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The rods of anti-parallel myosin molecules overlap at the centre of bipolar myosin filaments to produce an M-region (bare zone) that is free of myosin heads. Beyond the M-region edges, myosin molecules aggregate in a parallel fashion to yield the bridge regions of the myosin filaments. Adjacent myosin filaments in striated muscle A-bands are cross-linked by the M-band. Vertebrate striated muscle myosin filaments have a 3-fold rotational symmetry around their long axes. In addition, at the centre of the M-region, there are three 2-fold axes perpendicular to the filament long axis, giving the whole filament dihedral 32-point group symmetry. Here we describe the three-dimensional structure obtained by a single-particle analysis of the M-region of myosin filaments from goldfish skeletal muscle under relaxing conditions and as viewed in negative stain. This is the first single-particle reconstruction of isolated M-regions. The resulting three-dimensional reconstruction reveals details to about 55 Å resolution of the density distribution in the five main nonmyosin densities in the M-band (M6′, M4′, M1, M4 and M6) and in the myosin head crowns (P1, P2 and P3) at the M-region edges. The outermost crowns in the reconstruction were identified specifically by their close similarity to the corresponding crown levels in our previously published bridge region reconstructions. The packing of myosin molecules into the M-region structure is discussed, and some unidentified densities are highlighted.

Experiments in the cat have led to a concept of how the CNS controls micturition. In a previous study this concept was tested in a PET study in male volunteers, It was demonstrated that specific brainstem and forebrain areas are activated during micturition, It was unfortunate that this study did not involve women, because such results are important for understanding urge incontinence, which occurs more frequently in women than in men. Therefore, a similar study was done in 18 right-handed women, who were scanned during the following four conditions: (i) 15 min prior to micturition (urine withholding); (ii) during micturition; (iii) 15 min after micturition; and (iv) 30 min after micturition, Of the 18 volunteers, 10 were able to micturate during scanning and eight were not, despite trying vigorously. Micturition appeared to be associated with significantly increased blood flow in the right dorsal pontine tegmentum and the right inferior frontal gyrus, Decreased blood flow was found in the right anterior cingulate gyrus during urine withholding. The eight volunteers who were not able to micturate during scanning did not show significantly increased regional cerebral blood flow in the right dorsal, but did so in the right ventral pontine tegmentum, In the cat this region controls the motor neurons of the pelvic floor. In the same unsuccessful micturition group, increased blood flow was also found in the right inferior frontal gyrus, In all 18 volunteers, decreased blood flow in the right anterior cingulate gyrus was found during the period when they had to withhold their urine prior to the micturition condition. The results suggest that in women rind in men the same specific nuclei exist in the pontine tegmentum responsible for the control of micturition. The results also indicate that the cortical and pontine micturition sites are more active on the right than on the left side.

Light microscopy tracing studies have provided evidence that the pontine micturition center (PMC) projects to the area of the intermediolateral cell column of the sacral spinal cord. Although this region contains parasympathetic preganglionic motoneurons of the bladder and colon, it also contains many local interneurons and neurons projecting to supraspinal levels. The present study demonstrates that neurons in the PMC indeed project to preganglionic bladder motoneurons. Wheat germ agglutinin horseradish peroxidase was injected in the PMC and cholera toxin B subunit was injected in the bladder wall. Many anterogradely labeled fibers from the PMC were found to terminate on somata and dendrites of the retrogradely labeled preganglionic bladder motoneurons. The terminals were filled with many round vesicles and possessed an asymmetric synaptic cleft, suggesting an excitatory function. (C) 1997 Elsevier Science Ireland Ltd.

Although the brain plays a crucial role in the control of micturition, little is known about the structures involved. Identification of these areas is important because their dysfunction is thought to cause urge incontinence, a major problem in the elderly. In the cat, three areas in the brainstem and diencephalon are specifically implicated in the control of micturition: the dorsomedial pontine tegmentum, the periaqueductal grey, and the preoptic area of the hypothalamus. PET scans were used to test whether these areas are also involved in human micturition. Seventeen right-handed male volunteers were scanned during the following four conditions: (i) 15 min prior to micturition during urine withholding; (ii) during micturition; (iii) 15 min after micturition; (iv) 30 min after micturition. Ten of the 17 volunteers were able to micturate during scanning. Micturition was associated with increased blood flow in the right dorsomedial pontine tegmentum, the periaqueductal grey, the hypothalamus and the right inferior frontal gyrus. Decreased blood flow was found in the right anterior cingulate gyrus when urine was withheld. The other seven volunteers were not able to micturate during scanning, although they had a full bladder and tried vigorously to do so. In this group, during these unsuccessful attempts to micturate, increased blood pow was Sound in the right ventral pontine tegmentum, which corresponds with the hypothesis, formulated from results in cats, that this area controls the motor neurons of the pelvic poor Increased blood pow was also found in the right inferior frontal gyrus during unsuccessful attempts at micturition, and decreased blood pow in the right anterior cingulate gyrus was found during the withholding of urine. The results suggest that, as that of the cat, the human brainstem contains specific nuclei responsible for the control of micturition, and that the cortical and pontine micturition sites are predominantly on the right side.

The pelvic floor musculature plays an important role in behaviors such as defecation, micturition, mating behavior, and vomiting. A recent positron emission tomography (PET) study revealed that structures belonging to the emotional motor system are involved in the control of the pelvic floor during micturition. However, there also exist brain structures involved in the voluntary motor control of the pelvic floor, and the present PET study was designed to identify these structures. Six adult female volunteers were scanned with the bolus injection of (H2O)-O-15 during the following four conditions: (1) rest, (2) repetitive pelvic floor straining, (3) sustained pelvic floor straining, and (4) sustained abdominal straining. The results revealed that the superomedial precentral gyrus, the most medial portion of the motor cortex, is activated during pelvic floor contraction and the superolateral precentral gyrus during contraction of the abdominal musculature. In these conditions, significant activations were also found in the cerebellum, supplementary motor cortex, and thalamus. The right anterior cingulate gyrus was activated during sustained pelvic floor straining. No activations were found in subcortical structures belonging to the emotional motor system. The results are discussed in light of the existing literature on human control of the pelvic floor and micturition. (C) 1997 Wiley-Liss, Inc.

Light microscopy tracing studies have provided evidence that the pontine micturition center (PMC) projects to the area of the intermediolateral cell column of the sacral spinal cord. Although this region contains parasympathetic preganglionic motoneurons of the bladder and colon, it also contains many local interneurons and neurons projecting to supraspinal levels. The present study demonstrates that neurons in the PMC indeed project to preganglionic bladder motoneurons. Wheat germ agglutinin horseradish peroxidase was injected in the PMC and cholera toxin B subunit was injected in the bladder wall. Many anterogradely labeled fibers from the PMC were found to terminate on somata and dendrites of the retrogradely labeled preganglionic bladder motoneurons. The terminals were filled with many round vesicles and possessed an asymmetric synaptic cleft, suggesting an excitatory function. (C) 1997 Elsevier Science Ireland Ltd.

Although the brain plays a crucial role in the control of micturition, little is known about the structures involved. Identification of these areas is important because their dysfunction is thought to cause urge incontinence, a major problem in the elderly. In the cat, three areas in the brainstem and diencephalon are specifically implicated in the control of micturition: the dorsomedial pontine tegmentum, the periaqueductal grey, and the preoptic area of the hypothalamus. PET scans were used to test whether these areas are also involved in human micturition. Seventeen right-handed male volunteers were scanned during the following four conditions: (i) 15 min prior to micturition during urine withholding; (ii) during micturition; (iii) 15 min after micturition; (iv) 30 min after micturition. Ten of the 17 volunteers were able to micturate during scanning. Micturition was associated with increased blood flow in the right dorsomedial pontine tegmentum, the periaqueductal grey, the hypothalamus and the right inferior frontal gyrus. Decreased blood flow was found in the right anterior cingulate gyrus when urine was withheld. The other seven volunteers were not able to micturate during scanning, although they had a full bladder and tried vigorously to do so. In this group, during these unsuccessful attempts to micturate, increased blood pow was Sound in the right ventral pontine tegmentum, which corresponds with the hypothesis, formulated from results in cats, that this area controls the motor neurons of the pelvic poor Increased blood pow was also found in the right inferior frontal gyrus during unsuccessful attempts at micturition, and decreased blood pow in the right anterior cingulate gyrus was found during the withholding of urine. The results suggest that, as that of the cat, the human brainstem contains specific nuclei responsible for the control of micturition, and that the cortical and pontine micturition sites are predominantly on the right side.