Korean J Physiol Pharmacol.  2013 Aug;17(4):321-329. 10.4196/kjpp.2013.17.4.321.

Changes in c-Fos Expression in the Forced Swimming Test: Common and Distinct Modulation in Rat Brain by Desipramine and Citalopram

• Choi SH
• Chung S
• Cho JH
• Cho YH
• Kim JW
• Kim JM
• Kim HJ
• Kim HJ
• Shin KH

• KMID: 2285467
• DOI: http://doi.org/10.4196/kjpp.2013.17.4.321

Abstract

Rodents exposed to a 15-min pretest swim in the forced swimming test (FST) exhibit prolonged immobility in a subsequent 5-min test swim, and antidepressant treatment before the test swim reduces immobility. At present, neuronal circuits recruited by antidepressant before the test swim remain unclear, and also less is known about whether antidepressants with different mechanisms of action could influence neural circuits differentially. To reveal the neural circuits associated with antidepressant effect in the FST, we injected desipramine or citalopram 0.5 h, 19 h, and 23 h after the pretest swim and observed changes in c-Fos expression in rats before the test swim, namely 24 h after the pretest swim. Desipramine treatment alone in the absence of pretest swim was without effect, whereas citalopram treatment alone significantly increased the number of c-Fos-like immunoreactive cells in the central nucleus of the amygdala and bed nucleus of the stria terminalis, where this pattern of increase appears to be maintained after the pretest swim. Both desipramine and citalopram treatment after the pretest swim significantly increased the number of c-Fos-like immunoreactive cells in the ventral lateral septum and ventrolateral periaqueductal gray before the test swim. These results suggest that citalopram may affect c-Fos expression in the central nucleus of the amygdala and bed nucleus of the stria terminalis distinctively and raise the possibility that upregulation of c-Fos in the ventral lateral septum and ventrolateral periaqueductal gray before the test swim may be one of the probable common mechanisms underlying antidepressant effect in the FST.

Keyword

Antidepressant; Forced swimming test; Fos; Lateral septum

MeSH Terms

Amygdala
Animals
Antidepressive Agents
Brain
Citalopram
Desipramine
Neurons
Periaqueductal Gray
Rats
Rodentia
Swimming
Up-Regulation
Antidepressive Agents
Citalopram
Desipramine

Figure

• 

  Fig. 1 Schematic representation of the experimental procedures and groups. (A) the forced swimming test (FST) process consists of two sessions: a pretest swim (pTS, 15 min) and a test swim (5 min) 24 h later. (B) one set of rats was injected with 0.9% saline (SAL, 1 ml/kg, i.p.), desipramine (DMI, 15 mg/kg/ml, i.p.), or citalopram (CIT, 10 mg/kg/ml, i.p.) according to the antidepressant treatments schedule (0.5 h, 19 h, and 23 h after the pretest swim), but not exposed to the pretest swim. (C) another set of rats was treated with saline, desipramine or citalopram after the pretest swim according to the antidepressant treatments schedule. Behaviorally naïve rats not exposed to the forced swimming and antidepressant served as baseline controls (CON) for each set. All rats were sacrificed 1 h after the last antidepressant or saline injection. Abbreviations used: SAL, saline-treated rats not exposed to the pretest swim; DMI, desipramine-treated rats not exposed to the pretest swim; CIT, citalopram-treated rats not exposed to the pretest swim; pTS+SAL, pretest swim-exposed, saline-treated rats; pTS+DMI, pretest swim-exposed, desipramine-treated rats; pTS+CIT, pretest swim-exposed, citalopram-treated rats.

• 

  Fig. 2 Schematic diagrams adapted from the Paxinos and Watson atlas showing selected brain areas in which c-Fos-like immunoreactive cells were counted. PrL, prelimbic cortex (3.20~2.70 mm from bregma, 25×104 µm2); NAc core, nucleus accumbens core (1.70~1.00 mm from bregma, 10×104 µm2); NAc shell, nucleus accumbens shell (1.70~1.00 mm from bregma, 10×104 µm2); LSv, ventral lateral septal nucleus (1.00~0.70 mm from bregma, 10×104 µm2); dlBNST, dorsolateral bed nucleus of the stria terminalis (-0.26~-0.30 mm from bregma, 4×104 µm2); vBNST, ventral bed nucleus of the stria terminalis (-0.26~-0.30 mm from bregma, 12.5×104 µm2); PVN, hypothalamic paraventricular nucleus (-1.80~-1.88 mm from bregma); CeA, central nucleus of the amygdala (-1.88~-2.80 mm from bregma, 6×104 µm2); PVT, paraventricular thalamic nucleus (-3.30~-4.16 mm from bregma); LHb, lateral habenula (-3.30~-4.16 mm from bregma); PAG [periaqueductal gray (dm, dorsomedial; dl, dorsolateral; l, lateral; vl, ventrolateral)] (-6.30~-8.00 mm from bregma, 1×104 µm2); DR, dorsal raphe (-7.30~-8.00 mm from bregma); LC, locus ceruleus (-9.68~-10.04 mm from bregma).

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  Fig. 3 Effects of antidepressant treatments on the number of c-Fos-like immunoreactive cells in the ventral lateral septum in the FST. Saline, desipramine or citalopram was administered at 0.5 h, 19 h, and 23 h after the pretest swim as depicted in Fig. 1. Rats were killed 1 h after the last injection of antidepressant or saline. Behaviorally naïve rats not exposed to forced swimming or antidepressants served as baseline controls (CON). The results with antidepressant treatments obtained under basal conditions without the pretest swim (upper left) and after the pretest swim (lower left) are presented in the bar graphs. The results are presented as the means±standard error of the means (S.E.M). Significant differences among groups were determined by the nonparametric Kruskal-Wallis ANOVA followed by post hoc Mann-Whitney U test with Bonferroni correction (***p<0.00016 vs. CON; #p<0.00833 and ###p<0.00016 vs. pTS+SAL). Representative images at ×100 magnification show c-Fos-like immunoreactivity in the ventral lateral septum from rats with antidepressant or saline treatments after the pretest swim.

• 

  Fig. 4 Effects of antidepressant treatments on the number of c-Fos-like immunoreactive cells in the central nucleus of the amygdala during the FST. Experimental groups, animal numbers per group, and all the procedures are the same as described in Fig. 1. The results obtained with antidepressant or saline treatments alone (upper left) or in combination with prior exposure to pretest swim (upper right) are presented as bar graphs. Significant differences among groups were determined by the nonparametric Kruskal-Wallis ANOVA followed by post hoc Mann-Whitney U test with Bonferroni correction (*p<0.00833 and ***p<0.00016 vs. CON; ###p< 0.00016 vs. pTS+SAL). Representative images at ×100 magnification show c-Fos-like immunoreactivity in the central nucleus of the amygdala from rats with antidepressant or saline treatments alone (lower left) or in combination with prior exposure to pretest swim (lower right). Abbreviations used are the same as in Fig. 1.

• 

  Fig. 5 Effects of antidepressant treatments on the number of c-Fos-like immunoreactive cells in the dorsolateral bed nucleus of stria terminalis during the FST. Experimental groups, animal numbers per group, and all the procedures are the same as described in Fig. 1. The results obtained with antidepressant or saline treatments alone (upper left) or in combination with prior exposure to pretest swim (upper right) are presented as bar graphs. Significant differences among groups were determined by the nonparametric Kruskal-Wallis ANOVA followed by post hoc Mann-Whitney U test with Bonferroni correction (*p<0.00833 and ***p<0.00016 vs. CON; ###p<0.00016 vs. pTS+SAL). Representative images at ×100 magnification show c-Fos-like immunoreactivity in the dorsolateral bed nucleus of stria terminalis from rats with antidepressant or saline treatments alone (lower left) or in combination with prior exposure to pretest swim (lower right). Abbreviations used are the same as in Fig. 1.

• 

  Fig. 6 Effects of antidepressant treatments on the number of c-Fos-like immunoreactive cells in the ventrolateral periaqueductal gray during the FST. Experimental groups, animal numbers per group, and all the procedures are the same as described in Fig. 1. The results obtained with antidepressant or saline treatments alone (left upper) or in combination with prior exposure to pretest swim (right upper) are presented as bar graphs. Statistical significance of data with equal variances was assessed by one-way analyses of variance (ANOVAs) followed by post hoc Fisher's least significant difference (LSD) test and significance was accepted for p-values less than 0.05 (*p<0.05 and ***p<0.001 vs. CON; ###p< 0.001 vs. pTS+SAL). Representative images at ×40 magnification show c-Fos-like immunoreactivity in the ventrolateral periaqueductal gray from rats with antidepressant or saline treatments after the pretest swim (right). Abbreviations used are the same as in Fig. 1.

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