CSF NPTX2 is a biomarker of schizophrenia and supports a model that integrates across genetics, pharmacology, and behavior.

Climbing fibers (CFs) generate complex spikes (CS) and Ca²⁺ transients in cerebellar Purkinje cells (PCs), serving as instructive signals. The so-called 'all-or-none' character of CSs has been questioned since the CF burst was described. Although recent studies have indicated a sensory-driven enhancement of PC Ca²⁺ signals, how CF responds to sensory events and contributes to PC dendritic Ca²⁺ and CS remains unexplored. Here, single or simultaneous Ca²⁺ imaging of CFs and PCs in awake mice revealed the presynaptic CF Ca²⁺ amplitude encoded the sensory input’s strength and directly influenced post-synaptic PC dendritic Ca²⁺ amplitude. The sensory-driven variability in CF Ca²⁺ amplitude depended on the number of spikes in the CF burst. Finally, the spike number of the CF burst determined the PC Ca²⁺ influx and CS properties. These results reveal the direct translation of sensory information-coding CF inputs into PC Ca²⁺, suggesting the sophisticated role of CFs as error signals.

Significance: We report a unique form of neural plasticity in the visual cortex. Unlike well-known forms of neural plasticity, in which synaptic connections are slowly weakened or strengthened, we found that visual deprivation causes a rapid and transient “all-or-none” loss of local connections between pyramidal cells and parvalbumin-positive interneurons (Pyr→PV). After 1 d of visual deprivation, half of these connections are lost, whereas the spared ones remain unchanged; after 2 d of deprivation, the connectivity levels return to normal. Finally, we show that this early transient all-or-none loss of Pyr→PV connections is an obligatory step for subsequent changes in the cortical function induced by visual deprivation.

Sleep and circadian rhythm disruption (SCRD) is commonly observed in aging, especially in individuals who experience progressive cognitive decline to mild cognitive impairment (MCI) and Alzheimer’s disease (AD). However, precise molecular mechanisms underlying the association between SCRD and aging are not fully understood. Orexin A is a well-characterized “sleep neuropeptide” that is expressed in hypothalamic neurons and evokes wake behavior. The importance of Orexin is exemplified in narcolepsy where it is profoundly down-regulated. Interestingly, the synaptic immediate early gene NPTX2 is co-expressed in Orexin neurons and is similarly reduced in narcolepsy. NPTX2 is also down-regulated in CSF of some cognitively normal older individuals and predicts the time of transition from normal cognition to MCI. The association between Orexin and NPTX2 is further evinced here where we observe that Orexin A and NPTX2 are highly correlated in CSF of cognitively normal aged individuals and raises the question of whether SCRD that are typically attributed to Orexin A loss of function may be modified by concomitant NPTX2 down-regulation. Is NPTX2 an effector of sleep or simply a reporter of orexin-dependent SCRD? To address this question, we examined NPTX2 KO mice and found they retain Orexin expression in the brain and so provide an opportunity to examine the specific contribution of NPTX2 to SCRD. Our results reveal that NPTX2 KO mice exhibit a disrupted circadian onset time, coupled with increased activity during the sleep phase, suggesting difficulties in maintaining states. Sleep EEG indicates distinct temporal allocation shifts across vigilance states, characterized by reduced wake and increased NREM time. Evident sleep fragmentation manifests through alterations of event occurrences during Wake and NREM, notably during light transition periods, in conjunction with an increased frequency of sleep transitions in NPTX2 KO mice, particularly between Wake and NREM. EEG spectral analysis indicated significant shifts in power across various frequency bands in the wake, NREM, and REM states, suggestive of disrupted neuronal synchronicity. An intriguing observation is the diminished occurrence of sleep spindles, one of the earliest measures of human sleep disruption, in NPTX2 KO mice. These findings highlight the effector role of NPTX2 loss of function as an instigator of SCRD and a potential mediator of sleep disruption in aging.

Background: Deficits in interneuron and cholinergic circuits are noted in AD pathology, yet the precise mechanisms of their contribution to cognitive decline in the disease remain elusive. Neuronal Pentraxin 2 (NPTX2), a sensitive marker for synaptic activity and AD progression, is an immediate early gene expressed by pyramidal neurons that functions at excitatory synapses on Parvalbumin interneurons (PV‐IN) to cluster AMPA receptors and strengthen circuit inhibition. NPTX2 is later shed from some synapses into the cerebrospinal fluid (CSF), where reduced NPTX2 levels inversely correlate with hippocampal volume and cognitive performance in individuals with AD/MCI. Recent studies employing NPTX2‐SEP (Super‐Ecliptic pHluorin) as a marker of its synaptic trafficking have suggested that the diurnal oscillation of NPTX2 trafficking is important for circuit refinement, which is crucial for ensemble formation and memory updating.Method: We aim to investigate the mechanisms of NPTX2 synaptic trafficking by utilizing two‐photon imaging of NPTX2‐SEP in the somatosensory cortex while chemo‐ and optogenetically manipulating PV‐IN and cholinergic circuits, specifically the basal forebrain (BF) and cortical intrinsic cholinergic neurons.Result: We found that reducing PV‐IN activity leads to rapid shedding of NPTX2, whereas increasing PV‐IN activity results in elevated accumulation of NPTX2 at excitatory synapses on PV‐IN. This suggests that PV‐IN activity is a critical determinant for NPTX2 synaptic exocytosis and shedding and supports a model akin to spike‐timing‐dependent plasticity, wherein synapses are strengthened with correlated pre‐ and postsynaptic activity and weakened when presynaptic activity is not associated with postsynaptic activity. Direct activation of BF cholinergic neurons had minimal effect on NPTX2‐SEP. However, consistent with the observation that activation of nicotinic and muscarinic ACh receptors (AChR) can respectively increase and decrease cortical PV‐IN activity, chemogenetic activation of BF cholinergic neurons with mAChR blocker induced NPTX2 shedding, while nicotine also moderately induced its shedding. Additionally, chemo‐ and optogenetic activation of cortical intrinsic cholinergic interneurons reduced PV‐IN activity and induced NPTX2 shedding.Conclusion: These results underscore the significant roles of the ACh‐PV pathway in regulating NPTX2 synaptic trafficking and implicate deficits in NPTX2 shedding and circuit refinement due to the failure of the ACh‐PV pathway as a mechanism for cognitive decline in AD.

Background: Sleep and circadian rhythm disruption (SCRD) is prevalent in aging, particularly in individuals transitioning to mild cognitive impairment (MCI) and Alzheimer's disease (AD). Orexin A, a key neuropeptide regulating wakefulness, is reduced in conditions like narcolepsy. The synaptic immediate early gene NPTX2, co‐expressed in orexin neurons, serves as a sensitive biomarker for AD and has been linked to cognitive decline. The precise role of NPTX2 in SCRD, however, remains unclear. Method: NPTX2 and orexin A levels in cerebrospinal fluid (CSF) were analyzed in cognitively normal aged individuals and AD patients across two independent cohorts. In NPTX2 knockout (KO) mice, orexin A levels were measured using biochemical assays. Behavioral assessments and sleep EEG recordings were performed to investigate the contribution of NPTX2 to SCRD, focusing on circadian onset, vigilance states, sleep transitions, orexin signaling, neuronal synchronicity, and sleep spindle activity. Result: NPTX2 levels in CSF strongly correlated with orexin A in cognitively normal aged individuals but not in AD, suggesting a disruption in this association with disease progression. However, orexin A expression was not altered in NPTX2 KO and they exhibited disrupted circadian onset, increased activity during the sleep phase, and fragmented sleep characterized by increased wake‐to‐NREM transitions and altered vigilance state durations. Behavioral assays demonstrated an enhanced response to the orexin receptor 1 agonist TAK‐925 in NPTX2 KO mice, indicating altered orexin signaling. Sleep EEG analysis revealed shifts in power across frequency bands and reduced sleep spindles, an early marker of human sleep disruption. Conclusion: These findings demonstrate that NPTX2 loss of function instigates SCRD by disrupting sleep architecture, orexin signaling, and neuronal synchronicity. This supports the effector role of NPTX2 in sleep regulation and highlights its potential as a therapeutic target for sleep and circadian dysfunction in aging and neurodegenerative conditions.