Effects of electrical stimulation of the thoracic spinal cord on bladder and external urethral sphincter activity in the decerebrate cat

Summary Electrical stimulation of the spinal cord above the sacral segments was used to produce coordinated micturition in the paralysed decerebrate cat. Stimulation of the superficial aspect of the dorsolateral funiculus (DLF) within the lower thoracic (T9-T13) segments produced a bladder contraction coordinated with decreased activity in the external urethral sphincter (EUS) branch of the pudendal nerve during which time fluid was expelled. In addition, a similar response was observed with DLF stimulation at the boundary of the L5/L6 segments. At the second cervical spinal segment, however, stimulation of a more lateral and ventral portion of the superficial spinal white matter was the only effective site for producing micturition. The spinal cord-evoked response was comparable to the micturition evoked by electrical stimulation of the pontine micturition centre (PMC) within the brainstem. A bilateral lesion of the dorsal columns (DC) and the dorsolateral funiculi (DLF) at the lower thoracic levels abolished reflex micturition evoked by bladder distension. However stimulation rostral to the lesion, within the PMC or thoracic DLF, continued to produce coordinated bladder and sphincter response during voiding. Stimulation caudal to the lesion produced a decrease in pudendal nerve activity but did not produce a void or bladder pressure change. This reduction in pudendal nerve activity could be abolished with a second lesion of the superficial DLF caudal to the stimulation site. It was concluded that stimulation of the thoracic dorsolateral funiculus activates both ascending and descending fibres which can influence the bladder and/or sphincter muscles. The spinal cordevoked voiding was hypothesized to be due to activation of some portion of the ascending limb of the spinobulbospinal micturition reflex loop. The decreased activity produced by stimulation of the thoracic DLF caudal to a bilateral DC/DLF subtotal cord lesion may be mediated by fibres descending in the dorsolateral funiculus. The possibility that the spinal cord stimulation antidromically activated axons of neurons having segmental collaterals capable of influencing pudendal neural activity cannot be exclused at this time.     

Sacral dorsal horn neurone activity during micturition in the cat

The excitability of two groups of neurones located in different parts of the sacral spinal cord were examined during micturition in decerebrate adult cats. One group of cells, characterized by their activation by pudendal cutaneous afferents, was located in the dorsal commissure of the first and second sacral spinal segments. The second group, located in the dorsal horn of the first sacral spinal segment, was excited by group II muscle and cutaneous afferents. Micturition was evoked by distension of the urinary bladder or by electrical stimulation of the pontine micturition centre. Tonic firing was induced in the neurones by ejection of DL-homocysteic acid from the recording extracellular micropipette. The instantaneous firing frequency of 11/17 sacral dorsal grey commissure neurones was decreased from 7 to 100 % during micturition, and on average was about half of the prevoid firing frequency. It is hypothesized that these sacral neurones are interposed in polysynaptic excitatory pathways from sacral perineal afferents to sphincter motoneurones and that they are subject to direct postsynaptic inhibition during micturition. One other cell showed no change in firing during micturition, two displayed complex patterns of modulation, while 3/17 of the dorsal grey commissure neurones increased their firing rate 30 to 1000 % during micturition. It is hypothesized that the excited neurones may be part of the inhibitory pathways mediating postsynaptic inhibition of sphincter motoneurones or sacral primary afferent depolarization during micturition. Alternatively, they may be part of the excitatory urethral-bladder reflex circuitry. A small (5–15%) but significant decrease in firing was observed in 4/5 of the group II rostral sacral neurones examined; the firing of a fifth neurone was unchanged. The depression of group II neurones may serve to suppress unwanted hindlimb reflexes that could disrupt micturition.     

Reflex firing in the lumbar sympathetic outflow to activation of vesical afferent fibres

1. Activation of vesical afferent fibres in the Aγδ range by electrical stimulation of the pelvic nerve or by bladder distension elicited reflex firing in hypogastric nerves and in preganglionic nerves to the inferior mesenteric ganglion.

2. The multisynaptic reflex was present in cats with an intact spinal cord and in acute and chronic spinal animals (transections at T10—T12). The reflex pathway was partially crossed in the sacral cord, and in the periphery at the level of the inferior mesenteric ganglia. In contrast, an inhibitory response to raised intravesical pressure was mediated by a supraspinal inhibitory mechanism which was activated in parallel with the micturition reflex.

3. Since enhancement as well as depression of sympathetic firing accompanied reflex micturition, it is concluded that at least two distinct populations of lumbar preganglionic neurones are responsive to vesical afferent activity: one population being excited, the other depressed, during micturition. The latter population may be involved in an inhibitory feed-back mechanism on to the bladder.

     

Inhibitory effect of the nucleus reticularis pontis oralis on the pontine micturition center and pontine urine storage center in decerebrate cats

The influence of the nucleus reticularis pontis oralis (PoO) on the pontine micturition center (PMC) and pontine urine storage center (PUSC) was examined in decerebrate cats by electrical and chemical stimulations of the PMC, PUSC or PoO. Microinjection of carbachol into the rostral and dorsolateral part of the PoO rapidly inhibited reflex micturition and external urethral sphincter (EUS) activity. After confirming the inhibition of reflex micturition and EUS activity by microinjection of carbachol into the PoO, intravenous injection of atropine sulfate or its microinjection into the PoO recovered both reflex micturition and EUS activity. Microinjection of carbachol into the PMC evoked micturition and then inhibited reflex micturition, but intravenous injection of atropine or its microinjection into the PoO recovered reflex micturition. After confi rming the inhibition of reflex micturition and EUS activity by microinjection of carbachol into the PoO, electrical stimulation of the PUSC enhanced EUS activity, but electrical stimulation of the PMC failed to evoke micturition. However, electrical stimulation of the PMC evoked micturition after microinjection of atropine into the PoO. These results suggest that the PoO strongly inhibits the PMC and less strongly inhibits the PUSC. Therefore, the PoO seems to be the pontine micturition inhibitory area.     

骶髓排尿反射机制的形态学基础——HRP标记、溃变和免疫组化法的光、电镜研究

本文应用溃变、HRP标记和免疫组化相结合的方法,在电镜下观察了SPN区外周初级传入终末与节前神经元间的突触联系形式。证明生理状态下,两者之间存在直接突触联系。并进一步探讨了与节前神经元形成直接突触联系的初级传入终末的来源和性质。为解释反射性排尿形成机制的“脱抑制释放学说”提供了超微结构水平的形态学依据。     

Reflexes to sacral parasympathetic neurones concerned with micturition in the cat

1. Reflexes to sacral parasympathetic neurones were studied by electrophysiological techniques in decerebrate, in chloralose-anaesthetized, and in chronic spinal cats.2. Excitatory reflexes from pelvic nerve and sacral somatic afferent nerve fibres were present before and after chronic transection of the spinal cord, but the latencies differed markedly. It was concluded that the long-latency reflexes observed when the spinal cord was intact involved long-loop reflexes to the brain-stem. The weak, short-latency reflexes in the chronic spinal cat were never observed when the spinal cord was intact and could be due to reorganized spinal connexions. The short-latency reflexes are probably unimportant in normal micturition.3. Stimulation of afferent fibres in the pelvic or sacral somatic nerves produced short-latency inhibitory post-synaptic potentials (IPSPs) and inhibition of discharges in parasympathetic neurones. This inhibition was due to a spinal reflex.4. A local reflex was demonstrated in the pelvic plexus. This was probably a cholinergic axon reflex, but the remote possibility that it was a local cholinergic reflex involving sensory neurones in the bladder wall has not been excluded.     

Sacral spinal interneurones and the control of urinary bladder and urethral striated sphincter muscle function

Normally, during bladder filling (continence) and expulsion (micturition) there is a reciprocity between the pattern of activity in the urinary bladder sacral parasympathetic efferents and the somatic motoneurones innervating the striated external urethral sphincter muscle. The co-ordination of this pattern of reciprocal activity appears to be determined by excitatory and inhibitory actions of a variety of segmental afferents and descending systems with sacral spinal actions. These actions may in part be mediated through lower lumbar and sacral excitatory and inhibitory spinal interneurones. Over the past 30 years, both neuroanatomical and electrophysiological approaches have been used to reveal an ever-increasing richness in the neuronal network in the lower spinal cord related to the bladder and striated external urethral sphincter muscle. The purpose of this review is to present an overview of the identified excitatory and inhibitory spinal interneurones hypothesized to be involved in the central networks controlling the sacral bladder parasympathetic preganglionic neurones and striated urethral sphincter motoneurones during continence and micturition.     

大鼠脑桥排尿中枢和脊髓交感中枢之间的形态学研究

为研究大鼠排尿过程中交感神经同副交感神经协同作用的形态学基础,通过形态学方法,用生物素标记的葡聚糖胺(BDA)顺行标记从脑桥排尿中枢(PMC)投射到腰6至骶1(L6~S1)脊髓节段的神经末梢。将荧光金(FG)注入盆节逆行标记副交感神经节前神经元(PPNs),并且通过免疫组化的方法判断该逆标的神经元是否为胆碱能性的。于L1~L2节段IML区和L6~S1节段骶副交感核(SPN)分别注射辣根过氧化物酶(HRP)和麦芽凝集素结合的HRP(WGA-HRP),分别在L6~S1检测逆标神经元和L1~L2节段检测顺行标记终末。结果显示,于L1~L2节段IML区交感节前神经元所在部位注射HRP,在同侧SPN的背内侧发现有逆标神经元,且该神经元为非胆碱能神经元,其胞体显著小于PPNs(P<0.05)。BDA标记的神经末梢主要位于L6~S1节段双侧IML区,也是SPN的所在部位,并发现有些末梢和同侧逆标的HRP阳性神经元有紧密接触。SPN中电泳入WGA-HRP,发现在L1~L2节段IML区有顺标的神经末梢。上述结果提示,脑桥排尿中枢可能通过位于SPN背侧的中间神经元对L1~L2节段IML区内的交感节前神经元发挥调控作用。     

Gentle Perineal Skin Stimulation for Control of Nocturia

One of the major causes of nocturia is overactive bladder (OAB). Somatic afferent nerve stimuli are used for treating OAB. However, clinical evidence for the efficacy of this treatment is insufficient due to the lack of appropriate control stimuli. Studies on anesthetized animals, which eliminate emotional factors and placebo effects, have demonstrated an influence of somatic stimuli on urinary bladder functions and elucidated the underlying mechanisms. In general, the effects of somatic stimuli are dependent on the modality, location, and physical characteristics of the stimulus. Recently we showed that gentle stimuli applied to the perineal skin using a soft elastomer roller inhibited micturition contractions to a greater extent than a roller with a hard surface. Studies aiming to elucidate the neural mechanisms of gentle stimulation-induced inhibition reported that 1–10 Hz discharges of low-threshold cutaneous mechanoreceptive Aβ, Aδ, and C fibers evoked during stimulation with an elastomer roller inhibited the micturition reflex by activating the spinal cord opioid system, thereby reducing both ascending and descending transmission between bladder and pontine micturition center. The present review will provide a brief summary of (1) the effect of somatic electrical stimulation on the micturition reflex, (2) the effect of gentle mechanical skin stimulation on the micturition reflex, (3) the afferent, efferent, and central mechanisms underlying the effects of gentle stimulation, and (4) a translational clinical study demonstrating the efficacy of gentle skin stimuli for treating nocturia in the elderly with OAB by using the two roller types inducing distinct effects on rat micturition contractions. Anat Rec, 302:1824–1836, 2019. © 2019 American Association for Anatomy     

Sympathetic activity in the recto-rectal reflex of the guinea pig

In the guinea pig, defecation is controlled by the myenteric plexus, whose activity is modulated by the sacral spinal and supraspinal centers. The purpose of this study is to clarify the control of defecation reflex by sympathetic nerves. The propulsive contractions of the rectum produced by rectal distension (recto-rectal excitatory reflex response) were abolished after transection of the Th 13 and/or the L 4 segment. This response was reproduced again after removal of the lumbar segments (L1-4), division of the lumbar dorsal roots (L1-4), the lumbar splanchnic nerves or lumbar colonic nerves (LCN). The frequency of efferent discharges of LCN was increased slightly by rectal distension and remarkably increased after Th 13 and/or L 4 transection. Thus, there occurs during the recto-rectal reflex not only mucosal intrinsic reflex and sacral excitatory reflex via the pelvic nerves but also a lumbar inhibitory reflex via the colonic nerves, whose center may be located in the upper lumbar segments.But, the activity of the inhibitory center was depressed by the supraspinal center, so that an excitatory reflex is produced more dominantly than an inhibitory one in normal animals. All these extrinsic reflexes coordinate the activity of the myenteric plexus in defecation reflex.     

Electrical and chemical stimulations of the pontine micturition center

In an acute decerebrate cat, electrical stimulation of the pontine micturition center (PMC) resulted in micturition. Carbachol injection into the PMC also resulted in micturition. The pattern of changes in bladder pressure and the sphincter activity observed during carbachol-induced micturition was almost identical to that observed during reflex micturition. The injection site corresponded to the nucleus locus coeruleus alpha (LC alpha). These results suggest that activation of cholinoceptive neurons in the LC alpha presumably becomes a trigger to recruit any one of a number of neuronal circuits involved in micturition.     

Reflex changes in the urinary bladder after mechanical and thermal stimulation of the skin at various segmental levels in cats

Mechanical or thermal stimulation of various skin areas produced reflex changes in the urinary bladder in anesthetized cats. When the bladder was quiescent, mechanical or thermal stimulation of the skin resulted in a reflex increase in the tonus of the bladder only when the perineal area was stimulated. This cutaneo-vesical excitatory reflex was a spinal reflex with its efferent arc in the pelvic nerves. When there were spontaneous, large, rhythmic micturition contractions of the bladder at a frequency of 1–3/min, these contractions were usually inhibited by mechanical or thermal stimulation of the skin of the perineum, abdomen or chest in this order of effectiveness. Sometimes, the inhibition was followed by a subsequent excitation. The efferent arc for this reflex inhibition of the large micturition contractions was also in the pelvic nerves. For both the excitatory and the inhibitory cutaneo-vesical reflex responses, noxious stimulation was much more effective than nonnoxious stimulation.     

Characterization and restoration of altered inhibitory and excitatory control of micturition reflex in experimental autoimmune encephalomyelitis in rats

Multiple sclerosis (MS) is characterized by inflammatory lesions throughout the central nervous system. Spinal cord inflammation correlates with many neurological defecits. Most MS patients suffer from micturition dysfunction with urinary incontinence and difficulty in emptying the bladder. In experimental autoimmune encephalomyelitis (EAE) induced in female Lewis rats, a model of MS, we investigated at distinct clinical severity scores the micturition reflex by cystometrograms. All rats presenting symptomatic EAE suffered from micturition reflex alterations with either detrusor areflexia or hyperactivity. During pre-symptomatic EAE, a majority of rats presented with detrusor areflexia, whereas at onset of clinical EAE, detrusor hyperactivity was predominant. During progression of EAE, detrusor areflexia and hyperactivity were equally expressed. Bladder hyperactivity was suppressed by activation of glycine and GABA receptors in the lumbosacral spinal cord with an order of potency: glycine > GABA_B > GABA_A. Detrusor areflexia was transformed into detrusor hyperactivity by blocking glycine and GABA receptors. Spinalization abolished bladder activity in rats presenting detrusor hyperactivity and failed to induce activity in detrusor areflexia. Altogether, the results reveal an exaggerated descending excitatory control in both detrusor reflex alterations. In detrusor areflexia, a strong segmental inhibition dominates this excitatory control. As in treatment of MS, electrical stimulation of sacral roots reduced detrusor hyperactivity in EAE. Blockade of glycine receptors in the lumbosacral spinal cord suppressed the stimulation-induced inhibitory effect. Our data help to better understand bladder dysfunction and treatment mechanisms to suppress detrusor hyperactivity in MS.     

Functional role of lumbar sympathetic nerves and supraspinal mechanism in the defecation reflex of the cat

The role of the lumbar sympathetic nerves and supraspinal mechanism in the defecation reflex was investigated in 30 adult cats and 6 kittens. One or two propulsive contractions, whose mean pressure evoked was more than about 90 cmH2O (adult cats) and 50 cmH2O (kittens), were induced in the rectum of all animals by rectal distension. These propulsive contractions could be generated at the descending and the transverse colons. The removal of the supraspinal influence by spinal transection at T13 or removal of pelvic afferents to the supraspinal center by spinal transection at L abolished the propulsive contractions. Successive lumbar sympathectomy restored the contractions. Lumbar sympathectomy and the successive removal of the supraspinal influence did not affect the propulsive contractions. In both cases, the final exclusion of the sacral segments by pithing of the spinal cord abolished the propulsive contractions. These results suggest that the sacral excitatory reflex mediated via pelvic nerves and the lumbar inhibitory reflex mediated via lumbar sympathetic nerves can function during rectal distension in spinal cats and that the lumbar inhibitory reflex is suppressed by the supraspinal sympathetic inhibitory reflex activated by pelvic afferents in intact cats, as in guinea pigs, resulting in propulsive contractions.     

Evidence for a strychnine-sensitive mechanism and glycine receptors involved in the control of urethral sphincter activity during micturition in the cat

Micturition in the decerebrate cat is characterized by a coordinated bladder contraction and a simultaneous decrease in external urethral sphincter (EUS) efferent activity. Without the suppression of EUS activity, voiding is significantly impaired, resulting in a state sometimes referred to as bladder-sphincter dyssynergia. The aim of the present study was to determine whether glycinergic inhibition contributes to the suppression of EUS activity during micturition evoked by bladder distension or electrical stimulation of the pontine micturition center (PMC) in decerebrate cats. Using subconvulsive intravenous doses of strychnine (0.1–0.24 mg/kg), we examined changes in bladder and EUS electroneurographic (ENG) activity during micturition. Following subconvulsive doses of strychnine, tonic EUS ENG activity increased during bladder filling in five of six animals. In the presence of strychnine, it was possible to evoke reflex bladder contractions of similar duration and peak pressure to those observed before strychnine administration. However, there was an absence of suppression of EUS ENG activity during the bladder contractions in all the animals. To determine whether the changes in sphincter activity could be due to strychnine acting at glycine receptors on EUS motoneurons, sacral spinal tissue was processed for a structural protein (gephyrin) associated with the glycine receptor. Motoneurons in Onuf′s nucleus in S1 were identified using choline acetyltransferase immunohistochemistry and subsequently processed with a gephyrin monoclonal antibody. Abundant gephyrin labeling was evident throughout Onuf′s nucleus. Since Onuf′s nucleus is made up of EUS and other motoneuron populations, a sample of antidromically identified urethral and anal sphincter motoneurons were intracellularly labeled with tetramethylrhodamine dextran (TMR-D) and then processed with the gephyrin antibody. Using dual-beam confocal microscopy, gephyrin immunoreactivity was observed on the soma and proximal processes of individual EUS motoneurons in both male and female animals. It was concluded that a strychnine-sensitive mechanism contributes to the suppression of sphincter activity normally observed during voiding. Although glycinergic inhibition may affect several components of the circuitry responsible for micturition, it appears that the suppression of EUS motoneurons during micturition may be partly due to a direct glycinergic inhibition of the EUS motoneurons. Received: 3 June 1997 / Accepted: 22 September 1997     

Bladder afferent pathway and spinal cord injury: possible mechanisms inducing hyperreflexia of the urinary bladder

Lower urinary tract dysfunction is a common problem in patients with spinal cord injury (SCI). Since the coordination of the urinary bladder and urethra is controlled by the complex mechanisms in spinal and supraspinal neural pathways, SCI rostral to the lumbosacral level disrupts voluntary and supraspinal control of voiding and induces a considerable reorganization of the micturition reflex pathway. Following SCI, the urinary bladder is initially areflexic. but then becomes hyperreflexic because of the emergence of a spinal micturition reflex pathway. Recent electrophysiologic and histologic studies in rats have revealed that chronic SCI induces various phenotypic changes in bladder afferent neurons such as: (1) somal hypertrophy along with increased expression of neurofilament protein; and (2) increased excitability due to the plasticity of Na+ and K+ ion channels. These results have now provided detailed information to support the previous notion that capsaicin-sensitive, unmyelinated C-fiber afferents innervating the urinary bladder change their properties after SCI and are responsible for inducing bladder hyperreflexia in both humans and animals. It is also suggested that the changes in bladder reflex pathways following SCI are influenced by neural-target organ interactions probably mediated by neurotrophic signals originating in the hypertrophied bladder. Thus, increased knowledge of the plasticity in bladder afferent pathways may help to explain the pathogenesis of lower urinary tract dysfunctions after SCI and may provide valuable insights into new therapeutic strategies for urinary symptoms in spinal cord-injured patients.     

Organization of the neural switching circuitry underlying reflex micturition

The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain and spinal cord that coordinates the activity of the bladder and urethral outlet. Experimental studies in animals indicate that urine storage is modulated by reflex mechanisms in the spinal cord, whereas voiding is mediated by a spinobulbospinal pathway passing through a coordination centre in the rostral brain stem. Many of the neural circuits controlling micturition exhibit switch‐like patterns of activity that turn on and off in an all‐or‐none manner. This study summarizes the anatomy and physiology of the spinal and supraspinal micturition switching circuitry and describes a computer model of these circuits that mimics the switching functions of the bladder and urethra at the onset of micturition.     

内源性鸦片肽在骶髓排尿反射中的意义的形态学探讨—溃变法、HRP逆行标记法和免疫组化法相结合的光、电镜研究

本文通过溃变、HRP标记和免疫组化相结合的电镜观察,在证明骶髓副交感中枢区后根传入纤维的终末和副交感节前神经元树突之间存在轴-树突触的同时,发现初级传入终末又接受来源尚未确定的ENK样免疫阳性终末与之形成轴-轴突触。本文根据所观察的结果,探讨了ENK样成分对骶髓直接排尿反射的作用机制,并对其在逼尿肌与外括约肌的功能协调中的意义进行了讨论。本研究的结果为探讨截瘫患者反射性排尿的出现机制以及临床上用吗啡治疗膀胱痉挛以及应用纳洛酮加强慢性神经源性膀胱功能障碍患者逼尿肌的反射活动等的机制提供了形态学依据。     

Some properties of sympathetic neuron inhibition by depressor area and intraspinal stimulation

In Nembutal anesthesized cats single shock stimulation of the depressor area of the medulla oblongata evoked inhibition of spontaneous and glutamate-evoked activity of sympathetic preganglionic units. Single shocks to the lateral funiculus of the cervical or upper thoracic spinal cord in acute spinal cats evoked inhibition of the spontaneous and glutamate-evoked activity of single units and of the segmental reflex mass discharge evoked by spinal afferent stimulation. Cats studied 4 to 6 weeks after a complete transection of the spinal cord also showed, on stimulation of the lateral funiculus below the transection, an inhibition of the segmental reflex with time course similar to that seen in the acute spinal state, but of lower threshold and greater intensity. These results suggest that the inhibitory coupling between supraspinal levels and sympathetic preganglionic units is mediated, at least in part, by propriospinal neuronal system which survive after chronic spinal section. On the assumption that the observed changes in the properties of inhibition are due to plastic changes consequent to partial denervation the results also suggest that continuous descending tracts exist, and that both the continuous and the propriospinal descending tracts may be converging onto some common neural element.     

Central control of thermogenesis in mammals

Thermogenesis, the production of heat energy, is an essential component of the homeostatic repertoire to maintain body temperature in mammals and birds during the challenge of low environmental temperature and plays a key role in elevating body temperature during the febrile response to infection. The primary sources of neurally regulated metabolic heat production are mitochondrial oxidation in brown adipose tissue, increases in heart rate and shivering in skeletal muscle. Thermogenesis is regulated in each of these tissues by parallel networks in the central nervous system, which respond to feedforward afferent signals from cutaneous and core body thermoreceptors and to feedback signals from brain thermosensitive neurons to activate the appropriate sympathetic and somatic efferents. This review summarizes the research leading to a model of the feedforward reflex pathway through which environmental cold stimulates thermogenesis and discusses the influence on this thermoregulatory network of the pyrogenic mediator, prostaglandin E(2), to increase body temperature. The cold thermal afferent circuit from cutaneous thermal receptors ascends via second-order thermosensory neurons in the dorsal horn of the spinal cord to activate neurons in the lateral parabrachial nucleus, which drive GABAergic interneurons in the preoptic area to inhibit warm-sensitive, inhibitory output neurons of the preoptic area. The resulting disinhibition of thermogenesis-promoting neurons in the dorsomedial hypothalamus and possibly of sympathetic and somatic premotor neurons in the rostral ventromedial medulla, including the raphe pallidus, activates excitatory inputs to spinal sympathetic and somatic motor circuits to drive thermogenesis.