Aihua Pan

Olfactory experience modulates immature neuron development in postnatal and adult guinea pig piriform cortex.

Immature neurons expressing doublecortin (DCX+) are present around cortical layer II in various mammals including guinea pigs and humans, especially enriched in the paleocortex. However, little is known whether and how functional experience affects the development of this population of neurons. We attempted to explore a modulation by experience to layer II DCX+ cells in the primary olfactory cortex in postnatal and adult guinea pigs. Neonatal and 1-year-old guinea pigs were subjected to unilateral naris-occlusion, followed 1 and 2months later by morphometry of DCX+ cells in the piriform cortex. DCX+ somata and processes were reduced in the deprived relative to the non-deprived piriform cortex in both age groups at the two surviving time points. The number of DCX+ cells was decreased in the deprived side relative to internal control at 1 and 2months in the youths and at 2months in the adults post-occlusion. The mean somal area of DCX+ cells showed a trend of decrease in the deprived side relative to the internal control in the youths. In addition, DCX+ cells in the deprived side exhibited a lower frequency of colocalization with the neuron-specific nuclear antigen (NeuN) relative to counterparts. These results suggest that normal olfactory experience is required for the maintenance and development of DCX+ immature neurons in postnatal and adult guinea pig piriform cortex.

Somal and dendritic development of human CA3 pyramidal neurons from midgestation to middle childhood: a quantitative Golgi study.

The CA3 area serves a key relay on the tri‐synaptic loop of the hippocampal formation which supports multiple forms of mnemonic processing, especially spatial learning and memory. To date, morphometric data about human CA3 pyramidal neurons are relatively rare, with little information available for their pre‐ and postnatal development. Herein, we report a set of developmental trajectory data, including somal growth, dendritic elongation and branching, and spine formation, of human CA3 pyramidal neurons from midgestation stage to middle childhood. Golgi‐impregnated CA3 pyramidal neurons in fetuses at 19, 20, 26, 35, and 38 weeks of gestation (GW) and a child at 8 years of age (Y) were analyzed by Neurolucida morphometry. Somal size of the impregnated CA3 cells increased age‐dependently among the cases. The length of the apical and basal dendrites of these neurons increased between 26 GW to 38 GW, and appeared to remain stable afterward until 8 Y. Dendritic branching points increased from 26 GW to 38 GW, with that on the apical dendrites slightly reduced at 8 Y. Spine density on the apical and basal dendrites increased progressively from 26 GW to 8 Y. These data suggest that somal growth and dendritic arborization of human CA3 pyramidal neurons occur largely during the second to third trimester. Spine development and likely synaptogenesis on CA3 pyramidal cells progress during the third prenatal trimester and may continue throughout childhood. Anat Rec, 2013.

Formalin-induced increase in P2X(3) receptor expression in dorsal root ganglia: implications for nociception.

1 ATP‐gated P2X receptors in nociceptive sensory neurons participate in the transmission of pain signals from the periphery to the spinal cord. The effect of formalin on the expression of P2X3 receptors in dorsal root ganglia (DRG) was characterized using molecular and immunological approaches and the patch‐clamp technique. 2 Adult Sprague‐Dawley rats were injected with 100 µL of 5% formalin in the planar surface of the hindpaw and were killed 30 min and 1, 3, 6, 12, 24 and 48 h later for in vitro analyses. The expression and distribution of P2X3 receptors in the lumbar spinal cord and in L5/L6 DRG were examined; 24 and 48 h after formalin injection, currents in neurons were examined using whole‐cell patch‐clamp recording. 3 Western blots showed that anti‐P2X3 antibody recognized a major monomer of approximately 64 kDa in DRG. Immunoreactivity for P2X3 receptors was detected predominantly in the cytoplasm and plasma membrane of small (< 25 µm) and middle‐sized (25–50 µm) DRG neurons. Expression of the P2X3 transcript in the DRG was unchanged 30 min and 1 h after formalin injection, but increased after 12 h. There was no distinct change in P2X3 immunostaining of the spinal cord lamina at 30 min or 1 h after injection, but after 24 h P2X3 labelling increased. At 24 h after the formalin injection, currents in isolated small and middle‐sized DRG neurons were increased by 1 µmol/L α,β‐methylene‐ATP. These currents were completely inhibited by 1 µmol/L A‐317491, a potent and selective P2X3 receptor antagonist. 4 These data suggest that formalin injection leads to early upregulation of P2X3 expression in the spinal cord and DRG and that this may be one of the mechanisms giving rise to nociception.

Sortilin Fragments Deposit at Senile Plaques in Human Cerebrum

Genetic variations in the vacuolar protein sorting 10 protein (Vps10p) family have been linked to Alzheimer’s disease (AD). Here we demonstrate deposition of fragments from the Vps10p member sortilin at senile plaques (SPs) in aged and AD human cerebrum. Sortilin changes were characterized in postmortem brains with antibodies against the extracellular and intracellular C-terminal domains. The two antibodies exhibited identical labeling in normal human cerebrum, occurring in the somata and dendrites of cortical and hippocampal neurons. The C-terminal antibody also marked extracellular lesions in some aged and all AD cases, appearing as isolated fibrils, mini-plaques, dense-packing or circular mature-looking plaques. Sortilin and β-amyloid (Aβ) deposition were correlated overtly in a region/lamina- and case-dependent manner as analyzed in the temporal lobe structures, with co-localized immunofluorescence seen at individual SPs. However, sortilin deposition rarely occurred around the pia, at vascular wall or in areas with typical diffuse Aβ deposition, with the labeling not enhanced by section pretreatment with heating or formic acid. Levels of a major sortilin fragment ~15 kDa, predicted to derive from the C-terminal region, were dramatically elevated in AD relative to control cortical lysates. Thus, sortilin fragments are a prominent constituent of the extracellularly deposited protein products at SPs in human cerebrum.

Experimental epidural hematoma causes cerebral infarction and activates neocortical glial and neuronal genesis in adult guinea pigs

Epidural hematoma (EDH) is a type of life‐threatening traumatic brain injury. Little is known about the extent to which EDH may cause neural damage and regenerative response in the cerebral cortex. Here we attempted to explore these issues by using guinea pigs as an experimental model. Unilateral EDH was induced by injection of 0.1 ml autologous blood into the extradural space, with experimental effects examined at 7, 14, 30, and 60 days postlesion. An infarct developed in the cortex deep to the EDH largely after 7 days postlesion, with neuronal death occurred from layers I to V in the central infarct region, as evidenced by loss of immunoreactivity (IR) for neuron‐specific nuclear antigen (NeuN). Glial fibrillary acidic protein (GFAP) IR appeared as a cellular band surrounding the infarct and extending into the periinfarct cortex along the pia. Doublecortin (DCX) IR emerged in these same areas, with labeled cells appearing as astrocytic and neuronal profiles. DCX/GFAP colocalization was found in these regions commonly at 7 and 14 days postlesion, whereas DCX/NeuN‐colabeled neurons were detectable at 30 and 60 days postlesion. Subpopulations of GFAP‐, DCX‐, or NeuN‐immunoreactive cells colocalized with the endogenous proliferative marker Ki‐67 or bromodeoxyuridine (BrdU) after pulse‐chase with this birth‐dating marker. The results suggest that experimental EDH can cause severe neuronal loss, induce significant glial activation, and promote a certain degree of local neuronal genesis in adult guinea pig neocortex. These findings point to potential therapeutic targets for improving neuronal recovery in clinical management of EDH.

Effects of total saponins of Panax notoginseng on immature neuroblasts in the adult olfactory bulb following global cerebral ischemia/reperfusion

The main active components extracted from Panax notoginseng are total saponins. They have been shown to inhibit platelet aggregation, increase cerebral blood flow, improve neurological behavior, decrease infarct volume and promote proliferation and differentiation of neural stem cells in the hippocampus and lateral ventricles. However, there is a lack of studies on whether total saponins of Panax notoginseng have potential benefits on immature neuroblasts in the olfactory bulb following ischemia and reperfusion. This study established a rat model of global cerebral ischemia and reperfusion using four-vessel occlusion. Rats were administered total saponins of Panax notoginseng at 75 mg/kg intraperitoneally 30 minutes after ischemia then once a day, for either 7 or 14 days. Total saponins of Panax notoginseng enhanced the number of doublecortin (DCX) + neural progenitor cells and increased co-localization of DCX with neuronal nuclei and phosphorylated cAMP response element-binding/DCX + neural progenitor cells in the olfactory bulb at 7 and 14 days post ischemia. These findings indicate that following global brain ischemia/reperfusion, total saponins of Panax notoginseng promote differentiation of DCX + cells expressing immature neuroblasts in the olfactory bulb and the underlying mechanism is related to the activation of the signaling pathway of cyclic adenosine monophosphate response element binding protein.

Sorting Nexin 11 Regulates Lysosomal Degradation of Plasma Membrane TRPV3

The trafficking of ion channels to/from the plasma membrane is considered an important mechanism for cellular activity and an interesting approach for disease therapies. The transient receptor potential vanilloid 3 (TRPV3) ion channel is widely expressed in skin keratinocytes, and its trafficking mechanism to/from the plasma membrane is unknown. Here, we report that the vesicular trafficking protein sorting nexin 11 (SNX11) downregulates the level of the TRPV3 plasma membrane protein. Overexpression of SNX11 causes a decrease in the level of TRPV3 current and TRPV3 plasma membrane protein in TRPV3‐transfected HEK293T cells. Subcellular localizations and western blots indicate that SNX11 interacts with TRPV3 and targets it to lysosomes for degradation, which is blocked by the lysosomal inhibitors chloroquine and leupeptin. Both TRPV3 and SNX11 are highly expressed in HaCaT cells. We show that TRPV3 agonists‐activated Ca2+ influxes and the level of native TRPV3 total protein in HaCaT cells are decreased by overexpression of SNX11 and increased by knockdown of SNX11. Our findings reveal that SNX11 promotes the trafficking of TRPV3 from the plasma membrane to lysosomes for degradation via protein‐protein interactions, which demonstrates a previously unknown function of SNX11 as a regulator of TRPV3 trafficking from the plasma membrane to lysosomes.

Aberrant expression of the pore-forming KATP channel subunit Kir6.2 in hippocampal reactive astrocytes in the 3xTg-AD mouse model and human Alzheimer's disease.

Alzheimers disease (AD) is a progressive neurodegenerative disease characterized by beta-amyloid (Aβ) deposition, neurofibrillary tangles and cognitive decline. Recent pharmacologic studies have found that ATP-sensitive potassium (KATP) channels may play a role in AD and could be a potential therapeutic target. Interestingly, these channels are found in both neurons and astrocytes. One of the hallmarks associated with AD is reactive gliosis and a change in astrocytic function has been identified in several neuropathological conditions including AD. Thus the goal of this study was to examine whether the pore-forming subunits of KATP channels, Kir6.1 and Kir6.2, are altered in the hippocampus in a cell type-specific manner of the 3xTg-AD mouse model of AD and in human AD tissue obtained from the Chinese brain bank. Specifically, in old 3xTg-AD mice, and age-matched controls, we examined glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), Kir6.1 and Kir6.2 in hippocampal region CA1 with a combination of immunoblotting and immunohistochemistry (IHC). A time point was selected when memory impairment and histopathological changes have been reported to occur in 3xTg-AD mice. In human AD and age-matched control tissue IHC experiments were performed using GFAP and Kir6.2. In the hippocampus of 3xTg-AD mice, compared to wild-type controls, Western blots showed a significant increase in GFAP indicating astrogliosis. Further, there was an increase in Kir6.2, but not Kir6.1 in the plasma membrane fraction. IHC examination of hippocampal region CA1 in 3xTg-AD sections revealed an increase in Kir6.2 immunoreactivity (IR) in astrocytes as identified by GFAP and GS. In human AD tissue similar data were obtained. There was an increase in GFAP-IR in the stratum oriens (SO) and alveus (ALV) of CA1 concomitant with an increase in Kir6.2-IR in cells with an astrocytic-like morphology. Dual immunofluorescence revealed a dramatic increase in co-localization of Kir6.2-IR and GFAP-IR. Taken together, these data demonstrate that increased Kir6.2 is seen in reactive astrocytes in old 3xTg-AD mice and human AD tissue. These changes could dramatically alter astrocytic function and subsequently contribute to AD phenotype in either a compensatory or pathophysiological manner.

Sp8 expression in putative neural progenitor cells in guinea pig and human cerebrum.

Neural stem/progenitor cells have been characterized at neurogenic sites in adult mammalian brain with various molecular markers. Here it has been demonstrated that Sp8, a transcription factor typically expressed among mature GABAergic interneurons, also labels putative neural precursors in adult guinea pig and human cerebrum. In guinea pigs, Sp8 immunoreactive (Sp8+) cells were localized largely in the superficial layers of the cortex including layer I, as well as the subventricular zone (SVZ) and subgranular zone (SGZ). Sp8+ cells at the SGZ showed little colocalization with mature and immature neuronal markers, but co‐expressed neural stem cell markers including Sox2. Some layer I Sp8+ cells also co‐expressed Sox2. The amount of Sp8+ cells in the dentate gyrus was maintained 2 weeks after X‐ray irradiation, while that of doublecortin (DCX+) cells was greatly reduced. Mild ischemic insult caused a transient increase of Sp8+ cells in the SGZ and layer I, with the subgranular Sp8+ cells exhibited an increased colabeling for the mitotic marker Ki67 and pulse‐chased bromodeoxyuridine (BrdU). Sp8+ cells in the dentate gyrus showed an age‐related decline in guinea pigs, in parallel with the loss of DCX+ cells in the same region. In adult humans, Sp8+ cells exhibited comparable morphological features as seen in guinea pigs, with those at the SGZ and some in cortical layer I co‐expressed Sox2. Together, these results suggested that Sp8 may label putative neural progenitors in guinea pig and human cerebrum, with the labeled cells in the SGZ appeared largely not mitotically active under normal conditions.

Sortilin: a new player in dementia and Alzheimer-type neuropathology

Age-related dementias are now a major mortality factor among most human populations in the world, with Alzheimers disease (AD) being the leading dementia-causing neurodegenerative disease. The pathogenic mechanism underlying dementia disorders, and AD in particular, remained largely unknown. Efforts to develop drugs targeting the diseases hallmark lesions, such as amyloid plaque and tangle pathologies, have been unsuccessful so far. The vacuolar protein sorting 10p (Vps10p) family plays a critical role in membrane signal transduction and protein sorting and trafficking between intracellular compartments. Data emerging during the past few years point to an involvement of this family in the development of AD. Specifically, the Vps10p member sortilin has been shown to participate in amyloid plaque formation, tau phosphorylation, abnormal protein sorting and apoptosis. In this minireview, we update some latest findings from animal experiments and human brain studies suggesting that abnormal sortilin expression is associated with AD-type neuropathology, warranting further research that might lead to novel targets for the development of AD therapies.