(2R,6R)-hydroxynorketamine (HNK) reverses mechanical hypersensitivity in a model of localized inflammatory pain

The ketamine metabolite (2R,6R)-hydroxynorketamine, or (2R,6R)-HNK, was recently reported to evoke antinociception in response to a noxious thermal stimulus in healthy mice and reverse mechanical hypersensitivity in a murine model of neuropathic pain. This study reports the behavioral effects of (2R,6R)-HNK in male and female C57BL/6J mice exposed to a localized inflammatory pain condition and the broad pharmacological mechanism underlying this effect. Hind paw intraplantar injection of λ-carrageenan (CARR) caused inflammation and mechanical hypersensitivity in mice within 2 hours, lasting at least 48 hours. Intraperitoneal administration of (2R,6R)-HNK (10-30 mg/kg i.p.) 2 hours following CARR injection significantly reversed mechanical hypersensitivity within 1 hour in male and female mice, and the effect persisted for 24 hours following a single dose. The magnitude and timing of the analgesic effect of (2R,6R)-HNK were comparable to the non-steroidal anti-inflammatory drug carprofen. The reversal of hypersensitivity by (2R,6R)-HNK was blocked at 4 and 24 hours after administration by pretreatment with the AMPA receptor antagonist NBQX and was not accompanied by changes in locomotor activity. These findings reinforce the growing evidence supporting (2R,6R)-HNK as a novel analgesic in multiple preclinical pain models and further support an AMPAR-dependent mechanism of action. SIGNIFICANCE: The ketamine metabolite (2R,6R)-HNK reversed mechanical hypersensitivity associated with localized inflammation with onset less than one hour and duration greater than 24 hours in an effect comparable to the NSAID carprofen. Reversal of mechanical hypersensitivity by (2R,6R)-HNK is AMPAR-dependent.

Antinociceptive and Analgesic Effects of (2R,6R)-Hydroxynorketamine

Commonly used pain therapeutics, such as opioid medications, exert dangerous side effects and lack effectiveness in treating some types of pain. Ketamine is also used to treat pain, but side effects limit its widespread use. (2R,6R)-hydroxynorketamine (HNK) is a ketamine metabolite that potentially shares some beneficial behavioral effects of its parent drug without causing significant side effects. This study compared the profile and potential mechanisms mediating the antinociception activity of ketamine and (2R,6R)-HNK in C57BL/6J mice. Additionally, this study compared the reversal of mechanical allodynia by (2R,6R)-HNK with gabapentin in a model of neuropathic pain. Unlike the near-immediate and short-lived antinociception caused by ketamine, (2R,6R)-HNK produced late-developing antinociception 24 hours following administration. Pharmacological blockade of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors with 2,3-dioxo-6-nitro-7-sulfamoyl-benzo[f]quinoxaline (NBQX) prevented the initiation and expressionof (2R,6R)-HNK antinociception, suggesting the involvement of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor-dependent glutamatergic mechanisms in the pain reduction-like responses. Blockade of opioid receptors with naltrexone partially prevented the antinociceptive effect of ketamine but was ineffective against (2R,6R)-HNK. Furthermore, (2R,6R)-HNK did not produce dystaxia, even when tested at doses five times greater than those needed to produce antinociception, indicating a superior safety profile for (2R,6R)-HNK over ketamine. Additionally, (2R,6R)-HNK reversed mechanical allodynia in a spared nerve injury model of neuropathic pain with similar short-term efficacy to gabapentin (within 4 hours) while outperforming gabapentin 24 hours after administration. These findings support the further study of (2R,6R)-HNK as a potentially valuable agent for treating different types of pain and establish certain advantages of (2R,6R)-HNK treatment over ketamine and gabapentin in corresponding assays for pain. SIGNIFICANCE STATEMENT: The ketamine metabolite (2R,6R)-HNK produced antinociception in male and female mice 24 hours after administration via activation of AMPA receptors. The effects of (2R,6R)-HNK differed in time course and mechanism and presented a better safety profile than ketamine. (2R,6R)-HNK also reversed allodynia in SNI-operated animals within 4 hours of treatment onset, with a duration of effect lasting longer than gabapentin. Taken together, (2R,6R)-HNK demonstrates the potential for development as a non-opioid analgesic drug.

Distinct post-sepsis induced neurochemical alterations in two mouse strains

Sepsis associated encephalopathy, occurs in 70% of severe septic cases, following which survivors exhibit long-term cognitive impairment or global loss of cognitive function. Currently there is no clearly defined neurochemical basis of septic encephalopathy. Moreover, the lingering neurological complications associated with the severe acute respiratory syndrome CoV 2 (SARS-CoV-2) and the significant worsening in outcomes for those individuals with SARS-Cov-2 following sepsis underscore the need to define factors underlying the susceptibility to acute toxic encephalitis. In this study, differential neurochemical sequelae in response to sepsis (lipopolysaccharide (LPS)-induced endotoxemia and caecal ligation and puncture (CLP)), were evaluated in two inbred mouse strains, known to differ in behaviour, immune profile, and neurotransmitter levels, namely BALB/c and C57BL/6J. It was hypothesized that these strains would differ in sepsis severity, cytokine profile, peripheral tryptophan metabolism and central monoamine turnover. BALB/c mice exhibited more pronounced sickness behavioural scores, hypothermia, and significant upregulation of cytokines in the LPS model relative to C57BL/6J mice. Increased plasma kynurenine/tryptophan ratio, hippocampal serotonin and brainstem dopamine turnover were evident in both strains, but the magnitude was greater in BALB/c mice. In addition, CLP significantly enhanced kynurenine levels and hippocampal serotonergic and dopaminergic neurotransmission in C57BL/6J mice. Overall, these studies depict consistent changes in kynurenine, serotonin, and dopamine post sepsis. Further evaluation of these monoamines in the context of septic encephalopathy and cognitive decline is warranted. Moreover, these data suggest the continued evaluation of altered peripheral kynurenine metabolism as a potential blood-based biomarker of sepsis.

Mediation of the behavioral effects of ketamine and (2R,6R)-hydroxynorketamine in mice by kappa opioid receptors

Emerging evidence has implicated the endogenous opioid system in mediating ketamine's antidepressant activity in subjects with major depressive disorder. To date, mu opioid receptors have been suggested as the primary opioid receptor of interest. However, this hypothesis relies primarily on observations that the opioid antagonist naltrexone blocked the effects of ketamine in humans and rodents. This report confirms previous findings that pretreatment with naltrexone (1 mg/kg) just prior to ketamine (10 mg/kg) administration effectively blocks the behavioral effect of ketamine in the mouse forced swim test 24 h post-treatment. Furthermore, pharmacological blockade of kappa opioid receptors prior to ketamine administration with the selective, short-acting antagonist LY2444296 successfully blocked ketamine's effects in the forced swim test. Likewise, the ability of the ketamine metabolite (2R,6R)-hydroxynorketamine to reduce immobility scores in the forced swim test was also blocked following pretreatment with either naltrexone or LY2444296. These data support a potential role of kappa opioid receptors in mediating the behavioral activity of ketamine and its non-dissociate metabolite (2R,6R)-hydroxynorketamine.

Buprenorphine as a Treatment for Major Depression and Opioid Use Disorder

Rates of major depressive disorder (MDD) are disproportionally high in subjects with opioid use disorder (OUD) relative to the general population. MDD is often more severe in OUD patients, leading to compliance issues with maintenance therapies and poor outcomes. A growing body of literature suggests that endogenous opioid system dysregulation may play a role in the emergence of MDD. Buprenorphine, a mixed opioid receptor agonist/antagonist approved for the treatment of OUD and chronic pain, may have potential as a novel therapeutic for MDD, especially for patients with a dual diagnosis of MDD and OUD. This paper presents a comprehensive review of papers relevant to the assessment of buprenorphine as a treatment for MDD, OUD, and/or suicide compiled using electronic databases per Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The principal goal of this literature review was to compile the clinical studies that have interrogated the antidepressant activity of buprenorphine in opioid naïve MDD patients and OUD patients with comorbid MDD. Evidence supporting buprenorphine's superiority over methadone for treating comorbid OUD and MDD was also considered. Finally, recent evidence for the ability of buprenorphine to alleviate suicidal ideation in both opioid-naïve patients and opioid-experienced patients was evaluated. Synthesizing all of this information, buprenorphine emerges as a potentially effective therapeutic for the dual purposes of treating MDD and OUD.

Long-term increase in sensitivity to ketamine's behavioral effects in mice exposed to mild blast induced traumatic brain injury

Neurobehavioral deficits emerge in nearly 50% of patients following a mild traumatic brain injury (TBI) and may persist for months. Ketamine is used frequently as an anesthetic, analgesic and for management of persistent psychiatric complications. Although ketamine may produce beneficial effects in patients with a history of TBI, differential sensitivity to its impairing effects could make the therapeutic use of ketamine in TBI patients unsafe. This series of studies examined male C57BL/6 J mice exposed to a mild single blast overpressure (mbTBI) for indications of altered sensitivity to ketamine at varying times after injury. Dystaxia (altered gait), diminished sensorimotor gating (reduced prepulse inhibition) impaired working memory (step-down inhibitory avoidance) were examined in mbTBI and sham animals 15 min following intraperitoneal injections of saline or R,S-ketamine hydrochloride, from day 7-16 post injury and again from day 35-43 post injury. Behavioral performance in the forced swim test and sucrose preference test were evaluated on day 28 and day 74 post injury respectively, 24 h following drug administration. Dynamic gait stability was compromised in mbTBI mice on day 7 and 35 post injury and further exacerbated following ketamine administration. On day 14 and 42 post injury, prepulse inhibition was robustly decreased by mbTBI, which ketamine further reduced. Ketamine-associated memory impairment was apparent selectively in mbTBI animals 1 h, 24 h and day 28 post shock (tested on day 15/16/43 post injury). Ketamine selectively reduced immobility scores in the FST in mbTBI animals (day 28) and reversed mbTBI induced decreases in sucrose consumption (Day 74). These results demonstrate increased sensitivity to ketamine in mice when tested for extended periods after TBI. The results suggest that ketamine may be effective for treating neuropsychiatric complications that emerge after TBI but urge caution when used in clinical practice for enhanced sensitivity to its side effects in this patient population.

Translational relevance of fear conditioning in rodent models of mild traumatic brain injury

Mild traumatic brain injury (mTBI) increases the risk of posttraumatic stress disorder (PTSD) in military populations. Utilizing translationally relevant animal models is imperative for establishing a platform to delineate neurobehavioral deficits common to clinical PTSD that emerge in the months to years following mTBI. Such platforms are required to facilitate preclinical development of novel therapeutics. First, this mini review provides an overview of the incidence of PTSD following mTBI in military service members. Secondly, the translational relevance of fear conditioning paradigms used in conjunction with mTBI in preclinical studies is evaluated. Next, this review addresses an important gap in the current preclinical literature; while incubation of fear has been studied in other areas of research, there are relatively few studies pertaining to the enhancement of cued and contextual fear memory over time following mTBI. Incubation of fear paradigms in conjunction with mTBI are proposed as a novel behavioral approach to advance this critical area of research. Lastly, this review discusses potential neurobiological substrates implicated in altered fear memory post mTBI.

Sex differences in the modulation of mouse nest building behavior by kappa opioid receptor signaling

Emerging evidence suggests that females are less sensitive than males to the effects of kappa opioid receptor (KOR) ligands across multiple behavioral measures. The effects of the KOR agonist U50,488 and the KOR antagonist aticaprant were assessed on nest building behavior, an ethologically relevant indicator of overall well-being and affect, in adult male and female C57BL/6J mice. Females required a higher dose of U50,488 to suppress nesting, and a higher dose of aticaprant to restore U50,488-induced impairment of nesting. Females also required a higher dose of aticaprant to decrease immobility scores in the forced swim test. Pretreatment with the estrogen receptor modulator tamoxifen, at a dose which blocked estrogen receptors, augmented the effect of U50,488 on nesting in female mice, suggesting that estrogen receptors play a key role in attenuating the effects of KOR ligands in female mice. Together, these results suggest that females are less sensitive to KOR mediation, requiring a higher dose to achieve comparable results to males. This behavioral sensitivity, as measured by nesting, may be mediated by estrogen receptors. Together these studies highlight the importance of comparing sex differences in response to KOR regulation on behaviors related to affective states.

Behavioral effects of the kappa opioid receptor partial agonist nalmefene in tests relevant to depression

Compounds with high affinity at kappa and mu opioid receptors may have clinical utility in treating major depressive disorder. Nalmefene (NMF) is a partial kappa opioid receptor agonist and potent mu opioid receptor antagonist, but there has been no preclinical evaluation of NMF in rodent tests relevant to depression and anxiety. To address this, the effects of NMF on neurochemical and behavioral endpoints in C57BL/6J mice were examined and contrasted with a structurally related analog, naltrexone (NTX). NMF exhibited kappa opioid receptor agonist activity, measured as a reduction in extracellular dopamine release in the nucleus accumbens using in vivo microdialysis following acute but not chronic administration. In the mouse forced swim test, female mice were more responsive to higher doses of NMF and NTX compared to male mice. The behavioral effects of NMF in the forced swim test were blocked in Oprk1^-/- and Oprm1^-/- mice. Conversely, the effects of NTX were blocked only in Oprm1^-/- mice. These results indicate that both kappa and mu opioid receptors mediate the behavioral effects of NMF, but the effects of NTX in this test were modified only by mu opioid receptor engagement. Unlike NTX, NMF did not produce conditioned place aversion in either sex. Finally, NMF's activity in the marble burying test and forced swim test were retained following chronic administration. The sustained effects exerted by NMF on tests that are sensitive to antidepressant and anxiolytic compounds support further investigation of NMF as a potential therapeutic for depression.

Kappa Opioid Receptor Antagonists as Potential Therapeutics for Stress-Related Disorders

Exposure to stressful stimuli activates kappa opioid receptor (KOR) signaling, a process known to produce aversion and dysphoria in humans and other species. This endogenous opioid system is dysregulated in stress-related disorders, specifically in major depressive disorder (MDD). These findings serve as the foundation for a growing interest in the therapeutic potential of KOR antagonists as novel antidepressants. In this review, data supporting the hypothesis of dysregulated KOR function in MDD are considered. The clinical data demonstrating the therapeutic efficacy and safety of selective and mixed opioid antagonists are then presented. Finally, the preclinical evidence illustrating the induction of behaviors relevant to the endophenotypes of MDD and KOR antagonist activity in stress-naïve and stress-exposed animals is evaluated. Overall, this review highlights the emergent literature supporting the pursuit of KOR antagonists as novel therapeutics for MDD and other stress-related disorders.

Targeting opioid dysregulation in depression for the development of novel therapeutics

Since the serendipitous discovery of the first class of modern antidepressants in the 1950's, all pharmacotherapies approved by the Food and Drug Administration for major depressive disorder (MDD) have shared a common mechanism of action, increased monoaminergic neurotransmission. Despite the widespread availability of antidepressants, as many as 50% of depressed patients are resistant to these conventional therapies. The significant length of time required to produce meaningful symptom relief with these medications, 4-6 weeks, indicates that other mechanisms are likely involved in the pathophysiology of depression which may yield more viable targets for drug development. For decades, no viable candidate target with a different mechanism of action to that of conventional therapies proved successful in clinical studies. Now several exciting avenues for drug development are under intense investigation. One of these emerging targets is modulation of endogenous opioid tone. This review will evaluate preclinical and clinical evidence pertaining to opioid dysregulation in depression, focusing on the role of the endogenous ligands endorphin, enkephalin, dynorphin, and nociceptin/orphanin FQ (N/OFQ) and their respective receptors, mu (MOR), delta (DOR), kappa (KOR), and the N/OFQ receptor (NOP) in mediating behaviors relevant to depression and anxiety. Finally, putative opioid based antidepressants that are under investigation in clinical trials, ALKS5461, JNJ-67953964 (formerly LY2456302 and CERC-501) and BTRX-246040 (formerly LY-2940094) will be discussed. This review will illustrate the potential therapeutic value of targeting opioid dysregulation in developing novel therapies for MDD.

Dysregulation of the Lateral Habenula in Major Depressive Disorder

Clinical and preclinical evidence implicates hyperexcitability of the lateral habenula (LHb) in the development of psychiatric disorders including major depressive disorder (MDD). This discrete epithalamic nucleus acts as a relay hub linking forebrain limbic structures with midbrain aminergic centers. Central to reward processing, learning and goal directed behavior, the LHb has emerged as a critical regulator of the behaviors that are impaired in depression. Stress-induced activation of the LHb produces depressive- and anxiety-like behaviors, anhedonia and aversion in preclinical studies. Moreover, deep brain stimulation of the LHb in humans has been shown to alleviate chronic unremitting depression in treatment resistant depression. The diverse neurochemical processes arising in the LHb that underscore the emergence and treatment of MDD are considered in this review, including recent optogenetic studies that probe the anatomical connections of the LHb.

Ketamine Reverses Lateral Habenula Neuronal Dysfunction and Behavioral Immobility in the Forced Swim Test Following Maternal Deprivation in Late Adolescent Rats

Mounting evidence suggests that the long-term effects of adverse early life stressors on vulnerability to drug addiction and mood disorders are related to dysfunction of brain monoaminergic signaling in reward circuits. Recently, there has been a growing interest in the lateral habenula (LHb) as LHb dysfunction is linked to the development of mental health disorders through monoaminergic dysregulation within brain reward/motivational circuits and may represent a critical target for novel anti-depressants, such as ketamine. Here, we show that maternal deprivation (MD), a severe early life stressor, increases LHb intrinsic excitability and LHb bursting activity, and is associated with the development of increased immobility in the forced swim test (FST) in late-adolescent male rats. A single in vivo injection of ketamine is sufficient to exert prolonged antidepressant effects through reversal of this early life stress-induced LHb neuronal dysfunction and the response in the FST. Our assessment of ketamine’s long-lasting beneficial effects on reversal of MD-associated changes in LHb neuronal function and behavior highlights the critical role of the LHb in pathophysiology of depression associated with severe early life stress and in response to novel fast-acting antidepressants.

How do we facilitate international clinical placements for nursing students: A cross-sectional exploration of the structure, aims and objectives of placements

BACKGROUND

International clinical placements provide undergraduate students with a unique and complex clinical learning environment, to explore cultural awareness, experience different health care settings and achieve clinical competencies. Higher education institutions need to consider how to structure these placements to ensure appropriate and achievable aims and learning outcomes.

OBJECTIVES

In this study we described the structure, aims and learning outcomes associated with international clinical placement opportunities currently undertaken by Australian undergraduate nursing students in the Asia region.

PARTICIPANTS

Forty eight percent (n = 18) of the institutions invited responded. Eight institutions met the inclusion criteria, one of which offered three placements in the region, resulting in 10 international placements for which data were provided.

METHODS

An online survey tool was used to collect data during August and September 2015 on international clinical placements conducted by the participating universities. Descriptive data on type and numbers of placements is presented, along with results from the content analysis conducted to explore data from open ended questions on learning aims and outcomes.

RESULTS

One hundred students undertook 10 International Clinical Placements offered in the Asian region by eight universities. Variations across placements were found in the length of placement, the number of students participating, facilitator to student ratios and assessment techniques used. Five categories related to the aims of the programs were identified: 'becoming culturally aware through immersion', 'working with the community to promote health', 'understanding the role of nursing within the health care setting', 'translating theory into professional clinical practice', and 'developing relationships in international learning environments'. Four categories related to learning outcomes were identified: 'understanding healthcare and determinants of health', 'managing challenges', 'understanding the role of culture within healthcare' and 'demonstrating professional knowledge, skills and behaviour'.

CONCLUSIONS

International clinical placements in the Asia region appear to vary greatly from one education institution to the next with no clear consensus from either this study's findings or the literature on which structure, support and assessments lead to greater student learning.

A role for corticotropin-releasing factor signaling in the lateral habenula and its modulation by early-life stress

Centrally released corticotropin-releasing factor or hormone (extrahypothalamic CRF or CRH) in the brain is involved in the behavioral and emotional responses to stress. The lateral habenula (LHb) is an epithalamic brain region involved in value-based decision-making and stress evasion. Through its inhibition of dopamine-mediated reward circuitry, the increased activity of the LHb is associated with addiction, depression, schizophrenia, and behavioral disorders. We found that extrahypothalamic CRF neurotransmission increased neuronal excitability in the LHb. Through its receptor CRFR1 and subsequently protein kinase A (PKA), CRF application increased the intrinsic excitability of LHb neurons by affecting changes in small-conductance SK-type and large-conductance BK-type K⁺ channels. CRF also reduced inhibitory γ-aminobutyric acid-containing (GABAergic) synaptic transmission onto LHb neurons through endocannabinoid-mediated retrograde signaling. Maternal deprivation is a severe early-life stress that alters CRF neural circuitry and is likewise associated with abnormal mental health later in life. LHb neurons from pups deprived of maternal care exhibited increased intrinsic excitability, reduced GABAergic transmission, decreased abundance of SK2 channel protein, and increased activity of PKA, without any substantial changes in Crh or Crhr1 expression. Furthermore, maternal deprivation blunted the response of LHb neurons to subsequent, acute CRF exposure. Activating SK channels or inhibiting postsynaptic PKA activity prevented the effects of both CRF and maternal deprivation on LHb intrinsic excitability, thus identifying potential pharmacological targets to reverse central CRF circuit dysregulation in patients with associated disorders.

Hair corticosterone measurement in mouse models of type 1 and type 2 diabetes mellitus

In diabetes, glucocorticoid secretion increases secondary to hyperglycemia and is associated with an extensive list of disease complications. Levels of cortisol in humans, or corticosterone in rodents, are usually measured as transitory biomarkers of stress in blood or saliva. Glucocorticoid concentrations accumulate in human or animal hair over weeks and could more accurately measure the cumulative stress burden of diseases like chronic diabetes. In this study, corticosterone levels were measured in hair in verified rodent models of diabetes mellitus. To induce type 1 diabetes, C57BL/6J mice were injected with streptozotocin and blood and hair samples were collected 28days following induction. Leptin receptor deficient (db/db) mice were used as a spontaneous model of type 2 diabetes and blood and hair samples were collected at 8weeks of age, after the development of hyperglycemia and obesity. Corticosterone levels from serum, new growth hair and total growth hair were analyzed using an enzyme immunoassay. Corticosterone levels in new growth hair and serum were significantly elevated in both models of diabetes compared to controls. In contrast, corticosterone levels in old hair growth did not differ significantly between diabetic and non-diabetic animals. Thus, hair removal and sampling of new hair growth was a more sensitive procedure for detecting changes in hair corticosterone levels induced by periods of hyperglycemia lasting for 4weeks in mice. These results validate the use of hair to measure long-term changes in corticosterone induced by diabetes in rodent models. Further studies are now needed to validate the utility of hair cortisol as a tool for measuring the stress burden of individuals with diabetes and for following the effects of long-term medical treatments.

Reversal of Stress-Induced Social Interaction Deficits by Buprenorphine

BACKGROUND

Patients with post-traumatic stress disorder frequently report persistent problems with social interactions, emerging after a traumatic experience. Chronic social defeat stress is a widely used rodent model of stress that produces robust and sustained social avoidance behavior. The avoidance of other rodents can be reversed by 28 days of treatment with selective serotonin reuptake inhibitors, the only pharmaceutical class approved by the U.S. Food and Drug Administration for treating post-traumatic stress disorder. In this study, the sensitivity of social interaction deficits evoked by 10 days of chronic social defeat stress to prospective treatments for post-traumatic stress disorder was examined.

METHODS

The effects of acute and repeated treatment with a low dose of buprenorphine (0.25 mg/kg/d) on social interaction deficits in male C57BL/6 mice by chronic social defeat stress were studied. Another cohort of mice was used to determine the effects of the selective serotonin reuptake inhibitor fluoxetine (10 mg/kg/d), the NMDA antagonist ketamine (10 mg/kg/d), and the selective kappa opioid receptor antagonist CERC-501 (1 mg/kg/d). Changes in mRNA expression of Oprm1 and Oprk1 were assessed in a separate cohort.

RESULTS

Buprenorphine significantly reversed social interaction deficits produced by chronic social defeat stress following 7 days of administration, but not after acute injection. Treatment with fluoxetine for 7 days, but not 24 hours, also reinstated social interaction behavior in mice that were susceptible to chronic social defeat. In contrast, CERC-501 and ketamine failed to reverse social avoidance. Gene expression analysis found: (1) Oprm1 mRNA expression was reduced in the hippocampus and increased in the frontal cortex of susceptible mice and (2) Oprk1 mRNA expression was reduced in the amygdala and increased in the frontal cortex of susceptible mice compared to non-stressed controls and stress-resilient mice.

CONCLUSIONS

Short-term treatment with buprenorphine and fluoxetine normalized social interaction after chronic social defeat stress. In concert with the changes in opioid receptor expression produced by chronic social defeat stress, we speculate that buprenorphine's efficacy in this model of post-traumatic stress disorder may be associated with the ability of this compound to engage multiple opioid receptors.

Genetic variation in the behavioral effects of buprenorphine in female mice derived from a murine model of the OPRM1 A118G polymorphism

Pharmacogenetic studies have identified the non-synonymous single nucleotide polymorphism (A118G) in the human mu opioid receptor (MOR) gene (OPRM1) as a critical genetic variant capable of altering the efficacy of opioid therapeutics. To date few studies have explored the potential impact of the OPRM1 A118G polymorphism on the pharmacological effects of buprenorphine (BPN), a potent MOR partial agonist and kappa opioid receptor antagonist, which is approved by the FDA for the treatment of opioid addiction and chronic pain. The goal of these studies was to determine whether the MOR-mediated behavioral effects of BPN were altered in the Oprm1 A112G mouse model of the human OPRM1 A118G SNP. All studies were conducted in female, AA, AG and GG mice. BPN's maximal analgesic effect in the hot plate test was significantly blunted in AG and GG mice compared to wild type AA mice. Similarly, the BPN-induced reduction of latency to consume food in the novelty induced hypophagia test was blocked entirely in AG and GG mice compared to their AA littermates. In addition, GG mice exhibited marked reductions in psychostimulant hyperlocomotor activity compared to the AA group. In contrast, reduced immobility in the forced swim test, an effect of BPN mediated by kappa opioid receptors, was not affected by genotype. These studies demonstrate the ability of the Oprm1 A112G SNP to attenuate the analgesic, anxiolytic and hyperlocomotor effects of BPN. Overall, these data suggest that the OPRM1 A118G SNP will significantly impact the clinical efficacy of BPN in its therapeutic applications.

International clinical placements for Australian undergraduate nursing students: A systematic thematic synthesis of the literature

OBJECTIVES

International clinical placements provide undergraduate nursing students with the opportunity to experience or practice nursing care in diverse countries, settings, and cultures. This systematic review aims to ascertain the current knowledge on international clinical placements offered by undergraduate nursing programs in Australia. It seeks to explore three questions: (1) How have previous experiences of nursing students' international clinical placements been described? (2) How have participants and stakeholders determined if the placement has been successful? And (3) What benefits or challenges have been identified by stakeholders as a result of participating in international clinical placements?

DESIGN

A systematic thematic synthesis was undertaken.

DATA SOURCES

A search of electronic databases including CINAHL, Proquest Central, Scopus, PubMed, and Health Collection was undertaken between September and October 2014.

REVIEW METHODS

Key terms including 'international clinical placement', 'study abroad', 'international exchange', 'nursing', and 'Australia' were used to identify articles that appeared in peer-reviewed English language journals and that explored international clinical placements offered to undergraduate nursing students by Australian universities.

RESULTS

Eight studies were identified that meet the inclusion criteria, and through thematic analysis, five key themes were identified including developing cultural awareness and competence, providing a global perspective on health care, translation of theory to practice, growing personally through reflection, and overcoming apprehension to successfully meet the challenge. A comparison search of literature from Canada and the United Kingdom revealed that similar themes occurred internationally.

CONCLUSIONS

Although personal successes were identified by students undertaking international clinical placement, further research is required to identify all stakeholder experiences including those of the educators, the educational institutions, and travel providers supporting these placements and the communities where the placements take place.

Effect of acute swim stress on plasma corticosterone and brain monoamine levels in bidirectionally selected DxH recombinant inbred mouse strains differing in fear recall and extinction

Stress-induced changes in plasma corticosterone and central monoamine levels were examined in mouse strains that differ in fear-related behaviors. Two DxH recombinant inbred mouse strains with a DBA/2J background, which were originally bred for a high (H-FSS) and low fear-sensitized acoustic startle reflex (L-FSS), were used. Levels of noradrenaline, dopamine, and serotonin and their metabolites 3,4-dihydroxyphenyacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were studied in the amygdala, hippocampus, medial prefrontal cortex, striatum, hypothalamus and brainstem. H-FSS mice exhibited increased fear levels and a deficit in fear extinction (within-session) in the auditory fear-conditioning test, and depressive-like behavior in the acute forced swim stress test. They had higher tissue noradrenaline and serotonin levels and lower dopamine and serotonin turnover under basal conditions, although they were largely insensitive to stress-induced changes in neurotransmitter metabolism. In contrast, acute swim stress increased monoamine levels but decreased turnover in the less fearful L-FSS mice. L-FSS mice also showed a trend toward higher basal and stress-induced corticosterone levels and an increase in noradrenaline and serotonin in the hypothalamus and brainstem 30 min after stress compared to H-FSS mice. Moreover, the dopaminergic system was activated differentially in the medial prefrontal cortex and striatum of the two strains by acute stress. Thus, H-FSS mice showed increased basal noradrenaline tissue levels compatible with a fear phenotype or chronic stressed condition. Low corticosterone levels and the poor monoamine response to stress in H-FSS mice may point to mechanisms similar to those found in principal fear disorders or post-traumatic stress disorder.

High fat diet produces brain insulin resistance, synaptodendritic abnormalities and altered behavior in mice

Insulin resistance and other features of the metabolic syndrome are increasingly recognized for their effects on cognitive health. To ascertain mechanisms by which this occurs, we fed mice a very high fat diet (60% kcal by fat) for 17days or a moderate high fat diet (HFD, 45% kcal by fat) for 8weeks and examined changes in brain insulin signaling responses, hippocampal synaptodendritic protein expression, and spatial working memory. Compared to normal control diet mice, cerebral cortex tissues of HFD mice were insulin-resistant as evidenced by failed activation of Akt, S6 and GSK3β with ex-vivo insulin stimulation. Importantly, we found that expression of brain IPMK, which is necessary for mTOR/Akt signaling, remained decreased in HFD mice upon activation of AMPK. HFD mouse hippocampus exhibited increased expression of serine-phosphorylated insulin receptor substrate 1 (IRS1-pS(616)), a marker of insulin resistance, as well as decreased expression of PSD-95, a scaffolding protein enriched in post-synaptic densities, and synaptopodin, an actin-associated protein enriched in spine apparatuses. Spatial working memory was impaired as assessed by decreased spontaneous alternation in a T-maze. These findings indicate that HFD is associated with telencephalic insulin resistance and deleterious effects on synaptic integrity and cognitive behaviors.

Antidepressant effects of ketamine: mechanisms underlying fast-acting novel antidepressants

Newer antidepressants are needed for the many individuals with major depressive disorder (MDD) that do not respond adequately to treatment and because of a delay of weeks before the emergence of therapeutic effects. Recent evidence from clinical trials shows that the NMDA antagonist ketamine is a revolutionary novel antidepressant because it acts rapidly and is effective for treatment-resistant patients. A single infusion of ketamine alleviates depressive symptoms in treatment-resistant depressed patients within hours and these effects may be sustained for up to 2 weeks. Although the discovery of ketamine's effects has reshaped drug discovery for antidepressants, the psychotomimetic properties of this compound limit the use of this therapy to the most severely ill patients. In order to develop additional antidepressants like ketamine, adequate preclinical behavioral screening paradigms for fast-acting antidepressants need to be established and used to identify the underlying neural mechanisms. This review examines the preclinical literature attempting to model the antidepressant-like effects of ketamine. Acute administration of ketamine has produced effects in behavioral screens for antidepressants like the forced swim test, novelty suppression of feeding and in rodent models for depression. Protracted behavioral effects of ketamine have been reported to appear after a single treatment that last for days. This temporal pattern is similar to its clinical effects and may serve as a new animal paradigm for rapid antidepressant effects in humans. In addition, protracted changes in molecules mediating synaptic plasticity have been implicated in mediating the antidepressant-like behavioral effects of ketamine. Current preclinical studies are examining compounds with more specific pharmacological effects at glutamate receptors and synapses in order to develop additional rapidly acting antidepressants without the hallucinogenic side effects or abuse potential of ketamine.

Alterations in prefrontal cortical serotonin and antidepressant-like behavior in a novel C3H/HeJxDBA/2J recombinant inbred mouse strain

In the present study, two genetically related inbred mouse strains selectively bred for high and low fear-sensitized acoustic startle reflex (FSS) were assessed in the forced swim test model of anti-depressant action and central monoamine concentrations in several brain regions were investigated. These mice were generated through backcrossing C3H/HeJ mice on DBA/2J mice, followed by inbreeding for several generations. The high-FSS and low-FSS strains are known to differ in their acquisition and extinction of fear following auditory fear conditioning. Significantly increased concentrations of 5-HT and its metabolite 5-HIAA were observed in the medial prefrontal cortex (mPFC) but not in the hypothalamus, striatum, hippocampus, amygdala, or midbrain of high-FSS mice compared to low-FSS mice. In addition the concentration of DOPAC, the major metabolite of dopamine was also significantly increased in the mPFC. Furthermore, the high-FSS mice displayed significantly higher levels of immobility in the forced swim test but not the tail suspension test in comparison to the low-FSS group. The mPFC is not only important in the regulation of fear extinction, but also a key region of interest in the study of depression and maintenance of depressive-like behaviors. These data implicate serotonergic modulation in the mPFC in the maintenance of antidepressant-like behavior in a highly fearful mouse strain.

Differential lipopolysaccharide-induced immune alterations in the hippocampus of two mouse strains: effects of stress

Immunological activation may result in the development of depressive-like symptoms in a large percentage of patients treated with cytokine-based therapies. The mechanisms underlying susceptibility to cytokine-induced depression are currently unknown; however activation of the tryptophan catabolising enzyme indoleamine 2,3-dioxygenase (IDO) is associated with the induction of cytokine-induced depression. Peripheral administration of lipopolysaccharide (LPS) is one of the most commonly used immunological challenges in animal models of cytokine-induced depression. Inbred mouse strains are useful tools in the investigation of the neurobiology of psychiatric illnesses. In this study we hypothesised that two strains which differ in stress susceptibility, namely the BALB/c and C57BL/6J mice, would respond differentially to LPS and swim-stress in cytokine profile, corticosterone concentrations and mRNA expression of genes coding for the tryptophan metabolising enzymes, IDO1, IDO2, Tph1 and Tph2. The stress-sensitive BALB/c strain exhibited increased depressive-like behaviour and enhanced corticosterone concentrations in response to LPS. Furthermore, swim-stress attenuated the LPS-induced corticosterone response in BALB/c mice only. LPS significantly increased plasma interleukin (IL)-1β and tumour necrosis factor α (TNFα) concentrations to a greater extent in BALB/c mice. The LPS-induced increase in IL-1β mRNA expression was significantly attenuated by swim-stress in the hippocampus of C57BL/6J but not in BALB/c mice. TNFα mRNA expression was significantly increased in BALB/c mice only; this increase was attenuated by swim-stress. Tph1 mRNA expression was upregulated in the brainstem of C57BL/6J mice post-LPS and following the combination of swim-stress and LPS in BALB/c mice. In the hippocampus Tph1 and Tph2 mRNA expression was increased in C57BL/6J but not BALB/c mice in response to LPS challenge and swim-stress. Conversely, IDO2 but not IDO1 mRNA expression was significantly altered following swim-stress and LPS, particularly in the hippocampus of BALB/c mice. These data indicate altered central mRNA expression of tryptophan metabolising enzymes and immune activation in BALB/c mice compared to the normo-sensitive C57BL/6J strain.

Cardiac responses to mild hypoxic hypercapnia in newborn babies: no effect of sleep position

OBJECTIVE

To evaluate whether cardiac responses to a level of hypoxic hypercapnia that may be observed in rebreathing studies are altered with infant sleep position.

METHODOLOGY

Eighteen healthy term infants (< 5-days-old) were studied. Heart rate (HR) and HR variability were monitored during air breathing and during 3 min exposure to a mixture of 15% O2/3% CO2 in both the prone and supine positions. Power spectral analysis of HR was performed.

RESULTS

Heart rate was the only measured variable to be significantly changed in response to 15% O2/3% CO2. Hypoxic hypercapnia elicited no significant responses in power spectral HR variables. There was no effect of sleeping position on any of the measured variables.

CONCLUSIONS

There are no significant differences in cardiac responses to mild hypoxic hypercapnia between sleep positions and power spectral indices of the autonomic control of HR are not altered by sleep position in newborn babies.

Infant autonomic function is altered by maternal smoking during pregnancy

Sudden infant death syndrome (SIDS) is more prevalent in infants of smokers and may involve subtle alterations in autonomic control mechanisms. Autonomic function can be assessed using blood pressure responses to a passive head-up tilt and power spectral analysis of heart rate variability. This study aimed to determine if maternal smoking altered infants' responses to head-up tilt. Blood pressure and heart rate responses to a passive 70 degrees head-up tilt were compared in infants of smokers and non-smokers at 2-3 days and 3 months of age. There were no significant differences between groups in power spectral indices. At 2-3 days, the systolic pressure response to tilt was significantly different between groups (P<0.01). In infants of smokers, systolic pressure decreased by a mean (S.E.) of 7.7(1.1) mmHg, whereas in control infants it remained unchanged. At 3 months, systolic pressure in infants of smokers remained unchanged but increased in control infants by 6.2(2.1) mmHg (P<0.05). These results indicate that maternal smoking alters autonomically mediated cardiovascular responses in the infant.

Uterine luminal content of insulin-like growth factor (IGF)-I and endometrial expression of mRNA encoding IGF-binding proteins 1 and 2 during the oestrous cycle and early pregnancy in the ewe

Cyclic (n = 30) and pregnant (n = 29) Merino ewes were examined (n = 3 to 5 at most time points) over Days 0-16 and 0-22 after oestrus, respectively. As IGFBP activity was detected in some plasma and ULF samples, all samples were subjected to acid-gel chromatography before assay for IGF-I. After oestrus, the overall means of both groups of ewes showed lower ULF IGF-I content (Days 3 and 12), lower plasma IGF-I concentrations (Days 3-16), higher endometrial expression of mRNA encoding IGFBP-I (Days 12-16) and lower endometrial expression of mRNA encoding IGFBP-2 (Day 8). Between Days 0 and 16 after oestrus, the pregnant ewes had lower plasma IGF-I concentrations and higher endometrial expression of IGFBP-1 mRNA than did the cyclic ewes. The presence of IGF-I in the ULF throughout the oestrous cycle and early pregnancy suggests a role of IGF-I in early pregnancy, influencing both uterine growth and embryonic survival. The concomitant endometrial expression of mRNA encoding IGFBP-1 and IGFBP-2 suggests a role of these binding proteins in the regulation of IGF-I bioavailability in the uterine environment of the ewe.

The effect of fetal hypophysectomy with or without ACTH replacement on the molecular weight profile of enkephalin-containing peptides in the adrenal medulla of the fetal sheep

We have investigated the possible role of the fetal pituitary and ACTH in the control of the synthesis and post-translational processing of the enkephalin precursor, proenkephalin A (proEnk A), in the fetal sheep adrenal gland in late gestation. Fetal hypophysectomy (n = 8) or sham operations (n = 4) were performed between 109 and 118 days of gestation. At 138-139 days, either ACTH(1-24) (10.5 micrograms/0.24 ml saline per h, n = 4) was infused intravenously for 72 h into hypophysectomized fetal sheep or 0.9% (w/v) NaCl alone (0.24 ml/h, n = 4) was infused for 72 h into hypophysectomized fetal sheep and sham-operated animals. At the end of the infusion the pregnant ewe was killed and left or right adrenal glands (n = 12) were collected from the fetal sheep that were intact and given saline (Intact + sal; n = 4), hypophysectomized and given saline (Hx + sal; n = 4) and hypophysectomized and given ACTH (Hx + ACTH; n = 4). Each adrenal was homogenized in acid (acetic acid (1 mol/l)/HCl (20 mmol/l)/2-mercaptoethanol (0.2%)). After centrifugation, the supernatant was loaded onto a Sephadex G-75 column (2.0 x 50 cm), eluted at 80 ml/24 h and fractions were collected (5 ml, n = 42). An aliquot of each fraction (2 ml) was dried down prior to enzymatic digestion (trypsin/carboxypeptidase B) and oxidation with H2O2, and assay for methionine-O-enkephalin (immunoreactive Met-O-Enk).(ABSTRACT TRUNCATED AT 250 WORDS)

Epidermal growth factor and transforming growth factor alpha

I have attempted here to outline the basic biochemical knowledge that we have now secured on the EGF family of proteins. In the future we will learn much more about the differential role of EGF versus TGF-alpha, about the physiological significance of amphiregulin, the newest member of this family, and about the roles of TGF-alpha and amphiregulin in cancer. Many questions remain. What is the importance of these factors in embryogenesis and fetal development? Is there an involvement of the EGF-like domains of extracellular proteins in cell-to-extracellular-matrix interactions? Do these extracellular matrix EGF-like entities function in a similar manner to fibroblast growth factor in cell growth and in mediating the relationship of cells to the extracellular matrix? What is the significance of cell membrane-bound forms of EGF and TGF-alpha as potential cell-to-cell contact regulators? What is the role of the viral EGF-like proteins in the viral infective and transforming process? These and other questions will be addressed in the next decade. The key question has already been well stated: 'what is the normal physiological role of EGF during development and homeostasis? The answers to these and a host of other questions must be found before we can fully comprehend this important regulatory system' (Cohen, 1987).

Effect of adrenalectomy or long term cortisol or adrenocorticotropin (ACTH)-releasing factor infusion on the concentration and molecular weight distribution of ACTH in fetal sheep plasma

It is unclear whether the maturation of corticotrophs from the fetal to the adult type in the fetal sheep pituitary in late gestation is associated with changes in the sensitivity of the fetal pituitary to corticotrophic secretagogues and in the form of ACTH-containing peptides (IR-ACTH) secreted into the circulation. The maturation of the pituitary corticotroph population is known to be accelerated by intrafetal cortisol infusion and delayed by bilateral fetal adrenalectomy. We have therefore investigated the mol wt profile of IR-ACTH present in fetal sheep plasma from 110 days gestation until term (147 +/- 3 days) and determined whether intrafetal cortisol infusion between 105-117 days (2.5 mg cortisol/day), or bilateral fetal adrenalectomy can alter the mol wt profile of IR-ACTH in fetal sheep plasma. We have also investigated whether prior exposure to cortisol alters the subsequent responsiveness of the fetal pituitary to a long term infusion of ovine (o) CRF (10 micrograms oCRF/day). In the control group, the proportion of IR-ACTH which eluted in the low-mol wt (LMW) range (i.e. less than 12K) was significantly higher between 121-125 days (43.9 +/- 4.2%) than between 126-139 days (26.8 +/- 9.3%) but not different to that after 140 days gestation (29.9 +/- 5.5%). Between 110-117 days, cortisol infusion had no effect on the proportion of IR-ACTH in the LMW range (43.9 +/- 5.7%, saline infused; 44.1 +/- 2.4%, cortisol infused). Between 121-125 days, the proportion of IR-ACTH in the LMW range in the CRF-infused groups (with or without prior exposure to cortisol) was significantly lower (27.4 +/- 2.1%) than in the saline-infused control group. In contrast, after fetal adrenalectomy, the proportion of IR-ACTH in the LMW range between 126-139 days was significantly higher (48.0 +/- 6.7%) than in intact control animals (23.8 +/- 3.5%). We conclude that the change in the mol wt profile of IR-ACTH in fetal plasma after 125 days may be a consequence of changes in the morphological and/or functional characteristics of the corticotrophic cells in the fetal pituitary. Infusion of oCRF appears to accelerate the normal maturation of the fetal pituitary-adrenal relationship, and oCRF acting either directly or via secretion of cortisol may play a role in the posttranslational processing of POMC in the fetal sheep pituitary after 125 days gestation.

Different roles for the pituitary and adrenal cortex in the control of enkephalin peptide localization and cortico-medullary interaction in the sheep adrenal during development

We have investigated the effect of adrenocorticotrophic hormone (ACTH) replacement after fetal hypophysectomy on the pattern of localization of enkephalin-containing peptides (enkephalins) and phenylethanolamine N-methyltransferase (PNMT) in the fetal sheep adrenal. We have also investigated the relative roles of the fetal pituitary and adrenal cortex in determining the extent of the interdigitation of the peripheral adrenaline (AD)-containing cells of the adrenal medulla with the inner zones of the adrenal cortex in the late gestation fetus. Fetal hypophysectomy (Hx; n = 12) or sham operations (n = 8) were performed at 109-118d. At 138 or 139d, ACTH (1-24) (10.5 micrograms/h) was infused intravenously for 72 h into 4 Hx fetuses (Hx + ACTH group). Saline was infused for 72 h into 4 Hx fetuses (Hx + Sal) and into 4 sham-operated fetal sheep (Intact + Sal). Fetal adrenal glands were collected at autopsy from 141/2d Intact + Sal, Hx + Sal and Hx + ACTH groups, from 4 intact fetal sheep at 145-147d gestation (145/7d Intact group) and 4 Hx fetal sheep at 147-164d gestation (147/64d Hx group). Adrenals were also collected from 4 newborn lambs at 10-12d after birth (10/12d Newborn group). Using the peroxidase-antiperoxidase immunocytochemical staining method, sections of adrenal glands (10-12 microns) from all groups were stained anti-PNMT. Sections of adrenal glands from the 141/2d groups were also stained separately with anti-dopamine-beta-hydroxylase (anti-D beta H) and anti-enkephalin (anti-ENK).(ABSTRACT TRUNCATED AT 250 WORDS)

The molecular weight profile of enkephalin-containing peptides in the sheep adrenal gland changes during development

We have measured the content of enkephalin-containing peptides (ENK-containing peptides) in adrenal gland extracts from fetal sheep between 68-142 days gestation and from adult sheep. We investigated whether there are changes in the post-translational processing of ENK-containing peptides in the fetal sheep adrenal gland with increasing gestational age. ENK-containing peptides in adrenal extracts from fetal sheep (68-142 days gestation) and adult sheep were separated using gel filtration chromatography and the ENK immunoreactivity (ENK-IR) was measured using RIAs for Met-enkephalin-Arg6,Phe7 immunoreactivity (MERF-IR) and Met-o-enk immunoreactivity (MET-O-ENK-IR). The MET-O-ENK-IR in fetal and adult sheep adrenal extracts was distributed in four main peaks, which corresponded to mol wt (MW) ranges of more than 12, 7-12, 3-7, and less than 3 kDa. There was a significant increase (P less than 0.05) in the total ENK-IR content of the fetal adrenal between 68-78 (42.4 +/- 19.2 ng/adrenal) and 100-121 (320.1 +/- 142.6 ng/adrenal) days gestation. There was also a significant increase in the proportion of MET-O-ENK-IR and MERF in the less than 3 kDa range between 68-78 (MET-O-ENK, 6.8 +/- 2.7%; MERF, 10.3 +/- 1.4%) and 100-121 (MET-O-ENK, 24.4 +/- 5.1%; MERF, 26.2 +/- 5.8%) days gestation, with an associated decrease in the ratio of ENK-containing peptides in the high MW form (i.e. greater than 3 kDa) compared to those in the low MW (less than 3 kDa) forms (10.4 +/- 2.5 at 68-78 days gestation; 4.2 +/- 1.1 at 100-121 days gestation). There was also a significant decrease in the percentage of MET-O-ENK in the 12 kDa range after 139 days gestation (125-135 days gestation, 20.4 +/- 2.2%; 139-142 days gestation, 4.0 +/- 2.1%). Therefore, there is an increase in the proportion of the low MW forms of ENK-containing peptides in the fetal sheep adrenal with advancing gestational age, which may reflect changes in the post-translational processing of the precursor proenkephalin-A during development.

The fate and uptake of murine epidermal growth factor in the sheep

125I-Labelled murine epidermal growth factor (EGF) was injected or infused into conscious ewes through the jugular vein. Its disappearance from the circulation and the pattern of its distribution in other body tissues and compartments were observed. Single bolus injections of 125I-labelled EGF resulted in a transient peak of radioactive EGF in the circulation which occurred within 1 min of the injection. This was followed by a very rapid fall in radioactivity in the plasma (t1/2 approximately 1 min) and the gradual appearance of 125I-labelled EGF in the urine. Immunoprecipitable 125I-labelled EGF could be detected in urine within 5 min of the start of the experiment. 125I-Labelled EGF accumulated in the urine for several hours following the injection, although with increasing time a substantial amount of non-immunoprecipitable iodide was also found. The rate of disappearance of the 125I-labelled EGF from the plasma of the ewe was found to be faster than the rate of disappearance of free [125I]iodide that had been injected into the ewe. 125I-Labelled EGF was also administered by a continuous infusion following an initial bolus injection. This again resulted in a rapid initial fall in radioactivity in blood, followed by a slow rise throughout the period of the infusion. When the infusion was stopped, there was a 15-min period of rapid readjustment, after which the radioactivity in the blood fell at a much slower rate (t1/2 approximately 70 min) than was seen initially. Again, intact 125I-labelled EGF was transferred to urine throughout the experiment. At autopsy, 125I-labelled EGF was increased in bile, liver, thyroid and kidney. Although most of the 125I found in the thyroid was free iodide, some EGF-like material was also present. There was also EGF-like material found in both the kidney cortex and the kidney medulla. These results indicate that complex multi-compartment pathways for the uptake, distribution and clearance of 125I-labelled EGF exist in the sheep.

Simultaneous isolation of insulin-like growth factors I and II from adult sheep serum

Ovine insulin-like growth factors I and II (oIGF-I and oIGF-II) have been purified from adult sheep serum. oIGF-II-like receptor-binding activity and IGF-I-like immunoactivity were enriched on SP-Sephadex C-25, then purified using HPLC in the presence of a variety of counter ions. IGF-I- and IGF-II-like activities were separated using HPLC in the presence of 0.2% tetrabutylammonium phosphate at pH 7.0. The final recovery of oIGF-I was 82.6 micrograms from 3.2 litres of adult sheep serum (a yield of 17.6%), and the recovery of oIGF-II was 388 micrograms (a yield of 13.3%). Both IGF preparations were considered to be homogeneous as judged by single sharp peaks during analytical HPLC, and unique N-terminal amino acid sequences. Purified ovine IGFs had molecular weights similar to that of other IGFs (approximately 7000), and the first 30 N-terminal amino acids of both peptides were identical to their human counterparts. The isoelectric points of oIGF-I (pI approximately 8.2) and oIGF-II (pI approximately 6.8) were similar to those of human (h) IGFs (hIGF-I pI approximately 8.2; hIGF-II pI approximately 6.5), and the overall amino acid content of the ovine IGFs was also similar to that of IGFs from other species. oIGF-II preparations from fetal sheep and from adult sheep appeared to be identical. The isolation procedure represents one of general utility that can be easily modified to facilitate the isolation of recombinant IGFs from culture fluid.

Growth hormone and testosterone can independently stimulate the growth of hypophysectomized prepubertal lambs without any alteration in circulating concentrations of insulin-like growth factors

Castrated prepubertal lambs were hypophysectomized and then treated with GH and testosterone either alone or in combination over a series of 3-week treatment periods. Hypophysectomy resulted in a rapid reduction in skeletal growth rate which could be reversed by the administration of either GH (4 IU three times a week for 3 weeks) or testosterone propionate (10 mg daily for 3 weeks). When GH or testosterone treatment was withdrawn, skeletal growth fell to the post-operative rate. Combined treatment with both GH and testosterone was no more or less effective than either hormone given singly. The order of administration did not have any effect on the growth rate. Circulating concentrations of insulin-like growth factor-I (IGF-I) were reduced by hypophysectomy, but neither GH nor testosterone treatment, alone or in combination, had any effect on IGF-I concentrations. Concentrations of IGF-II rose following hypophysectomy, and again were not affected by any of the hormonal replacement treatments. In conclusion, both GH and testosterone could stimulate skeletal growth in the hypophysectomized lamb without any alteration of circulating IGF concentrations, and testosterone can clearly stimulate skeletal growth in the complete absence of GH.

Effect of fetal hypophysectomy on the localization of the catecholamine biosynthetic enzymes and enkephalins in the adrenal medulla of the fetal sheep

We have investigated the effect of fetal hypophysectomy on the localization of dopamine B-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT) and enkephalin-containing peptides in the fetal sheep adrenal, using immunocytochemical techniques. Staining with anti-DBH was observed throughout the adrenal medulla in the intact (140-146 days of gestation) and hypophysectomized fetal sheep (147-164 days of gestation) and the newborn lamb (10-12 days after birth). In the adrenal medulla of the late-gestation intact fetal sheep and newborn lamb, positive staining with anti-PNMT was observed in the peripheral rim of medullary cells adjacent to the adrenal cortex. After hypophysectomy, there was intense positive staining with anti-PNMT in the peripheral adrenal medullary cells and a small and variable proportion of central adrenal medullary cells were stained with anti-PNMT. In the adrenal gland of the intact fetal sheep and the newborn lamb, there was intense staining with anti-enkephalin in the peripheral rim of adrenal medullary cells. Staining with anti-enkephalin was less intense in the central medullary cells of the adrenal gland of the intact fetal sheep and the 10- to 12-day-old newborn lamb, and many unstained central medullary cells were present. After hypophysectomy, intense positive staining with anti-enkephalin was observed throughout the entire fetal adrenal medulla. Therefore, the fetal pituitary, either directly or indirectly through the adrenal cortex, plays a role in regulating the pattern of localization of both PNMT and enkephalin in the fetal sheep adrenal.

Effect of hypophysectomy on the growth and development of the sheep adrenal gland: a morphometric study

We have investigated the effect of gestational age and fetal hypophysectomy on the growth and development of the adrenal gland of the fetal sheep. The area of the fetal sheep adrenal medulla increased significantly (P less than 0.05) from 3.21 +/- 0.42 mm2 at 90-107 days to 6.09 +/- 0.26 mm2 at 120-126 days of gestation and there was a further significant increase (P less than 0.05) in the newborn period to 9.48 +/- 0.85 mm2. The adrenomedullary area of the hypophysectomised fetal sheep (7.47 +/- 1.10 mm2) was not significantly different from that of the fetal sheep at 140-146 days of gestation or from that of the newborn lamb. The ratio of the area of the adrenal occupied by the cells which contained adrenaline (adrenaline zone) to the area of the adrenal occupied by the cells which contained noradrenaline (noradrenaline zone) was unchanged between 90 days of gestation and 12 days after birth. After hypophysectomy, the ratio of the adrenaline to noradrenaline zone was not significantly different from that in the adrenal medulla of the 140-146 days fetal sheep and the 10-12 days newborn lamb.

Hypophysectomy of the fetal lamb leads to a fall in the plasma concentration of insulin-like growth factor I (IGF-I), but not IGF-II

The role of the pituitary gland in the regulation of the plasma concentrations of insulin-like growth factors (IGFs) in the late gestation sheep fetus has been examined. Singleton sheep fetuses were either hypophysectomized or sham-operated between days 110-120 of gestation. Blood samples were then collected via carotid cannulae at least three times weekly for the remainder of gestation. In some hypophysectomized fetuses T4 was administered (100 g/day) to overcome the hypothyroidism caused by hypophysectomy. Blood samples were also obtained from lambs during the perinatal period, neonatal lambs within 1-10 days after birth, and pregnant and nonpregnant adult ewes. All plasma samples were subjected to Sephadex G-50 gel filtration under acidic conditions (pH 2.3) to eliminate IGF-binding protein activity. The fractions containing the free IGF peptides were collected and assayed for IGF-I by heterologous RIA, and IGF-II by a homologous RRA. Plasma concentrations of IGF-I and IGF-II did not change with advancing gestational age in any fetal group and were not affected by the prolonged gestation that results from hypophysectomy. The mean plasma IGF-I and IGF-II concentrations in the sham fetuses were 112 +/- 8 and 1340 +/- 112 ng/ml, respectively. Hypophysectomy without thyroid hormone replacement resulted in a significant decrease in plasma IGF-I concentrations to 50 +/- 5 ng/ml, whereas IGF-II concentrations were not affected (1096 +/- 124 ng/ml). IGF-I concentrations in the hypophysectomized fetuses that received T4 were significantly increased (67 +/- 6.0 ng/ml) compared to those in the hypophysectomized fetuses that did not receive T4. The IGF-II concentrations in the hypophysectomized fetuses that received T4 were similar to those in the sham-operated fetuses (1120 +/- 112 ng/ml). At term IGF-I concentrations were increased (180 +/- 21 ng/ml) and IGF-II concentrations were decreased (264 +/- 25 ng/ml) compared to fetal values. Plasma IGF-I concentrations in the prepubertal lamb were similar to the fetal values. Pregnancy in the adult ewe was associated with a significant increase in IGF-II, but had no effect on IGF-I plasma concentrations. These data show that circulating IGF-I concentrations in the fetal lamb are under some pituitary and thyroid control, whereas IGF-II concentrations are independently of pituitary or thyroid status. We confirm, using a homologous assay, that fetal IGF-II concentrations are high and then decrease at term. These data also support the concept that a pregnancy-related factor may regulate plasma IGF-II concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Endocrine control of fetal growth

Fetal growth is regulated by fetal hormones in all species that have been studied. However, it is clear that strict definition of fetal growth must be applied in order that different studies and different species may be meaningfully compared. The experimental manipulation of fetal growth in vivo has been the main tool by which information in this area has been gained. Organ ablation experiments, with or without appropriate hormone replacement treatments, have been used now for nearly 50 years as a means of studying fetal growth. As the years have gone by, many of the original techniques have been refined beyond recognition, so that precise surgical or immunological approaches have now replaced the rather simpler earlier methods. However, the nature of the questions which are posed are still remarkably similar to those first formulated nearly 50 years ago. What regulates fetal growth? This article attempts to document the progress that has been made in the endocrine control of fetal growth.

Effect of gamma 3 or gamma 2 melanocyte stimulating hormone on steroidogenesis in the fetal sheep during late gestation

We have measured circulating concentrations of gamma 3 Melanocyte Stimulating Hormone (MSH) in fetal sheep between 111 and 145 days gestation. There was no significant effect of gestational age on the fetal plasma concentrations of gamma 3 MSH throughout this period. We have examined the role of gamma-MSH related peptides in the control of fetal adrenal steroidogenesis and found no significant change in fetal plasma cortisol or pregnenolone concentrations during a 60-72 h infusion of saline, gamma 2 MSH or gamma 3 MSH in sheep between 130 and 135 days gestation. Therefore although we have demonstrated the presence of gamma MSH related peptides in fetal sheep plasma during late gestation we have failed to demonstrate a role for gamma 3 or gamma 2 MSH in the changes in fetal steroid concentrations which occur prepartum.

Failure of acid-ethanol treatment to prevent interference by binding proteins in radioligand assays for the insulin-like growth factors

Acid-ethanol precipitation and gel filtration at acidic pH have been widely used to extract circulating binding proteins for insulin-like growth factor (IGF-I and IGF-II) from plasma or serum samples before radioligand assay for the respective IGFs. Gel filtration on Sephadex G-50 at neutral pH of neutralized acid-ethanol extracts of fetal and adult ovine plasma which had been incubated with 125I-labelled IGF-I or 125I-labelled IGF-II revealed that significant amounts of the IGF-binding protein activity survived the acid-ethanol extraction procedure. Radioimmunoassay for IGF-I in acid-ethanol extracts of plasma samples from fetal, neonatal and adult sheep yielded results which depended upon the method used for separation of the antibody-bound IGF-I tracer from the free IGF-I tracer. Acid gel filtration of ovine fetal and adult plasma was found to remove completely the IGF-binding protein activity. Radioimmunoassay for IGF-I in samples of fetal, neonatal and adult sheep plasma that had undergone acid gel chromatography yielded consistent results for both methods that were used to separate antibody-bound IGF-I tracer from the free tracer. Radioreceptor assays for IGF-II were similarly highly perturbed by the presence of binding protein in acid-ethanol extracts of ovine fetal and adult plasma. We conclude that acid-ethanol extraction can not be used reliably for the removal of IGF-binding proteins, and that only acid gel filtration is a completely safe and valid method.

Ontogeny of catecholamine-synthesizing enzymes and enkephalins in the sheep adrenal medulla: an immunocytochemical study

An immunocytochemical staining technique was used to investigate the development of the sheep adrenal medullary cells containing enkephalins and the catecholamine synthetic enzymes dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyl transferase (PNMT). No staining was observed in the adrenocortical cells with any of the antisera used in this study. Positive staining with anti-DBH was observed throughout the medulla in both adult and fetal adrenal glands from 80 days of gestation. Positive staining with anti-PNMT was observed in all glands from as early as 80 days of gestation, and staining with this antiserum was mainly confined to the peripheral medullary cells, which were adjacent to, and interdigitated between, the cells of the adrenal cortex. In the fetus between 80 and 120 days of gestation, staining for the enkephalins was observed in both the peripheral columnar and the central polygonal adrenal medullary cells. After 125 days of gestation and in the adult ewe, the peripheral columnar cells were uniformly stained with anti-enkephalin whereas many unstained cells were present in the central medullary region. Therefore, enkephalin-containing peptides are present in the catecholamine cells of the fetal and adult sheep adrenal and there appears to be a changing pattern in the distribution of the enkephalins in the fetal adrenal in late gestation.