5-HT1A receptor expression is modulated by corticosteroid receptor agonists in primary rat hippocampal culture

Long-lasting monoaminergic and behavioral dysfunctions in a mice model of socio-environmental stress during adolescence

Adolescence is one of the critical periods of development and has great importance to health for an individual as an adult. Stressors or traumatic events during this period are associated with several psychiatric disorders as related to anxiety or depression and cognitive impairments, but whether negative experiences continue to hinder individuals as they age is not as well understood. We determined how stress during adolescence affects behavior and neurochemistry in adulthood. Using an unpredictable paradigm (2 stressors per day for 10days) in Balb/c mice, behavioral, hormonal, and neurochemical changes were identified 20days after the cessation of treatment. Adolescent stress increased motor activity, emotional arousal and vigilance, together with a reduction in anxiety, and also affected recognition memory. Furthermore, decreased serotonergic activity on hippocampus, hypothalamus and cortex, decreased noradrenergic activity on hippocampus and hypothalamus, and increased the turnover of dopamine in cortex. These data suggest behavioral phenotypes associated with emotional arousal, but not depression, emerge after cessation of stress and remain in adulthood. Social-environmental stress can induce marked and long-lasting changes in HPA resulting from monoaminergic neurotransmission, mainly 5-HT activity.

Of rodents and humans: A comparative review of the neurobehavioral effects of early life SSRI exposure in preclinical and clinical research

Selective serotonin reuptake inhibitors (SSRIs) have been a mainstay pharmacological treatment for women experiencing depression during pregnancy and postpartum for the past 25 years. SSRIs act via blockade of the presynaptic serotonin transporter and result in a transient increase in synaptic serotonin. Long-lasting changes in cellular function such as serotonergic transmission, neurogenesis, and epigenetics, are thought to underlie the therapeutic benefits of SSRIs. In recent years, though, growing evidence in clinical and preclinical settings indicate that offspring exposed to SSRIs in utero or as neonates exhibit long-lasting behavioral adaptions. Clinically, children exposed to SSRIs in early life exhibit increased internalizing behavior reduced social behavior, and increased risk for depression in adolescence. Similarly, rodents exposed to SSRIs perinatally exhibit increased traits of anxiety- or depression-like behavior. Furthermore, certain individuals appear to be more susceptible to early life SSRI exposure than others, suggesting that perinatal SSRI exposure may pose greater risks for negative outcome within certain populations. Although SSRIs trigger a number of intracellular processes that likely contribute to their therapeutic effects, early life antidepressant exposure during critical neurodevelopmental periods may elicit lasting negative effects in offspring. In this review, we cover the basic development and structure of the serotonin system, how the system is affected by early life SSRI exposure, and the behavioral outcomes of perinatal SSRI exposure in both clinical and preclinical settings. We review recent evidence indicating that perinatal SSRI exposure perturbs the developing limbic system, including altered serotonergic transmission, neurogenesis, and epigenetic processes in the hippocampus, which may contribute to behavioral domains (e.g., sociability, cognition, anxiety, and behavioral despair) that are affected by perinatal SSRI treatment. Identifying the molecular mechanisms that underlie the deleterious behavioral effects of perinatal SSRI exposure may highlight biological mechanisms in the etiology of mood disorders. Moreover, because recent studies suggest that certain individuals may be more susceptible to the negative consequences of early life SSRI exposure than others, understanding mechanisms that drive such susceptibility could lead to individualized treatment strategies for depressed women who are or plan to become pregnant.

Synthesis, preclinical evaluation and molecular modelling of macrocyclic appended 1-(2-methoxyphenyl)piperazine for 5-HT1A neuroreceptor imaging

An efficient approach in the design and synthesis of a multi-functional chelating agent based on 1-(2-methoxyphenyl)piperazine for targeting 5-HT_1A receptors in brain was envisaged.

Anxiolytic effects of herbal ethanol extract from Gynostemma pentaphyllum in mice after exposure to chronic stress

In this study, the effects of herbal ethanol extracts of Gynostemma pentaphyllum (GP-EX), on chronic electric footshock (EF) stress-induced anxiety disorders were investigated in mice, which were orally treated with GP-EX (30 mg/kg and 50 mg/kg) once a day for 14 days, followed by exposure to EF stress (2 mA, with an interval and duration of 10 s for 3 min). After the final exposure to EF stress, the elevated plus-maze and marble burying tests were performed, and the levels of dopamine and serotonin in the brain, the serum levels of corticosterone, and the expression of c-Fos in the paraventricular nuclei (PVN) were determined. Treatment with GP-EX (30 mg/kg and 50 mg/kg) significantly recovered the number of entries into open arms and time spent on open arms, which was reduced by chronic EF stress. GP-EX (30 mg/kg and 50 mg/kg) also reduced the number of marbles buried, which was increased by chronic EF stress. In addition, electric EF stress significantly decreased the levels of dopamine and serotonin in the brain, which was recovered by treatment with GP-EX (30 mg/kg and 50 mg/kg). The serum levels of corticosterone, which were markedly increased by chronic EF stress, were reduced by treatment with GP-EX (30 mg/kg and 50 mg/kg). Chronic EF stress-induced increases in c-Fos expression were also markedly reduced by GP-EX (30 mg/kg and 50 mg/kg) in the PVN. These results suggest that GP-EX shows anxiolytic functions, determined by the elevated plus-maze and marble burying tests, which are mediated by modulating the activity of dopamine and serotonin neurons as well as the expression of c-Fos in the brain, and the serum levels of corticosterone. Clinical trials of herbal GP-EX and its bioactive components need further investigation.

Effects of repeated low-dose soman exposure on monoamine levels in different brain structures in mice

In order to better understand the effects of repeated low-dose exposure to organophosphorus (OPs) on physiological and behavioural functions, we analysed the levels of endogenous monoamines (serotonin and dopamine) in different brain areas after repeated exposure of mice to sublethal dose of soman. Animals were injected once a day for 3 days with 0.12 LD50 of soman (47 microg/kg, i.p.). They did not show either severe signs of cholinergic toxicity or pathological changes in brain tissue. 24 h after the last injection of soman, inhibition of cholinesterase was similar in plasma and brain (32% and 37% of inhibition respectively). Afterwards, recovery of cholinesterase activity was faster in the plasma than in the brain. Dopamine levels were not significantly modified. On the other hand, we observed a significant modification of the serotoninergic system. An increase of the 5-HIAA/5-HT ratio was maintained for 2 and 4 weeks after exposure in the hippocampus and the striatum respectively. This study provides the first evidence of a modification of the 5-HT turnover in the hippocampus and the striatum after repeated low-dose intoxication with a nerve agent. Further experiments are necessary to evaluate the relationship between these modifications and the unexpected neuropsychological disorders usually reported after chronic exposure of organophosphorus.

Effects of chronic restraint stress on feeding behavior and on monoamine levels in different brain structures in rats

Monoaminergic systems are important modulators of the responses to stress. Stress may influence feeding behavior, and the involvement of monoamines in the control of food intake is well recognized. We investigated the effects induced by chronic-restraint stress, 1 h a day, for 40 days, on eating behavior and on monoamines in distinct brain structures. Increased consumption of sweet pellets, and not of peanuts, was observed. Dopamine (DA), serotonin (5-HT), and their metabolites were measured by HPLC-EC. After chronic restraint, the results observed were decreased 5-HT in hippocampus, with increased 5-HIAA/5-HT; decreased 5-HIAA levels in cortex; reduction in DA in hippocampus, and increased levels in amygdala and hypothalamus; HVA increased in cortex, as well as HVA/DA ratio, while DOPAC/DA decreased. HVA decreased in hypothalamus, as well as HVA/DA, and DOPAC/DA and HVA/DA decreased in the amygdala. These results suggest that restraint stress differentially affects the activity of central dopaminergic and serotonergic neurons, and this may be related to the effects observed in eating behavior.

Astrocyte-mediated trophic support of developing serotonin neurons: effects of ethanol, buspirone, and S100B

Previously, this laboratory demonstrated that the development of serotonin (5-HT) neurons and S100B-immunopositive glia proximal to these neurons is impaired in the offspring of ethanol-fed rats. However, maternal treatment with a 5-HT(1A) agonist, e.g., buspirone or ipsapirone, between gestational days 13 and 20 prevented most of the ethanol-associated changes to developing 5-HT neurons and S100B-immunopositive glia in offspring. The present in vitro studies examined the hypothesis that the protective effects of a 5-HT(1A) agonist on ethanol-exposed, developing 5-HT neurons are mediated in part by astrocyte-produced factors such as S100B. Primary cultures of fetal 5-HT neurons were maintained in conditioned medium (CM) that was obtained from ethanol- and buspirone-treated astrocytes. In order to assess the potential contribution of S100B to the protective effects of buspirone, a mouse monoclonal antibody to S100B was added to the CM to block the biological effects of this protein. These studies demonstrated that CM, obtained from ethanol-treated astrocytes, was unable to support normal development of 5-HT neurons; there was a significant reduction in the number of 5-HT neurons/well. However, CM that was obtained from astrocytes that were co-treated with buspirone and ethanol prevented the ethanol-associated reduction, and the protective effects of buspirone required S100B. We also investigated whether exogenous S100B could protect 5-HT neurons from damage caused by direct exposure to ethanol. Direct exposure of fetal brainstem neurons to ethanol in chemically-defined medium was associated with a significant reduction in the number of 5-HT immunopositive neurons/well. However, exogenous S100B protected 5-HT neurons from the ethanol-associated reduction. Our observations suggest that the protective effects of buspirone on ethanol-exposed, developing 5-HT neurons are mediated in part by the astrocyte-produced factor S100B.

Potential involvement of S100B in the protective effects of a serotonin-1a agonist on ethanol-treated astrocytes

Previously, this laboratory found that the offspring of rats that consumed ethanol on a chronic basis prior to parturition exhibited a significant reduction in serotonin (5-HT) neurons and in astrocytes proximal to these neurons. This laboratory also showed that maternal treatment with a 5-HT(1A) agonist during the latter part of gestation prevented the reduction of 5-HT neurons and most of the astrocyte abnormalities. The present in vitro studies extended our prior in vivo work by examining the potential involvement of S100B with the protective effects of a 5-HT(1A) agonist, i.e., buspirone, on astrocytes. Astrocyte cultures were either maintained in chemically defined media in the presence and absence of ethanol and buspirone or in conditioned media that was generated by ethanol- and buspirone-treated astrocytes. A mouse monoclonal antibody to S100B was used to assess the potential involvement of S100B with the protective effects of buspirone. Additional in vitro studies measured the direct effects of S100B and ethanol on astrocyte proliferation. These investigations demonstrate that in vitro ethanol exposure reduces the number of astrocytes, and that treatment with the 5-HT(1A) agonist buspirone prevents the ethanol-associated reduction in astrocyte number. The protective effects of buspirone appear to be mediated by factors that are secreted by astrocytes; such factors likely include S100B. In addition, added S100B prevents an ethanol-associated reduction in [(3)H]-thymidine incorporation into proliferating astrocytes.

Heterodimerization of mineralocorticoid and glucocorticoid receptors at a novel negative response element of the 5-HT1A receptor gene

Negative regulation of neuronal serotonin (5-HT1A) receptor levels by glucocorticoids in vivo may contribute to depression. Both types I (mineralocorticoid) and II (glucocorticoid) receptors (MR and GR, respectively) participate in corticosteroid-induced transcriptional repression of the 5-HT1A gene; however, the precise mechanism is unclear. A direct repeat 6-base pair glucocorticoid response element (GRE) half-site 5'-TGTCCT separated by 6 nucleotides was conserved in human, mouse, and rat 5-HT1A receptor promoters. In SN-48 neuronal cells that express MR, GR, and 5-HT1A receptors, deletion or inactivation of the nGRE (negative GRE) eliminated negative regulation of the rat 5-HT1A or heterologous promoters by corticosteroids, whereas its inclusion conferred corticosteroid-induced inhibition to a heterologous promoter. Bacterially expressed recombinant MR and GR preferentially bound to the nGRE as a heterodimer, as identified in nuclear extracts of MR/GR-transfected COS-7 cells, and with higher affinity than MR or GR homodimers. In SN48 and COS-7 cells, concentration-dependent coactivation of MR and GR was required for maximal inhibitory action by corticosteroids and was abrogated in the L501P-GR mutant lacking DNA binding activity. Corticosteroid-mediated transcriptional inhibition was greater for MR/GR in combination than for MR or GR alone. These data represent the first identification of an nMRE/GRE and indicate that heterodimerization of MR and GR mediates direct corticosteroid-induced transrepression of the 5-HT1A receptor promoter.

Effect of p-chloroamphetamine on 5-HT1A and 5-HT7 serotonin receptor expression in rat brain

The aim of this study was to investigate if p-chloroamphetamine (PCA), which is neurotoxic to serotonin (5-HT) nerve terminals, was able to induce, like 3,4-methylenedioxymethamphetamine, a region-specific regulation of 5-HT1A receptor mRNA expression. The effect of PCA on the expression of 5-HT7 receptors, which share some pharmacological properties with 5-HT1A receptors, was comparatively studied. PCA (2 x 5 mg/kg) produced a lasting depletion of 5-HT content in the rat frontal cortex and hippocampus. In the hippocampus, the maximal 5-HT depletion was found on day 21 (-70%), whereas in the cortex, the highest 5-HT depletion was found on day 14 (-73%), with a partial but significant recovery on day 21. At the latter time point, 5-HT1A receptor mRNA expression was increased by 80% in the cortex and decreased by 50% in the hippocampus. The 5-HT1A receptor mRNA expression was also enhanced after exposure to PCA of rat cortical but not of hippocampal primary cultures. In regard to 5-HT7 receptor mRNA expression, the most remarkable change after PCA was the great increase (+200%) in the brain-stem. Binding studies to 5-HT1A receptors matched the changes in receptor mRNA expression. Gel shift assays revealed enhanced nuclear protein binding to the KB sequence with use of cortical but not hippocampal extracts of PCA-treated rats. Overall, the data show region-specific changes in 5-HT receptor-type expression that may not be entirely dependent on the neurotoxic effect of PCA on 5-HT terminals.

Homologous regulation of 5-HT1A receptor mRNA in adult rat hippocampal dentate gyrus

Short-term adrenalectomy induces a loss of mature granular neuronal phenotypes in the hippocampal dentate gyrus; injection of 5-HT1A receptor agonist reverses this effect. Adrenalectomy also induces an increase of expression of 5-HT1A receptor mRNA in the dentate gyrus. This study tested the effect of 5-HT1A agonist on this adrenalectomy-induced increase of 5-HT1A mRNA. Five, 9 and 18 days after adrenalectomy, 5-HT1A receptor mRNA is increased in the granular layer of the dentate gyrus. The increase is nearly 100% at day 18 after adrenalectomy. 5-HT1A agonist treatment decreased 5-HT1A mRNA both at 9 (20%) and 18 days (34%) after adrenalectomy. Our results indicated that a 5-HT1A agonist can partly reverse the adrenalectomy-induced increase of 5-HT1A mRNA and loss of mature granular neuronal phenotypes in hippocampal dentate gyrus.

Agonist- and antagonist-induced plasticity of rat 5-HT1A receptor in hippocampal cell culture

We examined the response and regulation of 5-HT1A receptor on hippocampal cultured fetal neurons grown in the absence of serotonin and steroids using three experimental designs: 1) functional response using an antibody against phosphorylated cyclic adenosine monophosphate response element binding protein (pCREB); 2) transcriptional regulation using in situ hybridization; and 3) translational expression using antipeptide 5-HT1A receptor antibody. Pretreatment of cultured hippocampal cells with the agonist 8-hydroxy-2-(di-N-propylamino)-tetralin (8-OH-DPAT) (10(-8) M) or ipsapirone (IPS) (10(-9) M) for 10 min blocked the forskolin-stimulated increase in pCREB immunoreactivity. In situ hybridization radioautography revealed that IPS (10(-9) M) decreased the 5-HT1A receptor mRNA expression (-33%) after a 24-h treatment. The decrease in 5-HT1A receptor mRNAwas accompanied by a change in protein immunoreactivity using a 5-HT1A receptor antipeptide antibody. Computer-assisted morphometric analyses showed a reduction in the 5-HT1A receptor immunoreactive (IR) intensity as compared to control 24 h after treatment with 8-OH-DPAT (10(-7)-10(-12) M) and IPS (10(-9) M). Thus, fetal hippocampal neurons have a functional 5-HT1A receptor that is downregulated at both the transcription and translation levels. In addition, we found increased 5-HT1A receptor-IR intensity (+17% approximately +39%) 24 h after treatment with the antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide (WAY 100635) (10(-7)-10(-12) M). Our results indicate that the 5-HT1A receptor is sensitive to both agonists (downregulation) and antagonists (upregulation) in hippocampal fetal neurons grown in the absence of serotonin and steroids.