The Thermal Nociception Test Device was developed as described by Hargreaves et al. (1988). Our PAWS device is an improvement on the Hargreaves conception. PAWS consists of a glass surface upon which the mice or rats are placed individually in Plexiglas cubicles. The glass surface temperature (either 30± 0.1°C or 25± 0.1°C) is maintained by a feedback-controlled, under-glass, forced-air heating system and is controlled by a thermocouple on the bottom of the glass plate.
The thermal nociceptive stimulus originates from a focused projection bulb mounted in a stimulus tower that is manually manipulated in a two-dimensional axis on ball bearing slides to permit the stimulus to be delivered separately to either hind paw of each test subject. This stimulus is positioned under the foot pad with the aid of an angled mirror mounted on the stimulus source, permitting an exact visual targeting of the stimulation site prior to stimulus initiation. A timer is automatically actuated with the light source, and response latency is defined as the time required for the paw to show an abrupt withdrawal.
Paw withdrawal is detected by motion sensors mounted on the stimulus tower that stops the timer and terminates the stimulus. Stimulus current from a regulated source is monitored continuously to determine the amperage delivered to the light source and, thereby, the magnitude of the radiant stimulus to which the paw is subjected. In all cases, a cut-off of 20 seconds is employed to avoid tissue injury.
Features of the device:
• CONCURRENT TESTING OF GROUPS OF ANIMALS
The large stimulus area combined with the easily adjustable stimulus probe allows for testing of up to 6 rats or mice in adjacent plastic enclosures.
• AUTOMATIC CUT OFF
Paw withdrawal leads to changes in reflectance; use of an array of 3 spatially arranged photo transistors ensure adequate sensitivity to movement and determination of latency.
• SURFACE TEMPERATURE CONTROLLER WITH DIGITAL DISPLAY
Thermocouple controlled feedback circuit controls the temperature of circulating air allowing selection of glass temperature for reliable baseline despite minor changes in room ambient temperature. A LED display updated at 10 Hz will indicate glass or stimulus temperature.
• THROUGH FLOOR STIMULUS LOCALIZATION
A mirror positioned on the moveable stimulus tower allows the investigator to position the stimulus by direct visualization of the plantar surface of the paw no matter the posture of the animal.
The full reference is given at: