Protective effect of the calcium antagonist nimodipine on discrimination learning deficits and impaired retention behavior caused by prenatal nitrite exposure in rats

Supplementation with dietary omega-3 PUFA mitigates fetal brain inflammation and mitochondrial damage caused by high doses of sodium nitrite in maternal rats

Objective

Food safety and nutrition during pregnancy are important concerns related to fetal brain development. In the present study, we aimed to explore the effects of omega-3 polyunsaturated fatty acids (PUFA ω-3) on exogenous sodium nitrite intervention-induced fetal brain injury in pregnant rats.

Methods

During pregnancy, rats were exposed to water containing sodium nitrite (0.05%, 0.15%, and 0.25%) to establish a fetal rat brain injury model. Inflammatory factors and oxidative stress levels were detected using enzyme-linked immunosorbent assay (ELISA) or flow cytometry. Subsequently, animals were divided into three groups: control, model, and 4% PUFA ω-3. Pregnancy outcomes were measured and recorded. Hematoxylin-eosin (H&E) staining and immunohistochemistry (IHC) were utilized to observe brain injury. ELISA, quantitative real-time PCR (qRT-PCR), western blot, flow cytometry, and transmission electron microscopy (TEM) were adopted to measure the levels of inflammatory factors, the NRF1/HMOX1 signaling pathway, and mitochondrial and oxidative stress damage.

Results

With the increase of sodium nitrite concentration, the inflammatory factors and oxidative stress levels increased. Therefore, the high dose group was set as the model group for the following experiments. After PUFA ω-3 treatment, the fetal survival ratio, average body weight, and brain weight were elevated. The cells in the PUFA ω-3 group were more closely arranged and more round than the model. PUFA ω-3 treatment relieved inflammatory factors, oxidative stress levels, and mitochondria damage while increasing the indicators related to brain injury and NRF1/HMOX1 levels.

Conclusions

Sodium nitrite exposure during pregnancy could cause brain damage in fetal rats. PUFA ω-3 might help alleviate brain inflammation, oxidative stress, and mitochondrial damage, possibly through the NRF1/HMOX1 signaling pathway. In conclusion, appropriately reducing sodium nitrite exposure and increasing PUFA omega-3 intake during pregnancy may benefit fetal brain development. These findings could further our understanding of nutrition and health during pregnancy.

Impaired Learning and Abnormal Open-field Behaviours of Rats After Early Postnatal Anoxia and the Beneficial Effect of the Calcium Antagonist Nimodipine

Perinatal anoxia/hypoxia is considered a serious risk factor for normal brain development. Anoxia induced by repeated asphyxia at 2 and 4 days after birth resulted in a transient hyperactivity in the small open-field, and a behavioural depression in adult open-field activity of male Wistar rats. The same treatment impaired adult learning behaviour in pole-jumping conditioned avoidance and appetitively motivated hole-board test situations. The calcium entry blocker nimodipine (in doses of 3 and 10 mg/kg) prevented the anoxia-induced changes in orientation motility in the open-field tests and almost fully antagonized the learning deficit in the hole-board test. The behavioural deficit seen during acquisition of the pole-jumping conditioned avoidance response was ameliorated to a lesser degree. The results indicate that the maintenance of calcium homeostasis during the early postnatal phase of brain development is crucial to prevent anoxia-induced behavioural abnormalities.

The influence of nimodipine, nicardipine and amlodipine on the brain free fatty acid level in rats with penicillin-induced seizures

1. The aim of this study was to investigate the effects of the calcium channel blockers, nimodipine, nicardipine and amlodipine, on the brain free fatty acid (FFA) level in rats with chemically-induced seizures. 2. The study was carried out on Hannover-Wistar rats. Animals were anesthetized and placed in a stereotaxic apparatus. Each of them received an injection of penicillin (5000 IU/5 microliters) into the left lateral ventricle (i.c.v.). Various doses (1, 3, 10 or 30 mg/kg) of nimodipine, nicardipine or amlodipine had been injected i.p. 30 min before the penicillin application. The rats were decapitated 5 min after the occurrence of epileptic seizures. FFAs were quantified by gas chromatography using the internal standard method. 3. The results demonstrate that i.c.v. injection of penicillin was associated with significant increase in the brain FFA concentration. Tested doses of nicardipine and amlodipine did not influence the increase of the brain free palmitic, stearic, oleic and arachidonic acid level while nimodipine prevented the accumulation of free palmitic, oleic and arachidonic acid in rats with penicillin-induced seizures. Statistically insignificant decrease of steric acid was observed in animals pretreated with nimodipine. 4. It maybe assumed that the brain FFA accumulation caused by i.c.v. penicillin administration is not predominantly associated with a disturbance in calcium homeostasis via L-type voltage-sensitive calcium channels, but by some other membrane and/or intracellular mechanisms.

Delayed neuronal migration of protein kinase Cgamma immunoreactive cells in hippocampal CA1 area after 48 h of moderate hypoxemia in the near term ovine fetus

The brain is uniquely sensitive to disturbances in energy and oxygen supply, particularly during the early stage of life. Since hypoxemia can indirectly activate the intracellular messenger protein kinase C (PKC), we studied the PKCgamma-immunoreaction in the fetal hippocampal CA1 region of naive (n=4), instrumented control (n=7), and instrumented hypoxemic fetuses (n=14), at a mean gestational age of 127 days. Forty-eight hours of mild to moderate hypoxemia, were followed by a 48-h recovery period. Hypoxemia resulted in an increase in carotid blood flow (137% of control), and a shift towards a higher percentage of high-voltage electrocortical activity. After recovery, the fetal brain was fixated by perfusion of both carotid arteries, sectioned and immunostained for PKCgamma. The distribution of PKCgamma-immunoreactive cells was significantly changed after 48 h of hypoxemia in that the migration of cells (from the ventricular region towards the stratum pyramidale) was delayed (p<0.01) compared to naive and instrumented control animals. In contrast to the distribution, the relative total optical density of PKCgamma-ir cells and fibres in the CA1 hippocampal area was not significant different between the animal groups. We conclude that hypoxemia delayed migration of PKCgamma-ir cells, without neuronal degeneration.

The influence of nimodipine and MK-801 on the brain free arachidonic acid level and the learning ability in hypoxia-exposed rats

1. The influence of voltage dependent calcium channel blocker (VDCC), nimodipine and N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 on the brain free arachidonic acid (FAA) level and on the learning ability in hypoxia-exposed rats was examined. 2. Some animals were decapitated after cerebral hypoxia had been obtained and the brain FAA level was determined by gas chromatography. The other animals were trained in a passive avoidance procedure and were exposed to hypoxic conditions immediately after the learning trial response had been acquired. A passive avoidance retention test was performed 24 hours later. 3. Various doses of nimodipine (0.03; 0.1; 0.3 and 1.0 mg/kg) and MK-801 (0.03; 0.1 and 0.3 mg/kg) had been injected 30 minutes before biochemical or behavioral procedures started. 4. It was found that hypoxia strongly increased the brain FAA level and impaired the retention of the passive avoidance response. 5. Pretreatment with 0.3 mg/kg and 1.0 mg/kg of nimodipine prevented the brain FAA accumulation. It has also been shown that all tested doses of nimodipine significantly improved the retention deficit in the animals exposed to hypoxia. 6. Neither the one of tested doses of MK-801 influenced significantly the increase of the brain FAA level and/or passive avoidance behavior in hypoxic animals. 7. These results confirm the hypothesis that the brain FAA accumulation and cognitive impairment, caused by hypoxia, are maybe associated with disturbances in calcium homeostasis and that nimodipine may be useful in ameliorating the hypoxia-induced brain tissue damage. Blocade of NMDA receptor-channel complex by MK-801 was not sufficient to prevent hypoxia-induced neuronal damage.

Hypoxia and brain development

Hypoxia threatens brain function during the entire life-span starting from early fetal age up to senescence. This review compares the short-term, long-term and life-spanning effects of fetal chronic hypoxia and neonatal anoxia on several behavioural paradigms including novelty-induced spontaneous and learning behaviours. Furthermore, it reveals that perinatal hypoxia is an additional threat to neurodegeneration and decline of cognitive and other behaviours during the aging process. Prenatal hypoxia evokes a temporary delay of ingrowth of cholinergic and serotonergic fibres into the hippocampus and neocortex, and causes an enhanced neurodegeneration of 5-HT-ir axons during aging. Neonatal anoxia suppresses hippocampal ChAT activity and up-regulates muscarinic receptor sites for 3H-QNB and 3H-pirenzepine binding in the hippocampus in the early postnatal age. The altered development of axonal arborization and pre- and postsynaptic cholinergic functions may be an important underlying mechanism to explain the behavioural deficits. As far as the cellular mechanisms of perinatal hypoxia is concerned, our primary aim was to study the putative importance of Ca2+ homeostasis of developing neurons by means of pharmacological interventions and by measuring the development of immunoexpression of Ca(2+)-binding proteins. We assessed that nimodipine, an L-type calcium channel blocker, prevented or attenuated the adverse behavioural and neurochemical effects of perinatal hypoxias, while it enhanced the early postnatal development of ir-Ca(2+)-binding proteins. The results are discussed in the context of different related research areas on brain development and hypoxia and ischaemia.

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.

Life-spanning behavioural and adrenal dysfunction induced by prenatal hypoxia in the rat is prevented by the calcium antagonist nimodipine

The long-term behavioural effects of prenatal chronic anaemic hypoxia were investigated in young (5 months old), late adult (19 months) and aged Wistar rats (23-26 months). Sodium nitrite (2 g/l) offered in the drinking water during the second half of pregnancy served to evoke prenatal hypoxia. In parallel to nitrite treatment the Ca2+ channel blocker nimodipine (10 mg/kg) or vehicle alone was administered intragastrically once daily. Open-field activity, intermale social behaviour, learning ability in a black-white discrimination paradigm and fear-induced emotionality were assessed at different ages. Plasma corticosterone response to novelty stress was measured by blood sampling through chronic venous canulas at the age of 28 months. The nitrite-exposed 5-month-old offspring started exploration in a novel open-field with considerable delay. This delayed start-latency was augmented in 19- and 23-month-old rats, pointing to exaggerated suppression of behavioural arousal. Nitrite-induced hypoxia decreased the duration of social interactions during ageing. Aged rats exposed to nitrite were unable to learn a black-white discrimination but showed a normal generalized conditioned fear response (immobility) to the test situation as a whole. The conditioned fear-induced vocalization was more frequent among hypoxic aged animals. The aged hypoxic rats displayed a prolonged plasma corticosterone stress response and had higher adrenal weight than their controls. The abnormal open-field, social, learning and emotional behaviours, as well as the altered plasma corticosterone response, were prevented by prenatal nimodipine treatment.

Nimodipine accelerates the postnatal development of parvalbumin and S-100 beta immunoreactivity in the rat brain

The effects of chronic maternal perinatal nimodipine treatment on the immunocytochemical distribution of the Ca(2+)-binding proteins parvalbumin (PV) and S-100 beta in neocortex and hippocampus were studied at the age of postnatal day (PD) 5, 7, 10, 14 and 20. The Ca2+ antagonist nimodipine (1000 ppm BAY e 9736 in daily food) was administered to pregnant rats starting at postconceptual day 11. The expression of PV exemplified in layer V of parietal and retrosplenial cortex and in all hippocampal layers of CA1 and CA3 was enhanced by more than two-fold in the offspring of nimodipine-treated dams at PD 10 compared with placebo-treated animals. The difference was no longer present at PD 14 and 20. Nimodipine administration also significantly increased the number of S-100 beta-immunopositive glial cells in upper neocortical layers I-III at PD 5 and 7. Again, the difference between nimodipine and placebo-treated animals disappeared after PD 10. The data indicate an accelerated development of PV and S-100 immunoreactivity in the postnatal forebrain as a result of perinatal blockade of the L-type Ca2+ current.

Postnatal development of hippocampal and neocortical cholinergic and serotonergic innervation in rat: effects of nitrite-induced prenatal hypoxia and nimodipine treatment

Postnatal development of ingrowing cholinergic and serotonergic fiber patterns were studied in the rat hippocampus and parietal cortex employing a histochemical procedure for acetylcholinesterase as a cholinergic fiber marker, and immunocytochemistry of serotonin for serotonergic fiber staining. The rat pups were killed at postnatal days 1, 3, 5, 7, 10, and 20. The development of cholinergic and serotonergic innervation was described and the fiber density quantified under normal conditions and after long-term prenatal anemic hypoxia induced by chronic exposure to sodium nitrite. Furthermore, a third group was studied in which the nitrite hypoxia was combined with a simultaneous treatment with the Ca(2+)-entry blocker nimodipine to test the neuroprotective potential of this drug. Quantitative measurement of fiber density from postnatal day 1 to day 20 yielded the following results: (i) both neurotransmitter systems revealed an age-dependent and an anatomically-organized developmental pattern; (ii) the serotonergic innervation of the dorsal hippocampus preceded that of cholinergic afferentation in postnatal days 1-3; (iii) prenatal hypoxia induced a transient delay in the innervation of parietal neocortex and dentate gyrus for both neurotransmitter systems, but left the innervation of the cornu ammonis unaffected; and (iv) the hypoxia-induced retardation of cholinergic and serotonergic fiber development was prevented by concomitant application of the Ca(2+)-antagonist nimodipine during the hypoxia. The results indicate that prenatal hypoxia evokes a temporary delay in the cholinergic and serotonergic fiber outgrowth in cortical target areas in a region-specific manner. The hypoxia-induced growth inhibition is prevented by the calcium antagonist nimodipine, which supports the importance of the intracellular Ca2+ homeostasis of cells and growth cones in regulating axonal proliferation.

Disruption of two-way active avoidance behavior produced by nimodipine

Nimodipine, a voltage-sensitive calcium channel blocker, has been suggested to be a procognitive drug. In the studies reported herein, we found that low doses of IP-injected nimodipine (0.5 and 0.05 mg/kg) impaired two-way active avoidance behavior. The acquisition phase of the training was the same for drug-treated and control animals. However, the nimodipine-injected rats achieved a significantly lower level of performance. The no-shock tests revealed much faster extinction of the learned behavior in drug-treated vs. control animals. These results could be interpreted as indicating learning-disruptive effects of nimodipine.

Nimodipine prevents the in vivo decrease in hippocampal extracellular acetylcholine produced by hypobaric hypoxia

Hypoxia decreases acetylcholine (ACh) synthesis and release in vitro, and ACh synthesis in vivo; however, its effect on extracellular concentration of ACh in vivo is not known. The calcium channel blocker nimodipine is a cerebrovascular dilator which also increases extracellular ACh in vivo. Therefore, it may provide protection from the effects of hypobaric hypoxia on the cholinergic system either via its effects on vascular function or by direct action on the nervous system. This study examined the effect of hypobaric hypoxia on extracellular ACh and choline levels, as measured by microdialysis, as well as the effects of nimodipine under hypoxia. Microdialysis guide cannulae were implanted into the hippocampal region of male Fischer rats so that probes would sample from the CA1 and DG regions. Animals were then exposed for eight hours to a simulated altitude of 5,500 m (18,000 ft) or tested at sea level for an equivalent duration. HPLC with electrochemical detection was used for analysis of the dialysates. At 5,500 m extracellular ACh levels in the placebo-treated group were significantly lower than the sea level group values. This decrement was reversed by nimodipine administered i.p. immediately preceding altitude ascent (10 mg/kg) and 250 min post-altitude ascent (10 mg/kg). These data suggest that nimodipine may provide protection from the detrimental effects of hypoxia on hippocampal cholinergic function.

Long-term cholinergic denervation caused by early postnatal AF64A lesion prevents development of Muscarinic receptors in rat hippocampus

The effect of early postnatal (day 8) intracerebroventricular injections of the putative cholinotoxin ethylcholine aziridinium mustard (AF64A) on development of cholinergic innervation and postsynaptic muscarinic acetylcholine receptors in the rat hippocampus was examined. The cholinotoxin applied at this stage of development leads to a permanent denervation of cholinergic fibres in the hippocampus in adulthood demonstrated by (immuno)histochemical methods and biochemical assays. Muscarinic receptor expression in the principal neurons of dentate gyrus and cornu ammonis was strongly reduced as studied by immunostaining with antibodies against muscarinic receptor proteins and binding assays with the muscarinic antagonist quinuclidinyl benzilate. Cholinoceptive interneurons and somatostatinergic interneurons are not affected by the developmental cholinergic lesion. Immunoreactivity to protein kinase C type I as a marker for inositolphosphate-related cellular activation systems slightly decreased in the apical dendrites of the hippocampal principal neurons. These findings indicate that damage to ingrowing cholinergic terminals in the hippocampus in the early postnatal period is a critical hazard for development of the muscarinic receptor system in the hippocampal principal neurons. These results are discussed for their significance to the neural mechanisms that underlie perinatal brain damage and associated cognitive dysfunction.

Behavioral and biochemical effects of early postnatal cholinergic lesion in the hippocampus

The effects of early postnatal (PD 8) intracerebroventricular injection of ethylcholine mustard aziridinium ion (AF64A) on development of open-field and cognitive behaviors and cholinergic markers in several brain areas were examined in the rat. The cholinotoxin was bilaterally administered in a dose range of 0.25 to 2.0 nmol. In the open-field tests, the cholinergic lesion caused a dose-dependent increase in activity at 20 days of age, while it resulted in lengthened latency to initiate exploration and decreased rearing activity at adulthood. Hole-board spatial learning was severely inhibited in adult age. The biochemical activity of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) in the hippocampus was markedly decreased in a dose-dependent manner, but was unchanged in the neocortex and striatum. Histochemical staining of AChE-positive fibers revealed a severe cholinergic denervation of the granular and pyramidal cell layers of the hippocampus. The results showed that a selective cholinergic deafferentation of the hippocampus at a critical stage of development leads to long-lasting abnormal open-field and spatial learning behaviors.

Behavioral and anatomical consequences of unilateral fornix lesions and the administration of nimodipine

Male Wistar rats subjected to unilateral fimbria-fornix transection by mechanical knife cut or to sham operations were tested in a water maze and in an open field. Half the animals in each group were treated with either 0.06 mg/kg nimodipine or vehicle, administered i.p. for 7 days, beginning the day of surgery. Animals were sacrificed and brains were processed for acetylcholine esterase (AChE) histochemistry. In the water maze, lesioned rats showed a significant impairment relative to the sham-operated animals. Nimodipine treatment did not improve performance. There were no differences among the groups in the observed frequencies of the open field behaviors of locomotion, hole-poke, rearing and grooming. A significant reduction of AChE-positive cell bodies was found in the medial septal region on the side of the lesion. There were no differences in water maze performance among groups of rats treated with 0.0, 0.5, 1.0, or 5.0 mg/kg nimodipine for 7 days, beginning the day of fimbria-fornix transection, in an attempt to determine any dose-dependent effect of the drug.