Role of hippocampal NO in the acquisition and consolidation of inhibitory avoidance learning

Nitric oxide (NO), an unconventional neurotransmitter in the brain, has been postulated as a retrograde intercellular messenger necessary for the induction, but not the maintenance phase, of activity-dependent forms of synaptic plasticity in the hippocampus. Here we report on the effects of an inhibitory avoidance learning task on hippocampal NO synthase (NOS) activity and on the effects of intrahippocampal infusion of a NOS inhibitor in the acquisition and consolidation of this task in rats. NOS activity increases by 45% in the hippocampus immediately after training (0 min) but not at 60 min after training. No changes were observed in cerebellar NOS activity. The bilateral intrahippocampal microinjection of nitro-arginine (NO-arg), an NOS inhibitor, provoked retrograde amnesia for the inhibitory avoidance when given 10 min before or immediately after training, but not 60 min after training. These results suggest that NO-regulated processes in the hippocampus play an important role at the time of training or very shortly thereafter of an inhibitory avoidance learning.

Learning-specific, time-dependent increase in [3H]phorbol dibutyrate binding to protein kinase C in selected regions of the rat brain

Several lines of evidence indicate that protein kinase C (PKC) participates in long-term potentiation (LTP) and in certain forms of learning. Here we describe a rapid, specific and time-dependent increase in [3H]phorbol-12,13-dibutyrate ([3H]PDBu) binding to membrane-associated PKC in selected brain regions of rats submitted to an inhibitory avoidance task. A quantitative film autoradiographic method was used to determine the amount and distribution of membrane-bound PKC in rats sacrificed at various time intervals after training. At 0, 30 and 120 min following training there was a prominent increase (up to 200%) in the binding of [3H]PDBu throughout the hippocampus relative to naive, shocked or habituated control groups. No significant changes in [3H]PDBu binding in any brain region were found at 180 min after training. Similar training-specific increments in the binding of [3H]PDBu were observed in the frontal, parietal and entorhinal cerebral cortices, amygdala and cerebellum. The maximal effect was seen at 30 min in the CA2 region of the hippocampus (+200%) and at 30 and 120 min after training in the amygdala (+170%) in comparison to naive control values. No alterations in [3H]PDBu binding were found in the other brain regions studied. The present findings, together with previous data reporting a similar temporal course in the effects of intrahippocampal or intraamygdala infusion of specific PKC inhibitors on memory, suggest that PKC activation plays a role in the acquisition and consolidation of an inhibitory avoidance learning.

Memory enhancement by intrahippocampal, intraamygdala, or intraentorhinal infusion of platelet-activating factor measured in an inhibitory avoidance task

Platelet-activating factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine), which is thought to be a retrograde messenger in long-term potentiation (LTP), enhances glutamate release and LTP through an action on presynaptic nerve endings. The PAF antagonist BN 52021 blocks CA1 LTP in hippocampal slices, and, when infused into rat dorsal hippocampus pre- or posttraining, blocks retention of inhibitory avoidance. Here we report that memory is affected by pre- or posttraining infusion of the PAF analog 1-O-hexadecyl-2-N-methylcarbamoyl-sn-glycerol-3-phosphocholine (mc-PAF) into either rat dorsal hippocampus, amygdala, or entorhinal cortex. Male Wistar rats were implanted bilaterally with cannulae in these brain regions. After recovery from surgery, the animals were trained in step-down inhibitory avoidance or in a spatial habituation task and tested for retention 24 h later. mc-PAF (1.0 microgram per side) enhanced retention test performance of the two tasks when infused into the hippocampus before training without altering training session performance. In addition, mc-PAF enhanced retention test performance of the avoidance task when infused into (i) the hippocampus 0 but not 60 min after training; (ii) the amygdala immediately after training; and (iii) the entorhinal cortex 100 but not 0 or 300 min after training. In confirmation of previous findings, BN 52021 (0.5 microgram per side) was found to be amnestic for the avoidance task when infused into the hippocampus or the amygdala immediately but not 30 or more minutes after training or into the entorhinal cortex 100 but not 0 or 300 min after training. These findings support the hypothesis that memory involves PAF-regulated events, possibly LTP, generated at the time of training in hippocampus and amygdala and 100 min later in the entorhinal cortex.

Muscarinic toxins from the venom of Dendroaspis snakes with agonist-like actions

The venom of some Dendroaspis snakes contains small proteins (7500 mol. wt) that inhibit the binding of radiolabelled muscarinic antagonist to brain synaptomal membranes. There were no peptides described among muscarinic ligands until Adem et al. (Biochim. biophys. Acta 968, 340-345, 1988) reported that muscarinic toxins (MTxs), MTx1 and 2 were able to inhibit 3H-QNB binding to rat brain membranes. Since MTxs inhibit around half of specific binding of 3H-quinuclidinyl benzilate (3H-QNB) and 3H-N-methyl-scopolamine (3H-NMS), which do not discriminate between subtypes of muscarinic receptors, it has been proposed that MTxs might selectively bind to some subtype. MTx1 and 2 from Dendroaspis angusticeps almost completely inhibit the binding of 3H-pirenzepine (3H-PZ), a preferential M1 muscarinic receptor subtype ligand to cerebral cortex synaptosomal membranes. A much higher concentration was needed to inhibit partially 3H-PZ binding to atrial muscarinic receptors. These results support the hypothesis that MTx1 and 2 may be M1 selective muscarinic ligands. Similar activities have been found in Dendroaspis polylepis and D. viridis venoms, but with lower affinities. The Ki obtained from inhibition curves of the binding of 3H-PZ showed that MTx1 has higher affinity for the putative M1 muscarinic receptor subtype, followed by MTx2. DpMTx has lower affinity, while DvMTx seems to have the lowest affinity. All these peptides are devoid of anticholinesterase activity. Dendrotoxin and fasciculin from D. angusticeps venom do not inhibit the binding of muscarinic radioligands to cerebral cortex membranes. The injection of MTxs into dorsal hippocampus of rats immediately after training in an inhibitory avoidance task improves memory consolidation, as does oxotremorine.(ABSTRACT TRUNCATED AT 250 WORDS)

Experiments suggesting a role for nitric oxide in the hippocampus in memory processes

Nitric oxide (NO) has been proposed to be involved in the induction of long-term potentiation (LTP) and in other processes. When coupled with weak tetanic stimulation, NO produces a long-term synaptic enhancement on its own. N-Nitroarginine (NO-Arg) inhibits NO-synthase, the enzyme that produces NO, and blocks LTP in hippocampal slices. We investigated the effect on memory of the pre- or post-training infusion of NO-Arg and of the post-training infusion of the No donor, S-nitroso-N-acetylpenicillamine (SNAP) into the hippocampus. Male Wistar rats were implanted bilaterally with cannulae in the dorsal hippocampus. After recovery from surgery, the animals were trained in step-down inhibitory avoidance using a 0.4-mA footshock and tested for retention 24 h later. NO-Arg (2.0 microgram) hindered retention test performance when infused either before or immediately after training, but not 30 or 60 min later. SNAP (5.0 microgram) enhanced retention test performance when given 0, 60, or 150 min, but not 300 min, after training. The results suggest that memory storage depends on NO-sensitive processes in the hippocampus, perhaps, as suggested in previous papers, LTP generated at the time of training.

Evidence for the involvement of hippocampal CO production in the acquisition and consolidation of inhibitory avoidance learning

Carbon monoxide (CO), produced through the action of haem oxygenase (HO) isoenzymes, has been recently postulated as a retrograde messenger in the early stages of long-term potentiation (LTP). In the present study, rats submitted to an inhibitory avoidance task there is a significant increase (+76%) in hippocampal HO activity immediately after training (0 min), but not at 60 min post-training. No changes were observed in cerebral cortical and cerebellar HO activity. Bilateral intrahippocampal infusion of the HO inhibitor zinc-protoporphyrin-IX (ZnPP) (2 micrograms side-1) caused full amnesia for inhibitory avoidance when given 10 min before training or immediately after training, but not 60 min after training. These findings provide evidence that CO production in the hippocampus is important for the early stages of memory processing of an inhibitory avoidance training.

Flutrimazole 1% dermal cream in the treatment of dermatomycoses: a multicentre, double-blind, randomized, comparative clinical trial with bifonazole 1% cream. Efficacy of flutrimazole 1% dermal cream in dermatomycoses. Catalan Flutrimazole Study Group

BACKGROUND

Flutrimazole is a new imidazole derivate. Its antifungal activity has been demonstrated in in vivo and in vitro studies to be comparable to that of clotrimazole and higher than bifonazole.

AIM

To compare the efficacy and tolerability of flutrimazole cream 1% with a reference drug, bifonazole, in the treatment of dermatomycoses, eligible for topical treatment exclusively.

METHODS

A multicentre, double-blind, randomized, parallel-group clinical trial was conducted. Patients with clinically and mycologically (KHO and/or culture) diagnosed fungal infection of the skin were included in this study and were randomized into two treatment groups: 1% flutrimazole or 1% bifonazole, applied to the affected area (target lesion) once a day. The principal criterion of efficacy, 'cure', was based on clinical and mycological assessment.

RESULTS

Four hundred and forty-nine patients were included in the study (228 flutrimazole, 221 bifonazole). 'Intention-to-treat' analysis of the data showed a difference between the treatments in terms of the rate of cure (clinical and mycological) after 4 weeks: 73% in the flutrimazole group and 65% in the bifonazole group (p = 0.05). From a safety point of view, flutrimazole and bifonazole were well tolerated, and the overall incidence of adverse effects (mainly mild local effects like irritation or burning sensation) was 5%.

CONCLUSIONS

One percent flutrimazole applied topically once a day in the treatment of fungal infections of the skin presents a better efficacy than bifonazole and a good tolerability.

Correlation between the pharmacology of long-term potentiation and the pharmacology of memory

The pharmacology of memory has been recently studied by the infusion of drugs into the hippocampus (HIP), amygdala (AMY), medial septum (MS), and entorhinal cortex (EC) at various times after training or at the time of retention testing. It was found to be remarkably similar to that of long-term potentiation (LTP). Memory and LTP are blocked early on by antagonists of glutamate N-methyl-D-aspartate (NMDA) or metabotropic receptors (mGLUs), by the antagonist of the presynaptic membrane receptor to PAF, BN 52021, by the inhibitor of heme oxygenase, ZnPP, by the inhibitor of NO synthase, N-nitro-arginine, by GABA type A receptor agonists, or by muscarinic blockers. Both memory and LTP are enhanced, at this early stage, by glutamate, mGLU agonists, GABA-A antagonists, muscarinic agonists, and norepinephrine. In the next 1-3 h, memory and LTP are accompanied by enhanced activity of protein kinases and are blocked by specific inhibitors of calcium/calmodulin dependent protein kinase II and protein kinase C. At the time of expression, memory and LTP are blocked by antagonists of glutamate AMPA receptors and are accompanied by an enhanced sensitivity of these receptors. Memories that depend on HIP are affected by drugs given into the HIP but not the MS or AMY, memories that depend on the AMY are affected by drugs given into the AMY, and memories that depend on the HIP, AMY, and MS are affected by drugs given into the three structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrahippocampal, but not intra-amygdala, infusion of an inhibitor of heme oxygenase causes retrograde amnesia in the rat

Zinc protoporhyrin-9 (ZnPP) is an inhibitor of heme oxygenase, the enzyme involved in the biosynthesis of carbon monoxide (CO). CO regulates the activity of glutamatergic synapses and has been proposed to play a role in the early phases of long-term potentiation. The present paper reports on the effect of ZnPP on memory of inhibitory avoidance and of habituation to a novel environment. The bilateral infusion of ZnPP (2 micrograms/side) into the dorsal hippocampus caused amnesia for the inhibitory avoidance task when given before training or 0 or 30 min, but not 60 or 100 min, after training. The immediate post-training intrahippocampal infusion of ZnPP also caused amnesia for the habituation task. The immediate post-training intra-amygdala infusion of ZnPP had no effect on retention of the avoidance task. The data are consistent with the hypotheses that memory involves long-term potentiation initiated at the time of training in the hippocampus, and that hippocampal but not amygdala long-term potentiation may be regulated by CO.

Flutrimazole 1% dermal cream in the treatment of dermatomycoses: a randomized, multicentre, double-blind, comparative clinical trial with 1% clotrimazole cream. Flutrimazole Study Group

In a multicentre, double-blind, randomized, parallel group clinical trial, the efficacy and tolerability of flutrimazole 1% dermal cream were compared with those of a reference compound, clotrimazole 1% dermal cream, applied topically twice daily for 4 weeks in patients with clinically and mycologically diagnosed fungal infection of the skin. A total of 484 patients were included in the study (244 patients received flutrimazole cream and 240 clotrimazole cream). According to an intention to treat analysis of the data, there was no difference between the treatments in terms of the rate of mycological cure after 4 weeks: 79% of patients in the clotrimazole group and 80% of patients in the flutrimazole group were mycologically cured (P = 0.83). From a safety point of view, flutrimazole and clotrimazole were well tolerated and the overall incidence of adverse reactions (mainly mild local reactions such as irritation or burning sensation) was 7%. This study shows that, in the treatment of fungal infections of the skin, topically applied flutrimazole has good efficacy, similar to that of clotrimazole, and is well tolerated.

Pharmacological evidence for a role of long-term potentiation in memory

Memory processes and long-term potentiation (LTP) are blocked at the time of their initiation by antagonists of glutamate NMDA or metabotropic receptors, by drugs that hinder the activity of carbon monoxide or the platelet-activating factor, and by GABA type A receptor agonists. In the next 2 h, memory and LTP are accompanied by an enhancement of the activity of calcium/calmodulin-dependent protein kinase II and of protein kinase C, and are blocked by inhibitors of these enzymes. At the time of expression, memory and LTP are blocked by antagonists of glutamate AMPA receptors. The effects of drugs on memory are seen upon their infusion into areas of the brain known to be responsible for the storage and retrieval of declarative memories (hippocampus, amygdala, medial septum, entorhinal cortex) and are both task- and structure-specific. When put together with other pharmacologic findings, with lesion and recording studies, and with data on transgenic animals showing deficits of both memory and LTP, the data reviewed here lend strong support to the hypothesis that LTP in these brain areas underlies memory processes.

Effect of antagonists of platelet-activating factor receptors on memory of inhibitory avoidance in rats

Platelet-activating factor (PAF) is present in the brain. It enhances glutamate release and long-term potentiation (LTP) through an action on synaptic membrane receptors sensitive to the antagonist, BN 52021, and has been proposed as a retrograde messenger in the genesis of LTP. In addition, PAF has other, metabolic actions mediated by microsomal receptors sensitive to the antagonist, BN 50730. We investigated the effect on memory of the pre- or post-training infusion of BN 52021 or BN 50730 into the hippocampus and that of BN 52021 in the amygdala and the entorhinal cortex. Male Wistar rats were implanted bilaterally with cannulae aimed at these brain regions. After recovery from surgery, the animals were trained in step-down inhibitory avoidance using a 0.5-mA foot shock and tested for retention 24 h later. BN 52021 (0.5 microgram/side) was amnestic when given into the hippocampus or the amygdala either before or immediately after training but not 30 or 100 min later. BN 52021 was also amnestic when given into the entorhinal cortex 100 but not 0 or 300 min after training. Intrahippocampally administered BN 50730 had no effect on memory. The findings are compatible with the suggestion from previous findings that memory of this task depends on the generation of LTP at the time of training in hippocampus and amygdala and, 90-180 min later, in the entorhinal cortex.

Memory of inhibitory avoidance in the rat is regulated by glutamate metabotropic receptors in the hippocampus

This experiment investigated the effect on memory, in rats, of the bilateral intrahippocampal post-training infusion of the glutamate metabotropic receptor (mGLUR) agonist, ACPD (1S, 2R-aminocyclopentane dicarboxylate) and of the mGLUR antagonist, MCPG ([RS]-alpha-methyl-4-carboxyphenyl glycine). Male Wistar rats were implanted bilaterally with cannulae in the CA1 region of the dorsal hippocampus. After recovery from surgery they were trained in a step-down inhibitory avoidance task and tested for retention 24h later. Immediately or 180min after training they received a bilateral intrahippocampal infusion of saline (0.5µl), ACPD (1.0 or 2.5µg/side), MCPG (2.5µg/side) or ACPD plus MCPG, in 0.5µl saline. Upon immediate post-training infusion, ACPD caused a dose-dependent enhancement of memory and MCPG was amnestic. The effect of MCPG was antagonized by the simultaneous administration of ACPD. When given 180min after training, the drugs had no effect on memory. The results indicate that the early phase of memory is regulated by mGLURs in the hippocampus, and support the suggestion that memory involves long-term potentiation initiated at the time of training in the hippocampus.

CNQX infused into entorhinal cortex blocks memory expression, and AMPA reverses the effect

Rats were trained in a step-down inhibitory avoidance task using a 0.8-mA foot shock and tested for retention 26 days later. Three to five days prior to the retention test they were bilaterally implanted with cannulae aimed at the entorhinal cortex. Ten minutes before testing they received an infusion, into the entorhinal cortex, of vehicle, ciano-nitro-quinoxaline-dione (CNQX; 0.5 micrograms), amino-hydroxy-methyl-isoxalone-propionate (AMPA; 1.0 or 2.5 micrograms), or AMPA (1.0 micrograms) plus CNQX (0.5 micrograms). CNQX blocked memory expression; the effect lasted less than 90 min. AMPA had no effect of its own, but at the lower dose level it counteracted the depressant influence of CNQX. It is not likely that the effect of CNQX could have been due to an influence on performance: In separate sets of experiments the bilateral intraentorhinal infusion of CNQX (0.5 micrograms) 10 min before training did not affect either acquisition or retention of the avoidance task or general activity during 3 min of free exploration in the training box. The results indicate that the integrity of AMPA receptors in the entorhinal cortex is necessary for memory expression.

Intrahippocampal or intraamygdala infusion of KN62, a specific inhibitor of calcium/calmodulin-dependent protein kinase II, causes retrograde amnesia in the rat

We investigated the effect of a bilateral post-training intracerebral infusion of KN62, a specific inhibitor of calcium/calmodulin-dependent protein kinase II (CaM-II), on memory. This enzyme plays a crucial role in the early phases of long-term potentiation. Male Wistar rats were implanted bilaterally with cannulae aimed at the CA1 region of the dorsal hippocampus or at the junction between the central and the basolateral nuclei of the amygdala. After recovery, rats were trained in step-down inhibitory avoidance using a 0.5-mA footshock and tested for retention 24 h later. At various times after training (0, 30, 120, or 240 min for the animals implanted into the hippocampus; 0 or 240 min for the animals implanted in the amygdala) they received, through the cannulae, an infusion of vehicle (0.1% dimethylsulfoxide in water) or KN62 (100 mumol/side). KN62 caused full retrograde amnesia when given 0 min after training into either the amygdala or the hippocampus. When given into the hippocampus 30 min post-training it had a partial amnestic effect. When given 120 min after training into the hippocampus, or 240 min after training into either structure, KN62 had no effect. The data suggest that the early phase of memory requires intact CaM-II activity in the amygdala and hippocampus and support the hypothesis that memory involves long-term potentiation initiated at the time of training in both structures.

Post-training intrahippocampal infusion of protein kinase C inhibitors causes amnesia in rats

This experiment investigated the effect on memory, in rats, of the bilateral intrahippocampal post-training infusion of two different inhibitors of protein kinase C activity, staurosporin and CGP41231. Male Wistar rats were implanted bilaterally with cannulae aimed at the CA1 region of the dorsal hippocampus. After recovery from surgery, they were trained in step-down inhibitory avoidance using a 0.5-mA footshock and tested for retention 24 h later. Immediately or 30, 120, or 180 min after training they received, through the cannulae, infusions of vehicle, staurosporin (1.0 microgram), or CGP41231 (2.5 micrograms). The two drugs caused full retrograde amnesia when given immediately or 30 min post-training, partial amnesia when given 120 min after training, and had no effect when given 180 min after training. The results support the suggestion that memory involves long-term potentiation initiated at the time of training in the hippocampus. Inhibitors of protein kinase C block the development of long-term potentiation when administered in the first 2 h after induction.

Naturally occurring benzodiazepines and benzodiazepine-like molecules in brain

Great progress has been made in the last five years in demonstrating the presence of benzodiazepines (BZDs) in mammalian tissues, in beginning studies on the origin of these natural compounds and in elucidating their possible biological roles. Many unanswered questions remain regarding the sources and the biosynthetic pathways responsible for the presence of BZDs in brain and their different physiological and/or biochemical actions. This essay will focus on recent findings supporting that: (1) BZDs are of natural origin; (2) mammalian brain contains BZDs in concentrations ranging between 5.10(-10) to 10(-8) M; (3) BZDs and BZD-like molecules are unevenly distributed in brain; the highest concentration is found in limbic structures (4) dietary source of BZDs might be a plausible explanation for their occurrence in animal tissues, including man; (5) the formation of BZDs-like molecules in brain is a possibility, experimentally supported; (6) BZDs like molecules including diazepam and N desmethyldiazepam are elevated in hepatic encephalopathy; (7) natural BZDs in the brain are involved in the modulation of memory processes. Future studies using the full range of biochemical, physiological, behavioral and molecular biological techniques available to the neuroscientist will hopefully continue to yield new and exciting information concerning the biological roles that BZDs might play in the normal and pathological functioning of the brain.

Memory processing by the limbic system: role of specific neurotransmitter systems

Experiments using localized infusions into selected brain structures of agonists and antagonists of various synaptic receptors, given before or after behavioral training, have led to the following conclusions: (1) Memory is processed shortly after training in the amygdala, medial septum and hippocampus by glutamatergic NMDA and AMPA receptors activated in that sequence. Cholinergic muscarinic receptors are activated concurrently with the former. GABAA receptors modulated by brain benzodiazepines and by beta-noradrenergic receptors inhibit the process. (2) The sequential involvement of NMDA and AMPA receptors suggests that long-term potentiation (LTP) of the synapses activated by the learning experiences in the hippocampus and/or amygdala and medial septum is the crucial event. Expression of this LTP at the time of testing is necessary for retrieval: AMPA receptor blockade in the hippocampus and amygdala at the time of testing hinders retrieval. This suggests that the LTP underlies the memory process itself. (3) The amygdala, medial septum and hippocampus mediate different types of memory and/or different components of memories. The entorhinal cortex, through mechanisms that require intact NMDA receptors and are inhibited by GABAA receptors, intervenes in post-training memory processing 90-180 min after the other limbic regions. The entorhinal cortex integrates consecutively acquired memories; this role could be maintained by the LTP that is generated after training in the amygdala, hippocampus and medial septum. Post-training intervention of the entorhinal cortex does not occur if this region is inhibited at the time of training.

A peptide muscarinic toxin from the Green Mamba venom shows agonist-like action in an inhibitory avoidance learning task

A peptide, muscarinic toxin 2 (MTX2), isolated from Dendroaspis angusticeps venom was previously shown to displace the specific binding of [3H]pirenzepine, a muscarinic M1 receptor ligand, from rat brain synaptosomal membranes. We have tested MTX2 for muscarinic agonist or antagonist actions in an inhibitory avoidance task in rats. Infusion of the muscarinic receptor antagonist scopolamine into the hippocampus of rats immediately after the training period produced amnesia, whereas the muscarinic agonist oxotremorine increased retention. When MTX2 was injected into the hippocampus of rats after the inhibitory avoidance task, it caused memory facilitation, which could be suppressed by the concomitant infusion of scopolamine. Hence, in this test, MTX2 showed muscarinic receptor agonist-like actions, which are probably mediated by the M1 subtype of muscarinic acetylcholine receptors.

Memory expression of habituation and of inhibitory avoidance is blocked by CNQX infused into the entorhinal cortex

Bilateral infusion of CNQX (1.0 micrograms) into the entorhinal cortex 10 min before retention tests blocked the expression of habituation to a novel environment and of step-down inhibitory avoidance in rats. Memory expression was found to be recovered in a second test session carried out 120 min after the infusions in the avoidance task; this was not measured in the habituation task. The data suggest that memory expression of these two tasks depends on non-NMDA receptor-mediated mechanisms, perhaps the expression of LTP, in the entorhinal cortex. Previous experiments had suggested similar mechanisms in the hippocampus and the amygdala. It is possible that, under normal conditions, memory expression may depend on the coordinated activity of the three brain structures.

Role of the amygdala, hippocampus and entorhinal cortex in memory consolidation and expression

1. Experiments using localized microinfusions of specific agonists and antagonists of neurotransmitter receptors have shown that the amygdala, hippocampus, medial septum and entorhinal cortex are involved in memory consolidation, storage and expression. The data are consistent with observations derived from lesion studies suggesting a role for these structures in memory processes, but permit many additional conclusions concerning the mechanisms involved and their timing. 2. Memories are initially processed by glutamatergic N-methyl-D-aspartate (NMDA) receptors in amygdala, hippocampus and medial septum, which are sensitive to amino-phosphono valerate (AP5). Memory of inhibitory avoidance is processed by the three structures; memory of habituation to a novel environment is processed only by the hippocampus. At the time of consolidation, immediately after training, gamma-aminobutyrate type A (GABA-A) receptors, modulated by endogenous benzodiazepines, play an inhibitory role, and cholinergic muscarinic and beta-noradrenergic transmission play a modulatory role. 3. From 90 to 180 min after training, memories are blocked by cyano-nitro-quinoxalinedione (CNQX) given into the amygdala, septum and hippocampus. CNQX blocks non-NMDA glutamatergic receptors. Also between 90 and 180 min after training, memory of the habituation and inhibitory avoidance tasks is blocked by the infusion of AP5 or of the GABA-A agonist, muscimol, into the entorhinal cortex. This late post-training intervention of the entorhinal cortex is essential for the integration of successively acquired memories, and occurs in response to the simultaneous activation of CNQX-sensitive synapses in amygdala and hippocampus. 4. The expression of memory is blocked by the infusion of CNQX, at the time of testing, into the amygdala and hippocampus (inhibitory avoidance), into the hippocampus but not the amygdala (habituation), or into the entorhinal cortex (for the two tasks). Since consolidation is blocked by AP5 infused into these structures (see above), the data agree with the hypothesis that memories are mediated by (or actually consist of) long-term potentiation (LTP) in these areas of the brain. LTP induction is blocked by AP5 and LTP expression is blocked by CNQX. It is possible that, at the time of memory expression, the entorhinal cortex is an output of the amygdala and hippocampus.

Atypical ectopic pregnancy

Most emergency physicians will agree that bleeding and abdominal pain in women of child-bearing age is considered an ectopic pregnancy until proven otherwise. Ectopic pregnancy remains the leading cause of maternal mortality in the United States. A high index of suspicion is necessary for early intervention and reduction in morbidity and mortality. Risk factors for ectopic pregnancy include previous salpingo-oophoritis, ectopic pregnancy, tubal surgery or ligation, use of an intrauterine device, hormonal therapy, and, more recently, in vitro fertilization. In addition, this case emphasizes the possibility of ectopic pregnancy in women with a history of hysterectomy without bilateral oophorectomy.

Evaluation of the methodological quality of clinical trial protocols. A preliminary experience in Spain

The methodological quality of 50 clinical trial protocols submitted to our hospital has been assessed by means of a check-list. The most frequent methodological deficiencies found were related to statistical analysis, selection criteria, sample size, incorrect use of placebo, homogeneity of the groups, concomitant medication, randomisation plan, monitoring of adverse events and study design. Lack of insurance for the patients and inadequacies in the investigators' brochure and case report forms were observed in a significant number of cases. The results suggest the importance of a multidisciplinary team in the elaboration of clinical trial protocols to prevent methodological errors.

Muscimol infused into the entorhinal cortex prior to training blocks the involvement of this area in post-training memory processing

Muscimol infusions into the entorhinal cortex (ERC) have previously been reported to impair the retention of passive avoidance learning, but only when infusions were delayed until 90min after training. In the present study, three experiments were carried out to examine further the effects of muscimol infusions into the ERC prior to training. In Experiment 1, muscimol infusions prior to training had no effect on retention, confirming earlier findings, but blocked the amnestic effect of a second muscimol infusion 90min post-training. In Experiment 2, muscimol infusions prior to training blocked the improvement of retention normally seen following a second training trial 2h after the first. In Experiment 3, the technique of summation of performance across training trials was used to confirm that the direct effects of muscimol infusions lasted less than 2h. The results indicate that the GABA-ergic mechanism in the ERC is normally involved in the formation of memory for passive avoidance, but if the ERC is inactivated at the time of training, memory formation is diverted to other structures, which appear less capable of integrating consecutive memories across time.

Memory expression is blocked by the infusion of CNQX into the hippocampus and/or the amygdala up to 20 days after training

Bilateral infusion of CNQX (0.5 microgram) into the amygdala and the dorsal hippocampus prior to a retention test blocked the expression of step-down inhibitory avoidance in rats 6, 13, or 20 days after training. Retention test performance recovered 90 min after the infusions. Pretest intrahippocampal CNQX (0.5 microgram) blocked the expression of habituation to a novel environment measured 20 days after training. The data suggest that memory expression depends on non-NMDA receptor-mediated mechanisms, perhaps the expression of LTP, up to at least 20 days after acquisition. These mechanisms operate in the hippocampus in both tasks and in the amygdala in the avoidance task.