Shifts in spatial synchronization of rabbit cortical potentials evoked by applying acetylcholine and amizil to the visual area

Acetylcholine solution application to the visual cortex of walking unrestrained rabbit led approximately in 5 minutes to a certain increase of the spatial synchronization of the cortical potentials at the small conditions, the the cortex, 24 EEG channels being used. Under the same conditions, the application of muscarinic antagonist amizil had an opposite more distinct effect. Endogenous cholinergic input increasing the spatial synchronization is supposed to play an important role in the formation of the spatiotemporal cortical potentials' organization necessary for the occurrence of complex behavioural acts.     

The participation of the cholinergic system of the rat sensorimotor cortex in regulating different types of movements

To study the role of the cholinergic system of the sensorimotor cortex in regulation of different manipulatory movements and locomotion of Wistar rats, the effects of injections of cholinergic drugs (a cholinergic agonist carbachol and an antagonist scopolamine) into the area of forepaw representation in the sensorimotor cortex on motor activity and performance of manipulatory movements (with prolonged and short pushing) were analyzed. The drugs were injected via special cannulae stereotaxically implanted into the cortex during surgery carried out under Nembutal anesthesia. Carbachol injections (0.03-3 micrograms in 1 microliter of physiologic solution) into the cortex resulted in a significant slowing down of both types of movements as well as an increase in locomotion in the open-field test. Injections of scopolamine (0.3-3 micrograms) into the same cortical area were accompanied by an increase in the number of fast manipulatory movements without significant changes in locomotor activity. The obtained evidence suggests that the cholinergic system of the sensorimotor cortex indifferent manners regulates the innate (locomotion) and acquired movements which require different periods of maintaining the muscle tone of the forepaw (short-time periods for the usual movements necessary for food taking from the narrow horizontal tube and prolonged periods for the learned slow movements with additional tactile and tonic components).     

Nerve growth factor increases stimulus-evoked metabolic activity in acetylcholine-depleted barrel cortex

Lesions of the basal forebrain deplete the neocortex of cholinergic fibers. Acetylcholine depletion in the somatosensory cortex of rats results in reduced stimulus-evoked activity in response to whisker stimulation. Previous studies demonstrate that embryonic basal forebrain transplants improve functional activity toward normal. It is not clear if the activity increase is due to cholinergic replacement or other factors present in the graft. In this study, we examined the possibility that nerve growth factor (NGF), a neurotrophin known as a survival factor and a specific protectant for cholinergic basal forebrain neurons, can preserve basal forebrain cells after a lesion and restore functional activity in the somatosensory cortex. We report that NGF alone is capable of restoring functional activity in the barrel cortex of animals with basal forebrain lesions, while vehicle injections of saline do not alter activity. Both high (10 mug) and low (5 mug) doses of NGF unilaterally injected into the lateral ventricle improved stimulus-evoked functional activity during bilateral whisker stimulation. The mechanism of NGF action is not clear since the restoration of functional activity in cortex was not accompanied by increased cholinergic activity as detected by acetylcholinesterase fiber staining. NGF may act directly on cortical neurons, although its site of action is not well defined.     

The role of acetylcholine in learning and memory

Pharmacological data clearly indicate that both muscarinic and nicotinic acetylcholine receptors have a role in the encoding of new memories. Localized lesions and antagonist infusions demonstrate the anatomical locus of these cholinergic effects, and computational modeling links the function of cholinergic modulation to specific cellular effects within these regions. Acetylcholine has been shown to increase the strength of afferent input relative to feedback, to contribute to theta rhythm oscillations, activate intrinsic mechanisms for persistent spiking, and increase the modification of synapses. These effects might enhance different types of encoding in different cortical structures. In particular, the effects in entorhinal and perirhinal cortex and hippocampus might be important for encoding new episodic memories.     

Neurochemical correlates of behaviour. Changes in acetylcholine, norepinephrine and 5-hydroxytryptamine concentrations in several discrete brain areas of the rat during behavioural excitation

—Acetylcholine, 5-hydroxytryptamine, and norepinephrine concentrations were measured in the telencephalon, diencephalon plus mesencephalon (midbrain), and pons-medulla oblongata of rats exhibiting behavioral excitation while working on a Sidman avoidance schedule and injected with 50 mg/kg iproniazid 16 hr before being given 2 mg/kg tetrabenazine. Acetylcholine concentrations in all three brain areas decreased and returned to normal levels at different times. The time course of increased response rates correlated best with the acetylcholine levels in the telencephalon. Both the 5-hydroxytryptamine and norepinephrine concentrations remained similar to the iproniazid control values during the period of behavioural excitation. However, the norepinephrine concentration in the midbrain showed a continuous decreasing trend toward naive control levels. These data suggest that changes in a cholinergic system in the telencephalon and a noradrenergic system in the midbrain operate in the maintenance of behavioural excitation.     

Presynaptic Nicotinic Cholinergic Receptors Labeled by [3H]Acetylcholine on Catecholamine and Serotonin Axons in Brain

Nicotinic cholinergic receptor binding sites labeled by [3H]acetylcholine were measured in the cerebral cortices, thalami, striata, and hypothalami of rats lesioned by intraventricular injection of either 6-hydroxydopamine or 5, 7-dihydroxytryptamine. In addition, [3H]acetylcholine binding sites were measured in the cerebral cortices of rats lesioned by injection of ibotenic acid into the nucleus basalis magnocellularis. [3H]Acetylcholine binding was significantly decreased in the striata and hypothalami of both 6-hydroxydopamine- and 5,7-dihydroxytryptamine-lesioned rats. There was no change in binding in the cortex or thalamus by either lesion. Ibotenic acid lesions of the nucleus basalis magnocellularis, which projects cholinergic axons to the cortex, did not alter [3H]acetylcholine binding. These results provide evidence for a presynaptic location of nicotinic cholinergic binding sites on catecholamine and serotonin axons in the striatum and hypothalamus.     

Cortical map reorganization without cholinergic modulation

Acetylcholine has been shown to modulate many forms of cortical plasticity. New evidence indicates that reorganization of adult primary auditory cortex is still possible after removal of cholinergic inputs. This finding suggests that acetylcholine may act less as a gate and more as a gain control on cortical plasticity.     

Aluminum-Induced Cholinergic Deficits in Different Brain Parts and Its Implications on Sociability and Cognitive Functions in Mouse

Aluminum is associated with etiology of many neurodegenerative diseases specially Alzheimer’s disease. Chronic exposure to aluminum via drinking water results in aluminum deposition in the brain that leads to cognitive deficits. The study aimed to determine the effects of aluminum on cholinergic biomarkers, i.e., acetylcholine level, free choline level, and choline acetyltransferase gene expression, and how cholinergic deficit affects novel object recognition and sociability in mice. Mice were treated with AlCl₃ (250 mg/kg). Acetylcholine level, free choline level, and choline acetyltransferase gene expression were determined in cortex, hippocampus, and amygdala. The mice were subjected to behavior tests (novel object recognition and social novelty preference) to assess memory deficits. The acetylcholine level in cortex and hippocampus was significantly reduced in aluminum-treated animals, as compared to cortex and hippocampus of control animals. Acetylcholine level in amygdala of aluminum-treated animals remained unchanged. Free choline level in all the three brain parts was found unaltered in aluminum-treated mice. The novel object recognition memory was severely impaired in aluminum-treated mice, as compared to the control group. Similarly, animals treated with aluminum showed reduced sociability compared to the control mice group. Our study demonstrates that aluminum exposure via drinking water causes reduced acetylcholine synthesis in spite of normal free choline availability. This deficit is caused by reduced recycling of acetylcholine due to lower choline acetyltransferase level. This cholinergic hypofunction leads to cognitive and memory deficits. Moreover, hippocampus is the most affected brain part after aluminum intoxication.     

Role of Acetylcholine in the Modulation of Activity of Neocortical Neurons in Awake Animals Performing an Instrumental Conditioned Reflex

We studied modulatory effects of the cholinergic system on the activity of sensorimotor cortex neurons related to realization of an instrumental conditioned placing reflex. Experiments were carried out on awake cats; multibarrel glass microelectrodes were used for extracellular recording of impulse activity of neurons in the sensorimotor cortex and iontophoretic application of synaptically active agents within the recording region. The background and reflex-related activity was recorded in the course of realization of conditioned movements, and then changes of spiking induced by applications of the testing substances were examined. Applications of acetylcholine and carbachol resulted in increases in the intensity of impulse reactions of neocortical neurons evoked by presentation of an acoustic signal and in simultaneous shortening of the response latencies. An agonist of muscarinic receptors, pylocarpine, exerted a similar effect on the evoked activity of sensorimotor cortex neurons. Blockers of muscarinic receptors, atropine and scopolamine, vice versa, sharply suppressed impulse reactions of cortical neurons to afferent stimulation and simultaneously increased latencies of these responses. Applications of an agonist of nicotinic receptors, nicotine, was accompanied by suppression of impulse neuronal responses, an increase in the latency of spike reactions to presentation of a sound signal, and a corresponding increase in the latency of a conditioned motor reaction. In contrast, application of an antagonist of nicotinic receptors, tubocurarine, significantly intensified neuronal spike responses and shortened their latency. The mechanisms underlying the effects of antagonists of membrane muscarinic and nicotinic cholinoreceptors and the role of activation of these receptors in the modulation of activity of pyramidal and non-pyramidal neocortical neurons related to realization of the instrumental motor reflex are discussed.     

THE ORIGIN OF THE ACETYLCHOLINE RELEASED FROM THE SURFACE OF THE CORTEX

—The specific radioactivity of acetylcholine liberated from the surface of the rabbit occipital cortex has been compared with that of the underlying cortical synaptosomal and vesicular acetylcholine at varying times after the administration of [N-Me-³H]choline. Choline was administered by diffusion from solutions placed in cups formed by Perspex cylinders applied to the surface of the cortex. Acetylcholine was collected by diffusion into these cups. The specific radioactivity of the acetylcholine declined progressively. The effect of stimulation of afferent cholinergic pathways was to cause a fall in the specific radioactivity of the released acetylcholine. However this was always higher than that of the synaptosomal or vesicular acetylcholine as represented by fractions P₂ and D of the authors’fractionation scheme. It is concluded that acetylcholine released from the cortex must come from a store or stores more recently synthesized than the endogenous acetylcholine of these subcellular fractions.     

Autoradiography of muscarinic cholinergic receptors in cortical and subcortical brain regions of C57BL/6 and DBA/2 mice

Mice of the inbred strains C57BL/6 and DBA/2 show strain-dependent behavioural differences which have been correlated with variations in brain cholinergic systems. In the present study, the density of muscarinic cholinergic receptors in both strains of mice was determined by autoradiographic methods using [³H]quinuclidinyl benzilate (QNB) and [³H]pirenzepine as ligands. C57BL/6 mice showed a significantly lower [³H]QNB binding level in the frontal cortex by one third as compared to DBA/2 mice. In the striatum and the cholinergic pontomesencephalic nucleus laterodorsalis tegmenti the [³H]QNB binding was lower in C57BL/6 by 28% and 31%, respectively. The [³H]pirenzepine binding level was found to be significantly higher in C57BL/6 temporal cortex (by 22%). These results are discussed in relation to interstrain differences in cholinergic cell density and in the activity of cholinergic enzymes.     

Effect of strychnine on the neuronal reactivity of the sensorimotor cortex and the temporary connection in rabbits

On awake nonimmobilized rabbits, evoked activity was studied of the sensorimotor cortex neurons in response to stimulation of the pyramidal tract, medial lemniscus and reticular nucleus of the midbrain tegmentum by stimuli of different frequencies, and driving reaction of cortical neurons to stimulation of these brain structures by series of stimuli of increasing frequency. Conditioned reflexes were also studied, established on the basis of combination of direct stimulation of the sensorimotor cortex and electrocutaneous stimulation. Application of the cortex of low concentration of strychnine solutions (less than 1%) heightened neurons reactivity and provides for the formation of temporary connection. Application of strychnine solutions of higher concentration (greater than 1%) led to opposite effects. Interconnection of electrical and behavioural effects is discussed.     

Differential Grey Matter Changes in Sensorimotor Cortex Related to Exceptional Fine Motor Skills

Functional changes in sensorimotor representation occur in response to use and lesion throughout life. Emerging evidence suggests that functional changes are paralleled by respective macroscopic structural changes. In the present study we used voxel-based morphometry to investigate sensorimotor cortex in subjects with congenitally malformed upper extremities. We expected increased or decreased grey matter to parallel the enlarged or reduced functional representations we reported previously. More specifically, we expected decreased grey matter values in lateral sensorimotor cortex related to compromised hand function and increased grey matter values in medial sensorimotor cortex due to compensatory foot use. We found a medial cluster of grey matter increase in subjects with frequent, hand-like compensatory foot use. This increase was predominantly seen for lateral premotor, supplementary motor, and motor areas and only marginally involved somatosensory cortex. Contrary to our expectation, subjects with a reduced number of fingers, who had shown shrinkage of the functional hand representation previously, did not show decreased grey matter values within lateral sensorimotor cortex. Our data suggest that functional plastic changes in sensorimotor cortex can be associated with increases in grey matter but may also occur in otherwise macroscopically normal appearing grey matter volumes. Furthermore, macroscopic structural changes in motor and premotor areas may be observed without respective changes in somatosensory cortex.     

Autoradiographic distribution of high affinity muscarinic and nicotinic cholinergic receptors labeled with [3H]acetylcholine in rat brain

The relative distribution of muscarinic and nicotinic cholinergic receptors labeled with [3H]acetylcholine was determined using autoradiography. [3H]Acetylcholine binding to high affinity muscarinic receptors was similar to what has been described for an M-2 distribution: highest levels of binding occurred in the pontine and brainstem nuclei, anterior pretectal area and anteroventral thalamic nucleus, while lower levels occurred in the caudate-putamen, accumbens nucleus and primary olfactory cortex. Nicotinic receptors were labeled with [3H]acetylcholine to the greatest extent in the interpeduncular nucleus, several thalamic nuclei, medial habenula, presubiculum and superior colliculus, and to the least extent in the hippocampus and inferior colliculus. By using autoradiography to localize cholinergic binding sites throughout the brain it was observed that the distributions of high affinity muscarinic and nicotinic sites labeled with the endogenous ligand, [3H]acetylcholine are different from each other and are different from distributions of muscarinic and nicotinic sites labeled with muscarinic and nicotinic antagonists.     

Effect of externally added carnitine on the synthesis of acetylcholine in rat cerebral cortex cells

Acetylcholine synthesis from radiolabelled glucose was monitored in cerebral cortex cells isolated from brains of suckling and adult rats. Acetylcholine synthesis was found much higher in suckling animals, both in the absence and presence of acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) inhibitor, paraoxon. Together with choline (20 μM), carnitine was found to stimulate acetylcholine synthesis in a synergistic way in cortex cells from adult rats (18%). Choline, however, was incapable of reversing an inhibitory effect exerted by carnitine on acetylcholine synthesis in cortex cells from suckling animals. Distribution of carnitine derivatives was found significantly different in the cells from young and old animals, the content of acetylcarnitine decreased with age with a corresponding increase of free carnitine. The observed differences in carnitine effect on acetylcholine synthesis suggested that high acetylcarnitine in cells capable of β-oxidation might be correlated with the lower level of acetylcholine synthesis.     

Effects of cholinergic drugs on growth hormone release

Acetylcholine and the cholinergic agonists, pilocarpine and physostigmine, increased GH release $\text{in}$$\text{vivo}$. The increase in GH release by pilocarpine was reversed by concurrent administration of the cholinergic receptor blocker, atropine, whereas atropine alone did not alter serum GH concentrations. Cholinergic stimulation of GH release appears to be partially mediated through a catecholaminergic system since the response was partially inhibited by pimozide, a dopamine receptor blocker, or phentolamine, an α-adrenergic receptor blocker. The cholinergic system may function physiologically to help regulate GH release.     

A spectral-correlational analysis of the electrical activity of the sensorimotor cortex and the internal geniculate body during a motor-polarization dominant]

By spectral-correlative analysis the dynamics was studied of structural changes of coherent relations of the electrical activity of the sensorimotor cortex and medial geniculate body (MGB) of the rabbit under motor polarization dominant created by the action of DC anode on the sensorimotor cortex area. It was shown, that in the power spectra of the MGB, besides the increase of the delta-region components in interstimulus intervals at the dominant, during the action of the sound stimulus a distinct maximum appeared in the alpha-rhythm range of the electrical activity of MGB of the "dominant" hemisphere. The coherence increase of the delta-range of the MGB and the sensorimotor cortex electrical activity in the "dominant" part of the brain was manifested exclusively in the period of sound stimulus action.     

Acute tolerance to ethanol on the release of acetylcholine from the cat cerebral cortex

Ethanol (1 g/kg, iv) produced a peak depression of acetylcholine release from the cat sensorimotor cortices within 30 min of the ethanol administration but recovery to control levels occurred in the following 30 min. However, the concentrations of ethanol in the blood and in the solution bathing the cortex remained stable during this recovery period. This example of acute tolerance to ethanol is possibly related to the well-known acute tolerance that develops to the behavioural effects of ethanol.     

Regulation by beta-adrenergic receptor and muscarinic cholinergic receptor activation of intracellular cyclic AMP and cyclic GMP levels in rat lung slices

The effects of adrenergic and cholinergic agents, present singly or in combination, on the levels of cyclic AMP and cyclic GMP in slices of rat lung were studied. It was found that isoproterenol increased pulmonary cyclic AMP levels about 3-fold, and this increase was abolished by propranolol, but not by phenoxybenzamine. Acetylcholine increased the cyclic GMP levels also about 3-fold (thus raising its tissue content above that of cyclic AMP), and this increment was largely reduced by atropine, but not by hexamethonium. While without effects on the cyclic GMP levels when present alone, isoproterenol antagonized acetylcholine in increasing cyclic GMP levels. Acetylcholine, while lacking effects on the basal levels of cyclic AMP, on the other hand, depressed the augmented levels caused by isoproterenol.The data presented indicate that cyclic GMP may mediate the cholinergic action in lung and that the pulmonary cyclic GMP levels are also closely regulated by β-adrenergic receptor activation.