Distribution of central cholinergic neurons in the baboon (Papio papio). I. General morphology

Cholinergic and Nadph-δ neurons in the pedunculopontine and laterodorsal tegmental nuclei of human and nonhuman primates

The brainstem pedunculopontine (PPN) and laterodorsal tegmental (LDTg) nuclei are involved in multifarious activities, including motor control. Yet, their exact cytoarchitectural boundaries are still uncertain. We therefore initiated a comparative study of the topographical and neurochemical organization of the PPN and LDTg in cynomolgus monkeys (Macaca fascicularis) and humans. The distribution and morphological characteristics of neurons expressing choline acetyltransferase (ChAT) and/or nicotinamide adenine dinucleotide phosphate diaphorase (Nadph-δ) were documented. The number and density of the labeled neurons were obtained by stringent stereological methods, whereas their topographical distribution was reported upon corresponding magnetic resonance imaging (MRI) planes. In both human and nonhuman primates, the PPN and LDTg are populated by three neurochemically distinct types of neurons (ChAT-/Nadph-δ+, ChAT+/Nadph-δ-, and ChAT+/Nadph-δ+), which are distributed according to a complex spatial interplay. Three-dimensional reconstructions reveal that ChAT+ neurons in the PPN and LDTg form a continuum with some overlaps with pigmented neurons of the locus coeruleus, dorsally, and of the substantia nigra (SN) complex, ventrally. The ChAT+ neurons in the PPN and LDTg are -two to three times more numerous in humans than in monkeys but their density is -three to five times higher in monkeys than in humans. Neurons expressing both ChAT and Nadph-δ have a larger cell body and a longer primary dendritic arbor than singly labeled neurons. Stereological quantification reveals that 25.6% of ChAT+ neurons in the monkey PPN are devoid of Nadph-δ staining, a finding that questions the reliability of Nadph-δ as a marker for cholinergic neurons in primate brainstem.

Distribution of cholinergic neurons in the brains of a lar gibbon and a chimpanzee

Using choline acetyltransferase immunohistochemistry, we describe the nuclear parcellation of the cholinergic system in the brains of two apes, a lar gibbon (Hylobates lar) and a chimpanzee (Pan troglodytes). The cholinergic nuclei observed in both apes studied are virtually identical to that observed in humans and show very strong similarity to the cholinergic nuclei observed in other primates and mammals more generally. One specific difference between humans and the two apes studied is that, with the specific choline acetyltransferase antibody used, the cholinergic pyramidal neurons observed in human cerebral cortex were not labeled. When comparing the two apes studied and humans to other primates, the presence of a greatly expanded cholinergic medullary tegmental field, and the presence of cholinergic neurons in the intermediate and dorsal horns of the cervical spinal cord are notable variations of the distribution of cholinergic neurons in apes compared to other primates. These neurons may play an important role in the modulation of ascending and descending neural transmissions through the spinal cord and caudal medulla, potentially related to the differing modes of locomotion in apes compared to other primates. Our observations also indicate that the average soma volume of the neurons forming the laterodorsal tegmental nucleus (LDT) is larger than those of the pedunculopontine nucleus (PPT) in both the lar gibbon and chimpanzee. This variability in soma volume appears to be related to the size of the adult derivatives of the alar and basal plate across mammalian species.

Immunohistochemical study of the brainstem cholinergic system in the alpaca (<em>Lama pacos</em>) and colocalization with CGRP

Several cholinergic regions have been detected in the brainstem of mammals. In general, these regions are constant among different species, and the nuclear complement is maintained in animals belonging to the same order. The cholinergic system of the brainstem has been partially described in Cetartiodactyla, except for the medulla oblongata. In this work carried out in the alpaca, the description of the cholinergic regions in this order is completed by the immunohistochemical detection of the enzyme choline acetyltransferase (ChAT). In addition, using double immunostaining techniques, the relationship between the cholinergic system and the distribution of calcitonin gene-related peptide (CGRP) previously described is analysed. Although these two substances are found in several brainstem regions, the coexistence in the same cell bodies was observed only in the laterodorsal tegmental nucleus, the nucleus ambiguus and the reticular formation. These results suggest that the interaction between ChAT and CGRP may be important in the regulation of voluntary movements, the control of rapid eye movement sleep and states of wakefulness as well as in reward mechanisms. Comparing the present results with others previously obtained by our group regarding the catecholaminergic system in the alpaca brainstem, it seems that CGRP may be more functionally related to the latter system than to the cholinergic system.

Subdivisions of the mesencephalon and isthmus in the lizard Gekko gecko as revealed by ChAT immunohistochemistry

The distribution of cholinergic cell bodies and fibers was examined in the mesencephalon and isthmus of Gekko gecko. Distinct groups with prominent labeled cells were observed in the cranial nerve motor nuclei and isthmic nuclei, and weak labeled cell bodies and fibers were observed in the mesencephalic nucleus of the trigeminal nerve and the central nucleus of the torus semicircularis. After discussing the topological relationships within the tectum and isthmus, we unify the nomenclature of the caudal deep mesencephalic nucleus in lizards and the rostral magnocellular nucleus isthmi in turtles that is similar in terms of the preisthmic position, nontopographic connections with the tectum, and the same midbrain origin to the magnocellular preisthmic nucleus in birds, and may be homologous to the superficial cuneiform nucleus in mammals. None of them belong to the cholinergic nucleus isthmi, as the latter has isthmus origin and topographic reciprocal connections with the tectum. We also discuss the origin and intrinsic function of the inner longitudinal tract of the thick ChAT-ir fibers that course through the mesencephalon and diencephalon. We review the subdivisions of the mesencephalon and isthmus of Gekko gecko as revealed by ChAT immunohistochemistry, as well as the limits of the diencephalo-mesencephalic, mesencephalic-isthmo, and isthmo-rhombocephalic by the ChAT-ir cell- and fiber-poor distribution, and discuss the caudal limit of the isthmus. Our research on the subdivisions of the mesencephalon and isthmus in G. gecko as revealed by ChAT immunohistochemistry will serve as the neuroanatomical basis for subsequent relevant studies of Gekko gecko.

Nuclear organization and morphology of cholinergic neurons in the brain of the rock cavy (Kerodon rupestris) (Wied, 1820)

The aim of this study was to conduct cytoarchitectonic studies and choline acetyltransferase (ChAT) immunohistochemical analysis to delimit the cholinergic groups in the encephalon of the rock cavy (Kerodon rupestris), a crepuscular Caviidae rodent native to the Brazilian Northeast. Three young adult animals were anesthetized and transcardially perfused. The encephala were cut in the coronal plane using a cryostat. We obtained 6 series of 30-μm-thick sections. The sections from one series were subjected to Nissl staining. Those from another series were subjected to immunohistochemistry for the enzyme ChAT, which is used in acetylcholine synthesis, to visualize the different cholinergic neural centers of the rock cavy. The slides were analyzed using a light microscope and the results were documented by description and digital photomicrographs. ChAT-immunoreactive neurons were identified in the telencephalon (nucleus accumbens, caudate-putamen, globus pallidus, entopeduncular nucleus and ventral globus pallidus, olfactory tubercle and islands of Calleja, diagonal band of Broca nucleus, nucleus basalis, and medial septal nucleus), diencephalon (ventrolateral preoptic, hypothalamic ventrolateral, and medial habenular nuclei), and brainstem (parabigeminal, laterodorsal tegmental, and pedunculopontine tegmental nuclei). These findings are discussed through both a functional and phylogenetic perspective.

Cholinergic profiles in the Goettingen miniature pig (Sus scrofa domesticus) brain

Central cholinergic structures within the brain of the even-toed hoofed Goettingen miniature domestic pig (Sus scrofa domesticus) were evaluated by immunohistochemical visualization of choline acetyltransferase (ChAT) and the low-affinity neurotrophin receptor, p75^NTR . ChAT-immunoreactive (-ir) perikarya were seen in the olfactory tubercle, striatum, medial septal nucleus, vertical and horizontal limbs of the diagonal band of Broca, and the nucleus basalis of Meynert, medial habenular nucleus, zona incerta, neurosecretory arcuate nucleus, cranial motor nuclei III and IV, Edinger-Westphal nucleus, parabigeminal nucleus, pedunculopontine nucleus, and laterodorsal tegmental nucleus. Cholinergic ChAT-ir neurons were also found within transitional cortical areas (insular, cingulate, and piriform cortices) and hippocampus proper. ChAT-ir fibers were seen throughout the dentate gyrus and hippocampus, in the mediodorsal, laterodorsal, anteroventral, and parateanial thalamic nuclei, the fasciculus retroflexus of Meynert, basolateral and basomedial amygdaloid nuclei, anterior pretectal and interpeduncular nuclei, as well as select laminae of the superior colliculus. Double immunofluorescence demonstrated that virtually all ChAT-ir basal forebrain neurons were also p75^NTR -positive. The present findings indicate that the central cholinergic system in the miniature pig is similar to other mammalian species. Therefore, the miniature pig may be an appropriate animal model for preclinical studies of neurodegenerative diseases where the cholinergic system is compromised. J. Comp. Neurol. 525:553-573, 2017. © 2016 Wiley Periodicals, Inc.

Neuroanatomical organization of the cholinergic system in the central nervous system of a basal actinopterygian fish, the senegal bichir Polypterus senegalus

Polypterid bony fishes are believed to be basal to other living ray-finned fishes, and their brain organization is therefore critical in providing information as to primitive neural characters that existed in the earliest ray-finned fishes. The cholinergic system has been characterized in more advanced ray-finned fishes, but not in polypterids. In order to establish which cholinergic neural centers characterized the earliest ray-finned fishes, the distribution of choline acetyltransferase (ChAT) is described in Polypterus and compared with the distribution of this molecule in other ray-finned fishes. Cell groups immunoreactive for ChAT were observed in the hypothalamus, the habenula, the optic tectum, the isthmus, the cranial motor nuclei, and the spinal motor column. Cholinergic fibers were observed in both the telencephalic pallium and the subpallium, in the thalamus and pretectum, in the optic tectum and torus semicircularis, in the mesencephalic tegmentum, in the cerebellar crest, in the solitary nucleus, and in the dorsal column nuclei. Comparison of the data within a segmental neuromeric context indicates that the cholinergic system in polypterid fishes is generally similar to that in other ray-finned fishes, but cholinergic-positive neurons in the pallium and subpallium, and in the thalamus and cerebellum, of teleosts appear to have evolved following the separation of polypterids and other ray-finned fishes.

Cognitive consilience: primate non-primary neuroanatomical circuits underlying cognition

Interactions between the cerebral cortex, thalamus, and basal ganglia form the basis of cognitive information processing in the mammalian brain. Understanding the principles of neuroanatomical organization in these structures is critical to understanding the functions they perform and ultimately how the human brain works. We have manually distilled and synthesized hundreds of primate neuroanatomy facts into a single interactive visualization. The resulting picture represents the fundamental neuroanatomical blueprint upon which cognitive functions must be implemented. Within this framework we hypothesize and detail 7 functional circuits corresponding to psychological perspectives on the brain: consolidated long-term declarative memory, short-term declarative memory, working memory/information processing, behavioral memory selection, behavioral memory output, cognitive control, and cortical information flow regulation. Each circuit is described in terms of distinguishable neuronal groups including the cerebral isocortex (9 pyramidal neuronal groups), parahippocampal gyrus and hippocampus, thalamus (4 neuronal groups), basal ganglia (7 neuronal groups), metencephalon, basal forebrain, and other subcortical nuclei. We focus on neuroanatomy related to primate non-primary cortical systems to elucidate the basis underlying the distinct homotypical cognitive architecture. To display the breadth of this review, we introduce a novel method of integrating and presenting data in multiple independent visualizations: an interactive website (http://www.frontiersin.org/files/cognitiveconsilience/index.html) and standalone iPhone and iPad applications. With these tools we present a unique, annotated view of neuroanatomical consilience (integration of knowledge).

Populations of subplate and interstitial neurons in fetal and adult human telencephalon

In the adult human telencephalon, subcortical (gyral) white matter contains a special population of interstitial neurons considered to be surviving descendants of fetal subplate neurons [Kostovic & Rakic (1980) Cytology and the time of origin of interstitial neurons in the white matter in infant and adult human and monkey telencephalon. J Neurocytol9, 219]. We designate this population of cells as superficial (gyral) interstitial neurons and describe their morphology and distribution in the postnatal and adult human cerebrum. Human fetal subplate neurons cannot be regarded as interstitial, because the subplate zone is an essential part of the fetal cortex, the major site of synaptogenesis and the 'waiting' compartment for growing cortical afferents, and contains both projection neurons and interneurons with distinct input-output connectivity. However, although the subplate zone is a transient fetal structure, many subplate neurons survive postnatally as superficial (gyral) interstitial neurons. The fetal white matter is represented by the intermediate zone and well-defined deep periventricular tracts of growing axons, such as the corpus callosum, anterior commissure, internal and external capsule, and the fountainhead of the corona radiata. These tracts gradually occupy the territory of transient fetal subventricular and ventricular zones.The human fetal white matter also contains distinct populations of deep fetal interstitial neurons, which, by virtue of their location, morphology, molecular phenotypes and advanced level of dendritic maturation, remain distinct from subplate neurons and neurons in adjacent structures (e.g. basal ganglia, basal forebrain). We describe the morphological, histochemical (nicotinamide-adenine dinucleotide phosphate-diaphorase) and immunocytochemical (neuron-specific nuclear protein, microtubule-associated protein-2, calbindin, calretinin, neuropeptide Y) features of both deep fetal interstitial neurons and deep (periventricular) interstitial neurons in the postnatal and adult deep cerebral white matter (i.e. corpus callosum, anterior commissure, internal and external capsule and the corona radiata/centrum semiovale). Although these deep interstitial neurons are poorly developed or absent in the brains of rodents, they represent a prominent feature of the significantly enlarged white matter of human and non-human primate brains.

Distribution and morphology of cholinergic, catecholaminergic and serotonergic neurons in the brain of Schreiber's long-fingered bat, Miniopterus schreibersii

The current study describes the nuclear parcellation and neuronal morphology of the cholinergic, catecholaminergic and serotonergic systems within the brain of a representative species of microbat. While these systems have been investigated in detail in the laboratory rat, and examined in several other mammalian species, no chiropterans, to the author's knowledge, have been examined. Using immunohistochemical stains for choline-acetyltransferase, tyrosine hydroxylase and serotonin, we were able to observe and document these systems in relation to the cytoarchitecture. The majority of cholinergic nuclei typically found in mammals were evident in the microbat, however we could not find evidence for choline-acetyltransferase immunopositive neurons in the Edinger-Westphal nucleus, parabigeminal nucleus, and the medullary tegmental field, as seen in several other mammalian species. A typically mammalian appearance of the catecholaminergic nuclei was observed, however, the anterior hypothalamic groups (A15 dorsal and ventral), the dorsal and dorsal caudal subdivisions of the ventral tegmental area (A10d and A10dc), and the ventral (pars reticulata) substantia nigra (A9v) were not present. The serotonergic nuclei were similar to that reported in all eutherian mammalian species studied to date. The overall complement of nuclei of these systems in the microbat, while different to the species examined in other orders of mammals, resembles most closely the complement seen in earlier studies of insectivore species, and is clearly distinguished from that seen in rodents, carnivores and primates. This data is discussed in terms of the phylogenetic relationships of the chiropterans.

Distribution and morphology of cholinergic, putative catecholaminergic and serotonergic neurons in the brain of the Egyptian rousette flying fox, Rousettus aegyptiacus

Over the past decade much controversy has surrounded the hypothesis that the megachiroptera, or megabats, share unique neural characteristics with the primates. These observations, which include similarities in visual pathways, have suggested that the megabats are more closely related to the primates than to the other group of the Chiropteran order, the microbats, and suggests a diphyletic origin of the Chiroptera. To contribute data relevant to this debate, we used immunohistochemical techniques to reveal the architecture of the neuromodulatory systems of the Egyptian rousette (Rousettus aegypticus), an echolocating megabat. Our findings revealed many similarities in the nuclear parcellation of the cholinergic, putative catecholaminergic and serotonergic systems with that seen in other mammals including the microbat. However, there were 11 discrete nuclei forming part of these systems in the brain of the megabat studied that were not evident in an earlier study of a microbat. The occurrence of these nuclei align the megabat studied more closely with primates than any other mammalian group and clearly distinguishes them from the microbat, which aligns with the insectivores. The neural systems investigated are not related to such Chiropteran specializations as echolocation, flight, vision or olfaction. If neural characteristics are considered strong indicators of phylogenetic relationships, then the data of the current study strongly supports the diphyletic origin of Chiroptera and aligns the megabat most closely with primates in agreement with studies of other neural characters.

Neurobiological mechanisms for the regulation of mammalian sleep-wake behavior: reinterpretation of historical evidence and inclusion of contemporary cellular and molecular evidence

At its most basic level, the function of mammalian sleep can be described as a restorative process of the brain and body; recently, however, progressive research has revealed a host of vital functions to which sleep is essential. Although many excellent reviews on sleep behavior have been published, none have incorporated contemporary studies examining the molecular mechanisms that govern the various stages of sleep. Utilizing a holistic approach, this review is focused on the basic mechanisms involved in the transition from wakefulness, initiation of sleep and the subsequent generation of slow-wave sleep and rapid eye movement (REM) sleep. Additionally, using recent molecular studies and experimental evidence that provides a direct link to sleep as a behavior, we have developed a new model, the cellular-molecular-network model, explaining the mechanisms responsible for regulating REM sleep. By analyzing the fundamental neurobiological mechanisms responsible for the generation and maintenance of sleep-wake behavior in mammals, we intend to provide a broader understanding of our present knowledge in the field of sleep research.

The immunohistochemical localization of neuronal nitric oxide synthase in the basal forebrain of the dog

The present work describes for the first time the anatomical distribution of neuronal nitric oxide synthase (nNOS) immunoreactivity and NADPH-d activity in the basal forebrain of the dog. As in other species, small, intensely nNOS-immunoreactive cells were seen within the olfactory tubercle, caudate nucleus, putamen, nucleus accumbens and amygdala. In addition, a population of mixed large and small nNOS positive cells was found in the medial septum, diagonal band and nucleus basalis overlapping the distribution of the magnocellular cholinergic system of the basal forebrain. Our results show that the distribution of NOS containing neurons in these nuclei in the dog is more extensive and uniform than that reported in rodents and primates. When double labeling of nNOS and NADPH-d was performed in the same tissue section most neurons were double labeled. However, a considerable number of large perikarya in the diagonal band and nucleus basalis appeared to be single labeled for nNOS. Thought a certain degree of interference between the two procedures could not be completely excluded, these findings suggest that NADPH-d histochemistry, which is frequently used to show the presence of NOS, underestimates the potential of basal forebrains neurons to produce nitric oxide. In addition, a few neurons mainly localized among the fibers of the internal capsule, appeared to be labeled only for NADPH-d. These neurons could be expressing a different isoform of NOS, not recognized by our anti-nNOS antibody, as has been reported in healthy humans and AD patients.

Development of the cholinergic system in the brain and retina of the zebrafish

We have analyzed the distribution pattern of choline acetyltransferase (ChAT) in the zebrafish brain and retina during ontogeny. ChAT-immunoreactive (ChAT-ir) neurons are observed in the prosencephalon from 60 h postfertilization (hpf) onwards, exclusively in the preoptic area (basal plate of p6) derived from the secondary prosencephalon. In the mesencephalon, ChAT-ir cells are observed in both the optic tectum and the tegmentum. Stained cells in the tegmentum are observed from 60 hpf onwards, while in the optic tectum they appear after hatching. In the rhombencephalon, ChAT-ir cells are first observed in the isthmic region (rh1) and in the medulla oblongata (rh5-rh7) at the end of embryonic life. The rhombencephalic cholinergic cell groups develop in a gradual caudorostral sequence. Motoneurons of the spinal cord are ChAT-ir from 48 hpf onwards. The retina displays ChAT-ir neuropil in both the inner and outer plexiform layers from embryonic life, whereas stained amacrine cells are only observed after hatching. The staining in the outer plexiform layer gradually decreases during juvenile development. The optic nerve axons show a transient expression of ChAT at the end of embryonic development. The early presence of ChAT immunolabeling suggests an important neuromodulator role for acetylcholine in the first developmental stages.

Cholinergic elements in the zebrafish central nervous system: Histochemical and immunohistochemical analysis

Recently, the zebrafish has been extensively used for studying the development of the central nervous system (CNS). However, the zebrafish CNS has been poorly analyzed in the adult. The cholinergic/cholinoceptive system of the zebrafish CNS was analyzed by using choline acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) histochemistry in the brain, retina, and spinal cord. AChE labeling was more abundant and more widely distributed than ChAT immunoreactivity. In the telencephalon, ChAT-immunoreactive (ChAT-ir) cells were absent, whereas AChE-positive neurons were observed in both the olfactory bulb and the telencephalic hemispheres. The diencephalon was the region with the lowest density of AChE-positive cells, mainly located in the pretectum, whereas ChAT-ir cells were exclusively located in the preoptic region. ChAT-ir cells were restricted to the periventricular stratum of the optic tectum, but AChE-positive neurons were observed throughout the whole extension of the lamination except in the marginal stratum. Although ChAT immunoreactivity was restricted to the rostral tegmental, oculomotor, and trochlear nuclei within the mesencephalic tegmentum, a widespread distribution of AChE reactivity was observed in this region. The isthmic region showed abundant AChE-positive and ChAT-ir cells in the isthmic, secondary gustatory and superior reticular nucleus and in the nucleus lateralis valvulae. ChAT immunoreactivity was absent in the cerebellum, although AChE staining was observed in Purkinje and granule cells. The medulla oblongata showed a widespread distribution of AChE-positive cells in all main subdivisions, including the octavolateral area, reticular formation, and motor nuclei of the cranial nerves. ChAT-ir elements in this area were restricted to the descending octaval nucleus, the octaval efferent nucleus and the motor nuclei of the cranial nerves. Additionally, spinal cord motoneurons appeared positive to both markers. Substantial differences in the ChAT and AChE distribution between zebrafish and other fish species were observed, which could be important because zebrafish is widely used as a genetic or developmental animal model.

The caudal sublenticular region/anterior amygdaloid area is the only part of the rat forebrain and mesopontine tegmentum occupied by magnocellular cholinergic neurons that receives outputs from the central division of extended amygdala

Ascending cholinergic projections and the central nucleus of the amygdala (CeA) have both been implicated in attentional and orienting mechanisms leading to adaptive behavioral responses. In view of this, the present study was carried out to identify relevant neuroanatomical relationships in the form of projections from the CeA and a related structure, the dorsolateral divison of the bed nucleus of the stria terminalis (dlBST), to parts of the basal forebrain and mesopontine tegmentum that contain magnocellular cholinergic neurons. The CeA and dlBST are components of the 'central division of extended amygdala'. Following injections of the anterogradely transported compounds, Phaseolus vulgaris-leucoagglutinin or biotinylated dextran amine, into the CeA or dlBST, sections were processed with immunohistochemical reagents to localize the anterograde tracer and choline acetyltransferase (ChAT). The trajectories of efferent projections from CeA and dlBST were qualitatively similar. Few ChAT-immunoreactive (ir) neurons were present within the extended amygdala or regions containing the dense terminations of its efferent projections, with the striking exception of the caudal sublenticular/anterior amygdaloid region. The ChAT-ir neurons there, however, were significantly smaller and weakly ChAT-ir as compared to those located outside of the dense extended amygdaloid terminations. In the mesopontine tegmentum, the robust downstream projection from the extended amygdala was centered medial to ChAT-ir neurons of the pedunculopontine tegmental nucleus. The differentiated character of the relationships between extended amygdala and forebrain and mesopontine districts containing ChAT-ir neurons that give rise to ascending projections may have significant implications for the control of cortical and diencephalic acetylcholine release and accompanying effects on attention, vigilance and locomotor activation.

Localization of choline acetyltransferase (ChAT) immunoreactivity in the brain of a caecilian amphibian, Dermophis mexicanus (Amphibia: Gymnophiona)

The organization of the cholinergic system in the brain of anuran and urodele amphibians was recently studied, and significant differences were noted between both amphibian orders. However, comparable data are not available for the third order of amphibians, the limbless gymnophionans (caecilians). To further assess general and derived features of the cholinergic system in amphibians, we have investigated the distribution of choline acetyltransferase immunoreactive (ChAT-ir) cell bodies and fibers in the brain of the gymnophionan Dermophis mexicanus. This distribution showed particular features of gymnophionans such as the existence of a particularly large cholinergic population in the striatum, the presence of ChAT-ir cells in the mesencephalic tectum, and the organization of the cranial nerve motor nuclei. These peculiarities probably reflect major adaptations of gymnophionans to a fossorial habit. Comparison of our results with those in other vertebrates, including a segmental approach to correlate cell populations across species, shows that the general pattern of organization of cholinergic systems in vertebrates can be modified in certain species in response to adaptative processes that lead to morphological and behavioral modifications of members of a given class of vertebrates, as shown for gymnophionans.

Distribution of the high-affinity choline transporter in the human and macaque monkey spinal cord

The distribution of the high-affinity choline transporter (CHT) was determined in the human and macaque monkey spinal cord using in situ hybridization histochemistry and immunohistochemistry. Signals for CHT mRNA were observed in somatic motor neurons, sympathetic preganglionic neurons, and neurons in the medial part of lamina VII. The mRNA for CHT was co-localized in single neurons with the mRNAs for vesicular acetylcholine transporter and cholineacetyltransferase. These same cholinergic neuronal groups were labeled by immunohistochemistry for human CHT. Of somatic motor neurons, smaller cell bodies of gamma-motor neurons were labeled very intensely, whereas larger cell bodies of alpha-motor neurons showed various degrees of labeling from weak to moderately intense. Human CHT is thus a novel cholinergic marker, which not only labels cholinergic neurons, but also reveals their heterogeneity.

Projections from the substantia nigra pars reticulata to the motor thalamus of the rat: single axon reconstructions and immunohistochemical study

This is a study in the rat of the distribution of specific neurotransmitters in neurones projecting from the substantia nigra reticulata (SNR) to the ventrolateral (VL) and ventromedial (VM) thalamic nuclei. Individual axons projecting from the SNR to these thalamic nuclei have also been reconstructed following small injection of the anterograde tracer dextran biotin into the the SNR. Analysis of reconstructions revealed two populations of SNR neurones projecting onto the VL and VM thalamic nuclei. One group projects directly onto the VM and VL, and the other projects to the VM/VL and to the parafascicular nucleus. In another set of experiments Fluoro-Gold was injected into the VL/VM to label SNR projection neurones retrogradely, and immunohistochemistry was performed to determine the distribution of choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT), gamma-aminobutyric acid (GABA), and glutamate in Fluoro-Gold-labelled SNR projection neurones. Most SNR-VL/VM thalamic projection neurones were immunoreactive to acetylcholine or glutamate, whereas only 25% of the projection neurones were found to be immunoreactive to GABA.

Distribution of choline acetyltransferase-immunoreactive structures in the lamprey brain

The distribution of cholinergic neurons and fibers was studied immunohistochemically in the brain of two species of lampreys (Petromyzon marinus and Lampetra fluviatilis), by using an antiserum against choline acetyltransferase (ChAT). The results obtained in both species were similar, but there appeared some interspecies differences. In the forebrain, cholinergic cells were present in the striatum, preoptic region, paraventricular nucleus, pineal and parapineal organs, habenula, and pretectum. The cranial nerve motoneurons (III, IV, V, VI, VII, IX, and X), the first and second spino-occipital nerves (so), and the ventral horn of the spinal cord showed a strong ChAT immunoreactivity. Additional cholinergic neurons were observed: the mesencephalic M5 nucleus of Schober, two different cell populations in the isthmic region, the efferent component of the eighth nerve, putative preganglionic parasympathetic cells, cells in the solitary tract nucleus, and the rhombencephalic reticular formation. Cholinergic fibers were widely distributed in the brain. Comparison with previous studies in other vertebrates suggests that major cholinergic pathways, like tectal innervation from the isthmic region, are also present in lampreys. Of particular interest was the prominent projection to the neurohypophysis from cholinergic neurons in the preoptic region and paraventricular nucleus. Present data were analyzed within the segmental paradigm, as was previously done in other vertebrates. Our results reveal that the organization of many cholinergic systems in the lamprey as, for example, in the striatal, preoptic, and isthmic regions, comprises features of the anamniote brain that remain common to all living amniotes studied so far, thus being conservative to a surprisingly high degree. Therefore, the distribution of ChAT-immunoreactive structures in the lamprey brain is, in general, comparable to that previously described in other vertebrate species.

Distribution of choline acetyltransferase (ChAT) immunoreactivity in the central nervous system of a chondrostean, the siberian sturgeon (Acipenser baeri)

All studies to date of cholinergic systems of bony fishes have been done in teleosts. To gain further insight into the evolution of the cholinergic systems of bony fishes, we have studied the brain of a chondrostean fish, the Siberian sturgeon (Acipenser baeri, Brandt), by using an antibody against choline acetyltransferase (ChAT). This study showed the presence of ChAT-immunoreactive (ChAT-ir) neurons in the preoptic region (parvocellular and magnocellular preoptic nuclei and suprachiasmatic nucleus), the periventricular and tuberal hypothalamus, the saccus vasculosus, the dorsal thalamus, and the habenula. The mesencephalic tegmentum contained ChAT-ir cells in the torus semicircularis and torus lateralis. The isthmus contained several cholinergic populations: the nucleus isthmi, the lateral nucleus of the valvula, the secondary visceral nucleus, and the dorsal tegmental nucleus. The motor neurons of the cranial nerves and the spinal motor column were strongly immunoreactive. The medial (sensory) trigeminal nucleus also contained a ChAT-ir neuronal population. The distribution of ChAT-ir neurons in the sturgeon brain showed some notable differences with that observed in teleosts, such as the absence of cholinergic cells in the telencephalon and the optic tectum. Several brain regions were richly innervated by ChAT-ir fibers, particularly the telencephalon, optic tectum, thalamus, posterior tubercle, and interpeduncular nucleus. The hypothalamo-hypophyseal tract, the tract of the saccus vasculosus, the fasciculus retroflexus, and an isthmo-mesencephalo-thalamic tract were the most conspicuous cholinergic bundles. Comparative analysis of these results suggests that teleosts have conserved most traits of the cholinergic system of the sturgeon, having acquired new cholinergic populations during evolution.

Cyto- and chemoarchitecture of basal forebrain cholinergic neurons in the common marmoset (Callithrix jacchus)

The cyto- and chemoarchitecture of basal forebrain cholinergic neurons (BFCN) was investigated in the lower primate, the common marmoset (Callithrix jacchus). A large population of magnocellular, hyperchromic, and choline acetyltransferase (ChAT)-positive neurons was detected in the marmoset basal forebrain. The distribution of these neurons was similar to those in higher primates. Thus, ChAT-positive neurons were observed in the medial septum (Ch2), the vertical (Ch2) and horizontal (Ch3) limbs of the diagonal band of Broca, and the nucleus basalis of Meynert (Ch4). The Ch4 complex was relatively well differentiated and displayed distinct sectors. We detected anterior (Ch4a, with a medial and a lateral subdivision), intermediate (Ch4i, with a dorsal and a ventral subdivision), and posterior (Ch4p) sectors in the marmoset Ch4. The Ch4i was relatively small while the Ch4p was large. Similar to the rodent, the marmoset Ch1 extended quite a distance posteriorly, and the Ch4p displayed a major interstitial component distributed within the globus pallidus, its medullary laminae, and the internal capsule. Virtually all of the marmoset BFCN displayed acetylcholinesterase activity, and low affinity (p75(NTR)) and high affinity (Trk) neurotrophin receptor immunoreactivity. A majority contained immunoreactivity for calbindin-D(28K) and calretinin. Many of the Ch4 neurons also displayed tyrosine hydroxylase immunoreactivity. The BFCN lacked galanin immunoreactivity, but were innervated by galanin-positive fibers. None of the marmoset BFCN were NADPH-d-positive. Thus, the BFCN display major anatomical and biochemical differences in the marmoset when compared with higher primates. The marmoset BFCN also display many characteristics common to other primates. This fact, combined with the relatively short life span of the marmoset, indicates that this species may be ideal for studies of age-related changes in the BFCN.

Distribution of choline acetyltransferase immunoreactivity in the brain of an elasmobranch, the lesser spotted dogfish (Scyliorhinus canicula)

Although the distribution of cholinergic cells is remarkably similar across the vertebrate species, no data are available on more primitive species, such as cartilaginous fishes. To extend the evolutionary analysis of the cholinergic systems, we studied the distribution of cholinergic neurons in the brain and rostral spinal cord of Scyliorhinus canicula by immunocytochemistry using an antibody against the enzyme choline acetyltransferase (ChAT). Western blot analysis of brain extracts of dogfish, sturgeon, trout, and rat showed that this antibody recognized similar bands in the four species. Putative cholinergic neurons were observed in most brain regions, including the telencephalon, diencephalon, cerebellum, and brainstem. In the retrobulbar region and superficial dorsal pallium of the telencephalon, numerous small pallial cells were ChAT-like immunoreactive. In addition, tufted cells of the olfactory bulb and some cells in the lateral pallium showed faint immunoreactivity. In the preoptic-hypothalamic region, ChAT-immunoreactive (ChAT-ir) cells were found in the preoptic nucleus, the vascular organ of the terminal lamina, and a small population in the caudal tuber. In the epithalamus, the pineal photoreceptors were intensely positive. Many cells of the habenula were faintly ChAT-ir, but the neuropil of the interpeduncular nucleus showed intense ChAT immunoreactivity. In the pretectal region, ChAT-ir cells were observed only in the superficial pretectal nucleus. In the brainstem, the somatomotor and branchiomotor nuclei, the octavolateral efferent nucleus, and a cell group just rostral to the Edinger-Westphal (EW) nucleus contained ChAT-ir neurons. In addition, the trigeminal mesencephalic nucleus, the nucleus G of the isthmus, some locus coeruleus cells, and some cell populations of the vestibular nuclei and of the electroreceptive nucleus of the octavolateral region exhibited ChAT immunoreactivity. In the reticular areas of the brainstem, the nucleus of the medial longitudinal fascicle, many reticular neurons of the rhombencephalon, and cells of the nucleus of the lateral funiculus were immunoreactive to this antibody. In the cerebellum, Golgi cells of the granule cell layer and some cells of the cerebellar nucleus were also ChAT-ir. In the rostral spinal cord, ChAT immunoreactivity was observed in cells of the motor column, the dorsal horn, the marginal nucleus (a putative stretch-receptor organ), and in interstitial cells of the ventral funiculus. These results demonstrate for the first time that cholinergic neurons are distributed widely in the central nervous system of elasmobranchs and that their cholinergic systems have evolved several characteristics that are unique to this group.

Quantification of cholinergic and select non-cholinergic mesopontine neuronal populations in the human brain

The pars compacta and pars dissipata of the pedunculopontine nucleus contain cholinergic cell group Ch5, and the laterodorsal tegmental nucleus contains cholinergic cell group Ch6. The pedunculopontine nucleus has been implicated in a variety of functions, including mediation of rapid eye movement sleep and in extrapyramidal motor function, although the role of cholinergic and non-cholinergic neurons is unclear. Quantitative neuroanatomical techniques were used to map the distribution of cholinergic neurons in the mesopontine nuclei of the adult human brain. In addition, the number and distribution of comparably sized non-cholinergic neurons at selected anatomical levels were compared. An antibody raised against human choline acetyltransferase was used to stain immunohistochemically the mesopontine neurons in six brains, ranging in age from 28 to 60 years. The rostrocaudal length of the Cb5/Ch6 cell complex was approximately 10 mm. The estimated total number of cells was similar for all brains, and varied by less than 7%. The estimated average number of cholinergic cells in the combined pedunculopontine and laterodorsal tegmental nuclei was approximately 20,000, with 30% of the cells in the pedunculopontine nucleus pars compacta, 57% in the pedunculopontine nucleus pars dissipata and 13% in the laterodorsal tegmental nucleus. There was no correlation between cell number and age. Within areas of mesopontine tegmentum occupied by the Ch5 cholinergic neurons, there were often more noncholinergic neurons than comparably sized cholinergic neurons. The present study provides detailed maps of the distribution and number of mesopontine cholinergic neurons in the normal human brain. Many non-cholinergic neurons are intermixed with the cholinergic pedunculopontine neurons. One region of the pedunculopontine nucleus pars dissipata containing few cholinergic neurons, located adjacent to the ventral border of the pedunculopontine nucleus pars compacta, may correspond to the midbrain-extrapyramidal area as defined previously in rodent and in non-human primate. These data will be useful for quantitative neuropathological studies concerning the role of both cholinergic and non-cholinergic mesopontine neurons in diseases proposed to affect these neurons, including Parkinson's disease, schizophrenia and progressive supranuclear palsy.

Nucleus subputaminalis (Ayala): the still disregarded magnocellular component of the basal forebrain may be human specific and connected with the cortical speech area

The small magnocellular group located within the rostrolateral extension of the basal forebrain was named and described as the nucleus subputaminalis in the human and chimpanzee brain by Ayala. Analysis of cytoarchitectonic and cytochemical characteristics of this cell group has been largely disregarded in both classical and more current studies. We examined the nucleus subputaminalis in 33 neurologically normal subjects (ranging from 15 weeks of gestation to 71 years-of-age) by using Nissl staining, choline acetyltransferase immunohistochemistry, acetyl cholinesterase histochemistry and nerve growth factor receptor immunocytochemistry. In addition, we applied reduced nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry and calbindin-D28k immunocytochemistry in three neurologically normal subjects. At the most rostrolateral levels we describe the previously poorly characterized component of the lateral (periputaminal) subdivision of the subputaminal nucleus, which may be human specific since it is not described in non-human primates. Moreover, we find the human subputaminal nucleus best developed at the anterointermediate level, which is the part of the basal nucleus that is usually much smaller or missing in monkeys. The location of subputaminal cholinergic neurons within the frontal lobe, the ascension of their fibers through the external capsule towards the inferior frontal gyrus, the larger size of the subputaminal nucleus on the left side at the most rostral and anterointermediate levels and the most protracted development among all magnocellular aggregations within the basal forebrain strongly suggest that they may be connected with the cortical speech area. These findings give rise to many hypotheses about the possible role of the subputaminal nucleus in various neurodegenerative, neurological and psychiatric disorders, particularly Alzheimer's disease and primary progressive aphasia. Therefore, future studies on the basal forebrain should more carefully investigate this part of the basal nucleus.

GABAergic and cholinergic basal forebrain and preoptic-anterior hypothalamic projections to the mediodorsal nucleus of the thalamus in the cat

The present study examined projections of GABAergic and cholinergic neurons from the basal forebrain and preoptic-anterior hypothalamus to the "intermediate" part of the mediodorsal nucleus of the thalamus. Retrograde transport from this region of the mediodorsal nucleus was investigated using horseradish peroxidase-conjugated wheatgerm agglutinin in combination with peroxidase-antiperoxidase immunohistochemical staining for glutamic acid decarboxylase and choline acetyltransferase. A relatively large number of retrogradely-labelled glutamic acid decarboxylase-positive neurons are located in the basal forebrain, amounting to more than 7% of the total population of glutamic acid decarboxylase-positive cells in this region. Moreover, retrogradely-labelled choline acetyltransferase-positive cells are interspersed among glutamic acid decarboxylase-positive neurons, accounting for about 6% of the total choline acetyltransferase-positive cell population in the basal forebrain. The glutamic acid decarboxylase-positive and choline acetyltransferase-positive retrogradely-labelled neurons are distributed throughout several regions of the basal forebrain, including the medial septum, the diagonal band of Broca, the magnocellular preoptic nucleus, the substantia innominata pars anterior, the substantia innominata pars posterior, and the globus pallidus where only a few retrogradely-labelled neurons were seen. The choline acetyltransferase-positive mediodorsal-projecting neurons are morphologically different from the choline acetyltransferase-positive neurons in the basal forebrain, suggesting that those projecting to the mediodorsal nucleus are a small proportion of the cholinergic neuronal population in the basal forebrain. In the preoptic-anterior hypothalamus, many retrogradely-labelled glutamic acid decarboxylase-positive cells were found, amounting to more than 7% of the total population of glutamic acid decarboxylase-positive cells in this region. These retrogradely-labelled glutamic acid decarboxylase-positive neurons are distributed throughout the preoptic-anterior hypothalamus in a continuous line with those in the basal forebrain, including the lateral preoptic area, the medial preoptic area, the bed nucleus of the stria terminalis, and the anterior and dorsal hypothalamic areas. The highest percentage of mediodorsal-projecting GABAergic neurons is in the anterior lateral hypothalamus where more than 25% of the total population of glutamic acid decarboxylase-positive cells project to the mediodorsal nucleus of the thalamus. Overall, of the large population of retrogradely-labelled neurons in the basal forebrain and preoptic-anterior hypothalamus, a significant proportion are glutamic acid decarboxylase-positive neurons (> 60% in the basal forebrain and > 30% in the preoptic-anterior hypothalamus), while the choline acetyltransferase-positive neurons amount to a smaller percentage of the neurons projecting to the mediodorsal nucleus (< 13% in the basal forebrain and < 2% in the preoptic-anterior hypothalamus). These results provide anatomical evidence of direct GABAergic projections from the basal forebrain and preoptic-anterior hypothalamic regions to the "intermediate" part of the mediodorsal nucleus in the cat. This GABAergic projection field could be the direct pathway by which the basal forebrain directly modulates thalamic excitability and may also be involved in mechanisms modulating electroencephalographic synchronization and sleep through the "intermediate" mediodorsal nucleus.

Effects of damage to the basal forebrain on brain glucose utilization: a reevaluation using positron emission tomography in baboons with extensive unilateral excitotoxic lesion

Neuronal loss in the basal forebrain cholinergic structures and frontotemporal hypometabolism are two characteristics of Alzheimer's disease, but their interrelations still are unsettled. We previously reported that unilateral electrolytic lesions of the nucleus basalis of Meynert in baboons were associated with marked but transient cortical hypometabolism. The current study reevaluates this issue using improved methodology. Baboons with unilateral ibotenic acid lesion of all three basal forebrain cholinergic structures (IBO group) were compared with sham-operated animals. The CMRglc was measured with high-resolution coronal positron emission tomography scanning coregistered with magnetic resonance imaging, before surgery and serially between 4 and 72 days afterward. Severe histologic basal forebrain damage and a decrease of more than 50% in cortical choline acetyltransferase activity were found postmortem in the IBO group. Transient and nonspecific hypometabolism was found in the needle track area in both groups. Compared with the sham-operated group, only marginally significant decreases in ipsilateral-contralateral CMRglc ratios were observed in the IBO group, affecting only 1 of 14 neocortical areas investigated (the anterior temporal cortex) at a single postsurgical time (day 14), and the posterior hippocampal region at days 14 and 38. Furthermore, there was no consistently significant correlation between ipsilateral-contralateral CMRglc ratios and cortical choline acetyltransferase activity values in any of the four regions analyzed. These results suggest that cholinergic deafferentation play at best a marginal role in the brain hypometabolism observed in Alzheimer's disease.

Organization of choline acetyltransferase-containing structures in the cranial nerve motor nuclei and spinal cord of the monkey

Cholinergic structures in the cranial nerve motor nuclei and ventral and lateral horns of the spinal cord of the monkey, Macaca fuscata, were investigated immunohistochemically with a monoclonal antibody against monkey choline acetyltransferase (ChAT). ChAT-immunoreactive perikarya and dendrites were present in the oculomotor, trochlear, abducent, trigeminal motor, facial and hypoglossal nuclei, nucleus of Edinger-Westphal, nucleus ambiguus, dorsal nucleus of the vagus, lamina IX of the cervical, thoracic and lumbar spinal cords, and intermediolateral nucleus of the thoracic spinal cord. The neuropil of the trigeminal motor, facial and hypoglossal nuclei, nucleus ambiguus and lamina IX of the cervical, thoracic and lumbar spinal cords contained many ChAT-positive bouton-like structures and they were seemingly in contact with perikarya and dendrites of motoneurons, suggesting that motoneurons in these nuclei are cholinoceptive as well as cholinergic. The oculomotor, trochlear and abducent nuclei, nucleus of Edinger-Westphal, dorsal nucleus of the vagus and intermediolateral nucleus of the thoracic spinal cord contained a small number of ChAT-immunoreactive bouton-like structures, but they did not contact with perikarya and dendrites of ChAT-positive neurons. These observations suggest that the organization of the motor nuclei is complex, at least regarding the cholinoceptivity.

Preganglionic parasympathetic neurons projecting to the sphenopalatine ganglion contain nitric oxide synthase in the rabbit

We have investigated the possible presence of nitric oxide synthase (NOS) and choline acetyltransferase (ChAT) in brainstem preganglionic parasympathetic neurons projecting to the sphenopalatine ganglion in rabbits, using combined retrograde axonal tracing and immunohistochemistry. Retrogradely labeled neurons were observed in the ipsilateral rostral medulla and caudal pons, in a region laterodorsal to the facial motor nucleus. Double-labeling experiments demonstrated that 75 +/- 5% of retrogradely labeled neurons contained NOS immunoreactivity, while all of retrogradely labeled neurons contained ChAT immunoreactivity. These observations suggest that nitric oxide could influence cholinergic transmission from preganglionic endings in the sphenopalatine ganglion.

Distribution of choline acetyltransferase immunoreactivity in the brain of anuran (Rana perezi, Xenopus laevis) and urodele (Pleurodeles waltl) amphibians

Because our knowledge of cholinergic systems in the brains of amphibians is limited, the present study aimed to provide detailed information on the distribution of cholinergic cell bodies and fibers as revealed by immunohistochemistry with antibodies directed against the enzyme choline acetyltransferase (ChAT). To determine general and derived features of the cholinergic systems within the class of Amphibia, both anuran (Rana perezi, Xenopus laevis) and urodele (Pleurodeles waltl) amphibians were studied. Distinct groups of ChAT-immunoreactive cell bodies were observed in the basal telencephalon, hypothalamus, habenula, isthmic nucleus, isthmic reticular formation, cranial nerve motor nuclei, and spinal cord. Prominent plexuses of cholinergic fibers were found in the olfactory bulb, pallium, basal telencephalon, ventral thalamus, tectum, and nucleus interpeduncularis. Comparison of these results with those obtained in other vertebrates, including a segmental approach to correlate cell populations, reveals that the cholinergic systems in amphibians share many features with amniotes. Thus, cholinergic pedunculopontine and laterodorsal tegmental nuclei could be identified in the amphibian brain. The finding of weakly immunoreactive cells in the striatum of Rana, which is in contrast with the condition found in Xenopus, Pleurodeles, and other anamniotes studied so far, has revived the notion that basal ganglia organization is more preserved during evolution than previously thought.

Cellular basis of pontine ponto-geniculo-occipital wave generation and modulation

1. Pontogeniculooccipital (PGO) waves are recorded during rapid eye movement (REM) sleep from the pontine reticular formation. 2. PGO wave-like field potentials can also be recorded in many other parts of the brain in addition to the pontine reticular formation, but their distribution is different in different species. Species differences are due to variation in species-specific postsynaptic target sites of the pontine PGO generator. 3. The triggering neurons of the pontine PGO wave generator are located within the caudolateral peribrachial and the locus subceruleus areas. 4. The transferring neurons of the pontine PGO generator are located within the cholinergic neurons of the laterodorsal tegmentum and the pedunculopontine tegmentum. 5. The triggering and transferring neurons of the pontine PGO wave generator are modulated by aminergic, cholinergic, nitroxergic, GABA-ergic, and glycinergic cells of the brainstem. The PGO system is also modulated by suprachiasmatic, amygdaloid, vestibular, and brainstem auditory cell groups.

Mesopontine organization of cholinergic and catecholaminergic cell groups in the normal and narcoleptic dog

Canine narcolepsy is a unique experimental model of a human sleep disorder characterized by excessive daytime sleepiness and cataplexy. There is a consensus recognition of an imbalance between cholinergic and catecholaminergic systems in narcolepsy although the underlying mechanisms remain poorly understood. Possible substrates could be an abnormal organization, numbers and/or ratio of cholinergic to catecholaminergic cells in the brain of narcoleptic dogs. Therefore, we sought to characterize the corresponding neuronal populations in normal and narcoleptic dogs (Doberman Pinscher) by using choline acetyltransferase (ChAT), nicotinamide adenosine dinucleotide phosphate (NADPH)-diaphorase, tyrosine hydroxylase (TH), and dopamine beta-hydroxylase (DBH). Cholinergic cell groups were found in an area extending from the central to the gigantocellular tegmental field and the periventricular gray corresponding to the pedunculopontine tegmental nucleus (PPT), the laterodorsal tegmental nucleus (LDT), and the parabrachial nucleus. An almost perfect co-localization of ChAT and NADPH-diaphorase was also observed. Catecholaminergic cell groups detected included the ventral tegmental area, the substantia nigra, and the locus coeruleus nucleus (LC). The anatomical distribution of catecholaminergic neurons was unusual in the dog in two important aspects: i) TH- and/or DBH-immunoreactive neurons of the LC were found almost exclusively in the reticular formation and not within the periventricular gray, ii) very few, if any TH-positive neurons were found in the central gray and dorsal raphe. Quantitative analysis did not reveal any significant differences in the organization and the number of cells identified in the LDT, PPT, and LC of normal and narcoleptic dogs. Moreover, the cholinergic to catecholaminergic ratio was found identical in the two groups. In conclusion, the present results do not support the hypothesis that the neurochemical imbalance in narcolepsy could result from abnormal organization, numbers, or ratio of the corresponding neuronal populations.

Cholinergic and noncholinergic tegmental pedunculopontine projection neurons in rats revealed by intracellular labeling

Morphological features of rat pedunculopontine projection neurons were investigated in in vitro preparation by using intracellular labeling with biocytin combined with choline acetyltransferase (ChAT) immunohistochemistry. These neurons were classified into two types (Type I and II), based on their electrical membrane properties: Type I had low-threshold Ca2+ spikes, and Type II had A-current. All Type I neurons (n = 17) were ChAT immunonegative (ChAT-). Type II neurons were either ChAT immunopositive (ChAT+; n = 49) or ChAT- (n = 20). In terms of topography in the tegmental pedunculopontine nucleus (PPN), Type I neurons were dispersed throughout the extent of the nucleus, whereas Type II neurons tended to be located more in the rostral and middle sections. Both Type I and II neurons consisted of small (long axis < 20 microns), medium (20-35 microns), and large (> 35 microns) cells. The small cells were round or oval; medium cells were round, triangular, or fusiform; and the large cells were primarily fusiform in shape. In terms of the soma size, there was a difference in Type I (15-38 microns) and Type II (11-50 microns) neurons, but no significant difference was found between Type II ChAT+ and ChAT- cells. Both types of neurons had three to six primary dendrites, but the dendritic field was more prominent in Type II neurons. Most of the axons originated from one of the primary dendrites, which gave off axon collaterals, some of which projected out of the nucleus. The intrinsic collaterals were thin and branched partly within the dendritic field of the parent cell. The extrinsic collaterals were thicker and could be grouped into three categories: 1) collaterals arborizing in the substantia nigra; 2) collaterals ascending mainly toward the thalamus, pretectal, and tectal area; and 3) collaterals descending toward the mesencephalic and/or pontine reticular formation. It was noted that the collaterals of both ChAT+ and ChAT-neurons were traced into the substantia nigra. There was no significant difference in antidromic latencies between Type I (m = 1.47 msec) and Type II (m = 1.36 msec) neurons following electrical stimulation of the substantia nigra.

Distribution and neurochemical character of substance P receptor (SPR)-immunoreactive striatal neurons of the macaque monkey: accumulation of SP fibers and SPR neurons and dendrites in "striocapsules" encircling striosomes

The striatal distribution of the substance P receptor (SPR) protein was examined in relation to its ligand, the neuro-peptide SP, as well as to the neurochemical and compartmental composition of the neostriatum in rhesus monkeys (Macaca mulatta) in immunohistochemical experiments. About 2% of striatal neurons, displaying varicose, virtually spine-free dendrites characteristic of large and medium-sized aspiny interneurons, expressed SPR immunoreactivity. SPR/choline acetyltransferase, SPR/somatostatin, SPR/GABA, SPR/calbindin D28k, and SPR/parvalbumin double immunolabeling experiments demonstrated that SPR-positive cells are either cholinergic or somatostatinergic. Comparison of SP and SPR immunoreactivities in double-labeled and adjacent single-labeled sections revealed compartment-specific match and mismatch between the densities of the peptide and receptor. A matching high density of SP fibers and SPR cells and dendrites was only observed in the rim of the striosome compartments. To our knowledge, this is the first evidence for an anatomical border comprised of dendritic processes that separate striatal compartments. We have termed these zones "striocapsules," because they encircle and encapsulate striosomal cell islands. In the striatal matrix, an abundance of SPR-labeled profiles was complemented with light SP staining. By contrast, in the core of the striosomes, SPR labeling was sparse and SP staining intense. SP-positive axon-like puncta frequently contacted SPR-positive dendrites in all striatal compartments. The SP receptor/ligand match indicates a sharp increase in the efficacy of SP action in the striocapsules, and suggests that the influence of SP might be heightened in this striatal subcompartment.

Preganglionic parasympathetic salivatory neurons in the brainstem contain markers for nitric oxide synthesis in the rabbit

The present study investigated the possible presence of markers for nitric oxide synthesis in brainstem preganglionic parasympathetic neurons involved in control of the submandibular and sublingual salivary glands of rabbits and rats. Retrograde axonal tracing was performed with biotinylated dextran to identify preganglionic parasympathetic salivatory neurons and combined with NADPH diaphorase histochemistry or nitric oxide synthase immunohistochemistry. The results of the double-labelling experiments demonstrated that most of the retrogradely labelled preganglionic parasympathetic neurons in rabbits contained the markers for nitric oxide synthesis, whereas, in rats most retrogradely labelled neurons lacked the markers for nitric oxide synthesis. These observations suggest that nitric oxide could influence ganglionic transmission in parasympathetic pathways controlling salivary secretion in the rabbit, but not in the rat.

Ultrastructural identification of cholinergic neurons in the external cuneate nucleus of the gerbil: acetylcholinesterase histochemistry and choline acetyltransferase immunocytochemistry

Using acetylcholinesterase histochemical and choline acetyltransferase immunocytochemical localization methods, this study has provided conclusive evidence for the existence of cholinergic neurons in the external cuneate nucleus of gerbils. By light microscopy, both acetylcholinesterase and choline acetyltransferase labelling was confined to the rostral portion of the external cuneate nucleus. Ultrastructurally, acetylcholinesterase reaction products were found in the nuclear envelope, cisternae of rough endoplasmic reticulum and Golgi saccules of some somata and large dendrites as well as in the membranes of small dendrites, myelinated axons and axon terminals. These neuronal elements were also stained for choline acetyltransferase; immunoreactivity was associated with nuclear pores, nuclear envelope, perikaryal membrane and all the membranous structures within the cytoplasm. Of the total choline acetyltransferase-labelled neuronal profiles analysed, 79% were myelinated axons, 15% dendrites, 4% somata and 2% axon terminals. The immunostained axon terminals consisted of two types containing either round (Rd type; 62.5%) or pleomorphic (Pd type; 37.5%) vesicles. Both were associated directly with choline acetyltransferase-positive dendrites. In contrast to the paucity of choline acetyltransferase-labelled axon terminals, numerous choline acetyltransferase-positive myelinated axons were present. It may thus be hypothesized that most, if not all, of the external cuneate nucleus cholinergic neurons are projection cells; such cells may give rise to axonal collaterals which synapse onto their own dendrites for possible feedback control. Choline acetyltransferase-positive dendrites were contacted by numerous unlabelled presynaptic boutons, 60% of which contained round or spherical synaptic vesicles (Rd boutons) and 40% flattened vesicles (Fd boutons), suggesting that these neurons are under strong inhibitory control. The preferential concentration of cholinergic components in the rostral external cuneate nucleus may be significant in the light of the highly organized somatotopy in the external cuneate nucleus and its extensive efferent projections to medullary autonomic-related nuclei. Our results suggest that the cholinergic neurons may be involved in somatoautonomic integration.