摘要:

WE reviewed 107 blood flow activation studies carried out with positron emission tomography and published between January 1993 and November 1996. These studies had reported their findings as peaks of significant difference in cerebral blood-flow (CBF) between two scans/tasks and had located the peaks in standardized stereotaxic space. We coded each task along several dimensions, including the type and rate of input and output, the types of cognitive processes, and the relative difficulty of tasks within a study. Based on this coding, a difference score (A–B) was calculated for each subtraction. Subsequently, the frequency distributions of the difference scores for subtractions yielding a peak in the anterior cingulate region (cingulate peak) were compared with those distributions obtained from subtractions without a cingulate peak (no cingulate-peak). The cingulate peak subtractions (n= 158) differed from the no cingulate peak subtractions (n= 229) in terms of difficulty level (p= 0.001) and the presence of a remote memory component (p= 0.01). Regional differences in the frequency distribution of certain task parameters, such as difficulty level, recent memory and the use of the hand for responding, were also observed when peaks found in the anterior cingulate cortex (ACC) were further classified as located in the rostralvscaudal ACC, supracallosalvssubcallosal ACC, and limbicvsparalimbic parts of the supracallosal ACC. We conclude that task difficulty plays a major role in modulating blood-flow response in the ACC, possibly interacting with other parameters such as the nature of the response and memory demands.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

The modulation of intracellular Ca2+concentration ([Ca2+]i) by the pro-inflammatory cytokine interleukin-1β (IL-1β) was assessed in synaptosomes loaded with the Ca2+-sensitive dye, Fura-2AM. IL-1β was found to exert a biphasic effect on the KCl-induced rise in [Ca2+]i, extending an inhibitory effect at lower (3.5 ng/ml) concentrations, and a stimulatory effect at high (100 ng/ml) concentrations. The inhibitory action of IL-1β on [Ca2+]iwas sensitive to pertussis toxin (PTX; 2 μg/ml), indicating a role for a PTX-sensitive G-protein, but was unaffected by the p42 mitogen-activated protein kinase kinase (MAP kinase kinase) inhibitor, PD 098059 (2 μM). In contrast, the stimulatory action of higher concentrations of IL-1β on [Ca2+]iwas blocked by PD 098059 and unaffected by PTX. We conclude that the biphasic actions of IL-1β on the KCl-induced rise in [Ca2+]iare mediated through activation of alternative second messenger pathways.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

FERRITIN contains most of the iron found in the brain, and the release of iron from ferritin has an essential role in iron-dependent lipid peroxidation. We examined the effect of cultured microglia on the ferritin-dependent lipid peroxidation of phospholipid liposomes monitored by the formation of thiobarbituric acid-reactive substances. Microglia stimulated by phorbol myristate acetate caused lipid peroxidation in the presence of ferritin. This lipid peroxidation was mediated by super-oxide produced by the microglia and iron released from the ferritin. Lipid peroxidation induced by activated microglia may be partly responsible for the oxidative damage that is thought to occur in Parkinson's disease and other neurodegenerative disorders.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

SEMI-QUANTITATIVE single cell RT-PCR techniques were used to determine the expression of mRNAs related to GABAergic and cholinergic neurotransmission in neurons of the rat globus pallidus and adjacent basal forebrain region. Neurons of the globus pallidus expressed relatively high levels of GAD67 and GABA vesicular transporter mRNA but undetectable levels of ChAT or ACh vesicular transporter mRNA. In contrast, nominally basal forebrain neurons co-expressed ChAT and GAD67 mRNAs and mRNAs for both ACh and GABA vesicular transporters. These results suggest that the neurons along the medial border of the globus pallidus may co-release GABA and ACh.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

FUNCTIONAL magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) are noninvasive techniques recently used to investigate cortical motor physiology. However, these modalities measure different phenomena, and in studies of human motor control they have given inconsistent results. We have developed a reproducible technique which co-registers TMS and fMRI, using a frameless method. In four normal subjects, the TMS map and fMRI activation were present on the primary motor cortex contralateral to the target hand, with some extension into primary sensory cortex. fMRI activation alone was also present in the medial motor cortex bilaterally and in the sensori-motor cortex ipsilateral to the target hand. This technique allows a more comprehensive evaluation of the physiologic events involved in motor control.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

NEURONAL responses were recorded from the striate cortex of monkeys trained to perform visual discrimination at locations in the visual field to which their attention was drawn. A subset of neurons showed vigorous responses to visual stimuli for trials in which the monkey was directing its attention to the respective receptive field location. In trials where attention is directed elsewhere, responses to the same stimuli were significantly reduced. In some cells the early response component was not modulated by attention, but later components were affected by the locus of attention. The results suggest the operation of a feedback in the paradigm that spotlights a topographically restricted area of V1 for further processing at higher levels.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

FUNCTIONAL magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were performed in six subjects during self-paced finger movement performance, tactile somatosensory stimulation and binaural auditory stimulation using identical stimulation paradigms. Both functional imaging modalities localized brain activity in adjacent areas of anatomically correct cortex. The mean distances measured between fMRI activity and the corresponding MEG dipoles were 10.1 mm (motor), 10.7 mm (somatosensory), 13.5 mm (auditory right hemisphere) and 14.3 mm (auditory left hemisphere). The distances found may reflect the correlation between electrophysiological and hemodynamic responses due to the different underlying substrates of neurophysiology measured by fMRI and MEG: BOLD contrastvsneuronal biomagnetic activity.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

BRAIN-DERIVED neurotrophic factor (BDNF) enhances survival and protects dopaminergic neurons from neurotoxicity. We have examined in primary cultures of fetal mesencephalic neurons the expression of BDNF transcripts and its regulation by glutamate receptor agonists. RT-PCR experiments showed in these cultures the expression of mRNA encoding for neurotrophin receptors TrkA, TrkB and TrkC as well as a differential expression of alternative BDNF gene transcripts derived from exons 1a, 1b, 1c and 1d. In adult rat mesencephalon we only detected BDNF mRNAs originated from exons 1a and 1c. Quantitative RT-PCR analysis of mesencephalic neurons revealed that NMDA, but not kainate treatment, significantly increased BDNF mRNAs derived from exons 1b and 1d. Our data indicate the existence in mesencephalic neurons of different and alternative promoters within the BDNF gene that may be differentially regulated by glutamate receptor stimulation.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

IN the central human retina, there are estimated to be nearly two L cone photoreceptors for each M cone. The extent to which this value varies across individuals is unclear and little is known about how the M:L cone ratio might change with retinal location. To address these questions, the ratio of M:L cone pigment mRNA was examined at different locations. For patches of central retina, the average M:L ratio was about 2:3 which decreased to about 1:3 for patches 40°eccentric. There were also large individual differences among the 23 eyes examined. The extremes differed in central M:L mRNA ratio by a factor of > 3. The measured differences in mRNA ratio are proposed to reflect differences in photo-receptor ratio. Such variations provide unique opportunities for understanding how the neural circuitry for color vision is affected by changes in cone ratio.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

ACTIVITY in the human supplementary motor area (SMA), primary motor cortex (M1), and the draining vein of the motor cortex during a visually triggered finger opposition task was measured by functional magnetic resonance imaging with a repetition time of 1 s. Sequential hemodynamic activation in these areas was revealed by cross-correlating a signal sequence in M1 directly with signal sequences from SMA and the draining vein, and applying polynomial fitting with the aid of Akaike's information criterion. We succeeded in detecting a time delay of approximately 0.5 s between the activations of SMA and M1, and a delay of nearly 1.3 s between the activations of M1 and its draining vein. The new combination of fMRI and data analysis techniques has attained a time resolution comparable to those in preceding studies that used shorter fMRI repetition times of 100–200 ms.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID