María Caballero-Bleda

Parallel input to the hippocampal memory system through peri- and postrhinal cortices

IN the rat, the rhinal cortices consist of the perirhinal, postrhinal and entorhinal cortices. The perirhinal and postrhinal cortices, which serve as major input sources to the entorhinal cortex, receive functionally different types of information. In this study we looked at the projections from the perirhinal and postrhinal cortices to the different parts of the entorhinal cortices using an anterograde tracing technique. Our results show that the perirhinal cortex preferentially projects to the lateral entorhinal cortex, whereas the postrhinal cortex mainly sends fibers to the medial entorhinal cortex. Since the lateral and medial entorhinal cortices are differentially connected with the hippocampus, we suggest that functionally different types of information are processed in parallel in the hippocampal memory system.

Projections from the presubiculum and the parasubiculum to morphologically characterized entorhinal-hippocampal projection neurons in the rat

The relations between the inputs from the presubiculum and the parasubiculum and the cells in the entorhinal cortex that give rise to the perforant pathway have been studied in the rat at the light microscopical level. Projections from the presubiculum and the parasubiculum were labeled anterogradely, and, in the same animal, cells in the entorhinal cortex that project to the hippocampal formation were labeled by retrograde tracing and subsequent intracellular filling with Lucifer Yellow. The distribution and the number of appositions between the afferent fibers and hippocampal projection neurons in the various layers of the entorhinal cortex were analyzed. The results show that layers I–IV of the entorhinal cortex contain neurons that give rise to projections to the hippocampal formation. The morphology of these projection neurons is highly variable and afferents from the presubiculum and the parasubiculum do not show a preference for any specific morphological cell type. Both inputs preferentially innervate the dendrites of their target cells. However, presubicular and parasubicular projections differ with respect to the layer of entorhinal cortex they project to. The number of appositions of presubicular afferents with cells that have their cell bodies in layer III of the entorhinal cortex is 2–3 times higher than with cells in layer II. In contrast, afferents from the parasubiculum form at least 2–3 times as many synapses on the dendrites of cells located in layer II than on neurons that have their cell bodies in layer III. Cells in layers I and IV of the entorhinal cortex receive weak inputs from the presubiculum and parasubiculum. Not only is the presubiculum different from the parasubiculum with respect to the distribution of projections to the entorhinal cortex, they also differ in their afferent and efferent connections. In turn, cells in layer II of the entorhinal cortex differ in their electrophysiological characteristics from those in layer III. Moreover, layer II neurons give rise to the projections to the dentate gyrus and field CA3/CA2 of the hippocampus proper, and cells in layer III project to field CA1 and the subiculum. Therefore, we propose that the interactions of the entorhinal-hippocampal network with the presubiculum are different from those with the parasubiculum.

Importance of Immunological and Inflammatory Processes in the Pathogenesis and THERAPY of Alzheimer's Disease

The contribution of autoimmune processes or inflammatory components in the etiology and pathogenesis of Alzheimers disease (AD) has been suspected for many years. The presence of antigen-presenting, HLA-DR-positive and other immunoregulatory cells, components of complement, inflammatory cytokines and acute phase reactants have been established in tissue of AD neuropathology. Although these data do not confirm the immune response as a primary cause of AD, they indicate involvement of immune processes at least as a secondary or tertiary reaction to the preexisting pathogen and point out its driving-force role in AD pathogenesis. These processes may contribute to systemic immune response. Thus, experimental and clinical studies indicate impairments in both humoral and cellular immunity in an animal model of AD as well as in AD patients. On the other hand, anti-inflammatory drugs applied for the treatment of some chronic inflammatory diseases have been shown to reduce risk of AD in these patients. Therefore, it seems that anti-inflammatory drugs and other substances which can control the activity of immunocompetent cells and the level of endogenous immune response can be valuable in the treatment of AD patients.

Subfield and layer-specific depletion in calbindin-D28K, calretinin and parvalbumin immunoreactivity in the dentate gyrus of amyloid precursor protein/presenilin 1 transgenic mice.

The depletion of neuronal calcium binding proteins deprives neurons of the capacity to buffer high levels of intracellular Ca(2+) and this leaves them vulnerable to pathological processes, such as those present in Alzheimers disease (AD). The aim of the present study was to investigate the expression of the calcium binding proteins, calbindin-D28K, calretinin and parvalbumin in the dentate gyrus (DG) of amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (Tg) mice and their non-Tg littermates, as well as the relation with the deposition of human amyloid beta (Abeta). We measured the expression of these three proteins at seven different rostro-caudal levels, and in the molecular, granular and polymorphic layers of the DG. We found that, except in the most caudal part of the DG, there is a substantial loss of calbindin-D28K immunoreactivity in all three layers of the DG in APP/PS1 mice compared with the non-Tg mice. Significant loss of calretinin immunoreactivity is present in most of the polymorphic layer of the DG of APP/PS1 mice compared with the non-Tg mice, as well as in the rostral and intermediate part of the inner molecular layer. Compared with the non-Tg mice parvalbumin immunoreactivity is significantly reduced throughout the whole polymorphic layer as well as in the rostral and intermediate part of the granular layer of DG in APP/PS1 mice. The relatively preservation of calbindin immunoreactivity in the caudal part of molecular and granular layers as well as calretinin immunoreactivity in the caudal part of polymorphic layer of the DG is likely related to the lower Abeta expression in those parts of DG. The present data suggest an involvement of calcium-dependent pathways in the pathogenesis of AD and indicate that there exists a subfield and layer-specific decrease in immunoreactivity which is related to the type of calcium-binding protein in APP/PS1 mice. Moreover, it seems that APP expression affects more the calbindin expression then parvalbumin and calretinin expression in the DG of APP/PS1 Tg mice.

Adult rat's offspring of alcoholic mothers are impaired on spatial learning and object recognition in the Can test

The aim of this study was to examine spatial and object recognition reference and working memory in adult offspring of Wistar rats exposed to ethanol in prenatal and/or preweaning period. For this purpose, four different conditions of the Can test were performed sequentially: spatial/object discrimination task, spatial orientation task, simple object recognition task and complex object recognition task. The results of present study shows: (1) the significant impairment in spatial learning and object recognition in animals exposed to alcohol during prenatal and/or preweaning period, (2) that cognitive dysfunction become increasingly evident with switching from simple to more sophisticated task, (3) that the most vulnerable period is the early neonatal period which corresponds to the third trimester gestational development in humans and (4) that during the developmental period, abrupt introduction or withdrawal of ethanol, rather than its continuous consumption, can produce higher cognitive deficit later on. In conclusion, moderate ethanol exposure during brain development produce long lasting impairment of spatial and recognition reference and working memory in adult rats offspring and these effects depend on the developmental period in which they were exposed to ethanol.

Neuroprotective effect of chronic verapamil treatment on cognitive and noncognitive deficits in an experimental Alzheimer's disease in rats

It is well known that disturbance of calcium homeostasis has a significant role in the development of neurodegenerative disorders, such as Alzheimers disease (AD). Our recent data suggest that acute treatment with the calcium antagonist verapamil can improve some behavioral deficits in an experimental model of AD. Therefore, the present study was done to establish the effect of chronically administered verapamil on cognitive and noncognitive behavior of rats with bilateral electrolitical lesions of nucleus basalis manocellularis (NBM)--an animal model of AD. The NBM lesions produce a deficit in performance of diverse behavior tests: active avoidance (AA), low level of fear (the open field test) as well as aggressive (the test of foot-shock induced aggression) and depressive (the learned helplessness test) behavior. Verapamil (1.0, 2.5, 5.0 and 10.0 mg/kg i.p.) or saline solution (1 ml/kg i.p.) were injected 24 hr after the lesion of NBM and then repeatedly administered during the next 8 days (twice a day). Performance of the two-way active avoidance test, the open field test, the foot shock-induced aggression test and the learned helplessness test were done on day 4 after the last verapamil or saline treatment (day 13 after the lesion). Verapamil in doses of 2.5 and 5.0 mg/kg significantly ameliorated the deficit in the performance of AA, the open field behavior, and the depression, but not the aggressive behavior. The obtained beneficial effect of chronic administered verapamil suggests that the regulation of calcium homeostasis during the early period after NBM lesions might be a reasonable way to prevent the behavioral deficits in an experimental model of AD.

Multiple binge alcohol consumption during rat adolescence increases anxiety but does not impair retention in the passive avoidance task.

We investigated the effect of binge alcohol consumption on anxiety-related behavior and memory in adolescent male Wistar rats. Three consecutive daily sessions of ethanol administration (5 g/kg) were repeated weekly for 4 weeks. The retention of passive avoidance was measured weekly, 48 h following the treatment. Three days after the last memory test a novel object exploration test was done. There was no significant difference in step-through latency between the groups, but the ethanol-treated group displayed a significantly higher incidence of defecation, and an increased number of boluses during the passive avoidance test. The latency to explore a novel object was also higher, while the duration of exploration was significantly lower. Together, these data suggest that binge alcohol consumption in adolescent rats does not impair their memory in passive avoidance tasks, but may significantly increase their anxiety.

Aging and time-of-day effects on anxiety in female Octodon degus

Animal models of anxiety have usually employed nocturnal species (e.g. rats and mice), and the tests used have been almost exclusively performed during the diurnal phase (lights on). Here, for the first time, we tested anxiety in a diurnal rodent, Octodon degus, according to its age (23 versus 40 months of age) and the time of the day. We employed three anxiety tests: object recognition, open field and light-dark tests, which were applied in the morning, at mid-day and in the late afternoon, respectively. Adult animals spent more time exploring a new object than aged animals. Nevertheless, there were no differences in the frequency of object exploration or in the latency to the first object approach between the groups. In the open field test, adult animals spent more time exploring (ambulation and rearing) than aged ones. Although both groups exhibited similar frequencies in transition from the dark to the light box in the light-dark test, adult animals spent significantly more time in the light, and expressed less anxiety when making the decision to cross over from the dark into the light area. In conclusion, there were no differences in anxiety between adult and aged animals in the morning session, although adult animals were more attentive when exploring a new object. However, in the mid-day and afternoon testing sessions, aged animals were more anxious than adults.

The flavonoid apigenin delays forgetting of passive avoidance conditioning in rats

The present experiments were performed to study the effect of the flavonoid apigenin (20 mg/kg intraperitoneally (i.p.), 1 h before acquisition), on 24 h retention performance and forgetting of a step-through passive avoidance task, in young male Wistar rats. There were no differences between saline- and apigenin-treated groups in the 24 h retention trial. Furthermore, apigenin did not prevent the amnesia induced by scopolamine (1mg/kg, i.p., 30 min before the acquisition). The saline- and apigenin-treated rats that did not step through into the dark compartment during the cut-off time (540 s) were retested weekly for up to eight weeks. In the saline treated group, the first significant decline in passive avoidance response was observed at four weeks, and complete memory loss was found five weeks after the acquisition of the passive avoidance task. At the end of the experimental period, 60% of the animals treated with apigenin still did not step through. These data suggest that 1) apigenin delays the long-term forgetting but did not modulate the 24 h retention of fear memory and 2) the obtained beneficial effect of apigenin on the passive avoidance conditioning is mediated by mechanisms that do not implicate its action on the muscarinic cholinergic system.

Barnes maze performance of Octodon degus is gender dependent

Gender differences in spatial navigation have been widely reported in nocturnal rodent species. Here, for the first time we report gender differences in spatial learning and memory of Octodon degus, a long-lived diurnal hystricomorph rodent. In the present study, 16 months old male and female O. degus were tested in the 18-holes Barnes circular maze. The acquisition session consisted of four daily 4 min trials, during 10 days. Seven days later, the retention test was performed. To avoid the effect of hormonal fluctuation on spatial navigation, both the acquisition and the retention tests, were performed in 21-day regular cycling females in a period that corresponds to the diestrus phase of the estrus cycle. At the beginning of the acquisition, female degus were significantly slower than males to find the escape hole, but the situation reversed afterwards. Moreover, during the course of acquisition, females made significantly less reference memory errors, working memory errors as well as omission errors, than males. In both sexes, motivation and learning ceiling effects were reached at days 5-6 of the training. During the acquisition, females used more frequently a spatial strategy, while males preferably applied either serial, random or opposite strategies. The observed cognitive differences between male and female O. degus existed only during the acquisition period but not during the retention, indicating that acquisition and consolidation are differently influenced by gender.