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PubMed1983

[Electrical connection between 2 bursting neurons in Helix pomatia].

In the parietal ganglion of some Helix pomatia snails two neurons with fast bursting activity were found instead of a single RPa1 neuron. Simultaneous recording of the activity from these neurons showed an almost complete synchronization of the membrane potential waves. Direct de- or hyperpolarization of the membrane of one of the neurons (either) resulted in de- or hyperpolarization of the other. Synchronous spontaneous modulation of electrical activity of the two neurons was also observed as well as synchronous modulation caused by the addition of a modulating factor to the external solution. Electrical coupling between these neurons is postulated.

Action Potentials↗
PubMedDate not supplied

[The structural organization of the synaptic connections of the motor neurons in the mammalian spinal cord].

Peculiarities of the synaptic organization of the motor neurons of the spinal cord of the rodents (rats), predators (cats), primates (Macaca rhesus monkeys) were studied in the early stages of the postnatal ontogenesis and in the adult animals. The motor nucleus region of the lumbar thickening was studied both in normal animals and after the experimental destruction of cerebral nuclei. A new view on the structural-spatial organization of the motor neuron dendrites, the branches of which are highly specialized in the perception of the efferent inputs, is gained. By means of light and electron microscope, the types of synapses, composed of the terminations of the fibers of three major supraspinal systems of the motor control (reticulo-, vestibulo- and rubro-spinal) were studied. Lower mammals are found to have electrotonic and mixed electro-chemical synapses, along with the chemical ones. The fundamental regularities of the distribution of the synaptic inputs of different modality on the somato-dendritic membranes of the motor neurons, specifically the grouping of the chemical synapses and definitive regions of the membrane and those of electrical ones in one microzone were stated. The functional significance of the different types of synapses is discussed with the reference to modern neurology data.

Animals↗
PubMed1998

Identification and connections of inspiratory premotor neurons in songbirds and budgerigar.

Recordings of extracellular unit activity in the ventrolateral medulla and of electromyographic activity in either the M. scalenus, a principal inspiratory muscle, or the abdominal expiratory muscles, were used to identify inspiratory related (IR) neurons. IR neurons extended from levels caudal to the obex through the caudal level of the descending vestibular nucleus. This distribution was found to correspond to that of a subset of cells retrogradely labeled from injections of neuronal tracers into the upper thoracic spinal cord, where motoneurons innervating the M. scalenus were located by retrograde transport. Injections of biotinylated dextran amine at the recording sites resulted in projections to the spinal cord and brainstem. Bulbospinal axons traveled in the lateral funiculus, predominantly contralaterally, and terminated in relation to the dendrites and cell bodies of motoneurons innervating the M. scalenus. Brainstem nuclei receiving projections from injections at IR loci included the retroambigualis, tracheosyringeal motor nucleus, ventrolateral nucleus of the rostral medulla, infraolivaris superior, ventrolateral parabrachial nucleus, and the dorsomedial nucleus of the intercollicular complex. In the finches, there were also bilateral projections to nucleus uvaeformis of the posterior thalamus. The spinal and brainstem projections are similar to those found in pigeon (Reinke and Wild, [1997] J. Comp. Neurol. 379:347-362), and probably mediate the intricate coordination of the vocal (syringeal) and respiratory systems for the control of vocalization. The distribution of IR neurons in birds is similar to that of the rostral ventral respiratory group (rVRG) in mammals.

Animals↗
PubMed1998

Functional streams and local connections of layer 4C neurons in primary visual cortex of the macaque monkey.

The primate visual system is composed of multiple, functionally specialized cortical areas. The functional diversity among areas is thought to reflect different contributions from early parallel visual pathways to the area V1 neurons providing input to "higher" cortical areas. The M pathway is believed to provide information about motion and contrast, via layer 4B of V1, to dorsal visual areas. The P pathway is believed to provide information about shape and color, via layer 2/3 of V1, to ventral visual areas, with specialized contributions from cytochrome-oxidase (CO) blob versus interblob neurons. However, the detailed anatomical relationships between the M and P pathways and the neurons in V1 that provide input to higher extrastriate cortical areas are poorly understood. To study these relationships, spiny stellate neurons in the M- and P-recipient layers of V1, 4Calpha and 4Cbeta, respectively, were intracellularly labeled, and their axonal and dendritic arbors were reconstructed. We find that neurons with dendrites in upper layer 4Calpha project axons to layer 4B and CO blobs in layer 2/3, thus relaying M input to these regions. Other neurons in lower layer 4Calpha provide M input to interblobs. These cells have either (1) dendrites restricted to lower layer 4Calpha and axons specifically targeting layer 2/3 interblobs, or (2) dendrites in lower 4Calpha and 4Cbeta and axons targeting blobs and interblobs. P-recipient layer 4Cbeta neurons have dense axonal arbors in both blobs and interblobs but not layer 4B. Quantitative analyses reveal that 4Calpha cells provide approximately five times more synapses than 4Cbeta cells to layer 4B, whereas 4Cbeta cells provide five times more synapses than 4Calpha cells to layer 2/3. These observations imply that M input is dominant in layer 4B. In layer 2/3, both blobs and interblobs receive M and P input, but the P input is dominant, and M input to interblobs derives exclusively from a subpopulation of M afferents that targets lower 4Calpha, not from afferents targeting only upper 4Calpha (cf. Blasdel and Lund, 1983). We speculate that the M and P pathways to interblobs are "X-like" linear systems, whereas blobs also receive nonlinear "Y-like" M input.

Animals↗
PubMed1976

[Postactivation inhibition of processes in interneurons transmitting the activity of lateral "descending" systems].

After-discharge depression of excitability is found in the interneurons specialized on transmission of activities from "lateral" descending systems. Many of these cells are propriospinal units sending axons to the lateral funicle (LF). Anti- und orthodromic spike potentials in these cells are followed by significant hyperpolarization. In some cells post-activation depression increased with a rise in intensity of LF stimulation that evoked antidromic discharge; inhibitory post-synaptic potentials were recorded in several units after LF stimulation subthreshold for evoking such discharges. Existance of inhibitory synaptic connections between neurons of the investigated group similar to recurrent connections in the motoneuronal pools is supposed.

Action Potentials↗
PubMed1999

Corticocortical associative neurons expressing latexin: specific cortical connectivity formed in vivo and in vitro.

Latexin, a carboxypeptidase A inhibitor, is expressed in a subset of neurons in the infragranular layers of the lateral cortex in the rat. We here show that latexin-expressing neurons exhibit ultrastructural features common to cortical pyramidal neurons. We show in combined retrograde tracing and immunofluorescent experiments that latexin-expressing neurons contribute to specific corticocortical pathways. Thus, injections of the retrograde tracer fluorogold into either the primary somatosensory (SI) or the primary motor (MI) cortical area labeled many latexin-expressing neurons in the infragranular layers of the secondary somatosensory (SII) and visceral sensory (Vi) areas. In contrast, tracer injections involving the thalamus, striatum, or contralateral SII and Vi exclusively labeled latexin-nonexpressing neurons in both the SII and Vi. Finally, we show that the correct corticocortical projections can be formed in organotypic slice cultures in vitro from latexin-expressing neurons: when slices of developing SII were cocultured with those from the SI and the thalamus, latexin-immunoreactive neurons in the SII projected preferentially to their normal SI target. The specific connectivity formed in vivo and in vitro by this molecularly distinct neuronal population reveals its characteristic manner of cortical organization and provides a unique model system to analyze mechanisms underlying the formation of precise corticocortical pathways.

Age Factors↗
PubMed1996

Adaptive changes in the somatotopic properties of individual thalamic neurons immediately following microlesions in connected regions of the nucleus cuneatus.

We examined the ability of thalamic neurons in the ventrobasal complex to show adaptive changes in receptive field properties following the loss of projections from the nucleus cuneatus. Thalamic responses to air jet stimulation were tested at multiple peripheral sites before and after making discrete microlesions in topographically-matched regions of the nucleus cuneatus. Prior to making a lesion, crosscorrelation analysis and orthodromic microstimulation were used to confirm the source of cuneate neurons projecting to the thalamic recording site. A total of 69 thalamic neurons were recorded from 29 rats. Following placement of a microlesion (100-200 microns diameter) in the nucleus cuneatus, 34 thalamic neurons did not show significant changes in stimulus-induced responses, possibly because the lesion was too small or because critical sites in the receptive field were not tested. The remaining 35 neurons were affected by cuneate microlesions, but the change in responsiveness varied according to stimulation site. When the most responsive site in the receptive field was examined, 24 neurons exhibited significant decreases and three neurons showed significant increases in responsiveness. Cuneate microlesions produced decreases at moderately responsive sites, but the reduction in response magnitude was smaller than at the most responsive site. When responses near the receptive field boundary were examined, 11 neurons displayed significant increases and only four neurons showed significant decreases. For two neurons without well-defined receptive field boundaries, cuneate microlesions caused new excitatory responses to emerge from sites that had formerly caused a slight inhibition of spontaneous activity. In all cases of increased responsiveness, the changes appeared on only one side of a neuron's receptive field. This asymmetry may account for the fact that the probability of detecting receptive field expansion increased from 27% (six of 22 experiments) to 71% (five of seven experiments) when the number of stimulation sites located throughout the receptive field was increased. These results indicate that the receptive field structure of individual neurons shows adaptive properties immediately after loss of the predominant ascending inputs.

Adaptation, Physiological↗
PubMedDate not supplied

Lateral inhibition as a possible mechanism for evaluating stimulus intensity.

This article presents results obtained by simulation modeling of neural networks which show that lateral inhibitory connections between neurons can in principle, when the parameters of these connections are selected appropriately, support the existence in the CNS of detectors for the intensity of an acting signal. A condition for the operation of the proposed detection mechanism is the physiologically demonstrated fact of an inverse proportional relationship between the latency of neuron responses to a threshold stimulus and the intensity of this stimulus.

Computer Simulation↗
PubMed2004

Dopamine-induced dispersion of correlations between action potentials in networks of cortical neurons.

The involvement of dopamine in the process of learning, at the cellular and behavioral levels, has been studied extensively. Evidently, dopamine is released from midbrain nuclei neurons on exposure to salient unpredicted stimuli and binds to neurons of cortical and subcortical structures, where its neuromodulatory effects are exerted. The neuromodulatory effects of dopamine at the synaptic and cellular levels are very rich, but it is difficult to extrapolate from these elementary levels what their effect might be at the behaviorally relevant level of neuronal ensembles. Using multi-site recordings from networks of cortical neurons developing ex vivo, we studied the effects of dopamine on connectivity within neuronal ensembles. We found that dopamine disperses correlations between individual neuronal activities while preserving the global distribution of correlations at the network level. Using selective D(1) and D(2) modulators, we show that both receptor types are contributing to dopamine-induced dispersion. Our results indicate that, at the neuronal ensemble level, dopamine acts to enhance changes in network connectivity rather than stabilize such connections.

Action Potentials↗
PubMed1997

[Behaviour after transplantation of brain cells into monkey models of Parkinson's disease].

OBJECTIVE: To observe the improved degree of pathogenic behaviour in monkey models of Parkinson's disease after transplantation of substantia nigra cells of human fetus. METHOD: 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was used to prepare monkey models of hemiparkinson's disease, i.e., early substantia nigra cells of human fetus were stereotaxically transplanted into PD monkey's behaviour for six months, using immuno-electromicroscopy to prove the transplanted survived neuron. RESULTS: After transplantation, the model monkey's motion slow and muscle hypertonia was apparently improved. Limb tremor almost disappeared, Right spontaneous rotation behavior relieved. Rotating frequency caused by APO became less than before transplanytation, and its effect could last a year. Under the immunoelectromicroscope, we observed that transplanted tyrosine hydroxylase positive neuron was connected with the host brain cells in synapse. CONCLUSION: Substantia nigra neuron transplanted into the PD monkey brain can establish synaptic connection with the host nervous cells. Pathogenic symptoms are improved and the effect may remain for a longer time.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1990

Global processing of visual stimuli in a neural network of coupled oscillators.

An oscillator neural network model is presented that is capable of processing local and global attributes of sensory input. Local features in the input are encoded in the average firing rate of the neurons while the relationships between these features can modulate the temporal structure of the neuronal output. Neurons that share the same receptive field interact via relatively strong feedback connections, while neurons with different fields interact via specific, relatively weak connections. This pattern of connectivity mimics that of primary visual cortex. The model is studied in the context of processing visual stimuli that are coded for orientation. We compare our theoretical results with recent experimental evidence on coherent oscillatory activity in the cat visual cortex. The computational capabilities of the model for performing discrimination and segmentation tasks are demonstrated.

Animals↗
PubMed2000

Effects of delay on the type and velocity of travelling pulses in neuronal networks with spatially decaying connectivity.

We study a one-dimensional model of integrate-and-fire neurons that are allowed to fire only one spike, and are coupled by excitatory synapses with delay. At small delay values, this model describes a disinhibited cortical slice. At large delay values, the model is a reduction of a model of thalamic networks composed of excitatory and inhibitory neurons, in which the excitatory neurons show the post-inhibitory rebound mechanism. The velocity and stability of propagating continuous pulses are calculated analytically. Two pulses with different velocities exist if the synaptic coupling is larger than a minimal value; the pulse with the lower velocity is always unstable. Above a certain critical value of the constant delay, continuous pulses lose stability via a Hopf bifurcation, and lurching pulses emerge. The parameter regime for which lurching occurs is strongly affected by the synaptic footprint (connectivity) shape. A bistable regime, in which both continuous and lurching pulses can propagate. may occur with square or Gaussian footprint shapes but not with an exponential footprint shape. A perturbation calculation is used in order to calculate the spatial lurching period and the velocity of lurching pulses at large delay values. For strong synaptic coupling, the velocity of the lurching pulse is governed by the tail of the synaptic footprint shape. Moreover, the velocities of continuous and lurching pulses have the same functional dependencies on the strength of the synaptic coupling strength gsyn: they increase logarithmically with gsyn for an exponential footprint shape, they scale like (In gsyn)1/2 for a Gaussian footprint shape, and they are bounded for a square footprint shape or any shape with a finite support. We find analytically how the axonal propagation velocity reduces the velocity of continuous pulses; it does not affect the critical delay. We conclude that the differences in velocity and shape between the front of thalamic spindle waves in vitro and cortical paroxysmal discharges stem from their different effective delays.

Algorithms↗