Physiological properties and receptive fields of mechanosensory neurones in the head ganglion of the leech: comparison with homologous cells in segmental ganglia.
(9/1895)
A study of the head ganglion of the leech was made to compare the properties of specific sensory cells in this ganglion with those of homologous neurones in the segmental ganglia. 1. In the head ganglion, cells were identified that had electrical properties, sensory modalities and adaptation properties similar to those of touch (T), pressure (P) and nociceptive (N) cells in the segmental ganglia. The cell bodies of these neurones were situated in characteristics positions that could be correlated with those in the segmental ganglia. Several lines of evidence suggested that they were primary sensory neurones. Fewer T, P and N neurones were identified in the head ganglion than would be expected from its six constituent segmental ganglia. 2. The receptive fields of identified T, P and N cells were situated on the external surface of the head and the interior of the mouth with considerable overlap. They were generally smaller in size than those situated on the main part of the body. The receptive fields were also displaced anteriorly so that some of them were situated in segments anterior to those of the innervating cells. 3. The morphology of the sensory cells in the head ganglion was studied by intracellular injection of horseradish perioxidase. The general branching characteristics of the cells and the structural appearance of their processes resembled those of homologous cells in the segmental ganglia. However, the routes taken to the periphery by some of the cells were not constant from head ganglion to head ganglion. This variability was confirmed by electrophysiological evidence, and differed from the constancy seen in segmental sensory cells. (+info)
Neural crest can form cartilages normally derived from mesoderm during development of the avian head skeleton.
(10/1895)
The lateral wall of the avian braincase, which is indicative of the primitive amniote condition, is formed from mesoderm. In contrast, mammals have replaced this portion of their head skeleton with a nonhomologous bone of neural crest origin. Features that characterize the local developmental environment may have enabled a neural crest-derived skeletal element to be integrated into a mesodermal region of the braincase during the course of evolution. The lateral wall of the braincase lies along a boundary in the head that separates neural crest from mesoderm, and also, neural crest cells migrate through this region on their way to the first visceral arch. Differences in the availability of one skeletogenic population versus the other may determine the final composition of the lateral wall of the braincase. Using the quail-chick chimeric system, this investigation tests if populations of neural crest, when augmented and expanded within populations of mesoderm, will give rise to the lateral wall of the braincase. Results demonstrate that neural crest can produce cartilages that are morphologically indistinguishable from elements normally generated by mesoderm. These findings (1) indicate that neural crest can respond to the same cues that both promote skeletogenesis and enable proper patterning in mesoderm, (2) challenge hypotheses on the nature of the boundary between neural crest and mesoderm in the head, and (3) suggest that changes in the allocation of migrating cells could have enabled a neural crest-derived skeletal element to replace a mesodermal portion of the braincase during evolution. (+info)
Long-term follow up of persistent hyperinsulinaemic hypoglycaemia of infancy.
(11/1895)
Twenty six children with hypoglycaemia were diagnosed and followed between 1975 and 1995. Diagnosis was confirmed by a high insulin:glucose ratio, and low free fatty acid and 3-hydroxybutyrate on fasting. All patients were treated with diazoxide at a maximum dose of 20 mg/kg/day. Requirement of a higher dose was considered as a failure of medical treatment and an indication for surgery. Sixteen children Responded to diazoxide; 10 failed to respond and underwent pancreatic resection. Six of the latter group started with symptoms in the neonatal period. Eleven of the 26 children have neurological sequelae. Head growth and neurological outcome correlated well. Additionally, non-specific electroencephalogram abnormalities (slow waves) appear to be indicative of subclinical hypoglycaemia during follow up. (+info)
Teratogen-induced cell death in postimplantation mouse embryos: differential tissue sensitivity and hallmarks of apoptosis.
(12/1895)
Teratogen-induced cell death is a common event in the pathogenesis associated with tissues destined to be malformed. Although the importance of this cell death is recognized, little information is available concerning the biochemistry of teratogen-induced cell death. We show that three teratogens, hyperthermia, cyclophosphamide and sodium arsenite induce an increase in cell death in day 9.0 mouse embryos with concurrent induction of DNA fragmentation, activation of caspase-3 and the cleavage of poly (ADP-ribose) polymerase (PARP). Teratogen-induced cell death is also selective, i. e., some cells within a tissue die while others survive. In addition, cells within some tissues die when exposed to teratogens while cells in other tissues are relatively resistant to teratogen-induced cell death. An example of the latter selectivity is seen in the cells of the developing heart, which are resistant to the cytotoxic potential of many teratogens. We show that the absence of cell death in the heart is accompanied by the complete lack of DNA fragmentation, activtion of caspase-3 and the cleavage of PARP. (+info)
Sequence interval within the PEST motif of Bicoid is important for translational repression of caudal mRNA in the anterior region of the Drosophila embryo.
(13/1895)
The Drosophila body organizer Bicoid (Bcd) is a maternal homeodomain protein. It forms a concentration gradient along the longitudinal axis of the preblastoderm embryo and activates early zygotic segmentation genes in a threshold-dependent fashion. In addition, Bcd acts as a translational repressor of maternal caudal (cad) mRNA in the anterior region of the embryo. This process involves a distinct Bcd-binding region (BBR) in the 3' untranslated region (UTR) of cad mRNA. Using cotransfection assays, we found that Bcd represses translation in a cap-dependent manner. Bcd-dependent translational repression involves a portion of the PEST motif of Bcd, a conserved protein motif best known for its function in protein degradation. Rescue experiments with Bcd-deficient embryos expressing transgene-derived Bcd mutants indicate that amino acid replacements within the C-terminal portion of the PEST motif prevent translational repression of cad mRNA but allow for Bcd-dependent transcriptional activation. Thus, Bcd contains separable protein domains for transcriptional and translational regulation of target genes. Maternally-derived cad protein in the anterior region of embryos interferes with head morphogenesis, showing that cad mRNA suppression by Bcd is an important control event during early Drosophila embryogenesis. (+info)
A clinical study of type 1 neurofibromatosis in north west England.
(14/1895)
A clinical study of patients on the North West Regional Genetic Register with neurofibromatosis type 1 (NF1) identified 523 affected cases from 304 families. In those for whom relevant information was available, 86.7% (383 of 442) had more than six cafe au lait patches, 83.8% (310 of 370) had axillary freckling, 42.3% (151 of 357) had inguinal freckling, and 63% (157 of 249) had Lisch nodules. Cutaneous neurofibromas were present in 59.4% (217 of 365) and 45.5% (150 of 330) were noted to have subcutaneous tumours. Plexiform neurofibromas were present in 15.3% (80 of 523). A positive family history of NF1 was found in 71.2% (327 of 459) and 28.8% (132 of 459) of affected patients were considered to be the result of a new mutation. Learning difficulties of varying severity occurred in 62% (186 of 300). CNS tumours associated with NF1 were reported in 9.4% (49) of patients, optic gliomas occurring in 25 of these, 4.8% of patients. Some degree of scoliosis was reported for 11.7% (61), 1.9% (10) had pseudoarthrosis, 4.3% (23) had epilepsy, and 2.1% (11) had spinal neurofibromas. Actuarial analyses were carried out for both optic glioma and malignant nerve sheath tumours and the data are presented. (+info)
The protein phosphatase inhibitor cantharidin induces head and foot formation in buds of Cassiopea andromeda (Rhizostomae, Scyphozoa).
(15/1895)
The polyps of Cassiopea andromeda produce spindle shaped, freely swimming buds which do not develop a head (a mouth opening surrounded by tentacles) and a foot (a sticky plate at the opposite end) until settlement to a suited substrate. The buds, therewith, look very similar to the planula larvae produced in sexual reproduction. With respect to both, buds and planulae, several peptides and the phorbolester TPA have been found to induce the transformation into a polyp. Here it is shown that cantharidin, a serine/threonine protein phosphatase inhibitor, induces head and foot formation in buds very efficiently in a 30 min treatment, the shortest yet known efficient treatment. Some resultant polyps show malformations which indicate that a bud is ordinary polyp tissue in which preparatory steps of head and foot formation mutually block each other from proceeding. Various compounds related to the transfer of methyl groups have been shown to affect head and foot formation in larvae of the hydrozoon Hydractinia echinata. These compounds including methionine, homocysteine, trigonelline, nicotinic acid and cycloleucine are shown to also interfere with the initiation of the processes which finally lead to head and foot formation in buds of Cassiopea andromeda. (+info)
Reduction of aneurysm clip artifacts on CT angiograms: a technical note.
(16/1895)
We describe a head tilt technique for use with CT angiography that reduces beam-hardening artifacts in patients with aneurysm clips. This simple maneuver directs the artifacts away from pertinent anatomy, thus increasing the chances for diagnostic accuracy. No significant changes in the CT angiographic protocol are required, and the maneuver can easily be combined with other artifact-minimizing strategies. (+info)