Disrupting astrocyte-neuron lactate transfer persistently reduces conditioned responses to cocaine

Abstract

A central problem in the treatment of drug addiction is the high risk of relapse often precipitated by drug-associated cues. The transfer of glycogen-derived lactate from astrocytes to neurons is required for long-term memory. Whereas blockade of drug memory reconsolidation represents a potential therapeutic strategy, the role of astrocyte-neuron lactate transport in long-term conditioning has received little attention. By infusing an inhibitor of glycogen phosphorylase into the basolateral amygdala of rats, we report that disruption of astrocyte-derived lactate not only transiently impaired the acquisition of a cocaine-induced conditioned place preference but also persistently disrupted an established conditioning. The drug memory was rescued by L-Lactate co-administration through a mechanism requiring the synaptic plasticity-related transcription factor Zif268 and extracellular signal-regulated kinase (ERK) signalling pathway but not the brain-derived neurotrophic factor (Bdnf). The long-term amnesia induced by glycogenolysis inhibition and the concomitant decreased expression of phospho-ERK were both restored with L-Lactate co-administration. These findings reveal a critical role for astrocyte-derived lactate in positive memory formation and highlight a novel amygdala-dependent reconsolidation process, whose disruption may offer a novel therapeutic target to reduce the long-lasting conditioned responses to cocaine.

Figure 1

Astrocyte-derived lactate is required for the acquisition of a cocaine-induced conditioned place preference (CPP). Experimental timeline is shown above the graphic. Data represent CPP mean score (±s.e.m.) expressed in seconds as time spent in cocaine compartment minus time spent in saline compartment. A two-way repeated-measures analysis of variance revealed a significant session × treatment interaction (F_3,44=4.467, P<0.05), and post hoc analyses demonstrated a significant preference for the compartment previously paired with cocaine injections in vehicle and 1,4-dideoxy-1,4-imino-D-arabinitol (DAB)+L-Lactate-treated animals (*P<0.05, ***P<0.001 compared with pretest score, n=15 and 11, respectively), while DAB- and DAB+L-Pyruvate-treated rats did not exhibit any preference (###P<0.001, n=13 and 11, respectively) compared with respective pretest conditions. BLA, basolateral amygdala.

Figure 2

Astrocyte-derived lactate modulates gene expression involved in conditioned responses to cocaine. mRNA levels are expressed relative to control animals. Cocaine-induced place preference correlated with increased Bdnf and Zif268 mRNA expression (*P<0.05, compared with Veh/Veh). This increase was abolished after 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) treatment (P>0.05 compared with Veh/Veh animals). Co-administration of DAB and L-Lactate rescued the expression of Zif268 mRNA (**P<0.01, compared with Veh/Veh) but not that of Bdnf (P>0.05, compared with Veh/Veh). Cocaine conditioning or intra-basolateral amygdala treatments did not alter Arc mRNA expression (P>0.05, compared with Veh/Veh). Bdnf measures, Veh/Veh n=5, Veh/cocaine n=5, DAB/cocaine n=8, DAB+L-Lactate/cocaine n=10; Zif268 measures, n=4, 4, 5 and 8, respectively; Arc measures, n=4, 7, 6 and 5, respectively.

Figure 3

A single injection of 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) into the basolateral amygdala (BLA) transiently disrupts already established cocaine-induced conditioned place preference (CPP). Experimental timeline is shown above the graphic. Data represent CPP mean score (±s.e.m.) expressed in seconds as time spent in cocaine compartment minus time spent in saline compartment. A two-way repeated-measures analysis of variance revealed a significant session × treatment interaction and post hoc analysis revealed a preference for the compartment previously paired with cocaine administration in all rats (F_5,19=3.301, *P<0.05 compared with pretest score, at test 1). DAB injections into the BLA 15 min prior test 2 prevented the expression of the place preference. This effect was prolonged for up to 2 days (on tests 3 and 4, #P<0.05 compared with vehicle-treated animals, *P<0.05 compared with pretest conditions). One week after treatment, both groups expressed a clear-cut preference for the compartment previously paired with cocaine administration (*P<0.05 compared with pretest conditions, Veh, n=10; DAB, n=11).

Figure 4

A double injection of 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) into the basolateral amygdala (BLA) permanently disrupt an already established cocaine-induced conditioned place preference (CPP). Experimental timeline is shown above the graphic. Data represent CPP mean score (±s.e.m.) expressed in seconds as time spent in cocaine compartment minus time spent in saline compartment. A two-way repeated-measures analysis of variance revealed a significant session × treatment interaction and post hoc analysis revealed a preference for the compartment previously paired with cocaine in all rats (F_5,10=3.126, ***P<0.001 compared with pretest score, at test 1). DAB injections into the BLA 15 min prior to test 2 immediately blocked the preference for the cocaine-paired compartment compared with vehicle-treated animals. A second bilateral administration of DAB into the BLA 5 h after test 2 prolonged the effect for up to 2 weeks (on tests 3 and 4, ##P<0.01 compared with vehicle animals, *P<0.05 compared with pretest conditions). Twenty-four hours after test 4, all rats were challenged with a cocaine priming injection (15 mg kg⁻¹ intraperitoneal (IP)). Whereas rats formerly treated with vehicle still exhibited a clear-cut preference for the compartment previously paired with cocaine administration, DAB-treated animals still did not exhibit any preference for the cocaine-paired compartment (test 5, ##P<0.01 compared with vehicle animals, ***P<0.001 compared with pretest conditions, Veh, n=11; DAB, n=11).

Figure 5

L-Lactate co-administration abolishes the 1,4-dideoxy-1,4-imino-D-arabinitol (DAB)-induced disruption of conditioned responses to cocaine and restores the expression of p-ERK (phosphorylated extracellular signal–regulated kinase) in the basolateral amygdala (BLA). (a) Experimental timeline is shown above the graphic. Data represent conditioned place preference (CPP) mean score (±s.e.m.) expressed in seconds as time spent in cocaine compartment minus time spent in saline compartment. A two-way repeated-measures analysis of variance revealed a significant session × treatment interaction and post hoc analysis revealed a preference for the compartment previously paired with cocaine in all rats (F_2,36=3.820, ***P<0.001 compared with pretest score at test 1). DAB injections into the BLA 15 min prior to test 2 immediately blocked the preference for the cocaine-paired compartment compared with vehicle-treated animals, whereas co-administration of DAB and L-Lactate permitted the expression of the cocaine-induced place preference (*P<0.05 compared with pretest conditions). A second bilateral administration of DAB into the BLA 5 h after test 2 prolonged the indifference for the cocaine compartment for up to 1 week, whereas rats that received a second (DAB+L-Lactate) administration exhibited a significant cocaine-seeking behaviour (test 3, #P<0.01 compared with vehicle animals, *P<0.05 compared with pretest conditions). (b) ERK protein phosphorylation (measured 15 min after test 3) was significantly decreased after the double administration of DAB into the BLA (#P<0.05, compared with the Veh group), while the double co-administration of (DAB+L-Lactate) restored the expression of p-ERK (*P<0.05, compared with the Veh group. Veh, n=7; DAB, n=8; DAB+L-Lactate, n=9).