Behavioral effects of xylamine-induced depletions of brain norepinephrine: interaction with LSD

Psychedelics: preclinical insights provide directions for future research

Recently, psychedelics have emerged as promising therapeutics for numerous neuropsychiatric disorders. While their potential in the clinic has yet to be fully elucidated, understanding their molecular and biological mechanisms is imperative as these compounds are becoming widely used both in therapeutic and recreational contexts. This review examines the current understanding of basic biology, pharmacology, and structural biology in an attempt to reveal both the knowns and unknowns within the field.

Lysergic Acid Diethylamide (LSD) for the Treatment of Anxiety Disorders: Preclinical and Clinical Evidence

Anxiety disorders (ADs) represent the sixth leading cause of disability worldwide, resulting in a significant global economic burden. Over 50% of individuals with ADs do not respond to standard therapies, making the identification of more effective anxiolytic drugs an ongoing research priority. In this work, we review the preclinical literature concerning the effects of lysergic acid diethylamide (LSD) on anxiety-like behaviors in preclinical models, and the clinical literature on anxiolytic effects of LSD in healthy volunteers and patients with ADs. Preclinical and clinical findings show that even if LSD may exacerbate anxiety acutely (both in "microdoses" and "full doses"), it induces long-lasting anxiolytic effects. Only two randomized controlled trials combining LSD and psychotherapy have been performed in patients with ADs with and without life-threatening conditions, showing a good safety profile and persisting decreases in anxiety outcomes. The effect of LSD on anxiety may be mediated by serotonin receptors (5-HT1A/1B, 5-HT2A/2C, and 5-HT7) and/or transporter in brain networks and circuits (default mode network, cortico-striato-thalamo-cortical circuit, and prefrontal cortex-amygdala circuit), involved in the modulation of anxiety. It remains unclear whether LSD can be an efficacious treatment alone or only when combined with psychotherapy, and if "microdosing" may elicit the same sustained anxiolytic effects as the "full doses". Further randomized controlled trials with larger sample size cohorts of patients with ADs are required to clearly define the effective regimens, safety profile, efficacy, and feasibility of LSD for the treatment of ADs.

Recent advances in the neuropsychopharmacology of serotonergic hallucinogens

Serotonergic hallucinogens, such as (+)-lysergic acid diethylamide, psilocybin, and mescaline, are somewhat enigmatic substances. Although these drugs are derived from multiple chemical families, they all produce remarkably similar effects in animals and humans, and they show cross-tolerance. This article reviews the evidence demonstrating the serotonin 5-HT2A receptor is the primary site of hallucinogen action. The 5-HT2A receptor is responsible for mediating the effects of hallucinogens in human subjects, as well as in animal behavioral paradigms such as drug discrimination, head twitch response, prepulse inhibition of startle, exploratory behavior, and interval timing. Many recent clinical trials have yielded important new findings regarding the psychopharmacology of these substances. Furthermore, the use of modern imaging and electrophysiological techniques is beginning to help unravel how hallucinogens work in the brain. Evidence is also emerging that hallucinogens may possess therapeutic efficacy.

Dissociation of multiple effects of acute LSD on exploratory behavior in rats by ritanserin and propranolol

Rats tested for 1 h in the Behavioral Pattern Monitor (BPM) after injection of the mixed serotonergic agonist d-lysergic acid diethylamide (LSD) exhibit a behavioral profile similar to that produced by various hallucinogenic 5HT-2 agonists. The characteristic effects of the hallucinogens include suppression of locomotor and exploratory behavior and a preferential decrease in entries into the center of the BPM during the initial half of the test session. After LSD, the initial suppression of responding is followed by a subsequent increase in locomotor activity that is not observed with other serotonergic agonists. In the present studies, the 5HT-1 and beta-adrenergic antagonist d,l-propranolol and the 5HT-2 antagonist ritanserin were administered individually or in combination prior to the acute administration of LSD to test for the involvement of these receptor subtypes in the mediation of the effects of LSD in the BPM paradigm. Propranolol (20 mg/kg) abolished the initial suppression of activity induced by 60 micrograms/kg LSD without affecting the subsequent increase in locomotion. Conversely, 2.0 mg/kg ritanserin failed to block the initial suppressive effects of 60 or 120 micrograms/kg LSD, but attenuated the LSD-induced increases in activity during the second half of the session. The combination of propranolol and ritanserin prevented both these effects of LSD. By contrast, the more selective 5HT-2 agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) (0.27 mg/kg) produced an initial suppression of activity in the BPM that was blocked by 2.0 mg/kg ritanserin and was not followed by a subsequent increase in activity. (ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral effects of xylamine-induced depletions of brain norepinephrine: interaction with amphetamine

Male rats were treated with a combination of systemic fluoxetine and intraventricular xylamine in order to deplete brain norepinephrine (NE) in the projection areas of the locus coeruleus. Liquid chromatographic measures confirmed that xylamine reduced hippocampal NE by 77%. Four days later, control and lesioned rats were tested following subcutaneous injections of either saline or 1.0 mg/kg amphetamine in a Behavioral Pattern Monitor which recorded the sequential patterns of their locomotor and investigatory (holepokes) responses. Relative to controls, NE-depleted rats exhibited no alteration in the amount of spontaneous locomotor activity or its rate of habituation, but made fewer rearings and holepokes, particularly early in the hour test session. When challenged with 1.0 mg/kg amphetamine, sham-lesioned rats exhibited the expected increases in locomotor activity, holepokes, rearings, and both entries into and time spent in the center of the chamber. The lesioned animals exhibited a potentiation of the amphetamine effect on center activity and a diminished effect of amphetamine on holepoking and rearings. Control and lesioned rats were again tested at 18 days postlesion using the same test paradigm. The previously noted effects of the lesions on spontaneous behavior were absent at 18 days. Furthermore, the ability of these NE depletions to alter the behavioral effects of 1.0 mg/kg amphetamine at 4 days postlesion largely disappeared by 18 days. These results are indicative of some compensatory mechanism(s) operating to restore normal function between 4 and 18 days after the introduction of the lesion.