LAUSR

Abstract Background A combination of ketamine‐xylazine (K‐X) is frequently used for anaesthesia in rats. Sex and age affect this cocktail dosage. Ketamine causes a hypnotic effect by blocking NMDA receptors located on the dendritic spine of the CA1 region. Objectives The present study aimed to find the optimal dosage of K‐X and its association with the changes in dendritic spine number of the CA1 region for aged and young rats of both sexes. Methods We injected 150–4 mg/kg of K‐X in young and 100–2 mg/kg in aged Wistar rats intraperitoneally and recorded the onset time and duration of anaesthesia and death percentage. Then, animals were sacrificed, brains removed, cut and after Golgi‐Cox staining, the total number of dendritic spines on CA1 was estimated. Results The findings showed that the onset time of anaesthesia lasted longer and its duration lasted shorter, and the number of mature spines decreased with aging, but sex caused no significant effect. The death percentages in young groups comprise 20% and in the aged groups were lower: 5% in males and 0.0% in females. Conclusions It seems 100–2 mg/kg of K‐X is an optimal dose in aged rats and retains an association with reduction of the mature dendritic spine of CA1.