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Biomedical subjects

A J Miller

Publications and source records attributed to A J Miller.

At least 127 records · Page 7Linked to original sources
PubMed1988

Response patterns of craniomandibular muscles with and without alterations in sensory feedback.

1. Surface EMG recordings were made bilaterally from the anterior part of the temporal muscle, superficial masseter muscle, and the suprahyoid complex of muscles while tracking mandibular incisor movement in three planes. This was done in 20 normal subjects with 16 different responses. Some responses involved clenching whereas other responses occurred with actual mandibular movement. 2. Each muscle demonstrated a probability of recruitment dependent on the response that correlated with the intensity of recruitment. The higher the probability of recruitment, the greater the intensity of muscle activity. 3. The anterior temporal muscle demonstrated no statistically significant difference in any of the responses between the left and right muscles. The masseter muscle also demonstrated bilateral symmetry. 4. The anterior part of the temporal muscle was recruited in more than 60% of its trials (60% to 100%) in ipsilateral laterotrusion, retrusion, fast vertical raising, clenching on the ipsilateral or intercuspal position, and mastication. The temporal muscle was recruited in less than 60% of its trials in contralateral and incisor clenching, and less than 30% in contralateral laterotrusion, protrusion, and opening. 5. The superficial masseter muscle was recruited in more than 60% of its trials in protrusion, vertical raising, all clenches, and mastication. The masseter muscle was recruited less than 60% in retrusion, ipsilateral laterotrusion, and opening. 6. The suprahyoid group of muscles was recruited in more than 60% of its trials in protrusion, opening, and mastication. This group of muscles was recruited less than 60% of the time in clenching, lateral movements, and rapid vertical raising of the mandible. 7. Applying a maxillary splint to seven subjects significantly decreased the recruitment of the anterior temporal and masseter muscles during mastication. The splint also modified the use of the masseter muscle during protrusion so that it was less active, but increased its recruitment during contralateral clenching. The suprahyoid muscle group was unaffected by the maxillary splint. 8. These data support the concept that movement of the mandible from the intercuspal or rest position develops a coactivation pattern that will excite or inhibit a given muscle regardless of whether clenching with occlusal contacts or no occlusal contact is involved. 9. The data also demonstrate that the maxillary splint can alter the use of the jaw elevator muscles, predominantly in mastication.

Adult↗
PubMed1988

Histochemical and electromyographic analysis of craniomandibular muscles in the rhesus monkey, Macaca mulatta.

The range of fiber composition was analyzed in four regions of the temporalis muscle of four normal rhesus monkeys. The middle region of the temporalis muscle contained significantly fewer type I fibers than the anterior region. Comparison of the same region between left and right temporalis muscles showed that a bilateral symmetry existed in the composition at the different comparable levels of the muscle except for the deep anterior temporalis. Biopsies were also taken from three muscles, the superficial anterior temporalis, superficial masseter, and the digastric muscles, of ten normal adult monkeys to determine the fiber composition. Both adult male and female monkeys demonstrated a low percentage of type I fibers in the anterior temporalis (less than 25%), and twice as many type I fibers in the masseter and digastric muscles (40 to 50%). The effect of applying a constant touch-pressure to the dorsal surface of the tongue using an acrylic wedge was studied subsequently in these ten animals. Behaviorally, the animals lowered their mandible more during the first 3 months of adapting to the tactile stimulus, and lowering of the mandible was accompanied by increased electromyographic activity (EMG) of the digastric muscle, but not of the anterior temporalis or masseter muscles. In fiber composition, only the anterior temporalis demonstrated a significant shift in percentage of type I fibers with a decrease during the first 3 months. In cross-sectional area, both the anterior temporalis and digastric muscles demonstrated a significant decrease for type I fibers during the 12 month period. Lowering the postural position of the mandible had more effect on the cross-sectional area of the individual fibers than on the metabolic activity of the muscles.

Animals↗
PubMed1988

Carcinogenesis in rats by cyclic N-nitrosamines containing sulphur.

The effects of chronic exposure to three sulphur-containing heterocyclic N-nitrosamines were determined after repeated oral administration to female Fischer 344 rats. Nitrosothiazolidine did not significantly affect the survival of the rats or the incidence of tumours at a total dose of 3.5 mmol. Nitrosodithiazine, an analogue of nitrosothiazolidine which contains an extra sulphur atom inserted between the carbons of its CH2-CH2 moiety, produced only three tumours (two of the nasal mucosa) in a group of 20 rats at a total dose of 1.75 mmol/rat. Nitrosothialdine, the all-cis 2,4,6-trimethyl analogue of nitrosodithiazine, was a potent carcinogen that significantly shortened the lifespan and produced oesophageal tumours in 70% of treated rats as well as numerous tumours of the tongue and liver; this outcome was unexpected because alpha-methyl substitution in other heterocyclic nitrosamines usually reduces or eliminates tumorigenicity. The results extend the data base on the carcinogenic activity of molecules containing both divalent sulphur and the nitrosamino function. The lack of significant carcinogenicity of nitrosothiazolidine in this study suggests that its presence in the human food supply presents a relatively minor risk.

Animals↗
PubMed1988

Craniomandibular bone density in the primate as assessed by computed tomography.

Ten normal rhesus monkeys, five juvenile and five adult animals, were analyzed for symmetry in bone density across the cranioskeleton with computed tomography (CT). Fifty contiguous axial CT scans were done using 1.5-mm thick scans between the lower mandibular border and inferior orbital ridge, and 3-mm thick scans from the inferior orbital ridge to the rostral level of insertion of the temporalis muscle. Eleven regions comprising areas of the lower mandibular border, lower ramus, upper ramus with condyle, the coronoid process, the zygomatic arch, and cranial bone were analyzed for symmetry using small regions of interest. Only one region, the condyle, demonstrated a statistically significant difference between the two sides with all other measured sites demonstrating the same bone mineral density bilaterally. Large area analysis of five regions--the lower mandibular border, upper ramus with condyle, the coronoid process, the zygomatic arch, and upper cranium--demonstrated no significant difference in the distribution of CT numbers. This analysis of bilateral distribution of bone density in the primate craniofacial skeleton demonstrates a basic symmetry that can be used to study altered patterns of neuromuscular function and their effects on bone density.

Aging↗
PubMed1988

The lymphatic drainage of the pericardial space in the dog.

The purpose of this study was to characterize definitively the lymphatic drainage system of the pericardial space in the dog. The reports on this subject, based on dissection experiments and acute dye injections, remain controversial, and our own previous studies have been incomplete. Seventeen dogs were studied using a radiographic technique. Micropulverized barium sulfate instilled into the pericardial sac was followed with serial chest x-rays in seven dogs with intact cardiac lymphatics, in seven dogs after section of the cardiac lymphatic drainage node (the cardiac lymph node) in the right upper mediastinum, and in three dogs after resection of cardiac drainage lymphatic nodes in the left upper mediastinum. These studies revealed that the lymphatic drainage of the pericardial space is via (a) the principal coronary lymphatic which drains from the left ventricular muscle and passes to the right upper mediastinum via the cardiac lymph node, (b) the lesser coronary lymphatic which drains the right ventricular muscle and passes to the left upper mediastinum, and (c) bilateral internal mammary (parasternal) lymphatic chains. These observations are important in planning experimental approaches to the effects of impairment of lymph drainage from the pericardial space. An understanding of the lymph drainage from the pericardial space may prove significant to understanding fibrotic reactions within it and the pathologic mechanisms of such entities as constrictive pericarditis.

Animals↗
PubMed1987

Inhibitory effects of thiols on a mutagenic contaminant from the synthesis of N-nitrosothiazolidine.

The effect of S9 and various thiols were studied for potential modifying effects on a mutagenic trace artifact ('NTHZ') formed during the synthesis of N-nitrosothiazolidine (NTHZ) from cysteamine, formaldehyde and nitrite. Induced and uninduced S9 prepared from Syrian hamster livers reduced mutagenic activity in Salmonella TA100. Incorporation of boiled S9 into the preincubation medium produced similar effects, indicating a non-enzymatic mechanism for the detoxification reaction. Thiols alone also lowered revertant yields, and inhibitory efficacy was, in general, related to the pKa of the compound. At equimolar concentrations mutagenic activity was reduced in the following order (pKa values in parentheses): Thioglycolate (10.7) greater than mercaptoethanol (9.6) greater than reduced glutathione (8.8) greater than cysteine (8.35) greater than cystine (8.2). N-Acetylcysteine (9.52) and cysteamine (8.35), however, did not fit this pattern. The results of this study suggest that normal hepatic mechanisms may minimize 'NTHZ' genotoxicity thereby reducing potential health risks associated with its exposure.

Animals↗
PubMed1986

Amino acid receptor mediated excitatory synaptic transmission in the cat red nucleus.

A study has been made of the effects of the selective N-methyl-D-aspartate receptor antagonist, 2-amino-5-phosphonovalerate (APV), and the broad spectrum excitatory amino acid antagonists, gamma-D-glutamylglycine (gamma-DGG), gamma-D-glutamylaminomethylsulphonate (GAMS), 4(p-chlorobenzoyl)-cis-piperazine-2, 3-dicarboxylate (pCB-PzDA) and kynurenate, have been examined on excitation evoked on neurones in the magnocellular red nucleus (m.r.n.) of the anaesthetized cat by stimulation of the interpositus nucleus (i.p.n.) and sensorimotor cortex, and by ionophoresed excitant amino acid agonists. The profile of activity of the excitatory amino acid antagonists on m.r.n. neurones was similar to that described on neurones in other areas of the central nervous system. APV selectively depressed responses to N-methyl-D-aspartate (NMDA), whereas the broader spectrum antagonists reduced responses to kainate and quisqualate as well as to NMDA. Neuronal responses to L-glutamate and L-aspartate were depressed by all the antagonists tested. I.p.n.-evoked monosynaptic responses of m.r.n. neurones were reversibly reduced by the broad spectrum antagonists, but were unaffected by APV. Cortically evoked mono- and polysynaptic excitatory responses were reversibly depressed by APV and the broad spectrum antagonist, pCB-PzDA. The action of APV corresponded with its ability to antagonize responses to NMDA. However, the cortically evoked responses appeared to be more sensitive to the actions of pCB-PzDA than to those of APV, although the former is a less effective antagonist of NMDA-induced excitation compared with APV. APV depressed excitation induced by cortical stimuli and L-glutamate and L-aspartate. However, there was no obvious correlation between the actions of the broad spectrum amino acid antagonists on synaptically evoked responses and those induced by L-glutamate or L-aspartate on the few neurones tested. These results are consistent with an amino acid being the transmitter in the interposito-rubral and cortico-rubral excitatory pathways which interacts with non-NMDA and both NMDA and non-NMDA receptors respectively. However, the identity of the transmitter acting at these receptors remains to be determined.

2-Amino-5-phosphonovalerate↗
PubMed1985

Neuromuscular adaptation of craniofacial muscles to altered oral sensation.

Experimentally induced changes in oral sensation to the tongue altered the use of specific craniofacial muscles. An acrylic wedge was anchored to the maxillary teeth of ten adult rhesus monkeys, providing a tactile-pressure sensation to the dorsal surface of the tongue. Fifteen craniofacial and tongue muscles were studied by electromyography during the first 6 months of adaptation. The results showed that there was an overall shift in those muscles that were normally tonically active in the craniofacial region. Muscles of the suprahyoid region, the geniohyoid and digastric, as well as the platysma muscle of the face, and the lateral pterygoid muscle were tonically active in more animals after placement of the wedge. In contrast to the enhanced activity of mandibular and facial muscles that function during mandibular depression, only the anterior temporalis muscle in the superficial and deep region demonstrated more tonic activity. The superficial and deep masseter regions, as well as the medial pterygoid muscle, demonstrated no change in their EMG activity. Only the lip muscles and mentalis demonstrated increased activity, whereas the facial muscles with more vertically oriented fibers did not demonstrate any increased activity. These findings suggest that a change in the tactile stimulation to the tongue can induce a new balance in the level of activity of specific craniofacial muscles and that this altered neuromuscular pattern can remain throughout the first 6 months of adaptation.

Adaptation, Physiological↗
PubMed1985

The study of the lymphatics of the heart: an overview.

A good number of studies on the cardiac lymph flow and the results of its impairment have been done, but the potential value of such experimental approaches is far from realized. An overview of the study of the cardiac lymphatics is presented to give perspective to its importance, and hopefully to stimulate the interest of more investigators.

Animals↗
PubMed1984

Morphologic response to changes in neuromuscular patterns experimentally induced by altered modes of respiration.

The present experiment was designed to test whether specific recordable changes in the neuromuscular system could be associated with specific alterations in soft- and hard-tissue morphology in the craniofacial region. The effect of experimentally induced neuromuscular changes on the craniofacial skeleton and dentition of eight rhesus monkeys was studied. The neuromuscular changes were triggered by complete nasal airway obstruction and the need for an oral airway. Alterations were also triggered 2 years later by removal of the obstruction and the return to nasal breathing. Changes in neuromuscular recruitment patterns resulted in changed function and posture of the mandible, tongue, and upper lip. There was considerable variation among the animals. Statistically significant morphologic effects of the induced changes were documented in several of the measured variables after the 2-year experimental period. The anterior face height increased more in the experimental animals than in the control animals; the occlusal and mandibular plane angles measured to the sella-nasion line increased; and anterior crossbites and malposition of teeth occurred. During the postexperimental period some of these changes were reversed. Alterations in soft-tissue morphology were also observed during both experimental periods. There was considerable variation in morphologic response among the animals. It was concluded that the marked individual variations in skeletal morphology and dentition resulting from the procedures were due to the variation in nature and degree of neuromuscular and soft-tissue adaptations in response to the altered function. The recorded neuromuscular recruitment patterns could not be directly related to specific changes in morphology.

Animals↗