Distribution of cholinergic neurons in rat brain: demonstrated by the immunocytochemical localization of choline acetyltransferase

The neuroanatomical location and cytological features of cholinergic neurons in the rat brain were determined by the immunocytochemical localization of the biosynthetic enzyme, choline acetyltransferase (ChAT). Perikarya labeled with ChAT were detected in four major cell groups: (1) the striatum, (2) the magnocellular basal nucleus, (3) the pontine tegmentum, and (4) the cranial nerve motor nuclei. Labeled neurons in the striatum were observed scattered throughout the neostriatum (caudate, putamen) and associated areas (nucleus accumbens, olfactory tubercle). Larger ChAT-labeled neurons were seen in an extensive cell system which comprises the magnocellular basal nucleus. This more or less continuous set of neuronal clusters consists of labeled neurons in the nucleus of the diagonal band (horizontal and vertical limbs), the magnocellular preoptic nucleus, the substantia innominata, and the globus pallidus. Labeled neurons in the pontine tegmentum were seen as a group of large neurons in the caudal midbrain, dorsolateral to the most caudal part of the substantia nigra, and extended in a caudodorsal direction through the midbrain reticular formation into the area surrounding the superior cerebellar peduncle. The neurons in this latter group constitute the pedunculopontine tegmental nucleus (PPT). An additional cluster of cells was observed medially adjacent to the PPT, in the lateral part of the central gray matter at the rostral end of the fourth ventricle. This group corresponds to the laterodorsal tegmental nucleus. Large ChAT-labeled neurons were also observed in all somatic and visceral motor nerve nuclei. The correspondence of the distribution of ChAT-labeled neurons identified by our methods to earlier immunocytochemical and acetylcholinesterase histochemical studies and to connectional studies of these groups argues for the specificity of the ChAT antibody used.

The central cholinergic system studied by choline acetyltransferase immunohistochemistry in the cat

An atlas of the distribution of cholinergic cell bodies, fibers, and terminals, as well as cholinoceptive cells, in the central nervous system of the cat (excluding the cerebellum) is presented from results obtained in immunohistochemical work on choline acetyltransferase. Cholinergic cell bodies are observed in more than forty areas, and cholinoceptive cells in sixty discrete areas of brain sections from the spinal cord to the olfactory bulb. The atlas is presented in seventy cross-sectional drawings of cat brain extending from the olfactory bulb to the upper cervical spinal cord.

Neuroblastoma x spinal cord (NSC) hybrid cell lines resemble developing motor neurons

We have developed a series of mouse-mouse neural hybrid cell lines by fusing the aminopterin-sensitive neuroblastoma N18TG2 with motor neuron-enriched embryonic day 12-14 spinal cord cells. Of 30 neuroblastoma-spinal cord (NSC) hybrids displaying a multipolar neuron-like phenotype, 10 express choline acetyltransferase, and 4 induce twitching in cocultured mouse myotubules. NSC-19, NSC-34, and their subclones express additional properties expected of motor neurons, including generation of action potentials, expression of neurofilament triplet proteins, and acetylcholine synthesis, storage, and release. In addition, NSC-34 cells induce acetylcholine receptor clusters on cocultured myotubes, and undergo a vimentin-neurofilament switch with maturation in culture, similar to that occurring in neuronal development. NSC cell lines appear to model selected aspects of motor neuron development in an immortalized clonal system.

Brain-derived neurotrophic factor increases survival and differentiated functions of rat septal cholinergic neurons in culture

Brain-derived neurotrophic factor (BDNF) was found to promote the survival of E17 rat embryo septal cholinergic neurons in culture, as assessed by a histochemical stain for acetylcholinesterase (AChE). A 2.4-fold increase in neuronal survival was achieved with 10 ng/ml BDNF. After initial deprivation of growth factor for 7 days, BDNF failed to bring about this increase, strongly suggesting that BDNF promotes cell survival and not just induction of AChE. BDNF was also found to increase the levels of cholinergic enzymes; choline acetyltransferase (ChAT) and AChE activities were increased by approximately 2-fold in the presence of 50 ng/ml BDNF. BDNF produced a 3-fold increase in the number of cells bearing the NGF receptor, as detected by the monoclonal antibody IgG-192. Although NGF had no additive effect with BDNF in terms of neuronal survival, suggesting that both act on a similar neuronal population, the combination of both produced an additive response, approximately a 6-fold increase, in ChAT activity.

The GDNF family ligands and receptors - implications for neural development

The glial cell line derived neurotrophic factor (GDNF) family has recently been expanded to include four members, and the interactions between these neurotrophic factors and their unique receptor system is now beginning to be understood. Furthermore, analysis of mice lacking the genes for GDNF, neurturin, and their related receptors has confirmed the importance of these factors in neurodevelopment. The results of such analyses reveal numerous similarities and potential overlaps in the way the GDNF and the nerve growth factor (NGF) families regulate development of the peripheral nervous system.

Gene targeting reveals a critical role for neurturin in the development and maintenance of enteric, sensory, and parasympathetic neurons

Neurturin (NTN) is a neuronal survival factor that activates the Ret tyrosine kinase in the presence of a GPI-linked coreceptor (either GFR alpha1 or GFR alpha2). Neurturin-deficient (NTN-/-) mice generated by homologous recombination are viable and fertile but have defects in the enteric nervous system, including reduced myenteric plexus innervation density and reduced gastrointestinal motility. Parasympathetic innervation of the lacrimal and submandibular salivary gland is dramatically reduced in NTN-/- mice, indicating that Neurturin is a neurotrophic factor for parasympathetic neurons. GFR alpha2-expressing cells in the trigeminal and dorsal root ganglia are also depleted in NTN-/- mice. The loss of GFR alpha2-expressing neurons, in conjunction with earlier studies, provides strong support for GFR alpha2/Ret receptor complexes as the critical mediators of NTN function in vivo.

The pedunculopontine tegmental nucleus: where the striatum meets the reticular formation

The pedunculopontine tegmental nucleus (PPTg) contains a population of cholinergic neurons (the Ch5 group) and non-cholinergic neurons. There appears to be functional interdigitation between these two groups, which both have extensive projections. The principal ascending connections are with thalamic nuclei and structures associated with the striatum, including the substantial nigra pars compacta. The descending connections are with a variety of nuclei in the pons, medulla and spinal cord, concerned with autonomic and motor functions. In the past, emphasis has been laid on the role of the PPTg in locomotion and behavioural state control. In this review, we emphasise the role of the PPTg in processing outputs from the striatum. The non-cholinergic neurons receive outflow from both dorsal and vental striatum, and lesions of the PPTg disrupt behaviour associated with each of these. Our review indicates that the PPTg is less concerned with the induction of locomotion and more concerned with relating reinforcement (information about which comes from the ventral striatum) with motor output from the dorsal striatum. The conclusions we draw are: (1) the PPTg is an outflow system for the striatum, but also forms a 'subsidiary circuit', returning information to striatal circuitry; in this, the PPTg has an anatomical organisation that resembles that of the substantia nigra. (2) As well as a role in the mediation of REM sleep, cholinergic PPTg neurons have an important role in the waking state, providing feedback into the thalamus and striatum. (3) The precise function of the computations performed on striatal outflow by the PPTg is uncertain. We discuss whether this function is complementary (parallel to other routes of striatal outflow), integrative (modifying other forms of striatal outflow) or both.

beta-Amyloid protein-induced Alzheimer's disease animal model

To investigate the toxicity of beta-amyloid protein which consisted of senile plaques of Alzheimer's disease (AD), this was infused into cerebral ventricle for 14 days by using mini-osmotic pump. The performance of the water maze task in beta-amyloid protein-treated rats was impaired. Choline acetyltransferase activity significantly decreased in the frontal cortex and hippocampus. These results suggest that the deposition of beta-amyloid protein in the brain is related to the impairment of learning and cholinergic neuronal degeneration, and that beta-amyloid protein-treated rats could be used as an animal model for AD.

Cholinergic and noradrenergic modulation of the slow (approximately 0.3 Hz) oscillation in neocortical cells

1. The pedunculopontine tegmental (PPT) cholinergic nucleus and the locus coeruleus (LC) noradrenergic nucleus were electrically stimulated to investigate their effects on the recently described slow oscillation (approximately 0.3 Hz) of neocortical neurons. Intracellular recordings of slowly oscillating, regular-spiking and intrinsically bursting neurons from cortical association areas 5 and 7 (n = 140) were performed in anesthetized cats. 2. Pulse trains to the PPT nucleus produced the blockage of rhythmic (approximately 0.3 Hz) depolarizing-hyperpolarizing sequences in 79% of tested cortical neurons and transformed this slow cellular rhythm into tonic firing. The latency of the cortical cellular response to PPT stimulation was 1.2 +/- 0.5 (SE) s and its duration was 15.9 +/- 1.9 s. The PPT-elicited suppression of the slow cellular oscillation was accompanied by an activation of the electroencephalogram (EEG) having a similar time course. Fast Fourier transform analyses of EEG activities before and after PPT stimulation showed that the PPT-evoked changes consisted of decreased power of slow rhythms (0-8 Hz) and increased power of fast rhythms (24-33 Hz); these changes were statistically significant. 3. The blockage of the slow cellular oscillation was mainly achieved through the diminution or suppression of the long-lasting hyperpolarizations separating the rhythmic depolarizing envelopes. This effect was observed even when PPT pulse trains disrupted the oscillation without inducing overt depolarization and increased firing rate. The durations of the prolonged hyperpolarizations were measured during a 40-s window (20 s before and 20 s after the PPT pulse train) and were found to decrease from 1.5 +/- 0.2 to 0.7 +/- 0.1 s. The values of the product resulting from the duration (in seconds), the amplitude (in millivolts), and number of such hyperpolarizing events within 20-s periods were 51.5 +/- 5 and 5.1 +/- 1.9 before and after PPT stimulation, respectively. 4. The PPT effect was suppressed by systemic administration of a muscarinic antagonist, scopolamine, but not by mecamylamine, a nicotinic antagonist. 5. The PPT effect on cellular and EEG cortical slow oscillation survived, although its duration was reduced, in animals with kainate-induced lesions of thalamic nuclei projecting to areas 5 and 7 (n = 3) as well as in animals with similar excitotoxic lesions leading to extensive neuronal loss in nucleus basalis (n = 2). These data indicate that the PPT effect is transmitted to neocortex through either thalamic or basal forebrain relays.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholinergic neurons in the pedunculopontine tegmental nucleus are involved in the mediation of prepulse inhibition of the acoustic startle response in the rat

The amplitude of the acoustic startle response (ASR) is markedly reduced when the startle eliciting pulse is preceded by a weak, non-startling stimulus at an appropriate lead time, usually about 100 ms. This phenomenon is termed prepulse inhibition (PPI) and has received considerable attention in recent years as a model of sensorimotor gating. We report here on experiments which were undertaken in order to investigate some of the neural mechanisms of PPI. We focused on the characterization of the cholinergic innervation of the pontine reticular nucleus, caudal part (PnC), an obligatory relay station in the primary startle pathway. The combination of retrograde tracing with choline acetyltransferase-immunocytochemistry revealed a cholinergic projection from the pedunculopontine tegmental nucleus (PPTg) and laterodorsal tegmental nucleus (LDTg) to the PnC. Extracellular recording from single PnC units, combined with microiontophoretic application of the acetylcholine (ACh) agonists acetyl-beta-methylcholine (AMCH) and carbachol revealed that ACh inhibits the majority of acoustically responsive PnC neurons. Neurotoxic lesions of the cholinergic neurons of the PPTg significantly reduced PPI without affecting the ASR amplitude in the absence of prepulses. No effect on long-term habituation of the ASR was observed. The present data indicate that the pathway mediating PPI impinges upon the primary acoustic startle circuit through an inhibitory cholinergic projection from the PPTg to the PnC.

Trophic effect of erythropoietin and other hematopoietic factors on central cholinergic neurons in vitro and in vivo

In vitro granulocyte colony-stimulating factor (G-CSF), macrophage colony-stimulating factor (M-CSF), erythropoietin (EPO), and erythroid differentiation factor (EDF) augmented choline acetyltransferase (ChAT) activity in mouse embryonic primary septal neurons and in cholinergic hybridoma cell line, SN6.10.2.2. This is similar to the effects seen with interleukin-3 (IL-3) or granulocyte-macrophage colony-stimulating factor (GM-CSF). Moreover, in vivo GM-CSF and EPO promoted survival of septal cholinergic neurons in adult rats which had undergone fimbria-fornix transections. These results suggest that some of the hematopoietic factors act on cholinergic neurons as 'neurotrophic factors' to influence the differentiation, maintenance and regeneration of these neurons.

Nitric oxide synthetase (NOS)-containing sympathoadrenal cholinergic neurons of the rat IML-cell column: evidence from histochemistry, immunohistochemistry, and retrograde labeling

Nitric oxide synthetase (NOS) can be selectively stained in neurons by either NADPH-diaphorase (i.e., NOS)-histochemistry or immunohistochemistry with antibodies raised against NOS, which apparently label identical reactive sites (Hope, B.T., G.J. Michael, K.M. Knigge, and S.R. Vincent, Proc. Natl. Acad. Sci. USA 88:2811-2814, '91). We provide histochemical evidence for the existence of a neuron-specific NOS-activity in autonomic neurons of the thoracic spinal cord. Among the four main preganglionic cell clusters investigated at mid-thoracic levels, Th7-10, the intermediolateral (IML)-cell column was the most prominently stained cell group. The histochemical staining was absent in other spinal cord neurons and non-neuronal cells, e.g., GFAP-positive glial cells. Staining was completely blocked by N omega-nitro-L-arginine (L-NNA), a potent NOS-inhibitor for brain and peripheral autonomic neurons, but was still observed in the presence of another NOS-inhibitor, N omega-monomethyl-L-arginine (MeArg). The NOS-activity co-localized with nearly half of the ChAT-immunostained neurons located in the mid-thoracic IML-cell column as quantified by cell counts in single and double-stained tissue sections. We conclude that NOS-activity-containing neurons represent a distinct group among cholinergic IML-neurons, which suggests a more general function of this newly defined subpopulation of the spinal cord autonomic system. In vivo Fast blue retrograde labeling combined with histochemical staining and immunostaining revealed that sympathoadrenal projection neurons belong to the distinct NOS and ChAT-positive IML-cell group.(ABSTRACT TRUNCATED AT 250 WORDS)

Dual adrenergic and cholinergic innervation of the cerebral arteries of the rat. An ultrastructural study

The innervation of the anterior cerebral artery of the rat was examined by electron microscopy and by the fluorescence method for localizing adrenergic nerves. Two groups of axon bundles were associated with the artery; one at the outer margin of the adventitia ( periadventitial bundles) and the other within the adventitia or at the adventitia-media border ( adventitial bundles). Periadventitial bundles consisted of nonmyelinated axons (0.1-2µ diam), some of which contained synaptic vesicles; in some bundles, myelinated axons were seen. Adventitial axons often contained many synaptic vesicles and were free of Schwann cell sheath in areas apposed to smooth muscle cells. The closest observed approach of axon to muscle cell was 800 A. No nerve fibers penetrated the medial muscle. After fixation with glutaraldehyde plus osmium, large (1000 A) granular and small (500 A) agranular vesicles were seen within many axon profiles. Small granular vesicles were rare. After permanganate fixation, terminal axons contained (besides large granular vesicles) either predominantly small granular vesicles or exclusively small agranular vesicles. Two days after sympathetic denervation, no axons containing small granular vesicles and no fluorescent fibers were seen. Adrenergic fibers were readily identified after injection of rats with 6-hydroxydopamine; small vesicles of adrenergic axons contained highly opaque granular cores, even in osmium-fixed material. Axons containing small agranular vesicles after 6-hydroxydopamine were considered cholinergic. The density of granulation of the large vesicles of adrenergic, but not cholinergic, axons was considerably enhanced following 6-hydroxydopamine. Both adrenergic and cholinergic axons come into close relationship with smooth muscle cells.

Dissociable effects on spatial maze and passive avoidance acquisition and retention following AMPA- and ibotenic acid-induced excitotoxic lesions of the basal forebrain in rats: differential dependence on cholinergic neuronal loss

Excitotoxic lesions of the basal forebrain were made by infusing either alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or ibotenic acid. Acquisition and performance of spatial learning in the Morris water maze, over a ten day, two trials per day, training regimen were unaffected by the AMPA-induced lesions which reduced cortical choline acetyltransferase activity by 70%. However, acquisition was significantly impaired in rats with ibotenic acid-induced lesions that reduced cortical choline acetyltransferase by 50%. Additionally, ibotenic acid-lesioned rats swam further than either sham or AMPA-lesioned rats, in the "training" quadrant during a probe trial, in which the escape platform was removed, suggesting a perseverative search strategy. Lesions induced with AMPA, but not ibotenate, significantly impaired the acquisition of "step-through" passive avoidance. Both AMPA- and ibotenate-induced lesions significantly impaired the 96 h retention of passive avoidance, but the effect of AMPA was greater on latency measures. Histological analysis revealed that AMPA infusions destroyed more choline acetyltransferase-immunoreactive neurons than did ibotenate infusions but, unlike ibotenate, spared the overlying dorsal pallidum and also parvocellular, non-choline acetyltransferase-immunoreactive neurons in the ventral pallidal/substantia innominata region of the basal forebrain. The impairment in acquisition of the water maze following ibotenate-induced basal forebrain lesions therefore appears unrelated to damage to cholinergic neurons of the nucleus basalis of Meynert and to depend instead on damage to pallidal and other neurons in this area. The AMPA- and perhaps also the ibotenate-induced impairment in the retention of passive avoidance appears to be more directly related to destruction of cholinergic neurons of the nucleus basalis. These data are discussed in the context of cortical cholinergic involvement in mnemonic processes.

Quantitative analysis of potassium channel mRNA expression in atrial and ventricular muscle of rats

The expression of 15 different potassium channel genes in rat atrial and ventricular muscle was quantitatively compared by use of an RNase protection assay. Of these genes, only five, Kv1.2, Kv1.4, Kv1.5, Kv2.1, and Kv4.2, were expressed at significant levels in cardiac muscle. In comparisons of atrial and ventricular RNA samples, transcripts from the Kv1.2 and Kv4.2 genes showed the largest differences in relative abundance. There was an approximately twofold decrease in total Kv4 subfamily mRNA expression in atrial muscle relative to ventricular muscle and a 70% increase in total Kv1 subfamily mRNA. Variation of potassium channel mRNA expression within the left ventricular wall was also examined. There was a large gradient of Kv4.2 expression across the ventricular wall, and Kv4.2 expression in epicardial muscle was more than eight times higher than in papillary muscle. Other potassium channel genes were expressed at relatively uniform levels across the ventricular wall. The results suggest that transcriptional regulation makes a significant contribution to the control of potassium channel expression in cardiac muscle and to the variation of the electrophysiological phenotype of myocytes from different regions of the myocardium.

Cholinergic and catecholaminergic afferents to the olfactory bulb in the hamster: a neuroanatomical, biochemical, and histochemical investigation

A series of neuroanatomical, biochemical, and histochemical studies have been conducted to determine the sources of cholinergic afferents to the main olfactory bulb (MOB) in the hamster. Following horseradish peroxidase (HRP) injections that are restricted to the MOB, retrograde neuronal labeling is observed bilaterally in the anterior olfactory nucleus, locus coeruleus, and raphe nuclei, and ipsilaterally in the ventral hippocampal rudiment, dorsal peduncular cortex, piriform cortex, nucleus of the lateral olfactory tract, anterior pole of the medial septal area and vertical limb of the diagonal band, nucleus of the horizontal limb of the diagonal band (HDB), and hypothalamus. Spread of HRP into the accessory olfactory bulb results in additional neuronal labeling ipsilaterally in the bed nucleus of the accessory olfactory tract, medial amygdaloid nucleus, and bed nucleus of the stria terminalis, and bilaterally in the posteromedial cortical amygdaloid nucleus. Retrograde tracing studies also have been conducted in cases with lesions in the basal forebrain or hypothalamus to assess the extent to which such lesions interrupt fibers of passage from other sources of centrifugal afferents, and the effects of such lesions on choline acetyltransferase (CAT) activity and catecholamine content in the MOB and on acetylcholinesterase (AChE) activity in the forebrain have been evaluated. Lesions in the basal forebrain reduce or eliminate CAT and AChE activity in the MOB in direct relationship to the extent of damage to the HDB. Norepinephrine (NE) content in the MOB also is reduced by basal forebrain lesions, but in relationship to damage of the medial forebrain bundle (MFB). The hypothalamic lesions have no effect on AChE activity in the forebrain or on CAT activity in the MOB, but they eliminate retrograde labeling in the locus coeruleus and raphe nuclei and reduce the NE content of the MOB to undetectable levels. The dopamine content of the MOB is not reduced by any of the lesions. Anterograde tracing studies have been conducted to compare the rostral projection patterns of the HDB with the distribution of AChE activity. Most of the rostrally directed axons travel in association with the MFB. A small component of axons travels in association with the lateral olfactory tract. Within the MOB, the axons terminate predominantly in the glomerular layer and in the vicinity of the internal plexiform layer. The projection and termination patterns of the HDB correspond well with the distribution of AChE activity. These various results indicate that the HDB is the major source of cholinergic afferents to the MOB.

Muscarinic M2 receptor mRNA expression and receptor binding in cholinergic and non-cholinergic cells in the rat brain: a correlative study using in situ hybridization histochemistry and receptor autoradiography

The goal of the present study was to identify the cells containing mRNA coding for the m2 subtype of muscarinic cholinergic receptors in the rat brain. In situ hybridization histochemistry was used, with oligonucleotides as hybridization probes. The distribution of cholinergic cells was examined in consecutive sections with probes complementary to choline acetyltransferase mRNA. Furthermore, the microscopic distribution of muscarinic cholinergic binding sites was examined with a non-selective ligand ([3H]N-methylscopolamine) and with ligands proposed to be M1-selective ([3H]pirenzepine) or M2-selective ([3H]oxotremorine-M). The majority of choline acetyltransferase mRNA-rich (i.e. cholinergic) cell groups (medial septum-diagonal band complex, nucleus basalis, pedunculopontine and laterodorsal tegmental nuclei, nucleus parabigeminalis, several motor nuclei of the brainstem, motoneurons of the spinal cord), also contained m2 mRNA, strongly suggesting that at least a fraction of these receptors may be presynaptic autoreceptors. A few groups of cholinergic cells were an exception to this fact: the medial habenula and some cranial nerve nuclei (principal oculomotor, trochlear, abducens, dorsal motor nucleus of the vagus). Furthermore, m2 mRNA was not restricted to cholinergic cells but was also present in many other cells throughout the rat brain. The distribution of m2 mRNA was in good, although not complete, agreement with that of binding sites for the M2 preferential agonist [3H]oxotremorine-M, but not with [3H]pirenzepine binding sites. Regions where the presence of [3H]oxotremorine-M binding sites was not correlated with that of m2 mRNA are the caudate-putamen, nucleus accumbens, olfactory tubercle and islands of Calleja. The present results strongly suggest that the M2 receptor is expressed by a majority of cholinergic cells, where it probably plays a role as autoreceptor. However, many non-cholinergic neurons also express this receptor, which would be, presumably, postsynaptically located. Finally, comparison between the distribution of m2 mRNA and that of the proposed M2-selective ligand [3H]oxotremorine-M indicates that this ligand, in addition to M2 receptors, may also recognize in certain brain areas other muscarinic receptor populations, particularly M4.

Basal forebrain magnocellular neurons stain for nerve growth factor receptor: correlation with cholinergic cell bodies and effects of axotomy

Recent evidence has demonstrated the presence of nerve growth factor (NGF) in areas of the central nervous system characterized by cholinergic innervation. We report that a unique population of rat basal forebrain magnocellular neurons that project to the cortex and hippocampus are immunoreactive to a monoclonal antibody to the NGF receptor. Removal of target contact results in a time-dependent loss or shrinkage of cells in the basal forebrain that stain for NGF receptor and acetylcholinesterase, suggesting that under normal conditions, basal forebrain cholinergic neurons utilize NGF for trophic support.

Survival of cholinergic forebrain neurons in developing p75NGFR-deficient mice

The functions of the low-affinity p75 nerve growth factor receptor (p75(NGFR)) in the central nervous system were explored in vivo. In normal mice, approximately 25 percent of the cholinergic basal forebrain neurons did not express TrkA and died between postnatal day 6 and 15. This loss did not occur in p75(NGFR)-deficient mice or in normal mice systemically injected with a p75(NGFR)-inhibiting peptide. Control, but not p75(NGFR)-deficient, mice also had fewer cholinergic striatal interneurons. Apparently, p75(NGFR) mediates apoptosis of these developing neurons in the absence of TrkA, and modulation of p75(NGFR) can promote neuronal survival. Cholinergic basal forebrain neurons are involved in learning and memory.

The neurotrophins BDNF, NT-3 and NT-4/5, but not NGF, up-regulate the cholinergic phenotype of developing motor neurons

Although developing motor neurons express low-affinity nerve growth factor (NGF) receptors, there is no known biological effect of NGF on developing or adult motor neurons. In this study, we found that, unlike NGF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4/5 (NT-4/5) stimulated cholinergic phenotype by increasing choline acetyltransferase (CAT) activity in cultures enriched with embryonic rat motor neurons. Ciliary neurotrophic factor (CNTF) also stimulated CAT activity. The effects of BDNF and NT-4/5 on CAT activity appeared to be synergistic with that of CNTF. Cotreatment with BDNF and NT-3 resulted in an additive effect, suggesting that signal transduction was mediated through different high-affinity receptors tyrosine kinases B and C (Trk B and Trk C). However, cotreatment with BDNF and NT-4/5 did not result in an increase in CAT activity greater than that of either BDNF or NT-4/5 alone, suggesting that their effects were mediated via the same receptor Trk B. Supporting our findings that spinal cholinergic neurons are responsive to trophic actions of members of the neurotrophin family, motor neuron-enriched cultures were found to express mRNA for Trk B and Trk C, which have been identified as high-affinity receptors for BDNF and NT-4/5, and NT-3, respectively.

Neurodevelopment. Parasympathetic neurons originate from nerve-associated peripheral glial progenitors

The peripheral autonomic nervous system reaches far throughout the body and includes neurons of diverse functions, such as sympathetic and parasympathetic. We show that the parasympathetic system in mice--including trunk ganglia and the cranial ciliary, pterygopalatine, lingual, submandibular, and otic ganglia--arise from glial cells in nerves, not neural crest cells. The parasympathetic fate is induced in nerve-associated Schwann cell precursors at distal peripheral sites. We used multicolor Cre-reporter lineage tracing to show that most of these neurons arise from bi-potent progenitors that generate both glia and neurons. This nerve origin places cellular elements for generating parasympathetic neurons in diverse tissues and organs, which may enable wiring of the developing parasympathetic nervous system.

Nicotine-induced protection of cultured cortical neurons against N-methyl-D-aspartate receptor-mediated glutamate cytotoxicity

The effects of nicotine on glutamate-induced cytotoxicity were examined using primary cultures of rat cortical neurons. The cell viability was significantly reduced when cultures were briefly exposed to glutamate or N-methyl-D-aspartate (NMDA) then incubated with normal medium for 1 h. A 1-h exposure of the cultures to kainate or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) reduced cell viability. Incubating cultures with nicotine for 1-24 h protected cortical neurons against glutamate cytotoxicity. Maximum protection against glutamate cytotoxicity was induced with a 2-h nicotine incubation. Exposure to nicotine for up to 2 h did not affect cell viability by itself although cell viability was reduced in a time-dependent manner when the exposure exceeded 4 h. Neuroprotection by nicotine was dependent on both the concentration and incubation period. Nicotine reduced the NMDA cytotoxicity but did not attenuate that of kainate and AMPA. The neuroprotective effects of nicotine against glutamate cytotoxicity were antagonized by mecamylamine and hexamethonium but not by atropine. These results indicate that nicotinic receptor stimulation induces neuroprotection against glutamate cytotoxicity mediated by NMDA receptors.

Cholinergic sprouting in the hippocampus: a proposed role for IL-1

Damage to the entorhinal afferents (i.e., perforant path) to the hippocampal dentate gyrus leads to sprouting of the remaining intact septal cholinergic afferents within the denervated outer molecular layer. To investigate the cellular and molecular events which may contribute to this sprouting response, we describe the temporal sequence of cellular changes in the denervated zone prior to the observed neural reorganization. Rats were given perforant path (PP) transections and sacrificed at various time points following the lesion, on Days (D) 1, 2, 3, 4, 5, 6, and 30. Coronal sections at the level of the dorsal hippocampus were immunostained to localize microglia (OX-42), interleukin-1 (IL-1), and astroctytes (GFAP). We observed a rapid increase in the number of immunoreactive microglia in the denervated molecular layer within the first day following PP transection. Parallel sections show a concomitant increase in the number of IL-1-positive cells. Maximal reactive changes (i.e., hypertrophy and increase in number) in GFAP-positive astrocytes are not observed until D5. This time course of events suggests a role of microglia in astrocyte activation in vivo via production of IL-1 and offers support for a proposed hypothesis postulating a cascade of glial events which may lead to cholinergic sprouting following PP transection.

Differential cholinergic innervation within functional subdivisions of the human cerebral cortex: a choline acetyltransferase study

The distribution of cholinergic fibers in the human brain was investigated with choline acetyltransferase immunocytochemistry in 35 cytoarchitectonic subdivisions of the cerebral cortex. All cortical areas and all cell layers contained cholinergic axons. These fibers displayed numerous varicosities and, on occasion, complex preterminal profiles arranged in the form of dense clusters. The density of cholinergic axons tended to be higher in the more superficial layers of the cerebral cortex. Several distinct patterns of lamination were identified. There were also major differences in the overall density of cholinergic axons from one cytoarchitectonic area to another. The cholinergic innervation of primary sensory, unimodal, and heteromodal association areas was lighter than that of paralimbic and limbic areas. Within unimodal association areas, the density of cholinergic axons and varicosities was significantly lower in the upstream (parasensory) sectors than in the downstream sectors. Within paralimbic regions, the non-isocortical sectors had a higher density of cholinergic innervation than the isocortical sectors. The highest density of cholinergic axons was encountered in core limbic structures such as the hippocampus and amygdala. These observations show that the cholinergic innervation of the human cerebral cortex displays regional variations that closely follow the organization of information processing systems.