptic potentials (EPSPs) and evoked inhibitory postsynaptic potentials (IPSPs) were similarly depressed by SPME, which at the same time increased the frequency of spontaneous GABAergic events and reduced that of spontaneous glutamatergic events. The effects of SPME on spontaneous and evoked IPSPs were prevented by the ionotropic glutamate receptor blocker kynurenic acid. In tetrodotoxin (TTX) solution, no change in either the frequency of spontaneous GABAergic and glutamatergic events or in the amplitude of responses of pyramidal neurons to 4 μmα‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) or 10 μmN‐methyl‐d‐aspartate (NMDA) was observed. On the same cells, SPME produced minimal changes in passive membrane properties unable to account for the main effects on synaptic transmission. The present data indicate that SPME exerted its action on CA1 pyramidal neurons via a complex network mechanism, which is hypothesized to involve facilitation of a subset of GABAergic neurons with widely distributed connections to excitatory and inhibitory cells in the CA1 area.
Long‐ but not medium‐term retention of olfactory memories in honeybees is impaired by actinomycin D and anisomycin
Authors: Wüstenberg Daniel , Gerber Bertram , Menzel Randolf
Published: March 2003

Although work in a wide variety of species and paradigms has demonstrated that long‐term memory is sensitive to the blocking of protein synthesis, previous studies have suggested that the honeybee might represent an exception to this rule. Retention tested one day after training was not impaired by the inhibition of translation by cycloheximide. Using blockers of either transcription (actinomycin D) or translation (anisomycin), we present experiments that reconcile this unusual finding by testing over longer retention periods. Honeybees were conditioned to associate an odourant with a sucrose reward. Typically, this leads to stable retention over days. However, injection of either drug led to lower retention after 4 days, whereas retention after 2 or sometimes even 3 days was unaffected. This dissociates two forms of memory: a protein synthesis‐independent, medium‐term memory (up to 3 days) and a protein synthesis‐dependent, long‐term memory lasting for at least 4 days.
A minigene of neural agrin encoding the laminin‐binding and acetylcholine receptor‐aggregating domains is sufficient to induce postsynaptic differentiation in muscle fibres
Authors: Meier Thomas , Marangi P. Angelo , Moll Joachim , Hauser Dominik M. , Brenner Hans‐R. , Ruegg Markus A.
Published: March 2003

The extracellular matrix molecule agrin is both necessary and sufficient for inducing the formation of postsynaptic specializations at the neuromuscular junction (NMJ). At the mature NMJ, agrin is stably incorporated in synaptic basal lamina. The postsynapse‐inducing activity of chick agrin, as assayed by its capability of causing aggregation of acetylcholine receptors (AChRs) on cultured muscle cells, maps to a 21 kDa, C‐terminal domain. Binding of chick agrin to muscle basal lamina is mediated by the laminins and maps to a 25 kDa, N‐terminal fragment of agrin. Here we show that an expression construct encoding a ‘mini’‐agrin, in which the laminin‐binding fragment was fused to the AChR‐clustering domain, is sufficient to induce postsynaptic differentiation in vivo when injected into non‐synaptic sites of rat soleus muscle. As shown for ectopic postsynaptic differentiation induced by full‐length neural agrin, myonuclei underneath the ectopic sites expressed the gene for the AChR ε‐subunit. Altogether, our data show that a ‘mini’‐agrin construct encoding only a small fraction of the entire agrin protein is sufficient to induce postsynapse‐like structures that are reminiscent of those induced by full‐length neural agrin or innervation by motor neurons.
Neurochemical characterization of individual vulnerability to addictive drugs in rats
Authors: Lucas Louis R. , Angulo Jesus A. , Moal Michel Le , McEwen Bruce S. , Piazza Pier V.
Published: March 2003

Rats exposed to a low‐light, low‐noise, novel environment exhibit differences in individual locomotor response to the novelty stressor. The categorization of rats in a locomotor screening procedure as low‐ (LR) or high‐responders (HR), where LRs are in the low locomotor range while HRs belong to the high locomotor range, is significant in that HRs show higher activity in mesencephalic dopaminergic projection neurons, and also show a higher propensity to self‐administer psychostimulants and other drugs of abuse compared with LRs. In this study, we examined the neurobiological basis of dopaminergic hyperactivity by comparing in HRs and LRs the steady‐state differences in regulatory inputs to mesencephalic (substantia nigra and ventral tegmental area: VTA) dopaminergic neurons. In particular, using in situ hybridization, we studied levels of mRNA for tyrosine hydroxylase (TH) and cholecystokinin (CCK) in the mesencephalon, and for preprodynorphin (DYN), preproenkephalin (PPE), and preprotachykinin (PPT) in the striatum and nucleus accumbens (Acb). We also evaluated TH levels by radioimmunocytochemistry (TH‐RIC) in striatal, accumbal and mesencephalic regions. HRs versus LRs had lower levels of neurochemicals belonging to the intrinsic inhibitory input to dopaminergic neurons in the VTA, e.g. lower TH‐RIC (–25%) and CCK‐mRNA (–48%). In contrast, HRs showed higher levels of parameters belonging to extrinsic facilitating inputs, e.g. higher PPE‐mRNA (+ 37%). In addition, HRs had higher DYN‐mRNA in Acb (+ 61%), which has been shown to be positively correlated with higher dopaminergic activity. These results enhance our knowledge of the neurobiological correlates of individual rats' propensities to develop drug‐intake and provide some putative mechanisms for the dopaminergic hyperactivity that characterizes drug‐prone animals.
Characterization of neuronal migration disorders in neocortical structures: quantitative receptor autoradiography of ionotropic glutamate, GABAA and GABAB receptors
Authors: Zilles Karl , Qü Meishu , Schleicher Axel , Luhmann Heiko J.
Published: March 2003

Epileptiform activity was previously described [Luhmann et al. (1998) Eur.J. Neurosci., 10, 3085–3094] in the neocortex of the adult rat following freeze lesioning of the newborn neocortex. After a survival time of 3 months, a small area of dysplastic cortex surrounded by histologically normal (exofocal) neocortex was observed. The dysplastic cortex is characterized by the formation of a small sulcus and a three‐ to four‐layered architecture. Two questions are addressed here: (i) is the hyperexcitability associated with changes in binding to major excitatory and inhibitory transmitter receptors in the dysplastic cortex?; and (ii) do such changes also occur in the exofocal cortex?

  Alterations in binding to glutamatergic N‐methyl‐d‐aspartate (NMDA), (±)‐α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA), kainate and GABAA and GABAB (γ‐aminobutyric acid) receptors are demonstrated with quantitative in vitro receptor autoradiography by using the ligands [3H]MK‐801, [3H]AMPA, [3H]kainate, [3H]muscimol and [3H]baclofen, respectively. In the dysplastic cortex, the binding to NMDA, AMPA and kainate receptors is significantly increased, whereas the binding to GABAA and GABAB receptors is reduced. Exofocal areas of the lesioned hemisphere show an imbalance between excitatory and inhibitory receptor binding with an up‐regulation of the binding to AMPA and kainate, and a down‐regulation to GABAA receptors. The binding to GABAB and NMDA receptors is not significantly changed in the exofocal areas.

  The imbalance between excitatory and inhibitory receptors may cause the hyperexcitability, as previously found in the identical experimental model, and may also induce epileptiform activity in the human cortex with migration disorders.
Calcium electrogenesis in neocortical pyramidal neurons in vivo
Authors: Paré Denis , Lang Eric J.
Published: March 2003

Much of what is known about Ca2+ electrogenesis in neocortical cells has been derived from in vitro studies. Since Ca2+ currents are controlled by various modulators, comparing these findings to in vivo data is essential. Here, we analysed tetrodotoxin (TTX)‐resistant, presumably Ca2+‐mediated potentials in intracellularly recorded neocortical neurons in vivo. TTX was applied locally to block Na+ channels. Its effectiveness was demonstrated by the elimination of fast spikes and orthodromic responses. In response to depolarizing current pulses bringing the membrane potential beyond ≈–33 mV, 71% of neurons generated high‐threshold Ca2+ spikes averaging 17 mV. This is in contrast with in vitro findings, where high‐threshold spikes could only be elicited following the blockade of K+ conductances. Consistent with this, neurons dialysed with K+ channel blockers in vivo generated high‐threshold spikes that had a lower threshold (≈–40 mV) and, with intracellular Cs+, a larger amplitude, indicating the presence of K+ currents opposing the activation of Ca2+ channels. Only 15% of cortical cells displayed low‐threshold Ca2+ spikes. To compare high‐threshold Ca2+ spikes evoked by synaptic stimuli or current injection, another group of cortical neurons was dialysed with QX‐314 and Cs+, in the absence of extracellular TTX. Synaptic stimuli applied on a background of membrane depolarization elicited presumed Ca2+ spikes whose amplitude varied in a stepwise fashion. Thus, although there are numerous similarities between in vivo and in vitro data, some significant differences were found, which suggest that the high‐voltage activated Ca2+ currents and/or the K+ conductances that oppose them are subjected to different modulatory influences in vivo than in vitro.
Transforming growth factor‐β mediates the neurotrophic effect of fibroblast growth factor‐2 on midbrain dopaminergic neurons
Authors: Krieglstein Kerstin , Reuss Bernhard , Maysinger Dusica , Unsicker Klaus
Published: March 2003

Fibroblast growth factor (FGF)‐2 is an established neurotrophic factor for dopaminergic (DAergic) neurons in the ventral midbrain. Its survival and differentiation‐promoting effects on DAergic neurons in vitro and in vivo are crucially dependent on the presence, numerical expansion and maturation of astroglial cells. We show now that transforming growth factor (TGF)‐β, an established trophic factor for DAergic neurons and product of astroglial cells, mediates the trophic effect of FGF‐2 on DAergic neurons cultured from the embryonic rat midbrain floor. Antibodies to TGF‐β that neutralize the isoforms ‐β1, ‐β2 and ‐β3 abolish the trophic effect of FGF‐2. FGF‐2 increases TGF‐β3 mRNA and amounts of biologically active TGF‐β determined in a mink lung epithelial cell assay in a time‐dependent manner. FGF‐2 also induces levels of active TGF‐β in neonatal rat astrocytes cultured from midbrain, striatum and cortex. We conclude that TGF‐β is required for mediating the survival promoting effect of FGF‐2 on DAergic and, possibly, cortical and striatal neurons grown in the presence of glial cells.
Protection of axotomized retinal ganglion cells by adenovirally delivered BDNF in vivo
Authors: Isenmann Stefan , Klöcker Nikolaj , Gravel Claude , Bähr Mathias
Published: March 2003

Following intraorbital transection of the optic nerve (ON) in rats, more than 80% of the retinal ganglion cell (RGC) population die by apoptosis within 14 days. Repeated intraocular injection of brain‐derived neurotrophic factor (BDNF) has been efficient in enhancing RGC survival following ON axotomy. The present study was designed to define a potential survival‐promoting effect of adenovirally administered BDNF on axotomized RGCs. A single injection of an adenoviral vector expressing the human BDNF gene from a CMV promoter/enhancer (Ad‐BDNF) enhanced RGC survival 14 days after axotomy by 40.3%. Moreover, a combinatory treatment regimen consisting of intraocular Ad‐BDNF administration and systemic application of the free radical scavenger, N‐tert‐butyl‐(2‐sulphophenyl)‐nitrone (S‐PBN), enhanced RGC survival by 63.0%. Our data demonstrate that adenoviral delivery of neurotrophic factors to the vitreous body is a feasible approach for the prevention of axotomy‐induced RGC death. Further, as shown for S‐PBN, therapeutic regimens that combine local virus‐mediated gene delivery with systemic administration of protective compounds, may offer promising strategies for future treatment also in human neurodegenerative conditions.
BDNF and NT‐3 applied in the whisker pad reverse cortical changes after peripheral deafferentation in neonatal rats
Authors: Calia Eustachio , Persico Antonio M. , Baldi Alfonso , Keller Flavio
Published: March 2003

It has been known for a long time that subcortical input drives the specification of cortical areas. Molecular signals mediating this instructive effect from the periphery are poorly understood. In foetal or neonatal rats, ablation of whisker follicles, transection of the infraorbital nerve, inhibition of axonal transport, but not impulse activity blockade, prevent formation of barrels in the primary somatosensory cortex (S1). These findings suggest that a chemical signal, possibly arising from the skin or the follicle, may be responsible for somatotopic pattern formation in S1. Neurotrophins promote survival and differentiation of primary sensory neurons, and are expressed in the whisker pad during development. Neonatal rats received gelfoam impregnated with NGF, BDNF or NT‐3 under the whisker pad following surgical denervation of whisker rows D and E on P0. Barrel formation in S1 was assessed on P7 by acetylcholinesterase histochemistry and 5‐HT‐immunohistochemistry. BDNF and NT‐3, but not NGF, promoted development of the cortical barrels corresponding to denervated whiskers. Furthermore, BDNF and NT‐3 prevented the lesion‐induced expansion of row C barrels, while NGF appeared to promote row C expansion. Our results suggest that BDNF and NT‐3 arising from the whisker pad are involved in the formation and/or maintenance of the barrel pattern in S1. These findings are potentially relevant for the prevention of sensory disturbances possibly due to reorganization of central sensory circuits after peripheral nerve lesions in humans.
A visuo‐somatomotor pathway through superior parietal cortex in the macaque monkey: cortical connections of areas V6 and V6A
Authors: Shipp S. , Blanton M. , Zeki S.
Published: March 2003

This report addresses the connectivity of the cortex occupying middle to dorsal levels of the anterior bank of the parieto‐occipital sulcus in the macaque monkey. We have previously referred to this territory, whose perimeter is roughly circumscribed by the distribution of interhemispheric callosal fibres, as area V6, or the ‘V6 complex’. Following injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA‐HRP) into this region, we examined the laminar organization of labelled cells and axonal terminals to attain indications of relative hierarchical status among the network of connected areas. A notable transition in the laminar patterns of the local, intrinsic connections prompted a sub‐designation of the V6 complex itself into two separate areas, V6 and V6A, with area V6A lying dorsal, or dorsomedial to V6 proper. V6 receives ascending input from V2 and V3, ranks equal to V3A and V5, and provides an ascending input to V6A at the level above. V6A is not connected to area V2 and in general is less heavily linked to the earliest visual areas; in other respects, the two parts of the V6 complex share similar spheres of connectivity. These include regions of peripheral representation in prestriate areas V3, V3A and V5, parietal visual areas V5A/MST and 7a, other regions of visuo‐somatosensory association cortex within the intraparietal sulcus and on the medial surface of the hemisphere, and the premotor cortex. Subcortical connections include the medial and lateral pulvinar, caudate nucleus, claustrum, middle and deep layers of the superior colliculus and pontine nuclei.

  From this pattern of connections, it is clear that the V6 complex is heavily engaged in sensory‐motor integration. The specific somatotopic locations within sensorimotor cortex that receive this input suggest a role in controlling the trunk and limbs, and outward reaching arm movements. There is a secondary contribution to the brain's complex oculomotor circuitry. That the medial region of the cortex is devoted to tightly interconnected representations of the sensory periphery, both visual and somatotopic—which are routinely stimulated in concert—would appear to be an aspect of the global organization of the cortex which must facilitate multimodal integration.
Organization of projections of rat retrosplenial cortex to the anterior thalamic nuclei
Authors: Shibata Hideshi
Published: March 2003

The organization of the projections from the retrosplenial cortex (Brodmann's area 29) to the anterior thalamic nuclei was examined in the rat with retrograde transport of the cholera toxin B subunit and anterograde transport of biotinylated dextran amine. Areas 29a and 29b project mainly ipsilaterally to the rostral two‐thirds of the anteroventral nucleus, with area 29a projecting more rostrodorsally than area 29b. Area 29c projects bilaterally to the ventromedial part of the anteroventral nucleus. The projections from area 29c are organized in a topographic pattern such that the rostral area 29c projects to the caudoventral part of the anteroventral nucleus, whereas the caudal area 29c projects to the more rostrodorsal parts. Caudal area 29d projects mainly ipsilaterally to the rostrodorsal part of the anteromedial nucleus, and the rostral and dorsal parts of the anteroventral nucleus, whereas rostral area 29d projects bilaterally to the caudodorsal part of the anteromedial nucleus and the caudolateral part of the anteroventral nucleus. All the areas of the retrosplenial cortex provide sparse projections, mainly ipsilateral, to the anterodorsal nucleus, with a crude topographic pattern such that the rostrocaudal axis of the retrosplenial cortex corresponds to the caudorostral axis of the anterodorsal nucleus. The results indicate that each area of the retrosplenial cortex has a distinct projection field within the anterior thalamic nuclei. This suggests that each of these projections transmits distinct information that is important for complex memory and learning functions, e.g. discriminative avoidance learning and spatial memory.
Chronic hyperammonemia impairs the glutamate–nitric oxide–cyclic GMP pathway in cerebellar neurons in culture and in the rat in vivo
Authors: Hermenegildo Carlos , Montoliu Carmina , Llansola Marta , Muñoz María‐Dolores , Gaztelu José‐María , Miñana María‐Dolores , Felipo Vicente
Published: March 2003

The aim of this work was to assess whether ammonia concentrations similar to the increase found in the brain of hyperammonemic rats (100 μm), impair N‐methyl‐d‐aspartate (NMDA) receptor‐mediated signal transduction. We first measured glutamate neurotoxicity, which in these neurons is mediated by activation of NMDA receptors, as an initial parameter reflecting activation of NMDA receptor‐mediated pathways. Long‐term treatment of cultured neurons with ammonia prevents glutamate‐induced neuronal death. The EC50 was 20 μm, and at 100 μm the protection was complete. The induction of the protective effect was not immediate, but took several hours.

  Treatment with 100 μm ammonia did not prevent a glutamate‐ or NMDA‐induced rise of intracellular calcium. Ammonia impaired the glutamate–nitric oxide–cGMP (3′,5′‐cyclic guanosine monophosphate) pathway in a dose‐ and time‐dependent manner. Glutamate‐induced formation of cGMP was reduced by 42%, while activation of nitric oxide synthase was not affected. Ammonia reduced by 31% cGMP formation induced by S‐nitroso‐N‐acetyl‐penicillamine (SNAP), a NO‐generating agent, confirming that the interference occurs at the level of guanylate cyclase activation by nitric oxide.

  To assess whether chronic moderate hyperammonemia in vivo also impairs the glutamate–nitric oxide–cGMP pathway, we determined by in vivo brain microdialysis in freely moving rats the formation of cGMP induced by NMDA. In hyperammonemic rats, the formation of cGMP induced by NMDA and SNAP was reduced by ca. 60 and 41%, respectively, indicating that chronic hyperammonemia in the animal in vivo also impairs the glutamate–nitric oxide–cGMP pathway. Impairment of this pathway can contribute to the neurological alterations found in hyperammonemia and hepatic encephalopathy.
AMPA receptors at primary afferent synapses in substantia gelatinosa after sciatic nerve section
Authors: Popratiloff A. , Weinberg R. J. , Rustioni A.
Published: March 2003

Increased excitability of superficial laminae of the spinal cord may contribute to the pathological pain consequent to peripheral nerve injury. Among several mechanisms that may be responsible for this occurrence is upregulation of receptors for glutamate in the spinal cord. To explore this possibility, we investigated changes in AMPA receptors in substantia gelatinosa of rats after section of the sciatic nerve. Immunofluorescence was performed on sections from the fourth lumbar segment. Quantitative analysis of digitally captured images suggested that staining for an antibody to a sequence shared by GluR2 and GluR3 (GluR2/3) was increased on the side ipsilateral to the lesion.

  To determine whether antigen accumulation was at synaptic sites and to probe whether it was selective for primary afferent terminals, we performed electron microscopy on immunogold‐labelled material. Gold particles coding for GluR2/3 subunits were counted from synaptic active zones of glomerular terminals in substantia gelatinosa that originate from small calibre afferent fibres, and from active zones of terminals of probable intrinsic origin. Counts were significantly increased on the side ipsilateral to the lesion only at synapses of primary afferent terminals. These results document selective upregulation of receptor protein at the synapse. This upregulation may contribute to the increased sensitivity of dorsal horn neurons following peripheral nerve injury.
Distribution of choline acetyltransferase immunoreactivity in the vestibular nuclei of normal and unilateral vestibular neurectomized cats
Authors: Tighilet B. , Lacour M.
Published: March 2003

Post‐lesion recovery of vestibular functions is a suitable model for studying adult central nervous system plasticity. The vestibular nuclei complex (VN) plays a major role in the recovery process and neurochemical reorganizations have been described at this brainstem level. The cholinergic system should be involved because administration of cholinergic agonists and antagonists modify the recovery time course. This study was aimed at analysing the postlesion changes in choline acetyltransferase immunoreactivity (ChAT‐Ir) in the VN of cats killed 1 week, 3 weeks or 1 year following unilateral vestibular neurectomy. ChAT‐positive neurons and varicosities were immunohistochemically labelled and quantified (cell count and surface measurement, respectively) by means of an image analysing system. The spatial distribution of ChAT‐Ir within the VN of control cats showed darkly stained neurons and varicosities mainly located in the caudal parts of the medial (MVN) and inferior (IVN) VN, the nucleus prepositus hypoglossi (PH) and, to a lesser extent, in the medial part of the superior vestibular nucleus (SVN). Lesion‐induced changes consisted in a significant increase in both the number of ChAT‐positive neurons (IVN, SVN) and the surface of ChAT‐positive varicosities (IVN, SVN, PH). They were observed bilaterally in the acute (1 year and 3 weeks) and compensated (1 year) cats for the SVN and PH, while they persisted only in the IVN on the lesioned side in the compensated cats. These findings demonstrate vestibular lesion‐induced reorganization of the cholinergic system in the IVN, SVN and PH which could contribute to postural and oculomotor function recovery.