Electrophysiological investigation of central neurons of the electroreceptor system of the skate

Bioelectrical responses of acoustico-lateral neurons to electrical stimulation of the ampullae of Lorenzini were investigated in acute experiments on the anesthetized Black Sea skateTrigon pastinaca. Three types of responses were found: a primary composite response, prolonged activity, and single unit activity. Excitation of the neurons corresponded to a more marked negative phase, and inhibition to a more marked positive phase of the primary response. The thresholds of the unit responses to adequate electrical stimulation were 10^–9–10^–10 A/mm² and the minimal latent period 20 msec. The spontaneous activity of some neurons clearly depended on the animal's respiration. The character of the response depended on stimulus polarity, as reflected in the appearance of on- and off-responses. A tonic type of response with features of adaptation was predominant. The dependence of some response parameters (latent period of on- and off-responses, firing rate, duration of the contrast interval, response thresholds) on those of the stimulus is analyzed. The mechanisms of these bioelectrical responses are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.1, pp.59–67, January–February, 1974.     

Tissue culture and plant regeneration of watermelon (Citrullus vulgaris Schrad. cv. Melitopolski)

Plants were regenerated from cotyledon and hypocotyl explants of watermelon (Citrullus vulgaris). The explants were cultured on a Murashige and Skoog's basal nutrient medium supplemented with auxin, cytokinin and auxin-cytokinin combinations. Green healthy nodular and compact callus was obtained in medium containing naphthalene acetic acid and benzylaminopurine. Shoot differentiation and root differentiation from the cotyledon and hypocotyl after callus formation in different media containing benzylaminopurine or naphthalene acetic acid, respectively. Shoot formation required benzylaminopurine. Kinetin proved ineffective in inducing shoot buds or shoots. Root differentiation occurred in a medium containing naphthalene acetic acid or indole acetic acid. There was a greater proliferation of roots on medium supplemented with naphthalene acetic acid. The regenerated shoots developed roots when transferred to medium containing naphthalene acetic acid and complete plantlets could be transferred to soil for further growth.Abbreviations BAP 6 Benzylaminopurine - NAA -Naphthalene acetic acid - MS Murashige and Skoog's medium - IAA Indole acetic acid - KN Kinetin     

Frequency characteristics of skate electroreceptive central neurons responding to electrical and magnetic stimulation

Responses of single neurons in the lateral lobes of the medulla to stimulation of the electroreceptive system by homogeneous sinusoidal electrical and magnetic fields were investigated in acute experiments on the skateRaja radiata. Thresholds of neuronal responses to electrical stimulation varied from 0.03 to 10 µV/cm. The optimal frequency ranges for electrical and magnetic reception were in the regions of 0.05–5 and 2–3 Hz respectively. The possible mechanisms and functional significance of frequency characteristics of central neurons are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. All-Union Cardiologic Scientific Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 464–470, July–August, 1984.     

Impulse activity of neurons of the visual and somatosensory regions of the cerebral cortex at different stages of goal-directed behavior

Impulse activity of neurones of the visual and somatosensory cortical areas was studied in free moving cats during performance of conditioned instrumental food-procuring reactions to the presentation of light or sound. It was established that the units of these cortical areas may participate in both all or individual stages of complex instrumental behaviour. The visual cortex neurones are more extensively involved in the formation of successive stages of the goal-directed behavioral act. Significant differences were revealed in the unit responses of the visual and somatosensory cortical areas at the moment of the switching on of the conditioned signal, at the period of "reinforcement anticipation", at the moment of appearance of milk, the reinforcing agent, and during reinforcement, when the milk was lapped by the animal.     

Gramicidin channels: a new mechanism for transmembrane transfer of ions (from high resolution x-ray structural studies of the antibiotic)]

The crystal structure of the membrane-active antibiotic-cyclopeptide gramicidin S complex with urea was determined by the X-ray structure analysis. The gramicidin S molecule possesses an antiparallel beta-structure, its slightly twisted 30-membered cycle has a roughly rectangular form about 4.8 x 13.6 A in size, with the lesser side being formed by the main chain atoms of Phe and Pro residues. The maximum size of the molecule is 22.9 A. A characteristic feature of the molecule is the position of the extended side chains of the Orn residues on one side of the molecular cycle in the form of peculiar "legs--tentacles". One of these legs is "fastened" by the intramolecular H-bond to O atom of the nearer Phe4 residue, the other being free. The distance between the terminal NE atoms of the Orn residues is 5.7 A. The side chains of the Phe and Orn2 residues have trans-orientation, those of the Val, Orn7, Leu residues gauche-orientation. For Val1 and Leu3 side chains statistical disorder of the terminal C atoms is realized. The pyrrolidine rings of the Pro residues adopt Cs-C beta-exo conformation. There are one urea and 20 water molecules per one antibiotic molecule in the structure. The positions of three water molecules are fully occupied, the others with the probability of 0.56-0.20. One of the "water" positions is occupied on 2/3 by water, and on 1/3 by the O atom of the alcohol. There is a complicated system of intra- and intermolecular H-bonds in the structure, with and without the participation of water, alcohol and urea molecules. The gramicidin S molecules, collecting around 3(1) axis according to the left-handed double helix, form the channels whose outside hydrophobic surface is built of the side uncharged radicals, the inside surface being built of the main chain atoms, mainly of the O and N atoms and of the ornithine "tails" with uncharged NE atoms at the termini. The outer diameter of the channel is 29-43 A, inner (without ornithine "tails") is about 12.7 A. At the expense of the change of these "tails" conformation, the inner diameter of the channel filled with water molecules may change from 3.4 up to 6.3 A. Thus, the ions and particles of a rather large size may pass through the channel. The gramicidin channels are discovered and described for the first time. The channels in the crystal structure are close-packed under the hexagonal law.(ABSTRACT TRUNCATED AT 400 WORDS)     

Study of the ultrastructural and functional expression of the hepatocyte genome under conditions of prolonged depression of protein biosynthesis by cycloheximide. III]

Dynamics of changes in mtRNA synthesis and mitochondria ultrastructure is strictly dependent on the level of inhibition of biosynthesis of cytoplasm proteins and "soluble" proteins of mitochondria by cycloheximide in hepatocytes: 1-6 hrs later a progressive weakening of protein synthesis is accompanied by a drop in mtRNA synthesis and essential destruction of mitochondria; from 12 to 24 hrs a partial restoration of protein biosynthesis induces the processes of the above-mentioned indexes normalization.     

192 Computer-aided search for novel anti-HIV-1 agents presenting peptidomimetics of broadly neutralizing antibodies against the virus envelope GP120 V3 loop

Computer-aided search for novel anti-HIV-1 agents that are able to imitate the pharmacophore properties of the antigen-binding site of a broadly neutralizing mAb 3074 against the envelope gp120 V3 loop was carried out followed by evaluation of their potential inhibitory activity by molecular modeling. In doing so, the following problems were solved: (1) the mAb 3074 amino acid residues responsible for specific binding to the HIV-1 V3 loop were identified from the X-ray structures of this antibody Fab in complexes with the MN, UR29, and VI191 V3 peptides (Jiang et al., 2010); (2) using these data, 2039 possible mAb-3074 peptidomimetics were found by pepMMsMIMIC presenting a public, web-oriented virtual screening platform (Floris et al., 2011); (3) the complexes of these compounds with the above V3 peptides were built by molecular docking and, based on their analysis, the four molecules exhibiting a high affinity to V3 in the in silico studies were selected as the most probable peptidomimetics of mAb 3074 (Figure 1); and (4) stability of the complexes of these molecules with the MN, UR29, and VI191 V3 peptides was estimated by molecular dynamics and free energy simulations. As a result, a key role in specific binding of the selected compounds to the V3 loop was shown to belong to π-π interactions between their aromatic rings and the conserved Phe20 and/or Tyr21 of the V3 immunogenic crown. Similarly to mAb 3074, these compounds were found to block the tip of the V3 loop forming its invariant structural motif, which contains residues critical for cell tropism (Andrianov et al., 2011; Andrianov et al., 2012). In addition, the complexes of interest do not undergo significant changes within the molecular dynamics calculations, exhibiting the low values of free energy of their formation. In this context, the compounds given in Figure 1 are considered as the promising basic structures for the design of novel, potent, and broad anti-HIV-1 drugs.     

Structural analysis of the envelope gp120 V3 loop for some HIV-1 variants circulating in the countries of Eastern Europe

The V3 loop on gp120 from human immunodeficiency virus type 1 (HIV-1) is a focus of many research groups involved in anti-AIDS drug development because this region of the protein is a principal target for neutralizing antibodies and a major determinant for cell tropism and syncytium formation. In this study, the nucleotide sequences of the env gene region coding the V3 loop were determined by DNA sequencing methods for four novel HIV-1 strains that circulate in the countries of Eastern Europe, such as Russia, Belarus, Ukraine, etc. Based on the empirical data obtained, the 3D structures of the V3 loops associated with these viral modifications were generated by computer modeling and then compared to discover similarities in the spatial arrangement of this functionally important site of gp120. Despite the HIV-1 genetic variety, several regions of the V3 loop that contain residues critical for cell tropism were shown to be structurally invariant, which may explain its exceptional role in a co-receptor usage. These data together with those on the biological activity of the V3 individual residues clearly show that these conserved structural motifs of gp120 represent potential HIV-1 weak points most suitable for therapeutic intervention.     

Sequence Polymorphism of the Mitochondrial DNA Control Region in Native and Invasive Populations of Harmonia axyridis (Coleoptera,Coccinellidae)

Russian Journal of Genetics - The harlequin ladybird Harmonia axyridis forms stable natural populations in East Asia and southern Siberia and spreading invasive populations in Europe, Africa, North...