In mammalian cells, the nuclear export receptor, Exportin 5 (Exp5), exports pre-microRNAs (pre-miRNAs) as well as tRNAs into the cytoplasm. In this study, we examined the function of HASTY (HST), the Arabidopsis ortholog of Exp5, in the biogenesis of miRNAs and tRNAs. In contrast to mammals, we found that miRNAs exist as single-stranded 20-to 21-nt molecules in the nucleus in Arabidopsis. This observation is consistent with previous studies indicating that proteins involved in miRNA biogenesis are located in the nucleus in Arabidopsis. Although miRNAs exist in the nucleus, a majority accumulate in the cytoplasm. Interestingly, loss-offunction mutations in HST reduced the accumulation of most miRNAs but had no effect on the accumulation of tRNAs and endogenous small interfering RNAs, or on transgene silencing. In contrast, a mutation in PAUSED (PSD), the Arabidopsis ortholog of the tRNA export receptor, Exportin-t, interfered with the processing of tRNA-Tyr but did not affect the accumulation or nuclear export of miRNAs. These results demonstrate that HST and PSD do not share RNA cargos in nuclear export and strongly suggest that there are multiple nuclear export pathways for these small RNAs in Arabidopsis.exportin 5 ͉ exportin-t ͉ miRNA G enetic analyses of the juvenile-to-adult transition in Arabidopsis have produced several genes required for the expression of the juvenile phase. The first genes to be identified were HASTY (HST) (1) and PAUSED (PSD) (2). Loss-of-function mutations in these genes have similar phenotypes. In addition to interfering with the expression juvenile traits, these mutations reduce the growth rate of the root and shoot, affect the morphology of the shoot apical meristem, cause aberrant phyllotaxy in the inflorescence, and disrupt floral morphogenesis (3-5). HST and PSD are members of the importin ␤ family of nucleocytoplasmic transport receptors (6, 7). PSD is the Arabidopsis ortholog of the tRNA export receptor, Exportin-t (Exp-t) (4, 5), and likely plays a role in tRNA export because it is capable of rescuing the tRNA export defect of a los1 mutation in Saccharomyces cerevisiae (4). The function of HST is more difficult to predict because its orthologs in S. cerevisiae and mammals have completely different functions. The mammalian ortholog of HST, Exportin 5 (Exp5), exports pre-microRNAs (pre-miRNAs) (8-11), tRNAs (12, 13), a viral hairpin RNA (14), and proteins associated with these and other double-stranded (ds) RNAs (15-17). The yeast ortholog of HST, Msn5p, exports several different types of phosphorylated proteins (18) and imports replication protein A (19), a protein involved in DNA replication and repair.miRNAs are endogenous 20-to 22-nt RNAs that negatively regulate gene expression at the posttranscriptional level (20,21). In plants, miRNAs function primarily by directing the cleavage of their targets in the middle of the miRNA recognition element; in animals, they act primarily as translational repressors. In animals, pre-miRNAs are excised from longer transcripts in the nuc...

The medial septum (MS) is required for theta rhythmic oscillations and grid cell firing in the medial entorhinal cortex (MEC). While GABAergic, glutamatergic, and cholinergic neurons project from the MS to the MEC, their synaptic targets are unknown. To investigate whether MS neurons innervate specific layers and cell types in the MEC, we expressed channelrhodopsin-2 in mouse MS neurons and used patch-clamp recording in brain slices to determine the response to light activation of identified cells in the MEC. Following activation of MS axons, we observed fast monosynaptic GABAergic IPSPs in the majority (Ͼ60%) of fast-spiking (FS) and low-threshold-spiking (LTS) interneurons in all layers of the MEC, but in only 1.5% of nonstellate principal cells (NSPCs) and in no stellate cells. We also observed fast glutamatergic responses to MS activation in a minority (Ͻ5%) of NSPCs, FS, and LTS interneurons. During stimulation of MS inputs at theta frequency (10 Hz), the amplitude of GABAergic IPSPs was maintained, and spike output from LTS and FS interneurons was entrained at low (25-60 Hz) and high (60 -180 Hz) gamma frequencies, respectively. By demonstrating cell type-specific targeting of the GABAergic projection from the MS to the MEC, our results support the idea that the MS controls theta frequency activity in the MEC through coordination of inhibitory circuits.

Epileptiform discharges recorded in the 4-aminopyridine (4-AP) in vitro epilepsy model are mediated by glutamatergic and GABAergic signaling. Using a 60-channel perforated multielectrode array (pMEA) on corticohippocampal slices from 2 to 3 week old mice we recorded interictal-and ictal-like events. When glutamatergic transmission was blocked, interictal-like events events no longer initiated in the hilus or CA3/CA1 pyramidal layers but originated from the dentate gyrus granule and molecular layers. Furthermore, frequencies of interictal-like events were reduced and durations were increased in these regions while cortical discharges were completely blocked. Following GABA A receptor blockade interictal-like events no longer propagated to the dentate gyrus while their frequency in CA3 increased; in addition, ictal-like cortical events became shorter while increasing in frequency. Lastly, drugs that affect tonic and synaptic GABAergic conductance modulate the frequency, duration, initiation and propagation of interictal-like events. These findings confirm and expand on previous studies indicating that multiple synaptic mechanisms contribute to synchronize neuronal network activity in forebrain structures.

Sazetidine-A seems to be a potent analgesic without causing neurologic side effects.

Network hyperexcitability is a feature of Alzheimer’ disease (AD) as well as numerous transgenic mouse models of AD. While hyperexcitability in AD patients and AD animal models share certain features, the mechanistic overlap remains to be established. We aimed to identify features of network hyperexcitability in AD models that can be related to epileptiform activity signatures in AD patients. We studied network hyperexcitability in mice expressing amyloid precursor protein (APP) with mutations that cause familial AD, and compared a transgenic model that overexpresses human APP (hAPP) (J20), to a knock-in model expressing APP at physiological levels (APPNL/F). We recorded continuous long-term electrocorticogram (ECoG) activity from mice, and studied modulation by circadian cycle, behavioral, and brain state. We report that while J20s exhibit frequent interictal spikes (IISs), APPNL/F mice do not. In J20 mice, IISs were most prevalent during daylight hours and the circadian modulation was associated with sleep. Further analysis of brain state revealed that IIS in J20s are associated with features of rapid eye movement (REM) sleep. We found no evidence of cholinergic changes that may contribute to IIS-circadian coupling in J20s. In contrast to J20s, intracranial recordings capturing IIS in AD patients demonstrated frequent IIS in non-REM (NREM) sleep. The salient differences in sleep-stage coupling of IIS in APP overexpressing mice and AD patients suggests that different mechanisms may underlie network hyperexcitability in mice and humans. We posit that sleep-stage coupling of IIS should be an important consideration in identifying mouse AD models that most closely recapitulate network hyperexcitability in human AD.