Chemogenetic selective manipulation of nucleus accumbens medium spiny neurons bidirectionally controls alcohol intake in male and female rats

The nucleus accumbens (NAc), considered the hub of reward circuitry, is comprised of two medium spiny neuron (MSN) subtypes that are classified by their enrichment of dopamine 1 (D1) or 2 (D2) receptors. While reports indicate that alcohol increases excitatory neurotransmission exclusively on NAc D1-MSNs in male rats, it remains unknown how NAc MSNs control alcohol intake in either sex. Therefore, this study investigated how NAc MSNs mediate alcohol intake by using Drd1a-iCre and Drd2-iCre transgenic rats of both sexes. Intra-NAc infusions of Cre-inducible viral vectors containing stimulatory (hM3Dq) or inhibitory (hM4Di) designer receptors exclusively activated by designer drugs (DREADDs) were delivered after 4-weeks of alcohol intake, and clozapine-N-oxide (CNO) was administered to selectively manipulate NAc MSNs. Our results show that activation of NAc D1-MSNs increased alcohol intake 1-, 4-, and 24-h after the start of drinking while inhibition decreased it 1-h after the start of drinking, with no sex differences observed at any time point. Activation of NAc D2-MSNs had no impact on alcohol intake while inhibition increased alcohol intake in Drd2-iCre rats for 1-h in males and 4-h in females. These findings suggest opposing roles for how NAc D1- and D2-MSNs modulate alcohol intake in rats of both sexes.

Preclinical evaluation of liposome-supported peritoneal dialysis for the treatment of hyperammonemic crises

Liposome-supported peritoneal dialysis (LSPD) with transmembrane pH-gradient liposomes was previously shown to enhance ammonia removal in cirrhotic rats and holds promise for the treatment of hyperammonemic crises-associated disorders. The main objective of this work was to conduct the preclinical evaluation of LSPD in terms of pharmacokinetics, ammonia uptake, and toxicology to seek regulatory approval for a first-in-human study. The formulation containing citric acid-loaded liposomes was administered intraperitoneally at two different doses once daily for ten days to healthy minipigs. It was also tested in a domestic pig model of hyperammonemia. The pharmacokinetics of citric acid and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was linear following intraperitoneal administration of medium and high dose. There was no systemic accumulation following daily doses over ten days. The systemic exposure to phospholipids remained low. Furthermore, the liposome-containing peritoneal fluid contained significantly higher ammonia levels than the liposome-free control, demonstrating efficient ammonia sequestration in the peritoneal space. This was indeed confirmed by the ability of LSPD to decrease plasmatic ammonia levels in artificially induced hyperammonemic pigs. LSPD was well tolerated, and no complement activation-related pseudoallergy reactions were observed. The safety profile, the linear pharmacokinetics of citric acid following repeated administrations of LSPD as well as the linear dose-dependent ammonia sequestration in the peritoneal space provide a strong basis for the clinical investigation of LSPD.

Locomotor sensitization to intermittent ketamine administration is associated with nucleus accumbens plasticity in male and female rats

Clinical evidence suggests superior antidepressant response over time with a repeated, intermittent ketamine treatment regimen as compared to a single infusion. However, the club drug ketamine is commonly abused. Therefore, the abuse potential of repeated ketamine injections at low doses needs to be investigated. In this study, we investigated the abuse potential of repeated exposure to either 0, 2.5, or 5 mg/kg ketamine administered once weekly for seven weeks. Locomotor activity and conditioned place preference (CPP) were assayed to evaluate behavioral sensitization to the locomotor activating effects of ketamine and its rewarding properties, respectively. Our results show that while neither males nor females developed CPP, males treated with 5 mg/kg and females treated with either 2.5 or 5 mg/kg ketamine behaviorally sensitized. Furthermore, dendritic spine density was increased in the NAc of both males and females administered 5 mg/kg ketamine, an effect specific to the NAc shell (NAcSh) in males but to both the NAc core (NAcC) and NAcSh in females. Additionally, males administered 5 mg/kg ketamine displayed increased protein expression of ΔfosB, calcium calmodulin kinase II alpha (CaMKIIα), and brain-derived neurotrophic factor (BDNF), an effect not observed in females administered either dose of ketamine. However, males and females administered 5 mg/kg ketamine displayed increased protein expression of AMPA receptors (GluA1). Taken together, low-dose ketamine, when administered intermittently, induces behavioral sensitization at a lower dose in females than males, accompanied by an increase in spine density in the NAc and protein expression changes in pathways commonly implicated in addiction.

Trichostatin A (TSA) facilitates formation of partner preference in male prairie voles (Microtus ochrogaster)

In the socially monogamous prairie voles (Microtus ochrogaster), the development of a social bonding is indicated by the formation of partner preference, which involves a variety of environmental and neurochemical factors and brain structures. In a most recent study in female prairie voles, we found that treatment with the histone deacetylase inhibitor trichostatin A (TSA) facilitates the formation of partner preference through up-regulation of oxytocin receptor (OTR) and vasopressin V1a receptor (V1aR) genes expression in the nucleus accumbens (NAcc). In the present study, we tested the hypothesis that TSA treatment also facilitates partner preference formation and alters OTR and V1aR genes expression in the NAcc in male prairie voles. We thus observed that central injection of TSA dose-dependently promoted the formation of partner preference in the absence of mating in male prairie voles. Interestingly, TSA treatment up-regulated OTR, but not V1aR, gene expression in the NAcc similarly as they were affected by mating - an essential process for naturally occurring partner preference. These data, together with others, not only indicate the involvement of epigenetic events but also the potential role of NAcc oxytocin in the regulation of partner preference in both male and female prairie voles.

Sex differences in social interaction behaviors in rats are mediated by extracellular signal-regulated kinase 2 expression in the medial prefrontal cortex

Considerable sex differences occur in the incidence and prevalence of anxiety disorders where women are more anxious than men, particularly in situations where social interaction is required. In preclinical studies, the social interaction test represents a valid animal model to study sex differences in social anxiety. Indeed, female rats engage less in conspecific interactions than their male counterparts, which are behaviors indicative of higher social anxiety in female rats. In this work, we implicated extracellular signal-regulated kinase 2 (ERK2) in the medial prefrontal cortex (mPFC) in mediating social interaction. Indeed, female rats' had lower ERK2 expression compared to male rats, and overexpression of ERK2 in the mPFC increases their social interaction to the level seen in their male counterparts. These data indicate that the sexually dimorphic expression of ERK2 mediates social anxiety-like behaviors.

Juvenile and adult rats differ in cocaine reward and expression of zif268 in the forebrain

Adolescents are more likely to experiment with and become addicted to drugs of abuse. A number of studies indicate that the developmental forebrain may be responsible for making adolescents vulnerable to the addictive properties of such drugs. The aim of this study was to first compare behavioral responses to novelty and cocaine between juvenile and adult rats and then compare levels of the immediate-early gene zif268 activation in several forebrain areas via in situ hybridization. We found that juveniles demonstrated higher locomotion scores and required a higher dose of cocaine than adults to establish a conditioned place preference. Additionally, at this higher dose, juvenile rats exhibited higher levels of zif268 mRNA in the prefrontal cortex compared with adults. A developmental effect for increased zif268 mRNA was also observed in the striatum and nucleus accumbens, but there was no interaction with the cocaine dose. These findings hold interesting implications for the study of the molecular mechanisms underlying juvenile drug addiction.

Lack of significant effect of bilastine administered at therapeutic and supratherapeutic doses and concomitantly with ketoconazole on ventricular repolarization: results of a thorough QT study (TQTS) with QT-concentration analysis

The effect of bilastine on cardiac repolarization was studied in 30 healthy participants during a multiple-dose, triple-dummy, crossover, thorough QT study that included 5 arms: placebo, active control (400 mg moxifloxacin), bilastine at therapeutic and supratherapeutic doses (20 mg and 100 mg once daily, respectively), and bilastine 20 mg administered with ketoconazole 400 mg. Time-matched, triplicate electrocardiograms (ECGs) were recorded with 13 time points extracted predose and 16 extracted over 72 hours post day 4 dosing. Four QT/RR corrections were implemented: QTcB; QTcF; a linear individual correction (QTcNi), the primary correction; and a nonlinear one (QTcNnl). Moxifloxacin was associated with a significant increase in QTcNi at all time points between 1 and 12 hours, inclusively. Bilastine administration at 20 mg and 100 mg had no clinically significant impact on QTc (maximum increase in QTcNi, 5.02 ms; upper confidence limit [UCL] of the 1-sided, 95% confidence interval, 7.87 ms). Concomitant administration of ketoconazole and bilastine 20 mg induced a clinically relevant increase in QTc (maximum increase in QTcNi, 9.3 ms; UCL, 12.16 ms). This result was most likely related to the cardiac effect of ketoconazole because for all time points, bilastine plasma concentrations were lower than those observed following the supratherapeutic dose.

Differential effects of social defeat in rats with high and low locomotor response to novelty

We compared the response to repeated social defeat in rats selected as high (HR) and low (LR) responders to novelty. In experiment 1, we investigated the behavioral and neuroendocrine effects of repeated social defeat in HR-LR rats. By the last defeat session, HR rats exhibited less passive-submissive behaviors than LR rats, and exhibited higher corticosterone secretion when recovering from defeat. Furthermore, in the forced swim test, while HR defeated rats spent more time immobile than their undefeated controls, LR rats' immobility was unaffected by defeat. In experiment 2, we compared the effects of repeated social defeat on body, adrenal, thymus, and spleen weights in HR-LR rats; moreover, we compared the effects of repeated social defeat on stress related molecules gene expression in these two groups of rats. Our results show that HR rats exhibited a decrease in thymus weight after repeated social defeat that was not present in LRs. Analyses of in situ hybridization results found HR-LR differences in 5-HT(2a) mRNA levels in the parietal cortex and 5-HT(1a) mRNA levels in the dorsal raphe. Moreover, LR rats had higher glucocorticoid receptor (GR) mRNA expression than HR rats in the dentate gyrus, and repeated social defeat decreased this expression in LR rats to HR levels. Finally, hippocampal mineralcorticoid receptor (MR)/GR ratio was reduced in HR rats only. Taken together, our results show a differential response to social defeat in HR-LR rats, and support the HR-LR model as a useful tool to investigate inter-individual differences in response to social stressors.

Individual differences in the effect of social defeat on anhedonia and histone acetylation in the rat hippocampus

Major depression is a growing problem worldwide with variation in symptoms and response to treatment. Individual differences in response to stress may contribute to such observed individual variation in behavior and pathology. Therefore, we investigated depressive-like behavior following exposure to repeated social defeat in a rat model of individual differences in response to novelty. Rats are known to exhibit either high locomotor activity and sustained exploration (high responders, HR) or low activity with minimal exploration (low responders, LR) in a novel environment. We measured anhedonia using the sucrose preference test in HR and LR rats following exposure to social defeat stress or in basal, non-defeated conditions. We then compared histone acetylation in the hippocampus in HR and LR defeat and non-defeated rats and measured mRNA levels of histone deacetylases (HDAC) 3, 4, 5, and Creb binding protein (CBP). We found that basally, HR rats consumed more sucrose solution than LR rats, but reduced consumption after exposure to defeat. LR rats' preference was unaffected by social defeat. We found that HR rats had higher levels of histone acetylation on H3K14 and H2B than LR rats in non-stress conditions. Following defeat, this acetylation pattern changed differentially, with HR rats decreasing acetylation of H3K14 and H2B and LR's increasing acetylation of H3K14. Acetylation on histone H4 decreased following defeat with no individual variation. Basal differences in CBP expression levels may underlie the observed acetylation pattern; however we found no significant effects of defeat in levels of HDACs 3, 4, 5 in the hippocampus.

[Diffuse arterial calcified elastopathy. A case report]

Diffuse arterial calcified elastopathy is a very rare and little known hereditary disease, characterized by diffuse calcifications of the arterial wall. It seems common in North Africa and in the Caucasian region. Its incidence appears to be underestimated in Morocco. Clinical pattern is dominated by renovascular hypertension often associated with symptoms of heart failure. Risk of sudden death from myocardial infarction is particularly important. Thus, the diagnosis of diffuse arterial calcified elastopathy must always be suspected in front of an apparently unexplained heart failure or renovascular hypertension occurring in an infant. We report a case of diffuse arterial calcified elastopathy discovered in a neonatal intensive care unit, during management of a cardiogenic shock in a 3-months old infant. This observation demonstrates the importance of systematic measurement of the arterial tension, family screening and the impact of the ultrasound in the detection of vascular calcifications. Treatment remains essentially symptomatic.

Repeated social defeat stress-induced sensitization to the locomotor activating effects of d-amphetamine: role of individual differences

RATIONALE

In this study, we sought to examine individual differences in stress-induced behavioral sensitization to d-amphetamine after repeated social defeat stress. In an effort to understand what mechanisms underlie stress-induced sensitization to d-amphetamine, we examined striatal gene expression of the dopamine receptor D(2). Additionally, we investigated if repeated social defeat was associated with changes in dendritic spine density in the hippocampus, prefrontal cortex, and nucleus accumbens of rats that exhibit stress-induced sensitization.

METHODS

Male rats were classified into high responders (HR) and low responders (LR) based on their locomotor response to a novel environment. Then, rats were either handled as a control or defeated on four occasions by aggressive rats. Two weeks after the last defeat, animals were challenged with one of three doses of d-amphetamine and their locomotor activity was recorded.

RESULTS

Non-defeated HR rats exhibited higher locomotor activity in response to d-amphetamine when compared to LR non-defeated rats. Fourteen days from the last repeated social defeat, LR rats and HR rats were behaviorally identical in response to acute injections of amphetamine. Furthermore, HR non-defeated rats had less D(2) mRNA expression in the nucleus accumbens core and dorsal striatum than do LR non-defeated rats. However, after repeated social defeat, HR and LR rats had identical D(2) mRNA expression in both the core and dorsal striatum. Finally, there were no changes in dendritic spine density in any of the brain areas examined in LR rats.

CONCLUSION

Repeated social defeat abolishes individual differences in behavioral responses to d-amphetamine which may be due to a down-regulation of striatal dopamine D(2) receptors in LR rats.

Effects of chronic environmental and social stimuli during adolescence on mesolimbic dopaminergic circuitry markers

Previously, we have shown that chronic exposure to environmental and social stimuli (ESS) during adolescence prevents the development of behavioral sensitization to amphetamine in adult rats. At the onset of the peripubertal-juvenile period (28-d) male rats were subjected to a 28-d long intermittent ESS protocol or handled as controls (NO-ESS). Twenty-four hours after the last session of ESS or NO-ESS, all rats started a regimen of behavioral sensitization to amphetamine (1mg/kg, i.p.), in which rats were injected every third day with amphetamine or saline on four occasions. Then following one week abstinence all rats were challenged with a lower dose of amphetamine (0.5mg/kg, i.p.) and their locomotor activity monitored for 2h. Our results showed that while NO-ESS rats developed behavioral sensitization to amphetamine, ESS rats did not develop this behavior. All rats were then sacrificed 3 days following the challenge to allow for amphetamine clearance. Since mesolimbic dopamine has been implicated in behavioral sensitization to amphetamine we compared messenger RNA (mRNA) expression of key dopamine-related molecules in the mesolimbic circuitry in ESS and NO-ESS rats. A decrease in dopaminergic D1 receptor (D1R) gene expression in the caudate-putamen (CPu) was associated with amphetamine sensitization in the controls, possibly as a result of a chronic increase in DA release. In contrast, amphetamine treatment did not modulate D1R mRNA levels in ESS rats. No change has been detected in any other dopaminergic markers [D2R, D3R, tyrosine hydroxylase (TH) or dopamine transporter (DAT) mRNAs]. Consequently, we conclude that ESS may inhibit the development of behavioral sensitization to amphetamine through preventing the decrease in CPu D1R mRNA levels.

Impact of peripheral elimination on the concentration-effect relationship of remifentanil in anaesthetized dogs

BACKGROUND

This study elucidates the impact of sampling site when estimating pharmacokinetic-pharmacodynamic (PK-PD) parameters of drugs such as remifentanil that undergo tissue extraction in the biophase. The interrelationship between the concentrations of remifentanil predicted for the effect compartment and those measured in arterial, venous, and cerebrospinal fluid were investigated under steady-state conditions.

METHODS

Following induction of anaesthesia with pentobarbital, an arterial cannula (femoral) and two venous catheters (jugular and femoral) were inserted. Electrodes were placed for EEG recording of theta wave activity. Each dog received two consecutive 5-min infusions for the PK-PD study and a bolus followed by a 60-min infusion was started for the steady-state study. Cerebrospinal fluid, arterial and venous blood samples were drawn simultaneously after 30, 40, and 50 min. At the end of the infusion, arterial blood samples were collected for pharmacokinetic analysis.

RESULTS

Remifentanil PK-PD parameters based on theta wave activity were as follows: apparent volume of distribution at steady-state (V(ss)) (231+/-37 ml kg(-1)), total body clearance (Cl) (63+/-16 ml min(-1) kg(-1)), terminal elimination half-life (t(1/2 beta)) (7.71 min), effect compartment concentration at 50% of maximal observed effect (EC(50)) (21+/-13 ng ml(-1)), and equilibration rate constant between plasma and effect compartment (k(e0)) (0.48+/-0.24 min). The mean steady-state cerebrospinal fluid concentration of 236 ng ml(-1) represented 52 and 74% of that in arterial and venous blood, respectively.

CONCLUSIONS

Our study re-emphasizes the importance of a sampling site when performing PK-PD modelling for drugs undergoing elimination from the effect compartment. For a drug undergoing tissue elimination such as remifentanil, venous rather than arterial concentrations will reflect more exactly the effect compartment concentrations, under steady-state conditions.

The search for the neurobiological basis of vulnerability to drug abuse: using microarrays to investigate the role of stress and individual differences

Basic neurobiological studies have led to great progress in our understanding of the mechanisms of action of drugs of abuse. Much has been learned about the brain response from the moment a psychoactive drug enters the organism onwards, including the psychological, neurobiological and peripheral effects of repeated drug administration, withdrawal and re-exposure. However, to relate this knowledge to the human experience requires further research on the antecedents of drug-taking behavior and the factors that predispose particular individuals to drug seeking and drug abuse. Thus, it is important to address several issues at the fundamental level: (1) Why are some individuals more vulnerable to drugs of abuse more than others? Is there a broader dimension or dimensions of emotional reactivity that contribute to this difference in vulnerability? (2) What is the effect of psychosocial stress on drug-seeking and drug-taking behavior, and are the effects distinct across individuals? (3) Since both drug-taking behavior and stress have sustained and pervasive effects on the brain, can we use microarrays to discern the "neural signature" or "neural phenotype" associated with these processes, and can we distinguish this signature across individuals with differing propensities to taking drugs? In the present paper, we summarize some of our early attempts at addressing these questions. We rely on animal studies aimed at characterizing the emotional and stress reactivity of rats with different propensities to self-administer drugs (high responders and low responders); we briefly describe the effect of a psychosocial stressor on these animals; we then detail a study using microarray technology aimed at investigating the "neural phenotype" associated with social defeat stress in the high vs. low responder animals. This "discovery" approach is used as a starting place for identifying novel mechanisms that might alter the vulnerability of different individuals to drug-seeking behavior. The power and limits of this approach, and its future directions, are discussed within this general framework.

Methamphetamine differentially regulates hippocampal glucocorticoid and mineralocorticoid receptor mRNAs in Fischer and Lewis rats

Fischer 344 (F344) and Lewis (LEW) rats differ in physiological regulation of the limbic-hypothalamo-pituitary-adrenal (LHPA) axis, such that F344 rats exhibit greater LHPA axis responses to a variety of stimuli. Furthermore, LHPA axis activity has been implicated in the development of sensitization to abused drugs, and F344 rats exhibit greater behavioral sensitization to psychostimulants. Accordingly, we hypothesized that there may be some overlap between the neurobiological mechanisms that underlie these strain differences in LHPA axis activity and in behavioral sensitization to psychostimulants. We examined the effects of acute and repeated methamphetamine (4 mg/kg) treatments on the regulation of hippocampal glucocorticoid receptors (GR mRNA) and mineralocorticoid receptors (MR mRNA) in F344 and LEW rats. Our results showed that acute treatment with methamphetamine (MAP) does not alter the level of expression of GR or MR mRNA in both strains. However, repeated treatments with MAP decreased the expression of hippocampal GR, but not MR mRNA specifically in F344 rats. The same repeated treatments had no effect on either GR or MR mRNA in LEW rats. This selective MAP regulation of the level of expression of hippocampal GR mRNA in F344 suggests that these receptors may play a role in the development of behavioral sensitization to MAP in this strain. The lack of alteration in hippocampal GR mRNA in LEW rats suggests that plasticity of hippocampal GR may not be critical for the development of behavioral sensitization to MAP in this strain.

Estrogen receptor β in the paraventricular nucleus of hypothalamus regulates the neuroendocrine response to stress and is regulated by corticosterone

The function of the second nuclear estrogen receptor, estrogen receptor beta (ERbeta), in the brain is largely unknown. The present study tested whether 1) ERbeta in the paraventricular nucleus (PVN) of the hypothalamus has a direct role in the hypothalamic-pituitary-adrenal (HPA) axis-mediated stress function, and 2) whether corticosterone (CORT) can regulate ERbeta gene expression in the PVN in the intact, cycling female rat. To test the first hypothesis a pure estrogen receptor antagonist, ICI182, 780, was microinjected into the PVN bilaterally and stress-induced CORT response to an acute stressor (15 min restraint) was measured at 0, 15, 30, 60 and 90 min time points. Estrogen antagonist-injected rats showed inhibited CORT levels at the peak (15 min) of the stress response compared with vehicle-injected animals. To test the second hypothesis, ERbeta mRNA levels were measured in the PVN using in situ hybridization histochemistry following sham surgery, adrenalectomy, and adrenalectomy with low or high CORT replacement. Adrenalectomy reduced ERbeta mRNA expression in the PVN, whereas CORT replacement fully reversed this effect in a dose-dependent fashion. Both antagonist inhibition of CORT response and CORT-mediated regulation of ERbeta mRNA were found to be estrus cycle-dependent in the intact, cycling female. These data suggest that ERbeta in the PVN may critically modulate the HPA axis response to stress and is, in turn, regulated by circulating CORT.

Simultaneous solid-phase extraction combined with liquid chromatography with ultraviolet absorbance detection for the determination of remifentanil and its metabolite in dog plasma

To establish pharmacokinetic/pharmacodynamic relationships, a selective and specific high-performance liquid chromatographic method was developed for the quantitation of remifentanil and its metabolite in dog plasma. The assay involves a solid-phase extraction and a reversed-phase chromatographic separation with ultraviolet detection (lambda=210 nm). The calibration curves are linear in the range of 7.89-1500 ng ml(-1). Intra-day assay variability is less than 7% for all standards evaluated. Good recovery, linearity, accuracy, and precision were achieved with the assay that proved readily applicable to pharmacokinetic studies in dogs.

Stress during adolescence alters behavioral sensitization to amphetamine

In humans, chronic intermittent and uncontrollable stress during adolescence is viewed as a key factor for vulnerability to drug abuse and development of psychopathologies later in life. Less is known about the long-term effects of chronic stress in animals during the juvenile period. Although there is evidence of cross sensitization during prenatal period and adulthood between chronic stress and amphetamine-induced behavioral sensitization in the rat, no studies have been conducted on cross sensitization between chronic variable stress in adolescence and behavioral sensitization to amphetamine. To address this question, at the onset of adolescence (28 days) male rats were subjected to 28 days of intermittent non-habituating social stress (isolation, novel environment, crowding, litter-shifting, subordination), or physical stress (restraint, swim, cold, ether, noise), or were handled as controls. Twenty-four hours after the last stressor or handling, all groups were exposed to a novel environment for 1 h, after which they underwent a regimen of behavioral sensitization to amphetamine. Our results showed that socially stressed rats have low locomotor activity in the novel environment, when compared to the control and physical groups who were identical in the same test. Even though socially stressed rats had lower locomotor activity in response to amphetamine injections, there were no significant differences during the training phase between the three groups at this dose of amphetamine. However, when tested for behavioral sensitization to amphetamine control and physically stressed rats showed a robust sensitization, socially stressed rats were significantly inhibited. We conclude that our chronic variable social stress protocol during adolescence inhibits behavioral sensitization to amphetamine during adulthood.

Anticancer activity of mycobacterial DNA: effect of formulation as chitosan nanoparticles

Mycobacterium phlei (M. phlei) DNA inhibits cancer cell division but is susceptible to degradation by DNase. Chitosan forms nanoparticulate polyelectrolyte complexes with DNA, and may thus reduce nuclease degradation. We have characterized chitosan-DNA nanoparticle formation, determined DNase susceptibility, and evaluated their antiproliferative activity. Nanoparticle diameter initially decreased with increasing phosphate charge density. However nanoparticle diameter increased above 6 micromol of phosphate. Particle aggregation occurred at 16.2 micromol phosphate and was related to reduced surface charge. Incorporation of DNA within chitosan nanoparticles significantly decreased degradation by DNase. The ability of M. phlei DNA-chitosan nanoparticles to inhibit melanoma cell division was determined relative to M. phlei DNA and a cationic liposomal M. phlei DNA formulation. M. phlei DNA had antiproliferative activity (MTT reduction, IC50 = 0.9 mg/ml) without intrinsic cytotoxicity (LDH release, ED50 > 50 microg/ml). Cationic polyphosphate chitosan nanoparticles were inert (antiproliferative IC50 > 1 mg/ml, ED50 > 1 mg/ml). M. phlei DNA-chitosan nanoparticles were 20-fold more potent than M. phlei DNA. Cationic DOTAP/DOPE liposomes were cytostatic (IC50 = 49 microg/ml) and cytotoxic (ED50 = 87 microg/ml), and complexation of M. phlei DNA resulted in a significant reduction of antiproliferative activity. Chitosan nanoparticles may therefore be appropriate delivery vehicles for M. phlei DNA.

Individual differences in novelty-seeking behavior in rats: a c-fos study

Novelty-seeking personality traits have been implicated in substance abuse and psychiatric disorders in humans. Novelty-seeking behaviors are also observed in rats, and individual rats exhibit substantial differences in expression of these behaviors. Thus, some rats exhibit low reactivity to novelty and high anxiety-like behavior and are termed low responders, while others are hyperresponsive to novelty and exhibit low anxiety-like behavior and are termed high responders. While we and others had shown differences in patterns of gene expression in high and low responding animals at rest, no studies have described their brain activation following an anxiety test. We report here that a 5-min exposure to an anxiogenic stressor induced distinct patterns of c-fos expression in the brains of high and low responding rats. When compared to low responders, high responding rats showed low expression of c-fos mRNA in the CA1 area of the hippocampus, but high c-fos mRNA levels in the olfactory area, the orbital cortex, the cingulate cortex, the dorsal striatum and the paraventricular nucleus of the hypothalamus. Given that c-fos is a trans-acting factor, we suggest that the short- and long-term consequences of the exposure to the anxiogenic stressor may also be quantitatively and anatomically different in these two groups of animals. Thus, these c-fos results demonstrate how experience may further exaggerate individual differences. Animals that differ in emotional reactivity not only exhibit basal differences in gene expression, but also react to novelty with different molecular responses, further increasing the neuronal differences between them.

Social defeat alters the acquisition of cocaine self-administration in rats: role of individual differences in cocaine-taking behavior

RATIONALE

It is known that social defeat can modulate cocaine self-administration. However, it is unclear whether this psychosocial stressor affects drug-taking behavior to the same extent across all individual animals, particularly those with differing propensities to self-administer psychostimulants.

OBJECTIVE

This study examined the effect of social defeat on cocaine self-administration in animals that differ in novelty-seeking behavior that predicts differences in drug self-administration.

METHODS

Male Sprague-Dawley rats were first classified into high-responder (HR) and low-responder (LR) groups. HR and LR rats were categorized based on their locomotor activity in a novel environment, with HR rats exhibiting higher locomotor activity than LR rats. Then, male rats were exposed on four occasions to an aggressive Long Evans male rat over the course of 4 days. Control rats were not exposed to the social defeat. All rats were subsequently implanted with jugular catheters and 3 days later placed into the self-administration box to study the acquisition of cocaine self-administration (0.25 mg per infusion).

RESULTS

HR non-defeated animals self-administered more cocaine than the LR non-defeated animals. Following social defeat, the acquisition of cocaine self-administration is significantly delayed in HR rats and enhanced in LR rats. CONCLUSION The unique patterns of responsiveness in the HR and LR animals suggest that social defeat plays a role of equalizer of individual differences in drug-taking behavior.

Neurobiological correlates of individual differences in novelty-seeking behavior in the rat: differential expression of stress-related molecules

It is well established that individual rats exhibit marked differences in behavioral responses to a novel environment. Rats that exhibit high rates of locomotor activity and sustained exploration in such an environment also exhibit high concentrations of stress-induced plasma corticosterone, linking this behavior to the stress system. Furthermore, these high-responding (HR) rats, in contrast to their low-responding (LR) counterparts, have a greater propensity to self-administer drugs. Thus, HR rats have been described as "novelty" seeking in that they are more active and explore novel stimuli more vigorously, despite the fact that this elicits in them high stress responses. In this study, we have further characterized the behavior of HR and LR rats in tests of anxiety and characterized their stress responses to either experimenter- or self-imposed stressors. We then investigated the physiological basis of these individual differences, focusing on stress-related molecules, including the glucocorticoid receptor (GR), the mineralocorticoid receptor (MR), corticotropin-releasing hormone (CRH) and pro-opiomelanocortin (POMC) in the context of the limbic-hypothalamo-pituitary adrenal axis. We have found that HR rats did not differ from LR in their basal expression of POMC in the pituitary. However, HR rats exhibited higher levels of CRH mRNA in the hypothalamic paraventricular nucleus but lower basal levels in the central nucleus of the amygdala. The basal expression of hippocampal MR is not different between HR and LR rats. Interestingly, the basal expression of hippocampal GR mRNA is significantly lower in HR than in LR rats. This low level of hippocampal GR expression in HR rats appears to be responsible, at least in part, for their decreased anxiety in exploring novelty. Indeed, the anxiety level of LR rats becomes similar to HR rats after the administration into the hippocampus of a GR antagonist, RU38486. These data indicate that basal differences in gene expression of key stress-related molecules may play an important role in determining individual differences in responsiveness to stress and novelty. They point to a new role of hippocampal GR, strongly implicating this receptor in determining individual differences in anxiety and novelty-seeking behavior.

Hippocampal type I and type II corticosteroid receptors are differentially regulated by chronic prazosin treatment

Two types of hippocampal corticosteroid receptors play an important role in regulating the secretion of corticosterone: type I receptors are thought to regulate both the basal and stress induced release of corticosterone whereas type II receptors seem to be involved only in the stress response. Although these receptors are known to be regulated by circulating levels of corticosterone, there is also evidence for a direct neural control independent of hormonal influences. Furthermore, several studies suggest differential regulation of type I and type II corticosteroid receptors, with greater hormonal control of type II and greater neural control of type I. In order to investigate this theory of differential regulation of type I and type II corticosteroid receptors, we studied the effect of chronic treatment with either vehicle or the alpha 1 noradrenergic antagonist prazosin (0.5 mg/kg, i.p), on hippocampal corticosteroid receptors. Rats in one group had intact adrenal glands, whereas rats in a second group were adrenalectomized, their plasma corticosterone levels being maintained in the physiological range by implantation of corticosterone pellets. Thus, in the first group, the effects of drug-induced changes in both noradrenergic transmission and corticosterone secretion on corticosteroid receptors were investigated, whereas in the second group, the influence of altered noradrenergic transmission was effectively isolated. The results of this experiment show that, in comparison to the vehicle treatment, chronic treatment with the alpha 1 receptor antagonist prazosin decreased the number of type I corticosteroid receptors in adrenalectomized animals with corticosterone substitutive therapy. This effect on type I was not evident in adrenal-intact animals. In contrast, the prazosin treatment reduced the number of type II corticosteroid receptors in adrenal-intact animals, but not in adrenalectomized animals with corticosterone substitutive therapy. It has also been demonstrated here that, in the adrenal-intact animals, chronic prazosin induces hypersecretion of corticosterone after stress, which may account for the reduction of type II corticosteroid receptors noted in this group. Taken together, these results support the theory that type I and type II are differentially regulated: type I receptors can be regulated by noradrenaline independently of corticosterone, whereas type II receptors seem to be adjusted by circulating levels of corticosterone. These results may also suggest possible pharmacotherapies of hypothalamo-pituitary-adrenal axis dysregulation, such as that occurring during depression, Alzheimer's disease and Cushing syndrome, by targeting type I corticosteroid receptors.

Opposite effects on hippocampal corticosteroid receptors induced by stimulation of beta and alpha 1 noradrenergic receptors

Central corticosteroid receptors play an important role in the regulation of the secretion of corticosterone. Although these receptors are thought to be regulated by circulating levels of corticosterone, there is evidence for direct neural control. For example, it has been shown that noradrenergic lesions can both increase and decrease corticosteroid receptors depending on the brain structure involved. In the present study, we investigated the role of different noradrenergic receptors in the rat, by examining the effect of the acute administration of agonists and antagonists of beta and alpha 1 noradrenergic receptors on hippocampal type I and type II corticosteroid receptor levels. The effects of these drugs were studied in adrenalectomized animals whose plasma levels of corticosterone were maintained in the physiological range by implantation of coritcosterone pellets. Our results show that the beta receptor agonist salbutamol (5 mg/kg) increased the number of type I and type II hippocampal corticosteroid receptors. This effect was blocked by the beta receptor antagonist propranolol (5 mg/kg), which had no effect on its own. In contrast, the alpha 1 receptor agonist phenylephrine (100 micrograms) reduced the number of type I and type II corticosteroid receptors, whereas the alpha 1 receptor antagonist prazosin (0.5 mg/kg) increased type I receptors. The effect of prazosin was attributed to an increase in the relative beta tonus resulting from blockade of alpha 1 receptors. Its effect was reversed by the simultaneous injection of the beta receptor antagonist propranolol. In conclusion, our results show that noradrenergic transmission can have both a facilitatory and an inhibitory action on central corticosteroid receptors by acting respectively on beta and alpha 1 noradrenergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Adoption reverses the long-term impairment in glucocorticoid feedback induced by prenatal stress

The development of the organism is subjected to critical and complex influences during the perinatal period. Prenatal and postnatal stresses can have different long-term behavioral effects, and appropriate postnatal manipulations can counteract the behavioral effects of prenatal stress. In the present study, we investigated the involvement of changes in the activity of the hypothalamo-pituitary-adrenal (HPA) axis in the long-term effects of prenatal and postnatal events and of interactions between them. We investigated stress-induced corticosterone secretion and hippocampal corticosteroid receptors in male adult rats submitted to prenatal and/or postnatal manipulations. Repeated restraint during the last week of pregnancy was used as prenatal stressor, and adoption at birth was used to change the postnatal environment. We found that (1) prenatal stress prolongs stress-induced corticosterone secretion in adult rats, which was attributed to the observed decrease in central corticosteroid receptors; (2) adoption, irrespective of the stress experience of the foster mother, reverses the effects of prenatal stress; and (3) adoption per se increases maternal behavior and decreases the stress-induced corticosterone secretion peak in the adult offspring. In conclusion, certain prenatal and postnatal manipulations appear to have opposite long-term effects on the activity of the HPA axis, and adoption, probably by modifying maternal behavior, can protect against the effects of prenatal stress. Thus, changes in the activity of the HPA axis may be one of the biological substrates of the long-term effects of certain perinatal events.

Prenatal stress increases the hypothalamo-pituitary-adrenal axis response in young and adult rats

Prenatal stress is considered as an early epigenetic factor able to induce long-lasting alterations in brain structures and functions. It is still unclear whether prenatal stress can induce long-lasting modifications in the hypothalamo-pituitary-adrenal axis. To test this possibility the effects of restraint stress in pregnant rats during the third week of gestation were investigated in the functional properties of the hypothalamo-pituitary-adrenal axis and hippocampal type I and type II corticosteroid receptors in the male offspring at 3, 21 and 90 days of age. Plasma corticosterone was significantly elevated in prenatally-stressed rats at 3 and 21 days after exposure to novelty. At 90 days of age, prenatally-stressed rats showed a longer duration of corticosterone secretion after exposure to novelty. No change was observed for type I and type II receptor densities 3 days after birth, but both receptor subtypes were decreased in the hippocampus of prenatally-stressed offspring at 21 and 90 days of life. These findings suggest that prenatal stress produces long term changes in the hypothalamo-pituitary-adrenal axis in the offspring.

The D1 dopamine agonist SKF 38393, but not the D2 agonist LY 171555, decreases the affinity of type II corticosteroid receptors in rat hippocampus and ventral striatum

Type I and type II brain corticosteroid receptors are regulated by adrenal hormones as well as being under neural control. Recent studies have indicated that neurotransmitters such as serotonin and noradrenaline are also involved in the regulation of corticosteroid receptors. In a previous study, we showed that dopamine also modulates activity of the corticosteroid receptor system. In the present study, we examined the roles of the dopamine D1 and D2 receptor subtypes in the regulation of corticosteroid receptors. Adrenalectomized rats whose corticosterone levels were maintained within normal limits by corticosterone replacement implants, were injected intraperitoneally with the D1 agonist SKF 38393 or the D2 agonist LY 171555. Corticosteroid receptors were assayed in the ventral striatum and hippocampus. We have shown that the D1 agonist SKF 38393 decreased type II receptor affinity in both regions, whereas the D2 agonist LY 171555 had no effects. The results show that the influence of the dopaminergic system on corticosteroid receptors appears to be mediated by D1 receptors.

Basal and stress-induced corticosterone secretion is decreased by lesion of mesencephalic dopaminergic neurons

There is evidence that certain psychopathological conditions are accompanied by a dysfunction in both the hypothalamo-pituitary-adrenal axis and dopaminergic systems, although the relationship between these two systems is as yet unclear. In the present study we investigated the effect of a specific lesion of dopamine mesencephalic neurons (Ventral Tegmental Area) on basal and stress-induced corticosterone secretion. Three weeks after injection of 6-OHDA, there was a depletion in dopamine in the frontal cortex and in the ventral and dorsal striatum, whereas norepinephrine and serotonin levels were unchanged. The dopamine-lesioned rats exhibited a lower basal and stress-induced corticosterone secretion than the sham-lesioned animals. The results indicate that the dopaminergic system may have a stimulatory influence on the hypothalamo-pituitary-adrenal axis.

The mesolimbic dopaminergic system exerts an inhibitory influence on brain corticosteroid receptor affinities

Central type I and type II corticosteroid receptors play a principle role in the regulation of corticosterone secretion. Although the binding capacity of these receptors is thought to be regulated essentially hormonally, there is also evidence for a direct neural control. For example, experimental manipulation of central serotoninergic and noradrenergic activities modifies the binding capacity of type I and type II corticosteroid receptors via a corticosterone-independent mechanism. In this study, we tested the effect of lesions of dopaminergic neurons in the ventral tegmental area on corticosteroid receptor binding capacity. The study was performed in adrenalectomized rats whose corticosterone levels were maintained within normal limits by corticosterone pellets and corticosterone in their drinking water during the dark period to generate the circadian rhythm. Binding properties of corticosteroid receptors were analysed in target regions of the lesioned neurons, including the ventral and dorsal striatum. Corticosteroid receptors in the hippocampus were also studied as a control as these lesions do not significantly affect dopamine content in this structure. Three weeks after the lesion, type II corticosteroid receptor affinity was increased in the ventral striatum. There was no effect on receptors in the dorsal striatum or hippocampus. Our results, together with other reports showing that dopamine inhibits the expression of corticosteroid receptors in the anterior pituitary, suggest that dopamine transmission exerts a negative control on central corticosteroid receptors.

Design of angiotensin II derivatives suitable for indirect affinity techniques: potential applications to receptor studies

The design of angiotensin II (A II)-derived probes suitable for indirect affinity techniques is presented. Biotin or dinitrophenyl moieties have been added at the N-terminus of A II, through aminohexanoic acid as spacer arm, to generate (6-biotinylamido)-hexanoyl-AII (Bio-Ahx-AII) and dinitrophenyl- aminohexanoyl-AII (Dnp-Ahx-AII). Monoiodinated and highly labeled radioiodinated forms of these probes have been prepared. The two bifunctional ligands displayed high affinities for rat liver A II receptors (Kd values in the nanomolar range) and their secondary acceptors: streptavidin and monoclonal anti-Dnp antibodies respectively. Bio-Ahx-AII and Dnp-Ahx-AII behaved as agonists on several AII-sensitive systems. Based on these structural assessments, the parent photoactivable azido probe: Bio-Ahx-(Ala1,Phe(4N3)8)A II. A II was synthesized and proved to possess similar biological properties than the non-azido compound. The hepatic A II receptor could be covalently labeled by the radioiodinated probe, with a particularly high yield (15-20%); SDS-polyacrylamide gel electrophoresis of solubilized complexes revealed specific labeling of a 65 Kdaltons binding unit, in agreement with previous data obtained with other azido AII-derived compounds. The potential applications of these probes are: i) receptor purification by combination of its photoaffinity labeling and adsorption of biotin-tagged solubilized hormone-receptor complexes on avidin gels. ii) cell labeling and sorting. iii) histochemical receptor visualization.