Decline In Choline Acetyltransferase Activity Research Articles

Precursor form of brain‐derived neurotrophic factor and mature brain‐derived neurotrophic factor are decreased in the pre‐clinical stages of Alzheimer's disease

Brain-derived neurotrophic factor (BDNF) is critical for the function and survival of neurons that degenerate in the late stage of Alzheimer's disease (AD). There are two forms of BDNF, the BDNF precursor (proBDNF) and mature BDNF, in human brain. Previous studies have shown that BDNF mRNA and protein, including proBDNF, are dramatically decreased in end-stage AD brain. To determine whether this BDNF decrease is an early or late event during the progression of cognitive decline, we used western blotting to measure the relative amounts of BDNF proteins in the parietal cortex of subjects clinically classified with no cognitive impairment (NCI), mild cognitive impairment (MCI) or mild to moderate AD. We found that the amount of proBDNF decreased 21 and 30% in MCI and AD groups, respectively, as compared with NCI, consistent with our previous results of a 40% decrease in end-stage AD. Mature BDNF was reduced 34 and 62% in MCI and AD groups, respectively. Thus, the decrease in mature BDNF and proBDNF precedes the decline in choline acetyltransferase activity which occurs later in AD. Both proBDNF and mature BDNF levels were positively correlated with cognitive measures such as the Global Cognitive Score and the Mini Mental State Examination score. These results demonstrate that the reduction of both forms of BDNF occurs early in the course of AD and correlates with loss of cognitive function, suggesting that proBDNF and BDNF play a role in synaptic loss and cellular dysfunction underlying cognitive impairment in AD.

Cognitive deficit associated with cholinergic and nerve growth factor down-regulation in experimental allergic encephalomyelitis in rats

Clinical symptoms in multiple sclerosis include cognitive dysfunction. Difficulties in learning and remembering new information represent the most common cognitive deficit and are associated with a general and progressive brain pathology. Possible pathogenetic mechanisms for neuronal damage such as neuroprotective strategies are under active investigation also in experimental allergic encephalomyelitis, the most widely used experimental model for multiple sclerosis. In this paper we demonstrate that a selective deficit in learning and memory performance, as investigated by the Morris water maze test, is a consistent feature in rat encephalomyelitis, which correlates with a decline in choline acetyltransferase activity and nerve growth factor mRNA level in cerebral cortex, hippocampus, and basal forebrain. Treatment aimed to restore acetylcholine content through chronic administration of selective acetylcholinesterase inhibitors (rivastigmine and donepezil) restores cognitive performance, choline acetyltransferase activity, and nerve growth factor mRNA expression.

Choline acetyltransferase activity and vesamicol binding in Rett syndrome and in rats with nucleus basalis lesions.

The decline in choline acetyltransferase activity has been identified previously within the brains of patients with Rett syndrome and Alzheimer's disease. The level of [3H]vesamicol binding to a terminal vesicular acetylcholine transporter is inversely related to the decline in cortical choline acetyltransferase activity in Alzheimer's disease, which may be due to compensatory processes within surviving cholinergic terminals. In order to investigate whether similar cholinergic compensatory processes are present in the Rett syndrome brain and are altered by normal aging, we investigated the density of cholinergic vesicular transporters in (i) the brains of Rett syndrome patients, and (ii) young and old rats with experimentally-induced cholinergic cell loss. In Rett syndrome, a significant decline in choline acetyltransferase activity within the putamen and thalamus was directly correlated with a decline in [3H]vesamicol binding. In both young and old rats, basal forebrain lesions decreased cortical choline acetyltransferase activity significantly, while [3H]vesamicol binding was unchanged. In contrast to young and old lesioned rats and patients with Alzheimer's disease, cholinergic cells in the brains of patients with Rett syndrome do not compensate for the loss of cholinergic cells by increasing acetylcholine vesicular storage.

Neuron-enriched cultures derived from spinal cord of 10-day-old chick embryos: Influence of neuropeptides on neuronal survival, proliferation and cholinergic expression

The developmental regulation of cell proliferation, survival and cholinergic expression by growth hormone-releasing hormone (GHRH) and somatostatin (SRIF) was investigated in neuronenriched cultures derived from 10-day-old embryonic chick spinal cord. In this study, 3H-thymidine incorporation into DNA was assessed, using two different applications, in order to determine both cellular proliferation and survival. The rate of neuroblast proliferation in both control and neuropeptide-treated cultures increased or remained the same up to day 6. However, in neuropeptide-treated cultures the magnitude of cell proliferation remained at levels higher than those observed in controls through day 6 and was most significant in SRIF-treated cultures at C4. In all groups, proliferation markedly declined by day 8. Survival of neuronal cells labelled at C4 remained high up to day 12 in all three groups, then drastically declined by day 17. Neuronal survival in the neuropeptide-treated cultures was also higher than in controls. Cholinergic expression, as assessed by activity of choline acetyltransferase (ChAT), responded differentially to neuropeptide treatment. Cultures treated with GHRH (100 nM) exhibited a long term significant enhancement in ChAT activity throughout the culture period, whereas those treated with SRIF (50 nM) expressed a transient decline in ChAT activity. Videometric analysis showed that both neuropeptides enhanced neuronal aggregation, neuritic arborization and neuritic length. These findings lead us to suggest that GHRH and SRIF may provide neurotrophic signals important not only for neuronal proliferation and survival but also for cholinergic neuronal expression. Furthermore, we propose that GHRH possesses specific cholinotrophic properties, whereas SRIF may act as a general neurotrophic factor.

Effect of ageing on response to nicotine in rabbit bronchial preparation

1. 1. Effect of ageing on the response to nicotine was tested in the bronchial muscle preparations from 5, 13, 100 and 125 week-old rabbits. The pD 2 value (potency) of nicotine significantly increased in the preparation from the 125 week-old rabbits. No age-related change was found in the pD 2 value of carbamylcholine or pA 2 value of atropine. 2. 2. No age-related change in characteristics of nicotine receptors. Choline acetyltransferase activity, the amount of acetylcholine released by nicotine and acetylcholineesterase activity decreased in the preparations from the 125 week-old rabbits. 3. 3. Decrease in the pD 2 value of nicotine in the preparation from the older rabbit is due to a decline in choline acetyltransferase activity followed by a reduction in the acetylcholine released, and not to a change in characteristics of nicotine receptors. 4. 4. These results also suggest that enzymes may be influenced more easily with age than drug receptors.

Neurotransmitter plasticity of cultured sympathetic neurones. Are the effects of muscle-conditioned medium reversible?

ABSTRACT Muscle-conditioned medium (CM) induces choline acetyltransferase (CAT) activity in primary cultures of new-born rat sympathetic neurones and depresses the development of tyrosine hydroxylase (TOH). By following these two enzymes, we have determined whether (1) the effects of CM are reversible and (2) the neurones progressively lose their sensitivity to CM with time in culture. When neurones were cultured in the presence of 50 % CM (CM+ medium), TOH activity developed slowly but CAT activity developed at a high rate. When the cultures were then switched to unconditioned medium (CM− medium), CAT activity remained elevated and continued to develop at higher rate than in cultures that were never exposed to CM. On the other hand, the switch to CM− medium was accompanied by a transition from a low to a high rate of TOH development. CAT induction by CM was thus essentially irreversible, whereas the impairment of TOH development was fully reversible. Conversely, we studied the effects of altering CM− to CM+ medium at progressively later culture days. CAT remained fully inducible for at least 2 to 3 weeks. On the other hand, TOH activity, which initially developed rapidly in CM− medium, first decreased to low levels after a switch to CM+ medium and then increased again, but at a slower rate. Neuronal depolarization by elevated K+ and exposure to CM have mirror-image, and antagonistic, effects on both CAT and TOH developments (Raynaud et al. 1987a). Walicke, Campenot & Patterson (1977) showed that a previous depolarization reduced the induction of cholinergic traits by a subsequent exposure to CM. We found that (1) such a depolarization only delayed the induction of CAT by several days and did not prevent the transition to a state of low TOH expression caused by CM and (2) an exposure of the cultures to elevated K+ after exposure to CM did not cause a decline in CAT activity. These data thus suggest that a state of high TOH expression can superimpose on a previously induced state of elevated CAT expression, but that the induction of CAT caused by a delayed exposure to CM is accompanied by a transition from a high to a lower state of TOH expression. In addition, neuronal depolarization does not stabilize the noradrenergic phenotype in a permanent manner and can not reverse cholinergic expression of sympathetic neurones to a purely noradrenergic phenotype.

Experimental febrile convulsions in the developing rat: effects on the cholinergic system.

The effects of hyperthermia-induced convulsions (HCs) on nicotinic and muscarinic receptor sites, choline acetyltransferase (ChAT), and acetylcholinesterase (AChE) in the rat were investigated. A series of 10 convulsions, evoked between 5 and 16 days of age, had marked effects on the development of the cholinergic system in the cerebellum and frontal cortex, but not in the hippocampus or hypothalamus. The concentration of muscarinic receptor sites in the cerebellum of the HC group was similar to that in controls at 2 days, greater than in controls at 8 days, but less than in controls at 55 days after the last convulsion. ChAT and AChE activities were increased at 2 days, similar at 8 days, and less than those in controls at 55 days. A decrease in muscarinic receptors and a decline in ChAT activity in the frontal cortex of the HC group were observed at 55 days after the last convulsion. The concentration of nicotinic receptor sites did not distinguish HC from control groups. A simple relationship between the experimental febrile convulsion and the cholinergic system was not found. The greatest effects were noted at 55 days after the last HC, which suggests that these may reflect secondary and possibly transsynaptic influences of the convulsion on cholinergic activity.

The influence of neurite-inducing agents on cholinergic activity in human neuroblastoma cells

Various factors capable of inducing morphological differentiation of neuroblastoma cells were studied to determine whether they may also specifically regulate cholinergic function in human cholinergic neuroblastoma cells MC-IXC. Choline acetyltransferase (CAT) activity was monitored to reflect cholinergic function while Mg2+ ATPase activity was monitored to reflect effects which are not related specifically to neuronal function. Among the agents, dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), D-α-tocopherol, ascorbic acid and dibutyryl-cAMP, only low doses of DMSO were found to selectively inhibit CAT activity while Mg2+ ATPase activity along with population growth remained unaffected. Of the three chemically related organic compounds tested (DMSO, DMF, DMA), DMSO was the least potent with regard to inhibition of population growth and Mg2+ ATPase activity while DMA was the most potent inhibitor. Sodium butyrate caused a decline in CAT activity while retinoic acid induced an enhancement. The combination of sodium butyrate with retinoic acid caused an enhancement of CAT activity similar in magnitude to that observed with retinoic acid alone. Lastly, CAT activity was found to be independent of population density unlike that in different neuroblastoma cell lines.8,12,19

Selective presynaptic cholinergic neurotoxicity following intrahippocampal AF64A injection in rats.

Compound AF64A, ethylcholine mustard aziridinium ion (0.4-8 nmol) was stereotaxically administered into rat dorsal hippocampus, and neurochemical changes were determined 5 days later. AF64A treatment, over an almost 10-fold dose range, resulted in a significant (up to 70%) decline in choline acetyltransferase activity. In the same tissue samples, Na+-dependent choline transport activity was also lowered, with most decreases ranging between 10 and 50% of controls; however, there was no significant correlation (r = 0.39) between these two parameters. Acetylcholinesterase activity was not affected by AF64A treatment when assayed by either histochemical or enzymatic methods. AF64A reduced acetylcholine levels by 43%, but did not alter norepinephrine content or serotonin uptake. These results demonstrate that AF64A can induce a specific, long-term reduction of cholinergic presynaptic biochemical markers in rat hippocampus. Thus, AF64A can serve as a useful new tool to study the cholinergic system and as an important agent to help develop animal models representing disorders of central cholinergic hypofunction.

Evidence for an agonist independent down regulation of hippocampal muscarinic receptors in kindling

Kindling induces a decline of hippocampal muscarinic cholinergic receptors. To test the hypthesis that the decline was mediated by the agonist, acetylcholine, adult male Sprague--Dawley rats were lesioned in the medial septum prior to kindling. Despite the marked destruction of presynaptic cholinergic terminals in the hippocampus, amygdala kindling proceeded normally and the hippocampal muscarinic receptor decline was not blocked. A small but significant decline in choline acetyltransferase activity was demonstrated in non-lesioned kindled rats. It is proposed that the kindling induced decline of hippocampal muscarinic receptors is mediated by repeated neuronal depolarization.

EFFECTS OF DEXAMETHASONE ON NEUROTRANSMITTER ENZYMES IN CHROMAFFIN TISSUE OF THE NEWBORN RAT

—Dexamethasone administration to newborn rats resulted in an increase in phenylethanolamine N-methyltransferase activity in superior cervical ganglia. The same treatment resulted in a decrease in tyrosine hydroxylase and choline acetyltransferase activities. The decline in choline acetyltransferase activity after dexamethasone treatment was only seen when the drug was given before 5 days of age. When dexamethasone was given to pregnant rats it caused an age-dependent decrease in choline acetyltransferase in the adrenals, superior cervical ganglia and para-aortic chromaffin tissue of the offspring. These results suggest that dexamethasone administration may delay the development of the preganglionic neurons of sympathetic ganglia. This in turn would delay the development of tyrosine hydroxylase but not phenylethanolamine N-methyltransferase.