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Objective To determine if there is atrophy of neuronal nuclei in the aging rat hippocampus.Methods The entire hippocampal formation in a cerebral hemisphere (on a random side) was removed from normal male SD rats aged 1, 2 and 3 years (each age-group 5 rats), serial sections (section thickness 40 |xm) were cut after embedding in a resin of glycol methacrylate, and 3-4 sections were systematically sampled and stained with periodic acid, Schiff' s reagent and hematoxylin. The nuclear sizes of hippocampal neurons were estimated with stereological methods, first, the nuclei were sampled in a uniform random way using the optical disector; then, a Feret diameter of the largest nuclear profile at its focal plane (optical section) was measured as the nuclear diameter, and the nuclear volume was measured at the clearest focal plane of the nucleolus with the nucleator. Results The mean diameters and volumes of the neuronal nuclei in the whole hippocampus were 8.7-9.2 |xm and 392-457 (Jim, respectively, in the 3 age-groups, without significant statistical difference between groups. There were no significant difference between groups, either, in the nuclear diameter or volume in each hippocampal region——the GA (hippocampus proper), dentate gyrus or subiculum. Conclusion In general, no age-related changes have been observed in the nuclear sizes of neurons in the whole hippocampus in the rat from middle to old age.
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Visuospatial memory (VSM) is the ability to represent and manipulate visual and spatial information. This cognitive function depends on the functioning of the hippocampal formation (HF), located in the medial portion of the temporal cortex. The present study aimed to investigate whether there is an association between the volume of the HF and performance in VSM tests. High-resolution structural images (T1) and neuropsychological tests evaluating VSM were performed on 31 healthy individuals. A VSM index was created by grouping 5 variables from 5 tasks (4 from the CANTAB battery and 1 from the Rey-Osterrieth Complex Figure test). Multiple linear regression models using the volumes of HF subregions as independent variables and the VSM index as the dependent variable were conducted to test the hypothesis that memory performance could be predicted by HF volumes. We also conducted analyses to explore the role of covariates that may mediate this relationship, specifically age and intelligence quotient (IQ). We found significant associations between the hippocampal subregions of the left hemisphere and the VSM index (F(7,22)=2.758, P=0.032, R2a=0.298). When IQ was accounted for as a covariate, we also found significant results for the right hemisphere (F(8,21)=2.804, P=0.028, R2a=0.517). We concluded that the bilateral hippocampal formations contributed to performance on VSM tasks. Also, VSM processing is essential for a diverse set of daily activities and may be influenced by demographic variables in healthy subjects.
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Humans , Hippocampus , Memory , Magnetic Resonance Imaging , Neuropsychological TestsABSTRACT
Objective To investigate the volume of hippocampal formation in normal adult using coronal magnetic resonance imaging. Methods 3D-fSPGR sequence was used to depict the brain in 68 healthy adult. The volume of hippocampus was calculated by drawing the outline of 10 coronal hippocampal formation images acquired equally form posterior border of rostrum corpus callosum to anterior border of the splenium. Data were analysed using the SPSS 17.0 software. Results In the coronal plane images of normal adult brain, the absolute volume of left and right hippocampal formation were 2 319.63-2 610.73 mm3 and 2 447.52-2 749.50 mm3 respectively . The relative volume of left and right hippocampal formation were 2 319 . 87-2 602 . 47 mm 3 and 2 443.96-2 755.89 mm3. There were no correlation between hippocampal volume and age (r = 0.084, P = 0.549. Significant gender differences (t=2.500, P=0.029) were observed between absolute volume of right hippocampal formation in the youth group. There were significant differences in the absolute volume (t = -2.571, P = 0.022), relative volume (t = 2.600, P = 0.021) among the right and left hippocampal formation. Significant absolute volume differences (P = 0.038) were observed between the middle-aged group and the youth group among the hippocampal formation of women. Conclusion No significant differences were observed in age, gender among the hippocampal volume of normal adult, and there was a significant difference between the left and right hippocampal formation volume.
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Objective To evaluate the dosimetric characteristics of hippocampal formation (HF) in the intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC).Methods Fifty-nine NPC patients underwent IMRT.Simultaneous integrated boost technology was used to determine the doses for the target areas.The dose ranges of the HF were collected by dose-volume histogram.The influence of T stage on the exposure doses ( Dmax,Dmean,D20,V10,V20,V30,and V40 ) were compared.Results The maximum dose for the HF (Dmax) ranged from 11.1 to 78.2 Gy(F =24.2,P ＜0.05) and the Dmean ranged from 3.2 to 44.6 Gy ( F =16.3,P ＜ 0.05 ).The Dmax and Dmean of the T1-2 stage patients were (40.8 ±9.4) Gy and ( 12.5 ±5.1 ) Gy,respectively,both significantly lower than those of the T3-4 stage patients [ (58.6± 14.8) Gy,(20.9± 9.3 ) Gy].The mean exposed volume of the T4 stage patients was significantly larger than that of the T1 and T2 stages patients.Conclusions In the IMRT of NPC,the HF receives rather high irradiation dose.T stage is the main factor influencing the dose,especially T3 and T4 stages deserve serious attention.
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ObjectiveTo investigate the effects of exercise on the hippocampal formation and the myelinated nerve fibers in the hippocampal formation of middle-aged rats. MethodsTen 14-month female SD rats were randomly divided into exercise group and sedentary group.Rats in the exercise group were forced to run on a treadmill for 4 months. After 4 months, spatial learning capacity of two group rats was tested using the Morris water maze.Then, the hippocampal formation and the myelinated nerve fibers in the hippocampal formation were quantitatively estimated using transmission electronic microscopy and stereological techniques. Results Treadmill running enhanced the spatial learning capacity of the rats. The volume of hippocampal formation and the total length of the myelinated nerve fibers in the hippocampal formation were significantly increased after 4 months exercise.However,there was no significant difference in the total volume of the myelinated fibers in the hippocampal formation between the two groups.The absolute distributions of the total length of the myelinated fibers in the hippocampal formation of two groups indicated that the exercise-induced increase of the total length of the myelinated nerve fibers in the hippocampal formation was mainly due to the increase of the myelinated fibers with small diameter. Conclusions Four months running exercise remarkably influence the spatial learning capacity,hippocampal formation and the myelinated fibers in the hippocampal formation of the middle-aged famale SD rats. The present results reveal a potential mechanism for the fact that exercise might improve brain function.
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ObjectiveTo investigate the effects of short-term enriched environment on the hippocampal formation and the myelinated fibers in the hippocampal formation of mid-aged male rats. MethodsTwenty 14-month old male SD rats were randomly divided into enriched group and standard group. Enriched rats were reared in enriched environment and standard rats were reared in standard environment for 4 months. Then, the spatial learning capacity of enriched rats and standard rats was tested with the Morris water maze. After the Morris water maze test, the total volume of the hippocampal formation and the myelinated nerve fibers in the hippocampal formation were quantitatively estimated with transmission electronic microscopy technique and stereological methods. Results There was not significant difference in the spatial learning capacity between enriched group and standard group. The total volume of the hippocampal formation of enriched rats was not significantly increased by 4.6% when compared with that of standard rats. The total volume, total length and mean diameter of the myelinated nerve fibers in the hippocampal formation of enriched rats were significantly increased when compared with those of standard rats. Conclusions Four-months enriched environment significantly affected the myelinated fibers in the hippocampal formation of mid-aged male SD rats. The present results might provide an important theoretical basis for searching the ethology strategy to delay the progress of brain aging in the future.
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ObjectiveTo investigate the effects of short-term enriched environment on the hippocampal formation and the myelinated fibers in the hippocampal formation of mid-aged female rats. Methods Twenty 14-month female SD rats were randomly divided into 10 enriched environment (EE) rats and 10 standard environment (SE) rats. EE rats were reared in enriched environment and SE rats were reared in standard environment for 4 months. Then, five rats were randomly selected from each group. The spatial learning capacity was assessed with Morris water maze. The hippocampal formation and the myelinated fibers in the rat hippocampal formation were quantitatively investigated with transmission electronic microscopy technique and stereological methods. Results Short-term enriched environment enhanced the spatial learning capacity of the mid-aged female rats. The total length and total volume of the myelinated fibers in the hippocampal formation of the EE rats was significantly increased by 43.3% and 47.4%, respectively, when compared to the SE rats. There was no significant difference in the hippocampal volume and the mean diameter of the myelinated fibers in the hippocampal formation between two groups. The increase of the total length of the myelinated nerve fibers in the hippocampal formation was mainly due to the increase of the myelinated fibers with small diameter. Conclusion Short-term enriched environment had significant effects on the spatial learning capacity and the myelinated fibers in the hippocampal formation of middle-aged female rats.
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Objective To explore the changes of the hippocampal formation and the myelinated nerve fibers in the hippocampal formation of aged female Long-Evans rat. Methods The hippocampal formation and the myelinated nerve fibers in the hippocampal formation of 5 young (6-month old), 5 middle-aged (18-month old) and 6 aged (28-month old) female Long-Evans rats were quantitatively investigated with the stereological techniques and transmission electronic microscope technique. Results There were no significant changes in the volume of hippocampal formation, the volume density, the total volume, the length density and the mean diameter of the myelinated nerve fibers in the hippocampal formation among young, middle-aged and aged rats. When compared to that of young rats, the total length of the myelinated nerve fibers in the hippocampal formation of middle-aged rats was significantly increased by 63.6%. When compared to that of middle-aged rats, the total length of the myelinated nerve fibers in the hippocampal formation of aged rats was significantly decreased by 47.5%. When compared to that of young rats, the total length of the myelinated nerve fibers in the hippocampal formation of aged rats was non-significantly decreased by 13.8%. Conclusion Although the reason why the total length of the myelinated nerve fibers in the hippocampal formation of middle-aged rats was longer than that of young rats needs further investigations, the present results together with our previous findings in white matter and cortex further suggest that there are age-related changes of the myelinated nerve fibers in the normal aged brains.
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OBJECTIVE: To search for right/left asymmetries in the dendritic trees of the neuronal populations and in the cell-free layer volumes of the human hipoccampal formation. METHOD: In necropsic material obtained from six male individuals we performed a quantitative Golgi study of the dendritic trees of dentate granules, CA3 and CA1 pyramidal neurons and a volumetric analysis of dentate gyrus molecular layer, strata oriens plus alveus and strata lacunosum-moleculare plus radiatum of CA3 and CA1 fields. RESULTS: We found inter-hemispheric asymmetries in the dendrites trees of all neurons, reaching the significant level in the number of granule cells dendritic segments (higher in the left than in the right hemisphere), dendritic branching density of CA3 pyramidal cells and mean dendritic length of CA1 apical terminal segments (higher in the right than in the opposite side). No volumetric differences were observed. CONCLUSION: This study points to different anatomical patterns of connectivity in the hippocampal formations of both hemispheres which may underlie functional asymmetries.
OBJETIVO: Pesquisar a existência de assimetrias direita/esquerda nas arborizações dendríticas neuronais e nos volumes das camadas não celulares da formação do hipocampo humano. MÉTODO: Efectuamos estudo quantitativo Golgi das arborizações dendríticas dos grânulos da fascia denteada e das células piramidais de CA3 e CA1, e uma análise estereológica dos volumes da camada molecular da fascia denteada, do strata oriens + alveus e do strata lacunosum-moleculare + radiatum de CA3 e de CA1 em material necrópsico colhido em 6 indivíduos do sexo masculino. RESULTADOS: Encontrámos assimetrias inter-hemisféricas nas arborizações dendríticas de todos os neurónios, significativas no número de segmentos dendríticos das células granulares (maior à esquerda do que à direita) na densidade de ramificação dendrítica das pirâmides de CA3 e no comprimento dendrítico médio dos segmentos apicais terminais das pirâmides de CA1 (maiores à direita do que à esquerda). Não encontramos diferenças volumétricas. CONCLUSÃO: Estes resultados alertam para diferentes padrões anatómicos de conectividade nas formações do hipocampo de ambos os hemisférios que podem fundamentar assimetrias funcionais.
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Adult , Humans , Male , Middle Aged , Dendrites , Golgi Apparatus , Hippocampus/cytology , Neurons/cytology , Pyramidal Cells/cytology , Cell Count , Cell Size , Staining and Labeling/methodsABSTRACT
The organization of the striatal projection fibers from the hippocampal formation (HF) was studied in the monkey with particular emphasis on specific projections of the ventral striatum. Retrograde tracers were injected into the five different regions of the ventral striatum such as the ventromedial caudate nucleus, ventral shell, central shell, and dorsal core of the nucleus accumbens (NA), and ventrolateral putamen. The ventromedial caudate nucleus and the shell of the NA received dense projections from the HF. Although the ventromedial caudate nucleus and the shell of the NA are both innervated by the HF, the shell receives the larger of these projections. This suggests that the HF is more strongly connected with the shell of the NA than with the ventromedial caudate nucleus. There are no differences between the ventral shell and central shell of the NA. Labeled neurons were mainly observed in the rostral parts of the dorsomedial CA1 and adjacent subicular complex (prosubiculum, subiculum, presubiculum, and parasubiculum) of the HF. These results suggest that the shell of the NA is the main converging site receiving hippocampal projections primarily related to integrating visuospatial and limbic information.
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Basal Ganglia , Caudate Nucleus , Haplorhini , Hippocampus , Neurons , Nucleus Accumbens , Primates , PutamenABSTRACT
In order to study damages on brain cells upon occlusion and reperfusion, brain infarction was induced by insertion of a single nylon thread, through the internal carotid artery, into a middle cerebral artery. After occlusion of 1 hr and reperfusion for variable duration, brain slices were used to observe changes in the brain morphology and in the pyramidal neurons of the himppocampal formation. In this study we found following results. 1) The operation took 20~30 min and about 30% of the operated animals were suitable for studying neurological aspects. 2) The TTC stain showed that about 23.9% of the total brain area was damaged in the 72 hr-reperfusioned sample. 3) The degree of brain edema was larger in the left hemisphere (damaged side) than in the right one (contralateral undamaged side). 4) Pyramidal cells of the damaged hippocampal formation showed features of necrosis such as shrinkage, large vacuole, swelling, and cell debris. 5) The numbers of survived cells per mm2 of the hippocampal formation were 93 in the undamaged animal, and 23 and 3 in the 3 and 7 days after reperfusion, respectively.
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Animals , Brain , Brain Edema , Brain Infarction , Carotid Artery, Internal , Hippocampus , Ischemia , Middle Cerebral Artery , Necrosis , Neurons , Nylons , Pyramidal Cells , Reperfusion , VacuolesABSTRACT
OBJECTIVES: Hippocampal formation and entorhinal cortex play a part in learning and memory. This study sought to investigate the change of cell-death controlling factors in the hippocampal formation and entorhinal cortex of aged rats. METHODS: Ten aged rats and ten controls were studied. We performed immunocytochemical method using antibodies against NOS, VIP, c-fos , bcl-2, bax and p53 and in situ hybridization. RESULTS: 1) The number of nNOS-immunoreactive(IR) neurons in the entorhinal cortex was significantly decreased in the aged rats(>30%). Morphologically, the number of dendritic branches seemed to be decreased and the length of dendrites showed a tendency to by shortened in the aged group. A major loss of nNOS mRNA positive neurons was observed in the hippocampal formation of the aged rats(>30%). 2) VIP-IR neurons were predominantly bipolar cell. VIP-IR cells were mildly decreased in the hippocampus and subiculum(30%). 4) Bcl-2 mRNA positive neurons were moderately decreased in the hippocampus, subiculum and entorhinal cortex(15-30%), and severely decreased in dentate gyrus of the aged rats(>30%). 5) Bax-IR neurons were similarly distributed between the control and the aged rats, but bax-IR neurons of the aged group, as compared to the control group, were weakly immunostained. 6) P53-IR neurons were only observed in hippocampal CA1 region of the aged rats. CONCLUSION: These results indicate the involvement of neuronal system containing NOS, VIP, c-fos, bcl-2 and p53 in the brain aging process, and provide the morphological evidence for the changes in immunoreactivity of cell-death controlling factors in the hippocampal formation and entorhinal cortex of aged rats.
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Animals , Rats , Aging , Antibodies , Brain , CA1 Region, Hippocampal , Dendrites , Dentate Gyrus , Entorhinal Cortex , Hippocampus , Immunohistochemistry , In Situ Hybridization , Learning , Memory , Neurons , RNA, MessengerABSTRACT
Asymmetrical distribution of the vasoactive intestinal polypeptide (VIP)-immunoreactive neurons in the hippocam-pal formation of rat nd iv/iv mouse was detected by the immunocytochemical method. The animals were divided into 3 groups and group I was subdivided into 4 groups according to sex and handedness determined by the paw-preference test : group I (male right-handedness (MR), male left-handedness (ML), female right-handedness (FR), female left-handedness (FL)), group II (female rats ovariectomized in neonatal period), group III (iv/iv mouse, situs solitus & inversus). The number of VIP-immunoreactive neurons were counted under the light microscope and the following results were obtained. 1. In MR of group I, the area containing the higher density of VIP neurons in the left hippocampal formation than the right were the CA1, CA3, dentate gyrus and subiculum. In ML, the area containing the higher density of VIP neurons in the left cortex were the level 2 of dentate gyrus, and the area exhibiting higher density in the right cortex were level 1, 3 of dentate gyrus. 2. The asymmetrical distributional pattern of VIP in ovariectomized rat (group II) was similar to male subgroups in group I. 3. In group III, there was no asymmetrical distribution of VIP-immunoreactive neurons. Above results show that asymmetrical distribution of VIP neurons are prominent in the right handedness or male groups, and the sexually dimorphic pattern of VIP is related directly or indirectly to gonadal steroids, but there seems to be no relationship between iv gene and asymmetrical distribution of VIP neurons in cerebral cortex.
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Animals , Female , Humans , Male , Mice , Rats , Cerebral Cortex , Dentate Gyrus , Functional Laterality , Gonads , Hippocampus , Immunohistochemistry , Neurons , Ovariectomy , Steroids , Vasoactive Intestinal PeptideABSTRACT
This study was conducted to Identify the effects of diazepam on stress-induced c-fos expression In rat brain. The rats were divided into 4 groups according to injection agents [0.9% isotonic saline 1ml, diazepam(5 mg/kg)] and restraint stress, respectively. Saline or diazepam was injected into the peritoneum of rats 10 minutes before the restraint groups were restrained in a wire chamber. Fos-immunoreactive neurons were calculated in the hippocampal area CA2, dentate gyrus, amygdalohippocampal area, paraventricular nucleus, ventral lateral geniculate nucleus, supramammillary nucleus, temporal cortex area 3, occipital cortex area 2, piriform cortex, and cingulate cortex area 3. The results were as follows: 1) In the hippocampal formation including hippocampal area CA2 and dentate gyrus, Fos expression increased significantly in the saline-injected restraint animals than in any other groups. A two-way factorial ANOVA retreated a significant erects of stress and diazepam, and a significant stress by diazepam interaction. 2) In amygdalohippocampal area, Fos expression increased significantly in the saline-injected restraint animals than in diazepam-injected animals. A two-way factorial ANOVA revealed a significant effects of stress and diazepam, but no significant Interaction of stress and diazepam. 3) In paraventricular nucleus, Fos expression increased significantly in the saline-injected restraint animals than in saline-Injected animals and diazepam-injected animals. A two-way factorial ANOVA revealed a significant effects of stress, no significant effects of diazepam, and no significant Interaction of stress and diazepam. 4) In ventral lateral geniculate nucleus, Fos expression Increased significantly in the saline-injected restraint animals than in diazepam-Infected animals and diazepam-injected restraint animals. A two-way factorial ANOVA revealed a significant effects of diazepam, no significant effects of stress, and no significant interaction of stress and diazepam. 5) In supramammillary nucleus, temporal cortex area 3, occipital cortex area 2, piriform cortex, and cingulate cortex area 3, there was no significant difference of Fos expression in each group. A two-way factorial ANOVA revealed no significant effects of stress and diazepam, and no significant interaction of stress and diazepam. These results suggest that the hippocampal formation is involved in the response to the stress and the tension reduction effect of diazepam.
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Animals , Rats , Brain , Dentate Gyrus , Diazepam , Gyrus Cinguli , Hippocampus , Neurons , Paraventricular Hypothalamic Nucleus , PeritoneumABSTRACT
Objective To investigate the effects of long-term replacement therapy of estrogen or compound estrogen on the deposition of beta-amyloid protein (A?) in ovariectomy (OVX) rat hippocampal formation. Methods Fifty seven-month-old female Sprague-Dawley rats were randomly divided into five groups: normal control, SHAM, OVX, OVX plus 17beta-estradiol (OVX/ERT), and OVX plus compound nylestriol tablet (OVX/NL). The ovariectomy was performed in OVX, OVX/NL and OVX/ERT rats and drugs were administered orally in OVX/NL and OVX/ERT rats for 35 weeks after the ovariectomy. Then the rats in all groups were sacrificed. Immunohisto-chemistry of A?, cell counting and imaging system were used to determine the change of A? deposition levels in OVX rat hippocampal formation. Results The numbers and optical density of A?-positive neurons of all hippocampal subregions and dentate gyrus in OVX rats were markedly higher than those of normal control, SHAM,OVX/NL, and OVX/ERT rats( P
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Objective To investigate the sex differences of the myelinated nerve fibers in the hippocampal formation of mid-aged standard and enriched rats. Methods Twenty 14-month Sprague-Dawley (SD) rats, 10 female and 10 male rats, were randomly divided into enriched group and standard group. Enriched rats were reared in enriched environment and standard rats were reared in standard environment for 4 months. Then, the total volume of the hippocampal formation and the myelinated nerve fibers in the hippocampus were quantitatively estimated by transmission electron microscopy and stereological methods. Results The total volume and mean diameter of the myelinated nerve fibers in the hippocampal formation of standard female rats were significantly bigger than those of standard male rats (P0.05). The mean diameter of the myelinated nerve fibers in the hippocampal formation of enriched female rats was significantly smaller than that of enriched male rats (P0.05). Conclusion The sex differences of the myelinated nerve fibers in the hippocampal formation of mid-aged standard and enriched rats are significantly different, which indicates the response to the enriched environment in the mid-aged male and female rats is different.
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Aim To investigate the age-related changes of TrkB mRNA in hippocampal formation of aged rats,and the effects of ginsenosides(GS),and provide reliable experimental evidence for anti-aging.Methods 24 Wistar female rats were randomly divided into 3 groups: Young,aged and GS group(fed with GS from 17 to 27 months).In situ hybridization(ISH) method was applied into qualifying and quantitating the TrkB mRNA expression in hippocampal formation.Results TrkB mRNA expression in aged CA3,CA1 and dentate gyrus decreased by 24.2%,13.4% and 50.6%(P
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Objective:To investigate the spatiotemporal distribution pattern of active ERK1/2 in rat hippocampal formation following pilocarpine-induced status epilepticus(SE) and to discuss its significance.Methods:The lithium-pilocarpine-induced model of SE was established to evaluate the phosphorylation forms of ERK1/2(p-ERK1/2) by immunohistochemistry and observe histopathology changes at different times after pilocarpine injection.Results:The p-ERK1/2 immunoreactivity was observed only in neurites of saline-treated rats hippocampal formation.In pilocarpine-treated rats,the hippocampal neurons showed a strong immunoreactivity of p-ERK1/2 in the body at 30 min which peaked at 2h after pilocarpine injection,while decreased markedly at 6h and returned to basal level at 12h.There were more immunoreactive positive cells in dentate gyrus than those in regions of CA1 and CA3.Many injured neurons were found in hippocampus of SE rats.Conclusion:MAPK ERK1/2 signal transduction pathway can be activated in SE induced by pilocarpine,and may play a critical role in the pathophysiological process of neuron injury and protection related to seizure,and even mediate further long-lasting morphological changes.
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Combining the immunogold-silver staining (IGSS) method with the image quantitative analytical study, changes in somatostatin(SOM)-like, neurons of the hippocampal formation were investigated in young (2 monthes), adult (10 monthes) and old (24 monthes) rats. The results were as follows:1. The number of the SOM-like neurons decreased gradually from the young to the old. Moreover, there was a significant difference among the three age groups (p
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Objective To observe the distribution of parvalbumin immunoreactive neurons in the hippocampal formation of human fetuses. Methods The distribution of parvalbumin immunoreactive neurons in the hippocampal formation of human fetuses at 30 week were investigated by ABC immunocytochemical technique. Results The abundant parvalbumin immunoreactive neurons were localized in all regions of hippocampal formation, especially in the stratum pyramidale. In the stratum oriens of CA1\|3, the triangle or shuttle parvalbumin immunoreactive neurons with some processes were smaller and scattered in this layer. In the stratum pyramidale, the parvalbumin immunoreactive neurons distributed densely, and the processes run out to the stratum oriens and stratum moleculare. In the stratum moleculare the parvalbumin immunoreactive neurons were sparser than in the stratum oriens and stratum moleculare. The parvalbumin immunoreactive neurons in hilus were denser in the hippocampal formation, compared with the other regions, however, delamination of them was not distinct. The processes of parvalbumin immunoreactive neurons run out to the dentate gyrus. The parvalbumin immunoreactive neurons in the dentate gyrus were mainly localized in the stratum granule. Few immunoreactive neurons distributed in the other layers, which were lightly stained and with no processes. In the subicular complex, the lightly stained neurons with few processes were mainly localized in the stratum pyramidale. Conclusion The abundant parvalbumin immunoreactive neurons presented in all regions of the hippocampal formation, especially in the stratum pyramidale. However, the ripe time of these neurons might be different, neurons in CA3 and hilus were earlier than in the dentate gyrus and subicular complex.