The distribution of cholinergic neurons in the human central nervous system

Choline acetyltransferase (ChAT), the enzyme responsible for the biosynthesis of acetylcholine, is presently the most specific marker for identifying cholinergic neurons in the central and peripheral nervous systems. The present article reviews immunohistochemical and in situ hybridization studies on the distribution of neurons expressing ChAT in the human central nervous system. Neurons with both immunoreactivity and in situ hybridization signals of ChAT are observed in the basal forebrain (diagonal band of Broca and nucleus basalis of Meynert), striatum (caudate nucleus, putamen and nucleus accumbens), cerebral cortex, mesopontine tegmental nuclei (pedunculopontine tegmental nucleus, laterodorsal tegmental nucleus and parabigeminal nucleus), cranial motor nuclei and spinal motor neurons. The cerebral cortex displays regional and laminal differences in the distribution of neurons with ChAT. The medial septal nucleus and medial habenular nucleus contain immunoreactive neurons for ChAT, which are devoid of ChAT mRNA signals. This is probably because there is a small number of cholinergic neurons with a low level of ChAT gene expression in these nuclei of human. Possible connections and speculated functions of these neurons are briefly summarized.     

Acetylcholinesterase in neurons of the rat cerebral cortex.

AChE-containing neurons have been demonstrated by electron-microscopical histochemistry in the neocortex of the rat. These cells are mainly located in layer VI. AChE activity is seen in the cisternae of the RER, in subsurface cisternae and in the dendritic membranes.     

Ultrastructure of cellular features permitting the regulation of human cerebral cortex microcirculation]

Microglia-like cells and endothelial cells may influence capillary blood output. 1) Microglia-like cells are sometimes interposed between two endothelial processes with which they are nexus-linked. In this position, they protude in vascular lumen which is considerably reduced. 2) Endothelial cells present no contractile filaments but their nucleus and surrounding cytoplasm may protude in vascular lumen, constituting a "coussinet-like" structure. Thus, regulation by specialized structures observed by Legait in brain arteries seems to occur even in the smallest ramifications of brain cortical vessels.     

Effect of vascular factors and aging on the ultrastructure of neurons of the human cerebral cortex

Neuronal ultrastructure of the frontal and temporal cerebral cortex has been studied in persons 36-, 39-, 50-, 70-year-old, died from the ischemic heart disease and 73-, 83-year-old, whose deaths are not connected with vascular pathology. The neurons can be divided into several groups, depending on osmiophilic degree of their nucleus and cytoplasm: I--electron-light, II--electron-opaque, III--with dark nucleus and light cytoplasm and IV--with light nucleus and dark cytoplasm. The protein-synthesizing apparatus (PSA) is subjected to the earliest and most essential disorders. Its changes in the I group of neurons at the age of 36-50 years are mainly of compensatory-adaptive character, while at the age of 73 and 83 years the dystrophic changes of the PSA result in hollowness of the cell, that evidently makes the base of the cell ageing mechanism. Presence of electron opaque neurons is not a sign of ageing, and depends on various pathology, in the given case on the ischemic heart disease, that causes certain vascular disorders in the brain. Variability of the ultrastructures of the electron opaque neurons and essential changes of some part of them, observed in the brain of the 72-year-old man confirm that the vascular factor is an important one in pathology of neurons. Dependence of lipofuscin appearance in neurons on the manifestation degree of the pathological process and ageing in them is discussed.     

Localization of ATPase in the cerebral cortex and its role in the functional activity of neurons]

By analogy of defensive conditioned reflex formation in rats using a cytochemical method, dependency of localization and concentration of the product of ATP-ase activity on neuronal and synaptic functional activity has been demonstrated. It corresponds to the notion that only a part of the cortical cells are simultaneously at the state of structural-functional activity. The experimental data demonstrate that the CNS excitation in the animals during the process of learning is connected with increasing ATP-ase activity in ultrastructures of the nucleolus, pericaryon and synapses of some neurons participating in the formation of trace processes in the brain.     

The effects of sleep on neurons in isolated cerebral cortex.

Slabs of cat parietal cortex with some 2 mm of underlying white matter were surgically isolated from the rest of the nervous system, without interference with the superficial blood supply. Wire micro-recording electrodes were inserted into the isolated cortex; bone, muscle and skin wounds were repaired and the animal allowed to recover from anaesthesia. The adequacy of surgical isolation was examined histologically 8--12 weeks after operation. Only one of the six preparations reported here showed surviving neural connections with the rest of the brain. Soon after operation, spontaneous bursts of neural activity appeared within the isolated area. These became more frequent until neural discharge was continuous but irregular. Our records were made from this time onwards. The interval distributions obtained from neurons within the isolated area did not differ significantly from log-normal curves. When the unrestrained animal fell asleep, there was no significant alteration in the model interval or geometric standard deviation of interval distributions recorded from cells in isolated cortex. The interval distributions of neurons in isolated cerebral cortex resembled those of neurons in the intact cortex of an alarmed animal. It is concluded that the reduction of modal interval that is shown by neurons in intact cortex when an animal falls asleep is probably due to the neural influence of infracortical structures.     

Directed differentiation of human pluripotent stem cells to cerebral cortex neurons and neural networks

Efficient derivation of human cerebral neocortical neural stem cells (NSCs) and functional neurons from pluripotent stem cells (PSCs) facilitates functional studies of human cerebral cortex development, disease modeling and drug discovery. Here we provide a detailed protocol for directing the differentiation of human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) to all classes of cortical projection neurons. We demonstrate an 80-d, three-stage process that recapitulates cortical development, in which human PSCs (hPSCs) first differentiate to cortical stem and progenitor cells that then generate cortical projection neurons in a stereotypical temporal order before maturing to actively fire action potentials, undergo synaptogenesis and form neural circuits in vitro. Methods to characterize cortical neuron identity and synapse formation are described.     

Glutamate dehydrogenase activity in motor cortex neurons during restoration of disrupted visual function]

The recovery of the visual function of rats throughout two weeks after deprivation period (keeping animals in dark chambers for 8 weeks from their birth) leads to a significant normalization of the activity level of glutomatedehydrogenase in the neurones of the III and V layers of the motor cortex. The changes of the enzyme activity in the neurones are accompanied by a diminution of their sizes. The obtained data together with the results of the previous studies (Busnuk, 1976), suggest that the elimination of the visual impulse activity in the early ontogenesis exerts a specific and reversible influence on the morpho-chemical differentiation of neurones both in the visual and in the motor cortical areas. The functional factors determining the direction of changes in the studied parameters of cortical neurones during deprivation and in the rate of their normalization during recovery of the visual function are discussed.     

The transsynaptic regulation of the septal-hippocampal cholinergic neurons

There is not yet a complete understanding of the functional interactions among various septal nuclei which regulate hippocampal function. Nevertheless, much has been learned histologically and biochemically about the major connections of the distinct areas of the septal complex and the chemical character of some of these pathways. The cholinergic septal-hippocampal pathway serves as a well defined link between these two important structures of the limbic system. Acetylcholine turnover rates in the hippocampus have been shown to increase or decrease proportionally to the activity of the cholinergic neurons originating in the septum. Moreover, these turnover rates have been shown to be modulated by intraseptal injections of agonists or antagonists of various neurotransmitters or neuromodulators which are stored in various cell groups located in the septum. By coupling this biochemical approach with techniques to study the receptor organization, greater detail concerning the transmitter and cotransmitter interactions among the various neuromodulators can be obtained.     

Transport of L-carnitine in isolated cerebral cortex neurons.

The accumulation of carnitine was measured in cerebral cortex neurons isolated from adult rat brain. This process was found to be lowered by 40% after preincubation with ouabain and with SH-group reagents (N-ethylmaleimide and mersalyl). The initial velocity of carnitine transport was found to be inhibited by 4-aminobutyrate (GABA) in a competitive way (Ki = 20.9 +/- 2.4 mM). However, of various inhibitors of GABA transporters, only nipecotic acid and very high concentrations of 1-[2-([(diphenylmethylene)amino]oxy)ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride (NO-711) acid decreased carnitine accumulation while betaine, taurine and beta-alanine had no effect. The GABA transporters expressed in Xenopus laevis oocytes did not transport carnitine. Moreover, carnitine was not observed to diminish the accumulation of GABA in cerebral cortex neurons, which further excluded a possible involvement of the GABA transporter GAT1 in the process of carnitine accumulation, despite the expression of this protein in the cells under study. The absence of carnitine transporter OCTN2 in rat cerebral cortex neurons (K. A. Na?ecz, D. Dymna, J. E. Mroczkowska, A. Bro?r, S. Bro?r, M. J. Na?ecz and R. Cecchelli, unpublished results), together with the insensitivity of carnitine accumulation towards betaines, implies that a novel transporting protein is present in these cells.     

Transformation of vestibular signals by neurons of the cat cerebral cortex

Unit activity of cortical vestibular projections in response to trapezoidal and sinusoidal rotation of the animal on a horizontal plane was investigated in unanesthetized immobilized cats. Neurons with tonic response representing non-specific cortical activation were distinguished from those responding phasically and displaying directional sensitivity, depending on which type of activity was elicited. It was shown that a complete picture of changes in the angular velocity of rotation can only be gained from the entire range of responses observed in direction-specific neurons. Transformation of vestibular signals by cortical neurons showed quasilinear properties, although linearity was maintained in the limited angular velocity range of 0 to 30–50 deg×sec^–1.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR. Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 5, 1987, pp. 613–622, September–October, 1987.