Micro-electrophoretic studies in the cat pulvinar region: effect of acetylcholine

Electroencephalographic abnormalities in patients with presenile dementia of the Alzheimer type: quantitative analysis at rest and during photic stimulation

In the present study, quantitative electroencephalographic (EEG) analysis was performed at rest and during photic stimulation (5, 10, and 15 Hz) in nine patients with presenile dementia of the Alzheimer type (AD; mean age at onset, 55 years) and nine sex- and age-matched control subjects. Compared with the normal controls, the AD patients had a significantly lower alpha-2 and beta band power in the resting EEG as well as a significant increase in delta and theta band power. EEG analysis during the photic stimulation demonstrated that the AD patients had a significantly lower EEG power during photic stimulation for the alpha (9.8-10.2 Hz) and beta bands (14.8-15.2 Hz) corresponding to photic stimulation at 10 Hz and 15 Hz, respectively. In addition, when we examined EEG changes from rest to the stimulus condition, the AD patients were found to show significantly smaller changes in EEG power mainly over the posterior regions, irrespective of the stimulus frequency. These findings provide evidence that AD patients have EEG abnormalities in both non-stimulus and stimulus conditions, and suggest diminished EEG reactivity to photic stimulation.

Neuronal activity in the peribrachial area: relationship to behavioral state control

Extensive studies have ascribed a role to the brainstem cholinergic system in the generation of rapid eye movement (REM) sleep and ponto-geniculo-occipital (PGO) waves. Much of this work stems from systemic and central cholinergic drug administration studies. The brainstem cholinergic system is also implicated in cortical activation via basal forebrain, thalamic, and hypothalamic relay neurons. This cholinergic ascending reticular activating hypothesis has also been suggested by in vivo experiments under anesthetics and by in vitro studies using cholinergic agonists in thalamic and hypothalamic slices. During the last ten years, brainstem cholinergic neurons have been discovered to be in the peribrachial area (PBL). With the discovery of PBL cholinergic neurons, many studies were devoted to the examination of PBL neuronal activity and their connectivity. This article reviews PBL neuronal activity in behaving animals and the anatomical features of these neurons in relation to behavioral state control. The role of the PBL in the generation of REM sleep, PGO waves, and the ascending reticular activating system (ARAS) has been evaluated at the cellular and neurochemical level. Based on recent literature, tentative mechanisms of REM sleep generation, PGO waves generation, and the cortical activation process are also outlined.

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.

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.

Neurotoxic lesions of the dorsolateral pontomesencephalic tegmentum-cholinergic cell area in the cat. II. Effects upon sleep-waking states

Kainic acid was injected bilaterally (4.8 micrograms in 1.2 microliters each side) into the dorsolateral pontomesencephalic tegmentum of cats in order to destroy the cholinergic neurons located in that region and thus to study the effects of their destruction upon sleep-waking states. The kainic acid produced a large area of nerve cell loss and/or gliosis centered in the dorsolateral tegmentum-cholinergic cell area, that includes the pedunculopontine tegmental (PPT) and laterodorsal tegmental (LDT) nuclei rostrally (A1-P2), and the parabrachial (PB) and locus coeruleus (LC) nuclei caudally (P3-P5). The mean loss of choline acetyltransferase (ChAT)-immunoreactive neurons within this area was 60% with a range from 25% to 85% across 11 cats. The mean loss of tyrosine hydroxylase (TH)-immunoreactive neurons, differentially distributed through the same region, was 35% with a range of 0-50%. Whereas the kainic acid lesions appeared to have only slight effects upon wakefulness and slow-wave sleep, they had marked effects upon paradoxical sleep (PS), which varied in degree across animals. In cats with the most extensive destruction of cholinergic neurons, PS was eliminated in the first few weeks following the lesion and then reappeared as isolated episodes characterized by sparse, low amplitude PGO spikes in association with few eye movements and an activated cortex, though in absence of neck muscle atonia. Although these PS-like episodes varied in amount, they were significantly less than baseline PS in percent and in duration for the group of 11 animals over one month recording. The PGO spike rate was significantly reduced; the EMG amplitude was significantly increased, marking a loss of neck muscle atonia. The percent of PS-like epochs, the rate of PGO spiking and the EMG amplitude on postlesion day 28 were found to be significantly correlated with the volume of the lesion within the dorsolateral pontine tegmentum-cholinergic cell area. The percent PS-like episodes and PGO spike rate were significantly correlated with the number of remaining ChAT-immunoreactive neurons, but not with the number of remaining TH-immunoreactive neurons within this region. These results suggest that cholinergic pontomesencephalic neurons may be critically involved in the generation of paradoxical sleep and its phasic events.

Cholinergic and non-cholinergic projections from the upper brainstem core to the visual thalamus in the cat

The projections of cholinergic and non-cholinergic neurons of the rostral brainstem reticular formation to the visual thalamic nuclei (dorsal lateral geniculate - LG, lateral posterior - LP, and perigeniculate - PG) were studied in cat by using the retrograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) combined with choline acetyltransferase (ChAT) immunohistochemistry. After thalamic injections, less than 10% of all retrogradely labeled neurons in the upper brainstem reticular core were located at most rostral (perirubral) levels where there are virtually no cholinergic elements. Approximately 75-80% of all HRP-positive neurons in the reticular formation were found between stereotaxic planes anterior 1 and posterior 2, in the peribrachial (PB) area of the pedunculopontine nucleus and in the laterodorsal tegmental (LDT) nucleus. The brainstem afferents to LG and PG thalamic nuclei essentially derive from PB neurons, with a small contribution from LDT cells, whereas the LP thalamic nucleus receives massive inputs from both PB and LDT brainstem nuclei. Of all HRP-positive elements visualized in the PB nucleus after an LG or a PG injection, 87% and 73%, respectively, were also ChAT-positive. Of all HRP-positive elements in the PB and LDT nuclei after an LP injection, 82% and 92%, respectively, were also ChAT-positive. The numbers of labeled neurons in the contralateral brainstem reticular nuclei reach 30% to 50% of the numbers found in the ipsilateral reticular formation. These findings reveal the existence of a prominent cholinergic projection from the brainstem reticular formation to the visual thalamic nuclei. Such a chemospecific projection is probably involved in phasic and tonic events of activated behavioral states.

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

The origins of the cholinergic and other afferents of several thalamic nuclei were investigated in the rat by using the retrograde transport of wheat germ agglutinin conjugated-horseradish peroxidase in combination with the immunohistochemical localization of choline acetyltransferase immunoreactivity. Small injections placed into the reticular, ventral, laterodorsal, lateroposterior, posterior, mediodorsal, geniculate, and intralaminar nuclei resulted in several distinct patterns of retrograde labelling. As expected, the appropriate specific sensory and motor-related subcortical structures were retrogradely labelled after injections into the principal thalamic nuclei. In addition, other basal forebrain and brainstem structures were also labelled, with their distribution dependent on the site of injection. A large percentage of these latter projections was cholinergic. In the brainstem, the cholinergic pedunculopontine tegmental nucleus was retrogradely labelled after all thalamic injections, suggesting that it provides a widespread innervation to the thalamus. Neurons of the cholinergic laterodorsal tegmental nucleus were retrogradely labelled after injections into the anterior, laterodorsal, central medial, and mediodorsal nuclei, suggesting that it provides a projection to limbic components of the thalamus. Significant basal forebrain labelling occurred only with injections into the reticular and mediodorsal nuclei. Only injections into the reticular nucleus resulted in retrograde labelling of the cholinergic neurons in the nucleus basalis of Meynert. The results provide evidence for an organized system of thalamic afferents arising from cholinergic and noncholinergic structures in the brainstem and basal forebrain. The brainstem structures, especially the cholinergic pedunculopontine tegmental nucleus, appear to project directly to principal thalamic nuclei, thereby providing a possible anatomical substrate for mediating the well-known facilitory effects of brainstem stimulation upon thalamocortical transmission.

Choline acetyltransferase immunoreactivity in the rat thalamus

The distribution of choline acetyltransferase immunoreactivity in the rat thalamus was investigated by using a specific monoclonal antibody and was compared with the pattern of acetylcholinesterase staining. The only choline acetyltransferase-immunoreactive cell bodies in the thalamus were in the medial habenula. A wide range of densities of immunoreactive fibers and varicosities was found. The highest densities of stained varicosities were in the anteroventral, reticular, lateral mediodorsal, and intralaminar nuclei. At the other extreme, the anterodorsal, ventroposteromedial, and paraventricular nuclei were almost devoid of immunoreactive varicosities. A light density of fibers was observed in several medial nuclei, including parataenial, reuniens, and gelatinosus. Most other nuclei contained moderately dense regions of varicose fibers that were often heterogeneous or patchy. The pattern of choline acetyltransferase immunoreactivity in the thalamus was in general similar to that of acetylcholinesterase. A marked discrepancy, however, was found in the anterodorsal nucleus, which was intensely stained for acetylcholinesterase but contained no apparent choline acetyltransferase immunoreactivity. Numerous physiologic studies have demonstrated striking effects of acetylcholine on thalamic activity. The present study provides a description of choline acetyltransferase-immunoreactive structures in the thalamic nuclei, providing a first step toward elucidating the anatomical basis for the physiologic and functional importance of cholinergic transmission in the thalamus.

Biochemical evidence for glutamate and/or aspartate as neurotransmitters in fibers from the visual cortex to the lateral posterior thalamic nucleus (pulvinar) in rats

The effects of visual cortex ablation on several neurotransmitter parameters in the lateral thalamic nucleus (pulvinar) in rats have been investigated. We found a 57% decrease in high affinity uptake of D-[3H]aspartate in the pulvinar after ablation of the ipsilateral visual cortex. The KCl-evoked release of exogenous D-[3H]aspartate and endogenous glutamate were decreased by 33 and 37%, respectively. Moreover, the contents of endogenous glutamate and aspartate were decreased by 35%, each. The glutamate decarboxylase and choline acetyltransferase activities and the contents of other amino acids were not affected by the lesion. Our biochemical data indicate that glutamate and/or aspartate may be transmitters in the fibers from visual cortex to pulvinar in rats.

Central cholinergic pathways in the rat: an overview based on an alternative nomenclature (Ch1-Ch6)

Monoclonal antibodies to choline acetyltransferase and a histochemical method for the concurrent demonstration of acetylcholinesterase and horseradish peroxidase were used to investigate the organization of ascending cholinergic pathways in the central nervous system of the rat. The cortical mantle, the amygdaloid complex, the hippocampal formation, the olfactory bulb and the thalamic nuclei receive their cholinergic innervation principally, from cholinergic projection neurons of the basal forebrain and upper brainstem. On the basis of connectivity patterns, we subdivided these cholinergic neurons into six major sectors. The Ch1 and Ch2 sectors are contained within the medial septal nucleus and the vertical limb nucleus of the diagonal band, respectively. They provide the major cholinergic projections of the hippocampus. The Ch3 sector is contained mostly within the lateral portion of the horizontal limb nucleus of the diagonal band and provides the major cholinergic innervation to the olfactory bulb. The Ch4 sector includes cholinergic neurons in the nucleus basalis, and also within parts of the diagonal band nuclei. Neurons of the Ch4 sector provide the major cholinergic innervation of the cortical mantle and the amygdala. The Ch5-Ch6 sectors are contained mostly within the pedunculopontine nucleus of the pontomesencephalic reticular formation (Ch5) and within the laterodorsal tegmental gray of the periventricular area (Ch6). These sectors provide the major cholinergic innervation of the thalamus. The Ch5-Ch6 neurons also provide a minor component of the corticopetal cholinergic innervation. These central cholinergic pathways have been implicated in a variety of behaviors and especially in memory function. It appears that the age-related changes of memory function as well as some of the behavioral disturbances seen in the dementia of Alzheimer's Disease may be related to pathological alterations along central cholinergic pathways.

Rotational behavior in the cat induced by electrical stimulation of the pulvinar-lateralis posterior nucleus complex: role of the cholinergic system

We studied the involvement of the cholinergic system in the contralateral head-eye-body turning induced in the cat through stimulation of the pulvinar-lateralis posterior nucleus complex (P-LP). In 17 cats through a cannula aimed at the P-LP, agonists and antagonists of the cholinergic system were injected. The electrical activity of the P-LP could be recorded through the same cannula or through electrodes attached to it. In addition, electrodes were implanted ipsilaterally in the dorsal hippocampus, caudate nucleus, amygdala, and superior colliculus to record through them and through one screw placed on the skull the electrical activity of those structures and of the cortical P-LP projection. Seven days after surgery, carbachol, an agonist of the cholinergic system was injected in the P-LP, and the behavior and electrical activity of the unrestrained cat (previously accustomed to a plastic cage) were recorded. A control volume of 0.9% NaCl was always injected previously. The usual drug volume injected was 1 microliter; occasionally, 2 microliter were injected. Weekly or biweekly sessions were conducted to determine (a) the threshold for cholinergic activation, (b) the threshold for turning behavior, (c) the blocking effect of local atropine sulfate injected previously, (d) the effect of haloperidol previously injected (locally or systemically), and (e) the effect of dioxolane, an exclusive muscarinic agonist. In 14 of 17 cats, contralateral turning behavior was evoked by carbachol. In two of the three cats that did not respond to carbachol, dioxolane induced turning. The effect of dioxolane was similar to that of carbachol when tried in five cats. Besides turning behavior, carbachol produced numerous symptoms due to cholinergic activation. Atropine blocked the rotational effect of carbachol in all cats, and haloperidol blocked it in 68% of them. Electrolytic coagulation of the dorsal hippocampus surrounding the P-LP did not disturb the effects induced by carbachol. These experiments show that both systems of the P-LP, cholinergic and catecholaminergic, are involved in the contralateral turning. We conclude that the effect induced by carbachol is due to activation of muscarinic receptors because it is totally blocked by local atropine sulfate and is reproduced by dioxolane, an exclusive muscarinic agonist.

Acetylcholine and somatically evoked inhibition on perigeniculate neurones in the cat

1 Perigeniculate neurones in cats were found to be inhibited by iontophoretically applied acetylcholine (ACh) and some of them by somatic sensory stimulation under certain experimental conditions. 2 Under chloralose anaesthesia, perigeniculate neurones could be divided into two groups with regard to their spontaneous activity, sensitivity to glutamate and reaction to sensory inputs. Somatic sensory stimulation clearly inhibited the glutamate discharges of those perigeniculate neurones which were characterized by a high sensitivity to glutamate and the absence of spontaneous activity. ACh had no clear inhibitory effect. 3 Under fluothane and urethane anaesthesia, no somatic sensory influence was noticed but ACh depressed almost all perigeniculate neurones. 4 In an unanaesthetized midpontine pretrigeminal preparation, the inhibitory effect of ACh was confirmed. 5 No conditions were found which the inhibitory influences of ACh and those of somatic sensory stimulation could be observed simultaneously on the same neurone. Therefore, it could not be established whether ACh mediates the somatic sensory influences on perigeniculate cells.

Inhibitory effects of acetylcholine on neurones in the feline nucleus reticularis thalami

1. Short iontophoretic pulses of acetylcholine (ACh) inhibited almost every spontaneously active cell encountered in the nucleus reticularis thalami of cats anaesthetized with a mixture of halothane, nitrous oxide and oxygen. On 200 cells the mean current needed to eject an effective inhibitory dose of ACh was 67 +/- 2 nA. When the ACh-evoked inhibition was mimicked by gamma-aminobutyric acid (GABA) or glycine on the same cell, the current required to release ACh was found to be approximately twice as great as that required to release an equally effective dose of GABA or glycine. 2. ACh inhibitions developed with a latency which was very much shorter than that for ACh excitation in cells of the ventrobasal complex. The latency of the ACh-evoked inhibition was as rapid as the onset and offset of the excitation of the same cells glutamate and their inhibition by GABA or glycine. 3. The firing pattern of ACh-inhibited neurones in the nucleus reticularis was characterized by periods of prolonged, high frequency bursts, and their mean firing frequency was 22 Hz. Raster dot displays and interspike interval histograms showed that whereas ACh suppressed the spikes that occurred between bursts much more readily than those that occurred during bursts, all spikes were equally sensitive to the depressant action of GABA and glycine. Large doses of ACh provoked or exaggerated burst activity. 4. ACh-evoked inhibition was extremely sensitive to blockade by short iontophoretic applications of atropine, which had no effect on the inhibitions evoked on the same cell equipotent doses of GABA or glycine. The ACh-evoked inhibitions were also antagonized by dihydro-beta-erythroidine released with slightly larger currents. When tested on the same cell, small iontophoretic applications of picrotoxin and bicuculline methoiodide blocked the inhibition evoked by GABA but had no effect on that evoked by ACh. Iontophoretic strychnine only rarely affected the inhibition evoked by ACh, while readily blocking the inhibition evoked on the same cell by an equipotent dose of glycine. In two cats, intravenous strychnine (1-2 mg/kg) had no effect on the ACh-evoked inhibition, while greatly reducing the sensitivity of the cell under study to glycine. 5. Only four out of forty-eight ACh-inhibted cells tested were inhibited by iontophoretic applications of either guanosine or adenosine 3':5'-phosphate. 6. Cells of the nucleus reticularis have been shown to have an inhibitory action on the thalamic relay cells, which are excited by ACh. It is suggested that the presence of both ACh excited and inhibited cells in different nuclei of the thalamus could be of considerable functional significance in gating sensory transmission through the thalamus.