Acetylcholinesterase induces long-term potentiation in CA1 pyramidal cells by a mechanism dependent on metabotropic glutamate receptors

Acetylcholinesterase (AChE) has additional functions within the central nervous system that are unrelated to cholinergic transmission. In the cerebellar cortex AChE has been shown to potentiate synaptic responses evoked by excitatory amino acids. Because AChE is also secreted from the terminal regions of cholinergic nerves within the hippocampus, this study investigates the actions of AChE on synaptic transmission in guinea pig hippocampal slices. Application of AChE produced a long-lasting potentiation of both the field epsp and the resulting population spike evoked by stimulation of the Schaffer/commissural-CA1 pathway. This effect was independent of any cholinergic receptor stimulation since it persisted in the presence of the cholinergic antagonists atropine and mecamylamine. Furthermore, the effect was not mimicked by butyrylcholinesterase despite its cholinolytic activity. However, the effect of AChE was dependent on metabotropic glutamate receptor stimulation since it was prevented by the metabotropic receptor antagonist (+/-)-alpha-methyl-4-carboxyphenylglycine. Perfusion with AChE therefore induces a long-lasting potentiation of hippocampal synaptic transmission which is reminiscent of the classical LTP produced by tetanic stimulation. Consequently the secreted protein could play an important role in the molecular mechanisms of learning and memory in vertebrates.

Secreted acetylcholinesterase: non-classical aspects of a classical enzyme

Recent evidence suggests that termination of cholinergic transmission is just one of the many ways in which acetylcholinesterase (AChE) could influence neuronal function. Neuronal AChE can be secreted from several brain regions, while purified AChE possesses several properties (in addition to its cholinesterase activity) that can affect neuronal function, including the abilities to influence certain membrane conductances, enhance excitatory amino acid transmission and hydrolyse peptides. Loss of AChE and its non-classical actions would have a profound effect on brain function in neurodegenerative diseases such as Alzheimer's disease where there is widespread loss of AChE-containing neurons.

Acetylcholinesterase and butyrylcholinesterase activities in cerebrospinal fluid from different levels of the neuraxis of patients with dementia of the Alzheimer type

Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities of cerebrospinal fluid (CSF) collected post mortem from the lateral ventricles, cisterna magna, and lumbar regions of the spinal cord of patients with a histologically confirmed diagnosis of Alzheimer's disease were compared with those of normal, age matched control patients, patients with dementia of non-Alzheimer aetiology, and patients with non-dementing neurological disorders. The AChE activity of the ventricular CSF of patients with Alzheimer's disease was 48% lower (p < 0.005) than that of age matched controls or patients with other types of dementia, and the AChE activity of CSF sampled from the basal cistern was 40% lower (p < 0.005) in patients with Alzheimer's disease. There were no significant differences between the AChE activity in Alzheimer's disease and control patients in CSF collected from the lumbar cistern. AChE activity was lower in CSF sampled from the basal and lumbar cistern of patients with dementia of non-Alzheimer aetiology, while ventricular activity was in the normal range. BuChE activity in ventricular CSF of Alzheimer's disease patients was 41% lower than normal (p < 0.05) and in the normal range in all other samples. The secretion of AChE from forebrain and hindbrain regions is reduced in Alzheimer's disease patients, leading to decreased ventricular and cisternal levels of the enzyme. Secretion from more caudal regions of the central nervous system seems to be unaffected by the disease, resulting in AChE in the lumbar CSF of patients with Alzheimer's disease being in the control range. Such altered secretion of AChE in the brain could have profound implications not only for cholinergic transmission in these patients but also for the proposed noncholinergic modulatory actions of AChE.

Presence of a soluble form of acetylcholinesterase in human ocular fluids

Samples of ocular fluid obtained from normal persons at necropsy and during eye surgery have been assayed for the presence of acetylcholinesterase. Measurable levels could be detected in all samples examined, but levels of acetylcholinesterase in vitreous humour were consistently higher than those in aqueous humour, indicating a possible retinal origin. Polyacrylamide gel electrophoresis revealed that the enzyme of ocular fluid had the same mobility as that of acetylcholinesterase from cerebrospinal fluid. It is probable that acetylcholinesterase is secreted from neuronal structures in the retina into the ocular fluid in an analogous manner to the secretion of acetylcholinesterase from brain neurones into cerebrospinal fluid.

Acetylcholinesterase activity in regions of mouse brain following acute and chronic treatment with a benzodiazepine inverse agonist

1. Chronic administration of the benzodiazepine inverse agonist FG 7142 has previously been shown to induce seizure activity in mice. In the present study we have investigated the effects of acute and chronic treatment with FG 7142 in mice on the levels of acetylcholinesterase activity in cortex, hippocampus, midbrain and striatum. We have also investigated the effects of acute and chronic stress in the form of handling (vehicle-injection) on acetylcholinesterase levels. 2. A single dose of FG 7142 produced a marked elevation of total acetylcholinesterase activities in the hippocampus and midbrain when compared with vehicle-injected control levels, but the levels were not different from those in unhandled animals. 3. Acute stress, in the form of vehicle-injection produced decreases in cortical and hippocampal soluble acetylcholinesterase activity but FG 7142 had no effect upon these stress-induced changes. 4. Total cortical and hippocampal acetylcholinesterase activities were increased by 56% and 16% respectively in the chronic FG 7142-treated mice that exhibited seizure activity (compared with vehicle-injected controls). 5. Soluble acetylcholinesterase activity in the midbrain was decreased to 82% of control levels only in animals that had undergone FG 7142-induced kindling. Smaller or no changes in acetylcholinesterase activity in the midbrain were observed in chronically FG 7142-treated animals that exhibited no seizure activity. 6. Mice that did not demonstrate seizure activity in response to chronic FG 7142 treatment showed alterations in the soluble acetylcholinesterase activities of the hippocampus and midbrain. 7. It is concluded that chronic treatment with the benzodiazepine inverse agonist FG 7142 produces alterations in the acetylcholinesterase activities of various brain regions, in a manner related to the kindling that can be produced by this treatment. 8. Chronic mild stress, in the form of repeated handling (vehicle injection), induced changes in brain activity with decreases in total activity occurring in the cortex and hippocampus, and an increase in soluble acetylcholinesterase activity occurring in the midbrain. 9. All these stress-induced changes appeared to be prevented by administration of FG 7142 at the time of the stress. It would appear therefore that FG 7142 can prevent the effects of chronic stress on brain acetylcholinesterase activity.

Secretion of acetylcholinesterase and butyrylcholinesterase from the guinea-pig isolated ileum

1. Strips of longitudinal muscle from guinea-pig ileum, retaining Auerbach's plexus, were superfused with oxygenated Krebs solution. Addition of 50 mM KCl led to a pronounced Ca2+-dependent increase in the activities of both acetylcholinesterase and non-specific cholinesterase (butyrylcholinesterase) in the perfusate but with no change in lactate dehydrogenase activity. 2. No release of acetylcholinesterase, either spontaneous or K+-evoked was observed in tissue freed of the nerve plexus, although release of butyrylcholinesterase still occurred. 3. Carbachol induced a marked Ca2+-dependent increase in the release of acetylcholinesterase but had no effect on the release of butyrylcholinesterase or lactate dehydrogenase. This carbachol-evoked increase in acetylcholinesterase release was blocked by hexamethonium but not by atropine. 4. Four readily soluble molecular forms of acetylcholinesterase and three soluble molecular forms of butyrylcholinesterase were present in innervated longitudinal muscle strips, but insignificant amounts of acetylcholinesterase were detected in denervated strips of muscle. Only one of the four molecular forms of acetylcholinesterase was recovered in the perfusates. 5. It is concluded that acetylcholinesterase is secreted from the nerves of Auerbach's plexus in response to depolarizing stimuli or to nicotinic cholinergic stimulation, while butyrylcholinesterase is secreted from non-neural elements, possibly the longitudinal muscle cells, of guinea-pig ileum in response to a depolarizing stimulus.

Release of acetylcholinesterase from the guinea-pig cerebellum in vivo

In the cerebellum there is scant evidence for cholinergic transmission but a large amount of acetylcholinesterase. Although it exists most commonly in a membrane-bound form, the release of a soluble form of this enzyme, within the cerebrum, has indicated that it may have a novel non-cholinergic role. In order to understand why the cerebellum is rich in acetylcholinesterase, the first step has been to investigate the possibility of its release in this structure. Following unilateral application of a depolarizing concentration of potassium ions, there was a large, sustained, calcium-dependent increase in release of acetylcholinesterase, specifically in the local cerebellar cortex; a marked enhancement of acetylcholinesterase release also occurred in the contralateral cerebellum, suggesting that the phenomenon reflected polysynaptic neuronal events. Indeed, systemic administration of harmaline, which modifies activity in certain cerebellar afferent pathways, induced a significant increase in acetylcholinesterase release in the cerebellar cortex. Local administration of the cholinomimetic, carbachol, had no effect. It is concluded that acetylcholinesterase is released from cerebellar neurons in association with physiological events, yet unrelated to cholinergic transmission.

Cholinesterase activities in cerebrospinal fluid of patients with senile dementia of Alzheimer type

Acetylcholinesterase (AChE) and nonspecific cholinesterase (nsChE) activities of lumbar ceresbrospinal fluid (CSF) from patients with a clinical or histological diagnosis of Alzheimer's disease have been compared with those of normal age-matched control patients and patients with dementia of non-Alzheimer aetiology. No significant differences in the AChE activity of lumbar CSF from histologically and clinically diagnosed Alzheimer's disease patients and normal age-matched controls were found, although they could be distinguished from controls and other dements by their lower lumbar CSF levels of nsChE activity and by their elevated ratio of AChE/nsChE. A lower level of AChE activity was observed in the lumbar CSF of patients with dementia of non-Alzheimer aetiology. The AChE and nsChE activities of ventricular CSF obtained at postmortem have also been examined. The AChE activity of the ventricular CSF of patients with histologically confirmed Alzheimer's disease was 66% lower than that of age-matched controls; these patients could also be distinguished from normals by their lower levels of nsChE and by the elevated ratio of AChE/nsChE activities. A molecular defect in the AChE in the ventricular CSF of Alzheimer patients is indicated by the finding that the enzyme failed to show inhibition by high concentrations of substrate. The lower level of AChE in ventricular CSF may reflect the changes in this enzyme in forebrain regions of Alzheimer patients. Although it is at present not possible to correlate the lower levels of nsChE found in CSF with any known brain pathology, the significantly altered ratio of AChE/nsChE activities in lumbar CSF may possibly form the basis for a diagnostic test of Alzheimer type dementia.

Acetylcholinesterase activity rises in rat cerebrospinal fluid post-ictally; effect of a substantia nigra lesion on this rise and on seizure threshold

The activity of acetylcholinesterase (AChE) in the cerebrospinal fluid (CSF) of rats increased by 53% following an electroconvulsive shock (ECS) while non-specific cholinesterase (nsChE) activity was unchanged. A flurothyl-induced seizure failed to elicit a change in the AChE activity of CSF. A bilateral lesion of the substantia nigra pars reticulata abolished the rise in AChE activity in the CSF but did not diminish the increase of seizure threshold which follows a convulsion. These data suggest that AChE is released from the substantia nigra following a seizure but indicate that the change is not associated with the rise in seizure threshold which occurs.

Acetylcholinesterase activity in regions of rat brain following repeated administration of electroconvulsive shock

It has previously been shown that 30 min after administration of a single elec troconvulsive shock (ECS) to rats there is a marked decrease in both soluble and total acetylcholinesterase (AChE) activity in the midbrain and hippocampus. In the current study it has been shown that AChE activity is unchanged in these regions (apart from a small rise in soluble AChE in the hippocampus) 30 min after the final ECS of a series of 10 (once daily for 10 days). Twenty-four hours after the last ECS there was a significant increase in total and membrane bound AChE activity in the striatum but not hippocampus, midbrain, cortex and amygdala. This change in the striatum may be associated with the change in GABA synthesis which has been shown to also occur in this region at the same time.

6-Hydroxydopamine-induced turning behaviour in the rat: the significance of acetylcholinesterase in cerebrospinal fluid

In the substantia nigra, acetylcholinesterase may have a novel function related not to cholinergic transmission, but to the homeostasis of dopaminergic nigrostriatal neurones. The initial aim of this study was thus to see whether, in the rat, release of the enzyme into cerebrospinal fluid would reflect turning behaviour following unilateral 6-hydroxydopamine lesions of varying severity. It was found that acetylcholinesterase levels, lower than those in the cerebrospinal fluid of control rats, were accompanied by marginal circling behaviour and a small loss of striatal dopamine: on the other hand, elevated acetylcholinesterase activity was observed in the cerebrospinal fluid of rats displaying vigorous turning behaviour and with large depletion of striatal dopamine. It has already been demonstrated that exogenous acetylcholinesterase, applied locally to nigral neurones, has both electrophysiological and behavioural effects reminiscent of dopamine agonists. Hence it is possible that exogenous acetylcholinesterase could modify turning behaviour resulting from unilateral striatal dopamine depletion. Purified acetylcholinesterase, administered by cisternal puncture, attenuated circling behaviour for up to 7 days. The possible mechanisms are discussed by which endogenous acetylcholinesterase in cerebrospinal fluid could serve as an index of dopamine depletion in the nigrostriatal pathway and how exogenous enzymes might alleviate the accompanying motor dysfunction.

Acetylcholinesterase activity in regions of the rat brain following a convulsion

The effects of electroconvulsive shock on the levels of acetylcholinesterase in several brain regions of the rat were studied. Hippocampus, mesencephalon, cortex, and striatum exhibited rapid changes in acetylcholinesterase activity during the first few minutes following the convulsion, whereas brainstem and basal forebrain levels remained unchanged. In both hippocampus and midbrain there was a sustained decrease in activity: the total acetylcholinesterase activity was decreased by up to 40% within 2 min of the convulsion and did not return to control values for another 3 h. Thirty minutes after a flurothyl-induced convulsion there was a similar fall in acetylcholinesterase activity in both these regions, whereas a subconvulsive electric shock produced no change. It is concluded that a convulsion produces significant short-term decreases in acetylcholinesterase activity in areas of the rat brain that are involved in the generation and propagation of seizures, and the question is raised of whether this is related to the increase in seizure threshold that follows a convulsion.