Flash responses of mouse rod photoreceptors in the isolated retina and corneal electroretinogram: comparison of gain and kinetics.

PURPOSE: To examine the amplification and kinetics of murine rod photoresponses by recording ERG flash responses in vivo and ex vivo from the same retina. We also aimed to evaluate the two available methods for isolating the rod signal from the ERG flash response, that is, pharmacology and paired flash method on the isolated retina. METHODS: Dark-adapted ERG responses to full-field flashes of green light were recorded from anesthetized (ketamine/xylazine) C57BL/6N mice. ERG flash responses to homogenous light stimuli arriving from the photoreceptor side were then recorded transretinally from the same retinas, isolated and perfused with Ringer's or Ames' solution at 37°C. The responses were analyzed to determine the a-wave kinetics as well as the estimated flash sensitivity and kinetics of the full rod responses derived with the paired flash protocol. The analysis was complemented with pharmacologic blockade of glutamatergic transmission in the isolated retina. RESULTS: The a-waves were of comparable size, sensitivity and kinetics in vivo and in the isolated retina, but the onset of the b-wave was delayed in the isolated retina. The Lamb-Pugh activation constants determined for the a-waves were similar in both preparations. The kinetics of the derived photoreceptor responses were similar in both conditions, although the responses were consistently slightly slower ex vivo. This was not explicable as a direct effect of ketamine or xylazine on the photoreceptors or as their indirect effect through hyperglycemia, as tested on the isolated retina. CONCLUSIONS: Through comparison to the corneal ERG, the transretinal ERG is a valuable tool for assaying the physiologic state of isolated retinal tissue. The rod photoreceptor responses of the intact isolated retina correspond well to those recorded in vivo. The origin of their faster kinetics compared to single cell recordings remains to be determined.

Bioactive glass microspheres as osteopromotive inlays in macrotextured surfaces of Ti and CoCr alloy bone implants: trapezoidal surface grooves without inlay most efficient in resisting torsional forces.

We have tested the efficacy of porous bioactive glass (BG) inlays in enhancement of implant osseointegration. A total of 24 sheep underwent bilateral surgical implantation of three parallel implants on the anteromedial cortical surface of each tibia. The disc-shaped implants made of Ti6Al4V or cobalt chromium (CoCr) alloys had two parallel surface grooves (trapezoidal space with bottom widening) filled with sintered 100% bioactive glass microspheres or a selected mixture of bioactive and biocompatible glass microspheres. The surface of uncoated control implants was smooth, grit-blasted or had unfilled grooves. A subgroup of control smooth CoCr implants was coated with two or three BG layers. Implant incorporation with bone was evaluated using torque testing to failure, scanning electron microscopy and morphometry at 12 and 25 weeks. A total of 144 in vivo implants and 16 ex vivo cemented control implants were analyzed. Control Ti6Al4V implants with unfilled trapezoidal grooves showed highest torsional failure loads with excellent ingrowth of new bone and remodeling of ingrown bone into lamellar bone. Implants with BG inlays and microroughened control Ti6Al4V implants showed significantly lower torsional failure loads than control Ti6Al4V implants with unfilled grooves. In conclusion, BG inlays failed to enhance biological implant fixation. Macrotextured surface was more effective than grit-blasting in promotion of mechanical incorporation.

Bioceramic inlays do not improve mechanical incorporation of grit-blasted titanium stems in the proximal sheep femur.

The aim of the present study was to determine, if bioactive glass (BG) surface inlays improve osseointegration of titanium implants in the proximal femur of adult sheep. In simulation of uncemented primary stems (nine animals), only the proximal part of the implants was grit-blasted and three surface slots of the grit-blasted region were filled with sintered BG microspheres. Primary stems were implanted using press-fit technique. In revision stem simulation (eight animals), grit-blasting was extended over the whole implant and seven perforating holes of the stem were filled by sintered BG granules. Revision stems were implanted with a mixture of autogenous bone graft and BG granules. Comparison with solid partially or fully grit-blasted control stems implanted in the contralateral femurs was performed in the primary and revision stem experiments at 12 and 25 weeks, respectively. Implant incorporation was evaluated by torsional failure testing and histomorphometry. Only one-third of the primary stems anchored mechanically to bone. The revision stems incorporated better and the BG inlays of the revision stems showed ingrowth of new bone. However, there were no significant differences in the torsional failure loads between the stems with BG inlays and the control stems. In conclusion, surface BG inlays gave no measurable advantage in mechanical incorporation of grit-blasted titanium implants. Overall, the proximal sheep femur, characterized by minimal amount of cancellous bone and the presence of adipocytic bone marrow, seemed to present compromised bone healing conditions.

Propofol modulates inner retina function in Beagles.

PURPOSE: To further understand a common veterinary anesthetic, propofol (2,6- di-isopropylphenol) and effects of infusion rates on the retinal neurons in Beagle dogs. METHODS: Standard full-field blue xenon-flash stimulation elicited responses of dark-adapted eyes, which were recorded from dogs before and after a propofol infusion rate increase. RESULTS: Electroretinogram b-waves increased significantly after the infusion rate increase and decreased with decline (P < 0.0001). Also, a weak significance (P = 0.041) for a-wave peak amplitude increase was found after infusion rate increase. The initial part (first 18 ms) of the leading edge of the a-wave remained unchanged. No significant differences in times to a- and b-wave peaks were found. CONCLUSION: Enhanced b-wave response and decline is due to sensitivity of postreceptoral cells, possibly interplexiform and amacrine cells, to propofol concentration.