Richard M. Allen

a biosensor generated via high-throughput screening quantifies cell edge src dynamics

Fluorescent biosensors for living cells currently require laborious optimization and a unique design for each target. They are limited by the availability of naturally occurring ligands with appropriate target specificity. Here we describe a biosensor based on an engineered fibronectin monobody scaffold that can be tailored to bind different targets via high throughput screening. This Src family kinase (SFK) biosensor was made by derivatizing a monobody specific for activated SFK with a bright dye whose fluorescence increases upon target binding. We identified sites for dye attachment and alterations to eliminate vesiculation in living cells, providing a generalizable scaffold for biosensor production. This approach minimizes cell perturbation because it senses endogenous, unmodified target, and because sensitivity is enhanced by direct dye excitation. Automated correlation of cell velocities and SFK activity revealed that SFK are activated specifically during protrusion. Activity correlates with velocity, and peaks 1–2 microns from the leading edge.

The competitive NMDA receptor antagonist LY235959 modulates the progression of morphine tolerance in rats

Abstract A rat warm-water tail-withdrawal procedure was used to examine the effects of chronic administration of the competitive NMDA receptor antagonist LY235959 in morphine tolerant rats. Morphine dose-dependently increased tail-withdrawal latencies from 55°C water. When morphine (10 mg/kg) was administered twice-daily for 7 days, the morphine dose-effect curves shifted 0.3–0.5 log unit to the right. When morphine was administered for an additional 7 days, the morphine dose-effect curve shifted 0.4 log unit further to the right. Co-administration of LY235959 (1, 3, 10 mg/kg) along with morphine prevented the development of tolerance observed during the second week of chronic morphine administration. Although the highest dose of LY235959 (10 mg/kg) partially reversed tolerance in five of seven rats, tolerance was not reversed by lower doses of LY235959. These data suggest that NMDA receptor antagonists may effectively prevent the progressive development of morphine tolerance at doses that are not sufficient to reverse pre-established morphine tolerance.

Role of morphine maintenance dose in the development of tolerance and its attenuation by an NMDA receptor antagonist.

Abstract Rationale: Current research shows that N-methyl-d-aspartate (NMDA) receptor antagonists attenuate the development of morphine tolerance in rodent antinociceptive assays. Objective: The purpose of this study was to determine the role of morphine maintenance dose in the attenuation of morphine tolerance by the competitive NMDA receptor antagonist, LY235959. Methods: A rat warm-water tail-withdrawal procedure was used to measure the antinociceptive effects of morphine and LY235959. In this procedure, the distal 8 cm of each rat’s tail is immersed in 40° (non-noxious) and 55°C (noxious) water, and the latency to remove the tail is recorded. Results: Morphine (0.3–10 mg/kg, SC) produced dose-dependent increases in tail-withdrawal latencies from the 55°C water. Following determination of the morphine dose-effect curves, rats were administered chronically one of three doses of morphine (10, 20, or 40 mg/kg) either alone or in combination with LY235959 (1.0, 3.0, or 5.6 mg/kg, SC) twice daily for 7 days. Chronic administration of 10, 20, and 40 mg/kg morphine produced rightward shifts in the morphine dose-effect curves of approximately 3-, 6-, and 12-fold, respectively. When LY235959 (1.0–5.6 mg/kg) was co-administered with 10 mg/kg morphine, the development of morphine tolerance was attenuated in a dose-dependent manner, with complete prevention observed following 3.0 mg/kg LY235959. LY235959 (1.0, 3.0 mg/kg) also attenuated the development of tolerance to 20 and 40 mg/kg morphine; however, tolerance was not completely prevented. Administering 3.0 mg/kg LY235959 along with 20 and 40 mg/kg morphine was functionally equivalent to treating rats with half the amount of morphine. Conclusion: These data suggest that the maintenance dose of morphine, and thus the magnitude of tolerance, can determine the effectiveness of an NMDA receptor antagonist to attenuate morphine tolerance.