Electroconvulsive seizures regulate gene expression of distinct neurotrophic signaling pathways

Abstract

Electroconvulsive therapy (ECT) remains the treatment of choice for drug-resistant patients with depressive disorders, yet the mechanism for its efficacy remains unknown. Gene transcription changes were measured in the frontal cortex and hippocampus of rats subjected to sham seizures or to 1 or 10 electroconvulsive seizures (ECS), a model of ECT. Among the 3500-4400 RNA sequences detected in each sample, ECS increased by 1.5- to 11-fold or decreased by at least 34% the expression of 120 unique genes. The hippocampus produced more than three times the number of gene changes seen in the cortex, and many hippocampal gene changes persisted with chronic ECS, unlike in the cortex. Among the 120 genes, 77 have not been reported in previous studies of ECS or seizure responses, and 39 were confirmed among 59 studied by quantitative real time PCR. Another 19 genes, 10 previously unreported, changed by <1.5-fold but with very high significance. Multiple genes were identified within distinct pathways, including the BDNF-MAP kinase-cAMP-cAMP response element-binding protein pathway (15 genes), the arachidonic acid pathway (5 genes), and more than 10 genes in each of the immediate-early gene, neurogenesis, and exercise response gene groups. Neurogenesis, neurite outgrowth, and neuronal plasticity associated with BDNF, glutamate, and cAMP-protein kinase A signaling pathways may mediate the antidepressant effects of ECT in humans. These genes, and others that increase only with chronic ECS such as neuropeptide Y and thyrotropin-releasing hormone, may provide novel ways to select drugs for the treatment of depression and mimic the rapid effectiveness of ECT.

Figure 1.

Plot of the mean abundances of each of the 8799 probe sets measured with the Affymetrix U34A rodent chip in the frontal cortex or hippocampus of rats that were exposed to either acute or chronic ECS (n = 10 per group; y axes) or sham control (n = 10 per group; x axes). Genes in white are those with ECS/control group ratios >1.5 or <0.67, with p <0.05, and passing minimum expression restrictions.

Figure 2.

The effect of sample size on the number of identified gene changes (Hits; p < 0.01, independent of fold change) is significant only for comparisons between sham- and ECS-treated rats. Groups of 2–10 were randomly composed from the hippocampus of acute sham-treated rats (sham), acute ECS-treated rats (ECS), or mixtures of rats from both groups (mixed). The number of hits was calculated for each microarray analysis of these samples, and this process was repeated 100 times for each sample size. Values are means ± SD. A calculation of 40 “theoretical chance” gene changes was based on p < 0.01 for the ∼4000 probes detected in the frontal cortex with at least a single present call in one group and a mean abundance >100.

Figure 3.

Venn diagram representation of the distribution of changes (p < 0.05, ratio of change >1.5 or <0.67) in the 120 unique genes in the frontal cortex and hippocampus after acute or chronic ECS. Genes are represented only if the corresponding probe was detected as present in at least 50% of samples in one group, and mean abundance exceeded 100. The overlaps of three genes between hippocampus chronic and frontal cortex acute could not be illustrated and are included in the tally of genes for these two tissues (shown in parentheses).

Figure 4.

Ability of the RT-PCR assay to detect small differences in genes identified by the Affymetrix microarray. The expression of three genes was measured for each sample (n = 10 rats per acute hippocampus group) and normalized to the GAPDH expression for that sample to account for variations in efficiency of the RT reaction. The normalized expression values (mean ± SEM × 10³) of each of the three genes differed significantly (p < 0.01; t test) between the sham and ECS-treated rats in the parent material and at the 0.75×, 0.5×, and 0.25× dilutions, except for the normalized rat heart EST189184 gene at the greatest dilution and GAPDH at all dilutions. The normalized expression values of each gene also decreased (p < 0.05; t test) at each dilution for all four genes compared with the one preceding it for both the sham and ECS groups, except for neuropilin at the 0.5× dilution.