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

4-(1-Naphthylvinyl)pyridine decreases brain acetylcholine in vivo, but does not alter the level of acetyl-CoA

The effects of intraperitoneally administered 4-(1-naphthylvinyl)pyridine (NVP; 200 mg/kg) on the concentrations of acetylcholine (ACh), choline (Ch), and acetyl-CoA (AcCoA) in rat striatum, cortex, hippocampus, and cerebellum were investigated. Twenty minutes after treatment, the content of ACh was significantly diminished, whereas that of Ch was increased. In response to stress (swimming for 20 min), these changes were enhanced. However, the AcCoA content did not change in any of the brain regions. It is thus very likely that the decrease of brain ACh concentration induced by NVP is due to the drug's effect on choline acetyltransferase (ChAT) and/or the reduction of the high-affinity Ch uptake, and not on the availability of AcCoA. Presumably, the pharmacologically diminished activity of ChAT may become the rate-limiting factor in the maintenance of ACh levels in cholinergic neurons.

Cholinergic differentiation of clonal rat pheochromocytoma cells (PC12) induced by factors contained in glioma-conditioned medium: enhancement of high-affinity choline uptake system and reduction of norepinephrine uptake system

The effects of glioma-conditioned medium (GCM) and factors contained in GCM on the neurochemical differentiation of the PC12 clone of rat pheochromocytoma cells were investigated. The results obtained are as follows. The accumulation of choline into PC12 cells proceeded through two uptake systems with high (Km = 3.20 microM) and low (Km = 65.2 muM) affinities as revealed by least-squares iterative fitting of a substrate-velocity curve to the data. Culturing of PC12 cells in the presence of GCM led to a 5-fold increase in the Vmax value of the high-affinity uptake system without affecting the Km of the high-affinity uptake system. Both Km and Vmax of the low-affinity uptake system were unaffected by the GCM treatment. The high-affinity choline uptake system in both GCM-treated and untreated PC12 cells was devoid of Na+ dependency and showed low sensitivity to hemicholinium-3. The ratio of [3H]acetylcholine converted from [3H]choline taken up by PC12 cells at 1 muM choline for 1 h was two-fold higher than that by untreated cells. PC12 possess a high-affinity norepinephrine uptake system. Culturing of PC12 cells in the presence of GCM led to a decrease in the rate of uptake of 3 muM norepinephrine to 43% of that in control cells. The 40-K and 10-K fractions isolated by gel filtration of GCM had both abilities to enhance the high-affinity choline uptake system and to suppress the high-affinity norepinephrine uptake system. From these observations it was concluded that GCM contains factors which induce the cholinergic neuronal differentiation of PC12 cells.

Effects of 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid (AH5183) on rat cortical synaptosome choline uptake, acetylcholine storage and release

The cholinergic vesicular uptake blocker, 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid (AH5183), had several effects on presynaptic cholinergic function that depended on the duration of treatment and dose. The synthesis, storage and release of newly synthesized [3H]ACh were monitored because the vesicular uptake of this pool of transmitter may be preferentially affected by the drug. Initially, high concentrations of AH5183 (over 10 microM) increased the spontaneous release but decreased the K+ depolarization-induced release of newly synthesized transmitter. [3H]Choline efflux was not altered by the drug. High affinity choline uptake was slightly (10-20%) inhibited by AH5183 in an apparently competitive but time-dependent manner. In contrast to its initial effects on [3H]ACh release, AH5183 (50nM-100 microM) very potently inhibited both the spontaneous and K+-induced release of [3H]ACh but not of [3H]choline after a 60 min preincubation. [3H]ACh levels in cytoplasmic (S3) and crude membrane (P3) fractions were not affected by a 2-min incubation with 10 microM AH5183. After a 60-min preincubation with this drug dose, however, the P3 and S3 levels of newly synthesized transmitter were decreased and increased, respectively. Subsequent fractionation of synaptosomes by sucrose-density gradient centrifugation revealed that these reductions in P3 [3H]ACh-levels were referable to reductions in two subfractions D and H that have been reported to contain low density vesicles and denser vesicles associated with plasma membranes, respectively.

Characterization of [3H]hemicholinium-3 binding associated with neuronal choline uptake sites in rat brain membranes

Hemicholinium-3 (HCh-3) is a potent and specific inhibitor of the high-affinity choline transport process (HAChT) localized on cholinergic neurons. In this study, the specific binding of [3H]HCh-3 (120 Ci/mmol) was characterized in crude synaptic membranes prepared from rat brain. The binding of [3H]HCh-3 to forebrain membranes was saturable, reversible and specific with an apparent Kd under optimal conditions of 35 nM and a Bmax of 56 fmol/mg protein. The potency of various HAChT inhibitors correlated with their apparent affinities for the specific [3H]HCh-3 binding site. The specific binding of [3H]HCh-3 exhibited an uneven regional distribution in the adult rat brain that corresponded to the activity of the HAChT in these regions. Transsection of the fornix, which causes a degeneration of the septal hippocampal cholinergic pathway, resulted in comparable reductions of the specific [3H]HCh-3 binding and the specific activity of choline acetyltransferase, a presynaptic marker for cholinergic terminals in the hippocampal formation; the lesion did not affect the specific activity of glutamic acid decarboxylase, a presynaptic marker for GABAergic neurons within the hippocampus. Maximal binding occurred in the presence of 200 mM NaCl: potassium, lithium, rubidium and calcium substituted poorly for sodium; and bromide, fluoride, iodide, sulfate and phosphate were less effective anions than chloride. Increasing concentrations of NaCl increased the affinity of the site for [3H]HCh-3 with no significant effect on the maximal number of sites; the enhancement of affinity was due to a selective slowing of the rate of dissociation of the ligand from its binding site. These findings indicate that [3H]HCh-3 binds to the carrier site mediating the HAChT on cholinergic neurons; thus, this radioligand may be a useful probe for investigating this presynaptic component (HAChT) of cholinergic neurons.

Incorporation of acetate into acetylcholine, acetylcarnitine, and amino acids in the Torpedo electric organ

The metabolism of acetate was investigated in the nerve-electroplaque system of Torpedo marmorata. In intact fragments of electric organ, radiolabeled acetate was incorporated into acetylcholine (ACh), acetylcarnitine (ACar), and three amino acids: aspartate, glutamate, and glutamine. These compounds were identified by TLC, high-voltage electrophoresis, column chromatography, and enzymic tests. The system responsible for acetate transport and incorporation into ACh displayed a higher affinity but a lower Vmax than that involved in the synthesis of ACar and amino acids. Choline, when added to the medium, increased the rate of acetate incorporation into ACh but decreased (at concentrations greater than 10(-5) M) that into ACar and amino acids. Monofluoroacetate slightly depressed ACh and ACar synthesis from external acetate but inhibited much more the synthesis of amino acids. During repetitive nerve stimulation, the level of the newly synthetized [14C]ACh was found to oscillate together with that of endogenous ACh, but the level of neither [14C]ACar nor the 14C-labeled amino acids exhibited any significant change as a function of time. This means that there is probably no periodic transfer of acetyl groups between ACh and the investigated metabolites in the course of activity. Acetate metabolism was also tested in the electric lobe (which contains the cell bodies of the neurons innervating the electric organ) and in Torpedo synaptosomes (which are nerve terminals isolated from the same neurons). Radioactive pyruvate and glutamine were also assayed in some experiments for comparison with acetate. These observations are discussed in connection with ACh metabolism under resting and active conditions in tissues where acetate is the preferred precursor of the neurotransmitter.

Effects of bilateral ibotenate-induced lesions of the nucleus basalis magnocellularis upon selective cholinergic biochemical markers in the rat anterior cerebral cortex

The relationship of choline acetyltransferase (ChAT) activity and high affinity binding of the potent and selective sodium-dependent choline uptake inhibitor [3H]hemicholinium-3 ([3H]HC-3) to high-affinity binding of the muscarinic agonist [3H](+)-cis-methyldioxolane ([3H](+)CD), the putative M1 selective antagonist [3H]pirenzepine ([3H]PZ) and the classical antagonist [3H](-)-quinuclidinyl benzilate ([3H](-)QNB) in homogenates of the rat neocortex was studied. ChAT activity was 42% lower in rats with ibotenate-induced lesions of the nucleus basalis magnocellularis (nbm) when compared to controls, and [3H]HC-3 binding was similarly reduced by 44%. However, equilibrium dissociation constants (Kd values) for [3H]HC-3 (0.8-1.0 nM), [3H](-)QNB (11-24 pM), [3H]PZ (4.0-4.3 nM) and [3H](+)CD (2.1-2.9 nM) were each unchanged. Mean Bmax values (total binding site densities) for [3H](+)CD were significantly altered in both hemispheres of the anterior cerebral cortex, showing a 25% reduction in the number of sites which display the highest affinity conformation for this potent muscarinic agonist. The decreased ChAT activity and [3H]HC-3 binding after nbm lesions were associated with only slight reductions in putative M1 muscarinic site density (14%) and [3H](-)QNB binding site density (13%). Thus, it appears that while [3H]PZ and [3H](-)QNB label predominantly postsynaptic muscarinic binding sites, a significant number of sites labeled by [3H](+)CD may be associated with presynaptic cholinergic nerve terminals. These data suggest that cholinergic input differentially regulates the drug binding sites of anterior cerebral cortical muscarinic receptors, exerting a substantial effect upon the highest affinity conformational state for agonists.

Activation of acetylcholine synthesis in cat sympathetic ganglia: dependence on external choline and sodium-pump rate

Acetylcholine synthesis in the perfused cat superior cervical ganglion is maximally activated without activation of release during a 10 min recovery in Locke solution following a 15 min period of Na-pump inhibition by perfusion with K-free Locke solution; choline (5 X 10(-5) M) being present throughout. This procedure combined with the use of very high rates of perfusion flow has now permitted an examination of the roles of choline uptake and Na in the activation of synthesis. The data were analysed by analysis of variance as a basis for assessing experimental error and by Bartlett's test to assess equality of variance. Significance of differences between groups was estimated from this analysis (see Appendix). By selective omission of choline, either with or without addition of hemicholinium-3 (HC-3), in the K-free or in the recovery period it was found that choline is only taken up for formation of acetylcholine in the recovery period. With the use of different concentrations of choline in the recovery period, and omission of choline in the K-free period, it was found that the rate of acetylcholine synthesis increased with increasing choline concentration in conformity with Michaelis-Menten kinetics. The choline concentration giving half-maximal synthesis rate was 3.6 microM. Addition of 10(-6) M-HC-3 during recovery completely abolished synthesis in the presence of 5 X 10(-6) M-choline, and 2.5 X 10(-7) M-HC-3 reduced it by 68%. These values for choline dependence and inhibitory potency of HC-3 are similar to those found for high affinity choline transport in brain synaptosomes, indicating that the same system operates in brain and in ganglia. In additional experiments in which choline was omitted in the K-free period and with 5 X 10(-5) M-choline in the recovery fluid a reduction of external Na to 50 mM during recovery did not reduce significantly the maximal rate of acetylcholine synthesis. Further reduction to 25 nM, which would be expected to abolish the Na gradient, reduced the rate of synthesis by only 18%. The presence of 2 X 10(-5) M-ouabain during recovery in normal Locke solution containing 5 X 10(-5) M-choline abolished synthesis. It is concluded that choline uptake for acetylcholine synthesis in ganglia is via the high affinity transporter; that the transport is rate limiting for acetylcholine synthesis and; that the transport process is intimately linked to Na-pump rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased metabolism of acetylcholine in brain of cats with Gm1 gangliosidosis

Acetylcholine metabolism was studied in cats with Gm1 gangliosidosis. Marked increases in acetylcholine synthesis (130% of controls) and K+-stimulated release of ACh (142-165% of controls) were observed in cortical and hippocampal brain slices of diseased cats. Cortical synaptosomes prepared from affected cats had significantly elevated rates of high affinity choline transport (131% of controls). These results indicate that in Gm1 gangliosidosis there is an unique disease-induced activation of cholinergic activity in the nervous system. These changes may result from disease-induced proliferation of functional cholinergic nerve endings and/or altered regulation of acetylcholine metabolism.

Diisopropylfluorophosphate inhibits choline efflux from the perfused rat hemidiaphragm

Acetylcholine (ACh) synthesis by motor nerve terminals requires an adequate supply of its precursor, choline. The results reported here show that diisopropylfluorophosphate (DFP), an acetylcholinesterase inhibitor commonly used in ACh release studies, reduces the rate of endogenous choline efflux from the perfused rat hemidiaphragm. Perfusion of the isolated hemidiaphragm with 10 microM or 100 microM DFP reduced choline efflux by 39% and 69% respectively. DFP administration to rats (6 mg/kg) also lowered the in vitro release of choline by 33%. The rate of ACh release from hemidiaphragm preparations perfused with DFP was significantly lower than the rate of release from preparations perfused with physostigmine, an acetylcholinesterase inhibitor which had no effect on choline efflux. The addition of choline (10-30 micron) to the perfusion medium restored the rate of ACh release from DFP-treated hemidiaphragms but did not further elevated ACh release from physostigmine-treated preparations. These results demonstrate that DFP inhibits choline efflux from the isolated hemidiaphragm and further suggest that, by limiting the availability of choline for ACh synthesis, DFP reduces the rate of ACh release.

Choline fluxes in synaptosomal membrane vesicles

Synaptic plasma membrane vesicles isolated from the highly cholinergic nervous tissue of insects were used to study the translocation of choline across the membrane via a high-affinity carrier-mediated mechanism energized by ion gradients as the sole driving force. The uphill movement of choline, energized mainly by the Na+ gradient, attained levels of choline severalfold the final equilibrium value at the peak of the overshoot. Efflux of choline required the presence of internal sodium ions and was promoted by external choline if Na+ was present. External choline inhibited choline efflux in the absence of sodium. It is concluded that the efflux of choline is in many aspects symmetrical with its uptake.

Effect of hypoxia on uptake and acetylation of [3H]choline in brain slices from adult and newborn guinea pigs

The synthesis of [3H]acetylcholine in brain slices from adult and newborn guinea pigs were suppressed by anaerobiosis. The uptake and acetylation of [3H]choline in the newborn brain were very low, compared to findings in slices of the adult brain. The most sensitive tissue to hypoxia was the striatum followed by the hippocampus. There were significant differences in the case of the frontal cortex.

Estradiol increases choline acetyltransferase activity in specific basal forebrain nuclei and projection areas of female rats

Administration of estradiol to gonadectomized female, but not male rats, is associated with increased activity of choline acetyltransferase in the medial aspect of the horizontal diagonal band nucleus, the frontal cortex, and CA1 of the dorsal hippocampus. Four other basal forebrain cholinergic nuclei did not show changes in choline acetyltransferase activity after estradiol. These data have implications for possible benefits of estradiol administration to patients with senile dementia of the Alzheimer's type.

Reconstitution of carrier-mediated choline transport in proteoliposomes prepared from presynaptic membranes of Torpedo electric organ, and its internal and external ionic requirements

Proteoliposomes made by a butanol-sonication technique from electric organ presynaptic membranes showed choline transport activity. In contrast to intact nerve terminals, the uptake of choline was dissociated from its conversion to acetylcholine in this preparation. The kinetics of choline uptake by proteoliposomes was best described by two Michaelis-Menten components. At a low concentration of choline, uptake was inhibited by hemicholinium-3 and required external Na+ and, thus, closely resembled high-affinity choline uptake by intact cholinergic nerve terminals. Choline transport could be driven by the Na+ gradient and by the transmembrane potential (inside negative) but did not directly require ATP. External Cl-, but not a Cl- gradient, was needed for choline transport activity. It is suggested that internal K+ plays a role in the retention of choline inside the proteoliposome. Proteoliposomes should prove a useful tool for both biochemical and functional studies of the high-affinity choline carrier.

The effects of neonatal thyroid deficiency on acetylcholine synthesis and glucose oxidation in rat corpus striatum

The effects of propylthiouracil (PTU)-induced thyroid deficiency on [14C]acetylcholine synthesis and 14CO2 production from [U-14C]glucose in vitro, by fine prisms of the corpus striatum were investigated in developing rats. Consistent with deficits in choline uptake and choline acetyltransferase activity (Kalaria et al.17), PTU-treatment from two days after birth significantly impaired (27-39%) [14C]acetylcholine synthesis in striatal tissue taken from 3- or 6-week-old animals. In the thyroid-deficient (Tx) animals, 14CO2 production from [14C]glucose was unchanged in incubations in the presence of 5 mM K+ but was significantly reduced (33%) in medium with 31 mM K+ concentration. The addition of 10 mM DL-3-hydroxybutyrate in incubations with 5 mM K+ persistently inhibited 14CO2 production by striatal samples from the Tx rats. The fraction acetylated of [3H]choline accumulated by striatal prisms was unaffected by the PTU-induced thyroid deficiency. These findings suggest the development of fewer cholinergic nerve terminals in striatum during neonatal thyroid deficiency. Cholinergic nerve terminals that develop seem unaffected in their capacity for K+-stimulation and in their ability to acetylate transported [3H]choline.

Halothane-induced alterations of glucose and pyruvate metabolism in rat cerebra synaptosomes

Synaptosomes isolated from rat cerebra were used to study the effects of the inhalational anesthetic, halothane, on cholinergic processes. To identify possible mechanisms responsible for the depression of acetylcholine synthesis, we examined the effects of halothane on precursor metabolite metabolism involved with supplying the cytosol with acetyl-CoA for acetylcholine synthesis. Three percent halothane/air (vol/vol) depressed 14CO2 evolution from labeled pyruvate and glucose. Steady-state 14CO2 evolution from [1-14C]glucose was depressed 84% by halothane, while 14CO2 evolution from [6-14C]glucose and [3,4-14C]glucose was decreased 67 and 52%, respectively, when compared with control conditions. Halothane inhibited the activities of both pyruvate dehydrogenase (14% depression) and ATP-citrate lyase (32% depression). Total synaptosomal acetyl-CoA concentrations were unaffected by halothane. Three percent halothane/air (vol/vol) caused a 77% increase in medium glucose depletion rate from 1.38 nmol (mg protein)-1 min-1 to 2.44 nmol (mg protein)-1 min-1. Production of lactate by the synaptosomes in the presence of halothane increased by 231% from a control rate of 1.44 nmol (mg protein)-1 min-1 to 4.77 nmol (mg protein)-1 min-1. Lactate production rate from pyruvate was also enhanced by 56% in the presence of halothane. These data lend support to the concept that the NAD+/NADH potential may be involved in the halothane-induced depression of acetylcholine synthesis.

Age-related reductions in rat atrial high affinity choline uptake, ACh synthesis, and ACh release. A brief note

We have developed a rat atrial mince preparation that can take up choline, acetylate it, and then release acetylcholine in a depolarization-dependent manner. We demonstrate that aging appears to reduce the functional cholinergic activity in this tissue, which may be important for understanding how senescence alters the regulation of cardiac activity.

Modulation of choline transport and acetylcholine synthesis in synaptosomes from different brain regions

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 Na+ in the incubation medium and when the sodium salts were replaced by Trisphosphate 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-ACh to 3H-Ch in the P2 pellet was 86, 81 and 69 per cent in hippocampus, striatum and cortex, respectively. Omission of sodium ions in the incubation medium reduced uptake of 3H-Ch by about 90 per cent at 1 microM 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 striatum compared with cortex and hippocampus. Apparent Km and Vmax were 0.9 X 10(-6)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 microM 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 proportion of 3H-ACh in the pellets.

Passive avoidance deficits in mice following ethylcholine aziridinium chloride treatment

High-affinity choline uptake (HACU) appears to be the rate-limiting step in the synthesis of the neurotransmitter acetylcholine. The present experiment was designed to examine the effects of irreversible inhibition of HACU by ethylcholine aziridinium chloride (ECA) on passive avoidance retention in mice. Animals were injected intracerebroventricularly, and one-trial passive avoidance retention evaluated 21 days later. A significant retention deficit was observed in ECA-treated animals upon retest 24 hours after training. ECA-induced changes in retention were accompanied by significant reductions in choline acetyltransferase (CAT) activity in only two of seven brain regions tested, hippocampus (48% of control) and cerebellum (76% of control). The results support the involvement of hippocampal cholinergic activity in mediation of passive avoidance learning.

The characterization of a sodium-dependent high affinity choline uptake system unassociated with acetylcholine biosynthesis

The cardiac ganglion of the horseshoe crab, Limulus polyphemus, was incubated in Chao's solution containing 0.01 microM [3H]choline at room temperature (25 +/- 2 degrees C) and the ganglion readily accumulated the radiolabel. The ganglion uptake of [3H]choline was linear over 60 min. Kinetic analysis revealed dual choline uptake systems within the cardiac ganglion, a high affinity uptake system (Km = 2.2 microM, Vmax = 0.16 pmoles/mg/min) and a low affinity system (Km = 92.3 microM, Vmax = 3.08 pmoles/mg/min). The high affinity uptake system was sodium-dependent and inhibited by micromolar concentrations of hemicholinium-3. A 15 min pre-exposure of the ganglion to Chao's solution containing 90 mM potassium stimulated a significant increase in choline uptake. There was no detectable synthesis of [3H]acetylcholine from the [3H]choline taken up by the cardiac ganglion. The major portion of the extractable label appeared in a fraction which co-electrophoresed with phosphorylcholine. These results suggest that the sodium-dependent high affinity [3H]choline uptake system of the cardiac ganglion subserves a specific requirement for choline which is unrelated to a cholinergic function.

Sodium-dependent high-affinity binding of [3H]hemicholinium-3 in the rat brain: a potentially selective marker for presynaptic cholinergic sites

This report describes the membrane binding properties of [3H]hemicholinium-3 ([3H]HC-3), a selective inhibitor of sodium-dependent high-affinity choline uptake (SDHACU) in cholinergic nerve terminals. Under the described assay conditions, [3H]HC-3 bind with a saturable population of high-affinity (apparent Kd = 1.9 nM) CNS membrane sites having the regional distribution: striatum much greater than hippocampus greater than cerebral cortex greater than cerebellum. High-affinity [3H]HC-3 binding is entirely dependent upon the presence of sodium chloride (EC50 = 35-50 mM) and is markedly reduced when other salts of sodium or monovalent ions are substituted. [3H]HC-3 binding is inhibited by choline (Ki = 6 microM) and acetylcholine (Ki = 35 microM) but markedly less sensitive to other cholinergic agents and metabolic inhibitors. In light of the similar ionic dependencies, regional distributions and pharmacological specificities of [3H]HC-3 binding and SDHACU, closely associated sites may be involved in both processes.

Radioactive choline uptake in the isolated rat phrenic nerve-hemidiaphragm preparation. A biochemical and autoradiographic study

When hemidiaphragms are stimulated via the phrenic nerve in the presence of 10 microM radioactive choline (Ch), the rate of radioactive Ch uptake in the endplate-rich area (EPA) is greater than that in the endplate-poor muscle (M). Ch uptake in the EPA is temperature-dependent, with a Q10 of 2.9 and an activation energy of 19.5 kcal/mol. It is inhibited in a Na+-depleted medium, in the absence of Ca2+, and by 10-20 microM hemicholinium-3 (HC-3) and it is not inhibited by alpha-bungarotoxin even when the muscle is completely paralyzed. In the absence of stimulation the rate of uptake in the EPA is slightly, but not significantly, greater than in M. Using autoradiography, we find an enhanced amount of isotope in the nerve terminals and their immediate vicinities compared with the muscle fibres, in both stimulated and unstimulated hemidiaphragms. There is no enhanced uptake of isotope into the nerve terminals in stimulated tissues in the presence of 26 microM HC-3. The uptake of isotope into the muscle is not altered by any of these treatments. There is a positive correlation between the initial rate of radioactive Ch uptake in the EPA and the amount of isotope in the nerve terminals (the mean corrected grain density above the nerve terminals). Without correcting for the large amount of diffusion that occurs, the ratio of the grain density above the synapses to that above the muscle fibres is 1.66 in tissue stimulated at 1 Hz, 1.04 in stimulated tissues in the presence of 26 microM HC-3, and 1.31 in unstimulated tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

The cholinergic system of the primitive streak chick embryo

The presence of neurotransmitters at stages of embryonic development prior to neurulation has been demonstrated in several systems. Although the functions of these molecules at early stages of embryogenesis have not been ascertained, it is possible that they are involved in aspects of cell migration, regulation of the synthesis of macromolecules, intercellular communication, and in the transmission of positional information during gastrulation. As an initial approach to the resolution of questions concerning the function of transmitters during early development, we have begun a study of the cholinergic system in the primitive streak chick embryo (Hamburger-Hamilton stages 3 + to 5). We have found that the chick embryo: (1) can use exogenously applied choline for the synthesis of acetylcholine; (2) possesses a true acetylcholinesterase, which is predominantly in the form of the 4-6s monomer; and (3) can take up exogenous choline through a sodium-dependent, high-affinity choline transport system. To date we do not have any evidence for the presence of nicotinic or muscarinic receptors at the primitive streak stage.

Possible mechanisms involved in the presynaptic cholinotoxicity due to ethylcholine aziridinium (AF64A) in vivo

AF64A is a toxin which can diminish irreversibly cholinergic transmission in vivo (1, 2). Disruption of neurotransmitter function in vivo is specific to the cholinergic system when AF64A is administered in nanomolar quantities (3, 4). The mechanisms involved appear to be mediated presynaptically (g). The neurochemical and behavioral consequences of AF64A administration are reminiscent of similar measures in patients with Alzheimer's disease (5, 6). Consequently, we have suggested tentatively that the AF64A treated animal may be explored as a potential animal model of this debilitating disease state (7). In this report we provide a brief overview of our recent findings using this compound in vivo, attempt to correlate these findings with those of others with similar aziridinium agnts in vitro, and propose a possible mechanism of action of AF64A in vivo, based on recent observations made in our laboratories.

Alterations in high affinity choline accumulation rate in rat cerebral cortex during anaesthesia with ketamine and pentobarbital

After i.p. injection of ketamine (75 mg/kg) or pentobarbital-Na (40 mg/kg) to rats, there was a rapid, then a steady decrease of the sodium-dependent high affinity choline (HAC) accumulation rate to a minimum. This minimum was followed by a rapid increase (ketamine) or a gradual rise (pentobarbital-Na). Immediately after the rats came out of anaesthesia, the accumulation rate had not yet completely recovered. We suggest the ketamine or pentobarbital-Na induce alterations in central cholinergic systems, i.e. changes in choline uptake and incorporation into acetylcholine. It is conceivable that interactions of cholinesterase inhibitors or corticosteroids with the anaesthetics are based upon some modification of these changes.

GM1 ganglioside facilitates the recovery of high-affinity choline uptake in the cerebral cortex of rats with a lesion of the nucleus basalis magnocellularis

The effect of repeated administrations of GM1 monosialoganglioside on high-affinity choline uptake (HACU) was investigated in the cerebral cortex of rats with a unilateral electrolytic lesion of the nucleus basalis magnocellularis. In saline-treated rats, 4 days after lesion, a 38% and 14% decrease in HACU-activity was found in the ipsilateral frontal and parietal cortex, respectively. A spontaneous recovery of HACU activity occurred within the next 20 days. In rats receiving daily injections of GM1 from the day of operation, no significant decrease in HACU activity was found in the lesioned hemisphere 4 days after the lesion. In contrast a 25% increase in HACU activity in the frontal area of the opposite hemisphere was detected. No effect of GM1 treatment could be seen on days 10 or 20 after lesion. The possibility that GM1 may exert its stimulatory effect on HACU independently of the well-known effect of gangliosides on neuronal sprouting is discussed.

Effects of organophosphorus compounds, O,O-dimethyl O-(2,2-dichlorovinyl)phosphate (DDVP) and O,O-dimethyl O-(3-methyl 4-nitrophenyl)phosphorothioate (fenitrothion), on brain acetylcholine content and acetylcholinesterase activity in Japanese quail

Effects of 2 organophosphorus compounds, O,O-dimethyl O-(2,2-dichlorovinyl)phosphate (DDVP) and O,O-dimethyl O-(3-methyl 4-nitrophenyl)phosphorothioate (fenitrothion), on the brain cholinergic system were investigated in Japanese quail. Cholinergic signs, such as salivation and convulsions in legs and wings, were seen 7-15 min after administration with DDVP (3-4 mg/kg) or 6-120 min after administration with fenitrothion (250-350 mg/kg). In the DDVP-treated quail (10 min after dosage of 3 mg/kg), free acetylcholine (ACh), labile-bound ACh, increased significantly and acetylcholinesterase (AChE) decreased to 28% of the value determined in untreated quail. In the fenitrothion-treated group (60 min after dosage of 300 mg/kg), only free ACh increased and AChE activity decreased to 20% of the control value. In vitro, DDVP and fenitrothion inhibited AChE activity in brain homogenate with an I50 of 10(-8) M and 10(-5) M, respectively. It appeared that both organophosphorus compounds might have essentially the same effect on the brain cholinergic system. There were only small differences in the effect on various fractions of ACh between the 2 compounds, although there was a hundred-fold range in dose.

Effects of acute and chronic administration of antidepressant drugs on the central cholinergic nervous system. Comparison with anticholinergic drugs

The purpose of this investigation was to study the effects of antidepressant drugs on the central cholinergic system of the rat after acute and chronic administration. Drugs (antidepressants and non-antidepressants) were first divided into highly potent, moderately potent or weak anticholinergic categories based upon the ability of each compound to displace [3H]-QNB [( 3H]quinuclidinyl benzilate from synaptosomal membranes. One antidepressant drug and one non-antidepressant drug, with similar anticholinergic properties, were chosen as representative agents of each category of anticholinergic potency. Acute administration of amitriptyline or atropine (highly potent anticholinergics) increased the level of high affinity uptake of choline in the hippocampus and striatum. Imipramine and thioridazine (moderately potent anticholinergics) increased the uptake of choline only in the striatum. After acute administration, the effects of nomifensine and d-amphetamine (weak anticholinergics) differed on striatal uptake of choline. Following 30 days pretreatment with any drug, an acute challenge dose of that drug no longer altered the uptake of choline in either region. After chronic administration, amitriptyline increased the density of muscarinic receptors in the cortex whereas atropine increased the density of receptors in the cortex, hippocampus and striatum. The other agents did not alter receptor parameters in the regions examined. Since the central cholinergic actions of the antidepressants were similar to the central actions of the non-antidepressants, it is concluded that the effects of the antidepressants on the central cholinergic nervous system are more closely related to the side effects of these agents than to their therapeutic mechanism of action.

Hierarchial thermodynamic approach to the brain

A thermodynamic approach to understanding the brain is presented. Thermodynamics may be extended to "higher than molecule" levels. The role of the concept of entropy in thermodynamic-based nonthermodynamic systems has been discussed. Static and dynamic structures, cooperative and competitive mechanisms and some of their neurobiological applications are discussed. Postsynaptic membrane noises, dynamic synaptic activity, synaptogenesis, plasticity, retinotopy and perception have been considered as self-organizing neural structures appearing at different hierarchical levels.

The neurochemistry of Alzheimer's disease and senile dementia

At this time we seem to be on the verge of opening two new fields of research on Alzheimer's disease. To treat the symptoms of this condition, an understanding of the factors regulating acetylcholine synthesis will be very important. Because of the vast amount of work on this neurotransmitter over the last 30 years, rapid progress in this area should be made. However, to truely conquer Alzheimer's disease, we need to learn what it is that attacks and apparently destroys the cholinergic neurons. While this second point may take a little more time to unravel, the work will be both exciting and very worth while.

Target influences on [3H]ACh synthesis and release by ciliary ganglion neurons in vitro

The developmental influence of neuron-target interaction upon transmitter synthesis from labeled precursor and the capacity to release labeled transmitter were examined in dispersed cell cultures of embryonic ciliary ganglion neurons by comparing cultures of neurons plated alone and neurons plated upon pectoral myotubes. Of the total ACh synthesized from radiolabeled choline by neurons plated alone, more than half is via a Na+-dependent path, but a larger fraction of the synthesis is Na+ insensitive in culture than in mature neurons in vivo. In addition, at 1 week in culture the neurons lacking target failed to significantly increase ACh synthesis from the labeled choline in response to a previous high [K+]0 depolarization. Synthetic responsiveness to depolarization is a characteristic of mature nerve terminals in this preparation. One week after plating neurons onto myotube cultures, synthesis of ACh from the exogenous precursor is double that of sibling cultures lacking muscle, and prior depolarization with [K+]0 results in an increase in labeled product. Release from the labeled transmitter pool by the neurons with myotubes was also enhanced. [3H]ACh release elicited by depolarization via a Ca2+-dependent mechanism was more than fivefold higher in the cocultures. The influence of coculture with myotubes upon neuronal development is not duplicated by the neurons themselves despite formation of apparent interneuronal synapses (G. Crean, G. Pilar, J. Tuttle, and K. Vaca, 1982, J. Physiol. (London). 331, 87-104), by "fibroblasts" or medium conditioned over myotube cultures. Neurons under these conditions neither increase synthesis of [3H]ACh in response to a prior depolarization nor demonstrate enhanced basal [3H]ACh synthesis and release. Thus, coculture of embryonic ciliary ganglion neurons with a striated muscle target has a somewhat specific inductive effect, enhancing the capacity for neuronal [3H]ACh synthesis and release toward mature levels. This influence of a readily accessible target upon ciliary neuron cholinergic development in vitro may reflect a normal neuromuscular interaction occurring during embryogenesis.

Neural crest origin of cardiac ganglion cells in the chick embryo: identification and extirpation

Using interspecific grafting of neural crest between quail and chick embryos, it was determined that the cardiac ganglia originate from the cranial region (somites 1-2) of the vagal neural crest (somites 1-7). Neuronal uptake of [3H]choline was used as an index of neuronal development in the chick atrium. Normal uptake was found to be quite high between Days 8 and 14 of incubation. Following extirpation of neural crest over somites 1 to 3 at stages 8 to 10, neuronal uptake in 8-day chick atrium was decreased by 25-60% depending on the stage at which the lesion was performed. It is thought that the residual uptake represents preganglionic terminals from the dorsal motor nucleus of the vagus. Embryos with extirpations of neural crest over somites 1-3 performed at stage 9 showed the greatest decrease of neuronal choline uptake and did not live beyond 11 days of incubation. However, hearts from embryos with partial lesions (performed at stage 10) were treated on incubation Days 12 and 15 for demonstration of acetylcholinesterase in the subepicardial plexus. These hearts showed much less extensive neural plexus with sparse, small cardiac ganglia.

Thyrotropin-releasing hormone (TRH) and its analog (DN-1417): interaction with pentobarbital in choline uptake and acetylcholine synthesis of rat brain slices

TRH or its analog DN-1417 (gamma-butyrolactone-gamma-carbonyl-L-histidyl-L-proliamide) given 15 min after intravenous (i.v.) administration of pentobarbital (30 mg/kg) markedly shortened the pentobarbital-induced sleeping time in rats. This effect was almost completely abolished by intracerebroventricular pretreatment with atropine methylbromide (20 micrograms/rat), thereby suggesting the involvement of cholinergic mechanism. The action mechanism was investigated using rat brain slices. TRH (10(-6)-10(-4)M) or DN-1417 (10(-7)-10(-5)M) caused significant increases in the uptake of [3H]-choline into striatal slices. TRH(10(-4)M) or DN-1417(10(-5)M) also stimulated the conversion of [3H]-choline to [3H]-acetylcholine in striatal slices. A 30% reduction of acetylcholine synthesis from [3H]-choline in hippocampal slices and a 40% reduction of [3H]-choline uptake in slices of cerebral cortex, hippocampus and hypothalamus were observed in rats pretreated with pentobarbital (60 mg/kg, i.v.). TRH or DN-1417 (20 mg/kg, i.v.) given 15 min after the administration of pentobarbital markedly reversed both of the pentobarbital effects. Direct application of pentobarbital (5 X 10(-4)M) to slices in vitro also caused a 20-40% reduction of [3H]-choline uptake of cerebral cortex, hippocampus and diencephalon. A concomitant application of TRH(10(-4)M) or DN-1417(10(-5)M) and pentobarbital abolished the pentobarbital effect. These results provide neurochemical evidence that the antagonistic effects of TRH and DN-1417 on pentobarbital-induced narcosis are closely related to alterations in the rat brain choline uptake and acetylcholine synthesis, which are considered to be measures of the activity of cholinergic neurons.

Selective retrograde labelling of vestibular efferent neurons with [3H]choline

Following administration of [3H]choline in the lateral semicircular canal of the cat labyrinth, bidirectional axoplasmic transport [3H]choline and its derivatives was shown by radioautography in the vestibular system. Light-microscopic radioautographs exhibited various patterns of radioautographic labelling. First, a diffuse reaction was observed in vestibular nuclei representing anterograde-labelled, vestibular nerve endings. Second, a heavy labelling limited to perikarya was detected in efferent vestibular neurons and corresponded to retrograde transport. The anterograde migration of [3H]choline is known to be non-selective and is related to synthesis of phospholipids, non-diffusable molecules. In contrast, the retrograde perikaryal labelling seems highly selective and related to the cholinergic specificity of the transmitter. The selectivity of such labelling offers a further possibility of identifying cholinergic neurons and is additional evidence that cholinergic mechanisms are involved in the efferent vestibular control.

The effect of the scorpion venom, tityustoxin, on high-affinity choline uptake in rat brain cortical slices

Tityustoxin (TsTx) inhibited high affinity choline uptake (HAChU) in cortical slices of the rat brain. The effect was dependent on the concentration of tityustoxin, energy source, incubation time, temperature, and the pH of the incubation medium. The inhibitory effect was dependent upon the presence of sodium and calcium ions in the incubation medium; barium ions could not replace calcium. Both tetrodotoxin and ethyleneglycol-tetra-acetic acid (EGTA) blocked the inhibitory effect of tityustoxin on high affinity choline uptake. On this evidence, it is suggested that the effect of tityustoxin might be related to its action on cell depolarization, causing an increase in the release of acetylcholine (ACh).

Mode of action of gamma-butyrolactone on the central cholinergic system

Gamma-butylactone (GBL), a drug depressing the central nervous system, produced marked increases in acetylcholine contents in rat brain hemispheric regions (striatum, hippocampus, cortex) and in striatal choline content without modifying choline acetyltransferase or acetylcholinesterase activities. In the hippocampus GBL also strongly decreased the acetylcholine turnover rate and inhibited the high affinity uptake of choline. Its increase in acetylcholine content was prevented by an acute electrolytic lesion of the medial septum but not by a wide array of drug treatments designed to interfere with neurotransmission in various pathways. The results are taken to indicate that GBL directly depresses the cholinergic septal-hippocampal afferents by interrupting impulse flow. In the striatum, too, GBL markedly depressed the acetylcholine synthesis rate but had no effect on the high affinity choline uptake process. Such dissociation of the two phenomena had previously been observed using other drugs and may denote that acetylcholine synthesis in this region is regulated differently from that in the hippocampus. By comparison, gamma-hydroxybutyric acid (GHBA), an active metabolite which shares with GBL the capacity to produce a somnolent state and depress impulse flow in the dopaminergic nigroneostriatal pathway, had no effect on either striatal acetylcholine content or on hippocampal high affinity choline uptake. The results suggest that GBL can be distinguished from GHBA in its neuropharmacological central cholinergic effects.

Role of dopamine receptors in the modulation of acetylcholine release in the rabbit hippocampus

Modulation of acetylcholine release was studied in slices of the rabbit hippocampus preincubated with 3H-choline and then continuously superfused with a medium containing 10 mumol/l hemicholinium-3. Electrical field stimulation of the superfused slices elicited an increase in tritium outflow, which was tetrodotoxin-sensitive and largely calcium-dependent. Stimulus-evoked acetylcholine release in the rabbit hippocampal slices was modulated by presynaptic muscarinic autoreceptors, as has been shown previously for the rat hippocampus. Drugs with affinity for alpha- and or beta-adrenoceptors did not affect the evoked overflow of tritium from rabbit hippocampal slices. In contrast, the dopamine receptor agonist apomorphine (0.1 or 1 mumol/l) and exogenous dopamine (1 or 10 mumol/l) significantly reduced the evoked outflow by about 10 or 20%, respectively. This effect was antagonized by haloperidol (0.01 mumol/l) but not by phentolamine (1 mumol/l). Attempts to enhance (using nomifensine 10 mumol/l) or reduce (using haloperidol, up to 1 mumol/l; or bretylium, 1 mmol/l for 5 min) endogenous dopaminergic transmission in the hippocampal slices did not affect stimulation evoked acetylcholine release. In conclusion, presynaptic dopamine receptors modulating acetylcholine release are present in the rabbit hippocampus, but they seem not to be of physiological significance.

Immunochemical studies of bovine and human choline-O-acetyltransferase using monoclonal antibodies

Immunochemical properties of bovine and human choline acetyltransferase (ChAT, EC 2.3.1.6, acetyl-CoA:choline-O-acetyltransferase) were studied using six monoclonal antibodies (AB1, AB5, AB6, AB7, AB8, and AB9) reactive with the enzyme. All antibodies except AB1 bound specifically to two proteins of 68,000 and 70,000 MW on "Western" blots of sodium dodecyl sulfate-polyacrylamide gels containing human or bovine ChAT. The enzyme was specifically absorbed to immobilized antibody and could not be eluted by low pH and/or high salt concentrations although the enzyme retained activity on the immunoabsorbent. Pure bovine enzyme consisting of the same two proteins as seen in the Western blotting studies was eluted from immobilized AB1 in the presence of sodium dodecyl sulfate. Although active enzyme could not be eluted from immobilized antibodies by standard conditions, various combinations of free and immobilized antibodies were effective in competing off bound enzyme. Free antibody AB1 quantitatively eluted the active enzyme from immobilized AB1. The different capacities of the antibodies to elute enzyme from various immunoabsorbents reflect interesting properties of both the enzyme and the antibodies.

Cortical modulation of cholinergic neurons in the striatum

Previous reports suggest the existence of a corticostriatal pathway which might use glutamate as the transmitter. In the present study, the possible influence of this pathway on striatal cholinergic neurons was investigated. Two weeks following surgical destruction of the cerebral cortex, the high affinity uptake of glutamate and choline into striatal synaptosomes was significantly reduced whereas GABA uptake was unaffected. In acute experiments (1 hour following decortication), only choline uptake was significantly reduced while the uptake of glutamate and GABA were not altered. Acute injection (2 minutes) of kainic acid into the striatum, 1 hour after decortication, reversed the effect of the decortication on choline uptake, perhaps by simulating an excitatory input to the striatum which was presumably removed by the cortical ablation. These observations are consistent with the existence of a cortical input (perhaps glutamatergic) to the striatum and suggest that striatal cholinergic neurons can be influenced by this cortico-striatal pathway.

Acetylcoenzyme A and acetylcholine in slices of rat caudate nuclei incubated with (-)-hydroxycitrate, citrate, and EGTA

The effects of (-)-hydroxycitrate (OHC) and citrate on the concentration of acetylcoenzyme A (acetyl-CoA) and acetylcholine (ACh) in the tissue and on the release of ACh into the medium were investigated in experiments on slices of rat caudate nuclei incubated in media with 6.2 or 31.2 mM K+, 0 or 2.5 mM Ca2+, and 0, 1, or 10 mM EGTA. OHC diminished the concentration of acetyl-CoA in the slices under all conditions used; in experiments with 2.5 mM OHC, the concentration of acetyl-CoA was lowered by 25-38%. Citrate, in contrast, had no effect on the level of acetyl-CoA in the tissue. Although both OHC and citrate lowered the concentration of ACh in the slices during incubations with 6.2 mM K+ and 1 mM EGTA, they had different effects on the content of ACh during incubations in the presence of Ca2+. The concentration of ACh in the slices was increased by citrate during incubations with 2.5 mM Ca2+ and 31.2 or 6.2 mM K+, but it was lowered or unchanged by OHC under the same conditions. The release of ACh into the medium was lowered or unchanged by OHC and lowered, unchanged, or increased by citrate. It is concluded that most effects of OHC on the metabolism of ACh can be explained by the inhibition of ATP-citrate lyase; with glucose as the main metabolic substrate, ATP-citrate lyase appears to provide about one-third of the acetyl-CoA used for the synthesis of ACh. Experiments with citrate indicate that an increased supply of citrate may increase the synthesis of ACh. The inhibitory effect of citrate on the synthesis of ACh, observed during incubations without Ca2+, is interpreted to be a consequence of the chelation of intracellular Ca2+; this interpretation is supported by the observation of a similar effect caused by 10 mM EGTA.

The turnover of acetylcholine in ligated sciatic nerves of the rat

The accumulation of acetylcholine (ACh) and choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities proximal to a crush on rat sciatic nerves was investigated after superfusion of the nerves in situ with or without inhibitors of ACh synthesis and/or AChE. 9 h after crushing of nerves, the ACh-content of the 5 mm segment of nerve immediately proximal to the crush was increased from 37 +/- 5 to 80 +/- 4 pmol (mean +/- SE), while ChAT-activity was increased to 112 +/- 10% and AChE-activity to 198 +/- 19% over that in non-ligated nerves. Superfusion of the nerves for 8 h with Krebs' bicarbonate medium had no effect on enzyme accumulations, but reduced the ACh content to 59 +/- 4 pmol. The presence of hemicholinium 3 (HC-3) (2 X 10(-5) M) in the superfusion medium reduced the ACh content markedly (to 17 +/- 2 pmol), but had no effect on enzyme accumulations at the crush. Adding eserine (10(-5) M) or soman (10(-6) M) to the superfusion medium increased ACh content to 133 +/- 8 pmol and 101 +/- 8 pmol, respectively, and markedly reduced AChE-activity; ChAT activity was not effected. Superfusion with a combination of HC-3 and eserine caused a marked reduction in ACh content compared with eserine alone; the effect was less with soman. The results are consistent with the view that the ACh which accumulates proximal to crush exists in a protective organelle, but that there is a continuous turnover of ACh due to leakage of ACh from the organelle, both during axonal transport and after accumulation.