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Results for “Neuronal Connectivity”

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At least 1,585 records · Page 88Linked to original sources
PubMed1986

Computing with neural circuits: a model.

A new conceptual framework and a minimization principle together provide an understanding of computation in model neural circuits. The circuits consist of nonlinear graded-response model neurons organized into networks with effectively symmetric synaptic connections. The neurons represent an approximation to biological neurons in which a simplified set of important computational properties is retained. Complex circuits solving problems similar to those essential in biology can be analyzed and understood without the need to follow the circuit dynamics in detail. Implementation of the model with electronic devices will provide a class of electronic circuits of novel form and function.

Action Potentials↗
PubMed2006

Responses of the rat medullary neurons to central penicillin microinjection.

BACKGROUND: The microinjection of penicillin in the medulla oblongata caused different alterations in the global respiratory output. The purpose of this paper was to study the involvement of impulse activity and the functional relationship of bulbar neurons in mechanisms underlying experimentally induced respiratory arrhythmias. METHODS: Extracellular activity of neurons and diaphragmatic electromyogram activity were recorded and analyzed. RESULTS: Penicillin microinjection increased the mean discharge rate of bulbar neurons and caused the prolongation of discharge of inspiratory neurons. Cross-correlation analysis revealed new excitatory connections between neurons and a high level of positive synchronization of neuronal activity. CONCLUSION: The local blockage of synaptic inhibition by penicillin within respiratory areas leads to drastic changes in the functioning of neuronal elements of the single respiratory network.

Action Potentials↗
PubMed1988

Brain development in the fetus, neonate and infant.

In structural brain development eight interrelated but distinguishable events can be recognized: (1) neuronal induction, (2) neuroblast proliferation, (3) neuronal migration, (4) neuronal selective aggregation, (5) neuronal differentiation and formation of specific patterns of connection, (6) neuronal death, (7) selective synapse elimination and (8) myelination. The basic mechanisms regulating these developmental events are genetically determined but at any stage of development epigenetic and environmental factors modulate the genetic regulation. This paper reviews representative samples of work in animal experiments and knowledge in human fetal brain development by several authors.

Aging↗
PubMed1991

Responses and anatomical connections of peripheral vestibular neurons innervating otolith organs.

The response patterns of the Scarpa's neurons and lateral vestibular nucleus (LVN) neurons that respond to lateral and antero-posterior tilting were investigated using cats. The following observations were made: 1) The Scarpa's neurons that respond to lateral tilting have directional sensitivity physiologically and may innervate the utricular macula; 2) The LVN neurons that respond to lateral tilting are found mostly in the ventral part of the LVN and also have directional sensitivity. They project toward the spinal cord into the lateral vestibulo-spinal tract.

Acoustic Maculae↗
PubMed1990

Fine structural characteristics and synaptic connections of trigeminocerebellar projection neurons in rat trigeminal nucleus oralis.

In order to classify the presynaptic terminals contacting trigeminocerebellar projection neurons (TCPNs) in rat trigeminal nucleus oralis (Vo), electron-microscopic examination of sequential thin sections made from TCPNs located in the border zone (BZ) of Vo, labeled by the retrograde transport of horseradish peroxidase, was undertaken. The use of BZ TCPNs, labeled in Golgi-like fashion so that many of their dendrites and axons were visible, allowed for the determination of the distribution of each bouton type along the soma and dendrites, as well as for the characterization of the morphology and synaptic relations of the labeled axon and its terminals. Three types of axon terminals contacting labeled BZ TCPNs have been recognized, depending upon whether they contain primarily spherical-shaped, agranular synaptic vesicles (S endings); predominantly flattened, agranular synaptic vesicles (F endings); or a population of pleomorphic-shaped, agranular synaptic vesicles (P endings). The S endings represent the majority of axon terminals contacting labeled BZ TCPNs and establish asymmetrical axosomatic and axodendritic synaptic contacts. Many S endings are situated in one of two types of synaptic glomeruli. One type of glomerulus has a large S ending at its core, whereas the other contains a small S ending. Large-S-ending glomeruli include only labeled distal dendrites of BZ TCPNs; small-S-ending glomeruli contain either a labeled soma, proximal dendrite, or distal dendritic shaft. The remaining S endings are extraglomerular, synapsing on distal dendrites. P endings are less frequently encountered and establish intermediate axosomatic and axodendritic synapses. These endings exhibit a generalized distribution along the entire somatodendritic tree. F endings make symmetrical axodendritic synapses with distal dendrites, are only found in glomeruli containing small S endings, and are the least frequently observed ending contacting labeled BZ TCPNs. The majority of axonal endings synapsing on labeled BZ TCPNs are located along distal dendrites, with only a relatively few synapsing terminals situated on proximal dendrites and somata. The axons of labeled BZ TCPNs arise from the cell body and generally give rise to a single short collateral near their points of origin. This collateral remains unbranched and generates several boutons within BZ, while the parent axon acquires a myelin sheath and, without branching further, travels dorsolaterally toward the inferior cerebellar peduncle. The collateral boutons resemble extraglomerular S endings. They contain agranular, spherical-shaped synaptic vesicles and make asymmetrical axodendritic synapses with small-diameter unlabeled dendritic shafts in the BZ neuropil.

Animals↗
PubMedDate not supplied

[Activation of glutamate ionotropic connections of sensorimotor cortex neurons during conditioning].

Changes in conditioned impulse reactions of neurons in sensorimotor cortex were studied during microiontophoretic application of glutamatergic and GABA ergic agonistic and antagonistic drugs. It was shown that ionotropic glutamate receptors (AMPA and NMDA) are activated by a conditioned stimulus. Not only large pyramidal neurons of deep cortical layers but surrounding short-axon inhibitory interneurons are involved in the reaction. It was shown that the activity of pyramidal neurons is under a constant inhibitory control from surrounding interneurons. This inhibition is involved in organization of excitatory cortical responses during conditioning.

2-Amino-5-phosphonovalerate↗
PubMed1991

Regeneration of functional synaptic connections between widely separated neurons in the adult mammalian central nervous system.

The responses to light of retinal ganglion cells with regenerated axons can be recorded from axons teased from peripheral nerve grafts replacing the optic nerve of the adult rat or hamster. These responses resemble those of normal retinal ganglion cells but can no longer be observed several months after grafting, concomitant with ongoing loss of the population of axotomized retinal ganglion cells. Synapses formed with neurons in the superior colliculus by retinal ganglion cell axons regenerated through peripheral nerve grafts mediate both excitatory and inhibitory responses. These experiments demonstrate that when provided with an appropriate milieu for elongation, neurons indigenous to the adult mammalian central nervous system can make functional reconnections with distant targets within the nervous system.

Animals↗
PubMed1989

Age related changes in neuron number in the mouse lateral vestibular nucleus.

The number of large neurons in the lateral vestibular nucleus of the mouse brain decreases in number after 25 months of age, from 488 at 25 months to 298 at 31 months. The number of small neurons in the nucleus remains constant up to 31 months of age. Large neurons accumulate lipofuscin from 25 months and their mean nuclear diameter increases significantly between 25 and 28 months of age. Small neurons contain very little lipofuscin even at 31 months of age and their mean nuclear diameter remains constant between 6 and 31 months. The difference in response of the two types of neurons to ageing may be due to their connections. Large neurons project to spinal motor neurons which decline in number with age and they receive projections from Purkinje cells in the anterior lobe of the cerebellum which also decline in number with age. Small neurons mainly project to the oculogyric nuclei in at least one of which (the abducens) there is no loss of neurons up to 31 months of age.

Aging↗
PubMed1988

Neuronal relationships between the dorsal periaqueductal nucleus and the inferior colliculus (nucleus commissuralis) in the cat. A Golgi study.

Cell types in the dorsal periaqueductal nucleus (PAGd) were studied with the aid of the rapid Golgi method in young cats. The neurons were subdivided into fusiform and stellate types with several varieties of the latter class according to the final destination of their axons. Fusiform neurons send their axons to the neuropil of the Ncom. In turn these neurons receive descending fibres from the nucleus commissuralis (Ncom) which seem to establish axo-dendritic contacts. Also commissural neurons receive contacts from ascending fibres of the PAGd. On the basis of Golgi material it is concluded that particular neuronal types of the PAGd could establish reciprocal connections with neuronal elements of the ventral part of the Ncom. The present study supports the hypothesis that the PAGd could be subdivided into discrete cell groups according to their afferent and efferent projections.

Animals↗
PubMed1987

Induced disruption in the connectivity of an identified neuron in the Drosophila ts mutant shibire.

Temperature-sensitive mutants permit the selective expression of mutant genotype. The Drosophila ts mutant shibire (shi) is paralytic at 30 degrees C; the probable primary effect of the mutation is disruption of membrane recycling. In studying the development of the giant fiber (GF) pathway during the pupal period, we find that shi flies exposed to heat pulse during early pupal states exhibit perturbation in the development of an identified neuron that links giant fibers to motoneurons of indirect flight muscles. Concomitantly, latency in activation of these muscles by the giant fiber pathway is significantly increased. Flies exposed to heat pulse during the late pupal period remain similar to control shi and wildtype flies in giant fiber pathway anatomy and muscle latency. Thus, the critical period of development of an identified neuron in a known motor pathway can be defined by its period of sensitivity to the shi defect. The time-dependent defect is apparently specific for cells that are at a developmental stage that is greatly dependent on membrane recycling processes. Use of this mutant will allow us to investigate the possible role of membrane recycling in development and to establish critical periods of neuronal development.

Animals↗