Pharmacokinetics and bioavailability after intramuscular injection of the 5-HT1A serotonin agonist R-8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) in domestic goats (Capra aegagrus hircus).

To determine the bioavailability and pharmacokinetic properties of the serotonin 5-HT1A receptor agonist R-8-OH-DPAT in goats, and 0.1 mg kg-1 R-8-OH-DPAT hydrobromide was administered intramuscularly (i.m.) and intravenously (i.v.) to six goats in a two-phase cross-over design experiment. Venous blood samples were collected from the jugular vein 2, 5, 10, 15, 20, 30, 40 and 60 min following treatment and analysed by liquid chromatography tandem mass spectrometry. Bioavailability and pharmacokinetic parameters were determined by a one-compartment analysis. Mean bioavailability of R-8-OH-DPAT when injected i.m. was 66%. The mean volume of distribution in the central compartment was 1.47 L kg-1 . The mean plasma body clearance was 0.056 L kg-1  min-1 . All goats injected i.v. and two of six goats injected i.m. showed signs of serotonin toxicity. In conclusion, R-8-OH-DPAT is well absorbed following i.m. injection and the observed pharmacokinetics suggest that administration via dart is feasible. Administration of R-8-OH-DPAT hydrobromide, at a dosage of 0.1 mg kg-1 , resulted in the observation of clinical signs of serotonin toxicity in the goats. It is suggested that dosages for the clinical use of the compound should be lower in order to achieve the desired clinical effect without causing serotonin toxicity.

Vortioxetine dose-dependently reverses 5-HT depletion-induced deficits in spatial working and object recognition memory: a potential role for 5-HT1A receptor agonism and 5-HT3 receptor antagonism.

We previously reported that the investigational multimodal antidepressant, vortioxetine, reversed 5-HT depletion-induced memory deficits while escitalopram and duloxetine did not. The present report studied the effects of vortioxetine and the potential impact of its 5-HT1A receptor agonist and 5-HT3 receptor antagonist properties on 5-HT depletion-induced memory deficits. Recognition and spatial working memory were assessed in the object recognition (OR) and Y-maze spontaneous alternation (SA) tests, respectively. 5-HT depletion was induced in female Long-Evans rats using 4-cholro-DL-phenylalanine methyl ester HCl (PCPA) and receptor occupancies were determined by ex vivo autoradiography. Rats were acutely dosed with vortioxetine, ondansetron (5-HT3 receptor antagonist) or flesinoxan (5-HT1A receptor agonist). The effects of chronic vortioxetine administration on 5-HT depletion-induced memory deficits were also assessed. 5-HT depletion reliably impaired memory performance in both the tests. Vortioxetine reversed PCPA-induced memory deficits dose-dependently with a minimal effective dose (MED) ≤0.1mg/kg (∼80% 5-HT3 receptor occupancy; OR) and ≤3.0mg/kg (5-HT1A, 5-HT1B, 5-HT3 receptor occupancy: ∼15%, 60%, 95%) in SA. Ondansetron exhibited a MED ≤3.0µg/kg (∼25% 5-HT3 receptor occupancy; OR), but was inactive in the SA test. Flesinoxan had a MED ≤1.0mg/kg (∼25% 5-HT1A receptor occupancy; SA); only 1.0mg/kg ameliorated deficits in the NOR. Chronic p.o. vortioxetine administration significantly improved memory performance in OR and occupied 95%, 66%, and 9.5% of 5-HT3, 5-HT1B, and 5-HT1A receptors, respectively. Vortioxetine's effects on SA performance may involve 5-HT1A receptor agonism, but not 5-HT3 receptor antagonism, whereas the effects on OR performance may involve 5-HT3 receptor antagonism and 5-HT1A receptor agonism.

Anxiolytic effects of Julibroside C1 isolated from Albizzia julibrissin in mice.

Julibroside C1 is a saponin-containing compound isolated from Albizzia julibrissin Durazz. In this study, we investigated the putative anxiolytic effects of Julibroside C1 using the elevated plus maze (EPM) in mice. Julibroside C1 at doses of 0.5 and 1 mg/kg significantly increased the time spent in the open arms and the number of entries into the open arms of the EPM compared to the control group. Moreover, the anxiolytic-like effects of Julibroside C1 (0.5 mg/kg) were blocked by WAY-100635 (5-HT1A receptor antagonist), bicuculline (GABA(A) receptor antagonist), and flumazenil (antagonist of the GABA(A) receptor benzodiazepine site). However, Julibroside C1 did not change locomotor activity or induce myorelaxant effects. We used quantitative receptor autoradiography to investigate the effects of Julibroside C1 on alterations in mouse brain receptors. After acute treatment with Julibroside C1 (0.5 mg/kg), [(3)H]-8-OH-DPAT binding was significantly decreased in the CA1 region of the hippocampus and [(3)H]-flunitrazepam binding was decreased remarkably in the cingulate cortex region. However, [(3)H]-muscimol binding did not show a significant change in any brain region. Taken together, our findings suggest that Julibroside C1 shows anxiolytic-like effects, which might be mediated by the 5-HT1A and GABA(A)-benzodiazepine receptor systems.

Neuron density and serotonin receptor binding in prefrontal cortex in suicide.

Although serotonin receptor and cytoarchitectonic alterations are reported in prefrontal cortex (PFC) in suicide and depression, no study has considered binding relative to neuron density. Therefore, we measured neuron density and serotonin transporter (SERT), 5-HT1A and 5-HT2A binding in matched suicides and controls. Suicides and normal controls (n=15 matched pairs) were psychiatrically characterized. Neuron density and binding were determined in dorsal [Brodmann area (BA) 9] and ventral (BA 47) PFC by stereology and quantitative autoradiography in near-adjacent sections. Binding index was defined as the ratio of receptor binding to neuron density. Suicides had lower neuron density in the gyrus of both areas. The binding index was lower for SERT in BA 47 but not in BA9; the 5-HT1A binding index was higher in BA 9 but not in BA 47, while the 5-HT2A binding index was not different between groups. SERT binding was lower in suicides in BA 47 but not BA 9, while 5-HT1A binding was higher in BA 9 but not BA 47. SERT binding negatively correlated with 5-HT1A binding in BA 47 in suicides. Neuron density decreased with age. The 5-HT1A binding index was higher in females than males. We found lower neuron density and lower SERT binding index in both PFC regions in suicides. More 5-HT1A binding with less SERT binding and the negative correlation in depressed suicides suggests post-synaptic receptor up-regulation, and it is independent of the difference in neuron density. Thus, abnormalities in both cortical neurons and in their serotonergic innervation are present in suicides and future studies will need to determine whether cortical changes reflect the trophic effect of altered serotonin innervation.

Serotonin 5-HT(1A) receptor binding sites in the brain of the pigeon (Columba livia).

Present knowledge about the serotonergic system in birdbrains is very limited, although the pigeon was used as an animal model in various studies focused on the behavioral effects of serotonergic transmission. In the mammalian brain the 5-HT(1A) receptor is the most widespread serotonin receptor type, and is involved in various functions. Less is known about the distribution of 5-HT(1A) receptors in the avian species. Therefore, we analyzed serotonin 5-HT(1A) receptor binding sites in the pigeon brain using quantitative in vitro receptor autoradiography with the selective radioligand [³H]-8-hydroxy-2-(di-n-propylamino)tetralin ([³H]-8-OH-DPAT). The receptor is differentially distributed throughout the pigeon brain. High levels of 5-HT(1A) receptors are found in the nucleus pretectalis (PT). Moderate densities were detected in the tectum, as well as in the telencephalic nidopallium and hyperpallium. Very low levels were found in the hippocampal formation, the amygdaloid complex, the basal ganglia, and several thalamic nuclei. Furthermore, local variations in 5-HT(1A) receptor densities support the concept of further subdivisions of the entopallium. The regional distribution patterns of 5-HT(1A) receptors mostly display a similar distribution as found in homologue brain structures of mammals.

The pharmacokinetics and pharmacological effect of (S)-5-OH-DPAT following controlled delivery with transdermal iontophoresis.

The pharmacokinetic (PK) and pharmacodynamic (PD) properties of the active (S)-enantiomer of the potent dopamine (DA) agonist 5-hydroxy-2-(N,N,-di-n-propylamino)tetralin (5-OH-DPAT) were investigated in a novel anesthetized animal model. First, the relationship between current density, in vivo transport, and plasma profile was characterized. Second, the effect of the anesthetic mixture, transdermal iontophoresis, and blood sampling on the striatal DA release (PD end point) was investigated. Third, the PK-PD relationship following transdermal iontophoresis was investigated during a controlled reversible pharmacological response. Given that striatal DA levels are unaltered during experimental procedures, this rat model can be used to investigate the PK-PD relationship. The in vivo flux was linearly correlated with the current density, indicating that drug delivery can be titrated by the current density. Following transdermal iontophoresis and intravenous infusion, a strong reversible effect was observed. Compartmental modeling showed that the relationship between plasma concentration and biomarker response is best characterized by an effect compartment, rather than an indirect response model. In addition, covariate analysis suggested that the delivery rate can affect the PD efficiency. Finally, PK-PD analysis revealed that steady delivery rates are translated into continuous dopaminergic stimulation. This can be of benefit for reducing side effects in the symptomatic treatment of Parkinson's disease with 5-OH-DPAT.

The in vitro and in vivo evaluation of new synthesized prodrugs of 5-OH-DPAT for iontophoretic delivery.

The feasibility of transdermal iontophoretic transport of 4 novel ester prodrugs of 5-OH-DPAT (glycine-, proline-, valine- and beta-alanine-5-OH-DPAT) was investigated in vitro and in vivo. Based on the chemical stability of the prodrugs, the best candidates were selected for in vitro transport studies across human skin. The pharmacokinetics and pharmacodynamic effects of the prodrug with highest transport efficiency, were investigated in a rat model. The in vitro transport, plasma profile and pharmacological response were analyzed with compartmental modeling. Valine- and beta-alanine-5-OH-DPAT were acceptably stable in the donor phase and showed a 4-fold and 14-fold increase in solubility compared to 5-OH-DPAT. Compared to 5-OH-DPAT, valine- and beta-alanine-5-OH-DPAT were transported less and more efficiently across human skin, respectively. Despite a higher in vitro transport, lower plasma concentration was observed following 1.5h current application (250 microAcm(2)) of beta-alanine-S-5-OH-DPAT in comparison to S-5-OH-DPAT. However the prodrug showed higher plasma concentrations post-iontophoresis, explained by a delayed release due to hydrolysis and skin depot formation. This resulted in a pharmacological effect with the same maximum as 5-OH-DPAT, but the effect lasted for a longer time. The current findings suggest that beta-alanine-5-OH-DPAT is a promising prodrug, with a good balance between stability, transport efficiency and enzymatic conversion.

Mechanistic studies of the transdermal iontophoretic delivery of 5-OH-DPAT in vitro.

A characterization and optimization of the in vitro transdermal iontophoretic transport of 5-hydroxy-2-(N,N,-di-n-propylamino)tetralin (5-OH-DPAT) is presented. The utility of acetaminophen as a marker of electroosmotic flow was studied as well. The following parameters of iontophoretic transport of 5-OH-DPAT were examined: drug donor concentration, electroosmotic contribution, influence of co-ions, current density, and composition of the acceptor phase. The steady-state flux (Flux(ss)) of acetaminophen was linearly correlated with the donor concentration and co-iontophoresis of acetaminophen did not influence the iontophoretic flux of 5-OH-DPAT, indicating that acetaminophen is an excellent marker of electroosmotic flow. Lowering the Na(+) concentration from 78 to 10 mM in the donor phase, resulted in a 2.5-fold enhancement of the Flux(ss). The Flux(ss) showed a nonlinear relation with the drug donor concentration and an excellent linear correlation with the current density. Reducing the pH of the acceptor phase from 7.4 to 6.2 resulted in a dramatic decrease of the Flux(ss) of 5-OH-DPAT, explained by a reduced electroosmotic flow and an increased counter-ion flow. Optimization of the conditions resulted in a maximum Flux(ss) of 5-OH-DPAT of 1.0 micromol x cm(-2) h(-1) demonstrating the potential of the iontophoretic delivery of this dopamine agonist for the symptomatic treatment of Parkinson's disease.

L-stepholidine reduced L-DOPA-induced dyskinesia in 6-OHDA-lesioned rat model of Parkinson's disease.

L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia (LID) remains a challenge in Parkinson's disease (PD) drug therapy. In the present study, we examined the effect of L-stepholidine (L-SPD), a known dual dopamine receptor agent, on LID in 6-hydroxydopamine (6-OHDA)-lesioned PD rat model. Daily administration of L-DOPA to PD rats for 22 days induced steady expression of LID, co-administration of L-SPD with L-DOPA significantly ameliorated LID without compromising the therapeutic potency of L-DOPA, indicating that L-SPD attenuated LID development. L-SPD alone elicited stable contralateral rotational behavior without inducing significant dyskinesia. Acute administration of L-SPD to rats with established LID produced significant relief of dyskinesia; this effect was mimicked by D(2) receptor antagonist haloperidol, but blunted by 5-HT(1A) receptor antagonist WAY100635. Furthermore, the mRNA level of 5-HT(1A) decreased significantly on 6-OHDA-lesioned striata, whereas chronic L-SPD treatment restored 5-HT(1A) receptor mRNA level on the lesioned striata. The present data demonstrated that L-SPD elicited antidyskinesia effects via both dopamine (D(2) receptor antagonistic activity) and nondopamine (5-HT(1A) agonistic activity) mechanisms.

Cortical serotonin 1A receptor levels are associated with depression in patients with dementia with Lewy bodies and Parkinson's disease dementia.

BACKGROUND: Serotonin 1A receptors (5-HT(1A)) have not been studied in dementia with Lewy bodies (DLB) or Parkinson's disease dementia (PDD) patients with depression. AIM: To examine 5-HT(1A) in DLB and PDD postmortem in relation to depression. METHODS: [(3)H]8-hydroxy-2-dipropylaminotetralin binding to 5-HT(1A) was determined in temporal cortex (Brodmann areas, BA20 and BA36) from 10 DLB patients, 17 PDD patients and 9 controls. RESULTS: 5-HT(1A) density was significantly higher in BA36 in combined DLB/PDD patients with depression, but was unaltered in BA20. CONCLUSION: Higher BA36 5-HT(1A) density in PDD and DLB patients than in control is dependent on whether the patient had experienced depression during life, not DLB/PDD diagnosis. A 5-HT(1A) antagonist adjuvant may improve treatment of depression in dementia.

WAY100635 prevents the changes induced by fluoxetine upon the 5-HT1A receptor functionality.

5-HT1A receptor-mediated signalling in rat brain was evaluated after chronic administration (14 days; s.c.) of the selective serotonin reuptake inhibitor (SRRI) fluoxetine (10 mg/kg/day) alone, or in combination with the 5-HT1A receptor antagonist WAY100635 (0.1 mg/kg/day). The density of 5-HT1A binding sites was unchanged following fluoxetine, WAY100635, or the combination of fluoxetine and WAY100635. However, the net stimulation of [35S]GTPgammaS binding induced by the 5-HT1A agonist 8-OH-DPAT was significantly attenuated in dorsal raphe nucleus (DRN), but not in hippocampus, after chronic fluoxetine. Moreover, depending of the area analysed, the basal binding of [35S]GTPgammaS was differentially affected by this treatment: increased in DRN and decreased in hippocampal dentate gyrus. Interestingly, the changes in [35S]GTPgammaS basal binding and on 5-HT1A receptors functionality were prevented by the concomitant administration of WAY100635. The inhibition of dorsal raphe firing by 8-OH-DPAT was also attenuated in fluoxetine-treated rats (ED50 = 2.12 +/- 0.32 microg/kg and 4.34 +/- 0.09 microg/kg, for vehicle and fluoxetine respectively), an effect which was also prevented by the concomitant administration of WAY100635 (ED50 = 2.10 +/- 0.58 microg/kg). Chronic administration of WAY100635 alone did not affect the 5-HT1A receptor-induced stimulation of [35S]GTPgammaS binding, nor the 8-OH-DPAT-induced inhibition of 5-HT neuron firing. These results demonstrate that the concomitant blockade of 5-HT1A receptors when administering fluoxetine prevents those adaptive changes of 5-HT1A receptor function associated with the chronic administration of this antidepressant. These findings could be relevant from the therapeutic point of view, and further support the potential benefit of treatments with a SSRI/5-HT1A receptor antagonist combination.

Serotonin-1A autoreceptor binding in the dorsal raphe nucleus of depressed suicides.

Serotonergic dysfunction is present in mood disorders and suicide. Brainstem 5-HT1A somatodendritic autoreceptors regulate serotonin neuron firing but studies of autoreceptor binding in the dorsal raphe nucleus (DRN) in depressed suicides report conflicting results. We sought to determine: (1) the anatomical distribution of 5-HT1A receptor binding in the DRN in depressed suicides and psychiatrically normal controls; and (2) whether sex differences in 5-HT1A binding in the DRN contribute to differences between depressed suicides and controls. Previously collected quantitative receptor autoradiograms of [3H]8-hydroxy-2-(di-n-propyl)aminotetralin (3H-8-OH-DPAT) in postmortem tissue sections containing the DRN from drug-free suicide victims (n=10) and matched controls (n=10) were analyzed. Less total receptor binding (fmol/mg tissuexmm3) was observed in the entire DRN in depressed suicides compared with controls (p<0.05). Group differences along the rostrocaudal extent of the DRN were observed for cross-sectional 5-HT(1A) binding (fmol/mg tissue) and receptor binding (fmol/mgxmm3, p<0.05). Cross-sectional 5-HT1A DRN binding in depressed suicides compared with controls was higher rostrally and lower caudally. The differences between depressed suicides and controls were present in males and females, although females had more binding than males. Less autoreceptor binding in the DRN of depressed suicides may represent a homeostatic response to less serotonin release, increasing serotonin neuron firing. More autoreceptor binding in rostral DRN might contribute to deficient serotonin release in ventromedial prefrontal cortex by lower neuronal firing.

Serotonin-caused phase shift of circadian rhythmicity in a photosensitive neuron.

In the sixth abdominal ganglion (sixth AG) of the crayfish, two photosensitive neurons are located and have been identified as caudal photoreceptors (CPRs). We have expanded our investigation on the role of 5-Hydroxytryptamine (5-HT) as a modulator of the spontaneous and light-induced activity of the CPR. We located, by using immunocytochemistry, neurons in the sixth AG that contain the 5HT1A receptor. The expression of these receptors was examined by binding assays with [3H] 8-hydroxy-2 (di-n-propylamino) tetralin ([3H(8-OH-DPAT). We examined the exogenous action of both 5HT and its agonist 8-OH-DPAT on the phase of circadian rhythms of the spontaneous electrical activity and the photoresponse of the CPR in the isolated sixth AG by conventional extracellular recording methods. Experiments were made on the adult crayfish Procambarus clarkii and Cherax quadricarinatus. Thirteen immunopositive neurons were located, principally near the ventral and dorsal surface of the sixth AG, with the mean diameter of their somata 20+/-3 microm. The specific binding data showed the presence of 5-HT1A receptors with a mean level of 22.4+/-6.6 fmol/mg of wet tissue. Spontaneous and light-induced electrical activity of the CPR showed circadian variations with their activity more intense at night than in the day. Exogenous application of 5-HT or 8-OH-DPAT causes a circadian phase-shift in electrical activity of the CPR. Taken together, these results lead us to believe the 5-HT acts as a modulator of circadian electrical activity of the CPR in the isolated sixth AG of crayfish. Moreover, it suggests that the 5-HT1A receptor participates in this modulation.

WAY-100635 antagonist-induced plasticity of 5-HT receptors: regulatory differences between a stable cell line and an in vivo native system.

We present evidence that the 5-hydroxytryptamine(1A) (5-HT(1A)) receptor antagonist, N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl}-N-(2-pyridinyl)cyclohexanecarboxamide (WAY-100635), can induce receptor internalization in a human (h)5-HT(1A) receptor Chinese hamster ovary (CHO-K1) cell system. Exposure of h5-HT(1A) CHO cells to WAY-100635 decreased the cell-surface h5-HT(1A) receptor density in a way that was both time (24-72 h) and concentration (1-100 nm) dependent.[(3)H]WAY-100635 and [(3)H]8-hydroxy-dipropylaminotetralin ([(3)H]8-OH-DPAT) saturation analyses demonstrated a significant reduction (50-60%) in total h5-HT(1A) receptor number in the WAY-100635-treated (100 nm; 72 h) compared with control cells. In WAY-100635-treated cells, the 8-OH-DPAT-mediated inhibition of forskolin (FSK)-stimulated cAMP accumulation was right-shifted and the maximal inhibitory response of 8-OH-DPAT was impaired compared with control cells. Similar results were obtained for 8-OH-DPAT-mediated Ca(2+) mobilization after WAY-100635 treatment. h5-HT(1A) receptors labeled with [(3)H]WAY-100635, as well as [(3)H]4-(2'-Methoxy)-phenyl-1-[2'-(N-2''-pyridinyl)-p-fluorobenzamido]ethyl-piperazine (MPPF), exhibited a time-dependent rate of cellular internalization that was blocked by endocytotic suppressors and was pertussis-toxin insensitive. In contrast, quantitative autoradiographic studies demonstrated that chronic treatment of rats with WAY-100635 for two weeks produced a region-specific increase in the 5-HT(1A) receptor density. In conclusion, prolonged exposure of an h5-HT(1A) cell-based system to the 5-HT(1A) antagonist, WAY-100635, induced a paradoxical internalization of cell surface receptor resulting in depressed functional activity. This suggests that an antagonist can influence 5-HT(1A) receptor recycling in vitro differently to in vivo regulatory conditions.

Pharmacokinetics and pharmacodynamics analysis of transdermal iontophoresis of 5-OH-DPAT in rats: in vitro-in vivo correlation.

Pharmacokinetics and dopaminergic effect of dopamine agonist 5-OH-DPAT in vivo were determined following transdermal iontophoresis in rats based on drug concentration in plasma (C(p)) and dopamine levels in striatum (C(DA)). Correlation of the in vitro transport with the pharmacokinetic-pharmacodynamic (PK-PD) profiles was characterized in the transport in dermatomed rat skin (DRS) and rat stratum corneum (RSC). The integrated in vivo PK-PD and in vitro transport models successfully described time course of C(p), C(DA), and in vitro flux in DRS and RSC. Population value of steady-state flux (J(ss)) in vivo (31 nmol/cm(2) . h with 95% confidence interval (CI) = 20-41) is closer to J(ss) in vitro in DRS (61 nmol/cm(2) . h, CI = 54-67) than in vitro J(ss) in RSC (98 nmol/cm(2) . h, CI = 79-117). On the other hand, skin release rate constant (K(R)) in vivo was similar to the K(R) in RSC (4.8/h, CI = 2.4-7.1 vs. 2.6/h, CI = 2.5-2.6). Kinetic lag time (t(L)) in vivo was negligible, which is close to in vitro t(L) in RSC (0.0 h, CI = 0.0-0.1). Based on nonlinear mixed-effect modeling, profiles of C(p) and C(DA) were successfully predicted using in vitro values of J(ss) in DRS with K(R) and t(L) in RSC. A considerable dopaminergic effect was achieved, indicating the feasibility to reach therapeutically effective concentrations of 5-OH-DPAT upon transdermal iontophoresis.

Diurnal rhythm in the levels of the serotonin 5-HT1A receptors in the crayfish eyestalk.

The crayfish eyestalk (ES) has been postulated as a possible circadian clock. 5-Hydroxytryptamine (5-HT) has been shown to play the role of a neurotransmitter or a modulator in the ES. However, little is known about the 5-HT receptors in the ES. The purpose of this work is to determine the specific binding sites using [(3)H]8-hydroxy-2(di-n-propylamino)tetralin ([(3)H]8-OH-DPAT), a specific agonist of the 5-HT(1A) receptor, and to characterize the diurnal rhythm in the binding by an autoradiography procedure in the crayfish ES. Data show the presence of a circadian rhythmicity in the level of the 5-HT(1A) receptors, principally in two regions: (a) the complex retina (R)-lamina ganglionaris (LG), with the acrophase at dusk and (b) the medulla terminalis (MT), where it was in antiphase. It is suggested that (1) the expression of levels of 5-HT(1A) receptors is modulated by light-dark (LD) cycles, (2) the level of 5-HT(1A) receptors in the R-LG and MT are in antiphase during the 24-h cycle, and (3) there is a different mechanism of action of LD cycles in each of these two anatomical regions of the crayfish ES.

Short-term constant light potentiation of large-magnitude circadian phase shifts induced by 8-OH-DPAT: effects on serotonin receptors and gene expression in the hamster suprachiasmatic nucleus.

Nonphotic phase-shifting of mammalian circadian rhythms is thought to be mediated in part by serotonin (5-HT) acting in the suprachiasmatic nucleus (SCN) circadian clock. Previously we showed that brief (1-3 days) exposure to constant light (LL) greatly potentiates nonphotic phase-shifting induced by the 5-HT agonist, (+/-)2-dipropyl-amino-8-hydroxyl-1,2,3,4-tetrahydronapthalene (8-OH-DPAT). Here we investigated potential mechanisms for this action of LL, including 5-HT receptor upregulation and SCN clock gene and neuropeptide gene expression. Autoradiographic analysis of ritanserin inhibition of [3H]8-OH-DPAT binding indicated that LL (approximately 2 days) did not affect 5-HT7 receptor binding in the SCN or dorsal raphe. Measurement of 5-HT1A autoreceptors in the median raphe and 5-HT1B receptors in the SCN also showed no effect of LL. In experiment 2, hamsters held under a 14-h light : 10-h dark photocycle (LD) or exposed to LL for approximately 2 days received an intraperitoneal injection of 8-OH-DPAT or vehicle at zeitgeber time (ZT) 6 or 0 and were killed after 2 h of dark exposure. 8-OH-DPAT suppressed SCN Per1 and Per2 mRNAs at both ZTs, as assessed by in situ hybridization. Per1 mRNA was also suppressed by LL alone. In addition, in situ hybridization of arginine vasopressin (AVP) mRNA and vasoactive intestinal polypeptide mRNA showed that LL significantly suppressed the former but not the latter. The LL-induced suppression of SCN Per1 mRNA and AVP mRNA may be involved in LL-induced potentiation of pacemaker resetting, especially as these data provide additional evidence that LL suppresses circadian pacemaker amplitude, thus rendering the clock more susceptible to phase-shifting stimuli.

Transdermal iontophoresis of the dopamine agonist 5-OH-DPAT in human skin in vitro.

The feasibility of transdermal iontophoretic delivery of a potent dopamine agonist 5-OH-DPAT was studied in vitro in side by side diffusion cells across human stratum corneum (HSC) and dermatomed human skin (DHS) according to the following protocol: 6 h of passive diffusion, 9 h of iontophoresis and 5 h of passive diffusion. The influences of the following parameters on the flux were studied: donor solution pH, NaCl concentration, drug donor concentration, current density and skin type. A current density of 0.5 mA cm(-2) was used, except for one series of experiments to study the current density effect. Probably due to the influence of the skin perm-selectivity and the competition with H(+), increase in pH from 3 to 5 resulted in a significant increase in flux. Further increase in pH to 6 did not further increase the flux. The iontophoretic transport was found to increase linearly with concentration and current density, providing a convenient way to manage dose titration for Parkinson's disease therapy. Increase in concentration of NaCl dramatically reduced the flux of 5-OH-DPAT as a result of ion competition to the transport. When DHS was used, the iontophoretic transport was less. Also, with DHS the response in flux profile, by switching the current on and off, was shallower than that with HSC. With the optimum condition, a delivery of 104 microg of 5-OH-DPAT per cm(2) patch per hour is feasible, indicating that the therapeutic level could be achieved with a smaller patch size than required in case of rotigotine. Thus, based on this in vitro study, transdermal iontophoretic delivery of 5-OH-DPAT is very promising.

Novel antipsychotics activate recombinant human and native rat serotonin 5-HT1A receptors: affinity, efficacy and potential implications for treatment of schizophrenia.

Serotonin 5-HT1A receptors are promising targets in the management of schizophrenia but little information exists about affinity and efficacy of novel antipsychotics at these sites. We addressed this issue by comparing binding affinity at 5-HT1A receptors with dopamine rD2 receptors, which are important targets for antipsychotic drug action. Agonist efficacy at 5-HT1A receptors was determined for G-protein activation and adenylyl cyclase activity. Whereas haloperidol, thioridazine, risperidone and olanzapine did not interact with 5-HT1A receptors, other antipsychotic agents exhibited agonist properties at these sites. E(max) values (% effect induced by 10 microM of 5-HT) for G-protein activation at rat brain 5-HT1A receptors: sarizotan (66.5), bifeprunox (35.9), SSR181507 (25.8), nemonapride (25.7), ziprasidone (20.6), SLV313 (19), aripiprazole (15), tiospirone (8.9). These data were highly correlated with results obtained at recombinant human 5-HT1A receptors in determinations of G-protein activation and inhibition of forskolin-stimulated adenylyl cyclase. In binding-affinity determinations, the antipsychotics exhibited diverse properties at r5-HT1A receptors: sarizotan (pK(i)=8.65), SLV313 (8.64), SSR181507 (8.53), nemonapride (8.35), ziprasidone (8.30), tiospirone (8.22), aripiprazole (7.42), bifeprunox (7.19) and clozapine (6.31). The affinity ratios of the ligands at 5-HT1A vs. D2 receptors also varied widely: ziprasidone, SSR181507 and SLV313 had similar affinities whereas aripiprazole, nemonapride and bifeprunox were more potent at D2 than 5-HT1A receptors. Taken together, these data indicate that aripiprazole has low efficacy and modest affinity at 5-HT1A receptors, whereas bifeprunox has low affinity but high efficacy. In contrast, SSR181507 has intermediate efficacy but high affinity, and is likely to have more prominent 5-HT1A receptor agonist properties. Thus, the contribution of 5-HT1A receptor activation to the pharmacological profile of action of the antipsychotics will depend on the relative 5-HT1A/D2 affinities and on 5-HT1A agonist efficacy of the drugs.

Differential effects of intra-midbrain raphe and systemic 8-OH-DPAT on VTA self-stimulation thresholds in rats.

RATIONALE: Intra-median raphe nucleus (MRN) administration of the 5-HT(1A) receptor agonist 8-OH-DPAT decreases lateral hypothalamic self-stimulation thresholds and is reported to have biphasic effects following systemic administration. These experiments attempted to extend the previous findings to mesolimbic pathway self-stimulation at ventral tegmental area (VTA) electrodes. OBJECTIVES: This study was conducted to provide comparative data for systemic and intra-dorsal raphe nucleus (DRN) and intra-MRN effects of 8-OH-DPAT on VTA self-stimulation. METHODS: Male Sprague-Dawley rats with VTA electrodes were trained to respond for electrical stimulation. Systemic and intra-midbrain raphe 8-OH-DPAT effects on rate-frequency thresholds were measured. Systemic administration of WAY 100635 was used to confirm 5-HT(1A) receptor mediation of 8-OH-DPAT effects. RESULTS: 8-OH-DPAT (0.003-0.3 mg kg(-1) SC) increased rate-frequency thresholds and decreased maximal response rates. WAY 100635 alone (0.0125-0.1 mg kg(-1) SC) did not alter these measures. Intra-DRN and intra-MRN 8-OH-DPAT (5.0 microg) decreased rate-frequency thresholds without altering maximal response rates. Intra-DRN 8-OH-DPAT (0.1-5.0 microg) induced a slight decrease and intra-MRN 8-OH-DPAT a slight increase in locomotor activity. WAY 100635 (0.1 mg kg(-1)) blocked effects of 8-OH-DPAT on VTA self-stimulation. CONCLUSION: These results confirm threshold-decreasing effects of intra-MRN 8-OH-DPAT and extend this to the DRN and to VTA thresholds. Monophasic dose dependent increases in VTA thresholds following systemic 8-OH-DPAT are not equivalent to reports for hypothalamic self-stimulation. Differences between studies may be attributable to stimulation site and/or differences in threshold measurement procedures. Effects of WAY 100635 in this study indicate 5-HT(1A) receptor mediation of these 8-OH-DPAT effects.