This protocol describes a method for the in vivo measurement of steroid hormones in brain circuit... more This protocol describes a method for the in vivo measurement of steroid hormones in brain circuits of the zebra finch. A guide cannula is surgically implanted into the skull, microdilysate is collected through a microdialysis probe that is inserted into the cannula, and steroid concentrations in the microdialysate are determined using the enzyme-linked immunosorbent assay (ELISA). In some cases, the steroids measured are derived locally (e.g., neural estrogens in males), whereas in other cases, the steroids measured reflect systemic circulating levels and/or central conversion (e.g., the primary androgen testosterone and the primary glucocorticoid corticosterone). A reverse-microdialysis ("retrodialysis") method that can be used to deliver pharmacological agents into the brain to influence local steroid neurochemistry as well as behavior is also discussed.
Steroid hormones synthesized in the brain, known as neurosteroids, influence neuroplasticity and ... more Steroid hormones synthesized in the brain, known as neurosteroids, influence neuroplasticity and behavior, including learning and memory, as well as recovery from neural injury. In particular, estradiol has been identified as a neurosteroid affecting neuronal plasticity and thus may play a role in learning and memory. Neuroestrogens are produced from androgens by the enzyme aromatase that is expressed in the brain. In some songbirds, aromatase is expressed at high levels in the hippocampus (HP), a brain region crucial for vertebrate learning and memory. To determine whether performing a memory task regulates aromatase levels in the HP via gene expression, zebra finches were subjected to either a memory acquisition or a memory recall test that required the localization of a food source in a four-armed maze. Immediately after completing the behavioral test, the HP of each bird was removed and frozen. Quantitative polymerase chain reaction (qPCR) was used to determine levels of aromata...
Estradiol is known to impact cognitive function including spatial learning and memory, with studi... more Estradiol is known to impact cognitive function including spatial learning and memory, with studies focused largely on rodent models. Estrogens can be produced peripherally or centrally as neuroestrogens, and the specific role for neuroestrogens in memory processes remains unresolved. Many songbirds possess remarkable spatial memory capabilities and also express the estrogen synthetic enzyme aromatase abundantly in the hippocampus, suggesting that locally-produced estrogens may promote the acquisition or retrieval of spatial memories in these birds. We examined the effect of estradiol on spatial memory in three contexts in the zebra finch: retrieval after discrimination training, retrieval after familiarization but without discrimination training, and memory acquisition, using a combination of estradiol implants and oral dosing with the aromatase inhibitor fadrozole (FAD). Retrieval of spatial memory in both contexts was impaired when estradiol production was blocked. However, spati...
The specificity of estrogen signaling in brain is defined at one level by the types and distribut... more The specificity of estrogen signaling in brain is defined at one level by the types and distributions of receptor molecules that are activated by estrogens. At another level, as our understanding of the neurobiology of the estrogen synthetic enzyme aromatase has grown, questions have emerged as to how neuroactive estrogens reach specific target receptors in functionally relevant concentrations. Here we explore the spatial specificity of neuroestrogen signaling with a focus on studies of songbirds to provide perspective on some as-yet unresolved questions. Studies conducted in both male and female songbirds have helped to clarify these interesting facets of neuroestrogen physiology.
... 2009 doi: 10.1676/09-027.1. Invasive Fire Ants Depredate Nest of Florida Scrub-Jay. Travis E.... more ... 2009 doi: 10.1676/09-027.1. Invasive Fire Ants Depredate Nest of Florida Scrub-Jay. Travis E. Wilcoxen 1, 2 and Michelle A. Rensel 1. ... General and Comparative Endocrinology 154:150160. CrossRef, PubMed. Sikes, PJ and KA Arnold. 1986. ...
The immune system is a necessary, but potentially costly, defense against infectious diseases. Wh... more The immune system is a necessary, but potentially costly, defense against infectious diseases. When nutrition is limited, immune activity may consume a significant amount of an organism's energy budget. Levels of dietary protein affect immune system function; high levels can enhance disease resistance. We exposed southern leopard frog [Lithobates sphenocephalus (=Rana sphenocephala)] tadpoles to high and low protein diets crossed with the presence or absence of the pathogenic amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) and quantified: (1) tadpole resistance to Bd; (2) tadpole skin-swelling in response to phytohaemagglutinin (PHA) injection (a measure of the T cell-mediated response of the immune system); (3) bacterial killing ability (BKA) of tadpole blood (a measure of the complement-mediated cytotoxicity of the innate immune system); and (4) tadpole growth and development. Tadpoles raised on a low-protein diet were smaller and less developed than tadpoles on a high-protein diet. When controlled for developmental stage, tadpoles raised on a low-protein diet had reduced PHA and BKA responses relative to tadpoles on a high-protein diet, but these immune responses were independent of Bd exposure. High dietary protein significantly increased resistance to Bd. Our results support the general hypothesis that host condition can strongly affect disease resistance; in particular, fluctuations in dietary protein availability may change how diseases affect populations in the field.
... Efectos de las Carreteras sobre la Disponibilidad de Alimento y la Incorporación de Energía e... more ... Efectos de las Carreteras sobre la Disponibilidad de Alimento y la Incorporación de Energía en Aphelocoma coerulescens. Gina M. Morgan, 1, 3 Raoul K. Boughton, 1, 2 Michelle A. Rensel, 1 and Stephan J. Schoech 1. ... Fahrig, L., JH Pedlar, SE Pope, PD Taylor, and JF Wegner. ...
This protocol describes a method for the in vivo measurement of steroid hormones in brain circuit... more This protocol describes a method for the in vivo measurement of steroid hormones in brain circuits of the zebra finch. A guide cannula is surgically implanted into the skull, microdilysate is collected through a microdialysis probe that is inserted into the cannula, and steroid concentrations in the microdialysate are determined using the enzyme-linked immunosorbent assay (ELISA). In some cases, the steroids measured are derived locally (e.g., neural estrogens in males), whereas in other cases, the steroids measured reflect systemic circulating levels and/or central conversion (e.g., the primary androgen testosterone and the primary glucocorticoid corticosterone). A reverse-microdialysis ("retrodialysis") method that can be used to deliver pharmacological agents into the brain to influence local steroid neurochemistry as well as behavior is also discussed.
Steroid hormones synthesized in the brain, known as neurosteroids, influence neuroplasticity and ... more Steroid hormones synthesized in the brain, known as neurosteroids, influence neuroplasticity and behavior, including learning and memory, as well as recovery from neural injury. In particular, estradiol has been identified as a neurosteroid affecting neuronal plasticity and thus may play a role in learning and memory. Neuroestrogens are produced from androgens by the enzyme aromatase that is expressed in the brain. In some songbirds, aromatase is expressed at high levels in the hippocampus (HP), a brain region crucial for vertebrate learning and memory. To determine whether performing a memory task regulates aromatase levels in the HP via gene expression, zebra finches were subjected to either a memory acquisition or a memory recall test that required the localization of a food source in a four-armed maze. Immediately after completing the behavioral test, the HP of each bird was removed and frozen. Quantitative polymerase chain reaction (qPCR) was used to determine levels of aromata...
Estradiol is known to impact cognitive function including spatial learning and memory, with studi... more Estradiol is known to impact cognitive function including spatial learning and memory, with studies focused largely on rodent models. Estrogens can be produced peripherally or centrally as neuroestrogens, and the specific role for neuroestrogens in memory processes remains unresolved. Many songbirds possess remarkable spatial memory capabilities and also express the estrogen synthetic enzyme aromatase abundantly in the hippocampus, suggesting that locally-produced estrogens may promote the acquisition or retrieval of spatial memories in these birds. We examined the effect of estradiol on spatial memory in three contexts in the zebra finch: retrieval after discrimination training, retrieval after familiarization but without discrimination training, and memory acquisition, using a combination of estradiol implants and oral dosing with the aromatase inhibitor fadrozole (FAD). Retrieval of spatial memory in both contexts was impaired when estradiol production was blocked. However, spati...
The specificity of estrogen signaling in brain is defined at one level by the types and distribut... more The specificity of estrogen signaling in brain is defined at one level by the types and distributions of receptor molecules that are activated by estrogens. At another level, as our understanding of the neurobiology of the estrogen synthetic enzyme aromatase has grown, questions have emerged as to how neuroactive estrogens reach specific target receptors in functionally relevant concentrations. Here we explore the spatial specificity of neuroestrogen signaling with a focus on studies of songbirds to provide perspective on some as-yet unresolved questions. Studies conducted in both male and female songbirds have helped to clarify these interesting facets of neuroestrogen physiology.
... 2009 doi: 10.1676/09-027.1. Invasive Fire Ants Depredate Nest of Florida Scrub-Jay. Travis E.... more ... 2009 doi: 10.1676/09-027.1. Invasive Fire Ants Depredate Nest of Florida Scrub-Jay. Travis E. Wilcoxen 1, 2 and Michelle A. Rensel 1. ... General and Comparative Endocrinology 154:150160. CrossRef, PubMed. Sikes, PJ and KA Arnold. 1986. ...
The immune system is a necessary, but potentially costly, defense against infectious diseases. Wh... more The immune system is a necessary, but potentially costly, defense against infectious diseases. When nutrition is limited, immune activity may consume a significant amount of an organism's energy budget. Levels of dietary protein affect immune system function; high levels can enhance disease resistance. We exposed southern leopard frog [Lithobates sphenocephalus (=Rana sphenocephala)] tadpoles to high and low protein diets crossed with the presence or absence of the pathogenic amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) and quantified: (1) tadpole resistance to Bd; (2) tadpole skin-swelling in response to phytohaemagglutinin (PHA) injection (a measure of the T cell-mediated response of the immune system); (3) bacterial killing ability (BKA) of tadpole blood (a measure of the complement-mediated cytotoxicity of the innate immune system); and (4) tadpole growth and development. Tadpoles raised on a low-protein diet were smaller and less developed than tadpoles on a high-protein diet. When controlled for developmental stage, tadpoles raised on a low-protein diet had reduced PHA and BKA responses relative to tadpoles on a high-protein diet, but these immune responses were independent of Bd exposure. High dietary protein significantly increased resistance to Bd. Our results support the general hypothesis that host condition can strongly affect disease resistance; in particular, fluctuations in dietary protein availability may change how diseases affect populations in the field.
... Efectos de las Carreteras sobre la Disponibilidad de Alimento y la Incorporación de Energía e... more ... Efectos de las Carreteras sobre la Disponibilidad de Alimento y la Incorporación de Energía en Aphelocoma coerulescens. Gina M. Morgan, 1, 3 Raoul K. Boughton, 1, 2 Michelle A. Rensel, 1 and Stephan J. Schoech 1. ... Fahrig, L., JH Pedlar, SE Pope, PD Taylor, and JF Wegner. ...
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