Segmental release of amino acid neurotransmitters from transcranial stimulation

The present study used microdialysis techniques in an intact rabbit model to measure the release of amino acids within the lumbar spinal cord in response to transcranial electrical stimulation. Dialysis samples from the extracellular space were obtained over a stimulation period of 90 minutes and were examined using high pressure liquid chromatography. Neuronal excitation was verified by recerding corticomotor evoked potentials (CMEPs) from the spinal cord. A significant increase in the release of glycine and taurine compared to sham animals was measured after 90 minutes of transcranial stimulation. Glutamate and aspartate release was not significantly elevated. GABA concentrations were consistently low. CMEP components repeatedly showed adequate activation of descending fiber pathways and segmental interneuron pools during dialysis sampling. Since glycine, and to a lesser extent taurine, have been shown to inhibit motor neuron activity and are closely associated with segmental interneuron pools, suprasegmental modulation of motor activity may be, in part, through these inhibitory amino acid neurotransmitters in the rabbit lumbar spinal cord.     

Potato Lectin: A Cell-Wall Glycoprotein

The activity and the amount of potato lectin were measured inpotato tuber slices (Solanum tuberosum cv. Huinkul) aeratedfor 48 h. Lectin was found in a soluble form, liberated to themedium and associated with insoluble structures. Polyacrylamidegel electrophoresis in denaturating conditions and immunologicaltechniques indicated that the lectins associated to cell wall,soluble or liberated to the medium, were identical. The cell-wallfraction was found to contain 65% of total lectin in the tuber.The possible role of potato lectin in tubers was discussed. (Received June 5, 1985; Accepted September 3, 1985)     

The cytoskeletal architecture of interdigitated microvilli in the photoreceptors of some nocturnal spiders

Summary The photoreceptor microvilli of some nocturnal spiders (Isopeda andOlios in theSparassidae, andClubiona in theClubionidae) are wide (80–140 nm), and microvilli from adjacent receptors are interdigitated. Because microvillar diameters are relatively large in relation to the thicknesses of thin sections, it is possible to examine cytoskeletal structures closely associated with the microvillar plasmalemmae directly.Retinae were treated with a specific inhibitor of cysteine proteases before primary fixation for electron microscopy in a Ca²⁺-chelating medium. Cytoskeletal components were stabilized with tannic acid. A variety of microvillar profiles was obtained, consistent with an assumption that they represent imperfect preservation of anin vivo plasmalemmal undercoat, inferred to consist of longitudinally-disposed microfilaments, presumptively bonded to the microvillar plasmalemma. The microvillar lumen is inferred to be empty of cytoskeletal components in life.This model is discussed in terms of 1. the cytoskeletal organisation of microvilli of the primitive photoreceptors of a leech (Blest et al. 1983), where the arrangement of microfilaments resembles that in the vertebrate intestinal brush-border; 2. the large complement of membrane-associated oligomeric actin in rhabdoms of crayfish, where identifiable microfilaments cannot be resolved within microvilli by transmission electron microscopy (de Couet et al. 1984), and a single visualizable axial filament of uncertain composition is linked to the plasmalemma by side-arms.     

Toxicity oft-butylhydroperoxide in hepatocyte monolayers exposed to hypoxia and reoxygenation

Summary Inasmuch as it is known that the toxicity of anesthetic agents is potentiated by hypoxia and that the reductive metabolism of these agents results in the formation of lipid hydroperoxides, we investigated the toxicity of hydroperoxides under low-oxygen concentrations. We found that hypoxia exacerbates the toxicity oft-butyl hydroperoxide, shifting the dose-response curve oft-butyl hydroperoxide vs. lysis of hepatocytes approximately an order of magnitude to the left. Furthermore, although at the end of a 4-h exposure to 0.5% O₂ hepatocyte monolayers seemed normal by three indices (release of⁵¹Cr and serum glutamate transaminase or exclusion of trypan blue), they were completely lysed after an additional 20 h reoxygenation at 20%. O₂. In contrast, monolayers exposed to 2% O₂ for 4 h seemed normal after 20 h reoxygenation. However, cells exposed to both a subtoxic dose of hydroperoxide and 4 h of 2% O₂, although seeming healthy at the end of the hypoxic period, were completely lysed within 20 h after reoxygenation. The study was supported by grant OH 00978 from the National Institutes for Occupational Safety and Health, Atlanta, Georgia.     

Boar sperm surface glycoproteins: Isolation,localization, and temporal expression during spermatogenesis

Boar sperm glycoprotein fractions were isolated by Lens culinaris hemagglutinin affinity chromatography of detergent-solubilized ejaculated spermatozoa, followed by preparative sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. In order to develop methods for further investigations of the sperm proteins, we proceeded with two of the isolated glycoproteins. Antibodies were raised in female rabbits against each of the two sperm glycoproteins. By a combination of immunosorbent chromatography, using the antibodies obtained, and preparative SDS polyacrylamide gel electrophoresis, highly purified sperm proteins were isolated. The sperm proteins were immobilized on Sepharose gel columns and specific immunoglobulin Fab fragments were enriched by affinity chromatography. The specificity of the Fab fragments was ascertained by immunoprecipitation analysis. The Fab fragments were used in indirect immunofluorescence analysis to localize the corresponding antigens on the surface of boar spermatozoa. Both antigens were exclusively confined to the postacrosomal region. Immunohistochemical staining of boar testis sections revealed that both antigens are expressed from the spermatid stage. This technique also revealed that one of the antigens congregated at the Golgi complex-acrosome region during spermatogenesis.     

Toxoplasma gondii: Microassay to differentiate toxoplasma inhibiting factor and interleukin 2

Using a sensitive, economical, and reproducible microassay, the relationship of toxoplasma inhibiting factor to interleukin 2 has been examined. The assay developed took advantage of the observation that (1) Toxoplasma gondii tachyzoites replicated efficiently in the murine monocytic cell line, RAW 264; (2) treatment of RAW 264 cells with toxoplasma inhibiting factor prevented intracellular replication of the parasite to an extent similar to that observed with identical treatment of freshly isolated murine peritoneal exudate cells; and (3) [³H]uracil incorporation was an efficacious means to quantify replication (or inhibition of replication) of tachyzoites within the cell line. Although toxoplasma inhibiting factor and interleukin 2 were both present in the same lectin -and antigen-stimulated splenocyte supernatant fluids, results from microassays strongly suggested that the molecules were two distinct entities.     

EFFECT OF CYANIDE AND ELECTRICAL STIMULATION ON PHOSPHOINOSITIDE METABOLISM IN LOBSTER NERVES

The contents of phosphoinositides, ATP, glucose and lactate in leg and claw nerves of the lobster were determined. Nerves were also analysed after cyanide poisoning, after electrical stimulation, and 1 h after removing the leg from the lobster. Cyanide poisoning decreased the levels of ATP and glucose and increased the content of lactate but did not alter the levels of phosphoinositides. Nerves left in situ for 1 h after disconnection from the central nervous system exhibited a decrease in the content of tri-phosphoinositides (TPI) of 50 per cent, without changes in ATP, glucose or lactate. The TPI change was reversed after incubation for 1 h in oxygenated seawater. Nerves labelled in vivo with ³²P were removed and stimulated at 50 Hz for 5 min. The turnover of TPI phosphorus increased on stimulation in both normal and cyanide-poisoned nerves. In contrast, turnover of ATP increased after stimulation in normal nerves but not in cyanide-treated nerves. We sought to determine whether polyphosphoinositides play a greater role in resting metabolism of the nerve or in the conducting mechanisms. Our results make more likely the involvement of TPI in permeability changes of neural membranes during excitation.     

Adenosine Triphosphate Inhibition of Yeast Trehalase

Yeast trehalase has been found to be inhibited non-competitively by adenosine triphosphate. Such a biological control could explain the accumulation of trehalose during the stationary phase of the growth curve.