Choroid plexus epithelial cells in primary culture: a model of 5HT1C receptor activation by hallucinogenic drugs

Experimental strategies to discover and develop the next generation of psychedelics and entactogens as medicines

Research on classical psychedelics (psilocybin, LSD and DMT) and entactogen, MDMA, has produced a renaissance in the search for more effective drugs to treat psychiatric, neurological and various peripheral disorders. Psychedelics and entactogens act though interaction with 5-HT_2A and other serotonergic receptors and/or monoamine reuptake transporters. 5-HT, which serves as a neurotransmitter and hormone, is ubiquitously distributed in the brain and peripheral organs, tissues and cells where it has vasoconstrictor, pro-inflammatory and pro-nociceptive actions. Serotonergic psychedelics and entactogens have known safety and toxicity risks. For these drugs, the risks been extensively researched and empirically assessed through human experience. However, novel drug-candidates require thorough non-clinical testing not only to predict clinical efficacy, but also to address the risks they pose during clinical development and later after approval as prescription medicines. We have defined the challenges researchers will encounter when developing novel serotonergic psychedelics and entactogens. We describe screening techniques to predict clinical efficacy and address the safety/toxicity risks emerging from our knowledge of the existing drugs: 1) An early-stage, non-clinical screening cascade to pharmacologically characterise novel drug-candidates. 2) Models to detect hallucinogenic activity. 3) Models to differentiate hallucinogens from entactogens. 4) Non-clinical preclinical lead optimisation technology (PLOT) screening to select drug-candidates. 5) Modified animal models to evaluate the abuse and dependence risks of novel psychedelics in Safety Pharmacology testing. Our intention has been to design non-clinical screening strategies that will reset the balance between benefits and harms to deliver more effective and safer novel psychedelics for clinical use. This article is part of the Special Issue on 'National Institutes of Health Psilocybin Research Speaker Series'.

In Vitro Models of the Blood–Cerebrospinal Fluid Barrier and Their Applications in the Development and Research of (Neuro)Pharmaceuticals

The pharmaceutical research sector has been facing the challenge of neurotherapeutics development and its inherited high-risk and high-failure-rate nature for decades. This hurdle is partly attributable to the presence of brain barriers, considered both as obstacles and opportunities for the entry of drug substances. The blood–cerebrospinal fluid (CSF) barrier (BCSFB), an under-studied brain barrier site compared to the blood–brain barrier (BBB), can be considered a potential therapeutic target to improve the delivery of CNS therapeutics and provide brain protection measures. Therefore, leveraging robust and authentic in vitro models of the BCSFB can diminish the time and effort spent on unproductive or redundant development activities by a preliminary assessment of the desired physiochemical behavior of an agent toward this barrier. To this end, the current review summarizes the efforts and progresses made to this research area with a notable focus on the attribution of these models and applied techniques to the pharmaceutical sector and the development of neuropharmacological therapeutics and diagnostics. A survey of available in vitro models, with their advantages and limitations and cell lines in hand will be provided, followed by highlighting the potential applications of such models in the (neuro)therapeutics discovery and development pipelines.

Advancing brain barriers RNA sequencing: guidelines from experimental design to publication

BACKGROUND

RNA sequencing (RNA-Seq) in its varied forms has become an indispensable tool for analyzing differential gene expression and thus characterization of specific tissues. Aiming to understand the brain barriers genetic signature, RNA seq has also been introduced in brain barriers research. This has led to availability of both, bulk and single-cell RNA-Seq datasets over the last few years. If appropriately performed, the RNA-Seq studies provide powerful datasets that allow for significant deepening of knowledge on the molecular mechanisms that establish the brain barriers. However, RNA-Seq studies comprise complex workflows that require to consider many options and variables before, during and after the proper sequencing process.

MAIN BODY

In the current manuscript, we build on the interdisciplinary experience of the European PhD Training Network BtRAIN ( https://www.btrain-2020.eu/ ) where bioinformaticians and brain barriers researchers collaborated to analyze and establish RNA-Seq datasets on vertebrate brain barriers. The obstacles BtRAIN has identified in this process have been integrated into the present manuscript. It provides guidelines along the entire workflow of brain barriers RNA-Seq studies starting from the overall experimental design to interpretation of results. Focusing on the vertebrate endothelial blood-brain barrier (BBB) and epithelial blood-cerebrospinal-fluid barrier (BCSFB) of the choroid plexus, we provide a step-by-step description of the workflow, highlighting the decisions to be made at each step of the workflow and explaining the strengths and weaknesses of individual choices made. Finally, we propose recommendations for accurate data interpretation and on the information to be included into a publication to ensure appropriate accessibility of the data and reproducibility of the observations by the scientific community.

CONCLUSION

Next generation transcriptomic profiling of the brain barriers provides a novel resource for understanding the development, function and pathology of these barrier cells, which is essential for understanding CNS homeostasis and disease. Continuous advancement and sophistication of RNA-Seq will require interdisciplinary approaches between brain barrier researchers and bioinformaticians as successfully performed in BtRAIN. The present guidelines are built on the BtRAIN interdisciplinary experience and aim to facilitate collaboration of brain barriers researchers with bioinformaticians to advance RNA-Seq study design in the brain barriers community.

The nonselective cation channel TRPV4 inhibits angiotensin II receptors

G-protein-coupled receptors (GPCRs) are a ubiquitously expressed family of receptor proteins that regulate many physiological functions and other proteins. They act through two dissociable signaling pathways: the exchange of GDP to GTP by linked G-proteins and the recruitment of β-arrestins. GPCRs modulate several members of the transient receptor potential (TRP) channel family of nonselective cation channels. How TRP channels reciprocally regulate GPCR signaling is less well-explored. Here, using an array of biochemical approaches, including immunoprecipitation and fluorescence, calcium imaging, phosphate radiolabeling, and a β-arrestin-dependent luciferase assay, we characterize a GPCR-TRP channel pair, angiotensin II receptor type 1 (AT1R), and transient receptor potential vanilloid 4 (TRPV4), in primary murine choroid plexus epithelial cells and immortalized cell lines. We found that AT1R and TRPV4 are binding partners and that activation of AT1R by angiotensin II (ANGII) elicits β-arrestin-dependent inhibition and internalization of TRPV4. Activating TRPV4 with endogenous and synthetic agonists inhibited angiotensin II-mediated G-protein-associated second messenger accumulation, AT1R receptor phosphorylation, and β-arrestin recruitment. We also noted that TRPV4 inhibits AT1R phosphorylation by activating the calcium-activated phosphatase calcineurin in a Ca2+/calmodulin-dependent manner, preventing β-arrestin recruitment and receptor internalization. These findings suggest that when TRP channels and GPCRs are co-expressed in the same tissues, many of these channels can inhibit GPCR desensitization.

d-Lysergic Acid Diethylamide (LSD) as a Model of Psychosis: Mechanism of Action and Pharmacology

d-Lysergic Acid Diethylamide (LSD) is known for its hallucinogenic properties and psychotic-like symptoms, especially at high doses. It is indeed used as a pharmacological model of psychosis in preclinical research. The goal of this review was to understand the mechanism of action of psychotic-like effects of LSD. We searched Pubmed, Web of Science, Scopus, Google Scholar and articles' reference lists for preclinical studies regarding the mechanism of action involved in the psychotic-like effects induced by LSD. LSD's mechanism of action is pleiotropic, primarily mediated by the serotonergic system in the Dorsal Raphe, binding the 5-HT2A receptor as a partial agonist and 5-HT1A as an agonist. LSD also modulates the Ventral Tegmental Area, at higher doses, by stimulating dopamine D₂, Trace Amine Associate receptor 1 (TAAR₁) and 5-HT2A. More studies clarifying the mechanism of action of the psychotic-like symptoms or psychosis induced by LSD in humans are needed. LSD's effects are mediated by a pleiotropic mechanism involving serotonergic, dopaminergic, and glutamatergic neurotransmission. Thus, the LSD-induced psychosis is a useful model to test the therapeutic efficacy of potential novel antipsychotic drugs, particularly drugs with dual serotonergic and dopaminergic (DA) mechanism or acting on TAAR₁ receptors.

Combined Effects of Neurotrophin Secreting Transplants, Exercise, and Serotonergic Drug Challenge Improve Function in Spinal Rats

Objectives. To determine the effects of neurotrophin-secreting transplants combined with exercise and serotonergic drug challenges on recovery of hindlimb function in rats with midthoracic spinal cord transection injuries. Methods. Spinalized animals received transplants of fibroblasts genetically modified to express brain-derived neurotrophic factor and neurotrophin-3 and daily cycling exercise. Hindlimb movement in an open-field test (BBB) was scored weekly. Serotonin agonists were used monthly to further stimulate motor function. Axonal growth was quantified in the transplant and at L5 using immunocytochemical markers. Weights of hindlimb muscles were used to assess muscle atrophy. Results. Neurotrophin-secreting transplants stimulated axonal growth, and cycling prevented muscle atrophy, but individual treatments did not improve motor scores. Combined treatments resulted in improvements in motor function. Serotonergic agonists further improved function in all groups, and transplant groups with exercise achieved weight-supporting levels following drug treatment. Conclusion. Combined treatments, but not individual treatments, improved hindlimb function.

A molecular characterization of the choroid plexus and stress-induced gene regulation

The role of the choroid plexus (CP) in brain homeostasis is being increasingly recognized and recent studies suggest that the CP has a more important role in physiological and pathological brain functions than currently appreciated. To obtain additional insight on the CP function, we performed a proteomics and transcriptomics characterization employing a combination of high resolution tandem mass spectrometry and gene expression analyses in normal rodent brain. Using multiple protein fractionation approaches, we identified 1400 CP proteins in adult CP. Microarray-based comparison of CP gene expression with the kidney, cortex and hippocampus showed significant overlap between the CP and the kidney. CP gene profiles were validated by in situ hybridization analysis of several target genes including klotho, CLIC 6, OATP 14 and Ezrin. Immunohistochemical analyses were performed for CP and enpendyma detection of several target proteins including cytokeratin, Rab7, klotho, tissue inhibitor of metalloprotease 1 (TIMP1), MMP9 and glial fibrillary acidic protein (GFAP). The molecular functions associated with various proteins of the CP proteome indicate that it is a blood-cerebrospinal fluid (CSF) barrier that exhibits high levels of metabolic activity. We also analyzed the gene expression changes induced by stress, an exacerbating factor for many illnesses, particularly mood disorders. Chronic stress altered the expression of several genes, downregulating 5HT2C, glucocorticoid receptor and the cilia genes IFT88 and smoothened while upregulating 5HT2A, BDNF, TNFα and IL-1b. The data presented here attach additional significance to the emerging importance of CP function in brain health and CNS disease states.

Head-twitch response in rodents induced by the hallucinogen 2,5-dimethoxy-4-iodoamphetamine: a comprehensive history, a re-evaluation of mechanisms, and its utility as a model

Two primary animal models persist for assessing hallucinogenic potential of novel compounds and for examining the pharmacological and neurobiological substrates underlying the actions of classical hallucinogens, the two-lever drug discrimination procedure and the drug-induced head-twitch response (HTR) in rodents. The substituted amphetamine hallucinogen, serotonin 2 (5-HT(2) ) receptor agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI) has emerged as the most popular pharmacological tool used in HTR studies of hallucinogens. Synthesizing classic, recent, and relatively overlooked findings, addressing ostensibly conflicting observations, and considering contemporary theories in receptor and behavioural pharmacology, this review provides an up-to-date and comprehensive synopsis of DOI and the HTR model, from neural mechanisms to utility for understanding psychiatric diseases. Also presented is support for the argument that, although both the two-lever drug discrimination and the HTR models in rodents are useful for uncovering receptors, interacting proteins, intracellular signalling pathways, and neurochemical processes affected by DOI and related classical hallucinogens, results from both models suggest they are not reporting hallucinogenic experiences in animals.

The serotonin 2C receptor potently modulates the head-twitch response in mice induced by a phenethylamine hallucinogen

RATIONALE

Hallucinogenic serotonin 2A (5-HT(2A)) receptor partial agonists, such as (+ or -)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), induce a frontal cortex-dependent head-twitch response (HTR) in rodents, a behavioral proxy of a hallucinogenic response that is blocked by 5-HT(2A) receptor antagonists. In addition to 5-HT(2A) receptors, DOI and most other serotonin-like hallucinogens have high affinity and potency as partial agonists at 5-HT(2C) receptors.

OBJECTIVES

We tested for involvement of 5-HT(2C) receptors in the HTR induced by DOI.

RESULTS

Comparison of 5-HT(2C) receptor knockout and wild-type littermates revealed an approximately 50% reduction in DOI-induced HTR in knockout mice. Also, pretreatment with either the 5-HT(2C) receptor antagonist SB206553 or SB242084 eradicated a twofold difference in DOI-induced HTR between the standard inbred mouse strains C57BL/6J and DBA/2J, and decreased the DOI-induced HTR by at least 50% in both strains. None of several measures of 5-HT(2A) receptors in frontal cortex explained the strain difference, including 5-HT(2A) receptor density, Galpha(q) or Galpha(i/o) protein levels, phospholipase C activity, or DOI-induced expression of Egr1 and Egr2. 5-HT(2C) receptor density in the brains of C57BL/6J and DBA/2J was also equivalent, suggesting that 5-HT(2C) receptor-mediated intracellular signaling or other physiological modulators of the HTR may explain the strain difference in response to DOI.

CONCLUSIONS

We conclude that the HTR to DOI in mice is strongly modulated by 5-HT(2C) receptor activity. This novel finding invites reassessment of hallucinogenic mechanisms involving 5-HT(2) receptors.

5-HT2A/2C receptor blockade regulates progenitor cell proliferation in the adult rat hippocampus

Adult hippocampal neurogenesis is reported to be a target of antidepressants, drugs of abuse and animal models of depression, suggesting a role for this form of structural plasticity in psychopathology. Serotonergic neurotransmission, which is implicated in several psychiatric diseases, has been reported to regulate adult hippocampal neurogenesis. Amongst the serotonergic receptors, the serotonin2A/2C (5-HT2A/2C) receptors play an important role in the actions of antidepressants and the effects of hallucinogenic drugs of abuse. We have used the mitotic marker 5'-bromo-2-deoxyuridine to address the effects of the 5-HT2A/2C receptors on the proliferation of adult hippocampal progenitors following acute or chronic treatment with the hallucinogenic partial agonists, (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) and lysergic acid diethylamide (LSD) and the antagonist, Ketanserin. Acute, and chronic, DOI and LSD treatments induced a strong behavioral activation, but did not alter adult hippocampal progenitor proliferation. In striking contrast, Ketanserin treatment resulted in a biphasic regulation with a significant decline (22%) in progenitor proliferation following a single treatment, and a robust increase (46%) observed following chronic administration. These results indicate that hallucinogenic drugs that primarily target the 5-HT2A/2C receptors, in contrast to other drugs of abuse, may not alter adult hippocampal neurogenesis. In addition, our results that enhanced adult hippocampal progenitor proliferation results from a sustained blockade of the 5-HT2A/2C receptors suggest that the 5-HT2A/2C receptors may be an important target for the neurogenic effects of antidepressant treatment.

The behavioral pharmacology of hallucinogens

Until very recently, comparatively few scientists were studying hallucinogenic drugs. Nevertheless, selective antagonists are available for relevant serotonergic receptors, the majority of which have now been cloned, allowing for reasonably thorough pharmacological investigation. Animal models sensitive to the behavioral effects of the hallucinogens have been established and exploited. Sophisticated genetic techniques have enabled the development of mutant mice, which have proven useful in the study of hallucinogens. The capacity to study post-receptor signaling events has lead to the proposal of a plausible mechanism of action for these compounds. The tools currently available to study the hallucinogens are thus more plentiful and scientifically advanced than were those accessible to earlier researchers studying the opioids, benzodiazepines, cholinergics, or other centrally active compounds. The behavioral pharmacology of phenethylamine, tryptamine, and ergoline hallucinogens are described in this review, paying particular attention to important structure activity relationships which have emerged, receptors involved in their various actions, effects on conditioned and unconditioned behaviors, and in some cases, human psychopharmacology. As clinical interest in the therapeutic potential of these compounds is once again beginning to emerge, it is important to recognize the wealth of data derived from controlled preclinical studies on these compounds.

Pharmacological profile of the 5-HT(2C) receptor agonist WAY-163909; therapeutic potential in multiple indications

The 5-HT(2C) receptor subtype has been implicated in a wide variety of conditions including obesity, anxiety, depression, obsessive compulsive disorder, schizophrenia, migraine and erectile dysfunction and as a consequence has received considerable attention as a target for drug discovery. Here we review the pharmacological, pharmacokinetic and toxicological profile of WAY-163909 {(7bR,10aR)-1,2,3,4,8,9,10,10a-octahydro-7bH-cyclopenta-[b][1,4]diazepino[6,7,1hi]indole}, a novel 5-HT(2C) receptor selective agonist. Consistent with a potential therapeutic utility in obesity, schizophrenia and depression WAY-163909 was found to have robust dose-dependent effects in animal models of obesity, psychotic-like behavior or depression.

WAY-163909 [(7bR, 10aR)-1,2,3,4,8,9,10,10a-Octahydro-7bH-cyclopenta-[b][1,4]diazepino[6,7,1hi]indole], a Novel 5-Hydroxytryptamine 2C Receptor-Selective Agonist with Anorectic Activity

The pharmacological profile of WAY-163909 [(7bR, 10aR)-1,2,3,4,8,9,10,10a-octahydro-7bH-cyclopenta-[b][1,4]diazepino[6,7,1hi]indole], a novel 5-hydroxytryptamine (HT)(2C) (serotonin) receptor-selective agonist is presented. WAY-163909 displaced [(125)I]2,5-dimethoxy-4-iodoamphetamine binding from human 5-HT(2C) receptor sites, in Chinese hamster ovary (CHO) cell membranes, with a K(i) value of 10.5 +/- 1.1 nM. Binding affinities determined for the human 5-HT(2A) and 5-HT(2B) receptor subtypes were 212 and 485 nM, respectively. In functional studies, WAY-163909 stimulated the mobilization of intracellular calcium in CHO cells stably expressing the human 5-HT(2C) receptor with an EC(50) value of 8 nM, and E(max) relative to 5-HT of 90%. WAY-163909 failed to stimulate calcium mobilization in cells expressing the human 5-HT(2A) receptor subtype (EC(50) >> 10muM) and was a 5-HT(2B) receptor partial agonist (EC(50) 185 nM, E(max) 40%). WAY-163909 exhibited negligible affinity (<50% inhibition at 1 muM) for other receptor sites examined, including human 5-HT(1A), D2, and D3 receptors, and the 5-HT transporter binding site in rat cortical membranes. WAY-163909 exhibited weak affinity for the human D4 (245 nM) and 5-HT(7) (343 nM) receptor subtypes and the alpha1 binding site in rat cortical membranes (665 nM). WAY-163909 produced a dose-dependent reduction in food intake in normal Sprague-Dawley rats (ED(50) = 2.93 mg/kg), an effect blocked by a 5-HT(2C) receptor antagonist but not by a 5-HT(2A) or 5-HT(2B) receptor antagonist. In addition, WAY-163909 decreased food intake in obese Zucker rats and diet-induced obese mice with ED(50) values of 1.4 and 5.19 mg/kg i.p., respectively, consistent with the potential utility of 5-HT(2C) receptor agonists as anti-obesity agents.

Hallucinogens

Hallucinogens (psychedelics) are psychoactive substances that powerfully alter perception, mood, and a host of cognitive processes. They are considered physiologically safe and do not produce dependence or addiction. Their origin predates written history, and they were employed by early cultures in a variety of sociocultural and ritual contexts. In the 1950s, after the virtually contemporaneous discovery of both serotonin (5-HT) and lysergic acid diethylamide (LSD-25), early brain research focused intensely on the possibility that LSD or other hallucinogens had a serotonergic basis of action and reinforced the idea that 5-HT was an important neurotransmitter in brain. These ideas were eventually proven, and today it is believed that hallucinogens stimulate 5-HT(2A) receptors, especially those expressed on neocortical pyramidal cells. Activation of 5-HT(2A) receptors also leads to increased cortical glutamate levels presumably by a presynaptic receptor-mediated release from thalamic afferents. These findings have led to comparisons of the effects of classical hallucinogens with certain aspects of acute psychosis and to a focus on thalamocortical interactions as key to understanding both the action of these substances and the neuroanatomical sites involved in altered states of consciousness (ASC). In vivo brain imaging in humans using [(18)F]fluorodeoxyglucose has shown that hallucinogens increase prefrontal cortical metabolism, and correlations have been developed between activity in specific brain areas and psychological elements of the ASC produced by hallucinogens. The 5-HT(2A) receptor clearly plays an essential role in cognitive processing, including working memory, and ligands for this receptor may be extremely useful tools for future cognitive neuroscience research. In addition, it appears entirely possible that utility may still emerge for the use of hallucinogens in treating alcoholism, substance abuse, and certain psychiatric disorders.

Ligand Dependency of 5-Hydroxytryptamine 2C Receptor Internalization

Agonist-induced internalization of G protein-coupled receptors (GPCRs) is a well characterized phenomenon believed to contribute to receptor desensitization. The 5-hydroxytryptamine (5-HT)2C subtype of serotonin receptor is a GPCR that we have shown to internalize upon agonist incubation. In this study, we have examined the effects of 5-HT2C receptor agonists serotonin, Ro 60-0175 [(S)-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine], and WAY-161503 [(4aR)-8,9-dichloro-2,3,4,4a-tetrahydro-1H-pyrazino[1,2-a]quinoxalin-5(6H)-one]; partial agonists mCPP [1-(m-chlorophenyl)piperazine] and DOI [(+)-1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane]; inverse agonists SB-206553 [N-3-pyridinyl-3,5-dihydro-5-methylbenzo(1,2-b:4,5-b')dipyrrole-1(2H)carboxamide] and mianserin; and neutral antagonists SB-242084 [6-chloro-5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-indoline] and 5-methoxygramine on the internalization of a C-terminal green fluorescent protein (GFP)-tagged 5-HT2C receptor (VSV isoform) expressed in transiently transfected human embryonic kidney cells. We detected internalization with an automated, cell-based fluorescence-imaging system (Arrayscan) and monitored function with intracellular Ca2+ measurements (flourometric imaging plate reader). The 5-HT2C-GFP construct exhibited appropriate pharmacology, and we observed that although all three agonists resulted in similar magnitudes of dose-dependent internalization, the partial agonists resulted in approximately 50% less internalization, and the inverse agonists and neutral antagonists failed to induce internalization. These results were confirmed by confocal microscopy. They demonstrate that the 5-HT2C receptor is internalized by incubation with agonists and partial agonists but not with inverse agonists or neutral antagonists.

Positive allosteric modulator of the human 5-HT2C receptor

The human 5-hydroxytryptamine-2C (5-HT2C) receptor has been the target of potential anxiolytics and antiobesity drugs, and its positive allosteric modulator was discovered to be l-threo-alpha-d-galacto-octopyranoside, methyl-7-chloro-6,7,8-trideoxy-6-[[(4-undecyl-2-piperidinyl)carbonyl]amino]-1-thiomonohydrochloride (2S-cis) (PNU-69176E). The drug at low micromolar concentrations (<25 microM) markedly enhanced [3H]5-HT binding (more than 300%) by increasing its affinity for low-affinity sites but with no appreciable effect on antagonist ([3H]mesulergine) binding. Functionally, PNU-69176E alone rendered receptors constitutively active, producing the pheno-types of 5-HT-activated receptors, as measured with mesulergine-sensitive guanosine 5'-O-(3-[35S]thio)triphosphate binding, transient inositol 1,4,5-triphosphate release, and [3H]inositol phosphate accumulation. These actions of PNU-69176E were observed with the human 5-HT2C receptor expressed in several mammalian cell lines (human embryonic kidney 293, NIH3T3, and SH-EP) at variable receptor densities (6 to 45 pmol/mg of protein), but not with analogous 5-HT and dopamine receptors (human 5-HT2A, 5-HT2B, 5-HT6, 5-HT7, and dopamine D2-long and D3 receptors). Structurally, PNU-69176E consists of a long alkyl chain and a polar moiety, including the alpha-d-galactopyranoside. Its analogs with shorter alkyl chains (methyl to n-hexyl instead of n-undecyl group) failed to enhance [3H]5-HT binding, and also long alkyl amides are without allosteric modulation. We propose that PNU-69176E may represent a new class of membrane receptor modulators, which probably need a long alkyl chain as a membrane anchor and target a selective polar head group to receptor modulatory sites near the membrane surface.

A unique phenotype of 5-HT2C, agonist-induced GTPgamma35S binding, transferable to 5-HT2A and 5-HT2B, upon swapping intracellular regions

1 The human 5-HT(2C) receptor, when expressed heterologously in various mammalian cell lines (HEK293, SH-EP and NIH-3T3) at various receptor densities (6 to 45 pmol mg(-1) protein), mediates robust agonist-induced GTPgamma(35)S binding from coupling to G(i) subtypes of G proteins, in addition to G(q/11). Such a phenotype, however, was not seen with the human 5-HT(2A) and 5-HT(2B) receptors, indicating their common pathway with 5-HT(2C) limited to G(q/11), not including G(i). 2 Because intracellular regions are largely responsible for signalling pathways, we prepared the chimeras of the 5-HT(2A) and 5-HT(2B) receptors where the second and third intracellular loops, and the C-terminal region were replaced with the 5-HT(2C) counterparts. 3 The chimeras showed robust agonist-induced GTPgamma(35)S binding. Relative intrinsic efficacies of agonists from the GTPgamma(35)S binding were nearly identical to the reported values for their parent receptors as measured with Ca(2+) or [(3)H]-inositol phosphate accumulation. Also the chimeras displayed the same ligand-binding properties as the parent receptors. 4 We conclude that the phenotype of agonist-induced GTPgamma(35)S binding is unique to 5-HT(2C) among the 5-HT(2) receptor family, and is transferable to 5-HT(2A) and 5-HT(2B), upon swapping intracellular sequences, without altering their receptor pharmacology.

RNA editing of the 5-HT(2C) receptor is reduced in schizophrenia

5-HT(2C) receptor (5HT(2C)R, serotonin-2C) RNA undergoes editing to produce several receptor variants, some with pharmacological differences. This investigation comprised two parts: the characterisation of 5-HT(2C)R RNA editing in a larger human control sample than previously examined, and a comparative study in subjects with schizophrenia. Secondary structure analysis of the putative edited region of the human 5-HT(2C)R gene predicted the existence of a double stranded (ds) RNA loop, essential for RNA editing in this receptor. RNA was then extracted from frontal cortex of five controls and five subjects with schizophrenia. RT-PCR products of the edited region were cloned and sequenced (n = 100). Reduced RNA editing, increased expression of the unedited 5-HT(2C-INI) isoform in schizophrenia (P = 0.001) and decreased expression of the 5-HT(2C-VSV) and 5-HT(2C-VNV) isoforms were detected in the schizophrenia group. In addition, two novel mRNA edited variants were identified: 5-HT(2C-MNI) and 5-HT(2C-VDI). Screening of the 5-HT(2C)R gene did not reveal any mutations likely to disrupt the dsRNA loop, suggesting that the reduced RNA editing in schizophrenia may instead be caused by altered activity of the editing enzyme(s). Since the unedited 5-HT(2C-INI) is more efficiently coupled to G proteins than the other isoforms, its increased expression in schizophrenia may lead to enhanced 5-HT(2C)R-mediated effects. The results also illustrate that potentially important receptor alterations may occur in schizophrenia which are not detectable merely in terms of receptor abundance.

In vitro autoradiography of serotonin 5-HT(2A/2C) receptor-activated G protein: guanosine-5'-(gamma-[(35)S]thio)triphosphate binding in rat brain

Agonist activation of G protein-coupled receptors induces an increase in the binding of guanosine 5'-(gamma-[(35)S]thio)triphosphate ([(35)S]GTPgammaS); this increase in binding has been used as a tool to investigate receptor interaction with the heterotrimer guanine nucleotide-binding regulatory protein (G protein). The present study uses agonist-stimulated [(35)S]GTPgammaS binding to characterize serotonin 5-HT(2A/2C) receptors in rat brain membrane fractions and demonstrate the anatomical localization of the receptors by in vitro autoradiography on slide-mounted sections. The stimulatory effect of the agonist [1-(2,5-dimethoxy-4-iodophenyl)]-2 aminopropane (DOI) is compared to that of serotonin (5-HT). Autoradiography revealed a similar localization of DOI- and 5-HT-stimulated binding of [(35)S]GTPgammaS in distinct areas of prefrontal and parietal cortex, consistent with previously reported 5-HT(2A) receptor distribution. Specific binding was demonstrated in the frontal and parietal cortex, medial prefrontal, and cingular and orbital-insular areas as well as in the hippocampal formation, septal areas, the nucleus accumbens, and the choroid plexus. MDL 100105, a specific 5-HT(2A) antagonist, and ketanserin, an antagonist of 5-HT(2A/2C) receptors, blocked DOI stimulation in all labeled areas, whereas 5-HT stimulation was only partially blocked (70-80%). A small but significant inhibition was observed with the specific antagonist of 5-HT(2C/2B), SB 206553. This autoradiographic technique provides a useful tool for measuring in situ changes in specific receptor-Gq protein coupling in anatomically discrete brain regions, under physiological and pathological conditions.

The effects of antipsychotic drugs on serotonergic activity in the rat hippocampus

The serotonergic activity in hippocampus was investigated following acute and chronic treatment with the antipsychotic drugs haloperidol and risperidone. Acute administration of risperidone, the serotonin(2) (5-HT(2)) receptor antagonist ketanserin, and the dopamine (DA)-D(2) receptor antagonist raclopride increased the 5-hydroxyindoleacetic acid/serotonin (5-HIAA/5-HT) ratio. In contrast, acute administration of haloperidol did not affect this ratio. Chronic administration of risperidone maintained the increased 5-HIAA/5-HT ratio; a challenge dose of risperidone after the chronic treatment and the subsequent washout period also maintained the increased ratio. Chronic administration of haloperidol as well as a challenge dose of haloperidol following chronic treatment did not affect the serotonergic activity in hippocampus. Administration of ketanserin or raclopride after chronic treatment and the washout period induced an additional increase in the 5-HIAA/5-HT ratio in risperidone-treated rats. Moreover, a challenge dose of ketanserin, but not raclopride, increased the 5-HIAA/5-HT ratio in haloperidol-treated rats. The present results indicate that acute and chronic treatment of haloperidol or risperidone modified serotonergic activity in the hippocampus in a different way. Moreover, the augmentation of serotonergic activity induced by risperidone did not seem to be solely related to dopaminergic or serotonergic properties and may be of particular relevance for the amelioration of schizophrenia symptoms.

The paradox of 5-methoxy-N,N-dimethyltryptamine: an indoleamine hallucinogen that induces stimulus control via 5-HT1A receptors

Stimulus control was established in rats trained to discriminate either 5-methoxy-N,N-dimethyltryptamine (3 mg/kg) or (-)-2,5-dimethoxy-4-methylamphetamine (0.56 mg/kg) from saline. Tests of antagonism of stimulus control were conducted using the 5-HT1A antagonists (+/-)-pindolol and WAY-100635, and the 5-HT2 receptor antagonist pirenperone. In rats trained with 5-MeO-DMT, pindolol and WAY-100635 both produced a significant degree of antagonism of stimulus control, but pirenperone was much less effective. Likewise, the full generalization of 5-MeO-DMT to the selective 5-HT1A agonist [+/-]-8-hydroxy-dipropylaminotetralin was blocked by WAY-100635, but unaffected by pirenperone. In contrast, the partial generalization of 5-MeO-DMT to the 5-HT2 agonist DOM was completely antagonized by pirenperone, but was unaffected by WAY-100635. Similarly, in rats trained with (-)-DOM, pirenperone completely blocked stimulus control, but WAY-100635 was inactive. The results obtained in rats trained with (-)-DOM and tested with 5-MeO-DMT were more complex. Although the intraperitoneal route had been used for both training drugs, a significant degree of generalization of (-)-DOM to 5-MeO-DMT was seen only when the latter drug was administered subcutaneously. Furthermore, when the previously effective dose of pirenperone was given in combination with 5-MeO-DMT (s.c.), complete suppression of responding resulted. However, the combination of pirenperone and WAY-100635 given prior to 5-MeO-DMT restored responding in (-)-DOM-trained rats, and provided evidence of antagonism of the partial substitution of 5-MeO-DMT for (-)-DOM. The present data indicate that 5-MeO-DMT-induced stimulus control is mediated primarily by interactions with 5-HT1A receptors. In addition, however, the present findings suggest that 5-MeO-DMT induces a compound stimulus that includes an element mediated by interactions with a 5-HT2 receptors. The latter component is not essential for 5-MeO-DMT-induced stimulus control, but is revealed in animals tested or trained with a 5-HT2-selective agonist such as (-)-DOM. Based upon the present data, we conclude that 5-MeO-DMT differs from DOM with respect to the serotonergic element that mediates stimulus control in the rat, but that it shares with DOM a functionally significant interaction with 5-HT2 receptors.

Agonist-induced GTPgamma35S binding mediated by human 5-HT(2C) receptors expressed in human embryonic kidney 293 cells

The 5-HT(2C) receptor as heterologously expressed in various mammalian cells mediates inositol 1,4,5-triphosphate (IP(3)) signal by activating G(q/11) subtypes of G proteins, but minimally promotes agonist-induced GTPgamma35S binding in membranes due to slow GTP turnover rates of the G proteins. Here we discovered robust (over 200%) agonist-induced GTPgamma35S binding mediated by the human receptor expressed in human embryonic kidney (HEK) 293 cells, and investigated its pharmacology. Agonists concentration-dependently increased GTPgamma35S binding in isolated membranes, which was competitively blocked by antagonists. Intrinsic efficacies of agonists from GTPgamma35S binding were comparable to those from IP(3) measurement. Pertussis toxin treatment largely blocked serotonin-induced GTPgamma35S binding, serotonin high affinity sites by 70% without altering the total binding sites, and reduced IP(3) release by 40%. GTPgamma35S-bound Galpha subunits from serotonin-activated membranes were mainly Galpha(i), judging from immobilization studies with various Galpha-specific antibodies. Inhibition of forskolin-stimulated cAMP formation, however, was not observed. Apparently, the 5-HT(2C) receptor-mediated GTPgamma35S binding is a unique phenotype observed in HEK293 cells, reflecting its coupling to pertussis toxin-sensitive G(i) subtypes, which contribute to the IP(3) signal, along with pertussis toxin-insensitive G(q/11) subtypes.

Serotonergic receptor subtypes and hallucinogen-induced stimulus control

More than a quarter century has passed since the demonstration that indoleamine and phenethylamine hallucinogens can function as discriminative stimuli in the rat, and that serotonergic systems are critically involved. During that period our knowledge of the physiology, pharmacology, biochemistry, and molecular biology of serotonergic receptors has increased exponentially; with each advance it has been necessary to reexamine our assumptions regarding hallucinogen-induced stimulus control. Of particular interest is the hypothesis that a drug may act, at a molecular level, upon multiple receptors to produce, at a behavioral level, a compound discriminative stimulus. The salience of the individual elements of such compound stimuli may be influenced by a variety of experimental factors including training dose, pretreatment time, the state of sensitization of the systems being acted upon, and the nature of the drugs chosen for tests of generalization. This article provides examples of experimental approaches to these complexities using selective agonists and antagonists, depletion-induced sensitization, and antagonist correlation analysis.

Direct agonists for serotonin receptors enhance locomotor function in rats that received neural transplants after neonatal spinal transection

We analyzed whether acute treatment with serotonergic agonists would improve motor function in rats with transected spinal cords (spinal rats) and in rats that received transplants of fetal spinal cord into the transection site (transplant rats). Neonates received midthoracic spinal transections within 48 hr of birth; transplant rats received fetal (embryonic day 14) spinal cord grafts at the time of transection. At 3 weeks, rats began 1-2 months of training in treadmill locomotion. Rats in the transplant group developed better weight-supported stepping than spinal rats. Systemic administration of two directly acting agonists for serotonergic 5-HT(2) receptor subtypes, quipazine and (+/-)-1-[2, 5]-dimethoxy-4-iodophenyl-2-aminopropane), further increased weight-supported stepping in transplant rats. The improvement was dose-dependent and greatest in rats with poor to moderate baseline weight support. In contrast, indirectly acting serotonergic agonists, which block reuptake of 5-HT (sertraline) or release 5-HT and block its reuptake (D-fenfluramine), failed to enhance motor function. Neither direct nor indirect agonists significantly improved locomotion in spinal rats as a group, despite equivalent upregulation of 5-HT(2) receptors in the lumbar ventral horn of lesioned rats with and without transplants. The distribution of immunoreactive serotonergic fibers within and caudal to the transplant did not appear to correspond to restoration of motor function. Our results confirm our previous demonstration that transplants improve motor performance in spinal rats. Additional stimulation with agonists at subtypes of 5-HT receptors produces a beneficial interaction with transplants that further improves motor competence.

Distribution and cellular localization of the serotonin type 2C receptor messenger RNA in human brain

The regional and cellular distribution of serotonin type 2C receptor messenger RNA was investigated in autopsy samples of human brain by in situ hybridization histochemistry. The main sites of serotonin receptor type 2C messenger RNA expression were the choroid plexus, cerebral cortex, hippocampus, amygdala, some components of the basal ganglia, the substantia nigra, the substantia innominata and the ventromedial hypothalamus, suggesting that this receptor might be involved in the regulation of different brain functions. Interestingly, in all regions examined, the serotonin type 2C receptor messenger RNA was always restricted to subpopulations of cells, suggesting a specific role, perhaps determined by regionality. A comparison of the in situ hybridization results with those previously obtained by means of radioligand binding experiments suggested that in most of the areas analysed the serotonin type 2C receptors were located at axon terminals.

Pharmacological characteristics and regulation of 5-HT receptor-stimulated phosphoinositide hydrolysis in the rat spinal cord

In slices from immature rat spinal cord, both 5-hydroxytryptamine (5-HT) and the 5-HT2A/C receptor agonists (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and alpha-methyl-5-HT (alpha-Me-5-HT) stimulate phosphoinositide (PI) hydrolysis. PI breakdown is also increased by the 5-HT3 receptor agonist 2-Me-5-HT but not by phenylbiguanide. The effect of either 5-HT or DOI is blocked by selective 5-HT2A receptor antagonists such as spiperone and ketanserin and more markedly by mixed 5-HT2 receptor antagonists, such as ritanserin, methysergide and mesulergine, with higher affinity at the 2C subtype. The effect of 2-Me-5-HT is blocked by 5-HT2 and not by 5-HT3 receptor antagonists, indicating that 5-HT3 receptors do not directly or indirectly take part in PI hydrolysis in the spinal cord. Moreover, lesion with neonatal capsaicin of thin primary afferents to the dorsal spinal cord enhances inositol phosphate formation stimulated by 5-HT or DOI but not by 2-Me-5-HT. This lesion also increases 5-HT2A and 5-HT2C receptor density. After neonatal injection of 5,7-dihydroxytryptamine, which results in a marked loss of 5-HT content in the cord, 5-HT and 5-HT2 receptor agonists also enhance PI breakdown without a concomitant change in receptor number. The results suggest that the 5-HT-stimulated PI response in the rat spinal cord is associated only with the 5-HT2 receptor class, in particular with the 5-HT2C subtype.

Serotonergic basis of antipsychotic drug effects in schizophrenia

Recent attention has been focused on the involvement of serotonin (5-HT) in the pathophysiology of schizophrenia and its role in mediating antipsychotic drug effects. There are two reasons for the new emphasis: the tremendous success of the so-called "atypical" antipsychotic drugs (a common feature of which is their high affinity for specific 5-HT receptor subtypes); and the elucidation of a complex family of 5-HT receptors whose function and pharmacology is only beginning to be understood. This paper will review the evidence that pertains to the role of 5-HT in mediating antipsychotic drug effects. The interaction of dopamine and 5-HT systems will be reviewed, and the mechanisms of action of atypical antipsychotic drugs will be evaluated in this context. The impact of serotonin on neurodevelopment, and the involvement of serotonin in the psychotomimetic and psychotogenic properties of hallucinogens, will be discussed. Together, these facts will be placed into the context of changes in serotonergic function in schizophrenia.

A comparison of N,N-dimethyltryptamine, harmaline, and selected congeners in rats trained with LSD as a discriminative stimulus

1. A series of N-substituted tryptamines was compared with a series of beta-carbolines in rats trained to discriminate LSD (0.1 mg/kg) from saline. 2. Intermediate levels of substitution were elicited by MDMT (76.4%), DMT (77.9%), and DET (48.7%). 6-F-DET produced 41.3% LSD-appropriate responding at a dose of 6.0 mg/kg but only 4 of 8 subjects completed the test session thus precluding statistical analysis. Bufotenine (25.8%) also failed to substitute. Although none of the tryptamines substituted completely for LSD, the pattern of substitution is consonant with what is known of their activity in humans. MDMT, DMT, and DET are well established in the literature as hallucinogens but the same cannot be said for 6-F-DET and bufotenine. 3. Of the beta-carbolines tested, none substituted for LSD completely and only harmane elicited intermediate substitution (49.5%). No significant generalization of the LSD stimulus to 6-methoxyharmalan, harmaline, or THBC was observed. Thus, in contrast to the tryptamines, scant ability to substitute for LSD was observed in the beta-carbolines tested. 4. Taken together, the present data indicate that the representative tryptamines employed in the present study exhibit greater similarity to the LSD stimulus than do representative beta-carbolines. The receptor interactions responsible for these differences remain to be determined.

Ependymal and choroidal cells in culture: characterization and functional differentiation

During the past 10 years, our teams developed long-term primary cultures of ependymal cells derived from ventricular walls of telencephalon and hypothalamus or choroidal cells (modified ependymal cells) derived from plexuses dissected out of fetal or newborn mouse or rat brains. Cultures were established in serum-supplemented or chemically defined media after seeding on serum-, fibronectin-, or collagen-laminin-coated plastic dishes or semipermeable inserts. To identify and characterize cell types growing in our cultures, we used morphological features provided by phase contrast, scanning, and transmission electron microscopy. We used antibodies against intermediate filament proteins (vimentin, glial fibrillary acidic protein, cytokeratin, desmin, neurofilament proteins), actin, myosin, ciliary rootlets, laminin, and fibronectin in single or double immunostaining, and monoclonal antibodies against epitopes of ependymal or endothelial cells, to recognize ventricular wall cell types with immunological criteria. Ciliated or nonciliated ependymal cells in telencephalic cultures, tanycytes and ciliated and nonciliated ependymal cells in hypothalamic cultures always exceeded 75% of the cultured cells under the conditions used. These cells were characterized by their cell shape and epithelial organization, by their apical differentiations observed by scanning and transmission electron microscopy, and by specific markers (e.g., glial fibrillary acidic protein, ciliary rootlet proteins, DARPP 32) detected by immunofluorescence. All these cultured ependymal cell types remarkably resembled in vivo ependymocytes in terms of molecular markers and ultrastructural features. Choroidal cells were also maintained for several weeks in culture, and abundantly expressed markers were detected in both choroidal tissue and culture (Na+-K+-dependent ATPase, DARPP 32, G proteins, ANP receptors). In this review, the culture models we developed (defined in terms of biological material, media, substrates, duration, and subculturing) are also compared with those developed by other investigators during the last 10 years. Focusing on morphological and functional approaches, we have shown that these culture models were suitable to investigate and provide new insights on (1) the gap junctional communication of ependymal, choroidal, and astroglial cells in long-term primary cultures by freeze-fracture or dye transfer of Lucifer Yellow CH after intracellular microinjection; (2) some ionic channels; (3) the hormone receptors to tri-iodothyronine or atrial natriuretic peptides; (4) the regulatory effect of tri-iodothyronine on glutamine synthetase expression; (5) the endocytosis and transcytosis of proteins; and (6) the morphogenetic effects of galactosyl-ceramide. We also discuss new insights provided by recent results reported on in vitro ependymal and choroidal expressions of neuropeptide-processing enzymes and neurosecretory proteins or choroidal expression of transferrin regulated through serotoninergic activation.

Serotonin 5HT2A receptor activation inhibits inducible nitric oxide synthase activity in C6 glioma cells

C6-glioma cells endogenously express both 5HT2A receptors and inducible nitric oxide synthase (iNOS). iNOS can be induced by transcriptional activation to produce nitric oxide (NO) in response to a challenge with lipopolysaccharide (LPS). Experiments were conducted to determine whether 5HT2A receptor activation could modify the production of NO in response to LPS. Incubation of 10 microg/ml LPS with C6-glioma cells for a period of 24 hours resulted in a 2.6 fold increase in nitrite levels, as a measure of NO levels, over vehicle treated controls. Co-incubation with the selective 5HT2A receptor partial agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) produced a dose-dependent inhibition of the LPS-induced nitrite levels of 22% with an IC50 of 16 nM. The full agonists serotonin (5HT) and alpha-methyl-5HT produced an inhibition of approximately 30% at a concentration of 1 microM. The inhibitory effect of 1 microM DOI was blocked by the 5HT2A receptor antagonists spiperone and ritanserin (10 nM). Inhibition of protein kinase C (PKC) using 100 nM chelerythrine prevented the DOI-mediated decrease in LPS-induced nitrite levels. Addition of DOI to the cells after 1 hr following the LPS addition did not produce a decrease in nitrite levels indicating iNOS was not modified post-translationally. The data demonstrate that iNOS activity can be modulated by serotonin 5HT2A receptor activation, most likely at the initiation of the induction process, via PKC. We therefore suggest that there may be a link between the serotonergic system and NO-mediated immune responses in the brain.

Generation of anti-peptide antibodies against serotonin 5-HT2A and 5-HT2C receptors

Anti-peptide antibodies were generated against several 13-17 amino acid regions of rat serotonin 5-HT2A and 5-HT2C receptors. Peptides containing terminal cysteine residues were conjugated to bovine serum albumin (BSA) and ovalbumin (OVA) with the cross-linking reagent sulfo-SMCC (sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate). Both the carrier protein and the number of peptide molecules per carrier molecule were changed during the immunization schedule. For the early immunizations, immunogens were BSA-peptides at ratios of 8-27 mol peptide per mol BSA. For the later boosts, immunogens were OVA-peptides at ratios of 1-2 mol peptide per mol OVA. The peptide constructs were used to immunize rabbits and chickens. Anti-peptide antibodies were purified from sera (rabbits) or egg yolks (hens) using peptide matrices. Cell lines expressing similar densities of rat 5-HT2A or 5-HT2C receptors were used to monitor the specificity of purified antibodies on immunoblots and in immunocytochemistry. A total of five out of the six rabbit antibodies were positive on immunoblots (three anti-5-HT2A and two anti-5-HT2C) and four were also positive in immunocytochemistry (three anti-5-HT2A and one anti-5-HT2C). None of the anti-peptide chicken antibodies were useful on immunoblots or in immunocytochemistry. Since there is a paucity of high affinity reagents selective for 5-HT2A or 5-HT2C receptors, these rabbit antibodies will be useful tools. The methods used to generate site-directed antibodies specific for 5-HT2A or 5-HT2C receptors should be applicable to other proteins.

The meta-chlorophenylpiperazine challenge test in cocaine addicts: hormonal and psychological responses

We report on the neuroendocrine and psychological responsivity of 31 cocaine addicts and 14 controls to the serotonergic agonist, meta-chlorophenylpiperazine (m-CPP) (0.5 mg/kg p.o.). Cocaine addicts were subdivided into subjects with aggressive tendencies and other features similar to those found in type 2 alcoholics and subjects without these features. Following m-CPP, aggressive and nonaggressive patients had a significantly blunted prolactin response compared to controls, but there was no difference between the two patient subgroups. There was no difference between the cortisol responses of nonaggressive patients and controls, but aggressive patients had a significantly blunted cortisol response compared to controls and nonaggressive patients. Both patient subgroups reported more intense "activation-euphoria" and "high" responses following m-CPP than controls. These results could indicate the existence of alterations along serotonergic pathways in cocaine addicts taken as a group. In addition, a subgroup of patients who could be described as type 2 cocaine addicts appear to be biologically different from healthy subjects and from other cocaine addicts as indicated by a greater cortisol blunting following m-CPP.

5-HT2A receptor-mediated regulation of brain-derived neurotrophic factor mRNA in the hippocampus and the neocortex

The influence of 5-HT receptor agonists on the expression of BDNF in brain was determined. Administration of a hallucinogenic 5-HT2A /2C receptor agonist, but not a 5-HT1A receptor agonist, resulted in a significant but differential regulation of BDNF mRNA levels in hippocampus and neocortex. In the hippocampus, the 5-HT2A /2C receptor agonist significantly decreased BDNF mRNA expression in the dentate gyrus granule cell layer but did not influence expression of the neurotrophin in the CA subfields. In parietal cortex and other neocortical areas, but not piriform cortex, the 5-HT2A /2C receptor agonist dramatically increased the expression of BDNF mRNA. The effect of the 5-HT2A /2C receptor agonist on BDNF mRNA in both the hippocampus and the neocortex was blocked by pretreatment with a selective 5-HT2A, but not 5-HT2C, receptor antagonist. The expression of BDNF mRNA in the hippocampus is reported to be decreased by stress, raising the possibility that the 5-HT2A receptor mediates this effect. Pretreatment with ketanserin, a 5-HT2A /2C receptor antagonist, significantly blocked the stress-induced downregulation of BDNF mRNA in hippocampus, in support of this hypothesis. The results of this study raise the possibility that regulation of BDNF expression by hallucinogenic 5-HT2A receptor agonists leads to adaptations of synaptic strength in the hippocampus and the neocortex that may mediate some of the acute and long-term behavioral effects of these agents.

(+/-)-1-(2,5-Dimethoxy-4-ethylthiophenyl)-2-aminopropane (ALEPH-2), a novel putative anxiolytic agent lacking affinity for benzodiazepine sites and serotonin-1A receptors

Serotonergic behavioral responses, effects on motor activity and core temperature, and binding properties of the novel putative anxiolytic amphetamine derivative (+/-)1-(2,5-dimethoxy-4-ethylthio-phenyl)-2-aminopropane (ALEPH-2), were examined in rodents in order to elucidate the mechanism underlying its anxiolytic-like effect. After peripheral administration in rats, ALEPH-2 induced some symptoms of the serotonergic syndrome, e.g. forepaw treading and flat body posture. Additionally, a decrease in motor activity was observed. No significant effects on the number of head shakes were observed after injection, although high inter-subject variability was noted. Higher doses of ALEPH-2, in the range exhibiting anxiolytic properties (4mg/kg), elicited significant hypothermia in mice. The affinity of the drug for 5-HT2A/2C receptors ([3H]ketanserin sites) was in the nanomolar range (Ki = 173 nM), whereas for 5-HT1A, benzodiazepine sites, and GABAA receptors, the affinity was micromolar of lower. Based on these results the mechanism of action and the anxiolytic-like properties of ALEPH-2 are discussed.

Activities of novel aryloxyalkylimidazolines on rat 5-HT2A and 5-HT2C receptors

Using transfected NIH 3T3 mouse fibroblast cell lines expressing the rat 5-HT2A and rat 5-HT2C receptor subtypes, and techniques of 2-[125I](+)-iodolysergic acid diethylamide ([125I]LSD) binding and serotonin (5-hydroxytryptamine, 5-HT)-stimulated phosphoinositide hydrolysis, we have characterized a new structural class of 5-HT receptor ligands, the aryloxyalkylimidazolines. These compounds were found to be potent competitors of [125I]LSD binding at both receptor subtypes (Ki approximately 5-200 nM) and to have efficacy ranging from potent competitive antagonists (IC50 approximately 25 nM) to moderately potent full agonists (EC50 approximately 200 nM). Some of these compounds are agonists at both receptor subtypes, while others are 5-HT2C receptor agonists with 5-HT2A receptor antagonist activity. None of the aryloxyalkylimidazolines reported here have 5-HT2A or 5-HT2C receptor selective antagonist activity. Since these compounds are novel structures, we compared them with a variety of reference 5-HT receptor ligands selected from other chemical classes that have previously been studied at 5-HT2A and 5-HT2C receptors in native tissues.

Behavioral effects of (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, (DOI) in the elevated plus-maze test

The serotonin (5-hydroxytryptamine, 5-HT) system has consistently been implicated in the actions of (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and other hallucinogens. Recent evidence suggest that the 5-HT2A/2C receptor subtypes may be major targets for such drugs in the CNS. DOI-treated hooded rats (0.1-5.0 mg/kg) and DOI treated ICR mice (0.1-2.0 mg/kg), displayed aversions at lower doses and anti-aversions at higher doses to the open arms of the plus-maze. Mianserin (0.5 mg/kg) and ketanserin (0.1 mg/kg) blocked the anti-aversive behavior, but only mianserin was effective at reversing the aversions produced by the higher doses of DOI in the ICR mice. DOI produced an intense aversion in the DBA/2 and anti-aversion in the C57/BL6 mice to the open arms of the plus-maze. These opposing actions of DOI in the plus-maze may be exploited in studying the neurobehavioral effects of hallucinogens. Since flumazenil was ineffective at blocking the DOI induced changes, it was concluded that the mechanism of DOI induced anxiolysis or anxiogenesis may not involve an action at the benzodiazepine receptors.

LSD and structural analogs: pharmacological evaluation at D1 dopamine receptors

The hallucinogenic effects of lysergic acid diethylamide (LSD) have been attributed primarily to actions at serotonin receptors. A number of studies conducted in the 1970s indicated that LSD also has activity at dopamine (DA) receptors. These latter studies are difficult to interpret, however, because they were completed before the recognition of two pharmacologically distinct DA receptor subtypes, D1 and D2. The availability of subtype-selective ligands (e.g., the D1 antagonist SCH23390) and clonal cell lines expressing a homogeneous receptor population now permits an assessment of the contributions of DA receptor subtypes to the DA-mediated effects of LSD. The present study investigated the binding and functional properties of LSD and several lysergamide and analogs at dopamine D1 and D2 receptors. Several of these compounds have been reported previously to bind with high affinity to serotonin 5HT2 (i.e., 3H-ketanserin) sites in the rat frontal cortex (K0.5 5-30 nM). All tested compounds also competed for both D1-like (3H-SCH 23390) and D2-like (3H-spiperone plus unlabeled ketanserin) DA receptors in rat striatum, with profiles indicative of agonists (nH < 1.0). The affinity of LSD and analogs for D2 like receptors was similar to their affinity for 5HT2 sites. The affinity for D1 like receptors was slightly lower (2- to 3-fold), although LSD and several analogs bound to D1 receptors with affinity similar to the prototypical D1 partial agonist SKF38393 (K0.5 ca. 25 nM). A second series of experiments tested the binding and functional properties of LSD and selected analogs in C-6 glioma cells expressing the rhesus macaque D1A receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Methylenedioxyamphetamine: a selective effect on cortical content and turnover of 5-HT

This study examined the effects of the hallucinogen, MDA, on brain content of monoamines and their metabolites in the rabbit. A single 1.8 mg/kg dose of MDA produced 30 to 64% increases in the 5-HT content of frontal cortex from 30 to 120 min after injection and a decrease in 5-HT turnover from 30 min to 8 h, but had no effect in hippocampus, caudate nucleus, or hypothalamus. A single 3.6 mg/kg dose of MDA also reduced the turnover of 5-HT in frontal cortex, but this was accompanied by a decrease in 5-HIAA with no increase in 5-HT. The 1.8 and 3.6 mg/kg doses of MDA had no significant or consistent effects on the contents of DA, DOPAC, HVA, and NE in any brain area examined. Chronic administration of MDA (3.6 mg/kg/day for 4 days) failed to produce any evidence of a neurotoxic action on 5-HT neurons. Higher doses could not be employed because the LD50 of MDA was approximately 5 mg/kg. This study has demonstrated that behaviorally effective and nonneurotoxic doses of MDA produce increases in the content and decreases in turnover of 5-HT in frontal cortex that resemble those of other hallucinogens such as LSD and DOM.

Evidence for two types of potassium current in rat choroid plexus epithelial cells

The whole-cell patch-clamp technique was applied to rat choroid plexus epithelial cells. The resting membrane potential was -53 mV. The whole-cell conductance was mainly K+ selective, and the K+ current observed appeared to contain two distinct components. Depolarizing voltage pulses (more positive than 0 mV) evoked time-dependent outward currents which resembled delayed-rectifying K+ currents in other tissues. The current exhibited time-dependent activation and, at potentials more positive than 40 mV, slower time-dependent inactivation. The reversal potential measured by tail current analysis showed a shift of 43 mV for a tenfold increase in extracellular K+ concentration ([K+]o). The current was reduced by extracellular 5 mM Ba2+, 5 mM tetraethylammonium (TEA+), 5 mM Cs+ and 1 mM 4-aminopyridine (4-AP). In contrast, hyperpolarizing voltage pulses evoked time-independent, inward-rectifying currents. The reversal potential measured by voltage-ramp commands showed a shift of 42 mV for a tenfold increase in [K+]o. The chord conductance did not appear to increase with increasing [K+]o. The current was reduced by extracellular 5 mM Ba2+ and 0.5 mM Cs+, but not by 5 mM TEA+ or 1 mM 4-AP. These data suggest that two populations of K+ channel contribute to the conductance of choroid plexus epithelial cells.

Involvement of 5-HT2C receptors in mediating the discriminative stimulus properties of m-chlorophenylpiperazine (mCPP)

Rats were trained to discriminate the 5-HT receptor agonist 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-HT1B/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-HT1A/B receptor agonist RU 24969 (0.25-2 mg/kg) substituted fully for mCPP. The 5-HT2A/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-HT1A or 5-HT3 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-HT1/2 receptor antagonist metergoline (0.125-1 mg/kg) completely blocked the mCPP cue whereas the 5-HT2A/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-HT2C receptors.

5-HT1C receptor-mediated phosphoinositide hydrolysis in the rat choroid plexus after chronic treatment with clozapine

Chronic treatment with clozapine (14 days; 10 and 25 mg/kg/day) decreases 5-HT1C receptor density but not affinity in rat choroid plexus measured with [3H]mesulergine. We now report the effects of the same clozapine treatment regimens on the function of 5-HT1C receptors (measured by maximal stimulation of 5-HT1C receptor-mediated phosphoinositide hydrolysis) in relation to receptor changes in rat choroid plexus. Quantitative 5-HT1C receptor autoradiography indicated that chronic clozapine treatment decreased, in a dose-related manner, 5-HT1C receptor binding sites labeled by antagonist ([3H]mesulergine) and agonist ([125I](+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, [125I]DOI) radioligands. However, only the higher dose of clozapine decreased statistically significantly the maximal 5-HT1C receptor-mediated phosphoinositide hydrolysis response. Chronic administration of haloperidol (0.5 mg/kg/day) did not change any of the 5-HT1C receptor parameters. In conclusion, chronic clozapine treatment is able to modulate the function of 5-HT1C receptors. This further strengthens the possibility that 5-HT1C receptors may contribute to some of the atypical effects of clozapine.

MDMA enhances associative and nonassociative learning in the rabbit

The rate of associative learning was assessed in the presence of saline versus methylenedioxymethamphetamine (MDMA) at doses of 0.95, 1.9, and 3.8 mg/kg. The conditioned stimuli (CSs) were lights and tones and the unconditioned stimulus (US) was a corneal air puff. Learning was enhanced by all but the highest dose of drug tested, and the enhancement was most pronounced when light was used as the conditioned stimulus. Nonassociative responding was assessed using unpaired presentations of the lights, tones, and air puffs. MDMA (1.9 mg/kg) produced a slight increase in the percentage of baseline responses but failed to produce an increase in the frequency of nonassociative responding in the presence of the lights or tones. MDMA produced a significant increase in the amplitude of the unconditioned response to the corneal air puff across the 10 sessions. This increase was taken as evidence for sensitization of the unconditioned response, a nonassociative learning phenomenon. In summary, MDMA, like the parent compound methylenedioxyamphetamine (MDA), enhances both conditioned and unconditioned responding. Because this dual effect has not been seen with related psychedelic compounds, the effect appears to be unique to this class of phenylethylamine drugs.

Adverse consequences of lysergic acid diethylamide

The continued endemic use of hallucinogenic drugs, and of LSD in particular, raises concern regarding their short and long term adverse consequences. The epidemiology of LSD abuse is reviewed suggesting an increase in LSD use among the young as the prevalence rates for other substances continues to fall. Evidence supports the association of LSD use with panic reactions, prolonged schizoaffective psychoses and post-hallucinogen perceptual disorder, the latter being present continually for as long as 5 years. Evidence does not support claims of genetic disorders arising from hallucinogens. In light of the foregoing, current data confirm earlier findings of long lasting psychopathology arising in vulnerable individuals from the use of LSD. A hypothetical long term molecular mechanism of adverse effects is proposed.

Modulation of 5-HT1C receptors and phosphoinositide system by ethanol consumption in rat brain and choroid plexus

The effect of chronic ethanol consumption (60 days) on 5-HT1C receptors as measured by [3H]mesulergine binding in the hippocampus, cortex, and choroid plexus of rats was investigated. The 5-HT1C receptor-mediated phosphoinositide hydrolysis in rat choroid plexus was also investigated. It was observed that chronic ethanol treatment significantly increased the 5-HT-stimulated [3H]inositol 1-phosphate ([3H]IP1) formation, as well as the density (Bmax) of 5-HT1C receptors without causing a significant change in affinity (KD) of [3H]mesulergine binding in rat choroid plexus. It was also observed that chronic ethanol consumption had no significant effect on the Bmax or KD of 5-HT1C receptor binding sites in the hippocampus and cortex brain regions of rats. These results thus suggest that chronic ethanol consumption causes an up-regulation of both 5-HT1C receptors and 5-HT1C receptor-mediated phosphoinositide hydrolysis in rat choroid plexus but has no significant effects on the 5-HT1C receptors in brain. These results also suggest that 5-HT1C receptors and their functional response may be involved in the pathogenesis of alcohol dependence.

LSD has high efficacy relative to serotonin in enhancing the cationic current Ih: intracellular studies in rat facial motoneurons

The effects of LSD (d-lysergic acid diethylamide) on rat facial motoneurons were compared to those of 5-hydroxytryptamine (5-HT) in brain slices by means of current clamp and single-electrode voltage-clamp recordings. As previously reported, 5-HT, in part by decreasing a resting potassium conductance, produced a reversible depolarization (approximately 5 mV), an increase in input resistance, and an enhancement in electrical excitability. LSD also produced an increase in electrical excitability, although with a much slower onset and longer duration. However, in contrast to 5-HT, LSD produced only a slight depolarization (1-2 mV). Moreover, in the presence of LSD the depolarizing effect of 5-HT was markedly attenuated. The 5-HT2/5-HT1C agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) produced effects intermediate between LSD and 5-HT. The LSD-induced increase in electrical excitability was completely reversed by spiperone, a 5-HT2/5-HT1A antagonist, and by ritanserin, a 5-HT2/5-HT1C antagonist; the effects of 5-HT were also reduced by these 2 antagonists, but complete blockade did not occur at the concentrations and durations tested. Surprisingly, LSD was found to enhance the hyperpolarization-activated nonspecific cation current Ih to a greater extent than did 5-HT; this enhancement was blocked by both spiperone and ritanserin. These results indicate that, despite having low efficacy relative to 5-HT in decreasing resting potassium conductance, LSD has high efficacy in enhancing the Ih current in rat facial motoneurons; possible mechanisms for this difference are discussed.

Up-regulation of 5-hydroxytryptamine2 and neurokinin-1 receptors associated with serotonin/substance P hyperinnervation in the rat inferior olive

The fate of serotonin and substance P receptors following serotonin/substance P hyperinnervation of CNS tissue was investigated in the inferior olivary complex of adult rats subjected to earlier intraventricular administration of 5,6-dihydroxytryptamine. [3H]8-hydroxy-2-(Dl-n-propylamino)tetralin, [3H]5-hydroxytryptamine, [3H]ketanserin and [125I]Bolton-Hunter-substance P were respectively used to label 5-hydroxytryptamine1A, 5-hydroxytryptamine1B, 5-hydroxytryptamine2 and neurokinin-1 receptor sites for quantitative ligand binding autoradiography. Only 5-hydroxytryptamine2 and neurokinin-1 sites were detected in the normal or serotonin/substance P-hyperinnervated inferior olivary complex. In the normal inferior olivary complex, the density of [3H]ketanserin binding (5-hydroxytryptamine2 receptors) was relatively low, being the highest in pars a of the caudal medial accessory olive and the principal olive; moderate in pars c of the caudal medial accessory olive; truly low in the medial and the lateral dorsal accessory olive, nucleus b and pars b of the caudal medial accessory olive; and negligible in the middle medial accessory olive, rostral medial accessory olive and the smaller subnuclei. [125I]Bolton-Hunter-substance P binding (neurokinin-1 receptors) appeared denser, being highest in nucleus beta and the middle medial dorsal accessory olive; moderate in the three portions of the caudal medial accessory olive, the lateral dorsal accessory olive and the dorsal cap of Kooy; low in the rostral medial accessory olive, the ventrolateral outgrowth and the dorsomedial cell column; and very low or null in the principal olive and the medial dorsal accessory olive. After serotonin/substance P hyperinnervation, there were striking increases in the apparent density of both populations of receptor. [3H]Ketanserin binding was now stronger in the most olivary subnuclei, including some in which it had not been found in the normal, such as the middle and the rostral medial accessory olive. [125I]Bolton-Hunter-substance P binding showed even greater elevations in a few subnuclei, such as the principal olive and the dorsomedial cell column; it was now detectable in the medial dorsal accessory olive, unchanged in the dorsal cap of Kooy and the ventrolateral outgrowth, and slightly decreased in the lateral dorsal accessory olive. The normal and altered distributions of both ligands did not match the respective patterns of serotonin and substance P innervation and hyperinnervation previously demonstrated with immunocytochemistry. In some sectors of the inferior olivary complex where both transmitters are presumably co-localized, there was no overlap in the distribution of the respective binding sites either in the normal or in the hyperinnervated state.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated cocaine modifies the neuroendocrine responses to the 5-HT1C/5-HT2 receptor agonist DOI

Endocrine responses to the serotonin (5-HT) 5-HT1C/5-HT2 agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) were utilised to evaluate cocaine-induced alterations in postsynaptic 5-HT receptor function. Rats received cocaine HCl (0, 5 or 15 mg/kg i.p.) twice daily for 7 days. Effects of DOI (0, 0.5, 2 or 10 mg/kg i.p.) on plasma adrenocorticotropic hormone (ACTH), corticosterone, prolactin, oxytocin and renin concentrations were assessed 42 h after the final cocaine injection. DOI dose dependently increased the plasma concentrations of each hormone. Cocaine potentiated the DOI-induced elevations of plasma ACTH, corticosterone and prolactin concentrations. In contrast, the oxytocin response was reduced, and the renin response was unaltered by cocaine exposure. The data suggest that 5-HT2 receptor-mediated responses for ACTH, corticosterone and prolactin secretion become supersensitive following repeated cocaine. In contrast, the 5-HT2 receptor-mediated response for oxytocin secretion is subsensitive. The cocaine-induced changes in postsynaptic 5-HT receptor function are likely a consequence of deficits in the function of 5-HT nerve terminals, that we have documented previously.