Weeks Of Chronic Treatment Research Articles

Regulation of Iron Homeostasis By PTG-300 Improves Disease Parameters in Mouse Models for Beta-Thalassemia and Hereditary Hemochromatosis

Hepcidin-Ferroportin axis dictates optimal absorption of dietary iron as well as systemic iron levels. This is crucial for providing sufficient iron needed for cellular functions while also preventing iron toxicity. PTG-300 (currently in a Phase 2 clinical study for beta-thalassemia) is a peptide mimetic of natural hepcidin that targets the major iron transporter, ferroportin, and causes its internalization & subsequent degradation. The pharmacodynamic effects of PTG-300 are the reductions in serum iron and transferrin-saturation (TSAT) due to reduced ferroportin expression on cells that store or recycle iron. We chose to demonstrate in two mouse models with iron dysregulation, that our hepcidin mimetics improve disease parameters by correcting dysregulated iron homeostasis. Beta-thalassemia is characterized by an imbalance in alpha-beta globin ratio in erythrocytes due to underlying beta-globin gene mutations. The excess alpha-globin, along with associated heme and iron, form "hemichrome" aggregates that integrate into the membranes of RBCs. The labile iron in these hemichromes generate ROS and are toxic to the cells, causing premature hemolysis of circulating RBCs and reduction in their lifespan. In a mouse model for beta-thalassemia, Hbbth3/+, we investigated the efficacy of a hepcidin mimetic in reducing hemichrome aggregation by limiting iron in the erythroid progenitors, and thereby reducing iron toxicity in RBCs. Subcutaneous injections of 1 mg/kg PN-8772 (analog of PTG-300 which has similar in vitro and in vivo potency) were administered every other day (Q2D) for a period of 4 weeks. At the end of the study, hemichrome aggregates were extracted from RBC membranes, and then analyzed on a TAU gel to quantify the cytoskeleton α-globin band intensities (Casu et al, Blood 2016). Hemichrome aggregates were reduced in groups treated with PN-8772 as compared to untreated controls, with concurrent improvements in hemoglobin and reductions in reticulocytes. Treatment with oral chelator Deferasirox (200 mg/kg; daily) did not show reduction in hemichrome aggregation, while it significantly lowered liver iron-overload. RBCs in Hbbth3/+ mice express aberrant morphologies due to the underlying hemichrome toxicity, similar to the phenotypes expressed in human beta-thalassemia. Chronic treatment with PN-8772 (as described above) also resulted in a significant reduction in aberrant morphologies that are indicative of hemolysis, viz. spherocytes & schistocytes. In a separate study, flow cytometry was used to monitor the survival of RBCs in Hbbth3/+ mice. At the end of 4 weeks of PTG-300 treatment (1 mg/kg, Q2D) the RBCs were marked by an in-life biotinylation method (Schmidt et al, Blood 2013) and subsequently followed over 49 days with continued treatment. There was a significant increase in survival of RBCs as compared to untreated controls. In summary, we demonstrate that by limiting iron in the developing erythroblasts and iron toxicity in RBCs, PTG-300 therapy has the potential to improve the quality of the RBCs and their oxygen carrying capacity, thereby ameliorating anemia. In beta-thalassemia, the clinical presentation includes secondary iron overload in various organs because of hyperabsorption of dietary iron, exacerbated by frequent blood transfusions that are required for management of anemia. Similarly, in hereditary hemochromatosis (HH) there is hyperabsorption of dietary iron leading to primary iron overload. We used a hemochromatosis mouse model (HFE) to demonstrate the effectiveness of PTG-300 therapy in limiting systemic iron toxicity by regulating TSAT and in preventing hyper-iron absorption. The model is characterized by homozygous deletion of HFE with severely low hepcidin levels and consequently very high TSAT (~100%). In this model, a single dose of PTG-300 at 2.5mg/kg reduced TSAT by ~60% at 10-hour post-dose, as compared to untreated controls. Sustained TSAT reduction by chronic treatment will therefore mitigate toxic effects of labile iron. Two weeks of chronic treatment with PTG-300 (2.5 mg/kg, Q2D) effectively prevented iron deposition in the liver. Overall our data suggests that PTG-300 has the potential to be an effective treatment in hemoglobinopathies, like beta-thalassemia, and Hereditary Hemochromatosis, by reducing systemic labile iron toxicity by limiting TSAT, preventing organ iron deposition & improving anemia (in case of thalassemia). Disclosures Taranath: Protagonist Therapeutics: Employment. Bourne:Protagonist Therapeutics: Employment. Zhao:Protagonist Therapeutics: Employment. Frederick:Protagonist Therapeutics: Employment. King:Protagonist Therapeutics: Employment. Liu:Protagonist Therapeutics: Employment.

The effect of Paracetamol exposure on hepatic and renal tissues during statin usage

Abstract Objective Statins and Paracetamol have widespread use in clinic and both drugs possess similar side effects; therefore, we investigated if drug-interaction occurs when the combination of these two drugs is used during therapy. Materials and methods A total of 32 (12–15 months old) grown-up male rats were divided into four groups: Control group, RSV group (10 mg/kg Rosuvastatin/daily), APAP group (50 mg/kg Paracetamol/5 days/weekly), RSV+APAP (10 mg/kg Rosuvastatin/daily+50 mg/kg Paracetamol/5 days/weekly). At the end of 8 weeks of chronic treatment, the blood and tissue samples were taken under the Ketamine and Xylasine anesthesia (50 mg/kg and 5 mg/kg, respectively). Results In the liver, sinusoidal dilatations, pyknotic nuclei and hemorrhagic foci are more frequently seen in the group receiving combination therapy; although serum liver functions among groups were not significantly different. Kidney histopathologic alterations in APAP and RSV+APAP groups were found more distinct than in RSV alone group. Inducible nitric oxide synthase activity was highly increased with combination therapy in liver and kidney tissues. Conclusion RSV-Paracetamol interaction may occur as an important drug interaction histopathologically even before it is manifested biochemically in the clinic.

Endothelin-1-induced remodelling of murine adult ventricular myocytes

The precise role of hormones binding to Gαq protein-coupled receptors (H-GαqPCRs) in chronic heart diseases remains poorly understood. To address this, we used a model of cultured adult rat ventricular myocytes stimulated with endothelin-1 (ET-1) or phenylephrine (PE) over a period of 8 days in vitro (DIV). Chronically treated cells showed an increased number of arrhythmogenic Ca2+ transients when electrically paced at 0.5Hz. While their post-rest behaviour was preserved, from DIV6 onwards the amplitude of caffeine-evoked Ca2+ transients was increased in hormone-treated cells, suggesting an elevated sarcoplasmic reticulum Ca2+ load. The duration of electrically evoked global Ca2+ transients gradually increased over the culturing time indicating decreased activity of processes removing cytosolic Ca2+. In treated cells, spontaneous Ca2+ sparks displayed smaller amplitudes from DIV6 onwards, and a slower decay period for PE (from DIV3) and for ET-1 (from DIV6). This cellular functional remodelling was associated with changes in gene expression: chronic ET-1 treatment decreased PKCγ transcripts, whereas PE increased PKCγ and SERCA2a transcripts as probed by qPCR. Western blot analysis confirmed the upregulation of PKCγ with PE. To study ET-1 receptor desensitization in vivo, osmotic minipumps containing either NaCl or ET-1 were implanted in mice and Ca2+ signalling was studied in acutely isolated ventricular myocytes after 2 weeks of chronic treatment. Interestingly, while cellular responses to isoproterenol stimulation were preserved in ET-1 treated animals, the inotropic response of myocytes to ET-1 stimulation was abrogated. We therefore conclude that chronic stimulation of cardiac myocytes by H-GαqPCRs induces cellular remodelling of Ca2+ cycling with altered PKCγ expression and promotion of arrhythmogenic cellular responses.

7D.10

Objective: It has been previously demonstrated that inflammation in adipose tissue may be implicated in vascular dysfunction (Circulation 2009; 119(12):1661–1670). A senescence-accelerated prone mouse (SAMP8) is a model of age-related cognitive decline and vascular dysfunction. Several studies demonstrated that SAMP8 suffers from increased oxidative stress and that accelerated senescence was associated with decreased eNOS and nNOS and increased oxygen radicals synthesis. Aim of the study was to investigate functional responses of small mesenteric arteries in a senescence-accelerated prone mouse (SAMP8) before and after chronic treatment with melatonin.Design and method: We investigated 7 SAMP8 and 7 SAMR1 normal controls. Mesenteric small resistance arteries were dissected and mounted on a wire myograph, according to Mulvany-Halpern technique (internal diameter about 200 μm). A concentration-response to norepinephrine (NE, from 10–9 to 10-5 Mol/l) was evaluated in vessels with intact prerivascular fat tissue (WF) and in vessels in which perivascular fat tissue was removed (NoF). Investigations were repeated in 7 SAMP8 and 7 SAMR1 after 54 weeks of chronic treatment with melatonin, an endogenous hormone with antioxidant and vasculoprotective properties. Results: In SAMR1 control mice anticontractile effect of perivascular fat was present (WF vs. NoF: ANOVA p = 0.04), while in aging SAMP8 mice the effect was less pronounced (WF vs. NoF: ANOVA p = NS) (see figure). Long-term treatment with melatonin had no effect in SAMR1 either in WF or NoF vessels, while it decreased the contractile response to norepinephrine in noF vessels of SAMP8 (ANOVA p < 0.001); the effect of melatonin treatment in WF vessels was not statistically significant. Conclusions: The anticontractile effect of perivascular fat is impaired in a senescence-accelerated prone mouse, compared with controls. A long-term treatment with melatonin seems to decrease contractile responses to norepinephrine in NOF mesenteric small arteries of SAMP8, thus restoring an anticontractile effect, probably through antioxidant mechanisms.

Nasal Application of the Galantamine Pro-drug Memogain Slows Down Plaque Deposition and Ameliorates Behavior in 5X Familial Alzheimer's Disease Mice.

The plant alkaloid galantamine is an established symptomatic drug treatment for Alzheimer's disease (AD), providing cognitive and global relief in human patients. However, as an acetylcholinesterase inhibitor, gastrointestinal side effects limit the dosage and duration of treatment. Memogain (Gln-1062), a pro-drug, liberates galantamine on cleavage by a carboxyesterase in the brain. The possibility to deliver Memogain intranasally may further circumvent side effects, allowing higher dosing compared to galantamine. In this study, the 5X Familial Alzheimer's Disease (5XFAD) mouse model was used to investigate the effect of chronic Memogain treatment on behavior and amyloid-β (Aβ) plaque deposition in the brain. Chronic intranasal dosage of 6 mg/kg body weight twice daily was tolerated well, whereas the double dose caused body weight loss in males and was less effective in some behavioral tests. 8 weeks of chronic treatment resulted in improved performance in behavioral tests, such as open field and light-dark avoidance, and in fear conditioning already at mildly affected stages at the age of 18 weeks compared to untreated controls. Furthermore, after treatment a significantly lower plaque density in the brain, i.e., in the entorhinal cortex (reduction 20% females, 40% males) and the hippocampus (19% females, 31% males) at the age of 18 weeks was observed. These results show that nasal application of Memogain effectively delivers the drug to the brain with the potential to retard plaque deposition and improve behavioral symptoms in AD similar to the approved galantamine.

Facilitation of Serotonin Signaling by SSRIs is Attenuated by Social Isolation

Hypofunction of the serotonergic system is often associated with major depression and obsessive compulsive disorder (OCD). Selective serotonin reuptake inhibitors (SSRIs) are commonly prescribed to treat these disorders, and require 3-6 weeks of chronic treatment before improvements in the symptoms are observed. SSRIs inhibit serotonin's transporter, and in doing so, increase extracellular serotonin concentrations. Thus, efficacy of SSRIs likely depends upon the brain's adaptive response to sustained increases in serotonin levels. Individual responsiveness to SSRI treatment may depend on a variety of factors that influence these changes, including ongoing stress. Social isolation is a passive, naturalistic form of chronic mild stress that can model depression in rodents. In this study, we examined how 20-day treatment with the SSRI citalopram (CIT) alters marble-burying (MB), open field behavior, and serotonin signaling in single- vs pair-housed animals. We used in vivo voltammetry to measure electrically evoked serotonin, comparing release rate, net overflow, and clearance. Pair-housed mice were significantly more responsive to CIT treatment, exhibiting reduced MB and facilitation of serotonin release that positively correlated with the frequency of electrical stimulation. These effects of CIT treatment were attenuated in single-housed mice. Notably, although CIT treatment enhanced serotonin release in pair-housed mice, it did not significantly alter uptake rate. In summary, we report that chronic SSRI treatment facilitates serotonin release in a frequency-dependent manner, and this effect is blocked by social isolation. These findings suggest that the efficacy of SSRIs in treating depression and OCD may depend on ongoing stressors during treatment.

Flibanserin Treatment Increases Appetitive Sexual Motivation in the Female Rat

Flibanserin is a mixed 5-HT1A agonist/5-HT2A antagonist that has been developed for the treatment of hypoactive sexual desire disorder in women. To assess the acute and chronic dose-response effects of flibanserin on measures of sexual desire and copulation in ovariectomized rats primed with estradiol benzoate (EB) alone or in combination with progesterone (P). In Experiment 1, sexually experienced ovariectomized (OVX) rats at one testing site were rendered fully sexually receptive with EB + P priming and tested weekly with a sexually active male in bi-level pacing chambers following daily flibanserin treatment for 28 days. In Experiment 2, sexually experienced OVX rats at a different testing site received EB alone and were tested weekly with sexually active males following daily flibanserin treatment. Female appetitive behaviors (solicitations, hops and darts, anogenital investigations), defensive behaviors, pacing, lordosis, and male copulatory responses (intromissions and ejaculations) were measured during each 30-minute copulation test. Acute flibanserin or 1 week of chronic flibanserin treatment did not modify sexual responses in fully (EB + P) or partially (EB-alone) primed females. After 2 weeks of chronic treatment, fully primed females displayed significantly more solicitations than the three other groups. After 3 weeks of chronic treatment, a significant increase in female solicitations was observed in both hormone-treatment groups. This study shows the first evidence that chronic, but not acute, flibanserin treatment augments appetitive sexual behaviors in OVX female rats primed with EB + P or EB alone. Given the positive effect of flibanserin in clinical trials, these results confirm previous reports that solicitations in the female rat are a predictive animal model of human female sexual desire.

Thyroid hormone affects both endothelial and vascular smooth muscle cells in rat arteries

SAR, China, Peopleˈs Republic of The effect of thyroid hormone on vascular cells is controversial. The present study investigated in isolated arteries [with and without endothelium; suspended for isometric tension measurement] whether or not thyroid hormone causes relaxations in, or alleviates endothelial dysfunction in diabetic animals.Triiodothyronine, (T3) did not relax aortae of control rats with or without endothelium but caused endothelium‐independent decreases in tension in mesenteric arteries, suggesting an endothelium‐independent vasodilator effect of the hormone.In femoral arteries of rats with streptozotocin‐induced Type 1 diabetes, A23187 caused the release of endothelium‐derived contracting factors (EDCF). After four weeks of chronic treatment with T3, the contractions to A23187 of preparations with endothelium were unchanged, but those without endothelium were augmented, suggesting that the release of EDCF was reduced. Thus, thyroid hormone affects both endothelial and vascular smooth muscle cells in rat arteries.

TP receptor antagonists (TXRAs): expensive irrelevance or wonder drugs strangled at birth?

TP receptor antagonists (TXRAs): expensive irrelevance or wonder drugs strangled at birth?

Chronic administration of DSP‐7238, a novel, potent, specific and substrate‐selective DPP IV inhibitor, improves glycaemic control and β‐cell damage in diabetic mice

The purpose of this study is to assess the in vitro enzyme inhibition profile of DSP-7238, a novel non-cyanopyrrolidine dipeptidyl peptidase (DPP) IV inhibitor and to evaluate the acute and chronic effects of this compound on glucose metabolism in two different mouse models of type 2 diabetes. The in vitro enzyme inhibition profile of DSP-7238 was assessed using plasma and recombinant enzymes including DPP IV, DPP II, DPP8, DPP9 and fibroblast activation protein alpha (FAPalpha) with fluorogenic substrates. The inhibition type was evaluated based on the Lineweaver-Burk plot. Substrate selectivity of DSP-7238 and comparator DPP IV inhibitors (vildagliptin, sitagliptin, saxagliptin and linagliptin) was evaluated by mass spectrometry based on the changes in molecular weight of peptide substrates caused by release of N-terminal dipeptides. In the in vivo experiments, high-fat diet-induced obese (DIO) mice were subjected to oral glucose tolerance test (OGTT) following a single oral administration of DSP-7238. To assess the chronic effects of DSP-7238 on glycaemic control and pancreatic beta-cell damage, DSP-7238 was administered for 11 weeks to mice made diabetic by a combination of high-fat diet (HFD) and a low-dose of streptozotocin (STZ). After the dosing period, HbA1c was measured and pancreatic damage was evaluated by biological and histological analyses. DSP-7238 and sitagliptin both competitively inhibited recombinant human DPP IV (rhDPP IV) with K(i) values of 0.60 and 2.1 nM respectively. Neither vildagliptin nor saxagliptin exhibited competitive inhibition of rhDPP IV. DSP-7238 did not inhibit DPP IV-related enzymes including DPP8, DPP9, DPP II and FAPalpha, whereas vildagliptin and saxagliptin showed inhibition of DPP8 and DPP9. Inhibition of glucagon-like peptide-1 (GLP-1) degradation by DSP-7238 was apparently more potent than its inhibition of chemokine (C-X-C motif) ligand 10 (IP-10) or chemokine (C-X-C motif) ligand 12 (SDF-1alpha) degradation. In contrast, vildagliptin and saxagliptin showed similar degree of inhibition of degradation for all the substrates tested. Compared to treatment with the vehicle, single oral administration of DSP-7238 dose-dependently decreased plasma DPP IV activity and improved glucose tolerance in DIO mice. In addition, DSP-7238 significantly decreased HbA1c and ameliorated pancreatic damage following 11 weeks of chronic treatment in HFD/STZ mice. We have shown in this study that DSP-7238 is a potent DPP IV inhibitor that has high specificity for DPP IV and substrate selectivity against GLP-1. We have also found that chronic treatment with DSP-7238 improves glycaemic control and ameliorates beta-cell damage in a mouse model with impaired insulin sensitivity and secretion. These findings indicate that DSP-7238 may be a new therapeutic agent for the treatment of type 2 diabetes.

Combination Antiplatelet Therapy with Aspirin and Clopidogrel: The Role of Antecedent and Concomitant Doses of Aspirin

Background: Numerous randomized studies have shown that the combination of clopidogrel with aspirin yields better clinical outcomes than monotherapy in patients with acute vascular events. However, the impact of the aspirin dose on the antiplatelet potency of clopidogrel is unclear. We sought to compare the antiplatelet profile of aspirin 81 mg (n = 252) versus aspirin 325 mg (n = 459) before and during conventional clopidogrel loading (300 mg), and/or clopidogrel maintenance (75 mg/daily) therapy. Methods: Secondary post hoc analysis of an existing dataset consisting of 711 patients after coronary stenting (n = 601) and ischemic stroke (n = 110) treated previously with aspirin for at least 1 month, and then with aspirin + clopidogrel for at least 7 days was performed. Platelet assessments include conventional and whole blood aggregometry, rapid cartridge-based analyzers, and expression of platelet/endothelial cell adhesion molecule-1, P-selectin, and GPIIb/IIIa activity by flow cytometry measured before and after addition of clopidogrel. Results: There was a small but consistent yet non-significant trend towards more potent platelet inhibition with aspirin 325 mg compared to aspirin 81 mg for every platelet activation parameter before addition of clopidogrel. However, after loading and/or 1 week of chronic treatment with clopidogrel + aspirin, measured platelet parameters became very similar between the groups, and identical for collagen-induced aggregation and PFA-100 analyzer readings. Conclusions: Before addition of clopidogrel, aspirin 325 mg has a tendency to provide stronger platelet inhibition than aspirin 81 mg. However, when clopidogrel and aspirin are used in combination, the higher aspirin dose does not translate into superior antiplatelet action. Given that the existing body of evidence supports the comparable efficacy and, particularly, superior safety of lower versus higher doses of aspirin, aspirin 81 mg should be the dose used in combination with clopidogrel.

Sex-related elevation in cortisol during chronic treatment with alprazolam associated with enhanced cognitive performance

There is evidence of more widespread use and abuse of benzodiazepines (BZPs) among elderly women. However, factors underlying this observation are poorly understood but could be related to more intense withdrawal reactions, which are a major risk factor for continued BZP use. We previously reported elevations in interdose morning plasma cortisol levels in healthy elderly individuals after chronic treatment with alprazolam, possibly consistent with increased hypothalamic-pituitary-adrenal (HPA) axis activity and drug withdrawal. In this study, we examined sex-related differences in this population. Twenty-five cognitively intact healthy elderly (13 women and 12 men) participated in a parallel, double-blind, placebo-controlled study that included a group that received acute and chronic (3 weeks) treatment with alprazolam (0.5 mg b.i.d.). Elderly women, but not men, experienced significant elevations in interdose morning plasma cortisol levels over 3 weeks of chronic treatment with alprazolam (0.5 mg b.i.d.) compared to placebo. In addition, higher morning plasma cortisol levels were significantly associated with better cognitive performance but not with higher plasma drug levels or greater degree of tolerance development to an acute alprazolam challenge. Elderly females experienced a greater interdose activation of the HPA axis during treatment with therapeutic doses of alprazolam than men, which could be related to drug withdrawal.

NKP608, an NK1 receptor antagonist, has an anxiolytic action in the social interaction test in rats.

Evidence is starting to accumulate that NK1 receptor antagonists might have anxiolytic effects in animal tests and in patients. To examine the effects of NKP608, a substance P antagonist acting at NK1 receptors, in various conditions of the social interaction test of anxiety and to determine its effects after 3 and 6 weeks of treatment. Rats were tested after vehicle, 0.01 or 0.1 mg/kg PO in three conditions of the social interaction test that varied in the level of anxiety generated. Thus pairs of rats were tested in an arena with which they were unfamiliar that was lit by high (HU) or low (LU) light and in the condition that generated the lowest level of anxiety, i.e. an arena with which they were familiar, lit by low light (LF). They were also tested after 3 and 6 weeks of treatment with 0.03 mg/kg and after 24 h withdrawal from these chronic treatments. NKP608 had significant anxiolytic effects at 0.01, 0.03 and 0.1 mg/kg PO in the HU and LU test conditions, but was without effect in the LF condition, except for an increased incidence of bite attacks at 0.1 mg/kg. The anxiolytic effect of 0.03 mg/kg remained after 3 weeks of chronic treatment and there was no anxiogenic effect after 24 h of drug withdrawal. Following 6 weeks of chronic treatment (0.03 mg/kg per day), tolerance had developed, but no anxiogenic withdrawal effect was seen 24 h after the last dose. These results provide further evidence that substance P may play a role in mediating states of anxiety and suggest that the selective NK1 receptor antagonist NKP608 may prove a useful anxiolytic compound.

14-12 - The effects of iorazepam and alprazolam on cognition in the elderly

Benzodiazepines with shorter elimination half-lives are widely prescribed In the elderly and generally thought to produce less cognitive toxicity than agents with longer half-lives such as diazepam. However, there are few stud• ies that have examined the cognitive effects of these agents In the elderly. This study assessed the acute and chronic effects on task perfonnance of high and low equivalent doses of alprazolam and lorazepam, two benzo• diazepines with relatively short half-lives. The relationship of these effects to age, plasma drug levels and duration of treatment was also examined. Eighty subjects (ages~7 yrs) participated In an NIMH-sponsored 3-week double-blind, placebo-controlled, parallel group study comparing low(0.25 mg bid) and hlgh-close (0.5 mg bid) alprazolam versus low(0.5 mg bid) and high-dose (1.0 mg bid) lorazepam. Both low and high doses of alprazolam and lorazepam produced significant impairments in the Buschke total recall in the Initial acute challenge. Chronic treatment was associated with minimal next-day effects. Acute rechallenge with high doses of alprazolam and 10• razepam after 3 weeks of chronic treatment was associated with significant less impairment than that observed In the Initial acute challenge, consistent with the development of tolerance. Nevertheless, rechallenge with low doses of lorazepam and alprazolam and high doses of lorazepam still produced significant Impairment compared to placebo. These findings suggest caution In the use of these medications In the elderly.

Anticonflict effect of MK-801 in rats: Time course and chronic treatment studies

The present study examined the time course and chronic treatment effects of the noncompetitive N-methyl-D-aspartate (NMDA) antagonist, MK-801 (dizocilpine), on conflict behavior in the conditioned suppression of drinking (CSD) paradigm, a repeated-measures conflict task. In daily 10-min sessions, water-restricted rats drank from a tube that was occasionally electrified (0.25- or 0.5-mA shocks signaled by a tone). Trained subjects (4 weeks of CSD testing) exhibited stable baselines for both punished responding and unpunished responding. In the first experiment, the effects of MK-801 administered IP were determined in female and male rats following a range of pretreatment intervals (i.e., 0.5–48 h). In female rats, 0.2 mg/kg MK-801 exerted an anticonflict effect at pretreatment intervals of 10–36 h, but not before 10 h or after 36 h. In male rats, qualitatively similar results were obtained; MK-801 (0.4 mg/kg) exerted anticonflict effects following pretreatment intervals of 6–14 h, but not before 6 or after 14 h. In the second experiment, chronic treatment of female rats with 0.04, 0.1, or 0.2 mg/kg MK-801 resulted in a dose-dependent anticonflict effect in CSD paradigm, which remained stable over the course of 5 weeks of chronic treatment. Punished responding returned to pretreatment levels within 2–3 days after discontinuation of chronic treatment with MK-801. These data suggest that MK-801 exerts a delayed anticonflict effect in both female and male rats with a qualitatively similar pattern, and that there is no tolerance to the anticonflict effect of MK-801 with chronic treatment.

Chronic bretazenil produces tolerance to chlordiazepoxide, midazolam, and abecarnil

The purpose of the present study was to determine if chronic treatment with a nonsedative benzodiazepine partial agonist would confer tolerance to the rate-decreasing effects of other benzodiazepine ligands in a fixed-interval procedure in rats. A separate group of rats was treated chronically with the sedative benzodiazepine full agonist, chlordiazepoxide, for comparison. It was hypothesized that tolerance would develop rapidly to chlordiazepoxide due to loss of reinforcement density at rate-decreasing doses and that there would probably be cross-tolerance to other rate-decreasing benzodiazepine ligands such as midazolam and abecarnil. Because bretazenil does not produce rate decreases, however, it was not expected that tolerance would be found to chlordiazepoxide, midazolam, or abecarnil. After 8–12 weeks of chronic treatment with either chlordiazepoxide or bretazenil, however (final dose of benzodiazepine = 30 mg/kg/day), tolerance was found to the rate-decreasing effects of chlordiazepoxide, midazolam, and abecarnil in both groups. It is concluded that such tolerance was most likely due to a saturation of benzodiazepine receptors by this high-affinity partial agonist.

The effects of selective and non-selective monoamine oxidase (MAO) inhibitors on conflict behavior in the rat

Conflict behavior in rats was examined over the course of several weeks of chronic treatment with selective and non-selective monoamine oxidase inhibitors (MAOIs). In daily 10min sessions, rats were trained to drink from a tube which was occasionally electrified (0.5mA). Electrification was signalled by the presence of a tone. Within 3-4 weeks, control (i.e. non-drug) conflict behavior had stabilized (30-40 shocks and 8-12ml water/session) and drug testing began. Chronic administration (two injections/day for 8 weeks) with a non-selective (i.e. MAO-A and MAO-B inhibiting) dose of pargyline (15mg/kg) resulted in a time-dependent increase in punished responding. In contrast, chronic administration of the MAO-A selective inhibitor (clorgyline; 1.0mg/kg, 2mg/kg), the MAO-B selective inhibitor deprenyl (5mg/kg) or MAO-B inhibiting doses of pargyline (1.0mg/kg, 5mg/kg) were without effect. Finally, chronic treatment with the combination of a low dose of clorgyline (1.0mg/kg) and a low dose of pargyline (1.0mg/kg) did result in a time-dependent increase in punished responding. These results suggest that inhibition of both MAO-A and MAO-B is required for the eventuation of the anxiolytic effect resulting from chronic MAOI treatment.

The Effect of Nortriptyline on Cognition

Despite widespread belief that antidepressants cause cognitive dysfunction, there has been surprisingly little systematic research that supports this view. With this in mind, our group sought to evaluate the effects of the tricyclic antidepressant nortriptyline on a variety of cognitive and psychomotor tasks. For the purposes of this report, we will focus on Buschke Total Recall. Seventy-eight patients (age range 21-81, mean age 49.95) who met RDC and DSM-III criteria for major depression (mean Hamilton score 20.82) voluntarily agreed to participate in a 6 week double-blind trial whereby they received either notriptyline (NT) or placebo (PBO) following a 1 week single-blind placebo. At each weekly visit the patient received a comprehensive neuropsychological battery which included the Buschke Selective Reminding Task. In addition at baseline, the patient was acutely challenged with the medication to which he was randomized (either PBO or 50 mg NT) and the neuropsychological battery including Buschke selective reminding test was repeated at 1.5 and 4 hrs. All patients received another acute challenge (either placebo or 50 mg nortriptyline) after 6 weeks of chronic treatment. Doses of NT were adjusted weekly to maintain therapeutic plasma levels. Data were analyzed by an analysis of variance with age group (young vs old-55 was the cutoff) and drug status (drug vs PBO) the between subject factors and time of assessment (weekly for the chronic effect and 1.5 & 4 hrs for the acute effect) as the within subject factor. In view of the effect of depression on memory, we used weekly Hamilton depression score as a covariate. The results indicated that there was no statistically significant difference between the NT (mean plasma level 87.94 ng/ml at wk6) vs PBO group with respect to the chronic effects on Buschke Total Recall. There was also no difference between NT vs PBO with respect to Buschke Total Recall after acute challenge at baseline and after acute rechallenge following 6 weeks chronic treatment with either NT or PBO.

The relationship between motor effects in rats following acute and chronic haloperidol treatment

Tardive dyskinesia (TD) is a serious and sometimes irreversible side-effect to long-term neuroleptic treatment. In order to find predictors for development of TD, it would be of interest to known whether susceptibility to develop acute side-effects increases the risk of TD development. The study investigated in female Sprague-Dawley rats the relationship between haloperidol-induced acute motor effects, assessed by means of the grid test and the open field test, and the chronic motor effect assessed as vacuous chewing movements (VCM). The doses of haloperidol were 1.2, 2.4 and 4.8 mg/kg IP in the acute experiments and haloperidol decanoate 38 mg/kg per 4 weeks IM in the chronic experiment. The VCM obtained at different timepoints during the 24 weeks of chronic treatment were highly correlated. However, no correlation was found between the motor effects in the acute and the chronic experiments. The study does not indicate any connection between susceptibility to acute side-effects on neuroleptics and later development of TD.

Reversal of stress-induced anhedonia by the dopamine receptor agonist, pramipexole.

Chronic exposure to mild unpredictable stress has previously been found to depress the consumption of a palatable (1%) sucrose solution, and to attenuate food-induced place preference conditioning. In this study the effects of pramipexole (SND-919), a dopamine D2 agonist, were studied during 7-9 weeks of chronic treatment. Pramipexole (1.0 mg/kg per day) reversed the suppression of sucrose intake in stressed animals, increasing sucrose intakes above the levels seen in untreated nonstressed controls. Pramipexole also increased sucrose intake in nonstressed animals; these effects were accompanied by increases in water intake and tended to correlate with weight loss. Drug-treated stressed animals also lost weight, but in this case water intake was unaffected. A second group of animals received a higher dose of pramipexole (2.0 mg/kg per day). The effects of the two doses were very similar. After three weeks of treatment, these animals were switched to a lower dose of pramipexole (0.1 mg/kg per day). Increases in sucrose intake were maintained over three weeks of treatment at the lower dose, with significant recovery of body weight. Two further groups received the same doses of pramipexole (1.0 mg/kg for 6 weeks or 2.0 mg/kg for 3 weeks followed by 0.1 mg/kg thereafter), but received intermittent (twice-weekly) drug treatment. Intermittent pramipexole treatments also tended to increase sucrose intakes, but the results were less consistent from week to week. Following 6-8 weeks of pramipexole treatment, food-induced place preference conditioning was studied in all animals.(ABSTRACT TRUNCATED AT 250 WORDS)