Interaction of Noradrenergic and Cholinergic Agonists with Ligands Increasing K-conductance of Guinea Pig Hippocampal Neurons, in vitro

Single electrode current clamp and voltage clamp recordings were employed to study the effects of noradrenergic agonists and a cholinergic agonist (carbachol, Cch) on the resting membrane potential of CA3 neurons in guinea pig hippocampal slices. Stimulation of muscarinic and beta-adrenergic receptors depolarized, and stimulation of alpha1-adrenergic receptor hyperpolarized, CA3 neurons but the membrane potential changes were small. Hyperpolarizations or outward currents induced by baclofen, adenosine or serotonin (5-HT) were strongly potentiated by alpha-noradrenergic agonists and suppressed by Cch at concentrations ten times lower than those having any direct effects on membrane potential. Both the enhancement of the baclofen-induced hyperpolarization by phenylephrine and its suppression by Cch were pronounced at low concentrations of baclofen, but diminished at higher concentrations. The modulatory effects persisted after blockade of sodium spikes by tetrodotoxin and after blockade of fast inhibitory and excitatory synaptic transmission by picrotoxin and 6-cyano-7-nitroquinoxaline-2,3-dione. Our data suggest that, through the postsynaptic interaction with ligands activating potassium conductance, noradrenergic and muscarinic receptor stimulation can exert a stronger inhibitory and excitatory effect on CA3 pyramidal neurons at their resting membrane potential than would be expected from the changes in membrane potential induced by these neuromodulators on their own.

Functional and biological test of a 20 channel implantable stimulator in sheep in view of functional electrical stimulation walking for spinal cord injured persons

A newly developed implantable stimulator with 20 output channels, mainly intended for the stimulation of lower extremities in paraplegics, was implanted in 6 sheep over a time period of 26 weeks. Five epineural electrodes each were used to contact various nerves at different locations to elicit hip and knee extension and flexion and to make carrousel and selective stimulation possible. Different electrode application strategies in view of paraplegic standing and walking were investigated. Additional implanted electrodes allowed M-wave monitoring for selectivity investigations in 3 sheep. Stimulator, electrode leads, and electrodes proved to be reliable. Selective stimulation with electrodes placed on the trunk of the sciatic nerve could be demonstrated but with bad reproducibility. Histological investigation of the tissues surrounding electrodes and leads showed the expected stable foreign body response. Strong hip and knee extension could be gained in all cases while only weak flexion forces could be elicited in most cases. Muscle biopsies showed that daily stimulation for 8 h at threshold level caused an increase in muscle Type I fibers and a decrease in Type IIc fibers. Implants and electrodes fulfill the most important functional and biological criteria for their clinical application for paraplegic walking. The intention to provide selective flexion functions via epineural stimulation could not be demonstrated sufficiently in this animal model.

Different receptor subtypes are involved in the serotonin-induced modulation of epileptiform activity in rat frontal cortex in vitro

The frontal cortex is innervated by serotonergic terminals from the raphe nuclei and it expresses diverse 5-HT receptor subtypes. We investigated the effects of 5-HT and different 5-HT receptor subtype-selective agonists on spontaneous discharges which had developed in rat cortical slices perfused with a Mg2+-free medium and the GABA(A) receptor antagonist picrotoxin. The frequency of synchronous discharges, recorded extracellularly in superficial layers (II/III) of the frontal cortex, was dose-dependently enhanced by 5-HT (2.5-40 microM). That excitatory effect was blocked by the 5-HT2 receptor selective antagonist ketanserin. The 5-HT2A/2C receptor-selective agonist DOI and the 5-HT4 receptor agonist zacopride also increased the frequency of spontaneous discharges. In the presence of ketanserin, 5-HT decreased the discharge rate; a similar effect was observed when the 5-HT1A receptor agonist 8-OH-DPAT or the 5-HT1B receptor agonist CGS-12066B was applied. The 5-HT3 receptor agonist m-CPBG was ineffective. In conclusion, 5-HT produces multiple effects on epileptiform activity in the frontal cortex via activation of various 5-HT receptor subtypes. The excitatory action of 5-HT, which predominates, is mediated mainly by 5-HT2 receptors. The inhibitory effects can be attributed to activation of 5-HT1A and 5-HT1B receptors.

Pruritometer 2: portable recording system for the quantification of scratching as objective criterion for the pruritus

Studies to evaluate therapies for itching (pruritus) related diseases often require the quantification of the itch sensation. Like all subjective symptoms the evaluation of itching is difficult and can only be done indirectly. With the Pruritometer 2 a measuring system is introduced that evaluates itching by detecting scratching movements. Based on the Pruritometer 1, that processes the signals of a piezoelectric vibration sensor, fixed on the midfinger of the patients dominant hand, and triggers a simple counter, the Pruritometer 2 allows to store the scratch activity during a 24 hours period. For each adjustable time slice of this time period, the amount of scratches and the scratch intensity are recorded. All data can be transferred to a PC via infrared link for further processing with a standard software package. An additional PC-software allows to set various parameters for optimal scratch detection and to test the patient attached system, also via the infrared link. All electronic components are shockproof encapsulated in a milled housing and are attached to a textile watchstrap that is worn by the patient like a wristwatch.

Opposite effects of antidepressants and corticosterone on the sensitivity of hippocampal CA1 neurons to 5-HT1A and 5-HT4 receptor activation

Using extracellular and intracellular ex vivo recording techniques we studied changes in the reactivity of hippocampal pyramidal CA1 neurons to serotonin (5-HT) and to the 5-HT1A- and 5-HT4 receptor agonists (+/-)-2-dipropylamino-8-hydroxy- 1,2,3 ,4-tetrahydronaphthalene hydrobromide (8-OH-DPAT) and zacopride, respectively, evoked by repeated electroconvulsive shock (ECS), imipramine and corticosterone treatments. Rats were subjected to ECS for 1 or 10 days, treated with imipramine for 1, 7, 14 or 21 days (10 mg/kg p.o., twice daily) and with corticosterone for 7 days (10 mg/kg s.c., twice daily). Hippocampal slices were prepared 2 days after the last treatment. Activation of 5-HT1A receptors decreased the amplitude of population spikes evoked by stimulation of the Schaffer/collateral-commissural pathway and hyperpolarized CA1 cells. Activation of 5-HT4 receptors increased the population spike amplitude and decreased the amplitude of slow afterhyperpolarization. Both repeated ECS and imipramine enhanced the effects related to 5-HT1A receptor activation and attenuated the effects of 5-HT4 receptor activation. The action of imipramine was significant after a 7-day treatment and reached a maximum after 14 daily applications, remaining at the same level in a group of animals treated for 21 days. Repeated corticosterone attenuated the inhibitory effect of 5-HT and 8-OH-DPAT on the population spike amplitude and enhanced the increase in population spike amplitude induced by zacopride. These findings indicate that antidepressant treatments and repeated corticosterone have opposite effects on hippocampal responsiveness to 5-HT1A and 5-HT4 receptor activation. In consequence, antidepressants enhance, whereas corticosterone reduces the 5-HT-mediated inhibition of hippocampal CA1 cells, which may be relevant to the antidepressant and pro-depressant effects of either treatment, respectively.

[Electrophysiologic tests for testing the effects of antidepressant drugs and corticosterone on reactivity of serotonin receptors in the hippocampus]

Disturbances in the serotonin (5-HT) system and the limbic-hypothalamo-pituitary-adrenal axis (LHPA) have been implicated in the pathophysiology of depression. It is well established that hippocampus is a central component of limbic circuitry that participates in the modulation of cognition, mood and behavior, and is involved in the control of the LHPA axis. Therefore, the hippocampus provides a unique environment to study the interplay between serotonergic system, antidepressants and corticosteroids. Activity of hippocampal cells can be modulated by 5-HT via inhibitory 5-HT1A and excitatory 5-HT4 receptors. Repeated treatment with antidepressants increases the responsiveness of hippocampal pyramidal neurons to the 5-HT1A and attenuates the responsiveness to the 5-HT4 receptor agonists, with a time course which correlates with the delayed onset of the therapeutic effect of antidepressants in humans. Moreover, repeated corticosterone, which may constitute a model of a prolonged nonadaptable stress, has opposite effect on hippocampal responsiveness to the 5-HT1A and 5-HT4 receptor activation. Such an action results in an enhancement of the 5-HT-mediated inhibition by antidepressants and a reduction in the inhibitory effect of 5-HT by corticosterone which may be relevant to antidepressant/antiaxiety and proaxiety effects, respectively, of both treatments.

Basic design and construction of the Vienna FES implants: existing solutions and prospects for new generations of implants

We can distinguish 3 generations of FES implants for activation of neural structures: 1. RF-powered implants with antenna displacement dependent stimulation amplitude; 2. RF-powered implants with stabilised stimulation amplitude; and 3. battery powered implants. In Vienna an 8-channel version of the second generation type has been applied clinically to mobilisation of paraplegics and phrenic pacing. A 20-channel implant of the second generation type for mobilisation of paraplegics and an 8-channel implant of the third generation type for cardiac assist have been tested in animal studies. A device of completely new design for direct stimulation of denervated muscles is being tested in animal studies. There is a limited choice of technologically suitable biocompatible and bioresistant materials for implants. The physical design has to be anatomically shaped without corners or edges. Electrical conductors carrying direct current (D.C.) have to be placed inside a hermetic metal case. The established sealing materials, silicone rubber and epoxy resin, do not provide hermeticity and should only embed DC-free components. For electrical connections outside the hermetic metal case welding is preferable to soldering; conductive adhesives should be avoided. It is advisable to use a hydrophobic oxide ceramic core for telemetry antenna coils embedded in sealing polymer. Cleaning of all components before sealing in resin is of the utmost importance as well as avoidance of rapid temperature changes during the curing process.

Neuropeptide Y reduces epileptiform discharges and excitatory synaptic transmission in rat frontal cortex in vitro

Neuropeptide Y reduced spontaneous and stimulation-evoked epileptiform discharges in rat frontal cortex slices perfused with a magnesium-free solution and with the GABA(A) receptor antagonist picrotoxin. To investigate the mechanism of that action, effects of neuropeptide Y on intrinsic membrane properties and synaptic responses of layer II/III cortical neurons were studied using intracellular recording. Neuropeptide Y (1 microM) had no detectable effect on the membrane properties of neurons. The evoked synaptic potentials were attenuated by neuropeptide Y. Moreover, the pharmacologically isolated excitatory postsynaptic potentials, mediated by N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors, were reversibly depressed by neuropeptide Y. The most pronounced inhibitory effect of neuropeptide Y was observed on late polysynaptic excitatory postsynaptic potentials. To assess a putative postsynaptic action of neuropeptide Y, N-methyl-D-aspartate was locally applied in the presence of tetrodotoxin. The N-methyl-D-aspartate-evoked depolarizations were unaffected by neuropeptide Y, which suggests that the depression of excitatory postsynaptic potentials was due to an action at sites presynaptic to the recorded neurons. These data show that neuropeptide Y attenuates epileptiform discharges and the glutamate receptor-mediated synaptic transmission in the rat frontal cortex. The above results indicate that neuropeptide Y may regulate neuronal excitability within the cortex, and that neuropeptide Y receptors are potential targets for an anticonvulsant therapy.

[EMG monitoring in functional electrostimulation]

When using functional electrical stimulation (FES), correct adjustment of stimulation parameters, and monitoring of the stimulated muscle is mandatory if tissue damage is to be avoided. Although several FES systems are already in regular use, a method for direct muscle monitoring is still lacking. This paper investigates the suitability of the electromyogram (EMG) for such a purpose. In six sheep, the right latissimus dorsi muscle (LDM) and the associated thoracodorsal nerve were exposed. Stimulation was effected via electrodes placed on the nerve. Three electrodes were placed in the LDM for EMG recording, and the tendon was connected to a force transducer for isometric force measurement. Stimulation was applied for one second (burst), followed by a three-second pause. The stimulation current was increased in 0.2 mA steps, starting at 0 mA and ending at 4 mA. Throughout the investigation, the EMG signal was monitored with an oscilloscope. In addition, the EMG signal and the force transducer signal were recorded for subsequent analysis. An analysis of the data of all six sheep revealed an almost linear relationship between muscle force and m-wave amplitude (magnitude of r = 0.95, p < 0.001). M-wave monitoring during EMG recording with three intramuscular electrodes is a reliable method of monitoring FES-induced muscle activity, but the absolute force cannot be measured.

Roles of group II metabotropic glutamate receptors in modulation of seizure activity

Evidence suggests that metabotropic glutamate receptors (mGluR) are involved in mediating seizures and epileptogenesis. In the present experiments, the selective, group II mGluR agonist (+)-2-aminobicyclo-[3.1.0]hexane-2,6-dicarboxylic acid (LY354740, 0.1-1.0 microM) inhibited spontaneous epileptiform discharges which developed in rat cortical slices in Mg2+-free medium. LY354740 (4-16 mg/kg) administered prior to an injection of pentylenetetrazol (80 mg/kg) or picrotoxin (3.2 mg/kg) produced a dose-dependent decrease in the number of mice exhibiting clonic convulsions, but had no effect on N-methyl-D-aspartate (NMDA, 150 mg/kg)-induced convulsions. LY354740 (4-16 mg/kg) did not affect lethality induced in mice by pentylenetetrazol, picrotoxin or NMDA. LY354740 potentiated the anticonvulsant activity of the conventional antiepileptic drug diazepam, significantly decreasing the ED50 for that drug's effect on pentylenetetrazol-induced convulsions by 30%, but had no influence on anticonvulsant activity of ethosuximide and valproic acid. A pharmacokinetic interaction between LY354740 and diazepam, leading to the lowering of the plasma level of free diazepam, was also demonstrated. Our data suggest that the group II mGluR agonist LY354740 possesses anti-seizure activity and may modify the effects of some conventional antiepileptic drugs.

Repeated corticosterone administration increases excitatory effect of 5-HT4 receptor agonist in the rat hippocampus

The objective of the present study was to investigate whether repeated exposure of rats to high level of corticosterone affects responses of CA1 hippocampal cells to the 5-HT4 receptor agonist zacopride. To assess responsiveness of CA1 neurons to zacopride we used extracellular recording of population spikes evoked in CA1 cells by the stimulation of the Schaffer/collateral-commissural pathway in hippocampal slices. Rats were treated with corticosterone for 7 days (10 mg/kg sc, twice daily), slices were prepared two days after the last treatment. Zacopride induced an increase in the amplitude of population spike and repeated corticosterone treatment enhanced this excitatory effect. It is concluded that repeated treatment with corticosterone increases the responsiveness of hippocampal CA1 neurons to the 5-HT4 receptor activation.

An antidepressant-induced decrease in the responsiveness of hippocampal neurons to group I metabotropic glutamate receptor activation

Imipramine, a serotonin and noradrenaline uptake inhibitor, is the prototypical tricyclic antidepressant. The effects of imipramine on neuronal responsiveness to the group I glutamate metabotropic (mGlu) receptor agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) were studied ex vivo, in the CA1 area of rat hippocampus, using extracellular and intracellular recording. DHPG increased the population spike amplitude, depolarized CA1 cells and decreased the slow afterhyperpolarization. Imipramine (20 microM) administered acutely in vitro did not change the effect of DHPG on population spikes. Repeated treatment with imipramine (10 mg/kg, twice daily, for 14 days) significantly attenuated the enhancing effect of DHPG (2.5 and 5 microM) on population spikes, as well as the DHPG-induced depolarization and the decrease in the slow afterhyperpolarization. Repeated treatment with imipramine had no effect on passive or active membrane properties of CA1 pyramidal cells. The results of the time-course experiment demonstrated that the imipramine-induced decrease in the responsiveness of CA1 cells to DHPG was apparent after a 7-day treatment; there was a further decrease after 14 days of treatment to a level which was not changed by longer (21-day) administration of imipramine. The attenuation of neuronal responsiveness to DHPG induced by a 14-day treatment was still detectable 7 days after imipramine withdrawal. It is concluded that repeated treatment with imipramine induces a decrease in the responsiveness of rat CA1 hippocampal neurons to group I mGlu receptor activation with a time course which correlates with the delayed onset of the therapeutic effect of antidepressants in humans. This suggests that alterations in mGlu receptors may contribute to antidepressant efficacy.

Imipramine-induced increase in the inhibitory effect of adenosine receptor activation in the hippocampus

Imipramine, a tricyclic antidepressant, is one of the main drugs used for the treatment of depression. We investigated the effects of the repeated administration of imipramine (10 mg/kg po for 14 days, twice daily) on adenosine receptor-mediated actions using extracellular and intracellular recording techniques in the rat hippocampal slices. Adenosine and 2-chloroadenosine dose-dependently decreased the amplitude of population spikes and the slope of the field excitatory postsynaptic potentials (fEPSPs) evoked in the CA1 cell layer and apical dendrites of the CA1 cells, respectively, by stimulation of the Schaffer collateral/commissural pathway. As revealed by intracellular recording, a membrane hyperpolarization and a strong attenuation of excitatory synaptic transmission contribute to the decrease in the population spikes and fEPSPs induced by adenosine and 2-chloroadenosine. The repeated administration of imipramine enhanced the effect of adenosine (3 microM) and 2-chloroadenosine (0.15 microM) on fEPSPs while the inhibition of population spikes was not changed. When higher concentration of 2-chloroadenosine (0.25 microM) was tested, repeated imipramine administration enhanced its inhibitory effect on population spikes but not on fEPSPs. The present report provides evidence that the inhibitory effect of adenosine receptor activation in the hippocampus is enhanced by repeated treatment with imipramine.

Long-term electromyogram recording from the posterior cricoarytenoid muscle as a potential biological trigger for phrenic pacing: results of an animal study

Diaphragm pacing has been used to restore respiration in approximately 1,000 patients worldwide suffering from high quadriplegia or from central alveolar hypoventilation syndrome. Compared with conventional mechanical ventilation, electrophrenic respiration (EPR) reduces the risk of pulmonary infections and increases the mobility of patients. Voluntary activation of the pacemaker during speech would improve patients' quality of life and allow application of EPR in a more physiological way. An animal study was performed to investigate the electromyogram (EMG) of the posterior cricoarytenoid (PCA) muscle and the movement of the glottis via impedance measurement (electroglottography) with the aim to examine reproducibility and stability of the recordings from the PCA muscle as a potential biological trigger for a phrenic pacemaker. The EMG of the PCA muscle was recorded via implanted electrodes for a 200 day period. The EMG signal proved stable for that period, artifacts caused by movements can be suppressed, and swallowing can be detected. In contrast, impedance measurement to detect movement of the glottis proved not useful. Based on the results of this study, the use of the PCA EMG as a biological trigger for a phrenic pacemaker has to be considered a realistic option.

Neuropeptide Y suppresses epileptiform activity in rat frontal cortex and hippocampus in vitro via different NPY receptor subtypes

Neuropeptide Y (NPY) and different NPY receptor (Y) subtype-selective agonists were tested for their effects on spontaneous epileptiform discharges which developed in rat cortical and hippocampal slices in Mg(2+)-free medium. Epileptiform activity, recorded extracellularly, was attenuated by NPY (0.5-1 microM) in both the frontal cortex and hippocampal CA3/CA1 pyramidal cell layers. In the cortex the Y1/5 selective agonist [Leu31 Pro34] NPY was more effective than the Y2 preferring agonist NPY13-36 and the Y2/5 preferring agonist NPY3-36. The suppression of epileptiform discharges induced by NPY in cortical slices was blocked by the selective Y1 receptor antagonist (R)-N2-(diphenylacetyl)-N-((4-hydroxyphenyl)methyl] argininamide (BIBP 3226). In the hippocampus, NPY13-36 and NPY3-36 were more effective than [Leu31 Pro34] NPY. In conclusion, the antiepileptic activity of NPY is mediated predominantly by the Y1 receptor subtype in the frontal cortex and by Y2 and probably Y5 receptors in the hippocampal CA3/CA1 areas.

MYOSTIM-FES to prevent muscle atrophy in microgravity and bed rest: preliminary report

Long-term flights in microgravity cause atrophy and morphological changes of skeletal muscles. Training with mechanical devices is insufficient regarding the required time to exercise and space for devices. The objective of this project is to develop a passive training method based on functional electrostimulation (FES) to preserve muscle mass and fiber composition with minimal impairment to the cosmonaut. For a pilot experiment on the MIR space station, a suitable 8 channel FES device was developed. It consists of electrode trousers that carry surface electrodes and cables, 2 interconnected 4 channel stimulators, and a laptop personal computer (PC) for stimulator programming and processing compliance data. An automatic extensive training of 4 muscle groups of the lower extremities is performed for 6 h/day, with 1 s on and 2 s off tetanic contractions at 20-30% of maximum tetanic muscle force. The synchronous activation of antagonists of the thigh and lower leg prevents uncoordinated movements.

Battery-powered implantable nerve stimulator for chronic activation of two skeletal muscles using multichannel techniques

Chronic activation of skeletal muscle is used clinically in representative numbers for diaphragm pacing to restore breathing and for dynamic graciloplasty to achieve fecal continence. The 3 different stimulation techniques currently used for electrophrenic respiration (EPR) all apply high frequency powered implants. It was our goal to make these stimulation methods applicable for EPR by a battery-powered nerve stimulator that would maximize the patient's freedom of movement. Additionally, the system should allow the implementation of multichannel techniques and alternating stimulation of 2 skeletal muscles as a further improvement in graciloplasty. Generally, the developed implantable nerve stimulator can be used for simultaneous and alternating activation of 2 skeletal muscles. Stimulation of the motor nerve is achieved by either single channel or multichannel methods. Carousel stimulation and sequential stimulation can be used for graciloplasty as well as for EPR. For EPR we calculated an operating time of the implant battery of 4.1 years based on the clinically used stimulation parameters with carousel stimulation. The multichannel pulse generator is hermetically sealed in a titanium case sized 65 x 17 mm (diameter x height) and weighs 88 g.

Personal computer supported eight channel surface stimulator for paraplegic walking: first results

Today functional electrical stimulation (FES) is used among other treatments to restore hand and arm function, to restore mobility of the lower extremities, for phrenic pacing, and in cardiomyoplasty. Common to all FES applications is that they require careful setup of stimulation parameters. To improve these tasks, personal computer (PC) based software for stimulation parameter evaluation and data acquisition was written. First, the described software was used to mobilize paraplegic patients in conjunction with an 12C bus controlled 8 channel surface stimulator. Electrodes were placed on each leg on the m. quadriceps and m. gluteus for hip and knee extension and the peroneal nerve to elicit flexion reflex. The fourth channel was used to correspond to subjects' individual needs. The stimulation patterns for standing up, walking, and sitting down easily could be set up and optimized by adjusting up to 128 stimulation parameters in a task-specific way.

Multifunctional implantable nerve stimulator for cardiac assistance by skeletal muscle

Different methods are used, clinically and experimentally, to assist severely impaired heart function by means of skeletal muscle. The efficiency of these methods is restricted by skeletal muscle losing strength after transpositioning and during conditioning and not being sufficiently resistant to fatigue. This is mainly due to the nonphysiological activation of the nerves by electrical stimulation. We have developed a battery operated, ECG triggered multichannel implant that is capable of implementing various advanced stimulation techniques. The stimulator can activate 2 skeletal muscles via the motor nerves. It allows for application of multichannel stimulation methods, i.e., carousel stimulation and sequential stimulation, as well as the programming of optimized pulse trains. Synchronization delay and burst duration can be automatically and dynamically adapted to the heart rate. The multichannel stimulator is hermetically sealed in a titanium case. Its calculated life span on the basis of the integrated battery is 3-5 years, depending on the programmed stimulation parameters. The implant dimensions are 65 x 17 mm (diameter x height), and it weighs 93 g. The implant has been tested in vitro as well as in vivo.

[Modular PC-based data acquisition and processing system for biological signals]

The data acquisition system described here is designed for biomedical research and permits the recording of up to eight biological signals simultaneously. A personal computer using the Windows 95 operating system is employed for data monitoring, data processing and analysis during experiments. The system has been designed for reliability, economy, flexibility and ease of handling, with the aim of achieving universal application. To avoid interface incompatibility, problems with transfer protocols and the data formats of commercially available products, analog signals are used for further processing. The individual input channels are electrically isolated from one another and the PC to avoid ground loops, and for reasons of safety. An isolated voltage supply is available for pre-amplifiers and bridges. A bandwidth of 0-5 kHz and the maximum sampling rate of 12.5 kHz suffice to pick up higher frequency signals such as EMG and ENG. The modular software and hardware concepts permit the use of almost any desktop or laptop PC as a central processing unit. The PC handless documentation, data acquisition, data analysis and the preparation of publications. If needed, further analytical functions can be added in modular form. Finally, the option of saving data in the ASCII format permits processing of results with such standard software packages as Excel, Access, Matlab and Origin.

Comparison of the effects of low and high concentrations of group I metabotropic receptor agonists on field potentials in the hippocampal CA1 region in vitro

We compared the effects of low and high concentrations of the selective group I metabotropic glutamate receptor (mGluR) agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG) and the nonselective mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid ((1S,3R)-ACPD) on extracellularly recorded potentials which were evoked in the rat hippocampal CA1 region by stimulation of the Schaffer collateral/commissural pathway and on intracellularly recorded electrophysiological properties of CA1 neurons, in vitro. At low concentrations (2.5 and 5 microM) DHPG and (1S,3R)-ACPD increased while at high concentrations (20 and 50 microM) they decreased population spike amplitudes. Simultaneous recordings of population spikes in the CA1 cell layer and field excitatory postsynaptic potentials (fEPSPs) in stratum radiatum of the CA1 area revealed that the enhancement of the population spike amplitude is not associated with any change in the fEPSP slope, but the decrease in population spikes is accompanied with a decrease in the fEPSP slope, suggesting that at high concentrations both agents may attenuate excitatory synaptic transmission in CA1 cells. DHPG and (1S,3R)-ACPD had a number of direct excitatory effects on CA1 pyramidal cells like a concentration-dependent depolarization and an inhibition of the slow afterhyperpolarization, which in all probability underlay the increase in the amplitude of population spikes. At high concentrations, both mGluR agonists strongly depolarized CA1 cells indicating that depolarization block of cell discharges may underlay the reduction in the population spike amplitude. Furthermore, robust cell discharges induced by the strong depolarizations, activate several secondary processes which may significantly contribute to the action of high concentrations of DHPG and (1S,3R)-ACPD. Therefore, the effects of low and high concentrations of the studied mGluR agonists may involve different mechanisms, at low concentrations the effects can be directly related to the activation of postsynaptically localized group I mGluRs while at higher concentrations the contribution of indirect effects may predominate.

Antidepressant treatment influences group I of glutamate metabotropic receptors in slices from hippocampal CA1 region

We investigated the effects of repeated electroconvulsive shock or imipramine treatment on inositol phosphate accumulation and on the reactivity of neurons to metabotropic glutamate (mGlu) receptor agonists in rat hippocampal slices. (1S,3R)-1-carboxycyclopentane-3-acetic acid (1S,3R-ACPD), a nonselective mGlu receptor agonist, caused a concentration-dependent increase in inositol phosphate in slices from the CA1 region of the hippocampus, an effect that was not modified by imipramine or electroconvulsive shock treatment. 1S,3R-ACPD or the selective agonist of the I group of mGlu receptor, (R,S)-3,5-dihydroxyphenylglycine ((R,S)-3,5-DHPG), produced a concentration-dependent increase of the population spike recorded in the CA1 cell layer. This effect of 1S,3R-ACPD was markedly attenuated by both repeated imipramine and electroconvulsive shock treatment, and the action of (R,S)-3,5-DHPG was markedly attenuated by prolonged imipramine treatment (electroconvulsive shock was not tested). Our results indicate that antidepressant treatment may induce a subsensitivity of group I mGlu receptors when assessed by electrophysiological but not biochemical measures.

Influence of imipramine treatment on the group I of metabotropic glutamate receptors in CA1 region of hippocampus

Effects of repeated imipramine treatment on inositol phosphates accumulation and on the reactivity of neurons to metabotropic glutamate receptor (mGlu) agonist (1S,3R)-1-carboxycyclopentane-3acetic acid (1S,3R-ACPD) were investigated in the rat hippocampal slices. The concentration-dependent increase in inositol phosphate accumulation in the slices from CA1 region of hippocampus induced by 1S,3R-ACPD was not modified by imipramine treatment. 1S,3R-ACPD produced a concentration-dependent increase in population spike amplitude recorded in the CA1 cell layer. This effect of 1S,3R-ACPD was markedly attenuated by repeated imipramine administration. Our results indicate that antidepressant treatment may induce a subsensitivity of mGlu receptors in the CA1 region of hippocampus when estimated by electrophysiological, but not biochemical measures.