Choline acetyltransferase and acetylcholinesterase abnormalities in senile dementia: Importance of biochemical measurements in human post-mortem brain specimens

Choline acetyltransferase and acetylcholinesterase have been assessed in human aging brains, in demented and agonal states. Choline acetyl transferase decreased during aging in normal brain when measured in the cerebral cortex. Choline acetyltransferase was also reduced in several other brain areas in patients with Alzheimer's disease and in one patient with Creutzfeldt-Jakob disease. Choline acetyltransferase was also reduced in bronchopneumonia and in some terminal conditions. On the contrary, the activity was not reduced in patients who died after cerebrovascular accidents. Acetylcholine esterase, although it followed the general trend of choline acetyltransferase, did not yield significant results.

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Sommario L'attività degli enzimi colina-acetil-transferasi e acetil-colina-esterasi è stata studiata nell'encefalo umano durante l'invecchiamento, nella demenza e nelle patologie terminali. La colina-acetil-transferasi è risultata decrescere con l'età nella corteccia frontale e significativamente diminuita in varie regioni dell'encefalo di soggetti affetti da malattia di Alzheimer e di Creutzfeldt Jacob. Corrispondentemente l'attività della colinoacetil-transferasi è risultata significativamente compromessa anche nelle patologie terminali quali il coma e la broncopolmonite terminale. In contrasto a questi risultati nell'encefalo di soggetti deceduti per accidenti cerebrovascolari la attività enzimatica è risultata normale. In oltre l'attività della acetilcolina-esterasi non ha mostrato significative variazioni in alcuno dei gruppi studiati.

     

Effect of central stimulants and depressants on mouse brain acetylcholine and choline levels

Brain concentrations of acetylcholine and choline were measured within 5–30 min after an i.p. injection of central stimulant or depressant drugs. The acetylcholine concentration in whole mouse brain of controls was 2.35 ± 0.06 μg/g wet wt. (16.1 nmol/g wet wt.) while the choline concentration was 6.52 ± 0.21 μg/g wet wt. (62.7 nmol/g). Physostigmine, 0.5 mg/kg, oxotremorine, 2 mg/kg free base, and haloperidol, 4 and 8 mg/kg, increased both acetylcholine and choline 20 min after administration. Pentobarbital, 55 mg/kg, and diazepam, 5–40 mg/kg, increased only acetylcholine without affecting choline. Atropine, 50 mg/kg, lowered acetylcholine without affecting choline. Haloperidol, 1 mg/kg, chlorpromazine, 10 mg/kg, reserpine, 2.5 mg/kg, 20 hr, desmethylimipramine, 20 mg/kg, and amphetamine, 7 and 15 mg/kg, had no effect on either acetylcholine or choline. No drug studied caused a simultaneous decrease in these two quaternary amines. The possible significance of these findings on the mechanism of action of these drugs is discussed.     

The effects of blepharorrhaphy induced depression of corneal cholinergic activity

Unilateral lid closure for 8 or more days had previously been shown to reduce rabbit corneal epithelial choline acetyltransferase (ChAc) activity without affecting lactic dehydrogenase activity or thymidine, uridine, leucine and alanine incorporation rates. In the present study, the reduction in ChAc activity was found to be associated with a similar reduction in acetylcholine (ACh) content, to a mean value of 16 and 17%, respectively, of control eye levels. However, on reopening the lids, ACh levels recovered much more rapidly, achieving a mean value 67% of control values (P > 0·05) in 48 hr while ChAc activity was only 23% of control eye levels at 48 hr and required more than 30 days to fully recover.Unilateral lid closure of 10 days was also associated with a small increase in corneal thickness, 0·46±0·09 mm vs. 0·41±0·04 mm (P < 0·05), and reductions in standing electrical potential, 5·5±7·8 mV vs. 13·2±15·2 mV (P < 0·05), and short circuit current, 2·7±2·6 μA vs. 4·9±3·5 μA (P < 0·05). On re-opening the lids, the short-circuit current recovered within 24 hr, the corneal thickness within 3 days and the resting potential within 4 days. Administration of ACh 10^?4m, pilocarpine 10^?4m, eserine 10^?6m or carbachol 10^?5m to the epithelial side of corneas mounted in chambers immediately after reopening the lids failed to elevate either the standing electrical potentials or short-circuit currents; a causal relationship between cholinergic activity and corneal electrical phenomena could not be demonstrated.     

Effects of food deprivation,discrimination experience and physostigmine on choline acetylase and acetylcholine esterase in the dorsal hippocampus and frontal cortex of rats

The effects of food deprivation and preliminary training treatments on choline acetylase and acetylcholine esterase activity in the dorsal hippocampus and frontal cortex of rats have been investigated. In addition, blood sugar and adrenal epinephrine levels were examined. The activity of choline acetylase and the levels of blood sugar and adrenal epinephrine were significantly altered during various stages of preliminary training but all values were comparable to pre-experimental levels before discrimination commenced. In addition, rats were injected physostigmine salicylate (0.25 mg/kg) or saline i.p. each day immediately after receiving three training trials on a food-motivated black-white task. The physostigmine injected rats were significantly better than the controls in rate learning.No differences were observed in choline acetylase activity in the dorsal hippocampus and frontal cortex in discriminating rats treated with physostigmine or saline. However, choline acetylase activity is lower in treated and control rats which did not discriminate at the end of the 14th session.     

Autoimmune neuromuscular disease induced by a preparation of choline acetyltransferase

An apparent fatal autoimmune disease was induced in guinea pigs by injection of a preparation of choline acetyltransferase in complete Freund's adjuvant. The animals probably died from respiratory failure based on the evidence from clinical, histological, and histochemical examination. At autopsy the pathogenic lesions were located at the neuromuscular junctions and near the nerves where choline actyltransferase was found. It is further proposed that this is a presynaptic autoimmune neuromuscular disease based on the finding of numerous target, as well as targetoid, fibers in muscle after histochemical staining. There was also denervation shown by electromyographic measurements in the form of positive sharp waves as well as fibrillation discharges.     

The role of hippocampal cholinergic mechanisms in the aquisition of a barpress response.

The role of hippocampal cholinergic mechanisms in learning a bar-press response reinforced with food was investigated. Firstly, an interstrain comparison showed that mice having a low choline acetyltransferase activity in the dorsal hippocampus were quicker to associate the barpress with reinforcement. Secondly, when the activity of this enzyme was reduced by a subseizure electrical stimulation of the hippocampus learning was accelerated. It is suggested that acetylcholine availability at the hippocampal synapses slowed the apparition of these learned responses.     

Brain vesicular acetylcholine transporter in human users of drugs of abuse

Limited animal data suggest that the dopaminergic neurotoxin methamphetamine is not toxic to brain (striatal) cholinergic neurons. However, we previously reported that activity of choline acetyltransferase (ChAT), the cholinergic marker synthetic enzyme, can be very low in brain of some human high-dose methamphetamine users. We measured, by quantitative immunoblotting, concentrations of a second cholinergic marker, the vesicular acetylcholine transporter (VAChT), considered to be a "stable" marker of cholinergic neurons, in autopsied brain (caudate, hippocampus) of chronic users of methamphetamine and, for comparison, in brain of users of cocaine, heroin, and matched controls. Western blot analyses showed normal levels of VAChT immunoreactivity in hippocampus of all drug user groups, whereas in the dopamine-rich caudate VAChT levels were selectively elevated (+48%) in the methamphetamine group, including the three high-dose methamphetamine users who had severely reduced ChAT activity. To the extent that cholinergic neuron integrity can be inferred from VAChT concentration, our data suggest that methamphetamine does not cause loss of striatal cholinergic neurons, but might damage/downregulate brain ChAT in some high-dose users. However, the finding of increased VAChT levels suggests that brain VAChT concentration might be subject to up- and downregulation as part of a compensatory process to maintain homeostasis of neuronal cholinergic activity. This possibility should be taken into account when utilizing VAChT as a neuroimaging outcome marker for cholinergic neuron number in human studies.     

Intravenously injected CDP-choline increases blood pressure and reverses hypotension in haemorrhagic shock: effect is mediated by central cholinergic activation

Intravenous (i.v.) administration of cytidine-5′-diphosphate choline (CDP-choline) (100, 250 and 500 mg/kg) increased blood pressure in normal rats and reversed hypotension in haemorrhagic shock. Choline (54 mg/kg; i.v.), at the dose equimolar to 250 mg/kg CDP-choline decreased blood pressure of rats in both conditions and caused the death of all hypotensive animals within 2-5 min. Equimolar dose of cytidine (124 mg/kg; i.v.) did not change cardiovascular parameters. Choline levels in plasma, lateral cerebral ventricle and hypothalamus increased after CDP-choline administration. Intracerebroventricular (i.c.v.) hemicholinium-3 pretreatment (20 μg), greatly attenuated the pressor effect of CDP-choline in both conditions. Atropine pretreatment (10 μg; i.c.v.) did not change the pressor effect of CDP-choline while mecamylamine (50 μg; i.c.v.) abolished the pressor response to drug. Besides, acetylcholine (1 μmol; i.c.v.) produced similar increases in blood pressure in normal and hypotensive conditions to that observed in CDP-choline given rats. CDP-choline (250 mg/kg; i.v.) increased plasma catecholamines and vasopressin levels but not plasma renin activity. Pretreatment of rats with either prazosin (0.5 mg/kg; i.v.) or vasopressin V₁ receptor antagonist, [β-mercapto,β,β-cyclopentamethylenepropionyl¹,O-Me-Tyr²-Arg⁸]vasopressin (10 μg/kg; i.v.), attenuated the pressor response to CDP-choline while simultaneous administration of these antagonists before CDP-choline injection completely blocked the pressor effect. Results show that i.v. CDP-choline increases blood pressure and reverses hypotension in haemorrhagic shock. Activation of central nicotinic cholinergic mechanisms by the increases in plasma and brain choline concentrations appears to be involved in the pressor effect of this drug. Moreover, the increases in plasma catecholamines and vasopressin levels mediate these effects.     

Effects of ageing and long-term hormone replacement on cholinergic neurones in the medial septum and nucleus basalis magnocellularis of ovariectomized rats

Ovariectomized aged rats, some of which received long-term hormone replacement with oestrogen or oestrogen plus progesterone, were evaluated for the number and size of basal forebrain cholinergic neurones, as well as relative levels of choline acetyltransferase (ChAT) and trkA mRNA, in order to determine whether effects on basal forebrain cholinergic cell survival and function correspond with differences in cognitive performance previously described. The results show that ageing combined with long-term loss of ovarian function produced substantial reductions in the levels of ChAT and trkA mRNA in the medial septum and nucleus basalis magnocellularis, relative to much younger ovariectomized controls. In contrast, no significant effects on the number or size of the cholinergic cells were detected, indicating that loss of ovarian function does not cause a loss of cholinergic neurones with age. Long-term hormone replacement had no apparent effect on the number of ChAT-positive neurones detected, and did not prevent the reductions in ChAT and trkA mRNA associated with ovariectomy and ageing. Collectively, the data suggest that ageing combined with long-term loss of ovarian function has a severe negative impact on basal forebrain cholinergic function, but not on cholinergic cell survival per se.