Biomedical subjects

A Begega

Publications and source records attributed to A Begega.

16 recordsLinked to original sources

PubMed2003

c-Fos expression in supramammillary and medial mammillary nuclei following spatial reference and working memory tasks.

To investigate brain substrates of spatial memory, neuronal expression of c-Fos protein was studied. Two groups of rats were trained in two spatial memory tasks in the Morris water maze, where the rats have to apply a reference memory rule or a working memory rule. In addition to the experimental groups, two control groups were used to study c-fos activation not specific to the memory processes studied. After immunohistochemical procedures, the number of c-Fos positive neuronal nuclei was quantified in the mammillary body (MB) region (medial mammillary nucleus [MMn] and supramammillary nucleus [SuM]). The results have shown that some MMn neurons expressed c-Fos nuclear immunoreactivity related to spatial working memory but not to spatial reference memory. The increased number of c-Fos immunoreactive neuronal nuclei in the SuM was related to spatial training but not to either working or reference memory demands of the tasks.

Animals↗

PubMed2002

Improvement of spatial memory by (R)-alpha-methylhistamine, a histamine H(3)-receptor agonist, on the Morris water-maze in rat.

This work aims to clarify the role of histamine in learning and memory. This is done by studying the effect of administration of the histamine precursor, L-histidine (His), and the agonist of the H(3) receptor (R)-alpha-methylhistamine (RAMH), on acquisition and retention of spatial reference memory in rats. Treatment with RAMH (10 mg/kg i.p.) facilitates recovery of spatial memory. In contrast, administration of His (500 mg/kg i.p.) does not affect the performance of this task. Moreover, pharmacological modulation of the cerebral histaminergic system does not impair the animal's behavioral flexibility, i.e. their ability to adapt to a new learning task in the same stimular context. Improved retention of spatial memory after a reduction in cerebral histamine confirms the modulating role of this neurotransmitter in memory processes.

Animals↗

PubMed2001

Effects of histamine precursor and (R)-alpha-methylhistamine on the avoidance response in rats.

The aim of this work is to clarify the role of histamine in learning and memory processes. In order to do this, the effect of administration of the histamine precursor, L-histidine (HIS) and of the agonist of the H(3) receptor, (R)-alpha-methylhistamine (RAMH), on active avoidance response in rats is studied. Treatment with RAMH (10 mg/kg i.p.) increased the number of avoidance responses produced during acquisition and retention of the learning. In contrast, administration of L-his (500 mg/kg i.p.) impairs performance in the shuttle-box. These results are consistent with a role for histamine in cognitive processes and suggest that a increase in cerebral histamine levels impair the acquisition of avoidance response, whereas reduced levels facilitate this acquisition.

Animals↗

PubMed2001

Effects of ageing on allocentric and egocentric spatial strategies in the Wistar rat.

This study was designed to assess the effect of ageing on spatial (allocentric and egocentric) strategies in rats. Two different tasks were designed for this purpose: one involving Morris' circular pool (distal extramaze cues) and another using the T water maze (egocentric cues). In the first task, the aged rats showed some difficulty in acquiring allocentric spatial learning skills. After increasing the number of trials in this task, there was no significant improvement in the performance of the aged group of rats compared to the adult group. However, in the second spatial task (using egocentric cues), both age groups gave a similar performance. Therefore, the effect of ageing on spatial learning depends on the strategy required to acquire this learning.

Journal Article↗

PubMed2000

Functional sex differences in the accessory olfactory bulb of the rat.

The aim of this study is to determine whether sex-related differences exist in the biosynthetic activity of the mitral cells within the mitral layer of the AOB. Possible functional changes over the estrus cycle and the potential effects of castration and androgenization are assessed. Biosynthetic activity was measured using silver staining of the argyrophilic proteins associated with the nucleolar organizer regions (Ag-NOR). Assisted by stereological methods, the following parameters were studied: mean number, percentage and mean area of Ag-NOR in estrus and diestrus females, intact males, castrated and androgenizated rats. We detected sex differences in a histochemical marker related to synthetic activity, an estrus cycle effect and changes resulting from the perinatal treatments. We conclude that this structurally dimorphic region is also functionally dimorphic.

Animals↗

PubMed2000

Effects of chronic alcohol consumption on spatial reference and working memory tasks.

The aim of this work was to determine the spatial memory impairments induced by chronic alcohol consumption in rats. The alcoholization process began on the 21st postnatal day and alcohol concentrations were gradually increased to reach a concentration of 20% that was maintained for 4 mon. Behavioral tests were performed in the Morris Water Maze (MWM). The first study assessed the effects of chronic alcohol intake on two reference memory tasks (a place learning with multiple trials and a new place learning carried out in the same experimental context). Alcohol-treated animals presented no overall impairment in their ability to process spatial information. Deficits were restricted to reduced behavioral flexibility in spatial strategies. The second study assessed working memory in two tasks in which information about platform location was only valid for one trial. In the first working memory task, the animals had to perform one trial per day and in the second task they were submitted to four trials per day. At the end of the second experiment, all animals were trained in a visual-cued task. In the second experiment, the most important deficits in alcohol-treated animals occur in spatial working memory tasks, and this impairment was independent of the intertrial interval used. In the second spatial working memory task, performance of the alcohol-treated animals in the earlier trials affected their performance in subsequent trials, suggesting that a process of proactive interference had taken place. The visual-cued task demonstrated that these behavioral impairments were produced without visuoperceptive impairments.

Adaptation, Psychological↗

PubMed1999

Age-related changes of the nucleolar organizer regions without neuron loss in medial mamillary bodies (hypothalamus) in old rats.

Age-related morphological and functional changes were studied in the medial mamillary nuclei of the hypothalamus (MMN). The number of nerve cells and the volume of MMN were estimated in both groups of Wistar rats, adult and old (3 and 22 months, respectively) using stereologic methods such as the optical fractionator and Cavalieri's method respectively. The number of neurons and glial cells remain inalterable with ageing but there was an age-dependent reduction in MMN volume. In the second experiment, functional changes in the MMN neurons were observed although there was no loss in neuron number. Several functional parameters of the Ag-NORs were quantified by a computer analysis system: area and number of Ag-NORs per neuron; number of neurons with one or several Ag-NORs and also surface of neuronal nucleus. The present study shows how ageing causes volumetric and functional changes in the MMN whereas the number of neurons and glial cells remain unchanged in the mamillary region. All these results confirm the effects of age on proteic synthesis activity in neurons of the MMN, showing a decreased neuronal activity in this region.

Aging↗

PubMed1999

Effects of mammillary body lesions on spatial reference and working memory tasks.

This work examines the effects of electrolytic mammillary body (MB) lesions on the performance of rats in different spatial memory tasks in the Morris water maze. The first experiment assessed the effect of MB lesion on performance in a spatial reference memory task (place learning with multiple trials). The second experiment examined the effect of a lesion in this nucleus on performance in a spatial working memory task (single-trial place learning). The results show that lesion of the MB impairs the animals performance in spatial working memory tasks but does not impair acquisition in spatial reference memory tasks (place learning, transfer task, reversal task) or in a visual-cued task. However, the deficit in the spatial working memory task does not appear to vary with the delay between acquisition and retention trials (30 s and 5 min). Our results demonstrate a clear role of the mammillary bodies in the processing of spatial information in a working memory task. Lesion of the MB impairs performance in a working memory task but does not affect reference memory processes.

Animals↗

PubMed1999

Unbiased estimation of the total number of nervous cells and volume of medial mammillary nucleus in humans.

In this study, we demonstrate that aging does not provoke any changes in neuronal number or in the glial cells of the medial mammillary nucleus (MMN) in humans. Three age groups were used: young (age 17-35), adult (age 50-57), and aged (age 70-88). Furthermore, no age-dependent volumetric changes were observed in the MMN. All the estimations were performed with stereological methods: an optical fractionator and Cavalier's principle. The total number of neurons cells was estimated using an optical fractionator and amounted to 32x10(3) in the young group, 24x103 in the adult group, and 29x103 in the aged group. The number of glial cells was 164x10(3), 187x103, 185x103, respectively. Thus, all three age groups had a neuron/glial ratio of about 1:5, 1:8, and 1:6, respectively. The MMN volume was estimated using the Cavalier's principle. The total volume was 6.98 mm3 in the young group, 6.66 mm3 in the adult group, and 6.80 mm3 in the aged group. We have demonstrated that neither the total number of neurons and glial cells nor the volume of MMN are affected by age.

Adolescent↗

PubMed1999

Hepatic cytochrome oxidase in rats with microsurgical cholestasis or portocaval shunt.

AIMS: portocaval shunt and extrahepatic cholestasis are experimental models of chronic hepatic insufficiency of different etiology and histological characteristics, and which probably also differ in the mechanism of impairment of oxidative metabolism. To test this hypothesis we measured hepatic cytochrome oxidase. METHODS: cytochrome oxidase was assayed with a histochemical technique in three groups of Wistar rats: A (n = 8) control; B (n = 8) microsurgical extrahepatic cholestasis; and C (n = 8) end-to-side portocaval shunt. RESULTS: cytochrome oxidase activity was lowest in group B, both in the left middle (p = 0.00019) and in the inferior caudate (p = 0.00014) hepatic lobes, and was highest in group C in both hepatic lobes, especially in the left middle lobe (p = 0.0029). CONCLUSION: the decrease in cytochrome oxidase activity in the liver of rats with extrahepatic cholestasis and the increase in animals subjected to portal flow deprivation demonstrate the different nature of the impairment in hepatic oxidative metabolism in these two pathological conditions.

Animals↗

PubMed1997

Changes in the nucleolar organizer regions in the tuberomammillar region after dehydration.

The existence of efferent connections between tuberomammillary (TM) and the supraoptic (SON) nuclei led us to study the morphological changes at these levels during dehydration induced in rats by repeated administration of hypertonic saline. The dehydration effects are evaluated by three parameters: nucleus area, argyrophilic nucleolar organizer regions (Ag-NOR) area, and mean number of Ag-NORs. These parameters reflect the level of transcriptional activity of the rRNA genes, which in turn is closely related to the protein synthesis activity of the cell. The technique used is argyrophilic staining which labels the nucleolar organizer regions (NORs) of the nucleoli in the neurons and their area, permitting their quantification with an image analysis system. The statistical analysis reflects the sensitivity to dehydration of these structures at TM level. Our results support the regulatory role of vasopressin secretion by SON through the histaminergic pathways arising from TM in rat dehydration processes.

Animals↗

PubMed1997

Portacaval shunt control animals: physiological consequences derived from the sham operation.

The portacaval shunt in the rat is a frequently used experimental model of portosystemic encephalopathy. Among other consequences of this surgical preparation is an important decrease in hepatic and testicular volume. Different sham-operation methods including a laparotomy were used as controls in each case. Given that the liver volume varies greatly in comparison to body weight in the sham-operated animals, this paper aims to evaluate the possible consequences of the sham operation. It concludes that control animals without manipulation, in addition to the respective controls of portacaval shunt, should be used in every case.

Analysis of Variance↗

PubMed1996

Behaviour laterality in male rats: influence of practice and stress.

During recent decades, the existence of cerebral and behavioural asymmetries has been manifested in many different animal species. In this work, the asymmetric spatial preference recorded in the water T-maze has been analysed. Fifty-five male rats were tested in this maze for 8 consecutive days. Spatial preference, the number of times each arm was chosen, and the percentages of animals that showed right, left, or no spatial preference were calculated. The results show the evolution of this asymmetric behaviour. Most of the animals tested preferred the right arm (populational laterality). Recently, the influence of factors such as stress and practice in the process of acquiring this behaviour has been investigated. We used 40 male rats divided into two groups with two different stress levels: water temperature at 21 degrees C and 14 degrees C. Our results, based on these two criteria, hypothesize that both variables, stress and practice, are involved in the acquisition of spatial preference behaviour.

Animals↗

PubMed1996

Ethanol- and diazepam-induced cytochrome oxidase activity in mammillary bodies.

This study aims to analyze the effect of the administration of diazepam and alcohol on cytochrome c oxidase activity (COX) in the mammillary bodies (MB) with a quantitative densitometry method. The histochemical reaction of the COX is used as a reflection of energy consumption. Our results show an increase in the COX activity after treatment with diazepam in the different nuclei of MB: medial medial nucleus (MMNm), lateral medial nucleus (MMN1), and lateral nucleus (LMN) of the MB, the MMNm and LMN being significantly more active compared to the MMN1. Furthermore, the consequences of administering these drugs become manifest in spatial learning (water T maze). The performance in a spatial discrimination task did not prove to be impaired.

Animals↗

PubMedDate not supplied

[Spatial learning and the hippocampus].

INTRODUCTION: Since publication of the book The hippocampus as a cognitive map by O'Keefe and Nadel in 1978, several theoretical and experimental works have supported the participation of the hippocampus in rodents in spatial processing. Since then, great advances have been made into understanding the potential role of the hippocampus in learning and memory processes, relegating a secondary role to the hypothesis that, in rodents, the hippocampus is restricted to the formation of a cognitive map. DEVELOPMENT: In this work, different forms of spatial navigation are analyzed (taxis, cartographic and route integration-based navigation) on a psychological and neurobiological level. The spatial function of the hippocampus proposed by O'Keefe and Nadel is discussed but a more general model is chosen that explains the function of the hippocampus in mammals, i.e. a model of relational memory. Therefore, in the context of relational memory we attempt to explain the different forms of spatial memory in rodents and present the most relevant experimental data that support a critical role for the hippocampus in this kind of memory. CONCLUSIONS: The studies reviewed in this work support an important role for the hippocampus in spatial processing. However, this does not appear to be its sole function and it possibly operates more widely also participating in relational memory.

Animals↗

PubMedDate not supplied

[Quantitative observations of non-neuronal and neuronal cells of the mammillary bodies during postnatal development].

The mammillary bodies are already shaped in the last stages of the fetal development, and you can differentiate clearly in them the medial mammillary nucleus (MMN) and lateral mammillary nucleus (LMN). All this allow to study the variations in cellular density, the relation between neuronal and glial cells, so as the number of nucleoli present in the neuronal cells and the nucleolar area variations through the postnatal development (0N, 2N, 4N, 8N, 16N and adult). The results show, demonstrate a different behaviour in the cellular stabilization and migration of the MMN and LMN, so as a cellular differentiation after 4N in both nucleus. All this is discussed with the data obtained from the nucleolar activity, as an index of synthesis and reflection of the neuronal maturing.

Animals↗