The origins of cholinergic and other subcortical afferents to the thalamus in the rat

The role of noradrenergic locus coeruleus neurons and neighboring cholinergic neurons of the pontomesencephalic tegmentum in sleep-wake states

Despite early suppositions that the noradrenergic (NA) locus coeruleus (LC) neurons play a critical role in the generation and tonic maintenance of wakefulness and paradoxical sleep, further studies indicated that these cells play a nonessential modulatory role in the regulation of these states. Thus, based upon evidence from pharmacological, lesion and single-unit recording studies, it now appears that NA neurons may be important for enhanced periods of attention or stress during wakefulness, though they are not necessary for the tonic maintenance of cortical activation or behavioral arousal during the state. From similar examinations, it has been found that the cessation of activity of NA LC neurons may normally be important in permitting the occurrence of the state of paradoxical sleep. Neighboring cholinergic neurons of the pontomesencephalic tegmentum may also be active during waking and play a role in facilitating thalamocortical activity and transmission, like NA neurons during that state. However, unlike the NA neurons, the cholinergic neurons play an active and essential role in the generation of the state of paradoxical sleep. Generation of the state of paradoxical sleep may depend upon the simultaneous activation of cholinergic neurons and cessation of NA LC neurons, that could be brought about by the intermediary action of local GABA neurons.

Paradoxical sleep and its chemical/structural substrates in the brain

As originally named for the ostensibly contradictory appearance of rapid eye movements and low voltage fast cortical activity during behavioral sleep, paradoxical sleep or rapid eye movement sleep, represents a distinct third state, in addition to waking and slow wave sleep, in mammals and birds. It is an internally generated state of intense tonic and phasic central activation that is contemporaneous with the inhibition of sensory input and motor output. In early studies, it was established that the state of paradoxical sleep was generated within the brainstem, and particularly within the pons. Pharmacological studies indicated an important role for acetylcholine as a neurotransmitter in the generation of this state. Local injections of cholinergic agonists into the pontine tegmentum triggered a state of paradoxical sleep marked by phasic ponto-geniculo-occipital spikes in association with cortical activation and neck muscle atonia. Following the immunohistochemical identification of choline acetyl transferase-containing neurons and their localization to the dorsolateral ponto-mesencephalic tegmentum, neurotoxic lesions of this major cholinergic cell group could be performed to assess its importance in paradoxical sleep. Destruction of the majority of the cholinergic cells, which are concentrated within the laterodorsal tegmental and pedunculopontine tegmental nuclei but extend also into the locus coeruleus and parabrachial nuclei in the cat, resulted in a loss or diminishment of the state of paradoxical sleep, ponto-geniculo-occipital spiking and neck muscle atonia. These deficits were correlated with the loss of choline acetyltransferase-immunoreactive neurons in the region, so as to corroborate results of pharmacological studies and single unit recording studies indicating an active role of these cholinergic cells in the generation of paradoxical sleep and its components. These cells provide a cholinergic innervation to the entire brainstem reticular formation that may be critical in the generation of the state which involves recruitment of massive populations of reticular neurons. Major ascending projections into the thalamus, including the lateral geniculate, may provide the means by which phasic (including ponto-geniculo-occipital spikes) and tonic activation is communicated in part to the cerebral cortex. Descending projections through the caudal dorsolateral pontine tegmentum and into the medial medullary reticular formation may be involved in the initiation of sensorimotor inhibition. Although it appears that the pontomesencephalic cholinergic neurons play an important, active role in the generation of paradoxical sleep, this role may be conditional upon the simultaneous inactivity of noradrenaline and serotonin neurons, evidence for which derives from both pharmacological and recording studies.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of the laterodorsal tegmental nucleus of the rat in experimental seizures

This study determined the effects of discrete microinjections of GABA agonists in the cholinergic nuclei of the pontomesencephalic tegmentum on spontaneous behavior and seizures induced by intravenous pentylenetetrazol, bicuculline or strychnine, in the rat. Injections of both the GABAA agonist piperidine-4-sulfonic acid and the GABAB agonist (-)baclofen in the laterodorsal tegmental nucleus produced a dose-dependent suppression of behavioral arousal and a reduction in the threshold of myoclonic and clonic but not tonic seizures induced by bicuculline and pentylenetetrazol. There were no significant effects on any type of strychnine seizure. Injections in the surrounding brainstem structures, including the pedunculopontine tegmental nucleus, had little effect on spontaneous behavior and did not significantly alter the thresholds of pentylenetetrazol-induced seizures. We have previously demonstrated that injections of GABA agonists in the central medial intralaminar nucleus of the thalamus have similar effects on behavior and seizures. Since the central medial nucleus receives important direct cholinergic projections from the laterodorsal tegmental nucleus, these two nuclei form a discrete ascending system which regulates seizure threshold.

Specificity in the projection patterns of accumbal core and shell in the rat

The efferent projections of the core and shell areas of the nucleus accumbens were studied with a combination of anterograde and retrograde tract-tracing methods, including Phaseolus vulgaris-leucoagglutinin, horseradish peroxidase and fluorescent tracers. Both the core and shell regions project to pallidal areas, i.e. ventral pallidum and entopeduncular nucleus, with a distinct topography in the sense that the core projection is located in the dorsolateral part of ventral pallidum, whereas the shell projects to the medial part of the subcommissural ventral pallidum. Both regions of the accumbens also project to mesencephalon with a bias for the core projection to innervate the substantia nigra-lateral mesencephalic tegmentum, and for the shell projection to reach primarily the ventral tegmental-paramedian tegmentum area. The most pronounced differences between core and shell projections exist in regard to the hypothalamus and extended amygdala. Whereas the core projects primarily to the entopeduncular nucleus including a part that invades the lateral hypothalamus, the shell, in addition, projects diffusely throughout the rostrocaudal extent of the lateral hypothalamus as well as to the extended amygdala, especially its sublenticular part. Both the core and shell of the accumbens have unmistakable striatal characteristics both histologically and in their connectional patterns. The shell, however, has additional features that are reminiscent of the recently described extended amygdala [Alheid G.F. and Heimer L. (1988) Neuroscience 27, 1-39; de Olmos J.S. et al. (1985) In The Rat Nervous System, pp. 223-334]; in fact, the possibility exists that the shell represents a transitional zone that seems to characterize most of the fringes of the striatal complex, where it adjoins the extended amygdala.

Electrophysiological properties of pedunculopontine neurons and their postsynaptic responses following stimulation of substantia nigra reticulata

Membrane properties and postsynaptic responses to stimulation of the substantia nigra reticulata (SNr) of the neurons in rat pedunculopontine nucleus (PPN) were studied in an in vitro parasagittal slice preparation using intracellular recording techniques. Based on electrical membrane properties, PPN neurons were classified into 3 types (types I, II and II). The unique feature of the type I neuron was the low threshold calcium spike while the type II neuron had various inward and outward rectifications. The type III neuron showed no such features as those observed in type I or II neurons. Some recorded neurons were intracellularly labeled with biocytin to study their morphology, and their transmitter phenotype was investigated by immunocytochemistry for choline acetyltransferase (ChAT). The type I and III neurons were found to be non-cholinergic, but 50% of the labeled type II neurons were immunopositive for ChAT. Morphological features of type II neurons were also different from type I or III neurons. The soma of the type II neuron was almost always more than twice as large as that of type I and III neurons. Inhibitory postsynaptic potentials (IPSPs) were induced in all 3 types of PPN neurons following stimulation of SNr. SNr-induced IPSPs were usually followed by a slow depolarizing potential from which rebound spikes were triggered. These rebound excitations were found only in type I and II neurons. These data indicate that heterogeneous groups of neurons exist in the PPN in terms of morphology, transmitter phenotypes and electrical membrane properties.

Light and electron microscopic evidence for a GABAergic projection from the caudal basal forebrain to the thalamic reticular nucleus in rats

Neurons in the magnocellular nucleus of the caudal basal forebrain extend an axonal projection which arborizes within the reticular nucleus of the thalamus. The present study addresses the ultrastructure and neurochemistry of this projection in rats. Many labeled terminals are apparent within the thalamic reticular nucleus following Phaseolus vulgaris leucoagglutinin injections into the caudal basal nucleus; anterogradely labeled axon terminals most commonly contact both somata and dendrites of reticular nucleus neurons with symmetric membrane specializations. Thus, the majority of the labeled terminals examined contrast with choline acetyltransferase positive terminals which have been previously identified as contacting dendrites and forming asymmetric synapses within this nucleus. Many of the neurons within the caudal basal nucleus which are retrogradely labeled following tracer injections into the thalamic reticular nucleus are gamma-aminobutyric acid (GABA) immunoreactive. In addition, following injections of Phaseolus vulgaris leucoagglutinin or fluoro-ruby into the caudal basal forebrain, some of the labeled axonal swellings and boutons within the thalamic reticular nucleus also contain glutamic acid decarboxylase. These results indicate that a significant component of the projection is GABAergic. These anatomical observations suggest that the projection from the caudal basal nucleus onto the thalamic reticular nucleus could facilitate the relay of information through the dorsal thalamus by inhibiting reticular nucleus neurons, and thus, in turn, disinhibiting thalamic relay neurons.

Generation patterns of immunocytochemically identified cholinergic neurons in rat brainstem

Combined [3H]thymidine autoradiographic and choline acetyltransferase (ChAT)-immunocytochemical techniques were used to answer questions concerning the generation of specific classes and subclasses of cholinergic neurons in rat brainstem. First, the generation of rostrally and caudally located neurons of the same class (i.e. somatic efferent oculomotor and hypoglossal nuclei, respectively) were compared. Results indicated that, although embryonic day 11 (E11) was the peak birthday for both nuclei, hypoglossal neurons were generated significantly earlier than oculomotor neurons, indicating a caudorostral generation gradient for brainstem somatic motor nuclei. Second, the generation patterns of 3 different subclasses of motor neurons at the same brainstem level were compared; namely those of the somatic efferent hypoglossal nucleus (XII), the general visceral efferent dorsal nucleus of the vagus (X), and the predominantly special visceral efferent nucleus ambiguus. All 3 subclasses of cholinergic cells had the same peak day (E11) and overall period of generation (E11-12). However, statistical analyses indicated a precocious generation of nucleus ambiguus, but no developmental differences between N, XII and N. X. It is suggested that nucleus ambiguus is formed earlier than N. XII and N. X, due to its more ventral location within a ventrodorsal neurogenetic gradient. Third, the generation patterns of different classes of large cholinergic neurons were examined. Specifically, the birthdays of cholinergic non-motor projection neurons of the pedunculopontine-laterodorsal tegmental nuclei (PPT-LDT) were contrasted to those of the cholinergic brainstem motor neurons. The peak birthdays of both rostrally and caudally located motor neurons were two days earlier than those of the PPT-LDT neurons. Thus, large cholinergic cells projecting to peripheral targets are born significantly earlier than those projecting within the CNS, even though the former are located more rostrally on the caudorostral neurogenetic gradient. This represents an apparent exception to the emerging rule that cholinergic neurons obey the general gradients of neurogenesis manifest in the regions of the central nervous system where they reside.

Ultrastructure of cholinergic synaptic terminals in the thalamic anteroventral, ventroposterior, and dorsal lateral geniculate nuclei of the rat

The principal relay nuclei of the thalamus receive their cholinergic innervation from two midbrain cholinergic groups: the pedunculopontine tegmental nucleus and the laterodorsal tegmental nucleus. The different thalamic nuclei exhibit populations of cholinergic axons which vary in density and morphology when examined at the light microscopic level. However, the ultrastructure of the cholinergic terminals in different thalamic nuclei has not been described. This study was undertaken to confirm that synaptic contacts are formed by cholinergic axons in several principal thalamic relay nuclei, to describe their ultrastructural morphology, and to identify the types of postsynaptic elements contacted by cholinergic synaptic terminals. The thalamic nuclei examined in this study are the dorsal lateral geniculate nucleus, ventroposteromedial nucleus, ventroposterolateral nucleus, and anteroventral nucleus. Our results confirm that cholinergic axons form synaptic terminals in these thalamic nuclei. Cholinergic synaptic terminals contact structures outside the characteristic synaptic glomeruli, are never postsynaptic, and have morphologies and postsynaptic targets which differ among the thalamic nuclei. In the ventroposterior nuclei, cholinergic terminals form asymmetric synaptic contacts onto larger dendrites in the extraglomerular neuropil. In the anteroventral nucleus, cholinergic terminals form both symmetric and asymmetric synaptic contacts onto dendrites and somata. Cholinergic terminals in the anteroventral nucleus are larger than those in other nuclei. In the dorsal lateral geniculate nucleus, cholinergic terminals contact both somata and dendrites in the extraglomerular neuropil, but the synaptic contacts in this nucleus are symmetric in morphology.

Afferent and efferent connections of the laterodorsal tegmental nucleus in the rat

The connections of the laterodorsal tegmental nucleus (LDTg) have been investigated using anterograde and retrograde lectin tracers with immunocytochemical detection. Inputs to LDTg were found from frontal cortex, diagonal band, preoptic areas, lateral hypothalamus, lateral mamillary nucleus, lateral habenula; the interpeduncular nucleus, ventral tegmental area, substantia nigra and retrorubral fields; the medial terminal nucleus, interstitial nucleus, supraoculomotor central grey, medial pretectum, nucleus of the posterior commissure, paramedian pontine reticular formation, paraabducens and paratrochlear region; the parabrachial nuclei and nucleus of the tractus solitarius. Terminal labelling from PHA-L injections of LDTg was found in infralimbic, cingulate and hippocampal cortex, lateral septum, septofimbrial and triangular nuclei, horizontal limb of diagonal band and preoptic areas; in the anterior, mediodorsal, reuniens, centrolateral, parafascicular, paraventricular and laterodorsal thalamic nuclei, rostral reticular thalamic nucleus, and zona incerta; the lateral habenula and the lateral hypothalamus. A number of brainstem structures apparently associated with visual functions were also innervated, mainly the superior colliculus, medial pretectum, medial terminal nucleus, paramedian pontine reticular formation, inferior olive, supraoculomotor, paraabducens and supragenual regions, prepositus hypoglossi and nucleus of the posterior commissure. Also innervated were substantia nigra compacta, ventral tegmental area, interfascicular nucleus, interpeduncular nucleus, dorsal and medial raphe, pedunculopontine tegmental region, parabrachial nuclei, and nucleus of the tractus solitarius. These findings suggest the LDTg to be a highly differentiated part of the ascending "reticular activating" system, concerned not only with specific cortical and thalamic regions, especially those associated with the limbic system, but also with the basal ganglia, and visual (particularly oculomotor) mechanisms. Additional links with the habenula-interpeduncular system are discussed in this context.

Secondary generalization of seizures from a cortical penicillin focus following stimulation of the basal forebrain

The basal forebrain has been implicated in the regulation of generalized motor convulsive activity particularly from amygdala kindling. The effect of electrical stimulation of the substantia innominata and ventral pallidal regions of the basal forebrain in rats with acute interictal penicillin foci in the frontal parietal neocortex was determined. Stimulation of this area resulted in generalized cortical EEG synchronization, an inconsistent effect on interictal spike frequency, and generalized seizures that were not prevented by atropine. The results support a role for these basal forebrain structures in the regulation of generalized seizures from a cortical focus mediated primarily through influences on thalamocortical pathways.

Brainstem genesis of reserpine-induced ponto-geniculo-occipital waves: an electrophysiological and morphological investigation

Several experimental results indicate that the peribrachial (PB) cholinergic area of the pedunculopontine nucleus is the final relay for the transfer of brainstem-generated pontogeniculo-occipital (PGO) waves to the thalamus. However, the mechanisms underlying the PGO-related activity of PB neurons remain unknown. In order to study these mechanisms, single unit recordings in the PB area were performed in reserpinized cats. Because PGO waves are closely related to rapid eye movements, our microelectrode explorations were also aimed to some structures of the preoculomotor network, namely, the superior colliculus (SC) and parts of the central tegmental field (FTC). We have found several classes of PGO-on cells in the PB area, most of them descharging 80 ms or less before the peak of PGO waves. These cell-classes comprised high-frequency bursting cells, slow-frequency bursting cells, and neurons discharging single spikes or doublets. Intracellular recordings showed that PGO-on single spikes arise from conventional excitatory postsynaptic potentials. Among PGO-related cells in structures outside the PB limits, it was found that most SC cells discharge during or after the PGO, whereas FTC cells increase their discharge rate several hundreds of ms before PGO waves, thus indicating that PGO waves are elaborated long before the activation of PB neurons. Massive retrograde labeling was found in FTC following horseradish peroxidase injections into the PB area. We suggest that long-lead FTC neurons provide an excitatory input to PGO-on PB neurons.

Cholinergic neurons of the feline pontomesencephalon. II. Ascending anatomical projections

Immunoreactivity for choline acetyltransferase (ChAT) was analyzed in unoperated cats and in cats in which stereotaxic lesions were made in the pedunculopontine and laterodorsal tegmental nuclei. The fine reaction product revealed moderate to dense ChAT-immunoreactive fiber plexuses throughout the telencephalon, diencephalon, and midbrain. A pontomesencephalic origin of cholinergic innervation to virtually every nucleus of the diencephalon, as well as to various midbrain and basal telencephalic sites was indicated in the cats with lesions, in which the optical density of ChAT-immunoreactivity was significantly decreased as compared to controls. Pontomesencephalic lesions produced no changes, however, in the density of ChAT staining in the cerebral cortex, basolateral amygdala, or caudate nucleus. In addition to ChAT-positive terminal fiber arborizations which were widely distributed, cholinergic fibers-of-passage were traced in the unoperated and operated feline brains. The general course of ChAT fibers cut in cross-section was followed in successive transverse levels, and although pathways originating from the pedunculopontine nucleus demonstrated orientations in every direction, many demonstrated a rostral course. A particularly dense aggregate of ascending ChAT-positive fibers was localized in the dorsolateral sector of the pedunculopontine area which could be followed at more rostral levels into the central tegmental fields and the compact part of the substantia nigra. From the central tegmental fields, numerous ChAT-immunopositive fibers cut in cross-section continued to course rostrally in the intralaminar, reticular and lateroposterior nuclei of the thalamus, and a distinct bundle of ChAT fibers coursing dorsolaterally was observed medial to the optic tract ascending to the lateral geniculate. ChAT fibers with dorsolateral orientations were additionally observed in the zona incerta, ventral anterior thalamus, and ansa lenticularis on route to the reticular thalamus, the globus pallidus, and the substantia innominata. Pathways consisting of fibers traced from ChAT-containing cells in the laterodorsal tegmental nucleus could be traced to medial structures such as the periaqueductal gray, ventral tegmental area and dorsal raphe. Medially placed ChAT fibers were additionally followed through the ventral tegmental area, the midline thalamus, and the hypothalamus, up to the medial and lateral septal nuclei. The trajectories of the ascending cholinergic pathways from the pontomesencephalon are discussed in relation to locally generated electrophysiological responses in the cat.

Immunohistochemical study of choline acetyltransferase-immunoreactive processes and cells innervating the pontomedullary reticular formation in the rat

The present study was undertaken to examine the cholinergic innervation of the brainstem reticular formation in an effort to understand the potential role of cholinergic neurons in processes of sensory-motor modulation and state control. The cholinergic cells and processes within the pontomedullary reticular formation were studied in the rat by application of peroxidase-antiperoxidase immunohistochemistry with silver intensification for choline-acetyltransferase (ChAT). ChAT-immunoreactive cells were located in the pontomesencephalic tegmentum within the laterodorsal and pedunculopontine tegmental (LDT and PPT) nuclei, where they numbered approximately 3,000 on each side and were scattered in the midline, medial, and lateral medullary reticular formation, where they numbered approximately 10,000 in total on each side. The cholinergic neurons within the reticular formation were commonly medium in size and gave rise to multiple dendrites that extended for considerable distances within the periventricular gray or the reticular formation, as is typical of other isodendritic reticular neurons. A prominent innervation of the entire pontomedullary reticular formation was evident by varicose ChAT-immunoreactive fibers that often surrounded large noncholinergic reticular neurons in a typical perisomatic pattern of termination, suggesting a potent influence of the cholinergic innervation on pontomedullary reticular neurons. The contribution of the pontomesencephalic cholinergic neurons to the innervation of the medial medullary and lateral pontine reticular formation was studied by retrograde transport of horseradish peroxidase conjugated wheat germ agglutinin (WGA-HRP) in combination with ChAT immunohistochemistry. A proportion of the cholinergic neurons within the laterodorsal tegmental nucleus (pars alpha) and the pedunculopontine tegmental nucleus were retrogradely labelled on the ipsilateral (10-15%) and contralateral (5-10%) sides from the medial medullary reticular formation, indicating a significant contribution to the cholinergic innervation of this region, which, however, also appeared to derive in part from intrinsic medullary cholinergic neurons. The major fiber system by which the medial medullary reticular formation was reached by the pontomesencephalic cholinergic neurons appeared to correspond to the lateral tegmentoreticular tract. Fibers passed from these cholinergic cells ventrally through the lateral pontine tegmentum, in the region of the subcoeruleus, where they also appeared to innervate by fibres en passage the noncholinergic neurons of the region. A significant proportion of the pontomesencephalic cholinergic neurons were retrogradely labelled from the lateral pontine tegmentum.(ABSTRACT TRUNCATED AT 400 WORDS)

Compartmental ordering of cholinergic innervation in the mediodorsal nucleus of the thalamus in human brain

The cholinergic innervation of the mediodorsal (MD) nucleus of the thalamus was visualized immunohistochemically in human brain postmortem, using an antibody against human choline acetyltransferase (ChAT). The ChAT staining of the MD nucleus was more intense than in the surrounding thalamic nuclei but weaker than that of the striatum. No ChAT-positive cell bodies were detected. The ChAT-positive neuropil was unevenly distributed, with patches of dense immunoreactivity contrasting with a weaker surrounding matrix. In adjoining sections stained for ChAT immunoreactivity and for acetylcholinesterase (AChE) activity, the zones enriched in ChAT-immunostained neuropil corresponded to AChE-rich regions. The three-dimensional reconstruction of the richest zone in AChE/ChAT activity evidenced a cylindrical organization throughout the rostrocaudal axis of the MD nucleus. Counts of ChAT-positive varicosities confirmed an inhomogeneous distribution; the density of varicosities was 30% higher in ChAT-rich regions than in surrounding matrix. These findings suggest that the activity of intrinsic neurons within the nucleus may be differentially regulated by cholinergic systems.

Histamine excites pedunculopontine neurones in guinea pig brainstem slices

Intracellular recordings were obtained from pedunculopontine tegmental nuclei neurones in guinea pig brainstem slices. These neurones were characterized by the presence of a slow regular firing (around 3 spikes/s), a broad action potential (more than 1 ms) and a transient rectification indicating the presence of an A current. Bath-application of histamine at 10(-4) or 10(-5) M induced a reversible increase in spontaneous firing. In presence of tetrodotoxin (1 microM), the effect of histamine was a reversible membrane depolarization. It was a direct effect as it persisted in presence of a low calcium/high magnesium solution. This excitatory action was presumably mediated by histamine H1 receptors as it could be blocked by the H1 receptor antagonist mepyramine but not by the H2 receptor antagonist cimetidine. A role in arousal is discussed.

Cholinergic synapses in the central nervous system: studies of the immunocytochemical localization of choline acetyltransferase

Cholinergic synapses can be identified in immunocytochemical preparations by the use of monoclonal antibodies and specific antisera to choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine (ACh) and a specific marker for cholinergic neurons. Electron microscopic studies demonstrate that the fibers and varicosities observed in light microscopic preparations of many brain regions are small-diameter unmyelinated axons and vesicle-containing boutons. The labeled boutons generally contain clear vesicles and one or more mitochondrial profiles. Many of these boutons form synaptic contacts, and the synapses are frequently of the symmetric type, displaying thin postsynaptic densities and relatively short contact zones. However, ChAT-labeled synapses with asymmetric junctions are also observed, and their frequency varies among different brain regions. Unlabeled dendritic shafts are the most common postsynaptic elements in virtually all regions examined although other neuronal elements, including dendritic spines and neuronal somata, also receive some cholinergic innervation. ChAT-labeled boutons form synaptic contacts with several different types of unlabeled neurons within the same brain region. Such findings are consistent with a generally diffuse pattern of cholinergic innervation in many parts of the central nervous system. Despite many similarities in the characteristics of ChAT-labeled synapses, there appears to be some heterogeneity in the cholinergic innervation within as well as among brain regions. Differences are observed in the sizes of ChAT-immunoreactive boutons, the types of synaptic contacts, and the predominant postsynaptic elements. Thus, the cholinergic system presents interesting challenges for future studies of the morphological organization and related function of cholinergic synapses.

Lower brainstem afferents to the cat posterior hypothalamus: a double-labeling study

Using a double-immunostaining technique with cholera toxin (CT) as a retrograde tracer, the authors examined the cells of origin and the histochemical nature of lower brainstem afferents to the cat posterior hypothalamus. The posterior hypothalamus, in particular the lateral hypothalamic area, receives substantial afferent projections from: substantia nigra, peripeduncular nucleus, ventral tegmental area, periaqueductal grey, mesencephalic reticular formation, peribrachial region including the locus coeruleus complex, rostral raphe nuclei and the rostral part of the nucleus magnus. In addition, a moderate number of retrogradely labeled neurons was found in: Edinger-Westphal nucleus, nucleus reticularis pontis oralis, nucleus reticularis magnocellularis, caudal lateral bulbar reticular formation around the nucleus ambiguus and lateral reticular nucleus and the nucleus of the solitary tract. The posterior hypothalamus receives: 1) dopaminergic inputs from A8, A9 and A10 cell groups; 2) noradrenergic inputs from A6 and A7 pontine, as well as A1 and A2 bulbar cell groups; 3) adrenergic inputs from C1 cell group in the caudal medulla; 4) serotoninergic inputs from the rostral raphe nuclei (B6, B7 and B8 cell groups); 5) cholinergic inputs from the peribrachial region of the dorsal pontine tegmentum as well as from the nucleus reticularis magnocellularis of the medulla; 6) peptidergic inputs such as methionine-enkephalin, substance P, corticotropin-releasing factor and galanin that originate mainly in the mesencephalic periaqueductal grey, the dorsal raphe nucleus and the peribrachial region of the dorsal pontine tegmentum.

Postnatal changes in the density and distribution of neurotensin-like immunoreactive fibers in the mediodorsal nucleus of the thalamus in the rat

A previous report (Inagaki et al., Brain Res. 260:143-146, '83) suggested that the peptide neurotensin is contained in neurons of the piriform cortex that project to the mediodorsal thalamic nucleus (MD) in young rats. To confirm this, we have studied the distribution of neurotensin-like immunoreactive (NTIR) fibers in MD during development, using three antisera directed at different parts of the neurotensin molecule (Emson et al., J. Neurochem. 38:992-999, '82). In adult rats, NTIR fibers in MD are sparse. They are located mostly at the medial edge of MD and in the adjacent midline thalamic nuclei, with a few poorly stained NTIR fibers in the central part of MD. In contrast, during the first postnatal week, both the medial and central portions of MD stain heavily for neurotensin. The density of NTIR fibers in MD then progressively decreases until the density typical of adult rats is reached, at about 5 weeks. Changes in the distribution of NTIR fibers in MD also occur. In 7-day-old rats, the patches of NTIR fibers in the medial and central parts of MD are contiguous, but by 10 days a sparsely immunoreactive zone forms between them. With maturation, this zone enlarges as the density of neurotensin staining decreases, until the medial contingent of NTIR fibers reaches its adult position at the medial edge of MD. From a comparison of the distribution of NTIR cells with that of cells that can be retrogradely labeled from MD or the midline thalamus, the probable source of the NTIR fibers to the central part of MD is in the deep layer of the piriform cortex, while the NTIR fibers to the medial edge of MD and the midline nuclei may arise from the preoptic region and the medial amygdala. In neonatal rats, neurons are found in the piriform cortex, the preoptic region, and the medial amygdala, which can be double-labeled both for neurotensin and with a retrograde tracer injected into MD and the midline thalamus. Projections of the preoptic region to the thalamus have a distribution similar to that of the medial population of NTIR fibers, whereas the distribution of piriform cortical afferents in central MD matches the central patch of NTIR fibers.

Substance P-containing neurons in the pontomesencephalic tegmentum of the human brain

We have employed immunohistochemical and computerized morphometric procedures to study substance P-containing neurons in the tegmentum of adult humans. An estimated 192,500 +/- 40,500 substance P-containing neurons were found in three main cytoarchitectural regions: the mesencephalic reticular formation, the central gray, and the pontine reticular formation. The morphology of the immunoreactive neurons varied according to the region in which they were found. On the basis of size alone two types of substance P-containing neurons, large and small, were readily distinguishable by eye and measurement. Within each of the three main regions it was possible to distinguish distinct subgroups using cell size, morphology and position. Large neurons were concentrated in the caudal midbrain (pedunculopontine tegmental nuclei), in the oral pontine reticular nucleus and in the lateral dorsal tegmental nucleus. In contrast, small neurons were concentrated in the rostral mesencephalic reticular formation (cuniform nuclei). Both small and large neurons were found in the midbrain and pontine raphe nuclei. In addition, small neurons were concentrated in discrete midline regions (the periaqueductal gray, the tegmental nuclei of the pontine central gray, and the interpeduncular nucleus). The findings suggest that the majority of neurons in the brainstem tegmental nuclei previously identified as cholinergic also contain substance P in humans.

Neuronal localization of the nerve growth factor precursor-like immunoreactivity in the rat brain

The distribution of the nerve growth factor precursor(proNGF)-like immunoreactivity was examined in the adult rat brain with affinity-purified antisera directed against synthetic peptides that reproduce sequences of the precursor protein. Immunoreactivity was localized in defined areas of the neocortex, hippocampal formation, thalamus/hypothalamus, striatum, olfactory bulb, pons and spinal cord, which are regions previously reported to contain NGF mRNA. Interestingly, immunoreactivity was also observed in the septum and diagonal band of Broca known to contain very low NGF mRNA levels. Using immunohistochemical methods combined with the retrograde transport of a protein gold complex we demonstrate that proNGF-like immunoreactivity is localized within neuronal cell bodies, in the cortex, hippocampus and septum. These results suggest that the immunological approach may not only identify NGF-synthesizing cells, but also cells which may accumulate proNGF or some cleavage products by an uptake mechanism.

Projections to the rostral reticular thalamic nucleus in the rat

Afferent pathways to the rostral reticular thalamic nucleus (Rt) in the rat were studied using anterograde and retrograde lectin tracing techniques, with sensitive immunocytochemical methods. The analysis was carried out to further investigate previously described subregions of the reticular thalamic nucleus, which are related to subdivisions of the dorsal thalamus, in the paraventricular and midline nuclei and three segments of the mediodorsal thalamic nucleus. Cortical inputs to the rostral reticular nucleus were found from lamina VI of cingulate, orbital and infralimbic cortex. These projected with a clear topography to lateral, intermediate and medial reticular nucleus respectively. Thalamic inputs were found from lateral and central segments of the mediodorsal nucleus to the lateral and intermediate rostral reticular nucleus respectively and heavy paraventricular thalamic inputs were found to the medial reticular nucleus. In the basal forebrain, afferents were found from the vertical and horizontal limbs of the diagonal band, substantia innominata, ventral pallidum and medial globus pallidus. Brainstem projections were identified from ventrolateral periaqueductal grey and adjacent sites in the mesencephalic reticular formation, laterodorsal tegmental nucleus, pedunculopontine nucleus, medial pretectum and ventral tegmental area. The results suggest a general similarity in the organisation of some brainstem Rt afferents in rat and cat, but also show previously unsuspected inputs. Furthermore, there appear to be at least two functional subdivisions of rostral Rt which is reflected by their connections with cortex and thalamus. The studies also extend recent findings that the ventral striatum, via inputs from the paraventricular thalamic nucleus, is included in the circuitry of the rostral Rt, providing further evidence that basal ganglia may function in concert with Rt. Evidence is also outlined with regard to the possibility that rostral Rt plays a significant role in visuomotor functions.

Nicotine conditions place preferences after intracerebral administration in rats

A single-trial place conditioning procedure, one treatment and one non-treatment during two daily conditioning sessions followed by a single test session on the 3rd day, was used to examine the place conditioning effects of intracerebrally administered nicotine. In the first series of experiments, Sprague-Dawley male rats were implanted unilaterally with guide cannulas aimed at the lateral ventricle. After 1 week, rats received either "treatment" (nicotine in 2 microliters phosphate buffer or 2 microliters of buffer alone) or "no treatment" (no injections) before being placed in the black or white compartment of a three-compartment place-conditioning apparatus for 20 min. The next day the rats received the opposite treatment before being conditioned in the opposite compartment. On day 3, animals had free access to the entire apparatus for 15 min and the time spent in each compartment was recorded automatically. Even though the rats exhibited a baseline bias for the black compartment, intracerebroventricular nicotine induced positive place preferences relative to buffer control, i.e. if treatments were paired with the black compartment, nicotine enhanced the preference for the black compartment, and if the treatments were paired with the white compartment, nicotine induced a preference for the white compartment. In addition, the nicotine-induced preference response was antagonized by the co-intraventricular administration of mecamylamine. In a second series of experiments, animals were implanted unilaterally with guide cannulas aimed at the pendunculopontine tegmental nucleus of the mesopontine tegmentum. Nicotine microinjection, 1.2-18.5 nmol in 0.5 microliter buffer, induced a dose-dependent positive place preference response.(ABSTRACT TRUNCATED AT 250 WORDS)

Single cholinergic mesopontine tegmental neurons project to both the pontine reticular formation and the thalamus in the rat

Microinjections of the cholinergic agonist carbachol into a caudal part of the pontine reticular formation of the rat induce a rapid eye movement sleep-like state. This carbachol-sensitive region of the pontine reticular formation is innervated by cholinergic neurons in the pedunculopontine and laterodorsol tegmental nuclei. The same population of cholinergic neurons also project heavily to the thalamus, where there is good evidence that acetylcholine facilitates sensory transmission and blocks rhythmic thalamocortical activity. The present study was undertaken to examine the degree to which single cholinergic neurons in the mesopontine tegmentum project to both the carbachol-sensitive region of the pontine reticular formation and the thalamus, by combining double fluorescent retrograde tracing and immunofluorescence with a monoclonal antibody to choline acetyltransferase in the rat. The results indicated that a subpopulation (5-21% ipsilaterally) of cholinergic neurons in the mesopontine tegmentum projects to both the thalamus and the carbachol-sensitive site of the pontine reticular formation, and these neurons represented the majority (45-88%) of cholinergic neurons projecting to the pontine reticular formation site. The percentage of cholinergic neurons with dual projections was higher in the pedunculopontine tegmental nucleus (6-27%) than in the laterodorsal tegmental nucleus (4-11%). In addition, mixed with cholinergic neurons in the mesopontine tegmentum, there was a small population of dually projecting neurons that did not appear to be cholinergic. Mesopontine cholinergic neurons with dual projections may simultaneously modulate neuronal activity in the pontine reticular formation and the thalamus, and thereby have the potential of concurrently regulating different aspects of rapid eye movement sleep.

Distribution of nerve growth factor receptor-like immunoreactivity in the adult rat central nervous system. Effect of colchicine and correlation with the cholinergic system--I. Forebrain

Nerve growth factor receptor, as recognized by the monoclonal antibody 192-IgG, was localized to multiple regions of the adult rat forebrain. Immunoreactive cell bodies and fibers were seen in both sensory and motor regions which are known to contain cholinergic and non-cholinergic neurons. Specifically, nerve growth factor receptor immunoreactivity was present in cells lining the olfactory ventricle, rostral portion of the lateral ventricle, in basal forebrain nuclei, caudate putamen, globus pallidus, zona incerta and hypothalamus. Immunoreactive cells which were situated subpially along the olfactory ventricle and anterior portions of the lateral ventricle, and in the arcuate nucleus resembled neuroglia but could not definitively identified at the light microscopic level. Animals pretreated with intracerebroventricular colchicine displayed significantly increased nerve growth factor receptor immunoreactivity in all previously positive neurons and particularly in the medial preoptic area and ventral premammillary nucleus of the hypothalamus. In such animals, receptor immunoreactivity also appeared in previously non-immunoreactive cells of the hippocampal CA3 region and polymorph layer of the dentate gyrus as well as in the mitral cell layer of the olfactory bulb. Nerve growth factor receptor-immunoreactive fibers and varicosities were seen in the olfactory bulb, piriform cortex, neocortex, amygdala, hippocampus, thalamus, olivary pretectal nucleus and hypothalamus. In most regions, such fiber-like immunoreactive structures likely represented axon terminals, although in some areas, neuroglial or extracellular localizations could not be excluded. In this context, diffuse, non-fibrillar receptor immunoreactivity occurred in the lateral habenular nucleus and medial terminal nucleus of the accessory optic tract. Furthermore, intense nerve growth factor receptor immunoreactivity occurred along certain regions of the pial surface on the ventral surface of the brain. The distribution of nerve growth factor receptor-immunoreactive cell bodies and fibers in multiple sensory and motor nuclei suggests wide-spread influences of nerve growth factor throughout the adult rat forebrain. There is a high degree of overlap with regions containing choline acetyltransferase immunoreactivity. However, significant disparities exist suggesting that certain nerve growth factor receptor-containing non-cholinergic neurons of the rat forebrain may also be affected by nerve growth factor.

Basal forebrain and mesopontine tegmental projections to the reticular thalamic nucleus: an axonal collateralization and immunohistochemical study in the rat

Using a double fluorescence retrograde labeling procedure, the present study sought to determine the degree to which basal forebrain and mesopontine tegmental neurons have axons that innervate both the reticular thalamic nucleus and the cerebral cortex. Immunofluorescence for choline acetyltransferase, somatostatin, and the calcium-binding protein parvalbumin was also performed to elucidate the neurochemical identity of basal forebrain and mesopontine tegmental inputs to the reticular thalamic nucleus. A significant portion (10-15%) of neurons in the basal forebrain and mesopontine tegmentum that were retrogradely labeled from the reticular thalamic nucleus were also found to be retrogradely labeled from the cortex. Many of these neurons stained positively for choline acetyltransferase. Of the basal forebrain neurons retrogradely labeled from the reticular thalamic nucleus, approximately 20% were found to be immunoreactive to choline acetyltransferase, whereas none was stained for somatostatin. A larger portion (up to 50%) of the basal forebrain neurons that were retrogradely labeled from the reticular thalamic nucleus were parvalbumin-immunoreactive, and some of these were also retrogradely labeled from the cortex. These results suggest that a subpopulation of cholinergic and non-cholinergic neurons in the basal forebrain and the mesopontine tegmentum may influence simultaneously the activity of neurons in the reticular thalamic nucleus and the cerebral cortex.

Cholinergic systems in the rat brain: IV. Descending projections of the pontomesencephalic tegmentum

Descending projections from cholinergic neurons in the pedunculopontine and laterodorsal tegmental nuclei, collectively referred to as the pontomesencephalotegmental (PMT) cholinergic complex, were studied by use of the fluorescent retrograde tracers fluorogold, true blue, or Evans Blue in combination with choline acetyltransferase (ChAT) immunohistochemistry of acetylcholinesterase (AChE) pharmacohistochemistry. Pedunculopontine somata positive for ChAT or staining intensely for AChE were retrogradely labeled with fluorescent tracers following infusions into the motor nuclei of cranial nerves 5, 7, and 12. ChAT-positive cells in both the pedunculopontine and laterodorsal tegmental nuclei demonstrated projections to the vestibular nuclei, the spinal nucleus of the 5th cranial nerve, deep cerebellar nuclei, pontine nuclei, locus ceruleus, raphe magnus nucleus, dorsal raphe nucleus, median raphe nucleus, the medullary reticular nuclei, and the oral and caudal pontine reticular nuclei. Fluorescent tracers used in combination with AChE pharmacohistochemistry corroborated these projections and, in addition, provided evidence for cholinergic pontomesencephalic projections to the lateral reticular nucleus and inferior olive. The majority of retrogradely labeled neurons demonstrating ChAT-like immunoreactivity were found ipsilateral to the injection site, but, in all cases, tracer-containing cholinergic cells contralateral to the infused side of the brain were detected also. More retrogradely labeled cells containing ChAT were observed in the pedunculopontine tegmental than in the laterodorsal tegmental nucleus following tracer injections at all sites with the exceptions of the locus ceruleus and dorsal raphe nucleus where the converse profile was observed. None of the pedunculopontine or laterodorsal tegmental cells immunopositive for ChAT or stained intensely for AChE contained retrogradely transported tracers following dye infusions into the cerebellar cortex or cervical spinal cord. Triple-label experiments using two tracers infused into different sites in the same animal revealed that individual ChAT-immunoreactive cells in the PMT cholinergic complex projected to more than one hindbrain site in some cases and had ascending projections as well. Certain ChAT-positive somata in the pedunculopontine and laterodorsal tegmental nuclei were found in close association with several fiber tracts, including the superior cerebellar peduncle, lateral lemniscus, dorsal tegmental tract, and medial longitudinal fasciculus.

The neuropeptide, Org 5878 (desenkephalin-gamma-endorphin, DE gamma E), affects local cerebral glucose utilization in freely moving rats

The effect of the antipsychotic peptide, Org 5878 (desenkephalin-gamma-endorphin, beta-endorphin-(6-17), on local cerebral glucose utilization was studied in freely moving male Wistar rats. Org 5878 (20 micrograms/kg, i.v.) or saline were given acutely and local cerebral glucose utilization was measured in 116 brain structures. Glucose uptake was not altered by Org 5878 in most brain areas, including areas of the nigrostriatal system, the cortex and the thalamus. However, significant reductions in glucose uptake were observed in the ventral tegmental area, the diagonal band complex, the hippocampus, the amygdala, the interpeduncular nucleus, the reticular nucleus of the thalamus and the cerebellum. These results indicate that the nigrostriatal and cortico-thalamic systems remain unaffected but the activity of the mesolimbic ventral tegmental area and of major target areas of cholinergic basal forebrain structures is selectively reduced following Org 5878 administration. It is concluded that the effect of Org 5878 on local cerebral glucose utilization is distinct from and more selective than that of antipsychotics currently used in the clinic.

Demonstration of muscarinic acetylcholine receptor-like immunoreactivity in the rat forebrain and upper brainstem

The distribution of muscarinic acetylcholine receptor protein (mAChR) in the rat forebrain and upper brainstem was described by using a monoclonal antibody (M35) raised against mAChR purified from bovine forebrain homogenates. A method is investigated for light microscopic (LM) and electronmicroscopic (EM) immunocytochemical visualization of reactivity to mAChR-proteins. Putative cholinoceptive neurons including their dendrites were found immunoreactive in the cortical mantle, hippocampus, basal ganglia, amygdala, thalamus and several midbrain regions. In the neocortex, immunoprecipitate with M35 was mainly present in layer 5 pyramidal cells, some layer 3 pyramidal neurons and layer 2 stellate cells, all including their characteristic dendritic profiles of both basal and apical dendrites. In the hippocampus, a variety of pyramidal, granular and non-pyramidal celltypes were stained in various hippocampal cell layers, in the dentate hilus and in stratum oriens of cornu ammonis. Moreover, positively reacting cells occurred in central and lateral amygdala, all parts of the basal ganglia and ventral pallidum. The thalamus was very richly provided with labeled neurons in several nuclei but notably numerous in the ventrolateral, anteroventral and geniculate nuclei. In cortex and hippocampus also some staining of astrocytes occurred. Electron microscopic study of the intracellular distribution of M35 immunoreactivity in all cases showed dense precipitates in the soma cytoplasm in close association with the golgi apparatus, but conspicuous absence near the endoplasmic reticulum. Immunoprecipitate can be followed within the dendritic tree along the microtubular transport system, up to proximal and distal postsynaptic membrane positions, apposing non labeled presynaptic endings. Muscarinic receptor subtype recognition by M35 will be discussed by comparing M35 distribution with cholinergic innervation patterns, muscarinic receptor ligand binding studies and localization of muscarinic receptor subtype mRNAs.

Degeneration of neurons in the thalamic reticular nucleus following transient ischemia due to raised intracranial pressure: excitotoxic degeneration mediated via non-NMDA receptors?

Transient global ischemia was produced in rats by cisternal fluid infusion, producing a negative cerebral perfusion pressure by elevating the intracranial pressure (ICP) 25-50 mm Hg above mean arterial pressure (MAP). Animals were allowed to survive for 2-7 days following a transient ischemic episode of 5-30 min. The brains were examined for signs of ischemic degeneration in Nissl-stained sections and adjacent sections reacted with antisera against glial fibrillary acidic protein (GFAP) or aspartate aminotransferase (AAT). Neurons in the thalamic reticular nucleus (RT), a pure population of gamma-aminobutyric acid (GABA)ergic neurons which project their axons to thalamic relay nuclei, were found to have the lowest threshold for degeneration in this model, consistently undergoing degeneration under conditions which completely spared the hippocampal CA1 from degeneration. Whereas it took up to 30 min of complete ischemia to produce degeneration of CA1 neurons when ICP was raised using room temperature infusion fluids, 15 min of ischemia under these conditions was sufficient to produce extensive degeneration of neurons in the entire ventral 3/4 of the RT. Prolonged (greater than 25 min) episodes of partial ischemia (ICP less than or equal to MAP) were also sufficient to produce massive degeneration of RT neurons. The lesion in the RT was most clearly evident in sections reacted with antisera to GFAP, labeling intensely reactive protoplasmic astrocytes within the regions of the RT where neuronal degeneration had occurred. Neuronal loss and accompanying proliferation of microglial cells were evident in Nissl-stained sections but the extent of the neuronal loss was most clearly obvious in sections reacted with an antisera to AAT, an enzyme present in detectable quantities in GABAergic neurons. Pretreatment with the non-competitive NMDA antagonist MK-801 at doses sufficient to completely prevent massive degeneration of the hippocampal CA1 failed to prevent the degeneration of RT neurons, suggesting that if RT degeneration involves an excitotoxic process it acts through non-NMDA receptors.

Cholinergic and monoaminergic innervation of the cat's thalamus: comparison of the lateral geniculate nucleus with other principal sensory nuclei

The cholinergic and monoaminergic innervation of the lateral geniculate nucleus (GL) and other thalamic nuclei in the cat was examined by using immunocytochemical and tract-tracing techniques. Cholinergic fibers, identified with an antibody to choline acetyltransferase (ChAT), are present in all layers of the GL. They are fine in caliber and exhibit numerous swellings along their lengths. The A layers, the magnocellular C layer, and the medial interlaminar nucleus are rich in cholinergic fibers that give rise to prominent clusters of boutons, while the parvicellular C layers contain fewer fibers that are more uniformly distributed. The interlaminar zones are largely devoid of ChAT-immunoreactive fibers. Double-label experiments show that cholinergic projections to the GL originate from two sources, the pedunculopontine reticular formation (PPT) and the parabigeminal nucleus (Pbg). The PPT contributes cholinergic fibers to all layers, while Pbg projections are limited to the parvicellular C layers. The lateral geniculate nucleus has a much greater density of cholinergic fibers than the other principal sensory nuclei: the density of fibers in the A layers is more than three times greater than that in the ventral posterior nucleus (VP) or the ventral division of the medial geniculate nucleus (GMv). In contrast, serotonin (5-HT)-immunoreactive fibers are distributed with equal density across the principal thalamic nuclei, while tyrosine hydroxylase (TH)-immunoreactive fibers (presumed to contain norepinephrine) are noticeably less dense in the GL than in the others. Monoaminergic fibers also differ from cholinergic fibers in their laminar distribution within the GL: both TH- and 5HT-immunoreactive fibers are distributed evenly across the layers and interlaminar zones and are slightly more abundant in the parvicellular C layers than in the other layers. Other thalamic nuclei rich in cholinergic fibers include the pulvinar nucleus, the ventral lateral geniculate nucleus, the intermediate nucleus of the lateral group, the lateral medial and suprageniculate nuclei (Graybiel and Berson: Neuroscience 5:1175-1238, '80), and the paracentral and central-lateral components of the intralaminar nuclei. This pattern matches the distribution of projections from the PPT and is similar, but not identical, to the pattern of acetylcholinesterase staining. The fact that most of the nuclei rich in cholinergic fibers have been implicated in visual sensory or visual motor functions suggests that cholinergic projections from the reticular formation play an especially important role in visually guided behavior.

Unitary characteristics of presumptive cholinergic tegmental neurons during the sleep-waking cycle in freely moving cats

A total of 260 neurons were recorded in the rostral pontine tegmentum of freely moving cats during the sleep-waking cycle. Of these, 207 neurons (80%) were located in the dorsal pontine tegmentum containing monoaminergic and choline acetyltransferase (ChAT)-immunoreactive, or cholinergic neurons. In addition to presumably monoaminergic PS-off cells (n = 51) showing a cessation of discharge during paradoxical sleep (PS) and presumably cholinergic PGO-on cells (n = 40) exhibiting a burst of discharge just prior to and during ponto-geniculo-occipital (PGO) waves, we observed tonic (n = 108) and phasic (n = 61) neurons exhibiting, respectively, tonic and phasic patterns of discharge during wakefulness and/or paradoxical sleep. Of 87 tonic cells histologically localized in the dorsal pontine tegmentum rich in cholinergic neurons, 46 cells (53%) were identified as giving rise to ascending projections either to the intralaminar thalamic complex (n = 26) or to the ventrolateral posterior hypothalamus (n = 13) or to both (n = 9). Two types of tonic neurons were distinguished: 1) tonic type I neurons (n = 28), showing a tonic pattern and high rates of discharge during both waking and paradoxical sleep as compared with slow wave sleep; and 2) tonic type II neurons (n = 20), exhibiting a tonic pattern of discharge highly specific to the periods of paradoxical sleep. Tonic type I neurons were further divided into two subclasses on the basis of discharge rates during waking: a) rapid (Type I-R; n = 17); and b) slow (Type I-S; n = 11) units with a discharge frequency of more than 12 spikes/s or less than 5 spikes/s, respectively. Like monoaminergic PS-off and cholinergic PGO-on cells, both tonic type II and type I-S cells were characterized by a long spike duration (median: 3.3 and 3.5 ms), as well as by a slow conduction velocity (median = 1.8 and 1.7 m/s). In the light of these data, we discuss the possible cholinergic nature and functional significance of these ascending tonic neurons in the generation of neocortical electroencephalographic desynchronization occurring during waking and paradoxical sleep.

Thalamic nuclei in Alzheimer disease: evidence against the cholinergic hypothesis of plaque formation

Recent studies provide evidence for a significant cholinergic projection from the nucleus basalis of Meynert (NbM) to the reticular and mediodorsal thalamic nuclei. We examined the incidence and distribution of plaques in the thalamus in order to determine whether in Alzheimer's disease degenerating cholinergic processes from the NbM induce the emergence of plaques according to the cholinergic hypothesis. The present study shows that degeneration of NbM neurons does not induce plaques in the thalamic nuclei it innervates, and that plaques appear more frequently in other thalamic nuclei that do not receive projections from the NbM.

Single neurones of the basal forebrain and laterodorsal tegmental nucleus project by collateral axons to the olfactory bulb and the mediodorsal nucleus in the rat

The branching pattern of axons arising from cells in the basal forebrain and laterodorsal tegmental nucleus of the pontine grey, was examined using the double retrograde transport of rhodamine- and coumarin-labelled latex microspheres injected into the olfactory bulb and the mediodorsal thalamic nucleus. About 30-50% of basal forebrain neurones were double-labelled, and approximately 30-40% of laterodorsal tegmental neurones were double-labelled ipsilateral to the injections. No contralateral single or double label was observed in the basal forebrain, but approximately 30% of the contralateral laterodorsal tegmental projection was also double-labelled.

The pedunculopontine nucleus in Parkinson's disease

This study demonstrated a significant loss of neurons within the lateral part of the pedunculopontine nucleus pars compacta in individuals with idiopathic Parkinson's disease and in individuals with combined Parkinson's and Alzheimer's disease. We also examined the extent of neuronal loss within the substantia nigra pars compacta, locus ceruleus, dorsal raphe nucleus, and nucleus basalis of Meynert. The number of pedunculopontine nucleus pars compacta neurons in the patients with Parkinson's or Parkinson's and Alzheimer's disease was reduced (average, 40%) in comparison with the number in control subjects or patients with Alzheimer's disease (p less than 0.01). This finding correlated significantly with the extent of loss of substantia nigra pars compacta neurons (p less than 0.01).

Neonatal enucleations reduce number, size, and acetylcholinesterase histochemical staining of neurons in the dorsal lateral geniculate nucleus of developing rats

Previous studies have demonstrated that transient patterns of acetylcholinesterase (AChE) activity are characteristic of geniculo-recipient regions of rat cortical area 17 during the second and third postnatal weeks of life. Neonatal enucleation results in a marked reduction of this transiently expressed cortical AChE. Parallel studies have demonstrated that the dorsal lateral geniculate nucleus (dLGN) also expresses AChE transiently during development. The present study examines neuronal number and size as well as AChE histochemical staining in the dLGN of normal and neonatally enucleated rat pups to determine whether changes in dLGN neurons could account for the decreased visual cortical AChE staining that results from neonatal enucleation. Changes in 4 parameters in dLGN were noted after neonatal enucleation. First, a 26-37% shrinkage in the volume of dLGN occurred contralateral to enucleation. Second, enucleation resulted in a loss of 16-30% of AChE-stained neuronal somata. Third, remaining AChE-positive neuronal somata appeared shrunken by approximately 40%. Fourth, intensity of AChE histochemical staining of individual dLGN neurons was reduced by approximately 24% following neonatal enucleation. These data suggest that loss of transient AChE activity in cortical area 17 consequent to neonatal enucleation is secondary to enucleation-induced alterations in the dLGN; these alterations include loss of neurons, shrinkage of neurons, and an apparent decrease in the ability of neurons to synthesize AChE. These data support the hypothesis that geniculocortical projection neurons express AChE transiently during development of geniculocortical connectivity and indicate that normal afferent connections and/or activity are important for the transient expression of AChE by these neurons.

Axonal arborizations of a magnocellular basal nucleus input and their relation to the neurons in the thalamic reticular nucleus of rats

A dense axonal plexus, arising in a portion of the magnocellular basal nucleus, was identified in the thalamic reticular nucleus in adult rats. The details of these axonal arbors as well as their relation to the neurons of the reticular nucleus were investigated by using Phaseolus vulgaris leucoagglutinin injections into the basal nucleus and intracellular injections of Lucifer yellow into reticular nucleus neurons. Axons arising in the caudal basal nucleus at the medial margin of the globus pallidus do not enter the dorsal thalamus but are confined to the reticular nucleus, where they arborize widely and densely. Neurons in the reticular nucleus are large, with sparsely spined and beaded dendrites, which radiate within the plane of the nucleus. Bouton-like swellings along basal nucleus axons are often found apposed to the somata of reticular nucleus neurons, although many are also apposed to dendrites. These morphological observations suggest a second potentially significant route, in addition to its well-known direct cortical projection, through which the magnocellular basal nucleus could influence cortical function: it may, by strategically modulating the excitability of reticular nucleus neurons, alter the general state of the thalamus and hence affect the initial transmission of information to the cortex.

Intracellular analysis of excitatory subthalamic inputs to the pedunculopontine neurons

Response patterns of the pedunculopontine (PPN) area neurons to electrical stimulation of the subthalamic nucleus (STH) were investigated in anesthetized rats. Intracellular recordings demonstrated that STH stimulation evoked short duration (mean value: 11.6 ms) depolarizing potentials which were identified as excitatory postsynaptic potentials (EPSPs) by intracellular current injection. These potentials were considered monosynaptic because the latency was constant in spite of changes in stimulus intensities. The conduction velocities of STH-PPN area afferents ranged from 1.2 to 8.3 m/s (mean value: 1.6 m/s). Similar results were obtained in rats with chronic unilateral coronal lesion just rostral to STH which eliminated the rostral afferents. In some neurons, EPSPs were followed by IPSPs. PPN area neurons were also antidromically activated by STH stimulation. Some of these neurons could also be antidromically activated by substantia nigra stimulation. We could differentiate PPN area projection neurons into two groups based on their conduction velocity. One group had a conduction velocity of 6.0 m/s and the second one 1.7 m/s. The morphology of 5 HRP-labeled PPN area neurons was analyzed. The somata were fusiform, polygonal and oval in shape, and the size varied from 152 to 1310 micron 2. Two to nine dendrites emerged from the somata and extended either radially or more in one direction (e.g. rostrocaudal). Axons arose, in general, from a proximal dendritic trunk close to the soma except one and branched near the soma. These data indicate a reciprocal connection between STH and PPN area and that STH exerts excitatory influence on PPN area neurons.

Human reticular formation: cholinergic neurons of the pedunculopontine and laterodorsal tegmental nuclei and some cytochemical comparisons to forebrain cholinergic neurons

Choline acetyltransferase immunohistochemistry showed that the human rostral brainstem contained cholinergic neurons in the oculomotor, trochlear, and parabigeminal nuclei as well as within the reticular formation. The cholinergic neurons of the reticular formation were the most numerous and formed two intersecting constellations. One of these, designated Ch5, reached its peak density within the compact pedunculopontine nucleus but also extended into the regions through which the superior cerebellar peduncle and central tegmental tract course. The second constellation, designated Ch6, was centered around the laterodorsal tegmental nucleus and spread into the central gray and medial longitudinal fasciculus. There was considerable transmitter-related heterogeneity within the regions containing Ch5 and Ch6. In particular, Ch6 neurons were intermingled with catecholaminergic neurons belonging to the locus coeruleus complex. The lack of confinement within specifiable cytoarchitectonic boundaries and the transmitter heterogeneity justified the transmitter-specific Ch5 and Ch6 nomenclature for these two groups of cholinergic neurons. The cholinergic neurons in the nucleus basalis (Ch4) and those of the Ch5-Ch6 complex were both characterized by perikaryal heteromorphism and isodendritic arborizations. In addition to choline acetyltransferase, the cell bodies in both complexes also had high levels of acetylcholinesterase activity and nonphosphorylated neurofilament protein. However, there were also marked differences in cytochemical signature. For example, the Ch5-Ch6 neurons had high levels of NADPHd activity, whereas Ch4 neurons did not. On the other hand, the Ch4 neurons had high levels of NGF receptor protein, whereas those of Ch5-Ch6 did not. On the basis of animal experiments, it can be assumed that the Ch5 and Ch6 neurons provide the major cholinergic innervation of the human thalamus and that they participate in the neural circuitry of the reticular activating, limbic, and perhaps also extrapyramidal systems.

Laminar and non-laminar patterns of acetylcholinesterase activity in the marsupial lateral geniculate nucleus

Acetylcholinesterase (AChE) distribution in the dorsal lateral geniculate nucleus (LGd) of 3 polyprotodont and 3 diprotodont marsupials has been compared with the cytoarchitecture and, as appropriate, with retinal terminal bands (RTBs) as demonstrated by tracers injected into the vitreous body. In this series those polyprotodont marsupials showing only partial segregation of retinal input (Virginia opossum and Tasmanian devil), display the least cell laminar differentiation. In them AChE staining is mainly diffuse but stronger in areas of greatest retinal terminal overlap. Segregation of visual input increases progressively in the remaining polyprotodont (eastern quoll) and in the diprotodonts (Tasmanian bettong, Tasmanian potoroo and brush-tailed possum), culminating in the last-named, in which segregation is most complete. Related to this development varying numbers of cell laminae/sublaminae appear and retinal terminal laminae/sublaminae (bands) are revealed. AChE activity can be correlated with both specific cell laminae/sublaminae and retinal terminal laminae/sublaminae in these complex LGds. Greatest AChE staining in every case is related to laminae/RTBs located in the medial part of the lateral (alpha) segment of LGd. Cytoarchitecturally, the ventral lateral geniculate nucleus (LGv), unlike the heterogeneous LGd, is remarkably homogeneous in the series of animals studied and shows well-stained AChE patches relating to areas receiving significant retinal input.

Origin of ascending and spinal pathways from the nucleus tegmenti pedunculopontinus in the rat

The distribution and collateralization of ascending and descending projections from neurons in the nucleus tegmenti pedunculopontinus (PPN) were studied in the rat by using retrograde transport of HRP, HRP/WGA, and fluorescent dyes. The PPN and its two subdivisions, the subnucleus compactus (PPNc) and subnucleus dissipatus (PPNd), were delineated on sagittal Nissl-stained sections by using cytoarchitectural features as guidelines. Large bilateral pressure injections of HRP and/or fluorescent dyes into the cervical cord retrogradely labeled moderate numbers of fusiform and polygonal PPN cells which ranged in size between 65 and 390 microns2. The labeled cells were scattered throughout the PPNd and were somewhat more numerous in the medial half of the subnucleus. The PPNc contained only occasional labeled cells in its ventralmost portion. Following single unilateral HRP/WGA injections in the striatum, globus pallidus, entopeduncular nucleus, subthalamus, or the substantia nigra, the distribution of the labeled cells was similar to that of the spinal cord-projecting PPN neurons. Multiple HRP injections were then made bilaterally in the substantia nigra and the entopeduncular nucleus and/or subthalamus in order to label the entire population of PPN neurons projecting to the basal ganglia. In this case, not only the PPNd but also the PPNc contained a substantial number of retrogradely labeled cells. The rostrally projecting PPN cells outnumbered 5.4 times those projecting to the spinal cord, and their somata were somewhat larger, ranging between 114 and 472 microns2. While both fusiform and polygonal shapes were encountered, the polygonal cell somata were more numerous. In the double-labeling experiments, Granular Blue and Diamidino Yellow Dihydrochloride were injected into the cervical cord and the entopeduncular nucleus or subthalamus. In general, these experiments confirmed the extensive overlap of forebrain- and spinal cord-projecting neurons within the PPNd and the quantitative preponderance of ascending neurons. They also demonstrated that these two projection systems originate largely from separate cell populations since the double-labeled cells always composed less than 5% of the labeled neurons. The results confirm the existence of a direct PPN projection to the spinal cord. This pathway originates mainly in the PPNd and appears to be quantitatively weaker than the PPN projections to the forebrain. The spinal cord-projecting cells are not spatially segregated from the cells projecting to the basal ganglia, but they represent a separate population of the PPN projection neurons.

Collateral projections of predorsal bundle cells of the superior colliculus in the rat

The deep layers of the superior colliculus contain cells which are premotor in the sense that they respond prior to the onset of shifts in gaze and send axons, by way of a pathway called the predorsal bundle, to the contralateral brainstem gaze centers and cervical spinal cord. Previous studies have suggested that these cells also contribute to other efferent pathways which arise in the deep layers. The present study examines the contributions of the cells of origin of the predorsal bundle to these additional pathways as a step toward understanding their roles in gaze mechanisms. In one series of experiments, retrograde tracers were used to compare the laminar distribution of predorsal bundle cells with the distributions of the cells of origin of three other pathways: those that project to the intralaminar region of the dorsal thalamus, those that project to the contralateral superior colliculus, and those that project to the ipsilateral brainstem tegmentum. Predorsal bundle cells were found primarily in stratum griseum intermedium sublayer b. This distribution overlaps extensively with the distribution of colliculus cells that project to the intralaminar region of the thalamus. In contrast, the majority of the colliculus cells that project to either the contralateral superior colliculus or the ipsilateral brainstem tegmentum do not overlap extensively with the predorsal bundle cells; instead, they are primarily located dorsal or ventral to sublayer b of stratum griseum intermedium. In a second series of experiments, two regions were injected with different retrograde fluorescent traces in single animals in order to study the collateral projections of the cells of origin of these pathways. The results indicate that many predorsal bundle cells project to the intralaminar region of the dorsal thalamus but that only a few contribute to the tectotectal pathway. The results also indicate that few tectotectal cells contribute to the ipsilateral tectobulbar pathway.

Brainstem projecting neurons in the rat basal forebrain: neurochemical, topographical, and physiological distinctions from cortically projecting cholinergic neurons

Magnocellular regions of the basal forebrain contain cholinergic neurons that project to the cerebral cortex. Neurons in the same basal forebrain regions innervate the brainstem. The present study investigated whether these brainstem projecting neurons are cholinergic, project also to the cortex, and share similar physiological properties as cortically projecting neurons. Data with retrograde tracing from various regions of the pons, medulla, and cortex combined with choline acetyltransferase immunofluorescence indicated that: 1) brainstem projecting neurons are usually segregated from cortically projecting and/or cholinergic neurons in the basal forebrain, 2) virtually no brainstem projecting neurons in the basal forebrain are cholinergic, and 3) only rarely do basal forebrain neurons have axon collaterals that project to both cortex and brainstem. Extracellular recordings from basal forebrain neurons confirmed the paucity of axonal collateralization and the topographic segregation between cortically and brainstem projecting basal forebrain neurons, and, in addition, showed that brainstem projecting neurons have a slower mean conduction velocity than cortically projecting neurons. These observations suggest that basal forebrain neurons projecting to the brainstem (pons, medulla) and the cortex represent separate cell populations in terms of projections, neurotransmitter content, distribution, and physiological properties.

In vitro electrophysiology of neurons in the lateral dorsal tegmental nucleus

The lateral dorsal tegmental nucleus (LDT) provides ascending cholinergic projections to forebrain structures such as prefrontal cortex, septum, habenula, and thalamus, but relatively little is known of the physiology of LDT neurons. Intracellular recordings from LDT neurons in guinea pig brain slices found that most neurons fired action potentials either tonically or in bursts. The voltage dependent characteristics of the neurons suggest that a prolonged afterhyperpolarization due to an outward potassium current and a low-threshold calcium conductance contributed to these two modes of firing. Intracellular injections of Lucifer Yellow and subsequent staining for NADPH-diaphorase activity permitted positive identification of cholinergic neurons.

Hypothalamic axons terminate on forebrain cholinergic neurons: an ultrastructural double-labeling study using PHA-L tracing and ChAT immunocytochemistry

A correlated light and electron microscopic study combining choline acetyltransferase immunocytochemistry with anterograde tracing of Phaseolus vulgaris leucoagglutinin revealed that axons of lateral hypothalamic neurons terminate on forebrain cholinergic projection cells. This finding is discussed in relation to direct and indirect corticopetal systems.

The cholinergic input to the superficial layers of the superior colliculus: an ultrastructural immunocytochemical study in the ferret

The cholinergic innervation of the superficial layers of the ferret's superior colliculus was investigated with a combination of electron microscopy and choline acetyltransferase immunohistochemistry. Cholinergic boutons in the superficial layers of the superior colliculus possess spherical vesicles and make predominantly asymmetrical synapses onto the profiles of small dendrites, as do the terminals of cortical and retinal axons. In most areas of the brain studied so far, cholinergic terminals tend to form synapses of the symmetrical variety.