Negr1 controls adult hippocampal neurogenesis and affective behaviors.

Recent genome-wide association studies on major depressive disorder have implicated neuronal growth regulator 1 (Negr1), a GPI-anchored cell adhesion molecule in the immunoglobulin LON family. Although Negr1 has been shown to regulate neurite outgrowth and synapse formation, the mechanism through which this protein affects mood disorders is still largely unknown. In this research, we characterized Negr1-deficient (negr1-/-) mice to elucidate the function of Negr1 in anxiety and depression. We found that anxiety- and depression-like behaviors increased in negr1-/- mice compared with wild-type mice. In addition, negr1-/- mice had decreased adult hippocampal neurogenesis compared to wild-type mice. Concurrently, both LTP and mEPSC in the dentate gyrus (DG) region were severely compromised in negr1-/- mice. In our effort to elucidate the underlying molecular mechanisms, we found that lipocalin-2 (Lcn2) expression was decreased in the hippocampus of negr1-/- mice compared to wild-type mice. Heterologous Lcn2 expression in the hippocampal DG of negr1-/- mice rescued anxiety- and depression-like behaviors and restored neurogenesis and mEPSC frequency to their normal levels in these mice. Furthermore, we discovered that Negr1 interacts with leukemia inhibitory factor receptor (LIFR) and modulates LIF-induced Lcn2 expression. Taken together, our data uncovered a novel mechanism of mood regulation by Negr1 involving an interaction between Negr1 and LIFR along with Lcn2 expression.

BK channel blocker paxilline attenuates thalidomide-caused synaptic and cognitive dysfunctions in mice.

Thalidomide is a widely prescribed immunomodulatory drug (iMiD) for multiple myeloma, but causes reversible memory loss in humans. However, how thalidomide causes cognitive dysfunction at a cellular and molecular level has not been demonstrated. We studied the effect of thalidomide on synaptic functions and cognitive behaviors using a mouse model. Thalidomide led to cognitive deficits in learning behavior in a passive avoidance test and in a novel object recognition test, increased anxiety in an elevated plus maze test, and increased depressive behaviors in a tail suspension test. Interestingly, thalidomide elevated big- or large-conductance, calcium-activated K+ (BK) channel expression in the plasma membrane and BK channel activity in the hippocampus. Thalidomide also increased the paired pulse ratio of excitatory postsynaptic current (EPSC), which suggests a decreased probability of glutamate release. Furthermore, the changes in the paired pulse ratio and in BK channel activity were blocked by paxilline, a BK channel blocker. Finally, we found that thalidomide-induced cognitive dysfunctions were restored by paxilline treatment. These results suggest that thalidomide-mediated BK channel hyperfunction is responsible for the pathological mechanism of thalidomide-associated reversible memory loss.

Cereblon Maintains Synaptic and Cognitive Function by Regulating BK Channel.

Mutations in the cereblon (CRBN) gene cause human intellectual disability, one of the most common cognitive disorders. However, the molecular mechanisms of CRBN-related intellectual disability remain poorly understood. We investigated the role of CRBN in synaptic function and animal behavior using male mouse and Drosophila models. Crbn knock-out (KO) mice showed normal brain and spine morphology as well as intact synaptic plasticity; however, they also exhibited decreases in synaptic transmission and presynaptic release probability exclusively in excitatory synapses. Presynaptic function was impaired not only by loss of CRBN expression, but also by expression of pathogenic CRBN mutants (human R419X mutant and Drosophila G552X mutant). We found that the BK channel blockers paxilline and iberiotoxin reversed this decrease in presynaptic release probability in Crbn KO mice. In addition, paxilline treatment also restored normal cognitive behavior in Crbn KO mice. These results strongly suggest that increased BK channel activity is the pathological mechanism of intellectual disability in CRBN mutations.SIGNIFICANCE STATEMENTCereblon (CRBN), a well known target of the immunomodulatory drug thalidomide, was originally identified as a gene that causes human intellectual disability when mutated. However, the molecular mechanisms of CRBN-related intellectual disability remain poorly understood. Based on the idea that synaptic abnormalities are the most common factor in cognitive dysfunction, we monitored the synaptic structure and function of Crbn knock-out (KO) animals to identify the molecular mechanisms of intellectual disability. Here, we found that Crbn KO animals showed cognitive deficits caused by enhanced BK channel activity and reduced presynaptic glutamate release. Our findings suggest a physiological pathomechanism of the intellectual disability-related gene CRBN and will contribute to the development of therapeutic strategies for CRBN-related intellectual disability.

Caspase-cleaved tau exhibits rapid memory impairment associated with tau oligomers in a transgenic mouse model.

In neurodegenerative diseases like AD, tau forms neurofibrillary tangles, composed of tau protein. In the AD brain, activated caspases cleave tau at the 421th Asp, generating a caspase-cleaved form of tau, TauC3. Although TauC3 is known to assemble rapidly into filaments in vitro, a role of TauC3 in vivo remains unclear. Here, we generated a transgenic mouse expressing human TauC3 using a neuron-specific promoter. In this mouse, we found that human TauC3 was expressed in the hippocampus and cortex. Interestingly, TauC3 mice showed drastic learning and spatial memory deficits and reduced synaptic density at a young age (2-3months). Notably, tau oligomers as well as tau aggregates were found in TauC3 mice showing memory deficits. Further, i.p. or i.c.v. injection with methylene blue or Congo red, inhibitors of tau aggregation in vitro, and i.p. injection with rapamycin significantly reduced the amounts of tau oligomers in the hippocampus, rescued spine density, and attenuated memory impairment in TauC3 mice. Together, these results suggest that TauC3 facilitates early memory impairment in transgenic mice accompanied with tau oligomer formation, providing insight into the role of TauC3 in the AD pathogenesis associated with tau oligomers and a useful AD model to test drug candidates.

Melatonin inhibits voltage-sensitive Ca(2+) channel-mediated neurotransmitter release.

Melatonin is involved in various neuronal functions such as circadian rhythmicity and thermoregulation. Melatonin has a wide range of pharmacologically effective concentration levels from the nanomolar to millimolar levels. Recently, the antiepileptic effect of high dose melatonin has been the focus of clinical studies; however, its detailed mechanism especially in relation to neurotransmitter release and synaptic transmission remains unclear. We studied the effect of melatonin at high concentrations on the neurotransmitter release by monitoring norepinephrine release in PC12 cells, and excitatory postsynaptic potential in rat hippocampal slices. Melatonin inhibits the 70mM K(+)-induced Ca(2+) increase at millimolar levels without effect on bradykinin-triggered Ca(2+) increase in PC12 cells. Melatonin (1mM) did not affect A2A adenosine receptor-evoked cAMP production, and classical melatonin receptor antagonists did not reverse the melatonin-induced inhibitory effect, suggesting G-protein coupled receptor independency. Melatonin inhibits the 70mM K(+)-induced norepinephrine release at a similar effective concentration range in PC12 cells. We confirmed that melatonin (100µM) inhibits excitatory synaptic transmission of the hippocampal Schaffer collateral pathway with the decrease in basal synaptic transmission and the increase in paired pulse ratio. These results show that melatonin inhibits neurotransmitter release through the blocking of voltage-sensitive Ca(2+) channels and suggest a possible mechanism for the antiepileptic effect of melatonin.

Surgical outcomes of laparoscopic cholecystectomy for severe acute cholecystitis.

The aim of this study was to evaluate the surgical outcomes of laparoscopic cholecystectomy (LC) in patients who were diagnosed with severe acute cholecystitis (SAC) and to clarify the useful treatment modalities of SAC. Of 112 patients who presented SAC, we selected 99 patients and divided them into 3 groups: 37 patients who underwent preoperative percutaneous transhepatic gallbladder drainage (PTGBD; group 1), 62 patients with SAC but not indicated for PTGBD (group 2), and 59 patients with acute and chronic cholecystitis (group 3). The conversion rate was 2.7% (1/37) in group 1, 6.5% (4/62) in group 2, and 1.7% (1/59) in group 3. In groups 1 and 2, the postoperative stay and operative time were longer than those in group 3 with significant difference, respectively (P<0.05). In group 2, there was correlation not only between postoperative stay and age but also between postoperative stay and ASA class (P<0.05). In group 2, there was no correlation between time to operation and operative time and also between time to operation and postoperative stay, however, there was surprisingly significant correlation between time to operation and conversion rate in SAC (P=0.018). In conclusion, PTGBD should selectively be performed in patients with severe comorbidities rather than improving surgical outcomes of LC for severe acute cholecystitis. If patients are not indicated for PTGBD, an early laparoscopic cholecystectomy is recommended because it can decrease conversion rate, although it cannot decrease operative time and postoperative stay.

Risk factors of postoperative anastomotic stricture after excision of choledochal cysts with hepaticojejunostomy.

The aim of this study was to investigate the risk factors of postoperative anastomotic stricture after excision of choledochal cysts and hepaticojejunostomy. Among 65 patients who underwent surgery for choledochal cyst between March 1995 and June 2005, we selected 34 adult patients who were diagnosed as having choledochal cyst. We divided patients into two groups, depending on postoperative anastomotic stricture developed or not. Medical records and radiological findings of each patient were reviewed retrospectively. H&E stain and Masson-Trichrome stain of each specimen of the resected cyst were performed, and thickness of cyst wall, the grade of fibrosis, loss of smooth muscle layer, loss of mucosa, and infiltration of inflammatory cells were measured. Of the 34 patients, excision of choledochal cyst and hepaticojejunostomy were done in 33 patients, and 1 patient with chronic pancreatitis underwent pylorus-preserving pancreaticoduodenectomy. Anastomotic stricture and intrahepatic duct stones postoperatively developed in eight patients; one patient of 19 type I cyst and seven patients of 15 type IVa, developing significantly more in the type IVa choledochal cyst (P<0.05). The size of choledochal cyst in the stricture group was 7.0 cm, and that of the non-stricture group, 4.2 cm, showing significant difference between the two groups (P<0.05). The stricture group presented shorter duration of symptoms (27.63+/-61.72 days; ranged, 1 approximately 180 days) than the non-stricture group (483.33+/-916.41 days; ranged, 1 approximately 3,560 days), and it was statistically significant (P<0.05). Pathologically, significant difference was found between anastomotic stricture and infiltration of inflammatory cells (P<0.05). The results indicate that anastomotic stricture is influenced by the type IVa choledochal cyst, size of cyst, duration of symptoms, and the grade of infiltration of inflammatory cells. Therefore, closed careful follow-up is important in patients who underwent cyst excision with hepaticojejunostomy for type IVa choledochal cyst. If the anastomotic stricture develops, nonoperative management should be recommended, rather than operation, as much as possible.