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Olfactory dysfunction precedes dementia in several neurodegenerative disorders such as Alzheimer’s disease (AD) or Parkinson’s Disease (PD), and AD/PD are associated with progressive sleep abnormalities. However, how sleep affects cognitive performance remains unclear, perhaps due to the complexities of the human nervous system. Here we demonstrate that the transparent model organism C. elegans which has well defined neural connection sleeps after repeated odor trainings. This provides us with a platform to dissect how sleep affects memory at a synaptic resolution. We identified that sleep after training is required for the animal to retain a long-term memory of the odor. We found that if animals do not sleep in the first two hours after training, memory is not consolidated. After identifying the neurons that are required for the memory, we show that the sensory-interneuron connections within the circuit are downscaled after sleep. Therefore, we found a time-specific requirement of sleep that modulates synaptic downscaling to preserve memory. Conversely, lack of sleep post-training erases the long-term memory and destabilizes the synaptic downscaling, indicating that modulating the amount of sleep is sufficient to modulate memory. These results make C. elegans an excellent tool to ask what molecular mechanisms, cell biological processes and circuit level reorganizations are engaged during sleep to promote memory. This understanding will provide insights into the functions of sleep that affects cognitive performance in neurodegenerative diseases.

In the mammalian inner ear, bicellular and tricellular tight junctions (tTJs) seal the paracellular space between epithelial cells. Tricellulin and immunoglobulin-like (Ig-like) domain containing receptor 1 (ILDR1, also referred to as angulin-2) localize to tTJs of the sensory and non-sensory epithelia in the organ of Corti and vestibular end organs. Recessive mutations of TRIC (DFNB49) encoding tricellulin and ILDR1 (DFNB42) cause human nonsyndromic deafness. However, the pathophysiology of DFNB42 deafness remains unknown. ILDR1 was recently reported to be a lipoprotein receptor mediating the secretion of the fat-stimulated cholecystokinin (CCK) hormone in the small intestine, while ILDR1 in EpH4 mouse mammary epithelial cells in vitro was shown to recruit tricellulin to tTJs. Here we show that two different mouse Ildr1 mutant alleles have early-onset severe deafness associated with a rapid degeneration of cochlear hair cells (HCs) but have a normal endocochlear potential. ILDR1 is not required for recruitment of tricellulin to tTJs in the cochlea in vivo; however, tricellulin becomes mislocalized in the inner ear sensory epithelia of ILDR1 null mice after the first postnatal week. As revealed by freeze-fracture electron microscopy, ILDR1 contributes to the ultrastructure of inner ear tTJs. Taken together, our data provide insight into the pathophysiology of human DFNB42 deafness and demonstrate that ILDR1 is crucial for normal hearing by maintaining the structural and functional integrity of tTJs, which are critical for the survival of auditory neurosensory HCs.

Prior studies of the modulation of the Na+ current by sympathetic stimulation have yielded controversial results. Separation of the Na+ and Ca2+ currents poses a problem in myocyte preparations. The gating of cloned Na+ channels is different in oocytes compared with mammalian expression systems. We have examined the sympathetic modulation of the alpha-subunit of the wild-type human cardiac Na+ channel (hH1) and the long QT-associated mutant, delta KPQ, expressed in human embryonic kidney cells.Stable cell lines of hH1 and delta KPQ were established in human embryonic kidney cells. Whole-cell and single-channel currents were measured with the patch-clamp technique. Sympathetic stimulation was effected by exposure to isoproterenol or 8-bromo-cAMP. Na+ channel activation and inactivation were determined using standard voltage clamp protocols. Ca2+:Na+ permeability ratio was determined under bi-ionic conditions.We observed a qualitatively different effect of sympathetic stimulation on the cardiac Na+ current from that reported in frog oocytes: activation and inactivation kinetics were shifted to more negative potentials. This shift was similar for both hH1 and delta KPQ. [delta V0.5 for inactivation: 8.3 +/- 1.7 mV, p0.001 (hH1); 6.8 +/- 0.9 mV, p0.001 (delta KPQ)]. Increased rate of closed-state inactivation contributed to the shifting of the inactivation-voltage relationship. Open-state inactivation was not affected as mean open times were unchanged. Reversal potential measurement in hH1 suggested a low Ca2+:Na+ permeability ratio of 0.017, uninfluenced by sympathetic stimulation. In delta KPQ, the size of the persistent relative to the peak current was increased with 8-bromo-cAMP from 3.0 +/- 0.7% to 4.3 +/- 0.6% (p = 0.056).Sympathetic stimulation exerts multiple effects on the gating of hH1. Similar effects are also seen in delta KPQ which may increase arrhythmia susceptibility in long QT syndrome by modifying the Na+ channel contribution to the action potential.