Evaluation of plasma polymer-coated contact lenses by electrochemical impedance spectroscopy.

The influence of ultra-thin (i.e., 5-50 nm) plasma polymer coatings on siloxane-based hydrogel contact lenses was investigated by electrochemical impedance spectroscopy (EIS). Impedance measurements as a function of frequency (Bode plots) were taken at regular intervals until steady impedance was obtained, indicating that the lenses were saturated. Appropriate equivalent circuit models were constructed to describe the salt intrusion characteristics of the plasma polymer-coated contact lenses. This provided information pertaining to the resistance and capacitance of interfacial and bulk layers in the plasma polymer-coated lenses. Resistance relates to ion permeability and capacitance for water uptake. This investigation showed that some of an ultra-thin layer of plasma polymer applied onto a dry hydrogel remains a contiguous film after the substrate hydrogel swells upon hydration. In some cases, however, the overall impedance of the coated lens is so low that the state of the plasma polymer layer after the hydration of the substrate hydrogel could not be judged by EIS.

Global cerebral blood flow, blood volume, and oxygen metabolism in patients with migraine headache.

OBJECTIVE: Migraine headaches with and without aura are representative of vascular headache states traditionally thought to be mediated by alterations in vascular tone. Validation of this theory has been hampered in part by technical difficulties inherent in the measurement of cerebral blood flow (CBF). The purpose of this study was to compare CBF measured during migraine and migraine-free states using PET. METHODS: Patients with a minimum of one migraine headache without aura per month (International Headache Society [IHS] criteria) underwent measurement of CBF, cerebral blood volume (CBV), oxygen extraction, and metabolism during an episode of spontaneous migraine headache. Imaging was repeated during a migraine-free period of at least 48 hours. PET radiotracers used were: CBF, H(2)15O; CBV, C15O; oxygen metabolism, 15O2. RESULTS: In nine patients (seven female and two male), global CBF (mL/min/100 g [SD]) was measured as 52.70 (6.9) during migraine and 59.65 (10.6) in the migraine-free state; p=0.028. CBV (mL/100 g [SD]) was 3.6 (0.43) during the symptomatic state and 3.8 (0.55) after the migraine; p=0.047. Oxygen metabolism (mL/min/100 g [SD]) was 3.68 (0.9) during migraine and 3.38 (1.02) without headache; p=0.211. The oxygen extraction ratio was 0.48 (0.15) and 0.41 (0.12) during migraine and migraine-free states, respectively; p=0.132. CONCLUSIONS: In patients experiencing migraine without aura, CBF and CBV are reduced during the headache phase. Cerebral oxygen metabolism and oxygen extraction are not significantly affected.

Endogenous opioids may modulate catecholamine secretion during high intensity exercise.

To determine the effect of endogenous opioids on catecholamine response during intense exercise [80% maximal oxygen uptake (VO2max)], nine fit men [mean (SE) VO2max, 63.9 (1.7) ml.kg-1.min-1; age 27.6 (1.6) years] were studied during two treadmill exercise trials. A double-blind experimental design was used with subjects undertaking the two exercise trials in counterbalanced order. Exercise trials were 20 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration of naloxone (N; 1.2 mmol.l-1; 3 ml) and the other after receiving a placebo (P; 0.9% saline; 3 ml). Prior to each experimental trial a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Immediately afterwards, each subject received bolus injection of either N or P. Blood samples were also collected after 20 min of continuous exercise while running. Epinephrine and norepinephrine were higher (P < 0.05) in the N than P exercise trial with mean (SE) values of 1679 (196) versus 1196 (155) pmol.l-1 and 24 (2.2) versus 20 (1.7) nmol.l-1, respectively. Glucose and lactate were higher (P < 0.05) in the N than P exercise trial with values of 7 (0.37) versus 5.9 (0.31) mmol.l-1 and 6.9 (1.1) versus 5.3 (0.9) mmol.l-1 respectively. These data suggest an opioid inhibition in the release of catecholamines during intense exercise.

Lesions of the retrosplenial cortex produce deficits in reversal learning of the rabbit nictitating membrane response: implications for potential interactions between hippocampal and cerebellar brain systems.

The effect of bilateral lesions of the retrosplenial cortex on discrimination reversal learning of the rabbit nictitating membrane response was examined. Results showed that animals with such lesions were not impaired in their ability to acquire a cross-modality discrimination, but were severely impaired in their ability to reverse the discrimination once it was learned. All animals failed at the reversal phase of the task because they displayed high levels of conditioned responding to both the CS+ and the CS-. Thus bilateral damage to the retrosplenial cortex results in deficits in reversal learning that are highly similar to those observed after bilateral hippocampectomy. These findings are interpreted within a conceptual framework that characterizes multisynaptic projections from the hippocampus to the retrosplenial cortex, and ultimately to the cerebellum, as responsible for the behavioral expression of learning-related changes in hippocampal pyramidal cell activity.

Hippocampal lesions disrupt classical conditioning of cross-modality reversal learning of the rabbit nictitating membrane response.

The role of the hippocampus and subiculum in classical conditioning of tone-light discrimination reversal learning of the rabbit nictitating membrane response was investigated using aspiration lesions of both limbic structures. Only two of seven animals with hippocampal-subicular damage successfully reached reversal criteria within 21 days of conditioning, although all hippocampectomized animals learned the initial discrimination at rates equivalent to those of two control groups. Thus, previously reported deficits in two-tone reversal learning seen after similar lesions are not due to increased within-modality generalization to the conditioned stimuli (CS) serving as the CS+ and CS-.