Human plasma contains cortisol (F) and corticosterone (B) at a ratio of ~10:1. B is well studied in mice and rats, which do not produce F due to absent adrenal Cyp17, but is largely neglected in humans. Differential transmembrane export of F > B by ABCB1 may account for accumulation of B in the CNS. Conversely, ABCC1, expressed in human adipose tissue, preferentially exports B>F. Here we tested the hypotheses that: (i) negative feedback suppression of the hypothalamic-pituitary-adrenal (HPA) axis is disproportionately sensitive to B; (ii) adipose tissue is disproportionately sensitive to F; and (iii) low plasma B contributes to impaired HPA axis negative feedback and increased F action in metabolic syndrome. We validated a stable isotope tracer for B in vitro and demonstrated distinct kinetics of B and F in vivo. In a randomised crossover study, we undertook ramped steady state infusion of B or F in 10 patients with Addison’s disease. Although levels of B were marginally lower than F, ACTH was similarly suppressed, and yet glucocorticoid-responsive transcripts in adipose tissue were much higher following F than B (PER1 2.2-fold and LPL 1.3-fold; p < 0.05). We assessed associations of ACTH-stimulated plasma B and F with features of metabolic syndrome in a cross-sectional study (n=279). Glucose tolerance was impaired with higher F (β=0.146, p=0.01) but lower B (β = -0.056, p = 0.05). These data support the concept of differential tissue sensitivity to B and F, whereby B suppresses the HPA axis more effectively than it induces adverse effects in adipose tissue. Enhanced CYP17 activity, causing ‘relative B deficiency’, may contribute to HPA axis activation and enhanced F action in adipose tissue in obesity. B therapy might allow control of HPA axis activation without inducing adverse metabolic effects. The ‘neglected second glucocorticoid’, corticosterone, may optimise glucocorticoid action in the human CNS, and simultaneously limit adverse metabolic effects driven by cortisol excess.

The mechanism of steroid transport and corticosterone secretion in the zona fasciculata-reticularis of rat adrenal cortex was investigated by measuring the subcellular distribution and concentrations of steroids following ACTH stimulation.

No description available.

Depression is a complex psychiatric illness that affects a large proportion of the population. Many researchers make use of preclinical animal models to study the behavioural and neurobiological characteristics of this disease. However, although a bias towards maladaptive thinking patterns and emotional responses is a cardinal symptom of depression, these symptoms have been rarely considered in preclinical models. One way to investigate maladaptive thinking is through the use of fear conditioning paradigms. Fear conditioning evaluates emotional memory by assessing a rodent’s ability to associate neutral cues with an aversive experience. It requires the activation of brain structures critically involved in emotion-related learning and memory processes, most notably the hippocampus and amygdala, to successfully learn the task. The primary goal of this dissertation was to gain a better understanding of the consequences of repeated corticosterone injections—a validated preclinical model of depression-- on emotionally driven behaviour, the involvement of the hippocampus and amygdala in mediating these behaviours, and whether the antidepressant, fluoxetine, can prevent the effects of corticosterone on these behaviours. To begin, in Chapter 2 I confirmed that the depressogenic effects of corticosterone in the forced swim test, which is a traditional behavioural assay for depression in rodents, are not due to procedural differences or non-specific motor effects. I then investigated the impact of repeated corticosterone injections on the learning and memory of delay and contextual fear conditioning. I examined whether altering the order in which rats recall context versus tone cued fear associations determines the magnitude of corticosterone’s effect on conditioned fear. I found that corticosterone dose-dependently increased freezing to contextual cues whereas freezing to tone cues was increased regardless of dose. Furthermore, the order of the presentation of context versus tone cues during recall determined whether corticosterone produced significant enhancements in freezing. In Chapter 4, I investigated whether neuronal activity in the hippocampus and amygdala after recall of contextual or tone cued fear was associated with the effects of corticosterone found in Chapter 3. Recall of contextual cues was associated with neuronal activity in specific sub regions of the amygdala without any observed changes in the hippocampus. In Chapter 5, I investigated whether repeated corticosterone injections would also enhance the learning and memory of trace fear conditioning, a task that is heavily reliant on the hippocampus. I found that corticosterone increased freezing during recall of trace cues and enhanced the acquisition of trace cues. The results from this chapter, taken together with the results from chapters 3 and 4, suggest that repeated corticosterone exposure readily enhances learning and memory processes that evoke emotional arousal. In Chapter 6, I asked whether repeated treatment with the antidepressant, fluoxetine, could prevent increased fear learning produced by repeated corticosterone injections. I found that fluoxetine decreased freezing behaviour in corticosterone rats during recall of tone cues. Overall, the results of this dissertation further our understanding of the effects of corticosterone on learning and memory tasks that evoke emotional arousal, support the use of fear conditioning as a measure of depression-like behaviour, and demonstrate that repeated corticosterone injections reliably produce a depressive phenotype in rats.

The main objectives of the current study were to obtain the complete cDNA sequence of an opioid-like receptor from an amphibian, the roughskin newt, Taricha granulosa, and investigate the receptor's tissue distribution and regulation following chronic exposure to the glucocorticoid corticosterone (CORT). Degenerate primers designed in highly conserved regions of characterized opioid receptors were used to amplify opioid-like receptor fragments from a newt brain cDNA library. Receptor fragments with high sequence identity to the orphanin opioid receptor type, also termed the 'opioid receptor-like' (ORL1) receptor, were selected for 3' and 5' RACE (rapid amplification of cDNA ends) reactions to obtain the full-length receptor cDNA sequence. By this approach, we obtained a cDNA sequence that putatively encodes a 368 amino acid protein with high sequence identity (57%) to the human ORL1 receptor. Therefore, hereafter we refer to this receptor as the newt ORL1-like (nORL) receptor. The nORL receptor also has identity with the mammalian kappa (K) opioid receptor at a number of residues that may enable it to recognize both ORL1- and K- receptor selective ligands. The tissue distribution of the nORL receptor was determined by reverse-transcriptase polymerase chain reaction (PCR). RNA from a variety of tissues was reverse-transcribed into cDNA using an oligo-dT primer, and the resultant cDNA was used as template in PCR reactions with nORL receptor-specific primers. Appropriately sized amplicons were produced in reactions with cDNA template originating from newt brain, spinal cord, and lungs. No amplification occurred in reactions with template cDNA from newt spleen, small intestine, heart, liver, sperm duct, bladder, or kidney. The regulation of the nORL receptor following chronic exposure to the glucocorticoid corticosterone was investigated using real-time PCR. Animals were exposed continuously to CORT for 10 days using surgically implanted Silastic capsules packed with CORT powder. Control animals received empty Silastic capsules, or no treatment. The relative quantitation of the nORL receptor messenger RNA (mRNA) was achieved by real-time PCR, and mRNA levels for the hormone-treated animals were compared to those of the controls. The same samples were used for the relative quantitation of intracellular glucocorticoid receptor (iGR) mRNA. There was no change in the expression of mRNA for the nORL receptor or the iGR following chronic exposure to CORT as compared to the controls. In conclusion, this study provides evidence for an opioid-like receptor in the roughskin newt that has high sequence identity to the mammalian ORL1 opioid receptor. To the best of our knowledge, this is the first complete opioid receptor cDNA sequence obtained for an amphibian. The nORL receptor appears to principally function in central nervous system (CNS) processes in the newt, as evidenced by its primary localization to brain and spinal cord. The role of the nORL receptor in the periphery may be limited to a function in the lungs, and awaits further investigation. The current study was also the first to investigate the effects of a stress hormone on the regulation of an opioid receptor in an amphibian. Our results indicate that chronic exposure to the stress hormone corticosterone does not impact the levels of nORL receptor or intracellular glucocorticoid receptor mRNA in the newt spinal cord. / Graduation date: 2003

In the wild, when an animal is exposed to predators or harsh conditions, the stress response is often associated with fleeing behaviors, which are seen as increased locomotor behavior. Handling-stress procedures and intracerebroventricular (icy) injection of corticotropin-releasing factor (CRF) have both been shown to cause an increase in locomotor activity in roughskin newts (Taricha granulosa). The present experiments were designed to determine if icv administration of corticosterone (CORT) prevents stress-induced locomotor increases in activity, if it prevents CRF-induced increases in locomotor activity, and if the time-course and pharmacological specificity of the CORT effects on locomotor activity fit the model for intracellular or membrane receptors. In experiment 1, newts which had been injected with CORT or dexamethasone (DEX) received a standardized handling-stress procedure. Corticosterone administration was able to suppress the increase in locomotor activity in newts exposed to handling-stress at 20 minutes after administration. This effect was transient (no longer present at 2 hours after the injection) and not mimicked by DEX, a synthetic glucocorticoid that binds to intracellular and not membrane receptors. In experiments 2 and 3, either CORT or DEX was administered in the same icy injection with CRF. CORT suppressed CRF-induced locomotor activity in some cases, but this action of CORT seems to be context dependent. Results for DEX-injected newts were confounded the failure of CRF to induced significant increases in locomotor activity. There was variability in the effect of CRF on locomotor activity across seasons. Based on time-course and specificity, it appears that CORT can modulate locomotor activity in newts through mechanisms involving the membrane receptor. Variability in the effects of CRF on locomotor activity in newts suggests there may be seasonal differences in responses to stress. / Graduation date: 1998

Pheromones are chemosensory cues released by an individual to cause a behavioral or physiological change in a conspecific. These changes can range from increasing a female's receptivity to altering hormone secretions in the body. The red-legged salamander (Plethodon shermani) is an emerging non-mammalian model for understanding the evolution of chemical communication due to their well-characterized pheromones. Plethodontid salamanders secrete pheromones from their submandibular gland, called mental gland pheromones. Previous studies showed that mental gland pheromones increased receptivity in females during courtship and also increased corticosterone (CORT) concentrations in males. CORT is a metabolic hormone that mediates vertebrate stress responses. To further understand the neuroendocrine mechanisms involved in behavioral and physiological responses to pheromones, I conducted several experiments. First, I investigated whether pheromones altered levels of two neuromodulators in the brain, gonadotropin-releasing hormone (GnRH) and arginine vasotocin (AVT) in P. shermani. GnRH is both a neuromodulator and hormone, and has strong effects on reproductive behavior. Additionally, AVT has broad behavioral effects in vertebrates, particularly in newts. I found that application of mental gland pheromones altered the number of GnRH-immunoreactive neurons, but had no effect on the number of AVT-immunoreactive neurons. Second, I examined the effects of AVT and AVP antagonist on courtship and mating in dusky salamanders (Desmognathus spp.). There was no effect of AVT or antagonist on reproductive behaviors in dusky salamanders. Finally, I investigated the role of increased CORT concentrations in male P. shermani. I first validated a non-invasive method to transdermally deliver CORT through a dermal patch. I then used dermal patches to exogenously elevate plasma CORT and examine the effects of CORT on behavior (activity and chemoinvestigation) and metabolism. CORT had no effect on behavior, but increased metabolic rates in male red-legged salamanders. Together these studies provide insight into the mechanisms by which pheromones work to alter behaviors and physiological functions in vertebrates. / Bayer School of Natural and Environmental Sciences; / Biological Sciences / PhD; / Dissertation;

During surgery, both anesthesia and tissue damage cause physiological stress responses in the body. The hypothalamic-pituitary-adrenal (HPA) axis is activated with increased levels of glucocorticoids. After surgical procedures the stress response may be a cause of postoperative morbidity and pre-emptive analgesic treatment can attenuate the stress response during the postoperative period. In laboratory animals, buprenorphine is a commonly used analgesic. Subcutaneous (s.c.) administration of buprenorphine is most common, but oral administration would be preferable in many cases, enabling administration without any handling of the rat. In this thesis we studied the surgical stress response in laboratory rats during surgery and in the postoperative period, and its modulation by s.c. injection and oral voluntary ingestion (VI) of buprenorphine. Corticosterone levels and the clinical parameters body weight, water intake and behavior were observed. The concentration of buprenorphine in plasma was measured as well as stock-related differences in postoperative recovery. During surgery and anesthesia there was a higher corticosterone release during a more severe surgery and corticosterone levels were reduced more effectively after buprenorphine treatment than after lidocaine treatment. Buprenorphine treatment, independent of the route of administration, led to better postoperative recovery in body weight and water intake compared to local anesthetics. VI of buprenorphine resulted in a suppression of plasma corticosterone levels compared to s.c. buprenorphine treatment and treatment with local anesthetics during the first day after surgical catheterization. The corticosterone levels of all buprenorphine treated groups had, by the second postoperative day, reverted to the normal diurnal rhythm of corticosterone secretion. Buprenorphine treatment increased locomotor activity in non-operated rats only. The effect of buprenorphine in operated rats could not be detected via the monitoring of locomotor activity or the time spent resting in the present study. Treatment with buprenorphine by VI has similar effects on postoperative plasma corticosterone levels in both Wistar and Sprague-Dawley rats. VI of buprenorphine resulted in a buprenorphine concentration in plasma at least as high as by s.c. treatment. Thus, administration by VI of buprenorphine appears to be an effective stress-reducing method for administrating postoperative analgesia to laboratory rats.

Both chronic psychosocial stress and chronic administration of corticosterone have been shown to alter serotonergic type 2A (5-HT2A) receptor activity. A non-invasive behavioural index of 5-HT2A receptor activity is the frequency of "wet dog shakes" (WDS) or serotonergic stereotypy. In addition to WDS, 5-HT2A receptors mediate effects on sexual behaviour in the rat, in particular, inhibition in the male and stimulation in the female. In the present series of experiments, the potential involvement of stress and corticosterone in the regulation of WDS and sexual behaviour in the male and female rat was investigated. In Experiments 1-4, chronic exposure to several different forms of psychosocial stress was found to facilitate female and inhibit male rat sexual behaviour while concurrently increasing the display of WDS in both sexes. In Experiment 5, nefazodone, an antidepressant with 5-HT2A antagonistic properties, blocked the effects of stress on WDS but not sexual behaviour in female rats. In Experiments 6-7, the corticosterone synthesis inhibitor, metyrapone, blocked the effects of stress on sexual proceptivity and WDS in female rats. Metyrapone blocked the effects of stress on WDS but not sexual behaviour in male rats. In Experiments 8-9, high doses of corticosterone administered chronically facilitated female and inhibited male rat sexual behaviour while concurrently increasing WDS in both sexes. In Experiments 10-11, the 5-HT2A antagonist ketanserin was found to completely attenuate the effects of corticosterone on sexual behaviour and WDS in both male and female rats. In Experiments 12-13, the acute administration of corticosterone was found to exert no effect on either sexual behaviour or WDS in male or female rats. The present results indicate that both chronic corticosterone treatment and exposure to chronic stress inhibit male and facilitate female sexual behaviour while concurrently increasing WDS behaviour. The stress-induced facilitation of WDS appears to be related to elevated corticosterone levels and is suggestive of increased 5-HT2A activity. Both corticosterone and stress exerted effects on sexual behaviour in the direction that would be predicted by increased 5-HT2A activity. While the effects of corticosterone on sexual behaviour appear to be mediated by 5-HT2A activity, the effects of stress on sexual behaviour do not appear to be related to either elevations in corticosterone levels or alterations in 5-HT2A activity.

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Psychology, Behavioral Neuroscience, 2008. / Includes bibliographical references.