Acta pharmacol. et toxicol. zyxwvutsrq 1985, 56, 193-198. From the *Department of Pharmacology, University of Uppsala, S-75124 Uppsala, and **Karolinska Institute, Department of Clinical Pharmacology, Huddinge Hospital, S-14186 Huddinge, Sweden zyx Modulation of Choline Transport and Acetylcholine Synthesis in Synaptosomes from Different Brain Regions BY Agneta Nordberg* and Anders Sundwall** (Received November zyxwvuts 5, 1984; Accepted November 20, 1984) Abstract: Uptake and biotransformation of radioactive choline (3H-Ch) have been studied in P2 fractions from different brain regions of mice treated with different doses of sodium pentobarbital (45-120 mg/kg intraperitoneally) or saline. Sodium dependent uptake (SDU) has been measured as the difference between results of incubations with Naf in the incubation medium and when the sodium salts were replaced by Tris- phosphate and sucrose. The uptake of radioactivity increased during the incubation with 3H-Ch but the proportion of 3H-ACh was the same at all time points. The proportion of 3H-ACb to 3H-Ch in the P2 pellet was 86, 81 and 69 per cent in hippocampus, striaturn and cortex, respectively. Omission of sodium ions in the incubation medium reduced uptake of 3H-Ch by about 90 per cent at zyxw 1 zyxwv pM Ch in the incubation medium and the proportion of 3H-ACh to 3H-Ch was only 10 to 20 per cent while the proportion of 3H-PhCh increased from insignificant amounts to between 20 to 30 per cent. There were quantitative regional differences in SDU, a two times greater uptake was obtained in the striaturn compared with cortex and hippocampus. Apparent K, and V,,, were 0.9 x M and 71 pmol/mg, respectively, for the cortex of untreated animals. The contribution of endogenous Ch from the P2 fraction to the incubation medium gave a final concentration of 0.5 pM Ch in the standard uptake experiments. The 3H-Ch uptake was significantly reduced in P2 fraction from cortex and hippocampus prepared from mice anaesthetized with sodium pentobarbital while the uptake in P2 fractions from the striatum was unaffected. Sodium pentobarbital treatment did not affect the pro- portion of 3H-ACh in the pellets. Keywords: Choline uptake - acetylcholine biosynthesis - brain regions - pentobarbital - physostigmine - mice. There is evidence that choline important for the regulation (Ch) transport is of acetylcholine (ACh) metabolism in the brain (Sparf 1973; Jope 1979). In addition to diffusion there appear to be two saturable transport systems, one with a rather low affinity for Ch, K, 5 x to 2 x M (Schuberth et al. 1966 8z 1967) and one with K, in the range of zyxwvuts 1 to 8 x M (Haga 1971; Hage & Noda 1973; Yamamura & Snyder 1972 & 1973). A transport system with a low affinity for Ch has also been demonstrated in many other tissues like human erythrocytes (K, 2 to 5 and 10-4 M) (Martin 1968; Diamond & Kennedy 1969). The high affinity Ch transport system in brain tissue which requires the presence of sodium in the incubation medium appears to be confined to cholinergic nerve terminals (Simon et al. 1976) and most of the Ch transported by this carrier is converted to ACh (Yamamura & Snyder 1973; Haga & Noda 1973; Kuhar et al. 1973). By study- ing drugs known to affect turnover of ACh, Kuhar et al. have shown that alteration of the activity in cholinergic neurones in vivo are fol- lowed by parallel changes in sodium dependent high affinity Ch uptake in vitro (Atweh et al. 1975). These findings have been confirmed and extended