A global competitive neural network

 A study is presented of a set of coupled nets proposed to function as a global competitive network. One net, of hidden nodes, is composed solely of inhibitory neurons and is excitatorily driven and feeds back in a disinhibitory manner to an input net which itself feeds excitatorily to a (cortical) output net. The manner in which the former input and hidden inhibitory net function so as to enhance outputs as compared with inputs, and the further enhancements when the cortical net is added, are explored both mathematically and by simulation. This is extended to learning on cortical afferent and lateral connections. A global wave structure, arising on the inhibitory net in a similar manner to that of pattern formation in a negative laplacian net, is seen to be important to all of these activities. Simulations are only performed in one dimension, although the global nature of the activity is expected to extend to higher dimensions. Possible implications are briefly discussed. Received: 21 November 1993/Accepted in revised form: 30 June 1994     

OMA1—An integral membrane protease?

OMA1 is a mitochondrial protease. Among its substrates are DELE1, a signaling peptide, which can elicit the integrated stress response, as well as the membrane-shaping dynamin-related GTPase OPA1, which can drive mitochondrial outer membrane permeabilization. OMA1 is dormant under physiological conditions but rapidly activated upon mitochondrial stress, such as loss of membrane potential or excessive reactive oxygen species. Accordingly, OMA1 was found to be activated in a number of disease conditions, including cancer and neurodegeneration. OMA1 has a predicted transmembrane domain and is believed to be tethered to the mitochondrial inner membrane. Yet, its structure has not been resolved and its context-dependent regulation remains obscure. Here, I review the literature with focus on OMA1's biochemistry. I provide a good homology model of OMA1's active site with a root-mean-square deviation of 0.9 Å and a DALI Z-score of 19.8. And I build a case for OMA1 actually being an integral membrane protease based on OMA1's role in the generation of small signaling peptides, its functional overlap with PARL, and OMA1's homology with ZMPSTE24. The refined understanding of this important enzyme can help with the design of tool compounds and development of chemical probes in the future.     

Genetic diversity of hop stunt viroid from symptomatic and asymptomatic citrus trees in Iran

Hop stunt viroid as the causal agent of cachexia disease has detected from citrus trees in different areas in Iran. Although cachexia has not been reported as a decline disease for citrus trees, it can impair crop quality and reduce plant yields. This study was undertaken to molecularly detect HSVd among different commercial citrus cultivars and determine genetic diversity of this viroid in Mazandaran province of Iran. Sampling was performed from symptomatic and symptomless citrus cultivars in Mazandaran province. HSVd specific primers were used for molecular detection. SSCP and sequencing were applied to assay HSVd genetic diversity. Results showed the detection of HSVd in all symptomatic Satsuma (25 out of 25), Clementine (25 out of 25), sweet lime (20 out of 20) and sweet orange cv. Valencia (7 out of 7), as well as, 31% (14 out of 22), 100% (12 out of 12) and 33% (5 out of 15) of page mandarin, lemon and grapefruit trees, respectively. 10 different HSVd genomes were identified by sequencing the SSCP profiles among which HSVd‐IR1 had the most frequency.     

A novel experimental method to estimate stress-strain behavior of intact coronary arteries using intravascular ultrasound (IVUS)

Most arterial mechanics studies have focused on excised non-coronary vessels, with few studies validating the application of ex-vivo results to in-vivo conditions. A method was developed for testing the mechanical properties of intact left anterior descending coronary arteries under a variety of conditions. Vascular deformation and pressure were simultaneously measured with intravascular ultrasound and a pressure transducer guidewire, respectively. Results suggest the importance of understanding in-vivo factors such as myocardial support, vascular tone and local pressure fluctuations when applying ex-vivo coronary characterization data. With further development, this method can more accurately characterize the true in-vivo constitutive behavior in normal and atherosclerotic coronaries.