CNQX infused into rat hippocampus or amygdala disrupts the expression of memory of two different tasks

The bilateral infusion of CNQX (0.5 or 1.25 micrograms) into the amygdala or dorsal hippocampus 10 min prior to a retention test partially blocked the expression of stepdown inhibitory avoidance in rats 24 h after training. When infused into both the amygdala and the hippocampus at a dose of 0.5 microgram. CNQX caused a complete blockade of the expression of that task. Retention test performance recovered 2 h after the infusions. In rats trained for habituation to a novel environment and tested 24 h later, pretest intrahippocampal CNQX (0.5 microgram) blocked the expression of retention at a dose of 0.5 microgram, and intra-amygdala CNQX (0.5 or 1.25 micrograms) had no effect. The data suggest that, up to at least 1 day after training, memory of the avoidance task depends on glutamate acting on non-NMDA receptors in both the hippocampus and the amygdala, whereas memory of the habituation task depends on non-NMDA receptor activity in the hippocampus but not the amygdala.

Benzodiazepines in the brain. Their origin and possible biological roles

Great progress has been made in the last 5 yr in demonstrating the presence of benzodiazepines (BDZs) 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 biosynthetic pathways responsible for the presence of BDZs in brain and their different physiological and/or biochemical actions. This essay will focus on recent findings supporting that: (1) BDZs are of natural origin; (2) mammalian brain contains BDZs in concentrations ranging between 5 x 10(-10)-10(-8) M; (3) dietary source of BDZs might be a plausible explanation for their occurrence in animal tissues, including man; (4) the formation of BDZ-like molecules in brain is a possibility, experimentally supported; (5) BDZ-like molecules including diazepam and N-desmethyldiazepam are elevated in hepatic encephalopathy; and (6) natural BDZs 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 exciting and new information concerning the biological roles that BDZs might play in the normal and pathological functioning of the brain.

Effect of various training procedures on performance in an elevated plus-maze: possible relation with brain regional levels of benzodiazepine-like molecules

Rats submitted to one, two, or seven sessions of exploration to a new environment (habituation) or exposed to an inhibitory avoidance training showed different degrees of anxiety, evaluated by the elevated plus-maze test. Also, the brain regional levels of benzodiazepine (BDZ)-like molecules in rats submitted to one, two, or seven sessions of habituation were differentially decreased with respect to nontrained rats. The percentage of time spent in the open arms of the elevated plus-maze for each group correlates with the data of decrease in the BDZ-like immunoreactivity in amygdala (r = 0.77, p < 0.0005), hippocampus (r = 0.68, p < 0.0005), and septum (r = 0.57, p < 0.005). These results suggest that the limbic system responds to anxiogenic experiences by changing the BDZ-like molecule levels in relation to the degree of anxiety and/or stress that accompany these experiences.

Anxiogenic effects of the intraamygdala injection of flumazenil, a benzodiazepine receptor antagonist

The effects of bilateral intraamygdala microinjection of flumazenil, a benzodiazepine receptor (BZD-R) antagonist, on the exploratory activity in an elevated plus maze were examined in chronically implanted rats. This compound induced a significant decrease in the time spent in the open arms, which is consistent with an anxiogenic action. No effect was observed after intrastriatal injections of flumazenil. Naive rats exposed to the elevated plus maze showed a rapid and selective decline in the content of BZD-like molecules in amygdala (-68%) but not in striatum and hippocampus. These data suggest that the anxiogenic effects of the intraamygdala injection of flumazenil is probably due to the blockade of BZD-like molecules released during the performance.

NMDA-receptor-dependent, muscimol-sensitive role of the entorhinal cortex in post-training memory processing

The bilateral infusion into the entorhinal cortex of the NMDA receptor antagonist, AP5 (5.0µg) or of the GABA(A) agonist, muscimol (0.03µg) 90min after training but not 30min before training, 0min after training or 10min before testing, hindered retention test performance 24h after inhibitory avoidance in rats. Glutamate (5.0µg) or picrotoxin (0.08µg) infused 90min after training had no effect. In animals trained with a low level footshock a second training session, 120min after the first, was needed in order to obtain a good retention test performance. This was taken to reflect summation of the consecutive memory traces left by the two training sessions. In these animals, the infusion of AP5 or muscimol into the entorhinal cortex between the two training sessions impeded their summation. The present results suggest that the entorhinal cortex plays a late role in memory processing, that this role does not need a hyperactivation of the entorhinal cortex, and that it is important for the interaction between consecutive memory traces.

Amnesia by post-training infusion of glutamate receptor antagonists into the amygdala, hippocampus, and entorhinal cortex

The blockers of glutamate receptors, aminophosphonovaleric acid (AP5) (5.0 micrograms) and cyano-nitroquinoxaline-dione (CNQX) (0.5 microgram), were infused bilaterally into the amygdala, dorsal hippocampus, or entorhinal cortex of rats through indwelling cannulae 0, 90, 180, or 360 min after step-down inhibitory avoidance training. Animals were tested for retention 24 h after training. In the amygdala or hippocampus, AP5 was amnestic when given 0 min after training and CNQX was amnestic when given 0, 90, or 180 min after training. In the entorhinal cortex, AP5 was amnestic when given 90 or 180 min after training and CNQX had no effect. The results suggest that a phenomenon sensitive first to AP5 and then to CNQX in the amygdala and hippocampus, probably long-term potentiation (LTP), is crucial to post-training memory processing. LTP in these two structures could underlie their role in memory consolidation and could explain the late involvement of the entorhinal cortex in post-training memory processing.

Neurotransmitter receptors involved in post-training memory processing by the amygdala, medial septum, and hippocampus of the rat

Rats were trained and tested in habituation to a novel environment and step-down inhibitory avoidance. Immediately after training in each task the animals received intra-amygdala, intraseptal, or intrahippocampal micro-injections of agonists and antagonists of various neurotransmitter receptors. In the habitation task, intrahippocampal, but not intra-amygdala or intraseptal administration of the NMDA receptor antagonist aminophosphornopentanoic acid (AP5, 5.0 micrograms) or of the muscarinic receptor antagonist, scopolamine (2.0 micrograms) caused amnesia and the indirect antagonist of GABA-A receptors, picrotoxin (0.08 microgram), caused retrograde facilitation. Intrahippocampal administration of the respective agonists, glutamate, oxotremorine, and muscimol, had effects of their own opposite to those of the blockers, and norepinephrine (0.3 microgram) caused memory facilitation. In the avoidance task, results obtained with drug infusions given into the three structures were very similar: in all cases, AP5, scopolamine, and muscimol were amnestic, and glutamate, oxotremorine, norepinephrine, and picrotoxin caused memory facilitation. In addition, also in the three structures, picrotoxin counteracted the amnestic effect of AP5 and/or scopolamine and the beta-adrenoceptor blocker, timolol (0.3 microgram), while ineffective on its own, attenuated all the effects of picrotoxin. The results suggest that similar synaptic mechanisms in the amygdala, medial septum, and hippocampus are involved in memory consolidation: NMDA, muscarinic, and beta-noradrenergic receptors stimulate and GABA-A receptors inhibit this process, and beta-noradrenergic receptors modulate the GABAergic synapses. In the avoidance task these mechanisms operate in the three structures: in habituation only those in the hippocampus are operative. Possibly in each structure these mechanisms regulate, if not actually consolidate, a different aspect, component, or form of memory.

Pharmacokinetic profile of [14C]flutrimazole following single topical application in normal and scarified skin of healthy volunteers

14C-labelled 1-[(2-fluorophenyl)(4-fluorophenyl)phenylmethyl]-1H- imidazole (flutrimazole, UR-4056, CAS 119006-77-8) was administered topically (dermally) in three male volunteers to normal skin and scarified skin, respectively. Blood, urine and faeces were collected and radioassayed by liquid scintillation counting techniques. After topical application to healthy skin area, less than 1% of flutrimazole was absorbed percutaneously from a 1% cream and the amount absorbed was excreted with the urine. Following administration of the drug to scarified skin, the proportions absorbed were very similar to those measured after application to normal skin. About 0.5% of the administered dose is recovered in urine. The absorbed amount of drug leads to very low concentrations in the circulation, lower than a few ng/ml.

Local and systemic tolerance of flutrimazole skin creams following single and repeated topical application in healthy volunteers

A double-blind, randomized phase I study was performed in 21 healthy volunteers to evaluate the dermal tolerance of skin creams containing 1% and 2% 1-[(2-fluorophenyl)(4-fluorophenyl)phenylmethyl]-1H-imidazole (flutrimazole, UR-4056, CAS 119006-77-8) or only the excipient, versus a commercial skin cream containing 1% clotrimazole. The study was carried out using the patch-test procedure performed in three stages: 1. single application in the back skin; 2. induction period (usage test) using three skin areas on the volar side of the forearm of each subject, where skin cream samples were applied once a day for a period of three weeks; and 3. after a wash-out period of two weeks, challenge applications in the back and forearm skin. The systemic tolerance of the formulations was also tested. There was no evidence of allergic sensitization after the application of flutrimazole creams, or their excipients, with signs of mild and doubtful skin reactions being observed in few subjects with all formulations. Furthermore, no systemic side effects after topical administration were detected throughout the study.

Differential diagnosis between dementia and depression: a study of efficiency increment

A battery of neuropsychological tests was examined to establish its value in differentiating mild dementia from depression. The battery was applied to 84 subjects: 31 dementia patients of several etiologies, 31 patients with major depression and 22 volunteers whose age and educational level was similar to that of the patients. The battery consisted of tests for immediate, recent and remote memory, the Mini Mental State examination, a screening test for language disorders, and tests measuring abstraction, calculation, judgement, praxic and gnosic functions. The results showed significant differences among the three groups in all memory tests. Deficits of abstraction, calculation, praxis and language functions were strongly associated with dementia. The epidemiological analysis of efficiency increment, with determination of sensitivity and specificity, showed a highly significant enhancement of efficiency for diagnostic purposes when the results of the tests were combined. These findings suggest that the entire battery of neuropsychological tests should be applied, and their results compared using the efficiency increment procedure, in order to establish a firm differential diagnosis between dementia and depression, and/or to detect the former when it is at a mild early stage.

Late posttraining memory processing by entorhinal cortex: Involvement of NMDA and GABAergic receptors

The NMDA receptor antagonist, D-2-amino-5-phosphonopentanoic acid (AP5) (5 micrograms) and the GABAA receptor agonist, muscimol (0.03 microgram) were infused bilaterally into the entorhinal cortex of rats 0, 90, 180, or 360 min after training in habituation to a novel environment or in step-down inhibitory avoidance. Animals were tested for retention 22 h after training in each task. AP5 and muscimol were amnestic for both tasks when given 90 or 180 min after training, but had no effect when given 0 or 360 min after training. In contrast, intraamygdala injections or AP5 or muscimol were amnestic when given 0 but not 90 min after inhibitory avoidance training. The results indicate that the entorhinal cortex plays a late but important role in posttraining memory processing; this role involves glutamatergic NMDA receptors and is inhibited by GABAA receptors. The intervention of the entorhinal cortex in posttraining memory processing is subsequent, and could be secondary, to that of the amygdala and other limbic structures.

Memory consolidation of a habituation task: role of N-methyl-D-aspartate, cholinergic muscarinic and GABA-A receptors in different brain regions

1. The immediate post-training microinjection of the N-methyl-D-aspartate receptor antagonist amino-5-phosphonopentanoic acid (5 micrograms) or of scopolamine, the cholinergic muscarinic antagonist (2 micrograms), into the dorsal hippocampus of rats caused retrograde amnesia for habituation to a novel environment, as measured by the number of rearings and crossings performed in a test session. In contrast, picrotoxin (0.08 microgram), the indirect GABA-A antagonist, caused retrograde memory facilitation. 2. Receptor agonists administered into the hippocampus had effects opposite to those of the respective antagonists: glutamate (5 micrograms) and oxotremorine (2 micrograms) enhanced memory and muscimol (0.03 microgram) was amnestic. 3. Aminophosphonopentanoic acid, scopolamine and picrotoxin had no effect when injected into the amygdala or medial septum. Our result contrasted with the recent report of an inhibitory avoidance task in which these drugs, at the doses used here, were effective when injected post-training into any of the three structures. 4. These findings suggest that similar neurotransmitter mechanisms operate in different brain regions in order to regulate memory consolidation processes; however, there is a specialization of these brain regions in relation to different types or components of memory.

The effect of flumazenil on acquisition, retention, and retrieval of spatial information

The effect of flumazenil, a benzodiazepine-receptor antagonist, was evaluated in a spatial-reference memory procedure in a water maze. Flumazenil (1.0, 3.0, and 10.0 mg/kg, ip) did not modify acquisition of spatial information. Retention was similar between control and experimental rats 24 h after the training phase, as all groups showed bias to the target quadrant in a free swim trial. However, 10 days later, only flumazenil-injected rats (3.0 mg/kg) showed bias to the target quadrant. Flumazenil did not affect retrieval of spatial information in a group of well-trained rats. These results suggest that a benzodiazepine-receptor mediated endogenous mechanism is activated during learning of spatial tasks and that its blockade facilitates retention of spatial information.

GABAA receptor modulation of memory: the role of endogenous benzodiazepines

GABAA receptors are known to downregulate memory consolidation processes: picrotoxin and bicuculline enhance memory, and benzodiazepines and muscimol depress it. The discovery of naturally occurring benzodiazepines in the brain prompted a recent investigation of whether these compounds could act as physiological regulators of the GABAA receptors involved in memory modulation. Different forms of learning cause a rapid reduction of benzodiazepine-like immunoreactivity in septum, amygdala and hippocampus; microinjection of the benzodiazepine antagonist flumazenil into these regions, at the time that consolidation is taking place, enhances memory. Ivan Izquierdo and Jorge Medina suggest that these and other findings indicate that benzodiazepines released in the septum, amygdala and hippocampus do indeed physiologically downregulate memory storage processes; moreover, benzodiazepine release could be modulated by the anxiety and/or stress associated with each type of learning.

Habituation and inhibitory avoidance training alter brain regional levels of benzodiazepine-like molecules and are affected by intracerebral flumazenil microinjection

The effects of habituation and inhibitory avoidance training on the rat brain regional levels of benzodiazepine (BZD)-like molecules and on central type BZD binding sites were examined. BZD-like immunoreactivity was decreased by 26-50% in the amygdala, cerebral cortex and septum of rats sacrificed immediately after stepping-down from the platform of an inhibitory avoidance apparatus (non-trained group) as compared to naive controls. Rats submitted to a second step-down session 20 h later (habituated group) have significantly lower BZD-like immunoreactivity in the septum (-60%) as compared to non-trained animals. Rats exposed to an inhibitory avoidance training, i.e. stepping-down and receiving a footshock (trained group), showed a significant reduction in the content of BZD-like molecules in cerebral cortex (-44%), amygdala (-68%), septum (-80%) and hippocampus (-82%) as compared to non-trained rats. In addition, the density of central type BZD binding sites was slightly increased in the hippocampus and septum of trained rats. No changes were observed in the apparent dissociation constant. No changes were observed in parallel measurements of [3H]-L-quinuclidinyl benzylate binding constants at cholinergic muscarinic binding sites. The immediate posttraining intrahippocampal bilateral injection of the central type BZD receptor antagonist flumazenil (10 nmol/hippocampus), enhanced the retention of habituation but not when injected in the amygdala or septum. In contrast, retention of the inhibitory avoidance task was significantly increased by flumazenil administered bilaterally into any of the 3 brain structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Memory facilitation by post-training intraperitoneal, intracerebroventricular and intra-amygdala injection of Ro 5-4864

Post-training i.p. (2.0 or 5.0 mg/kg), i.c.v. (2.5 micrograms/rat), or intra-amygdala (1.6-40 ng/amygdala) administration of Ro 5-4864 causes memory facilitation of step-down inhibitory avoidance in rats. The effect is expressed as an increased latency to step down in a retention test carried out 24 h after training. Ro 5-4864 is a blocker of the Cl(-)-channel associated with GABAA receptors, at a site sensitive to the antagonist, PK11195, and different from that sensitive to picrotoxin. PK11195, given i.c.v. (2.5 micrograms/rat) or into the amygdala (8 ng/amygdala), antagonized the effect of Ro 5-4864. Intra-amygdala picrotoxin administration (80 ng/amygdala) also caused retrograde memory facilitation, but its effect was not antagonized by PK11195. At a higher dose (40 ng/amygdala), PK11195 had an amnestic effect of its own, which suggests that it might be acting against an endogenous ligand of receptor to Ro 5-4864 in the Cl(-)-channel. These findings support the hypothesis that there is a GABAA mechanism in the amygdala normally involved in the modulation of the post-training memory processing of aversive learnings.

Changes in gentamicin pharmacokinetic profiles induced by mechanical ventilation

The influence of controlled mechanical ventilation (CMV) on the pharmacokinetic profile of gentamicin has been examined in 23 patients after elective open heart surgery. A parallel design was adopted in two groups of patients; 13 patients requiring CMV for at least 32 h after surgery, all of whom were able to breath spontaneously (SB) after 72 h (study group), and 10 patients who required CMV for only a brief period and who showed SB at 32 h postsurgery. Haemodynamic parameters remained stable throughout the study. Apparent volume of distribution (VZ), half-life (t1/2), total clearance (CL), peak (Cmax") and trough (Cmin") plasma levels at steady-state for target levels (6-8 microgram/ml), were measured. In the study group significant differences between CMV and SB conditions were found in VZ (mean 0.36 and 0.25 l/kg). t1/2 (mean 3.63 and 2.90 h) and Cmax" (mean 4.30 and 5.53 microgram/ml) while Cmin" (mean 1.06 microgram.ml-1 and 0.92 microgram.ml-1) did not change significantly. In contrast, the pharmacokinetics in the control group showed no differences. It appears that CMV leads to an increase in gentamicin Vz which accounts for the fall in Cmax" below the therapeutic dose range (less than 5 microgram/ml) recommended for gentamicin. It seems advisable to use a large dose of gentamicin in patients receiving CMV, even before the level is assessed.

Benzodiazepine receptor ligand influences on learning: an endogenous modulatory mechanism mediated by benzodiazepines possibly of alimentary origin

In rats, pre- but not post-training ip administration of either flumazenil, a central benzodiazepine (BZD) receptor antagonist, or of n-butyl-B-carboline-carboxylate (BCCB), an inverse agonist, enhanced retention of inhibitory avoidance learning. Flumazenil blocked the enhancing effect of BCCB, and the inhibitory effect of the BZD agonists clonazepam and diazepam also given pre-training. Post-training administration of these drugs had no effect. The peripheral BZD receptor agonist/chloride channel blocker Ro5-4864 had no effect on the inhibitory avoidance task when given ip prior to training, but it caused enhancement when given immediately post-training either ip or icv. This effect was blocked by PK11195, a competitive antagonist of Ro5-4864. These results suggest that there is an endogenous mechanism mediated by BZD agonists, which is sensitive to inverse agonists and that normally down-regulates the formation of memories through a mechanism involving GABA-A receptors and the corresponding chloride channels. The most likely agonists for the endogenous mechanism suggested are the diazepam-like BZDs found in brain whose origin is possibly alimentary. Levels of these BZDs in the cortex were found to sharply decrease after inhibitory avoidance training or mere exposure to the training apparatus.

Endogenous benzodiazepine modulation of memory processes

The immediate posttraining administration of the GABA antagonist, bicuculline, or of the Cl-channel blockers, picrotoxin or Ro 5-4864, enhances memory. These drugs are effective when injected into the amygdaloid nucleus. Intraamygdala muscimol has an opposite effect. All this suggests that memory is modulated at the posttraining period by GABA-A receptors. The pre-, but not posttraining systemic administration of benzodiazepines hinders, and that of inverse agonists, or of the benzodiazepine antagonist, flumazenil enhances retention of diverse tasks. Flumazenil, at doses lower than those that cause an enhancement, antagonizes the effect of benzodiazepine agonists and inverse agonists. This suggests that memory is modulated during acquisition by endogenous benzodiazepine receptor ligands: possibly the diazepam that was recently discovered in brain. Pretraining intraamygdala muscimol administration depresses memory, at doses several times higher than those that are effective posttraining. Pretraining Ro 5-4864 has no effect. This suggests that the release of endogenous benzodiazepines during training may modulate a GABA-A receptor complex, possibly in the amygdala, making it more sensitive to muscimol or Ro 5-4864 in the immediate posttraining period.

Bilateral injection of fasciculin into the amygdala of rats: effects on two avoidance tasks, acetylcholinesterase activity, and cholinergic muscarinic receptors

These experiments examined the effects of the bilateral injection of fasciculin-2 (FAS), a natural acetylcholinesterase (AChE) inhibitory peptide, into the amygdala of rats on acquisition and retention of two avoidance behaviors. Intraamygdala injection of FAS (150 ng/amygdala) produced a pronounced and long-lasting inhibition of AChE activity: 85% and 74% on day 2 and day 5, respectively. After 48 hr, FAS-treated animals showed no changes in training or test session performance in a step-down inhibitory avoidance task (training-test interval was 24 hr). In a 2-way shuttle avoidance task, intraamygdala FAS slightly reduced retention test performance without modifying training session scores. Two and five days after FAS injections into the amygdala, the density of muscarinic receptor decreased about 50% as measured by the specific bindings of 3H-quinuclidinyl benzilate and 3H-oxotremorine. No alterations were observed in the apparent dissociation constants. On the other hand, the central-type benzodiazepine receptor population of the amygdala remained unchanged, suggesting that FAS microinjection did not produce damage to neuronal components of these nuclei. In conclusion, the results presented have indicated that a clear-cut and long-lasting inhibition of AChE activity in the amygdala is not accompanied by a facilitation of learning and memory of two different avoidance tasks. Compensation of the increased cholinergic activity by a down-regulation of muscarinic receptors could account for these findings.

Post-training down-regulation of memory consolidation by a GABA-A mechanism in the amygdala modulated by endogenous benzodiazepines

In rats, amygdala benzodiazepine-like immunoreactivity decreases by 29% immediately after the animals step down from the platform of an inhibitory avoidance apparatus and decreases by a further 45% immediately after they receive a training footshock. The decrease is attributable to a release of diazepam or diazepam-like molecules. The immediate post-training intraamygdala injection of the central benzodiazepine antagonist flumazenil (10 nmole/amygdala) causes memory facilitation, and that of the GABA-A agonist muscimol (0.005 to 0.5 nmole) causes retrograde amnesia. Pretraining ip flumazenil administration (2.0 and 5.0 mg/kg) attenuates the effect of post-training muscimol by a factor of at least 100. The higher dose of pretraining flumazenil also causes memory facilitation. The data suggest that post-training consolidation is down-regulated by a GABA-A mechanism in the amygdala modulated by endogenous benzodiazepines released during training and at the time of consolidation.