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Biomedical subjects

C Collin

Publications and source records attributed to C Collin.

At least 37 records · Page 2Linked to original sources
PubMed1997

Glare disability and contrast sensitivity before and after cataract surgery.

PURPOSE: To determine whether brightness-induced glare decreases spatial contrast sensitivity and visual acuity in preoperative cataract patients with functional visual complaints and to compare preoperative with postoperative results. SETTING: Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada. METHODS: Twenty patients with a visual acuity of 20/70 or better at the time of chart selection and no other ocular pathology who were referred for cataract surgery were evaluated with the Optec 3000 vision tester to assess contrast sensitivity and visual acuity in the presence and absence of glare. Testing was done preoperatively and 1 and 3 months postoperatively. RESULTS: An analysis of variance indicated that there were statistically significant double interactions between the preoperative/postoperative and glare/no-glare variables and between the preoperative/postoperative and spatial frequency variables. Postoperatively, visual acuity and contrast sensitivity improved to within normal limits. There were no statistically significant differences in visual acuity and spatial contrast sensitivity between 1 and 3 months postoperatively. CONCLUSION: Spatial contrast sensitivity and glare testing provided objective assessment of patients who had good visual acuity yet also had functional complaints.

Adult↗
PubMed1997

Dendritic spine density and LTP induction in cultured hippocampal slices.

Transverse hippocampal slices were cut from 8- to 9-day-old rats and maintained in an interface chamber for periods of 1-4 wk, in tissue culture conditions. Neurons in the slice preserved their spatial organization and connectivity. Dendritic spine density in CA1 neurons was very low at 1 wk in culture, and long, filopodia-like structures were abundant. Spine density increased in these neurons nearly threefold during the course of 3 wk in vitro, to approach values of those of the normal, in vivo hippocampus. The magnitude of long-term potentiation (LTP) of reactivity of Ca1 to stimulation of CA3 neurons also increased during weeks in culture in parallel with the change in spine density. Chronic exposure of slices to drugs that interact with synaptic activity caused changes in their dendritic spine density. Blockade of the N-methyl-D-aspartate (NMDA) receptors with the receptor antagonist 2-aminophosphonovalerate (D-APV) or blockade of action potential discharges with tetrodotoxin (TTX) prevented dendritic spine development in immature cultures. Enhancing synaptic activity by blockade of GABAergic inhibition with picrotoxin did not affect spine density to a significant degree. D-APV-treated slices expressed larger LTP than controls. TTX-treated slices expressed smaller LTP than controls. Picrotoxin treated slices did not express LTP. It is proposed that LTP and dendritic spine density are correlated strongly during development, whereas they are not correlated in the more mature slice/culture of the hippocampus where spine density can be modulated by chronic exposure to blockers of synaptic activity, which will not affect LTP in a similar manner.

Action Potentials↗
PubMed1996

A follow-up study of patients hospitalized after minor head injury.

Minor head injury accounts for 95% of all head injury. In this study 62 patients, hospitalized after minor head injury, were assessed within 48 h, and invited to attend for review and retesting 3 months later. Thirty-five patients were followed up in this way and 11 more were interviewed over the telephone. There was significant improvement on all psychometric tests between initial evaluation and follow-up. Between 51% and 86% reported troublesome late post-concussional symptoms, of which headaches and tiredness were the most frequently reported symptoms. Length of post-traumatic amnesia (PTA) was related to severity of symptoms. Clinical levels of anxiety and stress were noted in approximately one-third of the whole group; 95% of the group had returned to work by 3 months with a mean absence rate of 9.4 days. The therapeutic implications of these results are discussed.

Adolescent↗
PubMed1995

Long-term synaptic transformation of hippocampal CA1 gamma-aminobutyric acid synapses and the effect of anandamide.

Evidence is presented for a distinctive type of hippocampal synaptic modification [previously described for a molluscan gamma-aminobutyric acid (GABA) synapse after paired pre- and postsynaptic excitation]: transformation of GABA-mediated synaptic inhibition into synaptic excitation. This transformation persists with no further paired stimulation for 60 min or longer and is termed long-term transformation. Long-term transformation is shown to contribute to pairing-induced long-term potentiation but not to long-term potentiation induced by presynaptic stimulation alone. Further support for such mechanistic divergence is provided by pharmacologic effects on long-term transformation as well as these two forms of long-term potentiation by Cl- channel blockers, glutamate and GABA antagonists, as well as the endogenous cannabinoid ligand anandamide.

Animals↗
PubMed1995

Dye-coupling in three-dimensional histoculture of rat lingual frenulum.

A three-dimensional histoculture of wet stratified squamous epithelium of rat lingual frenulum was cultured on a liquid-air interface. The tissue retained its morphology for many days in culture. During this period the vast majority of the epithelial cells remained viable and exhibited dye (lucifer yellow) coupling in all living epithelial strata. Dye coupling was determined using two methods: the conventional intracellular injection method, and a new method--"cut-loading." In the cut-loading method, an incision is made in the epithelium in the presence of dye, and intracellular diffusion of dye throughout the epithelium was measured using confocal microscopy. The basolateral surface of the lingual frenulum also acted as a substrate for neuroblastoma cells to grow without exogenously added trophic factors. These neuroblastoma cells grow neurites that establish contacts with epithelial cells. This preparation can serve as a model for investigating interactions among epithelial cells and between nerves and epithelial cells.

Animals↗
PubMed1995

Confocal microscopy of cells implanted into tissue blocks: cell migration in long-term histocultures.

In three-dimensional tissues in vivo, cells find themselves in a unique, heterogeneous microenvironment among various cellular and noncellular elements. Cells are greatly affected by and contribute to their physical and chemical microenvironments. However, live cells are currently studied predominantly in homogeneous monolayer cultures where newly established contacts might be fundamentally different from contacts in vivo. Several systems have been suggested to simulate the three-dimensional environment of real tissue. In this report, we describe a new system for studying cell behavior inside real tissues in vitro. By fluorescently labeling mouse tumor cells, them implanting them into cultured tissue blocks (histocultures), we have observed cellular location and followed their locomotion, within tissues in vitro for days. We discuss the potential of the described system for studying different aspects of cell behavior in a nativelike microenvironment.

Animals↗
PubMed1994

Assignment of the human cytokeratin 3 gene (KRT3) to 12q12-->q13 by FISH.

We used fluorescence in situ hybridization to localize the human gene for cytokeratin 3 (KRT3), a member of the type II subfamily of cytokeratins, within the human genome. The results show that KRT3 is located within chromosome region 12q12-->q13. All human type II keratin genes mapped to date have been assigned to chromosome 12, where they are likely to be organized into one homotypic cluster.

Chromosome Mapping↗
PubMed1994

Intracellular calcium signals are enhanced for days after Pavlovian conditioning.

Previous observations have implicated GABA as a neurotransmitter released by the vestibular sensory neurons ("hair cells") of the snail Hermissenda onto visual sensory neurons, the type B cells, whose cell bodies are the sites of biophysical and biochemical changes during and following Pavlovian conditioning. Still other observations demonstrated that light-GABA pairings that simulate stimuli presented during Pavlovian conditioning cause prolonged elevation of intracellular Ca2+ and transformation of GABA-induced synaptic inhibition into excitation. Intracellular Ca2+ signals in response to GABA perfused onto the postsynaptic type B terminal branches are shown here to be prolonged on days after conditioning, but not after control paradigms. These and past results demonstrate two separate sites, i.e., the cell body and the terminal branches, for learning-induced changes after Pavlovian conditioning.

Animals↗
PubMed1993

Reconstruction of ionic currents in a molluscan photoreceptor.

Two-microelectrode voltage-clamp measurements were made to determine the kinetics and voltage dependence of ionic currents across the soma membrane of the Hermissenda type B photoreceptor. The voltage-dependent outward potassium currents, IA and ICa(2+)-K+, the inward voltage-dependent calcium current, ICa2+ and the light-induced current, IIgt, were then described with Hodgkin-Huxley-type equations. The fast-activating and inactivating potassium current, IA, was described by the equation; IA(t) = gA(max)(ma infinity[1-exp(-t/tau ma)])3 x (ha infinity [1-exp(-t/tau ha)] + exp(-t/tau ha)) (Vm-EK), where the parameters ma infinity, ha infinity, tau ma, and tau ha are functions of membrane potential, Vm, and ma infinity and ha infinity are steady-state activation and inactivation parameters. Similarly, the calcium-dependent outward potassium current, ICa(2+)-K+, was described by the equation, ICa(2+)-K+ (t) = gc(max)(mc infinity(VC)(1-exp[-t/tau mc (VC)]))pc (hc infinity(VC) [1-exp(-t/tau hc)] + exp(-t/tau hc(VC)])pc(VC-EK). In high external potassium, ICa(2+)-K+ could be measured in approximate isolation from other currents as a voltage-dependent inward tail current following a depolarizing command pulse from a holding potential of -60 mV. A voltage-dependent inward calcium current across the type B soma membrane, ICa2+, activated rapidly, showed little inactivation, and was described by the equation: ICa2+ = gCa(max) [1 + exp](-Vm-5)/7]-1 (Vm-ECa), where gCa(max) was 0.5 microS. The light-induced current with both fast and slow phases was described by: IIgt(t) = IIgt1 + IIgt2 + IIgt3, IIgti = gIgti [1-exp(- ton/tau mi)] exp(-ton/tau hi)(Vm-EIgti) (i = 1, 2). For i = 3, /Igt(t) = gigt3m33h3(Vm - Eigt3)exp(-ton/Ton) x exp(-tfoff/t Off). Based on these reconstructions of ionic currents, learning-induced enhancement of the long lasting depolarization (LLD) of the photoreceptor'slight response was shown to arise from progressive inactivation of /A, lca2+ -K+, and lCa2+.

Animals↗
PubMed1993

GABA-mediated synaptic interaction between the visual and vestibular pathways of Hermissenda.

The synaptic convergence of the eyes and the vestibular hair cells in the nudibranch mollusc Hermissenda has been shown previously to mediate the learning of simple visual-vestibular associations. The neurotransmitter mediating this interaction between the visual and vestibular organs was characterized. HPLC chromatography, confirmed by mass spectroscopic analysis, demonstrated endogenous GABA in the statocysts, in a concentration approximately 150 times greater than in the whole CNS. Additional confirmation was provided by immunocytochemical localization of GABA in hair cell axons and branches that converge with photoreceptor terminal branches. Depolarization of the hair cells in the caudal region of the statocyst in response to positive current injection or vibratory stimulation caused a hyperpolarization and a cessation of the type B photoreceptor impulse activity. The inhibition of the B cell was unaffected by addition to the artificial sea water bath of the adrenergic antagonist yohimbine (250 microM), the cholinergic antagonist atropine (250 microM), and the serotonergic antagonist imipramine (50 microM). In contrast, the GABAA antagonist bicuculline (250 microM) significantly reduced the inhibitory interaction. Moreover, the GABA reuptake inhibitor guvisine (250 microM) increased the hyperpolarization. Pressure microapplication of GABA (12.5 or 25 microM) onto the terminal branches of the B cell resulted in a concentration-dependent hyperpolarization and cessation of spikes in the B cell. Depolarization of the caudal hair cell, or direct GABA application, decreased input resistance across the B cell soma membrane. Moreover, removal of chloride from the extracellular solution reduced inhibition of the B cell induced by GABA application or hair cell stimulation. Furthermore, application of the GABAB agonist baclofen hyperpolarized the type B cell and reduced or eliminated spontaneous impulse activity at the resting membrane potential. The reversal potentials for inhibition induced in all three procedures ranged from -70 to -80 mV and were consistent with mixed Cl- and K+ conductances. These results implicate GABA as the endogenous neurotransmitter mediating visual-vestibular interactions in this animal, and suggest a possible role of GABA in visual-vestibular associative learning.

Animals↗
PubMed1992

Long-term transformation of an inhibitory into an excitatory GABAergic synaptic response.

For a constant membrane potential, a predominantly inhibitory GABAergic synaptic response is shown to undergo long-term transformation into an excitatory response after pairing of exogenous gamma-aminobutyric acid (GABA) with postsynaptic depolarization or pairing of pre- and postsynaptic stimulation. Current- and voltage-clamp experiments suggest that this synaptic transformation is due to a shift from a net increase of conductance to a net decrease of conductance in response to GABA. GABA-induced elevation of intracellular calcium is prolonged after the same stimulus pairing and may, therefore, contribute to this synaptic transformation via Ca(2+)-activated phosphorylation pathways. This synaptic transformation, which does not follow unpaired stimulus presentations, occurs in a neuronal compartment spatially separated from the soma, which also changes during stimulus pairing.

Animals↗
PubMed1992

Characterization of human cytokeratin 2, an epidermal cytoskeletal protein synthesized late during differentiation.

Among the more than 30 different human proteins of the cytokeratin (CK) group of intermediate filament (IF) proteins, the significance of the epidermal polypeptide CK 2 (Moll et al., 1982, Cell 31, 11-24) has been repeatedly questioned in the literature. Here, we show, by in vitro translation and protein gel electrophoresis, that human epidermis from various body sites does indeed contain relatively large amounts of mRNA encoding a distinct polypeptide comigrating with native epidermal CK 2. We also report the isolation of a cDNA clone encoding the complete sequence of CK 2, which is a type II CK different from--but related to--epidermal CKs 1 and 5 on the one hand and corneal CK 3 on the other. The mRNA of approximately 2.6 kb encodes a polypeptide of 645 amino acids and M(r) 65,852, in good agreement with the value of 65.5 kDa previously estimated from gel electrophoresis. This human CK, the largest so far known, displays several features typical of CKs of stratified epithelia, including numerous repeats of glycine-rich tetrapeptides in the head and tail domains. Northern blot and in situ hybridizations have shown that CK 2 is expressed strictly suprabasally, usually starting in the third or fourth cell layer of epidermis, and this was confirmed at the protein level by immunohistochemistry using CK 2-specific antibodies. The protein has been detected as a regular epidermal component in skin samples from different body sites, albeit as a minor CK in "soft skin" (e.g., breast nipple, penile shaft, axilla), but not in foreskin epithelium and in other epithelia, in squamous metaplasias and carcinomas, or in cultured cell lines derived therefrom. We propose that CK 2 is a late cytoskeletal IF addition synthesized during maturation of epidermal keratinocytes which probably contributes to terminal cornification.

Amino Acid Sequence↗
PubMed1992

The role of calcium in prolonged modification of a GABAergic synapse.

Caudal hair cell impulses cause postsynaptic inhibition of ipsilateral type B photoreceptors in the snail Hermissenda. This inhibition is shown to be GABAergic according to a number of criteria. HPLC, mass spectrophotometric, and immunocytochemical techniques demonstrated the presence of GABA in the hair cells and their axons. GABA agonists and antagonists mimic and block the synaptic effect in a manner consistent with endogenous GABAergic transmission. Other properties, including I-V relations, conductance changes and reversal potentials, are comparable for exogenous GABA responses and endogenous effects of the hair cell impulses. This inhibitory synapse has been found to undergo a long-lasting transformation into an excitatory synapse if GABA release is paired with post-synaptic depolarization. GABA, via GABAA and GABAB receptors in the B cell, causes the opening of calcium sensitive chloride and potassium channels that leads to the post-synaptic hyperpolarization. GABA also induces a long-lasting intracellular calcium elevation at the terminal branches of the B cell that greatly outlasts the voltage responses. Synaptic transformation induced by pairings is caused by a decrease in both GABA induced chloride and potassium conductances in the post-synaptic B cell, as well as a significant prolongation of the intracellular calcium accumulation in the B cell's terminal axonal branches.

Animals↗