BDNF release is required for the behavioral actions of ketamine

Abstract

Background: Recent studies demonstrate that the rapid antidepressant ketamine increases spine number and function in the medial prefrontal cortex (mPFC), and that these effects are dependent on activation of glutamate α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors and brain-derived neurotrophic factor (BDNF). In vitro studies also show that activation of AMPA receptors stimulates BNDF release via activation of L-type voltage-dependent calcium channels (VDCC).

Methods: Based on this evidence, we examined the role of BDNF release and the impact of L-type VDCCs on the behavioral actions of ketamine.

Results: The results demonstrate that infusion of a neutralizing BDNF antibody into the mPFC blocks the behavioral effects of ketamine in the forced swim test (FST). In addition, we show that pretreatment with nifedipine or verapamil, two structurally-different L-type calcium channel antagonists, blocks the behavioral effects of ketamine in the FST. Finally, we show that ketamine treatment stimulates BDNF release in primary cortical neurons and that this effect is blocked by inhibition of AMPA receptors or L-type VDCCs.

Conclusions: Taken together, these results indicate that the antidepressant effects of ketamine are mediated by activation of L-type VDCCs and the release of BDNF. They further elucidate the cellular mechanisms underlying this novel rapid-acting antidepressant.

Keywords: BDNF; L-type VDCC; depression; glutamate; ketamine.

Figure 1.

Infusion of anti-BDNF antibody into the mPFC blocks the behavioral effects of ketamine in the FST. Rats received a bilateral infusion into the mPFC of a function-blocking anti-BDNF antibody (1µg/µl) 30min prior to a ketamine injection (10mg/kg i.p.), and immobility in the FST was determined 24 hours following the ketamine injection. (A) Ketamine significantly reduced the immobility time compared to vehicle-treated rats, and pretreatment with the function-blocking anti-BDNF antibody completely blocked this effect. Values are the mean ± SEM (n = 7–11; antibody x drug interaction, F_1,37 = 4.158, *p < 0.05). (B and C) Total swim time was divided into two epochs: the first 5 minutes and the second 5 minutes. Ketamine significantly reduced immobility time, which was blocked by the neutralizing antibody in both the first 5 minutes (ANOVA, F_3,37 = 3.357, *p < 0.05) and the second 5 minutes (ANOVA, F_3,37 = 3.630, *p < 0.05). (D) There was no effect on locomotor activity.

Figure 2.

L-type channel antagonists block the antidepressant behavioral effects of ketamine in the FST. Rats were injected i.p. with either nifedipine (10mg/kg) or verapamil (10mg/kg) 30min prior to a systemic ketamine injection (10mg/kg). 24 hours after the ketamine injection, immobility was measured in the FST. (A) Ketamine produced a significant decrease in immobility time over the entire 10min test that was completely blocked by pretreatment with nifedipine (n = 6; drug x drug interaction, F_1,20 = 7.023, *p < 0.05). (D) Verapamil pretreatment also completely blocked the effects of ketamine over the entire 10min test (n = 8; ANOVA, F_3,28 = 3.936, *p < 0.05). Fisher’s post-hoc least significant difference tests revealed a significant difference between vehicle-treated and ketamine-treated rats, pretreatment with verapamil and ketamine (p < 0.05), and verapamil and ketamine alone (p < 0.01). (B, C, E, and F) Immobility was also examined during the first (0–5min) and second (6–10min) time blocks of the 10min test. Ketamine significantly decreased immobility time compared to controls in the first and second epochs, and these effects was blocked by nifedipine (B and C) or verapamil (E and F) in the second epoch: (B) ANOVA, F_3,20 = 5.581, *p < 0.05; (C) ANOVA, F_3,20 = 10.067, *p < 0.05; (E) ANOVA, F_3,28 = 4.857, *p < 0.05; and (F) ANOVA, F_3,28 = 3.130, *p < 0.05. All values are the means ± SEM.

Figure 3.

Incubation of primary neuronal cultures with ketamine rapidly increases BDNF release. Primary cortical neuronal cultures were stimulated with 0.5 µM ketamine for 15 and 60min and for 6hr, and culture medium was collected for BDNF analysis. Ketamine significantly increased BDNF release into the culture media following 15min (n = 12; t[22] = 3.10,**p < 0.01), 60min (n = 6; t[10] = 3.33, **p < 0.01), and 6 hour (n = 3; t[4] = 3.14, *p < 0.05) incubations. All values are expressed as fold change compared to the control and are shown as means ± SEM.

Figure 4.

Ketamine-induced BDNF release is dependent on activation of glutamate-AMPA receptors and L-type VDCCs. (A) Cortical neurons were incubated with NBQX (50 µM) 20min prior to ketamine, and medium was collected 15min later (after ketamine). Incubation with the AMPA receptor antagonist completely blocked ketamine-induced BDNF release (n = 6; drug x drug interaction, F_1,20 = 13.209, *p < 0.01). (B) Pretreatment with verapamil (10 µM) also blocked ketamine-induced BDNF release (n = 9–10; drug x drug interaction, F_1,44 = 14.809, **p < 0.001). All values are expressed as fold change compared to the control and are shown as means ± SEM.