A morphometric method for correcting phytoplankton cell volume estimates

Cell volume calculations are often used to estimate biomass of natural phytoplankton assemblages. Such estimates may be questioned due to morphological differences in the organisms present. Morphometric analysis of 8 species representative of phytoplankton types found in the Great Lakes shows significant differences in cell constituent volumes. Volume of physiologically inert wall material ranges from nil, in some flagellates, to over 20% of the total cell volume in certain diatoms. Likewise, “empty” vacuole may comprise more than 40% of the total cell volume of some diatoms, but less than 3% of the volume of some flagellates. In the organisms investigated, the total carbon containing cytoplasm ranged from 52% to 98% of the total cell volume and the metabolizing biovolume ranged from 30% to 82%. Although these differences complicate direct biomass estimation, morphometric analysis at the ultrastructural level may provide ecologically valuable insights.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41732/1/709_2005_Article_BF01275650.pd

cGMP-Phosphodiesterase Inhibition Enhances Photic Responses and Synchronization of the Biological Circadian Clock in Rodents

The master circadian clock in mammals is located in the hypothalamic suprachiasmatic nuclei (SCN) and is synchronized by several environmental stimuli, mainly the light-dark (LD) cycle. Light pulses in the late subjective night induce phase advances in locomotor circadian rhythms and the expression of clock genes (such as Per1-2). The mechanism responsible for light-induced phase advances involves the activation of guanylyl cyclase (GC), cGMP and its related protein kinase (PKG). Pharmacological manipulation of cGMP by phosphodiesterase (PDE) inhibition (e.g., sildenafil) increases low-intensity light-induced circadian responses, which could reflect the ability of the cGMP-dependent pathway to directly affect the photic sensitivity of the master circadian clock within the SCN. Indeed, sildenafil is also able to increase the phase-shifting effect of saturating (1200 lux) light pulses leading to phase advances of about 9 hours, as well as in C57 a mouse strain that shows reduced phase advances. In addition, sildenafil was effective in both male and female hamsters, as well as after oral administration. Other PDE inhibitors (such as vardenafil and tadalafil) also increased light-induced phase advances of locomotor activity rhythms and accelerated reentrainment after a phase advance in the LD cycle. Pharmacological inhibition of the main downstream target of cGMP, PKG, blocked light-induced expression of Per1. Our results indicate that the cGMP-dependent pathway can directly modulate the light-induced expression of clock-genes within the SCN and the magnitude of light-induced phase advances of overt rhythms, and provide promising tools to design treatments for human circadian disruptions

JEAB and JABA on the World Wide Web: a report to readers.

The Journal of the Experimental Analysis of Behavior (JEAB) and the Journal of Applied Behavior Analysis (JABA) have both established home pages on the World Wide Web. Their addresses are: http://www.envmed.rochester.edu/wwwrap/beh avior/jeab/jeabhome.htm http://www.envmed.rochester.edu/wwwrap/beh avior/jaba/jabahome.htm An important feature of these pages is a powerful program that permits rapid full-text searches of a database consisting of the nearly 5,000 abstracts that have accompanied articles published in JEAB since 1958 and in JABA since 1968. An electronic version of a single article from each issue of each journal is now made available soon after the paper edition of the journal appears

Behavioral procedure and 60 Hertz exposure system for determining field detection by rats

A new system has been constructed to determine the threshold for detecting 60 Hertz electric fields by the rat. A variant of the Method of Constant Stimuli, which has been studied intensively by other investigators for determining the thresholds of animals to a variety of stimuli, will be used in the present study. The present report describes significant features of both the exposure system and behavioral paradigm designed to study the sensitivity of the rat to 60 Hertz electric fields