GABA concentrations in the striatum following repetitive cerebral ischemia

GABAergic neurons in the striatum are very sensitive to the effects of ischemia. The progressive decline in striatal GABA following transient forebrain ischemia in gerbils may be secondary to either a decreased production or an increase in reuptake mechanisms or both. The current experiment was designed to evaluate release of GABA by stimulation with K+ or inhibition of its uptake with nipecotic acid or their combination (K+ nipecotic) after repetitive forebrain ischemia in gerbils by in-vivo microdialysis on Days 1, 3, 5, and 14 following the insult. Infusion of nipecotic acid or potassium chloride, resulted in a significant increase in extracellular GABA. This response was significantly decreased in the post-ischemic animals. The synergistic effect of increased GABA concentrations by the infusion of nipecotic acid+potassium chloride seen in the controls was not evident in the post-ischemic animals. In conclusion, though there is a reduction in the extracellular GABA concentrations in the first week following an ischemic insult, restorative mechanisms are operative in the second week as seen by the increasing GABA concentrations.     

Catecholamine and MHPG plasma levels,platelet MAO activity,and3H-imipramine binding in heroin and cocaine addicts

This work evaluated in a population of heroin and heroin plus cocaine human addicts:

1. Norepinephrine (NE), epinephrine (Epi), and 3-methoxy-4-hydroxyphenylglycol (MHPG) (the principal metabolite of brain NE) plasma levels;
2. Monoamine oxidase (MAO) activity; and
3. ³H-imipramine specific binding to the amine carrier in platelets.

NE plasma levels were significantly lower in the short-term heroin user groups (1–3 and 4–6 yr), a finding not observed in both the long-term heroin user (>6 yr) and heroin plus cocaine user (>6 yr) groups. Epi levels changed in a similar manner, except that a significant increase was noted in heroin plus cocaine abusers. Conversely, dopamine and MHPG plasma levels increased with the duration of heroin use, and even more with cocaine abuse. Platelet MAO activity increased in all groups. Specific³H-imipramine binding sites showed an increase after 3 yr of heroin abuse and in all heroin plus cocaine addicts. In conclusion, short-term use of heroin decreases NE or Epi release, but with prolonged use, a slow adpatation occurs. In contrast, cocaine inhibits the neuronal Epi uptake, even in a situation of long duration of abuse. Probably the amine levels additionally regulate the amine carrier, resulting in changes that show a different pattern from major depression. These drugs of abuse may also influence directly or indirectly related enzymatic systems.     

Salivary apyrase of Aedes aegypti: characterization and secretory fate

Salivary gland homogenates of female adult Aedes aegypti hydrolyzed ATP and ADP thereby defining an apyrase activity. Activity is divalent cation dependent with an optimum pH of 9.0. ATPase and ADPase activities could not be dissociated thus suggesting the presence of a true apyrase enzyme. Apyrase activity is low on the day of emergence but increases to 160 mU per pair of glands on the second day. The site at which mosquitoes probed into warm polyacrylamide gels retains apyrase activity, confirming the secretory fate of this activity.     

The larval midgut of the cassava hornworm (Erinnyis ello)

Summary Columnar cells of the larval midgut of the cassava hornworm, Erinnyis ello, display microvilli with vesicles pinching off from their tips (anterior and middle midgut) or with a large number of double membrane spheres budding along their length (posterior midgut). Basal infoldings in columnar cells occur in a parallel array with many openings to the underlying space (posterior midgut) or are less organized with few openings (anterior and middle midgut). Goblet cells have a cavity, which is formed by invagination of the apical membrane and which occupies most of the cell (anterior and middle midgut) or only its upper part (posterior midgut). The infolded apical membrane shows modified microvilli, which sometimes (posterior midgut) or always (anterior and middle midgut) contain mitochondria. The cytoplasmic side of the membrane of the microvilli that contain mitochondria are studded with small particles. The results suggest that the anterior and middle region of the midgut absorbs water, whereas the posterior region secretes it. This results in a countercurrent flux of fluid, which is responsible for the enzyme recovery from undigested food before it is expelled. Intermediary and final digestion of food probably occur in the columnar cells under the action of plasma membrane-bound and glycocalix-associated enzymes.     

Non-ependymal cilia in the habenulae and the interpeduncular nucleus of the frog tadpole

Summary Cilia of the 9+2 pattern are found electron microscopically in nonependymal cells of the habenulae and the interpeduncular nucleus of the tadpole of Rana esculenta at an early stage of development (8 mm length, head to tip of tail). A comparison is made between these and the ependymal and sensory cilia in the same specimens. The cilia project into the neuropil emerging from a perikaryon rich in free ribosomes and displaying a prominent Golgi apparatus. These perikarya contain dense core vesicles. Synapses with vesicles of the clear spherical type have been observed along the ciliary shaft. On a purely morphologic basis the authors hypothesize that these cilia, at least in this early ontogenetic stage, may extend considerably the conducting surface of the cell and represent a sensory structure which could be stimulated by terminal processes belonging to distantly located cells. In addition, they could also be involved in the trophic exchange of material with the adjacent structures.     

High-resolution nuclear magnetic resonance determination of transfer RNA tertiary base pairs in solution. 1. Species containing a small variable loop.

Eight class I tRNA species have been purified to homogeneity and their proton nuclear magnetic resonance (NMR) spectra in the low-field region (-11 to -15 ppm) have been studied at 360 MHz. The low-field spectra contain only one low-field resonance from each base pair (the ring NH hydrogen bond) and hence directly monitor the number of long-lived secondary and tertiary base pairs in solution. The tRNA species were chosen on the basis of their sequence homology with yeast phenylalanine tRNA in the regions which form tertiary base pairs in the crystal structure of this tRNA. All of the spectra show 26 or 27 low-field resonances approximately 7 of which are derived from tertiary base pairs. These results are contrary to previous claims that the NMR spectra indicate the presence of resonances from secondary base pairs only, as well as more recent claims of only 1-3 tertiary resonances, but are in good agreement with the number of tertiary base pairs expected in solution based on the crystal structure. The tertiary base pair resonances are stable up to at least 46 degrees C. Removal of magnesium ions causes structural changes in the tRNA but does not result in the loss of any secondary or tertiary base pairs.     

Preferred conformations of protected homo-oligo-L-glutamate peptides in CDCl3 and CDCl3/TFA mixtures

A conformational analysis of protected glutamate homo-oligopeptides Z-[Glu(OEt)]_n-OEt (n = 2–7) was carried out in chloroform solution using high-resolution ¹H-nmr spectroscopy. At dilute peptide concentrations, the backbone NH and α-CH resonances are well resolved and can be assigned by combining extensive homonuclear decoupling experiments with data for co-oligopeptide derivatives. The structure of these peptides in solution was then assessed using information from chemical shifts, coupling constants, temperature coefficients, and titration of each oligomer with trifluoroacetic acid (TFA). The di- and tripeptides are found to be in disordered forms in deuterochloroform (CDCl₃) and CDCl₃/TFA mixtures. The tetrapeptide exhibits a folded structure with intramolecular hydrogen bonding at Glu² in CDCl₃ and undergoes a transition to increasingly disordered forms as TFA is added. The pentamer to heptamer show a folded structure with a strong intramolecular hydrogen bond at Glu² and a weaker hydrogen bond at Glu³, which are disrupted as these peptides go to random coils at high TFA/CDCl₃ ratios. In addition, the N-terminal portions of these glutamate peptides appear to be involved in side chain–main chain interactions. The results support the hypothesis that protected linear homo-oligopeptides may possess two or more segments of conformation with intramolecular folding preferred near the N-terminal portion.     

1H-nmr studies of polyoxyethylene-bound homo-oligo-L-methionines

The use of ¹H-nmr spectroscopy is demonstrated to be a useful analytical method to characterize the structure of synthetic peptides attached to soluble, macromolecular polyoxyethylene (POE) supports in the liquid-phase method (LPM) of peptide synthesis. We report an extensive 360-MHz ¹H-nmr study of POE-bound homo-oligo-L -methionine peptides. A combination of high field and selective saturation or Redfield pulse methods allows resolution of individual backbone NH and α-CH resonances of dilute peptides in the presence of strong resonances from macromolecular POE and/or protonated solvents. The nmr spectra for the POE-bound peptides in CDCl₃ are qualitatively similar to those of the low-molecular-weight Boc-L -Met_n-OMe peptide esters. This corroborates other observations that POE has little effect on peptide stucture. The backbone α-CH region of peptides is overlapped by signals from the terminal oxyethylene group of POE, but the peptide side-chain and low-field backbone NH resonances are well resolved. In trifluoroethanol the Boc-(L -Met)_n-NH-POE heptamer and octamer adopt the right-handed α-helical structure, and the present nmr studies provide evidence for two strong intramolecular hydrogen bonds to stabilize the helices. In water, the N-deblocked derivatives, (L -Met)_n-NH-POE oligomers adopt β-sheet structure and manifest well-resolved nonequivalent NH resonances with 6–7 Hz ³J_NH-CH coupling constants.     

Amblyomma americanum: characterization of salivary prostaglandins E2 and F2 alpha by RP-HPLC/bioassay and gas chromatography-mass spectrometry.

Secretagogue-induced saliva of the tick, Amblyomma americanum (L.) was fractionated by reversed-phase-high-performance liquid chromatography (RP-HPLC) and bioassayed in smooth muscle preparations. Material with retention times of authentic prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) were found to cause contraction of preparations of rat colon and rat stomach strips. Gas chromatography-mass spectra of selected ions of both HPLC-purified fractions confirmed the existence of PGE2 and PGF2 alpha. Bioassay of individual samples obtained from ticks stimulated to salivate with pilocarpine, dopamine + theophiline, or dopamine + theophiline + GABA indicated that all these secretagogues induced similar amounts of prostaglandin secretion, averaging 469 ng PGE2/ml. These pharmacological doses of prostaglandin are hypothesized to assist in tick feeding by inducing vasodilation and/or other pharmacological events in their hosts.