Tao-Tao Liu

Motor Cortex-Periaqueductal Gray-Spinal Cord Neuronal Circuitry May Involve in Modulation of Nociception: A Virally Mediated Transsynaptic Tracing Study in Spinally Transected Transgenic Mouse Model

Several studies have shown that motor cortex stimulation provided pain relief by motor cortex plasticity and activating descending inhibitory pain control systems. Recent evidence indicated that the melanocortin-4 receptor (MC4R) in the periaqueductal gray played an important role in neuropathic pain. This study was designed to assess whether MC4R signaling existed in motor cortex- periaqueductal gray- spinal cord neuronal circuitry modulated the activity of sympathetic pathway by a virally mediated transsynaptic tracing study. Pseudorabies virus (PRV)-614 was injected into the left gastrocnemius muscle in adult male MC4R-green fluorescent protein (GFP) transgenic mice (n = 15). After a survival time of 4–6 days, the mice (n = 5) were randomly assigned to humanely sacrifice, and spinal cords and brains were removed and sectioned, and processed for PRV-614 visualization. Neurons involved in the efferent control of the left gastrocnemius muscle were identified following visualization of PRV-614 retrograde tracing. The neurochemical phenotype of MC4R-GFP-positive neurons was identified using fluorescence immunocytochemical labeling. PRV-614/MC4R-GFP dual labeled neurons were detected in spinal IML, periaqueductal gray and motor cortex. Our findings support the hypothesis that MC4R signaling in motor cortex-periaqueductal gray-spinal cord neural pathway may participate in the modulation of the melanocortin-sympathetic signaling and contribute to the descending modulation of nociceptive transmission, suggesting that MC4R signaling in motor cortex- periaqueductal gray-spinal cord neural pathway may modulate the activity of sympathetic outflow sensitive to nociceptive signals.

Stimulation for the compact parts of pedunculopontine nucleus: An available therapeutic approach in intractable epilepsy

Many studies have shown that susceptibility to epilepsy is increased during nonrapid eye movement (NREM, slow-wave) sleep whereas rapid eyemovement (REM) sleep suppresses seizure occurrence. Therefore, it is postulated that rapid eye movement sleep is a natural antiepileptogenic system in the body during the human wake–sleep cycle [1–3]. Because it is demonstrated that stimulation of the pedunculopontine tegmental nucleus (PPTg) can enhance REM sleep successfully [4], PPTg has been highlighted as a target for deep brain stimulation for seizure treatment of intractable epilepsy [2,5,6]; however, the exact location of the optimal brain site for stimulation is not fully understood [7,8]. Recently, some studies have suggested that the neurons innervating motor structures are predominantly situated in the caudal parts of the PPTg, which divide into the dissipated part (dp) and compact part (cp) of the PPTg [9–11]. Nevertheless, it is still unclear whether cpPPTg or dpPPTg is tightly linked to motor projections. There is unequivocal agreement on the high and specific value of neurotropic pseudorabies virus (PRV) tracing for synaptic connectivity and neuroanatomical pathways in CNS by propagating retrogradely through chains of functionally connected neurons [11–16]. It is well known that PRV can provide a highly specific method of mapping the motor and sympathetic pathways innervating a variety of targets [12,17–19]. We explore the hypothesis that the functional integrity of synapses in the cpPPTg is essential tomotor projections andnot sympathetic projections. We had characterized projections from the left gastrocnemius muscle to the PPTg of the midbrain tegmentum in surgically sympathectomized [20,21]mice by using retrograde tracing techniques of PRV-614, expressing a novelmonomeric red fluorescent protein (mRFP1) under control of the cytomegalovirus immediate early promoter for direct visualization with the fluorescence microscope [22–24]. We found that injections of PRV-614 into the left gastrocnemius muscle labeled neurons in the cpPPTg and dpPPTg (Fig. 1), which was in line with a previous report showing that the PPTg control of the lumbar epaxial muscle produced a special posture by transneuronal tracer PRV-Bartha [25], suggesting that a direct neuronal circuit from the cpPPTg and dpPPTg to gastrocnemius muscle exists via the motor pathway. Otherwise, PRV-614/tyrosine hydroxylase (TH) and PRV614/tryptophan hydroxylase (TPH) double-labeled neurons were detected in the dpPPTg and not in the cpPPTg (Fig. 1), which was in agreement with our previous immunohistochemical study in investigating that PRV-614/tryptophan hydroxylase and PRV-614/tyrosine hydroxylase double-labeled neurons in the cpPPTg were not detected

The optimal acupoint for acupuncture stimulation as a complementary therapy in pediatric epilepsy

Fig. 1. Diagrams of the locations of auricular acupuncture points (Shen Men). It is well known that the auricular branch of the vagus nerve innervates the auricular concha and so provides noninvasive or minimally invasive access to the vagus nerve [47]. Wang et al. [48] had demonstrated the use of ear acupuncture (Shen Men) for preoperative anxiety by placing a needle in the concha, an area innervated by the vagus nerve. Metaphysical theories of “auriculotherapy” claim that 168 body points on the ear are connected to various body locations. The optimal acupoint for acupuncture stimulation as a complementary therapy in pediatric epilepsy

Possible mechanism of subthalamic nucleus stimulation-induced acute renal failure: A virally mediated transsynaptic tracing study in transgenic mouse model

The case report titled “acute renal failure in patients with bilateral deep brain stimulation” by Guimar~aes et al., indicated that effect of deep brain stimulation–subthalamic nucleus (DBS-STN) in hypothalamic centers remained a valid hypothesis which could explain an altered kidney function immediately after DBS-STN. Hypothalamic centers are well known to be important regions in the autonomic nervous system and have great significance for the emergence or maintenance of vascular tone and the release of vasopressin/ antidiuretic hormone. The retrograde transsynaptic tracer pseudorabies virus (PRV) has been widely used as a marker for multisynaptic connectivity in the brain. We would like to further complete the discussion of Guimar~aes et al. by using a virally mediated transsynaptic tracing study in the melanocortin-4 receptor (MC4R) green fluorescent protein (GFP) transgenic mouse model. Data from experiments in men and animal models have demonstrated that there is a close interaction between the kidney and the central nervous system. It is widely acknowledged that sympathetic influence in kidney functions is under control of hypothalamic nuclei. The melanocortin-4 receptor (MC4R) is expressed in numerous regions of brainstem and hypothalamus, and some findings indicated an important physiologic role for the MC4R in the regulation of renal sympathetic traffic by both leptin and insulin. We had characterized the projection from the kidney to STN and hypothalamic nuclei in an adult transgenic mouse line expressing GFP under the control of the MC4R promoter by using retrograde tracing techniques of PRV-614. We found that neurons expressing MC4R-GFP were distributed in STN and hypothalamic nuclei (Fig. 1), injections of PRV-614 into the kidney resulted in retrograde infection of neurons in STN and hypothalamic nuclei, PRV-614–infecting cells were most heavily concentrated in hypothalamic nuclei and distributed sparsely in STN, and most PRV-614–labeled cells specifically concentrated in the paraventricular hypothalamic nucleus (PVN). It was strikingly attractive that PRV-614/MC4R-GFP dual-labeled neurons were detected in the STN and PVN (Fig. 1), and PRV-614/tyrosine hydroxylase (TH), PRV-614/ tryptophan hydroxylase (TPH) dual-labeled neurons were detected in PVN (Fig. 1), not in STN, suggesting that different neuronal populations presented between the STN and PVN. Therefore, it was presumed that possible mechanism of the STN stimulation-induced acute renal failure involved between melanocortinergic, catecholaminergic, and serotonergic signals in hypothalamic centers, and melanocortinergic signals in STN. Because central regulation of sympathetic activity is a major component of melanocortinergic action and central serotonergic-positive and catecholaminergicpositive neurons participate in regulating sympathetic outflow, our data suggested that MC4R signaling between STN and hypothalamic nuclei involved in the sympathetic regulation of renal function. In conclusion, data presented here provided direct neuroanatomical evidence for the central melanocortin-sympathetic circuits from the STN and hypothalamic nuclei to the kidneys. Our observations strongly indicated that STN and hypothalamic nuclei was considered as a prominent neuronal circuit involved in the melanocortinergic regulation of renal function. Thereby, stimulation of STN may induce decreased renal blood flow (eg, secondary renal failure) by the central melanocortin-sympathetic mechanism. Further investigations will be required to research whether regional effects of DBSSTN on hypothalamic centers depend on the exact location of the contact in the STN area with a mouse model of STNDBS.

Posterior pedunculopontine tegmental nucleus may be involved in visual complaints with intractable epilepsy

Understanding the neural basis of vision remains a fundamental goal of neuroscience and has as much importance to studies of visual processing as to clinical studies of the visual disorders. Evidence suggests that the pedunculopontine tegmental nucleus (PPTg) may be an available therapeutic target for treatment of intractable epilepsy and Parkinsons disease [1–3]. Jenkinson et al. reported a case of induced oscillopsia caused by deep brain stimulation (DBS) of PPTg using infrared eye tracking [4]. It is known that visual symptoms are common in Parkinsons disease (PD), and the detection of visual symptoms is important for differential diagnosis and patient management [5]. It has been shown previously that there is strong cholinergic innervation from PPTg to lateral geniculate nucleus (LGN), and LGN receives as much as 40% of its input from PPTg [6,7]. There are several reports that in vivo activation of pedunculopontine tegmental nucleus (PPTg) neurons enhances visual responses in LGN without changing receptive field size by making these neurons more excitable [8,9]. Otherwise, some clinical studies point to a hyperexcitability of the visual cortex in patients with idiopathic generalized epilepsies [10–14]. Thereby, we postulate that PPTg may be involved in visual complaints in patients with intractable epilepsy. Recent anatomical and behavioral findings have led to the idea that there is a functionally heterogeneous nature of the PPTg region, and PPTg exhibits a wide heterogeneity in terms of its neurochemical properties (cholinergic, serotonergic, catecholaminergic, glutamatergic, and GABAergic cells) and connectivity with the corticostriatal architecture and the medial reticular formation [3,15–19]. Early studies of PPTg function concentrated on motor processes and behavioral state control, but recent work has emphasized its sensory function. This is involved in the important differences of PPTg subregions, which divide into the anterior and posterior portions [20–22]. Recent behavioral evidence suggests that the anterior and posterior portions of the PPTg are associated with different brain circuits and sensory processes [19,23]. Though accumulating reports highlight preferential projections by anterior PPTg (aPPTg) to substantia nigra pars compacta and by posterior PPTg (pPPTg) to ventral tegmental area [19,20,24], it is still unclear whether aPPTg or pPPTg is tightly linked to visual function. Over the past decade, transneuronal tracing with neurotropic pseudorabies viruses (PRV) has greatly advanced our understanding of multisynaptic circuits between the brain and peripheral tissue. Moore et al. have reported that cortical PRV-M201 injections resulted in transneuronal retrograde infection of the lateral geniculate nucleus (LGN), thalamic reticular nucleus (TRN), and retina [25]. We had

Melanocortin-4 receptor expression in the cuneiform nucleus is involved in modulation of opioidergic signaling

SummarySubstantial evidence has suggested that deep brain stimulation of the cuneiform nucleus has become a remarkable treatment option for intractable pain, but the possible mechanism is poorly understood. Using a melanocortin-4 receptor (MC4R)-green fluorescent protein (GFP) reporter knockin mouse, we showed that a large number of MC4R-GFP-positive neurons were expressed in the cuneiform nucleus. Immunofluorescence revealed that approximately 40%–50% of MC4R-GFP-positive neurons expressed mu opioid receptors, indicating that they were opioidergic signaling. Our findings support the hypothesis that MC4R expression in the cuneiform nucleus is involved in the modulation of opioidergic signaling.Substantial evidence has suggested that deep brain stimulation of the cuneiform nucleus has become a remarkable treatment option for intractable pain, but the possible mechanism is poorly understood. Using a melanocortin-4 receptor (MC4R)-green fluorescent protein (GFP) reporter knockin mouse, we showed that a large number of MC4R-GFP-positive neurons were expressed in the cuneiform nucleus. Immunofluorescence revealed that approximately 40%–50% of MC4R-GFP-positive neurons expressed mu opioid receptors, indicating that they were opioidergic signaling. Our findings support the hypothesis that MC4R expression in the cuneiform nucleus is involved in the modulation of opioidergic signaling.

NRG1-ErbB signalling promotes microglia activation contributing to incision-induced mechanical allodynia

Spinal microglia activation is one of the pathologic mechanisms involved in post‐operative pain, which results from surgical injuries in skin, fascia, muscle and small nerves innervating these tissues. Recent research has shown that neuregulin‐1 (NRG1) and its receptor erythroblastosis oncogene B (ErbB) family mediate microglia proliferation and chemotaxis contributing to the development of neuropathic pain. However, it is unclear whether NRG1‐ErbB signalling contributes to incision‐induced mechanical allodynia.

Hypothesis: CeM-PAG GABAergic circuits may be implicated in sudden unexpected death in epilepsy by melanocortinergic signaling.

Over the past ten years, we have increased our understanding of the neural correlates of sudden unexpected death in epilepsy (SUDEP). The study of patients with SUDEP provides unique opportunities to witness the sufficient or necessary conditions for the development of respiratory disorders and cardiac dysfunction [1,2]. Amajor clinical challenge in the neurologic field has been to develop newapproaches for controlling and preventing SUDEP in patients whose seizures do not respond to current pharmacological intervention [3]. In a recent report, the gammaaminobutyric acid (GABA) inhibitory interneurons have recently gained renewed interest as a potential target for the treatment of seizure generation and propagation [4,5]. The transgenic animal models support the general concept that dysfunctional GABAergic inhibitory neurotransmission is important for SUDEP, suggesting that GABAergic neural networks affected by epilepsy might be an interventional strategy for controlling and preventing SUDEP.

CeA-NPO circuits and REM sleep dysfunction in drug-refractory epilepsy

Sleep dysfunction is commonly symptom experienced by patients with refractory epilepsy [1,2]. The stages of sleep include rapid eye movement (REM), also known as active sleep (AS), and non-REM sleep. During REM sleep, the eyes move quickly in different directions, whereas that does not happen during non-REM sleep. Previous studies demonstrated that susceptibility to seizures is decreased during REM sleep, whereas non-REM sleep promotes seizure occurrence [3–7]. The study of REM behavior disorder in patients with epilepsy provides unique opportunities to develop new approaches for controlling and preventing refractory epilepsywhich does not respond to current pharmacological intervention.

The mechanism of electroacupuncture for predicting the efficacy of deep brain stimulation in pharmacoresistant epilepsy may be involved in the melanocortinergic signal

Intractable epilepsy is still one of the most confusing and enigmatic neurological disorders [1,2]. Deep brain stimulation targeted at the subthalamic nucleus (STN-DBS) is an alternative treatment for patients with uncontrolled symptoms of epilepsy [3], but predicting outcome before the operation is not possible. Electrical stimulation at acupoints was also efficient in treating medically refractory epilepsy, and Yan et al. and Meng et al. suggested that electroacupuncture at acupoints could predict the curative effect of STN-DBS for refractory epilepsy [4,5]. However, but the mechanisms of electroacupuncture for predicting the efficacy of electrical stimulation in pharmacoresistant epilepsy are still unclear. It is interesting to note that previous studies have demonstrated that epileptic seizures are tightly linked to an imbalance between the excitatory [glutamate (Glu), aspartate (Asp)] and inhibitory [GABA, glycine (Gly), and taurine (Tau)] neuronal transmitters [6]. Otherwise, it has been verified that the therapeutic mechanism of STN-DBS and electroacupuncture at acupoints is associated with the balance between the excitatory and inhibitory neuronal transmitters [7,8]. Accordingly, some authors suggested that the mechanism of electroacupuncture for predicting the efficacy of deep brain stimulation in pharmacoresistant epilepsy involved the metabolism of amino acids [4,5]. We would like to further discuss the possible mechanism of electroacupuncture for predicting the efficacy of deep brain stimulation in MC4R-GFP transgenic mice [9–12]. As data have accumulated over the last two decades, STN-DBS is now identified as an importantmodification of energymetabolism as reflected by changes in daily energy metabolism after stimulation surgery [13]. The study of Batisse-Lignier et al. [14] indicated that STN-DBS in patients affected glucose disposal of endogenous glucose production, suggesting that a cross talk between the central subthalamic nucleus and peripheral tissues may regulate glucose homeostasis. In addition, clinical findings have demonstrated that the therapeutic mechanisms of STN-DBS are closely related to the changes in cerebral glucosemetabolism [15,16]. Some neuroimaging studies using functional magnetic resonance imaging, single-photon emission computed tomography (SPECT), and positron emission tomography (PET) had revealed that glucose metabolism significantly increased in the left superior medial frontal gyrus, the middle frontal gyrus, and the right superior medial frontal gyrus following electroacupuncture at Hegu (LI 4) and Quchi (LI 11) [17,18], suggesting that the clinical effect of electroacupuncture at acupoints is also related to the changes in cerebral glucose metabolism. Therefore, we presume that the possible mechanism of electroacupuncture for predicting the efficacy of deep brain stimulation in pharmacoresistant epilepsy may be involved in the changes in cerebral glucose metabolism.