Effects of diethylcholine in two animal models of Parkinsonism tremors

Relative levels of cytoprotection produced by analogs of choline and the role of alpha7-nicotinic acetylcholine receptors

Several analogs of the acetylcholine precursor molecule choline have been widely studied as potential false cholinergic neurotransmitters with the therapeutic goal of using them to limit cholinergic neurotransmission. More recently, choline itself has been shown to act as a full, if low potency, agonist at the alpha7 subtype of the nicotinic acetylcholine receptor. This pharmacological property has been associated with the ability of nicotine and other related alpha7 receptor agonists to offer neuroprotection in a variety of experimental models. We confirm here that choline offers a significant degree of protection against the cytotoxicity induced by growth factor deprivation in differentiated PC-12 cells. Choline-induced cytoprotection ( approximately 1 mM) was about 3 orders of magnitude less potent than that for nicotine (EC(50) = 0.7 microM). Choline also exhibited only about 40% of the full cytoprotective effect of nicotine. Ethyl substitution for choline's N-methyl groups did not result in a significant improvement over choline as a cytoprotective agent. In contrast, pyrrolidinecholine exhibited much greater potency (EC(50) = 20 microM) and increased efficacy (about 55% of nicotine's effect) than choline. Like choline and nicotine, pyrrolidinecholine fully displaced [(125)I]alpha-bungarotoxin binding (K(i) = 33 microM) and chronic exposure to the analog increased cell surface binding sites. The cytoprotective effects of the analog were completely inhibited by coincubation with methyllycaconitine (MLA), a selective alpha7-nicotinic receptor antagonist. These findings are consistent with the possibility that the choline structure may serve as a template for the development of novel agents with both alpha7-nicotinic agonist activity and potential neuroprotective ability, as many of these compounds, including pyrrolidinecholine, are transported along with choline into the central nervous system.

Global in vivo replacement of choline by N-aminodeanol. Testing a hypothesis about progressive degenerative dementia: II. Physiological and behavioral effects

We have examined the progressive effects of replacement of dietary choline with NADe for a period of 120 days on a broad spectrum of behavioral and physiological functions known to involve the cholinergic system. The magnitudes of these effects tended to increase with time on the NADe diet, but those related to learning and memory were largely confined to the 60-120-day period. Neurochemical effects were concomitant with the replacement of Ch by NADe, being consistent with a hypocholinergic state as found in such progressive degenerative dementias as Alzheimer's disease. As cholinergic functioning was progressively impaired, basic physiological ("vegetative") processes appeared not to be affected. Apparently the rate at which the hypofunctional state developed was sufficiently slow for adjustments to occur, allowing the animal to adapt at a survival level to neurochemical changes. More complex behavioral functions were affected progressively, cognitive processes (e.g., learning and memory) being most sensitive and showing the least adaptability. We propose that the syndrome generated by NADe replacement of Ch represents an experimental model of progressive degenerative dementia.

Precursors of cholinergic false transmitters: central effects on blood pressure and direct interactions with cholinergic receptors

The purpose of this study was to determine whether a series of analogs of choline depress central cholinergic function in a manner consistent with the activity of their acetylated derivatives. Intracerebroventricular infusion of monoethylcholine (MECh), diethylcholine (DECh) and triethylcholine (TECh) inhibited the pressor response of unanesthetized rats to the subsequent intravenous injection of physostigmine (a well-characterized muscarinic response). The order of blocking potency was TECh greater than DECh greater than MECh greater than choline, directly opposite to the order of potency for elicitation of a central pressor response by their associated acetylated derivative (i.e. ACh greater than AMECh greater than ADECh = ATECh; Aronstam, Marshall and Buccafusco, 1988). In contrast, there was little selectivity between the analogs of choline in terms of their affinity for muscarinic receptors in the brainstem or cortex; the Ki's for inhibition of the binding of [3H]quinuclidinyl benzilate ranged from 0.33 to 0.95 mM). In terms of their affinity for nicotinic receptors (from the electric organ of Torpedo californica) the following order of potency was obtained: choline greater than MECh = DECh greater than TECh. Choline and MEC stimulated the binding of [3H]phencyclidine to the nicotinic ion channel (EC50's = 79 and 115 microM, respectively). At greater concentrations, all of the analogs inhibited ligand binding to the channel (Ki's from 0.2 to 10 mM), with the following order of potency: TECh greater than DECh greater than MECh greater than choline. These findings suggest that the inhibitory actions of these analogs of choline are related to their synthesis and release as false cholinergic neurotransmitters.

Effects of chronic dietary administration of the cholinergic false precursor N-amino-N,N-dimethylaminoethanol on behavior and cholinergic parameters in rats

The choline analog, N-amino-N,N-dimethylaminoethanol (NADe), was fed ad libitum (chloride salt; 0.5%) to weanling rats in a low choline, low methionine synthetic diet. Control rats were fed choline chloride (0.5%) in place of NADe. Initial observation and behavioral screen tests of grasp strength, startle reflex, righting reflex, analgesia (hot plate test) and body temperature did not reveal any toxic effects caused by NADe, although both experimental and control groups gained weight more slowly than rats fed standard lab chow. After 25 days on the diet, the performance of rats fed NADe in a one-trial passive avoidance test was significantly impaired compared to control rats. There was no difference between experimental and control rats in sensitivity to foot shock or in activity monitored in a closed field. A subjective, 6-component behavioral rating scale indicated rats fed NADe were resistant to handling but not aggressive. These behavioral results were similar in two separate feeding experiments using deuterium-labeled and unlabeled NADe. The twitch response of isolated rat phrenic nerve-diaphragms during stimulation did not show any impairment of neuromuscular function in rats fed NADe. Receptor binding experiments indicated there were no differences between experimental and control rats in tritiated quinuclidinyl benzilate [( 3H]QNB) binding capacity in cortex, heart and ileum. Competitive [3H]QNB binding with carbachol indicated there was no difference in the IC50's measured in cortex homogenates. Acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) activities in cortex were similar in experimental and control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic actions of false neurotransmitters: acetyldiethylcholine

Acetyldiethylcholine (AcDECh), a false transmitter at cholinergic synapses, binds to central muscarinic receptors with 14-fold lower affinity than acetylcholine (AcCh). The properties of this binding, including the limited extent of regional specificity and binding activation by N-ethylmaleimide, are those associated with weak agonists and antagonists. Intracerebroventricular injection of AcDECh or AcCh produces an increase in arterial blood pressure which is blocked by prior administration of atropine (10 nmol). While AcDECh is 17-fold less potent tha AcCh in producing the pressor response, the maximum pressure changes and time courses are comparable. AcDECh also binds to nicotinic receptors of Torpedo electric organs thereby inducing conformational changes in the receptor-ion channel complex that are associated with postsynaptic activation. In these nicotinic actions, however, AcDECh is 320-fold less active than AcCh.