Role Of Cholinergic Neurotransmission Research Articles

A new microdialysis-electrochemical device for in vivo simultaneous determination of acetylcholine and choline in rat brain treated with N-methyl-( R)-salsolinol

Acetylcholine (ACh) and choline (Ch) play a critical role in cholinergic neurotransmission and the abnormalities in their concentrations are related to several neural diseases. Therefore, the in vivo determination of ACh and Ch is important to the research on neurodegenerative disorders. In this work, electrochemical biosensors based on poly( m-(1,3)-phenylenediamine) (pmPD) and polytyramine (PTy) modified enzyme electrodes were fabricated. The electropolymerized pmPD polymer was used to exclude interfering substances and the PTy layer facilitated the immobilization of acetylcholinesterase (AChE) and choline oxidase (ChOx). Then, ACh/Ch sensor and Ch sensor were coupled with microdialysis to produce a novel device, which provides a sensitive and selective method for simultaneous determination of ACh and Ch. This method has detection limits of 63.0 ± 3.4 nM for ACh and 25.0 ± 1.2 nM for Ch. The integrated device was successfully applied to assessing the impact of endogenous neurotoxin N-methyl-( R)-salsolinol [1( R),2-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, ( R)-NMSal] on ACh and Ch concentration, which is of great benefit to understand the pathogenesis of Parkinson's disease.

Muscarinic receptor antagonism at the spinal cord level causes inhibitory effects on male rat sexual behavior

The role of cholinergic neurotransmission in male rat sexual behavior at the brain level has been studied by several researchers. However, little is known about its role at the spinal cord level. In this study, the effects of the intrathecal (IT) administration of the muscarinic receptor antagonist subtypes (MRAs) methoctramine (Meth), tropicamide (Trop) and 4-DAMP on male rat sexual behavior were evaluated during three ejaculatory series. Meth and Trop are preferring antagonists for the M2/M4 receptor subtypes, and 4-DAMP is a preferring antagonist for the M3 receptor subtype. All the MRAs tested noticeably inhibited male rat copulatory behavior, reflected by a reduction in the number of animals engaging in sexual behavior and a gradual decrease in the number of animals able to ejaculate. Significant increases in intromission latency (IL), ejaculation latency (EL) and post-ejaculatory interval (PEI) were observed. The ranking of inhibitory potency in all recorded parameters was Meth ≥ 4-DAMP > Trop. In theory, the effects of Meth and Trop could be a result of interaction with M2/M4 receptors. However, given that the M2 receptor constitutes the greatest population of muscarinic receptors at all spinal cord sites and given the high affinity for Meth on M2 receptors, the high potency in the inhibitory effects of Meth is indicative of the special role of M2 spinal receptors in the implementation of this behavior. The weaker effects of Trop could be linked to the smaller population of M4 receptors in the spinal cord, but some interaction with M2 receptors is probable. Since some differences in the pattern of inhibitory response between Meth and 4-DAMP were observed in this and a previous study, a possible role for M3 receptors must be considered. The data obtained in this study confirm the facilitating effect of acetylcholine (ACh) at the spinal cord level on male rat sexual behavior through muscarinic mechanisms, with an important influence on ejaculatory processes. These data support the hypothesis of the modulating role of ACh on male rat sexual behavior at the spinal cord level.

Nonenzymatic role of acetylcholinesterase in neuritic sprouting: Regional changes in acetylcholinesterase and choline acetyltransferase after neonatal 6-hydroxydopamine lesions

Acetylcholinesterase (AChE) is postulated to play a nonenzymatic role in the development of neuritic projections. We gave the specific neurotoxin, 6-OHDA to rats on postnatal day (PN) 1, a treatment that destroys noradrenergic nerve terminals in the forebrain while producing reactive sprouting in the brainstem. AChE showed profound decreases in the forebrain that persisted in males over the entire phase of major synaptogenesis, from PN4 through PN21; in the brainstem, AChE was increased. Parallel examinations of choline acetyltransferase, an enzymatic marker for cholinergic nerve terminals, showed a different pattern of 6-OHDA-induced alterations, with initial decreases in both forebrain and brainstem in males and regression toward normal by PN21; females were far less affected. The sex differences are in accord with the greater plasticity of the female brain and its more rapid recovery from neurotoxic injury; our findings indicate that these differences are present well before puberty. These results support the view that AChE is involved in neurite formation, unrelated to its enzymatic role in cholinergic neurotransmission. Further, the results for choline acetyltransferase indicate that early depletion of norepinephrine compromises development of acetylcholine systems, consistent with a trophic role for this neurotransmitter.

Impaired muscarinic regulation of excitatory synaptic transmission in the APPswe/PS1dE9 mouse model of Alzheimer's disease

Cholinergic hypothesis and amyloid cascade hypothesis are mainly proposed for Alzheimer's disease; however, the relationship between these hypotheses is poorly understood. To address the question of whether amyloid β-peptide pathology affects cholinergic neurotransmission, we examined the effect of a cholinesterase inhibitor, physostigmine, on field excitatory postsynaptic potentials (EPSPs) evoked by single-pulse stimulation in the CA1 region of the hippocampus of various APPswe/PS1dE9 transgenic mice with different degrees of amyloid β-peptide pathology. Reduced field EPSPs by physostigmine in transgenic mice at 3 months of age, when the mice had negligible amyloid β-peptide levels and no amyloid β-peptide deposits, were indistinguishable from those in age-matched wild-type mice. In contrast, reduced field EPSPs by physostigmine in transgenic mice at 5 months of age, when the mice had low amyloid β-peptide levels and subtle amyloid β-peptide deposits, were significantly lower than those in age-matched wild-type mice. Next, we characterized acetylcholine receptors, which play important roles in cholinergic neurotransmission, because physostigmine resulted in increased acetylcholine levels in the synaptic cleft. Different reductions of field EPSPs by physostigmine between transgenic and wild-type mice at 5 months of age were not affected by a nicotinic receptor antagonist, mecamylamine; however, reduced field EPSPs by physostigmine in both transgenic and wild-type mice were restored to basal levels by a muscarinic receptor antagonist, atropine. These results indicate that cholinergic modulation of glutamatergic transmission is already impaired at the onset of the formation of amyloid β-peptide deposits, and muscarinic receptor dysfunction is one of the causes of this impairment.

Reduction in CHT1-mediated choline uptake in primary neurons from presenilin-1 M146V mutant knock-in mice

The memory loss in Alzheimer's disease (AD) has been linked to cholinergic hypoactivity. Mutations in presenilin-1 (PS-1) may regulate cholinergic signaling, although their precise roles in cholinergic neurotransmission in AD are unsettled. Neuronal uptake of choline via the high affinity choline transporter (CHT1) is essential for cholinergic neurotransmission. CHT1 is a Na+-dependent, hemicholinium-3 (HC-3)-sensitive choline transporter. Although cholinergic neurons in the nucleus basalis of Meynert are a major source of cholinergic projections for the cerebral cortex, it is unclear whether cortical neurons exhibit intrinsic CHT1 activity that is altered in AD. We now report that primary cortical neurons express intrinsic and biologically active CHT1, and that, in these neurons, CHT1-mediated choline uptake activity is significantly reduced in PS-1 M146V mutant knock-in mice. Further kinetic studies using HC-3 binding and cell surface biotinylation assays showed that the PS-1 mutation inhibits CHT1 mediated choline uptake by reducing the ligand binding affinity of CHT1 without significantly altering levels of CHT1 expression in the plasma membrane. Since human neocortex has recently been shown to possess intrinsic cholinergic innervation, our results indicate that alterations in CHT1-mediated high affinity choline uptake in cortical neurons may contribute to Alzheimer's dementia.

Posttrial Administration of Cholinergic Drugs does not Affect Consummatory Successive Negative Contrast in Rats

Posttraining administration of cholinergic drugs modulates the consolidation of memory processes in several learning tasks. We studied the effect of the administration of atropine (cholinergic antagonist, Experiment 1) and physostigmine (acetylcholinesterase inhibitor, Experiment 2) immediately after the first session of reward downshift, and immediately after the last preshift session (Experiment 3) on a consummatory successive negative contrast procedure. Animals were given access to a high-value reward (32% sucrose solution), and surprisingly shifted to a low-value reward (4% sucrose solution) in a second phase. The results indicate that atropine and physostigmine have no effects on contrast. The role of cholinergic neurotransmission in the memory of surprising reward changes is discussed.

Neurobiology of butyrylcholinesterase

Butyrylcholinesterase is a serine hydrolase related to acetylcholinesterase that catalyses the hydrolysis of esters of choline, including acetylcholine. Butyrylcholinesterase has unique enzymatic properties and is widely distributed in the nervous system, pointing to its possible involvement in neural function. Here, we summarize the biochemical properties of butyrylcholinesterase and review the evidence that this enzyme has important roles in cholinergic neurotransmission and could be involved in other nervous system functions and in neurodegenerative diseases.

Neurotransmitter regulation of neural development: acetylcholine and nicotinic receptors.

Several neurotransmitter systems have been related to developmental processes during the past decade. In this review, we discuss the evidence that the nicotinic acetylcholine receptors could have an additional function during development that may be unrelated to their role in cholinergic neurotransmission in the vertebrate brain. Both temporal expression data and in vitro and in vivo studies with nicotinic agonists and antagonists have provided direct support for a role of nicotinic receptors in neural developmental processes such as neurite outgrowth and differentiation. A similar picture has emerged for other neurotransmitter and receptor systems as well, which generates a new view of neural processes during both development and mature life.

Effect of tetrahydroaminoacridine on sleep in healthy subjects

The present study investigated the impact of the cholinesterase inhibitor tetrahydroaminoacridine (THA; tacrine) on sleep in healthy subjects. According to the reciprocal interaction model of non-rapid eye movement (NREM) and REM sleep regulation, which postulates a primary role in cholinergic neurotransmission for the initiation and maintenance of REM sleep, it was expected that THA would lead to an earlier onset of REM sleep. In 12 healthy subjects aged from 21 to 50 years two different doses (20 mg, 40 mg) were administered 1 hour prior to bed time and compared to placebo. Only the higher dose of THA significantly shortened REM latency. No other significant effects on sleep architecture were observed, although administration of 40 mg tacrine was associated with a decrease in sleep efficiency and a prolongation of sleep latency. Blood plasma levels of tacrine and its metabolite 1-hydroxytacrine measured prior to sleep and during the first 90 min of sleep were significantly correlated with the onset of REM sleep in relation to the timing of drug administration (only for the 20 mg dose). The reversible cholinesterase inhibitor THA exerts effects on REM latency comparable to those observed with other cholinomimetic agents.

Localization of some neurotransmitters during developments hydroidomedusae

Neurotransmission in Cnidarians is known to occur mainly by peptidergic neuronal pathways; the role of cholinergic neurotransmission, that in other animals this involves both neurotransmission and developmental regulation, has never been shown with certainty. This histochemical-immunohistochemical study was performed, in different developmental stages of some hydroidomedusan species (characterized by different reproductive and developmental patterns) to investigate the presence and distribution of cholinesterase (ChE) activity, acetylcholine receptors, biogenic amines, and molecules immunologically related to secretory peptides (FMRF amide and VIP). The results showed that ChE (revealed by all the kinds of activities: AChE, PrChE, BuChE) is mainly present in developing or ‘juvenile’ structures. Biogenic amines are revealed by aldehyde-induced fluorescence at every stage studied, while peptide-like immunoreactivities are mainly present in differentiated structures. These findings support the hypothesis that all the chemical messengers here investigated arose very early in evolution, although, in some cases, with different functions. For most of the investigated species, similarities in the distribution pattern of markers generally reflect similarities in life cycle, rather than phylogenetic affinities.

Role of cholinergic neurotransmission in the amygdala on performances of passive avoidance learning in mice.

To clarify the role of cholinergic neurons in the amygdala on learning and memory, scopolamine was injected topically into the bilateral amygdala of mice, and the ability to perform two types of passive avoidance tasks (step-through and step-down) was investigated. On the first day mice performed the learning trial and on the second day their retention was tested. Scopolamine (0.5 or 1 microgram/site) was injected bilaterally into the amygdala 30 min before or immediately after the learning trial or 30 min before the testing trial. Scopolamine impaired the performance ability of the mice dose-dependently only when it was injected 30 min before the learning trial. The results coincided well with the effect of scopolamine injected intraperitoneally. Taken together, these results suggest that the site of action for scopolamine to cause anterograde amnesia is the amygdala, and that cholinergic neurons projecting to the amygdala play an important role in memory acquisition in the two passive avoidance tasks.

P-192 - Role of cholinergic neurotransmission in the amygdala on memory performances of mice

P-192 - Role of cholinergic neurotransmission in the amygdala on memory performances of mice

Cholinergic neurotransmission in human corpus cavernosum. I. Responses of isolated tissue

To investigate the role of cholinergic neurotransmission in erection, human penile corpus cavernosum tissue was studied. Electrical stimulation of strips of corpus cavernosum suspended in an organ chamber induced contractions and relaxations that were blocked by tetrodotoxin. The contractions also were blocked by bretylium and prazosin. Norepinephrine and phenylephrine contracted the isolated strips and this response was prevented by prazosin. Electrical stimulation-induced relaxations were enhanced by bretylium and physostigmine and partially blocked by atropine. The effect of atropine, but not that of physostigmine, was prevented by bretylium. Corporal strips contracted with norepinephrine relaxed to acetylcholine; this effect was blocked by atropine and enhanced by physostigmine. Strips lacking endothelium contracted normally with norepinephrine, but the relaxation caused by acetylcholine was virtually abolished. Thus endothelium lining the lacunar spaces within human corpus cavernosum is required for the relaxation caused by exogenous acetylcholine. There may be three neurotransmitter effector systems that control corpus cavernosum smooth muscle tone: adrenergic (excitatory), cholinergic (inhibitory), and nonadrenergic noncholinergic (inhibitory). Cholinergic nerves do not dilate or constrict directly the smooth muscle but may modulate other neuroeffector systems and/or the endothelium.

Ultrastructural localization of acetylcholinesterase in the synganglion of the tick, Dermacentor variabilis (Say).

Light- and electron-microscopic enzyme cytochemistry was used to localize acetylcholinesterase (AChE) activity in the synganglion (brain) of the tick Dermacentor variabilis. High AChE activity was observed throughout the neuropil as well as adjacent to most neuronal perikarya. Intracellular activity was not observed by light microscopy. By electron microscopy, reaction product was localized at the plasma membrane of glia and neurons. Enzyme activity was not associated with the olfactory globuli neurons. In other types of neurons, small amounts of reaction product were observed in the Golgi apparatus and nuclear envelope. Large neurosecretory neurons contained activity that appeared to be associated with deep invaginations of the plasma membrane as well as intracellular membranes. AChE activity was also associated with processes of both neurons and glia. In most peripheral nerves AChE activity was associated with virtually all axons. Clearly then, AChE is associated with glia and non-cholinergic neurons as well as with presumed cholinergic neurons. The widespread localization and large amounts of AChE in the tick brain exceeds that reported for other invertebrates and vertebrates. As has been suggested for other animals, AChE in the tick brain may have functions in addition to its known role in cholinergic neurotransmission.