Table 10.

Studies showing that HDAC inhibitors augment exposure-based fear extinction and rescue extinction learning deficits.

Drug/manipulat	Extinction training	Extinction retrieval	Longterm extinction	Route	Reference
HDAC1 KO (HPC)	ns	−#	ns	No drug	(Bahari-Javan et al., 2012)
HDAC2 KO in forebrain CamKII neurons	ns	+*#	ns	No drug	(Morris et al., 2013)
Vorinostat/SAHA	ns	+	ns	ip	(Fujita et al., 2012)
	ns	+ **	ns	ip	(Matsumoto et al., 2013)
	ns	+ **	ns	ip	(Hait et al., 2014)
TSA (trichostatin A)	ns	+*	ns	ip, HPC	(Lattal et al., 2007)
Sodium butyrate	−	+	+ (SR)	ip, HPC	(Stafford et al., 2012)
	ns	+	ns	ip	(Itzhak et al., 2012)
	ns	+	ns	ip, HPC	(Lattal et al., 2007)
Valproic acid	−	+*	ns	ip	(Bredy et al., 2007)
		+*	+ (Ren-A)	ip	(Bredy & Barad, 2008)
	+ **	+ **	+ (SR, Ren-N)	ip	(Whittle et al., 2013)
MS-275 (entinostat)	−	+ **	+ (SR, Ren-N)	ip	(Whittle et al., 2013)
Cl-994	ns	+ ***	+ (SR)	ip	(Graff et al., 2014)
FTY720 (fingolimod)	−	+ **	ns	ip	(Hait et al., 2014)

^*Partial extinction training: reduction of fear during the extinction training session was not to pre-conditioning levels,

^**facilitates rescue of impaired fear extinction;

^***facilitate remote memories combined with memory re-consolidation update paradigm;

^#extinction protocol based on a re-consolidation/update paradigm

+, Improved;-, impaired; ip, intraperitoneal injection; ns, not studied; HPC, intra-hippocampal administration; Ren-A, Fear renewal in the conditioning context; Ren-N, Fear renewal in a novel context; SR, spontaneous recovery; # reduced freezing levels at the beginning of extinction training