Effects of the histone deacetylase inhibitor sodium butyrate in models of depression and anxiety

Abstract

Histone modification, which affects the rate of transcription without altering DNA sequence, occurs in response to various psychiatric drugs and in several models of psychiatric disease. As increases in histone acetylation have been seen after treatment with antidepressants, we investigated whether directly increasing histone acetylation using a histone deacetylase inhibitor would have antidepressant effects. We administered sodium butyrate (NaB, 100 mg/kg, i.p.) to mice acutely (3 injections over 24 h) or chronically (twice daily for 21 days) and subjected them to a number of behavioral tests of antidepressant response. This dose of NaB had no effect on overall locomotor activity after either acute or chronic treatment. Acutely treated mice showed an increase in immobility in the forced-swim test (FST) and an increase in latency to consume in the novel environment of the novelty-induced hypophagia (NIH) paradigm, an anxiogenic effect. The effect of NaB on anxiety did not generalize to another test, the elevated zero maze, where it had no effect. Chronic treatment with NaB had no effect on latency to consume in the NIH or immobility in the FST. However, this dose did alter histone acetylation in the hippocampus. While H4 acetylation increased in the hippocampus 30 min following acute NaB, chronic treatment caused a decrease in AcH4. There were no changes in AcH3 following either treatment. While changes in chromatin structure may be involved in the mechanism of action of antidepressant drugs, these data suggest that increasing histone acetylation pharmacologically is not sufficient to produce antidepressant effects.

Figure 1

Acute, but not chronic, treatment with NaB increases immobility in the FST at doses that do not affect locomotor activity. Mice were given 3 injections of NaB over 24 hours (a) or treated twice daily for 21 days with NaB or DMI (b), and their locomotor activity was measured 1 hour after the last injection. Ambulations (left) and crossings (right) were measured in 5-minute bins for a total of 30 minutes in acutely treated mice (a). The higher dose of NaB (1.2 g/kg) caused significant hypolocomotion in the first 5 minutes, while the lower dose (100 mg/kg) had no effect (n=8). Chronic treatment with NaB (100 mg/kg) or DMI (12.5 mg/kg) had no significant effect on either ambulations (left) or crossings (right) over 60 minutes (b) (n = 30). A separate cohort of mice was given acute treatment with NaB or DMI, and immobility during a 6 minute FST was measured (c). There was a significant effect of treatment on immobility, with DMI significantly reducing immobility and NaB (100 mg/kg) significantly increasing immobility (n=5–6). After chronic treatment with twice-daily NaB (100 mg/kg) or DMI (12.5 mg/kg), DMI significantly reduced immobility in the FST, whereas NaB had no effect (d). Error bars indicate SEM. *p< 0.05 vs. saline; ** p< 0.01 vs. saline; ***p<0.001 vs. saline.

Figure 2

Acute treatment with NaB increased latency to consume peanut butter chips in the novel environment of the NIH paradigm. Mean latencies to consume in home and novel environment are shown. Mice were given 3 injections of NaB (AM and PM on Home Day 1 and AM on Novel day, 1 hr before test) or 1 injection of CDP (1 hr before test) before exposure to novel environment. There was an increase in latency to consume in the novel environment relative to the home cage (p<0.0001) and an increase in latency in NaB-treated animals as compared to saline-treated animals (*p<0.001) (n=9–10). Error bars indicate SEM.

Figure 3

Acute treatment with NaB had no effect on anxiety behavior in the elevated zero maze. Mice were given 3 injections of NaB over 24 hours and tested in the EZM 1hr following the last injection. NaB had no effect on time spent in the open quadrants (a), entries into the open quadrants (b), distance traveled in the open quadrants (c), or total distance traveled in the maze (d) (n = 6–7). Error bars indicate SEM.

Figure 4

Chronic treatment with NaB had no effect on latency to consume peanut butter chips in the novel environment of the NIH paradigm. Mean latencies to consume in home and novel environment are shown. Mice were treated with NaB or DMI for 22 days before exposure to novel environment. There was an increase in latency to consume in the novel environment relative to the home cage (p<0.001). There was a significant decrease in latencies in the novel environment in DMI-treated mice as compared to saline-treated animals, but no change in NaB-treated mice (*p<0.001) (n=9–10). Error bars indicate SEM.

Figure 5

Optical density of AcH staining normalized to total H3 staining is shown. Mice were given 3 injections of NaB over 24 hours and sacrificed 30 min after the last injection (a and b). Acute treatment with NaB dose-dependently increased AcH4 in the hippocampus (a), while only the higher dose of NaB (1.2 g/kg) significantly increased AcH3 in the hippocampus (b) (n = 5–7). A separate cohort of mice was injected with NaB for 21 days and sacrificed 30 minutes after the last injection (c and d). Chronic treatment with NaB decreased AcH4 in the hippocampus (c), while the level of AcH3 in the hippocampus did not change after chronic treatment with NaB (n=7–8). *p<0.05 vs. saline; **p<0.01 vs. saline; ***p<0.001 vs. saline. Error bars indicate SEM.