Fast-spiking Interneurons Contribute to Propofol-induced Facilitation of Firing Synchrony in Pyramidal Neurons of the Rat Insular Cortex

Neuronal subtype-dependent kinetics of EPSCs induced by thalamocortical projections from the ventroposteromedial thalamic nucleus to the insular cortex in rats

Cerebrocortical neurons receive glutamatergic inputs via thalamocortical projections, and their activities are simultaneously controlled by GABAergic interneurons. Few studies have demonstrated the difference in the amplitude of evoked excitatory postsynaptic currents (EPSCs) via thalamocortical projections onto glutamatergic excitatory (ENs) and GABAergic inhibitory neurons (INs); the strength of excitation among neural subtypes varies among sensory cortices. The present study aimed to reveal the profile of thalamocortical inputs to ENs and inhibitory neurons in the insular cortex (IC) by evaluating the amplitude and latency of EPSCs evoked in the connection from the ventroposteromedial (VPM) thalamic nucleus to the IC. Whole-cell patch-clamp recordings were prepared from ENs, fast-spiking neurons (FSNs), and non-fast-spiking neurons (NFSNs) in the middle layers (layer 4 and adjacent layers) of the IC. Photostimulation-induced EPSCs (pEPSCs) were evoked via the selective activation of thalamocortical axons via optogenetics. All the neuronal subtypes received direct excitatory inputs from the VPM, and pEPSCs recorded from FSNs had the greatest amplitude and shortest latency compared with those recorded from ENs and NFSNs. Under current-clamp conditions, FSNs almost invariably exhibited action potentials responding to photostimulation, whereas ENs and NFSNs often showed the failure of action potential induction. In addition to excitatory inputs, some neurons exhibited pEPSCs followed by outward GABAA receptor-mediated currents, which curtailed the pEPSC peak and aligned the timing of the action potential to photostimulation. These results suggested that FSNs play a role in the feedforward inhibition of EN activity in the upper layer of the IC. (244 words).

Lysophosphatidylcholine induced by fat transplantation regulates hyperalgesia by affecting the dysfunction of ACC perineuronal nets

The pathogenesis of hyperalgesia is complex and can lead to poor clinical treatment. Our study revealed that epididymal white adipose tissue (eWAT) from spared nerve injury (SNI) mice is involved in the occurrence of hyperalgesia after adipose tissue transplantation. We also showed that lysophosphatidylcholine (LPC) is enriched in the eWAT of SNI mice using non-targeted metabolomic analysis and verified that the levels of LPC in plasma and the anterior cingulate cortex (ACC) region increased following eWAT transplantation. Based on the immunohistochemistry results, we observed that LPC in the ACC region activated microglia via the TRPV1/CamkⅡ pathway. Meanwhile, the disruption of perineuronal nets (PNNs) around PV+ neurons in ACC promoted hyperalgesia, and the loss of PNNs and PV+ interneurons might be due to microglial phagocytosis. These findings elucidate the mechanism underlying hyperalgesia from the perspective of lipid metabolite LPC and PNNs and provide potential strategies for the treatment of hyperalgesia.

Propofol-Induced Fasciculations in a Patient With Obstructive Sleep Apnea: A Case Report

We report a case of a 39-year-old male patient who developed propofol-induced fasciculations during the induction of general anesthesia. The patient had a history of moderate obstructive sleep apnea and was intolerant to continuous positive airway pressure therapy. He subsequently underwent the insertion of a hypoglossal nerve stimulator as a viable surgical intervention. The patient had a drug-induced sleep endoscopy that showed a 100% obstruction at the velum and the oropharynx, mainly in the anteroposterior and lateral directions. The patient experienced a smooth induction and emergence from general anesthesia, except for a brief episode of myoclonus-like movement in the bilateral upper extremities after propofol administration. The patient recovered well and reported an improvement in his sleep quality and daytime symptoms.

A neural circuit from paratenial thalamic nucleus to anterior cingulate cortex for the regulation of opioid-induced hyperalgesia in male rats

Prolonged use of opioids can lead to increased sensitivity to painful stimuli, a condition referred to as opioid-induced hyperalgesia (OIH). However, the mechanisms underlying this contradictory situation remain unclear. This study elucidates the pivotal role of the paratenial thalamic nucleus (PT)-anterior cingulate cortex (ACC) neuronal circuit in the development of OIH in male rats. Immunofluorescence and electrophysiology experiments demonstrated aberrant activation of PT glutamatergic neurons (PTGlu) in rats with OIH. Optogenetic or chemogenetic activation of the PTGlu-ACC circuit aggravates mechanical and thermal hyperalgesia. Conversely, the inhibition of neuronal circuits showed analgesic effects. Additionally, PTGlu neurons project to both ACC pyramidal neurons and interneurons. Moreover, OIH affects the function of the ACC microcircuit, leading to decreased feedforward inhibition and an inhibitory/excitatory (I/E) imbalance in ACC pyramidal neurons. In conclusion, our findings highlighted the role of the PTGlu-ACC neuronal circuit in the development of opioid-induced hyperalgesia, suggesting that this circuit is a promising therapeutic target for addressing the side effects of opioids.

Differential synaptic mechanism underlying the neuronal modulation of prefrontal cortex, amygdala, and hippocampus in response to chronic postsurgical pain with or without cognitive deficits in rats

Chronic Postsurgical Pain (CPSP) is well recognized to impair cognition, particularly memory. Mounting evidence suggests anatomic and mechanistic overlap between pain and cognition on several levels. Interestingly, the drugs currently used for treating chronic pain, including opioids, gabapentin, and NMDAR (N-methyl-D-aspartate receptor) antagonists, are also known to impair cognition. So whether pain-related cognitive deficits have different synaptic mechanisms as those underlying pain remains to be elucidated. In this context, the synaptic transmission in the unsusceptible group (cognitively normal pain rats) was isolated from that in the susceptible group (cognitively compromised pain rats). It was revealed that nearly two-thirds of the CPSP rats suffered cognitive impairment. The whole-cell voltage-clamp recordings revealed that the neuronal excitability and synaptic transmission in the prefrontal cortex and amygdala neurons were enhanced in the unsusceptible group, while these parameters remained the same in the susceptible group. Moreover, the neuronal excitability and synaptic transmission in hippocampus neurons demonstrated the opposite trend. Correspondingly, the levels of synaptic transmission-related proteins demonstrated a tendency similar to that of the excitatory and inhibitory synaptic transmission. Furthermore, morphologically, the synapse ultrastructure varied in the postsynaptic density (PSD) between the CPSP rats with and without cognitive deficits. Together, these observations indicated that basal excitatory and inhibitory synaptic transmission changes were strikingly different between the CPSP rats with and without cognitive deficits.

SCFAs Ameliorate Chronic Postsurgical Pain-Related Cognition Dysfunction via the ACSS2-HDAC2 Axis in Rats

Patients with chronic postsurgical pain (CPSP) frequently exhibit comorbid cognitive deficits. Recent observations have emphasized the critical effects of gut microbial metabolites, like short-chain fatty acids (SCFAs), in regulating cognitive function. However, the underlying mechanisms and effective interventions remain unclear. According to hierarchical clustering and 16S rRNA analysis, over two-thirds of the CPSP rats had cognitive impairment, and the CPSP rats with cognitive impairment had an aberrant composition of gut SCFA-producing bacteria. Then, using feces microbiota transplantation, researchers identified a causal relationship between cognitive-behavioral and microbic changes. Similarly, the number of genera that generated SCFAs was decreased in the feces from recipients of cognitive impairment microbiota. Moreover, treatment with the SCFAs alleviated the cognitive-behavioral deficits in the cognitively compromised pain rats. Finally, we observed that SCFA supplementation improved histone acetylation and abnormal synaptic transmission in the medial prefrontal cortex (mPFC), hippocampal CA1, and central amygdala (CeA) area via the ACSS2 (acetyl-CoA synthetase2)-HDAC2 (histone deacetylase 2) axis. These findings link pain-related cognition dysfunction, gut microbiota, and short-chain fatty acids, shedding fresh insight into the pathogenesis and therapy of pain-associated cognition dysfunction.

Different Anesthetic Drugs Mediate Changes in Neuroplasticity During Cognitive Impairment in Sleep-Deprived Rats via Different Factors

Background

Perioperative neuro-cognitive disorders (PND) are preoperative and postoperative complications of multiple nervous systems, typically manifested as decreased memory and learning ability after surgery. It was used to replace the original definition of postoperative cognitive dysfunctions (POCD) from 2018. Our previous studies have shown that sevoflurane inhalation can lead to cognitive dysfunction in Sprague-Dawley rats, but the specific mechanism is still unclear.

Material/Methods

Thirty-six male Sprague-Dawley rats were randomly divided into 6 groups (n=6): the SD group was given 24-h acute sleep deprivation; Sevoflurane was inhaled for 2 h in the Sevo group. Two mL propofol was injected into the tail vein of rats in the Prop group. The rats in the SD+Sevo group and SD+Prop group were deprived of sleep before intervention in the same way as before.

Results

We noted significant behavioral changes in rats treated with SIK3 inhibitors or tau phosphorylation agonists before propofol injection or sevoflurane inhalation, with associated protein levels and dendritic spine density documented. Sevoflurane anesthesia-induced cognitive impairment following acute sleep deprivation was more pronounced than sleep deprivation-induced cognitive impairment alone and resulted in increased brain SIK3 levels, increased phosphorylation of total tau and tau, and decreased acetylation modifications. After using propofol, the cognitive function returned to baseline levels with a series of reversals of cognitive dysfunction.

Conclusions

These results suggest that sevoflurane inhalation via the SIK3 pathway aggravates cognitive impairment after acute sleep deprivation and that propofol anesthesia reverses the effects of sleep deprivation by affecting modifications of tau protein.