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PubMedDate not supplied

Nutrition during brain activation: does cell-to-cell lactate shuttling contribute significantly to sweet and sour food for thought?

Functional activation of astrocytic metabolism is believed, according to one hypothesis, to be closely linked to excitatory neurotransmission and to provide lactate as fuel for oxidative metabolism in neighboring neurons. However, review of emerging evidence suggests that the energetic demands of activated astrocytes are higher and more complex than recognized and much of the lactate presumably produced by astrocytes is not locally oxidized during activation. In vivo activation studies in normal subjects reveal that the rise in consumption of blood-borne glucose usually exceeds that of oxygen, especially in retina compared to brain. When the contribution of glycogen, the brain's major energy reserve located in astrocytes, is taken into account the magnitude of the carbohydrate-oxygen utilization mismatch increases further because the magnitude of glycogenolysis greatly exceeds the incremental increase in utilization of blood-borne glucose. Failure of local oxygen consumption to equal that of glucose plus glycogen in vivo is strong evidence against stoichiometric transfer of lactate from astrocytes to neighboring neurons for oxidation. Thus, astrocytes, not nearby neurons, use the glycogen for energy during physiological activation in normal brain. These findings plus apparent compartmentation of metabolism of glycogen and blood-borne glucose during activation lead to our working hypothesis that activated astrocytes have high energy demands in their fine perisynaptic processes (filopodia) that might be met by glycogenolysis and glycolysis coupled to rapid lactate clearance. Tissue culture studies do not consistently support the lactate shuttle hypothesis because key elements of the model, glutamate-induced increases in glucose utilization and lactate release, are not observed in many astrocyte preparations, suggesting differences in their oxidative capacities that have not been included in the model. In vivo nutritional interactions between working neurons and astrocytes are not as simple as implied by "sweet (glucose-glycogen) and sour (lactate) food for thought."

Anesthesia↗
PubMed2002

GABA(A) receptor modulation of the rewarding and aversive effects of ethanol.

Ethanol has been shown to exert many of its biochemical and behavioral effects through an interaction with the gamma-aminobutyric acid (GABA) receptor system. This review focuses on a subset of studies that has used self-administration, as well as place and taste conditioning, procedures to investigate a role for the GABA(A) receptor system in modulating the rewarding and aversive effects of ethanol. Potential advantages and disadvantages of each procedure are also discussed. A significant amount of evidence supports the suggestion that GABA(A) receptors are important modulators of the motivational effects of ethanol, although most of the findings have been obtained from studies examining oral ethanol self-administration. Relatively fewer studies have investigated ethanol place and taste conditioning. All self-administration studies reviewed used rats, whereas most conditioning studies used mice. Results of these studies show that GABA(A) antagonists and inverse agonists reduce ethanol self-administration under limited-access conditions. The effect of GABA(A) agonists on ethanol self-administration is less clear due to their bidirectional effects. GABA(A) receptor antagonists have been shown to increase ethanol-induced conditioned place preference and conditioned taste aversion in mice and decrease ethanol-induced conditioned taste aversion in rats. Issues related to interpretation and integration of these findings across models and species are considered. The integration of data from self-administration and conditioning procedures is necessary to define the role of GABA(A) receptors in modulating the rewarding and aversive effects of ethanol and may lead to the development of pharmacotherapies that target GABA(A) receptors to treat alcoholism in human beings.

Animals↗
PubMed2000

Enantioselective syntheses and sensory properties of the 3-mercapto-2-methylpentanols.

3-Mercapto-2-methylpentanol, a new powerful flavor compound, exhibits two stereocenters giving rise to two pairs of diastereomers. To determine differences in the sensory properties, all four diastereomers and enantiomers were stereo- and enantioselectively synthesized. A highly diastereoselective aldol reaction using a chiral auxiliary was one of the key steps in the synthesis. Further derivatization yielded the enantiopure compounds. Odor thresholds in air and water were determined.

Models, Chemical↗
PubMed1997

Perceptual and imaginary mixtures in chemosensation.

D. Algom and W.S. Cain (1991) reported similar interaction patterns for perceived and imaginary mixtures of odorants. However, their experimental design did not allow sensitive statistical testing to demonstrate differences between conditions. Three experiments on 16 mixtures of sucrose-citric acid mixtures yielded significantly different interaction pattern for perceived and imaginary mixtures. Inconsistencies in the degrees of suppression in the imaginary condition suggested that participants did not base their responses on the inspection of a mental image but on incomplete implicit or explicit knowledge of sensory interactions. Participants knew the phenomenon of mixture suppression and knew that its effects were level dependent, but they were unable to predict the exact intensity of a mixture on the basis of the intensities of its unmixed components.

Citric Acid↗
PubMed2004

Modeling the kinetics of flavour release during drinking.

Novel mathematical models for flavour release during drinking are described, based on the physiology of breathing and swallowing. Surprisingly, we conclude that most flavour molecules arriving in the nose are extracted from liquid left in the throat, after swallowing. The models are fit to real time flavour release data obtained using APCI-mass spectrometry. Before modelling, raw data are corrected for the effects of varying airflow rate, using the signal from acetone in exhaled air. A simple equilibrium batch extraction model correctly describes flavour release during the first breaths after swallowing a flavoured liquid. It shows that for eight volatiles, whose in vitro air-water partition coefficients vary by a factor of 500, the apparent in vivo air-saliva partition coefficients vary only by a factor of five. To interpret the kinetics of flavour release longer after swallowing, diffusion of flavour into the throat lining is included. This is done using a three-layer model for mass transfer in the throat. An analytical solution of this model gives good fits to typical data. These models de-couple the physiological and physico-chemical aspects of flavour release, clarifying the effect of behaviour on in-vivo flavour release.

Computer Simulation↗
PubMed2005

Chemometric modeling to relate antioxidants, neutral lipid fatty acids, and flavor components in chicken breasts.

Relationships among quality factors in retailed free-range, corn-fed, organic, and conventional chicken breasts (9) were modeled using chemometric approaches. Use of principal component analysis (PCA) to neutral lipid composition data explained the majority (93%) of variability (variance) in fatty acid contents in 2 significant multivariate factors. PCA explained 88 and 75% variance in 3 factors for, respectively, flame ionization detection (FID) and nitrogen phosphorus (NPD) components in chromatographic flavor data from cooked chicken after simultaneous distillation extraction. Relationships to tissue antioxidant contents were modeled. Partial least square regression (PLS2), interrelating total data matrices, provided no useful models. By using single antioxidants as Y variables in PLS (1), good models (r2 values > 0.9) were obtained for alpha-tocopherol, glutathione, catalase, glutathione peroxidase, and reductase and FID flavor components and among the variables total mono and polyunsaturated fatty acids and subsets of FID, and saturated fatty acid and NPD components. Alpha-tocopherol had a modest (r2 = 0.63) relationship with neutral lipid n-3 fatty acid content. Such factors thus relate to flavor development and quality in chicken breast meat.

Animals↗
PubMed2004

Cellular mechanisms involved in CO(2) and acid signaling in chemosensitive neurons.

An increase in CO(2)/H(+) is a major stimulus for increased ventilation and is sensed by specialized brain stem neurons called central chemosensitive neurons. These neurons appear to be spread among numerous brain stem regions, and neurons from different regions have different levels of chemosensitivity. Early studies implicated changes of pH as playing a role in chemosensitive signaling, most likely by inhibiting a K(+) channel, depolarizing chemosensitive neurons, and thereby increasing their firing rate. Considerable progress has been made over the past decade in understanding the cellular mechanisms of chemosensitive signaling using reduced preparations. Recent evidence has pointed to an important role of changes of intracellular pH in the response of central chemosensitive neurons to increased CO(2)/H(+) levels. The signaling mechanisms for chemosensitivity may also involve changes of extracellular pH, intracellular Ca(2+), gap junctions, oxidative stress, glial cells, bicarbonate, CO(2), and neurotransmitters. The normal target for these signals is generally believed to be a K(+) channel, although it is likely that many K(+) channels as well as Ca(2+) channels are involved as targets of chemosensitive signals. The results of studies of cellular signaling in central chemosensitive neurons are compared with results in other CO(2)- and/or H(+)-sensitive cells, including peripheral chemoreceptors (carotid body glomus cells), invertebrate central chemoreceptors, avian intrapulmonary chemoreceptors, acid-sensitive taste receptor cells on the tongue, and pain-sensitive nociceptors. A multiple factors model is proposed for central chemosensitive neurons in which multiple signals that affect multiple ion channel targets result in the final neuronal response to changes in CO(2)/H(+).

Acids↗
PubMed2003

Comparison of the responses of the chorda tympani and glossopharyngeal nerves to taste stimuli in C57BL/6J mice.

BACKGROUND: Recent progress in discernment of molecular pathways of taste transduction underscores the need for comprehensive phenotypic information for the understanding of the influence of genetic factors in taste. To obtain information that can be used as a base line for assessment of effects of genetic manipulations in mice taste, we have recorded the whole-nerve integrated responses to a wide array of taste stimuli in the chorda tympani (CT) and glossopharyngeal (NG) nerves, the two major taste nerves from the tongue. RESULTS: In C57BL/6J mice the responses in the two nerves were not the same. In general sweeteners gave larger responses in the CT than in the NG, while responses to bitter taste in the NG were larger. Thus the CT responses to cyanosuosan, fructose, NC00174, D-phenylalanline and sucrose at all concentrations were significantly larger than in the NG, whereas for acesulfame-K, L-proline, saccharin and SC45647 the differences were not significant. Among bitter compounds amiloride, atropine, cycloheximide, denatonium benzoate, L-phenylalanine, 6-n-propyl-2-thiouracil (PROP) and tetraethyl ammonium chloride (TEA) gave larger responses in the NG, while the responses to brucine, chloroquine, quinacrine, quinine hydrochloride (QHCl), sparteine and strychnine, known to be very bitter to humans, were not significantly larger in the NG than in the CT. CONCLUSION: These data provide a comprehensive survey and comparison of the taste sensitivity of the normal C57BL/6J mouse against which the effects of manipulations of its gustatory system can be better assessed.

Acids↗
PubMed2003

Release characteristics of flavor from spray-dried powder in boiling water and during rice cooking.

The release characteristics of flavor in boiling water and the flavor retention in the rice after cooking were investigated by using spray dried powder in encapsulated in or emulsified with d-limonene or ethyl n-hexanoate in cyclodextrin and maltodextrin, or in gum arabic and maltodextrin. The behavior of flavor release into the boiling water was well simulated by Avrami's equation. The retention of d-limonene and ethyl n-hexanoate in cooked rice was correlated in each case with the flavor amount of spray-dried powder added.

Caproates↗
PubMed1986

The roles of the recurrent nerve and the ventral nerve cord in the feeding response of the blowfly, Phormia regina M.

The interaction of sensory activities from internal stretch receptors and from external sugar receptors was studied in relation to proboscis extension and sucrose intake of the blowfly. The tarsal threshold for proboscis extension was elevated in flies after the recurrent nerve was cut. Cutting either the recurrent nerve or the ventral nerve cord did not alter the labellar thresholds for proboscis extension but did influence sucrose intake by prolonging the duration of intake. After the ventral nerve cord was cut, the flies did not stop ingestion as long as sugar receptors in the interpseudotracheal papillae were stimulated. Tonic impulse discharges from the intact recurrent nerve were divided into efferent and afferent types. Efferent impulses from the brain were thought to be transmitted to the hypocerebral ganglion-corpus cardiacum complex for regulation of opening and closing of the foregut valves, of peristaltic movements in the foregut. Afferent impulses were thought to be discharged from the foregut stretch receptors which detected peristaltic movements in the foregut.

Animals↗