Effects of Choline Administration on In Vivo Release and Biosynthesis of Acetylcholine in the Rat Striatum as Studied by In Vivo Brain Microdialysis (original) (raw)
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Brain Research, 1989
This study examined the possibility that membrane phospholipids might be a source of choline used for acetylcholine (ACh) synthesis. Slices of rat striatum or cerebellum were superfused with a choline-free or choline-containing (10, 20 or 40 #M) physiological solution with eserine. for alternating 20 min periods of rest or electrical stimulation. Superfusion media were assayed for choline and ACh. and slice samples taken before and after stimulation were assayed for choline, ACh, various phospholipids. protein and DNA. The striatal slices were able to sustain the stimulation-induced release of ACh, releasing a total of about 3 times their initial ACh contents during the 8 periods of stimulation and rest. During these 8 cycles, 885 pmol/ug DNA free choline was released from the slices into the medium, an amount about 45-fold higher than the initial or final free choline levels in the slices. Although repeated stimulation of the striatal slices failed to affect tissue levels of free tholine or of ACh, this treatment did cause significant. dose-related (i.e., number of stimulation periods) stoichiometric decreases in tissue levels of phosphatidylcholine (PC) and of the other major phospholipids; tissue protein levels also declined significantly. Addition of exogenous choline to the superfusion medium produced dose-related increases in resting and evoked ACh release. The choline also fully protected the striatal slices from phospholipid depletion for as many as 6 stimulation periods. Cerebellar slices liberated large amounts of free choline into the medium but did not release measurable quantities of ACh; their phospholipid and protein levels did not decline with electrical stimulation. These data show that membrane phospholipids constitute a reservoir of free choline that can be used for-ACh synthesis. When free choline is in short supply, ACh synthesis and release are sustained at the expense of this reservoir. The consequent reduction in membrane PC apparently is associated with a depletion of cellular membrane. The use of free choline by cholinergic neurons for two purposes, the syntheses of both ACh and membrane phospholipids, may thus impart vulnerability to them in situations where the supply of free choline is less than that needed for acetylation. INTRODUCI'ON Brain slices and minces continue to make and, upon depolarization, to release large amounts of acetylcholine (ACh) without exhibiting reductions in their contents of free choline or ACh even when they are superfused wiih a'choline-free medium" 0 ' 2 6-344J. However, addition to the choline-free medium of hemicholinium-3 (HC-3), a drug which blocks choline's high-affinity uptake into cholinergic terminals, stops the release of acetylcholine from nerve terminals, and decreases tissue acetylcholine levels. These findings were interpreted as suggesting that some of the choline used by the slices for acetylcholine synthesis originated in the phosphatidylcholine (PC) of neuronal membranes6: depolarization would cause a net hydrolysis of this PC, and the choline thus released into extracellular fluid would be taken up into cholinergic terminals for acetylation s .
3,4-Diaminopyridine and choline increase in vivo acetylcholine release in rat striatum
European Journal of Pharmacology, 1995
We investigated the effects of choline, 3,4-diaminopyridine and their combination on acetylcholine release from the corpus striatum of freely moving rats which were treated or not with atropine. Intraperitoneal administration of choline or intrastriatat administration of 3,4-diaminopyridine increased acetylcholine levels in striatal dialysates in a dose-dependent manner. When 3,4-diaminopyridine treatment was combined with choline, the observed effect was considerably greater than the sum of the increases produced by choline or 3,4-diaminopyridine alone. Administration of atropine (1/zM) in the dialysing medium was also found to be effective to stimulate striatal acetylcholine levels. 3,4-Diaminopyridine did not affect acetylcholine levels under these conditions. Whereas the choline-induced increase in acetylcholine release was significantly potentiated by atropine, co-administration of 3,4-diaminopyridine with choline failed to produce a further significant increase in the presence of atropine. These results suggest that a highly effective means for increasing acetylcholine release involves two concurrent treatments that increase neuronal choline levels and inhibition of the negative feedback modulation of acetylcholine release.
Pharmacological Research Communications, 1977
The effect of the administration of choline (Ch), phosphorylcholine (PCh) and dimethylaminoethanol (DMAE) on acetylcholine (ACh) level in the cerebral Cortex and the caudate nucleus was investigated in rats killed by focussed microwave radiations. Ch administered i.p. or i.v. up to the dose of 120 mg/]{g caused neither behavioural effects nor changes in ACh level. Similarly no effects were detected following administration of ecuimolar doses of PCh or DI:LkE. PCh (228 mg/K~_ i.p.) exerted a partial antagonism toward the decrease in striatal ACh induced by intraventricular administration of hemicholinium (HC-3). The intraadministration of PCh, Ch but not of DI, LkE also antaeffect of HC-3 on striatal ACh level but not on ventric ular gonized the cortical ACh.
Brain Research, 1973
As suggested by in vitro studies 7 brain tissue is unable to synthesize choline from its normal unmethylated precursors such as serine or monoaminoethanol. Similar conclusions could be drawn from in vivo experiments 1. An external supply of choline seems thus to be required for brain metabolism; in fact, this precursor is synthesized in the liver and probably transported by the plasma to the brain in a bound form (phosphatidylcholine)L However, several studies a,s,24 strongly suggest that free choline is the physiological precursor of acetylcholine (ACh) in brain. Indeed this molecule is taken up into brain synaptosomes by a carrier-mediated transport systemll,lZ, 21, apparently highly developed in cholinergic terminals 19. Such a dependence of neuronal tissue on external choline suggests that the availability of the precursor could be a limiting factor in ACh synthesis, or at least that the effect of drugs on choline uptake could be involved in some of their pharmacological actions.
Journal of Neurochemistry, 1980
High-affinity uptake of choline and choline acetyltransferase activity (ChAT) were measured in the striatum of rats treated for 45-60 days with haloperidol (1 mg/kg per 0s) and pimozide (1 mg/kg per 0s) daily and with fluspirilene (1 mg/kg i.m.) twice a week. Haloperidol and fluspirilene caused a 2976, and pimozide a 3896, increase in high-affinity uptake of choline. They also caused a significant decrease in ChAT activity: haloperidol, 20%; pimozide, 27%; and fluspirilene, 42%. In rats treated with fluspirilene for 65-80 days the metabolism of [3Hlcholine taken up by striatal synaptosornes was investigated. A 33% increase in total radioactivity, a significant increase in labelled acetylcholine (ACh), a relative decrease in labelled choline, and no change in labelled phosphorylcholine and betaine were found. It is concluded that the increase in high-affinity choline uptake caused by chronic administration of neuroleptic drugs is associated with a parallel increase in choline utilization for ACh formation. On the other hand, the decrease in ChAT activity does not appear to influence ACh formation.
On the Relationship Between [ 3 H]Choline Uptake Activation and [ 3 H]Acetylcholine Release
Journal of Neurochemistry, 1977
The depolarization-induced, calcium-dependent release of C3H]ACh from hippocampal synaptosomes was studied in a superfusion system. Release increased. with increasing depolarization. Barium and strontium effectively substituted for calcium during the depolarization, but magnesium inhibited the release. Releasable C3H]ACh is derived from the sodium-dependent component of the [3H]choline uptake which points out the physiologic importance of sodium-dependent choline transport. It is concluded that C3H]ACh release in this system has the same properties as neurotransmitter release in many other systems. Previous studies have shown that treatments which alter the activity of cholinergic neurons in uiuo result in parallel changes in sodium-dependent choline uptake in uitro. When synaptosomes were utilized from animals treated to reduce cholinergic activity, there was a reduced release following the reduced uptake. Conversely, when synaptosomes were taken from animals treated to increase sodium-dependent choline uptake, there was an increase in the release. It is concluded that the changes in sodium-dependent choline uptake in uitro consequent to changes in neuronal activity in uiuo result in parallel changes in releasable ACh. A comparison was made between the effect of a number of ions and agents on release and their effect on the in uitro, depolarization-induced activation of sodium-dependent choline uptake. Barium and strontium, ions which substitute for calcium in the release process, support the in uitro activation of uptake. Vinblastine and Bay a 1040, compounds which block release, prevented the in uitro activation of sodium-dependent choline uptake. However, magnesium blocked release in a dose-dependent manner, but did not block the activation of uptake in uitro. Rather, magnesium substituted for calcium and supported the activation of uptake in a dose-dependent fashion. It is concluded that acetylcholine release is not necessary for the activation of choline uptake.
Life Sciences, 1994
We examined the effects of exogenous choline (30, 60, 120 mg/kg, i.p.) on basal and scopolamine-evoked acetylcholine (ACh) release in awake animals, using in vivo microdialysis. After collection of 3-4 baseline dialysate samples (15 min each), rats received either saline or choline chloride and 4 additional samples were collected. All animals then received scopolamine hydrochloride (0.5 mg/kg, i.p.) and 6 additional samples were collected. Basal ACh release in animals receiving choline did not differ from that in rats given saline, nor from ACh release prior to choline administration. Scopolamine alone increased average ACh levels in dialysates from 1.22 + 0.54 to 11.18 f 3.07 pmol/l5 min (mean f SD; p = 0.001); administration of 60 mg/kg or 120 mg/kg of choline chloride significantly enhanced maximal scopolamine responses by about 55%. These results suggest that supplemental choline enhances evoked ACh release in hippocampus of freely-moving rats.
Neurochemistry International, 1993
Al~traet--In the central nervous system, choline is an essential precursor of choline-containing phospholipids in neurons and glial cells and of acetylcholine in cholinergic neurons. In order to study choline transport and metabolism in the brain, we developed a comprehensive methodical procedure for the analysis of choline and its major metabolites which involves a separation step, selective hydrolysis and subsequent determination of free choline by HPLC and electrochemical detection. In the present paper, we report the levels of choline, acetylcholine, phosphocholine, glycerophosphocholine and choline-containing phospholipids in brain tissue, cerebrospinal fluid and blood plasma of the untreated rat. The levels of free choline in blood plasma (11.4 #M), CSF (6.7 #M) and brain intracellular space (64.0 pM) were sufficiently similar to be compatible with an exchange of choline between these compartments. In contrast, the intracellular levels of glycerophosphocholine (1.15 mM) and phosphocholine (0.59 mM) in the brain were considerably higher than their CSF concentrations of 2.83 and 1.70/~M, respectively. In blood plasma, glycerophosphocholine was present in a concentration of 4.58 #M while phosphocholine levels were very low or absent (< 0.1 #M). The levels of phosphatidylcholine and lyso-phosphatidylcholine were high in blood plasma (1267 and 268 #M) but very low in cerebrospinal fluid (< 10 pM). We concluded that the transport of free choline is the only likely mechanism which contributes to the supply of choline to the brain under physiological conditions.
Acetylcholine release from dissociated striatal cells
Brain Research, 1995
To study the regulation of striatal acetylcholine (ACH) release, adult male rat striata were dissociated and incubated with 3H-choline to synthesize 3H-ACH. Fractional 3H-ACH effiux per min during continuous perifusion was: (1) tightly regulated; (2) dependent on calcium influx; (3) stimulated by 10 mM K + and 1 mM glutamate; and (4) comparable to ACH release detected by HPLC. Thus, acutely dissociated striata exhibit calcium-sensitive, voltage-dependent secretion of 3H-ACH and direct receptor-mediated stimulation of release through the glutamate receptor family. This new approach toward cholinergic secretory physiology will help clarify complex striatal circuitry. * Corresponding author. Fax: (1) (804) 982-1726. 0006-8993/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSD1 0006-8993(95)00996-5
Journal of neurochemistry, 2017
In addition to hydrolysis by acetylcholine esterase (AChE), acetylcholine (ACh) is also directly taken up into brain tissues. In the present study, we examined whether the uptake of ACh is involved in the regulation of synaptic ACh concentrations. Superfusion experiments with rat striatal segments pre-incubated with [(3) H]choline were performed using an ultra-mini superfusion vessel, which was developed to minimize superfusate retention within the vessel. Hemicholinium-3 (HC-3) at concentrations less than 1 μM, selectively inhibited the uptake of [(3) H]choline by the high affinity-choline transporter 1 (CHT1) and had no effect on basal and electrically evoked [(3) H]efflux in superfusion experiments. In contrast, HC-3 at higher concentrations, as well as tetraethylammonium (TEA, >10 μM), which inhibited the uptake of both [(3) H]choline and [(3) H]ACh, increased basal [(3) H]overflow and potentiated electrically evoked [(3) H]efflux. These effects of HC-3 and TEA were also obse...