Recent studies in rodents suggest that repeated and prolonged anesthetic exposure at early stages of development leads to cognitive and behavioral impairments later in life. However, the underlying ...mechanism remains unknown. In this study, we tested whether exposure to general anesthesia during early development will disrupt the maturation of synaptic circuits and compromise learning-related synaptic plasticity later in life.
Mice received ketamine-xylazine (20/3 mg/kg) anesthesia for one or three times, starting at either early (postnatal day 14 P14) or late (P21) stages of development (n = 105). Control mice received saline injections (n = 34). At P30, mice were subjected to rotarod motor training and fear conditioning. Motor learning-induced synaptic remodeling was examined in vivo by repeatedly imaging fluorescently labeled postsynaptic dendritic spines in the primary motor cortex before and after training using two-photon microscopy.
Three exposures to ketamine-xylazine anesthesia between P14 and P18 impair the animals' motor learning and learning-dependent dendritic spine plasticity (new spine formation, 8.4 ± 1.3% mean ± SD vs. 13.4 ± 1.8%, P = 0.002) without affecting fear memory and cell apoptosis. One exposure at P14 or three exposures between P21 and P25 has no effects on the animals' motor learning or spine plasticity. Finally, enriched motor experience ameliorates anesthesia-induced motor learning impairment and synaptic deficits.
Our study demonstrates that repeated exposures to ketamine-xylazine during early development impair motor learning and learning-dependent dendritic spine plasticity later in life. The reduction in synaptic structural plasticity may underlie anesthesia-induced behavioral impairment.
Peripheral nerve injury–induced mechanical allodynia is often accompanied by abnormalities in the higher cortical regions, yet the mechanisms underlying such maladaptive cortical plasticity remain ...unclear. Here, we show that in male mice, structural and functional changes in the primary somatosensory cortex (S1) caused by peripheral nerve injury require neuron-microglial signaling within the local circuit. Following peripheral nerve injury, microglia in the S1 maintain ramified morphology and normal density but up-regulate the mRNA expression of brain-derived neurotrophic factor (BDNF). Using in vivo two-photon imaging and
Cx3cr1
CreER
;
Bdnf
flox
mice, we show that conditional knockout of BDNF from microglia prevents nerve injury–induced synaptic remodeling and pyramidal neuron hyperactivity in the S1, as well as pain hypersensitivity in mice. Importantly, S1-targeted removal of microglial BDNF largely recapitulates the beneficial effects of systemic BDNF depletion on cortical plasticity and allodynia. Together, these findings reveal a pivotal role of cerebral microglial BDNF in somatosensory cortical plasticity and pain hypersensitivity.
Accumulating evidence has shown that repeated exposure to general anesthesia during critical stages of brain development results in long-lasting behavioral deficits later in life. To date, there has ...been no effective treatment to mitigate the neurotoxic effects of anesthesia on brain development. By performing calcium imaging in the mouse motor cortex, we show that ketamine anesthesia causes a marked and prolonged reduction in neuronal activity during the period of post-anesthesia recovery. Administration of the AMPAkine drug CX546 1-(1,4-benzodioxan-6-ylcarbonyl)piperidine to potentiate AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor activity during emergence from anesthesia in mice enhances neuronal activity and prevents long-term motor learning deficits induced by repeated neonatal anesthesia. In addition, we show that CX546 administration also ameliorates various synaptic deficits induced by anesthesia, including reductions in synaptic expression of NMDA (N-methyl-d-aspartate) and AMPA receptor subunits, motor training-evoked neuronal activity, and dendritic spine remodeling associated with motor learning. Together, our results indicate that pharmacologically enhancing neuronal activity during the post-anesthesia recovery period could effectively reduce the adverse effects of early-life anesthesia.
The anterior cingulate cortex (ACC) is thought to be important for acute pain perception as well as the development of chronic pain after peripheral nerve injury. Nevertheless, how ACC neurons ...respond to sensory stimulation under chronic pain states is not well understood. Here, we used an
two-photon imaging technique to monitor the activity of individual neurons in the ACC of awake, head restrained mice. Calcium imaging in the dorsal ACC revealed robust somatic activity in layer 5 (L5) pyramidal neurons in response to peripheral noxious stimuli, and the degree of evoked activity was correlated with the intensity of noxious stimulation. Furthermore, the activation of ACC neurons occurred bilaterally upon noxious stimulation to either contralateral or ipsilateral hind paws. Notably, with nerve injury-induced neuropathic pain in one limb, L5 pyramidal neurons in both sides of the ACC showed enhanced activity in the absence or presence of pain stimuli. These results reveal hyperactivity of L5 pyramidal neurons in the bilateral ACC during the development of neuropathic pain.
To determine alteration of dendritic spines and associated changes in the primary visual cortex (V1 region) related to unilateral optic nerve crush (ONC) in adult mice.
Adult unilateral ONC mice were ...established. Retinal nerve fiber layer (RNFL) thickness was measured by spectral-domain optical coherence tomography. Visual function was estimated by flash visual evoked potentials (FVEPs). Dendritic spines were observed in the V1 region contralateral to the ONC eye by two-photon imaging in vivo. The neurons, reactive astrocytes, oligodendrocytes, and activated microglia were assessed by NeuN, glial fibrillary acidic protein, CNPase, and CD68 in immunohistochemistry, respectively. Tropomyosin receptor kinase B (TrkB) and the markers in TrkB trafficking were estimated using western blotting and co-immunoprecipitation. Transmission electron microscopy and western blotting were used to evaluate autophagy.
The amplitude and latency of FVEPs were decreased and delayed at 3 days, 1 week, 2 weeks, and 4 weeks after ONC, and RNFL thickness was decreased at 2 and 4 weeks after ONC. Dendritic spines were reduced in the V1 region contralateral to the ONC eye at 2, 3, and 4 weeks after ONC, with an unchanged number of neurons. Reactive astrocyte staining was increased at 2 and 4 weeks after ONC, but oligodendrocyte and activated microglia staining remained unchanged. TrkB was reduced with changes in the major trafficking proteins, and enhanced autophagy was observed in the V1 region contralateral to the ONC eye.
Dendritic spines were reduced in the V1 region contralateral to the ONC eye in adult mice. Reactive astrocytes and decreased TrkB may be associated with the reduced dendritic spines.
Homeostasis of neural firing properties is important in stabilizing neuronal circuitry, but how such plasticity might depend on alternative splicing is not known. Here we report that chronic ...inactivity homeostatically increases action potential duration by changing alternative splicing of BK channels; this requires nuclear export of the splicing factor Nova-2. Inactivity and Nova-2 relocation were connected by a novel synapto-nuclear signaling pathway that surprisingly invoked mechanisms akin to Hebbian plasticity: Ca2+-permeable AMPA receptor upregulation, L-type Ca2+ channel activation, enhanced spine Ca2+ transients, nuclear translocation of a CaM shuttle, and nuclear CaMKIV activation. These findings not only uncover commonalities between homeostatic and Hebbian plasticity but also connect homeostatic regulation of synaptic transmission and neuronal excitability. The signaling cascade provides a full-loop mechanism for a classic autoregulatory feedback loop proposed ∼25 years ago. Each element of the loop has been implicated previously in neuropsychiatric disease.
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•Chronic spike blockade with tetrodotoxin causes homeostatic spike broadening•Alternative splicing of BK channels by exclusion of a specific exon is responsible•Synaptic homeostasis starts CaM kinase signaling to drive nuclear exit of Nova-2•Chronic inactivity and hyperactivity can initiate similar LTP-like events
Silencing neuronal activity triggers similar molecular mechanisms as activating neurons during long-term potentiation, demonstrating Hebbian mechanisms of homeostatic spike regulation.
Obsessive-compulsive disorder (OCD) is a mental disease with heterogeneous behavioral phenotypes, including repetitive behaviors, anxiety, and impairments in cognitive functions. The brain regions ...related to the behavioral heterogeneity, however, are unknown.
We systematically examined the behavioral phenotypes of three OCD mouse models induced by pharmacological reagents RU24969, 8-hydroxy-DPAT hydrobromide (8-OH-DPAT), and 1-(3-chlorophenyl) piperazine hydrochloride-99% (MCPP), and compared the activated brain regions in each model, respectively.
We found that the mouse models presented distinct OCD-like behavioral traits. RU24969-treated mice exhibited repetitive circling, anxiety, and impairments in recognition memory. 8-OH-DPAT-treated mice exhibited excessive spray-induced grooming as well as impairments in recognition memory. MCPP-treated mice showed only excessive self-grooming. To determine the brain regions related to these distinct behavioral traits, we examined c-fos expression to indicate the neuronal activation in the brain. Our results showed that RU24969-treated mice exhibited increased c-fos expression in the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), prelimbic cortex (PrL), infralimbic cortex (IL), nucleus accumbens (NAc), hypothalamus, bed nucleus of the stria terminalis, lateral division, intermediate part (BSTLD), and interstitial nucleus of the posterior limb of the anterior commissure, lateral part (IPACL), whereas in 8-OH-DPAT-treated mice showed increased c-fos expression in the ACC, PrL, IL, OFC, NAc shell, and hypothalamus. By contrast, MCPP did not induce higher c-fos expression in the cortex than control groups.
Our results indicate that different OCD mouse models exhibited distinct behavioral traits, which may be mediated by the activation of different brain regions.
Aging is accompanied by a progressive decrease in learning and memory function. Synaptic loss, one of the hallmarks of normal aging, likely plays an important role in age-related cognitive decline. ...But little is known about the impact of advanced age on synaptic plasticity and neuronal function
. In this study, we examined the structural dynamics of postsynaptic dendritic spines as well as calcium activity of layer 5 pyramidal neurons in the cerebral cortex of young and old mice. Using transcranial two-photon microscopy, we found that in both sensory and motor cortices, the elimination rates of dendritic spines were comparable between young (3-5 months) and mature adults (8-10 months), but seemed higher in old mice (>20 months), contributing to a reduction of total spine number in the old brain. During the process of motor learning, old mice compared to young mice had fewer new spines formed in the primary motor cortex. Motor training-evoked somatic calcium activity in layer 5 pyramidal neurons of the motor cortex was also lower in old than young mice, which was associated with the decline of motor learning ability during aging. Together, these results demonstrate the effects of aging on learning-dependent synapse remodeling and neuronal activity in the living cortex and suggest that synaptic deficits may contribute to age-related learning impairment.
Epithelial-mesenchymal transition (EMT) has been recognized as a key element of cell migration, invasion, and drug resistance in several types of cancer. In this study, our aim was to clarify ...microRNAs (miRNAs)-related mechanisms underlying EMT followed by acquired resistance to chemotherapy in glioblastoma (GBM). We used multiple methods to achieve our goal including microarray analysis, qRT-PCR, western blotting analysis, loss/gain-of-function analysis, luciferase assays, drug sensitivity assays, wound-healing assay and invasion assay. We found that miR-203 expression was significantly lower in imatinib-resistant GBM cells (U251AR, U87AR) that underwent EMT than in their parental cells (U251, U87). Ectopic expression of miR-203 with miRNA mimics effectively reversed EMT in U251AR and U87AR cells, and sensitized them to chemotherapy, whereas inhibition of miR-203 in the sensitive lines with antisense oligonucleotides induced EMT and conferred chemoresistance. SNAI2 was identified as a direct target gene of miR-203. The knockdown of SNAI2 by short hairpin RNA (shRNA) inhibited EMT and drug resistance. In GBM patients, miR-203 expression was inversely related to SNAI2 expression, and those tumors with low expression of miR-203 experienced poorer clinical outcomes. Our findings indicate that re-expression of miR-203 or targeting SNAI2 might serve as potential therapeutic approaches to overcome chemotherapy resistance in GBM.
Ion channels are found in a variety of cancer cells and necessary for cell cycle and cell proliferation. The roles of K+ channels in the process are, however, poorly understood. In the present study, ...we report that adenosine triphosphate (ATP)-sensitive potassium channel activity plays a critical role in the proliferation of glioma cells. The expression of KATP channels in glioma tissues was greatly increased than that in normal tissues. Treatment of glioma cells with tolbutamide, KATP channels inhibitor, suppressed the proliferation of glioma cells and blocked glioma cell cycle in G0/G1 phase. Similarly, downregulation of KATP channels by small interfering RNA (siRNA) inhibited glioma cell proliferation. On the other hand, KATP channels agonist diazoxide and overexpression of KATP channels promoted the proliferation of glioma cells. Moreover, inhibiting KATP channels slowed the formation of tumor in nude mice generated by injection of glioma cells. Whereas activating KATP channels promoted development of tumor in vivo. The effect of KATP channels activity on glioma cells proliferation is mediated by extracellular signal-regulated kinase (ERK) activation. We found that activating KATP channel triggered ERK activation and inhibiting KATP channel depressed ERK activation. U-0126, the mitogen-activated protein kinase kinase (MAPK kinase) inhibitors blocked ERK activation and cell proliferation induced by diazoxide. Furthermore, constitutively activated MEK plasmids transfection reversed the inhibitory effects of tolbutamide on glioma proliferation, lending further support for a role of ERK in mediating this process. Our results suggest that KATP channels control glioma cell proliferation via regulating ERK pathway. We concluded that KATP channels are important in pathological cell proliferation and open a promising pathway for novel targeted therapies.
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