Comparison of Negative Effects of R- and S-ketamine in Wistar Rats

Abstract

Ketamine induces several similar symptoms observed in schizophrenia in humans and is therefore used to establish a pharmacological model of schizophrenia in rodents [1]. There are two enantiomers of ketamine, R- and S‐ketamine, which differ in pharmacological properties and effects on psychiatric symptoms and brain metabolism in healthy participants [2]. S- ketamine has 4x higher binding affinity for NMDAR than R‐ketamine [2]. A common finding in preclinical studies is that R- ketamine causes fewer side effects than S- ketamine, suggesting that the side effects of (R,S)‐ketamine are due to the action of S‐ketamine rather than R-ketamine [3]. With our study, we aim to determine whether intermittent use of ketamine, as commonly used for medical purposes and recreational drug abuse, causes neurotoxic effects in animals similar to those characteristics of the ketamine model of schizophrenia. By analysing changes in the expression of the GAD67 enzyme, we will observe the changes in the GABAergic system and the association with the glutamatergic hypothesis of schizophrenia. Also, by analysing alterations in dopamine D1 receptor, we aim to detect changes in the cortical dopaminergic system.

Methods

The study will be performed on adult male Wistar rats. 18 animals will be divided into three groups, the first will receive R�ketamine, the second S-ketamine and the third will be a control group receiving

saline. We will use a sub-acute, intermittent ketamine dosing pattern, which consists of seven ketamine doses, applied every third day. A single dose of ketamine hydrochloride will be 15 mg/kg body weight.

After the ketamine treatment we will analyse changes in the dopaminergic and GABAergic systems in the isolated brains. We will perform western blot analysis for two biomarkers, D1 and GAD67; this procedure is used to study the expression levels of proteins of different sizes in individual brain regions. We will also perform immunohistochemical staining for GAD67 and D1 on brain tissue samples; a procedure, where antibody binding determines the tissue distribution of the antigen of interest.

Expected results

We expect to observe differences in expression of GAD67 and D1 between ketamine-treated groups and control and differences between S- and R-ketamine groups.

References

[1] J. Frohlich and JD. Van Horn, “Reviewing the ketamine model for schizophrenia,” J Psychopharmacol, vol. 28, no. 4, pp. 287– 302, 2014.

[2] I. Oye, O. Paulsen and A. Maurset, “Effects of ketamine on sensory perception: evidence for a role of N-methyl-D-aspartate receptors,” J Pharmacol Exp Ther, vol. 260, no. 3, pp. 1209–1213, 1992.

[3] P. Zanos, R. Moaddel, PJ. Morris, IM. Riggs, JN. Highland, P. Georgiou, ... and TD. Gould, “Ketamine and ketamine metabolite pharmacology: insights into therapeutic mechanisms,” Pharmacol. Rev, vol. 70, no. 3, pp. 621–660, 2018.