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Papers by Maria Horvat-Gordon

Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2016

Medullary bone is a specialized bone found in the marrow cavity of laying birds. It provides a si... more Medullary bone is a specialized bone found in the marrow cavity of laying birds. It provides a significant contribution to the calcium supply for egg shell formation. Medullary bone is distinguished from cortical bone by the presence of large amounts of a keratan sulfate proteoglycan (KSPG). The aims of the present experiment are to confirm the identity of the core protein of KSPG, identify a marker of medullary bone metabolism, and determine whether changes in keratan sulfate (KS) concentration in blood are associated with the egg-laying cycle. Using two different isolation techniques- one specific for bone and another for blood- we have identified bone sialoprotein (BSP) to be the core protein of this KSPG. We also determined that the amount of keratan sulfate (KS) in laying hen blood fluctuates in synchrony with the egg-laying cycle, and thus can serve as a specific marker for medullary bone metabolism. During the course of this investigation, we also found FGF-23 (phosphatonin) to be expressed in medullary bone, in synchrony with the egg-laying cycle. Western blotting was used to demonstrate the presence of this peptide in both laying hen blood and medullary bone extracts. The importance of FGF-23 (phosphatonin) and parathyroid hormone in normalizing the dramatic changes in plasma calcium and phosphorus during the 24h egg-laying cycle is discussed.

PLoS ONE, 2013

White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat ... more White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat stores to fuel migration. Adipose tissue produces hormones and signaling factors in a rhythmic fashion and may be controlled by a clock in adipose tissue or driven by a master clock in the brain. The master clock may convey photoperiodic information from the environment to adipose tissue to facilitate pre-migratory fattening, and adipose tissue may, in turn, release adipokines to indicate the extent of fat energy stores. Here, we present evidence that a change in signal from the adipokines adiponectin and visfatin may act to indicate body condition, thereby influencing an individual's decision to commence migratory flight, or to delay until adequate fat stores are acquired. We quantified plasma adiponectin and visfatin levels across the day in captive birds held under constant photoperiod. The circadian profiles of plasma adiponectin in non-migrating birds were approximately inverse the profiles from migrating birds. Adiponectin levels were positively correlated to body fat, and body fat was inversely related to the appearance of nocturnal migratory restlessness. Visfatin levels were constant across the day and did not correlate with fat deposits; however, a reduction in plasma visfatin concentration occurred during the migratory period. The data suggest that a significant change in the biological control of adipokine expression exists between the two migratory conditions and we propose a role for adiponectin, visfatin and adipose clocks in the regulation of migratory behaviors. Citation: Stuber EF, Verpeut J, Horvat-Gordon M, Ramachandran R, Bartell PA (2013) Differential Regulation of Adipokines May Influence Migratory Behavior in the White-Throated Sparrow (Zonotrichia albicollis). PLoS ONE 8(6): e59097.

Physiology & Behavior, 2005

The integration of oxytocin (OT) into behavioral science seems to hold considerable promise for a... more The integration of oxytocin (OT) into behavioral science seems to hold considerable promise for advancing our understanding of human health and development but methodological issues restrict the measurement of OT in large studies, in everyday social settings, or when repeated sampling is required. Measuring OT in saliva could overcome many of these limitations. In this paper, we rigorously evaluate the feasibility of doing so. A series of experiments leads to the conclusion that saliva does not contain oxytocin in measurable amounts, and that OT is not a valid salivary biomarker when measured by currently available immunological methods. Levels of immuno-reactive OT in saliva are primarily due to non-specific interference with antibody-antigen binding. We can state with a high degree of certainty that measurement of OT in saliva does not yield meaningful indices of individual differences or intra-individual change.

BMC Medical Research Methodology, 2011

PLoS ONE, 2013

Laying hens often experience unbalanced calcium utilization which can cause deficiencies in bone ... more Laying hens often experience unbalanced calcium utilization which can cause deficiencies in bone and egg mineralization. Because melatonin has been shown to affect bone mineralization in other animals, we examined whether treating hens with melatonin would affect eggshell thickness and improve skeletal performance, thereby reducing skeletal and egg shell defects. Birds were given a diet containing either low (30 mg/kg), medium (300 mg/kg), or high (3 mg/kg) concentrations of melatonin, or control feed through approximately one laying cycle. We examined the weight, length, and strength of egg, femur, tibia, and keel. Hens treated with a high concentration of melatonin showed significant strengthening in their femur and tibia, as measured by maximum force sustained and breaking force, compared to controls. Egg weights from hens treated with melatonin were significantly greater than those from hens that were not treated with melatonin. Conversely, egg shell mass of hens treated with melatonin was significantly lower than those of hens not treated with melatonin. Our data suggest that melatonin may affect the allocation of calcium to bone at the expense of egg shell mineralization.

Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2016

Medullary bone is a specialized bone found in the marrow cavity of laying birds. It provides a si... more Medullary bone is a specialized bone found in the marrow cavity of laying birds. It provides a significant contribution to the calcium supply for egg shell formation. Medullary bone is distinguished from cortical bone by the presence of large amounts of a keratan sulfate proteoglycan (KSPG). The aims of the present experiment are to confirm the identity of the core protein of KSPG, identify a marker of medullary bone metabolism, and determine whether changes in keratan sulfate (KS) concentration in blood are associated with the egg-laying cycle. Using two different isolation techniques- one specific for bone and another for blood- we have identified bone sialoprotein (BSP) to be the core protein of this KSPG. We also determined that the amount of keratan sulfate (KS) in laying hen blood fluctuates in synchrony with the egg-laying cycle, and thus can serve as a specific marker for medullary bone metabolism. During the course of this investigation, we also found FGF-23 (phosphatonin) to be expressed in medullary bone, in synchrony with the egg-laying cycle. Western blotting was used to demonstrate the presence of this peptide in both laying hen blood and medullary bone extracts. The importance of FGF-23 (phosphatonin) and parathyroid hormone in normalizing the dramatic changes in plasma calcium and phosphorus during the 24h egg-laying cycle is discussed.

PLoS ONE, 2013

White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat ... more White-throated sparrows increase fat deposits during pre-migratory periods and rely on these fat stores to fuel migration. Adipose tissue produces hormones and signaling factors in a rhythmic fashion and may be controlled by a clock in adipose tissue or driven by a master clock in the brain. The master clock may convey photoperiodic information from the environment to adipose tissue to facilitate pre-migratory fattening, and adipose tissue may, in turn, release adipokines to indicate the extent of fat energy stores. Here, we present evidence that a change in signal from the adipokines adiponectin and visfatin may act to indicate body condition, thereby influencing an individual's decision to commence migratory flight, or to delay until adequate fat stores are acquired. We quantified plasma adiponectin and visfatin levels across the day in captive birds held under constant photoperiod. The circadian profiles of plasma adiponectin in non-migrating birds were approximately inverse the profiles from migrating birds. Adiponectin levels were positively correlated to body fat, and body fat was inversely related to the appearance of nocturnal migratory restlessness. Visfatin levels were constant across the day and did not correlate with fat deposits; however, a reduction in plasma visfatin concentration occurred during the migratory period. The data suggest that a significant change in the biological control of adipokine expression exists between the two migratory conditions and we propose a role for adiponectin, visfatin and adipose clocks in the regulation of migratory behaviors. Citation: Stuber EF, Verpeut J, Horvat-Gordon M, Ramachandran R, Bartell PA (2013) Differential Regulation of Adipokines May Influence Migratory Behavior in the White-Throated Sparrow (Zonotrichia albicollis). PLoS ONE 8(6): e59097.

Physiology & Behavior, 2005

The integration of oxytocin (OT) into behavioral science seems to hold considerable promise for a... more The integration of oxytocin (OT) into behavioral science seems to hold considerable promise for advancing our understanding of human health and development but methodological issues restrict the measurement of OT in large studies, in everyday social settings, or when repeated sampling is required. Measuring OT in saliva could overcome many of these limitations. In this paper, we rigorously evaluate the feasibility of doing so. A series of experiments leads to the conclusion that saliva does not contain oxytocin in measurable amounts, and that OT is not a valid salivary biomarker when measured by currently available immunological methods. Levels of immuno-reactive OT in saliva are primarily due to non-specific interference with antibody-antigen binding. We can state with a high degree of certainty that measurement of OT in saliva does not yield meaningful indices of individual differences or intra-individual change.

BMC Medical Research Methodology, 2011

PLoS ONE, 2013

Laying hens often experience unbalanced calcium utilization which can cause deficiencies in bone ... more Laying hens often experience unbalanced calcium utilization which can cause deficiencies in bone and egg mineralization. Because melatonin has been shown to affect bone mineralization in other animals, we examined whether treating hens with melatonin would affect eggshell thickness and improve skeletal performance, thereby reducing skeletal and egg shell defects. Birds were given a diet containing either low (30 mg/kg), medium (300 mg/kg), or high (3 mg/kg) concentrations of melatonin, or control feed through approximately one laying cycle. We examined the weight, length, and strength of egg, femur, tibia, and keel. Hens treated with a high concentration of melatonin showed significant strengthening in their femur and tibia, as measured by maximum force sustained and breaking force, compared to controls. Egg weights from hens treated with melatonin were significantly greater than those from hens that were not treated with melatonin. Conversely, egg shell mass of hens treated with melatonin was significantly lower than those of hens not treated with melatonin. Our data suggest that melatonin may affect the allocation of calcium to bone at the expense of egg shell mineralization.