Surgery increases cell death and induces changes in gene expression compared with anesthesia alone in the developing piglet brain

<div><p>In a range of animal species, exposure of the brain to general anaesthesia without surgery during early infancy may adversely affect its neural and cognitive development. The mechanisms mediating this are complex but include an increase in brain cell death. In humans, attempts to link adverse cognitive development to infantile anaesthesia exposure have yielded ambiguous results. One caveat that may influence the interpretation of human studies is that infants are not exposed to general anaesthesia without surgery, raising the possibility that surgery itself, may contribute to adverse cognitive development. Using piglets, we investigated whether a minor surgical procedure increases cell death and disrupts neuro-developmental and cognitively salient gene transcription in the neonatal brain. We randomly assigned neonatal male piglets to a group who received 6h of 2% isoflurane anaesthesia or a group who received an identical anaesthesia plus 15 mins of surgery designed to replicate an inguinal hernia repair. Compared to anesthesia alone, surgery-induced significant increases in cell death in eight areas of the brain. Using RNAseq data derived from all 12 piglets per group we also identified significant changes in the expression of 181 gene transcripts induced by surgery in the cingulate cortex, pathway analysis of these changes suggests that surgery influences the thrombin, aldosterone, axonal guidance, B cell, ERK-5, eNOS and GABA_A signalling pathways. This suggests a number of novel mechanisms by which surgery may influence neural and cognitive development independently or synergistically with the effects of anaesthesia.</p></div

Changes in the expression of gene transcript thought to be important in the mediation of neural plasticity, long term potentiation, learning and memory, following a 6h isoflurane exposure.

<p>Changes in the expression of gene transcript thought to be important in the mediation of neural plasticity, long term potentiation, learning and memory, following a 6h isoflurane exposure.</p

Representative amplitude-integrated electroencephalographs (aEEGs) in response to 2h of isoflurane exposure (0 to 2h).

<p><b>A.</b> Continuous normal voltage (CNV) throughout. <b>B.</b> Low voltage, recovering to CNV by 2h.</p

Histology of TUNEL, CCasp-3, Iba-1 and GFAP.

<p>Representative photomicrograpths of TUNEL and CCasp-3 in the external capsule and the Iba-1 and GFAP in the thalamus of naïve (left column) and isoflurane exposed (right column) piglets. Arrows indicate TUNEL and CCasp-3 positive cells. CCasp-3 and Iba-1 are counterstained with cresyl violet. Inserts highlight cell activation and morphology (scale bar = 50μm).</p

Physiological variables for piglets at 1h intervals during the 6h exposure to isoflurane anaesthesia.

<p>Physiological variables for piglets at 1h intervals during the 6h exposure to isoflurane anaesthesia.</p

Amplitude-integrated electroencephalography.

<p>Findings for each piglet were scored using the de Vries and Hellstrom-Westas [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0166784#pone.0166784.ref027" target="_blank">27</a>] pattern classification. Three out of six piglets initially had a suppressed aEEG trace. All piglets had a normal aEEG trace by 1h. No piglet had seizures on 6-lead EEG. CNV: continuous normal voltage; DNV: discontinuous normal voltage; BS: burst suppression.</p