Environmental noise exposure modifies astrocyte morphology in hippocampus of young male rats.

BACKGROUND: Chronic exposure to noise induces changes on the central nervous system of exposed animals. Those changes affect not only the auditory system but also other structures indirectly related to audition. The hippocampus of young animals represents a potential target for these effects because of its essential role in individuals' adaptation to environmental challenges. OBJECTIVE: The aim of the present study was to evaluate hippocampus vulnerability, assessing astrocytic morphology in an experimental model of environmental noise (EN) applied to rats in pre-pubescent stage. MATERIALS AND METHODS: Weaned Wistar male rats were subjected to EN adapted to the rats' audiogram for 15 days, 24 h daily. Once completed, plasmatic corticosterone (CORT) concentration was quantified, and immunohistochemistry for glial fibrillary acidic protein was taken in hippocampal DG, CA3, and CA1 subareas. Immunopositive cells and astrocyte arborizations were counted and compared between groups. RESULTS: The rats subjected to noise exhibited enlarged length of astrocytes arborizations in all hippocampal subareas. Those changes were accompanied by a marked rise in serum CORT levels. CONCLUSIONS: These findings confirm hippocampal vulnerability to EN and suggest that glial cells may play an important role in the adaptation of developing the participants to noise exposure.

Capsaicin and N-arachidonoyl-dopamine (NADA) decrease tension by activating both cannabinoid and vanilloid receptors in fast skeletal muscle fibers of the frog.

Previous studies have indicated that vanilloid receptor (VR1) mRNA is expressed in muscle fibers. In this study, we evaluated the functional effects of VR1 activation. We measured caffeine-induced contractions in bundles of the extensor digitorum longus muscle of Rana pipiens. Isometric tension measurements showed that two VR1 agonists, capsaicin (CAP) and N-arachidonoyl-dopamine (NADA), reduced muscle peak tension to 57 ± 4 % and 71 ± 3% of control, respectively. The effect of CAP was partially blocked by a VR1 blocker, capsazepine (CPZ), but the effect of NADA was not changed by CPZ. Because NADA is able to act on cannabinoid receptors, which are also present in muscle fibers, we tested the cannabinoid antagonist AM281. We found that AM281 antagonized both CAP and NADA effects. AM281 alone reduced peak tension to 80 ± 6 % of control. With both antagonists, the CAP effect was completely blocked, and the NADA effect was partially blocked. These results provide pharmacological evidence of the functional presence of the VR1 receptor in fast skeletal muscle fibers of the frog and suggest that capsaicin and NADA reduce tension by activating both cannabinoid and vanilloid receptors.

Early-life exposure to noise reduces mPFC astrocyte numbers and T-maze alternation/discrimination task performance in adult male rats.

In this experiment, we evaluated the long-term effects of noise by assessing both astrocyte changes in medial prefrontal cortex (mPFC) and mPFC-related alternation/discrimination tasks. Twenty-one-day-old male rats were exposed during a period of 15 days to a standardized rats' audiogram-fitted adaptation of a human noisy environment. We measured serum corticosterone (CORT) levels at the end of the exposure and periodically registered body weight gain. In order to evaluate the long-term effects of this exposure, we assessed the rats' performance on the T-maze apparatus 3 months later. Astrocyte numbers and proliferative changes in mPFC were also evaluated at this stage. We found that environmental noise (EN) exposure significantly increased serum CORT levels and negatively affected the body weight gain curve. Accordingly, enduring effects of noise were demonstrated on mPFC. The ability to solve alternation/discrimination tasks was reduced, as well as the number of astroglial cells. We also found reduced cytogenesis among the mPFC areas evaluated. Our results support the idea that early exposure to environmental stressors may have long-lasting consequences affecting complex cognitive processes. These results also suggest that glial changes may become an important element behind the cognitive and morphological alterations accompanying the PFC changes seen in some stress-related pathologies.

Increased vascular permeability in the circumventricular organs of adult rat brain due to stimulation by extremely low frequency magnetic fields.

It has been demonstrated that the exposure of biological systems to magnetic fields (MFs) can produce several beneficial effects: tissue recovery in chronic wounds, re-establishment of blood circulation after tissue ischemia or in necrotic tissues, improvement after epileptic episodes, angiogenesis, etc. In the current study, the effects of extremely low frequency (ELF) MF on the capillaries of some circumventricular organs (CVOs) are demonstrated; a vasodilator effect is reported as well as an increase in their permeability to non-liposoluble substances. For this study, 96 Wistar male rats (250 g body mass) were used and divided into three groups of 32 rats each: a control group (no treatment); a sham ELF-MF group; and an experimental group subjected to ELF-MF (120 Hz harmonic waves and 0.66 mT, root mean square) by the use of Helmholtz coils. All animals were administered colloidal carbon (CC) intravenously to study, through optical and transmission electron microscopy, the capillary permeability in CVOs and the blood-brain barrier (BBB) in brain areas. An increase in capillary permeability to CC was detected in the ELF-MF-exposed group as well as a significant increase in vascular area (capillary vasodilation); none of these effects were observed in individuals of the control and sham ELF-MF groups. It is important to investigate the mechanisms involved in the phenomena reported here in order to explain the effects of ELF-MF on brain vasculature.

Curcumin protects against the oxidative damage induced by the pesticide parathion in the hippocampus of the rat brain.

UNLABELLED: One of the main concerns regarding organophosphate pesticides (OP) is their possible toxic effects. Doses that do not produce acute toxicity are capable of altering the structure and biochemistry of different tissues and organs by production of reactive oxygen species (ROS). Curcumin (CUR) is the main substance in Curcuma longa (Zingiberacea) rhizome that has strong antioxidant activity. However, the neuroprotective properties of curcumin against oxidative stress induced by prolonged exposure to parathion (PAR) is not clear. OBJECTIVE: The present work evaluated the protective effect of curcumin against the oxidative damage induced in the rat hippocampus by the OP PAR. METHODS: Forty female Wistar rats were distributed in four groups as follows: exposed to PAR by inhalation (PAR group); pre-treated with CUR and then exposed to PAR by inhalation, (CUR + PAR group); exposed to environmental air and treated with CUR in the food (CUR group); and exposed to environmental air (the control group). At the end of the handling process, the concentration of erythrocyte cholinesterase was monitored, as indicator of PAR intoxication and lipoperoxidation, immunohistochemistry for astrocytes, and activated microglia and apoptosis was determined in the hippocampus. RESULTS: In the present study, we show that the administration of CUR (200 mg/kg body weight) significantly diminished the oxidative damage in the hippocampus of rats exposed to the OP PAR. DISCUSSION: These data suggest that CUR may be an alternative to prevent neurodegenerative damage after pesticide exposure.

Selective estrogen receptor modulators regulate dendritic spine plasticity in the hippocampus of male rats.

Some selective estrogen receptor modulators, such as raloxifene and tamoxifen, are neuroprotective and reduce brain inflammation in several experimental models of neurodegeneration. In addition, raloxifene and tamoxifen counteract cognitive deficits caused by gonadal hormone deprivation in male rats. In this study, we have explored whether raloxifene and tamoxifen may regulate the number and geometry of dendritic spines in CA1 pyramidal neurons of the rat hippocampus. Young adult male rats were injected with raloxifene (1 mg/kg), tamoxifen (1 mg/kg), or vehicle and killed 24 h after the injection. Animals treated with raloxifene or tamoxifen showed an increased numerical density of dendritic spines in CA1 pyramidal neurons compared to animals treated with vehicle. Raloxifene and tamoxifen had also specific effects in the morphology of spines. These findings suggest that raloxifene and tamoxifen may influence the processing of information by hippocampal pyramidal neurons by affecting the number and shape of dendritic spines.

Chronic exposure of juvenile rats to environmental noise impairs hippocampal cell proliferation in adulthood.

Increasing evidence indicates that chronic exposure to environmental noise may permanently affect the central nervous system. The aim of this study was to evaluate the long-term effects of early exposure to environmental noise on the hippocampal cell proliferation of the adult male rat. Early-weaned Wistar rats were exposed for 15 days to a rats' audiogram-fitted adaptation to a noisy environment. Two months later, the rats were injected with the cellular proliferation marker 5΄bromodeoxiuridine (BrdU), and their brains were processed for immunohistochemical analysis. Coronal sections were immunolabeled with anti-BrdU antibodies to identify new-born cells in dentate gyrus (DG), cornu amonis areas CA1 and CA3. In addition, blood samples were obtained to evaluate corticosterone serum levels after noise exposure. All data are expressed as mean±standard deviation. For mean comparisons between groups, we used the Student t test. We found an increase in corticosterone serum levels after environmental noise exposure. Interestingly, noise-exposed rats showed a long-term reduction of proliferating cells in the hippocampal formation, as compared to controls. These findings indicate that chronic environmental noise exposure at young ages produces persistent non-auditory impairment that modifies cell proliferation in the hippocampal formation.

Early exposure to noise followed by predator stress in adulthood impairs the rat's re-learning flexibility in Radial Arm Water Maze.

OBJECTIVE: This study investigated the cognitive effect of chronic exposure to environmental noise on RAWM performance of juvenile rats, and the ability of adult rats exposed to a novel acute stress to perform in the RAWM as a function of whether or not they were exposed to environmental noise as juveniles. METHODS: We examined the consequences of exposure to noise during the juvenile-early periadolescent period on adulthood stress response by assessing cognitive performance in the RAWM. Male rats were exposed to environmental noise during the childhood-prepubescent period (21-35 PND), and their RAWM performance was tested at the end of the exposure to noise, and then again two months later when they had to cope with a new stressful event. RAWM execution included a 3-day training phase and a reversal learning phase on day 4. Escape latency, reference memory errors and working memory errors were compared between experimental and control groups. In addition, body weight gain and serum corticosterone levels were evaluated. RESULTS: Stressed rats demonstrated spatial impairment, as evidenced by poor execution on day 4. This effect was significantly noticeable in the doubly stressed group. Noise annoyance was evidenced by reduced body weight gain and increased serum corticosterone levels. CONCLUSIONS: Our results suggest that environmental noise may produce potent stress-like effects in developing subjects that can persist into adulthood, affecting spatial learning abilities. This cognitive impairment may restrict the subject's ability to learn under a new spatial configuration.

Expression of NK cells activation receptors after occupational exposure to toxics: a preliminary study.

The expression of NK cells activation receptors was assessed by comparative study of two groups of women workers at a chemical reagents factory, located in Zapopan, Jalisco, Mexico. Twenty of them were exposed to environmental toxics identified and quantified by gas chromatography, and 20 women unexposed to toxic substances. The expression of the surface markers CD56+ and CD3+, and of the activation receptors and co-receptors on NK cells was quantified by flow cytometry. To assess the cellular damage produced by chronic exposure to the toxics, the thiobarbituric acid reacting substances (TBARS) generated and the total plasma antioxidizing capacity (TPAC) were quantified in both groups. The exposed women had been exposed at least to 12 volatile toxic compounds, benzene, benz(a)pyrene, ethylbenzene, dimethylbenz(a)anthracene, xylene, toluene, styrene, chloroform, formaldehyde, iodine, chlorine and fluorine. Significant difference between the two groups was in the proportion of CD3 lymphocytes, 72.7+/-10.3% in the unexposed women versus 66.8+/-7.9% in the exposed group (p<0.05). The density of expression of NKG2D and NKp30 receptors was significantly higher in the unexposed women compared to the exposed group: NKG2D were 31.3+/-6.3 and NKp30 were 9.5+/-5.2 in the unexposed women and 5.14+/-2.9 (p<0.01) and 4.6+/-1.9 (p<0.05), respectively in the exposed women. No statistically significant differences were found in the expression of NKp80, NKp46 and 2B4 receptors. The concentration of TBARS was lower in women from the unexposed group than the corresponding data from women of the exposed group. However, no significant difference was observed in TPAC between the two groups studied. The results of this preliminary study suggest that from the five activation receptors and co-receptors of NK cells evaluated (NKp30, NKp46, NKp80, NKG2D and 2B4), only NKp30 and NKG2D receptor expression was diminished in women exposed to toxics when compared with data from unexposed women. These results suggest that the occupational exposure to mixture of toxics is one of the important factors in the diminution of the NK cell receptor expression.

Prefrontal serotonergic denervation induces increase in the density of 5-HT2A receptors in adult rat prefrontal cortex.

The 5-HTergic system and particularly 5-HT(2A) receptors have been involved in prefrontal cognitive functions, but the underlying mechanisms by which the serotonin (5-HT) system modulates these processes are still unclear. In this work, the effects of prefrontal 5-HTergic denervation on the density and expression levels of 5-HT(2A) receptors were evaluated by immunohistochemical and molecular biology studies in the prefrontal cortex (PFC). The [(3)H]-Ketanserin binding study revealed an increase in the B(max), along with no change in the binding affinity (K(D)) for 5-HT(2A) receptors. The increase in PFC of 5-HT(2A) receptor density in response to denervation was accompanied by increase in 5-HT(2A) receptor mRNA and protein levels. This increase in the number of 5-HT(2A) receptors may be interpreted as an adaptive plastic change, i.e., hypersensitivity; resulting from the selective pharmacological lesion of the raphe-proceeding 5-HTergic fibers to the PFC. Based on previous evidence, this could be strongly related to the abnormal expression of short-term memory.

Low tryptophan and protein in the diet during development increase the susceptibility to convulsions in adult rats.

Tryptophan (TRY) is the precursor for serotonin (5-HT) synthesis. Common maize has low protein content with low concentration of TRY and lysine. A diet based on two strains of corn differing in their TRY content were given to adult female rats, prior mating, during pregnancy and lactation. Same diets were offered to their male offspring after weaning until reaching 60-days old. The pattern and severity of the convulsive phenomenon induced by monosodium glutamate (MSG) in a well established model of Status epilepticus were evaluated in comparison with data from animals of two control groups: (a) rats fed a hypoproteic (8% protein) diet, and (b) rats fed a normal Purina chow diet (23% protein). Significant increased susceptibility to convulsions was observed in both groups of rats fed the corn-based diets. However, the animals fed the common corn-based diet (8-9% protein; 0.058% TRY) showed a higher susceptibility to convulsions than what was registered in animals fed a Quality Protein Maize (QPM)-based diet (8-9% protein; 0.1% TRY). It is concluded that low TRY concentration in the diet during development, produces lower rate of brain 5-HT synthesis, affecting development and maturation of GABAergic inhibitory cortical interneurons, with alteration of cortical excitability, contributing in part, to the increased susceptibility to convulsions, as shown in the experiments here reported.

Interactions Between Epilepsy and Plasticity.

Undoubtedly, one of the most interesting topics in the field of neuroscience is the ability of the central nervous system to respond to different stimuli (normal or pathological) by modifying its structure and function, either transiently or permanently, by generating neural cells and new connections in a process known as neuroplasticity. According to the large amount of evidence reported in the literature, many stimuli, such as environmental pressures, changes in the internal dynamic steady state of the organism and even injuries or illnesses (e.g., epilepsy) may induce neuroplasticity. Epilepsy and neuroplasticity seem to be closely related, as the two processes could positively affect one another. Thus, in this review, we analysed some neuroplastic changes triggered in the hippocampus in response to seizure-induced neuronal damage and how these changes could lead to the establishment of temporal lobe epilepsy, the most common type of focal human epilepsy.

Changes in the expression level of MAPK pathway components induced by monosodium glutamate-administration produce neuronal death in the hippocampus from neonatal rats.

Excessive Glutamate (Glu) release may trigger excitotoxic cellular death by the activation of intracellular signaling pathways that transduce extracellular signals to the cell nucleus, which determines the onset of a death program. One such signaling pathway is the mitogen-activated protein kinases (MAPK), which is involved in both survival and cell death. Experimental evidences from the use of specific inhibitors supports the participation of some MAPK pathway components in the excitotoxicity mechanism, but the complete process of this activation, which terminates in cell damage and death, is not clearly understood. The present work, we investigated the changes in the expression level of some MAPK-pathway components in hippocampal excitotoxic cell death in the neonatal rats using an experimental model of subcutaneous monosodium glutamate (MSG) administration on postnatal days (PD) 1, 3, 5 and 7. Data were collected at different ages through PD 14. Cell viability was evaluated using fluorescein diacetate mixed with propidium iodide (FDA-PI), and the Nissl-staining technique was used to evaluate histological damage. Transcriptional changes were also investigated in 98 components of the MAPK pathway that are associated with cell damage. These results are an evidence of that repetitive use of MSG, in neonatal rats, induces cell damage-associated transcriptional changes of MAPK components, that might reflect a differential stage of both biochemical and molecular brain maturation. This work also suggests that some of the proteins evaluated such as phosphorylated retinoblastoma (pRb) protein, which was up-regulated, could regulate the response to excitotoxic through modulation of the process of re-entry into the cell cycle in the hippocampus of rats treated with MSG.

The ATP levels in kidneys and blood are mainly decreased by acute ingestion of tullidora (Karwinskia humboldtiana).

Our previous acute toxicity studies with Karwinskia humboldtiana (Kh) in rats showed renal hemodynamic changes with a marked increase in the fractional excretion of sodium and morphological damage. To analyse the effects of Kh or 'tullidora' on energetic metabolism, a single dose of an oral preparation from the seed fruits was given to Wistar rats (1.25 g/kg). In tullidora-treated rats there was 8% mortality. ATP concentrations in renal tissue decreased significantly (control: 53.85+/-3.34, tullidora 38.28+/-5.31 micromol/g fresh tissue, P<0.05). Total blood (54.8+/-0.96, tullidora: 40.2+/-1.55 micromol/dL, P<0.01) and haemoglobin-ATP concentrations (3.69+/-0.12, tullidora: 2.56+/-0.11 micromol/g, P<0.01) were also significantly diminished. Moreover, the total protein in renal cortex from tullidora-treated rats decreased as compared to control group (control: 71.43+/-2.88, tullidora: 55.20+/-4.06 mg/g fresh tissue, P<0.05). In contrast, Na+-K+-ATPase activity in tullidora-treated animals was not different from control rats. These findings might partially explain the acute effects and mortality observed in the Kh treated rats.

Heterogeneity of Genetic Damage in Cervical Nuclei and Lymphocytes in Women with Different Levels of Dysplasia and Cancer-Associated Risk Factors.

The comet assay can be used to assess genetic damage, but heterogeneity in the length of the tails is frequently observed. The aims of this study were to evaluate genetic damage and heterogeneity in the cervical nuclei and lymphocytes from patients with different levels of dysplasia and to determine the risk factors associated with the development of cervical cancer. The study included 97 females who presented with different levels of dysplasia. A comet assay was performed in peripheral blood lymphocytes and cervical epithelial cells. Significant genetic damage (P ≤ 0.05) was observed only in patients diagnosed with nuclei cervical from dysplasia III (NCDIII) and lymphocytes from dysplasia I (LDI). However, the standard deviations of the tail lengths in the cervical nuclei and lymphocytes from patients with dysplasia I were significantly different (P ≤ 0.0001) from the standard deviations of the tail lengths in the nuclei cervical and lymphocytes from patients with DII and DIII (NCDII, NCDIII and LDII, LDIII), indicating a high heterogeneity in tail length. Results suggest that genetic damage could be widely present but only manifested as increased tail length in certain cell populations. This heterogeneity could obscure the statistical significance of the genetic damage.

Modification of dendritic development.

Since 1890 Ramón y Cajal strongly defended the theory that dendrites and their processes and spines had a function of not just nutrient transport to the cell body, but they had an important conductive role in neural impulse transmission. He extensively discussed and supported this theory in the Volume 1 of his extraordinary book Textura del Sistema Nervioso del Hombre y de los Vertebrados. Also, Don Santiago significantly contributed to a detailed description of the various neural components of the hippocampus and cerebral cortex during development. Extensive investigation has been done in the last Century related to the functional role of these complex brain regions, and their association with learning, memory and some limbic functions. Likewise, the organization and expression of neuropsychological qualities such as memory, exploratory behavior and spatial orientation, among others, depend on the integrity and adequate functional activity of the cerebral cortex and hippocampus. It is known that brain serotonin synthesis and release depend directly and proportionally on the availability of its precursor, tryptophan (TRY). By using a chronic TRY restriction model in rats, we studied their place learning ability in correlation with the dendritic spine density of pyramidal neurons in field CA1 of the hippocampus during postnatal development. We have also reported alterations in the maturation pattern of the ability for spontaneous alternation and task performance evaluating short-term memory, as well as adverse effects on the density of dendritic spines of hippocampal CA1 field pyramidal neurons and on the dendritic arborization and the number of dendritic spines of pyramidal neurons from the third layer of the prefrontal cortex using the same model of TRY restriction. The findings obtained in these studies employing a modified Golgi method, can be interpreted as a trans-synaptic plastic response due to understimulation of serotoninergic receptors located in the hippocampal Ammon's horn and, particularly, on the CA1 field pyramidal neurons, as well as on afferences to the hippocampus which needs to be further investigated.

Corn feeding during development induces changes in the number of serotonergic neurons in the raphe nuclei.

Serotonin (5-HT) plays a trophic role during brain development; chronic changes in cerebral concentration of this neurotransmitter during the critical stage of development can produce severe damage in the formation of the neural circuits. For the present work a hypoproteic (HYP) diet based on corn (CORN) meal which is deficient in tryptophan (TRY) was given to rats before and during pregnancy, which continued to the offspring until they reached 60 days of age. An isocaloric but hypoproteic diet containing normal amount of TRY, and normal chow (Ch) Purina were given with the same scheme to two groups of rats considered as controls. 5-HT immunohistochemistry was revealed by avidin-biotin complex (ABC) method to quantify serotonergic nerve cells in the nine raphe nuclei. The number of cells immunoreactive to 5-HT immunoreactive (5-HTir) were quantified by means of stereological analysis. Results demonstrated a significant variation in 5-HT expression in the raphe nuclei. Thus, a significant reduction in the number of 5-HTir cells in the rostral raphe nuclei was seen at all ages studied in the animals fed the corn diet, compared to data obtained from the control groups. This decrease was more evident between the postnatal ages of 30 and 60 days. It is concluded that the variations in the available TRY affect the brain cells producing 5-HT and the innervation of their target areas.

Excitotoxicity triggered by neonatal monosodium glutamate treatment and blood-brain barrier function.

It is likely that monosodium glutamate (MSG) is the excitotoxin that has been most commonly employed to characterize the process of excitotoxicity and to improve understanding of the ways that this process is related to several pathological conditions of the central nervous system. Excitotoxicity triggered by neonatal MSG treatment produces a significant pathophysiological impact on adulthood, which could be due to modifications in the blood-brain barrier (BBB) permeability and vice versa. This mini-review analyzes this topic through brief descriptions about excitotoxicity, BBB structure and function, role of the BBB in the regulation of Glu extracellular levels, conditions that promote breakdown of the BBB, and modifications induced by neonatal MSG treatment that could alter the behavior of the BBB. In conclusion, additional studies to better characterize the effects of neonatal MSG treatment on excitatory amino acids transporters, ionic exchangers, and efflux transporters, as well as the role of the signaling pathways mediated by erythropoietin and vascular endothelial growth factor in the cellular elements of the BBB, should be performed to identify the mechanisms underlying the increase in neurovascular permeability associated with excitotoxicity observed in several diseases and studied using neonatal MSG treatment.

From neurogenesis to neuroprotection in the epilepsy: signalling by erythropoietin.

Epilepsy is a disorder characterised by recurrent seizures and molecular events, including the activation of early expression genes and the post-translational modifications of functional proteins. These events lead to changes in neurogenesis, mossy fibre sprouting, network reorganisation and neuronal death. The role of these events is currently a matter of great debate, especially as they relate to protection, repair, or further brain injury. In recent years, accumulating data have supported the idea that erythropoietin (EPO) regulates biological processes including neuroprotection and neurogenesis in several diseases, such as epilepsy. This review summarises the role of EPO in some of the molecular mechanisms involved in these events that could direct a more detailed approach for its use as a therapeutic alternative in reducing epileptic seizures.

NKCC1 and KCC2 protein expression is sexually dimorphic in the hippocampus and entorhinal cortex of neonatal rats.

Seizure susceptibility appears to be greater in males than females during the early developmental stages of the brain when the gamma-aminobutyric acid (GABA), acting through its GABA-A receptor, predominantly produces neuronal depolarization. GABA-mediated excitation has been observed when the NKCC1 (chloride importer) expression level is higher than KCC2 (chloride exporter). In this study, the relative protein expression of NKCC1 and KCC2 over ß-actin was evaluated in the hippocampus and entorhinal cortex of male and female rats during postnatal days (PND) 1, 3, 5, 7, 9, 11, 13 and 15 using Western blotting assays. For both cerebral regions in the females, the NKCC1/ß-actin expression ratio was constant during all evaluated ages, whereas the KCC2/ß-actin expression ratio increased gradually until reaching a maximal level at PND9 that was nearly three- and ten-fold higher in the hippocampus and entorhinal cortex, respectively, compared with the initial level. In males, the NKCC1/ß-actin expression ratio was constant during the first week, peaking almost three-fold higher than the initial level at PND9 in the hippocampus and at PND11 in the entorhinal cortex and then returning to the initial values at PND13, whereas the KCC2/ß-actin expression ratio increased gradually to reach a maximal and steady level at PND5, which were nearly two- and four-fold higher in the hippocampus and entorhinal cortex, respectively, compared with the intial level. In conclusion, the NKCC1/ß-actin and KCC2/ß-actin expression ratios displayed a specific expression profile for each gender and cerebral region, which could be related with the differences in seizure susceptibility observed between genders.