Molecular biology of the vesicular ACh transporter

Contributions of Non-Neuronal Cholinergic Systems to the Regulation of Immune Cell Function, Highlighting the Role of α7 Nicotinic Acetylcholine Receptors

Loewi's discovery of acetylcholine (ACh) release from the frog vagus nerve and the discovery by Dale and Dudley of ACh in ox spleen led to the demonstration of chemical transmission of nerve impulses. ACh is now well-known to function as a neurotransmitter. However, advances in the techniques for ACh detection have led to its discovery in many lifeforms lacking a nervous system, including eubacteria, archaea, fungi, and plants. Notably, mRNAs encoding choline acetyltransferase and muscarinic and nicotinic ACh receptors (nAChRs) have been found in uninnervated mammalian cells, including immune cells, keratinocytes, vascular endothelial cells, cardiac myocytes, respiratory, and digestive epithelial cells. It thus appears that non-neuronal cholinergic systems are expressed in a variety of mammalian cells, and that ACh should now be recognized not only as a neurotransmitter, but also as a local regulator of non-neuronal cholinergic systems. Here, we discuss the role of non-neuronal cholinergic systems, with a focus on immune cells. A current focus of much research on non-neuronal cholinergic systems in immune cells is α7 nAChRs, as these receptors expressed on macrophages and T cells are involved in regulating inflammatory and immune responses. This makes α7 nAChRs an attractive potential therapeutic target.

Anatomic and functional mapping of human uterine innervation

OBJECTIVE

To better understand the physiology of pain in pelvic pain pathological conditions, such as endometriosis, in which alterations of uterine innervation have been highlighted, we performed an anatomic and functional mapping of the macro- and microinnervation of the human uterus. Our aim was to provide a 3-dimensional reconstruction model of uterine innervation.

DESIGN

This was an experimental study. We dissected the pelvises of 4 human female fetuses into serial sections, and treated them with hematoxylin and eosin staining before immunostaining.

SETTING

Academic Research Unit.

PATIENTS

None.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Detection of nerves (S100 +) and characterization of the types of nerves. The slices obtained were aligned to construct a 3-dimensional model.

RESULTS

A 3-dimensional model of uterine innervation was constructed. The nerve fibers appeared to have a centripetal path from the uterine serosa to the endometrium. Within the myometrium, innervation was dense. Endometrial innervation was sparse but present in the functional layer of the endometrium. Overall innervation was richest in the supravaginal cervix and rarer in the body of the uterus. Innervation was rich particularly laterally to the cervix next to the parametrium and paracervix. Four types of nerve fibers were identified: autonomic sympathetic (TH+), parasympathetic (VIP+), and sensitive (NPY+, CGRP1+ and VIP+). They were found in the 3 portions and the 3 layers of the uterus.

CONCLUSIONS

We constructed a 3-dimensional model of the human uterine innervation. This model could provide a solid base for studying uterine innervation in pathologic situations, in order to find new therapeutic approaches.

Neurochemical organization of the ventral striatum's olfactory tubercle

The ventral striatum is a collection of brain structures, including the nucleus accumbens, ventral pallidum and the olfactory tubercle (OT). While much attention has been devoted to the nucleus accumbens, a comprehensive understanding of the ventral striatum and its contributions to neurological diseases requires an appreciation for the complex neurochemical makeup of the ventral striatum's other components. This review summarizes the rich neurochemical composition of the OT, including the neurotransmitters, neuromodulators and hormones present. We also address the receptors and transporters involved in each system as well as their putative functional roles. Finally, we end with briefly reviewing select literature regarding neurochemical changes in the OT in the context of neurological disorders, specifically neurodegenerative disorders. By overviewing the vast literature on the neurochemical composition of the OT, this review will serve to aid future research into the neurobiology of the ventral striatum.

Acetylcholine signaling system in progression of lung cancers

The neurotransmitter acetylcholine (ACh) acts as an autocrine growth factor for human lung cancer. Several lines of evidence show that lung cancer cells express all of the proteins required for the uptake of choline (choline transporter 1, choline transporter-like proteins) synthesis of ACh (choline acetyltransferase, carnitine acetyltransferase), transport of ACh (vesicular acetylcholine transport, OCTs, OCTNs) and degradation of ACh (acetylcholinesterase, butyrylcholinesterase). The released ACh binds back to nicotinic (nAChRs) and muscarinic receptors on lung cancer cells to accelerate their proliferation, migration and invasion. Out of all components of the cholinergic pathway, the nAChR-signaling has been studied the most intensely. The reason for this trend is due to genome-wide data studies showing that nicotinic receptor subtypes are involved in lung cancer risk, the relationship between cigarette smoke and lung cancer risk as well as the rising popularity of electronic cigarettes considered by many as a "safe" alternative to smoking. There are a small number of articles which review the contribution of the other cholinergic proteins in the pathophysiology of lung cancer. The primary objective of this review article is to discuss the function of the acetylcholine-signaling proteins in the progression of lung cancer. The investigation of the role of cholinergic network in lung cancer will pave the way to novel molecular targets and drugs in this lethal malignancy.

Microvillous cells in the olfactory epithelium express elements of the solitary chemosensory cell transduction signaling cascade

The nasal cavity hosts an array of chemoresponsive cells, including the extended olfactory system and several other cells involved in detection of and responses to irritants. Solitary chemosensory cells (SCCs), which respond to irritants and bacteria, express the transient receptor potential channel TRPM5 an essential element of the taste transduction-signaling cascade. Microvillous cells (MVCs), non-neuronal cells situated in the apical layer of the main olfactory epithelium, also express TRPM5, but their function has not yet been clarified. TRPM5-positive MVCs, like SCCs, show a cholinergic phenotype expressing choline acetyl transferase (ChAT), but none of the other elements of the bitter taste transduction cascade could be detected. We reexamined TRPM5-positive MVCs with more sensitive gene expression and staining techniques to clarify whether they rely only on TRPM5 and ChAT or express other elements of the taste/SCC transduction cascade. Analyzing existing RNA sequencing data from whole olfactory mucosa and isolated olfactory sensory neurons, we determined that several elements of the taste/SCC transduction cascade, including taste receptors, are expressed in the olfactory mucosa in cells other than olfactory sensory neurons. Immunostaining confirmed the presence TRPM5 and ChAT in a subset of cells of the olfactory mucosa, which also showed the expression of PLCB2, gustducin, and T1R3. Specifically, these cells were identified as TRPM5-positive MVCs. Furthermore, we examined whether MVCs are innervated by trigeminal fibers, similarly to SCCs. Using antibodies against trigeminal nerve markers calcitonin gene-related peptide and substance P, we determined that, despite the cholinergic phenotype, most MVCs in the olfactory mucosa lacked consistent trigeminal innervation. Our findings indicate that MVCs, like SCCs, express all the elements of the bitter taste transduction cascade but that, unlike SCCs, they possess only sparse trigeminal innervation. The cholinergic phenotype of MVCs suggests a modulatory function of the surrounding olfactory epithelium, through the release of acetylcholine.

The unfolding landscape of the congenital myasthenic syndromes

Congenital myasthenic syndromes (CMS) are heterogeneous disorders in which the safety margin of neuromuscular transmission is impaired by one or more specific mechanisms. Since the advent of next-generation sequencing methods, the discovery of novel CMS targets and phenotypes has proceeded at an accelerated rate. Here, we review the current classification of CMS and describe our findings in five of these targets identified and investigated in our laboratory in the past 5 years. Defects in LRP4 hinder synaptic development and maintenance; the defects in PREPL are predicted to diminish filling of the synaptic vesicle with acetylcholine; and defects in SNAP25, Munc13-1, and synaptotbrevin-1 impede synaptic vesicle exocytosis.

Detailed muscular structure and neural control anatomy of the levator ani muscle: a study based on female human fetuses

BACKGROUND

Injury to the levator ani muscle or pelvic nerves during pregnancy and vaginal delivery is responsible for pelvic floor dysfunction.

OBJECTIVE

We sought to demonstrate the presence of smooth muscular cell areas within the levator ani muscle and describe their localization and innervation.

STUDY DESIGN

Five female human fetuses were studied after approval from the French Biomedicine Agency. Specimens were serially sectioned and stained by Masson trichrome and immunostained for striated and smooth muscle, as well as for somatic, adrenergic, cholinergic, and nitriergic nerve fibers. Slides were digitized for 3-dimensional reconstruction. One fetus was reserved for electron microscopy. We explored the structure and innervation of the levator ani muscle.

RESULTS

Smooth muscular cell beams were connected externally to the anococcygeal raphe and the levator ani muscle and with the longitudinal anal muscle sphincter. The caudalmost part of the pubovaginal muscle was found to bulge between the rectum and the vagina. This bulging was a smooth muscular interface between the levator ani muscle and the longitudinal anal muscle sphincter. The medial (visceral) part of the levator ani muscle contained smooth muscle cells, in relation to the autonomic nerve fibers of the inferior hypogastric plexus. The lateral (parietal) part of the levator ani muscle contained striated muscle cells only and was innervated by the somatic nerve fibers of levator ani and pudendal nerves. The presence of smooth muscle cells within the medial part of the levator ani muscle was confirmed under electron microscopy in 1 fetus.

CONCLUSION

We characterized the muscular structure and neural control of the levator ani muscle. The muscle consists of a medial part containing smooth muscle cells under autonomic nerve influence and a lateral part containing striated muscle cells under somatic nerve control. These findings could result in new postpartum rehabilitation techniques.

Functional and structural microanatomy of the fetal sciatic nerve

INTRODUCTION

The ultrastructure of a nerve has implications for surgical nerve repair. The aim of our study was to characterize the fascicular versus fibrillar anatomy and the autonomic versus somatic nature of the fetal sciatic nerve (SN).

METHODS

Immunohistochemistry for vesicular acetylcholine transporter, tyrosine hydroxylase, and peripheral myelin protein 22 was performed to identify cholinergic, adrenergic, and somatic axons, respectively, in the human fetal SN. Two-dimensional (2D) analysis and 3D reconstructions were performed.

RESULTS

The fetal SN is composed of one-third stromal tissue and two-thirds neural tissue. Autonomic fibers are predominant over somatic fibers within the neural tissue. The distribution of somatic fibers is initially random, but then become topographically organized after intra- and interfascicular rearrangements have occurred within the nerve.

CONCLUSIONS

The fetal model presents limitations but enables illustration of the nature of the nerve fibers and the 3D fascicular anatomy of the SN. Muscle Nerve 56: 787-796, 2017.

Alzheimer's disease: Targeting the Cholinergic System

Acetylcholine (ACh) has a crucial role in the peripheral and central nervous systems. The enzyme choline acetyltransferase (ChAT) is responsible for synthesizing ACh from acetyl-CoA and choline in the cytoplasm and the vesicular acetylcholine transporter (VAChT) uptakes the neurotransmitter into synaptic vesicles. Following depolarization, ACh undergoes exocytosis reaching the synaptic cleft, where it can bind its receptors, including muscarinic and nicotinic receptors. ACh present at the synaptic cleft is promptly hydrolyzed by the enzyme acetylcholinesterase (AChE), forming acetate and choline, which is recycled into the presynaptic nerve terminal by the high-affinity choline transporter (CHT1). Cholinergic neurons located in the basal forebrain, including the neurons that form the nucleus basalis of Meynert, are severely lost in Alzheimer’s disease (AD). AD is the most ordinary cause of dementia affecting 25 million people worldwide. The hallmarks of the disease are the accumulation of neurofibrillary tangles and amyloid plaques. However, there is no real correlation between levels of cortical plaques and AD-related cognitive impairment. Nevertheless, synaptic loss is the principal correlate of disease progression and loss of cholinergic neurons contributes to memory and attention deficits. Thus, drugs that act on the cholinergic system represent a promising option to treat AD patients.

Central cholinergic synaptic vesicle loading obeys the set-point model in Drosophila

Experimental evidence shows that neurotransmitter release, from presynaptic terminals, can be regulated by altering transmitter load per synaptic vesicle (SV) and/or through change in the probability of vesicle release. The vesicular acetylcholine transporter (VAChT) loads acetylcholine into SVs at cholinergic synapses. We investigated how the VAChT affects SV content and release frequency at central synapses in Drosophila melanogaster by using an insecticidal compound, 5Cl-CASPP, to block VAChT and by transgenic overexpression of VAChT in cholinergic interneurons. Decreasing VAChT activity produces a decrease in spontaneous SV release with no change to quantal size and no decrease in the number of vesicles at the active zone. This suggests that many vesicles are lacking in neurotransmitter. Overexpression of VAChT leads to increased frequency of SV release, but again with no change in quantal size or vesicle number. This indicates that loading of central cholinergic SVs obeys the "set-point" model, rather than the "steady-state" model that better describes loading at the vertebrate neuromuscular junction. However, we show that expression of a VAChT polymorphism lacking one glutamine residue in a COOH-terminal polyQ domain leads to increased spontaneous SV release and increased quantal size. This effect spotlights the poly-glutamine domain as potentially being important for sensing the level of neurotransmitter in cholinergic SVs.

Kinetics modeling and occupancy studies of a novel C-11 PET tracer for VAChT in nonhuman primates

INTRODUCTION

Deficits in cholinergic function have been found in the aged brain and in neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD). The vesicular acetylcholine transporter (VAChT) is a reliable biomarker for the cholinergic system. We previously reported the initial in vitro and ex vivo characterization of (-)-[(11)C]TZ659 as a VAChT specific ligand. Here, we report the in vivo specificity, tracer kinetics, and dose-occupancy studies in the nonhuman primate brain.

METHODS

MicroPET brain imaging of (-)-[(11)C]TZ659 was performed under baseline conditions in two male macaques. Tracer kinetic modeling was carried out using a two-tissue compartment model (2TCM) and Logan plot with arterial blood input function and using a simplified reference tissue model (SRTM) and Logan plot (LoganREF) without blood input. Specificity for VAChT was demonstrated by pretreatment with (+)-pentazocine, (-)-vesamicol, or S-(-)-eticlopride. Target occupancy (Occ) was calculated following pretreatment with escalating doses of (-)-vesamicol.

RESULTS

Baseline PET imaging revealed selective retention in the striatum with rapid clearance from the cerebellar hemispheres as a reference region. Total volume of distribution (VT) values derived from both 2TCM and Logan analysis with blood input revealed ~3-fold higher levels of (-)-[(11)C]TZ659 in the striatum than the cerebellar hemispheres. Injection of (-)-vesamicol either as a blocking or displacing agent significantly reduced striatal uptake of (-)-[(11)C]TZ659. In contrast, pretreatment with the sigma-1 ligand (+)-pentazocine had no impact. Pretreatment with the S-(-)-eticlopride, a dopamine D2-like receptor antagonist, increased striatal uptake of (-)-[(11)C]TZ659. Striatal binding potential (BPND, range of 0.33-1.6 with cerebellar hemispheres as the reference region) showed good correlation (r(2)=0.97) between SRTM and LoganREF. Occupancy studies found that ~0.0057 mg/kg of (-)-vesamicol produced 50% VAChT occupancy in the striatum.

CONCLUSION

(-)-[(11)C]TZ659 demonstrated specific and reversible VAChT binding and favorable pharmacokinetic properties for assessing the density of VAChT in the living brain.

Synthesis and biological characterization of a promising F-18 PET tracer for vesicular acetylcholine transporter

Nine fluorine-containing vesicular acetylcholine transporter (VAChT) inhibitors were synthesized and screened as potential PET tracers for imaging the VAChT. Compound 18a was one of the most promising carbonyl-containing benzovesamicol analogs; the minus enantiomer, (-)-18a displayed high potency (VAChT Ki=0.59 ± 0.06 nM) and high selectivity for VAChT versus σ receptors (>10,000-fold). The radiosynthesis of (-)-[(18)F]18a was accomplished by a two-step procedure with 30-40% radiochemical yield. Preliminary biodistribution studies of (-)-[(18)F]18a in adult male Sprague-Dawley rats at 5, 30, 60 and 120 min post-injection (p.i.) were promising. The total brain uptake of (-)-[(18)F]18a was 0.684%ID/g at 5 min p.i. and by 120 min p.i. slowly washed out to 0.409 %ID/g; evaluation of regional brain uptake showed stable levels of ∼0.800 %ID/g from 5 to 120 min p.i in the VAChT-enriched striatal tissue of rats, indicating the tracer had crossed the blood brain barrier and was retained in the striatum. Subsequent microPET brain imaging studies of (-)-[(18)F]18a in nonhuman primates (NHPs) showed high striatal accumulation in the NHP brain; the standardized uptake value (SUV) for striatum reached a maximum value of 5.1 at 15 min p.i. The time-activity curve for the target striatal region displayed a slow and gradual decreasing trend 15 min after injection, while clearance of the radioactivity from the cerebellar reference region was much more rapid. Pretreatment of NHPs with 0.25mg/kg of the VAChT inhibitor (-)-vesamicol resulted in a ∼90% decrease of striatal uptake compared to baseline studies. HPLC metabolite analysis of NHP plasma revealed that (-)-[(18)F]18a had a good in vivo stability. Together, these preliminary results suggest (-)-[(18)F]18a is a promising PET tracer candidate for imaging VAChT in the brain of living subjects.

PREPL deficiency with or without cystinuria causes a novel myasthenic syndrome

OBJECTIVE

To investigate the genetic and physiologic basis of the neuromuscular symptoms of hypotonia-cystinuria syndrome (HCS) and isolated PREPL deficiency, and their response to therapy.

METHODS

We performed molecular genetic, histochemical, immunoblot, and ultrastructural studies, investigated neuromuscular transmission in vitro in a patient with isolated PREPL deficiency, and evaluated the effect of pyridostigmine in this patient and in 3 patients with the HCS.

RESULTS

HCS is caused by recessive deletions involving the SLC3A1 and PREPL genes. The major clinical features of HCS are type A cystinuria, growth hormone deficiency, muscle weakness, ptosis, and feeding problems. The proband with isolated PREPL deficiency had myasthenic symptoms since birth and a positive edrophonium test but no cystinuria. She and 1 of 3 patients with HCS responded transiently to pyridostigmine during infancy. The proband harbors a paternally inherited nonsense mutation in PREPL and a maternally inherited deletion involving both PREPL and SLC3A1; therefore, the PREPL deficiency determines the phenotype. We detected no PREPL expression in the patient's muscle and endplates. Electrophysiology studies revealed decreased quantal content of the endplate potential and reduced amplitude of the miniature endplate potential without endplate acetylcholine receptor deficiency or altered endplate geometry.

CONCLUSION

Isolated PREPL deficiency is a novel monogenic disorder that causes a congenital myasthenic syndrome with pre- and postsynaptic features and growth hormone deficiency. The myasthenic symptoms in PREPL deficiency with or without cystinuria may respond to pyridostigmine in early life. We attribute the myasthenia to abrogated interaction of PREPL with adaptor protein 1.

Regional brain imaging of vesicular acetylcholine transporter using o-[125 I]iodo-trans-decalinvesamicol as a new potential imaging probe

In this study, the regional rat brain distribution of radioiodinated o-iodo-trans-decalinvesamicol ([(125) I]OIDV) was determined in vivo to evaluate its potential as a single-photon emission computed tomography (SPECT) imaging probe for vesicular acetylcholine transporter (VAChT). Following intravenous injection, [(125) I]OIDV passed freely across the blood-brain barrier and accumulated in rat brain. The accumulation of [(125) I]OIDV in rat brain was significantly reduced by coadministration of (+/-)-vesamicol (0.125 µmol). In contrast, the coadministration of σ-receptor ligands, such as (+)-pentazocine (0.125 µmol) as a σ-1 receptor ligand and (+)-3-(3-hydroxyphenyl)-N-propylpiperidine (0.125 µmol) as a σ-1 and σ-2 receptor ligands, barely affected the accumulation of [(125) I]OIDV in rat brain. These findings in vivo were corroborated by autoradiographic analysis ex vivo. The authors found that the tracer binds with pharmacological selectivity to VAChT in rat brain and predicted that it may likewise serve in translational SPECT imaging studies of this marker in the integrity of cholinergic innervations.

Localization of acetylcholine-related molecules in the retina: implication of the communication from photoreceptor to retinal pigment epithelium

It has been long speculated that specific signals are transmitted from photoreceptors to the retinal pigment epithelium (RPE). However, such signals have not been identified. In this study, we examined the retinal expression and localization of acetylcholine-related molecules as putative candidates for these signals. Previous reports revealed that α7 nicotinic acetylcholine receptors (nAChRs) are present in the microvilli of RPE cells that envelope the tips of photoreceptor outer segments (OS). Secreted mammalian leukocyte antigen 6/urokinase-type plasminogen activator receptor-related protein-1 (SLURP-1) is a positive allosteric modulator of the α7 nAChR. Therefore, we first focused on the expression of SLURP-1. SLURP-1 mRNA was expressed in the outer nuclear layer, which is comprised of photoreceptor cell bodies. SLURP-1 immunoreactivity co-localized with rhodopsin and S-opsin in photoreceptor OS, while choline acetyltransferase (ChAT) and high affinity choline transporter (CHT-1) were also expressed in photoreceptor OS. Immunoelectron microscopy identified that the majority of SLURP-1 was localized to the plasma membranes of photoreceptor OS. These results provide evidence that SLURP-1 is synthesized in photoreceptor cell bodies and transported to photoreceptor OS, where SLURP-1 may also be secreted. Our findings suggest that photoreceptor OS communicate via neurotransmitters such as ACh and SLURP-1, while RPE cells might receive these signals through α7 nAChRs in their microvilli.

Tail spasms in rat spinal cord injury: changes in interneuronal connectivity

Uncontrolled muscle spasms often develop after spinal cord injury. Structural and functional maladaptive changes in spinal neuronal circuits below the lesion site were postulated as an underlying mechanism but remain to be demonstrated in detail. To further explore the background of such secondary phenomena, rats received a complete sacral spinal cord transection at S(2) spinal level. Animals progressively developed signs of tail spasms starting 1 week after injury. Immunohistochemistry was performed on S(3/4) spinal cord sections from intact rats and animals were sacrificed 1, 4 and 12 weeks after injury. We found a progressive decrease of cholinergic input onto motoneuron somata starting 1 week post-lesion succeeded by shrinkage of the cholinergic interneuron cell bodies located around the central canal. The number of inhibitory GABAergic boutons in close contact with Ia afferent fibers was greatly reduced at 1 week after injury, potentially leading to a loss of inhibitory control of the Ia stretch reflex pathways. In addition, a gradual loss and shrinkage of GAD65 positive GABAergic cell bodies was detected in the medial portion of the spinal cord gray matter. These results show that major structural changes occur in the connectivity of the sacral spinal cord interneuronal circuits below the level of transection. They may contribute in an important way to the development of spastic symptoms after spinal cord injury, while reduced cholinergic input on motoneurons is assumed to result in the rapid exhaustion of the central drive required for the performance of locomotor movements in animals and humans.

Increased non-quantal release of acetylcholine after inhibition of endocytosis by methyl-β-cyclodextrin: the role of vesicular acetylcholine transporter

We investigated the role of the vesicular acetylcholine transporter in the mechanism of non-quantal (non-vesicular) secretion of neurotransmitter in the neuromuscular synapse of the rat diaphragm muscle. Non-quantal secretion was estimated electrophysiologically by the amplitude of end-plate hyperpolarization after inhibition of cholinesterase and nicotinic receptors (H-effect) or measured by the optical detection of acetylcholine in the bathing solution. It was shown that 1 mM methyl-β-cyclodextrin (MCD) reduced both endocytosis and, to much lesser extent, exocytosis of synaptic vesicles (SV) thereby increasing non-quantal secretion of acetylcholine with a concurrent decrease in axoplasm pH. During high-frequency stimulation of the motor nerve, that substantially increases vesicles exocytosis, the non-quantal secretion was further enhanced if the endocytosis of SV was blocked by MCD. In contrast, non-quantal secretion of acetylcholine did not increase when the MCD-treated neuromuscular preparations were superfused with either vesamicol, an inhibitor of vesicular transporter of acetylcholine, or sodium propionate, which decreases intracellular pH. These results suggest that the proton-dependent, vesamicol-sensitive vesicular transporters of acetylcholine, which become inserted into the presynaptic membrane during SV exocytosis and removed during endocytotic recycling of SV, play the major role in the process of non-quantal secretion of neurotransmitter.

Cholinergic innervation of pyramidal cells and parvalbumin-immunoreactive interneurons in the rat basolateral amygdala

The basolateral nucleus of the amygdala receives an extremely dense cholinergic innervation from the basal forebrain that is critical for memory consolidation. Although previous electron microscopic studies determined some of the postsynaptic targets of cholinergic afferents, the majority of postsynaptic structures were dendritic shafts whose neurons of origin were not identified. To make this determination, the present study analyzed the cholinergic innervation of the anterior subdivision of the basolateral amygdalar nucleus (BLa) of the rat using electron microscopic dual-labeling immunocytochemistry. The vesicular acetylcholine transporter (VAChT) was used as a marker for cholinergic terminals; calcium/calmodulin-dependent protein kinase II (CaMK) was used as a marker for pyramidal cells, the principal neurons of the BLa; and parvalbumin (PV) was used as a marker for the predominant interneuronal subpopulation in this nucleus. VAChT(+) terminals were visualized by using diaminobenzidine as a chromogen, whereas CAMK(+) or PV(+) neurons were visualized with Vector very intense purple (VIP) as a chromogen. Quantitative analyses revealed that the great majority of dendritic shafts receiving cholinergic inputs were CAMK(+) , indicating that they were of pyramidal cell origin. In fact, 89% of the postsynaptic targets of cholinergic terminals in the BLa were pyramidal cells, including perikarya (3%), dendritic shafts (47%), and dendritic spines (39%). PV(+) structures, including perikarya and dendrites, constituted 7% of the postsynaptic targets of cholinergic axon terminals. The cholinergic innervation of both pyramidal cells and PV(+) interneurons may constitute an anatomical substrate for the generation of oscillatory activity involved in memory consolidation by the BLa.

Localization of pre- and postsynaptic cholinergic markers in rodent forebrain: a brief history and comparison of rat and mouse

Rat and mouse models are widely used for studies in cognition and pathophysiology, among others. Here, we sought to determine to what extent these two model species differ for cholinergic and cholinoceptive features. For this purpose, we focused on cholinergic innervation patterns based on choline acetyltransferase (ChAT) immunostaining, and the expression of muscarinic acetylcholine receptors (mAChRs) detected immunocytochemically. In this brief review we first place cholinergic and cholinoceptive markers in a historic perspective, and then provide an overview of recent publications on cholinergic studies and techniques to provide a literature survey of current research. Next, we compare mouse (C57Bl/J6) and rat (Wistar) cholinergic and cholinoceptive systems simultaneously stained, respectively, for ChAT (analyzed qualitatively) and mAChRs (analyzed qualitatively and quantitatively). In general, the topographic cholinergic innervation patterns of both rodent species are highly comparable, with only considerable (but region specific) differences in number of detectable cholinergic interneurons, which are more numerous in rat. In contrast, immunolabeling for mAChRs, detected by the monoclonal antibody M35, differs markedly in the forebrain between the two species. In mouse brain, basal levels of activated and/or internalized mAChRs (as a consequence of cholinergic neurotransmission) are significantly higher. This suggests a higher cholinergic tone in mouse than rat, and hence the animal model of choice may have consequences for cholinergic drug testing experiments.

Synthesis and in vitro and in vivo evaluation of 18F-labeled positron emission tomography (PET) ligands for imaging the vesicular acetylcholine transporter

A new class of vesicular acetylcholine transporter inhibitor that incorporates a carbonyl group into the benzovesamicol structure was synthesized, and analogues were evaluated in vitro. (+/-)-trans-2-Hydroxy-3-(4-(4-[(18)F]fluorobenzoyl)piperidino)tetralin (9e) has K(i) values of 2.70 nM for VAChT, 191 nM for sigma(1), and 251 nM for sigma(2). The racemic precursor (9d) was resolved via chiral HPLC, and (+/-)-[(18)F]9e, (-)-[(18)F]9e, and (+)-[(18)F]9e were respectively radiolabeled via microwave irradiation of the appropriate precursors with [(18)F]/F(-) and Kryptofix/K(2)CO(3) in DMSO with radiochemical yields of approximately 50-60% and specific activities of >2000 mCi/micromol. (-)-[(18)F]9e uptake in rat brain was consistent with in vivo selectivity for the VAChT with an initial uptake of 0.911 %ID/g in rat striatum and a striatum/cerebellum ratio of 1.88 at 30 min postinjection (p.i.). MicroPET imaging of macaques demonstrated a 2.1 ratio of (-)-[(18)F]9e in putamen versus cerebellum at 2 h p.i. (-)-[(18)F]9e has potential to be a PET tracer for clinical imaging of the VAChT.

Coexistence of adrenergic and cholinergic nerves in the inferior hypogastric plexus: anatomical and immunohistochemical study with 3D reconstruction in human male fetus

Classic anatomical methods have failed to determine the precise location, origin and nature of nerve fibres in the inferior hypogastric plexus (IHP). The purpose of this study was to identify the location and nature (adrenergic and/or cholinergic) of IHP nerve fibres and to provide a three-dimensional (3D) representation of pelvic nerves and their relationship to other anatomical structures. Serial transverse sections of the pelvic portion of two human male fetuses (16 and 17 weeks' gestation) were studied histologically and immunohistochemically, digitized and reconstructed three-dimensionally. 3D reconstruction allowed a 'computer-assisted dissection', identifying the precise location and distribution of the pelvic nerve elements. Proximal (supra-levator) and distal (infra-levator) communications between the pudendal nerve and IHP were observed. By determining the nature of the nerve fibres using immunostaining, we were able to demonstrate that the hypogastric nerves and pelvic splanchnic nerves, which are classically considered purely sympathetic and parasympathetic, respectively, contain both adrenergic and cholinergic nerve fibres. The pelvic autonomic nervous system is more complex than previously thought, as adrenergic and cholinergic fibres were found to co-exist in both 'sympathetic' and 'parasympathetic' nerves. This study is the first step to a 3D cartography of neurotransmitter distribution which could help in the selection of molecules to be used in the treatment of incontinence, erectile dysfunction and ejaculatory disorders.

Synthesis and in vitro biological evaluation of carbonyl group-containing inhibitors of vesicular acetylcholine transporter

To identify selective high-affinity inhibitors of the vesicular acetylcholine transporter (VAChT), we have interposed a carbonyl group between the phenyl and piperidyl groups of the prototypical VAChT ligand vesamicol and its more potent analogues benzovesamicol and 5-aminobenzovesamicol. Of 33 compounds synthesized and tested, 6 display very high affinity for VAChT (K(i), 0.25-0.66 nM) and greater than 500-fold selectivity for VAChT over sigma(1) and sigma(2) receptors. Twelve compounds have high affinity (K(i), 1.0-10 nM) and good selectivity for VAChT. Furthermore, 3 halogenated compounds, namely, trans-3-[4-(4-fluorobenzoyl)piperidinyl]-2-hydroxy-1,2,3,4-tetrahydronaphthalene (28b) (K(i) = 2.7 nM, VAChT/sigma selectivity index = 70), trans-3-[4-(5-iodothienylcarbonyl)piperidinyl]-2-hydroxy-1,2,3,4-tetrahydronaphthalene (28h) (K(i) = 0.66 nM, VAChT/sigma selectivity index = 294), and 5-amino-3-[4-(p-fluorobenzoyl)piperidinyl]-2-hydroxy-1,2,3,4,-tetrahydronaphthalene (30b) (K(i) = 2.40 nM, VAChT/sigma selectivity index = 410) display moderate to high selectivity for VAChT. These three compounds can be synthesized with the corresponding radioisotopes so as to serve as PET/SPECT probes for imaging the VAChT in vivo.

Asymmetric regulation by estrogen at the cholinergic gene locus in differentiated NG108-15 neuronal cells

AIMS

Estrogen acts as a neurogenerative and neuroprotective factor in the cholinergic system. Choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) are regarded as markers of cholinergic neurons. The genes coding these proteins are located at a common locus, the cholinergic gene locus. However, few details concerning activation of the locus have been obtained. We examined the effect of estrogen on the activation pattern of the locus using a cholinergic cell line.

MAIN METHODS

NG108-15 neuronal cells, as a model of cholinergic neurons, were used. Dose-dependent effects of estradiol (E2) on the gene expression of ChAT and VAChT were quantitatively determined by a real-time RT-PCR. The expression of ChAT mRNA variants was qualitatively evaluated by RT-PCR using specific primers.

KEY FINDINGS

The expression of ChAT and VAChT mRNA was strongly enhanced with the induction of differentiation. The enhanced expression of ChAT mRNA was further increased dose-dependently by E2 (10(-10) to 10(-7)M), while that of VAChT mRNA did not respond to E2. The up-regulation of ChAT mRNA expression by E2 was abolished by co-treatment with a pure-antagonist of estrogen receptors. A qualitative analysis of ChAT mRNA variants revealed the R types, which share a common sequence with the VAChT gene, and type M ChAT mRNA to mainly be expressed, and that the appearance of these variants was not altered by E2.

SIGNIFICANCE

The cholinergic gene locus in differentiated NG108-15 neuronal cells is further activated by E2, but the effect is restricted to the transcription of ChAT gene.

Operons

Operons (clusters of co-regulated genes with related functions) are common features of bacterial genomes. More recently, functional gene clustering has been reported in eukaryotes, from yeasts to filamentous fungi, plants, and animals. Gene clusters can consist of paralogous genes that have most likely arisen by gene duplication. However, there are now many examples of eukaryotic gene clusters that contain functionally related but non-homologous genes and that represent functional gene organizations with operon-like features (physical clustering and co-regulation). These include gene clusters for use of different carbon and nitrogen sources in yeasts, for production of antibiotics, toxins, and virulence determinants in filamentous fungi, for production of defense compounds in plants, and for innate and adaptive immunity in animals (the major histocompatibility locus). The aim of this article is to review features of functional gene clusters in prokaryotes and eukaryotes and the significance of clustering for effective function.

Multiple protonation states of vesicular acetylcholine transporter detected by binding of [3H]vesamicol

Vesicular acetylcholine transporter (VAChT) is inhibited by (-)-vesamicol [(-)-trans-2-(4-phenylpiperidino)cyclohexanol], which binds tightly to an allosteric site. The tertiary alkylamine center in (-)-vesamicol is protonated and positively charged at acidic and neutral pH and unprotonated and uncharged at alkaline pH. Deprotonation of the amine has been taken to explain loss of (-)-vesamicol binding at alkaline pH. However, binding data deviate from a stereotypical bell shape, and more binding occurs than expected at alkaline pH. The current study characterizes the binding of (-)-vesamicol from pH 5 to pH 10 using filter assays, (-)-[3H]vesamicol (hereafter called [3H]vesamicol), and human VAChT expressed in PC12(A123.7) cells. At acidic pH, protons and [3H]vesamicol compete for binding to VAChT. Preexposure or long-term exposure of VAChT to high pH does not affect binding, thus eliminating potential denaturation of VAChT and failure of the filter assay. The dissociation constant for the complex between protonated [3H]vesamicol and VAChT decreases from 12 nM at neutral pH to 2.1 nM at pH 10. The simplest model of VAChT that explains the behavior requires a proton at site 1 to dissociate with pK1 = 6.5 +/- 0.1, a proton at site A to dissociate with pKA = 7.6 +/- 0.2, and a proton at site B to dissociate with pKB = 10.0 +/- 0.1. Deprotonation of the site 1 proton is obligatory for [3H]vesamicol binding. Deprotonation of site A decreases affinity (2.2 +/- 0.5)-fold, and deprotonation of site B increases affinity (18 +/- 4)-fold. Time-dependent dissociation of bound [3H]vesamicol is biphasic, but equilibrium saturation curves are not. The contrasting phasicity suggests that the pathway to and from the [3H]vesamicol binding site exists in open and at least partially closed states. The potential significance of the findings to development of PET and SPECT ligands based on (-)-vesamicol for human diagnostics also is discussed.

Cell type and function of neurons in the ascidian nervous system

Ascidians, or sea squirts, are primitive chordates, and their tadpole larvae share a basic body plan with vertebrates, including a notochord and a dorsal tubular central nervous system (CNS). The CNS of the ascidian larva is formed through a process similar to vertebrate neurulation, while the ascidian CNS is remarkably simple, consisting of about 100 neurons. Recent identification of genes that are specifically expressed in a particular subtype of neurons has enabled us to reveal neuronal networks at single-cell resolution. Based on the information on neuron subtype-specific genes, different populations of neurons have been visualized by whole-mount in situ hybridization, immunohistochemical staining using specific antibodies, and fluorescence labeling of cell bodies and neurites by a fluorescence protein reporter driven by neuron-specific promoters. Neuronal populations that have been successfully visualized include glutamatergic, cholinergic, gamma-aminobutyric acid/glycinergic, and dopaminergic neurons, which have allowed us to propose functional regionalization of the CNS and a neural circuit for locomotion. Thus, the simple nervous system of the ascidian larva can serve as an attractive model system for studying the development, function, and evolution of the chordate nervous system.

Immunohistochemical characterization and quantitative analysis of neurons in the myenteric plexus of the equine intestine

The present study was performed on whole-mount preparations to investigate the chemical neuroanatomy of the equine myenteric plexus throughout its distribution in the intestinal wall. The objective was to quantify neurons of the myenteric plexus, especially the predominant cholinergic and nitrergic subpopulations. Furthermore, we investigated the distribution of vasoactive intestinal polypeptide and the calcium-binding protein calretinin. Samples from different defined areas of the small intestine and the flexura pelvina were taken from 15 adult horses. After fixation and preparation of the tissue, immunofluorescence labeling was performed on free floating whole-mounts. Additionally, samples used for neuropeptide staining were incubated with colchicine to reveal the neuropeptide distribution within the neuronal soma. The evaluation was routinely accomplished using confocal laser-scanning microscopy. For quantitative and qualitative analysis, the pan-neuronal marker anti-HuC/D was applied in combination with the detection of the marker enzymes for cholinergic neurons and nitrergic nerve cells. Quantitative data revealed that the cholinergic subpopulation is larger than the nitrergic one in several different locations of the small intestine. On the contrary, the nitrergic neurons outnumber the cholinergic neurons in the flexura pelvina of the large colon. Furthermore, ganglia are more numerous in the small intestine compared with the large colon, but ganglion sizes are bigger in the large colon. However, comparison of the entire population of neurons in the different locations of the gut showed no difference. The present study adds further data on the chemoarchitecture of the myenteric plexus which might facilitate the understanding of several gastrointestinal disorders in the horse.

Ex vivo and in vivo evaluation of (2R,3R)-5-[(18)F]-fluoroethoxy- and fluoropropoxy-benzovesamicol, as PET radioligands for the vesicular acetylcholine transporter

Molecular imaging of the vesicular acetylcholine transporter (VAChT) using positron emission tomography (PET) may provide insights into early diagnosis and better understanding of Alzheimer's disease. We further characterized the VAChT ligand (2R,3R)-5-FEOBV (1) and developed new fluoropropoxy analogues. Ex vivo studies of the new nonradiolabeled analogues (2R,3R)-5-FPOBV (2) (k(D) = 0.7 nM) and (2S,3S)-5-FPOBV (3) (k(D) = 8.8 nM) were performed in rat brain and showed an enantioselective inhibition of (-)-5-[(125)I]-IBVM uptake in striatum, cortex, and hippocampus (e.g., 74% for 2 and only 54% for 3 in the cortex). Radiochemical procedures were developed to produce [(18)F]1 and [(18)F]2 as potential imaging agent for the VAChT. The radiochemistry was carried out in a one step procedure, with radiolabeling yields of 17 and 2.6% (range: 1-5.4), respectively, nondecay corrected with good specific activity: 124-338 GBq/micromol. The radiochemical purity was greater than 98%. The biological (ex vivo and in vivo) properties of these radioligands were evaluated in rats and showed a low (less then 0.1% of the injected dose) and homogeneous brain uptake. The in vivo PET study of [(18)F]2 performed in baboon also revealed rapid defluorination as the main problem. Therefore [(18)F]1 and [(18)F]2 appear to be unsuitable for in vivo imaging of the VAChT using PET.

ATP and acetylcholine, equal brethren

Acetylcholine was the first neurotransmitter identified and ATP is the hitherto final compound added to the list of small molecule neurotransmitters. Despite the wealth of evidence assigning a signaling role to extracellular ATP and other nucleotides in neural and non-neural tissues, the significance of this signaling pathway was accepted very reluctantly. In view of this, this short commentary contrasts the principal molecular and functional components of the cholinergic signaling pathway with those of ATP and other nucleotides. It highlights pathways of their discovery and analyses tissue distribution, synthesis, uptake, vesicular storage, receptors, release, extracellular hydrolysis as well as pathophysiological significance. There are differences but also striking similarities. Comparable to ACh, ATP is taken up and stored in synaptic vesicles, released in a Ca(2+)-dependent manner, acts on nearby ligand-gated or metabotropic receptors and is hydrolyzed extracellularly. ATP and acetylcholine are also costored and coreleased. In addition, ATP is coreleased from biogenic amine storing nerve terminals as well as from at least subpopulations of glutamatergic and GABAergic terminals. Both ACh and ATP fulfill the criteria postulated for neurotransmitters. More recent evidence reveals that the two messengers are not confined to neural functions, exerting a considerable variety of non-neural functions in non-innervated tissues. While it has long been known that a substantial number of pathologies originate from malfunctions of the cholinergic system there is now ample evidence that numerous pathological conditions have a purinergic component.

Cholinergic projections to the suprachiasmatic nucleus and lower subparaventricular zone of diurnal and nocturnal rodents

In nocturnal species cholinergic agonists alter circadian rhythm phase when injected intraventricularly or directly into the suprachiasmatic nucleus (SCN), but the phase shifts obtained differ depending upon the site being injected. Cholinergic projections reach the SCN of nocturnal laboratory rats, however, nothing is known about these projections in diurnal rodents. The first objective of this study was to evaluate the hypothesis that cholinergic projections to the SCN are only present in nocturnal species. The second objective was to evaluate the hypothesis that the lower part of the subparaventricular zone (LSPV) is a candidate for being a site that mediates the phase shifts observed when cholinergic agonists are injected intraventricularly. These hypotheses were tested in the diurnal unstriped Nile grass rat (Arvicanthis niloticus) and the nocturnal laboratory rat. Additionally, we evaluated if the light-dark (LD) cycle had an effect on the expression of the vesicular acetylcholine transporter (VAChT) in the SCN, LSPV, and in two control areas. Animals were kept in a 12:12 LD cycle and perfused at six time points. VAChT immunoreactivity was observed in the SCN, LSPV, and in the control areas of both species. The SCN and LSPV showed a differential distribution and density of cholinergic projections between the two species, but similar temporal patterns of VAChT expression were found across species. These results provide evidence for a differential cholinergic stimulation of the SCN between grass rats and laboratory rats that may reflect a rewiring of neural projections brought about by the adoption of a diurnal activity profile.

Vesicular acetylcholine transporter–immunoreactive axon terminals enriched in the pontine nuclei of the mouse

Information to the cerebellum enters via many afferent sources collectively known as precerebellar nuclei. We investigated the distribution of cholinergic terminal-like structures in the mouse precerebellar nuclei by immunohistochemistry for vesicular acetylcholine transporter (VAChT). VAChT is involved in acetylcholine transport into synaptic vesicles and is regarded as a reliable marker for cholinergic terminals and preterminal axons. In adult male mice, brains were perfusion-fixed. Polyclonal antibodies for VAChT, immunoglobulin G-peroxidase and diaminobenzidine were used for immunostaining. In the mouse brain, immunoreactivity was seen in almost all major cholinergic cell groups including brainstem motoneurons. In precerebellar nuclei, the signal could be detected as diffusely beaded terminal-like structures. It was seen heaviest in the pontine nuclei and moderate in the pontine reticulotegmental nucleus; however, it was seen less in the medial solitary nucleus, red nucleus, lateral reticular nucleus, inferior olivary nucleus, external cuneate nucleus and vestibular nuclear complex. In particular, VAChT-immunoreactive varicose fibers were so dense in the pontine nuclei that detailed distribution was studied using three-dimensional reconstruction of the pontine nuclei. VAChT-like immunoreactivity clustered predominantly in the medial and ventral regions suggesting a unique regional difference of the cholinergic input. Electron microscopic observation in the pontine nuclei disclosed ultrastructural features of VAChT-immunoreactive varicosities. The labeled bouton makes a symmetrical synapse with unlabeled dendrites and contains pleomorphic synaptic vesicles. To clarify the neurons of origin of VAChT-immunoreactive terminals, VAChT immunostaining combined with wheat germ agglutinin-conjugated horseradish peroxidase retrograde labeling was conducted by injecting a retrograde tracer into the right pontine nuclei. Double-labeled neurons were seen bilaterally in the laterodorsal tegmental nucleus and pedunculopontine tegmental nucleus. It is assumed that mesopontine cholinergic neurons negatively regulate neocortico-ponto-cerebellar projections at the level of pontine nuclei.

Glutamatergic functions of primary afferent neurons with special emphasis on vagal afferents

Glutamate has been identified as the main transmitter of primary afferent neurons. This was established based on biochemical, electrophysiological, and immunohistochemical data from studies on glutamatergic receptors and their agonists/antagonists. The availability of specific antibodies directed against glutamate and, more recently, vesicular glutamate transporters corroborated this and led to significant new discoveries. In particular, peripheral endings of various classes of afferents contain vesicular glutamate transporters, suggesting vesicular storage in and exocytotic release of glutamate from peripheral afferent endings. This suggests that autocrine mechanisms regulate sensory transduction processes. However, glutamate release from peripheral sensory terminals could also enable afferent neurons to influence various cells associated with them. This may be particularly relevant for vagal intraganglionic laminar endings, which could represent glutamatergic sensor-effector components of intramural reflex arcs in the gastrointestinal tract. Thus, morphological analysis of the relationships of putative glutamatergic primary afferents with associated tissues may direct forthcoming studies on their functions.

Transient suppression of the vesicular acetylcholine transporter in urinary bladder pathways following spinal cord injury

The aim of this study was to examine the expression profile of the vesicular acetylcholine transporter (VAChT), which is a cholinergic pre-synaptic marker, in the lower neural tract following spinal cord injury (SCI) and its effect on coordination of micturition. In adult female Sprague-Dawley rats, SCI was induced by complete transection of the spinal cord at T9. At various time points, 3, 7, 14 and 28 days, after SCI, cystometry was performed on conscious rats. Bladder areflexia was observed during the first week. Twenty-eight days after SCI the rats showed reflex contractions and voiding. The expression of VAChT was examined with immunohistochemistry. The number of VAChT-positive nerve terminals, which were surrounding neuronal soma, was transiently decreased in pelvic ganglion and spinal cord (L1, L2, L6 and S1). In particular VAChT terminals surrounding motor neurons in the ventral horn and autonomic pre-ganglion cells were dramatically decreased from 3 to 14 days after SCI. Similarly, and the number of VAChT-positive fibers in the bladder wall was also decreased. The intensity of VAChT terminals recovered in all above regions in conjunction with recovery of bladder function. These observations indicate that the transient decrease of the VAChT-positive nerve might cause a failure of cholinergic neuronal transmission along the urinary bladder tract after SCI. As the cholinergic system was recovered at least in rat, the functional recovery of neurogenic bladder syndrome in SCI patients may become possible by further understanding the mechanism underlying the recovery of cholinergic system in rat.

The vesicular acetylcholine transporter is present in melanocytes and keratinocytes in the human epidermis

The human epidermis holds the full machinery for cholinergic signal transduction. However, the presence of the vesicular transporter (vesicular acetylcholine (ACh) transporter (VAChT)) for both choline and ACh has never been shown in this compartment. The results of this study confirm the presence of VAChT in cutaneous nerves and in both epidermal melanocytes and keratinocytes as well as in their nuclei using immunofluorescence labelling in situ and in vitro, Western blot analysis of cellular and nuclear extracts and reverse transcription-PCR. These results underline that ACh/choline transport in the non-neuronal epidermis is no different from the neuronal pathway. However, the function of VAChT in the nucleus remains to be shown.

Changes in vesicular glutamate transporter 2, vesicular GABA transporter and vesicular acetylcholine transporter labeling of sacrocaudal motoneurons in the spastic rat

Spasticity of the midline musculature can significantly hinder performing transfers and lead to development of pressure sores. Currently, significant gaps exist in our knowledge of the pathophysiology involved in spasticity development following SCI, especially regarding the axial musculature. The goals of this study were: (1) to determine the effects of S(2) transection on the number and distribution of glutamatergic, GABAergic and cholinergic inputs on more caudal motoneurons, (2) to correlate these changes with the development of spasticity within the tail musculature, which are the caudal counterparts to the axial musculature. Animals with S(2) spinal transection were tested behaviorally for the progression of spasticity within the tail musculature. At 1, 2, 4, or 12 weeks post-injury, the animals were sacrificed and temporal changes in glutamatergic, GABAergic, and cholinergic inputs to sacrocaudal motoneurons were assessed using antibodies for the specific vesicular transporter of each neurotransmitter and confocal microscopy. At 1 week post-injury, when the tail musculature demonstrated decreased responsiveness, an overall increase in the ratio of excitatory to inhibitory input to sacrocaudal motoneurons was observed. From 2 to 12 weeks post-injury, when the tail musculature demonstrated increased reflex behavior, an overall decrease in the ratio of excitatory to inhibitory inputs was observed. Additionally, from 2 to 12 weeks following spinal transection, a progressive loss of cholinergic labeling of sacrocaudal motoneurons was observed. The increase in the overall level of excitation with a concomitant loss of cholinergic influence following spinal transection could, in part, explain the development of spasticity within the tail musculature.

Heterogeneity of neuromuscular junctions in striated muscle of human esophagus demonstrated by triple staining for the vesicular acetylcholine transporter, α-bungarotoxin, and acetylcholinesterase

During studies on enteric co-innervation in the human esophagus, we found that not all acetylcholinesterase (AChE)-positive motor endplates stained for alpha-bungarotoxin (alpha-BT) and the vesicular acetylcholine transporter (VAChT), respectively. Therefore, we probed for differences in neuromuscular junctions in human esophagus by using triple staining for VAChT, alpha-BT, and AChE followed by qualitative and quantitative analysis. To exclude that the results were caused by processing artifacts, we additionally examined the influence of a number of factors including post-mortem changes and the type and duration of fixation on the staining results. Four types of neuromuscular junction could be distinguished in human esophagus: type I with VAChT-positive and type II with VAChT-negative nerve terminals on a alpha-BT-positive and AChE-positive endplate area, type III with VAChT-positive nerve terminals on a alpha-BT-negative but AChE-positive endplate area, and type IV with VAChT-negative nerve terminals on a alpha-BT-negative but AChE-positive endplate area. On average, 32% of evaluated AChE-positive motor endplates were type I, 6% type II, 24% type III, and 38% type IV. Based on these results, we suggest that, in human esophagus, (1) the most reliable method for staining motor endplates is presently AChE histochemistry, (2) alpha-BT-sensitive and alpha-BT-resistant nicotinic acetylcholine receptors exist in neuromuscular junctions, and (3) different types of VAChT or transport mechanisms for acetylcholine probably exist in neuromuscular junctions.

Nicotinic cholinergic intercellular communication: implications for the developing auditory system

In this paper, research on the temporal and spatial distribution of cholinergic-related molecules in the lower auditory brainstem, with an emphasis on nicotinic acetylcholine receptors (nAChRs), is reviewed. The possible functions of acetylcholine (ACh) in driving selective auditory neurons before the onset of hearing, inducing glutamate receptor gene expression, synaptogenesis, differentiation, and cell survival are discussed. Experiments conducted in other neuronal and non-neuronal systems are drawn on extensively to discuss putative functions of ACh and nAChRs. Data from other systems may provide insight into the functions of ACh and nAChRs in auditory processing. The mismatch of presynaptic and postsynaptic markers and novel endogenous agonists of nAChRs are discussed in the context of non-classical interneuronal communication. The molecular mechanism that may underlie the many functions of ACh and its agonists is the regulation of intracellular calcium through nAChRs. The possible reorganization that may take place in the auditory system by the exposure to nicotine during critical developmental periods is also briefly considered.

Post-training intrahippocampal infusion of nicotine prevents spatial memory retention deficits induced by the cyclo-oxygenase-2-specific inhibitor celecoxib in rats

Recently, we demonstrated that intrahippocampal infusion of the cyclo-oxygenase (COX)-2-specific inhibitor celecoxib impaired spatial memory retention in the Morris water maze. In the present work, we investigated the effects of nicotine, infused in the rat dorsal hippocampus several minutes after infusion of celecoxib, on memory retention in the Morris water maze. Rats were trained for 3 days; each day included two blocks, and each block contained four trials. Test trials were conducted 48 h after surgery. As expected, bilateral intrahippocampal infusion of celecoxib (19 microg/side; 0.1 m) increased escape latency and travel distance in rats, indicating significant impairment of spatial memory retention. We also examined the effects of bilateral infusion of nicotine (0.5, 1.0 and 2.0 microg/side) on memory retention. Infusion of 1 microg nicotine significantly decreased escape latency and travel distance but not swimming speed, compared with controls, suggesting memory retention enhancement by nicotine at this concentration. In separate experiments, bilateral infusion of nicotine, infused 5 min after 0.1 m (19 microg/side) celecoxib infusion, was associated with escape latency, travel distance and swimming speed profiles very similar to those in control animals. Brain tissue sections from several of these animals were subjected to immunohistochemical staining analysis with anti-COX-2 antibodies. Quantification analysis by optical density measurements showed that the celecoxib infusion reduced the immunoreactivity of COX-2-containing neurons in the CA1 area of the hippocampus compared with controls, although this reduction was not significant. However, infusion of a combination of celecoxib and nicotine significantly increased this immunoreactivity compared with levels in control and celecoxib-infused groups. These results suggest that nicotine prevented or reversed the adverse effects of celecoxib on spatial memory retention and protected or restored the immunostaining pattern of COX-2 neurons in the rat dorsal hippocampus.

The evolving theory of basal forebrain functional-anatomical 'macrosystems'

The conceptual basis and continuing development of Alheid and Heimer's [Alheid, G.F., Heimer, L., 1988. New perspectives in basal forebrain organization of special relevance for neuropsychiatric disorders: the striatopallidal, amygdaloid and corticopetal components of substantia innominata. Neuroscience 27, 1-39] theory of basal forebrain organization based on the description of basal forebrain functional-anatomical 'macrosytems' is reviewed. It is posed that the macrosystem theory leads to a hypothesis that different macrosystems cooperate and compete to exert distinct influences on motor and cognitive function. Emergent corollaries include, e.g. that the organization of the outputs of different macrosystems should differ. Consistent with these considerations, extant literature and some unpublished data indicate that the input nuclei of macrosystems are not abundantly interconnected and macrosystems systems have distinct neuroanatomical relationships with basal forebrain and brainstem cholinergic and dopaminergic ascending modulatory systems. Furthermore, macrosystem outputs appear to be directed almost exclusively at the reticular formation or structures intimately associated with it. The relative merits of the theory of functional-anatomical macrosystems are discussed in relation to Swanson's model of cerebral hemisphere control of motivated behavior.

Restricted response of mesencephalic neural crest to sympathetic differentiation signals in the trunk

Lineage diversification in the vertebrate neural crest may occur via instructive signals acting on pluripotent cells, and/or via early specification of subpopulations towards particular lineages. Mesencephalic neural crest cells normally form cholinergic parasympathetic neurons in the ciliary ganglion, while trunk neural crest cells normally form both catecholaminergic and cholinergic neurons in sympathetic ganglia. In contrast to trunk neural crest cells, mesencephalic neural crest cells apparently fail to express the catecholaminergic transcription factor dHAND in response to BMPs in the head environment. Here, we show that migrating quail mesencephalic neural crest cells grafted into the trunk of host chick embryos colonise the sympathetic ganglia. While many express dHAND and form tyrosine hydroxylase (TH)-positive catecholaminergic neurons, the proportion that expresses either dHAND or TH is significantly smaller than that of quail trunk neural crest cells under the same conditions. Furthermore, the proportion of quail mesencephalic neural crest cells that is TH+ in the sympathetic ganglia decreases with time, while the proportion of TH+ quail trunk neural crest-derived cells increases. Thus, a subset of mesencephalic neural crest cells fails to express dHAND or TH in the sympathetic ganglia, while a further subset initiates but fails to maintain TH expression. Taken together, our results suggest that a subpopulation of migrating mesencephalic neural crest cells is refractory to catecholaminergic differentiation signals in the trunk. We suggest that this heterogeneity, together with local signals that repress catecholaminergic differentiation, may ensure that most ciliary neurons adopt a cholinergic fate.

Membrane and firing properties of glutamatergic and GABAergic neurons in the rat medial vestibular nucleus

In previous studies, neurons in the medial vestibular nucleus (MVN) were classified mainly into 2 types according to their intrinsic membrane properties in in vitro slice preparations. However, it has not been determined whether the classified neurons are excitatory or inhibitory ones. In the present study, to clarify the relationship between the chemical and electrophysiological properties of MVN neurons, we explored mRNAs of cellular markers for GABAergic (glutamic acid decarboxylase 65, 67, and neuronal GABA transporter), glutamatergic (vesicular glutamate transporter 1 and 2), glycinergic (glycine transporter 2), and cholinergic neurons (choline acetyltransferase and vesicular acetylcholine transporter) expressed in electrophysiologically characterized MVN neurons in rat brain stem slice preparations. For this purpose, we combined whole cell patch-clamp recording analysis with single-cell reverse transcription-polymerase chain reaction (RT-PCR) analysis. We examined the membrane properties such as afterhyperpolarization (AHP), firing pattern, and response to hyperpolarizing current pulse to classify MVN neurons. From the single-cell RT-PCR analysis, we found that GABAergic neurons consisted of heterogeneous populations with different membrane properties. Comparison of the membrane properties of GABAergic neurons with those of other neurons revealed that AHPs without slow components and a firing pattern with delayed spike generation (late spiking) were preferential properties of GABAergic neurons. On the other hand, most glutamatergic neurons formed a homogeneous subclass of neurons exhibiting AHPs with slow components, repetitive firings with constant interspike intervals (continuous spiking), and time-dependent inward rectification in response to hyperpolarizing current pulses. We also found a small number of cholinergic neurons with various membrane properties. These findings clarify the electrophysiological properties of excitatory and inhibitory neurons in the MVN, and the information about the preferential membrane properties may be useful for identifying GABAergic and glutamatergic MVN neurons electrophysiologically.

Vesicular acetylcholine transporter can be a morphological marker for the reinnervation to muscle of regenerating motor axons

This study was designed to evaluate whether the vesicular acetylcholine transporter (VAChT), which packages acetylcholine into synaptic vesicles, can be used as a marker for regenerating motor axon terminal. We examined motor axon regeneration in the tongue after hypoglossal nerve axotomy, using an anterograde tracer biotin-dextran (BD), retrograde tracer Fluoro-Gold (FG), electron microscopic (EM) observation, and VAChT immunocytochemistry. BD study demonstrated that outgrowth of thin regenerating axons into the frontal area of the tongue was firstly observed at 14 post-operative days, and presynaptic formation of neuromuscular junction (NMJ) was observed from 21 post-operative days. Under electron microscopic observation, reconstruction of new NMJs was observed within the interval between 21 and 28 days. VAChT-immunoreactive nerve terminals disappeared by 3 days after axotomy, slightly appeared at 14 post-operative days, and thereafter gradually increased in number from 21 to 28 post-operative days. The re-expression of VAChT positive presynaptic terminal was almost the same as those obtained in BD, FG and EM studies. Regenerating axons tip in the crush model of the hypoglossal nerve exhibited prominent VAChT immunoreactivity in growing tip of regenerating axons. These indicate that VAChT is an excellent morphological indicator for regenerating nerve terminals of motor neurons.

Regulation of vesicular neurotransmitter transporters

Neurotransmitters are key molecules of neurotransmission. They are concentrated first in the cytosol and then in small synaptic vesicles of presynaptic terminals by the activity of specific neurotransmitter transporters of the plasma and the vesicular membrane, respectively. It has been shown that postsynaptic responses to single neurotransmitter packets vary over a wide range, which may be due to a regulation of vesicular neurotransmitter filling. Vesicular filling depends on the availability of transmitter molecules in the cytoplasm and the active transport into secretory vesicles relying on a proton gradient. In addition, it is modulated by vesicle-associated heterotrimeric G proteins, Galphao2 and Galphaq, which regulate VMAT activities in brain and platelets, respectively, and may also be involved in the regulation of VGLUTs. It appears that the vesicular content activates the G protein, suggesting a signal transduction form the luminal site which might be mediated by a vesicular G-protein coupled receptor or, as an alternative, possibly by the transporter itself. These novel functions of G proteins in the control of transmitter storage may link regulation of the vesicular content to intracellular signal cascades.