The neural basis of a sensory filter in the Jamming Avoidance Response: No grandmother cells in sight

Summary The Jamming Avoidance Response (JAR), during which weakly electric fish modulate their electric organ discharge rate in response to a foreign electric signal of nearly the same frequency is strongest for frequency differences (f s) between 3–8 Hz. We have searched for neural correlates of this behavioral specificity. Single unit recordings in the anterior lateral line ganglion (ALLG), the posterior lateral line lobe (PLLL) and the torus semicircularis (TS) ofEigenmannia virescens were made during electrical stimulation simulating jamming by a nearby conspecific.Contrary to previously published reports (Scheich 1974, 1977) we conclude that f specificity does not lie in a single class of receptors or higher-order units in the PLLL tuned to the most effective f s. No tuning is seen at the receptor level of the PLLL. Specificity seems to be a population effect first visible at the level of the torus semicircularis, with individual units responding most strongly to different f s, but with most units tuned to approximately + and-4 Hz. By having cells tuned to a variety of f s but occurring in proportions corresponding to the observed behavior (and the degree to which f s impair electrolocation), animals would be better equipped to carry out other tasks such as detection of relative motion of objects in space and would also be better able to read complex stimuli corresponding to the more usual case of simultaneous jamming from several conspecifics (Partridge and Heiligenberg 1980).Units in the PLLL show slight differences in the timing of their firing to jamming signals presented at a frequency slightly above (+f) the fish's pacemaker frequency compared to those presented at a frequency slightly below (–f) (Scheich 1977). Firing pattern within the beat cycle produced by interaction of the fish's EOD, or an electrical mimic, S₁, and the foreign signal, S₂, is largely unaffected by the field orientation of the jamming signal. In the torus, by contrast, two classes of units are encountered which completely reverse the pattern of their firing within the beat cycle if the sign of the f is reversed. And, unlike the PLLL cells, those in TS respond differentially to different stimulus field geometries. Units of class 1 appear to compare T-unit input from different sites on the body surface (Heiligenberg and Bastian 1980) whereas those of class 2 additionally appear to receive input from E- and I-units in the PLLL. Abbreviations: see MethodsThis study was supported by grants from the National Science Foundation and the National Institutes of Health.     

Ectothiorhodospira vacuolata sp. nov., a new phototrophic bacterium from soda lakes

A new phototrophic bacterium was isolated from Jordanian and Kenyan alkaline salt lakes. Cells are rod shaped, 1.5 m wide and 2–4 m long, and motile by polar flagella. They divide by binary fission, and possess photosynthetic membranes as lamellar stacks similar to those in the other species of the genus Ectothiorhodospira and the brown colored Rhodospirillum species. The presence of bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series is indicated by the absorption spectra of living cells. Under certain growth conditions the cells form gas vacuoles, may become immotile and float to the top of the culture medium. Sulfide and thiosulfate are used as photosynthetic electron donors. During the oxidation of sulfide to sulfate, elemental sulfur is formed, which is accumulated outside the cells. The organisms are strictly anaerobic, do not require vitamins, are moderately halophilic and need alkaline pH-values for growth. The new species Ectothiorhodospira vacuolata is proposed.     

The combining site of the dinitrophenyl-binding immunoglobulin A myeloma protein MOPC 315

Magnetic-resonance techniques are used to refine the model of the combining site of the Fv fragment of the dinitrophenyl-binding mouse myeloma protein MOPC 315 constructed by Padlan, Davies, Pecht, Givol & Wright (1976) (Cold Spring Harbor Symp. Quant. Biol. 41, in the press). Light-absorption studies indicate a dinitrophenyl–tryptophan interaction in the Fv fragment of the type occurring in free solution. The Dnp-aspartate–tryptophan complex is therefore used as a starting point for the n.m.r. (nuclear-magnetic-resonance) analysis of the dinitrophenyl–Fv fragment interaction. Ring-current calculations are used to determine the geometry of the complex. The specificity of complex-formation between dinitrophenyl and tryptophan is confirmed by the lack of ring-current shifts of the dinitrophenyl resonances when tryptophan is replaced by any other aromatic amino acid. Proton n.m.r. difference spectra (at 270MHz), resulting from the addition of a variety of haptens to the Fv fragment, show that the combining site is highly aromatic in nature. Calculations on the basis of ring-current shifts define the geometry of the combining site, which involves a dinitrophenyl ring in van der Waals contact with four aromatic amino acid residues on the protein. The observation of a nuclear Overhauser effect on the H₍₃₎ resonance of the dinitrophenyl ring provides additional constraints on the relative geometry of the H₍₃₎ proton and an aromatic amino acid residue on the Fv fragment. The specificity of the Fv fragment for dinitrophenyl ligands arises from a stacking interaction of the dinitrophenyl ring with tryptophan-93_L, in an `aromatic box' of essentially tryptophan-93_L, phenylalanine-34_H and tyrosine-34_L; asparagine-36_L and tyrosine-34_L also contribute by forming hydrogen bonds with the nitro groups on the dinitrophenyl ring. The n.m.r. results also confirm that the antibody–hapten reaction may be visualized as a single encounter step. An Appendix shows the method of calculation of ring currents for the four aromatic amino acids and their use in calculating structures.     

Organization of the stomatogastric ganglion of the spiny lobster

Summary Three direct synaptic connections occur between neurons in the gastric and pyloric systems of the stomatogastric ganglion ofPanulirus interruptus. Two synapses are inhibitory, and one is electrical. This electrical synapse is both excitatory and inhibitory at different times. These synapses, and others within each system, let the two systems interact under some conditions. The synapses also form multisynaptic pathways which modulate the firing of many neurons in both systems. The consequences of these multisynaptic pathways are described and discussed.I thank Allen I. Selverston, Karen Sigvardt, Eve Marder, David Russell and Mary Chamberlin for criticizing a draft of this paper, Forrest Gompf and Doug Tissdale for technical support, and Nina Pollack and Betty Jorgensen for laboratory assistance. The research was supported by USPHS grant NS-12295 to BM and USPHS grant NS-09322 to Alien I. Selverston. BM was a USPHS NIH Postdoctoral Fellow in A.I. Selverston's laboratory during part of this research and is now a Research Fellow of the Alfred P. Sloan Foundation.     

Mutation in continuous cultures of Schizosaccharomyces Pombe. I. Dependence of the kinetics of mutation accumulation upon the growth-limiting nutrilite

The rate of spontaneous mutation to resistance to the 12,13-epoxytrichothecene trichodermin has been determined under different growth limiting conditions in continuous cultures of the microbial eukaryote Schizosaccharomyces pombe. In agreement with data obtained in bacterial systems by previous workers the kinetics observed for the accumulation of mutations is found to be dependent upon the nutrient used to limit the growth of the population. Under conditions of glucose-limitation mutation accumulation is directly proportional to the rate of cell division, while under histidine-limitation it is proportional to chronological time. Various possible explanations for these observations are discussed.     

RIBOSOMAL ACTIVITY IN PRENATAL MOUSE BRAIN

Abstract— Regulation of protein synthesis is important for the proper growth and development of the brain. Our previous work on the regulation of protein synthetic activity in fetal mouse brain cell suspensions showed that the rate of protein synthesis decreased during the prenatal period. In the present study, ribosomal activity of cell-free homogenates and purified ribosomes obtained from fetal neural tissue was measured. The post-mitochondrial supernatant (PMS) fraction actively incorporated amino acids into polypeptides using either endogenous mRNA or polyuridylic acid as template. The protein synthetic activity was dependent upon the age of the fetus. Ribosomes purified from this fraction were also active in protein synthesis. Incorporation of phenylalanine was linear for 20 min, and dependent upon the concentration of ribosomes and the pH 5 enzyme fraction. The age dependent decrease in protein synthetic activity observed with the post-mitochondrial supernatant fractions was not found when these purified ribosomes were employed. Ribosomes obtained from fetal, newborn or adult neural tissue were compared and found equally active in their protein synthetic capacity.     

The biosynthesis of trichothecin from acetate- [1,2- 13C2]

The coupling pattern of trichothecin biosynthesized from acetate-[1,2-¹³C₂] is in accord with previous enrichment studies. Multiple labelling was observed. Exogenous acetate has been shown to inhibit the utilization of glucose and the incorporation of radioactivity from pyruvate-[2-¹⁴C] and citrate-[1,5-¹⁴C] into the metabolites. Two pairs of ¹³C NMR assignments are interchanged.     

Neoflavonoids and the cinnamylphenol kuhlmannistyrene from Machaerium kuhlmannii and M. Nictitans

The trunkwood of Machaerium kuhlmannii contains methyl palmitate, 3-O-acetyloleanolic acid and sitosterol; the benzene derivatives 2,3-dimethoxyphenol, 2,6-dimethoxyphenol, 2-hydroxy-3-methoxyphenol, 2,3-dimethoxybenzaldehyde and methyl 3-(2-hydroxy-4-methoxyphenyl)-propionate; the isoflavonoids formononetin and (6aS,11aS)-medicarpin; the neoflavonoids (R)-3,4-dimethoxydalbergione, (R)-3,4-dimethoxydalbergiquinol, kuhlmanniquinol [(R)-3-(4-hydroxyphenyl)-3-(5-hydroxy-2,3,4-trimethoxyphenyl)-propene], dalbergin, kuhlmannin (6-hydroxy-7,8-dimethoxy-4-phenylcoumarin) and kuhlmannene (6-hydroxy-7,8-dimethoxy-4-phenylchrom-3-ene), as well as the cinnamylphenol kuhlmannistyrene [Z-1-(5-hydroxy-2,3,4-trimethoxybenzyl)-2-(2-hydroxyphenyl)-ethylene]. Five of these compounds, in addition to (R)-4′-hydroxy-3,4-dimethoxydalbergione, were also isolated from a trunkwood extract of M. nictitans. Structural assignments were confirmed by chemical interconversion and by the synthesis of (±)-kuhlmanniquinol.     

Absolute configurations of isoflavans

The absolute configurations of isoflavans and isoflavanquinones isolated from Cyclolobium, Dalbergia and Machaerium species were established by comparison of their ORD curves with that of (3S)-5,7,3′,4′-tetra-methoxyisoflavan and (3S)-7,4′-dimethoxyisoflavan-2′,5′-quinone, respectively. The assignments were checked by the ozonolysis of the isoflavan (?)-duartin to (R)-paraconic acid and the oxidation of isoflavans to isoflavanquinones. The PMR spectra of the dihydropyran ring of the isoflavans are discussed in terms of the preferred conformation of this ring.