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Biomedical subjects

A Jean

Publications and source records attributed to A Jean.

At least 73 records · Page 4Linked to original sources
PubMed1984

Medullary control of the pontine swallowing neurones in sheep.

The origin of the inputs from the medullary swallowing centre (dorsal region including the nucleus of the solitary tract, or ventral region corresponding to the reticular formation surrounding the nucleus ambigous) to the pontine swallowing neurones (PSNs) was studied in sheep anaesthetized with halothane. Out of 101 PSNs located in the posterior part of the trigeminal (Vth) motor nucleus, 46 were activated by stimulating either the dorsal (21 neurones) or the ventral (25 neurones) region of the ipsilateral medullary swallowing centre, 3-4 mm rostral from the obex. Thirty-one neurones out of the 46 were identified as alpha motoneurones supplying swallowing muscles (mylohyoïd, anterior body of digastric and medial pterygoïd). Their average activation latency through stimulation of the dorsal medullary region was about 1 ms longer than through stimulation of the ventral region (3.63 ms +/- 0.81 versus 2.72 ms +/- 0.32). To determine the origin of the medullary input to the PSNs, we tried to activate the medullary swallowing neurones (MSNs) antidromically through stimulating the posterior part of the Vth motor nucleus, which contains the swallowing motoneurones. Seventy-three MSNs were tested (25 located in the dorsal and 48 in the ventral region). None of the dorsal neurones tested could be antidromically activated by pontine stimulation: 15 ventral neurones showed a clear antidromic response (collision test) with an average latency of 2.5 ms +/- 0.73. These neurones, which send their axons into the pons, were all located in the reticular formation, above the nucleus ambiguus, 3-4 mm rostral from the obex.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1984

Brainstem organization of the swallowing network.

Swallowing is a complex motor sequence involving the coordinated contraction of several muscles in the mouth, pharynx, larynx and esophagus. The motor sequence of swallowing, which can be entirely performed without afferent feedback, is centrally programmed by a neuronal network. This network can be divided into three levels: an afferent level corresponding to the input arm to the network, that is mainly the solitary tract; an efferent level corresponding to the output arm of the network, that is the different pools of motoneurons involved in swallowing and localized within the trigeminal and hypoglossal nuclei and the nucleus ambiguus; an organizing level corresponding to the interneuronal network which programs the swallowing motor sequence. The 'swallowing interneurons' of the organizing level are localized in two medullary regions: a dorsal region including the nucleus of the solitary tract (NST) and the adjacent reticular formation, and a ventral region corresponding to the lateral reticular formation above the nucleus ambiguus. Neurons localized within the NST region are interneurons which largely go to make up the part of the network which initiates and programs swallowing. Originating from these neurons, the central swallowing command is relayed by the interneurons within the ventrolateral reticular formation before reaching the different groups of motoneurons which excite the swallowing reactions.

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PubMed1983

Connections between the ventral medullary swallowing area and the trigeminal motor nucleus of the sheep studied by tracing techniques.

The anatomical connections between two regions involved in swallowing, the medullary reticular formation around the nucleus ambiguous (ventral group of swallowing interneurons) and the trigeminal motor nucleus (NMV) were studied in sheep using anterograde and retrograde tracing techniques. [3H]leucine and HRP were injected into the ventral medulla and the NMV respectively. These injections were performed according to stereotaxic coordinates previously established by electrophysiological recording tests. The results show bilateral connections between the ventral medulla, 2-4 mm rostral to the obex, and the trigeminal motor nucleus. In addition, the same area of the ventral medulla is connected with the homologous contralateral region and with the facial, vagal and hypoglossal nuclei that are also involved in swallowing. Some connections between the ventral medulla and the NMV must be monosynaptic since aggregates of silver grains typical of axon terminals were observed on the cell bodies of trigeminal motoneurons. Obviously, the various connections shown to exist in this study may serve other functions than swallowing. Nevertheless, most of the results are consistent with the view that the ventral group of medullary swallowing interneurons are switching neurons that distribute the programmed swallowing excitation to the various motoneuron pools involved in deglutition.

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PubMed1975

A pontine primary relay for ascending projections of the superior laryngeal nerve,.

1. In sheep anaesthetized with fluothane, electrical stimulation of the superior laryngeal nerve (SLN), which contains most of the afferent fibres for swallowing, evokes potentials in the medial part of the ipsilateral thalamic VPM (nucleus ventro-postero-medialis) within about 5 msec. This region constitutes the secondary synaptic relay for the laryngeal impulses projecting to the frontal cortex concerned with swallowing. 2. SLN fibres are synaptically connected with cells of the NTS (nucleus of the tractus solitarius), 2-4 mm rostral to the obex (see Car and Jean, 1971). Coagulation of this region abolishes reflexly and cortically induced swallowing, but does not influence the thalamic or cortical responses induced by SLN stimulation. 3. SLN stimulation evokes potentials with a short latency (2 msec) in a restricted pontine area localized 5 mm from the midline and above the trigeminal motor nucleus, just in front of the central emergence of the facial nerve (i.e; about 12 mm rostral to obex). Restricted coagulation of this pontine region eliminates both the thalamic and the cortical projection of SLN. 4. Repetitive stimulation (2 V; 0.2 msec; 20-30 Hz) of this same pontine region produces rhythmic swallowing with characteristics quite similar to those of swallowing induced by SLN or bulbar stimulation. 5. Other data show that SLN fibres, or at least part of them, bifurcate after entering the brain stem (about 6 mm in front of the obex), and give a caudal branch, which reaches the bulbar swallowing centre (3 mm rostral to the obex) by running through the tractus solitarius; and a rostral branch terminating in the pons where the primary synaptic relay for the ascending laryngeal pathway is localized.

Animals↗
PubMed1975

Comparison of activity in pontine versus medullary neurones during swallowing.

1. On decerebellectomized sheep lightly anaesthetized with fluothane, the activity of 49 neurones in the pontine relay (see Car et al., 1975) was recorded with microelectrodes following stimulation of afferents in the superior laryngeal nerve (SLN), 2. These pontine neurones (PN) exhibited an "initial activity" (one or a few spikes) for stimulation either of the homolateral SLN (35 PN) or glossopharyngeal nerve (14 PN). This initial activity had a latency between 1.5 and 4 msec. When swallowing was induced by SLN stimulation, a later discharge appeared. This "swallowing activity" consisted of a variable burst of spikes. 3. The effect of curarization was tested for 13 PN. It always eliminated the "swallowing activity". 4. A clear antidromic response of 16 PN (26 tested PN) was induced by stimulating the thalamic VPM nucleus. This stimulation failed to elicit an antidromic response in medullary neurones (14 tested) located in the nucleus of the tractus solitarius. 5. It is concluded that PN are probably sensory relay neurones which inform higher nervous centres of the state of oropharyngeal receptors; whereas medullary swallowing neurones are really interneurones involved in the programming of the wallowing motor sequence.

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