Smajo Osmanovic

Enhancement of current induced by superfusion of GABA in locus coeruleus neurons by pentobarbital, but not ethanol

gamma-Aminobutyric acid (GABA), pentobarbital and ethanol were applied by bath superfusion to rat locus coeruleus (LC) neurons in a brain slice preparation. The GABA-induced current and conductance increase was measured with single-electrode voltage clamp. Pentobarbital potentiated the GABA-induced current and conductance increase in all LC neurons tested. In contrast, ethanol did not alter the current and conductance increase induced by bath application of GABA to LC neurons.

Baclofen increases the potassium conductance of rat locus coeruleus neurons recorded in brain slices

Baclofen causes a concentration-dependent inhibition of spontaneous firing, hyperpolarization and resistance decrease in locus coeruleus (LC) neurons recorded intracellularly in a brain slice preparation. The (-) isomer is active while the (+) isomer has little or no activity which indicates that the baclofen effect is stereoselective. Baclofen action on LC neurons is a direct postsynaptic effect since it remains in low Ca2+, high Mg2+ media. Baclofen actions on LC neurons are resistant to the GABAA antagonist bicuculline. The baclofen-induced hyperpolarization reverses at the K+ equilibrium potential, as estimated by the reversal potential of the post-stimulus hyperpolarization which follows an evoked train of action potentials. When the K+ concentration in the superfusion media is increased, the reversal potential for the baclofen-induced hyperpolarization shifts linearly with a slope of 61 mV per 10-fold change as predicted by the Nernst equation for a pure K+ conductance. The baclofen-induced K+ conductance increase is prevented by addition of the K+-channel blocker Ba2+ to the external media. Taken together, these data suggest that baclofen directly hyperpolarizes LC neurons by activation of GABAB receptors which leads to an increase in K+ conductance.

Functional significance of the apamin-sensitive conductance in rat locus coeruleus neurons.

The effects of apamin on rat locus coeruleus (LC) neurons were studied in a brain slice preparation with intracellular recording. Bath application of apamin (2-500 nM) reduced the amplitude of an intermediate component of the afterhyperpolarization (AHP) following single spontaneous action potentials, but did not change the size or time-course of fast and slow components of the AHP, spike amplitude or duration. Apamin blocked the early component of the post-stimulus hyperpolarization (PSH) which follows a train of action potentials. The size of the late component of PSH was sometimes augmented by apamin. Apamin increased the number of spikes evoked by a depolarizing current pulse and increased the slope of the spike frequency-current intensity relation. Accommodation of firing during long depolarizing pulses showed a biexponential time-course indicating 2 distinct components. Apamin specifically reduced the contribution of the fast component of accommodation and increased its time constant. These data indicate that the apamin-sensitive conductance is functionally important in accommodation at faster firing rates such as those seen during evoked spike trains in the present experiments, and which may occur in vivo during behavioral arousal and in anxiety or drug withdrawal syndromes.

Anomalous rectification in rat locus coeruleus neurons

Rat locus coeruleus neurons recorded under current clamp conditions show anomalous rectification (AR) as indicated by a progressive decrease in slope resistance measured with hyperpolarizing current pulses of increasing amplitude. AR was most prominent at potentials more negative than the K+ equilibrium potential. AR was strongly dependent on external K+ concentration and was blocked by external Ba2+ and Cs+, and intracellular injection of acetate.

Predicted refraction versus refraction outcome in cataract surgery after trabeculectomy

PurposeTo determine whether the manifest refraction after cataract surgery in eyes that had undergone previous trabeculectomy was different from the predicted refraction. SettingUniversity-based tertiary glaucoma service and 3 glaucoma private practices. MethodsRetrospective, interventional, case-control study. The medical records of patients with glaucoma and medically treated glaucoma suspects who underwent cataract extraction between January 1, 2004 and February 11, 2006 were reviewed. The axial length was measured by contact A-scan ultrasonography. The study group included 27 eyes of 25 patients who underwent phacoemulsification with intraocular lens implantation after trabeculectomy, whereas the control group included 52 eyes of 49 glaucoma patients or medically treated glaucoma suspects who underwent phacoemulsification with intraocular lens implantation only. The main outcome measure was the difference between the postphacoemulsification manifest refraction and predicted refraction between the 2 groups. ResultsThe difference between the mean final refraction and mean predicted refraction in the study group (−0.852±1.056 D) and the control group (−0.501±0.542 D) was not statistically significant (P=0.115). The mean intraocular pressure in the study group decreased significantly after trabeculectomy (25.9±8.9 to 9.6±4.3 mm Hg, P<0.001), and increased significantly after phacoemulsification (9.6±4.3 to 12.5±5.3, P=0.001). Lower prephacoemulsification intraocular pressure was weakly correlated with a myopic shift in final refraction (r=0.269, P=0.017). ConclusionsThough numerous variables can potentially influence the refractive outcome in cataract extraction after trabeculectomy, our study shows that the refractive outcome in these cases remained reasonably predictable. However, lower prephacoemulsification intraocular pressure was weakly correlated with a myopic shift in final refraction.

Objective measurement of periocular pigmentation.

Purpose: To evaluate the Minolta CR‐400 chromameter in objectively measuring periocular/facial pigmentation in subjects of different ethnicities.

Plug surface defects as a late complication of silicone punctal plugs.

Purpose: To report 3 cases of punctal plug surface defects as a cause of irritation complicating punctal plug therapy. Methods: Interventional case series and scanning electron microscopy (SEM) of punctal plugs. Results: Three patients were found to have punctal plug surface defects and local irritation of conjunctiva and inferonasal cornea 9, 40, and 69 months after placement of AquaFlo silicone punctal plugs for the treatment of dry eyes. SEM of the explanted plugs confirmed a defective collarette surface. In addition, unused AquaFlo plugs from different lots examined by SEM showed a rough irregular collarette surface that was not seen in unused plugs of Parasol silicone punctal plugs. Discussion: AquaFlo punctal plugs inherently have surface irregularities when compared with similar plug brands, which we suggest may predispose to plug breakdown over time, leading to mechanical irritation of the adjacent conjunctiva and cornea. This report highlights the local complications by AquaFlo punctal plugs associated with plug surface defects as a complication of punctal plug therapy.