Analysis of serum and endometrial progesterone in determining endometrial receptivity.

STUDY QUESTION: Is there a relationship between serum and endometrial progesterone (P4) levels, including P4 and metabolites (oestrone, oestradiol and 17α-hydroxyprogesterone), and endometrial receptivity? SUMMARY ANSWER: Serum P4 levels were not correlated with endometrial P4, nor associated with endometrial receptivity as determined by the ERA® test; however, endometrial P4 and 17α-hydroxyprogesterone levels were positively correlated and related to endometrial receptivity by ERA. WHAT IS KNOWN ALREADY: Acquisition of endometrial receptivity is governed by P4, which induces secretory transformation. A close relationship between serum P4 and pregnancy outcome is reported for hormone replacement therapy (HRT) cycles. However, the relationship between serum and uterine P4 levels has not been described, and it is unknown whether uterine receptivity depends more on serum or uterine P4 levels. STUDY DESIGN, SIZE, DURATION: A prospective cohort study was performed during March 2018-2019 in 85 IVF patients undergoing an evaluation-only HRT cycle with oestradiol valerate (6 mg/day) and micronised vaginal progesterone (400 mg/12 h). PARTICIPANTS/MATERIALS, SETTING, METHODS: Patients were under 50 years of age, had undergone at least one failed IVF cycle, had no uterine pathology, and had adequate endometrial thickness (> 6.5 mm). The study was conducted at IVI Valencia and IVI Foundation. An endometrial biopsy and a blood sample were collected after 5 days of P4 vaginal treatment. Measures included serum P4 levels, ERA®-based evaluation of endometrial receptivity, and endometrial P4 levels along with metabolites (oestrone, oestradiol and 17α-hydroxyprogesterone) measured by ultra-performance liquid chromatography-tandem mass spectrometry. MAIN RESULTS AND THE ROLE OF CHANCE: Seventy-nine women were included (mean age: 39.9 ± 4.6, BMI: 24.2 ± 3.9 kg/m2, endometrial thickness: 8.2 ± 1.4 mm). The percentage of endometria indicated as receptive by ERA® was 40.5%. When comparing receptive versus non-receptive groups, no differences were observed in baseline characteristics nor in steroid hormones levels in serum or endometrium. No association between serum P4 and endometrial steroid levels or ERA result was found (P < 0.05). When the population was stratified according to metabolite concentration levels, endometrial P4 and 17α-hydroxyprogesterone were significantly associated with endometrial receptivity (P < 0.05). A higher proportion of receptive endometria by ERA was observed when endometrial P4 levels were higher than 40.07 µg/ml (relative maximum) and a lower proportion of receptive endometria was associated with endometrial 17α-hydroxyprogesterone lower than 0.35 ng/ml (first quartile). A positive correlation R2 = 0.67, P < 0.001 was observed between endometrial P4 and 17α-hydroxyprogesterone levels. LIMITATIONS, REASONS FOR CAUTION: This study did not analyse pregnancy outcomes. Further, the findings can only be extrapolated to HRT cycles with micronised vaginal progesterone for luteal phase support. WIDER IMPLICATIONS OF THE FINDINGS: Our findings suggest that the combined benefits of different routes of progesterone administration for luteal phase support could be leveraged to ensure an adequate concentration of progesterone both in the uterus and in the bloodstream. Further studies will confirm whether this method can optimise both endometrial receptivity and live birth rate. Additionally, targeted treatment to increase P4 endometrial levels may normalise the timing of the window of implantation without needing to modify the progesterone administration day. STUDY FUNDING/COMPETING INTEREST(S): This research was supported by the IVI-RMA Valencia (1706-VLC-051-EL) and Consellería d'Educació, Investigació, Cultura, i esport Generalitat Valenciana (Valencian Government, Spain, GV/2018//151). Almudena Devesa-Peiro (FPU/15/01398) and Cristina Rodriguez-Varela (FPU18/01657) were supported by the FPU program fellowship from the Ministry of Science, Innovation and Universities (Spanish Government). P.D.-G. is co-inventor on the ERA patent, with non-economic benefits. The other authors have no competing interests. TRIAL REGISTRATION NUMBER: NCT03456375.

Can we increase the speed and efficacy of antidepressant treatments? Part II. Glutamatergic and RNA interference strategies.

In the second part we focus on two treatment strategies that may overcome the main limitations of current antidepressant drugs. First, we review the experimental and clinical evidence supporting the use of glutamatergic drugs as fast-acting antidepressants. Secondly, we review the involvement of microRNAs (miRNAs) in the pathophysiology of major depressive disorder (MDD) and the use of small RNAs (e.g.., small interfering RNAs or siRNAs) to knockdown genes in monoaminergic and non-monoaminergic neurons and induce antidepressant-like responses in experimental animals. The development of glutamatergic agents is a promising venue for antidepressant drug development, given the antidepressant properties of the non-competitive NMDA receptor antagonist ketamine. Its unique properties appear to result from the activation of AMPA receptors by a metabolite [(2S,6S;2R,6R)-hydroxynorketamine (HNK)] and mTOR signaling. These effects increase synaptogenesis in prefrontal cortical pyramidal neurons and enhance serotonergic neurotransmission via descending inputs to the raphe nuclei. This view is supported by the cancellation of ketamine's antidepressant-like effects by inhibition of serotonin synthesis. We also review existing evidence supporting the involvement of miRNAs in MDD and the preclinical use of RNA interference (RNAi) strategies to target genes involved in antidepressant response. Many miRNAs have been associated to MDD, some of which e.g., miR-135 targets genes involved in antidepressant actions. Likewise, SSRI-conjugated siRNA evokes faster and/or more effective antidepressant-like responses. Intranasal application of sertraline-conjugated siRNAs directed to 5-HT1A receptors and SERT evoked much faster changes of pre- and postsynaptic antidepressant markers than those produced by fluoxetine.

Effects of Hallucinogens on Neuronal Activity.

Hallucinogens evoke sensory, perceptual, affective, and cognitive effects that may be useful to understand the neurobiological basis of mood and psychotic disorders. The present chapter reviews preclinical research carried out in recent years in order to better understand the action of psychotomimetic agents such as the noncompetitive NMDA receptor (NMDA-R) antagonists and serotonergic hallucinogens. Our studies have focused on the mechanisms through which these agents alter cortical activity. Noncompetitive NMDA-R antagonists, such as phencyclidine (PCP) and MK-801 (dizocilpine), as well as the serotonergic hallucinogens DOI and 5-MeO-DMT, produce similar effects on cellular and population activity in prefrontal cortex (PFC); these effects include alterations of pyramidal neuron discharge (with an overall increase in firing), as well as a marked attenuation of the low frequency oscillations (0.2-4 Hz) to which neuronal discharge is coupled in anesthetized rodents. PCP increases c-fos expression in excitatory neurons from various cortical and subcortical areas, particularly the thalamus. This effect of PCP involves the preferential blockade of NMDA-R on GABAergic neurons of the reticular nucleus of the thalamus, which provides feedforward inhibition to the rest of thalamic nuclei. It is still unknown whether serotonergic hallucinogens also affect thalamocortical networks. However, when examined, similar alterations in other cortical areas, such as the primary visual cortex (V1), have been observed, suggesting that these agents affect cortical activity in sensory and associative areas. Interestingly, the disruption of PFC activity induced by PCP, DOI and 5-MeO-DMT is reversed by classical and atypical antipsychotic drugs. This effect suggests a possible link between the mechanisms underlying the disruption of perception by multiple classes of hallucinogenic agents and the therapeutic efficacy of antipsychotic agents.

Low serum progesterone on the day of embryo transfer is associated with a diminished ongoing pregnancy rate in oocyte donation cycles after artificial endometrial preparation: a prospective study.

STUDY QUESTION: Is there a relationship between serum progesterone (P) and endometrial volume on the day of embryo transfer (ET) with ongoing pregnancy rate (OPR) in artificial endometrium preparation cycles? SUMMARY ANSWER: Patients with serum P < 9.2 ng/ml on the day of ET had a significantly lower OPR but endometrial volume was not related with OPR. WHAT IS KNOWN ALREADY: A window of optimal serum P levels during the embryo implantation period has been described in artificial endometrium preparation cycles. A very low endometrial volume is related to poor reproductive outcome. STUDY DESIGN, SIZE, DURATION: Prospective cohort study with 244 patients who underwent ET in an oocyte donation cycle after an artificial endometrial preparation cycle with estradiol valerate and vaginal micronized progesterone (400 mg/12 h). The study period went from 22 February 2016 to 25 October 2016 (8 months). Sample size was calculated to detect a 20% difference in OPR (35-55%) between two groups according to serum P levels in a two-sided test (80% statistical power, 95% confidence interval (CI)). PARTICIPANTS/MATERIALS, SETTING, METHODS: Patients undergoing their first/second oocyte donation cycle, aged <50, BMI < 30 kg/m2, triple layer endometrium >6.5 mm and 1-2 good quality transferred blastocysts. A private infertility centre. Serum P determination and 3D ultrasound of uterine cavity were performed on the day of ET. Endometrial volume measurements were taken using a virtual organ computer-aided analysis (VOCAL™) system. The primary endpoint was OPR beyond pregnancy week 12. MAIN RESULTS AND ROLE OF CHANCE: About 211 of the 244 recruited patients fulfilled all the inclusion/exclusion criteria. Mean serum P on the day of embryo transfer was 12.7 ± 5.4 ng/ml (Centiles 25, 9.2; 50, 11.8; 75,15.8). OPRs according to serum P quartiles were: Q1: 32.7%; Q2: 49.1%; Q3: 58.5%; Q4: 50.9%. The OPR of Q1 was significantly lower than Q2-Q4: 32.7% versus 52.8%; P = 0.016; RR (95% CI): 0.62 (0.41-0.94). The mean endometrial volume was 3.4 ± 1.9 ml. Serum P on the day of ET did not correlate with endometrial volume. A logistic regression analysis, adjusted for all the potential confounders, showed that OPR significantly lowered between women with serum P < 9.2 ng/ml versus ≥9.2 ng/ml (OR: 0.297; 95%CI: 0.113-0.779); P = 0.013. The ROC curve showed a significant predictive value of serum P levels on the day of ET for OPR, with an AUC (95%CI) = 0.59 (0.51-0.67). LIMITATIONS, REASONS FOR CAUTION: Only the women with normal uterine cavity, appropriate endometrial thickness and good quality blastocysts transfer were included. Extrapolation to an unselected population or to other routes and/or doses of administering P needs to be validated. The role of endometrial volume could not be fully defined as very few patients presented a very low volume. WIDER IMPLICATIONS OF THE FINDINGS: The present study suggests a minimum threshold of serum P values on the day of ET that needs to be reached in artificial endometrial preparation cycles to optimize outcome. No upper threshold could be defined. STUDY FUNDING/COMPETING INTEREST(S): None. TRIAL REGISTRATION NUMBER: NCT02696694.

Phencyclidine-induced disruption of oscillatory activity in prefrontal cortex: Effects of antipsychotic drugs and receptor ligands.

The non-competitive NMDA receptor (NMDA-R) antagonist phencyclidine (PCP) markedly disrupts thalamocortical activity, increasing excitatory neuron discharge and reducing low frequency oscillations (LFO, <4Hz) that temporarily group neuronal discharge. These actions are mainly driven by PCP interaction with NMDA-R in GABAergic neurons of the thalamic reticular nucleus and likely underlie PCP psychotomimetic activity. Here we report that classical (haloperidol, chlorpromazine, perphenazine) and atypical (clozapine, olanzapine, quetiapine, risperidone, ziprasidone, aripripazole) antipsychotic drugs--but not the antidepressant citalopram--countered PCP-evoked fall of LFO in the medial prefrontal cortex (mPFC) of anesthetized rats. PCP reduces LFO by breaking the physiological balance between excitatory and inhibitory transmission. Next, we examined the role of different neurotransmitter receptors to reverse PCP actions. D2-R and D1-R blockade may account for classical antipsychotic action since raclopride and SCH-23390 partially reversed PCP effects. Atypical antipsychotic reversal may additionally involve 5-HT1A-R activation (but not 5-HT2A-R blockade) since 8-OH-DPAT and BAYx3702 (but not M100907) fully countered PCP effects. Blockade of histamine H1-R (pyrilamine) and α1-adrenoceptors (prazosin) was without effect. However, the enhancement of GABAA-R-mediated neurotransmission (using muscimol, diazepam or valproate) and the reduction of excitatory neurotransmission (using the mGluR2/3 agonist LY379268 and the preferential kainite/AMPA antagonist CNQX--but not the preferential AMPA/kainate antagonist NBQX) partially or totally countered PCP effects. Overall, these results shed new light on the neurobiological mechanisms used by antipsychotic drugs to reverse NMDA-R antagonist actions and suggest that agents restoring the physiological excitatory/inhibitory balance altered by PCP may be new targets in antipsychotic drug development.

Preclinical and clinical characterization of the selective 5-HT(1A) receptor antagonist DU-125530 for antidepressant treatment.

BACKGROUND AND PURPOSE: The antidepressant efficacy of selective 5-HT reuptake inhibitors (SSRI) and other 5-HT-enhancing drugs is compromised by a negative feedback mechanism involving 5-HT(1A) autoreceptor activation by the excess 5-HT produced by these drugs in the somatodendritic region of 5-HT neurones. 5-HT(1A) receptor antagonists augment antidepressant-like effects in rodents by preventing this negative feedback, and the mixed ß-adrenoceptor/5-HT(1A) receptor antagonist pindolol improves clinical antidepressant effects by preferentially interacting with 5-HT(1A) autoreceptors. However, it is unclear whether 5-HT(1A) receptor antagonists not discriminating between pre- and post-synaptic 5-HT(1A) receptors would be clinically effective. EXPERIMENTAL APPROACH: We characterized the pharmacological properties of the 5-HT(1A) receptor antagonist DU-125530 using receptor autoradiography, intracerebral microdialysis and electrophysiological recordings. Its capacity to accelerate/enhance the clinical effects of fluoxetine was assessed in a double-blind, randomized, 6 week placebo-controlled trial in 50 patients with major depression (clinicaltrials.gov identifier NCT01119430). KEY RESULTS: DU-125530 showed equal (low nM) potency to displace agonist and antagonist binding to pre- and post-synaptic 5-HT(1A) receptors in rat and human brain. It antagonized suppression of 5-hydroxytryptaminergic activity evoked by 8-OH-DPAT and SSRIs in vivo. DU-125530 augmented SSRI-induced increases in extracellular 5-HT as effectively as in mice lacking 5-HT(1A) receptors, indicating a silent, maximal occupancy of pre-synaptic 5-HT(1A) receptors at the dose used. However, DU-125530 addition to fluoxetine did not accelerate nor augment its antidepressant effects. CONCLUSIONS AND IMPLICATIONS: DU-125530 is an excellent pre- and post-synaptic 5-HT(1A) receptor antagonist. However, blockade of post-synaptic 5- HT(1A) receptors by DU-125530 cancels benefits obtained by enhancing pre-synaptic 5-hydroxytryptaminergic function.

Preferential in vivo action of F15599, a novel 5-HT(1A) receptor agonist, at postsynaptic 5-HT(1A) receptors.

BACKGROUND AND PURPOSE: F15599, a novel 5-hydroxytryptamine (5-HT)(1A) receptor agonist with 1000-fold selectivity for 5-HT compared with other monoamine receptors, shows antidepressant and procognitive activity at very low doses in animal models. We examined the in vivo activity of F15599 at somatodendritic autoreceptors and postsynaptic 5-HT(1A) heteroreceptors. EXPERIMENTAL APPROACH: In vivo single unit and local field potential recordings and microdialysis in the rat. KEY RESULTS: F15599 increased the discharge rate of pyramidal neurones in medial prefrontal cortex (mPFC) from 0.2 microg x kg(-1) i.v and reduced that of dorsal raphe 5-hydroxytryptaminergic neurones at doses >10-fold higher (minimal effective dose 8.2 microg x kg(-1) i.v.). Both effects were reversed by the 5-HT(1A) antagonist (+/-)WAY100635. F15599 did not alter low frequency oscillations (approximately 1 Hz) in mPFC. In microdialysis studies, F15599 increased dopamine output in mPFC (an effect dependent on the activation of postsynaptic 5-HT(1A) receptors) with an ED(50) of 30 microg x kg(-1) i.p., whereas it reduced hippocampal 5-HT release (an effect dependent exclusively on 5-HT(1A) autoreceptor activation) with an ED(50) of 240 microg x kg(-1) i.p. Likewise, application of F15599 by reverse dialysis in mPFC increased dopamine output in a concentration-dependent manner. All neurochemical responses to F15599 were prevented by administration of (+/-)WAY100635. CONCLUSIONS AND IMPLICATIONS: These results indicate that systemic administration of F15599 preferentially activates postsynaptic 5-HT(1A) receptors in PFC rather than somatodendritic 5-HT(1A) autoreceptors. This regional selectivity distinguishes F15599 from previously developed 5-HT(1A) receptor agonists, which preferentially activate somatodendritic 5-HT(1A) autoreceptors, suggesting that F15599 may be particularly useful in the treatment of depression and of cognitive deficits in schizophrenia.

A mechanical comparison of high-flexion and conventional total knee arthroplasty.

The question addressed in this study was whether high-flexion total knee arthroplasty (TKA) designs improve the mechanical behaviour of TKAs in high flexion and whether they maintain the mechanical performance of conventional TKAs at normal flexion angles. A finite element study was performed in which the mechanical behaviour of the conventional Sigma RP and the new high-flexion Sigma RP-F were compared, during a dynamic simulation of a high-flexion squatting activity. Forces, stresses, and contact positions were calculated during different stages of the simulations. In general, higher stresses were found with larger flexion angles for both designs. Mechanical parameters were similar in normal flexion. In high flexion, lower stress and deformation values were found for the high-flexion Sigma RP-F, except for the contact stress at the post of the insert. This study confirms that a high-flexion design can improve mechanical behaviour at high-flexion without changing the performance in normal flexion. Hence, although a high-flexion TKA may show a similar or better performance in comparison with a conventional TKA, high-flexion activities still cause an increase in the implant stress levels. Therefore, the patient's demand for large flexion angles may reduce the longevity of TKA implants.

In vivo actions of aripiprazole on serotonergic and dopaminergic systems in rodent brain.

RATIONALE: Aripiprazole is an atypical antipsychotic drug with high in vitro affinity for 5-HT(1A), 5-HT(2A) and dopamine (DA) D2 receptors. However, its in vivo actions in the brain are still poorly characterized. OBJECTIVE: The aim was to study the in vivo actions of aripiprazole in the rat and mouse brain. METHODS: Brain microdialysis and single-unit extracellular recordings were performed. RESULTS: The systemic administration of aripiprazole reduced 5-HT output in the medial prefrontal cortex (mPFC) and dorsal raphe nucleus of the rat. Aripiprazole also reduced extracellular 5-HT in the mPFC of wild-type (WT) but not of 5-HT(1A) (-/-) knockout (KO) mice. Aripiprazole reversed the elevation in extracellular 5-HT output produced by the local application of the 5-HT(2A/2C) receptor agonist DOI in mPFC. Aripiprazole also increased the DA output in mPFC of WT but not of 5-HT(1A) KO mice, as observed for atypical antipsychotic drugs, in contrast to haloperidol. Contrary to haloperidol, which increases the firing rate of DA neurons in the ventral tegmental area (VTA), aripiprazole induced a very moderate reduction in dopaminergic activity. Haloperidol fully reversed the inhibition in dopaminergic firing rate induced by apomorphine, whereas aripiprazole evoked a partial reversal that was significantly different from that evoked by haloperidol and from the spontaneous reversal of dopaminergic activity in rats treated with apomorphine. CONCLUSIONS: These results indicate that aripiprazole modulates the in vivo 5-HT and DA release in mPFC through the activation of 5-HT(1A) receptors. Moreover, aripiprazole behaves as a partial agonist at DA D2 autoreceptors in vivo, an action which clearly distinguishes it from haloperidol.

[Serotonergic control of prefrontal cortex]. / Control serotoninérgico de la corteza prefrontal.

INTRODUCTION AND DEVELOPMENT: The prefrontal cortex (PFC) plays a crucial role in higher brain functions such as working memory or cognition and controls, via the excitatory axons of pyramidal neurons, the activity of many subcortical motor and limbic areas. It receives a dense innervation from the brainstem aminergic nuclei, including the serotonergic raphe nuclei. Prefrontal function and metabolism is altered in patients with severe psychiatric disorders, like major depression or schizophrenia. Although the exact role of serotonergic neurotransmission in PFC remains largely unknown, the PFC contains a very large density or serotonin 5-HT1A (inhibitory) and 5-HT2A (excitatory) receptors. In addition, hallucinogens like LSD or DOI are agonists and atypical antipsychotics are antagonists at 5-HT2A receptors. In this review we focus on the main excitatory and inhibitory mechanisms through which serotonin modulates pyramidal and GABAergic neuron activity in the PFC. CONCLUSIONS: We report on the presence of 5-HT1A and 5-HT2A receptor-mediated responses in pyramidal neurons of the PFC that exert opposite effects on their activity when recorded in vivo in the anesthetized rat. Despite the large co-expression of both receptors in pyramidal neurons of the PFC, physiological amounts of 5-HT mainly inhibit pyramidal neurons. This is probably due to the distinct location of 5-HT1A and 5-HT2A in pyramidal neurons. Thus, 5-HT1A receptors are mainly localized in the axon hillock, where they may have a prominent inhibitory role in the control of pyramidal activity given their coupling to GIRK channels. Moreover, 5-HT can inhibit pyramidal neurons indirectly through the activation of 5-HT2A and 5-HT3 receptors localized in GABAergic interneurons and a subsequent increase in synaptic GABA inputs.

Control of serotonergic function in medial prefrontal cortex by serotonin-2A receptors through a glutamate-dependent mechanism.

We examined the in vivo effects of the hallucinogen 4-iodo-2,5-dimethoxyamphetamine (DOI). DOI suppressed the firing rate of 7 of 12 dorsal raphe (DR) serotonergic (5-HT) neurons and partially inhibited the rest (ED(50) = 20 microg/kg, i.v.), an effect reversed by M100907 (5-HT(2A) antagonist) and picrotoxinin (GABA(A) antagonist). DOI (1 mg/kg, s.c.) reduced the 5-HT release in medial prefrontal cortex (mPFC) to 33 +/- 8% of baseline, an effect also antagonized by M100907. However, the local application of DOI in the mPFC increased 5-HT release (164 +/- 6% at 100 microm), an effect antagonized by tetrodotoxin, M100907, and BAY x 3702 (5-HT(1A) agonist) but not by SB 242084 (5-HT(2C) antagonist). The 5-HT increase was also reversed by NBQX (AMPA-KA antagonist) and 1S,3S-ACPD (mGluR 2/3 agonist) but not by MK-801 (NMDA antagonist). AMPA mimicked the 5-HT elevation produced by DOI. Likewise, the electrical-chemical stimulation of thalamocortical afferents and the local inhibition of glutamate uptake increased the 5-HT release through AMPA receptors. DOI application in mPFC increased the firing rate of a subgroup of 5-HT neurons (5 of 10), indicating an enhanced output of pyramidal neurons. Dual-label fluorescence confocal microscopic studies demonstrated colocalization of 5-HT(1A) and 5-HT(2A) receptors on individual cortical pyramidal neurons. Thus, DOI reduces the activity of ascending 5-HT neurons through a DR-based action and enhances serotonergic and glutamatergic transmission in mPFC through 5-HT(2A) and AMPA receptors. Because pyramidal neurons coexpress 5-HT(1A) and 5-HT(2A) receptors, DOI disrupts the balance between excitatory and inhibitory inputs and leads to an increased activity that may mediate its hallucinogenic action.

Control of dorsal raphe serotonergic neurons by the medial prefrontal cortex: Involvement of serotonin-1A, GABA(A), and glutamate receptors.

Anatomical evidence indicates that medial prefrontal cortex (mPFC) neurons project to the dorsal raphe nucleus (DR). In this study, we functionally characterized this descending pathway in rat brain. Projection neurons in the mPFC were identified by antidromic stimulation from the DR. Electrical stimulation of the mPFC mainly inhibited the activity of DR 5-HT neurons (55 of 66). Peristimulus time histograms showed a silence of 150 +/- 9 msec poststimulus (latency, 36 +/- 1 msec). The administration of WAY-100635 and picrotoxinin partly reversed this inhibition, indicating the involvement of 5-HT(1A) and GABA(A) receptors. In rats depleted of 5-HT with p-chlorophenylalanine, the electrical stimulation of mPFC mainly activated 5-HT neurons (31 of 40). The excitations (latency, 17 +/- 1 msec) were antagonized by MK-801 and NBQX. Likewise, MK-801 prevented the rise in DR 5-HT release induced by electrical stimulation of mPFC. The application of 8-OH-DPAT in mPFC significantly inhibited the firing rate of DR 5-HT neurons and, in dual-probe microdialysis experiments, reduced the 5-HT output in mPFC and DR. Furthermore, the application of WAY-100635 in mPFC significantly antagonized the reduction of 5-HT release produced by systemic 8-OH-DPAT administration in both areas. These results indicate the existence of a complex regulation of DR 5-HT neurons by mPFC afferents. The stimulus-induced excitation of some 5-HT neurons by descending excitatory fibers releases 5-HT, which inhibits the same or other DR neurons by acting on 5-HT(1A) autoreceptors. Afferents from the mPFC also inhibit 5-HT neurons through the activation of GABAergic interneurons. Ascending serotonergic pathways may control the activity of this descending pathway by acting on postsynaptic 5-HT(1A) receptors.

The role of 5-HT1B receptors in the regulation of serotonin cell firing and release in the rat brain.

The release of 5-HT in terminal areas of the rodent brain is regulated by 5-HT1B receptors. Here we examined the role of 5-HT1B receptors in the control of 5-HT output and firing in the dorsal raphe nucleus (DR), median raphe nucleus (MnR) and forebrain of the rat in vivo. The local perfusion (30-300 microM) of the selective 5-HT1B receptor agonist CP-93,129 to freely moving rats decreased 5-HT release in the DR and more markedly in the MnR. Likewise, 300 microM CP-93,129 reduced 5-HT output in substantia nigra pars reticulata, ventral pallidum, lateral habenula and the suprachiasmatic nucleus. The effect of CP-93,129 was prevented by SB-224289, but not by WAY-100635, selective 5-HT1B and 5-HT1A receptor antagonists, respectively. SB-224289 did not alter dialysate 5-HT in any raphe nuclei. The intravenous administration of the brain-penetrant selective 5-HT1B receptor agonist CP-94,253 (0.5-2.0 mg/kg) to anesthetized rats decreased dialysate 5-HT in dorsal hippocampus and globus pallidus, increased it in MnR and left it unaltered in the DR and medial prefrontal cortex. SB-224289, at a dose known to block 5-HT1B autoreceptor-mediated effects (5 mg/kg), did not prevent the effect of CP-94,253 on MnR 5-HT. The intravenous administration of CP-94,253 (0.05-1.6 mg/kg) to anesthetized rats increased the firing rate of MnR, but not DR-5-HT neurons. The local perfusion of CP-94,253 in the MnR showed a biphasic effect, with 5-HT reductions at 0.3-3 microM and increase at 300 microM. These results suggest that 5-HT cell firing and release in midbrain raphe nuclei (particularly in the MnR) are under control of 5-HT1B receptors. The activation of 5-HT1B autoreceptors (possibly located on 5-HT nerve endings and/or varicosities within DR and MnR) reduces 5-HT release. The effects of higher concentrations of 5-HT1B receptor agonists seem more compatible with the activation of 5-HT1B heteroreceptors on inhibitory neurons.

How does pindolol improve antidepressant action?

Since 1994, the beta-adrenoceptor and 5-HT(1A/1B) receptor ligand pindolol has been used to accelerate or enhance the clinical effects of antidepressant drugs, such as the selective 5-HT reuptake inhibitors (SSRIs), that act primarily on 5-HT-containing neurones. Pindolol was initially thought to act by preventing the inhibition of 5-HT release, elicited by SSRIs and other 5-HT-acting drugs, as a result of its ability to antagonize the action of 5-HT at midbrain raphe 5-HT(1A) autoreceptors that control the activity of ascending 5-HT-mediated pathways. However, the partial agonist properties of pindolol at 5-HT(1A) receptors and beta-adrenoceptors suggest that other explanations for its action are also possible. In this article, recent controversial data on the mechanism of action of pindolol, which are crucial for the development of more rapid and efficient antidepressant therapies, will be discussed.

In vivo actions of the selective 5-HT1A receptor agonist BAY x 3702 on serotonergic cell firing and release.

We investigated the effects of the novel 5-HT1A receptor agonist BAY x 3702 on the serotonergic function in rat brain using single unit recordings in the dorsal raphe nucleus (DR) of anesthetized rats and in vivo microdialysis in freely moving rats. The administration of BAY x 3702 (0.25-4 microg/kg i.v.) suppressed the firing activity of 5-HT neurones. This effect was antagonized by a low dose of the selective 5-HT1A receptor antagonist WAY 100635 (5 microg/kg i.v.). In microdialysis experiments, BAY x 3702 (10-100 microg/ kg s.c.) reduced dose-dependently the 5-HT output in the dorsal and median raphe (MnR) nucleus, dorsal hippocampus (DHPC) and medial prefrontal cortex (mPFC) in a regionally selective manner. Maximal effects were observed in the MnR and mPFC, with reductions to approximately 15% of baseline at a dose of 0.1 mg/kg s.c. The decrease in 5-HT output produced in the DR and DHPC was more moderate, to 45% of baseline at 0.1 mg/kg s.c. BAY x 3702. WAY 100635 (0.3 mg/kg s.c.) completely antagonized the effect of BAY x 3702 (30 microg/kg s.c.). The application of BAY x 3702 in the DR (1-100 microM) reduced the local 5-HT output to 25% of baseline. In rats implanted with two dialysis probes (in DR and mPFC) the application of BAY x 3702 (30 microM) in the DR reduced the 5-HT output in the DR and that in mPFC. These effects were significantly antagonized by the co-perfusion of WAY 100635 (100 microM) in the DR. Overall, these results indicate that the systemic administration of BAY x 3702 reduces the 5-HT release with high potency through the activation of midbrain 5-HT1A receptors.

Striatal, pallidal, and pars reticulata evoked inhibition of nigrostriatal dopaminergic neurons is mediated by GABA(A) receptors in vivo.

Dopaminergic neurons express both GABA(A) and GABA(B) receptors and GABAergic inputs play a significant role in the afferent modulation of these neurons. Electrical stimulation of GABAergic pathways originating in neostriatum, globus pallidus or substantia nigra pars reticulata produces inhibition of dopaminergic neurons in vivo. Despite a number of prior studies, the identity of the GABAergic receptor subtype(s) mediating the inhibition evoked by electrical stimulation of neostriatum, globus pallidus, or the axon collaterals of the projection neurons from substantia nigra pars reticulata in vivo remain uncertain. Single-unit extracellular recordings were obtained from substantia nigra dopaminergic neurons in urethane anesthetized rats. The effects of local pressure application of the selective GABA(A) antagonists, bicuculline and picrotoxin, and the GABA(B) antagonists, saclofen and CGP-55845A, on the inhibition of dopaminergic neurons elicited by single-pulse electrical stimulation of striatum, globus pallidus, and the thalamic axon terminals of the substantia nigra pars reticulata projection neurons were recorded in vivo. Striatal, pallidal, and thalamic induced inhibition of dopaminergic neurons was always attenuated or completely abolished by local application of the GABA(A) antagonists. In contrast, the GABA(B) antagonists, saclofen or CGP-55845A, did not block or attenuate the stimulus-induced inhibition and at times even increased the magnitude and/or duration of the evoked inhibition. Train stimulation of globus pallidus and striatum also produced an inhibition of firing in dopaminergic neurons of longer duration. However this inhibition was largely insensitive to either GABA(A) or GABA(B) antagonists although the GABA(A) antagonists consistently blocked the early portion of the inhibitory period indicating the presence of a GABA(A) component. These data demonstrate that dopaminergic neurons of the substantia nigra pars compacta are inhibited by electrical stimulation of striatum, globus pallidus, and the projection neurons of substantia nigra pars reticulata in vivo. This inhibition appears to be mediated via the GABA(A) receptor subtype, and all three GABAergic afferents studied appear to possess inhibitory presynaptic GABA(B) autoreceptors that are active under physiological conditions in vivo.

GABAergic control of rat substantia nigra dopaminergic neurons: role of globus pallidus and substantia nigra pars reticulata.

Dopaminergic neurons in vivo fire spontaneously in three distinct patterns or modes. It has previously been shown that the firing pattern of substantia nigra dopaminergic neurons can be differentially modulated by local application of GABA(A) and GABA(B) receptor antagonists. The GABA(A) antagonists, bicuculline or picrotoxin, greatly increase burst firing in dopaminergic neurons whereas GABA(B) antagonists cause a modest shift away from burst firing towards pacemaker-like firing. The three principal GABAergic inputs to nigral dopaminergic neurons arise from striatum, globus pallidus and from the axon collaterals of nigral pars reticulata projection neurons, each of which appear to act in vivo primarily on GABA(A) receptors (see preceding paper). In this study we attempted to determine on which afferent pathway(s) GABA(A) antagonists were acting to cause burst firing. Substantia nigra dopaminergic neurons were studied by single unit extracellular recordings in urethane anesthetized rats during pharmacologically induced inhibition and excitation of globus pallidus. Muscimol-induced inhibition of pallidal neurons produced an increase in the regularity of firing of nigral dopaminergic neurons together with a slight decrease in firing rate. Bicuculline-induced excitation of globus pallidus neurons produced a marked increase in burst firing together with a modest increase in firing rate. These changes in firing rate were in the opposite direction to what would be expected for a monosynaptic GABAergic pallidonigral input. Examination of the response of pars reticulata GABAergic neurons to similar manipulations of globus pallidus revealed that the firing rates of these neurons were much more sensitive to changes in globus pallidus neuron firing rate than dopaminergic neurons and that they responded in the opposite direction. Pallidal inhibition produced a dramatic increase in the firing rate of pars reticulata GABAergic neurons while pallidal excitation suppressed the spontaneous activity of pars reticulata GABAergic neurons. These data suggest that globus pallidus exerts significant control over the firing rate and pattern of substantia nigra dopaminergic neurons through a disynaptic pathway involving nigral pars reticulata GABAergic neurons and that at least one important way in which local application of bicuculline induces burst firing of dopaminergic neurons is by disinhibition of this tonic inhibitory input.

Relationship between blood serotonergic variables, melancholic traits, and response to antidepressant treatments.

The relationship between peripheral serotonergic variables, melancholic traits, and clinical improvement after antidepressant treatment was examined in 83 drug-free major depressive patients. Plasma serotonin (5-HT) concentrations was lower in untreated melancholic patients (1.00 +/- 0.11 vs. 1.84 +/- 0.28 ng/mL, p < 0.008; N = 40 and 43, respectively). A tendency was observed for plasma 5-hydroxyindoleacetic acid (p < 0.06), whereas platelet 5-HT and plasma tryptophan did not differ between groups. After blood sampling and clinical ratings, treatment began with fixed doses of 5-HT uptake inhibitors (clomipramine or fluvoxamine), monoamine oxidase inhibitors, or tianeptine, a 5-HT uptake enhancer. There was no significant difference in response rates between patients with and without melancholic traits. The relationship between the clinical response at 6 weeks (>50% reduction of baseline Hamilton score) and the pretreatment values of biochemical variables was examined. Responders had a lower pretreatment platelet 5-HT (530 +/- 36 vs. 664 +/- 50 ng/10(9) platelets, p < 0.03; N = 44 and 39, respectively). Patients with a platelet 5-HT concentration above 800 ng/10(9) platelets had a lower response rate than those below this value (p < 0.003). This difference was maximal in the subgroup of patients treated with 5-HT uptake inhibitors (N = 49). In this subgroup, the response rates of patients with 5-HT concentrations below and above the cutoff point were, respectively, 70% and 17% (p < 0.001). A pretreatment platelet 5-HT value above 800 ng/10(9) platelets had a predictive value for a negative response of 92%. These results suggest the presence of biochemical differences in the peripheral serotonergic system between melancholic and nonmelancholic patients. The inverse relationship between the pretreatment platelet 5-HT content and clinical response may be useful in the investigation of the relationship between the 5-HT system and antidepressant response.