Imaging cytoplasmic cAMP in mouse brainstem neurons

Background  

cAMP is an ubiquitous second messenger mediating various neuronal functions, often as a consequence of increased intracellular Ca²⁺ levels. While imaging of calcium is commonly used in neuroscience applications, probing for cAMP levels has not yet been performed in living vertebrate neuronal tissue before.     

Radial particle distributions in a d.c. arc—maximum off-axis

It is shown that for some elements evaporated from the anode of a d.c. arc the position of the maximum concentration of atomic particles (i.e. atoms + ions) occurs not on the axis of the arc column but some distance away from the centre, this distance being largely determined by the inside diameter of the electrode crater. It is shown that the magnitude of the off-axis peak increases with increasing volatility of the element concerned, but decreases with increasing electrical power generated in the plasma as well as with decreasing ionisation potential of the buffer metal. The proposed mechanism for this phenomenon is based on the fact that, due to thermal repulsion, cool vapours do not readily mix with hot gases. Thus volatile sample components evaporating from regions not immediately beneath the anode spot would tend to diffuse laterally around the arc rather than vertically into the hot plasma.     

Engineering acyclic stereocontrol in the alkylation of vinylglycine-derived dianions: asymmetric synthesis of higher alpha-vinyl amino acids

A generalizable synthesis of higher L-alpha-vinyl amino acids is presented. The strategy pursued here involves the introduction of the amino acid side chain via the alkylation of a chiral, vinylglycine-derived dianionic dienolate, bearing the (-)-8-(beta-naphthyl)menthyl (d'Angelo) auxiliary. A model is presented that postulates a favored "exo-entended" conformation for this dienolate, leading to C(alpha)-alkylation at the si face. The model invokes internal amidate chelation to control ester enolate geometry and soft-soft interactions between the polarizable beta-naphthyl ring of the auxiliary and the extended pi-system of the dienolate to shield the re face. Heats of formation for four conformers of this dianion were calculated for their semiempirical optimized geometries (PM3). The results support the notion that in these vinylglycine-derived dianionic dienolates, "exo" conformations are considerable lower in energy than their "endo" counterparts, with the "exo-entended" conformation being most favorable. In fact, the d'Angelo auxiliary gives a greater degree of acyclic stereocontrol in this system when compared with the (-)-8-phenylmenthyl (Corey) and trans-2-(beta-naphthyl)cyclohexyl auxiliaries, using isobutyl iodide and benzyl bromide as model electrophiles. These dianions are generated from the corresponding dehydrobutyrine esters via sequential deprotonation with LDA and n-BuLi (2 equiv). When alkylations are carried out at -78 degrees C in THF-HMPA, they proceed in 65-81% yields, with both regiocontrol (deconjugative alpha-alkylation is preferred over gamma-alkylation) and a great degree of acyclic stereocontrol [91:9 to >/=98:2 diastereomeric ratios (10 examples)]. The auxiliary may be recovered in high yield (generally 90%) using a modification of Gassman's "anhydrous hydroxide" conditions, in which considerably higher temperatures are employed. Among the side chains introduced directly are those of butyrine, leucine, ornithine, phenylalanine, aspartate, valine, and norvaline. The lysine side chain is elaborated via a 4-step sequence from the alkylation product obtained with 1-chloro-4-iodobutane as electrophile. Importantly, to our knowledge, this work represents the first asymmetric synthesis of L-alpha-vinyl analogues of m-tyrosine, ornithine, and lysine, known time-dependent inhibitors for amino acid decarboxylases.     

Upward shifts in the masking pattern with increasing masker intensity

Masking patterns obtained with forward-masking paradigms and relatively intense maskers sometimes have their peaks at the masker frequency and sometimes at a frequency well above it. Here it is shown that which outcome is obtained depends upon certain temporal parameters of the procedure. Specifically, the masking pattern for a 2000-Hz tone showed a gradual shift toward higher frequencies as masker intensity was increased from 65 to 95 dB SPL when long signals (about 50 ms) and long masker-to-signal intervals (about 50 ms) were used, but the effect was absent or smaller when the signals and intervals were short. This shift did not occur with a 750-Hz masker. Upward shifts in the masking pattern with increasing masker intensity are in accord with the view that the peak of displacement of the traveling-wave envelope migrates basally with increasing intensity--an idea that has frequently been suggested as an explanation of the so-called half-octave shift so routinely seen in auditory fatigue experiments.     

Stable isotopic studies of earthworm feeding ecology in tropical ecosystems of Puerto Rico

Feeding strategies of earthworms and their influence on soil processes are often inferred from morphological, behavioral and physiological traits. We used (13)C and (15)N natural abundance in earthworms, soils and plants to explore patterns of resource utilization by different species of earthworms in three tropical ecosystems in Puerto Rico. In a high altitude dwarf forest, native earthworms Trigaster longissimus and Estherella sp. showed less (15)N enrichment ((15)N = 3-6 per thousand) than exotic Pontoscolex corethrurus ((15)N =7-9 per thousand) indicating different food sources or stronger isotopic discrimination by the latter. Conversely, in a lower altitude tabonuco forest, Estherella sp. and P. corethrurus overlapped completely in (15)N enrichment ((15)N = 6-9 per thousand), suggesting the potential for interspecific competition for N resources. A tabonuco forest converted to pasture contained only P. corethrurus which were less enriched in (15)N than those in the forest sites, but more highly enriched in (13)C suggesting assimilation of C from the predominant C(4) grass. These results support the utility of stable isotopes to delineate resource partitioning and potential competitive interactions among earthworm species. Copyright 1999 John Wiley & Sons, Ltd.     

Reductions in overshoot during aspirin use

The overshoot effect was measured before, during, and after the administration of a moderate dose of aspirin. Prior to the drug, detectability of the 6-ms, 3550-Hz signal was 5-11 dB worse when presented 2 ms after the onset of the 200-ms wideband masking noise than when presented 190 ms after masker onset. Following 4 days of aspirin use, detectability in the long-delay condition was unchanged from the predrug value, but (for four of the five subjects) detectability in the short-delay condition was improved by about 4-8 dB. Thus the overshoot effect was markedly reduced by aspirin because the drug partially counteracted the normally poor detectability for signals presented soon after masker onset. This paradoxical improvement in detectability was accompanied by an aspirin-induced loss in detectability of 5-16 dB for a 200-ms sample of that same signal presented in the quiet. Similar paradoxical effects have previously been obtained by inducing a temporary hearing loss with exposure to intense sound. It is presumed that the same basic mechanisms underlie the parallel outcomes. The so-called cochlear amplifier is discussed in this regard, and also the possibility that the known differences in those primary auditory fibers having high and low spontaneous rates may be involved. A supplementary experiment demonstrated that shifting audibility with either a wideband or a narrow-band background noise does not affect the overshoot effect in the same way as does aspirin or exposure to intense sound, further suggesting that the cochlear amplifier must be altered in order for overshoot to be diminished.     

Partial dissociation of spontaneous otoacoustic emissions and distortion products during aspirin use in humans

Otoacoustic emissions (OAEs) of two types--spontaneous and evoked distortion products--were studied before, during, and following a period of aspirin use. As previously reported, aspirin consumption uniformly reduced the spontaneous OAEs (SOAEs) to unmeasurable or extremely low levels. Aspirin consumption also reduced the amplitude of the evoked distortion products (EDPs) but did not eliminate them entirely. The amplitude of the EDP and its change with aspirin consumption were related to both the proximity of the EDP to the frequency of the SOAE and to the level of the primaries producing the EDP. At low primary levels, even with the SOAE absent (due to aspirin consumption, or suppression), EDPs near the SOAE frequency were 10-20 dB higher than when they were 100 Hz away from the SOAE frequency.