Brain plasticity and cognitive functions after ethanol consumption in C57BL/6J mice

Acute or chronic administrations of high doses of ethanol in mice are known to produce severe cognitive deficits linked to hippocampal damage. However, we recently reported that chronic and moderate ethanol intake in C57BL/6J mice induced chromatin remodeling within the Bdnf promoters, leading to both enhanced brain-derived neurotrophic factor (BDNF) expression and hippocampal neurogenesis under free-choice protocol. We performed here a series of cellular and behavioral studies to analyze the consequences of these modifications. We showed that a 3-week chronic free-choice ethanol consumption in C57BL/6J mice led to a decrease in DNA methylation of the Bdnf gene within the CA1 and CA3 subfields of the hippocampus, and upregulated hippocampal BDNF signaling pathways mediated by ERK, AKT and CREB. However, this activation did not affect long-term potentiation in the CA1. Conversely, ethanol intake impaired learning and memory capacities analyzed in the contextual fear conditioning test and the novel object recognition task. In addition, ethanol increased behavioral perseveration in the Barnes maze test but did not alter the mouse overall spatial capacities. These data suggested that in conditions of chronic and moderate ethanol intake, the chromatin remodeling leading to BDNF signaling upregulation is probably an adaptive process, engaged via epigenetic regulations, to counteract the cognitive deficits induced by ethanol.

Web-based tool for injury risk assessment of foreign body injuries in children

Web-based surveillance systems enhance the ability for identifying, estimating and assessing public health hazards. In this paper we describe the development of a Web-based surveillance registry called Susy Safe for inorganic foreign body injuries in children aged 0-14. The Susy Safe system, which collected 2103 cases during 2000-2002 in 19 European countries, allows for notifying from physicians over the internet thus taking advantage of Web reporting capabilities. Functions include automated risk analysis engine and results visualization. Risk analysis engine has been implemented in a Bayesian framework and provides an update estimate of the risk profile of the products causing injuries, effectively as new data become available. The system contributes to simplify the physician reporting and improve public health information dissemination within consumers and consumers' association. Also it gives physician and researcher the access of a large amount of data otherwise scattered all around in different hospitals. Finally, supplying a quantitative risk assessment for the identification of hazardous characteristics of objects, such as dimensions or shape, it works toward an improvement of consumer products' safety design.

Are FPCIs a source of increased risk for children? Results of a multicenter, experimental study comparing children's behaviour with FPCIs and toys

INTRODUCTION

Food Products Containing Inedibles (FPCIs) are believed to represent a source of higher choking risk in children. The aim of this study was to set up a controlled study, conducted on children aged 3-6 in a laboratory setting, in order to understand their behavior when interacting with FPCIs (with reference to mouthing activities, double nature recognition, and toy assembling ability).

METHOD

The experimental phase was divided into two sessions: a FPCI session and a Toy session, to which 247 children were randomly assigned. During these sessions children were observed in order to catch their mouthing activity according to the two types of objects available to them (FPCIs and Toys).

RESULTS

This study shows that: (a) children's behavior with respect to toys contained in FPCIs and toys presented alone is not significantly different; (b) children's ability to distinguish between the edible and non-edible part of the FPCI was very high; and (c) mouthing episodes of the inedible parts were negligible and comparable between FPCIs and toys presented alone. This strongly suggests that, with respect to choking risk, FPCIs are not per se distinguishable from toys containing small parts.

IMPACT ON INDUSTRY

Restrictions on the sale of FPCIs with small toys exist in the U.S. market. In Europe, FPCIs are allowed to be on sale, under the condition that, in case, they will follow the general regulatory requirements of small toys packaged and sold alone. In this case, they must provide age warnings and labels. Our findings do not justify the different attention that toys in FPCIs are at times afforded by regulators when compared to "stand alone" toys.

The cost of foreign body injuries in the upper aero-digestive tract: need for a change from a clinical to a public health perspective?

OBJECTIVE

This paper addressed the impact in terms of direct costs of the injuries in children due to foreign bodies in the upper aero-digestive tract.

METHODS

Two thousand one hundred and three consecutive cases were collected from 2000 to 2002 in 16 European hospitals, 1 hospital for each participating country, and referred to children aged until 14 who had FB injuries. Costs were based on the extraction of the FB procedures and on hospitalization length, based on DRGs. Determinants of costs and of length of stay (LOS) were analyzed using a multilevel model.

RESULTS

The major cost of the treatment of FB injuries is covered by the ENT Departments, which are usually the first choice of referral, directly from the patients. Children had a mean LOS of 2.13 days (95% C.I. 1.99-2.29). Treatment of the FB was associated with a mean cost of euro 1017.37 (95% C.I. 963.27-1073.51). In the multivariable analysis higher costs are related to the modality of arrival to the hospital by walk, to the site of the injury (ICD-933, ICD-934, ICD-935 in particular) and to the use of surgery in removing the FB.

DISCUSSION

Foreign bodies injuries are posing a great threat not only with regards to the clinical aspects but also from the public health perspective, their treatment being associated with high costs, in particular when surgery is needed.

Foreign bodies in the upper airways: the experience of two Italian hospitals

OBJECTIVE

To study the pattern of foreign bodies in the upper airways as emerging from the hospital records in the Bologna and Siena hospitals in Italy 1997-2002.

METHODS

A retrospective review of hospital records was performed using a standardized protocol. All injuries with ICD9 (International Classification of Diseases, 9'h revision) codes ranging from 931 to 934 which occurred in children age 0-14 were considered for the database.

RESULTS

One hundred ninety seven patients were included in the database with a diagnosis of Foreign Bodies (FB) over the study period, 78 with ICD931, 105 with ICD932, 12 with ICD933 and 2 with ICD934 discharge diagnosis. Of the 197 patients, 51.90% of the patients were males and the 48.10% were female. Median age was 4 (2, 6). At the moment of the injury, the child was eating (11%), playing (83%) or studying (4%) or cleaning ears (2%). The child was supervised by an adult in doing his/her activities at the moment of injury in the 84.2% of the cases. The child reached the hospital using always private transport (100%), never by using an emergency transport (0%). Most commonly, FB were extracted in ambulatory (95.4%), more rarely using an endoscopic procedure (4.1%), and never using surgery. Hospitalization was required in the 0.5% of cases (1).

CONCLUSIONS

Our study showed the substantial epidemiological similarity of the Italian data with the experience of other center in the world. The burden of chocking was very limited in our country, as proven by the limited access to emergency and more invasive procedures. Nevertheless, some consideration can be made from the preventive point of view. Quite surprisingly, the majority of injuries occurred under the supervision of an adult in playing or recreational activities.

Child mortality due to suffocation in Europe (1980-1995): a review of official data

This report outlines the current status of the official statistical data available concerning mortality rates for suffocation in children <15 years of age, stratified according to sex and country in Europe, in the years 1980-1995. The data source is the WHO Mortality Database, which comprises deaths registered in national vital registration systems, with underlying cause of death as coded by the relevant national authority. To assess the impact of the problem of suffocation, the total potential years of life lost have been calculated. In addition, for Italy, and for the years 1999-2000, data related to deaths and hospitalizations for foreign body in the pharynx and larynx are presented. In Italy, in the years 1999-2000, the ratio between the number of hospitalizations and the mortality rates is approximately one death every 10 hospitalizations (x 100,000). The European mortality rate exceeds nearly one death per 100,000 persons. No evidence of any geographical pattern or cyclic trend emerged from the analysis of this official data.

Psychological aspects of risk appraisal in asphyxiation accidents: a review of the factors influencing children's perception and behaviour

Psychological aspects determining children's behaviour in response to asphyxiation risk due to ingestion of foreign matter have been rarely and non-systematically examined in the literature. Aim of this report is to highlight--through a review of the most significant psychological research in the literature--which factors influence the behaviour, perception and assessments of children 0 to 14 years of age, in a risk situation. In particular, attention is focused on the direct experience of a child at risk, assuming that this experience can play a significant role in future dangerous situations. Outcomes of studies taken into consideration have highlighted the influence of age, sex, socio-economic status, parents' role, peer group, personal traits, television and personal experience. The latter refutes the initial hypotheses, showing an unexpected and clearly negative effect on future evaluation and behaviour in response to similar contexts of asphyxiation risk. The implications for research on asphyxiation due to ingestion of foreign matter are examined.

Selective inhibition of local excitatory synaptic transmission by serotonin through an unconventional receptor in the CA1 region of rat hippocampus

1. The modulation of synaptic transmission by serotonin (5-HT) was studied using whole-cell voltage-clamp and sharp-electrode current-clamp recordings from CA1 pyramidal neurones in transverse rat hippocampal slices in vitro. 2. With GABA(A) receptors blocked, polysynaptic transmission evoked by stratum radiatum stimulation was inhibited by submicromolar concentrations of 5-HT, while monosynaptic excitatory transmission and CA1 pyramidal neurone excitability were unaffected. The effect persisted following pharmacological blockade of 5-HT(1A) and 5-HT(4) receptors, which directly affect CA1 pyramidal neurone excitability. 3. Concentration-response relationships for 5-HT were determined in individual neurones; the EC(50) values for block of polysynaptic excitation and inhibition by 5-HT were approximately 230 and approximately 160 nM, respectively. The 5-HT receptor type responsible for the observed effect does not fall easily into the present classification of 5-HT receptors. 4. 5-HT inhibition of polysynaptic EPSCs persisted following complete block of GABAergic transmission and in CA1 minislices, ruling out indirect effects through interneurones and non-CA1 pyramidal neurones, respectively. 5. Monosynaptic EPSCs evoked by stimulation of CA1 afferent pathways appeared to be unaffected by 5-HT. Monosynaptic EPSCs evoked by stimulation of the alveus, which contains CA1 pyramidal neurone axons, were partially inhibited by 5-HT. 6. We conclude that 5-HT inhibited synaptic transmission by acting at local recurrent collaterals of CA1 pyramidal neurones. This may represent an important physiological action of 5-HT in the hippocampus, since it occurs over a lower concentration range than the 5-HT effects reported so far.

Tryptophan metabolism and hepatic encephalopathy. Studies on the sedative properties of oxindole

Oxindole administration (1-100 mg/kg i.p.) to mammals decreases locomotor activity, reduces muscular tone and blood pressure and at larger doses causes coma and death. Utilizing both HPLC and GC/MS, we showed that oxindole is present in the blood, brain and other organs of several animal species, including humans. We demonstrated that oxindole is a tryptophan metabolite able to significantly decrease neuronal excitability by modifying the function of voltage-operated sodium channels. Its synthesis requires the availability of indole, which is formed in the gut. When liver function is impaired, a sufficient amount of indole reaches systemic circulation and is oxidized into oxindole, which seems to be one of the responsible agents for the neurological symptoms found in the course of liver impairment.

Biochemical and electrophysiological studies on (S)-(+)-2-(3'-carboxybicyclo(1.1.1)pentyl)-glycine (CBPG), a novel mGlu5 receptor agonist endowed with mGlu1 receptor antagonist activity

The pharmacological profile of (S)-(+)-2-(3'-carboxybicyclo[1.1.1]pentyl)-glycine (CBPG) and of other group 1 metabotropic glutamate (mGlu) receptor agents were studied in BHK cells transfected with mGlu receptor subtypes or in native receptors in brain slices by measuring second messenger responses. The mGlu receptor-mediated changes in the electrophysiological properties of CA1 pyramidal cells of the hippocampus were also evaluated. In mGlu5a receptor transfected cells, CBPG behaved as a partial agonist, while in mGlu1alpha receptor transfected cells, it behaved as a glutamate antagonist. No effect was found on cAMP formation in cells transfected with mGlu2 receptors or mGlu4 receptors. In brain slices, CBPG neither affected phospholipase D-coupled glutamate receptors nor did it modify the responses to ionotropic receptor stimulation (at concentrations up to 1 mM). When tested in CA1 pyramidal cells of the hippocampus, CBPG (50-100 microM) caused depolarization, increased cell input resistance, and decreased action potential frequency adaptation and afterhyperpolarization. DHPG (3-100 microM), an agonist of both mGlu1 and mGlu5 receptors, and CHPG (1000 microM), a low affinity mGlu5 agonist, produced qualitatively similar effects. The actions of CBPG or CHPG were not modified by AIDA (300 microM), a selective mGlu1 receptor antagonist. Our results suggest that CBPG could be a useful tool for discriminating between mGlu1 receptor and mGlu5 receptor effects and that mGlu5 receptors are the receptors which are mainly responsible for the direct excitatory effects of mGlu receptor agonists on CA1 pyramidal cells.

Electrophysiological studies on oxindole, a neurodepressant tryptophan metabolite

1. The aim of the present work was to investigate the electrophysiological effects of oxindole, a tryptophan metabolite present in rat blood and brain, and recently proposed as a contributing factor in the pathogenesis of hepatic encephalopathy. 2. Using rat hippocampal slices in vitro and extra- or intracellular recordings, we evaluated oxindole effects on the neurotransmission of the CA1 region following orthodromic stimulation of the Schaffer collaterals. 3. Oxindole (0.3-3 mM) decreased the amplitude of population spikes extracellularly recorded at the somatic level and of the fEPSPs recorded at the dendritic level. In intracellular recordings, oxindole (0.1-3 mM) did not affect the resting membrane potential or the neuronal input resistance, but reduced the probability of firing action potentials upon either synaptic or direct activation of the pyramidal cells. 4. Oxindole (0.3-3 mM) increased the threshold and the latency of firing action potentials elicited by depolarizing steps without changing the duration or the peak amplitude of the spikes. It also significantly increased the spike frequency adaptation induced by long lasting (400 ms) depolarizing stimuli. 5. In separate experiments, performed by measuring AMPA or NMDA-induced responses in cortical slices, oxindole (1-3 mM) did not modify glutamate receptor agonist responses. 6. Our results show that concentrations of oxindole which may be reached in pathological conditions, significantly decrease neuronal excitability by modifying the threshold of action potential generation.

Electrophysiological effects of felbamate

Felbamate is a broad spectrum antiepileptic drug recently introduced into clinical practice for controlling seizures in patients affected by Lennox-Gastaut epilepsy, complex partial seizures or otherwise intractable epilepsies. However, the cellular mechanisms by which the drug exerts its anticonvulsant actions are not fully understood. The aim of the present article is to outline the possible mechanisms of action of felbamate as suggested by findings obtained with electrophysiological approaches.

Temporal correlation between adenosine outflow and synaptic potential inhibition in rat hippocampal slices during ischemia-like conditions

The temporal correlation between adenosine outflow and changes in field excitatory post synaptic potentials (fEPSP) occurring during ischemia-like conditions was investigated in rat hippocampal slices. Five-minute long ischemia-like conditions resulted in a 100% depression of fEPSP amplitude, followed by a complete recovery after 6-7 min of reperfusion. By reducing the duration of the ischemic insult to 2 min, fEPSP was depressed by 50%. During both 5 and 2 min of ischemia-like conditions, a significant increase in adenosine outflow was detected. During reperfusion, when fEPSP amplitude recovered completely, the adenosine level in the extracellular fluid returned to basal values. The strict relationship between the increase in adenosine outflow and fEPSP inhibition supports the hypothesis that adenosine is largely responsible for the synaptic transmission depression during cerebral ischemia.

Effect of the selective 5-HT1A receptor antagonist WAY 100635 on the inhibition of e.p.s.ps produced by 5-HT in the CA1 region of rat hippocampal slices

1. The actions of N-(2-(-4(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl) cyclohexane carboxamide (WAY 100635), a novel and selective 5-hydroxytryptamine1A (5-HT1A) antagonist, on excitatory postsynaptic potentials (e.p.s.ps) were investigated by use of intracellular recordings in pyramidal cells of the CA1 region of rat hippocampal slices. 2. WAY 100635 (10 nM) did not affect any of the investigated parameters of cell excitability such as membrane potential, total input resistance (Rin), firing threshold, action potential amplitude, action potential frequency adaptation, and slow afterhyperpolarization (sAHP) which follows repetitive firing of action potentials. WAY 100635 did not have any effect on either the slope or the amplitude of e.p.s.ps evoked by stimulation of the CA1 stratum radiatum. 3. Bath application of either 5-hydroxytryptamine (5-HT, 10-30 microM) or 5-carboxamidotryptamine (5-CT, 300 nM) hyperpolarized the membrane potential (deltaVm = -4.1 +/- 0.9 and -6.0 +/- 0.9 mV, respectively), and reduced Rin (-25 +/- 8% and -18 +/- 1%, respectively). 5-HT blocked the action potential frequency adaptation and significantly reduced the amplitude of the sAHP that follows repetitive firing of action potentials. 4. 5-HT significantly decreased the amplitude of evoked e.p.s.ps (-14 +/- 6%). This effect was greater in the presence of the GABA(A) receptor antagonist bicuculline (10 microM, -45 +/- 12%) and was mimicked by 5-CT (-49 +/- 5%). Both AMPA and NMDA components of e.p.s.ps were significantly reduced in amplitude by 5-HT (-38 +/- 8%, n = 6, and -29 +/- 12%, n = 3, respectively; P < 0.05). 5. WAY 100635 fully antagonized the hyperpolarization, the reduction of Rin, and the decrease in amplitude of e.p.s.ps elicited by 5-HT, while it did not affect the action of 5-HT on the action potential frequency adaptation. In the presence of WAY 100635, 5-HT elicited a depolarization which was blocked by 10-30 microM RS 23597-190, a selective 5-HT4 receptor antagonist. 6. Our data demonstrate that WAY 100635 is devoid of direct effects on CA1 pyramidal cell excitability and on evoked e.p.s.ps, while it fully antagonizes the effects of 5-HT on excitatory synaptic transmission and on hyperpolarization, without affecting the 5-HT4 receptor-mediated response. Since WAY 100635 selectively antagonizes 5-HT1A receptor-mediated actions of 5-HT, our data also demonstrate that the inhibitory action of 5-HT on excitatory synaptic transmission in CA1 is mediated by 5-HT1A receptors.

Antagonist properties of (-)-pindolol and WAY 100635 at somatodendritic and postsynaptic 5-HT1A receptors in the rat brain

1. The aim of the present work was to characterize the 5-hydroxytryptamine1A (5-HT1A) antagonistic actions of (-)-pindolol and WAY 100635 (N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl) cyclohexane carboxamide). Studies were performed on 5-HT1A receptors located on 5-hydroxytryptaminergic neurones in the dorsal raphe nucleus (DRN) and on pyramidal cells in the CA1 and CA3 regions of the hippocampus in rat brain slices. 2. Intracellular electrophysiological recording of CA1 pyramidal cells and 5-hydroxytryptaminergic DRN neurones showed that the 5-HT1A receptor agonist 5-carboxamidotryptamine (5-CT) evoked in both cell types a concentration-dependent cell membrane hyperpolarization and a decrease in cell input resistance. On its own, (-)-pindolol did not modify the cell membrane potential and resistance at concentrations up to 10 microM, but it antagonized the 5-CT effects in a concentration-dependent manner. Similar antagonism of 5-CT effects was observed in the CA3 hippocampal region. (-)-Pindolol also prevented the 5-HT1A receptor-mediated hyperpolarization of CA1 pyramidal cells due to 5-HT (15 microM). In contrast, the 5-HT-induced depolarization mediated by presumed 5-HT4 receptors persisted in the presence of 3 microM (-)-pindolol. 3. In the hippocampus, (-)-pindolol completely prevented the hyperpolarization of CA1 pyramidal cells by 100 nM 5-CT (IC50=92 nM; apparent KB=20.1 nM), and of CA3 neurones by 300 nM 5-CT (IC50=522 nM; apparent KB= 115.1 nM). The block by (-)-pindolol was surmounted by increasing the concentration of 5-CT, indicating a reversible and competitive antagonistic action. 4. Extracellular recording of the firing rate of 5-hydroxytryptaminergic neurones in the DRN showed that (-)-pindolol blocked, in a concentration-dependent manner, the decrease in firing elicited by 100 nM 5-CT (IC50=598 nM; apparent KB= 131.7 nM) or 100 nM ipsapirone (IC50= 132.5 nM; apparent KB= 124.9 nM). The effect of (-)-pindolol was surmountable by increasing the concentration of the agonist. Intracellular recording experiments showed that 10 microM (-)-pindolol were required to antagonize completely the hyperpolarizing effect of 100 nM 5-CT. 5. In vivo labelling of brain 5-HT1A receptors by i.v. administration of [3H]-WAY 100635 ([O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1 -piperazinyl)ethyl-N-(2-pyridyl)cyclo-hexane-carboxamide) was used to assess their occupancy following in vivo treatment with (-)-pindolol. (-)-Pindolol (15 mg kg[-1]) injected i.p. either subchronically (2 day-treatment before i.v. injection of [3H]-WAY 100635) or acutely (20 min before i.v. injection of [3H]-WAY 100635) markedly reduced [3H]-WAY 100635 accumulation in all 5-HT1A receptor-containing brain areas. In particular, no differences were observed in the capacity of (-)-pindolol to prevent [3H]-WAY 100635 accumulation in the DRN and the CAI and CA3 hippocampal areas. 6. Intracellular electrophysiological recording of 5-hydroxytryptaminergic DRN neurones showed that WAY 100635 prevented the hyperpolarizing effect of 100 nM 5-CT in a concentration-dependent manner (IC50=4.9 nM, apparent KB=0.25 nM). In CA1 pyramidal cells, hyperpolarization induced by 50 nM 5-CT was also antagonized by WAY 100635 (IC50 = 0.80 nM, apparent KB= 0.28 nM).

Electrophysiological effects of WAY 100635, a new 5-HT1A receptor antagonist, on dorsal raphe nucleus serotoninergic neurones and CA1 pyramidal cells in vitro

The novel 5-HT1A receptor antagonist WAY 100635 [(N-(2-(-4(2-metoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyc lohexane carboxamide)] has been tested on 5-HT1A receptor-mediated inhibition of firing and intracellularly recorded hyperpolarisation of serotoninergic cells of the dorsal raphe nucleus (DRN) and on hyperpolarisation of hippocampal CA1 pyramidal cells. WAY 100635 selectively blocked 5-HT1A receptor-mediated responses of 5-HT, 8-OH-DPAT, lesopitron and 5-CT. The antagonism of the hyperpolarisation elicited by 5-CT was competitive in the DRN and non competitive in CA1, probably because of the existence of a 5-HT1A receptor reserve in serotoninergic cells of DRN.

Felbamate decreases synaptic transmission in the CA1 region of rat hippocampal slices

The antiepileptic drug felbamate (FBM) is known to block N-methyl-D-aspartate receptor-mediated responses and to decrease voltage-sensitive Na+ and Ca+2 channels. The present work was aimed at investigating the actions of FBM on synaptic potentials in the hippocampus, a region frequently involved in epileptic discharges. In rat hippocampal slices, application of FBM (100-1300 microM, 10 min) elicited a concentration-dependent, fully reversible decrease in amplitude of electrically evoked population spikes recorded extracellularly from the CA1 pyramidal cell layer. In intracellular recordings, FBM (50-300 microM) decreased the amplitude of excitatory postsynaptic potentials and reduced the probability of firing action potentials upon synaptic activation. Action potential frequency adaptation (accommodation), which typically limits repetitive firing in CA1 pyramidal cells, was increased. By using a paired-pulse protocol, FBM (300 microM) depressed the amplitude of paired excitatory postsynaptic potentials, without affecting the facilitation of the second response. In nominally Mg(+2)-free solution, FBM (100 microM) blocked N-methyl-D-aspartate receptor-mediated synaptic excitatory postsynaptic potentials isolated by the presence of 10 microM 6-nitro-7-sulfamoylbenzo(f)quinoxaline hydrochloride, a selective alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist, and 10 microM bicuculline or 25 microM picrotoxin. This effect was not reversed by the addition of 300 microM Gly. All these effects contribute to decrease excitatory synaptic transmission and are likely to limit neuron recruitment and propagation of epileptic discharges.

Effects of the antiepileptic drug felbamate on long-term potentiation in the CA1 region of rat hippocampal slices

In the CA1 region of rat hippocampal slices, the antiepileptic drug 2-phenyl-1,3-propanediol dicarbamate (felbamate; 100-1300 microM) concentration-dependently decreased extracellularly recorded synaptic potentials. The effect was significant at 200 microM, and became maximal at 700 microM felbamate, with a 70% decrease in population spike amplitude and 25% reduction of dendritic field excitatory postsynaptic potential (fEPSP) slope. Both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor-mediated components of the fEPSP were decreased by 700 microM felbamate. Up to 300 microM felbamate did not affect long-term potentiation (LTP), whereas 500 microM decreased the magnitude of LTP. Higher concentrations of felbamate (700-1300 microM) blocked induction of somatic and dendritic LTP completely, but reversibly. It appears that the concentrations of felbamate which affect LTP are higher than those needed for its antiepileptic action.

Electrophysiological effects of N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl) cyclohexane carboxamide (WAY 100635) on dorsal raphe serotonergic neurons and CA1 hippocampal pyramidal cells in vitro

The aim of the present study was to examine the effects of N-(2-(4-2-methoxphenyl)-1-piperazinyl)ethyl)-N-(2-pyridnyl) cyclohexane carboxamide (WAY 100635) on 5-HT1A receptor-mediated responses in the dorsal raphe nucleus (DRN) and the CA1 hippocampal region. In DRN slices superfused with WAY 100635 (10 nM), the majority of putative 5-HT neurons increased their firing rate (13 +/- 2% of baseline rate). In addition, WAY 100635 completely prevented the decrease in firing rate produced by 5-HT (3-15 microM), 8-OH-DPAT (10 nM), 5-carboxamidotryptamine (20 nM) and lesopitron (100 nM). The antagonism exerted by WAY 100635 (IC50 = 0.95 +/- 0.12 nM against 15 microM 5-HT) was fully surmounted by increasing the concentration of 5-HT to 300 microM. In hippocampal slices, WAY 100635 (0.5-10 nM) did not alter the resting membrane potential or the membrane input resistance of intracellularly recorded CA1 pyramidal cells. However, WAY 100635 completely prevented (IC50 = 0.9-1.7 nM) the hyperpolarization and the decrease in membrane input resistance produced by 5-HT (15-30 microM) and by 5-carboxamidotryptamine (50-300 nM). In contrast, WAY 100635 affected neither the block of action potential frequency adaptation and slow afterhyperpolarization produced by 5-HT (15 microM) nor the hyperpolarization and decrease in membrane input resistance evoked by bath application of GABA(B) receptor agonist baclofen (10 microM). The cumulative concentration-hyperpolarization curve for 5-carboxamidotryptamine (3 nM-10 microM) was shifted to the right by WAY 100635 (apparent Kb = 0.23 +/- 0.07 nM), and the latter drug also reduced the maximal response to the agonist. These data show the WAY 100635 is a potent antagonist at 5-HT1A receptors, both in the DRN and in the CA1 region of the hippocampus. The antagonism is apparently competitive in the DRN and partly noncompetitive in the hippocampus. Kinetic characteristics of the antagonist-receptor interactions might account for these regional differences.

Electrophysiological, biochemical, neurohormonal and behavioural studies with WAY-100635, a potent, selective and silent 5-HT1A receptor antagonist

Although considerable progress has been made in characterising the 5-HT1A receptor using agonists, partial agonists or non-selective antagonists, further studies of 5-HT1A receptor function have been hindered by the lack of highly selective antagonists. The term 'silent' antagonist has been used for such compounds in order to distinguish them unequivocally from several 5-HT1A receptor partial agonists which were initially designated 'antagonists'. In this report we provide a comprehensive review of the biochemical, pharmacological and behavioural properties of the first potent, selective and silent 5-HT1A receptor antagonist, WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2- pyridinyl)cyclohexanecarboxamide trihydrochloride). WAY-100635 had an IC50 (displacement of specific [3H]8-OH-DPAT binding to 5-HT1A receptors in the rat hippocampus) of 1.35 nM and was > 100-fold selective for the 5-HT1A site relative to a range of other CNS receptors. [3H]WAY-100635 was also characterised as the first 5-HT1A antagonist radioligand, displaying the same regional distribution of binding sites as [3H]8-OH-DPAT in rat brain. As would be expected for the binding of an antagonist to a G-protein-coupled receptor, the Bmax of [3H]WAY-100635 specific binding was consistently 50-60% greater than that of the agonist radioligand, [3H]8-OH-DPAT. Mn2+, but not guanine nucleotides, inhibited [3H]WAY-100635-specific binding. [3H]WAY-100635 was also shown to bind selectively to brain 5-HT1A receptors in vivo, following intravenous administration to mice. In vitro electrophysiological studies demonstrated that WAY-100635 had no 5-HT1A receptor agonist actions, but dose-dependently blocked the effects of agonists at both the postsynaptic 5-HT1A receptor in the CA1 region of the hippocampus, and the somatodendritic 5-HT1A receptor located on dorsal raphe 5-HT neurones. In vivo, WAY-100635 also dose-dependently blocked the ability of 8-OH-DPAT to inhibit the firing of dorsal raphe 5-HT neurones, and to induce the '5-HT syndrome', hypothermia, hyperphagia and to elevate plasma ACTH levels. In the mouse light/dark box anxiety model, WAY-100635 induced anxiolytic-like effects. WAY-100635 had no intrinsic effect on cognition in the delayed-matching-to-position model of short-term memory in the rat, but reversed the disruptive effects of 8-OH-DPAT on motor motivational performance. These data clearly demonstrate that WAY-100635 is the first potent, selective and silent 5-HT1A receptor antagonist. Furthermore, [3H]WAY-100635 is the first antagonist radioligand to become available for 5-HT1A receptor binding studies both in vitro and in vivo. The positive effects of WAY-100635 in an anxiety model also indicate that a postsynaptic 5-HT1A receptor antagonist action may contribute to the anxiolytic properties of 5-HT1A receptor partial agonists.

EPSP-spike potentiation during primed burst-induced long-term potentiation in the CA1 region of rat hippocampal slices

Long-term potentiation induced by high-frequency stimulation in the CA1 region of the hippocampus exhibits EPSP-spike potentiation. This consists of an increase in population spike amplitude exceeding that predicted by EPSP potentiation alone. This phenomenon is apparently due to an increase in pyramidal cell excitability. Patterns of afferent stimuli which activate pyramidal cells to reproduce the theta rhythm observed in the hippocampus under physiological conditions, have been shown to induce LTP-like enhancement of synaptic responses in vitro. The aim of this study was to investigate the presence of EPSP-spike potentiation and/or changes in pyramidal cell excitability during the long-term potentiation induced in the CA1 region of rat hippocampal slices by theta-like patterns of stimuli: the primed burst and the patterned stimulation. Using extracellular recording, a significant leftward shift in the EPSP-spike relationship was found 30 min after primed burst or patterned stimulation. The magnitude of EPSP-spike potentiation induced by patterned stimulation was similar to that produced by high-frequency stimulation. Both were significantly greater than that induced by a primed burst, indicating that only a subset of pyramidal cells were potentiated by this kind of afferent activation. Modifications in synaptic efficacy and cell excitability brought about by a primed burst were investigated in 25 intracellularly recorded pyramidal cells. Consistent with extracellular results, it was found that only 11 out of 25 neurons receiving a primed burst were potentiated. In these cells the increase in probability of firing action potentials elicited by synaptic activation with test shocks was accompanied by enhanced cell excitability, but not by an increase in EPSP slope. High-frequency stimulation delivered 40 min after a primed burst invariably increased the EPSP slope, the probability of firing upon synaptic stimulation, and the excitability of cells. The presence of EPSP-spike potentiation and of increased excitability of potentiated cells during the primed burst-induced long-term potentiation strengthen the suggestion that theta pattern-induced synaptic potentiation can be considered similar to high-frequency stimulation and long-term potentiation and supports the notion that the EPSP-spike potentiation is a constitutive characteristic of long-term potentiation.

Electrophysiological interactions between 5-hydroxytryptamine and thyrotropin releasing hormone on rat hippocampal CA1 neurons

Intracellular recording from CA1 neurons of the rat hippocampal slice preparation was used to examine the possibility of functional interactions between 5-hydroxytryptamine (5-HT) and thyrotropin releasing hormone (TRH), which act as cotransmitters in other areas of the central nervous system. 5-HT (30 microM) elicited complex effects consisting of biphasic changes in membrane potential and a strong depression of the afterhyperpolarization (AHP) following a spike burst. TRH (10 microM) did not alter membrane potential or input conductance but it produced a partial block of the AHP. Under single-electrode voltage clamp, 5-HT and TRH both reduced the amplitude of voltage-activated total K+ currents. When the two substances were co-applied, their actions were occluded. The voltage-activated K+ current remaining in Ca(2+)-free solution lost its sensitivity to 5-HT and TRH, suggesting that the K+ current modulated by TRH and 5-HT was Ca(2+)-dependent, although TRH itself did not depress high-threshold voltage-activated Ca2+ currents. When a relatively small concentration (5 microM) of 5-HT was co-applied with an equimolar amount of TRH, the degree of block of the spike AHP was the sum of the two individual effects of these drugs. It is suggested that in hippocampal pyramidal cells 5-HT and TRH influenced neuronal excitability by depressing a Ca(2+)-dependent K+ current, a phenomenon perhaps mediated through a common intracellular second messenger pathway.

Effects of DAU 6215, a novel 5-hydroxytryptamine3 (5-HT3) antagonist on electrophysiological properties of the rat hippocampus

1. The aim of the present study was to test the effects of DAU 6215 (endo-N-(8-methyl-8-azabicyclo-[3.2.1]-octo-3-yl)-2,3-dihydro-2-ox o-1H- benzimidazole-1-carboxamide carboxamide hydrochloride), a newly synthesized, selective 5-hydroxytryptamine3 (5-HT3) antagonist, on the cell membrane properties and on characterized 5-HT-mediated responses of pyramidal neurones in the hippocampal CA1 region. 2. Administration of DAU 6215, even at concentrations several hundred fold its Ki, did not affect the cell membrane properties of pyramidal neurones, nor modify extracellularly recorded synaptic potentials, evoked by stimulating the Schaffer's collaterals. 3. Micromolar concentrations (15-30 microM) of 5-HT elicited several responses in pyramidal neurones that are mediated by distinct 5-HT receptor subtypes. DAU 6215 did not antagonize the 5-HT1A-induced membrane hyperpolarization and conductance increase, a response that was blocked by the selective 5-HT1A antagonist NAN-190 (1-(2-methoxyphenyl)-4-[4-(2-phtalamido)butyl- piperazine). Similarly, DAU 6215 did not affect the membrane depolarization and decrease in amplitude of the afterhyperpolarization, elicited by the activation of putative 5-HT4 receptors. 4. 5-HT increased the frequency of spontaneous postsynaptic potentials (s.p.s.ps) recorded in pyramidal neurones loaded with chloride. In agreement with previous observations, most of the s.p.s.ps were reversed GABAergic events, produced by the activation of 5-HT3 receptors on interneurones, because they persisted in the presence of the glutamate NMDA and non NMDA antagonists, D-aminophosphonovaleric acid (APV; 50 microM) and 6,7-dinitroquinoxaline-2,3-dione (DNQX; 25 microM), and were elicited by the selective 5-HT3 agonist, 2-methyl-5-HT (2-Me-5-HT, 50 microM). 5. The increase in frequency of s.p.s.ps induced by 5-HT was significantly antagonized by DAU 6215 in 70% of the cases, whereas the 5-HT3 antagonist always suppressed the effect of 2-Me-5-HT, at concentrations as low as 60 nM.6. The antagonistic effect of DAU 6215 was also tested on the 5-HT3-mediated block of induction of long-term potentiation (LTP), elicited by a primed burst (PB) stimulation. Extracellular recordings showed that low concentrations (60 nM) of DAU 6215 suppressed the inhibitory action of 5-HT onPB-induced LTP, without affecting the 5-HTlA-induced reduction in the amplitude of the population spike.7. These results provide evidence that DAU 6215 is an effective antagonist of the 5-HT3-mediated responses in the central nervous system and may offer a cellular correlate for the pharmacological effects of DAU 6215 as an anxiolytic and cognition enhancer.

Phosphorylation of the presynaptic protein B-50 (GAP-43) is increased during electrically induced long-term potentiation

The protein B-50 (F1, GAP-43) is a presynaptic-specific substrate of protein kinase C, functionally related to neurotransmitter release. An increase in phosphorylation of this protein has been proposed as a molecular mechanism underlying long-term potentiation (LTP). B-50 phosphorylation measured by quantitative immunoprecipitation in rat hippocampal slices incubated in the presence of radiolabeled inorganic phosphate was increased for at least 1 hr after the induction of LTP in the CA1 region. No significant changes in B-50 phosphorylation were observed in untetanized slices stimulated at low frequency. The direct demonstration of an increased phosphorylation of the protein B-50 during LTP is consistent with the hypothesis that presynaptic mechanisms contribute to maintenance of LTP.

Serotonin blocks the long-term potentiation induced by primed burst stimulation in the CA1 region of rat hippocampal slices

The effect of 5-hydroxytryptamine on the induction of long-term potentiation by a train of high frequency pulses (100 Hz; 1 s) or by a stimulation consisting of one burst of five pulses at 100 Hz delivered 170 ms after a single pulse (primed burst) was investigated in the CA1 region of the rat hippocampal slice in vitro with extracellular recordings. Superfusion with 5-hydroxytryptamine (3-30 microM) produced a concentration-dependent decrease in amplitude of the population spikes evoked by test stimuli. The presence of 5-hydroxytryptamine (30 microM) did not affect the magnitude of long-term potentiation produced by the high-frequency stimulation but it prevented the long-term potentiation induced by a primed burst. The action of 5-hydroxytryptamine was mimicked by the 5-hydroxytryptamine1A agonist 5-carboxamidotryptamine (0.3 microM) and blocked by the 5-hydroxytryptamine2/5-hydroxytryptamine1A antagonist spiperone (3 microM) or by the 5-hydroxytryptamine1/5-hydroxytryptamine2 antagonist methiothepin (1-10 microM). The selective 5-hydroxytryptamine2 antagonist ritanserin (1 microM) did not antagonize the block of long-term potentiation produced by 5-hydroxytryptamine. The selective 5-hydroxytryptamine3 antagonists (3-tropanyl)-1H-indole-3-carboxylic acid ester (ICS 205-930; 1 nM) and ondansetron (GR-38032; 30 nM) did not affect the reduction in the population spike produced by application of 5-hydroxytryptamine. In contrast, a primed burst delivered at the fifth minute of 5-hydroxytryptamine application in the presence of a 5-hydroxytryptamine3 antagonist induced a long-term potentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the nootropic drug oxiracetam on field potentials of rat hippocampal slices

1. The effect of the nootropic drug oxiracetam on hippocampal neurotransmission was investigated in the CA1 region of the rat hippocampal slice in vitro by use of extracellular recordings. 2. Superfusion of oxiracetam (0.1-100 microM) produced a concentration-dependent, wash-resistant (greater than 90 min), increase in initial slope and amplitude of the dendritic field excitatory postsynaptic potential (e.p.s.p.). This increase was maximal at a concentration of 1 microM (70%). 3. Input-output curves relating the initial slope to the amplitude of the afferent volley were significantly (P less than 0.05) steeper and showed a greater maximal response in the presence of 1 microM oxiracetam than in control conditions. 4. Two trains of high frequency stimulation (100 Hz, 0.4 s, 5 min apart) delivered in the stratum radiatum 30 min after washout of oxiracetam (1 microM) still elicited a long-term potentiation (LTP) of the field e.p.s.p. However, the absolute magnitude of the LTP produced did not differ from that obtained in untreated slices. 5. After induction and establishment of LTP, oxiracetam (1 microM) had a smaller (27%) and reversible effect on the evoked field e.p.s.p. 6. D-2-Amino-5-phosphonopentanoic acid (AP-5), at the same concentration (50 microM) which in our conditions prevented the induction of LTP, blocked the action of 1 microM oxiracetam and strongly depressed the effect of higher concentrations of the nootropic drug. 7. It is concluded that oxiracetam provokes an enduring increase of neurotransmission in the CA1 rat hippocampal region. This action appears to share some features with LTP as indicated by its persistence, sensitivity to AP-5 and lack of additivity with electrically-induced LTP.

GABAergic mechanisms in the CA3 hippocampal region during early postnatal life

The developmental pattern of GABAergic neurons in the rat hippocampus during the first week of postnatal life shows several particularities both from a morphological and physiological point of view: (1) GABA immunoreactive neurons which are initially localized in a deep and superficial layer, progressively disappear from these two layers. From the end of the first postnatal week, GABAergic neuronal somata appear throughout the whole hippocampus, but GABA immunoreactive terminal structures are not frequent until the second postnatal week. (2) Intracellular observations in slices reveal the presence in CA3 pyramidal neurons between P0 and P6 (postnatal days) of spontaneous giant depolarizing potentials (GDPs); these are mediated by GABA acting on GABAA receptors and modulated presynaptically by NMDA receptors. During this period of development, GABA and GABAA analogues have a depolarizing action at resting membrane potential. Bicuculline at this developmental stage blocks completely spontaneous and evoked synaptic potentials. During the second postnatal week, when GABA responses shift from depolarizing to hyperpolarizing, bicuculline induces spontaneous interictal discharges. It is suggested that the positive feedback of the GABAergic interneuron on the pyramidal neuron during the first week of life may account for the generation of GDPS which may play an important role in synaptogenesis.

The allosteric glycine site of the N-methyl-D-aspartate receptor modulates GABAergic-mediated synaptic events in neonatal rat CA3 hippocampal neurons

We report in this study that, in the presence of magnesium, bath application of micromolar concentrations of glycine have prominent effects on synaptic events and N-methyl-D-aspartate (NMDA) responses in neonatal but not in adult hippocampal slices. Intracellular recordings were made from 71 rat CA3 hippocampal neurons in neonatal slices. In keeping with our earlier study, during the first postnatal week, CA3 neurons exhibited giant depolarizing potentials (GDPs). These GDPs are mediated by gamma-aminobutyric acid (GABA) acting on type A GABA (GABAA) receptors and modulated presynaptically by NMDA receptors. In the majority of cells (18 out of 31), glycine (10-30 microM) increased the frequency of GDPs (from 0.14 to 0.29 Hz). This effect was mimicked by D-serine (10-20 microM) and blocked by the NMDA receptor antagonists D-(-)-2-amino-5-phosphonovalerate (50 microM) and DL-2-amino-7-phosphonoheptanoate (50 microM) and by the GABAA antagonist bicuculline (10 microM) but not by strychnine (1 microM). Subthreshold concentrations of glycine (or D-serine) and NMDA, when given together, enhanced synaptic noise and the frequency of GDPs. In the presence of tetrodotoxin (1 microM), glycine and D-serine (up to 50 microM) did not modify the NMDA-induced inward currents in CA3 pyramidal cells. However the reduction of NMDA-mediated currents by 7-chlorokynurenate (10-20 microM) was reversed by glycine and D-serine (100-200 microM). In contrast, glycine (up to 100 microM) had no effect on membrane potential, input resistance, or NMDA responses after postnatal day 10. It is concluded that GABA-mediated events are facilitated by glycine acting on presynaptically located NMDA receptors.

GABA mediated excitation in immature rat CA3 hippocampal neurons

Intracellular recordings from rat hippocampal neurons in vitro during the first postnatal week revealed the presence of spontaneous giant depolarizing potentials (GDPs). These were generated by the synchronous discharge of a population of neurons. GDPs reversed polarity at -27 and -51 mV when recorded with KCl or K-methylsulphate filled electrodes, respectively. GDPs were blocked by the GABAA receptor antagonist bicuculline (10 microM). Iontophoretic or bath applications of GABA (10-300 microM) in the presence of tetrodotoxin (1 microM), induced a membrane depolarization or in voltage clamp experiments an inward current which reversed polarity at the same potential as GDPs. The response to GABA was blocked in a non-competitive manner by bicuculline (10 microM) and did not desensitize. GABA mediated GDPs were presynaptically modulated by N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Their frequency was reduced or blocked by NMDA receptor antagonists and by the rather specific non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The frequency of GDPs was enhanced by glycine and D-serine (10-30 microM) in a strychnine insensitive manner. This effect was blocked by AP-5, suggesting that it was mediated by the allosteric modulatory site of the NMDA receptor. These observations suggest that most of the 'excitatory' drive in immature neurons is mediated by GABA acting on GABAA receptors; furthermore excitatory amino acids modulate the release of GABA by a presynaptic action on GABAergic interneurons.

The protein kinase C inhibitor 1-(5-isoquinolinesulphonyl)-2-methylpiperazine (H-7) disinhibits CA1 pyramidal cells in rat hippocampal slices

1. The effects of the protein kinase C (PKC) inhibitor 1-(5-isoquinolinesulphonyl)-2-methylpiperazine (H-7) on evoked synaptic potentials were investigated in the CA1 region of rat hippocampal slices by use of extracellular and intracellular recording techniques. 2. Extracellular recordings showed that superfusion with H-7 (10-100 microM) increased the amplitude of the population spike and the initial slope of the dendritic field e.p.s.p. H-7 also produced the appearance of multiple population spikes in the somatic region and in the dendritic field e.p.s.p. 3. H-7 (30 microM) induced the disappearance of intracellularly recorded inhibitory potentials elicited by orthodromic stimulation of CA1 pyramidal cells. At this concentration H-7 had no effect on resting membrane potential, input membrane resistance, and spike threshold. In voltage-clamped neurones H-7 blocked the antidromically evoked inhibitory currents and the spontaneous miniature inhibitory currents. 4. The hyperpolarizing effect of bath applied gamma-aminobutyric acid (GABA, 500 microM) or isoguvacine (30 microM) was not affected by 30 microM H-7. 5. Neither the PKC activity regulator sphingosine (10-40 microM) nor the H-7 analogue N-(2-guanidinoethyl)-5-isoquinolinesulphonamide (HA-1004, 20-50 microM) which is devoid of activity on PKC at these concentrations, affected the extracellularly recorded dendritic field e.p.s.p. or population spike. 6. It is concluded that the disinhibitory effect produced by H-7 is due to the block of a H-7-sensitive PKC which is involved in the spontaneous and evoked release of GABA.

Giant synaptic potentials in immature rat CA3 hippocampal neurones

1. Intracellular recordings were made from rat CA3 hippocampal neurones in vitro during the first eighteen days of postnatal life. The cells had resting membrane potentials more negative than -51 mV, action potentials greater than 55 mV and membrane input resistances of 117 +/- 12 M omega. An unusual characteristic of these cells was the presence of spontaneous giant depolarizing potentials (GDPs) which were observed during the first eight postnatal (P) days in over 85% of neurones. They were less frequent between P9 and P12 (48%) and disappeared after P12. 2. The GDPs were synchronously generated by a population of neurones; they reversed polarity at -27 mV when recorded with KCl-containing electrodes and at -51 mV with potassium acetate- or potassium methylsulphate-filled electrodes. 3. The GDPs were blocked by bath application of bicuculline (10 microM) or picrotoxin (100-200 microM). Exogenously applied gamma-aminobutyric acid (GABA; 0.2-1 mM) induced at resting membrane potential a bicuculline-sensitive membrane depolarization which reversed polarity at -25 and -51 mV when recorded with KCl- or potassium methylsulphate-filled electrodes respectively. 4. The GDPs were reduced in frequency or blocked by the N-methyl-D-aspartate (NMDA) receptor antagonists DL-2-amino-7-phosphonoheptanoate (AP-7; 50 microM), D(-)2-amino-5-phosphonovalerate (AP-5, 10-50 microM) and (+-)3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP, 10-50 microM) or NMDA channel blockers phencyclidine (2 microM) and ketamine (20 microM). 5. Stimulation of the hilus during the first week of life evoked a GDP followed by a hyperpolarization. The GDPs were generated by a population of synchronized neurones and reversed polarity at -27 mV with KCl-filled electrodes and at -52 mV with potassium acetate- or potassium methylsulphate-containing electrodes. 6. Bath application of bicuculline (1-10 microM) or picrotoxin (100-200 microM) reversibly blocked the evoked GDPs in the majority of cells. The NMDA receptor antagonists AP-5 (50 microM), AP-7 (50 microM) and CPP (30 microM) usually reduced the amplitude and the duration of the evoked GDPs. In neurones in which evoked GDPs were blocked by bicuculline, a NMDA-mediated component was revealed by increasing the strength or the frequency of stimulation. 7. During the second week of postnatal life, when spontaneous GDPs were extremely rare or absent, superfusion with bicuculline (10 microM) induced, as in adult slices, interictal discharges. These reversed polarity near 0 mV with KCl- or potassium acetate-containing electrodes and were reduced in amplitude and duration by AP-5 (50 microM).(ABSTRACT TRUNCATED AT 400 WORDS)

Flunarizine-induced parkinsonism in the elderly

Twenty-seven patients (19 women and 8 men, ages 63 to 88 years; mean, 74 years) displayed mild to moderate parkinsonism and altered ballistic motor performances during long-term flunarizine treatment. One month after, flunarizine withdrawal, 20 patients showed clear-cut improvements in both clinical features and ballistic motor performances; a complete recovery within 6 months was observed in all these patients but one, who still showed very mild slowness of movement. On the other hand, seven patients showed little clinical improvement and still maintained markedly altered ballistic motor performances 1 month after drug withdrawal. At the 2-month follow-up assessments, either they did not improve further or they deteriorated; they were successfully treated with L-dopa and, despite the ameliorations, after 12 to 24 months they still have definite parkinsonian syndrome. The authors conclude that (1) flunarizine, even at the recommended dose (10 mg daily), can induce reversible parkinsonism, at least in subjects older than 60; (2) the persistence of a marked symptomatology 2 months after flunarizine withdrawal should lead to starting treatment with antiparkinsonism drugs; (3) the study of ballistic movements is proposed as a useful tool for objective quantification and early detection of bradykinesia.

Phospholipase C activation induced by noradrenaline in rat hippocampal slices is potentiated by GABA-receptor stimulation

We have studied the effect of gamma-aminobutyric acid (GABA) and other GABA-receptor agonists (3-aminopropanesulphonic acid and muscimol) on the noradrenaline-induced stimulation of polyphosphoinositide metabolism in rat hippocampal slices. Formation of water-soluble inositol phosphates, and polyphosphoinositide metabolism were studied in hippocampal slices prelabelled with [3H]myoinositol. Noradrenaline induced formation of inositol mono-, bis- and trisphosphate during 10 min incubation in the presence of lithium; activation of phospholipase C by noradrenaline was also reflected by the hydrolysis of polyphosphoinositides and by the increased metabolism of phosphatidylinositol. GABA-receptor agonists were unable to activate per se phospholipase C; however, when added together with a low concentration of noradrenaline, they greatly potentiated the noradrenaline-stimulated polyphosphoinositide metabolism. We conclude that GABA-receptor agonists potentiate the effect of noradrenaline on polyphosphoinositide turnover and we discuss the role of this neurotransmitter interaction in the physiology of the hippocampus.

GABA-receptor stimulation enhances norepinephrine-induced polyphosphoinositide metabolism in rat hippocampal slices

The effect of gamma-aminobutyric acid (GABA)receptor stimulation on norepinephrine (NE)-induced metabolism of polyphosphoinositides (PIPs) was studied in rat hippocampal slices. Inositol phosphates (IPs), PIPs, and phosphatidic acid were measured. NE induced formation of IPs and phosphatidic acid in a dose-dependent manner with an EC50 of 4.5 microM. GABA, 3-aminopropanesulphonic acid (3APS) and muscimol did not affect PIPs breakdown, but they strongly increased (greater than 100%) PIPs metabolism induced by 1 microM NE. Their action was antagonized by bicuculline (10 microM). We discuss the implications of these findings in hippocampal neurotransmission.

Chronic caffeine treatment reduces caffeine but not adenosine effects on cortical acetylcholine release

The effects of both adenosine and caffeine on the release of acetylcholine (ACh) were investigated in slices of cerebral cortex taken from rats pretreated for 30 days with caffeine (100 mg kg-1 daily, dissolved in their drinking water) at rest and during electrical stimulation at frequencies of 0.2, 1 and 5 Hz. The effect of this treatment on adenosine binding sites was also investigated in cortical membranes using N-cyclohexyl-[3H]-adenosine ([3H]-CHA) as a ligand. The chronic caffeine treatment did not change animal growth patterns. Spontaneous exploratory activity appeared to be increased at the 3rd day but was unchanged at the 30th day when compared with controls. Caffeine-treatment increased the number of high affinity binding sites for [3H]-CHA by 64% over the control values. Low affinity binding site density and affinity constants were unaffected. Adenosine 30 microM added to the superfusion fluid decreased electrically stimulated ACh release both in rats drinking tap water and rats drinking caffeine. In rats drinking tap water, caffeine added to the superfusion fluid at a concentration of 50 microM enhanced ACh release, while at 0.5 mM it decreased ACh output from the slices. Both effects were abolished by pretreatment with caffeine in vivo. The results indicate that prolonged consumption of high doses of caffeine causes changes in the responsiveness of cholinergic neurones to caffeine. The change is not shared by adenosine, through whose recognition sites caffeine is believed to act. It is therefore possible that the adaptive changes following repeated caffeine administration involve either only the coupler-transducer mechanism activated by the antagonist, or effects unrelated to receptors.

Muscarinic mobilization of choline in rat cerebral cortex does not involve alterations of blood-brain barrier

Efflux of choline from the rat cerebral cortex in vivo was investigated using the cup technique. After removal of the dura mater, the cup was placed on the cortex. Transmission and scanning electron microscopy revealed that the cortex was separated from the cup solution (100-300 microliter) by basal lamina, pia mater, arachnoid (with discrete defects) and remainders of the subdural neurothelium. Two kinds of experiments were carried out to determine: efflux of unlabelled choline into the cup solution; and translocation of radioactivity from the plasma into the cup solution (via blood-brain barrier and leptomeningeal layers) during i.v. infusion of [3H]choline or [14C]inulin. The former process was highly temperature-sensitive in contrast to the latter. Penicillin-G-sodium, which is known to damage the blood-brain barrier, was added to the cup solution, enhanced efflux of unlabelled choline, and caused a 5-fold increase in the rates of translocation of radioactivity during infusion of either labelled choline or inulin. In contrast, physostigmine (3 X 10(-4) M, added to cup solution) failed to enhance 3H-translocation, but markedly facilitated the efflux of unlabelled choline; this effect was highly temperature-sensitive and was blocked by atropine. It is concluded that activation of muscarinic receptors enhanced the choline efflux from cortical tissue. This effect was caused by cellular mobilization of choline presumably through an action on the metabolism of phosphatidylcholine. The effect was not due to alterations in the translocation of choline from the plasma to the cup solution, i.e. through permeability changes in the blood-brain barrier and in the leptomeningeal 'barrier'.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological characterization of D-aminophosphonovaleric acid antagonism of amino acid and synaptically evoked excitations on frog motoneurones in vitro: an intracellular study

The effect of D-aminophosphonovaleric acid (D-APV) on the depolarizations induced by N-methyl-D-aspartate (NMDA), glutamate, aspartate or quisqualate was studied with intracellular recordings from frog motoneurones in vitro. D-APV (0.5-10 microM) produced a slight hyperpolarization of the motoneuronal membrane without significant changes in input conductance. In control and tetrodotoxin-containing solutions the depolarizations induced by NMDA were strongly reduced by D-APV while quisqualate depolarizations were unaffected. Responses to glutamate and aspartate were antagonized to an intermediate level. The relatively small conductance increases evoked by excitatory amino acids were unaltered in solutions containing D-APV. The amplitude of monosynaptic excitatory postsynaptic potentials (e.p.s.ps) was strongly depressed by D-APV. The amplitude of polysynaptic e.p.s.ps was little changed but their decay time was reduced. It is suggested that D-APV is a powerful and selective NMDA receptor antagonist and that an endogenous amino acid acting via NMDA receptors may be the transmitter of monosynaptic e.p.s.ps on frog motoneurones.

Adenosine decreases aspartate and glutamate release from rat hippocampal slices

The effect of adenosine and related compounds on the release of endogenous aspartate and glutamate from isolated, superfused rat hippocampal slices was studied at rest and during electrical stimulation of the stratum radiatum in the CA3/CA2 region, using a sensitive mass-spectrometric technique. Evoked extracellular potentials were recorded from the CA1 region. Adenosine, at 3 X 10(-4) M concentration, inhibited the stimulation-evoked potentials and prevented the stimulation-induced release of aspartate and glutamate. Similarly, 1-phenylisopropyladenosine (10(-6) M) and cyclohexyladenosine (10(-6) M) depressed both electrical and neurochemical responses to stimulation of the stratum radiatum. 8-Phenyltheophylline (5 X 10(-6) M) increased the release of aspartate and glutamate and antagonized the cyclohexyladenosine-induced inhibition of amino acid release. Our results support the hypothesis that adenosine modulates the electrophysiological responses to stimulation of stratum radiatum through a reduction of the release of the excitatory amino acids aspartate and glutamate.

Disappearance of low affinity adenosine binding sites in aging rat cerebral cortex and hippocampus

A1 adenosine receptor binding was investigated, using the selective agonist, [3H]cyclohexyladenosine, on membranes prepared from the cerebral cortex and hippocampus of 3- and 24-month-old rats. The Scatchard analysis of the binding results obtained in the cerebral cortex of young animals showed two distinct binding sites with apparent Kd of 2 and 24 nM and Bmax of 259 and 675 fmol/mg protein, respectively. Conversely, in the old rats only one population of high affinity binding sites with a Kd of 2.2 nM and a Bmax of 450 fmol/mg protein was found. Displacement curves of labelled ligand carried out on hippocampal membranes also demonstrate the disappearance of a low affinity subpopulation of A1 receptors in the old rat brain.

8-Phenyltheophylline potentiates the electrical activity evoked in hippocampal slices

The effects of 8-phenyltheophylline (8PT) were studied on coronal slices of rat hippocampus. 8PT was more potent than theophylline in enhancing the pyramidal cell responses evoked by stimulation of the stratum radiatum. 8PT dose dependently antagonized the depression of the excitatory postsynaptic potentials induced by cyclohexyladenosine and did not change the amplitude of antidromically evoked responses of pyramidal cells. These findings suggest that 8PT is a potentially powerful tool for studying adenosine neuromodulation in the CNS.

Electrical stimulation of the stratum radiatum increases the release and neosynthesis of aspartate, glutamate, and gamma-aminobutyric acid in rat hippocampal slices

The release of endogenous aspartic, glutamic, and gamma-aminobutyric acids (Asp, Glu, GABA, respectively) was measured in the effluent from superfused hippocampal slices using a new and sensitive mass spectrometric method. The stimulation of the stratum radiatum of the rat dorsal hippocampus caused a Ca2+-dependent increase in the release of these amino acids. This release was accompanied by an increase in the incorporation of [13C2] from [13C]glucose into Asp, Glu, and GABA, suggesting an increase in their neosynthesis. The removal of Ca2+ from the superfusion fluid brought about a marked decrease in Asp and Glu release at rest, and prevented their stimulation-evoked release and the appearance of population spikes. The results support the hypothesis that Asp and Glu are excitatory neurotransmitters in intrinsic hippocampal circuits and are possibly released from the Schaffer collaterals and commissural fibres. The increase in GABA release and neosynthesis during stimulation of the stratum radiatum could be related to recurrent inhibition evoked by transsynaptic stimulation of the pyramidal cells.

Mobilization of cellular choline by stimulation of muscarine receptors in isolated chicken heart and rat cortex in vivo

The effects of cholinesterase inhibitors and muscarinic agonists on efflux of choline were studied in isolated perfused chicken heart and rat cortex in vivo. In the heart, the phospholipase A2 inhibitor mepacrine (10(-4) M) reduced the choline efflux (1.1 nmol g-1 min-1) by 51 +/- 5% (N = 3), whereas several cholinesterase inhibitors (physostigmine, neostigmine and diisopropylfluorophosphate) and muscarinic agonists (acetylcholine, oxotremorine and bethanechol) caused an increase. The muscarinic increase in choline efflux appears to be specific, as the increase caused by 10(-6) M physostigmine (+113%), by 3 X 10(-7) M acetylcholine (+89%) or by 5 X 10(-4) M bethanechol (+29%) was blocked by atropine. Cholinesterase inhibitors and muscarinic agonists also caused a decrease in heart rate by about 50%. Papaverine (10(-5) M) blocked the physostigmine- or bethanechol-evoked increase in choline efflux, but left the decrease in heart rate unchanged. Choline efflux from rat cortex in vivo was studied using the "cup technique." During the experimental period (3 hr), resting efflux declined from 60 to 15 pmol cm-2 min-1. Again choline efflux was increased by physostigmine (+48%) or by bethanechol (+48%) added to the cup solution from 80 to 160 min, whereas a decrease was observed after atropine plus physostigmine (-36%) or atropine plus bethanechol (-26%). In conclusion, stimulation of muscarine receptors increased extracellular choline by mobilization of cellular choline presumably through an effect on phospholipid metabolism. The hypothesis is discussed that synthesis of acetylcholine in the brain may be supported by an autoregulation of precursor availability.

Levels and synthesis of glutamate and aspartate in the olfactory cortex following bulbectomy

Guinea pigs were unilaterally bulbectomised and the contents of aspartate, glutamate and GABA measured in slices of olfactory cortex taken from the lesioned and intact hemispheres. Two days after the operation there was a fall in the aspartate and glutamate levels, which persisted for over 120 days, whereas gamma-aminobutyric acid (GABA) showed a transient fall followed by a small rise. The fall in glutamate and aspartate was much greater in small, thin slices containing a high density of nerve terminals. The synthesis of 13C aminoacids from [13C]glucose during electrical stimulation was greater in the slices taken from the normal side than in those from the operated side. The GABA synthesis, however, was four times greater on the lesioned side. This time-course for the fall in acidic amino acids correlates with the fall in electrical responses, and this lends weight to the idea that aspartate and/or glutamate mediate synaptic transmission in the area.

Acute subcortical lesions modify cortical muscarinic receptors in human brain

Post-mortem determinations of muscarinic cholinergic receptor parameters by means of binding procedures were carried out in human brains. In patients who died from internal capsule stroke a significant increase in cortical (Brodmann area 8) muscarinic receptor density was present when compared to non-neurological controls. No significant changes were detected in cortical choline acetyltransferase. Subcortical structures such as thalamus and caudate nucleus seemed to undergo opposite effects. It is suggested that acute interruption of fibers ascending to the cortex from subcortical areas can alter muscarinic receptor properties in the cerebral cortex.