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M. Geyer

Lysergic Acid Diethylamide and Psilocybin Revisited

August 6, 2015 / LSD, Mushrooms / Psilocybin, Papers, Psychology, Publications / By /

Abstract

The past decade brought the beginnings of a renaissance in research on psychedelic drugs. Two articles in this issue of Biological Psychiatry signify that the resurrection of this long-ignored topic has begun to mature and bear at least the promise of fruit. In the early 1970s, the onset of the “War on Drugs” brought with it a near-total hiatus in serious research on psychedelic drugs, especially in the United States. The resumption of credible work in this area has come from Switzerland, where many of the original pioneering studies were initiated in the 1950s and 1960s.

Geyer, M. A. (2015). Lysergic Acid Diethylamide and Psilocybin Revisited. Biological psychiatry, 78(8), 516-518. http://dx.doi.org/10.1016/j.biopsych.2015.08.003
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Role of the 5-HT2A receptor in the locomotor hyperactivity produced by phenylalkylamine hallucinogens in mice

January 29, 2013 / Mescaline / Cacti, Neuroscience, Papers, Publications / By / , ,

Abstract

The 5-HT2A receptor mediates the effects of serotonergic hallucinogens and may play a role in the pathophysiology of certain psychiatric disorders, including schizophrenia. Given these findings, there is a need for animal models to assess the behavioral effects of 5-HT2A receptor activation. Our previous studies demonstrated that the phenylalkylamine hallucinogen and 5-HT2A/2C agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) produces dose-dependent effects on locomotor activity in C57BL/6J mice, increasing activity at low to moderate doses and reducing activity at high doses. DOI did not increase locomotor activity in 5-HT2A knockout mice, indicating the effect is a consequence of 5-HT2A receptor activation. Here, we tested a series of phenylalkylamine hallucinogens in C57BL/6J mice using the Behavioral Pattern Monitor (BPM) to determine whether these compounds increase locomotor activity by activating the 5-HT2A receptor. Low doses of mescaline, 2,5-dimethoxy-4-ethylamphetamine (DOET), 2,5-dimethoxy-4-propylamphetamine (DOPR), 2,4,5-trimethoxyamphetamine (TMA-2), and the conformationally restricted phenethylamine (4-bromo-3,6-dimethoxybenzocyclobuten-1-yl)methylamine (TCB-2) increased locomotor activity. By contrast, the non-hallucinogenic phenylalkylamine 2,5-dimethoxy-4-tert-butylamphetamine (DOTB) did not alter locomotor activity at any dose tested (0.1–10 mg/kg i.p.). The selective 5-HT2A antagonist M100907 blocked the locomotor hyperactivity induced by mescaline and TCB-2. Similarly, mescaline and TCB-2 did not increase locomotor activity in 5-HT2A knockout mice. These results confirm that phenylalkylamine hallucinogens increase locomotor activity in mice and demonstrate that this effect is mediated by 5-HT2A receptor activation. Thus, locomotor hyperactivity in mice can be used to assess phenylalkylamines for 5-HT2A agonist activity and hallucinogen-like behavioral effects. These studies provide additional support for the link between 5-HT2A activation and hallucinogenesis.

Halberstadt, A. L., Powell, S. B., & Geyer, M. A. (2013). Role of the 5-HT 2A receptor in the locomotor hyperactivity produced by phenylalkylamine hallucinogens in mice. Neuropharmacology, 70, 218-227. 10.1016/j.neuropharm.2013.01.014
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Multiple receptors contribute to the behavioral effects of indoleamine hallucinogens

January 20, 2011 / Ayahuasca, DMT, LSD, Mescaline / Cacti, Mushrooms / Psilocybin, Neuroscience, Papers, Psychology, Publications / By / ,

Abstract

Serotonergic hallucinogens produce profound changes in perception, mood, and cognition. These drugs include phenylalkylamines such as mescaline and 2,5-dimethoxy-4-methylamphetamine (DOM), and indoleamines such as (+)-lysergic acid diethylamide (LSD) and psilocybin. Despite their differences in chemical structure, the two classes of hallucinogens produce remarkably similar subjective effects in humans, and induce cross-tolerance. The phenylalkylamine hallucinogens are selective 5-HT(2) receptor agonists, whereas the indoleamines are relatively non-selective for serotonin (5-HT) receptors. There is extensive evidence, from both animal and human studies, that the characteristic effects of hallucinogens are mediated by interactions with the 5-HT(2A) receptor. Nevertheless, there is also evidence that interactions with other receptor sites contribute to the psychopharmacological and behavioral effects of the indoleamine hallucinogens. This article reviews the evidence demonstrating that the effects of indoleamine hallucinogens in a variety of animal behavioral paradigms are mediated by both 5-HT(2) and non-5-HT(2) receptors.

Halberstadt, A. L., & Geyer, M.A. (2011). Multiple receptors contribute to the behavioral effects of indoleamine hallucinogens. Neuropharmacology, 61(3), 364-381. http://dx.doi.org/10.1016/j.neuropharm.2011.01.017
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LSD but not lisuride disrupts prepulse inhibition in rats by activating the 5-HT2A receptor

November 25, 2009 / LSD, Papers, Publications / By / ,

Abstract

Rationale: Compounds that activate the 5-HT2A receptor, such as lysergic acid diethylamide (LSD), act as hallucinogens in humans. One notable exception is the LSD congener lisuride, which does not have hallucinogenic effects in humans even though it is a potent 5-HT2A agonist. LSD and other hallucinogens have been shown to disrupt prepulse inhibition (PPI), an operational measure of sensorimotor gating, by activating 5-HT2A receptors in rats.

Objective: We tested whether lisuride disrupts PPI in male Sprague–Dawley rats. Experiments were also conducted to identify the mechanism(s) responsible for the effect of lisuride on PPI and to compare the effects of lisuride to those of LSD.

Results: Confirming a previous report, LSD (0.05, 0.1, and 0.2 mg/kg, s.c.) reduced PPI, and the effect of LSD was blocked by pretreatment with the selective 5-HT2A antagonist MDL 11,939. Administration of lisuride (0.0375, 0.075, and 0.15 mg/kg, s.c.) also reduced PPI. However, the PPI disruption induced by lisuride (0.075 mg/kg) was not blocked by pretreatment with MDL 11,939 or the selective 5-HT1A antagonist WAY-100635 but was prevented by pretreatment with the selective dopamine D2/D3 receptor antagonist raclopride (0.1 mg/kg, s.c).

Conclusions: The effect of LSD on PPI is mediated by the 5-HT2A receptor, whereas activation of the 5-HT2A receptor does not appear to contribute to the effect of lisuride on PPI. These findings demonstrate that lisuride and LSD disrupt PPI via distinct receptor mechanisms and provide additional support for the classification of lisuride as a non-hallucinogenic 5-HT2A agonist.

Halberstadt, A. L, & Geyer, M. A. (2010). LSD but not lisuride disrupts prepulse inhibition in rats by activating the 5-HT2A receptor. Psychopharmacology, 208(2), 179–189. http://dx.doi.org/10.1007/s00213-009-1718-x
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Serotonin-Related Psychedelic Drugs

November 5, 2008 / LSD, Mescaline / Cacti, Mushrooms / Psilocybin, Neuroscience, Papers, Psychology, Publications / By / , ,

Abstract

Serotonergic hallucinogens include the prototypical compounds such as mescaline, psilocybin, and LSD, representing the chemical classes of phenethylamines, tryptamines, and ergolines. Known as psychedelics, these compounds induce dramatic alterations of perception, affect, consciousness, and the experience of self. As first discovered in animal studies and recently confirmed in humans, the psychological effects of psychedelics are primarily attributable to the activation of the 5-HT2A subtype of serotonin receptors in brain. Research on psychedelic compounds has provided important insights into the neurobiology of consciousness and naturally occurring psychotic states and may lead to further advances in the development of psychiatric pharmacotherapeutics.

Geyer, M. A., Nichols, D. E., & Vollenweider, F. X. (2009). Serotonin-related psychedelic drugs. 10.1016/B978-008045046-9.01160-8
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The effects of the preferential 5-HT2A agonist psilocybin on prepulse inhibition of startle in healthy human volunteers depend on interstimulus interval

February 14, 2007 / Mushrooms / Psilocybin, Neuroscience, Papers, Psychology, Psychotic Disorders, Publications / By / , , , ,

Abstract

Schizophrenia patients exhibit impairments in prepulse inhibition (PPI) of the startle response. Hallucinogenic 5-HT2A receptor agonists are used for animal models of schizophrenia because they mimic some symptoms of schizophrenia in humans and induce PPI deficits in animals. Nevertheless, one report indicates that the 5-HT2A receptor agonist psilocybin increases PPI in healthy humans. Hence, we investigated these inconsistent results by assessing the dose-dependent effects of psilocybin on PPI in healthy humans. Sixteen subjects each received placebo or 115, 215, and 315 mug/kg of psilocybin at 4-week intervals in a randomized and counterbalanced order. PPI at 30-, 60-, 120-, 240-, and 2000-ms interstimulus intervals (ISIs) was measured 90 and 165 min after drug intake, coinciding with the peak and post-peak effects of psilocybin. The effects of psilocybin on psychopathological core dimensions and sustained attention were assessed by the Altered States of Consciousness Rating Scale (5D-ASC) and the Frankfurt Attention Inventory (FAIR). Psilocybin dose-dependently reduced PPI at short (30 ms), had no effect at medium (60 ms), and increased PPI at long (120–2000 ms) ISIs, without affecting startle reactivity or habituation. Psilocybin dose-dependently impaired sustained attention and increased all 5D-ASC scores with exception of Auditory Alterations. Moreover, psilocybin-induced impairments in sustained attention performance were positively correlated with reduced PPI at the 30 ms ISI and not with the concomitant increases in PPI observed at long ISIs. These results confirm the psilocybin-induced increase in PPI at long ISIs and reveal that psilocybin also produces a decrease in PPI at short ISIs that is correlated with impaired attention and consistent with deficient PPI in schizophrenia.

Vollenweider, F. X, Csomor, P. A., Knappe, B., Geyer, M. A., & Quednow, B. B. (2007). The effects of the preferential 5-HT2A agonist psilocybin on prepulse inhibition of startle in healthy human volunteers depend on interstimulus interval. Neuropsychopharmacology, 32(9), 1876-1887. http://dx.doi.org/10.1038/sj.npp.1301324
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