I have used this method to extract total RNA from mouse brains.
It has worked extremelly well for me.

1. Homogenize tissue samples (1/2 of brain usually)
in 2 ml of TRIZOL.
2. Transfer to two 1.5 ml tubes (about 1 ml in each).
3. Incubate for 5 min at RT.
4. Add 200 µl of chloroform to each tube.
5. Cap tubes securely and shake vigorously by hand for 15 sec.
6. Incubate 3 min at RT.
7. Centrifuge samples @ 12,000 rpm for 15 min @ 4 C.
8. Transfer upper (clear) aqueous phase to a fresh set of tubes
(about 600 µl per tube).
9. Add 500 µl isopropanol to each tube.
10. Incubate @ RT for 10 min.
11. Centrifuge 12,000 rpm for 10 min @ 4 C.
12. Carefully remove supernatant. Make sure not to lose the pellet.
13. Wash pellet once with 1 ml of 75% ethanol per tube.
14. Mix by vortex and centrifuge @ 7,500 rpm for 5 min @ 4.
15. Carefully remove as much ethanol as possible
(do not lose the pellet).
16. Add 50 µl RNase free water per tube, vortex, and incubate
at 56 C 15 min.
17. Vortex tubes for 10 sec, then combine into one fresh
tube per sample.
18. SpeedVAC tubes 10-15min without heat to remove trace EtOH.
19. Dilute 1/100 in DEPC H2O and measure OD 260/280.
20. To determine RNA concentration multiply OD260 values
by 4000 µg/µl.
(40 µg/µl RNA per 1OD260) * (dilution factor 100) = 4000 µg/µl
21. OD260/OD280 ratio should be >1.8
22. Store RNA @ -70 C.
23. If necessary adust volume to achieve 3-4 µg/µl
(add H20 or speedVAC)
24. In hybridization reaction use 2 µl RNA in
6 µl hybridization buffer.

NOTE: DO NOT TOUCH ANYTHING W/O GLOVES,
CHANGE GLOVES OFTEN