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The dorsal striatum, with its functional microcircuits galore, serves as the primary gateway of the basal ganglia and is known to play a key role in implicit learning. Initially, excitatory inputs from the cortex and thalamus arrive on the direct and indirect pathways, where the precise flow of information is then regulated by local GABAergic interneurons. The balance of excitatory and inhibitory transmission in the dorsal striatum is modulated by neuromodulators such as dopamine and acetylcholine. Under pathophysiological states in the dorsal striatum, an alteration in excitatory and inhibitory transmission may underlie dysfunctional motor control. Here, we review the cellular connections and modulation of striatal microcircuits and propose that modulating the excitatory and inhibitory balance in synaptic transmission of the dorsal striatum is important for regulating locomotion.The dorsal striatum is best known for its role in decision-making, especially in action selection and initiation through the convergence of sensorimotor, cognitive, and motivational information (DeLong 1990;Smith et al. 1998;Balleine et al. 2007). As the primary input of the basal ganglia, the striatum receives glutamatergic inputs from the cortex and thalamus and in turn projects GABAergic outputs to the globus pallidus and substantia nigra pars reticulata (SNr). Inputs from the cortex and thalamus both form excitatory synaptic connections on medium spiny neurons (MSN) in which cortical afferents are from the sensory, motor, and associational cortex (Bolam et al. 2000), and thalamic afferents are from the intralaminar thalamic nuclei (Doig et al. 2010). These glutamatergic inputs are then processed in the dorsal striatum where numerous connections between various types of neurons exist. Thus, the complexity of neuronal circuits has made it difficult to elucidate the functional roles of the striatum. Recently, studies focused on interneurons that reside in the dorsal striatum have characterized the physiological features and functional connections. For example, parvalbumin-expressing fastspiking interneurons (PV-FSI) and neuropeptide-Y positive lowthreshold spiking interneurons (NPY-LTS) form synaptic connections with MSNs and regulate the firing activity of the principal neuron MSNs (Koos and Tepper 1999;Gittis et al. 2010;Chuhma et al. 2011). These interneurons were shown to have distinct firing patterns and connections, and thus they may exert different effects on MSNs. Other crucial connections are the cholinergic, dopaminergic, and serotonergic axons that strongly innervate the dorsal striatum. These projections are essential for modulating striatal circuits and disruption of such signaling can result in movement impairments and neurological disorders such as Huntington's disease (Lovinger 2010). This review summarizes recent reports of the microcircuits present in the dorsal striatum, although serotonergic signaling is excluded, and suggests a putative role for striatal microcircuits in motor dysfunction and/or hyperactivity that ...

Peripheral nerve injury can induce pathological conditions that lead to persistent sensitized nociception. Although there is evidence that plastic changes in the cortex contribute to this process, the underlying molecular mechanisms are unclear. Here, we find that activation of the anterior cingulate cortex (ACC) induced by peripheral nerve injury increases the turnover of specific synaptic proteins in a persistent manner. We demonstrate that neural cell adhesion molecule 1 (NCAM1) is one of the molecules involved and show that it mediates spine reorganization and contributes to the behavioral sensitization. We show striking parallels in the underlying mechanism with the maintenance of NMDA-receptor- and protein-synthesis-dependent long-term potentiation (LTP) in the ACC. Our results, therefore, demonstrate a synaptic mechanism for cortical reorganization and suggest potential avenues for neuropathic pain treatment.

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Many of the cellular and molecular mechanisms underlying astrocytic modulation of synaptic function remain poorly understood. Recent studies show that G-protein coupled receptor-mediated astrocyte activation modulates synaptic transmission in the nucleus of the solitary tract (NTS), a brainstem nucleus that regulates crucial physiological processes including cardiorespiratory activity. By using calcium imaging and patch clamp recordings in acute brain slices of wild-type and TRPV1 rats, we show that activation of proteinase-activated receptor 1 (PAR1) in NTS astrocytes potentiates presynaptic glutamate release on NTS neurons. This potentiation is mediated by both a TRPV1-dependent and a TRPV1-independent mechanism. The TRPV1-dependent mechanism appears to require release of endovanilloid-like molecules from astrocytes, which leads to subsequent potentiation of presynaptic glutamate release via activation of presynaptic TRPV1 channels. Activation of NTS astrocytic PAR1 receptors elicits cFOS expression in neurons that project to respiratory premotor neurons and inhibits respiratory activity in control, but not in TRPV1 rats. Thus, activation of astrocytic PAR1 receptor in the NTS leads to a TRPV1-dependent excitation of NTS neurons causing a potent modulation of respiratory motor output.

Previously we have demonstrated that leptin in the NTS activates leptin receptor (LepRb) and galanin‐expressing neurons which directly increases phrenic motor output via a NALCN‐dependent mechanism (Do et al, Cell Reports, 2020). We also reported that such NTS LepRb neurons are glutamatergic and project to the rostral ventral respiratory group (rVRG) and, interestingly, the dorsomedial hypothalamus (DMH). While the excitatory projections to the rVRG are consistent with the robust increase in integrated phrenic activity, projections to the DMH imply an integrative leptin‐dependent circuit. The DMH includes a significant number of LepRb expressing neurons and our previous preliminary work suggests that optogenetic activation of DMH LepRb neurons increases phrenic nerve activity (Chang et al, FASEB Abstr. 2018). Here we report that selective optogenetic activation of LepRb DMH neurons induces a robust increase, on discrete timescales, in integrated phrenic activity and inspiratory activity in vagal motoneurons. These DMH LepRb neurons are dominantly GABAergic confirmed by the expression of VGAT with in situ hybridization. Lastly, viral tracing studies reveals DMH LepRb neurons project to the arcuate nucleus, periaqueductal gray (PAG), and parabrachial nucleus (PBN). Together, these findings highlight a leptin‐dependent suprapontine circuit that, along with NTS LepRb neurons, is likely to participate in matching respiratory motor output to metabolism.

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