Mechanisms and Pharmacological Therapy of Intergenerational Neurocognitive Deficiencies Induced by Exposure to the General Anesthetic Sevoflurane

Background Neurocognitive deficits attributed to general anesthesia/surgery, referred to as postoperative neurocognitive disorder (PND), affect millions of patients. The mechanisms that initiate and maintain PND, however, which may serve as targets for pharmacological therapy, are poorly understood. Aims & Objectives We tested the following hypotheses in rats: 1) repeated exposure to sevoflurane initiates upregulation of the hypothalamic-pituitary-adrenal (HPA) axis and inflammation through mechanisms that involve increased Na+-K+-Cl- (NKCC1) Cl- importer/K+-2Cl- Cl- exporter ratios in hypothalamic arginine vasopressin (AVP)-producing magnocellular neurons, creating a positive feedback loop that perpetuates these abnormalities, leading to neurocognitive deficits in both exposed subjects and their offspring; 2) the NKCC1 inhibitor bumetanide or the glucocorticoid receptor (GR) antagonist RU486 can exert therapeutic effects by disrupting this positive feedback loop. Method Sprague Dawley male rats (generation F0) were exposed to 2.1% sevoflurane for 3 h on postnatal days 56 (P56), P58 and P60 (SEVO group). F0 male rats in the Bum + SEVO and RU486 + SEVO groups received bumetanide (1.84 mg/kg, i.p.), and RU486 (10 mg/kg, i.p.), respectively, before each sevoflurane exposure. All were mated on P90 to produce offspring (generation F1). Both generations were sequentially evaluated in behavioral tests starting on P100 (F0) and P60 (F1), followed by mechanistic studies. In addition, early effects were studied in tissue samples isolated 1 h after exposure to sevoflurane on P60. Results Consistent with persistently upregulated stress and inflammatory signaling, both early and sustained changes in F0 SEVO rats included increases in hypothalamic cFOS expression, increases in mRNA transcripts for Avp but not oxytocin, upregulated HPA axis signaling, increased levels of systemic and central inflammatory markers, and increased Nkcc1 mRNA/Kcc2 mRNA ratios in the brain. The F0 SEVO males also exhibited behavioral deficits in the elevated plus maze, prepulse inhibition of acoustic startle, and Morris water maze tests. In almost all of these measures F0 Bum + SEVO and RU486 + SEVO rats were protected from adverse effects of sevoflurane. Male offspring of F0 SEVO sires, but not Bum + SEVO or RU486 + SEVO sires, exhibited neurobehavioral deficits similar to those found in the F0 SEVO rats, as well as deficits in sociability and social novelty tests. F1 female offspring of F0 SEVO males showed only impaired spatial memory. Emerging studies suggest a role of the brain-gut-microbiome (BGM) axis in pathogeneses of a wide range of neurodevelopmental and neurodegenerative disorders, as well as PND. 16S rRNA gene sequencing revealed dysbiosis in gut microbiota diversity and in the ratio of firmicutes to bacteroidetes bacteria in F1 male offspring of F0 SEVO sires, but not of Bum + SEVO and RU486 + SEVO sires (F1 females were not affected). Discussion & Conclusions These findings suggest a role of the hypothalamic NKCC1/KCC2-GABAAR-AVP pathway in the sevoflurane-induced sustained upregulation of the HPA axis, inflammation, and neurocognitive abnormalities in both exposed rats and their future (largely male) offspring, as well as in male offspring’s BGM axis. The NKCC1 Cl- importer and GRs may represent targets for therapeutic prevention of sevoflurane-induced intergenerational PND.