Effects of intra-PVN infusion of RU486 on behavior in rats that
were chronically treated with CORT
We investigated the effects of RU486 on depressive- and anxiety-like
behaviors and the levels of GRs, MRs, and CRF in the PVN in rats that
were treated with CORT + vehicle. On day 16 during CORT consumption at
08:00, the rats received an intra-PVN infusion of RU486 for 7 days. As
shown in Fig. 3, rats that were treated with CORT + vehicle also
exhibited depressive-like behaviors in the FST
(F 3, 23 = 42.47, p < 0.01, Fig.
3A) and SPT (F 3, 23 = 7.599, p <
0.01, Fig. 3B) and anxiety-like behaviors in the SIT
(F 3, 23 = 24.03, p < 0.01, Fig.
3C) and NSFT (F 3, 23 = 6.225, p< 0.01, Fig. 3D). The intra-PVN infusion of RU486 did not
influence CORT-induced depressive- or anxiety-like behaviors (Fig.
3A-D). Western blot revealed that the intra-PVN infusion of RU486
restored GR expression in the PVN (F 3, 16 =
15.88, p < 0.01, Fig. 3F) without marked improvement in
MR levels in the PVN (Fig. 3E) and significantly decreased the MR/GR
ratio (F 3, 16 = 8.628, p < 0.01,
Fig. 3G). Unexpectedly, intra-PVN RU486 administration augmented the
increase in CRF levels compared with rats that were treated with CORT +
vehicle (F 3, 16 = 94.75, p <
0.01, Fig. 3H). These data suggest that although GR levels in the PVN in
rats that were treated with CORT + vehicle rats were restored to normal
by the intra-PVN infusion of RU486 alone, the MR/GR ratio was still
imbalanced, and CRF levels remained high. Thus, depressive- and
anxiety-like behaviors in rats that were chronically treated with CORT
were not inhibited.
Effects of intra-PVN infusion of spironolactone on
behavior in rats that were chronically treated with
CORT
To elucidate the involvement of MRs in the PVN in the behavioral
alterations that were induced by chronic CORT exposure, the MR
antagonist spironolactone was microinjected into the PVN on day 16 of
CORT consumption at 08:00 for 7 days. Depressive-like behavior,
including immobility time in the FST (Fig. 4A) and sucrose preference in
the SPT (Fig. 4B), were not reversed by intra-PVN spironolactone
administration. In contrast, the intra-PVN infusion of spironolactone in
CORT-exposed rats exerted anxiolytic-like effects, reflected by an
increase in social interaction in the SIT (F 3, 22= 18.76, p < 0.01, Fig. 4C) and a shorter feeding
latency in the NSFT (F 3, 22 = 19.07, p< 0.01, Fig. 4D).
The
intra-PVN injection of spironolactone reversed the decrease in MR levels
in the PVN that was induced by chronic CORT exposure
(F 3, 16 = 26.15, p < 0.01, Fig.
4E). Chronic CORT exposure significantly altered
GR
and CRF expression, and these
changes were
unaffected
by intra-PVN spironolactone administration (Fig. 4F, H). Because MR
levels returned to normal but GRs levels failed to recover, the MR/GR
ratio was two-times higher than normal and notably out of balance
(F 3, 16 = 7.344, p < 0.01, Fig.
4G). Based on these results, the CORT-induced decrease in MR levels in
the PVN may be associated with anxiety-like behavior, and intra-PVN
spironolactone administration restored MR levels to normal, which may be
related to its anxiolytic effect. Meanwhile, the failure of GR and CRF
levels and the MR/GR ratio to return to normal in the PVN in
CORT-treated rats may explain why the intra-PVN infusion of
spironolactone did not produce an antidepressant effect.
Effects of co-administration of RU486 and spironolactone
in the PVN on behavior and GR, MR and CRF levels in rats that were
chronically treated with
CORT
Accumulating evidence indicates that MRs cooperate with GRs in the
stress response (Spencer et al., 1998; Mattsson et al., 2009; Jadavji et
al., 2011). In this experiment, we co-administered the GR antagonist
RU486 and MR antagonist spironolactone in the PVN. RU486 was
microinjected in the PVN once daily beginning on day 16 of CORT
consumption at 08:00 for 7 days. Spironolactone was administered on the
same days, 40 min after RU486 administration. Combined GR and MR
blockade in the PVN in rats that were chronically treated with CORT
restored behavior in the FST (F 3,22 = 15.78,p < 0.01, Fig. 5A), SPT (F 3,22 =
9.56, p < 0.01, Fig. 5B), SIT
(F 3,22 = 16.68, p < 0.01, Fig.
5C) and NSFT (F 3,22 = 18.99, p <
0.01; Fig. 5D) and the levels of MRs (F 3,16 =
14.64, p < 0.01, Fig. 5E), GRs
(F 3,16 = 33.93, p < 0.01, Fig.
5F) and CRF (F 3,16 = 22.60, p <
0.01, Fig. 5H) in the PVN. Altogether, these data suggested
co-administration of the MR and GR antagonists in the PVN restored the
levels of MRs, GRs, and CRF and the MR/GR ratio in the PVN to normal in
CORT-exposed rats, thus inhibiting depressive- and anxiety-like
behaviors.