Transmission of HIV Drug Resistance and the Predicted Effect on Current First-line Regimens in Europe

Transmitted human immunodeficiency virus drug resistance in Europe is stable at around 8%. The impact of baseline mutation patterns on susceptibility to antiretroviral drugs should be addressed using clinical guidelines. The impact on baseline susceptibility is largest for nonnucleoside reverse transcriptase inhibitors.

Background. Numerous studies have shown that baseline drug resistance patterns may influence the outcome of antiretroviral therapy. Therefore, guidelines recommend drug resistance testing to guide the choice of initial regimen. In addition to optimizing individual patient management, these baseline resistance data enable transmitted drug resistance (TDR) to be surveyed for public health purposes. The SPREAD program systematically collects data to gain insight into TDR occurring in Europe since 2001.

Methods. Demographic, clinical, and virological data from 4140 antiretroviral-naive human immunodeficiency virus (HIV)–infected individuals from 26 countries who were newly diagnosed between 2008 and 2010 were analyzed. Evidence of TDR was defined using the WHO list for surveillance of drug resistance mutations. Prevalence of TDR was assessed over time by comparing the results to SPREAD data from 2002 to 2007. Baseline susceptibility to antiretroviral drugs was predicted using the Stanford HIVdb program version 7.0.

Results. The overall prevalence of TDR did not change significantly over time and was 8.3% (95% confidence interval, 7.2%–9.5%) in 2008–2010. The most frequent indicators of TDR were nucleoside reverse transcriptase inhibitor (NRTI) mutations (4.5%), followed by nonnucleoside reverse transcriptase inhibitor (NNRTI) mutations (2.9%) and protease inhibitor mutations (2.0%). Baseline mutations were most predictive of reduced susceptibility to initial NNRTI-based regimens: 4.5% and 6.5% of patient isolates were predicted to have resistance to regimens containing efavirenz or rilpivirine, respectively, independent of current NRTI backbones.

Conclusions. Although TDR was highest for NRTIs, the impact of baseline drug resistance patterns on susceptibility was largest for NNRTIs. The prevalence of TDR assessed by epidemiological surveys does not clearly indicate to what degree susceptibility to different drug classes is affected.

Clinical outcome of maraviroc-containing therapy in heavily pre-treated HIV-1-infected patients

Available data on the use of maraviroc (MVC) in clinical settings are limited. In this cohort study, the clinical outcomes of HIV-1-infected patients treated with MVC were analysed and the predictive values of different tropism assays were compared. Baseline viral tropism was assessed and compared by phenotypic (Trofile and MT-2) and genotypic assays. Virological and immunological responses were evaluated. In total, 62 predominantly extensively pre-treated patients started MVC [median GSS 2.0 (IQR 2.0-2.5)]. Tropism assays were performed on baseline samples of 58 patients (93.5%). Thirty-two samples (80.0%) were classified as R5 by Trofile, 41 (80.4%) by genotypic tropism test (GTT) and 17 (81.0%) by MT-2. At least two types of tropism assay were performed on samples from 39 patients, whereas in 15 patients all three assays were performed (concordance 84.8-94.1%). Plasma HIV-RNA was <50 copies/mL in 82.1%, 85.0% and 68.8% of patients after 12, 24 and 36 months, respectively; median CD4 cell increase was 199 (IQR 108-283), 291 (IQR 187-413) and 234 (IQR 106-444)cells/μL. The predictive values of different tropism assays were comparably high: at Month 24, 92.9% (Trofile and GTT) and 100.0% (MT-2) of patients had plasma HIV-RNA <50 copies/mL. Three patients stopped MVC treatment because of suspected side effects. Five patients died during follow-up. In this heavily pre-treated cohort, treatment with MVC was well tolerated and resulted in good immunological and virological responses. Results generated by the different tropism assays correlated well with each other and had a high predictive value.

Resveratrol preconditioning induces cellular stress proteins and is mediated via NMDA and estrogen receptors

Resveratrol pretreatment has been shown to provide neuroprotection in models of cerebral ischemia. This phenomenon, commonly termed preconditioning, promotes ischemic tolerance and may involve mild activation of endoplasmic reticulum stress pathways in the affected tissue. Systemic injection of resveratrol (2 x 10(-3), 2 x 10(-4), 1 x 10(-4) mg/kg) 30 min prior to a 4 h period of right middle cerebral artery occlusion significantly reduced infarct area in the insular region of rat prefrontal cortex. This affect was blocked when resveratrol treatment was combined with a non-selective estrogen receptor antagonist, or preceded by intracortical injection of an NMDA receptor antagonist. The neuroprotective effect of resveratrol was associated with reduced renal sympathetic nerve activity as well as induction of resident endoplasmic reticulum chaperone proteins, glucose-regulated proteins 78 and 94. The calcium-sensitive chaperone heat shock protein 70 and the cysteine protease m calpain did not respond to resveratrol pretreatment. However, a significant induction of heat shock protein 70 was observed in the contralateral cortex of resveratrol pretreated rats following 4 h of right middle cerebral artery occlusion. These data suggest that resveratrol preconditioning promotes ischemic tolerance in the short term, in part via effects mediated through activation of estrogen and NMDA receptors, as well as through mild activation of cellular stress proteins.

Role of oestrogen in the central regulation of autonomic function

1. In recent years, the role of oestrogen in women's health has been a subject of considerable scientific and popular debate. There is unquestionable evidence that oestrogen has both potent and long-lasting effects on several vital organ systems, including the cardiovascular system, the autonomic nervous system and, most recently, within the central nervous system itself. 2. The research and medical community continues to debate whether the benefits of oestrogen therapy outweigh the risks in the treatment of the symptoms of menopause, the attenuation of the risk for cardiovascular insults, such as stroke and heart disease, and even the retardation of the progression of Alzheimer's disease. 3. The recent evidence provided by the Heart and Estrogen/Progestin Replacement Study (HERS) II clinical trial suggesting that long-term exposure to combined oestrogen and progestin in post-menopausal women who have previously had a heart attack or stroke (for secondary prevention) may actually increase their risk of a subsequent cardiovascular insult has further fuelled the debate. However, there remain considerable gaps in our knowledge with respect to the actual mechanisms by which oestrogen exerts its various beneficial effects at the cellular level for the primary prevention of cardiovascular disease. This information is essential if we are to harness the positive aspects of oestrogen therapy in such a manner as to avoid or minimize the associated risks of increased oestrogen exposure in women who we know, with some certainty, to be at an increased risk of cancers of the uterus, cervix and breast tissue.

Estrogen limits ischemic cell death by modulating caspase-12-mediated apoptotic pathways following middle cerebral artery occlusion

Estrogen has received considerable attention as a potential therapeutic agent against various forms of neurodegenerative diseases including stroke. Experimental data in animal models of stroke have provided exhaustive evidence of the neuroprotective properties of this steroid hormone. Our laboratory in particular has demonstrated that acute estrogen treatment in male rats significantly reduced (approximately 50%) ischemic cell death within 4 h following permanent occlusion of the middle cerebral artery occlusion (MCAO). However, the cellular and molecular mechanisms implicated in the protective actions of estrogen in this experimental model have yet to be elucidated. Accumulating evidence suggests that in various in vivo and in vitro models, estrogen can be pro-apoptotic and that this effect may be mediated by an estrogen-induced up-regulation of the Fas/FasL system and the subsequent activation of caspase-12. We therefore hypothesized that under ischemic conditions following MCAO, estrogen would up-regulate protective endoplasmic reticulum (ER) stress pathways leading to caspase-12 activation, thus limiting infarct volume. Our results showed that estrogen significantly increased activated caspase-12 at 2, 3 and 4 h post-MCAO. Immunostaining of brain sections showed a significantly higher number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling positive cells in estrogen-treated animals at 4 h, but not at 2 h, post-MCAO. These findings correlate with previous observations that differences in infarct volume between saline and estrogen-treated animals are not seen until 3 and 4 h post-MCAO. A decrease in m-calpain expression was observed in the infarct region only at 4 h post-MCAO following estrogen pre-treatment, suggesting m-calpain may not be involved in regulating estrogen-induced caspase-12 activation. Based on these cellular changes correlated to estrogen pretreatment, we conclude that estrogen may up-regulate ER-specific apoptotic pathways, thus limiting the extent of necrotic cell death which is responsible for the spreading depression and growth of the infarct volume following MCAO.

Estrogen-mediated neuroprotection in the cortex may require NMDA receptor activation

Several studies have suggested that a potential mechanism for estrogen-mediated neuroprotection following experimental stroke is a result of modulating glutamate-mediated excitotoxicity. Our laboratory has shown that in male rats, estrogen injection (systemic or direct intracortical injection) resulted in an immediate depolarization of cortical neurons. Therefore, the present study was designed to investigate whether the estrogen-induced depolarization of cortical neurons was required in mediating the early events associated with this neuroprotection. We tested this hypothesis by co-injecting selective antagonists of the NMDA (MK-801) or AMPA (DNQX) glutamatergic receptors with estrogen. Systemic injection of estrogen significantly attenuated the MK-801-induced decrease in infarct volume following middle cerebral artery occlusion (MCAO). Similarly, when estrogen and MK-801 were co-injected directly into the cortex, no neuroprotection was observed. However, when estrogen or MK-801 was injected centrally 10 min prior to the injection of the other drug, significant neuroprotection was observed. This led us to hypothesize that estrogen-mediated neuroprotection required an initial activation of NMDA receptors. Furthermore, our results suggest that this estrogen-mediated neuroprotection was also associated with a significant increase in m-calpain and activation of an endoplasmic reticulum (ER) specific caspase-12. Finally, the results of current clamp experiments showed that estrogen significantly depolarized cortical neurons as well as enhanced NMDA-induced depolarization. Taken together, these results suggest that estrogen pretreatment may activate NMDA receptors resulting in modification of ER-associated molecular mechanisms involved in neuroprotection following MCAO.

Estrogen synthesis in the central nucleus of the amygdala following middle cerebral artery occlusion: Role in modulating neurotransmission

Stroke-induced lesions of the insular cortex in the brain have been linked to autonomic dysfunction (sympathoexcitation) leading to arrhythmogenesis and sudden cardiac death. In experimental models, systemic estrogen administration in male rats has been shown to reduce stroke-induced cell death in the insular cortex as well as prevent sympathoexcitation. The central nucleus of the amygdala has been postulated to mediate sympathoexcitatory output from the insular cortex. We therefore set out to determine if endogenous estrogen levels within the central nucleus of the amygdala are altered following stroke and if microinjection of estrogen into the central nucleus of the amygdala modulates autonomic tone. Plasma estrogen concentrations were not altered by middle cerebral artery occlusion (22.86+/-0.14 pg/ml vs. 21.24+/-0.33 pg/ml; P>0.05). In contrast, estrogen concentrations in the central nucleus of the amygdala increased significantly following middle cerebral artery occlusion (from 20.83+/-0.54 pg/ml to 76.67+/-1.59 pg/ml; P<0.05). Local infusion of an aromatase inhibitor, letrozole, into the central nucleus of the amygdala at the time of middle cerebral artery occlusion prevented the increase in estrogen concentration suggesting that this increase was dependent on aromatization from testosterone. Furthermore, bilateral microinjection of estrogen (0.5 microM in 200 nl) directly into the central nucleus of the amygdala significantly decreased arterial pressure and sympathetic tone and increased baroreflex sensitivity, and these effects were enhanced following co-injection with either an N-methyl-D-aspartate or non-N-methyl-D-aspartate receptor antagonist. Taken together, the results suggest that middle cerebral artery occlusion resulted in synthesis of estrogen within the central nucleus of the amygdala and that this enhanced estrogen level may act to attenuate overstimulation of central nucleus of the amygdala neurons to prevent middle cerebral artery occlusion-induced autonomic dysfunction.

Reduction in infarct size by local estrogen does not prevent autonomic dysfunction after stroke

Systemic estrogen administration in male rats has been shown to normalize the autonomic dysfunction and reduce the infarct size after permanent middle cerebral artery occlusion (MCAO). Therefore, the present investigation determined if local microinjection of estrogen at the site of the infarct also promoted recovery of autonomic function and reduction of the infarct size. Experiments were done in anesthetized (thiobutabarbitol sodium; 100 mg/kg) male Sprague-Dawley rats instrumented to record baseline and reflex changes in cardiovascular and autonomic parameters. The right middle cerebral artery was permanently occluded using bipolar coagulation. Local microinjection of estrogen into the insular cortex before MCAO significantly reduced the infarct size but did not attenuate the MCAO-induced autonomic dysfunction. Injection of ICI-182,780 alone significantly increased infarct area; however, the greater infarct area was not associated with enhanced autonomic dysfunction. These results suggest that within the insula, endogenous estrogen activity can affect the extent of MCAO-induced cell death, but extracortical central nervous system sites may be responsible for mediating the beneficial effects of estrogen on the autonomic disturbances.

Estrogen-induced recovery of autonomic function after middle cerebral artery occlusion in male rats

Several studies have provided evidence to suggest that estrogen results in a significant reduction (approximately 50%) in the size of the ischemic zone in the middle cerebral artery occlusion (MCAO) model of stroke in a rat. The current study was done to demonstrate whether this estrogen-induced reduction in infarct size is associated with normalization of the autonomic dysfunction observed in an acute model of stroke in male rats. Experiments were done in anesthetized (thiobutabarbitol sodium; 100 mg/kg) male Sprague-Dawley rats instrumented to record baseline and reflex changes in cardiovascular and autonomic parameters. Estrogen was intravenously administered 30 min before, immediately before, or 30 min after MCAO. Estrogen administration resulted in a recovery of autonomic function and prevented the detrimental changes in autonomic tone observed following a stroke. In addition, infarct size was significantly increased in the presence of the estrogen antagonist ICI-182,780. These results suggest that both pre- or poststroke estrogen administration prevents or reverses acute stroke-induced autonomic dysfunction and that endogenous estrogen levels in males can contribute to this neuroprotection.

Estrogen blocks the cardiovascular and autonomic changes following vagal stimulation in ovariectomized rats

The current investigation examines the effect of acute and chronic estrogen administration on baroreflex sensitivity and autonomic tone following 2 h of vagal afferent stimulation in ovariectomized female rats. Female Sprague-Dawley rats were ovariectomized and supplemented daily for 7 days with either estrogen (OVX-E2; 0.5 microg/kg; s.c.) or saline (OVX-S; 0.9%; s.c.). On the 8th day the animals were anaesthetized (sodium thiobutabarbitol; 100 mg/kg) and instrumented for recording blood pressure, heart rate and efferent vagal and renal nerve activities. The baroreflex was evoked using intravenous injection of various doses of phenylephrine hydrochloride (0.025, 0.05+/-0.1 mg/kg). Electrical stimulation of vagal afferents for 2 h produces autonomic imbalance characterized by sympathoexcitation and parasympathetic withdrawal. This protocol of vagal stimulation produced a significant increase in renal nerve activity (from 20+/-6 to 140+/-20 spikes/2 s) and decreases in both vagal nerve activity (from 22+/-3 to 10+/-2 spikes/2 s) and baroreflex sensitivity (from 0.55+/-0.05 to 0.3+/-0.05) in OVX-S female rats. However. vagal stimulation had no effect on baroreflex sensitivity or autonomic nerve activities in OVX-E2 rats. Administration of a single, bolus dose of estrogen (1 x 10(-2) mg/kg) to OVX-S rats immediately prior to termination of vagal stimulation blocked the changes in autonomic nerve activities and baroreflex sensitivity previously observed. These results suggest that both chronic and acute estrogen supplementation may provide resistance to the autonomic disturbances associated with visceral afferent activation.

Toxicity of PCB 28 in the rat liver: a quantitative ultrastructural study

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants that bioaccumulate in the food chain and thus pose a health risk to both humans and other animals. PCB 28 was administered via the diets to male and female Sprague-Dawley rats for 13 weeks in concentrations of 0.05, 0.5, 5 and 50 ppm. The chemical was mixed in corn oil and animals that served as controls received only corn oil in their diets. Use of transmission electron microscopy and stereology revealed significant (P < 0.05) elevations in the mean volume fraction (VF) of liver smooth reticulum (SER) profiles (5 and 50 ppm groups) in the females. Also, the hepatocytes of the male rats contained a significantly greater baseline VF of SER compared to those of the females. Statistically significant alterations were not detected in VP of mitochondria, rough endoplasmic reticulum, peroxisomes or lipid droplets. We estimated in Sprague-Dawley rats a no observable adverse effect level (NOAEL) of 0.5 ppm for congener 28.

Acute injection of 17beta-estradiol enhances cardiovascular reflexes and autonomic tone in ovariectomized female rats

Among the many benefits of long-term hormone replacement therapy to postmenopausal women is a significant reduction in risk for and progression of cardiovascular disease. However, long-term estrogen replacement therapy has been associated with several undesirable, and likely dose-dependent, side-effects. There is some evidence to suggest that the dose of estrogen which confers optimal beneficial effects on the cardiovascular system is much lower than that which is currently prescribed for postmenopausal women. The following experiments were conducted to determine the dose-response relationship of acutely administered estrogen on autonomic tone and reflex control of heart rate in ovariectomized Sprague-Dawley female rats. Rats were anaesthetized with sodium thiobutabarbital (100 mg/kg) and instrumented to record blood pressure, heart rate and efferent parasympathetic and sympathetic nerve activities. The sensitivity of the cardiac baroreflex was tested using intravenous injection of either phenylephrine hydrochloride (0.025-0.1 mg/kg) or sodium nitroprusside (0.0025-0.01 mg/kg). Intravenous injection of estrogen produced dose-dependent increases in the magnitude of the baroreflex sensitivity and parasympathetic tone while reducing sympathetic tone with a maximal effect observed at 1 x 10(-3) mg/kg. Prior administration of the selective estrogen receptor antagonist, ICI 182,780 blocked the estrogen-induced changes in baroreflex sensitivity and autonomic tone. These results demonstrate that acutely administered, low-dose estrogen has beneficial effects on autonomic tone and cardiovascular reflexes.

Autonomic and cardiovascular reflex responses to central estrogen injection in ovariectomized female rats

The role of estrogen in central autonomic nuclei was examined in ovariectomized female Sprague-Dawley rats supplemented daily for 7 days with either estrogen (5 microg/kg; sc) or saline (0.9%; sc). Animals were subsequently anaesthetized with sodium thiobutabarbital (Inactin; 100 mg/kg; ip) and instrumented to record blood pressure and heart rate. Efferent vagal parasympathetic (VPNA) and renal sympathetic (RSNA) nerve activities were recorded and used to assess baseline and reflexive changes in autonomic tone. The cardiac baroreflex was evoked using a single bolus injection of phenylephrine (0.1 mg/kg) both before and following either intrathecal injection of estrogen (0.5 microM; 1 microl) or bilateral injection of estrogen (0.5 microM; 100 nl/side) into several central autonomic nuclei. In estrogen-replaced rats, both the baseline and PE-evoked values for mean arterial pressure and RSNA were significantly decreased following injection of estrogen into the nucleus tractus solitarius (NTS), rostral ventrolateral medulla (RVLM), parabrachial nucleus (PBN), central nucleus of the amygdala (CNA) and the intrathecal space. Baseline heart rate and VPNA were significantly decreased following injection of estrogen into NTS, nucleus ambiguous (Amb), PBN and the intrathecal space. PE-evoked changes in heart rate and VPNA were significantly enhanced following injection of estrogen into these same nuclei. Injection of estrogen into the insular cortex (IC) produced significant decreases in baseline and PE-evoked RSNA only. The cardiac baroreflex was significantly enhanced following injection of estrogen into all nuclei and the intrathecal space. In saline-replaced females, injection of estrogen into NTS, RVLM, Amb and the intrathecal space had similar effects on both baseline and PE-evoked parameters although of a reduced magnitude compared to estrogen-replaced rats. However, no significant changes in autonomic tone and baroreflex function were observed following the injection of estrogen into the PBN, CNA or IC of saline-replaced rats. These results demonstrate a role for estrogen in central autonomic nuclei in female rats and suggest a possible alteration of estrogen receptor distribution or efficacy within the central nervous system of estrogen-deficient female rats.

Medullary and intrathecal injections of 17beta-estradiol in male rats

The following experiments were designed to investigate the role of estrogen in central autonomic nuclei on autonomic tone and reflex control of heart rate. Male Sprague-Dawley rats were anesthetized with sodium thiobutabarbital (100 mg/kg) and instrumented to record blood pressure and heart rate. Efferent vagal and renal nerve activities were recorded and used to assess changes in parasympathetic and sympathetic tone, respectively. The cardiac baroreflex was evoked using a single bolus injection of phenylephrine (0.1 mg/kg) both before and following either intrathecal injection of estrogen (0.5 microM; 1 microl) to influence sympathetic preganglionic neurons of the intermediolateral cell column or bilateral injection of estrogen (0.5 microM; 100 nl/side) into the nucleus tractus solitarius, rostral ventrolateral medulla or nucleus ambiguus. The cardiac baroreflex was significantly enhanced following both intrathecal and medullary injections of estrogen. Efferent vagal nerve activity was significantly increased following injection of estrogen into the nucleus tractus solitarius, nucleus ambiguus and the intrathecal space. Renal sympathetic nerve activity was significantly depressed following injection of estrogen into the nucleus tractus solitarius, rostral ventrolateral medulla and the intrathecal space. In all cases, simultaneous injection of estrogen with the selective estrogen receptor antagonist, ICI 182,780 (1 pM) blocked all previously observed changes in baroreflex function and autonomic tone. These results demonstrate a role for estrogen in the reflex control of heart rate and as a central modulator of autonomic tone in male rats.

17beta-estradiol modulates baroreflex sensitivity and autonomic tone of female rats

The following experiments examine the role of estrogen as a central modulator of autonomic tone and baroreflex sensitivity in the female rat. Female Sprague-Dawley rats were ovariectomized and then supplemented daily for 7 days with a fixed dose of estrogen (5 microg/kg; sc) to produce a stable level of estrogen similar to that present at proestrous (17 pg/ml). The rats were then anaesthetized with sodium thiobutabarbital (100 mg/kg) and instrumented to record blood pressure, heart rate and both vagal and renal efferent nerve activities. The sensitivity of the cardiac baroreflex was tested using intravenous injection of multiple doses of either phenylephrine hydrochloride or sodium nitroprusside. Estrogen-supplemented female rats exhibited a significantly enhanced BRS as compared to male rats from a previous study (0.78 vs. 0.5). Furthermore, bolus injection of estrogen (1x10(-2) mg/kg; iv) in estrogen-supplemented female rats produced a significant increase in vagal nerve activity and a significant decrease in renal nerve activity which together resulted in a further enhancement of the BRS (0.78 vs. 2.4). Injection of the selective estrogen receptor antagonist, ICI 182,780, into nucleus ambiguus and the intrathecal space of the spinal cord blocked the respective changes in parasympathetic and sympathetic nerve activities indicating that intravenously administered estrogen modulates baseline autonomic tone via the activation of central estrogen receptors.

PCB 128-induced ultrastructural lesions in the rat liver

PCB 128 (2,2',3,3',4,4'-hexachlorobiphenyl) prepared in 4% corn oil and mixed in diets was given to weanling Sprague-Dawley rats. The animals were placed in eight groups, each comprising 10 males or 10 females; each group received a diet that contained 0.05, 0.5 or 5 ppm PCB. Ten animals of each gender that served as the controls were given diets mixed with only corn oil. Thirteen weeks after the commencement of dosing, animals were euthanized and liver specimens were harvested and prepared for transmission electron microscopy. The architecture of the liver parenchymal cell was indistinguishable in the animals of the lowest concentration group from those in the controls. However, smooth endoplasmic reticulum profiles increased, and abnormal mitochondria were noted in the liver of rats, regardless of gender, from 0.5 and 5 ppm groups. Based on our previous work, PCB 128 is estimated to be equally toxic as PCB 153, another di-ortho substituted PCB congener.

PCB congener 126-induced ultrastructural alterations in the rat liver: a stereological study

Hepatocyte cytoplasmic alterations were morphometrically determined in male and female Sprague-Dawley rats fed PCB congener 126 (3,3',4,4',5-pentachlorobiphenyl) in concentrations of 0.1, 1.0, 10, 100 ppb or corn oil in diets for 13 weeks. A dose-dependent increase (P < 0.05) in the volume fraction of smooth endoplasmic reticulum (SER) and mitochondria was measured in the hepatocytes of the females. However, these cells of the male rats contained a significantly greater baseline volume fraction of SER compared to that in the females. Statistical differences were not detected in the volume fractions of rough endoplasmic reticulum, peroxisomes or lipid droplets of the hepatocytes in either the males or females. We conclude the increase in mitochondrial volume was a necessary cellular adaptation to meet the heightened energy demands by the SER to produce the necessary enzymes to detoxify the PCB. Morphometric analysis rather than a descriptive methodology allowed for a more accurate determination of the liver pathology induced by PCB 126.

Visceral afferent activation-induced changes in sympathetic nerve activity and baroreflex sensitivity

The following experiments were done to determine whether changes in baroreflex sensitivity evoked by cervical vagus nerve stimulation are due to sympathoexcitation mediated by the parabrachial nucleus. The relative contribution of cardiopulmonary and general gastric afferents within the cervical vagus nerve to the depression in baroreflex sensitivity are also investigated. Male Sprague-Dawley rats anesthetized with thiobutabarbital sodium (50 mg/kg) were instrumented to measure blood pressure and heart rate or for the continuous monitoring of renal sympathetic nerve activity. Baroreflex sensitivity was measured using bolus injections of phenylephrine. Electrical stimulation of the cervical vagus (with or without the aortic depressor nerve) or the abdominal vagus nerve produced a significant increase in renal nerve activity and a decrease in baroreflex sensitivity. Both of these effects were blocked after the microinjection of lidocaine into the parabrachial nucleus before nerve stimulation. Therefore, we conclude that an increase in the activity of cardiac, pulmonary, or general gastric afferents mediated the increased sympathetic output and decreased baroreflex sensitivity via a pathway involving the parabrachial nucleus.

Centrally mediated effect of 17beta-estradiol on parasympathetic tone in male rats

The following experiments were conducted to determine if peripherally administered estrogen has an effect on central autonomic tone and whether this change in tone results in an alteration in cardiovascular reflex control. Male Sprague-Dawley rats were anesthetized with thiobutabarbitol sodium (50 mg/kg) and instrumented to record blood pressure, heart rate, and vagal parasympathetic or renal sympathetic efferent nerve activity. Additional rats were instrumented to test the sensitivity of the cardiac baroreflex using intravenous injections of phenylephrine hydrochloride (0.025, 0.05, 0.1 mg/kg) or sodium nitroprusside (0. 0025, 0.005, 0.01 mg/kg) and plotting the cardiovascular responses. Intravenous injection of estrogen (10(-4), 10(-2), and 10(-1) mg/kg) produced a significant increase in vagal efferent activity and in baroreflex sensitivity. The bilateral microinjection of an estrogen receptor antagonist, ICI-182,780 (1 pM, 50 nl/side) into the nucleus ambiguus blocked both the estrogen-induced increase in vagal efferent activity and baroreflex sensitivity. These results demonstrate that in male rats estrogen acts centrally to enhance baroreflex sensitivity by increasing parasympathetic efferent tone.

The parabrachial nucleus mediates the decreased cardiac baroreflex sensitivity observed following short-term visceral afferent activation

Previous investigations have provided evidence demonstrating that the extracellular release of glutamate into the parabrachial nucleus was significantly enhanced following visceral afferent activation. This period of enhanced glutamate release into the parabrachial nucleus corresponded to a time during which the pressor response to a bolus phenylephrine injection was significantly enhanced, and the reflex bradycardia was attenuated. This decrease in the sensitivity of the baroreflex is suggestive of an enhanced sympathetic tone as a result of the vagal stimulation. The present investigation was done to determine if the decreased baroreflex sensitivity observed following short-term vagal stimulation is mediated by an increase in sympathetic activity and was dependent on the parabrachial synapse. Male Sprague-Dawley rats were anaesthetized with sodium thiobutabarbitol and instrumented to monitor blood pressure and heart rate and for the placement of a stimulating electrode on the left cervical vagus nerve. Femoral arterial blood samples were taken before, during and after 2 h of vagal stimulation which were later assayed for plasma catecholamines. The results showed that plasma norepinephrine levels decreased during, and were significantly elevated immediately following termination of the vagal stimulation, indicative of an increase in sympathetic tone. To determine if the parabrachial nucleus is involved in mediating an enhanced sympathetic activity following vagal stimulation, a second group of animals underwent an identical surgical preparation, vagal stimulation and blood sampling protocol with the addition of bilateral microinjections of either the reversible anaesthetic, lidocaine, or saline into the parabrachial nucleus. The results showed that reversible blockade of the parabrachial nucleus prior to the onset of the vagal stimulation was effective in blocking both the elevation in plasma norepinephrine levels and the depressed baroreflex sensitivity previously observed following 2 h of vagal stimulation. These results suggest that the parabrachial nucleus mediated the sympathoexcitation and consequent depression in baroreflex sensitivity observed following visceral afferent activation.

Role of 17beta-estradiol in the modulation of baroreflex sensitivity in male rats

Female mammals have an enhanced baroreflex sensitivity compared with their male counterparts, leading researchers to speculate that estrogen modulates autonomic tone. Therefore, this study tests the hypothesis that exogenous estrogen can enhance the baroreflex sensitivity of male rats. Male Sprague-Dawley rats anesthetized with thiobutabarbitol sodium (50 mg/kg) were instrumented to measure blood pressure and heart rate and for the intravenous injection of drugs. The baroreflex was tested using intravenous injections of phenylephrine (0.025, 0.05, and 0.1 mg/kg), and the cardiovascular responses were plotted to obtain a measure of the sensitivity of the cardiac baroreflex. Intravenous injection of estrogen produced dose-related increases in the baroreflex sensitivity due to an increase in the magnitude of the reflex bradycardia. In a separate group of animals, stimulation of the vagus nerve for 2 h resulted in a decrease in baroreflex sensitivity. This effect was blocked when estrogen (1 x 10(-2) mg/kg) was administered immediately before the end of stimulation. In conclusion, intravenous injection of estrogen in male rats significantly enhanced baroreflex sensitivity and blocked the attenuation in the baroreflex sensitivity observed after vagal stimulation.

Development of an injectable sustained-release formulation of morphine: antinociceptive properties in rats

The antinociceptive actions of morphine incorporated into an injectable chitosan-based gel were investigated in rats. Subcutaneous administration of 4.8 mg/kg morphine sulphate in a gel composed of N,O-carboxymethylchitosan (NOCC) and chitosan resulted in significant antinociception within 10 min that was maximal at 60 min and persisted for 6 h. In contrast, the same dose of morphine sulphate injected in sterile saline produced maximal responses at 30 min but only persisted for 2 h. NOCC/chitosan gel was easily injectable using a 22 guage needle and appears stable in long-term storage. No local or systemic adverse effects other than morphine-induced sedation were observed either at the time of injection or during the subsequent 48 h. We conclude that gels composed of chitosan and chitosan derivatives are effective matrices for sustained-release formulations of opioid analgesics capable of providing long-lasting antinociception.

PCB congener 77-induced ultrastructural alterations in the rat liver: a quantitative study

Liver alterations were estimated morphometrically in male and female Sprague-Dawley rats that were fed PCB congener 77 (3,3',4,4'-tetrachlorobiphenyl) in concentrations of 0.01, 0.1, 1, 10 ppm or corn oil in diets for 13 weeks. A dose-dependent increase in the volume of smooth endoplasmic reticulum (SER) and an elevation in the volume of mitochondria following administration of the highest congener concentration (10 ppm) were estimated in the female rats. Hepatocytes of the male rats contained a significantly greater baseline volume of both SER and mitochondria compared to that in the females. A statistically significant (P < 0.05) change in the volumes of either SER or mitochondria in the PCB-fed males was not revealed. The authors concluded that the increase in mitochondrial volume was probably a necessary cellular adaptation to meet the heightened energy demands required by the SER to detoxify the PCB. The use of morphometric rather than a descriptive methodology allowed for a better determination of the hepatic alterations induced by PCB 77.

Role of the insular cortex in the modulation of baroreflex sensitivity

Cervical vagal stimulation for 2 h results in a depressed baroreflex sensitivity produced by an enhanced sympathetic output, as indicated by increased plasma norepinephrine levels. The current study examined the role of the insular cortex in modulating the vagal stimulation-induced changes in baroreflex sensitivity. Male Sprague-Dawley rats were anesthetized with thiobutabarbitol sodium and instrumented for recording blood pressure, heart rate, intravenous drug administration, and vagal afferent nerve stimulation. Stereotaxic microinjections (300 nl) of either 5% lidocaine or 0.9% saline were made bilaterally into the insula. Thirty minutes after 2 h of vagal stimulation, the baroreflex was significantly depressed and plasma norepinephrine levels were significantly elevated in both groups. The baroreflex was also significantly depressed after bilateral lidocaine injections into the insula, independent of vagal stimulation. However, no significant change in plasma norepinephrine was observed, suggesting that an attenuated parasympathetic output contributed to the altered baroreflex. Taken together, the results suggest that the insular cortex modulates the cardiac baroreflex through a modulation of parasympathetic output.

The fear levels after transport of hens from cages and a free-range system

All end-of-lay hens must be transported from the production site to the site for slaughter, usually by road. The acts of being crated and transported are likely to be novel and potentially frightening. Frightened birds can be put into tonic immobility (TI), an unlearned, catatonic state, the duration of which is positively related to the fear level of the birds. Ninety ISA Brown free-range birds (in three groups of 30) and 90 caged ISA Brown birds (in similar groups) were transported (one group from cages and free-range per day) on a journey of 68 km (74 min approximately). On their return, each of the birds was subjected to TI. Although no significant differences were recorded between free-range and caged birds after they were transported (P = 0.087), in the comparison between the same birds after 7 wk, without transport, a significant difference in fear levels was observed (P < 0.001). The free-range birds were less frightened than the caged birds. No significant difference was ever found in fear levels for caged birds from different tiers. Handling and transport on this relatively short journey was apparently equally frightening for caged and free-range birds. It cannot be assumed that just because fear levels differ between free-range and caged birds, this difference will be apparent for all novel stimuli. If all birds, at all tiers, receive the same amount of human contact during the production period, there is no reason to expect differences to occur in fear levels of birds from different tiers.

Interaction of PCB congeners and 2,3,7,8-TCDD in the rat liver: an electron microscope study

Polyhalogenated aromatic compounds such as polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins continue to be environmental contaminants because of their bioaccumulation in the food chain and resistance to biodegradation. This study was undertaken to determine if WHO-IPCS PCB congeners or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) individually or their coadministration in rats produced morphological alterations in the liver. Groups (N = 5) of female Sprague Dawley rats received TCDD (0, 2.5, 25, 250, 1,000 ng/kg bw/day) or PCB (0, 2, 20 micrograms/kg bw/day) either alone, or each dose of PCB coadministered with that of TCDD. The test substances were dissolved in corn oil and given by gavage at 0.2 ml/100 g bw/day for 28 days. At the end of the experiment the rats were killed and liver samples were prepared for transmission electron microscopy. Electron micrographs of the liver from animals of the control groups revealed characteristic normal hepatocyte architecture. An increase in smooth endoplasmic reticulum (SER) profiles and a corresponding decrease in the profiles of rough endoplasmic reticulum (RER) proportional to the increased doses of the compounds was revealed in the micrographs. Coadministration of PCBs and TCDD induced greater SER proliferation and a greater decrease in the number of RER profiles compared to either compound administered individually. The PCBs and TCDD at the doses used apparently interacted to induce hepatic ultrastructural alterations. These changes may represent an attempt by the organism to metabolize and neutralize the effects of xenobiotics.

Modulation of the cardiac baroreflex following reversible blockade of the parabrachial nucleus in the rat

The parabrachial nucleus (PBN) has a prominent anatomical connection with the nucleus of the solitary tract as well as other central baroreflex centres which suggests a role for the PBN in the regulation of this cardiovascular reflex. This study examined the effects of a reversible, bilateral blockade of the PBN on the cardiac baroreflex. Male Sprague-Dawley rats were anesthetized with sodium butabarbitol and instrumented to monitor blood pressure and heart rate and for the intravenous administration of drugs. The cardiac baroreflex was evoked using bolus intravenous injections of phenylephrine (PE) and sodium nitroprusside (NaNp) at various doses and a graph of baroreflex sensitivity was constructed. Bilateral microinjections of the reversible anesthetic, lidocaine (5%, 300 nl), into the PBN did not significantly change baseline blood pressure or heart rate when compared to microinjections of saline (0.9%, 300 nl) into the PBN. The pressor or depressor responses evoked by bolus injections of PE or NaNp, respectively, were not significantly affected by the bilateral pretreatment of the PBN with lidocaine when compared to saline controls. However, approximately 30 min following lidocaine injection, the amplitudes of both the evoked-reflex bradycardia and reflex tachycardia were significantly increased by approximately 98%. The cardiovascular responses to various doses of PE and NaNp were graphed and baroreflex sensitivity curves were constructed. This graph showed an increased slope of the baroreflex sensitivity curve following lesions of the PBN. Reflex changes in heart rate returned to pre-lidocaine injection levels after approximately 2 h. The results of the present investigation suggest that the PBN participates in the modulation of the cardiac baroreflex which in turn suggests a role for this nucleus in the central integration of cardiovascular reflex function.

Morphological changes in the small intestine of the fetal pig after prenatal stimulation of the sow with ACTH

Twelve pregnant primiparous sows were catheterized on day 102 of gestation and randomly allocated to receive ACTH (days 112-113 of gestation [2d], days 105-parturition [10d]) or saline. At parturition the 3rd, 4th, 6th and 7th piglet born alive were sacrificed either at birth or at 6 h. The later group was fed bovine colostrum through a stomach tube at 30 min, 2 and 4 h of life. Following sacrifice, the small intestine of each piglet was excised, extended and measured. Piglets from sows in the 2d group tended to be heavier with longer small intestines than either the control or 10d groups. When the small intestine length was expressed as a function of body weight, the 10d group had the greatest ratio, suggesting that the pre-parturition maintenance of elevated cortisol levels either enhanced small intestine growth or attenuated overall weight gain. Two types of enterocyte granules were described at the level of the electron microscope: granular and opaque. Opaque granules from piglets born to sows in the 2d treatment group had both a lower volume fraction and were fewer per unit area when compared to those of either the saline or 10d treatments. The process of macromolecule uptake from the intestinal lumen appeared to have been interfered with as a result of an acute prenatal stimulation with ACTH. The above results suggest that in piglets, the level of circulating cortisol differentially controls the processes of IgG absorption, enterocyte replacement and small intestine growth through separate mechanisms. Further, these processes can be manipulated in the prenatal piglet.

Rapid development of tolerance to morphine in the formalin test

Previous reports have suggested that tolerance to the antinociceptive effects of morphine does not develop in the formalin test. To re-examine these findings, morphine was administered via multiple injections or continuous infusion from 0 to 4 days prior to testing with either the formalin or tail-flick test. Following twice daily injections (5.0 mg kg-1 s.c.), significant tolerance developed within 2 days with the formalin test but not until day 4 with the tail-flick test. Significant tolerance was noted with both tests 4 days following the implantation of osmotic mini-pumps (10 mg kg-1 day-1, s.c.). We conclude that in mice, tolerance to the analgesic effects of morphine develops rapidly with the formalin test.

Systemic injections of alpha-1 adrenergic agonists produce antinociception in the formalin test

The role of alpha 1 receptors in antinociception was investigated in the formalin test, a well established test of tonic pain. The effect of systemic injections of selective alpha 1-adrenergic agonists (phenylephrine and methoxamine), a mixed alpha agonist selective for alpha 2 receptors (ST-91), and 2 adrenergic antagonists (prazosin and idazoxan) was measured in groups of Long-Evans rats. All agonists tested produced significant antinociception in this test. Dose-response curves for each agonist were statistically parallel and equally efficacious (100% antinociception). Prior injection of 0.15 mg/kg prazosin (an alpha 1 antagonist) completely antagonized the antinociception produced by either an ED50 or a maximally effective dose of each agonist tested. Idazoxan (0.5 mg/kg), an alpha 2 antagonist, was without effect on the antinociception produced by phenylephrine or methoxamine. ST-91 produced significant antinociception in the presence of idazoxan although the response was different from that obtained with ST-91 alone. The observed antinociception in the formalin test was not due to drug-induced changes in peripheral inflammation as measured using plethysmometry. Moreover, none of the drugs tested produced significant changes in coordinated motor behavior (accelerated rotarod test) at doses that produced significant analgesia (ED50). We conclude that alpha 1 receptors contribute significantly to adrenergic analgesia in the formalin test by an undefined action on sensory processing mechanisms.

Development of the small intestine of piglets in response to prenatal elevation of glucocorticoids

The effects of prenatal adrenal stimulation and synthetic glucocorticoid supplementation on development of the gastro-intestinal tract of the piglet were investigated. Twelve pregnant sows were treated with either ACTH infusion, Isoflupredone injection or Saline between days 105 and 112 of gestation. Neonatal pigs were weighed, bled and sacrificed at 0 or at 6 h. Piglets sacrificed at 6 h were fed bovine colostrum. Transverse sections were prepared from the duodenum, jejunum and ileum for measurement of the villus amplification factor (VAF) and basal membrane circumference. Sows in the ACTH group showed an elevation in cortisol in response to infusion; this decreased after infusion and then rose again at parturition. Piglets from both the ACTH and Saline groups had more villus surface area per unit of body weight (BW) than those born to Isoflupredone-treated animals. The BW of the ACTH piglets was lower (P less than 0.05) than those of piglets in the other groups. When the weight of the stomach and the Small Intestine (SI) was expressed as a function of the body weight, the stomach and SI:BW ratio was larger (p less than 0.05) in pigs born to ACTH-treated sows. The circumference of the ileum was larger at 6 h than at 0 h. Control pigs had a higher concentration of bovine IgG at 4 and 6 h (P less than 0.05). Observations of the light microscopic preparations indicated a less organized epithelium in both ACTH and isoflupredone pigs sacrificed at 0 h. Light and EM preparations of ileum from ACTH pigs sacrificed at 6 h, showed an abundance of dark-stained vacuoles, characteristic of IgG-containing structures. These became less evident in piglets from the Isoflupredone group and even less so in the control groups. The consequences of these phenomena in terms of absorptive capacity are discussed.

Pharmacology of systemically administered domoic acid in mice

Domoic acid, a structural analogue of kainic acid, has been identified as the toxin that poisoned people who consumed contaminated blue mussels harvested from eastern Prince Edward Island in December of 1987. To investigate the pharmacology of domoic acid in vivo we injected groups of mice with serial dilutions of extracts of contaminated mussels and verified domoic acid concentrations using high performance liquid chromatography. Mice progressed through a series of behavioural changes that were both reproducible and dose-dependent. These behaviours formed the basis of a rating scale that was used to reliably quantitate domoic acid concentrations as low as 20 micrograms/mL. This scale was then used to compare the relative toxicity of domoic acid contained in four formulations: namely, (1) extracts of contaminated mussels, (2) pure domoic acid, (3) extracts of noncontaminated mussels that were "spiked" with pure domoate, and (4) extracts of the algal source of domoic acid. Interpolation of the resulting dose-response curves produced median toxic dose (TD50) values of 2.9, 3.9, 4.9, and 4.2 mg/kg for the four formulations, respectively. Statistical analysis of these data revealed that curves for all formulations of domoic acid were parallel, but that extracts of contaminated mussels were significantly more potent than any of the other formulations at low and intermediate doses of domoic acid. We further compared domoic acid toxicity with that produced by kainic acid. Dose-response curves for both compounds were statistically parallel and both toxins were equally efficacious. The TD50 values were 3.9 and 31.9 mg/kg for pure domoic acid and kainic acid, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation between cellular changes in supraoptic and paraventricular nuclei and water-drinking in neuroleptic-treated rats

The neuroleptics haloperidol and thioridazine were injected intraperitoneally in rats for 81 days. During this time the rats' water consumption was measured. Drug-treated animals drank significantly less water for the first 40 days of the experiment only. On day 82 the rats were perfused for electron microscopy. The rat's paraventricular and supraoptic nuclei were embedded, sectioned, stained for electron microscopy and viewed for morphological change. There were significantly more darkly staining neurons in the haloperidol-treated rats than in control rats. Thioridazine-treated rats had more dark neurons but the difference was not significant. These dark cells had the appearance of highly stimulated neurons. Some appeared to be degenerating.