Nucleus Reticularis Gigantocellularis Research Articles

Electrical stimulation of the cuneiform nucleus enhances the effects of rehabilitative training on locomotor recovery after incomplete spinal cord injury.

Most human spinal cord injuries are anatomically incomplete, leaving some fibers still connecting the brain with the sublesional spinal cord. Spared descending fibers of the brainstem motor control system can be activated by deep brain stimulation (DBS) of the cuneiform nucleus (CnF), a subnucleus of the mesencephalic locomotor region (MLR). The MLR is an evolutionarily highly conserved structure which initiates and controls locomotion in all vertebrates. Acute electrical stimulation experiments in female adult rats with incomplete spinal cord injury conducted in our lab showed that CnF-DBS was able to re-establish a high degree of locomotion five weeks after injury, even in animals with initially very severe functional deficits and white matter lesions up to 80-95%. Here, we analyzed whether CnF-DBS can be used to support medium-intensity locomotor training and long-term recovery in rats with large but incomplete spinal cord injuries. Rats underwent rehabilitative training sessions three times per week in an enriched environment, either with or without CnF-DBS supported hindlimb stepping. After 4 weeks, animals that trained under CnF-DBS showed a higher level of locomotor performance than rats that trained comparable distances under non-stimulated conditions. The MLR does not project to the spinal cord directly; one of its main output targets is the gigantocellular reticular nucleus in the medulla oblongata. Long-term electrical stimulation of spared reticulospinal fibers after incomplete spinal cord injury via the CnF could enhance reticulospinal anatomical rearrangement and in this way lead to persistent improvement of motor function. By analyzing the spared, BDA-labeled giganto-spinal fibers we found that their gray matter arborization density after discontinuation of CnF-DBS enhanced training was lower in the lumbar L2 and L5 spinal cord in stimulated as compared to unstimulated animals, suggesting improved pruning with stimulation-enhanced training. An on-going clinical study in chronic paraplegic patients investigates the effects of CnF-DBS on locomotor capacity.

Control of defensive behavior by the nucleus of Darkschewitsch GABAergic neurons

Abstract The nucleus of Darkschewitsch (ND), mainly composed of GABAergic neurons, is widely recognized as a component of the eye-movement controlling system. However, the functional contribution of ND GABAergic neurons (NDGABA) in animal behavior is largely unknown. Here, we show that NDGABA neurons were selectively activated by different types of fear stimuli, such as predator odor and foot-shock. Optogenetic and chemogenetic manipulations revealed that NDGABA neurons mediate freezing behavior. Moreover, using circuit-based optogenetic and neuroanatomical tracing methods, we identified an excitatory pathway from the lateral periaqueductal grey (lPAG) to the ND that induces freezing by exciting ND inhibitory outputs to the motor-related gigantocellular reticular nucleus, ventral part (GiV). Together, these findings indicate the NDGABA population as a novel hub for controlling defensive response by relaying fearful information from lPAG to GiV, a mechanism critical for understanding how the freezing behavior is encoded in the mammalian brain.

Brainstem nuclei responsive to cystometry in both endometriosis and cystitis rat models: C-fos immunohistochemistry study.

Although the co-occurrence of interstitial cystitis (IC) and endometriosis (ENDO) is remarkably high, the exact pathophysiology for this co-occurrence is unknown. The convergence of the inputs from the involved structures to the same neuronal centers may suggest neuronal hyperexcitability as a mechanism for this co-occurrence. The present study aimed to investigate the association between IC and ENDO, by studying the changes in brainstem responses to cystometry in a rat model of ENDO and cyclophosphamide (CYP)-induced IC using c-fos immunohistochemistry. Following cystometry the brainstem areas that had significant increase in c-fos expression in ENDO alone included: periaqueductal gray (PAG) nuclei, dorsal raphe nucleus, raphe obscurus nucleus, kolliker- Fuse areas, and area postrema. However, the brainstem areas that had increased significantly in the c-fos expression in the ENDO and CYP treated animals included: gigantocellular nucleus, lateral paragigantocellular nucleus, caudoventrolateral nucleus, rostroventrolateral/caudoventrolateral nucleus, lateral reticular nucleus, locus coeruleus, lateral PAG, raphe pallidus nucleus, raphe magnus nucleus, rostroventrolateral nucleus, dorsal motor nucleus of vagus, and solitary tract nucleus. Whereas only lateral parabrachial nucleus showed significant increase in c-fos expression in CYP treated animals alone. The results of the present study demonstrate the overlap of brainstem nuclei that are excited by urinary bladder under ENDO and IC conditions. The pattern of hyperexcitability of the brainstem nuclei may help in understating the pathophysiology of IC and ENDO conditions.

Modulation of the swallowing reflex by stimulation of the gigantocellular reticular nucleus in the rat

ObjectivesThe gigantocellular reticular nucleus (Gi) projects to the nuclues of the solitary tract nucleus (NTS) and the lateral reticular formation (LRF) above the nucleus ambiguus. The swallowing central pattern generator comprises the NTS and the LRF. The present study examined whether stimulation of the Gi affects the swallowing reflex. MethodsExperiments were performed on urethane-anesthetized rats. The swallowing reflex was evoked by repetitive electrical stimulation of the superior laryngeal nerve and responses were recorded from the mylohyoid muscle on an electromyogram. The Gi was stimulated electrically. In addition, glutamate was injected into the Gi. The Friedman's test, followed by the Wilcoxon signed-rank test with Bonferroni correction, were used to assess the effects of electrical stimulation of the Gi. The Wilcoxon signed-rank test was used to assess the effects of glutamate injection into the Gi. Differences were considered significant at the P < 0.05 level. ResultsThe number of swallows was significantly increased or decreased by electrical stimulation of the Gi or after injection of glutamate into the Gi. In both electrical stimulation of the Gi and injection of glutamate into the Gi, the onset latency of the first swallow was prolonged when the number of swallows was decreased but showed no change when the number of swallows was increased. ConclusionsThe present results suggest that the Gi is involved in the control of swallowing.

Rapid, activity-dependent co-release of GABA and glycine in the mouse brainstem

Presympathetic neurons in the ventrolateral and ventromedial medulla (VLM/VMM) control the sympathetic tone, and GABA was identified as a primary mechanism for sympathoinhibition. Intriguingly, there is evidence that both GABA and glycine efficiently inhibit sympathetic tone; however, the mechanism of glycine release is unknown. In this study, we tested the hypothesis that GABA and glycine are co-released in the VLM/VMM. Glycine is recycled by glycine transporter 2 (GlyT2), which is a reliable marker of glycinergic neurons. Therefore, we crossed heterozygous GlyT2Cre mice with floxed channelrhodopsin 2 (ChR2-EYFP) mice to generate GlyT2 reporter mice (GlyT2ChR2/EYFP), which were used to determine the mechanism of glycine release and reveal the location of glycinergic neurons. Whole-cell patch-clamp recordings from presympathetic VLM/VMM neurons revealed that GABA mediates most spontaneous inhibitory postsynaptic currents (sIPSCs); whereas increased activity of inhibitory inputs promotes the release of glycine. Light stimulation of glycinergic fibers expressing ChR2 in GlyT2ChR2/EYFP mice evoked IPSCs (eIPSCs) with glycinergic and GABAergic components. Bath application of GABAA receptors antagonist (bicuculline, 10 μM) decreased the amplitude of eIPSCs, suggesting that approximately 70% of the eIPSCs are generated by glycine. Moreover, blockade of GlyT2 partially diminished the glycinergic component of the light-evoked IPSCs. Using GlyT2ChR2/EYFP mice, we found that glycinergic fibers are abundant throughout the rostral brainstem, and GlyT2-expressing neurons were distributed within the ventral gigantocellular nucleus and medial reticular formation. Immunofluorescence labeling of glycine receptor subunits in the VLM/VMM revealed the expression of two prevalent forms of glycine receptors formed by α1 and α3. In summary, we found that GABA and glycine are co-released in the VLM/VMM, and blockage of GlyT2 decreased the amplitude of light-evoked IPSCs, suggesting that GABA and glycine are likely located in separate vesicles. Our data provide evidence for the co-inhibition of presympathetic neurons in the VLM/VMM by GABA and glycine and suggest that GABA controls the threshold excitability, while glycine is released on demand to increase the strength of inhibition. Supported by: NIDDK122842 and Tulane Brain Institute Marko Spark Innovation Research Fund This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Dystonia-like behaviors and impaired sensory-motor integration following neurotoxic lesion of the pedunculopontine tegmental nucleus in mice.

The pedunculopontine nucleus (PPTg) is a vital interface between the basal ganglia and cerebellum, participating in modulation of the locomotion and muscle tone. Pathological changes of the PPTg have been reported in patients and animal models of dystonia, while its effect and mechanism on the phenotyping of dystonia is still unknown. In this study, a series of behavioral tests focusing on the specific deficits of dystonia were conducted for mice with bilateral and unilateral PPTg excitotoxic lesion, including the dystonia-like movements evaluation, different types of sensory-motor integrations, explorative behaviors and gait. In addition, neural dysfunctions including apoptosis, neuroinflammation, neurodegeneration and neural activation of PPTg-related motor areas in the basal ganglia, reticular formations and cerebellum were also explored. Both bilateral and unilateral lesion of the PPTg elicited dystonia-like behaviors featured by the hyperactivity of the hindlimb flexors. Moreover, proprioceptive and auditory sensory-motor integrations were impaired in bilaterally lesioned mice, while no overt alterations were found for the tactile sensory-motor integration, explorative behaviors and gait. Similar but milder behavioral deficits were found in the unilaterally lesioned mice, with an effective compensation was observed for the auditory sensory-motor integration. Histologically, no neural loss, apoptosis, neuroinflammation and neurodegeneration were found in the substantia nigra pars compacta and caudate putamen (CPu) following PPTg lesion, while reduced neural activity was found in the dorsolateral part of the CPu and striatal indirect pathway-related structures including subthalamic nucleus, globus pallidus internus and substantia nigra pars reticular. Moreover, the neural activity was decreased for the reticular formations such as pontine reticular nucleus, parvicellular reticular nucleus and gigantocellular reticular nucleus, while deep cerebellar nuclei were spared. In conclusion, lesion of the PPTg could elicit dystonia-like behaviors through its effect on the balance of the striatal pathways and the reticular formations.

Use of a tissue clearing technique combined with retrograde trans-synaptic viral tracing to evaluate changes in mouse retinorecipient brain regions following optic nerve crush.

Successful establishment of reconnection between retinal ganglion cells and retinorecipient regions in the brain is critical to optic nerve regeneration. However, morphological assessments of retinorecipient regions are limited by the opacity of brain tissue. In this study, we used an innovative tissue cleaning technique combined with retrograde trans-synaptic viral tracing to observe changes in retinorecipient regions connected to retinal ganglion cells in mice after optic nerve injury. Specifically, we performed light-sheet imaging of whole brain tissue after a clearing process. We found that pseudorabies virus 724 (PRV724) mostly infected retinal ganglion cells, and that we could use it to retrogradely trace the retinorecipient regions in whole tissue-cleared brains. Unexpectedly, PRV724-traced neurons were more widely distributed compared with data from previous studies. We found that optic nerve injury could selectively modify projections from retinal ganglion cells in the hypothalamic paraventricular nucleus, intergeniculate leaflet, ventral lateral geniculate nucleus, central amygdala, basolateral amygdala, Edinger-Westphal nucleus, and oculomotor nucleus, but not the superior vestibular nucleus, red nucleus, locus coeruleus, gigantocellular reticular nucleus, or facial nerve nucleus. Our findings demonstrate that the tissue clearing technique, combined with retrograde trans-synaptic viral tracing, can be used to objectively and comprehensively evaluate changes in mouse retinorecipient regions that receive projections from retinal ganglion cells after optic nerve injury. Thus, our approach may be useful for future estimations of optic nerve injury and regeneration.

Descending pathways from the superior colliculus mediating autonomic and respiratory effects associated with orienting behaviour.

The ability to discriminate competing external stimuli and initiate contextually appropriate behaviours is a key brain function. Neurons in the deep superior colliculus (dSC) integrate multisensory inputs and activate descending projections to premotor pathways responsible for orienting, attention and defence, behaviours which involve adjustments to respiratory and cardiovascular parameters. However, the neural pathways that subserve the physiological components of orienting are poorly understood. We report that orienting responses to optogenetic dSC stimulation are accompanied by short-latency autonomic, respiratory and electroencephalographic effects in awake rats, closely mimicking those evoked by naturalistic alerting stimuli. Physiological responses were not accompanied by detectable aversion or fear, and persisted under urethane anaesthesia, indicating independence from emotional stress. Anterograde and trans-synaptic viral tracing identified a monosynaptic pathway that links the dSC to spinally projecting neurons in the medullary gigantocellular reticular nucleus (GiA), a key hub for the coordination of orienting and locomotor behaviours. In urethane-anaesthetized animals, sympathoexcitatory and cardiovascular, but not respiratory, responses to dSC stimulation were replicated by optogenetic stimulation of the dSC-GiA terminals, suggesting a likely role for this pathway in mediating the autonomic components of dSC-mediated responses. Similarly, extracellular recordings from putative GiA sympathetic premotor neurons confirmed short-latency excitatory inputs from the dSC. This pathway represents a likely substrate for autonomic components of orienting responses that are mediated by dSC neurons and suggests a mechanism through which physiological and motor components of orienting behaviours may be integrated without the involvement of higher centres that mediate affective components of defensive responses. KEY POINTS: Neurons in the deep superior colliculus (dSC) integrate multimodal sensory signals to elicit context-dependent innate behaviours that are accompanied by stereotypical cardiovascular and respiratory activities. The pathways responsible for mediating the physiological components of colliculus-mediated orienting behaviours are unknown. We show that optogenetic dSC stimulation evokes transient orienting, respiratory and autonomic effects in awake rats which persist under urethane anaesthesia. Anterograde tracing from the dSC identified projections to spinally projecting neurons in the medullary gigantocellular reticular nucleus (GiA). Stimulation of this pathway recapitulated autonomic effects evoked by stimulation of dSC neurons. Electrophysiological recordings from putative GiA sympathetic premotor neurons confirmed short latency excitatory input from dSC neurons. This disynaptic dSC-GiA-spinal sympathoexcitatory pathway may underlie autonomic adjustments to salient environmental cues independent of input from higher centres.

The Rostral Ventromedial and Lateral Medulla Are the Major Areas Responsive to Lung Cancer Progression among Brainstem Lung-Innervating Nuclei.

In recent years, the information crosstalk between the central nervous system and the periphery has been a hot topic, such as the brain-gut axis, brain-lung axis, etc. Among them, some studies have shown that brainstem nuclei activity can significantly affect the progression of peripheral tumor; however, regarding lung cancer, our understanding of the basic characteristics of the lung-innervating brain nuclei responsive to lung cancer progression remains deficient. Therefore, we used the pseudorabies virus for retrograde labeling of nerves to study the neural circuits between the lung and brain. We then established a mouse orthotopic lung cancer model and used the expression of the c-Fos gene in brain regions to characterize activated brain circuits and compared these results with those of the control group. We focused on c-Fos activity in nuclei associated with retrograde tracing regions of the brainstem. We found over 16 nuclei in the whole brain with direct or indirect lung innervation through neural retrograde labeling with the pseudorabies virus. We further revealed that the neuronal activity of the rostral ventrolateral reticular nucleus (RVL), caudal nucleus of Raphe (raphe obscurus nucleus, ROb), Raphe pallidus nucleus (RPa), and ventral gigantocellular reticular nucleus (GiV) in the rostral ventromedial and lateral medulla were significantly changed in an orthotopic lung cancer mouse model by the immunostaining of c-Fos early responsive protein. Thus, the distinctive rostroventral medulla area, functionally closely related to the vagus nerve, likely plays a role in central neural interaction with peripheral lung tumors and deserves future investigation.

Genetic tagging of the adenosine A2A receptor reveals its heterogeneous expression in brain regions.

The adenosine A2A receptor (A2AR), a G protein-coupled receptor, is involved in numerous and varied physiological and pathological processes, including inflammation, immune responses, blood flow, and neurotransmission. Accordingly, it has become an important drug target for the treatment of neuropsychiatric disorders. However, the exact brain distribution of A2AR in regions outside the striatum that display relatively low levels of endogenous A2AR expression has hampered the exploration of A2AR functions under both physiological and pathological conditions. To further study the detailed distribution of the A2AR in low-expression regions, we have generated A2AR knock-in mice in which the 3xHA-2xMyc epitope tag sequence was fused to the C-terminus of A2AR (A2AR-tag mice) via CRISPR/Cas9 technology. Here, using CRISPR/Cas9 technology, we have generated A2AR knock-in mice in which the 3xHA-2xMyc epitope tag sequence was fused to the C-terminus of A2AR (A2AR-tag mice). The A2AR-tag mice exhibited normal locomotor activity and emotional state. Consistent with previous studies, A2AR fluorescence was widely detected in the striatum, nucleus accumbens, and olfactory tubercles, with numerous labeled cells being evident in these regions in the A2AR-tag mouse. Importantly, we also identified the presence of a few but clearly labeled cells in heterogeneous brain regions where A2AR expression has not previously been unambiguously detected, including the lateral septum, hippocampus, amygdala, cerebral cortex, and gigantocellular reticular nucleus. The A2AR-tag mouse represents a novel useful genetic tool for monitoring the expression of A2AR and dissecting its functions in brain regions other than the striatum.

Pre-treatment with morphine prevents lipopolysaccharide-induced acute respiratory distress syndrome in rats via activation of opioid receptors

PurposeAcute respiratory distress syndrome (ARDS), a severe medical condition, is among the major causes of death in critically ill patients. Morphine is used as a therapeutic agent against severe pain. The mechanisms of its reactions over ARDS are not fully understood. The aim of this study was to assess the mechanism of morphine in rats with ARDS. MethodsRats were injected with lipopolysaccharide to induce ARDS, and some rats were pre-treated with graded doses of morphine in the lateral ventricles to assess survival and non-infected mortality. Immunohistochemical and HE staining were performed to measure MPO and CD68 activity in the lungs and lung injury. ELISA was conducted to detect the inflammatory factor levels in the plasma and BALF. Co-labeling of μ-opioid receptor (MOR) and c-Fos was observed in the brain tissues. MOR-positive cells in brain tissues were evaluated using immunohistochemistry. The effect of MOR antagonists on ARDS was examined in rats by pre-injection of naloxone or methylnaltrexone. The expression of MyD88, TLR4, and NF-κB was lastly assessed. ResultsDose-independent improvement was observed in respiratory capacity and lung injury in ARDS rats after morphine pre-injection, along with reduced inflammatory factors in the plasma and BALF. MOR-positive cells were elevated after morphine, which occurred within the ventral part of the gigantocellular reticular nucleus (GiV). Naloxone and methylnaltrexone blocked the effects of morphine via central and peripheral MOR. Morphine activated TLR pathway in a MyD88-dependent manner. ConclusionMorphine activates MOR within the GiV and the TLR pathway to attenuate ARDS in rats.

Mapping the human corticoreticular pathway with multimodal delineation of the gigantocellular reticular nucleus and high-resolution diffusion tractography

The corticoreticular pathway (CRP) is a major motor tract that transmits cortical input to the reticular formation motor nuclei and may be an important mediator of motor recovery after central nervous system damage. However, its cortical origins, trajectory and laterality are incompletely understood in humans. This study aimed to map the human CRP and generate an average CRP template in standard MRI space. Following recently established guidelines, we manually delineated the primary reticular formation motor nucleus (gigantocellular reticular nucleus [GRN]) using several group-mean MRI contrasts from the Human Connectome Project (HCP). CRP tractography was then performed with HCP diffusion-weighted MRI data (N = 1065) by selecting diffusion streamlines that reached both the cortex and GRN. Corticospinal tract (CST) tractography was also performed for comparison. Results suggest that the human CRP has widespread origins, which overlap with the CST across most of the motor cortex and include additional exclusive inputs from the medial and anterior prefrontal cortices. The estimated CRP projected through the anterior and posterior limbs of the internal capsule before partially decussating in the midbrain tegmentum and converging bilaterally on the pontomedullary reticular formation. Thus, the CRP trajectory appears to partially overlap the CST, while being more distributed and anteromedial to the CST in the cerebrum before moving posterior to the CST in the brainstem. These findings have important implications for neurophysiologic testing, cortical stimulation and movement recovery after brain lesions. We expect that our GRN and tract maps will also facilitate future CRP research.

Histomorphological Study of The Pons and Medulla Oblongata of African Striped Group Squirrel (Xerus erythropus)

The study was undertaken to investigate the histological and functional relationships between the pons and Medulla Oblongata of African Striped Ground Squirrel (Xerus erythropus). Twenty (20) adult African striped ground squirrels were divided in to two groups: 10 males and 10 females. The ground squirrels were obtained from the surrounding villages of Zaria Local Government, Kaduna State Nigeria. Each Squirrel was euthanized using ketamine hydrochloride at dose 80mg/kg BW followed by gentle perfusion with neutral formal saline. A pair of scissors, chisel and scalpel blade was used to gently extract the brain (craniotomy). The extracted brain was fixed in bouins solution for 24hours and processed histologically. The pons and medulla are composed of conspicuous nucleus abducens, nucleus facialis and nucleus trigeminal. The nucleus facialis was found dorsal to the paramedian pontine reticular formation as group of large multipolar neurons. A conspicuous nucleus abducens was found as clusters of medium neurons located lateral to the trigeminal nucleus. In myelencephalon, the cuneate fascicles, intermediate sulcus and lateral sulcus were not evident on dorsal surface but there were grossly visible pyramids and olivary prominence on the ventral surface. Similarly, the nucleus olivary were prominent, nucleus cochlearis and spinal nucleus trigemini were well developed, nucleus hypoglossi, raphe obscurus, lateral reticular nucleus, gigantocellular reticular nucleus were all very distinct. In conclusion, the presence of distinct nuclei in the pons and medulla oblongata gives squirrels fine voluntary skills with good motor coordination and balance and good visual acuity for improved diurnal adaptation.

The Cortical Motor System in the Domestic Pig: Origin and Termination of the Corticospinal Tract and Cortico-Brainstem Projections.

The anatomy of the cortical motor system and its relationship to motor repertoire in artiodactyls is for the most part unknown. We studied the origin and termination of the corticospinal tract (CST) and cortico-brainstem projections in domestic pigs. Pyramidal neurons were retrogradely labeled by injecting aminostilbamidine in the spinal segment C1. After identifying the dual origin of the porcine CST in the primary motor cortex (M1) and premotor cortex (PM), the axons descending from those regions to the spinal cord and brainstem were anterogradely labeled by unilateral injections of dextran alexa-594 in M1 and dextran alexa-488 in PM. Numerous corticospinal projections from M1 and PM were detected up to T6 spinal segment and showed a similar pattern of decussation and distribution in the white matter funiculi and the gray matter laminae. They terminated mostly on dendrites of the lateral intermediate laminae and the internal basilar nucleus, and some innervated the ventromedial laminae, but were essentially absent in lateral laminae IX. Corticofugal axons terminated predominantly ipsilaterally in the midbrain and bilaterally in the medulla oblongata. Most corticorubral projections arose from M1, whereas the mesencephalic reticular formation, superior colliculus, lateral reticular nucleus, gigantocellular reticular nucleus, and raphe received abundant axonal contacts from both M1 and PM. Our data suggest that the porcine cortical motor system has some common features with that of primates and humans and may control posture and movement through parallel motor descending pathways. However, less cortical regions project to the spinal cord in pigs, and the CST neither seems to reach the lumbar enlargement nor to have a significant direct innervation of cervical, foreleg motoneurons.

Intrinsic brainstem circuits comprised of Chx10-expressing neurons contribute to reticulospinal output in mice.

Glutamatergic reticulospinal neurons in the gigantocellular reticular nucleus (GRN) of the medullary reticular formation can function as command neurons, transmitting motor commands to spinal cord circuits to instruct movement. Recent advances in our understanding of this neuron-dense region have been facilitated by the discovery of expression of the transcriptional regulator, Chx10, in excitatory reticulospinal neurons. Here, we address the capacity of local circuitry in the GRN to contribute to reticulospinal output. We define two subpopulations of Chx10-expressing neurons in this region, based on distinct electrophysiological properties and soma size (small and large), and show that these populations correspond to local interneurons and reticulospinal neurons, respectively. Using focal release of caged glutamate combined with patch clamp recordings, we demonstrated that Chx10 neurons form microcircuits in which the Chx10 local interneurons project to and facilitate the firing of Chx10 reticulospinal neurons. We discuss the implications of these microcircuits in terms of movement selection.NEW & NOTEWORTHY Reticulospinal neurons in the medullary reticular formation integrate inputs from higher regions to effectively instruct spinal motor circuits. Using photoactivation of neurons in brainstem slices, we studied connectivity of reticular formation neurons that express the transcriptional regulator, Chx10. We show that a subpopulation of these neurons functions as local interneurons that affect descending commands. The results shed light on the internal organization and microcircuit formation of reticular formation neurons.

Progressive Pontine-Medullary Dysfunction Leads to REM Sleep Behavior Disorder Symptoms in a Chronic Model of Parkinson's Disease.

BackgroundClinical observations reveal that rapid eye movement (REM) sleep behavior disorder (RBD) often develops prior to alpha-synucleinopathies including Parkinson’s disease (PD). However, a causal relationship between alpha-synucleinopathy and Parkinsonian neurodegeneration has not been delineated.MethodsRats were chronically treated with rotenone and EEG and EMG signals were recorded for analysis of sleep behavior, assisted by video recording of body movements. C-fos expression and TUNEL staining were used to assess neuronal activation and apoptosis, respectively. Chemogenetic manipulation of brain stem nuclei was conducted to ameliorate RBD symptoms in rotenone-treated rats.ResultsRats chronically exposed to rotenone exhibited progressive RBD features, from EEG slowing to REM sleep motor behavior and NREM muscle activities. Temporally, these phenomena correlated well with progressive alpha-synuclein aggregation and neuronal apoptosis in the sublaterodorsal tegmental nucleus (SLD) and gigantocellular ventricular reticular nucleus in the brainstem. Chemogenetic activation of glutamatergic neurons in SLD alleviated RBD symptoms in the rotenone model.ConclusionTaken together, these results are consistent with a progressive degeneration in the REM sleep promoting and atonia circuit in early Parkinsonism that underlies the emergence of RBD symptoms, and demonstrate that the rotenone model is useful for further studies into RBD and its relationship to PD.

ACE2 expression in rat brain: Implications for COVID-19 associated neurological manifestations

We examined cell type-specific expression and distribution of rat brain angiotensin-converting enzyme 2 (ACE2), the receptor for SARS-CoV-2, in the rodent brain. ACE2 is ubiquitously present in brain vasculature, with the highest density of ACE2 expressing capillaries found in the olfactory bulb, the hypothalamic paraventricular, supraoptic, and mammillary nuclei, the midbrain substantia nigra and ventral tegmental area, and the hindbrain pontine nucleus, the pre-Bötzinger complex, and nucleus of tractus solitarius. ACE2 was expressed in astrocytes and astrocytic foot processes, pericytes and endothelial cells, key components of the blood-brain barrier. We found discrete neuronal groups immunopositive for ACE2 in brainstem respiratory rhythm generating centers, including the pontine nucleus, the parafascicular/retrotrapezoid nucleus, the parabrachial nucleus, the Bötzinger, and pre-Bötzinger complexes and the nucleus of tractus solitarius; in the arousal-related pontine reticular nucleus and gigantocellular reticular nuclei; in brainstem aminergic nuclei, including substantia nigra, ventral tegmental area, dorsal raphe, and locus coeruleus; in the epithalamic habenula, hypothalamic paraventricular and supramammillary nuclei; and in the hippocampus. Identification of ACE2-expressing neurons in rat brain within well-established functional circuits facilitates prediction of possible neurological manifestations of brain ACE2 dysregulation during and after COVID-19 infection.

Electrophysiological Study on the Influence of the Morphine Microiontophoresis on Firing Activity of Neurons in Nuclei Related to Acupuncture Analgesia

Background and Aim: Many nuclei such as periaqueductal central gray (PAG), raphe magnus nucleus (RMG) and gigantocellular reticular nucleus (Gi) are related in acupuncture analgesia. The aim of this study is to find the analgesic characteristics when dorsolateral periaqueductal gray (DLPAG), ventrolateral periaqueductal gray (VLPAG), RMG and Gi were individually stimulated in rat. Methods: Wistar rats (200~230g) were used in experiments. Rats were put in a small plastic box except the tail when the tail of a rat was stimulated by using radiant heat, tail flick latency (TFL), threshold of the painful response on account of the radiant heat was determined. The stimulus experiments were performed 3 to 5 days after inserting the electrodes. The current intensity for microiontophoresis is 30nA and time is 20s. Results: When DLPAG was locally stimulated in rats, the analgesia gradually appeared. Its characteristics resembled those of electroacupuncture at ST36 point. And then the analgesic effect appeared only in the period when VLPAG, RMG and Gi were individually stimulated in rats, but didn’t appear after cessation of stimulation. The rates of the excited neurons in the VLPAG, RMG and Gi were increased by microiontophoresis of morphine. Conclusion: There are mechanisms inhibiting the painful impulse in input of spinal cord by influence of endogenous morphine-type substance affecting neurons in VLPAG, RMG, and Gi among the mechanisms of electroacupuncture analgesia on ST36 point.

Kv2.1 expression in giant reticular neurons of the postnatal mouse brain

Previous experiments charted the development of behavioral arousal in postnatal mice. From Postnatal Day 3 (P3) to Postnatal Day 6 (P6) mice (a) become significantly more active, “arousable”; and (b) in large reticular neurons, nucleus gigantocellularis (NGC), patch clamp recordings reveal a significantly increased ability to fire high frequency trains of action potentials as are associated with elevated cortical arousal. These action potential trains depend on delayed rectifiers such as Kv2.1. Here we report tracking the development of expression of a delayed rectifier, Kv2.1 in NGC neurons crucial for initiating CNS arousal. In tissue sections, light microscope immunohistochemistry revealed that expression of Kv2.1 in NGC neurons is greater at day P6 than at P3. Electron microscope immunohistochemistry revealed Kv2.1 labeling on the plasmalemmal surface of soma and dendrites, greater on P6 than P3. In brainstem reticular neuron cell culture, Kv2.1 immunocytochemistry increased monotonically from Days-In-Vitro 3–10, paralleling the ability of such neurons to fire action potential trains. The increase of Kv2.1 expression from P3 to P6, perhaps in conjunction with other delayed rectifier currents, could permit the ability to fire action potential trains in NGC neurons. Further work with genetically identified NGC neurons is indicated.

Potassium channels and the development of arousal-relevant action potential trains in primary hindbrain neurons

Neurons in nucleus gigantocellularis (NGC) have been shown by many lines of evidence to be important for regulating generalized CNS arousal. Our previous study on mouse pups suggested that the development of NGC neurons’ capability to fire action potential (AP) trains may both lead to the development of behavioral arousal and may itself depend on an increase in delayed rectifier currents. Here with whole-cell patch clamp we studied delayed rectifier currents in two stages. First, primary cultured neurons isolated from E12.5 embryonic hindbrain (HB), a dissection which contains all of NGC, were used to take advantage of studying neurons in vitro over using neurons in situ or in brain slices. HB neurons were tested with Guangxitoxin-1E and Resveratrol, two inhibitors of Kv2 channels which mediate the main bulk of delayed rectifier currents. Both inhibitors depressed delayed rectifier currents, but differentially: Resveratrol, but not Guangxitoxin-1E, reduced or abolished action potentials in AP trains. Since Resveratrol affects the Kv2.2 subtype, the development of the delayed rectifier mediated through Kv2.2 channels may lead to the development of HB neurons’ capability to generate AP trains. Stage Two in this work found that electrophysiological properties of the primary HB neurons recorded are essentially the same as those of NGC neurons. Thus, from the two stages combined, we propose that currents mediated through Kv2.2 are crucial for generating AP trains which, in turn, lead to the development of mouse pup behavioral arousal.