Acute Spinal Cord Transection Research Articles

Boldine Alters Serum Lipidomic Signatures after Acute Spinal Cord Transection in Male Mice.

Traumatic spinal cord injury (SCI) results in wide-ranging cellular and systemic dysfunction in the acute and chronic time frames after the injury. Chronic SCI has well-described secondary medical consequences while acute SCI has unique metabolic challenges as a result of physical trauma, in-patient recovery and other post-operative outcomes. Here, we used high resolution mass spectrometry approaches to describe the circulating lipidomic and metabolomic signatures using blood serum from mice 7 d after a complete SCI. Additionally, we probed whether the aporphine alkaloid, boldine, was able to prevent SCI-induced changes observed using these 'omics platforms'. We found that SCI resulted in large-scale changes to the circulating lipidome but minimal changes in the metabolome, with boldine able to reverse or attenuate SCI-induced changes in the abundance of 50 lipids. Multiomic integration using xMWAS demonstrated unique network structures and community memberships across the groups.

Alginate hydrogel cross-linked by Ca2+ to promote spinal cord neural stem/progenitor cell differentiation and functional recovery after a spinal cord injuryhh.

Alginate capillary hydrogels seeded with differentiated cells can fill the lesion cavity and promote axonal regeneration after grafting into the injured spinal cord. Neural stem/progenitor cells (NSPCs) can potentially repair the spinal cord; however, effects of alginate hydrogels (AHs) on NSPCs remain unknown. In this study, we fabricated AHs cross-linked by Ca2+ and seeded hydrogels with rat embryonic day 14 NSPCs. Immunocytochemistry and electron microscopy show that NSPCs survive, proliferate and differentiate into neurons in vitro within the capillaries. After transplantation into an acute T8 complete spinal cord transection site in adult rats, approximately one-third (38.3%) of grafted cells survive and differentiate into neurons (40.7%), astrocytes (26.6%) and oligodendrocytes (28.4%) at 8 weeks post-grafting. NSPCs promote the growth of host axons within the capillaries in a time-dependent manner. Host axons make synapse-like contacts with NSPC-derived neurons within the hydrogel channels, and graft-derived axons extend into the host white and gray matter making putative synapses. This is paralleled by improved electrophysiological conductivity across the lesion and partial hindlimb locomotor recovery.

Anisotropic Alginate Hydrogels Promote Axonal Growth across Chronic Spinal Cord Transections after Scar Removal

We have previously reported that cell-seeded alginate hydrogels (AHs) with anisotropic capillaries can restore the continuity of the spinal cord and support axonal regeneration in a rat model of acute partial spinal cord transection. Whether similar effects can be found after transplantation into sites of complete chronic spinal cord transections without additional growth-promoting stimuli has not been investigated. We therefore implanted AHs into the cavity of a chronic thoracic transection following scar resection (SR) 4 weeks postinjury and examined electrophysiological and functional recovery as well as regeneration of descending and ascending projections within and beyond the AH scaffold up to 3 months after engraftment. Our results indicate that both electrophysiological conductivity and locomotor function are significantly improved after AH engraftment. SR transiently impairs locomotor function immediately after surgery but does not affect long-term outcomes. Histological analysis shows numerous host cells migrating into the scaffold channels and a reduction of fibroglial scaring around the lesion by AH grafts. In contrast to corticospinal axons, raphaespinal and propriospinal descending axons and ascending sensory axons regenerate throughout the scaffolds and extend into the distal host parenchyma. These results further support the pro-regenerative properties of AHs and their therapeutic potential for chronic SCI in combination with other strategies to improve functional outcomes after spinal cord injury.

Prokinetic effects of neurokinin-2 receptor agonists on the bladder and rectum of rats with acute spinal cord transection

The suitability of various neurokinin-2 (NK2) receptor agonists and routes of administration to elicit on-demand voiding of the bladder and bowel, as future therapy for individuals with spinal cord injury, was examined using a rat model. The current study examined the feasibility of alternative routes of administration, which are more practical for clinical use than intravenous (IV) administration. Voiding and isovolumetric cystometry were recorded in anesthetized, acutely spinalized, female rats after IV, subcutaneous (SC), intramuscular (IM), intranasal (IN), or sublingual (SL) administration of [Lys5,MeLeu9,Nle10]-NKA(4−10) (LMN-NKA). Administration of LMN-NKA (1–10μg/kg IV; 10−300μg/kg SC or IM; 15–1000μg/kg IN or 300–1500μg/kg SL) elicited rapid-onset, short-duration, dose-related increases in bladder pressure and voiding with the rank order for time of both onset and duration being IV < IN < SC = IM < SL. The incidence of voiding was dependent on the dose and route, with all routes resulting in a high voiding efficiency (~ 70%). Like LMN-NKA, neurokinin A (NKA 1–100μg/kg IV) and GR 64349 (0.1–30μg/kg IV or 1–300μg/kg SC) produced rapid-onset, short-duration increases in bladder pressure, as well as colorectal pressure. Administration of vehicle never produced bladder or rectal contractions or voiding. Transient hypotension was observed after IV injection of LMN-NKA, which was less pronounced after SC injection. Hypotension was not apparent with GR 64349. In conclusion, selective NK2 receptor agonists, administered through various non-IV routes of administration, may provide a safe, convenient, and efficacious method for inducing voiding.

MP8-18 THE ROLE OF THE BRAINSTEM IN TIBIAL INHIBITION OF THE MICTURITION REFLEX IN CATS

You have accessJournal of UrologyUrodynamics/Incontinence/Female Urology: Basic Research I1 Apr 2015MP8-18 THE ROLE OF THE BRAINSTEM IN TIBIAL INHIBITION OF THE MICTURITION REFLEX IN CATS Matthew Ferroni, Richard Slater, Bing Shen, Zhiying Xiao, Jicheng Wang, Andy Lee, James Roppolo, William de Groat, and Changfeng Tai Matthew FerroniMatthew Ferroni More articles by this author , Richard SlaterRichard Slater More articles by this author , Bing ShenBing Shen More articles by this author , Zhiying XiaoZhiying Xiao More articles by this author , Jicheng WangJicheng Wang More articles by this author , Andy LeeAndy Lee More articles by this author , James RoppoloJames Roppolo More articles by this author , William de GroatWilliam de Groat More articles by this author , and Changfeng TaiChangfeng Tai More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.285AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Tibial Nerve Stimulation (TNS) has been shown to significantly inhibit the micturition reflex when the bladder is distended by saline infusion or irritated by 0.25% acetic acid (AA) in cats. However, TNS inhibition of AA-induced bladder overactivity is lost after acute spinal cord transection at the level of T9/T10 indicating a supraspinal site of action. This study determines the role of the brainstem in TNS inhibition, which is important for understanding the mechanism of action of tibial neuromodulation therapy for overactive bladder. METHODS 16 cats under isoflurane anesthesia underwent decerebration by surgical transection rostral to the superior colliculi. Then, multiple saline cystometrograms (CMGs) were performed under á-chloralose anesthesia to elicit micturition reflex contractions (>30 cmH2O). 30 minutes of continuous TNS at three times threshold intensity for inducing toe movement was then applied during isovolumetric bladder contractions at frequencies of either 5Hz or 30Hz. After each stimulation, five consecutive CMGs were performed to assess post-stimulation changes of bladder capacity. CMGs were then performed during TNS at either 5Hz or 30Hz. Next, the same stimulation protocol was repeated during AA irritation. At the end of each experiment, naloxone (an opioid receptor antagonist) was administered either intravenously (1 mg/kg) or directly into the brainstem (2.0-4.0 mg in 0.1-0.2 cc) followed by a series of CMGs with/without TNS. ANOVA tests were used to determine statistical significance (p<0.05). RESULTS During saline infusion, 30 minutes of TNS significantly increased post-stimulation bladder capacity above controls with a mean increase of 27.2% (p<0.01) at a frequency of 5 Hz and 44.2% (p<0.01) at a frequency of 30 Hz. However, post-stimulation TNS inhibition was not observed during AA infusion. TNS applied during CMG significantly increased bladder capacity by 27.3% (saline, p<0.01) and 87.6% (AA, p<0.01) respectively over controls at 5 Hz, but failed to achieve significant inhibition at 30 Hz. Naloxone treatments significantly reduced control bladder capacity whether given intravenously (68.1% reduction, p<0.01) or directly into brainstem (58.8% reduction, p<0.01) and completely eliminated the acute TNS inhibition. CONCLUSIONS Our results suggest: (1) the brainstem plays an important role in TNS inhibition of both non-nociceptive (saline distention) and nociceptive (AA irritation) bladder reflexes while the cerebrum is not necessary; (2) opioid receptors in the brainstem are involved in TNS inhibition of the nociceptive bladder reflex. © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e79-e80 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.MetricsAuthor Information Matthew Ferroni More articles by this author Richard Slater More articles by this author Bing Shen More articles by this author Zhiying Xiao More articles by this author Jicheng Wang More articles by this author Andy Lee More articles by this author James Roppolo More articles by this author William de Groat More articles by this author Changfeng Tai More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

MP12-01 SPINAL METABOTROPIC GLUTAMATE RECEPTOR 5 INVOLVEMENT IN PUDENDAL INHIBITION OF NOCICEPTIVE BLADDER REFLEX IN CATS

INTRODUCTION AND OBJECTIVES: Spinal cord transection (SCT) results in disruption of the Ad-fiber mediated supraspinal voiding reflex with emergence of a C-fiber mediated spinal reflex. Pudendal nerve stimulation (PNS) can increase bladder capacity and reduce storage pressures in both acute and chronic spinal cord injury models. Metabotropic glutamate receptor 5 (mGluR5) is widely expressed in the CNS and has been shown to suppress excitatory transmission of the micturition reflex. This study investigates the role and location of mGluR5 in pudendal nerve inhibition of C-fiber mediated spinal bladder reflex using an acute SCT model. METHODS: Cystometrograms (CMGs) were performed on 12 cats under a-chloralose anesthesia. Saline control capacity was establish followed by acute SCT at T9/T10. CMGs were performed using 0.25% acetic acid (AA) to activate nociceptive C-fiber bladder afferents and induce spinal bladder reflexes. PNS was applied at 5 Hz at 2 and 4 times the threshold (T) for inducing anal twitch. Under isovolumetric conditions, MTEP (a selective mGluR5 antagonist) was given (3 mg/kg, i.v.) to determine its effect on PNS. Six of the cats were treated with propranolol (3 mg/kg, i.v.) prior to MTEP administration. Hexamethonium (10 mg/kg, i.v.) was given at the end of each experiment to block the spinal bladder reflex. RESULTS: Following T9/T10 SCT and AA irritation, CMGs showed a spinal bladder reflex resulting in low amplitude (<50 cmH2O), short duration (<30 s) contractions at a significantly lower bladder volume 78.69% 26.2% of saline control capacity. During AA irritation, MTEP resulted in a significant increase in control capacity from 71.77% 24.17% to 93.97 34.05% but did not significantly change maximal contraction amplitude. MTEP given after propranolol resulted in significantly reduced contraction amplitude from 18.57 5.2 to 6.62 3.0 cmH2O and significantly increased capacity from 56.91 25.8% to 78.53 31.94%. MTEP resulted in elimination of PNS inhibition at both 2T and 4T stimulation without changing the control capacity. Propranolol did not fully remove PNS inhibition, but MTEP after propranolol treatment completely eliminated the PNS inhibition. CONCLUSIONS: Our study reveals the presence of mGluR5 in the nociceptive C-fiber mediated spinal bladder reflex and substantiates the role of spinal mGluR5 in PNS inhibition of the nociceptive C-fiber mediated bladder reflex. Understanding of the location and neurotransmitters involved in PNS may help to create new therapies for overactive bladder.

Propranolol, but not naloxone, enhances spinal reflex bladder activity and reduces pudendal inhibition in cats.

This study examined the role of β-adrenergic and opioid receptors in spinal reflex bladder activity and in the inhibition induced by pudendal nerve stimulation (PNS) or tibial nerve stimulation (TNS). Spinal reflex bladder contractions were induced by intravesical infusion of 0.25% acetic acid in α-chloralose-anesthetized cats after an acute spinal cord transection (SCT) at the thoracic T9/T10 level. PNS or TNS at 5 Hz was applied to inhibit these spinal reflex contractions at 2 and 4 times the threshold intensity (T) for inducing anal or toe twitch, respectively. During a cystrometrogram (CMG), PNS at 2T and 4T significantly (P < 0.05) increased bladder capacity from 58.0 ± 4.7% to 85.8 ± 10.3% and 96.5 ± 10.7%, respectively, of saline control capacity, while TNS failed to inhibit spinal reflex bladder contractions. After administering propranolol (3 mg/kg iv, a β₁/β₂-adrenergic receptor antagonist), the effects of 2T and 4T PNS on bladder capacity were significantly (P < 0.05) reduced to 64.5 ± 9.5% and 64.7 ± 7.3%, respectively, of the saline control capacity. However, the residual PNS inhibition (about 10% increase in capacity) was still statistically significant (P < 0.05). Propranolol treatment also significantly (P = 0.0019) increased the amplitude of bladder contractions but did not change the control bladder capacity. Naloxone (1 mg/kg iv, an opioid receptor antagonist) had no effect on either spinal reflex bladder contractions or PNS inhibition. At the end of experiments, hexamethonium (10 mg/kg iv, a ganglionic blocker) significantly (P < 0.05) reduced the amplitude of the reflex bladder contractions. This study indicates an important role of β₁/β₂-adrenergic receptors in pudendal inhibition and spinal reflex bladder activity.

Somatic modulation of spinal reflex bladder activity mediated by nociceptive bladder afferent nerve fibers in cats.

The goal of the present study was to determine if supraspinal pathways are necessary for inhibition of bladder reflex activity induced by activation of somatic afferents in the pudendal or tibial nerve. Cats anesthetized with α-chloralose were studied after acute spinal cord transection at the thoracic T9/T10 level. Dilute (0.25%) acetic acid was used to irritate the bladder, activate nociceptive afferent C-fibers, and trigger spinal reflex bladder contractions (amplitude: 19.3 ± 2.9 cmH2O). Hexamethonium (a ganglionic blocker, intravenously) significantly (P < 0.01) reduced the amplitude of the reflex bladder contractions to 8.5 ± 1.9 cmH2O. Injection of lidocaine (2%, 1-2 ml) into the sacral spinal cord or transection of the sacral spinal roots and spinal cord further reduced the contraction amplitude to 4.2 ± 1.3 cmH2O. Pudendal nerve stimulation (PNS) at frequencies of 0.5-5 Hz and 40 Hz but not at 10-20 Hz inhibited reflex bladder contractions, whereas tibial nerve stimulation (TNS) failed to inhibit bladder contractions at all tested frequencies (0.5-40 Hz). These results indicate that PNS inhibition of nociceptive afferent C-fiber-mediated spinal reflex bladder contractions can occur at the spinal level in the absence of supraspinal pathways, but TNS inhibition requires supraspinal pathways. In addition, this study shows, for the first time, that after acute spinal cord transection reflex bladder contractions can be triggered by activating nociceptive bladder afferent C-fibers using acetic acid irritation. Understanding the sites of action for PNS or TNS inhibition is important for the clinical application of pudendal or tibial neuromodulation to treat bladder dysfunctions.

Agar-based bridges as biocompatible candidates to provide guide cues in spinal cord injury repair

Spinal bridge implants are strategic to provide growth surfaces for axonal regeneration after spinal cord injuries. The design of an appropriate substrate, one that is suitable for implantation, must involve careful testing of the biomaterial properties both in vitro and in vivo. The goal of this work was to test the structure, stability and biological response after spinal bridges implantation of several biopolymers, composed of mixtures of agar (AG), as structural matrix scaffold, with κ-carrageenan (Kc), gelatin (G), xanthan gum (Xn) and polysulfone (PS). Biopolymer structures were studied by environmental scanning electron microscopy, whereas the stability of gels was analyzed by in vitro degradation and swelling tests. The biocompatibility of these materials and their ability to promote cell growth and axonal regeneration were studied by implantation of spinal bridges containing empty linear channels in an acute rat spinal cord transection model at thoracic level (T8). All gel mixtures gave rise to porous structures and they were stables to degradation, excepting the AG+G mixture. Spinal bridges constructed from all mixtures were implanted during a month in adult rats. After this time a low host reaction occurred to all bridge materials as well as neurite and cell ingrowths through the empty channels. Neurites within the bridges were mostly peripheral sensory fibers such as those positive for CGRP, whereas there was a lack of regeneration of central axons crossing from the spinal tissue to bridges. Many of these neurites established closed contacts with non-myelin Schwann cells. The histological analysis revealed a high accumulation of collagen fibers within the channels. Unexpected was the apparent loss of channels linearity which affected the growth of neurites and cells, indicating the need for additional regeneration strategies and vertebrae bridge fixing.

Metallothionein deficiency leads to soleus muscle contractile dysfunction following acute spinal cord injury in mice.

Metallothionein (MT) is a small molecular weight protein possessing metal binding and free radical scavenging properties. We hypothesized that MT-1/MT-2 null (MT(-/-)) mice would display exacerbated soleus muscle atrophy, oxidative injury, and contractile dysfunction compared with the response of wild-type (WT) mice following acute spinal cord transection (SCT). Four groups of mice were studied: WT laminectomy, WT transection, MT(-/-) laminectomy (MT(-/-) lami), and MT(-/-) transection (MT(-/-) trans). Laminectomy animals served as surgical controls. Mice in SCT groups experienced similar percent body mass (BM) losses at 7 days postinjury. Soleus muscle mass (MM) and MM-to-BM ratio were lower at 7 days postinjury in SCT vs. laminectomy mice, with no differences observed between strains. However, soleus muscles from MT(-/-) trans mice showed reduced maximal specific tension compared with MT(-/-) lami animals. Mean cross-sectional area (microm(2)) of type I and type IIa fibers decreased similarly in SCT groups compared with laminectomy controls, and no difference in fiber distribution was observed. Lipid peroxidation (4-hydroxynoneal) was greater in MT(-/-) trans vs. MT(-/-) lami mice, but protein oxidation (protein carbonyls) was not altered by MT deficiency or SCT. Expression of key antioxidant proteins (catalase, manganese, and copper-zinc superoxide dismutase) was similar between the groups. In summary, MT deficiency did not impact soleus MM loss, but resulted in contractile dysfunction and increased lipid peroxidation following acute SCT. These findings suggest a role of MT in mediating protective adaptations in skeletal muscle following disuse mediated by spinal cord injury.

Intraurethral Stimulation Evokes Bladder Responses via 2 Distinct Reflex Pathways

Recent animal studies have shown that selective activation of pudendal nerve branches can evoke bladder responses through 2 distinct reflex pathways. We examined intraurethral electrical stimulation as a minimally invasive means of selectively activating these pathways in the cat. Bladder responses evoked by intraurethral electrical stimulation were measured in alpha-chloralose anesthetized male cats at different stimulation frequencies, stimulation intensities and intraurethral locations. Intraurethral electrical stimulation evoked inhibitory and excitatory bladder reflexes depending on stimulation frequency and location. Stimulation in the penile urethra 0 to 3 cm from the urethral meatus at 33 Hz evoked bladder contraction and at 10 Hz it evoked bladder relaxation. These responses were abolished after bilateral transection of the dorsal penile nerves. Stimulation in the membranous urethra 5 to 7 cm from the urethral meatus at 2, 10 and 33 Hz evoked bladder contractions. These responses were abolished after bilateral transection of the cranial sensory nerves. Following acute spinal cord transection bladder contractions were still evoked by 33 Hz stimulation in the penile urethra but not by stimulation at any frequency in the membranous urethra. Intraurethral electrical stimulation selectively evoked bladder responses by activating 2 distinct pudendal afferent pathways. Responses depended on stimulation frequency and location. Intraurethral electrical stimulation is a valid means of determining the pathways involved in bladder responses evoked by pudendal nerve stimulation.

Activation and inhibition of the micturition reflex by penile afferents in the cat

Coordination of the urinary bladder and the external urethral sphincter is controlled by descending projections from the pons and is also subject to modulation by segmental afferents. We quantified the effects on the micturition reflex of sensory inputs from genital afferents traveling in the penile component of the somatic pudendal nerve by electrical stimulation of the dorsal nerve of the penis (DNP) in alpha-chloralose anesthetized male cats. Depending on the frequency of stimulation (range, 1-40 Hz), activation of penile afferents either inhibited contractions of the bladder and promoted urine storage or activated the bladder and produced micturition. Stimulation of the DNP at 5-10 Hz inhibited distension-evoked contractions and increased the maximum bladder capacity before incontinence. Conversely, stimulation at 33 and 40 Hz augmented distension-evoked contractions. When the bladder was filled above a threshold volume (70% of the volume necessary for distension-evoked contractions), stimulation at 20-40 Hz activated de novo the micturition reflex and elicited detrusor contractions that increased voiding efficiency compared with distension-evoked voiding. Electrical stimulation of the DNP with a cuff electrode or percutaneous wire electrode produced similar results. The ability to evoke detrusor contractions by activation of the DNP was preserved following acute spinal cord transection. These results demonstrate a clear role of genital afferents in modulating the micturition reflex and suggest the DNP as a potential target for functional restoration of bladder control using electrical stimulation.

Hindlimb movement in the cat induced by amplitude-modulated stimulation using extra-spinal electrodes

Hindlimb movement in the cat induced by electrical stimulation with an amplitude-modulated waveform of the dorsal surface of the L5-S1 spinal cord or the L5-S1 dorsal/ventral roots was investigated before and after acute spinal cord transection at the T13-L1 level. Stimulation of the spinal cord or dorsal/ventral root at the same spinal segment induced similar movements including coordinated multi-joint flexion or extension. The induced movements changed from flexion to extension when the stimulation was moved from rostral (L5) to caudal (S1) spinal segments. Stimulation of a dorsal or ventral root on one side induced only ipsilateral hindlimb movement. However, stimulation on the dorsal surface of the spinal cord along the midline or across the spinal cord induced bilateral movements. The extension induced by stimulation of L7 dorsal root produced the largest ground reaction force that was strong enough to support body weight. Dorsal root stimulation induced a larger ground reaction force than ventral root stimulation and produced a more graded recruitment curve. Stepping at different speeds could be generated by combined stimulation of the rostral (L5) and the caudal (L6/L7) spinal segments with an appropriate timing between the different stimulation channels. Acute transection of the spinal cord did not change the responses indicating that the induced movements did not require the involvement of the supraspinal locomotor centers. The methods and the stimulation strategy developed in this study might be utilized to restore locomotor function after spinal cord injury.

ORIGINAL RESEARCH—BASIC SCIENCE: Effect of the Destruction of Cells Containing the Serotonin Reuptake Transporter on Urethrogenital Reflexes

ABSTRACT Introduction The urethrogenital (UG) reflex is an autonomic and somatic response that mimics some of the physiological changes seen during ejaculation. The UG reflex is tonically inhibited by neurons in the ventral medulla, an area containing serotonin neurons. Aim To examine the effect of lesions of brain neurons containing the serotonin reuptake transporter (SERT) on ejaculatory-like reflexes. Methods Anti-SERT saporin (80 nL, 1 mM) or saline was injected bilaterally into the ventrolateral medulla of male Sprague–Dawley rats. Ten to 18 days later, animals were deeply anesthetized and the presence of the UG reflex was examined before and after acute spinal cord transection (T9–10). Following the experiment the presence and number of serotonin and norepinephrine containing neurons (using tryptophan hydroxylase and dopamine beta-hydroxylase, respectively) was performed. Main Outcome Measures The UG reflex and cell counts. Results In saline-injected controls the UG reflex was not evoked in the anesthetized, intact preparation, indicating the presence of the supraspinal inhibition, as previously reported. Injection of anti-SERT saporin into the ventrolateral medulla allowed the UG reflex to be activated in the intact preparation, thus removed the inhibition. This was associated with a decrease in the number of serotonin neurons in the ventrolateral medulla and raphe. No change in the number of noradrenergic neurons was observed. Conclusion These studies suggest that ventral medullary neurons containing SERT are involved in the tonic inhibition of the UG reflex.

Spinal Micturition Reflex Mediated by Afferents in the Deep Perineal Nerve

Reflexes mediated by urethral sensory pathways are integral to urinary function. This study investigated the changes in bladder pressure and urethral sphincter activity resulting from electrical stimulation of afferents in the deep perineal nerve (DP), which innervates the urethra and surrounding muscles, before and after acute spinal cord transection (SCT) in cats anesthetized with alpha-chloralose monitored by blood pressure and heart rate. DP stimulation elicited bladder contractions before and after SCT but only if the bladder contained a sufficient volume of fluid (78% of the volume needed to cause distention-evoked reflex contractions). The volume dependency was mediated by a neuronal mechanism in the lumbosacral spinal cord and was not attributable to length-tension properties of the detrusor muscle. Stimulation at 2-40 Hz initiated bladder contractions, but 20-40 Hz was more effective than lower frequencies in evoking and sustaining bladder contractions for the duration of the stimulus train. Decreases in urethral sphincter activity occurred during sustained bladder contractions evoked by 20- to 40-Hz stimulation before and within 16 h after SCT. After SCT, average bladder pressure increases evoked by DP stimulation were smaller than those evoked before SCT, but in some animals, bladder pressures elicited by DP stimulation continued to increase as time after SCT increased and reached pretransection amplitudes at 8-16 h posttransection. These data confirm the presence of a spinal circuit that can mediate coordinated bladder-sphincter responses and show that afferents from the DP can activate this circuit under appropriate conditions.

Locations and morphologies of sympathetically correlated neurons in the T 10 spinal segment of the rat

We precisely localized and morphologically characterized sympathetically correlated neurons in the acutely transected spinal cord of the rat. We have shown that these neurons are likely members of the spinal networks that generate sympathetic activity after spinal cord transection. In humans with injured spinal cords, these networks are responsible for hypertensive crises that occur in response to ordinarily innocuous stimuli. We recorded from neurons in the dorsal horn of the T 10 spinal segment of anesthetized rats after acute spinal cord transection at C 2. Neurons with activities closely correlated to renal sympathetic nerve activity (RSNA) were considered to be putative components of spinal sympathetic systems. These neurons had receptive fields on the left flank and abdomen. After characterizing their ongoing activities, receptive fields, and degrees of correlation with RSNA, we juxtacellularly labeled neurons with biotinamide and subsequently reconstructed their somas and dendrites histologically. Confirming our earlier studies, sympathetically correlated neurons were found in dorsal horn laminae III, IV, and V. For the first time, we also identified sympathetically correlated neurons in laminae I and II. The dendrites of all sympathetically correlated neurons projected to multiple lamina. By virtue of the positions of their somas and the broad projections of their dendrites, we concluded that sympathetically correlated neurons may receive direct input both from supraspinal systems and from nociceptive and non-nociceptive primary afferents.

Evidence for Plateau Potentials in Tail Motoneurons of Awake Chronic Spinal Rats With Spasticity

Motor units of segmental tail muscles were recorded in awake rats following acute (1-2 days) and chronic (>30 days) sacral spinal cord transection to determine whether plateau potentials contributed to sustained motor-unit discharges after injury. This study was motivated by a companion in vitro study that indicated that after chronic spinal cord injury, the tail motoneurons of the sacrocaudal spinal cord exhibit persistent inward currents (I(PIC)) that cause intrinsically sustained depolarizations (plateau potentials) and firing (self-sustained firing). Importantly, in this companion study, the plateaus were fully activated at recruitment and subsequently helped sustain the firing without causing abrupt nonlinearities in firing. That is, after recruitment and plateau activation, the firing rate was modulated relatively linearly with injected current and therefore provided a good approximation of the input to the motoneuron despite the plateau. Thus in the present study, pairs of motor units were recorded simultaneously from the same muscle, and the firing rate (F) of the lowest-threshold unit (control unit) was used as an estimate of the synaptic input to both units. We then examined whether firing of the higher-threshold unit (test unit) was intrinsically maintained by a plateau, by determining whether more synaptic input was required to recruit the test unit than to maintain its firing. The difference in the estimated synaptic input at recruitment and de-recruitment of the test unit (i.e., change in control unit rate, DeltaF) was taken as an estimate of the plateau current (I(PIC)) that intrinsically sustained the firing. Slowly graded manual skin stimulation was used to recruit and then de-recruit the units. The test unit was recruited when the control unit rate was on average 17.8 and 18.9 Hz in acute and chronic spinal rats, respectively. In chronic spinal rats, the test unit was de-recruited when the control unit rate (re: estimated synaptic input) was significantly reduced, compared with at recruitment (DeltaF = -5.5 Hz), and thus a plateau participated in maintaining the firing. In the lowest-threshold motor units, even a brief stimulation triggered very long-lasting firing (seconds to hours; self-sustained firing). Higher-threshold units required continuous stimulation (or a spontaneous spasm) to cause firing, but again more synaptic input was needed to recruit the unit than to maintain its firing (i.e., plateau present). In contrast, in acute spinal rats, the stimulation did not usually trigger sustained motor-unit firing that could be attributed to plateaus because DeltaF was not significantly different from zero. These results indicate that plateaus play an important role in sustaining motor-unit firing in awake chronic spinal rats and thus contribute to the hyperreflexia and hypertonus associated with chronic injury.

Interactions between pelvic viscera and their striated musculature in the rat before and after acute spinal cord transection

Interactions between pelvic viscera and their striated musculature in the rat before and after acute spinal cord transection

Interactions between pelvic viscera and their striated musculature in the rat before and after acute spinal cord transection

Interactions between pelvic viscera and their striated musculature in the rat before and after acute spinal cord transection

L-DOPA and quipazine elicit air-stepping in neonatal rats with spinal cord transections.

Acute mid-thoracic spinal cord transection eliminates hindlimb air-stepping in neonatal rats suspended in harnesses and administered L-DOPA. Because spinal cord transection eliminates all descending inputs to the hindlimb locomotor circuits, this experiment determined if coadministration of L-DOPA and quipazine (serotonin receptor agonist) would induce hindlimb air-stepping in rat pups 24 hr after transection. Hindlimb steps of spinally transected pups that received L-DOPA or quipazine alone were infrequent and slow; hindlimb steps induced by L-DOPA + quipazine occurred more frequently and were faster than those elicited by either drug alone. These findings suggest that catecholaminergic and serotonergic systems both contribute to hindlimb stepping.