Influence of NO on the background activity and corticofugal responses of anterior hypothalamus neurons

In acute experiments on cats we studied the modulating influence of an NO donor, nitroglycerin (NG), and a blocker of NO synthase nitro-L-arginine, methyl esther (L-NAME), on the neuronal responses in the anterior hypothalamus evoked by stimulation of evolutionary heterogeneous cortical zones. Intracerebroventricular injections of NG and L-NAME relatively rarely resulted in fundamental changes in the types of cortically evoked responses (8.8%; 65 cases among 736 testings). Yet, 72% of the L-NAME injections evoked significant increases in the frequency of the neuronal background activity, while 64% of NG injections resulted in suppression of the background activit. Possible mechanisms of modifications of the synaptic efficiency in cortico-hypothalamic projections determined by shifts in the NO concentration are discussed.     

Simulation of mechanisms responsible for initiation and modulation of bursting activity in RPa1 neuron of theHelix snail

A mathematical model of bursting activity in the RPa1 neuron of theHelix snail has been developed. The model allowed us to describe the processes of initiation and augmentation of the bursting activity related to transient secretion of a modulatory factor. Based on the analysis of computer simulations of various mechanisms underlying the effect of a modulating factor on the ionic membrane conductances in the bursting neuron, we suggested that modulating factor evokes a transition of non-voltage-dependent sodium channels and hyperpolarization-activated outward current channels to an active state and influences the gating of voltage-dependent sodium channels.Neirofiziologiya/Neurophysiology, Vol. 27, No. 1, pp. 11–17, January–February, 1995.     

Osmoprotection of Salmonella enterica serovar Typhimurium by Ngamma-acetyldiaminobutyrate, the precursor of the compatible solute ectoine

N(gamma)-acetyl-2,4-diaminobutyrate (NADA), the precursor of the compatible solute ectoine, was shown to function as an osmoprotectant for the non-halophilic bacterium Salmonella enterica serovar Typhimurium. The addition of NADA-containing extracts of an ectoine synthase mutant of the broad salt-growing halophile Chromohalobacter salexigens DSM 3043(T) could alleviate the inhibitory effects of high salinity in S. enterica, which lacks the ectoine biosynthetic pathway. NADA, purified from extracts of the mutant, protected S. enterica against salinity stress. This osmoprotective effect was slightly lower than that of ectoine, but more potent than that of hydroxyectoine. Accumulation of purified NADA by S. enterica was demonstrated by (13)C-NMR spectroscopy and HPLC analysis. In addition, it was shown that NADA was taken up by S. enterica via the ProP and ProU transport systems, which are known to transport glycine betaine and proline. This finding provides evidence that these permeases can recognize a diaminoacid that carries an unsubstituted alpha-amino group. This is the first time that NADA has been connected with osmoprotective functions in non-halophilic bacteria.     

Identification of regions of the tomato gamma-glutamyl kinase that are involved in allosteric regulation by proline

The first step of proline biosynthesis is catalyzed by gamma-glutamyl kinase (GK). To better understand the feedback inhibition properties of GK, we randomly mutagenized a plasmid carrying tomato tomPRO1 cDNA, which encodes proline-sensitive GK. A pool of mutagenized plasmids was transformed into an Escherichia coli GK mutant, and proline-overproducing derivatives were selected on minimal medium containing the toxic proline analog 3,4-dehydro-dl-proline. Thirty-two mutations that conferred 3,4-dehydro-dl-proline resistance were obtained. Thirteen different single amino acid substitutions were identified at nine different residues. The residues were distributed throughout the N-terminal two-thirds of the polypeptide, but 9 mutations affecting 6 residues were in a cluster of 16 residues. GK assays revealed that these amino acid substitutions caused varying degrees of diminished sensitivity to proline feedback inhibition and also resulted in a range of increased proline accumulation in vivo. GK belongs to a family of amino acid kinases, and a predicted three-dimensional model of this enzyme was constructed on the basis of the crystal structures of three related kinases. In the model, residues that were identified as important for allosteric control were located close to each other, suggesting that they may contribute to the structure of a proline binding site. The putative allosteric binding site partially overlaps the dimerization and substrate binding domains, suggesting that the allosteric regulation of GK may involve a direct structural interaction between the proline binding site and the dimerization and catalytic domains.     

The high salt requirement of the moderate halophile Chromohalobacter salexigens DSM3043 can be met not only by NaCl but by other ions

The growth rate of Chromohalobacter salexigens DSM 3043 can be stimulated in media containing 0.3 M NaCl by a 0.7 M concentration of other salts of Na+, K+, Rb+, or NH4+, Cl-, Br-, NO3-, or SO4(2-) ions. To our knowledge, growth rate stimulation by a general high ion concentration has not been reported for any organism previously.     

The targeted force steps developed by a human wrist: Force trajectories under conditions of repetition or random alternation of different target levels

The targeted isometric force steps developed by a human wrist after an acoustic signal under conditions of regular repetition and random alternation (the Reg and Rnd modes) of three visually presented target levels (25 N, 35 N, and 50 N) were studied. The main components (MC) and postcorrections could be easily differentiated in the majority of the force trajectories (FT). Analysis of MC parameters has shown that the Rnd mode in comparison with the Reg one is characterized by a noticeable increase in mean amplitude errors of MC with respect to the target level; as a rule, mean errors were positive for the 25 N target level and negative for the 50 N level. An increase in the amplitude variability and a weaker correlation of the force amplitude and the peak value of the first force derivative by time (the maximum rate of the force increase) were also typical of the Rnd mode. It is concluded that when duration of force development is not limited from above, the motor program of such reaction (especially in the Rnd mode) is more liberal than in the case of limitations [5, 12]: values of the force increase rate, specified by the central program, determine the force amplitude in a less rigid manner. Program transferring, i.e., the use of the central program of a fast ballistic movement to make a fast isometric force step, is regarded as a possible reason for the above-mentioned discrepancy; the rigidity of the program of the fast movement is regarded to be determined by corresponding biomechanical limitations. Correlations of the amplitudes and durations of the FT MC varied a great deal for different tested persons and in different modes, but there was a substantial positive correlation in the majority of cases. This finding contradicts the widespread notions about principles of scaling, when scaling of some parameters and maintenance of other parameters of targeted motor reactions as invariants are postulated. Correspondence of the resulting data to the concept of the generalized motor programs and its modifications is discussed.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 389–399, September–October, 1993.