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M C Buhot

Publications and source records attributed to M C Buhot.

31 records · Page 2Linked to original sources
PubMed1994

Enhanced aggressive behavior in mice lacking 5-HT1B receptor.

The neuromodulator serotonin (5-hydroxytryptamine, 5-HT) has been associated with mood disorders such as depression, anxiety, and impulsive violence. To define the contribution of 5-HT receptor subtypes to behavior, mutant mice lacking the 5-HT1B receptor were generated by homologous recombination. These mice did not exhibit any obvious developmental or behavioral defects. However, the hyperlocomotor effect of the 5-HT1A/1B agonist RU24969 was absent in mutant mice, indicating that this effect is mediated by 5-HT1B receptors. Moreover, when confronted with an intruder, mutant mice attacked the intruder faster and more intensely than did wild-type mice, suggesting the participation of 5-HT1B receptors in aggressive behavior.

Aggression↗
PubMed1994

Effects of medial septal or unilateral hippocampal inactivations on reference and working spatial memory in rats.

The memory performances of rats receiving a reversible inactivation of either the medial septum or one side of the ventral hippocampus were compared in a radial arm maze task allowing the assessment of both working and reference memory. After pre-surgery training, rats were chronically equipped with bilateral cannulae into the ventral hippocampus and a single cannula into the medial septum. Following post-surgery retraining, animals received a series of test trials during which they received saline or lidocaine injections in either the medial septum or one side of the ventral hippocampus. Lidocaine injections in either structure resulted in both reference and working memory deficits. However, animals were more impaired after septal injections than after unilateral hippocampal injections. This result suggests that the septo-hippocampal formation acts as a functionally homogeneous structure essential for spatial processing.

Animals↗
PubMed1992

Exploratory activity and response to a spatial change in rats with hippocampal or posterior parietal cortical lesions.

Rats with bilateral lesions of posterior parietal cortex (PPC: Krieg's Area 7) or dorsal hippocampus (HIP) were compared with controls for their response to environmental change. In the first experiment, following subjects' exploration of a relatively homogeneous open-field environment, a stimulus-rat was introduced at a particular location beneath the glass floor. All groups selectively explored the location of the stimulus-rat, but only the control and PPC groups displayed habituation. On removal of the stimulus-rat, only the control group selectively re-explored the place where the stimulus-rat had been. A second experiment, similar to the first, used additional prominent visual cues beneath the floor. When the cues were spatially separate from the location of the stimulus-rat (Dissociated object condition), the same results were obtained as in the first experiment. When the additional cues were positioned close to the stimulus-rat location (Associated object condition), habituation occurred in all groups including the hippocampal group, and again the removal of the stimulus-rat resulted in a selective re-exploration of its former location in the control group only. However, a selective preference for staying at the stimulus-rat's previous location was found in PPC animals as in controls. Hippocampal rats failed to investigate the location of the missing stimulus in all conditions. The results confirm the role played by the hippocampus in spatial memory and suggest that the posterior parietal cortex is involved in the cognitive-demanding aspects of spatial encoding, particularly in environments that are poorly visually differentiated.

Animals↗
PubMed1992

Cognitive and noncognitive processes involved in selective object exploration: comparison between young adult and old rats.

The age effects on locomotor activity, object-oriented exploration, habituation, and response to a spatial change were studied in young adult and old rats using an object exploration test. In this test the spatial response was evaluated by the renewal of exploration of a familiar object after its repositioning. The specificity of the spatial response was determined by comparison with control animals not submitted to a spatial change. Male Wistar rats 6 and 24 months old were used. Results showed a significant decrement in locomotor activity, object exploration, and spatial reactivity in old rats. The habituation curve and the reactivity to a new object were preserved. Detail analyses suggest that the spatial deficit of old rats is due to an incapacity to detect the spatial change and not to their poor locomotor or exploratory activity. These results corroborate those obtained in spatial orientation tasks and support the idea that the lack of spatial response observed in old animals is more related to cognitive impairments than to other factors such as sensory, motor, or motivational differences.

Aging↗
PubMed1992

Visually guided locomotion, distractibility, and the missing-stimulus effect in hooded rats with unilateral or bilateral lesions of parietal cortex.

When hooded rats with bilateral lesions of Krieg's area 7 (parietal cortex) were trained to locomote toward visual targets in a runway, they ran less accurately than did controls, although unilaterals ran accurately. When flashing lights were presented unexpectedly during their run, bilateral parietals were less disrupted than were controls, but they failed to show total neglect. Unilateral paritals turned toward distracters on either side but turned preferentially toward distracters contralateral to the intact hemisphere, particularly when distracters occurred bilaterally and simultaneously. Effects due to the omission of expected distracters were similar in parietals and controls. Rat parietal cortex is not essential for the redirection of attention to stimuli notable for their unexpected presence or absence, but parietal cortex may resolve interhemispheric competition. The results suggest a homology between parietal cortex in rat and primate.

Animals↗
PubMed1992

Object exploration and reactions to spatial and nonspatial changes in hooded rats following damage to parietal cortex or hippocampal formation.

Hooded rats with bilateral lesions of the anterior part of the hippocampal formation (HIP), anterior region of the posterior parietal cortex (APC), or posterior region of the posterior parietal cortex (PPC) were compared with controls for their exploration of 5 objects in an open field, habituation of locomotion and object investigation, and response to spatial and nonspatial change. First, all groups displayed habituation of both locomotor and exploratory activity. Second, controls selectively reexplored displaced objects, and APC-lesioned rats reexplored all objects, whereas PPC- and HIP-lesioned rats failed to react to the spatial change. Third, a novel object induced reexploration in all groups. The results are consistent with the roles of the HIP and PPC in spatial information processing. Moreover, the APC and PPC are involved in attentional effortful processing and visuospatial information processing necessary for spatial representation, respectively.

Animals↗
PubMed1991

Effects of short-lasting inactivations of the ventral hippocampus and medial septum on long-term and short-term acquisition of spatial information in rats.

This study was aimed at testing the effects of a reversible inactivation of the hippocampal formation on long-term and short-term acquisition of spatial information. Rats chronically equipped with either bilateral cannulae into the ventral hippocampus or a single cannula into the medial septum had to locate, in a circular platform with 18 holes on the periphery, the unique hole leading to a hidden shelter in order to avoid bright light. In Expt. 1, following 16 days of training (1 trial/day, 24 h ITI) without physical intervention, the location of the correct hole was changed on both Days 17 and 23, and the rats were either sham-injected or injected with lidocaine. Both hippocampally and septally lidocaine-injected rats relearned the new location at a rate similar to corresponding sham-injected animals. In Expt. 2, a massed-trial version of the task was used, in which the rats had to learn a new hole location on each daily session (3 trials, ITI = 1 min). Animals were sham-injected or lidocaine-injected on alternate sessions. While sham-injected rats improved in orientational accuracy over successive trials, both hippocampally and septally lidocaine-injected rats failed to display any between-trial improvement. The impairment displayed by lidocaine-injected rats when their hippocampus was inactivated confirms the role of the hippocampus in short-term spatial memory (Expt. 2). In contrast, short-lasting inactivation of the hippocampus did not prevent long-term spatial learning (Expt. 1). These results suggest that the hippocampus could process information 'off-line' in the delay between temporally discontiguous learning trials, and show that short-term and long-term spatial learning rely on distinct neurobiological mechanisms.

Animals↗
PubMed1991

Spatial problem-solving in a wheel-shaped maze: quantitative and qualitative analyses of the behavioural changes following damage to the hippocampus in the rat.

The behaviour of sham-operated rats and rats with damage to the dorsal hippocampus was compared in a complex spatial problem-solving task using a 'hub-spoke-rim' wheel type maze. Compared to the classical Olton 8-arm radial maze and Morris water maze, this apparatus presents the animal with a series of possible alternative routes both direct and indirect to the goal (food). The task included 3 main stages: exploration, feeding and testing, as do the classic problem-solving tasks. During exploration, hippocampal rats were found to be more active than sham rats. Nevertheless, they displayed habituation and a relatively efficient circumnavigation, though, in both cases, different from those of sham rats. During test trials, hippocampal rats were characterized as being less accurate, making more errors than sham rats. Nevertheless, both groups increased their accuracy of first choices over trials. The qualitative analyses of test trial performance indicated that hippocampal rats were less accurate in terms of the initial error's deviation from the goal, and less efficient in terms of corrective behaviour than sham rats which used either the periphery or the spokes to attain economically the goal. Surprisingly, hippocampal rats were not limited to a taxon type orientation but learned to use the periphery, a tendency which developed over time. Seemingly, for sham rats, the problem-solving process took the form of updating information during transit. For hippocampal rats, the use of periphery reflected both an ability to discriminate its usefulness in reaching the goal via a taxis type behaviour, and some sparing of ability to generalize the closeness and the location of the goal. These results, especially the strategic correction patterns, are discussed in the light of Sutherland and Rudy's 'configurational association theory'.

Animals↗
PubMed1991

The effects of reversible inactivations of the hippocampus on exploratory activity and spatial memory.

This study was aimed at testing the effects of a reversible inactivation of the ventral hippocampus on behavior in response to a change, following a period of habituation with a hippocampus that functions normally. A new dishabituation paradigm was used, which allowed the testing of visuospatial memory. A salient stimulus was placed under the glass floor of the apparatus during initial exploration and was removed during the test session. The time spent above the zone where the stimulus was initially located indicated the rats' reaction to the change. Unlike the control rats who reacted to the removal of the salient stimulus by reexploring its previous location, lidocaine-injected subjects did not display any similar searching behavior. Experiment 2 examined the hypothesis that landmarks located under the floor could help hippocampus-inactivated animals to accurately react to the change. Two objects were located either close to the stimulus or some distance away from it. Even when the objects were closely associated to the stimulus, the same failure to react to the removal of the stimulus was found in lidocaine-injected rats. However, these animals displayed a higher activity level measured by the time spent on a "neutral" zone. This behavioral pattern suggests a specific localization deficit. The method of reversible inactivation appears to be a promising approach to the study of the time course of memory process with short-term experimental paradigms such as those used in the present study.

Animals↗
PubMed1991

The effects of superior colliculus lesions in hamsters: feature detection versus spatial localization.

This study was aimed at further documenting the effects of collicular lesions in exploratory activity in the hamster. Following habituation to a set of four objects placed in an open field, collicular and sham-operated hamsters were confronted to a change in the initial situation in which one object was replaced by a new one in a familiar location or in a new location, or a familiar object was moved to a new location, or was left in the same location (control condition). Hamsters sustaining lesions of the superior colliculus and sham-operated hamsters were found to habituate at the same rate. The surgical treatment modified the reactions to the spatial change. Intact hamsters reacted selectively to the new object, whatever its location. In contrast, collicular animals did not react to the familiar object when it was in a new location. Nevertheless, they were able to detect the new object when it replaced a familiar object at the same location. However, when the new object was at a new location, there was only a tendency in collicular hamsters to react to this change. When no change was made in the initial situation, no change in exploratory activity was observed in either group. These results, together with others, suggest that the rodent's superior colliculus is not directly involved in object discrimination, but plays a crucial role in the attentional components of spatial behavior.

Animals↗
PubMed1989

Changes in exploratory behaviour of hamsters following treatment with 8-hydroxy-2-(di-n-propylamino)tetralin.

The influence of the centrally active 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on the exploration of objects was studied in hamsters, using a radioactographic method. This spatial paradigm allows the study of the behavioural expression of underlying locomotor and cognitive (attentional, mnemonic, representative) mechanisms. The drug was found to enhance the cognitive components of the exploratory process, i.e. object-oriented exploration, habituation and, under certain temporal conditions, response-to-change, in a dose-dependent manner. Since drug-injected animals did not differ from controls when no object was present, 8-OH-DPAT probably has no role in non-oriented exploratory activity. The influence of time was further investigated by varying the duration of successive trials and intertrial intervals. In situations where the durations were extremely shortened (3-min trials/3-min intertrial intervals), drug-treated subjects, in contrast to control ones, exhibited a 'hypernormal' time course: they explored and habituated. 8-OH-DPAT appears to increase the efficiency of exploration possibly via a positive effect on arousal or attention. 8-OH-DPAT is assumed to act on 5-HT somatodendritic autoreceptors, lowering 5-HT utilization in the hippocampus, which is the main structure implicated in spatial memory. This exploration paradigm could be employed in the study of time components of environmental adaptation without the need to restrain subjects.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1989

Scopolamine impairs response-to-change based on distal cues in the rat.

The effect of a scopolamine injection (1 mg/kg, IP) on response-to-change behavior was investigated in two experiments. After exploration of a T-maze with one arm black and the other white (Trial 1), rats were tested with both arms either black or white (Trial 2). Experiment 1 revealed that the opportunity to make body turns into the arms did not help scopolamine-injected rats to locate the changed arm after visual exploration of the arms during Trial 1. Saline-injected animals chose the changed arm. In Experiment 2, rats were allowed to move freely into the arms during Trial 1. During Trial 2, they were tested either from the same start as that used during Trial 1 or from a different start 180 degrees from the original start. While scopolamine-injected animals reacted appropriately to the change when tested from the same start, they were impaired when tested from the opposite start. In both conditions, saline-injected animals chose the changed arm. These results, together with others, support the notion that the cholinergic system plays a crucial role in the processing of distal information.

Animals↗