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Results for “Neural Conduction”

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At least 415 records · Page 23Linked to original sources
PubMed1984

Solitary nucleus neurons transmitting vagal visceral input to the forebrain via a direct pathway in rats.

Electrical stimulation of the hypothalamus in rats anesthetized with chloralose-urethane evoked antidromic responses in 5% of the neurons in the nucleus tractus solitarius (NTS) which responded orthodromically to vagus nerve stimulation. The NTS neurons with such a direct forebrain projection (F-NTS neurons) were distributed mostly in the lateral part of the ipsilateral commissural NTS. Latencies of the antidromic responses ranged from 20 to 75 ms, indicating that the axons of the F-NTS neurons were unmyelinated. Orthodromic responses (latencies, 20 to 80 ms) were observed in 6 of 23 F-NTS neurons, to the same stimuli that evoked the antidromic responses. Sites that elicited antidromic responses in the F-NTS neurons upon stimulation covered almost all medial hypothalamic nuclei, but 65% were localized in the preoptic-anterior hypothalamic region. All orthodromic responses to activation of vagal afferent fibers (either myelinated or unmyelinated) were polysynaptic in nature. Three F-NTS neurons were found to project to two different hypothalamic regions, by axonal branching. In addition, the firing rate of most F-NTS neurons was not appreciably affected by norepinephrine-induced blood pressure increase. It is concluded that vagal visceral input is transmitted polysynaptically to the F-NTS neurons and is then conveyed to the forebrain via the direct pathway.

Animals↗
PubMed1985

Influence of molecular layer on pyramidal tract neurons.

Activity in layer I increases the excitability of pyramidal tract (PT) neurons, the effect being stronger on slow than on fast PT neurons. Extracellular recordings were made from lateral postcruciate cortex of domestic cats, using antidromic activation from medullary pyramid to identify and classify PT neurons. Their responses to contralateral forepaw (CFP) and direct cortical (Ctx) stimulation, 3 to 4 mm caudal to the recording site, were determined before and after placement of vertical cuts between the Ctx stimulating and recording sites. These cuts had a minor effect on the responses of PT neurons to CFP stimulation, but a strong effect on the responses to Ctx stimulation. Cuts through layers I and II markedly delayed the responses of slow PT neurons, but had no effect on fast PT neurons. After deeper cuts (II/III through V/VI), half the fast and half the slow PT neurons failed to respond to Ctx stimulation. Of those that did, fast PT responses were markedly delayed, but slow PT responses were only mildly affected. The Ctx-CFP interactions showed the familiar facilitation-depression sequence. The period of depression was unaffected by any of the vertical cuts, but disappeared after undercutting the stimulus site below layer VI. The period of facilitation depended primarily on layer I for its production, although deeper layers also contributed to the facilitation of fast PT neurons.

Animals↗
PubMed1985

Spinal neurons with branched axons traveling in both the dorsal and dorsolateral funiculi.

Antidromic search stimuli were delivered to cervical (C2-C3) dorsal and dorsolateral funiculi that were dissected apart from one another and from the rest of the spinal cord. Fifty-six neurons were antidromically identified in the dorsal horn of the lumbosacral enlargement. Of these neurons, 23 were activated antidromically from both the dorsal columns and the ipsilateral dorsolateral funiculus. The neurons were found at depths corresponding to laminae III and IV. About half of the neurons responded only to innocuous, tactile stimuli whereas the other half responded to both innocuous and noxious stimuli. The existence of neurons with branched axons ascending both the dorsal and dorsolateral funiculi raises the possibility that the dorsal column postsynaptic and spinocervical tracts may not be completely independent projections.

Animals↗
PubMed1986

Kinematic assessment of a functional role for recurrent inhibition and selective recruitment.

It has been proposed that recurrent inhibition, which is presumed to act more powerfully on type S than on FR or FF motoneurons, and a selective recruitment order of synergistic motoneurons may function to prevent slowly contracting muscles from impeding rapid contractions. The possibility that such mechanical interactions do occur was investigated kinematically by analysis of plantar flexion in the rat hind limb under loaded and unloaded muscle conditions. The left limb was denervated to isolate the lateral gastrocnemius-soleus nerve and muscles. Plantar flexion was induced before and after soleus denervation by posterior tibial-nerve stimulation with the ankle in one of three positions: (i) resting (unloaded), (ii) dorsiflexed (held by a restraint bar), or (iii) with ankle position set by a load applied in series to the intact Achilles tendon. With the initial ankle position near maximal dorsiflexion, peak velocities of foot movements associated with passive elastic muscle properties approached one-half or more of the values achieved by active contractile mechanisms. Under unloaded and loaded conditions, no evidence was found in support of mechanical interference by the slower contracting soleus muscle of maximal lateral gastrocnemius shortening responses. Contributions of soleus tension to foot velocity and acceleration began to emerge with loads greater than 3 N. These findings are in agreement with previous reports that the slow-contracting soleus muscle, though fully activated, cannot contribute effectively to plantar flexion movements at speeds above a critical level.

Animals↗
PubMed1987

Signs of hemifacial spasm created by chronic periodic stimulation of the facial nerve in the rat.

We show in this paper that daily electrical stimulation of the facial nerve near its entrance to the brain stem in rats results in abnormalities in the electromyographic response of the facial muscles that resemble those seen in patients with hemifacial spasm. After about 4 weeks of daily electrical stimulation of the facial nerve for 1 min/day, stimulation of the temporal branch of the facial nerve resulted in an abnormal EMG response from the mentalis/orbicularis oris muscles, consisting of an initial deflection with a latency of about 6 ms, followed by a burst of EMG activity lasting 10 to 50 ms. We found such "lateral spread" of antidromic activity in all 10 rats that were subjected to chronic stimulation, but not in normal rats and not in rats that had electrodes implanted but which had not been stimulated. Measurements of neural conduction times suggest that the location of the cross transmission that gives rise to this lateral spread response is central to the site where the facial nerve exits the brain stem, probably in the facial motor nucleus. We take these results to support the hypothesis that chronic stimulation of the facial nerve can change the facial nucleus in such a way that it becomes hyperactive, and cross transmission between neurons that are innervating different facial muscles is facilitated.

Animals↗
PubMed1995

A computational model for the neurobiological substrates of visual attention.

Two interesting and complex tasks are performed by the brain in the process of perception: the integration of characteristics leading to an easier recognition of a pattern as a whole (binding), and the extraction of properties that need to be detailed and analyzed (attention). Attention seems to have a reciprocal relation with binding, inasmuch as the latter promotes the composition of features and their dependencies, while the former selects a single characteristic independently of the remainder. Classically, binding is viewed as a process whereby sets of properties are gathered in representative entities, which are themselves linked to form higher level structures, in a sequence that culminates in the total integration of the pattern features in a localized construct. The convergent axonal projections from one cortical area to another would be the neurobiological mechanism through which binding is achieved. Attention comprises the selective excitation of neuronal networks or pathways that stand for specific pattern properties. The thalamus and its reticular nucleus would then be the anatomical substrate of the attentional focus. In this paper we propose a computational model aiming at bringing together the main (and apparently diverging) ideas about binding and attention. Based on experimental data, a neuronal network representing cortical pyramidal cells is assembled, and its structure and function are related to the binding and attention phenomena. Actually, the convergent projections that enlarge the visual receptive field are associated to binding, while a specific change in the pyramidal cell behavior is responsible for attention. Computer simulations are shown which reproduce the electrophysiology of pyramidal cells and mimic some interesting experimental results in visual attention. We conclude by conjecturing that attention is a driven interruption in the regular process of binding.

Algorithms↗
PubMed1994

Quantitative studies of fly visual sustained neurons.

We present a quantitative study of a neural network model [1] proposed for the sustained neurons in the fly visual system. Electrophysiological recordings of sustained neurons [2] are digitized and transferred to a computer. A numerical ordinary differential equation solver is used to simulate the model. In order to obtain an initial set of parameters, we introduce approximations to the model and obtain fits to parts of the response characteristics. These initial parameter values are then refined by optimization routines. The model is compared to data in 4 different experimental paradigms and in general is in good agreement with data. We conclude that the simplified versions of temporal and spatial adaptation mechanisms of the model capture the essential features of the dynamics of sustained neurons and that the refinement of the model requires further experimental studies to elucidate the number of stages involved in temporal adaptation as well as the precise shape of the relationship between the membrane potentials and the spike frequency for the sustained neurons.

Action Potentials↗
PubMed1992

Somatic motor efferents in multiple system atrophy with autonomic failure: a clinico-pathological study.

The myelinated fibers in the corticospinal tracts, ventral spinal roots, and the neurons in the ventral spinal horns were quantitatively examined in 8 autopsied cases of multiple system atrophy associated with autonomic failure. In these structures consisting of the somatic motor efferents, the main pathological feature was the size dependent-involvement of predominantly small-sized fibers and neurons. The small myelinated fibers were significantly depopulated, while the large myelinated fibers were well populated in the corticospinal tract. Neurons in the ventral horns were also involved, but those with a small diameter and located in the intermediate zone (Rexed's lamina VII, VIII) were markedly diminished. In the ventral spinal roots, in the fourth lumbar segments containing essentially no autonomic efferents, small myelinated fibers were also preferentially involved. These pathological changes in the small-sized fiber and neuron loss were examined in relation to the somatic and autonomic motor symptoms, particularly of pyramidal signs.

Aged↗