Author Correction: Forearc carbon sink reduces long-term volatile recycling into the mantle

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

Lipomatous Lesions of the Parotid Gland

PURPOSE

Lipomatous lesions of the parotid gland are rare and seldom considered in the initial diagnosis of a parotid mass. We report our experience in the management of patients with lipomatous lesions affecting the parotid gland.

PATIENTS AND METHODS

Retrospective analysis of all parotidectomies performed for neoplastic lesions in the maxillofacial unit between 1975 and 2003 and patients with lipomatous lesions involving the parotid gland were identified; 638 parotidectomies were performed in this period on 629 patients in which 660 neoplasms were identified. Eight patients were found to have lipomatous lesions and form the basis of this study.

RESULTS

Lipomatous lesions accounted for only 1.3% of parotid tumors and occurred more frequently in males, at a ratio of 3 to 1. The most common presentation was that of a slowly enlarging, painless mass. Computed tomography scan was the most frequent imaging modality undertaken, and in 3 patients a diagnosis of a lipoma was made preoperatively. Seven patients underwent a superficial parotidectomy and 1 patient had a total conservative parotidectomy because of the deep lobe location of the mass. Five patients were found to have a focal lipoma and 3 patients had diffuse lipomatosis. There were no recurrences. Temporary facial nerve palsy and Frey's syndrome were the most frequent complications.

CONCLUSION

Lipomatous lesions accounted for only 1.3% of all parotid tumors. There were no specific distinguishing clinical features in our patients, and an accurate preoperative diagnosis was made in 3 patients based on imaging investigations. A well-circumscribed lipoma was more common than diffuse lipomatosis. Superficial parotidectomy was the treatment of choice and there were no recurrences in our series.

Multiple synchronous and metachronous neoplasms of the parotid gland: The Chichester experience

Parotid neoplasms are usually solitary and multiple tumours occurring in an individual are uncommon. The incidence and implications of multiple synchronous and metachronous tumours remains relatively unknown. We reviewed the case notes of 606 patients who had parotidectomies for neoplastic lesions over a 30 year period and identified 30 patients (5%) with multiple primary tumours. There were 24 patients with synchronous tumours and 6 with metachronous tumours. Sixteen of the synchronous tumours (67%) were ipsilateral, whereas all six metachronous tumours were contralateral. Preoperative examination was effective at detecting bilateral tumours but poor at detecting multiple ipsilateral tumours. Multiple tumours were likely to be of the same histology (n=24, 80%) and Warthin's was by far the most common multiple tumour. Ipsilateral tumours of differing histological types and identical tumours other than Wartin's were uncommon. All but one patient had superficial parotidectomies and there were no recurrences.

Surgical management of incompletely excised basal cell carcinomas of the head and neck

We made a retrospective audit of all basal cell carcinomas excised in the Maxillofacial Units at St. Richard's Hospital, Chichester and the Worthing and Southlands NHS Trust between 1990 and 1999. A total of 3795 BCCs were excised. Of these, 3560 were completely excised (93.8%) and 235 were incompletely excised (6.2%), which compares favourably with other series. Of these, 84 patients had further excision, 11 had radiotherapy, and 140 were kept under review. Residual tumour was present in 45% of the re-excised specimens. Of the 140 cases managed by observation, 21% recurred. Notably, 31% of patients in the observation cohort died of other causes without recurrence. Incomplete excision was significantly more likely (P < 0.001) if multiple lesions were excised at the time of operation. Involvement of multiple margins was not a significant risk factor for recurrence in the 'observed' cohort. This study shows that a flexible strategy, which balances observation, further excision and radiotherapy, is superior to any single approach.

Changing frequency of parotid gland neoplasms--analysis of 560 tumours treated in a district general hospital

An analysis of all parotidectomies performed for neoplastic lesions in the maxillofacial unit at a district general hospital during a 26-year period between 1974-1999 was undertaken. The details analysed were age, sex, histology and temporal variations in the frequency of specific tumour types during the study period. A total of 538 parotidectomies performed on 529 patients in whom 560 tumours were present, formed the basis of this study. Marked variations were present in the age and sex distribution and relative frequency of specific tumour types in this study, when compared to previous reports. There were also differences in the age and sex distribution of pleomorphic adenoma and adenolymphoma (P <0.0001) in this study. The relative frequency of benign tumours and adenolymphoma increased, whereas that of pleomorphic adenoma decreased during the study period. In addition, there was a statistically significant decrease in the relative frequency of pleomorphic adenoma (P <0.0001) and an increase in adenolymphoma (P <0.0001) when comparisons were made with previous studies. This study from a defined population may be more representative of the true proportion of specific tumours in this population. The potential implications of the results on the investigation and treatment of parotid neoplasms is highlighted.

Evaluating cardiovascular disease prevention programs in African American communities

This article reports on an evaluation of community cardiovascular disease prevention projects. The evaluation protocol involved a monitoring system for documenting community activities. It showed improvements in cardiovascular disease prevention services, community actions, planned products, and new or modified community programs to prevent cardiovascular disease. Reports from focus group sessions provided analyses of participants' perceived behaviors and satisfaction with eight community-based cardiovascular disease prevention projects in African American communities. Modest improvements in blood pressure, blood cholesterol, dietary intake, and physical activity among a convenience sample of participants in the community were noted.

Indications for third molar surgery

Recent reports have suggested that the practice of prophylactic lower third molar surgery is widespread, possibly account for up to 50% of all patients treated. An objective effort to refute the findings of the previously published data was undertaken by the Maxillofacial Unit of a large district general hospital trust. A prospective study of 454 consecutive patients referred for third molar surgery demonstrated that in 96% of the patients, at least one nationally defined criteria for surgery was present. A concurrent retrospective audit of patients already on the waiting list for surgery identified that 97% had at least one valid criterion for surgery. Of those patients who presented with unilateral symptoms, over half had only the troublesome side removed. Only 11 out of 454 patients were accepted for treatment without a defined criterion, all of whom had partially erupted teeth. The evidence presented in the current study is compared with previously reported data and possible reasons for the variance are discussed.

Controversies in third molar surgery--the national view on review strategies

A national survey was conducted to establish the current practice of postoperative review of third molar surgery by the 255 fellows of the British Association of Oral and Maxillofacial Surgeons. Of the 216 complete responses, 134 say that they routinely reviewed all patients, while 67 did not. A further 15 fellows (7%) are currently considering their practice. Five (2%) stated that routine review should be compulsory and failure to do so was medically negligent. We conclude that a policy of selective rather than routine review is safe for most patients, but if a patient is under age, mentally retarded, taking psychoactive drugs, or has any other associated condition, then routine follow-up should be undertaken.

Michigan physicians' perceptions of their role in managing obesity

In a random sample of 211 primary-care physicians in Michigan, about 33% (n = 70) perceived their role in the prevention of obesity as coordinating and 39% (n = 82) as cooperative and of equal importance to that of other professionals. Perceived barriers to prevention of obesity were inadequate time to educate patients, method of reimbursement, and inadequate training in management of obesity. These results suggest that physicians' involvement in managing obesity can improve if they work closely with other health professionals.

Toward a symmetrical and an integrated framework of norms for nutrition communication in sub-Saharan Africa

Nutrition is crucial to national development; an undernourished or a malnourished population is at risk for infectious diseases that may reduce its working and productive capacities. Sub-Saharan Africa leads the world in the proportion of its population that is chronically malnourished. This article presents a symmetrical and an integrated framework of norms for nutrition communication. It uses three nutrition communication projects in Africa to illustrate the application of those norms. Based on that review, it concludes that a community-based framework should emphasize at the outset--and throughout program implementation and evaluation--the importance of folk media (e.g., Africa's "oramedia") as both formative and summative norms for planning, implementing, and evaluating nutrition communication programs in Africa.

Adaptive control for backward quadrupedal walking V. Mutable activation of bifunctional thigh muscles

1. In this, the fifth article in a series to assess changes in posture, hindlimb dynamics, and muscle synergies associated with backward (BWD) quadrupedal walking, we compared the recruitment of three biarticular muscles of the cat's anterior thigh (anterior sartorius, SAa; medial sartorius, SAm; rectus femoris, RF) for forward (FWD) and BWD treadmill walking. Electromyography (EMG) records from these muscles, along with those of two muscles (semitendinosus, ST; anterior biceps femoris, ABF) studied previously in this series, were synchronized with kinematic data digitized from high-speed ciné film for unperturbed steps and steps in which a stumbling corrective reaction was elicited during swing. 2. During swing, the relative timing of EMG activity for the unifunctional SAm (hip and knee flexor) was similar for unperturbed steps of FWD and BWD walking. The SAm was active before paw lift off and remained active during most of swing (75%) for both forms of walking, but there was a marked decrease in EMG amplitude after paw off during BWD and not FWD swing. In contrast, the relative timing of EMG activity for the SAa and RF, two bifunctional muscles (hip flexors, knee extensors), was different for FWD and BWD swing. During FWD swing, the SAa and the RF (to a lesser extent) were coactive with the SAm; however, during BWD swing, the SAa and RF were active just before paw lift off and then inactive for the rest of swing until just before paw contact (see 3). Thus the swing-phase activity of the SAa and RF was markedly shorter for BWD than FWD swing. 3. Activity in SAa and RF was also different during FWD and BWD stance. The RF was consistently active from mid-to-late stance of FWD walking, and the SAa was also active during this period in some FWD steps. During the stance phase of BWD walking, however, the onset of activity in both muscles consistently shifted to early stance as both muscles became active just before paw contact (the E1 phase). Activity in RF consistently persisted through most of BWD stance. The duration of SAa recruitment during BWD stance was more variable across cats with offsets ranging from mid- to late stance. 4. The activation patterns of the biarticular anterior thigh muscles during stumbling corrective reactions were, in general, similar to their different activations during FWD and BWD swing. The initial response to a mechanical stimulus applied to the dorsum of the paw that obstructed FWD swing was an augmentation of knee flexion and increased activity in ST and SAm. A mechanical stimulus applied to the ventral surface of the paw to obstruct BWD swing resulted in an initial conversion of hip extension to flexion and a slowing of knee flexion. There was a corresponding recruitment of SAa and RF and an enhancement of background activity in SAm. 5. The two forms of walking are differentiated by posture and limb dynamics, yet muscles participating in the basic flexor and extensor synergies are unchanged. Although central pattern generating (CPG) circuits determine the basic timing of these synergies, changes in the duration and waveform of muscle activity may depend on unique interactions among the CPG, supraspinal inputs that set posture and the animal's goal (to walk BWD or FWD) and motion-related feedback from the hindlimb. Output mutability to each muscle may depend on the balance of this tripartite input; muscles with immutable patterns may rely heavily on input from CPG circuits, whereas muscles with mutable patterns may rely more on form-specific proprioceptive and supraspinal inputs.

Labial sensory function following sagittal split osteotomy

A retrospective assessment of labial sensory function following sagittal split osteotomy was undertaken by a combination of record analysis, postal questionnaire and objective sensory testing. Case records for 90 sides operated upon by a single consultant surgeon between 1979 and 1992 identified a prevalence of persisting sensory changed at 2 years of 6.7%. A higher incidence of sensory change was seen in patients treated with intermaxillary fixation/upper border wires than those managed with buccal monocortical miniplates. Postal questionnaire returns for 67 consultant operated sides identified a higher incidence of sensory change than recorded in the notes. 5.9% had long term persisting anaesthesia. Another 28% had more variable subtle sensory impairment. A similar relation to method of fixation was seen. An association between duration of temporary sensory change and magnitude of forward mandibular advance was noted. Objective sensory testing validated the subjectively reported sensory status but also identified many patients self-assessed as normal had some undetected sensory impairment. Possible mechanisms for the above findings and implications for clinical practice are presented.

Evidence of positive force feedback among hindlimb extensors in the intact standing cat

1. The functional organization of heterogenic reflexes produced by activation of extensor force receptors (Golgi tendon organs) was studied in intact cats during stationary stance. Intramuscular stimulation (200 Hz, 20 ms) of hindlimb extensor muscles via chronically implanted electrodes was used to evoke weak muscle contractions and naturally activate Golgi tendon organ Ib afferents while cats stood unrestrained with each paw on a moveable triaxial force plate. 2. Intramuscular stimulation of every hindlimb extensor muscle tested in this study evoked excitatory responses that were widely distributed among hindlimb extensor muscles. Source and target specializations in the functional organization of this positive force feedback system were also observed. For example, stimulation of ankle extensors typically excited extensors and flexors at the ankle and hip (but not knee), whereas stimulation of hip extensors typically excited only extensors at all three joints. In addition, intramuscular stimulation of either lateral (LG) or medial (MG) gastrocnemius consistently inhibited soleus while exciting other extensors at the ankle and more proximal joints. 3. The electromyographic (EMG) reflex responses described above are attributed to the natural (via muscle contraction) activation of extensor group Ib afferents. Direct activation of intramuscular afferents by the stimulus was unlikely because there was no evidence that Ia afferents, which have the lowest electrical thresholds, were activated. Both the observed inhibition of the synergist, soleus, and the excitation of the antagonist, tibialis anterior, produced by gastrocnemius stimulation are opposite to the reflex effects that would be produced at the ankle by activation of gastrocnemius Ia afferents.(ABSTRACT TRUNCATED AT 250 WORDS)

Stance control in the chronic spinal cat

1. A longitudinal study of the control of quiet and perturbed stance was conducted before and for 1 yr after complete spinal transection (T12) in a cat trained to stand on a moveable force platform. 2. With daily training, the spinal cat recovered full weight support and some intermittent control of lateral stability within 1 mo. Within the second month postspinalization, the spinal cat achieved the ability to maintain independent, unassisted stance (no external support or stimulation) for up to 45 s during quiet stance, as well as for 62-97% of the trials of horizontal translations of the support surface. 3. Control of lateral stability in the spinal cat was severely compromised, however, as eventually the spinal cat always lost its balance. Head movements and the tendency for the hindlimbs to initiate stepping movements were more destabilizing than platform translations. 4. Our preliminary results indicate that the recovery of partial lateral stability of the hindquarters in the spinal cat is the product of passive muscle properties and segmental reflexes, which, in isolation can provide only limited balance control in the chronic spinal cat.

A multivariate analysis of weight-loss behavior

This study used a theoretical framework with multiple variables in multivariate analyses (factor, multiple regression, and path analyses) to investigate the sociopsychological predictors of weight loss. Responses from 309 participants of a comprehensive weight-loss program indicated that self-assurance was the most significant predictor of actual weight loss, followed by weeks completed. Other factors, such as program satisfaction and perceived importance, indirectly predicted weight loss through the intervening variables of self-assurance and weeks completed. Differences in the factors predicting weight loss were observed between completers and dropouts. The implications of these results for professionals concerned with weight control are discussed.

Functionally complex muscles of the cat hindlimb. I. Patterns of activation across sartorius

The cat sartorius (SA) can be divided functionally into an anterior (SAa), knee extensor portion and a medial (SAm), knee flexor portion; it can be further subdivided anatomically by multiple nerve branches into parallel longitudinal columns that terminate in a distributed insertion at the knee with a continuous range of moment arms. Thus, SA may be controlled by a discrete number of motoneuron task groups reflecting a small number of central command signals or by a continuum of activation patterns associated with a continuum of moment arms. To resolve this question, the activation patterns across the width of the SA were recorded with an electrode array during three kinematically different movements--treadmill locomotion, scratching and paw shaking, in awake, unrestrained cats. Uniformity of activation along the longitudinal axis was also examined because individual muscle fibers do not extend the length of the SA. In addition, the cutaneous reflex responses were recorded throughout all regions of the SA during locomotion. Two fascial surface-patch arrays, each carrying 4-8 pairs of bipolar EMG electrodes, were sutured to the inner surface of the SA, one placed proximally and the other more distally. Each array sampled separate sites across the anterior to medial axis of SA. During locomotion, two basic EMG patterns were observed: the two burst-per-step-cycle pattern typical of SAa and the single burst pattern typical of SAm. There was an abrupt transition in the pattern of activation recorded in the two parts of SA during locomotion, and no continuum in the activation pattern was observed. Stimulation of both sural and saphenous cutaneous nerves during locomotion produced reflex responses that were uniformly distributed throughout SA, in contrast to the regional differences noted during unperturbed walking. Similarly, during scratching and paw shaking all parts of the SA were active simultaneously but with regional differences in EMG amplitude. The abrupt functional border between SAa and SAm coincided with the division of the SA into a knee flexor vs. a knee extensor. In all cases, the quantitative and qualitative differences in SAa and SAm EMGs were uniformly recorded throughout the entire extent of SAa or SAm; i.e., there was no segregation of activity within either SAa or SAm. Furthermore, the time course of EMG from each proximal recording site was nearly identical to the corresponding distal site, indicating no segregation of function along the longitudinal axis of SA. These results indicate that SAa and SAm constitute the smallest functional modules that can be recruited in SA.(ABSTRACT TRUNCATED AT 400 WORDS)

Functionally complex muscles of the cat hindlimb. V. The roles of histochemical fiber-type regionalization and mechanical heterogeneity in differential muscle activation

Several cat hindlimb muscles that exhibit differential activation (activity that is restricted to a specific region of muscle) during natural movements were studied to determine the possible roles of 1) non-uniform distribution of histochemically-identified muscle fiber-types (semitendinosus, ST; tibialis anterior, TA) or 2) mechanical heterogeneity (biceps femoris, BF; tensor fasciae latae, TFL). Using chronic recording techniques, electromyographic (EMG) activity was recorded from multiple sites of each muscle during treadmill locomotion, ear scratch, and paw shake. Standard histochemical analysis was performed on each muscle to determine fiber-type distribution. The histochemically regionalized muscles (ST and TA) were differentially active during slow locomotion; the deep regions (high in type I [SO] fibers) were active, but the superficial regions (high in type IIB [FG] fibers) were inactive. Vigorous movements (fast locomotion, ear scratch, paw shake) produced additional, synchronous activation of the superficial regions. In all movements, ST and TA activation patterns were consistent with the existence of identically timed synaptic inputs to all motoneurons within each motoneuron pool, resulting in an orderly recruitment of each whole pool. The differential activation recorded from ST and TA during slow locomotion was presumably a consequence of the non-uniform distribution of the different muscle fiber types. In contrast, differential activation of the histochemically nonregionalized, mechanically heterogeneous muscles (BF and TFL) resulted from non-synchronous activation of different muscle regions. The selective activation of BF or TFL compartments was indicative of differential synaptic inputs to, and selective recruitment of, subpopulations of the motoneuron pool, with each motoneuron subpopulation exclusively innervating physically separate regions of the muscle consistent with the regions defined by the neuromuscular territories of the major nerve branches supplying each muscle. Individual neuromuscular compartments of BF and TFL differ in their mechanical arrangements to the skeleton and in their contribution to mechanical action(s) at the hip and knee joints. Selective neural activation of mechanically distinct compartments within a mechanically heterogeneous muscle can provide highly advantageous mechanical "options" for animals that perform kinematically diverse movements. With regard to EMG recording techniques, the results of this study emphasize the need for carefully chosen EMG sampling sites and the value of knowing the muscle histochemistry, neuromuscular and musculoskeletal anatomy and possible mechanical functions prior to recording EMG.

Functionally complex muscles of the cat hindlimb. IV. Intramuscular distribution of movement command signals and cutaneous reflexes in broad, bifunctional thigh muscles

Similarities between the muscle synergies associated with the flexion reflex and locomotion in reduced preparations have suggested that spinal circuits subserving these two motor tasks might share common interneurons. To test this hypothesis in functionally complex muscles, we studied the interaction between low-threshold cutaneous afferents and the locomotor central pattern generator (CPG) during treadmill locomotion in awake, intact cats. Electrical stimuli were delivered via implanted nerve cuff electrodes at all phases of locomotion, and EMGs were recorded from fourteen intramuscular subregions in eight bifunctional thigh muscles (adductor femoris, biceps femoris, caudofemoralis, gracilis, semimembranosus, semitendinosus, tensor fasciae latae, and tenuissimus). In addition, the EMG patterns recorded during locomotion were compared with those recorded during two other centrally driven rhythmical behaviors, scratching and paw shaking, to determine whether the functional relationships among these intramuscular subregions were fixed or task dependent. Four of the five broad, bifunctional muscles studied (biceps femoris, gracilis, semimembranosus, and tensor fasciae latae) had functional subunits that could be differentially activated in one or more of the three movements studied; adductor femoris was consistently uniformly activated despite its distributed skeletal attachments. The pattern of recruitment of the intramuscular functional subunits was movement-specific. The locomotor CPG and cutaneous reflex pathways both similarly subdivided some bifunctional muscles, but not others, into intramuscular subregions. The results of the present study confirm that some combinations of muscle subregions and cutaneous nerves constitute simple reciprocal categories of flexors and extensors, as described originally by Sherrington (1910). "Typical" low threshold excitatory or inhibitory reflex responses were produced in muscles or muscle subregions that were recruited as "net" flexors of extensors, respectively. However, muscles with complex activation patterns during walking often had very individualized, complex reflex responses during locomotion that did not conform to the background locomotion synergies. All of the reflex responses observed were mediated by low threshold cutaneous afferents. These data indicate that there are multiple, low threshold, excitatory and inhibitory cutaneous reflex pathways that have highly specialized connections with flexor and extensor muscles and even their intramuscular subregions. It is also clear that the premotoneuronal circuits mediating these cutaneous reflex effects are not necessarily synonymous with those of the locomotor CPG. These two systems do interact powerfully, however, suggesting some convergence. The nature of the convergence between the CPG and the many independent subsets of spinal interneurons mediating cutaneous reflexes is specialized and muscle subregion-specific.

Functionally complex muscles of the cat hindlimb. II. Mechanical and architectural heterogenity within the biceps femoris

The goal of this study was to analyze the architecture of the cat biceps femoris (BF), a multifunctional hamstring muscle, and to evaluate the relationships between muscle architecture, limb position, and muscle function during natural movement. The BF muscle consists of three neuromuscular compartments: anterior (BFa), middle (BFm) and posterior (BFp). Each compartment is innervated by a separate nerve branch. Nerve branch stimulation and 2-dimensional surface EMG recordings showed that individual compartment territories were discrete and non-overlapping with well-defined borders. Comparisons of the three compartments revealed consistent differences in architecture, relationship to the skeleton, and function. The BFa crossed only the hip joint and appears to function as a pure hip extensor. The BFm had equal lever arm lengths to the hip and knee joints, appears to function as a hip extensor, and may contribute to knee flexion or femoral rotation. The BFp had a greater lever arm to the knee, functions as a knee flexor, and may contribute to hip extension, femoral rotation or ankle extension. Measurements of individual fascicles from the three compartments revealed a surprising range of lengths, 3.3-12.0 cm. Microdissection of gold-stained tissue showed that fascicles from all compartments were comprised of interdigitated, short fibers (range: 0.6-5.0 cm; average 2.14 cm) arranged in-series in fascicles, running parallel to the origin-insertion axis of each muscle compartment. In regions of fiber interdigitation, the fiber endings were round and tapered (taper lengths: 1-11 mm) although flat, tapering endings like ribbons were occasionally found. As hip and knee joint angles were varied over physiological ranges corresponding to minimal to maximal muscle length, fascicles of the three compartments changed length disproportionately. Long BFa fascicles maximally lengthened 10-18%, consistent with in vivo length measures during treadmill locomotion. However, the long BFp fascicles lengthened 25-45%, and the relatively short fascicles near the BFm/BFp border maximally lengthened 45-53%. How do these unexpectedly large length changes affect sarcomere lengths? Using laser diffraction to measure sarcomeres, static fascicle and sarcomere lengths were compared in muscles that went into rigor mortis after fixing the hip and knee joint angles. Sarcomeres within the short BFm/BFp and long BFp fascicles consistently lengthened proportionately less than the whole fascicle. It remains to be determined how and where the fascicle length changes are dissipated in the connective tissue between the interdigitated muscle fibers and whether such a series-compliance operates during the large excursions over which this muscle normally works.

Role of tropoelastin fragmentation in elastogenesis in rat smooth muscle cells

Neonatal rat aortic smooth muscle cell cultures produce two major soluble elastin molecules termed protropoelastin (77 kDa) and tropoelastin (71 kDa). Cell layer extracts are protroproelastin-enriched, while protropoelastin, tropoelastin, and significant amounts of discrete elastin fragments (Mr of 66,000, 61,000, 56,000, and 45,000) are present in preparations from the medium of these cultures. To determine the role of the various elastin molecules in the metabolism of elastin in neonatal rat aortic smooth muscle cell cultures, the amino termini of these proteins were sequenced. All soluble elastin components present in the medium were purified as a single peak by high performance liquid chromatography; further separation of the components was achieved by polyacrylamide gel electrophoresis and electroblotting. The bands were excised and sequenced. The amino-terminal sequences of protropoelastin, tropoelastin, and the 66-kDa, 61-kDa, and 56-kDa fragments were identical: Gly-Gly-Val-Pro-Gly-Ala-Val-Pro-Gly-Gly. This sequence is identical with published amino-terminal sequences of tropoelastins from several other species. As expected, when the cell cultures were pulsed with [3H]valine, all the soluble elastin molecules were radioactive, while only protropoelastin appeared radioactive after [35S] cysteine pulsing. Since cysteine is present only in the carboxyl-terminal end of the molecule, all the data indicate that the cleavage of the elastin fragments identified in the culture are occurring at the carboxyl end of protropoelastin. These results are consistent with the original hypothesis that a precursor-product relationship exists between the 77-kDa and 71-kDa soluble elastin molecules. Based on known tropoelastin sequences and the molecular weights of the discrete fragments, additional fragmentation of protropoelastin and/or tropoelastin most likely occurs at the lysine/alanine-enriched domains presumably involved in cross-link formation.

Development of a screening questionnaire to study attrition in weight-control programs

Several environmental, social, personal and demographic factors are related to the likelihood that an individual will drop out of a weight-control program. This paper identifies such factors and proposes a research instrument to study attrition in adult weight-control programs.

Nutrition knowledge and concerns of health and physical education teachers

The results indicated that most (80%) of the teachers were fairly knowledgeable about the nutrition needs of athletes. However, while many teachers agreed that carbohydrates and fats were the main sources of muscular energy, 35% indicated that protein was the primary source of energy for muscular activity. Also, 12% agreed that the consumption of salt tablets during athletic events prevents muscle cramps. The results suggest nutrition education for HPE teachers is needed. Information provided to HPE teachers should address their three main nutrition concerns, which are a balanced diet for athletes, weight control, and fluid replacement.

The motor-unit population of the cat tenuissimus muscle

1. We studied the organization of motor units in the tenuissimus (TEN) muscle of pentobarbital-anesthetized cats. The cat TEN is a long, delicate straplike muscle that spans hip and knee, which has a very flat length-tension curve through 22 mm of length change. 2. The TEN motor nucleus, labeled by retrograde transport of several forms of horseradish peroxidase, was composed of 8-31 cells in different cats, of which about half were, on average, in the size range of alpha-motoneurons. TEN motoneurons were scattered through the ventrolateral portion of lamina IX, over a rostrocaudal distance of up to 6.5 mm, making it relatively easy to isolate individual TEN motor axons for single motor-unit stimulation. 3. Individual TEN muscle units were classified into four groups [fast-twitch, fatigable (FF), intermediate, fatigue-resistant (Fint), fast-twitch, fatigue-resistant (FR), and slow-twitch, fatigue resistant (S)] on the basis of "sag" and fatigue index mechanical properties, as in other cat hindlimb muscles. There was a relatively large proportion of Fint units (28%) in the TEN sample, and the range of tetanic tension (approximately 19-fold) was much smaller than found in other cat hindlimb muscles. 4. A majority of TEN muscle fibers could be classified into the three major histochemical types (IIB, IIA, and I) found in other cat muscles, but a substantial minority remained "unclassified." A single type Fint muscle unit was successfully depleted of glycogen for histochemical study. It exhibited a typical type IIB histochemical profile. 5. Despite its unusual morphology, the cat TEN contains the same types of motor units found in larger, more "typical" limb muscles.

Cross-correlation of EMG reveals widespread synchronization of motor units during some slow movements in intact cats

It is commonly assumed that the motor units comprising a single mammalian muscle will be recruited asynchronously at subtetanic firing rates to produce smoothly modulated force output. However, electromyograms from certain neck muscles, recorded by implanted bipolar "patch" electrodes having large contacts, often exhibited a rhythmic clustering of spike activity whose patterns suggested that motor-unit firing was synchronized both within and across muscles. We have developed a computerized processing system that digitizes EMG activity and calculates auto- and cross-correlation products of selected segments. The presence or absence of synchronization caused by neural mechanisms can be identified and differentiated from that due to the rhythmicity of the behavior itself (e.g. shaking) or due to cross-talk, according to the shapes of the resultant correlograms. These methods have so far been applied to the study of hindlimb and neck muscle EMG during various natural motor behaviors, but they provide a general, quantitative tool for the study of an important aspect of motor control that may be overlooked by conventional sampling and smoothing techniques.

A multiple-contact EMG recording array for mapping single muscle unit territories

The glycogen-depletion technique has become a well-established method for determining histologically the cross-sectional distribution of a single muscle unit. A major drawback of this method is its low yield of one depleted unit per experiment. Furthermore, this technique is particularly unsuited for determining the longitudinal distribution of single muscle units in long, broad muscles because of the formidable serial sectioning job that would be required. Our alternative, electrophysiological method utilizes a multiple-contact, two-dimensional EMG recording array to map efficiently the cross-sectional and longitudinal distributions of numerous single muscle units in anatomically diverse muscles. Additionally, architectural information on muscle fiber lengths, end-plate locations, motor subunit (MSU) arrangements and muscle conduction velocities can be determined.

Cat hindlimb motoneurons during locomotion. II. Normal activity patterns

Activity patterns were recorded from 51 motoneurons in the fifth lumbar ventral root of cats walking on a motorized treadmill at a range of speeds between 0.1 and 1.3 m/s. The muscle of destination of recorded motoneurons was identified by spike-triggered averaging of EMG recordings from each of the anterior thigh muscles. Forty-three motoneurons projected to one of the quadriceps (vastus medialis, vastus lateralis, vastus intermedius, or rectus femoris) or sartorius (anterior or medial) muscles of the anterior thigh. Anterior thigh motoneurons always discharged a single burst of action potentials per step cycle, even in multifunctional muscles (e.g., sartorius anterior) that exhibited more than one burst of EMG activity per step cycle. The instantaneous firing rates of most motoneurons were lowest upon recruitment and increased progressively during a burst, as long as the EMG was still increasing. Firing rates peaked midway through each burst and tended to decline toward the end of the burst. The initial, mean, and peak firing rates of single motoneurons typically increased for faster walking speeds. At any given walking speed, early recruited motoneurons typically reached higher firing rates than late recruited motoneurons. In contrast to decerebrated cats, initial doublets at the beginning of bursts were seen only rarely. In the 4/51 motoneurons that showed initial doublets, both the instantaneous frequency of the doublet and the probability of starting a burst with a doublet decreased for faster walking speeds. The modulations in firing rate of every motoneuron were found to be closely correlated to the smoothed electromyogram of its target muscle. For 32 identified motoneurons, the unit's instantaneous frequencygram was scaled linearly by computer to the rectified smoothed EMG recorded from each of the anterior thigh muscles. The covariance between unitary frequencygram and muscle EMG was computed for each muscle. Typically, the EMG profile of the target muscle accounted for 0.88-0.96 of the variance in unitary firing rate. The EMG profiles of the other anterior thigh muscles, when tested in the same way, usually accounted only for a significantly smaller fraction of the variance. Brief amplitude fluctuations observed in the EMG envelopes were usually also reflected in the individual motoneuron frequencygrams. To further demonstrate the relationship between unitary frequencygrams and EMG, EMG envelopes recorded during walking were used as templates to generate depolarizing currents that were applied intracellularly to lumbar motoneurons in an acute spinal preparation.(ABSTRACT TRUNCATED AT 400 WORDS)

Cat hindlimb motoneurons during locomotion. I. Destination, axonal conduction velocity, and recruitment threshold

Fine flexible wire microelectrodes chronically implanted in the fifth lumbar ventral root (L5 VR) of 17 cats rendered stable records of the natural discharge patterns of 164 individual axons during locomotion on a treadmill. Fifty-one out of 164 axons were identified as motoneurons projecting to the anterior thigh muscle group. For these axons, the centrifugal propagation of action potentials was demonstrated by the technique of spike-triggered averaging using signals recorded from cuff electrodes implanted around the femoral nerve. The axonal conduction velocity was measured from the femoral nerve cuff records. For 43/51 motoneurons, the corresponding target muscle was identified by spike-triggered averaging of signals recorded from bipolar EMG electrodes implanted in each of the anterior thigh muscles: vastus intermedius, medialis and lateralis, sartorius anterior and medialis, and rectus femoris. For 32/51 motoneurons, the recruitment threshold during locomotion was determined from the mean value of the rectified digitally smoothed EMG of the target muscle measured at the time when the motoneuron fired its first spike for each step. The recruitment threshold of every motoneuron was relatively constant for a given speed of walking, but for some units there were small systematic variations as a function of treadmill speed (range: 0.1-1.3 m/s). Recruitment thresholds were standardized with respect to the mean value of peak EMG activity of the target muscle during 16 s of walking at 0.5 m/s. For 28/51 motoneurons recorded in nine cats, recruitment thresholds (range: 3-93% of peak target muscle EMG) were linearly correlated (r = 0.51, P less than 0.02) to axonal conduction velocities (range: 57-117 m/s). In addition, for seven recorded pairs of motoneurons that projected to the same muscle in the same cat, the recruitment thresholds were ordered by relative conduction velocities. Taken together, these results are consistent with the notion that, in normal cat locomotion up to a medium trot, anterior thigh motoneurons are progressively recruited in an orderly fashion.

Cat hindlimb motoneurons during locomotion. III. Functional segregation in sartorius

Cat sartorius has two distinct anatomical portions, anterior (SA-a) and medial (SA-m). SA-a acts to extend the knee and also to flex the hip. SA-m acts to flex both the knee and the hip. The objective of this study was to investigate how a "single motoneuron pool" is used to control at least three separate functions mediated by the two anatomical portions of one muscle. Discharge patterns of single motoneurons projecting to the sartorius muscle were recorded using floating microelectrodes implanted in the L5 ventral root of cats. The electromyographic activity generated by the anterior and medial portions of sartorius was recorded with chronically implanted electrodes. The muscle portion innervated by each motoneuron was determined by spike-triggered averaging of the EMGs during walking on a motorized treadmill. During normal locomotion, SA-a exhibited two bursts of EMG activity per step cycle, one during the stance phase and one during the late swing phase. In contrast, every recorded motoneuron projecting to SA-a discharged a single burst of action potentials per step cycle. Some SA-a motoneurons discharged only during the stance phase, whereas other motoneurons discharged only during the late swing phase. In all cases, the instantaneous frequencygram of the motoneuron was well fit by the rectified smoothed EMG envelope generated by SA-a during the appropriate phase of the step cycle. During normal locomotion, SA-m exhibited a single burst of EMG activity per step cycle, during the swing phase. The temporal characteristics of the EMG bursts recorded from SA-m differed from the swing-phase EMG bursts generated by SA-a.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and innervation of short, interdigitated muscle fibers in parallel-fibered muscles of the cat hindlimb

The cat hindlimb contains several long, biarticular strap muscles composed of parallel muscle fascicles that attach to short tendons. Three of these muscles--sartorius, tenuissimus, and semitendinosus--were studied by dissecting individual gold-stained fibers and determining the surface distribution of acetylcholinesterase-stained end-plate zones. In each muscle, fascicles were composed of muscle fibers that ran only part of the fascicle length and tapered to end as fine strands that interdigitated with other tapering fibers within the muscle mass. Most muscle fibers measured 2-3 cm in length. Fascicles of muscle fibers were crossed by short transverse bands of endplates (1 mm wide by 1-5 mm long) that were spaced at fairly regular intervals from the origin to the insertion of the muscle. The endplate pattern suggested that the fiber fascicles were organized into multiple longitudinal strips. In the sartorius, the temporospatial distribution of electromyographic (EMG) activity evoked by stimulating fine, longitudinal branches of the parent nerve confirmed that each strip was selectively innervated by a small subset of the motor axons. These axons appeared to distribute their endings throughout the entire length of the fascicles, providing for synchronous activation of their in-series fibers.

Ia inhibitory interneurons and Renshaw cells as contributors to the spinal mechanisms of fictive locomotion

The activity of selected single alpha-motoneurons, Renshaw cells (RCs), and Ia inhibitory interneurons (IaINs) during fictive locomotion was recorded via microelectrodes in decerebrate (precollicular-postmammillary) cats in which fictive locomotion was induced by stimulation of the mesencephalic locomotor region. The interrelationships in the timing and frequency of discharge among these three interconnected cell types were determined by comparing their averaged step cycle firing histograms, which were normalized in reference to motoneuron activity recorded in ventral root filaments. Previous findings that RCs are rhythmically active during locomotion and discharge in phase with the motoneurons from which they are excited were confirmed, and further details of the phase relationships between RC and alpha-motoneuron activity during fictive locomotion were obtained. Flexor and extensor RCs became active after the onset of flexor and extensor motoneuron activity, respectively. Maximal activity in extensor RCs occurred at the end of the extension phase coincidental with the onset of hyperpolarization and a decrease in activity in extensor motoneurons. Maximal flexor RC activity occurred during middle to late flexion and was temporally related to the onset of reduced flexor motoneuron activity. The IaINs recorded in the present experiments were rhythmically active during fictive locomotion, as previously reported. The quadriceps IaINs were mainly active during the extension phase of the step cycle, along with extensor RCs. Thus the known inhibition of quadriceps IaINs by RCs coupled to quadriceps and other extensor motoneurons is obviously not sufficient to interfere with the appropriate phasing of IaIN activity and reciprocal inhibition during fictive locomotion, as had been speculated. Most of the quadriceps IaINs analyzed exhibited a decrease in discharge frequency at the end of the extension phase of the step cycle, which was coincidental with increased rates of firing in extensor RCs. These data are consistent with the possibility that extensor RCs contribute to the reduction in quadriceps IaIN discharge at the end of the extension phase of the step cycle. The possibility that IaIN rhythmicity during fictive locomotion arises from periodic inhibition, possibly from Renshaw cells, was tested by stimulating the reciprocal inhibitory pathway throughout the fictive step cycle. The amplitude of Ia inhibitory postsynaptic potentials (IPSPs) varied significantly throughout the fictive step cycle in 14 of the 17 motoneurons tested, and, in 11 of these 14 motoneurons, the Ia IPSPs were maximal during the phase of the step cycle in which the motoneuron was most

Elastase effect on the extracellular matrix of rat aortic smooth muscle cells in culture

The effect of elastase on the extracellular matrix of neonatal rat aortic smooth muscle cell cultures was monitored both chemically and ultrastructurally. Porcine pancreatic elastase was shown to decrease the elastin content in these cultures. Although chemically no distinction could be made between the elastin remaining in the culture matrix after elastase when compared to that in the nontreated cultures, the elastin was dramatically altered morphologically. The elastin assumed a "mottled" appearance after elastase treatment similar to that seen in vivo in emphysema models. A highly sensitive immunogold staining technique was used to detect elastin at the earliest stages of accumulation. Pulse experiments demonstrated an increase in protein synthesis by the cells 20 hr after elastase exposure. The culture system described here provides a model for probing in vivo elastase effects on elastin-containing tissues.

Aging effects on the elastin composition in the extracellular matrix of cultured rat aortic smooth muscle cells

Elastin accumulation in the extracellular matrix of cultured rat aortic smooth muscle cells was monitored as a function of age. The effect of the animal donor age and time in culture in single or consecutive passages on the cells' ability to accumulate total protein as well as elastin was evaluated. Smooth muscle cells were obtained from animals ranging in age from 2 d to 36 mo. Protein accumulation by the cells based on DNA content was similar regardless of which of the above aging parameters was examined. Although there were significant amounts of elastin present in the extracellular matrix of those cells originating from the younger animals (2 d and 6 wk old), little or none was detected in cell cultures derived from the oldest animals. A soluble elastin-like fraction which was isolated from the cultures of the 2-d-old rats seemed to be lacking in the cultures of cells from the 36-mo-old animals. This observation may, in part, explain the absence of insoluble elastin in the matrix of some cultures obtained from older animals. The data strongly suggest that the age of the donor animal from which the cells originate has the greatest influence on in vitro elastin accumulation.

Processing of soluble elastin in cultured neonatal rat smooth muscle cells

The synthesis and extracellular deposition of elastin by cultured neonatal rat aorta smooth muscle cells has been followed. The addition of beta-aminopropionitrile to the culture medium promotes accumulation of soluble precursors of elastin. Under such conditions, a protein possessing characteristics of a soluble elastin precursor with an apparent molecular weight of 77,000 was detected and partially purified. Pulse-chase studies suggested that this 77-kDa protein undergoes an extracellular, enzymatically catalyzed process to a 71-kDa protein. This 71-kDa protein is strikingly similar to tropoelastins isolated from other tissue systems, in which no evidence for higher molecular weight soluble precursors is at present available. Data presented in this communication suggest that the 77-kDa protein, which we have designated protropoelastin, represents a precursor to the tropoelastin moiety produced in the neonatal rat smooth muscle cell culture.

Activity of spindle afferents from cat anterior thigh muscles. I. Identification and patterns during normal locomotion

The naturally occurring activity patterns of anterior thigh muscle spindle afferents were recorded during unrestrained treadmill locomotion by means of floating microelectrodes chronically implanted in the fifth lumbar dorsal root ganglion. Conduction velocity of units from primary and secondary endings was determined by spike-triggered averaging of the signals from a chronically implanted nerve cuff. Activity from knee extensor muscle spindles generally occurred during periods of muscle lengthening, but was often greater for small stretches when the muscle was active (during stance phase of walking) than for larger stretches when the muscle was passive (swing phase), indicating fusimotor enhancement of spindle sensitivity in phase with extrafusal muscle recruitment. Activity from spindles in biarticular muscles acting across the knee and hip was more variable and complex than that seen in the pure knee extensors, and frequently included activity during rapid muscle shortening (swing phase) indicative of strong static fusimotor input. Changes in speed of gait caused changes in the range and velocity of muscle length excursions monitored by chronically implanted length gauges, but such changes were accompanied by only modest changes in spindle afferent activity, suggesting concurrent and compensatory changes in fusimotor influence on spindles. Activity from spindle secondary endings was generally lower, more regular, and less velocity dependent than that from primary endings, consistent with their lack of input from the dynamic fusimotor apparatus. The activity of all spindle afferents studied was similarly well modulated during extrafusal activity of the parent muscles, regardless of the kinematic conditions of muscle length and velocity during which this muscle work occurred. This suggests that the fusimotor apparatus is well orchestrated to regulate the static and dynamic sensitivity of primary spindle afferents at levels appropriate to the anticipated motion.

Distribution of the human jaw stretch reflex response elicited by percutaneous, localized stretch of jaw-closing muscles

In the present study homonymous and heteronymous projections of muscle spindle afferent fibers in the human jaw-closing system were investigated. Stretch reflex responses were elicited with percutaneous displacement stimuli applied to the belly of the anterior superficial divisions of temporalis and masseter muscles. The distribution of reflex responses in jaw-closing muscles was assessed. Reflex responses to this stimulus were observed in all jaw-closing muscles ipsilateral to the stimulated muscle, suggesting that the projection of spindle afferent fibers to jaw-closing muscles in humans is diffuse. Comparisons of homonymous and heteronymous reflex response amplitudes indicated that homonymous response amplitudes tended to be larger. However, the relative strength of heteronymous inputs to masseter motoneurons appeared to be stronger than those to temporalis motoneurons.

Single unit conduction velocities from averaged nerve cuff electrode records in freely moving cats

The conduction velocity of peripheral neurons recorded by wire microelectrodes implanted in intact, freely moving cats was determined on-line using the technique of spike-triggered averaging of nerve cuff electrode records described here. Axonal velocity was estimated from the conduction latency between two adjacent sets of tripolar recording electrodes inside a cuff, thereby avoiding uncertainties that could arise from differences in spike shape, variable conduction distance, or unknown stimulus utilization time. This method rendered conduction velocity values for individual afferent and efferent myelinated fibers ranging from 27 to 120 m/sec, estimated with an uncertainty of +/-5%. In addition, predictions from theoretical models relating extracellular potential amplitude, wavelength, and conduction velocity were confirmed experimentally for en passant records obtained from intact myelinated fibers.

Discharge patterns of hindlimb motoneurons during normal cat locomotion

Long-term recording from single lumbar motoneurons of intact cats revealed activation patterns fundamentally different from those seen in decerebrate preparations. In intact cats, motoneuron bursts showed marked rate modulation without initial doublets. Each unit's frequencygram generally resembled the envelope of the gross electromyogram simultaneously recorded from the corresponding muscle. Average and peak discharge rates increased for faster gaits. These findings suggest that, in cat locomotion, rate modulation is a more important contributor to force regulation than was previously thought.