The expression of transcription factors , such as thyroid hormone receptor beta 1 ( TRbeta 1 ) , and transcriptional co repressors , such as histone deactylase 3 ( HDAC 3 ) , was affected by Delta 9 THC in a dose dependent manner , whereby 15 microM Delta 9 THC caused a 2 . 8 fold inhibition of TRbeta 1 expression , but a 3 . 5 fold increase in HDAC 3 expression . ^^^