FGF2 treatment differentially impacts GAD65 and GAD67 mRNA expression in the forebrain of selectively bred high-responder and low-responder rats

Waselus M, Krolewski DM, Schrade S, Ilagan RA, Huh J, Perez J, Akil H, Watson SJ Jr
Society for Neuroscience. 2015.


The selectively bred lines of high-responder (bHR) and low-responder (bLR) rats, which display robust differences in anxiety-like behaviors, have previously been used in our laboratory to demonstrate the anxiolytic effect of systemic fibroblast growth factor 2 (FGF2) treatment (Perez et al., 2009). The effect of FGF2 administration on brain GABA-ergic function is largely unknown and of particular interest given the role of GABA in both anxiety and depression. Thus, we sought to examine the potential effects of FGF2 administration on GABA-synthesizing enzyme isoforms glutamate decarboxylase 65 (GAD65) and GAD67 in the brains of bHR and bLR rats. Adult male bHR and bLR Sprague-Dawley rats received single daily injections of either vehicle or FGF2 (5ng/g, i.p.) for 21-days. On the day after the last injection, rats were behaviorally assessed for anxiety-like behaviors and the brain was subsequently removed. Thin (10 μm) sections taken through the forebrain of each rat were used to examine the expression of GAD65 and GAD67 mRNA using radiolabeled in situ hybridization with cRNA probes. The effects of phenotype (bHR vs. bLR) and treatment (vehicle vs. FGF2) as well as the interaction between the two were statistically evaluated using a 2-way ANOVA with Tukey’s post-hoc tests for multiple comparisons when appropriate. Irrespective of treatment, bHR-bLR differences in GAD65 expression were observed in the prelimbic and infralimbic cortices as well as the core and shell subregions of the nucleus accumbens with bLRs having lower GAD65 expression compared to bHRs in all regions. Examination of GAD67 expression revealed that in the prelimbic and infralimbic cortices, bHR-bLR differences were limited to vehicle-treated rats and eliminated following FGF2 treatment. Moreover, FGF2-induced decreases in GAD67 expression in these regions, as well as the sensorimotor cortex, occurred selectively in bHR, but not bLR, rats. In summary, the reduced expression of GAD65 in bLRs relative to bHRs supports the previously proposed association between decreased GABA function and anxiety-like behaviors. However, the failure of FGF2 treatment to augment GAD65 or GAD67 mRNA in bLRs suggests that the anxiolytic effects of FGF2 in the bLR line may not be related to changes is GABA function in the regions selected for analysis. Future studies will further examine GAD65 and GAD67 expression in other brain regions including the hippocampus which is known to play a role in anxiety and mood disorders.