Delayed application of the anesthetic propofol contrasts the neurotoxic effects of kainate on rat organotypic spinal slice cultures

Preemptive Propofol Administration in Spinal Cord Injury: Effects on Pain-Induced Hypertension, Neuroinflammation, and Functional Recovery in Rats

Spinal cord injury (SCI) triggers secondary damage, including pain-induced hypertension, inflammation, and hemorrhage, impairing recovery. This study evaluated the efficacy of general anesthesia with preemptive propofol administration in mitigating secondary damage in SCI rats. SCI was induced in rats using a contusion model. Propofol (100 mg/kg) was administered intraperitoneally either 30 min before (preemptive) or 30 min after intermittent tail shock. Systolic blood pressure (SBP), body weight, food intake, inflammatory markers (interleukin-1 beta [IL-1β], interleukin-6 [IL-6]), hemorrhage markers, and serum levels of SCI biomarkers (glial fibrillary acidic protein [GFAP], myelin basic protein [MBP]) were measured. Functional recovery was assessed over 28 days using the Basso, Beattie, and Bresnahan (BBB) scale, horizontal ladder test, and rotarod test. Preemptive propofol administration effectively mitigated pain-induced hypertension, enhanced body weight and food intake, and reduced inflammatory markers to levels comparable to unstimulated SCI rats. In contrast, propofol administered post-stimulation was less effective. Preemptive administration significantly decreased GFAP levels and preserved MBP levels. Importantly, preemptive intervention reduced levels of hemoglobin and alpha hemoglobin, while post-stimulation intervention showed no significant effect on hemorrhage. Behavioral assessments demonstrated improved locomotor recovery, motor coordination, and balance in preemptively treated rats compared to delayed or no intervention. Preemptive administration of propofol effectively reduces pain-induced hypertension, inflammation, and gliosis while preserving myelin integrity and enhancing functional recovery in SCI rats. This intervention demonstrates significantly greater efficacy compared to delayed administration, underscoring the critical importance of timely treatment in mitigating secondary damage and improving outcomes after SCI.

GABAergic Mechanisms Can Redress the Tilted Balance between Excitation and Inhibition in Damaged Spinal Networks

Correct operation of neuronal networks depends on the interplay between synaptic excitation and inhibition processes leading to a dynamic state termed balanced network. In the spinal cord, balanced network activity is fundamental for the expression of locomotor patterns necessary for rhythmic activation of limb extensor and flexor muscles. After spinal cord lesion, paralysis ensues often followed by spasticity. These conditions imply that, below the damaged site, the state of balanced networks has been disrupted and that restoration might be attempted by modulating the excitability of sublesional spinal neurons. Because of the widespread expression of inhibitory GABAergic neurons in the spinal cord, their role in the early and late phases of spinal cord injury deserves full attention. Thus, an early surge in extracellular GABA might be involved in the onset of spinal shock while a relative deficit of GABAergic mechanisms may be a contributor to spasticity. We discuss the role of GABA A receptors at synaptic and extrasynaptic level to modulate network excitability and to offer a pharmacological target for symptom control. In particular, it is proposed that activation of GABA A receptors with synthetic GABA agonists may downregulate motoneuron hyperexcitability (due to enhanced persistent ionic currents) and, therefore, diminish spasticity. This approach might constitute a complementary strategy to regulate network excitability after injury so that reconstruction of damaged spinal networks with new materials or cell transplants might proceed more successfully.

Modulation of extrasynaptic GABAergic receptor activity influences glutamate release and neuronal survival following excitotoxic damage to mouse spinal cord neurons

Excitotoxic levels of released glutamate trigger a cascade of deleterious cellular events leading to delayed neuronal death. This phenomenon implies extensive dysregulation in the balance between network excitation and inhibition. Our hypothesis was that enhancing network inhibition should prevent excitotoxicity and provide neuroprotection. To test this notion, we used mouse organotypic spinal slice cultures and explored if excitotoxicity caused by the potent glutamate analogue kainate was blocked by pharmacological increase in GABA_A receptor activity. To this end we monitored (with a biosensor) real-time glutamate release following 1 h kainate application and quantified neuronal survival 24 h later. Glutamate release evoked by kainate was strongly decreased by the allosteric GABA_A modulator midazolam (10 nM) or the GABA agonist THIP (10 μM), leading to neuroprotection. On the contrary, much higher glutamate release was induced by the GABA antagonist bicuculline (20 μM) that inhibits synaptic and extrasynaptic GABA_A receptors. Gabazine (20 μM), an antagonist of synaptic GABA_A receptors, had no effect on glutamate release or neuroprotection. No effect was observed with the glycine antagonist strychnine or the glycine agonist L-alanine. These findings indicate that enhancement of GABA receptor activity was an effective tool to counteract excitotoxic death in spinal networks. In view of the potent activity by THIP, preferentially acting on extrasynaptic GABA_A receptors, the present data imply a significant role for extrasynaptic GABA_A receptors in sparing spinal cord neurons from injury.

General anesthesia combined with epidural anesthesia on the postoperative cognitive functions in pregnant women with dystocia

Effects of general anesthesia combined with epidural anesthesia on the postoperative cognitive functions in pregnant women with dystocia were investigated. Postoperative cognitive functions of 84 dystocia pregnant women treated with cesarean section were retrospectively analyzed. Patients who received general anesthesia were included in group A (n=42), and those who received general anesthesia combined with epidural anesthesia were included in group B (n=42). Mean arterial pressure (MAP), heart rate (HR) and bispectral index (BIS) at different time-points after anesthesia in the two groups of patients were observed and compared. Recovery of anesthesia such as the recovery time of spontaneous breathing, recovery time of orientation and time of eye opening were observed and compared between two groups of patients. Mini mental state examination (MMSE) scores were obtained and compared between the the groups of patients at different time-points after operation. Three vital signs (MAP, HR and BIS) were not significantly different between group A and B at the same time-point (P>0.05) and the maintenance of anesthesia was satisfactory. Compared with group A, postoperative recovery time of spontaneous breathing, recovery time of orientation and the time of eye opening in group B were all significantly shorter (P<0.05). In addition, MMSE scores of patients in group B, 2 and 12 h after operation were 24.33±1.61 and 26.41±1.83 points, respectively, which were significantly improved compared with those of patients in group A (20.45±1.58 and 22.39±1.72 points, respectively) (P<0.05). In conclusion, recovery of postoperative cognitive functions in pregnant women with dystocia who received general anesthesia combined with epidural anesthesia was shorter to that of those who only received general anesthesia.

Propofol Protects Rat Hypoglossal Motoneurons in an In Vitro Model of Excitotoxicity by Boosting GABAergic Inhibition and Reducing Oxidative Stress

In brainstem motor networks, hypoglossal motoneurons (HMs) play the physiological role of driving tongue contraction, an activity critical for inspiration, phonation, chewing and swallowing. HMs are an early target of neurodegenerative diseases like amyotrophic lateral sclerosis that, in its bulbar form, is manifested with initial dysphagia and dysarthria. One important pathogenetic component of this disease is the high level of extracellular glutamate due to uptake block that generates excitotoxicity. To understand the earliest phases of this condition we devised a model, the rat brainstem slice, in which block of glutamate uptake is associated with intense bursting of HMs, dysmetabolism and death. Since blocking bursting becomes a goal to prevent cell damage, the present report enquired whether boosting GABAergic inhibition could fulfill this aim and confer beneficial outcome. Propofol (0.5 µM) and midazolam (0.01 µM), two allosteric modulators of GABA_A receptors, were used at concentrations yielding analogous potentiation of GABA-mediated currents. Propofol also partly depressed NMDA receptor currents. Both drugs significantly shortened bursting episodes without changing single burst properties, their synchronicity, or their occurrence. Two hours later, propofol prevented the rise in reactive oxygen species (ROS) and, at 4 hours, it inhibited intracellular release of apoptosis-inducing factor (AIF) and prevented concomitant cell loss. Midazolam did not contrast ROS and AIF release. The present work provides experimental evidence for the neuroprotective action of a general anesthetic like propofol, which, in this case, may be achieved through a combination of boosted GABAergic inhibition and reduced ROS production.

Neuroprotective effect of propofol against excitotoxic injury to locomotor networks of the rat spinal cord in vitro

Although neuroprotection to contain the initial damage of spinal cord injury (SCI) is difficult, multicentre studies show that early neurosurgery under general anaesthesia confers positive benefits. An interesting hypothesis is that the general anaesthetic itself might largely contribute to neuroprotection, although in vivo clinical settings hamper studying this possibility directly. To further test neuroprotective effects of a widely used general anaesthetic, we studied if propofol could change the outcome of a rat isolated spinal cord SCI model involving excitotoxicity evoked by 1 h application of kainate with delayed consequences on neurons and locomotor network activity. Propofol (5 μm; 4-8 h) enhanced responses to GABA and depressed those to NMDA together with decrease in polysynaptic reflexes that partly recovered after 1 day washout. Fictive locomotion induced by dorsal root stimuli or NMDA and serotonin was weaker the day after propofol application. Kainate elicited a significant loss of spinal neurons, especially motoneurons, whose number was halved. When propofol was applied for 4-8 h after kainate washout, strong neuroprotection was observed in all spinal areas, including attenuation of motoneuron loss. Although propofol had minimal impact on recovery of electrophysiological characteristics 24 h later, it did not further depress network activity. A significant improvement in disinhibited burst periodicity suggested potential to ameliorate neuronal excitability in analogy to histological data. Functional recovery of locomotor networks perhaps required longer time due to the combined action of excitotoxicity and anaesthetic depression at 24 h. These results suggest propofol could confer good neuroprotection to spinal circuits during experimental SCI.