Masseteric reflex inhibition induced by afferent impulses in the hypoglossal nerve.
ABSTRACT Summary1.Effects of stimulation of the central cut end of the hypoglossal nerve on the masseteric reflex were studied in cats (spinal cord sectioned between C2 and C3). Hypoglossal stimulation with 1–3 pulses induced a prolonged suppression of the ipsilateral and contralateral masseteric reflex, with or without a facilitatory phase following the peak of suppression.2.The threshold of suppression was 2–3 times higher than the threshold for firing axons of hypoglossal motor neurons and maximal suppression was obtained when the hypoglossal nerve was stimulated with pulses supramaximal for these axons. Pulses of longer duration than necessary to induce suppression were usually required to induce facilitation.3.Hypoglossal influences on the masseteric reflex were almost completely abolished following section of the hypoglossal roots on the stimulated side, whereas the effects still remained following section of the glossopharyngeal, vagal and accessory nerve roots and the dorsal roots of C1 and C2 when the hypoglossal roots were left intact.4.Dihydro-β-erythroidine did not alter the hypoglossal effects on the masseteric reflex.5.Neither precollicular nor medullo-spinal transection altered these hypoglossal influences, whereas ponto-medullary transection completely abolished them.6.From these results it was concluded that afferent impulses in the hypoglossal nerve enter the brain stem primarily through the hypoglossal roots, ascend bilaterally in the brain stem via a polysynaptic route to the trigeminal motor nucleus and induce inhibition and facilitation of the masseteric monosynaptic reflex.
- Neurophysiology 01/1973; 5(4):342-344. · 0.17 Impact Factor
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ABSTRACT: Seven healthy volunteers showing a fourteenfold range in steady-state plasma concentrations on oral alprenolol (200 mg b.i.d.) were investigated by administration of 5 mg of the drug intravenously and then 50, 100, 150, and 200 mg as single oral doses. The rank order for individual steady-state plasma concentrations was the same as that for the relative bioavailability of the 200 mg dose. The area under the plasma concentration-time curve showed a nonlinear increase with the dose. As the relative availability was a good predictor of steady state while clearance after intravenous administration was not, it was concluded that differences in first-pass elimination markedly contribute to the interindividual variability in steady state plasma concentrations. After pentobarbital treatment, the area under the plasma concentration curve of the 200 mg dose was decreased to 32% and 59% of the pretreatment values in two subjects, but there was no change in the plasma half-life of alprenolol. This indicates induction of the first-pass extraction of alprenolol in man.Journal of Pharmacokinetics and Pharmacodynamics 04/1977; 5(3):193-205. · 1.46 Impact Factor
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ABSTRACT: The proprioceptive innervation of the tounge has been investigated in the Cynamolgus monkey by silver impregnation methods following unilateral section of lingual, hypoglossal, and cervical nerves. Muscle spindles were constantly present in the intrinsic and extrinsic muscles. They varied greatly in number, averaged half the length of lumbrical spindles, and showed an unusual arrangement of chain fibre nuclei. Other, inconstant proprioceptors included tendon endings, Ruffini endings, Pacinian corpuscles, paciniform and lamellated endings. Topologically, the endings other than spindles were extra-muscular, so that the overall pattern of proprioceptive innervation resembled that of skeletal muscle in general. Lingual nerve section was without apparent effect on the proprioceptors. Section of the hypoglossal nerve at its point of entry into the tongue caused severe depletiion of ipsilateral proprioceptors and of fusimotor nerves. In the anterior tongue there was evidence of transmedian overlap by efferent and afferent axons contained in the hypoglossal nerve. Hypoglossal section at the skull base caused degeneration of fusimotor nerves but not of proprioceptors. Section of (a), the connexion of C2-C3 ventral rami with the hypoglossal, together with section of (b), the ramus descendens hypoglossi, coused depletion of lingual proprioceptors; again there was evidence of transmedian overlap. Procedures (a) or (b) alone had a lesser effect. It was concluded that lingual proprioceptive afferent fibres occupy the distal hypoglossal nerve, leaving it in the ramus descendens and in the C2-C3 connexion to enter the spinal cord via nerves C2 and C3.Journal of Anatomy 06/1979; 128(Pt 3):523-52. · 2.23 Impact Factor