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Biomedical subjects

C Ambrogi Lorenzini

Publications and source records attributed to C Ambrogi Lorenzini.

At least 19 recordsLinked to original sources
PubMed2000

Effects of coupled perirhinal cortex and medial septal area, fimbria-fornix, entorhinal cortex tetrodotoxin inactivations on passive avoidance consolidation in the rat.

In order to ascertain the rat perirhinal cortex (PC) function during early consolidation of a passive avoidance response (PAR), and to ascertain whether there are some functional interactions with the medial septal area (MSA), the fimbria-fornix complex (FF) and the entorhinal cortex (EC), PC-MSA, PC-FF, and PC-EC coupled inactivations were performed immediately after the PAR acquisition session. Anesthetized male adult Wistar rats aged 60 days were treated with stereotaxical bilateral injections of TTX (5 ng in 0.5 microl saline) in the appropriate sites. Retrieval testing was performed 48 h later. It was shown that all three coupled inactivations were followed by significant PAR disruption. It may be concluded that PC is somehow active even during the first mnemonic phase following the acquisition session, thus better defining PC mnemonic involvement chronology. These results may be taken as indicating that during initial consolidation the engram is concurrently processed in more than one septal and parahippocampal site, each of which by itself is not absolutely necessary for the final engram formation.

Analysis of Variance↗
PubMed1999

Effects of combined medial septal area, fimbria-fornix and entorhinal cortex tetrodotoxin inactivations on passive avoidance response consolidation in the rat.

On the basis of previous experimental evidence, it has been concluded that the entorhinal cortex (EC), the fimbria-fornix (FF) complex and medial septal area (MSA) do not take part in the consolidation phase of passive avoidance response (PAR) memorization. On the other hand, a mnemonic role during consolidation of at least two of these structures has been argued, based on several considerations. In order to ascertain whether the EC and FF are still involved in PAR memorization during consolidation, the coupled fully reversible functional tetrodotoxin (TTX) inactivation of MSA, FF and EC was performed in rats having undergone a PAR training. In Experiment 1 MSA, FF and EC were inactivated pair-wise (FF and EC always bilaterally). Permanently cannulated animals were injected stereotaxically with TTX (5 ng in 0.5 microliter saline) or saline (0.5 microliter) immediately following PAR acquisition. It was shown that combined FF-EC inactivation induced PAR retention impairment, whereas FF-MSA and EC-MSA inactivation was not followed by amnesic effects. Having obtained a positive result, in Experiment 2 the combined FF-EC inactivation was performed at different post-acquisition delays (0.25 h, 1.5 h, 6 h), so as to assess the duration of their involvement in PAR consolidation. It was shown that only the coupled inactivation performed at the shortest post-acquisition delay was followed by amnesic effects. Thus EC and FF play a definite role during early consolidation. The results are discussed in relation to EC, FF, MSA, and hippocampal involvement in PAR memorization, as reported in previous studies, and to their connectivity.

Animals↗
PubMed1998

Entorhinal cortex and fimbria-fornix role in rat's passive avoidance response memorization.

The stereotaxic administration of tetrodotoxin (TTX) was employed to induce the fully reversible inactivation of the fimbria-fornix complex (FF) and of the entorhinal cortex (EC), in order to ascertain the role of these structures in the memorization of a passive avoidance response (PAR). On permanently cannulated rats TTX (5 ng in 0.5 microliter saline) or saline (0.5 microliter) was injected uni- or bilaterally, respectively, in the FF and in the EC, 60 min before PAR acquisition, immediately after PAR acquisition and 60 min before PAR retrieval, always performed 48 h after the acquisition trial. It was shown that EC unilateral or bilateral pre-acquisition inactivation was followed by amnesia, while TTX inactivation in post-acquisition and pre-retrieval had no effects. Identical results were obtained by TTX administration in FF. The experimental evidence indicates that both EC and FF play a role during acquisition of PAR engram. The results are discussed in comparison with previous ones concerning dorsal and ventral hippocampus TTX inactivation effects on rat's PAR, and in relation to hippocampal and medial septal area connectivity.

Animals↗
PubMed1994

Post-training nucleus basalis magnocellularis functional tetrodotoxin blockade effects on passive avoidance consolidation in the rat.

The tetrodotoxin (TTX) functional ablation technique was employed in order to evaluate the temporal coordinates of the rat's nucleus basalis magnocellularis (NBM) involvement in memory trace processing. Under ketamine general anesthesia, TTX (10 ng in 1 microliter saline) was stereotaxically administered to rats, either in one or both NBMs. TTX was injected to different groups of rats, respectively 15 min, 6, 24, 48, 96 h after passive avoidance acquisition testing. The rats underwent retrieval testing 48 h later, i.e. after full recovery from TTX effects. Results show that: (1) monolateral TTX blockade significantly impairs PAR conditioned responding if induced up to 6 h but not 24 h after acquisition testing; (2) bilateral TTX blockade dramatically impairs passive avoidance responding up to a 48-h delay but not 96 h after acquisition testing. The results indicate a very profound involvement of NBM in passive avoidance response consolidation. The experimental evidence is discussed together with previous functional ablation findings concerning amygdala, parabrachial nuclei and neocortex.

Amygdala↗
PubMed1994

Passive avoidance response distribution by post-training substantia nigra functional tetrodotoxin inactivation in the rat.

The tetrodotoxin (TTX) functional ablation technique was employed to assess the temporal coordinates of rat's substantia nigra (SN) in memory processing. TTX (10 ng in 1 microliter saline) was stereotaxically administered to rats under general ketamine anesthesia, either bilaterally or unilaterally. TTX was injected in different groups of rats respectively 0.25, 6, 24, and 48 hours after passive avoidance acquisition testing. Rats always underwent retrieval testing 48 hours later, after full recovery from TTX effects. The results show that: i) unilateral TTX blockade significantly impairs PAR only up to 0.25 h and not 6 h after acquisition testing, and ii) bilateral TTX blockade dramatically disrupts passive avoidance responding up to 24 but not 48 hours after acquisition testing. The results indicate a much more important SN role in memory processing than was previously assessed. The experimental evidence is discussed both in relation to previous TTX functional ablation findings (amygdala, parabrachial nuclei, nucleus basalis magnocellularis) and in relation to SN anatomical and functional connections with other subcortical structures.

Animals↗
PubMed1993

Forced extinction as a means to evaluate consolidation gradient of a passive avoidance response in the rat.

Passive avoidance response (PAR) consolidation gradient, and US (footshock) intensity/engram strength relationship were investigated by means of specific forced extinction procedure (30 min detention in the shock box without receiving punishment) in Wistar rats trained in the light-dark box apparatus. Different groups of rats (punished either with 0.8 or 1.2 mA footshock intensity) underwent detention at different postacquisition time delays: immediately or 1, 2, 4 days after acquisition training. By means of this purely behavioral paradigm, designed to investigate a specific PAR memory trace, previous results obtained by using diverse and sometimes unspecific memory-disrupting agents were fully confirmed: PAR strength and consolidation gradient are positively related to US intensity. The influence of differential generalization effects on extinction is discussed. An unexpected finding was that from engrams that are experimentally shown to be of unequal resistance to disruption, equal conditioned responses are obtained.

Animals↗
PubMed1993

Physical and optical shelter characteristics influence rat's preferences in a multiple Y-maze.

Rat's preference for covered or uncovered sections of a multiple Y-maze, measured as time spent under cover, was investigated. Surface area of covered and uncovered sections was the same. There were no light-intensity differences between uncovered and covered sections. Coverings were of two types: transparent or sanded plexiglas, affording respectively only physical or physical and optical protection. Both types of covering were placed either over discontinuous sections of the maze or continuously over one entire half of it. Male adult Wistar rats were employed. Rats exhibited maximal preference for the continuous sanded covering. They also exhibited a very similar significant preference for the continuous transparent covering and the discontinuous sanded one. Equal permanence time was measured in uncovered sections and under discontinuous transparent coverings. The results show that rats can recognize and choose shelter even when there is no light diminution under it. In fact they can very well discriminate between the several types of shelter, as shown by their significant longer permanence under the most protective and most continuous one. Finally, results are taken as basis for discussing whether the accepted "dark preference" of rats may be due solely to photophobia or also to the fact that normally darkness indicates a shelter.

Animals↗
PubMed1992

Minaprine cancels scopolamine effects on the rat's acquisition of passive avoidance responses in two multitrial paradigms.

The antiamnesic activity of minaprine has been studied in male Wistar rats. Two multitrial paradigms were employed: the light-dark box test (aversive stimulus: 0.6-mA foot-shocks) and the tail-handling test (aversive stimulus: manual tail-handling). In both paradigms, intraperitoneal scopolamine administration 30 min before testing significantly impaired the acquisition of the passive avoidance conditioned response. There were no significant differences in either paradigm between control rats and those to whom scopolamine and minaprine were simultaneously administered. These results show that minaprine fully protects the acquisition process of conditioned responses against scopolamine impairment not only in one-trial tests but also in multitrial paradigms. The effects of minaprine in reversing memory deficits are discussed in relation to its stimulating activity on central cholinergic systems.

Amnesia↗
PubMed1991

The behavior of the homozygous and heterozygous sub-types of rats which are genetically-selected for diabetes insipidus: a comparison with Long Evans and Wistar stocks.

Several aspects of spontaneous and conditioned behavior (food and water intake, locomotion and emotionality, passive and active avoidance acquisition and retention) of standard (albino and pigmented) rats, and rats heterozygous (HEDI) and homozygous (HODI) for diabetes insipidus, are reviewed. As would be expected, HODI rats have been repeatedly found to consume far more fluid than either HEDI or control rats. Pigmented rats appear to be more active than albinos. HODI rats exhibit less marked emotional responses than do control rats, among which the pigmented ones exhibit the highest emotionality. Light aversion is more evident in albino than in pigmented rats. No differences are found among HEDI, HODI and normal Long Evans rats. It is quite difficult to provide a clear-cut statement concerning inter-strain differences in passive avoidance behavior, possibly because of the variety of techniques employed. In any case, HODI rats do not perform worse than normal controls do. In one-way active avoidance paradigms, pigmented rats perform better than albinos, and the performance of HODI rats does not differ from that of controls. In two-way avoidance paradigms, albinos appear to outperform pigmented rats. Once again, there are no obvious differences between HODI and control animals. In addition to indicating that HODI rats may actually be less emotional than the other groups of rats reviewed here, the studies described once again fail to confirm the previously alleged functions of vasopressin in memory consolidation.

Animals↗
PubMed1991

Effects of nucleus basolateralis amygdalae neurotoxic lesions on aversive conditioning in the rat.

After bilateral stereotaxic administration of ibotenic acid on the n. basolateralis amygdalae, male adult rats were tested in the light-dark box apparatus to measure the time-course of the acquisition and retention of passive and active avoidance responses. The results show that after the lesions both passive avoidance and active avoidance acquisition were impaired. Passive avoidance responses were retained quite well, while active avoidance responses disappeared quickly. Conditioned freezing was almost completely absent. Thus it appears that the n. basolateralis plays a facilitatory role in all the conditioned responses which were investigated.

Amygdala↗
PubMed1991

Effects of nucleus basolateralis amygdalae neurotoxic lesions on some spontaneous activities in the rat.

Drinking, feeding, locomotion and exploratory activity of male Wistar rats were assessed after bilateral stereotaxic administration of ibotenic acid in the nucleus basolateralis amygdalae. Feeding, drinking and locomotion were measured in an activity cage, while exploratory activity was determined in a multiple Y-maze. In the 24-hour cycle, lesioned animals exhibited unvaried feeding, decreased drinking and increased locomotion. Exploration was also increased. The results show that this nucleus is not involved in quantitative feeding control, while it does exert a significant facilitatory influence on drinking. It also exerts an inhibitory influence on exploration and on locomotion.

Amygdala↗
PubMed1990

The rat's right-left preference during free exploration of a multiple Y-maze.

The right-left preference of Wistar, Sprague-Dawley, and Long Evans rats of both sexes was investigated in a multiple Y-maze in which the animals had to perform three consecutive right-left choices in order to go from the common starting point to one of the eight goal arms. The rats were free to explore the maze without being subjected to punishments or rewards. Care was taken to minimize inhibitory influences on exploration (low illumination, no handling to return the rats to home cage). The statistical analysis of the total right-left choices performed by the rats showed that three groups (Wistar females, Sprague-Dawley females, and Long Evans males) exhibited a preference for the right. This preference was not related either to sex or strain, but was possibly a species characteristic.

Animals↗
PubMed1988

Aversive conditioning of homozygous and heterozygous D.I. Brattleboro rats in the light-dark box.

Active and passive avoidance, and conditioned freezing acquisition and retention were studied in HODI and HEDI Brattleboro rats. All animals were from the same source and of the same age and sex. The light-dark box test was employed. 0.6 and 2.0 mA footshocks were administered for the same number (7) of daily trials. Extinction time-course was followed for seven consecutive daily trials. Passive avoidance: the conditioned response was acquired and retained equally well by all Ss and for both shock intensities. Active avoidance: for 0.6 mA shocks HODI Ss acquired and retained the response significantly better than HEDI Ss; for 2.0 mA shocks the response was acquired equally by both groups of Ss, and retained significantly better by HODI Ss. Freezing: in general, HODI Ss exhibited less freezing then HEDI Ss. The diverse conditioned behavior of HODI and HEDI Ss in this paradigm, which allows the contemporaneous investigation of several aversive responses, does not support the hypothesis that vasopressin deficiency impairs learning and memory in the rat.

Animals↗
PubMed1987

Effects of detention and illumination on rats' exploratory behavior in a two-box apparatus.

The effects of detention and lighting intensity on the exploratory behavior of male Wistar rats have been investigated by means of several types of two-box apparatus. Experiments consisted of six consecutive daily trials. Step-through latency values were taken up to 180 sec. Even a very short detention (10 sec) within the starting box exerted a powerful inhibitory influence on the exploratory behavior of the subjects. Uniformly well-lighted surroundings (both boxes) exerted an equally powerful inhibitory influence on the same behavior. This inhibition was only slightly decreased by the availability of visual cues. Only in the apparatus in which at least one box was dark was the exploratory behavior well maintained. Both detention and bright lighting inhibited selectively the exploratory, locomotor behavior of these animals and did not inhibit other motor activities. In fact, groomings and attempts (abortive passages from one box into the other) were repeatedly performed during the increased step-through latency. These activities are discussed as indicators of a conflict between drives.

Animals↗
PubMed1987

Spontaneous and conditioned behavior of Wistar and Long Evans rats.

Spontaneous behavior (locomotion, feeding, drinking, and exploration in a two box apparatus) as well as conditioned behavior (passive and active avoidance responding, and freezing in the light-dark box apparatus) were studied in naive male Wistar and Long Evans rats. Concerning spontaneous behavior, Long Evans rats were more active during both light and dark periods, and showed better exploratory performance than Wistar rats. Concerning conditioned behavior, Long Evans rats acquired and retained better active and passive avoidance responses, and exhibited longer initial freezing than Wistar rats in the range of 0.6-1.4 mA footshocks. The results better define the important behavioral differences existing between the two strains, Long Evans rats showing consistently a higher level of alertness and a better conditioned performance.

Animals↗
PubMed1986

Some factors influencing conditioned and spontaneous behavior of rats in the light-dark box test.

Step-through and exit latencies in the light-dark box test were used to examine the effects of unconditioned exploration, the physical characteristics of the apparatus and detention on passive and active avoidance. Experiment 1, in which the subjects (Ss) received inescapable shocks in the dark chamber, shows that omission of the free exploration of the apparatus does not significantly affect acquisition and retention of either of the learned responses. Further, passive avoidance, compared with active avoidance is, by far, the better consolidated response. Experiment 2, which is the reverse of Experiment 1, (the dark chamber becomes the safe box, and the punishments are administered in the light chamber) emphasizes the role played by the physical characteristics of the two chambers of the apparatus. This role is shown by the improvement of the active avoidance response. Experiment 3 confirms the importance of detention in influencing the behavior of conditioned and control Ss. These results underscore the basic differences of active and passive avoidance responses.

Animals↗
PubMed1985

Active and passive avoidance learning in homozygous D.I. Brattleboro rats.

In homozygous D.I. rats and in Long-Evans controls the contemporaneous evolution of learning and retention of active and passive avoidance responses was studied by means of the light-dark box test. Passive avoidance performance of homozygous D.I. rats was almost equal to that of control subjects, while their active avoidance performance showed a significant deficit. Also, in homozygous D.I. rats the duration of the first freezing after being placed in the apparatus was consistently longer than in control Ss. The longer duration of this inhibitory behavior has been taken as an indication of a diminished ability of homozygous D.I. rats to respond to stress. The possible role of this diminished response to stress in determining the active avoidance deficit is discussed.

Animals↗