Piazza, Giulia G; Iskandar, Georges; Hennessy, Vanessa; Zhao, Hannah; Walsh, Katie; McDonnell, Jeffrey; Terhune, Devin B; ... Kamboj, Sunjeev K; + view all Piazza, Giulia G; Iskandar, Georges; Hennessy, Vanessa; Zhao, Hannah; Walsh, Katie; McDonnell, Jeffrey; Terhune, Devin B; Das, Ravi K; Kamboj, Sunjeev K; - view fewer (2022) Pharmacological modelling of dissociation and psychosis: an evaluation of the Clinician Administered Dissociative States Scale and Psychotomimetic States Inventory during nitrous oxide ('laughing gas')-induced anomalous states. Psychopharmacology 10.1007/s00213-022-06121-9. (In press).

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Abstract

RATIONALE: A significant obstacle to an improved understanding of pathological dissociative and psychosis-like states is the lack of readily implemented pharmacological models of these experiences. Ketamine has dissociative and psychotomimetic effects but can be difficult to use outside of medical and clinical-research facilities. Alternatively, nitrous oxide (N2O) - like ketamine, a dissociative anaesthetic and NMDAR antagonist - has numerous properties that make it an attractive alternative for modelling dissociation and psychosis. However, development and testing of such pharmacological models relies on well-characterized measurement instruments. OBJECTIVES: To examine the factor structures of the Clinician Administered Dissociative States Scale (CADSS) and Psychotomimetic States Inventory (PSI) administered during N2O inhalation in healthy volunteers. METHODS: Secondary analyses of data pooled from three previous N2O studies with healthy volunteers. RESULTS: Effect sizes for N2O-induced dissociation and psychotomimesis were comparable to effects reported in experimental studies with sub-anaesthetic ketamine in healthy volunteers. Although, like ketamine, a three-factor representation of N2O-induced dissociation was confirmed, and a more parsimonious two-factor model might be more appropriate. Bayesian exploratory factor analysis suggested that N2O-induced psychosis-like symptoms were adequately represented by two negative and two positive symptom factors. Hierarchical cluster analysis indicated minimal item overlap between the CADSS and PSI. CONCLUSION: N2O and ketamine produce psychometrically similar dissociative states, although parallels in their psychosis-like effects remain to be determined. The CADSS and PSI tap largely non-overlapping experiences under N2O and we propose the use of both measures (or similar instruments) to comprehensively assess anomalous subjective states produced by dissociative NMDAR antagonists.

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