Lower Lip Retraction Research Articles

Synthesis and pharmacological evaluation of thiopyran analogues of the dopamine D3 receptor-selective agonist (4aR,10bR)-(+)-trans-3,4,4a,10b-tetrahydro-4-n-propyl-2H,5H [1]b enzopyrano[4,3-b]-1,4-oxazin-9-ol (PD 128907).

Benzopyranoxazine (+)-7 (PD 128907) is the most dopamine (DA) D3 receptor-selective agonist presently known. The only structural feature which distinguishes 7 from the analogous nonselective naphthoxazines is an oxygen atom in the 6-position. To extend this series of tricyclic DA agonists we used a classic bioisoster approach and synthesized thiopyran analogues of 7, which have a sulfur atom in the 6-position. We prepared trans-4-n-propyl-3,4,4a,10b-tetrahydro-2H,5H-[1]benzothiopyrano[4, 3-b]-1,4-oxazin-9-ol (9, trans-9-OH-PTBTO), its enantiomers ((+)-9 and (-)-9), the racemic cis-analogue (10), and the racemic trans-sulfoxide (11) and studied the potency and selectivity for DA receptors of these compounds. As with other rigid DA agonists, the highest affinity for DA receptors resided in one of the enantiomers, in this case the (-)-enantiomer of 9. On the basis of a single-crystal X-ray analysis of a key intermediate, the absolute configuration of (-)-9 was found to be 4aS,10bR, which is homochiral with (+)-(4aR,10bR)-7. In contrast to (+)-7 however, (-)-9 displayed no selectivity for any of the DA receptors. In addition, it has affinity for 5HT1A receptors. (+/-)-cis-4-n-Propyl-3,4,4a,10b-tetrahydro-2H,5H-[1]benzothiopyrano++ +[4,3-b]-1,4-oxazin-9-ol (10), which was expected to be inactive, displayed affinity and selectivity for the DA D3 receptor, whereas the sulfoxide 11 displayed some DA D3 selectivity, but with a lower affinity. Further pharmacological evaluation revealed that (-)-9 is a very potent full agonist at DA D2 receptors and a partial agonist at DA D3 receptors. The cis-analogue (+/-)-10 displayed the same profile, but with lower potency. These findings were confirmed in vivo: in reserpinized rats (-)-9 displayed short-acting activation of locomotor activity (DA D2 agonism) and also lower lip retraction and flat body posture, (5HT1A agonism). Compound (+/-)-10 had no effect on locomotor activity. In unilaterally 6-OH-DA lesioned rats, (-)-9 gave short-acting locomotor activation. Furthermore, in microdialysis studies in rat striatum, (-)-9 potently decreased DA release, confirming its activation of presynaptic DA D2 receptors.

In vivo estimates of efficacy at 5-HT1A receptors: effects of EEDQ on the ability of agonists to produce lower-lip retraction in rats.

Maximal responses are often used as a measure of intrinsic activity or efficacy, but cannot be directly equated to efficacy. Using irreversible antagonists, estimates of efficacy can be obtained that may be less dependent on specific conditions. To characterize the intrinsic activity of serotonin (5-HT)1A agonists by examining the effects of an irreversible antagonist on their ability to produce 5-HT1A receptor-mediated responses. The effects of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on the ability of 5-HT1A agonists to produce lower-lip retraction (LLR) in rats were studied. In the absence of EEDQ, each 5-HT1A agonist produced full effects, the rank order of potency being: S 14506 > 8-OH-DPAT > buspirone > ipsapirone. EEDQ decreased the number of 5-HT1A binding sites and shifted the dose-response curves (DRCs) of each agonist either to the right or, at higher EEDQ doses, to the right and downward. The manner in which these shifts occurred, however, differed among the compounds. For each agonist, all DRCs obtained after different doses of EEDQ were fitted to models proposed by Furchgott and Black and Leff, and the results indicated the following rank order of efficacy: ipsapirone < buspirone approximately 8-OH-DPAT < S 14506. 5-HT1A agonist-induced LLR appears to be mediated by 5-HT1A receptors, because the 5-HT1A antagonist, WAY 100635, shifted the agonist DRCs to the right in a parallel and dose-related manner, with pA2 values ranging from 7.8 to 8.1. Moreover, pretreatment with WAY 100635 protected against the antagonist activity of EEDQ. The results suggest that the effects of EEDQ on the ability of 5-HT1A agonists to produce LLR in rats may be useful to obtain estimates of their apparent efficacy at 5-HT1A receptors.

Ligand-5-HT 1A receptor interaction

In the present paper the general structure and pharmacophore of some 5-HT 1A receptor ligands are described. For several compounds (∼15) the intrinsic activity in lower lip retraction (postsynaptic, rat) and hypothermia (presynaptic, mice) tests was determined. For the identified functional presynaptic agonists and antagonists the influence on the brain serotonin level was examined. No direct correlation between the functional intrinsic activity and the influence on the level was observed. Molecular modelling revealed the possibility of the existence of different binding sites for different examined compounds.

On the bioactive conformation of NAN-190 (1) and MP3022 (2), 5-HT(1A) receptor antagonists.

Structural modifications of 1, a postsynaptic 5-HT(1A) receptor antagonist, provided its flexible (8, 12) and rigid (7, 9, 11, 13) analogues. Compounds 7, 8, 9, and 11 showed high 5-HT(1A) receptor affinity (K(i) = 4-72 nM). They acted as 5-HT(1A) postsynaptic receptor antagonists, since, like 1, they inhibited the behavioral syndrome, i.e., flat body posture (FBP) and forepaw treading (FT), in reserpine-pretreated rats as well as the lower lip retraction (LLR) in rats, both induced by 8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT), a 5-HT(1A) receptor agonist. Compound 12, which demonstrated high 5-HT(1A) receptor affinity (K(i) = 50 nM), revealed properties of a partial 5-HT(1A) receptor agonist: it induced LLR and, at the same time, inhibited FT in rats. Compound 13 (K(i) = 1600 nM) was not tested in a behavioral study. Restriction of the conformational freedom in 2, a full 5-HT(1A) receptor antagonist, yielded compound 14 with high 5-HT(1A) receptor affinity (K(i) = 47 nM) and partial agonist properties at postsynaptic 5-HT(1A) receptors in the above tests in vivo; i.e., it induced LLR and inhibited FBP and FT in rats. New constrained analogues of 1 and 2 (compounds 7 and 14, respectively) were also synthesized to recognize a bioactive conformation of those 5-HT(1A) receptor antagonists. On the basis of in vitro and in vivo investigations, binding and functional properties of compound 7 were found to reflect those of 1 at 5-HT(1A) receptors. On the other hand, compound 14, a rigid analogue of 2, showed a different activity in vivo in comparison with the parent compound. PM3 and MM calculations revealed the existence of three low-energy conformers of 7 and six of 14, all of them belonging to the extended family of conformations. The optimized structures of both analogues had a different angle between aromatic planes of terminal fragments; moreover, the heteroaromatic system of those molecules occupied various space regions. Our present study provides support to the hypothesis that the bioactive conformation of 1, responsible for its postsynaptic 5-HT(1A) receptor antagonism, is an extended linear structure represented by 7.

A search for new 5-HT1A/5-HT2A receptor ligands. In vitro and in vivo studies of 1-[omega-(4-aryl-1-piperazinyl)alkyl]indolin-2(1H)-ones.

A series of 1-¿omega-(4-aryl-1-piperazinyl)alkyl]indolin-2(1H)-one derivatives 2-14 was synthesized in order to obtain ligands with a dual 5-HT1A/5-HT2A activity. The majority of those compounds (2-5, 7, 10-13) exhibited a high 5-HT1A (Ki = 2-44 nM) and/or 5-HT2A affinity (Ki = 51 and 39 for 5 and 7, respectively). Induction of lower lip retraction (LLR) and behavioral syndrome and inhibition of these effects evoked by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) were used for determination the agonistic and antagonistic activity, respectively, at 5-HT1A receptors. The 5-HT2A antagonistic activity was assessed by the blocking effect on the head twitches induced by (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) in mice. Two of the tested compounds, 1-¿3-[4-(3-chlorophenyl)-1-piperazinyl]propyl¿-6-fluoroindolin-2(1 H)-one (5) and 1-¿3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl¿indolin-2(1H)-one (7), demonstrated a high 5-HT1A/5-HT2A affinity and an in vivo antagonistic activity towards both receptor subtypes.

The effects of 5-HT1A receptor agonists, 5-HT1A receptor antagonists and their interaction on the fear-potentiated startle response.

The present study investigated whether the anxiolytic effect of 5-HT1A receptor agonists on the fear-potentiated startle response could be antagonized by 5-HT1A receptor antagonists. Therefore, control and fear-potentiated startle amplitudes were measured after co-administration of vehicle, flesinoxan (10 mg/kg PO) or 8-OH-DPAT (0.3 mg/kg SC) and DU 125,530 (0, 1, 3 and 10 mg/kg SC), (+/-)-pindolol (0, 3, 10 and 30 mg/kg SC) or WAY 100,635 (0, 0.1, 0.3 and 1 mg/kg SC). Unexpectedly, the three antagonists themselves as measured in the vehicle-pretreatment groups dose-dependently decreased startle potentiation. Further, DU 125,530 and WAY 100,635 were able to reverse the attenuating effect of 8-OH-DPAT, while no antagonism of the flesinoxan effect on startle potentiation was found. In contrast, both the flesinoxan- and 8-OH-DPAT-induced lower lip retraction were antagonized by DU 125,530 and WAY 100,635, but not by (+/-)-pindolol. The findings of the present study suggest that drugs acting on 5-HT1A receptors differentially affect lower lip retraction and startle potentiation probably mediated by different neuronal populations.

A pharmacological validation of radiotelemetry in conscious, freely moving rats

Two reference substances were used in the present study. d-Amphetamine is a direct catecholamine-releasing agent which has a marked stimulant effect upon locomotor activity at low to moderate doses and induces stereotypy at higher doses. (±)8-Hydroxy-2-(di-n-propylamino)-tetraline [(±)8-OH-DPAT] is a selective 5-HT 1A receptor agonist which produces a well-defined behavioral syndrome and a dose-dependent hypothermia. The first aim of this study was to validate that the d-amphetamine-induced activity monitored by telemetry correlated to that concomitantly measured in automated cages and complement these measures with an ethologically based direct observational technique. d-Amphetamine (2.5 and 5.0 μmol/kg s.c.) stimulated locomotion as assessed with radiotelemetry, in automatic cages and by observation. Accompanying these behavioral effects was a concurrent increase (assessed by radiotelemetry) in heart rate but not in blood pressure. The second part of this study examined the pharmacological effects of (±)8-OH-DPAT (0.09–6.1 μmol/kg s.c.) on behavior (observation and activity) and temperature and on the cardiovascular system. (±)8-OH-DPAT induced the classical serotonergic syndrome of lower lip retraction, forepaw treading, and flattened body posture (observation), and this was accompanied by a concomitant hypothermia (radiotelemetry). (±)8-OH-DPAT also induced a dose-dependent and significant decrease in heart rate for 50 min of the 1-h long observation period. This was not accompanied by an increase in blood pressure in spite of the increased activity as seen with all three methods. These results show that radiotelemetry can be used as a tool to measure activity, core temperature, and the cardiovascular parameters in animals that are less stressed than those that are restrained for similar more invasive measurements, and that this technique can be used in combination with others to produce a more complete ethogram of the animal’s responses to pharmacological challenges.

Flesinoxan pretreatment differentially affects corticosterone, prolactin and behavioural responses to a flesinoxan challenge.

To determine whether alterations in 5-HT1A receptor mediated responses induced by a single injection with a selective 5-HT1A receptor agonist is a transient effect, or whether the (de)sensitisation is more persistent, rats were pretreated with the selective and full 5-HT1A receptor agonist, flesinoxan (3 mg/kg SC once daily) for either 1 day or 1 week. Twenty-four hour after the last pretreatment injection, rats were challenged with flesinoxan (3 mg/kg SC), and the effects on plasma corticosterone and prolactin levels, lower lip retraction and behaviour in the shock-probe burying test were determined. Several 5-HT1A receptor mediated responses were modified differentially following the flesinoxan pretreatment. However, all changes induced by a single flesinoxan injection remained present upon repeated flesinoxan administration. The differential changes in the responses to flesinoxan cannot easily be explained by differences in pre- or postsynaptically 5-HT1A mediated responses. The prolactin response to flesinoxan, which is thought to be mediated postsynaptically, was enhanced, whereas the corticosterone response to flesinoxan, which is also mediated postsynaptically, was attenuated. The presynaptically mediated lower lip retraction response was attenuated as well, whereas the behavioural effects of flesinoxan remained relatively unaffected following repeated flesinoxan administration. Upon prolonged flesinoxan pretreatment, the changes induced by a single flesinoxan injection remained present or increased further. Although repeated flesinoxan administration (1 day and 1 week) resulted in 20% lower plasma flesinoxan concentrations, this effect could not explain the neuroendocrine and behavioural findings.

Comparison of relative potencies of i.v. and i.c.v. administered 8-OH-DPAT gives evidence of different sites of action for hypothermia, lower lip retraction and tail flicks

8-Hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT)-induced temperature reduction, lower lip retraction and tail flick responses are widely used models of 5-HT 1A receptor function. To obtain information about the sites of receptors mediating these effects we measured these responses, parallel over wide dose ranges after intracerebroventricular (i.c.v., 0.6–67 μg/kg) and intravenous (i.v., 3–500 μg/kg) administration. Analysis of the dose–response curves provided evidence for a 9.8-fold ratio of the potency of 8-OH-DPAT following i.c.v. compared to i.v. administration on body temperature reduction (ED 50 values are 5.1 and 50 μg/kg, after i.c.v. and i.v. administration, respectively) and a 2.9-fold ratio in potency for lower lip retraction (ED 50 values are 29 and 86 μg/kg, after i.c.v. and i.v. administration, respectively). 8-OH-DPAT was less potent in the induction of tail flicks than of the other responses and had a lower potency after i.c.v. than after i.v. administration (ED 50 values, the first one extrapolated, are 526 and 246 μg/kg, after i.c.v. and i.v. administration, respectively). In addition, the i.c.v. ED 50 for temperature reduction was significantly lower than those for lower lip retraction or tail flick responses. The relative potency, that is, the ratio of i.v. and i.c.v. ED 50, was significantly higher for temperature reduction than for lower lip retraction or tail flick responses (ED 50 i.v./ED 50 i.c.v. values are 9.8, 2.9, and 0.47, respectively). These data provide evidence that distinct sites of action are involved in these models. Temperature reduction is mediated mainly by postsynaptic receptors in the close vicinity of the lateral ventricle. Receptors that mediate lower lip retraction are located more distantly in the brain, supporting previous evidence that they are somatodendritic autoreceptors, and receptors in the spinal cord are probably responsible for tail flick responses. © 1997 Elsevier Science B.V. All rights reserved.

New Benzocycloalkylpiperazines, Potent and Selective 5-HT1A Receptor Ligands

A series of 1-(benzocycloalkyl)-4-(benzamidolkyl)piperazine derivatives was prepared in order to obtain compounds with a high affinity and selectivity for 5-HT1A receptors. The modifications of aromatic substituents, the length of the alkyl chain, and the size of the ring were explored. Most of N-(1,2,3,4-tetrahydronaphthyl)-N'-(benzamidoethyl)piperazines (32-37) were bound to 5-HT1A receptors in a nanomolar range and presented a high degree of selectivity. After resolution, levorotatory enantiomers showed affinity and selectivity higher than those of dextrorotory ones for 5-HT1A sites. The agonist type activity of selected derivatives was also confirmed in vitro on the inhibition of the activation of adenylate cyclase induced by forskolin and, in vivo, on the induction of the lower lip retraction in rats.

Pharmacological profile of LY301317, a potent and selective 5-HT1A agonist

LY301317 ((4r)-(−)-4-(dipropylamino)-6-(5-oxazolinyl)-1,3,4,5-tetrahydrobenz[c,d]indole) has high affinity for the 5-HT1A receptor and weak affinity for the 5-HT1D and histamine-H1 receptors. No significant affinity was found for the other amine receptors studied. In rats, LY301317 produced potent in vivo effects that are characteristic of compounds with agonist activity at the 5-HT1A receptor, such as an increase in serum corticosterone concentration, a reduction in 5-HIAA concentration in brain tissue, induction of flat body posture and lower lip retraction (components of a serotonin syndrome), and a decrease of core body temperature. In pigeons trained to discriminate 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) from saline, full generalization to LY301317 was observed. LY301317 increased punished responding in both the pigeon and rat conflict tests for anxiolytic activity. LY301317 reduced immobility in the rat forced swim model used to indicate potential antidepressant activity. In pigeons, LY301317 blocked emesis induced by a chemical (ditolyguanidine), by a 5-HT3 agonist (m-(chlorophenyl)-biguanide), and by an oncolytic agent (cisplatin), as well as vomiting induced by conditioning to environmental stimuli (a model of anticipatory nausea and vomiting). In addition, LY301317 blocked cisplatin- and ipecac-induced vomiting in the dog and motion-induced emesis in the cat. It was concluded that LY301317 is an orally active, potent, and selective agonist for the 5-HT1A receptor with potential clinical utility as an anxiolytic, an antidepressant, and a broad-spectrum antiemetic. Drug Dev. Res. 40:17–34, 1997. © 1997 Wiley-Liss, Inc.

The effect of premolar extractions on the soft-tissue profile in adult African American females.

The present study was designed to evaluate the effect of four first premolar extractions on the soft tissue profile in African American patients. Pretreatment and posttreatment cephalograms of 28 adult female patients were assessed. The data were subjected to ANOVA, and correlation coefficients were performed between the significantly different dental and soft tissue variables. Variables that showed correlation at r value of greater than 0.6 were subjected to a stepwise multiple regression. The results of the study indicate that retraction of the lower lip correlates with retraction of both maxillary and mandibular anterior teeth. A ratio of 1.2:1 [corrected] was obtained between mandibular incisor retraction and retraction of the lower lip. The relationship between the upper lip and retraction of maxillary incisors was not significant. A ratio of 1.75:1 [corrected] was attained between maxillary incisor retraction and upper lip change. The upper lip correlated most strongly with lower lip retraction. Mandibular incisor angulation was the only hard-tissue variable that could be used as a predictor in a regression model to explain lip response to orthodontic therapy. Changes in the maxillary complex were more difficult to predict because of the complex nature of the soft-tissue integument and the details of muscle tension and soft-tissue tone that were lost by conversion of a three-dimensional structure into a roentgenographic cephalogram. A significant profile change did occur following the extraction of four first premolars and subsequent orthodontic therapy.

Modulation of 5-HT receptor subtype-mediated behaviours by corticosterone

Malfunction of the serotonergic system and dysregulation of the hypothalamo-pituitary-adrenocortical axis have been implicated in the pathophysiology of depression. Several studies provide evidence for reciprocal influences between glucocorticoids and 5-HT receptors. The effect of repeated treatment with a high dose of corticosterone (50 mg/kg s.c. twice daily for 4 days) on 5-HT receptor subtype-mediated behaviours was studied. It was found that in rats that were repeatedly treated with corticosterone the number of 2-chloro-6-(1-piperazinyl)pyrazine HCl (MK 212)-induced, 5-HT 2C receptor-mediated penile erections were reduced, whereas both MK 212 and (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)-induced 5-HT 2A receptor-mediated head shakes were increased. The (±)-8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT)-induced lower lip retraction mediated by presynaptic 5-HT 1A receptors was unchanged, whereas the open field activity induced by 8-OH-DPAT was enhanced in corticosterone pretreated rats. These changes in 5-HT receptor subtype-mediated behaviours were not seen after a single injection with corticosterone given 24 h or 5 days before. The results suggest that 5-HT 2A, 5-HT 2C and postsynaptic 5-HT 1A receptor-mediated behaviour can be modulated by repeated treatment with a high dose of corticosterone.

Modification of behavioral effects of 8-hydroxy-2-(di- n-propylamino)tetralin following chronic ethanol consumption in the rat: evidence for the involvement of 5-HT 1A receptors in ethanol dependence

Behavioral effects induced by 8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT; i.e., lower lip retraction, flat body posture, and forepaw treading) were examined in rats during ethanol withdrawal following a 2-week period of access to a liquid diet containing 9% (v/v) ethanol. After an 18 h withdrawal period, tolerance to 8-OH-DPAT-induced flat body posture and, conversely, sensitization to the effects of 8-OH-DPAT on lower lip retraction were observed in the 9% ethanol group as compared to control rats fed an isocaloric diet. In contrast, 8-OH-DPAT-induced forepaw treading in the 9% ethanol group was not significantly different in comparison to control rats. Plasma corticosterone levels were significantly higher in the ethanol-exposed group than in control animals, an effect which was not additive with the increase in corticosterone levels normally observed after the administration of low doses of 8-OH-DPAT. Altered flat body posture and lower lip retraction responses to a submaximal dose of 8-OH-DPAT (2.5 mg/kg i.p.) were still observed as late as 3 days after withdrawal of the 9% ethanol liquid diet, but were no longer apparent at 7 days. Interestingly, prominent ethanol withdrawal signs such as tremor and rigidity, while occurring on the first day, were completely absent on the third day. Taken together, these results indicate that chronic ethanol exposure differentially alters sensitivity to several pharmacological effects of the 5-HT 1A receptor ligand 8-OH-DPAT. They further support the involvement of 5-HT (5-hydroxytryptamine, serotonin) systems in alcohol abuse and therapeutic interventions using 5-HT 1A ligands.

Post-synaptic 5-HT1A receptor involvement in yawning and penile erections induced by apomorphine, physostigmine and mCPP in rats

Apomorphine and mCPP induced yawning associated with penile erections in rats, whereas physostigmine induced only yawns. Apomorphine-induced yawning and penile erections were antagonized by low doses of raclopride, whereas physostigmine-induced yawning and mCPP-induced effects were only partly inhibited at high doses of raclopride. Scopolamine as well as clozapine antagonized yawning and penile erections induced by apomorphine, mCPP and physostigmine. Similarly, the 5-HT1A agonists 8-OH-DPAT and S 14506 inhibited yawning and penile erections induced by apomorphine, mCPP and physostigmine, and at similar doses induced lower lip retraction and hyperreactivity to handling. The beta/5-HT1A antagonist tertatolol reversed the inhibitory effects of 8-OH-DPAT and S 14506 on drug-induced yawning and penile erections and increased apomorphine- and physostigmine-induced yawn frequency but not penile erection frequency. Like tertatolol, propranolol increased apomorphine- and physostigmine-induced yawn frequency, whereas ICI 118551 increased only physostigmine-induced yawning. 8-OH-DPAT- and S 14506-induced lower lip retraction and hyperreactivity to handling were also significantly antagonized by tertatolol. Finally, p-chlorophenylalanine pretreatment produced about 95% depletion in 5-HT in hypothalamus, hippocampus, striatum and frontal cortex and modified neither the responses of the inducing drugs nor the inhibitory effects of 8-OH-DPAT and S 14506 on drug-induced yawning and penile erections.(ABSTRACT TRUNCATED AT 250 WORDS)

The α2-selective adrenoceptor antagonist org 3770 (mirtazapine, Remeron®) enhances noradrenergic and serotonergic transmission

Org 3770 (mirtazapine, Remeron®) is an antidepressant with an atypical behavioural pharmacology. Org 3770 was found inactive in classical tests used to detect antidepressants, but showed antidepressant-like effects on REM sleep, in the DRL-72 (measuring impulse control) and in the (subchronic) bulbectomy model. Org 3770 has no effect on monamine reuptake, but preferentially blocks noradrenergic α2-auto- and heteroreceptors controlling noradrenaline and serotonin release. α2-Adrenoceptor antagonism in vivo was confirmed by blockade of clonidine-induced mydriasis and in conditioned taste aversion (CTA) experiments with idazoxan. Blockade of α2-autoreceptors in vivo was shown in microdialysis experiments where Org 3770 increased noradrenergic transmission (measured as DOPAC release). Org 3770 has a low affinity for 5-HT1A receptors but potently blocks 5-HT2 and 5-HT3 receptors. Surprisingly, Org 3770 showed 5-HT1A-like effects in CTA and caused lower lip retraction, a 5-HT1A mediated effect. Org 3770 increases serotonergic cell-firing in the dorsal raphe and increased 5-HT release in the hippocampus as measured by microdialysis. These effects are explained by noradrenergic enhancement of 5-HT cell firing and blockade of noradrenaline mediated inhibition of hippocampal 5-HT release. Because Org 3770 blocks 5-HT2 and 5-HT3 receptors, only 5-HT1-mediated transmission is enhanced. In conclusion, the noradrenergic activation by α2-autoreceptor-blockade and the consequent indirect enhancement of serotonergic transmission most probably underly the marked therapeutic activity of Org 3770. Blockade of 5-HT2 and 5-HT3 receptors likely prevents side effects associated with non-selective 5-HT activation and may also contribute to the anxiolytic and sleep-improving properties of Org 3770.

Structure‐Activity Relationship Studies of CNS Agents, Part 26 4‐[2‐(Cycloalkanecarboxamido)ethyl]‐1‐(2‐methoxyphenyl)‐piperazines: High‐Affinity 5‐HT1A Agonists

AbstractCycloalkanecarboxamido)ethyl‐1‐(2‐methoxyphenyl)piperazin es 8a–c, 8e, and 8h were obtained by acylation of 4‐(2‐aminoethyl)‐1‐(2‐methoxyphenyl)piperazine, and their 5‐HT1A, 5‐HT1A, 5‐HT2A and α receptor affinities were determined. It was found that the terminal cycloalkane moiety strongly stabilizes both the 5‐HT1A and 5‐HT2A receptor‐ligand complexes. It was demonstrated that the most active 5‐HT1A ligands 8e and 8h (Ki = 2.1 and 0.21 nM, respectively) behaved as potent agonists of these receptors, i.e. both derivatives mimicked 8‐OH‐DPAT in the lower lip retraction (LLR) model and the effect was susceptible to blockade by reasonable doses of the selective 5‐HT1A receptor antagonist (S)‐WAY‐100135.

The corticosterone-enhancing effects of the 5-HT 1A receptor antagonist, (S)-UH301, are not mediated by the 5-HT 1A receptor

We tried to antagonize the endocrine and behavioural changes induced by the selective 5-HT 1A receptor agonist, flesinoxan, with the putative 5-HT 1A receptor antagonist, (S)-UH301 (( S)-5-fluoro-8-hydroxy-2-(di- n-propylamino)tetralin). The interaction of (S)-UH301 (3 and 10 mg/kg s.c.) with flesinoxan (3 mg/kg s.c.) showed no antagonistic effects of (S)-UH301 on flesinoxan-induced corticosterone secretion. In fact, like flesinoxan (1 and 3 mg/kg s.c.), (S)-UH301 (3 and 10 mg/kg s.c.) itself dose dependently increased plasma corticosterone levels. Unlike flesinoxan, (S)-UH301 did not induce hyperglycemia, lower lip retraction and flat body posture. Moreover, flesinoxan-induced hyperglycemia and behavioural changes were effectively antagonized by (S)-UH301, showing potent 5-HT 1A receptor antagonistic effects of (S)-UH301. Therefore we conclude that (S)-UH301 is a potent 5-HT 1A receptor antagonist and that the (S)-UH301-induced corticosterone secretion is mediated by a non-5-HT 1A receptor mechanism.

Pharmacological characterization of enantiomers of 8‐thiomethyl‐2‐(di‐n‐propylamino)tetralin, potent and selective 5‐HT1Areceptor agonists

AbstractLY274600 and LY274601 are the S (−) and R (+) enantiomers, respectively, of 8‐thiomethyl‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT). In in vitro studies, both enantiomers have high and selective affinity for the 5‐HT1Areceptor. However, LY274600 produced submaximal inhibition of forskolin‐stimulated cyclase activity, which indicates that it is a partial agonist, whereas LY274601 produced maximal inhibition of cyclase activity, which indicates that it is a full agonist in this model. Both of these enantiomers had potent in vivo pharmacological effects in rats that are characteristic of 5‐HT1Areceptor agonists including (1) a reduction of hypothalamic 5‐HIAA levels, (2) an increase in serum corticosterone levels, (3) a reduction in hypothalamic 5‐HTP accumulation after decarboxylase inhibition, (4) an induction of 5‐HT1Abehavioral responses, e.g., flat posture and lower lip retraction, and (5) a lowering of body temperature. In these general pharmacological tests, both compounds had a potency equal to or greater than 8‐OH‐DPAT but had a greater oral activity. LY274601 appeared to be either slightly more potent or efficacious than LY274600. In the drug‐discrimination studies using pigeons trained to identify the effects of 8‐OH‐DPAT, LY274601 was significantly more potent than LY274600, but both were less potent than 8‐OH‐DPAT. Both enantiomers restored full sexual reflex function to rats that had reduced sexual capacity. In rats with normal capacity for sexual reflexes but reduced performance, the enantiomers caused decreases in ejaculatory latencies and postejaculatory latencies and increases in copulatory efficiency and rate. No consistent differences between the enantiomers could be demonstrated in these estimates of total sexual performance, erectile capacity, and sexual drive. Both enantiomers increased punished responding at lower doses than were needed to decrease unpunished responding in pigeons, an effect that is indicative of anxiolytic activity. LY274600, a partial agonist, produced a significantly greater change in punished responding than did LY274601, a full agonist. Both compounds induced dose‐related decreases in immobility time and defecation rate in the rat forced swim model, which represent reductions in stress‐induced “behavioral despair” and stress‐induced gastrointestinal motility. Collectively, these pharmacological studies have shown that the substitution of a thiomethyl for hydroxyl group at the 8 position on the 2‐(di‐n‐propylamino) tetralin structure resulted in selective and potent agonists for the 5‐HT1Areceptor similar to that of 8‐OH‐DPAT but with improved oral potency. The preclinical efficacy studies demonstrated possible utilites for these compounds in the treatement of either sexual response disorders, anxiety, or depression. © 1995 Wiley‐Liss, Inc.

The Selective α2-Adrenoceptor Antagonist Mirtazapine (Org 3770) Enhances Noradrenergic and 5-HT1A-Mediated Serotonergic Neurotransmission

Mirtazapine (Org 3770) is a selective antagonist at α2-adrenergic auto- and heteroreceptors, which are involved in regulation of neuronal noradrenaline (norepinephrine) and serotonin (5-hydroxytryptamine; 5-HT) release. It was identified as a potential antidepressant in rat sleep studies, showing characteristic REM sleep suppression, as well as activity in the bulbectomised rat and an operant behaviour model. However, mirtazapine does not inhibit monoamine reuptake and is inactive in classical tests predictive of antidepressant activity (antagonism of reserpine-induced hypothermia, Porsolt test, and muricidal behaviour). As an α2-antagonist, mirtazapine inhibits clonidine-induced mydriasis and resembles idazoxan in evoking conditioned taste aversion. In addition, mirtazapine induces lower lip retraction, a response characteristic of 5-HT1A receptor stimulation, and resembles the 5-HT1A agonist 8-hydroxy-dipropylaminotetraline (8-OH-DPAT) in producing conditioned taste aversion. Thus, mirtazapine may have indirect serotonin-enhancing effects, since its affinity for 5-HT1A receptors is low.