Optical coherence microscopy for the evaluation of a tissue-engineered artificial cornea.

A transparent artificial cornea derived from biological material is the ultimate goal of corneal research. Attempts at artificial corneal constructs produced from synthetic polymers have proved unsuccessful due to lack of biocompatibility and ability to integrate into the tissue. We have designed a corneal model derived from collagenous biological materials that has several advantages: it has low antigenicity and therefore small chance of eliciting an immune reaction, it can be broken down by the body's own cells and gradually replaced over time by natural materials, and it may contain signaling information for native cells, thereby inducing normal phenotype and behavior. In addition, a transparent corneal model has the potential to be used for testing of novel ophthalmic drugs or gene therapy approaches, eliminating the need for animal testing. We have used an optical coherence microscope (OCM) to evaluate both the structure of our tissue constructs over time in culture and the optical properties of the tissue itself. This imaging technique promises to be an important diagnostic tool in our efforts to understand the influence of mechanical forces, cell phenotype, and soluble factors on the transparency of corneal tissue.

Locomotor activity in the ischemic gerbil.

Previous studies have shown that within 24 h after ischemic insult, gerbils exhibit an increase in locomotor activity. Because activity gradually diminishes to normal levels with repeated testing, it has been argued that this behavior represents a reversible or transient effect of ischemia. The present study challenged this notion by testing ischemic gerbils at a time when increased activity is not observed with repeated testing. Ischemic (5-min bilateral carotid occlusion) and sham gerbils were tested for 14 consecutive days after reperfusion in an open-field apparatus (n = 6/condition). As previously reported, ischemic gerbils exhibited a significant increase in activity (days 1 and 2) which returned to control levels with repeated testing (days 13 and 14). A second group of ischemic and sham gerbils (n = 6/condition) were tested only on days 13 and 14 after reperfusion. In contrast to those tested repeatedly, these ischemic gerbils displayed increased locomotor activity as compared with sham controls. In addition, gerbils in the repeated testing conditions were evaluated in a semi-novel testing environment on days 15 and 16 after surgery. The locomotor activity of ischemic gerbils significantly increased in response to the semi-novel environment. These results suggest that the effects of ischemia on locomotor activity are not limited to a brief period after occlusion and may represent a permanent deficit. In addition, as previously suggested, this behavior may represent a deficit in habituation or spatial mapping rather than motor hyperactivity.

Neurotensin-induced hypothermia prevents hippocampal neuronal damage and increased locomotor activity in ischemic gerbils.

Hypothermia induced by surface cooling has shown to protect vulnerable regions of the brain during an ischemic insult. This study evaluated the neuroprotective efficacy of neurotensin, a potent hypothermic agent, using a 5-min carotid occlusion procedure in the gerbil. In Experiment 1, the dose-response and time course of neurotensin-induced hypothermia were evaluated (n = 5/dose). Central infusion of 10, 20, and 30 micrograms neurotensin were found to significantly decrease core body temperature of conscious gerbils within 30 min of administration. In Experiment 2, gerbils pretreated with 30 micrograms neurotensin were permitted to become hypothermic or were maintained at 37 degrees-38 degrees C (rectal) during ischemic insult. Other gerbils were pretreated with peptide vehicle prior to ischemic insult (at 37 degrees -38 degrees C) or underwent a sham procedure (n = 6/condition). At 24 h after surgery, gerbils were tested for increased locomotor activity in an open-field apparatus. Gerbils pretreated with peptide vehicle or neurotensin and maintained at 37 degrees-38 degrees C during ischemia had significantly higher activity levels compared to the other treated groups. In contrast, gerbils made hypothermic with neurotensin exhibited activity levels similar to sham gerbils. Histological assessment revealed that neurotensin-induced hypothermia protected the CA1 region from ischemic damage.