Forced swimming test and fluoxetine treatment: in vivo evidence that peripheral 5-HT in rat platelet-rich plasma mirrors cerebral extracellular 5-HT levels, whilst 5-HT in isolated platelets mirrors neuronal 5-HT changes

Breeding amiable animals? Improving farm animal welfare by including social effects in breeding programmes

Social interactions between individuals, such as co-operation and competition, are key factors in evolution by natural selection. As a consequence, evolutionary biologists have developed extensive theories to understand the consequences of social interactions for response to natural selection. Current genetic improvement programmes in animal husbandry, in contrast, largely ignore the implications of social interactions for the design of breeding programmes. Recently, we have developed theoretical and empirical tools to quantify the magnitude of heritable social effects, ie the heritable effects that animals have on their group mates’ traits, in livestock populations, and to utilise those effects in genetic improvement programmes. Results in commercial populations of pigs and laying hens indicate large heritable social effects, and the potential to substantially increase responses to selection in traits affected by social interactions. In pigs, including social effects into the breeding programme affected aggressive behaviour, both at mixing and in stable groups, indicating changes in the way dominance relationships are established and in aggressiveness. In laying hens, we applied selection between kin-groups to reduce mortality due to cannibalistic pecking. This resulted in a considerable difference in mortality between the low mortality line and the unselected control line in the first generation (20 vs 30%). Furthermore, changes in behavioural and neurobiological responses to stress were detected in the low mortality line, pointing to reduced fearfulness and stress sensitivity. These first results indicate that including social effects into breeding programmes is a promising way to reduce negative social interactions in farm animals, and possibly to also increase positive social interactions, by breeding animals with better social skills.

Longitudinal platelet reactivity to acute psychological stress among older men and women

Platelet reactivity to acute stress is associated with increased cardiovascular disease risk; however, little research exists to provide systematic methodological foundations needed to generate strong longitudinal research designs. Study objectives were: 1) to evaluate whether markers of platelet function increase in response to an acute psychological stress test among older adults, 2) to establish whether reactivity remains robust upon repeated administration (i.e. three occasions approximately 1 year apart), and 3) to evaluate whether two different acute speech stress tasks elicit similar platelet responses. The 149 subjects (mean age 71 years) gave a brief impromptu speech on one of two randomly assigned topics involving interpersonal conflict. Blood samples drawn at baseline and post-speech were assayed using flow cytometry for platelet responses on three outcomes (% aggregates, % P-selectin expression, and % fibrinogen receptor expression). Three-level hierarchical linear modeling analyses revealed significant stress-induced increases in platelet activation on all outcomes (p < 0.001). No significant habituation on any measure was found. Additional reactivity differences were associated with male gender, history of myocardial infarction, and use of aspirin, statins, and antidepressants. The results demonstrate that laboratory acute stress tests continued to produce robust platelet reactivity on three activation markers among older adults over 3 years.

Persistent versus transient depressive symptoms in relation to platelet hyperactivation: a longitudinal analysis of dementia caregivers

BACKGROUND

Depressive symptoms and caregiving stress may contribute to cardiovascular disease (CVD) via chronic platelet activation; however, it remains unclear whether this elevated activation constitutes a trait or state marker. The primary objective was to investigate whether persistent depressive symptoms would relate to elevated platelet activation in response to acute psychological stress over a three-year period.

METHODS

Depressive symptoms (Brief Symptom Inventory) were assessed among 99 spousal dementia caregivers (52-88 years). Platelet P-selectin expression was assessed in vivo using flow cytometry at three time-points over the course of an acute stress test: baseline, post-stress, and after 14 min of recovery. Two competing structural analytic models of depressive symptoms and platelet hyperactivity with three yearly assessments were compared.

RESULTS

Although depressive symptoms were generally in the subclinical range, their persistent elevation was associated with heightened platelet reactivity and recovery at all three-years while the change in depressive symptoms from the previous year did not predict platelet activity.

LIMITATIONS

These results focus on caregivers providing consistent home care, while future studies may extend these results by modeling major caregiving stressors.

CONCLUSIONS

Enduring aspects of negative affect, even among those not suffering from clinical depression are related to hemostatic changes, in this case platelet reactivity, which might be one mechanism for previously reported increase in CVD risk among elderly Alzheimer caregivers.

The lack of genotype-phenotype relationship between platelet serotonin concentration and serotonin transporter gene promoter polymorphism in healthy subjects

A polymorphism in the serotonin transporter gene (5-HTTLPR) is frequently studied for association with antidepressant treatment response, different personality traits, and psychiatric disorders. Baseline platelet serotonin (5-HT) concentration has been proposed to indicate a good or a poor treatment response to antidepressant drugs and to be associated with particular symptoms in psychiatric disorders. The aim of the study was to elucidate the genotype-phenotype relationship between platelet 5-HT concentration and 5-HTTLPR in healthy subjects. The frequency of 5-HTTLPR genotypes and alleles, as well as platelet 5-HT concentration was evaluated in 434 male and 86 female unrelated healthy medication-free Caucasian subjects of Croatian origin. A two-way ANOVA revealed no significant difference in platelet 5-HT concentration subdivided according to the particular 5-HTTLPR genotype, no significant effect of sex, no significant effect of genotype, and no significant interaction between sex and genotype on platelet 5-HT concentration. In addition, one-way ANOVA did not detect significant effects of homozygous S/S genotype, or homozygous L/L genotype on platelet 5-HT concentration. Our results showed a lack of significant association between platelet 5-HT concentration and 5-HTTLPR variants, suggesting that there is no functional relationship between 5-HTTLPR alleles and platelet 5-HT concentration in the large groups of healthy male and female medication-free Caucasian subjects, free of neuro-psychiatric disorders.

Effects of genetic group selection against mortality on behavior and peripheral serotonin in domestic laying hens with trimmed and intact beaks

Severe feather pecking is a maladaptive behavior in laying hens that may result in cannibalism and ultimately death of the victims. Selection methods in which the genetic effect of an animal on the survival of its group members is taken into account, i.e. 'group selection', have been shown to be very effective in reducing mortality due to feather pecking and cannibalism in laying hens. It has been suggested that fearfulness and serotonergic functioning are involved in the causation and development of feather pecking. We investigated effects of selection based on survivability in non-beak trimmed groups on fear-related behavior and peripheral 5-HT concentration and uptake in hens with trimmed or intact beaks, in a 2 x 2 factorial arrangement. Hens from the second generation of the low mortality line showed less fear-related behavior than control line hens. In addition, they displayed higher whole blood 5-HT concentrations and a lower platelet 5-HT uptake, indicating differences in functional activity of the 5-HT system. Beak trimming resulted in lowered levels of fear, and in a reduction of feather damage. Hens with trimmed and intact beaks did, however, not differ in peripheral 5-HT. The results imply that fearfulness and 5-HT activity are related to feather pecking without distinguishing between cause and effect. However, given that selection altered fear-related behaviors and peripheral 5-HT concentration and uptake, whereas beak trimming affected fearfulness and feather damage, but not 5-HT parameters, we suggest that peripheral 5-HT activity might reflect the predisposition to develop severe feather pecking under adverse conditions in laying hens.

Platelet serotonin uptake in drug-naïve depressive patients before and after treatment with citalopram

We investigated the kinetic parameters of serotonin (5-HT) uptake into platelets in a group of 26 drug-naïve patients suffering from major depression before and after 3-7 weeks of treatment with citalopram. The degree of depression was rated using the Hamilton Depression Rating Scale (HDRS). The 5-HT uptake characteristics in untreated depressive patients were not significantly different from those of normal subjects. The apparent Michaelis constant (K(M)) was significantly increased, the apparent maximal velocity (V(max)) was not different from baseline, and the uptake efficiency (V(max)/K(M)) was significantly decreased after citalopram treatment. A significantly positive correlation between K(M) and V(max) was found in all groups. There was a significantly lower V(max) and V(max)/K(M) in the female compared with the male depressed patients before citalopram treatment; a hypothesis was supported that lowered 5-HT uptake may reflect a gender-linked vulnerability to a serotonin-related depression. A significant negative correlation between 5-HT uptake efficiency and the initial HDRS score suggests that platelet 5-HT uptake can be used as a marker of effective depressive disorder pharmacotherapy. The initial severity of depression was significantly negatively correlated with V(max), which supported a hypothesis that the initial severity of depressive disorder could be related to the lower V(max).

Platelet serotonin level and its correlation with finger length relation

BACKGROUND

Serotonin is one of the neurotransmitters implicated in normal personality. Many psychobiological models of personality include some dimensions related to serotonin. Moreover, platelets have long been proposed as easily obtainable, neurological models of serotonergic neurons.

AIM

This study was done to examine whether measurement for platelet serotonin could aid as a marker for increased neuroticism trait amongst (arbitrarily named Group C) males and females having the tip of the little fingers below the distal finger mark on the adjacent ring fingers in both their outstretched hands compared to (arbitrarily named Group A) the males and females who have the tip of the little fingers above the distal finger mark on the adjacent ring fingers in both their outstretched hands.

MATERIALS AND METHODS

Platelet serotonin estimation was done by Elisa Method (LDN, Germany Kit) from randomly selected 48 healthy subjects [24 males (12 males belonging to Group A and 12 belonging to Group C) and 24 females (12 females belonging to group A and 12 females belonging to Group C)].

RESULTS

PRELIMINARY RESULTS SHOWED THAT THE PLATELET SEROTONIN LEVELS WERE SIGNIFICANTLY LOWER (LEVEL OF SIGNIFICANCE: 0.05 in t-Test analysis) in Group C males compared to those observed in Group A males and the platelet serotonin levels were also significantly lower (level of significance: 0.05 in t-Test analysis) in Group C females compared to those observed in Group A females.

CONCLUSION

Thus, it may be inferred that the platelet serotonin may be used as a biochemical marker for increased neuroticism trait in Group C subjects.

Behavioral and pharmacological validation of the gerbil forced-swim test: effects of neurokinin-1 receptor antagonists

Several studies have suggested that neurokinin-1 (NK1) receptor antagonists may have therapeutic potential as novel antidepressant drugs. To test these compounds preclinically, gerbils have become one of the preferred species in that they demonstrate close NK1 receptor homology with humans and bind NK1 antagonists with higher affinity than rats and mice. The intent of the present study was to determine whether the forced-swim test (FST), one of the most commonly used animal tests of antidepressant-like activity, could be adapted for use with the gerbil. Critical factors in the establishment of this assay included swim tank diameter, weight, and sex of the animals tested. Pharmacological validation of the FST using standard antidepressant compounds (eg fluoxetine, paroxetine, desipramine) resulted in decreased immobility time during the test, indicative of an antidepressant-like effect. Similar to results reported for the rat and mouse FST, the antipsychotic drug haloperidol increased immobility, whereas the psychostimulant, amphetamine decreased immobility, and anxiolytic drugs (eg buspirone) had no effect. Investigation into the locomotor effects of all compounds tested was consistent with previous reports in other species, with the exception of paroxetine, which produced hyperactivity at therapeutically effective doses in gerbils. In addition to standard antidepressants, NK1 antagonists (L-733060, MK-869, and CP-122721) all reduced immobility in the gerbil FST without affecting locomotor activity. Overall, these results suggest that the gerbil is an ideal species for use in the FST, and that this paradigm may have predictive validity for identifying novel antidepressant compounds.

Effect of cannabinoids on platelet serotonin uptake

Serotonin is involved in many of the same processes affected by cannabinoids; therefore, we investigated in vitro and in vivo effects of these drugs on the function of serotonin transporter. The effect of Delta(9)-tetrahydrocannabinol (Delta(9)-THC), endocannabinoid anandamide and synthetic cannabinoid receptor agonist WIN 55,212-2 on platelet serotonin uptake and membrane microviscosity was examined in 19 marijuana smokers and 20 controls. (1) Serotonin uptake was inhibited at higher doses of Delta(9)-THC (IC(50) = 139 micromol/l), anandamide (IC(50) = 201 micromol/l) or WIN 55,212-2 (IC(50) = 17.4 micromol/l); the inhibition was found non-competitive. Delta(9)-THC, anandamide and WIN 55,212-2 produced different effects on the membrane microviscosity. (2) Maximal velocity of platelet serotonin uptake was significantly increased in a group of chronic marijuana smokers suffering impairment of cognitive functions when compared with controls. Opposite effect of marijuana smoking on the serotonin uptake efficiency was observed in males beside females. In summary, this study provides evidence that (1) Activity of serotonin transporter is acutely affected by cannabinoids at relatively high drug concentrations; this effect is indirect and can be partially accounted for the changes in the membrane microviscosity. (2) Increase of maximal velocity of the serotonin uptake could be understood as adaptation change in the serotonergic system induced by chronic cannabis use. A hypothesis was supported that lowered serotonin uptake may reflect a gender-related differences in effects of psychoactive cannabinoids.

[Reduced serotonin levels in platelet-free plasma of adolescents with externalizing behaviour problems]

OBJECTIVES

A serotonergic dysfunction, in particular a reduced serotonergic neurotransmission in the frontal cortex and limbic brain regions, has been discussed in connection with the aetiology of aggressive and impulsive behaviour. Assessment of the activity in the central serotonergic system in children and adolescents is limited due to its technical complexity and ethical restrictions. Therefore, peripheral serotonergic parameters have been used as a model to obtain deeper insight into central serotonergic functions. The aim of this investigation is to examine the significance of plasma serotonin measurement with regard to behavioural problems in adolescents at risk for psychopathology.

METHODS

Within the framework of a prospective longitudinal study of children at risk, serotonin levels in platelet-free blood plasma were measured in a group of n = 10 adolescents aged 15 years with persistent externalizing behaviour (T-score > or = 60 on the "Externalizing Problems" scale of the CBCL) and in a control group of n = 20 mentally undisturbed adolescents. Groups were matched according to age and gender. Externalizing behaviour was assessed by means of a parent questionnaire, the Achenbach Child Behavior Checklist (CBCL).

RESULTS

Significantly lower levels of plasma serotonin were found in adolescents with persistent behaviour problems than in the control group. Significant negative correlations between serotonin levels and the CBCL scales "Aggressive Behavior" and "Externalizing Problems" were obtained for the total sample.

CONCLUSIONS

Earlier findings that described a serotonergic deficit as a key mechanism in the manifestation of aggressive and antisocial behaviour are confirmed for adolescents at risk taken from a community sample.

Effect of treatment on serum brain-derived neurotrophic factor levels in depressed patients

Researchers have reported that serum brain-derived neurotrophic factor (sBDNF) of drug-free depressed patients are lower than those of healthy controls and proposed that low sBDNF levels might reflect failure of neuronal plasticity in depression. In this study, we compared sBDNF levels of depressed patients (n = 28) before and after 8 weeks of antidepressant treatment, with those of healthy controls (n = 18) to test the hypothesis that initially low sBDNF levels of drug-free depressed patients will increase parallel with their clinical response to antidepressant treatment. The severity of depression and response to treatment were assessed with Hamilton Rating Scale for Depression (HAM-D). sBDNF was assayed with the sandwich ELISA method. Baseline sBDNF levels of patients (mean, 20.8 ng/ml; [S.D., 6.7]) were significantly lower than those of controls (mean, 26.8 ng/ml; [S.D., 9.3]; p = 0.015), and were negatively correlated with HAM-D scores (r = -0.49, p = 0.007). After 8 weeks of treatment, sBDNF levels of patients had increased significantly (mean, 33.3 ng/ml; [S.D., 9.9]; p < 0.001) and no longer differed from those of controls. These results support the hypothesis that BDNF might play a critical role in the pathophysiology of major depressive disorder and successful antidepressant treatment increases the attenuated BDNF levels in depressed patients.

Co-administration of fluoxetine and WAY100635 improves short-term memory function

The aim of this study was to determine whether the action of the antidepressant fluoxetine or the anxiolytic buspirone could be modified by specific 5-hydroxytriptamine (5-HT(1A)) receptor blockade in a short-term memory paradigm. Male Wistar rats were trained to perform the putative short-term memory task, delayed non-matching to position. WAY100635, a selective 5-HT(1A) receptor antagonist (0.15 mg/kg), was administered 15 min before either the selective serotonin reuptake inhibitor fluoxetine (3 mg/kg), or the partial 5-HT(1A) receptor agonist and dopamine D2 receptor antagonist, buspirone (0.3 mg/kg). 8-Hydroxy-di-n-propylamino tetralin (8-OH-DPAT), a full 5-HT(1A) receptor agonist (0.3 mg/kg), was also included in the study as a positive control. WAY100635 alone had no effect on any behavioural parameter measured (response accuracy, delay lever press activity and trial completion). 8-OH-DPAT impaired response accuracy in a delay-dependent manner, an effect reversed by WAY100635. Fluoxetine also impaired response accuracy delay-dependently. WAY100635 pretreatment not only reversed this deficit but improved response accuracy, in the presence of a significant deficit in trial completion. At the dose used, buspirone showed no significant differences compared to the control group. The data suggest that fluoxetine impairs short-term memory function by the indirect activation of 5-HT(1A) receptors, but that its co-administration with WAY100635 improves short-term memory function.

Impact of the CYP2D6 ultra-rapid metabolizer genotype on doxepin pharmacokinetics and serotonin in platelets

INTRODUCTION

CYP2D6 gene duplication causing ultrafast metabolism is one reason for failure in responding to CYP2D6-metabolized antidepressants. We studied the effect of the CYP2D6 duplication genotype on doxepin pharmacokinetics and platelet serotonin uptake and concentrations.

METHODS

Pharmacokinetics of trans (E)- and cis (Z)-doxepin and N-desmethyldoxepin were analyzed after a single dose of 75 mg doxepin in 11 ultrafast metabolizers (UM), 11 extensive metabolizers (EM) and 3 poor metabolizers (PM), identified by genotyping for CYP2D6 alleles *2, *3, *4, *5, *6, *9, *10, *35, *41 and specific analyses to characterize gene duplication. Platelet serotonin concentrations were measured by HPLC.

RESULTS

A trend for lower AUC of the active principle (sum of doxepin and N-desmethyldoxepin) in UMs versus EMs was detected (575 versus 1,000 nmol h/l, P=0.07), mainly due to the differences in desmethyldoxepin concentrations (P=0.003). Stereoselective analysis showed a significant effect of the UM genotype on (E)-doxepin pharmacokinetic parameters whereas those of (Z)-doxepin did not differ between the CYP2D6 genotype groups. The 75-mg doxepin dose had no effect on platelet serotonin concentration and uptake, but serotonin concentrations in platelets were significantly higher in UM in comparison to the EM and PM groups. At baseline, these concentrations were 462, 399, and 292 ng/10 platelets in UM, EM and PM (P<0.0001 for trend).

CONCLUSIONS

At the same dose, internal exposure to doxepin differed by more than ten-fold between the CYP2D6 genotype groups. CYP2D6 may have an effect on platelet serotonin explained by salvage pathways of 5-methoxytryptamine to serotonin mediated by CYP2D6; however, this finding requires further confirmatory experiments.

Serotonin transport kinetics correlated between human platelets and brain synaptosomes

RATIONALE

Blood platelets have been used extensively as a model system for investigating the role of the serotonin transporter (SERT) in various psychiatric disorders, especially depression. However, to date, it is not known whether platelet serotonin (5-HT) transport would be related to that in brain.

OBJECTIVES

We examined 5-HT transport kinetics simultaneously in human blood platelets and human cortical brain synaptosomes to determine whether they were correlated.

METHODS

Blood platelets and synaptosomes were obtained from 25 patients undergoing epileptic surgery. Synaptosomes were obtained from normal margins of surgical neuropathology specimens of anterotemporal cortex.

RESULTS

Platelet SERT V(max) was significantly correlated with brain SERT V(max) on linear regression (r=0.58, p<0.005), after controlling for the confounding effects of gender (t=-2.4, p=0.025) and time of day (t=2.1, p<0.05). Consistent with previous observations, there was a negative correlation between the maximum velocity (V(max)) of platelet 5-HT transport and pO2 (r=-0.52, p<0.01). Females had a significantly higher pO2 than males (F=4.9, p<0.05). After accounting for gender differences, addition of pO2 did not add further strength to the regression, given the aforementioned gender differences in pO2. The correlation between unadjusted values for platelet vs brain SERT V(max) was r=0.3, p=0.06.

CONCLUSIONS

These results suggest that a relationship may exist between 5-HT transport in platelets and cortical synaptosomes, when appropriate controls for confounding factors are employed.

Antidepressant-like actions of intra-accumbens infusions of allopregnanolone in ovariectomized Wistar rats

This study was aimed to verify the role of the nucleus accumbens (NAcc) in the antidepressant-like effects of allopregnanolone in ovariectomized rats forced to swim. The interaction between infusions of allopregnanolone (intra-NAcc) with systemic administrations of allopregnanolone, muscimol, fluoxetine and GABA-A antagonists was assessed. Results showed that allopregnanolone (intra-NAcc; 1.5 microg, p < 0.05; 2.0 microg, p < 0.05) or systemic injections of allopregnanolone (1.5 mg/kg, p < 0.05; 2.0 mg/kg, p < 0.05; s.c.) or muscimol (0.3 mg/kg, p < 0.05; 0.6 mg/kg, p < 0.05; i.p.) reduced immobility by increasing climbing in the forced swimming task (FST), whereas fluoxetine (1.0 mg/kg, p < 0.05; 2.0 mg/kg, p < 0.05; i.p.) reduced immobility by increasing swimming. Allopregnanolone (intra-NAcc; 0.5 microg/side) synergized with systemic doses of allopregnanolone (0.5 mg/kg; p < 0.05), muscimol (0.1 mg/kg; p < 0.05) or fluoxetine (0.5 mg/kg; p < 0.05) and reduced immobility by increasing climbing. Picrotoxin (0.125 mg/kg; i.p.) attenuated the synergism of the combination allopregnanolone (intra-NAcc; 0.5 microg/side) plus fluoxetine (i.p.) or allopregnanolone (s.c.) and the effects of allopregnanolone (intra-NAcc; 1.5 microg/side). Bicuculline (2.0 mg/kg; i.p.) attenuated the synergism between the combination allopregnanolone (intra-NAcc; 0.5 microg/side) plus muscimol (i.p.), but not the synergism of the combination allopregnanolone (intra-NAcc; 0.5 microg/side) plus allopregnanolone (s.c.). In conclusion, allopregnanolone (systemic injections or intra-NAcc), fluoxetine or muscimol produced antidepressant-like effects in the FST. Subthreshold doses of allopregnanolone (intra-NAcc) synergized with systemic subthreshold doses of fluoxetine, muscimol or allopregnanolone. Antagonists of the GABA-A receptor canceled the synergism.

Serotonin transporter kinetics in rats selected for extreme values of platelet serotonin level

By selective breeding of Wistar rats for the extreme values of platelet serotonin (5HT) level (PSL), we have developed earlier two sublines of animals differing markedly in this parameter. Further studies, performed on the protein and mRNA levels, revealed platelet serotonin transporter (5HTt) as parameter underlying mentioned differences in PSL between sublines. In this work, we have performed full-kinetic analysis of platelet serotonin uptake (PSU) in animals from the genetically selected sublines. The results demonstrated marked differences in maximal velocity (V(max)) of the 5HT transporter, as contrasted to the lack of any difference in the Michaelis constant (K(m)). High correlation between PSL and V(max) of PSU was demonstrated, revealing that the number of membrane 5HT transporter sites is under genetic control and responsible for marked differences in PSL between high- and low-5HT sublines. These results enabled further selective breeding of animals for the extremes of V(max) of platelet 5HT transporter, and so the development of more specific model "Wistar-Zagreb 5HT rats".

Synergistic interaction between ketoconazole and several antidepressant drugs with allopregnanolone treatments in ovariectomized Wistar rats forced to swim

This article was aimed to investigate the interest of the combination allopregnanolone plus ketoconazole in depression with the time-sampling method in the forced swimming task. Dose-response curves for fluoxetine (0.5, 1.0 or 2.0 mg/kg, twice day, during 2 weeks; i.p.), desipramine (0.5, 1.0 or 2.14 mg/kg, twice a day, during 2 weeks; i.p.), ketoconazole (6.25, 12.5, 25.0 and 37.5 mg/kg, once a day, during 2 weeks; i.p.) and allopregnanolone (0.5, 1.5, 2.0 mg/kg; once a day, during 2 weeks; s.c.) were established. Fluoxetine (1.0 mg/kg, p < 0.05; 2.0 mg/kg, p < 0.05) or ketoconazole (25.0 mg/kg, p < 0.05; 37.5 mg/kg, p < 0.05) produced antidepressant-like behavioral changes in swimming, highlighting a serotonergic mechanism while desipramine (1.0 mg/kg, p < 0.05; 2.14 mg/kg, p < 0.05) or allopregnanolone (1.5 mg/kg, p < 0.05; 2.0 mg/kg, p < 0.05) increased climbing behavior highlighting noradrenergic or dopaminergic effects. Subthreshold doses of fluoxetine (p < 0.05), desipramine (p < 0.05) or ketoconazole (p < 0.05) synergized with subthreshold doses of allopregnanolone and reduced immobility by increasing climbing. In conclusion, fluoxetine, desipramine, ketoconazole and allopregnanolone produced differential antidepressant-like actions in ovariectomized rats forced to swim. Ketoconazole, fluoxetine or desipramine synergized with allopregnanolone.

Schizophrenia-like behavioral changes after partial hippocampal kindling

The effect of hippocampal kindling on behavioral changes following 10 and 21 hippocampal afterdischarges (ADs) or electrographic seizures was examined in behaving rats. As compared to control, non-stimulated rats, 21 but not 10 hippocampal ADs resulted in a decrease in social contact, an increase in social isolation, and an increase in climbing and chasing behavior tested in an open field 3 days after cessation of kindling. Porsolt forced swimming test was not different among the control, 10- or 21-AD groups of rats. A deficit in sensorimotor gating, measured by prepulse inhibition of an acoustic startle, was observed in kindled as compared to control rats at 2 weeks after 21 ADs, but not after 10 ADs. Similarly, methamphetamine (1 mg/kg i.p.) induced higher locomotor activity in kindled rats, as compared to controls, after 21 ADs but not after 10 ADs. Spontaneous locomotor activity in a novel cage, without drug administration, was not different between kindled and control rats. These findings suggest that behavioral alterations after repeated hippocampal electrographic seizures may be mediated by increased dopaminergic functions, which may also mediate the psychiatric symptoms in human epileptic patients.

Evidence that the metabotropic glutamate receptor 5 antagonist MPEP may act as an inhibitor of the norepinephrine transporter in vitro and in vivo

The mechanisms through which blockade of metabotropic glutamate receptors 5 (mGluR5) results in anxiolytic and antidepressant effects are currently unknown. In the present study, we therefore hypothesized that the anxiolytic- and antidepressant-like profile of the noncompetitive mGluR5 receptor antagonist 2-ethyl-6-(phenylethynyl)-pyridine (MPEP) may be mediated by inhibition of the norepinephrine transporter (NET). Accordingly, we first examined the potency of MPEP to bind to or inhibit uptake at the NET as well as the dopamine and serotonin transporters (DAT and SERT, respectively). We also examined the simultaneous in vivo effects of MPEP and desipramine (DMI) on both NE-like oxidation current in the amygdala (AMY) and cell firing in the locus coeruleus (LC) by means of differential pulse voltammetry (DPV) coupled with electrophysiology. MPEP completely displaced the binding of [3H]-nisoxetine on human NET with a pKi of 6.63 +/- 0.02. In addition, MPEP was able to inhibit [3H]-NE uptake in LLCPK cells expressing human NET, with a pIC50 of 5.55 +/- 0.09. In vivo DPV data revealed that both MPEP (30 mg/kg i.p.) and DMI (10 mg/kg i.p.) significantly increased NE-like voltammetric responses levels in the AMY, whereas both compounds also significantly decreased cell firing monitored concomitantly from the second microelectrode in the LC. Collectively, the results of the present study provide potential new mechanisms through which MPEP exerts its anxiolytic and antidepressant effects.