Browsing by Subject "Corticosterone"
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Item Influence of ACTH/MSH peptides and corticosterone of habituation of prey catching behavior in the toad, Bufo cognatus(Texas Tech University, 1995-08) Carpenter, Anne MarieThe effect of adrenocorticotropin and melanotropin peptides, corticosterone, and the a-MSH antagonist, U-76188E, was studied on the acquisition and extinction of the prey-catching behavior in the toad, Bufo cognatus. Male toads were injected with corticosterone, porcine ACTH[l-39], a-MSH, (Nle4-D-Phe7)a-MSH, desacetyl- a-MSH, ACTH[4-10], a-MSH antagonist (U-76188E), or control vehicle 30 min prior to acquisition. ACTH[l-39], ACTH[4-10] and a-MSH significantly decreased the number of turning reactions during acquisition in relation to controls. The effect of these peptides was rapid, occurring within the first 20 min of acquisition. Corticosterone caused a significant decrease in the number of turning reactions, although this effect was not observed until 40 min after the onset of testing. (Nle^4-DPhe^ 7) a-MSH and des-acetyl-a-MSH did not influence acquisition. The a-MSH antagonist (U-76188E) abolished the behavioral response to a-MSH during acquisition, but did not significantly influence extinction. ACTH[ 1-391 was the only peptide to delay extinction. These data suggest that the ability of ACTH to facilitate acquisition is independent of interrenal corticosterone secretion. Furthermore, it appears that minor structural differences can dramatically influence the ability of ACTH/MSH peptides to modulate learning and memory processes in toads.Item An integrated evaluation of costs and benefits of corticosterone secretion through development(2007) Wada, Haruka; Jansen, Robert; Breuner, CreaghGlucocorticoids (GCs) play critical roles during development: transient increases in GCs facilitate anticipatory physiological changes and trigger ontogenetic transitions such as promoting fetal/embryonic organ maturation and initiating birth/hatching. In contrast, chronically elevated GCs can be detrimental to growth, cognition, and survival. Thus, animals going through substantial growth may have higher corticosteroid binding globulin (CBG) levels, or enhance negative feedback/tonic inhibition on the hypothalamic-pituitary-adrenal (HPA) axis to keep GCs levels low. Here I investigated these hypotheses using altricial white-crowned sparrow nestlings. I examined 1) the ontogeny of the corticosterone (CORT) response (both total and free hormone levels), 2) changes in corticosteroid receptor levels in brain with age, and 3) effects of acute and extended elevation of CORT on behavior and growth. In response to acute stress, nestlings showed a low HPA reactivity in total CORT during the first 1/3 of the nestling period. When free CORT is considered, this hyporesponsive period was extended to 2/3 of the nestling period, suggesting CBG is one of the mechanisms to keep free CORT low. These periods coincided with rapid mass gain and acquiring thermoregulatory ability. The low reactivity was partly due to a dampened sensitivity at pituitary level or higher as all stages of nestlings responded to adrenocorticotropic hormone challenges; however it was not due to an enhanced negative feedback/tonic inhibition on hypothalamus or hippocampus. When CORT levels were artificially elevated, I only observed detrimental effects on begging behavior and growth. These series of data elucidated the ontogeny of the HPA axis in altricial nestlings regarding CORT, binding globulin, and receptor levels. In addition, I found that measured effects of exogenous CORT are primarily costly and highly age-specific.Item An integrated evaluation of costs and benefits of corticosterone secretion through development(2007-05) Wada, Haruka, 1976-; Jansen, Robert K., 1954-; Breuner, Creagh W.Glucocorticoids (GCs) play critical roles during development: transient increases in GCs facilitate anticipatory physiological changes and trigger ontogenetic transitions such as promoting fetal/embryonic organ maturation and initiating birth/hatching. In contrast, chronically elevated GCs can be detrimental to growth, cognition, and survival. Thus, animals going through substantial growth may have higher corticosteroid binding globulin (CBG) levels, or enhance negative feedback/tonic inhibition on the hypothalamic-pituitary-adrenal (HPA) axis to keep GCs levels low. Here I investigated these hypotheses using altricial white-crowned sparrow nestlings. I examined 1) the ontogeny of the corticosterone (CORT) response (both total and free hormone levels), 2) changes in corticosteroid receptor levels in brain with age, and 3) effects of acute and extended elevation of CORT on behavior and growth. In response to acute stress, nestlings showed a low HPA reactivity in total CORT during the first 1/3 of the nestling period. When free CORT is considered, this hyporesponsive period was extended to 2/3 of the nestling period, suggesting CBG is one of the mechanisms to keep free CORT low. These periods coincided with rapid mass gain and acquiring thermoregulatory ability. The low reactivity was partly due to a dampened sensitivity at pituitary level or higher as all stages of nestlings responded to adrenocorticotropic hormone challenges; however it was not due to an enhanced negative feedback/tonic inhibition on hypothalamus or hippocampus. When CORT levels were artificially elevated, I only observed detrimental effects on begging behavior and growth. These series of data elucidated the ontogeny of the HPA axis in altricial nestlings regarding CORT, binding globulin, and receptor levels. In addition, I found that measured effects of exogenous CORT are primarily costly and highly age-specific.Item The effects of neonatal testosterone on the prepubertal female rat's response to different stressors(Texas Tech University, 1985-12) Smith, Constance JNot available