Biomedical subjects

J H Medina

Publications and source records attributed to J H Medina.

At least 19 recordsLinked to original sources

PubMed1995

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.

Animals↗

PubMed1995

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.

Analysis of Variance↗

PubMed1995

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)

Amygdala↗

PubMed1995

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.

Animals↗

PubMed1995

Apigenin, a component of Matricaria recutita flowers, is a central benzodiazepine receptors-ligand with anxiolytic effects.

The dried flower heads of Matricaria recutita L. (Asteraceae) are used in folk medicine to prepare a spasmolytic and sedative tea. Our fractionation of the aqueous extract of this plant led to the detection of several fractions with significant affinity for the central benzodiazepine receptor and to the isolation and identification of 5,7,4'-trihydroxyflavone (apigenin) in one of them. Apigenin competitively inhibited the binding of flunitrazepam with a Ki of 4 microM and had no effect on muscarinic receptors, alpha 1-adrenoceptors, and on the binding of muscimol to GABAA receptors. Apigenin had a clear anxiolytic activity in mice in the elevated plusmaze without evidencing sedation or muscle relaxant effects at doses similar to those used for classical benzodiazepines and no anticonvulsant action was detected. However, a 10-fold increase in dosage produced a mild sedative effect since a 26% reduction in ambulatory locomotor activity and a 35% decrement in hole-board parameters were evident. The results reported in this paper demonstrate that apigenin is a ligand for the central benzodiazepine receptors exerting anxiolytic and slight sedative effects but not being anticonvulsant or myorelaxant.

Animals↗

PubMed1994

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.

Amnesia, Retrograde↗

PubMed1994

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.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1993

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.

2-Amino-5-phosphonovalerate↗

PubMed1992

Interactions of phospholipids and free fatty acids with antidepressant recognition binding sites in rat brain.

The lipid microenvironment of cell membranes has been shown to regulate both neurotransmitter and hormone receptors. Preincubation of cortical synaptosomal membranes of rat brain with phospholipase A2 (PLA2) increases the number of [3H]imipramine ([3H]IMI) high affinity binding sites without altering Kd (Bmax control: 2.53 +/- 0.28 pmol/mg protein vs Bmax PLA2: 3.66 +/- 0.26 pmol/mg protein). The displacement curves of [3H]IMI binding in synaptosomal membranes with other tricyclic antidepressants are not affected by the presence of PLA2. The effect of PLA2 was prevented by incubation with EGTA (2 x 10(-3)) or bovine serum albumin (BSA; 1:1). In addition, end products of catalytic activity of PLA2 such as unsaturated fatty acids (arachidonic or oleic acids) mimicked the effect of PLA2. These effects were entirely prevented by preincubation with BSA. The in vitro addition of the acidic phospholipid phosphatidylserine isolated from bovine brain (BC-PS) produced a similar increase in Bmax. This action was also blocked by addition of BSA. On the other hand, palmitic acid, a saturated fatty acid, and lysophosphatidylserine (lysoPS) or lysophosphatidylethanolamine (lysoPE) failed to modify [3H]IMI binding sites. The chronic administration of tricyclic antidepressant (AD) resulted in a 25% decrease in [3H]IMI binding sites in synaptosomal membranes. Preincubation of these AD-treated membranes with PLA2 did not alter [3H]IMI binding, whereas the addition of unsaturated free fatty acids (FFA) produced a greater increase in the density of [3H]IMI binding sites in comparison with control membranes. Taken together, these findings suggest that unsaturated free fatty acids could play an important role in the regulation of the number of [3H]IMI high affinity binding sites in the mammalian brain.

Amitriptyline↗

PubMed1992

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.

Animals↗

PubMed1992

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.

2-Amino-5-phosphonovalerate↗

PubMed1992

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.

Animals↗

PubMed1992

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.

Amygdala↗

PubMed1992

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.

Amnesia, Retrograde↗

PubMed1992

Ethanol and the peripheral benzodiazepine receptor: in vivo and in vitro experiments.

1. The effect of chronic ethanol exposure on rat peripheral benzodiazepine receptors (PBR) was studied. 2. The binding of 3H-RO 5-4864 to PBR was increased (35.4%) in the kidneys of rats treated with 10% (v/v) ethanol for 12 weeks, but not in renal membranes isolated from rats exposed to ethanol 30% (v/v) during the same period. 3. Similarly, short-term administration of ethanol (4 weeks) did not alter the binding of 3H-RO 5-4864 to renal membranes. 4. To examine the possibility of a direct interaction of ethanol with PBR, in vitro experiments were carried out. Only high concentrations of ethanol (> 100 mM) caused a significant inhibition of 3H-RO 5-4864 binding in kidney, testis and cerebral cortex. 5. The results presented indicate that chronic ethanol exposure causes a time and dose-dependent increase in renal PBR.

Animals↗

PubMed1992

Down regulation of cerebral cortical 3H imipramine binding sites during chronic antidepressant treatment is independent of the central serotonergic innervation.

The effects of chronic antidepressant (AD) administration (amitryptiline 12 mg/Kg i.p., 20 days) on cerebral cortical [3H] imipramine binding sites were examined in control rats and in serotonergic denervated animals. Both treatments independently reduced the density of [3H] imipramine binding sites by 33-40%. Animals submitted to both treatments showed a slightly higher decrease in the Bmax (-50%). No alterations were observed in the apparent dissociation constant. Preincubation of cerebral cortical synaptosomal membranes with Triton X-100 (0.2% v/v), which preferentially dissolves the presynaptic component of the synaptosomes, reduced by 40% the maximal number of [3H] imipramine binding sites in control rats. In chronic AD treated rats or in serotonergic lesioned rats, membranes preincubated with Triton X-100 showed a 30% decrease in the number of [3H] imipramine sites in comparison to the sham group. The combination of both treatments produced an even larger decrease in the density of [3H] imipramine binding sites in Triton X-100 treated membranes (-55%) compared to the sham group. Taken together, these results strongly suggest that cerebral cortical [3H] imipramine binding sites located both pre- and postsynaptically, are down regulated by the long term AD administration independently of the integrity of the central serotonergic system.

5,7-Dihydroxytryptamine↗

PubMed1992

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.

2-Amino-5-phosphonovalerate↗

PubMed1991

Production of benzodiazepine-like compounds in bovine rumen.

The presence of benzodiazepine-like molecules was detected radioimmunologically in bovine rumen contents and in incubates of ruminal contents with homogenates of several common grasses. A similar production was found "in vivo" in samples obtained from a grazing cow with a rumen cannula.

Animals↗