D-lysergic Acid Diethylamide Research Articles

Serotonin model of schizophrenia: emerging role of glutamate mechanisms

The serotonin (5-HT) hypothesis of schizophrenia arose from early studies on interactions between the hallucinogenic drug LSD ( d-lysergic acid diethylamide) and 5-HT in peripheral systems. More recent studies have shown that the two major classes of psychedelic hallucinogens, the indoleamines (e.g., LSD) and phenethylamines (e.g., mescaline), produce their central effects through a common action upon 5-HT 2 receptors. This review focuses on two brain regions, the locus coeruleus and the cerebral cortex, where the actions of indoleamine and the phenethylamine hallucinogens have been shown to be mediated by 5-HT 2A receptors; in each case, the hallucinogens (via 5-HT 2A receptors) have been found to enhance glutamatergic transmission. In the prefrontal cortex, 5-HT 2A-receptors stimulation increases the release of glutamate, as indicated by a marked increase in the frequency of excitatory postsynaptic potentials/currents (EPSPs/EPSCs) in the apical dendritic region of layer V pyramidal cells; this effect is blocked by inhibitory group II/III metabotropic glutamate agonists acting presynaptically and by an AMPA/kainate glutamate antagonist, acting postsynaptically at non-NMDA glutamate receptors. A major alternative drug model of schizophrenia, previously believed to be entirely distinct from that of the psychedelic hallucinogens, is based on the psychotomimetic properties of antagonists of the NMDA subtype of glutamate receptor (e.g., phencylidine and ketamine). However, recently it has been found that many of the effects of the NMDA antagonists may also (1) involve 5-HT 2A receptors and (2) be mediated through excess activity at non-NMDA (i.e., AMPA/kainate) glutamate receptors. Moreover, pharmacological manipulations of glutamate transmission (e.g., by inhibitory metabotropic glutamate agonists) provide unexpected parallels between the actions of these two classes of drugs. Given an emerging recognition of the importance of alterations in glutamatergic transmission in the actions of both psychedelic hallucinogens an NMDA antagonists, this review concludes with of implications for the pathophysiology and therapy of schizophrenia.

Separation of D-lysergic acid diethylamide derivatives using micellar electrokinetic capillary chromatography.

By adjusting column temperature and applied electric field, a fast separation in micellar electrokinetic capillary chromatography was developed for the separation of D-lysergic acid diethylamide derivatives. A baseline separation of nine derivatives was accomplished with a run time of less than 12 min by utilizing elevated column temperature (60 degrees C) and an applied electric field of 387 V/cm. The number of plates generated per unit time for the separations completed at elevated temperatures was significantly higher when compared to separations at the same applied electric field but at lower temperatures (20 degrees C).

Separation of D-lysergic acid diethylamide derivatives using micellar electrokinetic capillary chromatography

Separation of D-lysergic acid diethylamide derivatives using micellar electrokinetic capillary chromatography

LSD and DOB: interaction with 5-HT2A receptors to inhibit NMDA receptor-mediated transmission in the rat prefrontal cortex.

Both the phenethylamine hallucinogen (-)-1-2, 5-dimethoxy-4-bromophenyl-2-aminopropane (DOB), a selective serotonin 5-HT2A,2C receptor agonist, and the indoleamine hallucinogen D-lysergic acid diethylamide (LSD, which binds to 5-HT1A, 1B, 1D, 1E, 1F, 2A, 2C, 5, 6, 7, dopamine D1 and D2, and alpha1 and alpha2 adrenergic receptors), but not their non-hallucinogenic congeners, inhibited N-methyl-D-aspartate (NMDA)-induced inward current and NMDA receptor-mediated synaptic responses evoked by electrical stimulation of the forceps minor in pyramidal cells of the prefrontal cortical slices. The inhibitory effect of hallucinogens was mimicked by 5-HT in the presence of selective 5-HT1A and 5-HT3 receptor antagonists. The inhibitory action of DOB, LSD and 5-HT on the NMDA transmission was blocked by the 5-HT2A receptor antagonists R-(+)-alpha-(2, 3-dimethoxyphenil)-1-[4-fluorophenylethyl]-4-piperidineme thanol (M100907) and ketanserin. However, at low concentrations, when both LSD and DOB by themselves only partially depressed the NMDA response, they blocked the inhibitory effect of 5-HT, suggesting a partial agonist action. Whereas N-(4-aminobutyl)-5-chloro-2-naphthalenesulphonamide (W-7, a calmodulin antagonist) and N-[2-[[[3-(4'-chlorophenyl)- 2-propenyl]methylamino]methyl]phenyl]-N-(2-hydroxyethyl)-4'-methoxy-b enzenesulphonamide phosphate (KN-93, a Ca2+/CaM-KII inhibitor), but not the negative control 2-[N-4'methoxybenzenesulphonyl]amino-N-(4'-chlorophenyl)-2-propeny l-N -methylbenzylamine phosphate (KN-92), blocked the inhibitory action of LSD and DOB, the selective protein kinase C inhibitor chelerythrine was without any effect. We conclude that phenethylamine and indoleamine hallucinogens may exert their hallucinogenic effect by interacting with 5-HT2A receptors via a Ca2+/CaM-KII-dependent signal transduction pathway as partial agonists and modulating the NMDA receptors-mediated sensory, perceptual, affective and cognitive processes.

Neural Rhythmicity, Feature Binding, and Serotonin: A Hypothesis

Natural selection favors animals that make successful predictive theories about the world. The first step in the formation of these theories is the construction of complex, multifea ture percepts. This process requires resolution of the binding problem, possibly via rhyth mic cortical oscillations, as suggested by von der Malsburg, Singer, Koch & Crick, and others. If the binding process were made rewarding, animals might enjoy theory-making and spontaneously become "smarter." I argue that the serotonergic raphe may have been used by evolution to link cortical binding with limbic reward centers and so serve as a neural substrate for the enjoyment of successful theory-making. I present evidence, from the study of such disorders as obsessive-compulsive disorder and autism and such drugs as d-lysergic acid diethylamide (LSD) and 3,4-methylenedioxymethamphetamine (MDMA), suggesting that rhythmicity, reward, and pattern recognition are causally linked. I also propose that the genus Homo has tied powerful symbol manipulation hardware ("language") to the binding/theory-making circuits, allowing the construction, rehearsal, and communication of sophisticated models of the world. I suggest that many interesting phenomena, such as music-induced euphoria, déjà vu, and the so-called "temporal lobe personality" can be explained by the interactions between these systems. NEURO SCIENTIST 5:79-85, 1999

The 5-hydroxytryptamine6 receptor-selective radioligand [3H]Ro 63-0563 labels 5-hydroxytryptamine receptor binding sites in rat and porcine striatum.

Ro 63-0563 [4-amino-N-(2,6 bis-methylamino-pyridin-4-yl)-benzene sulfonamide] is a high affinity 5-hydroxytryptamine6 (HT6) receptor antagonist with more than 100-fold selectivity for the 5-HT6 receptor compared with 69 other receptors and binding sites. The present study describes the properties of [3H]Ro 63-0563, the first selective 5-HT6 receptor radioligand. Specific binding of [3H]Ro 63-0563 (nonspecific binding defined in the presence of 10 microM methiothepin) to recombinant rat and human 5-HT6 receptors was saturable, rapid, and reversible with equilibrium dissociation constants (Kd) of 6.8 nM and 4.96 nM, respectively. The pharmacological profile of the rat 5-HT6 receptor labeled with [3H]Ro 63-0563 (methiothepin > D-lysergic acid diethylamide > clozapine approximately Ro 63-0563 > lisuride > ergotamine approximately Ro 04-6790 > 5-HT > amitriptyline approximately metergoline approximately mianserin approximately ritanserin > methysergide > mesulergine) was similar to that obtained by using either [3H]D-lysergic acide diethylamide or [3H]5-HT as radioligand. In equilibrium binding studies with rat striatal membranes, [3H]Ro 63-0563 labeled a single binding site with Kd and Bmax values of 11. 7 nM and 175 fmol/mg protein, respectively. In porcine striatal membranes, [3H]Ro 63-0563 also labeled a single binding site with Kd and Bmax values of 8.0 nM and 130 fmol/mg protein, respectively. The affinities of 14 5-HT6 receptor ligands at this binding site were similar to those found for the recombinant rat and human 5-HT6 receptor, which suggested the presence of 5-HT6 receptors in porcine striatum.

Analysis of lysergic acid diethylamide: comparison of capillary electrophoresis with laser-induced fluorescence (CE-LIF) with conventional techniques

The increasing use of the potent hallucinogenic drug d-lysergic acid diethylamide (LSD) makes the application of highly sensitive analytical techniques necessary. For an effective analysis of biological specimens a limit of detection in the sub-ng/ml range is required. Using capillary electrophoresis (CE) with laser-induced fluorescence detection it was possible to determine 0.1–0.2 ng LSD/ml blood. The conventionally used immunoassays and gas and high-performance liquid chromatographic methods have cut-off values and limit of detection, respectively, in the same range. Only tandem mass spectrometry techniques can be more sensitive. Therefore, CE can be considered a good complementary method to conventional immunological and chromatographic techniques for the forensic analysis of biofluids.

Effects of LSD, Ritanserin, 8-OH-DPAT, and Lisuride on Classical Conditioning in the Rabbit

d-Lysergic acid diethylamide (LSD), an agonist at the 5-HT 2A/2C and 5-HT 1A receptors, has previously been demonstrated to enhance associative learning as measured by accelerated acquisition of the rabbit’s classically conditioned nictitating membrane (NM) response. The present study examined further the role of these receptors in the action of LSD. LSD (30 nmol/kg, IV) significantly enhanced conditioned response (CR) acquisition to both tone and light conditioned stimuli (CSs), while the 5-HT 1A receptor agonists 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT; 50 and 200 nmol/kg) and lisuride (0.3–30 nmol/kg) had no effect. Ritanserin (6.7–6700 nmol/kg, SC), a selective 5-HT 2A/2C receptor antagonist, retarded acquisition of CRs to both tone and light CSs in a dose-dependent manner. Ritanserin (6.7–670 nmol/kg, SC) also dose dependently antagonized the enhancement of CR conditioning produced by LSD (30 nmol/kg, IV) to both tone and light CSs. We conclude that the enhancement of CR acquisition by LSD was due to an action at the 5-HT 2A/2C receptor. These results suggest that the 5-HT 2A/2C receptor plays an important role in learning.

`Candyflipping': Synergistic discriminative effect of LSD and MDMA

The co-administration of d-lysergic acid diethylamide (LSD; `Acid') and 3,4-methylenedioxymethamphetamine (MDMA; `Ecstasy'; `XTC'), has reached a prevalence that has allowed for the street terminology `candyflipping' to describe the combination. Internet sites indicate a significant enhancement of central effects with their simultaneous use. In this preliminary observation, male Fawn-Hooded rats were trained to discriminate 1.5 mg/kg MDMA and were, subsequently, tested with doses of MDMA (0.15 mg/kg) or LSD (0.04 mg/kg) that each produced a saline-like response. Co-administration of these doses of MDMA and LSD synergized to produce a maximal MDMA-like response. The possible mechanism for synergistic action upon central serotonergic neurons is discussed to explain the observed effect.

Epimerization studies of LSD using 1H nuclear magnetic resonance (NMR) spectroscopy.

A study was conducted to determine the conditions needed to achieve the equilibrium concentration for the epimerization of d-lysergic acid diethylamide (LSD) to iso-LSD. The reaction was followed by integration of the C-9 resonance of LSD and iso-LSD by proton nuclear magnetic resonance (NMR). The C-9 resonance of LSD and iso-LSD appear as singlets at 6.35 and 6.27 ppm respectively. Starting with pure LSD, the conversion to iso-LSD is attained at temperatures above 37 degrees C and pH levels over 7.0. At a pH of 7.0 or higher, the LSD/iso-LSD ratio of 9:1 is achieved after one week at 45 degrees C or two weeks at 37 degrees C. Starting with iso-LSD, the conversion to LSD requires more vigorous conditions. The 9:1 LSD/iso-LSD ratio is attained only after 6 weeks at a temperature of 45 degrees C and a pH of 9.7. At lower pH levels, the reaction proceeds more slowly. The 9:1 LSD/iso-LSD ratio is achieved whether the starting material is LSD or iso-LSD and therefore represents an equilibrium concentration (K = 9). In addition, the more vigorous conditions needed to achieve equilibrium of iso-LSD to LSD demonstrate the difficulty in extraction of the epimerizable proton of iso-LSD. This study is the first to quantitate the epimerization of LSD by NMR techniques and establishes the conditions needed to induce epimerization in solution.

Determination of LSD in blood by capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis (CE) with HeCd laser-induced fluorescence (LIF) detection and its application in forensic toxicology is demonstrated by the determination of d-lysergic acid diethylamide (LSD) in blood. Following precipitation of proteins, washing of the evaporated supernatant and extraction, the residue was reconstituted in methanol and injected electrokinetically (10 s, 10 kV). The total analysis time for quantification of LSD was 8 min using a citrate–methanol buffer, pH 4.0. With this buffer system it is possible to separate LSD, nor-LSD, iso-LSD and iso-nor-LSD. Using a specific sample preparation, electrokinetic injection, extended light path (bubble cell) capillaries and especially LIF detection ( λ ex 325 nm, λ em 435 nm), a limit of detection of 0.1–0.2 ng LSD per ml blood could be obtained. The limit of quantitation was about 0.4–0.5 ng/ml. The quantitative evaluation for LSD was carried out using methylergometrine as internal standard. The precision expressed as coefficient of variation (C.V.) and accuracy of the method were <20% and 86–110%, respectively. The application of the method to human blood samples from two forensic cases and a comparison with radioimmunoassay demonstrated that the results were consistent.

A risk profile of street youth in Northern California: Implications for gender-specific human immunodeficiency virus prevention

To assess human immunodeficiency virus (HIV) risk behaviors of street youth and to determine whether risk behaviors differ by gender or housing status. Using systematic street-based sampling in four Northern California cities, we recruited 429 street youth (mean age = 19.2 years). Participants completed a structured interview which was used to assess sexual and drug HIV risk behaviors. The majority of youth were heterosexual (85%), white (77%), male (68%), and currently without any type of stable housing (75%). Although 60% of the sample had had vaginal sex in the past 30 days, only 44% used a condom the last time they had sex. About one-third (32%) of the sample reported ever injecting drugs, and almost all reported lifetime use of multiple drugs including D-lysergic acid diethylamide (96%), marijuana (90%), alcohol (81%), cocaine (70%), and speed (70%). Compared to males, females were equally likely to use injection and noninjection drugs, but were more likely to be sexually active (P < .001), were more likely to have been diagnosed with a sexually transmitted disease (P = .005), and were less likely to report consistent condom use (P = .003) or intent to use condoms consistently in the future (P = .005). Compared with those with stable housing, youth who were currently without such housing reported higher rates of injection, and other drug use; females without stable housing were less likely to have used condoms the last time they had vaginal intercourse. The high level of HIV risk behavior in this street-based sample of youth, particularly females and youth without stable housing, suggests an urgent need for gender-specific prevention efforts and an increased range of housing options.

Elucidation of LSD in vitro metabolism by liquid chromatography and capillary electrophoresis coupled with tandem mass spectrometry.

The in vitro metabolism of D-lysergic acid diethylamide (LSD) by human liver microsomes was investigated. Tandem mass spectrometric techniques, using precursor and neutral loss scans, were employed in the initial search for drug metabolites. The determination of LSD human liver in vitro metabolites was performed by high-performance liquid chromatography and capillary electrophoresis coupled with tandem mass spectrometry. Two new in vitro metabolites, lysergic acid ethylamide (LAE) and 2-oxo-LSD, were positively identified; their structures were established by comparing with reference standards. Several other possible in vitro metabolites detected were suggested to be mono- and trioxylated metabolites of LSD. The major metabolic route of LSD by human liver microsomes is deethylation. Some results with LSD-positive human urine are presented. Among the LSD-related compounds detected in human urine specimens, iso-LSD was present at the highest concentration, followed by nor-LSD and isonor-LSD. Low concentrations of LAE and iso-LAE were also found in these urine specimens.

Effect of a Chiral 4-Alkyl Substituent in Hallucinogenic Amphetamines

The potency of hallucinogenic amphetamine derivatives of the 1-(2,5-dimethoxy-4-alkylphenyl)-2-aminopropane type drops dramatically when the length of the 4-alkyl substituent exceeds propyl or when the substituent is branched. This investigation was directed toward evaluating changes in behavioral and biochemical pharmacology resulting from introducing chirality into the 4-alkyl group of such analogues. Two diastereoisomeric derivatives of this class containing a 4-(R or S)-2-butyl substituent, 11a,b, respectively, were studied. A slight but nonsignificant potency difference in d-lysergic acid diethylamide tartrate (LSD)-like discriminative stimulus properties and equal affinity for [125I]-(R)-(2,5-dimethoxy-4-iodophenyl) isopropylamine-labeled serotonin 5-HT2A/C radioligand-binding sites were observed. Thus, the portion of the receptor that interacts with the 4-alkyl substituent on hallucinogenic amphetamines does not present a highly asymmetric environment to the ligand. However, since both test drugs had higher binding affinity but lower LSD-like behavioral potency than the prototype compound with a 4-methyl group ((2,5-dimethoxy-4-methylphenyl)isopropylamine, 2), 11a,b may differ in their receptor agonist efficacy from more behaviorally active compounds such as 2.

Involvement of 5-HT 2C receptors in mediating the discriminative stimulus properties of m-chlorophenylpiperazine (mCPP)

Rats were trained to discriminate the 5-HT receptor agonists m-chlorophenylpiperazine (mCPP; 1 mg/kg) from saline using a two-lever, water-reinforced drug discrimination task. The antidepressant trazodone (1–8 mg/kg), the 5-HT 1B/2C receptor agonists 1-( m-trifluoromethylphenyl)piperazine (TFMPP; 0.25–1 mg/kg) and MK 212 (0.125–1 mg/kg), and the mixed 5-HT 1A/B receptor agonist RU 24969 (0.25–2 mg/kg) substituted fully for mCPP. The 5-HT 2A/2C receptor agonists 1-(2,5-dimethoxy-4-iodophenyl) -2-aminopropane (DOI; 0.25–1 mg/kg) and d-lysergic acid diethylamide (LSD; 0.02–0.08 mg/kg) and the 5-HT releaser fenfluramine (0.5–2 mg/kg) also mimicked mCPP. Agonists selective for the 5-HT 1A or 5-HT 3 receptor or the 5-HT reuptake site produced saline-lever responding. The ergoline derivative mesulergine (0.5–4 mg/kg) produced a partial agonist/antagonist profile. The 5- HT 1 2 receptor antagonist metergoline (0.125–2 mg/kg) completely blocked the mCPP cue whereas the 5-HT 2A/2C receptor antagonists ketanserin and LY 53857 as well as all other 5-HT receptor antagonists failed to block the mCPP cue. The dopamine receptor antagonists SCH 23390 and haloperidol were also ineffective mCPP antagonists. Following pretreatment with the 5-HT synthesis inhibitor p-chlorophenylalanine (pCPA; 100 mg/kg/day) for 3 consecutive days, the discriminability of low doses of mCPP increased, whereas the effects of fenfluramine decreased. The present results suggest that the discriminative stimulus effects of mCPP in rats are mediated primarily by postsynaptic 5-HT 2C receptors.

Cross-tolerance studies of serotonin receptors involved in behavioral effects of LSD in rats.

Like hallucinogenic 5-HT2 agonists, LSD (d-lysergic acid diethylamide) produces characteristic decreases in locomotor activity and investigatory behaviors of rats tested in a novel environment. Because LSD is an agonist at both 5-HT1A and 5-HT2 receptors, however, the respective influences of these different receptors in the behavioral effects of LSD remain unclear. In particular, the paucity of selective 5-HT1A antagonists has made it difficult to assess the specific contribution of 5-HT1A receptors to the effects of LSD. An alternative approach to the delineation of receptor-specific effects is the use of cross-tolerance regimens. In the present studies, rats were pretreated with saline, 8-hydroxy-2(di-n-propylamino)-tetralin (8-OH-DPAT) (0.5 mg/kg SC), 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (1.0 mg/kg SC), or LSD (60 micrograms/kg SC), every 12 h for 5 or 8 days. Thirty-six hours later, rats were tested in a behavioral pattern monitor 10 min after injection of saline, 0.5 mg/kg 8-OH-DPAT, 1.0 mg/kg DOI, or 60 micrograms/kg LSD. As expected, tolerance to the decreases in locomotor activity produced by acute administrations of 8-OH-DPAT, DOI, or LSD occurred when rats were pretreated chronically with 8-OH-DPAT, DOI, or LSD, respectively. Furthermore, pretreatment with either 8-OH-DPAT or DOI produced cross-tolerance to LSD. These results support the hypothesis that the effects of LSD in this model reflect a combination of 5-HT1A and 5-HT2 effects and support the view that there is an interaction between 5-HT1A and 5-HT2 receptors.

Studies of the biochemical basis for the discriminative properties of 8-hydroxy-2-(di-n-propylamino)tetralin

The ability of a series of compounds to mimic the stimulus properties of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was compared to: (1) the affinity of these compounds for the 5-HT 1A receptor; and (2) their efficacy to inhibit forskolin-stimulated adenylate cyclase activity. Although for nine compounds (flesinoxan, MDL 73005EF, gepirone, ipsapirone, buspirone, tandospirone, yohimbine, L 657,743 and rauwolscine) complete cross generalization was associated with high affinity for the 5-HT 1A receptor, eltoprazine, d-lysergic acid diethylamide and BMY 7378 had pK D > 7.44, but did not show complete mimicry of 8-OH-DPAT. In addition, indorenate had a pK D of 7.88, yet the behavioral response was indistinguishable from the saline control. Because the above data indicated that affinity for the 5-HT 1A receptor was necessary, but not sufficient for a receptor ligand to mimic 8-OH-DPAT, the in vitro efficacy of the various compounds at the 5-HT 1A receptor was determined by measuring inhibition of forskolin-stimulated adenylate cyclase activity in hippocampal membranes. For a series of drugs (gepirone, ipsapirone, flesinoxan, buspirone, tandospirone, yohimbine, L 657,743 and rauwolscine) significant inhibition of forskolin-stimulated adenylate cyclase activity was observed, and these same drugs showed complete cross generalization. However, BMY 14802 and MDL 73005EF did not alter adenylate cyclase activity, yet completely mimicked the stimulus properties of 8-OH-DPAT. Eltoprazine had significant efficacy in inhibiting forskolin-stimulated adenylate cyclase activity, but only 30% of the responses following administration of this drug were on the 8-OH-DPAT-appropriate lever. Furthermore, although indorenate inhibited hippocampal adenylate cyclase activity, the behavioral response to this compound was indistinguishable from the saline control. The present study indicates that activation of the 5-HT 1A receptor negatively coupled to adenylate cyclase is neither necessary nor sufficient for a receptor ligandto mimic the stimulus properties of 8-OH-DPAT.

Molecular cloning and functional expression of 5-HT1E-like rat and human 5-hydroxytryptamine receptor genes.

Sequential polymerase chain reaction experiments were performed to amplify a unique sequence representing a guanine nucleotide-binding protein (G-protein)-coupled receptor from rat hypothalamic cDNA. Degenerate oligonucleotides corresponding to conserved amino acids from transmembrane domains III, V, and VI of known receptors [5-HT1A, 5-HT1C, and 5-HT2; 5-HT is serotonin (5-hydroxytryptamine)] were used as primers for the sequential reactions. The resulting product was subcloned and used to screen a rat genomic library to identify a full-length clone (MR77) containing an intronless open reading frame encoding a 366-amino acid seven-transmembrane domain protein. The human homolog was isolated, and its encoded protein had 93% overall amino acid identity with the rat sequence. Within the conserved transmembrane domains, the sequences exhibit approximately 52%, 59%, 65%, and 68% amino acid identity with the known rat 5-HT1A, rat 5-HT1B, rat 5-HT1D, and human 5-HT1E receptors, respectively. MR77 was subcloned into a eukaryotic expression vector system and expressed in CosM6 cells. Studies on broken cell preparations indicate that the expressed receptor exhibits 125I-labeled d-lysergic acid diethylamide (LSD) binding that can be displaced by serotonin but not by other biogenic amines. The specific binding is displaced by the selective 5-HT1D agonist sumatriptan but not by the mixed 5-HT1A/1D agonist 5-carboxyamidotryptamine. 125I-labeled LSD binding was competitively antagonized by the ergot alkaloids methysergide and ergotamine. HeLa cells transfected with the MR77 gene exhibited inhibition of adenylate cyclase in response to serotonin. MR77 is expressed at low levels throughout the brain, with the greatest expression in the cortex, hippocampus, and striatum. MR77 thus represents a 5-HT receptor of the 5-HT1 class, and we propose that, based on the pharmacological characterization, MR77 represents an additional 5-HT1E-like receptor.

Lysergic acid diethylamide is a partial agonist at 5-HT 2 receptors in ovine uterine artery of late pregnancy

d-Lysergic acid diethylamide (LSD) produced dose-dependent contractions (EC 50, 17.9 ± 2.1 nM) on isolated ovine uterine artery of late pregnancy, which were competitively antagonized by ketanserin. The maximal contraction to LSD was 51% of the 5-HT response. LSD competitively antagonized (pA 2 9.21) contractions produced to 5-hydroxytryptamine (5-HT). The results indicate that LSD is a partial agonist at 5-HT 2 receptors in ovine uterine artery.

Activity of serotonin (5-HT) receptor agonists, partial agonists and antagonists at cloned human 5-HT 1a receptors that are negatively coupled to adenylate cyclase in permanently transfected hela cells

The activity of serotonin (5-HT) receptor agonists, partial agonists and antagonists, and various other neurotransmitter receptor antagonists at human 5-HT 1A receptors that are negatively coupled to adenylate cyclase in permanently transfected HeLa cells was investigated. 5-HT 1A receptor-mediated inhibition of adenylate cyclase was studied by measuring inhibition of cAMP accumulation, induced by forskolin. At 100 μM forskolin produced a 100-fold increase in cAMP formation: 5-HT concentration dependently inhibited the cAMP formation; maximal inhibition was attained at 1 μM 5-HT and represented 90% of the stimulated cAMP formation. Full inhibition was observed with 5-HT 1A receptor agonists: N,N-dipropyl-8-hydroxy-2-aminotetralin (8-OH-DPAT) and flesinoxan, and non-selective 5-HT receptor agonists: d-lysergic acid diethylamide (d-LSD), RU 24,969, bufotenine, methysergide and tryptamine. The rank order of potency of the compounds for inhibiting the cAMP formation corresponded to the rank order of the binding affinities of the drugs for the 5-HT 1A receptor. Partial inhibition was obtained with submicromolar concentrations of buspirone, spiroxatrine and ipsapirone. A slight inhibition was observed with 1 μM 5-HT receptor agonist CP 93129 and 1 μM 5-HT receptor antagonists mesulergine and BW-501. No inhibition was found with: the 5-HT receptor agonists quipazine, sumatriptan and 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM); the 5-HT receptor antagonist ICS-205,930; and other neurotransmitter receptor antagonists such as pindolol, CGP 20712-A, prazosin, sulpiride and pyrilamine. Spiperone and pindolol fully antagonized the agonist-mediated inhibition of forskolin-stimulated cAMP formation. Partial inhibition of the agonist-mediated inhibition of forskolin-stimulated cAMP formation was apparent with 1 μM ocaperidone and 1 μM ipsapirone. It can be concluded that HeLa cells, permanently expressing human 5-HT 1A receptors, are a valid cellular system for studying the negative coupling of 5-HT 1A receptors to adenylate cyclase and the action of compounds thereupon.