Chronic intermittent hypoxia transiently increases hippocampal network activity in the gamma frequency band and 4-Aminopyridine-induced hyperexcitability in vitro

The effect of M-current activation on controller gain and obstructive sleep apnoea severity: a randomised controlled trial using flupirtine

Ventilatory control instability, or high loop gain (LG), contributes towards upper airway collapse in approximately one-third of people with obstructive sleep apnoea (OSA). A high LG can be the product of elevated chemosensitivity (controller gain) and/or an excessive ventilatory output (plant gain). Therapies such as carbonic anhydrase inhibitors (targeting plant gain) have been shown to reduce OSA severity; however, there is a lack of viable pharmacological options targeting controller gain. This study investigated the effect of flupirtine (400 mg), a KCNQ potassium channel opener, on LG and OSA severity in fifteen moderate-to-severe OSA patients through a randomised, double-blind, placebo-controlled trial. Despite the hypothesised potential of flupirtine to reduce LG by attenuating chemosensory activity, our findings revealed no significant effect on LG and OSA severity. The lack of overall efficacy of flupirtine is most likely due to multifactorial nature of OSA and the challenges of its management. Our findings suggest a need for a nuanced understanding of OSA pathogenesis and caution against the use of flupirtine in managing OSA. While, pharmacological modulation of ionic channels within the ventilatory control system presents a promising strategy, given the plethora of robust targets available, it remains to be determined whether an effective treatment can capitalise on a single predominant ionic current ubiquitous throughout the ventilatory system, or if a more successful approach necessitates the simultaneous modulation of multiple targets. This research enhances our understanding of the ventilatory control system's contribution to OSA and the complexity of finding a one-size-fits-all treatment. KEY POINTS: Around one-third of obstructive sleep apnoea (OSA) cases involve an unstable control of breathing, leading to airway collapse. This research examined whether the drug flupirtine could stabilise breathing control and reduce OSA severity in 15 patients. Flupirtine, which was expected to improve breathing control by reducing chemosensitivity, showed no significant benefit for OSA. While targeting ionic channels in the breathing system is promising, the search for an effective OSA treatment may require addressing multiple targets simultaneously.

Repeated High-dose Fentanyl Administration in Rats Reveals Minimal Tolerance to Unconsciousness, Bradycardia, Muscle Rigidity, and Respiratory Depression

BACKGROUND

Fentanyl is a synthetic opioid that is widely used in anesthesiology, but its illicit use is rapidly increasing. At high doses, fentanyl induces unconsciousness and muscle rigidity, the mechanisms of which are poorly understood. Since animal models are needed to study these effects, the aim of this study was to establish a rat model of fentanyl abuse and investigate the effects of repeated high-dose fentanyl injections on loss of righting reflex, heart rate, respiratory depression, muscle, and brain activity.

METHODS

Male and female Sprague-Dawley rats were studied (n = 40). A bolus of 100 µg/kg fentanyl was administered intravenously twice a week for 5 consecutive weeks. Time to return of righting reflex after fentanyl injection and changes in electromyography/electroencephalography activity as well as heart rate were analyzed. Additionally, arterial blood gas analysis for evaluation of ventilation was performed. Mixed-effect models with Dunnett test and effect sizes were used for statistical analysis.

RESULTS

Repeated injections resulted in a U-shaped change in time to return of righting reflex with the longest latency after the first exposure (median, 50 [first to third quartile, 36 to 56] min) and the shortest after the fifth exposure (16 [13 to 33] min). After fentanyl administration, heart rate dropped immediately by 225 beats/min (95% CI, 179 to 271; F = 3,952.16; P < 0.001), while electromyography activity increased by 291% (95% CI, 212 to 370; F = 27.51; P < 0.001) and partial pressure of arterial carbon dioxide increased by 49.4 mmHg (95% CI, 40.6 to 58.2; F = 75.97; P < 0.001) within 5 min after injection. Additionally, pH decreased by 0.48 (95% CI, 0.41 to 0.54; F = 142.00; P < 0.01), and partial pressure of arterial oxygen decreased by 50.4 mmHg (40.8 to 60.0; F = 57.90; P < 0.001). Repeated fentanyl exposures did not significantly affect the extent of these changes (EMG, F = 1.63, P = 0.237; partial pressure of arterial carbon dioxide, F = 1.23, P = 0.312; heart rate, F = 1.05, P = 0.400; pH, F = 3.05, P = 0.066; arterial partial pressure of oxygen, F = 3.35, P = 0.052). Electroencephalography analysis revealed that repeated fentanyl exposures elicited significantly higher absolute power in frequencies greater than 20 Hz as indicated by an area under the receiver operator characteristics curve greater than 0.7.

CONCLUSIONS

The authors established a rodent model of repeated high-dose fentanyl administration. Overall, significant evidence of tolerance was not observed after 10 exposures of high-dose fentanyl for any of the analyzed parameters. These results suggest that tolerance does not develop for fentanyl-induced unconsciousness, muscle rigidity, or respiratory depression.

Cracking the code: the clinical and molecular impact of aminopyridines; a review (2019-2024)

Aminopyridines belong to a class of compounds that are monoamino and diamino derivatives of pyridine. They work primarily by blocking voltage-gated potassium channels in a dose-dependent manner. Essential heterocycles used extensively in synthetic, natural products, and medicinal chemistry are aminopyridine and its derivatives. A vast array of biological and pharmacological effects can result from the interaction of aminopyridine rings with different enzymes and receptors, due to their unique structural properties. Aminopyridine research is continually growing, and there are now greater expectations for how it may aid in the treatment of numerous disorders. This review article will serve as an innovative platform for researchers investigating aminopyridine compounds, intending thoroughly to examine both traditional and novel synthesis strategies in addition to investigating the various biological characteristics displayed by these adaptable heterocycles. We attempt to provide valuable insights that will contribute to further progress in the synthesis and utilization of aminopyridines in various fields.

Sleep and epilepsy: A clinical and pathophysiological overview

The interaction between sleep and epilepsy is complex. A better understanding of the mechanisms linking sleep and epilepsy appears increasingly important as it may improve diagnosis and therapeutic strategies in patients with epilepsy. In this narrative review, we aim to (i) provide an overview of the physiological and pathophysiological processes linking sleep and epilepsy; (ii) present common sleep disorders in patients with epilepsy; (iii) discuss how sleep and sleep disorders should be considered in new therapeutic approaches to epilepsy such as neurostimulation; and (iv) present the overall nocturnal manifestations and differential diagnosis between epileptic seizures and parasomnia.

Associations between spontaneous electroencephalogram oscillations and oxygen saturation across normobaric and hypobaric hypoxia

High-altitude indoctrination (HAI) trains individuals to recognize symptoms of hypoxia by simulating high-altitude conditions using normobaric (NH) or hypobaric (HH) hypoxia. Previous studies suggest that despite equivalent inspired oxygen levels, physiological differences could exist between these conditions. In particular, differences in neurophysiological responses to these conditions are not clear. Our study aimed to investigate correlations between oxygen saturation (SpO₂ ) and neural responses in NH and HH. We recorded 5-min of resting-state eyes-open electroencephalogram (EEG) and SpO₂ during control, NH, and HH conditions from 13 participants. We applied a multivariate framework to characterize correlations between SpO₂ and EEG measures (spectral power and multiscale entropy [MSE]), within each participant and at the group level. Participants were desaturating during the first 150 s of NH versus steadily desaturated in HH. We considered the entire time interval, first and second half intervals, separately. All the conditions were characterized by statistically significant participant-specific patterns of EEG-SpO₂ correlations. However, at the group level, the desaturation period expressed a robust pattern of these correlations across frequencies and brain locations. Specifically, the first 150 s of NH during desaturation differed significantly from the other conditions with negative absolute alpha power-SpO₂ correlations and positive MSE-SpO₂ correlations. Once steadily desaturated, NH and HH had no significant differences in EEG-SpO₂ correlations. Our findings indicate that the desaturating phase of hypoxia is a critical period in HAI courses, which would require developing strategies for mitigating the hypoxic stimulus in a real-world situation.

Tabernaemontana arborea and ibogaine induce paroxysmal EEG activity in freely moving mice: involvement of serotonin 5-HT1A receptors

Several Apocynaceae species, most notably Tabernanthe iboga, Voacanga africana and many Tabernaemontana species, produce ibogan-type alkaloids. Although a large amount of information exists about the Tabernaemontana genus, knowledge concerning chemistry and biological activity remains lacking for several species, especially related to their effects on the central nervous system (CNS). The aim of this study was to evaluate the effect of Tabernaemontana arborea Rose ex J.D.Sm. (T. arborea) hydroalcoholic extract (30, 56.2 and 100 mg/kg, i.p.) and two of its main alkaloids (ibogaine and voacangine, 30 mg/kg, i.p.) on electroencephalographic (EEG) activity alone and in the presence of the chemical convulsant agent pentylenetetrazole (PTZ, 85 mg/kg, i.p.) in mice. EEG spectral power analysis showed that T. arborea extract (56.2 and 100 mg/kg) and ibogaine (30 mg/kg, i.p.) promoted a significant increase in the relative power of the delta band and a significant reduction in alpha band values, denoting a CNS depressant effect. Voacangine (30 mg/kg, i.p.) provoked an EEG flattening pattern. The PTZ-induced seizures were not modified in the presence of T. arborea, ibogaine, or voacangine. However, sudden death was observed in mice treated with T. arborea extract at 100 mg/kg, i.p., combined with PTZ. Because T. arborea extract (100 mg/kg, i.p.) and ibogaine (30 mg/kg, i.p.), but not voacangine (30 mg/kg, i.p.), induced paroxysmal activity in the EEG, both were explored in the presence of a serotonin 5-HT_1A receptor antagonist (WAY100635, 1 mg/kg, i.p.). The antagonist abolished the paroxysmal activity provoked by T. arborea (100 mg/kg, i.p.) but not that observed with ibogaine, corroborating the participation of serotonin neurotransmission in the T. arborea effects. In conclusion, high doses of the T. arborea extract induced abnormal EEG activity due in part to the presence of ibogaine and involving serotonin 5-HT_1A receptor participation. Nevertheless, other possible constituents and mechanisms might participate in this complex excitatory activity that would be interesting to explore in future studies.

Perinatal inflammation and gestational intermittent hypoxia disturbs respiratory rhythm generation and long-term facilitation in vitro: partial protection by acute minocycline

Perinatal inflammation triggers breathing disturbances early in life and affects the respiratory adaptations to challenging conditions, including the generation of amplitude long-term facilitation (LTF) by acute intermittent hypoxia (AIH). Some of these effects can be avoided by anti-inflammatory treatments like minocycline. Since little is known about the effects of perinatal inflammation on the inspiratory rhythm generator, located in the preBötzinger complex (preBötC), we tested the impact of acute lipopolysaccharide (LPS) systemic administration (sLPS), as well as gestational LPS (gLPS) and gestational chronic IH (gCIH), on respiratory rhythm generation and its long-term response to AIH in a brainstem slice preparation from neonatal mice. We also evaluated whether acute minocycline administration could influence these effects. We found that perinatal inflammation induced by sLPS or gLPS, as well as gCIH, modulate the frequency, signal-to-noise ratio and/or amplitude (and their regularity) of the respiratory rhythm recorded from the preBötC in the brainstem slice. Moreover, all these perinatal conditions inhibited frequency LTF and amplitude long-term depression (LTD); gCIH even induced frequency LTD of the respiratory rhythm after AIH. Some of the alterations were not observed in slices pre-treated in vitro with minocycline, when compared with slices obtained from naïve pups, suggesting that ongoing inflammatory conditions affect respiratory rhythm generation and its plasticity. Thus, it is likely that alterations in the inspiratory rhythm generator and its adaptive responses could contribute to the respiratory disturbances observed in neonates that suffered from perinatal inflammatory challenges.

Alterations in Piriform and Bulbar Activity/Excitability/Coupling Upon Amyloid-β Administration in vivo Related to Olfactory Dysfunction

BACKGROUND

Deficits in odor detection and discrimination are premature symptoms of Alzheimer's disease (AD) that correlate with pathological signs in the olfactory bulb (OB) and piriform cortex (PCx). Similar olfactory dysfunction has been characterized in AD transgenic mice that overproduce amyloid-β peptide (Aβ), which can be prevented by reducing Aβ levels by immunological and pharmacological means, suggesting that olfactory dysfunction depends on Aβ accumulation and Aβ-driven alterations in the OB and/or PCx, as well as on their activation. However, this possibility needs further exploration.

OBJECTIVE

To characterize the effects of Aβ on OB and PCx excitability/coupling and on olfaction.

METHODS

Aβ oligomerized solution (containing oligomers, monomers, and protofibrils) or its vehicle were intracerebroventricularlly injected two weeks before OB and PCx excitability and synchrony were evaluated through field recordings in vivo and in brain slices. Synaptic transmission from the OB to the PCx was also evaluated in slices. Olfaction was assessed through the habituation/dishabituation test.

RESULTS

Aβ did not affect lateral olfactory tract transmission into the PCx but reduced odor habituation and cross-habituation. This olfactory dysfunction was related to a reduction of PCx and OB network activity power in vivo. Moreover, the coherence between PCx-OB activities was also reduced by Aβ. Finally, Aβ treatment exacerbated the 4-aminopyridine-induced excitation in the PCx in slices.

CONCLUSION

Our results show that Aβ-induced olfactory dysfunction involves a complex set of pathological changes at different levels of the olfactory pathway including alterations in PCx excitability and its coupling with the OB. These pathological changes might contribute to hyposmia in AD.