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At least 19 recordsLinked to original sources
PubMed1994

Selective cortical decrease of high-affinity choline uptake carrier in Alzheimer's disease: an autoradiographic study using 3H-hemicholinium-3.

3H-hemicholinium-3 (3H-HC-3) binding, a marker of the presynaptic high-affinity choline uptake carrier (HACU), was measured by autoradiography in several brain regions of 17 Alzheimer's disease (AD) patients and of 11 matched controls. A significant decrease in the density of 3H-HC-3 binding sites was found in entorhinal cortex, hippocampus and layers I-III of the frontal cortex. By contrast, in the caudate-putamen the number of 3H-HC-3 binding sites in AD cases was comparable to that of control striata. These data concur with previous results using classical presynaptic markers and reflect the loss in the activity of HACU, and, hence, in the synthesis of acetylcholine, that selectively occurs in cortical areas of AD brains due to the degeneration of presynaptic cholinergic terminals arising from the basal forebrain. However, the relatively low mean reduction in HACU in cortical areas (-40%), together with the apparent indemnity of this marker in certain severely demented AD cases, suggest that AD dementia cannot be explained simply by the loss of presynaptic terminals originating in the basal forebrain. These data seem to be a good explanation for the poor response to cholinergic replacement in AD.

Aged↗
PubMed1977

Effect of sulfur substitution for the noncarbonyl oxygen in hemicholinium-3 and acetyl-seco-hemicholinium-3. Synthesis, biological activity, and structure-toxicity relationships.

As a continuation of our efforts to develop and study inhibitors which act presynaptically on neuromuscular function, sulfur analogues of hemicholinium-3 (HC-3, 1) and acetyl-seco-hemicholinium-3 (AcHC-3, 3) were prepared. In each case sulfur is substituted for the noncarbonyl oxygen in HC-3 (1) and AcHC-3 (3). As expected on the basis of conformational differences between acetylcholine and acetylthiocholine both of the thio analogues are produced in the seco form and do not cyclize spontaneously or when subjected to aqueous, acidic conditions up to 100 degrees C. Both compounds are stable in aqueous pH 7.4 solutions at 37 degrees C and in slightly acidic D2O solutions for more than 24 h. While thio-seco-hemicholinium 3 (11) is stable in the presence of acetylcholinesterase and butyrylcholinesterase in H2O at pH 7.4, acetylthio-seco-hemicholinium-3 (12) reacts within seconds to form the hemiacetal form of thiohemicholinium-3 (16). Mouse toxicity studies (LD50) indicate that while 12 is approximately as toxic as HC-3 (1) and AcHC-3 (3), 11 is 226 times less toxic. As in the studies with 1 and 3, mice were protected from 11 by choline and slightly by neostigmine. It is of interest, however, that almost equal and intermediate protection against 12 was afforded by choline and neostigmine. Structure-toxicity relationships of 1,3,11, 12, and 16 are discussed.

Acetylation↗
PubMed1990

Phospholipase A2 and 3H-hemicholinium-3 binding sites in rat brain: a potential second-messenger role for fatty acids in the regulation of high-affinity choline uptake.

The involvement of phospholipase A2 (PLA2) and fatty acid release in the regulation of sodium-dependent high-affinity choline uptake in rat brain was assessed in vitro through the use of the specific binding of 3H-hemicholinium-3 (3H-HCh-3). Addition of arachidonic acid and other unsaturated fatty acids to rat striatal membranes in vitro resulted in a dose-dependent, temperature-independent activation of 3H-HCh-3 binding. Scatchard analysis revealed that these changes in binding result from a 2-fold increase in the affinity and capacity of 3H-HCh-3 binding. Saturated fatty acids, lysophospholipids, and phospholipids did not affect specific 3H-HCh-3 binding. Addition of defatted BSA to membranes, which had been treated previously with arachidonic acid, completely reversed the increase in specific 3H-HCh-3 binding. However, several inhibitors of fatty acid metabolism, including nordihydroguaiaretic acid, indomethacin, catalase, and superoxide dismutase, did not alter arachidonic acid-induced changes in 3H-HCh-3 binding, suggesting that unsaturated fatty acids, and not their metabolites, are directly responsible for the observed activation of specific 3H-HCh-3 binding. Additionally, unsaturated fatty acids dose-dependently inhibited high-affinity 3H-choline uptake in rat striatal synaptosomes, apparently due to the disruption of synaptosomal integrity. The phospholipase A2 inhibitors quinacrine hydrochloride, trifluoperazine, and 4-bromophenacylbromide dose-dependently inhibited potassium depolarization-induced activation of specific 3H-HCh-3 binding in slices of rat brain in vitro. Similarly, both quinacrine and trifluoperazine inhibited the metabolism of phospholipids and the release of fatty acids evoked by either elevated KCl or calcium ionophore A23187. These results support the involvement of PLA2 and subsequent fatty acid release in the increase of 3H-HCh-3 binding in cholinergic neurons and suggest that activation of PLA2 may be the penultimate step in regulating the velocity of sodium-dependent choline transport.

Animals↗
PubMed1987

Blockade and recovery of cholinergic transmission in rats treated with hemicholinium 3.

Nerve-induced responses of parotid gland and gastrocnemius muscle were reduced by HC-3 (1 mg kg-1) in proportion to the number of stimuli. Contractions by somatic muscle at 100 Hz were abolished after 6.0 X 10(3) stimuli while 14 X 10(3) were applied at 20 Hz before secretion was blocked. As stimulus rate was decreased, blockade of secretion resulted from fewer stimuli but no difference in ACh content was found between stimulated and unstimulated glands. When stimuli were withheld for 1.5 h transmission recovered temporarily; initial secretory flow rate was only 50% of that in untreated controls when stimulation resumed. In both organs, the time during which responses were sustained, however, was much shorter than when the preparations were stimulated initially. After choline, recovery of transmission was dose-dependent: 150 mg kg-1 were required to restore responsiveness to the muscle and the gland comparable to that in HC-3-treated rats stimulated for the first time. Resting recovery, when stimuli are withheld, probably depends upon stored transmitter becoming mobilized rather than on de novo transmitter synthesis because the endogenous choline in plasma is only 1/1000 of that following exogenous choline.

Acetylcholine↗
PubMed1976

Synthesis and structure-toxicity relationships of three new stable analogues of acetyl-seco-hemicholinium-3.

In order to develop and study inhibitors of neuromuscular function which act presynaptically, three stable analogues of acetyl-seco-hemicholinum-3 (AcHC-3,2) were prepared. These analogues have 2-ethoxyethyltrimethylammonium, 4-oxopentyltrimethylammonium, and n-pentyltrimethylammonium moieties substituted for the 2-acetylethyltrimethylammonium (acetylcholine) moieties of AcHC-3 (2) to form the ether 2, ketone 4, and alkane 5 analoggues of AcHC-3 (2). Although AcHC-3 (2) has been shown to undergo deesterification rapidly in basic solutions and slowly at pH 7.4, it has been found to be stable in H2O or D2O under slightly acidic conditions. All of the analogues are stable for extended time under both slightly acidic conditions and at pH 7.4 in H2O or D3O. It has been found that 2 reacts with acetylcholinesterase and butyrylcholinesterase within seconds in H2O at pH7.4. However, deesterification of 2 with subsequent cyclization to the hemiacetal form of hemicholinium-3 (HC-3, 1) is prevented at pH 7.4, possibly by an irreversible binding of 2 to the enzyme. The analogues 3-5, however, do not react under identical conditions. Mouse toxicity studies (LD50) indicate that 2 is approximately as toxic as HC-3 (1), whereas 3, 4, and 5 are 14.2, 23.8, and 43.1 times less toxic, respectively. The toxic effects of 3-5, like 1 and 2, are antagonized by choline but not by neostigmine in mice. Structure-activity relationships of 2-5 are discussed.

Animals↗
PubMed1979

Pharmacological activities of acetal derivatives of hemicholinium no. 3.

Acetal derivatives of hemicholinium no. 3 (HC-3) were synthesized and their chemical structures were confirmed by spectrophotometric evidence and elemental analysis. The acetals elicited a biphasic pattern of neuromuscular inhibition in the cat: (a) an immediate inhibition (early phase block) was judged to be curare-like as responses to acetylcholine (close i.a.) were abolished by acetal administration and reversal of inhibition was effected by neostigmine (25 micrograms/kg); (b) a slow, progressive inhibition of transmission (late phase block) was considered HC-3-like as it occurred only during high frequency stimulation and was antagonized by small doses of choline (1--3 mg/kg). In comparison to HC-3, significanlty greater curare-like activity was noted following acetal administration in vivo and in vitro. Mouse toxicity and cat nerve--muscle studies revealed the acetals to be HC-3-like but 1/2 to 1/3 as active as the parent compound. Cholinesterase inhibition by HC-3 and the acetals was low (I50 greater than 0.1 mM) and did not account for differences in activities. Acetal-elicited hypotension in the cat was attributed to postsynaptic ganglionic blockade and histamine release. Studies employing the 14C-(N-methyl) acetals furnished no evidence of the bioactivation (O-dealkylation) of the acetals to HC-3 in the cat in vivo or in cat liver in vitro. Chromatographic analysis afforded no evidence of molecular modifications of 14C-HC-3 or of the 14C-acetals in these systems.

Acetals↗
PubMed1982

Peripheral toxicity of hemicholinium-3 in mice.

1 The site (i.e. peripheral or central) of the toxicity produced by hemicholinium-3 in mice was investigated. 2 Hemicholinium-3 was measured fluorometrically and acetylcholine was determined by gas chromatography after intraventricular or intraperitoneal administration of hemicholinium-3. 3 Hemicholinium-3 was not detected in the brain nor were acetylcholine levels decreased in the brain after systemic administration. 4 The dose-response curve following intraventricular administration demonstrated that hemicholinium-3 was not as lethal after central administration as it was after peripheral administration. 5 Approximately 24% of a 75 microgram intraventricular dose of hemicholinium-3 was found in the periphery at death. 6 These results suggest that hemicholinium-3 manifests its toxicity primarily in the periphery.

Acetylcholine↗
PubMed1977

Biological evaluation of some biphenyl analogs of acetyl-seco-hemicholinium No. 3.

The oxygen atoms in the esteratic moiety of acetyl-seco-hemicholinium No. 3 (AcHC-3) were replaced with carbon to form the ether, ketone and aliphatic analogs. Also, the thio and acetylthio-seco analogs of hemicholinium No. 3 (HC-3) were studied. When evaluated in the rabbit sciatic nerve-gastrocnemius muscular preparation all of the analogs caused neuromuscular blockades in two or three separate phases. The first phase of blockade caused by the ketone and thio analogs was rapid in onset and reversed by neostigmine. It was presumably competitive in type. The first phase of blockade caused by the ether and aliphatic analogs was increased by neostigmine and was concluded to be of the non-competitive type. All analogs caused a second phase of blockade that was reversed by choline and is typical of HC-3. A third blockade was found following the ether and ketone analogs. All of the analogs were more active as inhibitors of the true and pseudocholinesterases than was HC-3. All of the analogs were much less potent as inhibitors of acetylcholine synthesis than was AcHC-3. The implications of these findings are discussed.

Acetylcholine↗
PubMed1982

Uptake and metabolism of choline by the embryonic heart of the chick in vitro.

1. The uptake and metabolism of [14C]choline was investigated in isolated hearts from 4- to 14-day-old chick embryos. 2. A high-affinity uptake system of choline was present in hearts from all ages of embryos examined: the Km values were 9-11 muM, while the Vmax values ranged from 5 (14-day ventricles) to 77 (4-day atria) pmol choline/mg protein/min. 3. Hemicholinium-3, metabolic inhibitors, low temperature and low Na+ concentrations reduced the high-affinity uptake process. 4. The accumulated choline was converted mainly into phosphorylcholine in 4-day hearts, while the percentage of conversion into acetylcholine increased in older embryos.

Animals↗
PubMed1981

Mechanism of action of muscarine on the longitudinal muscle of the guinea-pig isolated ileum.

1 DL-Muscarine elicited a contraction of the ileal longitudinal muscle of the guinea-pig and the contraction was characterized by an after-response. 2 Physostigmine (20 x 10(8) M) potentiated the contraction of the longitudinal muscle elicited by DL-muscarine. 3 Hemicholinium-3 (HC-3) caused a rightward shift of the dose-response curve to DL-muscarine on the ileal longitudinal muscle of the guinea-pig ileum. 4 beta-Bungarotoxin (10 microgram/ml) significantly (P < 0.025) reduced the contraction elicited by DL-muscarine (2.5 X 10(-8) M) suggesting presynaptic release of acetylcholine as an indirect mechanism of action of DL-muscarine. 5 Morphine (1.0 x 10(-8) M) significantly (P < 0.05) reduced the contractions elicited by DL-muscarine (2.5 x 10(-8) M) further suggesting presynaptic release of acetylcholine as an indirect mechanism of action of DL-muscarine. 6 A subthreshold dose of DL-muscarine (2.0 x 10(-10) M) potentiated the effect of acetylcholine (2.5 x 10(-8) M) and the potentiation was blocked by beta-bungarotoxin.

Acetylcholine↗