Search

Search Results

• 1. [Article] Neurobiology of Seasonal Life-history Transitions

  Many animals exhibit seasonal changes in life-history stages, and these seasonal transitions are often accompanied by dramatic switches in behavior. While the neuroendocrine mechanisms that regulate such ...

  Citation × Citation Citation Abstract Copy Title: Neurobiology of Seasonal Life-history Transitions Author: Lucas, Ashley Rae Year: 2015 Many animals exhibit seasonal changes in life-history stages, and these seasonal transitions are often accompanied by dramatic switches in behavior. While the neuroendocrine mechanisms that regulate such behavioral transitions are poorly understood, arginine vasotocin (AVT) and neuropeptide Y (NPY) are excellent candidates because they regulate reproductive and feeding behavior, respectively. In this study, I asked if seasonal changes in AVT and/or NPY are concomitant with spring migration away from the breeding grounds, as male and female red-sided garter snakes (Thamnophis sirtalis parietalis) are transitioning from reproductive to non-reproductive behavior during this time. To address this question, I collected male and female snakes in different migratory stages during the spring and fall. Brains were processed for AVT and NPY immunohistochemistry and the total number of immunoreactive (-ir) cells quantified for each individual. As predicted, males had significantly more AVT-ir cells in the preoptic area and bed nucleus of the stria terminalis, brain regions important for courtship behavior, during the spring mating season compared to the fall. Females had significantly more AVT-ir cells in the preoptic area during the spring compared to the fall and, surprisingly, did not exhibit seasonal changes in NPY. In contrast, males had significantly more NPY-ir cells in the cortex, a region important for spatial memory, and in the posterior hypothalamus during the fall compared to the spring, which likely reflects increased feeding behavior during the summer foraging period. Neither AVT- nor NPY-ir cell number varied significantly with migratory status, indicating that seasonal changes in these neuropeptides are not directly related to migration. I then asked if the observed seasonal changes in AVT and NPY in males and females are related to the transition from reproductive to non-reproductive states. Compared to courting males, non-courting males had significantly more AVT-ir cells in the supraoptic nucleus and more NPY-ir cells in the cortex. AVT- and NPY-ir cells did not differ between unmated and mated females. Collectively, my results suggest that AVT and NPY play a role in regulating seasonal transitions in male reproductive behavior, rather than regulating migration per se. Further, these data indicate that both AVT and NPY are regulating reproductive behavior differently in males versus females. These data provide the framework for future studies examining the mechanisms regulating transitions between reproductive, migratory and foraging behaviors. Title: Neurobiology of Seasonal Life-history Transitions Author: Lucas, Ashley Rae Year: 2015 Many animals exhibit seasonal changes in life-history stages, and these seasonal transitions are often accompanied by dramatic switches in behavior. While the neuroendocrine mechanisms that regulate such behavioral transitions are poorly understood, arginine vasotocin (AVT) and neuropeptide Y (NPY) are excellent candidates because they regulate reproductive and feeding behavior, respectively. In this study, I asked if seasonal changes in AVT and/or NPY are concomitant with spring migration away from the breeding grounds, as male and female red-sided garter snakes (Thamnophis sirtalis parietalis) are transitioning from reproductive to non-reproductive behavior during this time. To address this question, I collected male and female snakes in different migratory stages during the spring and fall. Brains were processed for AVT and NPY immunohistochemistry and the total number of immunoreactive (-ir) cells quantified for each individual. As predicted, males had significantly more AVT-ir cells in the preoptic area and bed nucleus of the stria terminalis, brain regions important for courtship behavior, during the spring mating season compared to the fall. Females had significantly more AVT-ir cells in the preoptic area during the spring compared to the fall and, surprisingly, did not exhibit seasonal changes in NPY. In contrast, males had significantly more NPY-ir cells in the cortex, a region important for spatial memory, and in the posterior hypothalamus during the fall compared to the spring, which likely reflects increased feeding behavior during the summer foraging period. Neither AVT- nor NPY-ir cell number varied significantly with migratory status, indicating that seasonal changes in these neuropeptides are not directly related to migration. I then asked if the observed seasonal changes in AVT and NPY in males and females are related to the transition from reproductive to non-reproductive states. Compared to courting males, non-courting males had significantly more AVT-ir cells in the supraoptic nucleus and more NPY-ir cells in the cortex. AVT- and NPY-ir cells did not differ between unmated and mated females. Collectively, my results suggest that AVT and NPY play a role in regulating seasonal transitions in male reproductive behavior, rather than regulating migration per se. Further, these data indicate that both AVT and NPY are regulating reproductive behavior differently in males versus females. These data provide the framework for future studies examining the mechanisms regulating transitions between reproductive, migratory and foraging behaviors. Close

• 2. [Article] Neuropeptide Y: A potential Marker for a Life-History Transition in the Red-Sided Garter Snake (Thamnophis sirtalis)

  It is essential for organisms to exhibit appropriate behaviors as they transition from one life-history stage to another. While such life-history transitions are critical to both individual survival and ...

  Citation × Citation Citation Abstract Copy Title: Neuropeptide Y: A potential Marker for a Life-History Transition in the Red-Sided Garter Snake (Thamnophis sirtalis) Author: Richards, Daelyn Year: 2014 It is essential for organisms to exhibit appropriate behaviors as they transition from one life-history stage to another. While such life-history transitions are critical to both individual survival and reproductive fitness, we know very little about the underlying mechanisms. This project explores a potential mechanism regulating the transition of red-sided garter snakes (Thamnophis sirtalis) from reproductive to foraging behavior. After emerging from winter dormancy, male snakes engage in mate searching and mating behavior followed by a transition to foraging. Neuropeptide Y (NPY) is a neurohormone that controls appetite and feeding behavior in all organisms studied. We previously demonstrated that NPY cell number in the brain is increased in snakes exhibiting feeding behavior. In this study, we asked if brain NPY is involved in regulating the transition from courtship to foraging behavior under natural field conditions. To address this question, courting and foraging snakes were collected from the field and their behavioral preference confirmed by testing on a Y-maze. Snakes were then euthanized and the brains collected. An immunohistochemistry assay was performed for NPY; immunoreactive cells were counted manually. Quantification of NPY cell number in three different brain regions is currently being finalized (cortex, amygdala, and hypothalamus). We hypothesize that male snakes exhibiting feeding behavior will have more NPY cells than male snakes exhibiting mating behavior. If our hypothesis is supported, these data will provide evidence that NPY plays a role in mediating an important life-history transition between reproductive and feeding behaviors under natural field conditions. Title: Neuropeptide Y: A potential Marker for a Life-History Transition in the Red-Sided Garter Snake (Thamnophis sirtalis) Author: Richards, Daelyn Year: 2014 It is essential for organisms to exhibit appropriate behaviors as they transition from one life-history stage to another. While such life-history transitions are critical to both individual survival and reproductive fitness, we know very little about the underlying mechanisms. This project explores a potential mechanism regulating the transition of red-sided garter snakes (Thamnophis sirtalis) from reproductive to foraging behavior. After emerging from winter dormancy, male snakes engage in mate searching and mating behavior followed by a transition to foraging. Neuropeptide Y (NPY) is a neurohormone that controls appetite and feeding behavior in all organisms studied. We previously demonstrated that NPY cell number in the brain is increased in snakes exhibiting feeding behavior. In this study, we asked if brain NPY is involved in regulating the transition from courtship to foraging behavior under natural field conditions. To address this question, courting and foraging snakes were collected from the field and their behavioral preference confirmed by testing on a Y-maze. Snakes were then euthanized and the brains collected. An immunohistochemistry assay was performed for NPY; immunoreactive cells were counted manually. Quantification of NPY cell number in three different brain regions is currently being finalized (cortex, amygdala, and hypothalamus). We hypothesize that male snakes exhibiting feeding behavior will have more NPY cells than male snakes exhibiting mating behavior. If our hypothesis is supported, these data will provide evidence that NPY plays a role in mediating an important life-history transition between reproductive and feeding behaviors under natural field conditions. Close

• 3. [Article] Seasonal and Sex Differences in the Effects of Melatonin on Brain Arginine Vasotocin in Green Treefrogs (Hyla cinerea): Relationship to Melatonin Receptor 1a

  Critical life history events such as breeding, migration and hibernation must take place in the correct environmental context to minimize deleterious consequences on survival and reproductive fitness. ...

  Citation × Citation Citation Abstract Copy Title: Seasonal and Sex Differences in the Effects of Melatonin on Brain Arginine Vasotocin in Green Treefrogs (Hyla cinerea): Relationship to Melatonin Receptor 1a Author: Howard, Christina Marie Year: 2014 Critical life history events such as breeding, migration and hibernation must take place in the correct environmental context to minimize deleterious consequences on survival and reproductive fitness. Neuroendocrine mechanisms synchronizing internal physiological states with extrinsic environmental cues are vital to timing life history events appropriately. Secretion of the pineal hormone melatonin is sensitive to light and temperature cues, which provides a physiological indicator of time of day and time of year for organisms. Melatonin influences seasonal reproduction in a variety of vertebrates, likely by altering the synthesis and/or release of reproductive neuropeptides in the brain. The neuropeptides arginine vasotocin and its mammalian homologue, arginine vasopressin, are well-known modulators of reproductive and sociosexual behavior across vertebrate taxa, and are likely targets of melatonin in the context of seasonal reproduction. There is extensive evidence that vasotocin/vasopressin innervation in the brain is subject to seasonal variation, and that this variation is frequently sexually dimorphic. However, evidence that melatonin directly modulates this important neuropeptide system is lacking. Melatonin receptor 1a (MT1 in mammals) may be responsible for mediating melatonin's influence on brain vasotocin, as it is known to regulate seasonal reproduction in a variety of vertebrates. In the present study, I asked whether melatonin influences brain vasotocin in male green treefrogs (Hyla cinerea), and compared the distribution of melatonin receptor 1a in the brain of green treefrogs between sexes and seasons. Adult male and female green treefrogs were collected from field sites in Louisiana during the summer breeding season. Summer animals were acclimated to lab conditions for 3 weeks, then euthanized and their brains collected. Winter animals were maintained in the lab for four months under incrementally changing photo-, thermo-, and hygroperiod regimes that mimicked the transition to winter in their natural habitat, followed by euthanasia and brain collection. A subset of winter males (Experiment 1) were implanted with melatonin-filled or blank silastic capsules for a period of one month prior to euthanasia and brain collection. Brains of these males were processed for vasotocin immunohistochemistry. I quantified AVT-ir cell number in Experiment 1 males in the nucleus accumbens (NAcc), amygdala and caudal striatum (AMG), preoptic area (POA), suprachaismatic nucleus (SCN), and ventral hypothalamus (VH). Melatonin did not influence brain vasotocin-ir cell number in any brain region. Brains from untreated summer and winter males and females were collected and processed for MT1 immunohistochemistry. MT1-ir cells were quantified in the NAcc, striatum (STR), AMG, POA, SCN, and VH. In all regions quantified, reproductively active males had significantly more MT1-ir cells than nonreproductive males. Within the summer breeding season, males had significantly more MT1-ir cells in the NAcc than did reproductively active females. In all other regions there was no significant difference in MT1-ir cell number between reproductively active males and females. Collectively, these data suggest that melatonin modulates vasotocin via MT1. These findings assist in elucidating the neuroendocrine mechanisms by which vertebrates integrate seasonal cues with physiology to correctly time critical life history events. Title: Seasonal and Sex Differences in the Effects of Melatonin on Brain Arginine Vasotocin in Green Treefrogs (Hyla cinerea): Relationship to Melatonin Receptor 1a Author: Howard, Christina Marie Year: 2014 Critical life history events such as breeding, migration and hibernation must take place in the correct environmental context to minimize deleterious consequences on survival and reproductive fitness. Neuroendocrine mechanisms synchronizing internal physiological states with extrinsic environmental cues are vital to timing life history events appropriately. Secretion of the pineal hormone melatonin is sensitive to light and temperature cues, which provides a physiological indicator of time of day and time of year for organisms. Melatonin influences seasonal reproduction in a variety of vertebrates, likely by altering the synthesis and/or release of reproductive neuropeptides in the brain. The neuropeptides arginine vasotocin and its mammalian homologue, arginine vasopressin, are well-known modulators of reproductive and sociosexual behavior across vertebrate taxa, and are likely targets of melatonin in the context of seasonal reproduction. There is extensive evidence that vasotocin/vasopressin innervation in the brain is subject to seasonal variation, and that this variation is frequently sexually dimorphic. However, evidence that melatonin directly modulates this important neuropeptide system is lacking. Melatonin receptor 1a (MT1 in mammals) may be responsible for mediating melatonin's influence on brain vasotocin, as it is known to regulate seasonal reproduction in a variety of vertebrates. In the present study, I asked whether melatonin influences brain vasotocin in male green treefrogs (Hyla cinerea), and compared the distribution of melatonin receptor 1a in the brain of green treefrogs between sexes and seasons. Adult male and female green treefrogs were collected from field sites in Louisiana during the summer breeding season. Summer animals were acclimated to lab conditions for 3 weeks, then euthanized and their brains collected. Winter animals were maintained in the lab for four months under incrementally changing photo-, thermo-, and hygroperiod regimes that mimicked the transition to winter in their natural habitat, followed by euthanasia and brain collection. A subset of winter males (Experiment 1) were implanted with melatonin-filled or blank silastic capsules for a period of one month prior to euthanasia and brain collection. Brains of these males were processed for vasotocin immunohistochemistry. I quantified AVT-ir cell number in Experiment 1 males in the nucleus accumbens (NAcc), amygdala and caudal striatum (AMG), preoptic area (POA), suprachaismatic nucleus (SCN), and ventral hypothalamus (VH). Melatonin did not influence brain vasotocin-ir cell number in any brain region. Brains from untreated summer and winter males and females were collected and processed for MT1 immunohistochemistry. MT1-ir cells were quantified in the NAcc, striatum (STR), AMG, POA, SCN, and VH. In all regions quantified, reproductively active males had significantly more MT1-ir cells than nonreproductive males. Within the summer breeding season, males had significantly more MT1-ir cells in the NAcc than did reproductively active females. In all other regions there was no significant difference in MT1-ir cell number between reproductively active males and females. Collectively, these data suggest that melatonin modulates vasotocin via MT1. These findings assist in elucidating the neuroendocrine mechanisms by which vertebrates integrate seasonal cues with physiology to correctly time critical life history events. Close