Olfactory performance of rats after selective deafferentation of the olfactory bulb by 3-methyl indole

Rats trained to detect propyl acetate and valeric acid and to discriminate between propyl acetate and amyl acetate and between valeric acid and butyric acid were injected with a low dose of 3-methyl indole, a treatment that produces well-defined and selective deafferentation of the olfactory bulbs. Treatment completely deafferented most but not all bulbar loci for aliphatic acids and at least disrupted those for propyl and amyl acetate. In posttreatment tests, experimental rats performed somewhat but not significantly more poorly than controls and about as well on the acid detection and discrimination tasks as on the corresponding acetate tests.     

Effects of short chain fatty acids on seedlings

Abstract. Primary roots of lettuce show no appreciable diminution of sensitivity of SCFA between 24 and 72 h, so it is likely that all actively growing primary roots are susceptible to inhibition by SCFA. While roots do not recover from long exposures to high concentrations of SCFA, partial recovery is seen following exposure to intermediate levels.
SCFA inhibit elongation of lettuce and turnip hypocotyls as well as roots. However, higher concentrations are required to produce a given inhibition of hypocotyl. In contrast with the inhibition of roots, inhibition of shoots is markedly dependent on the chain length of the fatty acid. Thus, either access to sites of action or action at the sites differs between shoots and roots of the same seedling plants.     

Olfactory discrimination ability for aliphatic c6 alcohols as a function of presence, position, and configuration of a double bond

The ability of human subjects to distinguish between aliphatic C6 alcohols differing in presence, position, or configuration (i.e., cis-trans geometry) of a double bond was tested. In a forced-choice triangular test procedure, 20 subjects were repeatedly presented with all 21 binary combinations of the seven stimuli and asked to identify the bottle containing the odd stimulus. I found (a) that as a group, the subjects performed significantly above chance level in all tasks but two and thus were clearly able to discriminate between most of the odor pairs presented; (b) marked interindividual differences in discrimination performance, ranging from subjects who were able to significantly distinguish between all 21 odor pairs to subjects who failed to do so with 10 of the tasks; (c) that odor pairs involving two hexenols were significantly more difficult to discriminate than odor pairs that involved hexanol and one of the hexenols; (d) that odor pairs involving hexenols sharing the same geometry but differing in the position of the double bond by only one carbon atom were significantly more difficult to distinguish than odor pairs that involved hexenols differing by two carbon atoms; (e) that odor pairs involving 4-hexenols were significantly easier to discriminate than 3-hexenols, which, in turn, were significantly easier to distinguish than 2-hexenols; and (f) that odor pairs involving two cis-hexenols were significantly more difficult to discriminate than odor pairs that involved two trans-hexenols. These findings demonstrate that the presence as well as the position and configuration of a double bond affected discriminability in a systematic manner and suggest that these molecular structural features may be important determinants of the interaction between stimulus molecule and olfactory receptor and thus may affect odor quality of aliphatic alcohols.     

Performance of mice in discrimination of liquor odors: behavioral evidence for olfactory attention

We examined performance of mice in discrimination of liquor odors by Y-maze behavioral assays. Thirsty mice were initially trained to choose the odor of a red wine in the Y-maze. After successful training (>70% concordance for each trained mouse), the individual mice were able to discriminate the learned red wine from other liquors, including white wine, rosé wine, sake, and plum liqueur. However, when the mice were tested to distinguish fine differences between 2 brands of red wine, their performance significantly varied among the individual trained mice. Among 10 mice tested, 2 mice were able to discriminate between the red wines (>75% concordance) whereas 6 mice failed to distinguish between them (50-67% concordance, where chance could be assumed to be 50%). More importantly, 2 other mice exhibited lower than 30% concordance, indicating that they were more attracted to the nonrewarded red wine compared with the learned one. This result suggested that the individual mice directed attention to different subsets of volatile components emanating from the rewarded red wine, when they were trained to choose the liquor odor in the Y-maze. Selective attention of mice was also observed in Y-maze behavioral assays using the mixtures of 3 or less pure odorants. Additionally, we also observed that the olfactory attention of mice could be modified through their learning experiences.     

Entamoeba invadens: restriction of ploidy by colonic short chain fatty acids

The DNA content of Entamoeba parasites appears to be regulated by an unusual mechanism. This conclusion, however, was based on experiments that examined parasites grown in media that did not contain short chain fatty acids (SCFAs) normally found in the colonic lumen. Since one of these SCFAs, butyrate, is known to affect DNA replication in eukaryotic cells, we examined the effect of SCFAs on Entamoeba trophozoite DNA content. Similar to reports from others, we found that Entamoeba invadens trophozoite cultures grown in conventional medium (TYI-S-33) contained cells with 2N, 4N, 8N, and 16N amounts of DNA. In contrast, cultures grown in TYI medium containing colonic SCFAs added in place of glucose contained a minor population with 2N, a major population with 4N, and very few cells with higher amounts of DNA. SCFAs also prevented the normal increase in the number of nuclei per cell in trophozoites that were induced to encyst. These results suggest that E. invadens trophozoite stage parasites growing in the intestine in the presence of high amounts of SCFAs have a ploidy range restricted to 2N/4N. Axenic growth of trophozoites in the absence of SCFAs, however, appears to allow trophozoites to increase the amount of DNA per cell, which they must do during the normal encystment process.     

Olfactory discrimination of urine odors from five species by tufted capuchin (Cebus apella)

Urine collected from New World monkeys (tufted capuchin, squirrel monkey, cotton-top tamarin) and Old World monkeys (rhesus macaque, Japanese macaque), was used as the odor stimuli. Two adult tufted capuchins were trained on a successive odor-discrimination task with two odors, 30 trials each, in one session per day. Responses to one of the two odors (S+) were reinforced by sweet water. The monkeys failed to discriminate between the urine from the two species of macaques but could discriminate among the urine from the three species of New World monkeys. Furthermore, similarity of urine odors was analyzed by multi-dimensional scaling (MDS) and a cluster analysis. These analysis suggested that the tufted capuchin can distinguish differences among New World monkeys but not between the macaques. The natural distribution of the tufted capuchin overlaps with that of other New World monkeys, but it does not overlap with those of Old World monkeys. Consequently, it can be concluded that this difference in olfactory recognition in the tufted capuchin reflects their sympatric and allopatric relationships with other species.     

Growth of Synthrophomonas wolfei on unsaturated short chain fatty acids

The anaerobic fatty acid-degrading syntrophic bacterium, Syntrophomonas wolfei, was grown in pure culture with either trans-2-pentenoate, trans-2-hexenoate, trans-3-hexenoate, and trans, trans-2,4-hexadienoate as the substrate. Trans-2-pentenoate was fermented to acetate, propionate, butyrate, and valerate. Acetate, butyrate, and hexanoate were produced from the six-carbon mono- and di-unsaturated acids. Propionate was also product from the trans,trans-2,4-hexadienoate which suggested this compound was degraded by another pathway in addition to -oxidation. The transient production of trans-2-hexenoate from trans-3-hexenoate suggested that the position of the double bound shifted from carbon-3 to carbon-2 prior to -oxidation. The specific growth rate decreased with increasing carbon length and degree of unsaturation. Molar growth yields ranged from 8.4 to 17.5 mg (dry wt.) per mmol and suggested that energy was conserved not only from substrate-level phosphorylation, but also from the reduction of unsaturated substrate.     

Asymmetric suppression of components in binary aldehyde mixtures: behavioral studies in the laboratory rat

The aim of the present study was to assess component interaction in the perception of the 2 aldehydes butanal and heptanal when presented in binary mixtures to rats. A further aim was to develop a behavioral paradigm for testing suppression of components in mixtures using rodent subjects. Thirsty rats were initially trained to discriminate between the 2 aldehydes butanal and heptanal in an olfactometer using a go/no-go discrimination task. This involved rats learning to place their noses in a sniff port where odors were presented and to lick a tube for water reward when one of the aldehydes was presented (S+) while withholding licking at the tube to the other, unrewarded, aldehyde (S-). A mixture condition was then introduced into the task, whereby a proportion of trials involved presentation of a combination of the 2 aldehydes as an additional unrewarded condition. Rats readily learned to withhold licking on trials when the mixture was presented. The concentration of the nonrewarded (S-) aldehyde in the mixture was then systematically decreased, whereas the concentration of the S+ component was held constant. This eventually caused the S+ component in the mixture to suppress detection of the S-, as shown by an increasing number of lick responses (false alarms) on trials when the mixture was presented. These suppressing effects occurred well above the detection threshold for the S- aldehyde presented alone. Results showed asymmetric suppression in the mixture condition such that butanal suppressed detection of heptanal at much lower concentrations than vice versa. A second experiment showed that when both butanal and heptanal were present in a binary mixture at the same concentration (10(-6) volume %), then rats responded to the mixture as if only butanal was present. These findings are discussed in terms of butanal having higher mobility and being able to compete more effectively than heptanal for occupation of shared receptor sites.     

Stimulatory effect of short chain fatty acids on the epithelial cell proliferation in rat large intestine

1. Short chain fatty acids [SCFA: acetate 75, propionate 35, butyrate 20 (microM)] introduced intraluminally into the colon increased the mitotic index and the labeling index of the large intestinal epithelial cells within 60 min in fasted rats. 2. Epithelia that lacked direct contact with SCFA were also stimulated. 3. SCFA did not have such a stimulatory effect either in vagotomized rats or in sympathectomized rats. 4. These results suggest that SCFA stimulate epithelial cell proliferation in the large intestine of fasted rats via the autonomic nervous system.     

Isotopomer enrichment assay for very short chain fatty acids and its metabolic applications

The present work illustrated an accurate GC/MS measurement for the low isotopomer enrichment assay of formic acid, acetic acid, propionic aicd, butyric acid, and pentanoic acid. The pentafluorobenzyl bromide derivatives of these very short chain fatty acids have high sensitivity of isotopoic enrichment due to their low natural isotopomer distribution in negative chemical ionization mass spectrometric mode. Pentafluorobenzyl bromide derivatization reaction was optimized in terms of pH, temperature, reaction time, and the amount of pentafluorobenzyl bromide versus sample. The precision, stability, and accuracy of this method for the isotopomer analysis were validated. This method was applied to measure the enrichments of formic acid, acetic acid, and propionic acid in the perfusate from rat liver exposed to Krebs–Ringer bicarbonate buffer only, 0–1 mM [3,4-¹³C₂]-4-hydroxynonanoate, and 0–2 mM [5,6,7-¹³C₃]heptanoate. The enrichments of acetic acid and propionic acid in the perfusate are comparable to the labeling pattern of acetyl-CoA and propionyl-CoA in the rat liver tissues. The enrichment of the acetic acid assay is much more sensitive and precise than the enrichment of acetyl-CoA by LC-MS/MS. The reversibility of propionyl-CoA from succinyl-CoA was confirmed by the low labeling of M1 and M2 of propionic acid from [5,6,7-¹³C₃]heptanoate perfusates.     

The sniff is part of the olfactory percept

In this review, we use data obtained primarily from humans to argue that sniffs are not merely a stimulus carrier but are rather a central component of the olfactory percept. We argue that sniffs 1) are necessary for the olfactory percept, 2) affect odorant intensity perception and identity perception, 3) drive activity in olfactory cortex, 4) are rapidly modulated in an odorant-dependent fashion by a dedicated olfactomotor system, and 5) are sufficient to generate an olfactory percept of some sort even in the absence of odor.     

Olfactory discrimination ability of human subjects for enantiomers with an isopropenyl group at the chiral center

The ability of 20 human subjects to distinguish between nine enantiomeric odor pairs sharing an isopropenyl group at the chiral center was tested in a forced-choice triangular test procedure. I found (i). that as a group, the subjects were only able to significantly discriminate the optical isomers of limonene, carvone, dihydrocarvone, dihydrocarveol and dihydrocarvyl acetate, whereas they failed to distinguish between the (+)- and (-)-forms of perillaalcohol, perillaaldehyde, isopulegol and limonene oxide; (ii). marked interindividual differences in discrimination performance, ranging from subjects who were able to significantly discriminate between eight of the nine odor pairs to subjects who failed to do so with six of the nine tasks; and (iii). that with none of the nine odor pairs the antipodes were reported to differ significantly in subjective intensity when presented at equal concentrations. Additional tests of the chemesthetic potency and threshold measurements of the optical isomers of dihydrocarvone, dihydrocarveol, and dihydrocarvyl acetate suggest that the discriminability of these three enantiomeric odor pairs is indeed due to differences in odor quality. Analysis of structure-activity relationships suggest that the combined presence of (i). an isopropenyl group at the chiral center; (ii). a methyl group at the para-position; and/or (iii). an oxygen-containing group at the meta-position allows for the discrimination of enantiomeric odor pairs.     

Effects of short chain fatty acids on radicle emergence and root growth in lettuce

Abstract. Short chain fatty acids inhibit both radicle emergence and root growth in lettuce. The transition from ineffectual to inhibitory levels occurs abruptly. Root growth is more sensitive to lower concentrations than radicle emergence and is invariant with chain length. The effect of short chain alcohols on radicle emergence is similar to that of short chain acids, but their comparatively severe inhibition of root growth varies with chain length. Alkanes of the same chain lengths have no noticeable effect. Respiration is not altered by a representative short chain fatty acid (heptanoic). Lettuce seeds are sensitized to phytochrome-absorbed light by short chain fatty acids as found by Berrie and co-workers.     

Decoding Temporal Information Through Slow Lateral Excitation in the Olfactory System of Insects

Sensory information is represented in a spatio-temporal code in the antennal lobe, the first processing stage of the olfactory system of insects. We propose a novel mechanism for decoding this information in the next processing stage, the mushroom body. The Kenyon cells in the mushroom body of insects exhibit lateral excitatory connections at their axons. We demonstrate that slow lateral excitation between Kenyon cells allows one to decode sequences of activity in the antennal lobe. We are thus able to clarify the role of the existing connections as well as to demonstrate a novel mechanism for decoding temporal information in neuronal systems. This mechanism complements the variety of existing temporal decoding schemes. It seems that neuronal systems not only have a rich variety of code types but also quite a diversity of algorithms for transforming different codes into each other.     

Branched chain amino acids as source of specific branched chain volatile fatty acids during the fermentation process of fish sauce

Summary.  The source of the formation of branched chain volatile fatty acids (VFA) in fish sauce was investigated. Certain branched VFA were derived from the degradation of specific amino acids as iso-butyric acid from valine and iso-valeric acid from leucine. Short and long straight chain VFA were significantly higher in the linoleic acid added sample than in the control but did not significantly bring changes to the branched chain VFA. It is suggested that straight chain VFA developed from fish fats. Alanine and isoleucine did not have a clear influence on the production of volatile fatty acids. Received November 23, 2001 Accepted June 20, 2002 Published online December 18, 2002 RID="*" ID="*" Part of this paper was presented in the 7th International Congress on Amino Acids and Proteins in Vienna, Austria from August 6–10, 2001. Authors' address: Norlita G. Sanceda, Ph.D., Institute of Environmental Science for Human Life, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112, Japan, Fax: + 81-3-5978-5805, E-mail: lita@cc.ocha.ac.jp