Novel method of monitoring electroencephalography at the site of microdialysis during chemically evoked seizures in a freely moving animal

Allosteric Modulators of Sigma-1 Receptor: A Review

Allosteric modulators of sigma-1 receptor (Sig1R) are described as compounds that can increase the activity of some Sig1R ligands that compete with (+)-pentazocine, one of the classic prototypical ligands that binds to the orthosteric Sig1R binding site. Sig1R is an endoplasmic reticulum membrane protein that, in addition to its promiscuous high-affinity ligand binding, has been shown to have chaperone activity. Different experimental approaches have been used to describe and validate the activity of allosteric modulators of Sig1R. Sig1R-modulatory activity was first found for phenytoin, an anticonvulsant drug that primarily acts by blocking the voltage-gated sodium channels. Accumulating evidence suggests that allosteric Sig1R modulators affect processes involved in the pathophysiology of depression, memory and cognition disorders as well as convulsions. This review will focus on the description of selective and non-selective allosteric modulators of Sig1R, including molecular structure properties and pharmacological activity both in vitro and in vivo, with the aim of providing the latest overview from compound discovery approaches to eventual clinical applications. In this review, the possible mechanisms of action will be discussed, and future challenges in the development of novel compounds will be addressed.

Correlations between acetylcholinesterase inhibition, acetylcholine levels and EEG changes during perfusion with neostigmine and N6-cyclopentyladenosine in rat brain

Organophosphate poisoning can result in seizures and subsequent neuropathology. In order to improve treatment strategies in organophosphate intoxication, the relationship between acetylcholinesterase inhibition, extracellular levels of acetylcholine, and electroencephalogram (EEG) changes was investigated during local perfusion of the reversible acetylcholinesterase inhibitor neostigmine in the hippocampus and striatum of freely moving rats. Acetylcholinesterase activity and acetylcholine levels were measured by microdialysis, and EEG signals were recorded from an electrode placed near the microdialysis probe. A non-linear relationship between the acetylcholinesterase activity and the extracellular amount of acetylcholine was found, the latter being approximately three times higher in the striatum than in the hippocampus upon infusion with 10(-4) M neostigmine. Highly accumulated extracellular acetylcholine significantly correlated with significant relative power increases of the EEG-gamma2-band and a significant relative power decrease in the beta2-band. Co-infusion of the adenosine A1 agonist N6-cyclopentyladenosine partly prevented acetylcholine accumulation, rendered both powers towards control values, and abolished the acetylcholine-EEG correlation. In view of the latter relationship, it is concluded that prevention of acetylcholine accumulation as a concept for neuroprotection in case of organophosphate poisoning, is worth to be further investigated.

Preparation for the in vivo recording of neuronal responses in the visual cortex of anaesthetised marmosets (Callithrix jacchus)

The marmoset is becoming an important model for studies of primate vision, due to factors such as its small body size, lissencephalic brain, short gestational period and rapid postnatal development. For many studies of visual physiology (including single-cell recordings), it is a requirement that the animal is maintained under anaesthesia and neuromuscular block in order to ensure ocular stability. However, maintaining such a small animal (290-400 g) in good physiological condition for long periods requires expert attention. This becomes particularly important in the case of recordings from visual association cortex, where neuronal responses are known to be highly sensitive to factors such as the type and dose of anaesthetic, and the animal's physiological balance. The present protocol summarises our laboratory's experience over the last decade in developing a preparation for the study of marmoset visual cortex. It allows excellent recording from extrastriate areas for periods of at least 48 h, including the continuous study of isolated single cells for several hours.

Intracerebral microdialysis: 30 years as a tool for the neuroscientist

1. Microdialysis is an established technique for studying physiological, pharmacological and pathological changes of a wide range of low molecular weight substances in the brain extracellular fluid. Many studies have proven its sensitivity in sampling the extracellular space in discrete brain locations, such as the striatum, and monitoring the action of exogenous substances. 2. The two main areas of application of microdialysis are the recovery of endogenous substances, primarily the neurotransmitters, and the infusion of drugs through the microdialysis cannula (retrodialysis). 3. Microdialysis in awake animals is the tool of choice for studying the relationship between changes in behaviour and neurotransmitters in certain brain areas. In addition, the concomitant recording of the electroencephalogram at the site of microdialysis has been shown to be extremely useful in determining the role of certain neurotransmitters in paroxysmal activity. 4. Clinical applications of microdialysis have included monitoring of ischaemic injury, subarachnoid haemorrhage, trauma and epilepsy. With the recent availability of standardized equipment, the use of microdialysis in the neurological clinic is likely to become more common.

EEG measurements by means of radiotelemetry after intracerebroventricular (ICV) cannulation in rodents

The utility of implanted radiotelemetry transmitters for the measurement of electroencephalogram (EEG), locomotor activity, body temperature and cardiovascular parameters has been well documented. This paper focuses on the methodology, of combining radiotelemetry with intracerebroventricular (ICV) cannulation. The two excitatory neuropeptides, orexin-A and orexin-B, can only be given by ICV injection, therefore we examined their effects on the normal sleep-wake cycle of rodents in the present study. The effects of orexins on sleep architecture have been extensively studied in tethered models demonstrating increased levels of wakefulness. In this study, both orexin neuropeptides, especially orexin-A, increase wakefulness within the first sleep period followed by an increase in slow wave (SW) sleep and paradoxical sleep (PS), towards the end of a 5-h recording period which may be a rebound phenomena. The present study has demonstrated that ICV cannulation can be used effectively in studying the effects of pharmacological agents on the sleep-wake cycle of rodents by measuring EEG and EMG by radiotelemetry.

A simple method for measuring EEG in freely moving guinea pigs

This paper describes a method of measuring EEG in guinea pigs by means of temporarily attached superficial electrodes with radiotelemetry equipment. This represents an alternative approach to more conventional methods of monitoring EEG in animals, which necessitate surgical implantation of electrodes. The novel approach of using superficial electrodes was compared with the cortical screw electrode technique, in a nerve agent-induced seizure model. In both cases, radiotelemetry techniques were used for data capture to facilitate monitoring of nerve agent-induced seizures in freely moving non-tethered guinea pigs. The advantages and disadvantages of the technique are discussed, for example the saving in resources and the benefits to animal welfare.

SCH 23390 affords protection against soman-evoked seizures in the freely moving guinea-pig: a concomitant neurochemical, electrophysiological and behavioural study

We studied the role of striatal dopamine (DA) release in seizure activity evoked by the subcutaneous administration of the cholinesterase inhibitor pinacolyl methylphosphonofluoridate (soman), in the guinea-pig. The involvement of the dopamine receptor subtypes was studied by systemic administration of the D(1)-like receptor antagonist SCH 23390 (0.5 mg kg(-1)) or the D(2)-like receptor antagonist sulpiride (30 mg kg(-1)). Microdialysis and HPLC with electrochemical detection were used to monitor changes in extracellular levels of striatal DA and its metabolites, acetylcholine and choline. These data were correlated with changes in the striatal and cortical electroencephalogram and observation of predefined clinical signs. We found that the blockade of the D(1) receptor with SCH 23390 can inhibit seizure activity, while blockade of the D(2) receptor with sulpiride can augment the evoked seizure activity. These results clarify the involvement of the dopaminergic system in soman-evoked seizures.

Changes in striatal electroencephalography and neurochemistry induced by kainic acid seizures are modified by dopamine receptor antagonists

We investigated the involvement of striatal dopamine release in electrographic and motor seizure activity evoked by kainic acid in the guinea pig. The involvement of the dopamine receptor subtypes was studied by systemic administration of the dopamine D(1) receptor antagonist, R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390; 0.5 mg kg(-1)), or the dopamine D(2) antagonist, (5-aminosulphonyl)-N-[(1-ethyl-2-pyrrolidinyl)-methyl]-2-methoxybenzamide (sulpiride, 30 mg kg(-1)). Microdialysis and high performance liquid chromatography were used to monitor changes in extracellular levels of striatal dopamine and its metabolites, glutamate, aspartate and gamma-amino-butyric acid (GABA). These data were correlated with changes in the striatal and cortical electroencephalographs and clinical signs. We found that, although neither dopamine receptor antagonist inhibited behavioural seizure activity, blockade of the dopamine D(1)-like receptor with SCH 23390 significantly reduced both the 'power' of the electrical seizure activity and the associated change in extracellular striatal concentration of glutamate, whilst increasing the extracellular striatal concentration of GABA. In contrast, blockade of the dopamine D(2)-like receptor with sulpiride significantly increased the extracellular, striatal content of glutamate and the dopamine metabolites. These results confirm previous evidence in other models of chemically-evoked seizures that antagonism of the dopamine D(1) receptor tends to reduce motor and electrographic seizure activity as well as excitatory amino-acid transmitter activity, while antagonism of the dopamine D(2) receptor has relatively less apparent effect.

SCH 23390: the first selective dopamine D1-like receptor antagonist

SCH 23390, the halobenzazepine (R)-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5- tetrahydro-1H-3-benzazepine, is a highly potent and selective dopamine D1-like receptor antagonist with a K(i) of 0.2 and 0.3 nM for the D1 and D5 dopamine receptor subtypes, respectively. In vitro, it also binds with high affinity to the 5-HT2 and 5-HT1C serotonin receptor subtypes. However, the doses required to induce a similar response in vivo are greater than 10-fold higher than those required to induce a D1-mediated response. Previous in vivo pharmacological studies with SCH 23390 have shown it to abolish generalized seizures evoked by the chemoconvulsants: pilocarpine and soman. These studies provide evidence of the potential importance of D1-like dopaminergic receptor mechanisms in facilitating the initiation and spread of seizures. The inference from a majority of studies is that the activation of dopamine D1 receptors facilitates seizure activity, whereas activation of D2 receptors may inhibit the development of seizures. SCH 23390 has also been used in studies of other neurological disorders in which the dopamine system has been implicated, such as psychosis and Parkinson's disease. Apart from the study of neurological disorders, SCH 23390 has been extensively used as a tool in the topographical determination of brain D1 receptors in rodents, nonhuman primates, and humans. In summary, SCH 23390 has been a major tool in gaining a better understanding of the role of the dopamine system, more specifically the D1 receptor, in neurological function and dysfunction.