Noradrenergic modulation of neuronal responses to n-methyl-d-aspartate in the vestibular nuclei: an electrophysiological and immunohistochemical study

Norepinephrine modulates wakefulness via α1 adrenoceptors in paraventricular thalamic nucleus

Norepinephrine (NE) neurons in the locus coeruleus (LC) play key roles in modulating sleep and wakefulness. Recent studies have revealed that the paraventricular thalamic nucleus (PVT) is a critical wakefulness-controlling nucleus in mice. However, the effects of NE on PVT neurons remain largely unknown. Here, we investigated the mechanisms of NE modulating wakefulness in the PVT by using viral tracing, behavioral tests, slice electrophysiology, and optogenetics techniques. We found that the PVT-projecting LC neurons had few collateral projections to other brain nuclei. Behavioral tests showed that specific activation of the LC-PVT projections or microinjection of NE into the PVT accelerated emergence from general anesthesia and enhanced locomotion activity. Moreover, brain slice recording results indicated that NE increased the activity of the PVT neurons mainly by increasing the frequency of spontaneous excitatory postsynaptic currents via α1 adrenoceptors. Thus, our results demonstrate that NE modulates wakefulness via α1 adrenoceptors in the PVT.

Altered monoaminergic levels, spasticity, and balance disability following repetitive blast-induced traumatic brain injury in rats

Spasticity and balance disability are major complications following traumatic brain injury (TBI). Although monoaminergic inputs provide critical adaptive neuromodulations to the motor system, data are not available regarding the levels of monoamines in the brain regions related to motor functions following repetitive blast TBI (bTBI). The objective of this study was to determine if mild, repetitive bTBI results in spasticity/balance deficits and if these are correlated with altered levels of norepinephrine, dopamine, and serotonin in the brain regions related to the motor system. Repetitive bTBI was induced by a blast overpressure wave in male rats on days 1, 4, and 7. Following bTBI, physiological/behavioral tests were conducted and tissues in the central motor system (i.e., motor cortex, locus coeruleus, vestibular nuclei, and lumbar spinal cord) were collected for electrochemical detection of norepinephrine, dopamine, and serotonin by high-performance liquid chromatography. The results showed that norepinephrine was significantly increased in the locus coeruleus and decreased in the vestibular nuclei, while dopamine was significantly decreased in the vestibular nuclei. On the other hand, serotonin was significantly increased in the motor cortex and the lumbar spinal cord. Because these monoamines play important roles in regulating the excitability of neurons, these results suggest that mild, repetitive bTBI-induced dysregulation of monoaminergic inputs in the central motor system could contribute to spasticity and balance disability. This is the first study to report altered levels of multiple monoamines in the central motor system following acute mild, repetitive bTBI.

The effect of intraoperative lidocaine versus esmolol infusion on postoperative analgesia in laparoscopic cholecystectomy: a randomized clinical trial

Background

As a part of multimodal analgesia for laparoscopic cholecystectomy, both intraoperative lidocaine and esmolol facilitate postoperative analgesia. Our objective was to compare these two emerging strategies that challenge the use of intraoperative opioids. We aimed to assess if intraoperative esmolol infusion is not inferior to lidocaine infusion for opioid consumption after laparoscopic cholecystectomy.

Methods

In this prospective, randomized, double-blind, non-inferiority clinical trial, 90 female patients scheduled for elective laparoscopic cholecystectomy received either intravenous (IV) lidocaine bolus 1.5 mg/kg at induction followed by an infusion (1.5 mg/ kg/h) or IV bolus of esmolol 0.5 mg/kg at induction followed by an infusion (5–15 μg/kg/min) till the end of surgery. Remaining aspect of anesthesia followed a standard protocol apart from no intraoperative opioid supplementation. Postoperatively, patients received either morphine or tramadol IV to maintain visual analogue scale (VAS) scores ≤3. The primary outcome was opioid consumption (in morphine equivalents) during the first 24 postoperative hours. Pain and sedation scores, time to first perception of pain and void, and occurrence of nausea/vomiting were secondary outcomes measured up to 24 h postoperatively.

Results

Two patients in each group were excluded from the analysis. The postoperative median (IQR) morphine equivalent consumption in patients receiving esmolol was 1 (0–1.5) mg compared to 1.5 (1–2) mg in lidocaine group (p = 0.27). The median pain scores at various time points were similar between the two groups (p > 0.05). More patients receiving lidocaine were sedated in the post-anesthesia care unit (PACU) than those receiving esmolol (p < 0.05); however, no difference was detected later.

Conclusion

Infusion of esmolol is not inferior to lidocaine in terms of opioid requirement and pain severity in the first 24 h after surgery. Patients receiving lidocaine were more sedated during their stay in PACU than those receiving esmolol.

Trial registration

ClinicalTrials.gov- NCT02327923. Date of registration: December 31, 2014.

Excitatory effect of norepinephrine on neurons in the inferior vestibular nucleus and the underlying receptor mechanism

The central noradrenergic system, originating mainly from the locus coeruleus in the brainstem, plays an important role in many physiological functions, including arousal and attention, learning and memory, anxiety, and nociception. However, little is known about the roles of norepinephrine (NE) in somatic motor control. Therefore, using extracellular recordings on rat brainstem slices and quantitative real-time RT-PCR, we investigate the effect and mechanisms of NE on neuronal activity in the inferior vestibular nucleus (IVN), the largest nucleus in the vestibular nuclear complex, which holds an important position in integration of information signals controlling body posture. Here, we report that NE elicits an excitatory response on IVN neurons in a concentration-dependent manner. Activation of α1 - and β2 -adrenergic receptors (ARs) induces an increase in firing rate of IVN neurons, whereas activation of α2 -ARs evokes a decrease in firing rate of IVN neurons. Therefore, the excitation induced by NE on IVN neurons is a summation of the excitatory components mediated by coactivation of α1 - and β2 -ARs and the inhibitory component induced by α2 -ARs. Accordingly, α1 -, α2 -, and β2 -AR mRNAs are expressed in the IVN. Although β1 -AR mRNAs are also detected, they are not involved in the direct electrophysiological effect of NE on IVN neurons. All these results demonstrate that NE directly regulates the activity of IVN neurons via α1 -, α2 -, and β2 -ARs and suggest that the central noradrenergic system may actively participate in IVN-mediated vestibular reflexes and postural control. © 2016 Wiley Periodicals, Inc.