Serotonin in the leech central nervous system: anatomical correlates and behavioral effects

Summary Stridulation of grasshoppers is controlled by hemisegmental pattern generator subunits which probably are restricted to the metathoracic ganglion complex (TG3-complex). The coordination of left and right pattern generator subunits depends on commissures of the TG3-complex (Ronacher 1989). The coordination of the stridulatory movements was studied in Chorthippus dorsatus males with partial mediosagittal incisions in the TG3-complex.Animals bearing anterior incisions in the TG3-complex, by which all commissures of the metathoracic neuromere and the first abdominal neuromere were transected, were still able to produce bilaterally coordinated species-specific stridulatory movements. Commissures of the T3- and A1-neuromere, thus, are not necessary, and the A2-, A3-commissures are sufficient for this coordination (Figs. 3, 4).Animals with partial posterior incisions, extending until A1, had deficits in their stridulation pattern; the coordination between the hindlegs was impaired though not completely lost (Fig. 6). This is discussed in view of the structure of stridulation interneurons identified in a related grasshopper species (Omocestus viridulus).These results indicate an unexpected substantial contribution of the abdominal neuromeres A2 and A3 to the control of stridulatory movements. This constitutes an interesting parallel to the flight control system of locusts where interneurons located in the first 3 abdominal neuromeres also appear to contribute to the flight pattern generator (Robertson et al. 1982).Abbreviations A1–A3 abdominal neuromeres 1–3 - T3 metathoracic neuromere - TG3-complex metathoracic ganglion complex including A1–A3     

Hydrogen evolution by subchloroplast preparations of photosystem II from pea and spinach,

Covalent coupling of bovine rhodopsin to CPG-thiol glass was used for separation of CNBr peptides. It is shown that cysteine residues 322 and 323 in the C-terminal cytoplasmic fragment of rhodopsin are modified with palmitic acid.     

The mechanistic nature of the membrane potential dependence of sodium-sugar cotransport in small intestine

Summary Methods are described which demonstrate the use of unidirectional influx of¹⁴C-tetraphenylphosphonium (¹⁴C-TPP⁺) into isolated intestinal epithelial cells as a quantitative sensor of the magnitude of membrane potentials created by experimentally imposed ion gradients. Using this technique the quantitative relationship between membrane potential () and Na⁺-dependent sugar influx was determined for these cells at various Na⁺ and -methylglucoside (-MG) concentrations. The results show a high degree of dependence for the transport Michaelis constant but a maximum velocity for transport which is independent of . No transinhibition by intracellular sugar (40mm) can be detected. Sugar influx in the absence of Na⁺ is insensitive to 1.3mm phlorizin and independent of . The mechanistic implications of these results were evaluated using the quality of fit between calculated and experimentally observed kinetic constants for rate equations derived from several transport models. The analysis shows that for models in which translocation is the potential-dependent step the free carrier cannot be neutral. If it is anionic, the transporter must be functionally asymmetric. A model in which Na⁺ binding is the potential-dependent step (Na⁺ well concept) also provides an appropriate kinetic fit to the experimental data, and must be considered as a possible mechanistic basis for function of the system.     

Cholinergic- and Adrenergic-Stimulated Inositide Hydrolysis in Brain: Interaction, Regional Distribution, and Coupling Mechanisms

Carbachol and norepinephrine were used as agonists to compare and contrast cholinergic and adrenergic stimulation of inositide breakdown in rat brain slices. Carbachol acts through a muscarinic (possibly M1) receptor and norepinephrine acts through an alpha 1 adrenoceptor. Studies in cerebral cortical slices indicated that both agonists stimulated the production of inositol-1-phosphate and glycerophosphoinositol. Although the initial rates for the stimulation of inositol phosphate release were similar for the two ligands, the response to norepinephrine continued for 60 min and was larger compared with carbachol which plateaued at 30 min. The presence of carbachol did not affect the ED50 for norepinephrine. Concentrations of carbachol near the ED50 in combination with norepinephrine resulted in an additive response whereas maximal concentrations of carbachol and norepinephrine resulted in a less than additive response in the cortex. This negative interaction was also seen in the hippocampus and hypothalamus but not in the striatum, brainstem, spinal cord, olfactory bulb, or cerebellum. Norepinephrine had a larger response than carbachol in the hippocampus, striatum, and spinal cord, but the reverse was true in the olfactory bulb. Manganese (1 mM) stimulated the incorporation of [3H]inositol into phosphatidylinositol (PtdIns) four- to fivefold but not into polyphosphoinositides. The stimulation by manganese of PtdIns labelling increased the nonstimulated release of inositol phosphates but did not affect the stimulated release of inositol phosphates by carbachol or norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Midbody sealing after cytokinesis in embryos of the sea urchin Arabacia punctulata

Summary Cytokinesis consists of a contractile phase followed by sealing of the connecting midbody to form two separated cells. To determine how soon the midbody sealed after cleavage furrow contraction, the fluorescent dye Lucifer Yellow CH(457.3 M.W.) was microinjected into cells at various intervals after cleavage had begun. Mitotic PtK₂ cells were recorded with video-microscopy so that daughter cells in the epithelial sheet could be identified for several hours after cell division. One daughter cell of each pair followed was microinjected to determine whether the dye diffused into the other daughter cell. For intervals up to four hours after the beginning of cytokinesis, diffusion took place between daughter cells. After this time the dye did not spread between daughter cells. In sea urchin blastomeres of the first, second and third divisions, Lucifer Yellow passed between daughter blastomeres only during the first 15 min after cytokinesis. If one cell of a two-cell, four-cell or eight-cell embryo was microinjected more than 15 min after the last cleavage, the dye remained in the injected cell and was distributed to all progeny of that cell, resulting in blastulae that were either one-half, one-quarter or one-eighth fluorescent, respectively. Thus, although cleavage furrow contraction takes approximately the same amount of time in sea urchin blastomeres and PtK₂ cells, the time of midbody sealing differs dramatically in the two cell types. Our results also indicate the importance of knowing the mitotic history of cells when injecting dyes into interphase cells for the purpose of detecting gap junctions.     

Alterations in the structure of the electrical double layer adjacent to a charged membrane arising from electromagnetically induced changes in the activity of membrane bound enzymes

Electromagnetic fields of very low amplitude have been reported to influence a number of cellular functions. Many of these effects have a high degree of frequency specificity. Herein it is suggested that some of these reported results could be explained by a fieldinduced alteration in the enzymic activity of integral membrane proteins. It is shown that such a field-induced transition from an initial nonequilibrium steady-state to a final nonequilibrium steady-state can lead to an alteration in the concentration profiles of those charged species in the cell's ambient electrolyte that comprise the so-called electrical double layer. Examples of variations in the concentration profiles of those ions that react with a membrane-bound enzyme, as well as nonreacting ionic species, are given. The modulation of such effects by systematic variations in extracellular pH and ionic strength is discussed.     

Communicating junctions and calmodulin: Inhibition of electrical uncoupling inXenopus embryo by calmidazolium

Summary This paper reports the inhibitory effects of calmidazolium (CDZ), a calmodulin inhibitor, on electrical uncoupling by CO₂. Membrane potential and coupling ratio (V ₂/V₁) are measured in two neighboring cells ofXenopus embryos (16 to 64 cell stage) for periods as long as 5.5 hr. Upon exposure to 100% CO₂, control cells consistently uncouple even if the CO₂ treatments are repeated every 15 min for 2.5 hr. CDZ (5×10^–8–1×10^–7 m) strongly inhibits uncoupling. The inhibition starts after 30, 50 and 60 min of treatment with 1×10^–7, 7×10^–8 and 5×10^–8 m CDZ, respectively, is concentration-dependent and partially reversible. In the absence of CO₂, CDZ also improves electrical coupling. CDZ has no significant effect on membrane potential and nonjunctional membrane resistance. These data suggest that calmodulin or a calmodulin-like protein participates in the uncoupling mechanism.     

Kinetic Effects of Terbium Ions on Muscarinic Acetylcholine Receptors of Murine Neuroblastoma Cells

Preincubation of murine neuroblastoma cells (clone N1E-115) with terbium chloride resulted in a significant potentiation of carbachol-mediated increase in cyclic GMP formation. This effect was accompanied by a shift of the peak response from 30 s to 120 s and a 6-fold decrease in carbachol concentration producing half-maximal responses, in addition to a significant increase in the Hill coefficient. Terbium ions also caused a significant decrease in the affinity and an increase in the maximum binding of [3H]quinuclidinyl benzilate to muscarinic receptors, the change in affinity being mainly due to a decrease in the association rate. Preincubation of cells with 1 mM carbachol for 4 h (the desensitized state of the muscarinic receptor) resulted in a decrease in the ability of terbium to alter [3H]quinuclidinyl benzilate binding. The effects of terbium reported here might be due to its affecting muscarinic receptor-effector coupling, which is considered to be lost upon receptor desensitization.     

Models of localized energy coupling

It is proven that any model of localized protonmotive energy coupling that relies upon properties of a homogeneous surface phase must, when operated in the steady state, lead to bulk phase electrochemical potentials for protons that are as large as those required by the delocalized chemiosmotic theory. To obtain models consistent with experiments supporting localized energy coupling requires some kind of surface heterogeneity for the proton conducting pathways. Two general classes of heterogeneous surface models are mentioned. One class involves phase-separated lipid domains. The second class involves hydrogen-bonded chains in proteins that traverse the membrane laterally.     

Dye coupling in the organ of Corti

Summary Dye-coupling in an in vitro preparation of the supporting cells of the guinea-pig organ of Corti was evaluated by use of the fluorescent dyes, Lucifer Yellow, fluorescein and 6 carboxyfluorescein. Despite the presence of good electrical coupling in Hensen cells (coupling ratios >0.6) the spread of Lucifer yellow was inconsistent. Hensen cells are very susceptible to photoinactivation, i.e., cell injury upon illumination of intracellular dye; and this in conjunction with Lucifer Yellow's charge and K+-induced precipitability may account for its variability of spread. Fluorescein and 6 carboxyfluorescein, on the other hand, spread more readily and to a greater extent than Lucifer Yellow, often spreading to cell types other than those of Hensen. Dye spread is rapid, occurring within a few minutes. These results suggest that molecules of metabolic importance also may be shared by the supporting cells of the organ of Corti.