Dissociable Perceptual Effects of Visual Adaptation

Neurons in the visual cortex are responsive to the presentation of oriented and curved line segments, which are thought to act as primitives for the visual processing of shapes and objects. Prolonged adaptation to such stimuli gives rise to two related perceptual effects: a slow change in the appearance of the adapting stimulus (perceptual drift), and the distortion of subsequently presented test stimuli (adaptational aftereffects). Here we used a psychophysical nulling technique to dissociate and quantify these two classical observations in order to examine their underlying mechanisms and their relationship to one another. In agreement with previous work, we found that during adaptation horizontal and vertical straight lines serve as attractors for perceived orientation and curvature. However, the rate of perceptual drift for different stimuli was not predictive of the corresponding aftereffect magnitudes, indicating that the two perceptual effects are governed by distinct neural processes. Finally, the rate of perceptual drift for curved line segments did not depend on the spatial scale of the stimulus, suggesting that its mechanisms lie outside strictly retinotopic processing stages. These findings provide new evidence that the visual system relies on statistically salient intrinsic reference stimuli for the processing of visual patterns, and point to perceptual drift as an experimental window for studying the mechanisms of visual perception.     

Polypyrimidine Tract Binding Protein Prevents Activity of an Intronic Regulatory Element That Promotes Usage of a Composite 3��-Terminal Exon

Alternative splicing of 3′-terminal exons plays a critical role in gene expression by producing mRNA with distinct 3′-untranslated regions that regulate their fate and their expression. The Xenopus α-tropomyosin pre-mRNA possesses a composite internal/3′-terminal exon (exon 9A9′) that is differentially processed depending on the embryonic tissue. Exon 9A9′ is repressed in non-muscle tissue by the polypyrimidine tract binding protein, whereas it is selected as a 3′-terminal or internal exon in myotomal cells and adult striated muscles, respectively. We report here the identification of an intronic regulatory element, designated the upstream terminal exon enhancer (UTE), that is required for the specific usage of exon 9A9′ as a 3′-terminal exon in the myotome. We demonstrate that polypyrimidine tract binding protein prevents the activity of UTE in non-muscle cells, whereas a subclass of serine/arginine rich (SR) proteins promotes the selection of exon 9A9′ in a UTE-dependent way. Morpholino-targeted blocking of UTE in the embryo strongly reduced the inclusion of exon 9A9′ as a 3′-terminal exon in the endogenous mRNA, demonstrating the function of UTE under physiological circumstances. This strategy allowed us to reveal a splicing pathway that generates a mRNA with no in frame stop codon and whose steady-state level is translation-dependent. This result suggests that a non-stop decay mechanism participates in the strict control of the 3′-end processing of the α-tropomyosin pre-mRNA.     

How to become comfortable talking about sex to your patients.

Dealing with patients'' sex-related complaints is uncomfortable for many physicians. It can become more comfortable if the physician learns to apply his or her clinical knowledge of sexuality in combination with specific interpersonal interviewing skills. The level of comfort can be increased if the physician accepts his or her professional limitations in providing therapy and knows what other sources of care are available.     

Determination of the biological activity of Clostridium difficile toxins in in vivo and in vitro experiments

The biological activity of the filtrates of 29 C. difficile strains was studied in vivo (suckling white mice) and in vitro (cell cultures of different species and origin). The action of the filtrates on the experimental models in vivo was evaluated from the cytotoxic effect index, while in vitro the intensity of the cytotoxic effect was evaluated from the percentage of dead cells in the monolayer. The results of the comparative determination of toxicity characteristics in vivo and in vitro demonstrated that cell cultures were more sensitive experimental models than suckling white mice. The use of cell cultures permitted the quantitative evaluation of the cytotoxic activity of the filtrates under study, as well as the detection of their cell-directed action at minimal concentrations.     

Effect of alpha-fetoprotein on isolated mouse oocytes

Data are presented which indicate a possible action of alpha-fetoprotein (AFP) on female germinal cells. The in vitro maturation of mature mice oocytes was significantly inhibited when mouse AFP replaced albumin in the culture medium. In addition, the degenerative aspect of oocytes cultured with AFP seemed to indicate that this me?otic inhibition was caused by a premature degeneration of oocytes rather than by a blockage at a specific stage of maturation. Thus AFP, perhaps through its ligands, may play a role in the reduction of germinal cells during fetal and immediate post-natal life rather than in the arrest of me?osis at the diplotene stage.     

Prey-capture techniques and prey preferences of Corythalia canosa and Pystira orbiculata, ant-eating jumping spiders (Araneae, Salticidae)

Corythalia canosa from Florida is an unusual salticid because it is known to eat ants. This species' specialized behaviour for catching ants is described in detail for the first time and compared to its behaviour for catching other insects. Pystira orbiculata from Queensland is shown to be another ant-eating salticid, although its behaviour for catching ants seems less specialized than that of C. canosa. Three different types of tests of prey preference were carried out. In each type of test C. canosa and P. orbiculata took ants in preference to other insects. Another species of salticid, Trite planiceps from New Zealand, failed to eat ants in these tests, although T. planiceps often attacked then released the ants. Corythalia canosa's and P. orbiculata's preference for ants, and their prey-specific predatory behaviour for catching ants, are shown not to depend on prior experience with ants.