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T R Scott

Publications and source records attributed to T R Scott.

At least 91 records · Page 5Linked to original sources
PubMed1990

Complex attributes of lateral hypothalamic neurons in the regulation of feeding of alert rhesus monkeys.

To elucidate the roles of glucose-sensitive (GS) and glucose-insensitive (GIS) cells of the lateral hypothalamic area (LHA), single neuron activity was recorded during 1) microelectrophoretic administration of chemicals, 2) a conditioned bar press feeding task, 3) gustatory, 4) olfactory, and 5) electrical brain stimulation. GS and GIS neurons showed different firing rate changes during phases of the task, and the responses were highly influenced by the palatability of the food and the motivational (hunger or satiety) state of the animal. The two groups of cells also differed in their responsiveness to gustatory and olfactory stimuli: GS neurons were more likely to respond to tastes and odors than GIS cells. Taste- and odor-responsive GS neurons were primarily suppressed by electrophoretically applied noradrenaline and were localized ventromedially within the LHA. The chemosensitive GIS cells, being organized along a dorsolateral axis, were especially excited by dopamine. The two sets of neurons had distinct connections with associative (orbitofrontal, prefrontal) cortical areas. GS and GIS cells, thus, appear to have differential and complex attributes in the control of feeding.

Animals↗
PubMed1990

Effect of cholecystokinin on taste responsiveness in rats.

Alterations in taste responsiveness have been suggested to mediate the suppression of feeding that accompanies exogenous administration of cholecystokinin (CCK). We tested this possibility in electrophysiological and behavioral experiments. First we monitored taste-evoked activity in the nucleus tractus solitarii of anesthetized rats during intravenous injection of 2 or 6 micrograms/kg of CCK or vehicle. We found no significant effects on taste activity during the 30-min period after CCK administration. Then we employed a conditioned taste-aversion paradigm to measure the rat's perceived intensity of a series of glucose concentrations under the same three experimental conditions. At 2 micrograms/kg, CCK had no effect; at 6 micrograms/kg there was a significant increase in the perceived intensity of 2 of the 15 test solutions, which we attribute to elevated vagal tone. The potential contribution of gastric distension was eliminated in the electrophysiological study and was minimized by brief exposures to stimuli in the behavioral experiment. Thus CCK administration, in the absence of significant gastric distension, does not appear to alter taste responsiveness.

Animals↗
PubMed1990

Immunity to Pasteurella multocida in protein-deficient chickens.

Studies were conducted to determine the effects of dietary protein restriction on the humoral immunity (HI) and cell-mediated immunity (CMI) of chickens. New Hampshire chickens were separated into two dietary treatment groups: basal, containing 3,200 kcal/kg and 21% protein; or protein restricted (PR), containing 3,200 kcal/kg and 7% protein. In studies involving HI, half of the birds in each dietary treatment were vaccinated against fowl cholera at 4 and 8 wk of age. Blood samples were collected weekly beginning at 4 wk of age. Overall, unvaccinated birds had lower titers than vaccinated birds and PR groups generally showed lower titers than basal groups. All birds were challenged by palatine cleft inoculation of live, virulent Strain X-73 of Pasteurella multocida. The vaccinated PR group survived live challenge as well as the vaccinated basal group, but all unvaccinated birds died as a result of the challenge, regardless of antibody titer. In studies involving CMI, half of the birds in each dietary treatment were vaccinated at 5 wk of age. At 2 to 3 wk postvaccination, representative birds from each treatment were bled for total and differential blood counts. Also, birds were sacrificed and spleen cells collected. Cells were cultured in Roswell Park Memorial Institute (RPMI) medium with phytohemagglutinin-M (PHA-M), sonicated P. multocida (X-73), or RPMI only.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Interference with the humoral immune response in diverse genetic lines of chickens. II. The effect of colloidal carbon.

Two experiments were conducted to study the difference in humoral immune responses between lines of chickens selected for high (H) or low (L) antibody production to sheep red blood cells (SRBC). Prior to i.v. immunization with SRBC or Brucella abortus (BA), chicks of both lines were injected with either 2, 3 or 4 ml carbon suspension (59 mg carbon/ml) per kg body weight; controls were not injected. In both the H and L line, a higher dose of carbon showed a more progressive depression of the total antibody titer to SRBC during the initial stage of the primary response. The 2ME-resistant antibody titers to SRBC showed the same tendency during the latter phase of the primary response. However, chicks treated with 3 ml carbon had lower 2ME-resistant antibody titers than any other group. Following i.m. reimmunization with SRBC, the previous treatment with carbon doses enhanced total antibody titers throughout the secondary response, when compared to the controls. The 3 ml carbon-treated chicks had the highest total anti-SRBC titers in the secondary response. The secondary 2ME-resistant anti-SRBC titers were not affected by the carbon doses. Carbon treatment did not affect the antibody titers to BA. No differences between the H and L line were found in the effects of carbon on the humoral immune responses to SRBC or BA.

Animals↗
PubMed1989

In vitro thymidine uptake and incorporation into thymic and bursal lymphocytes from young hypothyroidic chickens.

Experiments were conducted to evaluate the ability of thymic and bursal lymphocytes from hypothyroidic chicks to take up 3H-thymidine. To produce hypothyroidism, chicks were fed a diet containing thiouracil (0.1%) from day of hatch to 3 weeks of age. At 1, 2 and 3 weeks of age, body weights were significantly lower for hypothyroid chicks, and at 2 and 3 weeks of age, the relative weights of the thymus and bursa were significantly less than those of controls. Furthermore, chicks treated with thiouracil had significantly lower serum concentrations of 3,5,3'-triiodothyronine (T3) and thyroxine (T4). Thymic cells from hypothyroid chicks incorporated less 3H-thymidine at 1 and 3 weeks of age as assessed by liquid scintillation counting and autoradiography. Liquid scintillation counts for labeled bursal cells from hypothyroid chicks were not lower at 1 week of age, but the counts were lower at 3 weeks of age. Autoradiographic studies with bursal cells revealed that 3H-thymidine incorporation was less, but not significantly less, in medium-size lymphocytes from thiouracil-treated chicks at both 1 and 3 weeks of age. Thymidine incorporation into large bursal cells was affected more by thiouracil treatment at 1 than 3 weeks of age.

Animals↗
PubMed1988

Taste responses in the nucleus tractus solitarius of the chronic decerebrate rat.

The ingestive behavior of decerebrate rats has been studied for some time, yet little is known of its neural substrates. While taste fibers in rats proceed from hindbrain to thalamus and ventral forebrain, these regions return centrifugal fibers to the hindbrain by which lower-order taste activity may be influenced. We examined the functional characteristics of taste neurons in the nucleus tractus solitarii (NTS) of chronic decerebrate rats in which this reciprocal communication was disrupted and compared them with those of intact controls. Nine Wistar rats were decerebrated at the supracollicular level. After a minimum of one week recovery, they were immobilized with Flaxedil, anesthetized locally and prepared for recording. The responses of 50 taste cells were isolated bilaterally from the NTS of these animals, while the activity of 50 additional neurons was recorded from 12 intact rats under the same conditions. Taste stimuli included 7 Na-Li salts, 3 sugars, HCl and citric acids, quinine HCl and NaSaccharin. Mean spontaneous activity in decerebrates was 6.5 spikes/s, 36.0% lower than the level in intact animals. Mean evoked activity was reduced by 32.6%. Analyses of the effects of stimulus quality, intensity and time course of the responses all indicated that the decrease in activity was attributable to the inability of taste cells in decerebrate rats to respond to demands for high discharge rates. This deficit could be responsible for the failure of these animals to develop conditioned taste aversions. Neurons from decerebrate preparations did, however, retain the broad sensitivity across stimuli that characterized taste cells in intact preparations. It was also typical that most neuron response profiles from decerebrates could be grouped into 3 loose clusters with peak sensitivities to acid-salt, salt or sugar. An analysis of similarities among stimulus activity profiles indicated that Na-Li salts, sugars and an acid-quinine complex represented 3 groups of stimulus quality; in intact animals, the primary distinction was between sweet and non-sweet stimuli. Moreover, the response to sodium saccharin lost its bitter component in decerebrates. These findings were in general agreement with those derived from acute decerebrate rats.

Animals↗
PubMed1988

Interference with the humoral immune response in diverse genetic lines of chickens. I. The effect of carrageenan.

Two experiments were conducted in which the effect of carrageenan (CGN) on humoral immune response of chicks selected on either high (H) or low (L) antibody production to sheep red blood cells (SRBC) was determined. H and L line chicks were injected i.p. with different doses of CGN prior to immunization with SRBC or Brucella abortus (BA). Four weeks later chicks were reimmunized with the same antigens. In general, control H and L chicks had significantly higher total anti-SRBC titers than CGN-treated chicks in primary response. Also, total anti-BA titers were significantly higher in control chicks than CGN-treated chicks on days 3 and 5 following primary immunization and on days 0 and 7 of the secondary response. Overall, the 2-mercaptoethanol (2ME)-resistant anti-SRBC titers did not differ significantly among the CGN-treated groups. However, control chicks tended to have higher anti-BA 2ME-resistant titers from day 14 p.i. of primary response on. Regardless of antigen or CGN treatment, the H line chicks had significantly higher titers than L line chicks. However, the CGN treatments did not affect the antibody response to BA nor to SRBC differently between L and H line chicks. It would appear that since CGN is cytotoxic for macrophages, selection for antibody production did not result in different abilities of the macrophages of these chicken lines to respond to an antigenic challenge.

Animals↗
PubMed1988

Methods of single unit recording from medullary neural substrates in awake, behaving guinea pigs.

An electrophysiological procedure that permits extracellular single neuronal recording in the medulla of unanesthetized, freely behaving animals is described. System components consist of 1) a flexible, single-strand microwire as recording electrode; 2) a miniature, skull-mounted miniature microdrive used for isolation of single unit activity; and 3) a head-mounted voltage follower that conditions and stabilizes the neuronal signals prior to amplification and transmission for further processing. A unique advantage of this procedure is the latitude and provision for microwire replacement in the event that multiple penetrations are desired or the tip of the microwire recording electrode is insulated as a result of gliomatosis. With minor modification, this technique can be used for single unit recording virtually anywhere along the supra-segmental neuraxis. Technical aspects of this procedure, together with details of design and fabrication of implantable devices, chronic instrumentation procedure, and potentials for other chronic applications, are discussed.

Action Potentials↗
PubMed1988

The responsiveness of neurones in the frontal opercular gustatory cortex of the macaque monkey is independent of hunger.

1. In order to determine whether the responsiveness of neurones in the primary gustatory cortex is influenced by hunger, the activity of neurones in the gustatory cortex in the frontal operculum was recorded while macaque monkeys (Macaca fascicularis) were fed to satiety. The responses of single neurones in the gustatory cortex to the prototypical taste stimuli glucose, NaCl, HCl and quinine hydrochloride, and to fruit juice, were measured before, while, and after the monkey was fed to satiety with glucose or fruit juice. 2. While behaviour turned from avid acceptance to active rejection upon repletion, the responsiveness of the neurones to the stimulus array, including the satiating solution, was unmodified. 3. It is concluded that in the gustatory cortex in the frontal operculum, neuronal responses to gustatory stimuli are not influenced by the normal transition from hunger to satiety. This is in contrast to the responses of a population of neurones recorded in the hypothalamus, which only occur to the taste of food when the monkey is hungry. Thus the neurones in the primary gustatory cortex are involved in a motivation-independent analysis of gustatory stimuli, whereas the hypothalamic neurones may be more closely related to the influence of motivational state on behavioural responsiveness to gustatory stimuli.

Action Potentials↗
PubMed1988

Taste responses in the nucleus tractus solitarius of sodium-deprived rats.

1. Maintenance of sodium balance is crucial to mammals and is expressed in the innate salt appetite. With depletion, sodium preference is exaggerated, hypertonic solutions accepted and salt balance restored. This compensatory behaviour is thought to result from a centrally induced change in taste responsiveness. This proposal was tested by recording taste activity from ninety-four single neurones in the nucleus tractus solitarius of sodium-replete (N = 44) and of deprived (N = 50) rats. Twelve Wistar rats were given a nominally sodium-free diet for 10-13 days, and the resulting sodium depletion confirmed by flame photometry of their urine. Nine rats provided control data. Taste stimuli included five concentrations of NaCl (0.003-0.3 M) plus eight other salts, acids, sugars and alkaloids. 2. Taste responsiveness was generally reduced in sodium-depleted rats. Spontaneous activity was 33% lower while responses to sodium salts lagged by a mean of 30%, to acids by 25% and to bitter salts and quinine by 17%. Mean activity to sugars was 60% higher in the deprived group. 3. Activity in sugar- and salt-profile neurones was most affected. In deprived animals responses to sodium salts were lower by 80% among salt-profile cells while among sugar-profile neurones activity to these stimuli was nearly 10 times greater than in controls. These changes in activity resulted in a dramatic shift in the participation of sodium- and sugar-profile cells in the afferent signal for NaCl. In replete animals 60% of sodium-induced activity was transmitted through salt-profile cells while only 1% occurred in sugar-profile neurones. In deprived subjects this situation was nearly reversed as 7% of the total NaCl response was conveyed through salt-profile cells while the contribution of neurones with sugar-profiles rose to 46%. 4. Multidimensional stimulus spaces based on average activity in each of four identifiable neurone subgroups demonstrated a shift in the affiliation of sodium salts away from bitter and acid stimuli and towards sugars. 5. These results confirm earlier findings from the chorda tympani that sodium deprivation suppresses activity evoked by sodium salts. However the application of more recent analytical procedures permits quite a different interpretation of this finding. The overall decrease is merely the net effect of a shift in the major responsibility for encoding sodium from salt-profile neurones to those whose primary sensitivity is to sugars.(ABSTRACT TRUNCATED AT 400 WORDS)

Acids↗
PubMed1988

Erythrocyte alloantigen diversity and some immunological effects of the B system in related New Hampshire strains.

Chickens from the Lester J. Dreesen strain of New Hampshires and a small (SBL) and a large (LBL) bursa line derived from it were tested with previously prepared reagents for 10 erythrocyte alloantigen systems. Eight systems were shown to be segregating in one or more of the three related lines. Immunogenetic analysis of the hemagglutination reactions resulted in genotype assignments for seven of the systems. The number of alleles segregating at the respective alloantigen loci were three A, five B, three C, two D, two I, two L, and two P. All seven segregating systems displayed considerable divergence in gene frequencies among two or more of the lines. The B1B1 chicks produced significantly higher peak titers against sheep red blood cells than B6B6 chicks; in adults the order of response of genotypes was B1B1, B6B6, B5B5. Peripheral blood leukocytes from groups of adults and 5-wk old chickens responded consistently to phytohemagglutinin-M according to their B genotypes, in the order B1B1, B5B5, B6B6. Serum immunoglobulin G (IgG) concentrations determined at various ages were higher in the LBL than the SBL strain, even after bursectomy. Genes influencing serum IgG levels may be closely linked to one or more of the blood group systems.

Animals↗
PubMed1988

Genetic variation of plasma growth hormone and its genetic association with growth traits in young chickens.

A pedigreed, randomly mated population of 25 sire families was assessed for genetic variation in body weight, gain, and plasma growth hormone (GH) under conditions of reduced temperature brooding (26.7 C) from day of hatch to 7 days of age. Heritability estimates (h2) for 7-day body weight and gain were moderate to high. The calculated h2 for GH was moderate. Plasma levels of GH were not phenotypically or genotypically correlated with body weight or gain.

Animals↗
PubMed1988

Inhibition of rat liver glutathione S-transferase isoenzymes by acrolein.

The in vitro effect of the toxin and teratogen, acrolein, on the fetal rat liver glutathione S-transferase isoenzyme, YcYfetus, was investigated and compared with acrolein's effect on some of the adult rat liver glutathione S-transferase isoenzymes. Acrolein was found to inhibit all the isoenzymes investigated and double-reciprocal plots suggest that inhibition is either noncompetitive or mixed-type noncompetitive. It is therefore attractive to suggest that should a similar situation arise in vivo, it may provide one mechanism for the teratogenicity of acrolein.

Acrolein↗
PubMed1987

The isolation of a fetal rat liver glutathione S-transferase isoenzyme with high glutathione peroxidase activity.

A previously uncharacterized glutathione S-transferase isoenzyme which is absent from normal adult rat livers has been isolated from fetal rat livers. The enzyme was purified using a combination of affinity chromatography, CM-cellulose column chromatography and chromatofocusing. It is composed of two non-identical subunits, namely, subunit Yc (Mr 28,000) and a subunit (Mr 25,500) recently reported by us to be uniquely present in fetal rat livers and which we now refer to as subunit 'Yfetus'. The enzyme which we term glutathione S-transferase YcYfetus has an isoelectric point of approx. 8.65 and has glutathione S-transferase activity towards a number of substrates. The most significant property of the fetal isozyme is its high glutathione peroxidase activity towards the model substrate cumene hydroperoxide. We suggest that this isozyme serves a specific function in protecting fetuses against the possible teratogenic effects of organic peroxides.

Amino Acids↗
PubMed1987

The taste system encodes stimulus toxicity.

Attempts to define the organization of the taste system in terms of the physical characteristics of stimuli have been largely unsuccessful. We recorded taste-evoked neural activity in the rat's hindbrain and determined that stimuli could be effectively organized along a physiological dimension which corresponds to stimulus toxicity. Taste is a visceral sense that mediates between the external and internal chemical environments. Its responsiveness to a wide range of chemicals and its organization along a dimension which promotes the organism's physiological welfare ideally suit it to that purpose.

Action Potentials↗
PubMed1987

Blood glucose level affects perceived sweetness intensity in rats.

Electrophysiological data indicate that hyperglycemia is associated with decreased neural taste responsiveness to 1.0 M glucose, but not to 0.01 M quinine HCl, in the rat's hindbrain. The present behavioral experiment was conducted to determine whether this suppression of neural activity is manifested in a reduced intensity perception to glucose, but not quinine. Each rat learned to avoid 1.0 M glucose through development of a conditioned taste aversion. Perceived intensity was then measured in control and in hyperglycemic rats by the extent to which they generalized to each test concentration of glucose. Experimental subjects treated moderate glucose concentrations (0.6-2.0 M) as if their intensity perceptions were reduced by 47%. This is consistent with the mean reduction of 43% in taste-evoked neural activity associated with hyperglycemia. A corresponding experiment gave no indication of a change in intensity perception to quinine as a function of hyperglycemia, again in accord with earlier electrophysiological results. We conclude that nutritional state may selectively affect gustatory sensitivity in the rat.

Animals↗