Repeated lysergic acid diethylamide (LSD) reverses stress-induced anxiety-like behaviour, cortical synaptogenesis deficits and serotonergic neurotransmission decline

This rodent study (2022) assessed the effects of LSD administration on anxiety-like behaviour, on the cortical dendritic spines and on the activity of serotonin neurons in mice exposed to chronic restraint stress. LSD dose of 30 µg/kg (daily for 7 days) prevented the stress-induced anxiety-like behaviour and the stress-induced decrease of cortical spine density. LSD acutely decreased the firing activity of serotonin neurons, yet repeated LSD increased their basal firing rate and restored the low serotonin firing induced by stress. Overall, repeated LSD prevents the exacerbation of anxiety-like behaviour following chronic stress exposure, but has no behavioural effects in non-stressed mice.

Abstract

“Lysergic acid diethylamide (LSD) is a serotonergic psychedelic compound receiving increasing interest due to putative anxiolytic and antidepressant properties. However, the potential neurobiological mechanisms mediating these effects remain elusive. Employing in vivo electrophysiology, microionthophoresis, behavioural paradigms and morphology assays, we assessed the impact of acute and chronic LSD administration on anxiety-like behaviour, on the cortical dendritic spines and on the activity of serotonin (5-HT) neurons originating in the dorsal raphe nucleus (DRN) in male mice exposed to chronic restraint stress. We found that while the acute intraperitoneal (i.p.) administration of LSD (5, 15 and 30 and 60 μg/kg) did not produce any anxiolytic or antidepressant effects in non-stressed mice, the dose of 30 µg/kg (daily for 7 days) prevented the stress-induced anxiety-like behaviour and the stress-induced decrease of cortical spine density. Interestingly, while LSD acutely decreased the firing activity of 5-HT neurons, repeated LSD increased their basal firing rate and restored the low 5-HT firing induced by stress. This effect was accompanied by a decreased inhibitory response of 5-HT neurons to microiontophoretic applications of the 5-HT_1A agonist 8-OH-DPAT (8-hydroxy-N,N-dipropyl-2-aminotetralin). In conclusion, repeated LSD prevents the exacerbation of anxiety-like behaviour following chronic stress exposure, but has no behavioural effects in non-stressed mice. These effects are paralleled by increased cortical spinogenesis and an enhancement of 5-HT neurotransmission which might be due to 5-HT_1A receptors desensitization. Increased cortical spine density and enhancement of serotonergic neurotransmission may thus represent a candidate mechanism which mediates the therapeutic effects of serotonergic psychedelics on stress-induced anxiety.”

Authors: Daniel De Gregorio, Antonio Inserra, Justine P. Enns, Athanasios Markopoulos, Michael Pileggi, Youssef El Rahimy, Martha Lopez-Canul, Stefano Comai & Gabriella Gobbi

Summary

INTRODUCTION

Psychedelic compounds have come to the forefront as potential therapeutics in psychiatry, but the mechanisms mediating their therapeutic effects remain elusive. In our previous study, we observed that LSD decreases the firing activity of serotonergic (5-HT) neurons in the DRN and dopaminergic neurons in the ventral tegmental area.

LSD at low doses enhances sociability and the social novelty preference by potentiating the 5-HT2A and AMPA responses in glutamatergic neurons and activating the mTORC1 complex in excitatory neurons of the medial prefrontal cortex.

LSD is a serotonergic agent with anxiolytic properties, and it may affect the neurobiology of stress-induced anxiety and depression. However, the effects of repeated LSD on 5-HT neurotransmission in baseline conditions or under a chronically stressful condition remains unknown.

Here, we tested if repeated administration of LSD could prevent the development of anxiety-like behavior and stress-induced cortical spinogenesis and 5-HT neurotransmission decline.

Effects of acute LSD treatment on the head twitch response in non-stressed animals

Mice treated with LSD showed increased head twitches after injection of 30, 40 and 60 g/kg, compared to vehicle or lower LSD doses.

Effects of acute LSD treatment on anxiety- and depressive-like behavior in non-stressed animals

We performed a battery of behavioral tests to investigate the ability of different doses of LSD to modulate anxiety-like and depression-like behaviors. The time spent in the light compartment was the same for all animals after the EPM. Mice were placed in a novel arena to undergo the novelty suppressed feeding test, and the open field test and forced swim test were performed. A main effect of treatment was observed over the total distance traveled and the number of entries into the center of the arena. No significant differences were found between the experimental groups. We found that the 60 g/kg dose of LSD produced a significant increase in grooming duration and rearing episodes, but the 30 g/kg dose did not. Furthermore, there were no differences found regarding the immobility time in relation to the dose of LSD.

Repeated LSD administration prevents chronic-stress induced anxiety-like behavior

We tested the ability of LSD to prevent the development of anxiety-like behavior following chronic restraint stress. Stressed mice showed no differences in locomotion compared to controls, and repeated LSD had no effect on the distance traveled at the tested doses. CS mice treated with LSD at the dose of 30 g/kg/day for 7 days had a statistically higher number of entries in the center of the arena compared to CS mice treated with veh, indicating an anxiolytic-like effect of the 7-day repeated LSD regimen.

Repeated LSD administration prevents chronic stress-induced anxiety-like behavior in the light-dark box test and in the novelty suppressed feeding test, but not in the elevated plus maze test

To further assess the protective effects of LSD over stress-induced anxiety-like behavior, mice were exposed to CS and tested in the EPMT, LDBT and NSFT. In the LDB test, CS mice spent less time in the open arms, spent more time in the closed arms, and entered less the open arms than veh mice. The repeated LSD treatment failed to alter any of these parameters.

The LSD treatment did not affect the time spent in the light compartment of the LDBT, but stress did, and the interaction of the two did as well. The same cohort of mice was tested in the novel arena and the homecage. The repeated LSD at the dose of 30 g/kg prevented the exacerbation of stress-induced anxiety-like behavior.

Chronic restraint stress does not exacerbate depressive- and anhedonic-like behavior

We assessed whether the CS paradigm produced depressive- and/or anhedonic-like behavior in mice using the sucrose preference test and the forced swim test. We found no differences in immobility time or sucrose preference due to stress or repeated LSD.

Repeated LSD administration prevents the chronic stress-induced reduction of cortical spine density. This effect was observed in the mPFC where repeated LSD administration increased the number of dendritic spines while also preventing the stress-induced reduction in the number of apical dendritic spines.

Acute LSD decreases 5-HT DRN firing activity in anesthetized mice, similar to the response previously observed in non-stressed rats. Repeated LSD prevents the development of stress-induced anxiety-like phenotype and the decrease in cortical spinogenesis. LSD completely shut down DRN 5-HT activity at the dose of 30 g/kg, and repeated administration of this dose for 7 days prevented the development of stress-induced anxiety-like behavior. LSD significantly increased the number of spontaneous cell firing events in DRN5-HT neurons and the coefficient of variation percentage, suggesting that LSD triggered a more irregular firing activity than veh.

The mean 5-HT neural activity of mice treated with LSD was skewed compared to mice treated with veh.

To determine whether the increased DRN 5-HT firing after repeated LSD administration was due to altered 5-HT1A autoreceptor sensitivity, we performed in vivo electrophysiological recordings with multi-barreled electrodes for microionthophoretic ejections. LSD treatment reduced the inhibitory response to the 5-HT1A agonist. To confirm that the 8-OH-DPAT does not affect the 5-HT7 receptor, we administered the 5-HT7 receptor antagonist SB269970 10 min prior to the acute cumulative injections of 8-OH-DPAT. This did not affect the inhibitory effect of cumulative injection of 8-OH-DPAT in 7-day vehicle-treated animals.

Repeated LSD administration prevents the stress-induced decline of 5-HT DRN neurons firing

Chronic unpredictable stress decreases 5-HT neuronal activity in the DRN, and a repeated LSD regimen prevents this decline. Moreover, a 7-day repeated LSD regimen increases 5-HT neuronal activity in stressed mice, compared to stressed mice treated with veh.

DISCUSSION

Psychedelic compounds have come to the forefront as potential novel therapeutics in psychiatry. Repeated administration of LSD during stress exposure prevented the development of anxiety-like behavior and increased spine density in naive animals, suggesting an anxiolytic-like effect of repeated LSD under anxiogenic conditions.

Studies on patients experiencing anxiety and distress associated with a terminal disease reported rapid and sustained improvements in anxiety scores. Preclinical evidence concerning the anxiolytic- and antidepressants-like effects of LSD remains controversial. However, repeated administration of LSD (0.13 mg/kg daily for 11 days) reversed the stress-induced deficits in active avoidance learning and normalized 5-HT2A receptor-mediated hippocampal 5-HT signaling in a model of depression. In the present study, LSD did not elicit anxiolytic- and/or antidepressant-like effects in naive mice. However, it did prevent the exacerbation of stress-induced anxiety-like behavior in a 15 day-chronic restraint stress paradigm.

Antidepressants and psychedelic compounds induce neurogenesis and synaptogenesis, which attenuate the negative effects of stress and depression on hippocampal and prefrontal cortex plasticity.

DMT increased memory in mice, but repeated LSD administration decreased cortical dendritic spines density in females, but not male rats. LSD also increased synaptic plasticity in brain organoids and increased expression of proteins involved in synaptogenesis and plasticity.

LSD increases the density of apical dendritic spines in the mPFC and potentiates the 5-HT neurotransmission, and can prevent the decrease of 5-HT firing activity after a 15 day restraint stress protocol.

The behavioral outcomes of this study should be interpreted in light of their limitations, as the chronic stress paradigm used in this study did not induce depressive-like behavior. However, the results may be related to the direct effects of LSD on memory. In this study, LSD prevented the development of anxiety-like phenotype and 5-HT decline following the stress procedure. However, the effect of LSD on sex remains unclear.

Repeated administration of low doses of LSD prevents the exacerbation of stress-induced anxiety-like behavior without affecting depressive-like behavior or other behavioral measures. Moreover, repeated LSD administration increases dendritic spine density in mPFC pyramidal neurons and prevents the stress-induced decrease in cortical dendritic spines density.