Haloperidol-Induced Catalepsy and Its Correlations with Acetylcholinesterase Activity in Different Brain Structures...

Antipsychotic medicines are used to treat several psychological disorders and some symptoms caused by dementia and schizophrenia. Haloperidol (Hal) is a typical antipsychotic usually used to treat psychosis; however, its use causes motor or extrapyramidal symptoms (EPS) such as catalepsy. Hal blocks the function of presynaptic D2 receptors on cholinergic interneurons, leading to the release of acetylcholine (ACh), which is hydrolyzed by the enzyme acetylcholinesterase (AChE).

This study was designed to investigate the Hal-inhibitory effects on AChE activity in regions representative of the cholinergic system of mice and potential associations between cataleptic effects generated by Hal using therapeutic doses and their inhibitory effects on AChE.

The distribution of the AChE activity in the different regions of the brain followed the order striatum > hippocampus > (prefrontal cortex/hypothalamus/ cerebellum) > brainstem > septo-hippocampal system. In ex vivo assays, Hal inhibited AChE activity obtained from homogenate tissue of the striatum, hippocampus, and septo-hippocampal system in a concentration-dependent manner. The inhibitory concentration of 50% of enzyme activity (IC₅₀) indicated that the septo-hippocampal system required a higher concentration of Hal (IC₅₀ = 202.5 µmol·L^-1) to inhibit AChE activity compared to the striatum (IC₅₀ = 162.5 µmol·L^-1) and hippocampus (IC₅₀ = 145 µmol·L^-1). In in vivo assays, male Swiss mice treated with concentrations of Hal higher than 0.1 mg·kg^-1 induced cataleptic effects. Positive correlations with Spearman's correlation were observed only between the lack of cataleptic effect and the decreased AChE activity of the hippocampus in the mice treated with 0.01 mg·kg^-1 of Hal but not in the striatum and septo-hippocampal system.

Our results suggest that Hal could increase cholinergic effects via AChE inhibition, in addition to its dopamine antagonist effect, as an alternative approach to the treatment of behavioral disturbances associated with dementia.