5 Hz repetitive TMS increases anticipatory motor activity in the human cortex

In the present study, we analyzed how high-frequency repetitive transcranial magnetic stimulation (rTMS) of the primary motor hand area (M1-Hand) shapes anticipatory motor activity in frontal areas as indexed by the contingent negative variation (CNV). Eight right-handed volunteers received real or sham 5 Hz rTMS at an intensity of 90% resting motorthreshold (1500 stimuli per session). Real but not sham rTMS to left M1-Hand induced a site-specific increase in amplitude of the late component of the CNV at the electrode C3 overlaying the site of stimulation. The increase in pre-movement activity in the stimulated cortex may reflect an increase in facilitatory drive from connected motor areas, enhanced responsiveness of the stimulated cortex to these inputs or both. (c) 2005 Elsevier Ireland Ltd. All rights reserved.

Attentional modulation of visual cortex activity following right parietal damage in humans

Pathological inattention following parietal damage causes perceptual impairments for visual stimuli in the contralesional hemifield. Here we used functional magnetic resonance imaging (fMRI) to examine visual cortex activity in parietal patients as they performed a spatial attention task. Righthemisphere patients and healthy controls viewed counterphasing checkerboards in which coloured targets appeared briefly within the contralesional and ipsilesional hemifields. In separate fMRI runs participants focused their attention covertiy on the left or right hemifield, or on both hemifields concurrentiy. They were required to detect coloured targets that appeared briefly within the attended hemifield(s), and to withhold responses to distractor stimuli. Neural activit}' was significantly attenuated in early visual areas within the damaged hemisphere. Crucially, although attention significantiy modulated early visual activit}' within the intact (left) hemisphere, there was relatively littie modulation of activity within the affected hemisphere. Our findings suggest that parietal lesions alter early cortical responses to contralesional visual inputs.

Spontaneous and stimulus-evoked intrinsic optical signals in primary auditory cortex of the cat

Spontaneous and tone-evoked changes in light reflectance were recorded from primary auditory cortex (A1) of anesthetized cats (barbiturate induction, ketamine maintenance). Spontaneous 0.1-Hz oscillations of reflectance of 540- and 690-nm light were recorded in quiet. Stimulation with tone pips evoked localized reflectance decreases at 540 nm in 3/10 cats. The distribution of patches activated by tones of different frequencies reflected the known tonotopic organization of auditory cortex. Stimulus-evoked reflectance changes at 690 nm were observed in 9/10 cats but lacked stimulus-dependent topography. In two experiments, stimulus-evoked optical signals at 540 nm were compared with multiunit responses to the same stimuli recorded at multiple sites. A significant correlation (P < 0.05) between magnitude of reflectance decrease and multiunit response strength was evident in only one of five stimulus conditions in each experiment. There was no significant correlation when data were pooled across all stimulus conditions in either experiment. In one experiment, the spatial distribution of activated patches, evident in records of spontaneous activity at 540 nm, was similar to that of patches activated by tonal stimuli. These results suggest that local cerebral blood volume changes reflect the gross tonotopic organization of A1 but are not restricted to the sites of spiking neurons.

The human temporal cortex: Characterization of neurons expressing nitric oxide synthase, neuropeptides and calcium-binding proteins, and their glutamate receptor subunit profiles

Immunocytochemical techniques were used to examine the distribution of neurons immunoreactive (-ir) for nitric oxide synthase (nNOS), somatostatin (SOM), neuropeptide Y (NPY), parvalbumin (PV), calbindin (CB) and calretinin (CH), in the inferotemporal gyros (Brodmann's area 21) of the human neocortex. Neurons that colocalized either nNOS or SOM with PV, CB or CR were also identified by double-labeling techniques. Furthermore, glutamate receptor subunit profiles (GluR1, GluR2/3, GluR2/4, GluR5/6/7 and NMDAR1) were also determined for these cells. The number and distribution of cells containing nNOS, SOM, NPY, PV, CB or CR differed for each antigen. In addition, distinct subpopulations of neurons displayed different degrees of colocalization of these antigens depending on which antigens were compared. Moreover, cells that contained nNOS, SOM, NPY, PV, GB or CR expressed different receptor subunit profiles. These results show that specific subpopulations of neurochemically identified nonpyramidal cells may be activated via different receptor subtypes. As these different subpopulations of cells project to specific regions of pyramidal calls, facilitation of subsets of these cells via different receptor subunits may activate different inhibitory circuits. Thus, various distinct, but overlapping, inhibitory circuits may act in concert in the modulation of normal cortical function, plasticity and disease.

Dendritic branching patterns of pyramidal cells in the visual cortex of the new world marmoset monkey, with comparative notes on the old world macaque monkey

The basal dendritic arbors of 442 supragranular pyramidal cells in visual cortex of the marmoset monkey were compared by fractal analyses. As detailed in a previous study,(1) individual cells were injected with Lucifer Yellow and processed for a DAB reaction product. The basal dendritic arbors were drawn, in the tangential plane, and the fractal dimension (D) determined by the dilation method. The fractal dimensions were compared between cells in ten cortical areas containing cells involved in visual processing, including the primary visual area (Vi), the second visual area (V2), the dorsoanterior area (DA), the dorsomedial area (DM), the dorsolateral. area (DL), the middle temporal area (MT), the posterior parietal area (PP), the fundus of the superior temporal area (FST) and the caudal and rostral subdivisions of inferotemporal cortex (ITc and ITr, respectively). Of 45 pairwise interareal comparisons of the fractal dimension of neurones, 20 were significantly different. Moreover, comparison of data according to previously published visual processing pathways revealed a trend for cells with greater fractal dimensions in higher cortical areas. Comparison of the present results with those in homologous cortical areas in the macaque monkey(2) revealed some similarities between the two species. The similarity in the trends of D values of cells in both species may reflect developmental features which, result in different functional attributes.

Pyramidal neurones in macaque visual cortex: Interareal phenotypic variation of dendritic branching patterns

The basal dendritic arbors of over 500-layer III pyramidal neurones of the macaque cortex were compared by fractal analyses, which provides a measure of the space filling (or branching pattern) of dendritic arbors. Fractal values (D) of individual cells were compared between the cytochrome oxidase (CO)-rich blobs and CO-poor interblobs, of middle and upper layer III, and between sublaminae, in the primary visual area (Vi). These data were compared with those in the CO compartments in the second visual area (V2), and seven other extrastriate cortical areas. (V4, MT, LIP, 7a, TEO, TE and STP). There were significant differences in the fractal dimensions, and therefore the dendritic branching patterns, of cells in striate and extrastriate areas. Of the 55 possible pairwise comparisons of fractal dimension of neurones in different cortical areas (or CO compartments), 39 proved to be significantly different. The markedly different morphologies of pyramidal cells in the different cortical areas may be one of the features that determine the functional signatures of these cells by influencing the number of inputs received by, and propagation of potentials through, their dendritic arbors.

Relationships between non-occupational cadmium exposure and expression of nine cytochrome P450 forms in human liver and kidney cortex samples

This study was undertaken to assess associations between age, gender, cigarette smoke and non-workplace cadmium exposure, and liver pathology and inter-individual variation in cytochrome P450 (CYP) expression in human tissues. Autopsy specimens of twenty-eight Queensland residents whose ages ranged from 3 to 89 years were analyzed for the presence of nine CYP protein isoforms by immunoblotting. All subjects were Caucasians and their liver cadmium contents ranged from 0.11 to 3.95 kg/g wet weight, while their kidney cadmium contents were in the range of 2 to 63 mug/g wet weight. CYP1A2, CYP2A6, CYP2D6, CYP3A4, and CYP3A5 were detected in liver but not in kidney, and CYP1A1 and CYP1B1 were not found in liver or kidney. Lowered liver CYP2C8/19 protein contents were found to be associated with liver pathology. Importantly, we show elevated levels of CYP2C9 protein to be associated with cadmium accumulation in liver. No mechanism that explains this association is apparent, but there are two possibilities that require further study. One is that variation in CYP2C9 protein levels may be, in part, attributed to an individual's non-workplace exposure to cadmium, or an individual's CYP2C9 genotype may be a risk factor for cadmium accumulation. A positive correlation was found between liver CYP3A4 protein and subject age. Levels of liver CYPIA2 protein, but not other CYP forms, were increased in people more exposed to cigarette smoke, but there was no association between CYPIA2 protein and cadmium. CYP2A6 protein was found in all liver samples and CYP2A6 gene typing indicated the absence of CYP2A6 null allele (CYP2A6(D)) in this sample group, confirming very low prevalence of homozygous CYP2A6(D) in Caucasians. CYP2A6 gene types W/W, WIC, and CIC were not associated with variations in liver microsomal CYP2A6 protein. CYP2D6 protein was absent in all twenty-five kidney samples tested but was detectable in liver samples of all but two subjects, indicating the prevalence of the CYP2D6 null allele (CYP2D6(D)) in this sample group to be about 7%, typical of Caucasian populations. (C) 2001 Elsevier Science Inc. All rights reserved.

Host preference and host suitability in an egg-pupal fruit fly parasitoid, Fopius arisanus (Sonan) (Hym., Braconidae)

The relative oviposition rate of the parasitoid Fopius arisanus (Sonan) was investigated across three frugivorous tephritid species, Bactrocera tryoni Froggart, Bactrocera jarvisi (Tryon) and Bactrocera cucumis French. Choice and no-choice tests were both used. The suitability of these three species for sustaining larval development and survival to the adult stage was also assessed. Fopius arisanus parasitized all three tephritid species. regardless of the method of exposure, but showed stronger preference for B. tryoni and B. jarvisi over B. cucumis. Superparasitism was extremely rare. Successful development of F. arisanus varied across host species. Bactrocera tryoni yielded significantly more parasitoids than B. jarvisi, but no wasps emerged from B. cucumis puparia. Tests were set up in replicated trials. but results were not homogeneous across trials. We discuss the host relationships of F. arisanus with reference to this variation and in relation to host suitability for larval development.

Spermine modulation of the glutamate(NMDA) receptor is differentially responsive to conantokins in normal and Alzheimer's disease human cerebral cortex

The pharmacology of the N -methyl-d-aspartate (NMDA) receptor site was examined in pathologically affected and relatively spared regions of cerebral cortex tissue obtained at autopsy from Alzheimer's disease cases and matched controls. The affinity and density of the [H-3]MK-801 binding site were delineated along with the enhancement of [H-3]MK-801 binding by glutamate and spermine. Maximal enhancement induced by either ligand was regionally variable; glutamate-mediated maximal enhancement was higher in controls than in Alzheimer's cases in pathologically spared regions, whereas spermine-mediated maximal enhancement was higher in controls in areas susceptible to pathological damage. These and other data suggest that the subunit composition of NMDA receptors may be locally variable. Studies with modified conantokin-G (con-G) peptides showed that Ala(7)-con-G had higher affinity than Lys(7)-con-G, and also defined two distinct binding sites in controls. Nevertheless, the affinity for Lys(7)-con-G was higher overall in Alzheimer's brain than in control brain, whereas the reverse was true for Ala(7)-con-G. Over-excitation mediated by specific NMDA receptors might contribute to localized brain damage in Alzheimer's disease. Modified conantokins are useful for identifying the NMDA receptors involved, and may have potential as protective agents.