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At least 955 records · Page 53Linked to original sources
PubMed1983

Study of inhibitory effect of amygdaloid stimulation on auditory response of medial geniculate body (MGB) and analysis of transmissive pathway of the said effect.

Experiments performed on 103 rabbits immobilized with Flaxedil, and the recording of the electrical discharges of single MGB neuron caused by clicks, burst or sustained tone showed marked inhibition of the reaction of 47 out of 75 (62.7%) MGB units responding to sound stimuli, when the amygdaloid complex was stimulated. The latent period of such an inhibitory effect was 5-12 msec and its duration about 2-13 msec. Evoked responses with the latency of 1-2 msec for the stimulation of medial, central and lateral nuclei of amygdala could be recorded from the temporal and parietal cortex. The largest response was recorded from Woolsey's AI area of the temporal cortex. Stimulation of the Woolsey's AI auditory area could also result in a distinct inhibition of the spontaneous as well as the evoked discharges of MGB neurons in response to sound stimulation. Moreover, application of 1% procaine to the surface of auditory cortex could block the inhibitory effect of the amygdala on the MGB neurons. Based on the facts mentioned above, the authors have reason to believe that the inhibitory effect of the amygdaloid complex on the activity of MGB units might be transmitted via the amygdala-auditory cortex-MGB circuit. The biological significance of such an suppressive effect has been discussed.

Acoustic Stimulation↗
PubMed1978

[Reactions of neurons in the reticular and ventral anterior thalamic nuclei to stimulation of the ventrolateral nucleus of the thalamus and motor cortex].

Responses of 137 neurons located in oral parts of reticular (R) and ventral anterior (VA) thalamic nuclei to electrical stimulation of the ventrolateral nucleus (VL) and motor cortex (MI) were studied in 17 cats immobilized with d-tubocurarine. 10.5% of the investigated neurons responded to VL stimulation by antidromic spike (latency 0.7--3.0 ms). 11.0% of the neurons responded antidromically to MI stimulation (latency 0.4--4.0 ms). Neurons with axon sending one branch to VL and the other to MI were found. 78.9% of the neurons responded to VL stimulation with orthodromic excitation (after stimulation of MI this type of response was found only in 52.5% of neurons). 55.6% of R and VA neurons responded to VL stimulation by discharges composed of 3--20 spikes with frequency of 130--530/per second. After MI stimulation discharges of the same type were observed only in 30.5% of the investigated neurons. Inhibition was found in 6.8% of the studied neurons. 55.7% of R and VA neurons demonstrated the convergence of the effects from VL and MI. Corticofugal influences from MI on responses of R and VA neurons to the VL testing stimuli could be inhibitory as well as excitatory.

Action Potentials↗
PubMed1982

Cellular and biophysical mechanisms contributing to regulation of reflex excitability of inking behavior in Aplysia.

Inking behavior in Aplysia offers a simple test system whereby it is possible to examine the cellular and biophysical determinants of a simple behavior and its ability to undergo a short-term behavioral modification. The features of the behavior and its underlying neural circuit, as well as the intrinsic biophysical properties of the effector motor neurons, have been analyzed. Inking behavior shows a selective sensitivity to long-duration stimuli, which appears due to presence of a voltage-dependent fast K+ current and a slow buildup of synaptic input in the ink gland motor neurons. The ability of the behavior to undergo a short-term modification of reflex-excitability appears due to the activation of a prolonged synaptic current in the ink motor neurons.

Animals↗
PubMed1981

How is respiratory rhythm generated?

The time course of respiratory activity, e.g., the the abrupt transitions between the inspiratory (1) and expiratory (E) phases, can be explained by several types of interaction between brainstem respiratory neurons. 1) Reciprocal inhibition: Inhibition of E neurons by I neurons, and of I neurons by E neurons, has been demonstrated, a mechanism that prevents occurrence of activity in one set of populations during the period of activity of another set of populations. 2) Recurrent inhibition: During each respiratory phase, activity in recurrent loops gradually rises to levels sufficient to inhibit ongoing activity and produce abrupt phase-switching. a) I leads to E phase-switching: By use of lung inflation tests, several categories of I neurons in the region of the ventrolateral nucleus of tractus solitarius (NTS) have been specified; in particular, a population of late-I neurons has been found that may function to terminate the I phase. b) E leads to I phase-switching: Several populations of medullary neurons (early-E, late-E, and EI) have been found with responses to lung inflation that suggest that they may play a role in determining E phase duration and E leads to I switching; in particular, a population of early-E neurons in the NTS has been found whose discharge properties suggest that they may function to delay the onset of the succeeding I phase. 3) Recurrent excitation: There is evidence for the existence of recurrent excitatory actions among I neurons that may produce the augmenting pattern of I neurons' discharges.

Animals↗
PubMed1981

Interactions between brainstem respiratory neurons.

Interactions between brainstem respiratory neurons underlie respiratory rhythmogenesis. Several techniques to study these interactions are discussed. Cross-correlation analysis of the firing patterns of pairs of respiratory neurons revealed a high probability of interaction and/or shared inputs between neurons that are immediate neighbors, and the lack and ubiquitous connections between neurons located in different regions. Neuroanatomical studies demonstrated a previously unobserved brainstem projection to the ventrolateral nucleus of tractus solitarius, an important brainstem respiratory-related structure, from a small cluster of neurons in the contralateral ventrolateral medulla several millimeters rostral to the obex; subsequent recordings have shown these neurons to have expiratory firing patterns. Modeling studies suggested that neurons hypothesized to produce inspiratory phase termination should begin firing late in the inspiratory phase and should be excited by lung inflation. Subsequent extracellular recordings have shown that neurons with these properties constitute a significant fraction of neurons in the region of te ventrolateral nucleus of tractus solitarius. The results of these studies indicate that rhythmogenesis results from highly specific interactions between limited subpopulations of respiratory neurons.

Animals↗
PubMed1981

Where are the real respiratory neurons?

Transection experiments establish that the mechanisms responsible for the generation of the basic breathing pattern are located in the medulla. Several populations of neurons with activity patterns related to this motor pattern are readily recorded in the medulla, and much information has been obtained in the past 10 years about the physiology of these medullary respiratory neurons and their possible interconnections, inputs, and interactions. This evidence does not support the hypothesis that the basic alternations between expiration and inspiration is the result of a stable oscillatory network containing only the presently known medullary respiratory neurons. It is proposed that conventional extracellular recording methods have missed important parts of the medullary respiratory mechanism.

Animals↗
PubMed1978

[Inhibition in neurology].

The author recalls three examples of inhibition in neurology: -- in the somatic sensory area inhibition halo around the excited zone; -- in the organisation of painful perception, inhibition by stages of nociceptive impulses; -- in anterior limbic system, inhibition of excitations without concern with the given operationnal programme. From these three examples, he recalls that inhibition and excitation always go together in the functioning of nervous system; but, between the acceptation of the work inhibition in the two first examples and the third one, an important semantic slipping happens. It squares with the crossing of the clinical level to the physiological level.

Aged↗
PubMed1994

Responses of respiratory-modulated facial nerve activity to activation of the ventrolateral subarea of the nucleus of the tractus solitarius.

The purpose of the present study was to examine respiratory-modulated facial nerve activity (FNA) in response to activation of the ventrolateral subarea of the nucleus of the tractus solitarius (vlNTS). The cat was anesthetized with sodium pentobarbital and then vagotomized bilaterally, paralyzed and ventilated artificially. End-tidal fractional concentration of CO2 was maintained at hyperoxic normocapnia. Partial occipital craniotomy was performed to expose the obex. Activities of the phrenic and the facial nerves were simultaneously recorded. The vlNTS was excited by electrical current (80 Hz frequency, 0.5 ms pulse duration and a variety of current from 12.5 to 50 microA) and glutamate (30-100 nl, 0.5 M). Three responsive patterns for both nerves were observed in response to vlNTS activation. First, inspiratory facial nerve activity (iFNA) and phrenic nerve activity (PNA) were decreased (p < 0.01), while expiratory facial nerve activity (eFNA) was not changed. Second, iFNA and PNA were diminished (p < 0.01) but eFNA was enhanced. Third, iFNA was decreased whereas PNA was enhanced. These results suggest that there might be a neural pathway projecting from the vlNTS to the facial nuclei to modulate respiratory-modulated facial nerve activities.

Animals↗
PubMed1994

The 5-HT4 receptor mediates 5-hydroxytryptamine-induced rise in short circuit current in the human jejunum in vitro.

BACKGROUND: 5-Hydroxytryptamine (5-HT) is a potent intestinal secretagogue for chloride and a mediator of diarrhea in the carcinoid syndrome. 5-HT-induced chloride secretion is seen as a change in short circuit current (Isc) in muscle-stripped, chambered human jejunum. The aim of this study was to determine which 5-HT receptors mediate a 5-HT-induced change in Isc in the human jejunum. METHODS: Segments of jejunum obtained from patients (n = 23) having obesity surgery were stripped of muscularis, and the mucosal sheets were mounted in flux chambers and short-circuited. By a cumulative method, a 5-HT-induced change in Isc was measured in the presence or absence of 0.2 mumol/L of neural conduction inhibitor tetrodotoxin or 5-HT receptor antagonists (n = 4 to 5): 10 mumol/L 5-HTP-DP, a 5-HT1p antagonist; 0.1 mumol/L ketanserin, a 5-HT2 antagonist; 0.3 mumol/L ondansetron, a 5-HT3 antagonist; 0.05 and 1 mumol/L ICS 205-930, a selective 5-HT3 antagonist at 0.05 mumol/L and also a 5-HT4 antagonist at 1 mumol/L or more; and 0.01 mumol/L GR 113808, a new selective 5-HT4 antagonist. A chloride-free solution or furosemide (100 mumol/L) was used to show the relationship of a 5-HT-induced change in Isc to chloride secretion. RESULTS: Data were analyzed by ANOVA; p < 0.05 was significant. The chloride-free solution and furosemide significantly (p < 0.05) depressed the maximum change in Isc. Significant shifts occurred in the median effective concentration (1.5 +/- 0.2 mumol/L) for 5-HT in the presence of 1 mumol/L ICS 205-930 (3 +/- 0.2) and 0.03 mumol/L GR 113808 (2.4 +/- 0.2), but not in the presence of 5-HTP-DP (1.2 +/- 0.4), methysergide (1.8 +/- 0.3), ketanserin (2.4 +/- 0.6), ondansetron (1.6 +/- 0.1), 0.05 micron ICS 205-930 (1.3 +/- 0.1), or tetrodotoxin (1.4 +/- 0.4). CONCLUSIONS: In the human jejunum in vitro, a 5-HT-induced change in Isc is mediated through a tetrodotoxin-insensitive pathway by the 5-HT4 receptor. Antagonists to this receptor may be useful in the treatment of diarrhea in carcinoid syndrome.

Chloride Channels↗
PubMed1994

Modeling the thalamocortical loop.

This work proposes a mathematical model for the thalamic gateway to the cortex. In this model, the ionic currents considered and the structural details are in accordance with the biomedical experimental data. To validate the model, three series of simulations were performed in different levels of complexity. First, some experiments show that the model captures the electrophysiological properties of a single thalamic cell, that is, the relay and burst modes of operation. Second, a complete neural network representing the thalamic gateway to the cortex is assembled and the influences of the cortical projections over the thalamus are analysed. Some interesting results about how the cortex opens and closes the thalamic gate, and the relation of this control policy with the phenomenon of attention, are shown. Finally, a third set of simulations establishes some mechanisms of interaction between neighboring thalamic regions, especially a form of somatosensory competition. The paper also hints at possible theoretical explanations for clinical facts like counterirritation, acupuncture analgesia and variations in the sensibility of somatosensory perception. The model seems to be an interesting and new way of understanding the thalamocortical interactions.

Action Potentials↗