Isotopic labeling of synaptosomes that accumulate choline and the effect of narcotic drugs

Intra-retrosplenial cortical grafts of cholinergic neurons: functional incorporation and restoration of high affinity choline uptake

Fetal septal neurons transplanted into the deafferented retrosplenial cortex (RSC) of rats have been shown to reinnervate the host brain and ameliorate spatial memory deficits. In the present study we examined the effects of implanting cholinergic neurons on high affinity choline uptake (HACU) in the denervated RSC and the correlational relationship between this cholinergic parameter and the level of behavioral recovery. Three groups of animals were used: 1) normal control rats (NC), 2) rats with lesions of the fornix and cingulate pathways (FX), and 3) lesioned rats with fetal septal grafts in the RSC (RSCsep-TPL). We found that intra-RSC septal grafts produced significant increases in HACU, and that recovery of HACU was significantly correlated with the improvements in the performance of spatial reference memory, spatial navigation, and spatial working memory tasks. We have also investigated the ability of the host brain to modulate the activity of the implanted neurons. In particular we evaluated the effect of the animals' performance in a 6-arm radial maze task on high affinity choline uptake (HACU). Animals in each of the NC, FX, and RSCsep-TPL groups were randomly assigned one of the following subgroups: 1) rats that performed the maze task before the determination of HACU (BEH), or 2) rats that did not perform the maze task before the determination of HACU (NON-BEH). Significant increases were observed in the NC and RSCsep-TPL groups, but not in the FX animals, indicating that fetal septal grafts in the RSC can become functionally incorporated with the host neural circuitry, and that the activity of the implanted cholinergic neurons can be modulated by the host brain.

High affinity choline transport and acetylCoA production in brain and their roles in the regulation of acetylcholine synthesis

This review describes recent advances made in the understanding of the regulation of acetylcholine synthesis in brain with regard to the availability of its two precursors, choline and acetylCoA. Choline availability appears to be regulated by the high affinity choline transport system. Investigations of the localization and inhibition of this system are reviewed. Procedures for measuring high affinity choline transport and their shortcomings are described. The kinetics and effects of previous in vivo and in vitro treatments on high affinity choline transport are reviewed. Kinetic and direct coupling of the transport and acetylation of choline are discussed. Recent investigations of the source of acetylCoA used for the synthesis of acetylcholine are reviewed. Three sources of acetylCoA have recently received support: citrate conversion catalyzed by citrate lyase, direct release of acetylCoA from mitochondria following its synthesis from pyruvate catalyzed by pyruvate dehydrogenase, and production of acetylCoA by cytoplasmic pyruvate dehydrogenase. Investigations indicating that acetylCoA availability may limit acetylcholine synthesis are reviewed. A model for the regulation of acetylcholine synthesis which incorporates most of the reviewed material is presented.

Development of high affinity choline uptake and associated acetylcholine synthesis in the rat fascia dentata

The ontogenic development of hemicholinium-sensitive, high affinity choline uptake and the synthesis of acetylcholine from exogenous choline have been studied in particulate preparations of the rat fascia dentata. Between 6 days of age and adulthood the rate of high affinity choline uptake increases 3-fold, when expressed with respect to protein, and 125-fold, when expressed independently of protein. This process develops most rapidly during the period around 16-17 days of age, similar to the ontogenesis of choline acetyltransferase activity. This observation supports the idea that cholinergic septohippocampal boutons develop mainly at this time. Unlike choline acetyltransferase activity, the velocity of high affinity choline uptake increases to as much as 161% of the adult value at about 30 days of age. It is suggested that at 25-31 days of age a relatively high endogenous septohippocampal firing rate increases the rate of choline uptake. At 6 days of age we detected no synthesis of acetylcholine from the accumulated choline. Uptake-synthesis coupling develops mainly between 6 and 13 days of age, earlier than any other presynaptic cholinergic property. Acetylcholine synthesis from exogenous choline develops in paralled with high affinity choline uptake, but developmental increases in uptake velocity result in comparable increases in synthesis rate only after a delay of several days. Some limiting factor other than choline acetyltransferase activity appears to link the accumulation of exogenous choline to acetylcholine synthesis during development.