Extracellular Serotonin Levels Research Articles

Sex-specific 24-h profile of extracellular serotonin levels in the medial prefrontal cortex

The medial prefrontal cortex (mPFC) controls emotional responses in many species, receiving serotonergic innervation from the dorsal and median raphe nucleus (DRN and MRN). To examine the sex difference in 24-h profiles of extracellular serotonin (5HT) levels in the mPFC, an in vivo microdialysis study was performed using intact male, diestrous female, and proestrous female rats. Dialysates were automatically collected by a microdialysis probe from the mPFC every 30 min for more than 24 h under freely moving conditions. The levels of 5HT in dialysates were quantified by high performance liquid chromatography. Extracellular 5HT levels exhibited episodic changes in the mPFC of both sexes of rats, with both diestrous and proestrous females exhibiting a clear diurnal change; the 5HT levels were high during the dark phase, but low during the light phase. In contrast, male rats exhibited relatively high 5HT levels throughout the day without significant diurnal changes. At mathematically analyzed trough, males showed higher 5HT levels than diestrous or proestrous females. The overall 24-h 5HT levels in males were significantly greater than proestrous females, but were not different from diestrous females. Further, stereological methods were used to examine the number of tryptophan hydroxylase (TrpH), but no sex differences in the number of TrpH immunoreactive cells in the DRN and MRN were observed. These results suggest that sex and/or the gonadal steroid environment may affect the 24-h profile of extracellular 5HT in the mPFC of rats without changes in the number of 5HT neurons in the DRN and MRN.

Systemic administration of ghrelin increases extracellular dopamine in the shell but not the core subdivision of the nucleus accumbens

The gut-hormone ghrelin endogenously binds to the ghrelin receptor (GHS-R) to promote foraging and feeding behaviours mainly via the hypothalamic arcuate nucleus (ARC). GHS-Rs are also expressed in midbrain dopaminergic neurons of the ventral tegmental area (VTA) suggesting that ghrelin may modulate the mesolimbic dopamine (DA) system. In support of this hypothesis, previous results have shown that intraventricular administration of ghrelin in rats increases DA levels in the nucleus accumbens (NAc). In the present study, the systemic doses of ghrelin capable of triggering central activation were first determined, and growth hormone (GH) levels were used as a marker of ghrelin-induced activation. Similar dose regimen was then used to measure ghrelin-induced effects on extracellular levels of monoamines in the shell and core subdivisions of the NAc using microdialysis in freely moving rats. We show that subcutaneous (s.c.) administration of ghrelin produced an increase in basal plasmatic ghrelin concentrations that was paralleled by enhanced GH secretion. In addition, a significant increase in extracellular levels of DA was observed specifically in the NAc shell, with no effect in the core subdivision. Extracellular serotonin (5-HT) levels were also affected in the shell subregion, but without reaching statistical significance. Increased extracellular DA levels in the NAc shell have been typically associated with the acute reinforcing effects of addictive drugs. The present findings therefore suggest that systemic ghrelin may modulate the valence of reinforcers such as food and drugs of abuse by interfering with mesolimbic DA activity.

Effect of different challenge doses after repeated citalopram treatment on extracellular serotonin level in the medial prefrontal cortex: In vivo microdialysis study

In order to elucidate the relevance between the delayed onset of clinical efficacy of selective serotonin re-uptake inhibitors (SSRI) and extracellular 5-HT levels in the medial prefrontal cortex, the present study compared the ability of low-dose (3 mg/kg) and high-dose (30 mg/kg) citalopram to increase extracellular 5-HT levels in the medial prefrontal cortex following repeated citalopram treatment using in vivo microdialysis. An SSRI, citalopram, was given 10 mg/kg, s.c. twice daily for 6 days and once on the seventh day in rats. On the eighth day, rats received a single injection of citalopram (3 or 30 mg/kg s.c.), and extracellular 5-HT levels were assessed in the medial prefrontal cortex of rats using in vivo brain microdialysis. There was no significant difference in basal extracellular 5-HT levels between the repeated citalopram group and the repeated saline group. The low-challenge dose of citalopram (3 mg/kg) produced significantly greater increases (170-200% at each time point) in the repeated citalopram group than in the repeated saline group (150%). The high-challenge dose of citalopram (30 mg/kg), however, increased extracellular 5-HT levels by 200-250% of basal levels in the repeated citalopram group, which was similar to the increases in the repeated saline group. Repeated SSRI treatment enhances the effect of low-dose SSRI on extracellular 5-HT levels but not that of high-dose SSRI.

Impairment of the serotonergic control of feeding in adult female rats exposed to intra-uterine malnutrition

We have previously shown that adult female rats exposed to intra-uterine malnutrition were normophagic, although obese and resistant to insulin-induced hypophagia. The present study aimed at examining aspects of another important catabolic component of energy homeostasis control, the hypothalamic serotonergic function, which inhibits feeding and stimulates energy expenditure. Pregnant dams were fed ad libitum or were restricted to 50 % of ad libitum intake during the first 2 weeks of pregnancy. Control and restricted 4-month-old progeny were studied. The restricted rats had increased body adiposity with normal daily food intake but failed to respond with hypophagia to an intracerebroventricular injection of serotonin (5-hydroxytryptamine; 5-HT). Stimulation, by food ingestion, of extracellular levels of serotonin in medial hypothalamus microdialysates was more pronounced and lasted longer in the restricted than in the control rats. In the restricted group, hypothalamic levels of 5-HT 2C receptor protein tended to be reduced (P = 0.07) while the levels of 5-HT1B receptor and serotonin transporter proteins were significantly elevated (36 and 79 %, respectively). In conclusion, female rats undernourished in utero had normophagic obesity as adults but had an absence of serotonin-induced hypophagia and low hypothalamic levels of the 5-HT 2C receptor. Compensatory adaptations for the functional serotonergic impairment were evidenced, such as an enhanced release of serotonin in response to a meal allied to up-regulated hypothalamic 5-HT1B and transporter expression. Whether these compensations will persist in later life warrants further investigation. Moreover, it cannot be ruled out that the serotonergic component of energy expenditure was already impaired, thus contributing to the observed body-fat phenotype.

The molecular background of sex difference in depressive disorders: still an enigma

There is no doubt that adult females are significantly more often affected by depression and anxiety disorders than males. Virtual every study enrolls more women than men and it is assumed that the number of women suffering from depression doubles that of men. Interestingly, this difference is not present before adolescence. Not only the incidence and prevalence of depression is gender-specific, the same is true for the clinical phenomenology. The female excess is more pronounced in comorbid depression and anxiety and less in the pure forms. Other forms affecting women to a significantly higher degree than other subtypes are the so-called atypical depression [1] and somatic depression [2]. The main pathophysiological concept of depression relies on the biogenic amine 5-hydroxytryptophan (5HT) named serotonin. There is convincing evidence that the central serotonergic system plays a key role in the development, treatment and response rate of this affective disorder. Serotonin depletion induces depression in vulnerable subjects. Pharmacological restoration of high extracellular serotonin level relieves symptoms and is associated with termination of depressive episodes, which are frequently observed in the Western population and represent a relevant socioeconomic and medical problem. So far, the unequivocal facts for which strong evidence exist from epidemiologic studies and animal experiments. For in vivo studies on brain function in depression and other psychiatric disorders, nuclear medicine imaging provides a valuable and powerful imaging tool. By positron emission tomography, the serotonin transporter, the serotonin 2A and the serotonin 1A receptor binding potential (BP) can be selectively quantified. In this regard, particular interest is put on PET with [carbonyl-C]WAY-100635, a highly selective ligand for the 5-HT1A receptor that is the main inhibitory serotonergic receptor subtype. One should expect that, based on the overwhelming evidence for the predominance of female depressive patients, this armamentarium can easily visualise the molecular sex differences in the serotonergic system. However, the results remain inconsistent despite that the majority of investigators demonstrated a reduction of 5-HT1A receptor BP in distinct brain regions of depressive subjects [3–5], whereas no significant 5-HT1A receptor BP difference was found in patients with major depressive disorder (MDD) in comparison to controls in another comparable study by Parsey et al. [6]. Given that females show a significant predominance in depression, the consideration of a sex difference in 5-HT1A receptor BP is quite compelling. Indeed, a very recent study demonstrated a higher 5-HT1Areceptor BP and a lower serotonin transporter BP in females compared to males in healthy subjects [7]. Some years earlier, Parsey et al. also demonstrated a higher 5-HT1A receptor BP in females in several brain regions playing a role in mood disorders [8]. The study of Stein et al. in this EJNMMI issue focused on the 5-HT1A receptor BP in a sample of young healthy volunteers, determining the structure by two independent methods with the surprising result that there was a trend to though nonsignificant lower 5-HT1A receptor BP in females than in males [9]. These results were obtained by both an automated template-based method and by visual region of Eur J Nucl Med Mol Imaging (2008) 35:2156–2158 DOI 10.1007/s00259-008-0928-5

Neurochemical, behavioral, and physiological effects of pharmacologically enhanced serotonin levels in serotonin transporter (SERT)-deficient mice

Serotonin transporter (SERT) knockout (-/-) mice have an altered phenotype in adulthood, including high baseline anxiety and depressive-like behaviors, associated with increased baseline extracellular serotonin levels throughout life. To examine the effects of increases in serotonin following the administration of the serotonin precursor 5-hydroxy-L-tryptophan (5-HTP) in SERT wild-type (+/+), heterozygous (+/-), and -/- mice. 5-HTP increased serotonin in all five brain areas examined with approximately 2- to 5-fold increases in SERT+/+ and +/- mice, and with greater 4.5- to 11.7-fold increases in SERT-/- mice. Behaviorally, 5-HTP induced exaggerated serotonin syndrome behaviors in SERT-/-, mice with similar effects in male and female mice. Studies suggest promiscuous serotonin uptake by the dopamine transporter (DAT) in SERT-/- mice, and here, the DAT blocker GBR 12909 enhanced 5-HTP-induced behaviors in SERT-/- mice. Physiologically, 5-HTP induced exaggerated temperature effects in SERT-deficient mice. The 5-HT1A antagonist WAY 100635 decreased 5-HTP-induced hypothermia in SERT+/+ and +/- mice with no effect in SERT-/- mice, whereas the 5-HT7 antagonist SB 269970 decreased this exaggerated response in SERT-/- mice only. WAY 100635 and SB 269970 together completely blocked 5-HTP-induced hypothermia in SERT+/- and -/- mice. These studies demonstrate that SERT-/- mice have exaggerated neurochemical, behavioral, and physiological responses to further increases in serotonin, and provide the first evidence of intact 5-HT7 receptor function in SERT-/- mice, with interesting interactions between 5-HT1A and 5-HT7 receptors. As roles for 5-HT7 receptors in anxiety and depression were recently established, the current findings have implications for understanding the high anxiety and depressive-like phenotype of SERT-deficient mice.

Antidepressant-Like Pharmacological Profile of a Novel Triple Reuptake Inhibitor, (1S,2S)-3-(Methylamino)-2-(naphthalen-2-yl)-1-phenylpropan-1-ol (PRC200-SS)

Due to the putative involvement of dopaminergic circuits in depression, triple reuptake inhibitors are being developed as a new class of antidepressant, which is hypothesized to produce a more rapid onset and better efficacy than current antidepressants selective for serotonin or norepinephrine neurotransmission. (1S,2S)-3-(Methylamino)-2-(naphthalen-2-yl)-1-phenylpropan-1-ol (PRC200-SS), a new triple reuptake inhibitor, potently bound to the human serotonin, norepinephrine, and dopamine transporters with K(d) values of 2.3, 0.63, and 18 nM, respectively. Inhibition of serotonin, norepinephrine, and dopamine uptake by PRC200-SS was also shown in cells expressing the corresponding transporter (K(i) values of 2.1, 1.5, and 61 nM, respectively). In vivo, PRC200-SS dose-dependently decreased immobility in the forced-swim test in rats and in the tail-suspension test in mice, models predictive of antidepressant activity, with effects comparable with imipramine. These results in the behavioral models did not seem to result from the stimulation of locomotor activity. Consistent with the in vitro data and behavioral effects, peripheral administration of PRC200-SS (5 and 10 mg/kg i.p.) significantly increased extracellular levels of serotonin and norepinephrine in the medial prefrontal cortex, and of serotonin and dopamine in the core of nucleus accumbens, with reduction of levels of 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid compared with levels for saline control. Furthermore, PRC200-SS self-administration, which was used as a marker of abuse liability, was not observed with rats. Therefore, it seems that PRC200-SS may represent a novel triple reuptake inhibitor and possess antidepressant activity.

Excess of serotonin affects embryonic interneuron migration through activation of the serotonin receptor 6

The discovery that a common polymorphism (5-HTTLPR, short variant) in the human serotonin transporter gene (SLC6A4) can influence personality traits and increase the risk for depression in adulthood has led to the hypothesis that a relative increase in the extracellular levels of serotonin (5-HT) during development could be critical for the establishment of brain circuits. Consistent with this idea, a large body of data demonstrate that 5-HT is a strong neurodevelopmental signal that can modulate a wide variety of cellular processes. In humans, serotonergic fibers appear in the developing cortex as early as the 10th gestational week, a period of intense neuronal migration. In this study we hypothesized that an excess of 5-HT could affect embryonic cortical interneuron migration. Using time-lapse videometry to monitor the migration of interneurons in embryonic mouse cortical slices, we discovered that the application of 5-HT decreased interneuron migration in a reversible and dose-dependent manner. We next found that 5-HT6 receptors were expressed in cortical interneurons and that 5-HT6 receptor activation decreased interneuron migration, whereas 5-HT6 receptor blockade prevented the migratory effects induced by 5-HT. Finally, we observed that interneurons were abnormally distributed in the cerebral cortex of serotonin transporter gene (Slc6a4) knockout mice that have high levels of extracellular 5-HT. These results shed new light on the neurodevelopmental alterations caused by an excess of 5-HT during the embryonic period and contribute to a better understanding of the cellular processes that could be modulated by genetically controlled differences in human 5-HT homeostasis.

Effect of a novel neurotensin analog, NT69L, on nicotine-induced alterations in monoamine levels in rat brain

NT69L, is a novel neurotensin (8–13) analog that participates in the modulation of the dopaminergic pathways implicated in addiction to psychostimulants. NT69L blocks nicotine-induced hyperactivity as well as the initiation and expression of sensitization in rats. Recent evidence suggests that stimulation of mesocorticolimbic dopamine system, with influences from the other monoamine systems, e.g. norepinephrine and serotonin, is involved in nicotine's reinforcing properties. The aim of the present study was to investigate the effect of pretreatment with NT69L on nicotine-induced changes in monoamine levels in the rat brain using in vivo microdialysis. Acute or chronic (0.4 mg/kg, sc, once daily for 2 weeks) administration of nicotine elicited increases in extracellular levels of dopamine, dopamine metabolites, norepinephrine, or serotonin in medial prefrontal cortex, nucleus accumbens shell, and core of rats. Pretreatment with NT69L (1 mg/kg, intraperitoneally, ip) administered 40 min before nicotine injection significantly attenuated the acute nicotine-evoked increases in norepinephrine levels in medial prefrontal cortex, dopamine and serotonin in nucleus accumbens shell. After chronic nicotine administration, pretreatment of NT69L markedly reversed the increase in dopamine levels in the nucleus accumbens core. NT69L's attenuation of some of the biochemical effects of acute and chronic nicotine is consistent with this peptide's attenuation of nicotine-induced behavioral effects. These data further support a role for NT69L or other neurotensin receptor agonists to treat nicotine addiction.

Serotonin immunoreactivity in auditory brainstem neurons of the postnatal monoamine oxidase-A knockout mouse

Altered levels of extracellular serotonin (5-HT) during development cause structural abnormalities in the neural projections of sensory systems. To better understand the potential role of 5-HT in the development of auditory system projections, we examined 5-HT immunoreactivity (IR) in auditory brainstem nuclei of postnatal mice. We previously observed 5-HT-IR in the lateral superior olive (LSO) of wild type mice. In the current study, we used a genetic model (monoamine oxidase-A knockout mouse) in which brain 5-HT levels are abnormally high to improve detection of 5-HT. In the cochlear nucleus of this knockout, 5-HT-IR cell bodies were observed in the dorsal cochlear nucleus (DCN), a primary relay to the inferior colliculus (IC). In the superior olivary complex, 5-HT-IR somata were observed in the LSO, another relay to the IC. Labeled somata were also observed within the IC itself. The 5-HT immunostaining in all 3 regions was transient and was not observed beyond postnatal day 8. These results suggest that 5-HT may play a role in the branching and refinement of DCN and LSO axon collaterals within the IC, as well as IC axon collaterals within the medial geniculate body. The pattern of expression indicates that 5-HT has a developmental role in select populations of neurons of the ascending auditory pathway prior to any influences of sound-evoked activity.

Loudness Dependence of Auditory Evoked Potentials as Indicator of Central Serotonergic Neurotransmission: Simultaneous Electrophysiological Recordings and In Vivo Microdialysis in the Rat Primary Auditory Cortex

Serotonin released in synapsis is one of the key neurotransmitters in psychiatry and psychopharmacology. The loudness dependence of auditory evoked potentials (LDAEP) has been proposed as a marker for central serotonergic neurotransmission. Several findings in animals and humans support this hypothesis. However, the in vivo measurement of cortical extracellular serotonin levels has never been performed simultaneously with the recording of auditory evoked potentials. The interrelationship between low cortical serotonergic activity and strong LDAEP is yet to be proven. The auditory evoked potentials were recorded in the epidura above the primary auditory cortex of male Wistar rats whereas extracellular serotonin levels in the primary auditory cortex were measured by in vivo microdialysis before and after i.p. application of the selective serotonin reuptake inhibitor citalopram. At baseline, the correlation of coefficients between the LDAEP, especially of the N1 component, and extracellular serotonin levels in the primary auditory cortex was negative. The increase of serotonin levels after citalopram application was significantly related to a decrease of LDAEP of the N1 component (r=-0.86, p=0.003). These data support the view that the LDAEP is closely modulated by cortical serotonergic activity. Thus, the LDAEP might serve as an inversely related marker of synaptically released serotonin in the CNS.

In-vitro and in-vivo characterization of JNJ-7925476, a novel triple monoamine uptake inhibitor

Triple reuptake inhibitors, which block the serotonin transporter (SERT), norepinephrine transporter (NET) and dopamine transporter (DAT) in the central nervous system have been described as therapeutic alternatives for classical selective serotonin reuptake inhibitors, with advantages due to their multiple mechanisms of action. JNJ-7925476 ( trans-6-(4-ethynylphenyl)-1,2,3,5,6,10b-hexahydropyrrolo[2,1-a]isoquinoline) is a selective and potent inhibitor of the SERT, NET, and DAT ( K i = 0.9, 17 and 5.2 nM, respectively). Following subcutaneous dosing in rat, JNJ-7925476 was rapidly absorbed into the plasma, and drug concentrations in the brain tracked with those in the plasma but were 7-fold higher. The ED 50 values for JNJ-7925476 occupancy of the SERT, NET, and DAT in rat brain were 0.18, 0.09 and 2.4 mg/kg, respectively. JNJ-7925476 (0.1–10 mg/kg, s.c.) rapidly induced a robust, dose-dependent increase in extracellular serotonin, dopamine, and norepinephrine levels in rat cerebral cortex. The compound also showed potent antidepressant-like activity in the mouse tail suspension test (ED 50 = 0.3 mg/kg, i.p.). These results demonstrate that JNJ-7925476 is a triple reuptake inhibitor with in-vivo efficacy in biochemical and behavioral models of depression.

Neurochemical responses to antidepressants in the prefrontal cortex of mice and their efficacy in preclinical models of anxiety-like and depression-like behavior: a comparative and correlational study

Marble burying and forced swimming behavior are widely used and sensitive tests for identifying clinically effective antidepressant drugs, although the underlying neurobiology of these behaviors is not fully elucidated. The objective of this study was to determine the relationship between the behavioral effects of antidepressant drugs and their ability to modulate extracellular neurotransmitter levels in the prefrontal cortex. The effects of fluoxetine, fluvoxamine, citalopram, imipramine, and desipramine (0 to 60 mg/kg by oral gavage, except fluoxetine at 0 to 40 mg/kg) were studied independently in CD-1 mice in the marble-burying task, forced swim task and on extracellular concentrations of serotonin, norepinephrine, and dopamine in the prefrontal cortex by freely moving microdialysis. Fluvoxamine, fluoxetine, and citalopram all suppressed marble-burying behavior, but produced no change in immobility time in the forced swim test. In contrast, imipramine and desipramine suppressed both marble-burying behavior and increased swimming time in the forced swim test, although desipramine mildly suppressed locomotor activity at the maximal dose. Fluvoxamine, fluoxetine, and citalopram all increased extracellular levels of cortical serotonin. Desipramine and imipramine increased extracellular dopamine levels. Fluoxetine, desipramine, and imipramine increased extracellular norepinephrine levels. Correlational analysis revealed a positive correlation between efficacy of drugs in the forced swim test and cortical extracellular dopamine levels, whereas a positive correlation was found between efficacy in the marble-burying test and extracellular serotonin levels. Although marble burying and forced swimming behavior have strong predictive validity in tests of antidepressant action, each assay appears to be underpinned by entirely different neurochemical systems.

Effects of Ion Channel Blockers on Basal Hippocampal Monoamine Levels in Freely Moving Diabetic and Non-Diabetic Rats

This study characterized the ion channel activities in the hippocampus of diabetic rats by monitoring the levels of monoamines. Extracellular levels of serotonin and dopamine were measured in the hippocampus of awake, freely moving streptozotocin-induced diabetic rats, spontaneously diabetic rats, and non-diabetic rats, using in vivo microdialysis. Sodium, calcium, and potassium ion channel blockers were used to assess the ion channel activities. The results suggest that there are no abnormalities in the ion channels of diabetic brain, but the reduced levels of monoamines could be due to any problems of reuptake, release, and rate of breakdown of these molecules.

Influence of brain catecholamines on the development of fatigue in exercising rats in the heat.

The purpose of the present study was to identify the effects of an acute injection of a dual dopamine (DA)/noradrenaline (NA) reuptake inhibitor (bupropion) on exercise performance, thermoregulation and neurotransmitters in the preoptic area and anterior hypothalamus (PO/AH) of the rat during exercise in the heat. Body core temperature (T(core)), brain temperature (T(brain)) and tail skin temperature (T(tail)) were measured. A microdialysis probe was inserted in the PO/AH, and samples for measurement of extracellular DA, NA and serotonin (5-HT) levels were collected. Rats received either bupropion (17 mg kg(-1); hot-BUP) or saline (1 ml kg(-1); hot) 20 min before the start of exercise and ran at a speed of 26 m min(-1) until exhaustion in a warm environment (30 degrees C). Rats also ran until exhaustion in a cool environment (18 degrees C; cool). Running time to exhaustion was significantly influenced by the ambient temperature, and it was increased by bupropion in the heat (cool, 143.6 +/- 21 min; hot, 65.8 +/- 13 min; hot-BUP, 86.3 +/- 7.2 min). T(core) and T(brain) at exhaustion were significantly higher in the bupropion group compared to the cool and hot groups, respectively. T(tail) measured at exhaustion was not significantly different between the two hot conditions. Extracellular concentrations of DA and NA in the PO/AH increased during exercise, and was significantly higher in the bupropion than in cool and hot groups (P < 0.05). No differences were observed between groups for 5-HT levels. These results suggest that DA and NA in the PO/AH might be responsible for the increase in exercise performance and T(core) and T(brain) in the bupropion group in hyperthermia. Moreover, these results support previous findings in humans that acute bupropion ingestion increases T(core) during exercise in the heat, indicating the possibility of an important role for DA and NA in thermoregulation.

Regulation of extracellular serotonin levels and brain-derived neurotrophic factor in rats with high and low exploratory activity

Serotonin (5-HT) system has a significant role in anxiety- and depression-related states and may be influenced by brain-derived neurotrophic factor (BDNF). This study examined extracellular 5-HT levels and expression of BDNF in rats with persistently low or high levels of exploratory activity (LE and HE, respectively). Baseline extracellular levels of 5-HT as assessed by in vivo microdialysis in conscious animals were similar in both groups in medial prefrontal cortex (PFC) and dentate gyrus (DG). No differences were found in parachloroamphetamine-induced 5-HT release in either region. However, LE animals had significantly higher levels of 5-HT transporter (5-HTT) binding in PFC and a larger increase in extracellular 5-HT levels after administration of citalopram (1 μM) into this area by retrograde dialysis. No difference in 5-HTT levels was found in hippocampus, while perfusion with citalopram was accompanied by a greater increase in extracellular 5-HT in the HE group in this brain region. LE-rats had higher levels of BDNF mRNA in the PFC but not hippocampus. In contrast, levels of nerve growth factor mRNA were similar in these brain regions of LE- and HE-rats. The differential regulation of 5-HT-ergic system in LE- and HE-rats in PFC and hippocampus may form the basis for their distinct anxiety-related behaviours.

Reciprocal effects of combined administration of serotonin, noradrenaline and dopamine reuptake inhibitors on serotonin and dopamine levels in the rat prefrontal cortex: the role of 5-HT1A receptors

The purpose of the present study was to examine, by in vivo microdialysis technique, the effects of triple acting monoamine reuptake inhibitors, constructed by combinations of a selective serotonin reuptake inhibitor citalopram with a noradrenaline/dopamine reuptake inhibitor methylphenidate and a serotonin/noradrenaline reuptake inhibitor venlafaxine with a dopamine reuptake inhibitor GBR12909, on extracellular levels of serotonin (5-HT), noradrenaline (NA) and dopamine (DA) in the prefrontal cortex (PFC) of anaesthetized rats. At the highest dose tested, adjunctive methylphenidate (10 mg/kg s.c.) to citalopram markedly attenuated by 63% the extracellular levels of 5-HT as compared to the levels induced by citalopram (5 mg/kg i.p.) alone, whereas the overall DA concentrations significantly increased to about 149% of those induced by methylphenidate alone. Similarly, the combination of venlafaxine with GBR12909 (10 mg/kg s.c.) caused a reduction of 5-HT levels to 66% of the levels induced by venlafaxine (10 mg/kg i.p.) alone, whereas the overall DA levels increased to 151% of the venlafaxine-treated group. The extracellular levels of NA were only marginally affected by the treatments with combined reuptake inhibitors compared to the effects induced by methylphenidate or venlafaxine alone. The modulatory effects of combined administration of the DA/NA reuptake inhibitors with the 5-HT reuptake inhibitors (citalopram and venlafaxine) on potentiation of DA and attenuation of 5-HT efflux were completely reversed by a pre-treatment with the 5-HT(1A) receptor antagonist WAY-100635. These findings suggest a crucial role played by the 5-HT(1A) receptors in balancing the reuptake inhibitory efficacy for the enhancement of 5-HT and DA transmission in the PFC by the drugs combining the reuptake inhibition of all three monoamines.

Increased extracellular 5‐HT but no change in sleep after perfusion of a 5‐HT1A antagonist into the dorsal raphe nucleus of rats

The 5-HT(1A) receptor antagonist 4-Iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide hydrochloride (p-MPPI) (10 microM) was perfused into the dorsal raphe nucleus (DRN) to study simultaneously the effects of the drug on the DRN and frontal cortex extracellular serotonin (5-hydroxytryptamine, 5-HT) levels and concurring behavioural states. Waking, slow wave sleep and rapid eye movement sleep were determined by polygraphic recordings during microdialysis perfusion and extracellular sample collection. The samples were analysed by microbore high-performance liquid chromatography coupled with electrochemical detection for analysis of 5-HT. p-MPPI perfusion into the DRN (n = 6) produced a sixfold 5-HT increase in the DRN during all behavioural states. The increased 5-HT level was most likely related to the blockage of 5-HT(1A) receptors in the DRN by p-MPPI. No significant effect was seen on sleep. Despite the dramatic increase in DRN extracellular 5-HT produced by p-MPPI, only a transient and nonsignificant effect on sleep was recorded. It is suggested that the usual coupling between 5-HT level and behavioural state may be lost when an excessive serotonergic output is pharmacologically achieved.

P.2.b.014 Extracellular serotonin levels and expression of neurotrophic factors in rats with high or low novelty-related activity

Despite the standardization of the phlebotomy procedure, blood analysis is occasionally requested after recommended hours with the excuse that the patient is still fasting. We aimed to examine the influence of prolonged fasting and mild physical activity on routine laboratory tests.The study was conducted on 30 volunteers (27 female) median age 40 y (20–59). Blood samples were taken in the morning (7:00–8:00 a.m.) and early afternoon (1:00–2:00 p.m.) after prolonged fasting and usual daily activities. Serum glucose (GLU), urea, creatinine, triglyceride, uric acid (UA), iron and electrolytes were analyzed on Roche cobas 6000 c501 and complete blood count on Siemens ADVIA 2120i. Statistical significance between the two measurements was tested using paired t-test or Wilcoxon test according to data distribution. Clinical significance was judged against calculated reference change values (RCV).A statistically significant decrease was found for red blood cell count, hemoglobin, hematocrit, mean corpuscular volume (MCV), GLU, urea, creatinine, triglycerides and electrolytes, whereas white blood cell count and iron were significantly increased. Judging against desirable bias derived from biological variation, a significant change was found for all the analytes except MCV, platelet count, UA and triglycerides. A clinically significant change was not found for any of the tested analytes when compared to RCV.Prolonged fasting and mild activity will not influence the medical decision for healthy subjects with normal results. Despite the present statistically significant change, the clinically significant change was not shown. However, the study did not include pathological results which have to be interpreted more carefully.

Pharmacological characterization of JNJ-28583867, a histamine H 3 receptor antagonist and serotonin reuptake inhibitor

Wake-promoting agents such as modafinil are used in the clinic as adjuncts to antidepressant therapy in order to alleviate lethargy. The wake-promoting action of histamine H 3 receptor antagonists has been evidenced in numerous animal studies. They may therefore be a viable strategy for use as an antidepressant therapy in conjunction with selective serotonin reuptake inhibitors. JNJ-28583867 (2-Methyl-4-(4-methylsulfanyl-phenyl)-7-(3-morpholin-4-yl-propoxy)-1,2,3,4-tetrahydro-isoquinoline) is a selective and potent histamine H 3 receptor antagonist ( K i = 10.6 nM) and inhibitor of the serotonin transporter (SERT) ( K i = 3.7 nM), with 30-fold selectivity for SERT over the dopamine and norepinephrine transporters. After subcutaneous administration, JNJ-28583867 occupied both the histamine H 3 receptor and the SERT in rat brain at low doses (< 1 mg/kg). JNJ-28583867 blocked imetit-induced drinking (3–10 mg/kg i.p.), confirming in vivo functional activity at the histamine H 3 receptor and also significantly increased cortical extracellular levels of serotonin at doses of 0.3 mg/kg (s.c.) and higher. Smaller increases in cortical extracellular levels of norepinephrine and dopamine were also observed. JNJ-28583867 (3–30 mg/kg p.o.) showed antidepressant-like activity in the mouse tail suspension test. JNJ-28583867 (1–3 mg/kg s.c.) caused a dose-dependent increase in the time spent awake mirrored by a decrease in NREM. Concomitantly, JNJ-28583867 produced a potent suppression of REM sleep from the dose of 1 mg/kg onwards. JNJ-28583867 has good oral bioavailability in the rat (32%), a half-life of 6.9 h and a C max of 260 ng/ml after 10 mg/kg p.o. In summary, JNJ-28583867 is a combined histamine H 3 receptor antagonist-SERT inhibitor with in vivo efficacy in biochemical and behavioral models of depression and wakefulness.