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R Jaffard

Publications and source records attributed to R Jaffard.

At least 109 records · Page 6Linked to original sources
PubMed1983

Facilitation of memory consolidation by post-training electrical stimulation of the medial septal nucleus: is it mediated by changes in rhythmic slow activity?

Sinusoidal (100 Hz) electrical stimulation was applied at a weak intensity (7.5 muA peak to peak) through bipolar electrodes located in the medial septal nucleus after partial acquisition of an appetitive operant conditioning task in a Skinner box. Analysis of performance in a retention test 24 hr later showed that (i) the presence of stimulation electrodes by itself impaired retention-test performance, and (ii) electrical stimulation applied 30 sec after the end of the acquisition session improves retention; this facilitatory effect disappeared when the treatment was delayed 15 min. Both impairment and facilitation were found to vary (considerably) among subjects. Electrodes located in the center of the medial septal nucleus led to both a greater impairment in unstimulated subjects and a greater facilitation in stimulated subjects than more anterior placements in the vicinity of the diagonal band. Finally, spectral analysis of hippocampal EEG showed that stimulation had no effect on rhythmic slow activity (RSA). These results are discussed in relation to studies showing that RSA is associated with memory-storage processes and our own hypothesis which underlines the importance of activation of septo-hippocampal cholinergic neurons in the early stages of these mnemonic processes.

Animals↗
PubMed1983

[Accelerated forgetting and increased proactive interference after long-term alcohol consumption in the mouse].

Male Mice of the BALB/c strain were given a solution of 15% ethanol as its only source of fluid for 8 months. 2 months after alcohols was omitted from the diet they were tested for memory and compared to two control groups which received either an isocaloric solution of sucrose or tap water. Memory was tested by using spontaneous alternation (S.A.) in a T maze as a learning paradigm involving two forced trials (acquisition) followed by a free trial (retention). The 1st experiment was aimed at studying the spontaneous alteration rate as a function of the acquisition-test interval. It was found that for a short interval (5 min) the S.A. rate did not differ between the experimental aid control subjects but that it decreases more rapidly over time (1 h and 24 h) in alcohol treated subjects. The second experiment was aimed at determining whether this accelerated forgetting might not be explained by an excess of proactive interference. Results showed that when experimental subjects remembered for 1 h informations associated with a first acquisition, they were no longer able to remember those associated with a second acquisition when the interval between the two acquisitions was 5 h. Such proactive interference was not found in control subjects. These results suggest that, as in humans, prolonged alcohol consumption results in accelerated forgetting and increased proactive interferences.

Alcoholism↗
PubMed1982

[Facilitation of memory consolidation induced by electrical stimulation of the medial septal nucleus in BALB/c mice (author's transl)].

Sinusoidal (100Hz) electrical stimulation was applied at a weak intensity (7.5microA peak to peak) to the medial septal nucleus after partial acquisition of an appetitive operant conditioning task in a Skinner box. Analysis of performance recorded 24 hrs later during a retention session shows that (i) implantation alone impaired performance; (ii) electrical stimulation applied 30 sec. after the end of the acquisition session improves retention; this facilitatory effect disappears when the treatment is delayed 15 min. Furthermore spectral analysis of hippocampal EEG showed that there was no significant modification of theta rhythms. These results are discussed in relation to studies in the literature which demonstrate that RSA (rhythmical slow activity) is associated with memory-storage processes and our own hypothesis which underlines the importance of activation of septo-hippocampal cholinergic neurons in the early stages of these mnemonic processes.U

Animals↗
PubMed1981

[Quantitative relation between the spectral density of spontaneous bioelectric activity and the excitability of commissural synapses of the CA1 area of the dorsal hippocampus of conscious mice].

Power spectra of the spontaneous electrical activity of CA1 field of dorsal hippocampus and the amplitude of responses evoked to commissural stimulation were compared in waking Mice. The magnitude of excitatory post-synaptic potentials was found to be positively correlated with the power in 5 and 6 Hz while this correlation became negative for 8-9 Hz. Similar, although weaker correlations were found for the population spike responses and for a late potential, suggesting that different types of modulation are involved.

Animals↗
PubMed1981

Posttraining changes in excitability of the commissural path-CA1 pyramidal cell synapse in the hippocampus of mice.

Mice were partially trained on a bar-press operant conditioning task on continuous reinforcement (CRF). The amplitude of population excitatory postsynaptic potentials (EPSPs) evoked by commissural stimulation of the Ca2 field of the dorsal hippocampus was found to significantly increase 1 h after training and then to decrease. This phenomenon was either not observed or much less evident in mice could not learn the task or which had already been trained on this task.

Animals↗
PubMed1980

Changes in hippocampal cholinergic activity following learning in mice.

A short bar-press operant conditioning acquisition session with food reward on continuous reinforcement was shown to induce a decrease (13.5%) of hippocampal choline acetyltransferase activity in mice. Such an effect seems to be specific to this kind of learning since no change was observed in several control groups, including a group of mice submitted to another type of conditioning in the same apparatus. It is suggested that these enzymatic modifications might be responsible for the delayed improvement of performance observed on retention of this task.

Acetylcholinesterase↗
PubMed1977

Effects of hippocampal electrical stimulation on longterm memory and on cholinergic mechanisms in three inbred strains of mice.

Two sets of experiments have been carried out in an attempt to determine the role of hippocampal cholinergic mechanisms in a long-term memory storage. Three inbred strains of mice were presented with two different learning tasks in order to estimate their long-term retention abilities as well as changes in this ability after a post-trial hippocampal stimulation. In parallel experiments the enzymes involved in acetylcholine metabolism were studied under different experimental conditions. Our results indicate: (a) The capacity for long-term memory of the BALB/c line is much greater than that of either the C57BL/6 or C57BR strain. (b) Hippocampal post-trial electrical stimulation leads to an improvement of this capacity in the BALB/c strain. This phenomenon is less pronounced in C57BL/6 and non-existent in C57BR mice. (c) Choline acetyltransferase activity in the hippocampus is significantly higher in BALB/c than in the other two strains. In BALB/c this enzyme activity is greatly changed by the post-trial stimulation whereas in the C57BL/L strain only a slight variation of enzyme activity is observed. No modification occurs in C57BR. The results suggest that the more active acetylcholine synthesizing enzyme in the hippocampus of BALB/c may be related to a greater acetylcholine availability, thus favoring the establishment of a long-term memory, perhaps by releasing greater amounts of acetylcholine in the hippocampus immmediately after the learning session. The electrical stimulation of the hippocampus acts to magnify or accelerate this phenomenon. It is suggested that the efficiency of the stimulation would be related to the genetically determined higher cholinergic activity of the hippocampus.

Acetylcholine↗
PubMed1976

[Changes in cholinergic mechanisms and in learning in three strains of inbred mice after electric stimulation of the dorsal hippocampus].

Two experiments investigated the neurochemical correlates of hippocampal stimulation effects on learning in three inbred strains of Mice. In the 1st experiment, it was shown that subseizure electrical stimulation of the dorsal hippocampus, 30 sec. after a partial appetitive learning session (1) improved 24 hrs. delayed performances of BALB/c Mice (2) had little but significant effect on C57BL/6 (3) had no effect on C57BR animals. The second experiment was aimed at studying the stimulation effect on hippocampal cholinergic mechanisms by testing the two main enzymes involved in acetylcholine synthesis and degradation (choline acetyltransferase = ChAc and acetylcholinesterase = AChE). The major findings of this experiment were as follows: (1) stimulation induced a 3 hrs. delayed improvement of ChAc activity for the BALB/c strain (2) a similar but less important effect was observed in C57BL/6 Mice (3) there was no effect for C57BR animals. These result further support the view that cholinergic hippocampal mechanisms act upon memory consolidation.

Acetylcholinesterase↗
PubMed1976

[Passive avoidance in two inbred strains of mice: conditioned emotional response and specific avoidance].

Specific response inhibition and generalized behavioral suppression (conditioned emotional response) contributions to a step-through passive avoidance performance are tested in two inbred strains of mice. For this purpose response contingent (0 sec.) and delayed punishment (from 5 to 60 sec.) are used in the learning session. The results of the test session (24 hr later) show that in the BALB/c strain, the response contingent component is very important (i.e. delaying the punishment produces a rapid decrease of the step-through latency). On the otherhand the latency remains unaffected in C57 BL/6 mice, showing that conditioned emotional response is the major determinant of the passive avoidance performance in this strain. These results might at least partially explain some contradictory results about memory differences between inbred strains of mice. Moreover they show that more sophisticated behavioral analysis is necessary whenever interstrain comparisons or genetic analysis are used for studying learning and memory.

Animals↗
PubMed1976

The role of hippocampal cholinergic mechanisms in the aquisition of a barpress response.

The role of hippocampal cholinergic mechanisms in learning a bar-press response reinforced with food was investigated. Firstly, an interstrain comparison showed that mice having a low choline acetyltransferase activity in the dorsal hippocampus were quicker to associate the barpress with reinforcement. Secondly, when the activity of this enzyme was reduced by a subseizure electrical stimulation of the hippocampus learning was accelerated. It is suggested that acetylcholine availability at the hippocampal synapses slowed the apparition of these learned responses.

Acetylcholinesterase↗
PubMed1975

[Distrubance in retention of a conditioned feeding behavior in mice by subconvulsant electrical stimulation of the cerebral cortex].

A bilateral 80 s stimulation of the parieto-occipital cortex was applied 200 s after a former partial acquisition test in a Skinner box. It has resulted in an impairment of the performances obtained 24 h later through a second test. This effect was greater the greater the stimulus, this latter being always kept under threshold values of post-discharges. These results seem to reveal that reminiscence phenomena are under the control of neocortex, in a somewhat discrete way which does not produce any retrograde amnesia.

Amnesia, Retrograde↗