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Biomedical subjects

H Gad

Publications and source records attributed to H Gad.

8 recordsLinked to original sources
PubMed2005

Malignant bone tumors in Kuwait: a 10-year clinicopathological study.

Between 1995 and 2004, 142 malignant bone tumours comprising 76 primary and 66 secondary tumours were identified in the Pathology Department of Al-Sabah Hospital, Kuwait. Pathological fracture was the presenting sign in 35% of the cases. The mean incidence of primary tumours/year was 3.3 cases/million inhabitants. The primary tumours showed a male predilection and 42% occurred below the age of 20 years. The most frequent in the descending order of frequency were Ewing's sarcoma, multiple myeloma, osteosarcoma, chondrosarcoma and non-Hodgkin's lymphoma. The femur was the most common site for secondary tumours; more than half of the tumours with metastases at this site originated in the breast. The high frequency of Ewing's sarcoma is noteworthy and requires further investigation.

Adolescent↗
PubMed2000

Fission and uncoating of synaptic clathrin-coated vesicles are perturbed by disruption of interactions with the SH3 domain of endophilin.

Coordination between sequential steps in synaptic vesicle endocytosis, including clathrin coat formation, fission, and uncoating, appears to involve proteinprotein interactions. Here, we show that compounds that disrupt interactions of the SH3 domain of endophilin with dynamin and synaptojanin impair synaptic vesicle endocytosis in a living synapse. Two distinct endocytic intermediates accumulated. Free clathrin-coated vesicles were induced by a peptide-blocking endophilin's SH3 domain and by antibodies to the proline-rich domain (PRD) of synaptojanin. Invaginated clathrin-coated pits were induced by the same peptide and by the SH3 domain of endophilin. We suggest that the SH3 domain of endophilin participates in both fission and uncoating and that it may be a key component of a molecular switch that couples the fission reaction to uncoating.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Endophilin/SH3p4 is required for the transition from early to late stages in clathrin-mediated synaptic vesicle endocytosis.

Endophilin/SH3p4 is a protein highly enriched in nerve terminals that binds the GTPase dynamin and the polyphosphoinositide phosphatase synaptojanin, two proteins implicated in synaptic vesicle endocytosis. We show here that antibody-mediated disruption of endophilin function in a tonically stimulated synapse leads to a block in the invagination of clathrin-coated pits adjacent to the active zone and therefore to a block of synaptic vesicle recycling. We also show that in a cell-free system, endophilin is not associated with clathrin coats and is a functional partner of dynamin. Our findings suggest that endophilin is part of a biochemical machinery that acts in trans to the clathrin coat from early stages to vesicle fission.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Dissociation between Ca2+-triggered synaptic vesicle exocytosis and clathrin-mediated endocytosis at a central synapse.

We have tested whether action potential-evoked Ca2+ influx is required to initiate clathrin-mediated synaptic vesicle endocytosis in the lamprey reticulospinal synapse. Exo- and endocytosis were temporally separated by a procedure involving tonic action potential stimulation and subsequent removal of extracellular Ca2+ (Ca2+e). A low concentration of Ca2+ ([Ca2+]e of 11 microM) was found to be required for the induction of early stages of endocytosis. However, the entire endocytic process, from the formation of clathrin-coated membrane invaginations to the generation of synaptic vesicles, proceeded in the absence of action potential-mediated Ca2+ entry. Our results indicate that the membrane of synaptic vesicles newly incorporated in the plasma membrane is a sufficient trigger of clathrin-mediated synaptic vesicle endocytosis.

Animals↗
PubMed1997

Synaptic vesicle endocytosis impaired by disruption of dynamin-SH3 domain interactions.

The proline-rich COOH-terminal region of dynamin binds various Src homology 3 (SH3) domain-containing proteins, but the physiological role of these interactions is unknown. In living nerve terminals, the function of the interaction with SH3 domains was examined. Amphiphysin contains an SH3 domain and is a major dynamin binding partner at the synapse. Microinjection of amphiphysin's SH3 domain or of a dynamin peptide containing the SH3 binding site inhibited synaptic vesicle endocytosis at the stage of invaginated clathrin-coated pits, which resulted in an activity-dependent distortion of the synaptic architecture and a depression of transmitter release. These findings demonstrate that SH3-mediated interactions are required for dynamin function and support an essential role of clathrin-mediated endocytosis in synaptic vesicle recycling.

Amino Acid Sequence↗
PubMed1997

Sustained neurotransmitter release: new molecular clues.

Chemical synapses convey impulses at high frequency by exocytosis of synaptic vesicles. To avoid failure of synaptic transmission, rapid replenishment of synaptic vesicles must occur. Recent molecular perturbation studies have confirmed that the recycling of synaptic vesicles involves clathrin-mediated endocytosis. The rate of exocytosis would thus be limited by the capacity of the synaptic clathrin machinery unless vesicles could be drawn from existing pools. The mobilization of vesicles from the pool clustered at the release sites appears to provide a mechanism by which the rate of exocytosis can intermittently exceed the rate of recycling. Perturbation of synapsins causes disruption of vesicle clusters and impairment of synaptic transmission at high but not at low frequencies. Both clathrin-mediated recycling and mobilization of vesicles from the reserve pool are thus important in the replenishment of synaptic vesicles. The efficacy of each mechanism appears to differ between synapses which operate with different patterns of activity.

Animals↗
PubMed1995

Synaptic vesicle depletion in reticulospinal axons is reduced by 5-hydroxytryptamine: direct evidence for presynaptic modulation of glutamatergic transmission.

5-hydroxytryptamine (5-HT; serotonin) is known to depress glutamatergic synaptic transmission in the spinal cord of vertebrates. To test directly whether 5-HT inhibits synaptic glutamate release, we examined its effect on the ultrastructure of synaptic vesicle clusters in giant reticulospinal axons in a lower vertebrate (lamprey; Lampetra fluviatilis). The size of these axons makes it possible to selectively expose only a part of the presynaptic element to 5-HT, while another part of the same axon is maintained in control solution. Action potential stimulation at 20 Hz for 20 min caused a marked reduction in the number of synaptic vesicles in active zones maintained in control solution, while in the part exposed to 5-HT (20 microM) the number of synaptic vesicles per active zone was approximately 3-fold higher. In contrast, 5-HT had no effect on the number of vesicles in resting axons. To examine whether 5-HT acts by reducing presynaptic Ca2+ influx, intra-axonal recordings of Ba2+ potentials were performed. No reduction of the axonal Ba2+ potential could be detected after application of 20 or 200 microM 5-HT. The present results show that 5-HT reduces the rate of synaptic exocytosis in reticulospinal axons. The effect appears to be mediated by a mechanism distinct from the presynaptic Ca2+ channels.

Action Potentials↗