Modulation of central serotonergic neurotransmission by risperidone: underlying mechanism(s) and significance of action

Sodium valproate in pregnancy: what are the risks and should we use a shared decision-making approach?

BACKGROUND

Despite significant teratogenic risks, sodium valproate is still widely prescribed in many countries to women of childbearing age, as a mood stabiliser in bipolar disorder and also in epilepsy. The UK has recently banned valproate use in women who are not in a pregnancy prevention programme. Whilst this ruling reflects prevailing clinical practice, it also highlights an ongoing debate about when (if ever) a woman who is or could become pregnant should be allowed to choose to take valproate.

MAIN BODY

We review the benefits and harms of drugs available for bipolar disorder and epilepsy in women of childbearing age, with a particular focus on teratogenic risk. We speculate on hypothetical rare situations in which potential benefits of valproate may outweigh potential harms in such women. We also review the literature on shared decision-making - on which there is now a NICE guideline and numerous evidence-based decision tools. Drawing on previous work by experts in shared decision-making, we offer a list of 'frequently asked questions' and a matrix of options to support conversations with women about continuing or discontinuing the drug in (or in anticipation of) pregnancy. We also consider whether shared decision-making is an appropriate paradigm when considering whether to continue a teratogenic drug.

CONCLUSION

We conclude that because valproate in pregnancy remains the subject of such debate, there is scope for further research - not only into the relative efficacy and safety of alternatives to it - but also into the dynamics of communication and shared decision-making in this situation.

Access to the CNS: Biomarker Strategies for Dopaminergic Treatments

Despite substantial research carried out over the last decades, it remains difficult to understand the wide range of pharmacological effects of dopaminergic agents. The dopaminergic system is involved in several neurological disorders, such as Parkinson's disease and schizophrenia. This complex system features multiple pathways implicated in emotion and cognition, psychomotor functions and endocrine control through activation of G protein-coupled dopamine receptors. This review focuses on the system-wide effects of dopaminergic agents on the multiple biochemical and endocrine pathways, in particular the biomarkers (i.e., indicators of a pharmacological process) that reflect these effects. Dopaminergic treatments developed over the last decades were found to be associated with numerous biochemical pathways in the brain, including the norepinephrine and the kynurenine pathway. Additionally, they have shown to affect peripheral systems, for example the hypothalamus-pituitary-adrenal (HPA) axis. Dopaminergic agents thus have a complex and broad pharmacological profile, rendering drug development challenging. Considering the complex system-wide pharmacological profile of dopaminergic agents, this review underlines the needs for systems pharmacology studies that include: i) proteomics and metabolomics analysis; ii) longitudinal data evaluation and mathematical modeling; iii) pharmacokinetics-based interpretation of drug effects; iv) simultaneous biomarker evaluation in the brain, the cerebrospinal fluid (CSF) and plasma; and v) specific attention to condition-dependent (e.g., disease) pharmacology. Such approach is considered essential to increase our understanding of central nervous system (CNS) drug effects and substantially improve CNS drug development.

Chronic administration of risperidone in a rat model of schizophrenia: a behavioural, morphological and molecular study

In the present work we analyzed the effect of the chronic administration of risperidone (2mg/kg over 65 days) on behavioural, morphological and molecular aspects in an experimental model of schizophrenia obtained by bilateral injection of ibotenic acid into the ventral hippocampus of new-born rats. Our results show that during their adult lives the animals with hippocampal lesions exhibit different alterations, mainly at behavioural level and in the gene expression of dopamine D(2) and 5-HT(2A) receptors. However, at morphological level the study performed on the prefrontal cortex did not reveal any alterations in either the thickness or the number of cells immunoreactive for c-Fos, GFAP, CBP or PV. Overall, risperidone administration elicited a trend towards the recovery of the values previously altered by the hippocampal lesion, approaching the values seen in the animals without lesions. It may be concluded that the administration of risperidone in the schizophrenia model employed helps to improve the altered functions, with no significant negative effects.

Locus coeruleus and dorsal raphe neuron activity and response to acute antidepressant administration in a rat model of Parkinson's disease

In addition to noradrenergic and serotonergic systems, dopaminergic neurotransmission seems to play an important role in the aetiopathogenesis of, and recovery from, depression. Moreover, the incidence of depression is higher in patients affected by diseases where the dopaminergic system is highly impaired, such us Parkinson's disease. Here, we investigated the effects of dopamine degeneration on the activity and response to antidepressants of locus coeruleus (LC) noradrenergic and dorsal raphe nucleus (DRN) serotonergic neurons. To this end, single-unit extracellular recordings were performed in control and 6-hydroxydopamine (6-OHDA)-lesioned animals. In this latter group, LC neurons showed a lower basal firing rate as well as less sensitivity to the administration of the serotonin reuptake inhibitor, fluoxetine. The rest of electrophysiological parameters and the response to the administration of the α2-adrenoceptor agonist, clonidine and the noradrenaline reuptake inhibitor, reboxetine remained unaltered. In the DRN, dopamine depletion did not modify the basal electrophysiological characteristics and the response to clonidine or fluoxetine administration. In contrast, the administration of reboxetine more efficiently induced an inhibitory effect in the lesioned group. In additional analyses it was observed that while in control animals, LC and DRN basal firing rate was significantly correlated, this relationship was lost after the 6-OHDA lesion. In conclusion, dopaminergic degeneration alters LC neuron basal activity, the relationship/synteny between both nuclei, and their response to antidepressants. These findings shed fresh light on our understanding of the role of dopamine in depression and the mechanism action of antidepressants.

Repeated risperidone treatment increases the expression of NCAM and PSA-NCAM protein in the rat medial prefrontal cortex

The present study investigates whether the anti-schizophrenic drug risperidone may evoke changes in the expression of NCAM/PSA-NCAM proteins, an indispensable element in the remodeling of synaptic arrangements, in the medial prefrontal cortex (mPFC). Rats were treated with risperidone (0.2 mg/kg, i.p.) either once or repeatedly (once a day, for 21 days). The expression of NCAM and PSA-NCAM proteins was analyzed via western blot and immunohistochemistry at intervals of 3 h and 3, 6, and 9 days after the single or the last risperidone dose. Repeated (but not acute) administration of risperidone was found to increase the expression of NCAM-180, NCAM-140 and PSA-NCAM proteins at 3 or 6 days after treatment. PSA-NCAM immunoreactivity was found in cell bodies, perisomatic-like sites, and in the neuropil of the mPFC. Neither single nor repeated risperidone administration changed the number of PSA-NCAM neurons in the mPFC. In contrast, the repeated risperidone treatment increased the number of PSA-NCAM perisomatic-like sites and the length density of PSA-NCAM positive neuropil at 3 days after the last injection. The data obtained indicate that risperidone, given repeatedly, may promote the remodeling of the structure of presumably GABA-ergic interneurons and that it may evoke the rearrangement of the synaptic contact in the mPFC.

Effects of disulfiram and dopamine beta-hydroxylase knockout on cocaine-induced seizures

The antialcoholism drug disulfiram has shown recent promise as a pharmacotherapy for treating cocaine dependence, probably via inhibition of dopamine beta-hydroxylase (DBH), the enzyme that catalyzes the conversion of dopamine (DA) to norepinephrine (NE). We previously showed that DBH knockout (Dbh -/-) mice, which lack NE, are susceptible to seizures and are hypersensitive to the psychomotor, rewarding, and aversive effects of cocaine, suggesting that disulfiram might exacerbate cocaine-induced seizures (CIS) by inhibiting DBH. To test this, we examined CIS in wild-type and Dbh -/- mice following administration of disulfiram or the selective DBH inhibitor nepicastat. We found that Dbh genotype had no effect on CIS probability or frequency, whereas disulfiram, but not nepicastat, increased the probability of having CIS in both wild-type and Dbh -/- mice. Both disulfiram and nepicastat increased CIS frequency in wild-type but not Dbh -/- mice. There were no genotype or treatment effects on serum cocaine levels, except for an increase in disulfiram-treated Dbh -/- mice at the highest dose of cocaine. These results suggest that disulfiram enhances CIS via two distinct mechanisms: it both increases CIS frequency by inhibiting DBH and increases CIS frequency in a DBH-independent manner.

Quantification and pharmacological characterization of dialysate levels of noradrenaline in the striatum of freely-moving rats: release from adrenergic terminals and modulation by alpha2-autoreceptors

Information concerning striatal levels of noradrenaline (NA) remains inconsistent. Here we have addressed this issue using a sensitive method of HPLC coupled to amperometric detection. The NA reuptake-inhibitor, reboxetine, selectively elevated levels of NA versus dopamine (DA), and NA levels were also selectively elevated by the alpha2-adrenoceptor (AR) antagonist, atipamezole. The actions of atipamezole were mimicked by the preferential alpha2A-AR antagonist, BRL44408, while JO-1 and prazosin, preferential antagonists at alpha2C-ARs, caused less marked elevations in NA levels. In contrast to antagonists, the alpha2-AR agonist, S18616, decreased NA levels and likewise suppressed those of DA. Unilateral lesions of the substantia nigra with 6-hydroxydopamine depleted DA levels without affecting those of NA. Further, the D3/D2 receptor agonist, quinelorane, decreased levels of DA without modifying those of NA. However, the D3/D2 receptor antagonists, haloperidol and raclopride, and the DA reuptake-inhibitor, GBR12935, elevated levels of both DA and NA. Levels of 5-HT (but not of NA or DA) were increased only by the 5-HT reuptake-inhibitor, citalopram. They were decreased by S18616 and prazosin, reflecting the inhibitory and excitatory influence of alpha2- and alpha1-ARs, respectively, upon serotonergic pathways. In conclusion, NA in the striatum is derived from adrenergic terminals. Its release is subject to tonic, inhibitory control by alpha2-ARs, possibly involving both alpha2A- and alpha2C-AR subtypes, though their respective contribution requires clarification. A role of dopaminergic terminals in the reuptake of NA likely explains the elevation in its levels elicited by DA reuptake-inhibitors and D3/D2 receptor antagonists.

Brain region and dose effects of an olanzapine/fluoxetine combination on extracellular monoamine concentrations in the rat

Clinical studies of patients with treatment-resistant depression have shown that combined treatment with fluoxetine and olanzapine rapidly and significantly improved depressive symptoms. The present study used in vivo microdialysis to investigate the brain regional and dose effects of these drugs on extracellular monoamine concentrations in the rat prefrontal cortex, hypothalamus, nucleus accumbens and striatum. In the prefrontal cortex, the olanzapine/fluoxetine combination (3/10 mg/kg, respectively) increased catecholamine concentrations to a significantly greater extent than either drug alone (dopamine mean+/-S.E.M. percent of baseline: olanzapine (120 +/- 12.4), fluoxetine (123 +/- 6.2), combination (185 +/- 8.8); norepinephrine: olanzapine (124 +/- 7.2), fluoxetine (126 +/- 5.0), combination (215 +/- 15.8)). The combination also increased serotonin concentrations to 156 +/- 11.0% of baseline, but to a lesser extent than fluoxetine alone (210 +/- 14.5%). Similar synergistic effects of the combination were observed in the hypothalamus, but not in the other regions studied. The dose response effects of the drugs alone and in combination were complex, but larger doses of the combinations produced greater monoamine concentration increases than smaller dose combinations. The effects of the olanzapine/fluoxetine combination are meaningful in prefrontal cortex and hypothalamus due to their hypothesized role in the etiology and pharmacotherapy of depression. The wide-ranging neurochemical effects of this drug combination may make it particularly useful as a treatment for complex, resistant depressions.

Acute and subacute effects of risperidone and cocaine on accumbens dopamine and serotonin release using in vivo microvoltammetry on line with open-field behavior

In vivo microvoltammetry was used to detect dopamine (DA) and serotonin (5-HT) release from nucleus accumbens (NAcc) of freely moving, male, Sprague-Dawley laboratory rats, while animals' locomotor (forward ambulations) and stereotypic behavior (fine movements of sniffing and grooming) were monitored at the same time with infrared photobeams. Monoamine release mechanisms were determined by using a depolarization blocker (gamma-butyrolactone, gamma BL). Miniature carbon sensors (BRODERICK PROBES microelectrodes) smaller than a human hair were used in conjunction with a semidifferential electrochemical circuit to detect release of each monoamine in separate signals and within seconds. The purpose was to evaluate the neuropharmacology of the 5-HT(2)/DA(2) antagonist risperidone in its current therapeutic role as an atypical antipsychotic medication as well as in its potential role as pharmacotherapy for cocaine psychosis and withdrawal symptoms. Acute (single drug dose) and subacute (24-h follow-up studies in the same animal, no drug administration) studies were performed for each treatment group. The hypothesis for the present studies is derived from a growing body of evidence that cocaine-induced psychosis and schizophrenic psychosis share similar neurochemical and behavioral manifestations. Results showed that (1) Acute administration of risperidone (2 mg/kg sc) significantly increased DA and 5-HT release in NAcc above baseline (habituation) values (P<.001) while locomotion and stereotypy were virtually unaffected. In subacute studies, DA release did not differ from baseline (P>.05), whereas 5-HT release was significantly increased above baseline (P<.001). Locomotion increased over baseline but not to a significant degree, while stereotypy was significantly increased above baseline (P<.05). (2) Acute administration of cocaine (10 mg/kg ip) significantly increased both DA and 5-HT release above baseline (P<.001), while locomotion and stereotypy were significantly increased over baseline (P<.001). In subacute studies, DA decreased significantly below baseline (P<.001) and significant decreases in 5-HT release occurred at 15, 20, 50 and 55 min (P<.05). Behavior increased above baseline but did not reach a statistically significant degree. (3) Acute administration of risperidone/cocaine (2 mg/kg sc and 10 mg/kg ip, respectively) showed a significant block of the cocaine-induced increase in DA release in the first hour (P<.001) and 5-HT release in both hours of study (P<.001). Cocaine-induced locomotion and stereotypy were blocked simultaneously with the monoamines (P<.001). In subacute studies, DA and 5-HT release returned to baseline while locomotion and stereotypy increased insignificantly above baseline. Thus, (a) these studies were able to tease out pharmacologically the critical differences between presynaptic and postsynaptic responses to drug treatment(s) and these differences may lead to more effective therapies for schizophrenic and/or cocaine psychosis. (b) Taken together with other data, these acute studies suggest that risperidone may possibly act via inhibition of presynaptic autoreceptors to produce the observed increases in accumbens DA and 5-HT release, whereas cocaine may be acting at least in part via serotoninergic modulation of DA postsynaptically. The subacute data suggest that pharmacokinetics may play a role in risperidone's action and that neuroadaptation may play a role in the mechanism of action of cocaine. Finally, the ability of risperidone to block cocaine-induced psychostimulant neurochemistry and behavior during acute studies while diminishing the withdrawal symptoms of cocaine during subacute studies suggests that risperidone may be a viable pharmacotherapy for cocaine psychosis and withdrawal.

The "two-headed" latent inhibition model of schizophrenia: modeling positive and negative symptoms and their treatment

RATIONALE

Latent inhibition (LI), namely, poorer performance on a learning task involving a previously pre-exposed non-reinforced stimulus, is disrupted in the rat by the dopamine (DA) releaser amphetamine which produces and exacerbates psychotic (positive) symptoms, and this is reversed by treatment with typical and atypical antipsychotic drugs (APDs) which on their own potentiate LI. These phenomena are paralleled by disrupted LI in normal amphetamine-treated humans, in high schizotypal humans, and in schizophrenia patients in the acute stages of the disorder, as well as by potentiated LI in normal humans treated with APDs. Consequently, disrupted LI is considered to provide an animal model of positive symptoms of schizophrenia with face, construct and predictive validity.

OBJECTIVES

To review most of the rodent data on the neural substrates of LI as well as on the effects of APDs on this phenomenon with an attempt to interpret and integrate these data within the framework of the switching model of LI; to show that there are two distinct LI models, disrupted and abnormally persistent LI; to relate these findings to the clinical condition.

RESULTS

The nucleus accumbens (NAC) and its DA innervation form a crucial component of the neural circuitry of LI, and are involved at the conditioning stage. There is a clear functional differentiation between the NAC shell and core subregions whereby damage to the shell disrupts LI and damage to the core renders LI abnormally persistent under conditions that disrupt LI in normal rats. The effects of shell and core lesions parallel those produced by lesions to the major sources of input to the NAC: entorhinal cortex lesion, like shell lesion, disrupts LI, whereas hippocampal lesion, like core lesion, produces persistent LI with changes in context, and basolateral amygdala (BLA) lesion, like core lesion, produces persistent LI with extended conditioning. Systemically induced blockade of glutamatergic as well as DA transmission produce persistent LI via effects exerted at the conditioning stage, whereas enhancement of DA transmission disrupts LI via effects at the conditioning stage. Serotonergic manipulations can disrupt or potentiate LI via effects at the pre-exposure stage. Both typical and atypical APDs potentiate LI via effects at conditioning whereas atypical APDs in addition disrupt LI via effects at pre-exposure. Schizophrenia patients can exhibit disrupted or normal LI as a function of the state of the disorder (acute versus chronic), as well as persistent LI.

CONCLUSIONS

Different drug and lesion manipulations produce two poles of abnormality in LI, namely, disrupted LI under conditions which lead to LI in normal rats, and abnormally persistent LI under conditions which disrupt it in normal rats. Disrupted and persistent LI are differentially responsive to APDs, with the former reversed by both typical and atypical APDs and the latter selectively reversed by atypical APDs. It is suggested that this "two-headed LI model" mimics two extremes of deficient cognitive switching seen in schizophrenia, excessive and retarded switching between associations, mediated by dysfunction of different brain circuitries, and can serve to model positive symptoms of schizophrenia and typical antipsychotic action, as well as negative symptoms of schizophrenia and atypical antipsychotic action.

Effects of clozapine on the efflux of serotonin and dopamine in the rat brain: the role of 5-HT1A receptors

In vivo microdialysis in conscious rats was used to examine the effect of clozapine on serotonin (5-hydroxytryptamine, 5-HT) efflux in the prefrontal cortex and dorsal raphe nucleus and dopamine efflux in the prefrontal cortex. Both systemic and local administration of clozapine (systemic, 10 or 20 mg/kg, i.p.; local, 100 microM) increased 5-HT efflux in the dorsal raphe. However, in the prefrontal cortex, dialysate 5-HT increased when clozapine (100 microM) was administered through the probe, while no effect was observed when it was administered systemically. By pretreatment with the selective 5-HT1A receptor antagonist p-MPPI (3 mg/kg, i.p.), systemic treatment of clozapine (10 mg/kg, i.p.) significantly increased 5-HT efflux in the prefrontal cortex. This result suggests that the ability of clozapine to enhance the extracellular concentrations of 5-HT in the dorsal raphe attenuates this drug's effect in the frontal cortex, probably through the stimulation of 5-HT1A somatodendritic autoreceptors in the dorsal raphe. We also found that pretreatment with p-MPPI (3 mg/kg, i.p.) attenuated by 45% the rise in cortical dopamine levels induced by clozapine (10 mg/kg, i.p.). These findings imply that the reduction in serotonergic input from the dorsal raphe nucleus induced by clozapine could lead to an increase in dopamine release in the prefrontal cortex.

Reciprocal autoreceptor and heteroreceptor control of serotonergic, dopaminergic and noradrenergic transmission in the frontal cortex: relevance to the actions of antidepressant agents

The frontal cortex (FCX) plays a key role in processes that control mood, cognition and motor behaviour, functions which are compromised in depression, schizophrenia and other psychiatric disorders. In this regard, there is considerable evidence that a perturbation of monoaminergic input to the FCX is involved in the pathogenesis of these states. Correspondingly, the modulation of monoaminergic transmission in the FCX and other corticolimbic structures plays an important role in the actions of antipsychotic and antidepressant agents. In order to further understand the significance of monoaminergic systems in psychiatric disorders and their treatment, it is essential to characterize mechanisms underlying their modulation. Within this framework, the present commentary focuses on our electrophysiological and dialysis analyses of the complex and reciprocal pattern of auto- and heteroreceptor mediated control of dopaminergic, noradrenergic and serotonergic transmission in the FCX. The delineation of such interactions provides a framework for an interpretation of the influence of diverse classes of antidepressant agent upon extracellular levels of dopamine, noradrenaline and serotonin in FCX. Moreover, it also generates important insights into strategies for the potential improvement in the therapeutic profiles of antidepressant agents.

Mirtazapine enhances frontocortical dopaminergic and corticolimbic adrenergic, but not serotonergic, transmission by blockade of alpha2-adrenergic and serotonin2C receptors: a comparison with citalopram

Mirtazapine displayed marked affinity for cloned, human alpha2A-adrenergic (AR) receptors at which it blocked noradrenaline (NA)-induced stimulation of guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]-GTPgammaS) binding. Similarly, mirtazapine showed high affinity for cloned, human serotonin (5-HT)2C receptors at which it abolished 5-HT-induced phosphoinositide generation. Alpha2-AR antagonist properties were revealed in vivo by blockade of UK-14,304-induced antinociception, while antagonist actions at 5-HT2C receptors were demonstrated by blockade of Ro 60 0175-induced penile erections and discriminative stimulus properties. Mirtazapine showed negligible affinity for 5-HT reuptake sites, in contrast to the selective 5-HT reuptake inhibitor, citalopram. In freely moving rats, in the dorsal hippocampus, frontal cortex (FCX), nucleus accumbens and striatum, citalopram increased dialysate levels of 5-HT, but not dopamine (DA) and NA. On the contrary, mirtazapine markedly elevated dialysate levels of NA and, in FCX, DA, whereas 5-HT was not affected. Citalopram inhibited the firing rate of serotonergic neurons in dorsal raphe nucleus, but not of dopaminergic neurons in the ventral tegmental area, nor adrenergic neurons in the locus coeruleus. Mirtazapine, in contrast, enhanced the firing rate of dopaminergic and adrenergic, but not serotonergic, neurons. Following 2 weeks administration, the facilitatory influence of mirtazapine upon dialysate levels of DA and NA versus 5-HT in FCX was maintained, and the influence of citalopram upon FCX levels of 5-HT versus DA and NA was also unchanged. Moreover, citalopram still inhibited, and mirtazapine still failed to influence, dorsal raphe serotonergic neurons. In conclusion, in contrast to citalopram, mirtazapine reinforces frontocortical dopaminergic and corticolimbic adrenergic, but not serotonergic, transmission. These actions reflect antagonist properties at alpha2A-AR and 5-HT2C receptors.

Reboxetine attenuates forced swim test-induced behavioural and neurochemical alterations in the rat

The forced swim test is a behavioural paradigm that is predicative of antidepressant activity in rodents. Until recently, research has focused on the ability of antidepressant drugs to decrease immobility in the forced swim test paradigm, but the neurochemical sequelae induced by swim stress, or the neurochemical basis of antidepressant-induced behavioural changes have received little attention. In this regard, we have recently demonstrated that forced swim test exposure increases serotonergic activity in the amygdala, frontal cortex and hippocampus and dopamine turnover in the striatum. In addition, forced swim test-exposure activates the hypothalamic pituitary adrenal axis. The purpose of the present study was to examine the effect of treatment with the selective noradrenaline reuptake inhibitor reboxetine (3, 10 and 30 mg/kg; i.p.) on immobility and defaecation scores in the forced swim test, and on forced swim test-induced neurochemical and hypothalamic pituitary adrenal axis changes in the rat. Reboxetine treatment (10 and 30 mg/kg) significantly decreased immobility and defaecation in the forced swim test in dose dependent manner. Furthermore, reboxetine produced a dose dependent attenuation of forced swim test-induced increases in serotonin turnover in the amygdala and frontal cortex and dopamine turnover in the striatum. Reboxetine (30 mg/kg) produced a modest, but non-significant, attenuation of forced swim test-induced increases in serum corticosterone concentrations. These data demonstrate that, in addition to the behavioural activity of reboxetine in the rat forced swim test paradigm, a dose-dependent attenuation of swim stress-induced increases in serotonergic and dopaminergic activity occurred in a region specific manner. These are the first data to demonstrate that treatment with the selective noradrenaline reuptake inhibitor, reboxetine can impact on the activity of other neurotransmitter systems in response to stress. Moreover, these data further demonstrate that this paradigm is a valuable tool in studying the effect of antidepressants, on both behaviour and swim stress-related alterations in central neurotransmitter function and hypothalamic pituitary adrenal axis activity in the rat.