bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in morphology and behaviour of retinal growth cones before and after crossing the midline of the mouse chiasm – a confocal microscopy study
Authors: Chan S. O. , Wong K. F. , Chung K. Y. , Yung W. H.
Published: March 2003

The growth of retinal axons was investigated in different regions of the optic chiasm in C57 pigmented mouse embryos aged embryonic day 13 (E13) to E15. Individual retinal axons and their growth cones were labelled anterogradely by DiI and imaged using a confocal imaging system. In aldehyde‐fixed embryos, retinal growth cones display a simple form in the optic nerve and become more complex in morphology in the chiasm. The complex form is particularly prominent in those axons that turn to the ipsilateral tract in the premidline region of chiasm. Moreover, complex growth cones are also commonly found in axons in the postmidline chiasm, which are markedly different in morphology from those axons in the premidline region, suggesting that the postmidline chiasm contains a novel environment for the pathfinding of retinal axons. In another experiment, the dynamic growth of retinal axons is studied in a brain slice preparation of the living retinofugal pathway. Retinal axons show an intermittent growth across the premidline and postmidline chiasm. Extensive remodelling of growth cone form followed by a shift in growth direction is commonly seen during the pause periods, indicating that signals that guide axon growth across the chiasm are not restricted to the midline, but are laid down throughout the chiasm. Moreover, dramatic changes in axon trajectory are noted first at the premidline chiasm where the uncrossed axons segregate from the crossed axons, and second at the postmidline chiasm where specific sorting of retinal axons according to their position in the dorsal ventral retinal axis and their ages are known to take place. These results show that there are two distinct environments, separated by the midline in the chiasm, where axons show different responses to local guidance cues and develop the distinct fibre orders.
Cellular prion protein localization in rodent and primate brain
Authors: Salès Nicole , Rodolfo Katia , Hässig Raymonde , Faucheux Baptiste , Di Giamberardino Luigi , Moya Kenneth L.
Published: March 2003

The presence of an abnormal, protease‐resistant form of the prion protein (PrP) is the hallmark of various forms of transmissible spongiform encephalopathies (TSE) which can affect a number of mammalian species, including humans. The normal, cellular form of this protein, PrPc, while abundant in brain is also present in many tissues and a number of species. In order to address the unresolved question of the precise localization of normal cerebral PrPc, we used a free‐floating immunohistochemistry procedure to localize the protein at both the light and the electron microscopic levels in the brain of three TSE‐sensitive species: hamster, macaque and humans. This method shows that PrPc is abundant in synaptic terminal fields in olfactory bulb, limbic‐associated structures and in the striato‐nigral complex, whereas many other regions of the hamster brain are essentially devoid of immunoreactivity. With the striking exception of the olfactory nerve, in which axons are continually growing throughout life, PrPc is not abundant in fibre pathways. PrPc distribution in the primate hippocampus and cortex is very similar to the distribution observed in hamster. PrPc was present at synaptic profiles as shown by immunoelectron microscopy, but was not detectable in neuronal perikaryon either by light or electron microscopy. Our results show that PrPc is abundant in a number of brain structures known for ongoing plasticity, and are consistent with the hypothesis that the protein also plays a role in synaptic function.
Human FGF‐1 gene delivery protects against quinolinate‐induced striatal and hippocampal injury in neonatal rats
Authors: Hossain Mir Ahamed , Fielding Kevin E. , Trescher William H. , Ho Tang , Wilson Mary Ann , Laterra John
Published: March 2003

Fibroblast growth factors (FGFs) are cell mitogens and differentiating factors with neuroprotective properties in the CNS. We have already shown that endothelial cells genetically engineered to secrete human FGF‐1 (RBEZ‐FGF) survive implantation to neonatal rat brain (Johnston et al. (1996) J. Neurochem.67, 1643–1652]. In this study, the effects of cell‐based FGF‐1 gene delivery on quinolinate‐induced neurotoxicity in the developing rat brain were examined. Control endothelial cells (RBE4), and RBEZ‐FGF cells were implanted into right striatum at post‐natal day (PND) 7. On PND 10, quinolinate (150 nmol), an endogenous N‐methyl‐d‐aspartate (NMDA) receptor agonist, or vehicle alone was injected into striatum ipsilateral to cell implantation. Injury was quantified in coronal sections obtained from PND 17 animals by comparing striatal and hippocampal volumes ipsilateral and contralateral to the site of quinolinate injection. Human FGF‐1 specific transgene expression in vivo was shown by Northern blot and RT‐PCR up to 14 days after cell implantation in control animals, and up to 4 days after quinolinate exposure. Quinolinate reduced the size of ipsilateral striatum by 37% and hippocampus by 38% in animals preimplanted with control endothelial cells. In contrast, quinolinate reduced the size of striatum by only 14% and had no effect on hippocampal size in animals preimplanted with RBEZ‐FGF cells. Thus, FGF‐1 gene delivery protected the developing striatum and hippocampus from quinolinate‐induced volume loss by 62% and 100%, respectively. Intrastriatal quinolinate resulted in a significant decrease in density of NOS+ CA3 hippocampal neurons (–38%) without affecting the density of NOS+ neurons in hippocampal regions CA1, dentate gyrus or striatum. This response of CA3 NOS+ neurons appeared to be only partially reversed by FGF‐1 gene delivery. Our results show that intracerebral FGF‐1 gene expression within the developing brain can protect striatum and hippocampus from quinolinate‐mediated injury.
Effects of chronic alcohol consumption or Diazepam administration on item recognition and temporal ordering in a spatial working memory task in mice
Authors: Borde Nathalie , Jaffard Robert , Béracochéa Daniel
Published: March 2003

This study was aimed at determining the effects of either Diazepam administration or chronic alcohol consumption (CAC) on spatial memory measured by concurrent discriminations in an eight arm radial maze using mice as subjects. Two different protocols involving a non‐matching rule were used to evaluate either temporal order (recurrent items) or item recognition (non‐recurrent items). Results showed that both Diazepam administration and CAC produced a memory deficit which was primarily observed in the temporal task, whereas item recognition was spared. These data show that Diazepam and CAC produced similar memory impairments. Thus, our study stressed the potential importance of the GABA/BDZ dysfunction in the production of organic amnesia of alcoholic origin. The overall analysis of the data suggests that both CAC and Diazepam injections would impair forms of memory sustained by automatic or incidental learning.
Re‐establishment of direct synaptic connections between sensory axons and motoneurons after lesions of neonatal opossum CNS (Monodelphis domestica) in culture
Authors: Lepre M. , Fernandéz J. , Nicholls J. G.
Published: March 2003

For functional recovery after spinal cord injury, regenerating fibres need to grow and to reform appropriate connections with their targets. The isolated central nervous system of neonatal opossums aged 1–9 days has been used to analyse the precision with which neurons become reconnected during regeneration. In culture these preparations maintain their electrical activity and show rapid outgrowth through spinal cord crushes or cuts. By recording electrically and by staining with horseradish peroxidase, we first demonstrated that direct reflex connections were already present at birth between sensory fibres in one segment and motoneurons in the same segment and in adjacent segments. As in previous experiments, 5 days after the spinal cord had been crushed, labelled sensory fibres grew across the lesion to reach the next segment (Woodward et al. (1993) J. Exp. Biol., 176, 77–88;Varga et al. (1995a) Eur. J.Neurosci., 7, 2119–2129, Varga et al. (1995b) Proc. Natl. Acad. Sci. USA, 92, 10959–10963). Beyond the lesion the labelled axons abruptly changed direction, traversed the spinal cord and terminated on labelled motoneurons in the ventral horn. In preparations that had regenerated dorsal root stimulation once again initiated ventral root reflexes. Electron micrographs revealed synapses made by labelled sensory axons on motoneurons. Double staining of growing sensory axons and radial glial fibres showed close association, suggesting guidance. These results indicate that the original pathway is re‐established during repair and that appropriate connections are reformed after injury.
Associative and limbic regions of monkey striatum express high levels of dopamine D3 receptors: effects of MPTP and dopamine agonist replacement therapies
Authors: Morissette Marc , Goulet Martin , Grondin Richard , Blanchet Pierre , Bédard Paul J. , Di Paolo Thérèse , Lévesque Daniel
Published: March 2003

The role of the dopamine D3 receptor subtype in the central nervous system is still not well understood. It has a distinct and restricted distribution, mostly associated with limbic territories of the striatum (olfactory tubercle and the shell of nucleus accumbens) in rat brain. Dopaminergic denervation induced by a 6‐hydroxydopamine lesion of the nigrostriatal system in rat down‐regulates the expression of the D3 receptor. In the present study, we investigated the functional neuroanatomy of the dopamine D3 receptor subtype in the monkey (Macaca fascicularis) basal ganglia. We also studied the effect of administration of the dopaminergic neurotoxin 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) and chronic D1‐like (SKF 82958) or D2‐like (cabergoline) agonist treatments on dopamine D3 receptor levels using receptor autoradiography. Our results clearly show that the distribution of D3 receptors in the monkey is more closely related to associative and limbic components of the striatum (caudate‐putamen), as compared with its sensorimotor counterpart. Hence, D3 receptors may be more specifically involved in cognitive and motivational aspects of striatal functions, which are elaborated in prefrontal, temporal, parietal, cingulate and limbic cortices. Moreover, MPTP administration significantly decreased levels of D3 receptors and this effect was reversed or compensated by a chronic treatment with a D1‐like, but not a D2‐like, receptor agonist. The D3 receptor may represent an important target for adjunct or direct therapy designed to improve cognitive deficits observed in patients with Parkinson's disease, schizophrenia and other illnesses with frontal lobe cognitive disturbances.
Absence of short‐wavelength sensitive cones in the retinae of seals (Carnivora) and African giant rats (Rodentia)
Authors: Peichl Leo , Moutairou Kabirou
Published: March 2003

Most non‐primate mammals have two types of cone: short‐wavelength sensitive (S) and middle‐to‐long‐wavelength sensitive (M/L) cones. In two species of African giant rats, Cricetomys gambianus and C. emini, and in two species of earless seals, Phoca hispida and P. vitulina, the retinal cone types and cone distributions were assessed with antibodies specific for the M/L‐cone opsin and the S‐cone opsin, respectively. All four species were found to completely lack S‐cones, while M/L‐cones were present in low densities. M/L‐cone densities, rod densities and cone/rod ratios were determined across the retina. Cone proportions are about 0.3–0.5% in C. gambianus, 0.5–0.8% in C. emini, and 1.5–1.8% in P. hispida. An absence of S‐cones has previously been reported in a few nocturnal mammals. As earless seals are visually active during night and day, we conclude that an absence of S‐cones is not exclusively associated with nocturnality. The functional and comparative aspects are discussed.
Short‐lasting exposure to one odour decreases general reactivity in the olfactory bulb of adult rats
Authors: Buonviso N. , Gervais R. , Chalansonnet M. , Chaput M.
Published: March 2003

We investigated in adult rats whether a relatively short exposure to a novel odour can lead to changes in reactivity of olfactory bulb principal neurons. Naive rats were exposed to isoamyl acetate for 20 min per day either for 6 consecutive days or for a single 20‐min exposure. Control group was non‐exposed. Under anaesthesia, responsiveness of each recorded single mitral/tufted cell was tested towards isoamyl acetate and four other odours. Results show that the proportion of responding cells in the exposed groups decreased drastically when compared to controls. In the two experimental groups recorded 24 h following the last exposure, mitral/tufted cells show a significant decrease in the number of excitatory responses. In parallel, the number of non‐responsive cells increased by at least a fourfold factor. This decrease in reactivity was not selective towards the odour used during the exposure but concerned any of the five test‐odours presented during recordings. Finally, this lower responsiveness was long lasting as it was still observed 10 days after the end of the last exposure. This preliminary study points out the importance of even limited sensory experience in neural representation of odours.
Influence of Gz and Gi2 transducer proteins in the affinity of opioid agonists to μ receptors
Authors: Garzón Javier , Castro Marián , Sánchez‐Blázquez Pilar
Published: March 2003

The affinity displayed by different opioids to μ receptors (ORs) was determined in mouse brain membranes incubated with antibodies directed to Gα subunits of the guanine nucleotide‐binding proteins Gi2 and Gz. Assays were conducted with 10 pm125I‐Tyr27‐β‐endorphin in the presence of 300 nmN,N‐diallyl‐Tyr‐(α‐aminoisobutyric acid)2‐Phe‐Leu‐OH (ICI‐174 864), which prevented the binding of the iodinated neuropeptide to δ‐ORs. Gpp(NH)p or the preincubation of mouse brain membranes with IgGs to Gi2α or Gzα subunits, promoted reductions in the affinity exhibited by the labelled probe. The potencies of β‐endorphin, [D‐Ala2,N‐MePhe4,Gly‐ol5]‐enkephalin (DAMGO) and [D‐Pen2,5]enkephalin (DPDPE) were reduced after impairing the coupling of μ‐ORs to Gi2 or Gz proteins. Morphine showed a loss of affinity towards the μ‐OR after preincubation of membranes with IgGs to Gzα subunits. However, it retained its potency after treatment with the anti‐Gi2α IgGs. Conversely, [D‐Ala2, D‐Leu5]enkephalin (DADLE) and [D‐Ser2, Leu5] enkephalin‐Thr6 (DSLET) showed decreased affinity to μ‐ORs after treatment with anti‐Gi2α IgGs, with no noticeable change following the use of IgGs to Gzα subunits. The affinity exhibited by the opioid antagonists naloxone, naltrexone, naloxonazine and [Cys2,Tyr3,Orn5,Pen7 amide]somatostatin analogue (CTOP) remained unchanged after either treatment. Therefore, the affinity exhibited by opioid agonists of μ‐ORs, but not antagonists, depends on the nature of the G‐protein coupled to these receptors.
Two types of TTX‐resistant and one TTX‐sensitive Na+ channel in rat dorsal root ganglion neurons and their blockade by halothane
Authors: Scholz A. , Appel N. , Vogel W.
Published: March 2003

The clinically employed general anaesthetic halothane was shown to exert action on the peripheral nervous system by suppressing spinal reflexes, but it is still unclear which mechanisms underlie this action. The present study addressed the question whether blockade of tetrodotoxin‐sensitive (TTXs) and ‐resistant (TTXr) Na+‐channels in rat dorsal root ganglia (DRG) neurons by halothane could explain its peripheral effects. Two types of TTXr Na+‐currents, fast and slow, with distinct activation and inactivation kinetics were found in small (< 25 μm) and medium sized (25–40 μm) DRG neurons. These currents were blocked by halothane with IC50 values of 5.4 and 7.4 mmol/L, respectively. Additionally, in a concentration‐dependent manner halothane accelerated the inactivation kinetics of both currents and shifted the inactivation curves to more hyperpolarized potentials. Neither the activation curves of both TTXr Na+‐currents were influenced by halothane nor a voltage‐dependent block at test potentials of the currents was seen. In contrast to that of fast current, the time‐to‐peak for slow current was changed in the presence of halothane. The TTXs Na+‐current which prevailed in large neurons (> 40 μm) was blocked by halothane with an IC50 of 12.1 mmol/L. Its inactivation curve was also shifted to more hyperpolarized potentials and the inactivation kinetics accelerated with increasing halothane concentration. Similarly to TTXr Na+‐currents, the activation curve of TTXs Na+‐current and its time‐to‐peak were not influenced by halothane. It is suggested that two types of TTXr Na+‐currents can explain the heterogeneity in kinetic data for TTXr Na+‐currents. Furthermore, the incomplete blockade of Na+‐currents might underlie the incomplete reduction of spinal reflexes at clinically used concentrations of halothane.
Intracellular Ca2+during metabolic activation of KATPchannels in spontaneously active dorsal vagal neurons in medullary slices
Authors: Ballanyi Klaus , Kulik Anna
Published: March 2003

Intracellular Ca2+([Ca2+]i) and membrane properties were measured in fura‐2 dialysed dorsal vagal neurons (DVN) spontaneously active at a frequency of 0.5–5 Hz. [Ca2+]iincreased by about 30 nmupon rising spike frequency by more than 200% due to 20–50 pA current pulses or 10 μmserotonin. It fell by 30 nmupon block of spiking by current‐injection, tetrodotoxin or Ni2+and also during hyperpolarization due to γ‐aminobutyric acid or opening of adenosine triphosphate (ATP) ‐sensitive K+(KATP) channels with diazoxide. KATPchannel‐mediated hyperpolarizations during anoxia or cyanide produced an initial [Ca2+]idecrease which reversed into a secondary Ca2+rise by less than 100 nm. Similar moderate rises of [Ca2+]iwere observed during block of aerobic metabolism under voltage‐clamp as well as in intact cells, loaded with fura‐2 AM. The magnitude of the metabolism‐related [Ca2+]itransients did not correlate with the amplitude of the KATPchannel‐mediated outward current. [Ca2+]idid not change during diazoxide‐induced or spontaneous activation of KATPoutward current observed in 10% of cells after establishing whole‐cell recording. Increasing [Ca2+]iwith cyclopiazonic acid did not activate KATPchannels. [Ca2+]iwas not affected upon block of outward current with sulphonylureas, but these KATPchannel blockers were effective to reverse inhibition of spike discharge and, thus, the initial [Ca2+]ifall upon spontaneous or diazoxide‐, anoxia‐ and cyanide‐induced KATPchannel activation. A sulphonylurea‐sensitive hyperpolarization and [Ca2+]ifall was also revealed in the early phase of iodoacetate‐induced metabolic arrest, whereas after about 20 min, occurrence of a progressive depolarization led to an irreversible rise of [Ca2+]ito more than 1 μm. The results indicate that KATPchannel activity in DVN is not affected by physiological changes of intracellular Ca2+and the lack of a major perturbance of Ca2+homeostasis contributes to their high tolerance to anoxia.
Presynaptic protein interactions in vivo: evidence from botulinum A, C, D and E action at frog neuromuscular junction
Authors: Raciborska Dorota A. , Trimble William S. , Charlton Milton P.
Published: March 2003

The present study examines the paralytic action of botulinum neurotoxins at their natural target, the neuromuscular junction. We asked whether syntaxin, synaptosome‐associated protein of 25 kDa (SNAP‐25) and vesicle‐associated membrane protein (VAMP/synaptobrevin), the proteins proteolysed by botulinum, are susceptible to cleavage in frog nerve terminals, and whether they form complexes in vivo. In control terminals, the three SNAREs were distributed in broad bands at 1 μm intervals, at sites consistent with presynaptic Ca2+ channels. Within 3 h, botulinum A, C, D and E (BoNT/A/C/D/E) blocked nerve‐evoked muscle contractions but their effects on substrate immunoreactivity varied. The effect of BoNT/A on either C‐terminus or N‐terminus immunoreactivity of SNAP‐25 was undetectable after 3‐h incubation, although C‐terminus immunoreactivity was reduced after 24 h; N‐terminus immunoreactivity was not affected even after 36 h. BoNT/E reduced C‐terminus immunoreactivity of SNAP‐25 1.5 h after toxin application when transmitter release was blocked, but required 24 h to reduce N‐terminus immunoreactivity. BoNT/C reduced syntaxin immunoreactivity after 24‐h incubation but did not affect SNAP‐25. BoNT/D reduced VAMP immunoreactivity at 3 h while it increased SNAP‐25 C‐terminal staining fourfold. BoNT/A and BoNT/C applied together for 24 h reduced syntaxin immunoreactivity and that of both C‐ and N‐terminus of SNAP‐25, indicating that retention of SNAP‐25 N‐terminus after cleavage by BoNT/A depended on intact syntaxin. Therefore, we infer that SNAP‐25 interacts with VAMP and with syntaxin in vivo. Neurotoxin action abolished only 40–60% of SNAP‐25, VAMP or syntaxin immunoreactivity suggesting that distinct pools of these proteins, not immediately involved in triggered exocytosis, are resistant to proteolysis.
Differential expression of alternative splice variants of β‐arrestin‐1 and ‐2 in rat central nervous system and peripheral tissues
Authors: Komori Naoka , Cain Sandra D. , Roch Jean‐Marc , Miller Kenneth E. , Matsumoto Hiroyuki
Published: March 2003

Members of arrestin/β‐arrestin protein family are thought to participate in agonist‐mediated desensitization of G‐protein‐coupled receptors, including rhodopsin and β2‐adrenergic receptor. Unlike in human and cow, splice variants of this protein family in rat have not been studied extensively, and there has been no report on their existence at protein level. Hence, a previous report by others on the localization of both β‐arrestin‐1 and ‐2 in a wide range of innervated rat tissues could imply their broad receptor specificity. In this report we show the presence of two alternatively spliced forms of β‐arrestin‐1 in several rat tissues using both reverse transcription–polymerase chain reaction and Western immunoblot. Splicing of β‐arrestin‐1 pre‐mRNA appears to be subject to differential regulation between the rat CNS and peripheral tissues. In contrast, we detected no splice variants of β‐arrestin‐2 in rat. A comparison of the genomic DNA sequences of bovine and rat β‐arrestin‐2, where the splicing of bovine β‐arrestin‐2 mRNA has been reported, revealed a high degree of homology in their organization of exons and introns as well as certain differences that might be responsible for the different processing of β‐arrestin‐2 mRNA in the two species. Our two‐dimensional isoelectric focusing gels using rat spinal cord and heart tissues demonstrate isoelectric heterogeneity of rat β‐arrestin‐1, suggesting that β‐arrestin‐1 is subject to post‐translational modification unlike β‐arrestin‐2.
An animal model of autism: behavioural studies in the GS guinea‐pig
Authors: Caston J. , Yon E. , Mellier D. , Godfrey H. P. , Delhaye‐Bouchaud N. , Mariani J.
Published: March 2003

Autism is a human behavioural pathology marked by major difficulties in abnormal socialization, language comprehension and stereotypic motor patterns. These behavioural abnormalities have been associated with corticocerebral and cerebellar abnormalities in autistic patients, particularly in vermal folia VI and VII. Progress in understanding this disease has been hindered by the absence of a non‐primate animal model. GS guinea‐pigs are a partially inbred, non‐ataxic guinea‐pig strain with cerebellar and corticocerebral abnormalities similar to those reported to exist in human patients with autism. In order to determine if GS guinea‐pigs represent an animal model of autism, their behaviour was compared with that of Hartley strain guinea‐pigs. GS animals learned a motor task significantly more rapidly than Hartley guinea‐pigs, but performed it in a more stereotypic manner and were less influenced by environmental stimuli than Hartleys. GS animals exhibited significantly less exploratory behaviour in a novel environment and were significantly less responsive to 50–95 dBA pure tones than Hartley guinea‐pigs. In a social interaction assay, GS guinea‐pigs interacted significantly less frequently with each other or with Hartley guinea‐pigs than Hartleys did under the same conditions. GS behaviour thus exhibits autistic‐like behaviour patterns: motor stereotypy, lack of exploration and response to environment and poor social interaction. Coupled with the neuropathological findings, this abnormal behaviour suggests that GS guinea‐pigs could be a useful animal model of autism.
The expression of the glial glutamate transporter protein EAAT2 in motor neuron disease: an immunohistochemical study
Authors: Fray Anne E. , Ince Paul G. , Banner Steven J. , Milton Ian D. , Usher Philip A. , Cookson Mark R. , Shaw Pamela J.
Published: March 2003

Emerging evidence suggests that a disturbance of the glutamate neurotransmitter system may be a contributory factor to motor neuron injury in motor neuron disease. Previous autoradiographic and immunoblotting studies have suggested that there may be reduced expression of glutamate transporter proteins in pathologically affected areas of the CNS in motor neuron disease. This study further explores the possible alteration in expression of the excitatory amino acid transporter protein EAAT2 in MND, by examining the protein expression in situ, in frozen sections, using immunohistochemistry. The aim of the study was to compare the distribution and density of EAAT2 in the motor cortex and spinal cord of MND cases (n = 16) compared with neurologically normal controls (n = 12), matched for relevant parameters. A novel, previously characterized, monoclonal antibody to EAAT2 was employed. EAAT2 immunoreactivity in motor neuron disease and control cases was compared using relative optical density measurements generated by computerized image analysis. In the motor cortex, EAAT2 immunoreactivity was laminated comprising a superficial intense band (corresponding to layers 1 and 2); a paler middle band (layer 3 and part of 5) and a more intense deep layer (layers 5 and 6). In the spinal cord, the ventral horn showed strong immunoreactivity with dense perisomatic staining around motor neuron cell bodies, the substantia gelatinosa showed moderate diffuse staining and the intermediate spinal laminae showed weak staining. This general pattern of immunoreactivity was preserved in the motor neuron disease cases. However, in the motor neuron disease cases compared with controls, the optical density values for EAAT2 immunoreactivity were significantly reduced in all grey matter regions of the lumbar spinal cord (P < 0.001) and were increased in the middle laminae of the motor cortex (P < 0.05). This study indicates that glutamate transporter pathology in motor neuron disease may be a more complex phenomenon than previously recognized.
The layout of orientation and ocular dominance domains in area 17 of strabismic cats
Authors: Löwel Siegrid , Schmidt Kerstin E. , Kim Dae‐Shik , Wolf Fred , Hoffsümmer Frank , Singer Wolf , Bonhoeffer Tobias
Published: March 2003

In the primary visual cortex of strabismic cats, the elimination of correlated activity between the two eyes enhances the segregation of the geniculocortical afferents into alternating ocular dominance domains. In addition, both tangential intracortical fibres and neuronal synchronization are severely reduced between neurons activated by different eyes. Consequently, ocular dominance columns belonging to different eyes are functionally rather independent. We wondered whether this would also affect the organization of orientation preference maps. To this end, we visualized the functional architecture of area 17 of strabismic cats with both optical imaging based on intrinsic signals and double labelling of orientation and ocular dominance columns with [14C]2‐deoxyglucose and [3H]proline. As expected, monocular iso‐orientation domains had a patchy appearance and differed for the two eyes, leading to a clear segregation of the ocular dominance domains. Comparison of ‘angle maps’ revealed that orientation domains exhibit a pinwheel organization as in normally reared cats. Interestingly, the map of orientation preferences did not show any breaks at the borders between ocular dominance columns: iso‐orientation domains were continuous across these borders. In addition, iso‐orientation contours tended to cross the borders of adjacent ocular dominance columns at right angles. These data suggest that the basic relations between the layout of orientation maps and ocular dominance columns are not disturbed by artificial decorrelation of binocular input. Therefore in cat area 17, the orientation map does not seem to be modified by experience‐dependent changes of thalamic input connections. This suggests the possibility that use‐dependent rearrangement of geniculocortical afferents into ocular dominance columns is due to Hebbian modifications whereby postsynaptic responsivity is constrained by the scaffold of the orientation map.
GABA‐dependent generation of ectopic action potentials in the rat hippocampus
Authors: Avoli Massimo , Methot Mario , Kawasaki Hiroto
Published: March 2003

Intracellular recordings from CA3 pyramidal cells of rat hippocampus in a slice preparation revealed the occurrence of interictal epileptiform discharges and synchronous GABA‐mediated potentials during application of 4‐aminopyridine (4AP, 50 μm). The synchronous GABA‐mediated potential consisted of a sequence of early hyperpolarization, long‐lasting depolarization (LLD), and late hyperpolarization. Action potentials of variable amplitude occurred at the peak of the early hyperpolarization and during the LLD rising phase (48 of 64 cells); they were not prevented by membrane hyperpolarization and displayed inflections that were reminiscent of the initial segment‐somatodendritic (IS‐SD) fractionation. Interictal discharges were blocked by excitatory amino acid receptor antagonists, while both GABA‐mediated potentials and action potentials of variable amplitude continued to occur (n = 10). The latter events were still recorded in the presence of the GABAB receptor antagonist CGP‐35348 (0.5–1 mm, n = 4), but were abolished by the GABAA receptor antagonist bicuculline methiodide (BMI, 10 μm, n = 5). Localized application of BMI (20 μm, n = 6) or tetrodotoxin (TTX, 5 μm, n = 3) to the CA1 stratum radiatum blocked the variable amplitude action potentials; these effects were not seen when BMI (n = 4) or TTX (n = 4) were applied to the CA3 stratum radiatum, although both procedures made LLDs disappear. Our findings indicate that action potentials of variable amplitude recorded from CA3 pyramidal cells in the 4AP model are generated at or near the terminal region of the Schaffer collaterals and that they represent TTX‐sensitive ectopic events. These action potentials are generated at this site by a BMI‐sensitive (and thus GABAA‐mediated) mechanism. We propose that the ectopic action potentials reflect an increased excitability of axon terminals that is presumably caused by [K+]o elevations associated with the 4AP‐induced synchronous GABA‐mediated potential.
Spatial‐frequency tuning and geniculocortical projections in the visual cortex (areas 17 and 18) of the pigmented ferret
Authors: Baker Gary E. , Thompson I. D. , Krug K. , Smyth D. , Tolhurst D. J.
Published: March 2003

We have examined the spatial‐frequency selectivity of neurons in areas 17 and 18 of the adult pigmented ferret, by measuring how the amplitude of response depends on the spatial‐frequency of moving sinusoidal gratings of optimal orientation and fixed contrast. Neurons in area 17 of the ferret respond optimally to low spatial frequencies [average 0.25 cycles per degree (c/deg)], much lower than the optima for cat area 17. The tuning curves are of the same form as those found in cat and monkey: unimodal with bandwidths in the range 0.8–3.5 octaves. Neurons in area 18 of the ferret respond optimally to even lower spatial frequencies (average 0.087 c/deg) than area 17 neurons, and the distributions of optimal spatial frequency for areas 17 and 18 hardly overlap. In both cortical areas, the bandwidth of the tuning curves is inversely correlated with optimal spatial frequency. This marked difference in tuning between the two cortical areas is probably attributable to differential geniculo‐cortical projections. Small injections of fluorescent latex microspheres or horseradish peroxidase (HRP) were made into area 17 or area 18 in order to investigate the populations of geniculate neurons projecting to the two cortical areas. After injections into area 17, labelled neurons are found predominantly in the geniculate A layers, with a few neurons labelled in the C layers. Conversely, after an area 18 injection, similar numbers of labelled neurons are found in the C layers as in the A layers. Soma‐size analysis of the neurons in the A‐layers suggests the existence of two populations of relay neurons, which project differentially to areas 17 and 18. The different geniculate inputs and the different spatial‐frequency tuning in areas 17 and 18 may imply that the two cortical areas process visual information more in parallel than in series.
The cytokine network of Wallerian degeneration: IL‐10 and GM‐CSF
Authors: Be′eri Hadassah , Reichert Fanny , Saada Ann , Rotshenker Shlomo
Published: March 2003

Wallerian degeneration (WD) is the inflammatory response of peripheral nerves to injury. Evidence is provided that granulocyte macrophage colony stimulating factor (GM‐CSF) contributes to the initiation and progression of WD by activating macrophages and Schwann, whereas IL‐10 down‐regulates WD by inhibiting GM‐CSF production. A significant role of activated macrophages and Schwann for future regeneration is myelin removal by phagocytosis and degradation. We studied the timing and magnitude of GM‐CSF and IL‐10 production, macrophage and Schwann activation, and myelin degradation in C57BL/6NHSD and C57BL/6‐WLD/OLA/NHSD mice that display normal rapid‐WD and abnormal slow‐WD, respectively. We observed the following events in rapid‐WD. The onset of GM‐CSF production is within 5 h after injury. Production is steadily augmented during the first 3 days, but is attenuated thereafter. The onset of production of the macrophage and Schwann activation marker Galectin‐3/MAC‐2 succeeds that of GM‐CSF. Galectin‐3/MAC‐2 production is up‐regulated during the first 6 days, but is down‐regulated thereafter. The onset of myelin degradation succeeds that of Galectin‐3/MAC‐2, and is almost complete within 1 week. IL‐10 production displays two phases. An immediate low followed by a high that begins on the fourth day, reaching highest levels on the seventh. The timing and magnitude of GM‐CSF production thus enable the rapid activation of macrophages and Schwann that consequently phagocytose and degrade myelin. The timing and magnitude of IL‐10 production suggest a role in down‐regulating WD after myelin is removed. In contrast, slow‐WD nerves produce low inefficient levels of GM‐CSF and IL‐10 throughout. Therefore, deficient IL‐10 levels cannot account for inefficient GM‐CSF production, whereas deficient GM‐CSF levels may account, in part, for slow‐WD.
Induction of long‐term potentiation at spinal synapses by noxious stimulation or nerve injury
Authors: Sandkühler Jürgen , Liu Xianguo
Published: March 2003

Use‐dependent long‐term potentiation of synaptic strength (LTP) is an intensively studied model for learning and memory in vertebrates. Induction of LTP critically depends on the stimulation parameters of presynaptic fibres with synchronous high‐frequency bursts being most effective at many central synapses. It is, however, not known whether naturally occurring discharge patterns may induce LTP and whether LTP has any biological function in sensory systems. Here we have investigated the LTP of excitatory synaptic transmission between primary afferent C‐fibres, many of which are nociceptors, and neurons in rat superficial spinal dorsal horn. LTP that lasted for 4–6 h could not only be induced by electrical stimulation of sural nerve but also by natural stimulation of heat‐, mechano‐ or chemosensitive nociceptors in the skin or by acute nerve injury. Maintenance of LTP was not affected when afferent nerves were cut 1 h or 5 min after noxious skin stimulation, indicating that an ongoing afferent barrage is not required. Natural noxious stimuli induced LTP in animals which were spinalized but were ineffective in intact animals. Thus, induction of LTP is suppressed by tonically active supraspinal descending systems. We conclude that the natural non‐synchronized discharge patterns that are evoked by noxious stimulation may induce LTP and that this new form of LTP may be an underlying mechanism of afferent induced hyperalgesia.
Quinolinic acid‐induced inflammation in the striatum does not impair the survival of neural allografts in the rat
Authors: Duan Wei‐Ming , Widner Håkan , Cameron Reynolds M. , Brundin Patrik
Published: March 2003

It has been suggested that inflammation related to intracerebral transplantation surgery can affect the survival of intrastriatal neural allografts. To test this hypothesis, we transplanted dissociated embryonic mesencephalic tissue from one of two rat strains, Lewis (allogeneic grafts) or Sprague–Dawley (syngeneic grafts), to the striatum of Sprague–Dawley rats. The target striatum was either intact or had received a local injection of quinolinic acid 9 days earlier, in order to induce a marked inflammation. At 6 or 12 weeks after transplantation, there was no significant difference between the different groups regarding the number of surviving grafted tyrosine hydroxylase immunoreactive neurons. However, the graft volume of both the syngeneic and allogeneic implants was significantly larger in the quinolinate‐lesioned than in the intact striatum. There were dramatically increased levels of expression of major histocompatibility complex class I and II antigens, marked infiltrates of macrophages, activated microglia and astrocytes, and accumulation of large numbers of CD4 and CD8 positive T‐lymphocytes in the quinolinate‐lesioned striatum. In contrast, these immunological markers were much less abundant around both syngeneic and allogeneic grafts placed in intact striatum. We conclude that severe inflammation caused by quinolinic acid does not lead to rejection of intrastriatal neural allografts.
5HT1A‐receptors and behaviour under chronic stress: selective counteraction by testosterone
Authors: Flügge G. , Kramer M. , Rensing S. , Fuchs E.
Published: March 2003

Behaviour of chronically stressed male tree shrews is characterized by a reduction in scent marking, self‐grooming and overall locomotor activity. It has been proposed that this subordination behaviour is related to the down‐regulation of 5HT1A‐receptors occurring in distinct brain regions of the animals. The high cortisol concentrations which accompany chronic stress are supposed to induce 5HT1A‐receptor down‐regulation. Because chronic stress in males also decreases androgen levels we investigated whether behaviour and 5HT1A‐receptor expression could be renormalized by testosterone replacement.

 Male tree shrews were submitted to subordination stress for 28 days, while during the last 18 days, one

group was treated with testosterone and one with vehicle. Scent marking, self‐grooming, and overall locomotor activity were monitored, and cortisol levels were measured in morning urine during the whole experiment. Brain 5HT1A‐receptors were quantified by in vitro receptor autoradiography.

 Although in subordinate animals cortisol levels remained high during the testosterone treatment, 5HT1A‐receptors in the hippocampal formation and the occipital cortex were renormalized to control levels by the androgen, but 5HT1A‐receptors in the ventromedial thalamic nucleus did not return to base line levels. Scent marking and self‐grooming behaviour were both renormalized by testosterone, but overall locomotor activity did not return to base line levels.

 These data indicate that a balance between glucocorticoids and androgens is necessary to maintain ‘normal’ numbers of the monoamine receptors. The fact that both, 5HT1A‐receptors and certain behaviours can be renormalized by the sex steroid supports the view that 5HT1A‐receptor are involved in the regulation of stress behaviour. However, the fact that overall locomotor activity was not returned to baseline indicates that different types of behaviour are distinctly regulated.
Differential acetylcholine and GABA release from cultured chick retina cells
Authors: Santos Paulo F. , Carvalho Ana L. , Carvalho Arsélio P. , Duarte Carlos B.
Published: March 2003

In the present work we investigated the mechanisms controlling the release of acetylcholine (ACh) and of γ‐aminobutyric acid (GABA) from cultures of amacrine‐like neurons, containing a subpopulation of cells which are simultaneously GABAergic and cholinergic. We found that 81.2 ± 2.8% of the cells present in the culture were stained immunocytochemically with an antibody against choline acetyltransferase, and 38.5 ± 4.8% of the cells were stained with an antibody against GABA. Most of the cells containing GABA (87.0 ± 2.9%) were cholinergic. The release of acetylcholine and GABA was mostly Ca2+‐dependent, although a significant release of [3H]GABA occurred by reversal of its transporter. Potassium evoked the Ca2+‐dependent release of [3H]GABA and [3H]acetylcholine, with EC50 of 31.0 ± 1.0 mm and 21.6 ± 1.1 mm, respectively. The Ca2+‐dependent release of [3H]acetylcholine was significantly inhibited by 1 μm tetrodotoxin and by low (30 nm) ω‐conotoxin GVIA (ω‐CgTx GVIA) concentrations, or by high (300 nm) nitrendipine (Nit) concentrations. On the contrary, the release of [14C]GABA was reduced by 30 nm nitrendipine, or by 500 nmω‐CgTx GVIA, but not by this toxin at 30 nm. The release of either transmitters was unaffected by 200 nmω‐Agatoxin IVA (ω‐Aga IVA), a toxin that blocks P/Q‐type voltage‐sensitive Ca2+ channels (VSCC). The results show that Ca2+‐influx through ω‐CgTx GVIA‐sensitive N‐type VSCC and through Nit‐sensitive L‐type VSCC induce the release of ACh and GABA. However, the significant differences observed regarding the Ca2+ channels involved in the release of each neurotransmitter suggest that in amacrine‐like neurons containing simultaneously GABA and acetylcholine the two neurotransmitters may be released in distinct regions of the cells, endowed with different populations of VSCC.
Axonal injury and peripheral nerve grafting in the thalamus and cerebellum of the adult rat: upregulation of c‐jun andcorrelation with regenerative potential
Authors: Vaudano E. , Campbell G. , Hunt S. P. , Lieberman A. R.
Published: March 2003

The protooncogene c‐junis highly expressed for long periods in axotomized PNS neurons. This may be related to their growth and regeneration. In contrast, axotomized CNS neurons show only a small and transient upregulation of c‐jun. It has been suggested that there may be a correlation between this failure to maintain high levels of c‐junexpression after axotomy and abortive CNS axonal regeneration. We have studied, byin situhybridization and immunohistochemistry, the c‐junresponse after stab wound lesion, and after peripheral nerve grafting in the thalamus and cerebellum of the adult rat. A lesion elicits upregulation of c‐junin thalamic neurons ipsilateral to the lesion. This is most evident and prolonged in neurons such as those of the thalamic reticular nucleus, which have an established propensity to regenerate. After peripheral nerve grafting, the c‐junresponse in thalamic neurons is enhanced, mostly in neurons which have axons regenerating along the grafts. These neurons also upregulate growth‐associated protein 43 (GAP‐43). By comparison, injured Purkinje cells of the cerebellum which do not regenerate their axons along a graft, do not upregulate either c‐junorGAP‐43, although they increase their expression of p75. Thus CNS neurons able to regenerate their axons along a peripheral nerve graft are those in which c‐junis induced after injury, and c‐junmay play a critical role in the control of gene programs for axonal regeneration. Moreover, the observed differences in the ability of CNS neurons to regenerate their axons may relate to a difference in their intrinsic molecular response to axotomy.
Expression of the mRNA for the β2 subunit of the voltage‐dependent sodium channel in rat CNS
Authors: Levy‐Mozziconacci Annie , Alcaraz Gisèle , Giraud Pierre , Boudier Jeanne‐Andrée , Caillol Ghislaine , Couraud François , Autillo‐Touati Amapola
Published: March 2003

Expression of the voltage‐dependent sodium channel has been analysed in adult rat central nervous system by Northern blotting and in situ hybridization. Northern blots showed that all the territories studied express β2 transcripts, albeit with widely varying levels (with cerebellum >> hippocampus > brain > brainstem > spinal cord). In situ hybridization confirmed that in these structures, all the neuronal cell bodies contain β2 mRNA; expression was particularly high in the granule cells of the cerebellum, in both pyramidal cell layer and dentate gyrus in the hippocampus, and in spinal cord motor neurons. Northern blots also showed that RNA extracted from optic nerve and cultured cortical astrocytes contained β2 mRNA, while it was totally absent from sciatic nerve.In situ hybridization evidenced the presence of a numerous population of β2‐positive cells in cerebellum white matter, spinal cord white matter, and in corpus callosum, where frontal sections showed labelled cells arranged in the chain‐like or row pattern typical of interfascicular oligodendrocytes. Combination of antiglial fibrillary acid protein (GFAP) immunofluorescent histochemistry with detection of β2 mRNA evidenced that expression of the transcripts was indeed restricted to GFAP‐negative cells in white matter.
Potentiometric study of resting potential, contributing K+ channels and the onset of Na+ channel excitability in embryonic rat cortical cells
Authors: Maric Dragan , Maric Irina , Smith Susan V. , Serafini Ruggero , Hu Qian , Barker Jeffery L.
Published: March 2003

Resting membrane potential (RMP), K+ channel contribution to RMP and the development of excitability were investigated in the entire population of acutely dissociated embryonic (E) rat cortical cells over E11–22 using a voltage‐sensitive fluorescent indicator dye and flow cytometry. During the period of intense proliferation (E11–13), two cell subpopulations with distinct estimated RMPs were recorded: one polarized at ∼–70 mV and the other relatively less‐polarized at ∼–40 mV. Ca2+o was critical in sustaining the RMP of the majority of less‐polarized cells, while the well‐polarized cells were characterized by membrane potentials exhibiting a ∼Nernstian relationship between RMP and [K+]o. Analysis of these two subpopulations revealed that > 80% of less‐polarized cells were proliferative, while > 90% of well‐polarized cells were postmitotic. Throughout embryonic development, the disappearance of Ca2+o‐sensitive, less‐polarized cells correlated with the disappearance of the proliferating population, while the appearance of the K+o‐sensitive, well‐polarized population correlated with the appearance of terminally postmitotic neurons, immuno‐identified as BrdU–, tetanus toxin+ cells. Differentiating neurons were estimated to contain increased K+i relative to less‐polarized cells, coinciding with the developmental expression of Cs+/Ba2+‐sensitive and Ca2+‐dependent K+ channels. Both K+ channels contributed to the RMP of well‐polarized cells, which became more negative toward the end of neurogenesis. Depolarizing effects of veratridine, first observed at E11, progressively changed from Ca2+o‐dependent and tetrodotoxin‐insensitive to Na+o‐dependent and tetrodotoxin‐sensitive response by E18. The results reveal a dynamic development of RMP, contributing K+ channels and voltage‐dependent Na+ channels in the developing cortex as it transforms from proliferative to primarily differentiating tissue.