A novel role for PSD-95 in mediating ethanol intoxication, drinking and place preference

Abstract

The synaptic signaling mechanisms mediating the behavioral effects of ethanol (EtOH) remain poorly understood. Post-synaptic density 95 (PSD-95, SAP-90, Dlg4) is a key orchestrator of N-methyl-D-aspartate receptors (NMDAR) and glutamatergic synapses, which are known to be major sites of EtOH's behavioral actions. However, the potential contribution of PSD-95 to EtOH-related behaviors has not been established. Here, we evaluated knockout (KO) mice lacking PSD-95 for multiple measures of sensitivity to the acute intoxicating effects of EtOH (ataxia, hypothermia, sedation/hypnosis), EtOH drinking under conditions of free access and following deprivation, acquisition and long-term retention of EtOH conditioned place preference (CPP) (and lithium chloride-induced conditioned taste aversion), and intoxication-potentiating responses to NMDAR antagonism. PSD-95 KO exhibited increased sensitivity to the sedative/hypnotic, but not ataxic or hypothermic, effects of acute EtOH relative to wild-type controls (WT). PSD-95 KO consumed less EtOH than WT, particularly at higher EtOH concentrations, although increases in KO drinking could be induced by concentration-fading and deprivation. PSD-95 KO showed normal EtOH CPP 1 day after conditioning, but showed significant aversion 2 weeks later. Lithium chloride-induced taste aversion was impaired in PSD-95 KO at both time points. Finally, the EtOH-potentiating effects of the NMDAR antagonist MK-801 were intact in PSD-95 KO at the dose tested. These data reveal a major, novel role for PSD-95 in mediating EtOH behaviors, and add to growing evidence that PSD-95 is a key mediator of the effects of multiple abused drugs.

Figure 1

PSD-95 KO show hypersensitivity to the sedative/hypnotic effects of EtOH. (a) Baseline rotarod performance was impaired in KO relative to WT, as demonstrated by lower latencies to fall on all trials but the first (n = 10–13/genotype). (b) Injection of 1.75 g/kg EtOH caused ataxia (as indicated by negative delta latency to fall) that was no different between genotypes (n = 10–15/genotype). (c) Injection of 3.0 g/kg EtOH caused hypothermia (as indicated by negative delta temperature) that was no different between genotypes (n = 7–14/genotype). (d) Injection of 3.0 g/kg EtOH produced a significantly prolonged sedative/hypnotic response in KO relative to WT (n = 8–11/genotype). (e) Injection of 30 mg/kg pentobarbital produced a similar sedative/hypnotic response in both genotypes (n = 6–8/genotype). (f) Blood EtOH levels following injection with 3.5 g/kg EtOH did not differ between genotypes (n = 5–11/genotype). Data are Means ± SEM. *P < 0.05 versus WT

Figure 2

PSD-95 KO show reduced EtOH drinking. (a) When offered a single (15%) concentration of EtOH, KO consumed significantly less EtOH and (b) had a significantly lesser preference for EtOH than WT (n = 8–9/genotype). (c) When offered increasing concentrations of EtOH, KO consumed significantly less EtOH at 9% and 11% concentrations and (d) had significantly lesser preference at 9% and 11% concentrations relative to WT (n = 12/genotype). (e) Prior to EtOH deprivation, KO consumed significantly less (15%) EtOH than WT. KO, but not WT, consumed significantly more EtOH 1 day after deprivation, relative to pre-deprivation baseline, and this elevation returned to baseline over the next 3 days. (f) KO showed significantly lesser preference for EtOH than WT during pre-deprivation baseline, and KO, but not WT, showed a significant increase in preference 1 day (but not 2–4 days) post-deprivation, relative to pre-deprivation baseline (n = 8/genotype). Data are Means ± SEM. **P < 0.01, *P < 0.05 versus WT/same concentration or period, ##P < 0.01 versus KO baseline

Figure 3

PSD-95 KO show long-term loss of EtOH conditioned place preference. (a) Schematic of study design. (b) WT and KO showed significant preference for the EtOH-paired compartment 1 day after conditioning. When tested 14 days after conditioning, WT retained a significant preference for the EtOH-paired side while KO showed a significant aversion to the EtOH-paired side. (c) Both genotypes preferred the EtOH-paired side, as measured by cumulative time spent in that compartment, 1 day after conditioning. (d) WT preference for the EtOH-paired side was intact 14 days post-conditioning, while KO showed an increasing aversion to the EtOH-paired side, as measured by cumulative time spent in the EtOH-paired side (n = 10/genotype). Data are Means ± SEM. #P < 0.05 versus 50% chance/same genotype, **P < 0.01 versus WT/same test day

Figure 4

PSD-95 KO show impaired lithium chloride conditioned taste aversion. (a) WT and KO showed high, similar malaise scores following LiCl injection. (b) KO had a significantly lower aversion index than WT during probe tests 1 and 14 days after conditioning. The aversion index was significantly above chance in WT, not KO, on both test days (n = 8–10/genotype). Data are Means ± SEM. #P < 0.05 versus 50% chance/same genotype, **P < 0.01 versus WT/same test day

Figure 5

PSD-95 KO show intact EtOH-potentiating effects of MK-801. (a) WT and KO pre-treated with MK-801 showed a greater ataxic response to EtOH than mice pre-treated with vehicle (VEH) (n = 9–13/genotype/treatment). (b) MK-801 pre-treatment did not alter the hypothermic response to EtOH, regardless of genotype (n = 8–13/genotype/treatment). (c) WT and KO pre-treated with 0.2 mg/kg MK-801 showed a greater sedative/hypnotic response to EtOH than mice pre-treated with vehicle (n = 8–11/genotype). Data are Means ± SEM. #P < 0.05 versus VEH/same genotype, ##P < 0.01 versus VEH/same genotype, **P < 0.01 WT versus KO