The mGlu2/3 Receptor Agonists LY354740 and LY379268 Differentially Regulate Restraint-Stress-Induced Expression of c-Fos in Rat Cerebral Cortex

Abstract

Metabotropic glutamate 2/3 (mGlu2/3) receptors have emerged as potential therapeutic targets due to the ability of mGlu2/3 receptor agonists to modulate excitatory transmission at specific synapses. LY354740 and LY379268 are selective and potent mGlu2/3 receptor agonists that show both anxiolytic- and antipsychotic-like effects in animal models. We compared the efficacy of LY354740 and LY379268 in attenuating restraint-stress-induced expression of the immediate early gene c-Fos in the rat prelimbic (PrL) and infralimbic (IL) cortex. LY354740 (10 and 30 mg/kg, i.p.) showed statistically significant and dose-related attenuation of stress-induced increase in c-Fos expression, in the rat cortex. By contrast, LY379268 had no effect on restraint-stress-induced c-Fos upregulation (0.3-10 mg/kg, i.p.). Because both compounds inhibit serotonin 2A receptor (5-HT2AR)-induced c-Fos expression, we hypothesize that LY354740 and LY379268 have different in vivo properties and that 5-HT2AR activation and restraint stress induce c-Fos through distinct mechanisms.

Figure 1

Schematic diagrams of coronal brain sections at Bregma + 2.7 mm according to the atlas [27]. Fos-positive cells were counted within the gray frame for the prelimbic cortex (A) or the infralimbic cortex (B).

Figure 2

Restraint stress upregulated c-Fos in the PrL (a) and IL (b) cortex. Pretreatment with the mGlu2/3 agonist LY354740 (10 mg/kg, i.p.) attenuated the restraint-induced increase in c-Fos expression in both the PrL and IL cortex. ∗ indicates significantly different from vehicle + home cage; ∗∗∗P < 0.001. ^# indicates significantly different from vehicle + restraint stress; ^## P < 0.01. One-way ANOVA with Newman-Keuls post hoc test. Each bar represents the mean (±SEM), n = 7-8.

Figure 3

Restraint stress upregulated c-Fos in the PrL (a) and IL (b) cortex. Pretreatment with the mGlu2/3 agonist LY379268 (0.3–3 mg/kg, i.p.) had no effect on the restraint-induced increase in c-Fos expression in the PrL and IL cortex. Pretreatment with alprazolam (3 mg/kg, i.p.) attenuated the c-Fos response in the PrL and IL cortex. ∗ indicates significantly different from vehicle + home cage; ∗∗∗P < 0.001. ^# indicates significantly different from vehicle + restraint stress; ^## P < 0.01, ^### P < 0.001. One-way ANOVA with Newman-Keuls post hoc test. Each bar represents the mean (±SEM), n = 7-8.

Figure 4

(a) Restraint stress upregulated c-Fos in the PrL cortex. Pretreatment with the mGlu2/3 agonist LY354740 (10 and 30 mg/kg, IP) but not LY379268 (10 mg/kg, i.p.) reversed restraint-induced increase in c-Fos expression in the PrL cortex. ∗∗ indicates significantly different from vehicle + home cage; P < 0.01, ∗∗∗P < 0.001; ^# indicates significantly different from vehicle + restraint stress; ^## P < 0.01. One-way ANOVA with Newman-Keuls post hoc test. Each bar represents the mean (±SEM), n = 7-8. (b) Representative photomicrographs of the prelimbic cortex showing c-Fos-labeled neurons of rats treated either with vehicle (Veh), LY (LY354740 30 mg/kg), vehicle + stress (vehicle + restraint stress), or LY + stress (LY354740 30 mg/kg + restraint stress). Restraint stress increased the number of Fos-positive-labeled cells and pretreatment with LY354740 (30 mg/kg) reversed the effect. LY354740 alone did not enhance Fos immunoreactivity. Scale bar = 100 μm.

Figure 5

DOI produced an increase in c-Fos in the PrL (a) and IL (b) cortex. Pretreatment with LY354740 (3 and 10 mg/kg) attenuated the DOI-induced increase in the PrL and IL cortex. ∗ indicates significantly different from vehicle; ∗∗∗P < 0.001, ^# indicates significantly different from DOI; ^## P < 0.01, ^### P < 0.001. One-way ANOVA with Newman-Keuls post hoc test. Each bar represents the mean (±SEM), n = 7-8.