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Here we describe for the first time the distinctive pharmacological profile for (3S)-3-(2,3-difluorophenyl)-3-methoxypyrrolidine (IRL752), a new phenyl-pyrrolidine derivative with regioselective central nervous system transmission-enhancing properties. IRL752 (3.7-150 µmol/kg, s.c.) was characterized through extensive in vivo studies using behavioral, tissue neurochemical, and gene expression as well as microdialysis methods. Behaviorally, the compound normalized tetrabenazine-induced hypoactivity, whereas it was unable to stimulate basal locomotion in normal animals or either accentuate or reverse hyperactivity induced by amphetamine or MK-801. IRL752 induced but minor changes in monoaminergic tissue neurochemistry across noradrenaline (NA)- and dopamine (DA)-dominated brain regions. The expression of neuronal activity-, plasticity-, and cognition-related immediate early genes (IEGs), however, increased by 1.5-fold to 2-fold. Furthermore, IRL752 dose-dependently enhanced cortical catecholamine dialysate output to 600%-750% above baseline, whereas striatal DA remained unaltered, and NA rose to ∼250%; cortical and hippocampal dialysate acetylcholine (ACh) increased to ∼250% and 190% above corresponding baseline, respectively. In line with this cortically preferential transmission-promoting action, the drug was also procognitive in the novel object recognition and reversal learning tests. In vitro neurotarget affinity and functional data coupled to drug exposure support the hypothesis that 5-hydroxytryptamine 7 receptor and α2(C)-adrenoceptor antagonism are key contributors to the in vivo efficacy and original profile of IRL752. The cortical-preferring facilitatory impact on catecholamine (and ACh) neurotransmission, along with effects on IEG expression and cognition-enhancing features, are in line with the potential clinical usefulness of IRL752 in conditions wherein these aspects may be dysregulated, such as in axial motor and cognitive deficits in Parkinson disease. SIGNIFICANCE STATEMENT: This report describes the distinctive preclinical profile of (3S)-3-(2,3-difluorophenyl)-3-methoxypyrrolidine (IRL752). Its in vivo neurochemical, behavioral, microdialysis, and gene expression properties are consistent with a cortically regioselective facilitatory impact on catecholaminergic and cholinergic neurotransmission accompanied by cognitive impairment-reversing features. The pharmacological characteristics of IRL752 are in line with the clinical usefulness of IRL752 in conditions wherein these aspects may be dysregulated, such as in axial motor and cognitive deficits in Parkinson disease.

IRL790 ([2-(3-fluoro-5-methanesulfonylphenoxy)ethyl](propyl)amine, mesdopetam) is a novel compound in development for the clinical management of motor and psychiatric disabilities in Parkinson disease. The discovery of IRL790 was made applying a systems pharmacology approach based on in vivo response profiling. The chemical design idea was to develop a new type of DA D3/D2 receptor type antagonist built on agonist rather than antagonist structural motifs. We hypothesized that such a dopamine antagonist with physicochemical properties similar to agonists would exert antidyskinetic and antipsychotic effects in states of dysregulated dopaminergic signaling while having little negative impact on physiologic dopamine transmission and, hence, minimal liability for side effects related to dopamine-dependent functions. At the level of in vivo pharmacology, IRL790 displays balancing effects on aberrant motor phenotypes, reducing l-DOPA-induced dyskinesias in the rodent 6-hydroxydopamine lesion model and reducing psychostimulant-induced locomotor hyperactivity elicited by pretreatment with either d-amphetamine or dizocilpine, without negatively impacting normal motor performance. Thus, IRL790 has the ability to normalize the behavioral phenotype in hyperdopaminergic as well as hypoglutamatergic states. Neurochemical and immediate early gene (IEG) response profiles suggest modulation of DA neurotransmission, with some features, such as increased DA metabolites and extracellular DA, shared by atypical antipsychotics and others, such as increased frontal cortex IEGs, unique to IRL790. IRL790 also increases extracellular levels of acetylcholine in the prefrontal cortex and ventral hippocampus. At the receptor level, IRL790 appears to act as a preferential DA D3 receptor antagonist. Computational docking studies support preferential affinity at D3 receptors with an agonist-like binding mode. SIGNIFICANCE STATEMENT: This paper reports preclinical pharmacology along with molecular modeling results on IRL790, a novel compound in clinical development for the treatment of motor and psychiatric complications in advanced Parkinson disease. IRL790 is active in models of perturbed dopaminergic and glutamatergic signaling, including rodent 6-hydroxydopamine l-DOPA-induced dyskinesias and psychostimulant-induced hyperactivity, in a dose range that does not impair normal behavior. This effect profile is attributed to interactions at dopamine D2/D3 receptors, with a 6- to 8-fold preference for the D3 subtype.

The most common approach to in vivo pharmacokinetic and pharmacodynamic analyses involves sequential analysis of the plasma concentration - and response - time data, such that the plasma kinetic model provides an independent function, driving the dynamics. However, in situations when plasma sampling may jeopardize the effect measurements or is scarce, nonexistent, or unlinked to the effect (e.g., in intensive care units, pediatric or frail elderly populations, or drug discovery), focusing on the response-time course alone may be an adequate alternative for pharmacodynamic analyses. Response-time data inherently contain useful information about the turnover characteristics of response (target turnover rate, half-life of response), as well as the drug’s biophase kinetics (biophase availability, absorption half-life, and disposition half-life) pharmacodynamic properties (potency, efficacy). The use of pharmacodynamic time-response data circumvents the need for a direct assay method for the drug and has the additional advantage of being applicable to cases of local drug administration close to its intended targets in the immediate vicinity of target, or when target precedes systemic plasma concentrations. This review exemplifies the potential of biophase functions in pharmacodynamic analyses in both preclinical and clinical studies, with the purpose of characterizing response data and optimizing subsequent study protocols. This article illustrates crucial determinants to the success of modeling dose-response-time (DRT) data, such as the dose selection, repeated dosing, and different input rates and routes. Finally, a literature search was also performed to gauge how frequently this technique has been applied in preclinical and clinical studies. This review highlights situations in which DRT should be carefully scrutinized and discusses future perspectives of the field.

The in vitro affinity of a compound for its target is an important feature in drug discovery, but what remains is how predictive in vitro properties are of in vivo therapeutic drug exposure. We assessed the relationship between in vitro potency and clinically efficacious concentrations for marketed small molecule drugs (n = 164) and how they may differ depending on therapeutic indication, mode of action, receptor type, target localization, and function. Approximately 70% of compounds had a therapeutic unbound plasma exposure lower than in vitro potency; the median ratio of exposure in relation to in vitro potency was 0.32, and 80% had ratios within the range of 0.007 to 8.7. We identified differences in the in vivo-to-in vitro potency ratio between indications, mode of action, target type, and matrix localization, and whether or not the drugs had active metabolites. The in vitro-assay variability contributions appeared to be the smallest; within the same drug target and mode of action the within-variability was slightly broader; but both were substantially less compared with the overall distribution of ratios. These data suggest that in vitro potency conditions, estimated in vivo potency, required level of receptor occupancy, and target turnover are key components for further understanding the link between clinical drug exposure and in vitro potency.

Translation across species and from in vitro to in vivo is a central tenet in drug discovery pharmacology. Successful implementation requires proper assessment of both in vivo potency and efficacy. This notwithstanding, in vivo data is typically defined mostly in terms of ligand-to-target binding affinity, similar to in vitro studies. As in vivo potency and efficacy involve a combination not only of drug, but also partitioning, target, and drug-target-complex events and processes, ignoring some of the central differences between in vivo and in vitro may result in serious miscalculations of in vivo efficacious exposure for translational predictions. We compare potency measures derived from two basic pharmacodynamic model situations: A 'closed' in vitro system defining target binding of a ligand when both concentrations remain essentially static, and an 'open' in vivo system where target turnover dynamics and elimination of the drug-target complex are also included. Corresponding equilibrium (steady-state) expressions in the central pharmacokinetic compartment are derived and presented. Three representative variants of 'open' in vivo systems are discussed, showing relationships for ligand-target complex and ligand for each of the systems and graphically illustrating corresponding shapes. The examples include i) two ligands competing for one target, ii) two targets competing for one ligand (/drug), and iii) target-ligand (/drug) interactions in a peripheral PK compartment. The expanded in vivo potency EC50 expression emphasises the contribution from target-related biology parameters that need accounting for, and particularly that 'closed' system (in vitro) properties should not be first choice when ranking compounds in vivo ('open' system).

Obesity increases risk of falling, but the effect of bariatric surgery on fall-related injuries is unknown. The aim of this study was therefore to study the association between bariatric surgery and long-term incidence of fall-related injuries in the prospective, controlled Swedish Obese Subjects study. At inclusion, body mass index was ≥ 34 kg/m2 in men and ≥38 kg/m2 in women. The surgery per-protocol group (n = 2007) underwent gastric bypass (n = 266), banding (n = 376), or vertical banded gastroplasty (n = 1365), and controls (n = 2040) received usual care. At the time of analysis (31 December 2013), median follow-up was 19 years (maximal 26 years). Fall-related injuries requiring hospital treatment were captured using data from the Swedish National Patient Register. During follow-up, there were 617 first-time fall-related injuries in the surgery group and 513 in the control group (adjusted hazard ratio 1.21, 95% CI, 1.07-1.36; P = 0.002). The incidence differed between treatment groups (P

Potency is a central parameter in pharmacological and biochemical sciences, as well as in drug discovery and development endeavors. It is however typically defined in terms only of ligand to target binding affinity also in in vivo experimentation, thus in a manner analogous to in in vitro studies. As in vivo potency is in fact a conglomerate of events involving ligand, target, and target-ligand complex processes, overlooking some of the fundamental differences between in vivo and in vitro may result in serious mispredictions of in vivo efficacious dose and exposure. The analysis presented in this paper compares potency measures derived from three model situations. Model A represents the closed in vitro system, defining target binding of a ligand when total target and ligand concentrations remain static and constant. Model B describes an open in vivo system with ligand input and clearance (Cl(L)), adding in parallel to the turnover (ksyn, kdeg) of the target. Model C further adds to the open in vivo system in Model B also the elimination of the target-ligand complex (ke(RL)) via a first-order process. We formulate corresponding equations of the equilibrium (steady-state) relationships between target and ligand, and complex and ligand for each of the three model systems and graphically illustrate the resulting simulations. These equilibrium relationships demonstrate the relative impact of target and target-ligand complex turnover, and are easier to interpret than the more commonly used ligand-, target- and complex concentration-time courses. A new potency expression, labeled L50, is then derived. L50 is the ligand concentration at half-maximal target and complex concentrations and is an amalgamation of target turnover, target-ligand binding and complex elimination parameters estimated from concentration-time data. L50 is then compared to the dissociation constant Kd (target-ligand binding affinity), the conventional Black & Leff potency estimate EC50, and the derived Michaelis-Menten parameter Km (target-ligand binding and complex removal) across a set of literature data. It is evident from a comparison between parameters derived from in vitro vs. in vivo experiments that L50 can be either numerically greater or smaller than the Kd (or Km) parameter, primarily depending on the ratio of kdeg-to-ke(RL). Contrasting the limit values of target R and target-ligand complex RL for ligand concentrations approaching infinity demonstrates that the outcome of the three models differs to a great extent. Based on the analysis we propose that a better understanding of in vivo pharmacological potency requires simultaneous assessment of the impact of its underlying determinants in the open system setting. We propose that L50 will be a useful parameter guiding predictions of the effective concentration range, for translational purposes, and assessment of in vivo target occupancy/suppression by ligand, since it also encompasses target turnover - in turn also subject to influence by pathophysiology and drug treatment. Different compounds may have similar binding affinity for a target in vitro (same Kd), but vastly different potencies in vivo. L50 points to what parameters need to be taken into account, and particularly that closed-system (in vitro) parameters should not be first choice when ranking compounds in vivo (open system).

Summary Background Bariatric surgery is associated with remission of diabetes and prevention of diabetic complications in patients with obesity and type 2 diabetes. Long-term effects of bariatric surgery on microvascular complications in patients with prediabetes are unknown. The aim of this study was to examine the effects of bariatric surgery on incidence of microvascular complications in patients with obesity stratified by baseline glycaemic status. Methods Patients were recruited to the Swedish Obese Subjects (SOS) study between Sept 1, 1987, and Jan 31, 2001. Inclusion criteria were age 37–60 years and BMI of 34 kg/m 2 or greater in men and 38 kg/m 2 or greater in women. Exclusion criteria were identical in surgery and control groups and designed to exclude patients not suitable for surgery. The surgery group (n=2010) underwent gastric bypass (265 [13%]), gastric banding (376 [19%]), or vertical-banded gastroplasty (1369 [68%]). Participants in the control group (n=2037) received usual care. Bodyweight was measured and questionnaires were completed at baseline and at 0·5 years, 1 year, 2 years, 3 years, 4 years, 6 years, 8 years, 10 years, 15 years, and 20 years. Biochemical variables were measured at baseline and at 2 years, 10 years, and 15 years. We categorised participants into subgroups on the basis of baseline glycaemic status (normal [fasting blood glucose concentration Findings 4032 of the 4047 participants in the SOS study were included in this analysis. We excluded four patients with suspected type 1 diabetes, and 11 patients with unknown glycaemic status at baseline. At baseline, 2838 patients had normal blood glucose, 591 had prediabetes, 246 had screen-detected diabetes, and 357 had established diabetes. Median follow-up was 19 years (IQR 16–21). We identified 374 incident cases of microvascular disease in the control group and 224 in the surgery group (hazard ratio [HR] 0·56, 95% CI 0·48–0·66; p Interpretation Bariatric surgery was associated with reduced risk of microvascular complications in all subgroups, but the greatest relative risk reduction was observed in patients with prediabetes at baseline. Our results suggest that prediabetes should be treated aggressively to prevent future microvascular events, and effective non-surgical treatments need to be developed for this purpose. Funding US National Institutes of Health, Swedish Research Council, Sahlgrenska University Hospital Regional Agreement on Medical Education and Research, and Swedish Diabetes Foundation.

IMPORTANCE: Bariatric surgery is an established treatment for obesity, but knowledge on the long-term incidence of revisional surgery is scarce. OBJECTIVE: To determine the incidence and type of revisional surgery after bariatric surgery in 26 years of follow-up of participants in the Swedish Obese Subjects (SOS) study. DESIGN, SETTING, AND PARTICIPANTS: The SOS study is a prospective nonrandomized controlled study comparing bariatric surgery (banding, vertical banded gastroplasty [VBG], and gastric bypass [GBP]) with usual care. The bariatric surgeries in the SOS study were conducted at 25 public surgical departments in Sweden. Men with body mass index values of 34 or higher and women with body mass indexes of 38 or higher were recruited to the surgery group of the SOS study between September 1, 1987, and January 31, 2001, and follow-up continued until December 31, 2014. Data analysis occurred from November 2016 to April 2018. INTERVENTIONS: Banding, VBG, or GBP. MAIN OUTCOMES AND MEASURES: Revisional surgeries, analyzed using data from questionnaires, hospital records, and the Swedish National Patient register through December 31, 2014. RESULTS: A total of 2010 participants underwent surgery. The age range was 37 to 60 years. A total of 376 participants underwent banding (18.7%), while 1365 had VBG (67.9%) and 266 had GBP (13.2%). During a median follow-up of 19 years, 559 participants (27.8%) underwent first-time revisional surgery, including 354 conversions to other bariatric procedures (17.6%), 114 corrective surgeries (5.6%), and 91 reversals to normal anatomy (4.5%). Revisional surgeries (conversions, corrective surgery, and reversals) were common after banding (153 of 376 [40.7%]) and VBG (386 of 1365 [28.3%]) but relatively rare after GBP (20 of 266 [7.5%]). Patients who had banding and VBG primarily underwent conversions to GBP or reversals. Incidence of reversals was 5 times higher after banding than after VBG (40.7% vs 7.5%; unadjusted hazard ratio, 5.19 [95% CI, 3.43-7.87]; P

There is a medical need for safe and efficacious anti-obesity drugs with acceptable side effect profiles. To mitigate the challenge posed by translating target interaction across species and balancing beneficial vs. adverse effects, a positron emission tomography (PET) approach could help guide clinical dose optimization. Thus, as part of a compound differentiation effort, three novel selective CB1 receptor (CB1R) antagonists, developed by AstraZeneca (AZ) for the treatment of obesity, were compared with two clinically tested reference compounds, rimonabant and taranabant, with regard to receptor occupancy relative to dose and exposure. A total of 42 PET measurements were performed in 6 non-human primates using the novel CB1R antagonist radioligand [(11)C]SD5024. The AZ CB1R antagonists bound in a saturable manner to brain CB1R with in vivo affinities similar to that of rimonabant and taranabant, compounds with proven weight loss efficacy in clinical trials. Interestingly, it was found that exposures corresponding to those needed for optimal clinical efficacy of rimonabant and taranabant resulted in a CB1R occupancy typically around ∼20-30%, thus much lower than what would be expected for classical G-protein coupled receptor (GPCR) antagonists in other therapeutic contexts. These findings are also discussed in relation to emerging literature on the potential usefulness of 'neutral' vs. 'classical' CB1R (inverse agonist) antagonists. The study additionally highlighted the usefulness of the radioligand [(11)C]SD5024 as a specific tracer for CB1R in the primate brain, though an arterial input function would ideally be required in future studies to further assure accurate quantitative analysis of specific binding.

Pattern recognition is a key element in pharmacodynamic analyses as a first step to identify drug action and selection of a pharmacodynamic model. The essence of this process is going from data to insight through exploratory data analysis. There are few formal strategies that scientists typically use when the experiment has been done and data collected. This report attempts to ameliorate this deficit by identifying the properties of a pharmacodynamic model via dissection of the pattern revealed in response-time data. Pattern recognition in pharmacodynamic analyses contrasts with pharmacokinetic analyses with respect to time course. Thus, the time course of drug in plasma usually differs markedly from the time course of the biomarker response, as a consequence of a myriad of interactions (transport to biophase, binding to target, activation of target and downstream mediators, physiological response, cascade and amplification of biosignals, homeostatic feedback) between the events of exposure to test compound and the occurrence of the biomarker response. Homing in on this important-but less often addressed-element, 20 datasets of varying complexity were analyzed, and from this, we summarize a set of points to consider, specifically addressing baseline behavior, number of phases in the response-time course, time delays between concentration- and response-time courses, peak shifts in response with increasing doses, saturation, and other potential nonlinearities. These strategies will hopefully give a better understanding of the complete pharmacodynamic response-time profile.

Translation across species and from in vitro to in vivo is a central tenet in drug discovery pharmacology. Successful implementation requires proper assessment of both in vivo potency and efficacy. This notwithstanding, in vivo data is typically defined mostly in terms of ligand-to-target binding affinity, similar to in vitro studies. As in vivo potency and efficacy involve a combination not only of drug, but also partitioning, target, and drug-target-complex events and processes, ignoring some of the central differences between in vivo and in vitro may result in serious miscalculations of in vivo efficacious exposure for translational predictions. We compare potency measures derived from two basic pharmacodynamic model situations: A 'closed' in vitro system defining target binding of a ligand when both concentrations remain essentially static, and an 'open' in vivo system where target turnover dynamics and elimination of the drug-target complex are also included. Corresponding equilibrium (steady-state) expressions in the central pharmacokinetic compartment are derived and presented. Three representative variants of 'open' in vivo systems are discussed, showing relationships for ligand-target complex and ligand for each of the systems and graphically illustrating corresponding shapes. The examples include i) two ligands competing for one target, ii) two targets competing for one ligand (/drug), and iii) target-ligand (/drug) interactions in a peripheral PK compartment. The expanded in vivo potency EC

The individual weight loss response to obesity treatment is diverse. Here we test the hypothesis that the weight loss response to the CB1 receptor antagonist rimonabant is influenced by endogenous levels of receptor agonists. We show that baseline anandamide levels and body weight independently contribute to predict the treatment response to rimonabant in rodents, demonstrating that addition of biomarkers related to mode of action is relevant for a personalized health care approach to obesity treatment.

Diet-induced obesity (DIO) resulting from consumption of a high fat diet (HFD) attenuates normal neuronal responses to leptin and may contribute to the metabolic defense of an acquired higher body weight in humans; the molecular bases for the persistence of this defense are unknown. We measured the responses of 23 brain regions to exogenous leptin in 4 different groups of weight- and/or diet-perturbed mice. Responses to leptin were assessed by quantifying pSTAT3 levels in brain nuclei 30 minutes following 3 mg/kg intraperitoneal leptin. HFD attenuated leptin sensing throughout the brain, but weight loss did not restore central leptin signaling to control levels in several brain regions important in energy homeostasis, including the arcuate and dorsomedial hypothalamic nuclei. Effects of diet on leptin signaling varied by brain region, with results dependent on the method of weight loss (restriction of calories of HFD, ad lib intake of standard mouse chow). High fat diet attenuates leptin signaling throughout the brain, but some brain regions maintain their ability to sense leptin. Weight loss restores leptin sensing to some degree in most (but not all) brain regions, while other brain regions display hypersensitivity to leptin following weight loss. Normal leptin sensing was restored in several brain regions, with the pattern of restoration dependent on the method of weight loss.

Objective The physiology of the weight-reduced (WR) state suggests that pharmacologic agents affecting energy homeostasis may have greater efficacy in WR individuals. Our aim was to establish a protocol that allows for evaluation of efficacy of weight maintenance agents and to assess the effectiveness of AZD2820, a novel melanocortin 4 receptor (MC4R) agonist in such a paradigm. Methods MC4R agonist was administered in stratified doses to mice who were either fed high-fat diet ad libitum (AL) throughout the study; or stabilized at a 20% reduced body weight (BW), administered the drug for 4 weeks, and thereafter released from caloric restriction while continuing to receive the drug (WR). Results After release of WR mice to AL feeding, the high-dose group (53.4 nmol/day) regained 12.4% less BW than their vehicle-treated controls since the beginning of drug treatment. In WR mice, 10.8 nmol/day of the agonist was sufficient to maintain these animals at 95.1% of initial BW versus 53.4 nmol/day required to maintain the BW of AL animals (94.5%). Conclusions In the WR state, the MC4R agonist was comparably efficacious to a five-fold higher dose in the AL state. This protocol provides a model for evaluating the mechanisms and quantitative efficacy of weight-maintenance strategies and agents.

Our article in this journal some 15 years ago focussed on the role of serotonin (5-HT) autoreceptors in the mechanism of action of antidepressant drugs. Specifically in this regard, the results were summarised of rat microdialysis studies carried out to examine: (a) the relative importance of 5-HT1A and 5-HT1B autoreceptors, including (b) possible regional variation, and (c) potential changes in autoreceptor responsiveness following chronic selective serotonin reuptake inhibitor administration. In the present reflection piece, I recap some of the key findings against a brief background and provide an account of their bearing within the context of subsequent endeavours in the antidepressant drug research and development field. I conclude by shortly commenting on selected topics relevant to novel, interesting advances and avenues for future research.

The implication of the cannabinoid receptor 1 (CB(1) receptor) in several pathophysiological states has sparked the development of selective antagonists. Here we compare binding of the antagonists [(3) H]-AZ12491187, [(3) H]-taranabant and [(3) H]-rimonabant to intact human embryonic kidney cells stably expressing recombinant human CB(1) receptors (CB1r cells). Unlabelled ligands decreased the total binding of the three radioligands with closely the same order of potency: i.e. AZ12288553∼AZ12491187∼taranabant>rimonabant. Nondisplaceable (i.e. nonspecific) binding to the CB1r cells was the same as total binding to the wells containing untransfected cells and it was more pronounced for [(3) H]-AZ12491187 and [(3) H]-rimonabant than for [(3) H]-taranabant. [(3) H]-Rimonabant and (to a lesser extent) [(3) H]-AZ12491187 were also prone to bind nonspecifically to the walls of the wells. Compared to the other radioligands, [(3) H]-rimonabant displayed lower potency for the CB(1) receptors in saturation binding studies and faster association and dissociation in kinetic experiments. When dissociated, the three radioligands also showed prominent rebinding to the cells in medium only. This could be relieved by the presence of excess of unlabelled ligand and of bovine serum albumin (BSA) but a combination thereof was most efficient. The long 'residence time' of AZ12491187 at the CB(1) receptor (because of slow dissociation and prominent rebinding) and its pronounced incorporation into the membranes of the cells could contribute to long-lasting in vivo CB(1) receptor blockade.

5-Hydroxytryptamine 1A (5-HT(1A)) receptors have been suggested as a target for the treatment of irritable bowel syndrome (IBS). A recent clinical trial investigating the efficacy of the selective 5-HT(1A) antagonist AZD7371 [3(R)-(N,N-dicyclobutylamino)-8-fluoro-3,4-dihydro-2H-1-benzopyran-5-carboxamide (R,R)-tartrate monohydrate] showed no symptomatic improvement in IBS patients. We characterized the mechanisms mediating potential analgesic effects of AZD7371 in a model of colorectal distension (CRD)-induced visceral pain in rats to understand its mechanism of action and the lack of clinical efficacy. Visceromotor and cardiovascular responses (telemetry) were assessed in conscious rats during noxious CRD (80 mm Hg). Effects of AZD7371 (3-300 nmol/kg i.v.; 1-30 micromol/kg p.o.) and a reference 5-HT(1A) antagonist, WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridyl)cyclohexanecarboxamide maleate salt; 3-300 nmol/kg i.v.), were assessed. Effects of intracerebroventricular AZD7371 were also evaluated. Intravenous AZD7371 or WAY-100635 and oral AZD7371 dose-dependently inhibited visceromotor responses to CRD (ED(50), 203, 231, and 14 micromol/kg, respectively). In telemetrized rats, oral AZD7371 inhibited visceromotor responses to CRD without affecting the concomitant hypertensive and tachycardic responses. Intracerebroventricular AZD7371 did not affect visceromotor responses, whereas it inhibited micturition. None of the doses tested induced visible gross side effects. AZD7371, likely acting at a spinal site, inhibited the visceromotor but not the cardiovascular responses to visceral pain in the CRD model in rats. Although agents effective on multiple pain-related readouts in the CRD model (e.g., pregabalin or clonidine) alleviate IBS symptoms, AZD7371, which is effective on only one pain-related pseudoaffective readout, does not. Data from preclinical CRD models of visceral pain need to be interpreted cautiously as it relates to their clinical translational value.

Background: The endocannabinoid system functions through two well characterized receptor systems, the CB1 and CB2 receptors. Work by a number of groups in recent years has provided evidence that the system is more complicated and additional receptor types should exist to explain ligand activity in a number of physiological processes.

Given the complexity of pharmacological challenge experiments, it is perhaps not surprising that design and analysis, and in turn interpretation and communication of results from a quantitative point of view, is often suboptimal. Here we report an inventory of common designs sampled from anti-inflammatory, respiratory and metabolic disease drug discovery studies, all of which are based on animal models of disease involving pharmacological and/or patho/physiological interaction challenges. The corresponding data are modeled and analyzed quantitatively, the merits of the respective approach discussed and inferences made with respect to future design improvements. Although our analysis is limited to these disease model examples, the challenge approach is generally applicable to the vast majority of pharmacological intervention studies. In the present five Case Studies results from pharmacodynamic effect models from different therapeutic areas were explored and analyzed according to five typical designs. Plasma exposures of test compounds were assayed by either liquid chromatography/mass spectrometry or ligand binding assays. To describe how drug intervention can regulate diverse processes, turnover models of test compound-challenger interaction, transduction processes, and biophase time courses were applied for biomarker response in eosinophil count, IL6 response, paw-swelling, TNFα response and glucose turnover in vivo. Case Study 1 shows results from intratracheal administration of Sephadex, which is a glucocorticoid-sensitive model of airway inflammation in rats. Eosinophils in bronchoalveolar fluid were obtained at different time points via destructive sampling and then regressed by the mixed-effects modeling. A biophase function of the Sephadex time course was inferred from the modeled eosinophil time courses. In Case Study 2, a mouse model showed that the time course of cytokine-induced IL1β challenge was altered with or without drug intervention. Anakinra reversed the IL1β induced cytokine IL6 response in a dose-dependent manner. This Case Study contained time courses of test compound (drug), challenger (IL1β) and cytokine response (IL6), which resulted in high parameter precision. Case Study 3 illustrates collagen-induced arthritis progression in the rat. Swelling scores (based on severity of hind paw swelling) were used to describe arthritis progression after the challenge and the inhibitory effect of two doses of an orally administered test compound. In Case Study 4, a cynomolgus monkey model for lipopolysaccharide LPS-induced TNFα synthesis and/or release was investigated. This model provides integrated information on pharmacokinetics and in vivo potency of the test compounds. Case Study 5 contains data from an oral glucose tolerance test in rats, where the challenger is the same as the pharmacodynamic response biomarker (glucose). It is therefore convenient to model the extra input of glucose simultaneously with baseline data and during intervention of a glucose-lowering compound at different dose levels. Typically time-series analyses of challenger- and biomarker-time data are necessary if an accurate and precise estimate of the pharmacodynamic properties of a test compound is sought. Erosion of data, resulting in the single-point assessment of drug action after a challenge test, should generally be avoided. This is particularly relevant for situations where one expects time-curve shifts, tolerance/rebound, impact of disease, or hormetic concentration-response relationships to occur.

It is well recognized that the hypothalamus is of central importance in the regulation of food intake and fat mass. Recent studies indicate that it also plays an important role in the regulation of bone mass. Melanin concentrating hormone (MCH) is highly expressed in the hypothalamus and has been implicated in regulation of energy homeostasis. We developed MCHR1 inactivated mice to evaluate the physiological role of this receptor. Interestingly, the MCHR1−/− mice have osteoporosis, caused by a reduction in the cortical bone mass, while the amount of trabecular bone is unaffected. The reduction in cortical bone mass is due to decreased cortical thickness. Serum levels of c-telopeptide, a marker of bone resorption, are increased in MCHR1−/− mice, indicating that the MCHR1−/− mice have a high bone turnover osteoporosis. In conclusion, the MCHR1−/− mice have osteoporosis, indicating that MCHR1-signalling is involved in a tonic stimulation of bone mass.

Some clinical reports suggest that tricyclic antidepressants which block both noradrenaline and serotonin (5-HT) reuptake (SNRIs) are more effective than selective 5-HT reuptake inhibitors (SSRIs) in treating severe depression. Moreover, one neurochemical study reported larger increases in extracellular 5-HT in rat frontal cortex in response to the tricyclic antidepressant imipramine compared to the SSRI fluoxetine. However, imipramine, which blocks both 5-HT and noradrenaline reuptake, also binds with relatively high affinity to receptors for noradrenaline, histamine and acetylcholine. Thus, to test the hypothesis that compounds that inhibit both 5-HT and noradrenaline reuptake produce larger increases in 5-HT efflux, we compared the effects of acute systemic administration of several SNRIs and SSRIs. Extracellular 5-HT was measured using microdialysis probes implanted in the diencephalon and frontal cortex of unanesthetized rats. We tested the SSRIs paroxetine (0.3-10 mg/kg), citalopram (10-20 mg/kg) and fluoxetine (10 mg/kg), the nonselective tricyclic antidepressant imipramine (20 mg/kg) and the more selective SNRIs duloxetine (3-30 mg/kg) and venlafaxine (30-50 mg/kg). During the lights-off period, paroxetine and duloxetine increased 5-HT in the diencephalon approximately 300 and approximately 200%, respectively. During the lights-on period, paroxetine and duloxetine each increased 5-HT approximately 400% in the diencephalon. In the frontal cortex, both paroxetine and duloxetine increased 5-HT approximately 200%. Citalopram and venlafaxine each increased 5-HT in the diencephalon approximately 300%. Fluoxetine and imipramine increased 5-HT in the diencephalon by approximately 125 and approximately 80%, respectively. Thus, these results do not support the hypothesis that compared to SSRIs, compounds which inhibit both 5-HT and noradrenaline reuptake have a larger acute effect on extracellular 5-HT.

Patients with chronic hepatic encephalopathy (HE) may present affective symptoms and antidepressant drug treatment in this condition is not uncommon. The present microdialysis study investigated treatment with the chronic antidepressant venlafaxine (VEN) in experimental HE with regard to tentative changes in pharmacokinetic and/or pharmacodynamic parameters. Three weeks after portacaval shunt (PCS) or sham operation in rats, VEN (10 mg/kg daily) was administered by implanted osmotic minipumps. VEN treatment for 14 days resulted in higher concentrations of VEN in PCS rats than in sham controls in serum and brain compartments, and the VEN levels in serum and brain were strongly inter-correlated. The serum N-desmethylvenlafaxine concentration did not differ between the groups, but correlated with the serum VEN levels. The other VEN metabolites were below the quantification limits. VEN treatment for 9-12 days significantly stimulated locomotion and rearing in the open field in sham controls, but failed to do so in the PCS rats. The concentrations of noradrenaline, dopamine, 5-HT, and 5-HIAA in neocortical dialysates were higher in PCS than in sham rats after 14 days of VEN treatment, but the elevations reached statistical significance only in the case of dopamine and 5-HIAA. In summary, there were significant pharmacokinetic and pharmacodynamic alterations in rats with experimental HE as compared to controls. The described experimental HE model may be useful for continued pharmacokinetic/pharmacodynamic interaction studies to unravel the pathophysiological consequences of HE on the CNS.

Energy intake (EI) is a pivotal biomarker used in quantification approaches to metabolic disease processes such as obesity, diabetes, and growth disorders. Eating behavior is however under both short-term and long-term control. This control system manifests itself as tolerance and rebound phenomena in EI, when challenged by drug treatment or diet restriction. The paper describes a model with the capability to capture physiological counter-regulatory feedback actions triggered by energy imbalances. This feedback is general as it handles tolerance to both increases and decreases in EI, and works in both acute and chronic settings. A drug mechanism function inhibits (or stimulates) EI. The deviation of EI relative to a reference level (set-point) serves as input to a non-linear appetite control signal which in turn impacts EI in parallel to the drug intervention. Three examples demonstrate the potential usefulness of the model in both acute and chronic dosing situations. The model shifts the predicted concentration-response relationship rightwardly at lower concentrations, in contrast to models that do not handle functional adaptation. A fourth example further shows that the model may qualitatively explain differences in rate and extent of adaptation in observed EI and its concomitants in both rodents and humans.

Rats were administered venlafaxine (10 mg/kg per day) for 14 days by using subcutaneously implanted osmotic minipumps. The present study assessed the distribution of VEN in different compartments, whether the VEN concentration in the compartments correlated, the effect of VEN on dialysate monoamine levels and on the spontaneous open-field behavior, and possible relations between the pharmacokinetic and pharmacodynamic parameters. The venlafaxine level in serum after sustained treatment was about 25% of the concentration in brain parenchyma and much higher than in brain dialysate. There was a clear correlation between venlafaxine concentrations in blood and brain compartments. The sustained venlafaxine challenge resulted in higher neocortical concentration of serotonin and noradrenaline, lower 5-hydroxyindole-3-acetic acid levels and increased locomotor activity in the central part of the test arena as compared to controls. No correlations were found between the venlafaxine concentration and brain monoamine parameters or the open-field behaviors. We conclude that, although species differences in pharmacokinetic properties for venlafaxine between rat and man exist, the pharmacokinetic correlations found after sustained treatment add information to the in vivo nature of the drug. Also, more studies like the present need to be performed to find the pharmacokinetic/pharmacodynamic interrelations for drugs like VEN.

THE NMDA receptor antagonist phencyclidine (PCP) has low micromolar affinity for the 5-HT reuptake site, but it is uncertain whether PCP blocks 5-HT reuptake when given systemically to rats in behaviourally stimulating doses. We here report for the first time that systemically administered PCP (5 mg/kg, s.c.) increases extracellular 5-HT levels in the rat medial prefrontal cortex (to 322%) and dorsal hippocampus (to 233%). Increases were found also when citalopram (1 microM) was included in the perfusion medium (to 184 and 180%, respectively). Extracellular 5-HIAA concentrations increased during both conditions, and extracellular GABA decreased in the dorsal hippocampus. It is concluded that systemic PCP treatment elevates extracellular 5-HT levels, probably through mechanisms other than a blockade of 5-HT reuptake.

Clozapine and the novel putative, antipsychotic S 16924 ((1-(benzodioxane-5-yl)-3-[3-(4-fluorophenacyl)pyrrolidine]-1-o xapropane HCl) share significant affinity for alpha1-adrenoceptors and 5-HT1A autoreceptors in vitro and display an 'atypical' behavioural profile in in vivo models used for detecting potential neuroleptic effects. In the present study, in vivo microdialysis was used to examine the effect of clozapine and S 16924 on 5-HT overflow in the rat ventral hippocampus, and to assess the relative role of putative alpha1-adrenoceptor antagonist and 5-HT1A autoreceptor agonist properties of the drugs in this regard. S 16924 (0.1-3 mg/kg, s.c.) reduced dialysate 5-HT in a dose- and time-dependent fashion by maximally approximately 70% from baseline 40-60 min after injection. Clozapine (0.1-10 mg/kg, s.c.) reduced 5-HT overflow in the same manner, with a maximum effect of approximately 60% from baseline, obtained after 60-80 min. The 5-HT decrease elicited by S 16924 (1.0 mg/kg, s.c.) was significantly, though only partially, antagonized by pretreatment with the selective 5-HT1A receptor antagonist WAY 100635 (0.3 mg/kg, s.c.). The selective alpha1-adrenoceptor agonist cirazoline (0.02 mg/kg, i.p.) alone did not significantly attenuate the effect of S 16924 (1.0 mg/kg, s.c.) on 5-HT overflow. Combined treatment with both WAY 100635 and cirazoline, however, totally reversed the 5-HT-suppressing effect of S 16924 (1.0 mg/kg, s.c.). By comparison, when given separately, neither WAY 100635 (0.3 mg/kg, s.c.) nor cirazoline (0.02 mg/kg, i.p.) antagonized the clozapine (0.3 mg/kg, s.c.)-induced decrease of 5-HT in ventral hippocampus dialysates. In the presence of both WAY 100635 and cirazoline, the response to this dose of clozapine was however significantly, though modestly, attenuated. In contrast, the WAY 100635/cirazoline combination failed to antagonise the 5-HT decrease resulting from a higher dose (3.0 mg/kg, s.c.) of clozapine. We conclude that both alpha1-adrenoceptor antagonist and 5-HT1A receptor agonist properties of clozapine and S 16924 contribute to the 5-HT release-reducing action of these drugs. Whereas these factors apparently explain the effect of S 16924 fully, additional mechanism(s) appear to be involved in the case of clozapine. With regard to the interplay between alpha1-adrenoceptor and 5-HT1A (auto)receptor mechanisms in the control of 5-HT release in the rat forebrain, the present data suggest that an excitation mediated by the former is outweighed by the simultaneous activation of the latter-inhibitory-receptors.

Portal-systemic encephalopathy (PSE) is associated with an increased brain tissue turnover of serotonin (5-HT). Despite increased 5-HT metabolism, brain 5-HT release in rats with a portacaval shunt (PCS) seems to be unaltered. Although this may indicate that the overall 5-HT output is unaltered in PSE, it is also possible that the 5-HT release pattern might be altered in some way. In the present study, the potassium-evoked frontal neocortical release of 5-HT was studied in experimental chronic PSE. KCI (60 mM) produced marked increases in the 5-HT output compared with basal values both in PCS and sham rats. Simultaneously, the KCI challenge resulted in significant elevations in the 5-HT release of PCS compared with sham. In Ca2+-free medium, the difference between PCS and sham rats in the KCl-evoked release of 5-HT was abolished. In the presence of TTX (1 mM), both groups displayed increased extracellular 5-HT levels. Again, a difference with higher amplitude of the 5-HT release in PCS compared with sham was evident. It is concluded that in experimental chronic PSE an augmented neocortical 5-HT release compared with the normal in vivo situation is available. The possible mechanism(s) responsible for the difference in neocortical 5-HT output between PCS and sham-operated rats in response to the KCl-challenge is discussed.

Portal-systemic encephalopathy (PSE) is associated with increased brain turnover of serotonin (5-HT) in vivo but the brain 5-HT output seems to be unaltered. Recent results suggest, however, that an augmented neocortical 5-HT release in experimental chronic PSE may prevail under certain conditions. In the present study, neocortical extracellular 5-HT and 5-hydroxyindoleacetic-3-acid (5-HIAA) levels were measured in portacaval shunted (PCS) rats and sham-operated controls following local administration of p-chloroamphetamine (pCA) and d-fenfluramine (dFEN), two specific 5-HT releasing agents. The basal neocortical extracellular 5-HT concentrations were unaltered and the 5-HIAA levels were elevated in experimental PSE, supporting an unchanged brain 5-HT output despite elevated brain 5-HT metabolism. Perfusion with pCA or dFEN (5 microM; one 20-min pulse) produced marked increases in brain 5-HT release both in PCS and sham-operated rats compared with corresponding basal values. While no difference in the 5-HT response to dFEN administration was seen between sham (5-HT levels increased by 330%) and PCS (500%) rats, a clear difference (p

Ammonia has been shown to cause release of neurotransmitters such as serotonin (5-hydroxytryptamine; 5-HT) from synaptosomal preparations in vitro. In the present study, frontal neocortical extracellular levels of 5-HT and its major metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), were determined in vivo by the use of microdialysis in portacaval shunted (PCS) rats, an experimental model of chronic hepatic encephalopathy (HE), prior to and after an acute coma-inducing administration of ammonium acetate (NH4Ac; 5.2 mmol/kg, i.p.). PCS rats displayed elevated (P0.01) 5-HIAA but unaltered 5-HT extracellular levels compared with controls, supporting the contention of an increased neocortical 5-HT metabolism but unaltered neuronal 5-HT output in chronic HE. However, a transient elevation of extracellular 5-HT levels was observed when PCS-NH4Ac rats were in coma. Increased brain ammonia may thus augment neuronal 5-HT release in chronic HE, which in turn could be a causative for precipitation of more severe stages of HE.

Portal-systemic encephalopathy (PSE) is associated with increased brain turnover of serotonin (5-hydroxytryptamine; 5-HT). Despite this metabolic increase, neuronal release of 5-HT is unaltered in neocortex of portacaval shunted (PCS) rats. In the present study, frontal neocortical extracellular 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) levels were determined in PCS rats and sham-operated controls prior to, as well as, after acute challenge with L-tryptophan (L-TRP; a bolus dose of 280 mg/kg i.p. followed by 5 consecutive hourly doses of 50 mg/kg). Neither basal 5-HT nor 5-HIAA extracellular levels were significantly altered in PCS rats compared to controls. L-TRP administration resulted in unaltered extracellular 5-HT but elevated 5-HIAA levels in PCS and sham rats. These findings do not suggest that changes in brain neuronal 5-HT release play any major functional role in the pathogenesis of chronic PSE. The present data also emphasize the importance of distinguishing between brain 5-HT metabolism and brain 5-HT release.

Recent open clinical studies suggest that pindolol and buspirone may enhance the efficacy and/or shorten the latency to antidepressant action of selective serotonin reuptake inhibitors (SSRI) in unipolar major depressive disorder. The present investigation addressed the possibility that these agents share the ability to enhance the extracellular 5-hydroxytryptamine (5-HT)-elevating response to the SSRI citalopram. For the purpose, in vivo microdialysis in the rat ventral hippocampus was employed. (-)-Pindolol (8 mg/kg s.c.) augmented the citalopram (5 mg/kg s.c.)-induced rise of extracellular 5-HT levels, whereas buspirone (5 mg/kg s.c.) failed to do so. This effect of (-)-pindolol probably reflects its ability to block 5-HT1A autoreceptors, thereby abating the citalopram-induced indirect activation of these sites (secondary to the inhibition of 5-HT reuptake and elevation of extracellular 5-HT in the midbrain raphe). The lack of effect of buspirone in this model indicates that the clinically observed antidepressant augmentation action of buspirone is not mediated indirectly, via enhanced extracellular levels of 5-HT.

Twelve N,N-dipropyl-substituted derivatives of trans-2-arylcyclopropylamine have been prepared and assayed for their ability to displace [(3)H]-8-OH-DPAT from rat brain 5-HT(1A) receptors. The new derivatives include phenyl (7a), bromo- (7b) and fluorophenyl (7c-e), 2-methoxy-5-fluorophenyl (7h), and 2-hydroxy-5-fluorophenyl (7l) as well as trifluoromethylphenyl (7f) and 2,3-dichlorophenyl (7g) analogues. In the present series of compounds, electron-withdrawing substituents in the phenyl ring appear to decrease the affinity for 5-HT(1A) receptors. In contrast, electron-rich aryl groups, such as 2- or 3-thienyl (7j and 7k, respectively), provide compounds with high affinity. The additional bulk produced by the aromatic moiety in the 2-benzothienyl derivative 7i appears to be detrimental to 5-HT(1A) receptor affinity. The racemic mixtures of the interesting 7j and 7l were resolved into the enantiomers; 7j and 7l exhibited a high enantiomeric 5-HT(1A) receptor affinity ratio (75-fold and 100-fold, respectively). The enantiomers of 7j and 7l were evaluated in vivo by use of biochemical and behavioral tests in rats. Compound (1R,2R)-7j behaved as a partial agonist whereas (1R,2S)-7l appeared as an efficacious 5-HT(1A) receptor agonist, stimulating both autoreceptors and postsynaptic receptors.

The inhibition of serotonin (5-HT) release produced by antidepressants varying in relative selectivity for blocking uptake of 5-HT and noradrenaline (NA) was compared. Release was measured by microdialysis in anesthetized rats with nerve terminal 5-HT uptake inhibited by local infusion of citalopram (1 μM) through a dialysis probe in hippocampus. With 5-HT uptake first blocked in hippocampus, systemic injection of uptake inhibitors produced decreases in dialysate 5-HT, presumably due to autoreceptor stimulation in the raphe. The largest decreases (about 60–70%) in 5-HT were produced by the selective 5-HT uptake inhibitors sertraline, paroxetine and citalopram. Nonselective blockers caused less suppression of release. Thus, the maximum decrease in 5-HT was 35% after clomipramine, a less selective 5-HT uptake inhibitor, and ⩽ 30% after the nonselective 5-HT/NA uptake blockers imipramine and amitriptyline, 5-HT was not decreased after maprotiline, a selective NA uptake blocker. Pretreatment with (+)WAY 100135 to block 5-HT 1A autoreceptors, abolished the inhibition of 5-HT release produced by systemic sertraline, clomipramine and imipramine. One explanation for the difference between selective and nonselective inhibitors with respect to central 5-HT release, is the excitatory effect of ( α 1 ) adrenergic receptor stimulation on 5-HT neuronal discharge. However, pretreatment with α -methyl- p -tyrosine to deplete NA, did not influence the inhibition of 5-HT release produced by imipramine.

The clinical efficacy of antidepressants that block serotonin (5-hydroxytryptamine, 5-HT) reuptake may be restrained by indirect activation of autoreceptors. In vivo microdialysis in rat hippocampus was used to assess the release-inhibitory properties of the 5-HT reuptake inhibitors citalopram and paroxetine. When reuptake was first blocked by infusing citalopram into the hippocampus, systemic administration of citalopram or paroxetine resulted in a 50–70% decrease in hippocampal 5-HT overflow. This presumably reflected the inhibition of 5-HT release subsequent to reuptake blockade in the raphe nuclei and, in turn, activation of somatodendritic autoreceptors. In support, pretreatment with (±)-pindolol or(+)-WAY100135 ((+)-N-tert-butyl-3-(4- (2-methoxyphenyl)piperazine-1-yl)-2-phenylpropanamide dihydrochloride), to block 5-HT1A autoreceptors, abolished the decrease in 5-HT produced by systemic injection of the uptake blockers.

The two diphenylbutylpiperazinepyridinyl derivatives, FG5865 and FG5893, have a unique receptor binding profile in that they show very high and essentially equipotent affinities for both 5-HT 1A and 5-HT 2 receptors. The present report describes the acute effects of FG5865 and FG5893 on presynaptic 5-hydroxytryptamine (5-HT) neuronal function in the rat CNS, using established ex vivo and in vivo neurochemical techniques. Post-mortem measurements of tissue levels of 5-HT, its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and of the formation of 5-hydroxytryptophan (5-HTP; after inhibition of aromatic amino acid decarboxylase by NSD 1015) showed that FG5865 (0.1–20 mg/kg, s.c.) and FG5893 (0.1–20 mg/kg, s.c.) dose dependently decreased the synthesis and the metabolism/turnover of 5-HT - this to an extent comparable to the reference 5-HT 1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin. Reserpine (5 mg/kg, s.c.) pretreatment did not prevent the FG5893-induced decrease of 5-HT synthesis rate. In contrast, about 25–50 times higher doses of FG5865 were required to produce a comparable decrease in brain 5-HT synthesis in reserpinized vs. non-pretreated rats. In in vivo microdialysis experiments, both FG5865 (0.1–3.0 mg/kg, s.c) and FG5893 (0.3–1.0 mg/kg, s.c.) caused a marked and dose-dependent decrease of 5-HT release in the ventral hippocampus. Pretreatment with the 5-HT 1A receptor antagonist, (±)-pindolol (8 mg/kg, s.c.), abolished the FG5865 (0.3 mg/kg, s.c.)-induced reduction of 5-HT release, and (−)-pindolol (8 mg/kg, s.c.) similarly reversed the FG5893 (0.3 mg/kg, s.c.)-induced decrease. Local infusion of FG5865 into the ventral hippocampus (10 μM, 20-min pulse) resulted in a rapid and transient elevation of the 5-HT output, an effect that was independent of extracellular Ca 2+ , FG5893, on the other hand, did not affect the 5-HT release upon local administration. The results demonstrate that FG5865 and FG5893 potently affect a range of neurochemical indices of rat brain 5-HT neuronal activity in vivo, in a way consistent with indirect (FG5865) and direct (FG5865 and FG5893) stimulation of the 5-HT 1A autoreceptors in the raphe nuclei.

The present study addressed the possibility that disinhibition of serotonin (5-HT) autoreceptor-mediated negative feedback might potentiate the elevation of nerve terminal 5-HT output induced by selective 5-HT reuptake blockade. To this end, rats were given citalopram and the 5-HT autoreceptor-blocking agents (S)-UH-301 (5-HT1A) and (-)-penbutolol (5-HT1A/1B), and the effect on extracellular 5-HT in the ventral hippocampus was monitored by means of in vivo microdialysis. Citalopram (5 mg/kg, s.c.) approximately doubled the 5-HT output, a response that was markedly augmented by (S)-UH-301 (3 mg/kg, s.c.) and (-)-penbutolol (8 mg/kg, s.c.) and by combined treatment with (S)-UH-301 (3 mg/kg, s.c.) plus (-)-penbutolol (1 microM; via the dialysis perfusion medium), but not by (-)-penbutolol (1 microM) alone. These findings provide evidence that 5-HT, in particular 5-HT1A, autoreceptor-mediated negative feedback mechanisms are pivotal in determining the nerve terminal 5-HT output level after 5-HT reuptake inhibition. These findings have important implications for the interplay between different processes controlling 5-HT transmission in vivo and might possibly offer a lead toward novel, therapeutically exploitable principles.

Racemic 5-methoxy-2-methyl-2-dipropylaminotetralin (3) has been prepared by a short synthetic route, in which the N,N-dipropyliminium perchlorate of 5-methoxy-2-tetralone (4) is a key intermediate. Racemic 3 was resolved by crystallization of the corresponding diastereomeric di-p-toluoyltartrates. The enantiomeric excess (%ee) of the phenolic derivatives of (+)-(R)- and (−)-(S)-3 [(+)-(R)- and (−)-(S)-2] was determined by 1HNMR spectroscopic analysis of the corresponding diastereomeric (−)-(R)-1,1′-binaphthyl-2,2′-diylphosphoric acid salts utilizing 13C satellites. X-ray crystallography established the absolute configuration of (−)-(S)-2 · HCl. The enantiomers of 2 were tested for hippocampal output of 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, and dihydroxyphenylacetic acid in rats by use of in vivo microdialysis. The (−)-(S)-enantiomer appeared to affect 5-HT-turnover, whereas (+)-(R)-2 was inactive. Results obtained provide support for the previously reported hypothesis that the inactivity of (−)-(S)-2 at central DA receptors is caused by the steric bulk of the C(2)-methyl group. This makes it possible to define a “DA D2 receptor essential volume.” © 1993 Wiley-Liss, Inc.