Cholinergic Axons Research Articles

Neurochemical coding compared between varicose axons and cell bodies of myenteric neurons in the guinea-pig ileum

The discrete functional classes of enteric neurons in the mammalian gastrointestinal tract have been successfully distinguished on the basis of the unique combination of molecules and enzymes in their cell bodies (“chemical coding”). Whether the same chemical coding exists in varicose axons of different functional classes has not been systematically tested. In this study, we quantified the coexistence of markers that define classes of nerve cell bodies in the myenteric plexus of the guinea-pig ileum, in varicose axons of the same neurons. Profound differences between the combinations of immunohistochemical markers in myenteric nerve cell bodies and in their varicosities were identified. These discrepancies were particularly notable for classes of neurons that had previously been classified as cholinergic, based on immunoreactivity for choline acetyltransferase (ChAT) in their cell bodies. To detect cholinergic varicose axons of enteric neurons in this study, we used antiserum against the vesicular acetylcholine transporter (VAChT). ChAT-immunoreactivity has been reported to be consistently co-localized with 5-hydroxytryptamine (5-HT) in interneuronal cell bodies, yet only 29±5% (n=4) of 5-HT-immunoreactive varicosities contained vesicular acetylcholine transporter (VAChT). Somatostatin coexists with ChAT-immunoreactivity in a class of descending interneuron but only 21±1% (n=4) of somatostatin-immunoreactive varicosities were VAChT-immunoreactive. Comparable discrepancies were also noted for non-cholinergic markers. The results suggest that chemical coding of cell bodies does not necessarily reflect chemical coding of varicose axon terminals and that the assumption that nerve cell bodies that contain ChAT are functionally cholinergic may be questionable.

Prolonged Disynaptic Inhibition in the Cortex Mediated by Slow, Non-α7 Nicotinic Excitation of a Specific Subset of Cortical Interneurons

Cholinergic activation of nicotinic receptors in the cortex plays a critical role in arousal, attention, and learning. Here we demonstrate that cholinergic axons from the basal forebrain of mice excite a specific subset of cortical interneurons via a remarkably slow, non-α7 nicotinic receptor-mediated conductance. In turn, these inhibitory cells generate a delayed and prolonged wave of disynaptic inhibition in neighboring cortical neurons, altering the spatiotemporal pattern of inhibition in cortical circuits.

Selective optogenetic stimulation of cholinergic axons in neocortex

Acetylcholine profoundly affects neocortical function, being involved in arousal, attention, learning, memory, sensory and motor function, and plasticity. The majority of cholinergic afferents to neocortex are from neurons in nucleus basalis. Nucleus basalis also contains projecting neurons that release other transmitters, including GABA and possibly glutamate. Hence, electrical stimulation of nucleus basalis evokes the release of a mixture of neurotransmitters in neocortex, and this lack of selectivity has impeded research on cholinergic signaling in neocortex. We describe a method for the selective stimulation of cholinergic axons in neocortex. We used the Cre-lox system and a viral vector to express the light-activated protein channelrhodopsin-2 in cholinergic neurons in nucleus basalis and their axons in neocortex. Labeled neurons depolarized on illumination with blue light but were otherwise unchanged. In anesthetized mice, illumination of neocortex desynchronized the local field potential, indicating that light evoked release of ACh. This novel technique will enable many new studies of the cellular, network, and behavioral physiology of ACh in neocortex.

N-cadherin induces partial differentiation of cholinergic presynaptic terminals in heterologous cultures of brainstem neurons and CHO cells

N-cadherin is a calcium-sensitive cell adhesion molecule commonly expressed at synaptic junctions and contributes to formation and maturation of synaptic contacts. This study used heterologous cell cultures of brainstem cholinergic neurons and transfected Chinese Hamster Ovary (CHO) cells to examine whether N-cadherin is sufficient to induce differentiation of cholinergic presynaptic terminals. Brainstem nuclei isolated from transgenic mice expressing enhanced green fluorescent protein (EGFP) under the control of choline acetyltransferase (ChAT) transcriptional regulatory elements (ChATBACEGFP) were cultured as tissue explants for 5 days and cocultured with transfected CHO cells for an additional 2 days. Immunostaining for synaptic vesicle proteins SV2 and synapsin I revealed a ~3-fold increase in the area of SV2 immunolabeling over N-cadherin expressing CHO cells, and this effect was enhanced by coexpression of p120-catenin. Synapsin I immunolabeling per axon length was also increased on N-cadherin expressing CHO cells but required coexpression of p120-catenin. To determine whether N-cadherin induces formation of neurotransmitter release sites, whole-cell voltage-clamp recordings of CHO cells expressing α3 and β4 nicotinic acetylcholine receptor (nAChR) subunits in contact with cholinergic axons were used to monitor excitatory postsynaptic potentials (EPSPs) and miniature EPSPs (mEPSPs). EPSPs and mEPSPs were not detected in both, control and in N-cadherin expressing CHO cells in the absence or presence of tetrodotoxin (TTX). These results indicate that expression of N-cadherin in non-neuronal cells is sufficient to initiate differentiation of presynaptic cholinergic terminals by inducing accumulation of synaptic vesicles; however, development of readily detectable mature cholinergic release sites and/or clustering of postsynaptic nAChR may require expression of additional synaptogenic proteins.

Chronic IL-1β-Mediated Neuroinflammation Mitigates Amyloid Pathology in a Mouse Model of Alzheimer’s Disease without Inducing Overt Neurodegeneration

Neuroinflammation is a local tissue response to injurious stimuli in the central nervous system (CNS) and is characterized by glial reactivity, induction of cytokines and chemokines, and vascular permeability. The cytokine interleukin (IL)-1β is rapidly induced following CNS insult, and is chronically expressed in neurodegenerative disorders such as Alzheimer's disease (AD). We recently developed a novel method of sustained IL-1β production in the brain to study the link between IL-1β and AD pathogenesis. Utilizing this model, we have previously demonstrated reduction of plaque size and frequency accompanied by a robust neuroinflammatory response. These observations were limited to a single early time point in the course of AD plaque deposition and did not investigate other neurodegenerative endpoints. To extend these observations to other stages of disease progression and evaluate additional pathologic markers, we investigated the effects of age and duration of IL-1β overexpression in the APPswe/PS-1dE9 AD model on a congenic C57BL/6 background. We now report that IL1β overexpression leads to decreased 6E10 immunopositive plaque pathology regardless of age or duration. We also investigated whether IL-1β overexpression led to neuronal apoptosis or cholinergic axonal degeneration in the context of this AD model. Although we could demonstrate apoptosis of infiltrating inflammatory cells, we found no evidence for IL-1 associated apoptosis of neurons or cholinergic axon degeneration even after 5 months of chronic neuroinflammation. Together, these observations point to a neuroprotective role for IL-1β in AD neuropathogenesis.

Optogenetic release of ACh induces rhythmic bursts of perisomatic IPSCs in hippocampus.

Acetylcholine (ACh) influences a vast array of phenomena in cortical systems. It alters many ionic conductances and neuronal firing behavior, often by regulating membrane potential oscillations in populations of cells. Synaptic inhibition has crucial roles in many forms of oscillation, and cholinergic mechanisms regulate both oscillations and synaptic inhibition. In vitro investigations using bath-application of cholinergic receptor agonists, or bulk tissue electrical stimulation to release endogenous ACh, have led to insights into cholinergic function, but questions remain because of the relative lack of selectivity of these forms of stimulation. To investigate the effects of selective release of ACh on interneurons and oscillations, we used an optogenetic approach in which the light-sensitive non-selective cation channel, Channelrhodopsin2 (ChR2), was virally delivered to cholinergic projection neurons in the medial septum/diagonal band of Broca (MS/DBB) of adult mice expressing Cre-recombinase under the control of the choline-acetyltransferase (ChAT) promoter. Acute hippocampal slices obtained from these animals weeks later revealed ChR2 expression in cholinergic axons. Brief trains of blue light pulses delivered to untreated slices initiated bursts of ACh-evoked, inhibitory post-synaptic currents (L-IPSCs) in CA1 pyramidal cells that lasted for 10's of seconds after the light stimulation ceased. L-IPSC occurred more reliably in slices treated with eserine and a very low concentration of 4-AP, which were therefore used in most experiments. The rhythmic, L-IPSCs were driven primarily by muscarinic ACh receptors (mAChRs), and could be suppressed by endocannabinoid release from pyramidal cells. Finally, low-frequency oscillations (LFOs) of local field potentials (LFPs) were significantly cross-correlated with the L-IPSCs, and reversal of the LFPs near s. pyramidale confirmed that the LFPs were driven by perisomatic inhibition. This optogenetic approach may be a useful complementary technique in future investigations of endogenous ACh effects.

Acute myocardial infarction induces bilateral stellate ganglia neural remodeling in rabbits

Myocardial infarction (MI) results in cardiac nerve sprouting in the myocardium. Whether or not similar neural remodeling occurs in the stellate ganglia (SGs) is unknown. We aimed to test the hypothesis that MI induces bilateral SG nerve sprouting. Acute MI was created by coronary artery ligation in rabbits (n=12). Serum nerve growth factor (NGF) level was measured by enzyme-linked immunosorbent assay. The hearts and bilateral SGs were harvested for immunohistochemistry after 1 week in six rabbits and after 1 month in six rabbits. Immunostaining for tyrosine hydroxylase (TH), growth-associated protein 43 (GAP43), choline acetyltransferase (ChAT), and synaptophysin (SYN) was performed to determine the magnitude of nerve sprouting. Tissues from six normal rabbits were used as controls. Nerve density was determined by computerized morphometry. Myocardial infarction results in increased serum NGF levels at 1 week (1519.8±632.2 ng/ml) that persist up to 1 month (1361.2±176.3 ng/ml) as compared to controls (89.6±34.9 ng/ml) (P=.0002 and P=.0001, respectively). Immunostaining demonstrated nerve sprouting and hyperinnervation in both SGs after MI. The nerve densities (μm(2)/ganglion cell) in SG 1 week after MI and 1 month after MI and those in control groups, respectively, were as follows: GAP43: 278±96, 225±39, and 149±57 (P=.01); SYN: 244±152, 268±115, and 102±60 (P=.02); TH: 233±71, 180±50, and 135±68 (P=.047); ChAT: 244±100, 208±46, and 130±41 μm(2)/cell (P=.01). Myocardial infarction increases serum NGF levels and induces nerve sprouting and hyperinnervation in bilateral SGs for at least 1 month after MI. The hyperinnervation includes both adrenergic axons and cholinergic axons in the SG.

Form of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A nonphosphorylated at tyrosine 145 and 147 is enriched in the nuclei of astroglial cells, adult hippocampal progenitors, and some cholinergic axon terminals

Compelling lines of evidence indicate that overexpression of dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) in subjects with trisomy 21 (Down syndrome[DS]) contributes to the abnormal structure and function of the DS brain. In the present study, we used a novel, phospho-dependent antibody recognizing DYRK1A only with nonphosphorylated tyrosine 145 and 147 (DYRK1A Tyr-145/147P(-)), to investigate the expression pattern of this DYRK1A species in trisomic and disomic human and mouse brains. Immunoblotting and dephosphorylation experiments demonstrated higher levels of DYRK1A Tyr-145/147P(-) in postnatal trisomic brains in comparison with controls (by ∼40%) than those of the DYRK1A visualized by three other N- and C-terminally directed antibodies to DYRK1A. By immunofluorescence, the immunoreactivity to DYRK1A Tyr-145/147P(-) was the strongest in the nuclei of astroglial cells, which contrasted with the predominantly neuronal localization of DYRK1A visualized by the three other antibodies to DYRK1A we used. In addition, DYRK1A Tyr-145/147P(-) was enriched in the nuclei of neuronal progenitors and newly born neurons in the adult hippocampal proliferative zone and also occurred in some cholinergic axonal terminals. Our data show a distinctive expression pattern of DYRK1A forms nonphosphorylated at Tyr-145 and Tyr-147 in the brain tissue and suggest that DS subjects may exhibit not only upregulation of total DYRK1A, but also more subtle differences in phosphorylation levels of this kinase in comparison with control individuals.

Cholinergic axon length reduced by 300 meters in the brain of an Alzheimer mouse model

Modern stereological techniques have been used to show that the total length of the cholinergic fibers in the cerebral cortex of the APPswe/PS1deltaE9 mouse is reduced by almost 300 meters at 18 months of age and has a nonlinear relationship to the amount of transgenetically-induced amyloidosis. These data provide rigorous quantitative morphological evidence that Alzheimer's-like amyloidosis affects the axons of the cholinergic enervation of the cerebral cortex.

Innervation Patterns of Autonomic Axons in the Human Endocrine Pancreas

The autonomic nervous system regulates hormone secretion from the endocrine pancreas, the islets of Langerhans, thus impacting glucose metabolism. The parasympathetic and sympathetic nerves innervate the pancreatic islet, but the precise innervation patterns are unknown, particularly in human. Here we demonstrate that the innervation of human islets is different from that of mouse islets and does not conform to existing models of autonomic control of islet function. By visualizing axons in three dimensions and quantifying axonal densities and contacts within pancreatic islets, we found that, unlike mouse endocrine cells, human endocrine cells are sparsely contacted by autonomic axons. Few parasympathetic cholinergic axons penetrate the human islet, and the invading sympathetic fibers preferentially innervate smooth muscle cells of blood vessels located within the islet. Thus, rather than modulating endocrine cell function directly, sympathetic nerves may regulate hormone secretion in human islets by controlling local blood flow or by acting on islet regions located downstream.

Neural cell adhesion molecule ablation in mice causes hippocampal dysplasia and loss of septal cholinergic neurons

The neural cell adhesion molecule (NCAM) is implicated in nervous system development and plasticity. In humans, abnormal NCAM expression has been linked to the pathogenesis of neuropsychiatric and neurodegenerative disorders accompanied by cognitive dysfunctions. Impaired cognition is also observed in NCAM-deficient (NCAM(-/-) ) mice. Considering the importance of the septal cholinergic nuclei and the hippocampus for cognition, we performed quantitative morphological analyses of these areas in young and adult (2 and 13 months old, respectively) NCAM(-/-) mice and wild-type (NCAM(+/+) ) littermates. In young mice, we found lower numbers of septal cholinergic neurons in NCAM(-/-) than in NCAM(+/+) mice. Despite deficient numbers of neurons, total lengths of cholinergic axons and choline acetyltransferase protein levels in the hippocampus of NCAM(-/-) mice were normal. The hippocampus of NCAM(-/-) mice was atrophic, notably in the CA3 subfield and the dentate gyrus (DG). The atrophy appeared to have different primary causes in the two subfields: loss of pyramidal cells in CA3 and reduced branching and volume of granule cell dendrites in the DG. The frequency of dendritic spines on dentate granule cells in NCAM(-/-) mice was normal. Numbers of parvalbumin-positive (PV(+) ) interneurons were reduced in NCAM(-/-) mice in proportion to subfield volume loss, and the ratios of principal cells to PV(+) interneurons were similar to those of NCAM(+/+) mice. None of the observed abnormalities was exaggerated or alleviated in adult NCAM(-/-) mice. Our observations indicate that NCAM ablation causes structural abnormalities in the hippocampus and the forebrain cholinergic system in adult mice, which may contribute to impaired cognition in NCAM(-/-) mice.

Nicotine excites hypothalamic arcuate anorexigenic proopiomelanocortin neurons and orexigenic neuropeptide Y neurons: similarities and differences

Two of the biggest health problems facing us today are addiction to nicotine and the increased prevalence of obesity. Interestingly, nicotine attenuates obesity, but the underlying mechanism is not clear. Here we address the hypothesis that if weight-reducing actions of nicotine are mediated by anorexigenic proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus, nicotine should excite these cells. Nicotine at concentrations similar to those found in smokers, 100-1,000 nM, excited POMC cells by mechanisms based on increased spike frequency, depolarization of membrane potential, and opening of ion channels. This was mediated by activation of both α7 and α4β2 nicotinic receptors; by itself, this nicotine-mediated excitation could explain weight loss caused by nicotine. However, in control experiments nicotine also excited the orexigenic arcuate nucleus neuropeptide Y (NPY) cells. Nicotine exerted similar actions on POMC and NPY cells, with a slightly greater depolarizing action on POMC cells. Immunocytochemistry revealed cholinergic axons terminating on both cell types. Nicotine actions were direct in both cell types, with nicotine depolarizing the membrane potentials and reducing input resistance. We found no differences in the relative desensitization to nicotine between POMC and NPY neurons. Nicotine inhibited excitatory synaptic activity recorded in NPY, but not POMC, cells. Nicotine also excited hypocretin/orexin neurons that enhance cognitive arousal, but the responses were smaller than in NPY or POMC cells. Together, these results indicate that nicotine has a number of similar actions, but also a few different actions, on POMC and NPY neurons that could contribute to the weight loss associated with smoking.

Projections from the rat pedunculopontine and laterodorsal tegmental nuclei to the anterior thalamus and ventral tegmental area arise from largely separate populations of neurons

Cholinergic and non-cholinergic neurons in the brainstem pedunculopontine (PPT) and laterodorsal tegmental (LDT) nuclei innervate diverse forebrain structures. The cholinergic neurons within these regions send heavy projections to thalamic nuclei and provide modulatory input as well to midbrain dopamine cells in the ventral tegmental area (VTA). Cholinergic PPT/LDT neurons are known to send collateralized projections to thalamic and non-thalamic targets, and previous studies have shown that many of the afferents to the VTA arise from neurons that also project to midline and intralaminar thalamic nuclei. However, whether cholinergic projections to the VTA and anterior thalamus (AT) are similarly collateralized is unknown. Ultrastructural work from our laboratory has demonstrated that cholinergic axon varicosities in these regions differ both morphologically and with respect to the expression and localization of the high-affinity choline transporter. We therefore hypothesized that the cholinergic innervation to these regions is provided by separate sets of PPT/LDT neurons. Dual retrograde tract-tracing from the AT and VTA indicated that only a small percentage of the total afferent population to either region showed evidence of providing collateralized input to the other target. Cholinergic and non-cholinergic cells displayed a similarly low percentage of collateralization. These results are contrasted to a control case in which retrograde labeling from the midline paratenial thalamic nucleus and the VTA resulted in higher percentages of cholinergic and non-cholinergic dual-tracer labeled cells. Our results indicate that functionally distinct limbic target regions receive primarily segregated signaling from PPT/LDT neurons.

A transgenic mouse model reveals fast nicotinic transmission in hippocampal pyramidal neurons

The relative contribution to brain cholinergic signaling by synaptic- and diffusion-based mechanisms remains to be elucidated. In this study, we examined the prevalence of fast nicotinic signaling in the hippocampus. We describe a mouse model where cholinergic axons are labeled with the tauGFP fusion protein driven by the choline acetyltransferase promoter. The model provides for the visualization of individual cholinergic axons at greater resolution than other available models and techniques, even in thick, live, slices. Combining calcium imaging and electrophysiology, we demonstrate that local stimulation of visualized cholinergic fibers results in rapid excitatory postsynaptic currents mediated by the activation of α7-subunit-containing nicotinic acetylcholine receptors (α7-nAChRs) on CA3 pyramidal neurons. These responses were blocked by the α7-nAChR antagonist methyllycaconitine and potentiated by the receptor-specific allosteric modulator 1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxanol-3-yl)-urea (PNU-120596). Our results suggest, for the first time, that synaptic nAChRs can modulate pyramidal cell plasticity and development. Fast nicotinic transmission might play a greater role in cholinergic signaling than previously assumed. We provide a model for the examination of synaptic properties of basal forebrain cholinergic innervation in the brain.

Comparative analysis of the nucleus basalis of Meynert among primates

Long projection axons from the Ch4 cell group of the nucleus basalis of Meynert (nbM) provide cholinergic innervation to the neurons of the cerebral cortex. This cortical cholinergic innervation has been implicated in behavioral and cognitive functions, including learning and memory. Recent evidence revealed differences among primate species in the pattern of cholinergic innervation specific to the prefrontal cortex. While macaques displayed denser cholinergic innervation in layers I and II relative to layers V and VI, in chimpanzees and humans, layers V and VI were as heavily innervated as the supragranular layers. Furthermore, clusters of cholinergic axons were observed within the prefrontal cortex of both humans and chimpanzees to the exclusion of macaque monkeys, and were most commonly seen in humans. The aim of the present study was to determine whether the Ch4 cell group was modified during evolution of anthropoid primates as a possible correlate of these changes in cortical cholinergic innervation. We used stereologic methods to estimate the total number of choline acetyltransferase-immunoreactive magnocellular neurons within the nbM of New World monkeys, Old World monkeys, apes, and humans. Linear regression analyses were used to examine the relationship of the Ch4 cell group with neocortical volume and brain mass. Results showed that total nbM neuron numbers hyposcale relative to both neocortical volume and brain mass. Notably, the total number of nbM neurons in humans were included within the 95% confidence intervals for the prediction generated from nonhuman data. In conclusion, while differences in the cholinergic system exist among primate species, such changes appear to involve mostly axon collateral terminations within the neocortex and, with the exception of the relatively small group of cholinergic cells of the subputaminal subdivision of the nbM at the anterointermediate and rostrolateral levels, are not accompanied by a significant extra-allometric increase in the overall number of subcortical neurons that provide that innervation.

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.

A Paradigm-Changing Surprise from Dentate Gyrus Granule Cells— Cilium-Localized p75NTR May Drive Their Progenitor Cell Proliferation

Ubaldo Armato*,Balu Chakravarthy,Anna Chiarini,Ilaria Dal Prà,James F. Whitfield-A Paradigm-Changing Surprise from Dentate Gyrus Granule Cells-Cilium-Localized p75NTR May Drive Their Progenitor Cell Proliferation

Partial, selective survival of nitrergic neurons in chagasic megacolon

One frequent chronic syndrome of Chagas’ disease is megacolon, an irreversible dilation of a colonic segment. Extensive enteric neuron loss in the affected segment is regarded as key factor for deficient motility. Here, we assessed the quantitative balance between cholinergic and nitrergic neurons representing the main limbs of excitatory and inhibitory colonic motor innervation, respectively. From surgically removed megacolonic segments of four patients, each three myenteric wholemounts (from non-dilated oral, megacolonic and non-dilated anal parts) was immunohistochemically triple-stained for choline acetyltransferase, neuronal nitric oxide synthase (NOS) and the panneuronal human neuronal protein Hu C/D. Degenerative changes were most pronounced in the megacolonic and anal regions, e.g. bulked, honeycomb-like ganglia with few neurons which were partly enlarged or atrophic or vacuolated. Neuron counts from each 15 ganglia of 12 megacolonic wholemounts were compared with those of 12 age- and region-matched controls. Extensive neuron loss, mainly in megacolonic and anal wholemounts, was obvious. In all three regions derived from megacolonic samples, the proportion of NOS-positive neurons (control: 55%) was significantly increased: in non-dilated oral parts to 61% (p = 0.003), in megacolonic regions to 72% (p < 0.001) and in non-dilated anal regions to 78% (p < 0.001). We suggest the chronic dilation of megacolonic specimens to be due to the preponderance of the nitrergic, inhibitory input to the intestinal muscle. However, the observed neuronal imbalance was not restricted to the dilated regions: the non-dilated anal parts may be innervated by ascending, cholinergic axons emerging from less affected, more anally located regions.

Histological Determination of the Areas Enriched in Cholinergic Terminals and m2 and m3 Muscarinic Receptors in the Mouse Central Auditory System

Cholinergic projections to auditory system are vital for coupling arousal with sound processing. Systematic search with in situ hybridization and immunohistochemistry indicated that the ventral nucleus of the medial geniculate body and the nucleus of the brachium of the inferior colliculus constituted cholinergic synaptic sites in the brainstem auditory system, containing a significant number of cholinergic axon terminals and m2 receptor-expressing cell bodies.

Neuronal and Axonal Loss Are Selectively Linked to Fibrillar Amyloid-β within Plaques of the Aged Primate Cerebral Cortex

The amyloid-beta peptide (Abeta) deposited in plaques in Alzheimer's disease has been shown to cause degeneration of neurons in experimental paradigms in vivo and in vitro. However, it has been difficult to convincingly demonstrate toxicity of native amyloid deposits in the aged and Alzheimer brains. Here we provide evidence that the fibrillar conformation of Abeta (fAbeta) deposited in compact plaques is associated with the pathologies observed in Alzheimer brains. fAbeta containing compact but not diffuse plaques in the aged rhesus cortex contained activated microglia and clusters of phosphorylated tau-positive swollen neurites. Scholl's quantitative analysis revealed that the area adjacent to fAbeta, containing compact but not diffuse plaques in aged rhesus, aged human, and Alzheimer's disease cortex, displays significant loss of neurons and small but statistically significant reduction in the density of cholinergic axons. These observations suggest that fAbeta toxicity may not be restricted to cultured cells and animal injection models. Rather, fAbeta deposited in native compact plaques in aged and AD brains may exert selective toxic effects on its surrounding neural environment.