Detrimental effects of postnatal exposure to propofol on memory and hippocampal LTP in mice

Hippocampal SIRT1-Mediated Synaptic Plasticity and Glutamatergic Neuronal Excitability Are Involved in Prolonged Cognitive Dysfunction of Neonatal Rats Exposed to Propofol

Neonates who receive repeated or prolonged general anesthesia before the age of 4 are at a significantly higher risk of developing cognitive dysfunction later in life. In this study, we investigated the effects of repeated neonatal propofol exposure on hippocampal synaptic plasticity, neuronal excitability, and cognitive function. Adeno-associated SIRT1 virus with CaMKIIɑ promotor and a viral vector carrying the photosensitive gene ChR2 with the CaMKIIɑ promotor, as well as their control vectors, were stereotaxically injected into the hippocampal CA1 region of postnatal day 5 (PND-5) rats. PND-7 rats were given intraperitoneal injection of 60 mg/kg propofol or fat emulsion for three consecutive days. Western blotting, Golgi staining, and double immunofluorescence staining were used to evaluate the SIRT1 expression, synaptic plasticity, and the excitability of neurons in the hippocampal CA1 region. The Morris water maze (MWM) test was conducted on PND-30 to assess the learning and memory abilities of rats. Repeated neonatal propofol exposure reduced SIRT1 expression, suppressed synaptic plasticity, decreased glutamatergic neuron excitability in the hippocampus, and damaged learning and memory abilities. Overexpression of SIRT1 attenuated propofol-induced cognitive dysfunction, excitation-inhibition imbalance, and synaptic plasticity damage. After optogenetic stimulation of glutamatergic neurons in the hippocampal CA1 region, the learning and memory abilities of rats exposed to propofol were improved on PND-30. Our findings demonstrate that SIRT1 plays an important role in cognitive dysfunction induced by repeated neonatal propofol exposure by suppressing synaptic plasticity and neuronal excitability.

Prophylactic Melatonin Treatment Ameliorated Propofol-Induced Cognitive Dysfunction in Aged Rats

Considering the fact that melatonin acts as protective agent in various cognitive impairment, we decided to explore the precise effect of pretreatment with melatonin on cognitive function, mitochondrial activity, apoptosis and synaptic integrity in aged rats anesthetized by propofol. We first randomly allocated the thirty Sprague Dawley rats into three groups: Control vehicle-treated group (Con), Propofol-treated group (Pro) and Melatonin + Propofol group (Mel + Pro). The Barnes maze, open field and contextual fear conditioning test were employed to evaluate spatial memory, exploratory behavior and general locomotor activity, and hippocampus-dependent learning and memory ability, respectively. Moreover, mitochondrial function (including reactive oxygen species, mitochondrial membrane potential and ATP levels) and apoptosis were detected in the regions of hippocampus (HIP) and prefrontal cortex (PFC). The results of behavioral tests suggested that melatonin improved propofol-induced memory impairment in aged rats. Melatonin mitigated mitochondrial dysfunction and decreased the apoptotic cell counts in the regions of HIP and PFC. Furthermore, prophylactic melatonin treatment also reversed the propofol-induced inactivation of PKA/CREB/BDNF signaling and synaptic dysfunction. On the whole, our results indicated that melatonin ameliorated the propofol-induced cognitive disorders via attenuating mitochondrial dysfunction, apoptosis, inactivation of PKA/CREB/BDNF signaling and synaptic dysfunction.

Impact of anesthesia exposure in early development on learning and sensory functions

Each year, millions of children undergo anesthesia, and both human and animal studies have indicated that exposure to anesthesia at an early age can lead to neuronal damage and learning deficiency. However, disorders of sensory functions were not reported in children or animals exposed to anesthesia during infancy, which is surprising, given the significant amount of damage to brain tissue reported in many animal studies. In this review, we discuss the relationship between the systems in the brain that mediate sensory input, spatial learning, and classical conditioning, and how these systems could be affected during anesthesia exposure. Based on previous reports, we conclude that anesthesia can induce structural, functional, and compensatory changes in both sensory and learning systems. Changes in myelination following anesthesia exposure were observed as well as the neurodegeneration in the gray matter across variety of brain regions. Disproportionate cell death between excitatory and inhibitory cells induced by anesthesia exposure can lead to a long-term shift in the excitatory/inhibitory balance, which affects both learning-specific networks and sensory systems. Anesthesia may directly affect synaptic plasticity which is especially critical to learning acquisition. However, sensory systems appear to have better ability to compensate for damage than learning-specific networks.

Effects of compound 21, a non‑peptide angiotensin II type 2 receptor agonist, on general anesthesia‑induced cerebral injury in neonatal rats

General anesthesia has a great impact on neurodevelopment. However, the mechanisms underlying this effect and therapeutic methods to address it remain limited. The present study aimed to investigate the effects of compound (C)21, a non-peptide angiotensin II type 2 receptor agonist, on general anesthesia-induced cerebral injury in neonatal rats. Neonatal Sprague Dawley rats (postnatal day 7) were randomly divided into three groups (n=6 per group): The control, isoflurane and C21+ isoflurane (C21) group. General anesthesia was induced through inhalation of 1.3% isoflurane. Apoptosis and synaptic structure were analyzed. The levels of peroxisome proliferator-activated receptor (PPAR)-α were detected using an enzyme-linked immunosorbent assay. BCL2, apoptosis regulator (Bcl-2) expression was also measured. Compared with the control group, the cerebral cortex, hippocampus, amygdala and hypothalamus in the isoflurane group had significantly more apoptotic cells (P<0.05). The nuclei of the control group were round and transparent, while shrunken nuclei and condensed chromatin were visible in the isoflurane group. A reduction in synapse number was observed in the isoflurane group compared with the control. By contrast, nuclei shrinkage and the decrease in synaptic number was improved in the C21 group. PPAR-α and Bcl-2 expression, at the mRNA and protein levels, was significantly reduced in the isoflurane group compared with the control (P<0.05). C21 treatment reduced the decrease in PPAR-α and Bcl-2 in the cerebral cortex, hippocampus, amygdala and hypothalamus (P<0.05). Collectively, it was demonstrated that C21 prevented apoptosis and synaptic loss induced by general anesthesia in neonatal rats by enhancing the expression of PPAR-α and Bcl-2.

The recovery from transient cognitive dysfunction induced by propofol was associated with enhanced autophagic flux in normal healthy adult mice

Propofol is the most widely accepted intravenous anesthetic available for clinical use. However, neurotoxicity of propofol in the developing brain has been reported. This study investigated the effects of propofol on cognitive function in normal healthy adult mice. Thirty-three GFP-LC3 adult mice were included. Propofol was injected for anesthesia (n = 22). The sham control (n = 11) received intralipid injections. The mice completed a Y-maze test on 3 and 7 days after being anesthetized. Western blotting, immunofluorescence staining, and transmission electron microscopic (TEM) analyses were performed with their hippocampi. In addition, we conducted a separate ex vivo experiment using organotypic hippocampal slice cultures (OHSCs) to investigate the effects of propofol on induced autophagy. There was a significantly lower percentage of alternation in the Y-maze test on day 3 after propofol anesthesia than the control, but no difference was observed on day 7. Western blot analyses and immunofluorescence assays showed that the levels of cognitive function-related proteins significantly decreased in the propofol group compared to the control on day 3 but had recovered by day 7. In terms of autophagy-related proteins, western blot analyses and immunofluorescence assays showed that propofol increased autophagic induction, flux, and degradation of autophagosomes. Ex vivo experiments showed that propofol enhanced autophagic flux of the induced autophagy. In conclusion, although transient cognitive dysfunction occurred, adult mice recovered their cognitive function after the administration of propofol anesthesia. And this finding may be associated with enhanced autophagic flux.

Impairments of spatial learning and memory following intrahippocampal injection in rats of 3-mercaptopropionic acid-modified CdTe quantum dots and molecular mechanisms

With the rapid development of nanotechnology, quantum dots (QDs) as advanced nanotechnology products have been widely used in neuroscience, including basic neurological studies and diagnosis or therapy for neurological disorders, due to their superior optical properties. In recent years, there has been intense concern regarding the toxicity of QDs, with a growing number of studies. However, knowledge of neurotoxic consequences of QDs applied in living organisms is lagging behind their development, even if several studies have attempted to evaluate the toxicity of QDs on neural cells. The aim of this study was to evaluate the adverse effects of intrahippocampal injection in rats of 3-mercaptopropionic acid (MPA)-modified CdTe QDs and underlying mechanisms. First of all, we observed impairments in learning efficiency and spatial memory in the MPA-modified CdTe QD-treated rats by using open-field and Y-maze tests, which could be attributed to pathological changes and disruption of ultrastructure of neurons and synapses in the hippocampus. In order to find the mechanisms causing these effects, transcriptome sequencing (RNA-seq), an advanced technology, was used to gain the potentially molecular targets of MPA-modified CdTe QDs. According to ample data from RNA-seq, we chose the signaling pathways of PI3K–Akt and MPAK–ERK to do a thorough investigation, because they play important roles in synaptic plasticity, long-term potentiation, and spatial memory. The data demonstrated that phosphorylated Akt (p-Akt), p-ERK1/2, and c-FOS signal transductions in the hippocampus of rats were involved in the mechanism underlying spatial learning and memory impairments caused by 3.5 nm MPA-modified CdTe QDs.