Assessing the impact of non-dilating the eye on full-field electroretinogram and standard flash response.

We investigated the possibility of performing electroretinography (ERG) in non-pharmacologically dilated eyes using brighter flash (time-integrated) luminance. Photopic (N = 26; background 25.5 cd·m(-2), white LED flashes) and scotopic ERG (N = 23, green LED flashes) luminance response functions were obtained simultaneously in a dilated (DE) and non-dilated eye (NDE). In the NDE, photopic V (max) b-wave amplitude was reduced by 14% (P < 0.0001), implicit time prolonged (P < 0.0001), and retinal sensitivity (log K) decreased by 0.38 log units (P < 0.0001) with no effect on a-wave. Using a xenon strobe light (N = 6) to increase flash luminance, V (max) remained lower by about 12% in the NDE (P = 0.02). V (max) with LED and xenon was achieved at 3.9 ± 1.0 cd·s·m(-2) and 3.3 ± 0.81 cd·s·m(-2) in the DE and 10.6 ± 1.2 cd·s·m(-2) and 12.3 ± 1.90 cd·s·m(-2) in the NDE, that is an increase of 0.43 and 0.57 log unit (P < 0.0001), respectively. Increasing background luminance by 0.50 log units (80 cd·m(-2), N = 4) resulted in implicit time normalization but not V (max) amplitude. Rod V (max) was decreased by 7% in NDE (P < 0.05) and sensitivity reduced by 0.40 log units (P < 0.0001), but our data suggest that the luminance may have not been sufficient to reach V (max) in all participants in the NDE and that the sensitivity change may have been due to an inadequate inter-stimulus interval. For the photopic ERG, increasing flash luminance is not sufficient to compensate for the smaller pupil size, whereas for the scotopic ERG, more data are needed to establish proper inter-stimulus interval to perform recordings in a non-pharmacologically dilated.

Circadian variation in the electroretinogram and the presence of central melatonin.

The light/dark cycle is the most important circadian clock synchronizer for mammals and humans. Circadian rhythms of dopamine and melatonin production in the retina have been reported to follow the light and dark cycle, but their impact on rod and cone functioning is not clear. The purpose of this study was to assess diurnal variations (morning vs. evening) in retinal function as measured with the photopic and scotopic electroretinogram (ERG). We also tried to correlate our results with the presence or absence of melatonin secretion in the saliva. Photopic and scotopic luminance-response functions were obtained in 29 participants at 11:00 (when melatonin should not be present) and 23:00 (when melatonin should be present). From the luminance-response function, Vmax, log K and slope parameters were derived. In scotopic condition, a significant increase of 6% in Vmax amplitude was observed in evening compared to morning (P = 0.03) along with a prolonged b-wave implicit time of 8% (P = 0.01) and an increase in rod sensitivity in evening compared to morning (P = 0.02). As expected, these changes in rod function were accompanied by a higher concentration of melatonin in saliva samples in the evening (P = 0.01). In photopic condition, only a prolonged a-wave implicit time of 5% was observed in evening when compared to morning (P = 0.02). Our findings suggest that the rod system is favored during night time, when circulating melatonin is present. Although statistically significant changes were observed, the day vs. night difference observed in the present study appears to be too small to impact significantly upon clinical assessment of retinal function.

Two PC12 pheochromocytoma lines sealed in hollow fiber-based capsules tonically release L-dopa in vitro.

Two PC12 cell-derived lines have been studied following encapsulation into polymer-based hollow fibers with respect to secreted catecholamines and their metabolites. Cellular encapsulation provides a chronic microperfusion environment within which basally secreted PC12 products can be readily measured. Encapsulated PC12 cells grown and held under the conditions specified in this report basally release amounts exceeding their total cellular stores of the dopamine precursor L-DOPA and the electrochemically active dopamine metabolites DOPAC and HVA during 45-min static incubations. Under these same conditions, these cells release less than 0.1% of their total cellular store of dopamine. Depolarizing incubations enhance dopamine secretion eightyfold and enhance secretion of L-DOPA, HVA, and DOPAC about twofold. The relative composition of products basally secreted differs between PC12-derived cell lines, and an inverse relationship exists between basal release of L-DOPA and total cellular store of dopamine. These results further indicate that selected PC12 cell lines are potentially a source of both dopamine and L-DOPA in therapeutic cellular replacement applications.