Background

Experimental evidence shows postnatal exposure to anesthesia negatively affects brain development. The PDZ2 domain, mediating protein–protein interactions of the postsynaptic density-95 protein, serves as a molecular target for several inhaled anesthetics. The authors hypothesized that early postnatal disruption of postsynaptic density-95 PDZ2 domain interactions has persistent effects on dendritic spines and cognitive function.

Methods

One-week-old mice were exposed to 1.5% isoflurane for 4 h or injected with 8 mg/kg active postsynaptic density-95 wild-type PDZ2 peptide along with their respective controls. A subset of these mice also received 4 mg/kg of the nitric oxide donor molsidomine. Hippocampal spine density, long-term potentiation, novel object recognition memory, and fear learning and memory were evaluated in mice.

Results

Exposure of 7-day-old mice to isoflurane or postsynaptic density-95 wild-type PDZ2 peptide relative to controls causes: (1) a long-term decrease in mushroom spines at 7 weeks (mean ± SD [spines per micrometer]): control (0.8 ± 0.2) versus isoflurane (0.4 ± 0.2), P < 0.0001, and PDZ2MUT (0.7 ± 0.2) versus PDZ2WT (0.4 ± 0.2), P < 0.001; (2) deficits in object recognition at 6 weeks (mean ± SD [recognition index]): naïve (70 ± 8) versus isoflurane (55 ± 14), P = 0.010, and control (65 ± 13) versus isoflurane (55 ± 14), P = 0.045, and PDZ2MUT (64 ±11) versus PDZ2WT (53 ± 18), P = 0.045; and (3) deficits in fear learning at 7 weeks and memory at 8 weeks (mean ± SD [% freezing duration]): Learning, control (69 ± 12) versus isoflurane (52 ± 13), P < 0.0001, and PDZ2MUT (65 ± 14) versus PDZ2WT (55 ± 14) P = 0.011, and Memory, control (80 ± 17) versus isoflurane (56 ± 23), P < 0.0001 and PDZ2MUT (73 ± 18) versus PDZ2WT (44 ± 19) P < 0.0001. Impairment in long-term potentiation has fully recovered here at 7 weeks (mean ± SD [% baseline]): control (140 ± 3) versus isoflurane (137 ± 8), P = 0.560, and PDZ2MUT (136 ± 17) versus PDZ2WT (128 ± 11), P = 0.512. The isoflurane induced decrease in mushroom spines was preventable by introduction of a nitric oxide donor.

Conclusions

Early disruption of PDZ2 domain-mediated protein–protein interactions mimics isoflurane in decreasing mushroom spine density and causing learning and memory deficits in mice. Prevention of the decrease in mushroom spine density with a nitric oxide donor supports a role for neuronal nitric oxide synthase pathway in mediating this cellular change associated with cognitive impairment.

Editor’s Perspective
What We Already Know about This Topic
  • PDZ2 domains of postsynaptic density-95 proteins bind to the NR2 subunit of the N-methyl-d-aspartate (NMDA) receptor and promote synaptogenesis

  • PDZ2 domains are molecular targets for inhalational anesthetics

What This Article Tells Us That Is New
  • Disruption of PDZ2 domain-mediated protein–protein interactions or a 4-h-long isoflurane anesthesia in 7-day-old mice induced comparable lasting deficits in synaptogenesis and cognitive function, and these effects were prevented by administration of the nitric oxide donor molsidomine

  • These experimental observations suggest the involvement of a pathway involving the NMDA receptor, postsynaptic density protein-95, and nitric oxide signaling in isoflurane exposure-induced cognitive impairment in mice

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