Suppression of parasympathetic reflex vasodilatation in the lower lip of the cat by isoflurane, propofol, ketamine and pentobarbital: implications for mechanisms underlying the production of anaesthesia

Mesoscopic mapping of hemodynamic responses and neuronal activity during pharmacologically induced interictal spikes in awake and anesthetized mice

Imaging hemodynamic responses to interictal spikes holds promise for presurgical epilepsy evaluations. Understanding the hemodynamic response function is crucial for accurate interpretation. Prior interictal neurovascular coupling data primarily come from anesthetized animals, impacting reliability. We simultaneously monitored calcium fluctuations in excitatory neurons, hemodynamics, and local field potentials (LFP) during bicuculline-induced interictal events in both isoflurane-anesthetized and awake mice. Isoflurane significantly affected LFP amplitude but had little impact on the amplitude and area of the calcium signal. Anesthesia also dramatically blunted the amplitude and latency of the hemodynamic response, although not its area of spread. Cerebral blood volume change provided the best spatial estimation of excitatory neuronal activity in both states. Targeted silencing of the thalamus in awake mice failed to recapitulate the impact of anesthesia on hemodynamic responses suggesting that isoflurane's interruption of the thalamocortical loop did not contribute either to the dissociation between the LFP and the calcium signal nor to the alterations in interictal neurovascular coupling. The blood volume increase associated with interictal spikes represents a promising mapping signal in both the awake and anesthetized states.

Effects of N-Methyl-D-aspartate receptor (NMDAR) and Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα) on learning and memory impairment in depressed rats with different charge by modified electroconvulsive shock

Background

With the development of modified electroshock therapy (MECT), it has become necessary to increase the electric quantity in order to achieve a good antidepressant effect, but this increase will lead to more serious learning and memory impairment. The purpose of this study was to investigate the intrinsic mechanism of cognitive impairment induced by high-energy electroconvulsive shock (MECS, an animal model of MECT).

Methods

Rats were randomly divided into 6 groups: control (C, n=6), M0, M60, M120, M180, and M240 groups (MECS at 0, 60, 120, 180, and 240 mC stimulation intensity after 80 mg/kg propofol, with 12 rats in each group). Their depression-like behavior and learning and memory ability were evaluated by sucrose preference test (SPT), open field test (OFT), and Morris water maze test (MWM). The expression of phospho-NMDA receptor 1 (GluN1), GluN2A, GluN2B, Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα), p-T305-CaMKII, and postsynaptic densities-95 (PSD-95) in hippocampus were detected by western blot. The co-expression of CaMKIIα and GluN2B subunit was detected by co-immunoprecipitation (CO-IP).

Results

The chronic unpredictable mild stresses (CUMS) procedure successfully induced depression-like behavior in rats, which was improved in varying degrees after MECS. The results showed that the expression of GluN1, GluN2A, GluN2B, and PSD-95 decreased with the increase of charge, while p-T305-CaMKII increased, which led to the deterioration of learning and memory ability, but the expression change of CaMKIIα was not statistically significant.

Conclusions

Increase in the MECS charge adjusts the synaptic plasticity by changing the binding amount of CaMKIIα and its subunit GluN2B and the level of CaMKII autophosphorylation, thereby impairing learning and memory functions.

Mesoscopic Mapping of Ictal Neurovascular Coupling in Awake Behaving Mice Using Optical Spectroscopy and Genetically Encoded Calcium Indicators

Unambiguously identifying an epileptic focus with high spatial resolution is a challenge, especially when no anatomic abnormality can be detected. Neurovascular coupling (NVC)-based brain mapping techniques are often applied in the clinic despite a poor understanding of ictal NVC mechanisms, derived primarily from recordings in anesthetized animals with limited spatial sampling of the ictal core. In this study, we used simultaneous wide-field mesoscopic imaging of GCamp6f and intrinsic optical signals (IOS) to record the neuronal and hemodynamic changes during acute ictal events in awake, behaving mice. Similar signals in isoflurane-anesthetized mice were compared to highlight the unique characteristics of the awake condition. In awake animals, seizures were more focal at the onset but more likely to propagate to the contralateral hemisphere. The HbT signal, derived from an increase in cerebral blood volume (CBV), was more intense in awake mice. As a result, the “epileptic dip” in hemoglobin oxygenation became inconsistent and unreliable as a mapping signal. Our data indicate that CBV-based imaging techniques should be more accurate than blood oxygen level dependent (BOLD)-based imaging techniques for seizure mapping in awake behaving animals.

Syntheses of Analogues of Propofol: A Review

Propofol (2,6-diisopropylphenol) is an intravenous sedative/hypnotic agent that is used extensively for introduction and maintenance of general anaesthesia, sedation of critically ill patients and procedural sedation (e.g., endoscopy). Propofol has a rapid onset and offset of action and shows only minimal accumulation upon prolonged use. Propofol is only sparingly soluble in water and is currently marketed in 10% soybean oil-based lipid emulsion. Propofol’s anaesthetic properties were discovered over forty years ago, and it has been in clinical use for over thirty years. The main use of propofol remains as an anaesthetic but, over the years, analogues have been developed with varying properties from anticancer, anticonvulsant and antioxidant. In addition, large synthetic efforts have been made towards improving propofol’s water-solubility, its activity, and elucidating its structure–activity­ relationship and exact mechanism of action have been made. This review provides an overview of the research pertaining to propofol-like molecules and covers the efforts of synthetic chemists towards propofol analogues over the last 40 years.

1 Introduction

2 History

3 Early Work

4 Improving Water Solubility

5 The Importance of the Phenol

6 Exploring the Structure–Activity Relationship and Attempts to Improve Activity

7 Anticancer Activity

8 Anticonvulsant Properties

9 Antioxidant Activity

10 Photoactive Labelling to Elucidate Mechanism of Action

11 Photoregulation

12 Conclusion

Anesthesia with sevoflurane or isoflurane induces severe hypoglycemia in neonatal mice

Sevoflurane and isoflurane are among the most commonly used general anesthetics for children including infants, but their impact on metabolism, especially on blood glucose level, in children is not well understood. We investigated the impacts of anesthesia of neonatal (7–8 days old) and adult (2–3 months old) mice with the inhalational anesthetics 2.5% sevoflurane or 1.5% isoflurane, or the injectable anesthetics propofol (150 mg/kg) or avertin (375 mg/kg), for up to 6 hours. We found that sevoflurane and isoflurane induced severe hypoglycemia in neonatal mice and that this phenomenon was specific to the inhalational anesthetics because the injectable anesthetics propofol and avertin did not induce hypoglycemia. Surprisingly, the inhalational anesthesia induced hyperglycemia instead in adult mice. We also demonstrated that the inhalational anesthesia-induced hypoglycemia was a major cause of death for the neonatal mice receiving intranasal administration of saline prior to anesthesia. These studies revealed severe hypoglycemia in neonatal mice during anesthesia with sevoflurane or isoflurane. If this phenomenon also occurs in human, our findings would warrant closely monitoring blood glucose level and maintaining it in the normal range in infants receiving inhalational anesthesia.

Novel propofol derivatives and implications for anesthesia practice

Propofol (2,6-diisopropylphenol) is the most commonly used intravenous agent for induction of anesthesia. It is also used for maintenance of anesthesia and sedation in both Intensive Care Units and outpatient procedural settings. Its success in the clinical setting has been a result of its rapid onset, short duration of action, and minimal side effects despite disadvantages associated with its oil emulsion formulation. Early attempts to alter the standard emulsion or to develop new formulations with cyclodextrins and micelles to resolve issues with pain upon injection, the need for antimicrobial agents, and possible hyperlipidemia have mostly failed. With these challenges in the foreground, attention has now shifted to the use of more prodrugs and exogenous alternatives, the success of which is yet to be determined. These new agents must offer significant clinical advantages over the well-entrenched, generic propofol oil emulsion to justify higher costs and to be well received in the increasingly cost-conscious healthcare marketplace.

Are neuronal voltage-gated calcium channels valid cellular targets for general anesthetics?

The effects of anesthetics and analgesics on ion channels have been the subject of intense research since recent reports of direct actions of anesthetic molecules on ion channel proteins.  It is now known that ligand-gated channels, particularly γ-amino-butyric acid (GABAA) and N-methyl-D-aspartate (NMDA) receptors, play a key role in mediating anesthetic actions, but these channels are unable to account for all aspects of clinical anesthesia such as loss of consciousness, immobility, analgesia, amnesia, and muscle relaxation.  Furthermore, an assortment of voltage-gated and background channels also display anesthetic sensitivity and a key question arises: What role do these other channels play in clinical anesthesia? These channels have overlapping physiological roles and pharmacological profiles, making it difficult to assign aspects of the anesthetic state to individual channel types.  Here, we will focus on the function of neuronal voltage-gated calcium channels in mediating the effects of general anesthetics.

The experimental and clinical pharmacology of propofol, an anesthetic agent with neuroprotective properties

Propofol (2,6-diisopropylphenol) is a versatile, short-acting, intravenous (i.v.) sedative-hypnotic agent initially marketed as an anesthetic, and now also widely used for the sedation of patients in the intensive care unit (ICU). At the room temperature propofol is an oil and is insoluble in water. It has a remarkable safety profile. Its most common side effects are dose-dependent hypotension and cardiorespiratory depression. Propofol is a global central nervous system (CNS) depressant. It activates gamma-aminobutyric acid (GABA A) receptors directly, inhibits the N-methyl-d-aspartate (NMDA) receptor and modulates calcium influx through slow calcium-ion channels. Furthermore, at doses that do not produce sedation, propofol has an anxiolytic effect. It has also immunomodulatory activity, and may, therefore, diminish the systemic inflammatory response believed to be responsible for organ dysfunction. Propofol has been reported to have neuroprotective effects. It reduces cerebral blood flow and intracranial pressure (ICP), is a potent antioxidant, and has anti-inflammatory properties. Laboratory investigations revealed that it might also protect brain from ischemic injury. Propofol formulations contain either disodium edetate (EDTA) or sodium metabisulfite, which have antibacterial and antifungal properties. EDTA is also a chelator of divalent ions such as calcium, magnesium, and zinc. Recently, EDTA has been reported to exert a neuroprotective effect itself by chelating surplus intracerebral zinc in an ischemia model. This article reviews the neuroprotective effects of propofol and its mechanism of action.

Occurrence of parasympathetic vasodilator fibers in the lower lip of the guinea-pig

The present study was designed to examine whether there are parasympathetic vasodilator fibers in the lower lip of the guinea-pig. Electrical stimulation of the central cut end of the lingual nerve of guinea-pigs evoked intensity- and frequency-dependent decreases in lower lip blood flow and systemic arterial blood pressure (SABP). Pretreatment with guanethidine, a postganglionic sympathetic nerve blocker and antihypertensive drug (30 mg kg(-1), s.c., 24 h prior to experiments), reduced the magnitude of the decrease in SABP while the intensity- and frequency-dependent increases of the lip blood flow occurred by the lingual nerve stimulation only on the side ipsilateral to stimulation. Increases in the lip blood flow evoked by lingual nerve stimulation in guanethidine pretreated guinea-pigs were reduced by hexamethonium (an autonomic ganglion cholinergic blocker) in a dose-dependent manner. When fluoro-gold (a retrograde neural tracer) was injected into the lower lip, labeled neurons were observed in the ipsilateral otic ganglion. The present study indicates the presence of parasympathetic vasodilator fibers originating from the otic parasympathetic ganglion in the guinea-pig lower lip, similar to those reported previously in rats, cats, rabbits and humans.

Involvement of A1 adenosine receptors and neural pathways in adenosine-induced bronchoconstriction in mice

High levels of adenosine can be measured from the lungs of asthmatics, and it is well recognized that aerosolized 5'AMP, the precursor of adenosine, elicits robust bronchoconstriction in patients with this disease. Characterization of mice with elevated adenosine levels secondary to the loss of adenosine deaminase (ADA) expression, the primary metabolic enzyme for adenosine, further support a role for this ubiquitous mediator in the pathogenesis of asthma. To begin to identify pathways by which adenosine can alter airway tone, we examined adenosine-induced bronchoconstriction in four mouse lines, each lacking one of the receptors for this nucleoside. We show, using direct measures of airway mechanics, that adenosine can increase airway resistance and that this increase in resistance is mediated by binding the A(1) receptor. Further examination of this response using pharmacologically, surgically, and genetically manipulated mice supports a model in which adenosine-induced bronchoconstriction occurs indirectly through the activation of sensory neurons.

Effects of isoflurane on parasympathetic vasodilatation in the rat submandibular gland

Volatile anesthetics have been known to suppress parasympathetic reflex vasodilatation in the lower lip and palate. However, in the submandibular gland, little is known about the effects of these anesthetics on the parasympathetic vasodilatation elicited by reflex and direct (i.e., non-reflex) activation of the parasympathetic vasodilator mechanisms. Although both parasympathetic vasodilatations were inhibited by isoflurane in a concentration- and time-dependent manner, the effects of continuous administration of the alpha(1)-adrenoceptor agonist methoxamine were markedly different: The reflex vasodilatation was not affected by methoxamine, while the direct vasodilatation was significantly reduced. Picrotoxin (GABA(A) receptor antagonist) attenuated the inhibitory effect of isoflurane on direct vasodilatation and the systemic arterial blood pressure. These findings suggest that the isoflurane-induced inhibitory effects on direct vasodilatation are produced by a decrease of peripheral vascular tone by GABAergic mechanisms, whereas those on the reflex vasodilatation are produced exclusively by the inhibition of the reflex center.

Role of muscarinic cholinergic transmission in Edinger-Westphal nucleus-induced choroidal vasodilation in pigeon

Activation of the parasympathetic ciliary ganglion input to the choroid causes increases in choroidal blood flow. We examined the role and the type of muscarinic receptors within the choroid that are involved in these increases in choroidal blood flow, using electrical stimulation of the nucleus of Edinger-Westphal (EW) to activate the ciliary ganglion input to choroid in ketamine anesthetized pigeons. Baseline choroidal blood flow and its EW-evoked increases measured as peak and total (area under the curve) responses were determined using laser Doppler flowmetry. The EW-evoked responses were reduced dose-dependently after administration of 4-diphenyl-acetoxy-N-methylpiperedine (4-DAMP), a relatively selective antagonist of M3 type muscarinic receptors, with a maximal mean decrease of 86% (peak response) and 93% (total response) at a dose of 10 microg kg(-1)i.v. without a significant effect on baseline choroidal blood flow, heart rate or systemic arterial blood pressure. Atropine, a non-selective antagonist of muscarinic receptors, decreased the EW-evoked responses to a lesser extent than 4-DAMP after intravenous administration of 1 mg kg(-1)(by 67% for peak response and by 53% for total response) or topical administration of a 5% solution (by 41% for peak response and by 62% for total response), both of which increased heart rate and systemic arterial blood pressure without a consistent effect on baseline choroidal blood flow. In contrast, himbacine (i.p. 10 microg kg(-1)), a relatively selective antagonist of M2 type muscarinic receptors, increased the EW-evoked parasympathetic cholinergic vasodilation (by 93% for the peak response and by 142% for the total response) without a significant effect on heart rate, systemic arterial blood pressure or baseline choroidal blood flow. The results of our study suggest a major role of M3 type muscarinic receptors in the EW-evoked increases in choroidal blood flow. Based on findings that the ciliary ganglion input to choroid does not synthesize nitric oxide but inhibitors of NO production do block EW-evoked choroidal vasodilation, it seems likely that the M3 receptors acted on by 4-DAMP are present on choroidal endothelial cells and mediate choroidal vasodilation via stimulation of endothelial release of nitric oxide. In contrast, M2 muscarinic receptors may play a presynaptic role in downregulating EW-evoked parasympathetic cholinergic vasodilation in avian choroid.

Correlation between degree of inhibition of parasympathetic reflex vasodilation and MAC value for various inhalation anesthetics

Parasympathetic reflex vasodilation was elicited in the lower lip by stimulation of the central cut end of the lingual nerve in urethane plus alpha-chloralose-anesthetized, vago-sympathectomized cats. A dose-related inhibition of this response was induced by the inhalation anesthetics isoflurane, halothane, sevoflurane, and enflurane, the ID50 values being 0.94%, 0.82%, 1.74%, and 2.0%, respectively. These results indicate that the ID50 value is approximately two-thirds of the published MAC (for isoflurane, halothane, sevoflurane, and enflurane, 1.6%, 1.2%, 2.6%, and 2.4%, respectively) value for such anesthetics, suggesting that parasympathetic reflex vasodilation is more susceptible than somato-somatic reflexes to inhibition by inhalation anesthetics.

Nervous control of blood flow in the orofacial region

The blood vessels of orofacial tissues are innervated by cranial parasympathetic, superior cervical sympathetic, and trigeminal nerves, a situation somewhat different from that seen in body skin. This review summarizes our current knowledge of the nervous control of blood flow in the orofacial region, and focuses on what we know of the respective roles of sympathetic, parasympathetic, and trigeminal sensory nerves in the regulation of blood flow in this region, with particular attention being paid to the mutual interaction between them.