The selective norepinephrine reuptake inhibitor atomoxetine counteracts behavioral impairments in trimethyltin-intoxicated rats.

This study was carried out to assess the behavioral effects of the non-psychostimulant drug atomoxetine, in rats prenatally-exposed to the organic compound trimethyltin chloride (TMT) and in spontaneously hypertensive rat (SHR), two rodent models of Attention Deficit/Hyperactivity Disorder (ADHD). At birth, neonatal reflexes (righting, cliff aversion, forelimb placing, forelimb grasping, bar holding and startle) had an earlier onset (i.e. percent of appearance) and completion (maximum appearance, i.e. 100% of the brood exhibiting each reflex) in prenatally TMT-exposed and SHR pups as compared to control groups. Two months after birth, TMT-exposed and SHR rats showed impaired cognitive performances in both the step-through passive avoidance test and the shuttle box active avoidance test. Atomoxetine (1, 3 and 6 mg/kg, i.p.), already at the lowest dose tested, improved learning and memory capacity of prenatally TMT-exposed rats and SHR; while methylphenidate (1, 3 and 6 mg/kg, i.p.), used here as positive control, elicited a significant cognitive enhancing effect only at the higher doses. In the open field test, both TMT-exposed rats and SHR displayed enhanced locomotor activity. Methylphenidate further increased locomotor activity in all groups, whereas atomoxetine reduced the enhanced locomotor activity of TMT-exposed rats and SHR down to the level of controls. These results suggest that prenatal TMT-exposure could be considered as a putative experimental model of ADHD and further support the effectiveness of atomoxetine in the ADHD pharmacotherapy. Furthermore, despite the similar effect of the two drugs on cognitive tasks, they exhibit distinct profiles of activity on locomotion, in ADHD models.

Tin chloride enhances parvalbumin-positive interneuron survival by modulating heme metabolism in a model of cerebral ischemia.

SnCl(2) has been reported to increase the expression of heme-oxygenase 1 (HO-1), a major antioxidant enzyme, and to decrease ischemic injury, in non-nervous tissues. This study examined the neuroprotective effect of SnCl(2) in the hippocampus of rats submitted to cerebral ischemia. SnCl(2) was administered 18 h before bilateral carotids obstruction. Changes in HO-1 expression and activity, heme content, inducible nitric oxide synthase (iNOS) expression and parvalbumin positive interneuron survival were studied. Thereafter both behavior and memory recovery were tested. The administration of SnCl(2) increased the expression of HO-1 protein and HO activity in the hippocampus and concomitantly decreased heme content at both mitochondrial and nuclear level. Furthermore, ischemized animals showed a strong increase in iNOS expression in the hippocampus, where a loss of parvalbumin positive interneurons also occurred. Pre-treatment with SnCl(2), decreased both iNOS expression in ischemized rats and increased cell survival. The beneficial effects of SnCl(2) were prevented by concomitant treatment with SnMP, a strong inhibitor of HO activity. SnCl(2) also caused an improvement in short term memory recovery. Our results showed that following SnCl(2) administration, HO-1 is strongly induced in the hippocampus and modulate iNOS expression, resulting in a strong neuroprotective effect.

Increased D-aspartate brain content rescues hippocampal age-related synaptic plasticity deterioration of mice.

Until recently, free d-amino acids were thought to be involved only in bacterial physiology. Nevertheless, today there is evidence that D-serine, by acting as co-agonist at NMDARs, plays a role in controlling neuronal functions in mammals. Besides D-serine, another D-amino acid, D-aspartate (D-Asp), is found in the mammalian brain with a temporal gradient of occurrence: high in embryo and low in adult. In this study, we demonstrate that D-Asp acts as an endogenous NMDAR agonist, since it triggers currents via interaction with each of NR2A-D receptor subunits. According to its pharmacological features, we showed that oral administration of D-Asp strongly enhances NMDAR-dependent LTP in adulthood and, in turn, completely rescues the synaptic plasticity decay observed in the hippocampus of aged animals. Therefore, our findings suggest a tantalizing hypothesis for which this in-embryo-occurring D-amino acid, when "forced" over its physiological content, may disclose plasticity windows inside which it counteracts the age-related reduction of NMDAR signaling.

Dopamine D3 receptor knock-out mice exhibit increased behavioral sensitivity to the anxiolytic drug diazepam.

Dopamine D(3) receptors (DRsD3) seem to have a pivotal role in mood disorders. Using the elevated plus maze (EPM) and the novelty-induced grooming test (NGT), we assessed the responses of DRD3-deficient (D(3)(-/-)) mice to the acute treatment (different testing time) with the anxiolytic drug, diazepam. D(3)(-/-) mice treated with diazepam (0.1 or 0.5mg/kg) exhibited a better behavioral response in the EPM than their wild type (WT). Furthermore, in D(3)(-/-) mice, but not in WT, 1mg/kg diazepam induced anxiolytic effects at all testing times. The contribution of DRsD3 in the anxiolytic effects of diazepam was confirmed by similar results obtained in EPM by using the selective DRD3 antagonist U99194A (10mg/kg) in combination with diazepam, in WT animals. D(3)(-/-) mice treated with diazepam (all doses), also showed a decrease in grooming behavior. However, the [(3)H]flunitrazepam autoradiographic analysis revealed no significant changes in D(3)(-/-) mice compared to WT, suggesting that if γ-aminobutyric acid receptor GABA(A) changes are involved, they do not occur at the level of binding to benzodiazepine site. These data suggest that D(3)(-/-) mice exhibit low baseline anxiety levels and provide the evidence that the DRD3 is involved in the modulation of benzodiazepine anxiolytic effects.

Fatty acid amide hydrolase (FAAH) inhibition enhances memory acquisition through activation of PPAR-alpha nuclear receptors.

Inhibitors of fatty acid amide hydrolase (FAAH) increase endogenous levels of anandamide (a cannabinoid CB(1)-receptor ligand) and oleoylethanolamide and palmitoylethanolamide (OEA and PEA, ligands for alpha-type peroxisome proliferator-activated nuclear receptors, PPAR-alpha) when and where they are naturally released in the brain. Using a passive-avoidance task in rats, we found that memory acquisition was enhanced by the FAAH inhibitor URB597 or by the PPAR-alpha agonist WY14643, and these enhancements were blocked by the PPAR-alpha antagonist MK886. These findings demonstrate novel mechanisms for memory enhancement by activation of PPAR-alpha, either directly by administering a PPAR-alpha agonist or indirectly by administering a FAAH inhibitor.

Anandamide-induced behavioral disruption through a vanilloid-dependent mechanism in rats.

RATIONALE: Endocannabinoids are involved in a variety of behavioral and physiological processes that are just beginning to be understood. In the five-choice serial reaction-time task, exogenous cannabinoids have been found to alter attention, but endocannabinoids such as anandamide have not been studied. OBJECTIVES: We used this task to evaluate the effects of anandamide in rats. Since anandamide is a ligand for not only cannabinoid receptors but also transient receptor potential vanilloid 1 (TRPV1) receptors, and as recently suggested, peroxisome proliferator-activated nuclear receptor-alpha (PPARalpha), we also determined whether anandamide's effects in this task were mediated by each of these receptors. MATERIALS AND METHODS: Whenever one of five holes was illuminated for 2 s, a food pellet was delivered if a response occurred in that hole during the light or within 2 s after the light. RESULTS: Anandamide increased omission errors and decreased responding during inter-trial intervals. These effects were blocked by the TRPV1 antagonist capsazepine, but not by the cannabinoid-receptor antagonist rimonabant or the PPARalpha antagonist MK886. Testing with open-field activity and food-consumption procedures in the same rats suggested that the disruption of operant responding observed in the attention task was not due to motor depression, anxiety, decreased appetite, or an inability to find and consume food pellets. CONCLUSIONS: The vanilloid-dependent behavioral disruption induced by anandamide was specific to the operant attention task. These effects of anandamide resemble effects of systemically administered dopamine antagonists and might reflect changes in vanilloid-mediated dopamine transmission.

Identification of dopamine D1-D3 receptor heteromers. Indications for a role of synergistic D1-D3 receptor interactions in the striatum.

The function of dopamine D(3) receptors present in the striatum has remained elusive. In the present study evidence is provided for the existence of dopamine D(1)-D(3) receptor heteromers and for an intramembrane D(1)-D(3) receptor cross-talk in living cells and in the striatum. The formation of D(1)-D(3) receptor heteromers was demonstrated by fluorescence resonance energy transfer and bioluminescence resonance energy transfer techniques in transfected mammalian cells. In membrane preparations from these cells, a synergistic D(1)-D(3) intramembrane receptor-receptor interaction was observed, by which D(3) receptor stimulation enhances D(1) receptor agonist affinity, indicating that the D(1)-D(3) intramembrane receptor-receptor interaction is a biochemical characteristic of the D(1)-D(3) receptor heteromer. The same biochemical characteristic was also observed in membrane preparations from brain striatum, demonstrating the striatal co-localization and heteromerization of D(1) and D(3) receptors. According to the synergistic D(1)-D(3) intramembrane receptor-receptor interaction, experiments in reserpinized mice showed that D(3) receptor stimulation potentiates D(1) receptor-mediated behavioral effects by a different mechanism than D(2) receptor stimulation. The present study shows that a main functional significance of the D(3) receptor is to obtain a stronger dopaminergic response in the striatal neurons that co-express the two receptors.

Behavioral effects of saredutant, a tachykinin NK2 receptor antagonist, in experimental models of mood disorders under basal and stress-related conditions.

The present study was made to investigate the role of tachykinin NK2 receptors in the expression of stress-related behaviors in animals. Under basal conditions, intraperitoneal (i.p.) administration of the selective tachykinin NK2 receptor antagonist, saredutant (1 and 3 mg/kg) or diazepam (1 mg/kg) exerted anxiolytic-like effects in rodents, as they reduced grooming score of Wistar male rats tested in the novelty-induced grooming sampling test (NGT) and increased percentage of time and entries in open arms of Swiss male mice tested in the elevated plus maze (EPM) test. After previous exposure to stress-related conditions, as induced by a 2-min forced swim made 5 min prior to the EPM test, saredutant but not diazepam, exhibited anxiolytic-like effects in mice. To study the antidepressant-like activity of tachykinin NK2 receptor antagonist under basal conditions, different groups of rats were injected i.p. with saredutant (2.5, 5 and 10 mg/kg) or the tricyclic antidepressant, clomipramine (50 mg/kg) and tested in the forced swim test (FST), a widely used antidepressant-responsive test. The influence of stress-related conditions was studied in rats subjected to electric foot-shocks (1 mA, 1 s) 24, 5 and 1 h prior to FST, after drugs injection. In the FST, clomipramine decreased the immobility time only under basal conditions, but not after application of acute foot-shocks. To the contrary, saredutant-treated rats also exhibited more active behavior in FST after previous exposure to stressors. These results give further support to the hypothesis that tachykinin NK2 receptors may be a therapeutic target for pharmacological treatment of stress-related diseases, such as anxiety and depression.

Behavioral effects of dietary cholesterol in rats tested in experimental models of mild stress and cognition tasks.

Abnormalities in serum cholesterol levels of patients with mood disorders have been identified in epidemiological studies. However, evidence for an influence of dietary cholesterol on behavioral models is poor. Here, we investigated the behavioral changes of Wistar male rats fed a 2% cholesterol-enriched diet for 2 months in experimental models of depression and anxiety, such as the forced swim test (FST) paradigm and the novelty-induced grooming sampling test (NGT). The correlation between behavioral depression and impaired cognitive capacity was also examined testing rats in the Morris water maze (MWM) task one day after the FST. Different groups of rats fed various dietary regimens, were subjected to acute or repeated treatment (14 days) with clomipramine hydrochloride (50 or 25 mg/kg), diazepam (1 mg/kg) or with the peripheral benzodiazepine receptors (PBRs) antagonist, isoquinoline PK11195 (1 mg/kg) injected intraperitoneally (i.p.). Rats fed the cholesterol-enriched diet showed a significant decrease of grooming score in the NGT and of immobility time in the FST in comparison to animals fed a standard diet. Furthermore, the anxiolytic and antidepressant effects of diazepam and clomipramine were not affected by the different diets. Only after repeated treatment, PK11195 impaired the performance of animals fed a standard diet in the FST, and exhibited an anxiolytic-like profile in animals fed either the cholesterol-enriched or the standard diet. The improved performance in the FST was followed by a better learning performance in the acquisition phase of the MWM. These results suggest that effects of cholesterol-enriched diet on the behavioral reaction of rats in experimental models of mild stress may involve PBRs. They deserve attention in order to clarify the clinical correlation between plasma cholesterol levels and mood disorders in humans.

Endocannabinoids and neurodegenerative diseases.

The cannabinoid CB1 and CB2 receptors, the endogenous endocannabinoid (EC) ligands anandamide (AEA) and 2-arachidonylethanolamide, and the degradative enzymes fatty acid amide hydrolase (FAAH) and monoglyceride lipase (ML) are key elements of the EC system implicated in different physiological functions including cognition, motor activity and immune responses. Thus, both the possible neuroprotective role of ECs and their modulating action on neurotransmitter systems affected in several neurodegenerative diseases such as Alzheimer's disease (AD), Huntington's disease (HD) and multiple sclerosis (MS) are currently under investigation. Accumulating data show an unbalance in the EC system (i.e. decrease of neuronal cannabinoid CB1 receptors, increase of glial cannabinoid CB2 receptors and over-expression of FAAH in astrocytes) in experimental models of AD as well as in post-mortem brain tissue of AD patients, suggesting its possible role in inflammatory processes and in neuroprotection. However, the mechanisms of the EC modulation of immune response are not fully understood. By contrast, in HD a reduced EC signaling, given both by the loss of cannabinoid CB1 receptors and decrease of ECs in brain structures involved in movement control as basal ganglia, has been well documented in preclinical and clinical studies. Thus, in the present review we discuss recent data concerning the role of the EC system in the pathophysiology of AD and HD, two neurodegenerative diseases characterized by cognitive deficit and motor impairment, respectively. We focus on the effects of compounds modulating the EC system (agonists/antagonists of cannabinoid CB1 and CB2 receptors, or inhibitors of ECs metabolism processes) on the symptoms and/or progression of neurodegenerative diseases.

Behavioral effects of the beta3 adrenoceptor agonist SR58611A: is it the putative prototype of a new class of antidepressant/anxiolytic drugs?

A large body of evidence corroborates the notion that deficiencies of serotonergic system are likely involved in the pathogenesis of both depression and anxiety. Activation of beta(3) adrenoceptors has been shown to increase brain tryptophan content suggesting an elevation of brain serotonin (5HT) synthesis. SR58611A is a selective beta(3) adrenergic agent possessing a profile of antidepressant activity in routine rodents' experimental models of depression. The present study was undertaken to evaluate in rodents the antidepressant properties of SR58611A and to assess its putative anxiolytic value in experimental models of depression and anxiety. Compared to the control group, SR58611A (0.1, 1, 5 or 10 mg/kg) caused a dose-dependent reduction in immobility of Wistar male rats in the forced swim test. The maximum dose appeared to be equivalent to an effective dose of clomipramine (50 mg/kg). In addition, acute injection of SR58611A induced in rats a dose-dependent decrease in grooming response to a novel environment (novelty-induced grooming test). For any dose, the effect was lower than that of diazepam (1 mg/kg). Chronic treatment with SR58611A resulted also in an increased social interaction time in the social interaction test without affecting motor activity of rats. Furthermore, similarly to diazepam a chronic treatment with the highest doses of SR58611A was followed by increased exploratory behavior in Swiss male mice exposed to the elevated plus maze test. These effects are mediated by beta(3) adrenoceptors since i.p. pretreatment with the selective beta(3) adrenoceptor antagonist SR59230A (5 mg/kg) blocked the effects of SR58611A. Finally, also the 5HT antagonist methysergide (2 mg/kg) prevented the antidepressant and anxiolytic-like activity of SR58611A indicating that 5HT transmission is strictly involved in its action.

Cognitive effects of SL65.0155, a serotonin 5-HT4 receptor partial agonist, in animal models of amnesia.

Given that several data suggest the involvement of serotonergic (5-HT) system, particularly the serotonin 5-HT(4) receptors, in memory processes; this study was undertaken to investigate the role of serotonin 5-HT(4) receptors in different experimental models of amnesia in male Swiss mice or in male Sprague-Dawley rats, tested in learning and memory tasks. Amnesia was induced in mice by intracerebroventricular (i.c.v.) injection of beta-amyloid 1-42 fragment (BAP 1-42; 400 pmol/mouse) or of galanin (GAL) 1-29 (3 microg/mouse). Another group of animals was exposed to carbon monoxide (CO). Treatments were made 14 days, 15 min or 8 days prior to the learning trial of a step-through passive avoidance paradigm, respectively. Latency to re-enter the dark box appeared to be reduced in all treatment groups. Intraperitoneal (i.p.) administration of SL65.0155 (5-(8-amino-7-chloro-2,3-dihydro-1,4-benzodioxin-5-yl)-3-[1-(2-phenylethyl)-4-piperidinyl]-1,3,4-oxadiazol-2(3H)-one-monohydrochloride), a serotonin 5-HT(4) receptor partial agonist (1 mg/kg/day), for 7 days prior to the learning trial, inhibited the amnesic effect of both peptides increasing the latency to re-enter the dark box also in mice exposed to CO. In rats with ibotenate-induced lesions of the nucleus basalis magnocellularis (NBM) or prenatally exposed to methylazoxymethanol (MAM), SL65.0155 (1 mg/kg/day, i.p.) administered for 7 days, improved the learning and memory capacity in animals tested in shuttle-box active avoidance and radial maze tests. These findings give further support to the hypothesis of SL65.0155 cognition-enhancing activity across a range of tasks.

Amnesia induced by beta-amyloid fragments is counteracted by cannabinoid CB1 receptor blockade.

Administration of drugs activating cannabinoid CB(1) receptors in the brain induces memory deficit in rodents, and blockade of these receptors may restore memory capacity in these animals. Central administration of beta-amyloid or beta-amyloid fragments may also lead to memory disturbances. This study was undertaken to study the involvement of cannabinoid CB(1) receptors in amnesia induced by beta-amyloid fragments in mice tested in a step-through passive avoidance paradigm. Pre-training intracerebroventricular (i.c.v.) injection of beta-amyloid fragments, beta-amyloid peptide-(25-35) (4, 8 or 16 nmol/mouse) or beta-amyloid peptide-(1-42) (200, 400, 800 pmol/mouse) 7 days prior to the learning trial reduced in a dose-dependent manner the retention of passive avoidance response. This effect was observed in two retention tests, 1 and 7 days after the learning trial. The two beta-amyloid fragments showed similar potency in reducing retention of passive avoidance behavior. This effect was counteracted by a single intraperitoneal (i.p.) injection of the cannabinoid CB(1) receptor antagonist, N-(piperidin-l-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A, 1 mg/kg), made 30 min prior to the second retention test. The injection of SR141716A per se did not affect memory capacity of mice. The i.c.v. administration of beta-amyloid peptide-(25-35) (8 nmol/mouse) or of beta-amyloid peptide-(1-42) (400 pmol/mouse) made 30 min prior to the learning trial failed to affect the retention capacity of mice as measured 1 and 7 days later. Also, the i.p. injection of SR 141716A (1 mg/kg) made 30 min prior to the learning trial did not influence the behavioral response of mice injected with beta-amyloid peptide-(25-35) (8 nmol/mouse) or of beta-amyloid peptide-(1-42) (400 pmol/mouse) 7 days prior to the learning trial. These results show that beta-amyloid fragments induce a dose-dependent memory deficit. Their effect on memory retention depends upon the time of administration and seems to involve cannabinoid CB(1) receptors in the brain.

Long-lasting behavioral changes induced by pre- or neonatal exposure to diazepam in rats.

Prenatal treatment with small doses of diazepam may counteract the effect of physical stress in rats, normalizing the time course of neonatal reflexes and the behavioral responses in adulthood. However, prenatal administration of diazepam in greater doses may induce desensitization of gamma-aminobutyric acid A (GABA(A)) receptors and induce hypersensitivity to convulsants. This study was designed to examine in rats the influence of prenatal or neonatal diazepam treatment on development of neonatal reflexes, as index of brain maturation, and susceptibility to pentylenetetrazol-induced convulsions in adulthood. Pregnant Wistar rats were injected with diazepam 2.5 mg/kg/day, intraperitoneally (i.p.) on days 14-21 of pregnancy. Offspring showed a delay in the appearing of neonatal reflexes (cliff aversion, forelimb placing, forelimb grasping and bar holding) except for righting and startle reflexes. At 50 days of age, male rats showed a greater sensitivity to pentylenetetrazol compared to controls. In contrast, females showed a decreased susceptibility to convulsions. The appearance of reflexes in pups exposed to diazepam during neonatal life appeared to be similar to that of controls. Only the appearance of cliff aversion and startle reflexes appeared to be delayed in animals exposed neonatally to diazepam as compared to controls. In adulthood, female rats exposed in early neonatal life to diazepam again showed a resistance to pentylenetetrazol-induced convulsions as compared to male animals. These data suggest that prenatal exposure to diazepam induces long-lasting behavioral changes, which may be influenced by sex-dependent factors.