Summary Sleep is thought to consolidate changes in synaptic strength, but the underlying mechanisms are unknown. We investigated the cellular events involved in this process in ocular dominance plasticity (ODP) - a canonical form of in vivo cortical plasticity triggered by monocular deprivation (MD) and consolidated by sleep via undetermined, activity-dependent mechanisms. We find that sleep consolidates ODP primarily by strengthening cortical responses to non-deprived eye stimulation. Consolidation is inhibited by reversible, intracortical antagonism of NMDA receptors (NMDARs) or cAMP-dependent protein kinase (PKA) during post-MD sleep. Consolidation is also associated with sleep-dependent increases in the activity of remodeling neurons, and in the phosphorylation of proteins required for potentiation of glutamatergic synapses. These findings demonstrate that synaptic strengthening via NMDAR and PKA activity is a key step in sleep-dependent consolidation of ODP.

SUMMARY Sleep consolidates experience-dependent brain plasticity, but the precise cellular mechanisms mediating this process are unknown [1]. De novo cortical protein synthesis is one possible mechanism. In support of this hypothesis, sleep is associated with increased brain protein synthesis [2, 3] and transcription of mRNAs involved in protein synthesis regulation [4, 5]. Protein synthesis in turn is critical for memory consolidation and persistent forms of plasticity in vitro and in vivo [6, 7]. However, it is unknown if cortical protein synthesis in sleep serves similar functions. We investigated the role of protein synthesis in the sleep-dependent consolidation of a classic form of cortical plasticity in vivo (ocular dominance plasticity: ODP [8, 9]) in the cat visual cortex. We show that intracortical inhibition of mammalian target of rapamycin (mTOR)-dependent protein synthesis during sleep abolishes consolidation, but has no effect on plasticity induced during wakefulness. Sleep also promotes phosphorylation of protein synthesis regulators (i.e. 4E-BP1 and eEF2) and the translation (but not transcription) of key plasticity-related mRNAs (ARC and BDNF). These findings show that sleep promotes cortical mRNA translation. Interruption of this process has functional consequences, as it abolishes the consolidation of experience in the cortex.

Ocular dominance plasticity in the developing primary visual cortex is initiated by monocular deprivation (MD) and consolidated during subsequent sleep. To clarify how visual experience and sleep affect neuronal activity and plasticity, we continuously recorded extragranular visual cortex fast-spiking (FS) interneurons and putative principal (i.e., excitatory) neurons in freely behaving cats across periods of waking MD and post-MD sleep. Consistent with previous reports in mice, MD induces two related changes in FS interneurons: a response shift in favor of the closed eye and depression of firing. Spike-timing-dependent depression of open-eye-biased principal neuron inputs to FS interneurons may mediate these effects. During post-MD nonrapid eye movement sleep, principal neuron firing increases and becomes more phase-locked to slow wave and spindle oscillations. Ocular dominance (OD) shifts in favor of open-eye stimulation-evident only after post-MD sleep -are proportional to MD-induced changes in FS interneuron activity and to subsequent sleep-associated changes in principal neuron activity. OD shifts are greatest in principal neurons that fire 40-300 ms after neighboring FS interneurons during post-MD slow waves. Based on these data, we propose that MD-induced changes in FS interneurons play an instructive role in ocular dominance plasticity, causing disinhibition among open-eye-biased principal neurons, which drive plasticity throughout the visual cortex during subsequent sleep.period shifts neuronal responses in primary visual cortex in favor of open-eye stimulation. Sleep is essential for consolidating ocular dominance plasticity (ODP) in cat visual cortex (1, 2). Specifically, post-MD sleep is required to potentiate open-eye responses in cortical neurons-a process mediated via intracellular pathways involved in long-term potentiation of glutamatergic synapses (1, 3). However, the changes in network activity (during waking experience and subsequent sleep) that mediate ODP remain unknown.One long-standing hypothesis is that ODP is gated by the balance of excitation and inhibition in the visual cortex during the critical period. This idea is supported by findings that ODP is enhanced either by increasing GABAergic neurotransmission before the critical period (4) or by reducing GABA signaling after the critical period (5-8). It has been suggested that, during the critical period, MD itself alters the balance of excitation and feedback inhibition within the visual cortex by depressing the activity of fast-spiking (FS) interneurons (9, 10). In support of this idea, ODP is first detectable in the extragranular cortical layers [i.e., 2/3, 5, and 6 (11)], where depression of FS interneuron activity has been reported after brief MD. These layers are characterized by abundant reciprocal intralaminar connections between FS interneurons and pyramidal neurons (12, 13). In contrast, in layer 4, where ODP is initially weak or absent (11), connections between FS interneurons and pyramidal neurons can be strengthened by MD ...

The mechanisms that govern the formation of ␣-synuclein (␣-syn) aggregates are not well understood but are considered a central event in the pathogenesis of Parkinson's disease (PD). A critically important modulator of ␣-syn aggregation in vitro is dopamine and other catechols, which can prevent the formation of ␣-syn aggregates in cell-free and cellular model systems. Despite the profound importance of this interaction for the pathogenesis of PD, the processes by which catechols alter ␣-syn aggregation are unclear. Molecular and biochemical approaches were employed to evaluate the mechanism of catechol-␣-syn interactions and the effect on inclusion formation. The data show that the intracellular inhibition of ␣-syn aggregation requires the oxidation of catechols and the specific noncovalent interaction of the oxidized catechols with residues 125 YEMPS 129 in the C-terminal region of the protein. Cell-free studies using novel near infrared fluorescence methodology for the detection of covalent proteinortho-quinone adducts showed that although covalent modification of ␣-syn occurs, this does not affect ␣-syn fibril formation. In addition, oxidized catechols are unable to prevent both thermal and acid-induced protein aggregation as well as fibrils formed from a protein that lacks a YEMPS amino acid sequence, suggesting a specific effect for ␣-syn. These results suggest that inappropriate C-terminal cleavage of ␣-syn, which is known to occur in vivo in PD brain or a decline of intracellular catechol levels might affect disease progression, resulting in accelerated ␣-syn inclusion formation and dopaminergic neurodegeneration. ␣-Synuclein (␣-syn)2 (NACP, synelfin), a small, neuron-specific protein, was first linked to PD by genetic analysis of families with autosomal dominant inheritance of the disease. Genetic analysis discovered a point mutation in the ␣-syn gene (SNCA), resulting in an amino acid conversion of Ala 53 to Thr (1). Subsequently, ␣-syn protein was detected in Lewy bodies within the dopaminergic neurons of the substantia nigra pars compacta (2), the intracellular proteinaceous inclusions characteristic of PD and related disorders. Since this discovery, the process of ␣-syn aggregation has been proposed to underlie dopaminergic degeneration that occurs in PD. Therefore, delineating the mechanisms of ␣-syn aggregation and its pathophysiological role in neurodegeneration has been the focus of many investigations.Although the in vivo factors that regulate ␣-syn aggregation are not well understood, mechanisms involving genetic and environmental factors have been proposed. Genetic analysis has uncovered two additional missense mutations in SNCA (A30P and E46K) (3, 4) as well as triplication of the SNCA genomic region (5). Mutations of ␣-syn or gene triplication may increase the rate of ␣-syn aggregation (6, 7), impair cellular degradation (8), or increase the amount of cytosolic ␣-syn beyond the critical concentration required to initiate polymerization (9). Most PD cases are sporadic and involve aggregation...

Sleep has been observed in several invertebrate species, but its presence in marine invertebrates is relatively unexplored. Rapid-eye-movement (REM) sleep has only been observed in vertebrates. We investigated whether the cuttlefish Sepia officinalis displays sleep-like states. We find that cuttlefish exhibit frequent quiescent periods that are homeostatically regulated, satisfying two criteria for sleep. In addition, cuttlefish transiently display a quiescent state with rapid eye movements, changes in body coloration and twitching of the arms, that is possibly analogous to REM sleep. Our findings thus suggest that at least two different sleep-like states may exist in Sepia officinalis.

Ocular dominance plasticity (ODP) in the cat primary visual cortex (V1) is induced during waking by monocular deprivation (MD) and consolidated during subsequent sleep. The mechanisms underlying this process are incompletely understood. Extracellular signal-regulated kinase (ERK) is activated in V1 during sleep after MD, but it is unknown whether ERK activation during sleep is necessary for ODP consolidation. We investigated the role of ERK in sleep-dependent ODP consolidation by inhibiting the ERK-activating enzyme MEK in V1 (via U0126) during post-MD sleep. ODP consolidation was then measured with extracellular microelectrode recordings. Western blot analysis was used to confirm the efficacy of U0126 and to examine proteins downstream of ERK. U0126 abolished ODP consolidation and reduced both phosphorylation of eukaryotic initiation factor 4E (eIF4E) and levels of the synaptic marker PSD-95. Furthermore, interfering with ERK-mediated translation by inhibiting MAP kinase-interacting kinase 1 (Mnk1) with CGP57380 mimicked the effects of U0126. These results demonstrate that ODP consolidation requires sleep-dependent activation of the ERK-Mnk1 pathway.

An automatic procedure, allowing the prospective registration of brain MRI images and the acquisition of nearly identical brain volumes (coverage and orientation) in longitudinal exams, is presented. This procedure, based on a fast registration algorithm and a tailored pulse sequence, is used to reposition single voxels for 1H MRS data acquired in vivo. The impact of the repositioning method on the extent of voxel overlap and on the reproducibility of metabolite concentration measurements is studied. A statistically significant increase in voxel overlap and generally decreased short-term measurement variability (decreased coefficients of variation and increased reproducibility coefficients) are observed. Differences in the long-term variances of metabolite concentrations and concentration ratios measured using the eye and automatic repositioning scheme, however, do not reach statistical significance. The improved workflow associated with the use of the automatic repositioning process, which obviates the need for skilled operator intervention for voxel repositioning, suggests that approaches similar to the one presented here may be a standard element in tomorrow's longitudinal MRI and MRS exams.

BackgroundRecent findings indicate that certain classes of hypnotics that target GABAA receptors impair sleep-dependent brain plasticity. However, the effects of hypnotics acting at monoamine receptors (e.g., the antidepressant trazodone) on this process are unknown. We therefore assessed the effects of commonly-prescribed medications for the treatment of insomnia (trazodone and the non-benzodiazepine GABAA receptor agonists zaleplon and eszopiclone) in a canonical model of sleep-dependent, in vivo synaptic plasticity in the primary visual cortex (V1) known as ocular dominance plasticity.Methodology/Principal FindingsAfter a 6-h baseline period of sleep/wake polysomnographic recording, cats underwent 6 h of continuous waking combined with monocular deprivation (MD) to trigger synaptic remodeling. Cats subsequently received an i.p. injection of either vehicle, trazodone (10 mg/kg), zaleplon (10 mg/kg), or eszopiclone (1–10 mg/kg), and were allowed an 8-h period of post-MD sleep before ocular dominance plasticity was assessed. We found that while zaleplon and eszopiclone had profound effects on sleeping cortical electroencephalographic (EEG) activity, only trazodone (which did not alter EEG activity) significantly impaired sleep-dependent consolidation of ocular dominance plasticity. This was associated with deficits in both the normal depression of V1 neuronal responses to deprived-eye stimulation, and potentiation of responses to non-deprived eye stimulation, which accompany ocular dominance plasticity.Conclusions/SignificanceTaken together, our data suggest that the monoamine receptors targeted by trazodone play an important role in sleep-dependent consolidation of synaptic plasticity. They also demonstrate that changes in sleep architecture are not necessarily reliable predictors of how hypnotics affect sleep-dependent neural functions.