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At least 271 records · Page 15Linked to original sources
PubMed1996

Coloboma contiguous gene deletion encompassing Snap alters hippocampal plasticity.

Mice heterozygous for the semidominant mutation coloboma (Cm/+) display several distinct pathologies including head bobbing, ophthalmic deformation, and locomotor hyperactivity. The Cm/+ mutation comprises a contiguous gene defect which encompasses deletion of the gene Snap encoding the presynaptic nerve terminal protein SNAP-25 that is an integral component of the synaptic vesicle docking and fusion complex. Indeed, SNAP-25 is required for axonal growth and for the regulated release of neurotransmitters at the synaptic cleft. As an extension of our studies on the behavioral deficits exhibited by these mutants, including evaluation of the hyperkinesis and dopamine-related behavioral pharmacology that might be related to attention-deficit hyperactivity disorder in humans, we have studied spontaneous electroencephalographic and evoked potential recordings in the dentate gyrus of halothane-anesthetized Cm/+ and normal (+/+) littermates to evaluate potential physiological abnormalities of synaptic function in these mice. While sensory activation elicited by brief (10 sec) tail-pinch produced 1-2 min of theta rhythmic activity in +/+ mice, theta induction was markedly reduced in Cm/+ mice. There were no significant differences in dentate afferent-evoked population excitatory postsynaptic potential (pEPSP) slopes, pEPSP facilitation, or population spike (PS) amplitudes; however, paired-pulse inhibition of dentate PS amplitudes was significantly increased in Cm/+ mice. Furthermore, although brief high-frequency stimulation of the perforant path produced robust long-term potentiation (LTP) of synaptic responses in the dentate gyrus of +/+ mice, LTP was attenuated in Cm /+ mice. It has been previously demonstrated that dopamine (DA) neurotransmission is essential for induction of one type of hippocampal theta rhythm and also may modulate hippocampal LTP, suggesting that alterations in DA synaptic transmission may underlie the behavioral abnormalities, in particular the hyperactivity, associated with Cm/+ mutant mice.

Animals↗
PubMed2000

Frontonasal dysplasia, macroblepharon, eyelid colobomas, ear anomalies, macrostomia, mental retardation, and CNS structural anomalies: another observation.

We report a Japanese girl with brachycephaly, a wide forehead, hypertelorism, macroblepharon with eyelid colobomas, ectropion, a broad nasal root, a depressed nasal tip, macrostomia, a small and grooved chin, ear anomalies, a structural anomaly of the corpus callosum, dilatation of the fourth ventricle, a urogenital sinus, and mental retardation. Cause and inheritance are unknown.

Abnormalities, Multiple↗
PubMed2004

Elevated thalamic low-voltage-activated currents precede the onset of absence epilepsy in the SNAP25-deficient mouse mutant coloboma.

Recessive mutations in genes encoding voltage-gated Ca2+ channel subunits alter high-voltage-activated (HVA) calcium currents, impair neurotransmitter release, and stimulate thalamic low-voltage-activated (LVA) currents that contribute to a cortical spike-wave epilepsy phenotype in mice. We now report thalamic LVA current elevations in a non-Ca2+ channel mutant. EEG analysis of Coloboma (Cm/+), an autosomal dominant mutant mouse lacking one copy of the gene for a synaptosomal-associated protein (SNAP25) that interacts with HVA channels, reveals abnormal spike-wave discharges (SWDs) in the behaving animal. We compared the biophysical properties of both LVA and HVA currents in Cm/+ and wild-type thalamic neurons and observed a 54% increase in peak current density of LVA currents evoked at -50 mV from -110 mV in Cm/+ before the developmental onset of seizures relative to control. The midpoint voltage for steady-state inactivation of LVA currents in Cm/+ was shifted in a depolarized direction by 8 mV before epilepsy onset, and the mean time constant for decay of LVA Ca2+ currents at -50 mV was also prolonged. No significant differences were found in recovery from inactivation of LVA currents or in HVA current densities and kinetics. Our data demonstrate that a non-Ca2+ channel subunit gene mutation leads to potentiated thalamic LVA currents that precede the appearance of SWDs and that altered somatodendritic HVA currents are not required for abnormal thalamocortical oscillations. We suggest that presynaptic release defects shared by these mutants lead to postsynaptic LVA excitability increases in thalamic pacemaker neurons that favor rebound bursting and absence epilepsy.

Action Potentials↗
PubMed1999

Frontonasal dysplasia, macroblepharon, eyelid colobomas, ear anomalies, macrostomia, mental retardation, and CNS structural anomalies. A new syndrome?

We report a Brazilian girl, born to normal and non-consanguineous parents and presenting, among other signs, brachyacrocephaly, a wide forehead, hypertelorism, wide palpebral fissures with multiple eyelid colobomas, a broad and high nasal root, an absent nasal tip, a wide columella, a long and smooth philtrum, a carp-like mouth, macrostomia, a thin upper lip with midline notching, submucous cleft of the soft palate, a small and grooved chin, ear anomalies, Dandy-Walker anomaly, a structural anomaly of the corpus callosum, grey matter heterotopia, and mental retardation. The whole clinical picture of the present patient suggests a 'new' type of frontonasal dysplasia and main differential diagnosis includes the acrofrontofacionasal dysostosis 2 syndrome (MIM 201181). Other differential diagnoses are discussed.

Abnormalities, Multiple↗
PubMed1989

Iris reconstruction by coloboma repair.

If a pupil becomes irreversibly miotic during cataract surgery it is helpful to perform an iridotomy to facilitate lens expression. Reconstructing the pupil with one or two iris sutures is advisable in order to prevent coloboma-related problems. We describe a method of iridoplasty that involves using a vanadium steel suture attached to a long, straight needle. This technique can be used in an eye with surgically low pressure as well as in an eye with elevated vitreous pressure.

Anterior Chamber↗