Distributions of molecular forms of acetylcholinesterase and butyrylcholinesterase in nervous tissue of the cat

Reduced epicardial vagal nerve density and impaired vagal control in a rat myocardial infarction-heart failure model

BACKGROUND

Autonomic remodeling, characterized by sympathetic activation and vagal withdrawal, contributes to heart failure (HF) progression. However, the exact mechanism(s) responsible for vagal withdrawal in HF remain(s) unclear, and whether HF causes epicardial autonomic nerve remodeling is unknown.

METHODS AND RESULTS

Myocardial infarction (MI) was produced in 14 Sprague-Dawley rats, and 10 sham surgery rats served as the control. MI-HF was confirmed 2 months after the surgery by echocardiography and hemodynamic measurement. Cervical vagal nerve stimulation was delivered to examine the heart rate slowing effect. Whole heart acetylcholinesterase histochemistry was used to examine the epicardial autonomic nerve remodeling at dorsal ventricles (remote from the infarcted area). Compared with the control animals, the same vagal nerve stimulation had less heart rate slowing effect in MI-HF group. Both epicardial nerve bundle length-density (2.56±0.60 μm/mm² versus 1.68±0.46 μm/mm², P=.001) and branching point-density (1.24±0.25 points/mm² versus 0.66±0.18 points/mm², P<.001) were lower in MI-HF rats. The chemically stained epicardial nerve bundles contain both sympathetic (tyrosine hydroxylase positive) and vagal (choline acetyltransferase positive) fibers. However, within the stained nerve bundle, the chemical color corresponds mainly with the vagal fibers.

CONCLUSIONS

Whole heart acetylcholinesterase histochemistry revealed a decreased ventricular epicardial vagal nerve density in MI-HF rats, which may contribute to impaired cardiac vagal control in HF.

Huperzine A as a neuroprotective and antiepileptic drug: a review of preclinical research

Huperzine A (HupA) is an acetylcholinesterase (AChE) inhibitor extracted from Huperzia Serrata, a firmoss, which has been used for various diseases in traditional Chinese medicine for fever and inflammation. More recently, it has been used in Alzheimer's disease and other forms of dementia with a presumed mechanism of action via central nicotinic and muscarinic receptors. HupA is marketed as a dietary supplement in the U.S. This article reviews newly proposed neuroprotective and anticonvulsant HupA properties based on animal studies. HupA exerts its effects mainly via α7nAChRs and α4β2nAChRs, thereby producing a potent anti-inflammatory response by decreasing IL-1β, TNF-α protein expression, and suppressing transcriptional activation of NF-κB signaling. Thus, it provides protection from excitotoxicity and neuronal death as well as increase in GABAergic transmission associated with anticonvulsant activity.

Morphological pattern of intrinsic nerve plexus distributed on the rabbit heart and interatrial septum

Although the rabbit is routinely used as the animal model of choice to investigate cardiac electrophysiology, the neuroanatomy of the rabbit heart is not well documented. The aim of this study was to examine the topography of the intrinsic nerve plexus located on the rabbit heart surface and interatrial septum stained histochemically for acetylcholinesterase using pressure-distended whole hearts and whole-mount preparations from 33 Californian rabbits. Mediastinal cardiac nerves entered the venous part of the heart along the root of the right cranial vein (superior caval vein) and at the bifurcation of the pulmonary trunk. The accessing nerves of the venous part of the heart passed into the nerve plexus of heart hilum at the heart base. Nerves approaching the heart extended epicardially and innervated the atria, interatrial septum and ventricles by five nerve subplexuses, i.e. left and middle dorsal, dorsal right atrial, ventral right and left atrial subplexuses. Numerous nerves accessed the arterial part of the arterial part of the heart hilum between the aorta and pulmonary trunk, and distributed onto ventricles by the left and right coronary subplexuses. Clusters of intrinsic cardiac neurons were concentrated at the heart base at the roots of pulmonary veins with some positioned on the infundibulum. The mean number of intrinsic neurons in the rabbit heart is not significantly affected by aging: 2200 ± 262 (range 1517-2788; aged) vs. 2118 ± 108 (range 1513-2822; juvenile). In conclusion, despite anatomic differences in the distribution of intrinsic cardiac neurons and the presence of well-developed nerve plexus within the heart hilum, the topography of all seven subplexuses of the intrinsic nerve plexus in rabbit heart corresponds rather well to other mammalian species, including humans.

Near-complete adaptation of the PRiMA knockout to the lack of central acetylcholinesterase

Acetylcholinesterase (AChE) rapidly hydrolyzes acetylcholine. At the neuromuscular junction, AChE is mainly anchored in the extracellular matrix by the collagen Q, whereas in the brain, AChE is tethered by the proline-rich membrane anchor (PRiMA). The AChE-deficient mice, in which AChE has been deleted from all tissues, have severe handicaps. Surprisingly, PRiMA KO mice in which AChE is mostly eliminated from the brain show very few deficits. We now report that most of the changes observed in the brain of AChE-deficient mice, and in particular the high levels of ambient extracellular acetylcholine and the massive decrease of muscarinic receptors, are also observed in the brain of PRiMA KO. However, the two groups of mutants differ in their responses to AChE inhibitors. Since PRiMA-KO mice and AChE-deficient mice have similar low AChE concentrations in the brain but differ in the AChE content of the peripheral nervous system, these results suggest that peripheral nervous system AChE is a major target of AChE inhibitors, and that its absence in AChE- deficient mice is the main cause of the slow development and vulnerability of these mice. At the level of the brain, the adaptation to the absence of AChE is nearly complete.

Morphologic pattern of the intrinsic ganglionated nerve plexus in mouse heart

BACKGROUND

Both normal and genetically modified mice are excellent models for investigating molecular mechanisms of arrhythmogenic cardiac diseases that may be associated with an imbalance between sympathetic and parasympathetic nervous input to the heart.

OBJECTIVE

The purpose of this study was to (1) determine the structural organization of the mouse cardiac neural plexus, (2) identify extrinsic neural sources and their relationship with the cardiac plexus, and (3) reveal any anatomic differences in the cardiac plexus between mouse and other species.

METHODS

Cardiac nerve structures were visualized using histochemical staining for acetylcholinesterase (AChE) on whole heart and thorax-dissected preparations derived from 25 mice. To confirm the reliability of staining parasympathetic and sympathetic neural components in the mouse heart, we applied a histochemical method for AChE and immunohistochemistry for tyrosine hydroxylase (TH) and/or choline acetyltransferase (ChAT) on whole mounts preparations from six mice.

RESULTS

Double immunohistochemical labeling of TH and ChAT on AChE-positive neural elements in mouse whole mounts demonstrated equal staining of nerves and ganglia for AChE that were positive for both TH and ChAT. The extrinsic cardiac nerves access the mouse heart at the right and left cranial veins and interblend within the ganglionated nerve plexus of the heart hilum that is persistently localized on the heart base. Nerves and bundles of nerve fibers extend epicardially from this plexus to atria and ventricles by left dorsal, dorsal right atrial, right ventral, and ventral left atrial routes or subplexuses. The right cranial vein receives extrinsic nerves that mainly originate from the right cervicothoracic ganglion and a branch of the right vagus nerve, whereas the left cranial vein is supplied by extrinsic nerves from the left cervicothoracic ganglion and the left vagus nerve. The majority of intrinsic cardiac ganglia are localized on the heart base at the roots of the pulmonary veins. These ganglia are interlinked by interganglionic nerves into the above mentioned nerve plexus of the heart hilum. In general, the examined hearts contained 19 ± 3 ganglia, giving a cumulative ganglion area of 0.4 ± 0.1 mm(2).

CONCLUSION

Despite substantial anatomic differences in ganglion number and distribution, the structural organization of the intrinsic ganglionated plexus in the mouse heart corresponds in general to that of other mammalian species, including human.

Epicardial neural ganglionated plexus of ovine heart: anatomic basis for experimental cardiac electrophysiology and nerve protective cardiac surgery

BACKGROUND

Sheep are routinely used in experimental cardiac electrophysiology and surgery.

OBJECTIVE

The purpose of this study was to (1) ascertain the topography and architecture of the ovine epicardial neural plexus (ENP), (2) determine the relationships of ENP with vagal and sympathetic cardiac nerves and ganglia, and (3) evaluate gross anatomic differences and similarities of ENP in humans, sheep, and other species.

METHODS

Ovine ENP and extrinsic sympathetic and vagal nerves were stained histochemically for acetylcholinesterase in whole heart and/or thorax-dissected preparations from 23 newborn lambs, with subsequent examination by stereomicroscope.

RESULTS

Intrinsic cardiac nerves extend from the venous part of the ovine heart hilum along the roots of the cranial (superior) caval and left azygos veins to both atria and ventricles via five epicardial routes: dorsal right atrial, middle dorsal, left dorsal, right ventral, and ventral left atrial nerve subplexuses. Intrinsic nerves proceeding from the arterial part of the heart hilum along the roots of the aorta and pulmonary trunk extend exclusively into the ventricles as the right and left coronary subplexuses. The dorsal right atrial, right ventral, and middle dorsal subplexuses receive the main extrinsic neural input from the right cervicothoracic and right thoracic sympathetic T(2) and T(3) ganglia as well as from the right vagal nerve. The left dorsal is supplied by sizeable extrinsic nerves from the left thoracic T(4)-T(6) sympathetic ganglia and the left vagal nerve. Sheep hearts contained an average of 769 +/- 52 epicardial ganglia. Cumulative areas of epicardial ganglia on the root of the cranial vena cava and on the wall of the coronary sinus were the largest of all regions (P <.05).

CONCLUSION

Despite substantial interindividual variability in the morphology of ovine ENP, right-sided epicardial neural subplexuses supplying the sinoatrial and atrioventricular nodes are mostly concentrated at a fat pad between the right pulmonary veins and the cranial vena cava. This finding is in sharp contrast with a solely left lateral neural input to the human atrioventricular node, which extends mainly from the left dorsal and middle dorsal subplexuses. The abundance of epicardial ganglia distributed widely along the ovine ventricular nerves over respectable distances below the coronary groove implies a distinctive neural control of the ventricles in human and sheep hearts.

Acetylcholine synthesis by choline acetyltransferase of a peripheral type as demonstrated in adult rat dorsal root ganglion

pChAT is a splice variant of a peripheral type encoded alternatively by the gene for choline acetyltransferase of the common type (cChAT), the enzyme responsible for acetylcholine synthesis. Immunohistochemistry using pChAT antiserum has successfully visualized many known peripheral cholinergic cells, whereas most cChAT antibodies failed to do so. As, however, accumulating evidence indicates that pChAT expression also occurs in various non-cholinergic neurons, we examined possible acetylcholine production by pChAT in rat dorsal root ganglion as a model. The present study indicated that the ganglion neurons possessed pChAT, but never cChAT, mRNA and protein. Our detailed analysis further showed that, despite low enzyme activities of both choline acetyltransferase and acetylcholinesterase, the level of acetylcholine in the ganglion was as high as to that in various brain regions receiving cholinergic innervation. By using immunoprecipitation methods, we here provide evidence that pChAT definitely has enzyme activity enough to supply physiological concentrations of acetylcholine in the ganglion. We propose that pChAT contributes both to acetylcholine neurotransmission in physiologically identified cholinergic cells and to functions yet unknown in non-cholinergic neurons. Thus pChAT provides a new window on the role of neuronal acetylcholine.

Detection of basal and potassium-evoked acetylcholine release from embryonic DRG explants

Spontaneous and potassium-induced acetylcholine release from embryonic (E12 and E18) chick dorsal root ganglia explants at 3 and 7 days in culture was investigated using a chemiluminescent procedure. A basal release ranging from 2.4 to 13.8 pm/ganglion/5 min was detected. Potassium application always induced a significant increase over the basal release. The acetylcholine levels measured in E12 explants were 6.3 and 38.4 pm/ganglion/5 min at 3 and 7 days in culture, respectively, while in E18 explant cultures they were 10.7 and 15.5 pm/ganglion/5 min. In experiments performed in the absence of extracellular Ca2+ ions, acetylcholine release, both basal and potassium-induced, was abolished and it was reduced by cholinergic antagonists. A morphometric analysis of explant fibre length suggested that acetylcholine release was directly correlated to neurite extension. Moreover, treatment of E12 dorsal root ganglion-dissociated cell cultures with carbachol as cholinergic receptor agonist was shown to induce a higher neurite outgrowth compared with untreated cultures. The concomitant treatment with carbachol and the antagonists at muscarinic receptors atropine and at nicotinic receptors mecamylamine counteracted the increase in fibre outgrowth. Although the present data have not established whether acetylcholine is released by neurones or glial cells, these observations provide the first evidence of a regulated release of acetylcholine in dorsal root ganglia.

Brain and cerebrospinal fluid cholinesterases in Alzheimer's disease, Parkinson's disease and aging. A critical review of clinical and experimental studies

Acetylcholinesterase (AChE), an enzyme responsible for the break-down of acetylcholine, is found both in cholinergic and non-cholinergic neurons in the central nervous system. In addition to its role in the catabolism of acetylcholine, AChE have other functions in brain, e.g. in the processing of peptides and proteins, and in the modulation of dopaminergic neurons in the brain stem. Several clinical and experimental studies have investigated AChE in brain and cerebrospinal fluid (CSF) in aging and dementia. The results suggest that brain AChE and its molecular forms show interesting changes in dementia and aging. However, CSF-AChE activity is not a very reliable or sensitive marker of the integrity and function of cholinergic neurons in the basal forebrain complex. Additional work is needed to clarify the role of AChE abnormality in the formation of pathology changes in patients with Alzheimer's disease.

The role of acetylcholinesterase in denervation supersensitivity in the frog cardiac ganglion

1. The sensitivity of normal and denervated cardiac ganglion cells to the cholinergic agonists acetylcholine and carbamylcholine (carbachol) were compared in the frog, Rana pipiens. Acetylcholine and carbachol bind to the same acetylcholine receptors, but, unlike acetylcholine, carbachol is resistant to hydrolysis by acetylcholinesterase. 2. Sensitivity was assessed by the peak depolarization elicited in response to a sustained pulse of ligand emitted from a pipette positioned 10 microns from the ganglion cell surface. This technique allows the sensitivity of the entire cell to be recorded with a single measurement. 3. The acetylcholine sensitivity of normal cardiac ganglion cells was increased by inhibiting extracellular acetylcholinesterase with echothiophate. 4. Denervation increased the sensitivity of cardiac ganglion cells to acetylcholine but not to carbachol. 5. Following the inhibition of extracellular acetylcholinesterase with echothiophate, sensitivity to acetylcholine was similar in normal and in denervated ganglion cells. 6. The increased sensitivity to acetylcholine of cardiac ganglion cells following denervation is caused by a reduction in the hydrolysis of the transmitter by acetylcholinesterase rather than by changes in the number and/or properties of acetylcholine receptors.

Postnatal development of acetylcholinesterase in, and cholinergic projections to, the cat superior colliculus

The postnatal development of cholinergic afferents to the superior colliculus in neonatal cats was studied by using acetylcholinesterase (AChE) histochemistry, choline acetyltransferase (ChAT) immunohistochemistry, and retrograde transport of horseradish peroxidase (HRP). In the adult cat, the pattern of AChE staining was laminar specific. AChE was distributed continuously in the stratum griseum superficiale (SGS) but was organized as patches in the stratum griseum intermediate (SGI). Diffuse AChE staining also was present in the stratum griseum profundum (SGP) and the dorsolateral periaqueductal gray (PAG). At birth, however, AChE staining was barely detectable in the SGS and, aside from a few isolated labeled neurons, was absent from the SGI, SGP, and PAG. By 7 days postnatal (dpn), staining in the SGS was more apparent but did not change appreciably in the deeper laminae. A substantial increase in AChE staining occurred in the SGS at 14 dpn (several days after eye opening), at which time patches in the SGI first became apparent. By 28 dpn, the complete laminar-specific adult AChE staining pattern was present, though the staining intensity did not reach the adult level until 56 dpn. A protracted maturation of both AChE staining and ChAT immunoreactivity also was observed in the sources of cholinergic afferents to the superior colliculus, which include the parabigeminal nucleus, and the pedunculopontine (PPN) and lateral dorsal tegmental (LDTN) nuclei. AChE and ChAT-immunoreactive staining in each nucleus was weak at birth but increased during the ensuing 2 weeks. At 21 dpn, however, ChAT immunoreactivity virtually disappeared in the parabigeminal nucleus and significantly decreased in PPN and LDTN. The ChAT immunoreactivity in these nuclei then gradually increased reaching maximum levels by 28 dpn. At 35 dpn, AChE staining showed a significant, though temporary (4 weeks), decrease in the parabigeminal nucleus, but not in the PPN and LDTN, that subsequently increased to the adult level of staining at 70 dpn. The absence of AChE in the SGI in neonatal animals was correlated, at least in part, with a paucity of neurons in the brainstem cholinergic cell groups labeled by retrograde transport of HRP from the superior colliculus. Injections of HRP into the superior colliculus retrogradely labeled many neurons in the parabigeminal nucleus, but few, if any, neurons in the PPN or LDTN at 1 dpn. Retrogradely labeled neurons also were observed in the substantia nigra pars reticulata, albeit fewer in neonates than in adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Allelic variants of acetylcholinesterase: genetic evidence that all acetylcholinesterase forms in avian nerves and muscles are encoded by a single gene

Two acetylcholinesterase (AcChoEase) polypeptide chains, alpha and beta, are expressed in avian nerves and muscles with apparent molecular masses of 110 and 100 kDa, respectively. We now show that individual quails express alpha, beta, or both AcChoEase polypeptide chains. By mating studies we show that the two AcChoEase polypeptides are autosomal and segregate as codominant alleles in classical Mendelian fashion. Biochemical studies of the two allelic AcChoEase polypeptides indicate that they have the same turnover number, have the same Km for acetylcholine, are immunoprecipitated to the same extent with a monoclonal anti-AcChoEase antibody, and can assemble with equal efficiency into multimeric forms. Thus there are no obvious functional differences between the two alleles. In heterozygotes, the rates of synthesis of the two polypeptides are identical, suggesting that there are no differences in expression of these two genes. Within an individual, nerves and muscles always express the same AcChoEase forms isolated from muscle indicates that all AcChoEase forms are comprised of the same allelic polypeptide chains. In contrast to the nicotinic acetylcholine receptors that appear to be encoded by complex multigene families, our studies on AcChoEase show that all forms of this important synaptic component in electrically excitable cells are encoded by a single gene. Thus differences in assembly and localization of the multiple synaptic forms of AcChoEase must arise through posttranscriptional events, posttranslational modifications of a similar AcChoEase polypeptide chain or both.

Maintenance by glycyl-L-glutamine in vivo of molecular forms of acetylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat

The 24-hr intracarotid infusion of plasma-treated glycyl-L-glutamine (3 microM) produced significant enhancement of the monomeric G1 and tetrameric G4 forms of acetylcholinesterase of the cat superior cervical ganglion 48 hr after denervation, in comparison with denervated, noninfused controls. No significant effect of glycyl-L-glutamine could be demonstrated 4 or 6 days after denervation. These findings are consistent with the conclusion, drawn from a previous in vitro study, that glycyl-L-glutamine acts at a stage prior to the aggregation of the G1 form into higher polymers to maintain the acetylcholinesterase content of denervated ganglia. It is proposed that the dipeptide may regulate the transcription of the DNA for acetylcholinesterase to its corresponding mRNA.

Effects of glycyl-L-glutamine in vitro on the molecular forms of acetylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat

Normal and preganglionically denervated cat superior cervical ganglia were sectioned and cultured for 24 or 48 hr, with or without preliminary inactivation of acetylcholinesterase, and in the presence or absence of 10(-5) M glycyl-L-glutamine. They were then homogenized, and the molecular forms of acetylcholinesterase were analyzed by sucrose gradient sedimentation. We observed an increased proportion of the globular monomeric G1 form, and to a lesser extent of the dimeric G2 and tetrameric membranous G4 forms, of acetylcholinesterase in the glycyl-L-glutamine-treated compared with the control cultures. There was only a small increase in the total acetylcholinesterase activity and no significant variation in the activity of the metabolic enzyme lactate dehydrogenase. It therefore seems likely that glycyl-L-glutamine, or the endogenous neurotrophic factor, maintains acetylcholinesterase in the preganglionically denervated ganglia in vivo by specifically increasing the biosynthesis of the monomeric G1 form, but not that of other proteins; these trophic factors do not seem to promote the polymerization of G1 into the more complex G2 and G4 forms.