Peripheral administration of lactate produces antidepressant-like effects

Abstract

In addition to its role as metabolic substrate that can sustain neuronal function and viability, emerging evidence supports a role for l-lactate as an intercellular signaling molecule involved in synaptic plasticity. Clinical and basic research studies have shown that major depression and chronic stress are associated with alterations in structural and functional plasticity. These findings led us to investigate the role of l-lactate as a potential novel antidepressant. Here we show that peripheral administration of l-lactate produces antidepressant-like effects in different animal models of depression that respond to acute and chronic antidepressant treatment. The antidepressant-like effects of l-lactate are associated with increases in hippocampal lactate levels and with changes in the expression of target genes involved in serotonin receptor trafficking, astrocyte functions, neurogenesis, nitric oxide synthesis and cAMP signaling. Further elucidation of the mechanisms underlying the antidepressant effects of l-lactate may help to identify novel therapeutic targets for the treatment of depression.

Figure 1

Peripheral administration of l-lactate increases extracellular l-lactate concentration in the hippocampus. (a) Intraperitoneal injection of l-lactate (1 g kg⁻¹) increases blood lactate concentration. Data are the mean±s.e.m., n=5 mice per group. (b) Intraperitoneal l-lactate administration results in a significant elevation of hippocampal extracellular l-lactate concentration during phase 2, as measured with an l-lactate biosensor inserted within the hippocampus. Results are the mean±s.e.m., n=5 mice per group. (c) Data in (b) expressed as area under the curve during phases 1 and 2. *P<0.05 compared with vehicle-treated mice (Student’s t-test).

Figure 2

l-Lactate induces antidepressant-like effects in the forced swim test and regulates downstream signaling and target genes. (a) Acute peripheral administration of l-lactate produces antidepressant-like effects in the forced swim test (FST). Mice received a single intraperitoneal injection of vehicle (0.9% NaCl, n=17), l-lactate (1 g kg⁻¹, n=17) or desipramine (20 mg kg⁻¹, n=12) and were subjected to behavioral testing 1 h later. Both l-lactate and desipramine significantly reduced immobility in the FST as analyzed by one-way analysis of variance (ANOVA), followed by Tukey's post hoc test (F_2,4=6.564, P<0.05). Data are the mean±s.e.m. **P<0.01 compared with vehicle-treated mice. (b–d) Phosphorylation levels of glycogen synthase kinase-3α (GSK3α), GSK3β and cAMP response element-binding protein (CREB) in the hippocampus were reduced 1 h after a single intraperitoneal injection of l-lactate, as shown by western blot analysis. Data are the mean±s.e.m., n=10 mice per group. *P<0.05 compared to vehicle-treated mice (Student’s t-test). (e–g) Quantitative PCR analysis revealed that a single intraperitoneal injection of l-lactate regulated the expression of Arc, cyclooxygenase-2 (COX-2) and nitric oxide synthase 1 (NOS1) mRNAs. Arc mRNA level was increased in the hippocampus of l-lactate- compared with vehicle-treated mice. COX-2 and NOS1 mRNA levels were decreased in the hippocampus of l-lactate- compared with vehicle-treated mice. Data are the mean±s.e.m. (vehicle n=16, l-lactate n=17). *P<0.05 compared with vehicle-treated mice (Student’s t-test).

Figure 3

Chronic peripheral administration of l-lactate produces antidepressant-like effects in the chronic corticosterone paradigm. Mice received a single subcutaneous injection of corticosterone (20 mg kg⁻¹) or vehicle (2% dimethyl sulfoxide (DMSO) in sesame oil) on each of 21 consecutive days. Corticosterone-treated mice were given intraperitoneal injections of vehicle (0.9% NaCl), l-lactate (1 g kg⁻¹) or desipramine (20 mg kg⁻¹) daily for 21 days. At 24 h after the last injection, mice were tested in the forced swim test (FST), tail suspension test (TST) and saccharin preference test (SPT). (a and b) Chronic administration of l-lactate and desipramine (n=9 and n=10, respectively) abolished the increased immobility induced by corticosterone treatment in the FST (F_3,45=15.041) and TST (F_3,45=14.253). (c) Chronic peripheral administration of l-lactate reversed the corticosterone-induced decrease in saccharin preference (F_3,33=4.436). Data are the mean±s.e.m. One-way analysis of variance (ANOVA) followed by Tukey's post hoc test. **P<0.01 and *P<0.05 compared with vehicle + vehicle-treated mice (n=10); ^##P<0.01 and ^#P<0.05 compared with corticosterone + vehicle-treated mice (n=8).

Figure 4

Chronic peripheral administration of l-lactate produces antidepressant-like effects in the open-space FST and regulates target gene expression. (a) Mice were exposed to the open-space FST according to Stone and Lin. During pretest (days 1–4), mice were subjected to four consecutive daily swim sessions. During treatment (days 1–19), mice received daily intraperitoneal administrations of vehicle (0.9% NaCl, n=8), l-lactate (1 g kg⁻¹, n=10) or desipramine (20 mg kg⁻¹, n=10) and were subjected to a swim session twice a week (at days 2, 5, 9, 12, 16 and 19). Two-ways repeated-measures analysis of variance (ANOVA) followed by Bonferroni post hoc test revealed a significant increase in immobility time for all groups after pretest (F_3,72=29.377, ^###P<0.001 compared with day 1). Chronic injection of l-lactate and desipramine significantly reduced immobility time as analyzed by Tukey's post hoc test (F_2,120=3.961, *P<0.05 compared with vehicle-treated mice). (b–g) Chronic peripheral l-lactate administration regulates the expression of p11 (b), S100β (c), Hes5 (d), phosphodiesterase-4D (PDE4D) (e), nitric oxide synthase 1 (NOS1) (f) and NOS1AP (g) expression in the hippocampus of animals subjected to the open-space FST. Quantitative PCR and western blot analysis revealed that p11, S100β and Hes5 mRNA and protein levels were increased in the hippocampus of l-lactate- compared with vehicle-treated mice, whereas PDE4D and NOS1 mRNA and protein levels were decreased in the hippocampus of l-lactate- compared with vehicle-treated mice. Data are the mean±s.e.m., n=11 mice per group. *P<0.05, **P<0.01 compared with vehicle-treated mice (Student’s t-test). FST, forced swim test.