Abstract: This study was conducted to examine if intraperitoneal lithium at high dose, sufficient to induce conditioned taste aversion learning, increases expression of Hippocampal Cholinergic Neurostimulating Peptide (HCNP) and choline acetyltransferase (ChAT) in the brain septo-hippocampal system. Quantitative real-time RT-PCR analysis demonstrated that an intraperitoneal injection of lithium chloride (0.15 M, 12 mL kg-1) acutely increases HCNP mRNA levels in the hippocampus. ChAT immunoreactivities in the medial septal nucleus and the hippocampus, which were determined by immunohistochemistry and western blot analysis, also increased with intraperitoneal lithium. These results suggest that intraperitoneal lithium may acutely activate the septo-hippocampal cholinergic system, via increasing expression of HCNP and ChAT. Additionally, we suggest that activation of the septo-hippocampal cholinergic system with increased HCNP expression may be a part of lithium`s action as unconditioned stimulus in conditioned taste aversion learning.