Activation of prefrontal parvalbumin interneurons ameliorates working memory deficit even under clinically comparable antipsychotic treatment in a mouse model of schizophrenia.

One of the critical unmet medical needs in schizophrenia is the treatment for cognitive deficits. However, the neural circuit mechanisms of them remain unresolved. Previous studies utilizing animal models of schizophrenia did not consider the fact that patients with schizophrenia generally cannot discontinue antipsychotic medication due to the high risk of relapse. Here, we used multi-dimensional approaches, including histological analysis of the prelimbic cortex (PL), LC-MS/MS-based in vivo dopamine D2 receptor occupancy analysis for antipsychotics, in vivo calcium imaging, and behavioral analyses of mice using chemogenetics to investigate neural mechanisms and potential therapeutic strategies for working memory deficit in a chronic phencyclidine (PCP) mouse model of schizophrenia. Chronic PCP administration led to alterations in excitatory and inhibitory synapses, specifically in dendritic spines of pyramidal neurons, vesicular glutamate transporter 1 (VGLUT1) positive terminals, and parvalbumin (PV) positive GABAergic interneurons located in layer 2-3 of the PL. Continuous administration of olanzapine, which achieved a sustained therapeutic window of dopamine D2 receptor occupancy (60-80%) in the striatum, did not ameliorate these synaptic abnormalities and working memory deficit in the chronic PCP-treated mice. We demonstrated that chemogenetic activation of PV neurons in the PL, as confirmed by in vivo calcium imaging, ameliorated working memory deficit in this model even under clinically comparable olanzapine treatment which by itself inhibited only PCP-induced psychomotor hyperactivity. Our study suggests that targeting prefrontal PV neurons could be a promising therapeutic intervention for cognitive deficits in schizophrenia in combination with antipsychotic medication.

A novel micro-ECoG recording method for recording multisensory neural activity from the parietal to temporal cortices in mice.

Characterization of inter-regional interactions in brain is essential for understanding the mechanism relevant to normal brain function and neurological disease. The recently developed flexible micro (µ)-electrocorticography (µECoG) device is one prominent method used to examine large-scale cortical activity across multiple regions. The sheet-shaped µECoG electrodes arrays can be placed on a relatively wide area of cortical surface beneath the skull by inserting the device into the space between skull and brain. Although rats and mice are useful tools for neuroscience, current µECoG recording methods in these animals are limited to the parietal region of cerebral cortex. Recording cortical activity from the temporal region of cortex in mice has proven difficult because of surgical barriers created by the skull and surrounding temporalis muscle anatomy. Here, we developed a sheet-shaped 64-channel µECoG device that allows access to the mouse temporal cortex, and we determined the factor determining the appropriate bending stiffness for the µECoG electrode array. We also established a surgical technique to implant the electrode arrays into the epidural space over a wide area of cerebral cortex covering from the barrel field to olfactory (piriform) cortex, which is the deepest region of the cerebral cortex. Using histology and computed tomography (CT) images, we confirmed that the tip of the µECoG device reached to the most ventral part of cerebral cortex without causing noticeable damage to the brain surface. Moreover, the device simultaneously recorded somatosensory and odor stimulus-evoked neural activity from dorsal and ventral parts of cerebral cortex in awake and anesthetized mice. These data indicate that our µECoG device and surgical techniques enable the recording of large-scale cortical activity from the parietal to temporal cortex in mice, including somatosensory and olfactory cortices. This system will provide more opportunities for the investigation of physiological functions from wider areas of the mouse cerebral cortex than those currently available with existing ECoG techniques.

MicroLED neural probe for effective in vivo optogenetic stimulation.

The MicroLED probe enables optogenetic control of neural activity in spatially separated brain regions. Understanding its heat generation characteristics is important. In this study, we investigated the temperature rise (ΔT) characteristics in the brain tissue using a MicroLED probe. The ΔT strongly depended on the surrounding environment of the probe, including the differences between the air and the brain, and the area touching the brain tissue. Through animal experiments, we suggest an in situ temperature monitoring method using temperature dependence on electrical characteristics of the MicroLED. Finally, optical stimulation by MicroLEDs proved effective in controlling optogenetic neural activity in animal models.

Ice nucleation activity in various tissues of Rhododendron flower buds: their relevance to extraorgan freezing.

Wintering flower buds of cold hardy Rhododendron japonicum cooled slowly to subfreezing temperatures are known to undergo extraorgan freezing, whose mechanisms remain obscure. We revisited this material to demonstrate why bud scales freeze first in spite of their lower water content, why florets remain deeply supercooled and how seasonal adaptive responses occur in regard to extraorgan freezing in flower buds. We determined ice nucleation activity (INA) of various flower bud tissues using a test tube-based assay. Irrespective of collection sites, outer and inner bud scales that function as ice sinks in extraorgan freezing had high INA levels whilst florets that remain supercooled and act as a water source lacked INA. The INA level of bud scales was not high in late August when flower bud formation was ending, but increased to reach the highest level in late October just before the first autumnal freeze. The results support the following hypothesis: the high INA in bud scales functions as the subfreezing sensor, ensuring the primary freezing in bud scales at warmer subzero temperatures, which likely allows the migration of floret water to the bud scales and accumulation of icicles within the bud scales. The low INA in the florets helps them remain unfrozen by deep supercooling. The INA in the bud scales was resistant to grinding and autoclaving at 121(∘)C for 15 min, implying the intrinsic nature of the INA rather than of microbial origin, whilst the INA in stem bark was autoclaving-labile. Anti-nucleation activity (ANA) was implicated in the leachate of autoclaved bud scales, which suppresses the INA at millimolar levels of concentration and likely differs from the colligative effects of the solutes. The tissue INA levels likely contribute to the establishment of freezing behaviors by ensuring the order of freezing in the tissues: from the primary freeze to the last tissue remaining unfrozen.

mRNA expression of the Nurr1 and NGFI-B nuclear receptor families following acute and chronic administration of methamphetamine.

Nur-related 1 (Nurr1) and nerve growth factor inducible-B (NGFI-B) constitute closely related subgroups of the nuclear receptor superfamily. One to three hours after 4 mg/kg acute methamphetamine (METH) administration, the levels of Nurr1 mRNA were significantly higher in the prelimbic (PrL), primary motor (M1) and primary somatosensory (S1) cortices and ventral tegmental area (VTA), as compared with the basal level. Pretreatment with 0.5 mg/kg of SCH23390 prevented the acute METH-induced increase in Nurr1 mRNA levels in these brain regions. One to three hours after 4-mg/kg acute METH administration, the levels of NGFI-B mRNA increased significantly in the PrL, M1, S1, striatum, and nucleus accumbens core (AcbC). Pretreatment with either 0.5 mg/kg of MK-801 or 0.5 mg/kg of SCH23390 prevented the acute METH-induced increase in NGFI-B mRNA levels in these brain regions. The levels of mRNAs were determined 3 h after a challenge injection of either saline or 4 mg/kg METH at the three-week withdrawal point in rats which had previously been exposed to either saline or METH (4 mg/kg/day) for 2 weeks. After the saline challenge, the group chronically exposed to METH displayed significantly higher levels of Nurr1 mRNA in the PrL, S1 and VTA, and of NGFI-B mRNA in the PrL, M1, S1, striatum and AcbC than did the group chronically treated with saline. The groups chronically exposed to METH failed to increase Nurr1 mRNA in the VTA, and NGFI-B mRNA in the AcbC, when challenged with 4 mg/kg METH. These results suggest that Nurr1 and NGFI-B mRNA play differential roles upon exposure to METH.

mRNA expression of activity-regulated cytoskeleton-associated protein (arc) in the amygdala-kindled rats.

Activity-regulated cytoskeleton-associated protein (arc) is an immediate early gene (IEG) whose mRNA is targeted to dendrites of activated synapses. The present study investigated the expression of three IEGs, arc and two transcription factors (NGFI-B and Nurr 1), in regions of the brain of rats that were subjected to a single afterdischarge-inducing electrical stimulation of the left amygdala and in the amygdala-kindled rats that developed consecutive generalized seizures. One hour after a single stimulus was administered to non-kindled rats, mRNA levels of arc and Nurr1 increased significantly in the ipsilateral piriform cortex and medial amygdaloid nucleus. mRNA levels of NGFI-B increased significantly in the left piriform cortex, basolateral amygdaloid nucleus and medial amygdaloid nucleus. In the amygdala-kindled rats, mRNAs of the three IEGs increased significantly in bilateral brain regions including the piriform cortex and dentate gyrus at 0.5-1 h after the last generalized kindled seizure, and returned near to basal levels by 6 h after. Photographic emulsion autoradiograms showed that the arc mRNA signals induced by the last generalized kindled seizures were associated with the cell bodies of the dentate granule cell layer and extended beyond the granule cell layer into the molecular layer, which contains the dendrites of granule cells. These results support that arc serves as an effector IEG whose mRNA is associated with synaptic reorganization in kindling.