Neurocomputational mechanisms underlying perception and sentience in the neocortex

The basis for computation in the brain is the quantum threshold of "soliton," which accompanies the ion changes of the action potential, and the refractory membrane at convergences. Here, we provide a logical explanation from the action potential to a neuronal model of the coding and computation of the retina. We also explain how the visual cortex operates through quantum-phase processing. In the small-world network, parallel frequencies collide into definable patterns of distinct objects. Elsewhere, we have shown how many sensory cells are meanly sampled from a single neuron and that convergences of neurons are common. We also demonstrate, using the threshold and refractory period of a quantum-phase pulse, that action potentials diffract across a neural network due to the annulment of parallel collisions in the phase ternary computation (PTC). Thus, PTC applied to neuron convergences results in a collective mean sampled frequency and is the only mathematical solution within the constraints of the brain neural networks (BNN). In the retina and other sensory areas, we discuss how this information is initially coded and then understood in terms of network abstracts within the lateral geniculate nucleus (LGN) and visual cortex. First, by defining neural patterning within a neural network, and then in terms of contextual networks, we demonstrate that the output of frequencies from the visual cortex contains information amounting to abstract representations of objects in increasing detail. We show that nerve tracts from the LGN provide time synchronization to the neocortex (defined as the location of the combination of connections of the visual cortex, motor cortex, auditory cortex, etc.). The full image is therefore combined in the neocortex with other sensory modalities so that it receives information about the object from the eye and all the abstracts that make up the object. Spatial patterns in the visual cortex are formed from individual patterns illuminating the retina, and memory is encoded by reverberatory loops of computational action potentials (CAPs). We demonstrate that a similar process of PTC may take place in the cochlea and associated ganglia, as well as ascending information from the spinal cord, and that this function should be considered universal where convergences of neurons occur.

The Use of Isoflurane and Adjunctive Magnesium Chloride Provides Fast, Effective Anaesthetization of Octopus vulgaris

A wide variety of substances have been used to anaesthetise invertebrates, but many are not anaesthetics and merely incapacitate animals rather than preventing pain. In essence, the role of an ideal general anaesthetic is to act as a muscle relaxant, an analgesic, an anaesthetic, and an amnesic. To achieve all these properties with a single substance is difficult, and various adjuvants usually need to be administered, resulting in a cocktail of drugs. In a clinical setting, the vast majority of patients are unaware of surgery being carried out and have no memory of it, so they can claim to have felt no pain, but this is much more difficult to demonstrate in invertebrates. Here, we show that 1% MgCl2, a muscle relaxant, is a useful adjuvant for the clinical anaesthetic isoflurane on Octopus vulgaris when applied alone in seawater for 10 min before the clinical anaesthetic. After this, full anaesthesia can be achieved in 5 min using 1% isoflurane insufflated into the saline still containing MgCl2. Full recovery takes place rapidly in about 10 to 15 min. The depth of anaesthesia was monitored using changes in respiratory rate, chromatophore pattern, and withdrawal movements of the arms and siphon. This methodology reduces stress on the animal and minimises the quantity of anaesthetic used.

COVID-19 vulnerabilities are intensified by declining human serum albumin levels

What is the topic of this review?

Human serum albumin (HSA) a common factor in COVID‐19 vulnerabilities.

What advances does it highlight?

Understanding of HSA capacity, and systemic vulnerabilities to COVID‐19. Raising HSA in COVID‐19 patients may alleviate systemic injury caused by diminished native HSA binding. A change in fluid therapy administration into the portal system of the liver is proposed to safely raise HSA levels.

Does the Brain Function as a Quantum Phase Computer Using Phase Ternary Computation?

Here we provide evidence that the fundamental basis of nervous communication is derived from a pressure pulse/soliton capable of computation with sufficient temporal precision to overcome any processing errors. Signalling and computing within the nervous system are complex and different phenomena. Action potentials are plastic and this makes the action potential peak an inappropriate fixed point for neural computation, but the action potential threshold is suitable for this purpose. Furthermore, neural models timed by spiking neurons operate below the rate necessary to overcome processing error. Using retinal processing as our example, we demonstrate that the contemporary theory of nerve conduction based on cable theory is inappropriate to account for the short computational time necessary for the full functioning of the retina and by implication the rest of the brain. Moreover, cable theory cannot be instrumental in the propagation of the action potential because at the activation-threshold there is insufficient charge at the activation site for successive ion channels to be electrostatically opened. Deconstruction of the brain neural network suggests that it is a member of a group of Quantum phase computers of which the Turing machine is the simplest: the brain is another based upon phase ternary computation. However, attempts to use Turing based mechanisms cannot resolve the coding of the retina or the computation of intelligence, as the technology of Turing based computers is fundamentally different. We demonstrate that that coding in the brain neural network is quantum based, where the quanta have a temporal variable and a phase-base variable enabling phase ternary computation as previously demonstrated in the retina.

SARS-CoV-2 Bound Human Serum Albumin and Systemic Septic Shock

The emergence of the COVID-19 virus and the subsequent pandemic have driven a great deal of research activity. The effects of COVID-19 are caused by the severe respiratory syndrome coronavirus 2 (SARS-CoV-2) and it is the underlying actions of SARs-CoV-2 virions on the endothelial glycocalyx that we consider here. One of the key factors in COVID-19 infection is its almost unique age-related profile, with a doubling in mortality every 10 years after the age of 50. The endothelial glycocalyx layer is essential in maintaining normal fluid homeostasis, but is fragile and prone to pathophysiological damage. It is physiologically significant in capillary microcirculation and in fluid distribution to the tissues. Human serum albumin (HSA), the most abundant protein in plasma, is created in the liver which also maintains its concentration, but this reduces by 10-15% after 50 years of age. HSA transports hormones, free fatty acids and maintains oncotic pressure, but SARS-CoV-2 virions bind competitively to HSA diminishing its normal transport function. Furthermore, hypoalbuminemia is frequently observed in patients with such conditions as diabetes, hypertension, and chronic heart failure, i.e., those most vulnerable to SARS-CoV-2 infection. Hypoalbuminemia, coagulopathy, and vascular disease have been linked in COVID-19 and have been shown to predict outcome independent of age and morbidity. Hypoalbuminemia is also known factor in sepsis and Acute respiratory distress syndrome (ARDS) occurs when fluids build-up in the alveoli and it is associated with sepsis, whose mechanism is systemic, being associated with the fluid and logistic mechanisms of the circulation. Glycocalyx damage is associated with changes plasma protein concentration, particularly HSA and blockage of albumin transport can produce the systemic symptoms seen in SARS-CoV-2 infection and sepsis. We therefore conclude that albumin binding to SARS-CoV-2 virions may inhibit the formation of the endothelial glycocalyx by inhibition of albumin transport binding sites. We postulate that albumin therapy to replace bound albumin might alleviate some of the symptoms leading to sepsis and that clinical trials to test this postulation should be initiated as a matter of urgency.

The role of non-coding RNAs in neuroprotection and angiogenesis following ischemic stroke

Stroke is the leading cause of death and physical disability worldwide. Non-coding RNAs (ncRNAs) are endogenous molecules that play key roles in the pathophysiology and retrieval processes following ischemic stroke. The potential of ncRNAs, especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) in neuroprotection and angiogenesis highlights their potential as targets for therapeutic intervention. In this review, we document the miRNAs and lncRNAs that have been reported to exert regulatory actions in neuroprotective and angiogenic processes through different mechanisms involving their interaction with target coding genes. We believe that exploration of the expression profiles and the possible functions of ncRNAs during the recovery processes will help comprehension of the molecular mechanisms responsible for neuroprotection and angiogenesis, and may also contribute to find biomarkers and targets for future stroke intervention.

Long non-coding RNAs and cell death following ischemic stroke

Stroke is a major cause of morbidity and mortality worldwide, and extensive efforts have focused on the improvement of therapeutic strategies to reduce cell death following ischemic stroke. Uncovering the cellular and molecular pathophysiological processes in ischemic stroke have been a top priority. Long noncoding RNAs (lncRNAs) are endogenous molecules that play key roles in the pathophysiology of cerebral ischemia, and involved in the neuronal cell death during ischemic stroke. In recent years, a bulk of aberrantly expressed lncRNAs have been screened out in ischemic stroke insulted animals. LncRNAs along with their targets could affect the genetic machinery at molecular levels, and exploring their functions and mechanisms may be a promising option for ischemic stroke treatment. In this review, we summarize the current knowledge for lncRNAs in ischemic stroke, focusing on the role of specific lncRNAs that may underlie cell death to find possible therapeutic targets.

A Comparative Study of Cell Specific Effects of Systemic and Volatile Anesthetics on Identified Motor Neurons and Interneurons of Lymnaea stagnalis (L.), Both in the Isolated Brain and in Single Cell Culture

1. A comparative descriptive analysis of systemic (sodium pentobarbital, sodium thiopentone, ketamine) and volatile (halothane, isoflurane, enflurane) general anesthetics revealed important differences in the neuronal responses of identified motor neurons and interneurons in the isolated central nervous system (CNS) and cultured identified neurons in single cell culture of Lymnaea stagnalis (L.). 2. At high enough concentrations all anesthetics eventually caused cessation of spontaneous or evoked action potentials, but volatile anesthetics were much faster acting. Halothane at low concentrations caused excitation, thought to be equivalent to the early excitatory phase of anesthesia. Strong synaptic inputs were not always abolished by pentobarbital. 3. There were cell specific concentration-dependent responses to halothane and pentobarbital in terms of membrane potential, action potential characteristics, the after hyperpolarization and patterned activity. Individual neurons generated specific responses to the applied anesthetics. 4. The inhalation anesthetics, enflurane, and isoflurane, showed little concentration dependence of effect, in contrast to results obtained with halothane. Enflurane was faster acting than halothane and isoflurane was particularly different, producing quiescence in all cells types studied at all concentrations studied. 5. Halothane, enflurane, the barbiturate general anesthetics, pentobarbital, and sodium thiopentone and the dissociative anesthetic ketamine, produced two distinctly different effects which could be correlated with cell type and their location in the isolated brain: either a decline in spontaneous and evoked activity prior to quiescence in interneurons or paroxysmal depolarizing shifts (PDS) in motor neurons, again prior to quiescence, which were reversed when the anesthetic was eliminated from the bath. In the strongly electrically coupled motor neurons, VD1 and RPD2, both types of response were observed, depending on the anesthetic used. Thus, with the exception isoflurane, all the motor neurons subjected to the anesthetic agents studied here were capable of generating PDS in situ, but the interneurons did not do so. 6. The effects of halothane on isolated cultured neurons indicates that PDS can be generated by single identified neurons in the absence of synaptic inputs. Further, many instances of PDS in neurons that do not generate it in situ have been found in cultured neurons. The nature of PDS is discussed.

Sense and Insensibility - An Appraisal of the Effects of Clinical Anesthetics on Gastropod and Cephalopod Molluscs as a Step to Improved Welfare of Cephalopods

Recent progress in animal welfare legislation stresses the need to treat cephalopod molluscs, such as Octopus vulgaris, humanely, to have regard for their wellbeing and to reduce their pain and suffering resulting from experimental procedures. Thus, appropriate measures for their sedation and analgesia are being introduced. Clinical anesthetics are renowned for their ability to produce unconsciousness in vertebrate species, but their exact mechanisms of action still elude investigators. In vertebrates it can prove difficult to specify the differences of response of particular neuron types given the multiplicity of neurons in the CNS. However, gastropod molluscs such as Aplysia, Lymnaea, or Helix, with their large uniquely identifiable nerve cells, make studies on the cellular, subcellular, network and behavioral actions of anesthetics much more feasible, particularly as identified cells may also be studied in culture, isolated from the rest of the nervous system. To date, the sorts of study outlined above have never been performed on cephalopods in the same way as on gastropods. However, criteria previously applied to gastropods and vertebrates have proved successful in developing a method for humanely anesthetizing Octopus with clinical doses of isoflurane, i.e., changes in respiratory rate, color pattern and withdrawal responses. However, in the long term, further refinements will be needed, including recordings from the CNS of intact animals in the presence of a variety of different anesthetic agents and their adjuvants. Clues as to their likely responsiveness to other appropriate anesthetic agents and muscle relaxants can be gained from background studies on gastropods such as Lymnaea, given their evolutionary history.

The Soliton and the Action Potential - Primary Elements Underlying Sentience

At present the neurological basis of sentience is poorly understood and this problem is exacerbated by only a partial knowledge of how one of the primary elements of sentience, the action potential, actually works. This has consequences for our understanding of how communication within the brain and in artificial brain neural networks (BNNs). Reverse engineering models of brain activity assume processing works like a conventional binary computer and neglects speed of cognition, latencies, error in nerve conduction and the true dynamic structure of neural networks in the brain. Any model of nerve conduction that claims inspiration from nature must include these prerequisite parameters, but current western computer modeling of artificial BNNs assumes that the action potential is binary and binary mathematics has been assumed by force of popular acceptance to mediate computation in the brain. Here we present evidence that the action potential is a temporal compound ternary structure, described as the computational action potential (CAP). The CAP contains the refractory period, an analog third phase capable of phase-ternary computation via colliding action potentials. This would best fit a realistic BNN and provides a plausible mechanism to explain transmission, in preference to Cable Theory. The action potential pulse (APPulse), is made up of the action potential combined with a coupled synchronized soliton pressure pulse in the cell membrane. We describe a model of an ion channel in a membrane where a soliton deforms the channel sufficiently to destroy the electrostatic insulation thereby instigating a mechanical contraction across the membrane by electrostatic forces. Such a contraction has the effect of redistributing the force lengthways thereby increasing the volume of the ion channel in the membrane. Na ions, once attracted to the interior, balance the forces and the channel reforms to its original shape. A refractory period then occurs until the Na ions diffuse from the adjacent interior space. Finally, a computational model of the action potential (the CAP) is proposed with single action potentials significantly including the refractory period as a computational element capable of computation between colliding action potentials.

Emerging Roles of microRNAs in Ischemic Stroke: As Possible Therapeutic Agents

Stroke is one of the leading causes of death and physical disability worldwide. The consequences of stroke injuries are profound and persistent, causing in considerable burden to both the individual patient and society. Current treatments for ischemic stroke injuries have proved inadequate, partly owing to an incomplete understanding of the cellular and molecular changes that occur following ischemic stroke. MicroRNAs (miRNA) are endogenously expressed RNA molecules that function to inhibit mRNA translation and have key roles in the pathophysiological processes contributing to ischemic stroke injuries. Potential therapeutic areas to compensate these pathogenic processes include promoting angiogenesis, neurogenesis and neuroprotection. Several miRNAs, and their target genes, are recognized to be involved in these recoveries and repair mechanisms. The capacity of miRNAs to simultaneously regulate several target genes underlies their unique importance in ischemic stroke therapeutics. In this Review, we focus on the role of miRNAs as potential diagnostic and prognostic biomarkers, as well as promising therapeutic agents in cerebral ischemic stroke.

Dose-dependent effects of the clinical anesthetic isoflurane on Octopus vulgaris: a contribution to cephalopod welfare

Recent progress in animal welfare legislation relating to invertebrates has provoked interest in methods for the anesthesia of cephalopods, for which different approaches to anesthesia have been tried but in most cases without truly anesthetizing the animals. For example, several workers have used muscle relaxants or hypothermia as forms of "anesthesia." Several inhalational anesthetics are known to act in a dose-dependent manner on the great pond snail Lymnaea stagnalis, a pulmonate mollusk. Here we report, for the first time, on the effects of clinical doses of the well-known inhalational clinical anesthetic isoflurane on the behavioral responses of the common octopus Octopus vulgaris. In each experiment, isoflurane was equilibrated into a well-aerated seawater bath containing a single adult O. vulgaris. Using a web camera, we recorded each animal's response to touch stimuli eliciting withdrawal of the arms and siphon and observed changes in the respiratory rate and the chromatophore pattern over time (before, during, and after application of the anesthetic). We found that different animals of the same size responded with similar behavioral changes as the isoflurane concentration was gradually increased. After gradual application of 2% isoflurane for a maximum of 5 min (at which time all the responses indicated deep anesthesia), the animals recovered within 45-60 min in fresh aerated seawater. Based on previous findings in gastropods, we believe that the process of anesthesia induced by isoflurane is similar to that previously observed in Lymnaea. In this study we showed that isoflurane is a good, reversible anesthetic for O. vulgaris, and we developed a method for its use.

GABA(A)- and AMPA-like receptors modulate the activity of an identified neuron within the central pattern generator of the pond snail Lymnaea stagnalis

To examine the neurochemistry underlying the firing of the RPeD1 neuron in the respiratory central pattern generator of the pond snail, Lymnaea stagnalis, we examined electrophysiologically and pharmacologically either "active" or "silent" preparations by intracellular recording and pharmacology. GABA inhibited electrical firing by hyperpolarizing RPeD1, while picrotoxin, an antagonist of GABA(A) receptors, excited silent cells and reversed GABA-induced inhibition. Action potential activity was terminated by 1 mM glutamate (Glu) while silent cells were depolarized by the GluR agonists, AMPA, and NMDA. Kainate exerted a complex triphasic effect on membrane potential. However, only bath application of AMPA desensitized the firing. These data indicate that GABA inhibits RPeD1 via activation of GABA(A) receptors, while Glu stimulates the neuron by activating AMPA-sensitive GluRs.

Aripiprazole: the evidence of its therapeutic impact in schizophrenia

INTRODUCTION

An ideal antipsychotic would rapidly stabilize acute psychotic symptoms and maintain the patient, without relapse, for prolonged periods in the absence of extrapyramidal, endocrine, diabetic, or cardiovascular side effects, and without weight gain. The dopamine partial agonist aripiprazole is compared with this ideal and with conventional antipsychotics, such as haloperidol, and with atypical antipsychotics.

AIMS

To review the evidence for the clinical impact of aripiprazole in the treatment of patients with schizophrenia.

EVIDENCE REVIEW

There is clear evidence that aripiprazole is as effective as haloperidol in reducing the positive and negative symptoms of schizophrenia and schizoaffective disorder. In patients with schizophrenia, aripiprazole has been shown to stabilize acute psychotic symptoms, prevent relapse in stabilized patients, and maintain patients with schizophrenia following acute relapse. Furthermore, in common with other atypical antipsychotics, aripiprazole appears to be associated with a lower incidence of side effects than typical antipsychotics and may reduce discontinuation of drug therapy. Evidence also suggests that aripiprazole may be associated with a lower incidence of extrapyramidal symptoms than conventional antipsychotics, but further long-term studies concerning tardive dyskinesia are required. Studies on the cost effectiveness of aripiprazole, as well as the quality of life and general functioning of patients taking the drug are still required, although there is some evidence of improved quality of life. Further evidence comparing aripiprazole with other atypical antipsychotics would be welcome.

CLINICAL VALUE

In conclusion, aripiprazole is an atypical antipsychotic suitable for first-line use in patients with schizophrenia. Its clinical value in relation to other atypical antipsychotics remains to be elucidated.

Pramipexole in restless legs syndrome: an evidence-based review of its effectiveness on clinical outcomes

INTRODUCTION

Restless legs syndrome (RLS) affects 5-15% of adults, but is often unrecognized and consequently misdiagnosed. The International Restless Legs Scale (IRLS) has been developed and validated to assess the severity of RLS. Currently, the most common treatment for RLS is levodopa, but this may lead to augmentation of symptoms. Pramipexole has been developed as an alternative treatment for patients diagnosed with RLS.

AIMS

The objective of this article is to review the evidence of the effectiveness of pramipexole for the clinical management of patients with RLS.

EVIDENCE REVIEW

There is clear evidence that pramipexole reduces the leg movements associated with RLS, as measured by improvements in both the IRLS and the Clinical Global Impression (CGI) score. There is also moderate evidence that the drug improves sleep quality. Pramipexole clearly improves the anxiety and depression often associated with RLS. Augmentation may be associated with pramipexole treatment, but the evidence is contradictory and augmentation may be more associated with patients pretreated with levodopa or with patients with primary RLS rather than those with secondary RLS. Pramipexole therapy appears to be well tolerated, with only mild-to-moderate adverse events reported.

OUTCOMES SUMMARY

Pramipexole reduces leg movements in RLS, and is well tolerated. Further investigation is required to confirm the preliminary evidence that pramipexole restores normal sleep architecture and restores a normal quality of life in patients with RLS. Health economic studies would be valuable in demonstrating the true impact of pramipexole on the social burden of RLS.

Anesthetic treatment blocks synaptogenesis but not neuronal regeneration of cultured Lymnaea neurons

Trauma and injury necessitate the use of various surgical interventions, yet such procedures themselves are invasive and often interrupt synaptic communications in the nervous system. Because anesthesia is required during surgery, it is important to determine whether long-term exposure of injured nervous tissue to anesthetics is detrimental to regeneration of neuronal processes and synaptic connections. In this study, using identified molluscan neurons, we provide direct evidence that the anesthetic propofol blocks cholinergic synaptic transmission between soma-soma paired Lymnaea neurons in a dose-dependent and reversible manner. These effects do not involve presynaptic secretory machinery, but rather postsynaptic acetylcholine receptors were affected by the anesthetic. Moreover, we discovered that long-term (18-24 h) anesthetic treatment of soma-soma paired neurons blocked synaptogenesis between these cells. However, after several hours of anesthetic washout, synapses developed between the neurons in a manner similar to that seen in vivo. Long-term anesthetic treatment of the identified neurons visceral dorsal 4 (VD4) and left pedal dorsal 1 (LPeD1) and the electrically coupled Pedal A cluster neurons (PeA) did not affect nerve regeneration in cell culture as the neurons continued to exhibit extensive neurite outgrowth. However, these sprouted neurons failed to develop chemical (VD4 and LPeD1) and electrical (PeA) synapses as observed in their control counterparts. After drug washout, appropriate synapses did reform between the cells, although this synaptogenesis required several days. Taken together, this study provides the first direct evidence that the clinically used anesthetic propofol does not affect nerve regeneration. However, the formation of both chemical and electrical synapses is severely compromised in the presence of this drug. This study emphasizes the importance of short-term anesthetic treatment, which may be critical for the restoration of synaptic connections between injured neurons.

Seasonal plasticity of synaptic connections between identified neurones in Lymnaea

Here we investigate the synaptic connectivity of the giant dopamine containing neurone (RPeDI) of Lymnaea stagnalis during the winter months, in wild and laboratory bred animals. RPeD1 is one of the three neurones forming the respiratory central pattern generator (CPG) in Lymnaea and initiates ventilation under normal circumstances. Many of the follower cells of RPeD1 are ventilatory motor neurones. The connections of RPeD1 to its follower cells were investigated using standard intracellular recording techniques and dopamine was applied to the follower cells using a puffer pipette. During February and early March, RPeD1 was functionally disconnected from its follower cells, but connections reappeared towards the end of March. Most functionally disconnected cells failed to respond to applied dopamine, consistent with the hypothesis that there is down regulation of dopamine receptors in the follower cells of RPeD1 in the winter months. Behaviourally, Lymnaea that survive the winter, are not active at this time and do not indulge in lung ventilation, but stay quiescent. Thus functional disconnection of neurones from the CPG may be either a cause or a consequence of this change in behaviour.

Effect of volatile anaesthetics on the electrical activity and the coupling coefficient of weakly electrically coupled neurones

1. The application of the volatile anaesthetics, halothane and isoflurane (1% v/v and 2% v/v), to the CNS of Lymnaea reduced the firing frequency of the small weakly coupled pedal A cluster (PeA) neurones, which eventually become quiescent. There was no change in their resting membrane potential. 2. Met-enkephalin significantly increased the coupling coefficient between PeA neurones. 3. The volatile anaesthetics decreased the coupling coefficient even in the presence of met-enkephalin. 4. These effects were dose dependent and the effects of halothane were more rapid than those of isoflurane, reflecting their different anaesthetic potencies.

Modulation of reconstructed peptidergic synapses and electrical synapses by general anaesthetics

1. The actions of clinically relevant concentrations of general anaesthetics on reconstructed peptidergic synapses and electrical synapses in the intact brain of the mollusc Lymnaea stagnalis (L.) are described. 2. At identified, reconstructed, FMRFamidergic synapses, chemical synaptic transmission is completely blocked in 2% halothane. 3. Inhibitory postsynaptic responses to directly applied FMRFamide are maintained in 2% halothane and are enhanced in 1% halothane, unlike excitatory responses which are abolished at this concentration. 4. Met-enkephalin normally produces inhibitory responses on postsynaptic PeA neurones, but these are non-reversibly abolished by halothane, whose presence induces novel, dose-dependent, enkephalinergic depolarising responses. 5. The biophysical effects of volatile anaesthetics and sodium pentobarbital on neuronal membranes have been described and they are shown to have opposite dose-dependent effects on input resistance, input conductance and time constant of the electrically coupled neurones VD1 and RPD2. 6. Volatile anaesthetics decouple the neurones VD1 and RPD2 in a dose dependent manner, whilst sodium pentobarbital either enhances coupling or has no effect, depending on the concentration used.

Serotonergic innervation of the foot of the pond snail Lymnaea stagnalis (L.)

The aminergic innervation of the foot of Lymnaea stagnalis was investigated using electron microscopy, immunocytochemistry, and HPLC. The foot was found to contain large amounts of serotonin and dopamine, though at lower concentrations than are found in nervous tissue. Serotonin containing tissue was concentrated in the ventral surface of the foot, under ciliated areas of the epidermis where it occurred in varicosities, with fine tracts joining these varicosities. Varicosities also occurred in deeper tissues, probably adjacent to mucus cells. Positive fluorescence for serotonin in axons was found in nerves innervating the foot, but few neuronal cell bodies containing serotonin were detected, indicating that most of the innervation was coming from the central ganglia. Axon varicosities were found using TEM on ciliated cells, mucus cells, and muscle cells as well as interaxonal junctions (possibly non-synaptic) within nerves. The neuronal varicosities contacting the ciliated cells and mucus cells contained mostly dense-cored vesicles of between 60 and 100 nm in diameter. Smaller, lucent vesicles also occurred in these terminals. The origin and significance of this innervation is discussed. It is suggested that both serotonin and dopamine may play a large role in controlling ciliary gliding by the foot.

Low concentrations of caffeine raise intracellular calcium concentration only in the presence of extracellular calcium in cultured molluscan neurons

1. The effects of low concentrations of caffeine (100 and 300 microM) on the intracellular calcium concentration [Ca2+]i in four cultured, identified neurons of the pond snail Lymnaea stagnalis (L) were investigated. 2. Intracellular CA2+ levels in these neurons were measured with the cell-permeable Ca2+ indicator Fura-2/AM, both in the presence and absence of extracellular Ca2 (o-Ca2+/EGTA). 3. In the presence of Ca2+ in the external medium, caffeine was found to induce a substantial elevation in the free [Ca2+]i in all cell types. 4. In some cases, the rise in [Ca2+]i was found to be both time- and concentration-dependent. 5. Low doses of caffeine did not produce any appreciable rise in [Ca2+]i in the absence of Ca2+ in the external medium, but calcium was still available from stores, as clinical concentrations of halothane rose [Ca2+]i in the absence of extracellular calcium. 6. These results indicate that the actions of caffeine, when applied at low concentrations, are dependent on extracellular calcium.

Halothane affects both inhibitory and excitatory synaptic transmission at a single identified molluscan synapse, in vivo and in vitro

In the isolated CNS of Lymnaea, a peptidergic neuron termed VD4 makes monosynaptic connections with identified pedal A cluster neurons. In this study, the pedal A (PeA) neurons were further divided into two subgroups depending upon whether they received an inhibitory or excitatory input from VD4. PeA cells inhibited by VD4 were designated PeA(I), whereas those excited by VD4 were termed PeA(E). Both inhibitory and excitatory effects of VD4 stimulation on the PeA(I) and PeA(E) cells, respectively, were mimicked by exogenous FMRFamide in culture (in vitro), implicating this or a related peptide as the transmitter utilized at the VD4-to-PeA synapses. We tested the ability of the general anesthetic, halothane, to affect either the inhibitory or the excitatory peptidergic synapses between VD4 and the PeA neurons, both in the isolated CNS (in vivo) and at the in vitro reconstructed synapses. In the presence of 1% halothane, the excitatory synaptic potential between VD4 and the PeA(E) cells was either depressed or completely abolished, whereas the inhibitory synaptic potential between VD4 and the PeA(I) cells was unaffected in the presence of 1% halothane. The inhibitory potential between VD4 and the PeA(I) cells was, however, blocked in 2% halothane. In order to determine halothane' 5 site of action, exogenous FMRFamide was applied to both PeA(E) and PeA(I) cells in the presence of 1 or 2% halothane. In 1% halothane, the excitatory responses produced by FMRFamide were substantially reduced or abolished, whereas the inhibitory responses to FMRFamide were maintained and enhanced in duration in 1% halothane. In 2% halothane, the inhibitory responses to exogenous FMRFamide remained unchanged. It, therefore, appears that halothane exerts effects at both the pre- and postsynaptic level of the synapse, although presynaptic transmitter release is probably not substantially affected until a concentration of 2% halothane is reached. Our data provide the first evidence that clinically relevant concentrations of halothane (1-2%) affect both excitatory and inhibitory peptidergic synaptic transmission between identified neurons in the nervous system. Furthermore, excitatory transmission is abolished at lower anesthetic concentrations than inhibitory transmission.

Halothane-induced synaptic depression at both in vivo and in vitro reconstructed synapses between identified Lymnaea neurons

1. In the present study we tested the ability of the general anesthetic, halothane, to affect synaptic transmission at in vivo and in vitro reconstructed peptidergic synapses between identified neurons of Lymnaea stagnalis. 2. An identified respiratory interneuron, visceral dorsal 4 (VD4), innervates a number of postsynaptic cells in the central ring ganglia of Lymnaea. Because VD4 has previously been shown to exhibit immunoreactivity for FMRFamide-related peptides, it was hypothesized that these peptides may be utilized by VD4 during synaptic transmission. In the intact, isolated CNS of Lymnaea, we have identified novel connections between VD4 and the pedal A (PeA) cells. We demonstrate that VD4 makes inhibitory connections with the PeA neurons, in particular PeA4, and that these synaptic responses are mimicked by exogenous application of FMRFamide. 3. The synaptic transmission between VD4 and the PeA cells in an intact, isolated CNS preparation was completely blocked in 2%, but not 1% halothanc. Interestingly, the postsynaptic responses (PeA) to exogenous FMRFamide were maintained in the presence of both 1 and 2% halothane. 4. To determine the specificity of the observed responses and to determine the precise synaptic site of anesthetic action, we reconstructed the VD4/PeA synapses in vitro. After isolation from their respective ganglia, both cell types extended processes and established neuritic contact. We demonstrated that not only did the presynaptic neuron reestablish the appropriate inhibitory synapses with the PeA neurons, but that the PeA cells also maintained their responsiveness to exogenous FMRFamide. 5. Superfusion of the in vitro synaptically connected VD4 and PeA cells with 2% halothane completely abolished the synaptic transmission between these cells. However, even higher concentrations of 4% halothane failed to block the responsiveness of the PeA neurons to exogenous FMRFamide. Moreover, both 1 and 2% halothane enhanced the duration of the postsynaptic response to exogenously applied FMRFamide. These data suggest that the halothane-induced depression of synaptic transmission most likely occurred at the presynaptic level. 6. This study provides the first direct evidence that peptidergic transmission in the nervous system may also be susceptible to the actions of general anesthetics. In addition, we utilized a novel approach of in vitro reconstructed synapses for studying the effects of general anesthetics on monosynaptic transmission in the absence of other synaptic influences.

5-HT receptors on identified Lymnaea neurones in culture: pharmacological characterization of 5-HT3 receptors

1. The selective agonist, 1-(m-chlorophenyl)-biguanide (m-CPBG) and antagonist, 3-tropanyl-3,5-dichlorobenzoate (MDL 72222) were used to characterize the 5-HT3 receptors in cultured identified neurones; the serotonin-containing cerebral giant cells (CGCs) and some follower neurones in the buccal ganglia of Lymnaea stagnalis. 2. 5-HT and its agonists were pressure ejected, while the 5-HT antagonists were bath applied. 3. Although m-CPBG evoked mostly depolarizing responses, hyperpolarizing responses were sometimes evoked. 4. At 10(-4) M, m-CPBG failed to mimic the responses of 5-HT, but at a concentration higher, 10(-3) M, pressure-ejected m-CPBG mimicked most 5-HT responses. 5. The 5-HT2 antagonist ketanserin failed to block the m-CPBG-evoked responses, whilst partially blocking the 5-HT responses. 6. These results suggest the presence of 5-HT3 receptors similar to those found in mammalian neurones, and that multiple subtypes of these receptors may be present in Lymnaea neurones.

Optical monitoring of movements in small animals and in semi-intact preparations

A system has been developed for monitoring motor patterns both in small animals and in semi-intact preparations. Using a video recording system, the optical image of the selected object is projected onto a TV monitor to which is attached a pair of photosensitive resistors or diodes. The signals from the photosensor are amplified, filtered prior to being recorded, or stored using commercially available data capture systems. Use of the paired photosensitive elements allows us to avoid changes in background illumination, using a differential amplification function, during different patterns of activity of monitored organs or animals and also allows us to record activity from several different organs or systems simultaneously. The simplicity of the system enables us to perform simultaneous monitoring of both effector movements and neuronal activity via multi-channel microelectrode recordings. We have tested this system using semi-intact preparations of the freshwater pulmonate snail, Lymnaea stagnalis. Examples of different types of recordings are presented.

5-HT receptors on identified Lymnaea neurones in culture: pharmacological characterization of 5-HT2 receptors

1. Pressure ejection techniques were used to investigate the identify of receptors mediating 5-HT (5-Hydroxytryptamine) effects on the serotonin-containing cerebral giant cells (CGCs) of the cerebral ganglia and some of their follower motorneurones from the buccal ganglia of Lymnaea stagnalis in culture. 2. The vertebrate 5-HT2 receptor agonist alpha-methylserotonin maleate (10(-4) M), inhibited most of the neurones inhibited by 5-HT (10(-3) M). Others were excited by both agonists. In cells where 5-HT failed to evoke any effects, the 5-HT2 agonist also lacked an effect. 3. Bath application of the 5-HT2 receptor antagonists ketanserin and methysergide (10(-4) M), not only blocked spike generation, but also reduced both the excitatory and inhibitory responses to both 5-HT and alpha-methylserotonin maleate, while the 5-HT3 antagonist MDL 72222 (10(-4) M) failed to block alpha-methylserotonin maleate effects. 4. At 10(-3) M, alpha-methylserotonin maleate increased the amplitudes of the hyperpolarizing responses in a dose-dependent manner. These responses were blocked by ketanserin (10(-4) M). 5. The above results suggest that 5-HT2 receptors are involved in the responses of the CGCs and the buccal motorneurones to 5-HT in Lymnaea stagnalis. The pharmacological characterization of these receptors indicates that the compounds that interact with the 5-HT2 receptors in mammals also interact with the 5-HT2 receptors in molluscs.

Nitric oxide synthase-immunoreactive cells in the CNS and periphery of Lymnaea

The presence and distribution of nitric oxide synthase (NOS) in the CNS and peripheral organs (buccal muscles, oesophagus, salivary glands, foot, mantle and pneumostome) of the pulmonate mollusc, Lymnaea stagnalis were studied using an antiserum developed against rat cerebellar NOS. NOS-immunopositive neurones in Lymnaea were localized predominantly in the buccal ganglia as well as in distinct areas of the cerebral and suboesophageal ganglia. NOS-immunoreactive terminals were also found on the somata of some central neurones. In the periphery, NOS-immunostaining was detected only in a few neurones in the pneumostome area and in the osphradial ganglion. In addition, approximately 100 NOS-immunopositive cells have been found in the salivary glands. Our data supports other recent reports indicating that NO may be a signal molecule in the CNS of molluscs.

Effects of met-enkephalin on electrical coupling between identified neurons in the pulmonate snails, Helix and Lymnaea

1. The effects of met-enkephalin on electrical coupling between molluscan neurons have been investigated using the isolated brains of Helix pomatia and Lymnaea stagnalis. 2. In the presence of both serotonin and met-enkephalin, non-rectifying electrical coupling is strongly facilitated between identified respiratory neurons in Helix, whilst coupling between putative, serotonin-containing, ciliomotoneurons in Lymnaea is facilitated by met-enkephalin alone. 3. Facilitation of coupling by met-enkephalin is weaker in the strongly coupled neurons, VD1/RPaD2 of Lymnaea. 4. These data suggest that met-enkephalin can modulate different groups of electrically coupled cells and may be involved in coordination of motor patterns.

Nitric oxide activates buccal motor patterns in Lymnaea stagnalis

The mollusc, Lymnaea stagnalis, has been used as a model to study the mechanisms of nitric oxide (NO)-dependent processes in the CNS. Putative NO-containing neurones in Lymnaea are localized in the buccal ganglia, predominantly in areas where sensory neurones known to regulate feeding are found. The NO-generating substance, S-nitrosocysteine (S-NC, 5 x 10(-5)-10(-3 M) activates feeding movements of the buccal mass and modulates the activity of buccal motoneurones. An inhibitor of NO synthase, NG-methyl-L-arginine (10(-4) M) decreases the frequency of background buccal movements and has opposite effects to S-NC on the buccal motoneurones. We suggest that NO is a messenger in the CNS of Lymnaea and may be involved in coordination of feeding motor patterns.

Differential effects of general anaesthetics on identified molluscan neurones in situ and in culture

1. The only unifying principle of general anaesthesia is that general anaesthetics interact with membrane components and no single cellular mechanism appears to explain their widespread effects in the central nervous system. 2. The gastropod mollusc, Lymnaea stagnalis, provides an excellent model system for studies on general anaesthetics because it has large, uniquely identifiable nerve cells. Several of these cells are interneurones with identified neurotransmitters and monosynaptic connections to other cells. 3. Recent work on Lymnaea neurones suggests that calcium currents are depressed by volatile general anaesthetics applied in the clinical range, whilst evidence from other preparations indicates that there is a rise in intracellular calcium concentration following application of these substances. 4. Identified Lymnaea neurones have different responses to applied anaesthetics, irrespective of the anaesthetic used. Following application of halothane, barbiturates and several other anaesthetic agents, some cells gradually become quiescent after a short period, whilst in others a series of paroxysmal depolarizing shifts occur prior to quiescence. 5. Cultured neurones of Lymnaea, Helisoma and related species retain their characteristic action potential types and neurotransmitter identity. Their responses to anaesthetics are similar to those in the intact brain. They may also form synapses in culture. Thus, they are a useful tool for studying the cellular and subcellular actions of general anaesthetics.

Respiratory behaviour in Lymnaea stagnalis: pharmacological and cellular analyses

Using pharmacological and microelectrode approaches, evidence is presented here to suggest that exogenously applied dopamine can coordinate respiratory behavioural patterns and that its effects are reproduced using transmitter precursor such as L-DOPA. It is possible that dopamine reproduces sensory inputs to the respiratory network. Interactions between different transmitter substances underlie modifications of rhythmic discharges and enkephalins are able to modulate the respiratory rhythm.

Coordination of locomotor and cardiorespiratory networks of Lymnaea stagnalis by a pair of identified interneurones

1. The morphology and electrophysiology of a newly identified bilateral pair of interneurones in the central nervous system of the pulmonate pond snail Lymnaea stagnalis is described. 2. These interneurones, identified as left and right pedal dorsal 11 (L/RPeD11), are electrically coupled to each other as well as to a large number of foot and body wall motoneurones, forming a fast-acting neural network which coordinates the activities of foot and body wall muscles. 3. The left and right sides of the body wall of Lymnaea are innervated by left and right cerebral A cluster neurones. Although these motoneurones have only ipsilateral projections, they are indirectly electrically coupled to their contralateral homologues via their connections with L/RPeD11. Similarly, the activities of left and right pedal G cluster neurones, which are known to be involved in locomotion, are also coordinated by L/RPeD11. 4. Selective ablation of both neurones PeD11 results in the loss of coordination between the bilateral cerebral A clusters. 5. Interneurones L/RPeD11 are multifunctional. In addition to coordinating motoneuronal activity, they make chemical excitatory connections with heart motoneurones. They also synapse upon respiratory motoneurones, hyperpolarizing those involved in pneumostome opening (expiration) and depolarizing those involved in pneumostome closure (inspiration). 6. An identified respiratory interneurone involved in pneumostome closure (visceral dorsal 4) inhibits L/RPeD11 together with all their electrically coupled follower cells. 7. Both L/RPeD11 have strong excitatory effects on another pair of electrically coupled neurones, visceral dorsal 1 and right parietal dorsal 2, which have previously been shown to be sensitive to changes in the partial pressure of environmental oxygen (PO2). 8. Although L/RPeD11 participate in whole-body withdrawal responses, electrical stimulation applied directly to these neurones was not sufficient to induce this behaviour.