Developmental docosahexaenoic and arachidonic acid supplementation improves adult learning and increases resistance against excitotoxicity in the brain.

Through metabolic imprinting mechanisms a number of bioactive molecules including polyunsaturated fatty acids affect brain functions in the developmental age and longer-lasting beneficial effects are expected. In this study pregnant rats were offered diets either containing no docosahexaenoic acid (DHA) and arachidonic acid (AA) (Placebo diet) or an excess amount of these long chain polyunsaturated fatty acids (LC-PUFA) (Supplement diet) up to the time of weaning. Bilateral N-methyl-D-aspartate (NMDA) induced neurodegeneration in the entorhinal cortex of offspring in the age of 4 months was used as a tool to investigate the neuroprotective property of the developmentally supplemented DHA and AA treatments. Hippocampus-dependent spatial learning was measured in Morris water maze and the extent of neuronal lesion in the injected brain area was evaluated. Under baseline condition, in intact or sham-lesioned rats, the Morris water maze performance was superior in the supplemented group compared to the placebo controls. NMDA-lesion in the entorhinal cortex area decreased spatial learning in the supplement-treated rats while insignificantly diminished it in the placebo controls. The same supplementation attenuated the lesion size induced by the NMDA injection into the entorhinal and ventral hippocampal areas. We concluded that LC-PUFA supplementation during fetal and early postnatal development results in long-term enhancement of spatial learning ability of the offspring and offers resistance against excitotoxic brain lesion which lasts up to the adult age.

Beta-amyloid pathology in the entorhinal cortex of rats induces memory deficits: implications for Alzheimer's disease.

Alzheimer's disease is characterized by the presence of senile plaques in the brain, composed mainly of aggregated amyloid-beta peptide (Abeta), which plays a central role in the pathogenesis of Alzheimer's disease and is a potential target for therapeutic intervention. Amyloid plaques occur in an increasing number of brain structures during the progression of the disease, with a heavy load in regions of the temporal cortex in the early phases. Here, we investigated the cognitive deficits specifically associated with amyloid pathology in the entorhinal cortex. The amyloid peptide Abeta(1-42) was injected bilaterally into the entorhinal cortex of rats and behavioral performance was assessed between 10 and 17 days after injection. We found that parameters of motor behavior in an open-field as well as spatial working memory tested in an alternation task were normal. In contrast, compared with naive rats or control rats injected with saline, rats injected with Abeta(1-42) showed impaired recognition memory in an object recognition task and delayed acquisition in a spatial reference memory task in a water-maze, despite improved performance with training in this task and normal spatial memory in a probe test given 24 h after training. This profile of behavioral deficits after injection of Abeta(1-42) into the entorhinal cortex was similar to that observed in another group of rats injected with the excitotoxic drug, N-methyl-d-aspartate. Immunohistochemical analysis after behavioral testing revealed that Abeta(1-42) injection induced a reactive astroglial response and plaque-like deposits in the entorhinal cortex. These results show that experimentally-induced amyloid pathology in the entorhinal cortex induces selective cognitive deficits, resembling those observed in early phases of Alzheimer's disease. Therefore, injection of protofibrillar-fibrillar Abeta(1-42) into the entorhinal cortex constitutes a promising animal model for investigating selective aspects of Alzheimer's disease and for screening drug candidates designed against Abeta pathology.

Chronic excess of corticosterone increases serotonergic fibre degeneration in aged rats.

Evidence is presented for the potentiating role of corticosterone on axonal degeneration of serotonergic neurones during ageing. Aged rats, 24 months old, were implanted subcutaneously with 2 x 100 mg pellets of corticosterone. Serotonergic and cholinergic (ChAT- and NADPHd-positive) fibre degenerations in the anteroventral thalamic nucleus (AVT) were measured 2 months after corticosterone implantation. Numbers of immunoreactive serotonergic raphe and mesolimbic cholinergic neurones were also quantified. Basal plasma corticosterone and adrenocorticotropin (ACTH) concentrations were assayed at 2, 4, 6, and 8 weeks after implantation in the plasma and at 1, 2, 4 and 6 weeks in urine. The degree of serotonergic fibre aberrations in the AVT increased significantly after corticosterone exposure, while that of ChAT-positive and NADPHd-stained axon aberrations showed a modest but nonsignificant increase. A positive correlation between the magnitudes of serotonergic and cholinergic fibre aberrations appeared in the AVT, but only in the corticosterone-treated rats. The number of serotonin immunopositive neurones in the raphe nuclei after corticosterone decreased marginally, while that of mesopontine ChAT-positive neurones was not influenced. Measurements of basal plasma corticosterone and ACTH, as well as urine corticosterone, revealed that the steroid implantation increased the plasma corticosterone level for at least 4 weeks and decreased ACTH level for at least 6 weeks. By the week 8, the pituitary-adrenal function was apparently restored. However, at sacrifice, both the weight of adrenal glands and that of thymus remained reduced, indicating the long-lasting effects of corticosterone on target tissues. It is concluded that the raphe serotonergic neurones and their projecting fibres are sensitive to corticosterone excess in aged rats and become more vulnerable to degeneration processes than under normal ageing conditions. Cholinergic neurones of brainstem origin, which also express massive NADPHd activity, are more resistant against corticosterone, but their axon degeneration correlates to serotonergic fibre degeneration.

Postnatal maternal deprivation produces long-lasting modifications of the stress response, feeding and stress-related behaviour in the rat.

The hypothalamo-pituitary-adrenal (HPA) axis plays a central role both in the regulation of the stress response, and in the control of feeding behaviour. Sensitivity of the HPA axis to respond to stress varies both during ontogeny and between individuals, and can be altered by neonatal events. The aim of our experiments was to determine whether early events that affect the HPA axis could also induce persistent modifications in food intake (quantitatively and qualitatively), as well as alterations of anxiety-related behaviour. Twenty-four-hour maternal deprivation was introduced at two different periods of HPA maturation, on day 5 (DEP5) or day 14 (DEP14) after birth. Sequential measurements of plasma levels of adrenocorticotropin hormone (ACTH) and corticosterone showed that this deprivation altered the HPA axis of adults; the response to restraint stress was prolonged in DEP5 and a higher ACTH peak appeared in DEP14. The neonatal stress also produced long-lasting modifications of rat behaviour, as DEP14 adults became more anxious. Standard food intake decreased in both groups of deprived rats. Diet preferences also changed, as carbohydrate intake decreased in DEP5 rats. Corticosteroid receptor binding did not vary in the hippocampus of the deprived rats. The modifications of the stress response and the behaviour parameters could be due to the alteration of corticosteroid receptors in the hypothalamic paraventricular nucleus and/or corticotropin-releasing hormone or vasopressin function, but these parameters have yet to be determined. This early stress paradigm altering feeding behaviour could become an interesting model for research into human eating disorders.

Temporal and spatial dynamics of corticosteroid receptor down-regulation in rat brain following social defeat.

The experiments explored the nature and time course of changes in glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) binding in homogenates of various brain regions and pituitary of male Wistar rats following social defeat stress. One week after defeat, the binding capacity of GRs was decreased in the hippocampus and the hypothalamus while no changes were observed in the parietal cortex and the pituitary. The number of MRs remained at the same level as in undefeated rats. Three weeks postdefeat, the initially down-regulated GR returned to baseline level in the hippocampus and the hypothalamus. However, GR binding was now decreased in the parietal cortex. Severe down-regulation of MRs was detected in the hippocampal and septal tissue. The results show that brief but intense stress like social defeat induces a long-lasting down-regulation of corticosteroid receptors and that the temporal dynamics of these changes are not only differential for GRs and MRs but also for brain sites.

Blunted pituitary-adrenocortical stress response in adult rats following neonatal dexamethasone treatment.

Glucocorticoids have a prominent impact on the maturation of the stress-related neuroendocrine system and on the postnatal establishment of adaptive behaviour. The present study aimed at investigating the stress responsiveness of the hypothalamo-pituitary-adrenocortical (HPA) axis in young and adult rats after neonatal treatment with the synthetic glucocorticoid agonist, dexamethasone. Newborn male Wistar rats were injected s.c. with 1 microg/g dexamethasone on postnatal days 1, 3 and 5. Circulating adrenocorticotropic hormone (ACTH) and corticosterone concentrations were measured in the resting state and following a 30-min cold stress at the age of 10 days, as well as after a 30-min restraint stress at the age of 14 weeks. Also in adults, pituitary and adrenocortical hormone responsiveness was evaluated after i.v. administration of 2 microg/kg corticotropin releasing hormone (CRH). In addition, glucocorticoid (GR) and mineralocorticoid receptor (MR) binding capacities were assessed in the pituitaries of adult rats. The results showed that at day 10 basal ACTH concentration was elevated while the cold stress-evoked ACTH response was attenuated in the dexamethasone-treated rats. As adults, treated rats showed a suppressed elevation of both ACTH and corticosterone plasma concentrations in response to restraint, while basal hormonal concentrations were not altered. There was no difference in the magnitude of the CRH-induced elevation of ACTH and corticosterone concentrations initially; however, the dexamethasone-treated animals showed a prolonged secretion of both hormones. These animals also showed a selective decrease in pituitary GR binding capacity. Neonatal dexamethasone treatment strongly suppressed body weight gain, and adrenal and thymus weights in the early phase of postnatal development. By adulthood, the body and adrenal weights were normalized while thymus weight was greater than in controls. These findings indicate that neonatal dexamethasone treatment permanently alters HPA axis activity by reducing stress responses to cold and restraint probably through supra-pituitary actions, and by decreasing the effectiveness of feedback through a diminished GR binding in the pituitary.

Early postnatal treatment with ACTH4-9 analog ORG 2766 improves adult spatial learning but does not affect behavioural stress reactivity.

Studies on adult animals and humans have shown that the ACTH4-9 analog ORG 2766 influences cognitive performance and possibly has neurotrophic effects. For this reason we studied the effect of ORG 2766 applied in early postnatal life when brain structures and neuronal pathways are still developing. Our aim was to see whether such treatment during development would result in permanent changes in adult behavioural performance. Pups received subcutaneous injections of 1 microg/g bodyweight ACTH4-9 analog ORG 2766 on day 1, 3 and 5 after birth. Control animals in the same nest received saline injections. When the animals had reached an adult age of 3 months they were subjected to a series of tests to measure their behavioural performance. In the first experiment, behavioural stress responses and anxiety were measured by subjecting the rats to the following tests: open field, defensive burying, elevated plus maze, and conditioned fear test. In a second experiment, adult cognitive function was measured in the Morris water-maze, a hippocampus-related spatial learning test, and in the active avoidance test, a more amygdala-related nonspatial test. The results showed that animals treated with ORG 2766 during early postnatal life learned faster in the spatial Morris water-maze. The treatment had a positive effect on performance during the acquisition phase of the learning task, while memory retrieval was not affected. Learning in the nonspatial active avoidance task did not change due to the postnatal ACTH4-9 treatment. In addition, there were no differences in the open field test, the defensive burying test, elevated plus maze and the conditioned fear test. The latter supports the conclusion that the differences in water-maze performance was due to a difference in learning speed, rather than a difference in anxiety or behavioural stress reactivity. Analysis of [3H]CORT binding capacity measured after the learning tests revealed no differences in the hippocampal MR and GR concentration between non-treated and treated animals.

Long-lasting deficient dexamethasone suppression of hypothalamic-pituitary-adrenocortical activation following peripheral CRF challenge in socially defeated rats.

The present study focuses on the long-term changes in the regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis following two short-lasting episodes of intensive stress in the rat stress model of social defeat and the possible similarities with HPA functioning in human affective disorders. Male Wistar rats experienced social defeats on 2 consecutive days by an aggressive male conspecific. The long-term effect of these defeats on resting and ovine corticotropin-releasing factor (oCRF; intravenous (i.v.) 0. 5 microg/kg) induced levels of plasma ACTH and corticosterone (CORT) were measured 1 and 3 weeks later. In a second experiment the glucocorticoid feedback regulation of HPA function was tested in a combined dexamethasone (DEX)/CRF test (DEX; 25 microg/kg s.c., 90 min before oCRF injection, 0.5 microg/kg). The oCRF challenges were performed between 11.00 and 13.00 h (about three hours after start of the light phase). One week after defeat the ACTH response to CRF was significantly enhanced in defeated rats as compared to controls. Three weeks after defeat the ACTH response was back to control levels. The increased ACTH response 1 week after the stressor was not reflected in higher CORT levels. Neither were baseline ACTH and CORT levels affected by the prior stress exposure. DEX pretreatment inhibited pituitary adrenocortical activity, reflected both in reduced baseline and response values of ACTH and CORT. The ACTH response to CRF following DEX administration was significantly higher in defeated rats as compared to controls both at one and three weeks after defeat. A reduced DEX suppression of baseline secretion of ACTH appeared 3 weeks after defeat. The same tendency was apparent in response and baseline values of CORT. The differences in CORT between socially stressed and control treated rats, however, did not reach significance. The possible role of changes in glucocorticoid-(GR) and mineralocorticoid receptor (MR) binding in the altered regulation of HPA activity following defeat were studied in brain and pituitary of male Wistar rats 1 and 3 weeks after defeat. One week after defeat GR-binding decreased in hippocampus and hypothalamus. No changes were observed in GR-binding in the pituitary nor in MR-binding in any of the regions analysed. Three weeks after defeat GR-binding recovered in hippocampus and hypothalamus but at this time MR-binding in hippocampal tissue was seriously decreased. In a fourth experiment vasopressin (AVP) and CRF stores in the external zone of the median eminence (ZEME) were measured by quantitative immunocytochemistry one and three weeks after defeat and compared with controls. Social defeat failed to induce a change in the immunocytochemical stores of AVP or CRF. The present findings show that in rats short-lasting stressors like defeat induce long-lasting, temporal dynamic changes in the regulation of the HPA axis. Since these changes in time are reflected in GRs and MRs in different brain areas an altered corticosteroid receptor binding might play an important role in the affected HPA activity following defeat.

Selective decline of 5-HT1A receptor binding sites in rat cortex, hippocampus and cholinergic basal forebrain nuclei during aging.

The effect of aging on 5-HT1A receptor binding in several forebrain areas associated with the basal forebrain cholinergic system was investigated in rats of 3-, 24- and 30-months-old by receptor autoradiography and biochemical binding assay using [3H]8-OH-DPAT as a ligand. Autoradiographic measurements demonstrated a marked region-specific decline of ligand binding in: (i) regions of the basal forebrain cholinergic cell groups, i.e. the medial septum, diagonal band nuclei and magnocellular nucleus basalis, (ii) the frontal and parietal neocortex and (iii) the dentate gyrus of the hippocampus. No change or only a slight decrease of the 5-HT1A receptor density was found in other areas investigated: the CA1 and CA3 sectors of hippocampus, the cingular and perirhinal cerebral cortex and the lateral septum. The autoradiographic findings were substantiated by the biochemical binding assay, which revealed a comparable loss of 5-HT1A receptor in the hippocampus and neocortex at the age of 30 months. The results clearly show that with increasing age the decrement of 5-HT1A receptor binding in the rat forebrain is remarkably region-selective and particularly affects the cholinergic cell groups that innervate cortex and hippocampus. This phenomenon appears to be especially significant in relation to the neuronal substrates underlying the age-related alterations of mood and cognition.

Permanent upregulation of hippocampal mineralocorticoid receptors after neonatal administration of ACTH-(4-9) analog ORG 2766 in rats.

The development of brain corticosteroid receptors may be permanently modified by perinatal hormone treatments, in particular by hormones of the hypothalamic-pituitary-adrenal axis. Changes in binding characteristics of corticosteroid receptors were investigated in rats treated subcutaneously with 1 microg/g body wt of the ACTH-(4-9) analog peptide ORG 2766 once daily at postnatal days 1, 3 and 5. [3H]Corticosterone (CORT) binding capacity (Bmax) and affinity (Kd) were determined at 1-, 2- and 3-weeks old and adult ages in the hippocampal cytosol by using saturation analysis. Mineralocorticoid type receptor (MR) and glucocorticoid receptor (GR) sites were measured separately with single-point analysis applying a selective glucocorticoid ligand RU 28362 saturating GR. An increase in [3H]CORT binding capacity was found during postnatal development which remained permanently high up to adult age. Separate analysis of MR and GR expression indicated that the increment in the number of corticoid receptor sites was due to an increase in number of MRs in both the young and adult rats. It was concluded that neonatal injections of ACTH-(4-9) peptide resulted in a permanent and selective upregulation of hippocampal MRs, which may underlie the previously observed increased vigilance and novelty-induced behavioral reactivity of the peptide-treated adult rats (Felszeghy, K., Sasvari, M. and Nyakas, C., Horm. Behav., 27 (1993) 380-396).

Long-term selective down-regulation of brain glucocorticoid receptors after neonatal dexamethasone treatment in rats.

The development of corticosteroid receptors may be permanently modified by perinatal hormonal influences. Changes in binding characteristics of corticosteroid receptors were examined in rats treated sc. with 1 microgram/g dexamethasone (DEX) on postnatal day (PND) 1 and subsequently two more times on PND 3 and 5 in several brain areas. [3H]Corticosterone (CORT) binding capacity (Bmax) and affinity (Kd) were determined at 3 weeks old and adult ages by using saturation analysis. The mineralocorticoid type receptor (MR) and the glucocorticoid receptor (GR) sites were measured separately with single point analysis applying a selective glucocorticoid ligand RU 28362 saturating GR. The decrease in CORT binding was due to a selective GR decrement in all structures and the MR concentration was not changed considerably. The basal levels of plasma CORT were not permanently influenced by neonatal DEX. In conclusion, DEX given during the first week of life resulted in long-term and selective down-regulation of GR and this decrement was independent of the actual circulating CORT level.

Beneficial effect of chronic nimodipine treatment on behavioral dysfunctions of aged rats exposed to perinatal ethanol treatment.

The long-term effects of prenatal and early postnatal ethanol exposure were assessed in adult (5-month), aged (24-month), and senescent (30-month) rats on non-aggressive intermale social behavior, and on black-white discrimination and spatial learning behaviors. Furthermore, the effects of chronic application of the Ca(2+) channel blocker nimodipine, which reportedly improves behavioral function in aging, were studied on the ethanol-induced behavioral deficits during aging. The results showed that the perinatal alcohol treatment suppressed social behavior by reducing the frequency and duration of social interactions at all ages. Black-white discrimination behavior and appetitively motivated learning in a hole-board were also markedly disturbed. Several measures of social and spatial learning behaviors of ethanol-exposed rats revealed progressive functional decline with aging. Chronic oral treatment with nimodipine improved the social activity and normalized the cognitive behavioral capabilities of aged and senescent rats exposed to ethanol. We concluded that: (1) the behavioral disabilities caused by perinatal ethanol toxicity are persistent in the rat lifespan and become more pronounced with aging; and (2) administration of nimodipine in the aging period improves, with a long-lasting efficacy, the ethanol-induced behavioral dysfunctions in aged rats.

Behavioral depression: opposite effects of neonatal dexamethasone and ACTH-(4-9) analogue (ORG 2766) treatments in the rat.

Permanent changes in novelty-induced arousal and behavioral depression were studied in adult male Wistar rats having received sc injections of 1 micrograms/g body wt dexamethasone (DEX) or ACTH-(4-9) analogue (ORG 2766), or the combined treatment of these substances at Postnatal Days 1, 3, and 5. Treatment with DEX increased immobility in the Porsolt's water immersion and closed-field tests, delayed start latency, and attenuated orientation motility in an open-field, and enhanced defensive burying activity. On the contrary, the ACTH peptide caused more active behavior, resulted in an increased motility in the Porsolt's test, and decreased immobility in the closed-field chamber compared to controls. Behavioral reactivity of rats after combined DEX and ACTH peptide treatments was comparable to that of saline controls. The hormone treatments did not alter basal and stress-induced circulating corticosterone levels assessed at the adult age. The data suggest that neonatal DEX strengthens the development of brain mechanisms supporting behavioral depression in response to stressful situations, while ORG 2766 has principally an opposite effect and is able to compensate the long-term aberrant behavioral effects of neonatal DEX treatment.

[Maternal behavior after the administration of morphine or naloxone to pregnant female rats and the pain sensitivity and brain mu-opioid receptors in the progeny]. / Materinskoe povedenie posle vvedeniia beremennym samkam krys morfiia i naloksona, bolevaia chuvstvitel'nost' i miu-opioidnye retseptory mozga potomkov.

Morphine or naloxone injected twice a day (10 mg/kg/day) to rat females from 15 to 18 days of gestation had no effect on their litter size or body weight of pups. Time necessary for the female to bring pups into the nest from the opposite end of the cage, that is a characteristic of maternal care and negatively correlated with the mean body weight of the pup in the litter, did not change after treatment with drugs during gestation. Newborns treated with mu-opioid receptor ligands during intrauterine development had an elevated number of 3H-naloxone binding sites in the brain. However, the number of 3H-naloxone binding sites on the 9 and 16 days of life, as well as pain thresholds under electric stimulation of the tail at a month age were equal in these rats and offsprings of the intact or saline treated mothers.

Neuroendocrine and neurochemical consequences of long-term sleep deprivation in rats: similarities to some features of depression.

The paradigm of long-term sleep deprivation was used as a model of chronic inescapable stress in rats. Several basic metabolic parameters (body weight changes, food and water intake, rectal temperature, serum glucose and creatinine), adrenal and thyroid secretion, norepinephrine and dopamine content and turnover in discrete brain regions, and open field behaviour were examined in the course of the exposure to experimental stress. Sleep deprivation over 7-9 days caused complete physical exhaustion of the animals. It was accompanied by hypothermia and hyperphagia. Adrenal activity was characterized by significant hypercorticism, but also by a relative decrease of the responsiveness to ACTH. A gradual decrease in the thyroid secretion was observed. Sleep deprivation elicited a depletion of norepinephrine in the hypothalamus and decreased its turnover, whereas hippocampal norepinephrine content decreased without considerable turnover alterations. Striatal dopamine content and turnover remained unaffected. Behavioural depression and altered open field activity were also observed in exhausted animals. Long-term sleep deprivation, therefore, seems to reproduce some of the biological correlates of the depressive illness, and may be useful in studying the development of coping failure as a result of chronic stress exposure.