Protistan parasites as mortality drivers in cold water crab fisheries.

From a historical perspective, several protistan taxa, including the recently re-aligned Microsporidia, have been associated with or identified as causes of mortalities in crustacean populations. Depending upon the host species, associated protistan prevalences could be as low as 5% or approach 100%. It has generally been assumed that reported prevalences translated directly into significant mortalities that could impact the distribution and abundance of affected populations. However, this assumption may be incorrect especially when the dynamics of host-pathogen-environment interactions are not entirely understood. We will discuss the presumed impact of several protistan pathogens on temperate and cold water commercial crab species. By using selected examples such as a ciliate in the Dungeness crab (Cancer magister) and Hematodinium sp. infections in North Pacific crabs, we will attempt to contrast differences between prevalence and mortality, acute and chronic infections/mortalities, age or size selectivity of affected population, and geographically restricted and widespread epizootics. We will also briefly discuss the potential impact of environmental changes such as climate change and ocean acidification on both host and protistan pathogen.

Dynamic mapping at the laminar level of odor-elicited responses in rat olfactory bulb by functional MRI.

We have applied functional MRI (fMRI) based on blood oxygenation level-dependent (BOLD) image-contrast to map odor-elicited olfactory responses at the laminar level in the rat olfactory bulb (OB) elicited by iso-amyl acetate (10(-2) dilution of saturated vapor) with spatial and temporal resolutions of 220x220x1,000 micro(m) and 36 s. The laminar structure of the OB was clearly depicted by high-resolution in vivo anatomical MRI with spatial resolution of 110x110x1,000 micro(m). In repeated BOLD fMRI measurements, highly significant (P < 0.001) foci were located in the outer layers of both OBs. The occurrence of focal OB activity within a domain at the level of individual glomeruli or groups of glomeruli was corroborated on an intra- and inter-animal basis under anesthetized conditions with this noninvasive method. The dynamic studies demonstrated that the odor-elicited BOLD activations were highly reproducible on a time scale of minutes, whereas over tens of minutes the activations sometimes varied slowly. We found large BOLD signal (DeltaS/S = 10-30%) arising from the olfactory nerve layer, which is devoid of synapses and composed of unmyelinated fibers and glial cells. Our results support previous studies with other methods showing that odors elicit activity within glomerular layer domains in the mammalian OB, and extend the analysis to shorter time periods at the level of individual glomeruli or groups of glomeruli. With further improvement, BOLD fMRI should be ideal for systematic analysis of the functional significance of individual glomeruli in olfactory information encoding and of spatiotemporal processing within the olfactory system.

Increased tricarboxylic acid cycle flux in rat brain during forepaw stimulation detected with 1H[13C]NMR.

NMR spectroscopy was used to test recent proposals that the additional energy required for brain activation is provided through nonoxidative glycolysis. Using localized NMR spectroscopic methods, the rate of C4-glutamate isotopic turnover from infused [1-(13)C]glucose was measured in the somatosensory cortex of rat brain both at rest and during forepaw stimulation. Analysis of the glutamate turnover data using a mathematical model of cerebral glucose metabolism showed that the tricarboxylic acid cycle flux [(V(TCA)] increased from 0.49 +/- 0.03 at rest to 1.48 +/- 0.82 micromol/g/min during stimulation (P < 0.01). The minimum fraction of C4-glutamate derived from C1-glucose was approximately 75%, and this fraction was found in both the resting and stimulated rats. Hence, the percentage increase in oxidative cerebral metabolic rate of glucose use (CMRglc) equals the percentage increases in V(TCA) and cerebral metabolic rate of oxygen consumption (CMRO2). Comparison with previous work for the same rat model, which measured total CMRglc [Ueki, M., Linn, F. & Hossman, K. A. (1988) J. Cereb. Blood Flow Metab. 8, 486-4941, indicates that oxidative CMRglc supplies the majority of energy during sustained brain activation.