Disruption of facial emotion perception occurs in neuropsychiatric disorders where the expression of emotion is dulled or blunted, for example depersonalization disorder and schizophrenia. It has been suggested that, in the clinical context of emotional blunting, there is a shift in the relative contribution of brain regions subserving cognitive and emotional processing. The non-competitive glutamate receptor antagonist ketamine produces such emotional blunting in healthy subjects. Therefore, we hypothesised that in healthy subjects ketamine would elicit neural responses to emotional stimuli which mimicked those reported in depersonalization disorder and schizophrenia. Thus, we predicted that ketamine would produce reduced activity in limbic and visual brain regions involved in emotion processing, and increased activity in dorsal regions of the prefrontal cortex and cingulate gyrus, both associated with cognitive processing and, putatively, with emotion regulation. Measuring BOLD signal change in fMRI, we examined the neural correlates of ketamine-induced emotional blunting in eight young right-handed healthy men receiving an infusion of ketamine or saline placebo while viewing alternating 30 s blocks of faces displaying fear versus neutral expressions. The normal pattern of neural response occurred in limbic and visual cortex to fearful faces during the placebo infusion. Ketamine abolished this: significant BOLD signal change was demonstrated only in left visual cortex. However, with ketamine, neural responses were demonstrated to neutral expressions in visual cortex, cerebellum and left posterior cingulate gyrus. Emotional blunting may be associated with reduced limbic responses to emotional stimuli and a relative increase in the visual cortical response to neutral stimuli.
The 813C values of several seagrasses were considerably less negative than those of terrestrial C3 plants and tended The marine monocotyledonous angiosperms, the seagrasses, have many interesting adaptations to their submerged environment (9,18). One of these is the adaptation of their photosynthetic physiology to enable the direct assimilation of inorganic carbon from seawater. The leaf anatomy of seagrasses is very different from that of terrestrial plants. The leaves have no stomata, and almost all of the chloroplasts are located in a single layer of thick walled epidermal cells. The mesophyll is comprised of highly vacuolated cells, containing very few chloroplasts, interspersed with large gas lacunae (2, 10). Evidence exists that the lacunal gas may become enriched in 02, relative to atmospheric levels, during periods of active photosynthesis (11). It is possible that the photosynthetic apparatus of seagrasses may be exposed to higher than atmospheric 02 concentrations. This situation is known to promote photorespiration (6) and is rarely, if ever, encountered by terrestrial plants in the natural environment.The photosynthetic pathway used by seagrasses to fix carbon is of interest. This interest has been stimulated by reports that the carbon isotope ratios of seagrasses resembled those of C4 plants rather than C3 plants and that C4 acids were labeled early during 14C fixation by Thalassia testudinum (1)(2)(3) 10 MATERIALS AND METHODSPlant Material. Both species were collected near Magnetic Island, North Queensland. T. hemprichii (Ehrenb.) Aschers was collected from an intertidal reefflat in Cockle Bay and H. spinulosa (R. Br.) Aschers from a subtidal location at 5-to 10-m depth off Nobby Head. Leafy shoots with attached rhizomes and roots were transported to the laboratory, stored in aerated seawater in the dark overnight, and used the following day. Only young leaves, free from visible epiphytes, were used for experiments. Segments of the youngest mature T hemprichii leaves (1.5-2.0 cm long) or groups of 8 to 10 leaves at the tips of H. spinulosa branches were selected.Medium for "4C-labeling. Millipore-filtered seawater was buffered with N,N-bis(2-hydroxyethyl)glycine (final concentration, 20 mM), acidified with HCI to below pH 4 and purged overnight with humidified C02-free air at 25 C. The pH was adjusted to 8.22 with carbonate-free NaOH and then NaH14CO3 was added to a final concentration of 2.2 mm with a specific radioactivity of 26 ,uCi ,Imofl' for T. hemprichii experiments and 9 liCi tmol' for H. spinulosa experiments.14C-labeling Procedure. Experiments were conducted at 25 C in a shaking water bath (about 50 oscillations/min). Light (about 100 w m-2) was provided from a mercury vapor lamp, filtered through 10 cm of water. Leaf material was preilluminated for at least 30 min in Millipore-filtered seawater or in nonradioactive medium equivalent in all other respects to the labeling medium. It was then quickly blotted to remove adhering unlabeled medium which would otherwise decrease the s...
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