Rat Hippocampal Formation Research Articles

The influence of the ketogenic diet on the elemental and biochemical compositions of the hippocampal formation.

A growing body of evidence demonstrates that dietary therapies, mainly the ketogenic diet, may be highly effective in the reduction of epileptic seizures. All of them share the common characteristic of restricting carbohydrate intake to shift the predominant caloric source of the diet to fat. Catabolism of fats results in the production of ketone bodies which become alternate energy substrates to glucose. Although many mechanisms by which ketone bodies yield its anticonvulsant effect are proposed, the relationships between the brain metabolism of the ketone bodies and their neuroprotective and antiepileptogenic action still remain to be discerned. In the study, X-ray fluorescence microscopy and FTIR microspectroscopy were used to follow ketogenic diet-induced changes in the elemental and biochemical compositions of rat hippocampal formation tissue. The use of synchrotron sources of X-rays and infrared allowed us to examine changes in the accumulation and distribution of selected elements (P, S, K, Ca, Fe, Cu, Zn, and Se) and biomolecules (proteins, lipids, ketone bodies, etc.) with the micrometer spatial resolution. The comparison of rats fed with the ketogenic diet and rats fed with the standard laboratory diet showed changes in the hippocampal accumulation of P, K, Ca, and Zn. The relations obtained for Ca (increased level in CA3, DG, and its internal area) and Zn (decreased areal density in CA3 and DG) were analogous to those that we previously observed for rats in the acute phase of pilocarpine-induced seizures. Biochemical analysis of tissues taken from ketogenic diet-fed rats demonstrated increased intensity of absorption band occurring at 1740 cm(-1), which was probably the result of elevated accumulation of ketone bodies. Moreover, higher absolute and relative (3012 cm(-1)/2924 cm(-1), 3012 cm(-1)/lipid massif, and 3012 cm(-1)/amide I) intensity of the 3012-cm(-1) band resulting from increased unsaturated fatty acids content was found after the treatment with the high-fat diet. This article is part of a Special Issue entitled "Status Epilepticus".

Orexinergic theta rhythm in the rat hippocampal formation: In vitro and in vivo findings.

Previous in vivo data suggested that orexin neuropeptides (ORX(A) and ORX(B) ) synthetized in hypothalamic neurons were involved in the mechanism of generation of the hippocampal formation theta rhythm. Surprisingly, this suggestion has never been directly proved by experiments using intraseptal or intrahippocampal administration of orexins. In this study, involving the use of in vitro hippocampal formation slices and in vivo model of anesthetized rat, we provide the first convergent electropharmacological evidence that in the presence of both ORX(A) and ORX(B) the hippocampal formation neuronal network is capable of producing oscillations in the theta band. This effect of orexin peptides was antagonized by selective blockers of orexin receptors (OX1 R and OX2 R), SB 334867 and TCS OX2 29, respectively. These results provide evidence for a novel, orexinergic mechanism responsible for the production of theta rhythm in the hippocampal formation neuronal network.

Fornical and nonfornical projections from the rat hippocampal formation to the anterior thalamic nuclei.

ABSTRACTThe hippocampal formation and anterior thalamic nuclei form part of an interconnected network thought to support memory. A central pathway in this mnemonic network comprises the direct projections from the hippocampal formation to the anterior thalamic nuclei, projections that, in the primate brain, originate in the subicular cortices to reach the anterior thalamic nuclei by way of the fornix. In the rat brain, additional pathways involving the internal capsule have been described, linking the dorsal subiculum to the anteromedial thalamic nucleus, as well as the postsubiculum to the anterodorsal thalamic nucleus. Confirming such pathways is essential in order to appreciate how information is transferred from the hippocampal formation to the anterior thalamus and how it may be disrupted by fornix pathology. Accordingly, in the present study, pathway tracers were injected into the anterior thalamic nuclei and the dorsal subiculum of rats with fornix lesions. Contrary to previous descriptions, projections from the subiculum to the anteromedial thalamic nucleus overwhelmingly relied on the fornix. Dorsal subiculum projections to the majority of the anteroventral nucleus also predominantly relied on the fornix, although postsubicular inputs to the lateral dorsal part of the anteroventral nucleus, as well as to the anterodorsal and laterodorsal thalamic nuclei, largely involved a nonfornical pathway, via the internal capsule. © 2015 The Authors Hippocampus Published by Wiley Periodicals, Inc.

Visualizing variations of signal processing in and signal propagation trough the rat hippocampal formation by combined electrophysiological and fMRI measurements

Visualizing variations of signal processing in and signal propagation trough the rat hippocampal formation by combined electrophysiological and fMRI measurements

Graph analysis of the anatomical network organization of the hippocampal formation and parahippocampal region in the rat.

Graph theory was used to analyze the anatomical network of the rat hippocampal formation and the parahippocampal region (van Strien et al., Nat Rev Neurosci 10(4):272–282, 2009). For this analysis, the full network was decomposed along the three anatomical axes, resulting in three networks that describe the connectivity within the rostrocaudal, dorsoventral and laminar dimensions. The rostrocaudal network had a connection density of 12 % and a path length of 2.4. The dorsoventral network had a high cluster coefficient (0.53), a relatively high path length (1.62) and a rich club was identified. The modularity analysis revealed three modules in the dorsoventral network. The laminar network contained most information. The laminar dimension revealed a network with high clustering coefficient (0.47), a relatively high path length (2.11) and four significantly increased characteristic network building blocks (structural motifs). Thirteen rich club nodes were identified, almost all of them situated in the parahippocampal region. Six connector hubs were detected and all of them were located in the entorhinal cortex. Three large modules were revealed, indicating a close relationship between the perirhinal and postrhinal cortex as well as between the lateral and medial entorhinal cortex. These results confirmed the central position of the entorhinal cortex in the (para)hippocampal network and this possibly explains why pathology in this region has such profound impact on cognitive function, as seen in several brain diseases. The results also have implications for the idea of strict separation of the “spatial” and the “non-spatial” information stream into the hippocampus. This two-stream memory model suggests that the information influx from, respectively, the postrhinal–medial entorhinal cortex and the perirhinal–lateral entorhinal cortex is separate, but the current analysis shows that this apparent separation is not determined by anatomical constraints.Electronic supplementary materialThe online version of this article (doi:10.1007/s00429-015-0992-0) contains supplementary material, which is available to authorized users.

The effect of vitamin supplementation on the toxic effects of dichlorvos on the microanatomy of rat hippocampal formation

Dichlorvos (DDVP) is a widely used pesticide that is toxic to animals and humans but study of its effect on the microanatomy of the brain is scanty. This study was designed to investigate the ameliorating effect of vitamin supplementation on DDVP-induced neurotoxicity in the hippocampus of Wistar rats. 25 male Wistar rats were separated into unexposed group and those exposed to DDVP (1000 mg/L) through inhalation either without, or with vitamin E, vitamin C or red palm oil supplementation. Treatment lasted for 14 days after which rats were sacrificed by ketamine anaesthesia. Hippocampal biopsies were processed into paraffin blocks and H&E stained sections were evaluated by light microscopy. DDVP administration elicited toxicity in the dentate gyrus, cornuammonis1 (CA1) and cornuammonis 3 (CA3) regions. There was pyknosis and alteration of the microanatomy of dentate granule cells and pyramidal cells of CA1 and CA3. DDVP-induced toxicity was mitigated by vitamins E, C and red palm oil in the dentate gyrus, but partially in CA1 and CA3. Inhalational DDVP induces toxicity in the hippocampus of rats and this could affect memory. Toxicity of DDVP is partially ameliorated by vitamins E, C and red palm oil.Keywords: Dichlorvos, dentate gyrus, cornuammonis, hippocampus, red palm oil.

Effect of Acetaldehyde Intoxication and Withdrawal on NPY Expression: Focus on Endocannabinoidergic System Involvement.

Acetaldehyde (ACD), the first alcohol metabolite, plays a pivotal role in the rewarding, motivational, and addictive properties of the parental compound. Many studies have investigated the role of ACD in mediating neurochemical and behavioral effects induced by alcohol administration, but very little is known about the modulation of neuropeptide systems following ACD intoxication and withdrawal. Indeed, the neuropeptide Y (NPY) system is altered during alcohol withdrawal in key regions for cerebrocortical excitability and neuroplasticity. The primary goal of this research was to investigate the effects of ACD intoxication and withdrawal by recording rat behavior and by measuring NPY immunoreactivity in hippocampus and NAcc, two brain regions mainly involved in processes which encompass neuroplasticity in alcohol dependence. Furthermore, on the basis of the involvement of endocannabinoidergic system in alcohol and ACD reinforcing effects, the role of the selective CB1 receptor antagonist AM281 in modulating NPY expression during withdrawal was assessed. Our results indicate that (i) ACD intoxication induced a reduction in NPY expression in hippocampus and NAcc; (ii) symptoms of physical dependence, similar to alcohol’s, were scored at 12 h from the last administration of ACD; and (iii) NPY levels increased in early and prolonged acute withdrawal in both brain regions examined. The administration of AM281 was able to blunt signs of ACD-induced physical dependence, to modulate NPY levels, and to further increase NPY expression during ACD withdrawal both in hippocampus and NAcc. In conclusion, the present study shows that complex plastic changes take place in NPY system during ACD intoxication and subsequent withdrawal in rat hippocampal formation and NAcc. The pharmacological inhibition of CB1 signaling could counteract the neurochemical imbalance associated with ACD, and alcohol withdrawal, likely boosting the setting up of homeostatic functional recovery.

Effects of amitriptyline and fluoxetine on synaptic plasticity in the dentate gyrus of hippocampal formation in rats

Background:Several studies have been shown that antidepressant drugs have contradictory effects on cognitive processes. Therefore, the aim of this study was to investigate the effects of amitriptyline and fluoxetine on synaptic plasticity in the dentate gyrus (DG) of the hippocampal formation in rat.Materials and Methods:Experimental groups were the control, the fluoxetine, and amitriptyline. The rats were treated for 21 days and then, paired pulse facilitation/inhibition (PPF/I) and long-term potentiation (LTP) in perforant path-DG synapses were assessed (by 400 Hz tetanization). Field excitatory post-synaptic potential (fEPSP) slope and population spike (PS) amplitude were measured.Results:The results of PPF/I showed that PS amplitude ratios were increased in 10-70 ms inter-stimulus intervals in the amitriptyline group compared to the control group. In the fluoxetine group, EPSP slope ratios were decreased in intervals 30, 40, and 50 ms inter-stimulus intervals compared to the control group. The PS-LTP was significantly lower in the fluoxetine and the amitriptyline groups with respect to the control group.Conclusion:The results showed that fluoxetine and amitriptyline affect synaptic plasticity in the hippocampus and these effects is probably due to the impact on the number of active neurons.

Number and regional distribution of GAD65 mRNA-expressing interneurons in the rat hippocampal formation

In rodent models for neuropsychiatric disorders reduced number of hippocampal interneurons have been reported, but the total number of GABAergic neurons in the normal rat hippocampus is yet unknown. We used in situ hybridization method to label the 65 isoform of glutamic acid decarboxylase (GAD65) and counted the number of GAD65 mRNA-expressing neurons along the entire septo-temporal axis of the hippocampus. We found that 2/3 of the interneurons were in Ammon's horn (61,590) and 1/3 in the dentate gyrus (28,000). We observed the following numbers in Ammon's horn: CA3 area 33,400, CA2 area 4,190, CA1 area 24,000 and in the dentate gyrus: 6,000 in the molecular and 9,000 in the granule cell layers and 13,000 in the hilus. GAD65 mRNA-expressing neurons were significantly more numerous in dorsal than in ventral hippocampus. The ratio between interneurons and principal cells was lowest in the granule cell layer (0.9%) and highest in hilus (21%). In Ammon's horn this ratio was constant being 13% in CA3 and 8% in CA1-2 areas. In the entire hippocampal formation, the interneuron/principal cell ratio was 6%, with a significant difference between Ammon's horn (9.5%) and the dentate gyrus (2.8%) including the hilus. Such low ratios could suggest that even a limited loss of GABAergic neurons in the hippocampus may have a considerable functional impact.

Prolonged protein deprivation differentially affects calretinin- and parvalbumin-containing interneurons in the hippocampal dentate gyrus of adult rats

Protein deprivation is a detrimental nutritional state that induces several deleterious changes in the rat hippocampal formation. In this study, we compared the effects of protein deprivation in the number of parvalbumin (PV)-immunoreactive and calretinin (CR)-immunoreactive interneurons of the dentate gyrus, which are involved in the control of calcium homeostasis and fine tuning of the hippocampal circuits. Two month-old rats were randomly assigned to control and low-protein diet groups. The rats of the latter group were fed with a low-protein diet (8% casein) for 6 months. All animals were perfused at 8 months of age. The number of neurons expressing CR in the molecular layer and in the hilus of dentate gyrus was reduced in protein-deprived rats. Conversely, protein deprivation increased the number of PV-containing interneurons in the dentate granule cell layer and hilus. These results support the view that protein deprivation may disturb calcium homeostasis, leading to neuronal death including GABAergic interneurons expressing CR. In the other hand, the up-regulation of PV cells may reflect a protective mechanism to counteract the calcium overload and protect the remaining neurons of the dentate gyrus.

Evaluation of the protective effects of tocotrienol-rich fraction from palm oil on the dentate gyrus following chronic restraint stress in rats

Exposure to chronic restraint stress has been shown to cause a number of morphological changes in the hippocampal formation of rats. Tocotrienol, an isoform of vitamin E, exhibits numerous health benefits, different from those of tocopherol. Recent studies have demonstrated that tocotrienol prevents stress-induced changes in the gastric mucosa, thus indicating that it may also protect other organs such as the brain from the damaging effects of stress. Therefore, the aim of the present study was to investigate the protective effect of tocotrienol-rich fraction (TRF) extracted from palm oil on the dentate gyrus of rats following exposure to chronic restraint stress. Thirty-six male Sprague Dawley rats were divided into four groups: control, stress, tocotrienol and combination of stress and tocotrienol. Animals were stressed by restraining them for 5 hours every day for 21 consecutive days. TRF was administered via oral gavage at a dose of 200 mg/kg body weight. Our results showed that the plasma corticosterone level was significantly increased in response to stress, compared to the control. The results confirmed previous findings that chronic restraint stress suppresses cellular proliferation and reduces granule cell number in the dentate gyrus. However, TRF supplementation failed to prevent or minimize these stress-induced changes. Therefore, we conclude that TRF at the current dosage is not effective in preventing the morphological changes in the dentate gyrus induced by chronic restraint stress.

Protective effects of a catechin-rich extract on the hippocampal formation and spatial memory in aging rats

Green tea (GT) displays strong anti-oxidant and anti-inflammatory properties mostly attributed to (−)-epigallocatechin-3-gallate (EGCG), while experiments focusing on other catechins are scarce. With the present work we intended to analyze the neuroprotective effects of prolonged consumption of a GT extract (GTE) rich in catechins but poor in EGCG and other GT bioactive components that could also afford benefit. The endpoints evaluated were aging-induced biochemical and morphological changes in the rat hippocampal formation (HF) and behavioral alterations. Male Wistar rats aged 12 months were treated with GTE until 19 months of age. This group of animals was compared with control groups aged 19 (C-19M) or 12 months (C-12M). We found that aging increased oxidative markers but GTE consumption protected proteins and lipids against oxidation. The age-associated increase in lipofuscin content and lysosomal volume was also prevented by treatment with GTE. The dendritic arborizations of dentate granule cells of GTE-treated animals presented plastic changes accompanied by an improved spatial learning evaluated with the Morris water maze. Altogether our results demonstrate that the consumption of an extract rich in catechins other than EGCG protected the HF from aging-related declines contributing to improve the redox status and preventing the structural damage observed in old animals, with repercussions on behavioral performance.

Progress of elemental anomalies of hippocampal formation in the pilocarpine model of temporal lobe epilepsy—an X-ray fluorescence microscopy study

In the present paper, X-ray fluorescence microscopy was applied to follow the processes occurring in rat hippocampal formation during the post-seizure period. In the study, one of the status epilepticus animal models of epilepsy was used, namely the model of temporal lobe epilepsy with pilocarpine-induced seizures. In order to analyze the dynamics of seizure-induced elemental changes, the samples taken from seizure-experiencing animals 3 h and 1, 4, and 7 days after proconvulsive agent administration were analyzed. The obtained results confirmed the utility of X-ray fluorescence microscopy in the research of mechanisms involved in the pathogenesis and progress of epilepsy. The topographic and quantitative elemental analysis of hippocampal formations from different periods of epileptogenesis showed that excitotoxicity, mossy fibers sprouting, and iron-induced oxidative stress may be the processes responsible for seizure-induced neurodegenerative changes and spontaneous recurrent seizures occurring in the chronic phase of the pilocarpine model. The analysis of correlations between the recorded elemental anomalies and quantitative parameters describing animal behavior in the acute period of pilocarpine-induced status epilepticus showed that the areal densities of selected elements measured in the latent period strongly depend on the progress of the acute phase. Especially important seem to be the observations done for Ca and Zn levels which suggest that the intensity of the pathological processes such as excitotoxicity and mossy fibers sprouting depend on the total time of seizure activity. These results as well as dependencies found between the levels of S, K, and Cu and the intensity of maximal seizures clearly confirm how important it is to control the duration and intensity of seizures in clinical practice.

Single-Transmembrane Domain IGF-II/M6P Receptor: Potential Interaction with G Protein and Its Association with Cholesterol-Rich Membrane Domains

The IGF-II/mannose 6-phosphate (M6P) receptor is a single-transmembrane domain glycoprotein that plays an important role in the intracellular trafficking of lysosomal enzymes and endocytosis-mediated degradation of IGF-II. The receptor may also mediate certain biological effects in response to IGF-II binding by interacting with G proteins. However, the nature of the IGF-II/M6P receptor's interaction with the G protein or with G protein-coupled receptor (GPCR) interacting proteins such as β-arrestin remains unclear. Here we report that [(125)I]IGF-II receptor binding in the rat hippocampal formation is sensitive to guanosine-5'-[γ-thio]triphosphate, mastoparan, and Mas-7, which are known to interfere with the coupling of the classical GPCR with G protein. Monovalent and divalent cations also influenced [(125)I]IGF-II receptor binding. The IGF-II/M6P receptor, as observed for several GPCRs, was found to be associated with β-arrestin 2, which exhibits sustained ubiquitination after stimulation with Leu(27)IGF-II, an IGF-II analog that binds rather selectively to the IGF-II/M6P receptor. Activation of the receptor by Leu(27)IGF-II induced stimulation of extracellular signal-related kinase 1/2 via a pertussis toxin-dependent pathway. Additionally, we have shown that IGF-II/M6P receptors under normal conditions are associated mostly with detergent-resistant membrane domains, but after stimulation with Leu(27)IGF-II, are translocated to the detergent-soluble fraction along with a portion of β-arrestin 2. Collectively these results suggest that the IGF-II/M6P receptor may interact either directly or indirectly with G protein as well as β-arrestin 2, and activation of the receptor by an agonist can lead to alteration in its subcellular distribution along with stimulation of an intracellular signaling cascade.

Opto-fMRI analysis for exploring the neuronal connectivity of the hippocampal formation in rats

In recent years, optical stimulation of neurons that bear a light-gated cation channel, “Optogenetics”, has opened a new avenue for exploring neuronal connectivity of the nervous system. In this study, we applied a technique, “Opto-fMRI”, which combined optogenetics with blood oxygenation level-dependent (BOLD) functional MRI (fMRI), for examining the neuronal connectivity of the hippocampal formation in rats. Although the hippocampal formation is very important for memory formation and retrieval, there is little information on its neuronal connectivity, especially on its longitudinal axis of connection. For this purpose, we utilized a transgenic rat strain, expressing the light-gated cation channel channelrhodopsin-2 (ChR2) under the regulation of the Thy1.2 promoter which permits the expression of the integrated gene in neurons. After optical stimulation targeting the dentate gyrus of the transgenic rat, we detected BOLD response of not only the dentate gyrus (DG) but also at the CA3 area. In addition, we detected the longitudinal-axis activation of the hippocampus after optical stimulation. Our study suggests that Opto-fMRI could be a tool for exploring the neuronal connectivity of the hippocampal formation, to understand the neural basis of memory formation and retrieval.

Inhibition of long‐term potentiation by CuZn superoxide dismutase injection in rat dentate gyrus: Involvement of muscarinic M1 receptor

Long-term potentiation (LTP) and long-term depression represent important processes that modulate synaptic transmission that carries out a key role in neural mechanisms of memory. Many studies give strong evidences on a role of the reactive oxygen species in the induction of LTP in CA1 region of hippocampal slices that was inhibited by adding the scavenger enzyme superoxide dismutase (SOD1). Previous data showed that SOD1 is secreted by many cellular lines, including neuroblastoma SK-N-BE cells through microvesicles by an ATP-dependent mechanism; moreover, it has been shown that SOD1 interacts with human neuroblastoma cell membranes increasing intracellular calcium levels via a phospholipase C-protein kinase C pathway activation. The aim of this study was to investigate the effect of intracerebral injection of SOD1 or the inactive form of enzyme (ApoSOD) on the modulation of synaptic transmission in dentate gyrus of the hippocampus in urethane anesthetized rats. The results of the present research showed that intracerebral injection of SOD1 and ApoSOD in the dentate gyrus of the rat hippocampal formation inhibits LTP induced by high-frequency stimulation of the perforant path. This result cannot be only explained by the dismutation of oxygen radical induced by SOD1 since also ApoSOD, that lacks the enzymatic activity, carries out the same inhibitory effect on LTP induction.

Variations in elemental compositions of rat hippocampal formation between acute and latent phases of pilocarpine-induced epilepsy: an X-ray fluorescence microscopy study

There is growing experimental evidence that tracing the elements involved in brain hyperexcitability, excitotoxicity, and/or subsequent neurodegeneration could be a valuable source of data on the molecular mechanisms triggering or promoting further development of epilepsy. The most frequently used experimental model of the temporal lobe epilepsy observed in clinical practice is the one based on pilocarpine-induced seizures. In the frame of this study, the elemental anomalies occurring for the rat hippocampal tissue in acute and silent periods after injection of pilocarpine in rats were compared. X-ray fluorescence microscopy was applied for the topographic and quantitative elemental analysis. The differences in the levels of elements such as P, S, K, Ca, Fe, Cu, and Zn between the rats 3 days (SE72) and 6 h (SE6) after pilocarpine injection as well as naive controls were examined. Comparison of SE72 and control groups showed, for specific areas of the hippocampal formation, lower levels of P, K, Cu, and Zn, and an increase in Ca accumulation. These results as well as further analysis of the differences between the SE72 and SE6 groups confirmed that seizure-induced excitotoxicity as well as mossy fiber sprouting are the mechanisms involved in the neurodegenerative processes which may finally lead to spontaneous seizures in the chronic period of the pilocarpine model. Moreover, in the light of the results obtained, Cu seems to play a very important role in the pathogenesis of epilepsy in this animal model. For all areas analyzed, the levels of this element recorded in the latent period were not only lower than those for controls but were even lower than the levels found in the acute period. The decreased hippocampal accumulation of Cu in the phase of behavior and EEG stabilization, a possible inhibitory effect of this element on excitatory amino acid receptors, and enhanced seizure susceptibility in Menkes disease (an inherited Cu transport disorder leading to Cu deficiency in the brain) suggest a neuroprotective role rather than neurodegenerative and proconvulsive roles of Cu in pilocarpine-induced epilepsy.

Interactions of neurotransmitter systems during postnatal development of the rat hippocampal formation: Effects of cisplatin

The distribution of neuroimmunohistochemical markers for the serotoninergic, noradrenergic, glutamatergic and GABAergic systems (respectively, 5HT2AR, β1AR, GluR 2/3 and GAD65/67) was determined in the hippocampal formation at stages PD11, PD17 and PD30 of postnatal development of untreated rats and cisplatin-treated rats after a single injection of the drug at 10days of life. In the different time points the neurons of the dentate gyrus and Cornu Ammonis progressively acquire mature morphological characteristics, and cell genesis, migration of interneurons and differentiation of mossy cells occur.Cisplatin induced decrease in immunoreactivity for most of the selected neurotransmitter markers, thereby altering the postnatal development of circuits in the hippocampal formation. Cisplatin also brought out clear evidence for an interaction between excitatory and inhibitory neurotransmitter markers during the postnatal maturation of cells and fiber projections containing GluR2/3 and GAD65, despite the fact that glutamatergic neurons and GABAergic interneurons are divergent in their source of genesis and in their mode of migration. In fact, GluR2/3 immunofluorescence was increased in the principal cells early, at PD11, possibly to reduce the calcium influx into the cell. Moreover, cisplatin might cause a loss of GABAergic interneurons early and reduction of fiber projections to hippocampal layers due to altered cell migration or to cell injury; late changes, particularly in GAD67 cell number in the dentate gyrus did not result in redistribution or recovery in treated rats. With the use of cisplatin it has been demonstrated here for the first time that the critical differentiation of dentate gyrus hilar β1AR and GluR2/3 mossy cells takes place between PD11 and PD17. Changes in neurotransmitter marker immunopositivity occurred subsequently to cytoarchitectural changes in the dentate gyrus and Cornu Ammonis which were already evident one day after cisplatin injection, suggesting that degeneration and cell loss may have occurred.Cisplatin was found to be a useful tool for following CNS development and for understanding how hippocampal neuronal networks react to injury. Furthermore, cisplatin-induced neurotoxicity may be used to reveal useful information on the genesis, migration and distribution, and differentiation of distinct types of hippocampal neurons.

Sprouting of Nervous Fibers and Upregulation of C‐X‐C Chemokine Receptor Type 4 Expression in Hippocampal Formation of Rats with Enhanced Spatial Learning and Memory

Hippocampal mossy fiber sprouting following training in the Morris water maze (MWM) is associated with spatial learning, memory and neural plasticity. The C-X-C chemokine receptor type 4 (CXCR4) is the main receptor for stromal cell-derived factor-1 (SDF-1), which is a chemokine that can regulate axonal elongation. This study aimed to investigate the relationship between the morphological plasticity of hippocampal formation and CXCR4 expression. A model of spatial learning and memory was established in rats by training using the MWM. Mossy fiber sprouting in the striatum oriens of the CA3 area of the hippocampus was found in trained rats by Neo-Timm's method. As shown by immunohistochemistry, the CXCR4 immunopositive neurons were distributed in all layers and areas of hippocampal formation. There were no differences among groups regarding the distribution or shape of the immunopositive neurons. However, the immunoreactive staining intensity was increased in trained rats as compared with the control rats. Both CXCR4 gene transcription and translation were significantly upregulated in the trained group as compared with the control group (P < 0.01). Morphological plasticity in the form of axonal sprouting in the hippocampal formation can be induced by enhanced spatial learning and memory activity, and CXCR4 mRNA and protein expression is upregulated, indicating a positive correlation between CXCR4 expression and axonal sprouting.

Impairments to the Establishment of the Various Hippocampal Fields in Rats as a Long-Term Consequence of Acute Perinatal Hypoxia

The aim of the present work was to study the long-term consequences of acute normobaric hypoxia during the perinatal period on the establishment of the hippocampal formation in rats. The experiments showed that hypoxia on day 2 of postnatal development led to significant damage to the structure of the hippocampal field, which showed different levels of sensitivity to the harmful factor. On day 20, all fields showed cell death and depletion of the pyramidal cell layers. The most marked neuron death occurred in fields CA4 and CA3. On day 30, a significant level of neuron death persisted in field CA4, though it decreased in field CA3 and was not seen in field CA1; neuron death in the granule layer of the dentate fascia increased. In addition, there were decreases in the sizes of pyramidal neuron bodies in all hippocampal fields. All hippocampal fields also showed activation of astrocyte reactions, which was more marked in field CA4, where gliosis persisted to prepubertal age (30 days).