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Journal of Neuroscience Research Dec 2019Four major discoveries on the function of the pedunculopontine nucleus (PPN) have significantly advanced our understanding of the role of arousal in neurodegenerative... (Review)
Review
Four major discoveries on the function of the pedunculopontine nucleus (PPN) have significantly advanced our understanding of the role of arousal in neurodegenerative disorders. The first was the finding that stimulation of the PPN-induced controlled locomotion on a treadmill in decerebrate animals, the second was the revelation of electrical coupling in the PPN and other arousal and sleep-wake control regions, the third was the determination of intrinsic gamma band oscillations in PPN neurons, and the last was the discovery of gene transcription resulting from the manifestation of gamma activity in the PPN. These discoveries have led to novel therapies such as PPN deep brain stimulation (DBS) for Parkinson's disease (PD), identified the mechanism of action of the stimulant modafinil, determined the presence of separate mechanisms underlying gamma activity during waking versus REM sleep, and revealed the presence of gene transcription during the manifestation of gamma band oscillations. These discoveries set the stage for additional major advances in the treatment of a number of disorders.
Topics: Acetylation; Animals; Arousal; Calcium Channels; Central Nervous System Stimulants; Decerebrate State; Deep Brain Stimulation; GABAergic Neurons; Gait; Gamma Rhythm; Gene Expression Regulation; Histones; Humans; Modafinil; Neurodegenerative Diseases; Parkinson Disease; Pedunculopontine Tegmental Nucleus; Protein Processing, Post-Translational; Sleep, REM; Transcription, Genetic; Wakefulness
PubMed: 30916810
DOI: 10.1002/jnr.24417 -
American Journal of Physiology. Heart... Jun 2019Autonomic dysreflexia (AD) often occurs in individuals living with spinal cord injury (SCI) and is characterized by uncontrolled hypertension in response to otherwise... (Comparative Study)
Comparative Study
Autonomic dysreflexia (AD) often occurs in individuals living with spinal cord injury (SCI) and is characterized by uncontrolled hypertension in response to otherwise innocuous stimuli originating below the level of the spinal lesion. Visceral stimulation is a predominant cause of AD in humans and effectively replicates the phenotype in rodent models of SCI. Direct assessment of sympathetic responses to viscerosensory stimulation in spinalized animals is challenging and requires invasive surgical procedures necessitating the use of anesthesia. However, administration of anesthesia markedly affects viscerosensory reactivity, and the effects are exacerbated following spinal cord injury (SCI). Therefore, the major goal of the present study was to develop a decerebrate rodent preparation to facilitate quantification of sympathetic responses to visceral stimulation in the spinalized rat. Such a preparation enables the confounding effect of anesthesia to be eliminated. Sprague-Dawley rats were subjected to SCI at the fourth thoracic segment. Four weeks later, renal sympathetic nerve activity (RSNA) responses to visceral stimuli were quantified in urethane/chloralose-anesthetized and decerebrate preparations. Visceral stimulation was elicited via colorectal distension (CRD) for 1 min. In the decerebrate preparation, CRD produced dose-dependent increases in mean arterial pressure (MAP) and RSNA and dose-dependent decreases in heart rate (HR). These responses were significantly greater in magnitude among decerebrate animals when compared with urethane/chloralose-anesthetized controls and were markedly attenuated by the administration of urethane/chloralose anesthesia after decerebration. We conclude that the decerebrate preparation enables high-fidelity quantification of neuronal reactivity to visceral stimulation in spinalized rats. In animal models commonly used to study spinal cord injury, quantification of sympathetic responses is particularly challenging due to the increased susceptibility of spinal reflex circuits to the anesthetic agents generally required for experimentation. This constitutes a major limitation to understanding the mechanisms mediating regionally specific neuronal responses to visceral activation in chronically spinalized animals. In the present study, we describe a spinalized, decerebrate rodent preparation that facilitates quantification of sympathetic reactivity in response to visceral stimuli following spinal cord injury. This preparation enables reliable and reproducible quantification of viscero-sympathetic reflex responses resembling those elicited in conscious animals and may provide added utility for preclinical evaluation of neuropharmacological agents for the management of autonomic dysreflexia.
Topics: Anesthetics, Intravenous; Animals; Autonomic Dysreflexia; Chloralose; Decerebrate State; Disease Models, Animal; Hemodynamics; Kidney; Male; Rats, Sprague-Dawley; Reflex; Spinal Cord; Sympathetic Nervous System; Urethane
PubMed: 30875256
DOI: 10.1152/ajpheart.00724.2018 -
American Journal of Physiology.... May 2019Recent findings have shown that muscle contraction evokes an exaggerated pressor response in type 1 diabetes mellitus (T1DM) rats; however, it is not known whether the...
Recent findings have shown that muscle contraction evokes an exaggerated pressor response in type 1 diabetes mellitus (T1DM) rats; however, it is not known whether the mechanoreflex, which is commonly stimulated by stretching the Achilles tendon, contributes to this abnormal response. Furthermore, the role of mechano-gated Piezo channels, found on thin-fiber afferent endings, in evoking the mechanoreflex in T1DM is also unknown. Therefore, in male and female streptozotocin (STZ, 50 mg/kg)-induced T1DM and healthy control (CTL) rats, we examined the pressor and cardioaccelerator responses to tendon stretch during the early stage of the disease. To determine the role of Piezo channels, GsMTx-4, a selective Piezo channel inhibitor, was injected into the arterial supply of the hindlimb. At 1 wk after STZ injection in anesthetized, decerebrate rats, we stretched the Achilles tendon for 30 s and measured pressor and cardioaccelerator responses. We then compared pressor and cardioaccelerator responses to tendon stretch before and after GsMTx-4 injection (10 µg/100 ml). We found that the pressor (change in mean arterial pressure) response [41 ± 5 mmHg ( = 15) for STZ and 18 ± 3 mmHg ( = 11) for CTL ( < 0.01)] and cardioaccelerator (change in heart rate) response [18 ± 4 beats/min for STZ ( = 15) and 8 ± 2 beats/min ( = 11) for CTL ( < 0.05)] to tendon stretch were exaggerated in STZ rats. Local injection of GsMTx-4 attenuated the pressor [55 ± 7 mmHg ( = 6) before and 27 ± 9 mmHg ( = 6) after GsMTx-4 ( < 0.01)], but not the cardioaccelerator, response to tendon stretch in STZ rats and had no effect on either response in CTL rats. These data suggest that T1DM exaggerates the mechanoreflex response to tendon stretch and that Piezo channels play a role in this exaggeration.
Topics: Animals; Blood Pressure; Decerebrate State; Diabetes Mellitus, Experimental; Female; Hindlimb; Intercellular Signaling Peptides and Proteins; Male; Muscle Contraction; Muscle, Skeletal; Physical Conditioning, Animal; Rats, Sprague-Dawley; Reflex; Spider Venoms
PubMed: 30840487
DOI: 10.1152/ajpregu.00294.2018 -
Physiological Reports Jan 2019Mechanical signals within contracting skeletal muscles contribute to the generation of the exercise pressor reflex; an important autonomic and cardiovascular control...
Mechanical signals within contracting skeletal muscles contribute to the generation of the exercise pressor reflex; an important autonomic and cardiovascular control mechanism. In decerebrate rats, the mechanically activated channel inhibitor GsMTx4 was found to reduce the pressor response during static hindlimb muscle stretch; a maneuver used to investigate specifically the mechanical component of the exercise pressor reflex (i.e., the mechanoreflex). However, the effect was found only during the initial phase of the stretch when muscle length was changing and not during the later phase of stretch when muscle length was relatively constant. We tested the hypothesis that in decerebrate, unanesthetized rats, GsMTx4 would reduce the pressor response throughout the duration of a 30 sec, 1 Hz dynamic hindlimb muscle stretch protocol that produced repetitive changes in muscle length. We found that the injection of 10 μg of GsMTx4 into the arterial supply of a hindlimb reduced the peak pressor response (control: 15 ± 4, GsMTx4: 5 ± 2 mmHg, P < 0.05, n = 8) and the pressor response at multiple time points throughout the duration of the stretch. GsMTx4 had no effect on the pressor response to the hindlimb arterial injection of lactic acid which indicates the lack of local off-target effects. Combined with the recent finding that GsMTx4 reduced the pressor response only initially during static stretch in decerebrate rats, the present findings suggest that GsMTx4-sensitive channels respond primarily to mechanical signals associated with changes in muscle length. The findings add to our currently limited understanding of the channels that contribute to the activation of the mechanoreflex.
Topics: Animals; Blood Pressure; Decerebrate State; Hindlimb; Intercellular Signaling Peptides and Proteins; Male; Muscle Contraction; Muscle, Skeletal; Rats; Rats, Sprague-Dawley; Reflex; Spider Venoms
PubMed: 30632294
DOI: 10.14814/phy2.13974 -
Neuroscience Jan 2019People with Rett Syndrome (RTT), a neurodevelopmental disorder caused by mutations in the MECP2 gene, have breathing abnormalities manifested as periodical...
People with Rett Syndrome (RTT), a neurodevelopmental disorder caused by mutations in the MECP2 gene, have breathing abnormalities manifested as periodical hypoventilation with compensatory hyperventilation, which are attributable to a high incidence of sudden death. Similar breathing abnormalities have been found in animal models with Mecp2 disruptions. Although RTT-type hypoventilation is believed to be due to depressed central inspiratory activity, whether this is true remains unknown. Here we show evidence for reshaping in firing activity and patterns of medullary respiratory neurons in RTT-type hypoventilation without evident depression in inspiratory neuronal activity. Experiments were performed in decerebrate rats in vivo. In Mecp2-null rats, abnormalities in breathing patterns were apparent in both decerebrate rats and awake animals, suggesting that RTT-type breathing abnormalities take place in the brainstem without forebrain input. In comparison to their wild-type counterparts, both inspiratory and expiratory neurons in Mecp2-null rats extended their firing duration, and fired more action potentials during each burst. No changes in inspiratory or expiratory neuronal distributions were found. Most inspiratory neurons started firing in the middle of expiration and changed their firing pattern to a phase-spanning type. The proportion of post-inspiratory neurons was reduced in the Mecp2-null rats. With the increased firing activity of both inspiratory and expiratory neurons in null rats, phrenic discharges shifted to a slow and deep breathing pattern. Thus, the RTT-type hypoventilation appears to result from reshaping of firing activity of both inspiratory and expiratory neurons without evident depression in central inspiratory activity.
Topics: Action Potentials; Animals; Decerebrate State; Disease Models, Animal; Male; Medulla Oblongata; Methyl-CpG-Binding Protein 2; Neurons; Phrenic Nerve; Rats, Sprague-Dawley; Rats, Transgenic; Respiration; Rett Syndrome; Wakefulness
PubMed: 30458221
DOI: 10.1016/j.neuroscience.2018.11.011 -
Neuron Dec 2018Response to danger needs to be rapid and appropriate. In humans, nocifensive behaviors often precede conscious pain perception. Much is known about local spinal cord...
Response to danger needs to be rapid and appropriate. In humans, nocifensive behaviors often precede conscious pain perception. Much is known about local spinal cord circuits for simple reflexive responses, but the mechanisms underlying more complex behaviors remain poorly understood. We now describe a brainstem circuit that controls escape responses to select noxious stimuli. Tracing experiments characterized a highly interconnected excitatory circuit involving the dorsal spinal cord, parabrachial nucleus (PBNl), and reticular formation (MdD). A combination of chemogenetic, optogenetic, and genetic ablation approaches revealed that PBNl neurons are activated by noxious stimuli and trigger robust escape responses to heat through connections to the MdD. Remarkably, MdD neurons receive excitatory input from the PBN and target both the spinal cord and PBN; activation of these neurons phenocopies the behavioral effects of PBNl neuron stimulation. These findings identify a substrate for controlling appropriate behavioral responses to painful stimuli.
Topics: Adenosine Triphosphate; Animals; Brain Stem; Calcitonin Gene-Related Peptide; Decerebrate State; Luminescent Proteins; Mice; Mice, Inbred C57BL; Mice, Transgenic; Nerve Tissue Proteins; Neural Pathways; Nociceptors; Optogenetics; Pain; Pain Perception; Spinal Cord; Tachykinins; Transduction, Genetic
PubMed: 30449655
DOI: 10.1016/j.neuron.2018.10.037 -
Neurourology and Urodynamics Nov 2018To assess bladder smooth muscle function and innervation after long-term lower spinal root transection in canines.
AIMS
To assess bladder smooth muscle function and innervation after long-term lower spinal root transection in canines.
METHODS
Thirteen female mixed-breed hound dogs underwent bladder decentralization, which included transection of all sacral dorsal and ventral roots caudal to L7 and hypogastric nerves, bilaterally (n = 3); all sacral roots and hypogastric nerves plus transection of L7 dorsal roots, bilaterally (n = 4); or a sham operation (n = 6). At a year after initial surgery, bladder function was assessed in vivo by stimulation of the pelvic plexus. The bladder tissue was harvested for ex vivo smooth muscle contractility studies. Remaining bladder was evaluated for nerve morphology immunohistochemically using neuronal marker PGP9.5, apoptotic activity using terminal deoxynucleotidyl transferase dUTP nick end labeling, and histopathology using a hematoxylin and eosin stain.
RESULTS
Sacral root decentralization did not reduce maximum strength of pelvic plexus stimulation-induced bladder contraction, although long-term sacral dorsal and ventral root plus L7 dorsal root transection significantly decreased contraction strength. Electric field stimulation-induced contractions of the detrusor from all decentralized animals were preserved, compared to controls. Viable nerves and intramural ganglia were visualized in the bladder wall, regardless of group. There was no difference in amount of apoptosis in bladder smooth muscle between groups.
CONCLUSION
Bladder smooth muscle cells maintain their function after long-term bladder decentralization. While pelvic plexus-induced bladder contractions were less robust at 1 year after lower spinal root transection, the absence of atrophy and preservation of at least some nerve activity may allow for successful surgical reinnervation after long-term injury.
Topics: Animals; Decerebrate State; Dogs; Electric Stimulation; Female; Hypogastric Plexus; In Situ Nick-End Labeling; Muscle Contraction; Muscle, Smooth; Nerve Regeneration; Spinal Nerve Roots; Urinary Bladder
PubMed: 30024057
DOI: 10.1002/nau.23765 -
Journal of Applied Physiology... Sep 2018Spinal cord injury (SCI) at the level of cervical segments often results in life-threatening respiratory complications and requires long-term mechanical ventilator...
Spinal cord injury (SCI) at the level of cervical segments often results in life-threatening respiratory complications and requires long-term mechanical ventilator assistance. Thus restoring diaphragm activity and regaining voluntary control of breathing are the primary clinical goals for patients with respiratory dysfunction following cervical SCI. Epidural stimulation (EDS) is a promising strategy that has been explored extensively for nonrespiratory functions and to a limited extent within the respiratory system. The goal of the present study is to assess the potential for EDS at the location of the phrenic nucleus (C-C) innervating the diaphragm: the main inspiratory muscle following complete C cervical transection. To avoid the suppressive effect of anesthesia, all experiments were performed in decerebrate, C cervical transection, unanesthetized, nonparalyzed ( n = 13) and paralyzed ( n = 7) animals. Our results show that C segment was the most responsive to EDS and required the lowest threshold of current intensity, affecting tracheal pressure and phrenic nerve responses. High-frequency (200-300 Hz) EDS applied over C segment (C-EDS) was able to maintain breathing with normal end-tidal CO level and raise blood pressure. In addition, 100-300 Hz of C-EDS showed time- and frequency-dependent changes (short-term facilitation) of evoked phrenic nerve responses that may serve as a target mechanism for pacing of phrenic motor circuits. The present work provides the first report of successful EDS at the level of phrenic nucleus in a complete SCI animal model and offers insight into the potential therapeutic application in patients with high cervical SCI. NEW & NOTEWORTHY The present work offers the first demonstration of successful life-supporting breathing paced by epidural stimulation (EDS) at the level of the phrenic nucleus, following a complete spinal cord injury in unanesthetized, decerebrate rats. Moreover, our experiments showed time- and frequency-dependent changes of evoked phrenic nerve activity during EDS that may serve as a target mechanism for pacing spinal phrenic motor networks.
Topics: Animals; Blood Pressure; Carbon Dioxide; Cervical Cord; Decerebrate State; Electric Stimulation; Epidural Space; Heart Rate; Male; Phrenic Nerve; Rats; Rats, Sprague-Dawley; Recovery of Function; Respiration; Respiratory Muscles; Spinal Cord Injuries
PubMed: 29771608
DOI: 10.1152/japplphysiol.00895.2017 -
The Journal of Neuroscience : the... May 2018Higher vertebrates, including humans, are capable not only of forward (FW) locomotion but also of walking in other directions relative to the body axis [backward (BW),...
Higher vertebrates, including humans, are capable not only of forward (FW) locomotion but also of walking in other directions relative to the body axis [backward (BW), sideways, etc.]. Although the neural mechanisms responsible for controlling FW locomotion have been studied in considerable detail, the mechanisms controlling steps in other directions are mostly unknown. The aim of the present study was to investigate the distribution of spinal neuronal networks controlling FW and BW locomotion. First, we applied electrical epidural stimulation (ES) to different segments of the spinal cord from L2 to S2 to reveal zones triggering FW and BW locomotion in decerebrate cats of either sex. Second, to determine the location of spinal neurons activated during FW and BW locomotion, we used c-Fos immunostaining. We found that the neuronal networks responsible for FW locomotion were distributed broadly in the lumbosacral spinal cord and could be activated by ES of any segment from L3 to S2. By contrast, networks generating BW locomotion were activated by ES of a limited zone from the caudal part of L5 to the caudal part of L7. In the intermediate part of the gray matter within this zone, a significantly higher number of c-Fos-positive interneurons was revealed in BW-stepping cats compared with FW-stepping cats. We suggest that this region of the spinal cord contains the network that determines the BW direction of locomotion. Sequential and single steps in various directions relative to the body axis [forward (FW), backward (BW), sideways, etc.] are used during locomotion and to correct for perturbations, respectively. The mechanisms controlling step direction are unknown. In the present study, for the first time we compared the distributions of spinal neuronal networks controlling FW and BW locomotion. Using a marker to visualize active neurons, we demonstrated that in the intermediate part of the gray matter within L6 and L7 spinal segments, significantly more neurons were activated during BW locomotion than during FW locomotion. We suggest that the network determining the BW direction of stepping is located in this area.
Topics: Animals; Biomechanical Phenomena; Cats; Decerebrate State; Electric Stimulation; Electrophysiological Phenomena; Epidural Space; Female; Gray Matter; Immunohistochemistry; Locomotion; Lumbosacral Region; Male; Nerve Net; Proto-Oncogene Proteins c-fos; Spinal Cord
PubMed: 29678875
DOI: 10.1523/JNEUROSCI.2951-17.2018 -
American Journal of Physiology.... May 2018µ-Opioid G protein-coupled receptors (MOR) interact with ion channels to decrease neuronal excitability. In humans, intrathecal administration of the MOR agonist...
µ-Opioid G protein-coupled receptors (MOR) interact with ion channels to decrease neuronal excitability. In humans, intrathecal administration of the MOR agonist fentanyl inhibits the exercise pressor reflex, an effect that can be attributed to either the opening of inward rectifying potassium channels (GIRK) or the closing of N-type calcium channels. The purpose of this study was to determine if the highly selective MOR agonist [d-Ala, N-MePhe,Gly-ol]-enkephalin (DAMGO) attenuates the exercise pressor reflex and which of these two channels are responsible for this effect. In decerebrate rats, we determined the effect of intrathecal injection of either tertiapin-LQ, which blocks the GIRK channel or ω-conotoxin-GVIA, which blocks the N-type calcium channel on the exercise pressor reflex, which was evoked by contracting the triceps surae muscles. Initially, we established that intrathecal injection of DAMGO inhibited the exercise pressor reflex relative to no intrathecal injection or intrathecal saline injection ( P < 0.001, n = 5). We then found that intrathecal injection of two doses of tertiapin-LQ (1 and 10 µg) had no effect on the exercise pressor reflex ( n = 6 and n = 7, respectively; P > 0.05). Importantly, neither dose of tertiapin-LQ prevented the DAMGO-induced inhibition of the exercise pressor reflex. Last, we found that intrathecal injection of ω-conotoxin-GVIA markedly attenuated the exercise pressor reflex ( P < 0.001, n = 7). The cardioaccelerator response to contraction did not appear to be effected in any of the experiments. We conclude that N-type voltage-gated calcium channel inhibition appears to be the mechanism by which MOR activation inhibits the exercise pressor reflex in decerebrate rats.
Topics: Analgesics, Opioid; Animals; Calcium Channel Blockers; Calcium Channels, N-Type; Calcium Signaling; Decerebrate State; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; G Protein-Coupled Inwardly-Rectifying Potassium Channels; Injections, Spinal; Ion Channel Gating; Male; Muscle Contraction; Muscle, Skeletal; Neural Inhibition; Neurons, Afferent; Physical Exertion; Potassium Channel Blockers; Rats, Sprague-Dawley; Receptors, Opioid, mu; Reflex; Spinal Cord
PubMed: 29341826
DOI: 10.1152/ajpregu.00380.2017