Biology subjects

Farrar, V. S.

Publications and source records attributed to Farrar, V. S..

4 recordsLinked to original sources

bioRxiv2022

Prior parental experience attenuates hormonal stress responses and alters hippocampal glucocorticoid receptors in both sexes of the biparental rock dove

In the face of challenges, animals must balance investments in reproductive effort versus their own survival. Physiologically, this tradeoff may be mediated by glucocorticoid release by the hypothalamic-pituitary-adrenal (HPA) axis and prolactin release from the pituitary to maintain parental care. The degree to which animals react to, and recover from, stressors likely affects their ability to maintain parental behavior and ultimately, fitness. However, less is known about how the stress response changes when animals gain parental experience, and what mechanisms may underlie any effect of experience on hormonal stress responses. To address these questions, we measured the corticosterone (CORT) and prolactin (PRL) stress response in both sexes of the biparental rock dove (Columba livia) that had never raised chicks versus birds that had fledged at least one chick. We measured both CORT and PRL at baseline and after an acute stressor (30 minutes restraint). We also measured negative feedback ability by administering dexamethasone, a synthetic glucocorticoid that suppresses CORT release, and measuring CORT and PRL after 60 minutes. All hormones we measured when birds were not actively nesting, allowing us to assess any lasting effects of parental experience beyond the parental care period. Birds with parental experience had lower stress-induced and negative-feedback CORT, and higher stress-induced PRL than inexperienced birds. In a separate experiment, we measured glucocorticoid receptor subtype expression in the hippocampus, a key site of negative feedback regulation. We found that experienced birds expressed higher glucocorticoid receptors than inexperienced controls, which may mediate their ability to attenuate the hormonal stress response. Together, these results shed light on potential mechanisms by which gaining experience may improve parental performance and fitness. Summary statementExperienced rock dove parents show lower corticosterone and higher prolactin levels after an acute stressor than birds without parental experience and increased glucocorticoid receptor expression in the hippocampus may mediate this effect.

animal behavior and cognition↗

bioRxiv2021

Prolactin maintains parental responses and alters reproductive axis gene expression, but not courtship behaviors, in both sexes of a biparental bird

Prolactin, a hormone involved in vertebrate parental care, is hypothesized to inhibit reproductive hypothalamic-pituitary-gonadal (HPG) axis activity during parenting, thus maintaining investment in the current brood as opposed to new reproductive efforts. While prolactin underlies many parental behaviors in birds, its effects on other reproductive behaviors, such as courtship, remain unstudied. How prolactin affects neuropeptide and hormone receptor expression across the avian HPG axis also remains unknown. To address these questions, we administered ovine prolactin (oPRL) or a vehicle control to both sexes in experienced pairs of the biparental rock dove (Columba livia), after nest removal at the end of incubation. We found that oPRL promoted parental responses to novel chicks and stimulated crop growth compared to controls, consistent with other studies. However, we found that neither courtship behaviors, copulation rates nor pair maintenance differed with oPRL treatment. Across the HPG, we found oPRL had little effect on gene expression in hypothalamic nuclei, but increased expression of FSHB and hypothalamic hormone receptor genes in the pituitary. In the gonads, oPRL increased testes size and gonadotropin receptor expression, but did not affect ovarian state or small white follicle gene expression. However, the oviducts of oPRL-treated females were smaller and had lower estrogen receptor expression compared with controls. Our results highlight that some species, especially those that show multiple brooding, may be able to maintain mating behavior despite elevated prolactin. Thus, mechanisms may exist for prolactin to promote investment in parental care without concurrent inhibition of reproductive function or HPG axis activity.

animal behavior and cognition↗

bioRxiv2021

Prolactin and prolactin receptor expression in the HPG axis and crop sac during parental care in both sexes of a biparental bird (Columba livia)

During breeding, multiple circulating hormones, including prolactin, facilitate reproductive transitions in species that exhibit parental care. Prolactin underlies parental behaviors and related physiological changes across many vertebrates, including birds and mammals. While circulating prolactin levels often fluctuate across breeding, less is known about how relevant target tissues vary in their prolactin responsiveness via prolactin receptor (PRLR) expression. Recent studies have also investigated prolactin (PRL) gene expression outside of the pituitary (i.e., extra-pituitary PRL), but how PRL gene expression varies during parental care in non-pituitary tissue (e.g., hypothalamus, gonads) remains largely unknown. Further, it is unclear if and how tissue-specific PRL and PRLR vary between the sexes during biparental care. To address this, we measured PRL and PRLR gene expression in tissues relevant to parental care, the endocrine reproductive hypothalamic-pituitary-gonadal (HPG) axis and the crop (a tissue with a similar function as the mammalian mammary gland), across various reproductive stages in both sexes of a biparental bird, the rock dove (Columba livia). We also assessed how these genes responded to changes in offspring presence by adding chicks mid-incubation, simulating an early hatch when prolactin levels were still moderately low. We found that pituitary PRL expression showed similar increases as plasma prolactin levels, and detected extra-pituitary PRL in the hypothalamus, gonads and crop. Hypothalamic and gonadal PRLR expression also changed as birds began incubation. Crop PRLR expression correlated with plasma prolactin, peaking when chicks hatched. In response to replacing eggs with a novel chick mid-incubation, hypothalamic and gonadal PRL and PRLR gene expression differed significantly compared to mid-incubation controls, even when plasma prolactin levels did not differ. We also found sex differences in PRL and PRLR that suggest gene expression may allow males to compensate for lower levels in prolactin by upregulating PRLR in all tissues. Overall, this study advances our understanding of how tissue-specific changes in responsiveness to parental hormones may differ across key reproductive transitions, in response to offspring cues, and between the sexes.

animal behavior and cognition↗

bioRxiv2020

Isolating the role of corticosterone in the hypothalamic-pituitary-gonadal genomic stress response

The negative impacts of stress on reproduction have long been studied. A large focus of investigation has centered around the effects of the adrenal steroid hormone corticosterone (CORT) on a system of tissues vital for reproduction, the hypothalamus of the brain, the pituitary gland, and the gonads (the HPG axis). Investigations of the role of CORT on the HPG axis have predominated the stress and reproductive biology literature, potentially overshadowing other influential mediators. To gain a more complete understanding of how elevated CORT, characteristic of the stress response, affects the activity of the HPG axis, we experimentally examined its role at the level of the genome in both male and female rock doves (Columba livia). We exogenously administrated CORT to mimic circulating levels during the stress response, specifically 30 min of restraint stress, an experimental paradigm known to increase circulating corticosterone in vertebrates. We examined all changes in genomic transcription within the HPG axis as compared to both restraint-stressed birds and vehicle-injected controls, as well as between the sexes. We report causal and sex-specific effects of CORT on the HPG stress response at the level of the transcriptome. Restraint stress caused 1567 genes to uniquely differentially express while elevated circulating CORT was responsible for the differential expression of 304 genes. Only 108 genes in females and 8 in males differentially expressed in subjects who underwent restraint stress and those who were given exogenous CORT. In response to CORT elevation characteristic of the stress response, both sexes shared the differential expression of 5 genes, KCNJ5, CISH, PTGER3, CEBPD, and ZBTB16, all located in the pituitary. The known functions of these genes suggest potential influence of elevated CORT on immune function and prolactin synthesis. Gene expression unique to each sex indicated that elevated CORT affected more gene transcription in females than males (78 genes versus 3 genes, respectively). To our knowledge, this is the first study to isolate the role of CORT in HPG genomic transcription during a stress response. These results provide novel targets for new lines of further investigation and therapy development. We present an extensive and openly accessible view of the role corticosterone in the HPG genomic stress response, offering novel gene targets to inspire new lines of investigation of stress-induced reproductive dysfunction. Because the HPG system is well-conserved across vertebrates, these data have the potential to inspire new therapeutic strategies for reproductive dysregulation in multiple vertebrate systems, including our own.

physiology↗