PubMed Health⌕ Search

Biomedical subjects

E S Luschei

Publications and source records attributed to E S Luschei.

8 recordsLinked to original sources
PubMed1979

Temporomandibular joint meniscectomy--effects on joint structure and masticatory function in macaca fascicularis.

The postoperative effects of unilateral temporomandibular joint meniscectomy on joint structure and masticatory function were evaluated in four mature Macaca fascicularis and compared with one control. Mandibular movement during mastication was monitored objectively with an optoelectronic tracking system within four months and again within twelve months postmeniscectomy in each animal. Temporomandibular joint structure was documented radiographically and histologically. Results showed that degenerative joint disease was produced in the postsurgical joint, and that the morphological changes were location-dependent. Fibrous ankylosis was observed histologically in three animals. The contralateral joints were not affected morphologically, except for bony resorption of the articular eminence noted microscopically in one animal. Radiographically, however, the joint appeared normal. Variable alterations in masticatory patterns were observed following unilateral meniscectomy. While there appeared to be an association between temporomandibular joint structure and masticatory function, radiographic and microscopic observation of morphological alterations in the joint did not result in predictable functional limitations in chewing pattern.

Animals↗
PubMed1978

The strength of the reflex response to sinusoidal stretch of monkey jaw closing muscles during voluntary contraction.

1. Rhesus monkeys were trained to exert steady biting forces of 3--60 N for 1--2 sec. This behaviour was well maintained while sinusoidal or step opening and closing movements were imposed on the jaw. 2. The amplitude of the force modulation during sinusoidal stretching was divided by the amplitude of movement to obtain the magnitude of stiffness. This estimate was made at frequencies from 2 to 50 Hz at amplitudes of 100 and 500 micrometer (half the peak-to-peak movement at the incisors). 3. Peak magnitudes of stiffness were seen with frequencies of 8--15 Hz when the amplitude of movement was small; there was a great deal of variation between individual animals. This variation was most striking with mean forces of 25--35 N. The stiffness was greatest in animals that showed considerable spontaneous tremor, and the highest levels of stiffness were often recorded with frequencies near which tremor amplitude was large. A marked phase lag in the force response was often seen during small amplitude stretching at 8--30 Hz. 4. Estimates of stiffness for larger amplitude (500 micrometer) stretching showed less variation; the magnitude of stiffness showed maximum values below 10 Hz and a minimum at 15--30 Hz. Force always showed a phase lead on position although this lead became small in the frequency range where with smaller movement there had been phase lags. The magnitude of stiffness increased with increasing mean force. 5. Bilateral electrolytic lesions were made in the brain stems of three animals; they reduced by over 95% the expected number of cells in the mesencephalic nucleus of the fifth cranial nerve on either side. These lesions interrupted the afferent pathway for the stretch reflex and so abolished excitatory electromyogram (e.m.g.) responses to step stretches of the jaw closing muscles. 6. Such reflex responses as persisted after the lesions were small and inhibitory. E.m.g. silences followed both step stretch and release; the response to release was a 'load compensation' that could not be attributed to spindle afferents. 7. After the lesions the responses to movements of 100 micrometer showed neither negative values for the phase nor marked peaks in the stiffness magnitude at low frequencies; these features therefore take origin in the action of the stretch reflex. The stiffness that was measured after the lesions may be attributed to the non-reflex components resisting stretch, particularly to the properties of the contracting muscles. Thus, the phase of the force response was markedly advanced at all frequencies and the stiffness seen for 100 micrometer was similar to that for 500 micrometer. Stiffness increased with increasing mean force, as before surgery. 8. Vector subtraction of the stiffness seen at each frequency after interrupting the stretch reflex from that seen before doing so gave a quantitative estimate of the strength of the stretch reflex. The reflex activity calculated in this way showed attenuation and progressive phase lag as the frequency increased above 10 Hz...

Afferent Pathways↗
PubMed1975

Role of monkey precentral cortex in control of voluntary jaw movements.

Monkeys were trained to produce a low, steady biting force for 0.5-2.5 s, and then a rapid forceful bite in response to a visual stimulus. After large bilateral lesions of the precentral face area, monkeys emitted repetitive forceful bites on the apparatus, but could not perform the force-holding task. They eventually relearned the task, but the force exerted was never as steady as it was prelesion, and often oscillated at about 2 and/or 5-6 Hz. After retraining, two animals with large bilateral lesions of the face area produced median RT responses equal to or only slightly longer than their prelesion performance, indicating that neural pathways not involving the precentral cortex can mediate quick visual RT responses. The variability of RTs was permanently increased, probably as a result of the persistent unsteadiness of the force-holding response. Incomplete bilateral lesions of the precentral face area, a complete unilateral lesion of that area, and bilateral lesions adjacent regions of cortex produced either mild, transient difficulties with the biting taks, or no problems at all. The results indicate that the precentral cortex has a role in the control of voluntary jaw movements. Lesions caused difficulty in controlling, but not producing, closing jaw movements, thereby suggesting that this role is predominantly to inhibit jaw-closing motoneurons or the systems that excite them. Electrical stimulation studies of the face area of the precentral cortex of the unanesthetized monkey point to the same conclusion.

Animals↗
PubMed1975

Discharge of spindle afferents from jaw-closing muscles during chewing in alert monkeys.

The discharge of muscle spindle afferents from monkey spindle afferents from monkey jaw-closing muscles was studied during mastication of natural foods by extracellular recording from the fibers or cell bodies of the tract and mesencephalic nucleus of the fifth nerve. In all, 39 muscle afferents were studied. The spindle associated with 18 of the afferents was positively identified by the afferent's response to gentle, localized palpation of either the temporalis or masseter muscle. Discharge patterns were observed during mastication, and in the majority of cases the qualitative passive response characteristics of the spindle afferent were determined. During steady chewing spindle afferent discharge typically paused briefly during the initial rapid upward part of the chewing cycle. Firing generally began as the jaw slowed its upward movement, and firing rates during the slow grinding portion of the upward movement were within the range of 50-80 spikes/s. All spindles exhibited a brisk discharge during the opening movement, typically within the range of 100-150 spikes/s. One-third of the spindle afferents exhibited a brief, high-frequency burst of firing at the very beginning of the opening movement, presumably as a result of stretch applied to a spindle just previously subjects to fusimotor excitation. Although the results of the study make it clear that spindles in jaw-closing muscles are coactived along with the extrafusal muscle fibers, the fusimotor bias does not seem capable of sustaining discharge in the face of rapid shortening of the muscle. Furthermore, the fact that discharge rate during opening, when the jaw-closing motoneurons are quiescent, is much higher than at any part of the closing cycle, when the motoneurons are active, suggests that the muscle spindles cannot provide the primary excitatory drive to the motoneurons.

Acoustic Stimulation↗
PubMed1975

Variability of neuropathologic lesions in experimental methylmercurial encephalopathy in primates.

Acute and chronic intoxications of rhesus monkeys with methylmercury produced lesions in the central nervous system (CNS) with different distributions. Neuronal degeneration and astroglial proliferation predominated in the dentate nucleus, lateral geniculate nucleus, thalamus and pontine nuclei in 2 monkeys that received 2 mg/kg/day for 17 and 18 days, whereas pseudolaminar necrosis and astroglial proliferation were observed in the cerebral crotex, maximally in the calcarine and insular regions, in 4 monkeys that received 0.5 to 0.8 mg/kg/day for 3 to 8.5 months. Mercury concentrations in the CNS were much higher in the acutely intoxicated animals than in the chronically intoxicated animals, but the correlation between concentrations of mercury and the histologic destruction was not precise.

Animals↗
PubMedDate not supplied

Human and macaque mastication: a quantitative study.

Significant differences exist between human and Macaca fascicularis patterns of mandibular movement during mastication. Macaque patterns display less asymmetry, more uniformity, and limited lateral excursions when compared to humans for mastication of the same food. Different anatomical structures between the two species offer explanations of the different patterns that were observed. Researchers should use caution when using macaques as models for human mastication.

Animals↗