Role of Midbrain Central Gray in Pain-Induced Defensive Boxing of Rats
Method Page 2

Title/Summary Page

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Pages 2 - 3

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Figures 1-7
Pages 8 - 9 - 10 - 11 - 12- 13 - 14

Page 15


Animals were 31 male rats over 150 days old and weighing 250-420 g. Experimental data were obtained from 19 rats, 12 of which were highly inbred DA agoutis and 7 of which were F 1 hybrid crosses between the DA and the Wag-Rij inbred albino. The remaining 6 DA's and 6 hybrids served' as normal controls.


Boxing and flinch tests were conducted in a clear Plexiglas chamber, 8 in. high with an 8 x 6 in. steel grid floor. The grids were connected via a scrambler switch to a 600 V a.c. power source with a variable resistance in series (minimum of 400 Kohm). Removal of a partition yielded an 8 x 9.5 in. chamber, which was used for escape tests. On one wall was a collapsible 2.5 X 7 in. wooden platform, elevated 3 in. off the floor.

The open field apparatus consisted of a 42 in. square wooden enclosure with 3 ft. high walls. The floor was divided into twenty-five 8.4 in. squares, and aside from 0.5 in. tan stripes outlining the squares, all other surfaces were painted black.

Surgery and Histology

Pairs of rats were anesthetized (60 mg/kg sodium pentobarbitol i.p.) and were given stereotaxically placed lesions aimed at the midbrain central gray. Two or three lesions were made bilaterally by 10 mA radio-frequency current for 20-40 sec through electrodes insulated except for a 1 mm tip.

Animals were placed in individual cages for recovery. If feeding had not recovered within 2 days, the rat was given gastric intubation of 10 cc of a liquid diet twice daily.

For histological assessment of lesions, animals were sacrificed by overdose of anesthesia and perfused with 0.9% saline followed by 10% Formalin. The brain was hardened in 10% Formalin and saline for 2 days and transferred to saturated sucrose solution for one day. Then it was cut into 50 micron sections, stained with neutral red and mounted. Tissue damage and gliosis were estimated for levels spaced every 0.2 mm from AP -1.4 to +4.0 and plotted on drawings taken from the atlas of Pellegrino and Cushman [23].

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