The Sustained Antidepressant Effects of Ketamine Are Independent of the Lateral Habenula

Abstract

Ketamine is known to have a rapid and lasting antidepressant effect. Recent studies have shown that ketamine exerts it rapid antidepressant effect by blocking burst firing in the lateral habenula (LHb). Whether the sustained antidepressant effect of ketamine occurs through the same mechanism has not been explored. Here, using male rats, we found that local infusion of (R,S)-ketamine into the LHb resulted in a rapid antidepressant-like effect 1 h after infusion, which almost returned to baseline levels after 24 h. Intra-LHb injection of (S)-ketamine also showed a significant antidepressant-like effect 1 h after injection, which recovered at 24 h. No significant antidepressant-like effect was found at 1 or 24 h after the administration of (R)-ketamine into the LHb. Injection of (2R,6R)-hydroxynorketamine, a ketamine metabolite, into the LHb did not result in any obvious antidepressant-like effect 1 or 24 h after injection. Systemic administration of (R,S)-ketamine (intraperitoneally) significantly suppressed LHb bursting activity at 1 h, but the inhibitory effect was reversed 24 h after injection. No significant effect of (R,S)-ketamine on miniature excitatory postsynaptic potentials of LHb neurons was found at 1 or 24 h after systemic application. Our study demonstrated that the sustained antidepressant-like effect of ketamine may not depend on burst firing of LHb neurons.SIGNIFICANCE STATEMENT Ketamine exerts it rapid antidepressant effect by blocking burst firing in the lateral habenula (LHb). However, whether the sustained antidepressant effect of ketamine occurs through the same mechanism has not been explored. In the present study, we demonstrated that the sustained antidepressant effect of ketamine may not depend on the burst firing of LHb neurons. This finding may lead to a novel perspective on LHb in the antidepressant effect of ketamine.

Keywords: AMPAR; NMDAR; antidepressant; bursting firing; ketamine; lateral habenula.

Figure 1.

The antidepressant effects of systemic or intra-LHb injection of (R,S)-ketamine in CRS rats. A, Schematic illustration of experimental protocol. B, Effect of intraperitoneal injection of (R,S)-ketamine on the LMA. n.s., Not significant. n = 6–9. C, Effect of intraperitoneal injection of (R,S)-ketamine on the immobile time in the FST. ***p < 0.001; n = 6–8. D, Effect of intraperitoneal injection of (R,S)-ketamine on the latency to immobility onset of FST. *p < 0.05, **p < 0.01; n = 6–8. E, Effect of intraperitoneal injection of (R,S)-ketamine on the SPT. *p < 0.05; n = 6–9. F, Schematic illustration of experimental protocol. G, The verified infusion sites. H, Effect of intra-LHb injection of (R,S)-ketamine on the LMA. n.s., Not significant. n = 7–10. I, Effect of intra-LHb injection of (R,S)-ketamine on the immobile time in the FST. ***p < 0.001, n.s., not significant. n = 7–9. J, Effect of intra-LHb injection of (R,S)-ketamine on the latency to immobility onset of FST. **p < 0.01, n.s., not significant. n = 6–8. K, Effect of intra-LHb injection of (R,S)-ketamine on SPT. ***p < 0.001, n.s., not significant. n = 6–9. Six rats were removed from the analysis for incorrect cannulae placement (H–K). LMA, Locomotion activity.

Figure 2.

The antidepressant effects of systemic injection of (R,S)-ketamine in CRS rats following LHb lesions. A, Schematic illustration of experimental protocol. B, A representative Nissl-stained brain section from the lesion group. C, Effect of intraperitoneal injection of (R,S)-ketamine on the LMA. n.s., Not significant. n = 6–8. D, Effect of intraperitoneal injection of (R,S)-ketamine on the immobile time in the FST. *p < 0.05, **p < 0.01; n = 6–8. E, Effect of intraperitoneal injection of (R,S)-ketamine on the latency to immobility onset of FST. *p < 0.05, **p < 0.01; n = 6–8. F, Effect of intraperitoneal injection of (R,S)-ketamine on the SPT. *p < 0.05, **p < 0.01; n = 6–9. Seven rats were removed from the analysis for incorrect LHb lesions (C–F). LMA, Locomotion activity.

Figure 3.

The antidepressant effects of intra-LHb injection of (R)-ketamine or (S)-ketamine in CRS rats. A, Schematic illustration of experimental protocol of (R)-ketamine. B, The verified infusion sites. C, Effect of intra-LHb injection of (R)-ketamine on the LMA. n.s., Not significant. n = 6–10. D, Effect of intra-LHb injection of (R,S)-ketamine on the immobile time in the FST. n.s., Not significant. n = 6–9. E, Effect of intra-LHb injection of (R)-ketamine on the latency to immobility onset of FST. n.s., Not significant. n = 6 and 7. F, Effect of intra-LHb injection of (R)-ketamine on the SPT. n.s., Not significant. n = 6–8. Five rats were removed from the analysis for incorrect cannulae placement (C–F). G, Schematic illustration of experimental protocol of (S)-ketamine. H, The verified infusion sites. I, Effect of intra-LHb injection of (S)-ketamine on the LMA. n.s., Not significant. n = 6–10. J, Effect of intra-LHb injection of (S)-ketamine on the immobile time in the FST. ***p < 0.001, n.s., not significant. n = 6–8. K, Effect of intra-LHb injection of (S)-ketamine on the latency to immobility onset of FST. **p < 0.01, n.s., not significant. n = 6–9. L, Effect of intra-LHb injection of (S)-ketamine on SPT. *p < 0.05, n.s., not significant. n = 6–9. Four rats were removed from the analysis for incorrect cannulae placement (I–L). LMA, Locomotion activity.

Figure 4.

The antidepressant effects of intra-LHb injection of (S)-ketamine in CRS rats. A, Schematic illustration of experimental protocol of (S)-ketamine. B, The verified infusion sites. C, Effect of intra-LHb injection of (S)-ketamine on the LMA. n.s., Not significant. n = 6–10. D, Effect of intra-LHb injection of (S)-ketamine on the immobile time in the FST. ***p < 0.001, n.s., not significant. n = 6–8. E, Effect of intra-LHb injection of (S)-ketamine on the latency to immobility onset of FST. **p < 0.01, n.s., not significant. n = 6–9. F, Effect of intra-LHb injection of (S)-ketamine on SPT. *p < 0.05, n.s., not significant. n = 6–9. Four rats were removed from the analysis for incorrect cannulae placement (G–L). LMA, Locomotion activity.

Figure 5.

The antidepressant effects of intra-LHb injection of (2R,6R)-HNK in CRS rats. A, Schematic illustration of experimental protocol. B, The verified infusion sites. C, Effect of intra-LHb injection of (2R,6R)-HNK on the LMA. n.s., Not significant. n = 6–8. D, Effect of intra-LHb injection of (2R,6R)-HNK on the immobile time in the FST. n.s., Not significant. n = 6–8. E, Effect of intra-LHb injection of (2R,6R)-HNK on the latency to immobility onset of FST. n.s., Not significant. n = 6 and 7. F, Effect of intra-LHb injection of (2R,6R)-HNK on the SPT. n.s., Not significant. n = 6–8. Three rats were removed from the analysis for incorrect cannulae placement (C–F). LMA, Locomotion activity.

Figure 6.

Effect of systemic injection of (R,S)-ketamine on bursting activity of LHb neurons. A, Schematic illustration of experimental protocol. B, Recording sites of each tetrode and example traces and average spike waveform of LHb neurons. C, Percentage of spikes in bursting and number of bursts per minute of LHb neurons from control and CRS rats. ***p < 0.001; n = 38 and 39. D, Effect of systemic administration of (R,S)-ketamine on the percentage of spikes in bursting and the number of bursts per minute of LHb neurons. **p < 0.01, ***p < 0.001, n.s., not significant. n = 20. E, Cumulative distribution of interspike intervals (ISIs). **p < 0.01, n.s., not significant.

Figure 7.

Effect of systemic injection of (R,S)-ketamine on mEPSC of LHb neurons and expression of GluR1. A, Schematic illustration of experimental protocol. B, Recording sites of each tetrode and example mEPSC traces of LHb neurons. C, Effect of systemic administration of (R,S)-ketamine on the cumulative distribution of mEPSC amplitude of LHb neurons. ***p < 0.001; n = 12–15. D, Effect of systemic administration of (R,S)-ketamine on the cumulative distribution of mEPSC interevents interval and average frequency of LHb neurons. *p < 0.05; n = 12–15. E, Effect of systemic administration of (R,S)-ketamine on the expression of GluR1 in LHb. **p < 0.01; n = 6–8.