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PubMed2004

Connectivities and synchronous firing in cortical neuronal networks.

Network connectivities ((-)k) of cortical neural cultures are studied by synchronized firing and determined from measured correlations between fluorescence intensities of firing neurons. The bursting frequency (f) during synchronized firing of the networks is found to be an increasing function of (-)k. With f taken to be proportional to (-)k, a simple random model with a (-)k dependent connection probability p((-)k).has been constructed to explain our experimental findings successfully.

Action Potentials↗
PubMed1984

[Ultrastructural changes in the neurons and interneuronal connections of the lateral hypothalamic area in rats at different times of food deprivation].

Changes in bodies of neurons, their processes and synapses in the lateral hypothalamic area (LHA) in rats at various time (1, 3, 5 and 7 days) of food deprivation have been studied electron microscopically. The changes in the posterior part of the LHA are the first and in the middle part of the LHA are the last to appear. The number of altered bodies of the neurons, their processes, synapses and severity of their injury during all the time of fasting is the greatest in the posterior and the least in the middle part of the LHA. The character of the ultrastructural changes is unitypical everywhere. Dendrites, especially those of middle and large size are the first to be injured. Their changes immediately acquire destructive character (vacuolization of dendroplasm, appearance of complex membranous bodies, swelling and destruction od microtubules and neurofilaments). One of peculiar features of the destructive changes of the neuronal processes and synapses is invagination of adjoining areas of axons and synapses into the dendrite. In the bodies of the neurons the changes appear later than in the dendrites and at first they are of functional character and only beginning from the 5th day of fasting certain signs of destructive disorders are noted. With increasing time of fasting, the injury is growing more severe and a greater and a greater number of the neuronal bodies, processes and synapses are involved into the pathological process.

Animals↗
PubMed2005

Morphology, electrophysiology and functional input connectivity of pyramidal neurons characterizes a genuine layer va in the primary somatosensory cortex.

Cortical layer V classically has been subdivided into sublayers Va and Vb on cytoarchitectonic grounds. In the analysis of cortical microcircuits, however, layer Va has largely been ignored. The purpose of this study was to investigate pyramidal neurons of layer Va in view of their potential role in integrating information from lemniscal and paralemniscal sources. For this we combined detailed electrophysiological and morphological characterization with mapping of intracortical functional connectivity by caged glutamate photolysis in layer Va of rat barrel cortex in vitro. Electrophysiological characterization revealed pyramidal cells of the regular spiking as well as the intrinsically burst firing type. However, all layer Va pyramidal neurons displayed uniform morphological properties and comparable functional input connectivity patterns. They received most of their excitatory and inhibitory inputs from intracolumnar sources, especially from layer Va itself, but also from layer IV. Those two layers were also the main origin for transcolumnar excitatory inputs. Layer Va pyramidal neurons thus may predominantly integrate information intralaminarly as well as from layer IV. The functional connectivity maps clearly distinguish layer Va from layer Vb pyramidal cells, and suggest that layer Va plays a unique role in intracortical processing of sensory information.

Animals↗
PubMed2000

The role of putative glutamatergic neurons and their connections in the locomotor central pattern generator of the mollusk, Clione limacina.

In the pteropod mollusk Clione limacina, locomotor rhythm is produced by the central pattern generator (CPG), due mainly to the activity of interneurons of groups 7 (active in the phase of the dorsal flexion of the wings) and 8 (active in the phase of the ventral flexion). Each of these groups excites the neurons active in the same phase of the locomotor cycle, and inhibits the neurons of the opposite phase. In this work, the nature of connections formed by group 7 interneurons was studied. Riluzole (2-amino-6-trifluoro-methoxybenzothiazole), which is known to inhibit the presynaptic release of glutamate, suppressed the action of the type 7 interneurons onto the follower neurons of the same and of the antagonistic phase of the locomotor cycle. The main pattern of rhythmic activity of CPG with alternation of two phases could be maintained after suppression of inhibitory connections from group 7 interneurons to antagonistic neurons. This suggests redundancy of the mechanisms controlling swimming rhythm generation, which ensures the reliable operation of the system.

Animals↗
PubMedDate not supplied

[Effect of GABA on a temporary connection in a neuronal population of the sensorimotor cortex in rabbits].

Evoked activity of sensorimotor cortical neurones in response to stimulation of the pyramidal tract, medial lemniscus and reticular nucleus of the midbrain tegmentum; driving reaction of cortical neurones at stimulation of these brain structures of growing frequency, and conditioned reflexes elaborated by combination of direct stimulation of the sensorimotor cortex and electrocutaneous stimulation were studied in awake nonimmobilized rabbits. Application to the cortex of GABA solutions of low concentration (less than or equal to 1%) emphasizes the evoked neuronal responses, facilitates the appearance of driving reaction and contributes to the manifestation of the temporary connection. Application of GABA solutions of higher concentration (greater than 2%) leads to opposite effects. Positive correlation is found between electrical and behavioural phenomena. The described experimental approach may be used for analysis of various types of influences on temporary connection formation.

Action Potentials↗
PubMed1983

The effects of stimuli on the activity and functional connectivity of local neuronal groups in the cat auditory cortex.

Simultaneous extracellular recordings from one electrode of 'local' groups of 3-6 neurons were obtained from the auditory cortex of unanesthetized, paralyzed cats. The activity and functional connectivity of local microenvironments were examined under various auditory stimuli. Single cell response patterns were examined using peri-stimulus (PST) histograms and functional connectivity among neighboring cells by the cross renewal density (CRD) histograms. Analysis of the PST histograms suggested that a high percentage of single cells demonstrated different response patterns to different stimuli. Analysis of the CRD histograms suggested, on the one hand, that only small numbers of neighboring cells behaved as if there were direct connections from one cell to another, and that these direct connections appeared to be excitatory. On the other hand, many cell pairs shared input from shared sources which lay outside the local groups. The majority of functional connections were altered by at least one of the stimuli delivered, thus demonstrating the system's plasticity. It is suggested that long-term gates at the synaptic level are responsible for this phenomenon.

Action Potentials↗
PubMedDate not supplied

[A statistical analysis of the functional connections between the neurons of the visual and motor cortex in different forms of conditioned-reflex behavior].

In experiments on cats with elaboration of delayed alimentary operant reflexes to light organization was studied of interneuronal cortical connections. By means of cross-correlation analysis the dynamics of intra- and interstructural neuronal network was revealed at the level of cortical projections (visual and motor) of cats brain zones at three forms of behaviour: CR realization, in intersignal period with the presence and absence of operant movements. Depending on the forms of behaviour, predominance of "informational" or "motivational" interneuronal connections was observed.

Animals↗
PubMed1995

Formation of connections between cultured identified neurones from the pleural ganglion of the pteropod mollusc Clione limacina.

A cluster of electrically interconnected neurosecretory cells (the 'white cells') involved in the control of reproductive behavior was identified in the right pleural ganglion of the marine mollusc, Clione limacina. Pleural ganglia also contain large neurons (PL1 and PL2) having no connections with each other and with the white cells. Most isolated white cells put into the simple unconditioned medium (50% L-15) adhered to the bottom of uncoated dishes and demonstrated neurite outgrowth for 7-10 days. If growing processes overlapped, the white cells formed electrical connections with each other, but they formed no connections with the PL1 and PL2 neurons. It is concluded that in the case which was under study cellular intrinsic properties were sufficient for the formation of 'correct' connections between neurones.

Animals↗
PubMed1983

Interactions between cat striate cortex neurons.

A series of simultaneous recordings from several striate cortex neurons were made in paralyzed, anesthetized cats. Recordings were obtained with one or two bundles of extra fine wires and originated from one and two cortical orientation columns. Standard PST histograms and, in some cases, response planes were used to analyse the neuronal receptive fields. Functional connectivity between neurons was assessed by cross-correlation of their spike trains. It was found that 61% of neuronal pairs found within a column shared the same input, either excitatory or inhibitory, Even if neurons in a pair belonged to two different columns separated by 1mm lateral distance, 40% of pairs still exhibited shared input coordination. This type of coordination could also encompass all combinations of simple and complex fields in the pair. Direct connections between neurons were found almost exclusively within columns: excitatory connections were found in 20% of cases and inhibitory in 8%. Direct connections were often accompanied by the other types of interactions. Only one example of excitatory and one of inhibitory direct connections were found between columns. In both cases preferred orientations were almost identical.

Animals↗
PubMed1984

Stability of new electrical connections between adult Helisoma neurons is influenced by preexisting neuronal interactions.

The factors responsible for the selective stability of new electrical connections between regenerating, adult Helisoma neurons (5, 6) were examined. In particular the alternative hypotheses that the normal reduction in strength of a specific connection is dependent on the formation of a new stable connection or the maintenance of a preexisting connection were tested. To this end, single neurons were eliminated either by microdissection or photoinactivation. Formation of stable 5-5 [i.e., left neuron 5 (L5) to right neuron 5 (R5)] coupling was prevented by removal of a single neuron 5 soma. The time course of the normally transient neuron 5-4 connection in these ganglia, however, was the same as that of control preparations. Thus the 5-4 connection is transient even when stable 5-5 coupling is unable to develop. After removal of a single neuron 4 soma, however, the 5-4 connection was stabilized. This was despite the concurrent development of stable 5-5 coupling in these preparations. Similar results were obtained when neurons were eliminated by photoinactivation, a procedure that kills axonal processes in addition to the neuronal cell body. Morphological examination of untreated neurons by Lucifer Yellow CH stain showed that neurite outgrowth was not prevented by either of the techniques employed to eliminate single neurons. It is concluded that the development of the new, stable 5-5 electrical connection does not influence the transient nature of the 5-4 connection. The presence of both neurons 4, however, which have a preexisting connection, is required for reduction of 5-4 coupling. Thus preexisting neurons and/or their connections appear to play a role in the stability of new connections in this adult nervous system.

Animals↗
PubMed1997

Two distinct populations of tectal neurons have unique connections within the retinotectorotundal pathway of the pigeon (Columba livia).

The tectofugal pathway is a massive ascending polysynaptic pathway from the tectum to the thalamus and then to the telencephalon. In birds, the initial component of this pathway is known as the tectorotundal pathway; in mammals, it is known as the tectopulvinar pathway. The avian tectorotundal pathway is highly developed; thus, it provides a particularly appropriate model for exploring the fundamental properties of this system in all amniotes. To further define the connectivity of the tectorotundal projections of the tectofugal pathway, we injected cholera toxin B fragment into various rotundal divisions, the tectobulbar projection, and the ventral supraoptic decussation of the pigeon. We found intense bilateral retrograde labeling of neurons that stratified within layer 13 and, in certain cases, granular staining in layer 5b of the optic tectum. Based on these results, we propose that there are two distinct types of layer 13 neurons that project to the rotundus: 1) type I neurons, which are found in the outer sublamina of layer 13 (closer to layer 12) and which project to the anterior and centralis rotundal divisions, and 2) type II neurons, which are found in the inner sublamina of layer 13 (closer to layer 14) and which project to the posterior and triangularis rotundal divisions. Only the labeling of type I neurons produced the granular dendritic staining in layer 5b. An additional type of tectal neuron was also found that projected to the tectobulbar system. We then injected Phaseolus vulgaris-leucoagglutinin in the optic tract and found that the retinal axons terminating within tectal layer 5b formed narrow radial arbors (7-10 microm in diameter) that were confined to layer 5b. Based on these results, we propose that these axons are derived from a population of small retinal ganglion cells (4.5-6.0 microm in diameter) that terminate on the distal dendrites of type I neurons. This study strongly indicated the presence of a major bilateral oligosynaptic retinotectorotundal pathway arising from small retinal ganglion cells projecting to the rotundus with only a single intervening tectal neuron, the proposed type I neuron. We suggest that a similar organization of retinotectopulvinar connections exist in reptiles and in many mammals.

Afferent Pathways↗
PubMed2005

Olfactory inputs to hypothalamic neurons controlling reproduction and fertility.

In order to gain insight into sensory processing modulating reproductive behavioral and endocrine changes, we have aimed at identifying afferent pathways to neurons synthesizing luteinizing hormone-releasing hormone (LHRH, also known as gonadotropin-releasing hormone [GnRH]), a key neurohormone of reproduction. Injection of conditional pseudorabies virus into the brain of an LHRH::CRE mouse line led to the identification of neuronal networks connected to LHRH neurons. Remarkably, and in contrast to established notions on the nature of LHRH neuronal inputs, our data identify major olfactory projection pathways originating from a discrete population of olfactory sensory neurons but fail to document any synaptic connectivity with the vomeronasal system. Accordingly, chemosensory modulation of LHRH neuronal activity and mating behavior are dramatically impaired in absence of olfactory function, while they appear unaffected in mouse mutants lacking vomeronasal signaling. Further visualization of afferents to LHRH neurons across the brain offers a unique opportunity to uncover complex polysynaptic circuits modulating reproduction and fertility.

Animals↗
PubMed1985

Medullary respiratory-related neurons with axonal connections to rostral pons and their function in termination of inspiration.

In urethane-anaesthetized, paralyzed and artificially ventilated rabbits, medullary respiration-related neurons (RRU) were classified according to the phase relation of their burst discharge to phrenic nerve activity. Phase-bound inspiratory (I) or expiratory (E) neurons were discriminated from phase-spanning expiratory-inspiratory (EI) or inspiratory-expiratory (IE) units. Mechanisms of termination of inspiration by electrical stimulation of rostral pontine nuclei (Nc. parabrachialis medialis; Lc. coeruleus) were examined firstly to demonstrate whether RRU receive descending excitatory and inhibitory afferents as well as ascending efferents and secondly to analyse the time course of the neuronal pathways involved. Of 120 RRU, 38 neurons were demonstrated to receive pontine afferents. About 33% of all E neurons became orthodromically excited during rostral pons stimulation whereas 18.2% of all I cells became orthodromically inhibited. Some RRU were shown to project up to the rostral pons. 50% of these were of the phase-spanning IE type. The onset of inspiratory inhibition induced by rostral pons stimulation occurred 3.4 ms after the onset of single electrical pulse stimulation. Based on these results a neuronal model for a pontine mechanism terminating inspiration is proposed.

Animals↗
PubMed1997

Distribution and connections of inspiratory premotor neurons in the brainstem of the pigeon (Columba livia).

We have recorded extracellular, inspiratory-related (IR) unit activity in the medulla at locations corresponding to those of neurons retrogradely labeled by injections of retrograde tracers in the lower brachial and upper thoracic spinal cord, injections that covered cell bodies and dendrites of motoneurons innervating inspiratory muscles. Bulbospinal neurons were distributed throughout the dorsomedial and ventrolateral medulla, from the spinomedullary junction through about 0.8 mm rostral to the obex. Almost all of the 104 IR units recorded were located in corresponding parts of the ventrolateral medulla, rostral to nucleus retroambigualis, where expiratory related units are found. Injections of biotinylated dextran amine at the recording sites labeled projections both to the spinal cord and to the brainstem. In the lower brachial and upper thoracic spinal cord, bulbospinal axons traveled predominantly in the contralateral dorsolateral funiculus and terminated in close relation to the dendrites of inspiratory motoneurons retrogradely labeled with cholera toxin B-chain. In the brainstem, there were predominantly ipsilateral projections to the nucleus retroambigualis, tracheosyringeal motor nucleus (XIIts), ventrolateral nucleus of the rostral medulla, infraolivary superior nucleus, ventrolateral parabrachial nucleus, and dorsomedial nucleus of the intercollicular complex. In all these nuclei, except XIIts, retrogradely labeled neurons were also found, indicating reciprocity of the connections. These results suggest the possibility of monosynaptic connections between inspiratory premotor neurons and inspiratory motoneurons, which, together with connections of IR neurons with other brainstem respiratory-vocal nuclei, seem likely to mediate the close coordination that exists in birds between the vocal and respiratory systems. The distribution of IR neurons in birds is similar to that of the rostral ventral respiratory group (rVRG) in mammals.

Animals↗
PubMed1997

Transients, metastability, and neuronal dynamics.

This paper is about neuronal dynamics and how their special complexity can be understood in terms of nonlinear dynamics. There are many aspects of neuronal interactions and connectivity that engender the complexity of brain dynamics. In this paper we consider (i) the nature of this complexity and (ii) how it depends on connections between neuronal systems (e.g., neuronal populations or cortical areas). The main conclusion is that simulated neural systems show complex behaviors, reminiscent of neuronal dynamics, when these extrinsic connections are sparse. The patterns of activity that obtain, under these conditions, show a rich form of intermittency with the recurrent and self-limiting expression of stereotyped transient-like dynamics. Despite the fact that these dynamics conform to a single (complex) attractor this metastability gives the illusion of a dynamically changing attractor manifold (i.e., a changing surface upon which the dynamics unfold). This metastability is characterized using a measure that is based on the entropy of the time series' spectral density.

Animals↗