Gastrointestinal transit and digestibility of maltitol, sucrose and sorbitol in rats: a multicompartmental model and recovery study.

Using data obtained with a dye marker and the gavage technique, the kinetics of gastrointestinal transit of different loads of sugar substitutes (maltitol, sorbitol) and sugar (sucrose) in the rat were analysed using a linear multicompartmental model over a range from the realistic to the non-physiologic high, of carbohydrate intake levels and using only a few experimental time points. The model gave detailed insight into intestinal propulsion and gastrocecal transit time. Rate constants of transport between the compartments investigated were determined; they showed characteristics which could be related to the substance and the dosage administered. Analyses of the gastrointestinal content and calculations of the intestinal net water movement showed that the digestibility and absorption of the disaccharide sugar alcohol, maltitol, in the small gut depended inversely on the dose ingested. For all substances tested, caloric availability in the small intestine was calculated. At a physiological low level of maltitol intake, the results also indicated an insignificant calorie-saving effect in comparison to sucrose, an effect based mainly on the slow absorption rate of the maltitol cleavage product sorbitol.     

Piroxicam-induced analgesia: Evidence for a central component which is not opioid mediated

Piroxicam is a nonsteroidal anti-inflammatory drug with a potent analgesic effect. In order to establish whether the analgesic action of Piroxicam has a central component, we studied the effect of the drug on the nociceptive orbicularis oculi reflexes evoked by electrical stimulation of the cornea and supraorbital nerve in healthy subjects. Piroxicam significantly suppressed the corneal reflex and R3 component of the blink reflex by 28% (p<0.05) and 50% (p<0.01), respectively. This effect was not reversed by the i.v. injection of naloxone. Beta-endorphin levels did not change. Piroxicam administration induces distinct inhibitory changes in nociceptive reflexes, which suggests that the analgesic action of the drug has a central component. The ineffectiveness of naloxone, and the lack of beta-endorphin changes, indicate that this central action is independent of the opioid system; other pain regulatory systems are probably involved.     

Rapid generation of region specific probes by chromosome microdissection and their application.

The strategy presented here to identify unequivocally cryptic chromosomal rearrangements has relevance to both prenatal and postnatal cytogenetic analysis as well as the analysis of tumour-associated chromosome rearrangements. Microdissection and in vitro amplification of specific chromosomal regions are performed, followed by labelling for fluorescent in situ hybridization (FISH) to normal metaphase chromosomes (Micro-FISH). Micro-FISH probes have been used successfully to determine the derivation of chromosome segments unidentifiable by standard chromosome banding analysis. Micro-FISH probes (created in less than 24 hours) now make it possible to identify explicitly the chromosome constitution of virtually all cytologically visible chromosome rearrangements.     

Aberrant splicing of neural cell adhesion molecule L1 mRNA in a family with X-linked hydrocephalus.

A locus for X-linked hydrocephalus (HSAS), which is characterized by mental retardation and enlarged brain ventricles, maps to the same subchromosomal region (Xq28) as the gene for neural cell adhesion molecule L1. We have found novel L1 mRNA species in cells from affected members of a HSAS family containing deletions and insertions produced by the utilization of alternative 3' splice sites. A point mutation at a potential branch point signal in an intron segregates with the disease and is likely to be responsible for the abnormal RNA processing. These results suggest that HSAS is a disorder of neuronal cell migration due to disruption of L1 protein function.     

A candidate mouse model for Prader-Willi syndrome which shows an absence of Snrpn expression.

The best examples of imprinting in humans are provided by the Angelman and Prader-Willi syndromes (AS and PWS) which are associated with maternal and paternal 15q11-13 deletions, respectively, and also with paternal and maternal disomy 15. The region of the deletions has homology with a central part of mouse chromosome 7, incompletely tested for imprinting effects. Here, we report that maternal duplication for this region causes a murine imprinting effect which may correspond to PWS. Paternal duplication was not associated with any detectable effect that might correspond with AS. Gene expression studies established that Snrpn is not expressed in mice with the maternal duplication and suggest that the closely-linked Gabrb-3 locus is not subject to imprinting. Finally, an additional new imprinting effect is described.     

The peripheral myelin protein gene PMP-22 is contained within the Charcot-Marie-Tooth disease type 1A duplication.

Charcot-Marie-Tooth disease (CMT1) is the most common form of inherited peripheral neuropathy. Although the disease is genetically heterogeneous, it has been demonstrated that the gene defect is the most frequent type (CMT1A) is the result of a partial duplication of band 17p11.2. Recent studies suggested that the peripheral hypomyelination syndrome in the trembler (Tr) mouse, a possible animal model for CMT1 disease, is associated with a point mutation in the peripheral myelin protein-22 gene (pmp-22). Expression of pmp-22 is particularly high in Schwann cells, and the protein is found in peripheral myelin. We now report that the human PMP-22 gene is contained within the CMT1A duplication. We therefore, suggest that increased dosage of the PMP-22 gene may be the cause of CMT1A neuropathy.     

Small nuclear ribonucleoprotein polypeptide N (SNRPN), an expressed gene in the Prader-Willi syndrome critical region.

Prader-Willi syndrome (PWS) is associated with paternally derived chromosomal deletions in region 15q11-13 or with maternal disomy for chromosome 15. Therefore, loss of the expressed paternal alleles of maternally imprinted genes must be responsible for the PWS phenotype. We have mapped the gene encoding the small nuclear RNA associated polypeptide SmN (SNRPN) to human chromosome 15q12 and a processed pseudogene SNRPNP1 to chromosome region 6pter-p21. Furthermore, SNRPN was mapped to the minimal deletion interval that is critical for PWS. The fact that the mouse Snrpn gene is maternally imprinted in brain suggests that loss of the paternally derived SNRPN allele may be involved in the PWS phenotype.     

Clonal expansion of p53 mutant cells is associated with brain tumour progression.

Tumour progression is a fundamental feature of the biology of cancer. Cancers do not arise de novo in their final form, but begin as small, indolent growths, which gradually acquire characteristics associated with malignancy. In the brain, for example, low-grade tumours (astrocytomas) evolve into faster growing, more dysplastic and invasive high-grade tumours (glioblastomas). To define the genetic events underlying brain tumour progression, we analysed the p53 gene in ten primary brain tumour pairs. Seven pairs consisted of tumours that were high grade both at presentation and recurrence (group A) and three pairs consisted of low-grade tumours that had progressed to higher grade tumours (group B). In group A pairs, four of the recurrent tumours contained a p53 gene mutation; in three of them, the same mutation was found in the primary tumour. In group B pairs, progression to high grade was associated with a p53 gene mutation. A subpopulation of cells were present in the low-grade tumours that contained the same p53 gene mutation predominant in the cells of the recurrent tumours that had progressed to glioblastoma. Thus, the histological progression of brain tumours was associated with a clonal expansion of cells that had previously acquired a mutation in the p53 gene, endowing them with a selective growth advantage. These experimental observations strongly support Nowell's clonal evolution model of tumour progression.     

Dynamin is a GTPase stimulated to high levels of activity by microtubules.

Dynamin was initially identified in calf brain tissue as a protein of relative molecular mass 100,000 which induced nucleotide-sensitive bundling of microtubules. Purified dynamin showed only trace ATPase activity. But in combination with an activating factor removed during the purification, it exhibited microtubule-activated ATPase activity and dynamin-induced bundles showed evidence of ATP-dependent force production. Dynamin is the product of the Drosophila gene shibire, which has been implicated in synaptic vesicle recycling and, more generally, in the budding of endocytic vesicles from the plasma membrane. Dynamin also shows extensive homology with proteins that participate in vacuolar protein sorting and spindle pole-body separation in yeast, and in interferon-induced viral resistance in mammals. All members of this family contain consensus sequence elements consistent with GTP binding near their amino termini, although none has been shown to have GTPase activity. We report here that dynamin is a specific GTPase which can be stimulated to very high levels of activity by microtubules.     

Specific low-affinity recognition of major histocompatibility complex plus peptide by soluble T-cell receptor.

The T-cell receptor is necessary and sufficient for recognition of peptides presented by major histocompatibility complex molecules. Other adhesion molecules, like CD4 or CD8, play an auxiliary role in antigen recognition by T cells. Here we analyse T-cell receptor (TCR) binding using a soluble rather than a cell-bound receptor molecule. A TCR-immunoglobulin chimaera is constructed with the variable and the first constant regions of both the TCR alpha- and beta-chains linked to the immunoglobulin light-chain constant regions. This soluble TCR is expressed, assembled and secreted as an alpha beta heterodimer by a myeloma cell line transfected with the recombinant genes. Furthermore, the soluble TCR is biologically active: it specifically inhibits antigen-dependent activation of the relevant T-cell clones and thus discriminates between proper and irrelevant peptides presented by major histocompatibility complex molecules.