The effect of iron ion injection on acetylcholine (ACh) turnover was studied in the cerebral cortex of male Sprague-Dawley rats. Rats were divided into 3 groups: rats of the Fe-group were injected with 500 nmol of Fe(3+) in the left sensorimotor cortex, rats of the HCl-group were injected with HCl-acidified saline (pH 1.8) in the left sensorimotor cortex, and a shamoperated group acted as a control (Sham-group).
On both sides of the cortex, the choline acetyltransferase (CAT) activity of the HCI- and Fe-groups decreased 30 min after, increased 6h after, and then decreased 24h after the injection compared with the activity of the Sham-group. A no time was there any difference between the CAT activities of the HCl- and Fe-groups. On both sides of the cortex, the ACh content of the HCl- and Fe-groups decreased transiently 24h after injection, but there was no difference in ACh content between the two groups. In the left cortex of the Fe- and HCl-groups, acetylcholinesterase (AChE) activity, which showed no difference between the two groups, decreased 30 min after injection.
These findings suggested that cortical neurons especially AChergic neurons might be irritated by a transient increase in intracranial pressure due to brain edema induced by the injection of acid into the cortex, as no specific effct of Fe(3+)-injection was observed in this study.