Effect of adult onset hypothyroidism on behavioral parameters and acetylcholinesterase isoforms activity in specific brain regions of male mice

•Adult male mice were rendered hypothyroid through 1% w/v KClO4 administration•Passive avoidance task supported learning and memory deficits in hypothyroid mice•EPM and OF tests indicated anxiety-like behavior and reduced locomotor activity•Hypothyroidism caused brain region-specific inhibition of AChE fractions activity

Thyroid hormones (TH) are essential for normal development and function of mammalian central nervous system (CNS); TH dysregulation has been implicated in several cognitive and behavioral deficits related to dysfunctions of neurotransmitter systems. In the present study, we investigated the effects of adult onset hypothyroidism on the activity of acetylcholinesterase (AChE) and on related behavioral parameters. For this purpose we used adult male Balb/cJ mice that were divided randomly into euthyroid and hypothyroid animal groups. Animals were rendered hypothyroid through administration of 1% w/v KClO4 in their drinking water for 8 weeks. At the end of the treatment, learning/memory procedures were examined through step-through passive avoidance task while fear/anxiety was assessed using elevated plus-maze (EPM) and open-field (OF) tests. AChE activity was determined colorimetrically in two different fractions, salt-soluble fraction (SS) (containing mainly the G1 isoform) and detergent-soluble fraction (DS) (containing mainly the G4 isoform) in cerebral cortex, cerebellum, midbrain, hippocampus and striatum. Our results indicate that adult onset hypothyroidism caused significant memory impairment and increased fear/anxiety. Moreover, the activity of both isoforms of AChE was reduced in all brain regions examined in a brain region- and isoform-specific manner.