Naunyn-Sdlmiedehcrg's Arch Pharmacol (1996ll354}O()(Jrvou 5:;1-O()()~J5I '\\!. 5 C' Springcr-Vcrlag 1996 ORIGINAL ARTIC'LE
Miguel Re}'es-Parada . Cecilia Scorza . Verónica Romero Rodolfo Silveira . Jorge H. Medina . Danice Andrus . David E. Nichols . Bruce K. Cassels ( + )-1-(2,5-Dimethoxy+ethylthlophenyl )-2-aminopropane (ALEPH-2), a novel putative anxiolytic agent lacking affinity for benzodiazepine sites and serotonin-1A receptors , ~.__.-~,•.: = - Mastercopv...... •••...... •.....••• Please ¡n5ert YOur corrections in Received: 20 March 1996/Accepted: 28 May 1996 ... this topy and send lhis copy lo
Abstract Serotonergic behavioral responses, efTects on Phenylisopropylaminesthe pubJisher . Rat . J motor activity and core temperature, and binding Hypothermia . Psychedelics properties of the novel putative anxiolytic amphe!a• mine derivative (± )1-(2,5-dimethoxy-4-ethylthlo• phenyl)-2-aminopropane (ALEPH-2), we~e examined Introductlon in rodents in order to elucidate the mcchamsm lInderly• ing' its anxiolytic-Iike effect. After peripheral adminis• The incidence of undesirable side effects concomitant tration in rats, ALEPH-2 induced some symptoms of with benzodiazepine treatments has generated a great the serotonergic syndrome. e.g. forepaw treading ahd deal of interest in the search for new anxiolytic agents flat body posture. Additionally, a decrease in motor with mechanisms of action other than those of the activity was observed. No significant efTects on the c1assical benzodiazepines. Thus far, the most likely number of head shakes were observed after injection, therapelltic alternatives seem to be drllgs that act lIpon although high inter-sllbject variability was noted. the serotonergic system (Barrett and Vanover 1993). Higher doses of ALEPH-2, in the range exhibiting Thus, serotonin 5-HT lA receptor agonists (fllll and anxiolytic properties (4mg/kg), elicited significant hy• partial) (De Vry et al. 1991), 5-HT 2 antagonists (lIsually pothermia in mice. The affinity of the drug for non selective 2A/2C agents) (Koek et al. (992) and 5-HT 2Aí2C receptors (eH]ketanserin sites) was in the 5-HT3 antagonists (Costall and Naylor 1991) ha ve nanomolar range (K¡ = 173 nM), whereas for 5-HTIA, shown anxiolytic efTectsin severa) behavioral models of benzodiazepine sites, and GABAA receptors, the affi• anxiety and, in some cases, in human c1inical trials nity was micromolar or lower. Based on these results (Feighner et al. 1982; Gammans et al. 1992). the mechanism of action and the anxiolytic-Iike proper• It is known that methoxylated and alkylthio ties of ALEPH-2 are discussed. phenethylamine derivatives afTect serotonergic ne~ro• transmission in many ways (Nichols 1994). Halluctno• Key words ALEPH-2 . Serotonin receptor binding . genic 2,5-dimethoxy amphetamine derivatives, for in• Anxiolytics . Serotonin syndrome . stance. are' potent and selective 5-HT 2A/2C ligands (Glennon et al. 1984). Para-substituted analogues such as p-methylthio- and p-methoxyamphetamine (PMA) are potent 5-HT releasing agents (Huang et al. 1992; M. Reyes-Parada (181)' c. Scorza' V. Romero' R. Silveira Nichols et al. 1993; Nichols 1994). Additionally. PMA Cell Biology Division, Instituto de Investigaciones Biológicas is a selective monoamine oxidase-A inhibitor (Green Clemente Estable, Avda. Italia 3318, Montevideo, Uruguay and El Hait (980). However, anxiolytic efTectshave not 1.H. Medina been reported for any members of these c1asses of Instituto de Biología Celular, Facultad de Medicina, Paraguay 2155, (1 (21) Buenos Aires, Argentina drugs. We ha ve recently shown that ( ± )1-(2,5-dimethoxy- D. Andrus1f-. Nichols }. 4-ethylthiophenyl)-2-aminopropane Jl..,(ALEPH-2), J.-... Deparlment or Medicinal Chemistry and MoleclIlar Pharmac.ology, Purdue Universily, School or Pharmacy and Pharmacal SClences, a phenethylamine derivative which has been reported West Larayette, IN 47907, USA to have psychedelic effects in hllmans (Shulgin and O.K. Cassels Shulgin 1991), exhibits an anxiolytic-like profile in mice Department or Chemistry, Faclllty or Sciences. Universidad de and rats in the elevated plus maze test as well as in the Chile. Casilla 653, Santiago, Chile elevated T -maze test (Scorza et al. 1996). , ,,' In the presenl study we report the behavioral In all hchavioral studies, the cxperilllents "cre pcrformed (serotonergic syndrorne). biochernical (binding proper• betweeÍl 09:00 and 12:30h. The observers (two for each expcri• ment) were always blind to the drug trcatment condilion of the ties) and physiological (eITecls on body temperature) animals. profile of ALEPH-2, in comparison with Ihe actions of some structurally related phenethylamine derivatives without anxiolytic properties, in an eITort to elucidate Radioligand binding studics the mechanism underlying its putative anxiolytic effect. 5-IIT rc('eplllr hillt/i"lf. 11.previously descrihcd proccdurc was em• ployed IJohnson et al. 1990). Brieny, the frontal cortelt or hippocam• Method. pal brain regions from 20--40 male Sprague-Dawley rats (175~2oo g, Harlan laboratories, Indianapolis) were pooled and homogenized (Brinkman Polytron, setting 6 for 2 )( 20s) in four or eight volumes Drrlll.~. II.lEPH·2, ( ± 11·{2.5.dimetholty-4-bromophenyl)-2·amino. of 0.32 M sucrose for frontal cortex or hippocampus, respectively. propane (DOR) and (± )1-(2,4,5-trimethoxyphenyl)-2-amino• The homogenate was centrifuged at 36000)( g for 10 min, and the propane (TMII.-2), all as hydrochloride salts, were synthesized fo1• reslllting pellets were resuspended in the same volume of sucrose lowing published procedures (Shulgin and Shulgin 1991). II.mif• sollltion. Separate aliquots of tissue were frozen at - 70 C until lamine was generously donated by ASTRII. II.rcus II..R. (Sweden). assay. Cinanserin was a gift from the Squibb 1nstitute for Medieal Re• For each separate experiment, a tisslle aliquot was thawed slowly search. 8-Hydroxy-N,N-dipropylamino lelralin (8-0H-DPII. T) was and diluted 1: 25 with 50 mM Tris HCI (pH = 7.4). The horno• from RBI USII., and 5·HT was from SIGMII.. eH]kelanserin, eH] genate was then incubated at 37 C for 10 min and centrifuged twice 8-0H-DPII.T, eH] nunitrazepam ([JH]FNZ) and [lH]muscimol at 36500)( g for 10 min, with an intermittent wash with buffer. The were purchased from New England Nuclear (Roston) at specific resulting pellet was resuspended in 50 mM Tris HCI containing activities of 61.9, 132.8. 87 and 20 Ci/mmol, respectively. 0.5 mM NazEDT 11.,0.1% Na ascorbate, and 10 mM pargyline HCI. 11.11drugs were dissolved in the corresponding vehicle (saline or In eltperiments with [JH]ketanserin, 5.7 mM CaClz was included. water), on the same day the assays were performed. In the hehavioral 11.second preincubation for 10 min at 37 C was conducted, and the studies, volumes injected were 1 ml/kg and 5 ml/kg body weight in homogenate suspensions were than cooled in an ice bath. 11.11eltpcri• rats and miee, respeclively. ments were pcrformed with triplicate determinations using the ap• propriate buffer, to which 200-400 IIg of protein was added, in a final volume of 1 mI. The contents of the tubcs were allowed to equilibrate Behavioral studies for 15 min at 37 C bcfore filtering through Whatman GF/C filters using a cell harvester (Brandel, Gaithersburg Md., USII.) followed . . . '" . . by two 5 mi washes using iee-cold Tris buffer. Specific binding Anrmab. Male Wlstar rats (Instlluto de InvestigacIOnes BlOloglcas was defined as that displaceablewith 10 ~IM cinanserin in the Cle.mente Estable an.imal stock) weighing 200-24~ g were used. [)H] ketanserin and with 10 ~IM 5-IH in the [)H] 8-01-l-DPII.T lI..ntmals were housed In groups of 5-6, under a 12-h.hght/dark cycle binding studies, respectively. Filters were air-dried. placed in scintil- (hghts on at 08: 00 and off at 2~ 00) at 22 ± 1 c. wlth free access to:tt: lation vials with 10011 of Ecolite scinlillation cocktail. and allowed food and waler. lo sit overnight before counting at an elliciency of 37%. Five to sÍ)( concentrations of radioligands were used in both 5-HT .~ymlrollJe. The rats were placed separalely in cages 5 min [)H]kelanserin and [)H]8-0H-DPAT saturalion eltperimenls. before the i.p. injection of equimolar doses of Ihe drugs (30 IImol/kg). [JH]ketanserin bound to a single site (Hill coefficient 1.08 ± 0.06) Control animals received saline under Ihe same conditions. Immedi• with a Ron•• of 180 ± 19 fmol/mg protein and a Ko of 0.83 ately after injection, each animal was placed in an individual plastic ± 0.08 nM. eH]8-0H-DPII.T bound to a single sile (HiII coeffic• eage (60)( 60 )( 36 cm) equipped with photobeams, and its motor ient 1.00 ± 0.01) with a Ron•• of 110 ± 10 fmol/mg prolein and activity, defined as the number of beam crosses, was scored during 30 min (Seorza et al. 1996). During the same period, observation druga K[) toofdisplace0.67 ± 0.100.75 nM.nM e"]T~ ketanserinability of 8-9or eH]-8-0H-DPATconcentrations of wastesl sessions lasting 45 s each, beginning 3 min after the injection of the determined in drug displacement studies. drug, were repeated every 3 mino Recíprocal forepaw treading, hind·
limb abduction and nat body posture were scored using a ranked BDZ (/11<1 GII.BAA receptor I>i"dillll studies. The affinity of AlEPH-2 intensity scale, where O = absent, I = equivocal, 2 = present, 3 = in• for the central Iypc BDZ receptor was measured using eH]FNZ. tense (the maximum score. summed over Ihe 10 observation periods, Briefly, for each assay, triplieate or quadruplicate membrane sam• amounted lo 30 for each symptom¡'animal)(Trieklebank et al. 1985). pies containing 200-400 ~Ig protein, determined by the Lowry method, were suspended in 1 mi Tris-HCI buffer, pH 7.3 and ¡ncu• lIead shClkes. In the first series of experiments, rats were injected i.p. bated at 4 'c for 60 min with 0.7 nM eH]FNZ. Non-specific bind• with II.lEPH-2 at the same dose used in the 5-HT syndrome studies ing was determined by parallel incubation in the presence of 3 ~IM (8.7 mg free base/kg, 30 IJmol/kg) and with a reportedly anxiolytic FNZ or c10nazepam and amounted to 5-15% of the total. Mem• dose (4 mg free base/kg, 13 IImol/kg). Control animals received sa• branes were harvested by rapid filtration through GF¡B filters with line and a group of rats injected i.p. with the 5-HT ZA/ZC agonist DOB 3 washes using 5 mi of the incubation buffer each time. Then, filters (0.5 mg free base/kg, 1.6 ~Imol/kg) was included as a positive control. were dried and transferred to vials with scintillation cocktail (2.5 mi Immediately after injection rats were placed in the observation cage diphenoltyloltazole-xylene) and the radioactivity was measured with and the number of head shakes, defined as rapid side to side 40% efficiency. rotations of the head and ears (Bedard and Pycock 1977), was GARAA receptors were assayed using eH]muscimol as the quantified for 30 mino radioligand. Each assay run in triplieate used 100-150 IIg protein In the second series of experiments, the ability of II.LEPJI·2 to incubated in 1 011Tris-HCI buffer, pH 7.4,with 13 nM [3H]mus• prevent DOB-induced head shakes was evaluated. Rats were pre· cimol for 30 min at 4 'C. Non-specific binding was measured by treated with either saline or ALEPH-2 (4 mg/kg i.p) and 30 min later performing the incubation in the presence of 100 IJM GARA and the animals were injected with DOD (0.5 mg/kg). Immediately represented 10-20"10 or the total. The membranes were harvested after injection of DOR, head shakes were quantified as described arter addition of 5 mi ice-cold buffer by rapid filtration through above. Whatman GF/C filters followed by two washes with 5 mi of buffer. 3
EITeets on body lemperature
Allilllllb. Male CFI mice (lnstiluto de InvesligacillOes Diológkas Clemente Eslahle animal stock) weighing 25- 35 g were used. Ani· mals were housed in groups of 1012. under a 12·h Iighl:dark cyde (Iighls on at OR: O() and oITat 20: 001 at 22 ± I e wilh free access lo food and waler.
Fi~. I Chemkal struclure llf ALEPI-f-2 '1.I'p"lh("IIIill. MI'use core lemperalure was measured hy inserting the prohe of a dígital thermomeler approxímalely 2.5 cm into the reclum while lighlly reslraining the animal immediatcly hefore (to) Motor Activity and 10. 20. 30. 60 and 120 min after an i.p. injectil'n of saline or 200 drugs. The resulls are expressed as Ihe change in body temperature (~t). with respecl to the basal lemperalure. measured at Ihe hegin• DSahne ning of the experiment (tol (Martin et al. I992). ti" ISO ~ Aml"amln~ " .AI"ph-2 Slllli.~IÍflll (IIwlpis. Means ± SEM were calculaled and are pre• e §TMA-2 u 100 sented for each experimental group. In the 5-IH syndrome, e head shakes. motor activity and hypolhermia sludies. statistical tini significance was assessed by analysis of variance (ANOV Al followed. al SO when appropriale, by Mann- Whítney V -test and Student's I-test. In the receptor binding studies. data were analyzed using Ihe com• puter programs EDDA and Ligand as descrihed by McPherson O (McPherson 1985). In all cases the significance level was found to be Treatment P < 0.05. Fig.2 EITects on locomotor aClivity induced by equimolar doses of phenelhylamine derivatives. The measurements were made immedi• alely after i.p. injection of the drugs. Each bar represents the R•• ults mean ± SEM of beam crosses (lf 10 rats per condition. -significant diITerence (r < 0.05 ANOVA-Sludenl's I-les!.) Behavioral studies AII drugs tested significantly decreased the number of Table I shows the results of the effects of equimolar beam crosses as compared with controls. doses (30 ~lmol/kg) of phenethylamine derivatives on The effects of ALEPH-2 on head shake behavior components of the serotonin syndrome. Amiflamine. are summarized in Tables 2 and 3. As is shown in Table a selective monoamine oxidase-A inhibitor and TMA· 2, the dnig did not induce the response to a significant 2, a psychoactive phenethylamine derivative (Shulgin extent at either of the two assayed doses. However, we and Shulgin 1991) with relatively weak affinity for noted that many rats (7 out of 10) did not display the 5-HT 2A/2e receptors (Glennon et al. 1984) were in• behavioral response. while a large number of head c1uded in this study. AIl the drugs tested induced re• shakes (mea n ± SEM = 22 ± 2) were observed in the sponses suggesting activation of 5-HT receptors, and remainder of the group. Almost the same behavior was were very potent inducers of the flat body posture observed at both dose levels. Additionally, ALEPH-2 response. The most interesting difference was the signi• was very potent in preventing the head shakes induced ficant ability of ALEPH-2 to e1icit forepaw treading, by nOB, Table 3. a behavior that has been associated with the selective activation of 5·HT I A receptors (Tricklebank 1985). It is worth pointing out that all behavioral responses began Effects on body temperature almost immediately after injection. Figure 2 compares the motor activity elicited by When mice were injected with increasing doses of injection of the different phenethylamine derivatives. -ALEPH-2 (1,2,4,8 mg/kg), a dose-dependent decrease
Table I Behavioral.0.00.0SalíneTMA-2scoresAmiflamine0.0for phenethylamine derivati~es 262546±1.3± 0.50.7-0.8-26 ± 0.5-Forepaw treading ALEPI-f-2 components induced by three Abduction I-findlimbFlatindividualbody posture5-I-fT syndrome 25 ± 0.7-
Each sign was scored at 3 min intervals during 30 min on a ranked intensity scale (0-31. The measurements started 3 min after i.p. injection of equimolar doses (30 ~mol/kgl of Ihe drugs. and lasted 45 s each. Values given are the mean scores ± SEM or 10 rats per condition. ·sígnificant difference (P < 0.05 ANOVA-Mann-Whilney V-test.) /4
.' // T.h1~ 1 Ilc"d sh,,\¡.:s indm:cd "y dilTcrcnl doscs of ALEI'H·2 30 min arter ALEPH-2 (Fig. 3B). Thc lempernture re• / ------lurned lo baseline wilhin 120 min after injection of lhe / ALEI'II·2 ALEI'II·2 Saline Don drug (dala not shown). 8-0H-DPAT at a dose of (4 mg/kg) (R.7 mg/kgl (0.5 mg/kg) 0.5 mg/kg "i.p., was injecled as a positivc control, and Hc"d sh"kcs 6.6 ± 10.3 6.2 ± R.2 2.7 ± 0.9 2R ± 4.5· produced basically the same time-cottrsc as ALEPH·2 (Fig.3B). Thc numt>cr of hcad shakes w"s c(lunled during 30 mino The measuremenls werc made immedialely after i.p. injcclion of each drug. Values given are Ihe mean scores ± SEM of 10 rals per condition. e~ccpl in Ihe case of DOn (11 = 6) . • significanl diITerence Radioligand sludies (P <0.05 ANOVA·M¡lnn·Whilney U·lest) Table 4 lists the K¡ values delermined for ALEPH-2 using the four radioligand binding assays ulilized in this study (see Materials and methods). At [3H]ketan• Saline + DOD AlEPH·2 + DOD serin binding sites, ALEPH-2 has an affinity in the nanomolar range, which is about three times lower and Head shakes 31 ± 4.2 3.4 ± 4.2· about seven times higher than the structurally related Rals were injecled wilh eilher saline or ALEPH·2 30 min before drugs DOB and TMA-2, respectively. 008. The number of head shakes was counled during 30 mino The At the [3H]8-0H-DPAT site, ALEPH-2 has an measurmenls were made immedialely afler i.p. injeclion of DOD. affinity in the micromolar range. The K¡ of ALEPH-2 Values given are lhe mean scores ± SEM of 8 rals per condilion. for the [3H]8-0H-DPAT site is similar to that of DOB • significanl diITercnce (P < 0.05 ANOVA·Mann· Whilney U ·les,", and about five times lower than that of TMA-2. ALEPH-2 does not recognize cenlral BDZ binding ALEPH-2 sites or GABAA receptors. The K¡ values for eH]FNZ and [3H]muscimol binding sites are higher than lOOJ.lM. ~ e .oJ•• ••E ••• .oJ •• •• Q. 11 E •.. Dlscusslon •• .oJ 1- •.• >- 11 "Oo ':¡••• A few reports exist describing the subjective effects ID <]~ of ALBPH-2 in humans. Like a number of other o 4-su bsti tuted- 2,5-dimethoxyam pheta mine deri vatives, M ALEPH-2 is regarded as a psychedelic drug (Shulgin o 2 ) 4 S 6 7 8 and Shulgin 1991). However, like other 4-alkylthio de• rivatives, this drug seems to difTer from c1assical (a) Dos!! (mgjKg) psychedelics, tending to produce a sta le of emotional detachment and anhedonia (Shulgin and Shulgin 1991; u~ 00 Nichols 1994). :..- -o 5 • B-OH-DPAT •• (05 mg/l
ND, nol dclerl1lined
has been associaled wilh lheir affinily for 5-HT 2 sub• clive 5-HT 2 anlagonisls showing anxiolytic profiJes in type receplors (Yap and Taylor 1983; Glennon and behavioral tests (Barrett and Vanover 1993; Koek et al. Lucki 1988; Glennon 1990). 1992). However, the psychedelic efTeclsof ALEPH-2 in The findings put forth above suggesled lo us the humans and its ability to induce some serotonergic possibility that ALEPH-2 might be a 5-HT1A ligand. syndrome responses in a way similar to other Nevertheless, the radioligand displacement studies serotonergic transmission enhancers suggest that showed that the drug has a very weak affinily for these ALEPH-2 is an agonist rather than an antagonist at receptors. Furthermore, these studies revealed that 5-HT 2 receptors. ALEPH-2 has a remarkably high affinity for 5-HT 2A/2C However, 5-HT 2 agonists, including psycho• receptors ([3H]ketanserin sites) which. like that of tomiJT!etic amphetamine deriva tives, elicit no consis• other 2,5-dimethoxy amphetamine derivalives, corre• tent anxiogenic-like responses in different behavioral lates well with its reporled hallucinogenic polency in models. Also, the anxiolytic effects of 5-HT2 antago• humans (Glennon et al. 1984; Sadzot el al. 1989; Shul• nists can be overcome by agonists of these receptors. In gin and Shulgin 1991). As expecled, lhe drug has no addition, it has been suggested that 5-HT 2 receptors affinity for benzodiazepine siles or GABAA receplors, may play an inhibitory role on plus-maze behavior and ruling ~)Utthe possibilily of ils anxiolylic-like activity that a down-regulation of these receptors may be re• being mediated by in lhese systems. sponsible for the anxioJytic profile observed 48 h after A ralher intriguing result was lhe observation that mianserin administration (Benjamin et al. 1992). Thus, ALEPH-2 also behaved in a difTerent way from ils a different explanation for the. mechanism of aclion hallucinogenic congeners regarding ils effecls on the couJd be offered. It has recenlly been reported that the head shake response. Head shakes are a normal beha• selective blockade of 5-HT 2C receptors seems to be vior in rats, but lhe administralion of selective responsible for lhe anxiolytic activity of non selective 5• 5-HT 2A/2C agonists c1early increases their number (Yap HT 2A/le anlagonists (Kennett 1992; Kennett et al. and Taylor 1983; Glennon and Lucki 1988; and see 1994). Furthermore, the reJatively selective 5-HT 2C Table 2, DOB effecls). As was observed, ALEPH-2 not agonist m-chlorophenylpiperazine (m-CPP), which is only did not significanlly elicit this response, but was anxiogenic in humans and rodents (Kahn et al. 1988; even able to prevent the behavior induced by DOB Kennett et al. 1989: M urphy et al. 1991), induces hyper• injected 30 min later. It is worth pointing out that in the thermia in rats (Wozniak et al. 1989; Murphy et al. case of the head shakes induced by ALEPH-2 a large 1991; Klodzinska and Chojnacka-Wójcik 1992). inter-subject variability was observed. This last finding Considering the un usual combination of effects could be a correlate of the highly variable effects ob• exerted by ALEPH-2 in rats, e.g. hypothermic and served in humans (Shulgin and Shulgin 1991). anxiolytic-like activity and the inabilily to consistently In agreement with previous observations (Scorza et induce head shakes, it may be possible that this drug al. 1996), ALEPH-2 induced a decrease in motor acti• could act as an antagonist at 5-HT 2C receplors, and still vity, an effect which was also produced by the other retain its 5-HT2A agonist aclion. In this sense, it is phenethylamine derivatives evaluated. interesting to speculate about the role of 5-HT 2C recep• Even though the sum of the results reported here tors in the effects of psychedelics in humans. Basically, does not completely c1arify the mechanism by which all hallucinogenic drugs are non-selective with regard ALEPH-2 behaves as an anxiolytic in rodents and to 5-HT2A and 5-HT2C receptors (Glennon et al. 1992), further studies are needed, for example using diverse but the relative contribution of eacl1 receptor to the 5-HT antagonists, we feel that several new hypotheses overall effect of these substances has not been e1uci• must be considered. Thus, the simplest possibility is dated. NevertheJess, Sanders-Bush and colleagues have that ALEPH-2 acts as an antagonist or a weak partial demonstrated that several structuraJly di verse haJluci• agonist of 5-HT 2A/2C receptors, since the drug dis• nogens are agonists at 5-HT 2C receptofs (Burris et al. played a relatively high affinity for these sites and 1991; Sanders-Bush and Breeding 1991). Thus, consid• blocks a behavioral response induced by an agonist. ering the difTerences between cJassical psychedeJics and There exists well documented evidence for non-sele- ALEPH-2, this compound, and perhaps other sulfur- containing phenethylallline derivatives. Illight be lIseful tent serotonin 5-llTlc rceeptor agonist. J Pharmacol Eltp Thcr tools to dissect the difTerent cOlllponents of the psyche- 25l!:l!91 l!l)6 delic experience, Costall O, Naylor "119911 Anxiolytic.: elTects llf 5-IIT.1 antagllnists in imimals. In: Rodgers RJ. C'oopcr SJ (edsl 5-11T lA agllnists. 5-11T) Additionally. 5-HT". cholecystokinin or glutamate antagonists and bcnzodialcpines: their wmparati\c hchavioural receptor-mediated effects cannot be discarded as e1ici- pharmacolllgy. Wiley, C'hiehester, England, pp 133157 l tors of the anxiolytic response, but the lack of struc- C'ritchley MAE, lIandley SL (I987) ElTects in thc X-maze anxicty tural similarity between ALEPH-2 and drugs that af- model of agents acting al 5-HT. and 5-HTz reeeptors. Psycho- fect these receptors acts against this explanation for the pharmaeology 93:502 506 De Vry J. Glaser T. Schuurman T, Schrcihcr R. Traher J 119911 mechanism of action ofthis phenethylamine derivative, 5-IIT'A rcceptors in anxiety. In: Briley M, File SE leds) Another possible explanation for the anxiolytic-like New concepts in amiety. C'RC' Press. Boca Raton. n. pp activity of ALEPH-2, is the formation of some active 94129 could be responsible for the in vivo actions. Obviollsly co~panso~ of h~splrone and .dlazepa~l m outpatlents wlth gene· , . -,.. ralrzed anxlety dlsorder. J Clrn Psychlatry 43: 103·107 t~ISmetabolite.~etabol~tepossiblywouldoa notsulfoxidebe detected,or a sulfone,m the !.!l..!!!!..Whic~eighner ammans J~,RE,Merideth.StringfellowC'H, JC,Hend.ricksonHvizdos AJ,~A Seidehamel(198~1 Dou~le.blindRJ, Cohn bmdmg studles, Expenments to determme the effects of JB, Wilcox CS, Fabre LF, Pecknold JC, Smith WT, Rickels a possible ALEPH-2 metabolite are currently being K (1992) Use of buspirone in patienls with generalized anxiety performedo disorder and coexisting depressive symptoms. A meta-analysis of A dd't' I t t' 'b'l't' th ' t eight randomized controlled studies. Neuropsychobiology n a 1 lona ,emp mg POS~I 011 Y IS o e eXls ~n~e 25: 193-201 of a new mechamsm for allevJatmg anxlety. Thls IS Glennon RA (1990) Do c1assical hallllcinogens act as 5-HT z agonists based on the fact that ALEPH-2 does not show affinity or antagonists? Neuropsychopharmacology 3:509-517 for 5- HT lA or benzodiazepine receptors, thus ruling Glenn?n ~A, Lucki 1(1988) Behavioral models o~serotonin receptor out a mode of action similar to those of the most widely aC~lvatlOn. In: Sanders-Bush E (ed) Serotonm. Humana Press. d 'l' d 1 h' ALEPH 2 'h b C'lrrton Park, N.J., pp 253-294 use anxlo yl1c r~gs, ~ t IS sense, - ~Ig t e Glennon RA, Tileler M, McKenney JD (1984) Evidence for 5.HTz a useful tool to mvestlgate such a hypothetlcal new involvement in the mechanism of action of hallucinogenic agents. mechanism. tife Sci 35:2505-2511 Fi~ally, although this possibility seems even less Glennon RA,. R?gghupathi R, "arly~el P, .Tei~ler M, leonhardt likely, A LEPH-2 might have some action of 5-HT S (1992) BlIldlllg of phenylalkyl?mllle denvatl\es at 5-HT le: ~nd .. , . lA 5-HT 1 serotonlll receptors: eVldence for a lad of selectlvlty. autoreceptorso There eXlsts mcreasmg eVldence that J Med Chem 35:734-740 5-HT1A autoreceptors (Iocated in the raphe nuclei) are Grccn Al, El Hait MAS 1198011'·Methllxyamphctaminc, a polent functionally different from the 5-HT lA receptors reversible inhibitor of type-A monoamine oxidase in vitro and in located postsynaptically (See for example Radja et al. vivo. J Pharm Pharmacol 32:262-266 1992). Because the radioligand experiments for 5-HT Gudclsky GA, Koemg !1. Meltzer HY (I9l!61 The~mo~egulatory . '. lA responses to serotonlll 15-HT) receptor sllmulallon m the rat. receptors were only done usmg hlppocampal mem- Evidence for opposing roles of 5-HTz and 5-HT'A receptors. branes, i.e., postsynaptic receptors, we cannot discard Neuropharmacology 25:1307-1313 a possible contribution of 5-HTtA autoreceptors to the Handley Sl, McBlane JW, Critchley MAE, Njllng'e K (19931 Mul- anxiolytic-like effects of ALEPH-2. tiple serotonin. mechanism in a~i.mal models (lf anxiety: e~viron- menlal, emotlOnal and cogmtlve factors. Behav Bram Res 58:203-210 Huang X, Marona-Lewicka O, Nichols DE (1992)I'·Methylthioam• Aeknowledgements The critical comments and helpful suggeslions by Pror. F. G. GraelT are greatly appreciated. This work was par• phetamine is a potent new nonneurotoxic serotonin-releasing agent. Eur J Pharmacol 229: 3 1-38 tially supported by CONIC'YT grant 94/038, International Founda• Johnson MP, Mathis CA, Shulgin AT, HolTman AJ, Nichols DE tion for Science (IFS), International Program in Chemical Sciences (1990) zll]-2-(205-dimethoxy-4-iodophenyl)aminoethane ([ I Z ll]• (IPICS), PEDECIBA (Uruguay), and NIH granl DA02189 (D.E.N.). e M. Reyes-Parada was the recipient of a research fellowship from 2-C-1) as a label for the 5-HTz receptor in ral frontal cortex. Pharmacol Biochem Behav 35:211-217 CONICYT (Uruguay). It was also partíally supported by FON• Kahn RS, Van Praag HM, Welzler S, Asnis GM, Ban G (1988) DECYT grant N' 89/915 (Chile). Serotonin and anxiety revisited. Biol Psychiatry 23: 189-208 Kennelt GA (1992) 5·HT ICreceptor antagonists have anxiolytic-like actions in the rat social interaction test. 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