Episodic-like memory deficits in the APPswe/PS1dE9 mouse model of Alzheimer's disease: relationships to beta-amyloid deposition and neurotransmitter abnormalities

Transgenic mice made by crossing animals expressing mutant amyloid precursor protein (APPswe) to mutant presenilin 1 (PS1dE9) allow for incremental increases in Abeta42 production and provide a model of Alzheimer-type amyloidosis. Here, we examine cognition in 6- and 18-month old transgenic mice expressing APPswe and PS1dE9, alone and in combination. Spatial reference memory was assessed in a standard Morris Water Maze task followed by assessment of episodic-like memory in Repeated Reversal and Radial Water maze tasks. We then used factor analysis to relate changes in performance in these tasks with cholinergic markers, somatostatin levels, and amyloid burden. At 6 months of age, APPswe/PS1dE9 double-transgenic mice showed visible plaque deposition; however, all genotypes, including double-transgenic mice, were indistinguishable from nontransgenic animals in all cognitive measures. In the 18-month-old cohorts, amyloid burdens were much higher in APPswe/PS1dE9 mice with statistically significant but mild decreases in cholinergic markers (cortex and hippocampus) and somatostatin levels (cortex). APPswe/PS1dE9 mice performed all cognitive tasks less well than mice from all other genotypes. Factor and correlation analyses defined the strongest correlation as between deficits in episodic-like memory tasks and total Abeta loads in the brain. Collectively, we find that, in the APPswe/PS1dE9 mouse model, some form of Abeta associated with amyloid deposition can disrupt cognitive circuits when the cholinergic and somatostatinergic systems remain relatively intact; and that episodic-like memory seems to be more sensitive to the toxic effects of Abeta.

Regulation of cholinergic gene expression by nerve growth factor depends on the phosphatidylinositol-3'-kinase pathway

Nerve growth factor (NGF) exerts anti-apoptotic, trophic and differentiating actions on sympathetic neurons and cholinergic cells of the basal forebrain and activates the expression of genes regulating the synthesis and storage of the neurotransmitter acetylcholine (ACh). We have been studying the intracellular signaling pathways involved in this process. Although, in the rat pheochromocytoma cell line PC12, NGF strongly activates the mitogen-activated protein kinase (MAPK) pathway, prolonged inhibition of MAPK kinase (MEK) activity by PD98059 or U0126 did not affect the ability of NGF to up-regulate choline acetyltransferase (ChAT) or to increase intracellular ACh levels. In contrast, the treatment with the phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002, but not with its inactive analogue LY303511, completely abolished the NGF-induced production of ACh. Inhibition of PI3K also eliminated the NGF effect on the intracellular ACh level in primary cultures of septal neurons from E18 mouse embryos. Blocking the PI3K pathway prevented the activation of cholinergic gene expression, as demonstrated in RT/PCR assays and in transient transfections of PC12 cells with cholinergic locus promoter-luciferase reporter constructs. These results indicate that the PI3K pathway, but not the MEK/MAPK pathway, is the mediator of NGF-induced cholinergic differentiation.

Blood‐cell‐specific acetylcholinesterase splice variations under changing stimuli

Developmental and trauma-induced mechanism(s) that modify inflammation and immune responses in blood cells were recently found to be regulated by acetylcholine. Here, we report corresponding blood cell-specific changes in acetylcholinesterase splice variants. Plasmon resonance and flow cytometry using acetylcholinesterase variant-specific antibody probes, revealed a progressive increase in myeloid cell fractions expressing the apoptosis-related acetylcholinesterase-S variant from newborns to adult controls and post-delivery mothers. Hematopoietic cell fractions positive for the myeloproliferative acetylcholinesterase-R variant, were similarly high in post-partum blood, both intracellular and on the cell surface. Moreover, intracellular acetylcholinesterase-S protein amounts as reflected by fluorescence intensity measurements remained unchanged in myeloid cells from post-partum mothers as compared with matched controls. Unlike brain neurons, which over-express intracellular acetylcholinesterase-R under stress, lymphocytes from post-partum mothers presented increased surface acetylcholinesterase-S and pronounced decreases in both the expression and contents of surface acetylcholinesterase-R. Peripheral stimuli-induced modulations in acetylcholine regulation may hence reflect blood cell lineage-dependent acetylcholinesterase splice variations.

The acetylcholine innervation of cerebral cortex: new data on its normal development and its fate in the hAPP(SW,IND) mouse model of Alzheimer's disease

To follow on prior studies of the cerebral cortex, we examined the acetylcholine innervation in the developing hippocampus of rat, by means of light and electron microscopic immunocytochemistry with a highly sensitive antibody against choline acetyltransferease. As in neocortex, the growth of this innervation mostly occurred within the first two weeks after birth. A preliminary ultrastructural survey indicated that a vast majority of these ChAT-immunostained axon varicosities were asynaptic during development as in the adult. In parallel, we quantified the cholinergic innervations of cerebral cortex and hippocampus in transgenic mice overexpressing human beta-amyloid peptide (hAPP(SW,IND)). A selective, widespread, plaque independent cholinergic denervation was thus demonstrated, first in hippocampus and then neocortex, in addition to a non-selective, plaque-dependent, local neurotoxic effect of aggregated beta-amyloid on ACh and 5-HT axons.

Relationships between cholinergic phenotype and acetyl-CoA level in hybrid murine neuroblastoma cells of septal origin

High susceptibility of cholinergic neurons to neurotoxic signals may result from their utilization of acetyl-CoA for both energy production and acetylcholine synthesis. SN56 cholinergic cells were transfected stably with cDNA for choline acetyltransferase. Transfected cells (SN56ChAT2) expressed choline acetyltransferase activity and acetylcholine content, 17 times and 2 times higher, respectively, than did nontransfected cells. Transfection did not change pyruvate dehydrogenase but decreased the acetyl-CoA level by 62%. Differentiation by cAMP and retinoic acid caused an increase of choline acetyltransferase activity and decrease of acetyl-CoA levels in both cell lines. Negative correlation was found between choline acetyltransferase activity and acetyl-CoA level in these cells. SN56ChAT2 cells were more susceptible to excess NO than were native SN56 cells, as evidenced by the thiazolyl blue reduction assay. Thus, the sensitivity of cholinergic neurons to pathologic conditions may depend on the cholinergic phenotype-dependent availability of acetyl-CoA.

The non-neuronal cholinergic system in humans: expression, function and pathophysiology

Acetylcholine, a prime example of a neurotransmitter, has been detected in bacteria, algae, protozoa, and primitive plants, indicating an extremely early appearance in the evolutionary process (about 3 billion years). In humans, acetylcholine and/or the synthesizing enzyme, choline acetyltransferase (ChAT), have been found in epithelial cells (airways, alimentary tract, urogenital tract, epidermis), mesothelial (pleura, pericardium), endothelial, muscle and immune cells (mononuclear cells, granulocytes, alveolar macrophages, mast cells). The widespread expression of non-neuronal acetylcholine is accompanied by the ubiquitous presence of cholinesterase and receptors (nicotinic, muscarinic). Thus, the non-neuronal cholinergic system and non-neuronal acetylcholine, acting as a local cellular signaling molecule, has to be discriminated from the neuronal cholinergic system and neuronal acetylcholine, acting as neurotransmitter. In the human placenta anti-ChAT immunoreactivity is found in multiple subcellular compartments like the cell membrane (microvilli, coated pits), endosomes, cytoskeleton, mitochondria and in the cell nucleus. These locations correspond with the results of experiments where possible functions of non-neuronal acetylcholine have been identified (proliferation, differentiation, organization of the cytoskeleton and the cell-cell contact, locomotion, migration, ciliary activity, immune functions). In the human placenta acetylcholine release is mediated by organic cation transporters. Thus, structural and functional differences are evident between the non-neuronal and neuronal cholinergic system. Enhanced levels of acetylcholine are detected in inflammatory diseases. In conclusion, it is time to revise the role of acetylcholine in humans. Its biological and pathobiological roles have to be elucidated in more detail and possibly, new therapeutical targets may become available.

Evolutional study on acetylcholine expression

Acetylcholine (ACh) is a well-known neurotransmitter in the cholinergic nervous systems of vertebrates and insects; however, there is only indirect evidence for its presence in lower invertebrates, such as plants and fungi. We therefore investigated the expression of ACh in invertebrates (sea squirt, sea urchin, trepang, squid, abalone, nereis, sea anemone, coral and sponge), plants (arabidopsis, eggplant, bamboo shoot, cedar, hinoki, pine, podcarp, fern, horsetail and moss), fungi (yeast and mushroom) and bacteria by assaying ACh content and synthesis, focusing on the presence of two synthetic enzymes, choline acetyltransferase (ChAT) and carnitine acetyltransferase (CarAT). Using a specific radioimmunoassay, ACh was detected in all samples tested. The levels varied considerably, however, with the upper portion of bamboo shoots having the highest content (2.9 micromol/g). ACh synthesis was also detected in all samples tested; moreover, the activity in most samples from the animal kingdom, as well as bamboo shoots and the stem of the shiitake mushroom, were sensitive to both ChAT and CarAT inhibitors. Levels of ACh synthesis were lower in samples from other plants, fungi and bacteria and were insensitive to ChAT and CarAT inhibitors. These findings demonstrate the presence of ACh and ACh-synthesizing activity in evolutionally primitive life as well as in more complex multicellular organisms. In the context of the recent discovery of non-neuronal ACh in various mammalian species, these findings suggest that ACh been expressed in organisms from the beginning of life, functioning as a local mediator as well as a neurotransmitter.

Congenital myasthenic syndrome associated with episodic apnea and sudden infant death

The sudden infant death syndrome has multiple etiologies. Some congenital myasthenic syndromes can cause sudden infant death syndrome by apnea, but the frequency of this etiology is unknown. We report here a young patient with sudden respiratory crises culminating in apnea followed by recovery, against a background of no or variable myasthenic symptoms without dyspnea. One sib without myasthenic symptoms and one sib who only had mild ptosis died previously during febrile episodes. Studies reported by us elsewhere traced the proband's illness to mutations in choline acetyltransferase. Here, we describe in detail the morphologic investigations and electrophysiologic findings, which point to a presynaptic defect in acetylcholine resynthesis or vesicular filling, in the proband. Analysis of DNA from a sib who previously died of sudden infant death syndrome revealed the same choline acetyltransferase mutation. Thus, mutations in choline acetyltransferase may be a cause of sudden infant death syndrome as, theoretically, could other presynaptic myasthenic disorders.

Ion channel variation causes epilepsies

The discovery of genetically transmissible form of epilepsy associated with a mutation in a gene that codes for a subunit of a ligand-gated channel shined a new light in this field of neurological diseases. Because this gene (CHRNA4) codes for a neuronal nicotinic acetylcholine receptor subunit, functional studies could be designed to evaluate the alterations caused by this mutation. Since this initial observation, five mutations were identified and determination of their functional properties initiated. These experiments were extended to pairwise expression of the control and mutated allele to mimic the heterozygote human genotype. The first common functional trait identified so far, in four of these mutants, is an increased sensitivity to the acetylcholine, suggesting that these mutations may cause a gain of function. An alternative possibility that cannot be excluded is that conditions in the brain are such that these higher responding receptors may be more prone to desensitization. The importance of ionic channels as cause of epilepsies was further demonstrated with the identification of the association between the benign neonatal epilepsy and mutations in genes coding for potassium channel subunits (KCNQ2, KCNQ3). Additional evidences were brought by the identification of mutations in voltage-dependent sodium channels (SCN1A, SCN1B) in a form of generalized epilepsy with febrile seizures.

Independent patterns of transcription for the products of the rat cholinergic gene locus

The cholinergic phenotype requires the expression of the vesicular acetylcholine transporter and choline acetyltransferase proteins. Both genes are encoded at one chromosomal location called the cholinergic gene locus. We have identified by in situ hybridization histochemistry distinct patterns of transcription from the cholinergic gene locus in the subdivisions of the rat cholinergic nervous system. The vesicular acetylcholine transporter and choline acetyltransferase are co-expressed in cholinergic neurons at all developmental stages in all major types of cholinergic neurons. The relative levels of vesicular acetylcholine transporter and choline acetyltransferase transcripts, however, change substantially during development in the CNS. They also differ dramatically in distinct subdivisions of the mature cholinergic nervous system, with vesicular acetylcholine transporter mRNA expressed at high levels relative to choline acetyltransferase mRNA in the peripheral nervous system, but at equivalent levels in the CNS. Expression of the R-exon, the presumptive first non-coding exon common to both the vesicular acetylcholine transporter and choline acetyltransferase, was not detectable at any developmental stage in any of the cholinergic neuronal subtypes in the rat nervous system. Thus, in contrast to less complex metazoan organisms, production of the vesicular acetylcholine transporter and choline acetyltransferase via a common differentially spliced transcript does not seem to occur to a significant extent in the rat. We suggest that separate transcriptional start sites within the cholinergic gene locus control vesicular acetylcholine transporter and choline acetyltransferase transcription, while additional elements are responsible for the specific transcriptional control of the entire locus in cholinergic versus non-cholinergic neurons. Independent transcription of the vesicular acetylcholine transporter and choline acetyltransferase genes provides a mechanism for regulating the relative expression of these two proteins to fine-tune acetylcholine quantal size in different types of cholinergic neurons, both centrally and peripherally.

Synaptic exocytosis and nervous system development impaired in Caenorhabditis elegans unc-13 mutants

C. elegans mutants defective in unc-13 exhibited severe behavioral abnormalities including paralyzed locomotion and slow pharyngeal pumping and irregular defecation cycle. Consistent with the phenotypes, the mutants accumulated abnormally high levels of the neurotransmitter acetylcholine and were resistant to acetylcholinesterase inhibitors. The unc-13 gene was expressed in most, if not all, neurons when analyzed by using chimeric constructs consisting of the unc-13 promoter and green fluorescence protein or beta-galactosidase reporter gene. While Ca(2+)-regulated acetylcholine release is lacking, the mutants were still able to release acetylcholine in vivo and in vitro at similar levels to that mediated by the regulated mechanism. Double mutants defective in both unc-13 and other genes involved in synaptic transmission showed the Unc-13 phenotype, rather than other mutant phenotypes, in terms of locomotion as well as of acetylcholine accumulation. Furthermore, electron microscopic reconstruction of the mutant nervous system uncovered that a majority of neurons developed and connected as those in the wild type except for subtle abnormalities including inappropriate connections through gap junctions and morphological alterations of neurons. These results demonstrate that the unc-13 gene product plays an essential role at a late stage in Ca(2+)-regulated synaptic exocytosis. Neurotransmitters released through the Ca(2+)-regulated mechanism are required for, but do not play major roles in the nervous system development. The large amount of Ca(2+)-independent neurotransmitter release observed in the unc-13 mutants suggests that there may be a distinct mechanism from evoked or spontaneous release in neurotransmission.

Expression patterns of mouse repressor element-1 silencing transcription factor 4 (REST4) and its possible function in neuroblastoma

The expression pattern of the repressor element-1 silencing transcription factor (REST) also known as the neuron-restrictive silencer factor (NRSF) and its truncated forms have been analyzed in the neuroblastoma cell lines, NS20Y and NIE115 and in NIH3T3 cells. The neuroblastoma cell lines express transcripts of REST/NRSF and its neuron-specific truncated form REST4; with REST4 being the major transcript. NIH3T3 cells express predominantly REST/NRSF, with no detectable REST4. The cellular localization of REST4, determined using a REST4-GFP fusion protein, was shown to be nuclear. Mutational analysis implicates the zinc finger domains as the nuclear-targeting signal. Analysis of reporter-gene activities in the NS20Y cell line showed that the presence of four RE-1/NRSE sequences did not affect promoter activity. However, coexpression of exogenous REST4 produces a small increase in promoter activity of the reporter plasmid, whereas expression of exogenous REST/NRSF leads to repression. In the NIH3T3 cell line, the RE-1/NRSE sequence leads to repression of reporter-gene activity, whereas introduction of exogenous REST4 leads to de-repression. These data indicate that REST4 does not act as a transcriptional repressor. However, they support a mechanism where REST4 can block the repressor activity of REST/NRSF.

Somatomotor neuron-specific expression of the human cholinergic gene locus in transgenic mice

We examined the expression pattern of the vesicular acetylcholine transporter in the mouse nervous system, using rodent-specific riboprobes and antibodies, prior to comparing it with the distribution of vesicular acetylcholine transporter expressed from a human transgene in the mouse, using riboprobes and antibodies specific for human. Endogenous vesicular acetylcholine transporter expression was high in spinal and brainstem somatomotor neurons, vagal visceromotor neurons, and postganglionic parasympathetic neurons, moderate in basal forebrain and brainstem projection neurons and striatal interneurons, and low in intestinal intrinsic neurons. Vesicular acetylcholine transporter expression in intrinsic cortical neurons was restricted to the entorhinal cortex. The sequence of the mouse cholinergic gene locus to 5.1kb upstream of the start of transcription of the vesicular acetylcholine transporter gene was determined and compared with the corresponding region of the human gene. Cis-regulatory domains implicated previously in human or rat cholinergic gene regulation are highly conserved in mouse, indicating their probable relevance to the regulation of the mammalian cholinergic gene locus in vivo. Mouse lines were established containing a human transgene that included the vesicular acetylcholine transporter gene and sequences spanning 5kb upstream and 1.8kb downstream of the vesicular acetylcholine transporter open reading frame. In this transgene, the intact human vesicular acetylcholine transporter was able to act as its own reporter. This allowed elements within the vesicular acetylcholine transporter open reading frame itself, shown previously to affect transcription in vitro, to be assessed in vivo with antibodies and riboprobes that reliably distinguished between human and mouse vesicular acetylcholine transporters and their messenger RNAs. Expression of the human vesicular acetylcholine transporter was restricted to mouse cholinergic somatomotor neurons in the spinal cord and brainstem, but absent from other central and peripheral cholinergic neurons. The mouse appears to be an appropriate model for the study of the genetic regulation of the cholinergic gene locus, and the physiology and neurochemistry of the mammalian cholinergic nervous system, although differences exist in the distribution of cortical cholinergic neurons between the mouse and other mammals. The somatomotor neuron-specific expression pattern of the transgenic human vesicular acetylcholine transporter suggests a mosaic model for cholinergic gene locus regulation in separate subdivisions of the mammalian cholinergic nervous system.

Genetic defects in acetylcholine signalling promote protein degradation in muscle cells of Caenorhabditis elegans

A myosin-lacZ fusion, expressed in 103 muscle cells of Caenorhabditis elegans, reports on how proteolysis in muscle is controlled by neural and intramuscular signals. Upon acute starvation, the fusion protein is degraded in the posterior 63 cells of the body-wall muscle, but remains stable in 32 anterior body-wall muscles and 8 vulval muscle cells. This distinction correlates with differences in the innervation of these cells. Reporter protein in the head and vulval muscles becomes labile upon genetic ‘denervation’ in mutants that have blocks in pre-synaptic synthesis or release of acetylcholine (ACh) or post-synaptic reception at nicotinic ACh receptors (nAChR), whereas protein in all 103 muscles is stabilized by the nicotinic agonist levamisole in the absence of ACh production. Levamisole does not stabilize muscle protein in nAChR mutants that are behaviorally resistant to levamisole. Neural inputs thus exert negative control over the proteolytic process in muscle by stimulating muscle nicotinic ACh receptors.

[Modulation of experimental myasthenia gravis by IVIg]

Myasthenia Gravis (MG) is an autoimmune disease mediated by antibodies directed against the acetylcholine receptor (AChR). Treatment by IVIg is effective in acute forms of myasthenia gravis. In order to determine the in vivo effects of the various fractions of human immunoglobulins, we used an experimental model of myasthenia gravis in SCID mice. To this end, thymic cells from MG patients are transferred to these mice according to a well defined protocol. When establishing of the model, we noticed the appearance of anti-AChR antibodies and the loss of AChR expression at the muscle level. After treatment with IVIgG or IVIgM, the mice displayed a lower anti-AChR antibody titer compared to control mice (albumin treated) and the loss of the AChR number at the muscle was significantly reduced. These results obtained from one MG patient indicate that the human immunoglobulin preparations induce significant effects on pathogenic parameters in the SCID mouse model. Therefore this model is interesting to approach the mechanisms of action of human immunoglobulins and deserves further investigation.

Extraneuronal cholinergic system in lymphocytes

Acetylcholine (ACh) is well known as a neurotransmitter in both the central and peripheral nervous systems in mammalian species. Both muscarinic and nicotinic ACh receptors have been identified in lymphocytes isolated from thymus, lymph node, spleen, and peripheral blood, and their stimulation by muscarinic and nicotinic agonists elicits a variety of functional and biochemical effects. On the basis of these findings, it has been postulated that the parasympathetic nervous system may play a role in immune-neurohumoral crosstalk. However, ACh present in the blood of several species has been localized to lymphocytes from various origins using radioimmunoassay. Moreover, using Northern blots or reverse transcription-polymerase chain reaction, expression of choline acetyltransferase, an ACh synthesizing enzyme, has been identified in human blood mononuclear leukocytes, human leukemic T-cell lines, and rat lymphocytes. Stimulation of T-lymphocytes with phytohemagglutinin activates the lymphoid cholinergic system, as evidenced by increased synthesis and release of ACh, increased acetylcholinesterase activity, and the increased expression of mRNA encoding choline acetyltransferase and ACh receptors. The observation that muscarinic receptor stimulation by ACh or agonists increases in [Ca(2)+](i) and up-regulates c-fos expression strongly argues that ACh synthesized and released from T-lymphocytes acts as an autocrine and/or paracrine factor regulating immune function. In summary, these data present a compelling picture in which immune function is not only regulated by the cytokine system, but is also under the control of an independent, lymphoid cholinergic system.

Cholinergic strategies for Alzheimer's disease

Alzheimer's disease is a devastating degenerative disorder of the central nervous system that results in gradual deterioration of cognitive function and severe alteration of personality. Degeneration of neurons in the nucleus basalis Meynert, the origin of the major cholinergic projections to the neocortex, occurs early in the course of the disease, and is correlated with the cognitive decline. This link between cholinergic dysfunction in the basal-cortical system and cognitive deficits has focused scientific efforts on developing tools to elucidate the neurobiological role of the cholinergic system in cognition and to develop therapeutic interventions in the disorder. An important step in understanding the mechanisms underlying cognitive dysfunction has been the development of in vivo rodent models that mimic some of the features of Alzheimer's disease. Acute excitotoxic or immunotoxic lesions of the nucleus basalis in rodents have revealed a role of the basal-cortical system in attention, learning and memory. More recent advances in developing mouse gene technology offer newer models to systematically examine the underlying neuropathological cascade leading to dysfunctions in mnemonic processing. Using in vivo rodent models, several cholinergic enhancement strategies have been tested and proven to be effective in alleviating lesion-induced cognitive deficits, including neuropharmacological approaches (acetylcholinesterase inhibitors), neurotrophic factor administration (nerve growth factor), and transplantation of cholinergic-enriched fetal grafts. Successful results have also been obtained using ex vivo gene transfer to deliver nerve growth factor or acetylcholine to compromised regions of the basal-cortical system. Gene therapy may be of particular interest for clinical applications, because this approach provides a method for topographically restricted and selective delivery of therapeutic genes and their products to afflicted areas of the brain. Advanced techniques in molecular biology (e.g., exogenous regulatable gene transfer) and newly developed tools of modern neuroscience (e.g., neural precursor cells) will be important contributions for deciphering the biological bases of neuronal degeneration and for refining therapeutic strategies for Alzheimer's disease.

The cholinergic gene locus

Messenger RNAs and the cognate gene(s) encoding choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT) have been cloned from mammals and several other animal classes in the last decade. These have provided molecular tools for investigating acetylcholine synthesis and packaging into synaptic vesicles, the genesis of cholinergic vesicles, and the development and senescence of the cholinergic nervous system. VAChT and ChAT have been found to share a common gene locus and regulatory elements for gene transcription. The cholinergic gene locus represents a previously undiscovered type of neuronal transcriptional unit controlling chemically coded neurotransmission. In vitro assays for the transport function of VAChT have shed light on the bioenergetics of amine accumulation in secretory vesicles. Manipulation of VAChT expression in vivo has demonstrated unequivocally the primacy of vesicular exocytosis as the mode of transmitting quanta of acetylcholine at the neuromuscular junction, as in vivo manipulation of acetylcholinesterase levels has demonstrated the importance of acetylcholine metabolism in the regulation of complex functions such as cognition. Light and electron microscopic visualization of VAChT, complementing previous ChAT immunohistochemistry, has improved understanding of the genesis and function of the cholinergic vesicle, neuron, and synapse. These advances should accelerate the development of "cholinergic" pharmacological and gene therapeutic approaches to treatment of human diseases that are associated with cholinergic surfeit and insufficiency.

Acute stress facilitates long-lasting changes in cholinergic gene expression

Acute traumatic stress may lead to post-traumatic stress disorder (PTSD), which is characterized by delayed neuropsychiatric symptoms including depression, irritability, and impaired cognitive performance. Curiously, inhibitors of the acetylcholine-hydrolysing enzyme acetylcholinesterase may induce psychopathologies that are reminiscent of PTSD. It is unknown how a single stressful event mediates long-term neuronal plasticity. Moreover, no mechanism has been proposed to explain the convergent neuropsychological outcomes of stress and of acetylcholinesterase inhibition. However, acute stress elicits a transient increase in the amounts released of the neurotransmitter acetylcholine and a phase of enhanced neuronal excitability. Inhibitors of acetylcholinesterase also promote enhanced electrical brain activity, presumably by increasing the survival of acetylcholine at the synapse. Here we report that there is similar bidirectional modulation of genes that regulate acetylcholine availability after stress and blockade of acetylcholinesterase. These calcium-dependent changes in gene expression coincide with phases of rapid enhancement and delayed depression of neuronal excitability. Both of these phases are mediated by muscarinic acetylcholine receptors. Our results suggest a model in which robust cholinergic stimulation triggers rapid induction of the gene encoding the transcription factor c-Fos. This protein then mediates selective regulatory effects on the long-lasting activities of genes involved in acetylcholine metabolism.

VAMP-1 and VAMP-2 gene expression in rat spinal motoneurones: differential regulation after neuronal injury

Vesicle-associated membrane protein (VAMP; synaptobrevin) is involved in the molecular regulation of transmitter release at the presynaptic plasma membrane. VAMP exists in two isoforms, VAMP-1 and VAMP-2, which are transcribed from two separate genes and differentially expressed in the nervous system. In situ hybridization was used to examine whether VAMP isoform mRNA expression may be altered by experimental manipulations. The effect of nerve injury on VAMP-1 and VAMP-2 mRNA levels in motoneurones of the rat lumbar spinal cord was compared with lesion-induced changes in the expression of choline acetyl transferase (ChAT) and alpha-calcitonin gene-related peptide (alpha-CGRP) mRNA. After unilateral sciatic nerve transection (axotomy), VAMP-1 mRNA expression decreased significantly in parallel with a downregulation of ChAT mRNA in axotomized motoneurones compared with the corresponding motoneurones on the contralateral unlesioned side. There was a rapid decrease in VAMP-1 and ChAT mRNA levels at 2 days after axotomy, and at 7 days there was a 65% decrease in VAMP-1 mRNA and a 48% decrease in ChAT mRNA. VAMP-1 mRNA levels continued to decrease at 14 and 21 days, while ChAT mRNA levels had returned to normal at this time. In contrast, VAMP-2 and alpha-CGRP mRNA levels were upregulated in axotomized motoneurones. A significant increase for both VAMP-2 and alpha-CGRP mRNA levels was present 2 days after axotomy, and a maximum was reached after 7 days for alpha-CGRP mRNA (163%) and after 14 days for VAMP-2 mRNA (587%). Immunohistochemical analysis did not reveal any detectable changes in VAMP-1- or VAMP-2-like immunoreactivity in the motoneurone cell soma after axotomy. In the proximal end of the transected sciatic nerve, there was an increase in VAMP-1- and VAMP-2-LI, which was most prominent at 2 days after lesion. The results show that, in axotomized spinal motoneurones, VAMP-1 mRNA is downregulated and VAMP-2 mRNA is upregulated, indicating differential regulation of the two separate VAMP genes and differential roles for the two VAMP isoforms in the regulation of exocytosis after nerve injury.

Upstream sequencing and functional characterization of the human cholinergic gene locus

The 5' flanking region of the human VAChT gene was sequenced to approx 5350 bases upstream of the initiating methionine codon of the VAChT open reading frame (orf). The 5' flanks of the human and rat cholinergic gene loci were compared to identify regions of local sequence conservation, and therefore of potential regulatory importance. Several discrete domains of high homology, including a cluster of far-upstream cis-active consensus motifs, a neuronally restrictive silencer element consensus sequence, and additional conserved sequences within the putative nerve growth factor response domain of the locus, were identified. The probable start of transcription of the VAChT gene was deduced from mapping of sequences of rat and human VAChT cDNAs onto the 5' flanking regions of the human and rat cholinergic gene loci. The actual utilization of a putative 5' VAChT exon in rat central nervous system (CNS) tissue was assessed by in situ hybridization histochemistry. RNA transcripts containing both VAChT and ChAT protein-coding sequences were abundant in spinal cord motoneurons, sympathetic preganglionic cells, basal forebrain, striatum, and cranial motor nuclei. R-exon-containing transcripts could be detected only at low levels in these cell groups, implying that most transcription of VAChT proceeds from a promoter downstream of the R-exon. To assess the structural requirements for expression of the VAChT gene without bias regarding the actual start of transcription, a 5' fragment of the human gene corresponding to approximately 3 kb of sequence extending upstream from within the presumed 5' untranslated region of VAChT itself was fused to a luciferase-encoding reporter and transfected into VAChT-expressing and nonexpressing human and rat cell lines. This portion of the VAChT gene provided strong promoter expression in both cholinergic and noncholinergic cell lines. Deletion of the putative neuronally restrictive silencer element (NRSE) resulted in enhanced transcription in all cell lines. Lack of differential expression of VAChT transcription in VAChT-expressing vs non-VAChT-expressing cell lines suggested that additional enhancer elements controlling cell-specific expression of the VAChT gene exist further upstream in the cholinergic locus 5' flank. Conservation of potential cis-active elements within a 1.4 kb sequence immediately upstream of the NRSE in both rat and human cholinergic gene loci suggests that this domain is required for cholinergic-specific regulation of VAChT and ChAT gene transcription.

Culture density regulates both the cholinergic phenotype and the expression of the CNTF receptor in P19 neurons

The P19 embryonal carcinoma cells differentiate into neurons, astrocytes, and fibroblast-like cells following induction with retinoic acid. The cells mature into functional neurons, as determined by their ability to release neurotransmitters in a Ca(2+)- and depolarization-dependent manner. P19 neurons in culture represent a mixed population in terms of their neurotransmitter phenotype. The cholinergic phenotype of these neurons is modulated by culture density. Cholinergic markers, such as the vesicular acetylcholine transporter, acetyl cholinesterase, and choline acetyltransferase, are expressed in about 85% of the cells in sparse cultures and are largely suppressed at high cell densities. In contrast, glutamate release is enhanced in dense P19 neuronal cultures. The factor mediating the density effect is concentrated exclusively on the cell membrane of P19 neurons and not on the nonneuronal cells, which also differentiate from P19 embryonal carcinoma cells. This membrane-associated component retains its functionality, even after membrane fixation. The downregulation of the cholinergic properties in dense cultures is paralleled by a downregulation of the alpha subunit of the ciliary neurotrophic factor (CNTF) receptor. Thus, it is suggested that the membrane-associated factor, which mediates the density effect, downregulates the cholinergic phenotype by inhibiting the responsiveness of these neurons to CNTF. We further suggest that the P19 cell line can serve as a model system for the study of neurotransmitter phenotype acquisition and plasticity throughout neuronal differentiation.

Essential role of neocortical acetylcholine in spatial memory

The cholinergic system plays a crucial role in learning and memory. Lesions of cholinergic nuclei, pharmacological manipulations of cholinergic systems, intracerebral transplantation of fetal tissue and anatomical changes in cholinergic pathways during ageing have all been correlated with altered cognitive behaviour. However, it has not been proved that regional acetylcholine is causally required for learning and memory. Here we describe how we achieved a permanent and selective impairment of learning and memory by damaging the nucleus basalis magnocellularis, a nucleus that provides the major cholinergic innervation of the neocortex, in adult rats. To test the hypothesis that acetylcholine is essential for restoration of cognitive function, we implanted genetically modified cells that produce acetylcholine into denervated neocortical target regions. After grafting, rats with increased neocortical acetylcholine levels showed a significant improvement in a spatial navigation task. Acetylcholine is thus not only necessary for learning and memory, as previously argued, but its presence within the neocortex is also sufficient to ameliorate learning deficits and restore memory following damage to the nucleus basalis.

Enhanced acetylcholine secretion in neuroblastoma x glioma hybrid NG108-15 cells transfected with rat choline acetyltransferase cDNA

Neuroblastoma x glioma hybrid NG108-15 cells and mouse neuroblastoma N18TG-2 and N1E-115 cells were transiently transfected with the sense cDNA coding for rat choline acetyltransferase (ChAT). All transfected cell lines showed a high level of ChAT activity. ACh secretion was monitored by recording miniature end-plate potentials (MEPPs) in striated muscle cells that had been co-cultured with transfected cells. The number of muscle cells with synaptic responses and the MEPP frequency were higher in co-culture with transfected NG108-15 cells than with control or mock cells. No synaptic response was detected in muscle cells co-cultured with transfected N18TG-2 or N1E-115 cells. The results show that ACh secretion into the synaptic cleft was enhanced due to ChAT overexpression in NG108-15 hybrid cells but not in neuroblastoma cells.