bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reticular stimulation evokes suppression of CA1 synaptic responses and generation of theta through separate mechanisms
Authors: Jiang Fengli , Khanna Sanjay 
Published: January 2004

AbstractThe induction of hippocampal theta by reticular stimulation involves a relay to the hippocampus via the posterior hypothalamic–supramammillary region and then the medial septum. Interestingly, sensory‐ or behaviour‐induced theta is accompanied by suppression of hippocampal field CA1 synaptic responses. In the present study, performed on anaesthetized rats, we observed that reticular stimulation also induced a suppression of the CA1 pyramidal cell population spike and the corresponding dendritic field excitatory postsynaptic potential evoked by field CA3 stimulation. This suppression was observed at stimulation intensity below the threshold for generation of CA1 theta and was maximal at stimulation intensities at the threshold for theta. The frequency and amplitude of theta waves, by contrast, increased further with increasing reticular stimulation voltage. Neural inactivation by microinjection of the local anaesthetic procaine (20% w/v, 0.1–0.2 µL) or the inhibitory ligand gamma aminobutyric acid (0.8 m, 0.5 µL) in the posterior hypothalamic regions, especially the ipsilateral medial supramammillary region, or the medial septum attenuated both the suppression of CA1 pyramidal cell synaptic excitability and theta generation. However, the effects of microinjection on suppression and theta were not always in parallel. Furthermore, the effect of microinjection of gamma aminobutyric acid on reticularly elicited suppression was observed from relatively fewer sites in the posterior hypothalamus as compared with that on theta activation. These results suggest that reticular stimulation evokes an inhibition of CA1 pyramidal cell excitability that (i) is mediated, at least in part, via medial supramammillary and septal regions, but (ii) involves a separate neural pathway from theta generation.
Properties of delay‐period neuronal activity in the primate prefrontal cortex during memory‐ and sensory‐guided saccade tasks
Authors: Tsujimoto Satoshi , Sawaguchi Toshiyuki 
Published: January 2004

AbstractThe dorsolateral prefrontal cortex (DLPFC) is involved in visuospatial short‐term (or working) memory. Its cellular basis has been widely examined using the delayed‐response paradigm in nonhuman primates. Sustained delay‐period activity in DLPFC neurons with directional difference (i.e. directional delay‐period activity) has been thought to represent visuospatial short‐term (or working) memory. However, little is known about the activity of these neurons during a delay period when the sensory input remains. To address this issue, we examined neuronal activity in the DLPFC while macaque monkeys performed a memory‐guided saccade (MGS) task and a delayed visually guided saccade (VGS) task. The MGS task required a memory‐guided saccade for a remembered target location. The VGS task had the same temporal sequence as the MGS task, but the sensory stimulus remained during the delay period. We found that most of the DLPFC neurons with directional delay‐period activity showed sustained activation during the ‘delay’ period in the VGS task only (‘V‐neurons’, 49%), or in both tasks (‘MV‐neurons’, 46%). Neurons showing directional delay‐period activity in the MGS task only (‘M‐neurons’) were only 5% of the DLPFC neurons with directional delay‐period activity. These findings indicate that most DLPFC neurons that are active during the delay period are also active when the sensory stimulus remains, suggesting that DLPFC neurons driven by mnemonic information are also driven by sensory input. Such sustained representation of information should have potential utility in flexible cognitive controls of behaviour.
The serum‐ and glucocorticoid‐induced kinase SGK inhibits mutant huntingtin‐induced toxicity by phosphorylating serine 421 of huntingtin
Authors: Rangone Hélène , Poizat Ghislaine , Troncoso Juan , Ross Christopher A. , MacDonald Marcy E. , Saudou Frédéric , Humbert Sandrine 
Published: January 2004

AbstractHuntington's disease (HD) is caused by abnormal polyglutamine (polyQ) expansion in the protein huntingtin. We have previously demonstrated the importance of the insulin‐like growth factor I (IGF‐1)/Akt pathway in HD. Indeed, upon IGF‐1 activation, Akt phosphorylates polyQ‐huntingtin at serine 421 and abrogates its toxicity. In addition, we have demonstrated that Akt is altered in the brain of HD patients. Here, we investigate the role of the serum‐ and glucocorticoid‐induced kinase (SGK) in HD. We show that SGK phosphorylates huntingtin at serine 421 and that phosphorylation can protect striatal neurons against polyQ‐huntingtin‐induced toxicity. We find that SGK levels are increased in the brain of HD patients. Using a cellular model of HD, we demonstrate that the SGK dysregulation induced by polyQ‐huntingtin occurs via the p38/MAPK pathway. Collectively, our results strongly suggest the involvement of SGK in HD and further imply that IGF‐1 downstream signalling is a key transduction pathway that regulates the toxicity of huntingtin.
Kv1 currents mediate a gradient of principal neuron excitability across the tonotopic axis in the rat lateral superior olive
Authors: Barnes‐Davies Margaret , Barker Matthew C. , Osmani Fatima , Forsythe Ian D. 
Published: January 2004

AbstractPrincipal neurons of the lateral superior olive (LSO) detect interaural intensity differences by integration of excitatory projections from ipsilateral bushy cells and inhibitory inputs from the medial nucleus of the trapezoid body. The intrinsic membrane currents active around firing threshold will form an important component of this binaural computation. Whole cell patch recording in an in vitro brain slice preparation was employed to study conductances regulating action potential (AP) firing in principal neurons. Current‐clamp recordings from different neurons showed two types of firing pattern on depolarization, one group fired only a single initial AP and had low input resistance while the second group fired multiple APs and had a high input resistance. Under voltage‐clamp, single‐spiking neurons showed significantly higher levels of a dendrotoxin‐sensitive, low threshold potassium current (ILT). Block of ILT by dendrotoxin‐I allowed single‐spiking cells to fire multiple APs and indicated that this current was mediated by Kv1 channels. Both neuronal types were morphologically similar and possessed similar amounts of the hyperpolarization‐activated nonspecific cation conductance (Ih). However, single‐spiking cells predominated in the lateral limb of the LSO (receiving low frequency sound inputs) while multiple‐firing cells dominated the medial limb. This functional gradient was mirrored by a medio‐lateral distribution of Kv1.1 immunolabelling. We conclude that Kv1 channels underlie the gradient of LSO principal neuron firing properties. The properties of single‐spiking neurons would render them particularly suited to preserving timing information.
Pyruvate limits zinc‐induced rat oligodendrocyte progenitor cell death
Authors: Kelland Eve E. , Kelly Mary D. , Toms Nick J. 
Published: January 2004

AbstractA growing body of evidence suggests that excessive Zn2+ release plays a key role in inducing neuronal death during central nervous system injury. However, the possible cytotoxicity of extracellular Zn2+ to oligodendrocyte lineage cells remains unknown. Employing cultures of rat oligodendrocyte progenitor cells (OPC), we report here that OPC are vulnerable to increased extracellular Zn2+ levels and that pyruvate limits Zn2+‐induced OPC death. Zn2+‐induced concentration‐dependent (pEC50 = −4.1 ± 0.1) OPC death, which was insensitive to both α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor (Evans Blue) and l‐type Ca2+ channel (nicardipine) inhibition. Neither kainate nor nicardipine influenced OPC 65Zn2+ accumulation, in contrast with the Zn2+ ionophore, pyrithione. Cytotoxic extracellular Zn2+ concentrations failed to increase OPC reactive oxygen species production and the antioxidant reagents, trolox, N,N′‐diphenyl‐1,4‐phenylenediamine and N‐tert‐butyl‐α‐phenylnitrone did not afford significant protection from Zn2+ insults. The apoptotic inducer staurosporine induced the appearance of known apoptotic markers [pyknotic nuclei and caspase‐3 specific (120 kDa) α‐fodrin cleavage fragment], events not reproduced with Zn2+ insults. Zn2+ insults were also insensitive to the pan‐caspase inhibitor Z‐VAD‐fmk. However, pyruvate afforded significant OPC protection from lethal Zn2+ insults. We conclude that cultured OPC are vulnerable to Zn2+ insults, via a nonoxidative stress and noncaspase‐3‐based mechanism, involving Zn2+ inhibition of OPC glycolysis.
Enhanced generation of intracellular Aβ42 amyloid peptide by mutation of presenilins PS1 and PS2
Authors: Takeda Kazuya , Araki Wataru , Tabira Takeshi 
Published: January 2004

AbstractThe accumulation of amyloid β‐peptide (Aβ) in the brain is a critical pathological process in Alzheimer's disease (AD). Recent studies have implicated intracellular Aβ in neurodegeneration in AD. To investigate the generation of intracellular Aβ, we established human neuroblastoma SH‐SY5Y cells stably expressing wild‐type amyloid precursor protein (APP), Swedish mutant APP, APP plus presenilin 1 (PS1) and presenilin 2 (PS2; wild‐type or familial AD‐associated mutant), and quantified intracellular Aβ40 and Aβ42 in formic acid extracts by sensitive Western blotting. Levels of both intracellular Aβ40 and Aβ42 were 2–3‐fold higher in cells expressing Swedish APP, compared with those expressing wild‐type APP. Intracellular Aβ42/Aβ40 ratios were approximately 0.5 in these cells. These ratios were increased markedly in cells expressing mutant PS1 or PS2 compared with those expressing their wild‐type counterparts, consistent with the observed changes in secreted Aβ42/Aβ40 ratios. High total levels of intracellular Aβ were observed in cells expressing mutant PS2 because of a marked elevation of Aβ42. Immunofluorescence staining additionally revealed more intense Aβ42 immunoreactivity in mutant PS2‐expressing cells than in wild‐type cells, which was partially colocalized with immunoreactivity for the trans‐Golgi network and endosomes. The data collectively indicate that PS mutations promote the accumulation of intracellular Aβ42, which appears to be localized in multiple subcellular compartments.
Superior tactile performance and learning in professional pianists: evidence for meta‐plasticity in musicians
Authors: Ragert Patrick , Schmidt Alexander , Altenmüller Eckart , Dinse Hubert R. 
Published: January 2004

AbstractMusician's brains constitute an interesting model for neuroplasticity. Imaging studies demonstrated that sensorimotor cortical representations are altered in musicians, which was assumed to arise from the development of skilled performance. However, the perceptual consequences of the cortical changes remain elusive. Here we ask whether cortical reorganization induced by professional musical skill training is paralleled by the evolution of other, unrelated perceptual abilities. We therefore studied psychophysically tactile spatial acuity as an indirect marker of cortical changes in professional pianists and non‐musician control subjects using a simultaneous two‐point discrimination paradigm. We show that long‐lasting piano practising resulted in lower spatial discrimination thresholds in comparison to non‐musicians. In musicians, individual discrimination thresholds were linearly correlated with the daily training duration, indicating a direct link between tactile acuity and the degree of piano practising. To investigate whether the superior acuity in pianists is subject to further improvement, we used a Hebbian stimulation protocol of tactile coactivation known to improve spatial tactile acuity. Three hours of coactivation further reduced their discrimination thresholds. The coactivation‐induced gain in pianists was significantly larger in comparison to control subjects and correlated with the years of heavy daily practising (>3 h/day), but not with the total years including casual playing. Our results suggest that despite already high‐level performance in pianists, Hebbian learning was more effective in musicians than in controls. This implies stronger capacities for plastic reorganization and points to enhanced learning abilities implicating a form of meta‐plasticity in professional pianists.
Selective cholinergic denervation of the cingulate cortex impairs the acquisition and performance of a conditional visual discrimination in rats
Authors: Winters Boyer D. , Robbins Trevor W. , Everitt Barry J. 
Published: January 2004

AbstractResults from excitotoxic lesion studies have implicated the cingulate cortex and its basal forebrain afferents in the acquisition and performance of conditional discrimination tasks. In the present work, we sought to clarify the role of specifically cholinergic projections from the vertical limb nucleus of the diagonal band (VDB) to the cingulate cortex in conditional visual discrimination (CVD) learning and performance in rats. We injected the cholinergic immunotoxin 192 IgG‐saporin into the cingulate cortex to produce selective retrograde lesions of the cholinergic neurons projecting from the VDB to the cingulate cortex with the aim of sparing afferents of non‐cingulate regions that can be disrupted by excitotoxic or immunotoxic VDB injections and non‐cholinergic VDB projections that can also be damaged by excitotoxic lesions. Rats sustaining selective cholinergic denervation in this manner were significantly impaired relative to sham‐operated animals in the acquisition and performance of a CVD rule of the type ‘If lights are flashing FAST, press the left lever; if SLOW, press right’. Asymptotic performance of the lesion group was substantially lower than for control rats, indicating an enduring performance deficit. This impairment was associated with a selective disruption on trials with the FAST flashing stimulus. The results confirm the involvement of cholinergic innervation of the cingulate cortex in CVD performance; however, the nature of the deficit suggests a role for cholinergic modulation in task‐relevant stimulus processing rather than stimulus‐response learning per se.
Neonatal 5HT activity antagonizes the masculinizing effect of testosterone on the luteinizing hormone release response to gonadal steroids and on brain structures in rats
Authors: Murray J. F. , Dakin C. L. , Siddiqui A. , Pellatt L. J. , Ahmed S. , Ormerod L. J. A. , Swan A. V. , Davies D. C. , Wilson C. A. 
Published: January 2004

AbstractHypothalamic 5HT concentrations are transiently lower in male compared to female Wistar rats in the second week post partum (pp) and our previous findings have shown that pharmacologically potentiating 5HT activity over this period feminizes certain aspects of sexually differentiated behaviours in adult males and androgenized females. In order to investigate whether neonatal testosterone and 5HT interact to influence physiological and morphological brain sexual differences, females, androgenized females and males were treated with the 5HT2 agonist (−) [2,5 dimethoxy‐4‐iodophenyl]‐2‐amino propane HCl [(−) DOI], over days 8–16 pp. In androgenized females (250 µg testosterone proprionate, day 2 pp) (−) DOI prevented the delay in vaginal opening, but did not prevent the androgen‐induced constant oestrus in females treated with 100 µg TP, day 2 pp. (−) DOI overcame the neonatal androgen effect in suppressing the positive feedback of ovarian steroids in a few males and androgenized females. (−) DOI had a feminizing effect on the volume of the anteroventral periventricular nucleus (normally smaller in males), by significantly increasing its volume in male and androgenized females. It also had a significant antagonistic effect on the testosterone‐induced increase in the volume of the sexually dimorphic nucleus of the preoptic area in males and androgenized females. These findings support the view that raised 5HT activity in the second week of life antagonizes the masculinizing effect of neonatal testosterone.
The significance of chicory to the diet of common duiker at Grants valley, Eastern Cape Province, South Africa
Authors: Kigozi Fred 
Published: January 2004

AbstractSouth Africa is considered one of the top four chicory (Chichorium intybus) producing countries of the world and commercial growing of the plant in the country is restricted to a small area in three districts of the Eastern Cape Province. Faecal analysis technique was used to study the diet of common duiker (Sylvicapra grimmia Linnaeus, 1758) in a chicory growing region at Grants valley. One of the principal items in the diet of these antelopes was chicory and the crop provided more than one third (35.6%) of the winter diet and a substantial proportion (14.4%) of the spring diet of common duiker. These findings confirmed earlier reports of common duiker feeding on cultivated crops and may have profound implications for the South African chicory industry. The study also confirmed earlier findings that common duiker are selective feeders and predominantly browsers, consuming only a very small proportion of monocotyledonous plants.
Seasonal occurrence and local movements of the grey‐headed (brown‐necked) parrot Poicephalus fuscicollis suahelicus in southern Africa
Authors: Symes Craig T. , Perrin Michael R. 
Published: January 2004

AbstractSeasonal movements of grey‐headed (brown‐necked) parrots were recorded in parts of its range and are likely a response to breeding and availability of specific food sources. Breeding occurred in the northern Kruger National Park and lowveld near the Mutale–Luvhuvhu river confluence from April to August. Aggregations and movements of birds occurred during the post‐breeding season (August–December) in response to seasonally abundant food sources. In north‐eastern South Africa, grey‐headed parrots occurred at Levubu, following the breeding season and their arrival in the area was correlated with the availability of unripe Mabola Plum, Parinari curatellifolia fruit. Similar regional movements occurred in Zimbabwe, the Caprivi of northern Namibia and Zambia. During these movements, flocks of up to 50 individuals were observed, whilst during breeding months singletons and pairs were more frequently seen. This increased abundance in time and space suggests that seasonal migratory movements occur.
Phenology of figs in Budongo Forest Uganda and its importance for the chimpanzee diet
Authors: Tweheyo Mnason , Lye Kåre A. 
Published: January 2004

AbstractThis paper reports on the phenological patterns of figs in Budongo Forest, Uganda, and how it relates to chimpanzee food availability in different seasons. In addition, we analysed the dung of chimpanzees to understand the composition of fruits in their diet. The aim of our study was to assess Ficus phenology and how it affects chimpanzee diet. Fifteen species of figs were monitored for fruit (syconium) and leaf phenology between June 2000 and 2001. Ficus fruit production varied significantly between and within species, and also with tree trunk and crown diameters. Fig fruit production was asynchronous and individual fig trees produced crops from one to five times in a year. In addition to fruits, chimpanzees fed on young leaves of some Ficus species. Shedding of old Ficus leaves coincided with the dry season, followed by appearance of young leaves. The dry season in Budongo is a period of general fruit scarcity. The combination of fig fruits and young leaves make up the most important food in the diet of chimpanzees. From the chimpanzee dung, more than 78% of seeds comprised fig ‘seeds’ (nutlets) and the rest of the diaspores were from other tree species. Our findings suggest that chimpanzees disperse large number of diaspores in their dung, thereby serving as important agents of natural forest regeneration.
Population dynamics of small mammals at Mlawula, Swaziland
Authors: Mahlaba T. A. M. , Perrin M. R. 
Published: January 2004

AbstractPopulation density, biomass and composition of a small mammal community in an Acacia nigrescens savanna were studied over 12 months from August 2000. The community consisted of Mus minutoides (A. Smith 1834), Mastomys natalensis (A. Smith 1834), Lemniscomys rosalia (Thomas 1904), Crocidura hirta (Peters 1952), Steatomys pratensis (Peters 1846); and on one occasion, Graphiurus murinus (Desmarest 1822) was caught. M. minutoides was the dominant species in the site. Species richness was found to vary significantly with the time of the year. The density of M. minutoides was significantly high in winter and low in the other seasons, the ratio of males to females was found to be equal, and pregnant females were caught from November to May. The biomass of small mammals in the area (also density and numbers) was generally low (mean biomass 212 g ha−1). The occurrence of new individuals in catches remained high throughout the study, suggesting a high mortality or emigration rate or a combination of the two.
Growth responses of a woody species to clipping and goat saliva
Authors: Rooke Tuulikki 
Published: January 2004

AbstractStudies on the role of mammalian herbivore saliva in plant–animal interactions have mostly focused on graminoid species and bovine saliva. A trial was performed in Botswana with clipping treatments to simulate browsing of shoots and the application of goat saliva on the woody species Combretum apiculatum Sonder (Combretaceae). Treatments were performed during early growing season while shoot growth was rapid, and responses of trees were recorded later in the same season. Clipped shoots with saliva had significantly enhanced shoot growth (tripled in length) and leaf production (2.7 times more leaves) compared to clipped shoots without saliva. However, unclipped shoots still grew more than clipped shoots, with or without saliva treatment.
Use of indigenous ecological knowledge of the Maasai pastoralists for assessing rangeland biodiversity in Tanzania
Authors: Mapinduzi Arnold L. , Oba Gufu , Weladji Robert B. , Colman Jonathan E. 
Published: January 2004

AbstractThis paper incorporates the indigenous ecological knowledge (IEK) of the Maasai pastoralists and ecological methods to assess effects of grazing and cropping on rangeland biodiversity at macro‐ and micro‐landscape scales in northern Tanzania. The joint surveys with pastoralists identified indicator plant species and their associations with micro‐landscapes and livestock grazing suitability (i.e. for cattle and small ruminant grazing), while traditional calf‐pasture reserves (alalili pl. alalilia) were evaluated for preservation of rangeland biodiversity. The macro‐landscapes comprising the cool high plateau (osupuko pl. isipuki) and montane forest highland (endim) were included in the survey. At micro‐landscape scales, the osupuko was classified into uplands (orkung'u), slopes (andamata) and dry valley bottomlands (ayarata). The micro‐landscapes were assessed in terms of herbaceous plant species and woody species richness and risks of soil erosion. Biodiversity varied at both the macro‐ and micro‐landscape scales and in accordance with the land‐use types. Greater plant species diversity and less erosion risks were found in the pastoral landscapes than in the agro‐pastoral landscapes. The calf‐grazing pastures had greater herbaceous species richness than the non‐calf pastures, which in turn had more woody species. The study concludes that the indigenous systems of landscape classification provides a valuable basis for assessing rangeland biodiversity, which ecologists should incorporate into ecological surveys of the rangelands in East Africa in the future.