Subsequent maternal separation exacerbates neurobehavioral abnormalities in rats neonatally exposed to sevoflurane anesthesia

Abstract

Several recent studies suggest that in the human population, a routine, short anesthetic in otherwise healthy infants is void of neurodevelopmental insult. On the other hand, many human retrospective epidemiological studies report evidence of cognitive abnormalities in children after testing those who had different anesthesia-requiring procedures in early childhood. We tested in a rat model whether post-anesthesia stressful environmental factors can contribute to developmental abnormalities that were initiated by a relatively short exposure to sevoflurane, the most widely used anesthetic in pediatric anesthesia, whose polyvalent actions include enhancement of gamma-aminobutyric acid type A receptor (GABAAR) activity. Postnatal day 6 (P6) male Sprague-Dawley rats were anesthetized with sevoflurane for 60 min. To simulate subsequent stress, the animals were subjected to a single maternal separation for 180 min at P10. To study the role of GABAAR-mediated depolarization, subgroups of P6 rats received a single injection of the Na+-K+-2Cl− (NKCC1) inhibitor, bumetanide, prior to initiation of anesthesia with sevoflurane. Rats that were exposed to sevoflurane had decreased hypothalamic K+-2Cl− (KCC2) mRNA level (F(2,13) = 3.839, P = 0.049), increased NKCC1/KCC2 mRNA ratio (F(2,13) = 5.043, P = 0.024) and increased corticotropin-releasing hormone (CRH) mRNA level (F(2,12) = 9.450, P = 0.003) at P10, the age at which maternal separation was imposed. Adult rats, neonatally exposed to a combination of sevoflurane and maternal separation, exhibited increases in the escape latencies greater than animals exposed to sevoflurane only (P = 0.012), and only rats in the sevoflurane plus maternal separation group spent significantly less time in the target quadrant during the Morris water maze test (F(4,55) = 4.856, P = 0.002). Bumetanide ameliorated abnormalities induced by sevoflurane and a combination of sevoflurane plus maternal separation. Neonatal exposure to sevoflurane may sensitize to stressors later in life, and post-exposure stress may exacerbate neurodevelopmental abnormalities even after a relatively short exposure to sevoflurane in rodents. The NKCC1 downregulation prior to exposure to the anesthetic may be therapeutic.

Role of epigenetic mechanisms in transmitting the effects of neonatal sevoflurane exposure to the next generation of male, but not female, rats

“…The sample sizes in this study were based on previous experience with the same experimental techniques. [6][7][8]…”

“…Adult F0 rats, exposed to sevoflurane as neonates, had significantly higher total corticosterone responses to restraint stress compared with F0 controls [males, t (8) ¼À8.09, P<0.001; and females, t (8) ¼À3.05, P¼0.015]. These increases in corticosterone responses were because of higher concentrations of corticosterone 10 min after restraint (P<0.001, males, Fig.…”

“…7 Serum corticosterone was measured using commercial ELISA kits (Cayman Chemical Company, Ann Arbor, MI, USA) following the manufacturer's instructions. 7,8 Editor's key points Early exposure to general anaesthetics can result in persistent cognitive dysfunction in adult animals, but effects on their offspring are unknown. Offspring of rats exposed to sevoflurane as neonates were investigated for behavioural abnormalities, changes in brain gene expression and deoxyribonucleic acid methylation in the genes' promoters.…”

“…The mRNA levels for Nkcc1, Kcc2 in the PVN of the hypothalamus and hippocampus, and for Gr in the hippocampus were analysed via qRTePCR as previously described. 7,8…”

“…Thus, NKCC1 inhibition before anaesthesia was protective, whereas anaesthetised neonatal rats had hypothalamic upregulated Nkcc1 and downregulated Kcc2 messenger ribonucleic acid (mRNA) concentrations even in adulthood. 7,8 During the second postnatal week, GABA A R-mediated neuronal signalling undergoes a fundamental transition from predominantly depolarising/stimulatory to inhibitory caused by concomitant developmental downregulation of NKCC1 and, most importantly, upregulation of neuron-specific KCC2. This shift is brain region-and sex-dependent, occurring earlier in females.…”