A reduced number of hippocampal granule cells does not associate with an anhedonia-like phenotype in a rat chronic mild stress model of depression

Figures & data

Table I.  Description of the experimental groups of rats used in the present study.

Experimental group	Abbreviations	Description	N
Unchallenged 4 weeks	U-4	Left unchallenged for 4 weeks	11
Unchallenged 8 weeks	U-8	Left unchallenged for 8 weeks	11
Chronic mild stress 4 weeks	CMS-4	Exposed to 4 weeks of CMS which resulted in a decrease of the sucrose consumption	8
Chronic mild stress 8 weeks	CMS-8	Exposed to 8 weeks of CMS which resulted in a decrease of the sucrose consumption	8
Chronic mild stress resilient group	CMS-R	Exposed to 8 weeks of CMS which did not result in a decrease of the sucrose consumption	10

Figure 1  Experimental design. Experimental design and groups compared for the following hypothesis: CMS induces anhedonia-like behavior and diminishes hippocampal cell proliferation and the total number of granule cells in a time-dependent manner. U-4, unchallenged 4 weeks (n = 10); U-8, unchallenged 8 weeks (n = 8); CMS-8, chronic mild stress 8 weeks (n = 8); CMS-R, chronic mild stress resilience (n = 8); and CMS-4, chronic mild stress 4 weeks (n = 10).

Table II.  Significant differences in sucrose intake between the experimental groups.

Compared groups	Time-points (weeks)	Groups compared with Bonferroni test	Bonferroni correlation (p)	Comment
CMS-4/U-4	Baseline	CMS-4/U-4	>0.05	ns
	1		>0.05	ns
	2		< 0.01	**
	3		>0.05	ns
	4		< 0.01	**
CMS-8/U-8/CMS-R	Baseline	CMS-8/U-8	>0.05	ns
	1		>0.05	ns
	2		< 0.05	*
	3		>0.05	ns
	4		>0.05	ns
	5		< 0.01	**
	6		< 0.05	*
	7		< 0.05	*
	Baseline	CMS-8/CMS-R	>0.05	ns
	1		>0.05	ns
	2		< 0.05	*
	3		< 0.01	**
	4		< 0.001	***
	5		< 0.001	***
	6		< 0.01	**
	7		< 0.001	***
	0–7	U-8/CMS-R	>0.05	ns

p-Values for significant differences between the compared experimental groups. The data were analyzed by two-way repeated measures (ANOVA), followed by Bonferroni post hoc group comparisons. U-4, unchallenged 4 weeks (n = 10); U-8, unchallenged 8 weeks (n = 8); CMS-4, chronic mild stress 4 weeks (n = 10); CMS-8, chronic mild stress 8 weeks (n = 8); and CMS-R, chronic mild stress resilience (n = 8).

Figure 2  Sucrose intake during the experiment. Influence of 4- and 8 weeks of chronic stress on sucrose consumption. The data were analyzed by two-way ANOVA for repeated measures, followed by Bonferroni post hoc group comparisons (Table II). U-4, unchallenged 4 weeks (n = 10); CMS-4, chronic mild stress 4 weeks (n = 10); U-8, unchallenged 8 weeks (n = 8); CMS-8, chronic mild stress 8 weeks (n = 8), and CMS-R, chronic mild stress resilience (n = 8). Data are mean ± SEM.

Figure 3  Cell proliferation in the hippocampal vGCL in the experimental groups. Cell proliferation in the vGCL after exposure to 4- and 8 weeks of CMS. Data were analyzed by one-way ANOVA followed by Bonferroni post hoc test. The statistical significance was set at *p < 0.05. U-4, unchallenged 4 weeks (n = 10); U-8, unchallenged 8 weeks (n = 8); CMS-4, chronic mild stress 4 weeks (n = 10); CMS-8, chronic mild stress 8 weeks (n = 8); and CMS-R, chronic mild stress resilience (n = 8). Data are mean ± SEM.

Figure 4  BrdU positive cells in the GCL of the VHF. (A) U-4, unchallenged 4 weeks, (B) CMS-4, chronic mild stress 4 weeks, (C) U-8, unchallenged 8 weeks, (D) CMS-8, chronic mild stress 8 weeks group, and (E) CMS-R, chronic mild stress resilience group. BrdU positive cells or cell clusters appear in red, the mature neurons appear in green. Scale bar: 100 μm.

Figure 5  The total cell number in the vGCL in the experimental groups. Total cell number in the vGCL after exposure to 4- and 8 weeks of CMS. Data were analyzed by one-way ANOVA followed by Bonferroni post hoc test. The statistical significance was set at p < 0.05, *p < 0.05, **p < 0.01. U-4, unchallenged 4 weeks (n = 10); U-8, unchallenged 8 weeks (n = 8); CMS-4, chronic mild stress 4 weeks (n = 10); CMS-8, chronic mild stress 8 weeks (n = 8); and CMS-R, chronic mild stress resilience (n = 8). Data are mean ± SEM.

Table III.  CE and CV values for estimates of the total number of granule cells in the ventral part of the hippocampal formation.

Experimental groups	CE values	CV values
U-4	0.079	0.13
CMS-4	0.076	0.14
U-8	0.07	0.17
CMS-8	0.066	0.105
CMS-R	0.079	0.12

The group means of CE of the individual estimates are presented for the estimates of total cell number for each group. The CV of the mean estimates of cell numbers of each whole experimental group was calculated as standard deviation of group mean/group mean. U-4, unchallenged 4 weeks (n = 10); U-8, unchallenged 8 weeks (n = 8); CMS-4, chronic mild stress 4 weeks (n = 10); CMS-8, chronic mild stress 8 weeks (n = 8); and CMS-R, chronic mild stress resilience (n = 8).

Table IV.  Changes in volume of the vGCL and the ventral Ammon's horn among the experimental groups.

	U-4			CMS-4			U-8			CMS-8
	Mean ± SD	CV	CE	Mean ± SD	CV	CE	Mean ± SD	CV	CE	Mean ± SD	CV	CE
GCL	0.13 ± 0.0034	0.0088	0.043	0.12 ± 0.0037	0.085	0.039	0.13 ± 0.0035	0.09	0.047	0.13 ± 0.0041	0.08	0.044
Ammon's horn	4.08 ± 0.068	0.052	0.034	3.96 ± 0.092	0.046	0.04	3.94 ± 0.09	0.073	0.028	4.15 ± 0.14	0.086	0.021

The group means of CE of the individual estimates are presented for the estimates of total cell number for each group. The CV of the estimates of cell numbers for each experimental group was calculated as standard deviation of the group mean. GCL, granule cell layer; CV, coefficient of variation; CE, coefficient of error; U-4, unchallenged 4 weeks (n = 10); CMS-4, chronic mild stress 4 weeks (n = 10); U-8, unchallenged 8 weeks (n = 8); and CMS-8, chronic mild stress 8 weeks (n = 8).