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Biomedical subjects

C M Mistretta

Publications and source records attributed to C M Mistretta.

At least 19 recordsLinked to original sources
PubMed1990

Developmental neurobiology of salt taste sensation.

A principal process in the homeostatic control of sodium levels is salt intake, and the sense of taste has a primary role in regulating ingestion. Because ingestion of sodium chloride (NaCl) is essential for life, the taste system for salt sensation might be expected to exhibit mature functional characteristics from very early development. However, major changes in gustatory nerve responses to NaCl take place during development. In sheep and rat, the peripheral nerve responses to NaCl are of low magnitude during early development. Progressively, the taste system acquires an increasing proportion of fibers that respond maximally to NaCl. The sodium responsiveness emerges in the context of shifting peripheral innervation patterns and the apparent addition of functional receptor membrane channels sensitive to the sodium transport blocker, amiloride. These developmental processes can be altered by early manipulation of sodium in the diet.

Action Potentials↗
PubMed1990

Convergence in mammalian nucleus of solitary tract during development and functional differentiation of salt taste circuits.

To determine the type and extent of neural rearrangements that are made during functional differentiation of circuits for salt taste processing, we determined receptive field size and salt response characteristics of second-order taste cells in 3 age groups of sheep. Neurophysiological recordings were made from single cells in the nucleus of the solitary tract (NST) in fetal, perinatal, and postnatal sheep. Responses to NH4Cl, NaCl, and KCl were measured, and location and number of fungiform papillae in the receptive field were determined by stimulating individual papillae with anodal electrical current. The data are compared with previous, parallel measures from chorda tympani nerve afferent taste fibers to permit conclusions about convergence or divergence onto second-order cells. Receptive field size of second-order taste neurons increases during development, in contrast to the decrease in field size observed previously for chorda tympani nerve fibers during the same period. Furthermore, receptive fields of second-order cells are significantly larger than those of first-order fibers at perinatal and lamb ages, but not fetal. Thus, there is convergence of first-order taste afferents onto brain-stem neurons, and the convergence increases remarkably between fetal and perinatal periods. Associated with the increase in convergence are increased salt response frequencies relative to afferent fibers for NaCl in perinatal animals and lambs, and for KCl in lambs. The increase in frequencies occurs before NST neurons are functionally mature, as indicated by the rapid response adaptation of many cells in young animals. Convergence in NST during development apparently functions to maximize gain for processing neural responses to NaCl. In the periphery, response frequencies to NaCl are very low in fetuses, and increase progressively during development. In the NST, NaCl response frequencies are high even in fetuses, and remain high. The process of convergence onto second-order cells is accomplished with maintenance of order in afferent projections because receptive fields of NST neurons are composed of fungiform papillae that are clustered together, not dispersed over the tongue. Our quantification of taste receptive field size at 2 neural levels provides strong evidence for increasing convergence in the NST during development. Altering patterns of afferent neural input and geometry of second-order neurons may have a role in establishing convergence. The convergence has an apparently special function: to increase gain for NaCl taste sensation. Therefore, neural rearrangements during differentiation of salt taste pathways result in specific functional outcomes.

Ammonium Chloride↗
PubMed1989

Anatomy and neurophysiology of the taste system in aged animals.

In summary, the recent data from quantitative studies of taste buds in old humans, rhesus monkeys, and rats complement neurophysiological data on taste responses from aged rats and lead to the general conclusion that the peripheral taste system is maintained structurally and functionally across the life span. Although some statistically significant differences were observed, the magnitude of these differences would not lead one to predict altered taste preferences or feeding behavior in old animals. The robust nature of the peripheral sense of taste in old age appears to be in sharp contrast to other sensory systems. Not only do receptors alter with age, but accessory organs, such as the lens in the visual system, also alter structurally so that sensory function is compromised. One factor contributing to maintenance of the receptor organ of taste bud and papilla is the turnover and replacement of taste bud cells and surrounding epithelial cells. Recent studies in aged mice indicate no differences in turnover time in epithelial mucosa lining the mouth. There are no data on turnover time, however, for taste bud cells or for gustatory papilla epithelium in old animals. Alterations in taste bud cell or membrane receptor turnover could affect function. In other cell types and receptors, age-related differences in membrane lipids, proteins, and fluidity characteristics are reported. Membrane changes such as these are proposed to account for age-related differences in response properties of the system of cardiac muscarinic receptors, a system in which density of receptors does not alter. The small, but statistically significant, differences in neurophysiological responses to taste stimuli from the chorda tympani nerve might well relate to age-related differences in membrane receptors. Not only is there an absence of data on turnover time or membrane characteristics for taste bud cells in old age, but there are no observations on the ultrastructure of taste buds in old animals. The taste bud is a complex structure, composed of many cells and different cell types, with a specific orientation and access to the oral cavity via the taste pore, and with extensive associations with the innervating afferent fibers. Ultrastructural observations could provide information on changes in synapses and other nerve/cell contacts--in microvilli and taste pore structure, and in numbers of various cell types within the bud. Such data will be essential to understanding the nature and extent of age-related alterations in the taste system.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1988

Developmental decrease in size of peripheral receptive fields of single chorda tympani nerve fibers and relation to increasing NaCl taste sensitivity.

During development in rats, sheep, and humans, the taste system acquires increasing responsiveness to NaCl, compared with a variety of other salts and chemicals. To better understand the neural basis of changes in salt taste responses, we studied receptive field size and response properties of single chorda tympani nerve fibers in fetal, perinatal, and postnatal sheep. Individual fungiform papillae were stimulated electrically with 5 microA anodal current to determine the location and number of papillae in receptive fields. Response characteristics of NH4Cl, NaCl, and KCl were determined for the entire field. Receptive fields were dissected for later histological reconstruction and taste bud identification. Median receptive field size decreased during development. Field sizes in lambs were smaller than those in younger animals. This decrease was accompanied by an increase in the NaCl/NH4Cl response ratio of single fibers and an increase in the proportion of fibers and associated fields that responded with higher frequency to NaCl, compared with NH4Cl. In addition, for fibers across all age groups, receptive field size correlated negatively with the NaCl/NH4Cl response ratio; that is, fields most responsive to NaCl had fewer papillae than those most responsive to NH4Cl. For all fibers, receptive field size correlated with response frequencies to NH4Cl and KCl but not NaCl. For NaCl-best fibers, receptive field size correlated with the response frequencies to all 3 salts. There was no relation between number of taste buds in a single fungiform papilla and the response frequency elicited during electrical stimulation of the papilla.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1988

Morphology of chorda tympani fiber receptive fields and proposed neural rearrangements during development.

The average number of fungiform papillae in receptive fields of single chorda tympani nerve fibers decreases during development in sheep, and a greater proportion of small receptive fields that are highly responsive to NaCl, compared with NH4Cl, is acquired. To learn whether there also are developmental differences in the number of taste buds within the papillae in mapped receptive fields, we studied the morphology of receptive fields and fungiform papillae, and also counted fibers in the chorda tympani nerve, in fetal, perinatal, and postnatal sheep. Whether defined as the number of fungiform papillae or as the number of taste buds within papillae, receptive fields of chorda fibers decrease developmentally. Initially, however, there is an increase, and subsequently a decrease, in the number of taste buds per field. The differences in field size cannot be attributed to developmental alterations in numbers of fungiform papillae because the total number of papillae on the tongue remains constant. The average number of taste buds per papilla, however, also increases and then decreases, and the increase in perinatal animals is accompanied by the appearance of large, multipored taste buds. Because there is a significant relation between fungiform papilla size and number of taste buds in the papilla, papilla size could be one regulating factor for taste bud number. Furthermore, the number of chorda tympani nerve fibers apparently increases up to perinatal stages and then decreases postnatally, providing another potential regulating factor for the number of taste buds.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Demonstration of sensory innervation of rat tongue with anterogradely transported horseradish peroxidase.

Wheat germ agglutinin-horseradish peroxidase injected into the petrosal ganglion in rats was transported to the posterior tongue in the glossopharyngeal nerve. Labelled fibers innervated the ipsilateral foliate papilla only, but both ipsi-and contralateral sides of the single circumvallate papilla. Somatosensory fibers in the posterior tongue also were labelled. Label crossed transcellularly from the afferent fibers into taste bud cells. Use of this method provides more detailed knowledge of sensory innervation of the tongue than previously available.

Animals↗
PubMed1986

Effects of dietary NaCl deprivation during early development on behavioral and neurophysiological taste responses.

In order to determine whether the gustatory system can be modified by restricting dietary NaCl during early development, neurophysiological taste responses were recorded in rats at various times after deprivation, and behavioral taste preferences were measured in adults. Rats deprived of dietary NaCl from the third day of gestation to 12 days postnatally and then placed on a NaCl-replete diet had chorda tympani nerve responses similar to those of nondeprived rats when recordings were made at 28 days of age and older; however, preferences for NaCl solutions over water were significantly less than those of controls when tested at adulthood. NaCl deprivation in pups from the third day of gestation to approximately 35 days postnatally resulted in altered chorda tympani nerve responses to NaCl but not to other stimuli such as NH4Cl and KCl. Therefore, restriction of dietary NaCl at a period in the rat's development when peripheral and central taste responses are changing results in short-term alterations in peripheral neural responses and in long-term changes in preference behaviors.

Animals↗
PubMed1986

Taste responses from the chorda tympani nerve in young and old Fischer rats.

To determine whether neurophysiological taste responses are different in young and old rats, recordings were made from the whole chorda tympani nerve which innervates taste buds on the anterior tongue. Fischer 344 male and female rats in three age groups were studied: 5 to 7 months, 23 to 25 months, and 29 to 32 months. Chemical stimuli included single concentrations of five salts, two acids, sucrose and quinine hydrochloride, and concentration series of the five salts. Neural response magnitudes were expressed as ratios relative to the NaCl(0.1M) response. Substantial neural responses were obtained to all chemicals at all ages. Response ratios for NH4Cl and sucrose, however, increased significantly with age; ratios for MgCl2 and citric acid decreased. Ratios for HCl decreased when data from either sex were analyzed separately. Shapes of response/concentration functions for NaCl, but not other salts, also differed with age. In general, though, the magnitudes of all age-related differences were small and neural recordings demonstrate that the peripheral taste system functions well in old age.

Acids↗
PubMed1986

Quantitative anatomical study of taste buds in fungiform papillae of young and old Fischer rats.

To determine if differences in neural taste responses relate to taste bud loss in old age, taste buds were counted in fungiform papillae of Fischer 344 rats aged 4 to 6 months, 20 to 24 months, and 30 to 37 months. Papillae anterior to the intermolar eminence on one half of the tongue were examined in serial sections. Presence or absence of a taste bud was noted and taste bud diameter was measured. Average percentages of papillae that contained a taste bud in the three groups were 99.6, 99.3, and 94.7%. This is a significant age-related difference but actual number of taste buds lost in the oldest rats was small. Taste bud diameter did not differ with age and general anatomical characteristics of buds were similar in all groups. Thus, anatomical observations on taste bud maintenance in rats over a wide age range, coupled with neurophysiological data, demonstrate that the integrity of the peripheral gustatory system is not altered greatly in old age.

Aging↗
PubMed1985

Transganglionic transport of HRP from the circumvallate papilla of the rat.

To learn whether horseradish peroxidase (HRP) injections in gustatory papillae on the tongue can be used to study central topographical projections of taste buds and papillae, injections were made into the circumvallate papilla in rats. Labeled central projections after papilla injections were compared to projections after applying HRP to the cut glossopharyngeal nerve. Papilla injections result in HRP transport by afferent and efferent fibers of the glossopharyngeal nerve, and the pattern of central projections is similar to that after labeling the cut nerve. Projections include a separation in the brainstem of afferent, dorsally located fibers and efferent, ventrally located fibers. Afferent fibers project to the solitary nucleus and the trigeminal system. Efferent projections label muscle motorneurons in the nucleus ambiguus and the cells of origin of parasympathetic preganglionic fibers, which from the inferior salivatory nucleus. The parasympathetic neurons labeled after papilla projections are preganglionic fibers to Remak's ganglia in the tongue; post-ganglionic fibers of these ganglia are the secretomotor supply to the von Ebner's glands. In summary, injections of HRP into gustatory papillae reliably label central projections of the papilla and can be used for studies to discern topography in central projections of the taste system. Injections into the circumvallate papilla also have demonstrated that the parasympathetic neurons innervating von Ebner's glands are located in the inferior salivatory nucleus.

Animals↗
PubMed1985

Age does not affect numbers of taste buds and papillae in adult rhesus monkeys.

Taste buds and papillae in tongues of rhesus monkeys were examined and counted to determine if there are age-related differences in general morphology or numbers of receptor organs. Tongues from 15 monkeys in five groups aged 4-31 years were studied with light microscopy. Fungiform, circumvallate, and foliate papillae were examined and taste buds in each papilla type were counted. Numbers of papillae did not differ with age through 31 years; however, at 24 years and older, fungiform papillae were reduced in number in some animals that had lost tongue tips due to trauma. There were no age-related differences in numbers of taste buds in any of the three gustatory papilla types, nor did taste bud diameter alter with age. From data on each papilla type, estimates were made of total numbers of lingual taste buds. Totals ranged from about 8,000 to 10,000 and there were no age-related differences. These results support other recent reports that taste buds are not decreased in number in old rats or humans. Since taste bud numbers and general morphology are maintained even in old age, any age-related differences in taste behavior cannot be attributed to gross degenerative changes in lingual taste buds.

Aging↗
PubMed1979

Age-related differences in salt taste acuity.

Salt taste detection thresholds were measured in 76 adults aged 23 to 92 years using a forced-choice staircase procedure, with distilled water rinses between all stimuli. Although an age-related decrease in salt taste acuity was observed, the decrement was smaller than previously reported in other studies. Past reports have probably exaggerated taste deficits in the elderly, because adequate rinse procedures and controls for subject response biases have not been incorporated in threshold measures.

Adult↗
PubMed1978

Taste responses in sheep medulla: changes during development.

Response characteristics of taste neurons in the sheep solitary tract and nuclei alter during development. Solitary tract cells in younger fetuses respond to stimulation of the tongue with fewer salts and acids than do cells in older fetuses, lambs, and adults. Further, responses to specific salts and acids develop in a particular sequence, not randomly. These changes may relate to maturation of taste receptor sites.

Age Factors↗
PubMed1973

Swallowing in fetal sheep.

Swallowing was measured in fetal sheep by using electromagnetic flowmeter heads chronically implanted in the fetal esophagus. The fetus swallows 20 to 200 milliliters of amniotic fluid in two to seven discrete episodes per day. The episodes are 1 to 9 minutes in duration and occur at seemingly random intervals. Swallowing is influenced by the condition of the fetus and may be the first manifestation of eating and drinking behavior.

Amniotic Fluid↗
PubMed1973

The gustatory sense in foetal sheep during the last third of gestation.

1. Histological studies revealed that presumptive taste buds are present in the foetal sheep tongue at 50 days. By 100 days the taste buds appear morphologically mature.2. To determine if foetal taste buds are functional, electrophysiological recordings were made of activity in the chorda tympani nerve of sheep foetuses. Single and multi-fibre preparations were studied in foetuses aged 100 days to term.3. Responses were recorded to lingual stimulation with salts, acids, glycerol, glycine, sodium saccharin, quinine HCl and amniotic fluid. Responses of the foetal chorda tympani to lingual stimulation with a series of monochloride salts and with increasing concentrations of one salt were similar to responses recorded in lambs and adults.4. The peripheral gustatory system of the foetal sheep is functional for at least the last third of gestation. Foetal taste experiences may influence the formation of adult taste preferences or may aid the foetus in monitoring its environment.

Acetates↗