Acetylcholine in mind: a neurotransmitter correlate of consciousness?
The cholinergic system is one of the most important modulatory neurotransmitter systems in the brain and controls activities that depend on selective attention, which are an essential component of conscious awareness. Psychopharmacological and pathological evidence supports the concept of a ‘cholinergic component’ of conscious awareness. Drugs that antagonize muscarinic receptors induce hallucinations and reduce the level of consciousness, while the nicotinic receptor is implicated as being involved in the mechanism of action of general (inhalational) anaesthetics. In degenerative diseases of the brain, alterations in consciousness are associated with regional deficits in the cholinergic system. In Alzheimer’s disease (AD), there is a loss of explicit (more than implicit) memory and hypoactivity of cholinergic projections to the hippocampus and cortex, while the visual hallucinations experienced by subjects with Dementia with Lewy bodies (DLB) are associated with reductions in neocortical ACh-related activity. In Parkinson’s disease, the additional loss of pedunculopontine cholinergic neurones, which control REM (rapid eye movement) sleep or dreaming, is likely to contribute to REM abnormalities, which also occur in DLB. Widespread basal-forebrain and rostral brainstem cholinergic pathways, which include converging projections to the thalamus, appear to be located strategically for generating and integrating conscious awareness. Alleviation of a range of cognitive and non-cognitive symptoms by drugs that modulate the cholinergic system, which are being developed for the treatment of AD and related disorders, could be caused by changes in consciousness.
Trends Neurosci. 1999 Jun;22(6):273-80
Dimethylaminoethanol (deanol) metabolism in rat brain and its effect on acetylcholine synthesis.
Specific methods utilizing combined gas chromatography mass spectrometry were used to measure the metabolism of [2H6] deanol and its effects on acetylcholine concentration in vitro and in vivo. In vitro [2H6]deanol was rapidly taken up by rat brain synaptosomes, but was neither methylated nor acetylated. [2H6]Deanol was a weak competitive inhibitor of the high affinity transport of [2H4]choline, thus reducing the synthesis of [2H4]acetylcholine. In vivo [2H6]deanol was present in the brain after i.p. or p.o. administration, but was not methylated or acetylated. Treatment of rats with [2H6]deanol significantly increased the concentration of choline in the plasma and brain but did not alter the concentration of acetylcholine in the brain. Treatment of rats with atropine (to stimulate acetylcholine turnover) or with hemicholinium-3 (to inhibit the high affinity transport of choline) did not reveal any effect of [2H6]deanol on acetylcholine synthesis in vivo. However, since [2H6]deanol did increase brain choline, it may prove therapeutically useful when the production of choline is reduced or when the utilization of choline for the synthesis of acetylcholine is impaired.
J Pharmacol Exp Ther. 1979 Dec;211(3):472-9
Deanol acetamidobenzoate inhibits the blood-brain barrier transport of choline.
Competition by deanol (dimethylaminoethanol) with choline for uptake from the bloodstream into the brain was demonstrated by simultaneous intracarotid administration of carbon 14-labeled choline with deanol (plus tritiated water and indium 113m, to calculate a brain uptake index) and by measuring the brain uptake of 14C-labeled choline mixed with sera from rats pretreated with deanol (300 or 500 mg/kg 8 or 30 minutes earlier). The inhibition constant for inhibition of choline uptake by deanol (159 micrograms) was actually lower than the Michaelis constant for choline itself (442 micrograms); hence, the affinity of the carrier mechanism for deanol is at least as great as it is for choline. Deanol administration also elevated blood choline levels; thus, the effect of the drug on brain choline (and acetylcholine) levels is the result of the increase it produces in blood choline and the suppression it causes in choline uptake. These findings may explain discrepant results from laboratories seeking increases in brain acetylcholine or clinical improvement in patients with tardive dyskinesia after deanol treatment.
Ann Neurol. 1978 Oct;4(4):302-6
Phosphatidylethanolamine and sarcolemmal damage during ischemia or metabolic inhibition of heart myocytes.
Phosphatidylethanolamine (PE) is a nonbilayer-preferring and fusogenic phospholipid. It is kept in the bilayer configuration by interaction with other phospholipids in biologic membranes. However, reorganization of the membrane phospholipids could lead to expression of the nonbilayer nature of PE and induce bilayer instability. During ischemia a transbilayer reorganization of sarcolemmal PE is observed, and results have been published that suggest a lateral phase separation in the inner sarcolemmal leaflet phospholipids. These reorganizations and the subsequent expression of the nonbilayer behavior of PE are proposed to form the basis for sarcolemma destabilization and destruction. Lowering the PE content of myocytes, especially of the sarcolemma, is then expected to attenuate myocyte damage after simulated ischemia or metabolic inhibition. Culturing neonatal rat heart myocytes in the presence of N,N-dimethylethanolamine resulted in the synthesis of the bilayer-preferring N,N-dimethyl-PE and a lowering of the ratio between nonbilayer- and bilayer-preferring phospholipids from 0.58 to 0.30. This change in phospholipid composition did not impair cell functioning but did result in a strong attenuation of cell damage on ischemia or metabolic inhibition. A good correlation between the nonbilayer-preferring phospholipid content and the degree of cell damage was obtained (r = 0.98). These results provide further evidence that physicochemical properties of the sarcolemmal phospholipids play a crucial role in the sarcolemmal disruption during prolonged ischemia and/or reperfusion.
Am J Physiol. 1995 Feb;268(2 Pt 2):H773-80
Pharmacological interventions against aging through the cell plasma membrane: a review of the experimental results obtained in animals and humans.
As was shown in a recent review by this author (Ann NY Acad Sci., 928: 187-199, 2001), oxyradicals cannot be considered only as harmful by-products of the oxidative metabolism, but living cells and organisms implicitly require their production. This idea is supported by numerous facts and arguments, the most important of which is that the complete inhibition of the oxyradical production by KCN (or by any block of respiration) kills the living organisms long before the energy reserves would be exhausted. This new theoretical approach not only helps our understanding of the normal functions of the living organisms, such as the basic memory mechanisms in the brain cells, but also helps in identifying the site-specific, radical-induced damaging mechanisms that represent the undesirable side effects of oxygen free radicals. First of all, these effects make the cell plasma membrane vulnerable and cause a series of intracellular functional disorders, as described by the membrane hypothesis of aging (MHA). The logical way for any antiaging intervention therefore should be to increase the available number of loosely bound electrons inside the plasma membrane that are easily accessible for OH(*) free radical scavenging. The present review summarizes the available knowledge regarding the theory of the use of membrane-related antiaging pharmaca, like centrophenoxine (CPH), tested in both animal experiments and human clinical trials. A modified, developed version of CPH coded as BCE-001 is also reported.
Ann N Y Acad Sci. 2002 Apr;959:308-20; discussion 463-5
Split face study on the cutaneous tensile effect of 2-dimethylaminoethanol (deanol) gel.
BACKGROUND/AIMS: Beyond subjective assessments, the effect of skin tensors is difficult to assess. The present 2-phase randomized double-blind split face study was designed to compare the effect of a gel containing 3% 2-dimethylaminoethanol (deanol, DMAE) with the same formulation without DMAE. METHODS: In a first pilot study, sensorial assessments and measures of the skin distension under suction were performed in eight volunteers. In a second study conducted in 30 volunteers, shear wave propagation was measured. RESULTS: Large interindividual variations precluded any significant finding in the first study. The DMAE formulation showed, however, a significant effect characterized by increased shear wave velocity in the direction where the mechanical anisotropy of skin showed looseness. CONCLUSION: The DMAE formulation under investigation increased skin firmness.
Skin Res Technol. 2002 Aug;8(3):164-7