Osvaldas Ruksenas

Effects of hormonal contraceptives on mental rotation and verbal fluency

Cognitive abilities, such as verbal fluency and mental rotation, are most sensitive to changes in sex steroids but poorly studied in the context of hormonal contraceptive usage. Therefore, we investigated the performance of mental rotation and verbal fluency in young (21.5±1.8 years) healthy oral contraceptive (OC) users (23 women) and non-users (20 women) during the follicular, ovulatory and luteal phases of the menstrual cycle. Salivary 17β-estradiol, progesterone and testosterone levels were assayed to evaluate hormonal differences between groups and the phases of the menstrual cycle. To assess the effects of progestins having androgenic/anti-androgenic properties, OC users were subdivided into the third and new generation OC users. In addition, positive and negative affects as factors possibly affecting cognitive performance were evaluated. Salivary 17β-estradiol and progesterone levels were significantly lower in hormonal contraception users. Level of salivary testosterone was slightly lower in the OC users group with significant difference only during ovulatory phase. Naturally cycling women performed better on verbal fluency task as compared to OC users. Subjects who used the third generation (androgenic) OCs generated significantly fewer words as compared to new generation (anti-androgenic) OC users and non-users. The third generation OC users demonstrated significantly longer RT in MRT task as compared to non-users. The MRT, verbal fluency and mood parameters did not depend on the phase of menstrual cycle. The parameters of the PANAS (Positive and Negative Affect Schedule) scales did not differ between OC users and non-users. Our findings show that hormonal contraception has an impact on verbal and spatial abilities. Different performances between users of oral contraceptives with androgenic and anti-androgenic properties suggest an essential role for the progestins contained in OCs on cognitive performance.

Two discrete components of the 20 Hz steady-state response are distinguished through the modulation of activation level

OBJECTIVE To investigate the modulation of amplitude and phase precision of the auditory steady-state response (SSR) to 20 Hz stimulation in two conditions varying in the level of activation. METHODS Click stimuli (20 Hz) were applied while subjects were sitting upright silently reading a book of interest (high activation level) and while subjects were sitting in a reclined position with eyes closed and the lights turned off (low activation level). Sixty-one channel EEG data was wavelet transformed, the amplitude and phase precision measures extracted and decomposed by the multi-subject non-negative multi-way factorization (NMWF). RESULTS The NMWF decomposition of amplitude and phase precision measures resulted in the observation of two distinct components: a component at the frequency of stimulation--20 Hz SSR and a component emerging at 40 Hz--20 Hz SSR-related 40 Hz activity. Modulation by the activation level was observed only for 20 Hz SSR-related 40 Hz activity as increased amplitude and phase precision during low activation level. No such effects were observed for 20 Hz SSR. CONCLUSION The discrete components of the 20 Hz SSR are distinguished through modulation of activation level, 20 Hz SSR-related 40 Hz being higher in low activation state. SIGNIFICANCE The biological modulation of 20 Hz SSR-related 40 Hz activity by the level of activation points to a physiological nature of this activity beyond a mere periodic effect in relation to the 20 Hz activity.

Corneal stromal ablation with femtosecond ultraviolet pulses in rabbits.

Purpose To determine the effectiveness of femtosecond ultraviolet (UV) pulses in ablating corneal stroma in a rabbit model and to compare the healing response between eyes treated with femtosecond UV pulses and eyes treated with standard excimer photorefractive keratectomy. Setting Laser Research Center, Vilnius University, Vilnius, Lithuania. Design Experimental study. Methods Myopic photoablation using a femtosecond UV solid‐state laser system was applied to corneas of pigmented rabbits. Experiments in 16 eyes were performed for optimization of the laser system parameters (fluence, spot size, pulse repetition rate) and calibration of ablation rate. In 7 rabbits, deep femtosecond UV ablation (∼130 μm) in 1 eye and shallow ablation (∼30 μm) in the contralateral eye were performed. Nine rabbits received an approximately 30 μm ablation with femtosecond UV pulses in 1 eye and with a conventional excimer system in the contralateral eye. Two eyes were used as controls. The ablation process and surface‐temperature dynamics were monitored and recorded. Surface quality and haze development were evaluated. Rabbits were humanely killed 0 to 6 months after surgery, and eyes were enucleated for histological examination. Results Rabbit corneas ablated with femtosecond UV pulses or excimer laser radiation were similar in terms of the corneal wound‐healing process, surface quality, and histology. Conclusions The experiments indicate the feasibility of clinical application of femtosecond UV lasers for stromal ablation. The ability to switch between laser harmonics allows fast changeover from infrared to the UV mode, implying that a wide range of ophthalmic procedures can be performed using a single solid‐state laser device. Financial Disclosure Ms. Gabryte and Mr. Danielius are paid employees of Light Conversion Ltd. Mr. Danielius is a shareholder of Light Conversion Ltd. No other author has a financial or proprietary interest in any material or method mentioned.

Effect of attention on 40 Hz auditory steady-state response depends on the stimulation type: Flutter amplitude modulated tones versus clicks

Auditory steady-state responses (ASSRs) are used to test the ability of local cortical networks to generate gamma frequency activity in patients with psychiatric disorders. For the effective use of ASSRs in research and clinical applications, it is necessary to find a comfortable stimulation type and to know how ASSRs are modulated by the tasks given to the subjects during the recording session. We aimed to evaluate the suitability of flutter amplitude modulated tone (FAM) stimulation for generation of ASSRs: subjective pleasantness of FAMs and attentional effects on FAM-elicited 40Hz ASSRs were assessed. Commonly used click stimulation was used for comparison. FAMs produced ASSRs that were stable over the variety of tasks - they were not modulated by attentional demands during the task; responses to clicks were reduced and less synchronized during distraction. FAM stimuli were rated as less unpleasant and less arousing than click stimuli, thus being more pleasant to the subjects. Our findings suggest that FAM stimulation might be more suitable in conditions, where attention is difficult to control, i.e. in clinical settings.

The effect of acetylcholine on Characeae K+ channels at rest and during action potential generation

The role of acetylcholine (ACh) as a signalling molecule in plants was investigated using a model system of Characeae cells. The effect of ACh on conductance of K+ channels in Nitella flexilis cells and on the action potential generation in Nitellopsis obtusa cells after H+-ATPase inhibition, where repolarization occurs after the opening of outward rectifying K+ channels, was investigated. Voltage-clamp method based on only one electrode impalement was used to evaluate the activity of separate potassium ion transport system at rest. We found that ACh at high concentrations (1 mM and 5 mM) activates K+ channels as the main membrane transport system at the resting state involved in electrogenesis of Characeaen membrane potential. We observed that ACh caused an increase in duration of AP repolarization of cells in K+ state when plasmalemma electrical characteristics are determined by large conductance K+ channels irrespective of whether AP were spontaneous or electrically evoked. These results indicate interference of ACh with electrical cellular signalling pathway in plants.

Corneal shaping and ablation of transparent media by femtosecond pulses in deep ultraviolet range.

PURPOSE: To assess the performance of a newly developed solid‐state femtosecond ultraviolet (UV) laser system in corneal ablation. SETTING: Vilnius University, Laser Research Centre, Vilnius, Lithuania. METHODS: Femtosecond pulses in the deep UV range (205 nm) were obtained by the generation of the fifth‐harmonic of an amplified Yb:KGW laser system (fundamental output at 1027 nm). Coupled with galvanometric beam‐scanning mirrors, this system allowed ablation shaping of transparent media, including poly(methyl methacrylate) (PMMA), collagen, and ex vivo porcine corneas. The surfaces of ablated structures were characterized using a noncontact confocal optical profiler. RESULTS: Spherical structures were successfully formed in all 3 materials tested. A 10.0 diopter refraction change in the cornea was produced in 180 seconds. The resulting surface quality was significantly higher (roughness length >100 μm versus approximately 6 μm) in gelatin and ex vivo corneas than in PMMA. CONCLUSION: The solid‐state femtosecond UV laser system seems an attractive alternative to the currently used ophthalmic argon–fluoride excimer laser system because of its small footprint, silent operation, and ability to generate femtosecond light pulses at both 1027 nm (suitable for flap creation) and 205 nm (corneal ablation). Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Go and NoGo: modulation of electrophysiological correlates by female sex steroid hormones

RationaleThe behavioral and electrophysiological responses in a Go/NoGo task are objective measures of executive functioning that may be impaired in clinical conditions. Prior to the wider application of Go/NoGo tasks in clinics, it is tempting to evaluate factors causing modulation of the responses.ObjectiveWe aimed to evaluate the effect of different levels of female sex steroids on Go/NoGo task-related ERPs in healthy females.MethodsThirty-four young healthy females performed an equiprobable (50/50) auditory Go/NoGo task. Amplitudes and latencies of N2 and P3 peaks from Fz, Cz, and Pz electrodes were evaluated. 17β-estradiol and progesterone levels in saliva samples were measured. Electrophysiological measures were correlated to 17β-estradiol and progesterone concentrations.ResultsThe diverse pattern of modulation of P3 latencies was shown: higher levels of 17β-estradiol contributed to Go-P3 latency prolongation, and higher levels of progesterone contributed to NoGo-P3 latency shortening. Higher levels of 17β-estradiol were associated with more negative frontal N2 amplitude in both conditions.ConclusionsThe relationship between electrophysiological correlates of executive functioning to individual hormonal levels points to a broader range of variation sources in healthy subjects which might mask or pronounce between-group differences in clinical studies.

The effects of Ni2+ on electrical signaling of Nitellopsis obtusa cells

The effect of nickel (Ni) on the generation of plant bioelectrical signals was evaluated in Nitellopsis obtusa, a Characean model organism. Conventional glass-microelectrode technique and K+-anaesthesia method in current-clamp and voltage-clamp modes were used for the measurement and analysis of electrical parameters. Ni2+ treatment rapidly influenced the action potential (AP) parameters namely, excitation threshold, AP peak and duration, membrane potential at various voltages and dynamics of ion currents. We conclude that altered electrical signaling pathway in the test organism constituted the early target for Ni toxicity imposition. The observed Ni interference could be ascribed to disturbed [Ca2+]cyt content, impaired Cl− and K+ channels activity resulting in decreased excitability and repolarization rate in generated AP.

Gain of spinal motoneurons measured from square and ramp current pulses.

The gain of motoneurons (MNs) characterizes how variations in synaptic input are transformed in to variations in output firing and muscle contraction. Experimentally gain is often defined as the frequency-current relation observed in response to injected suprathreshold square current pulses or current ramps during intracellular recording. The gain of MNs is strongly affected by adaptation: transient gain in response to depolarization is usually higher than steady state gain measured during sustained depolarization. The transient and the stationary gain of neurons are separate entities that can be selectively modified. Here we investigated how the transient and the stationary gain of spinal MNs obtained from responses to square current pulses are related to gain estimated from the responses to the current ramps. We found, that the gain in response to current ramps is identical to the steady state gain during sustained depolarization. Therefore, gain modulation is more fully characterized with square current pulses than with current ramps.

DNA Damage in Bone Marrow Cells Induced by Ultraviolet Femtosecond Laser Irradiation

BACKGROUND DATA Research on the damaging effect of ultraviolet (UV) laser irradiation on the DNA of live organisms is still scarce, although UV lasers are increasingly being used in therapeutics and surgical treatment. OBJECTIVE In this study we investigated the effect of new-generation 205-nm femtosecond solid-state laser irradiation on the DNA of murine bone marrow cells in vitro. MATERIALS AND METHODS Mouse bone marrow cells in distinct plates were exposed to different doses of 205-nm femtosecond laser irradiation. Single-cell gel electrophoresis, or comet, assay was used for DNA damage measurement. RESULTS Our study revealed intensity-dependent genotoxic, genotoxic-cytotoxic, or cytotoxic impact of laser irradiation. The lowest doses we used (0.0175-0.105 J/cm(2)) induced DNA photodamage in irradiated cells directly, medial doses (0.175 and 0.35 J/cm(2)) caused both direct damage of genetic material and irreversible injury of cells structure whereas the highest doses (1.05-4.2 J/cm(2)) caused the death of most irradiated cells. It is worrisome that even comparatively low doses of irradiation were genotoxic. Exposure to the lowest-intensity irradiation (0.0175 J/cm(2)) caused a highly significant (p < 0.0001) increase in DNA strand breaks of bone marrow cells: the mean ± SEM %DNA score in the comet tail was 9.96 ± 0.56 compared with 3.58 ± 0.80 for controls. Investigation of the effects of low and medial intensities of irradiation showed a dosage-effect relationship of R(2) = 0.84, P < 0.01. CONCLUSION New-generation 205-nm femtosecond laser irradiation produced a genotoxic effect by inducing strand breaks in the DNA of murine bone marrow cells in vitro. Research on the possible genotoxic effects of this laser on corneal and skin epithelial cells in vivo is needed.