Neural mechanisms to incorporate visual counterevidence in self-movement estimation

In selecting appropriate behaviors, animals should weigh sensory evidence both for and against specific beliefs about the world. For instance, animals measure optic flow to estimate and control their own rotation. However, existing models of flow detection can be spuriously triggered by visual motion created by objects moving in the world. Here, we show that stationary patterns on the retina, which constitute evidence against observer rotation, suppress inappropriate stabilizing rotational behavior in the fruit fly Drosophila. In silico experiments show that artificial neural networks (ANNs) that are optimized to distinguish observer movement from external object motion similarly detect stationarity and incorporate negative evidence. Employing neural measurements and genetic manipulations, we identified components of the circuitry for stationary pattern detection, which runs parallel to the fly's local motion and optic-flow detectors. Our results show how the fly brain incorporates negative evidence to improve heading stability, exemplifying how a compact brain exploits geometrical constraints of the visual world.

Neural mechanisms to incorporate visual counterevidence in self motion estimation

In selecting appropriate behaviors, animals should weigh sensory evidence both for and against specific beliefs about the world. For instance, animals measure optic flow to estimate and control their own rotation. However, existing models of flow detection can confuse the movement of external objects with genuine self motion. Here, we show that stationary patterns on the retina, which constitute negative evidence against self rotation, are used by the fruit fly Drosophila to suppress inappropriate stabilizing rotational behavior. In silico experiments show that artificial neural networks optimized to distinguish self and world motion similarly detect stationarity and incorporate negative evidence. Employing neural measurements and genetic manipulations, we identified components of the circuitry for stationary pattern detection, which runs parallel to the fly's motion- and optic flow-detectors. Our results exemplify how the compact brain of the fly incorporates negative evidence to improve heading stability, exploiting geometrical constraints of the visual world.

Bone mineral density reference norms for Hong Kong Chinese

The aim of this study was to establish bone mineral density (BMD) reference norms for Hong Kong Chinese using Hologic QDR 2000 and 4500 densitometers, and to estimate the prevalence of osteoporosis in the population. Altogether, 4,274 subjects (2,415 females and 1,859 males), aged 9-94 years old, were recruited using a combination of private solicitation and public advertising from schools, community centers, nursing homes, housing estates, and the general community in Hong Kong. Among females, BMD increased by 20% at the total hip and 48% at the lumbar spine between ages 10 and 20 but remained essentially constant between ages 20 and 40. Between ages 40 and 70, BMD declined by 17% at the total hip and 23% at the spine. Total hip BMD continued to drop after age 70 but little change in spine BMD was observed. Among males, BMD increased by 45% at the total hip and 77% at the spine between age 10 and 30. Between ages 30 and 80, total hip BMD decreased by 20%. Lumbar spine BMD decrease was milder, showing a loss of 4% between ages 30 to 50 and remaining relatively constant afterwards. The prevalence of osteoporosis was consistently overestimated when using Hologic-supplied Caucasian cutoffs as compared with local Chinese cutoffs. The prevalence of osteoporosis among Chinese women 50 years or older was 37% and 16% at the spine and total hip, respectively, while that among Chinese men 50 years or older was 7% and 6% at the spine and total hip, respectively. Prior studies have been limited by size or restricted to women. This study represents the largest sample of Hong Kong Chinese amassed to date, provides continuous BMD reference values from ages 10 to 85 for both women and men, and yields more reliable estimates of the prevalence of osteoporosis for the population.

Tissue specificity of lymphocyte migration into sheep gingival tissue

T cells show a bias in their migration pathways: some migrate preferentially to peripheral lymph nodes, some to mucosal tissues and some to peripheral tissues such as skin. The aim here was to determine the types of T cells that migrate preferentially into inflamed gingival tissue and compare this migration to that found in inflamed subcutaneous and mucosal tissues. The experiments were designed so that the simultaneous 3 h localization of two, differentially radiolabelled, lymphocyte populations (subcutaneously and mucosally derived) into sites of purified protein derivative/bacillus Calmette-Guerin-induced, delayed-type hypersensitivity, inflammatory lesions in skin, bowel and gingiva in the sheep model could be compared. The relative migration of two populations in each of the tissues was expressed as a ratio of the radioactivity of intestinal/subcutaneous lymphocytes recovered from that tissue. From nine experiments, the ratios [mean+/-S.E.M. (n)] for skin, bowel and gingiva were 0.53+/-0.02 (84), 1.98+/-0.11 (85), and 0.73+/-0.05 (29), respectively. These findings suggest that inflammation in skin and gingiva favoured the localization of subcutaneously derived lymphocytes (ratio significantly <1, P<0.025), while in bowel, the localization of intestinally derived lymphocytes was favoured (ratio significantly >1, P<0.025). Statistical analysis demonstrated that the relative localization of the two lymphocyte populations to the gingival lesions differed significantly from that for inflamed skin and bowel lesions (P<0.05). When tumour necrosis factor-alpha was used as a non-antigenic inflammatory agent to induce lymphocyte migration into skin and gingiva, a similarly greater increase in the localization of subcutaneously derived lymphocytes was detected, but the relative localization of lymphocytes was not significantly different between the two tissues. Therefore, it appears that there is tissue specificity in the migration of lymphocytes into the inflamed gingival tissues and that antigen is required for distinct tissue-specific lymphocyte traffic to occur.

Cyclosporine A inhibits lymphocyte migration into ovine peripheral nerve allografts

Lymphocyte migration into nerve allografts was measured to estimate the cyclosporine A (CsA) dose required to suppress rejection. Twelve outbred sheep received daily subcutaneous CsA at 0, 5, 10, or 15 mg/kg/day for 2 weeks prior to implantation of multiple heterotopic subcutaneous nerve grafts. Lymphocyte migration was determined after 7 days by an intravenous pulse of autologous 111indium-labeled lymphocytes and subsequent quantitation of gamma radioactivity in nerve tissue (CPM/g, mean +/- SEM). Measurement by radioimmunoassay revealed a dose-dependent increase in blood cyclosporine levels. Lymphocyte migration into autografts (404+/-44) was significantly less than migration into allografts (16,554+/-2,049), in control animals (P < 0.01). A dose-dependent inhibition of lymphocyte migration into nerve allografts was observed with counts of 7,662+/-1,692, 4,083+/-1,112, and 1,561+/-232 in sheep receiving 5, 10, or 15 mg/kg/day of CsA, respectively. Daily CsA administration produced effective blood levels and immunosuppression sufficient to inhibit lymphocyte migration into nerve allografts.

The traffic of resting lymphocytes through delayed hypersensitivity and chronic inflammatory lesions: a dynamic equilibrium

This essay is designed as a partial summary of the work of several students and colleagues from our laboratory. For the most part the experimental data have been published and this seminar represents an attempt to summarize, integrate and speculate on this work. In some situations the speculation is rather unrestrained and it is hoped that it will provoke discussion, controversy and better future experiments. Reference is made to the original articles and to recent reviews. In addition, since we have had the advantage of reading the other contributions to this volume, there is considerable reference to other chapters. We and others have argued in other publications that it is imperative to understand the normal physiological traffic of lymphocytes before one can adequately interpret data describing lymphocyte migration through pathological tissues. It has been useful to compare data derived from traffic through lymph nodes because there is considerable information on the individual lymph node with respect to blood-lymphocyte delivery and blood flow, prenodal input via peripheral lymphatics and, particularly in sheep, in the numbers and phenotypic analysis of the lymphocytes exiting lymph nodes in postnodal or efferent lymph (see Young, this volume). We consider the terms prenodal for afferent and post-nodal for efferent to be synonomous. In this volume, a significant contribution has been made by Cahill et al which describes the astonishing degree of lymphocyte traffic which occurs in fetal life prior to antigenic challenge. At the other extreme, in disease states, there is often profound activation of lymphocytes. This is most apparent in viral infections like HIV and SIV (Rosenberg et al, this volume) and also in the various models of diseases such as EAE (Hickey and Kulidjian et al, this volume). It is a central tenet of our paper that resting and activated lymphocyte migration need to be considered separately and that they are very different.

Lymph and interstitial fluid dynamics in labial gingival tissues of sheep

Lymphatic drainage and circulation in periodontal tissues have been cited as important components of host defence and pathogenic mechanisms, but quantitative data are sparse because of the technical difficulties associated with small animal lymphatic studies. However, the lymphatic vessels draining the periodontal tissues and surrounding region are sufficiently large in sheep to permit surgical placement of lymphatic catheters. Consequently, lymph and recirculating lymphocytes can be continuously collected and this permits the quantitative assessment of local immune responses in these tissues. We have studied the lymphatic drainage pathways from the labial gingival tissues in sheep by two methods. First, in a series of anatomical studies (n = 6), a complex of Evan's blue dye and albumin was injected into the labial gingival tissues. One hour after injection the animals were sacrificed and the submandibular and cervical regions were dissected to expose the stained lymphatics. This anatomical study demonstrated 2 major drainage pathways: 1) cervical lymph ducts and; 2) efferent prescapular lymphatics. Secondly, to compare the relative importance of these two drainage pathways, radiolabeled protein (125I-albumin) was injected directly into the gingival tissues and its appearance in the cervical and prescapular lymph was measured (n = 7). Despite the technical difficulties encountered in the experiments, data collected showed that over 7.5 h, 64.7% of the injected protein was recovered in the prescapular and cervical lymph vessels (31.8 +/- 6.5% and 32.9 +/- 8.5%, respectively). In addition, 11.9 +/- 2.1% of the injected protein was transported to the blood by routes not involving the cannulated cervical and prescapular lymph vessels. With most of the remaining radiolabeled protein (17.9 +/- 4.9%) recovered from the injection site, we were able to account for approximately 95% of the injected protein. This study suggests that the lymph drainage from this region in the sheep model could provide one of the best described closed and contained systems and thus, could be a useful system for future continuous monitoring of inflammatory responses during experimental periodontal diseases.

Enriched feeding formula and immune responses and outcome after Listeria monocytogenes challenge in mice

Immunocompromised malnourished patients are at high risk of developing serious opportunistic infection. This study examined the effect of feeding a special nutrient-enriched formula (Immun-Aid) on immune responses and mortality in mice challenged with Listeria monocytogenes. Two protocols were followed. In the first protocol, the animals were challenged with microorganisms when the experimental formula was introduced as the sole source of their nutrition. There was no significant effect on total T-lymphocyte number, but the proportion of helper T cells increased by day 7, resulting in a higher helper/suppressor (H/S) T lymphocyte ratio as well. Response to the mitogen phytohemagglutinin (PHA) was slightly higher on day 3 but came down and was comparable with that of control animals by day 7. Natural killer cell activity was slightly higher on day 7. Other immunologic parameters were unchanged. There was no significant difference in mortality between the two groups. In the second protocol, the animals were fed the experimental diet for 7 days before the infectious challenge. There was a slight increase in the total number of T lymphocytes on day 7. The numbers of helper and suppressor T lymphocytes were unchanged, but H/S was slightly higher on day 3 in the experimental group. Response to PHA was again higher on day 3 but plateaued on day 7. Natural killer cell activity was not altered. Mortality after infectious challenge was slightly but significantly decreased in the group of animals fed the enriched special formula. These results indicate a slight enhancement of selected parameters of immunity in mice fed the specially enriched formula and show that prior feeding with this formula for several days may partly protect against infectious challenge, resulting in reduced mortality.

Effect of two feeding formulas on immune responses and mortality in mice challenged with Listeria monocytogenes

Cell-mediated immunity and natural killer cells play an important role against facultative intracellular organisms. The effect of two commercially available tube feeding formulas used for patients with acute or chronic debilitating and life-threatening illnesses was studied in mice challenged with Listeria monocytogenes. C57BL/6 X DBA/2 F1 hybrid mice were given ad libitum access to one of two formulas or to chow. Sixty mice in each of the feeding groups were challenged with 4.8 X 10(3) organisms intraperitoneally. Mortality was significantly less in animals fed Impact, a formula enriched with arginine, RNA and selected fatty acids. This was associated with reduced number of viable organisms in the spleen on day 7 after challenge. There was no difference in the spleen/body weight index between the different groups. Delayed cutaneous hypersensitivity was slightly higher in the Impact group but this was not statistically significant. Natural killer cell activity was significantly higher in the Impact group compared with the other two feeding regimens. These observations suggest that selective manipulation of the composition of tube feeding formulas may have a significant impact on immune responses and on morbidity and mortality following infectious challenge.

Immunopathology of chronic cadmium administration in mice

Young male mice were given drinking water containing 50 ppm cadmium (Cd) for 3 weeks, and were killed 0, 3 and 6 weeks after the cessation of treatment. At 0 weeks, suppression in the number of splenic plaque-forming cells in response to sheep red blood cell immunization was noted 5 days after antigen injection, but not 7 days after injection. Plasma IgG concentration and thymic factor activity were unaffected at 0 weeks. The number of circulating lymphocytes tended to be less in the Cd-treated mice at all times. Cd treatment had no effect upon liver and kidney weights, and upon the weights and the lymphocyte contents of the thymus and spleen at any of the observation times. Employing immunofluorescence with anti-mouse IgG and C3, no evidence of an autoimmune response was found in the kidney of the treated mice at 0 and 3 weeks. Mitochondrial abnormalities in the renal proximal tubule cells were noted at 0 weeks in the Cd-treated mice. The Cd concentrations of the liver and kidneys remained high at all observation times. The results suggest that a modest dose of Cd produces some depression of the immune system, and the biological half-life of Cd is long.

Serum thymic hormone activity in genetically-obese mice

1. Serum thymic hormone was assayed in genetically-obese (C57B1/6J ob/ob) mice and lean controls (+/+, +/-) of the same strain. 2. The thymic hormone activity was higher in the majority of the obese animals compared with non-obese mice. 3. The number of antibody-forming cells in the spleen expressed as a proportion of the total mononuclear cells was increased in the obese mice. 4. It is suggested that obesity is associated with significant changes in the thymic hormone levels which may alter the relative proportion of lymphocyte subsets and cell-mediated immunity.

Serum thymic factor activity in deficiencies of calories, zinc, vitamin A and pyridoxine

Cell-mediated immunity is invariably impaired in protein-energy malnutrition. The effect of selected nutrient deficiencies on serum thymic factor activity was assessed in deprived rats and pair-fed controls. Deficits of calories, zinc or pyridoxine resulted in significant lowering of serum thymic factor activity whereas vitamin A deficiency did not have any effect. It is suggested that variants nutrients modulate different steps of cell-mediated immunity and that reduced thymic hormone activity may be the underlying mechanism of imparied immunity in some but not all nutritional deficiencies.

Single nutrient deficiency and cell-mediated immune responses. I. Zinc

The thymus of rats provided zinc-deficient diet weighed less than the thymus of animals fed zinc-containing control diet. The antibody-forming cell response in the spleen was reduced. Cytotoxic response of spleen cells of zinc-deficient mice immunized in vivo was decreased whereas after sensitization in vitro the response was comparable to that seen in zinc-replete animals. Natural killer cell activity and antibody-dependent cell-mediated cytotoxicity were increased, particularly the former. These observations suggest that dietary zinc intake is an important factor modulating cell-mediated immune responses.

Spleen hemolytic plaque-forming cell response and generation of cytotoxic cells in genetically obese (C57Bl/6J ob/ob) mice

Cell-mediated immune responses were evaluated in genetically obese (C57Bl/6J ob/ob) mice and lean controls. The thymus and spleen weighed less and contained fewer mononuclear cells in obese animals compared with controls. The total number of direct and indirect plaque-forming cells in the spleen of obese mice immunized intraperitoneally with sheep red blood cells was reduced, however, when the results were expressed as plaques/10(6) mononuclear cells, the proportion of antibody-producing cells was higher in the obese. Ob/ob mice immunized in vivo with allogeneic EL-4 lymphoma cells showed markedly diminished capacity to generate cytotoxic cells, whereas such response after in vitro immunization was comparable in the two groups of animals. These observations suggest that altered cell-mediated immune response in obese animals is the result of a deleterious microenvironment.

Iron status, immune response and susceptibility to infection

Nutritional factors can modulate immune responses. The concentration of iron, amongst other nutrients, influences host defence mechanisms. In experimentally induced iron deficiency in animals, morbidity and mortality on bacterial challenge are increased several-fold. Cell-mediated immunity and intra-cellular bacterial killing by polymorphonuclear leucocytes are impaired in iron-deficient individuals. This impairment is likely to be mediated by the effect of iron lack on cell proliferation, DNA synthesis and activity of iron-containing and iron-dependent enzymes involved in killing and elimination of microbes. Conversely, the availability of the free iron is a critical determinant for bacterial multiplication. It is not surprising then that epidemiological and clinical data on the frequency of infections--bacterial, fungal and others--in iron-deficient, iron-overloaded and healthy groups differ so widely. Vulnerability to infection based on the individual's iron status must be the net result of the effect of iron, or the lack of it, on microbial growth on the one hand and on immunocompetence of the host on the other. The key to keeping these interactions within physiological bounds is 'optimal iron nutrition'.

Polymorphonuclear leucocyte function in hypothyroidism

The quantitative nitroblue-tetrazolium test demonstrated that polymorphonuclear leucocytes from patients with hypothyroidism reduced the dye less well than leucocytes from euthyroid persons. The ability of these cells to ingest and kill staphylococci were unimpaired. The abnormality of the nitroblue-tetrazolium test in hypothyroid patients was corrected after their treatment with thyroxine.

The effect of mass on frequency

Two experiments are described where an apparent decrease in frequency was detected when the optical path was in the vicinity of a mass. In the first experiment the 21-centimeter absorption line from Taurus A was observed near occultation by the sun. In the second experiment the frequency of a portable cesium clock was compared with the frequency of a similar clock which transmits its signals from Cape Fear, North Carolina. A decrease of frequency of the received signals as a function of the distance between the two clocks was apparent. Several relevant observations (the red shift of lines from the sun, the Mossbauer determination of the gravitational red shift, and the cosmological red shif) are discussed in view of the present results. confirmation.