Intracerebellar Microinjection of an H4 Agonist Impairs Memory Consolidation in Open Field and Rotarod Tasks in Mice

Abstract

The cerebellum is known to participate in motor functions, but the role of the histaminergic system, and specifically the H4 receptors, in its functions is still unclear. In the present study, we investigated the effects of intravermis microinjections of an H4 receptor agonist (VUF-8430) on mice behavior undergoing a rotarod (Experiment 1) and open field (Experiment 2) test. The cerebellar vermis of male mice was implanted with a single guide cannula. All experiments were performed on two consecutive days: exposure (R1-first day in the rotarod test or OF1-first day in the open field test), followed by re-exposure (R2-second day in the rotarod test or OF2-second day in the open field test) 24 h later. The animals received saline (SAL) or VUF (0.15 nmol; 0.49 nmol; 1.48 nmol/0.1 μl) administered intravermis immediately after R1 or OF1. The data were analyzed using one-way ANOVA and Duncan's post hoc test. In Experiment 1, the drug led to a decrease of consolidation latency for the VUF 0.49 and VUF 1.48 groups compared to the control SAL group in R2. In Experiment 2, the VUF 1.48 group had a significant increase in freezing time in the open field in OF2 compared to OF1. These results suggests that the H4 agonist VUF 8430 at its highest dose (1.48 nmol) impairs memory consolidation in open field and rotarod tasks in mice (Graphical abstract).