Pellet Removal Research Articles

Synthesis and characterization of nonstoichiometric NiGa 2O 4 transparent thin films

Transparent nickel gallate spinel films were synthesized by means of an inter-diffusion reaction between NiO ceramics and (0 0 1) β-Ga 2O 3 single crystalline substrates at 1300 °C and annealed at various temperatures after removal of NiO pellets. The as-prepared films were characterized by X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, and optical absorption spectroscopy. It is revealed that the transparent reaction layers are single phase crystalline spinel with preferred orientations. Results from the EDX analysis show a homogeneous composition after equilibration, with a Ga/Ni atomic ratio of about 2.4 and 2.7 for samples quenched from 1300 °C and 1400 °C, respectively. Optical absorption spectra of spinel films are dominated by ligand field transitions of Ni 2+ ions in octahedral sites with overlapping absorption bands of Ni 2+ ions on tetrahedral sites.

Increased production of faecal pellets by the benthic harpacticoid Paramphiascella fulvofasciata: importance of the food source

The re-use of faecal pellets in the water column before sinking to the seaXoor is known as an important pathway in marine food webs. Especially planktonic cope- pods seems to be actively use their faecal pellets. Since benthic copepods (order Harpacticoida) live in the vicinity of their pellets, it remains unclear how important these pel- lets are for their feeding ecology. In the present study a lab- oratory experiment was conducted to analyse the importance of faecal pellets for the feeding ecology of the harpacticoid Paramphiascella fulvofasciata and its grazing pressure on two diatom species (Seminavis robusta, Navic- ula phyllepta). By quantifying the amount and volume of the produced faecel pellets in diVerent treatments, it was tested to what extent the food source and the lack of faecal pellets would inXuence the production of faecal pellets. We found that the grazing pressure of P. fulvofasciata depended on the diatom density since only a top-down eVect could be found on the smaller Navicula cells during its initial exponential growth phase. The grazer had a nega- tive eVect on the diatom growth and controlled the cell den- sity to about 4,000 cells/cm 2 . In spite of the fact that the addition of faecal pellets did not show a signiWcant positive eVect on the assimilation of diatoms, the removal of faecal pellets strongly promoted the pellet production. Especially when grazing on Navicula the harpacticoid P. fulvofasciata produced signiWcantly more and smaller faecal pellets when the pellets were removed. This outcome illustrates the need for faecal pellets of this harpacticoid copepod when grazing on the diatom Navicula. Apart from its selection for smaller diatom cells, it was suggested that the colonisation of heterotrophic bacteria enriched these pellets. This study is the Wrst to indicate that trophic upgrading occurs on fae- cal pellets and not only on the initial autotrophic food sources per se.

Degradation of copepod fecal pellets: key role of protozooplankton

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 367:1-13 (2008) - DOI: https://doi.org/10.3354/meps07611 FEATURE ARTICLEDegradation of copepod fecal pellets: key role of protozooplankton Louise K. Poulsen1,2,*, Morten H. Iversen3 1Danish Institute for Fisheries Research, Department of Marine Ecology and Aquaculture, Kavalergården 6, 2920 Charlottenlund, Denmark 2Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark 3Alfred-Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany *Email: lkpoulsen@bio.ku.dk ABSTRACT: Copepod fecal pellets are often degraded at high rates within the upper part of the water column. However, the identity of the degraders and the processes governing the degradation remain unresolved. To identify the pellet degraders we collected water from Øresund (Denmark) approximately every second month from July 2004 to July 2005. These water samples were divided into 5 fractions (<0.2, <2, <20, <100, <200 µm) and total (unfractionated). We determined fecal pellet degradation rate and species composition of the plankton from triplicate incubations of each fraction and a known, added amount of fecal pellets. The total degradation rate of pellets by the natural plankton community of Øresund followed the phytoplankton biomass, with maximum degradation rate during the spring bloom (2.5 ± 0.49 d–1) and minimum (0.52 ± 0.14 d–1) during late winter. Total pellet removal rate ranged from 22% d–1 (July 2005) to 87% d–1 (May). Protozooplankton (dinoflagellates and ciliates) in the size range of 20 to 100 µm were the key degraders of the fecal pellets, contributing from 15 to 53% of the total degradation rate. Free-living in situ bacteria did not affect pellet degradation rate significantly; however, culture-originating bacteria introduced in association with the pellets contributed up to 59% of the total degradation rate. An effect of late-stage copepod nauplii (>200 µm) was indicated, but this was not a dominating degradation process. Mesozooplankton did not contribute significantly to the degradation. However, grazing of mesozooplankton on the pellet degraders impacts pellet degradation rate indirectly. In conclusion, protozooplankton seems to include the key organisms for the recycling of copepod fecal pellets in the water column, both through the microbial loop and, especially, by functioning as an effective ‘protozoan filter’ for fecal pellets. KEY WORDS: Bacteria · Copepod · Degradation rate · Dinoflagellates · Fractionated plankton community · Protozoan filter · Nauplii Full text in pdf format Information about this Feature Article NextCite this article as: Poulsen LK, Iversen MH (2008) Degradation of copepod fecal pellets: key role of protozooplankton. Mar Ecol Prog Ser 367:1-13. https://doi.org/10.3354/meps07611Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 367. Online publication date: September 11, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Dietary n-3 Polyunsaturated Fatty Acids Enhance Hormone Ablation Therapy in Androgen-Dependent Prostate Cancer

Hormone ablation therapy typically causes regression of prostate cancer and represents an important means of treating this disease, particularly after metastasis. However, hormone therapy inevitably loses its effectiveness as tumors become androgen-independent, and this conversion often leads to death because of subsequent poor responses to other forms of treatment. Because environmental factors, such as diet, have been strongly linked to prostate cancer, we examined the affects of dietary polyunsaturated fatty acids (PUFAs; at 1.5 wt%) on growth of androgen-dependent (CWR22) and androgen-independent (CWR22R) human prostatic cancer xenografts, the acute response of CWR22 tumors to ablation therapy, and their progression to androgen independence. Significant diet-induced changes in tumor n-3 or n-6 PUFA content had no affect on CWR22 or CWR22R tumors growing with or without androgen support, respectively. However, dietary changes that increased tumor eicosapentaenoic acid and linoleic acid content enhanced responses to ablation therapy, measured by cancer cell apoptosis and mitosis. In addition, relapse to androgen-independent growth (measured by renewed increases in tumor volume and serum prostate-specific antigen after ablation) positively correlated with tumor arachidonic acid content. There was no correlation between expression of 15-lipoxygenase isozymes or their products and tumor growth or responses to ablation. In conclusion, dietary n-3 PUFA may enhance the response of prostate cancer to ablation therapy and retard progression to androgen-independent growth by altering tumor PUFA content.

Submicron-Sized Gamma-HMX: II. Effect of Pressing on Phase Transition

In a previous article we described the preparation and initial characterization of a novel submicron-sized HMX (sm-HMX). Using Raman spectroscopy, the sm-HMX was found to be the gamma polymorph and to be stable with respect to conversion to beta-HMX under ambient conditions for at least a year. Pressing of sm-HMX powder in a small diameter pellet press at pressures from 10,000 to 31,000 psi and 1- to 5-min hold times was found to promote the gamma-to-beta polymorphic phase transition. The fraction converted and rate of conversion versus time after pellet removal from the press were found to fit a sigmoidal curve, indicating nucleation and growth as a possible polymorphic transition mechanism.

Traditional medical removal of gunshot pellets: traditional medical treatment or traditional deceit?

Traditional medical removal of gunshot pellets: traditional medical treatment or traditional deceit?

No Effect of Morphine on Ventral Tegmental Dopamine Neurons during Withdrawal

Substantial evidence indicates that the ventral tegmental area (VTA) of the mesocorticolimbic dopaminergic (DA) system has a key role in mechanisms of opiate dependence. Although DA neurons have been studied extensively, little is known about their activity and their response to acute morphine during morphine dependence. We recorded the activity of VTA DA neurons in five groups of anesthetized rats: drug-naive (naive) rats, morphine-dependent [(MD) implanted with pellets] rats, and three groups of withdrawn rats. Withdrawals either were precipitated by naltrexone or occurred spontaneously 24 h or 15 d after pellet removal. We confirmed that acute morphine in naive rats produced a marked increase in the firing of VTA DA neurons. We also found that the basal firing rate of VTA DA neurons was markedly higher in MD than in naive rats; however, in MD rats, acute morphine failed to increase DA activity. We confirmed inhibition of VTA DA activity in MD rats in response to precipitated withdrawal; however, this inhibition resulted only in a normalization of the firing rate to that of naive animals. In rats that had spontaneous withdrawal after 24 h or 15 d, the activity of VTA DA neurons was similar to that of naive rats, and an acute injection of morphine failed to alter their activity. Our results indicate that VTA DA neurons show long-lasting tolerance to the acute effect of morphine after withdrawal. These findings show that VTA DA neural activity is unlikely to be a factor in the altered behavioral responses that occur with acute morphine or naltrexone administration after chronic opiate exposure.

Increased Sensitivity to Salmonella enterica Serovar Typhimurium Infection in Mice Undergoing Withdrawal from Morphine Is Associated with Suppression of Interleukin-12

We have shown previously that withdrawal from morphine induces immunosuppression in mice. The present study reports the effects of morphine withdrawal on infection with Salmonella enterica serovar Typhimurium. Mice were made dependent on morphine by the implantation of a slow-release morphine pellet for 96 h. Controls received a placebo pellet. Withdrawal was induced by pellet removal. Mice were inoculated intraperitoneally with Salmonella 24 h postwithdrawal. Morphine withdrawal sensitized mice to Salmonella infection, as evidenced by increased mortality, shortened mean survival time, and increased bacterial load in the blood, spleen, and liver. Examination of the levels of a panel of proinflammatory cytokines in sera of infected, morphine-withdrawn mice showed that morphine withdrawal inhibited the elevation of interleukin-12p70 (IL-12p70). The production of IL-12p40 in morphine withdrawal mice was also suppressed. The administration of exogenous IL-12 significantly decreased the bacterial burden in morphine-withdrawn mice. These studies show a correlation between the suppression of IL-12 production and a heightened susceptibility to Salmonella infection in mice undergoing withdrawal from morphine.

Role of endothelin (ET A) receptors in neonatal morphine withdrawal

We have previously demonstrated role of central endothelin (ET) receptors in neonatal morphine tolerance. The present study was conducted to investigate involvement of central ET receptors in neonatal rat morphine withdrawal. The aim was to determine activation of G-proteins coupled to opioid and ET receptors by morphine and ET ligands in neonatal rat brains during morphine withdrawal. Pregnant female rats were rendered tolerant to morphine by chronic exposure to morphine pellets over 7 days. Withdrawal was induced on day 8 by removal of pellets. Rat pups were delivered by cesarean section 24 h after pellet removal. G-protein stimulation induced by morphine; ET-1; ET A receptor antagonist, BMS182874; and ET B receptor agonist, IRL1620, was determined in the brain of neonatal rats undergoing morphine withdrawal by [ 35S]GTPγS binding assay. Morphine-induced maximal stimulation of G-protein in morphine withdrawal group (83.60%) was significantly higher compared to placebo control group (66.81%). EC 50 value for ET-1-induced G-protein stimulation during morphine withdrawal (170.60 nM) was higher than control (62.5 nM). BMS182874, did not stimulate GTP binding in control but significantly increased maximal stimulation of G-proteins in morphine withdrawal (86.07%, EC 50 = 31.25 nM). IRL1620-induced stimulation of G-proteins was similar in control and morphine withdrawal. The present findings indicate involvement of central ET A receptors in neonatal morphine withdrawal.

Morphine withdrawal sensitizes mice to lipopolysaccharide: Elevated TNF-α and nitric oxide with decreased IL-12

Mice made dependent on morphine using slow-release morphine pellets for 96 h were withdrawn by removal of pellets, followed by a sublethal dose of LPS 24 h later. These animals exhibited 100% lethality. Animals withdrawn from placebo pellets receiving LPS all survived, as did morphine-withdrawn mice receiving saline. Morphine-withdrawn LPS-treated animals had elevated serum TNF-α and nitric oxide levels, and depressed IL-12 levels compared to controls. Anti-TNF-α antibody given prior to LPS challenge afforded significant protection to morphine-withdrawn animals. These studies show that morphine withdrawal sensitizes to LPS lethality via increased production of TNF-α.

Characterization of motor skill and instrumental learning time scales in a skilled reaching task in rat

Successful motor skill learning requires repetitive training interrupted by rest periods. In humans, improvement occurs within and between training sessions reflecting fast and slow components of motor learning [Karni A, Meyer G, Rey-Hipolito C, Jezzard P, Adams MM, Turner R, et al. The acquisition of skilled motor performance: fast and slow experience-driven changes in primary motor cortex. Proc Natl Acad Sci USA 1998;95:861–8]. Here, these components are characterized in male and female rats using a model of skilled forelimb reaching and are compared to time scales of instrumental learning. Twenty female and 14 male adult Long–Evans rats were pre-trained to operate a motorized door (via a sensor in the opposite cage wall) to access a food pellet by tongue. Latencies between pellet removal and door opening were recorded as measures of instrumental learning. After criterion performance was achieved, skilled forelimb reaching was requested by increasing the pellet–window distance to 1.5 cm. Reaching success was recorded per trial. Mean latencies decreased exponentially over sessions and no improvement within-session was found. Skill learning over eight training sessions followed an exponential course in females and a sigmoid course in males. Females acquired the skill significantly faster than males starting at higher baseline levels ( P < 0.001) but reaching similar plateaus. Within-session improvement was found during the sessions 1–3 in females and 1–4 in males. Performance at the end of session 1 was not carried over to session 2. Learning curves of individual animals were highly variable. These findings confirm in rat that motor skill learning has fast and slow components. No within-session improvement is seen in instrumental learning.

Pumping Up Arteries: Estrogen shows beneficial effect (Estrogen replacement therapy)

Hormone replacement therapy's power to cool hot flashes and bolster bone has earned it a reputation as a youth-sustaining pill for postmenopausal women. Scientists have long reasoned that it could help fight heart disease too, in part because premenopausal women have a much lower incidence of the condition than men do; during menopause, estrogen concentrations plummet and the risk for women begins to catch up to that for men. However, a long-term study on a large group released this year--the Heart and Estrogen Replacement Study (HERS)--found that hormone replacement therapy didn't reduce the risk of cardiovascular disease, casting doubt on its benefits in this realm of health care. Now, Mullick and colleagues add fuel to the debate by demonstrating that estrogen protects the vascular system even after treatment stops--at least in rats. What's more, the work lends support to a possible mechanism for the newfound cardiovascular benefits. The researchers had previously found that estrogen protects arteries from age-associated damage. To probe whether this benefit persists after treatment, they implanted pellets that released either estrogen, progesterone, both, or nothing into 26 Sprague-Dawley rats whose ovaries had been removed so they wouldn't churn out estrogen and progesterone. A fifth group received no implant. After 12 months of hormone treatment, the researchers took out the pellets and allowed 1 month for the hormones to wash away. They then excised the carotid arteries from each rat and measured two indicators of vascular health: arterial stiffness and permeability--the ease with which a test substance seeps through the blood vessel lining. Stiff arteries are associated with high blood pressure because the rigid vessels can't expand properly, and increased permeability promotes the development of atherosclerosis by allowing lipids to more easily penetrate and accumulate in the vascular wall. Estrogen treatment led to a 34% improvement in flexibility, measured by the arteries' ability to expand with increasing pressure. And estrogen or a combination of estrogen and progesterone blocked passage of a fluorescent test molecule called TRITC-dextran through the artery wall: Only 64% as much of the compound permeated these vessels as it did those subjected to the other treatments. Previous results suggested that estrogen prevents vascular stiffening by limiting harm from so-called advanced glycation end products (AGEs), which arise from reactions between glucose and proteins and are thought to irrevocably alter proteins and thwart their functions. To find out whether the hormones in this study could be acting by limiting AGE-induced damage, the investigators assessed concentrations of the AGE pentosidine. Even a month after removal of the hormone pellets, concentrations of pentosidine were 50% lower in arteries from rats treated with either estrogen or a combination of estrogen and progesterone than from rats in the other groups. Because the researchers stopped the hormone treatments 1 month before taking measurements, the data indicate that estrogen's benefits persist even after therapy ends. Results from the new study need to be confirmed in women, and estrogen-based therapy--even when used to confer well-established benefits--is controversial because it might boost the risk of breast and other cancers. But if the results hold up, they'll add weight to the notion that this type of hormone treatment blocks some of the vascular changes that come with increasing age. --Christie Aschwanden; suggested by James M. Harper A. E. Mullick, B. A. Walsh, K. M. Reiser, J. C. Rutledge, Chronic estradiol treatment attenuates stiffening, glycoxidation, and permeability in rat carotid arteries. Am. J. Physiol. Heart Circ. Physiol. 281 , H2204-H2210 (2001). [Abstract] [Full Text]

Lead contamination of seabirds harvested with lead shot — implications to human diet in Greenland

Lead contamination of seabirds from the use of lead shot in Greenland was studied in thick-billed murre hunted at Nuuk in November 1998. In each bird shot pellets were located and counted using X-ray. The birds were skinned and viscera, head, wings and legs removed, after which the carcass was cooked. The soup and breast meat were then analyzed for lead after removal of visible shot pellets. In the soup the lead concentration was quite low, mean 6.3 μg/l (95% confidence interval between 4.4 and 8.2 μg/l), whereas breast meat lead values have a mean of 0.22 μg/g (wet weight basis; 95% confidence interval between 0.10 and 0.36 μg/g). This is more than 10 times higher than in birds not killed with lead shot. We found no correlation between lead concentration measured and number of pellets recorded in the whole bird or in the soup or in meat. The study indicates that lead in the meat exists as small lead fragments, left during the passage of pellets through the breast. Because of inhomogeneous lead distribution in samples, the uncertainty of estimated lead concentration in breast meat is high. Based on this study, it is concluded that birds killed with lead shot are a significant source of lead, probably the most important single source, of the diet of many people in Greenland. We estimate an intake of 50 μg lead from eating one boiled murre with soup. In addition people will occasionally eat whole lead shot pellets which have documented health effects. An intake of 50 μg lead is about twice as much as the daily average lead intake from all dietary sources in Denmark, about 25 times the daily lead intake from other marine food items in Greenland, and about one-fourth of the accepted tolerable daily intake.

The Strength and the High Temperature Behaviors of Self-reducing Pellets Containing EAF Dust.

The objective of this work was to study the cold and hot behaviors, that is, cold compressive strength, decrepitation, swelling, compressive strength after heating and efficiency of zinc removal of self-reducing pellets containing coal fines and EAF dust. Pellets with 3 and 5 wt% Portland cement, 12 wt% CaCO3 and without additive were produced. The effect of binder addition on the cold compressive strength was studied during 28 days. For the study of the high temperature behavior, pellets were submitted to thermal cycles with different heating intensities. The best results of cold compressive strength were obtained with 5 and 3 wt% Portland cement due to hydration of components that are contained in this binder. Pellets with Portland cement (3 and 5 wt%), after drying, did not present decrepitation, showing a correlation between the decrepitation, moisture content and mechanical strength of the pellet. Abnormal swelling was observed in pellets submitted to the thermal cycle with lower heating intensity. Such abnormal swelling was due to the growth of whiskers, and as consequence, it was recorded a maximum swelling (higher than 30%). With the gasification of carbon promoted by the release of H2O(g) and CO2(g) from the Portland cement and CaCO3, it was possible to obtain a higher zinc removal as compared to the value obtained with pellets with outadditives, mainly at 1124°C.

Estrogen withdrawal-induced human breast cancer tumour regression in nude mice is prevented by Bcl-2

We recently showed that estrogen induces expression of the anti-apoptotic protein, Bcl-2 in MCF-7 human breast cancer cells. Since estrogen-dependent breast tumours can regress following estrogen withdrawal, we hypothesized that stable Bcl-2 expression would prevent estrogen-withdrawal induced regression of MCF-7 tumours. We therefore established tumours in ovariectomized female nude mice implanted with an estrogen-release pellet using untransfected MCF-7 cells or MCF-7 cells stably transfected with a Bcl-2 cDNA sense or antisense expression vector. All tumours grew at similar rates indicating that Bcl-2 levels have no effect on tumour formation. After removal of the estrogen pellet, Bcl-2 antisense tumours and untransfected MCF-7 tumours regressed means of 49% and 52%, respectively, after estrogen pellet removal whereas Bcl-2 sense tumours were significantly stabilized. Regressing tumours displayed characteristics of apoptotic cells. These results show that Bcl-2 can prevent hormone-dependent breast tumour regression and are consistent with the notion that decreased Bcl-2 levels following estrogen withdrawal renders hormone-dependent breast tumour cells sensitive to apoptotic regression.

Sources of plants colonizing experimentally disturbed patches in an acidic grassland, in eastern England

1 The sources of propagules for regeneration in an acidic grassland were identified from analysis of differences in colonization between plots subject to surface (0–5 cm) soil disturbance and plots where surface soil had been replaced by ‘seed‐free’ soil from deeper soil horizons (30–35 cm), and between plots with and without the removal of rabbit pellets. 2 After 1 year, 10 species had a significantly higher cover on plots where the seed bank had been left intact. These included Agrostis capillaris (the dominant species prior to disturbance), Myosotis arvensis and Veronica arvensis. 3 Five species, including Sagina apetala, Senecio jacobaea and Veronica arvensis, showed significantly higher cover on plots where rabbit pellets were left in situ. 4 From calculations it appeared that rabbit‐dispersed seeds accounted for 15% of the developing higher plant cover, other means of dispersal from outside the plot accounted for 40%, and regeneration from the seed bank accounted for 45%. 5 Similar calculations suggested that three higher plant species, Geranium molle, Myosotis arvensis and Senecio jacobaea, appeared to depend most on non‐rabbit dispersed seed for colonization of bare ground. 6 High concentrations of Urtica dioica in pellets contrasted with its poor establishment in the experiment. However, the other common species in the pellets, Sagina apetala, Senecio jacobaea and Veronica arvensis, all established in greater numbers on the plots where the pellets were not removed. 7 Seed bank content correlated well with the pattern of regeneration for Agrostis capillaris, Holcus lanatus, Myosotis arvensis and Veronica arvensis. However, removal of the seed bank did not have a significant effect on the regeneration of either of the most common species in the seed bank, Rumex acetosella and Sagina apetala. 8 No species appeared to be reliant on only one mechanism for regeneration from seed in disturbed areas in this community.

Typical antipsychotics lead to 5-HT 2A receptor blockade In vivo in schizophrenic patients: Initial single photon emission tomography (SPET) findings

A method is described that permits the simultaneous quantitation of norepinephrine (NE), dopamine (DA) serotonin (5-HT) and their respective major metabolites, 3-methoxy-4 hydroxy phenylglycol (MHPG), 3-methoxytyramine (3-MT), dihydroxyphenyl acetic acid (DOPAC) and 5-hydroxyindole acetic acid (5-HIAA) in discrete brain regions. The ratio of MHPG/NE, DOPAC/DA and 5-HIAA/5-HT was used to assess the effects of the chronic administration of the narcotic antagonist, naltrexone, and its withdrawal on the regional activity of neurons that contain NE, DA and 5-HT respectively. Chronic administration of naltrexone (8 days) is associated with a significant increase in the ratio of 5-HIAA/5-HT and DOPAC/DA in the frontal cortex and dorsal hippocampus respectively. Under this condition the thalamic concentration of 3-MT in 4 of 8 animals is also significantly elevated. In contrast, the mesolimbic forebrain exhibited a decrease in the MHPG/NE ratio (4 out of 8 animals). One day following naltrexone pellet removal the above ratios, as well as the mean content of 3-MT in the thalamus, returned to control values. At this time the content of 3-MT in the thalamus (5 of 5 animals) and frontal cortex (3 of 9 rats) was appreciably elevated, while its content in the dorsal hippocampus was significantly reduced (6 of 9 rats). These data suggest that the activity of several central monoaminergic neuronal systems are regulated by an opioid input that is tonically active.

Time course of the changes in central nitric oxide synthase activity following chronic treatment with morphine in the mouse: Reversal by naltrexone

1. 1. The time course of the effect of chronic administration of morphine on the activity of nitric oxide synthase (NOS) in the brain regions and spinal cord of the mouse was determined. The effect of naltrexone by itself on the NOS activity and that induced by morphine also were determined. 2. 2. Male Swiss Webster mice were implanted subcutaneously with a pellet containing 25 mg of morphine free base for 4 days. Placebo pellet implanted mice served as controls. 3. 3. Twenty-four hours after treatment with morphine, NOS activity decreased in the cerebellum, midbrain, cortex and remainder of the brain as well as in the spinal cord. Forty-eight and 72 hr after the treatment with morphine, NOS activity increased in the cerebellum and cortex, but no change was observed in the other brain regions and spinal cord. Twenty-four hours after morphine pellet removal (withdrawal), NOS activity in all brain regions and the spinal cord had returned to normal. 4. 4. Implantation of a pellet containing 10 mg of naltrexone did not alter NOS activity in any brain region or spinal cord for 24, 48 and 72 hr or 24 hr after removal of the pellet. 5. 5. Implantation of a naltrexone pellet in conjunction with a morphine pellet blocked the changes in NOS activity in the brain region and spinal cord induced by morphine. 6. 6. It is concluded that the initial decrease in NOS activity by morphine may be related to enhanced motor activity, whereas the increase in NOS activity in certain brain regions may be associated with tolerance-physical dependence development. Additionally, the changes in central NOS activity by morphine appear to be mediated by opioid receptors because they were blocked by concurrent treatment with naltrexone.

Blockade of morphine supersensitivity by an antisense oligodeoxynucleotide targeting the delta opioid receptor (DOR-1).

An antisense oligodeoxynucleotide (ODN) targeting 20 bases of the coding sequence of the cloned delta opioid receptor (DOR-1), a mismatched ODN (different from the antisense ODN at 4 bases) or saline was administered to 3 groups of CD-1 mice implanted with naltrexone pellets (7.5 mg) for 7 days. Morphine supersensitivity (i.e., increased potency as defined by decreased morphine ED50 values) was observed 24 h after pellet removal (day 8) in mice treated with saline or mismatch ODN, but not in antisense ODN treated mice. Antisense ODN alone had no effect on basal nociceptive thresholds or morphine analgesia but reduced the analgesic potency of the delta, opioid agonist [D-Ala2]deltorphin II. These data suggest that the delta2 opioid receptor system participates in the adaptive changes contributing to increased morphine potency following chronic naltrexone treatment.

Effect of morphine on proopiomelanocortin gene expression and peptide levels in the hypothalamus

Opiates have been reported to suppress POMC in the medial basal hypothalamus (MBH) but studies have been complicated by the fact that acutely, in the rat, opiates stimulate corticosterone and inhibit gonadal steroid release, which could both affect POMC in brain. We have therefore examined POMC gene expression and peptide levels in the MBH of castrated rats after 10 days of treatment with subcutaneous morphine or placebo pellets and after pellet removal. POMC mRNA was measured by solution hybridization assay and β-endorphin (β-EP) and α-MSH were measured by RIA. In castrated male rats, the mean POMC mRNA concentration in the MBH was 1.67 ± 0.11 pg/μg RNA in the control animals and decreased to 1.17 ± 0.11 pg/μg RNA in the morphine-treated animals ( P < 0.01). Similarly in castrated, estradiol replaced female rats, the mean POMC mRNA level in the MBH was 1.36 ± 0.19 pg/μg RNA and decreased to 0.82 ± 0.08 pg/μg RNA after morphine treatment ( P < 0.05). β-EP levels were not significantly different in either study. When castrated male rats were similarly morphine pelleted and killed either on day 10 or 2 days later after pellet removal, the mean POMC mRNA level again fell from 1.83 ± 0.21 in the controls to 1.28 ± 0.20 pg/μg RNA after 10 days of morphine; 2 days after pellet removal levels remained suppressed at 0.80 ± 0.08 pg/μg RNA ( P < 0.01). In this study the concentrations of β-EP and α-MSH were both noted to decline in the MBH after morphine treatment ( P < 0.05). When the forms of β-EP in the MBH were characterized by HPLC, a decrease in the concentration of β-EP was again seen after morphine but no significant differences in the pattern of β-EP processing or in the relative amounts of β-EP 1–31 compared to β-EP 1–27 and β-EP 1–26 were noted in morphine-treated animals. There was also no significant effect of 10 −6−10 −4 M morphine on basal or KCl-stimulated release of β-EP or γ 3-MSH release from the perifused rat hypothalamus in vitro. We conclude that morphine suppresses POMC gene expression in the hypothalamus of chronically treated male and female rats. Persistent changes were also noted during morphine withdrawal. In some cases this was accompanied by a fall in β-EP peptide content. These effects were seen in castrated animals with and without sex steroid replacement and are thus independent of the effects of morphine on the pituitary-gonadal axis. These results show that opiate drugs modify endogenous opioid systems in the brain and provide further support for the hypothesis that such changes may contribute to mechanisms of opiate dependence and withdrawal.