Reelin-immunoreactivity in the hippocampal formation of 9-month-old wildtype mouse: effects of APP/PS1 genotype and ovariectomy

Reelin, an extracellular matrix protein has an important role in the migration, correct positioning and maturation of neurons during development. Though it is generally down-regulated in the postnatal period, expression of this large glycoprotein continues in the adult brain in some cell populations. In the present study, we examined the distribution of reelin-immunoreactivity (-ir) in the hippocampal formation of 9-month-old wildtype mice (WT). Then, reelin-ir in normal mice was compared to that of transgenic mice (APP/PS1) carrying mutated human APP and PS1 genes, which are linked to the familial form of Alzheimer's disease (AD). The APP/PS1 mice were additionally burdened with a second risk factor for AD, namely depletion of circulating gonadal hormones by ovariectomy (APP/PS1 + OVX). The analyses revealed that in adult WT reelin-ir is expressed by Cajal-Retzius cells and a subgroup of interneurons throughout the hippocampal formation. In addition, layer II projection neurons in the lateral entorhinal subfields are reelin-ir. Interestingly, ovariectomy decreases the number of reelin-ir cells in the hilus in WT mice, whereas AD-related genotype alone induces only a non-significant reduction. Unexpectedly, additional stress, e.g., depletion of gonadal hormones, does not aggravate the slight reduction in the reelin cell number in the APP/PS1 mice. We propose that the changes in normal reelin-ir are linked to disturbances in repair mechanisms in which APP/PS1 and gonadal hormones are involved and which are perturbed in neurodegenerative conditions, namely AD.     

The majority of brain mast cells in B10.PL mice is present in the hippocampal formation

In the healthy mammalian CNS, mast cells (MCs) are thought to be located mostly in the thalamus. In this study, we have systematically assessed the presence of MCs in the hippocampal formation (HF) and in the thalamus of normal male and female B10.PL mice. Giemsa⁺ and Toluidine Blue⁺ MCs were detected by histomorphometric analyses at perivascular and intraparenchymal sites of both the hippocampus and the entorhinal cortex. We found a mean number of 4.4 MCs in the HF of female and 3.3 MCs in male B10.PL mice. In contrast to the HF, no MCs were present in the thalamus of these mice. Notably, all HF-MCs showed immunoreactivity for Kit, the receptor for the MC growth and maturation factor SCF, as assessed by FITC–avidin/Kit double labelling. We demonstrate that the majority of brain MCs is found in the hippocampus and entorhinal cortex of B10.PL mice, though the total number of MCs is small compared to other mouse strains or rats. The presence of most brain MCs in the HF of B10.PL mice suggests a potential role of MCs in hippocampal physiology and pathology.     

Palmitone prevents pentylenetetrazole-caused neuronal damage in the CA3 hippocampal region of prepubertal rats

Palmitone is a secondary metabolite of polyketide origin extracted from leaves of Annona diversifolia Saff. (Annonaceae). We found that palmitone possesses anticonvulsant properties against penicillin-, 4-AP-, and pentylenetetrazole (PTZ)-caused seizure in adult animals. Some convulsants as PTZ cause neuronal damage in different brain regions such as the CA3 hippocampal region. Our objective was to evaluate if palmitone protects against PTZ-caused seizures and hippocampal neuronal damage in prepubertal rats. We used 32 prepubertal Wistar rats (30–35 days old) divided into four groups of 8 animals; group I was the control group, group II received a single PTZ dose of 50 mg/kg ip, group III received a single palmitone dose of 50 mg/kg ip, and group IV received a palmitone dose of 50 mg/kg ip plus a PTZ dose of 50 mg/kg ip. Ten days after administration, the animals were killed using pentobarbital anesthesia (35 mg/kg). The brains were removed and were embedded in paraffin. Coronal cuts of 7 μm were obtained from −2.8 to −3.3 from Bregma. Each section was stained with cresyl violet-eosin. We evaluated the number of normal and abnormal neurons in the CA3 hippocampal region in a 10,000 μm² section. It was observed that palmitone did not prevent the PTZ-caused seizure but palmitone prevents the PTZ-caused neuronal damage in the CA3 hippocampal region.     

Plasticity in the barrel cortex of the adult mouse: transient increase of GAD-immunoreactivity following sensory stimulation

Summary Sensory experience during perinatal life and adulthood modifies physiological and anatomical characteristics of the central nervous system. So far, this phenomenon has been studied in situations of complete or partial sensory deprivation. We here report that increased sensory stimulation, during four days, of a number of whisker follicles on the face of the adult mouse results in an increased immunoreactivity of glutamic acid decarboxylase (the biosynthetic enzyme of the inhibitory neurotransmitter GABA) in the somatosensory cortex of the adult mouse. Effects were limited to a column of tissue corresponding to the representation of the stimulated follicles and lasted two days beyond stimulation. These findings suggest that sensory stimulation transiently modifies local cortical processing.     

Kindling is associated with the formation of novel mossy fibre synapses in the CA3 region

Summary A Golgi and electron microscopy study of the hippocampal CA3 region was performed on control and kindled Wistar rats. The observations provide evidence that, in epileptic rats, mossy fibres sprout and establish novel synapses with the basilar dendrites of CA3 pyramidal neurons. These newly-developed synapses showed the typical features of mossy synapses observed in the stratum lucidum, including the appearance of complex giant spines. The morphological changes reported here may represent a histopathological substrate for the epilepsy in the absence of overt signs of a hippocampal lesion.     

双氢睾酮对快速老化小鼠海马CA1区突触可塑性和N-甲基-D-天冬氨酸受体1的影响

目的 探讨双氢睾酮(DHT)对快速老化小鼠(SAMP8)海马CA1区突触可塑性和N-甲基-D-天冬氨酸受体1(NMDAR1)的影响.方法 6月龄雄性SAMP8小鼠21只随机分为假手术组、去势组及去势+DHT补充治疗组,每组7只.DHT剂量为1mg/(kg·d),皮下注射21d后,通过Golgi染色观察海马CA1区顶树突树突棘的变化;免疫组织化学及图像分析检测突触素和NMDAR1表达的改变.结果 1.Golgi染色,去势组海马CA1区顶树突树突棘个数明显减少;DHT补充治疗后,树突棘个数明显增多.2.去势组海马CA1区突触素和NMDAR1的表达明显减少,平均吸光度值明显低于其他组(P<0.05).DHT补充治疗能明显增加突触素和NMDAR1的表达.结论 DHT可调节海马CA1区突触可塑性,使树突棘密度增多.DHT对突触可塑性的影响可能与其调节锥体细胞的NMDAR1有关.     

Regulation of long-term depression by increases in [guanosine 3',5'-cyclic monophosphate] in the hippocampal CA1 region of freely behaving rats

A role for guanosine 3',5'-cyclic monophosphate (cGMP) and the protein kinase G (PKG) pathway in synaptic long-term depression (LTD) in the hippocampal CA1 region has been proposed, based on observations in vitro, where, for example, increases of [cGMP] result in short-term depression (STD) coupled with a reduction in presynaptic glutamate release. To date, no evidence exists to support that LTD in the intact, freely behaving animal involves these mechanisms. We examined the effect of increases of [cGMP] on basal transmission and electrically-induced STD at hippocampal CA1 synapses in vivo. We found that elevating [cGMP] dose-dependently caused a chemically-induced STD which occluded electrically-induced STD. Repeated administration of Zaprinast, an inhibitor of cGMP-degrading phosphodiesterase, resulted in persistent LTD (>24 h). Paired-pulse analysis supported a presynaptic mechanism of action. Application of an inhibitor of soluble guanylate cyclase prevented LTD induced by low-frequency stimulation (LFS), and impaired LFS-STD elicited in the presence of Zaprinast. These data suggest the involvement of cGMP in LTD in the CA1 region of freely behaving adult rats.     

Immunohistochemical evidence of plasticity of γ-aminobutyric acid neurons in the red nucleus and adjacent reticular formation after contralateral cerebellectomy in the adult cat

A comparative mapping of γ-aminobutyric acid neurons identified by means of glutamic acid decarboxylase (GAD) immunohistochemistry was performed in the red nucleus (RN) in both intact and hemicerebellectomized adult cats (21 days postoperative). In the deafferented RN (controlateral to the lesion) as well as in the adjacent dorsolateral reticular formation, a marked increase in the number of GAD-positive perikarya was observed. In this mesencephalic area, some neurons may therefore increase their endogenous levels of immunodetectable GAD, as a response to cerebellar deafferentation. This can be viewed as one of the events contributing to functional recovery.     

Mitochondrial dysfunction in CA1 hippocampal neurons of the UBE3A deficient mouse model for Angelman syndrome

Angelman syndrome (AS) is a severe neurological disorder caused by a deficiency of ubiquitin protein ligase E3A (UBE3A), but the pathophysiology of the disease remains unknown. We now report that in the brains of AS mice in which the maternal UBE3A allele is mutated (m−) and the paternal allele is potentially inactivated by imprinting (p+) (UBE3A m−\p+), the mitochondria are abnormal and exhibit a partial oxidative phosphorylation (OXPHOS) defect. Electron microscopy of the hippocampal region of the UBE3A m−\p+ mice (n = 6) reveals small, dense mitochondria with altered cristae, relative to wild-type littermates (n = 6) and reduced synaptic vesicle density. The specific activity of OXPHOS complex III is reduced in whole brain mitochondria in UBE3A m−\p+ (n = 5) mice versus wild-type littermates (n = 5). Therefore, mitochondrial dysfunction may contribute to the pathophysiology of Angelman syndrome.     

Continuous blockade of GABA-ergic inhibition induces novel forms of long-lasting plastic changes in apical dendrites of the hippocampal cornu ammonis 1 (CA1) in vitro

Hippocampal long-term potentiation (LTP) is considered as a fundamental mechanism for learning and memory formation. A role for GABA was reported for the induction and early but not late maintenance of LTP. We have now investigated whether GABA-receptor function is involved in the prolonged maintenance of LTP (>4 h) at afferent synapses at apical dendrites of cornu ammonis 1 (CA1)-pyramidal neurons in hippocampal slices in vitro. Our data demonstrate that GABA-receptor mediated events are not required for conventional, tetanically-induced early- or late-LTP in the hippocampal CA1-region in vitro. Inhibition of GABA-ergic transmission did not negatively influence either early- or late-LTP. In contrast, an additional facilitation was observed at time points corresponding to the establishment of late-LTP (after 3–4 h). Investigation of a second, non-tetanized control input to the same neuronal population revealed that the elevated potentiation of late-LTP in the tetanized input was not LTP-specific. Therefore, we have examined, whether continuous application of GABA-receptor inhibitors also affected the time course of the recorded potentials when a low-frequency stimulation protocol was used. Under these conditions two distinct forms of a late-onset potentiation occurred 5–6 h after drug application. Investigation of mechanisms responsible for this prolonged enhancement of potentials revealed that the higher form of potentiation (potentiation levels above 200%) was dependent on presynaptic activity and N-methyl-d-aspartate (NMDA)-receptor activation, whereas the lower form (potentiation less than 200%) did not require these mechanisms. However, the latter potentiation was prevented by nifedipine, an L-type voltage-dependent calcium channel inhibitor.     

Synaptic formation in subsets of glutamatergic terminals in the mouse hippocampal formation is affected by a deficiency in the neural cell recognition molecule NB-3

The neural cell recognition molecule NB-3, which is also referred to as contactin-6, is a member of the contactin subgroup molecules that are expressed prominently in the developing nervous system after birth. In mice, an NB-3 deficiency impairs motor coordination and reduces the synaptic density between parallel fibers and Purkinje cells in the cerebellum. Here, we studied the role of NB-3 in the formation of glutamatergic synapses in the hippocampal formation. At postnatal day 5, NB-3 immunoreactivity was detected in the subiculum, the stratum lacunosum–moleculare of the CA1 region and the hilus of the dentate gyrus. NB-3 expression in the strata radiatum and oriens was weak, and it was very weak in the granule cell layer of the dentate gyrus, the pyramidal cell layer of regions CA3 to CA1 and the stratum lucidum. NB-3-positive puncta partially overlapped with vesicular glutamate transporter 1 (VGLUT1) and 2 (VGLUT2), excitatory presynaptic markers, but not with vesicular GABA transporter (VGAT), an inhibitory presynaptic marker. The density of VGLUT1 and VGLUT2 puncta in the regions where NB-3 was strongly expressed in wild-type mice was reduced by ∼20–30% in NB-3 knockout mice relative to wild-type mice, whereas that of VGAT puncta was not affected by NB-3 deficiency. Thus, NB-3 has key roles in the formation of glutamatergic, but not GABAergic, synapses during postnatal development of the hippocampal formation as well as the cerebellum.