A sleep-active basalocortical pathway crucial for generation and maintenance of chronic pain.

Poor sleep is associated with the risk of developing chronic pain, but how sleep contributes to pain chronicity remains unclear. Here we show that following peripheral nerve injury, cholinergic neurons in the anterior nucleus basalis (aNB) of the basal forebrain are increasingly active during nonrapid eye movement (NREM) sleep in a mouse model of neuropathic pain. These neurons directly activate vasoactive intestinal polypeptide-expressing interneurons in the primary somatosensory cortex (S1), causing disinhibition of pyramidal neurons and allodynia. The hyperactivity of aNB neurons is caused by the increased inputs from the parabrachial nucleus (PB) driven by the injured peripheral afferents. Inhibition of this pathway during NREM sleep, but not wakefulness, corrects neuronal hyperactivation and alleviates pain. Our results reveal that the PB-aNB-S1 pathway during sleep is critical for the generation and maintenance of chronic pain. Inhibiting this pathway during the sleep phase could be important for treating neuropathic pain.

REM sleep promotes experience-dependent dendritic spine elimination in the mouse cortex.

In many parts of the nervous system, experience-dependent refinement of neuronal circuits predominantly involves synapse elimination. The role of sleep in this process remains unknown. We investigated the role of sleep in experience-dependent dendritic spine elimination of layer 5 pyramidal neurons in the visual (V1) and frontal association cortex (FrA) of 1-month-old mice. We found that monocular deprivation (MD) or auditory-cued fear conditioning (FC) caused rapid spine elimination in V1 or FrA, respectively. MD- or FC-induced spine elimination was significantly reduced after total sleep or REM sleep deprivation. Total sleep or REM sleep deprivation also prevented MD- and FC-induced reduction of neuronal activity in response to visual or conditioned auditory stimuli. Furthermore, dendritic calcium spikes increased substantially during REM sleep, and the blockade of these calcium spikes prevented MD- and FC-induced spine elimination. These findings reveal an important role of REM sleep in experience-dependent synapse elimination and neuronal activity reduction.

Sevoflurane induces neuronal activation and behavioral hyperactivity in young mice.

Sevoflurane, a commonly used anesthetic, may cause agitation in patients. However, the mechanism underlying this clinical observation remains largely unknown. We thus assessed the effects of sevoflurane on neuronal activation and behaviors in mice. Ten-day-old mice received 2% sevoflurane, 1% isoflurane, or 6% desflurane for 10 minutes. The behavioral activities were recorded and evaluated at one minute after the loss of righting reflex in the mice, which was about two minutes after the anesthetic administration. The neuronal activation was evaluated by c-Fos expression and calcium imaging at one minute after the anesthetic administration. Propofol, which reduces neuronal activation, was used to determine the cause-and-effect of sevoflurane. We found that sevoflurane caused an increase in neuronal activation in primary somatosensory cortex of young mice and behavioral hyperactivity in the mice at one minute after the loss of righting reflex. Desflurane did not induce behavioral hyperactivity and isoflurane only caused behavioral hyperactivity with borderline significance. Finally, propofol attenuated the sevoflurane-induced increase in neuronal activation and behavioral hyperactivity in young mice. These results demonstrate an unexpected sevoflurane-induced increase in neuronal activation and behavioral hyperactivity in young mice. These findings suggest the potential mechanisms underlying the sevoflurane-induced agitation and will promote future studies to further determine whether anesthetics can induce behavioral hyperactivity via increasing neuronal activation.

Efficient Position Decoding Methods Based on Fluorescence Calcium Imaging in the Mouse Hippocampus.

Large-scale fluorescence calcium imaging methods have become widely adopted for studies of long-term hippocampal and cortical neuronal dynamics. Pyramidal neurons of the rodent hippocampus show spatial tuning in freely foraging or head-fixed navigation tasks. Development of efficient neural decoding methods for reconstructing the animal's position in real or virtual environments can provide a fast readout of spatial representations in closed-loop neuroscience experiments. Here, we develop an efficient strategy to extract features from fluorescence calcium imaging traces and further decode the animal's position. We validate our spike inference-free decoding methods in multiple in vivo calcium imaging recordings of the mouse hippocampus based on both supervised and unsupervised decoding analyses. We systematically investigate the decoding performance of our proposed methods with respect to the number of neurons, imaging frame rate, and signal-to-noise ratio. Our proposed supervised decoding analysis is ultrafast and robust, and thereby appealing for real-time position decoding applications based on calcium imaging.

Somatostatin-Expressing Interneurons Enable and Maintain Learning-Dependent Sequential Activation of Pyramidal Neurons.

The activities of neuronal populations exhibit temporal sequences that are thought to mediate spatial navigation, cognitive processing, and motor actions. The mechanisms underlying the generation and maintenance of sequential neuronal activity remain unclear. We found that layer 2 and/or 3 pyramidal neurons (PNs) showed sequential activation in the mouse primary motor cortex during motor skill learning. Concomitantly, the activity of somatostatin (SST)-expressing interneurons increased and decreased in a task-specific manner. Activating SST interneurons during motor training, either directly or via inhibiting vasoactive-intestinal-peptide-expressing interneurons, prevented learning-induced sequential activities of PNs and behavioral improvement. Conversely, inactivating SST interneurons during the learning of a new motor task reversed sequential activities and behavioral improvement that occurred during a previous task. Furthermore, the control of SST interneurons over sequential activation of PNs required CaMKII-dependent synaptic plasticity. These findings indicate that SST interneurons enable and maintain synaptic plasticity-dependent sequential activation of PNs during motor skill learning.

Neuropathic Pain Causes Pyramidal Neuronal Hyperactivity in the Anterior Cingulate Cortex.

The anterior cingulate cortex (ACC) is thought to be important for acute pain perception as well as the development of chronic pain after peripheral nerve injury. Nevertheless, how ACC neurons respond to sensory stimulation under chronic pain states is not well understood. Here, we used an in vivo two-photon imaging technique to monitor the activity of individual neurons in the ACC of awake, head restrained mice. Calcium imaging in the dorsal ACC revealed robust somatic activity in layer 5 (L5) pyramidal neurons in response to peripheral noxious stimuli, and the degree of evoked activity was correlated with the intensity of noxious stimulation. Furthermore, the activation of ACC neurons occurred bilaterally upon noxious stimulation to either contralateral or ipsilateral hind paws. Notably, with nerve injury-induced neuropathic pain in one limb, L5 pyramidal neurons in both sides of the ACC showed enhanced activity in the absence or presence of pain stimuli. These results reveal hyperactivity of L5 pyramidal neurons in the bilateral ACC during the development of neuropathic pain.

Microglia limit the expansion of ß-amyloid plaques in a mouse model of Alzheimer's disease.

BACKGROUND: Microglia are known as resident immune cells in the brain. ß-amyloid (Aß) plaques in the brain of Alzheimer's disease (AD) are surrounded by microglia, but whether and how microglia affect the formation and maintenance of plaques remains controversial. METHODS: We depleted microglia by injecting diphtheria toxin (DT) in CX 3 CR1 CreER/+ :R26 DTR/+ (CX 3 CR1-iDTR) mice crossed with APPswe/PSEN1dE9 (APP/PS1) mice. Intravital time-lapse imaging was performed to examine changes in the number and size of Congo Red-labeled amyloid plaques over 1-2 weeks. We also examined spine density and shaft diameter of dendrites passing through plaques in a PSAPP mouse model of AD (PS1 M146L line 6.2 × Tg2576) crossed with Thy1 YFP H-line mice. RESULTS: We found that DT administration to CX 3 CR1-iDTR mice efficiently ablated microglia within one week and that microglia repopulated in the second week after DT administration. Microglia depletion didn't affect the number of amyloid plaques, but led to ~13% increase in the size of Aß plaques within one week. Moreover, microglia repopulation was associated with the stabilization of plaque size during the second week. In addition, we found dendritic spine loss and shaft atrophy in the distal parts of dendrites passing through plaques. CONCLUSION: Our results demonstrate the important role of microglia in limiting the growth of Aß plaques and plaque-associated disruption of neuronal connection.