Compensatory attenuation of cortical apoptosis by SK2 downregulation following ketamine anesthesia

A single exposure to general anesthetic can induce acute increase in neuronal apoptosis of the neonatal brain; however, how the brain counteracts the anesthetic-induced neurotoxicity remains unknown. The aim of this study is to explore how the neonatal cerebral cortex responds to anesthetic-induced neuronal apoptosis and the underlying mechanisms involved.

Postnatal day 7 rats received intraperitoneal ketamine injections. Apoptotic neurons in the primary somatosensory cortex (S1) were quantified via immunohistochemistry. Whole-cell patch-clamp recordings were performed to assess neuronal activity of pyramidal neurons, including small conductance Ca²⁺-activated potassium (SK) channel-mediated medium afterhyperpolarization (mAHP) currents and spike frequency. SK2 expression was analyzed via Western blot, with genetic manipulation (overexpression/knockdown) to investigate its role in apoptosis regulation. SK2 ubiquitination and the ubiquitin-proteasome system (UPS) involvement were probed by co-immunoprecipitation and proteasomal inhibitor MG132.

Ketamine induced an acute surge in S1 neuronal apoptosis (mean ± SEM, control vs. ketamine, 1386.11 ± 253.63/mm³ vs. 2229.07 ± 239.78/mm³, P = 0.0247), followed by a significant reduction at 24 h post-anesthesia (1281.35 ± 316.07/mm³ vs. 554.24 ± 59.43/mm³, P = 0.0417). This compensatory anti-apoptotic response coincided with attenuated SK channel-mediated mAHP currents (487.33 ± 38.00 pA vs. 355.33 ± 23.49 pA, P = 0.0058), which consequently enhanced neuronal spike frequency. Concurrently, both total (0.75 ± 0.04, P = 0.0156) and surface (0.76 ± 0.02, P = 0.0078) expression of SK2 channels were decreased in S1. SK2 overexpression reversed elevated neuronal excitability and blocked apoptotic reduction, while SK2 knockdown mimicked the pro-excitability and anti-apoptotic effects. SK2 downregulation relied on UPS-dependent degradation: MG132 restored SK2 levels, normalized spike frequency, and inhibited apoptotic reduction.

The developing cortex compensates for ketamine-induced neuronal apoptosis by suppressing subsequent physiological apoptosis. This anti-apoptotic response is critically mediated by increased neuronal activity, driven by UPS-dependent SK2 downregulation.