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T R Scott

Publications and source records attributed to T R Scott.

At least 127 records · Page 7Linked to original sources
PubMed1982

Amino acids as taste stimuli. I. Neural and behavioral attributes.

The physiological importance of L-amino acids implies that the gustatory system should be sensitive to their presence in the environment. This notion is reinforced by research showing that rats are able to self-regulate their dietary consumption of amino acids and other important nutrients. This paper describes two studies which begin a systematic evaluation of the neural and behavioral effects of L-amino acids on gustation in the rat. The first experiment defined the neural thresholds, intensity-response functions and time courses of whole chorda tympani nerve responses to 12 stimuli. Thresholds varied from 10(-4) M (arginine) to 8 X 10(-2) M (proline), with pH-related amino acids being low and those reported by humans to be sweet being high. Maximum neural effectiveness, relative to the resting level of neural activity, ranged from 108% (2.0 M lysine-hydrochloride) to 8% (0.1 M leucine), with pH-related stimuli evoking the greatest activity. Neural time courses were varied, and often did not include well-defined phasic and tonic components. The second experiment measured the rat's preferences in 24-h two-bottle tests. Preference thresholds were typically lower than neural thresholds, presumably due to extra-chorda tympani input involved in the perception of flavor. They ranged from 2 X 10(-6) M (methionine) to 6 X 10(-2) m (leucine) and were in good agreement with psychophysically defined humar thresholds. Seven stimuli were preferred at low concentrations, but only two (alanine, leucine) continued to be appetitive as intensity increased. Preferences were predictable for 10 of the 12 stimuli from psychophysical reports. Rats also rejected amino acids in direct proportion to their toxicity, demonstrating the protective function of the taste-hedonic system.

Amino Acids↗
PubMed1982

Amino acids as taste stimuli. II. Quality coding.

Two experiments were performed in rats to evaluate the relative taste qualities of 12 L-amino acids, each at a concentration which evoked half the maximum response for that chemical. The first study involved recording the activity of 40 individual chorda tympani fibers to the stimulus series. Only 34% of the evoked responses resembled the short latency phasic-tonic activity which characterizes gustatory responses to inorganic salts and acids. 32% had latencies exceeding 1 s; another 27% consisted of only a phasic burst lasting less than 1 s. The remaining 7% were inhibitory. Both long latency and purely phasic activity were stimulus selective: 61% of the former were in response to Gly or Pro while 69% of the latter were evoked by Cys-HCl, Lys-HCl or His. Response inhibition was not associated with either specific fibers or stimuli. Thus amino acids, which to humans represent a class of perceptually complex stimuli, show a corresponding complexity of evoked neural properties in the rat. The second study employed a conditioned taste aversion paradigm to assess the qualitative similarity of each amino acid to the others and to the 4 prototypical taste stimuli; NaCl, HCl, quinine-HCl and sucrose. Some amino acids showed strong generalization to a single gustatory prototype (Pro and Gly to sucrose; Cys-HCl to HCl); others generalized well to multiple prototypes (e.g. Arg to sucrose and NaCl). Several showed poor generalization to all 4 prototypical tastes, calling into question the assumption that these 4 totally encompass the gustatory domain.

Animals↗
PubMed1982

Effects of blood sampling by cardiac puncture on subsequent body weights of broilers.

The effects of blood sampling via cardiac puncture in broiler chicks 2 to 4 weeks of age on subsequent body weights were examined in three experiments. No differences were found in chicks bled or stabbed with 18, 22, or 25-gauge needles when compared to chicks not blood sampled. However, male chicks bled at both 2 and 3 weeks of age with a 25-gauge needle demonstrated elevated body weights at 8 weeks of age when compared to chicks not blood sampled.

Animals↗
PubMed1981

Circulating levels of corticosterone in the serum of developing chick embryos and newly hatched chicks.

Circulating levels of corticosterone were determined in chick embryos from 10 to 21 days of incubation using eggs from a Leghorn breeder flock. In Experiment 1, eggs were incubated from 10 to 20 days for daily embryonic blood collection. To verify stage of development with day of incubation, embryo right middle toe lengths were measured concurrent with blood sampling. Serum from three embryos was pooled into one sample and the corticosterone content of 10 samples per day of incubation was determined using a radioimmunoassay procedure. The levels of corticosterone from day 10 to 14 fluctuated slightly and then increased rapidly until 16 days of incubation. At this time serum corticosterone remained relatively constant through day 18 with an apparent increasing trend up to day 20. The use of toe lengths to assure no day-to-day overlap in embryonic development proved effective. In Experiment 2, newly hatched (day 21) chicks were sorted into four 3-hr periods ranging from early to late hatching. Blood samples were collected from five individual chicks during four 15-min sampling periods for each of the four hatch times. Serum corticosterone levels were not affected by sampling periods or hatch times.

Animals↗
PubMed1976

Gustatory neural coding in the pons.

Third-order neurons from the pontine taste area (PTA) were analyzed in accordance with the across-fiber pattern theory of gustatory neural coding. Single neuron responses, evoked by chemical stimulation of the tongue, were recorded from the PTA of acute Nembutalized rats. They reveal that PTA neurons are broadly sensitive to stimuli representing the 4 putative basic taste qualities. Of 35 neurons, 33 responded to at least 3 of the 4 quality classes. Time course analyses indicate that stimuli which are shown to be alike in behavioral studies exhibit similar temporal response sequences. Correlations between all possible pairs of response patterns indicate that like-tasting chemicals elicit similar profiles of activity across the neural population. A multidimensional analysis indicates that three underlying physico-chemical dimensions (as yet undefined) bear upon the neural responses. In certain of their response properties, PTA neurons are like those of the (second-order) solitary nucleus; in other respects they auger the characteristics seen in the (fourth-order) thalamic neurons. It is concluded that the PTA is functionally as well as anatomically intermediate between the solitary nucleus and thalamus in the taste processing chain.

Animals↗