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Objectives: Chronic and heavy ketamine use has been associated with persistent neurocognitive impairment and structural brain abnormalities. Blood levels of neurofilament light chain (NFL) was recently proposed as a measure of axonal integrity in several neuropsychiatric disorders. We aimed to characterise the axonal neurotoxicity of chronic ketamine use and its relationship to relevant clinical outcomes. Methods: We enrolled 65 treatment-seeking ketamine-dependent patients (55 males and 10 females) and 60 healthy controls (51 males and 9 females). Blood NFL levels measured by single molecule array (SiMoA) immunoassay. We compared NFL levels between groups and used regression analyses to identify clinical variables related to NFL levels. Results: Ketamine-dependent patients had significantly higher NFL levels compared to controls (p < 0.001). A multivariate regression showed that age (p < 0.05) and lifetime history of major depressive disorder (MDD) (p < 0.01) predicted high NFL blood levels in patients. Subsequent group comparisons showed that specifically ketamine-dependent patients with a lifetime history of MDD had significantly increased NFL levels than those without (p < 0.05). Conclusions: These results suggest substantial neuroaxonal alterations following chronic and heavy ketamine use. The pronounced increase of NFL levels in the MDD subgroup warrants further investigation of a potential neuroaxonal vulnerability of depressed patients to ketamine.

Objectives: To explore the hypothesis that plasma levels of neurofilament light chain (NfL), a marker of neuroaxonal pathology, are elevated in chronic cocaine users (CU) and longitudinally associated with changes in cocaine use. Methods: As part of the Social Stress Cocaine Study (SSCP), we assessed 35 CU and 35 stimulant-naive healthy controls (HC) at baseline and at a 4-month follow-up. Plasma NfL levels were determined from blood samples using single molecule array (SIMOA) technology. Substance use was subjectively assessed with an extensive interview and objectively measured via toxicological analysis of urine and 4-month hair samples. Results: In a generalized linear model corrected for sex, age, and body mass index, NfL plasma levels were elevated in CU compared to HC (p<0.05). A moderate positive correlation between cocaine hair concentration and NfL levels was also found in CU (r(s)=0.36, p=0.03). Changes in cocaine hair concentration (group analysis of increasers vs. decreasers) over the 4-month interval predicted NfL levels at follow-up (p=0.002), indicating a rise in NfL with increased cocaine use and a reduction with decreased use. No associations between use or change of use of other substances (including the cocaine adulterant levamisole) and NfL levels were found (r(s)<0.28, p>0.05). Conclusions: Our findings demonstrate that NfL is a sensitive marker for assessing cocaine-related brain pathology, supporting the utility of blood NfL analysis in addiction research. The results also suggest that cocaine use should be considered a potential confounder in diagnostic applications and clinical studies using NfL.

Abstract3,4-Methylenedioxymethamphetamine (MDMA, “Ecstasy”) use has been linked to persistent alterations of the brain serotonergic (5-HT) system in animal and human studies, but the molecular underpinnings are still unclear. Cytoskeletal structures such as neurofilament light chain (NfL) are promising markers of drug-induced brain toxicity and may be involved in MDMA neurotoxicity. The brain-derived neurotrophic factor (BDNF) promotes the growth and sprouting of 5-HT neurons and its differential response to MDMA administration was suggested to mediate dose- and region-dependent 5-HT damage by MDMA. However, the role of BDNF pre-treatment in preventing MDMA neurotoxicity and the potential effects of MDMA on NfL are still elusive. Therefore, a differentiated 5-HT neuronal cell line obtained from rat raphe nucleus (RN46A) was treated in vitro with either MDMA, BDNF, MDMA + BDNF, or vehicle. Cell viability (measured by MTT) and intracellular NfL levels (immunocytochemistry assay) were reduced by MDMA, but partially rescued by BDNF co-treatment. Our findings confirmed that BDNF levels can influence MDMA-induced 5-HT damage, and support BDNF to be a crucial target for neuroprotective interventions of the 5-HT system. We also provide evidence on the sensitivity of NfL to MDMA neurotoxicity, with potential implications for in-vivo monitoring of drug-induced neurotoxicity.

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Sodium oxybate (γ-hydroxybutyrate, GHB) is an endogenous GHB/GABAB receptor agonist, clinically used to promote slow-wave sleep and reduce next-day sleepiness in disorders such as narcolepsy and fibromyalgia. The neurobiological signature of these unique therapeutic effects remains elusive. Promising current neuropsychopharmacological approaches to understand the neural underpinnings of specific drug effects address cerebral resting-state functional connectivity (rsFC) patterns and neurometabolic alterations. Hence, we performed a placebo-controlled, double-blind, randomized, cross-over pharmacological magnetic resonance imaging study with a nocturnal administration of GHB, combined with magnetic resonance spectroscopy of GABA and glutamate in the anterior cingulate cortex (ACC). In sum, 16 healthy male volunteers received 50 mg/kg GHB p.o. or placebo at 02:30 a.m. to maximize deep sleep enhancement and multi-modal brain imaging was performed at 09:00 a.m. of the following morning. Independent component analysis of whole-brain rsFC revealed a significant increase of rsFC between the salience network (SN) and the right central executive network (rCEN) after GHB intake compared with placebo. This SN-rCEN coupling was significantly associated with changes in GABA levels in the ACC (pall &lt; 0.05). The observed neural pattern is compatible with a functional switch to a more extrinsic brain state, which may serve as a neurobiological signature of the wake-promoting effects of GHB.

Delta (1 – 4 Hz) EEG/MEG activity is generally indicative of loss of consciousness and cortical down states, particularly when it is diffuse and high amplitude. Remarkably, however, drug challenge studies of several diverse classes of pharmacological agents—including antiepileptics, GABA-B-ergics, anticholinergics, and psychedelic tryptamines—demonstrate that participants appear to be neurophysiologically “down” (EEG activity resembling cortical down states) even when they are not psychologically “out” (unconscious). Of those substances that are safe to use in healthy volunteers, some may be highly valuable research tools for investigating which neural activity patterns are sufficient for consciousness or its absence.