The effect of long-term lithium treatment on the incorporation and distribution of 32P-orthosphosphate into the phospholipids from rat synaptosomes.

Rats were treated with lithium added to their diet for five weeks (40 mmol LiCl/kg diet). Mean plasma concentration was 0.45 mmol Li+/plasma. The investigation was divided into two sections. I) In an in vivo experiment in which the rats were injected with 32P-orthosphosphate for 20 hours, and with carbamoylcholine for 20 min. prior to their death, the distribution of 32P in the synaptosomal phospholipids, phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and phosphatidylcholine (PC), was investigated. II) An in vitro experiment which was carried out in order to establish the effect of carbamoylcholine on the incorporation of 32P into total phospholipids from extracted synaptosomes. In I) the incorporation of 32P-orthosphosphate into PI from carbamoylcholine-stimulated rats was significantly lower than from unstimulated rats, whereas there was no difference between the incorporation of 32P into PI from synaptosomes from control animals and lithium-treated animals. In II) the incorporation of 32P-orthosphosphate was significantly lower in unstimulated synaptosomes from lithium-treated rats than from control rats, while the increase in the 32P-incorporation after stimulation followed the same pattern with regard to synaptosomes from control rats and lithium-treated rats. The results support the idea of lithium exerting an effect on basal synaptosomal activity but not on stimulated synaptosomal activity.