Biomedical subjects

S Maren

Publications and source records attributed to S Maren.

44 records · Page 3Linked to original sources

PubMed1994

Water deprivation enhances fear conditioning to contextual, but not discrete, conditional stimuli in rats.

Water-deprived and nondeprived rats were fear conditioned with a discrete tone conditional stimulus (CS) and an aversive footshock unconditional stimulus (US). Twenty-four and 48 hr following conditioning, conditional fear to the tone CS and the context cues of the conditioning chamber, respectively, were assessed by measuring freezing behavior. Water deprivation had no effect on baseline responding to either tone or contextual stimuli. Following either 1 or 3 tone-shock pairings, however, water deprivation selectively enhanced conditional freezing to the contextual cues of the training chamber; conditional freezing to the tone was unaffected by water deprivation. These results are consistent with the view that water deprivation affects fear conditioning via an influence on the hippocampus.

Animals↗

PubMed1993

Postsynaptic factors in the expression of long-term potentiation (LTP): increased glutamate receptor binding following LTP induction in vivo.

Several lines of evidence indicate that LTP in the hippocampus is associated with a change in the properties of postsynaptic glutamate receptors. In the present study, we used quantitative autoradiography to examine the binding properties of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) and N-methyl-D-aspartate subclasses of glutamate receptors in frozen brain sections obtained from rats in which perforant-path LTP was induced in vivo. Induction of LTP resulted in a selective increase in [3H]AMPA binding in those hippocampal subfields receiving perforant-path axons. Increases in [3H]AMPA binding in dentate gyrus (stratum moleculare) were highly correlated with the magnitude of LTP recorded in this structure. Scatchard analyses of [3H]AMPA and 6-cyano-7-nitro-[3H]quinoxaline-2,3-dione (an AMPA receptor antagonist) binding in the dentate gyrus indicated that LTP induction resulted in an increase in the number of AMPA receptor binding sites. No changes in the binding of 3H-labeled N-[1-(thienyl)cyclohexyl]piperidine (an N-methyl-D-aspartate receptor antagonist) were observed in any hippocampal subfield. These results suggest that a modification in postsynaptic AMPA receptors plays a role in the expression of synaptic enhancement following LTP induction in the hippocampus.

Animals↗

PubMed1992

Long-term potentiation is associated with increased [3H]AMPA binding in rat hippocampus.

The location and nature of the changes underlying long-term potentiation (LTP) remain controversial issues. In this study, we tested the possibility that changes in binding properties of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA/quisqualate and N-methyl-D-aspartate (NMDA) subtype of glutamate receptors are associated with LTP. LTP was elicited in vivo by stimulation of the perforant pathway in anesthetized rats. One hour following stimulation the animals were sacrificed. We performed quantitative ligand binding autoradiography on frozen brain sections using [3H]AMPA and [3H]N-(1-(2-thienyl)cyclohexyl)-3,4-piperidine ([3H]TCP) to label the AMPA/quisqualate and the NMDA receptors, respectively. No changes in [3H]TCP binding were detected in any of the treatment groups. However, increases in [3H]AMPA binding were observed only in animals that exhibited LTP. These increases were bilateral and present in several subfields of the hippocampus and cortical areas. Administration of the NMDA receptor antagonist, ketamine, prior to tetanic stimulation prevented both the increase in binding and the induction of LTP. These results suggest that changes in the characteristics of AMPA/quisqualate receptors are a biochemical correlate of LTP.

Analysis of Variance↗

PubMed1992

Effects of the novel NMDA receptor antagonist, CGP 39551, on field potentials and the induction and expression of LTP in the dentate gyrus in vivo.

The effects of the novel competitive N-methyl-D-aspartate (NMDA) receptor antagonist, CGP 39551 [the carboxyethylester of CGP 37849; DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid], on extracellular field potentials and long-term potentiation (LTP) induced in the dentate gyrus by stimulation of the perforant path were studied in anesthetized rats. CGP 39551 attenuated the population spike (PS) and excitatory postsynaptic potential (EPSP) amplitude of dentate field potentials, reduced the NMDA receptor-mediated component of train-evoked burst potentials, and prevented the induction of LTP. The decrease in PS and EPSP amplitude produced by CGP 39551 was observed mainly in non-potentiated synaptic populations; potentiated field potentials were only minimally affected by drug treatment. These results are consistent with receptors may contribute in a tonic manner to the state of dentate granule cell excitability. Finally, the differential modulation of potentiated and non-potentiated synapses by CGP 39551 suggests that a change in some properties of postsynaptic AMPA receptors is involved in the expression of LTP.

2-Amino-5-phosphonovalerate↗

PubMed1991

Basolateral amygdaloid multi-unit neuronal correlates of discriminative avoidance learning in rabbits.

Basolateral (BL) amygdaloid multi-unit activity was recorded as male albino rabbits learned to avoid a foot-shock unconditioned stimulus (US) by stepping in an activity wheel to an acoustic (pure tone) warning stimulus (CS+). A second tone (CS-) of different auditory frequency than the CS+ was presented in an irregular order on half of the conditioning trials but was never followed by the US. BL amygdaloid neurons developed, in the first session of conditioning, enhanced CS-elicited discharges relative to discharges recorded during pretraining with tones and noncontingent US presentations (excitatory plasticity), and greater discharges to the CS+ than to the CS- (discriminative plasticity). The discriminative plasticity attained maximal magnitude as the rabbits reached the asymptote of behavioral discrimination, and persisted during post-asymptotic training. Peak excitatory plasticity occurred in the session of the first significant behavioral discrimination and declined during the asymptotic and post-asymptotic stages of training. Similar patterns of excitatory and discriminative plasticity in structures directly interconnected with the BL nucleus (anterior cingulate cortex; medial dorsal thalamic nucleus) and effects of lesions suggest that the neurons in these areas participate in a circuit involved in mediation of avoidance learning.

Amygdala↗

PubMed1991

A negative correlation between the induction of long-term potentiation and activation of immediate early genes.

In the present study we examined the relationship between the induction of long-term potentiation (LTP) in the dentate gyrus of anesthetized rats and activation of immediate early genes (IEGs; c-fos and zif/268) using several different high-frequency stimulation paradigms. Stimulation parameters that effectively induced LTP were not associated with IEG activation. Conversely, stimulation parameters that failed to induce LTP consistently resulted in IEG activation. These results suggest that there is a negative correlation between IEG activation and LTP, and that activation of IEGs is neither necessary nor sufficient for the induction of LTP.

Animals↗

PubMed1991

Differential effects of ketamine and MK-801 on the induction of long-term potentiation.

Ketamine and MK-801 are phencyclidine (PCP)-like noncompetitive antagonists of the N-methyl-D-aspartate (NMDA) receptor that produce a use-dependent blockade of the NMDA receptor-coupled channel. Recent studies have suggested that the binding properties of these drugs to the NMDA receptor in-vitro are different. In the present study, the effects of ketamine and MK-801 on the induction of long-term potentiation (LTP) were compared at perforant path--granule cell synapses in anaesthetized rats. LTP was observed in animals treated with either saline or MK-801, but not in those treated with ketamine. These results reveal that ketamine and MK-801 differentially modulate the induction of LTP, and we propose that this differential modulation may be related to the different binding properties of the drugs.

Animals↗

PubMedDate not supplied

Contextual and auditory fear conditioning are mediated by the lateral, basal, and central amygdaloid nuclei in rats.

A large body of literature implicates the amygdala in Pavlovian fear conditioning. In this study, we examined the contribution of individual amygdaloid nuclei to contextual and auditory fear conditioning in rats. Prior to fear conditioning, rats received a large electrolytic lesion of the amygdala in one hemisphere, and a nucleus-specific neurotoxic lesion in the contralateral hemisphere. Neurotoxic lesions targeted either the lateral nucleus (LA), basolateral and basomedial nuclei (basal nuclei), or central nucleus (CE) of the amygdala. LA and CE lesions attenuated freezing to both contextual and auditory conditional stimuli (CSs). Lesions of the basal nuclei produced deficits in contextual and auditory fear conditioning only when the damage extended into the anterior divisions of the basal nuclei; damage limited to the posterior divisions of the basal nuclei did not significantly impair conditioning to either auditory or contextual CS. These effects were typically not lateralized, although neurotoxic lesions of the posterior divisions of the basal nuclei had greater effects on contextual fear conditioning when the contralateral electrolytic lesion was placed in the right hemisphere. These results indicate that there is significant overlap within the amygdala in the neural pathways mediating fear conditioning to contextual and acoustic CS, and that these forms of learning are not anatomically dissociable at the level of amygdaloid nuclei.

Acoustic Stimulation↗