Spinal CCL2 Promotes Central Sensitization, Long-Term Potentiation, and Inflammatory Pain via CCR2: Further Insights into Molecular, Synaptic, and Cellular Mechanisms / 神经科学通报·英文版

Mounting evidence supports an important role of chemokines, produced by spinal cord astrocytes, in promoting central sensitization and chronic pain. In particular, CCL2 (C-C motif chemokine ligand 2) has been shown to enhance N-methyl-D-aspartate (NMDA)-induced currents in spinal outer lamina II (IIo) neurons. However, the exact molecular, synaptic, and cellular mechanisms by which CCL2 modulates central sensitization are still unclear. We found that spinal injection of the CCR2 antagonist RS504393 attenuated CCL2- and inflammation-induced hyperalgesia. Single-cell RT-PCR revealed CCR2 expression in excitatory vesicular glutamate transporter subtype 2-positive (VGLUT2) neurons. CCL2 increased NMDA-induced currents in CCR2/VGLUT2 neurons in lamina IIo; it also enhanced the synaptic NMDA currents evoked by dorsal root stimulation; and furthermore, it increased the total and synaptic NMDA currents in somatostatin-expressing excitatory neurons. Finally, intrathecal RS504393 reversed the long-term potentiation evoked in the spinal cord by C-fiber stimulation. Our findings suggest that CCL2 directly modulates synaptic plasticity in CCR2-expressing excitatory neurons in spinal lamina IIo, and this underlies the generation of central sensitization in pathological pain.

Whole-Brain Mapping of Direct Inputs to and Axonal Projections from GABAergic Neurons in the Parafacial Zone / 神经科学通报·英文版

The GABAergic neurons in the parafacial zone (PZ) play an important role in sleep-wake regulation and have been identified as part of a sleep-promoting center in the brainstem, but the long-range connections mediating this function remain poorly characterized. Here, we performed whole-brain mapping of both the inputs and outputs of the GABAergic neurons in the PZ of the mouse brain. We used the modified rabies virus EnvA-ΔG-DsRed combined with a Cre/loxP gene-expression strategy to map the direct monosynaptic inputs to the GABAergic neurons in the PZ, and found that they receive inputs mainly from the hypothalamic area, zona incerta, and parasubthalamic nucleus in the hypothalamus; the substantia nigra, pars reticulata and deep mesencephalic nucleus in the midbrain; and the intermediate reticular nucleus and medial vestibular nucleus (parvocellular part) in the pons and medulla. We also mapped the axonal projections of the PZ GABAergic neurons with adeno-associated virus, and defined the reciprocal connections of the PZ GABAergic neurons with their input and output nuclei. The newly-found inputs and outputs of the PZ were also listed compared with the literature. This cell-type-specific neuronal whole-brain mapping of the PZ GABAergic neurons may reveal the circuits underlying various functions such as sleep-wake regulation.

A Critical Time-Window for the Selective Induction of Hippocampal Memory Consolidation by a Brief Episode of Slow-Wave Sleep / 神经科学通报·英文版

Although extensively studied, the exact role of sleep in learning and memory is still not very clear. Sleep deprivation has been most frequently used to explore the effects of sleep on learning and memory, but the results from such studies are inevitably complicated by concurrent stress and distress. Furthermore, it is not clear whether there is a strict time-window between sleep and memory consolidation. In the present study we were able to induce time-locked slow-wave sleep (SWS) in mice by optogenetically stimulating GABAergic neurons in the parafacial zone (PZ), providing a direct approach to analyze the influences of SWS on learning and memory with precise time-windows. We found that SWS induced by light for 30 min immediately or 15 min after the training phase of the object-in-place task significantly prolonged the memory from 30 min to 6 h. However, induction of SWS 30 min after the training phase did not improve memory, suggesting a critical time-window between the induction of a brief episode of SWS and learning for memory consolidation. Application of a gentle touch to the mice during light stimulation to prevent SWS induction also failed to improve memory, indicating the specific role of SWS, but not the activation of PZ GABAergic neurons itself, in memory consolidation. Similar influences of light-induced SWS on memory consolidation also occurred for Y-maze spatial memory and contextual fear memory, but not for cued fear memory. SWS induction immediately before the test phase had no effect on memory performance, indicating that SWS does not affect memory retrieval. Thus, by induction of a brief-episode SWS we have revealed a critical time window for the consolidation of hippocampus-dependent memory.

Localization of vesicular inhibitory amino acid transporter (VIAAT) in the submandibular salivary gland throughout the postnatal development of mice / Localización del transportador vesicular de aminoácidos inhibidores (VIAAT) en la glándula salival submandibular durante el desarrollo postnatal de ratones

According to recent studies, it is highly possible that the occurrence of vesicular inhibitory amino acid transporter (VIAAT) is a good marker of GABA-signaling not only in the brain, but also in extra-brain tissue cells containing GABA and GAD. In view of this, the present study was attempted to localize VIAAT-immunoreactivity in the submandibular gland of mice. In the present study, the submandibular glands of male mice at various postnatal developmental stages were examined for detailed localization of VIAAT-immunoreactivity in immunohistochemistry at light microscopic level. The immunoreactivity for VIAAT was localized in epithelial cells of proximal and distal excretory ducts with the striated portion more intensely immunopositive at young postnatal stages. No significant immunoreactivity was seen in the acinar cells throughout the postnatal development. In addition, the immunoreactivity for VIAAT was detected in the salivary parasympathetic ganglionic neurons, but not in any nerve fibers surrounding the glandular cells. Furthermore, VIAAT-immunoreactivity was found in smooth muscle cells forming the outermost layer of intralobular arterioles. From the present findings, it is possible that GABA plays roles as paracrine and autocrine regulators in the saliva secretion as well as the gland development.

Según estudios recientes, es altamente posible que la aparición del transportador vesicular de aminoácidos inhibidores (VIAAT) sea un buen marcador de señalización de GABA no sólo en el cerebro, sino también en células de tejido extra-cerebrales que contienen GABA y GAD. En el presente estudio se intentó localizar inmunoreactividad a VIAAT en la glándula submandibular de ratones. En el presente estudio, se examinaron las glándulas submandibulares de ratones machos en las distintas etapas del desarrollo postnatal para la localización detallada de inmunoreactividad a VIAAT inmunohistoquímicamente a nivel de microscopía óptica. La inmunorreactividad para VIAAT se localizó en las células epiteliales de los conductos excretores proximal y distal, con mayor intensidad en la porción estriada en las etapas tempranas. No se observó inmunoreactividad significativa en las células acinares durante el desarrollo postnatal. Además, se detectó la inmunoreactividad para VIAAT en las neuronas ganglionares parasimpáticas salivales, pero no en las fibras nerviosas que rodean las células glandulares. Además, la inmunoreactividad a VIAAT se encuentra en las células del músculo liso que forman la capa más externa de las arterias interlobulillares. En base a estos hallazgos, es posible que GABA tenga una función como regulador autocrino y paraparacrino en la secreción de saliva, así como en el desarrollo de la glándula.